Facial skin temperature and its relationship with overall thermal sensation during winter in Changsha, China.

Facial skin temperature has been applied to evaluate thermal comfort in a few studies, but the related theoretical basis is not sufficient. We conducted a climate-controlled experiment in winter. The air temperatures were 12, 15, 18, 21, and 24°C, and the relative humidity was set to 60%. During exposure (140 min), the subjects were in a sedentary state, and their thermal sensation, comfort, and acceptability of perceived thermal environments were documented many times. iButton instruments were used to continuously and automatically record skin temperatures on the forehead, nose, right ear, right cheek, left cheek, left ear, and chin. The measurement accuracy of the corrected skin temperature was within 0.1°C after calibrating each i-Button. The experimental results showed that the skin temperatures at different measurement points varied significantly. The forehead skin temperature was the highest, whereas the nose, being the facial part, exhibited the lowest skin temperature (except 24°C). The uneven degree of the skin temperature distribution increased as air temperature decreased. Correlation analysis confirmed that the facial skin temperature can be used to evaluate thermal sensation. Nose skin temperature and the average skin temperature of the forehead, nose, and chin are the most suitable indicators of thermal sensation. The correlation between facial skin temperature and the thermal sensation was significantly higher after 15 min of exposure time than that during 0-15 min. This study provides a theoretical basis for using facial skin temperature to dynamically monitor thermal sensations.