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1、ManandHisEnvironmentBodyheatlosses.Thehumanbody,likeanyotherheatengine,consumesfuel(food)togenerateheat.Theheatleavesthebodyintheformofradiationandconvectionfromtheskin,evaporationofmoisturefromporesintheskin,andinthebreath.Radiationandconvectionoccuronlyiftheairtemperatureorthesurroundingsarebelowb
2、loodheat.Ifapproachingorabovethiscondition,thesweatglandsexpandandheatisrejectedsolelybyevaporation.Highrelativehumiditycoupledwithhightemperaturerenderslifeincreasinglydifficult.Atlowtemperatures,thebloodvesselsnearthesurfaceoftheskincloseup,leavingtheepidermisdryandactingasaninsulator.Shiveringisa
3、provisionofnaturetocausemuscularactivityandhenceincreasebloodcirculation.Humancomfort.Fourfactorsaffectcomfort:airtemperature,radiation,relativehumidity,andairmovement.Mostthermometersmeasureairtemperaturebutarenotinfluencedbyinfrared(long-wave)radiation,becausetheirglassenvelopesareopaquetosuchradi
4、ation.Thehumanbody,however,mayreceiveheatfromaradiantsource;ifso,airtemperaturemustbereducedifbodyheatreleaseistoremainnormal.Conversely,ifthebodyislosingheatbyradiationtoitssurroundings,suchastothecoldwallsofaroom,theairtemperaturemustberaisedforanequaldegreeofcomfort.Thestudyofradianteffectsiscomp
5、lex.Themeanradianttemperatureinanenclosedspaceisthemeanofallthesurfacesboundingthespaceinproportiontotheirareasandtemperature,thelatterbeingcalculablefromtheknownconductivityofthematerialsandanassumedtemperaturedifferencebetweeninsideandoutside.Thiscalculationgivesonlyanapproximation;suchfactorsasth
6、eeffectofalargeareaofwindow,whichmaybecoldinwinterandhotinsummer,producevariationsindifferentpartsofaroom.Moreover,thebodyitselfissizeable,anditsresponsevariesaccordingtodifferencesofclothing.Thematterisfurthercomplicatedbytheintroductionofheatedsurfacestowarmthespaceandbytheentranceofheatthroughwin
7、dowsviasunshine.Acloseapproximationtomeanradianttemperaturemaybeobtainedbytheuseofglobethermometer(Fif.1),consistingofanordinarythermometerinablackened,hollowmetalsphereaboutsixinches(15centimeters)in
