text: For a simple volume with two openings, the cross wind flow rate can be calculated using the following equation:
  where  is the far-field wind speed;  is a local pressure drag coefficient for the building, defined at the location of the upstream opening;  is a local pressure drag coefficient for the building, defined at the location of the downstream opening;  is the cross-sectional area of the upstream opening;  is the cross-sectional area of the downstream opening;  is the discharge coefficient of the upstream opening; and  is the discharge coefficient of the downstream opening.
  For rooms with single opening, the calculation of ventilation rate is more complicated than cross ventilation due to the bi-directional flow and strong turbulent effect. The ventilation rate for single-sided ventilation can be accurately predicted by combining different models for mean flow, pulsating flow and eddy penetration. The mean flow rate for single-sided ventilation is determined by:
  where
  l = width of the window;
  h = elevation of the top edge of the window;
  z = elevation of neural level (where inside and outside pressure balance);
  z = reference elevation where the wind velocity is measured (at 10 m) and
   = mean wind velocity at the reference elevation.
  As observed in the equation (1), the air exchange depends linearly on the wind speed in the urban place where the architectural project will be built. CFD (Computational Fluid Dynamics) tools and zonal modelings are usually used to design naturally ventilated buildings. Windcatchers can assist wind-driven ventilation by guiding air in and out of structures.