Short-term dynamic thermal perception and physiological response to step changes between real-life indoor and outdoor environments

Dynamic thermal environments may achieve higher thermal comfort levels than steady-state conditions. This is attributed to the impact of thermal alliesthesia and short-term adaptation phenomena on thermal perceptions. However, few studies have explored the combined effect of these two phenomena in transient environments. This study examined the short-term dynamic thermal perceptions and physiological responses of 50 subjects exposed to step-change indoor and different outdoor environments, including underneath an elevated building (UEB) and sunlit areas. Environmental parameters were monitored using a microclimate station, while physiological parameters were characterized by mean and local skin temperatures and sweat rate. Results show that short-term transitions lead to thermal alliesthesia and adaptation. When thermal environment changed, overshoot in thermal sensation persisted for at least 5 min, and its influence on thermal comfort increased and then diminished at around 5 min, at which point thermal adaptation began to occur. The current thermal comfort was affected by the preceding thermal status: in the strong alliesthesia zone, a 1.00 scale decrease in dTSV resulted in a 0.44 scale increase in dTCV; whereas in the moderate alliesthesia zone, a slight dTSV within 1.00 scale could positively affect dTCV. Skin temperature of exposed segments correlated better with TSV than those of unexposed ones. Still, skin temperatures had lower correlations with TSV compared with other static experiments. Besides thermal alliesthesia and adaptation effects, sweat accumulation and evaporation are possible reasons for the low correlations. The findings may have implications in adopting dynamic features outdoors for better design of thermal environment.