How do winds affect buoyancy-driven ventilation in buildings?

This paper examines theoretically the effects of wind on buoyancy-driven ventilation via some new analytical solutions recently developed by the authors. Three air change rate parameters are introduced to characterise respectively the effects of thermal buoyancy, the envelope heat loss and the wind force. The wind can either assist or oppose the airflow. For the first time, it has been found that for opposing winds, there are two stable ventilation flow rates for a given set of wind and thermal parameter, i.e. the natural ventilation flow exhibits hysteresis. Simple non-dimensional graphs are presented for calculating ventilation flow rates, and for sizing ventilation openings. Using the simple examples, this paper provides architects and engineers with some practical guidelines on how to use these non-dimensional graphs in their concept design.