Upper limits for indoor air humidity to avoid uncomfortably humid skin

The hypothesis that skin humidity in itself could be a cause of discomfort was tested with forty persons exposed to five levels of skin humidity. In addition, the effect of fabric material against the skin (cotton versus polyester) and of environmental temperature/clothing insulation on perceived discomfort was studied at one high level of skin humidity. Under all experimental conditions, skin humidity was controlled by the combination of vapor permeability of the experimental clothing ensemble and the thermal environment. The subjects perceived the condition of their skin to be less acceptable with increasing skin humidity at thermal neutrality. No effect of clothing material against the skin or of environmental temperature/clothing insulation was observed. A model was developed that predicts the percentage of persons dissatisfied due to humid skin as a function of the relative humidity of the skin. Existing models of heat and mass transfer can predict the relative skin humidity from thermal environmental parameters, clothing and activity. The new skin humidity model applies for sedentary, thermally neutral persons. The model was used to specify upper limits for indoor air humidity required to avoid discomfort caused by skin humidity. The model predicts that the relative air humidity may be close to 100% without causing much discomfort from humid skin among thermally neutral persons performing sedentary work.