Last edited 05 Jul 2021

Mechanical ventilation of buildings

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[edit] Introduction

Ventilation is necessary in buildings to remove ‘stale’ air and replace it with ‘fresh’ air:

Very broadly, ventilation in buildings can be classified as ‘natural’ or ‘mechanical’.

Natural ventilation is generally preferable to mechanical ventilation as it will typically have lower capital, operational and maintenance costs. However, there are a range of circumstances in which natural ventilation may not be possible:

Some of these issues can be avoided or mitigated by careful design, and mixed mode or assisted ventilation might be possible, where natural ventilation is supplemented by mechanical systems.

[edit] Types of mechanical ventilation

Where mechanical ventilation is necessary it can be:

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[edit] Typical mechanical ventilation systems for commercial buildings

In commercial developments, mechanical ventilation is typically driven by air handling units (AHU) connected to ductwork within the building that supplies air to and extracts air from interior spaces. Typically AHU comprise an insulated box that forms the housing for; filter racks or chambers, a fan (or blower), and sometimes heating elements, cooling elements, sound attenuators and dampers. In some situations, such as in swimming pools, air handling units might include dehumidification. See Air handling units for more information.

Where mechanical ventilation includes heating, cooling and humidity control, this can be referred to as Heating Ventilation and Air Conditioning (HVAC). See Heating Ventilation and Air Conditioning for more information.

Extracting internal air and replacing it with outside air can increase the need for heating and cooling. This can be reduced by re-circulating a proportion of internal air with the fresh outside air, or by heat recovery ventilation (HRV) that recovers heat from extract air to pre-heat incoming fresh air using counter-flow heat exchangers. See Heat recovery ventilation for more information.

The design of mechanical ventilation systems is generally a specialist task, undertaken by a building services engineer. Whilst there are standards and rules of thumb that can be used to determine air flow rates for straight-forward situations, when mechanical ventilation is combined with heating, cooling, humidity control and the interaction with natural ventilation, thermal mass and solar gain, the situation can quickly become very complicated.

This, along with additional considerations, such as the noise generated by fans, and the impact of ductwork on acoustic separation means it is vital building services are considered at the outset of the building design process, and not seen as an add-on.

See Building services engineer for more information.

[edit] Building management systems

Mechanical ventilation may be controlled by a building management system (BMS) to maximise occupant comfort and minimise energy consumption. Regular inspection and maintenance is necessary to ensure that systems are operating optimally and that occupants understand how systems are operated.

See Building management system for more information.

[edit] Building regulations requirements

Ventilation in buildings is regulated by Part F of the building regulations. Approved document F includes standards for ventilation and air quality for all buildings and requirements for the prevention of condensation. The types of ventilation covered include; mechanical, passive stack, background and purge (rapid).

It is supported by the Domestic Ventilation Compliance Guide, which provides detailed guidance about the installation, inspection, testing, commissioning and provision of information when installing fixed ventilation systems in new and existing dwellings.

See Approved document F for more information.

[edit] Related articles on Designing Buildings Wiki

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