Study on the daily thermal radiation iso-disturbance on a building by trees in summer

Abstract

Many studies have demonstrated that the cooling and energy-saving effects of planting trees around buildings vary depending on their location. However, most research has focused on a limited number of representative planting sites. This study evaluates the reduction in thermal radiation absorbed by walls over a single day due to trees, defined as daily thermal radiation disturbance (T_RDD). Using a combination of experiments and ENVI-met software simulations, we established a coordinate system to map the T_RDD distribution of trees at various locations around a building. The findings reveal that trees at different locations exhibit isoT_RDD lines, which are symmetrical about the building’s centerline. Trees planted along these isoT_RDD lines exert equal effects on T_RDD. The isoT_RDD lines form a series of ellipses that decay in two stages with increasing distance between the tree crowns and the walls (D_W-T): rapid decay when D_W-T is less than 3 m and slower decay beyond 3 m. Additionally, we found a linear positive correlation between the change in the sky view factor (ΔSVF) on the wall surface caused by trees and the T_RDD. Trees near the north and south walls, as well as those along the building's diagonal, primarily block sky-scattered radiation (R²>0.97). Trees around the east and west walls block both sky-scattered and direct solar short-wave radiation (R²>0.85). This indicates a significant relationship between isoT_RDD and SVF of the building. The methodology proposed in this study allows for a comprehensive assessment of the spatial evolution of T_RDD for trees around the building, providing a scientific basis for the spatial design of trees to optimize cooling and energy savings. Moreover, the relationship between ΔSVF and T_RDD enables rapid calculations and comparisons of the cooling effects of trees at different locations.