Addressing Corrosion, Cleaners, And Coil Maintenance
In a recent conversation, Haydu gave his insights on what hvacr service contractors need to know about coil maintenance. For starters, he said, don’t assume that the air in the area of the country you live in is not corrosive to coils.
Corrosion Severity Across The U.S.Absence of salt does not mean absence of corrosives. Coils need cleaning more than twice a year “even if you’re not in a salt Absence of salt does not mean absence of corrosives. Coils need cleaning more than twice a year “even if you’re not in a salt environment,” said Haydu. If you’re in Nebraska rather than Florida, don’t assume that the environment is safe for your coils.
Conditions other than salt can lead to increased coil corrosion, said Haydu. These include irrigation systems of acid rain, sulfur water, fertilizers, potash, pesticides, and animal urine. All these, as well as fossil fuel emissions and CO2, contribute to form corrosive environments. (See Figure 1.)
Even insects can lead to corrosion if they are drawn into the coil by the fan, as chemicals released by their decomposition are corrosive, said Haydu.
We haven’t even mentioned bird droppings. Do we really need to? It’s all bad news if coils aren’t cleaned often enough.
Cleaning should be done, at a minimum, once per quarter, said Haydu. In areas with severe corrosive atmospheres, such as coastal shops, houses, or condominiums, it may be required as often as monthly to maintain an energy-efficient operating system.
Service Tech ErrorsIn the best of all possible worlds, service technicians would be taught suitable methods for coil cleaning — and would follow them. But this is not the best of all possible worlds, so information needs to be reinforced from time to time.
Haydu pointed out that “In most cases, when service technicians clean coils, they do one of two things”:
1. They hose it down with just water. This can actually create more corrosion because it activates the corrosive deposits adhered to the coil. It can also encourage growth of fungi or biological contaminants.
Think about it. If you let your automobile set at the beach for a week, and then only rinsed it with water, do the salts flush off? The answer is no. It takes a cleaner to break the surface tension and flush the salts from the surface, explained Haydu. This is the same as with any corrosive atmospheric deposit.
2. When using highly aggressive cleaners, “They tend to spray it on real quick and not in a uniform manner, because many of these aggressive cleaners sting or burn the applicator when it gets on their skin or face and eyes.”
Another problem with highly aggressive cleaners is that while removing the soils, they can also remove good metal from the fin surface, said Haydu. While the result is a shiny coil, it can also mean a weakened fin; if the cleaner contains more than 10 ppm of halogens and is not thoroughly rinsed from the coil surface, the residue can continue to attack the coil metallurgy.
“Selection of a coil cleaner is important,” wrote Haydu recently, “since the cleaner has to both neutralize and remove deposits from the surface of the coil.
“Alkaline and acidic cleaners are the most widely used,” he continued. “The base ingredient of a coil cleaner should not be of such a harsh nature that it attacks the metal, coil coating, or the personnel applying the cleaner.”
Haydu professes a preference for surfactants for coil cleaning. “They penetrate and lift soils from coils,” he said, without attacking the base alloy. With increasing emphasis on higher efficiencies, the industry will probably see more fins/in. tightening the space for airflow through the coil.
“Therefore, it will become even more critical to maintain a clean coil so that the airflow is not restricted,” said Haydu. “Studies by power companies have shown that a 10% to 20% efficiency improvement can be achieved by properly maintaining coil cleanliness.” This is a big energy saving.
Fins And CoatingsAnother thing service contractors and technicians may overlook is straightening the fins. “If fins are all bent over, they are restricting airflow,” said Haydu. Fin combs that straighten fins were made for various fin/in. configurations. Use them wisely.
By use of the properly spaced fin comb to straighten the fins, bent fins can be fixed. Haydu pointed out many manufacturers are using enhanced, lanced, or raised fins. When straightening these fins, one has to be careful not to comb too deep as it can damage or bend the enhanced or lanced fin. The enhanced or lanced fin helps create a greater vortex of airflow over the fin, increasing its efficiency, explained Haydu. When they become damaged, this decreases their efficiency. It also aids in trapping atmospheric corrosives that can increase localized corrosion.
Keeping the coil clean aids in reducing galvanic corrosion at the points of dissimilar metal, such as the fin and tube interface and “U” bends, where brazing has taken place in construction of the coil.
However, Haydu said he prefers aluminum/copper coils with a quality coating that has been dip applied to the coil. “I believe this provides the owner with a more economical option than copper/copper coils,” he said, “and in most cases, coated aluminum/copper coils will have a longer life span.”
Haydu also noted that some engineers are using UV light to aid in the control of biological growth on evaporator coils. Haydu feels that coil coatings should be UV inhibited. He said his rule of thumb would be an inhibitor that is equal to 10-year Florida sun exposure.
Publication date: 12/17/2001