28254382-ventilation-calculating-the-efficiency-of-energy-recovery-ventilation.pdf

7/28/2019 28254382-Ventilation-Calculating-the-Efficiency-of-Energy-Recovery-Ventilation.pdf

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4100 N. FAIRFAX DR., SUITE 200 ARLINGTON, VIRGINIA 22203

2003

GUIDELINE for CALCULATINGTHE EFFICIENCY

OF ENERGY

RECOVERY

VENTILATION

AND ITS EFFECT

ON EFFICIENCY

AND SIZING OF

BUILDING HVAC

SYSTEMS

Guideline V


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Price $10.00 (M) $20.00 (NM) Copyright 2003, by Air-Conditioning and RefrigerationInstitute

Printed in U.S.A. Registered United States Patent and Trademark Office

IMPORTANT

SAFETY DISCLAIMER

ARI does not set safety standards and does not certify or guarantee the safety of any products, components or systemsdesigned, tested, rated, installed or operated in accordance with this standard/guideline. It is strongly recommended

that products be designed, constructed, assembled, installed and operated in accordance with nationally recognizedsafety standards and code requirements appropriate for products covered by this standard/guideline.

ARI uses its best efforts to develop standards/guidelines employing state-of-the-art and accepted industry practices.ARI does not certify or guarantee that any tests conducted under its standards/guidelines will be non-hazardous orfree from risk.

Note:

This is a new guideline.


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TABLE OF CONTENTS

SECTION PAGE

Section 1. Purpose ........................................................................................................................1

Section 2. Scope ...........................................................................................................................1

Section 3. Definitions ...................................................................................................................1

Section 4. Information Requirements...........................................................................................3

Section 5. General Principles .......................................................................................................4

Section 6. Calculating the Recovery Efficiency Ratio for the Energy Recovery VentilationComponent ..................................................................................................................4

Section 7. Integrating the Efficiency of the Energy Recovery Component with the

Efficiency of Cooling and Heating Equipment ...........................................................5

Section 8. Calculating the Effect of Energy Recovery Ventilation on Cooling SystemEfficiency ....................................................................................................................6

Section 9. Calculating the Effect of Energy Recovery Ventilation on Heating SystemEfficiency ....................................................................................................................6

Section 10. Sizing...........................................................................................................................6

Section 11. Implementation............................................................................................................6

APPENDICES

Appendix A. References - Normative...............................................................................................8

Appendix B. References - Informative .............................................................................................8

Appendix C. Sample Calculations - Informative..............................................................................9

Appendix D. Comparing Typical Combined Efficiency and Energy Analysis Results in aVariety of Climates Informative.............................................................................12

FIGURE

Figure 1. Generic Configuration of an Air-to-Air Heat Exchanger Used for Energy Recoveryin Ventilation Applications .........................................................................................2

TABLE FOR APPENDICES

Table D1. Sample Calculation Results for Five Climates..........................................................12


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ARI Guideline V-2003

1

CALCULATING THE EFFICIENCY OF ENERGY RECOVERYVENTILATION AND ITS EFFECT ON EFFICIENCY AND

SIZING OF BUILDING HVAC SYSTEMS

Section 1. Purpose

1.1 Purpose. The purpose of this guideline is to establisha method of calculating the energy efficiency of appliedEnergy Recovery Ventilation components and of heating,ventilating, and/or air-conditioning systems utilizing suchcomponents at selected operating conditions. It alsoprovides guidance on proper sizing of cooling and heatingequipment when such energy recovery components areapplied.

1.1.1 Intent. This guideline is intended for theguidance of the industry, including engineers,installers, contractors and users. It provides a means

for calculating the impact of applied energy recoveryequipment on the energy efficiency of the heating,ventilating and air-conditioning system at a singleselected operating condition. The guideline is not arating system for Energy Recovery Ventilation(ERV) Equipment, nor does it provide a means ofestimating annual energy use.

1.1.2 Review and Amendment. This guideline issubject to review and amendment as technologyadvances.

Section 2. Scope

2.1 Scope. This guideline applies to energy recoveryventilation component applications and combinations ofenergy recovery components with unitary heating,ventilating, and air-conditioning equipment incorporatingmechanical ventilation with outside air.

2.1.1 This guideline applies only to energyrecovery applications utilizing components tested andrated in accordance with ARI Standard 1060.

2.1.2 Because non-certified data is required forthe calculations, the results should not be consideredto be certified.

Section 3. Definitions

All terms in this document follow the standard industrydefinitions in the current edition ofASHRAE Terminology ofHeating, Ventilation, Air Conditioning and Refrigerationand ASHRAE Standard 84, unless otherwise defined in thissection.

3.1 Coefficient of Performance (COP). A ratio of the

cooling/heating capacity in watts [W] to the power inputvalues in watts [W] at any given set of Rating Conditionsexpressed in watts/watt [W/W].

3.2 Combined Efficiency (CEF). The efficiency of asystem incorporating an ERV component with a unitarypackaged air conditioner, heat pump, etc. Units varyaccording to the application. CEF may be expressed in

Btu/(Wh) or in W/W.

3.3 Effectiveness. The measured energy recoveryEffectiveness not adjusted to account for that portion of thepsychrometric change in the leaving supply air (Figure 1,

Station 2) that is the result of leakage of entering exhaust air(Figure 1, Station 3) rather than exchange of heat ormoisture between the airstreams. The equation fordetermining Effectiveness is given in ARI Standard 1060,Appendix C.

3.4 Energy Efficiency Ratio (EER). A ratio of the coolingcapacity in Btu/h to the power input values in watts at anygiven set of Rating Conditions expressed in Btu/(Wh).

3.5 Energy Recovery Ventilation (ERV) Equipment.Units which employ air-to-air heat exchangers to recoverenergy from exhaust air for the purpose of pre-conditioning

outdoor air prior to supplying the conditioned air to thespace, either directly or as part of an air-conditioning (toinclude air heating, air cooling, air circulating, air cleaning,humidifying and dehumidifying) system. Also referred to asthe air-to-air heat exchanger (AAHX).

3.5.1 Heat Pipe Heat Exchanger. A deviceemploying tubes charged with a fluid for the purposeof transferring sensible energy from one air stream toanother. Heat transfer takes place through thevaporization of the fluid exposed to the warmer airstream and condensation of the fluid in the cooler airstream.

3.5.2 Plate Heat Exchanger. A device for thepurpose of transferring energy (sensible or total) fromone air stream to another with no moving parts. Thisexchanger may incorporate parallel, cross or counterflow construction or a combination of these toachieve the energy transfer.


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2

3.5.3 Rotary Heat Exchanger. A deviceincorporating a rotating cylinder or wheel for thepurpose of transferring energy (sensible or total)from one air stream to the other. It incorporates heattransfer material, a drive mechanism, a casing orframe, and includes any seals, which are provided toretard the bypassing and leakage of air from one airstream to the other.

3.6 Exhaust Air Transfer Ratio (EATR). The tracer gas

concentration difference between the leaving supply air(Figure 1, Station 2) and the entering supply air (Figure 1,Station 1) divided by the tracer gas concentration differencebetween the entering exhaust air (Figure 1, Station 3) andthe entering supply air (Figure 1, Station 1) at the 100%rated air flow rate, expressed as a percentage.

3.7 Fan/Motor Efficiency, Fan/Motor. The product of thefan efficiency and the motor efficiency including drivelosses (mechanical, electrical and/or electronic asapplicable) for each airstream.

3.8 Net Effectiveness. The measured energy recovery

Effectiveness adjusted to account for that portion of thepsychrometric change in the leaving supply air (Figure 1,Station 2) that is the result of leakage of entering exhaust air(Figure 1, Station 3) rather than exchange of heat ormoisture between the airstreams. The derivation of NetEffectiveness is given in ARI Standard 1060, Appendix C.

3.9 Net Supply Air Flow. That portion of the leavingsupply air (Figure 1, Station 2) that originated as enteringsupply air (Figure 1, Station 1). The Net Supply Air Flow isdetermined by subtracting air transferred from the exhaustside of the AAHX from the gross air flow measured at thesupply air leaving the heat exchanger and is given by theequation:

( )EATR1

flowair

supplyLeaving

FlowAir

SupplyNet

=

3.10 Outdoor Air Correction Factor. The entering supplyair flow (Figure 1, Station 1) divided by the measured(gross) leaving supply air flow (Figure 1, Station 2).

3.11 Pressure Drop. The difference in static pressurebetween the entering air and the leaving air for a givenairstream.

3.11.1 Exhaust Pressure Drop. The difference instatic pressure between the entering exhaust air(Figure 1, Station 3) and the leaving exhaust air

(Figure 1, Station 4).

3.11.2 Supply Pressure Drop. The difference instatic pressure between the entering supply air(Figure 1, Station 1) and the leaving supply air(Figure 1, Station 2).

Figure 1. Generic Configuration of an Air-to-Air Heat Exchanger Used for EnergyRecovery in Ventilation Applications

AAHX

Station 4 Station 3

Station 2Station 1

Leaving Supply Air

(Supply Air)

Entering Supply Air

(Outdoor Air)

Entering Exhaust Air

(Return Air)

Leaving Exhaust Air

(Exhaust Air)


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3

3.12 Published Rating. A statement of the assigned valuesof those performance characteristics at stated RatingConditions, by which a unit may be chosen for itsapplication. These values apply to all ERV Equipment oflike size and type (identification) produced by the samemanufacturer. The term Published Rating includes therating of all performance characteristics shown on the unitor published in specifications, advertising or other literaturecontrolled by the manufacturer, at stated Rating Conditions.

3.12.1 Application Rating. A rating based on testsperformed at application Rating Conditions (otherthan Standard Rating Conditions).

3.12.2 Standard Rating. A rating based on testsperformed at Standard Rating Conditions.

3.13 Rating Conditions. Any set of operating conditionsunder which a single level of performance results, and whichcause only that level of performance to occur.

3.13.1 Standard Rating Conditions. RatingConditions used as the basis of comparison forperformance characteristics.

3.14 Recovery Efficiency Ratio (RER). The efficiency ofthe energy recovery component in recovering energy fromthe exhaust airstream is defined as the energy recovereddivided by the energy expended in the recovery process.Units vary according to the application. For Combined

Efficiency with EER, the RER is expressed in Btu/(Wh).For Combined Efficiency with COP, the RER is expressedin W/W.

3.15 "Should." "Should" is used to indicate provisionswhich are not mandatory but which are desirable as goodpractice.

3.16 Standard Air. Air weighing 0.075 lb/ft3, whichapproximates dry air at 70F and at a barometric pressure of29.92 in Hg.

3.17 Supply Air Flow. The measured (gross) leavingsupply air flow (Figure 1, Station 2). Also referred to as therated air flow.

Section 4. Information Requirements

4.1 Net Effectiveness. Ratings of Net Effectiveness atapplication Rating Conditions and air flow rates are requiredto perform calculations of efficiency. ARI certified ratingsfor Net Effectiveness are available at ARI Standard 1060Standard Rating Conditions.

4.2 Blower Power. A value for blower power input isrequired to perform the Combined Efficiency calculation. Ifmanufacturers data for blower power is not available, itmay be calculated from component pressure loss andFan/Motor Efficiency in accordance with this section and6.1.

4.2.1 Pressure Drop. Supply and ExhaustPressure Drop values at application RatingConditions and air flow rates are required to performcalculations of efficiency.

4.2.2 Fan/Motor Efficiency. Values forFan/Motor Efficiency may be required to calculatethe RER of the component as applied. Fan/MotorEfficiency is used with the pressure loss of theenergy recovery component to determine the blowerpower consumed in the process of recovering energy.

4.2.3 Determining Fan/Motor Efficiency.

4.2.3.1 When motor power is known:

MotorS

A2

1Fan

Motor

FanMotor/Fan

PwrK

KQP

Pwr

Pwr

=

=

1

where:

A/S = Air density ratio (ratioof the air density to thedensity of Standard

Air)Fan/Motor= Fan/Motor EfficiencyK1 = 746K2 = 6356PFan = Total static pressure

across the fan, in H2OPwrFan = Fan Power, WPwrMotor = Motor Power, WQ = Air flow rate, cfm

4.2.3.2 When the fan curve is available:

md

FanS

A2

1FanMotor/Fan

PwrK

KQP

= 2

where:

d = Drive efficiencym = Motor efficiencyPwrFan = Fan Power, Hp


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4

4.2.3.3 When fan, motor and driveefficiencies are known:

mdfMotorFan = 3

where:

f = Fan efficiency

4.3 Unitary Equipment Efficiency. The EER or COP ofthe unitary equipment is required to perform calculations ofCEF.

Calculations at Standard Rating Conditions may be used toprovide an indication of comparative performance. Tocharacterize actual performance, application RatingConditions should be used.

System selection, fan configuration, energy recoveryEffectiveness and outdoor air conditions can impact theapplied EER of the unitary equipment. Changes in air flow

rate, fan operating point or coil entering condition of theunitary equipment should be taken into account incalculating applied EER prior to completing the CombinedEfficiency calculation.

Standard Ratings EER at Standard Rating Conditionsshould be used when conditions (e.g. coil enteringconditions and air flow rate) for the system match StandardRating Conditions for the unitary equipment.

Application Ratings EER at application Rating Conditionsshould be used if conditions (e.g. coil entering conditionsand/or air flow rate) vary from Standard Rating Conditionsfor the unitary equipment.

4.4 Load Ratio, Y. The percentage of the system load(heating, cooling, humidification and/or dehumidification)met by the energy recovery component is designated as Yfor the purposes of the calculations in this guideline.

The system load is the sum of the building load and theventilation load.

capacitynetSystem

capacitynetAAHXY = 4

Section 5. General Principles

5.1 General Principle. The general principle of allefficiency calculations is to determine the energy input orcost for a given useful energy output. In the case of ERVequipment, this is the recovered space conditioning energydivided by the power used to recover that energy. This canbe expressed as a Recovery Efficiency Ratio (RER):

consumedpowerelectricTotal

eredrecovenergyngconditioniNetRER= 5

where the net space conditioning energy can be eitherheating, humidification, cooling, dehumidification or acombination thereof and the total electric power consumedincludes the power required to move air through both sides

of the AAHX as well as any additional power, such as thewheel drive motor in a Rotary Heat Exchanger.

The power required to move air through the AAHX is afunction of the Supply and Exhaust Pressure Drop valuesthrough the AAHX, as well as the Fan/Motor Efficiency ofthe air-moving device. The power required to rotate aRotary Heat Exchanger can be measured directly.

Section 6. Calculating the Recovery EfficiencyRatio for the Energy Recovery Ventilation

Component

6.1 Calculating the RER for the Energy Recovery Device.Consult manufacturers data for information on fan powerconsumption or pressure loss for the component. TheRERis calculated in Equations 6a, 6b and/or 6c:

compblwr

31mintotalnetTotal

PwrPwr

)h-(hmRER

+

=

&

6a

compblwr

31pminsensiblenetSensible

PwrPwr

)t-(tcmRER

+

=

&

6b

compblwr

31minlatentnetLatent

PwrPwr

)-(mRER

+

=

&

6c

where:

cp = Specific heat of air, Btu/lbF

h1 = Total enthalpy of the entering supplyair, Btu/lb (Figure 1, Station 1)

h3 = Total enthalpy of the entering

exhaust air, Btu/lb (Figure 1, Station3)

em& = Mass flow rate of the entering

exhaust air, lb/h (Figure 1, Station 3)

minm& = The lesser of sm& and em& , lb/h


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5

sm& = Mass flow rate of leaving supply air,

lb/h (Figure 1, Station 2)

Pwrcomp = Direct power input to the AAHXcomponent, not included in blowerpower, W

Pwrblwr = Sum of the blower power for boththe supply and the exhaustairstreams, W (represents theadditional fan power imposed by theintroduction of the energy recoverycomponent into the two airstreams;may be obtained from actual blowerpower from manufacturers data)

MotorFanC

PQ

= 7

where:

C = Required unit conversionconstant

P = Pressure loss of thecomponent for the supplyand exhaust airstreams, inH2O

Note: Other alternatives (such ascomparison of operating points on afan curve) that accuratelycharacterize the additional fan powerrequired by the component are

acceptable means of obtainingblower power.

t1 = Dry-bulb temperature of the entering

supply air, F (Figure 1, Station 1)

t3 = Dry-bulb temperature of the entering

exhaust air, F (Figure 1, Station 3)

net = Net Effectiveness (sensible, latent, ortotal, as applicable), as defined inARI Standard 1060 and determinedin accordance with ARI Standard

1060

1 = Humidity ratio of the entering supplyair, lb (water)/lb (dry air) (Figure1,Station 1)

3 = Humidity ratio of the enteringexhaust air, lb (water)/lb (dry air)(Figure 1, Station 3)

Section 7. Integrating the Efficiency of theEnergy Recovery Component with the Efficiency

of Cooling and Heating Equipment

7.1 CEF can be defined on a comparable basis to existingEER and COP ratings, based on the performance of theindividual components. The basic principle (illustrated herefor the cooling case) is:

n1n21

n1n21

powerpowerpowerpower

coolingcoolingcoolingcooling

consumedpowerelectricTotal

deliveredcoolingNetCEF

++++++

=

=

8

When an AAHX is combined with a unitary air conditioner,the AAHX provides a portion of the system cooling capacityand the vapor compression cycle of the unitary airconditioner provides the rest. Consistent with the basicprinciple,

nconsumptiopowerelectricTotalcapacitycoolingNetEER= 9

The cooling system Combined Efficiency (CEFcooling) of aunitary air conditioner with an AAHX cooling componentcan be defined as:

nconsumptiopowerelectricunitary

nconsumptiopowerelectricAAHX

capacitycoolingnetunitary

capacitycoolingnetAAHX

coolingCEF

+

+= 10a

The heating system Combined Efficiency (CEFheating) of aunitary air conditioner with an AAHX heating componentcan be defined as:

nconsumptiopowerelectricunitary

nconsumptiopowerelectricAAHX

capacityheatingnetunitary

capacityheatingnetAAHX

heatingCEF

+

+= 10b

Section 8. Calculating the Effect of EnergyRecovery Ventilation on Cooling System

Efficiency

8.1 Calculating the Effect of the ERV on Cooling SystemCEF. The CEFcooling is calculated from the RER of theAAHX (RERAAHX) and the EER of the packaged equipment(EERUnitary) according to the following expression:

UnitaryEER/)

cY-(1RER/

cY

1

coolingCEF

AAHX +=

11a


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6

where:

capacitycoolingnetsystem

capacitycoolingnetAAHXYc = (from 4.4)

and RER is expressed in Btu/(Wh).

8.2 Note that RER can be calculated on the basis of total

energy recovery, latent recovery or sensible recoveryEffectiveness. The selection of the RER basis will dependon the analysis being conducted: use total for cooling anddehumidification, latent for dehumidification only andsensible for cooling without dehumidification.

Section 9. Calculating the Effect of EnergyRecovery Ventilation on Heating System

Efficiency

9.1 Calculating the Effect of ERV on Heating SystemCEF. The CEFheating is calculated from the RER of the

AAHX (RERAAHX) and the COP of the packaged equipment(COPUnitary) according to the following expression:

UnitaryCOP/)

hY-(1RER/

hY

1

heatingCEF

AAHX +=

11b

where:

capacityheatingnetsystem

capacityheatingnetAAHXYh = (from 4.4)

and RER is expressed in W/W.

9.2 Note that RER can be calculated on the basis ofsensible recovery, latent recovery or total energy recoveryEffectiveness. The selection of the RER basis will dependon the analysis being conducted: use sensible for heatingonly, latent for humidification and total for heating andhumidification.

Section 10. Sizing

10.1 Sizing. In evaluating the impact of energy recoveryon CEF, it is important to recalculate the system size basedon the load reduction provided by the energy recoverycomponent at design conditions. Comparisons of systemswith and without energy recovery should take this intoaccount.

10.2 Methods. Equipment should be sized with loadreduction provided by energy recovery at design conditions.If not already accounted for in equipment selection, HVACequipment should be reselected in accordance with 10.3.

10.3 HVAC Equipment Load Reduction Factor. Anestimate of the reduction in equipment size is provided bythe capacity of the energy recovery component at designconditions according to the expression:

( )

=

recovery

energywithout

capacityEquipment

Y1

recoveryenergy

withcapacityequipment

Required

12

Section 11. Implementation

11.1 Conditions. This guideline may be used to compareefficiencies of different systems at a set of standardconditions or for a specific set of conditions reflecting aspecific application. The user should note that, like unitaryEER values for Standard Rating Conditions, RER values for

Standard Rating Conditions (for example, ARI Standard1060 Standard Rating Conditions and a value for fanefficiency) can provide a rational comparison of differentenergy recovery components. Note that the RER for theenergy recovery component as applied can vary with climateor conditions. This is due to the fact that the energyrecovered is dependent on the difference between outdoorair and exhaust air conditions and thus varies widely, whilethe energy used (Pressure Drop x Fan/Motor Efficiency) ismore consistent for a given air flow rate.

11.2 Blower Power. The blower power calculationspresented in the guideline are for the sole purpose of

determining the incremental parasitic losses due to theaddition of the energy recovery component to the airstreams.They do not describe the air-moving efficiency of aventilation system in supplying outside air; nor do theydescribe the fan efficiency of unitary systems, which isincluded in unitary energy efficiency ratings. Fanplacement, cabinet design and related system effects, whilethey can impact the efficiency of air delivery, are notaddressed in this guideline.

11.3 Applications. While the guideline provides a methodof determining efficiency of the energy recovery and ofsystems incorporating energy recovery, it is not intended to

be used to set minimum equipment efficiencies for heatingor cooling equipment in general. It is only applicable whereoutside air is being introduced into the system; the benefit ofenergy recovery to the Combined Efficiency is directlydependent on the amount of outdoor air provided and theindoor and outdoor conditions.

11.4 Calculated Results. The guideline provides amethodology for determining RER and CEF for a singlepoint at specified design conditions. If it is desired toevaluate the seasonal impact of energy recovery, it isnecessary to perform the guideline calculations for a series


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of representative conditions or, preferably, perform anenergy analysis. See Appendix D for example resultscomparing CEF and energy analysis calculations for avariety of climates.

11.5 Accuracy. The accuracy of the calculations is limitedby the cumulative tolerances in testing and reporting ofStandard and Application Ratings, estimates of Fan/MotorEfficiency, etc.

11.6 Sensible Heat Ratio. Care should be exercised inselecting energy recovery components and coolingequipment to provide adequate moisture removal forhumidity control in cooling. Combinations of equipmentthat result in a sensible heat ratio matching the load willprovide improved humidity control over those that do not.

11.7 Additional Guidance. Other guidelines or standards,such as local codes and ASHRAE Standard 90.1, maycontain specific requirements for energy recovery.


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8

APPENDIX A. REFERENCES NORMATIVE

None.

APPENDIX B. REFERENCES INFORMATIVE

B1 Listed here are standards, handbooks and otherpublications which may provide useful information andbackground, but are not considered essential. References inthis appendix are not considered part of the guideline.

B1.1 ANSI/ARI Standard 390-2001, SinglePackage Vertical Air-Conditioners and Heat Pumps,2001, Air-Conditioning and Refrigeration Institute,4100 North Fairfax Drive, Suite 200, Arlington, VA22203, U.S.A.

B1.2 ANSI/ARI Standard 430-99, Central StationAir Handling Units, 1999, Air-Conditioning and

Refrigeration Institute, 4100 North Fairfax Drive,Suite 200, Arlington, VA 22203, U.S.A.

B1.3 ANSI/ARI Standard 1060-2001,Rating Air-To-Air Heat Exchangers For Energy Recovery

Ventilation Equipment, 2001, Air-Conditioning andRefrigeration Institute, 4100 North Fairfax Drive,Suite 200, Arlington, VA 22203, U.S.A.

B1.4 ANSI/ASHRAE/IESNA Standard 90.1-2001, Energy Standard for Buildings Except Low-Rise Residential Buildings, 2001, American NationalStandards Institute/American Society of Heating,

Refrigerating and Air-Conditioning Engineers,Inc./Illuminating Engineering Society of NorthAmerica, 25 West 43rd Street, 4th Floor, New York,NY 10036 U.S.A/1791 Tullie Circle, N.E., Atlanta,GA 30329, U.S.A./120 Wall Street, Flo07 17, NewYork, NY 10005

B1.5 ANSI/ASHRAE Standard 84-1991,Methodof Testing Air-to-Air Heat Exchangers, 1991,American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 1791 Tullie CircleN.E., Atlanta, GA 30329, U.S.A.

B1.6 ARI/ASHRAE

/

ISO 13256-1, Water-SourceHeat Pumps Testing and Rating for Performance Part I: Water-to Air and Brine-to-Air Heat Pumps,

1998, Air-Conditioning and RefrigerationInstitute/American Society of Heating, Refrigeratingand Air-Conditioning Engineers, Inc./InternationalOrganization for Standardization, 4100 North FairfaxDrive, Suite 200, Arlington, VA 22203, U.S.A./1791Tullie Circle N.E., Atlanta, GA 30329, U.S.A./CasePostale 56, CH-1211, Geneva 21 Switzerland.

B1.7 ARI Standard 210/240-2003, Unitary AirConditioning and Air Source Heat Pump Equipment,2003 Air-Conditioning and Refrigeration Institute,4100 North Fairfax Drive, Suite 200, Arlington, VA22203, U.S.A.

B1.8 ARI Standard 310/380-93, PackagedTerminal Air-Conditioners and Heat Pumps (CSA-

C744-93) (ANSI/ARI 310/380-93), 1993, Air-Conditioning and Refrigeration Institute, 4100 NorthFairfax Drive, Suite 200, Arlington, VA 22203,U.S.A.

B1.9 ARI Standard 330-98, Water SourceHeatPumps, 1998, Air-Conditioning and RefrigerationInstitute, 4100 North Fairfax Drive, Suite 200,Arlington, VA 22203, U.S.A.

B1.10 ARI Standard 340/360-2000, Commercialand Industrial Unitary Air-Conditioning and Heat

Pump Equipment, 2000, Air-Conditioning andRefrigeration Institute, 4100 North Fairfax Drive,Suite 200, Arlington, VA 22203, U.S.A.

B1.11 ASHRAE Handbook,Fundamentals, 2001,American Society of Heating, Refrigerating and Air-

Conditioning Engineers, Inc., 1791 Tullie CircleN.E., Atlanta, GA 30329, U.S.A.

B1.12 ASHRAE Handbook, Systems andEquipment, 2000, American Society of Heating,Refrigerating and Air-Conditioning Engineers, Inc.,1791 Tullie Circle N.E., Atlanta, GA 30329, U.S.A.

B1.13 ASHRAE Terminology of Heating,Ventilation, Air-Conditioning, and Refrigeration,Second Edition, 1991, American Society of Heating,Refrigerating and Air-Conditioning Engineers, Inc.,1791 Tullie Circle, N.E., Atlanta, GA 30329, U.S.A.

B1.14 System Energy Efficiency Ratio,

Establishing the Recovery Efficiency Ratio for Air-to-

Air Energy Recovery Heat Exchangers and Their

Effect on HVAC System Energy Efficiency, 2002,Arthur D. Little, Inc., Acorn Park, Cambridge, MA02140, U.S.A.


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9

APPENDIX C. SAMPLE CALCULATIONS INFORMATIVE

C1 Cooling example, enthalpy recovery and EER:

where:

net total = 0.70 (70%)

Q = 1000 cfmC = 44.25 ftlbf/min/Wp = 1 in H2O Exhaust and Supply Pressure Drop [1 in H2O = 5.192 lb/ft

2]h1- h3 = 13.447 Btu/lb outdoor air at 95

oF dry-bulb/78 oF wet-bulb, return air at 75oF dry-bulb/63 oF wet-bulb

Air = 0.075 lb/ft3

Fan/Motor = 0.84 motor efficiency x 0.50 fan efficiency = 0.42Pwrcomp = 50 W for an enthalpy wheel ( = 0 for a plate or heat pipe heat exchanger)

From Equation 6a, RERTotal is given by:

( ) ( )

( ) ( )( )( ) ( )( )

( ) ( )[ ] ( ) ( )[ ]

( ) ( ) ( ) ( )( )

( )

)hW/(Btu58.69RER

W73.608

h/Btu05.358,42

W50W73.558

h/Btu05.358,42

W50

42.0W

min/lbft25.44

ft/lb192.5min/ft1000ft/lb192.5min/ft1000

hmin/60lb/Btu447.13ft/lb075.0min/ft100070.0

PwrC

pQpQ

hhQ

PwrPwr

)h-(hmRER

Total

f

2323

33

compMotor/Fan

exhaustplysup

31Airtotalnet

compblwr

31mintotalnetTotal

=

=+

=

+

+

=

+

+

=

+

=

&

For a direct expansion system with EER=10 and where the ERV component (AAHX) is handling 30% of the system load atdesign conditions, the CEFcooling is given by Equation 11a:

( )

)hW/(Btu46.13CEF

107.0

58.693.0

1

EERY1

RERY

1CEF

cooling

Unitaryc

AAHXc

cooling

=

+=

+

=


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10

C2 Cooling example, sensible recovery and EER:

where:

net sensible = 0.70 (70%)Q = 1000 cfm

C = 44.25 ftlbf/min/Wp = 1 in H2O Exhaust and Supply Pressure Drop [1 in H2O = 5.192 lb/ft

2]t1- t3 = 20

oF (outdoor air at 50 oF, return air at 70oF)

Air = 0.075 lb/ft3

cp = Specific heat of dry air = 0.24 Btu/lboF

Fan/Motor = 0.84 motor efficiency x 0.50 fan efficiency = 0.42Pwrcomp = 0 W for a plate or heat pipe heat exchanger (would be greater than 0 for an enthalpy wheel)

From Equation 6b, RERsensible is given by:

( )

( ) ( )( )( ) ( )( )

( ) ( )[ ]( ) ( )( )

( )( ) ( )( )( )( )

)hW/(Btu1.27RER

W73.558

h/Btu120,15

W0

42.0W

min/lbft25.44


hmin/60F20Flb/Btu24.0ft/lb075.0min/ft100070.0

Pwr

C

pQpQ

)t-(tcQ

PwrPwr

)t-(tcmRERRER

sensible

f

2323

oo33

comp

Motor/Fan

exhaustplysup

31pAirsensiblenet

compblwr

31pminsensiblenetsensiblesensible

=

=

+

+

=

+

+

=

+

==

&

For a direct expansion system with EER=10 and where the ERV component (AAHX) is handling 30% of the system load atdesign conditions, the CEFcooling is given by Equation 11a:

( )

)hW/(Btu34.12CEF

107.0

1.273.0

1

EERY1

RERY

1CEF

cooling

Unitary

c

AAHX

ccooling

=

+=

+=


15/16


11

C3 Heating example, sensible recovery and COP:where:

net sensible = 0.70 (70%)Q = 1000 cfm

C = 44.25 ftlbf/min/WZ = 1 W/3.413 Btu/hp = 1 in H

2O Exhaust and Supply Pressure Drop [1 in H

2O = 5.192 lb/ft2]

t1- t3 = 20oF (outdoor air at 50 oF, return air at 70oF)

Air = 0.075 lb/ft3

COP = 2.93 (for the heat pump)RERCOP AAHX = RER of energy recovery expressed as a dimensionless value

cp = Specific heat of dry air = 0.24 Btu/lboF

Fan/Motor = 0.84 motor efficiency x 0.50 fan efficiency = 0.42Pwrcomp = 0 W for a plate or heat pipe heat exchanger (would be greater than 0 for an enthalpy wheel)

From Equation 6b, RERsensible (= RERCOP AAHX)is given by:

( )

( ) ( )( )( ) ( )( )

( )

( )( )[ ]( ) ( ) ( )

( )( ) ( ) ( )( )( )

93.7RER

h/Btu413.3

W1

W73.558

h/Btu120,15

Btu413.3

W1

42.0W

min/lbft25.44


hmin/60F20Flb/Btu24.0ft/lb075.0min/ft100070.0

Z

Pwr

C

pQpQ

)t-(tcQ

RERPwrPwr

)t-(tcmRER

AAHXCOP

f

2323

oo33

comp

Motor/Fan

exhaustplysup

31pAirsensiblenet

AAHXCOPcompblwr

31pminsensiblenetsensible

=

=

+

=

+

+

=

=+

=

&

For a heat pump system with COP = 2.93 and where the ERV component (AAHX) is handling 30% of the system load at

design conditions, the CEFheating is given by Equation 11b:

( )

6.3CEF

93.27.0

93.73.0

1

COPY1

RERY

1CEF

heating

Unitary

h

AAHXCOP

hheating

=

+=

+=


16/16


12

APPENDIX D. COMPARING TYPICAL COMBINEDEFFICIENCY AND ENERGY ANALYSIS RESULTS IN A

VARIETY OF CLIMATES INFORMATIVE

As stated in the purpose, Combined Efficiency for cooling is calculated at a selected operating condition. As such, it is useful for

determining the impact of energy recovery on system efficiency, equipment sizing and peak load at design conditions. It does notconstitute a rating system for energy recovery, nor does it substitute for energy analysis in determining energy and/or economicsavings. A 20% increase in Combined Efficiency for cooling may or may not represent a 20% savings in energy usage, dependingon the climate and the percentage of the total load represented by the outside air. Table D1 below provides examples of howCombined Efficiency, equipment sizing and savings from energy analysis can vary differently with climate. These results areillustrative only; note that energy analysis can vary widely with assumptions, component selection, control strategy, etc. Users areadvised to perform an energy analysis for the specific application in order to evaluate the impact of energy recovery on energy useor economics.

Table D1. Sample Calculation Results for Five Climates

Location CombinedEfficiency,

cooling,

Btu/(Wh)

Annual CoolingSavings ($)

Annual HeatingSavings ($)

Fan EnergyUsed ($)

Annual NetSavings ($)

System Sizing(1-Y)

Miami 13.35 672 17 129 559 72%

Kansas City 12.78 212 570 129 652 76%

Minneapolis 12.19 82 845 129 798 79%

Tucson 11.84 265 196 129 331 82%

Seattle 10.60 9 455 129 334 91%

Assumptions:

a. Unitary capacity of 10 tons and EER of 10.1 for coolingb. Gas heat at 80% efficiencyc. Air flow rate of 1200 cfm outside air (approximately 30% outdoor air)d. Energy recovery enthalpy effectiveness of 75%e. Energy analysis with commercially available software and bin weather data from TMY-2f. Office building schedule 8 a.m. to 8 p.m., six days per week, energy costs at $6.52/MMBtu, electricity at $0.079/kWh

28254382-ventilation-calculating-the-efficiency-of-energy-recovery-ventilation.pdf

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