f h Usingoursameexample,letsexaminehowthis hasthepotentialforcreatingaproblem.Assume h th t ti l f ti bl A thatthebuildingdesignchangestouseamuch higher qualityglassthatwill reducethesensible higherquality glass that will reduce the sensible portionofthedesignloadfrom80,000Btu/hr to 47,000Btu/hr.This reducestheSHRto0.70. Somedesignersprefertosetthesupplyair So e des g e s p e e to set t e supp y a temperatureat55Forusea20F temperature differential(RoomDBSupplyDB)withoutregard fortheactualsensible h f h l bl heatratiooftheroom.
b id tifi d Thesecurvedlines representthechangesin drybulbandwetbulb y temperaturesasair passesthroughatypical coolingcoil.Theseare commonlyreferredtoas commonly referred to as coilcurves mixture of the two (C)ĪirQuantity Air QuantityBeforeproceeding,one moresetofcurvesonthe psychrometric chartmust beidentified. The air entering the cooling coil may be Theairenteringthecoolingcoilmaybe 100%recirculated(A),100%outdoor(B),ora mixtureofthetwo(C). Humidity ratio can be expressed as pounds of Humidityratiocanbeexpressedaspoundsof moistureperpoundofdryair,orasgrains of moistureperpoundofdryair.Thereare7000 moisture per pound of dry air There are 7000 grainsofwaterinapound.To appreciatethe magnitudeoftheseunitsofmeasurement,at magnitude of these units of measurement at sealevelonepoundof70F airoccupies approximately13.5cubicfeet,andonegrain approximately 13 5 cubic feet and one grain ofwaterinthatairweighs abouttwo thousandths(0.002)ofanounce thousandths (0 002) of an ounceįorexample,at25F,onepoundofdryaircanabsorbandhold19.14grains ofwater at30Fitcanabsorb24.19grains at35Fitcanabsorb29.94grains andsoon.Eachoftheseconditionsisasaturationpoint
saturated It can hold no more moisture Whenairisatasaturatedcondition,moisture enteringtheairdisplacesmoisturewithinthe entering the air displaces moisture within the air.Thedisplacedmoistureleavestheairin theformoffinedroplets.Whenthiscondition the form of fine droplets When this condition occursinnature,it iscalledfog
When the drybulb wetbulb and dewpoint Whenthedry bulb,wet bulb,anddew point temperaturesarethesame,theairis saturated.Itcanholdnomoremoisture.
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