EFFECTS OF DYNAMIC AIRFLOW ON HUMAN THERMAL PERCEPTION UNDER HOT ENVIRONMENT

Experiment with human subjects exposed to different square-wave airflows

Abstract

 Natural cross ventilation not only removes the heat load generated indoors, but also increases convective and evaporative heat loss from human skin to improve indoor thermal comfort of residential houses in the summer season. Opening of windows to increase air movement through cross ventilation has been always used as an environmental adaptive behavior in many countries including Japan. Existing research about fluctuating airflow mainly focused on sinusoidal or random airflow. This study investigated the perceptual and physiological responses of 10 college-aged subjects to square wave airflows of different cycles (2 min, 10 min and 30 min) under different temperature levels ( 28 ℃ and 32 ℃). Their thermal sensation, thermal comfort, thermal pleasure, and air movement sensation were investigated. In addition to subjective perceptions, a physiological parameter and skin temperature were also monitored. Main conclusions are obtained as follows:

 

 (1) The skin temperature difference among different body parts were smaller under the air temperature (32℃) than that under 28 ℃. The variation in skin temperature also showed an individual difference.

 (2) Under air temperature of 32 ℃, no subject reported “hot” thermal sensation when exposed to square-wave air flow with 2-min or 10-min cycles. However, subjects reported “hot” thermal sensation for 28% of the exposure time to airflow with 30-min cycle.

 (3) Subjects’ pleasantness showed a decreasing tendency under the square-wave airflow with 30-minute cycle period under both 28 ℃ and 32 ℃ thermal exposure. The mean pleasantness was highest in the condition of 32 ℃ air temperature with square-wave airflow (10-min cycle).

 (4) The mean thermal sensations reported by subjects were lower than corresponding PMV values, indicating the cooling effect of dynamic airflows on human thermal comfort in warm environment.

 

 In future research, it is necessary to increase sample size to enable analysis of the effects of gender and age on the cooling effect of cross ventilation on thermal comfort.