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

• Published in: The Science of the total environment 2023-02, Vol.859 (Pt 2), p.160408, Article 160408
• Main Authors: Zheng, Xiaona, Hu, Wentao, Luo, Shuang, Zhu, Zhiquan, Bai, Yujie, Wang, Weiwen, Pan, Lan
• Format: Article
• Language: English
• Subjects: Air Pollutants - analysis; air temperature; Aspect ratio; China; Cities; Cooling effect; energy; environment; Humans; Microclimate; Models, Theoretical; Pedestrians; Scaled Outdoor Measurement of Urban Climate and Health (SOMUCH); Temperature; vegetation; Vertical greenery systems; Wind; wind speed
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2022.160408

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. [Display omitted] •Vertical greenery systems (VGSs) reduced wind speed by 38.0 % and 21.0 % in streets (H/W = 1 and 2), respectively.•Canyon air cooled by VGSs was more pronounced at the pedestrian level than at the upper level.•Canyon air and ground on the side closer to VGSs had a higher temperature reduction.•The narrower street (H/W = 2) with VGSs tended to receive a better cooling effect.