“Low GWP” HFO and HFO/HFC blends

Aspects on the development of HFO and HFO/HFC refrigerants

The decision to use the “low GWP” refrigerant R1234yf in mobile air conditioning systems for passenger cars (R1234yf) also led to the development of alternatives for further mobile applications as well as stationary refrigeration, air conditioning and heat pump systems.

Primary objectives are the use of single-component refrigerants and of mixtures with significantly reduced GWP and similar thermodynamic properties as the HFCs that are currently used predominantly.

An essential basic component for this is R1234yf (CF3CF=CH2). This refrigerant belongs to the group of hydro-fluoro-olefins (HFO), i.e. unsaturated HFCs with molecular double bonds. This group of HFOs also includes another substance called R1234ze(E), which has been mainly used as a propellant for PU foam and aerosol. R1234ze(E) (CF3CH=CFH) differs from R1234yf in its molecular structure.

Both substances are the preferred choice in terms of their properties and are also used as basic components in HFO/HFC blends. The Global Warming Potential is very low − R1234yf with GWP 4 and R1234ze(E) with GWP 7. However, these refrigerants are flammable (safety class A2L), meaning the refrigerant quantity in the system must be considered in light of the installation location. In addition, open questions remain concerning the long-term stability in stationary systems where long life cycles are common. Furthermore the volumetric refrigerating capacity is relatively low: For R1234yf it is close to the level of R134a, and more than 20% lower for R1234ze(E).

There is also some uncertainty concerning flammability. In safety data sheets, R1234ze(E) is declared as non-flammable. However, this only applies to its transport and storage. When used as a refrigerant, a higher reference temperature for flammability tests of 60°C applies. At this temperature, R1234ze(E) is flammable and therefore classified in safety class A2L, like R1234yf.

R1234ze(E) is sometimes referred to as a R134a substitute, but its volumetric refrigerating capacity is more than 20% lower than that of R134a or R1234yf. The boiling point (-19°C) also greatly restricts the application at lower evaporation temperatures. Its preferred use is therefore in liquid chillers and high temperature applications. For further information: Refrigerants for special applications.

The list of further potential HFO refrigerants is relatively long. However, there are only few fluids that meet the requirements in terms of thermodynamic properties, flammability, toxicity, chemical stability, compatibility with materials and lubricants. These include e.g. the non-flammable (safety group A1) low-pressure refrigerants R1224yd(Z), R1233zd(E), R1336mzz(E), R1336mzz(Z) and R514A (blend of R1336mzz(Z)/R1130(E)). These are primarily an option for liquid chillers with large turbo-compressors, and they can be used with positive displacement compressors in high-temperature applications as well as ORC systems. Further information: Refrigerants for special applications

R1224yd(Z) and R1233zd(E) belong to the group of HCFO (hydro-chloro-fluoro-olefins); they have a (very) low ozone depletion potential (ODP). Upon release into the atmosphere, however, the molecule rapidly disintegrates.

On the other hand, there are currently no candidates from the HFO family with similar volumetric refrigerating capacity such as R22/R407C, R404A/R507A and R410A available for commercial use. Direct alternatives for these refrigerants with significantly lower GWPs must therefore be “constructed” as a mixture of R1234yf and/or R1234ze(E) with HFC refrigerants, possibly also small proportions of hydrocarbons, CO2 or other suitable molecules.

However, due to the properties of the HFC refrigerants suitable as blend components, flammability and GWP are related diametrically to one another. In other words: Blends as alternatives to R22/R407C of GWP < approx. 900 are flammable. This is also true for alternatives for R404A/R507A in blends of GWP < approx. 1300 and for R410A in blends of GWP < approx. 2000. The reason for this is the high GWP of each of the required non-flammable components. There are a few exceptions: Further development projects.
For R134a alternatives, the situation is more favorable. Due to the already quite low GWP of R134a, a blend with R1234yf and/or R1234ze(E) allows a formulation of non-flammable refrigerants with a GWP of approx. 600.

Thus, primarily two directions for development are pursued:

  • Non-flammable HFC alternatives (blends) with GWP values according to the above mentioned limits – safety group A1. Regarding safety requirements, these refrigerants can then be utilized similar to currently used HFCs.
  • Flammable HFC alternatives (blends) with GWP values below the above mentioned possible limits – according to safety group A2L (for refrigerants of lower flammability). This group of refrigerants will be subject e.g. to charge limits according to the current standards for A2L refrigerants.

Meanwhile, there are development projects using refrigerant components with a much higher volumetric refrigerating capacity and pressure than R1234yf and R1234ze(E). These can then be used to “formulate” mixtures with R32 as an alternative to R410A, which are optimised for certain properties. Additional information: Further development projects.

R134a alternatives

In addition to the flammable HFO refrigerants R1234yf and R1234ze(E) already described, non-flammable mixtures are now also available as R134a alternatives. As previously mentioned, the initial situation is most favorable for these.

They achieve GWP values of approx. 600 − less than half of 134a (GWP100 = 1430). In addition, this type of blends can have azeotropic properties, so that they can be used like pure refrigerants.

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 regarding the blend composition.

The refrigerants are listed in the ASHRAE nomenclature under R513A (Chemours) and R450A (Honeywell).

The same category also includes the refrigerant blends R516A (ARKEMA ARM 42) sowie 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 combination, declared by the manufacturer Honeywell 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 temperature 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 cpacity compared to R515B.

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 Properties) 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.

Further development projects with “Low GWP” refrigerants

For specific applications, Chemours has developed a non-flammable (A1) R410A alternative, which is marketed in selected countries and regions under the trade name OpteonTM XP41 – listed by ASHRAE as R463A.

It is a mixture of R32, R125, R1234yf, R134a and CO2 with a GWP of 1494. Despite the high proportion of R32 and R1234yf, flammability is suppressed by mixing with R125, R134a and CO2.

Regarding thermodynamics, the differences to R410A are comparatively small. The addition of CO2, however, leads to a distinct temperature glide, which may cause certain limitations for the application and places particular demand on the design of the heat exchangers.

All mixture components and their properties are well known, which means there are no additional particularities regarding material compatibility in comparison to the already known R410A alternatives.

The supply of compressors for laboratory or field tests requires an individual review of the specific application and a special agreement.

Some time ago, Honeywell has unveiled the new development of a non-flammable (A1) R410A alternative under the trade name Solstice® N-41 – listed by ASHRAE as R466A.

R466A is a mixture of R32, R125 and R13I1 (CF3I − tri-fluoroiodomethane), an iodine-methane derivative not previously used in refrigeration. CF3I is not flammable, as is R125, which means that the refrigerant is not flammable (A1), even with the relatively high proportion of R32 (A2L).

Despite the noticeable proportion of R125 with a GWP of 3500, the total GWP is 733 (AR4) and therefore in the range of R32 and R452B, which are however classified as A2L.

From a thermodynamic point of view, the differences between R410A and R466A are relatively small. Volumetric refrigerating capacity, pressure levels and discharge temperature are slightly higher, the refrigerant mass flow deviates slightly more (about 15 to 20% higher). The temperature glide is also very low.

Hence, R466A appears to be a promising substitute for R410A. However, due to the CF3I share, there are still uncertainties regarding long-term chemical stability and material compatibility under the special requirements of the refrigeration cycle.

Further investigation is required, so a final assessment of R466A is currently not possible. In any case, as matters stand, this refrigerant cannot be used in state-of-the-art systems (retrofit). The supply of compressors for laboratory tests requires an individual review of the specific application as well as a special agreement.

AGC Chemicals propagates R1123 ( CF2=CHF) mixed with R32, partially with addition of R1234yf, as an alternative to R410A and pure R32. It is a HCFO with very low ozone depletion potential (ODP). R1123 has a significantly higher volumetric refrigeration capacity than R1234yf or R1234ze(E) and is advantageous in this respect. However, the pressure level is even higher than of R32 and the critical temperature is only about 59°C. Apart from that, there are unanswered questions about the chemical long-term stability under the special requirements of the refrigeration cycle. According to the safety data sheet, this substance is also subject to very stringent safety requirements.

A final assessment of these mixtures is therefore currently not possible.

Comment from a compressor manufacturer’s point of view

It should be an aim to limit the product variety currently becoming apparent and to reduce the future supply to a few “standard refrigerants”. It will not be possible for component and equipment manufacturers nor for installers and service companies to deal in practice with a larger range of alternatives.

Current HFC-
AlternativesComponents / Mixture components for “Low GWP” alternatives (Examples)



A1~ 600
A1~ 300⑥
A1< 150⑥
A2L< 150
A2L< 10
R404A/R507A GWP 3922/3985A1< 2500①
A1~ 1400
A2L< 250
A2L③< 150
A2< 150
R22/R407C GWP 1810/1774A1900..1400
A2L< 250
A2L< 150
A2< 150
A1< 1500
A1< 750
A2L< 750
A2L~ 400..750

Potential mixture components for “Low GWP” alternatives (examples) (status as of 09.2020)

Refrigerating capacity, mass flow, discharge gas temperature similar to R404A
Only low percentage – due to temperature glide (CO2) and flammability (R290)
R32/HFO blends show lower refrigerating capacity than reference refrigerant, the addtion of CO2 leads to high temperature glide
Approx. values according to IPCC IV (AR4)
R13I1 (CF3I − tri-fluoroiodomethane) is an iodine-methane derivative.
⑥ Lower volumetric refrigerating capacity than reference refrigerant

Current HFC-Refrigerants“Low GWP” Alternatives for HFC refrigerant
Trade NameComposition
(with blends)
AR4 (AR5)
in °C
Glide in K
1430 ①
HoneywellR1234ze(E)/134a604 (547)A1-240.6
R456AAC5X ⑥Koura (Mexichem)R32/1234ze(E)/134a687 (627)A1-304.8
R513AOpteonTM XP10ChemoursR1234yf/134a631 (573)A1-300
R513ADaikin Chemical
R515B ②HoneywellR1234ze(E)/227ea293 (299)A1-190
R471A ②HoneywellR1234ze(E)/1336mzz(E)/227ea148 (148)A1-173.2
R1234yfvarious4 (< 1)A2L-300
various7 (< 1)A2L-190
R444AAC5 ⑥Koura (Mexichem)R32/152a/1234ze(E)92 (89)A2L-3410
R516AARM-42ArkemaR1234yf/R152a/R134a142 (131)A2L-290

3922/3985   (R22/R407C)
1387 (1273)A1-466.2
R449AOpteonTM XP40ChemoursR32/125/1234yf/
1397 (1282)A1-465.7
Forane® 449Arkema
R452AOpteonTM XP44ChemoursR32/125/1234yf2140 (1945)A1-473.8
ChemoursR32/1234yf239 (238)A2L-485.7
R454ADaikin Chemical
R457BARM-20b ⑦ArkemaR32/1234yf/152a251 (251)A2L-476.1
R454C OpteonTM XL20ChemoursR32/1234yf148 (146)A2L-467.8
HoneywellR32/1234yf/CO2148 (146)A2L-5212.8
R457A ②ARM-20aArkemaR32/1234yf/152a139 (139)A2L-437.2
R465AARM-25ArkemaR32/1234yf/290145 (143)A2-5211.8
R468ADaikin ChemicalR32/1234yf/1132a148 (147)A2L-5112.3
R22/R407CGWP 1810/1774R449COpteonTM
ChemoursR32/125/1234yf/134a1251 (1146)A1-446.1
R32various 675 (677)A2L-520
ChemoursR32/125/1234yf698 (676)A2L-510.9
ChemoursR32/1234yf466 (467)A2L-511.0
XP41 ⑩
1494 (1377)A1-5912.2
HoneywellR32/125/13I1(CF3I)733 (696)A1-520.7

“Low GWP” alternatives for HFC refrigerants (status as of 09.2020)

The relatively low GWP allows the use of R134a also on longer term.
Lower volumetric refrigerating capacity than reference refrigerant
AR4: according to IPCC IV // AR5: according to IPCC V – time horizon 100 years
Rounded values
Total glide from bubble to dew line at 1 bar (abs.)
Development product



BITZER experiences and products for HFOs and HFO/HFC blends

BITZER was involved early on in various projects with HFO/HFC blends and was thus able to gain important insight into the use of these refrigerants. Semi-hermetic reciprocating compressors of the ECOLINE series as well as CS. and HS. screw compressors can already be used with this new generation of refrigerants. Several of them have already been qualified and approved, the respective performance data is available on the BITZER SOFTWARE.

Scroll compressors of the ORBIT GSD6..VL and GSD8..VL series are approved and released for the use of the R32/HFO mixtures R452B and R454B.

Further information on the application of HFOs and HFO/HFC blends

Further information on the application of HFOs and HFO/HFC blends see brochure A-510, section 6.