Distribution of Incident Solar Radiation and Temperature of Ground Surface Surrounded by Buildings

Abstract

Ground surface temperature is a major element of the thermal environment, that is, atmospheric temperature and radiation to building or human body, and its characteristics should be predicted. While most former studies on this problem have focused on the thermal characteristics of surface materials, the amount of absorbed solar radiation which is converted to ground surface temperature also varies with the surrounding buildings which cut off the insolation. This study investigates the calculation method and characteristics of actual incident solar radiation and ground surface temperature in built up areas. First, after considering the sky factor, incident solar radiation and interreflection between walls and ground surface, the thermal characteristics of the ground surface in a two dimensional urban canyon are clarified. (1) The smaller the ratio of wall height to floor (ground surface) width, the larger the change of sky factor and incident solar radiation. (2) Floors in a east-to-west canyon are exposed to the largest amount of solar radiation in the summer and the smallest in the winter. This is opposite for north-to-south canyon. (3) The influence of interreflection between walls and floor on the rise of floor temperature is small compared to the influence of road orientation and the ratio of wall height to floor width. (4) The highest floor surface temperature in an east-to-west canyon may appear not in midday but after sunrise or before sunset. Subsequently, after the methods of calculating the distribution of the sky factor, incident solar radiation and ground surface temperature in three dimensional urban space are mentioned, the incident solar radiation and ground surface temperature in the Shinjuku area with many high rise buildings are investigated as a case study. Especially, the calculated distribution of ground surface temperature is compared with the thermal infrared image obtained by aircraft remote sensing. (5) The sky factor on the ground surrounded by high rise buildings in the Shinjuku area is 0.2〜0.6. (6) The ratio of incident solar radiation per day to total horizontal radiation is 0.2〜0.7. (7) Calculated distribution of ground surface temperature roughly agrees with the thermal infrared image. Consideration of incident solar radiation is as indispensable as that of materials for estimating the thermal environment.