Modeling the Hygrothermal Behavior of Green Walls in Comsol Multiphysics®: Validation Against Measurements in a Climate Chamber

Urban heat islands (UHI) impact human health and increase energy consumption. Urban vegetation and green walls (GW) can counteract UHI. A GW consist of vegetation and substrate compartments mounted on the outer leaf of a building wall. Three main GW benefits decrease the building’s surface temperature: shading, insulation, and evapotranspiration. The latter is a challenging calculation when modeling their hygrothermal (heat and moisture) behavior. This work aims to model and validate the hygrothermal behavior of GW by integrating a multiphysics model coupling heat and moisture transport equations in Comsol Multiphysics®. In the model, heat sink terms represent plants' and substrates' transpiration and evaporation. The model’s output (temperature) is compared against experimental measurements from four green wall-test panels (GW-TPs) evaluated in a climate chamber. The model showed that the GW-TPs reduced the temperature at the GW substrate's rear by 0.57 ± 0.15 °C and at the building's surface from 0.89 to 1.14 °C, wherein the air cavity accounts for a major proportion. However, the reductions are low compared to previous work, which might be explained due to the boundary conditions as radiation was not considered. Leaf area density (LAD) and substrate’s water saturation (Sr) were varied, obtaining higher temperature reduction of the building’s surface as the parameters’ values increased.