Numerical study of the influence of albedo on the microclimate of Bergpolder Zuid, Rotterdam

The rapid trend towards urbanization has increased the popularity of studies investigating urban microclimates. Factors such as the Urban Heat Island (UHI) effect and summer-time heat waves can have a significant influence on outdoor thermal comfort levels and building energy demand. For the investigation of urban microclimates, historically, observational approaches (such as field measurements) have been employed and lately, with the advancements in computing power, computational methods are becoming more popular because of the possibility to conduct scenario analysis. Computational Fluid Dynamics (CFD) is one of these computational methods which has proven to have the potential to accurately predict urban microclimate. Compared to other computational methods employed to investigate urban microclimate (i.e. Energy Balance Models), CFD has the capability to couple flow field with the temperature field at the cost of more computational resources. In this study, CFD simulations are performed to predict urban temperatures in the Bergpolder Zuid region, located in Rotterdam. The area is planned to be renovated and one of the aims is to increase its climate resilience. Based on the municipal drawings of the Bergpolder region, a high-resolution computational domain is generated. The computational domain has a hexagonal shape with an edge length of 2.4 kilometer and a height of 400 meter. In total, the grid consists of 6,610,456 hexahedral cells. The simulations are performed using the 3D unsteady Reynolds-averaged Navier-Stokes (URANS) equations in combination with the realizable k-epsilon turbulence model. Several physical phenomena influencing urban microclimate such as wind flow and heat transfer (conduction, convection and radiation) are considered in the simulations. As for evapotranspiration, during morning (6:00 - 11:00 h) and afternoon (15:00 - 18:00 h) a constant and uniform sink value of 80W/m2 is imposed and during noon time (11:00 - 15:00 h) the sink value is specified as 130 W/m2 (at the ground level). Meteorological data used in this study is obtained from the hourly averaged dataset of the Royal Dutch Meteorological Institute (KNMI) by the Rotterdam weather station, which is located near Rotterdam airport, 4 km northwest of Bergpolder Zuid. In the first part of this research, resulting surface temperatures on the region were validated using experimental data from high-resolution thermal infrared satellite imagery, which were recorded during the heat wave of July 2006. The resulting average surface temperatures showed a deviation of 7.9% with the satellite imagery data. In the second part, the investigation focused on the effect of different physical parameters, such as thermal diffusivity and albedo on outdoor thermal comfort, considering the validated time range. Preliminary results show that changing the thermal diffusivity of the building materials and albedo value of the ground cover can influence the average surface temperatures in an urban environment significantly. Complete results regarding the effect of physical parameters on outdoor thermal comfort are still being evaluated and the results will be available in the full paper.