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 (SleepingbagHT) and the smart sleeping bag with power turned off (SleepingbagCON). 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 SleepingbagHTcould 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 SleepingbagCONwithin 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.