This paper reviews the current literature on discharge coefficients (CD) of openings and compares different studies for wind-driven cross-ventilation. Considerable variation of discharge coefficients with opening porosity, configuration (shape and location in the faade), wind angle and Reynolds number is shown. Consequently, the use of a constant CD value such as that given in textbooks or other sources might be an invalid simplification.
To accurately estimate the natural ventilation of outdoor spaces surrounded by low-rise buildings using a wind tunnel requires correct representation of the natural wind regime combined with appropriately scaled building models and testing method. Existing outdoor ventilation studies are largely based on wind speed and estimated air change rates. Wind speeds mainly influence: peoples comfort, safety in pedestrian areas, the heat transfer between outdoor surfaces and airflow, and evaporation from wet surfaces.
The author describes how to improve the usual formula to calculate air flow rate through an opened hopper window.Improvements consist in better taking into account the geometry of such windows when estimating their opened area and also in adapting to this type of windows the model used to take into account the influence of wind and of thermal draught.Improved model gives a good comparison with on site measured data from the literature.
There is a resurgence of interest in naturally ventilated offices. Most of the time, cooling the buildings is possible with the opening of windows. Simulations with the softwere TAS were made and showed that window opening allow a sufficient day or night ventilation rate, even if wind characteristics are not favourable. The optimal size, shape and location of the window apertures to reach sufficient ventilation rates has been studied along with the impact of the wind orientation and the building degree of protection on these ventilation rates.
Multi-storey buildings with double-skin facade are not numerous and there is little experience of their behaviour in operation.In this study the authors analyze the impact of the double-skin orientation, the impact of the wind orientation, and the degree of wind protection on the facades. Simulations were realized too.
Wind pressure measurements corresponding to the various configurations of a detached houseshould be conducted by wind tunnel tests using a comparatively large geometric scale model because a building of extremely small size is targeted.
The authors recently reported the detailed experimental results on that the discharge coefficient of the openings exposed to the wind driven airflow clearly changes depending upon the windangle and consequent conditions. A full-scale building model in a wind tunnel has been used for theexperiment. In this paper, the mechanism of the change is discussed more deeply, and the predictionmethods of the discharge coefficient are tested by the new experimental results for different conditions of opening size and location.
In case of cross ventilation through the large opening, it is well known that the inflow directionat the opening is not normal to the opening. Authors proposed the simplified prediction method of theinflow direction at the inlet opening and the airflow rate simultaneously. It is also well known that the use of general discharged coefficient (CD) values is not suitable for the calculation of cross ventilation rate. First reason is that the simple connection of the pressure loss coefficient of an opening ( ?? as the reciprocal of square CD) in series under-estimates the airflow rate.
Airflow through openings in a cross ventilated building scale model was investigated in a windtunnel and by numerical predictions. Predictions for a wind direction perpendicular to the building showed an airflow pattern consisting of streamlines entering the room, that originated from approximately the same upstream area in the undisturbed boundary layer and a direction of the flow into the room dependent on opening location with velocity vectors pointing away from the stagnation point.