Types of mechanical ventilation used in commercial/industrial buildings
There are many types of mechanical ventilation in buildings. But for commercial or industrial premises, mechanical ventilation is typically driven by air handling units (AHU). The AHUs are connected to ductwork within the building that supplies air to and extracts air from interior spaces. Where mechanical ventilation includes heating, cooling, and humidity control, this can be referred to as a heating, ventilation and air conditioning (HVAC) system.
Extracting internal air and replacing it with outside air can increase the need for heating and cooling depending on the ambient air temperature. However, this can be reduced by re-circulating a proportion of the internal air with the fresh outside air, or by using heat recovery ventilation (HRV) that recovers heat from the extracted air to pre-heat incoming fresh air.
Supply and extract only systems
Mechanical ventilation systems can have both supply and extract vents assisted by fans. These systems may also include filters to ensure a higher standard of indoor air quality, coupled with heating and/or cooling coils.
Mechanical supply-only systems work by drawing outside air into a building in which inside air will escape through the building enclosure (cracks in walls, poorly sealed windows etc.) and extract fan ducts (if they are installed). This system is suitable for houses and occupied offices that need to be supplied by constant fresh air.
Mechanical extract-only systems are used mostly when the air is prone to contamination such as in kitchens or bathrooms where there is a need for constant and predictable extraction of air. The principle of working behind this system is based on pulling air out from a room using exhaust fan ducts. It often doesn’t have any particular component to pull outside air back into a room.
There are a few disadvantages of using this type of mechanical ventilation system:
- They have the potential to drive moist indoor air into wall cavities that could condense and create mould build-up and building fabric problems.
- The mechanical ventilation systems tend to create pressure imbalances within buildings.
- Both supply-only and extract-only mechanical ventilation systems require natural ventilation to work effectively.
For the best results, we recommend a building ventilation system that utilises both supply and extract capabilities.
Balanced ventilation systems
A balanced or fully ducted ventilation system is the most effective solution for creating a clean and optimum environment for employees. It utilises fully controlled and balanced ventilation. This system applies both supply and extract fans, introducing fresh air and exhausts dirty air in equal quantities, hence the name “balanced ventilation”. This allows for much safer use, keeping the pressures within the building at a steady level.
This type of ventilation system is most effective when you apply it in a well-sealed building, where other infiltration sources are reduced, like keeping windows and doors closed.
The most efficient way to operate such a system is to include heat exchange, whereby thermal energy is transferred between the outgoing and incoming airstreams, otherwise known as a heat recovery system.
Heat Recovery Ventilation (HRV)
Heat recovery ventilation (HRV) recovers heat from the air that has been extracted from a room. Heat recovery is a method that is increasingly used to reduce the temperature demands and energy costs of buildings.
By recovering the residual heat in the exhaust air, the fresh air introduced into the ventilation system is pre-heated. Heat recovery systems typically recover about 60–95% of the heat in the exhaust air and can significantly improve the energy efficiency of buildings.
An important thing to consider before introducing a mechanical ventilation heat recovery (MVHR) system in your building is to make sure your building is correctly sealed. It would be a huge waste of time, effort and money controlling ventilation and attempting heat recovery when your building leaks air (and heat) through poor seals. In the end, you would be fighting a losing battle and wasting money.