ASHRAE recently hosted an informative webcast titled “The Future of Refrigerants: Unitary and VRF Systems.” Some of the topics touched on during the presentation included the future of low-GWP refrigerant options for unitary products, whether future refrigerant retrofits will be possible, and some of the challenges involved when working with flammable refrigerants.

As with all alternative refrigerants, there are tradeoffs between efficiency, GWP, capacity, and glide. Safety is also a consideration, given that many alternative refrigerants are mildly flammable (A2L). The panelists reviewed the advantages and disadvantages of most of the alternatives that are currently being considered for unitary and VRF systems.

LOW-GWP ALTERNATIVES FOR R-410A

Panelist Steve Kujak, director of next-generation refrigerant research at Ingersoll Rand, discussed the pros and cons of lower-GWP alternatives that are similar to R-410A, including R-466A, R-452B, R-454B and R-32 (see Table 1).

“R-466A is a blend of R-32, R-125, and R-13I1, with a composition of 49 percent R-32 with nonflammable agents of R-125 and R-13I1 to make it a nonflammable refrigerant blend,” he said. “This will be the only refrigerant in this class that will be nonflammable and have a GWP of less than 750. Capacities and efficiencies are similar to R-410A, and the glide is less than 3°F.”

R-452B is an A2L blend comprised of 67 percent R-32, along with R-125 and R-1234yf to optimize properties. Capacity and efficiency are similar to R-410A, and glide is less than 3°F, said Kujak. He went on to explain that R-452B is optimized to work with current R-410A lubricants, and it can be considered a true drop-in replacement for R-410A designs.

R-454B is an A2L blend that is composed of 69 percent R-32, with the remainder being R-1234yf. R-454B is basically R-452B without R-125 to lower the GWP to the lowest possible value, said Kujak. Capacities and efficiencies are similar, and glide is also less than 3°F. The GWP value of 460 is the lowest of all the candidates, he said, which is the primary attribute of interest with this candidate.

“The last candidate, and by far the most adopted candidate at this point, is R-32,” said Kujak. “It is used in its pure form and is an A2L refrigerant. Capacity is higher than R-410A by about 8 percent, and efficiencies are similar. R-32 has no glide, which is a plus, but the glides for the other alternatives are not much of a concern, since they are small or less than 3°F.”

Kujak studied the actual performance of these alternatives in an air-cooled water chiller designed for R-410A and found that the COPs for all of the alternatives were similar, regardless to the change in ambient conditions, and all were similar to R-410A. Capacities were similar for alternatives to R-410A, except for R-32, which had a higher capacity. The big difference observed was the difference in compressor discharge temperature. All of the refrigerants had higher compressor discharge temperatures than R-410A, with pure R-32 being the highest. In fact, he noted that there have been many discussions about whether it may be necessary to incorporate compressor discharge temperature cooling into R-32 designs.

“In our testing, the compressor discharge protection limit of 130° to 135°C was reached with R-32 at about 45°C ambient,” he said. “The other alternatives did not reach this R-410A compressor design limit. Also interesting to note was the change in compressor discharge temperature versus ambient temperature — R-32 temperatures continued to grow, while all the other alternatives were unaffected by the changing ambient temperature. This is a result and a function of the differences in thermodynamic properties of pure R-32 and blends of R-32 with the other refrigerants.”

The takeaway, according to Kujak, is that there are several good R-410A alternatives available that will allow a smooth transition from R-410A to a variety of R-410A-like refrigerants that have GWPs ranging from 460 to about 730.

“Handling the flammability aspects of some of these alternatives would have to be considered, but overall, components are compatible with the operating pressures, heat exchangers, and compressor designs,” he said. “In the end, two transitions are likely, with the unitary product category having an interim GWP and a final GWP step, with plenty of market fragmentation by refrigerant type across product families and by regional global HFC phasedown regulations.”

LOW-GWP ALTERNATIVES FOR R-22

Panelist Sarah Kim, scientist and project leader at Arkema Fluorochemicals, discussed alternatives to R-22 that have GWPs below 300. These include the A2L refrigerants R-454A, R-444B, and ARM-20b, as well as R-290 (propane), which is an A3 refrigerant (see Table 2).

“The thermodynamic cycle performances of R-454A, R-444B, and ARM-20b were evaluated and compared to R-22, as well as R-290,” said Kim. “With R-22 being the baseline refrigerant, R-454A showed a slight decrease in COP, followed by ARM-20b, and R-444B. But all three were shown to be a close match, considering the fact that cycle calculations do not include heat transfer or pressure drop effects.”

R-290 showed comparable efficiency to R-22, she said, and in terms of capacity, ARM-20b showed 5 percent higher capacity, followed by R-454A. R-444B showed slightly lower capacity, and R-290 had a 10 percent drop in capacity. R-454A, R-444B, and ARM-20b have been researched extensively at Oakridge National Laboratory, with R-444B and ARM-20b tested in both mini split and rooftop units. R-290 was also tested in a mini split, and R-454A was tested in a rooftop unit.

“The results showed that R-290 had a higher COP compared to R-22 when tested in a mini split [under Air-Conditioning, Heating and Refrigeraiton Institute (AHRI) conditions], whereas the A2L refrigerants showed a slightly lower COP,” said Kim. “In terms of capacity, ARM-20b provided the closest match to R-22 among the A2L refrigerants, while R-290 showed about an 8 percent drop in capacity, consistent with the cycle calculation. As the test units were designed specifically for R-22, performance can be improved for A2L refrigerants and new equipment.”

R-444B showed higher compressor discharge temperatures by about 4°F in both rooftop and mini split units, while other refrigerants showed lower discharge temperatures, she said. R-290 showed much lower values than R-22.

“In terms of mass flow, A2L refrigerants were within 15 percent of R-22 mass flow, suggesting a similar or same-sized TXV can be used, while R-290 showed significantly lower mass flow, which will require different parts in addition to consideration of higher flammability of this refrigerant,” said Kim. “Among the refrigerants tested, ARM-20b was the closest match in discharge temperature and mass flow to the baseline R-22 refrigerant. Part of the study also included optimization of the refrigerant charge. For all three A2L refrigerants, about 15 percent less refrigerant was charged while providing similar or higher capacity than R-22, which is mainly due to the lower refrigerant liquid densities of these refrigerants.”

RETROFITS/FLAMMABILITY

One of the burning questions for many in the industry is whether or not any of these alternative refrigerants can be retrofitted into existing equipment. Douglas Tucker, director of industry and government relations for Mitsubishi Electric US, noted that this is often not possible.

“First, the product safety listings for equipment are dependent on one particular refrigerant or set of refrigerants,” he said. “So regardless of safety classification, even if you’re going from an A1 refrigerant to an A1 refrigerant, you will void that product safety listing, unless it’s part of the set of refrigerants for which it’s listed. Second, manufacturers would not allow the retrofit of a new refrigerant into existing equipment if it’s under warranty. That would void the warranty.”

Retrofitting is also a safety issue, particularly where flammable refrigerants are concerned.

“When it comes to retrofitting with flammable refrigerants, I have a short answer: No, don’t do it,” said Kujak. “The equipment is designed around a nonflammable refrigerant, while new equipment will be designed and certified around safety protocols for flammable refrigerants.”

Kim added that most of the R-410A-like replacements are A2L refrigerants, which are mildly flammable and, therefore, should not be retrofitted into existing equipment.

“There is one exception that is proposed to be nonflammable, and that’s R-466A, which is still pending classification at the moment,” she said. “It has a different kind of molecule that contains iodine in it, so we expect that it would exhibit a different type of system chemistry.”

Handling flammable refrigerants was the topic of Tucker’s presentation, and he discussed some of the rigorous measures that are being put in place to ensure the safety of those working with these materials. He noted that while developed countries have a long history of safely transporting flammable gases and cylinders, the risk profile — while low — is somewhat different for bulk refrigerant versus pre-charged systems.

“A2L refrigerants and pre-charged systems will require measures to prevent ignition of leaked refrigerant during transport,” said Tucker.

In the field, the presence of refrigerant and possible ignition sources together with human interaction during installation and service present a higher risk, said Tucker. This risk can be mitigated by proper technician training and certification and enforcement of regulations, as well as adhering to product safety standards and installation codes that prescribe safe construction and leak containment during operation. That includes proper leak detection, clearances from combustibles, separation from ignition sources, and ventilation, he said.

“However, the risk profile can vary by equipment type and application,” said Tucker. “For unitary and VRF systems, the probability of leaks is relatively low. But for VRF equipment in particular, close attention must be paid, so the refrigerant quantity limit is not exceeded in the event of a leak into occupied spaces.”

As the use of flammable refrigerants increases, risk assessment studies, the development of standardized procedures, and training of personnel on flammability issues are all of the utmost importance, he said.

“ASHRAE Research Project 1807 (Guidelines for flammable refrigerant handling, transporting, storing, and equipment servicing and installation) covers all of these topics in greater detail,” said Tucker. “The final report was published recently and is available for free to ASHRAE members.”

The HVACR industry is continuing to move toward lower-GWP refrigerants, and as can be seen here, manufacturers — as well as trade associations — are devoting a lot of time, energy, and resources to making sure the transition to these alternatives goes as smoothly as possible.

Publication date: 6/10/2019

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