## 3 Results and Discussion
### Environmental Impact Analysis  
TEWI was the metric used in this study to investigate the equivalent emissions of different refrigerants and refrigeration cycle designs. According to Equation (23), it is apparent that the total CO\({}_{2}\)-eq emission comprises two parts: direct and indirect emissions. Direct emissions are mainly dependent on the GWP value and refrigerant leakage rate. An increase in the GWP of refrigerants as well as a higher leakage rate results in higher CO\({}_{2}\)-eq emissions. Figure 9(a) represents the influence of GWP and leakage rate on CO\({}_{2}\) emissions for 10 years of refrigeration system operation, with the recovery factor assumed to be 0.7. The indirect emissions of a refrigeration system depend on the power consumption of the cycle and the emissions relevant to the energy sources used to operate the refrigeration system. Systems with higher efficiency consume less energy to produce the same cooling/heating and have lower CO\({}_{2}\)-eq emissions. In addition, various energy sources, such as fossil fuels and renewable energy, have different contributions to CO\({}_{2}\)-eq emission. When the share of clean energy sources increases, indirect emissions of the refrigeration systems are reduced. Figure 9(b) shows the influence of the COP and CO\({}_{2}\)-eq emission factor (kg per kWh) on indirect CO\({}_{2}\)-eq emissions. These results reveal that the impact of indirect emissions dominates the total CO\({}_{2}\)-eq emissions over the lifetime of a refrigeration system in most cases. Hence, it is essential to consider the refrigeration system's efficiency when introducing a low GWP refrigerant as an alternative to a refrigerant with a high GWP value. The use of hydrocarbons with much lower GWP values than R134a decreased the direct emissions of a refrigeration system. Figure 11 shows the direct CO\({}_{2}\)-eq emissions of the system when operating with hydrocarbons or R134a for 10 years. It can be seen that R134a significantly contributed to CO\({}_{2}\)-eq emissions, whereas using hydrocarbons with very low GWP values mitigated the CO\({}_{2}\)-eq emissions remarkably. Figure 9: The influence of (**a**) IHX and (**b**) vapor injection on different exergy parameters (T\({}_{\text{source}}\) and T\({}_{\text{sink}}\) of \(-5\) and \(35\)\({}^{\circ}\)C, respectively). As mentioned above, the improvement in the efficiency of the refrigeration system decreases the total CO\({}_{2}\)-eq emissions. The influence of the selection of hydrocarbons instead of R134a and the improved design of the refrigeration system on total CO\({}_{2}\)-eq emissions is shown in Figure 12. The results depicted that hydrocarbons as an alternative to R134a decreased the CO\({}_{2}\)-eq emissions significantly, while R600a had lower emissions because of its higher efficiency than other studied refrigerants. The improved designs, including an internal heat exchanger and flash tank vapor injection, reduced the CO\({}_{2}\)-eq emissions by between 1% and 8%. Figure 11: Logarithmic direct CO\({}_{2}\)-eq emissions of hydrocarbons and R134a at different leakage rates. Figure 10: Emissions (kg CO\({}_{2}\)-eq) of a refrigeration system as a function of different parameters: (a) direct and (b) indirect. Emissions from electricity consumption depend on the sources of energy used for electricity generation, and they differ from country to country. If a country has low carbon electricity generation, the total equivalent emissions are relatively low. Hence, to investigate the emissions of a refrigeration system, it is imperative to consider the CO\({}_{2}\)-eq emission factor as a determinant criterion. Figure 13 shows the total emission of the refrigeration system when operating with R290 in different countries. According to the results, in a country such as Sweden, where the main electricity generation sources are renewable clean energy, the total emissions are much lower than in other countries.