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外文翻译
本科生外文翻译
学院名称:
机械工程学院
年级专业:
07建环2班
指导教师:
冯炼
学生姓名:
乔宣铭
学生学号:
20071585
二〇一一年4月——二〇一一年6月
Thermalcomfortinthefuture-Excellenceandexpectation
P.OleFangerandJørnToftum
InternationalCentreforIndoorEnvironmentandEnergy
TechnicalUniversityofDenmark
Abstract
Thispaperpredictssometrendsforeseeninthenewcenturyasregardstheindoorenvironmentandthermalcomfort.Onetrenddiscussedisthesearchforexcellence,upgradingpresentstandardsthataimmerelyatan“acceptable”conditionwithasubstantialnumberofdissatisfied.Animportantelementinthisconnectionisindividualthermalcontrol.Asecondtrendistoacknowledgethatelevatedairtemperatureandhumidityhaveastrongnegativeimpactonperceivedairqualityandventilationrequirements.FuturethermalcomfortandIAQstandardsshouldincludetheserelationshipsasabasisfordesign.ThePMVmodelhasbeenvalidatedinthefieldinbuildingswithHVACsystemsthatweresituatedincold,temperateandwarmclimatesandwerestudiedduringbothsummerandwinter.Innon-air-conditionedbuildingsinwarmclimatesoccupantsmaysensethewarmthasbeinglessseverethanthePMVpredicts,duetolowexpectations.AnextensionofthePMVmodelthatincludesanexpectancyfactorisproposedforuseinnon-air-conditionedbuildingsinwarmclimates.TheextendedPMVmodelagreeswellwithfieldstudiesinon-air-conditionedbuildingsofthreecontinents.
Keywords:
PMV,Thermalsensation,Individualcontrol,Airquality,Adaptation
ASearchforExcellence
Presentthermalcomfortstandards(CENISO7730,ASHRAE55)acknowledgethatthereareconsiderableindividualdifferencesbetweenpeople’sthermalsensationandtheirdiscomfortcausedbylocaleffects,i.e.byairmovement.Inacollectiveindoorclimate,thestandardsprescribeacompromisethatallowsforasignificantnumberofpeoplefeelingtoowarmortoocool.Theyalsoallowforairvelocitiesthatwillbefeltasadraughtbyasubstantialpercentageoftheoccupants.
Inthefuturethiswillinmanycasesbeconsideredasinsufficient.Therewillbeademandforsystemsthatallowallpersonsinaspacetofeelcomfortable.Theobviouswaytoachievethisistomovefromthecollectiveclimatetotheindividuallycontrolledlocalclimate.Inoffices,individualthermalcontrolofeachworkplacewillbecommon.Thesystemshouldallowforindividualcontrolofthegeneralthermalsensationwithoutcausinganydraughtorotherlocaldiscomfort.Weknowtherangeofoperativetemperaturesrequiredinaworkplacetosatisfynearlyeverybody(Wyon1996;Fanger1970)andweknowthesensitivitytodraughtfromawiderangeofstudies.Asearchforexcellenceinvolvesprovidingallpersonsinaspacewiththemeanstofeelthermallycomfortablewithoutcompromise.
ThermalComfortandIAQ
Presentstandardstreatthermalcomfortandindoorairqualityseparately,indicatingthattheyareindependentofeachother.Recentresearchdocumentsthatthisisnottrue(Fangetal.1999;Toftumetal.1998).Theairtemperatureandhumiditycombinedintheenthalpyhaveastrongimpactonperceivedairquality,andperceivedairqualitydeterminestherequiredventilationinventilationstandards.Researchhasshownthatdryandcoolairisperceivedasbeingfreshandpleasantwhilethesamecompositionofairatanelevatedtemperatureandhumidityisperceivedasstaleandstuffy.Duringinhalationitistheconvectiveandevaporativecoolingofthemucousmembraneinthenosethatisessentialforthefreshandpleasantsensation.Warmandhumidairisperceivedasbeingstaleandstuffyduetothelackofnasalcooling.Thismaybeinterpretedasalocalwarmdiscomfortinthenasalcavity.ThePMVmodelisthebasisforexistingthermalcomfortstandards.Itisquiteflexibleandallowsforthedeterminationofawiderangeofairtemperaturesandhumiditiesthatresultinthermalneutralityforthebodyasawhole.Buttheinhaledairwouldbeperceivedasbeingverydifferentwithinthiswiderangeofairtemperaturesandhumidities.Anexample:
lightclothingandanelevatedairvelocityorcooledceiling,anairtemperatureof28ºCandarelativehumidityof60%maygivePMV=0,buttheairqualitywouldbeperceivedasstaleandstuffy.Asimultaneousrequestforhighperceivedairqualitywouldrequireanairtemperatureof20-22oCandamodestairhumidity.ModerateairtemperatureandhumiditydecreasealsoSBSsymptoms(Krogstadetal.1991,Anderssonetal.1975)andtheventilationrequirement,thussavingenergyduringtheheatingseason.Andevenwithair-conditioningitmaybebeneficialandsaveenergyduringthecoolingseason.
PMVmodelandtheadaptivemodel
ThePMVmodelisbasedonextensiveAmericanandEuropeanexperimentsinvolvingoverathousandsubjectsexposedtowell-controlledenvironments(Fanger1970).Thestudiesshowedthatthethermalsensationiscloselyrelatedtothethermalloadontheeffectormechanismsofthehumanthermoregulatorysystem.ThePMVmodelpredictsthethermalsensationasafunctionofactivity,clothingandthefourclassicalthermalenvironmentalparameters.Theadvantageofthisisthatitisaflexibletoolthatincludesallthemajorvariablesinfluencingthermalsensation.ItquantifiestheabsoluteandrelativeimpactofthesesixfactorsandcanthereforebeusedinindoorenvironmentswithwidelydifferingHVACsystemsaswellasfordifferentactivitiesanddifferentclothinghabits.ThePMVmodelhasbeenvalidatedinclimatechamberstudiesinAsia(deDearetal.1991;Tanabeetal.1987)aswellasinthefield,mostrecentlyinASHRAE’sworldwideresearchinbuildingswithHVACsystemsthatweresituatedincold,temperateandwarmclimatesandwerestudiedduringbothsummerandwinter(Cenaetal.1998;Doninietal.1996;deDearetal.1993a;Schilleretal.1988).ThePMVisdevelopedforsteady-stateconditionsbutithasbeenshowntoapplywithgoodapproximationattherelativelyslowfluctuationsoftheenvironmentalparameterstypicallyoccurringindoors.Immediatelyafteranupwardstep-wisechangeoftemperature,thePMVmodelpredictswellthethermalsensation,whileittakesaround20minattemperaturedown-steps(deDearetal.1993b).
Fieldstudiesinwarmclimatesinbuildingswithoutair-conditioninghaveshown,however,thatthePMVmodelpredictsawarmerthermalsensationthantheoccupantsactuallyfeel(BrageranddeDear1998).Forsuchnon-air-conditionedbuildingsanadaptivemodelhasbeenproposed(deDearandBrager1998).Thismodelisaregressionequationthatrelatestheneutraltemperatureindoorstothemonthlyaveragetemperatureoutdoors.Theonlyvariableisthustheaverageoutdoortemperature,whichatitshighestmayhaveanindirectimpactonthehumanheatbalance.Anobviousweaknessoftheadaptivemodelisthatitdoesnotincludehumanclothingoractivityorthefourclassicalthermalparametersthathaveawell-knownimpactonthehumanheatbalanceandthereforeonthethermalsensation.Althoughtheadaptivemodelpredictsthethermalsensationquitewellfornon-air-conditionedbuildingsofthe1900’slocatedinwarmpartsoftheworld,thequestionremainsastohowwellitwouldsuitbuildingsofnewtypesinthefuturewheretheoccupantshaveadifferentclothingbehaviourandadifferentactivitypattern.
WhythendoesthePMVmodelseemtooverestimatethesensationofwarmthinnonair-conditionedbuildingsinwarmclimates?
Thereisgeneralagreementthatphysiologicalacclimatizationdoesnotplayarole.Onesuggestedexplanationisthatopenablewindowsinnaturallyventilatedbuildingsshouldprovideahigherlevelofpersonalcontrolthaninair-conditionedbuildings.Wedonotbelievethatthisistrueinwarmclimates.Althoughanopenablewindowsometimesmayprovidesomecontrolofairtemperatureandairmovement,thisappliesonlytothepersonswhoworkclosetoawindow.Whathappenstopersonsintheofficewhoworkfarawayfromthewindow?
Andinwarmclimates,thenormalstrategyinnaturallyventilatedbuildingsistocoolthebuildingduringthenightandthenclosethewindowssometimeduringthemorningwhentheoutdoortemperatureexceedstheindoortemperature.Anotherobstacleisofcoursetrafficnoise,whichmakesopenwindowsinmanyareasimpossible.Webelievethatinwarmclimatesair-conditioningwithproperthermostaticcontrolineachspaceprovidesabetterperceivedcontrolthanopenablewindows.
Anotherfactorsuggestedasanexplanationtothedifferenceistheexpectationsoftheoccupants.WethinkthisistherightfactortoexplainwhythePMVoverestimatesthethermalsensationofoccupantsinnon-air-conditionedbuildingsinwarmclimates.Theseoccupantsaretypicallypeoplewhohavebeenlivinginwarmenvironmentsindoorsandoutdoors,maybeeventhroughgenerations.Theymaybelievethatitistheir“destiny”toliveinenvironmentswheretheyfeelwarmerthanneutral.Ifgivenachancetheymaynotonaveragepreferanenvironmentthatisdifferentfromthatchosenbypeoplewhoareusedtoair-conditionedbuildings.Butitislikelythattheywouldjudgeagivenwarmenvironmentaslesssevereandlessunacceptablethanwouldpeoplewhoareusedtoair-conditioning.Thismaybeexpressedbyanexpectancyfactor,e,tobemultipliedwithPMVtoreachthemeanthermalsensationvoteoftheoccupantsoftheactualnon-air-conditionedbuildinginawarmclimate.Thefactoremayvarybetween1and0.5.Itis1forair-conditionedbuildings.Fornon-air-conditionedbuildings,theexpectancyfactorisassumedtodependonthedurationofthewarmweatherovertheyearandwhethersuchbuildingscanbecomparedwithmanyothersintheregion