Subjective and objective quality of sleep with radiant or convection cooling systems: a randomized, cross-over trial

Sleep is influenced by environmental factors, and hot ambient temperature undermines sleep quality. Considering the global warming, it becomes increasingly important to keep bedroom temperature cool in the summer. Today, two electrical cooling systems are available: convection and radiant. Convection air cooling system supplies cooled air-flow. Radiant cooling system cools the room through radiation from the cooled surfaces, moisture condensation on which is prevented by reheated refrigeration cycle system. The present study was a randomized, cross-over trial setting room air temperature at 26 ℃ to compare subjective and objective quality of sleep between convection and radiant cooling in 7 healthy women. Subjective and objective quality of sleep were assessed by Oguri-Shirakawa-Azumi Sleep Inventory and EEG-based sleep parameters, respectively. Compared with convection cooling, radiant cooling provided lower relative humidity and air flow. Refreshness, one of the 4 indices of subjective quality of sleep, was higher with radiant cooling. Among the EEG-based sleep parameters, sleep efficiency was higher and sleep latency was shorter with radiant cooling. In spite of similar ambient room temperature, difference in cooling (radiant vs. convection) and/or dehumidifying (ordinary air conditioning vs. reheated refrigeration cycle) method provided difference in thermal comfort affecting subjective and objective quality of sleep.