Biofilm Growth in Commercial HVAC Systems

Hvac System Cleaning

What is Biofilm Growth?

It doesn’t take much for mold or bacteria to build a little home for themselves. Typically, high humidity levels will provide enough moisture to support life for an initial organism, and then, in the case of mold, they can send spores into various other reaches of the area, which if the area is also humid, will allow for further growth; or in the case of bacteria, the microorganisms can slowly creep over a surface and propagate this way. If however, the organisms are fortunate enough to begin their life in a more than humid environment, like say, an evaporator coil with fins that are each coated in a steady flow of sweat, or a condensation pan with a healthy pool of standing water, then these baby organisms have the possibility of creating a much more dynamic and enduring colony. This type of colony is called a biofilm.

“Understanding Microorganisms in Biofilm.” American Pharmaceutical Review. Jeanne Moldenhauer, Ph.D. October 12, 2018.

When a biofilm is formed, the communities of microorganisms are enclosed in a protective extracellular polymeric substance matrix. The matrix allows for adherence to living tissues, natural and artificial surfaces as well as to other microorganisms in the community. The biofilm also provides a defense mechanism to prevent eradication. Another benefit is that the biofilm makes the microbes stronger and more resistant to attack, e.g., antimicrobials, disinfectants, and host immune defenses. These sophisticated defense mechanisms make it difficult to identify the organisms, much less eradicate them.

​In the world of indoor air conditioning, biofilms generally present in the evaporator coils, chillers, and cooling towers.

In the world of dental hygiene, biofilms present at the gum-line, and in between teeth; they are more commonly known by the name: plaque.

Why this is bad:

♦ Build up of slime impedes air flow, thereby:

◊ Increasing energy costs

◊ Overworking the system and diminishing the lifespan of equipment

♦ Over time, slime causes corrosion, thereby requiring premature replacement for equipment

♦ Biofilms threaten the health of occupants by providing an (almost) impenetrable fortress for bacteria such as legionella

What are traditional cleaning options?

♦ Hot water with pressure (will not kill amoebas)

♦ Chlorine Bleach (will not kill amoebas)

»» While chlorine and hot water can kill the bacteria residing in the biofilm, there are other biofilm inhabitants who are immune to these cleaning techniques… they’re called amoebas. During a hot water or bleach powered cleaning session, certain bacteria, like legionella, can find safe harbor inside the amoebas, and then repopulate the biofilm once the cleaning process has ended.

♦ UV spectrum lights (too limited)

♦ Enzyme Cleaners (will not kill all bacteria—will become food for bacteria)

♦ Hydrogen Peroxide (will not kill all bacteria)

♦ High pH Alkaline (corrosive)

Acids (corrosive)

How Power Vac America Cleans Biofilms—If you can’t beat ‘em, join ‘em!

We use living bacteria to attack the biofilm in the form of a probiotic cleaning product. Because the probiotics are alive, they continue to work after application (versus enzyme cleaners, which only work during application.

Importantly, our probiotic cleaner can be applied without turning the units off for extended periods of time—in fact, the efficacy of the cleaner is increased by the agitation caused by the running unit. Through continuous movement, the good bacteria are kept active and moving, ensuring that the product gets to all the nooks and crannies.  This makes the probiotic cleaner an ideal option for jobsites that cannot have prolonged downtime, such as plants and hospitals.

In a case study from February 2018, probiotic coil cleaner was applied to an evaporator coil located in a Florida hospital. The hospital’s air flow was severely restricted. Conventional cleaning would have required a four man crew, and access to the shut-off unit for at least eight hours.

Instead, with the probiotic cleaner, the coil was cleaned by a two man crew, and the unit was only off for two hours (the time it took to apply the cleaner). Three days later, the air flow started to see significant improvement. By the seventh day following cleaning, airflow was restored to 85% of manufacturer’s specifications. Also important, at no time was there an odor in the AHU.