Alternatives for R114 and R12B1

R227ea and R236fa are considered suitable substitutes, even though they may no longer be used in new installations in the EU since 2020, due to their high GWP.

R227ea cannot be seen as a full replacement. Although tests and experience in real plants show favorable results, the critical temperature of 102°C limits the condensing temperature to 85 .. 90°C with conventional plant technology.

R236fa provides more favourable conditions at least in this regard – the critical temperature is above 120°C. A disadvantage, however, is the lower volumetric refrigerating capacity. It is similar to R114 and 40% below the performance of R124, which is still widely used for extra high temperature applications.

R600a (isobutane) will be an interesting alternative if safety regulations allow the use of hydrocarbons (safety group A3). With a critical temperature of 135°C, condensing temperatures of 100°C and more are within reach. The volumetric refrigerating capacity is almost identical to R124.

The "low GWP" refrigerant R1234ze(E) ("Low GWP" HFOs and HFO/HFC blends) can also be regarded as a potential candidate for extra high temperature applications. Compared to R124, its refrigerating capacity is 10 to 20% higher, its pressure level about 25% higher. At identical refrigerating capacities, the mass flow differs only slightly. Its critical temperature is 109°C, which would enable an economical operation up to a condensing temperature of about 90°C. However, like R1234yf, R1234ze(E) shows low flammability and is therefore classified into the new safety group A2L. The corresponding safety regulations must be observed.

As no sufficient operating experience is available so far, the suitability of this refrigerant for long-term use cannot be assessed yet.

For high temperature heat pumps in process technology and special applications at high temperatures, the low pressure refrigerants based on HFO and HCFO developed primarily for systems with turbo compressors are also potentially suitable ("Low GWP" HFOs and HFO/HFC blends as alternatives to HFCs). They are characterised by very high critical temperatures (> 130°C), which enable economical operation at condensing temperatures of sometimes well above 100°C. However, only purpose-built compressors and system components can be used here. Another advantage is their very low GWP and the classification in safety group A1 (non-flammable, non-toxic).

Characteristics of HFO (HCFO) low pressure refrigerants (status as of 09.2020)



Composition (with blends)


Safety group

Boiling temp. [°C]

Critical temp. [°C]



4 (1)






5 (1)






- (7)






9 (2)






R1336mzz(Z)/ R1130(E)

7 (2)




A detailed evaluation is not yet possible with respect to the chemical stability of the refrigerants and lubricants at the very high operating temperatures and the long service life required for industrial systems.

Special applications also include cogeneration systems – "Organic Rankine Cycle" (ORC), which become increasingly important. In addition to the potentially suitable substances listed in the table above, a series of other fluids are possible, depending on the temperature level of the heat source and heat sink.

They include the so far mostly used R245fa (GWP 1050) with a critical temperature of 154°C and a boiling temperature of 15.1°C.
Solvay offers further refrigerants for ORC applications, containing the base component R365mfc. A product with the trade name Solkatherm® SES36 already presented several years ago contains perfluoropolyether as a blend component. It is an azeotropic blend with a critical temperature of 178°C. Meanwhile two zeotropic blends containing R365mfc and R227ea have been developed whose critical temperatures are 177°C and 182°C, due to different mixing ratios. They are available under the trade names Solkatherm® SES24 and SES30.
In ORC systems, zeotropic behavior may be advantageous. In the case of single-phase heat sources and heat sinks, the temperature difference at the so-called "pitch point" can be raised by the gliding evaporation and condensation. This leads to improved heat transmission due to the higher driving average temperature difference.