At rest, the human body produces ab

At rest, the human body produces about 400 Btu/h (117 W) of energy. Moderate activities like walking can raise this amount to 750 Btu/h (220 W), while strenuous activities can cause the body to generate up to 1200 Btu/h (351 W). Thermal comfort is achieved when the human body is able to dissipate the heatand moisture it produces by metabolic action in order to maintain a stable, normal body temperature. In other words, thermal equilibrium must exist between the body and its environment.The human body loses or transfers heat to the surroundingair and surfaces in the following ways.Conduction• Conductionisthetransferofheatfrom the warmertothe cooler particles of a medium or of two bodies in direct contact, occurring without perceptible displacement ofthe particles themselves.• Conductionaccountsforaverysmallportionofthetotalheat loss from the body.Convection• Convectionisthetransferofheatbythecirculatory motionof the heated parts of a liquid or gas owing to a variation in density and the action of gravity. In other words, the body gives off heat to the surrounding cooler air.• A largedifferentialbetweenairandskintemperatureandincreased air motion induce more heat transmission by convection.Radiation• Radiationistheprocessby whichheatenergyintheformof electromagnetic waves is emitted by a warm body, transmitted through an intervening space, and absorbed by a cooler body. No air motion is required for the transfer of heat.• Lightcolorsreflect whiledarkcolorsabsorbheat;poorreflectors make good radiators.• Radiantheatcannottravelaroundcornersandisnotaffected by air motion.Evaporation• Heatisrequiredfortheevaporativeprocessofconvertingbody moisture into a vapor.• Heatlossbyevaporationincreases withair motion.• Evaporativecoolingisespeciallybeneficial whenhighairtemperatures, humidity, and activity levels exist.