Temperature-driven single-sided ventilation through a large rectangular opening

As part of an investigation into the night-time cooling of commercial buildings by single-sided natural ventilation through open windows, a computational fluid dynamics study was performed to analyse the impact on the airflow rate of the dimensions and position of a large rectangular opening and of the temperature difference between inside and outside air. An empty room (4.9×2.6×3.9m3, length × height × width) with a rectangular opening in the outside wall was assumed and the Bernoulli formula used to calculate discharge coefficients Cd. Experimental results served for spot verification of CFD results. The vertical position of the opening was found to have the greatest impact on the discharge coefficient (factor >1.5 between bottom and top position for an opening of 1.6×1.6m2). Cd is also influenced by the opening width and wall thickness. By contrast, the horizontal distance of the opening from the wall and the opening area are of minor importance only. As the temperature differences between inside and outside increase, an asymptotic Cd value is reached (>6K). Airflow patterns are shown and their effect on Cd discussed. The need for further experimental and simulation work is identified.