The impact of building configurations and anthropogenic heat on daily urban air temperature cycles

Abstract

Urban air temperature reflects the impact of urbanization on thermal and dynamics of urban climate. To understand the physical mechanism of building configurations and anthropogenic heat on daily urban air temperature cycles, an improved lumped urban air temperature model was provided. The surface energy balance equation for the improved and previous lumped urban air temperature model were compared. The effective depth of thermal mass and sub-surface temperature of urban surfaces in the previous model can be determined, which are usually chosen from model studies. These two parameters have a significant impact on the thermal storage. The models were evaluated and applied to the city of Hong Kong. Thermal storage is shown to have significant impact on the amplitude and phase term of daily air temperature cycle. Moreover, the building configurations can affect the solar radiation gain and redistribution in the sub-facets, which indirectly influenced the urban air temperature. The results show that the ventilation rate, building height and plan area ratio play important roles on daily cycle of urban air temperature, while the anthropogenic heat plays a less significant role. The main distinction of the improved model is its simplicity and less computation cost for practice use for engineers and urban planners. Two important parameters are emphasized, relative convective heat transfer number, λ, and time constant, τ. The two parameters provide some insights on how to control the urban thermal environment in an engineering way.