And even as those papers were being presented, Mark McLinden, of the Applied Chemicals and Materials Division for the National Institute of Standards and Technology (NIST), used a plenary session to predict that what is being worked on now “is all there is … really — we are bumping up against the physical limits of the chemistry.”

Low Global Warming

A paper presented by Xudong Wang of the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) updated conference attendees on AHRI’s Low Global Warming Potential Alternative Refrigerants Evaluation Program (Low-GWP AREP). At the time of the conference, Wang said that 38 low-GWP refrigerants were tested during the first phase in a variety of products including compressors, air conditioners, heat pumps, chillers, transport refrigeration, and ice makers. In addition, he said AHRI launched a second phase of testing in the beginning of 2014 that includes newly developed refrigerants and performance testing under high-ambient conditions that were not covered in the first phase. He noted the purpose was to identify potential replacements for high-GWP refrigerants, but not to prioritize them.

Low Compressor-discharge Temperature

Barbara Minor of DuPont, speaking on behalf of a team from DuPont, Thermo King, and Ingersoll Rand, addressed the issue of the high GWP of HFC-404A and the need for an alternative. She noted a developmental refrigerant presently called DR-34 (with a provisional ASHRAE designation of 452a). She described it as “a nonflammable refrigerant with low compressor-discharge temperature similar to R-404A, which closely matches all other properties and performance. This refrigerant will be particularly suitable for transport refrigeration where compressor cooling is difficult to manage under a wide range of ambient conditions.”

Finding the Right Replacement

The technical art of finding the best replacement for a high-GWP refrigerant was shown in a paper presented by Radia Eldeeb on behalf of a team of researchers representing the University of Maryland. They looked at three refrigerants currently being studied and defined as low-GWP refrigerants in a 10.55 kW heat pump. One is HFC-32 (currently used in blends), while the other two are developmental refrigerants.

“The test results show that HFC-32 is superior compared to R-410A in regards to cooling and heating capacities, while L41a is superior compared to R-410A in regards to COP, and D2Y60 is superior compared to R-410A in regards to compressor discharge temperature,” she said. “Generally, L41a is superior in terms of SEER and HSPF values compared to other alternative refrigerants.”

Low GWP in A/C

In looking at low-GWP alternatives to both hydrochlorofluorocarbon (HCFC)-22 and HFC-410A, Ankit Sethi reported on progress he and his colleagues at Honeywell Intl. Inc. have made. “Experimental results suggest that, without significant system modifications, L-20 can match the performance of R-22 across the range of ambient temperatures observed in various countries in the Middle East. Hence, L-20 is a promising low-global warming replacement for R-22 in cooling-only systems designed to work in regions. Theoretical results indicate that in hydronic systems, L-20 would be expected to have reasonable efficiency with an operating envelope very similar to R-410A. Hence, L-20 seems to be an attractive R-410A replacement in hydronic systems,” he said.

“Preliminary evaluations of higher- and medium-pressure blends also show promise in positive displacement chiller applications. However, there are tradeoffs in performance, flammability, and GWP that need to be made.”

HFOs

A report presented by Thomas Leck, on behalf of colleagues at DuPont, detailed some of the research regarding HFO refrigerants. He also presented a case for such research and how HFOs could end up working in stationary systems. (HFO-1234yf is already being used in automotive air conditioning.)

“In the interest of improved environmental sustainability, a new class of refrigerant molecule has been developed, the hydrofluoroolefin. While the very low, direct GWP values of these molecules are attractive, none of the HFOs, by themselves, are fully satisfactory for use in conventional stationary a/c system designs for reasons of concern about low capacity and flammability. Blended refrigerant candidates have been developed to provide better overall safety and performance while retaining significant environmental sustainability properties versus the legacy refrigerants.”

Publication date: 9/1/2014

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