10.-EPRI-NMAC_HVAC Testing, Adjunsting and Balancing Guideline.pdf

HVAC Testing, Adjusting, and Balancing Guideline

Technical Report

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Equipment

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HVA

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EPRI Project ManagerM. Pugh


HVAC Testing, Adjusting, andBalancing Guideline1003092

Final Report, October 2001

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CITATIONS

This report was prepared by

EPRI Nuclear Maintenance Applications Center (NMAC)1300 W.T. Harris Blvd.Charlotte, NC 28262

This report describes research sponsored by EPRI.

The report is a corporate document that should be cited in the literature in the following manner:

HVAC Testing, Adjusting, and Balancing Guideline, EPRI, Palo Alto, CA: 2001. 1003092.

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REPORT SUMMARY

BackgroundHeating, ventilating, and air conditioning (HVAC) systems serve a key function in nuclear powerplants. Reliable operation and maintenance of these systems are crucial to sustained plantoperation and availability. In many cases, these systems are required to be operable andfunctioning according to plant technical specifications. Maintenance and engineering personnelare often required to understand HVAC system operation and purpose, periodically test andmaintain system components, and respond to problems. The ability of plant personnel todiagnose and troubleshoot HVAC problems quickly and accurately is vital to maintain plantavailability.

Objectives• To provide guidance to nuclear plant personnel involved in the balancing of HVAC systems

for nuclear power facilities

• To present an overview of the requirements for developing and performing air and hydronicsystems balancing in order to optimize system performance and ensure that the system meetsall heating, cooling, and flow requirements

• To provide guidance on nuclear power plant HVAC systems, which consist of many differentcomponents that function together as a dynamic system

• To provide inexperienced and experienced engineers with the background necessary toperform testing, adjusting, and balancing activities on HVAC systems

ApproachIn cooperation with the Nuclear HVAC Utility Group (NHUG) and interested NuclearMaintenance Applications Center (NMAC) members, a task group of utility engineers andindustry experts was formed. This group met several times during one year to identify andprepare the guidance found in this report. Experience-proven practices and techniques wereidentified and discussed during this effort and are summarized in this report for use by all powerplant personnel.

ResultsThis report provides a practical approach that can be used by power plant personnel to diagnoseand troubleshoot HVAC system and component performance problems. The guideline isvaluable for both the component and system engineer and provides fundamental background andtechniques for testing, adjusting, and balancing HVAC systems, including information oncommonly used testing instruments and how they are used, flow measurement techniques,balancing processes and steps, and troubleshooting techniques. Additionally, commonly usedHVAC equipment and systems are discussed, and useful reference information, includingcommonly used equations and airflow measurement methodologies, is provided.

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EPRI PerspectiveThe information contained in this guide represents a significant collection of technicalinformation (including techniques and good practices) related to the testing, adjusting, andbalancing of HVAC systems in power plants. Assemblage of this information provides a singlepoint of reference for power plant personnel, now and in the future. The intended audience ofthis guide includes component, maintenance, and system engineers involved in testing,maintaining, operating, and troubleshooting HVAC systems. This guide will be helpful inevaluating system problems, selecting new and replacement components, and understandingHVAC system performance and reliability.

KeywordsDesign engineersPlant support engineeringPlant maintenancePlant operationsHVAC

EPRI Licensed Material

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ACKNOWLEDGMENTS

The following individuals participated on the task group for this report and provided valuableassistance and plant-specific information during its development:

Ray Runowski, Chairman PSEG, Salem

Peter Breglio, Vice-Chairman Proto-Power Corp

Lee Warnick Dominion Generation, North Anna

Mike Pugh EPRI NMAC

Dennis Adams Exelon, Quad Cities

Frank Johnston Niagara Mohawk, Nine Mile Point

David Scott Nuclear Management Company, Monticello

Eric Banks NUCON

Erick Jun OPPD, Fort Calhoun

Mike Fraughton Pacificorp, Naughton

Clint Medlock Power Generation Technologies

John Cichello PSEG, Hope Creek

Ray Rosten Sequoia Consulting Group

Mike Tulay Sequoia Consulting Group

Deep Ghosh Southern Company

Bob Campbell TVA Corporate

Mark Schwan TVA, Browns Ferry

Mike Walker TVA, Sequoyah

Sam Linginfelter TVA, Watts Bar

Tim Parker TXU, Comanche Peak

Lenny Murphy Vermont Yankee

Burt Copeland Wolf Creek Nuclear Operating Company


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CONTENTS

1 INTRODUCTION.................................................................................................................. 1-1

1.1 Purpose of the Report ............................................................................................... 1-1

1.2 Scope of the Report .................................................................................................. 1-1

1.3 Key Points................................................................................................................. 1-3

2 LIST OF ACRONYMS ......................................................................................................... 2-1

3 HVAC TESTING, ADJUSTING, AND BALANCING GUIDANCE ........................................ 3-1

3.1 Generic Process for Existing System Troubleshooting .............................................. 3-1

3.1.1 Identifying the Issue.............................................................................................. 3-3

3.1.1.1 Communicating Issues at a Nuclear Power Plant.......................................... 3-3

3.1.1.2 Common Symptoms Observed/Measured in HVAC Systems........................ 3-4

3.1.2 Defining the Problem ............................................................................................ 3-4

3.1.2.1 General Guidance......................................................................................... 3-4

3.1.2.2 Common Ventilation System Problems ......................................................... 3-5

3.1.2.3 Common System Blockage Problems ........................................................... 3-5

3.1.2.4 Fan Degradation Problems ........................................................................... 3-6

3.1.3 Determining and Validating Operating Conditions................................................. 3-7

3.1.4 Comparing to Previous Conditions........................................................................ 3-8

3.1.4.1 Comparison to Design Requirements/Historical Performance ....................... 3-8

3.1.4.2 Sources of Design Information ...................................................................... 3-9

3.1.5 Determine If Symptoms Could Adversely Affect HVAC System Performanceor Reliability ................................................................................................................. 3-10

3.1.6 Perform HVAC System Walkdown/Evaluation .................................................... 3-11

3.1.7 Develop Troubleshooting Plan............................................................................ 3-12

3.1.7.1 Determine What Measurements Are Appropriate ........................................ 3-13

3.1.7.2 Determine Who Will Perform the Measurements......................................... 3-13

3.1.7.3 Determine How Measurements Will Be Taken ............................................ 3-14


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3.1.8 Perform Recommended Tests/Measurements.................................................... 3-14

3.1.9 Determine If Troubleshooting Plan Provides Adequate Indication of theProblem ....................................................................................................................... 3-14

3.1.9.1 Evaluating HVAC System Performance Problems ...................................... 3-14

3.1.9.2 Typical Causes of HVAC System Performance Problems........................... 3-15

3.1.10 Develop Corrective Actions ............................................................................. 3-16

3.1.10.1 Typical Adjustments for HVAC System Performance Problems................. 3-17

3.1.10.2 Rebalancing HVAC Systems ..................................................................... 3-18

3.2 Generic Process for New/Existing Air System Balancing......................................... 3-18

3.2.1 Review Design and System Documentation ....................................................... 3-18

3.2.2 Perform System Walkdown ................................................................................ 3-19

3.2.3 Define Critical System Lineup............................................................................. 3-20

3.2.4 Operate System to Determine Overall System Flow ........................................... 3-21

3.2.5 Measure Flow in Branch Ducts ........................................................................... 3-21

3.2.6 Measure/Adjust Each Terminal Device in Each Branch ...................................... 3-21

3.2.6.1 General Considerations .............................................................................. 3-21

3.2.6.2 Balancing by Ratio Method......................................................................... 3-21

3.2.7 Re-Measure Total System Flow.......................................................................... 3-22

3.2.8 Simulate Dirty Filter and Wetted Coil Conditions................................................. 3-22

3.2.9 Final Balance or Adjustment in the Clean Mode ................................................. 3-22

3.3 Generic Process for Temporary Air System Balancing or Rebalancing ................... 3-23

3.3.1 Planning Steps ................................................................................................... 3-23

3.3.2 Execution............................................................................................................ 3-24

3.3.3 Review and Documentation................................................................................ 3-24

3.4 Generic Process for New/Existing Water System Balancing.................................... 3-25

3.4.1 Review Design and System Documentation ....................................................... 3-25

3.4.2 Perform Walkdown of the Water System ............................................................ 3-25

3.4.3 Prerequisites ...................................................................................................... 3-26

3.4.4 Operate System to Determine Overall System Flow ........................................... 3-27

3.4.5 Water Balancing Process ................................................................................... 3-27

3.5 Generic Process for Temporary Water System Balancing or Rebalancing .............. 3-28

3.5.1 Planning Steps ................................................................................................... 3-28

3.5.2 Execution............................................................................................................ 3-29

3.5.3 Review and Documentation................................................................................ 3-30


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4 INSTRUMENTATION .......................................................................................................... 4-1

4.1 Types of TAB Instrumentation ................................................................................... 4-1

4.1.1 Airflow Measuring Instruments.............................................................................. 4-1

4.1.1.1 U-Tube Manometer....................................................................................... 4-1

4.1.1.2 Inclined/Vertical Manometer.......................................................................... 4-2

4.1.1.3 Electronic (Digital) Manometer...................................................................... 4-3

4.1.1.4 Pitot Tube ..................................................................................................... 4-4

4.1.1.5 Pressure Gauge (Magnehelic®)..................................................................... 4-8

4.1.1.6 Rotating Vane Anemometer (Mechanical Type) ............................................ 4-8

4.1.1.7 Electronic Rotating Vane Anemometer.......................................................... 4-9

4.1.1.8 Deflecting Vane Anemometer ..................................................................... 4-10

4.1.1.9 Thermal Anemometer ................................................................................. 4-11

4.1.1.10 Flow Measuring Hood................................................................................ 4-12

4.1.1.11 Smoke Devices.......................................................................................... 4-12

4.1.2 Hydronic Instruments......................................................................................... 4-13

4.1.2.1 Pressure Test Gauge.................................................................................. 4-13

4.1.2.2 Differential Pressure Gauge........................................................................ 4-14

4.1.3 Rotation Measuring Instruments ......................................................................... 4-14

4.1.3.1 Chronometric Tachometer........................................................................... 4-14

4.1.3.2 Contact Tachometer (Digital) ...................................................................... 4-14

4.1.3.3 Optical (Photo) Tachometer ........................................................................ 4-15

4.1.3.4 Electronic Tachometer (Stroboscope) ......................................................... 4-15

4.1.3.5 Dual-Function Tachometer.......................................................................... 4-16

4.1.4 Temperature Measuring Instruments .................................................................. 4-17

4.1.4.1 Glass Tube Thermometers.......................................................................... 4-17

4.1.4.2 Dial Thermometers...................................................................................... 4-17

4.1.4.3 Thermocouple Thermometers ..................................................................... 4-18

4.1.4.4 Electronic Thermometers ............................................................................ 4-18

4.1.4.5 Portable Noncontact Thermometers............................................................ 4-18

4.1.4.6 Psychrometers ............................................................................................ 4-18

4.1.4.7 Electronic Thermohygrometers ................................................................... 4-19

4.1.4.8 Color Strip Temperature Indicators ............................................................. 4-20

4.1.5 Electrical Measuring Instruments ........................................................................ 4-20

4.1.5.1 Voltammeter ............................................................................................... 4-20


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4.1.6 Hydronic Flow Measuring Devices...................................................................... 4-21

4.1.6.1 Venturi Tube and Orifice Plate .................................................................... 4-21

4.1.6.2 Annular Flow Indicator ................................................................................ 4-21

4.1.6.3 Calibrated Balancing Valves ....................................................................... 4-22

4.1.6.4 Ultrasonic Flow Meters................................................................................ 4-22

4.1.6.5 V-Cone Flow Meters ................................................................................... 4-22

4.1.6.6 Coriolis Flow Meter ..................................................................................... 4-22

4.1.6.7 Vortex Shedding Flow Meter ....................................................................... 4-23

4.1.6.8 Location of Flow Devices ............................................................................ 4-23

4.2 Applications for TAB Instrumentation ...................................................................... 4-23

4.2.1 Airflow Measuring Instruments............................................................................ 4-23

4.2.2 Hydronic Measuring Instruments ........................................................................ 4-25

4.2.3 Rotation Measuring Instruments ......................................................................... 4-25

4.2.4 Temperature Measuring Instruments .................................................................. 4-26

4.3 Recommended Accuracy of TAB Instrumentation ................................................... 4-27

5 AIR AND WATER FLOW MEASUREMENT TECHNIQUES ................................................ 5-1

5.1 Airside Flow Measurement ........................................................................................ 5-1

5.1.1 Pitot Tube Traverse Methods................................................................................ 5-1

5.1.1.1 Equal Area Method ....................................................................................... 5-2

5.1.1.2 Log Linear Method........................................................................................ 5-6

5.1.1.3 Tchebycheff Method.................................................................................... 5-10

5.1.1.4 Documentation of Traverse Data................................................................. 5-12

5.1.1.5 Airflow Traverse Qualification...................................................................... 5-12

5.1.1.6 Examples .................................................................................................... 5-13

5.2 Water Side Flow Measurement ............................................................................... 5-18

5.2.1 Background ........................................................................................................ 5-18

5.2.2 Differential Pressure Producers .......................................................................... 5-19

5.2.2.1 Principle of Measurement ........................................................................... 5-19

5.2.3 Multiport Averaging Pitots ................................................................................... 5-19


5.2.4 Pitot Tube Traverse ............................................................................................ 5-19


5.2.5 Ultrasonic Flow Meters ....................................................................................... 5-20



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5.2.6 Magnetic Flow Meters........................................................................................ 5-20


5.2.7 Turbine Flow Meters ........................................................................................... 5-20


6 LESSONS LEARNED.......................................................................................................... 6-1

6.1 How Abnormal Flow Alignment Affects Fan Performance ......................................... 6-2

6.2 Estimating Filter Pressure Gradients for Clean and Dirty Conditions ......................... 6-1

6.3 Typical Failure Mechanism for Duct Access Doors.................................................... 6-2

6.4 Typical Failure Mechanism for an Inlet Damper......................................................... 6-2

6.5 Typical Failure Mechanism for an Air-Handling Unit Fan........................................... 6-2

6.6 Pitot Tube Employment and Failure Mechanisms...................................................... 6-3

6.7 Misuse of Measurement Equipment .......................................................................... 6-4

6.8 System and Component Interactions......................................................................... 6-5

6.9 How Flow Disturbances Can Affect Flow Measurement ............................................ 6-6

6.10 Proper Use of an Electronic Micromanometer ........................................................... 6-6

6.11 Consideration of System Operating Conditions ......................................................... 6-7

6.12 Low Airflow in the Auxiliary Building Ventilation System............................................ 6-7

7 REFERENCES .................................................................................................................... 7-1

A TYPES OF HVAC SYSTEMS..............................................................................................A-1

A.1 Generic HVAC Functions ..........................................................................................A-1

A.1.1 General Area Ventilation.......................................................................................A-1

A.1.2 Equipment/Area Cooling.......................................................................................A-1

A.1.3 Radioactivity Control Ventilation ...........................................................................A-2

A.1.3.1 Nuclear Air Cleanup......................................................................................A-2

A.2 Air Systems Designated by the Buildings Serviced...................................................A-2

A.2.1 Containment/Reactor Building ..............................................................................A-3

A.2.1.1 General Description ......................................................................................A-3

A.2.1.2 Standby Gas Treatment System ...................................................................A-3

A.2.1.3 Containment Cooling.....................................................................................A-4

A.2.1.4 Containment Power Access Purge or Minipurge ...........................................A-4

A.2.1.5 Containment Refueling Purge .......................................................................A-4

A.2.1.6 Containment Combustible Gas Control .........................................................A-4


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A.2.2 Turbine Building....................................................................................................A-5

A.2.3 Auxiliary Building ..................................................................................................A-5

A.2.4 Control Room .......................................................................................................A-5

A.2.5 Emergency Electrical Switchgear Rooms .............................................................A-6

A.2.6 Control Cable Spreading Room............................................................................A-6

A.2.7 Diesel Generator Building.....................................................................................A-6

A.2.8 Battery Rooms......................................................................................................A-6

A.2.9 Fuel-Handling Building..........................................................................................A-6

A.2.10 Personnel Facilities.............................................................................................A-7

A.2.11 Pump Houses .....................................................................................................A-7

A.2.12 Radwaste Building ..............................................................................................A-7

A.2.13 Technical Support Center ...................................................................................A-7

A.3 Types of Water Systems Supporting HVAC Systems ................................................A-7

A.3.1 Hot Water Heating Systems..................................................................................A-8

A.3.2 Chilled Water Systems .........................................................................................A-8

A.3.3 Hot and Chilled Water Systems with Ethylene or Propylene Glycol ......................A-8

A.3.4 Chiller Condenser Water Flow ..............................................................................A-9

A.3.5 Raw Water or Service Water Flow ........................................................................A-9

A.3.6 Coil Performance Equations .................................................................................A-9

A.4 Example of an HVAC System Diagram .....................................................................A-9

B TYPES OF HVAC EQUIPMENT..........................................................................................B-1

B.1 Fans..........................................................................................................................B-1

B.1.1 Types of Fans.......................................................................................................B-4

B.1.1.1 Centrifugal Fans ..........................................................................................B-4

B.1.1.2 Axial Fans....................................................................................................B-5

B.1.1.3 Tubular Centrifugal Fans .............................................................................B-8

B.1.1.4 Propeller Fans .............................................................................................B-8

B.1.2 Types of Fan Drivers and Drives ..........................................................................B-8

B.1.2.1 Belt Drive.....................................................................................................B-8

B.1.2.2 Direct Drive..................................................................................................B-9

B.1.2.3 Variable Speed Motor Drive.........................................................................B-9

B.2 Dampers ...................................................................................................................B-9

B.2.1 Types of Dampers ................................................................................................B-9

B.2.1.1 Isolation Dampers........................................................................................B-9


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B.2.1.2 Control Dampers .......................................................................................B-10

B.2.1.3 Inlet Vane Dampers ...................................................................................B-13

B.2.1.4 Backdraft Dampers ....................................................................................B-13

B.2.1.5 Fire Dampers.............................................................................................B-14

B.2.1.6 Smoke Dampers........................................................................................B-14

B.2.1.7 Louvers......................................................................................................B-14

B.2.2 Damper Actuators...............................................................................................B-14

B.3 Heating and Cooling Coils.......................................................................................B-15

B.3.1 Steam Coils ........................................................................................................B-15

B.3.2 Hot Water Heating Coils .....................................................................................B-15

B.3.3 Cooling Coils ......................................................................................................B-15

B.3.3.1 Refrigerant/Direct Expansion Coils ............................................................B-15

B.3.3.2 Chilled Water Cooling Coils .......................................................................B-16

B.3.4 Electric Heating Coils..........................................................................................B-17

B.4 Filters ......................................................................................................................B-17

B.4.1 Dust Filters/Prefilters/Postfilters..........................................................................B-17

B.4.2 HEPA Filters.......................................................................................................B-17

B.4.3 Charcoal Adsorbers............................................................................................B-18

B.4.4 Sand Filters ........................................................................................................B-18

B.5 Terminal Devices ....................................................................................................B-18

B.5.1 Single-Duct.........................................................................................................B-19

B.5.2 Dual-Duct, Nonmixing.........................................................................................B-19

B.5.3 Dual-Duct, Mixing ...............................................................................................B-20

B.5.4 Single-Duct with Heating Coil .............................................................................B-20

B.5.5 Fan-Powered, Variable Volume (Parallel) ...........................................................B-21

B.5.6 Fan-Powered, Constant Volume (Series)............................................................B-21

B.5.7 Low-Temperature Fan Terminals........................................................................B-22

B.5.8 Fan-Powered, Quiet ...........................................................................................B-22

B.5.9 Fan-Powered, Low-Profile ..................................................................................B-23

B.6 Ductwork.................................................................................................................B-23

B.6.1 General ..............................................................................................................B-23

B.6.2 Duct Leakage Classifications..............................................................................B-24

B.6.2.1 Allowable Leakage by Radiological Control Criteria ...................................B-24

B.6.2.2 Additional Leakage Criteria........................................................................B-25


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B.6.2.3 Air Cleaning System Configuration and Leakage Classes .........................B-25

B.6.3 Duct Construction ...............................................................................................B-25

B.6.3.1 Materials....................................................................................................B-25

B.6.3.2 Rectangular and Round Ducts...................................................................B-26

B.6.3.3 Flat Oval Ducts ..........................................................................................B-27

B.6.3.4 Fibrous Glass Ducts ..................................................................................B-27

B.6.3.5 Flexible Ducts............................................................................................B-27

B.6.3.6 Plenums and Apparatus Casings...............................................................B-27

B.6.3.7 Acoustical Treatment .................................................................................B-27

B.6.3.8 Hangers.....................................................................................................B-27

B.7 Instrument Test Ports ..............................................................................................B-28

B.8 Airflow Measuring Stations......................................................................................B-29

B.8.1 Multiport with Integral Air Straightener ................................................................B-29

B.8.2 Traverse Probe...................................................................................................B-29

B.8.3 Pitot Traverse Station .........................................................................................B-30

B.8.4 Hot Wire Sensor .................................................................................................B-31

B.8.5 Orifice Plates ......................................................................................................B-32

B.9 Humidifiers ..............................................................................................................B-32

B.9.1 Heated Pan Humidifiers......................................................................................B-33

B.9.2 Direct Steam Injection Humidifiers......................................................................B-33

B.9.3 Electrically Heated, Self-Contained Steam Humidifiers.......................................B-33

B.9.4 Atomizing Humidifiers.........................................................................................B-33

B.9.5 Wetted Media Humidifiers...................................................................................B-34

B.10 Dehumidifiers .....................................................................................................B-34

B.11 Centrifugal Pumps ..............................................................................................B-35

C TYPICAL HVAC TAB DOCUMENTATION .........................................................................C-1

C.1 Typical Documentation Requirements.......................................................................C-1

C.2 Testing, Adjusting, and Balancing Forms ..................................................................C-1

D EQUATIONS AND CALCULATIONS..................................................................................D-1

D.1 Fundamental Equations ............................................................................................D-1

D.2 Conduit, Pipe, and Duct Friction Loss Equations.......................................................D-5

D.3 Airflow Equations ....................................................................................................D-10

D.4 Fan Equations.........................................................................................................D-13


xvii

D.5 Pump Equations......................................................................................................D-18

D.6 Electrical Equations.................................................................................................D-20

D.7 Noise and Vibration Equations ................................................................................D-23

D.8 Drives, Belts, and Pulleys........................................................................................D-24

D.9 Areas and Circular Equivalents of Ducts .................................................................D-26

E ANALYTICAL METHODS ...................................................................................................E-1

E.1 Introduction ...............................................................................................................E-1

E.2 System Airflow and Pressure Loss Analysis..............................................................E-1

E.2.1 System Diagram Development .............................................................................E-2

E.2.2 Analysis Using Generic and Custom Computer Modeling Software......................E-2

E.2.2.1 Generic Spreadsheet Software....................................................................E-3

E.2.2.2 Computer Modeling Software ......................................................................E-3

E.3 Thermal and Pressure Loss Analysis and Balancing of HVAC Water/LiquidSystems ...................................................................................................................E-4

E.3.1 HVAC Heat Exchanger Analysis...........................................................................E-4

F ALTERNATE FLOW MEASUREMENT USING TRACER GAS........................................... F-1

G DEFINING ACFM AND SCFM WHEN PERFORMING TAB ACTIVITIES ...........................G-1

G.1 Effect of Temperature on CFM..................................................................................G-1

G.2 Effect of Pressure on CFM........................................................................................G-2

G.3 Effect of Moisture Variation on CFM..........................................................................G-3

G.4 Correction Formulas for ACFM and SCFM................................................................G-5

H LISTING OF KEY POINTS..................................................................................................H-1


xix

LIST OF FIGURES

Figure 1-1 Fundamental Elements of the HVAC TAB Process Addressed in this Report ........ 1-2

Figure 3-1 Preliminary Evaluation for Troubleshooting and Rebalancing HVAC Systems ....... 3-2

Figure 3-2 Operating Conditions Measured for HVAC System Troubleshooting ...................... 3-8

Figure 3-3 Factors Affecting the Need for Detailed HVAC System Troubleshooting .............. 3-10

Figure 3-4 Detailed HVAC System Troubleshooting and TAB Activities ................................ 3-11

Figure 4-1 Typical U-Tube Manometer.................................................................................... 4-2

Figure 4-2 Typical Inclined/Vertical Manometer....................................................................... 4-3

Figure 4-3 Typical Electronic (Digital) Manometer ................................................................... 4-4

Figure 4-4 Pitot Tube Details................................................................................................... 4-5

Figure 4-5 Typical Negative Static Pressure Pitot Tube and Manometer orMicromanometer Hookup ..................................................................................... 4-5

Figure 4-6 Typical Positive Static Pressure Pitot Tube and Manometer orMicromanometer Hookup ..................................................................................... 4-6

Figure 4-7 Typical Pressure Gauge......................................................................................... 4-8

Figure 4-8 Typical Mechanical Rotating Vane Anemometer .................................................... 4-9

Figure 4-9 Typical Electronic Rotating Vane Anemometer .................................................... 4-10

Figure 4-10 Typical Thermal Anemometer ............................................................................ 4-11

Figure 4-11 Typical Flow Hood ............................................................................................. 4-12

Figure 4-12 Typical Smoke Gun............................................................................................ 4-13

Figure 4-13 Typical Contact Reflective Tachometer .............................................................. 4-15

Figure 4-14 Typical Electronic Tachometer ........................................................................... 4-16

Figure 4-15 Typical Sling Psychrometer................................................................................ 4-19

Figure 4-16 Typical Electronic Hygrometer ........................................................................... 4-20

Figure 5-1 Traverse Qualification .......................................................................................... 5-13

Figure A-1 Turbine Room Ventilation One-Line Diagram .....................................................A-10

Figure B-1 Typical Fan Performance Curve ...........................................................................B-2

Figure B-2 Fan Outlet Velocity Profiles...................................................................................B-3

Figure B-3 Terminology for Centrifugal Fan Components.......................................................B-5

Figure B-4 Terminology for Axial and Tubular Centrifugal Fans ............................................B-7

Figure B-5 Multiblade Volume Dampers...............................................................................B-12

Figure B-6 DX Coil ...............................................................................................................B-16

Figure B-7 Single-Duct Configuration ...................................................................................B-19


xx

Figure B-8 Dual-Duct, Nonmixing Configuration ...................................................................B-20

Figure B-9 Dual-Duct, Mixing Configuration .........................................................................B-20

Figure B-10 Single-Duct with Heating Coil Configuration......................................................B-21

Figure B-11 Fan-Powered, Variable Volume, Parallel Configuration ....................................B-21

Figure B-12 Fan-Powered, Constant Volume Series Configuration......................................B-22

Figure B-13 Fan-Powered, Quiet Configuration....................................................................B-22

Figure B-14 Fan-Powered, Low-Profile Configuration ..........................................................B-23

Figure B-15 Instrument Test Port .........................................................................................B-28

Figure B-16 Multiport Air Measuring Station with an Integral Air Straightener.......................B-29

Figure B-17 Traverse Probe Air Measuring Station ..............................................................B-30

Figure B-18 Pitot Traverse Station .......................................................................................B-31

Figure B-19 Multipoint Insertion Mass Flow Element............................................................B-31

Figure B-20 Single-Stage Horizontal Pump (Single-Suction)................................................B-36

Figure B-21 Single-Stage Horizontal Pump (Double-Suction) ..............................................B-36

Figure C-1 Fan Data ..............................................................................................................C-2

Figure C-2 Round Duct Traverse Data Sheet .........................................................................C-3

Figure C-3 Rectangular Duct Traverse Data Sheet ................................................................C-4

Figure C-4 Grille/Register Data Sheet ....................................................................................C-5

Figure F-1 Typical Schematic for Using Tracer Gas Testing Methods .................................... F-1

Figure F-2 Tracer Gases Exhausted into a Room with a Single Exhaust Point....................... F-2

Figure G-1 Change in Air Volume as a Function of Temperature ...........................................G-2

Figure G-2 Change in Air Volume as a Function of the Change in Absolute Pressure fora Constant Mass.................................................................................................G-3

Figure G-3 Change in Air Volume as a Function of Temperature for VariousPercentages of Moisture Content........................................................................G-4


xxi

LIST OF TABLES

Table 3-1 Typical Adjustments for HVAC Dampers ............................................................... 3-17

Table 3-2 Typical Adjustments for HVAC Fans ..................................................................... 3-18

Table 4-1 Airflow Measuring Instruments .............................................................................. 4-24

Table 4-2 Hydronic Measuring Instruments ........................................................................... 4-25

Table 4-3 Rotation Measuring Instruments............................................................................ 4-25

Table 4-4 Temperature Measuring Instruments..................................................................... 4-26

Table 4-5 Air and Hydronic Measuring Instruments............................................................... 4-27

Table 5-1 Equal Area Method for a Rectangular Duct ............................................................. 5-3

Table 5-2 Equal Area Method for a Round Duct ...................................................................... 5-5

Table 5-3 Log Linear Method for a Rectangular Duct.............................................................. 5-6

Table 5-4 Log Linear Method for a Round Duct....................................................................... 5-6

Table 5-5 Tchebycheff Method for a Rectangular Duct ......................................................... 5-10

Table 5-6 Tchebycheff Method for a Round Duct .................................................................. 5-12

Table 5-7 Example of the Equal Area Method for a Rectangular Duct................................... 5-13

Table 5-8 Example of the Log Tchebycheff Method for a Round Duct................................... 5-15

Table 5-9 Log Linear Method for a Rectangular Duct............................................................ 5-16

Table 5-10 Weighting Values to Be Applied to Each Velocity ................................................ 5-16

Table 5-11 Velocities after the Weighting Values Are Applied ............................................... 5-17

Table B-1 General Fan Attributes...........................................................................................B-6

Table B-2 Orifice Plate Characteristics.................................................................................B-32


1-1

1 INTRODUCTION

1.1 Purpose of the Report

This report provides guidance to nuclear plant personnel involved in the balancing of heating,ventilating, and air conditioning (HVAC) systems for nuclear power facilities. The guideprovides an overview of the requirements for developing and performing air and hydronicsystems balancing to optimize system performance and ensure that the system meets all heating,cooling, and flow requirements. HVAC systems for nuclear power plants consist of manydifferent components, which function together as a dynamic system. These systems are subject tochanges—some the result of intrusive modifications and some caused by gradual componentchanges, such as component wear and instrument drift—that require periodic system balancingto maintain optimum system performance.

This guide will provide inexperienced and experienced engineers with the background necessaryto develop testing, adjusting, and balancing (TAB) procedures as well as an overview of testinginstruments used, documentation of test data, troubleshooting guidelines, and references.

1.2 Scope of the Report

Figure 1-1 shows the scope of this report. The figure captures the fundamental elements of theHVAC TAB process and relates each major element to a section and/or appendix in this report.

Figure 1-1 illustrates that the fundamental goal of HVAC TAB is to establish or restore systemparameters to design conditions. System parameters can be air or water flow, heat removal rates,building air pressure, required temperatures, and humidity. To accomplish this restoration, theengineer should systematically proceed through each element so as not to adversely affect orfurther degrade system performance. Much of Section 3 is devoted to troubleshooting techniquesthat support TAB activities.


Introduction

1-2

Figure 1-1Fundamental Elements of the HVAC TAB Process Addressed in this Report


Introduction

1-3

Section 3 first provides a schematic flow chart for troubleshooting existing plant systems withdetailed implementation guidance. Section 3 then offers guidance on conducting HVAC TABactivities for balancing new or existing air and water plant systems as well as temporarybalancing or rebalancing of air and water systems. Section 4 describes the variousinstrumentation used during HVAC TAB activities, and Section 5 provides air and water flowmeasurement techniques. These three sections constitute the core of the report and aresupplemented with information that may be useful to experienced or newly assigned HVACsystem engineers.

Section 6 provides the reader with a compilation of lessons learned from the experiences ofnumerous utility personnel during HVAC system TAB and troubleshooting activities. Section 7lists the references used to produce this report.

Appendices A through D provide an excellent source of fundamental information regardingHVAC systems and components in nuclear power plants that may be beneficial to lessexperienced HVAC system engineering personnel. Appendix A describes various HVACsystems installed in nuclear power plants and provides an example of a typical HVAC systemdiagram. Appendix B describes numerous types of components that are installed in HVACsystems and provides fundamental background information on the different types and designs ofHVAC components. Appendix C provides numerous examples of typical HVAC documentationused during the TAB processes. Appendices D and E provide guidance for calculating HVACsystem parameters using standard equations and commercially available software. Section 5 issupplemented by Appendix F, which discusses an alternate method for airflow measurement.Appendix G provides guidance on defining actual cubic feet per minute (ACFM) and standardcubic feet per minute (SCFM) when performing TAB activities.

1.3 Key Points

Throughout this report, key information is summarized in “Key Points.” Key Points are boldlettered boxes that succinctly restate information covered in detail in the surrounding text,making the key point easier to locate.

The primary intent of a Key Point is to emphasize information that will allow individuals to takeaction for the benefit of their plant. The information included in these Key Points was selectedby NMAC personnel and the consultants and utility personnel who prepared and reviewed thisguide.

The Key Points are organized according to the three categories: O&M Costs, Technical, andHuman Performance. Each category has an identifying icon, as shown below, to draw attentionto it when quickly reviewing the guide.


Introduction

1-4

Key O&M Cost Point

Emphasizes information that will result in reduced purchase, operating, ormaintenance costs.

Key Technical Point

Targets information that will lead to improved equipment reliability.

Key Human Performance Point

Denotes information that requires personnel action or consideration in orderto prevent injury or damage or ease completion of the task.

Appendix H contains a listing of all key points in each category. The listing restates each keypoint and provides reference to its location in the body of the report. By reviewing this listing,users of this guide can determine if they have taken advantage of key information that the writersof this guide believe would benefit their plants.


2-1

2 LIST OF ACRONYMS

AABC – Associated Air Balance Council

ABV – auxiliary building ventilation

ACFM – actual cubic feet per minute

ACU – air control/conditioning/cleanup unit

AHU – air-handling unit

ALARA – as low as reasonably achievable

AISC – American Institute of Steel Construction

AISI – American International Supply Incorporated

AMCA – Air Movement and Control Association

ANSI – American National Standards Institute

ASME – American Society of Mechanical Engineers

ASHRAE – American Society of Heating, Refrigerating, and Air Conditioning Engineers

ASTM – American Standards for Testing and Materials

BI – backward inclined

BWR – boiling water reactor

CEDM – control element drive mechanism

CFCU – containment fan cooling unit

CM – corrective maintenance

CREVS – control room emergency ventilation system


List of Acronyms

2-2

CRDM – control rod drive mechanism

DC – direct current

DDC – direct digital controls/dual-duct configuration

DI – deionized

DOP – dioctyl phthalate

DX – direct expansion

ECCS – emergency core cooling system

ESF – engineered safety feature

FSAR – final safety analysis report

gpm – gallons per minute

GRDs – grilles, registers, and diffusers

HELB – high-energy line break

HEPA – high-efficiency particulate-air filter

HVAC – heating, ventilating, and air conditioning

I&C – instrumentation and control

IEEE – Institute of Electrical and Electronics Engineers, Inc.

IGV – inlet guide vane

INPO – Institute of Nuclear Power Operation

IST – in-service testing

JCO – justification for continued operation

LCO – limited condition of operation

LCD – liquid crystal display

LED – light-emitting diode

LEL – lower explosive limit


List of Acronyms

2-3

LER – licensee event report

LOCA – loss-of-coolant accident

NC – noise criteria

NEBB – National Environmental Balancing Bureau

NFPA – National Fire Protection Association

NHUG – Nuclear HVAC Utilities Group

NMAC – Nuclear Maintenance Applications Center

NP – nuclear power

NPSH – net positive suction head

NRC – Nuclear Regulatory Commission

NSR – non-safety-related

O&M – operation and maintenance

OBD – opposed blade dampers

OEM – original equipment manufacturer

OSHA – Occupational Safety and Health Association

P&ID – process and instrumentation drawing

PM – predictive or preventive maintenance

PREACS – pump room exhaust air cleanup system

PWR – pressurized water reactor

RC – room criteria

RG – regulatory guide

RH – relative humidity

RO – reverse osmosis

rpm – revolutions per minute


List of Acronyms

2-4

RTD – resistance temperature detector

SCFM – standard cubic feet per minute

(Note: SCFM is standard cubic feet per minute at 60°F (16°C ) and 14.7 psia (101 kPa). Becausenot all countries convert SCFM to SI units in the same way, these measurements are notconverted to SI units in this report.)

SBGT – standby gas treatment system (also noted as SGTS)

SEF – system effects factors

SMACNA – Sheet Metal and Air Conditioning Contractors’ National Association

SR – safety-related

TAB – testing, adjusting, and balancing

TOB – terminal opposed blade damper

TR – technical report

TS – technical specification

TSC – technical support center

VAV – variable air volume

w.g. – water gauge


3-1

3 HVAC TESTING, ADJUSTING, AND BALANCINGGUIDANCE

3.1 Generic Process for Existing System Troubleshooting

This section presents a generic process for troubleshooting HVAC performance problems thatlead to TAB activities to rebalance the system. The generic process is divided into a PreliminaryEvaluation (see Figure 3-1) and a detailed Troubleshooting Process (see Figure 3-4) that maylead to testing, adjusting, or balancing the HVAC system under evaluation.


HVAC Testing, Adjusting, and Balancing Guidance

3-2

Figure 3-1Preliminary Evaluation for Troubleshooting and Rebalancing HVAC Systems

For the purposes of this report, the terms used in TAB are defined as follows:

Testing – The use of specialized and calibrated instruments to measure temperatures, pressures,rotational speeds, electrical characteristics, velocities, and air and water quantities for anevaluation of equipment and system performance [1].

Adjusting – The final setting of balancing devices (such as dampers and valves), adjusting fanspeeds and pump impeller sizes, and setting automatic control devices (such as thermostats andpressure controllers) to achieve optimum system performance and efficiency during normaloperation [1].

Balancing – The methodical regulation of system fluid flows (air or water) through the use ofacceptable procedures to achieve the desired or specified airflow or water flow [1].



3-3

3.1.1 Identifying the Issue

3.1.1.1 Communicating Issues at a Nuclear Power Plant

A performance issue may be communicated to a system/component HVAC engineer in a numberof ways. The issue could be a problem observed by maintenance personnel, a symptom of a moreserious problem, or a management directive to take corrective action. In any case, thesystem/component HVAC engineer must gain a clear understanding of the issue before a rootcause determination can be obtained or derived. It is a process of eliminating the “non-issues”and understanding and acting systematically on the remaining issues. A clear understanding ofthe issue is therefore essential for this process to be successful in the fewest number of iterations.

HVAC system performance issues and component failures may be communicated to an HVACsystem/component engineer in any of the following ways:

• Maintenance work order

• Failed in-service test

• Control room alarms

• Corrective action report

• Performance monitoring (condition monitoring reports)

• Telephone call

• Operations rounds or turnover sheets

• Vendor technical bulletins

• Institute of Nuclear Power Operation (INPO)/U.S. Nuclear Regulatory Commission (NRC)reported industry events

• Engineer walkdowns

Key to addressing any issue is understanding that the plant-specific design/licensing bases needto be maintained throughout the troubleshooting, TAB, and corrective action processes. Inaddition, plant-specific administrative interfaces should be coordinated in accordance with eachplant’s existing procedures (that is, control room interface and operator interface).


Key to addressing any issue is understanding that the plant-specificdesign/licensing bases need to be maintained throughout the troubleshooting,TAB, and corrective action processes.



3-4

3.1.1.2 Common Symptoms Observed/Measured in HVAC Systems

Insufficient airflow can be evidenced by direct velocity measurement performed as part ofroutine surveillance.

Insufficient cooling or heating may indicate reduced system airflow or a change in branchairflow. These symptoms may also be attributed to either heat transfer problems with heating orcooling coils or temperature control system problems. These conditions are usually most evidentduring ambient temperature extremes.

Changes to building/building zone pressure or differential pressure can be evidenced bydirectional airflow changes at the building or zone boundary. To troubleshoot this condition, athorough knowledge of system design is required because many independent factors can affectstructure pressures.

Key O&M Cost Point

The HVAC system may operate without an alarm; however, improperlymaintained system balancing may increase energy costs of operation. Lackof attention to the system balancing can be indicated by insufficient coolingand/or heating in the building or by problems with areas that requirepositive or negative pressure.

3.1.2 Defining the Problem

3.1.2.1 General Guidance

As previously noted, the HVAC engineer should clearly define the problem before proceedingwith system troubleshooting. The engineer should then identify the scope and nature of the issueto determine the severity of the problem and the extent to which the problem has been previouslyobserved in the plant or operating system. To accomplish this, the HVAC engineer shouldunderstand how the problem could apply to other systems/HVAC components of similar designand applications. The engineer should also attempt to validate the information (symptom) toensure that it is reasonable, technically accurate, and representative of observed conditions. Aface-to-face interview with the personnel communicating the HVAC system performance issueshould be considered. Contacting outside sources, such as the National Environmental BalancingBureau (NEBB) web site, the original equipment manufacturer (OEM), or NRC InformationNotices may also provide insight into whether the problem has occurred on other HVACsystems/components of the same design installed in similar applications.


The HVAC engineer should understand how the problem could apply toother systems/HVAC components of similar design and applications.



3-5

3.1.2.2 Common Ventilation System Problems

An exhaust system for potentially contaminated areas typically discharges to the plant stack.Because a change in operation of any fan in such a system can affect the performance of otherfans in the system, fan problems can significantly impact overall system operation.

Depending on the station design basis, these systems might be considered variable volumesystems. This is true if the station design allows for portions of the common exhaust system to besecured individually.

Some ventilation exhaust systems installed in newer facilities may be designed with velocitycontrol systems. These systems have been designed to maintain fan airflow at a constant rate orto vary airflow in order to maintain a structure or a boundary at a prescribed differential pressure.The velocity controls may be installed on the supply side, exhaust side, or both. Before acquiringfield performance data for any variable volume system, it must first be determined in whatsystem operating mode the data will be taken. For systems that control to a specific staticpressure or differential pressure, data can be taken when the system is controlling at set point.

System lineup should be recorded when acquiring air balance data on systems or subsystems thatcan be affected by other ventilation systems. This practice can allow for post-test evaluation ofdiscrepancies and can eliminate the need for re-testing the system.

Key O&M Cost Point

System lineup should be recorded when acquiring air balance data onsystems or subsystems that can be affected by other ventilation systems.

3.1.2.3 Common System Blockage Problems

Particulates - Particulates in the airstream travel through all ventilation systems. Over time,these particulates collect on obstructions in the system. Depending on the installed air filteringsystem (if any) and the nature of the collection points, accumulated dirt can have a seriousimpact on system performance. Typical collection points are coils, velocity diffusers, turningvanes, dampers, filters, air monitoring devices, and some fan blades.

Insulation - In some cases, defective or improperly installed duct lining (insulation) breaksdown with time and may cause system performance problems by plugging coils and reducingsystem airflow.

Coils - Coils act as an unintended filter in many systems. Most standard filters have limitedefficiency and some bypass flow. System dirt can build up on coils, possibly compromisingsystem performance. Routine preventive maintenance (PM) may include inspecting and cleaningpackage unit coils or large system coils; however, branch system coils are not often inspected ona regular basis.



3-6

Velocity Diffusers - Velocity diffusers are obstructions (typically perforated metal plates orscreens) usually installed in package equipment or terminal boxes. They ensure uniform airflowacross coils or velocity sensors. For diffusers installed in package equipment, routine PM mayinclude periodic inspection and cleaning, but for diffusers installed in terminal devices (such asvariable air volume [VAV] boxes or constant velocity boxes), internal inspections are nottypically part of the PM program. Over time, debris buildup can cause significant degradation insystem performance.

Turning Vanes - Most systems with rectangular ductwork have turning vanes at elbowsthroughout the system. The clearance between the vanes is usually sufficiently wide (typicallymore than 4 inches [10 cm]) to prevent obstruction by dirt and debris. Occasionally, turningvanes may become blocked with foreign material or debris, adversely affecting systemperformance. In some cases, turning vane blades have been found detached and lodged againstinternal duct components, causing airflow restriction.

Dampers - The clearance between damper blades is typically wide enough to prevent systemblockage caused by dirt or debris. However, many terminal registers are equipped with terminalopposed blade dampers (TOBs). These dampers are installed to facilitate terminal balance inmost systems. The open blade clearance for this type of damper is typically about 1 inch (2.5cm). If previous balancing work has left the TOBs in the nearly closed position, the effective freearea of the damper can, over time, be seriously affected by the buildup of dirt on the damperblades.

The failure of volume damper linkage has been known to cause a restriction in system airflow.Typically, when splitter damper linkage fails, the damper blade will fail to one side of the “Y” orbranch fitting. This condition can result in a significant “out-of-balance” condition. Multibladevolume dampers and control dampers can experience total or partial linkage failure, resulting inan out-of-balance condition. Drive axle slippage on control dampers can also result in incompleteopening or closing of the damper.

3.1.2.4 Fan Degradation Problems

Belt Drives - Belt drive fans are subject to performance degradation caused by a reduction in fanspeed. Slipping belts can reduce fan speed significantly; however, in severe cases, the conditionis usually detected promptly because of the noise generated.

Sheave wear can also reduce fan speed slightly. Variable pitch sheaves are factory installed onmany fans to allow for field balance during startup. Variable pitch sheaves tend to wear fasterthan fixed sheaves. Sheave wear is typically more severe on smaller sheaves installed on thedrive motor, effectively reducing the fan speed. If the replacement fixed sheave is sized based onrevolutions per minute (rpm) data taken from a drive operating with a severely worn sheave, theresult can be a permanent reduction in fan rpm.



3-7

Dirty Fan Blades - Most fan designs are not subject to severe performance degradation as aresult of dirt or debris collection on the blades. Backward inclined (BI) blade designs aretypically self-cleaning. However, BI fans that operate at low speed with high particulates havebeen found with significant buildup of debris on the blades near the hub. Virtually anycentrifugal fan design is subject to fouling from large objects.

Forward curve fan designs are susceptible to significant performance degradation as a result ofdebris caught in the blades. The blade shape for this fan is ideally suited to capture anyparticulate—from fine dust to larger pieces of debris. If repeated problems with loaded fanblades are identified, consideration should be given to improve filtration for supply fans orchanging fan design for exhaust systems.

In some cases, an out-of-balance condition indicated by fan vibration data may be caused bydebris accumulation on fan wheels.

Fan Wheel Clearance - Wheel clearance and centering are critical parameters in somecentrifugal fans. Excess wheel clearance increases bypass flow and reduces discharge airflow.Wheel clearance can be inadvertently changed by maintenance activities, such as bearingreplacement. Refer to the manufacturer’s recommendation for setting wheel clearance.

Rotation - Incorrect rotation is routinely found to be the cause of fan performance problems. Aroutine precaution to check fan rotation when work is performed that disconnects three-phasepower supplies is recommended. For many smaller, single-phase fan motors, rotation can bechanged at the junction box. Care should be taken to ensure that the as-left rotation is correct.

Different fan designs result in different symptoms when rotating backwards. Tubeaxial andpropeller fans move air in the wrong direction. The output of most centrifugal fans issignificantly reduced when the fan operates in the wrong direction. However, reverse rotation ofa BI fan in centrifugal tubular and power roof ventilators can result in near-design flow, maskingthe incorrect rotation.

3.1.3 Determining and Validating Operating Conditions

After the issue is clearly defined, the next step in the troubleshooting process is to determinewhich operating conditions should be measured or additional information collected as well ashow that information will be validated. Typically, the engineer should consider measuring any ofthe plant, system, or component parameters noted in Figure 3-2.



3-8

Figure 3-2Operating Conditions Measured for HVAC System Troubleshooting

Measurements should be taken using calibrated instruments and reviewed for consistency againstsystem design basis documents or outputs.

3.1.4 Comparing to Previous Conditions

3.1.4.1 Comparison to Design Requirements/Historical Performance

The next step in troubleshooting is to compare the measured parameter(s) against the most recentor historical operating conditions. The engineer should attempt to detect trends in performance.If only one isolated parameter changed since the previous conditions were monitored, the firstaction might be to validate the calibration of the instrumentation used to take the most recentmeasurement.

However, if the comparison reveals that a number of parameters have changed or that thechanges are following a trend and are degrading over time, further investigation is warranted.The measured data should be compared against maintenance history and design requirementsthat can be found in documents such as the following:

• Fan curve

• Nameplate data



3-9

• Fan configuration drawings

• In-service testing (IST) baseline data

• Fan and motor data sheets

• System pressure curve

• Vendor technical manuals

• Parts and materials list

• Recommended replacement parts list

The engineer should consider reviewing equipment history and examining the data trends fromthe computer monitoring systems to determine if the change has been sudden or gradual. Areview of recent preventive and corrective work orders for conditions and work performed(including filter changes and vibration readings) should also be considered. A review of recentperformance testing results on related pieces of equipment may also be helpful.

Consideration of industry-wide historical operating conditions of the fan and components, eitherat other nuclear sites or at other utilities, should be considered an option at this stage of thetroubleshooting process.

3.1.4.2 Sources of Design Information

The design documents noted in Section 3.1.4.1 might not provide all of the design informationrelated to the HVAC system in which the fan and other components are installed. As such, thefollowing sources of design information should also be considered:

• HVAC system design calculations

• HVAC system descriptions

• Design basis documents

• System process and instrumentation drawings (P&IDs)

• HVAC duct/piping drawings and layouts

• Materials management information system

• Component/system technical specifications

• Component procurement specifications

• Final safety analysis report (FSAR)

• Component assembly drawings



3-10

3.1.5 Determine If Symptoms Could Adversely Affect HVAC System Performanceor Reliability

The engineer should make this determination considering the factors shown in Figure 3-3.

Figure 3-3Factors Affecting the Need for Detailed HVAC System Troubleshooting

Figure 3-3 illustrates that this determination is subjective and varies depending on the level ofconservatism of each engineer and possibly on the work processes and scheduling controls inplace. If the conditions warrant further investigation and more detailed troubleshooting, theengineer should refer to the detailed troubleshooting guidance provided in Sections 3.1.6 through3.1.9. If the conditions do not warrant detailed troubleshooting, the engineer should considercontinued or increased monitoring of the HVAC system performance parameters, including thetest parameters. Experience and conservatism may result in performing increased monitoring anddetailed troubleshooting to a reasonable extent.

The person performing the troubleshooting should also ensure that the identifier of the issue ismade aware of the actions taken to that point as well as the justification for not performing anyfurther troubleshooting activities at that time. This feedback is denoted on Figure 3-1 with adotted line.



3-11

3.1.6 Perform HVAC System Walkdown/Evaluation

Figure 3-4Detailed HVAC System Troubleshooting and TAB Activities

Figure 3-4 is a continuation of Figure 3-1 and shows the steps associated with the more detailedaspects of troubleshooting at both the HVAC system and component levels. The engineer shouldthen perform an eyewitness, hands-on inspection of the equipment to validate the issue andsubsequently define the actual problem. A field walkdown of the HVAC system/component(s) isrecommended at this point. After these actions are taken, the engineer should be able tounderstand the issue that was initially communicated, identify the actual symptom(s) of theHVAC system performance, and begin to focus the scope of further troubleshooting efforts(including measurement of operating conditions).

Key Technical Point

The engineer should perform an eyewitness, hands-on inspection of theequipment to validate the issue and subsequently define the actual problem.A field walkdown of the HVAC system/component(s) is recommended at thispoint.



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As a result of the walkdown, the following types of information should be determined anddocumented:

• System lineup

• Damper indications and positions

• Overall system configuration

• Component configuration

• Evidence of damaged or broken equipment

3.1.7 Develop Troubleshooting Plan

Key O&M Cost Point

Development of a detailed troubleshooting plan can save money and time byreducing repetitive efforts and providing a structured approach todetermining the problem.

Prior to making any physical adjustments to the system, a detailed troubleshooting plan shouldbe developed, taking into consideration all of the data collected thus far in the evaluation.Primarily, the troubleshooting plan should address the following issues to ensure that thetroubleshooting effort will not adversely affect or jeopardize system performance:

• Technically correct problem statement

• Troubleshooting tools to be used

• Personnel assignments for implementers and verifiers

• Actions needed

• Expected results of each troubleshooting step

• The process used during troubleshooting

• Anticipated alarms and actuations

• Acceptance criteria for each test/inspection/measurement

• The awareness of possible consequences of initial intrusion into equipment (for example,attaching test equipment, lifting leads, and applying power)

• Contingency actions based on the actual readings/measured results

• Documentation requirements

• Personnel safety and “as low as reasonably achievable” (ALARA) issues

• Component/system configuration controls

• Clear definition of work area boundaries and scope of equipment

• Appropriate reference material (including drawings, technical manuals, procedures, andvisual aids)



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• Provisions for the preservation of evidence

• Communication and work hold-points

• Degree to which technical measurements and test results are quantified and documented

• How the system/component will be restored to design conditions

• Reference to administrative controls to define and manage risk

• Reference to the appropriate postmaintenance testing procedures

• Appropriate levels of review/approval in accordance with plant administrative procedures

• Consideration of plant-specific criteria for performing root cause analysis as well as how theanalysis will be handled

Typically, the level of detail of the plan and the approval authority depend on the risk andcomplexity of the troubleshooting activities and the significance of the failure.

Key Technical Point

Prior to making any physical adjustments to the system, a detailedtroubleshooting plan should be developed, taking into consideration all ofthe data collected thus far in the evaluation.

3.1.7.1 Determine What Measurements Are Appropriate

Typically, the following four critical parameters are measured when troubleshooting an HVACsystem that is not performing in accordance with its original design basis. These as-found/baseline readings need only be recorded if they were not already taken during systemtroubleshooting or if they have changed since the initial measurements were taken.

• Fan measurements, including pressure, power, speed, and rotation direction

• Flow

• Temperature

• Static pressure

3.1.7.2 Determine Who Will Perform the Measurements

Test/measurement personnel should meet the qualification and certification requirementsstipulated by each nuclear utility. Personnel should be familiar with the design of the subjectHVAC system and the operation of the test equipment.



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Personnel should be familiar with the design of the subject HVAC systemand the operation of the test equipment.

3.1.7.3 Determine How Measurements Will Be Taken

Section 4 provides guidance on the various types of instrumentation available to measure HVACsystem parameters. Instrumentation should be selected considering such factors as instrumentaccuracy, type of system parameter being measured, physical constraints regarding themeasurement, cost, and schedule.

3.1.8 Perform Recommended Tests/Measurements

Section 5 provides guidance on numerous air and water flow measurement techniques. Thetests/measurements should follow the troubleshooting plan and should be taken in a methodicaland structured manner.

3.1.9 Determine If Troubleshooting Plan Provides Adequate Indication of theProblem

3.1.9.1 Evaluating HVAC System Performance Problems

If the troubleshooting plan does not provide an adequate indication of the performance problem,the HVAC engineer should first consider revising the plan. Through an iterative effort, anappropriate set of tests/measurements should be developed to enable the identification of the rootcause of the performance problem.

The information collected and/or measured should be evaluated to determine if the root cause(s)of the system performance problems can be identified. This is performed by taking any of thefollowing actions:

• Comparing static pressures

• Comparing actual flow to the design flow noted on the fan curve

• Comparing all measured data to any previous TAB reports

If the troubleshooting plan provides an adequate indication of the performance problem, theHVAC engineer should develop the necessary corrective actions to restore the system to designconditions.



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3.1.9.2 Typical Causes of HVAC System Performance Problems

A few of the most common causes of HVAC system performance problems are noted in thissection. The following list is for illustrative purposes only and does not necessarily include allcauses of system performance degradation:

• Inadequate fan performance

• Worn or damaged turning vanes

• Worn, damaged, or missing flow straighteners

• Improper damper performance or adjustment

• Loss of pressure boundary (duct leakage)

• Plugged coils (airside or water side)

• Improper performance (that is, inadvertent closing) of fire dampers

• Airflow monitoring station plugging

• Dirty/damaged/missing/obstructed air distribution grilles

• Excessively dirty filters

• Damaged flex connections

• Inadvertent changes to system configuration

• Adverse ambient and environmental conditions

Multiple causes may exist for a given system. In these cases, system adjustments should beperformed methodically and documented in order to provide a clear indication of the effect eachparameter has on the overall system performance. The actual determination of root cause is aniterative process.



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Key Technical Point

The most common causes of HVAC system performance problems includethe following:














3.1.10 Develop Corrective Actions

The resulting corrective actions may encompass HVAC adjusting and rebalancing. A list ofcorrective action options follows:

• Perform component maintenance and/or repair

• Reconfigure the system

• Adjust system parameters (See Section 3.1.10.1)

• Rebalance the HVAC system (See Section 3.1.10.2)

The following activities are inherent to most utility corrective actions and should not beoverlooked when developing a corrective action plan for an HVAC system:

• Perform cause analysis (root cause analysis may take place after the HVAC systemperformance has been restored)

• Take the necessary actions to prevent recurrence



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3.1.10.1 Typical Adjustments for HVAC System Performance Problems

Key O&M Cost Point

Adjustments to dampers are generally less expensive to perform;modifications to fans generally involve modifications that can become costly.

Adjustments of HVAC systems typically involve adjusting parameters associated with fans anddampers. In most cases, the HVAC engineer should first ensure that dampers are in adjustmentbefore changing any fan parameters. Table 3-1 describes typical adjustments that may beconsidered for dampers.

Table 3-1Typical Adjustments for HVAC Dampers

Type of DamperType of Adjustment

Isolation Balancing Backdraft Modulating

Blade position/alignment Yes Yes Yes Yes

Spring position Yes N/A Yes N/A

Counterweight position N/A N/A Yes N/A

Shaft locks/quadrant locks N/A Yes N/A N/A

Linkage Yes Yes Yes Yes

Actuator adjustment Yes Yes N/A Yes



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Table 3-2 describes typical adjustments that may be considered for fans.

Table 3-2Typical Adjustments for HVAC Fans

Type of FanType of Adjustment

Centrifugal Axial

Adjust speed (sheave) Yes Yes

Inlet guide vane adjustment Yes Yes

Blade pitch N/A Yes

Belt tension Yes Yes

Re-center fan wheel Yes Yes

Drive alignment Yes Yes

3.1.10.2 Rebalancing HVAC Systems

The HVAC system/component engineer should consider retaking the readings as a first option ifthe corrective actions taken have not alleviated the performance problems. The data should thenbe evaluated to determine whether the resulting system/component performance is acceptable.These actions can be repeated as necessary in an iterative fashion until design requirements aremet. The engineer should then document the final data and configuration.

Sections 3.2 through 3.5 provide additional guidance on balancing new or existing air and/orwater systems and on temporary balancing/rebalancing of these systems.

3.2 Generic Process for New/Existing Air System Balancing

For additional or supporting information regarding the process presented in this report, seeSection 5 of NEBB “Procedural Standards for Testing, Adjusting, and Balancing ofEnvironmental Systems” [1].

3.2.1 Review Design and System Documentation

The first step in the balancing procedure is to become familiar with the complete systemoperation. This requires the engineer to review the reference design documents (such as airflowdiagrams, ductwork physical drawings, P&IDs, control logic drawings and details, electricalschematics, system descriptions, operating procedures, and reference specifications). The systemdesign requirements, such as total fan flow, main line and branch flows, individual terminalflows, and general area pressures, should be documented prior to performing any systembalancing to establish the appropriate acceptance criteria.



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Key Technical Point

The first step in the balancing procedure is to become familiar with thecomplete system operation.

In order to provide a complete plan of the system balancing, a markup of the plant physicaldrawings and/or the P&IDs should be prepared, depicting the locations of airflow measurements.All test locations should be labeled on the drawing.

Appendix A provides information on various HVAC systems commonly found at nuclear powerplants. Appendix B provides an overview of the various system components often installed inthese systems.

3.2.2 Perform System Walkdown

Prior to starting each system’s TAB work, a walkdown of the system should be made todetermine testability. A general walkdown of major system components, such as fans and filterhousings, should be performed to ensure that maintenance activities are not underway or needed.The following items should be evaluated at a minimum:

• Identify test port locations (that is, review for adequacy, number, and location); install newtest ports as necessary

• Ensure that scaffolding and ladders are available for access to test ports and/or balancingdevices

• Inspect the condition of the components (including balancing damper locking devices, as-leftposition indication, and installation of test ports)

• Ensure that communications equipment is available (for example, radios and sound-poweredphones)

• Verify that adequate lighting is available at the flow measurement and adjustment locations

• Inspect the HVAC system room/envelope walls, penetration seals, floors, and ceilings;confirm that all doors, windows, and other penetrations are positioned as required

• Verify that test equipment is available, in working condition, and possesses currentcalibration certificates

• Inspect damper positions

• Ensure that filters are installed or, if not installed, simulate their pressure gradients

Key Technical Point

Prior to starting each system’s TAB work, a walkdown of the system shouldbe made to determine testability. A general walkdown of major systemcomponents, such as fans and filter housings, should be performed to ensurethat maintenance activities are not underway or needed.



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Air Movement and Control Association (AMCA) Publication 201-90 [2] provides additionalinformation, if warranted by the HVAC engineer. System effects are pressure losses that may notbe initially accounted for in the initial fan selection and may result from undesirable fan inlet anddischarge conditions, such as the following:

• Improper inlet and/or outlet connections or configuration

• Nonuniform inlet flow

• Swirl at the fan inlet

System effects are normally introduced because of space or economic restrictions. For example,because of a fan’s location in relation to other equipment, it may be necessary to install an elbowclose to the fan discharge. This adds a system effect whose magnitude needs to be determined forthe particular configuration, based on the system effect curves found in AMCA 201-90 [2].

System effects can be accounted for by pressure drop calculations through the use of systemeffect factors (SEFs). Guidance for use and determination of SEFs for various fan configurationsis provided in AMCA 201-90 [2].

SEFs are given in terms of pressure loss value in units of inches of water gauge ( w.g.). The SEFis added directly to other calculated system losses to determine the system resistance and is usedto predict the fan performance when connected to the system.

When performing air balancing, system effects can cause low flow (high-pressure drops). TheHVAC engineer needs to be aware that this may occur. To account for low system flows, theHVAC engineer should observe the inlet and outlet conditions of the system fan and determinewhether any system effect may have been introduced.

For troubleshooting purposes, refer to AMCA Publication 202-98 [3] for initial symptom/causediagnosis. System effects are normally associated with low airflow or a high-pressure drop in asystem. Other causes, such as closed dampers or dirty filters, may also be attributed to lowairflow and high-pressure drops in a system. Refer to the fan/ductwork configurations providedin AMCA 201-90 [2] or other design books to determine whether system effects are affectingsystem airflow.

3.2.3 Define Critical System Lineup

The following actions should be taken to properly define the critical system lineup:

• Identify the condition of any filter in the system.

• If the system has multiple modes of operation, identify and balance the system to the criticalmode of operation. Check air and/or water flows with the system configured for the othermodes of operation, and initiate design changes as necessary to document any deviation.

• Define air/water flow parameters.

• Establish room/envelope differential pressure requirements.



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3.2.4 Operate System to Determine Overall System Flow

The following are key actions necessary to determine overall system flow:

• Begin air balancing with the supply system and repeat for the exhaust/return system.

• Obtain the total system flow. The HVAC engineer should select the flow measurementlocation, which could be at the fan suction or discharge or at multiple branch locations.

• Verify fan flow, pressure (total or static), and motor performance with the fan curve.

• Adjust flow as needed to approximately 120% of design flow (within system limitations). Toaccomplish this, the following actions may be considered:

– Adjust the inlet and outlet flow control dampers

– Change the fan blade pitch

– Adjust the inlet fan vanes (if present)

– Adjust or replace the fan/motor sheave

3.2.5 Measure Flow in Branch Ducts

Typically, the measurement should begin with the supply system and be repeated for the exhaustside. The HVAC engineer should adjust flow in branches to achieve approximately 10%additional flow using volume dampers for each branch.

3.2.6 Measure/Adjust Each Terminal Device in Each Branch

3.2.6.1 General Considerations

Flow should be adjusted to achieve approximately ±20% for each grille, if zone flow remainsacceptable. Plant-specific acceptance criteria should be referenced to ensure that designconditions are being considered.

3.2.6.2 Balancing by Ratio Method

The ratio method is commonly used to measure/adjust flow at terminal devices in branch lines.The following is a summary of this method:

1. Obtain the airflow at the last outlet on a branch.

2. Calculate the percentage of outlet flow to design flow at this point.

3. Obtain the next outlet flow upstream.




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5. Compare the percentages of the two points measured. If the percentages are within 10% ofone another, do not make adjustments. If they are not within 10%, make an adjustment to themost upstream outlet to bring the percentages closer together.

6. Obtain the next outlet flow upstream.


8. Compare the percentages of the two points measured. If the percentages are within 10% ofone another, do not make adjustments. If they are not within 10%, make an adjustment to themost upstream outlet to bring the percentages closer together.

9. Repeat the process until all the outlets on the branch are proportioned.

10. Move to the next branch and repeat the process.

11. When the individual outlets have been adequately adjusted on the branches, the branch linevolume dampers can be proportioned using the same process.

12. If the resulting total airflow requires adjustment, make a fan speed or blade adjustment, orreadjust the volume dampers and splitters and repeat the process.

13. Perform a final readout of the system.

3.2.7 Re-Measure Total System Flow

Adjustments should be made to total flow to the upper limit of plant-specific designrequirements. This can be accomplished by adjusting the fan or the main flow control damper.

3.2.8 Simulate Dirty Filter and Wetted Coil Conditions

Certain ventilation systems are needed to maintain credited design conditions, and these systemsshould be capable of generating design flows even with a dirty filter condition. Thus, it isnecessary to balance such systems with simulated dirty filter and wetted coil conditions.

Dirty filter and wetted coil conditions should be simulated on both the supply and exhaustportions of the system. Total flow should again be measured. Adjustments should be performedin an iterative manner to maintain total flow within the design tolerances of the system.

3.2.9 Final Balance or Adjustment in the Clean Mode

A final balance or adjustment should be made in the clean mode, considering plant-specific zonedifferential pressure gradients, zone temperatures, and humidity requirements.



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3.3 Generic Process for Temporary Air System Balancing or Rebalancing

Temporary balancing of a building’s ventilation system may be required when performingmaintenance on ventilation system components or while structural boundaries for the system(that is, walls and ceilings) are breached for other activities. Usually activities that could disrupta building’s ventilation system(s) are of short duration, the consequences of the disruption arenot significant, and upsetting the system balance can be tolerated for a short period. However,licensed nuclear facilities have to maintain their ventilation systems in order to comply with theirlicensing. When system conditions arise that are not explicitly addressed by the facility’s license,the licensee should evaluate the proposed configuration for compliance with the applicablelicense requirements.

Most nuclear facilities have to maintain their ventilation systems to enhance the movement of airfrom areas of low contamination toward areas of higher contamination. A basic corollary to thisrequirement is for the facilities to maintain a boundary and pressure differential or pressuregradient (∆P) between the environment and facility components with radioactive materials. Theboundary is usually a building structure, and the pressure differential is created by the building’sventilation system. If a specific pressure gradient is required to be maintained, the ventilationsystem or portions of it may have to be temporarily balanced while any equipment used tomaintain that building’s pressure gradient is removed from service for maintenance.

Temporary balancing uses the same techniques as initial balancing, except that the processbegins based on the as-found system balance. The basic steps for temporary balancing areaddressed in Sections 3.3.1 through 3.3.3.

3.3.1 Planning Steps

The following preliminary steps should be performed for temporary air system balancing orrebalancing:

1. Determine system design requirements and objectives.

2. Determine system licensing requirements (for example, FSARs and technical specifications[TSs]).

3. Verify system performance under the current configuration.

4. Determine the effect of the temporary condition on system performance.

5. Determine the system configuration necessary to maintain license requirements and designobjectives during the temporary condition.

6. Determine the sequence of component manipulations required to transition from the currentconfiguration to the temporary configuration, including changes in the condition (that is,breaching a wall).



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7. Determine which system parameters to monitor during the transition to the temporarycondition.

8. Determine the sequence of component manipulations required to restore the system to itsoriginal configuration and which system parameters to monitor during the transition.

9. Prepare work documents as required by the facility’s license and administrative controls,including a “back-out” provision for situations in which monitored parameters indicateconditions adverse to license requirements. Use standard balancing forms whenever possible;however, facility- and activity-specific forms may be desirable to consolidate data andfacilitate review and evaluation.

3.3.2 Execution

The following are the steps in executing temporary air system balancing or rebalancing:

1. If required, pre-brief the personnel involved or affected by the proposed change.

2. Document the initial configuration and critical parameters.

3. Verify that the configuration is compatible with the planned manipulations.

4. Sequence through the manipulations toward the temporary configuration.

5. Adjust controls to compensate for the actual system performance for the temporary balance.(This is similar to a final balance in an initial test and balance.)

6. Document the temporary configuration and critical parameters.

7. Verify that the work that required temporary balance has been completed.

8. Document the post-work temporary configuration and critical parameters.

9. Verify that the configuration is compatible with the planned manipulations for restoration.

10. Sequence through manipulations toward the initial configuration.

11. Adjust controls to compensate for actual system performance to achieve a final balance.

12. Document the final configuration and critical parameters.

13. Verify that the overall system performance is not affected.

3.3.3 Review and Documentation

The following steps describe reviewing and documenting temporary air system balancing orrebalancing:

1. Evaluate the data collected during the manipulations and temporary balancing described inSection 3.3.2.



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2. Determine the minimum critical activities and monitoring parameters for the possibility offuture similar work.

3. Document the entire evolution for future reference, and create actions for any lessonslearned.

3.4 Generic Process for New/Existing Water System Balancing

3.4.1 Review Design and System Documentation

The first step in the water balancing procedure is to become familiar with the complete systemoperation. This requires the engineer to review the reference design documents, including thewater flow diagrams, piping layout drawing, P&IDs, valve lineup, system descriptions, operatingprocedures, and component design requirements. The system design flow requirements (such aspump flow, system head pressure, branch flows, and flows to various coolers and heatexchangers) should be documented and appropriate acceptance criteria established prior toperforming any system adjustments.

In order to understand the scope of the balancing effort, the piping layout drawing should beused in conjunction with the water flow diagram and the P&IDs to depict the locations of flowmeasurements. The location of the balancing valves in the system should be noted.

Appendix A is provided to familiarize the reader with various HVAC systems commonly foundat nuclear power plants. Appendix B provides an overview of the various system componentsoften installed in these systems.

The water systems commonly used in HVAC systems are closed-loop chilled-water systems,closed-loop hot-water systems, open-loop chiller-condenser water systems, and the plantservice/river/raw water system. Balancing of the plant service water system will not be addressedin this document. The closed-loop water system is the most prevalent design employed at nuclearpower plants in support of HVAC systems; Section 3.5, “Generic Process for Temporary WaterSystem Balancing or Rebalancing,” considers this type of water system in the description.

The processes are provided for an initial balance of the water system, and some of the steps maynot be applicable to or recommended for rebalancing.

3.4.2 Perform Walkdown of the Water System

Prior to starting of the water balancing work, a walkdown of the system is recommended. Thefollowing items should be evaluated at a minimum:

• Identify the adequacy of any existing flow measurement stations, such as installed orificeplates. If water flow measurements are taken with the ultrasonic flow meter, identify flowmeasurement locations.

• The piping systems used in HVAC applications are usually insulated. Initiate a work orderfor insulation removal as deemed necessary according to plant procedure.



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• Ensure that scaffolding and ladders are available for access to flow measurement stations andbalancing valves.

• Inspect the lineup of the various components in the system (including pump, balancingvalves, and pressure gauges).

• Verify that all required pressure and temperature gauges are calibrated.

• Ensure that communications equipment is available (for example, radios and sound-poweredphones).

• Verify that adequate lighting is available at the flow measurement and adjustment locations.

• Verify that test equipment is available and in working condition and properly calibrated.

• Ensure that the pump suction strainer is flushed and/or clean.

Key Technical Point

Prior to starting the water balancing work, a walkdown of the system isrecommended.

3.4.3 Prerequisites

The following actions should be taken prior to starting any system adjustments to properly definethe critical system lineup:

1. On the recirculation pump curve, note the design point.

2. Note the design features of the various components in the system.

3. Open all isolation and balancing valves to the full-open position.

4. For cooling or heating systems with three-way (thermostatically controlled) mixing valves,close the valve port to the bypass line and open the valve port to the coil/terminal unit/heatexchanger.

5. Clean all strainers (and remove startup strainers, if present).

6. Verify that the system has been flushed and the water is clean.

7. Check the pump rotation.

8. Check the expansion tank for proper charge.

9. Verify that the system has been adequately vented and the air vent valves are closed.

10. Verify that the system makeup water valve is fully open and the pressure reducing valve iscorrectly set. In addition, verify the correct setting of any relief valve, if one is present in thesystem.

11. Check the operation of all three-way mixing valves.



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12. Check and set the operating temperature of the chiller or the boiler.

13. Ensure that applicable sections of the system air balancing are complete.

If the system has multiple modes of operation, identify and balance the system to its criticalmode of operation. Check the flows with the system aligned for the other modes of operation,and initiate design changes as necessary to document any deviation.

3.4.4 Operate System to Determine Overall System Flow

Perform the following steps to determine overall system flow:

• Start the recirculating water pump and adjust the balancing valve at the discharge of therecirculating pump to obtain system design water flow. Verify that the operating point is onthe pump curve.

• Adjust flow as needed to approximately 110–120% of the design flow without overloadingthe pump motor. To accomplish this, the following actions may be considered:

– Adjust the main system balancing valve

– Change the pump impeller size (personnel may need to procure a new impeller if alarger size is needed or grind off the impeller to obtain a smaller size)

3.4.5 Water Balancing Process

A reverse-return system is characterized by water that flows through similar components (that is,those components with the same pressure drops) and is configured so that the flow to the firstcomponent is the last one out to the return loop. The system is self-balancing, and it is notnecessary to adjust the flow through those similar components.

The following items should be considered in the water balancing process:

• In a multiple chiller or boiler system, adjust flow through each unit, starting with the one atthe farthest location. Make adjustments as necessary to obtain about +110% of the designflow.

• Each coil/terminal unit should have a balancing valve for flow adjustments. Adjust thebalancing valve to obtain design flow (-0, +10%) through the coil/terminal units whileverifying and maintaining pump design flow.

• For systems with three-way (thermostatically controlled) mixing valves, adjust the balancingvalve in the coil/terminal unit bypass piping. With the three-way mixing valve open to thecoil/terminal unit and closed to the bypass line, note the pressure drop through thecoil/terminal unit/heat exchanger. With the three-way mixing valve open to the bypass lineand closed to the coil/terminal unit/heat exchanger, adjust the balancing valve in the bypassline to obtain the same pressure drop as previously recorded through the coil/terminal unit/heat exchanger.



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• In systems with two-way (thermostatically controlled) valves, the pump usually has a pumpbypass or minimum system flow line with a modulating valve. With the two-way valvesclosed, adjust the pump bypass valve to obtain the necessary minimum flow for maintainingpump stability. Use information from the pump curve if it is not provided in the designdocuments.

• Allow the system to operate for 4 to 12 hours to let it equalize, and record the following data:

– Pump and pump motor data: nameplate data, flow, inlet and outlet pressures, andvolt amps

– Chiller or boiler: nameplate data, flow, inlet and outlet temperatures and pressures,volt amps, and ∆P

– Coil/terminal units: flow, inlet and outlet temperature and pressures, volt amps,and ∆P

3.5 Generic Process for Temporary Water System Balancing orRebalancing

A temporary water system is often installed to facilitate maintenance activities or replacement ofa component in the permanent system. For example, if a chiller(s) in a vital system (systemnecessary for plant operation) must be replaced while the plant is online, a temporary systemconsisting of a temporary chiller(s) with a pump may be installed to provide chilled water to thepermanent system. If such a system is installed, it will be necessary to balance it.

Temporary balancing requires the same techniques that initial balancing does; however, thepermanent system may not need any adjustments. The basic steps for temporary balancing areaddressed in the Sections 3.5.1 through 3.5.3.

3.5.1 Planning Steps

The following steps compose the planning phase of temporary water system balancing orrebalancing:

1. Determine makeup water requirements.

2. Determine the process to hydrostatically test any temporary piping installation prior toputting the temporary section in service.

3. Determine the process to functionally test the temporary system.

4. Determine the effect of the temporary system on the permanent system design requirementsand objectives.

5. Determine system licensing requirements (for example, FSAR and TSs).

6. Verify system performance under the current configuration.



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7. Determine the effect of the temporary system on the permanent system performance.

8. Determine the system configuration necessary to maintain license requirements and designobjectives during the temporary condition.

9. Determine the sequence of component manipulations required to transition from the currentconfiguration to the temporary configuration and vice versa.

10. Determine which system parameters to monitor during the transition to the temporarycondition.

11. Determine the sequence of component manipulations required to restore the system to itsoriginal configuration and which system parameters to monitor during the transition.

3.5.2 Execution

The following are the steps in executing temporary water system balancing or rebalancing:

1. If required, pre-brief the personnel involved or affected by the proposed change.

2. Document the initial configuration and critical parameters.

3. Verify that the configuration is compatible with the planned manipulations.

4. Sequence through the manipulations toward temporary configuration.

5. Adjust or install controls to allow the system to perform adequately in the temporary balanceconfiguration.

6. Document the temporary configuration and critical parameters.

7. Verify that the work that required temporary balance has been completed.

8. Document the post-work temporary configuration and critical parameters.

9. Verify that the configuration is compatible with the planned manipulations for restoration.

10. Sequence through the manipulations toward initial configuration.

11. Adjust controls to compensate for actual system performance to achieve a final balance.

12. Document the final configuration and critical parameters.

13. Verify that the overall system performance is not affected.



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3.5.3 Review and Documentation

The following steps describe reviewing and documenting temporary water system balancing orrebalancing:

1. Evaluate the data collected during the manipulations and temporary balancing described inSection 3.5.2.

2. Determine the minimum critical activities and monitoring parameters for the possibility ofperforming similar work in the future.

3. Document the entire evolution for future reference, and create actions for any lessonslearned.


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4 INSTRUMENTATION

Section 4.1 presents various types of TAB instrumentation commonly used to measure thesystem or component parameters presented in this report. Section 4.2 provides several tables thatillustrate the proper application of many of these instruments. Section 4.3 provides a table thatillustrates recommended ranges, accuracy, and calibration schedules for different types of TABinstrumentation.

4.1 Types of TAB Instrumentation

4.1.1 Airflow Measuring Instruments

4.1.1.1 U-Tube Manometer

The manometer is a simple and useful means of measuring partial vacuum and pressure for airand hydronic systems. It is so universally used that both the inch (mm) of water and inch (mm)of mercury have become accepted units of pressure measurements. In its simplest form, amanometer consists of a U-shaped glass tube partially filled with a liquid, such as tinted water oroil. The difference in height between the two fluid columns denotes the pressure differential.U-tube manometers are made in different sizes and are recommended for measuring pressuredrops above 1.0 inch w.g. (250 Pascals [Pa]) across filters, coils, fans, terminal devices, andsections of ductwork; they are not recommended for readings less than 1.0 inch w.g. (250 Pa).

Key Technical PointsManometer tubes should be chemically clean to be accurate and filled withthe correct fluid.Mercury is not an acceptable fluid for HVAC TAB work because of itspotential hazardous effects on personnel and on plant equipment.

Figure 4-1 illustrates a typical U-tube manometer commonly used in HVAC systems.


Instrumentation

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Figure 4-1Typical U-Tube Manometer (Courtesy of Meriam, Inc.)

4.1.1.2 Inclined/Vertical Manometer

The inclined and/or vertical manometer for airflow pressure reading is usually constructed froma solid, transparent block of plastic. It has an inclined scale that provides accurate air pressurereadings below 1.0 inch w.g. (250 Pa) and a vertical scale for reading greater pressures. Insteadof water, this instrument uses colored oil that is lighter than water. This means that although thescale reads in inches (mm) of water, it is longer than a standard rule measurement. Whenever amanometer is used, the oil must be at the same temperature as the environment in which themanometer will be used and of the correct specific gravity; otherwise, the reading will not becorrect. The manometer must be set level and mounted so that it does not vibrate.

Key Technical Point

When air pressures are extremely low, a micromanometer (hook gauge) orsome other more sensitive instrument should be used to ensure accuracy.

Figure 4-2 illustrates a typical inclined/vertical manometer commonly used in HVAC systems.


Instrumentation

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Figure 4-2Typical Inclined/Vertical Manometer (Courtesy of Meriam, Inc.)

4.1.1.3 Electronic (Digital) Manometer

The electronic manometer is designed to provide accurate readings at very low differentialpressures. Some multimeters measure an extremely wide range of pressures from 0.0001 to 60.00inches w.g. (0.025 to 15,000 Pa). Airflow and velocity are automatically corrected for the densityeffect of barometric pressure and temperature if the appropriate sensors are attached. Readingscan be stored and recalled with average and total functions. A specially designed grid enables thereading of face velocities at filter outlets, coil face velocities, and exhaust hood openings. Somemultimeters provide additional functions, such as temperature measurements.

Because the meter uses a time-weighted average for each reading, it is often difficult to measureand identify the pulsations in pressure. For this reason, it may be difficult to repeat single-pointreadings, especially at lower velocities.

Key Technical Point

The technical manual for the electronic manometer should be referenced todetermine if it provides results in ACFM, SCFM, or both. If the temperaturesensor is not used, the instrument reading on at least one electronicmanometer should be adjusted by calculation to either actual or standardconditions (ACFM or SCFM).


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Figure 4-3 illustrates a typical electronic (digital) manometer commonly used in HVAC systems.

Figure 4-3Typical Electronic (Digital) Manometer (Courtesy of Shortridge, Inc.)

4.1.1.4 Pitot Tube

The standard pitot tube, which is used in conjunction with a suitable pressure measuring device,provides a simple method of determining the air velocity in a duct. The pitot tube is of doubleconcentric tube construction, consisting of a 1/8-inch (3.2-mm) outside diameter inner tube (totalpressure) which is concentrically located inside of a 5/16-inch (8.0-mm) outside diameter outertube (static pressure). The outer “static” tube has eight equally spaced, 0.04-inch (1-mm)diameter holes around the circumference of the outer tube, located 2-1/4 inches (57 mm) backfrom the nose or open end of the pitot tube tip. Figure 4-4 illustrates typical details of a pitottube. Figures 4-5 and 4-6 illustrate typical configurations of pitot tubes.


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Figure 4-4Pitot Tube Details

Figure 4-5Typical Negative Static Pressure Pitot Tube and Manometer or Micromanometer Hookup


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Figure 4-6Typical Positive Static Pressure Pitot Tube and Manometer or Micromanometer Hookup

Smaller pitot tubes, commonly referred to as micro tubes, are available for use in smallerducting. They are designed to maintain the ratio of the hole spacing for both the total pressureand static pressure sensors but can not, by design, maintain the actual dimensions. These tubesare typically used when the cross-sectional area of the pitot tube is greater than 1/30 of the cross-sectional area of the ducting, with the pitot tube in the fully inserted position. At the base end, ortube connection end, the inner tube is open ended as at the head, and the outer tube has a sideoutlet tube connector perpendicular to the outer tube and directly parallel with and pointing inthe same direction as the head end of the pitot tube.

Both tubes have a 90º radius bend in them, located near the measuring end. This bend allows theopen end of the inner “impact” tube to be positioned so that it faces directly into the airstreamwhen 1) the main shaft of the pitot tube is perpendicular to the duct and 2) the side outlet staticpressure tube outlet connector is pointed in a parallel direction, with airflow (±10º) facingupstream.

Key Technical Point

Measurement of airstream total pressure is achieved by connecting the innertube outlet connector to one side of a manometer or gauge. If measuring apositive pressure, the pitot tube is connected to the high-pressure side of thepressure measuring device.


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Key Technical Point

Measurement of airstream static pressure is achieved by connecting the outertube side outlet connector to one side of a manometer or gauge. If measuringa negative pressure, the pitot tube is connected to the low-pressure side ofthe pressure measuring device.

Key Technical Point

Measurement of airstream velocity pressure is achieved by connecting boththe inner and the outer tube connectors to opposite sides of a manometer orgauge. The total pressure line is connected to the high-pressure port of thetest instrument, and the static pressure line is connected to the low-pressureside.

Accuracy of the measurements depends on the uniformity of flow and completeness of traverse.Several shapes and sizes of pitot tubes are available for different applications. A reasonably largespace is required, adjacent to the duct penetration, for maneuvering the instrument. Care shouldbe taken to avoid pinching the instrument tubing.

If static pressure, velocity pressure, and total pressure are to be measured simultaneously, threedraft gauges can be connected—depending on the specific application. In any case, the threevalues measured will then fulfill the equation: TP = SP + VP, where TP = total pressure, SP =static pressure, and VP = velocity pressure. In conducting tests, it is often sufficient to measureonly two of these three pressures because the third can be obtained by simple addition orsubtraction. Care should be taken, however, that the signs of the pressures monitored are correct.

If measuring velocity pressure, regardless of whether the ducting is at a positive or negativepressure, the pitot tube is connected to the pressure sensing instrument the same way. The totalpressure side is always connected to the high-pressure side of the instrument, and the staticpressure side is always connected to the low-pressure side of the instrument.

If measuring static pressures within the duct is required, the pitot-tube-to-instrument connectionwill be affected. If measuring a negative pressure duct, the static pressure port from the pitot tubemust be connected to the low-pressure side of the instrument. If the static pressure in the duct isat a positive pressure, the pitot tube must be connected to the high-pressure side of theinstrument.

The various connections between the pitot tube and gauge are frequently made with a good gradeof clear surgical tubing. Precaution must be taken so that all passages and connections are dry,clean, and free of leaks, sharp bends, and other obstructions. The branching out of the rubberhose can be accomplished by the use of a T-fitting or a two-stem nipple adapter.

The lines and various connections should be periodically tested for leaks. This leak check shouldbe performed as an integrated test to ensure that no one component may be attributing toerroneous readings.


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4.1.1.5 Pressure Gauge (Magnehelic®)

The Magnehelic® pressure gauge is operated by magnetic field linkage only, which makes itextremely sensitive and accurate. However, the construction of the gauge makes it resistant toshock and vibration. A zero calibration screw is located on the plastic cover. There areapproximately 30 available pressure ranges for this instrument.

Measurements should be made in midrange of the scale. The gauge should not be mounted on avibrating surface. The gauge should be held in the same position as when it is zeroed and shouldbe checked against a known pressure source with each use (some models are designed forvertical use only). Figure 4-7 illustrates a typical Magnehelic® pressure gauge commonly used inHVAC systems.

Figure 4-7Typical Pressure Gauge (Courtesy of Dwyer, Inc.)

4.1.1.6 Rotating Vane Anemometer (Mechanical Type)

The basic propeller or rotating vane anemometer consists of a lightweight, wind-driven wheelconnected through a gear train to a set of recording dials that read the linear feet (meters) of airpassing through the wheel in a measured length of time. At low velocities, the friction drag of themechanism is considerable. To compensate for this, a gear train that overspeeds is commonlyused. For this reason, the correction is often additive at the lower range and subtractive at theupper range, with the least correction in the middle of the 200–2000 feet per minute (ft/min)(1–10 meters per second [m/s]) ranges. Most older instruments are not sensitive enough for usebelow 200 ft/min (1 m/s). Newer instruments can read velocities as low as 30 ft/min (0.15 m/s).

Because other instruments read in feet (meters), a timing instrument must be used to determinevelocity. Readings are usually timed for one minute, in which case the anemometer reading(when corrected according to a calibration curve) will give the result in feet per minute or metersper minute. For moderate velocities, it may be satisfactory to use a one-half minute timedinterval, repeated as a check.


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In the case of coils or filters, an uneven airflow is frequently found because of entrance or exitconditions and/or stratification. These variations are taken into account by moving the instrumentin a fixed pattern traverse to cover the entire surface so that the varying velocities may be addedand averaged. NEBB “Procedural Standards for Testing, Adjusting, and Balancing ofEnvironmental Systems” [1] provides additional guidance on how these instruments may beused. Figure 4-8 illustrates a typical mechanical rotating vane anemometer commonly used inHVAC systems.

Key Technical Point

In the case of coils or filters, an uneven airflow is frequently found becauseof entrance or exit conditions and/or stratification.

Figure 4-8Typical Mechanical Rotating Vane Anemometer

4.1.1.7 Electronic Rotating Vane Anemometer

The electronic rotating vane anemometer is a battery-operated, direct digital or analog readoutanemometer. Some have interchangeable remote rotating vane heads. The digital readout of thevelocity is automatically averaged for a fixed period, depending on the measured velocity andthe type of instrument. Analog instruments are direct readout with a choice of velocity scales.Figure 4-9 illustrates a typical electronic rotating vane anemometer commonly used in HVACsystems.


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Figure 4-9Typical Electronic Rotating Vane Anemometer

4.1.1.8 Deflecting Vane Anemometer

The deflecting vane anemometer operates by having pressure exerted on a vane that causes apointer to indicate that measured value. It does not depend on air density because of the sensingof pressure differential to indicate velocities. The instrument is provided and always used with adual-hose connection between the meter and the probes, except as noted in the followingparagraph.

One type of deflecting vane anemometer uses three interchangeable velocity probes: the lo-flow,diffuser, and pitot probes. The lo-flow probe is used in conjunction with the 0–300 ft/min (0–1.5m/s) scale for measuring terminal air velocities in rooms or open spaces and for measuring facevelocities at ventilating hoods, spray booths, and fume hoods. The lo-flow probe is directlymounted to the anemometer without the use of hoses. The pitot probe is used to measureairstream velocities in ducts. The diffuser probe is used to measure air velocity through bothsupply and return air terminals, using the proper air terminal “K or Ak” factor (effective area) forthe airflow calculation. This will return a result in cubic feet per minute (ft3/min).


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4.1.1.9 Thermal Anemometer

The operation of the thermal anemometer depends on the fact that the resistance of a heated wirewill change with its temperature. The probe of this instrument is provided with a special type ofwire element that is supplied with current from batteries contained in the instrument case. As airflows over the element in the probe, the temperature of the element is changed from those thatexist in still air, and the resistance change is indicated as velocity on the indicating scale of theinstrument. This instrument is used to measure very low air velocities (such as a filter velocity),room velocity, and the velocity of hood openings. Figure 4-10 illustrates a typical thermalanemometer commonly used in HVAC systems.

Figure 4-10Typical Thermal Anemometer (Courtesy of TSI, Inc.)

The probe that is used with this instrument is directional and must be located at the proper pointon the diffuser, grille, or traverse, as indicated by the manufacturer. Probes are subject to foulingby dust and corrosive air. Because this type of instrument displays data for standard conditions,corrections must be made if actual feet per minute are to be recorded.


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4.1.1.10 Flow Measuring Hood

The flow measuring hood is a device that covers the terminal air outlet device to facilitate takingair velocity or airflow. The conical or pyramid shaped hood can be used to collect all of the airsupplied to or returned from an air terminal and guide it over flow measuring instrumentation.Hoods are generally constructed so that the outlet tapers down to an effective area of 1 ft 2

(0.09 m2). A velocity measuring grid and calibrated manometer in the hood will read the airflowin cubic feet per minute.

The balancing cone or hood should be tailored for the particular job. The large end of the coneshould be sized to fit over the complete diffuser and should have a gasket around the perimeter toprevent leakage. Some digital instruments have memory, averaging, and printing capabilities.Flow measuring hoods should not be used where the discharge velocities of the terminal deviceare excessive or severely stratified. The best results are obtained when the flow measuring hoodhas repeat readings on similar terminals in the same direction. Figure 4-11 illustrates a typicalflow hood commonly used in HVAC systems.

Figure 4-11Typical Flow Hood

4.1.1.11 Smoke Devices

Smoke devices generally are used to study airflow and detect leaks. These devices come invarious sizes with different durations of burning time. Smoke devices employ a chemicalreaction from which highly visible, nontoxic smoke readily mixes with air, simplifying theobservation of flow patterns. When testing for leaks, sufficient smoke should be used to fill avolume 15 to 20 times larger than the duct or enclosure volume to be tested. Air motion ratesbelow 10 ft/min (0.5 m/s) can be measured with a stopwatch and distance determinations.


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Smoke sticks conveniently come in different sizes and provide an indicating stream of smoke.Some produce a single puff of smoke, and others smoke continuously for a few minutes to amaximum of 10 minutes. Smoke guns are valuable in tracing air currents and determining thedirection and velocity of airflow and the general behavior of either warm or cold air inconditioned rooms. Figure 4-12 illustrates a typical smoke gun commonly used in HVACsystems.

Figure 4-12Typical Smoke Gun

Aspirated fine powders, such as zinc sterate, may also be used in locating drafts, determining thevelocity of slow moving currents in a room, and obtaining a better understanding of air motion.The fine powders suspend in air for a significant time and float with the air currents. The powdercan be used to mark leakage points on doors with gaskets because it tends to stick to the surfaceat the leak. Zinc sterate and other powders are usually chemically inert and may often be usedwhere chemical smoke is prohibited.

4.1.2 Hydronic Instruments

4.1.2.1 Pressure Test Gauge

The calibrated pressure test gauge should be of a minimum “Grade A” quality; have a Bourdontube assembly made of stainless steel, alloy steel, Monel, or bronze; and a nonreflecting whiteface with black letter graduations conforming to ANSI/ASME Specification B40.1 [4]. Testgauges are usually 3-1/2 to 6 inches (8.9 to 15.2 cm) in diameter, with bottom or backconnections. Dials are available with pressure, vacuum, or compound ranges.

Dial gauges are used primarily for checking pump pressure; coil, chiller, and condenser pressuredrops; and pressure drops across orifice plates, valves, and other flow calibrated devices.

Pressure ranges should be selected so that the pressures to be measured fall in the middle two-thirds of the scale range. The gauge should not be exposed to pressures greater than themaximum dial reading. Similarly, a compound gauge should be used where it could be exposedto negative pressure (vacuum). Pressure pulsations can be reduced or eliminated by installing aneedle valve between the gauge and the system equipment or piping. Under extreme pulsatingconditions, a pulsation dampener or snubber may be installed.


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4.1.2.2 Differential Pressure Gauge

A differential pressure gauge is a dual-inlet, “Grade A” dual Bourdon tube pressure gauge with asingle indicating pointer on the dial face, indicating the pressure differential between the twomeasured pressures. The gauge can be calibrated in psi, inches w.g., or inches mercury. Thedifferential pressure gauge will automatically read the difference between two pressures.

Using a single test gauge, the gauge is alternately valved to the high-pressure side and the low-pressure side to determine the pressure differential. Such an arrangement eliminates any problemconcerning gauge elevations and virtually eliminates errors as a result of gauge calibration.

4.1.3 Rotation Measuring Instruments


Care should be taken when using any rotating measuring instrument inorder to avoid personal injury caused by inadvertent contact with therotating equipment.

4.1.3.1 Chronometric Tachometer

The chronometric tachometer is considered by some to be obsolete; however, it is still used. Itcombines a revolution counter and a stopwatch in one instrument. In using this instrument, its tipis placed in contact with the rotating shaft. Care should be taken to avoid personal injury when inproximity to the rotating element. The tachometer spindle will then turn with the shaft, althoughthe instrument will not indicate. To take a reading, the push button is pressed and then quicklyreleased. This sets the meter hand to zero, winds the stopwatch movement, and simultaneouslystarts both the revolution counter and the stopwatch.

Because the timing is automatically synchronized with the operation of the revolution counter,the human error that can occur when a revolution counter and separate stopwatch are used iseliminated. In general, the chronometric tachometer is the preferred type of instrument when theshaft end is accessible and has a countersunk hole.

Newer hand tachometers are available, capable of producing instantaneous rpm measurementreadings on a dial face (eddy current type); solid-state instruments with digital readouts are alsoavailable.

4.1.3.2 Contact Tachometer (Digital)

Contact tachometers are available in either liquid crystal display (LCD) or light-emitting diode(LED) displays in multi-ranges. Some have a memory feature to recall the last reading as well asmaximum and minimum readings. In addition, most have a measuring wheel for linear speeds.Figure 4-13 illustrates a typical contact reflective tachometer commonly used in HVAC systems.


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Figure 4-13Typical Contact Reflective Tachometer

4.1.3.3 Optical (Photo) Tachometer

The optical or photo tachometer uses a photocell that counts the pulses as the object rotates.Then, by use of a transistorized computer circuit, the tachometer produces a direct rpm reading(either digital or analog) on the instrument dial. Several features make it adaptable for use inmeasuring fan speeds. It is completely portable and is equipped with long-life batteries as itslight and power source. It has good accuracy, and any error can be reduced by using more thanone reflective marker at a different location on the rotating device. Its calibration can becontinually checked on most jobs by directing its beam to a fluorescent light and comparing theindicated reading against 7,200 on the rpm scale (at 60 Hz).

The optical tachometer does not have to be in contact with the rotating device. It indicatesinstantaneous speeds using a contrasting mark on the rotating device or reflective tape. It is agood instrument to use on in-line fans and other equipment where shaft ends are not accessible.It also may be used on equipment rotating at high speed.

4.1.3.4 Electronic Tachometer (Stroboscope)

The stroboscope is an electronic tachometer that uses an electrically flashing light. Thefrequency of the flashing light is electronically controlled and adjustable, and when it is adjustedto equal the frequency of the rotating machine, the machine will appear to stand still. Figure 4-14illustrates a typical stroboscope commonly used in HVAC systems.


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Figure 4-14Typical Electronic Tachometer (Stroboscope)

The stroboscope does not need to make contact with the machine being checked. Rather, thestroboscope light needs to be pointed toward the machine to illuminate a moving part for theoperator. The light flashes are of extremely short duration, and their frequency is adjustable byturning a knob on the stroboscope. When the frequency of the light flashes is the same as thespeed of the moving part being viewed, the part will be seen distantly only once each cycle, andthe moving part will appear to stand still. The corresponding frequency, or rpm, can be read froman analog or digital scale on the instrument.

Care should be taken to avoid reading multiples (or harmonics) of the actual rpm. Readingsshould be started at the lower end of the scale. The number of flashes per second should beslowly increased until a single image is obtained. To ensure that the reading is not a harmonic ofthe actual rotational speed, increase the number of flashes per minute by twice the current value.If a double image is observed, the original reading was the true rpm of the equipment. What isbeing observed is that the strobe is operating at twice the speed of the true rpm. If, on the otherhand, a single image is obtained after doubling the number of flashes per minute, the strobe wasset at a subharmonic of the actual rpm. This process should be repeated until the first doubleimage is obtained. The last reading before the double image appears will be the actual rpm of therotating equipment. The best results are obtained when the strobe is shined on a rotating objecthaving one unique mark, such as a keyway on the end of a shaft.

4.1.3.5 Dual-Function Tachometer

The dual-function tachometer provides both optical and contact measurements of rotation andlinear motions. Many allow a choice of up to 19 ranges, depending on the application. A digitaldisplay always indicates the unit of measurement to identify the operating range. The memoryfeature may often be used to recall the last, maximum, minimum, and/or average readings. Thistachometer’s compact size and light weight allow easy one-handed operation.


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4.1.4 Temperature Measuring Instruments

4.1.4.1 Glass Tube Thermometers

Mercury-filled glass tube thermometers have a useful temperature range from -40°F (-40°C) toover 400°F (204°C). They are available in a variety of standard temperature ranges, scalegraduations, and lengths. Mineral spirits thermometers have a typical useful range of -40°F to200°F (-40°F to 93°C).

The complete stem immersion calibrated thermometer, as the name implies, must be used withthe stem completely immersed in the fluid in which the temperature is to be measured. Ifcomplete immersion of the thermometer stem is not possible or practical, a correction must bemade for the amount of emergent liquid column. Thermometers calibrated for partial stemimmersion are more commonly used in conjunction with thermometer test wells designed toreceive them. No emergent stem correction is required for the partial stem immersion type.

When the temperatures of the surrounding surfaces are substantially different from the measuredfluid, there is considerable radiation effect upon the thermometer reading if the thermometer isleft unshielded or otherwise unprotected. Proper shielding or aspiration of the thermometer bulband stem can minimize these radiation effects. Thermometer wells are used to house the testthermometer at the desired location and permit the removal and insertion of a thermometerwithout requiring the removal or loss of the fluid in the system.

4.1.4.2 Dial Thermometers

Dial thermometers have either a rigid stem or a flexible capillary. They are constructed withvarious size dial heads, 1-3/4 to 5 inches (4.5 to 12.7 cm), with a stainless steel encapsulatedtemperature sensing element. Hermetically sealed, dial thermometers are rust-, dust-, and leak-proof and are actuated by sensitive bimetallic helix coils. Some can be field calibrated. Sensingelements range in length from 2-1/2 to 24 inches (6.4 to 61 cm) and are available in manytemperature ranges, with and without thermometer wells.

Dial thermometers are more rugged and more easily read than are glass tube thermometers, andthey are fairly inexpensive. Small dial thermometers usually use a bimetallic temperature sensingelement in the stem.

The flexible capillary dial thermometer has a large temperature sensing bulb connected to theinstrument with a capillary tube. The instrument contains a Bourdon tube, as with pressuregauges. The temperature sensing system consisting of the bulb, capillary tube, and Bourdon tubeand is charged with either a liquid or a gas. Temperature changes at the bulb cause the containedliquid or gas to expand or contract, causing a pointer to move over a graduated scale.

In using a dial thermometer, the stem or bulb must be immersed a sufficient distance to allowthis part of the thermometer to reach the temperature being measured. Because dial thermometershave a relatively long time lag, enough time must be allowed for the thermometer to reach asteady temperature measurement.


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4.1.4.3 Thermocouple Thermometers

Thermocouple thermometers and analog or digital pyrometers, normally used in measurementsof surface temperatures in heating and air conditioning applications, use a thermocouple as asensing device and a scale calibrated for direct reading of temperatures. Thermocoupletemperature sensing elements are remote from the instrument case and connected to it by wire orcables.

In piping and duct applications, note that the surface temperature of the conduit is not equal tothe gas or fluid temperature and that a relative comparison is more reliable than an absolutereliance on readings at a single circuit or terminal unit.

4.1.4.4 Electronic Thermometers

There are many types of rugged, lightweight, battery powered digital electronic thermometersthat are highly accurate with interchangeable probes and/or sensors. Types include resistancetemperature detectors (RTDs), thermistors, thermocouples, and diode sensors with either LCD orLED displays. Response time and ease of use vary among models and types.

Electronic thermometers may be used to check air or liquid temperatures, either immersed in thefluid stream or from surfaces. Resistance thermometers have longer response times than thethermocouple type. Electronic thermometers have the advantages of remote reading, goodprecision, and a flexible temperature range. Additionally, some electronic thermometers havemultiple connection points on the instrument case and a selector switch, enabling the use of anumber of temperature sensors placed in different locations and read one at a time by use of theselector switch.

4.1.4.5 Portable Noncontact Thermometers

These devices are rugged and simple to use. Most are equipped with a laser pointer to facilitatedetermining the location of the temperature measuring point. These devices work on theprinciple of infrared energy (which all objects above absolute zero radiate), rapidly respond totemperature changes, and, at close ranges, are useful for determining hot spots. The averageeffective range depends on the size of the object being measured and the clarity of the airbetween the object and the detector.

4.1.4.6 Psychrometers

The sling psychrometer consists of two liquid-filled thermometers, one of which has a cloth wickor sock around its bulb. The two thermometers are mounted side-by-side on a frame fitted with ahandle by which the device can be whirled with a steady motion through the surrounding air. Thewhirling motion is periodically stopped to permit readings of the wet and dry bulb thermometers(in that order) to be taken until consecutive readings become steady. Because of evaporation, thewet bulb thermometer indicates a lower temperature than the dry bulb thermometer does (unlessthe airstream is at 100% relative humidity [RH]; then both the wet bulb and dry bulbtemperatures are the same). The difference is known as the wet bulb depression. Figure 4-15illustrates a typical sling psychrometer commonly used in HVAC systems.


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Figure 4-15Typical Sling Psychrometer

Accurate wet bulb readings require an air velocity of 1000–1500 ft/min (5–7.5 m/s) across thewick; otherwise, a correction must be made. Therefore, an instrument with an 18-inch (46-cm)radius should be whirled at a rate of two revolutions per second. Significant errors will result ifthe wick becomes dirty or dry; therefore, a constant supply of distilled water should be used.Temperatures below 32°F (0°C) require special handling conditions.

Digital battery powered versions of the sling psychrometer are available that blow the ambientair over the wetted wick. These instruments are accurate and can be placed into confined areaswhere there is insufficient room to whirl a sling psychrometer.

4.1.4.7 Electronic Thermohygrometers

Unlike the psychrometer, the thermohygrometer does not use the cooling effect of the wet bulbto determine the moisture content in the air. Instead, a thin film capacitance sensor is used as asensing element in many instruments. As the moisture content and temperature change, theresistance in the sensor changes proportionally. The readout is normally in percent RH. Becausethe instruments do not rely upon evaporation for measurement, the need for airflow across thewetted wick or sock is eliminated. The sensing element needs only to be held in the sampled air.Typical measuring rate is 10–98% RH, 32–140°F (0–60°C). Figure 4-16 illustrates a typicalelectronic hygrometer commonly used in HVAC systems.


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Figure 4-16Typical Electronic Hygrometer

The thermohygrometer can be used to determine the psychrometric properties of air in much thesame way as the sling psychrometer. The reading can be plotted on a standard psychrometricchart from which all other psychrometric properties of the air can be determined. At RHs above90%, the accuracy of the sensor is decreased because of swelling of the sensing element.

4.1.4.8 Color Strip Temperature Indicators

These simple devices employ a temperature sensitive, chemically treated spot on a strip thatchanges color at certain specified temperatures. There are no moving parts, and employment isusually specified by the manufacturer.

4.1.5 Electrical Measuring Instruments


Care should be used when working around energized electrical equipment.

4.1.5.1 Voltammeter

The clamp-on voltammeter, with digital or analog readout, is used for taking field electricalmeasurements. This voltammeter often has trigger operated, clamp-on transformer jaws thatpermit the taking of current readings without interrupting electrical service. Most meters haveseveral scale ranges in amperes and volts. Two voltage test leads are furnished, which may bequick-connected into the voltammeter.


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When using the voltammeter, the proper range should first be selected. When in doubt, the usershould begin with the highest range for both voltage and amperage scales. Readings may betaken at the motor leads or from the load terminals of the starter. To determine the amperages ofsingle-phase motors, the clamp should be placed around one wire after the motor has beenstarted. When involved with three-phase current, readings should be taken on each of the threewires and averaged. If the average voltage delivered to the motor varies by more than a few voltsfrom the nameplate rating of the motor, several things can occur. A rise in voltage may damagethe motor and cause a drop in the amperage reading. A drop in the voltage will cause a rise in theamperage and may cause the overload protectors on the starter to trip. In either case, it isadvisable to document and report high- or low-voltage situations.

To measure voltage with portable test instruments, the meter should be set to the most suitablerange and the test lead probes connected firmly against the terminals or other surfaces of the lineunder test.

4.1.6 Hydronic Flow Measuring Devices

4.1.6.1 Venturi Tube and Orifice Plate

The venturi tube or orifice plate is a specific, fixed area reduction in the path of fluid flow,installed to produce a flow restriction and a pressure drop. The pressure differential (theupstream pressure minus the downstream pressure) is related to the velocity of the fluid. Thepressure differential also is equated to the flow in gallons per minute (gpm) (cubic meters persecond); however, the pressure drop is not equal to the velocity pressure drop. By accuratemeasurement of the pressure drop with a manometer at flow rates from zero fluid velocity to amaximum fluid velocity, established by a maximum practical pressure drop, a calibrated flowrange may be established. The flow range may then be plotted on a graph that reads pressuredrop versus flow rate, or the manometer scale may be graduated directly in the flow rate values.

The venturi tube, because of the streamlining effect of both the entrance and the recovery cone,produces a lower pressure loss for the same flow rate. Although the full venturi tube can beextremely accurate with no appreciable system pressure loss, it must then be extremely long.Unless such accuracy is required, a modified version with a shortened entrance and recoverycones may be employed. The modified tube generally provides adequate accuracy withacceptable system pressure losses for environmental systems.

4.1.6.2 Annular Flow Indicator

The annular flow indicator is a flow sensing and indicating system that is an adaptation of theprinciple of the pitot tube. The upstream sensing tube has a number of holes that face the flowand so are subjected to the total pressure (velocity pressure plus static pressure). The holes arespaced to be representative of equal annular areas of the pipe, in the manner of selecting pitottube traverse points. An equalizing tube arrangement within the upstream tube averages thepressures sensed at the various holes, and this pressure is transmitted to a pressure gauge. Thedownstream tube is similar to a reversed impact tube and senses a pressure equal to the staticpressure with minimum velocity pressure; this pressure is also transmitted to a gauge. Thedifference between the two pressures will indicate flow in gallons per minute. A differentialpressure gauge is used to directly read the pressure differential.


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4.1.6.3 Calibrated Balancing Valves

Calibrated balancing valves perform dual duty as flow measuring devices and as balancingvalves. They are similar to ordinary balancing valves; however, the manufacturer has 1) providedpressure taps into the inlet and outlet and 2) calibrated the device by setting up known flowquantities while measuring the resistance that results from the different valve positions. Thesepositions usually are graduated on the valve body (as a dial), and the handle has a pointer toindicate the reading. The manufacturer typically provides a chart or graph that illustrates thepercentage open to the valve (the dial settings), the pressure drop, and the resulting flow.

4.1.6.4 Ultrasonic Flow Meters

Ultrasonic flow meters are nonintrusive devices that measure fluid flow using ultrasonic soundwaves transmitted across the direction of flow within the pipe. When faced with a system flowbalance or when questions of adequate flow arise, these instruments may be significant whenthere are no system-installed flow orifices, which is normally the case. These ultrasonic flowmeasuring devices have been found to be as labor-saving at balancing a hydronic system as anair data multimeter is in balancing a ventilation system. However, because there is an element ofuncertainty regarding the application and the resulting accuracy of these devices, the user shouldconsider referring to the guidance found in EPRI TR-109634, Flow Meter Guideline [5].

4.1.6.5 V-Cone Flow Meters

The v-cone flow meter is a differential pressure flow measurement device, somewhat similar tothe venturi tube or orifice plate. A cone is positioned in the center of the pipe to increase thevelocity of the flowing fluid and create a differential flow rate. Two taps are provided to allowsensing the high and low pressures. Compared to other techniques, this device generally providesaccurate results with shorter lengths of straight pipe upstream and downstream of the measuringelement.

4.1.6.6 Coriolis Flow Meter

The principle of measurement for the Coriolis mass flow meter is based on the concept of anelement of fluid traveling at constant velocity in a pipe. This element of fluid exhibits zeroacceleration because the velocity is constant. If the pipe were rotated at the same time that theelement of fluid passes through, a Coriolis acceleration component would be produced on thefluid. The Coriolis acceleration component produces a force on the pipe that is proportional tothe mass flow rate and, as such, is the measured value in this type of flow meter. The Coriolisforce is induced by sinusoidally vibrating the tube in which the fluid is flowing about an axisformed between the inlet and the outlet sides of the tube, at the natural frequency of the device.On the inlet side of the tube, the fluid flows away from the axis of rotation while on the outletside, the flow is toward the axis of rotation. At any time, each half of the tube has a Coriolisacceleration force that is equal but opposite in direction.


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4-23

4.1.6.7 Vortex Shedding Flow Meter

The principle of measurement for a vortex flow meter is based on a phenomenon first explainedby von Kármán in 1912. This phenomenon can be produced when a bluff body is immersed in asteady stream of fluid. As the flow approaches the bluff body, the flow is split into two streams.The instability of the shear layer as a result of this splitting of the flow causes the fluid to roll upinto a well-defined vortex. After formation, the vortex sheds, and a second vortex begins to formon the opposite side of the bluff body. Under steady flow, the time required for the formation ofthe first and second vortexes is the same, and the formation time is proportional to the velocity ofthe fluid stream.

4.1.6.8 Location of Flow Devices

Flow measuring devices, including the orifice, venturi, and other types described in this section,give accurate and reliable readings only when fluid flow in the line is uniform and free ofturbulence. Because pipe fittings, such as elbows and valves, create turbulence andnonuniformity of flow, flow measuring elements must be installed far enough away from elbows,valves, and other sources of flow disturbance to permit both turbulence to subside and flow toregain uniformity.

Key Technical Point

Flow measuring elements should be installed far enough from elbows, valves,and other sources of flow disturbances.

This rule applies particularly to conditions upstream of the measuring element and, to a lesserextent, to conditions downstream. The manufacturers of flow measuring devices usually specifythe lengths of straight pipe required upstream and downstream of the measuring element.Lengths are specified in numbers of pipe diameters, so that the actual required lengths depend onthe size of the pipe. Requirements vary with the type of element and the types of fittings at theends of the straight pipe runs, ranging from about 5 to 25 pipe diameters upstream and 2 to 5pipe diameters downstream.

4.2 Applications for TAB Instrumentation

4.2.1 Airflow Measuring Instruments

Table 4-1 lists the commonly employed airflow measuring instruments along with theirrecommended uses and limitations. Section B.8 describes different types of permanentlyinstalled airflow measuring devices.


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Table 4-1Airflow Measuring Instruments

Instrument Recommended Uses Limitations

U-tubemanometer

Measurement of pressure of air andgas above 1.0 w.g. (250 Pa) andmeasuring low manifold gas pressures.

The manometer should be clean and used withthe correct fluid. It should not be used forreadings under 1 inch (2.5 cm) of differentialpressure.

Vertical inclinedmanometer

Measurement of pressure of air andgas above 0.02 inch w.g. (50 Pa).

Normally used with a pitot tube or astatic probe for the determination ofstatic, total, and velocity pressures induct systems.

Field calibration and leveling are requiredbefore each use. For extremely low pressures,a micromanometer or some other sensitiveinstrument should be used to ensure maximumaccuracy.

Micromanometer(electronic)

Measurement of very low pressures orvelocities.

Used for the calibration of otherinstrumentation.

Because some instruments use a time-weighted average for each reading, it is difficultto measure pressure with pulsations.

Pitot tube Used with a manometer for thedetermination of total, static, andvelocity pressures.

Its accuracy depends on the uniformity of flowand completeness of duct traverse. The pitottube and tubing must be dry, clean, and free ofleaks and sharp bends or obstructions.

Pressure gauge(Magnehelic®)

Used with static probes for thedetermination of static pressure orstatic pressure differential.

Readings should be made in midrange ofscale, zeroed and held in the same position,and checked against a known pressure sourcewith each use.

Anemometerrotating vane(mechanical andelectronic)

Measurement of velocities at airterminals, air inlets, and filters or coilbanks.

The total inlet area of the rotating vane must bein measured airflow. Correction factors mayapply.

Anemometerdeflecting vane

Measurement of velocities at airterminals and air inlets.

Instruments should not be used in extremetemperatures or contaminated conditions.

Anemometerthermal

Measurement of low velocities such asroom air currents and airflow at hoods,troffers, and other low-velocityapplications.

Care should be taken to endure the proper useof the instrument probe. Probes are subject tofouling by dust and corrosive air. Should not beused in a flammable or explosive atmosphere.Temperature corrections may apply.

Flow measuringhood

Direct measurement (in cubic feet perminute [cubic meters per second]) ofair distribution devices.

Flow measuring hoods should not be usedwhere the velocities of the terminal devices areexcessive. Flow measuring hoods redirect thenormal pattern of air diffusion that creates aslight, artificially imposed pressure drop in theduct branch at the terminal device. Somemanufacturers make provisions to correct forthis pressure drop. The capture hood usedshould provide a uniform velocity profile at thesensing grid or device.


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4-25

4.2.2 Hydronic Measuring Instruments

Table 4-2 lists the commonly employed hydronic measuring instruments along with theirrecommended uses and limitations.

Table 4-2Hydronic Measuring Instruments


Pressure testgauge(calibrated)

Static pressure measurements ofsystem equipment and/or piping.

Pressure gauges should be selected so thatthe pressures to be measured fall in themiddle two-thirds of the scale. The gaugeshould not be exposed to a pressure greateror less than the dial range. Pressures shouldbe applied slowly in order to prevent severestrain and possible loss of accuracy of thegauge.

Pressure gauge(differential)

Differential pressure measurementsof system equipment and/or piping.

Same limitations as the pressure test gauge.

Flow measuringdevices

Used to obtain highly accuratemeasurement of volume flow rates influid systems.

Must be used in accordance with therecommendations of the equipmentmanufacturer.

4.2.3 Rotation Measuring Instruments

Table 4-3 lists the commonly employed rotation measuring instruments along with theirrecommended uses and limitations.

Table 4-3Rotation Measuring Instruments


Revolutioncounter

Contact measurement of rotatingequipment speed.

Requires direct contact of the rotating shaft.Must be used in conjunction with accuratetiming devices.

Chronometrictachometer

Contact measurement of rotatingequipment speed.

Requires direct contact of the rotating shaft.

Contacttachometer

Contact measurement of rotating andlinear speeds.

Requires direct contact of the rotating shaftor device to be measured.

Electronictachometer(stroboscope)

Noncontact measurement of rotatingequipment.

Readings must be started at the lower end ofthe scale in order to avoid reading multiples(or harmonics) of the actual rpm.

Opticaltachometer

Noncontact measurement of rotatingequipment.

Must be held close to the object and at thecorrect angle. The rotating device must usereflective markings.

Dual-functiontachometer

Contact or noncontact measurementof rotating equipment and linearspeeds.

Same limitations as the optical tachometer.


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4.2.4 Temperature Measuring Instruments

Table 4-4 lists the commonly employed temperature measuring instruments along with theirrecommended uses and limitations.

Table 4-4Temperature Measuring Instruments


Glass tubethermometers

Measurement of temperatures of airand fluids.

Ambient conditions may impact themeasurement of fluid temperature. Glasstube thermometers require immersion in fluidor adequate test wells. Some applicationsprohibit the use within the work area ofinstruments containing mercury.

Dialthermometers

Measurement of temperatures of airand fluids.

Ambient conditions may impact themeasurement of fluid temperature. The stemor bulb must be immersed a sufficientdistance in the fluid in order to record anaccurate measurement. The time lag ofmeasurement is relatively long.

Thermocouplethermometers

Measurement of surfacetemperatures of pipes and ducts.

Surface temperatures of pipes and ductsmay not equal the fluid temperature withinbecause of the thermal conductivity of thematerial.

Electronicthermometers

Measurement of temperatures of airand fluids. Measurement of surfacetemperatures of pipes and ducts.

Use this instrument within the recommendedrange. Use thermal probes in accordancewith the recommendations of themanufacturer.

Portablenoncontactthermometers

Identification of hot spots onequipment, general area temperaturemeasurement, and checking thetemperature of uninsulated ducts.

Does not work effectively in dusty or smokyatmospheres. The size of the measuring spotis a function of the thermometer’s distancefrom the object.

Psychrometers Measurement of dry and wet bulb airtemperatures.

Accurate wet bulb measurements require anair velocity between 1000 and 1500 ft/min (5and 7.5 m/s) across the wick, or a correctionmust be made. Dirty or dry wicks will result insignificant error.

Electronicthermo-hygrometer

Measurement of dry and wet bulb airtemperatures and direct reading ofRH.

The accuracy of measurement above 90%RH is decreased as a result of swelling of thesensing element.


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4.3 Recommended Accuracy of TAB Instrumentation

Table 4-5 provides recommended ranges, accuracy, and calibration schedules for different typesof TAB instrumentation and is presented for illustrative purposes only. Licensees typically haveplant- or site-specific measuring and test equipment calibration and accuracy requirements,which should always be used in lieu of the values listed in Table 4-5.

Table 4-5Air and Hydronic Measuring Instruments

Function Range Minimum Accuracy TypicalCalibrationSchedule

Rotation measuring instrument 0 to 5000 rpm ±2% 24 months

-40 to -120°F(-40 to -84°C)

Within 1/2 of scale division 12 monthsTemperature measuring(immersion) instrument

0 to 220°F(-18 to 104°C)

Within 1/2 of scale division 12 months

-40 to -120°F(-40 to -84°C)

Within 1/2 of scale division 12 monthsTemperature measuring (air)instrument

0 to 220°F(-18 to 104°C)

Within 1/2 of scale division 12 months

Electrical measuring instrument 0 to 6000 Vac

0 to 100 amperes

0 to 30 Vdc

3% of full scale

3% of full scale

3% of full scale

12 months

12 months

12 months

Air pressure measuringinstrument

0 to 0.5 inch w.g.(0 to 125 Pa)

0 to 1 inch w.g.(0 to 250 Pa)

0 to 5 inches w.g.(0 to 1250 Pa)

0 to 18 inches w.g.(0 to 4500 Pa)

±0.01 inches w.g. (±2.5 Pa)

±0.02 inches w.g. (±5 Pa)

±0.20 inches w.g. (±50 Pa)

±0.50 inches w.g. (±125 Pa)

12 months


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Table 4-5 (cont.)Air and Hydronic Measuring Instruments

Function Range Minimum Accuracy TypicalCalibrationSchedule

Pitot tube 18 inches (45 cm) orlonger

36 inches (90 cm)

Not applicable Not applicable

Air velocity measuringinstrument

Minimum range of100 to 3000 ft/min(0.5 to 15 m/s)

±10% when used inaccordance with themanufacturer’srecommendations

12 months

Humidity measuring instrument 0 to 90% RH 2% RH range 12 months

Air volume measuringinstrument (direct reading flowhood)

Minimum range 50 to2500 CFM (typical)

±5% when used inaccordance with themanufacturer’srecommendations

12 months

Temperature measuringinstrument (contact)

Minimum range of0 to 240°F(-18 to 115°C)

±1% of full scale 12 months

Hydronic pressure measuringinstrument

0 to 30 psi (0 to 207kPa)

0 to 60 psi (0 to 414kPa)

0 to 200 psi (0 to 1.38MPa)

30 in. Hg to 30 psi(101 to 207 kPa)

30 in. Hg to 60 psi(101 to 414 kPa)

±1% of full scale

±1% of full scale

±1% of full scale

±1% of full scale

±1% of full scale

12 months

Hydronic differential pressureinstrument

Minimum range of

0 to 36 in. Hg (0 to121 kPa)

±1% of full scale 12 months


5-1

5 AIR AND WATER FLOW MEASUREMENTTECHNIQUES

5.1 Airside Flow Measurement

Airside flow measurement is normally accomplished in an air distribution system by firstestablishing the fan performance per AMCA-203 [6]. Ducted airflow measurements are typicallydetermined using the pitot traverse measurement technique. The pitot traverse measures flowingair velocity pressures and static pressures across a traverse plane in a duct location where airflowis as close to uniform flow as possible. The pitot traverse readings are tabulated, and air densityis determined. The pitot traverse data are used to determine the average velocity of the airflow.The density is determined in order to convert the airflow to standard volumetric airflow in SCFMor ACFM.

For coil face measurement techniques, refer to American Society of Heating, Refrigerating, andAir Conditioning Engineers (ASHRAE) “Flow Measurements at Coil Faces with VaneAnemometers: Statistical Correlation and Recommended Field Measurement Procedure” [7].

In cases where traverse readings cannot be obtained, anemometers can be used to measure the airvelocity at terminal locations; alternate flow measurement techniques (such as the tracer gastechnique described in Appendix F) can also be used.

5.1.1 Pitot Tube Traverse Methods

The volumetric flow rate through a cross-sectional area of ducting can be determined bymeasuring the local velocities at enough points to establish the average velocity at the traverselocation. The flow rate is calculated by taking the average of all velocity readings atpredetermined traverse points (depending on the method) and multiplying this average by thecross-sectional area of the duct. As a rule, based on the equal area rectangular duct method, thetraverse should consist of a minimum of 16 readings—but need not be more than 64 readings.The minimum and maximum number of readings is different for the three methods (that is, theequal area, log linear, and log Tchebycheff methods) described in Sections 5.1.1.1 through5.1.1.3.

The location of the traverse in a duct is very important. Ideally, airflow should be fullydeveloped and uniform at the traverse location; the only exception is lower velocities nearer tothe duct edge. The pitot tube must be held within ±10° of the airstream direction to ensure theaccuracy of this method. For the most accurate results, the traverse location should be at least


Air and Water Flow Measurement Techniques

5-2

eight duct diameters (the larger of the two values for rectangular ducts when the two sides arenot equal) downstream of any disturbances and a minimum of two diameters upstream of anydisturbances. When this is not possible (in many existing duct systems), the accuracy of thetraverse location should be evaluated when obtaining flow rates.

Currently, three methods can be used to determine the layout of a traverse: equal area, log linear,and log Tchebycheff (the original spelling is Chebyshev). Sections 5.1.1.1 through 5.1.1.3provide illustrations of these methods, which are also used to determine the location of the testports to be installed in the ducting.

All three methods will return almost identical results for round ducts. However, substantialdifferences between the log linear and the log Tchebycheff methods can exist when compared tothe equal area method results for rectangular ducts. This difference results in part from the equalarea method not taking into account the lower velocities near the duct wall. In most cases, apositive error (that is, overestimated flow rate compared to the other two methods) nearly alwaysresults when the equal area method is used. Results using the equal area method should beclosely evaluated because overestimation is nonconservative when flow is near requiredminimum values. The evaluation of flow measurement method, adjacent flow disturbances, theinstrument type, the variation among test personnel, and nonstandard air conditions are allfactors that should be considered.

Key Technical Point

Results using the equal area method should be closely evaluated if they arenear minimum acceptance values.

5.1.1.1 Equal Area Method

Rectangular Ducts

The most common method used in the United States is the equal area method. For a rectangularduct, this method divides the traverse plane into equal areas with the centers of each area nogreater than 6 inches (15.2 cm) from the center of an adjacent area. The exception to this is invery large ducts where the total number of velocity readings would exceed 64. Under thesecircumstances, the distance between points may be greater than 6 inches (15.2 cm). The equalarea method does not take into account the reduced airflow at the perimeter of the duct as do theother two methods. Each velocity reading is given equal weight in the averaging process. Forrectangular ducts, to determine the number of points that the pitot tube is to be positioned insidethe duct or where the test ports are to be located on the duct, take either the L (x) axis or the M(y) axis, in inches, and divide by six. If this number has a remainder, round up to the next higherinteger with no remainder. This is the minimum number of points to be used on this axis.



5-3

Example:

Assume a duct that has a dimension of 19 inches in the M (y) axis and 30 inches in the L (x) axis.

To calculate the minimum numbers of points at which the pitot tube is to be positioned inside theduct when traversing the 19-inch (M) axis, perform the following:

N = M(y)/6

N = 19/6 = 3.17 (This is rounded up to 4.)

This means the minimum number of points at which the pitot tube will be positioned is four.

Using a mathematical method:

Pitot Position 1 (PP1): (M/N)/2 = (19/4)/2 = 2.375” from the edge of the duct.

Pitot Position 2: M/N + PP1 = 19/4 + 2.375 = 7.125” from the edge of the duct.



Table 5-1Equal Area Method for a Rectangular Duct

Distance from the Edge of the Duct

(Multiply the duct dimension that the pitot tube is to traverse across by the numbersbelow, based on the number of points per test port. This distance is how far the pitot tube

will be from the edge of the duct for each point.)

Numberof Points

1 2 3 4 5 6 7 8

4 0.125 0.375 0.625 0.875

5 0.100 0.300 0.500 0.700 0.900

6 0.083 0.250 0.417 0.583 0.750 0.917

7 0.071 0.214 0.357 0.500 0.643 0.786 0.929

8 0.063 0.188 0.313 0.438 0.563 0.688 0.813 0.938

The position points can also be determined using Table 5-1:

Pitot Position 1: 19 x 0.125 = 2.375” from the edge of the duct.






5-4

If we desire to traverse the 30” (L) side, to calculate the position of the test ports that will need tobe installed on the duct, perform the following:

Total number of test ports to be installed:

N = 30/6 = 5.0 (This is the minimum number of test ports that will need to be installed.)

Using a mathematical method:

Test Port Position 1: (L/N)/2 = (30/5)/2 = 3.0” from the edge of the duct.

Test Port Position 2: (L/N) + TTP1 = (30/5) + 3.0 = 9.0” from the edge of the duct.




Calculate the position of each test port with regard to the edge of the duct using Table 5-1:

Test Port Position 1: 30 x 0.10 = 3.0” from the edge of the duct.





Round Ducts

The equal area method can also be applied for round ducts. It divides the cross-sectional area ofthe traverse plane into equal area “doughnuts.” Typically, two traverse planes are established 90°apart. The distance between each velocity measurement point increases as the traverse progressesfrom the edge of the duct (lower velocity) toward the center of the duct (higher velocity).Conversely, the distance between points decreases as the traverse passes the center of the ductand progresses to the opposite edge. No velocity readings are taken in the center of the duct. Theminimum number of readings can be 12 for very small ducts or up to 40 for very large ducts.Standard practice suggests ducts that are 8 inches (20.3 cm) in diameter or smaller should use 12points (6 in each plane); ducts between 8 and 12 inches (20.3 and 30.4 cm) should use 16 points(8 in each plane); and ducts larger than 12 inches (30.4 cm) should use a total of 20 or 40 points(10 or 20 in each plane). For ducts smaller than 12 (30.4 cm) inches, a micro pitot tube should beused. In all cases, each velocity reading is given equal weight in the averaging process.



5-5

Table 5-2Equal Area Method for a Round Duct


(Multiply the duct diameter by the number below)

Points perDiameter(Traverse)

1 2 3 4 5 6 7 8 9 10

1–6 0.043 0.146 0.296 0.704 0.854 0.957

1–8 0.032 0.105 0.194 0.323 0.677 0.806 0.895 0.968

1–10 0.026 0.082 0.146 0.226 0.342 0.658 0.774 0.854 0.918 0.974

1–20 1 and11

2 and12

3 and13

4 and14

5 and15

6 and16

7 and17

8 and18

9 and19

10 and20

1–10 0.013 0.039 0.067 0.097 0.129 0.165 0.204 0.250 0.306 0.388

11–20 0.612 0.694 0.750 0.796 0.835 0.871 0.903 0.933 0.961 0.987

Example:

Assume a round duct that has a diameter of 18 inches. Using Table 5-2, calculate the pitot tubeposition in each plane:













5-6

5.1.1.2 Log Linear Method

The second method is known as the log linear method and is based on the Nikuradse formula forfully developed flow. This is not a common method and is more complex than the other twomethods. Each velocity measurement point is based on a logarithmic distribution in one plane.The pitot tube position for each test port location uses a logarithmic value. This method is furthercomplicated by the weighting values applied to each velocity reading for a rectangular duct, asopposed to a round duct, where all velocity readings are weighted equally. For a rectangularduct, each velocity reading is multiplied by a weighting value (for example, 2/96, 3/96, 5/96, or6/96); all of these weighted values are then added to arrive at the average air velocity.

This method differs from the equal area for a round duct in that it uses three test port penetrationsthat are 60º apart, as opposed to the two duct penetrations that are 90º apart. Tables 5-3 and 5-4illustrate the log linear method. The minimum number of points for a rectangular duct is 26 andcan be anywhere from 18 to 30 for a round duct.

Twenty-six total points are shown.

Table 5-3Log Linear Method for a Rectangular Duct

Distance from the Center of the Duct – (x or L) or (y or M)PointNumber

1 2 3 4 5 6 7

x or L ±0.408 ±0.408 ±0.408 ±0.408 ±0.132 ±0.132 ±0.132

y or M ±0.466 ±0.408 ±0.250 0 ±0.466 ±0.250 ±0.132

F 2/96 2/96 5/96 6/96 3/96 3/96 6/96

Three diameters are shown, with each diameter having six points.

Table 5-4Log Linear Method for a Round Duct


(Multiply the duct diameter by the number below)

Pointsper

Diameter

1 2 3 4 5 6 7 8 9 10

6 0.032 0.135 0.321 0.679 0.865 0.968

8 0.021 0.117 0.184 0.345 0.655 0.816 0.883 0.979

10 0.019 0.077 0.153 0.217 0.362 0.638 0.783 0.847 0.923 0.981



5-7

Example:

Assume a rectangular duct that has a dimension of 17” x 17” and that there is a transition to around duct with a diameter of 18”. For the rectangular duct, the test ports are to be added to thebottom of the duct. According to Table 5-3, this would be along the L (x) axis. Test ports need tobe installed at the 1 and 5 positions relative to the duct centerline.

Test Port Position 1(1): 17 x 0.408 = 6.94” away from the center of the duct.

Because it is not always practical to mark the duct using the center as the reference point, theedge of the duct should be used. Because the center of the duct is 8.5” from the edge, subtracting6.94 from 8.5 will give the location relative to the edge of the duct.

Test Port Position 1(1): 8.5 – 6.94 = 1.56” from the edge of the duct.

Perform the same operation to determine the position of the second test port (number 5 onTable 5-3):

Test Port Position 2(5): 17 x 0.132 = 2.24” from the center of the duct.

Test Port Position 2(5): 8.5 – 2.24 = 6.26” from the edge of the duct.

Once the duct center has been reached, the 8.5 will now be additive and not subtractive.


Test Port Position 3(5): 8.5 + 2.24 = 10.74” from the edge of the duct.


Test Port Position 4(1): 8.5 + 6.94 = 15.44” from the edge of the duct.

After the test port position has been determined, the ports would be drilled out and test portcovers installed. The next step will be to determine the pitot tube position at each duct test portpenetration.

According to Table 5-3, it is determined that the pitot tube will traverse along the M (y) axis.Test ports one and four will have the same pitot tube spacing but differ from test ports two andthree, which are also the same. Likewise, test ports one and two and test ports three and fourhave several pitot positions that are the same: position one and five and positions three and six.To calculate pitot positions 1, 2, 3, and 4 below the center of the duct, for test ports 1 and 4perform the following:

Pitot Position 1: 17 x 0.466 = 7.92” from the center of the duct.

Pitot Position 1: 8.5 – 7.92 = 0.58” from the edge of the duct.



5-8







To calculate the pitot positions that are above the centerline of the duct, perform the following:


Pitot Position 1: 8.5 + 7.92 = 16.42” from the edge of the duct.







To calculate the pitot tube positions below the duct centerline for points 5, 6, and 7, at test ports2 and 3, perform the following:





5-9





The calculation for those points above the centerline of the duct is as follows:







The round duct is calculated in the same was as the equal area method; however, the values fromTable 5-4 are used. To calculate the test port location, first calculate the circumference of theduct using the following formula:

C = 2 π r

where:

C = circumference (inches)

π = 3.14159

r = radius (inches)



5-10

Divide the circumference by 360 (because there are 360 degrees in a circle), and multiply thisnumber by 60 (because the test ports are 60 degrees apart). This will give the distance betweenthe test ports.

2 x π x 9 = 56.55”

56.55/360 = 0.1571 x 60 = 9.42” (This is how far apart the test ports will be from oneanother.)

5.1.1.3 Tchebycheff Method

The third method is known as the log Tchebycheff method. It is similar to the log linear methodfor both the rectangular and round ducts; however, it is less complicated. This method uses alogarithmic distribution of velocities near the wall of the duct and polynomial distributionelsewhere. Tables 5-5 and 5-6 describe this method. All velocities are weighted equally.

Five rows are shown, with each row having six points.

Table 5-5Tchebycheff Method for a Rectangular Duct

Rows or Points per Row Distance from Centerline – (x or L) or (y or M)

5 0 ±0.212 ±0.426

6 ±0.063 ±0.265 ±0.439

7 0 ±0.134 ±0.297 ±0.447

Example:

Using Table 5-5, assume a duct that has a dimension of 30” in the L (x) axis and 19” in the M (y)axis. To determine the location of the test ports that are to be installed on the bottom of the duct,perform the following:

Test Port Position 1: 30 x 0.439 = 13.17” from the center of the duct.

Test Port Position 1: 15 – 13.17 = 1.83” from the edge of the duct.





5-11




Test Port Position 4: 15 + 1.89 = 16.89” from the edge of the duct.





To calculate the pitot tube position for each test port, use the 5-point section from Table 5-5 asfollows:


Test Port Position 1: 9.5 – 8.09 = 1.41” from the edge of the duct.






Test Port Position 4: 9.5 + 4.03 = 13.53” from the edge of the duct.



5-12


Test Port Position 5: 9.5 + 8.09 = 17.59” from the edge of the duct.

Two diameters are shown, with each radius having four points.

Table 5-6Tchebycheff Method for a Round Duct

Distance from the Edge of the Duct(Multiply the duct diameter by the number below)

Pointsper

Diameter1 2 3 4 5 6 7 8 9 10

6 0.032 0.138 0.312 0.688 0.862 0.968

8 0.024 0.100 0.194 0.334 0.666 0.806 0.900 0.976

10 0.019 0.076 0.155 0.205 0.357 0.643 0.795 0.845 0.924 0.981

The round duct is calculated in the same way as the equal area method; however, the values fromTable 5-6 are used.

5.1.1.4 Documentation of Traverse Data

Figures C-2 and C-3 illustrate the documenting of traverse data for round and rectangular ducts,respectively.

5.1.1.5 Airflow Traverse Qualification

To determine if a traverse is located at a qualified position, apply the following from Figure 5-1.For any given traverse, round or rectangular, first find either the highest velocity in feet perminute or velocity pressure in inches of water. Divide this number by 10. Of all the readingscombined, 75% or greater must be equal to or greater than this number. If the traverse does notmeet these criteria, the traverse must not be used and will need to be relocated. Relocation of thetraverse may require that more than one traverse will need to be located at various branch linesservicing the system.

As of this writing, this qualification standard is currently under review. The new proposal is asfollows:

• A total of 80–90% of the velocity measurements is greater than 10% of the maximumvelocity for any given traverse.

• Airflow should be at right angles to the traverse plane.



5-13

Figure 5-1Traverse Qualification (Courtesy of AMCA 203)

5.1.1.6 Examples

The following examples are for use in calculating the airflow from a traverse and determining ifit is in a qualified location:

• The equal area method for a rectangular duct

• The log Tchebycheff method for a round duct

• The log linear method for a rectangular duct

• Traverse qualification method

Example: Equal Area Method for a Rectangular Duct

Given a 17” x 17” duct with a design flow rate of 4500 SCFM and a velocity profile shown inTable 5-7, calculate the airflow using the equal area method.

Table 5-7Example of the Equal Area Method for a Rectangular Duct

Position 2-1/8”* 6-3/8” 10-5/8” 14-7/8”

1 ft/min 2078 2164 2235 2107

2 ft/min 2184 2091 2162 2125

3 ft/min 2259 2193 2199 2341

4 ft/min 2326 2371 2423 2432

Subtotal ft/min 8847 8819 9019 9005* 1 inch = 2.5 cm



5-14

Total ft/min = 8847 + 8819 + 9019 + 9005 = 35,690 ft/min

Average ft/min = 35,690/16 = 2231 ft/min

Duct area, in square feet = 17” x 17”/144 = 289 in2/144 = 2.01 ft2

Airflow in ft3/min = 2.01 ft2 x 2231 ft/min = 4484 ft3/min

Percent of design = 4484/4500 x 100 = 99.6% of design



5-15

Example: Log Tchebycheff Method for a Round Duct

For round duct of 18” that has a design of 4500 ft 3/min and the velocity profile shown in Table 5-8, calculate the airflow using the logTchebycheff method.

Table 5-8Example of the Log Tchebycheff Method for a Round Duct

Position 0.34”* 1.37” 2.79” 3.69” 6.43” 11.57” 14.31” 15.21” 16.63” 17.66” Subtotal

Vertical 2,113 2,123 2,192 2,178 2,192 2,626 2,738 2,749 2,522 2,231 23,664

Horizontal 2,549 2,605 2,588 2,492 2,349 2,525 2,818 2,808 2,616 2,197 25,547

* 1 inch = 2.5 cm

Total ft/min = 23664 + 25547 = 49,211 ft/min

Average ft/min = 49,211/20 = 2461 ft/min

Duct area in square feet = π r2 /144 = 3.14159 x 92/144 = 254.47 in2/144 = 1.77 ft2

Airflow in ft3/min = 1.77 ft2 x 2461 ft/min = 4356 ft3/min


Example: Log Linear Method for a Rectangular Duct

Given a 17” x 17” duct with a design flow rate of 4500 SCFM and a velocity profile shown in Table 5-9, calculate the airflow usingthe log linear method.



5-16

Table 5-9Log Linear Method for a Rectangular Duct

Position 0.58”*(1 and 5)

1.56”(2)

4.25 “(3 and 6)

6.26”(7)

8.50”(4)

10.74”(7)

12.75”(3 and 6)

15.44(2)

16.42(1 and 5)

1.56” (1) 1848 1818 2059 2161 2048 1907 1826

6.26” (5) 1867 2088 2206 2172 2197 1930

10.74” (5) 2332 2303 2224 2265 2290 2111

15.44” (1) 1716 1847 2410 2472 2423 2373 2223

* 1 inch = 2.5 cm

Table 5-10 shows the weighting values to be applied to each velocity.

Table 5-10Weighting Values to Be Applied to Each Velocity


1.56”(2)

4.25”(3 and 6)

6.26”(7)

8.50”(4)

10.74”(7)

12.75”(3 and 6)

15.44”(2)

16.42”(1 and 5)

1.56” (1) 2/96 2/96 5/96 6/96 5/96 2/96 2/96

6.26” (5) 3/96 3/96 6/96 6/96 3/96 3/96

10.74” (5) 3/96 3/96 6/96 6/96 3/96 3/96

15.44” (1) 2/96 2/96 5/96 6/96 5/96 2/96 2/96

* 1 inch = 2.5 cm



5-17

Table 5-11 shows the velocities after the weighting values are applied.

Table 5-11Velocities after the Weighting Values Are Applied


1.56”(2)

4.25”(3 and 6)

6.26”(7)

8.50”(4)

10.74”(7)

12.75”(3 and 6)

15.44”(2)

16.42”(1 and 5)

1.56” (1) 38.5 37.9 107.2 135.1 106.7 39.7 38.0

6.26” (5) 58.3 65.3 137.9 135.8 68.7 60.3

10.74” (5) 72.9 72.0 139.0 141.6 71.6 66.0

15.44” (1) 35.7 38.5 125.5 154.5 126.2 49.4 46.3

Subtotal 205.4 76.4 370.0 276.9 289.6 277.4 373.2 89.1 210.6

* 1 inch = 2.5 cm

ft/min = 205.4 + 76.4 + 370.0 + 276.9 + 289.6 + 277.4 + 373.2 + 89.1 + 210.6 = 2168.6 ft/min

Duct area in square feet = 17” x 17”/144 = 289 in2/144 = 2.01 ft2

Airflow in CFM = 2.01 ft2 x 2168.6 FPM = 4359 ft3/min


Example: Traverse Qualification Method

Using the previous example, determine if the traverse location is qualified.



5-18

First, identify the velocity that is the highest and the total number of points that compose thetraverse. The highest velocity is 2472 ft/min, located at the center of the duct at positions 8.5inches and 15.44 inches, and the total number of traverse points is 26. The highest velocity valueis then divided by 10.

2472/10 = 247.2

For any traverse, 75% of the total number of points must be larger than this calculated number.

Therefore:

26 x 0.75 = 19.5 (At least 20 of the 26 velocity readings must be above the value of247.2 ft/min.)

Because there are no readings less than 247 ft/min, this is a qualified traverse. If, however, therehad been more than six velocity readings that were less then 247, this traverse would need to berelocated or other methods would need to be applied.

5.2 Water Side Flow Measurement

5.2.1 Background

The TAB process for water systems is described in Sections 3.4 and 3.5. In general, water sideflow measurement normally consists of direct measurement of a pressure drop across an orificeor ultrasonic measurement techniques that directly measure water flow rate.

Section 2 of EPRI TR-109634 [5] provides a detailed description of flow measurement principlesalong with information on the following:

• Continuity of flow equation

• Bernoulli’s equation of energy

• Reynolds number

Section 2.12 of EPRI TR-109634 [5] provides a table comparing the relative costs of employingvarious types of flow meters for measuring water flow.

Sections 5.2.2 through 5.2.8 are excerpts from EPRI TR-109634 [5] that are provided as anoverview of the various methods available to measure the flow of incompressible fluids. EPRITR-109634 [5] should be consulted for additional information on mathematical equations used tocalculate flow using each type of measuring device.



5-19

5.2.2 Differential Pressure Producers

5.2.2.1 Principle of Measurement

The principle of measurement is based on the introduction of a differential pressure device (suchas orifice, nozzle, and venturi) into a flow stream for which a fluid is measured. The introductionof the differential pressure device creates a dynamic pressure difference between the upstreamand downstream sides of the device. The square root of the differential pressure is proportional tothe velocity of the fluid. Differential-pressure-producing flow meters determine an area-averagedthroat velocity from the measured pressure differential.

5.2.3 Multiport Averaging Pitots


The principle of measurement is based on a determination of the area-averaged velocity of theflow in a pipe through which fluid is running full. The multiport averaging pitot allows themeasurement of differential pressure between the high upstream pressure (also called the impactor stagnation pressure) and the lower downstream pressure (also called the suction pressurebecause it is lower than the pipe static pressure).

The multiport averaging pitot operates like a classical pitot tube, with the following exceptions:

• Instead of a static wall tap, an averaging pitot senses low pressure on the downstream side ofthe tube, increasing the net differential pressure measured by the flow element.

• The multiport averaging pitot has multiple ports (some types have multiple ports on both theupstream and downstream sides), which are located so that if weighted equally, the ports arerepresentative of the average flow in the pipe.

• Certain types of multiport averaging pitot tubes have a noncircular shape in order to negateboundary layer separation problems associated with cylindrical-shaped averaging pitot tubes.This design tends to provide a consistent point of separation over a large range of Reynoldsnumbers.

5.2.4 Pitot Tube Traverse


The principle of measurement for a pitot tube traverse is based on the integration of equalannular area point velocities over the flow area. As a result, this method provides the averageflow through the pipe (if the pipe is full). The pitot tube traverse method is used extensively inthe cooling tower industry to accurately determine the flow of water in the riser pipes of bothnatural and mechanical draft cooling towers. The pitot tube traverse is based on a minimum oftwo perpendicular traverses of the pipe diameter. This methodology is intended to accuratelyprovide an average fluid velocity profile at the measurement plane.



5-20

5.2.5 Ultrasonic Flow Meters


Ultrasonic flow meters operate by transmitting an ultrasonic signal into a flow stream todetermine the velocity of the fluid. The velocity is then converted to a volumetric flowmeasurement, using the flow area dimensions and flow profile coefficient. The following typesof ultrasonic flow meters are used for measurement of flow in closed conduits:

• Transit-time

• Doppler

• Cross-correlation

Although all methods provide a viable means of measuring fluid flow, the transit-time and cross-correlation methods are the most applicable for measuring fluid flow.

5.2.6 Magnetic Flow Meters


The magnetic flow meter is based on Faraday’s law of electromagnetic induction. When aconductive fluid passes through an applied magnetic field, a voltage is generated at right anglesto the axis of fluid flow and the applied magnetic field. The generated output voltage is asummation of individual voltages generated by differential volumes moving at discrete velocitiesacross the plane of the pipe. In 1961, Shercliff demonstrated that the voltage output signalrepresents the average velocity for an asymmetric velocity profile. If the magnetic field isconstant and the distance between the electrodes is fixed, the induced voltage is directlyproportional to the average velocity of the fluid.

5.2.7 Turbine Flow Meters


The principle of measurement for a turbine flow meter is based on a rotating element, which ispositioned in the flow stream such that the rotational speed of the rotor is proportional to thefluid stream velocity and, therefore, the flow through the measurement plane. A turbine flowmeter (the primary element) typically outputs a low-amplitude frequency signal, which is inputinto a signal conditioner (the secondary element). The signal conditioner converts the meteroutput to an analog signal proportional to the flow. Each meter has a characteristic K-factor,which relates output frequency to a volumetric unit (for example, pulses per gallon). These typesof flow devices are generically categorized as linear flow meters.


6-1

6 LESSONS LEARNED

6.1 How Abnormal Flow Alignment Affects Fan Performance

Situation: Within 12 hours of placing an air-handling unit (AHU) in an abnormal flow alignment,the fan experienced catastrophic failure. Subsequent review identified the abnormal flow paththat had resulted in the operation of the fan at a point on its curve outside of its associatedoperating class limits.

Key O&M Cost Point

Lesson learned: When setting up a fan, the operating class limits for that fanmust not be exceeded. Operating a fan outside its associated limits may leadto catastrophic failure.

6.2 Estimating Filter Pressure Gradients for Clean and Dirty Conditions

Situation: The initial balancing of a nuclear air cleanup system was performed using a simulatedfilter differential pressure for clean and dirty conditions to protect the air cleanup components. Asubsequent system flow check after installation of the permanent filters identified flows higherthan expected. A review of filter pressure drop identified that the actual clean filter condition wasless than the design values, which are based on the manufacturer’s nominal values. Theassociated fan was slowed down to achieve its design airflow.

Key Technical Point

Lesson learned: The manufacturer’s data for nominal pressure drop may behigher than the actual pressure drop and may result in airflow that isgreater than design.


Lessons Learned

6-2

6.3 Typical Failure Mechanism for Duct Access Doors

Situation: During a control room isolation, it was identified that the main control room pressureswere less than required. Subsequent system troubleshooting identified an access door, open in acommon duct, which penetrated the pressure boundary. The access door had apparently openedfrom duct vibration and years of system startups and shutdowns. The access door and similarcritical duct access doors were secured closed using screws.

Key Technical Point

Lesson learned: Duct access doors should have a positive closing mechanismthat is not subject to opening as a result of vibration and system starts andstops.

6.4 Typical Failure Mechanism for an Inlet Damper

Situation: During a system engineer walkdown, the normal main control room pressure wasidentified lower than expected. A subsequent walkdown of the equipment identified that the inletdamper to the operating AHU was not fully open. The damper was “helped” open, and theoperating AHU was left in service until maintenance could be performed.

Key Technical Point

Lesson learned: Periodic monitoring of building pressures can identifyequipment problems prior to failure and avoid potentially detrimentalsystem effects.

6.5 Typical Failure Mechanism for an Air-Handling Unit Fan

Situation: During a system engineer walkdown, the normal main control room pressure wasidentified lower than expected. A strobotach was used and identified an operating AHU fanspeed that was less than the latest performance data. Although no sounds were audible, the beltswere found to be loose and slipping, resulting in a fan flow rate of approximately 70% of design.

Key Technical Point

Lesson learned: Slipping belts are not always audible, and a strobotachshould be used to verify fan speed when fan flows are in question.


Lessons Learned

6-3

6.6 Pitot Tube Employment and Failure Mechanisms

Situation: During routine performance of standby gas treatment system (SBGT) testing,problems were encountered while verifying the train flow prior to performing the in-place filterleak test. Train flow data are obtained by performing 20-point pitot traverses in the two SBGTsystem exhaust ducts. These ducts are located in the base of the plant vent stack and areconstructed of 30-inch (76-cm) steel pipe. The traverse is located in a vertical section of pipeapproximately seven diameters downstream of any restriction. Flow for the north pipe was stableand reasonable; however, data taken for the south pipe yielded results that were inconsistent withexpected values. The surveillance test was suspended and troubleshooting commenced.

The flow test was re-performed with a different pair of technicians collecting the data, andsimilar results were obtained. The results of the flow data for the north and south pipes weresignificantly below the SBGT train design flow. Train design flow is 9000 ft3/min, and the resultsindicated flow in the 4000-ft3/min range. To confirm train flow, a vane anemometer was used tomeasure the average velocity at the SBGT suction grille on the refueling floor. These resultsyielded a flow of slightly more than 9000 ft3/min.

Based on the data obtained from the suction grille face traverse, the technicians’ attention wasfocused on the test equipment used on the south pipe pitot traverse. The pitot tube was closelyinspected and found to be in good condition. The 0- to 0.5-inch (0- to 13-mm) inclinedmanometer was then inspected. This manometer is fitted with integral shutoff valves at the high-and low-pressure connections, which allowed the device to be transported without fear of losingthe measuring fluid. A small leak on the high-pressure shutoff valve was discovered. Both valveswere replaced and the flow test repeated. Results of the test were acceptable, and the surveillancetest was resumed.

Key Technical Point

Lesson learned: Pitot tubes should be closely inspected prior to each use.During subsequent checks of pitot tubes, one was discovered with an internalcrack in the impact velocity sensing line. A simple way to check the impactpressure line is to connect the pitot tube to a pressure measuring device andpressurize the impact line, block the sensing port, and observe the pressuremeasuring device for any pressure decay.

Key Technical Point

Lesson learned: Inclined manometers with integral shut-off valves should bechecked for leaks in these valves. These valves contain two O-rings and mayclose off tightly but leak when opened for use. In addition, these valvesshould never be opened more than three-fourths of a turn: opening themmore than this can result in the failure of the sealing O-ring to make contactwith the sealing surface in the valve body.


Lessons Learned

6-4

Key Technical Point

Lesson learned: The tubing used to connect the pitot tube to the pressuremeasuring device should be verified to ensure that it is in good condition andfree of any leaks. The tightness of the impact line can be verified bypressurizing it and blocking the impact port on the pitot tube. However, thestatic sensing line cannot be tested in this manner. A visual inspection is thebest method of verifying the connecting tubing.

6.7 Misuse of Measurement Equipment

Situation: During a routine surveillance test to perform airflow measurements, airflows wereincorrectly recorded because of instrument misuse.

Technicians were to perform an airflow measurement on a safety-related AHU. They were usinga standard pitot tube that was attached to a 0- to 10-inch (0- to 25.4-cm) vertical inclinedmanometer. The instruments were obtained from the instrumentation and control (I&C) shop,which has a temperature controlled environment. The test instruments were taken to the joblocation and set up. The ambient temperature of the job location was lower than that in the I&Cshop.

The manometer uses a liquid as its indicating medium. Setup of the manometer consisted ofleveling the instrument, attaching the pressure sensing lines, and zeroing the display. After thiswas accomplished, the technicians took a break before returning to the job site.

After they returned, they began to perform the required surveillance test. After all of the datapoints were obtained, the airflow was calculated. The calculated airflow was found to be belowthe lower limit of the technical specification (TS) limits, which required the licensee to enter intoa limited condition of operation (LCO) of 24 hours.

After further evaluation, it was determined that the fluid in the manometer may have shrunk as aresult of the cooler environment in which the instrument was being used. Because the manometerhad not been re-zeroed after it had been introduced into the new temperature environment, thezero point had shifted to below the actual indicating zero point of the instrument.

After re-zeroing the manometer in the new environment, airflow measurements were performedagain. The test results indicated that the airflow was within the acceptable limits of the TS, andthe LCO was exited.

Key O&M Cost Point

Lesson learned: The technicians likely did not understand the limitations oftheir instrumentation. When moving a fluid-based instrument from oneenvironment to another, ample time should be allotted for the liquid to cometo equilibrium, or frequent checks should be made to ensure that the basepoint has not changed.


Lessons Learned

6-5

6.8 System and Component Interactions

Situation: The original task was to replace the adjustable sheaves on all six exhaust fans and twosupply fans with a fixed sheave assembly. The modification documents were prepared by designengineering to accomplish this task. A maintenance contractor working with the licenseediscussed this modification with maintenance management and suggested that this modificationwould be a candidate for using a timing belt arrangement with a cogged wheel in lieu of usingfixed sheaves.

Maintenance selected an arrangement for using a cogged wheel and a timing belt. This changecaused the fan speed to increase, and design engineering recalculated the resulting airflow as~4% increase (which was within the ±10% tolerance of the airflow requirements of the system).

The modification was completed and the fans returned to service. After the fans were returned tooperation, the fan breakers tripped. It was determined that the originally 60-Hp (4.5-W) fanmotors had been rewound to provide 75 Hp (5.6 W); however, the electrical motor cables werenever replaced. A review of the cable design determined that it was adequate for 100-ampservice. The breaker setting was 105 amps. Because the breakers can take ~25% over the rating,they were reset for 110 amps. This additional load was then given to the electrical engineeringdepartment to revise the diesel loading calculation. However, the calculation determined that thediesels could not support the increase in load.

The mechanical engineering department then determined that the inlet guide vanes (IGV) on thefans could be throttled closed ~15% to decrease the load and still be able to maintain the propercable load and breaker set point. The airflow for the fans was measured and found to be too low(~15% below the required amount). The airflow requirement was further reviewed to determineif the lower airflows were sufficient for this application. New (75-Hp) fan motors were alsoordered for this application.

During this time, the fans operated for approximately five days when both the inboard andoutboard bearings failed. New bearings were ordered by maintenance without coordinating withdesign engineering. After receipt, it was discovered that the bearings would not fit into thebearing housing, which then had to be modified. A calculation also was required to ensure thesuitability of the new bearings for this application. During the final step, it was discovered thatthe fan guard would not fit back over the new belts and bearings. A new fan guard was thenspecified and procured.

Key O&M Cost Point

Lesson learned: Postulate system effects prior to proceeding with whatappears to be a minor design modification.


Lessons Learned

6-6

6.9 How Flow Disturbances Can Affect Flow Measurement

Situation: This plant has four control room emergency ventilation system (CREVS) fans; eachfan is rated at 1000 ACFM and tested every 18 months to be within 900–1100 ACFM. Three ofthe four CREVS fans have two sets of test ports in the fan suction ductwork: one at ground levelin a short section of duct between the filter heater and filter housing and one in a straight sectionof duct in the overhead. The overhead test port location is not easily accessible; however, thereare many diameters of straight duct before and after the test ports. Both locations are 12-inch(30.5-cm) round duct. Prior testing had been done using a hot-wire anemometer at the groundlevel test ports. The next surveillance test was performed with an electronic air data multimeterat the overhead test ports. The individual CREVS unit was declared inoperable as a result of aflow measurement of 794 ACFM (the previous surveillance test had measured 917 ACFM). Thethrottling valve on the fan suction was adjusted to increase the fan flow rate. Testing of the othertwo units with test ports in straight duct resulted in similar out-of-specification lowmeasurements. A licensee event report (LER) was submitted. Test results showed that althoughthe two different instruments provided slightly different results, using the same instrument at thetwo locations provided results differing by over 10%.

Key Technical Point

Lesson learned: Flow measurement in a duct at a location with flowdisturbances can be significantly different (in this case over 10% greater)than at a location of long straight duct.

6.10 Proper Use of an Electronic Micromanometer

Situation: During a training class, an electronic micromanometer was used that had a temperatureprobe for automatically converting velocity measurements to standard conditions (that is, flowresult was SCFM). Station personnel then purchased two electronic micromanometers ofdifferent models by the same manufacturer. During system testing by two individuals, conflictingflow results were obtained. One person did not use the temperature probe and instead used thetemperature correction calculation to convert the instrument reading to SCFM. The other personused the temperature probe and assumed that the velocity reading was automatically converted tostandard conditions for SCFM results. Closer review of the instruction manuals determined thatusing the temperature probe converts to actual conditions (that is, flow results in ACFM) and thatthese models do not have the option for converting the velocity reading to standard conditions. Ifthe temperature probe is not used, the instrument reading must be converted by calculation toeither ACFM or SCFM results.

Key Technical Point

Lesson learned: Some electronic micromanometers provide a velocityreading that automatically converts to actual flow results (that is, ACFM) byusing the temperature probe. If the temperature probe is not used, theinstrument reading corresponds to neither SCFM nor ACFM.


Lessons Learned

6-7

6.11 Consideration of System Operating Conditions

Situation: The station’s emergency core cooling system (ECCS) pump room exhaust air cleanupsystem (PREACS) fans consist of two redundant standby fans, each rated at 36,000 ft3/min. Thefan flow rate (fan inlet damper position) was controlled by suction vacuum. A plant modificationwas performed, which changed the flow control method from a “suction vacuum” signal to a fan“discharge flow” signal. The controls for each fan were modified and individually functionallytested. Functional testing did not include simultaneous start of both fans. A few months later,during emergency bus functional testing, both ECCS PREACS fans automatically started asdesigned in response to a simulated safety injection signal—but then both fans tripped.

Investigation concluded that the fans had tripped when suction vacuum exceeded a trip point.The high-suction vacuum trip had not been modified and was still required in the controls. Whenfans were started individually, the trip point was not exceeded. A justification for continuedoperation (JCO) was written, and controls were put in place to have the fans start at 18,000ft3/min (one-half the flow rate), with administrative controls to manually adjust one fan to fullflow if only one fan is available.

Six months later, during functional testing on a different emergency bus, both ECCS PREACSfans automatically started as designed in response to a simulated safety injection signal, and thenboth fans again tripped. Investigation concluded that the testing following the previous recoveryeffort had not actually performed a complete system functional test, with dampers in theunfiltered lineup. That testing had pre-positioned all of the affected dampers, and then manuallystarted the fans—both individually and simultaneously. An attempt was made to provide a time-delay to allow for damper repositioning prior to fan start; however, this did not resolve theproblem. Extensive troubleshooting was performed, with round-the-clock engineering andtechnician coverage for over two weeks as the system was studied and tested. System controlswere adjusted and modified, and the previous JCO and administrative controls were revised toallow the system to be declared operable. Several plant modifications were initiated in order tocorrect the design concerns.

Key Technical Point

Lesson learned: All possible system operating conditions need to be fullyconsidered during the design and functional test phases.

6.12 Low Airflow in the Auxiliary Building Ventilation System

Situation: Because of low airflow conditions in the auxiliary building ventilation (ABV) system,a team of engineers from design, testing, and systems was assembled to troubleshoot the cause ofthe low-flow condition. The team was divided into smaller teams as follows. Some were toprepare the necessary documents to submit to the U.S. NRC to assure them that the plant couldbe operated safely even though the airflow through the ABV system was lower than theminimum specified in the TSs. Others prepared documents to realign the system for optimumconditions, and still others reviewed drawings of the building and the system to determine otherpossible corrective actions.


Lessons Learned

6-8

One engineer was assigned the task of performing a system walkdown for proper damperalignments. The result of the walkdown was the identification of a fire damper that was onlypartially closed (it did not drop properly and hung up in mid-position). If the fire damper hadbeen completely closed, an alarm would have sounded in the control room. The reduced airflowthrough that duct section caused higher airflow through another duct section that contained ahigh-energy line break (HELB) damper. The HELB damper closed, as it should have with anincrease of more than 25% airflow through it. This closure caused the reduction in the overallsystem airflow rate and is the reason that the TS airflow through the filters was inadequate(below 10% of nominal flow). When the fire damper was repositioned, the HELB damperreopened—and the system flow rate returned to normal.

Key O&M Cost Point

Lesson learned: The most important part of the TAB work occurs prior tothe start of the work: understanding how the system works and performingthe walkdown.


7-1

7 REFERENCES

In-Text References

1. National Environmental Balancing Bureau (NEBB), Procedural Standards for Testing,Adjusting, and Balancing of Environmental Systems. Sixth Edition, 1998.

2. Air Movement and Control Association (AMCA) 201-90, “Fans and Systems,” 1990.

3. Air Movement and Control Association (AMCA) 202-98, “Troubleshooting,” 1998.

4. American National Standards Institute/American Society of Mechanical Engineers(ANSI/ASME) Specification B40.1, “Gauges, Pressure Indicating, Dial Type, ElasticElement,” 1991.

5. Flow Meter Guideline. EPRI, Palo Alto, CA: 1999. TR-109634.

6. Air Movement and Control Association (AMCA) 203-95, “Field Performance Measurementof Fan Systems,” 1995.

7. H. J. Sauerer and R. H. Howell, “Flow Measurements at Coil Faces with VaneAnemometers: Statistical Correlation and Recommended Field Measurement Procedure.”American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE)Transaction. Vol. 96 (1990).

8. American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE),“Nuclear Facilities,” Applications Handbook. 1999.

9. Nuclear Regulatory Commission, Regulatory Guide 1.140, “Design, Testing andMaintenance Criteria for Normal Ventilation Exhaust System Air Filtration and AdsorptionUnits of Light-Water–Cooled Nuclear Power Plants.” (Revision 1, 1979; Revision 2, 2001).

10. Code of Federal Regulations, Title 10 Nuclear Regulatory Commission, Part 20, “Standardsfor Protection Against Radiation.”

11. Nuclear Regulatory Commission, Regulatory Guide 1.52 dated March 1,1978, “Design,Testing, and Maintenance Criteria for Post Accident Engineered Safety Feature AtmosphereCleanup System Air Filtration and Adsorption Units of Light-Water–Cooled Nuclear PowerPlants.” June 1973. (Revision 1, 1976; Revision 2, 1978; Revision 3, 2001).


References

7-2

12. Code of Federal Regulations, Title 10 Nuclear Regulatory Commission, Part 100,“Revocation, Suspension, and Modification of Licenses and Construction Permits forCause.”

13. Code of Federal Regulations, Title 10 Nuclear Regulatory Commission, Part 50, AppendixA, “General Design Criteria for Nuclear Power Plants.”

14. American National Standards Institute/American Society of Mechanical Engineers(ANSI/ASME) N509, “Nuclear Power Plant Air Cleaning Units and Components,” 1989.

15. American National Standards Institute/American Society of Mechanical Engineers(ANSI/ASME) AG-1, “Code on Nuclear Air and Gas Treatment,” 1997.

16. American National Standards Institute/American Society of Mechanical Engineers,(ANSI/ASME) N510, “Testing of Nuclear Air Treatment Systems.” 1995.

17. Institute of Electrical and Electronics Engineers, Inc., IEEE 484, “Recommended Practice forInstallation Design and Installation of Vented Lead-Acid Batteries for StationaryApplications,” 1996.

18. HVAC Fans and Dampers Maintenance Guide. EPRI, Palo Alto, CA: 1999. TR-112170.

19. American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE),Chapter 18, HVAC Systems and Equipment Manual.

20. American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE),Chapter 41, Applications Manual.

21. National Fire Protection Association (NFPA) Standard 90A, “Standard for the Installation ofAir Conditioning and Ventilating Systems,” 1999.

22. Underwriters Laboratories (UL) Standard 181, “Factory-Made Air Ducts and AirConnectors.”

23. National Fire Protection Association (NFPA) Standard 91, “Standard for Exhaust Systemsfor Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids,” 1999.

24. Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA), “HVACDuct Construction Standards – Metal and Flexible,” 1995.

25. Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA),“Rectangular Industrial Duct Construction Standards,” 1980.

26. American Institute of Steel Construction (AISC), “Manual of Steel Construction,” 1989.

27. American International Supply, Inc. (AISI), “Cold Formed Steel Design Manual,” 1989.

28. USNRC Generic Letter 89-13, “Service Water System Problems Affecting Safety-RelatedEquipment,” July 18, 1989.


References

7-3

29. American Society of Testing and Materials (ASTM) E 2029-99, “Standard Test Method forVolumetric and Mass Flow Rate Measurement in a Duct Using Tracer Gas Dilution,” 1999.

30. American National Standards Institute/American Society for Heating, Refrigerating, and AirConditioning Engineers (ANSI/ASHRAE) 111-88, “Practices for Measurement, Testing,Adjusting, and Balancing of Building Heating, Ventilation, Air Conditioning, andRefrigeration Systems,” 1988.

Other References

Associated Air Balance Council (AABC), “Procedures for Testing, Adjusting and Balancing.”

American Conference of Governmental Industrial Hygienists, Industrial Ventilation. 24th Edition,2001.

American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE),“Testing, Adjusting, and Balancing,” HVAC Applications.

American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE),“1997 Fundamentals,” Inch-Pound Edition, 1997.

Hydramotor Actuator Application and Maintenance Guide. EPRI, Palo Alto, CA: 2000.TR-112181.

Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA), HVACSystems - Testing, Adjusting and Balancing. Second Edition, July 1993.


A-1

A TYPES OF HVAC SYSTEMS

This appendix describes the various types of HVAC systems that are commonly installed in anuclear power plant. Much of the information contained in this appendix has been presentedgenerically in several industry-wide standards; ASHRAE “1999 Applications Handbook Chapter25 – Nuclear Facilities” [8] provides additional information on HVAC system design.

There are two types of commercial nuclear power plants currently in operation in the UnitedStates: the pressurized water reactor (PWR) and the boiling water reactor (BWR). The systemsdescribed in this appendix are typical of these two types of nuclear power plants but are notrepresentative of any particular plant design. Furthermore, a system described here may beapplicable to one type of nuclear power plant and not to the other. As such, users should consulttheir own plant-specific system design documents to determine system design parameters andconfigurations. This appendix also provides an example of a typical nuclear HVAC processairflow diagram.

A.1 Generic HVAC Functions

An HVAC system at a nuclear power plant will typically perform one of the following functions:

• Ventilation

• Equipment/area cooling

• Filtration (radioactivity control ventilation)

A.1.1 General Area Ventilation

These applications are common for the main plant areas and individual buildings (for example,the radwaste building and the turbine building). The ventilation systems normally used in theseapplications include large supply and exhaust fans. Heating coils are installed on the supply side.In addition, the ventilation requirements consider the relative building pressure requirementswith respect to adjacent buildings and the outside atmosphere.

A.1.2 Equipment/Area Cooling

These systems are designed to provide cooling to essential components necessary for safeshutdown or mitigation of an accident. The building exhaust and supply are sized to maintain thebuilding temperatures in a range that maximizes equipment life by keeping ambient temperaturesreasonably low (usually less than 104°F [40°C] for unoccupied spaces and less than 80°F [27°C]for occupied spaces).


Types of HVAC Systems

A-2

These systems may be in the form of a simple ventilation system, consisting of a supply and/orexhaust fan; an area/room cooler; or cooling coils installed on the normal ventilation supply unitsfor the building. Equipment area/cooling systems are normally maintained in normal alignmentand are automatically actuated during an accident event. Other systems are used only during anaccident event, such as those used for cooling the diesel generator units, emergency service waterpumps, and ECCS/engineered safety feature (ESF) pump rooms. A room cooler consists of fancoil units supplied by a safety-related cooling water source from either the plant service water oran ESF chilled water system.

A.1.3 Radioactivity Control Ventilation

Ventilation systems may control the flow of potentially radioactive effluent by 1) maintainingthe building or area at a negative (or positive) pressure relative to adjacent buildings and theoutside atmosphere and/or 2) using a nuclear air cleanup unit.

A.1.3.1 Nuclear Air Cleanup

The air cleanup unit usually consists of a demister, an electric heater, a prefilter, a high-efficiency particulate-air (HEPA) filter, and a charcoal adsorber followed by a second HEPAfilter or a final filter. The non-safety-related units are used for filtering air from exhaust systemsprior to release into the atmosphere and may be governed by Regulatory Guide (RG) 1.140 [9].This ensures that the plant maintains off-site radioactive releases within the limits required by10CFR20 [10] for normal operations. These units are typically found on ventilation exhaustsystems within buildings housing radioactive or potentially radioactive materials. They may alsobe found on vent headers, such as waste gas disposal or condenser vacuum exhaust.

The safety-related units are used for filtering air in the event of a design basis accident and maybe governed by RG 1.52 [11]. These units may be used for filtering exhaust air or for filteringsupply or recirculation air for habitability zones, such as the main control room and/or technicalsupport center (TSC). For exhaust units, the system is used for maintaining the associatedbuilding pressure at a slight negative pressure, typically -0.25 inch w.g. (-63 Pa), to ensure thatall leakage is into the building and properly filtered prior to being exhausted. This ensures thatthe off-site radioactive release is within the limits required by 10CFR100 [12] for accidentmitigation. The supply/recirculation filter unit is typically a component of the associatedhabitability zone’s ventilation system. This system maintains the habitability zone at a slightpositive pressure, typically 0.125 inch w.g. (32 Pa), to ensure that all leakage is directed outward.This ensures that the operator and TSC staff dose is maintained within the limits required by10CFR50, Appendix A [13]. These safety-related systems are typically designed to ANSI N509[14] or the AG-1 Code [15] and are tested in accordance with ASME N510 [16].

A.2 Air Systems Designated by the Buildings Serviced

The buildings in which heating and cooling services are installed can also designate HVACsystems at nuclear power plants.



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A.2.1 Containment/Reactor Building

A.2.1.1 General Description

The containment/reactor building completely encloses the primary containment, auxiliaryequipment, and refueling areas. Under normal conditions, the reactor building HVAC systemmaintains the design space conditions and minimizes the release of radioactivity to theenvironment. The HVAC system consists of a 100% outside air ventilation system. Outside air isfiltered, heated, or cooled as required prior to being distributed throughout the various buildingareas. Supplemental cooling in localized areas is provided by area/room coolers. The exhaust airflows from areas with the least contamination to the areas with higher levels of contamination.Prior to its exhaust to the environment, potentially contaminated air is filtered. All exhaust airlocations are monitored for radioactivity prior to discharging air into the environment. To ensurethat no unmonitored exfiltration occurs during normal operations, the ventilation systemsmaintain the reactor building at a negative pressure relative to the atmosphere.

A.2.1.2 Standby Gas Treatment System

Upon detection of abnormal plant conditions (such as high radiation in the exhaust air path) orupon loss of negative pressure, the normal HVAC system is deactivated and the reactor buildingisolated. After it is isolated using fast-closing, low-leakage isolation dampers, the reactorbuilding serves as a secondary containment boundary. This boundary is designed to contain anyleakage from the primary containment or refueling area following an accident.

After the secondary containment is isolated, the standby gas treatment system (SGTS) is startedto draw down the secondary containment and maintain the building at a negative pressurerelative to the environment. The SGTS exhausts air from the secondary containment to theenvironment through a safety-related filtration system. The capacity of the SGTS is based on theamount of exhaust air needed to reduce the pressure in the secondary containment in about 120seconds and maintain it at a negative pressure for the duration of the accident event. In additionto the SGTS, some designs include safety-related recirculating air systems within the secondarycontainment to mix, cool, and/or treat the air during accident conditions. These recirculationsystems use portions of the normal ventilation system ductwork.

Safe shutdown components are usually located in the secondary containment and, if the isolatedsecondary containment area is not cooled during accident conditions, it is often necessary todetermine the maximum temperatures that could be reached during the accident event. Allsafety-related components in the secondary containment must be environmentally qualified tooperate at these temperatures. In most plant designs, safety-related unit area/room coolersprovide the necessary cooling for the ECCS pumps.



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A.2.1.3 Containment Cooling

The following systems are typical for containment cooling in a PWR plant.

Reactor Containment Coolers - These units remove most of the heat load. Distribution of theair supply depends on the containment layout and the location of the major heat sources.

Reactor Cavity AHUs or Fans - These units are usually transfer fans without coils that providecool air to the reactor cavity.

Control Rod or Control Element Drive Mechanism (CRDM or CEDM) AHUs - The CRDMand CEDM are usually cooled by an induced-draft system using exhaust fans. Because the flowrates, pressure drops, and heat loads are generally high, it is desirable to cool the air before it isreturned to the containment atmosphere.

Essential Reactor Containment Cooling Units - The containment air cooling system (or a partof it) is normally designed to provide cooling after a postulated accident. The system is capableof performing at high temperature, high pressure, high humidity, and a high level ofradioactivity. Cooling coils can be provided with chilled water and/or raw service water. Systemdesign must accommodate both normal and accident conditions. The ductwork is designed toendure the rapid pressure buildup associated with accident conditions. Fan motors are sized tohandle the high-density air associated with accident conditions.

A.2.1.4 Containment Power Access Purge or Minipurge

This system usually consists of a supply and filtered exhaust system. At some plants, thesesystems are licensed to operate continuously and at others, they are operated as needed for pre-access into the containment.

A.2.1.5 Containment Refueling Purge

Ventilation is required to control the level of airborne radioactivity during refueling operation.Because the reactor is not under pressure during refueling, there are no restrictions on the size ofthe penetrations through the containment boundary. Large openings of 42 to 48 inches (106 to122 cm), each protected by double containment isolation valves, may be provided. The requiredventilation rate is typically based on one air change per hour. The system consists of a supplyAHU, double containment isolation valves at each supply and exhaust containment penetration,and an exhaust fan. As a minimum, HEPA filtration is recommended.

A.2.1.6 Containment Combustible Gas Control

In case of a loss-of-coolant accident (LOCA), when a strong solution of sodium hydroxide orboric acid is sprayed into the containment, various metals react and produce hydrogen. Inaddition, if some of the fuel rods are not covered with water, the fuel rod cladding can react with



A-5

steam at elevated temperatures to release hydrogen into the containment. Therefore, redundanthydrogen recombiners are needed to remove the air from the containment atmosphere,recombine the hydrogen with the oxygen, and return the air to the containment. The recombinersmay be backed up by special exhaust filtration trains.

A.2.2 Turbine Building

The HVAC system in the turbine building typically provides both general ventilation and heatremoval. In a BWR plant, radioactive steam is directly supplied to the main turbine, and a leak inthe general area could cause a release of airborne radioactivity. Release of airborne radioactivityis a possibility in turbine buildings, and thus the buildings are typically maintained at a negativepressure. The exhaust air from the turbine building is exhausted to the environment using non-safety-related filtration systems. Filtration requirements are based on the plant and siteconfiguration.

In a PWR plant, the air is typically exhausted to the outside without filtration, and no radiationdetection equipment is required.

A.2.3 Auxiliary Building

The auxiliary building contains a large amount of support equipment, much of which handlespotentially radioactive material. The building is usually air conditioned for equipment protection,and the exhaust air is filtered prior to its discharge into the environment to minimize the releaseof radioactivity.

The HVAC system is a once-through ventilation system. Localized cooling systems (that is,area/room coolers) augment the ventilation system as needed. The building is maintained atnegative pressure relative to the environment.

Sometimes, the normal and essential cooling functions may be provided by an area/room coolerthat has 1) normal and essential cooling coils and 2) a safety-related fan powered from a Class1E bus. The normal coil is served by the normal chilled water system and the essential coil fromthe ESF chilled water system or the plant service water system.

A.2.4 Control Room

The control room HVAC system serves the control room habitability zone, that is, those spacesthat must be maintained habitable following a postulated accident to allow the orderly shutdownof the reactor. The control room HVAC system performs the following functions:

• Controls the environmental conditions in the main control room

• Pressurizes or isolates the control room to prevent infiltration

• Reduces the radioactivity level in the room

• Protects the area from hazardous chemical fume intrusion

• Protects the area from noxious fumes, such as smoke from surrounding or outside areas



A-6

A.2.5 Emergency Electrical Switchgear Rooms

These rooms house the electrical switchgear that operates essential or safety-related equipment.The switchgear rooms are usually cooled in order to ensure that useful life of the electricalcomponent in the room is maintained and to prevent the loss of power circuits as a result oftemperature-related problems.

A.2.6 Control Cable Spreading Room

These rooms are located directly above and/or directly below the main control room. They maybe cooled by the same AHUs that serve the switchgear rooms or the main control room orindependently cooled and/or ventilated with a dedicated system.

A.2.7 Diesel Generator Building

The diesel generator building is usually ventilated with 100% outside air. The ventilation systemconsists of a combination of a supply fan and an exhaust fan or one of the two fans with exhaustor inlet louvers.

A.2.8 Battery Rooms

Batteries produce the necessary dc control power for use during loss of off-site power. In safety-related systems, battery rooms are normally maintained in standby status. Batteries generatehydrogen during charging and are temperature dependent for prolonging service life ormaintaining adequate capacity. Different types of batteries are available, and the optimumtemperature for all batteries is 77°F (25°C) for maintaining service life and capacity. Older plantsmay not meet this temperature requirement because the battery room may be ventilated simply tocontrol the amount of hydrogen. In these cases, the minimum room design temperature should befactored into the capacity sizing of the batteries. Higher room temperatures should be consideredin evaluating the service life of the batteries and determining the hydrogen evolution rate. Theexhaust system is designed to limit the hydrogen concentration to about 2% of the room volumeor the lowest of the levels specified by IEEE 484 [17], Occupational Safety and HealthAssociation (OSHA), and the lower explosive limit (LEL). If the ventilation rate is notdetermined based on the hydrogen generation rate, it can be established at a minimum rate of oneair change per hour.

A.2.9 Fuel-Handling Building

New and spent fuel is stored in the fuel-handling building. The building is air conditioned forequipment protection and ventilated with a once-through air system to control airborneradioactivity. Normally, the level of airborne radioactivity is so low that the normal exhaust maynot be filtered, although it is typically monitored. If significant airborne radioactivity is detected,the building is isolated and a safety-related exhaust system activated to maintain the area at anegative pressure.



A-7

A.2.10 Personnel Facilities

For nuclear power plants, this area usually includes decontamination facilities, laboratories, andmedical treatment rooms.

A.2.11 Pump Houses

Cooling water pumps are protected by houses that are often ventilated by fans to remove the heatfrom the pump motors. If the pumps are essential or safety-related, the ventilation equipment isalso classified as safety-related.

A.2.12 Radwaste Building

Radioactive waste other than spent fuel is stored, shredded, baled, or packaged for disposal inthis building. The building is air conditioned for equipment protection and ventilated to controlpotential airborne radioactivity. The air may require filtration through HEPA filters and/orcarbon adsorbers prior to release to the atmosphere.

A.2.13 Technical Support Center

The TSC is a facility located close to or within the control room complex and is designed for useby plant management and technical support personnel to provide assistance to control roomoperators during accident conditions.

In case of an accident, the TSC HVAC system must provide the same comfort and radiologicalhabitability conditions maintained in the control room. The system is generally designed tocommercial HVAC standards. An outside air filtration system (composed of HEPA-charcoal-HEPA) pressurizes the facility with filtered outside air during emergency conditions. The TSCHVAC system is not typically designed to safety-related standards.

A.3 Types of Water Systems Supporting HVAC Systems

Two types of water systems are commonly used in HVAC systems for temperature control: thehot water heating system and the chilled water cooling system.

For a hot water system, a hot water or a steam boiler is used as the heat source. If a steam boileris used as the heat source, a steam-to-water heat exchanger is used to generate hot water. For achilled water system, a water chiller is used as the cooling source. The chiller may be air-cooledor water-cooled. In the case of a water-cooled system, a condenser water system is used to rejectchiller condenser heat.



A-8

A.3.1 Hot Water Heating Systems

The hot water system consists of a boiler (electric, natural or propane gas, or fuel oil fired), arecirculating water pump, and piping network interconnecting various heating coils. The hotwater heating coils are used to heat air as needed for temperature control of various areas. Theflow to each heating coil is controlled by a two- or three-way control valve that modulates oropens and closes to control the flow of hot water to the heating coils. The control valves areusually thermostatically controlled. The flow rate of the hot water to the heating coil is based onthe temperature drop across the inlet and outlet of the heating coil. The total system flow is basedon the average temperature differential across the various heating coils.

System flow (gpm) = Total Heating Load (Btu/hr)/(∆T x 500)

where:

∆T is the average temperature differential across the various heating coils

500 is a constant, based on the specific heat and density of the water

A.3.2 Chilled Water Systems

The chilled water system consists of a chiller (centrifugal, reciprocating, screw, or absorptiontype), a recirculating water pump, and a piping network interconnecting various cooling coils.The chilled water-cooling coils are used to cool air as needed for space temperature or humiditycontrol of various areas. The chilled water flow to each cooling coil is usually controlled with atwo- or three-way control valve that modulates or opens and closes to control the flow of chilledwater to the cooling coils. The control valves are usually thermostatically controlled. Chilledwater flow to the cooling coil is based on the temperature rise in the chilled water flow across theinlet and outlet of the cooling coil. The total system flow is based on the average temperaturedifferential across the various cooling coils.

System flow (gpm) = Total Sensible Heat Load (Btu/hr)/(∆T x 500)

where:

∆T is the average temperature differential across the various cooling coils

500 is a constant, based on the specific heat and density of the water

A.3.3 Hot and Chilled Water Systems with Ethylene or Propylene Glycol

The user should be aware that the addition of glycol in the system affects the selection criteria ofthe heat transfer source (that is, chiller or boiler), the size of the cooling or heating coils, theperformance of the recirculating water pump, and the pressure loss in the piping system. Forexample, a 20% glycol/80% water mixture in a heating or cooling system reduces the heattransfer capacity by as much as 10% and the pump efficiency by about 5% and increases thesystem pressure drop by about 25% at 50°F (10°C).



A-9

The constant of 500 used in the flow rate calculation needs to be corrected for systems withglycol because the amount of glycol in the system affects the heat transfer rate.

Correction factor: 500 (ρ/ρw) Cp

where:

ρ = Fluid density, lb/ft3

ρw = Density of water at 60°F, lb/ft3

Cp = Specific heat of fluid, Btu/lb °F

A.3.4 Chiller Condenser Water Flow

The condenser water system consists of a water-cooled chiller, a recirculating water pump, andan open- or closed-loop heat sink. Often a heat sink is used to reject the compression heat of achiller. The condenser water flow is sized based on the chiller selection, and the chillermanufacturer usually furnishes the condenser water flow rate.

A.3.5 Raw Water or Service Water Flow

Raw water or service water may be used as a source of cooling water in heat exchangers installedin HVAC systems.

A.3.6 Coil Performance Equations

The following equations are provided to assist the user when determining coil performance,ensuring that temperature and pressure corrections are made as needed:

Total heat load, q (Btu/h) = 4.5 x Airflow (ft3/min) x ∆h (change in air enthalpy)

Sensible heat load, q (Btu/h) = 1.1 x Airflow (ft3/min) x ∆T (change in air temperature)

Latent heat load, q (Btu/h) = 4840 x Airflow (ft 3/min) x ∆W (change in air humidityratio)

A.4 Example of an HVAC System Diagram

Figure A-1 illustrates a typical HVAC system diagram. It is provided for illustrative purposesonly and should not be used to perform plant-specific evaluations or analyses.



A-10

Figure A-1Turbine Room Ventilation One-Line Diagram


B-1

B TYPES OF HVAC EQUIPMENT

The information provided in Sections B.1 and B.2 is extracted from EPRI TR-112170, HVACFans and Dampers Maintenance Guide [18]. TR-112170 [18] provides additional information onfan and motor condition assessment as well as fan and damper maintenance issues andrecommendations.

B.1 Fans

The primary mechanical component in a ventilation system is the fan. Some industrialapplications require fans to move not only air, but also dispersed quantities of solid materials. Innuclear power plant applications, fan systems are typically designed for “clean-air” service. Thisallows the system designer to select from almost any of the basic fan types. Table 18.2 ofASHRAE “HVAC Systems and Equipment Manual” [19] describes the essential characteristicsof various fan types.

A suitable type of fan can be selected so that the conditions and requirements unique to a givenapplication can usually be accommodated. Four types of fans are available for selection by thedesigner:

• Centrifugal

• Axial

• Propeller

• Tubular centrifugal

Regardless of the type of fan, performance and selection criteria are described by the airflowquantity and developed pressure. For a given fan speed and size, the airflow quantity delivered isdirectly related to the pressure loss imparted between the fan inlet and outlet. These performanceparameters are plotted on a graph and result in a curve that describes the amount of flow that fanscan deliver at a given pressure (see Figure B-1). Additional information available on typical fancurves can include required horsepower and efficiency throughout the operational range of flowsand pressures described by the curve.


Types of HVAC Equipment

B-2

Figure B-1Typical Fan Performance Curve (Courtesy of AMCA 201-90)

In addition to methods directly related to the fan, dampers in ducted systems can also be adjustedto effectively increase or decrease flow within the limits of the fan curve. This adjustment can beaccomplished automatically or manually. Many ducted systems incorporate flow sensing devicesthat provide a control signal to a damper actuator that adjusts damper position as required todeliver the desired flow. In addition, manual balancing dampers are positioned to establish theinitial system flow conditions and are adjusted as necessary to selectively deliver flow to thevarious areas served by the ducted fan system. In either case, damper adjustments alter thesystem’s pressure characteristics, defining the operational point on the fan curve.



B-3

Ventilation systems most frequently include ductwork to distribute and direct airflow throughoutthe desired spaces and areas that they serve. Ducted systems also provide the designer withadditional flow control options because the systems accommodate modulating or manualbalancing dampers. System design should include an evaluation of the length of straight ductsections connected directly to the discharge of the fan. If insufficient straight duct is installed onthe fan’s discharge, performance is compromised because of the additional pressure lossesimparted. This system effect results from the flow profile at various distances from the dischargeof each type of fan (see Figure B-2). For axial fans, the minimum effective duct length isdetermined by the fan diameter and the resulting air velocity at design flow. For centrifugal fans,the minimum effective duct length is determined by the ratio of blast area and outlet area inconjunction with the orientation of the first fitting attached to the straight duct. The longer thestraight section attached to the fan discharge, the less the resulting pressure loss. For properapplication of SEFs to a specific ducted configuration, see AMCA 201-90 [2].

Figure B-2Fan Outlet Velocity Profiles (Courtesy of AMCA 201-90)



B-4

Although nuclear power plant facilities have large equipment rooms and service areas, theprimary ventilation system fans are typically large and, therefore, require long straight dischargeducts to minimize system effect pressure loss and maximize performance. This requirement isfrequently difficult to accommodate, resulting in flow patterns that tax the prescribed capabilitiesof the specified fan.

Un-ducted ventilation systems (for example, wall-mounted propeller fans and roof-mountedpropeller or centrifugal fans) are used in applications designed to transfer air between twospaces.

B.1.1 Types of Fans

B.1.1.1 Centrifugal Fans

Centrifugal fans are the most widely used because of their efficiency in moving both large andsmall quantities of air over a wide pressure range (see Figures B-3 and B-4a). The fan operatesby using a rotating impeller mounted inside of a scroll-type housing to impart energy to the air.For a given set of performance requirements (such as airflow quantity and developed pressure),centrifugal fans are typically larger than their vaneaxial counterparts. Flexibility in performancecharacteristics can be achieved in part by selecting from the available impeller styles. Theimpeller blades can be forward curved, backward curved, airfoil, or radial. For greatestefficiency, backward curved airfoil-shaped blades are usually preferred. Some space savingmight be realized with forward curved impeller wheel design. Standard configurations alsoinclude single- or double-width impellers and inlets. There is one drawback to a double-width,dual-inlet centrifugal fan. In dual-inlet systems with inlet vane damper control, potentialimplications exist for bearing damage if one of the inlet dampers fails to open or close. In thiscase, with one inlet damper open and the other closed, there is an unbalanced force on theimpeller of the fan. This will cause excess thrust wear on the impeller bearings. This thrust wearcan limit bearing life and result in unnecessary maintenance or equipment unavailability if theproblem goes unresolved. The consequences of this maintenance issue are normally taken intoconsideration during the design of the system.

Available drive types include direct and belt drive. Airflow quantity delivered by centrifugal fanscan be adjusted by means of inlet vanes positioned in line with the air inlet. By adjusting theposition of these vanes (partially open and closed), pressure loss is imparted to the airstream,altering the operating point on the fan head-flow curve. As pressure is induced to the airstreamby the inlet vanes, flow decreases as described by the fan curve (see Figure B-1). The speed ofthe impeller wheel can also be altered on belt-driven fans by changing the sheave sizes. Thisalters the speed of the wheel and, therefore, the performance characteristics of the fan. Themaximum impeller speed is limited by design and should not be exceeded. However, with thistype of alteration, the fan produces new flow and pressure characteristics and operates at flowand pressure conditions different from those described by the original fan curve. As can be seenin Figure B-3, the discharge of a centrifugal fan can be slightly obstructed by the lip of the scrollhousing. The reduced cross-sectional area of the discharge that results from this obstruction iscalled the blast area and is considered when determining the configuration of ductwork attachedto the discharge of a centrifugal fan.



B-5

Figure B-3Terminology for Centrifugal Fan Components (Courtesy of AMCA 201-90)

B.1.1.2 Axial Fans

In general, fans in the axial flow category tend to be smaller and less expensive than a centrifugalfan with comparable capacity. However, a unique characteristic of an axial fan is an increasedlevel of noise. Silencers can be installed to compensate for this effect; however, an additionalresistance is imparted to the system with this device. In this fan, as in all axial flow fans, airflows parallel to the fan shaft. Additionally, the fan hub and propeller blades are placed within acylindrical housing. Guide vanes are used before and/or after the blades to reduce airstreamrotation. The hub ratio in these types of fans is typically high, with fairly large hub diameters.The blades extend radially from the hub outward toward the housing, with the blade tips in fairlyclose tolerance with the inside of the housing surface. Flow in axial fans can be controlled by



B-6

adjusting the pitch of the blades. Stamped marks are provided on the blade shafts, which can berotated to produce different performance characteristics. In addition, templates can be obtainedfrom the fan manufacturer that result in more accurate positioning of the blades. As withcentrifugal fans, axial fans can be configured with either direct or belt drives. For belt drives,sheave sizes can be changed to alter the fan’s performance characteristics. Table B-1 provides ageneral characterization of fan types; Figure B-4 presents commonly used terminology for axialand tubular centrifugal fans.

Table B-1General Fan Attributes

Fan Attribute Axial Centrifugal

Cost Less expensive More expensive

Volumetric flow Higher Lower

Static pressure rise Lower Higher

Size vs. flow capacity Smaller Larger

Design complexity Simpler More complex



B-7

Figure B-4Terminology for Axial and Tubular Centrifugal Fans (Courtesy of AMCA 201-90)



B-8

B.1.1.3 Tubular Centrifugal Fans

Tubular centrifugal fans generally consist of a single-width airfoil wheel arranged in a cylinderto discharge air radially against the inside of the cylinder. Air is then deflected parallel with thefan shaft to provide straight-through flow. Vanes are sometimes used to recover static pressureand to straighten the airflow. The selection range is generally about the same as the scroll-type,BI or airfoil bladed wheel: approximately 50–85% of wide-open volume. However, becausethere is no housing of the turbulent airflow path through the fan, static efficiency is reduced to amaximum of about 72%, and the noise level is increased.

Frequently, the straight-through flow results in significant space saving, which is the mainadvantage of using tubular centrifugal fans.

B.1.1.4 Propeller Fans

Propeller fans are usually backward curved blade-type and can also be categorized as axial flow.However, these fans are distinguishable by their small hub ratios and lack of any substantialhousing and are used in applications that require air to be transferred—un-ducted—betweenspaces. Large-diameter propeller fans can be applied to move significant quantities of air, butdeveloped pressures are lower than those available with centrifugal or axial fans. They can oftenbe found in roof and wall exhaust applications. Control is possible with belt drive configurationsbut is usually not required because pressure variances across the fan do not occur in un-ductedapplications.

B.1.2 Types of Fan Drivers and Drives

Multiple options are available for the type of drive system used for fan applications; the twoprimary methods used are belt drive and direct drive. For nuclear installations, fans with externaldrives have a potential to allow air infiltration through the drive shaft opening and bearing. Careshould be exercised when applying this arrangement to potentially contaminated areas. Specialattention should be paid in sealing the seams of a drive belt tube in belt drive systems and inchecking for and repairing seal, shaft, and/or bearing leakage in direct drive systems duringregular maintenance.

B.1.2.1 Belt Drive

The most widely used drive method is the belt drive. This application is the most economical andprovides for good flexibility in range of application. With this system, the fan-to-motorconnection is established with a drive pulley (sheave) on the motor, a drive belt (“V” or cog),and a fan pulley. Fan speeds are determined by both the motor speed and the ratio of the pulleyson the motor and fan, allowing the fan and motor combination to be closely tuned to the serviceapplication. Furthermore, if future system changes alter the ventilation demand, a new sheave orpulley can be installed that will change the performance characteristics of the fan. Note thatinstalling a new sheave or pulley effectively produces a different fan performance curve. Prior toimplementing this type of change, a new system curve should be established and plotted with thenew fan curve to ensure that operation will not occur in an unstable region of the fan curve.



B-9

B.1.2.2 Direct Drive

Direct drive systems typically require less maintenance than belt drive systems because of thelack of replaceable belts and pulleys. In addition, fewer losses are expected in the powertransmission between the fan and motor. However, the disadvantage with this type of system isthe limited range of delivery flows and pressures available with the standard model fan andmotor combination. Speeds are limited to available motor speeds. When used with standardmodel fans, the range of resulting performance curves might not allow for optimum applicationto the subject system characteristics.

B.1.2.3 Variable Speed Motor Drive

This system incorporates an electronic control that sends a variable signal to the motor, whichmodulates the speed in accordance with the requirements of the system. This type of applicationis useful when consistent flows must be maintained in systems that have variable conditions.Sensors are placed at critical points in the ventilation system to monitor flow. As conditionschange (for example, filters load and fume hoods are placed in service), the sensors generate asignal and relay the change to the controller, which in turn modulates the fan speed to re-establish the design flow. These applications are sensitive to the associated installationparameters recommended by the manufacturers and should not be used unless the minimumrequirements for the location of sensors can be met. In addition, the variable speed drive systemsare far more expensive than the conventional drives.

B.2 Dampers

Dampers are used in ventilation systems to control environment pressures, temperatures, andflow rates. The types of dampers that are most commonly used in the nuclear industry are theisolation, control, backdraft, and fire damper. Dampers can be constructed with parallel oropposed blades, which can be flat or airfoil-shaped. Parallel blade dampers are better suited forisolation applications because of the undesirable flow pattern through the blades at partially openpositions. Either type of damper will benefit from an airfoil blade design, which will improveperformance of the system by reducing pressure loss associated with an open damper bladeobstructing the airstream.

B.2.1 Types of Dampers

B.2.1.1 Isolation Dampers

Isolation dampers are used to prevent the flow of air from one area to another and to containmetallic, silicone, or other types of seals (such as rubber and plastic). The seals are provided toensure that a leak tight seal exists when the damper is in the closed position. Frequently, twoisolation dampers are provided in series to ensure adequate protection for the area served. Thesedampers can be designed in both parallel and opposed blade configurations. Parallel bladeisolation damper design should be carefully constructed and installed with an appropriateactuator to ensure that the blades are positioned exactly parallel to the airstream when in the openposition. This will minimize the obstruction in the airstream and result in an optimized (that is,low) pressure drop associated with the open damper under full-flow conditions.



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Parallel blade dampers are generally more rugged, less expensive, and simpler in design thanopposed blade dampers. Parallel blade dampers should not be used in modulating applicationsbecause of their nonlinear flow characteristics (differences are described in detail in ASHRAE“Applications Manual” [20]). The flow characteristics of an opposed blade damper are morelinear than those of parallel blade dampers.

A further specialized type of isolation damper is the “bubble tight” damper. The bubble tightdamper provides the optimum effectiveness in airflow isolation between spaces. Whereas mostisolation dampers are rated for various amounts of leakage (based on the area of the damper),bubble tight dampers can provide zero leakage at reasonable differential pressures. Thesedampers often resemble valves in appearance and bulk, with a single blade providing a positiveseal. A heavy-duty actuator that will produce sufficient closing torque to the sealing surfaces isalso required. The cost of these dampers is high, and enhanced structural support is oftenrequired.

B.2.1.2 Control Dampers

Control dampers are used to balance ventilation system flow rates and pressures. Controldampers include two-position and modulating dampers. Specialty isolation dampers used in thenuclear industry vary in design while most control dampers are either parallel blade or opposedblade. The control damper can be operated automatically (using an actuator) to modulate thedamper and to allow an appropriate amount of airflow to achieve the desired operating parameter(that is, flow rate or temperature). As in the isolation damper, the actuator can be driven bypressurized air, an electric motor, or a motor-hydraulic unit (that is, electrohydraulic). Thedamper can also be operated manually and secured at the desired position based on similaroperating conditions. The control flexibility of a manual damper is limited because it is setinfrequently, usually during a system balance. Opposed blade configurations are normally thepreferred option because these dampers are usually positioned at some point between fully openand fully closed. This positioning eliminates the directionally deflected downstream flowcharacteristic of the parallel blade damper. In addition, the flow characteristics of an opposedblade damper are more linear than those of parallel blade dampers.

Most ventilation systems include manual balancing dampers. These dampers are usuallymanipulated only during the initial terminal air balance or subsequent balance verificationefforts. The following are the four primary types of manual balancing dampers:

• Terminal opposed blade dampers (OBDs or TOBs) are part of the supply, return, or exhausttermination device. These termination devices are commonly called diffusers, grilles, outlets,or registers; however, each has a specific function-related definition.

• Duct restricting volume dampers, usually referred to simply as volume dampers, can be 1)single or multiple blade and 2) parallel or opposed blade. These dampers are designed torestrict the flow through the duct by reducing the free area (see Figure B-5).



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• Splitter dampers are installed at duct branch fittings or “Y” fittings. These dampers areusually made from a single sheet of metal hinged at the neck of the fitting, with one or moreadjusting rods at the movable end. The dampers control the flow through the branch duct bycontrolling the effective cross-section of the branch and main duct.

• Scoop dampers are similar to splitter dampers but are used only with supply air outlets thatare installed on the main supply or trunk ducts. These dampers can be constructed from asingle sheet or multiple curved blades attached to rails. The damper movable end is extendedinto the airstream to direct the required airflow out of the outlet.



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Figure B-5Multiblade Volume Dampers (Courtesy of SMACNA)



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B.2.1.3 Inlet Vane Dampers

In some applications, dampers are added at the inlet of a fan. In many cases, this is done tocontrol the fan’s output characteristics or inlet swirl of the flow. In other cases, it is done tocontrol other system characteristics, such as system resistance. These inlet vane dampers oftenhave radially mounted blades. The movement of the blades can be used to induce variabledirection swirl or to reduce flow to a fan, which will affect the operating point on the fan curve.

Inlet vane dampers with fixed vanes are called inlet guide vanes (IGVs). IGVs are used toenhance the performance characteristics of a fan. The need for IGVs is determined during thedesign of a particular system. IGVs are often used with axial flow fans and compressors. Theyprovide direction to the flow before it enters the rotating blades.

Inlet vane dampers and IGVs should be maintained similarly to the other dampers and turningvanes. For variable vane dampers, the seals should be inspected to ensure that no damage hasoccurred and that the seal is sufficiently leak tight. The dampers should be inspected to ensurethat no debris is or could be caught in them. Debris in the dampers or ductwork could get caughtin the fan, causing damage. The dampers should be operated at a reasonable frequency, bothmanually and with any associated actuators. This operation will allow for the identification ofany inappropriate wear or mechanism damage. Finally, the components of the damper and theactuator should be visually inspected for signs of wear and/or damage.

In dual inlet systems with inlet vane damper control, potential implications exist for bearingdamage if one of the inlet dampers fails to open or close. In this case, with one inlet damper openand the other closed, there is an unbalanced force on the impeller of the fan. This unbalancedforce will cause excess thrust wear on the impeller bearings, illustrating the importance of properinspection of these dampers.

B.2.1.4 Backdraft Dampers

Backdraft dampers are used to allow the flow of air in one direction only. They also preventbackflow through nonoperating fans. This type of damper is useful in preventing the spread ofcontamination during times of unwanted reverse airflow (which could occur when a ventilationsystem is intentionally or unintentionally shut down). The backdraft damper is designed so thatthe damper blades will open when there is a differential pressure across the damper in the correctairflow direction. The damper blade linkage might have counterweights attached so that only asmall differential pressure will force open the damper. If the differential pressure across thedamper is eliminated or if a reverse differential pressure is created, the damper will close—preventing the flow of air in the reverse direction. There are drawbacks to backdraft dampers,however. There is an increased head loss associated with forcing the damper open and, becauseof the relatively small differential pressure that is needed to manipulate the damper, frictionlosses can alter the damper performance and even prevent its operation.



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B.2.1.5 Fire Dampers

Fire protection dampers are used to mitigate the spread of fire from one location to another byproviding a barrier between areas that would otherwise share a pathway through which a firecould spread. As with many large commercial structures, nuclear plants have partitions, floors,and ceilings capable of confining a fire to a given area for some specified time. When an air ductpasses through one of these fire barriers, a fire damper is generally required. Some of thesedampers are held open by fusible links, and others are actuated by smoke detectors or similardevices.

B.2.1.6 Smoke Dampers

Smoke dampers are used to control the spread of smoke through a ventilation system. Thesedampers might have actuators or be self-actuated and activated in a manner similar to firedampers. Although fire dampers are rated by hours of fire resistance, smoke dampers are ratedby leakage at pressure.

B.2.1.7 Louvers

Louvers are bladed assemblies designed for installation at interfaces between HVAC systemsand the outdoors. Louvers prevent weather (that is, precipitation) and large airborne objects (forexample, birds and leaves) from entering the system. Adjustable louvers operate like parallelblade dampers; however, they do not travel 90 degrees to full-open—rather, travel is limited toensure that a downward-sloped surface is presented to the outside of the building. Depending onclimate, louvers might be required to isolate freeze-sensitive components (that is, steam coils orchilled water coils) from freezing temperatures when the ventilation system is not operating.

B.2.2 Damper Actuators

Damper actuators are used to control the position of the dampers based on given input signals.These actuators could modulate the damper to any number of positions, or they could control thedamper to only the open or closed positions. The input signals are typically sent from a controllerthat monitors specific parameters. When a monitored parameter travels outside of a specifiedrange, the controller sends a signal to the actuator, which then adjusts the damper to bring theparameter back into the specified range. The typical monitored parameters are temperature, flowrate, and pressure. Actuators primarily used in the nuclear power industry are the electric,electrohydraulic, and pneumatic. The electric actuator is a motor connected to the damper anduses gears to adjust the damper. The electrohydraulic actuator uses a motor to pressurize ahydraulic system. The input signals are sent to the hydraulic system that controls the position ofa piston, connected to the damper linkage. The pneumatic actuator uses pressurized air and amanifold to control the damper position. Pneumatic actuators are typically pneumatic pistonactuators. Compressed air acts on a flexible diaphragm to position a shaft connected to thedamper.



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B.3 Heating and Cooling Coils

Air heating and cooling coils are used to heat or cool the air under forced convection. The totalcoil surface may consist of a single coil section or several coil sections assembled into a bank.The coils described in this section apply primarily to comfort heating and cooling for personneland equipment.

B.3.1 Steam Coils

Steam coils can be categorized as basic steam, steam distributing, or face-and-bypass. Basicsteam coils generally have smooth tubes with fins on the airside. The steam supply connection isat one end, and the tubes are pitched toward the condensate return, which is usually at theopposite end. Steam distributing coils most often incorporate perforated inner tubes thatdistribute steam evenly along the entire coil. The perforations perform like small steam ejectorjets that, when angle positioned in the inner tube, assist in removing condensate from inside theouter tube. Face-and-bypass steam coils have short sections of steam coils separated by airbypass openings. Airflow through the coil section or the bypass section is controlled by coil-and-bypass dampers that are linked together. As a freeze protection measure, large installations useface-and-bypass steam coils with vertical tubes.

B.3.2 Hot Water Heating Coils

Normal temperature hot water heating coils can be categorized as booster coils or standardheating coils. Booster coils (duct-mounted or reheat) are commonly found in variable air volumesystems. Standard heating coils are used in run-around systems, makeup air units, and heatingand ventilation systems. Most use the standard construction materials of copper tube andaluminum fins.

B.3.3 Cooling Coils

Fin and tube coils for cooling and dehumidifying air are made in two general classes: directexpansion and chilled water.

B.3.3.1 Refrigerant/Direct Expansion Coils

Direct expansion (DX) coils, as illustrated in Figure B-6, are commonly used in air conditioningrefrigeration applications as well as many types of commercial refrigeration systems. To becooled or dehumidified, air is circulated through the finned surface. In these coils, refrigerantevaporates inside the tubes, while air flows over the fins. Multiple rows and various tube patternsare used to achieve the desired heat transfer from the air to the circulating refrigerant. Coppertubes with copper or aluminum fins are most commonly used for efficient heat transfer.



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Figure B-6DX Coil (Courtesy of RAE Corporation)

Air conditioning systems need to operate efficiently at maximum design loads and partial loadconditions. Many types of system capacity controls are used to match the load requirement withsystem capacity. With refrigerant evaporator coils, this generally takes place in the form ofsurface reduction and/or one of the following:

• Single circuit

• Face split circuits

• Row split circuits

• Intertwined circuits

VAV systems use buildup coil banks or large AHUs with one refrigeration system. To balancesystem-capacity-to-load requirements, some form of face or row control is required. During thetime of reduced capacity, it is imperative to maintain a fully active dehumidification process atthe heat transfer coil. This is best accomplished by row control on standard DX coils or by use of“intertwined” refrigerant circuits. Row control is used for partial load surface balance.Whichever circuit is deactivated first results in full-face area operation of the remaining circuit,keeping the full volume of air in contact with active coil surfaces.

B.3.3.2 Chilled Water Cooling Coils

In this type of coil, chilled water or brine circulates through the tubes to the coil, and air flowsover the fins attached to the outside surface of the tubes. In most coils that use water as thecooling medium, the flow of water and air through the coil is in the opposite direction of eachother. Such an arrangement is known as counterflow. Parallel flow, in which the water and airflow through the coil in the same direction, is seldom used in commercial applications because ofthe additional surface required for a given set of conditions. In the counterflow design, the coldwater enters the coil where the coldest air is leaving the coil. In parallel flow, the cold waterenters the coil at the end the warm air is entering.



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Inlet water connections to chilled water cooling coils are usually made at the bottom tapping sothat the water flow is up through the coil and out the top tapping. There are two reasons forconnecting water coils in this manner. First, all of the air in the coil will be pushed ahead of thewater and accumulate in the top part of the coil, where it can be vented easily. Second, the coilwill remain completely filled with chilled water even though the control valve is closed.

B.3.4 Electric Heating Coils

An electric heating coil consists of a length of resistance wire (commonly nickel/chromium) towhich a voltage is applied. The resistance wire may be bare or sheathed.

B.4 Filters

HVAC filtration systems can be designed to remove either radioactive particles and/orradioactive gaseous iodine from the airstream. These systems filter potentially contaminatedexhaust air prior to discharge to the environment and may also filter potentially contaminatedmakeup air for power plant control rooms and TSCs.

The composition of the filter train is dictated by the type and concentration of the contaminant,the process air conditions, and the filtration levels required by the applicable regulations (forexample, RG 1.52 [11], RG 1.140 [9], ASME AG-1 [15], ASME N509 [14], 10CFR20 [10], and10CFR100 [12] [for the United States]). Filter trains may consist of one or more of the followingcomponents: prefilters, HEPA filters, charcoal filters (adsorbers), sand filters, heaters, anddemisters.

B.4.1 Dust Filters/Prefilters/Postfilters

Dust filters are selected for the efficiency required by the particular application and according toASHRAE. They are often used as prefilters for the special filters (listed in Sections B.4.2through B.4.4) to prevent them from being loaded with atmospheric dust and to minimizereplacement costs. Dust filters are also often used as postfilters downstream of the carbon filterin lieu of downstream HEPAs. In addition, these filters are used in supply side inlet applicationsto minimize dust entry into the plant.

B.4.2 HEPA Filters

Nuclear HEPA filters are used where there is a risk of particulate airborne radioactivity. Theconstruction and pre-use quality assurance (QA) testing of HEPA filters is specified in DOEstandards. The construction and QA testing of HEPA filters for use in nuclear power plants isspecified in ASME Standards AG-1 [15], N509 [14], and N510 [16]. Filter performancerequirements are based on penetration at a specified airflow and static pressure. For a 0.3-µmparticle, the penetration at rated airflow must not exceed 0.03%. HEPA filters are in-place testedand inspected when first installed and tested periodically thereafter. One or both of the followingmethods may be used for in-place testing of a stage of filtration: 1) mass flow testing of the stageas a whole or 2) testing of the individual filters and frame that make up the stage. In pre-use andin-place tests, an approved challenge agent, such as the aerosol dioctyl phthalate (DOP), must beused.



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B.4.3 Charcoal Adsorbers

Activated charcoal adsorbers are used mainly to remove radioactive iodine in its vapor orgaseous state. Bed depths are typically 2 or 4 inches (25 or 50 mm) but may be deeper. Thesefilters typically have an efficiency of 99.9% for elemental iodine and 95–99% for organic iodine.Charcoal filters lose efficiency rapidly as RH increases. They are often preceded by a heatingelement to keep the RH of the entering air below 70%.

Electric heating coils and/or demisters may be used to meet the RH conditions required forcharcoal filters. For safety-class systems, electric heating coils should be connected to theemergency power supply. Interlocks should be provided to prevent heater operation when theexhaust fan is de-energized.

Demisters (mist eliminators) are required to protect HEPA and charcoal filters if entrainedmoisture droplets are expected in the airstream. Demisters should be fire resistant.

B.4.4 Sand Filters

Sand filters consist of multiple beds of sand and gravel through which air is drawn. The air entersan inlet tunnel that runs the entire length of the filter. Smaller cross-sectional laterals runningperpendicular to the inlet tunnel distribute the air across the base of the sand. The air risesthrough several layers of various sizes of sand and gravel, typically at a rate of 5 ft/min (25mm/s). It is then collected in the outlet tunnel for discharge to the atmosphere.

B.5 Terminal Devices

A terminal is defined as a point where the controlled medium (fluid or energy) enters or leavesthe distribution system. In air systems, these terminals may be variable air or constant volumeboxes, registers, grilles, diffusers, louvers, and hoods. In water systems, these may be heattransfer coils, fan coil units, convectors, or finned-tube radiation or radiant panels.

Air terminals are the most noise-sensitive of all HVAC products because they are almost alwaysmounted in or directly over occupied spaces. They usually determine the residual backgroundnoise level from 125 to 2,000 Hz. The term air terminals has historically been used to describe anumber of devices that control airflows into occupied spaces at the zone (or individualtemperature control area) level. There are two types: those that control the amount of airflow to atemperature zone (air control units [ACUs] or, more commonly, boxes) and those that distributeor collect the flow of air (grilles, registers, and diffusers [GRDs]). On some occasions, the twofunctions are combined. Because these two elements are both the final components in manybuilt-up air delivery systems and the components closest to the building occupants, bothelements are critical components in the acoustical design of a space. A critical interplay alsoexists between acoustics and the primary function of these devices, providing a proper quantityof well-mixed air to the building occupants.



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Diffusers are commonly specified and reported in noise criteria (NC), rather than room criteria(RC). In most cases, there is no difference between NC and RC for diffusers because theyusually peak in the 500–2,000 Hz region, and the resultant numerical specification is the samefor both NC and RC.

Different types of terminal devices and physical configurations are described in Sections B.5.1through B.5.9.

B.5.1 Single-Duct

This basic terminal consists of casing, a damper, a damper actuator, and associated controls. Inresponse to control signals from a thermostat or other source, the terminal varies the airflowthrough a single-duct handling hot or cold air (see Figure B-7). In some applications, the sameterminal is used for both heating and cooling; a dual-function thermostat, together with thenecessary changeover circuitry, makes this possible. Controls can be pneumatic, electric, analog-electronic, or direct digital electronic. Accessories such as round outlets, multiple outlets, andsound attenuators may be added. The single-duct terminal is most often used in an interior zoneof the building for cooling only.

Figure B-7Single-Duct Configuration (Courtesy of Titus, Inc.)

B.5.2 Dual-Duct, Nonmixing

Essentially the same as two single-duct terminals side-by-side, this terminal modulates the flowof hot and cold air in two separate streams supplied by a dual-duct central AHU (see Figure B-8).Because there is no provision for mixing the two airstreams, this terminal should not be used forsimultaneous heating and cooling, which would result in stratification in the discharge duct.(When stratification occurs, the several outlets served by the terminal may deliver air atnoticeably different temperatures.) The nonmixing dual-duct terminal is best used in an exteriorzone, in which zero-to-low airflow can be tolerated as the temperature requirement shifts fromcooling to heating.



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Figure B-8Dual-Duct, Nonmixing Configuration (Courtesy of Titus, Inc.)

B.5.3 Dual-Duct, Mixing

Here the terminal is designed specifically for mixing hot (or tempered ventilation) and cold air inany proportion (see Figure B-9). When the terminal is equipped with pneumatic controls, there isa velocity sensor in the hot air inlet but none in the cold air inlet. A velocity sensor at thedischarge measures the total flow of air and sends the signal to the cold air controller. In themixing cycle, the hot airflow changes first, and a change in cold airflow follows in order tomaintain a constant total (mixed) volume. When equipped with direct digital controls (DDCs),both hot and cold inlets have velocity sensors, with the summation of flows computed by themicroprocessor. No discharge velocity sensor is used. This dual-duct terminal is often used in anexterior zone of a building or to ensure proper ventilation rates.

Figure B-9Dual-Duct, Mixing Configuration (Courtesy of Titus, Inc.)

B.5.4 Single-Duct with Heating Coil

Figure B-10 shows a single-duct terminal with a heating coil (either the hot water or the electrictype) added. The hot water coil is usually modulated by a proportioning valve controlled by thesame thermostat that controls the terminal. Control for the electric coil is either 100% on/off orin steps of capacity, energized by contactors in response to the room thermostat working througha multiple-step relay. The single-duct terminal with heating coil is most often used in an exteriorzone with moderate heating requirements because the terminal normally handles its minimumcubic feet per minute in the heating mode. A dual minimum cubic feet per minute or “flip-flop”control can be added for increased heating airflow.



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Figure B-10Single-Duct with Heating Coil Configuration (Courtesy of Titus, Inc.)

B.5.5 Fan-Powered Variable Volume (Parallel)

Figure B-11 illustrates a fan-powered, variable volume, parallel terminal. In this terminal, a fanis added to recirculate plenum air for heating only. The heating cycle occurs generally when theprimary air is off or at minimum flow. Heat is picked up as the recirculated air is drawn from theceiling space and the fan motor. Additional heat can be provided by a hot water or electric coilon the terminal. Because the fan handles only the heating airflow (which is usually less than thatfor cooling), the fan can be sized smaller than in the series flow terminal. During the coolingcycle, the fan is off, and cool primary air is supplied from the central system. A backdraftdamper prevents reverse flow through the fan. The flow of the primary air is regulated byvariable air volume controls. This type of terminal is used in exterior zones.

Figure B-11Fan-Powered, Variable Volume, Parallel Configuration (Courtesy of Titus, Inc.)

B.5.6 Fan-Powered, Constant Volume (Series)

Figure B-12 illustrates a fan-powered, constant volume, series terminal. The fan runscontinuously, fed by a mixture of primary and plenum air. The more primary air is forced in, theless plenum air is drawn in. The result is variable volume from the central system and constantvolume (and sound) to the room. Because the central system needs only to deliver air as far asthe fan, the inlet static pressure can be lower than in the parallel flow terminal. The fan, however,is sized to handle the total airflow. These terminals are often used in applications where constantbackground sound and continuous airflow are desired.



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Figure B-12Fan-Powered, Constant Volume Series Configuration (Courtesy of Titus, Inc.)

B.5.7 Low-Temperature Fan Terminals

The fan terminal, with its inherent mixing, is well suited to handle the very cold air delivered bysystems designed for air much colder than with conventional 55°F (13°C) supply systems. Inorder to use standard diffusers, the primary air must be raised to a conventional supplytemperature before it enters the room. A common solution is to mix the primary air withrecirculated air with a fan-powered terminal. Although the most common application uses aseries flow unit, many applications have been used with parallel units with a constantly runningfan. The low-temperature terminal has a special casing and insulation.

B.5.8 Fan-Powered, Quiet

This constant volume terminal uses special design and construction features that provideunusually quiet operation (see Figure B-13). The primary air section is enclosed in a sound-attenuating chamber. Instead of the usual primary air butterfly damper, there is a speciallydesigned damper assembly mounted in the primary air section enclosure. This air valve reducesnoise-producing turbulence. Other quiet performance features are a more rigid casing, specialbaffling, and a fan specially selected for low noise levels. Terminals of this type are used inbroadcast studios, libraries, and other applications where a minimum-noise, premium-qualityterminal is required.

Figure B-13Fan-Powered, Quiet Configuration (Courtesy of Titus, Inc.)



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B.5.9 Fan-Powered, Low-Profile

Figure B-14 illustrates a fan-powered, low-profile terminal. This constant or variable volumeterminal has a vertical dimension of only 10.5 inches (27 cm) for all sizes in order to minimizethe depth of ceiling space required. Often the recirculating fan is laid flat on its side with its shaftvertical. In localities where building heights are limited, the low-profile terminal saves enoughspace to allow extra floors to be included in a high-rise structure. Ceiling space can be as little as12–14 inches (30.4–35.5 cm) deep. The low-profile terminal is also useful in buildingsconstructed with precast concrete channel floors. The terminal can fit into the channel space withno extra depth required.

Figure B-14Fan-Powered, Low-Profile Configuration (Courtesy of Titus, Inc.)

B.6 Ductwork

B.6.1 General

Ducts are the means by which air is transported from the fan to the terminal devices. Ducts areavailable in numerous configurations but most commonly have rectangular, circular, or ovalcross-sectional configurations, are constructed of single or double walls, and can vary in thedegree of allowable leakage (airtightness). Typical materials used to fabricate ducts aregalvanized, galvaneal, aluminized steel, stainless steel, fiberglass, PVC-coated, brass, copper,and bronze.

In ASHRAE standards, duct construction is generally classified by application and pressure.HVAC systems in administrative, training, or off-site buildings are usually designed ascommercial systems. In addition, some buildings that contain HVAC systems are built toindustrial designs, and some that are built to nuclear-unique design requirements exceed theASHRAE standard for industrial designs.



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The following duct fittings are most commonly employed in a commercial or industrialapplication:

• Crosses – conical, lateral, with or without reducers

• Elbows – stamped, standing seam, or welded gore

• Laterals – with or without reducers

• Offsets

• Reducers – concentric or eccentric

• Saddles – 90° conical saddle, 90° saddle, or 45° saddle

• Takeoffs – 90° shoe takeoff or register box takeoff

• Tees – bull-nose, conical with or without reducers, 90° tee with or without reducer

• Wye branches

B.6.2 Duct Leakage Classifications

Section SA-4500 of ASME AG-1 [15] provides pressure boundary leakage guidance. Thesection references a nonmandatory Appendix SA-B, which describes procedures to determineallowable leakage for ductwork.

The referenced Appendix SA-B provides additional guidance on determining the allowableleakage for air cleaning, air conditioning, and ventilation systems. This guidance can be used todetermine duct construction, installation, and test requirements. The appendix presents a methodfor determining allowable leakage based on health physics requirements (such as theradioactivity concentration, the maximum permissible concentration, and the iodine protectionfactor) and provides typical sample problems. Optional guidance is also provided fordetermining alternate leakage criteria based on air cleaning and air cooling system effectivenessand expected system installation qualities.

B.6.2.1 Allowable Leakage by Radiological Control Criteria

For normal plant operating conditions, 10CFR20 [10] sets limits on the airborne radioactivematerial concentrations in areas of nuclear facilities in which plant personnel may be present.These limits are given by 10CFR20, Appendix B, Table 1. Section B-1200 of Appendix SA-Bprovides procedures for determining the maximum duct out-leakage based on the maximumpermissible concentration (MPC) as determined by 10CFR20.103, paragraphs a and b. Underaccident conditions, 10CFR100 [12] establishes the limits for airborne radioactive material.



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B.6.2.2 Additional Leakage Criteria

Additional leakage criteria may be developed to meet plant-specific ALARA criteria. Additionalcriteria may take the form of specifying air cleaning system effectiveness or system qualityparameters. It is recommend that the basis for any additional criteria be documented to allow thefuture evaluation of test data. The following examples of criteria, which have been previouslyestablished in industry standards, are identified in Section B 1300 of Appendix SA-B:

• Air cleaning system effectiveness

• Air cooling effectiveness

• System quality

B.6.2.3 Air Cleaning System Configuration and Leakage Classes

An air cleaning system can be defined schematically in terms of three spaces and twocomponents. The three spaces may be either exterior or interior and are 1) the contaminatedspace, 2) the protected space, and 3) the interspace. The interspace may be contaminated or cleanin relation to the air cleaning system located within the interspace. The two components are thefan and the air cleaning unit. The three spaces represent the possible locations for different partsof the air cleaning system. The contaminated and protected spaces also include the points ofsystem origin and termination, respectively. The interspace refers to all other spaces—contaminated or clean—where the air cleaning system or its parts may be located.

Section B 1400 of Appendix SA-B defines leakage classes. Leakage Class II indicates that,because of system configuration and location, a higher leakage rate may be allowable. LeakageClass I indicates that a more stringent leakage rate is required.

B.6.3 Duct Construction

B.6.3.1 Materials

For commercial materials, National Fire Protection Association (NFPA) Standard 90A [21] isused as a guide standard by many building code agencies. NFPA Standard 90A [21] invokesUnderwriters Laboratories (UL) Standard 181 [22], which classifies ducts as follows:

• Class 0 – Air ducts and air connectors having surface burning charateristics of zero

• Class 1 – Air ducts and air connectors having a flame-spread index of less than 25 (withoutevidence of continued progressive combustion) and a smoke-developed index of less than 50.



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For industrial materials, NFPA Standard 91 [23] is widely used for duct systems conveyingparticulates and removing flammable vapors (including paint-spraying residue) and corrosivefumes. Particulate-conveying duct systems are generally classified as follows:

• Class 1 covers nonparticulate applications, including makeup air, general ventilation, andgaseous emission control

• Class 2 is imposed on moderately abrasive particulate in light concentration, such as thatproduced by buffing and polishing

• Class 3 consists of highly abrasive material in low concentration, such as that produced fromabrasive cleaning, dryers and kilns, and boiler breeching

• Class 4 is composed of highly abrasive particulates in high concentration

• Class 5 applies to corrosive applications, such as acid fumes

Galvanized steel, uncoated carbon steel, or aluminum are most frequently used for industrial airhandling. Aluminum ductwork is not used for systems conveying abrasive materials and, whentemperatures exceed 400°F (204°C), galvanized steel is not recommended. Ductwork materialfor systems handling corrosive gases, vapors, or mists must be selected carefully.

B.6.3.2 Rectangular and Round Ducts

For commercial design, Sheet Metal and Air Conditioning Contractors’ National Association(SMACNA) “HVAC Duct Construction Standards – Metal and Flexible” [24] lists constructionrequirements for rectangular steel ducts and includes combinations of duct thicknesses,reinforcement, and maximum distance between reinforcements.

Round ducts are inherently strong and rigid and are generally the most efficient and economicalducts for air systems. The dominant factor in round duct construction is the ability of the materialto withstand the physical damage caused by installation and negative pressure requirements.

For industrial design, SMACNA “HVAC Duct Construction Standards – Metal and Flexible”[24] gives information for the selection of material thickness and reinforcement members forspiral and nonspiral industrial round ducts. SMACNA “Rectangular Industrial Duct ConstructionStandards” [25] is available for selecting material thickness and reinforcement members forindustrial ducts. The data contained in this manual give the duct construction for any pressureclass and panel width. Each side of a rectangular duct is considered a panel. Usually, the foursides of a rectangular duct are built of material with the same thickness. Ducts are sometimesbuilt with the bottom plate thicker than the other three sides.

The designer often selects a combination of panel thickness, reinforcement, and reinforcementmember spacing to limit the deflection of the duct panel to a design maximum. Any shape oftransverse joint or intermediate reinforcement member that meets the minimum requirement ofboth section modulus and the moment of inertia may be selected.



B-27

B.6.3.3 Flat Oval Ducts

For commercial applications, seams and transverse joints are generally the same as thosepermitted for round ducts. Flat oval ducts are typically used for positive pressure applicationsunless special designs are used. Hanger designs and installation details for rectangular ductsgenerally apply to flat oval ducts.

B.6.3.4 Fibrous Glass Ducts

Fibrous glass ducts are a composite of rigid fiberglass and a factory-applied facing (typicallyaluminum or reinforced aluminum), which serves as a finish and vapor barrier. This material isavailable in molded round sections or in board form for fabrication into rectangular or polygonalshapes. Duct systems of round and rectangular fibrous glass are generally limited to 2400 ft/min(12 m/s) and ±2 inches (±500 Pa) of water. Molded round ducts are available in higher pressureratings than are board form ducts.

B.6.3.5 Flexible Ducts

Flexible ducts typically connect mixing boxes, light troffers, diffusers, and other terminals to theair distribution system. Because unnecessary length, offsetting, and compression of these ductssignificantly increase airflow resistance, flexible ducts should be kept as short and straight aspossible, fully extended, and supported to minimize sagging.

B.6.3.6 Plenums and Apparatus Casings

SMACNA “HVAC Duct Construction Standards – Metal and Flexible” [24] shows details onfield-fabricated plenum and apparatus casings. Sheet metal thicknesses and reinforcement forplenum and casing pressure outside the range of -3 to +1 inches (-750 to +250 Pa) of water canbe based on SMACNA “Rectangular Industrial Duct Construction Standards” [25].

B.6.3.7 Acoustical Treatment

Metal ducts are frequently lined with acoustically absorbent materials to reduce aerodynamicnoise. Although many materials are acoustically absorbent, duct liners must also be resistant toerosion and fire and have properties compatible with the ductwork fabrication and erectionprocesses. For higher velocity ducts, double-wall construction using a perforated metal liner isfrequently specified.

B.6.3.8 Hangers

For commercial applications, SMACNA “HVAC Duct Construction Standards – Metal andFlexible” [24] describes commercial HVAC system hangers for rectangular, round, and flat ovalducts. When special analysis is required for larger ducts or loads or for other hangerconfigurations, American Institute of Steel Construction (AISC) “Manual of Steel Construction”[26] and AISI “Cold Formed Steel Design Manual” [27] should be used.



B-28

For industrial applications, the AISC “Manual of Steel Construction” [26] and the AISC “ColdFormed Steel Design Manual” [27] give design information for industrial duct hangers andsupports. The SMACNA standards for round and rectangular industrial ducts [24, 25] as well asmanufacturers’ schedules include duct design information for supporting ducts at intervals of upto 35 feet (8.9 m).

B.7 Instrument Test Ports

Instrument test ports make it easy and economical to provide openings for pitot tubes and othertest instruments in order to measure static pressures and air velocities. The hole is sealed off witha heavy screw cap and gasket, as shown in Figure B-15. Unless otherwise specified, a flat gasketis supplied to prevent air leakage around the base; however, in some cases, the test port can beconfigured with a curved base and a special gasket to accommodate a curved duct.

Figure B-15Instrument Test Port (Courtesy of Ventfabrics, Inc.)

Key Technical Point

Instrument test ports attached with rivets and sealed with gaskets may notbe suitable for nuclear plant applications requiring zero-leakage.

Instrument test ports are typically available in a variety of sizes, with total heights varying toaccommodate different thicknesses of insulation. The most common heights are 1-3/8 inches (3.5cm), which will accommodate 1 inch (2.5 cm) of duct insulation, and 2-3/8 inches (6 cm), whichwill accommodate 2 inches (5 cm) of duct insulation.



B-29

B.8 Airflow Measuring Stations

Airflow measuring stations are permanent devices installed in an appropriate length of duct inorder to measure attributes about the airflow at that given location. Several types of stations aredescribed in Sections B.8.1 through B.8.5.

B.8.1 Multiport with Integral Air Straightener

Figure B-16 shows a multiport, self-averaging pitot traverse station with an integral airstraightener-equalizer honeycomb cell. Many of these types of stations are capable ofcontinuously measuring fan discharges or ducted airflow with an accuracy of 2% or better. Amultiport pitot tube traverse station offers its high degree of measuring accuracy by virtue ofprecisely located sensors, honeycomb airflow processing, and instantaneous pneumaticaveraging of multiple pressure values. Some airflow measuring stations use a process known assymmetrical averaging, which requires that all stages in the averaging process occur at a pointwhere there is a balanced array of sensors present, ensuring that each sensed pressure is given thesame “equal weight” in the averaging process.

Figure B-16Multiport Air Measuring Station with an Integral Air Straightener (Courtesy of AirMonitoring Corp.)

B.8.2 Traverse Probe

Figure B-17 shows an airflow traverse station that uses one or more traverse probes (factorymounted in a rigid welded galvanized casing) to sense and average separate total and staticpressure traverses of an airstream. Multiple sets of total and static pressure sensing points,positioned along the length of each probe, traverse the airstream in single lines across the duct



B-30

and average the sensed pressures in separate internal manifolds. Factory-installed static and totalpressure signal tubing connects the individual probes, terminating at the galvanized casing forfield connection. These types of air measuring stations are suited for installations in ductwork,fan inlets, and other configurations operating at temperatures ranging from -20ºF to 400ºF (-29ºCto 204ºC).

Figure B-17Traverse Probe Air Measuring Station (Courtesy of Air Monitoring Corp.)

B.8.3 Pitot Traverse Station

The pitot traverse station is a flow traverse station that combines a honeycomb air straightener-equalizer with proven multipoint, self-averaging pitot technology. As shown in Figure B-18,these types of air measuring stations provide the means to measure low air volumes of 20 to1700 ft3/min in small-diameter round ducts within 2% of actual airflow.



B-31

Figure B-18Pitot Traverse Station (Courtesy of Air Monitoring Corp.)

B.8.4 Hot Wire Sensor

One or more mass flow measuring devices (for example, a hot wire sensor) measure theinstantaneous average mass velocity. Figure B-19 provides typical illustrations of one of thesedevices.

Figure B-19Multipoint Insertion Mass Flow Element (Courtesy of Kurz Instruments, Inc.)



B-32

In some models, each sensor uses a unique sensor circuit that eliminates output changes causedby temperature variations. The circuit also allows the sensor cable to be shortened or lengthenedwithout affecting the calibration. This is especially useful for sensors having remote sensorelectronics.

B.8.5 Orifice Plates

The measurement of fluid (water) flow is necessary to permit the intelligent, safe, and efficientoperation of equipment used in nuclear power facilities. This includes measurement of air, gas,water, and steam flows. An orifice plate is commonly used for these measurements because itprovides a measurable pressure drop based on a given flow and velocity. An orifice plate can beconsidered a type of flow meter that typically exhibits the characteristics shown in Table B-2.

Table B-2Orifice Plate Characteristics

Characteristic Value

Accuracy ±1% to 5% full scale

Range of control 3:1 to 5:1

Pressure loss High (typically >5 psi [34.5 kPa] for water applications)

Straight piping requirements(upstream)

10–40 pipe diameters

Straight piping requirements(downstream)

2–6 pipe diameters

An orifice provides flow metering in the following manner. As a compressible fluid passesthrough a nozzle, a drop in pressure and a simultaneous increase in velocity result. By assumingthe type of flow (for example, adiabatic), it is possible to calculate, from the properties of thefluid, the required area for the cross-section of the nozzle so that the flowing fluid may just fillthe provided space. This calculation indicates that for all compressible fluids, the nozzle formmust first be converging—but eventually, if the pressure drops sufficiently, the nozzle form mustbecome diverging to accommodate the increased volume caused by the expansion. The smallestcross-section of the nozzle is called the throat, and the pressure at the throat is the critical flowpressure.

B.9 Humidifiers

Humidifiers should be installed where the air can absorb the vapor. The temperature of the airbeing humidified must exceed the dew point of the space being humidified. When fresh or mixedair is humidified, the air may need to be preheated to allow absorption to take place.



B-33

B.9.1 Heated Pan Humidifiers

These units offer a broad range of capacities and may be heated by a heat exchanger suppliedwith either steam or hot water. They may be installed directly under the duct, or they may beinstalled remotely and feed vapor through a hose. In either case, a distribution manifold shouldbe used.

Steam heat exchangers are commonly used in heated pan humidifiers, with steam pressuresranging from 5 to 15 psig (34.5 to 103.4 kPa). Hot water heat exchangers are also used in panhumidifiers, generally at a water temperature higher than 240°F (116°C).

All pan humidifiers should have water regulation and some form of drain or flush system. Whenraw water is used, periodic cleaning is required to remove the buildup of minerals. Care shouldbe taken to ensure that all water is drained off when the system is not in use to avoid thepossibility of bacterial growth in the stagnant water.

B.9.2 Direct Steam Injection Humidifiers

These units cover a wide range of designs and capacities. Because steam is water vapor underpressure and at high temperature, the process of humidification can be simplified by addingsteam directly into the air. This is an isothermal process because the temperature of the airremains almost constant as the moisture is added. For this type of humidification system, thesteam source is usually a central steam boiler at low pressure. When steam is supplied from asource at a constant supply pressure, humidification responds quickly to system demand. Acontrol valve may be modulating or two-position in response to a humidity sensor/controller.Steam can be introduced into the airstream through one of the following devices:

• Single or multiple steam-jacketed manifold

• Non-jacketed manifold or panel distribution system

B.9.3 Electrically Heated, Self-Contained Steam Humidifiers

These units convert ordinary tap water to steam by electrical energy using either electrodes orresistance heater elements. The steam is generated at atmospheric pressure and discharged intothe duct system through dispersion manifolds. If the humidifier is a freestanding unit, the steamis discharged directly into the air through a fan. Some units allow the use of softened ordemineralized water, which greatly extends the time between cleanings.

B.9.4 Atomizing Humidifiers

Water treatment should be considered if mineral fallout from hard water is a problem. Optionalfilters may be required to remove the mineral dust from the humidified air. Depending on theapplication and the water condition, atomizing humidifiers may require a reverse osmosis (RO)or a deionized (DI) water treatment system to remove the minerals. Wetted parts should be ableto resist the corrosive effects of DI and RO water.



B-34

The following are the three main categories of atomizing humidifiers:

• Ultrasonic humidifiers – use a piezoelectric transducer submerged in demineralized water

• Centrifugal humidifiers – use a high-speed disk that slings water to its rim

• Compressed-air nozzle humidifiers

B.9.5 Wetted Media Humidifiers

Rigid media humidifiers use a porous core. Water is circulated over the media while air is blownthrough the openings. These humidifiers are adiabatic, cooling the air as it is humidified. Rigidmedia cores are often used for the dual purposes of winter humidification and summer cooling.They depend on the airflow for evaporation, and the rate of evaporation varies with airtemperature, humidity, and velocity.

Wetted media humidifiers have inherent filtration and scrubbing properties as a result of thewater-washing effect in the filter-like channels. Because only pure water is evaporated,contaminants collected from the air and water must be flushed from the system. A continuousbleed or regular pan flushing is recommended to minimize the accumulation of contaminants inthe pan and on the media.

B.10 Dehumidifiers

Dehumidification systems are typically employed where control of humidity and moisture iscritical. Technologically advanced dehumidification coils can extract maximum amounts ofmoisture under difficult conditions. With the addition of a remote condenser, somedehumidification systems can provide cool, dry air to the conditioned space. An automaticchangeover thermostat allows the system to maintain the desired room temperature in bothsummer and winter.

The operation of most dehumidifiers is completely automatic. A humidistat starts thedehumidifier upon a buildup of humidity in the room and stops when the set point is reached.

An optional water-heating coil may be added to a dehumidifier to provide hot water for industrialprocesses. Some computer-designed dehumidification systems take moisture-laden air from theconditioned space and pass it over the deep row dehumidification coil. The temperature of thisair is lowered to its dew point temperature, and water is condensed from the air. This air isimmediately passed through a re-heat coil, raising the temperature equal to a combination ofsensible and latent heat from the refrigeration cycle. The air leaving the dehumidifier is 10 to 15degrees warmer than the air entering. This warmer air adds room heating and is beneficial duringcold months.



B-35

B.11 Centrifugal Pumps

Centrifugal or kinetic pumps are typically used to provide fluid flow to HVAC systems forheating or cooling. Typically, centrifugal pumps are classified by one of two casingconfigurations: volute or diffuser. A volute is a spiral-like form; as the liquid is discharged fromthe impeller into the volute casing, 1) the volute areas increase at a rate proportional to thedischarge of liquid from the impeller and 2) a constant velocity exists around the periphery of theimpeller. This velocity is then diffused in the casing nozzle.

The other common casing classification is diffuser construction. A diffuser is actually a series ofvanes surrounding the impeller that accept the discharge of liquid from the impeller. The vanesefficiently reduce the velocity in order to increase pump head and, in the case of a multistagepump, direct this lower velocity fluid into vaned return channels that guide the liquid to the inletor eye of the next stage impeller. In the case of single-stage pumps, the discharge from thediffuser is collected in a surrounding casing, which guides the liquid out of the pump through thedischarge nozzle.

The single-stage centrifugal pump is often installed in HVAC systems. A design feature ofsingle-stage pumps is the configuration of the inlet of the impeller. The two major types ofsuction configurations are single-suction and double-suction. A single-suction configuration isoften employed with a radially split casing to achieve higher design pressures and temperatures.The disadvantage of the single-suction configuration is that it typically requires higher netpositive suction head (NPSH) than a double-suction configuration. In a double-suction pump, theflow comes from a single source and splits—doubling the inlet area. The doubling of the inletarea subsequently lowers the inlet velocity and thus the NPSH required.

Figures B-20 and B-21 illustrate the differences between the single-suction and double-suctionhorizontal pumps.



B-36

Figure B-20Single-Stage Horizontal Pump (Single-Suction)

Figure B-21Single-Stage Horizontal Pump (Double-Suction)


C-1

C TYPICAL HVAC TAB DOCUMENTATION

C.1 Typical Documentation Requirements

As noted in Section 1, the documentation used to record HVAC system parameters is oftencustomized by each plant. In some cases, the documentation is a hard-copy form that theengineer/technician uses to manually record data. In other cases, the data entry may beperformed electronically. In most cases, these forms are then used as input for performingcalculations, either using the equations noted in Appendix D or using computer programs (that is,a spreadsheet or commercially available software).

Some documentation is designed to allow for data entry and calculation. In these cases, the formrecords the data measured and is structured to allow the engineer/technician to perform thenecessary calculations on the same document.

The examples and methods of documenting/calculating HVAC system parameters are providedfor illustrative purposes only. Documentation requirements and calculation procedures vary fromplant to plant, and the information provided in this report should not be used in lieu of plant-specific procedures.

C.2 Testing, Adjusting, and Balancing Forms

Figures C-1 through C-4 illustrate means by which HVAC TAB information may bedocumented. The forms are examples provided for illustrative purposes only.


Typical HVAC TAB Documentation

C-2

Fan DataMOTOR: Nameplate As Found Measured

Data (Avg.)As Left MeasuredData (Avg.)

Initial/Date

Full Load Current, ampsFull Load Voltage, voltsSpeed, rpm

MISCELLANEOUS:Locked Rotor Current, amps HorsepowerModel No. Serial No.Service Factor Power FactorFrame EfficiencyDrive sheave size, in. Dia. Fan to Motor Shaft CenterlineManufacturerMotor Frame Adjustment

FAN:Rotation From Outlet Belt SizeBelt Tension No. of BeltDrive Sheave size, in. Dia.

Description Design As FoundMeasured Data

As LeftMeasured Data

Initial/Date

Inlet Total Press., in. H2O,Discharge Total Press., in. H2OFan Total Press., in. H2OMeasured Flow, cfmInlet Air TemperatureAir Flow (Fan Curves)

MOTOR MISCELLANEOUS INFORMATIONDescription As Found Measured Data As Left Measured Data

Full Load Current, amps A B C Avg. A B C Avg.

Full Load Voltage, volts AB BC AC Avg. AB BC AC Avg.

Motor Speed, rpm

Figure C-1Fan Data



C-3

ROUND DUCT TRAVERSE DATA SHEETDate: System: Pitot #:Time: Test Location: (Elev)Duct Dia.: in. Duct Area:Number of readings in Traverse (n): Area Served:Sum of Readings: fpm/n = fpm (Vt ) Avg, VelocityActual Velocity: fpm (Vt ) X ft2 (Dt ) = acfmSystem Mode of Operation:Pre Temperature = Post Temperature = Avg Temperature =Pre Static Pressure = Post Static Pressure = Avg Static Pressure =Altitude Correction Factor = Temperature Correction Factor =Total Correction Factor X Air Flow Reading = Corrected Air Flow Barometric Pressure = SCFM =Traverse Readings Traverse Readings Traverse ReadingsPoints VP FPM Points VP FPM Points VP FPM

1 11 212 12 223 13 234 14 245 15 256 16 267 17 278 18 289 19 29

10 20 30 Total FPM = Total FPM = Total FPM =Required Flow = Actual Flow = % Difference Flow =

Figure C-2Round Duct Traverse Data Sheet



C-4

RECTANGULAR DUCT TRAVERSE DATA SHEETDate: System: Pitot #:Time: Test Location: (Elev) Duct Dim. X = inDuct Area: in2. / 144 in2 = ft2 Duct Cross Section AreaNumber of readings in (Trav) Traverse (n):Sum of Readings: fpm/n = fpm (Vt ) Avg, VelocityActual Velocity: fpm (Vt ) X ft2 (Duct Area ) = acfmSystem Mode of Operation:Pre Temperature = Post Temperature = Avg Temperature =Pre Static Pressure = Post Static Pressure = Avg Static Pressure =Altitude Correction Factor = Temperature Correction Factor =Total Correction Factor X Air Flow Reading = Corrected Air Flow Required Flow = Actual Flow = % Difference Flow =Barometric Pressure = SCFM =Trav Reading 1 Reading 2 Reading 3 Reading 4 Reading 5 Reading 6Points V.P. FPM V.P. FPM V.P. FPM V.P. FPM V.P. FPM V.P. FPM

12345678910

TotalTrav Reading 7 Reading 8 Reading 9 Reading 10 Reading 11 Reading 12Points V.P. FPM V.P. FPM V.P. FPM V.P. FPM V.P. FPM V.P. FPM

12345678910

Total

Figure C-3Rectangular Duct Traverse Data Sheet



C-5

System:Location: Operating Mode:

Grille/Register Outlet Design As Found As LeftDate Room Area Served ID # Size AK VEL CFM VEL CFM VEL CFM Initial

Total = Total = Total =

Air Balance Engineer: Date: % Diff. % Diff.

Figure C-4Grille/Register Data Sheet


D-1

D EQUATIONS AND CALCULATIONS

Note: In some cases, dimensional constants have been added to ensure proper units. Because thisis not always the case, a dimensional analysis is highly recommended.

D.1 Fundamental Equations

Ideal gas law

P = ρRT (PV = mRT) Eq. D-1

2

22

1

11

T

VP

T

VP= Eq. D-2

where:

P = absolute pressure of the gas (lbf/ft2)

ρ = gas density (lbm/ft3)

R = gas constant (ft-lbf/lbm – Rankine [°R])

T = absolute temperature of the gas (°R)

V = gas volume (ft3)

m = mass of the gas (lbm)

Continuity equation

VAm ⋅⋅= ρ& Eq. D-3

where:

m& = mass flow rate across (lbm/min)

ρ = fluid density (lbm/ft3)

A = area (ft2)

V = fluid velocity (ft/min)


Equations and Calculations

D-2

Q = AV Eq. D-4

where:

Air Water

Q = volumetric flow rate (ft3/min) (gpm)

A = cross-sectional area of the duct (ft2) (ft2)

V = fluid velocity (ft/min) (ft/s)

Kinematic viscosity

ρµν =

Eq. D-5

where:

ν = kinematic viscosity (ft2/s)

µ = absolute viscosity (lbm/ft ⋅⋅⋅⋅ s)


Reynolds number

ν⋅=

720Re hVD

Eq. D-6

Re = 8.56 DhV for standard air Eq. D-7



D-3

P

ADh

⋅= 4 for noncircular pipes Eq. D-8

where:

Re = Reynolds number


Dh = hydraulic diameter (inches)

ν = fluid kinematic viscosity (ft2/s)

A = cross-sectional area (ft2)

P = wetted perimeter (ft)

Bernoulli’s equation

lossHzg

V

g

pz

g

V

g

p+++

⋅=++

⋅ 2

222

1

211

22 ρρEq. D-9

where:

p = static pressure (lbf/ft2)

V= velocity (ft/s)

z = elevation (ft)

Hloss = head loss (ft)

g = local acceleration due to gravity (ft/s2)




D-4

Total pressure

Pt = Pv + Ps Eq. D-10

where:

Pt = total pressure (in. w.g.)

Pv = velocity pressure (in. w.g.)

Ps = static pressure (in. w.g.)

Sensible heat ratio

( ) qq

q SHR

latentsensible

sensible

+= Eq. D-11

total

dB

q

T 0.24 = SHR

∆∆

Eq. D-12

where:

SHR = sensible heat ratio

qsensible = sensible heat (Btu/h)

qlatent = latent heat (Btu/h)

∆ TdB = dry bulb temperature difference of the air (°F)

∆ qtotal = change in total heat content of the supply air (Btu/lbm)

Humidity ratio

ΩΩΩΩ w

w

pp

p

−= 62198.0 Eq. D-13

where:

ω = humidity ratio (lbm of moisture/lbm of dry air)

pw = partial pressure of water vapor (psia)

p = total mixture pressure (psia)



D-5

D.2 Conduit, Pipe, and Duct Friction Loss Equations

Darcy-Weisbach equation

=

g

v

D

Lfhl 2

2

Eq. D-14

where:

f = friction factor (as defined below)

L = pipe length (ft)

D = pipe diameter (ft)

v = fluid velocity (ft/s2)

g = 32.2

Fanning friction factor: 4

f

For fully developed laminar flow: f =Re

64

For smooth conduit walls with turbulent flow:

25.0Re

3164.0=f Re<105 Eq. D-15

where:

Re = Reynolds number

237.0Re

221.00032.0 +=f 105< Re < 3 ⋅ 106

Eq. D-16

Fully rough flow:

+=

εD

flog214.1

1Eq. D-17



D-6

Colebrook equation for turbulent flow regime:

+−=

fDf Re

7.182log274.1

1 εEq. D-18

where:

ε = material absolute roughness factor (ft)

Churchill’s friction factor correlation (valid for the entire range of laminar, critical, and turbulentflows):

( )12

1

2

312

Re

88

++

= −BAf Eq. D-19

where:

169.0

7.3Re

7ln457.2

+

−=

D

kA

16

Re

37530

=B

Hazen-Williams equation

167.1852.11

022.3

⋅=

DC

vLhl Eq. D-20

where:

hl = head loss (ft )

L = pipe length (ft)

v = average velocity (ft/s)

C = roughness factor 140 for new steel pipe, 130 for new cast iron pipe, and 110 forriveted pipe

D = pipe internal diameter (ft)



D-7

Valve and fitting losses in pipes

=

g

VKhl 2

2

Eq. D-21

=

D

LfK Eq. D-22

pCQ ∆= v & Eq. D-23

where:

hl = head loss (ft )

K= geometry and size dependent loss coefficient

f = friction factor

D

L

= equivalent length in pipe diameters

Q& = volumetric flow rate (gpm)

Cv = valve coefficient, gpm at ∆p = 1 psi

∆p = pressure drop (psi)

Resistance coefficient for sudden and gradual enlargements in pipe

K = 2.6 sin2

θ(1-β2)2 for θ ≤ 45° Eq. D-24

K = (1-β2)2 for 45°< θ ≤ 180° Eq. D-25

The value of resistance coefficients K is based on the velocity in the small pipe. To obtain the Kvalues in terms of the larger pipe, divide the equations by β4,

where:

β = d1/d2

d1 = diameter of the small pipe (in.)

d2 = diameter of the large pipe (in.)



D-8

Resistance coefficient for sudden and gradual contractions in pipe

K = 0.8 sin2

θ(1-β2) for θ ≤ 45° Eq. D-26

K = 0.52

sinθ

(1-β2) for 45°< θ ≤ 180° Eq. D-27

The value of resistance coefficients K is based on the velocity in the small pipe. To obtain the Kvalues in terms of the larger pipe, divide the equations by β4,

where:

β = d1/d2

d1 = diameter of the small pipe (in.)

d2 = diameter of the large pipe (in.)

Equivalent of resistance coefficient and flow coefficient:

K

dCv

49.29 ⋅= Eq. D-28

where:

Cv = flow coefficient

d = nominal pipe diameter (in.)

K = resistance coefficient

Flow-through nozzles, orifices, and venturis

cd gg

pgAYCQ

/

)144(2)48052.760( 1 ρ

∆⋅=& Eq. D-29

41 β−= C

Cd

Eq. D-30



D-9

where:

=Q& volumetric flow rate (gpm)

Y = expansion factor of fluid (value = 1 for incompressible fluids)

Cd = discharge coefficient

C = flow coefficient

A1 = cross-sectional area of the device (ft2)


∆p = pressure drop across the device (lbf/in2)

ρ = fluid density at upstream conditions (lbm/ft3)

gc = gravitational constant (32.174 lbm ft/lbf s2)

β = d1/d2

d1 = diameter of the device (in.)

d2 = diameter of the pipe (in.)

Duct fitting losses

Tp = C ⋅ Vp Eq. D-31

where:

Tp = total pressure drop (in. w.g.)

C = fitting loss coefficient

Vp = velocity pressure (in. w.g.)



D-10

D.3 Airflow Equations

Note: In these equations, standard air is defined as dry air (0% RH) at 59°F and 14.696 psia.

Flow-through orifice

Airflow for a sharp-edged orifice with pipe taps located 1 inch on either side of the orifice (forduct diameters 2–14 inches):

ρh

dKQ o26 ⋅⋅=& Eq. D-32

hdKQ o ⋅⋅⋅= 8.21& for standard air Eq. D-33

where:

=Q& volumetric flow rate (ft3/min)

K = coefficient of airflow

do = diameter of the orifice (in.)

ρ = air density (lbm/ft3)

h = pressure drop across the orifice (in. w.g.)

Converting velocity pressure to velocity (for standard air):

vPV 4005= Eq. D-34

where:





D-11

Fluid flow equation

ghV 2= Eq. D-35

where:

V = velocity (ft/s)

g = acceleration due to gravity (32.2 ft/s2)

h = head (ft w.g.)

Calculating air density

T

PP s

b

+

=6.13

325.1

ρ Eq. D-36

where:

ρ = air density (lbm/ft3)

Pb = barometric pressure (in. Hg)


T = absolute temperature (°R)

Calculating the correction factor for velocity with a change in density

½

0.075

CF

=

ρEq. D-37

where:

CF = correction factor

0.075 = density of standard air (lbm/ft3)

ρ = new calculated density(lbm/ft3)



D-12

Calculating the average velocity corrected for density

Vc = Vm ⋅ CF Eq. D-38

where:

Vc = corrected velocity (ft/min)

Vm = measured velocity (ft/min)

CF = correction factor for new density

Calculating air volume with a correction for density

Q = A ⋅ Vc Eq. D-39

where:

Q = quantity of airflow (ft3/min)

A = area in (ft2)

Vc = corrected velocity (ft/min)

Calculating actual (local or true) velocity when flows are taken with a heated wireanemometer

=

530

P

29.92V V

bmeasuredactual

T Eq. D-40

where:


Pb = barometric pressure (in. Hg)

T = dry bulb temperature (°R)



D-13

Calculating corrected velocity to standard conditions when using a manometer

SCFMACFMT

PP

DB

SB

=⋅

+⋅

+

69.459

69.529

921.29

6.13Eq. D-41

where:

TDB = temperature, dry bulb (°F)

PB = pressure, barometric (in. Hg)

PS = pressure, static (in. w.g.)

ACFM = actual cubic feet per minute

SCFM = standard cubic feet per minute

Air changes per hour and cubic feet per minute from air changes per hour

Volume Room

)Q (60 ACH

&

= Eq. D-42

where:

ACH= air changes per hour

Q& = quantity of airflow (ft3/min)

Room Volume = room volume (ft3)

D.4 Fan Equations

Fan total pressure = Pt1-Pt2 Eq. D-43

Pt1= 0 if the fan draws directly from the atmosphere

Pt2 = pv1 if the fan discharges directly to the atmosphere



D-14

Fan static pressure = Pt-Pv Eq. D-44

= Ps2-Pt1

Fan velocity pressure

2

1097

= V

Pv ρ Eq. D-45

2

4005

= V

Pv for standard air Eq. D-46

where:


Pt = total pressure (in. w.g.)


ρ = density (lbm/ft3 )

V = duct air velocity (ft/min)

Subscripts 1, 2 = upstream and downstream of the fan, respectively

Fan total efficiency

Fi

tt P

PQ&=η Eq. D-47

where:

PFi = Fan input power (HP)

Fan static efficiency

t

sts P

Pηη = Eq. D-48

where:




D-15

Fan system effect pressure loss

2

oo 1097

V C SEF

= ρ Eq. D-49

where:

SEF = fan-system-effect pressure loss, in. w.g. (Pa)

Co = fan-system-effect loss coefficient, dimensionless

ρ = density (lbm/ft3 )

and for centrifugal fans, where:

Vo = inlet velocity based on area at the inlet collar, or outlet velocity based on the outletarea (ft/min)

and for axial fans, where:

Vo = inlet or outlet velocity based on the area calculated from the fan diameter (ft/min)

Fan output power or air horsepower

6356

PQ P t

Fo

&

= for a compressibility factor of 1 Eq. D-50

where:

PFo = Fan output power (HP)

Pt = total pressure rise (in. w.g.)

Fan motor power or fan brake horsepower

DηFi

Mo

PP = Eq. D-51

where:

PMo = Motor output power (HP)

PFi = Fan input power (HP)

ηD = Motor drive efficiency



D-16

Fan motor efficiency

Mi

Mo

P 1.341

P=Mη Eq. D-52

where:

ηM = Fan motor efficiency

PMo = Motor output power (HP)

PMi = Motor input power (HP)

Fan energy consumption

PMi MF

PQ

ηη ⋅⋅⋅=

8520

&

Eq. D-53

where:

PMi = Fan motor power (kW)

Q& = airflow volume (ft3)

P = fan pressure (in. w.g.)

ηF = fan efficiency (%)

ηM = motor efficiency (%)

Temperature rise through the fan (motor out of the airstream)

F

PT

ηs371.0 ∆⋅

=∆ Eq. D-54

where:

∆T = temperature rise through the fan (°F)

∆Ps = static pressure rise through the fan (in. w.g.)

ηF= fan efficiency (%)



D-17

Fan Law No. 1

1

2

1

2

1

2

Pd

Pd

N

N

Q

Q==

&

&

Eq. D-55

Fan Law No. 22

1

2

2

1

2

2

1

2

1

2

=

=

=

Pd

Pd

Q

Q

N

N

P

P

s

s

&

&

Eq. D-56

Fan Law No. 3: Power varies with the cube of the fan speed (for motors of 10 horsepower andlarger)

3

1

2

3

1

2

3

1

2

1

2

=

=

=

Pd

Pd

Q

Q

N

N

BHP

BHP&

&

Eq. D-57

Fan Law No. 3: Amperage varies as the cube of the air volume (for motors of 10 horsepowerand larger)

3

1

2

3

1

2

3

1

2

1

2

=

=

=

Pd

Pd

Q

Q

N

N

I

I&

&

Eq. D-58

Fan Law No. 3: Brake horsepower varies as the square root of the static pressures cubed32

1

2

1

2

=

s

s

P

P

BHP

BHPEq. D-59

where:

2Q& = new volume of airflow (cubic feet per minute)

1Q& = original volume of airflow (cubic feet per minute)

N2 = new fan speed (rpm)

N1 = original fan speed (rpm)

Pd2 = new pitch diameter of the motor sheave

Pd1 = original pitch diameter of the motor sheave

PS2 = new static pressure (in. w.g)

PS1 = original static pressure (in. w.g.)

BHP2 = new brake horsepower (hp)

BHP1 = original brake horsepower (hp)

I2 = new amperage (amps)

I1 = original amperage (amps)



D-18

Fan Laws and Density

Air volume remains constant with changes in air density. A fan is a constant volume machineand will handle the same airflow, regardless of air density. It must be remembered, however, thatmany instruments are calibrated for standard air density (70°F at 29.92 in Hg) and any change inair density will require a correction factor for the instrument.

Static pressure and brake horsepower vary in direct proportion to density

=

=

1

2

1

2

1

2

ρρ

BHP

BHP

P

P

s

sEq. D-60

where:

ρ1 = original density (lbm/ft3)

ρ2 = new density (lbm/ft3)

Air velocity pressure for pitot traverse2

1,

= ∑

=nPP

n

iivv Eq. D-61

where:


i = nth reading

n = total number of readings

D.5 Pump Equations

Pump efficiency and power equations

3960

γ⋅⋅= HQWHP

&

Eq. D-62

p

HQBHP

ηγ

⋅⋅⋅=

3960

&

Eq. D-63

2

1

2

1

2

=

∆∆

Q

Q

P

P&

&

Eq. D-64



D-19

where:

WHP = water horsepower

H = head (ft)

γ = specific weight (ft3/lbm)

BHP = brake horsepower

ηp = pump efficiency (%)

∆P = pressure difference (psi)

1Q& = volumetric flow rate (gpm)

Cavitation Index

( )2

2

o

vo

V

pp

⋅−

=ρ

σ Eq. D-65

where:

po = pressure at reference point o

pv = vapor pressure

Vo = velocity at reference point o

Pump NPSH

( )( )

+−−±+

−+=

g

VLBS

SG

PPPNPSHA va

2

31.2 2

Eq. D-66

where:

NPSHA = net positive suction head available (ft w.g.)

P = pressure above liquid (psig)

Pa = atmospheric pressure (psia)



D-20

Pv = vapor pressure of liquid at pumping temperature (psia)

SG = specific gravity at pumping temperature (ft3/lbm)

S = static height of liquid above (+) or below (-) grade (varies per pump type) (ft)

B = distance above grade from pump centerline (ft)

L = suction system friction losses (ft)

V = velocity of fluid at pump inlet nozzle (ft/s)


D.6 Electrical Equations

Brake horsepower, single-phase circuit

746

PF A V BHP

⋅⋅⋅= ηEq. D-67

Brake horsepower, three-phase circuit

746

PF A V1.732 BHP

⋅⋅⋅⋅= ηEq. D-68

where:

BHP = brake horsepower

V = volts (for three-phase circuits, this is average volts)

A = amps (for three-phase circuits, this is average amps)

η = motor efficiency

PF = power factor

1.732 = constant ( 3 ) for three-phase circuits



D-21

Calculating brake horsepower using no-load amps (for motors of 10 horsepower andlarger)

NLA)0.5 (FLA

NLA)0.5 (RLA HP BHP

c

n

⋅−⋅−= Eq. D-69

Calculating field corrected full load amps

FLAc = Vn ⋅ FLAn / Vm Eq. D-70

where:

HPn = nameplate horsepower

RLA = running load amps, field measured

NLA = no-load amps (motor sheave in place and belts removed)

FLAc = full load amps, field corrected

Vn = nameplate volts

FLAn = nameplate full load amps

Vm = volts, field measured

Single-phase power factor

AV

WPF

⋅= Eq. D-71



D-22

Three-phase power factor

AV

WPF

⋅⋅=

732.1Eq. D-72

where:

PF = power factor

W = power (watts)

V = voltage (volts)

A = amperage (amps)

1.732 = constant ( 3 ) for three-phase circuits

Voltage unbalance equation

%V = ∆D max /Vavg ⋅ 100 Eq. D-73

where:

%V = % voltage unbalance (should not exceed 2%)

∆D max = maximum deviation from average voltage

Vavg = average voltage (volts)

Current unbalance equation

%C = ∆D max / Cavg ⋅ 100 Eq. D-74

where:

%C = % current unbalance (should not exceed 10%)

∆D max = maximum deviation from average amps

Cavg = average amperage (amps)



D-23

Percent of slip of induction motors and synchronous speed

% = (NS – Nr) / NS ⋅ 100 Eq. D-75

Ns = 120 ⋅ f/p

where:

% = percent of slip

NS = synchronous speed (rpm)

Nr = rotor speed (rpm)

f = frequency (Hz)

p = number of poles (not pairs of poles)

D.7 Noise and Vibration Equations

Fan sound power level

⋅= −210

log10W

Lw Eq. D-76

where:

Lw = fan sound power level (dB)

Log = logarithm to base 10

W = power (kW)

Blade passage frequency

60

nNBPF = Eq. D-77

where:

BPF = blade passage frequency (Hz)

N = fan speed (rpm)

n = number of blades



D-24

Strouhal number

V

Df ⋅= 5NStrouhal Eq. D-78

where:

StrouhalN = Strouhal number

f = vortex shedding frequency (Hz)

V = velocity (ft/s)

D = characteristic dimension (ft)

D.8 Drives, Belts, and Pulleys

Drive equation

Nm ⋅ Dm = Nf ⋅ Df Eq. D-79

where:

Nm = speed of the motor shaft (rpm)

Dm = pitch diameter of the motor sheave (ft)

Nf = speed of the fan sheave (rpm)

Df = pitch diameter of the fan sheave (ft)

Blade tip speed

12NTip

ND ⋅⋅= π Eq. D-80

where:

NTip = blade tip speed (in/min)

π = 3.14

D = blade diameter (in.)

N = rotational speed (rpm)



D-25

Belt length

4C

d) - (D d) (D

2 C2 L

2

++⋅+⋅= πEq. D-81

where:

L = belt pitch length

C = center-to-center distance of the shafts

π = 3.14

D = pitch diameter of the large sheave

d = pitch diameter of the small sheave

Drive-belt losses for V-belt drives

LD = 9.4 – 4.65127 ln PM for fractional power motors Eq. D-82

LD = 9.4 – 1.86747 ln PM for motors from 1 to 10 horsepower Eq. D-83

LD = 6.2 – 0.477724 ln PM for motors from 10 to 100 horsepower Eq. D-84

LD = 4.0 for motors over 100 horsepower Eq. D-85

ηD = 1.0 – LD/100 Eq. D-86

where:

LD = drive belt losses

PM = motor power (kW)

ηD = drive efficiency (%)



D-26

D.9 Areas and Circular Equivalents of Ducts

Rectangular duct

A = ab/144 Eq. D-87

where:

A = area of the duct (ft 2)

a = length of one side of rectangular duct (in.)

b = length of adjacent side of rectangular duct (in.)

Round duct

A = πR2/144 Eq. D-88

where:

A = area of the duct (ft 2)

π = 3.14

R = radius (in.)

Flat oval duct

Area of the rectangle plus the area of the circle

Segment of a circle

A = πR2N/360 Eq. D-89

where:

A = area (ft2)

πR2 = area of the circle (ft2)

R = radius of circle (ft)

N = number of degrees in the arc

360 = constant, degrees in a circle



D-27

Triangle

A = bh/2 Eq. D-90

where:

A = area (ft2)

b = base of the triangle (ft)

h = height of the triangle (ft)

Circular equivalent for a rectangular duct

π/4ab=eD Eq. D-91

Circular equivalent for a rectangular duct for equal friction and capacity

0.25

0.625

b) (a

ab1.30

+=eD Eq. D-92

where:

De = equivalent duct diameter (in.)

a = length of one side of rectangular duct (in.)

b = length of adjacent side of rectangular duct (in.)

Circular equivalent for a flat oval duct for equal friction and capacity

0.25

0.625

A1.55

PDe = Eq. D-93

where:

area A = (πb2/4) + b (a – b)

perimeter P = πb + 2 (a – b)

a = major dimension of flat oval duct (in.)

b = major dimension of flat oval duct (in.)



D-28

References

American Conference of Governmental Industrial Hygienists (ACGIH), Industrial Ventilation –A Manual of Recommended Practice. 2001.

American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc. (ASHRAE),ASHRAE Handbook – Fundamentals. 1997.

E. A. Avallone and T. Baumeister III, Marks’ Standard Handbook for Mechanical Engineers.McGraw Hill. 1997.

Crane Co., Technical Paper No. 410. “Flow of Fluids through Valves, Fittings, and Pipe,” 1985.

R. G. Culham, Fans Reference Guide. Ontario Power Generation. 2001.

F. C. McQuiston and J. D. Parker, Heating, Ventilating, and Air Conditioning. John Wiley &Sons, Inc. 1994.

Sheet Metal and Air Conditioning Contractors’ National Association, Inc. (SMACNA), HVACSystems – Testing, Adjusting and Balancing. 1986.


E-1

E ANALYTICAL METHODS

E.1 Introduction

In situ TAB of nuclear HVAC systems can be difficult and expensive for several reasons,including required system operability (safety and licensing concerns), interference/distraction tonormal plant operation, and radiological exposure. For these reasons, the nuclear HVACengineer may consider alternative analytical methods as a “first cut” approach in accomplishinga full system balance. Preliminary analytical analyses will help in determining initial positionsand sizes for various flow balancing components (such as dampers, restrictors, orifice plates, andvalves) and the effect that identified system changes will have on overall airflow quantities anddistribution. This type of approach will also help to reduce the amount of time required fortemporary field construction and measurement activities along with system inoperability duringthe TAB process.

Key O&M Cost Point

Because of required system operability (safety and licensing concerns),interference/distraction to normal plant operation, and radiologicalexposure, the nuclear HVAC engineer may consider alternative analyticalmethods as a “first cut” approach in accomplishing a full system balance.

This appendix addresses several analytical methods that may be used as tools in troubleshootingand determining system modification effects and “best guess” positions of components (such asdampers and valves) as an efficient initial method in the nuclear HVAC TAB process.

E.2 System Airflow and Pressure Loss Analysis

Historically, the design of duct distribution systems has followed several basic methods,including the equal friction method and the static regain method. The equal friction methoddetermines duct size based on the assumption of a constant pressure loss per unit length of thesystem. The static regain method is based on the objective of sizing each branch-to-main-ductsection to obtain a constant static driving pressure for the supply of air to the correspondingbranch outlets. More recently, additional methods of duct distribution optimization (for example,the T method) have been developed and are more focused on initial system costs and the presentworth of energy.


Analytical Methods

E-2

E.2.1 System Diagram Development

To understand the dynamics of the HVAC system being analyzed, the engineer should firstdevelop a system one-line or nodal diagram that represents the ductwork and associatedcomponents to the degree of detail required. The diagram should be set up by duct/fittingsections and sufficiently detailed in order to evaluate the conditions at branches, majorequipment (including fan system effects), and balancing locations (such as fans, dampers, andflow measurement locations).

After the system diagram is developed, any available test and balance information that exists forthe current as-built system configuration may be used to assist the engineer in a baselineevaluation of the major plenum and branch flows. Hand calculations may then be performed toverify expected pressure and airflow measurement values based on observed conditions orchanges.

System effects based on fan placement in relation to system ductwork size, transitions, andfittings should also be evaluated to determine the possible magnitude of the resultant pressurelosses. Analytical methods supported by computer analyses may also be applied and are furtherdescribed in Sections E.2.2 through E.2.2.2. If significant disparity exists between analyticalcalculations and existing test data, the identified locations in question should be further tested.

Using this initial analytical approach should save significant time and the associated expenseafter a full system test and balance effort. This effort will also help to enhance the engineer’sknowledge of the operation and dynamics of the subject HVAC system.

E.2.2 Analysis Using Generic and Custom Computer Modeling Software

Regardless of the design method chosen, using a hand calculation approach in solving forpressure loss in each section of a distribution system can become laborious because of theiterative nature of the solution process. A variety of companies, including the major HVACequipment vendors (for example, Carrier and Trane), offer generic computer design software forinitial design and sizing of HVAC distribution systems. These programs are primarily structuredto permit the HVAC design engineer to input a proposed system configuration while allowingthe user to size the ductwork plenums and branch distribution.

Most nuclear HVAC engineers, however, are not required to design completely new ventilationsystems based on the pre-existing facilities and systems they support. Therefore, analysis is morefocused on operation and flow evaluation/balancing of existing HVAC systems. Methods forcalculating airflow and associated pressure loss of these systems are suitable for computerprograms that can provide iterative analysis capability and data tracking. Several of thesemethods and programs are discussed in Sections E.2.2.1 and E.2.2.2.


Analytical Methods

E-3

E.2.2.1 Generic Spreadsheet Software

HVAC engineers have taken advantage of generic software (for example, Microsoft, Lotus andCorel) to formulate simple to complex spreadsheet programs that will calculate and update theflow and pressure in a defined duct network system. The calculation algorithms are programmedinto the spreadsheet, allowing the program to calculate current airflow and pressure values foreach duct section on an iterative, cascading basis. This type of programming method, however, issomewhat limited in its rigor of analysis, based on the complexity of the assumed convergencecriteria and the inflexibility of defining dynamic system variables (including fan performance,system effects, and damper and component variable position).

E.2.2.2 Computer Modeling Software

Various architect/engineering (A/E) and engineering analysis organizations have developedspecific computer modeling programs to analyze nuclear HVAC systems. These models havebeen used to determine the margins and existing conditions of the plant’s current design andlicensing basis. Also, a benchmarked system model can be used to support JCO in lieu of fullsystem airflow test and measurement.

Some of these thermal-hydraulic software-modeling programs, available for use by the HVACnuclear engineer in a generic format (for example, PROTO-HVACTM), meet nuclear-grade qualityassurance program requirements. There are many advantages to using these types of analysisprograms for more accurately determining key operating and balancing conditions. Dependingon the complexity of the modeling input developed and the software used, the following outputcapabilities can be provided:

• Calculation of steady pressures, temperatures, and airflows throughout complex HVAC ductdistribution systems

• Change in alignment of flow paths or selection of predefined specific system operatingmodes

• Selection of fan operating status and fan performance curves (that is, design, actual,degraded, or new)

• Evaluation of system effects based on the subject HVAC system configuration

• Determination of balancing/volume damper throttle position (manually or automatically) as afunction of flow or pressure set point

• Specification of leak tightness of dampers or components as a function of pressure conditions

• Various component pressure losses as a function of a fixed or variable flow parameter

• Duct friction factor adjustment

• Specification of local airflow conditions (for example, temperature, pressure, elevations, andpsychrometric conditions)

• Flags to alert the user of abnormal conditions (for example, reverse flow, excessive leakage,less than minimum specified flow, and fan runout)

• Flexibility in output report information and formatting


Analytical Methods

E-4

A significant reduction in the time required to final balance the subject HVAC system is one ofthe benefits of developing a detailed computer simulation model. In addition, once this model isdeveloped and benchmarked, it can be used to support JCOs or proposed system modifications inlieu of in situ testing.

E.3 Thermal and Pressure Loss Analysis and Balancing of HVACWater/Liquid Systems

Analytical methods for assisting the engineer in the TAB of the water/liquid side of the HVACsystem are similar to those discussed in Section E.2 for the air/gas side. Because of the largertolerance in analytical inaccuracy of these hydraulic systems, liquid systems are by naturenormally less difficult to analyze. In most nuclear plants, HVAC system engineers do not havedirect responsibility for the liquid side of their subject systems. For that reason, this guidelinedoes not further describe specific analysis methods used to evaluate the complexity of thesesupporting systems (which include service water, emergency service water, chilled water, andclosed cooling water).

E.3.1 HVAC Heat Exchanger Analysis

The major component that provides the thermal interface between the air/gas and liquid side ofthe HVAC system is the fan or duct coil. Many devices are used in the various HVAC plantsystems, including containment fan coil units (CFCUs), room unit coolers, in-duct DX coils, in-duct chilled water and service water coils, in-duct steam and hot water heating coils, and preheatglycol coils. Many of these heat exchange devices must be balanced periodically on both theair/gas and water/liquid sides to satisfy licensing basis performance requirements (that is, thosefound in USNRC Generic Letter 89-13 [28]).

Numerous analytical methods, including hand calculations, generic software spreadsheets, andcomputer modeling software, are used in conjunction with in situ testing to verify thermalperformance. In addition, various A/Es and engineering analysis organizations have developedspecific heat exchanger, fan coil, service water and chilled water, and refrigerant chillercomputer modeling programs to analyze these systems and components. Some of these thermal-hydraulic software-modeling programs, available for use by the nuclear engineer or technician ina generic format (for example, PROTO-HXTM and PROTO-FLOTM), meet nuclear-grade qualityassurance program requirements.


F-1

F ALTERNATE FLOW MEASUREMENT USING TRACERGAS

Sulfur hexafluoride has been used as a tracer gas to test control room envelope in-leakage and tomeasure the airflow rate in ducting. ASTM E 2029-99 [29] is used as a standard for this method.Using the standard alone is insufficient without the experience and technique of trainedindividuals.

Not all duct configurations are capable of delivering an accurate pitot tube traverse. Systems inwhich turbulence and twisted configurations detract from good pitot tube results tend to be suitedfor the tracer gas technique. Applications range from the unit vent on a PWR to turbine buildingexhaust in a BWR. Figure F-1 illustrates a typical schematic for using tracer gas testing methods.

Figure F-1Typical Schematic for Using Tracer Gas Testing Methods

Tracer gas is injected at a known concentration at a known flow rate. After being fully mixed, itis sampled to measure the change in concentration that is commensurate with the flow rate in thesystem. Regardless of the application, the injection gas and mass flow meter should be calibratedfor the expected flow rate application.

Typical equipment used in the process consists of the following:

• Mass flow meter

• Mass flow control valve

• Calibration gas

• Injection gas


Alternate Flow Measurement Using Tracer Gas

F-2

• Injection manifold

• Sample pump

• Sample manifold

• Sample analyzer

Typical applications include not only airflow measurement in a ducting system but also damperleakage or fan flow rate measurement. The fan flow rate may be ducted or may be an applicationwhere the un-ducted fan exhausts into a room with a single exhaust point. In any case,re-entrainment of exhausted tracer gas should be accounted for. This application is shown inFigure F-2.

Figure F-2Tracer Gases Exhausted into a Room with a Single Exhaust Point


G-1

G DEFINING ACFM AND SCFM WHEN PERFORMINGTAB ACTIVITIES

When referring to airflow in HVAC systems, the convention is cubic feet per minute (CFM) orft3/min. However, when considering the change in air density for varying conditions oftemperature, pressure, and RH (moisture content), the term CFM becomes unclear. Moreappropriate units are actual cubic feet per minute (ACFM) and standard cubic feet per minute(SCFM) when performing specific airflow measurements and associated calculations for HVACsystems.

ACFM is defined as the flow rate measured under stated operating conditions corrected for localeffects (for example, true air density). ACFM is the actual operating volumetric flow ratecondition for a specific HVAC system at the specific location of observation. SCFM is the actualflow rate converted back to standard reference conditions. This conversion can be attainedanalytically by using the relationship presented in the ideal gas law (described further in thisappendix). The only time that ACFM and SCFM have the same value is at the establishedstandard reference conditions.

One of the most commonly used standard reference conditions is dry air (0% RH) at a pressureof 14.7 psia and temperature of 70ºF, as documented by ASHRAE in ANSI/ASHRAE 111-1988[30]. The Nuclear HVAC Utility Group (NHUG) also endorses these standard referenceconditions.

G.1 Effect of Temperature on CFM

Throughout the ranges of pressure and temperature applicable to most HVAC systems, air can betreated as an ideal gas. Therefore, the “ideal gas” relationship PV=mRT or P= ρRT (seeAppendix D for definitions of terms) can be applied to various analyses when determining theeffect that variations in temperature, pressure, and moisture content have on air volume anddensity.

As illustrated in Figure G-1, as the temperature of a fixed mass of dry air increases, the volume itoccupies also increases. The curve in Figure G-1 is based on the mass of dry air that wouldoccupy 100 cubic feet of volume at standard conditions. The figure shows that if airflow weremeasured at the temperature extreme of 10ºF, an 11% difference would be realized between thisACFM value and the standard condition at 70ºF. This also reflects a total volumetric differenceof 18%, which the same air mass would occupy over the temperature range (10–110ºF) indicated


Defining ACFM and SCFM When Performing Tab Activities

G-2

in Figure G-1. Based on this effect, a significant under-prediction of airflow at low temperaturesor over-prediction at higher temperatures could occur if measurements are not corrected back tostandard conditions. In addition, for many calculations requiring the rigor and accuracywarranted in the operation of nuclear power plants, this level of change would not be acceptableif left uncorrected.

Figure G-1Change in Air Volume as a Function of Temperature

G.2 Effect of Pressure on CFM

Applying the ideal gas law relationship for variations in absolute pressure at a constanttemperature for dry air provides for the associated change in volume. For most HVAC systems,this change is not very significant, based on the small changes in differential operating pressure(0–15 in. w.g.) realized through the system (supply-to-return ducting). However, thesechanges—in conjunction with local atmospheric pressure conditions during the time ofmeasurement—could be more significant and should be evaluated.

The curve in Figure G-2 is based on the mass of dry air that would occupy 100 cubic feet ofvolume at standard conditions of 14.696 psia. Figure G-2 reflects the change in volume thatwould be realized from conditions associated with a change in absolute (total) pressure between11.75 psia and 15.25 psia. This range of conditions could be realized, based on variouscombinations of weather (high or low barometric pressure), altitude (for example, Denver,Colorado vs. Miami, Florida), and system operating pressure variations applicable to the specificTAB performed.



G-3

Figure G-2Change in Air Volume as a Function of the Change in Absolute Pressure for a ConstantMass

Therefore, a TAB engineer/technician measuring ACFM on an HVAC system located in Denver,Colorado (with an atmospheric pressure of 11.75 psia) could realize as much as a 25% differencein airflow versus the same system located and tested in Miami, Florida (with an atmosphericpressure of 14.696 psia).

G.3 Effect of Moisture Variation on CFM

The difference as a result of moisture between ACFM and SCFM becomes more significant asthe air becomes more saturated. The behavior of the dry air and water vapor mixture is based onthe principle defined by Dalton’s law of partial pressures, as shown in Equation G-1.

(Pa + Pw)V = (na + nw)RT Eq. G-1

where:

Pa = partial pressure of the air

Pw = partial pressure of the water vapor

V = total volume of the mixture

na = number of moles of the air

nw = number of moles of the water vapor

R = universal gas constant

T = temperature



G-4

Each constituent (water vapor and air) exerts part of the total pressure of the gas mixture andshares a proportional part of the total volume. For dry air, the partial pressure (Pw) and thenumber of moles (nw) of water vapor are equal to zero; therefore, the air mass occupies the entirevolume. As the dry air begins to combine with and retain water vapor, the value of nw (number ofmoles) increases. In addition, the value of Pw is based on the temperature of the mixture. It canbe seen by Equation G-1 that as moisture percentage increases, a larger volume of air and itsequivalent mass are displaced by the water vapor.

Figure G-3 illustrates the effect that moisture content has on the change in air volume for thetemperature range above and below standard conditions. The curve for dry air (shown in FigureG-1) is compared to the curve for saturated air (having a moisture content of 100% RH). FigureG-3 shows that at low temperatures, the volumetric differences are not significant because thepartial pressure value of the water vapor (Pa) is small. However, as temperature increases, thepartial pressure value of the water vapor becomes significant, occupying a greater amount of thetotal mixture’s volume and displacing that portion of dry air mass associated with the originalvolume.

Figure G-3Change in Air Volume as a Function of Temperature for Various Percentages of MoistureContent



G-5

G.4 Correction Formulas for ACFM and SCFM

As described in Section G.3, local effects of temperature, pressure, and moisture content cansignificantly affect air density (the amount of air mass for a given volume) and the resultantHVAC system’s airflow measured by the TAB engineer/technician. Equation G-2 provides ameans to calculate the local air density (ρ) based on the defined variables of temperature,pressure, and RH (for wet and dry bulb temperatures):

( )( )

+⋅

−

⋅

+−+⋅−⋅⋅−

+

⋅=

−−

69.459 35.53

27006.13

41.0159.0296.0 378.0 6.13

73.70

123

DB

WBDBSBWBWB

SB

T

TTPPTT

PP

ρ

Eq. G-2

where:

PB = pressure, barometric (in. Hg) at the measurement location

PS = pressure, static (in. w.g.) at the measurement location

TWB = temperature, wet bulb (°F) at the measurement location

TDB = temperature, dry bulb (°F) at the measurement location

Airflow values measured by the TAB engineer/technician depending on the measurement device,may be corrected for density effects (based on air velocity) by using Equation G-3.

MCFMACFM 075.0 ⋅=ρ

Eq. G-3

where:

ACFM = actual CFM

ρ = density of air (lbs/ ft3)

MCFM = measured CFM



G-6

ACFM can be converted to standard reference conditions of SCFM by using Equation G-4:

ACFMT

PP

SCFMDB

SB

⋅

+⋅

+

=69.459

69.529

921.29

6.13

Eq. G-4

where:

SCFM = standard CFM

PB = pressure, barometric (in. Hg) at the measurement location

PS = pressure, static (in. w.g.) at the measurement location

TDB = temperature, dry bulb (°F) at the measurement location

ACFM = actual CFM


H-1

H LISTING OF KEY POINTS

The following list provides the location of “Key Point” information in this report.

Key O&M Cost Point

Emphasizes information that will reduce purchase, operating, ormaintenance costs.

ReferencedSection

Page Number Key Point

3.1.1.2 3-4 The HVAC system may operate without an alarm; however, improperlymaintained system balancing may increase energy costs of operation.Lack of attention to the system balancing can be indicated byinsufficient cooling and/or heating in the building or by problems withareas that require positive or negative pressure.

3.1.2.2 3-5 System lineup should be recorded when acquiring air balance data onsystems or subsystems that can be affected by other ventilationsystems.

3.1.7 3-12 Development of a detailed troubleshooting plan can save money andtime by reducing repetitive efforts and providing a structured approachto determining the problem.

3.1.10.1 3-17 Adjustments to dampers are generally less expensive to perform;modifications to fans generally involve modifications that can becomecostly.

6.1 6-1 Lesson learned: When setting up a fan, the operating class limits forthat fan must not be exceeded. Operating a fan outside its associatedlimits may lead to catastrophic failure.

6.7 6-4 Lesson learned: The technicians likely did not understand thelimitations of their instrumentation. When moving a fluid-basedinstrument from one environment to another, ample time should beallotted for the liquid to come to equilibrium, or frequent checks shouldbe made to ensure that the base point has not changed.

6.8 6-5 Lesson learned: Postulate system effects prior to proceeding with whatappears to be a minor design modification


Listing of Key Points

H-2

Key O&M Cost Point

Emphasizes information that will reduce purchase, operating, ormaintenance costs.

6.12 6-8 Lesson learned: The most important part of the TAB work occurs priorto the start of the work: understanding how the system works andperforming the walkdown.

E.1 E-1 Because of required system operability (safety and licensingconcerns), interference/distraction to normal plant operation, andradiological exposure, the nuclear HVAC engineer may consideralternative analytical methods as a “first cut” approach inaccomplishing a full system balance.



H-3

Key Technical Point


ReferencedSection


3.1.6 3-11 The engineer should perform an eyewitness, hands-on inspection ofthe equipment to validate the issue and subsequently define the actualproblem. A field walkdown of the HVAC system/component(s) isrecommended at this point.

3.1.7 3-13 Prior to making any physical adjustments to the system, a detailedtroubleshooting plan should be developed, taking into consideration allof the data collected thus far in the evaluation.

3.1.9.2 3-16 The most common causes of HVAC system performance problemsinclude the following:














3.2.1 3-19 The first step in the balancing procedure is to become familiar with thecomplete system operation.



H-4

Key Technical Point


3.2.2 3-19 Prior to starting each system’s TAB work, a walkdown of the systemshall be made to determine testability. A general walkdown of majorsystem components, such as fans and filter housings, should beperformed to ensure that maintenance activities are not underway orneeded.

3.4.2 3-26 Prior to starting the water balancing work, a walkdown of the system isrecommended.

4.1.1.1 4-1 Manometer tubes should be chemically clean to be accurate and filledwith the correct fluid.

Mercury is not an acceptable fluid for HVAC TAB work because of itspotential hazardous effects on personnel and on plant equipment.

4.1.1.2 4-2 When air pressures are extremely low, a micromanometer (hookgauge) or some other more sensitive instrument should be used toensure accuracy.

4.1.1.3 4-3 The technical manual for the electronic manometer should bereferenced to determine if it provides results in ACFM, SCFM, or both.If the temperature sensor is not used, the instrument reading on atleast one electronic manometer should be adjusted by calculation toeither actual or standard conditions (ACFM or SCFM).

4.1.1.4 4-6 Measurement of airstream total pressure is achieved by connectingthe inner tube outlet connector to one side of a manometer or gauge. Ifmeasuring a positive pressure, the pitot tube is connected to the high-pressure side of the pressure measuring device.

4.1.1.4 4-7 Measurement of airstream static pressure is achieved by connectingthe outer tube side outlet connector to one side of a manometer orgauge. If measuring a negative pressure, the pitot tube is connected tothe low-pressure side of the pressure measuring device.

4.1.1.4 4-7 Measurement of airstream velocity pressure is achieved by connectingboth the inner and the outer tube connectors to opposite sides of amanometer or gauge. The total pressure line is connected to the high-pressure port of the test instrument, and the static pressure line isconnected to the low-pressure side.

4.1.1.6 4-9 In the case of coils or filters, an uneven airflow is frequently foundbecause of entrance or exit conditions and/or stratification.



H-5

Key Technical Point


4.1.6.8 4-23 Flow measuring elements should be installed far enough from elbows,valves, and other sources of flow disturbances.

5.1.1 5-2 Results using the equal area method should be closely evaluated ifthey are near minimum acceptance values.

6.2 6-1 Lesson learned: The manufacturer’s data for nominal pressure dropmay be higher than the actual pressure drop and may result in airflowthat is greater than design.

6.3 6-2 Lesson learned: Duct access doors should have a positive closingmechanism that is not subject to opening as a result of vibration andsystem starts and stops.

6.4 6-2 Lesson learned: Periodic monitoring of building pressures can identifyequipment problems prior to failure and avoid potentially detrimentalsystem effects.

6.5 6-2 Lesson learned: Slipping belts are not always audible, and astrobotach should be used to verify fan speed when fan flows are inquestion.

6.6 6-3 Lesson learned: Pitot tubes should be closely inspected prior to eachuse. During subsequent checks of pitot tubes, one was discoveredwith an internal crack in the impact velocity sensing line. A simple wayto check the impact pressure line is to connect the pitot tube to apressure measuring device and pressurize the impact line, block thesensing port, and observe the pressure measuring device for anypressure decay.

6.6 6-3 Lesson learned: Inclined manometers with integral shut-off valvesshould be checked for leaks in these valves. These valves contain twoO-rings and may close off tightly but leak when opened for use. Inaddition, these valves should never be opened more than three-fourths of a turn: opening them more than this can result in the failureof the sealing O-ring to make contact with the sealing surface in thevalve body.

6.6 6-4 Lesson learned: The tubing used to connect the pitot tube to thepressure measuring device should be verified to ensure that it is ingood condition and free of any leaks. The tightness of the impact linecan be verified by pressurizing it and blocking the impact port on thepitot tube. However, the static sensing line cannot be tested in thismanner. A visual inspection is the best method of verifying theconnecting tubing.

6.9 6-6 Lesson learned: Flow measurement in a duct at a location with flowdisturbances can be significantly different (in this case over 10%greater) than at a location of long straight duct.



H-6

Key Technical Point


6.10 6-6 Lesson learned: Some electronic micromanometers provide a velocityreading that automatically converts to actual flow results (that is,ACFM) by using the temperature probe. If the temperature probe is notused, the instrument reading corresponds to neither SCFM nor ACFM.

6.11 6-7 Lesson learned: All possible system operating conditions need to befully considered during the design and functional test phases.

B.7 B-28 Instrument test ports attached with rivets and sealed with gaskets maynot be suitable for nuclear plant applications requiring zero-leakage.



H-7


Denotes information that requires personnel action or consideration in orderto prevent injury or damage or ease completion of the task.

ReferencedSection


3.1.1.1 3-3 Key to addressing any issue is understanding that the plant-specificdesign/licensing bases need to be maintained throughout thetroubleshooting, TAB, and corrective action processes.

3.1.2.1 3-4 The HVAC engineer should understand how the problem could apply toother systems/HVAC components of similar design and applications.

3.1.7.2 3-14 Personnel should be familiar with the design of the subject HVAC systemand the operation of the test equipment.

4.1.3 4-14 Care should be taken when using any rotating measuring instrument inorder to avoid personal injury caused by inadvertent contact with therotating equipment.

4.1.5 4-20 Care should be used when working around energized electricalequipment.

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