Integrated effects of overhanging shading devices and aspect ratios on microclimatic performance in street canyons: Scaled outdoor experiments

Overhanging shading devices (OSDs) are increasingly implemented to improve thermal comfort. Yet, the effects of street-scale OSDs on ventilation, thermal, and visual comfort under different canyon aspect ratios (H/W) remain unclear. This study conducted scaled outdoor experiments in a subtropical city to investigate the coupled effects of OSDs and H/W on street-canyon microclimate. OSDs reduce canyon wind speed by 25% and 52% for H/W = 1 and 2, respectively. The cooling is concentrated mainly beneath the OSDs at both canyon sides. The maximum reductions in east-facing and west-facing wall temperatures at 0.15 m height (pedestrian level) are 9.7 °C and 10.6 °C for H/W = 1, respectively, compared with 4.5 °C and 4.4 °C for H/W = 2. At the west-facing side, pedestrian-level air temperature decreases by 1.8 °C for H/W = 1, but increases by 1.4 °C for H/W = 2. In the wider street canyon (H/W = 1), OSDs reduce physiological equivalent temperature (PET) by 9.6 °C and 10.1 °C, and illuminance by 163.6 klux and 190.1 klux at the east-facing and west-facing sides, respectively, but increase PET and illuminance by 3.8 °C and 39.0 klux at the center. In the narrower street canyon (H/W = 2), PET and illuminance decrease by 6.8 °C and 141.9 klux at the east-facing side, 7.4 °C and 144.7 klux at the center, and 7.1 °C and 180.5 klux at the west-facing side, respectively. An effectiveness index is introduced, indicating that OSDs simultaneously improve thermal and visual comfort at both sides for H/W = 1, whereas excessive shading yields a slightly negative effect for H/W = 2. These findings support shading design in subtropical cities and provide reliable validation for numerical simulations.