Building ventilation removes stale air and replaces it with fresh air, measured in air changes per hour (ACH). Proper ventilation is important for healthy indoor air quality, removing chemicals and controlling humidity. Natural ventilation relies on pressure differences, while mechanical ventilation uses fans and HVAC ducts. The type of system used impacts energy efficiency and must be carefully considered.
Building ventilation is the process of removing stale air from inside a building and replacing it with fresh air from outside. This process is part of a building’s heating, ventilation, and air conditioning (HVAC) system, which is typically designed and installed by a mechanical or HVAC contractor. Building ventilation is measured in terms of air changes per hour (ACH), which is the percentage of the volume of air that is removed and replaced from the building each hour. This can range from 5 ACH in a tightly sealed building to 1.5 ACH in a sparsely built home.
Proper ventilation is vital to maintaining healthy indoor air quality within a building. As humans carry out basic metabolic processes, they release carbon dioxide into the air. Household items like paint, furniture and flooring often contain chemicals that can release gases into the air. Building ventilation helps remove chemicals and carbon dioxide and replace them with fresh air. Ventilation systems are also used to control humidity levels and reduce odors within a building.
Natural ventilation systems do not require fans, HVAC equipment or ducts. Instead they rely on the pressure differences between the outside and inside areas to help move air. Pressure changes occur constantly in a building and can be caused by wind, temperature changes or human activities. A natural building ventilation system uses windows, louvers, and operable grilles to help air enter or leave a building. While natural systems are very effective at producing air changes, they generally fail to control humidity levels, especially in hotter regions.
Mechanical ventilation systems use fans to draw fresh air indoors and rely on HVAC ducts to distribute the air throughout the building. The fresh air is known as “supply air” and passes through the building’s air handling units as it enters the home. When supply air is introduced into a room, the existing ‘return air’ is forced into the exhaust grilles, where it flows back through the duct network and is discharged to the outdoors.
The type of ventilation system used in a building can have a significant impact on the energy efficiency of the building. A natural building ventilation system does not consume energy to operate fans or air handlers, but instead allows heated or cooled air to escape through open windows and vents. Mechanical ventilation systems require energy to run fans and equipment, but don’t allow as much conditioned air to escape through vents or windows. The energy efficiency of each type of ventilation system must be carefully weighed against the ventilation needs of a building before selecting a system.
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