Cooling effect of elevated ambient air velocity on thermal comfort when sitting after walking

Sitting after walking is a common combination of activities in temporally occupied spaces (TOSs). The heat accumulated during walking can deteriorate the thermal comfort of occupants who sit for <= 15 min in the TOSs. Compared to reducing the ambient temperature, increasing the ambient air velocity may ensure thermal comfort and energy saving in TOSs. However, previous studies and current standards failed to consider the cooling effect of air movement for dwell times <= 15 min after walking. In this study, 20 male college students walked at 4 km/h for 15 min at 26 degrees C and 0.05 m/s. They then sat for 15 min in two operative temperatures (26 degrees C and 29 degrees C) and five levels of ambient air velocity (0.05 m/s, 0.42 m/s, 0.67 m/s, 0.92 m/s, and 1.08 m/s), for a total of 10 environmental combinations. The relative humidity was controlled in the range of 35-50%. The results showed that ambient air velocities of 0.42-0.67 m/s and 0.92-1.08 m/s could compensate for operative temperature drops of 3 degrees C and 6 degrees C, respectively, after sitting for <= 15 min during summer. The neutral, preferred, and acceptable ambient air velocities were compared. The predicted mean vote considering the cooling effect of the elevated airflow in ASHRAE Std. 55 overestimated the thermal sensitivity of the occupants. A summer comfort zone for the condition of sitting for <= 15 min after walking was obtained to guide the environmental design of TOSs.

Automated summary

Sitting after walking is a common activity combination in temporally occupied spaces. Increasing ambient air velocity can enhance thermal comfort and energy saving in these spaces. However, the cooling effect of air movement after walking for less than 15 minutes has been overlooked in previous studies and standards.