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 changed significantly compared to rural areas. The temperatures measured in urban areas are, due to the urban heat island (UHI) effect, higher compared to the rural temperatures. The UHI intensities are increasing with higher building densities and growing cities. Space cooling and heating demands of buildings are strongly affected by the local microclimate at the building sites. Due to the climate change and the limited energy resources, energy saving and sustainability are nowadays important issues. A significant part of the global energy consumption is used for space cooling and space heating of buildings. Thus its minimization for buildings in urban areas has great energy saving potential. Most building energy simulation (BES) models were developed for stand-alone buildings and therefore do not consider effects of the urban microclimate. This can lead to inaccurate predictions of the space cooling and heating demands for buildings in urban areas. The aim of this paper is to investigate the urban microclimate and its potential influence on the energy demand of buildings in an urban context by conducting detailed flow, radiation and building energy simulations at the urban neighborhood scale. CitySim is used for the radiation and building energy simulations. In CitySim detailed radiation models for solar and longwave radiation are implemented that can account for the radiation exchange between neighbouring buildings. The flow around the buildings is modelled by running CFD (computational fluid dynamics) simulations using OpenFOAM. As a result it is shown, how the temperatures and wind speeds can strongly differ within different urban areas. Further an approach is presented, to consider the local microclimate in the building energy simulation tool CitySim.