Scaled outdoor experimental investigation of thermal environment and surface energy balance in deep and shallow street canyons under various sky conditions

Abstract

This study investigates the characteristics of the thermal environment and surface energy balance (SEB) in idealized outdoor scaled street canyons with different height-to-width ratios (H/W = 0.5 and 2, H = 0.5 m) in a humid subtropical climate from 2019 to 2020. The surface temperature, air temperature, albedo, and SEB components are compared between the deep and shallow canyons under clear, partially cloudy, and cloudy sky conditions. The interior air of the mimic buildings in both canyons showed significant vertical temperature gradients, and the outdoor air temperature in the shallow canyon showed a significant horizontal difference. The wall surfaces in the deep street canyon exhibited a stronger vertical temperature gradient during the daytime. In winter, higher interior air temperature within mimic buildings and slightly lower outdoor air temperature were found in the deep street canyon compared to the shallow one. Sky conditions played an important role in the SEB. The clear sky days showed slightly higher albedo than the cloudy and partially cloudy days. Shallow canyons showed a dominant contribution from the ground heat storage under clear and partially cloudy skies, while the deep canyon showed a similar contribution from the ground, walls, and roof. Lastly, the dependence of storage heat flux on net-all-wave radiation flux was found stronger under clear skies than under partially cloudy skies in all cases and months studied. These results provide an enhanced understanding of indoor and outdoor thermal environment and the data may help to improve numerical simulations under different sky conditions for urban climate studies.