Elevated airflow can maintain sleep quality and thermal comfort of the elderly in a hot environment

The effect of elevated airflow on sleep quality was investigated with 18 elderly. Three airflow conditions were set: ceiling fan/30°C/max.0.8 m/s and mean 0.7 m/s, task fan/30°C/max.0.8 m/s and mean 0.6 m/s, and thermally neutral /27°C/0.2 m/s. Sleep quality was evaluated objectively by analysis of electroencephalogram signals that were continuously monitored during the sleeping period. Urinary cortisol concentrations were analyzed to measure the activity of sympathetic nervous system. No significant difference in sleep quality, thermal comfort, or cortisol concentration was found between the ceiling fan and the neutral condition. The duration of total sleep time decreased by 35 minutes, the duration of REM sleep decreased by 15 minutes, and the cortisol concentration in the morning increased by 50 ng/mL in the task fan than the other two conditions. Compared with ceiling fan, less heat load was removed in the task fan condition, possibly due to the lower air speed. This study shows that even small heat load led to reduced sleep quality and overactive sympathetic nervous system of the elderly. By supplying an airflow of 0.8 m/s evenly over the human body, the elderly could maintain sleep quality and thermal comfort at an air temperature that was 3 K higher than the neutral temperature.