Green roofs in a Mediterranean climate: energy performances based on in-situ experimental data

Green roofs appear to be an appealing solution for sustainable constructions because they could produce different advantages for the building, especially at an energy level. Nevertheless, usually dynamic models adopted for the simulation of the green roof performances require the knowledge of several parameters, which are often difficult to estimate, in order to properly define the thermal exchanges with the external environment. In this paper, in order to overcome this limitation, dynamic hourly simulations were performed by means of TRNSYS software, employing experimental climatic data and the monitored temperatures in an experimental green roof. In order to contemplate the overall effect of the vegetated roof, the temperature at interface with the structural roof was provided as the boundary condition in the building model. Simulation results have shown that, at annual level in the considered climatic context, a non-insulated green roof provides the best results due to the significant reduction of the cooling energy demand, with annual savings of 34.9% in continuous operation and of 34.7% in intermittent operation. The effect of the green roof was also detected in the second to last floor of the investigated building. The results further highlighted the capability of the green roof to consistently improve the indoor thermal comfort in both winter and summer season.