Effect of change rates and directions of air temperature ramps on thermal responses of occupants under warm summer conditions

Understanding thermal comfort in dynamic environments is vital for developing various air temperature control strategies that consider energy flexibility. However, studies on the quantitative effects of air-temperature change rates and directions on human thermal responses in thermal environments with temperature ramps (TRs) are limited. In this study, 22 sex-balanced young adults were recruited to investigate the thermal perceptions and physiological responses to room air TRs at rates of 0.10–0.30 °C/min in a climate chamber. The results revealed that the air temperature change direction had no effect on the mean skin temperature (T_skin) but significantly affected the thermal sensation vote (TSV), that is, the TSV was approximately 0.5 scales lower when the temperature was decreasing than when it was increasing (P < 0.05). Moreover, the slow change rates of T_skin within the range of ±0.07 °C/min had no significant effect on dynamic TSV, unlike that in step-change environments with higher change rates. The head was the most thermally sensitive body part with the highest TSV/T_skin values and change rates of T_skin (up to ±0.08 °C/min) in warm TR environments. In most cases, the thermal response of limbs was delayed. The thermal experience and adaptation levels of occupants may play essential roles in thermal perceptions within TR environments. Preliminary thermal comfort models suitable for hot summer climates were proposed in this study, which could be used in TR control strategies, such as intermittent cooling or demand response control.