Mechanical ventilation can be categorised into four types of system:
Supply
Where air is introduced into the space from somewhere else, generally outside.
Mechanical supply ventilation system description and common application:
A simple system consists of a fan collecting air from outside of the space, a filter, supply duct work and a grille or outlet into the space. Sophistication can be added in the form of heating, fan speed control, noise attenuation, dampers and volume control based on (for example) Carbon Dioxide levels in the space.
An application example would be an outdoor air supply to an occupied commercial space designed to flush away the products of respiration.
Extract
Where the air is taken (extracted) from the space and delivered somewhere else, generally outside.
Mechanical extract ventilation system description and common application:
A simple system consists of a fan collecting air from the space, a filter, extract duct work and a grille or hood. Sophistication can be added in the form of odour control system, fan speed control, noise attenuation, fire dampers and volume control.
An application example would be a commercial kitchen cooking hood and extract system to remove the steam, airborne grease and odours from above the cooking area.
Balanced
Where a supply and extract system work together to achieve a particular design aim. This system can be used to create the desired pressure in the space.
Mechanical balanced ventilation system description and common application:
A simple system consists of a supply and extract fan collecting from and supplying to the space, a form of filtration, duct work and a grille. Sophistication can be added in the form of heating, fan speed control, noise attenuation, dampers, and volume control.
An application example would be a laboratory where pathogens were handled. The balanced system design would ensure the air pressure inside the laboratory would be negative compared with the rooms adjacent. This way air can only leak into the space not out.
Energy Recovery Ventilation
(ERV)-where a specially designed system transfers energy from extract air and delivers it to the supply air. These systems reduce the energy required to condition the supply air entering the space. This energy demand can be significant at certain times of the season.
Mechanical energy recovery ventilation (ERV) system description and common application:
A simple system consists of a supply and extract fan collecting from and supplying to the space, energy transfer device, a form of filtration, duct work and a grille. Sophistication can be added in the form of sterilizer, heating, fan speed control, noise attenuation, dampers, and volume control based on (for example) Carbon Dioxide levels in the space.
An application example would be a space that requires high quantities of outdoor air year-round. A ball room where there is a high density of people needing outdoor air to flush away the products of respiration. An ERV would reduce the load on the air conditioning system at certain times of the year.