Combat Hidden HVAC Contaminants

09/28/2012 | By Janelle Penny

Find, target, and treat buildup anywhere in your system

Chemical use may be unavoidable on coils, which are susceptible to biofilm, a buildup of hard-to-remove microbial growth. Coil fins are easily damaged, which rules out hard manual scrubbing.

Deferring HVAC maintenance doesn’t just impair efficiency – it can also lead to breakdowns that eventually necessitate a premature and highly expensive replacement.

When your staff is constantly swamped with service calls, it’s hard to find the time for basic inspections and treatments. Unfortunately, this seemingly time- and money-saving move costs much more in the long run.

The Sources of HVAC Issues
Return air ductwork (if you have it) and the air handling unit are likely to attract grime first, notes Matt Mongiello, president of the National Air Duct Cleaners Association (NADCA).

Coils attract biofilm, a stubborn mix of microorganisms. Areas you often don’t have time to inspect can also spread contaminants, adds Mike White, chair of NADCA’s education committee.

“The air handling unit should be filtered, but depending on the type of filter you use and the frequency with which you’re changing that filter, there can be a lot of accumulation,” Mongiello explains.

Cool, moist places with dirt and dust accumulation, such as VAV boxes, present the optimal breeding ground for microbial growth. Left unchecked, that buildup can eventually spread to the ductwork, White adds.

If your staff is forced to constantly scramble in order to keep buildings running, it may be best to spring for a professional inspection.

Decode Cleaning Solution Claims

Antimicrobial pesticides like these are used to clean hard surfaces within HVAC components, such as air handlers, fans, coils, and duct interiors. What do these common descriptions actually mean?

Sanitizer Kills a high percentage (99.9%) of bacteria on a surface, but not necessarily all bacteria. Designed to reduce contamination to safe levels. Registered pesticides, such as sanitizers, disinfectants, and fungicides, are not approved for use in ductwork due to potential human health implications if building occupants breathe in the chemicals.
DISINFECTANT Targets a specific microorganism species, but may be effective against fungi and viruses as well as bacteria. Use in coils, drain pans, and other air handler parts. Not approved for use in ductwork.
FUNGICIDE Destroys fungi, yeast, and/or fungal spores that may threaten human health. Not approved for use in ductwork.
FUNGISTAT, BACTERIOSTAT, OR ALGAESTAT Inhibits the growth of fungi, bacteria, and algae, that don’t pose a threat to human health. These can be used in ductwork, though it’s best to deep clean before proceeding with chemicals, notes Mike White, chair of NADCA’s education committee.
Other Claims Cleaning products that aren’t registered as pesticides may be permissible for ductwork use. Check the label for approved uses first and ensure you only use the cleaner in authorized areas of the HVAC system.

Products approved for ductwork will state at least one of these claims:
  • Fungistatic
  • Bacteriostatic
  • Inhibits odor-causing bacteria and fungi
  • Inhibits bacteria, fungi, or algae that cause stains and damage
  • Inhibits fungi and algae growth
  • General claims about cleaning (indicates non-pesticidal use)
“Some facilities managers are under the notion that their supply ductwork never gets dirty because they’ve always had filters and a good program, but that’s not always the case,” Mongiello explains. “Sometimes people are surprised at the amount of dirt in their supply ductwork.”

Diagnose and Treat Issues
If you spot buildup, don’t start with the heavy artillery. In many cases, source cleaning is sufficient, White says.

For example, there are no antimicrobial disinfectants or sanitizers (the strongest categories of HVAC cleaning chemicals) with EPA approval for use in ductwork due to health concerns, so trying gentler methods first is the best way to start.

“If you find contamination, the first step is source removal,” White explains. “If you have some internally lined insulation that’s coming apart and becoming airborne, go in and clean that and then put a coating on it to refurbish the material.”

A HEPA vacuum and brush are often all that’s needed for ducts, White adds. For large installations, consider hiring a cleaner to walk through and contact-vacuum contaminated areas.

When in doubt, call in a professional, Mongiello recommends – an improper cleaning could contaminate clean areas.

“Brushing removes the adhered particles from the sides of the ductwork,” White says. “When you put the system under negative pressure and air-sweep the inside, it brings everything back to the HEPA vacuum.”

Ultraviolet disinfection lighting is gaining popularity, Mongiello notes, but its value depends on how you use it, what it’s used for, and whether it passes your cost-benefit analysis. The specialty lighting minimizes microbial growth in places like coils, plenums, and exterior HVAC applications, but bulbs can be costly to install and change, Mongiello says.

Coils especially benefit from chemical cleaning, particularly when you need to dissolve already accumulated enzymes. Like any cleaning solution, check to ensure you’re using something that’s EPA-registered for this use.

Acid-based compounds like phosphoric and hydrofluoric acid solutions are most often used on condenser coils due to the type of soiling associated with their outdoor location, according to NADCA’s guide to HVAC cleaning chemicals.

Alkaline cleaners, which contain chemicals like sodium hydroxide, are best to combat greasy soils. Coils often require chemical assistance because biofilm and greasy soils are very difficult to remove and their aluminum fins are easily damaged, the guide notes.

After the Deep Clean
Once you’ve removed accumulated debris, examine your inspection and cleaning schedule. Despite the all-too-common FM time shortage, don’t defer this maintenance step – the longer you let grime build up, the more you risk an early breakdown.

A proper self-inspection starts with merely looking at the system yourself, Mongiello says.

For instance, when it’s time to change the filters in the air handling unit, peer inside with a flashlight and assess the condition. As with any other building issue, prevention is key.

“Go back to the units and have somebody look at it. If you don’t have the manpower, hire a contractor who can give you an update on what needs to be done,” White says. “It’s a lot cheaper to keep the system up and running efficiently than to wait until it breaks down.”


Janelle Penny is associate editor of BUILDINGS.


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