Experimental Investigation of Assumptions Used to Quantify Airflows through a Window under Cross Natural Ventilation

As natural wind is continuously fluctuating in both speed and direction, quantifying instantaneous wind-driven natural ventilation rate can be difficult, and often an average effect is used to stabilize the fluctuations. This work performs an experimental investigation to assess the validity of assumptions often used in quantifying airflows through an opening under cross natural ventilation condition. In the experiment, the three velocity components are analyzed for flows approaching and through an open window exposed to natural wind. Detailed airflows are also examined across an open window to investigate velocity profiles at the opening. Finally, ventilation rates are calculated to assess the use of constant discharge coefficients for wind-driven natural ventilation, and show for the experimental conditions that the traditional orifice flow rate calculation using a constant discharge coefficient CD = 0.65 results in an underestimate by 17% compared to a detailed calculation based on seven airspeed measurements within the window opening.