The effects of programmed air temperature changes on sleep quality and energy saving in bedroom

Bedroom air-conditioning is often programmed to cause the air temperature to follow either a Rise-Fall or an inverted Fall-Rise shaped course during the night, and there are rational arguments for both. The effects of these two programmed air temperature changes were investigated by creating three thermal conditions: a reference condition with constant temperature (26 °C), a Rise-Fall change condition (26 °C-27 °C-28 °C-27 °C-26 °C), and a Fall-Rise change condition (28 °C-27 °C-26 °C-27 °C-28 °C). Twelve healthy young people (6 females and 6 males, mean age 23 years) slept in a climate chamber with multiple of their physiological parameters monitored continuously. No significant difference in thermal comfort or sleep quality was found among the three conditions. The subjects had better next-day performance in the Fall-Rise condition than in the other two conditions. Simulation results show that compared with the reference condition, the total cooling load of a simulated bedroom is reduced by 27.8% in the Rise-Fall and 34.3% in the Fall-Rise condition. These results indicate that a slight increase of air temperature within thermal comfort range during the later period of sleeping (as simulated in the Fall-Rise condition) could better prepare the body for wake up, and also could save energy.