Striving for Super Efficiency

Striving for Super Efficiency


The three basic components used in the manufacture of microchannel coils are parallel flow aluminum tubes (purple in illustration above), enhanced aluminum fins (red), and header manifolds (green). These components are combined by alternating tube and fin sections — a layer of tube atop a layer of fin atop a layer of tube, etc. This combination of fins and tubes is captured at both ends by the header manifolds. (Illustration courtesy of Johnson Controls.)

Manufacturers Continue to Tweak, Improve Upon Design of Condenser Coils


Long ago, the industry determined that the combination of copper tubing and aluminum fins provided the most efficient transfer of thermal heat in condenser coils.

Manufacturers of residential units are not necessarily on that same page — or that line of thinking — today.

Most manufacturers, if not all, are revising, have revised, or continue to revise their outdoor coil construction. One of the main objectives, of course, is to increase heat transfer efficiency, as energy efficiency is high on every homeowner’s wish list.

In the end, each manufacturer believes it has engineered and/or perfected — at least up to now — the most-efficient coil design. Some, like Goodman Manufacturing, have made changes as a direct result of the efficiency offered from R-410A refrigerant.

The NEWS asked major manufacturers to discuss the residential condenser coil changes that are occurring in the marketplace. Though not all responded, those that did provided great detail as to what’s happening with the component.


MICROCHANNEL TECHNOLOGY
Many years ago York engineers were concerned about 3 major issues concerning the industry.

“The first was efficiency, whether it was a 12 SEER or 13 SEER minimum,” said Andy Armstrong, director of marketing, Johnson Controls-Unitary Products. “We were confident that condenser coils would be challenged with new efficiencies.”

The second issue to address, he explained, was size. “The industry’s answer to efficiency has always been tied to bigger heat transfer surfaces,” he said. “Both application size restrictions and raw material usage made bigger and bigger coils an untenable long-term solution.”

The last issue involved sustainability. “We needed to make products that used less materials to begin with, and then, after use were easier to recycle and reuse,” said Armstrong.

In the case of Johnson Controls and York, they turned to microchannel technology, technology that has been used in the automotive industry for some time now. According to believers in the design, heat transfer efficiency and improvement in reliability are achieved through a higher level of corrosion resistance. (Johnson Controls uses the name MicroChannel.)

“Today, Johnson Controls believes that MicroChannel technology is the solution to all three challenges,” said Armstrong.

“With better heat transfer efficiency, MicroChannel allows us to economically reach the efficiency levels demanded by our customers. Not only do we reach higher efficiency levels, we reach them in a much smaller footprint. And from a sustainability standpoint, MicroChannel allows us to use far fewer raw materials.”


STATING ITS CASE

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Goodman said its unit with SmartCoil™ and R-410A refrigerant use 25 percent less refrigerant and the overall unit requires 15 percent less volume.

Johnson Controls is so convinced it has the answer, a year ago it produced a white paper on the subject, titled “Microchannel Technology: Benefits of Microchannel Technology in HVAC Applications.” (For the full report, go to www.us-ac.com.)

In the white paper, it states three basic components are used in the manufacture of microchannel coils: parallel-flow aluminum tubes, enhanced aluminum fins, and header manifolds.

According to the Johnson Controls’ report, these components are combined by alternating tube and fin sections — a layer of tube atop a layer of fin atop a layer of tube, and so forth. It said this combination of fins and tubes is captured at both ends by the header manifolds.

“Separator plates are located within the header manifolds to segment the coil assembly into two distinct sections: a desuperheating section, where the refrigerant gas transitions from gas to liquid, and a subcooling section, where the liquid refrigerant is further cooled below its saturated temperature,” it states in the report.

The manufacturer’s report also points out several advantages of microchannel technology when compared to traditional copper tube and aluminum fin designs. Per Johnson Controls, that list includes improved heat transfer properties, smaller size and weight, improved durability and serviceability, improved corrosion protection, and reduced refrigerant charge up to 50 percent. The report goes on to state its case and proof for each advantage it listed.

“Looking towards the future, January 2010, one of the current refrigerant options, R-22, can no longer be used in the manufacture of HVAC equipment and will be entirely replaced with R-410A, a more environmentally friendly refrigerant,” it states in the white paper. “Microchannel addresses all of the current and foreseeable future challenges in the HVAC industry.”

Armstrong was just as definitive. “Although R-410A refrigerant is better for the environment than R-22, no one would argue that the less we use any greenhouse gas, the better,” he said.

“With our current MicroChannel 5-ton 13 SEER product, we use one-half as much refrigerant as our closest competitor and one-third as much as another. When considering energy and time used in recovery, this statistic alone has dramatic effects for this industry and our environment.”

He added, “When the Johnson Controls-built unit has completed its useful life, an all-aluminum coil is far easier to recycle than its tube-and-fin counterparts. With an eye on the future, Johnson Controls engineers have taken a smaller box to a higher level.”