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Modes of ventilation

In general, natural ventilation can be induced by cross ventilation or stack ventilation and they can be either passive or active in nature. Cross ventilation technique use the natural wind force to direct the air movement through a building. When wind impact on a building it produces positive pressure on the windward side and relative negative pressure on the leeward side and these difference in pressures drive the airflow through the building. In order to achieve good cross ventilation effect, openings such as windows, doors and other openings are required at the different facings of the building. The stack ventilation technique utilizes the temperature between inside and outside of a building. When the room temperature is greater than outside, the warm indoor air will rise and exit and cooler, denser air from below can enter.

The natural ventilation can be further enhanced by wind driven ventilation technique. These techniques can be either passive or active in nature however the primary driving force for providing ventilation are primarily caused by wind.

 Passive wind driven ventilation technique (Fig-1)

This is probably the simplest form of its kind through window opening and ridge vents. This type of natural ventilation in a building can be optimized to cut down the need for artificial cooling.

However, major limitations are

  • This ventilation technique in unpredictability as wind patterns availability vary for different region according to seasons and more over for large buildings some physical limitations exists. Hence its application on its own cannot be considered to be a primary ventilation method.
  • A problem often cited with typical ridge vents is that they stop the rise of this hot air with the "inverted V" that sits on top of the vent.
  •  Active wind driven ventilation technique (Fig-2)

    Wind e ventilators commercially available in various sizes rotate in its vertical axis to create updraft inside the turbine which extracts air and in the absence of wind, they can still facilitate ventilator using the stack effects. These types of installations are usually on the top of the roof where higher wind speeds are available for most buildings.