A new simulation tool for the evaluation of energy performances of green roofs

Among the different adoptable solutions for building envelopes, of particular interest is the green roof which allows us to obtain, at the same time, energy, economic and environmental benefits using solar energy as a source for its operation. The aim of the proposed study is to evaluate the energy and economic savings achievable through the installation of an additional green roof stratigraphy on a variety of traditional roofs. The analysis was carried out with reference to the climatic conditions of the Calabria region (Italy), classified as Mediterranean. Such assessment has been achieved by the use of a thermal model in dynamic regime formulated by the authors that allows us to determine the heat transfer in roofs with a green cover. The model is based on two energy balance equations for the vegetation and soil layer. The model has been implemented into the software tool ThermoGR that allows us to evaluate the thermal exchanges of a green roof with indoor and outdoor environments and the seasonal energy savings due to the presence of the green stratigraphy. The reduction of the thermal load through the roof, due to the green roof, is used to perform an economic analysis based on the calculation of the cost of the energy saved per square meter of roof surface during the airconditioning period both in summer and in winter. This analysis is used to identify the constructive typologies on which the application of the green roof is more advantageous.