Page - 356 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2016,9, 240 KimandLeefocusedonheatingperformanceenhancementof theCO2heatpumpsystemusing wasteheat fromthestacks in fuel cellEVs [89,90]. In [89], aheatercore thatusedstackcoolantwas placedupstreamofacabinheater topreheat incomingair into thecabinheater. Theperformanceof thisheatpumpsystemwithheatercorewascomparedwiththatofaconventionalheatingsystemwith heatercoreandthatofaheatpumpsystemwithoutheatercore. Theheatingcapacityof theheatpump systemwithheatercore,whichusedrecoveredheat fromthestackcoolant,was improvedby100% over theheatpumpsystemwithoutheater coreandby70%over the conventionalheatingsystem withheater core. Furthermore, thecoolant to theairheatpumpsystemwithheater core showeda significantlybetterperformance thantheair toairheatpumpsystemwithheatercore. Lee et al. [90] concludedthatwhenthewasteheat fromthestackcoolantwasusedas theevaporatingheatsource, theheatpumpusingR744 couldprovide sufficient heating capacity andheatingCOPunder cold weatherconditions. 3.2. SupplementalExternalHeatSource Inaddition to thewasteheatdischargedfrominteriorelectricdevices inEVs,asanassistedheat source, thereareotherheatpumpcombinedsystemswithexternalheat. Solar-assistedheatpumpAC systemsareone interestingoptionforEVclimatecontrol systemssincesolarcells cannotonlyprovide aheat insulating layer, but also recharge thebattery. This conceptwasalsoapplied tomotor train unitsbyYin[91]. In [92],asolarcontrollerandanACcontrollerweredesigned. Thesolarcontroller managedthebattery fatures, suchaschargingandover-dischargingprotection,andcommunicated with thevehiclecontrol system.Theexperimental results showedthat thesolar-assistedheatpump ACsystemcouldoperatestably in theheatingmodeaswellas in thecoolingmode. In [93], solarcells coveredtheroofofacompactcar,andcouldgenerateabout225Wofpower. Thesolar-assistedheat pumpACsystemcould improvetherefrigeratingcapacitybyabout8%,whichsignificantlyreduced thepeakcooling loadandthedrivingmileage lossesof theEV.Zhao[94]declaredthat twohoursof generatingelectricitycapacitybyasolarpanelcouldkeepthesolar-assistedsystemrunningforhalf anhour. In [95], aheatpumpsystemwith integratedthermoelectricmoduleswasproposed. Theauthors discussedtheapplicationof this techniquetoprovidesupplementalheatingforEVs.Atanambient temperatureof´17.8˝C, the integratedautomotiveACsystemcouldachieveanadditional2kWof heatingcapacitywithalmost thesameCOPcomparedtotheheatpumpsystemwithout thermoelectric modules. The test results showedthat this integratedsystemcould increase theheatingcapacity inan energy-efficientway,especially forcoldclimateoperation. ThePTCheater isanotheradditionalheat source.Kim et al. [96] investigatedacombinedsystem consistingofaheatpumpandaPTCheaterasaheatingunit inEVs. Comparedto thestandardof thePTCheateratan indoor temperatureof20˝C, theheatingcapacitywas increasedby59%for the combinedsystem,andtheCOPwas increasedby100%for theheatpumpsystem.Theconclusions showedthat theheatpumpcycleshouldbealwaysoperatedforbetterefficiency,andthePTCheater shouldbe controlled for better performance. Therefore thePTCheater andheat pumpcombined systemisanoptionalACsystemforEVs,especially inextremelycoldweatherconditions. 4.Conclusions TheheatpumpACsystemseemstobe themost reasonablesolution tocontrol theclimateofEVs, althoughtherearecurrentlymanyothersolutionsusedinEVs. In thispaper,anextensive literature reviewhasbeenperformedontheprogressofheatpumpACsystemsfor theEV. Not only single air sourceheatpumpsystems,whichhavebeenwidely consideredbymany researchers,havebeencomprehensivelyanalyzed,butalsomultiplesourceheatpumpsystemshave beenincluded. InsingleairsourceheatpumpACsystems,manyadvancedtechnologiesandstrategies weredescribed, suchasalternativerefrigerants, the inverter technology,novel components, aswellas innovativesystemstructures. Theseadvancedtechnologiescan improve theACsystemefficiencyand 356