Microclimate and urban morphology effects on building energy demand in different European cities

In the building sector, initiatives for Nearly Zero Energy Buildings (NZEBs) are gaining importance to tackle climate change and decrease energy consumption. Ever-greater efforts from developers are required to achieve such a goal, and energy audits are becoming increasingly sophisticated. Nevertheless, Building Energy Models (BEMs) are still often employed considering the building as self-standing, neglecting the urban morphology and the local climate conditions. In this study, the Urban Heat Island (UHI) phenomenon has been investigated using the Urban Weather Generator tool (UWG). The UHI intensity (i.e. the increase in urban air temperature compared to the rural one) has been analysed comparing two different urban configurations: the reference district is conceived referring to existing European suburbs whereas the enhanced district is characterized by high-efficiency buildings and UHI mitigation strategies. Urban canyon air temperatures have been calculated as a function of the above district configurations, city locations corresponding to 3 European climate zones, and district geometries (6 cases, differing in building spacing and height). The results show an increase in urban air temperatures ranging from 0.8 °C in winter to 2.0 °C in summer. In a second stage, the heating and cooling consumption of a residential building in EnergyPlus environment has been tested under the different urban weather conditions and district characteristics. When rural weather data are used as input, the yearly air-conditioning needs are underestimated by 10%. Concerning the two urban configurations, whilst the annual energy consumption of the enhanced design is only 2.2% less than the reference case, splitting the heating and the cooling load, the difference is closer to 8%, with opposite trends for heating and cooling.