HFO refrigerants such as R1234yf (GWP = 4), R454A (GWP = 238), and R454C (GWP = 148) are in safety class A2L, meaning they are highly flammable. All refrigerants starting with a 4 are mixtures of other refrigerants and have a temperature slip point that depends on the refrigerant and dew point temperature.

• R454A is a mixture of 35% R32 and 65% R1234yf, with a temperature slip point of 5.6K at a dew point of 40°C.
• R454C is a mixture of 21.5% R32 and 78.5% R1234yf, with a temperature slip point of 6.79K at a dew point of 40°C.

An HFO is actually an unsaturated HFC and contains fluorine, so these will eventually disappear as well. The HFC refrigerant R32 (GWP = 675) is also an A2L refrigerant, meaning that not every A2L refrigerant is an HFO, but every HFO is an A2L refrigerant.

R744 (CO2) has a low critical temperature of 30.98°C at 73.77 bar(a). Above this temperature, the system operates transcritically. Low evaporator temperatures can only be used in subcritical mode because of the high compressed gas temperature. This can be done in booster systems and cascade systems with, for example, R717 or R290 in the high-pressure section. CO2 is also used as a refrigerant via a thermosiphon heat exchanger with R290 on the evaporator side.

Primarily, the COP (Coefficient of Performance) of CO2 is poor. For example, with a hypothetical 100% compressor efficiency, the COP at -10°C / +20°C = 5.70, while with R290 = 7.53 at -10°C / +27.4°C.

In transcritical operation, the discharge pressure should be controlled depending on the discharge gas outlet temperature from the gas cooler to keep the COP as least bad as possible. This can be improved by applying, for example, parallel compression or post-cooling of the compressed gases coming out of the gas cooler.

CO2 provides good opportunities to recover heat, even at high temperatures, but then of course that heat must be usable. If so, a lot of energy can be saved on that side. Euro-Cold has gained extensive experience with CO2 and can therefore provide you with extensive information.

R290 (propane) falls in the A3 safety class (highly flammable) but is energetically very favourable and can be used safely with proper precautions. It is widely used in chillers, heat pumps and refrigeration and freezer systems.

Other natural refrigerants in installations using BOCK compressors and other components such as separators, fluid tanks, plate heat exchangers and valves from Euro-Cold's range are the A3 refrigerants: 
R1270 (C3H6)
R1150 (C2H4)
R600 + R600a (butane + iso-butane C4H10).