Manual S

Residential Equipment SelectionSecond Edition, Version 1.00

Public Review Draft 1.00 April 17, 2013

ISBN # 978-1892765-58-6

The Second Edition of ACCA Manual S is the

Air Conditioning Contractors of America

guide for selecting and sizing heating and cooling equipment forsingle family homes, and low-rise multi-family dwellings.

Commenters must use the ACCA Response Form -- available

from www.acca.org/ansi -- to comment on this document.

The completed comment form is to be emailed to

standards-sec@acca.org; noting "Manual S Public

Comment from {your last name}" in the subject line.

The ANSI Public Review period is 10 May through 24 June 2013.

Public COMMENTS ARE DUE 24 June 2013

Glenn-XPSHighlight

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Copyright and Disclaimer

This publication and all earlier working/review drafts of this publication are protected by copyright. Bymaking this publication available for use, ACCA does not waive any rights in copyright to this publication.No part of this publication or earlier working/review drafts of this publication may be reproduced, storedin a retrieval system or transmitted in any form by any technology without written permission from ACCA.Address requests to reproduce, store, or transmit to: Chris Hoelzel at the ACCA offices in Arlington,Virginia.

2013, Air Conditioning Contractors of America2800 Shirlington Road, Suite 300Arlington, VA 22206www.acca.org

Adoption by ReferencePublic authorities and others are encouraged to reference this document in laws, ordinances, regulations,administrative orders, or similar instruments. Any deletions, additions, and changes desired by the adopt-ing authority must be noted separately. The term adoption by reference means references shall be lim-ited to citing of title, version, date and source of publication.

Disclaimer and Legal NoticeDiligence has been exercised in the production of this publication. The content is based on an industry con-sensus of recognized good practices drawn from published handbooks, manuals, journals, standards,codes, technical papers, research papers, magazine articles, textbooks used for engineering curriculums,and on information presented during conferences and symposiums. ACCA has made no attempt to question,investigate or validate this information, and ACCA expressly disclaims any duty to do so. The commen-tary, discussion, and guidance provided by this publication do not constitute a warranty, guarantee, orendorsement of any concept, observation, recommendation, procedure, process, formula, data-set, product,or service. ACCA, members of the Manual S Review Committee, and the document reviewers do not war-rant or guarantee that the information contained in this publication is free of errors, omissions, misinter-pretations, or that it will not be modified or invalidated by additional scrutiny, analysis, or investigation.The entire risk associated with the use of the information provided by this standard is assumed by the user.

ACCA does not take any position with respect to the validity of any patent or copyright rights asserted in con-nection with any items, process, procedures, or apparatus which are mentioned in or are the subject of thisdocument, and ACCA disclaims liability of the infringement of any patent resulting from the use of or relianceon this document. Users of this document are expressly advised that determination of the validity of any suchpatent or copyright, and the risk of infringement of such rights, is entirely their own responsibility. Users ofthis document should consult applicable federal, state, and local laws and regulations. ACCA does not, by thepublication of this document, intend to urge action that is not in compliance with applicable laws, and thisdocument may not be construed as doing so. Nothing in this manual should be construed as providing legaladvice, and the content is not a substitute for obtaining legal counsel from the readers own lawyer in theappropriate jurisdiction or state.

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Acknowledgments

The author, Hank Rutkowski, P.E., ACCA Technical Consultant, gratefully acknowledges the diverse expertise embodied in

the membership of the ACCA Manual S Advisory Committee:

Manual S, Second Edition, Reviewers and Advisors:

Mechanical Contractors

Dan Foley, Foley Mechanical Inc.; Lorton, VA

Ellis G. Guiles, Jr. P.E., TAG Mechanical Systems, Inc.; Syracuse, NY

Jolene O. Methvin, Bay Area Air Conditioning & Heating; Crystal River, FL

John D. Sedine, Engineered Heating and Cooling, Inc.; Walker, MI

Daryl F. Senica, Senica Air Corporation, Inc.; Spring Hill, FL

Kenneth B. Watson, Roscoe Brown, Inc.; Murfreesboro, TN

Instructors

Jack Bartell, Virginia Air Distributors, Inc.; Midlothian, VA

John Pete Jackson, Alabama Power Company; Mobile, AL

Arthur T. Miller, Community College of Allegheny County; Oakdale, PA

Fred G. Paepke, Fitzenrider, Inc.; Defiance, OH

John F. Parker, J. Parker Consulting Services; Clanton, AL

Thomas A. Robertson, Baker Distributing Company, Inc.; New Haven, MO

David E. Swett, Omaha Public Power District; Omaha, NE

Original Equipment Manufacturers

Pamela Androff, Mitsubishi Electric Cooling & Heating; Suwanee, GA

Tom Fesenmyer, Emerson Climate Technologies, AC Division; Sidney, OH

Raymond A. Granderson, Rheem Manufacturing Company - A/C Division; Fort Smith, AR

J. Kelly Hearnsberger, Goodman Manufacturing Company; Houston, TX

Tom Johnson, Lennox Industries Inc.; Dallas, TX

Eric Weiss, The Trane Company; Tyler, TX

Robert Lambert, Carrier Residential and Commercial Systems; Indianapolis, IN

ConsultantsCharles S. Barnaby, Wrightsoft Inc.; Lexington, MA

Stan Johnson, Consultant; Austin, TX

Michael Lubliner, Washington State University - Extension Energy Program; Olympia, WA

Jack Rise, Jack Rise HVAC Technical Training; Tampa, FL

Henry T. Rutkowski, P.E., HTR Consulting, Inc.; Dover, OH

William W. Smith, Elite Software, Inc.; College Station, TX

Brent Ursenbach, Salt Lake County Planning & Development; Salt Lake City, UT

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Richard F. Welguisz, HVAC Consultant; Tyler, TX

Jon Winkler, National Renewable Energy Laboratory (NREL); Golden, CO

Association and Other ParticipantsTimothy M. Donovan, Sheet Metal Workers Local 265; Carol Stream, IL

Glenn C. Hourahan, P.E., Air Conditioning Contractors of America (ACCA); Arlington, VA

Edward Janowiak, Eastern Heating & Cooling Council (EHCC); Mt Laurel, NJ

Warren B. Lupson, Air-Conditioning, Heating and Refrigeration Institute (AHRI); Arlington, VA

Patrick L. Murphy, Refrigeration Service Engineers Society (RSES); Des Plaines, IL

Extended Reviewer to the CommitteeRon Bladen, Fairfax County Building Plan Review Department; Fairfax, VA

Special Thanks and AppreciationJohn D. Sedine for his guidance and leadership as the Committee Chair.

Staff Liaison TechnicalGlenn C. Hourahan, P.E., ACCA; Arlington, VA

Staff Liaison Production, Publishing, and EditingChristopher N. Hoelzel, ACCA; Arlington, VA

Publishing ConsultantPage layout and electronic publishing provided by Carol Lovelady, Lovelady Consulting; Roswell, GA

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Dedication

Personal Dedication

Professional Dedication

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Overview

This manual provides procedures for selecting and sizing residential cooling equipment, heat pumps, furnaces and boil-ers. These procedures emphasize the importance of using performance data that correlates sensible and latent coolingcapacity with all the variables that affect performance. Similar principles apply to heat pump selection and sizing, and tofurnace and boiler selection and sizing. All guidance produces installed, design condition capacity that is appropriate forthe applicable building load(s), but is less than, or equal to, the over sizing limit allowed for a given type of equipment.

This manual has been divided into two parts - a 'normative' portion and an 'informative' portion. The two, up-front nor-mative sections provide all the equipment selection and equipment sizing criteria necessary to implement the standard'srequirements (there are no additional selection requirements or sizing requirements in the balance of the document):

Section N1 - General RequirementsSection N2 - Equipment Size Limits

The informative sections and informative appendices in the balance of this document provide discussion and guidancerelated to procedure intent and use; includes example problems that detail application of the procedure. These informa-tive presentations are provided to augment practitioner understanding and application of the normative portion:

Sections 1 to 4 - Basic Concepts and IssuesSections 5 to 10 - Central Ducted System and Hydronic Heating ExamplesSections 11 to 13 - Ductless Air-Air EquipmentAppendix 1 to 5 - Implementation GuidanceAppendix 6 to 15 - Related InformationAppendix 16 to 21 - Ancillary Pages

Commentary on Over Size Limits for Cooling-Only Equipment and Heat PumpsFor Manual S guidance, the target value for equipment size is 100% (1.00 factor) of the smallest defensible value for theManual J total cooling load (sensible load plus latent load). When indoor humidity control for entire cooling season (thesummer design condition, and all part-load conditions) is an issue, total cooling capacity must be as close as possible to thetarget value on the high side, or total cooling capacity may be a little less than the target value (0.90 is the absolute mini-mum factor). Normative Section N2, Tables N1-1 and N1-2 provides upper and lower limits for the installed coolingcapacity of various types of cooling-only equipment and heat pump equipment.

If cooling season humidity control is not an issue, and if heating season energy use is an issue, the over size limit for heatpump equipment cooling capacity is equal to the Manual J total cooling load plus 15,000 Btuh. This reduces winter energyuse because it increases the amount of seasonal heat provided by the compressor, and reduces the amount of seasonalheat provided by an electric heating coil. Normative Section N2, Table A1-2 shows this guidance.

There is no energy use benefit for over sizing cooling-only equipment, regardless of the summer humidity control issue,or the cold winter weather issue. In other words, the 15,000 Btuh exemption does not apply to any type of cooling-onlyequipment. Even when there is no latent cooling load, summer comfort is improved by adequate room air motion, so theequipment must run as much a possible. As far as energy use is concerned, compressor cycling degrades seasonal effi-ciency, so the equipment must be a small as possible.

There is no energy use benefit for over sizing heat pump equipment installed in a location that has a mild winter climate.This is because electric coil heat is not an issue when the thermal balance point for equipment that has little or no excesscooling capacity is below, at, or slightly above, the Manual J winter design temperature for outdoor air. Therefore, theplus 15,000 Btuh limit does not apply to any type of heat pump equipment installed in a location that has mild winterweather. Also note that on-off cycling degrades seasonal heating efficiency when the outdoor air temperature is above thethermal balance point, and on-off cycling degrades seasonal cooling efficiency, so excess cooling capacity increasesannual energy use. Even if there is no latent cooling load, summer comfort is improved by adequate room air motion, sothe equipment must run as much a possible.

This overview is not part of the this standard. It is merely informative and does not contain requirements necessary for conformance to the standard. It has not been processedaccording to the ANSI requirements for a standard, and may contain material that has not been subject to public review or a consensus process. Unresolved objectors oninformative material are not offered the right to appeal at ACCA or ANSI.

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Standard Size IssuesResidential HVAC equipment is mass produced for economies of scale. Cooling-only equipment and heat pumps havesignificant jumps in nominal size. The over size limits specified in Table N2-1 and Table N2-2 allow for substantial devia-tion from the target value because of the realties of the market place.

n For central ducted equipment, the nominal condenser capacity for single compressor speed equipment may startat 1-1/2 tons, and typically increases in ton steps, but there tends to be a 1 ton jump from 4-tons to 5-tons. SomeOEM's do not have a 1-1/2 ton product (2 tons is the smallest size).

Effective total cooling capacity may be increased or reduced by a mismatch for nominal condenser-evaporator tonnage values,but this is generally a 2,000 Btuh adjustment, more or less.

The primary reason for mismatching condenser-evaporator tonnage values is to obtain correspondence between the evaporatorcoil sensible heat ratio and the Manual J sensible heat ratio.

OEM expanded performance data may not be readily available for condenser-evaporator combinations that deviate from thebasic matched-size product.

Product availability and delivery time depends on what is commonly purchased vs. what may possibly be purchased.

n For ducted equipment, the nominal condenser-side capacity for a multi-speed or variable-speed compressor typi-cally increases in 1-ton steps.

This type of equipment will cycle or modulate between low and high compressor speed for a large number of part-load hours.There is significant latent capacity for this mode of operation, so the undesirable effect of excess cooling capacity, as far as indoorhumidity control is concerned, is somewhat less than what it would be for single-speed equipment.

However, there is a low limit to equipment cooling capacity. When the cooling load is below this limit, the compressor cycles onand off. So for these part-load hours, indoor humidity control is similar to the control provided by single-speed equipment. Inother words, excess cooling capacity is an important issue for a significant number of part-load hours.

n Ductless equipment may be as small as one ton (or less), and may have ton steps (or less) to 5 tons. However, aduct system is required to distribute capacity among a group of rooms that are not part of a common open space.

Room cooling loads typically range from less than 1,000 Btuh to less than 4,000 Btuh.

Indoor air motion occurs in the space that is near the indoor coil, and less so for a common space that is beyond the throw of theindoor coil's grille, and not at all for remote spaces that have partition walls (with or without partition doors).

Some indoor coils are designed to serve a duct system. However, the available static pressure of the equipment's blower, and thetype of duct fittings, establishes the distribution limits (distances) of the duct runs.

Efficiency IssueIn general, high SEER values are at the expense of latent capacity and indoor humidity control. Excess cooling capacity, isa bigger issue for contemporary high SEER equipment than it was for older, lower SEER equipment.

Job Economics and Practitioner TalentProper use of expanded performance data (or the software equivalent) does not require much time, and is relatively sim-ple, providing the data is readily available. However, practitioner access to this data may be limited to products producedby one OEM, or a few OEM's. In addition, expanded performance data may not be readily available for various con-denser-evaporator size matches.

n Business issues typically limit practitioner access to the entire collection of available products.

n Time-is-money issues limit the scope of the available equipment capacity investigation.

n Price-point issues may eliminate classes of equipment that have preferred attributes, as far as excess capacity andhumidity control are concerned.

n Fine tuning equipment selection by blower Cfm adjustments, and/or condenser-evaporator size matching, takestime and skill.

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ConclusionThe possibility of a comfort problem, humidity problem, or mold-mildew problem increases with the amount of excesscooling capacity. The equipment sizing goal is to have no excess total cooling capacity. Tolerance for upside deviationdepends on the Manual J sensible heat ratio (JSHR). For example, a 1.18 over size factor is more compatible with an0.90 JSHR, and less compatible with an 0.75 JSHR.

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Overview of Size Limits for Residential HVAC Equipment

Equipment a

Tested andRated by theAHRI

Attributes ofLocal Climate

Notes b, c

Issue Minimum (deficient) and Maximum(excessive) Capacity Factors. d

CoolingCapacity

(Btuh)

Single Speed Compressor Multi- and Variable Speed Compressor

Air-Air GLHP e GWHP f Air-Air GLHP e GWHP f

Air-Air andWater-AirCooling-Only& Heat Pump

Mild Winteror

Has a LatentCooling Load

Total 0.90 to 1.15 1.25 0.90 to 1.20 0.90 to 1.25

Latent Minimum = 1.00. Preferred maximum = 1.50 (may exceed 1.5 if no reasonable alternative).

Sensible Minimum = 0.90. Maximum determined by total and latent capacities.

Air-Air andWater-AirHeat PumpOnly

Cold Winterand

No LatentCooling load

Total Maximum capacity = Manual J total cooling load plus 15,000 Btuh; Minimum factor = 0.90

Latent Latent capacity for summer cooling is not an issue.

Sensible Not an issue (determined by the limits for total cooling capacity).

a) Central ducted; ductless single-split; ductless multi-split equipment. AHRI: Air Conditioning, Heating and Refrigeration Institute.b) Mild winter: Heating degree days for base 65F divided by cooling degree days for base 50F less than 2.0. Cold winter = 2.0 or more.c) Latent cooling load: Manual J sensible load divided by Manual J total load less than 0.95. No latent load = 0.95 or more.d) Minimum and maximum capacity factors operate on the total, latent, and sensible capacity values produced by an accurate Manual J load

calculation (per Section 2 of the Eighth Edition of Manual J, version 2.0 or later). Multiply a size factor by 100 to convert to a percentage. Forexample, 1.15 excess capacity = 115% excess capacity.

e) GLHP: Ground loop heat pump (water in buried closed pipe loop).f) GWHP: Ground water heat pump (ground water from well, pond, lake, river, etc., flows though equipment and is discarded).

ElectricHeatingCoils

Furnaces;Heat Pumpsupplement;emergency

Load (Btuh) Maximum KW Minimum Capacity Factor Maximum Capacity Factor

15,000 5.0 Satisfy Load See Maximum KW

> 15,000 See Min and Max 0.95 1.75

Minimum and maximum capacity factors operate on the heating load produced by an accurate Manual J load calculation. Multiply a size factorby 100 to convert to a percentage.

Natural Gas,Oil, PropaneFurnaces

Duty Minimum Output Capacity Maximum Output Capacity

Heating only

1.001.40

Heating-Cooling Preferred

Heating-Cooling Allowed 2.00

Minimum and maximum capacity factors operate on the heating load produced by an accurate Manual J load calculation. Multiply a size factorby 100 to convert to a percentage. For heating-cooling duty, blower performance must be compatible with the cooling equipment.

Electric, andFossil FuelWaterBoilers

Duty Minimum Output Capacity Maximum Output Capacity

Gravity or forced convectionterminals in the space, watercoil in duct or air-handler.

1.00 1.40

Minimum and maximum capacity factors operate on the heating load produced by an accurate Manual J load calculation. Multiply a size factorby 100 to convert to a percentage. Refer to OEM guidance if boiler is used for potable water heat, or snow melting.

Hot WaterCoils

Duty Minimum Factor Maximum Factor

Gravity or forced convection terminals in the space.1.00

Two-position1.25

Throttling1.50Water coil in duct or air-handler.

Minimum and maximum capacity factors operate on the heating load produced by an accurate Manual J load calculation. Multiply a size factorby 100 to convert to a percentage. Two-position= open-close valve; Throttling = Full modulating 2-way or 3-way valve.

Electric and Fossil Fuel Water Heaters The space heating load is the Manual J load. The total load is the space heating load plus thepotable water load. Refer to OEM guidance for selection and sizing guidance.

Dual Fuel Systems Heat pump sizing rules apply, heating equipment sizing rules apply, see Section N2-12.

Ancillary Dehumidification See Section N2-13. May allow +15,000 Btuh excess cooling capacity for cold winter climate.

Humidifiers Minimum capacity humidification load, excess capacity dependent on smallest size available

AHAM Cooling and Heat Pump Equipment See Section N2-15 for sizing rules.

Direct Evaporative Cooling Equipment See Section N2-15 for sizing rules.

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Prerequisites and Learned Skills

Manual S assumes the practitioner is familiar with residential comfort conditioning systems and equipment, load calcula-tions, procedures for selecting and sizing air distribution hardware, and duct design and airway sizing procedures. Theprerequisites for using Manual S procedures are summarized here:

n A general understanding of the concepts, components, arrangements, procedures, requirements and terminologythat pertain to residential building construction and residential comfort systems.

n Experience with designing residential heating and cooling systems for comfort applications.

n Mastery of residential load calculation methods and procedures (the full version of ACCA Manual J, EighthEdition).

n Mastery of air distribution principles, and experience with using manufacturer's performance data to select andsize supply air hardware and return air hardware, and associated devices (ACCA Manual T).

n Mastery of duct design principles, and experience with designing duct systems (ACCA Manual D, Third Edition).

n A general understanding of HVAC operating and safety controls, control strategies, and control cycles.

n Experience with designing HVAC systems that adjust performance to maintain space temperature set-points atfull-load conditions, and at all part-load conditions (i.e., mastery of capacity control issues and strategies).

n Installing and commissioning refrigerant-cycle equipment and fuel burning equipment; and related power sup-plies, controls and vents.

n Installing and commissioning HVAC systems and components (per the ACCA HVAC Quality InstallationSpecification).

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Table of Contents

Sections N1 and N2 are normative, andare part of this standard.

Section N1

Definitions and General RequirementsN1-1 DefinitionsN1-2 RoundingN1-3 Target Value DeterminationN1-4 Altitude Vs. Load CalculationsN1-5 OEM Performance DataN1-6 Return Duct Load EffectN1-7 Engineered Ventilation Load EffectN1-8 InterpolationN1-9 Altitude Vs. Equipment PerformanceN1-10 Air Distribution RequirementN1-11 Degree Day Data

Section N2

Equipment Size LimitsN2-1 ScopeN2-2 Compliance with Sizing LimitsN2-3 Alternative MethodN2-4 ClimateN2-5 Sizing MetricsN2-6 AHRI-Rated Cooling-Only EquipmentN2-7 AHRI Heat Pump EquipmentN2-8 Electric Heating CoilsN2-9 Fossil Fuel FurnacesN2-10 Water BoilersN2-11 Water Heater Used for Space HeatN2-12 Dual Fuel SystemsN2-13 Ancillary Dehumidification EquipmentN2-14 Humidification EquipmentN2-15 AHAM-Rated AppliancesN2-16 Direct Evaporative CoolingN2-17 OEM Performance Verification Path

Sections 1 through 13 are merelyinformative, and are not part of the thisstandard.

Section 1

Equipment Size Issues and Limits1-1 Momentary Loads1-2 Excess Capacity vs. Performance1-3 Indoor Humidity Issues1-4 Summer Dehumidification1-5 Equipment Sizing Methods1-6 Cooling-Only Equipment Size

1-7 Heat Pump Equipment Size1-8 Interpolation1-9 Application Compatibility Caveats1-10 Electric Heating Coil Size1-11 Fossil Fuel Furnace Size1-12 Dual Fuel Systems1-13 Hot Water Boilers and Water Heaters1-14 AHAM Appliances1-15 Ancillary Dehumidification Equipment1-16 Humidification Equipment1-17 Evaporative Cooling Equipment1-18 Over Sizing Authority for Heat Pumps1-19 Power Disruptions1-20 Set-up and Set-Back1-21 Performance Expectations1-22 Energy and Op-Cost Calculations

Section 2

Cooling-Only and Heat PumpEquipment Selection2-1 Load Calculation2-2 Equipment Operating Limits2-3 Seasonal Efficiency Rating2-4 Expanded Performance Data2-5 Sizing Cooling Equipment2-6 Sizing Heat Pumps2-7 Thermal Balance Point Diagram2-8 Balance Point Manipulation2-9 Balance Point Use2-10 Supplemental Heat2-11 Emergency Heat2-12 Auxiliary Heat2-13 High Limit Temperature for Heating Coils2-14 Design Blower Cfm for Cooling2-15 Design Blower Cfm for Heating2-16 Design Blower Cfm for Duct Sizing2-17 Blower Data2-18 Component Pressure Drop Data2-19 Operating and Safety Controls2-20 System Start Up and Set Point Recovery2-21 Air Zoning Controls2-22 Ductless Split Controls

Section 3

Furnace and Water Boiler Selection3-1 Load Calculation3-2 Operating Limits3-3 Seasonal Efficiency Rating3-4 Performance Data3-5 Furnace Temperature Limit Calculations

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3-6 Water Temperature Limit Calculations3-7 Design Value for Furnace Blower Cfm3-8 Furnace Blower Data3-9 Component Pressure Drop Data3-10 Adequate Blower Pressure3-11 Equipment Sizing3-12 Fuel Burning and Combustion Venting3-13 Operating and Safety Controls3-14 Air Zoning Controls3-15 System Start Up and Set Point Recovery

Section 4

Humidity Control and EvaporativeCooling Equipment4-1 Ancillary Dehumidification4-2 . . . . . Whole House Dehumidifier Examples4-3 Ventilation Dehumidifier Examples4-4 Evaporative Cooling4-5 Winter Humidification Equipment

Section 5

Central Ducted Air-Air Cooling Examples5-1 Latent Cooling Load Issues5-2 Sensible Heat Ratio Issues5-3 Maximum Capacity for Cooling-Only Equipment5-4 Maximum Cooling Capacity for Heat

Pump Equipment5-5 Minimum Cooling Capacity5-6 Total Cooling Capacity Value5-7 Latent and Sensible Capacity Values5-8 Equipment Selection Examples5-9 Attributes of the Example Dwelling5-10 Balanced Climate Humid Summer Example5-11 Hot-Humid Climate Example5-12 Dry Summer Cold Winter Example5-13 Moderate Latent Load Applications5-14 Multi-Speed Performance5-15 Variable-Speed Performance5-16 Product Comparison Study5-17 Compare Fayetteville Equipment5-18 Compare Brunswick Equipment5-19 Compare Bosie Equipment

Section 6

Central Ducted Air-Air Heat Pump HeatingExamples6-1 Balance Point Diagram6-2 Electric Coil Heat6-3 Heating Performance Examples6-4 Balanced Climate Example6-5 Hot-Humid Climate Example6-6 Dry Summer Cold Winter Example6-7 Multi-Speed and Variable-Speed Design

6-8 Heating Performance for Two-Speed Equipment6-9 Heating Performance for Variable-Speed

Equipment6-10 Entering Air Temperature and Heating

Capacity Depend on Blower Cfm6-11 Use of Minimum Compressor Speed Data

Section 7

Central Ducted Furnace Examples7-1 Heating Load7-2 Maximum Heating Capacity7-3 Minimum Heating Capacity7-4 Blower Cfm7-5 Air Temperature Limits7-6 Equipment Selection Examples7-7 Attributes of the Example Dwelling7-8 Balanced Climate Humid Summer Example7-9 Hot-Humid Climate Example7-10 Dry Summer Cold Winter Example7-11 Oil or Propane Furnace7-12 Electric Furnace

Section 8

Dual Fuel Heating Guidance and Examples8-1 Economic Question8-2 Heat Pump Outputs and Energy Inputs8-3 Furnace Outputs and Energy inputs8-4 Economic Balance Point8-5 Break-Even COP8-6 Water-Air Heat Pump8-7 Return on Investment8-8 Furnace Sizing8-9 Heat Pump Sizing8-10 Retrofit Application8-11 Economic Balance Points - Fayetteville8-12 Economic Balance Points - Brunswick8-13 Economic Balance Points - Boise

Section 9

Water-Air Equipment Examples9-1 Redundant Guidance9-2 Entering Water Temperature9-3 Balanced Climate Humid Summer Example9-4 Hot-Humid Climate Example9-5 Dry Summer Cold Winter Example9-6 Multi-Speed Performance9-7 Variable-Speed Performance . . . . . . . . .

Section 10

Hydronic Heating Equipment Examples10-1 Hot Water Heating System Design10-2 Space Heating Load

TOC

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10-3 Maximum Space Heating Capacity10-4 Minimum Space Heating Capacity10-5 Water Temperature Limits10-6 Equipment Selection Examples10-7 Attributes of the Example Dwelling10-8 Cold Winter Example10-9 Mild Winter Humid Climate Example10-10 Hydronic Air Handler10-11 Engineered Ventilation10-12 Freeze Protection

Section 11

Ductless Single-Split Equipment11-1 Applications11-2 Design Goals11-3 Outdoor Equipment11-4 Indoor Equipment11-5 Performance Data and Guidance11-6 Expanded Performance Data11-7 Air Distribution11-8 Blower Data11-9 Duct System Design11-10 Equipment Selection and Sizing

Section 12

Ductless Multi-Split Systems12-1 Applications12-2 Design Goals12-3 Outdoor Equipment12-4 Indoor Equipment12-5 Performance Data and Design Guidance12-6 Expanded Performance Data for Cooling12-7 Expanded Performance Data for Heating12-8 Air Distribution12-9 Blower Data12-10 Duct System Design12-11 Equipment Selection and Sizing

Section 13

Single-Package Equipment13-1 Applications13-2 Design Goals13-3 Equipment Attributes13-4 PTAC and PTHP Rating Data13-5 Home Appliance Rating Data13-6 Expanded Performance Data for Cooling13-7 Expanded Performance Data for Heating13-8 Air Distribution and Noise13-9 Equipment Size13-10 Heating Performance

Appendices 1 through 21, and the Index,are merely informative, and are not part ofthe this standard.

Appendix 1

Basic Concepts for Air System EquipmentA1-1 Load CalculationsA1-2 Operating Conditions for Cooling EquipmentA1-3 Operating Conditions for Heat Pump HeatingA1-4 Operating Conditions for Forced Air FurnacesA1-5 Design Values for Supply Air CfmA1-6 Sensible Heat RatioA1-7 Cooling Cfm Determined by DesignA1-8 Prerequisites for Equipment SelectionA1-9 Expanded Performance DataA1-10 Blower Performance DataA1-11 Component Pressure Drop DataA1-12 Performance Data FormatsA1-13 Standard FormatsA1-14 AHRI Certification Data

Appendix 2

Entering Air CalculationsA2-1 Summary of ProcedureA2-2 Dry-Bulb and Wet-Bulb at the Return GrilleA2-3 Return Duct LoadsA2-4 Dry-Bulb and Wet-Bulb at the Exit

of the Return DuctA2-5 Outdoor Air FractionA2-6 Entering Dry-Bulb and Wet-Bulb

Temperatures for Raw Air VentilationA2-7 Entering Dry-Bulb and Wet-Bulb

Temperatures for Heat Recovery VentilationA2-8 Comprehensive ExampleA2-9 Entering Air Worksheet for CoolingA2-10 Entering Air Worksheet for HeatingA2-11 Entering Air Worksheet Psychrometrics

Appendix 3

Searching OEM Data for CandidateEquipmentA3-1 Total Capacity MethodA3-2 Ballpark Cfm MethodA3-3 Ballpark Cfm Calculation

Appendix 4

Requirements for ExpandedPerformance DataA4-1 Cooling Capacity ValuesA4-2 Compressor Heating Capacity ValuesA4-3 Temperature Range for Air-Air CoolingA4-4 Temperature Range for Water-Air Cooling

TOC

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A4-5 Temperature Range for Air-Air HeatingA4-6 Temperature Range for Water-Air HeatingA4-7 Compressor Speed for Expanded Cooling DataA4-8 Compressor Speed for Expanded Heating DataA4-9 Indoor Blower Speed for Expanded DataA4-10 InterpolationA4-11 Additional Reporting Requirements

Appendix 5

Altitude EffectsA5-1 Psychrometric CalculationsA5-2 Altitude Affects Equipment PerformanceA5-3 Air-Air Cooling EquipmentA5-4 Water-Air Cooling EquipmentA5-5 Hot Water Coil or Chilled Water CoilA5-6 Electric Heating CoilA5-7 Gas BurnerA5-8 Oil BurnerA5-9 Hot-Gas CoilA5-10 Heat Pump HeatingA5-11 Blower PerformanceA5-12 Duct System PerformanceA5-13 Duct System DesignA5-14 Effect on Duct System Operating PointA5-16 Air-to-Air Heat Exchangers

and Desiccant Wheels

Appendix 6

Energy and Op-Cost CalculationsA6-1 Heat Pump Heating - Reducing Use

of Electric Coil HeatA6-2 Intuitive IndicatorA6-3 Simplified IndicatorA6-4 Alternative to the Degree Day Ratio MethodA6-5 Basic Bin-Hour CalculationA6-6 Advanced MethodsA6-7 Weather Data for Energy ModelingA6-8 Proximity Issues for Weather Data Use

Appendix 7

Moisture and Condensation IssuesA7-1 Design Values for Indoor HumidityA7-2 Moisture Issues for WinterA7-3 Moisture Issues for Summer

Appendix 8

Condensation CalculationsA8-1 Condensation on SurfacesA8-2 Dew-Point TemperatureA8-3 Condensation ModelsA8-4 Minimum Surface TemperatureA8-5 Minimum R-Value

A8-6 Condensation on Interior SurfacesA8-7 Condensation on Exterior GlassA8-8 Winter Condensation in Structural PanelsA8-9 Summer Condensation in Structural PanelsA8-10 Condensation Inside of Duct RunsA8-11 Condensation Outside of Duct RunsA8-12 Condensation SoftwareA8-13 Consequences of HumidityA8-14 Consequences of CondensationA8-15 Building Science Software

Appendix 9

Water-Loop Issues for Water-Air Heat PumpsA9-1 Once-Through WaterA9-2 Earth-Loop WaterA9-3 Buried Water-Loop DesignA9-4 Piping GeometryA9-5 Length of Buried PipeA9-6 Summary of Design IssuesA9-10 Other IssuesA9-11 Energy CalculationsA9-12 Comprehensive Guidance and Software

Appendix 10

Multi-Split PipingA10-1 Pipe NamesA10-2 Basic Two-Pipe SystemA10-3 Two-Pipe Recovery SystemA10-4 Three-Pipe Recovery System

Appendix 11

Furnace Cycling EfficiencyA11-1 Part-Load Efficiency CurvesA11-2 Part-Load Efficiency EquationsA11-3 Energy Use and Furnace Over Sizing

Appendix 12

Matching Evaporators and Condensing UnitsA12-1 Evaporator PerformanceA12-2 Condensing Unit PerformanceA12-3 Refrigerant-Side Operating PointA12-4 Optimum Refrigerant-Side Balance Point

Appendix 13

Performance Models for Cooling-Onlyand Heat Pump EquipmentA13-1 Performance Model UseA13-2 Altitude Effects -- General SolutionA13-2 Air-Air Cooling ModelA13-3 Modeling an Exhibit of Air-Air DataA13-5 Presentation Adjustment

TOC

xx

A13-6 Air-Air Heating ModelA13-7 Water-Air Cooling ModelA13-8 Deficient Format for Cooling DataA13-9 Modeling an Exhibit of Water-Air DataA13-10 Error CheckA13-11 Water-Air Equation Set UseA13-12 Water-Air Cooling ExampleA13-13 Water-Air Heating ModelA13-14 OEM Data Format IssuesA13-15 Modeling Issues and CaveatsA13-16 Accuracy of OEM Data

Appendix 14

Air-Air Heat Pump Supply Air TemperatureA14-1 Balance-point DiagramA14-2 Supply Air TemperaturesA14-3 Supplemental KW Run FractionA14-4 Two Stages Improve PerformanceA14-5 Sizing Supplemental HeatA14-6 Staging Supplemental Heat

Appendix 15

Whole-House Dehumidifier PerformanceA15-1 Latent Load vs. Month of YearA15-2 Expanded Capacity DataA15-3 Dehumidifier Performance Equations

Appendix 16

Glossary

Appendix 17

Symbols, Acronyms and Abbreviations

Appendix 18

Summary of Tables and EquationsA18-1 Psychrometric Equations for AirA18-2 State Point of Air - Altitude Effect

Appendix 19

Supporting Detail For Equipment|Sizing ExamplesA19-1 Dwelling Performance and AttributesA19-2 Balanced Climate with Summer HumidityA19-2 Warm and Very Humid ClimateA19-3 Cold Winter Hot Dry Summer ClimateA19-4 Moderate Climate with Some HumidityA19-5 Cold Winter Hot Humid SummerA19-6 Hot Dry ClimateA19-7 Bin Weather Data

Appendix 20

Related Resources

Appendix 21

Blank FormsA21-1 Entering Air ConditionA21-2 Friction Rate Worksheet

TOC

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TOC

xxii

Section N1

Definitions and General Requirements

This section defines terminology that is unique to thestandard. It also summarizes mandatory requirementsand procedures that generally apply to equipment selec-tion and sizing efforts.

N1-1 DefinitionsTerminology that is directly related to showing compli-ance equipment sizing limit guidance is defined below,and also appears in the glossary.

Total Cooling Load

For equipment sizing, the sum of the sensible coolingload and the latent cooling load for the summer designcondition.

Heating Load

For equipment sizing, the heating load for the winterdesign condition.

Target Value

The target value is the Manual J total cooling load for thesummer design condition, for the space served by cool-ing-only equipment, or heat pump equipment.

n Section N1-3 summarizes the requirements forproducing a target value. Section N1-4 deals withaltitude, as it affects load calculations.

n The target value and equipment sizing rules deter-mine the minimum and maximum limits for total(sensible plus latent) cooling capacity. There alsoare lower and upper limits for latent coolingcapacity, for sensible cooling capacity, and forelectric coil heating capacity. Section N2 providesrelated guidance and limit values.

AHRI Equipment

OEM air conditioning and heat pump products testedand rated by the Air-Conditioning, Heating, and Refrig-eration Institute (AHRI).

AHAM Equipment

OEM air conditioning and heat pump products that arecertified by the Association of Home Appliance Manufac-turers (AHAM).

AHRI Rating Test for Cooling

For air-air equipment cooling, the Cooling-A test for95F/80F/67F air (per ANSI/AHRI Standard 210/240).For water-air equipment cooling, the 85F water in, 95Fwater out, 80F/67F air test (AHRI Standard 320-98).

Full Compressor Speed

For single-speed equipment, full compressor speed is theonly available compressor speed. For staged equipment,full compressor speed is the maximum available com-pressor speed. For variable-speed equipment, full com-pressor speed is the AHRI rating speed (see next item).

AHRI Rating Speed

Variable-speed compressors (typically by inverter tech-nology) operate over a range of speeds. For this

This section is part of the this standard.

N1-1

Capabilities, Sensitivities and Defaults

Capability relates to mathematical modeling. Forexample, load calculation procedures use mathemati-cal models for fenestration loads, structural surfaceloads, duct loads and engineered ventilation loads. Acredible procedure has a model for outdoor condi-tions, and for every load producing item associatedwith the structure, and its comfort system. Equipmentperformance data provides an other example of amathematical model.

Sensitivity relates to the variables in a mathematicalmodel. For example, a fenestration model may onlyapply to clear, single pane, wood frame assemblies, orit may apply to any product listed in the NFRC direc-tory. The credibility of the model depends on how itssensitivities match up with the valuables that affectthe fenestration load. An equipment performancemodel has its own set of sensitivities.

Fixed defaults are standard inputs for sensitivity val-ues. For example, the Manual J leakage values for asealed duct system are 0.12 Cfm/SqFt for supply runsand 0.24 Cfm/SqFt for return runs (this is one of fiveleakage options). Fixed defaults must be technicallydefensible (based on physical and/or theoreticalresearch). Using one, worst-case compass directionfor the front door of a production home is a blatantexample of improper use of a fixed default.

Adjustable defaults simplify model use for commonoccurrences. For example, if day-to-day work typi-cally relates to dwellings that have clear, double pane,wood frame fenestration, the practitioner may use aform, or software setting, that is designed or set-up tosolve this particular problem. The danger is that suchforms and settings are used when they do not apply tothe project at hand.

equipment, full compressor speed is the speed used forthe AHRI rating test that produces the advertised valuefor total cooling Btuh.

n Expanded cooling performance data for full com-pressor speed is used for equipment sizing.

n Knowledge of the actual compressor speed value(Rpm, for example) for the AHRI rating test forcooling is not required for equipment sizing.

n It may be that a compressor can operate at speedsthat exceed the speed used for the AHRI rating testfor cooling, but cooling performance for this speedor speeds is not used for equipment sizing.

AHRI Rating Test for Heating

For air-air equipment, the compressor heating test for47F outdoors. For water-air equipment , the compressorheating test for 70F entering water temperature.

Enhanced Compressor Speed

Heat pump balance point diagrams, and supplementalelectric coil size, are normally based on expanded heatingperformance data for the compressor speed that is usedfor the AHRI rating test that produces the advertisedcompressor heating capacity value for a 47F outdoor airtemperature, or a 70F entering water temperature.

For single-speed equipment, there is only one compressorspeed. The maximum available compressor speedapplies to staged equipment. For variable-speed equip-ment, this may be the compressor speed for the AHRI rat-ing test for heating, or the compressor may be able tooperate at a higher speed (enhanced speed).

When applicable, expanded heating performance datafor enhanced speed is used for balance point diagrams,and for supplemental electric coil sizing, providing thatenhanced speed is continuously available for an unlim-ited amount of time. Enhanced cooling performance isnot used to size equipment (see AHRI Rating Speed).

Applied Capacity

Applied capacity is the amount of equipment cooling orcompressor heating capacity for the operating circum-stances produced by the summer design condition, or thewinter design condition.

n Applied cooling capacity is for the full compressorspeed. For variable speed cooling and heat pumpequipment, full compressor speed is the AHRI rat-ing speed, as defined on the next page.

n Applied compressor heating capacity is normallyfor the compressor speed used for the AHRI ratingtest for heating, but may be for enhanced speedwhen enhanced speed is continuously availablefor an unlimited amount of time.

n Sensible, latent, and total cooling capacity valuesdepend on the blower Cfm, and the summerdesign condition values for outdoor air tempera-ture or entering water temperature, entering airwet-bulb temperature, and entering air dry-bulbtemperature.

n Heat pump heating capacity depends on blowerCfm, and the winter design condition values foroutdoor air temperature or entering water tem-perature, and entering air dry-bulb temperature.

n Applied capacity values must be for the enteringair condition that corresponds to the circum-stances that affect the load calculations for coolingand heating. See Sections N1-6 and N1-7.

n Applied capacity values cooling and heating mustbe fully interpolated values when equipmentmanufacturers's data conditions do not exactlymatch the operating conditions for the summer orwinter design condition. More detail is provide bySection N1-8.

n For elevations above 2,500 Feet, applied capacityvalues for cooling and heating must be adjustedfor altitude, or follow OEM guidance if an adjust-ment is required for 2,500 feet, or less. See Sec-tion N1-9.

Full Capacity

For single-speed equipment, full capacity refers to opera-tion at the only available compressor speed. For stagedequipment, full capacity refers to operation at the maxi-mum available compressor speed. For variable-speedequipment, full capacity refers to performance when thecompressor operates at the AHRI rating test speed forcooling, or the AHRI rating test speed for heating.

Maximum and Minimum Capacity

For staged equipment and variable-speed equipment,maximum and minimum capacity refers to the highestand lowest compressor speeds allowed by the OEM'sdesign. For some variable speed equipment, maximumcompressor speed may exceed the full-capacity speed(see enhanced speed).

Over Size Factor

The over size factor (OSF) equals the applied equipmentcapacity value divided by the target value.

OSF = Applied capacity value / Target value

Over Size Limit

The over size limit (OSL) is the acceptable amount of defi-cient or excess applied capacity, as it relates to the targetvalue. The over size factor must be within the boundariesof the over size limit.

Section N1

N1-2

Minimum OSL OSF Maximum OSL

Section N2 provides OSL values.

Expanded Performance Data

Cooling performance data, or heating performance datathat correlates sensible and latent cooling capacity, orheating capacity, with all the operating variables thataffect the capacity values. Original equipment manufac-turers (OEMs) provide this data in electronic orhard-copy form, or as an interactive computer model. Therange of the data, as defined by the available choice ofoperating variables (compressor speed, burner stage orturndown ratio, blower Cfm, outdoor air temperature,entering water temperature, entering wet-bulb tempera-ture, entering dry-bulb temperature, for example) mustbe compatible with the summer or winter design condi-tions used for the load calculation.

Excess Latent Capacity

Excess latent capacity equals the latent capacity valueindicated by an OEM's expanded cooling performancedata minus the latent load for the summer design condi-tions. Both values are for the operating circumstances thatapply to the summer design conditions used to computethe cooling loads.

Whole-House Dehumidifier

Ancillary dehumidification equipment that is designed toprocess indoor air (the cabinet has an inlet for indoor air,and an outlet for discharge air). The equipment may havea duct interface with the primary equipment's duct sys-tem, or may have its own independent duct system, ormay be an unducted, movable appliance. Its purpose is toprovide a high limit (55% RH) for indoor humidity whenthe momentary sensible load is significantly less than thedesign (summer condition) load, and the momentarylatent load is relatively large, about equal to, or greaterthan the summer design load. The dehumidifier mayhold a lower indoor humidity set-point when equipmentcapacity exceeds the moisture load for 55% RH indoors.When outdoor air and indoor air are mixed in a duct teeand used as input to a whole-house dehumidifier, thedehumidifier is a ventilation dehumidifier, as far asequipment selection and sizing guidance is concerned.

Ventilation Dehumidifier

Ancillary dehumidification equipment that is designed toprocess indoor air and outdoor air (the cabinet has inletsfor indoor air and outdoor air, and an outlet for dischargeair). The dehumidifier will have a duct run to outdoor air ,plus duct runs that interface with the primary equip-ment's duct system. Its purpose is to provide a high limit(55% RH) for indoor humidity when the momentary sen-sible load is significantly less than the design (summercondition) load, and the momentary latent load is rela-tively large, about equal to, or greater than the summer

design load. The dehumidifier may hold a lower indoorhumidity set-point when equipment capacity exceeds themoisture load for 55% RH indoors.

N1-2 RoundingThere will be occasions where the OSF value is slightlydifferent than the OSL value; a 1.201 to 1.209 OSF vs. a1.20 limit, or a 0.891 to 0.899 OSF vs. a 0.90 limit, for exam-ple. For the purpose of comparing the over size factor tothe over size limit, ignore everything after the third deci-mal place, and round up or down to the second decimalplace. For example:

1.201 to 1.205 = 1.20

1.206 to 1.209 = 1.21

0.891 to 0.895 = 0.89

0.896 to 0.899 = 0.90

N1-3 Target Value DeterminationA target value for equipment size must be provided by anaggressive, accurate load calculation that has the appro-priate capabilities and sensitivities. The general require-ments are summarized here.

n The load calculation, and all the details of the loadcalculation, must be for a specific dwelling, itsequipment, and its distribution system, for a spe-cific location.

n In regard to the preceding bullet item, one set ofdesign calculations is sufficient for two or moreidentical dwellings (floor plan and constructiondetails), providing the dwellings face the samecompass direction, and have an identical set ofsystem loads.

n The ANSI standard for performing a residentialload calculation is the latest verison of theunabridged version of Manual J, Eighth Edition.

n Alternative load calculation methods must havesimilar capabilities and sensitivities, and defensi-ble procedures (see the sidebar on the first page ofthis section).

n The abridged version of the Eighth Edition ofManual J may, or may not, be an alternativemethod. This may be used if the attributes of thedwelling's construction and comfort system com-ply with the Abridged Edition Check List in frontof the abridged manual.

n The load calculation must be based on informationobtained by a careful and accurate survey of plansand drawings, or a site inspection.

n The load calculation must account for systemloads produced by the HVAC equipment and its

Section N1

N1-3

air or water distribution systems, as applicable tothe particular application.

n For the guidance in this standard, boiler andheater size is based on the load calculation heatingload. Refer to other guidance if the boiler or waterheater provides heat for any other purpose (typi-cally for potable water, perhaps for snow melting).

n There shall be no explicit safety factor applied toany step of the load calculation procedure, or tothe final value.

n There shall be no implicit safety factor (fudginginput data) applied to any step of the load calcula-tion procedure.

N1-4 Altitude Vs. Load CalculationsAltitude sensitive psychrometrics determine the psy-chrometric properties of outdoor air and indoor air. Infil-tration loads and ventilation loads depend on an altitudeadjustment for air density.

n Manual J weather data and related procedureshave altitude sensitivity.

n The load calculations for the example problems inthe informative sections of this document areadjusted for altitudes above sea level, even if theeffect is small..

n Load calculation procedures and software mustprovide altitude sensitivity.

n Altitude also affects equipment performance, seeSection N1-9.

N1-5 OEM Performance DataComprehensive (expanded) OEM performance datamust be used to select and size equipment, and to designthe air distribution system. Appendix 4 summarizes thereporting requirements for determining applied capacity.Related commentary and exhibits appear at variousplaces in the informative sections of this document, and inthe example problem sections.

n Cooling capacity may be reported as total capacityand sensible capacity, or as total capacity with acoil sensible heat ratio.

n OEM data provides sensible heating capacity val-ues for compressor heat, furnace heat, boiler heat,water heater heat, electric coil heat, and water-coilheat.

n OEM data provides, as applicable, operatingrange limits for ambient air temperature, for enter-ing air or water temperature, for leaving air orwater temperature, for air or water temperaturerise, and for air or water temperature drop.

n When applicable, a complete set of blower Cfm vs.external static pressure data is required for air dis-tribution system design. Air-side components thatwere in place (produced a pressure drop) duringthe blower test must be identified by OEM.Air-side components that are not identified asbeing in-place for the blower test (by blower tablefootnotes, or by an OEM letterhead response to astakeholder request for information), must betreated as a source of external airflow resistance.

n For air distribution system design, air-side pres-sure drop data is required for any type of coil, fil-ter, or air-side component that produces air flowresistance that is not accounted for by the OEM'sblower data.

n Refrigeration cycle equipment, fossil fuel heatingequipment, electrical resistance heating equip-ment, and hydronic heating equipment that isselected and sized without the aid of adequateperformance data, is not in compliance with Man-ual S guidance.

n When adequate performance data is not availableto authorized stakeholders, or when the availabledata is incomplete, the OEM must process designinformation provided by a stakeholder (typically apractitioner), and return values for total, sensibleand latent cooling capacity; for compressor heat-ing capacity; or for fossil fuel, electrical resistance,or hydronic equipment heating capacity, as appli-cable. When applicable, also provide operatingrange limits, temperature rise limits, and tempera-ture drop limits.

Sensitivity to Heat Sink and HeatSource Temperature

OEM performance data for air-air equipment shows thatrefrigeration equipment capacity depends on the temper-ature of the outdoor air. For cooling, this is the design out-door air temperature used for the cooling loadcalculation. For compressor heating, this is the designoutdoor air temperature used for the heating loadcalculation.

OEM performance data for water-air equipment showsthat equipment capacity depends on the temperature ofthe water entering the equipment. For cooling, this is thewarmest temperature expected for the cooling season(the local ground water temperature, or a much warmertemperature for a buried, closed-loop system). For com-pressor heating, this is the coldest temperature expectedfor the heating season (the local ground water tempera-ture, or a much cooler temperature for a buried,closed-loop system).

Section N1

N1-4

For buried, closed-loop (GLHP) systems, maximum andminimum water temperatures depend on a multitude ofvariables that affect the water-loop design. Water-loopdesign requires relevant expertise and software. Sec-tion 9-2 provides default guidance for maximum andminimum water temperature, see also Appendix 9.

n For this standard, default guidance for enteringwater temperature is used for example problems.

n Default guidance for entering water temperaturemay be used for preliminary equipment selectionand sizing.

n Final selection and sizing decisions must be basedon the specific details of the water-loop design.

n This standard defers to water-loop design guid-ance provided by other authority (local code,industry guidance, OEM guidance, for example).

Sensitivity to Blower Cfm

OEM performance data for cooling-only and heat pumpequipment shows that cooling performance, and com-pressor heating performance, depend on blower Cfm.Any blower Cfm listed in the OEM's performance datamay be used for equipment selection, but it is best to use amid-range value in case a minor performance adjustmentis required after the equipment is installed.

The heating capacity of a hot water coil depends (in part)on airflow Cfm through the coil. This may, or may not, beequal to the blower Cfm, depending on the location of thecoil.

The temperature rise through a furnace heat exchanger,electric resistance coil, or hot water heating coil dependson the Cfm flowing through the device.

Sensitivity to Water GPM

OEM performance data for water-air refrigeration cycleequipment shows that cooling performance, and com-pressor heating performance, depend on the water flowrate (Gpm). The OEM may require a water flow rate for anopen (once though water system), and a different flowrate for a water-loop system.

Hot water coil performance depends on coil Gpm. Waterflow rate is a water temperature rise issue for boilers andwater heaters.

Sensitivity to Entering Air Condition

OEM performance data for cooling-only and heat pumpequipment shows that total, sensible and latent capacitydepends on the condition of the entering air. OEM perfor-mance data for hot water coils shows that heating capac-ity depends on the dry-bulb temperature of the enteringair.

n For wet-coil cooling, the total, sensible, and latentcapacity values for size limit calculations must bebased on the entering air wet-bulb and dry-bulbtemperatures for the summer design condition.

n For dry-coil cooling (higher elevations, or a dry cli-mate at a lower elevation), the total and sensiblecapacity values for size limit calculations must bebased on a dry-coil value for entering air wet-bulband a dry-bulb temperature for the summerdesign condition.

n For compressor or water-coil heating, equipmentcapacity depends on the entering dry-bulb tem-perature for the winter design condition.

n The entering air temperature (typically dry-bulb,possibly dry-bulb and wet-bulb) for the summerdesign condition, or the winter design condition,must comply with OEM limits for entering airtemperature, and for leaving air temperature.

n The condition of the air entering the equipmentmay be the same as the condition of the room air(no return duct or engineered ventilation load).

n The condition of the air entering the equipmentmay just depend on the sensible and latent returnduct loads (no engineered ventilation loads).

n The condition of the air entering the equipmentmay just depend on the sensible and latent engi-neered ventilation loads (no return duct loads).

n The condition of the air entering the equipmentmay depend on the return duct loads and the engi-neered ventilation loads.

N1-6 Return Duct Load EffectA sensible duct load affects the dry-bulb and wet-bulbtemperatures of the entering air. A latent duct load affectsthe wet-bulb temperature of the entering air.

n The condition (dry-bulb and wet-bulb tempera-tures) of the air entering the return duct is the con-dition of the air at the return grille (the indoor airdesign condition used for the load calculation).

n For cooling, the condition of the air leaving thereturn duct depends on the sensible and latentloads for the return duct.

n For heating the dry-bulb temperature of the airleaving the return duct depends on the sensiblereturn duct load.

Implementation

Section A2-3 shows how a version of Manual JWorksheet G is used to evaluate return duct loads.Appendix 1 provides tables of default values that may beused to estimate the condition of the air leaving the returnduct. Appendix 2 has procedures and equations that

Section N1

N1-5

provide mathematical solutions to specific problems. Themain issues are summarized here:

n The psychrometric equations for duct loadsdepend on an altitude correction factor (ACF).

Sensible Btuh = 1.1 x ACF x Cfm x Temp. DifferenceLatent Btuh = 0.68 x ACF x Cfm x Grains DifferenceFigure A5-1 provides ACF values.

n Altitude sensitive psychrometrics determine therelationship between dry-bulb temperature,wet-bulb temperature, relative humidity, andhumidity ratio.

n For consistency, the procedures and examples inthis document have altitude sensitivity, even if theeffect is small.

Related Forms and Software Tools

Appendix 21 provides a blank Worksheet G form, andforms for implementing Appendix 2 procedures. SomeManual J software products have an altitude sensitivepsychrometrics module. Other sources for psychrometricsoftware are available. These software tools are relativelysimple to use.

N1-7 Engineered Ventilation Load EffectFor indoor air quality, a relatively small amount of out-door air may be mixed with a much larger amount ofreturn air before it enters the comfort system equipment.A sensible ventilation load affects the dry-bulb andwet-bulb temperatures of the entering air. A latent venti-lation load affects the wet-bulb temperature of the enter-ing air.

n If there are no return duct loads, the return airdry-bulb and wet-bulb temperatures depend onthe dry-bulb and wet-bulb temperatures at thereturn grille.

n Section N1-6 guidance determines the conditionof the return air if the return duct is in an uncondi-tioned space.

n Outdoor air dry-bulb and wet-bulb temperaturesfor cooling depend on the summer design valuesfor the load calculation. Outdoor air dry-bulb tem-perature for heating depends on the winter designvalue for the load calculation.

n The condition of the mixed air depends on the out-door air cfm and the return air Cfm. At the air han-dler, outdoor air Cfm plus return air Cfm equalsblower Cfm.

n The condition of the outdoor air that is mixed withreturn air may depend on the use and effective-ness of heat recovery equipment (sensible only, orsensible and latent recovery).

Implementation

Appendix 1 provides tables of default values that may beused to estimate the condition of the air leaving the returnduct, and the condition of mixed air. Appendix 2 has pro-cedures and equations that provide mathematical solu-tions to specific problems. The main issues aresummarized here:

n For a given location, an outdoor air Cfm value, or aprocedure to determine an outdoor air Cfm valueis specified by a local code or governing authority,or local authority may be silent on this issue.

n A fresh air Cfm value per an industry standard,such as ASHRAE 62.2, may be used if engineeredventilation is not locally mandated by a code orauthority.

n Mixed air psychrometrics determine the relation-ship between outdoor air Cfm, return air Cfm; andthe associated dry-bulb temperatures, wet-bulbtemperatures, and humidity ratios.

n Altitude sensitive psychrometrics determine therelationship between dry-bulb temperature,wet-bulb temperature, relative humidity, andhumidity ratio.

n For consistency, the procedures and examples inthis document have altitude sensitivity, even if theeffect is small.

Related Forms and Software Tools

Appendix 21 provides forms for implementing Appen-dix 2 procedures. Some Manual J software products havean altitude sensitive psychrometrics module. Othersources for psychrometric software are available. Thesesoftware tools are simple to use.

N1-8 InterpolationPublished OEM performance data typically has steps inthe data set, outdoor air dry-bulb temperature in 10Fincrements, for example. A full interpolation across theset of relevant variables is required when equipmentcapacity values are extracted from OEM performancedata. This may require two or more simultaneous inter-polations. For example, sensible cooling capacity for agiven blower Cfm depends on outdoor air temperature,entering wet-bulb temperature, and entering dry-bulbtemperature. Exact interpolation is used through out thisdocument, even if the effect is small.

N1-9 Altitude Vs. Equipment PerformanceThe performance of most types of heating-cooling equip-ment is affected by altitude. For example, OEM equip-ment performance data is for sea level air density, socooling capacity, or furnace heating capacity, is

Section N1

N1-6

somewhat less than indicated by the performance datawhen the equipment operates at 5,000 feet of elevation.The HVAC industry traditionally ignores this effect foraltitudes of 2,500 Feet, or less. The guidance in this stan-dard defers to this habit, because the effect is small.

Unless the guidance in this standard is superceded byspecific OEM instructions pertaining to installation ataltitude, equipment performance must be adjusted foraltitudes above 2,500 feet. Appendix 5 guidance andde-rate factors may be used for this purpose when OEMliterature does not provide specific guidance for productuse at higher elevations.

N1-10 Air Distribution RequirementFor equipment that serves an air distribution system,blower power must be adequate for the air flow resistanceproduced by all air-side components that are external tothe OEM's blower data, and the airflow resistance pro-duced by the duct fittings, and straight duct runs in thecritical circulation path.

n A circulation path is the supply air path from theblower to a space, plus the return path from thespace, back to the blower.

n The critical circulation path is the path that has thelargest pressure drop for the path's airflow rate.

- The circulation paths are parallel paths.

- If the blower has enough power for the path that hasmost airflow resistance (path pressure drop), it hasmore than enough power for all other paths.

- Adjusted balancing dampers in the lower resistancepaths make blower power correct for all paths.

n An external pressure dissipating component maybe a filter, cooling coil, or heating coil installed in,or at, an air handler or furnace cabinet. This wouldbe any piece of equipment that was not in place forthe blower test that provided the values for theblower performance table.

n A supply grille, a return grille, a balancingdamper, a zone damper, and a duct coil are exam-ples of external pressure dissipating componentsthat may be installed in a circulation path.

n External static pressure (ESP) is the pressure thatmoves the air though all pressure dissipatingitems that are external to the blower data.

n Available static pressure (ASP) is the pressure thatmoves the air though the fittings and straight runsin the critical circulation path.

n Available pressure equals external pressureminus the pressure dissipated by components thatare external to the blower data.

n The available static pressure, and the total effec-tive length (fitting equivalent lengths plus straightrun lengths) of the critical circulation path (TEL),determines the friction rate value (pressure dropper 100 feet of duct) for duct airway sizing.

n The Manual D Friction Rate Worksheet summa-rizes a procedure that evaluates the preceding bul-let items and determines when blower power iscompatible with reasonable duct airway sizes, andduct air velocity limits.

n The Friction Rate Worksheet procedure may beperformed by hand on any piece of physical orelectronic paper.

N1-11 Degree Day DataPer Table N2-2, the limit for excess cooling capacity forheat pump equipment depends on the ratio of heatingdegree days to the base 65F (HDD-65) to the coolingdegree days to the base 50F (CDD-50). A significantincrease in excess total cooling capacity is allowed if thisratio is 2.0, or more, providing that the sensible heat ratiofor the total and sensible cooling loads for the summerdesign condition is less than 0.95. The Condition B sizingrule for heat pump equipment applies when the answerto both questions is yes.

Degree day information is provided by the sources listedbelow. This data is not homogenized. For a given loca-tion, there will be differences in the degree day ratio,depending on the source of the data. This is not an issuefor locations that are decidedly cold, or decidedly warm,but it is an issue for locations that are at the tipping pointfor the 2.0 DD-ratio test.

Section N1

N1-7

Degree Day Data ComparisonFor Bosie, ID, and Vicinity

ASHRAENote 1

BoiseAir Port

Caldwell Lucky PeakDam

7NStation

HDD-65 5,658 5,698 ~ ~

CDD-50 3,036 2,624 ~ ~

DD Ratio 1.86 2.13 ~ ~

NOAANote 2

BoiseAir Port

Caldwell Lucky PeakDam

7NStation

HDD-65 5,727 5,606 5,730 6,325

CDD-50 2,856 3,119 2,840 2,527

DD Ratio 2.01 1.80 2.02 2.50

1) CD-ROM in back of the in the 2009 ASHRAE Handbook ofFundamentals.

2) NOAA: Annual Degree Days to Selected Bases, 1971-2000;Climatography of the United States No. 81; Supplement No. 2

Figure N1-1

Figure N1-1 (previous page) provides an example of thedegree day values and degree day ratios, for the Bosie, ID,area. Note that the results of the degree day ratio test areexactly opposite, depending on the data source. Also notethat the NOAA data has degree day values for threenearby locations, vs. one location for the ASHRAE data.All of these locations are close to each other, and the con-sensus per the Figure N1-1 ratios, is that the Boise areaqualifies for the Condition B sizing rule.

Figure N1-1 thinking is not software friendly. Therefore,the practitioner must specify the HDD-65 and CDD-50values for the location of interest. Either of the followingdata sources may be used.

ASHRAE Weather Data

Climatic design information (including degree day data)for 5,564 locations is provided by a CD-ROM in back ofthe in the 2009 ASHRAE Handbook of Fundamental (orthe latest version of this data base). To access this data,load Chapter 14 from the ASHRAE CD, and click on thefollowing link in the first paragraph of Chapter 14.

The complete data tables for all 5,564 stations are con-tained on the CD-ROM that accompanies this book.

Or use the computer's operating system to open CD files.Right-click on the CD, and use Explore command to openthe Program Files Folder. Double left-click (DLC) on thisfolder, DLC on the ASHRAE folder, DLC on the 2009ASHRAE Handbook folder, DLC on the Stations folder,DLC on the StaList_P.pdf file; then find the state of inter-est, then DLC on the town of interest.

NOAA Degree Day Data

Heating and cooling degree day values for various basetemperatures are provided by the following NOAA doc-ument. This may be downloaded from the NOAA website at no cost.

Annual Degree Days to Selected Bases, 1971-2000;Climatography of the United States No. 81; SupplementNo. 2; National Climate Data Center, Asheville N.C.

http://cdo.ncdc.noaa.gov/climatenormals/clim81_supp/CLI

M81_Sup_02.pdf.

Section N1

N1-8

Section N2

Equipment Size Limits

Heating-cooling equipment is sized for comfort and effi-ciency. For climates that have significant summer humid-ity, excess compressor capacity is minimized foroptimum indoor humidity control and refrigeration cycleefficiency. For dry summer climates, latent cooling capac-ity is not an issue, so the combined heating season effi-ciency of a heat pump compressor and the electric heatingcoil benefits from excess compressor capacity for cooling.There is no benefit from over sizing electric heating coilsand fossil fuel heating equipment. Guidance pertainingto equipment sizing limits take these issues into account.

N2-1 ScopeThis section provides sizing limits for the followingequipment. See Part 2 and Part 3 of this document forapplication guidance and example problems.

AHRI-rated cooling-only equipment

AHRI-rated heat pump equipment

Electric heating coils

Fossil fuel furnaces

Hot water boilers and water heaters

Dual fuel systems

Ancillary dehumidification equipment

Winter humidification equipment

AHAM-certified appliances

Direct evaporative cooling equipment

N2-2 Compliance with Sizing LimitsFor refrigeration cycle equipment, acceptable size is dem-onstrated by showing that a capacity value extractedfrom OEM performance data is in a limited range whencompared to a Manual J load value. There is only onedata set for equipment that operates at one compressorspeed, so there is no question about which data set to usefor equipment sizing. Since multi-speed and vari-able-speed equipment may have two or more sets of per-formance data, the data set that must be used forequipment sizing is specified here:

ECM Step and Variable Blower Speed Equipment

For the equipment sizing guidance in this standard,equipment that operates at one compressor speed is sin-gle-speed equipment, regardless of the technology usedto control indoor blower speed, and outdoor fan speed forair-air equipment.

n Compressor speed staging or modulation has adramatic effect on system performance, as far ascompressor run time at part-load is concerned.

n Blower/fan speed modulation may have a usefuleffect on compressor run time at part-load, but thisis not equivalent to the benefit offered by compres-sor speed control.

Single Compressor Speed Equipment

For single-speed equipment, there is one compressorspeed and a corresponding data set. Therefore, expandedcooling performance data for the only possible compres-sor speed must be used for equipment sizing.

Multi Compressor Speed Equipment

For two or more distinct compressor speeds, there may beperformance data for each compressor speed (typicallylow, or stage one speed; and high, or stage two speed).The expanded cooling performance data for high-speed(full compressor capacity) must be used for equipmentsizing.

Variable Compressor Speed Equipment

At this time (early 2013), data presentation for variablecompressor speed equipment (that typically uses invertertechnology), varies with the product. In general, there aredata exhibits for maximum capacity, an intermediatecapacity, and minimum capacity. An OEM may provideall three sets, a maximum-minimum set, or just the datafor maximum capacity; or no data at all (just the AHRI rat-ing values).

The concepts of maximum capacity and full capacity aredefined by this document. Per Section N1-1, full capacityis the capacity for the compressor speed used for theAHRI rating test for cooling. It may be that maximumcapacity is the same as full capacity, or it may be that max-imum capacity is for a compressor speed that exceeds thevalue used for a AHRI rating test (i.e., for the maximumcompressor speed allowed by the OEM's design).

For this document, enhanced speed refers to compressorspeeds that exceed the speed used for th e AHRI ratingtest for heating or cooling. Enhanced speed may, or maynot, be available on a continuous basis (i.e., enhancedspeed may have a time limit triggered by a monitoredrefrigeration-side, electric power, or motor heat variable).

The expanded cooling performance data for the compres-sor speed used for the AHRI rating test that produces the

N2-1

advertised value for AHRI total cooling capacity must beused for equipment sizing. The actual compressor speedvalue used for the rating test is of interest, but this infor-mation is not required for equipment sizing.

n The AHRI rating test is common to all products.

n Product SEER is based on the AHRI rating test.

n This eliminates questions pertaining to what max-imum or full capacity terminology actuallymeans.

n This eliminates questions pertaining to enhancedspeed availability, and endurance.

n This eliminates questions about actual compres-sor speed values.

Data Availability

Availability of expanded performance data for full-cool-ing capacity is a mandatory requirement for equipmentselection and sizing. This applies to equipment that oper-ates at a single compressor speed, two or more compres-sor speeds, and to equipment that has the variable-speedfeature.

n Figures A1-22, A1-23, A1-24 and A1-26 showexamples of expanded performance data for sin-gle-speed equipment that has one indoor coil.

n Figures 5-11 and 5-12 show examples of expandedperformance data for two-speed and vari-able-speed equipment that has one indoor coil.

First stage data, or minimum speed data is very usefulto system designers and energy use modelers, but is notused for equipment sizing.

n Figures A1-27, A1-28 and A1-29 show examples ofexpanded performance data for equipment thathas two or more indoor coils.

Data Attributes

Acceptable cooling data must correlate total capacity andsensible capacity (or sensible heat ratio) with outdoor airtemperature or entering water temperature, indoor coil(blower) Cfm, entering air wet-bulb temperature, andentering air dry-bulb temperature.

Acceptable heat pump heating data must correlate com-pressor heating capacity with outdoor air temperature orentering water temperature, indoor coil (blower) Cfm,and entering air dry-bulb temperature, plus a defrostcycle adjustment for air-air heat pumps.

n OEM data presentation formats may be differentthan the noted exhibits, but the noted sensitivitiesare a mandatory requirement.

n Data delivery may be by paper or electronic tablessimilar to the figures cited above, or may be a

calculation engine that processes operating condi-tion data, and returns capacity values.

n When refrigeration cycle equipment has two ormore indoor coils, the expanded performancedata must be for the configuration that will beinstalled (a given set of indoor units served by anoutdoor unit), when the compressor is operatingat the AHRI rating speed.

N2-3 Alternative MethodThe equipment sizing goal is to show that equipmentlatent and sensible capacities are compatible with Man-ual J cooling loads when the equipment operates at sum-mer design conditions. The OEM performanceverification path applies when published expanded per-formance data is not commonly available to anOEM-authorized audience, when available data isincomplete for intended equipment use, or when anauthorized party needs help with, and/or confirmationof, available data use (see Section N2-17).

N2-4 ClimateThe over size limit (OSL) for cooling-only equipment andheating-only equipment does not depend on the type ofclimate. The over size limit for heat pump cooling capac-ity does depend on the type of climate.

For heat pumps, practitioners should consider the energyand economic benefits of excess cooling capacity whenthe following conditions simultaneously occur:

n The Manual J sensible heat ratio (JSHR) for thesummer design day cooling load is 0.95 or higher.

n For the location of interest, the ratio of heatingdegree days, base 65F to cooling degree days,base 50.0F is 2.0 or greater. (For this purpose,64.4F data is equivalent to 65F data.)

N2-5 Equipment Sizing MetricsAccurate Manual J load calculations provide target val-ues for equipment capacity. Manual J, Section 2 definesproper use of Manual J procedures. Comprehensive per-formance data provides heating-cooling capacity values.

Accurate values for the condition of the outdoor air,indoor air, and entering air must be used for equipmentselection. Appropriate entering water temperature val-ues for heating and cooling are required for water-airequipment. See Sections A1-2, A1-3, A1-4, A1-10.

Expanded performance data must be used for equipmentselection and sizing. Such data may be a table that coversan adequate range of operating scenarios, or equipmentperformance software that processes conditional inputfor a comprehensive range of operating scenarios.

N2-2

Section N2

n The advertised rating value for total coolingcapacity for air-air or water-air equipment mustnot be used for excess capacity calculations, or forequipment sizing and selection.

Equipment performance must be evaluated for theactual operating circumstances for the summer designcondition.

n Equipment selection must not be based on stan-dard sizes. For example, the size implied by the018, 024, 030, 036, 042, 048 and 060 code valuesembedded in equipment model numbers.

n Equipment selection and sizing requires valuesfor total and latent cooling capacity for the equip-ment operating conditions caused by the summerdesign conditions for outdoor air and indoor air;and when applicable, the effect of return ductloads, and/or engineered ventilation loads. Plusan entering water temperature for water-airequipment.

n Appendix 4 summarizes the attributes and sensi-tivities of adequate performance data.

For Furnaces and Heating Coils:

Performance data that provides input Btuh or KW values,and output Btuh values, must be used for equipmentselection and sizing. An accurate entering air tempera-ture value is required to verify compliance with a leavingair temperature limit.

For all Equipment:

Conform to the OEM's engineering guidance pertainingto operating limits for design issues such as blower Cfm,OAT, EWT, EDB, EWB, LAT, etc. Conform to the effi-ciency rating requirement (SEER, HSPF, AFUE, EER, orCOP value) mandated by local codes and regulations.

N2-6 AHRI-Rated Cooling-Only EquipmentFor cooling-only equipment, excess cooling capacity mayhave an undesirable affect on comfort, depending on howmuch summer humidity control and air distributioneffectiveness suffer from short operating cycles. Shortoperating cycles also reduce seasonal efficiency, andincrease operating cost, but this is a secondary effect.

Target Value for Total Cooling Capacity

The target value for cooling equipment selection and siz-ing is the total Manual J cooling load (sensible load pluslatent load) for summer design conditions, for the roomsand spaces served by the cooling equipment.

Size Limit Values for Total Capacity

Table N2-1 determines maximum and minimum totalcapacity values for cooling-only equipment. The

equipment may be single-package ducted, or split-sys-tem ducted with the indoor coil in an air handler, oradded to a furnace, or ductless split equipment with oneor more indoor coils, or a packaged terminal air condi-tioner (PTAC).

Water-to-air equipment has two possible values for themaximum size because latent capacity and indoorhumidity control improves as the entering water temper-ature gets colder.

n Open piping systems (once-through water) have acolder entering water temperature (typicallyground water temperature) than buriedearth-loop systems.

n Buried earth-loop system water may be 90F orwarmer during late summer. Performance is simi-lar to air-cooled performance when loop water

N2-3

Section N2

Size Limits for Cooling-Only Equipment

EquipmentType

SingleSpeed

TwoSpeed

VariableSpeed

Air-Air Max = 1.15Min = 0.90

Max = 1.20Min = 0.90

FS

Max = 1.20Min = 0.90

RS

Water-Airpipe loopsystem

Max = 1.15Min = 0.90

Max = 1.20Min = 0.90

FS

Max = 1.20Min = 0.90

RS

Water-Airopen pipingsystem

Max = 1.25Min = 0.90

Max = 1.25Min = 0.90

FS

Max = 1.25Min = 0.90

RS

ZoneDamperSystems

To minimize excess air issues, zone dampersystems must have as little excess coolingcapacity as possible when full-cooling capacity iscompared to the Manual J block load for thespace served.

1) This table applies to central ducted equipment, ductless 1:1 splitequipment, ductless multi-split equipment, and packagedterminal air conditioning (PTAC) equipment.

2) FS = Full compressor speed; RS = The compressor speed usedfor the AHRI rating test for advertising total cooling Btuh.

3) OEM expanded performance data for continuous operation, andthe operating conditions for a summer design day, determinetotal cooling capacity, latent capacity, and sensible capacity.

4)Target value = MJ8 block load (sensible Btuh plus latent Btuh) forthe space served by the equipment.

5) Maximum total cooling capacity = Maximum limit x Target value.Minimum total cooling capacity = Minimum limit x Target value.

6) The latent capacity value extracted from OEM data must beequal to, or greater than, the latent load, and should not bemore than 150% of the latent load (1.00 to 1.50 factor).

7) Applied sensible capacity (after adjustment for excess latentcapacity, when applicable) must not be less than 90% (0.90factor) of the sensible load.

8) Maximum equipment size may be determined by theperformance verification path (see Section N2-17).

Table N2-1

temperature is similar to the outdoor airtemperature.

Latent Capacity Limits for Cooling Equipment

After sizing for total capacity, the corresponding latentcapacity value extracted from OEM data must be equal to,or greater than, the latent load, and should not be morethan 150% of the latent load (1.00 to 1.50 factor).

n Condensing side performance vs. evaporator sideperformance has a significant affect on latentcapacity. Use a condenser-evaporator combina-tion that is compatible with the Manual J sensibleheat ratio.

The variables that affect evaporator side performanceare; face area, number of rows, coil circuiting, fins perinch, and the type of refrigerant metering device.

For a given outdoor-indoor set, these variables may bemanipulated (by OEM design) to meet a coil sensibleheat ratio goal for a given set of operating conditions.

n Equipment may, or may not, be designed for lowcoil sensible heat ratios (enhanced moistureremoval). Use products that are compatible withthe Manual J sensible heat ratio.

n For minor adjustments, latent capacity increaseswith decreasing blower Cfm, and vice versa.

Low Limit for Sensible Cooling Capacity

After sizing for total capacity and qualifying latent capac-ity, the corresponding sensible capacity, after adjustmentfor excess latent capacity (when applicable) must not beless than 90% of the sensible load (0.90 factor).

n Half of the excess latent capacity indicated by theOEM's performance data is added to the OEM'ssensible capacity value. Then the sum is comparedto the Manual J sensible load.

n The 90% limit is not an issue when the over sizefactor (OSF) for total capacity is 1.0 or greater.

n The 90% limit may, or may not, be an issue as theOSF for total capacity tends toward 0.90.

The sensible capacity consequence of a decreasing OSFfor total capacity depends on the Manual J sensible heatratio, and the amount of excess latent capacity.

Sensible capacity decreases with a decreasing sensibleheat ratio.

Sensible capacity tends to decrease as excess latentcapacity increases (thus, the rational for the 1.50 or lessfactor for excess latent capacity).

n The 90% limit for sensible capacity is a summerdesign condition issue. Equipment that has an 0.90OSF for total cooling capacity will have adequate

(or more than adequate) sensible capacity atpart-load (for about 99% of the summer hours).

n For wet-coil applications, smaller equipment(total capacity OSF less than 1.0) improvespart-load humidity control.

OEM Performance Data Sensitivity

For air-air equipment, the operating variables are com-pressor speed, indoor coil (blower) Cfm, outdoor airdry-bulb (OAT), entering air wet-bulb (EWB), and enter-ing air dry-bulb (EDB). The cooling performance valuesare total capacity (TC Btuh), sensible capacity (SC Btuh),latent capacity (LC Btuh), and coil sensible heat ratio(CSHR). The power input values are compressor watts(CKW), blower watts (BKW), and total package watts(TKW). The efficiency for code/utility compliance is theSEER value for the AHRI rating test. The operating limitsfor the equipment are the maximum and minimum out-door air temperature values, the maximum and mini-mum conditions for entering air, and blower Cfm limits.

For water-to-air equipment, entering water temperaturereplaces outdoor air dry-bulb. Water-side Gpm, pressuredrop, and pumping power values are added to the pre-ceding list. The efficiency for code/utility compliance isthe EER value for the AHRI rating test.

Ancillary OEM Data

Duct system design must be based on a comprehensiveblower table, or graph. Pressure drop tables, or graphs,are required for all air-side components that were not inplace when the blower was tested (usually an accessoryfilter, but verify that a cooling coil and a standard filterwere in place for the blower test). For ductless equipment,grille performance data is used to evaluate air distribu-tion effectiveness. Investigate the standard and optionalsafety and operating controls, and select a control pack-age that is suitable for the application.

Deliverables

Provide a copy of the block load calculation for summercooling, per Section N1-3, and a list of the operating con-ditions for a summer design day (see Figure A1-21), sup-ported by a copy of the entering air calculations. Providecopies of the OEM's expanded performance data, operat-ing limits, and applicable ancillary data. Document thedesign value for the blower Cfm or blower speed setting,and show that this is in the range allowed by the OEM(the air system design must be compatible with this value,per Manual D procedures). Provide a copy of the calcula-tions that show design condition cooling capacity is in theacceptable range for the total, latent and sensible loads,per Section N2-6 guidance. Provide a list of the operatingand safety controls for the installation.

N2-4

Section N2

N2-7 AHRI-Rated Heat Pump EquipmentFor heat pump equipment, excess cooling capacity mayhave an undesirable affect on comfort, depending on howmuch summer humidity control and air distributioneffectiveness suffer from short operating cycles. Whensummer humidity control is not an issue, and when heat-ing energy and cost are a significant portion of annualenergy use and cost, the limit on heat pump coolingcapacity may be substantially increased for