## 3 Results and Discussion
### Energy Analysis
\begin{table}
\begin{tabular}{c c c c} \hline  & **SS** & **IHX** & **ECO** \\ \hline R134a & 59.8 & 71.7 & 57.9 \\ R290 & 58.9 & 70.4 & 57.1 \\ R600a & 50.3 & 62.2 & 49.2 \\ R1270 & 65.2 & 76.9 & 63.1 \\ \hline \end{tabular}
\end{table} 
Table 2: Discharge temperatures (\({}^{\circ}\)C) for different refrigerants and configurations. Figure 4: Relative pressure ratio using R134a as the reference. Figure 3: Relative compressor power using R134a as the reference. had a lower heating capacity than R134a. Although R134a had a lower latent heat of condensation than R600a, this could be compensated with the much higher mass flow rate of R134a than that of R600a. Hence, the heating capacity of R134a was found to be higher than R600a. As it is not desired to obtain lower heating capacity in many applications using a low GWP alternative refrigerant to HFCs, this problem could be solved by appropriating the equipment, e.g., the compressor. Figure 6 shows the relative coefficients of performance of the systems with different configurations and refrigerants. According to the results, the heating COP of the system when operating with R600a was higher than that using other refrigerants. This can be explained by its lower power consumption compared with other refrigerants, although it had the lowest heating capacity. The increase in power consumption was greater than the increase in heating capacity when the cooling capacity was kept constant. The heating COP of the system when using R290 and R1270 was lower than that using the baseline refrigerant. Figure 5: Relative heating capacity using R134a as the reference. Figure 6: Relative COP using R134a as the reference. The influences of the utilization of the IHX and vapor injection on performance parameters are shown in Figure 7. The influence of utilizing the IHX and vapor injection was obtained by dividing the performance parameters using the IHX or flash tank vapor injection by a similar parameter in the single-stage cycle. As can be seen, the heating capacity decreased when utilizing the IHX and vapor injection, while the reduction in heating capacity was greater with vapor injection than with IHX. For example, the heating capacity when using R290 decreased by approximately 4.2% when using vapor injection, while it decreased by 1.4% with the IHX. The heating COP increased with the IHX and vapor injection, while the enhancement when using vapor injection was greater than that using IHX. Considering the heating COP improvement, the refrigerant that benefited the most from the IHX was the R600a, with approximately a 3.8% increase in the heating COP, while utilizing the IHX decreased its heating capacity by 1.7%. A mass flow rate reduction in both cases, with the IHX and vapor injection, was observed. By contrast, the decrease in mass flow rate reduction with the IHX was 10.5% for tested refrigerants, and it was 2.2% with vapor injection. The compressor power consumption decreased with both IHX and vapor injection. The reduction in power consumption was much higher when using vapor injection than the IHX. According to the results, the reductions in power consumption with the IHX and vapor injection were 4.2% and 12.7%, respectively. The IHX and vapor injection utilization had a reverse influence on the compression pressure ratio and discharge temperature. It was shown that they had a weak influence on the compression pressure ratio. The pressure ratio decreased with the IHX by almost 1.6%, but it increased slightly (less than 0.3%) with a vapor injection.