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 (TRDD). Using a combination of experiments and ENVI-met software simulations, we established a coordinate system to map the TRDD distribution of trees at various locations around a building. The findings reveal that trees at different locations exhibit isoTRDD lines, which are symmetrical about the building’s centerline. Trees planted along these isoTRDD lines exert equal effects on TRDD. The isoTRDD lines form a series of ellipses that decay in two stages with increasing distance between the tree crowns and the walls (DW-T): rapid decay when DW-T is less than 3m and slower decay beyond 3m. 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 TRDD. 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 isoTRDD and SVF of the building. The methodology proposed in this study allows for a comprehensive assessment of the spatial evolution of TRDD 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 TRDD enables rapid calculations and comparisons of the cooling effects of trees at different locations.