Exploring the evapotranspirative cooling effect of a green façade

Abstract

• External wall behind the green layers were up to 7°C cooler than shade sails. • The gap temperatures behind green façade were always cooler than ambient air. • The gap temperatures behind green façade were cooler than gap behind shade sail. • The contribution of the evapotranspirative to overall gap cooling was to be 35%. Green façades are one of many innovative solutions widely applied to buildings to reduce energy consumption. Green façades can mitigate urban heat through evapotranspiration and shading; however, the relative contribution of interception of solar radiation (shade cooling) versus transpiration (evapotranspirative cooling) is not well understood. This study investigates the cooling provided by different façades, including green façades and shade sails, to quantify the relative impacts of evapotranspiration and shading. The temperature of the ambient air, gaps (areas behind the façades), and external walls behind the façades were measured and compared during different weather conditions. According to the results, during hot sunny days, the external wall temperatures behind the green façade were up to 7°C cooler than those behind the shade sail. Furthermore, the temperatures behind the green façade and shade sail were always cooler than the ambient air, by up to 11 and 6.8°C, respectively, indicating that the evapotranspirative cooling contributed 25-35% of the overall gap cooling induced by the green façades. The thermal benefits provided by the green façade indicated that they could contribute effectively to the sustainability of the building design and constitute an effective nature-based solution to city-scale urban heat and building energy use. The setup of temperature sensors (yellow circles) relative to the external wall and the a) green façade, d) shade sale and g) control – without façade. Diurnal temperature changes from the ambient air to the external wall behind the green façades (b: north-facing; c: west-facing), shade sails (e: north-facing; f: west-facing), and without façades (h: north-facing; i: west-facing) under sunny conditions. Note the difference in temperature scale of the north (b, e and h) and west facing façades (c, f and i). .