Ventilation is movement of air, typically between an indoor space and the outside. When people or animals are present, ventilation is especially necessary to evacuate the carbon dioxide produced and renew the oxygen used up. It is also needed to remove other pollutants (smoke, chemicals, etc.) from the space. Ventilation air can also be used to heat, cool, humidify and dehumidify the space and to filter particles or contaminants from the air.

In office buildings and other standard applications, a percentage of the total air that is circulated is evacuated outside and compensated by outside air. The time it takes to completely turn over the air volume of a room is considered the ventilation rate and it is measured in air exchanges per hour. Inadequate ventilation in a space occupied by people can cause the level of carbon dioxide to increase leading to sleepyness.

If there is something burning (a fireplace, gas heater, candle, oil lamp, etc.) more oxygen is replaced by carbon dioxide (and possibly other poisonous gases and smoke) and more ventilation is needed. If there is a chimney then the additional need of ventilation just refers to replacing the warmer air that leaves by convection through the chimney with fresh air.

Ventilation in a structure is also needed for removing water vapor, produced by breathing, burning, and cooking, and for removing smells, e.g. from a toilet or kitchen. If water vapor is permitted to accumulate, it may damage the insulation or interior finish. A dehumidifier may also be appropriate for removing moisture in the air.

Types of ventilation

• Natural ventilation: Natural ventilation occurs when the air in a space is changed with outdoor air without the use mechanical systems, such as a fan. Most often natural ventilation is assured though operable windows but it can also be achieved through temperature and pressure differences between spaces.
• Forced ventilation as in direct, dedicated or local exhaust ventilation
  • Fume hood
  • Biological safety cabinet
• Dilution ventilation as in general building or room ventilation
• Heat recovery ventilation

See also

• Solar chimney
• Sick building syndrome
• Heating, Ventilation and Air-Conditioning
• Stack effect

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