Investigating the impact of urban microclimate on building thermal performance: A case study of dense urban areas in Hong Kong.

• The urban microclimate effects are considered in an urban scale building simulation. • Building energy model is coupled with a high-resolution urban climate model. • Average overheating risks are underestimated by 140% without considering urban microclimate. • The building thermal performance is highly affected by neighboring urban contexts. • Subdivided flats in old buildings are more susceptible to the extreme heat event. Urban microclimate conditions could be an important factor influencing building thermal performance. However, most studies on urban building energy modeling (UBEM) use the typical meteorological year (TMY), often developed from observations of exposed/ rural sites, as input weather data. This study aims to assess the impacts of urban heat on building thermal performance by coupling a high-resolution urban climate simulation with UBEM. The simulated building thermal performance was compared with and without urban microclimate considerations, using weather data from the TMY, weather observations from an urban oasis, and outputs from the urban climate model. The physical parameters of typical building archetypes used in the UBEM were calibrated against indoor-measured data during summer days. Without considering urban microclimate, there was an underestimation of up to 140% of the average overheating risks of urban buildings. Furthermore, neighboring urban contexts and building ventilation rates considerably affected the thermal performance of individual buildings within high-density urban areas. The study reveals that neglecting the influence of the urban microclimate can result in a notable error in the building thermal performance assessment even at the urban level. [ABSTRACT FROM AUTHOR]