Establishment and validation of a solar radiation model for a living wall system

Abstract

Living wall systems attached to building facades act as energy barriers by blocking solar radiation. Light goes through the plant canopy and reaches the substrate surface instead of the building wall. The amount of solar radiation that reaches the substrate surface dictates the amount of heat transferred indoors, which affects the energy efficiency of the building envelope. The leaf inclination and leaf area index (LAI) describe the structural features of the canopy, which affects transmittance of radiation. The fraction of radiation intercepted by a canopy and the fraction transmitted to the substrate surface can be modeled based on the geometric parameters of the plants and the canopy's relative position to the sun. By modifying Campbell's ellipsoidal model, a new living-wall solar radiation (LWSR) model that computes solar transmission in vertical canopies was established. The model's accuracy was evaluated against experimental measurements of a living wall in Wuhan, China, through spring, summer, and fall. The simulated values were closer to the actual value and the accuracy was higher in comparison with Campbell's ellipsoidal model. The LWSR model can simulate living walls with different orientations and canopy structures. The simulation results reflect different magnitudes of radiation attenuation by living wall canopies as a function of leaf inclination and LAI.