Green walls for a sustainable control of building microclimate

The Urban Heat Island (UHI) phenomenon induces harmful outdoor comfort conditions, an increase in pollutants concentration, an excessive energy consumption related to the greater use of air conditioning systems and a raise of the frequency and magnitude of electricity demand peaks. In the Mediterranean area the urban warming and the solar heat gain in buildings need to be controlled in a sustainable way for keeping the indoor temperature at comfortable values. Green roofs and green walls can mitigate the heat events related to UHI, lower the indoor temperatures, cut energy loads on buildings, enhance human thermal comfort conditions and increase the buildings thermal insulation in winter. Experimental tests were carried out at the University of Bari (Italy) starting from summer 2014, aiming to analyze the influences of different climbing plants, as main components of green systems, applied on building walls. Three vertical walls, made of perforated bricks, were built. They were equipped with a sealed structure, on their backside, in order to realize prototypes of buildings in scale. The first wall was covered with Pandorea jasminoides variegated, the second with Rhyncospermum jasminoides, the third wall was kept uncovered and used as control. Several climatic parameters concerning the walls and the ambient conditions were collected during the experimental test by means of a data logger and sensors. High definition infra-red images for each wall were recorded using a Thermal Imaging Camera for analyzing the surface temperature of the plants and of the walls. The daylight temperatures observed on the walls protected with plants during warm days were lower than the respective temperatures of the control wall up to 5 °C; the nighttime temperatures observed during cold days were higher than the respective temperatures of the control wall up to 3°C.