The effects of local body cooling on thermal comfort and sleep quality in a hot environment were investigated in an experiment with 16 male subjects. Sleep quality was evaluated subjectively, using questionnaires completed in the morning, and objectively, by analysis of electroencephalogram (EEG) signals that were continuously monitored during the sleeping period. Compared with no cooling, the largest improvement in thermal comfort and sleep quality was observed when the back and head (neck) were both cooled at a room temperature of 32°C. Back cooling alone also improved thermal comfort and sleep quality, although the effects were less than when cooling 1,2 Disturbed nocturnal sleep also has consequential effects on health, increasing the risk of obesity, Type 2 diabetes, and cardiovascular disease. 3,4 The thermoregulatory system and the sleep regulating mechanisms have been shown to be strongly linked in humans, 5,6 and this was later confirmed by many studies that show high or low air temperatures, even moderately different from the neutral temperature, could significantly decrease sleep quality. 7-10 However, in many areas with long and hot summers, indoor air temperatures are very high. For example, in southern China, the indoor air temperature was found to be higher than 34°C in natural ventilated buildings during the summer season. 11 A survey in Indonesia found that the indoor air temperatures were higher than 32°C in naturally ventilated residential buildings. 12 Global warming that leads to higher temperatures will create still hotter indoor conditions. Attention is now being paid to how climate change may degrade the indoor thermal environment in buildings.13 It has been reported that heat-related deaths correlate, not just with daytime temperature, but also with nighttime temperatures. The highest risk factor for heat-related death is a bedroom located on the second floor without air-conditioning. 14 A study in 79 households in Greenland showed that in summer 19% of all bedroom temperature were above 26°C although the outside temperatures averaged no more than 9.5°C.
15Full air-conditioning may be one of the easiest ways to improve thermal environment. However, large amounts of cool air (often recirculated room air, for residential buildings) must be supplied to maintain indoor temperatures at acceptable levels in the entire building (including unoccupied areas), leading to increased energy consumption.
16Thus, especially in areas with hot summers, the long summer period
