Integrated impacts of cool coatings, street orientations, and height variability on urban cooling in 3D high-rise building arrays: CFD simulation

Abstract

Using cool coatings on building envelopes and modifying urban morphologies, such as street orientations and building height variability, are recognized as effective urban cooling strategies. However, few studies evaluate the integrated cooling performance of these strategies in three-dimensional (3D) high-rise building arrays. Moreover, most existing performance evaluations of cool coatings focus on temperature drop, while rarely considering coating costs. As a novel contribution, this study systematically investigates the combined impacts of cool coatings (cool roofs (CR), cool roofs & walls (CR&W), cool roofs & east-west walls (CR&EWW), and cool roofs & high-rise walls (CR&HW)), street orientations (north-south vs. east-west), and building height layouts (uniform-height vs. varied-height) on building surface temperature and pedestrian-level microclimate under three summer solar heating conditions (8 am, 12 pm, and 4 pm) using computational fluid dynamics simulations. Uniquely, cooling intensity (°C/m²) is proposed to quantify the average surface temperature drop per unit of cool-coated surface area by incorporating coating costs into cooling performance evaluation. Results indicate that cool coatings reduce direct sunlit surface temperatures by up to 7.5 °C, with ensemble-average building envelope drops of 0.36–1.63 °C, while their impacts on pedestrian-level air temperature (drop < 0.3 °C) and wind velocity ratio (variation < 0.06) are minimal. CR&W, CR&EWW, and CR&HW cause significantly greater ensemble-average temperature drops than CR; however, when coating costs are considered, CR&W is less cost-effective than other configurations. CR&EWW and CR&HW offer a good trade-off between cooling effect and coating costs. Moreover, north-south orientation generally shows superior cooling performance with cool coatings over east-west orientation. Height variability differentially influences the cool coating performance for high-rise and low-rise buildings. This study offers valuable insights for optimizing the spatial deployment of cool coatings in compact subtropical cities.