ASHRAE look at latest trends in low-GWP refrigerants

ASHRAE look at latest trends in low-GWP refrigerants

During an ASHRAE webcast called ‘The Future of Refrigerants: Unitary and VRF Systems’, topics 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 trade-offs between efficiency, GWP, capacity, and glide. Safety is also a consideration, given that many alternative refrigerants are mildly flammable (A2L). The panellists reviewed the advantages and disadvantages of most of the alternatives that are currently being considered for unitary and variable refrigerant flow (VRF) systems.

Low-GWP alternatives for R410A

Panellist Steve Kujak, director of next-generation refrigerant research at Ingersoll Rand, discussed the pros and cons of lower-GWP alternatives that are similar to R410A, including R466A, R452B, R454B and R32. View / Download the table as a PDF

Kujak studied the actual performance of these alternatives in an air-cooled water chiller designed for R410A and found that the COPs for all of the alternatives were similar, regardless to the change in ambient conditions, and all were similar to R410A. Capacities were similar for alternatives to R410A, except for R32, 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 R410A, with pure R32 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 R32 designs.

“In our testing, the compressor discharge protection limit of 130–35°C was reached with R32 at about 45°C ambient,” he said. “The other alternatives did not reach this R410A compressor design limit. Also, interesting to note was the change in compressor discharge temperature versus ambient temperature – R32 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 R32 and blends of R32 with the other refrigerants.”

The takeaway, according to Kujak, is that there are several good R410A alternatives available that will allow a smooth transition from R410A to a variety of R410A-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 R22

Panellist Sarah Kim, scientist and project leader at Arkema Fluorochemicals, discussed alternatives to R-22 that have GWPs below 300. These include the A2L refrigerants R454A, R444B, and ARM-20b, as well as R290 (propane), which is an A3 refrigerant. View / Download the table as a PDF

“The thermodynamic cycle performances of R454A, R444B, and ARM-20b were evaluated and compared to R22, as well as R290,” said Kim. “With R22 being the baseline refrigerant, R454A 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.”

R290 showed comparable efficiency to R22, she said, and in terms of capacity, ARM-20b showed 5% higher capacity, followed by R454A. R444B showed slightly lower capacity, and R290 had a 10% drop in capacity. R454A, R444B, and ARM-20b have been researched extensively at Oakridge National Laboratory, with R444B and ARM-20b tested in both mini split and rooftop units. R290 was also tested in a mini split, and R454A was tested in a rooftop unit.

“The results showed that R290 had a higher COP compared to R22 when tested in a mini split (under Air-Conditioning, Heating and Refrigeration 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 R22 among the A2L refrigerants, while R290 showed about an eight percent drop in capacity, consistent with the cycle calculation. As the test units were designed specifically for R22, performance can be improved for A2L refrigerants and new equipment.”

R444B showed higher compressor discharge temperatures by about 4°F in both rooftop and mini split units, while other refrigerants showed lower discharge temperatures, she added. R290 showed much lower values than R22.

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.”

“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 non-flammable refrigerant, while new equipment will be designed and certified around safety protocols for flammable refrigerants.”

Kim added that most of the R410A-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 non-flammable, and that’s R466A, 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.”

ASHRAE Research Project 1807 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 HVAC&R 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.

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