Urban microclimate impact on ventilation and thermal performance of multi-family residential buildings: two case studies in different climates and urban settings

Urban settings change the microclimate around buildings and resulting thermal comfort inside.  This paper presents a method to consider microclimatic conditions, especially the effect of wind variations around the building, which impacts natural ventilation rates and indoor operative temperatures. Air and surface temperature and wind speeds were studied using ENVImet for two areas located in Cadiz (Spain) and London (United Kingdom), representing temperate and hot European climates and moderate and dense urban settings.  The outputs of these microclimate simulations provided the spatial and temporal distribution of wind speed and directions at the building facades of two multi-family residential buildings located in the middle of the simulated areas (one in London and one in Cadiz) and the surface temperatures of surrounding buildings. These were used as boundary conditions to the EnergyPlus models of the two buildings to investigate their impact on achievable natural ventilation rates and the indoor thermal environment. Data for the case-studies were available through the ReCO2ST project. The ENVImet hourly wind speed values were used as input to the Air Flow Network models of EnergyPlus for the calculation of the wind pressure and the ventilation rates of the two buildings. The hourly surface temperatures calculated by ENVImet were assigned to the shading surface in front of the main façade of the case-study building located in Cadiz, to investigate its impact on thermal radiation emission and indoor operative temperatures. This was done by using the “Surrounding surface” objects of EnergyPlus V9.3.0. It was found that ventilation rates are reduced (in comparison to meteorological weather files) and this reduction impacts negatively on internal operative temperatures. The surface temperature of the facing building has a further negative impact during daytime, increasing the maximum indoor operative temperature.  A thermal comfort analysis was carried out indicating that the selection of a suitable weather file and microclimatic conditions is essential for more accurate predictions of internal thermal comfort and will assist in the sizing of passive and active systems to avoid overheating.