Effects of indoor thermal exposure on human dynamic thermal adaptation process

Abstract

The effects of indoor thermal exposure on human thermal adaptation is a time-dependent process, and deconstructing the human thermal response in a dynamic process helps to reveal the thermal adaptation mechanism. Although many researchers have studied human thermal comfort under different indoor thermal conditions in cross-sectional field investigations, the temporal variation of the human thermal response in the adaptation process remains to be further studied. To study the combined effect of indoor thermal stress and exposure duration on human thermal adaptation, a follow-up study was performed on 30 subjects for nine weeks: they were exposed to three different heating intensities in winter (unheated room, low-level heated room, and high-level heated room). Subjects’ physiological responses to the thermal environmental changes were monitored, and psychological assessment was conducted with questionnaires at indoor temperatures of 14, 18, and 22 °C in a climate chamber in each week. The results showed that indoor thermal exposure exhibited a temporal cumulative effect on human thermal adaptation, and the physiological and psychological adaptation processes were not necessarily synchronous. Prolonged indoor cold exposure not only increased the acceptability of human body to cold exposure, but also elevated the vigilance to warm exposure; skin temperature was increased and sympathetic activity was decreased characterized by lower LF/HF ratio in cold exposure. The research results provide implications for the control of indoor thermal environments based on human adaptability.