Clothing thermal insulation when sweating and when non-sweating

Abstract

Heat transfer through clothing is an important topic related to thermal comfort in environmental engineering and functional clothing design. The total heat transmitted through clothing is commonly considered as the sum of the dry heat transfer and the evaporative heat transfer. The clothing thermal insulation measured at a non-perspiring condition, e.g. using a dry thermal manikin, is frequently used to calculate the dry heat transfer when the body is perspiring or even sweating heavily. The effect of perspiration on clothing thermal insulation to dry heat transfer is not well understood, although it is widely speculated that perspiration reduces the thermal insulation as a result of wetting the clothing ensemble. In this investigation, the clothing thermal insulation under very low perspiration and very heavy perspiration have been measured using a novel perspiring fabric thermal manikin. It was found that clothing thermal insulation is reduced during perspiration and the amount of reduction varied from 2% to 8% related to the water accumulation within clothing ensembles. This finding suggests that the ‘after chill’ effect on wearers after heavy exercise may not only be caused by heat absorption due to the desorption and evaporation of water within clothing, but also due to the reduced clothing thermal insulation. It also suggests that, for clothing that can absorb a large amount of moisture during sweating, clothing thermal insulation measured on dry manikins may need to be corrected when applied to calculating the dry heat loss (sometimes used for calculating the moisture vapour resistance) on a sweating manikin and predicting the thermal comfort during sweating.