Effects of phased sleeping thermal environment regulation on human thermal comfort and sleep quality

Sleeping thermal environment in winter has been generally regulated to avoid the influence of cold exposure on human thermal experience and sleep quality. However, existing studies have focused primarily on manipulating the thermal environment either before or during sleep, and it remains unclear whether these two phases of sleeping thermal environments exert identical influences on human thermal states and sleep quality. This study aims to investigate the coupling effect of pre-sleep and during-sleep thermal environment regulations on human thermal comfort and sleep quality. Experiments were conducted under four conditions using different combinations of pre-sleep and during-sleep thermal environments. The human thermal state and sleep quality were determined via physiological monitoring and subjective assessments. The data confirmed that (1) warmer pre-sleep thermal environment within human thermoregulation range decreased sleep latency, (2) sleep fragmentation increased monotonically with thermal discomfort in bed climate, and (3) excessively warm sensation (higher than 0.8) was counter-productive for sleep quality improvement. Additionally, correlations between thermal sensation and thermal environments were determined, and the principles for pre-sleep and during-sleep thermal environment regulation were proposed, including consistency in key zones of bed climate and difference in heating intensity. The results provided implications with regard to human thermal perception control and personalized device usage for creating a suitable sleeping thermal environment.