"Low GWP" HFO refrigerant R1234yf

The ban on the use of R134a in mobile air conditioning systems within the EU has triggered a series of research projects. In addition to CO2 technology (CO₂ in car air conditioning systems), refrigerants with very low GWP values and similar thermodynamic properties as R134a have been developed.

In early 2006, two refrigerant mixtures were introduced under the names "Blend H" (Honeywell) and "DP-‍1" (DuPont). INEOS Fluor followed with another version under the trade name AC-‍1. In the broadest sense, all of these refrigerants were blends of various fluorinated molecules.

During the development and test phase it became obvious that not all acceptance criteria could be met, and thus further examinations with these blends were discontinued.
Consequently, DuPont (meanwhile Chemours) and Honeywell bundled their research and development activities in a joint venture which focused on 2,3,3,3- tetrafluoropropene (CF3CF=CH2). This refrigerant, designated R1234yf, belongs to the group of hydro fluoro olefins (HFO). These refrigerants are unsaturated HFCs with a chemical double bond.

The global warming potential is extremely low (GWP = 4). When released to the atmosphere, the molecule rapidly disintegrates within a few days, resulting in a very low GWP. This raises certain concerns regarding the long-term stability in refrigeration circuits under real conditions.
However, extensive testing has demonstrated the required stability for mobile air conditioning systems.

R1234yf has lower flammability as measured by ASTM 681, but requires significantly more ignition energy than R152a, for instance. Due to its low burning velocity and the high ignition force, it received a classification of the new safety group "A2L" according to ISO 817. In extensive test series, it has been shown that a potentially increased risk of the refrigerant flammability in MAC systems can be avoided by implementing suitable constructive measures. However, some investigations (e.g. by Daimler) also showed an increased risk. This is why various manufacturers have again intensified the development of alternative technologies.

Toxicity investigations have shown very positive results, as well as compatibility tests of the plastic and elastomer materials used in the refrigeration circuit. Some lubricants show increased chemical reactivity which, however, can be suppressed by a suitable formulation and/or addition of "stabilizers".

Operating experiences gained from laboratory and field trials to date allow a positive assessment, particularly with regard to performance and efficiency behaviour. For the usual range of mobile air conditioning operation, refrigerating capacity and coefficient of performance (COP) are within a range of 5% compared with that of R134a. Therefore, it is expected that simple system modifications will provide the same performance and efficiency as with R134a.

The critical temperature and pressure levels are also similar, while the vapour densities and mass flows are approximately 20% higher. The discharge gas temperature with this application is up to 10 K lower.

With a view to the relatively simple conversion of mobile air conditioning systems, this technology prevailed up to now over the competing CO2 systems.

However, as already explained before, due to the flammability of R1234yf, investigations focus on other technical solutions. This includes active fire-extinguishing devices (e.g. with argon), but also enhancements of CO2 systems.

For detailed information on "Low GWP" HFOs and blends: "Low GWP" HFOs and HFO/HFC blends as alternatives to HFCs.