Energy Balance in Green Façades

Increasing urban green infrastructure in cities can contribute to improve urban climate in summer reducing buildings surface temperature and urban air temperature especially in Southern Europe. The use of vegetated vertical systems is a sustainable passive technology for improving the energy efficiency of buildings in cities. It results in the reduction of the energy consumption for air conditioning. The application of vertical green systems requires the knowledge of the energy performance of the applied greenery system. The heat and mass transfer between the external environment, the green facades and the building surface determine the building microclimate. Solar radiation, long wave infrared radiation, convective heat transfer and evapotranspiration are the main mechanism of heat transfer in green façades. The paper describes the main mechanisms concerning heat flow in green facades. The mechanisms described by means of mathematical formulas can be used in simulation models for predicting temperatures in buildings. The greenery system was described by a schematic representation and four layers were defined. The energy balance was defined for each layer and all the terms involved in the energy exchange between the layers were defined as a function of the plant, the weather conditions and the characteristics of the wall.