Virtual wall: Numerical model on interaction between trees and building façade to quantify heat exchange and microclimate in urban context

When simulating a building's energy demand, the tree surroundings should be accounted in their shade and reshaping microclimate, just representing an envelope layer as a virtual wall. This study delves into the effects of such tree-induced virtual walls on building energy dynamics, with a dataset derived from 24 distinct samples of building façades and adjacent trees within a campus environment. An experiment was designed to validate microclimate simulation that captures variations in sheltered radiation and temperature reductions. The study introduces and calculates the dynamic and static equivalent heat transfer coefficients and thermal resistances for the virtual wall. The findings reveal significant correlations between the calculated coefficients and resistances, and various factors such as seasonality, weather conditions, and façade orientation. The equivalent thermal resistance value for south façade is highest on sunny days, reaching up to 3.7 m2·K/W, and on cloudy days, east façade has the highest equivalent heat transfer coefficient and thermal resistance values, at around 8.5 W/m2·K and 10.3 m2·K/W, respectively. Moreover, the study reveals that the tree's impact is primarily determined by its height and canopy area, with the equivalent heat transfer coefficient negatively correlated with tree height and canopy area, and positively correlated with building height.