A study on evaporative cooling capacity of a novel green wall to control ventilating air temperature

Abstract

Green buildings include structures that have passive indoor environmental control benefits, while green walls and roofs may offer extensive water holding capacity, reduced run out time, sound absorption, and fortified biodiversity in urban settings. Conventional green walls additionally provide passive cooling benefits via surface evaporation and plants' transpiration. In this study, a novel green wall comprised of bio-receptive porous concrete tiles was tested for its ability to act as an evaporative cooling pad. Ryegrass was grown on its surface, and air passed through the vegetated wall to determine its evaporative cooling effect. This novel green wall evaporative cooling pad (GWECP) showed a maximum cooling effectiveness of 0.97 with a maximum temperature reduction of −25.58 °C with 50 °C inlet air temperature. The effect of vegetation layer height was further examined, where a grass layer 30 cm in height showed a maximum cooling rate of −9.57 ± 0.79 kW, and a grass layer 22.5 cm in height showed a maximum evaporation rate of 3.36 ± 0.08 g s−1 when challenged with different inlet air conditions ranging from 25 °C to 50 °C. As a novel evaporative cooling system, the GWECP had maximum cooling and evaporation coefficients of 10.7 kW m−2 C−1 and 1.18 g s−1, respectively. This data set suggests a prospective application for this GWECP as an energy-efficient cooling system for ventilated air by providing carbon-free indoor air-cooling for any extremely warm outdoor weather conditions with the other associated benefits of green walls.