## 3 Results and Discussion
### Energy Analysis  
The relative mass flow rate of the refrigerants is presented in Figure 2. According to the results, all selected hydrocarbons had a lower mass flow rate than R134a. The mass flow rates of selected hydrocarbons were 44% to 49% lower than that of R134a. When the cooling capacity is fixed (10 kW in this study), a higher value of latent heat of vaporization lowers mass flow rates [29]. As presented in Table 1, the latent heat of vaporization of R134a was much lower than that for the hydrocarbons, and consequently, R134a exhibited a larger mass flow rate than the selected hydrocarbons. To investigate whether the selected hydrocarbons could work with the existing compressor as possible drop-in replacements for R134a, the suction volumetric flow should be taken into account. Although the suction volumetric flow is proportional to the mass flow rate, it is also inversely proportional to the suction density of the refrigerant. From Table 1, it is apparent that the density of hydrocarbons is lower than the R134a. So, taking into account the mass flow rate and suction density values of the hydrocarbons simultaneously, it was observed that the densities of R290 and R1270 were lower than that of R134a by almost the same proportion as the mass flow rate. This means that the compressor size for operation with R290 and R1270 cannot be reduced compared with operation with R134a. The ratio between the mass flow rate and suction density for R600a was much lower than that for R134a. Still, this discrepancy could negatively influence heating and cooling capacities when reducing the R600a compressor size because the capacity is proportional to the mass flow rate. The compressor discharge temperature for different configurations and refrigerants is shown in Table 2. Compared with R134a as baseline refrigerant, it was found that R1270 had a higher discharge temperature, but R290 and R600a had lower discharge temperatures than R134a. These results suggest that a safe substitution of R290 and R600a for R134a is possible, and a lower discharge temperature of R290 and R600a could increase the longevity of the compressor and reduce oil aging. R1270 exhibited approximately a 2% higher discharge temperature than R134a in the tested operating temperature, which must be considered when choosing this refrigerant as an alternative to R134a. It was also revealed that the IHX had a significant influence on discharge temperature. The discharge temperature increased dramatically (between 19% and 25%) with the IHX, but utilizing vapor injection decreased the discharge temperature by approximately 3.8%. It is interesting to note that R600a had the lowest discharge temperature compared with the other tested refrigerants. Using the IHX had the worst influence on this refrigerant, as approximately a 25% increase in discharge temperature was observed when using the IHX single-stage cycle with R600a. Considering the effect of both the refrigerant and configuration, it can be concluded that the IHX configuration when using R1270 is not suitable to supply a high heat sink temperature, as the discharge temperature was relatively high in this case. Figure 2: Relative mass flow rate using R134a as the reference. Figures 3 and 4 represent the relative compressor power consumption and compression pressure ratios, respectively. The compressor's power consumption when using R1270 and R290 was higher than that when using R134a by approximately 1.5% to 2%, whereas it was lower when using R600a as an alternative refrigerant. According to the results, all hydrocarbons had a lower pressure ratio than R134a. The relative heating capacities of the refrigeration systems with different configurations and refrigerants are presented in Figure 5. The latent heat of condensation and the mass flow rate affect the heating capacity [29]. R1270 and R290 had higher heating capacities than R134a, as they had a much greater latent heat of condensation, but R600a