Designing a smart electrically heated sleeping bag to improve wearers’ feet thermal comfort while sleeping in a cold ambient environment

In this study, a novel smart electrically heated sleeping bag was developed by incorporating a proportional–integral–derivative heating control system into a traditional sleeping bag. The smart sleeping bag was aimed to maintain human feet temperature within the thermoneutral range (i.e. 25.0–34.0℃) by automatically adjusting the heat power to the feet region based on real-time human toe temperatures. Subsequently, the performance of the newly developed smart sleeping bag in improving human thermal comfort was investigated by human trials. Eight female subjects underwent two 8-hour sleep trials, that is, the smart sleeping bag with power turned on (Sleepingbag HT ) and the smart sleeping bag with power turned off (Sleepingbag CON ). All trials were performed at an air temperature of 6.1 ± 0.5℃ (i.e. the EN 13537 defined comfort temperature for females), relative humidity of 80 ± 5% and air velocity of 0.4 ± 0.1 m/s. It was found that Sleepingbag HT could maintain both the foot and toe temperatures within the thermal neutral range as well as keep the local-, and whole-body thermal and comfort sensations in thermal neutral state throughout the 8-hour cold exposure. In contrast, linearly decreasing foot and toe temperatures and aggravated local-, and whole-body thermal and comfort sensations were detected in Sleepingbag CON within a 4.5-hour cold exposure. It could thus be concluded that the smart electrical heating sleeping bag was able to provide wearers an 8-hour comfortable sleep in the studied cold environment.