Cold but comfortable? Application of comfort criteria to cold environments.

Abstract

Fanger defined two physiological criteria that are basic requirements for people's perception of thermal neutrality and, eventually, thermal comfort. Mean skin temperature and evaporative heat loss are defined as functions of metabolic rate. The equations are derived from experiments in light clothing at or close to normal indoor climate. Relations between skin temperature and sweating on the one hand and thermal sensation and comfort on the other are well recognized; the precise description of the relationships vary and may differ from normal indoor environments to more extreme thermal stress. In moderately cold environments (around +10 degrees C) ISO/DIS 7730 and ISO/DIS 11079 prescribe significantly different responses. Evaluation of the rationale behind the comfort criteria and the basic heat transfer equations in the two models reveals some clear differences. By modification of the sweating criteria and some of the heat transfer equations, predictions become much more similar. It is concluded that the basic comfort criteria may apply also to moderately cold and cold environments, but must consider the complex heat transfer through multilayer clothing in a more adequate way. The suggested, modified comfort criteria incorporated either in the PMV-index or in the IREQ-index, provide more realistic and reliable prediction of heat balance and conditions for comfort in cool and cold environments.