It is important to understand the general nature of natural ventilation and these guidelines provide some insight to the concept of natural ventilation.
In hot, humid climates, maximize air velocities in the occupied zones for bodily cooling. In hot, arid climates, maximize airflow throughout the building for structural cooling, particularly at night when the temperature is low.
Take advantage of topography, landscaping, and surrounding buildings to redirect airflow and give maximum exposure to breezes. Use vegetation to funnel breezes and avoid wind dams, which reduce the driving pressure differential around the building. Site objects should not obstruct inlet openings.
Shape the building to expose maximum surface area to breezes.
Use architectural elements such as wing walls, parapets, and overhangs to promote airflow into the building interior.
The long facade of the building and the majority of the door and window openings should be oriented with respect to the prevailing summer breezes. If there is no prevailing direction, openings should be sufficient to provide ventilation regardless of wind direction.
Windows should be located in opposing pressure zones. Two openings on opposite sides of a space increase the ventilation flow. Openings on adjacent sides force air to change direction, providing ventilation to a greater area. The benefits of the window arrangement depend on the outlet location relative to the direction of the inlet airstream.
If a room has only one external wall, better airflow is achieved with two widely spaced windows.
If the openings are at the same level and near the ceiling, much of the flow may bypass the occupied level and be ineffective in diluting contaminants there.
The stack effect requires vertical distance between openings to take advantage of the stack effect; the greater the vertical distance, the greater the ventilation.
Openings in the vicinity of the Neutral Pressure Level (NPL) are least effective for thermally induced ventilation. If the building has only one large opening, the NPL tends to move to that level, which reduces the pressure across the opening.
An inlet window smaller than the outlet creates higher inlet velocities. The rule of thumb is to have the outlet area 50% larger than the inlet area, assuming that they do not have a tendency to reverse roles with changes in wind direction.
Openings with areas much larger than calculated are sometimes desirable when anticipating increased occupancy or very hot weather.
Horizontal windows are generally better than square or vertical windows. They produce more airflow over a wider range of wind directions and are most beneficial in locations where prevailing wind patterns shift.
Window openings should be accessible to and operable by occupants.
Casement type windows are much less effective in comparison to sliding windows.
Inlet openings should not be obstructed by indoor partitions. Partitions can be placed to split and redirect airflow, but should not restrict flow between the building's inlets and outlets.
Vertical airshafts or open staircases can be used to increase and take advantage of stack effects. However, enclosed stair-cases intended for evacuation during a fire should not be used for ventilation.
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