Effects of different vertical façade greenery systems on pedestrian thermal comfort in deep street canyons

Vertical greenery systems (VGSs) have been adopted in city planning operations to mitigate excess heat in hot and humid subtropical cities. This study focused on the influence of different arrangements of vertical greening on pedestrian thermal comfort and particulate matter with a diameter of 10 µm (PM₁₀) in street canyons. In this paper, the ENVI-met computational fluid dynamics (CFD) method was used to investigate the effects of different façade greenery arrangements with the same amount of greenery in the Nan Hai Yi Ku (NHYK) industrial district. On-site measurements were used to validate the simulation results in a transition season. The results showed that greening façades could improve pedestrians' thermal comfort with physiological equivalent temperature (PET) value reductions varying from 0.17 °C to 1.4 °C. Under a certain amount of greenery, the critical factor determining pedestrians' thermal comfort was the coverage rate of the greening façade near the pedestrian level. Specifically, increasing the greening façade coverage near the lower parts of street canyons could enhance the pedestrian-level cooling effect. In addition, the VGSs positively affected the pedestrian-level air quality in the street canyons. Nevertheless, the changes in pedestrian-level PM₁₀ concentration induced by the presence of VGSs were not very obvious under the building-parallel wind direction.