Dirty Sock Syndrome

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Dirty Sock Syndrome

“Ooooh that smell / Can’t you smell that smell” – Eliminate Microbial Odors

Lynyrd Skynryd was not singing about the smell dirty socks, but refrain still applies, as some commercial and residential HVAC systems can smell like a high school gym locker, a phenomenon aptly named “Dirty Sock Syndrome.”

The smelly problem originates in heat pumps and HVAC cooling coils from dead, decaying microorganisms. Although different options exist for controlling these odorous occurrences, the most effective and practical is UV-C technology.

In HVAC Systems

When it comes to cooling coils, microbial buildup starts on day one. A/C components are not made in sterile environments, meaning that microbes cover all of their parts along with a small amount of lubricant.

During the first cooling event following installation, condensate brings life to the microbes, which initially use the lubricant as a food source. Recirculated air contains a variety of organic materials and microbial species that aide ongoing decay and microbial proliferation. Microbial decay (rotting) is the process by which organic substances are broken down into simpler forms of matter — including gas molecules and acids. Even the carcasses of the original organisms begin to decompose shortly after death, setting the stage for a cumulative cycle of microbial growth.

In Heat Pumps

During certain times of the year when a heat pump may warm in the morning hours and then cool at noon and later hours, it can produce condensate during this cooling cycle to fuel growth for up to 16 hours — only to release odor and toxins during the next morning’s warming hours. Heat pump coil temperatures are often not sufficient to kill the ever-increasing microbes. Those that may die simply serve as a future food source for continued proliferation.

Dirty Sock Solutions

Accepted methods for the complete killing of microorganisms include:

Heat—although used in several types of food production (canning) to kill microorganisms of all kinds, it has limited application in residential systems, and it leaves carcasses behind that will serve as a future food source.

Chlorinated compounds—chlorine (bleach), works amazingly well as it not only kills microbes, it rips up their carcasses to limit them as a potential food source. But bleach is corrosive, and requires routine application…and it stinks.

UV-C—it kills microbes of all kinds and types and, like bleach, rips up their carcasses and other organic materials. However, UV-C produces very little heat, no odor, and leaves no secondary contamination behind — and it operates continuously, which means no build-up of microbial matter occurs, ever. UV-C is thus the most reliable and efficient means of eliminating the odor.

Using UV-C

To cure “Dirty Sock Syndrome”, UV-C products must be installed and maintained correctly. Follow ASHRAE recommendations and locate the lamp just downstream of the cooling coil and operate it 24/7/365. Operating continuously means that even 1 microwatt of UV-C wavelength energy will add up to 2.3 million microwatt-seconds in a month’s time. That’s more than enough to kill any microbes on coil and drain pan surfaces. It’s also enough to kill and remove growth and debris already on a coil if installed as a retrofit.

UV-C will do some amazing work, but there are a few things that will help prior to its installation, where possible:

  • Clear drain lines and traps.
  • Correct drain line angles.
  • Make sure traps are sufficient and primed.
  • Seal water and air leaks.

UV-C products’ superiority cannot be denied. According to many contractors, ultraviolet germicidal irradiation systems are less expensive than a proper coil cleaning procedure and/or antimicrobial application. Moreover, when a coil cleaning isn’t practical, UV-C can be installed.

To read the original article that appeared in ACHR News entitled, “Dirty Sock Syndrome: What It Is, How to Prevent It,” click here