Abstract:TheperformanceoftwoalternativerefrigerantsHFC134aandHCFC123forcentrifugalchillersisdescribed.Thesafety,efficiencyandotherfactorsofthesetworefrigerantsarecompared.Intermsofsafetyperformance,HFC134ahasanadvantage;Intermsofefficiency,HCFC123isslightlyhigherthanHFC134a;SincetheODPofHCFC123isnotzero,itwillberestrictedanddisabledundertheMontrealProtocol,amandatorytreaty.TheKyotoProtocolalsorequireslimitingHFCsemissions.Intheend,theriskanalysisoftheuseofHCFC123wascarriedoutincombinationwithChina'snationalconditions,anditwasconcludedthatHFC134ashouldbecomethemainstreamofalternativeagentsatpresent.

Keywords:centrifugalchiller;HFC134a;HCFC123;property

HCFC123unitsaremanufacturedwithoutcharge,andtheymustbechargedonsiteandleakdetection,whichundoubtedlyincreasesthepossibilityofrefrigerantlossandincreasesthedifficultyoffieldwork.

BecausetheHFC134achillerisoperatedunderpositivepressure,theydonotneedapumpingrecoverysystem,whiletheHCFC123unitisoperatedundernegativepressure,andthepumpingrecoverydevicemustbeinstalledtoavoidairandwatersteamenteringtheunit.Obviously,theextractionandrecoveryequipmentincreasesthecomplexityoftheunitandthedifficultyofmaintenance.Atthesametime,italsohasacertainimpactontheunitperformance,becausetheremaybeapartofairinsidethecondenserduringtheactualrefrigerationprocess,whichwillincreasethecondensingpressureandreducetheCOPofthesystem.

WhenHCFC123unitruns,thecondenserisunderpositivepressureandtheevaporatorisundernegativepressure,whichisunfavorabletothemechanicalseal,soHFC134aisbetterthanHCFC123.Conversely,highpressureoperationmayleadtothepossibilityofincreasedleakage,butmodernindustrialtechnologyhasmadesignificantprogressinreducingleakageandoperatingmanagementofrefrigerants.Table2showstheannualleakageratesofdifferentunits,anditcanbeseenthattheleakageofHFC134aunitissmaller.

Usually,thesizeoftheunitwithhigheroperatingpressureissmaller,thevolumerefrigerationcapacityislarger,andtherefrigerantchargeamountissmaller.Atthesametime,whentherefrigerantisrecovered,thepositivepressuremakesiteasytoremovetherefrigerantfromthechiller,andthereisnopumpingrecoveryequipment,whicheliminatestheneedtorepairit.

3Security[3]

Thesafetyperformanceofrefrigerantscannotbeignored,accordingtothelateststandardGB7778-2001formulatedbythestate.Themethodoftoxicityquantificationandflammabilityquantificationisusedtoclassifyrefrigerants,whichismorescientificandwidelyusedatpresent.

Toxicityreferstotheabilityofarefrigeranttobetoxicorlethaltohumanhealthunderacuteorprolongedexposure,inhalationoringestion.Refrigerantsareclassifiedaccordingtotheirtoxicityandflammability,asshowninTable3.LettersAorBindicatethedegreeoftoxicity,andnumbers1,2or3indicatethedegreeofflammability.

BothHCFC123andHFC134aarenon-combustiblerefrigerants,butHCFC123ismoretoxicthanHFC134a.

4Efficiency

Thechoiceofrefrigerantaffectstheefficiencyoftherefrigerationcycle.Table4showsthevalueofCOPofrefrigerantHFC134aandHCFC123underdifferentworkingconditions.ThetheoreticalefficiencyofHFC134ais3%~5%lowerthanthatofHCFC123.Withtheincreaseofsupercooling,theCOPofHFC134aimprovesfasterthanthatofHCFC123.Intheactualrefrigerationcycle,duetothebetterthermalconductivityofrefrigerantHFC134aandtheinfluenceofnon-condensiblegasonHCFC123,theCOPgapbetweenthetwowillbenarrowed[4].

Itisworthnotingthattheefficiencygapbetweenthetwoissmallcomparedtothe50%energysavingrateproposedbythe"EnergyefficientDesignStandardforPublicBuildings".Whenthenewtechnologyisusedtoimprovetheperformanceoftheunit,thecontributiontoenergysavingisgreater,whichisobviouslyseeninFigure2.Theefficiencyafterusingthedualheadisincreasedby25.3%comparedwiththesinglehead,andtheefficiencyafterusingthedualheadfrequencyconversioncanbeincreasedby49.8%.

5OtherAspects

TheKyotoProtocolclearlyprovidesforthecontrolandreductionofitsemissions.However,HFCsaccountedforlessthan2%ofallgreenhousegasemissionsin2000,andarescheduledtobecontrolledtolessthan3%by2050(source:IPCC:IntergovernmentalPanelonClimateChange),whichshowsthatHFCScontributeonlyasmallpartoftheoverallgreenhousegasproblem.ORNLhasproposedamorecomprehensiveevaluationofthegreenhouseeffectofrefrigerant,calledthetotalequivalentwarmingfactorTEWI.Itnotonlyincludesthedirectgreenhouseeffectoftherefrigerantitself,butalsoincludestheindirectgreenhouseeffectcausedbytheemissionofCO2duetotheenergyconsumptionoftherefrigerationunit.Literature[5]showsthatinthetotalequivalentwarmingfactorTEWI,thedirectequivalentwarmingfactorTEWI(D)accountsforasmallproportion(lessthan5%),whiletheindirectequivalentwarmingfactorTEWI(I)accountsformorethan95.4%ofTEWI,indicatingthatthecharacteristicparameterGWPoftherefrigerationworkingmediumhasnosignificantinfluenceonTEWI.HCFC123hasanon-zeroODPandtheMontrealProtocolhasprovidedforitsphase-outprocess.Itisworthnotingthatdevelopedcountrieshavesignificantlyacceleratedthephase-outtime,andtheoutputofHCFC123isfacingarapiddecline,andEUregulationshaveacceleratedthephase-outofHCFC123.Thisundoubtedlybringstwopotentialriskstodevelopingcountries:1)theproductionofHCFC123isverysmall,theapplicationscopeisnarrow,andtheproductionisconcentratedindevelopedcountries,andtheproductionofHCFCindevelopedcountriesisnowfacingarapiddecline,thepriceofHCFC123isboundtoriseduetotheproductionreduction,andtherepairandmaintenancecostsoftheunitareboundtofacerisingrisks;2)DevelopedcountrieswilleventuallyphaseouttheHCFC123unit,anditsfollow-uptechnicalresearchanddevelopmentfortherefrigerantproducthasbeenbasicallyatastandstill,bringingpotentialriskstothefollow-uptechnologyoftheproduct,aswellaspartssupplyproblems.HCFC123unitspurchasedtodaywillfacerefrigerantsupplyandtechnicalmaintenancerisksforalongtimeduringtheirlifecycle,asshowninFigure3.

6ConcludingRemarks

AccordingtothecomparativeanalysisofHFC134aandHCFC123'soperatingpressure,refrigerationefficiency,safetyperformanceandotheraspects,itisconcludedthatHFC134aunitoperatesunderpositivepressure,hasnopumpingandrecoverydevice,andhasasmallerrefrigerantleakagerate;TheefficiencyofHFC134aunitisslightlylowerthanthatofHCFC123unit,andthegapbetweenthetwounitscanbefurtherreducedbyadoptingnewtechnologytoimprovetheunit.HFC134ahasbettersafetyperformance.Insummary,comparedwithHCFC123,HFC134ahasthecharacteristicsoflowprice,goodpracticability,excellentsafetyperformance,reliability,smallproductsize,andnomandatoryeliminationprovisions.HFC134aisbeingusedmoreandmorewidely,inadditiontocentrifugalandscrewchillersproducedbymajormanufacturers,itisalsousedinautomotiveairconditioners,refrigeratedtrucks,medicalrespiratorsandotherequipment.

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