Numerical analysis of outdoor thermal comfort of block-scale vertical greening systems in a hot humid climate

Vertical greening systems (VGS) offer a promising solution for mitigating urban heat. Despite their potential benefits, research on the optimal greenery coverage ratio (GCR) and effective formation strategies are limited. This study aims to fill this gap by examining how GCR and appropriate VGS formation affect outdoor temperature at the block scale. Using ENVI-met, six VGS scenarios were evaluated to assess their impact on air temperatures and pedestrian comfort. Results indicate that increasing the pedestrian-level greenery improves thermal comfort. Notably, Vertical VGS formations outperformed horizontal ones in reducing surface temperatures and enhancing comfort. Specifically, adding 50% or more greenery on vertical surfaces of south-facing facades resulted in an average air temperature reduction of 0.36 degrees C, a decrease in average predicted mean vote (PMV) values exceeding 0.9, and a maximum surface temperature drop (Tse) of 9.91 degrees C. This study highlights the effectiveness of VGS in improving pedestrian comfort in hot humid climates.Abbreviations: VGS: Vertical greening systems; GI: Green infrastructure; GCR: Greenery coverage ratio; Ta: Air temperature; MRT: Mean radiant temperature; Tse: surface temperature; PET: Physiological equivalent temperature; SET: Standard effective temperature; PMV: Predicted mean vote; H/W: Aspect ratio; LAI: Leaf area index