Cleaning Microchannel Coils
A little TLC goes a long way
Keeping any kind of air conditioning or refrigeration coil clean is important for proper heat exchange, and microchannel coils are no exception. As these types of coils continue to grow in popularity, technicians should know that the microchannel cleaning procedures can differ from those for cleaning standard fin-and-tube coils.
Microchannel condenser coils are all-aluminum coils with multiple flat tubes containing small channels (microchannels) through which refrigerant flows. Heat transfer is maximized by the insertion of angled and louvered fins between the flat tubes. The coils are designed to be lighter, more durable, provide better heat transfer, and require less refrigerant charge than conventional tube-and-fin coils.
Mike Heidenreich, vice president of product engineering, Luvata HTS (Heat Transfer Solutions) Division, noted that because microchannel coils are typically thinner in depth than conventional plate fin-and-tube heat exchangers, microchannel coils tend to accumulate more dirt on the coil’s face and less inside the fin pack. Therefore, cleaning them must take into consideration the difference in construction.
Luvata’s recommended cleaning procedure for microchannel coils:
Step 1: Disconnect power to the unit — This should be done before any service work on any electrical equipment. In addition, appropriate personal protective equipment (safety glasses, gloves, etc.) should be worn.
Step 2: Remove surface debris — Remove surface dirt, leaves, fibers, etc. with a vacuum cleaner (preferably with a brush or other soft attachment rather than a metal tube). Blow compressed air from the inside out, and use a non-metallic soft-bristle brush to help with heavier particles, if necessary. Do not impact or scrape the coil with the vacuum tube or air nozzle.
Step 3: Rinse — Do not use any chemicals (including those advertised as coil cleaners) to wash microchannel heat exchangers, as they can cause corrosion. Rinse only. Hose the microchannel heat exchanger off gently, preferably from the inside out and top to bottom, running the water through every fin passage until it comes out clean.
“Microchannel fins are stronger than traditional tube-and-fin coil fins, but still need to be handled with care,” Heidenreich said. “Be careful not to bang the hose into the coil. In addition, we recommend putting your thumb over the end of the hose rather than using a nozzle end because the resulting spray is gentler and the possibility for impact damage is less.”
It is possible to clean a microchannel heat exchanger with a pressure washer, but — as with any coil-finned surface — extra care must be taken as it is possible to irreparably damage the coil, Heidenreich added.
“Use a wide-angle spray nozzle (no pencil nozzles) and only spray the coil at 90 degrees to the coil face,” he said. “Keep the nozzle at least 24 inches away from the coil face. Gently use a sweeping back and forth motion maintaining the 90-degree angle at all times.”
Step 4: Optional blow dry — Microchannel heat exchangers, because of their fin geometry, tend to retain water. Depending on the specific design and installation of the coil, it may be beneficial to blow or vacuum out the rinse water from a unit to speed up drying.
CHEMICAL CLEANERS OR DETERGENTS
Although Luvata’s recommendations strongly urge rinsing microchannel coils with water only, it’s possible that, in some extreme cases, a cleaner might be necessary. A general service bulletin from Trane Unitary Light and Large Commercial Units, “Microchannel Coil Servicing Guidelines,” addresses this possibility.
“Only in extreme cases should any type of chemical cleaner or detergent be used on microchannel coils,” it says. “If it becomes absolutely necessary because water alone did not clean the coil, specify a cleaner that is pH neutral (an alkaline cleaner that is no higher than eight on the pH scale and an acidic cleaner that is no lower than six on the pH scale) and does not contain any hydrofluoric acids.
“Be sure to follow the instructions provided with any cleaner chosen,” the bulletin states. “Keep in mind it is still mandatory that the coils are thoroughly rinsed with water after the application of the cleaner, even if the instructions specify a no-rinse cleaner. Cleaners or detergents that are left on the coil due to improper rinsing will significantly increase the possibility of corrosion damage on the microchannel coil.”
Kevin Gurley, engineering/sales manager, Peerless of America II Inc., added that steam cleaning is probably one of the best ways to clean coils, but that method isn’t always readily accessible.
Gurley also recommended using coil cleaners with caution.
“When using commercially available cleaners, always follow the directions carefully,” he said. “They typically indicate that the coils must be rinsed thoroughly to remove all detergent and debris.”
And only use cleaners specifically designed for coils, he added, as some cleaners not designed for coils can be harsh and will attack the copper or aluminum..
“The important thing is to keep the coils clean,” Gurley said. “They cannot exchange heat properly if they are dirty.”
SIDEBAR: Cleaning Small-diameter Copper Coils
Small-diameter copper tube coils are designed to provide many of same advantages of microchannel coils, including their small size, light weight, low material costs, high heat transfer coefficients, and low refrigerant charge.
Keeping these coils clean is just as important as keeping microchannel coils clean, but the procedures are slightly different because of the difference in construction. For example, the tubes in round-tube plate-fin coils are, as the name indicates, round, unlike the flat shape used in microchannel coils.
Nigel Cotton, MicroGroove team leader for the Copper Alliance, offered insights on cleaning small diameter round-tube plate-fin (RTPF) coils. “RTPF coils are easy to clean and offer good condensate drainage,” Cotton told The NEWS. “The plate fins in RTPF coils are typically vertically oriented, and water drains easily from the top to the bottom of the sheets. The tubes penetrate the sheets at right angles, and water can easily flow around them. The same holds true for RTPF coils made from smaller-diameter copper tubes. There may be more tubes penetrating the plate fins, but water flows easily around the smaller-diameter tubes.
“HVACR contractors are performing a valuable service by cleaning coils on a regular basis in both commercial and residential settings,” Cotton added. “RTPF coil cleaning methods are well-established, and a variety of cleaning solutions and foam sprays are available in the marketplace for this purpose. When cleaning RTPF coils, a fin comb can be used to straighten fins, which further restores the coil efficiency to its original value. Fins in microchannel coils are not continuous between the tube rows. Each fin edge needs to be individually straightened, if bent.”
Publication date: 9/12/2016