|COPIOUS COILS: A wide range of coil types are deigned to match specific applications. Pictured here, top row: a condenser coil and a steam distributing coil; bottom row: evaporator, hot water, and chilled water coils. Photo Courtesy of Precision Coils|
These aren’t your grandfather’s coils. Today’s coils are smaller, lighter, and more efficient than ever. These components are multifaceted and are suitable for use with hydrocarbons (HCs), natural refrigerants such as carbon-dioxide (CO2), and traditional hydrofluorocarbons (HFCs). And, the ever-adapting units will likely continue to evolve as the more changes that occur, the more the industry improves its equipment to meet these challenges.
“The main driver in the past few years was applying CO2 for commercial refrigeration. With the recent Significant New Alternatives Policy [SNAP] proposal by the U.S. Environmental Protection Agency [EPA], HCs and other new refrigerants are gaining interest,” said Mike Heidenreich, vice president of product engineering, Luvata HTS Division. “We have been involved with our customers in evaluating new refrigerants and developing coils for those applications.”
According to Heidenreich, a significant driver with HCs is refrigerant charge minimization, which creates a demand for small-diameter tubes and compact coil surfaces.
“We’ve introduced coils with tube diameters as small as 5 mm in Europe and ¼ inch in North America,” Heidenreich said.
“With some of the new refrigerants having improved thermodynamic efficiency over the ‘unacceptable’ HFCs and some with worse thermodynamic efficiency, we need to look at each application and develop the best solution. This is while facing increasing minimum efficiency standards by the U.S. Department of Energy [DOE].”
Kevin Gurley, technical sales engineer, Peerless of America II, agreed with Heidenreich that, as DOE and EPA requirements continue to increase and multiply, it is very important to consider alternative coil technologies. “Over the past couple of years, there has been increasing demand for evaporators and condensers that are optimized for use with natural refrigerants such as CO2, R290, and R600A,” Gurley said.
Peerless of America II has developed several ecofriendly heat exchanger options to help meet these challenges, including a 5-mm all-aluminum condenser with a patent pending “nonconventional” design, he added.
“The small diameter helps reduce the refrigerant charge and allows for high burst strength,” Gurley said. “This coil is also designed to reduce the fouling effects of environmental dust and debris. The all-aluminum design reduces the chance for formicary corrosion, and a single continuous (monolithic) tube/fin increases tube fin efficiency for optimal heat transfer. The only connections are to the copper stubs that are supplied with the coils for ease of installation. This reduces the chance for leaks, which is more critical than ever with these natural refrigerants.”
David Pflum, general manager, precision coils business unit, Unison Comfort Technologies, said one of the biggest trends in the HVACR industry and the coils industry, in particular, is the adoption of Web-based software and mobile applications.
“Our customers want quick, easy, and convenient access to information,” Pflum said. “We’re finding that our customers want to work from anywhere. They don’t want to be tied to a desk or a desktop computer. Also, many of our customers have a multitude of devices, and they want the information to be available across those devices and different operating systems. All these things are driving our industry to develop Web-based software and mobile applications for our customers.”
He noted Precision Coils soon will be releasing an app that will prompt the user to collect the data necessary to specify a replacement coil while they’re at the job site. This will save time by eliminating trips back to the site to collect additional information.
Another trend, according to Pflum, is a movement toward smaller-diameter fin-tube and microchannel coils, which offer higher heat transfer efficiency and/or lower cost. “There are many advantages to moving toward these smaller-diameter tube and microchannel coils, including smaller heat exchangers, smaller coils, and reduced weight. Another advantage of this is that the systems that employ these types of coils require less refrigerant, and reducing the amount of refrigerant in systems is a hot-topic issue right now with climate change.”
Microchannel coils grew out of the automobile industry; many car radiators employ microchannel coils, and that construction technique and technology is moving into the HVAC industry, Pflum said. “We typically see the microchannel coils in 10-ton systems or smaller. They provide some really nice advantages in those smaller-tonnage systems, such as cost savings, refrigerant savings, and high efficiencies. In addition, microchannel coils are all-aluminum. In many applications, that’s good because they’re fairly resistant to most corrosion, but a downside of a microchannel coil is it typically can’t be repaired. If it gets damaged in the field or springs a leak, it needs to be replaced.”
Finally, Pflum mentioned coil-testing technology using tracer gas is moving from the OEM level to the smaller-volume custom coil manufacturer level, particularly in the replacement coil market.
“The active tracer gas is helium or hydrogen, and we have sensing devices that can sense those gases in very diluted concentrations. This allows for testing and helps us find coil leaks that are much smaller than those that can be detected in a water bath. The benefit here is quality assurance for the customer. It’s important to our customers, and we see that technology being adopted now in lower-volume coil manufacturing.”
Steven Wand, president and CEO, Alcoil, agrees that growth in the use of microchannel coils is the trend to watch. “It’s really the next generation of technology that’s permeating the HVAC industry,” he said.
In fact, Wand sees microchannel as a revolution along the lines of scroll compressors replacing reciprocating compressors and brazed-plate heat exchangers replacing shell-and-tube heat exchangers. He noted a number of major manufacturers in the residential and commercial markets are using microchannel coils as their condenser coils in air-cooled equipment, and, within the past few years, microchannels have been making inroads into the evaporator and heat pump markets.
“We’re seeing heat pump manufacturers using microchannels, and we’re seeing people use them as evaporators for cooling coils and dehumidification coils. Those are going to be the next new growth areas in the marketplace,” Wand said.
Wand cautioned that microchannel coils require a high degree of accuracy when charging. “You can’t just put in a pound of refrigerant and see what happens,” he said. And, being all-aluminum, they are more susceptible to physical damage than traditional copper tubes. But, the benefits outweigh the negatives.
“The traditional copper tube heat exchanger will be displaced because it’s heavier, uses twice as much metal, and has a lower energy efficiency [than a microchannel coil],” Wand said.
“All of those are driving the microchannel market, and any time the price of copper goes up, it drives it up even faster. We all know the world continues to put a high premium on copper, so, in the long-term, the move to microchannels is inevitable. It’s a matter of the technology being accepted and integrated and more suppliers of microchannel coils being available to meet the demands of the marketplace.”
Microchannel coil technology also received a shout-out from Nigel D. Cotton, MicroGroove team leader for the International Copper Association. “Although larger-diameter copper tubes are still vital today in many applications, copper tubes having outer diameters that are 7 millimeters, 5 millimeters, or even smaller are emerging as the new benchmark,” he said.
MicroGroove tubes are employed in products from a large number of OEMs. According to Cotton, 15 million units containing MicroGroove tubes have already been produced globally. This figure includes room air conditioners and residential air conditioners as well as heat pumps, refrigerated transport systems, and commercial condensers.
“The use of MicroGroove tubes typically raises the capacity and the energy efficiency of these systems while also reducing the material usage and volume of refrigerant charge.
The HVAC industry has a well-earned reputation for creating innovative new products that meet the demands of regulations and the desires of contractors and their customers, and the coil market is no exception.
Publication date: 6/8/2015