Numerical simulation of wind-driven natural ventilation: Effects of loggia and facade porosity on air change rate

Building envelope geometry has an important impact on cross-ventilation performance. Presence of external architectural structures (e.g. a loggia), and opening surfaces can all affect ventilation performances. All these factors lead to deviation in the wind-driven ventilation rates predicted by semi-empirical models (correlations). Thus, this study is focused on the effects of a loggia and window opening size on cross-flow ventilation rates estimated by Computational Fluid Dynamics (CFD). CFD has been validated on field measurements in a low-rise building, with a steady-state Reynolds-Averaged Navier-Stokes (RANS) model. Ventilation performance is evaluated for buildings with or without a loggia with different opening sizes and various wind conditions. We find the presence of the loggia reduces the average air change rate by 27%, except for one wind direction at which a vortex is formed in the loggia and directs the airflow into the opening. However, the empirical models based on the orifice equation fail to precisely predict the ventilation rate for large windward-side windows. Large windows should be installed on the façade exposed to the prevailing wind, so as to enhance ventilation performance.