The effects of shading devices on outdoor thermal and visual comfort in Southern China during summer

Abstract

Shading effectively alleviates heat stress caused by heatwaves and urban heat islands. Artificial shading is a viable alternative to urban greenery when tree planting is impracticable. While tree shade has been studied extensively, the effects of shading devices on the microclimate and illuminance are not well understood. To examine the influence of shading devices on outdoor thermal and visual comfort, we conducted on-site meteorological observations and surveys (n = 1272) on a university campus in Guangzhou during the summer of 2018. In ENVI-met simulations, various shading device properties were compared, including materials, transparency, and size. Simulation results indicate that shading devices reduced mean radiant temperature, Physiological Equivalent Temperature (PET), and Universal Thermal Climate Index (UTCI) up to 24.8 °C, 12.0 °C and 5.9 °C, respectively. However, there was a negligible reduction in air temperature and wind speed. Opaque materials and glass covers with 10% transparency decreased illuminance by 73%–83% and 65%–75%, respectively. Moreover, the size threshold for optimal cooling effects differs in locations with different sky view factors and tree shade. Our survey reveals that reducing the illuminance by > 90,000 lux and sun sensation vote from +2.5 to +1 can lower the thermal sensation vote by up to one vote. As shading devices decrease illuminance and thermal indices, the cross-modal effect between visual and thermal comfort would need to be considered in optimizing the design of shading devices. Further observation and numerical simulation of outdoor microclimate and illuminance are necessary to validate this cross-modal effect in other climatic regions.