## 3 Results and Discussion  
### Variation Effects of Evaporation Temperature on Economic Performance of ORC System  
In this study, the ORC system operated under subcritical condition. Both R123 and R245 fa are dry working fluids with positive slopes of the saturation vapor curves. Therefore, after the isentropic expansion process to produce work, these two working fluids are at a superheated state. The upper limit of the evaporation temperature (inlet temperature of expander) was set to the temperature corresponding to the maximum entropy value on the saturated vapor curve near critical region of working fluid in \(T\)-s diagram. The condensation temperature was set at 27 \({}^{\circ}\)C and the heat source temperature was set at 197 \({}^{\circ}\)C.  
Figure 2 depicts the total cost of ORC system at different evaporation temperatures. In the figure, it can be seen that the total cost of ORC system with R123 as working fluid decreases with the increase of evaporation temperature, while, for the ORC system with R245 fa as working fluid, its total cost  
increases. With the increase of evaporation temperature, as for the R123 system, its heat transfer area in evaporator decreases. The output power of expander increases first and then decreases. The heat transfer area in condenser decreases. The work consumed by pump increases. The investment reduction rate of the evaporator is greater than the increase rate of the expander investment, so the total investment of system decreases as a whole. As for R245 fa system, the heat transfer areas in both evaporator and condenser decreases. Both the output power of expander and the work consumed by pump increases. The investment reduction rate of the evaporator is less than the increase rate of the expander investment, so the total investment increases as a whole. Figure 3 depicts the net earnings (NE) of ORC system at different evaporation temperatures. In the figure, it can be seen that, with the increase of evaporation temperature, the net earnings (NE) of the R123 system increase first and then decreases, while, for the R245 fa system, its net earnings (NE) increase. Multiplying the output power by the working fluid flow, the product obtained is sold in units of on-grid electricity price within one year. This income is the net earnings (NE) of ORC system. With the increase of evaporation temperature, the flow rate of R123 decreases while the output work increases. When the two items are multiplied, the net earnings (NE) of ORC system show a maximum at the evaporation temperature of 120 \({}^{\circ}\)C. As for the R245 fa system, the reduction rate of mass flow rate of working fluid is less than the increase rate of output work of system, thus the net earnings (NE) of system increases. Figure 3: Net earnings (NE) of ORC system at different evaporation temperatures. Figure 2: Total cost of ORC system at different evaporation temperatures. an optimal value at the evaporation temperature of 120 \({}^{\circ}\)C, while, for R245 fa system, the value increases with the increase of evaporation temperature. The present value of total profit in system service life of ORC system is related to two factors, total cost and net earnings of the system. The latter affects the value greatly. For the R123 system, the net earnings reach maximum at the evaporation temperature of 120 \({}^{\circ}\)C and the total cost of the system is small. Therefore, the present value of total profit in system service life has a maximum value at 120 \({}^{\circ}\)C. For R245 fa system, its increase rate of net earnings is greater than that of total cost of the system. Therefore, its present value of total profit in system service life increases with the increase of evaporation temperature.