Adjustment of outdoor thermal environment in a Central Business District with high-reflective material and rooftop greening

Central Business Districts are important component of urban economy development. But their dense infrastructure often exacerbates the urban heat island effect, leading to uncomfortable thermal environments. As Central Business Districts continue to proliferate globally, the importance of enhancing the thermal environment through appropriate building design cannot be ignored. In the past decades, high-reflective materials and roof greening are popularly recognized as energy-efficient envelope technologies. They can effectively lower the ambient temperature in the vicinity and enhance human comfort. However, the efficacy of these technologies in modulating the outdoor thermal environment has yet to be conclusively proven in Central Business Districts with high-density blocks and super high-rise buildings. In the current research, a representative Central Business Districts in Shenzhen, China was chosen as an example to analyze the influence of high-reflective materials and roof greening on outdoor thermal environment. The simulation model was developed with ENVI-met and successfully validated with field measurement data. The findings revealed a maximum reduction of 0.11 ℃ in outdoor air temperature was observed with the high-reflective material being applied on the rooftops. Meanwhile, compared to the initial block Case 0, the maximum increment of MRT reached 2.83 ℃ when the high-reflective material was applied to both facades and rooftops, which may lead to discomfort of pedestrians. For super high-rise buildings, the influence of rooftop greening on the outdoor thermal environment at the pedestrian level is negligible, exhibiting a mere 0.1 ℃ temperature reduction compared to case 0.