Horizontal Heat Impacts of a Building on Various Soil Layer Depths in Beijing City

Abstract

There is a lot of research on the urban thermal environment, mainly on air temperature. However, fewer studies focus on soil temperature that is influenced by built environment, especially on the horizontal heat impacts from buildings. In this research, soil temperature was investigated at different depths in Beijing, China, to compare the differences between two locations. One was next to the building and the other was far away from the building (10 m). The locations are referred to as site A and site B, respectively. These two sites were chosen to compare the differences in soil temperatures between them to present the horizontal heat impact from facade. The results show that facades caused horizontal heat impacts on the soil at different depths in the winter, spring, and summer. Basically, facades functioned as heat sources to the soil surrounding them. The mean temperature differences between the two sites were 3.282, 4.698 and 0.316 K in the winter, spring and summer, respectively. Additionally, the thermal effects of the buildings were not only exhibited as higher soil temperatures but the temporal appearance of the maximum and minimum temperature was also influenced. Buildings functioned as heat sources to heat soil in the winter and spring and stabilized soil temperature so that it would not fluctuate too much in the summer. Additionally, the coefficient of variation indicates that buildings primarily increased the soil temperature in the winter and spring and stabilized the soil temperature in the summer.

Horizontal heat impacts of a bare facade on air temperature in an adjacent green plot within pedestrian heights in Beijing

“…Equation (12) indicates that the higher the surface temperature is, the higher the sensible heat flux. The higher surface soil layer temperature at site A in the former study 39 corresponded to the higher surface temperature. For the air temperature, the mean values were 302.89 K and 302.78 K (the difference was 0.11 K) for site A and site B, respectively, indicating the horizontal heat flux from the facade.…”

“…The horizontal heat impact from the facade increased the rate of air warming in the surrounding area at various heights, which was a result similar to the high increasing rate of surface soil layer temperature recorded in this study, as well as the temperature difference between surface soil layer at site A and site B in former research. 39 This result means that the facade heated the adjacent air and soil horizontally. The surface temperature of the facade would affect the surrounding air temperature and surface soil layer temperature.…”

“…Similar levels of solar radiation and atmospheric counter radiation did not account for that difference. Nevertheless, the ground radiation was higher at site A than at site B due to the different surface soil layer temperatures, 39 which were caused by the horizontal heat flux between the building and soil. Therefore, under the stronger ground radiation and horizontal heat impacts, the DT a varied with a larger range at 0.02 m than at any other heights.…”

“…According to the black body radiation law, 40 the ground radiation is directly related to the surface soil layer temperature. According to continuous monitoring, the average soil surface layer temperature was 287.51 and 300.66 K in the spring and summer, respectively, 39 indicating lower ground radiation in the spring than in the summer. Similar phenomena were observed in previous studies.…”

“…According to a previous study conducted at the same time and place as this research, the average surface soil layer temperatures at site A and site B were 301.10 and 300.66 K (the difference was 0.44 K), respectively. 39 The sensible heat flux could be calculated with equation (12) 51,52…”