Recent challenges in the realm of urban studies concern better understanding of microclimatic conditions. Changes in urban climate affect cities at local and global scales, with consequences for human health, thermal comfort, building energy use, and anthropogenic emissions. The extent of these impacts may vary due to different morphologies and materials of the built environment. The present contribution summarizes the results of a multi-year effort concerned with the extent and implications of urban heat in Vienna, Austria. For this purpose, high-resolution weather data across six locations are obtained and analyzed. This allowed for an objective assessment of urban-level climatic circumstances across distinct low-density and high-density typologies. Subsequently, a systematic framework was developed for identification of essential properties of the built environment (geometric and material-related) that are hypothesized to influence microclimate variation. Results point to a number of related (positive and negative) correlations with microclimatic tendencies. Additionally, the impact of this location-specific weather data on building performance simulation results is evaluated. The results suggest that buildings' thermal performance is significantly influenced by location-specific microclimatic conditions with variation of mean annual heating load across locations of up to 16.1 kWhm −2 ·a −1 . The use of location-independent weather data sources (e.g., standardized weather files) for building performance estimations can, thus, result in considerable errors.
Recently, the interest in urban weather modeling methods has been steadily increasing. This is in part due to the insight that thermal building performance simulations are typically undertaken with standardized weather files that provide a rather general perspective on urban weather conditions. This may lead toward errors in conclusions drawn from modeling efforts. In this context, present contribution reports on the potential of different approaches to generate location-dependent urban meteorological data. We compare the meteorological output generated with the Weather Research and Forecasting (WRF) model, Urban Weather Generator, and morphing approach. These methods were compared based on empirical data (air temperature, humidity, and wind speed) collected from two distinct urban locations in Vienna, Austria, over 5 study periods. Our results suggest significant temporal and spatial discrepancies in resulting modeling output. Results further suggest better predictive performance in the case of high-density urban areas and under warmer and extreme conditions in spring and summer periods, respectively.
Global increase of urban population has brought about a growing demand for more dwelling space, resulting in various negative impacts, such as accelerated urbanization, urban sprawl and higher carbon footprints. To cope with these growth dynamics, city authorities are urged to consider alternative planning strategies aiming at mitigating the negative implications of urbanization. In this context, the present contribution investigates the potential of urban densification to mitigate the heat island effects and to improve outdoor thermal conditions. Focusing on a quite densely urbanized district in Vienna, Austria, we carried out a set of simulations of urban microclimate for pre- and post-densification scenarios using the parametric modelling environment Rhinoceros 3D and a set of built-in algorithms in the Rhino’s plug-in Grasshopper. The study was conducted for a hot summer period. The results revealed a notable solar shielding effect of newly introduced vertical extensions of existing buildings, promoting temperature decrease and improved thermal conditions within more shaded urban canyons and courtyards. However, a slight warming effect was noted during the night-time due to the higher thermal storage and lower sky view factor.
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