Impact of computational domain on the prediction of buoyancy-driven ventilation cooling

Traditional solar heated cavity structures such as solar chimneys make use of the stored solar energy in the interior wall to enhance natural ventilation of buildings but integration of photovoltaic devices into the exterior wall of such a structure can result in different proportions of heat distribution on both interior and exterior walls. This paper presents results of CFD simulation of the buoyancy-driven airflow and heat transfer in vertical cavities of different heights and widths with different total heat fluxes and wall heat distributions for ventilation cooling. Two sizes of computational domain were used for simulation – a small domain same as the physical size of a cavity and a large extended domain that is much larger than the cavity. The predicted natural ventilation rate and heat transfer coefficient have been found to depend on not only the cavity size and the quantity and proportion of heat distribution on the cavity walls but also the domain size. The difference in the predicted ventilation rate or heat transfer coefficient using the small and large domains is generally larger for wider cavities where heat distribution on two vertical walls is highly asymmetrical; incoming air would be distorted from symmetrical distribution across the inlet opening; and/or significant reverse flow would occur at the outlet opening. The difference in the heat transfer coefficient is generally less than that in the ventilation rate. In addition, a cavity with symmetrical heating has a higher ventilation rate but lower heat transfer coefficient than does an asymmetrically heated cavity.