A calculation method for the view factor between a wall and other feature surfaces under the influence of spherical canopy

Radiation heat transfer is one of the main modes of heat exchange for building exterior walls. When a tree is added to the site, the view factor (VF) between the exterior wall and surrounding surfaces, such as walls and floors, is affected, thus significantly impacting the radiation heat transfer of the exterior wall. In order to quantitatively analyze the impact of trees with spherical canopy on the radiation heat transfer process of exterior walls, a method for calculating the VF between the exterior wall and adjacent surfaces using the optical projection simulation method was proposed. The VF between the wall surface and the adjacent surface, as well as the visibility between the wall and ground surfaces when obstructed by the spherical canopy, can be approximately calculated. Finally, the VFs calculated are used to establish the radiation heat equations according to network diagram for radiation heat transfer. By comparing theoretical values with the measured values of irradiation intensity and radiosity intensity, it was found that the error rate of the optical projection simulation method does not exceed 3%. This method can be used to further study the effects of factors such as canopy's diameter, wall-canopy distance, and planting orientation on the disturbance of radiation heat transfer of building exterior walls.