Internal airflow sensitivity in a naturally ventilated atrium subject to variation in external wind conditions

Design guidelines for natural ventilation in buildings normally focus on the potential hourly air change (ACH) rates based on the building space parameters. Critically, external airflow design data is often assumed on the basis of a single mean wind speed and an associated prevailing wind direction. This can result in significant variation in ventilation rates and comfort conditions when non-design external wind conditions prevail. This paper examines the influence of variations in external wind conditions on internal building airflows using a CFD model for the atrium space of a naturally ventilated building. External wind speeds from 25% to 250% of the mean site wind speed were examined. For a single wind speed, the relationship between wind direction and air change rates was also found to be approximately linear for wind directions between 0o and 90o (orthogonal and parallel) to the vent openings, but non-linear for other directions (90o to 135o).