Coils and motors are the two most expensive components of an air conditioner. Understanding the environment your unit operates in should help you decide whether or not you should go with the added cost of coated coils. Coil corrosion is an expensive problem which ultimately leads toward replacement of an entire system.
What Causes Corrosion on HVAC Coils
Environmental hazards ranging from salt-air to off-gassing of food waste can significantly shorten mechanical systems work lives. Many work environments such as food processing plants, wastewater treatment plants, and paper mills face hazards such as salt, hydrogen sulfide, sulfuric acid, hydrofluoric acid, ammonia, chlorine, hydrogen chloride, sulfur, uric acid, etc. In these environments, coated coils can significantly increase the lifespan of equipment. Corrosion from hazardous environments can create pinhole leaks in coils, fins, tubes, fans and even cabinets. Estimations show that 40% of failure in industrial applications is a result of corrosion according to CED Engineering.
The Two Most Common Types of Coil Corrosion
There are two common forms of corrosion, and they can be observed in as few as 2-3 weeks after installation. Typically, you won’t notice corrosion for 1 to 4 years.
Pitting is a form of corrosion that is caused by fluorides and chlorides and is visible to the naked eye. Fluorides are prevalent in wastewater treatment plants while you find chlorides in products like detergents, fabric softeners, paint strippers, snow melting crystals, etc.
Condensation carries negatively charged chloride/fluoride ions down the metal surface. These negative ions attack the oxide film that usually protects the metal. This process essentially forms a corrosion fueled battery that consumes copper. Once pits have developed in the copper tubes they continue through the copper until a pinhole leak is created, causing the refrigerant to leak.
Formicary corrosion is a result of organic acids such as acetic and formic acids. Acetic acids are found in a lot of household products like vinegar, adhesives, cleaning solvents, paneling, particle board, silicone caulking, foam insulation and dozens of other products readily found at home, work or industrial places. You find Formic acid in cosmetics, tobacco and wood smoke, disinfectants, plywood, latex paints, and dozens of other materials. Formicary corrosion is typically not visible to the naked eye, but sometimes blue-gray or black deposits can be seen on the surface. Formicary corrosion creates an ant-nest type sub-surface networks of microscopic tunnels. Eventually one of these makes it through the coil resulting in coil leakage.
Selecting the Appropriate Coating For Your Application
Choosing the right coating for your coil can save you thousands of dollars in reapplication or replacement costs over the life of a unit. There are several factors to consider when choosing a coating.
Volatile Organic Compounds (VOC’s)
Heat Transfer – Air Conditioners are built to exchange heat from one place to another. When you coat coils with additional material, it inhibits a coils ability to transfer heat. Heat loss from coatings can easily be accounted for when designing a system, but when retrofitting, a coated coil might not perform to its manufactured specification. Generally speaking, the thinner the coating, the better the heat transfer is going to be. Choosing a coating that will minimize thermal loss will also save you in operational costs.
Durability – Selecting a coating appropriate for your environment is critical for longevity. There are four underlying coatings used for HVAC equipment: Polyurethanes, Epoxies, Fluoropolymers & Silanes. Each varies in durability, thickness, and hydrophobicity.
Hydrophobicity – How well water runs off the coating. Coils that can shed water quickly are more efficient and less prone to a residue or organic build up.
Anti-microbial – Closely related to the hydrophobicity of a coating, anti-microbial coatings will inhibit growth on a coil. “Dirty Sock Syndrome” is odor emanating from air conditioners and heat pumps that arises from the decay of accumulated organic debris by microorganism activity — similar to sewers, plumbing traps, and other rotting, decomposing organic material…and their volatile organic compounds (VOC’s). Coated Coils that shed water or are anti-microbial will prevent stinky coils.
Volatile Organic Compounds (VOC’s) – While Dirty Sock Syndrome can be responsible for VOC’s the coating used to protect the coils can also be a significant contributor to VOC’s themselves. Many jurisdictions including California are moving towards stricter standards of VOC’s in paints and HVAC coatings are no exception. Currently, there is only one coating we’re aware of that is compliant with new zero VOC legislation and it’s Aqua Aero.
Coated Coils & Cabinet Options
For three opinions all you need is two people. We have our preferred coatings but recognize everybody has their own needs and preferences. We’re familiar with every major process and brand and can do most of them in our factory. The decision of what we coat and how we do it is yours. Some of our customers prefer only coated coils while others need protection for the entire cabinet and coils.
Aqua-Aero (Coil & Cabinet)
Phenicon by Sherwin Williams (Coil)
Power Coating (Cabinet)
Sherwin Williams (Cabinet)
Standard colors are white and gray. Sherwin Williams color matching available.
Select your favorite one on the Build Yours tool, or we’ll work with you to help find the best coating for your application.