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1、HeatPumpTechnologyHeatflowsnaturallyfromahighertoalowertemperature.Heatpumps,however,areabletoforcetheheatflowintheotherdirection,usingarelativelysmallamountofhighqualitydriveenergy(electricity,fuel,orhigh-temperaturewasteheat).Thusheatpumpscantransferheatfromnaturalheatsourcesinth
2、esurroundings,suchastheair,groundorwater,orfromman-madeheatsourcessuchasindustrialordomesticwaste,toabuildingoranindustrialapplication.Heatpumpscanalsobeusedforcooling.Heatisthentransferredintheoppositedirection,fromtheapplicationthatiscooled,tosurroundingsatahighertemperature.Some
3、timestheexcessheatfromcoolingisusedtomeetasimultaneousheatdemand. Inordertotransportheatfromaheatsourcetoaheatsink,externalenergyisneededtodrivetheheatpump.Theoretically,thetotalheatdeliveredbytheheatpumpisequaltotheheatextractedfromtheheatsource,plustheamountofdriveenergysupplied.
4、Electrically-drivenheatpumpsforheatingbuildingstypicallysupply100kWhofheatwithjust20-40kWhofelectricity.Manyindustrialheatpumpscanachieveevenhigherperformance,andsupplythesameamountofheatwithonly3-10kWhofelectricity. Becauseheatpumpsconsumelessprimaryenergythanconventionalheatingsy
5、stems,theyareanimportanttechnologyforreducinggasemissionsthatharmtheenvironment,suchascarbondioxide(CO2),sulphurdioxide(SO2)andnitrogenoxides(NOx).However,theoverallenvironmentalimpactofelectricheatpumpsdependsverymuchonhowtheelectricityisproduced.Heatpumpsdrivenbyelectricityfrom,f
6、orinstance,hydropowerorrenewableenergyreduceemissionsmoresignificantlythaniftheelectricityisgeneratedbycoal,oilorgas-firedpowerplants. ThetwomainheatpumptypesAlmostallheatpumpscurrentlyinoperationareeitherbasedonavapourcompression,oronanabsorptioncycle.Thesetwoprincipleswillbebrief
7、lydiscussedinthefollowingtwosections.Theoretically,heatpumpingcanbeachievedbymanymorethermodynamiccyclesandprocesses.TheseincludeStirlingandVuilleumiercycles,single-phasecycles(e.g.withair,CO2ornoblegases),solid-vapoursorptionsystems,hybridsystems(notablycombiningthevapourcompressi
8、onandabsorptioncycle)andel
