Solar radiation is a significant factor affecting indoor air-conditioning loads. When sunlight directly reaches the human body, it impacts the heat exchange between the body and the surrounding environment, consequently affecting thermal sensation. The change in temperature of an environment in which a body is in thermal neutrality is related to the energy consumption of the air-conditioning system and human thermal comfort. In this study, a winter experiment was conducted in an artificial climate chamber using a solar radiation simulation device to control the intensity of the solar radiation. The subjects wore typical clothing and performed sitting and walking tasks (at speeds of 3.2 km/h and 5 km/h). Physiological parameters and thermal sensation questionnaires were analyzed to determine the heat exchange characteristics between the bodies and the surrounding environment under the combined effects of solar radiation and different activity levels. Further more, the displacement law of the thermal comfort zone was examined. The results showed that, compared with the case of solar radiation, as the activity level increased, the proportion of evaporation heat exchange increased, the proportions of convective heat exchange and radiant heat exchange decreased, the thermal comfort zone shifted downward, and the environmental temperature required to maintain a comfortable state in winter decreased. This study provides a reference for design parameters to improve the efficiency of air-conditioning systems.

Human thermal regulation models reflect the physiological response of the human body to the surrounding thermal environment. However, existing thermal regulation models do not account for the non-uniform impact of solar radiation on indoor thermal environments and the human body. Therefore, a new model was established by modifying the thermal regulation model of the human body to include local exposure to direct sunlight in buildings. First, the calculation of mean radiant temperature was revised by distinguishing direct and indirect areas. Second, the calculations of skin and clothing temperatures and heat loss in the model were modified by distinguishing direct and indirect parts. In addition, solar radiation heat gain was added to the heat transfer calculations. After experimental verification, the modified model demonstrated a relative error of less than 5% in predicting mean skin temperature, and approximately 4% in predicting total heat loss. Using the model, the mean skin temperature at different activity levels was predicted, and the thermal comfort zone offset laws of the human body as a whole and in direct parts were explored at different solar radiation intensities. The results show that the acceptable air temperature of the overall body at 400 W/m² is 2 ℃ lower than that at 200 W/m². This study provides a theoretical basis for zoning control of indoor environments under direct sunlight.