Field monitoring in Mediterranean climate to quantify thermal performances of vertical greening systems

Green envelopes can provide environmental and ecological benefits in dense urban areas, improving air quality, mitigating Urban Heat Island effect, reducing energy use for air conditioning. The present study is based on field monitoring of the pilot project INPS Green Façade, built in Genoa (Italy) to quantify its environmental, economic, and social benefits. The vertical greening system was installed on the south wall of an office building built early in the last century and renovated in the 1980’s, owned by INPS (National Institute of Social Insurance). The facade is exposed to solar radiation several hr/day in summer and 1–2 hr/day during winter. The external walls are constituted by two layers of masonry spaced by a 51 cm air gap (resulting from the retrofitting works), with a layer of 5 cm of insulating material. An experimental investigation allows evaluating the thermal performances of a well vegetated vertical greening system during summer and winter. This study demonstrates that a green layer can mitigate outdoor and surface temperatures, thus improve conform conditions and reduce building surfaces warming up (contributing to urban heat island mitigation). The cooling capacity of vertical greening systems, with air temperature difference up to 10°C, can be exploited to reduce energy demand for air conditioning during summer. Although the energy saving for cooling strongly depends on several factors, the results obtained show a potential significant reduction of energy need for air cooling. The consequence of the vertical greening system on energy demand during winter is more complex to define because combined effects can be registered: prevention from solar radiation, shielding from the wind and a natural ventilation of the cavity.