Urban Building Energy and Climate (UrBEC) simulation: Example application and field evaluation in Sai Ying Pun, Hong Kong

The energy performance of a building in a dense city depends to some extent on its surroundings. The impact of the built form, together with anthropogenic heat gains from traffic and building HVAC exhaust, determines external environmental conditions at the Urban Canopy Layer. Existing building energy models are limited in accounting for micro-scale variations of the urban microclimate, which may significantly modify a building's energy performance in density cities. This paper presents the Urban Building Energy and Climate (UrBEC) model, a coupled urban microclimate model (UMM) and building energy model (HTB2) developed to assess the time varying energy performance of a cluster of buildings and the combined heat gains to the external space from direct and reflected solar radiation, traffic and the exhaust from HVAC systems in a high-density city. The simulation results were evaluated by comparison with field measurement data collected from the Sai Ying Pun neighbourhood in Hong Kong, on a summer and winter day. Predicted and measured air and surface temperature at the four locations were found to be in reasonable agreement. Simulation results indicate an average of 1-3 ºC of temperature rise in street canyons compared with the ambient air in summer. Street level air is predicted to be 0.6 ºC warmer than those at higher levels (20m +). Anthropogenic heat from traffic and building HVAC exhaust are the dominant contributors to temperature rise in street canyons in summer, exceeding the contribution from urban surfaces. The predicted building cooling demand is expected to increase up to 15 % in summer due to the warming effect in street canyons. The UrBEC model runs significantly faster than current CFD-based approaches. Therefore, the model has the potential to support early stage design and planning decisions in a dense city