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HFOs and HFO/HFC blends For quite some time a blend has been applied on a larger scale in real systems – this was developed by Chemours and is called OpteonTM XP-10. Results available today are highly satisfactory. This is also true for an R134a alternative designated Solstice® N-13 and offered by Honeywell which, however, differs regard- ing the blend composition. The refrigerants are listed in the ASHRAE nomenclature under R513A (Chemours) and R450A (Honeywell). The same category also includes the re- frigerant blends R516A (ARKEMA ARM 42) as well as R456A (Koura/Mexichem AC5X). All options show refrigerating capacity, power input, and pressure levels similar to R134a. Thus, components and system technology can be taken over, only minor changes like superheat adjustment of the expansion valves are necessary. Polyolester oils are suitable lubricants which must meet special requirements, e.g. for the utilization of additives. Prospects are especially favorable for supermarket applications in the medium temperature range in a cascade with CO2 for low temperature, just as in liquid chillers with higher refrigerant charges where the use of flammable or toxic refrigerants would require comprehensive safety measures. A special case is the refrigerant R515B: an azeotropic mixture of R1234ze(E) and small amounts of R227ea. This combina- tion, declared by the manufacturer Honey- well as an R134a alternative, is non- flammable (A1) despite the very low GWP of approx. 300. However, as with the previously described R1234ze(E), this can only be considered an alternative under certain restrictions. The volumetric refrigerating capacity is also more than 20% lower than that of R134a or R1234yf. This category of substitutes also includes R471A (Honeywell), a blend of R1234ze(E), R1336mzz(E) and R227ea. R1336mzz(E) is a non-flammable HFO low-pressure refrigerant which can also be used with turbo compressors and for high tempera- ture heat pumps. Due to the two main HFO components, the GWP of the blend is < 150, but it is still non-flammable (A1). A disadvantage, however, is the even lower volumetric refrigerating capacity compared to R515B. Substitutes for R404A/R507A and R410A Since the available HFO molecules (R1234yf and R1234ze) show a consider- ably smaller volumetric refrigerating capaci- ty than the above mentioned HFC refriger- ants, relatively large HFC proportions with high volumetric refrigerating capacity must be added for the particular alternatives. The potential list of candidates is rather limited, one option is R32 with its relatively low GWP of 675. However, one disadvantage is its flamma- bility (A2L), resulting also in a flammable blend upon adding fairly large proportions in order to increase the volumetric refriger- ating capacity while maintaining a favor- able GWP. For a non-flammable blend, on the other hand, a fairly large proportion of refriger- ants with high fluor content (e.g. R125) must be added. A drawback here is the high GWP of more than approx. 900 for non-flammable R22/R407C alternatives and more than approx. 1300 with options for R404A/ R507A. Compared to R404A/ R507A, however, this means a reduction down to a third. The future drastic "phase-down" of F-Gases, e.g. as part of the EU F-Gas Regulation, already leads to a demand for R404A/ R507A substitutes with GWP values clearly below 500. Although this is possible with an adequate composition of the blend (high proportions of HFO, R152a, possibly also hydrocarbons), the disadvantage will be its flammability (safety groups A2L or A2). In this case, the application will have higher safety requirements and will need an ad- equately adjusted system technology. R410A currently has no non-flammable alternatives for a broader use in commercial applications. Either R32 (see page 23) as pure substance or blends of R32 and HFO can be used. Due to its high volumetric re- frigerating capacity, this requires a very high proportion of R32, which is why only GWP values from approx. 400 to 500 can be achieved. With a higher HFO proportion, the GWP can be reduced even further, but at the cost of a clearly reduced refrigerating capacity. All blend options described above with R1234yf and R1234ze(E) show a more or less distinct temperature glide due to boil- ing point differences of the individual com- ponents. The same criteria apply as de- scribed in context with R407C. Beyond that, the discharge gas temperature of most R404A/R507A alternatives is consi- derably higher than for these HFC blends. In single stage low temperature systems this may lead to restrictions in the com- pressor application range or require special measures for additional cooling. In trans- port applications or in low temperature systems with smaller condensing units, the compressors used can often not meet the required operating ranges, due to the high discharge gas temperatures. This is why refrigerant blends based on R32 and HFO with a higher proportion of R125 have also been developed. The GWP is slightly above 2000, but below the limit of 2500 set in the EU F-Gas Regulation from 2020. The main advantage of such blends is their moderate discharge gas temperature, which allows the operation within the typi- cal application limits of R404A. The following table (Tab. 4) shows the potential blend components for the alter- natives described above. With some re- frigerants the mixture components for R22/R407C and R404A/R507A substitutes are identical, but their distribution in per- cent is different. In the meantime, Chemours, Honeywell, Arkema, Mexichem and Daikin Chemical have offered corresponding chemical vari- ants for laboratory and field tests, and in some cases already for commercial use. A number of refrigerants are still declared as being under development and are only made available for testing purposes under special agreements. Until now, trade names are often used although a larger number of HFO/HFC blends are already listed in the ASHRAE nomenclature. 25PDF Image | REFRIGERANT REPORT 21
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