## 5 Conclusions  
Considering traditional and classical indicators mainly focus on the present economic performance evaluation, a relatively new indicator, which is called present value of total profit in system service life, is proposed in this paper. Economic performance of ORC systems with R123 and R245 fa as working fluid was analyzed using five traditional economic indicators (total cost, net earnings, payback period, return on investment, and levelized energy cost) and the relatively new indicator. From the calculation results, the following conclusion can be drawn. (1) Considering the variation effects of evaporation temperature on economic performance of ORC system, for R123 system, its payback period (PP), return on investment (ROI), and levelized energy cost (LEC) reach optimal at the evaporation temperature of 125 \({}^{\circ}\)C and its net earnings (NE) and present value of total profit in system service life have the optimal value at the evaporation temperature of 120 \({}^{\circ}\)C. Considering that the total cost of the system is relatively low when the evaporation temperature is 125 \({}^{\circ}\)C, this is the optimal evaporation temperature for R123 system. As for R245 fa system, its payback period (PP), return on investment (ROI), and levelized energy cost (LEC) reach optimal at the evaporation temperature of 122 \({}^{\circ}\)C. When above 122 \({}^{\circ}\)C, its growth rate of total cost of the system accelerates, while its growth rates of net earnings and present value of total profit in system service life slow down. Therefore, 122 \({}^{\circ}\)C is the optimal evaporation temperature for R245 fa system. (2) Considering the variation effects of condensation temperature, three indicators, payback period (PP), return on investment (ROI), and levelized energy cost (LEC) of ORC system, which are based on the ratio of net earnings to total cost of system, have an optimal value of condensation temperature. R123 and R245 fa systems have optimal condensation temperatures of 33 \({}^{\circ}\)C and 27 \({}^{\circ}\)C, respectively. (3) Considering the variation effects of heat source temperature, with the increase of heat source temperature, there are three increasing indicators: total cost, net earnings, and present value of total profit in system service life. R123 and R245 fa systems have optimal heat source temperatures of 217 \({}^{\circ}\)C and 177 \({}^{\circ}\)C, respectively. (4) Considering the variation effects of mass flow rate of heat source, with the increase of mass flow rate of heat source, although the total cost of system increases, the net earnings, return on investment, and present value of total profit in system service life increase. Meanwhile, the payback period and levelized energy cost decrease. Therefore, the economic performance of system becomes better and better with the increase of mass flow rate of heat source. (5) If the above four variation effects are considered comprehensively, the results show that the optimal evaporation temperature of R123 is 125 \({}^{\circ}\)C, optimal condensation temperature is 33 \({}^{\circ}\)C, and optimal heat source temperature is 217 \({}^{\circ}\)C. For R245 fa, the optimal evaporation temperature is 122 \({}^{\circ}\)C, optimal condensation temperature is 27 \({}^{\circ}\)C, and optimal heat source temperature is 177 \({}^{\circ}\)C. The investment in heat exchanger accounted for the largest proportion, followed by expander, then pump, and the least was the investment in working fluid. (6) The economic performance of an ORC demonstration project was reported. The investment in heat exchanger accounted for the largest proportion, followed by expander, working fluid accounts for the third, and the least was the investment in pump. Conceptualization, X.Z. ; Data curation, M.C. ; Formal analysis, M.C. and X.Y. ; Funding acquisition, X.Z. and H.G. ; Methodology, X.Z. and X.Y. ; Writing--original draft, X.Z. ; and Writing--review and editing, H.G. and J.W.