Influences of variable thermal exposures on walking thermal comfort in hot summer - Physio-psychological responses

To improve walkability in warm-biased cities, it is important to study thermal comfort experienced by walking pedestrians in complex urban continuums with variable microclimates. In this study, the heat exchange between a walking human body and its variable ambient was studied by measuring 70 human subjects' skin temperatures, sweating, heart rates, and surveying their mixed thermal perceptions, and monitoring the meteorological parameters in their immediate surroundings in two complex urban continuums. The extent of variable thermal exposures characterized by simultaneously varying wind and solar radiation during walking was described by the index Reverse Dynamic Thermal Environment (R_DTE), and its impacts on the physio-psychological responses of the human subjects were studied. It is concluded that about 36% of produced heat would be accumulated within the body during a 10 min' walking under variable thermal exposures with an air temperature over 28.0 °C. The sweating rate is highly related to the R_DTE rather than the mean skin temperature deviation from the neutral one (ΔT_sk). An increased extent of variable thermal exposures significantly improves the thermal comfort when a walking person's skin wettedness (w) is over 0.4, whereas it causes discomfort when w is below 0.2. While some more work are still needed to further understand the dynamic thermal responses, these preliminary findings shed light on assessing and improving walking thermal comfort by creating variable thermal exposures in the urban continuums on hot days.