The effects of personal comfort systems on sleep: A systematic review

Creating a comfortable thermal environment is the necessary measure to safeguard human sleep quality but it requires a substantial amount of energy. Personal comfort systems have the potential to improve sleep while significantly reducing energy consumption compared to typical air conditioning systems. Despite some studies reporting favorable outcomes when using personalized approaches to cooling or heating in bedrooms, a comprehensive summary of the impact of personal comfort systems on sleep is lacking. This systematic review of 25 sleep studies estimates the effect of personal comfort systems on sleep quality, sleep stages and sleeping thermal comfort. Configuration of personal comfort systems and sample characteristics are summarized and compared. Calculated effect sizes show that using personal comfort systems are generally effective in improving sleep quality and sleeping thermal comfort. However, there are potential negative effects of personal heating on slow wave sleep and personal cooling on pre-sleep thermal comfort. Relatively mild contact temperatures for both heating and cooling and steady air velocities below 0.9 m/s in warm environments are preferred. The head and feet are the most frequently targeted body parts for cooling and heating, respectively. Most subjects were aged between 17 and 40 years, suggesting a lack of data for both children and the elderly. Four future research directions are proposed: personal cooling at pre-bed phase, human subject tests with radiant systems, dynamic control strategies, and application of machine learning approaches.