Energy analysis of a green façade in summer: an experimental test in Mediterranean climate conditions

Energy performance of a double-skin green facade in Mediterranean climate was investigated. Experimental data were collected at a green facade prototype realized at the University of Bari. The green facade thermal behaviour was assessed under different summertime weather scenarios. To point out the plants influence, a comparison was carried out between microclimatic conditions and energy transfer at the covered wall, behind the vegetation, and at an un-vegetated wall. Experimental data concerning the walls surface, the air gap in the green facade and the external air were used to perform statistical analyses and to evaluate the heat fluxes. At daytime, the green facade provided a reduction of the wall surface temperature up to 9.9 °C, while air relative humidity behind the vegetation rose up to 18.7%. Surface and air warming were found at night-time. A time-shift was detected between the maximum surface temperature of the covered and of the bare wall. The analysis of the energy flux through the two walls highlighted a sensible reduction in the covered wall, equal to 62% during daytime. Solar and LWIR radiative and convective fluxes were generally lower in the covered wall. Latent heat due to evapotranspiration was evaluated, as well. Net radiation was found to be the most influencing parameter for latent heat transfer. A simplified relationship was proposed to quantify latent heat due to evapotranspiration. The formula based on the net radiation, as input parameter, was found to be the most suitable. The findings of this research contribute to the knowledge of the effects provided by green facades in terms of cooling and heating, influence on the proximity microclimatic conditions and overall energy transfer.