Transient human thermophysiological and comfort responses indoors after simulated summer commutes

Zhai, Y.C., Zhao, S., Yang, Y., Wei, N., Xu, Q., Zhang, H., Arens, E , Building and Environment ,157 (2019), 257-267

The current study investigates the transient human physiological and comfort responses during sedentary activity following a period of elevated activity in a hot condition. Such metabolic and thermal down-steps are common in buildings as occupants arrive after commuting in summer. It creates a serious problem for thermostatic control, since arriving occupants find their transition uncomfortably warm at temperatures that resident occupants find comfortable. Fifty-nine participants (29 men, 30 women) dressed in 0.6 clo were tested while sedentary for 60 min in 26 °C, after having been exposed to 30 °C for 15 min, during which they performed activities metabolically simulating commuting: sitting (SE - 1.2 met), or doing three levels of stair-step exercises: low (LEx- 2.2 met), medium (MEx - 3.0 met), and high (HEx - 4.4 met). Subjective comfort and physiological responses (metabolic rate, skin temperature, skin blood flow rate, heart rate, core temperature, and skin wettedness) were collected. Results show that sedentary conditions at 26 °C became comfortable and acceptable within 2 min, but thermal sensation required much longer to change from ‘warm’ or ‘hot’ to ‘neutral’: 0, 8, 17, 30 min after SE, LEx, MEx, HEx respectively. Skin wettedness and core temperature did not recover within the 60 min. The delays are mainly due to body heat stored during the exercise. A room temperature of 26 °C may not provide sufficient cooling after summer commuting. Localized convective cooling of transitional spaces and work areas by ceiling or desk fans represent a way to enhance comfort recovery.

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