Article

Streamlined CFD simulation framework to generate wind-pressure coefficients on building facades for airflow network simulations

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Abstract

Building energy modeling software generally comes with capable airflow network solvers for natural ventilation evaluation in multi-zone building energy models. These approaches rely on arrays of pressure coefficients representing different wind directions derived from simple box-shaped buildings without contextual obstructions. For urban or obstructed sites, or more complex building shapes, however, further evaluation is needed to avoid geometric oversimplification. In this study, we present an automated and easy-to-use simulation workflow for OpenFOAM-based exterior airflow simulations to generate arrays of pressure coefficients for arbitrary building shapes and contextual situations. The workflow is compared to other methods commonly used to obtain pressure coefficients for natural ventilation analysis. Finally, we assess for which climate zones and building types modelers should rely on more accurate CFD-based pressure coefficients and where it may be justifiable to rely on easier and readily available analytical approaches to determine pressure coefficients. Results suggest that existing workflows lead to significant error in predicted comfort hours for climates in the Global South and modelers should consider CFD-based facade pressure coeficients.

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... This workflow is a simplification in comparison to Computational Fluid Dynamics (CFD)based simulations that calculate context-specific pressure coefficients which can be used to more accurately evaluate predicted energy savings and thermal comfort conditions. The applicability of these methods should be largely informed by the density of the urban environment and the climate of interest, as larger deviations could be witnessed when utilizing the simplified models (Cheung & Liu, 2011;Dogan & Kastner, 2021). Moreover, when informing design strategies and comparing alternatives, the metrics used to evaluate comfort differ substantially. ...
... In other words, when is increasing model complexity by including CFD simulations more justifiable? In line with recent literature on warmer climates, the results have indicated that a large variation in annual discomfort hours is seen when CFD calculations are introduced in the AFN simulation (Dogan & Kastner, 2021). We find that in instances where crossventilation is being considered, a larger discrepancy can be seen between the method that includes internal wind speeds and the methods that assume a constant speed. ...
... Generally, there are two approaches to perform airflow simulation in buildings, which are as follows: computational fluid dynamics (CFD) and multizone modelling, of which the former one can provide more accurate and refined characterization of the flow field but at considerably higher computational cost and time [55][56][57]. Therefore, aiming at rapid simulation with adequate accuracy, the Airflow module in the i-IAQ toolbox applies multizone modelling for ventilation and infiltration simulation of the target building. ...
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