Indoor Air Quality Airflow Measurement for Today’s …€¦ · Indoor Air Qualityfor Acceptable Airflow Measurement for Today’s GREEN Buildings. ... Net Building Pressure = Pressurization

Airflow Measurementfor Acceptable

Indoor Air Quality Airflow Measurement for Today’s

GREEN Buildings


Indoor Air Quality

AS DESIGNERS WHY SHOULD YOU CARE ABOUT AIRFLOW

MEASURMENT?


Indoor Air Quality

� LEED POINTS, maintain minimum outside airflow rates

prescribed by ASHRAE 62.1-2007 constant and variable airflow HVAC systems.

� Provide stable, compartmentalized NET Pressure Control

� Improve temperature control, reduce envelope moisture,

space humidity issues and infiltration of contaminants.

� Comply with ADA requirements.

� Reduce Energy, Increase system efficiency,

� Minimizing wasted conditioning of excess outside and

supply air.

� SAVE MONEY ON DESIGNS WITH REAL TIME VERFICATION.

Significantly Improve Performance Designs w/ Air Flow

Measurement.


Indoor Air Quality

Maintain the minimum outside airflow rates

prescribed by ASHRAE 62.1-2007 on both constant

and variable airflow occupancy spaces.

Airflow Measurement can Significantly Improve the

Performance of Buildings


Indoor Air Quality ASHRAE 62.1-2010

1. PURPOSE

1.1 The purpose of this standard is to specify minimum

ventilation rates and other measures intended to

provide indoor air quality that is acceptable to human

occupants and that minimizes adverse health

effects.


Indoor Air Quality

5.1.1 Designing for Air Balancing. The ventilation air

distribution system shall be provided with means

to adjust the system to achieve at least the minimum

ventilation airflow as required by Section 6 under

any load condition.

ASHRAE 62.1-2010


Indoor Air Quality

5.3 Ventilation System Controls. Mechanical ventilation

systems shall include controls, manual or

automatic, that enable the fan system to operate whenever

the spaces served are occupied. The system

shall be designed to maintain no less than the minimum

outdoor airflow as required by Section 6

under any load condition.

Note: Variable Air Volume (VAV) systems with fixed

outdoor air damper positions must comply

with this requirement at minimum system primary airflow.

ASHRAE 62.1-2010


Indoor Air Quality

6.1.1 Ventilation Rate Procedure. The prescriptive

design procedure presented in Section 6.2, in which

outdoor air intake rates are determined based on space

type/application, occupancy level, and floor area, shall

be permitted to be used for any zone or system.

6.1.2 IAQ Procedure. This performance-based design

procedure (presented in Section 6.3), in which the

building outdoor air intake rates and other system

design parameters are based on an analysis of

contaminant sources, contaminant concentration limits,

and level of perceived indoor air acceptability, shall be

permitted to be used for any zone or system.

ASHRAE 62.1-2010


Indoor Air Quality

Variety of effects on airflow

Uncontrolled Minimum Outside Air Intake Damper

� Wind Effect

� Stack Effect

� Damper Hysteresis.

� Mixed air plenum pressure uncertainty

with any VAV system.

Techniques relying on damper position only


Indoor Air Quality

Wind pressure fluctuation uncertainty

EXAMPLE


Indoor Air Quality

Cross wind effect example:

EXAMPLE

Fixed Damper Hysteresis - CV System - 15mph Cross Wind(full size damper)

50%

60%

70%

80%

90%

100%

110%

1 2 3 4 5

Run Number (30 samples/run)

% o

f S

etp

oin

t

Close/Open

Open/Close


Indoor Air Quality

Stack effect results in similar uncertainty

EXAMPLE


Indoor Air Quality

Errors are compounded on VAV systems

EXAMPLE


Indoor Air Quality

Fixed Damper Hysterisis - CV System

(full size damper)

50%

60%

70%

80%

90%

100%

110%

1 2 3 4 5


% o

f S

etp

oin

t

Close/Open

Open/Close

Regardless, Damper linkage hysteresis is

significant ……

EXAMPLE


Indoor Air Quality

Damper Under Active Control - Light & Variable Wind

50%

60%

70%

80%

90%

100%

110%

1 2 3 4 5


% o

f S

etp

oin

t

Control

An answer is active control of minimum OA intake flow rates

EXAMPLE


Indoor Air Quality

Provide stable, compartmentalized NET pressure control to improve temperature control, reduce envelope moisture, space humidity and unfiltered infiltration of contaminants.


Performance of Your Building

Thermal Dispersion Airflow Measurement


Indoor Air Quality

Net Building Pressure = Pressurization Flow = In - Out

= AHU Intake - [AHU Exhaust + Local Exhaust(s)]

AHU Exhaust

AHU Intake

Local Exhaust(s)

Pressurization Flow

Only A HVAC System can pressurize your building!

Building Pressure Model

Control of Relief Air and Building PressureEXAMPLE


Indoor Air Quality

Building

QSA

QRA

Traditional Static Pressure ControlSupply/Return Fan Systems (alternate method)

MDAMD

MD

Control

SP

Control

MD

EXAMPLE


Indoor Air Quality

Building

Building Pressure Model: QP=QOA-QRE

QP

QSA

QRAQRE

QOA

Mathematical Equivalent:

QRec + QOA = QSA

QRec + QEX = QRA

QOA - QEX = QSA - QRA

QRec

Inherent problem Relief Airflow is Difficult to

Measure Accurately & Repeatable!

AMD

AMD

AMD

AMD

Ref. 2007

ASHRAE

Applications

Handbook 46.10,

Fig. 18

EXAMPLE


Indoor Air Quality

Building

Building Pressure Model: QP=QSA-QRA

QP

QSA

QRA

Traditional Pressure Solution

Control

AMDMDAMD

MD

Control

AMD2

Pos

Ref. 2007

ASHRAE

Applications

Handbook

46.10, Fig. 18

EXAMPLE


Indoor Air Quality

CV/VAV (multiple AHU’s) – [low or high-rise]

Systems with single minimum OA ERV, minimum OA mode

Notes:

1. Modulate ERV OA and EX fans to maintain duct static (w/reset)

2. Modulate OA dampers to maintain AHU OA at each zone.

3. OA-EX=QP at each zone.

4. BEST METHOD: Modulate AHU EX dampers to maintain QP at each zone.

Comments:

1. This method compensates for all external and system pressure effects.

OA

RA1

SA1

EX

RA2

SA2

OA1

EX1

OA2

EX2

Pressurization

UnitOA

MD

MD

SPOAFan

OA2

AMD

AMD

OA1

MD

MD

QP1

SP

QP2

EX Fan

AMD

AMD

EXAMPLE


Indoor Air Quality

Reduce energy by increasing

system efficiency while

simultaneously minimizing

wasted conditioning of excess

outside and supply air.



EXAMPLE


Indoor Air Quality

Volumetrically track fans to

reduce fan power

consumption and improve

building pressure and

temperature control.

Control outside air

intake flow rates to

reduce wasted

conditioning of

excess outside air.Volumetrically track

individual floors to improve

pressure and temperature

control.

Install in VAV boxes to

reduce system pressure

and fan horsepower. Also

reduce wasted reheat.Control room volumetric off set control

(labs/clean rooms) to reduce system pressure

and fan horsepower.

Energy Saving Opportunities


Indoor Air Quality

Provide a sustainable

design by assuring design

performance over the life of

the building.




Indoor Air Quality

8. INDOOR ENVIRONMENTAL QUALITY (IEQ)

8.3 Mandatory Provisions

8.3.1.2 Outdoor Air Delivery Monitoring

8.3.1.2.1 Spaces Ventilated by Mechanical Systems.

A permanently mounted, direct total outdoor airflow

measurement device shall be provided that is capable

of measuring the system minimum outdoor airflow

rate. The device shall be capable of measuring flow within an

accuracy of ±15% of the minimum outdoor airflow rate. The device

shall also be capable of being used to alam1 the building operator or

for sending a signal to a building central monitoring system when

flow rates are not in compliance.

Exception: Constant volume air supply systems that use a damper

position feedback system are not required to have a direct total outdoor

airflow measurement device.

ASHRAE 189.1


Indoor Air Quality

10.3.2.1.4.1 Outdoor Airflow Measurement.

The Plan for Operation shall document procedures for implementing

a regular outdoor airflow monitoring program after building

occupancy. The Plan shall include minimum verification frequencies

of airflows supplied by mechanical ventilation systems at the system

level. Verification shall be performed using hand-

held airflow measuring instruments appropriate for

such measurements or permanently installed

airflow measuring stations. Hand-held airflow measuring

instruments or airflow measuring stations used for airflow

verifications must be calibrated no more than 6 months prior to such

verifications.

ASHRAE 189.1


Indoor Air Quality

10.3.2.1.4.2 Outdoor Airflow Verification Procedures. The plan

procedures shall contain the following requirements:

a. For each mechanical ventilation system where direct outdoor airflow

measurement is required according to Section 8.3.1.2, a procedure shall

be in place to react when the outdoor airflow is 15% or more lower

than minimum outdoor airflow rate. It shall be verified that the device

that measures outdoor air flow rate is actually measuring the flow rate

within ±15% of the sensor output reading at the minimum outdoor

airflow rate. If the sensor is not within ±15%, it shall be recalibrated.

Verification of outdoor airflow shall be done on a

quarterly basis and records maintained onsite. Direct

outdoor airflow measurement devices shall be

calibrated at the manufacturer's recommended interval

or at least annually.

ASHRAE 189.1

LEED - Energy and Sustainability

Airflow Measurement OpportunitiesPrerequisite or Credit Description NC SCHOOLS CS

EA Prerequisite 1 Fundamental Commissioning Required Required Required

EA Prerequisite 2 Minimum Energy Performance Required Required Required

EA Credit 1 Optimize Energy Performance 1-19 points 1-19 points 3-21 points

EA Credit 3 Enhanced Commissioning 2 points 2 points 2 points

EA Credit 5 Measurement and Verification 3 points 2 points NA

IEQ Prerequisite 1 Minimum IAQ Performance Required Required Required

IEQ Prerequisite 2 ETS (tobacco smoke) Control Required Required Required

IEQ Prerequisite 3 Minimum Acoustical Performance NA Required NA

IEQ Credit 1 Outdoor Air Delivery Monitoring 1 Point 1 Point 1 Point

IEQ Credit 2 Increased Ventilation 1 Point 1 Point 1 Point

IEQ Credit 3/3.1 Construction Management Plan (constr.) 1 Point 1 Point 1 Point

IEQ Credit 3.2 Construction Management Plan (occup.) 1 Point 1 Point NA

IEQ Credit 6.2 Controllability of Systems - Thermal 1 Point 1 Point 1 Point

IEQ Credit 7/7.1 Thermal Comfort - Design 1 Point 1 Point 1 Point

IEQ Credit 7.2 Thermal Comfort - Verification 1 Point 1 Point NA

IEQ Credit 9 Enhanced Acoustical Performance NA 1 Point NA

IEQ Credit 10 Mold Prevention NA 1 Point NA

ID Credit 1 Innovation in Design 1-5 points 1-4 points 1-5 points


Indoor Air Quality

These losses have a significant affect

a owner’s bottom line!

* Based on 7 people/1,000 sq.ft.

Approx.

TD

EXAMPLE

Annual Wage/PersonAnnual Loss/Person

@5%Annual Loss/sq.ft.*

Airflow Cost/sq.ft.

$20,000 $1,000 $7

$40,000 $2,000 $14

$60,000 $3,000 $21

$80,000 $4,000 $28

$100,000 $5,000 $35

Min OA <

$0.12/sq.ft.on a

typical 20,000 CFM

system


Indoor Air Quality

Airflow Measurement Technologies ?

TechnologyTechnology Review


Indoor Air Quality

Different Styles of Airflow Measurements


Indoor Air Quality

Theory of Operation

Q = κΑ

dB + C (ρvd

µ)

m

(TH – TA)

Thermal Dispersion: airflow

is determined by measuring

the power and ∆T of a

heated sensor in a moving

air stream.

Power ∆T

velocity

Temperature

Sensing

Thermistor

Self-heated

Thermistor

Thermal Dispersion Technology


Indoor Air Quality

Signal to TransmitterUnprocessed Signal toTransmitter

0.000

0.500

1.000

1.500

2.000

2.500

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Airflow (fpm)

Sensor

Outp

ut

(Volts)

Sensor

Outp

ut

(in.w

.g.)

High Sensitivity at Low Velocities

A large signal change,

especially at lower airflow

rates, is ideal for HVAC

applications.

Sensitivity Increases

∆



Indoor Air Quality

Signal ComparisonUnprocessed Signal to Transmitter

0.000

0.500

1.000

1.500

2.000

2.500

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Airflow (fpm)

Sensor

Outp

ut

(Volts)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Sensor

Outp

ut

(in.w

.g.)

Unprocessed Signal Comparison

Vortex

Shedding

∆P Style Systems

Thermal Dispersion



Indoor Air Quality

0.000

0.500

1.000

1.500

2.000

2.500

3.000

3.500

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Airflow (fpm)

Sensor

Outp

ut (V

olts)

0.0

2.0

1.8

∆

Multi-point Factory Calibration to NIST Traceable Standards



Indoor Air Quality Long Term Stability

-2.0%

-1.5%

-1.0%

-0.5%

0.0%

0.5%

1.0%

1.5%

2.0%

-3000 -2500 -2000 -1500 -1000 -500 0

Days

% A

irfl

ow

Err

or

(of

read

ing

)

5000 FPM

2000 FPM

1000 FPM

100 FPM

Composite

7 years and counting


Indoor Air Quality

Average & Output

Calculate Airflow

& Temperature

Calculate Airflow

& Temperature

Calculate Airflow

& Temperature

Calculate Airflow

& Temperature

Convert Voltages

to Binary

Convert Voltages

to Binary

Convert Voltages

to Binary

Convert Voltages

to Binary

No Averaging Error



Indoor Air Quality

Standoff (no duct)

Insertion (through duct wall)

Internal (inside duct or plenum)

Duct & Plenum Probes

Ducts, Plenums & OA Intakes


Indoor Air Quality

Throat Mount

Face Mount

Forward Mount

Fan Inlet Sensors


Indoor Air Quality Fan Performance Losses?

12-blade plenum fan

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 10 20 30 40 50 60

Fan Speed

Refe

ren

ce C

FM

Open Inlet

Face Mount

Inlet Screen

Pitot Array


Indoor Air Quality

Averaging Pitot Array Stations with Honeycomb

Averaging Pitot Array Probes

Combination Pitot Array/Damper with Honeycomb

Combination Pitot Array & Dampers

∆P Across Louver

Air Monitor Corporation, FAN-E

Trane, Traq Damper

Ruskin, IAQ-50

Piezo Fan Inlet Rings

∆∆∆∆P Style Products


Indoor Air Quality

Total Pressure Inlet

Static Pressure Inlets

Total Pressure Tap

Static Pressure Tap

∆p=ptotal-pstatic

V=4005 x ∆p√

√V=k2∆pgc

ρ

Traditional Pitot Tubes and Arrays

Note: Accuracy is dependent on:

1. Pressure transducer performance.

2. Air density

3. Turndown

PITOT-STATIC TUBES vs. VELOCITY PRESSURE ARRAY


Indoor Air Quality Fan Inlet Piezometer Rings

� Piezometer “piezo” fan inlet rings

∆p=pthroat-pentry

√V= k2∆pgc

ρ

Note: k factor is dependent on:

1. Entry conditions

2. Turndown

Note: pentry is very dependent on

entry conditions

Note: pthroat is very dependent on

wheel position and inlet cone

geometry


Indoor Air Quality

Pressure Signal To TransducerUnprocessed Signal to Transmitter

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Airflow (fpm)

Sensor

Outp

ut

(in.w

.g.)

∆P Devices (% FULL SPAN Dilemma)

Transmitter Turn-down Error

Accuracy deteriorates to

the square of the turn-

down!

(i.e. 4:1 turndown = 16x

less accuracy)

∆∆∆∆P Devices

Sensitivity Decreases


Indoor Air Quality

≠≠≠≠0.1% of Full Scale 1% of Full Scale

∆P TRANDUCERS ARE NOT ALIKE


Indoor Air Quality

Based on Manufacturer’s Specifications

Transducer Accuracy: 0.1% of natural span (full scale)

(not including pitot array)Transducer Useable

Natural

Span

F.S. FPM

(@100% span)

F.S. FPM

(@80% span)5,000 2,500 1,000 500 250 100

10 12,665 10,132 0.3% 1.3% 8.4% 40.1% 225% 488%

5 8,955 7,164 0.2% 0.6% 4.1% 17.6% 153% 365%

2 5,664 4,531 0.1% 0.3% 1.6% 6.6% 30.2% 249%

1 4,005 3,204 0.1% 0.8% 3.3% 13.8% 178%

0.5 2,832 2,266 0.1% 0.4% 1.6% 6.6% 55.5%

0.25 2,003 1,602 0.2% 0.8% 3.3% 22.6%

0.1 1,266 1,013 0.1% 0.3% 1.3% 8.4%

0.05 896 716 0.2% 0.6% 4.1%

Airflow Rate (FPM)Uncertainty


Indoor Air Quality

Based on Manufacturer’s Specifications

Transducer Accuracy: 1% of natural span (full scale)

(not including pitot array)

∆P Transmitter Comparison

Transducer Useable

Natural

Span

F.S. FPM

(@100% span)

F.S. FPM

(@80% span)5,000 2,500 1,000 500 250 100

10 12,665 10,132 3.3% 13.8% 177.7% 332.7% 597% 1363%

5 8,955 7,164 1.6% 6.6% 55.5% 248.6% 444% 990%

2 5,664 4,531 0.6% 2.6% 17.6% 153.2% 303.3% 657%

1 4,005 3,204 1.3% 8.4% 40.1% 225.2% 488%

0.5 2,832 2,266 0.6% 4.1% 17.6% 153.2% 365.0%

0.25 2,003 1,602 2.0% 8.4% 40.1% 273.5%

0.1 1,266 1,013 0.8% 3.3% 13.8% 177.7%

0.05 896 716 1.6% 6.6% 55.5%

Airflow Rate (FPM)Uncertainty


Indoor Air Quality

VAV Single Pressure Zone

Supply/Return Fan with Relief at AHU

OA

AMD TSRecommended 150 fpm min recommended

BS

Relief

RF

AMD

AMD

MD

MD

MD

SF SP


Indoor Air Quality VAV multi-zone pressurization

Supply/Return Fan with Relief at AHU

AMD

AMD

VAV RAtyp.

AMD AMD AMD AMD

AMD AMD AMD AMDRF

SP

150 fpm min

recommended

OA

AMD TS

BS

Relief

Sequence: VAV_SF_RF_Relief_MultiZonePressure

AMD

AMD

MD

MD

Individual Pressure Zone

MD

SF SP


Indoor Air Quality Application Specific Airflow Measurement

Ideal for medical/laboratory/clean room airflow tracking

and accurate VAV box airflow measurement.

Lower space noise, reheat and fan energy costs

Improves pressure, ventilation and comfort control Electronic Low Flow Terminal Probe

Documents

Indoor Air Quality Airflow Measurement for Today’s …€¦ · Indoor Air Qualityfor Acceptable Airflow Measurement for Today’s GREEN Buildings. ... Net Building Pressure = Pressurization