## 3 Results and Discussion
### The Effect of Different Factors on the System Performance of Two Heat Pumps  
Figures 11-13 show the effects of different factors on the system performance of the R515B-1 subcritical heat pump and R744/R1234 yf (90/10) transcritical heat pump. Table 8 shows the cost of the R515B-1 subcritical heat pump and R744/R1234 yf (90/10) transcritical heat pump, which was obtained through market research (more accurate data provided by cooperative enterprises). \begin{table}
\begin{tabular}{c c} \hline \hline
**Device** & **Cost Equations** \\ \hline R515B-1 subcritical heat pump & \(63.38\times Q_{h}\) \\ R744/R1234 yf (90/10) transcritical heat pump & \(204.2\times Q_{h}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: The costs of two types heat pump. Figure 10: The effect of condensation temperature on the system performance of different refrigerants (subcritical cycle). Figure 9: The effect of evaporation temperature on the optimal system performance of different mixed refrigerants (transcritical cycle). The calculation method of PP is shown in Equation (12). \[PP= \frac{cost_{\text{tran}}-cost_{\text{sub}}}{\Delta W\cdot k_{d}} \tag{12}\]  
where \(\text{cost}_{\text{tran}}\) and \(\text{cost}_{\text{sub}}\) are the costs of the R744/R1234 yf (90/10) transcritical heat pump and R515B-1 subcritical heat pump, respectively; \(\Delta\)W is the difference in power consumption between the two systems; and \(\text{k}_{\text{el}}\) is the cost of electricity (USD 0.214/kWh) [33]. 3.1 The Effect of \(\text{T}_{\text{e}}\) on the System Performance of Different High-Temperature Heat Pumps  
Figure 11 shows the effect of evaporation temperature on the system performance of R515B-1 and R744/R1234 yf (90/10) applied to the subcritical heat pump and transcritical heat pump, respectively, as well as the expected cost recovery period of the R744/R1234 yf (90/10) transcritical heat pump compared to that of the R515B-1 subcritical heat pump. Figure 11a shows the changes in power consumption and heating capacity of the two heat pump systems with evaporation temperature. It can be observed from the figure that as the evaporation temperature increases, the power consumption of both heat pump systems decreases. At the same time, the heating capacity of the transcritical heat pump gradually decreases, while the heating capacity of the subcritical heat pump gradually increases. This is mainly because as the evaporation temperature increases, the evaporation pressure of both systems increases. At this time, the high pressure of the subcritical heat pump remains unchanged, while the high pressure of the transcritical heat pump decreases. Therefore, the compressor pressure ratio of the two systems decreases to varying degrees, ultimately leading to a decrease in power consumption of both systems. The increase in evaporation pressure reduces the unit heating capacity of the subcritical heat pump, while the increase in evaporation pressure increases the refrigerant flow rate. Because the influence of refrigerant flow rate is greater than that of unit heating capacity, the total heating capacity of the subcritical heat pump increases. In the transcritical heat pump, the reduction in unit heating capacity is greater, resulting in a decreasing trend in the total heating capacity of the transcritical heat pump. In addition, compared to the R515B-1 subcritical heat pump, the R744/R1234 yf (90/10) transcritical heat pump consumes less power and has a higher heating capacity; its heating capacity is only lower than that of the R515B-1 subcritical heat pump at higher evaporation temperatures. Figure 11b shows the variation in COP with evaporation temperature for the two heat pump systems. It can be observed from the figure that the COP of the R744/R1234 yf (90/10) transcritical heat pump is generally higher than that of the R515B-1 subcritical heat pump, and the COP of both systems increases with the increase in evaporation temperature.