Simulation of buoyancy-induced flow in open cavities for natural ventilation

Solar heated open cavities including solar chimneys and double façades were studied for enhancing natural ventilation of buildings. A commercial CFD package was used to predict buoyant air flow and flow rates in the cavities. The CFD model was validated against measured data from the literature and good agreement between the prediction and measurement was achieved. The effect of the cavity width of solar chimneys and double façades on the buoyancy-induced ventilation rate was investigated. It was found that there existed an optimum cavity width for maximising the buoyancy-induced flow rate and the optimum width was between 0.55 and 0.6 m for a solar chimney of 6 m high. The ventilation rate in a double façade of four-storeys high generally increased with cavity width but decreased with floor level from bottom to top. Integration of photovoltaics into a double façade increased the ventilation rate while reducing its variation from floor to floor.