Field assessment of winter outdoor 3-D radiant environment and its impact on thermal comfort in a severely cold region

According to the Code for Design of Civil Buildings (GB 50352-2005), the severely cold region of China is defined as the area where the monthly mean air temperature is lower than or equal to −10 °C in January, and is lower than or equal to 25 °C in July, and mean relative humidity is higher than or equal to 50% in July. This study investigates outdoor 3-D short- and long-wave radiant flux densities (K_i and L_i) from six perpendicular directions, and their effects on human thermal comfort during winter daytime in a severely cold region of China. Mean radiant temperature T_mrt, the representative parameter of the radiant environment, was determined by the “six-directional method”. Physiologically Equivalent Temperature PET, and Universal Thermal Climate Index UTCI were used to quantify denizens' perception of the thermal environment, particularly the response to the outdoor radiant environment. Results showed that building obstacles significantly influenced K_i and L_i components, and thus T_mrt, and human thermal comfort and stress. The absorbed long-wave radiant flux densities by human body especially those from the horizontal directions primarily affected the magnitude of T_mrt, while the absorbed short-wave radiant flux densities by human body mainly governed the fluctuation of T_mrt. Furthermore, a simplified method of estimating T_mrt for the severely cold region was obtained from two representative radiant variables. The consideration of T_mrt as an independent variable to represent the radiant environment can be used to accurately estimate PET and UTCI in winter in the severely cold region.