Mechanical ventilation

Mechanical or artificial ventilation employs the use of mechanical equipment for effective air circulation. It is provided in those circumstances where satisfactory standard of ventilation in respect to air quality or control-ability cannot be attained in natural ways. This system is costly buts increases efficiency and the control of individuals over the ventilation system.

Types of mechanical ventilation systems

  • Extraction system
  • Plenum system
  • Extraction-plenum system
  • Air-conditioning

Extraction/Exhaust system

This system is based on the principle of creation of vacuum in the rooms by exhausting the vitiated air by the means of a propeller type fans (exhaust fans). Air inlets are formed at the height of 1.2 to 1.8 m and the outlets are provided at the opposite side of the rooms through which air enters. The extraction of stale air enables the entry of fresh air by means of opening or windows. This system is useful for the extraction of odours, smoke, dust particles, etc. from kitchens, bathrooms, industrial plants, etc.

Plenum System/Supply system

In this system fresh air is forced into the room and the vitiated air is allowed to leave through ventilators. There air inlet is selected in the side where air quality is at its purest. The incoming air is forced into the building after passing through a fine screen. A constant stream of air is continuously forced down the screen and is drawn up by a blower fan.

After the removal of mechanical impurities further disinfection can be carried out by introduction of ozone. The ventilation by plenum mode can either be downward or upward. In the downward ventilation, the incoming air is allowed to enter at the ceiling height and while mixing the vitiated air during its downward journey and taken out from the outlets at the floor level. In upward ventilation the air enter through the floor level and exists at the roof level. This ventilation system is costly and is used in factories, conference halls, theatres, big offices, etc.

Extraction-Plenum system

This is an extension of the plenum system in which extraction fans are used for the exit of the vitiated air from the room. This system is adopted where the delivery of fresh air is sluggish or where it is necessary to discharge vitiated air containing obnoxious fumes from bathroom and factories.


This is the best system of artificial ventilation in which provision is made for filtration, heating or cooling, humidifying or de-humidifying the air thus creating the most comfortable environment and working conditions.

Guidelines for natural ventilation
Recommended fresh air supply

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