A model developed for predicting thermal comfort during sleep in response to appropriate air velocity in warm environments

Abstract

Using air movement to improve sleeping environments is widely practiced in summer; while research into how to evaluate thermal comfort and sleep quality under such non-uniform environments is lacking, due to the greatly reduced ability of occupants to adjust to the immediate environments during sleep. This study conducted climate chamber sleeping experiments under a combination of conditions of temperature (28 / 30 / 32 °C), relative humidity (50% / 80%), and air velocity (0.39 / 0.69 / 1.17 m / s). The results showed that the appropriate air velocities alleviated the thermal discomfort caused by higher temperature and humidity; however, when the temperature was higher than 32 °C and coupled with high humidity, the cooling efficiency of air velocity was reduced significantly. The subjective evaluations of sleep quality were consistent with the measured sleep indicators - Total Sleep Time (TST), Sleep Onset Latency (SOL), and Slow Wave Sleep (SWS) - indicating that recall-based sleeping evaluations after waking up could reflect the actual sleep quality to some degree. A developed PMVs model was proposed considering three aspects of the body heat exchanges: the parts in contact with the mattress (e.g. back, buttocks), the parts covered by the quilts or clothes (e.g. abdomen, chest), and the parts directly exposed to the air (e.g. head, arms, legs). The upper temperature and humidity limits, appropriate air velocity zones, and different bedding thermal insulation levels were thus obtained. The work can guide the application of local ventilation devices in sleeping environments in summer and contribute to reducing the use of air conditioners and achieving energy savings in residential buildings. • Explore sleep thermal comfort in warm-humid environments with air movement. • Increased airflows improve the sleeping thermal comfort except for hot-humid condition. • Subjective evaluations are consistent with measured sleep indicators such as Total Sleep Time (TST). • Develop a PMVs model including three heat exchange aspects with/without body coverings. • Appropriate temperature, humidity and air velocity designs are obtained by PMVs model.