Most modern homes need mechanical ventilation systems to provide satisfactory indoor air quality. Many poorly ventilated homes have mold and mildew growing in wall cavities, high levels of airborne chemicals, combustion byproducts, or high utility bills. It’s
Ventilation Systems Protect People and Preserve Buildings
Properly designed ventilation systems perform three important tasks.
- They protect human health by diluting airborne pollutants and by supplying fresh air.
- Ventilation improves comfort by eliminating odors and reducing drafts.
- Ventilation systems preserve structures by controlling airborne moisture, thus preventing moisture condensation.
Mechanical ventilation systems move air through the home using fans and ducts. Electric controls regulate airflow to provide ventilation where and when the home needs it. Contractors built many homes over the years that ventilate only by bathroom, kitchen fans, openable windows, and unintentional air infiltration through the building envelope. This un-controlled ventilation sometimes provides good indoor air quality and sometimes not.
Air Leakage is Wasteful and Polluting
Controlling air leakage through the building envelope is the first step to designing healthy and efficient buildings.
Air leakage happens when wind, temperature differences, or HVAC systems force air into and out of a building through unintentional leaks in walls, floors, ceilings, windows, and doors. Of course, air leakage can bring fresh air into the home, but just as often the air is polluted by crawl spaces, attics, lawn chemicals, and dust.
Three Requirements for Ventilation Systems
A ventilation strategy should dilute and/or remove both the background emissions and the occupant-related emissions, in order to minimize exposure to pollutants. As a result, current standards and regulations, such as ASHRAE 62.2-2016 and others in Europe, often prescribe ventilation strategies requiring three constraints on airflow rates:
- A constant airflow based on a rough estimation of the emissions of the buildings: for instance, one that considers size of the home and the number and type of occupants, or combinations of these.
- Minimum airflows (for instance during unoccupied periods).
- Provisions for short-term airflows to dilute a source pollutant generated by activities as cooking, showering, house cleaning, and painting.