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Volume 03 ,Number5,September-October1998JournalofResearchoftheNationalInstituteofStandardsandTechnology[J .Res.Natl.Inst.Stand.Technol. 03 ,52 9(1998)] ConferenceReport

REFRIGERANTSFORTHE21 ST CENTURYASHRAE/NISTREFRIGERANTSCONFERENCEGaithersburg,MDOctober6-7,1997Reportpreparedby PiotrA.DomanskiBuildingEnvironmentDivision,Buildingan dFireResearchLaboratory,NationalInstituteofStandardsan dTechnology,Gaithersburg,M D0899-0001 Availableonline:ttp;//www.nist.gov/jres 1. Introduction

TheRefrigerantsorth e21stCentury"onferencewasth ethirdrefrigerantsconferencejointlyorganizedbyth eAmericanSocietyofHeating,Refrigeratingan d Air-ConditioningngineersASHRAE)ndhe NationalnstitutefStandardsndechnology.he conferencesin1989an d993coveredtechnicalissuesrelatedto th eimplementation ofozone-safe refrigerants.Withlobalarmingeginningoeplacezonedepletionasth eworld'smostsignificant environmentalproblem,th e1997conferencewas relatedto both ozonedepletionndglobalwarming.Thegoalofheon -

ferencewasoeviewvailable ir-conditioningndrefrigerationtechnologiestoassesstheirsuitabilityfo rth eyearsoomeinviewofth etw oglobalnviron-mentalproblems. The2-dayconferenceconsisted of16 comprehensivepresentations;eachdayendedwithapaneldiscussion.Table ontainsheitlesnduthorsofth epaperspresented.Thetopics included contemporaryan d future fluorochemicals,natural"luids,ncludingydro-carbons,arbondioxide,nd ir,ndecondaryoopsystemssingmmoniandtherhemicals.nehundredninetyprofessionals t tendedth econference.

T hepurpose of thisreportistosummarizemuch of th ematerialpresented.Formorein-depth information referto th econferenceproceedingsavailable from AS HRAE{http:/www. ASHRAE. org).2. EnvironmentalConcerns:zoneDepletionand GlobalWarming

Aftertheirintroductionin1930,chlorofluorocarbons (CFCs)ndydrochlorofluorocarbonsHCFCs)e- camehepreferredefrigerantsormostpplicationsbecauseoftheiravorable ttributes,ncludingafetyan dhighefficiency.However,theirrecentimplicationinth eozonedepletionphenomenaresultedinaphase-out.Thephase-outschedule was firstformulated by th eMontrealrotocoln98 7ndasad eore stringenturingollow-upnternationaleetings.Predominant lternativesoCFCsndHCFCsam efromhehydrofluorocarbonHFC)amily.Although mostHFCs av e owerGlobalWarmingPotential(GWP)hanheluidsheyreupposedoeplace,someountriesootonsiderFCssheinalsolutionbecauseconcernsboutglobalwarminghaveintensified.Thisraisesth equestion:whichrefrigerantshould th eindustryus einth efuture?

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Volume 03 ,Number5,September-October 99 8JournalofResearchoftheNationalInstituteofStandardsandTechnologyTable1.aperspresentedatth eASHRAE/NIST RefrigerantsConferencean dincludedinth econferenceproceedingsAuthorDanielL.Albritton JamesM.Calm DavidDidion CharlesE.BullockJosteinPettersenPierreWeissJacquesGouguetHorstH.Kruse ThomasTiedemannFredJ.KellerHongmeiLiangMoshenFarzadLe eW.BurgettMichaelD.ByarsKennethJ.SchultzPaulM. eLarminatPredragS.Hrnjak GeorgeR.GilesRichardG.HuntGeorgeF.Stevenson JamesG.CrawfordKeshavS.SanvordenkerH.MichaelHughesDonaldB.Bivens BarbaraH.MinorMarkO.McLindenEricW.LemmonRichardT.Jacobsen

Affiliation NOAA-Boulder,CO EngineeringConsultantGreatFalls,VANIST-Gaithersburg,M D CarrierCorporationSyracuse,NY SINTEFTrondheim,NorwayEL FAtochemLevallois,France UniversityofHannoverGermany CarrierCorporationSyracuse, NY

The TraneCompanyLaCrosse,W I

YorkInternationalCorquefouCedex,France UniversityofIllinoisatUrbanaChampaign,IL NormalairGarrettLtd.Yeovil,U.K.

The TraneCompanyTyler ,TX Consultant-AnnArbor,MIAlliedSignal,Inc.-Buffalo,NY DuPontde Nemours&Co.Wilmington,DE NIST-Boulder,CO NIST-Boulder,CO UniversityofIdaho,Moscow,ID

Title OzoneDepletionan dGlobalWarmingTrade-OffsinRefrigerantSelections:ast,Present,nd Future TheoreticalPerformance ofCarbonDioxide inSubcriticalan dTranscriticalCycles ExperimentalResultsofCarbonDioxidein CompressionSystemsCurrentndProjectedUs eofRefrigerantsnEuropeExperiencewithHCRefrigerantsan dProjectionsfo rFutureApplicationsAssessmentofPropaneasaRefrigerantin ResidentialAir-ConditioningndHeatPumpApplicationsAbsorptionSystems:TheFuture,MoreThan aNiche?N ew Developments toExpandth eUs eofAmmonia The Benefitsnd PenaltiesAssociatedwith th eUs eofSecondaryLoopsAi ras Refrigerantfo rth e21stCenturyHeatPumpTechnologyonth eHorizonStatusofCF Can dHCFCAlternativesContemporaryFluorocarbons Fluoroethersnd OtherNext-Generation FluidsThermodynamicPropertiesfo rth e AlternativeRefrigerants

DanielL.Albrittonprovided tatuseport nhe currentscientificunderstandingofozonedepletion an d globalwarming. eonsidershelobalwarmingproblemtobemoredifficulttoolve.Albrittonom-mentedhatutureenerationsmayookuponhesolvingofth eozonedepletionissueasnapprentice-shipfo rdealingwithglobalwarming.Hepointedout thatthesetw ogeophysical phenomenaarenotindepen- dentofac h ther lthoughhe yrereated nhe internationalcenebywodifferentregulatorygree-ments:th eFramework Convention fo rClimateChangean dth eMontrealProtocol.Albrittonpresentedafe wke ypointsfromth e995scientificassessmentby th eIntergovernmental Panelon ClimateChange(IPCC).Hestressedth eimportance ofunderstandingwhichfactsconcerningth eclimatesys-te mweknowwellan dwhichfactswestatewithless confidence.orxample,heprinciplesof atural

greenhouseeffectar everywellunderstoodan dar enot disputed.Basic physicsdemonstrates thatCO 2an dothergreenhouseasesra partfhenfraredadiation emittedatth esurfacean dwarmth eearth'sclimate.Convincingdatashow thatgreenhousegasescaused byhumanctivitiesrencreasingnhe tmospherean dar etrappingmoreheat.Itseemsreasonableto pre-dictthatcontinuedemissionswillcauseglobalclimatechange.Thishangemaybe veryignificant, lteringtemperaturean drainfallpatternsndaffectingvegeta-tionan dth ewellbeingof livingspecies.Theissuesar eto oomplexopredictonfidentlyocalvariationsofclimatean ddetailedeffects.Theimportantconclusion comingro mhePC Ceportshatglobal-average earthtemperatureshaveincreased overth epastcentury,an dth ebalanceofevidencesuggestsadiscerniblehu -man influence.Thehuman-inducedclimatechangeoc- cursslowlyan dwillbedifficulttoreverse.

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Volume 03 ,Number5,September-October 99 8JournalofResearchoftheNationalInstituteofStandardsandTechnology3. Trade-OffsinRefrigerantSelection

Predictingtowhatdegreeclimatechangeissuesma yaffectrefrigerantchoicesinth efutureisdifficult.Welldocumented research showsthatthereareno refrigerantcandidates thatwouldsatisfyal lselectioncriteria(Calman dDidion).Thelistofdesiredrefrigerantpropertiesisextensive.Inadditiontohavinggoodthermodynamicproperties,anidealrefrigerantshouldbenonflammable,nontoxic,stableinsideth esystem,an dunstable in th eatmosphere withharmlessdecompositionproducts.Practicalon -siderationscallfo rlowcostan dfullcompatibilitywithsystemmaterialsncludingubricantsndmachining fluids.Theenvironmentalcriteriaincludeth eimpactofth eefrigerantnhetratosphericzoneayerndclimate.

An"ideal"refrigerantdoesnotexist,an dth eproba-bilityoffindingon einth efutureisclosetozero.This statementsupportedbymolecularcreeningof llelementsndheevelopednderstandingnow chemicalomposition eterminespropertiesofom -pounds.Thelistofelementsfo rrefrigerantsdentifiedbyMidgleyn930onsistedfarbon,itrogen,oxygen,ydrogen,luorine,ulfur,hlorine,ndbromine.T heconcernsaboutth eozonelayernarrowed thislistbyremovingchlorinean dbromine,ndexten-siveresearchduringhe lastdecadehas otexpandedth elistatall.Therefore,selectingrefrigerantsfo rth e21stcentury isnotaboutchoosingbetweenseveralidealrefrigerants waitingfo rimplementationorlookingfo racompound thatwillsatisfythisvoid.It isaboutscreeningalimitedpoolofrefrigerants,ac hofwhichha stswnwell-documenteddemerit. ence,heefrigerantelection processequires arefulnalysisuring hichllfluid'sadverseeffectshavetobe properlyweighted.

Arefrigerant'scontributiontoclimatechangehasdirectan dindirectcomponent .T hedirectcomponentisaresultofarefrigerantbeingagreenhousegas.When releasedtoth eatmosphere,ittrapspartofth einfraredradiation.T hemeasureofth edirecteffectfo ragivengasisits GWPIt isaratio ofits heattrappingcapabilitytothatofth ereferencegas,commonlycarbondioxide.Theindirectcomponentisrelatedtoth ecarbondioxidereleasedinth eprocessofproducingelectricityneededfo roperatingth erefrigeration system.T hefuelorfuelmix used to generate electricity, th econversionrate,an d othersystemeffectsimpactth eindirect effect.Arefrig-erantinfluencesth eindirecteffectthroughitsthermo-dynamicfficiency.ormostefrigerationndir- conditioningpplications,hendirectomponent as th edominanteffecton th eglobalwarming.

4. HFCandOtherCarbon-Based Refrigerants HFCshavebecometh epredominantzeroozonede-pletingotentialODP)lternativesorFCsndHCFCs.ThetransitiontoHFCsha snotoccurredwith-

out difficulties,mainlybecauseoflubricantcompatibil-ityproblems.However,itstillhasbeenth emostprag-maticmovewayro mozone-depletingluids.Whendiscussingth eimpacton earth'sclimate,th eproponents ofHFCsstressth eimportanceofth esystemefficiencyan dth eindirecteffecton globalwarming.Becauseth edirecteffectis resultofth erefrigerant'spresencein th eatmosphere,hekeytoenvironmentallycceptableusesoaveminimalefrigerantscapero mhesystem.fHFCsreontainedn ystemndheiremissionsre inimal,heirirectontributionoclimatechangewillbe minimalaswell(Sanvordenker).BecauseothertypesofzeroODPrefrigerantscould bemorepreferablehanHFCs,everal rganizationshavenvestigatedluorinated thers, lcohols,mines,an diliconndulfurompounds.hevaluationcriteriaincluded thermodynamicperformance,toxicity,flammability,tability,tmosphericifetime, anu-facturingeasibility,ndcost.nmostcases,heub -stancesunderconsiderationwerelarge,morecomplex moleculesequiringmulti-stepynthesisoutes.orexample,-234fEbgnd-234fEaberehe ost promisingsubstitutesfo rR-11ndR123.Thethermo-dynamicperformanceofhemajorityofnvestigated fluidswas worse than thatofHFCs.Only6 of30 exam-ined fluidshad predicted performancewithin 5% ofth eHFC theytargetedtoreplace.NoneappearedtohaveabalanceofrefrigerantattributesohallengeHFCsnvaporcompressionequipment(Bivensan dMinor).

5. AlternativestoHFCsTechnologyMorethanhalfofth econferenceprogramwa sdedi-catedotherechnologieshanFCs.dmittedly,

noneofhese ptionsreompletely ew .he yre either idelyppliednertainpplicationse.g.,ammonia orabsorption)ortheyhavebeen knownsinceth epre-CFC times,i.e.,before1930,likecarbon dioxideorhydrocarbons,ndwere iscardedbecauseofow efficiencyor safetyconcerns .Allconcepts discussed in thiscategory us erefrigerantshavingalowerGW PthanHFCs.Ammoniaha sbeenusedfo rover00years.tislow-costefrigerantithxcellenthermodynamic propertiesnd eroGWP; owever,tsoxicndflammable.Becauseofthesepropertiesnd trong

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Volume 03 ,Number5,September-October 99 8JournalofResearchoftheNationalInstituteofStandardsandTechnologyodor,ammonia did notgainacceptancein directcooling an dispracticallyimitedtopplicationsnwateran d liquidhillers.Theowostofammonia asbeenstrongactororelectingtorargeystemswhererefrigeranthargemaybe undredsrhousandsofkilograms.uc hystemsreypicallyse dnood processingan dindustrialapplications.Recentenviron-mentalconcernshavepromotedth eus eofammoniain smallercapacitysystems;however,ammonia'slackofcompatibilitywith coppermakesitalessattractiveop- tionfo rsmallmachines .Absorptionisnotherwell-establishedan dcentury-oldtechnology.Itha salonghistoryofusingenviron-mentallysaferefrigerantssuchasammoniaan dwater. InheUnitedtates,bsorptionystemsresedmostlynargeapacitypplications.Availabilityoffreewaste heator lo wga sratesfavorth eselectionofan absorptionystem.n re emarketwithconomicsbeinghegoverningelectionactor,bsorptionosestolectric-driveaporompression.tppearshatclimatehangeoncerns il lotavorbsorptionsystemsbecauseheyendtohave lowerefficiencyan dhigherindirectimpactonclimatechangethantheirelectric-drivecompetitor(Burgettetal.).Propanewasuseds refrigerantnhepre-CFCs era.Considering thatamajority ofth eearlyrefrigerantswereitherlammable,oxic,rboth,ropane'sflammabilitywasnotsomuchadifferentiatingfeatureastsow.he isappearanceofpropane-chargedsystemsro mhemarketwas ueopersonalafetyconcerns .Current fferingsfhydrocarbon-chargedsystemsmaybeconsideredas compromisebetween personalsafety an denvironmentalsafety.Hydrocarbonproponentsinsist that th eexplosivebehaviorofpropane an disobutanecan be managed with reasonable precau-tionaryefforts.Hydrocarbons eree-introducednefrigeratorsinGermanyn993.Today,ydrocarbon-chargedsystems av e lmost00%markethareofGerman refrigerator/freezerproduction (Kruse an dTiedemann) .Thissuccessisnotuniformin al lofEurope;th emarket-

in gismainlylimited to Northern an dCentralEuropeancountries.Smallsystemsusinghydrocarbonshaveth e potentialofbecomingmorecommon;however,largersystemswithlargerrefrigerantchargesmay havediffi-cultiesngainingmarketcceptancebecauseofhe inherentriskofflammablefluids.Thehort tmosphericiveimesofhydrocarbonsmakeheirGWPsloseoero,ndheirxcellentthermophysicalpropertiesssure fficiencieshatre comparabletothoseofHFCs.Becausedesignchangesnecessaryomitigateafetyisks ssociatedwithhe us eofflammableefrigerantsddostohe ydro-carbon-chargedsystem,itisappropriatetoconsiderth e

possiblefficiencymprovementchievedhenhesameadditionalcostisappliedto production ofan HFCsystem.Consequently,bothsystemswillhaveth esame priceagndanbevaluatedsoheirdirectndindirectimpactson climate change.A study presented at th eonferenceKelleret . l)howedthatnexampleR410Asplitsystemredesigned tohaveth esamecostas th eropaneystemad owermpactnlimate change.henalysisor indowir-conditionershowedapropaneystemtobemarginallybetterthanth eR410Asystemperunitofinvestment.Carbondioxideha several ttractivepropertiesndwas ls ousedbeforehedventofCFCs.TwoCO 2handicaps,ighressurendowyclefficiency,causeditsdemisewhenCFCsndHCFCswereintro-duced.heseO2 andicapstillemainhallengestodaywhenapplication ofCO 2isrevisited.Becauseofth elo wcriticaltemperature,CO 2operatesin atranscrit-icalcyclewithsupercriticalga scoolinginsteadofgascondensingfheonventionalapor-compression cycle.nmprovementnyclefficiencyaneachieved by matchingth elarge temperatureglide ofth esupercriticalCO 2withheglideofheheat-transferfluid.Cycle fficiencyofcarbon ioxidean lsobe considerablymprovedyeducinghrottlingossesthroughhesefnfficientxpanderBullock).Othereaturesfarbonioxidee.g.,ompressorpressureratio,heattransfercoefficient,ndaturation temperatureversuspressurerelationship) refavorablefo ritsapplication asarefrigerantan dexplain th einten-siveCO 2researcheffortundertaken inrecentyearsin severalcountries(Pettersen).Air deservesth enameofa"naturalrefrigerant"morethanan yfluid.Air-cyclerefrigeration,originallya19thcenturynvention,smostwidelyse dnerospaceapplications.Becauseofitslowcriticalpoint, irdoesnotndergo hasehangendemainss as throughout th erefrigeration processfo rair-conditioning applications.In general,thisresultsin higherenergy us e comparedo aporompressionycle.fficiencyimprovementsmayomero mmprovedompressordesignthrough th eus eofcomputationalfluiddynamicsinth edesignprocess(Gilesetal.).

Thetrendto limitrefrigerantemissionspromotesth eapplicationofindirectrefrigeration an dair-conditioning usingsecondaryloops.Insuchsystems,th eheat-trans-fe rfluidisused to exchange heatbetweenth eair-condi-tioned/refrigeratedspacean dth emachinerealizingth ethermodynamicycle.omefheequirementsorheat-transferluidsreheam esorefrigerants.Heat-transferfluidsshouldbe nontoxic,nonflammable,environmentallyriendly,table,ndompatiblewith commonengineeringmaterials.Highthermalconduc-tivity,ighpecificeat,ndowiscosityrehedesiredtransportpropertiesHrnjak).

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Volume 03 ,Number5,September-October 99 8JournalofResearchoftheNationalInstituteofStandardsandTechnologyTheadvantageofsecondaryloopsisso significant fo rcommercialargeuildingshatheyrelreadypredominantlyse dnuc hnstallations.urrently,supermarketsaredrawingattention asapotentiallyne wareaorpplicationfecondaryoops.econdaryloopsmaypaveth ewa yoncreasedus eofammonia

an dydrocarbonsecauseecondaryoopystems assurehatheefrigerantwillotbeeakedohe conditioned/refrigeratedarea.6. ConcludingComments

Theonferencerovided orumorresentingdiverseviewson possibleresponsesto th eozonedeple-tionan d globalwarmingproblems.Aconsensusopinionwasnotdeveloped,norwason eexpected.T hetaskofselecting"thebest"refrigerantfo rth e21stcenturywillbedifficultbecauseth emeritsofdifferentrefrigerants resultfrom acomplexcombination ofseveralattributes;th emostmportanteingzoneepletionotential,systemfficiency,irectglobalwarming,afety,nd cost.ecausehesettributesayarryifferentweightsin different application and countries,th emeritsofth econsideredrefrigerantsar eviewedwithacorre-spondinglackofuniformity.If refrigerantselectionfo rth efutureisnotaffectedbyregulatorymeasures,tissafetopredictthatHFCswillcontinuetobe dominantfo rdecadesoom ebecauseoftheirhigh fficiency,personalafety,ndth eurrenttrongpositionnhe market.It isalsocertainthatth esearchfo rne wan dth e refinementofmatureechnologieswillontinuenn efforttoproduceenvironmentallyfriendlysolutionsfo rth eyearstocome.

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