A model with regard to wet heat loss from skin surface was made taken the effect of humidity on thermal sensation into consideration. The present model is consisted of two control regions an—environmental region where the rate of moisture exceeds the maximum environmental capacity to accept evaporated moisture and an environmental region where the rate of moisture is less than the environmental capacity. We call the former region I and the latter region II.
In region I, by applying and developing wettedness model by Gagge et al with regard to skin evaporation, the evaporative heat loss in this region is given by the following equation.
He=κ
hc (Ψ
sXss-Xa)
Wwhere,
He: wet heat loss from skin surface
κ: modified Lewis relation
hc: convective heat transfer coefficient for the human body
Ψ
s: percentage humidity at skin surface
Xss: saturated humidity ratio at skin temperature
Xa: humidity ratio in ambient air
W: wettedness by Gagge et al
Although percentage humidity Ψ
sfor the boundary layer at skin surface is always unity in wettedness model, that in the present model is assumed to be not always unity and to have close relationship to environment humidity. As a consequence of surveying from clothing worn, air movement and so forth, we obtained a relation between percentage humidity at skin surface and that in ambient air.
In region II, man's ability to squeeze out the moisture is assumed to have a certain limit. A moisture control center regulates the quantity of moisture and wet heat loss is given by the following equation.
He=G⋅Lwhere,
G: quantity of moisture (insensible perspiration and sweat secretion, at comfort condition, only insensible perspiration)
L: latent heat
Heat balance between man and his environment is expressed by considering four main heat loss terms in a steady state—radiation, convection, evaporation and respiration. Based on the rational heat balance equation derived, a comfort chart was proposed as an index of comfortable sensation and for enviromental assessment and the proposed comfort line was compared with experimental data and theoretically derived comfort lines by earlier workers.
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