A scaled outdoor experimental study of the urban thermal environment in street canyons with green walls under various weather conditions

Abstract

• A scaled outdoor experiment studied thermal effects of green walls (GWs) in street canyons. • With aspects ratios AR = 1.5 and 2, cooling effect due to GWs was greater in upper heights of street walls. • GWs induced larger cooling effect on narrower street canyons (AR = 1.5 and 2) than with AR = 1. • Wall cooling due to GWs was stronger on sunny days (22.1 °C) than on cloudy or rainy days. A scaled outdoor experiment was conducted to examine the thermal effects of west-facing green walls (GWs) in street canyons with different street aspect ratios (building height/street width, H/W = AR = 1, 1.5, and 2, H = 1.2 m) under different weather conditions in humid-subtropical Guangzhou, China. Compared with the control cases ( AR = 1, 1.5, and 2), the wind speed at the height of 0.3 m (0.25 H ) was reduced by 15%-34% in GW cases under three weather conditions (sunny, cloudy and rainy). On a typical sunny day, significant wall temperature ( T wall ) reduction in GW cases was observed due to the thermal effects of GWs, with maximum values at 1.1 m (above the ground) reached 15.9, 21.2, and 22.1 °C for AR = 1, 1.5, and 2, respectively. The maximum ground temperature ( T ground ) reductions in GW cases were 1.5, 5.5, and 5.7 °C as AR = 1, 1.5, and 2, respectively. Moreover, GWs maximally reduced air temperature ( T air ) at 0.1 m height (equal to the pedestrian level in real cities) by 0.5, 1.0, and 1.0 °C when AR = 1, 1.5, and 2, respectively. Compared with sunny days, the weaker solar radiation and higher relative humidity on cloudy and rainy days suppressed the thermal effects of GWs on T wall , T ground , and T air in street canyons.