Vegetation as a passive system for enhancing building climate control

Building indoor air temperature depends on several different parameters related to the climate of the region, the building itself and its use. The main parameters influencing the microclimate are: external air temperature and relative humidity, incident solar radiation, long wave radiation exchange between the building surfaces and its surroundings, incidence and speed of the wind, air exchanges, physical and thermal properties of the building's envelope materials, design variables such as building dimensions and orientation, presence of artificial light, electrical equipment. A sustainable technology for improving the energy efficiency of buildings and to mitigate urban heat island is the use of green roofs and walls. The green technology can allow the physical shading of the building and promote evapotranspiration in summer and increase the thermal insulation in winter. An experimental test was carried out at the University of Bari (Italy). Three vertical walls, made with perforated bricks, were tested: two were covered with plants (one with Pandorea jasminoides variegated, the second with Rhyncospermum jasminoides) while the third wall was kept uncovered and used as control. A system composed by a data logger and sensors was used to measure and record the following parameters: temperature of the wall surface under solar radiation and of the surface on the other side of the wall, solar radiation falling on the wall, and external air temperature. The use of the green walls during cold months allowed increasing the thermal insulation performance of the walls by keeping the external surface temperature in nighttime hours up to about 2.8°C over the surface temperature of the wall not covered with plants.