Influence of plant coverage on the total green roof energy balance and building energy consumption

This study quantifies the influence of green roof plant coverage on the building energy consumption and the substrate energy balance components. The analysis started with the implementation of a green roof model that accounts for the effects of plant coverage into the U.S. Department of Energy (DOE) building energy simulation program, EnergyPlus. Using the DOE reference building models, thirty different cases were simulated considering different green roof plant coverage, building type, and building age for two different climates. The results indicated that the green roof substrate surface temperature decreases with increasing plant coverage. This temperature decrease is primarily due to the decrease in the amount of absorbed solar radiation on the substrate surface and also an increase in the substrate surface evaporation. For the base-case simulation, due to the plant shading effects, the total daily received radiation at the bare-soil surface is 32% (6.2 kWh m−2) higher than that at the fully-covered green roof substrate surface. Furthermore, the annual cooling (heating) load decreases (increases) with the rate of 13 (0.88) kWh m−2 of plant coverage area. The aim of this study is to show the importance of considering plant coverage in green roof simulations and building energy demand predictions.