The function of coils in heating and cooling systems is to transfer heat from one medium to another, either extracting heat from a building and expelling it outside or vice versa. Depending on the application, different technologies are available to ensure thermal energy is transferred as efficiently and cost-effectively as possible.
TYPES OF COILS
Several types of coils are available for both residential and commercial heat-transfer applications. One kind of coil technology that has become especially popular in recent years is MicroGroove.
“The International Copper Association refers to round-tube, plate-fin [RTPF] coils made from smaller diameter copper tubes as MicroGroove technology,” said Nigel Cotton, MicroGroove team leader for the International Copper Association. “Such coils are used by OEMs as condensers and evaporators in diverse refrigeration, air conditioning, and heat pump applications, from the very small to the very large.
“The RTPF construction of MicroGroove technology is easy to clean and defrost because water does not get trapped between flat tubes, as is the case with microchannel coils.
The core advantage of MicroGroove technology, Cotton said, is that the internal heat transfer coefficient [HTC] of a smaller-diameter, inner-grooved tube is much higher compared to larger-diameter, smooth-walled tubes. Hence, less material and refrigerant are required for a given performance, whether the capacity is hundreds of watts or hundreds of kilowatts.
David Pflum, vice president and general manager, Precision Coils, said Precision offers finned copper tube steam and hot water heating coils; chilled water and refrigerant DX cooling coils; and refrigerant condensing coils in 1-, 5/8-, ½-, 3/8-, and 5/16-inch tube diameters that are used in HVAC and commercial heating, cooling, and condensing applications.
“Precision Coils builds coils for new construction, OEM, and made-to-order replacements,” Pflum said. “Also, [we offer] insulated coil cabinets with integral drain pans, which we call Thermicoil. [They are] efficient, cost-effective, durable, configurable, and customizable.”
Peerless of America II Inc. offers several heat exchanger options for evaporators and condensers, said Kevin Gurley, engineering/sales manager, Peerless of America II Inc. “These include 3/8- and ½-inch plate fin coils; 3/8-, 5/8-, and ¾-inch off-center coils; 5/16-inch wraparound coils; and Skyve coil technology,” he said. “The copper/aluminum 3/8- and ½-inch plate fin coils are built with the tubing mechanically expanded into the fins. This traditional coil construction has a great tube-and-fin bond for excellent heat transfer. These coils are used in a variety of refrigeration applications and can be built from a range of 3.5-18 fins per inch. The low-FPI coils are used in low- and ultra-low-temperature evaporator applications as well as condensers where fouling is a concern.”
Over the years, coils have gotten smaller and more efficient, Cotton said. “New refrigerants are motivating manufacturers to adopt MicroGroove technology because the smaller-diameter copper tubes support higher pressures and use less refrigerant,” he said. “MicroGroove technology is unique [in that it uses] existing copper manufacturing technology to make products that are lighter, more compact, and more energy efficient without increasing size or weight. Such products use less material than would otherwise be the case.”
“In the copper tube market, we are seeing a trend toward smaller-diameter tubes, such as 5/16-inch [tubes]. These smaller diameters, in some applications, offer higher efficiency,” Pflum said. “New refrigerants are being developed in response to climate-change concerns. These refrigerants can operate at higher pressures; therefore, the coil must be designed and constructed accordingly.”
Gurley said coil technology has changed in several ways over the years, including adopting smaller tubing sizes. “Manufacturing processes have also changed to accommodate cost-effective solutions. New refrigerants have also played a role in coil changes. We look for the coil market to continue to evolve for years to come. Peerless still maintains some of the older coil technologies to serve certain markets that would have been forgotten, and we continue to be innovative by creating new coil options to serve the newest demands. The trend seems to be smaller and more durable coils that can be cleaned easily. Something that always remains the same is that coils cannot function properly unless they are clean.”
CLEAN COILS ARE HAPPY COILS
To that end, Doug Gildehaus, director of product development for Nu-Calgon, said the company has developed coil-cleaning solutions to accommodate newer coil technologies. “Surfactant options have evolved that have allowed us to continually improve coil cleaners for the best cleaning outcome even as the market changes,” he said. “Also, there have been packaging evolutions that have allowed Nu-Calgon to tailor a product for a specific market segment. A good example is Nu-Calgon’s Tri-Clean 2x, which is a specially formulated coil cleaner for residential and light commercial applications, where it can be dispensed in a hassle-free container without the need for a separate sprayer.”
Different kinds of coils require different kinds of cleaning solutions and methods, Gildehaus added. “Nu-Calgon offers a complete portfolio of liquid and aerosol-based cleaners for any coil location, construction, and cleaning challenge. Whether it’s a residential or commercial system, outdoor or indoor, located in food processing areas, or located where water for rinsing is available or not, Nu-Calgon has a solution. The company also has coil cleaners with foaming or non-foaming chemistries, products listed in the EPA’s [U.S. Environmental Protection Agency’s] Safer Choice Program, and cleaners that are OEM-approved for all aluminum coils, including microchannel. Nu-Calgon also offers a product called Evap-Fresh in liquid and aerosol formats, which is a cleaner and disinfectant for indoor coils where there is mold and mildew on the heat exchanger.”
THE FUTURE OF COIL TECHNOLOGY
As the U.S. Department of Energy (DOE), EPA, and other regulatory agencies continue to issue increasingly stringent rules governing refrigerants, appliance energy consumption, emissions, and more, manufacturers are expecting coil technology to continue to evolve to be more efficient, innovative, and cost-effective.
Cotton predicts copper will remain the material of choice for heat-exchanger coils due to its higher thermal conductivity. “The International Copper Association supports research on the use of copper tubes in diverse residential and commercial applications, including air conditioners, heat pumps, and refrigeration equipment,” he said.
Pflum said he anticipates continued trends toward smaller tube diameters, new tube shapes, enhanced heat transfer tubing, and new high-efficiency fin designs. Additionally, there is “increasing interest in mobile-enabled selection software,” he said.
And, as coil technology continues to change, so will coil-cleaning options, Gildehaus said. “[There is an] ongoing evolution of some OEMs moving from traditional copper tube/aluminum fin coils to all-aluminum-constructed coils, including microchannel construction, [which] presents an educational opportunity to make sure contractors use the appropriate coil cleaner for each coil construction. Nu-Calgon offers OEM-approved coil cleaners for these newly designed aluminum coils.”
Another trend Gildehaus has seen is the increase in high-efficiency a/c units with larger coils. “Cleaning the coils in these units is an important part of preventive maintenance needed to keep them running at optimal efficiency. Though not a trend, we’re amazed that some contractors still try to clean coils with water alone. That’s like taking a shower without soap. Cleaning coils with water does not effectively remove debris that can affect system performance.”
Manufacturers are also exploring new coating options, Gurley said. “This is affecting multiple industries and will most likely continue to increase. We continuously explore various coating options for corrosion resistance and condensate-shedding capabilities.”
In the next few years, coils will likely become smaller and more versatile, Cotton said.
“Improved methods of manufacturing, such as noninvasive pressure expansion, are increasing yield, making it easy to make RTPF coils from smaller-diameter copper tubes,” he said. “[There will be] smaller coils, innovative designs, more markets, and new applications.”
Publication date: 6/6/2016