## 3 Results
### Economic Analysis  
Section 3.3 discusses effects of internal and external factors on the energy saving potential of the ACS-OAR system. We can tell that feed air temperature and humidity not only affect the \(ESR\) and \(COP\) of OAR directly, but also play a decisive role in the optimization of the approach temperature of heat exchangers, as well as the evaporation temperature and flow ratio of the generators, which is crucial for the initial cost and operation cost of the ACS-OAR system. We conducted an economic analysis under variable feed air working conditions in Beijing to demonstrate the profitability of the proposed system. Assumptions for the economic analysis are listed in Table 5.  
According to Equation (37), \(DPP\) is directly related to project revenue (\(Pr\)) and cost of the OAR (\(C_{acs}\)). While \(Pr\) is in direct proportion to \(ESR\), which is almost exclusively determined by \(AT_{sahler}\). Therefore, the key point to confirm \(Pr\) is the optimization of \(AT_{sahler}\). As for the \(C_{acs}\), it includes the capital cost of instruments, maintenance cost, management cost, and operating cost. The maintenance cost is set annually as 4.63% of the capital cost. The management cost is considered annually as 20% of the operating labor cost. Figure 10: Influences of feed air temperature and humidity ratio on: (**a**) \(ESR\); (**b**) \(COP\); (**c**) \(AT_{sahler}\). \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline Life cycle of the system & 25 year \\ Annual working hours & 8000 h \\ Average electricity price & 0.09 USD/kWh \\ Interest rate IR & 8\% \\ Discounted rate DR & 2.5\% \\ Tax rate & 25\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Assumptions for the economic analysis. Compared to the operating of CASUs, workload for the operating of the OAR is relatively small; thus, additional labor cost is ignored. Additionally, no cost is obtained for heat source since the heat source for the OAR is the compression waste heat. Furthermore, the electricity consumption of the fans and pumps for intercoolers and ACTs in conventional ACSs can fully satisfy the electricity demand of the fans and pumps for the OAR. Thus, no additional operating cost is needed for the OAR. As the main equipment of the OAR are heat exchangers, the capital costs of the OAR are estimated by the heat transfer area, which is also strongly affected by the \(AT_{sahcx}\). Considering the effects of \(AT_{sahcx}\) on the two important variables (\(Pr\) and \(C_{acs}\)) of \(DPP\), designed \(AT_{sahcx}\) will be optimized to achieve desirable economic evaluation indicators. Table 6 shows the monthly \(ESR\) calculated according to the variable feed air working conditions under different \(AT_{sahcx}\). As can be seen from Table 6, the largest and smallest electricity consumption of conventional ACS occur in July and January, respectively. Conversely, the largest \(ESR\) (7.01%) occurs in January with \(AT_{sahcx}\) at 5 \({}^{\circ}\)C, whereas \(ESR\) in July approaches approximately zero due to the high dewpoint temperatures of inhaled air at the inlets of second- and third-stage compressors, which are higher than 40 \({}^{\circ}\)C. In this condition, cooling produced by an OAR can still be supplied to the pre-cooling stage of compressed air before the molecular sieve stage. The annual average \(ESR\) of the ACS-OAR in Beijing is from 4.41% to 2.68%, as \(AT_{sahcx}\) increases from 5 to 20 \({}^{\circ}\)C. Project revenue can be calculated based on \(ESR\) and electricity consumption values. Direct capital cost of conventional cooling system is calculated based on the most unfavorable month, i.e., July, in which the heat transfer rates of intercoolers are the highest. The heat transfer area of OAR equipment corresponding to different \(AT_{sahcx}\) was calculated. It is worth noting that heat transfer areas are not all based on the most unfavorable month, as a higher humidity of feed air in an unfavorable month permits a higher approach temperature.