Wind and buoyancy driven natural ventilation in double skin façades

The computational fluid dynamics (CFD) modelling activity presented in this work aims at investigating the reliability of the assumptions employed in a double skin façades (DSFs) simplified model, developed for the integration of naturally ventilated DSFs in building simulation (BS) tools. The simplified fluid-dynamic model considers both the wind action, by means of pressure coefficients (Cp) on the openings, and the buoyancy inside the ventilated channel. Both the BS and the CFD models have been assessed using the database of an experimental campaign carried out in a full scale test facility, named ‘The Cube’, and made available by the Department of Civil Engineering of Aalborg University. The results show a good agreement between the CFD and BS models in terms of predicted temperature increase, with a maximum deviation of 15%. Both models exhibit a high sensitivity to the imposed differential wind pressure, which depends on the Cp source employed. The determination of proper Cp values for the specific case is, hence, a crucial aspect. Moreover, the CFD analysis offers a deeper insight on surface heat transfer and suggests the need to take into account the interplay between thermal and wind-driven convection, which ultimately gives rise to a mixed convection phenomenon.