Mold doesn't require standing water to grow. High humidity is moisture enough for mold spores to germinate. High relative humidity levels in air-handling units occur anytime outdoor air dew points are above the cooling coil discharge temperature (typically 61°F). Air discharged from the cooling coils under these conditions usually has a relative humidity level of 90 percent or higher. Provided food is present, this is all it takes for mold to grow in an air distribution system.
Condensation is another problem, occurring whenever air comes in contact with surfaces that are cooler than the dew point of the surrounding air. This makes cold ductwork a prime area for unwanted moisture. This moisture can condense into liquid at the wrong place and the wrong time, wetting building components such as ceiling tiles, drywall, and carpeting, and setting the stage for mold growth.
Among solutions currently being offered involve the use of closed-cell, elastomeric foam. According to proponents of this approach, the foam won't absorb moisture. Its smooth surface also inhibits the accumulation of dirt that can serve as food for mold.
Properly installed and maintained, elastomeric foam is an effective deterrent to biological contamination, proponents said. Even if closed-cell foam duct lining gets dirty or wet, its smooth surface makes it easy to clean.
Proper insulation practices, along with good maintenance practice, are an owner's best defense.
Publication date: 10/02/2006