*3.2. R161–R41–R1234ze(E)*

The second mixture analyzed is a combination of R161, R41, and R1234ze(E). This composition is similar to the first mixture, but the R32 refrigerant has been replaced with R161, which also belongs to the HFC group. It has a very low GWP (equal to 12). In this mixture, R161 and R41 are highly flammable, while R1234ze(E) belongs to the 2 L class; therefore, it can be assumed that ternary mixtures will also belong to the highest flammability class. Each mixture component has a GWP below 150 (Figure 7a), so none of the points exceeded the strictest limit. Similar to the previously considered mixture, the normal boiling point of mixtures with high proportions of R1234ze(E) precludes the use of part of the composition in low temperature systems (Figure 7b). The heterogeneity of the mixtures is a serious problem in both the high- and low-temperature systems. Due to the very high temperature glides of this mixture for both analyzed cycles, only the narrow range of compositions meet the criterion of the maximum <sup>Δ</sup>*t*glide of 10 K, as presented in Figure 8.

**Figure 7.** Summary of the basic properties for the R161–R41–R1234ze(E) mixture: (**a**) GWP and (**b**) normal boiling point.

**Figure 8.** Temperature glide at the evaporation pressure for cooling cycles with R161–R41–R1234ze(E) mixture as refrigerant: (**a**) AC system (*t*e/*t*c = 0/30 ◦C); (**b**) low-temperature system (*t*e/*t*c = −30/30 ◦C).

The similarity to the previous mixture can also be seen in the COP and volumetric capacity charts (Figure 9). The areas of the highest values of these parameters are mutually exclusive, so it is necessary to consider which of the values will be more important for the end user. Considering the low cooling capacity of split air-conditioning devices, it can be concluded that higher energy efficiency will be more beneficial. Choosing a mixture with mass fractions of 0.8/0.1/0.1 will result in a much higher COP compared to a mixture with mass fractions of 0.1/0.8/0.1. An additional advantage is also a lower temperature glide.

In the case of mixtures predestined for operation in low-temperature circuits, the choice of a mixture with the 0.8/0.1/0.1 composition gives an additional advantage resulting from a significantly lower temperature of the medium after the compression process (see Figure 10b). Lowering this temperature by more than 30 K will be crucial for the operation of the system, especially in the summer. Discharge temperature drop will result in the lack of restrictions in terms of thermal stability of oils or the need for additional cooling of the compressor working elements. Compared to the 0.1/0.8/0.1 composition, the pressure ratio does increase, but its value remains at an acceptable level of 7.55 (Figure 10a). The mixture R161–R41–R1234ze(E) with mass fractions of 0.8/0.1/0.1 seems to be optimal also for low-temperature cycles, where for the assumed operating parameters it obtains COP = 2.2, with a volumetric cooling capacity of 1129 kJ/m<sup>3</sup> (Figure 10c,d).

**Figure 9.** Volumetric cooling capacity (**a**) and (**b**) the COP for air-conditioning system (*t*e/*t*c = 0/30 ◦C) with R161–R41– R1234ze(E) mixture as refrigerant.

**Figure 10.** Low-temperature system parameters (*t*e/tc = −30/30 ◦C) of the R161–R41–R1234ze(E) mixture: (**a**) pressure ratio; (**b**) temperature of the refrigerant vapour at the compressor discharge; (**c**) volumetric cooling capacity; and (**d**) COP.
