Buoyancy-driven natural ventilation of a room with large openings

The buoyancy-driven natural ventilation of a room with large lower and higher level openings is investigated by both theoretical analysis and CFD simulation. Pressure-based formulae are developed for the prediction of the height of neutral plane and airflow rate, and three different flow modes are identified according to the position of the neutral level: (I) when the neutral height is at intermediate level of the lower opening; (II) when the neutral height has no intersection with openings; (III) when the neutral height is at the intermediate level of the higher opening. CFD simulation is then performed to cross-check the validity of the formulae derived. Good agreement is achieved for the airflows of flow mode (I) both quantitatively and qualitatively, and the discrepancy is less than 18% for neutral level prediction and 7% for airflow rate prediction. But poor agreement is observed for flow mode (III) with discrepancies over 30% at some points, although the predictions on airflow rate generally show the same trend. Guidelines are also developed in relation to the opening design based on the analytical model developed and the CFD simulation.