Wind-tunnel analysis of natural ventilation in a generic building in sheltered and unsheltered conditions: Impact of Reynolds number and wind direction

Natural ventilation is generally preferred to mechanical ventilation because it saves energy and protects the outdoor atmospheric environment. The present work focuses on the air change rate (ACH) of a generic building for single-sided and cross-ventilation arrangements. This topic was studied on small-scale building models of cubic shape in a boundary layer wind tunnel. Experiments were carried out by simulating the atmospheric boundary layer (ABL) over suburban terrain that impinges a building model standing alone or surrounded by other buildings in a symmetrical 3 x 3 pattern. The spacing density of building models, flow incidence angle, velocity, and ventilation arrangement were major parameters for quantifying the ventilation performance. Hot-wire anemometry was used to determine the flow characteristics, and a tracer gas system was applied to measure the ACH. The ACH obtained for the isolated building proved larger than for the sheltered case, as expected. In the latter case, the ventilation is more efficient for less densely spaced buildings. For the isolated building, a linear relationship between the ACH and the flow velocity can be justified for both ventilation types. For the cross-ventilation setup, a model equation is proposed. It quantifies the dependence of the ACH on the flow velocity and incidence angle.