Thermal and draught perception in fluctuating stratified thermal environments with intermittent impinging jet ventilation

This study proposes a new integrated air supply strategy of impinging jet ventilation (IJV) and intermittent airflow to improve indoor thermal comfort. Vertical thermal stratification is created by the IJV, and a fluctuating thermal environment is created by the intermittent airflow. Three pulsating periods (3 min, 5 min, and 7 min), two supply air temperatures (18 degrees C and 16 degrees C), and four air supply velocities (1.8 m/s steady, 1.5/2.1 m/s, 0.9/ 2.7 m/s, and 0/3.6 m/s) were designed. In both steady and fluctuating indoor environments, fifteen college students were asked to report their perceptions of thermal sensation, thermal comfort, thermal preference, ankle air movement acceptability and preference, and perceived air quality. The results showed that pulsating airflow could lower the mean air temperature above 0.6 m and raise it below 0.6 m. Furthermore, pulsating airflow could reduce overall and local thermal sensation by up to 0.21 and 0.28 scale unit, respectively, and the thermal sensation difference between the head and the foot by up to 0.23 scale unit. While in neutral thermal conditions, the pulsating period of 3 min had the best cooling effect of the 10 cases, but the corresponding percentage of mean dissatisfied ankle draught was 4.3% higher than in the steady operation case. Draught sensation is so closely related to ankle thermal sensation that extending the pulsating periods to 5 or 7 min could reduce ankle draught risk by up to 12.3%. The perceived air quality did not differ significantly between the steady and intermittent cases. The intermittent operation of IJV was shown to have superior cooling performance in order to improve indoor thermal comfort.