Experimental study of draft-related local discomfort in a room with stratum ventilation

Abstract

Given increased air movement in rooms with stratum ventilation, draft may be a major cause of local thermal discomfort. However, there was a lack of comprehensive study on the draft risk of stratum ventilation and its causation. Hence, this study systematically conducted the subjective assessment of draft and examined its influencing factors in a stratum-ventilated room. Thermal sensation, preferences for air movement and air temperature, as well as thermal acceptability were surveyed. The subjects were exposed to different combinations of supply airflow rate and room air temperature, which created thermal conditions from slightly cool to slightly warm. Results showed that compared with supply airflow rate, room air temperature exerted more significant effects on the subjective responses to air movement. Regarding draft sensation, the upper body segments were more susceptible to supply airflow rate and room air temperature than the lower body segments. For room air temperature of 24 °C, the slightly cool sensation resulted in high draft rates, while room air temperature of 26 °C and above could significantly decrease draft risk. Air movement preference was closely correlated to overall thermal sensation. An overall thermal sensation value of −0.4 was found to be the lower limit to provide a draft rate less than 20%, and a value of −0.1 was the most desired overall thermal sensation as a majority of subjects wanted air movement to remain unchanged. Taking both the preferred air movement and temperature into account, room air temperature of around 26–27 °C was recommended to achieve satisfactory thermal environment.