As seen in the October issue of

Micro-channel Evaporator-coil Technology

An overview of all-aluminum micro-channel evaporator-coil technology, including technical differences HVAC professionals need to be aware of when installing or servicing.

B y M a t t L a t t a n z i a n d D o u g P r i e s t l e y

All images courtesy of NORDYNE. A n example of an aluminum micro-channel evaporator coil.

n recent years, formicary corrosion has wreaked havoc on tion, laminates, oil based paints, paneling, plywood, silicone the heating and cooling industry. As the No. 1 cause of caulking, latex paints, cosmetics, disinfectants, deodorizers, Ievaporator-coil leaks, formicary corrosion has gotten worse wallboard and other common household/construction prod- for a host of reasons: Chinese-manufactured drywall, tighter ucts). In areas such as the southeastern Unites States, all four home construction, different materials used in insulation and of these components are commonly found inside the central carpeting, new adhesives and more. The list of blame goes on A/C system. But if one component can be eliminated, so can and on. Regardless of the cause, HVAC manufacturers have the corrosion—and the resulting leaks. been quick to address the problem with fast fixes, such as coatings and different lubricants, as well as long-term product H istory of micro-channel changes such as all-aluminum coil construction. The automotive industry shares many of the same manufac- turing challenges faced in HVAC: cost, size and weight. In What is formicary corrosion? the early 1990s, the automotive industry had a significant Formicary literally means “ants’ nest.” So, formicary cor- challenge relative to air-conditioning systems—the industry rosion, as it relates to evaporator coils, is referring to small had to transition from R-12 to more environmentally friendly wandering pits that resemble the tunnels in an ants’ nest. R-134a, a that operates at slightly higher condens- This corrosion attacks copper and copper alloys exclusively, ing pressures. and is prevalent in southern climates with high . Faced with these issues, the automotive industry inves- Four components are necessary for formicary corrosion to tigated alternative coil technologies to improve the perfor- happen: copper, moisture, oxygen and an organic acid (from mance of their systems while maintaining or reducing size such items as adhesives, cabinets, countertops, foam insula- and weight. The answer was all-aluminum micro-channel coil

14 RSES Journal OCTOBER 2012 www.rsesjournal.com Four components are necessary for formicary “ corrosion to happen: copper, moisture, oxygen and an organic acid...

braze joint. Additionally, the product quality is further ampli- fied due to one homogeneous braze joint as opposed to more than 300 braze joints typically found on standard copper- tube/aluminum-fin coils. The two manifolds facilitate a two-pass process. In the first pass, the high-pressure superheated refrigerant is de-su- perheated and condensed into a liquid. The second pass sub- cools the liquid refrigerant below its saturation temperature prior to entering an expansion device. A close-up view of a micro-channel evaporator-coil’s all- This construction provides a coil that is typically 50% aluminum construction. lighter and uses, on average, 50% less refrigerant when com- pared to a copper-tube/aluminum-fin coil design. Heat trans- technology. It became the industry standard, and now, 20 fer is also enhanced, leading to smaller, more-efficient coils. years later, this technology is being used in residential heat- Additionally, the all-aluminum uniform design provides a ing and cooling systems. structurally robust coil. The biggest benefit, however, is rela- tive to formicary corrosion. O verview and benefits Micro-channel coils are aluminum-extruded channels that What technicians need to know are mechanically brazed to aluminum fins. The coil has three Many online HVAC forums are filled with misinformation basic components: micro-channel tubes, aluminum fins and about installing and maintaining micro-channel evapora- two manifolds. All three components are brazed together in tor coils. The coils are not more complicated than tradition- a hydrogen/nitrogen brazing . The lack of oxygen and al copper-tube/aluminum-fin coils, but they are more sensi- water in the brazing process ensures a robust reliable tive to accurate charging. If technicians have questions about www.rsesjournal.com OCTOBER 2012 RSES Journal 15 A traditional copper coil showing formi- cary corrosion. Field failure in this par- ticular coil occurred just two months from manufacture date.

installing or servicing these coils, they should go directly to their distributor or the manufacturer, as other online answers may be incorrect. The coils are not more I nstallation The installation of micro-channel evaporator coils follows complicated than traditional the same process as a traditional fin-in-tube coil. The install- copper-tube/aluminum-fin coils, er will need to: “ gBraze with nitrogen; gInstall a liquid-line filter-drier; but they are more sensitive gFollow the triple evacuation method; and gWeigh in the additional charge. to accurate charging.

These are the same practices that should be followed when installing any HVAC component or system. Installers should always refer to the manufacturer’s instal- flakes can form on the inside of the copper and can clog the lation instructions for the proper size or metering device. narrow micro-channels inside the coil. In many cases, the Some micro-channel coils may have dual applications and evaporator coil has a filter screen at the inlet of the metering may need a piston or TXV change. The installation of these device that also can become clogged by oxidation flakes. Al- metering devices is very similar to a copper-tube/aluminum- ways install the liquid-line filter-drier as close to the evapora- fin coil, and no special tools are required. In most cases, braz- tor as possible. This will catch any debris or moisture before ing is not necessary when installing a TXV. entering the metering device. It is best practice to have a small flow of nitrogen when When evacuating the system, technicians should use the brazing in any lineset, but it is critical with micro-chan- triple evacuation method and always use a micron gauge nel coils. If the installer brazes without nitrogen, oxidation to determine if the correct vacuum is reached. Do not rely

16 RSES Journal OCTOBER 2012 www.rsesjournal.com One of the benefits of micro-channel coils is that they require less refrigerant. However, this means there is also less room “for error when charging the system, as technicians need to be within ounces of the correct charge, not pounds.

on a gauge set alone to determine if the correct vacuum is room for error when charging the system, as technicians need reached. to be within ounces of the correct charge, not pounds. When charging a micro-channel system, any additional charge C harging should be weighed in with a scale. Technicians One of the benefits of micro-channel coils is that they re- should not use a bathroom or fish-type scale, as they do not quire less refrigerant. However, this means there is also less have the accuracy of the refrigeration scale. When adding

www.rsesjournal.com OCTOBER 2012 RSES Journal 17 T his close-up view of a micro-channel evaporator coil shows the micro-channels and fins.

charge to dial in the system, add small amounts of refrigerant izing in residential systems. Lattanzi is a member of ASHRAE at a time. It is also necessary to allow the system to level out and serves on various AHRI committees. For more information, in between adding refrigerant. Wait a minimum of 10 min- e-mail [email protected] or visit www.heynordyne.com. utes between each addition. To ensure accuracy, gauge sets should use the shortest Doug Priestley is the Technical Services Supervisor at NORDYNE hoses possible—not a hose that is as long as the technician and based out of the company’s O’Fallon, MO, corporate office. is tall. Since micro-channel systems use less refrigerant, the Priestley oversees HVAC contractor training materials, including trapped liquid in the high-side hose can affect the charge lev- online courses and NATE-recognized continuing education hours. els in the system. Always use some type of low-loss fittings on For more information, e-mail [email protected] or visit your gauge set, and meter the trapped refrigerant in the high- www.nordyneu.com. side hose back into the system through the low-side hose. Re- member to meter the refrigerant during this process. If there are any questions regarding the charge levels in a micro-channel system, it might be necessary to remove 1. First vacuum: Pull the system down to the entire amount of refrigerant and weigh it back into the system. 1,500 microns. R epair 2. Break the vacuum with nitrogen; release If a micro-channel evaporator coil needs a repair, the techni- nitrogen. cian should refer to the specific manufacturer’s installation in- 3. Second vacuum: Pull the system down to structions. Repair kits using epoxy do exist, but in many cases, a coil replacement might be a better or preferred option. 1,500 microns.

While providing much greater resistance to formicary cor- vacuation Method 4. Break the vacuum with nitrogen; release rosion, micro-channel evaporator coils are not more difficult E to install or service if the technician follows standard indus- nitrogen. try practices and the manufacturer’s instructions. Obtaining 5. Third vacuum: Pull the system down to a the correct system charge can be accomplished efficiently and within a reasonable period of time. minimum of 500 microns.

The Triple 6. Charge the system. Matt Lattanzi is the Director of Product and Warranty Manage- ment at NORDYNE, a heating and cooling manufacturer special-

18 RSES Journal OCTOBER 2012 www.rsesjournal.com