Effects of vertical greenery systems on the spatiotemporal thermal environment in street canyons with different aspect ratios: A scaled experiment study

Abstract

Many studies have focused mainly on the thermal and energy performance of VGSs on a building scale; however, little is known about the cooling effect of VGSs in street canyons and its response to different aspect ratios (building height/street width, H/W). Therefore, a scaled outdoor experiment was conducted to investigate the spatiotemporal variation of the urban wind and thermal environment caused by west-facing vertical greenery systems (VGSs) in street canyons with H/W = 1 and 2 in the subtropical city of Guangzhou, China. On a typical hot day (26th Oct. 2021), VGSs reduced wind speed by 38.0 % and 21.0 % in street canyons with H/W = 1 and 2, respectively. Compared with the reference cases, the temperature regimes of VGS cases (H/W = 1 and 2), including west-facing wall temperature (Tw-west), east-facing wall temperature (Tw-east), ground temperature (Tg), and air temperature (Ta), were all significantly decreased. Because of the cooling effect of VGSs, the maximum reduction of Tw-west in the upper level of street canyons with H/W = 1 and 2 was 20.3 and 16.8 °C, respectively. The maximum reduction of Tg in the center of the VGS case with H/W = 2 was 4.6 °C, which was more pronounced than in the VGS case with H/W = 1 (1.8 °C). The maximum reduction of Ta at the pedestrian level along the central axis of street canyons with H/W = 1 and 2 was 0.8 and 1.6 °C, respectively, which was more pronounced than at the upper level. The reduction of Tw-west in the upper level and of Tg and Ta in the VGS case with H/W = 2 was greater than that in the VGS case with H/W = 1 due to lower wind speed and albedo.