Ventilation

• Natural ventilation – takes advantage of warm air rising, as well as differences in air movement and currents from one side of the building to another
• Mechanical ventilation – requires dedicated ductwork and fans to distribute fresh air evenly throughout the building
• Mixed mode – uses a combination of natural and mechanical ventilation to meet a building’s varying needs.

Fresh air is provided via windows that open, air vents in the walls, and (more occasionally) roof spaces. Using natural ventilation can allow increased air rates to provide a degree of cooling in the space.

This can be achieved by using openings in different sides of the building and at different heights. The use of highly glazed lobby and atria areas can also increase the ventilation rates, and is becoming a common feature in newer, naturally ventilated buildings.

Variation in ventilation rates can be achieved by either altering the speed of the fans or by using ‘dampers’ which restrict the airflow in the ductwork. Many systems allow a proportion of exhaust air to be re-circulated into the space, reducing the amount of fresh air needing to be conditioned (heated or cooled) to match the internal conditions.

Where re-circulation is not possible, some of the heat (or coolness) from the exhaust air can be recovered using specialist equipment. However, as this increases fan energy consumption, a careful cost/benefit assessment will be required before installing any heat recovery system.

• The use of natural ventilation at the building periphery, with windows which open and air vents. Spaces deeper into the building, or in areas that require a more controlled environment (such as computer server rooms) are supplied with dedicated mechanical ventilation (and sometimes cooling) to ensure comfortable conditions are maintained
• Using natural ventilation for most of the year, and mechanical ventilation (and sometimes cooling) in the summer months, to ensure the space is provided with adequate ventilation and kept comfortably cool