Improving building heat evacuation by urban form optimization: the case from Xi'an, China

Anthropogenic heat emission is a crucial factor contributes to the urban heat island (UHI) phenomenon and a series of urban climatic disasters. People are discovering urban planning strategies to lower such negative influences. As an important component of anthropogenic heat emission, the intensities and evacuations of building heat emissions (BHE) are impacted by the urban forms to a large extent. In this study, we aim to develop the urban planning strategies from the perspective of improving BHE evacuations. To this end, the air flow and temperature fields in 42 urban blocks were simulated. On average, BHE increased the canopy UHI intensity by 1.03 degrees C and 1.36 degrees C in the residential and mix-used blocks, respectively. Decreasing the building density had a benefit at promoting BHE evacuation for all the blocks. However, the floor area ratio variation had minor impacts on the increases of UHI intensity caused by BHE in the residential blocks, but significant impacts on those in the mix-used blocks. The regression formulas that described the relationships between the increase of UHI intensity caused by BHE and the urban form indicators were provided. The formulas could be used as a tool to evaluate the urban form designs. As an example of utilization, the formulas were used for a renewal planning of a district (containing 18 urban blocks), combined with the genetic algorithm. In the renewal project, the land use intensity was maintained, while the district-averaged UHI increase caused by BHE was reduced by 0.3 degrees C.