At the 15th International Refrigeration and Air Conditioning Conference at Purdue University papers were presented at a session titled Evaluating Alternative Refrigerants and Technologies.
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, used a plenary session to predict that what is being worked on now “is all there is — 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 delegates on AHRI’s Low Global Warming Potential Alternative Refrigerants Evaluation Program (Low-GWP AREP).
At the time of the conference, Mr Wang said that 38 low-GWP refrigerants were tested during the first phase in a variety of products: compressors, air conditioners, heat pumps, chillers, transport refrigeration, and ice makers.
In addition, he said AHRI launched a second phase of testing in 2014 that included newly developed refrigerants and performance testing under high-ambient conditions, which were not covered in the first phase.
Wang noted the purpose was to identify potential replacements for high-GWP refrigerants, but not to prioritise 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 DR-34 (with a provisional ASHRAE designation of 452a). She described it as “a non-flammable 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.”
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 at the University of Maryland.
The team 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 with R-410A in regards to cooling and heating capacities, while L41a is superior compared with R-410A in regards to COP, and D2Y60 is superior compared with R-410A in regards to compressor discharge temperature,” she said. “Generally, L41a is superior in terms of SEER and HSPF values compared with 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 that Honeywell International has 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,” said Mr Sethi.
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.”
This article was first published in The Air Conditioning, Heating and Refrigeration News
In speaking to an audience of engineers and researchers from throughout the world this July at Purdue University, Mark McLinden of the applied chemicals and materials division of the National Institute of Standards and Technology noted that ongoing research is the end of the line, and that analysts are bumping up against the physical limits of chemistry.
When asked if there will be a fifth generation of refrigerants, he responded, very matter of factly: no.
It should be noted at this point that the final generation of refrigerants still has to sort itself out. But, by my count, there are about 60 refrigerants considered low-GWP HFCs, HFOs, or naturals currently being studied and tested to create cooling and refrigeration.
Many are in the field being used. That number has to work its way down to a more manageable figure, given the limit as to how many canisters can fit in service vans. But, it won’t be one or two. It could be dozens.
The point Dr McLinden is making is that what is currently being worked on is all there is or will be. For contractors, what emerges from this research will be what they’ll be working with for years to come.
Peter Powell is refrigeration editor for ACHR News