A simulation study on building-scale strategies for urban heat island mitigation and building energy consumption: Case study in Japan

The urban heat island (UHI) phenomenon and high building energy consumption are increasingly being associated with urbanization. Various strategies have been proposed for UHI mitigation and energy conservation in buildings. Nonetheless, the combined effects of the multiple strategies must be studied. This study clarifies the individual and combined effects of commonly used building-scale strategies (i.e., replacing ground materials, adding greenery, adjusting window-to-wall ratios, using high-performance glazing, increasing insulation thickness in the building envelope, changing roof surfaces, and adjusting air-conditioning operating temperatures) on UHI mitigation and building energy consumption reduction in both summer and winter. The selected strategies were implemented in a city block in Yokohama, Japan using a surface energy balance (SEB) simulation model. The simulation results demonstrated that planting tall deciduous trees was the most effective individual strategy for mitigating UHI and reducing energy consumption. While the highest UHI mitigation and energy savings were achieved by implementing all tested strategies simultaneously, a combination of water-retaining pavement, adjusting the air-conditioning operating temperature (28 °C in summer and 20 °C in winter), and a 100 mm insulation layer in the building envelope along with a green roof, demonstrated substantial effectiveness with fewer strategies. The interactions among these strategies provided either additive or offset effects. Therefore, selecting strategies with distinct action targets is crucial to maximize the combined effectiveness.