Ventilation is the process of replacing stale indoor air with fresh outdoor air. It is essential for maintaining the health, wellbeing, and comfort of building occupants. The importance of ventilation can be summarised as follows:

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• Providing sufficient oxygen to support breathing.

• Diluting and removing indoor pollutants, including body odours and carbon dioxide produced by occupants.

• Removing excess heat generated within the building.

• Supplying combustion air for fuel-burning appliances.

• Reducing relative humidity levels to minimise the risk of condensation and mould growth.

• Assisting in the removal of smoke during a fire emergency.

 

In domestic buildings, ventilation is commonly achieved through infiltration. Infiltration refers to the natural movement of air into and out of a building through small gaps, cracks, and openings in the building fabric. This air movement is mainly driven by wind forces and temperature differences between the indoor and outdoor environments.

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Small commercial buildings are often ventilated using similar principles to those applied in residential buildings. However, as buildings become larger and more complex, natural ventilation alone may no longer provide adequate air exchange, making mechanical ventilation necessary. Mechanical ventilation is particularly important in the following situations:

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• Areas with high occupant density, where the available space is less than 3.5 m³ per person.

• Deep-plan buildings, where natural cross-ventilation becomes ineffective beyond approximately 15 m between external walls, and single-sided ventilation is generally ineffective beyond 6 m from an external wall.

• Buildings where windows cannot be opened due to factors such as traffic noise, security concerns, or outdoor air pollution.

• Spaces requiring precise control of temperature and humidity.

• Areas where contaminants are generated more rapidly than can be removed through natural ventilation.

• Rooms that require positive pressurisation, such as clean rooms, to prevent the ingress of dust and airborne contaminants.

• Tall, sealed buildings where wind-driven and stack-effect ventilation would otherwise create excessive and uncontrolled airflow.