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Ventilation/HVAC Systems
In the past, efforts to reduce energy usage led some school planners to seal buildings tightly. Some buildings that are tightly sealed do not provide adequate ventilation for building occupants. Common IAQ problems in schools are often the result of inadequate ventilation in buildings that are too tightly sealed.
Ventilation considerations and HVAC system design and operation are critical components of any school IAQ management plan.
- Ventilation is the process of bringing fresh air into a building and exhausting stale indoor air out of the building.
- HVAC systems are the tools used in most schools to control fresh air intake, exhaust old, stale air, and control indoor temperature and humidity.
- In the process of bringing fresh air into a school and expelling stale indoor air, a properly functioning HVAC system can control odors and reduce pollutants that cause most IAQ problems inside buildings.
- School HVAC systems should be designed and operated to provide a minimum outdoor air ventilation rates consistent with the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 62.1 Standard which for classrooms is about 15 cubic feet per minute (cfm) of outdoor air per person.
Without adequate ventilation, pollutants can build up inside the building and result in IAQ-related complaints. According to a 199 report from the National Center for Education Statistics of the U.S. Department of Education approximately 25 percent of schools describe unsatisfactory ventilation, while 20 percent of schools told of unsatisfactory IAQ. In addition, 36 percent of all school officials rated their facility's heating and ventilation systems as a less than adequate building feature.
Common IAQ Problems Related to HVAC Systems
When HVAC systems are poorly designed, operated, or maintained, they can create IAQ problems. Common HVAC system problems and related IAQ issues include:
- Closed outdoor vents or dampers that do not allow for adequate fresh air intake (sometimes vents are closed to save energy) – Without adequate fresh air, a building may develop a variety of IAQ problems
- Obstructed outdoor screens on the fresh air intakes – When screens are blocked, obstructions can prevent adequate fresh air, or debris in the screen can bring outdoor pollutants into the building
- Filters that have not been changed on a regular basis – Filters only work to prevent potential contaminant sources from entering the building if they are changed regularly
- Moisture in drip pans and ductwork – Moisture can lead to mold growth. If mold grows in one part of the HVAC system, it can be distributed throughout the school
- Poor outside air quality – If the air outside the school is contaminated with chemicals, smog, mold, pollen, and/or vehicle exhaust, the outdoor air intakes can bring contaminant sources into the school