Energy behaviour of the green layer in green façades

The spread of green infrastructures in a city should improve climate and comfort conditions. Green vertical systems associated with buildings have been identified as the ones which offer significant opportunities to a sustainable transition. Such systems improve the energy efficiency of the buildings. Green façades can reduce building surface temperature and urban air temperature and, at the same time, reduce energy consumption for air conditioning and increase envelope insulation. The comprehension of the energy behaviour of the vegetated vertical solutions is complex, but essential for a more correct and advantageous application of this technology. The main objective of this paper is to provide tools to develop simulation models useful to describe and predict the energy functioning of the green façades. The paper proposes an analysis of the green layer, considering its schematic representation and all the heat transfer mechanisms occurring. Thermal exchanges take place by means of shortwave and longwave radiation transfer, convection and evapotranspiration. The latter is very significant for the green façades and deserves particular attention in its determination. To describe the functioning of the system, knowledge of some inputs parameters was necessary: the external weather conditions and the layers thermophysical characteristics. The energy balance model was defined and applied using the data collected at the experimental farm of the University of Bari. The applied formula describing the latent heat transfer in green layer was positively validated.