Effects of solar radiation on human thermal comfort under different activity intensities —— a chamber study

Global warming and accelerated urbanization have exposed urban residents to more severe threats of heat waves and extreme high temperatures. During daily commuting, people are inevitably exposed to solar radiation environments, enduring prolonged direct solar exposure, which poses significant health risks. This study investigates the thermal comfort of outdoor populations under varying activity intensities using an artificial climate chamber equipped with a solar radiation simulation device. By analyzing subjective evaluations of the thermal environment and physiological parameter changes, the relationship between physiological parameters and thermal sensation in active populations is explored. Results reveal a strong linear correlation between thermal sensation and metabolic rate under direct solar radiation. At an activity intensity of 4 km/h, the goodness-of-fit R2 values for thermal sensation and metabolic rate under solar radiation levels of 0 W/m2, 300 W/m2, and 500 W/m2 are 0.896, 0.882, and 0.759, respectively. The correlation between thermal sensation and mean skin temperature yields an R2 of 0.681, with the comfortable mean skin temperature range for the population identified as 33.75°C–34.15°C. Compared to active individuals (4 km/h), solar radiation exhibits a more pronounced impact on the thermal sensation of standing populations.