Urban heat island impacts on cooling energy demand of residential buildings at the city scale: a case study of Hong Kong

Abstract

Urban heat island (UHI) effects contribute to not only higher cooling energy demand of buildings but also an increase in peak demand. While UHI effects vary across a city, limited research has been conducted on the effects of microclimate on building energy demand at the city scale. To address the knowledge gap, this study uses city-scale high-resolution UHI data to assess the microclimate impacts on summer cooling energy demand of residential buildings in a subtropical high-density city at the tertiary planning unit (TPU) scale. Comparing the rural TPUs with the urban TPUs, the results reveal that cooling energy demand in urban TPUs can be up to five times higher than that in rural TPUs. A rise of 1000 °C·h in daytime UHI degree hours (UHIdh) linearly increases cooling energy demand by 4.7 kWh per square meter of building floor area. Furthermore, an increase of 1000 °C·h in UHIdh and 1 °C in maximum temperature corresponds linearly to peak cooling load increases of 0.5 kW and 1.02 kW, respectively. Conversely, nighttime UHIdh exhibits a non-linear relationship with cooling energy demand. This study underscores the nuanced differences between UHI metrics and cooling energy demand and provides maps to guide targeted mitigation and energy-saving interventions.