Sleep thermal comfort and the energy saving potential due to reduced indoor operative temperature during sleep

The optimal human body thermal conditions for comfortable sleep differ significantly from the optimal body thermal conditions for being awake. With the body covering such as a blanket representing a higher insulation value than the typical indoor attire suggests that a significant indoor temperature reduction during sleep may be available. With known skin temperature and heat loss rate required for comfortable sleep, a numerical model was developed for a 50th percentile male to calculate the desired thermal environment for sleep. The results show that the thermal environment represented by the operative temperature of the room can be reduced to around 15 degrees C to maintain sleep thermal comfort. This is significantly less than the thermal environment required by the building codes and ASHRAE comfort standard, which suggests that the heating system output may be reduced, which translates to potential energy savings and improved quality of thermal environment for sleep thermal comfort. As a part of a field study, data collected from a radiant ceiling heated house show that the operative temperatures exceed the desired thermal environment conditions for comfortable sleep. A calculation on the peak heating day with the building characteristics was performed with reduced heating set points during sleep. It was found that up to 10% of the heating energy may be reduced. The eQuest energy simulations show that an approximately 2% saving in total space heating demand can be achieved for 1 degrees C set-point reduction during the 8 h nighttime. (c) 2012 Elsevier Ltd. All rights reserved.