A nature-based system for improving Mediterranean buildings’ performance: contribution to energy saving by heat transfer reduction and influence of climatic parameters

Urban environments can be turned greener and more sustainable by letting in vegetation. The application of green façades on buildings’ vertical surfaces is a viable option that brings various advantages. This study focuses on the energy benefit provided by an evergreen green façade in Mediterranean climate conditions. The results came from a long experimental campaign, heat fluxes evaluation and statistical analyses. The thermal behaviour of the experimental green façade was analysed all year round, highlighting differences between warm and cold periods and between time of the day. The main advantage was assessed in terms of energy saving, defined as heat flux reduction through the wall covered with vegetation in comparison with an unvegetated wall. The study pointed out that energy saving was achieved throughout the year, but in different time of the day based on the season. A daytime energy saving was obtained in warm periods due to the shading effect and the plants evapotranspiration. A night-time benefit was reached in cold periods mainly thanks to the thermal and wind barrier action of the green layer. The results showed daily mean values of energy saving equal to 11.47 W m-2 for a warm period and to 3.23 W m-2 for a cold period. The statistical analysis highlighted that the energy saving was positively influenced by external air temperature especially at daytime. Overall, higher energy saving was provided by the green façade when higher external air temperature values were recorded. This research contributes to fill existing literature gaps on the yearly behaviour of green façades and on the energy benefits these provide.