Experimental study on thermal comfort of sleeping people at different air temperatures

• We investigated thermal comfort and sleep quality in human subjects.
• Human sleep quality was sensitive to change of air temperature.
• Skin temperature increased with air temperature during the sleeping period.
• The thermal neutral temperature of sleeping people was higher.

Current thermal comfort theories and standards are mainly concerned with people in waking state. The effects of air temperature on sleep quality and thermal comfort of sleeping people were investigated in this study by experimenting on human subjects. Sleep quality was evaluated by subjective questionnaires performed in the morning as well as electroencephalogram (EEG) signals, which were continuously recorded during the all-night sleep period. Subjective assessments on thermal comfort were performed both before and after sleep. Analysis on EEG signals indicated that the subjects took longer time to fall asleep and experienced shorter period of slow wave sleep (SWS) when the room temperatures moderately deviated from neutral. Consistently, they reported poorer subjective sleep quality in such conditions. The returned subjective questionnaires on thermal comfort from subjects reflected that the thermal comfort temperature was higher in sleep compared with that in waking state. Their skin temperatures were increased with air temperature and fluctuated during the sleeping period. In view of the distinctive requirements from waking people, it makes sense to study the thermal comfort of sleeping people. The results also have practical implications on energy savings in bedrooms.