Analysis of Space-Conditioning Loads in Commercial Buildings

AnalysisofSpace-ConditioningLoadsinCommercialBuildingsKatieCoughlin,EdwardCubero,AkhilMathur,andGregoryRosenquistEnergyAnalysis&EnvironmentalImpactDepartmentEnergyTechnologiesAreaLawrenceBerkeleyNationalLaboratory June15,2020

ThisworkwassupportedbytheAssistantSecretaryforEnergyEfficiencyandRenewableEnergy,OfficeofBuildingTechnology,State,andCommunityPrograms,oftheU.S.DepartmentofEnergyunderLawrenceBerkeleyNationalLaboratoryContractNo.DE-AC02-05CH1131.

ERNESTORLANDOLAWRENCEBERKELEYNATIONALLABORATORY

LBNL-2001339

Disclaimer

ThisdocumentwaspreparedasanaccountofworksponsoredbytheUnitedStatesGovernment.Whilethisdocumentisbelievedtocontaincorrectinformation,neithertheUnitedStatesGovernmentnoranyagencythereof,norTheRegentsoftheUniversityofCalifornia,noranyoftheiremployees,makesanywarranty,expressorimplied,orassumesanylegalresponsibilityfortheaccuracy,completeness,orusefulnessofanyinformation,apparatus,product,orprocessdisclosed,orrepresentsthatitsusewouldnotinfringeprivatelyownedrights.Referencehereintoanyspecificcommercialproduct,process,orservicebyitstradename,trademark,manufacturer,orotherwise,doesnotnecessarilyconstituteorimplyitsendorsement,recommendation,orfavoringbytheUnitedStatesGovernmentoranyagencythereof,orTheRegentsoftheUniversityofCalifornia.TheviewsandopinionsofauthorsexpressedhereindonotnecessarilystateorreflectthoseoftheUnitedStatesGovernmentoranyagencythereof,orTheRegentsoftheUniversityofCalifornia.ErnestOrlandoLawrenceBerkeleyNationalLaboratoryisanequalopportunityemployer.

Acknowledgements

TheauthorswouldliketothankLixingGuforgeneratingtheEnergyPlussimulationdata.

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TableofContents

1. Introduction...................................................................................................................................................4 1.1. Overviewofmethodology...................................................................................................................5 1.2. Outlineofthisreport.............................................................................................................................6

2. SummaryofEnergyPlusBuildingsandOutput.............................................................................6 2.1. Buildingprototypesandclimatezones.........................................................................................6 2.1.1. CommercialReferenceBuildings...........................................................................................................6 2.1.2. ClimateZones.................................................................................................................................................9 2.1.3. RepresentativeCities..................................................................................................................................9 2.1.4. SummaryofEachCommercialReferenceBuilding....................................................................11

2.2. Systemtypes..........................................................................................................................................16 2.3. Systemnodesandsystemvariables............................................................................................17 2.4. Zonedefinitionsandzonevariables............................................................................................20 2.5. DataavailabledirectlyfromEnergyPlus...................................................................................21

3. ThermodynamicEquations..................................................................................................................22 3.1. MassBalance..........................................................................................................................................22 3.2. EnergyBalance.....................................................................................................................................24 3.2.1. Sensibleheatbalance...............................................................................................................................24 3.2.2. Latentheatbalance...................................................................................................................................27

4. ValidationofCalculationMethods....................................................................................................29 5. Results...........................................................................................................................................................32 6. Conclusions.................................................................................................................................................46 References.................................................................................................................................................................48

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ListofFigures

Figure2-1 ClimateZoneClassification.....................................................................................................10 Figure2-2 TypicalHVACSystemandZoneNodes..............................................................................19 Figure4-1 RelationshipbetweenFanEnergyandMassFlowRateforVariableAirVolume

HVACSysteminMediumOfficeBuilding.........................................................................31 Figure4-2 ValidationCheckSummaryforAtlantaSystems...........................................................32 Figure5-1 WeekdayCoolingLoadProfiles:NewConstructionMediumOfficeandStand-

AlongRetail,Houston,Phoenix,andChicagoClimates..............................................35 Figure5-2 WeekdayCoolingLoadProfiles:Post-1980ConstructionMediumOfficeand

Stand-AlongRetail,Houston,Phoenix,andChicagoClimates................................36 Figure5-3 MonthlyBuildingLoadProfiles:NewConstructionMediumOfficeand

SecondarySchool,Houston,Phoenix,andChicagoClimates..................................38 Figure5-4 Sensiblevs.LatentLoadsinHoustonandPhoenix......................................................39 Figure5-5 LatentLoadsandHumidityRatios:SelectBuildingTypesinHouston,Phoenix,

andChicago...................................................................................................................................41 Figure5-6 TotalCoolingLoadasafunctionofOutdoorAirTemperatureforvarious

SensibleHeatRatiobins,MediumOfficeandStand-AloneRetail.........................43 Figure5-7 TotalCoolingPowerasafunctionofSensibleHeatRatiofortwoOutdoorAir

Temperaturebins,MediumOfficeandStand-AlongRetail......................................45 Figure5-8 DistributionofSensibleHeatRatiosforaSelectionofClimateZonesand

BuildingTypes.............................................................................................................................46

ListofTables

Table2-1 CommercialBuildingPrototypes............................................................................................7 Table2-2 DistributionofCommercialFloor-spacebyVintagein2020.....................................8 Table2-3 ClimateZonesandRepresentativeCities.........................................................................10 Table2-4 PrototypeBuildingCharacteristics.....................................................................................14 Table2-5 HVACSystemtypesforPrototypeBuildings..................................................................17 Table2-6 HVACSystemNodeandSystemAirPropertyVariableNames..............................18 Table2-7 RelationshipbetweennumberofHVACsystems(x)andcorresponding

numberofZones(nx)servedbyeachsystemwithZoneAirPropertyVariableNames..............................................................................................................................................21

Table2-8 SmallOfficeHVACSystemandZoneNodeswithEnergyPlusVariableNames22 Table4-1 HVACSystemandZoneLoadsreportedbyEnergyPlus............................................30 Table5-1 AverageCoolingCapacityperSquareFootbyBuildingTypeandClimateZone

............................................................................................................................................................34

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1. Introduction

Spaceconditioningend-uses,whichincludeheating,cooling,andventilation,representasignificantfractionofcommercialbuildingenergyuse,withawidevarietyofheatingandcoolingtechnologyoptionsavailableinthemarket.Intheinterestofimprovingtheoverallefficiencyofheating,ventilationandair-conditioning(HVAC)technologies,governments,utilitiesandprivatesectorentitieshaveimplementedavarietyofmarkettransformationpoliciesthataimtoinfluenceconsumerpurchasedecisions.Toevaluatethecostsandbenefitsofsuchprograms,analyststypicallypostulateahypotheticaldefaultequipmentchoice,andcompareittoonethatprovidescomparableservicewithlowerenergyand/orpoweruse.Thecorrespondingreducedoperatingcostprovidesabenefitthatoffsetsthepotentialhighercostofimprovedefficiency.Typically,life-cyclecostorcash-flowanalysesareusedtoquantifytheneteconomicbenefit.Theseanalysesrequirethecapabilitytoassesshowagivenequipmentdesignwouldperformacrossabroadrangeofcharacteristics,bothofthebuildingandofthelocalweather.Whiletheseassessmentscanbeperformedusingcustomizedbuildingsimulations,itisgenerallynotpracticaltodevelopandvalidatedetailedbuildingsimulationcodetocoverallthepotentialvariationsofequipmentdesignandinstallation.Analternative,andsomewhatsimpler,approachistosolelyusedetailedbuildingsimulationstogeneratetimeseriesofheatingandcoolingloadsincommercialbuildings.Theseloadscanthenbeusedasinputtomoredetailed,stand-aloneengineeringmodelsthatsimulateHVACsystemperformanceunderdifferentequipmentdesigns.Thisapproachwasusedtoevaluatearangeofhigh-efficiencycommercialpackagedairconditionerdesignoptionsfortheDepartmentofEnergy’sApplianceandEquipmentStandardsProgram(DOE-EERE2015).Whiletheremaybesomelossofprecisionrelativetofullsimulation,theaccuracyofthisapproachissufficientforpracticalapplicationsofcost-benefitanalysis.Thisreportdescribesthedevelopmentofadatabaseofcommercialbuildingheatingandcoolingloads,generatedusingtheEnergyPlussoftwarepackage,awholebuildingenergyusemodelsupportedbytheDepartmentofEnergy(DOE-EERE2020a).EnergyPlustakesasinputasetofconfigurationfilesthatdescribethebuildingitself(size,zoning,envelopecharacteristics,etc.)andthevarioussystemswithinit(HVAC,lighting,waterheating,etc.).Thisanalysisusesapubliclyavailablecollectionofcommercialreferencebuildings(CRB),comprisedofsixteenbuildingtypesandthreevintages(DOE-EERE2020b;Deruetal2011).Eachbuildingissimulatedineighteendifferentlocations,coveringawiderangeofclimaticconditions.TheprototypebuildingdescriptionfilesassignthetypeofHVACequipmentused,andcapacitiesacrossclimatezones.Asdescribedinthenextsection,thisanalysisusesEnergyPlusoutputtodisaggregatetheHVACloadsintolatentandsensiblecomponents,andtoseparatetherelativecontributionsfromincomingventilationairvs.airrecirculatedfromtheconditionedzones.Thisdisaggregationreflectsthefactthattherearedifferentphysicaldriversforthesecomponentloads.Therefore,itshouldbepossibletoconstructsimplecorrelationmodelsrelatingbuildingandclimatevariablestothecomponentloadsthataremoreaccuratethan

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suchestimatesofthetotalload.Thisaspectoftheproblemwillbeexploredinasecondreport,whichwilldescribehowtheHVACloadscanbemodifiedtorepresentalternativeassumptionsaboutbuildingenvelopecharacteristics,internalloads,andclimatevariables.

1.1. Overviewofmethodology

EnergyPlusrepresentsabuildingasasetofzonesthatareservedbyaspecificHVACsystem.ThesystemsintheCRBdatasetcoverawiderangeoftechnologiesincludingpackagedsingle-zonesystems,chillers,unitarypackagedequipment,amongothers.EnergyPlusrepresentsthefunctionalunitsoftheHVACequipmentthroughaseriesofnodes;examplesinclude:thecoolingcoil,theheatingcoil,andtheventilationfan.Conceptually,thisanalysisdefinesanairloopforthesystemasthepathtakenbyapacketofairasitpasseseachnodeintheHVACsystem,travelstotheconditionedspacethroughthesupplyduct,andthenreturnstotheHVACsystemwhereitismixedwithoutdoorairbeforebeginningthenextloop.Ateachnode,EnergyPlusdeterminesthephysicalairconditionsasafunctionoftheheataddedorremovedbytheHVACsystemcomponentsand/orzonalloads.TheHVACloaddatabaseisbuiltfromEnergyPlusoutputconsistingof10-minutetimeseriesofthemassflow,airconditions(dry-bulbtemperature,humidityratio,andheatcapacity)andotherrelevantdata,foreachsysteminthebuilding,forafullyear.Thesedataarecollectedattheminimumsetofnodesneededtofullydescribetheenergy,moistureandmassbalancerelationsaroundtheairloopformedbythesystemandthezonesthatitserves.Whilebothheatingandcoolingoperationsareconsideredinthisreport,mostoftheeffortisdirectedtowardstheunderstandingofcoolingloads,whicharemorecomplexduetothepresenceoflatentloads.Theaircirculatinginabuildingconsistsofdryairplusacertainquantityofwatervapor.Whenheatisaddedtoanairpacket,thetemperaturechanges,buttheamountofwatervaporintheairisnotaffected.Whenheatisremovedfromanairpacket,ifthetemperaturedropislargeenough,somemoisturewillcondenseout.Whenthewatervaporcondenses,itreleasesenergy,whichactsasanadditionalloadontheHVACsystem.Thisenergy,orheatofvaporization,isreferredtoasthelatentload.Thetemperaturechangewithoutachangeinmoisturecontentisreferredtoasthesensibleload.AlmostalltheHVACsystemsmodeledintheCRBsetarecontrolledbasedonthedry-bulbtemperatureintheconditionedspace(theonlyexceptionsareoperatingroomsinthehospitalandoutpatientprototypes).Withnodirectcontrolofhumidity,removalofmoisturefromtheincomingventilationairisanimportantfunctionoftheHVACsysteminhumidclimates.Itisexpectedthatthemagnitudeofthelatentload,andcorrespondingHVACenergyuse,todependprimarilyonlocalclimateconditionsandonbuildingcharacteristicsthatcorrelatewithoccupancy.Asnotedabove,tomorefullyunderstandthedriversonHVACloadingandenergyuse,thisanalysisseparatesthetotalspaceconditioningloadsintofourcomponents:thelatentand

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sensibleloads,andtheportionofeachassociatedwithoutdoorairvs.theairrecirculatedfromtheconditionedspace.ThedisaggregationisperformedusingbasicthermodynamicequationsandtheairconditionsreportedbyEnergyPlus,asdescribedinSection3.Theloadsarecalculatedforeachsystemwithinabuilding,whichallowscomparisonsofsimilarsystemsacrossbothbuildingtypesandclimatezones.Whilethermodynamicsallowstheloadstobeseparatedintolatentandsensiblecomponents,theHVACsystemdealswithbothsimultaneously,sounderstandinghowthesystemenergyusedependsonlatentvs.sensibleloadismorecomplicated.Inthispaper,dataareusedforthesamebuildingandsystemacrossdifferentclimatestoestimatetherelativeimportanceoflatentloadstooverallenergyuse.Thetime-seriesdataarebinnedaccordingtothevalueofoutdoordry-bulbtemperatureandhumidityratio.Withinasingledry-bulbtemperaturebin,thevariationofenergyusewithhumidityratioprovidesanestimateoftheimportanceoflatentloadstooverallenergyuse.Thegoalofthisinitialanalysisistoprovideageneralpictureoftherelativeimportanceoflatentvs.sensibleloads,andofthecontributionofoutdoorventilationairtotheloadsandrelatedenergyconsumption.Asecondreportwilldescribehowtheloaddatabaseassembledherecanbeusedtodevelopestimatesofpotentialimpactsonenergyuseofequipmentdesignchanges,changestothebuildingenvelope,orchangestoclimateconditions.

1.2. Outlineofthisreport

Section2providesadescriptionoftheclimatezonesandthecommercialreferencebuildingsusedinthisanalysis,includingasummaryofthezonelayoutandtheHVACsystemcharacteristicsforeachbuilding.Italsoprovidesaschematicdescriptionoftheorganizationofsystemnodes,andidentifythespecificEnergyPlusoutputvariablesthatareusedheretodescribetheairloop.Section3presentsthemassandenergybalanceequations,withlatentandsensibleloadstreatedseparately.Italsoidentifiesthecontributiontotheloadsfromincomingoutdoorairvs.theairrecirculatedfromthezones.Section4validatestheapproachpresentedbycomparingtheloadscalculatedfromairconditionstothosedirectlyreportedbyEnergyPlus.TheresultsanddiscussionarepresentedinSection5.

2. SummaryofEnergyPlusBuildingsandOutput

Thissectionprovidesasummaryofthebuildingprototypes,theclimatezonesandrepresentativecities,andtheheatingandcoolingsystemsinthemodeledbuildings.Italsoprovidesaschematicdescriptionofthearrangementofnodesforeachsystemtype,andtheselectionofnodesandoutputvariablesusedinthisanalysis.

2.1. Buildingprototypesandclimatezones

2.1.1. CommercialReferenceBuildings

TheDepartmentofEnergy(DOE)hasdevelopedbuildingprototypes,referredtoastheDOEReferenceBuildings,whicharemeanttobeusedtomodelannualHVACenergyusein

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EnergyPlus(Deruetal2011).TheDOECommercialReferencebuildingsrepresentcommonbuildingtypesintheU.S.commercialbuildingstockandconsistof16buildings(15commercialbuildingsandonemultifamilyresidentialbuilding)inthreevintages:pre-1980,post-1980,andnewconstruction.The16buildingsandthreevintagesrepresentapproximatelytwothirdsoftheU.S.commercialbuildingstock.Thethreevintageshavethesameareaandoperatingschedules,thedifferencesarefoundinbuildingcharacteristicssuchasinsulation,lighting,HVACequipmentefficiency.AsreportedinDeruatal2011,Table2-1belowdisplaysthe16buildingtypesandtheirsquarefootage.Table2-1 CommercialBuildingPrototypes

BuildingType SquareFootageCoolingCapacity(tonspersq.ft.)

Chicago Houston PhoenixSmallOffice 5,500 0.0018 0.0020 0.0020MediumOffice 53,628 0.0023 0.0024 0.0025LargeOffice 498,588 0.0018 0.0019 0.0019PrimarySchool 73,960 0.0020 0.0022 0.0022SecondarySchool 210,887 0.0031 0.0033 0.0030Stand-AloneRetail 24,692 0.0022 0.0025 0.0023StripMall 22,500 0.0021 0.0025 0.0024Supermarket 45,000 0.0034 0.0029 0.0028QuickServiceRestaurant 2,500 0.0054 0.0055 0.0055FullServiceRestaurant 5,500 0.0047 0.0048 0.0048SmallHotel 43,200 0.0018 0.0019 0.0020LargeHotel 122,120 0.0017 0.0018 0.0016Hospital 241,351 0.0034 0.0037 0.0034OutpatientHealthcare 40,946 0.0036 0.0038 0.0039Warehouse 52,045 0.0008 0.0007 0.0007MidriseApartment 33,740 0.0017 0.0016 0.0017

RepresentativenessofCommercialReferenceBuildingsoftheU.S.BuildingStock

TofurtherinvestigatehowrepresentativetheCRBdatasetisofthefullbuildingstock,the2012CommercialBuildingEnergyConsumptionSurvey(CBECS)data(DOE-EIA2012)andcommercialfloor-spaceprojectionsfromtheAnnualEnergyOutlook(AEO)2020(DOE-EIA2020)areusedtoestimatethedistributionoffloor-spacebybuildingtypeandvintagecategoryintheyear2020.AsshownbelowinTable2-2,thethreevintagecategoriesarePre-1980,1980-2003,2004-2012,and2013to2020.TheAEOCommercialDemandModuledocumentation(DOE-EIA2014)providesanalgorithmforretiringbuildingfloor-space,whichwasappliedtotheCBECS2012datatoestimatethequantityoffloor-spaceinthatsurveythatwouldhavebeentakenoutofthebuildingstockby2020.TheAEO2020projectionofnewconstructionfortheyears2013-2020wasthenusedtopopulatethevintagecategory2013-2020.TheresultsaresummarizedinTable2-2.Thesixthcolumnofthistableshowsthepercentofallfloor-spaceallocatedtothatbuildingtype,andtheseventhcolumnliststheCRBprototypesthatmaptothatbuildingtype.NotetheAEOmapsoutpatienthealthcarebuildingstotheirsmallandlargeofficecategories.Smallofficecorrespondstobuildingfloor-spacelessthanorequalto50,000squarefeet.

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Table2-2 DistributionofCommercialFloor-spacebyVintagein2020

BuildingType

VintageCategory PercentofFloor-spacein2020 Prototypes

Pre-1980

1980-2003

2004-2012

2013-2020

Assembly 48% 31% 11% 10% 11% Noneavailable

Education 43% 30% 12% 14% 14% Primaryschool,Secondaryschool

FoodSales 35% 37% 16% 12% 1% Supermarket

FoodService 44% 34% 9% 13% 2%Full-serviceRestaurant,Quick-serviceRestaurant

HealthCare 44% 22% 17% 17% 3% Hospital

Lodging 33% 37% 12% 19% 7%SmallHotel,MidriseApartment,LargeHotel

LargeOffice 39% 44% 7% 11% 10% LargeOffice,MediumOffice

SmallOffice 39% 37% 12% 12% 10% SmallOffice,Outpatient

Mercantile/Services 33% 39% 14% 15% 18% Stripmall,Stand-aloneRetail

Warehouse 31% 37% 16% 15% 15% WarehouseOther 44% 34% 8% 14% 8% NoneavailableAllBuildings 38% 36% 12% 14% 100% The‘Assembly’(theatres,churches,etc.)and‘Other’AEOcommercialbuildingcategoriesarenotincludedintheCRBprototypes.About50%ofthe‘Other’categoryreferstovacantbuildings,mostofwhichpresumablywouldberepresentedbytheexistingprototypesiftheywereoccupied.Hence,about15%ofallfloor-spacedoesnothaveacorrespondingprototype.ItseemsreasonabletoassumethatthePre-1980and1980-2003vintagecategoriesarewell-representedbythePre-1980andPost-1980vintageprototypes.Thesevintagesrepresent74%oftotalfloor-space.TheNewvintageprototypecorrespondstoASHRAE90.1-2004coderequirementspublishedin2004,anditislikelythatsomefractionofbuildingsconstructedafter2004aredesignedtomorerecentcodes.Themagnitudeofthisfractiondependsbothonwhatbuildingcodewascurrentintheyearofconstruction,andwhatthecodecompliancerateis.State-by-statebuildingcodeadoptiondataareavailablefromtheU.S.DepartmentofEnergy’sBuildingEnergyCodesProgram(DOE-BECP2019)forDecember2019.Basedonthesedata,asofDecember2019,statesrepresenting19percentoftheUSpopulationhaveabuildingcodemorestringentthanASHRAE90.12013,42percenthavecodesequaltoASHRAE90.1-2013,7percenthavecodesequaltoASHRAE90.1-2010,20%havecodesequaltoASHRAE90.1-2007,and11percenthavecodeslessstringentthanASHRAE90.1-

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2007orhavenostatewidecode.Roughly,fromthisitisinferredthatabout80percentofthepopulationisinstateshavingcodesthataremorethanfiveyearsoutofdate,and20percentisstateswithcodesadoptedwithinthelastfewyears.Basedonthisbreakdown,ofthe12%ofbuildingfloor-spaceinvintagecategory2004-2012,roughly9%wouldbesubjecttocodescomparableto2004(i.e.codes5ormoreyearsout-of-datein2012).Theremainder,plusthefloor-spaceinthe2013-2020category,leadstoanestimateof17%offloor-spacethatmightbesubjecttomorestringentcodesthanarerepresentedintheCRBprototypes.Adoptionratesdonotnecessarilyreflectcompliance.Enforcingcodecompliancecanbeexpensive,andanextensivereviewofavailabledatahasindicatedwidelyvaryingcompliancerates(Williamsetal.2013).Manystateslacksufficientdatatoestimatecompliance.Hence,a50%compliancerateacrossallstateswasassumed.Thus,ofthe17%offloor-spacepotentiallysubjecttomorestringentcodes,itisassumedthatabout9%arecompliant;roundingtoonedigitofprecision,thisestimatesuggeststhatabout10%offloor-spacewouldcomplywithcodesmorestringentthanthe“New”prototype.Insummary,theseestimatessuggestthatabout15%offloor-spacedoesnothaveaCRBprototype,andabout10%offloor-spacemaybesubjecttomorestringentcodesthanaremodeledintheCRBprototypes.Whiletheseareupperboundsbasedonlyonbuildingandvintagecategory,theydoindicatethatabout75%offloor-spaceisatleastinthegeneralcategoriesmodeledbytheCRBprototypes.

2.1.2. ClimateZones

TheclimatezonesusedinDeruetal2011werebasedonbasedonBriggsetal2003,which

developedclimatezonesforDOEandASHRAE2004(Briggsetal2003).Asshown

belowinFigure2-1,theseclimatezonesconsistofeightareasacrosstheU.S.,in

mostlyeast-westbandswithzoneonebeingthesouthernmostandzoneeight,which

isnotpicturedasitslocationissolelyinAlaska,beingthenorthernmostpartofthe

country.TheU.S.isalsodividedintoverticalsubdivisions:moist(A),dry(B),and

marine(C).Intotalthereare16climatezonesasshowninSource:Figure1Climatezoneclassification(Deruatal2011)Figure2-1below.

2.1.3. RepresentativeCities

Deruetal2011chosearepresentativecitywhichbalancedtherepresentativenessoftheclimateandthenumberofbuildingsineachclimatezone.Therepresentativecityweatherfileisusedtosimulatethehourlyweatheroverthecourseofatypicalmeteorologicalyear(TMY)foreachbuilding’ssimulation.TheTMYdataconsistofindividualcalendarmonthsofhistoricdata,chosenfromyearswhichrepresentmedianoraverageweather;hence,TMYdatadonotincludemoreextremeweathereventssuchasheatorcoldwaves.Table2-3displaysthe16climatezonesandtherepresentativecitiesusedforweatherdata.

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Source:Figure1Climatezoneclassification(Deruatal2011)Figure2-1 ClimateZoneClassification

Table2-3 ClimateZonesandRepresentativeCities

ClimateZone ClimateType RepresentativeCity1A Hot-Humid Miami,FL2A Hot-Humid Houston,TX2B Hot-Dry Phoenix,AZ3A Hot-Humid/Mixed-Humid Atlanta,GA

3B–CA Hot-Dry LosAngeles,CA3B–other Hot-Dry LasVegas,NV

3C Marine SanFrancisco,CA4A Mixed-Humid Baltimore,MD4B Mixed-Dry Albuquerque,NM4C Marine Seattle,WA5A Cold Chicago,IL5B Cold Boulder,CO6A Cold Minneapolis,MN6B Cold Helena,MT7 VeryCold Duluth,MN8 Subarctic Fairbanks,AK

Source:Table2SelectedCommercialReferenceBuildingModelLocations(Deruatal2011)

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2.1.4. SummaryofEachCommercialReferenceBuilding

Belowisasummaryofthenewconstructionvintageofthe16referencebuildings.Table2-4attheendofthissectionsummarizesthecharacteristicsofeachbuilding.

SmallOffice

Thesmallofficebuildingisarectangular,onefloorbuildingconsistingoffivezones:acorezoneandfourperimeterzones.Eachzoneisservedbyapackagedsinglezone(PSZ)unitwithadirect-expansion(DX)coilforairconditioningandagasfurnaceforheating.Economizersarenotusedinthesmallofficeprototypebuilding.

MediumOffice

Themediumofficebuildingisarectangular,threestorybuildingwithfivezonesperfloor:acorezoneandfourperimeterzones.Fornewconstructionandpost-1980buildings,eachfloorisservedbyapackagedvariableairvolume(VAV)system,withaDX-coilforair-conditioning,zone-levelelectricreheatcoils,andagasfurnaceforheating.Differentialdrybulbeconomizersareusedinallclimatezonesexceptforthehot-humidzones(1A,2A,3A,and4A).Thefloorplanandoccupancydonotchangebyfloor.

LargeOffice

Thelargeofficeisarectangular,twelvestorybuildingwithfivezonesperfloor:acorezoneandfourperimeterzones,aswellasasingle-zonebasement.ThebuildinghasatwochillersandaboilerwhichserveaVAVsystemoneachfloorandthebasement.Eachzoneexceptforthebasementhaselectricreheatcoils.Differentialdrybulbeconomizersareusedinallclimatezonesexceptforthehot-humidzones(1A,2A,3A,and4A).Thefloorplanandoccupancydonotchangebyfloor.

PrimarySchool

Theprimaryschoolisaonefloorbuildingintheshapeoftheletter“E”,composedofthreepodswhichcontaintheclassrooms,andamainbuildingwithagym,cafeteria,kitchen,library,offices,lobby,bathrooms,andamaincorridor.Eachpodconsistsof5zones,with4classroomsandacorridorzone.EachpodandthemainbuildingisservedbyapackagedVAVsystem,withaDXcoilforair-conditioning,zonelevelelectricreheatcoils,andaboilerforheating.Thegym,cafeteria,andkitchenareeachservedbytheirownpackagedsinglezonerooftopunitwithaDX-coilforcoolingandagasfurnaceforheating.

SecondarySchool

Thesecondaryschoolbuildingisatwofloorbuildingintheshapeoftheletter“E”,composedofthreetwo-floorpodswhichcontainclassrooms,atwo-floormainbuildingwithalobby,offices,alibrary,bathrooms,andamaincorridor,andtwogyms,acafeteria,akitchen,andanauditorium.EachpodandthemainbuildingareservedbyachillerandboilerwithaVAVairdistributionsystemwithelectricreheatineachzone.Thetwogyms,theauditorium,cafeteria,andkitchenaresinglezones,eachservedbytheirownpackagedsinglezonerooftopunitwithaDX-coilforcoolingandagasfurnaceforheating.

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StandAloneRetail

Thestand-aloneretailbuildingisarectangular,onefloorbuildingwithfourconditionedzones:thepointofsalearea,thefrontretailarea,alargecoreretailzone,andabackzone.EachzoneisservedbyapackagedsinglezonerooftopunitwithaDX-coilforcoolingandagasfurnaceforheating.Differentialdrybulbeconomizersareusedinthecoreretailzoneinallclimatezonesexceptforthehot-humidzones(1A,2A,3A,and4A).Thebackspacezoneusesaneconomizerinclimatezones4B,5B,6B,and7.

StripMall

Thestripmallbuildingisarectangular,onefloorbuildingconsistingoftwolargestoresandeightsmallerstoreswhichareallconnected.Onelargestoreislocatedattheendofthebuilding,followedbyfoursmallstores,anotherlargestore,andfourmoresmallstores.EachstoreisasinglezoneandservedbyapackagedsinglezonerooftopunitwithaDXcoilforcoolingandafurnaceforheating.Differentialdrybulbeconomizersareusedinlargestore1inclimatezones3B,3C,4B,4C,5B,and6Bandlargestore2inclimatezones3Band4B.

Supermarket

Thesupermarketbuildingisarectangular,onefloorbuildingconsistingofsixzones:sales,produce,drystorage,deli,bakery,andoffices.EachzoneisservedbyapackagedsinglezoneunitwithaDX-coilforcoolingandagasfurnaceforheating.Differentialdrybulbeconomizersareusedinthedrystorage,sales,andproducezonesinallclimatezonesexceptforthehot/mixed-humidzones(1A,2A,3A,and4A).

QuickServiceRestaurant

Thequickservicerestaurantbuildingisasquare,onefloorbuildingconsistingoftwoequallysizedconditionedzones.EachzoneisservedbyapackagedsinglezonerooftopunitwithaDXcoilandafurnacetoprovidecoolingandheating.Differentialdrybulbeconomizersareusedinthediningroominclimatezones3B,3C,4B,4C,5B,and6B.

FullServiceRestaurant

Thefullservicerestaurantbuildingisasquare,onefloorbuildingconsistingoftwozones,alargerdiningroomandasmallerkitchen.EachzoneisservedbyapackagedsinglezonerooftopunitwithaDXcoilforcoolingandafurnaceforheating.Differentialdrybulbeconomizersareusedinallclimatezonesexceptforthehot/mixed-humidzones(1A,2A,3A,and4A).

Warehouse

Thewarehousereferencebuildingisarectangular,onefloorbuildingwiththreezones:offices,afinestoragearea,andabulkstoragearea.TheofficesandthefinestoragezonesareeachservedbyaunitarypackagedprecisionaircooledunitwithaDX-coilforcoolingandagasfurnaceforheating.Thebulkstorageareaisnotcooled,buthasagasfiredunitheatercoiltoprovideheating.Differentialdrybulbeconomizersareusedinallclimate

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zonesexceptforthehot/mixed-humidzones(1A,2A,3A,and4A)inthefinestoragearea,andclimatezones4B,5B,and6Bintheofficezone.

LargeHotel

Thelargehotelisarectangular,6floorbuildingwithabasement.Thefirstfloorofthehotelconsistsofalobby,acafé,laundry,amechanicalroom,astorageroom,andtworetailspaces.Theremainingfivefloorsconsistofhotelrooms.Floorstwothroughfivehave42guestrooms,thesixthfloorhas11guestroomsalongwithabanquethallandarestaurant.Thehotelisservedbytwochillersforairconditioningandaboilerforheating.AVAVdistributionsystemwithelectriczonereheatisusedforthefirstfloor,therestaurant,andthebanquethall.Adedicatedoutsideairsystemisusedtoprovideventilationfortheguestroomsandeachguestroomhasafancoilforcoolingandheatingwithintheroom.TheVAVzonesuseadifferentialdrybulbeconomizerinallclimatezonesexceptforthehot/mixed-humidzones(1A,2A,3A,and4A).

SmallHotel

Thesmallhotelisarectangular,fourfloorbuildingwith77guestrooms.EachguestroomsisservedbyaPTACwithaDX-coilforcoolingandanelectricindividualspaceheaterforheating.Thereare12packagedsinglezoneunitswithaDX-coilforcoolingandagasfurnaceforheating,thatservethecommonspacesofthehotel:corridors,lounges,meetingrooms,laundryrooms,offices,andtheexercisecenter.Adifferentialdrybulbeconomizerisusedinthelaundryroominclimatezones3B,3C,4B,4C,5B,and6B.

Hospital

Thehospitalisarectangular,fivefloorbuildingwithabasement.Thehospitalconsistsofanemergencyroom,anintensivecareunit,operatingrooms,patientrooms,physicaltherapy,offices,alobby,labs,nurse’sstations,adininghall,kitchen,andconditionedcorridors.Thehospitalisservedbyachillerforairconditioningandaboilerforheating.ACAVairdistributionsystemisusedfortheemergencyroom,operatingrooms,theintensivecareunit,andsomepatientrooms.TheremainderofthehospitalusesaVAVairdistributionsystemwithelectricreheat.TheVAVzonesuseadifferentialdrybulbeconomizerinallclimatezonesexceptforthehot/mixed-humidzones(1A,2A,3A,and4A).

OutpatientHealthcare

Theoutpatienthealthcarebuildingisirregularshapedandthreefloors.Theoutpatienthealthcarebuildingconsistsofexamrooms,offices,alobby,waitingrooms,pre-operatingroom,operatingrooms,storage,restrooms,physicaltherapy,andstafflounges.Thebuildingisservedbytwopackagedvariableairvolumesystems,withaDX-coilforair-conditioningandaboilerforheating.EachzonehasaVAVboxwithelectricreheatcoils.Adifferentialdrybulbeconomizerisusedinallclimatezonesexceptforthehot/mixed-humidzones(1A,2A,3A,and4A).

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MidriseApartments

Themidriseapartmentisarectangularshaped,fourfloorbuilding.Themidriseapartmentbuildingconsists31identicalapartmentsandoneofficewhichisthesamesizeasanapartment.EachapartmentandtheofficeisservedbyaseparateunitarysplitsystemwithaDX-coilforairconditioningandagasfurnaceforheating.

SummaryofPrototypeBuildingCharacteristics

AsreportedintheDOEreferencebuildingscorecardspreadsheets,whichareavailableontheDOEreferencebuildingwebsite(DOE-EERE2020b),Table2-4displaysthecharacteristicsofthe16prototypebuildings.Theoccupantsperzonearenotawholenumberastheyarebasedonaveragesfromvariousdatasources,whicheitherestimateanaveragenumberofpeopleperspace(suchasahotelroom)orthesquarefootageperoccupantforaspecificbuildingtype.MoredetailsontheoccupancyoftheprototypebuildingscanbefoundinDeruetal2011.Eachprototypebuildingisassignedanoperatingscheduleforenduseequipment.Asnotedearlier,almostalltheHVACsystemsmodeledintheCRBsetarecontrolledbasedonthedry-bulbtemperatureintheconditionedspace(exceptionsarenotedbelow).Inmostcases,thereisaweekdayandaweekendoperatingschedule,whichdoesnotchangebyclimatezone.TheoperatingschedulescanbefoundintheDOEreferencebuildingscorecardspreadsheets.

Table2-4 PrototypeBuildingCharacteristics

Building ZoneSquarefootage People

Lights(W/sq.ft.)

PlugandProcess(W/sq.ft.)

Ventilation(cfm)

CoolingSetpoint(°F)

HeatingSetpoint(°F)

SmallOffice

Core 1,611 8.05 1 1 171 75.2 69.8Perimeter1 1,221 6.11 1 1 129 75.2 69.8Perimeter2 724 3.62 1 1 77 75.2 69.8Perimeter3 1,221 6.11 1 1 129 75.2 69.8Perimeter4 724 3.62 1 1 77 75.2 69.8

MediumOffice

Core* 10,587 52.93 1 1 1,122 75.2 69.8Perimeter1* 2,232 11.16 1 1 236 75.2 69.8Perimeter2* 1,413 7.06 1 1 150 75.2 69.8Perimeter3* 2,232 11.16 1 1 236 75.2 69.8Perimeter4* 1,413 7.06 1 1 150 75.2 69.8

LargeOffice

Basement 38,353 95.88 1 1 2,032 75.2 69.8Core** 27,258 136 1 1 2,888 75.2 69.8Perimeter1** 3,374 16.87 1 1 357 75.2 69.8Perimeter2** 2,174 10.87 1 1 230 75.2 69.8Perimeter3** 3,374 16.87 1 1 357 75.2 69.8Perimeter4** 2,174 10.87 1 1 230 75.2 69.8

PrimarySchool

Pod1 14,467 307.20 1.27 1.25 5,085 75.2 69.8Pod2 14,467 307 1.27 1.25 5,085 75.2 69.8Pod3 12,723 266.70 1.25 1.23 4,399 75.2 69.8Mainbuilding 23,261 161.89 1.05 0.80 4,375 75.2 69.8Gym 3,843 107.21 1.40 0.46 2,272 75.2 69.8Kitchen 1,808 25.19 1.20 17.70 427 75.2 69.8

15


Lights(W/sq.ft.)


Ventilation(cfm)



Cafeteria 3,391 226.04 1.40 2.36 4,790 75.2 69.8

SecondarySchool

Pod1 31,689 640 12.24 10.22 10,442 75.2 69.8Pod2 31,689 640 12.24 10.22 10,442 75.2 69.8Pod3 31,689 640 12.24 10.22 10,442 75.2 69.8Mainbuilding 61,440 295 10.09 5.91 8,895 75.2 69.8Gym 34,703 2,392 15.07 5.00 50,684 75.2 69.8Auditorium 10,635 988 9.69 5.00 16,748 75.2 69.8Kitchen 2,325 36 12.92 222.27 610 75.2 69.8Cafeteria 6,717 449 15.07 19.27 9,512 75.2 69.8

Stand-AloneRetail

BackSpace 4,089 13.63 0.8 0.75 604 75.2 69.8CoreRetail 17,227 258.40 1.7 0.3 5,087 75.2 69.8PointofSale 1,623 24.35 1.7 2 479 75.2 69.8FrontRetail 1,623 24.35 1.7 0.3 479 75.2 69.8FrontEntry 129 1.94 1.1 0 0 75.2 69.8

StripMall

LargeStore1 3,750 56.25 11.33 2.03 523 75.2 69.8SmallStore1 1,875 28.12 11.33 2.03 261 75.2 69.8SmallStore2 1,875 28.12 8.64 2.03 261 75.2 69.8SmallStore3 1,875 28.12 8.64 2.03 261 75.2 69.8SmallStore4 1,875 28.12 8.64 2.03 261 75.2 69.8LargeStore2 3,750 56.25 6.50 2.03 523 75.2 69.8SmallStore5 1,875 28.12 6.50 2.03 261 75.2 69.8SmallStore6 1,875 28.12 6.50 2.03 261 75.2 69.8SmallStore7 1,875 28.12 6.50 2.03 261 75.2 69.8SmallStore8 1,875 28.12 6.50 2.03 261 75.2 69.8

Super-market

Office 956 4.78 1.10 0.75 101 75.2 69.8DryStorage 6,694 22.31 0.80 0.75 988 75.2 69.8Deli 2,419 19.35 1.70 5.00 714 75.2 69.8Sales 25,025 200.20 1.70 0.50 7,389 75.2 69.8Produce 7,657 61.26 1.70 0.50 2,261 75.2 69.8Bakery 2,250 18.00 1.70 5.00 664 75.2 69.8

QuickServiceRestaurant

Dining 1,250 83.33 2.1 12 393 75.2 69.8

Kitchen 1,250 6.25 1.2 28 24 78.8 66.2

FullServiceRestaurant

Dining 4,001 266.77 2.1 5.6 1,259 75.2 69.8

Kitchen 1,501 7.50 1.2 35 28 78.8 66.2

WarehouseOffice 2,550 5.00 1.1 0.75 24 75.2 69.8FineStorage 14,999 0.00 1.4 0 164 80 60.8BulkStorage 34,497 0.00 0.9 0.25 378 0 45

LargeHotel

BasementandFloor1 42,600 640 1.1 0.7 3,035 75.2 69.8

GuestRooms 68,888 290 0.9 0.9 1,428 75.2/86† 69.8/60.8†Banquet&Restaurant 8,252 482 1.3 11.8 2,267 75.2 69.8

SmallHotel Guestrooms 27,758 765.91 1.10 1.3 2,310 75.2 69.8

16


Lights(W/sq.ft.)


Ventilation(cfm)



Corridor-FLR1 1,620 0.00 0.50 0.0 80 75.2 69.8Corridor-FLR2 1,350 0.00 0.50 0.0 66 75.2 69.8Corridor-FLR3 1,350 0.00 0.50 0.0 66 75.2 69.8Corridor-FLR4 1,350 0.00 0.50 0.0 66 75.2 69.8FrontLounge 1,755 52.71 1.10 1.4 893 75.2 69.8FrontOffice 1,404 10.03 1.10 1.2 212 75.2 69.8Restroom 351 1.00 0.90 1.0 0 75.2 69.8MeetingRoom 864 43.20 1.30 1.2 915 75.2 69.8MechanicalRoom 351 0.00 1.50 0.0 17 75.2 69.8

EmployeeLounge 351 10.54 1.20 7.2 179 75.2 69.8

LaundryRoom 1,053 10.53 0.60 2.0 290 75.2 69.8ExerciseCenter 351 10.54 0.90 1.1 223 75.2 69.8

Hospital

CAV1 18,900 157 1.2 2.1 1,565 72 70CAV2 8,250 41 1.9 4.4 3,711 72/65⟡ 70/65⟡VAV1 109,298 472 1.1 0.9 26,713 72 70VAV2 104,902 620 1.0 2.0 42,284 72 70

OutpatientHealthCare

Floor1 14,186 175 1.1 3.4 4,381 72/65⟡ 70/65⟡

Floor2and3 26,760 224 1.0 0.9 4,248 72 70

MidriseApartment

Apartment^ 950 2.50 0.4 0.5 90 75 70Office 950 2.00 1.2 6.1 42 75 70

* MediumOfficehasthreefloors.MultiplyCoreandPerimeterzonesbythreetoobtaintotalsquarefootage.**LargeOfficehastwelvefloors.MultiplyCoreandPerimeterzonesbytwelvetoobtaintotalsquarefootage.^ MidriseApartmenthas31apartments.MultiplyApartmentzoneby31toobtaintotalsquarefootage.† Thisisthesetpointtemperaturefortheguestroomcorridors.⟡ Thisistheoperatingroomtemperature.

2.2. Systemtypes

AsreportedintheDOEreferencebuildingscorecardspreadsheets,whichareavailableontheDOEreferencebuildingwebsite(DOE-EERE2020b),Table2-5summarizestheHVACsystemsusedineachbuilding.ForeachHVACsystem,thefan-typeisspecifiedasadraw-throughorblow-through,bothofwhicharedescribedinSection2.3.

17

Table2-5 HVACSystemtypesforPrototypeBuildings

BuildingType HVACType* Zones Cooling# Heating FanType ReheatEconomizer**SmallOffice PSZ 5 DX GasFurnace Draw-through No NoMediumOffice MZ_VAV 15 DX GasFurnace Draw-through Yes YesLargeOffice MZ_VAV 61 Chiller Boiler Draw-through Yes Yes

PrimarySchoolMZ_VAV 22 DX Boiler Draw-through Yes YesPSZ 3 DX GasFurnace Draw-through No Yes

SecondarySchool

MZ_VAV 41 Chiller Boiler Draw-through Yes YesPSZ 5 DX GasFurnace Draw-through No Yes

StandAloneRetail PSZ 4 DX GasFurnace Blow-through No Yes

StripMall PSZ 10 DX GasFurnace Blow-through No YesSupermarket PSZ 6 DX GasFurnace Draw-through No YesQuickServiceRestaurant PSZ 2 DX GasFurnace Draw-through No Yes

FullServiceRestaurant PSZ 2 DX GasFurnace Draw-through No Yes

Warehouse PSZ 3 DX GasFurnace Blow-through No Yes

LargeHotelMZ_VAV 16 Chiller Boiler Draw-through Yes YesFanCoil 179 Chiller Boiler Draw-through No NoDOAS 179 Chiller Boiler Draw-through No No

SmallHotelPTAC 77 DX Elec.Resistance Draw-through No NoPSZ 12 DX GasFurnace Draw-through No No

HospitalMZ_CAV 93 Chiller Boiler Draw-through No NoMZ_VAV 68 Chiller Boiler Draw-through Yes Yes

OutpatientHealthcare MZ_VAV 118 DX Boiler Draw-through Yes Yes

MidriseApartment

UnitarySplitSystem 32 DX GasFurnace Blow-through No No

*HVACTypes:PSZ=packagesinglezone;MS_VAV=multi-zonesystem,variableairvolume;MS_CAV=multi-zonesystem,constantairvolume;DOAS=dedicatedoutdoorairsystem;PTAC=packagedterminalairconditioner.

#Cooling: DX=direct-expansion.#Economizer:Economizersarenotusedinclimatezones1A,2A,3A,and4A.

2.3. Systemnodesandsystemvariables

Eachheating,ventilating,andair-conditioning(HVAC)systemisdefinedas:x =theindexoftheHVACsystem,Typex =thetypeofsystemx,N =numberofHVACsystemsinthebuilding,sox=1,…N.AnHVACsystemmayservemultiplezones;thetotalzonesservedbysystem,x,is:

18

nx =numberofzonesbeingservedbyHVACsystem,x.ForeachHVACsystem,x,therearethefollowingsystemnodes:rax =returnair,rfax =reliefair,oax =outdoorair,max =mixedairinlet,ccx =coolingcoilinlet(sameasthemaxnodeinadraw-throughsystem),hcx =heatingcoilinlet,sfx =supplyfaninlet(sameasthemaxnodeinablow-throughsystem),andsax =supplyair.Figure2-2depictsanHVACsystemandthezonesitserves.TwotypesofHVACsystemsaredepictedinFigure2-2;adraw-throughsystem,wherethesupplyfandrawsthemixedairthroughthecoolingandheatingcoils,andablow-throughsystem,wherethesupplyfandrawsinmixedairandthenblowsitthroughthecoolingandheatingcoils.ThesystemnodesarelabeledtoshowtheirlocationwithintheHVACsystem.AsnotedinFigure2-2,thesupplyairdeliveredtoeachzonemaypassthroughareheatcoilinordertoconditiontheairbeforeitisdeliveredtothezone.Finally,someoftheairfromazonemaybeexhausted,eitherthroughthereliefairnode,or(forkitchensandlaundry)directlythoughazonalexhaustnode;thezoneairthatisnotexhaustedisreturnedbacktotheHVACsystemtobereconditioned.Table2-6summarizesthevariablenamesofeachairpropertyateachsystemnode.TheHVACsystemnodesareindexedbytheletterj.Ateachnode,j,ofsystemx,therearethefollowingairproperties:!̇j_x =massflowrate(kg/s),Tj_x =dry-bulbtemperature(°C),cp_j_x =specificheat(kJ/kg-°C),wkg_j_x =humidityratio(kgwater/kgdryair),andvwe_j_x =latentheatofvaporization(kJ/kg).

Table2-6 HVACSystemNodeandSystemAirPropertyVariableNames

SystemNode

SystemAirPropertyMassFlow

RateDry-Bulb

Temperature SpecificHeatHumidityRatio

LatentHeatofVaporization

ReturnAir !̇ra_x Tra_x cp_ra_x wkg_ra_x vwe_ra_xReliefAir !̇rfa_x Trfa_x cp_rfa_x wkg_rfa_x vwe_rfa_xOutdoorAir !̇oa_x Toa_x cp_oa_x wkg_oa_x vwe_oa_xMixedAirInlet !̇ma_x Tma_x cp_ma_x wkg_ma_x vwe_ma_xCoolCoilInlet !̇cc_x Tcc_x cp_cc_x wkg_cc_x vwe_cc_xHeatCoilInlet !̇hc_x Thc_x cp_hc_x wkg_hc_x vwe_hc_xSupplyFanInlet !̇sf_x Tsf_x cp_sf_x wkg_sf_x vwe_sf_xSupplyAir !̇sa_x Tsa_x cp_sa_x wkg_sa_x vwe_sa_x

19

Figure2-2 TypicalHVACSystemandZoneNodes

Mixed Air / Cool Coil

Inlet

Zone 1

Zone 2

Zone nx

SupplyAir

Zone 1:Inlet Air

ReturnAir

Zone 2:Out Air

Zone 1:Outlet Air

Zone nx:Outlet Air

Zone 2:Inlet Air

Zone nx:Inlet Air

Zone 1:Exh Air

(if appl.)

All Zones:Exh Air

(if appl.)

Zone 2:Exh Air

(if appl.)Cooling Coil Heating Coil

SupplyFan

Reheat Coil 1 (if applicable)

HVAC Draw-through System xReheat Coil 2 (if applicable)

Reheat Coil nx (if applicable)

HeatCoilInlet

SupplyFanInlet

ReliefAir

OutdoorAir

Zone nx:Exh Air

(if appl.)

Mixed Air / Supply Fan

Inlet

CoolCoilInlet

Cooling Coil Heating Coil

SupplyFan

HVAC Blow-through System x

HeatCoilInlet

SupplyAir

ReliefAir

OutdoorAir

ReturnAir

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2.4. Zonedefinitionsandzonevariables

AllzonesinabuildingthatareservedbyanHVACsystemaremappedtooneoftheNsystemsinthebuilding.Zonevariablesaredefinedbybothazoneindex,andtheindex,x,oftheHVACsystemservingthatzone.Thezoneindexisincrementedinstepsof1uptothenumberofzones,nx,servedbyanHVACsystem,x,whichisexpressedasfollows:z =theindexofthezone,nx =numberofzonesbeingservedbyHVACsystem,x,soz=1,…nx.Foreachzone,z,beingservedbyanHVACsystem,x,therearethefollowingnodes:ziz =zoneinlet,zmz =zonemeanorlocationatthecenterofthezone,zoz =zoneoutlet,andzexz =zoneexhaust,Thezonenodesareindexedbytheletterk.Ateachnode,k,ofzonez,therearethefollowingairproperties:!̇k_z_x =massflowrate(kg/s),Tk_z_x =dry-bulbtemperature(°C),cp_k_z_x =specificheat(kJ/kg-°C),wkg_k_z_x =humidityratio(kgwater/kgdryair),andvwe_k_z_x =latentheatofvaporization(kJ/kg).Somezonesmayhaveanexhaustfan(forexampleinkitchens);hence,thesystemairloopmayincludeanadditionalquantityofairexhausted.Theairpropertiesofboththemassflowexhaustedout,andthatreturnedtotheHVACsystemfromeachzone,z,aresimilartotheairpropertiesofthezonemeanmassflowrate.Table2-7illustrateshowzones,theirassociatedHVACsystem,airpropertiesandmassflowratesareindexed.

21

Table2-7 RelationshipbetweennumberofHVACsystems(x)andcorrespondingnumberofZones(nx)servedbyeachsystemwithZoneAirPropertyVariableNames

SystemNo.

ZoneNo. ZoneNode

ZoneAirPropertyMassFlowRateintoZone

Dry-BulbTemperature

SpecificHeat

HumidityRatio

LatentHeatof

Vaporization

1

1ZoneInlet !̇zi_1_1 Tzi_1_1 cp_zi_1_1 wkg_zi_1_1 vwe_zi_1_1ZoneMean !̇zm_1_1 Tzm_1_1 cp_zm_1_1 wkg_zm_1_1 vwe_zm_1_1ZoneOutlet !̇zo_1_1 Tzo_1_1 cp_zo_1_1 wkg_zo_1_1 vwe_zo_1_1ZoneExhaust !̇zex_1_1 Tzex_1_1 cp_zex_1_1 wkg_zex_1_1 vwe_zex_1_1

• • • • • • •• • • • • • •• • • • • • •

n1

ZoneInlet !̇zi_n1_1 Tzi_n1_1 cp_zi_n1_1 wkg_zi_n1_1 vwe_zi_n1_1ZoneMean !̇zm_n1_1 Tzm_n1_1 cp_zm_n1_1 wkg_zm_n1_1 vwe_zm_n1_1ZoneOutlet !̇zo_n1_1 Tzo_n1_1 cp_zo_n1_1 wkg_zo_n1_1 vwe_zo_n1_1ZoneExhaust !̇zex_n1_1 Tzex_n1_1 cp_zex_n1_1 wkg_zex_n1_1 vwe_zex_n1_1

• • • • • • • •• • • • • • • •• • • • • • • •

N

1ZoneInlet !̇zi_1_N Tzi_1_N cp_zi_1_N wkg_zi_1_N vwe_zi_1_NZoneMean !̇zm_1_N Tzm_1_N cp_zm_1_N wkg_zm_1_N vwe_zm_1_NZoneOutlet !̇zo_1_N Tzo_1_N cp_zo_1_N wkg_zo_1_N vwe_zo_1_NZoneExhaust !̇zex_1_N Tzex_1_N cp_zex_1_N wkg_zex_1_N vwe_zex_1_N

• • • • • • •• • • • • • •• • • • • • •

nN

ZoneInlet !̇zi_nN_N Tzi_nN_N cp_zi_nN_N wkg_zi_nN_N vwe_zi_nN_NZoneMean !̇zm_nN_N Tzm_nN_N cp_zm_nN_N wkg_zm_nN_N vwe_zm_nN_NZoneOutlet !̇zo_nN_N Tzo_nN_N cp_zo_nN_N wkg_zo_nN_N vwe_zo_nN_NZoneExhaust !̇zex_nN_N Tzex_nN_N cp_zex_nN_N wkg_zex_nN_N vwe_zex_nN_N

2.5. DataavailabledirectlyfromEnergyPlus

ThelabellingofsystemandzonalnodesdescribedabovevariesacrossthedifferentEnergyPlusbuildingprototypes.Asanexample,Table2-8belowsummarizestheEnergyPlusvariablenamesfortheHVACsystemandzonenodesofinterestforthePSZHVACsystemsinthesmallofficebuildingprototype.TheEnergyPlusvariablesnamesofthesenodesinotherbuildingprototypesmaybedifferent,butthenodesarealwayspresentunder.ForeachofthenodeslistedinTable2-8,EnergyPlusprovidestheassociatedairproperties.Thenodeairpropertiesareinturnusedtodisaggregatethesensibleandlatentloads,asdiscussedinSection3.

22

Table2-8 SmallOfficeHVACSystemandZoneNodeswithEnergyPlusVariableNames

SystemorZone

NodeInformationName Notation EnergyPlusVariableName

System ReturnAir rax SUPPLYEQUIPMENTINLETNODESystem OutdoorAir oax OAINLETNODESystem ReliefAir rfax OARELIEFNODE

System MixedAirInlet maxCOOLCNODE(Draw-through);FANNODE(Blow-through)

System CoolingCoilInlet ccx COOLCNODESystem HeatingCoilInlet hcx HEATCNODESystem SupplyFanInlet sfx FANNODESupply SupplyAir sax SUPPLYEQUIPMENTOUTLETNODEZone ZoneInlet ziz DIRECTAIRINLETNODEZone Zone zmz ZONEMEANZone ZoneOutlet zoz RETURNAIRNODEZone ZoneExhaust zexz EXHASUTAIRNODE

3. ThermodynamicEquations

ThissectionpresentsthethermodynamicequationsusedtocalculatesensibleandlatentloadsfromthesystemandzoneairpropertiespresentedinSection2.Asnotedearlier,EnergyPlusgeneratessystemandzoneairpropertiesatnodesthroughouttheHVACsystemaswellasthezonesservedbytheHVACsystem.Usingtheequationsandairpropertydataouranalysisseparatesthetotalspaceconditioningloadsintofourcomponents:thelatentandsensibleloads,andtheportionofeachassociatedwithoutdoorairvs.theairrecirculatedfromtheconditionedspace.Section4validatesthecalculationsbycomparingthecalculatedtotallatentandsensiblespaceconditioningloadstothosegeneratedbyEnergyPlus.ThefourcomponentloadsassociatedwiththeoutdoorairandrecirculatedaircannotbevalidatedasEnergyPlusdoesnotdisaggregatesensibleandlatentloadstothislevel.

3.1. MassBalance

Thesensiblespace-conditioningandlatentcoolingprovidedbyanHVACsystemcanbedisaggregatedintotheloadsremovedorprovidedfromtwoairflowsthatcirculatewithintheairloopforthesystem;therecirculatedreturnairflowandtheoutdoorairflow.Thenetmassflowratearoundthesystemisconstant,soairenteringfromoutsideisalwaysbalancedbyexhaustingpartofthereturnairthroughthesystemreliefoutletnode.Thisisinadditiontoanyairexhausteddirectlythroughzoneexhaustnodes.Thetotalflowofairfromthezonesbacktothesystemiscalledthereturnair:forHVACsystem,x,therelationshipbetweenreturnair,zoneair,andexhaustairisrepresentedbythefollowingexpression:!̇!"_$ = ∑ !̇%&_%_$

'!%() − ∑ !̇%*$_%_$

'!%() = ∑ !̇%+_%_$

'!%() , (1)

23

where:∑ !̇%&_%_$'!%() =sumofinletzonemassflowratesservedbyHVACsystem,x,

∑ !̇%*$_%_$'!%() =sumofzonemassflowratesexhaustedfromthezonesservedbyHVAC

systemx,and∑ !̇%+_%_$'!%() =sumofoutletmassflowratesfromthezonesservedbyHVACsystemx.

ThereliefairistheamountofreturnairexhaustedinordertokeepthemassflowrateconstantwhenoutdoorairisdrawnintotheHVACsystem.TheoutdoorairmassflowratedrawnintotheHVACsystemisequaltothemassflowrateofthereliefairplusthesumofthezonemassflowratesthathavebeenexhausted,asshownbythefollowingexpression:!̇+"_$ = !̇!,"_$ + ∑ !̇%*$_%_$

'!%() , (2)

Therecirculatedairisdefinedastheportionofreturnairflowratethatisnotexhausted:!̇!-!-_$ = !̇!"_$ − !̇!,"_$ , (3)where:!̇!-!-_./.$ =returnairmassflowraterecirculatedtotheHVACsystem,x.Themixedairflowrateisequaltothesumoftherecirculatedairflowrateandtheoutdoorairflowrate:!̇0"_$ = !̇!-!-_$ + !̇+"_.$ . (4)ThemixedairflowrateisalsoequaltotheHVACsystem’ssupplyairflowrate;!̇."_$ = !̇0"_$ . (5)ForHVACsystem,x,thesupplyairmassflowrateequalsthesumofthemassflowratesintoeachzone:!̇."_$ = ∑ !̇%&_%_$

'!%() . (6)

Thezoneairmassflowraterepresentsbothairflowintoandoutofthezone,includinginfiltration,whichisgenerallysmall.Thesumofthemassflowratesdeliveredtoallzoneswithinthebuildingdefinesthetotalmassflowrateofthebuilding,!̇1234:!̇1234 = ∑ !̇."_$5

$() . (7)

24

3.2. EnergyBalance

Section3.2explainshowthesensibleandlatentcomponentsofthespacecoolingandheatingloadsarecalculated.EnergyPlususesweatherdataalongwithbuildingcharacteristicstocalculatetheheatgeneratedataspecifictime-step,andthencalculatestherateofcoolingorheatingrequiredbytheHVACsystemtomaintainthezonalset-pointtemperatures(DOE-EERE2018).Inthisreport,thetotalcoolingorheatingrateoftheHVACsystemisdisaggregatedintotheventilationloadandthezonalload,andthenfurtherdisaggregatedintosensibleandlatentcomponentsbasedonairpropertiesatdifferentpointsthroughouttheHVACsystem.Theairpropertiesusedintheloadcalculationsaretemperature,humidityratio,massflowrate,specificheat,andlatentheatofvaporization.Theventilationloadiscalculatedusingtheventilationrateforeachprototypebuildingandtheairpropertiesoftheoutdoorairandthesupplyairforaspecifictime-step.Thezonalloadsarecalculatedusingthechangeinairpropertiesbetweenthezoneinletnode(whereairentersazone)andthezoneoutletnode(whereairiseitherexhaustedtotheoutdoorsorreturnedtotheHVACsystem)foratime-step.Thezoneloadsrepresenttheamountofcoolingorheatingrequiredtooffsettheinternalgainsorlossesineachzone.Internalloadsrepresenttheloadsfrompeople,lighting,equipment,infiltration,windows,andwalls.

3.2.1. Sensibleheatbalance

Systemsensibleload

WithinHVACsystemx,therateofsensibleloadremovedorprovidedbetweenanodeupstreamofthesupplyairnodeandthesupplyairnodeisdeterminedwiththefollowingexpression:ℎ._6_$ = +7̅_6_$ × !̇6_$ × (/6_$ − /."_$), (8)where,ℎ._6_$ =rateofsensibleloadremovedorprovidedbyHVACsystem,x,betweenthe

upstreamandsupplyairnodes(kW),+7̅_6_$ =meanvalueofthespecificheatbetweentheupstreamandsupplyairnodes

(kJ/kg-°C),!̇6_$ =massflowrateatsupplyairnode(kg/s),and/6_$ =dry-bulbairtemperatureattheupstreamnode(°C),and/."_$ =dry-bulbairtemperatureatthesupplyairnode(°C).Therateofsensibleloadcalculatedinequation8representsthetotalsensibleloadandincludesboththeeffectsofrecirculatedreturnairandtheoutdoorair.Outdoorairdrawnintothesystemisusedtomeetcode-relatedventilationrequirementswhicharetypicallybasedonbuildingoccupancy.ForHVACsystemsequippedwitheconomizers,additionaloutdoorairisdrawnintotheHVACsystemattimeswhentheoutdoorairconditionsaresuitableforspace-coolingandcandisplacetheneedformechanicalcooling.

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Atoutdoorairconditionswhenmechanicalcoolingisneeded,theHVACsystemmustconditiontheoutdoorairtoremovethesensibleandlatentload.Whenmechanicalheatingisneeded,theHVACsystemconditionstheoutdoorairtoaddsensibleload.Indevelopingenergybalanceequationsaroundtheairloop,theheatrejectedfromthesupplyfanmustalsobeaccountedforaspartofthesensibleload.Fordraw-throughHVACsystems,thefan’seffectontheairproperties(e.g.,toincreasethedry-bulbtemperature)iscapturedinequation8aboveasthesupplyairnodeisafterthesupplyfan.Forblow-throughsystems,assumingtheupstreamnodeisbeforethefan,equation8alsocapturesthefan’seffectontheairproperties.TherateofsensibleloadremovedorprovidedbyHVACsystemxtotheoutdoorairflow,inordertobringitsairpropertiestosupplyairconditions,isexpressedas:ℎ._+"_$ = +7̅_+"_$ × !̇+"_$ × (/+"_$ − /."_.$), (9)where,ℎ._+"_$ =rateofsensibleloadremovedorprovidedtotheoutdoorairflow(kW),and+7̅_+"_$ =meanvalueofthespecificheatbetweentheoutdoorairandsupplyairnodes

(kJ/kg-°C).TherateofsensibleloadremovedorprovidedbyHVACsystemxtotherecirculatedreturnairflow,inordertobringitsairpropertiestosupplyairconditionsisexpressedasfollows:ℎ._!-!-_$ = +7̅_!-!-_$ × !̇!-!-_$ × (/!-!-_$ − /."_.$), (10)where,ℎ._!-!-_$ =rateofsensibleloadremovedorprovidedtotherecirculatedair(kW),and+7̅_!-!-_$ =meanvalueofthespecificheatbetweentherecirculatedreturnairandsupply

airnodes(kJ/kg-°C).Theoutdoorandrecirculatedairflowsarecombinedintoasinglestream,withairpropertiesdenotedasthemixednodema_x.TherateofsensibleloadremovedorprovidedbyHVACsystemxtothemixedairflowis:ℎ._0"_$ = +7̅_0"_$ × !̇0"_$ × (/0"_$ − /."_.$), (11)where,ℎ._0"_$ =rateofsensibleloadremovedorprovidedbyHVACsystem,x,inordertobring

mixedairpropertiestosupplyairconditions(kW),and+7̅_0"_$ =meanvalueofthespecificheatbetweenthemixedairandsupplyairnodes

(kJ/kg-°C).

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Becausethemixedairflowisthecombinationoftherecirculatedreturnairflowrateandtheoutdoorairflowrate,thesensibleloadduetothemixedairflowrateisequaltothesumoftheloadsattributedtoeachairstream:ℎ._0"_$ = ℎ._!-!-_$ + ℎ._+"_$ . (12)ThesupplyairfromHVACsystem,x,isusedtoconditiononeormorezones,z.SometypesofHVACsystems(e.g.,variableairvolume)utilizereheatcoilsforeachzonetoraisethedrybulbairtemperatureofthesupplyair,ifneeded,tomeeteachzone’ssetpointtemperature.Therateofsensibleloadprovidedbetweensupplyairnodeandeachofthezoneinletnodesis:ℎ._!9_$ = ∑ (+7̅_:_!9%_$ × !̇%&_%_$ × (/."_$ − /%&_%_$)'!

%() ), (13)where,ℎ._!9_$ =rateofsensibleloadprovidedfromthereheatcoilstoallzonesconditionedby

HVACsystemx(kW),and+7̅_:_!9_$ =meanvalueofthespecificheatbetweenthesupplyairandthezoneinletair

nodesforeachzone(kJ/kg-°C).ThesystemloadremovedorprovidedbyHVACsystemx,andallreheatcoilsthatareutilizedtoprovideadditionalsensibleloadisdeterminedwiththefollowingexpression:ℎ._$ = ℎ._0"_$ + ℎ._!9_$ = ℎ._!-!-_$ + ℎ._+"_$ + ℎ._!9_$ . (14)where,ℎ._$ =rateoftotalsensibleloadremovedorprovidedbyHVACsystem,x,andall

reheatcoilsservingzonesthatarespaceconditionedbyHVACsystem,x(kW).

Zonesensibleload

Thezonalloadassociatedwiththeinternalgainsfrompeople,plugloads,lighting,andothermiscellaneousloads,isdeterminedbythefollowingexpression:ℎ._%_$ = ∑ (+7̅_:_%_$ × !̇%&_%_$ × (/%+_%_$ − /%&_%_$)'!

%() ), (15)where,ℎ._%_$ =rateofsensibleloadremovedorprovidedforallzonesservedbyHVACsystem

x(kW),and+7̅_:_%_$ =meanvalueofthespecificheatbetweenthezoneinletairandzoneoutletair

nodesforeachzone(kJ/kg-°C).

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Someofthesensibleloadremovedorprovidedforallthezonesmaybedirectlyexhaustedfromthezone.TheexhaustedaircarriesawaypartofthesensibleloadthatwouldotherwisehavebeenputontheHVACsystem.Thesensibleloadassociatedwiththezoneexhaustairis:ℎ._%*$_$ = ∑ (+7̅_:_%_$ × !̇%*$_%_$ × (/%+_%_$ − /%&_%_$)'!

%() ), (16)where,ℎ._%*$_$ =rateofsensibleloadexhaustedfromzonez(kW).Thenetzonalloadsplustheloadintroducedbyoutdoorair,adduptothetotalsensibleloadonthesystem;hence:ℎ._$ = (ℎ._%_$ − ℎ._%*$_$) + ℎ._+"_$ + ℎ._!9%_$ . (17)Asnotedabove,thesensibleloadremovedorprovidedbyHVACsystem,x,andallreheatcoilscanalsobeexpressedas:ℎ._$ = ℎ._!-!-_$ + ℎ._+"_$ + ℎ._!9%_$ , (18)withthesensibleloadinrecirculatedairflowequaltoℎ._!-!-_$ = ℎ._%_$ − ℎ._%*$_$ . (19)

3.2.2. Latentheatbalance

Systemlatentload

WithinHVACsystemx,therateoflatentcoolingloadremovedbetweenanodeupstreamofthesupplyairnodeandthesupplyairnodeisdeterminedwiththefollowingexpression:ℎ2_6_$ = !̇6_$ × 1;*_6_$ × (2:4_6_$ −2:4_."_$), (20)where,ℎ2_6_$ =rateoflatentcoolingloadremovedbyHVACsystem,x,betweentheupstream

andsupplyairnodes(kW),!̇6_$ =massflowratebetweentheupstreamandsupplyairnodes(kg/s),1;*_6_$ =latentheatofvaporizationfortheupstreamnode(kJ/kg)ascalculatedwith

thefollowingexpression=2500.9 + 1.85895 × /6_$ ,and2:4_6_$ =humidityratioattheupstreamairnode(kgwater/kgdryair).

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Followingthesameprocedureusedforthesensibleloads,latentloadscanbedisaggregatedintothoseassociatedwiththerecirculatedandtheoutdoorairflows.Theequationsbelowsummarizethevariouscomponentsoflatentload.Thelatentcoolingloadremovedfromtheoutdoorairstreamis:ℎ2_+"_$ = !̇+"_$ × 1;*_+"_$ × (2:4_+"_$ −2:4_."_$). (21)where,ℎ2_+"_$ =rateoflatentcoolingloadremovedbyHVACsystem,x,inordertobring

outsideairpropertiestosupplyairconditions(kW),and1;*_+"_$ =latentheatofvaporizationattheoutdoorairnode(kJ/kg).Thelatentcoolingloadremovedfromtherecirculatedreturnairflowis:ℎ2_!-!-_$ = !̇!-!-_$ × 1;*_!-!-_$ × (2:4_!-!-_$ −2:4_."_$), (22)where,ℎ2_!-!-_$ =rateoflatentcoolingloadremovedbyHVACsystem,x,inordertobring

recirculatedreturnairpropertiestosupplyairconditions(kW),and1;*_!-!-_$ =latentheatofvaporizationattherecirculatedreturnairnode(kJ/kg).Thetotallatentcoolingrate,whichisidenticaltotheloadremovedbetweenthemixedandsupplyairnodesis:ℎ2_$ = ℎ2_0"_$ = !̇0"_$ × 1;*_0"_$ × (2:4_0"_$ −2:4_."_$), (23)where,ℎ2_0"_$ =rateoflatentcoolingloadremovedbyHVACsystem,x,inordertobringmixed

airpropertiestosupplyairconditions(kW),and1;*_0"_$ =latentheatofvaporizationbetweenatthemixedairnode(kJ/kg),andℎ2_$ =rateoftotallatentloadremovedbyHVACsystem,x(kW).Thetotallatentloadisthesumoftheoutdoorandrecirculatedcomponents:ℎ2_$ = ℎ2_!-!-_$ + ℎ2_+"_$ . (24)

Zonelatentload

Thezonallatentloadassociatedwiththeinternalgainsfrompeople,infiltrationetc.is:ℎ2_%_$ = ∑ (!̇%&_%_$ × 1;*_%&_%_$ × (2:4_%+_%_$ −2:4_%&_%_$)'!

%() ), (25)

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where,ℎ2_%_$ =rateoflatentcoolingloadremovedfromallzones,whichHVACsystem,x,is

serving(kW).Ifairisexhausteddirectlyfromthezone,thelatentloadremovedis:ℎ2_%*$_$ = ∑ (!̇%*$_%_$ × 1;*_%&_%_$ × (2:4_%+_%_$ −2:4_%&_%_$)'!

%() ), (26)where,ℎ2_%*$_$ =rateoflatentloadremovedfromallzonesthatisexhaustedasexhaustair

(kW).ThetotallatentloadonHVACsystemxis:ℎ2_$ = (ℎ2_%_$ − ℎ2_%*$_$) + ℎ2_+"_$ . (27)Asnotedabove,thelatentloadremovedbyHVACsystem,x,canalsobeexpressedas:ℎ2_$ = ℎ2_0"_$ =ℎ2_!-!-_$ + ℎ2_+"_$ , (28)withthelatentloadinrecirculatedairflowequaltoℎ2_!-!-_$ = ℎ2_%_$ − ℎ2_%*$_$ . (29)

4. ValidationofCalculationMethods

Inthisanalysis,thermodynamicrelationspresentedinSection3,alongwiththeairpropertiesoutputbyEnergyPlus,areusedtocalculatethedisaggregatedlatentandsensibleloadsfortheoutdoorandrecirculatedairstreams.TheloadsarecalculatedasloadsontheindividualHVACsystems.Thevariousindividualloadsthatoccurineachzone,duetopeople,envelopegains,andequipmentarecapturedintheHVACsystemloadassociatedwiththerecirculatedair.Thissectionalsodescribesthemethodsusedtovalidatethethermodynamiccalculations.Thisvalidationstepisusedtoconfirmthatthedivisionofsensibleandcoolingloadsintocontributionsfromtherecirculatedandoutdoorairstreamsprovidescorrectestimatesoftheseseparateloads.EnergyPlusdirectlyreportstheheatingandcoolingratesforthesystemcoils,assummarizedinTable4-1.Thistablesummarizesthevariablenames,notation,andequationnumbersfortheloadspresentedinSection3,andthecorrespondingEnergyPlusvariablenames,iftheyexist.Themethodsaretestedbycomparingtheloadscalculatedfromairconditions,foreachsystem,withthecoilratesoutputbyEnergyPlusdirectly.In

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thediagnostics,dataoutputatbotha10-minuteanda1-hourtimestepareused.TheactualtimestepusedinEnergyPlusismuchshorter,andadaptstothedetailsofloadbalance.Hence,theoutputdatarepresentaveragesovertheoutputtimestep.InorderfortheresultstomatchtheEnergyPlusoutput,twoadjustmentsarenecessary.Asnotedabove,fordraw-throughsystemsthesupplyfannodeisaftertheheatingandcoolingcoilnodes;hence,tomatchthecalculationstothereportedheatingandcoolingcoilratesacorrectionmustbemadeforthefanheatenergy(whichisalwaysincludedinthecalculationsinthisanalysis).Theotheradjustmentistoaccountforthefactthatduringhoursoflowloadthesystemmaycycleonandoff,whichisnotalwaysreflectedintheEnergyPluscoolingcoilrates.TheequationspresentedinSection3arevalidforanytimestep,aslongasthephysicalquantitiesareinterpretedcorrectly.Atthehourlytimestep,thedatashouldbeinterpretedasaveragesoverthehour,withanyperiodofthetimewherethesystemcyclestotheoffstateincludedintheaverage.FortheEnergyPlusoutput,whilethemassflowandfanheatoutputaretrueaveragesinthissense,thesensibleandlatentcoolingratesreportedforsomesystemsaretheratescalculatedonlyforthetimewhenthesystemisrunning.Hence,tomatchthetruehourlyaverage,theseratesneedtobeadjustedforthecyclingratio,fcyc,whichthisanalysisdefinesasthefractionoftheoutputtimestepthatthesystemison.Table4-1 HVACSystemandZoneLoadsreportedbyEnergyPlusSystemorZone VariableName

VariableNotation

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System

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ℎ!_#(11),(12),(13)

COOLINGCOILSENSIBLECOOLINGRATEminusFANELECTRICRATEfordraw-throughsystems(whenℎ!_#>0)

SensibleHeatingLoadHEATINGCOILAIRHEATINGRATEplusFANELECTRICRATEfordraw-throughsystems(whenℎ!_#<0)

LatentCoolingLoad ℎ$_#(24),(25),(26)

COOLINGCOILLATENTCOOLINGRATE

Reheat SensibleHeatingLoad ℎ!_%&'_# (14) VAVBOXREHEATCOILHEATINGCOILHEATINGRATE

Zone

SensibleCoolingLoadℎ!_'_# (16)

ZONEAIRSYSTEMSENSIBLECOOLINGRATE(whenℎ!_'_#>0)

SensibleHeatingLoadZONEAIRSYSTEMHEATINGRATE(whenℎ!_'_#<0)

LatentCoolingLoad ℎ$_'_# (27) NotavailableForUnitarySplitSystems,usedintheMid-riseApartmentprototypes,noadjustmentisnecessary.ForPTACSandDOASsystems,onlythefanheatadjustmentisneeded.Fortheothersystems,thereportedfanenergyisusedtocalculatethecyclingratio,withthemethoddependingonwhetherthesystemissingle-orvariable-speed.Forsingle-speedsystems(PSZandMS_CAV),thecyclingratioforagivenperiodisequaltotheratioofthefanenergyinthatperiodtothereportedmaximumfanenergyoverallperiods;thelatter

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correspondstoperiodswhenthesystemdoesn’tcycle.Forvariablespeedsystems(MS_VAVandFanCoil)themethodismorecomplicated,asthesesystemscanreducethemassflowtoaminimumvaluebeforetheybegincycling.ThisbehaviorisillustratedinFigure4-1,whichshowsascatterplotofthefanenergyvs.themassflowrate,foraVAVsystemintheMediumOffice-Newprototype.Asdemandforcoolingdecreases,themassflowandfanenergydecrease,buteventuallyreachaminimumvalue(representedbytheredcircleinFigure4-1),belowwhichthesystemstartstocycle.Itisconfirmedthatthesystemiscyclingintheselowmassflowhoursbecausetherelationshipbetweenmassflowandfanenergybecomeslinear.Hence,cyclingoccursonlyinthosehoursinwhichthemassflow/fanenergyarebelowthesystemminimum,andduringthesehoursthecyclingratioisequaltothefanenergyforthehourdividedbythesystemminimumvalue.

Figure4-1 RelationshipbetweenFanEnergyandMassFlowRateforVariableAir

VolumeHVACSysteminMediumOfficeBuildingForbothfixedandvariablespeedsystems,tocorrectforcycling,theEnergyPlusreportedsensibleandlatentcoolingcoilratesweremultipliedbythecyclingratioandtheresultingvalueswerecomparedtoourcalculationsbasedonairconditions.AsummaryofthisvalidationcheckispresentedinFigure4-2.ThisfigureshowsascatterplotofannualvaluesofthelatentandsensibleloadsreportedbyEnergyPlus(withtheadjustmentsdescribedabove)vs.thosecalculatedfromtheairconditions.ThedataareforallthesystemsandbuildingsinAtlanta,withthesensibleloadsshownassolidbluedotsandthelatentloadsasopenredsquares.Theaxesarelogarithmictoaccommodatethewiderangeofsystemsizes.Almostallsystemshaveadiscrepancyoflessthanafractionofapercent.Outofatotalof442systemsinthedatabasetherearefivethatshowlargediscrepanciesbetweenthecalculatedandreportedloads.AlltheerrorsariseforCAVsystems,inPre-1980vintageSecondarySchoolandLargeHotel.BycomparingtheCAVsystemdatatothedatafortheVAVsystemsthatservethesamezonesinthePost-1980andNewvintages,itis

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surmisedthattheloadscalculatedfromairconditionsarecorrectandthereisaproblemwiththeEnergyPlusreportedcoilrates.

Figure4-2 ValidationCheckSummaryforAtlantaSystems

5. Results

Thefullsimulationdatabaseconsistsof10-minutetime-stepdata,forafullyear,forthe16buildingtypes,3vintagesand18climatezones.Withinthe16buildingtypes,thereareseveralhundredindividualsystemsforwhichthenodaldataarecollected.Toconvertthesetoacomprehensiblesummaryform,twoprocessingstepsareusedanddescribedbelow.Thefirststepistoprovidesomenormalizationsothatloadscanbecomparedacrosssystemsofdifferentsizes.TheHVACsizingispartofthebuildingprototypedefinition,andcapacitiesvaryfromabout2,000Btu/hrforthesmallestPSZcoolingcoilstoafewmillionBTU/hrforthelargestVAVsystems.Tofacilitatecomparisonbetweensystems,thedataarenormalizedtorepresentquantitiesper-square-footofconditionedspace.Theareaofconditionedspaceassignedtoasystemisdefinedastheareaofallzonesservedbythatsystem.Theaveragecapacitypersquarefootbybuildingtypeforthreeclimatezonesisshownin

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Table5-1.Thedataareforcoolingsystemcapacity,heatingsystemcapacity,andreheatcoilcapacity,summedoverallsystemsinabuilding.ThetableshowstheNewandPre-1980vintagesforcomparison(zoneareasdonotchangeasafunctionofvintage).Thesystemtypesinthebuildingareindicatedinparenthesesbelowthebuildingtype.Thecoloredbarsinthetableareanotherindicationofmagnitude.Evenafternormalizationtoper-square-footthereisconsiderablevariationinthecapacitiesbybuildingtypeandvintage.Ingeneral,fornewervintages,thebuildingenvelopeimprovementsallowsystemstobedown-sizedbyuptoafactoroftwo.Heatingcapacitiesaremoresensitivetoclimatethancoolingcapacities.Thebuildingswithhighoccupancy(hotels,apartment,schools)havethelargestcapacityper-square-foot.Thesecondprocessingstepistousetime-averagingtoconverttheten-minutetimeseriesdatatoamorecompactrepresentationofloadshapes.Toaccomplishthis,hourlyloadprofilesbymonthandday-typewereconstructed.Theday-typesaredefinedasweekdayandweekend.Theseprofilesarecalculatedbyaveragingtheloadinagivenmonthandhouroverallthedaysofthatday-type.Normalizationandtime-averagingareappliedtoeachofthefourcomponentloads,foreachbuildingandvintage,inalloftheclimatezones.Inthefiguresofthissectiontheloadresultsareillustratedforafewselectedbuildingtypes(MediumOffice,Stand-aloneRetail,andSecondarySchool,newvintage),inthreeclimates.TheplotsusePhoenix,HoustonandChicagoasrepresentativeofhot-dry,hot-humidandcoldclimates.Thefulldatabasecontainsallbuildings,vintagesandclimatezones.Figure5-1showshourly,weekdaycoolingloadprofilesforAprilandAugust,decomposedintothelatent/sensibleandventilation/recirculatedcomponents.Thefigureshowstwonewconstructionbuildingtypes:MediumOfficeontheleft(whichusesaVAVsystem),andStand-aloneRetailontheright(singlespeedPSZsystems),inthethreeclimatelocations.Intheseplots,theventilationloadsareshowningreen,andtherecirculatedloadsinblue.Thesensiblecontributionisplottedusingsolidbars,andthelatentcontributionisshownwithopenbars.Onthehorizontalaxis,foreachhour,thedataforMarchandAugustareshownside-by-side.Theverticalscaleineachplotisthesame.Fromthefigure,itisclearthattheventilationcomponentoflatentloadsisdominantinallclimates,particularlyfortheStand-aloneRetailbuilding.Inthehot-humidclimate(Houston),ventilationsensibleandlatentloadsareapproximatelyequal.Inthehot-humidandhot-dryclimates,shoulderseasoncooling(April)isdominatedbytherecirculatedsensiblecoolingloads,presumablyfromenvelopegains.Figure5-2showsthesameweekdaycoolingloadprofilesbutforthepost-1980constructionbuildingtypes.AsevidencedbyFigure5-2,theoverallcoolingloadineachbuildingtypeisgreaterduetolessrestrictiveenergycoderequirementswhichthebuildingshadtocomplywith.

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Table5-1 AverageCoolingCapacityperSquareFootbyBuildingTypeandClimateZone

Capaci ty BTu/hr/SqFtCity Cool ing Heating Reheat Cool ing Heating Reheat

FULLSERVICERESTAURANT CHICAGO-OHARE 105 293 131 338(PSZ) HOUSTON 107 213 141 255

PHOENIX 105 177 148 227LARGEHOTEL CHICAGO-OHARE 523 416 12 596 489 28(DOAS, Fan Coi l , VAV) HOUSTON 510 377 11 703 415 21

PHOENIX 543 334 10 748 361 17LARGEOFFICE CHICAGO-OHARE 119 23 41 136 23 57(VAV) HOUSTON 122 12 36 156 11 46

PHOENIX 122 7 31 155 5 39MIDRISEAPARTMENT CHICAGO-OHARE 385 517 924 1035(Spl i t System) HOUSTON 352 319 648 620

PHOENIX 378 243 714 464OUTPATIENT CHICAGO-OHARE 95 15 53 111 13 74(VAV) HOUSTON 99 4 45 123 5 61

PHOENIX 100 3 43 126 3 58PRIMARYSCHOOL CHICAGO-OHARE 199 343 64 233 364 95(CAV/VAV, PSZ) HOUSTON 215 251 51 311 299 90

PHOENIX 215 207 44 321 250 76SECONDARYSCHOOL CHICAGO-OHARE 350 730 56 349 760 125(CAV/VAV, PSZ) HOUSTON 361 525 46 414 558 83

PHOENIX 360 441 38 430 464 67SMALLHOTEL CHICAGO-OHARE 1046 1310 1250 1637(PTACS, PSZ) HOUSTON 1138 980 1372 1013

PHOENIX 1149 820 1436 766SMALLOFFICE CHICAGO-OHARE 116 183 249 319(PSZ) HOUSTON 128 176 258 325

PHOENIX 131 172 258 329STRIPMALL CHICAGO-OHARE 255 406 531 716(PSZ) HOUSTON 292 248 543 402

PHOENIX 283 208 536 305SUPERMARKET CHICAGO-OHARE 311 558 466 711(PSZ) HOUSTON 282 436 362 510

PHOENIX 268 382 331 440WAREHOUSE CHICAGO-OHARE 61 93 116 164(CAV) HOUSTON 49 62 73 93

PHOENIX 49 48 68 66

New Buidl ings Pre-1980 Bui ldings

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Figure5-1 WeekdayCoolingLoadProfiles:NewConstructionMediumOfficeand

Stand-AlongRetail,Houston,Phoenix,andChicagoClimates

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Figure5-2 WeekdayCoolingLoadProfiles:Post-1980ConstructionMediumOffice

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MonthlyvariationinloadsisillustratedinFigure5-3.TheplotshowsthenewconstructionMediumOfficeontheleft,andthenewconstructionSecondarySchoolontheright.Inthisplot,thehourlydataaresummedtoprovideasinglevalueforeachmonthandday-type.Thismetriciscomparabletoatypicaldailyload.Theloadsareagaindividedintolatent/sensibleandventilation/recirculated,withheatingloadsincludedinorange.Theheatingloadonthesystemcoilisseparatefromtheheatingprovidedbyreheatcoils,asthesetwotypesofsystemcanpotentiallybeoperateddifferently.IntheCRBprototypes,reheatisonlyusedformulti-zoneHVACsystems,toensurethatzoneswithdifferentloadscanmaintainthebuildingset-pointtemperature.Inheatingseason,thereheatcoilsareusedifazonerequiresmoreheatthanthesupplyairtemperaturethatisprovidedbytheheatingcoil.Duringcoolingseason,thereheatcoilsareusedtoincreasethesupplyairtemperatureifazonerequireslesscooling,orinsomecases,requiresheatingwhileanotherzonerequirescooling.OurreviewoftheEnergyPlusoutputfortheCRBbuildingsindicatesthatthereisnosignificantreheatduringthesummercoolingseason(May-September),ascanbeseeninFigure5-3.Reheatforhumiditycontrolisonlyusedincertainzonesofthehospitalandoutpatienthealthcarebuildings.Reheatwasnotusedforhumiditycontrolinanyotherbuilding.ThefigureshowsthattheSecondarySchoolloadsaregenerallyhigher,duetohigheroccupancy.Becauseofthecorrespondinghigherventilationrequirement,theseloadsareagaindominatedbytheventilationcomponent.Theventilationairstreamincludestheuseofeconomizers,whichareusedonlyindryerclimates.AsnotedpreviouslyinTable2-5,economizersarenotusedinclimatezonesthatarehumidandwarm(i.e.,southeasternportionoftheU.S.).Economizersareprimarilyusedinshouldermonths(i.e.,notinthesummerandwintermonths)andtendtoreducesensibleloadsbutcouldincreaselatentloadsiftheoutdoorairishumid.Figure5-4providesanotherviewoftherelativesizeoflatentandsensibleloads,showingthreebuildingtypes(MediumOffice,Stand-aloneRetailandSecondarySchool,allNewvintage),andtwoclimates.Thepercentoftotalloadthatissensible/latentareplottedonthevertical/horizontalaxes,withsolidmarkersforMarchandopenmarkersforAugust.Eachpointrepresentsonesysteminthebuilding.InPhoenix,latentloadsneverexceed20%,whileforHoustontheycanapproach60%oftotalload.Thevariationinthepercentoflatentvs.sensiblecanvarysignificantlyfordifferentsystemswithinasinglebuilding,forexampleforStand-aloneRetail,dependingonwhetherthesystemprovidesventilationair.

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Figure5-3 MonthlyBuildingLoadProfiles:NewConstructionMediumOfficeand

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Figure5-4 Sensiblevs.LatentLoadsinHoustonandPhoenixFigure5-5presentsmoredetailonlatentloadsandhumidityconditions.Thefiguresontheleftsideofthegridprovideasenseofhowtheoperationoftheventilationsystemcorrelateswithlatentloads.Thesefiguresshow,forMediumOffice-Newinthethreeclimatezones,theventilationandrecirculatedlatentloadsplottedasbars(leftaxis),and

40

tworatiosplottedaslines(rightaxis).Thetworatiosarethepercentofmassflowaroundtheairloopthatismadeupbyoutdoorair(lightgrey),andtheratioofsensibletototalload(sensibleheatratioorSHR,blackline).Onthehorizontalaxisisthehourofdayandthemonth,withovernighthoursexcluded.Theaxesarethesameforallplots.Asexpected,inallclimatestheSHRisanti-correlatedwiththepercentofoutdoorair.TheplotforHoustonshowsapatternofhighventilationineveninghours,whichthendropsrapidlyasthesystemoperationisreducedovernight.Highventilationcausesthelatentloadstospike.InPhoenixventilationisreducedmid-dayduringhotmonths.BothPhoenixandChicagouseaneconomizertoprovidecoolingduringshouldermonths,iftheoutdoorairtemperatureisbelowthereturnairtemperature.Theventilationrateandminimumoutdoorairflowscheduledoesnotchangebyclimatezone(DOE-EERE2020b).Theplotsontheright-handsideofFigure5-5showscatterplotsofthesupply-nodehumidityratio(y-axis)vs.theoutdoorairhumidityratio(x-axis).Theweekdayhoursareplotted,dividedintotwogroups:6a.m.to8p.m.,whenbuildingscanbeexpectedtobeoccupied(bluemarkers),andtherestofthehours,duringwhichtimethebuildingislikelytobeunoccupied(redmarkers).Inthisplot,foreachclimate,dataforalltheVAVsystemsacrossallbuildingsthathaveVAVsystemsareincludedintheplot.TherationaleisthattheoperationofaVAVsystemduringoccupiedhoursshouldnotbedependentonthebuildingtype.Overallthisplotshowsthat,duringoccupiedhours,thesupply-nodehumidityleveliscorrelatedwithoutdoorhumidityuptoapointwhereitlevelsoffatavaluedeterminedbythecoolingcoilconditions,approximately0.008.Duringoff-hours,introductionofventilationairwithoutadditionalconditioningcausessupply-nodeconditionstorisesignificantlyinChicagoandHouston,butnotintherelativelydryclimateofPhoenix.Notethatsupply-nodeconditionsarenotidenticaltozoneconditions.

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Figure5-5 LatentLoadsandHumidityRatios:SelectBuildingTypesinHouston,

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Figure5-6andFigure5-7illustratethedependenceonSHRofbothtotalcoolingloadandtheenergyusedforcooling.Inbothfigures,thedataforasinglesystemacrossallclimatezonesandhoursoftheyearareusedtocreatetheplot.ThetwosystemschosenforthesefiguresaretheMediumOfficeVAV_1system(whichservesthebottomfloor),andtheStand-aloneRetailPSZ-2system(whichservesthecoreretailarea).Thetwosystemsareofcomparablesize,andthedatahavenotbeennormalizedtoper-square-footintheseplots.InFigure5-6,thetotalcoolingloadisplottedagainsttheoutdoorairtemperature(OAT)forarangeofdifferentSHRvalues.Tocreatethisplot,thehourlydataarefirstbinnedaccordingtothevaluesofOATandSHR.OATbinMcorrespondstotemperaturesintherange[M*10,(M+1)*10]degreesFahrenheit(degF),andSHRbinNcorrespondstoSHRvaluesintherange[N*0.1,(N+1)*0.1].TheintegerlabelsonthedifferentcurvescorrespondtothevalueofNforthatSHRbin.Onthex-axis,theOATbinisindicatedbythetemperatureatthebinmid-point.Withineachbinthehourlyloadsareaveraged.Figure5-6showsthatthereisageneralincreaseofthetotalloadasSHRdecreases,asexpectedduetothecontributionoflatentload.Whatismoreinterestingisthatthecurvesseemtoclusterintotwogroups,withSHRequalto0.7orless,andSHRequalto0.8andabove.ForthelowSHRcurves,theincreaseinloadasafunctionofOATissteeper,andathigherOATsthemagnitudeoftheloaddifferenceisquitesignificant.Thepatternisgenerallythesameforbothsystemtypes.

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Figure5-6 TotalCoolingLoadasafunctionofOutdoorAirTemperaturefor

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Figure5-7providesavisualizationofthewaythecoolingcoilenergyusevarieswithSHR.ThisfigurealsoillustratesthedegreeofhourlyandseasonalvariabilitythatishiddenbytheaveraginginFigure5-6.TocreateFigure5-7,dataareusedacrossallclimatezonesforthetwosystemsofFigure5-6.TheverticalaxisofthescatterplotsshowsthehourlyHVACenergyuseforcooling(reportedbyEnergyPlus),scaledtothemaximumvalueoverallthedata.ThehorizontalaxisshowstheSHR.Eachpointintheplotrepresentsonehourforonesystem.Tocontrolfortemperatureconditions,thedataareorganizedintoOATbins.TheplotshowshoursforwhichtheOATisbetween70-80degFasbluedots,andhoursforwhichtheOATisbetween80-90degFasorangedots.ToprovideasenseofhowtheOATandSHRconditionscorrelatedwithspecificclimates,thedataforPhoenixareoverlaidwithopenblacksquares,andthedataforHoustonareoverlaidwithopenblacktriangles.Whilethereisagreatdealofscatterinthedata,thereisacleartrendtowardsincreasingenergyuseasSHRdecreases.Therateofincreaseisquantifiedbyintroducingtworegressionlines;theequationsfortheseregressionlinesareprovidedintheplot(colorsoftheequationsandregressionlinescoordinatewiththemarkers).Thetwosystemsshowsimilartendencies;inthelowerOATbin,therateofincreaseinpoweruseastheSHRdecreasesisapproximatelythesameforbothbuildings,butinthehigherOATrangethepowerconsumptionoftheStand-aloneRetailPSZsystemismoresensitivetoSHRthantheVAVsystem.Overall,foradecreaseofSHRfrom0.8to0.6,thegaininaveragepowerconsumption,asrepresentedbytheregressionlines,is20%-30%.Figure5-8showsthedistributionofSHRvalues(computedonanhourlybasis)acrossaselectionofclimatezonesandbuildingtypes.Thedistributionsarerepresentedasbox-and-whiskerplots,withtheboxwidthdefiningthe25thand75thpercentilesofthedistribution,thewhiskersthe5thand95thpercentiles,andthehorizontallinethemedian.Buildingtypesareshownasdifferentcolors,andclusteredtogetherwithinaclimatezone.TheclimatezonesarerepresentedbyHouston,Phoenix,SanFrancisco,ChicagoandBoulder.Theplotshows,notsurprisingly,thattheSHRdistributionsaresimilaracrossdryclimates,andacrosshumidclimates,irrespectiveofwhetherthesearehotorcold.Hence,thedistributionsforHoustonandChicagoareverysimilar,asarethoseforPhoenixandBoulder.ThelowervaluesandbroaderrangeofSHRfortheMidriseApartmentbuildingreflectsthehigherventilationloads(basedonoccupancy),since,asnotedabove,latentloadsareprimarilyventilationdriven.

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Figure5-7 TotalCoolingPowerasafunctionofSensibleHeatRatiofortwo

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Figure5-8 DistributionofSensibleHeatRatiosforaSelectionofClimate

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6. Conclusions

Thisreportdescribesthedevelopmentofadatabaseofspace-conditioningloadsforcommercialbuildings,basedonprototypesdevelopedfortheEnergyPlussimulationsoftware,withaparticularfocusoncoolingloads.Theprototypescoversixteenbuildingtypesandthreevintages,whichweresimulatedineighteenclimatezones.Inadditiontosimplygeneratingtheloads,detailedinformationaboutairconditionsattheappropriateEnergyPlussystemnodestodisaggregatetheloadsintofourcategorieswereused:sensibleandlatentload,eachseparatedintothecomponentduetoincomingventilationair,andthecomponentduetoairrecirculatedfromtheconditionedzones.ThesedisaggregatedloadsarecalculatedforeachHVACsystemthatispresentinabuilding.AsstatedinSection2,eachvintageofcommercialbuildingprototypeshasthesameset-pointtemperatures,ventilationrates,HVACsystems,internalloads,andenvelopecharacteristicsacrossthe16climatezones.Whileintheactualbuildingstock,buildingenvelopes,HVACsystems,internalloads,andset-pointswouldvary,thedisaggregatedloadsinthisreportprovideapictureofthevariationofcoolingandheatingloadsacrossclimatezones.Asnotedintheintroduction,inasecondphaseofthisproject,theresultsdescribedherewillbeusedtoconstructalargersampleofloadsthatreflectabroaderrangeofcharacteristicsinthecommercialbuildingstockthanarerepresentedintheprototypereferencebuildings.Thedisaggregationofthebuildingloadsintofourcomponentsservesthispurposebecauseitreflectsrealphysicaldifferencesinthevariousdriversofspaceconditioningloads.Loadsassociatedwithventilationairaredrivenbyclimateconditionsandincomingmassflow;massflowiscorrelatedtoventilationcoderequirementsbasedonoccupancy,scheduleandsquarefootage,andpotentialuseofeconomizers.Thesensibleloadsassociatedwithrecirculatedairaredrivenbyenvelopegainsorlosses,lightingand

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equipment.Buildingoccupancyandinfiltrationratesaffectbothrecirculatedsensibleandlatentloads.Bycorrelatingvariablesdrivingthefourcomponentloadswiththeloadsthemselves,simplemodelscanbedevelopedtoaccountforchangestothebuildingfeatures,use,orlocation.Forexample,abroaderrangeofclimatescanbemodeledsimplybyadjustingtheairconditionsoftheincomingventilationair.Changestothebuildingenvelopesuchaswindowimprovementsthatreducesolargain,canbemodeledbyadjustingtherecirculatedsensibleloads.Changestoeitherventilationcodesortobuildingoccupancycanbemodeledbyadjustingtheventilationairmassflow.Aseachbuildingsystemisconsideredseparately,thesimulationdatacanalsobeusedtomodelthediversityofloadsonagivenequipmenttypebasedonthetypesofzonesitserves.Moredetailonthisapproachtodevelopingasetofbuildingloadcharacteristicsmorebroadlyreflectiveofthecommercialbuildingstockwillbedescribedinasecondreport.Thisreporthasalsoextensivelyconsideredtherelativeimportanceoflatentloads,foragivenbuildingandsystem,astheclimateconditionsvary.Boththemagnitudeofthetotalloadonthesystemandthesystemenergyusevarysignificantlyinmovingfromdrytohumidclimates.Thisisimportantbecausegeneralconsiderationsofbuildingloadsoftenrelyondriverssuchascoolingdegreedaysthatconsideronlyoutdoorairtemperature,whichapplydirectlyonlytothesensibleloads.TotheextentthatHVACsystemsrelyonlowcoiltemperaturestoprovideanyneededdehumidificationofventilationair,themagnitudeoflatentloadsmayalsoconstrainthewaysystemdesignscanbealteredtoimproveefficiency.Forexample,investigationofdifferentapproachestotheremovaloflatentvs.sensibleheatwasamajorfeatureofthedesignfinalistsfortheGlobalCoolingPrize(GlobalCoolingPrize2019).Adatatablecontainingasummaryoftheloaddataacrossallbuildings,systemsandclimatesexaminedforthisreportisalsoavailableinExcelformat.Thetableincludesannual,coolingseasonandheatingseasonvaluesforthefourcomponentloads,aswellasinformationonventilationairflowandothersummarydata.

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References

Briggsetal(2003).Briggs,R.S.,R.G.Lucas,T.Taylor.(2003).ClimateClassificationforBuildingEnergyCodesandStandards:Part2-ZoneDefinitions,MapsandComparisons,TechnicalandSymposiumPapers.ASHRAEWinterMeeting,Chicago,IL.January2003.Atlanta,GA:AmericanSocietyofHeating,RefrigeratingandAir-ConditioningEngineers.(LastaccessedOctober2009.)http://resourcecenter.pnl.gov/html/ResourceCenter/1420.htmlDOE-BECP(2019).U.S.DepartmentofEnergy-OfficeofEnergyEfficiencyandRenewableEnergy,BuildingEnergyCodesProgram.StateCodeAdoptionTrackingAnalysis.Washington,D.C.(LastAccessedMarch13,2020)https://www.energycodes.gov/state-code-adoption-tracking-analysisDOE-EERE(2015).U.S.DepartmentofEnergy-OfficeofEnergyEfficiencyandRenewableEnergy.DirectFinalRuleTechnicalSupportDocument:EnergyEfficiencyProgramForConsumerProductsAndCommercialAndIndustrialEquipment:Small,Large,AndVeryLargeCommercialPackageAirConditioningandHeatingEquipment.Washington,DC.Chapter7.December2015.https://www.regulations.gov/document?D=EERE-2013-BT-STD-0007-0105DOE-EERE(2018).U.S.DepartmentofEnergy-OfficeofEnergyEfficiencyandRenewableEnergy.EnergyPlusVersion8.9.0Documentation,EngineeringReference.Washington,DC.March2018.(Lastaccessed:March6,2020)https://energyplus.net/sites/all/modules/custom/nrel_custom/pdfs/pdfs_v8.9.0/EngineeringReference.pdfDOE-EERE(2020a).U.S.DepartmentofEnergy-OfficeofEnergyEfficiencyandRenewableEnergy,BuildingTechnologyOffice.EnergyPlus.Washington,DC.(LastaccessedFebruary20,2020.)https://energyplus.net/DOE-EERE(2020b).U.S.DepartmentofEnergy-OfficeofEnergyEfficiencyandRenewableEnergy.CommercialReferenceBuildings.Washington,DC.(LastaccessedFebruary20,2020.)https://www.energy.gov/eere/buildings/commercial-reference-buildingsDOE-EIA(2012).U.S.DepartmentofEnergy-EnergyInformationAdministration.2012CommercialBuildingsEnergyConsumptionSurvey.Washington,DC.(Lastaccessed:March6,2020.)https://www.eia.gov/consumption/commercial/data/2012/DOE-EIA(2014).U.S.DepartmentofEnergy-EnergyInformationAdministration.CommercialDemandModuleoftheNationalEnergyModelingSystem:ModelDocumentation2014.Washington,DC.August2014.(Lastaccessed:March6,2020.)https://www.eia.gov/outlooks/aeo/nems/documentation/commercial/pdf/m066(2014).pdf

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DOE-EIA(2020).U.S.DepartmentofEnergy-EnergyInformationAdministration.AnnualEnergyOutlook2020.Washington,DC.Releasedate:January29,2020.https://www.eia.gov/outlooks/aeo/Deruetal(2011).M.Deru,K.Field,D.Studer,K.Benne,B.Griffith,P.Torcellini,B.Liu,M.Halverson,D.Winiarski,M.Rosenberg,M.Yazdanian,J.Huang,andD.Crawley.U.S.DepartmentofEnergyCommercialReferenceBuildingModelsoftheNationalBuildingStock.TechnicalReportNREL/TP-5500-46861.February2011.NationalRenewableEnergyLaboratory,Golden,CO.https://www.nrel.gov/docs/fy11osti/46861.pdfGlobalCoolingPrize(2019).(Lastaccessed:March6,2020.)https://globalcoolingprize.org/about-the-global-cooling-prize/Williamsetal(2013).A.Williams,E.Vine,S.Price,A.Sturges,G.Rosenquist.TheCostofEnforcingBuildingEnergyCodes:Phase1.LBNL-6181E.April2013.LawrenceBerkeleyNationalLaboratory,Berkeley,CA.https://ees.lbl.gov/publications/cost-enforcing-building-energy-codes

Analysis of Space-Conditioning Loads in Commercial Buildings

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