Air Scrub University

Here are some helpful pieces of information obtained from the Environmental Protection Agency regarding indoor air quality and air conditioning.

Many HVAC components are particularly important to maintaining good IAQ. Tips for optimum functioning are listed below.

Coils and Drain Pans

  • Malfunctioning coils, including dirty coils, can waste energy and cause thermal discomfort.
  • Standing water will accumulate if the drain pan is not properly designed and maintained, creating a microbial habitat.
  • Proper sloping and frequent cleaning of the drain pans is essential to good indoor air quality.

Humidification and Dehumidification Equipment

  • Wet surfaces should be properly drained and periodically treated as necessary to prevent microbial growth.
  • Duct linings should not be allowed to become moist from water spray.

Air Filters

  • Use filters to remove particles from the air stream.
  • Filters should be replaced on a regular basis, on the basis of pressure drop across the filter, or on a scheduled basis.
  • Fans should be shut off when changing the filter to prevent contamination of the air.
  • Filters should fit tightly in the filter housing.
  • Low efficiency filters (ASHRAE Dust Spot rating of 10%-20%), if loaded to excess, will become deformed and even “blow out”, leading to clogged coils, dirty ducts, reduced indoor air quality and greater energy use.
  • Higher efficiency filters are often recommended as a cost-effective means of improving IAQ performance while minimizing energy consumption.
  • Filtration efficiency should be matched to equipment capabilities and expected airflows.

A small amount of dust on duct surfaces is normal. Parts of the duct susceptible to contamination include areas with restricted airflow, duct lining, or areas of moisture or condensation. Problems with biological pollutants can be prevented by:

  • Minimizing dust and dirt build-up (especially during construction or renovation)
  • Promptly repairing leaks and water damage
  • Keeping system components dry that should be dry
  • Cleaning components such as coils and drip pans
  • Good filter maintenance
  • Good housekeeping in occupied spaces.

Duct leakage can cause or exacerbate air quality problems and waste energy. Sealed duct systems with a leakage rate of less than 3% will usually have a superior life cycle cost analysis and reduce problems associated with leaky ductwork. Common problems include:

  • Leaks around loose fitting joints.
  • Leaks in return ducts in unconditioned spaces or underground can draw contaminants from these spaces into the supply air system.

Humidity and Microbial Growth
In addition to thermal comfort, the control of relative humidity is important to limit the growth of microorganisms such as mold and dust mites. To control microorganisms, it is best to keep relative humidity below 60% (to control mold) and 50% (to control dust mites) at all times, including unoccupied hours. High relative humidity can foster proliferation of mold and dust mites. See also