The effect of thermal transience on the perception of thermal comfort

Introduction: The present study tested the hypothesis that at any given ambient temperature (Ta), thermal comfort (TC) is not only a function of the temperature per se, but is also influenced by the temperatures rate of change and direction. Methods: Twelve healthy young (age: 23 ± 3) male participants completed experimental trials where Ta increased from 15° to 40 °C (heating) and then decreased from 40 to 15 °C (cooling). In one trial (FAST), the rate of change in Ta was maintained at 1 °C.min⁻¹, and in the other (SLOW) at 0.5 °C.min⁻¹. During each trial participants provided ratings of TC at 3-min intervals to determine their thermal comfort zone (TCZ). Results: In the FAST trial, participants identified TCZ at an Ta between 22 ± 4 and 30 ± 4 °C during heating and between 25 ± 3 and 33 ± 3 °C during cooling phase (p = .003), and in the SLOW trial between 21 ± 3 and 33 ± 4 °C during heating and between 23 ± 4 and 34 ± 3 °C during cooling phase (p = .012). During the heating phase TCZ was established at a lower range of Ta, compared to cooling phase. The difference between the heating and cooling phases in preferred range of Ta was more pronounced in the FAST compared to SLOW trial. Conclusion: TCZ is influenced not only by the prevailing temperature, but also by the direction and the rate of the change in Ta. Faster changes in Ta (1 °C.min⁻¹) established the TCZ at a higher Ta during cooling and at a lower Ta during heating phase.