REFRIGERANTS
environmental lobbyists, are the hazardous chemicals used by the early refrigeration industry. They are natural only in the sense they are found in nature, but being manufactured in chemical plants, they are actually synthetic. They would be more honestly termed ‘Hazrefs’ rather than ‘Natrefs’, the generic description favoured by environmentalists.
But this ‘back to the future’ approach is
unnecessary. A new family of fluorochemicals, the hydrofluoro-olefins (HFO), can, in combination with other components including some HFCs and other components, provide very low GWP refrigerants. The American Society for Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) has introduced a new safety classification of A2L, which is a lower flammable classification than A2 but still flammable, to facilitate the development of HFOs. R32 has been re-classified as A2L enabling it to be used in new equipment as a
replacement for nonflammable R410A. To meet the demands of increasingly restrictive regulatory regimes, the ultimate goal is to develop a range of refrigerant compositions sustainable in the long term, which combine low GWPs, nonflammability, low toxicity, good efficiency for use in both new and existing equipment. The end point will be to establish refrigerants having these properties with GWPs similar to, or even lower, than CO2
. There will be stepping-stones along the way which will involve the adoption of compositions with higher GWPs (than CO2
)
but considerably lower than the refrigerants in common use today. Traditional thinking in the RAC industry has favoured single fluids and azeotropic or near azeotropic mixtures, eg R11, R12, R502, R22, R404A, R507, R410A, which have zero or low temperature glides. Glide was generally assumed to result in operational problems, particularly the potential fractionation of blends due to the large difference in boiling points of the components, eg R407C, R407A. However, practical experience since the 1990s has shown that blends with wide glides have not presented such problems; R407C has been in practical use for over 20 years. This is hugely important because this experience supports our view that fluids with wider glides will provide the pathway to the development
of new refrigerants with very low GWPs combined with nonflammability. Recently, nonflammable compositions with lower GWPs than R404A, R507 and R410A have been developed for retrofitting existing installations. R448A and R449A, with GWPs just below 1,400, are being used to replace R404A and R507 in existing refrigeration equipment. R470B, with a GWP of @750, a recent addition to this list, is also nonflammable and suitable for use in existing installations to replace R404A and R507. Replacing R410A continues to be a goal for refrigerant suppliers because of its high GWP (over 2,000). R32 is being used in some splits but is not suitable for use in existing R410A equipment due to its flammability. Furthermore, R32 with a GWP of 675 is not sustainable longer term and will fall foul of ever tightening international regulations. R466A is being marketed as a nonflammable replacement for R410A but is not suitable as a retrofit. Another refrigerant, R470A with a GWP under 1,000, has recently been introduced as a nonflammable, retrofit replacement for R410A. This focus on direct GWP of refrigerants is unfortunately necessary due to the modus operandi of environmental legislators. As outlined above, the GWPs of replacements are reducing. There will be stages in this whole development process. The next step could be to commercialise nonflammable compositions with GWPs below 750, and then blends below 150. There are already some compositions with GWPs less than 150 but they are flammable with safety classification of A2L so unsuitable in a retrofit situation and limited for use in new equipment due to building codes. The final stage in this process is a
nonflammable refrigerant or refrigerants to replace R410A, R404A and R507 in new equipment with GWP close to or even below one. In our view, this will mean some changes will be needed to the design of RAC equipment – but they will retain the basic Rankine cycle and enable current technology with such items as existing compressors, evaporators, condensers etc to be used. Although the Holy Grail, it is not impossible technically and avoids the industry going ‘back to the future’.
www.acr-news.com
Decemb
December 2020 19
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
