Studying the impact of local urban heat islands on the space cooling demand of buildings using coupled CFD and building energy simulations

Syracuse, NY

Surface as well as air temperatures are due to the urban heat island effect higher in urban compared to their surrounding rural areas. These increased temperatures have a strong impact on the building energy performance in urban environments and thermal comfort as well as health of inhabitants of these environments. At smaller scales, local heat islands are formed within urban environments, which have the same negative impacts. In this study, we investigate the influence of local heat islands on the space cooling demand of buildings. Commonly, climate information from one weather station is used for building performance simulations within a whole city. This climate information cannot take local hot spots into account, what can lead to inaccurate space cooling demand predictions. Here, we model the local urban climate with CFD (Computational Fluid Dynamics) simulations. With CFD also the local convective heat transfer coefficients (CHTC) for the building surfaces can be predicted. These local CHTC can strongly vary locally due to differences in local wind speeds. The commonly used coefficients are mostly based on measurements at facades of stand-alone buildings, where the local wind speeds are higher compared to urban areas. This study shows a dependency of the space cooling demands on the local urban climate. Space cooling demands are higher in areas with high local temperatures, where the winddriven ventilation is decreased. Additionally to the higher local temperatures also the local CHTC are lower leading to lower heat losses from the buildings. It can be concluded that it is important to account for the local microclimate to accurately predict the space cooling demand of buildings in urban environments.

https://surface.syr.edu/ibpc/2018/EP2/5