Influence of morphologies on the microclimate in urban neighbourhoods

In the past decades the portion of the population living in urban areas has continuously increased. Due to the high building density, the microclimate in urban areas changes significantly compared to rural areas. The temperatures measured in urban areas are higher compared to the rural temperatures due to the urban heat island (UHI) effect. Furthermore, the longwave and solar radiation exchanges are influenced by shadowing, reflections between buildings and reduced sky view factors. The local urban microclimate has an influence on the energy demand of buildings and on human comfort and health in urban areas. In summer the human comfort in urban areas can decrease due to higher air and surface temperatures and lower wind speeds compared to rural areas. The local urban microclimate is difficult to predict because of the complex interaction of physical phenomena across a large range of time and length scales. Few guidelines exist for architects to mitigate UHI effects or its impacts. The aim of this paper is to model the urban microclimate with CFD and building energy simulations and to investigate in detail the influence of different urban building morphologies on the urban microclimate. This approach and the results of this study can be used to find measures to mitigate the UHI effect. The results show that building façade surface temperatures are mainly influenced by the distance between buildings. For urban morphologies with similar surface temperatures, the air temperatures can still strongly vary due to different wind flow patterns causing different rates of removing heat by wind.