Substitutes for R404A/R507A and R410A

Since the available HFO molecules (R1234yf and R1234ze) show a considerably smaller volumetric refrigerating capacity than the above mentioned HFC refrigerants, 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 flammability (A2L), resulting also in a flammable blend upon adding fairly large proportions in order to increase the volumetric refrigerating capacity while maintaining a favorable GWP.

For a non-flammable blend, on the other hand, a fairly large proportion of refrigerants 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 adequately adjusted system technology.

R410A currently has no non-flammable alternatives for a broader use in commercial applications. Either R32 (R32 as substitute for R22) as pure substance or blends of R32 and HFO can be used. Due to its high volumetric refrigerating 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 boiling point differences of the individual components. The same criteria apply as described in context with R407C.

Beyond that, the discharge gas temperature of most R404A/R507A alternatives is considerably higher than for these HFC blends.

In single stage low temperature systems this may lead to restrictions in the compressor application range or require special measures for additional cooling. In transport 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 onwards. The main advantage of such blends is their moderate discharge gas temperature, which allows the operation within the typical application limits of R404A.

The following table (Potential mixture components) shows the potential blend components for the alternatives described above. With some refrigerants the mixture components for R22/R407C and R404A/R507A substitutes are identical, but their distribution in percent is different.

In the meantime, Chemours, Honeywell, Arkema, Mexichem and Daikin Chemical have offered corresponding chemical variants 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.

The following table ("Low GWP" alternatives) lists a range of currently available refrigerants or refrigerants declared as development products. Due to the large number of different versions and the potential changes in development products, the tables (Refrigerant data) only list data of alternatives for R134a, R404A/R507A and R410A which are already commercially available.

For testing the "Low GWP" refrigerants, AHRI (USA) has initiated the "Alternative Refrigerants Evaluation Program (AREP)". It has investigated and evaluated several of the products mentioned below ("Low GWP" alternatives) as well as halogen-free refrigerants.