Design for Maximum Ventilation

Cross Ventilation

Without outlet openings, there may be no effective air movement through a building, even in the case of strong winds. It is essential that windows are located on opposite walls to encourage cross ventilation. Also, because of obstructions within the building, air flow may lose its kinetic energy, each time it is diverted around an obstacle. Internal walls, furniture, etc. can effectively stop low velocity air flow. Therefore, it is better to have partitions clear of the floor and ceiling.
The air flow depends directly on the difference in pressure at the openings. The main parameters influencing the air flow levels are the inlet and outlet surface of the openings, the wind velocity and direction, the temperature difference between the indoor and outdoor environment, the relative position of the openings, and the relative wind shadowing of the building.

Orientation of openings

If the elevation is 90 degree to the wind direction then there is maximum pressure and maximum air velocity. Therefore, orient the building in such a way that the largest openings are facing the wind direction. However, when the openings are at 45 degree to the wind direction, there is better average indoor velocity and better distribution.

Position of openings

To be effective air movement must be directed at the body surface. Air movement should be through the living zone. When the inlet is at a high level, the air flow happens only along the ceiling, regardless of the outlet. Pressure build up happens in front of the solid areas of the elevation. This will govern the direction of the indoor air stream and this will be independent of the outlet opening position.

Size of openings

Largest air velocity happens if the inlet is small and the outlet is large. The total force is acting on a small area and forcing air through the opening at a high pressure. If the inlet opening is large, air velocity will be low but the volume of air passing in unit time will be higher. Therefore, large inlet openings are desirable when the wind direction is not constant, or airflow through the whole space is required.

Wing Walls

To increase the cooling effectiveness of natural ventilation techniques, especially on sites with low outdoor air velocity and variable wind directions, it is possible to incorporate wing walls into the building design. Wing walls project outward next to a window even a slight breeze against the wall creates a high pressure zone on one side and low on the other. The pressure differential draws outdoor air in through one open window and out the adjacent one.

cross ventilation wind walls