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 15min, 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 the60 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.
People often feel uncomfortably warm and sweaty in their workspace after commuting there by walking or cycling in summer. This is because body heat stored during the commute takes a substantial time to dissipate. People complaining about this uncomfortable transition may cause operators to lower the thermostat setpoint, causing long-term overcooling and wasting energy. In addition, space cooling is slow, requiring minutes to take effect. This study addresses how to improve comfort in the transition by increasing the availability of convective cooling, where the response time is in seconds. Thirty-five subjects (17 men and 18 women) dressed in 0.6 clo entered a test room after exercising at 4.4 met for 15 min in 30 ºC. The exercise emulates the commute activity in summer. The test room was controlled to 24, 26, and 28 ºC, with and without the option of cooling using fan-produced horizontal airflow. Subjects were sedentary for 60 minutes, during which subjective thermal responses and physiological responses were measured. The enhanced convective and evaporative heat loss caused by fans significantly shortened the time needed to reach thermal comfort after the exerciseinduced thermal stress and improved the final comfort level. Compared to a typical indoor condition of 24 ºC and still air, 26 and 28 ºC with fans provided equal or better comfort more quickly, and inherently required much less energy to do so. Our study suggests that personally controlled air movement should be available in spaces where thermal and metabolic down-steps take place.
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