Heat transfer mechanisms in vertical green systems and energy balance equations

The use of vegetated vertical systems is a sustainable technology for improving the energy efficiency of buildings in cities in order to reduce the energy consumption for air conditioning in summer and to increase the thermal insulation in winter. increasing urban green infrastructure (ugi) in a city can contribute to improve urban climate in summer reducing buildings surface temperature and urban air especially in southern europe. the application of vertical green systems requires the knowledge of the energy performance of the applied greenery system. the choice of the green facades depends on the local climate, water availability, building shape. the presence of green facades affects the building microclimate all day, by reducing heat waves during the warm periods and heat losses from the building in the cold period. 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 mechanisms of heat transfer in a green façade. the paper describes the main parameters concerning heat flow in green facades that can be used in simulation models for predicting temperatures in buildings using the external weather conditions as model inputs. the input parameters are: external air temperature and relative humidity, solar radiation, wind velocity and direction, plants and building characteristics. the green facade was described by a schematic representation, four layers were defined: the green layer, the external surface of the building wall, the internal surface of the building wall, the air inside the building. 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 constructive characteristics of the wall