Figure 2.
Simplified schematic of heat exchange between humans and their environment. Net metabolic heat production (Mnet) is the combination of resting heat production plus that associated with physical activity, minus any external work being performed. Dry heat exchange (R+C) is determined by the gradient between mean skin temperature (Tsk) and ambient dry-bulb temperature (Tdb) unless there is a significant source of radiant heat that elevated mean radiant temperature (Tr). Dry heat exchange is bidirectional. Evaporative heat exchange (E), on the other hand, is unidirectional (loss only) and is determined by the gradient between the water vapor pressure of the skin (Psk) and the ambient water vapor pressure (Pa). The sum of Mnet ± (R+C) − E determines heat storage, which in turn, determines core temperature (Tc).