## 3 Exergoeconomic Analysis
### Exergy Cost Balance and Thermoeconomic Indicators  
The Specific Exergy Costing (SPECO) cost method consists of three steps [34]. In the first step, the exergy flows are identified, for which a process flow diagram is made where the exergetic inputs and outputs flows are known due to exergetic analysis. In the second step, the different flows between the inputs and outputs are defined for the performance evaluation of each component of the process. Then, in the third step, the cost balances and auxiliary equations are presented, which are presented in Table 1.  
The cost of a k-component is the sum of the costs due to the capital investment \(\left(\dot{Z}_{k}^{CI}\right)\) and the operation and maintenance costs \(\left(\dot{Z}_{k}^{OM}\right)\), as shown in Equation (13). \[\dot{Z}_{K}=\ \dot{Z}_{k}^{CI}+\dot{Z}_{k}^{OM} \tag{13}\]  
The exergetic costs balance for control volumes in the stationary state is made by means of Equation (14), which establishes that the total cost of the exergetic output flows, is equal to the cost of the exergetic inlet flow plus the capital costs and other costs [32]. \[\sum_{j=1}^{n}\dot{C}_{j,k,in}+\dot{Z}_{K}=\sum_{j=1}^{m}\dot{C}_{j,k,out}, \tag{14}\]  
The exergetic balances obtained by applying Equation (14) to each of the components of the different WHR systems using ORC are shown in Table 1. The total exergy cost of a flow can be defined as shown in Equation (15). \[\dot{C}_{j}=c_{j}\dot{E}_{j} \tag{15}\]  
where the term \(c_{j}\) is the leveled cost per unit of exergy. For the analysis of ITC1 and ITC 3 in the WHR based on SORC and RORC, the costs per unit of exergy of stream 11 and 1A are null, because they have negligible purchase and sale costs. The cost rates associated with the input and output are defined in a similar way to the exergy rates, which were presented previously for each WHR configuration [10]. The cost rates obtained are used to calculate the average costs per unit of input and output flow for each component, according to the methodology defined by [PERSON] [34]. For component k of the WHR system, the cost associated with the fuel is calculated using Equation (16), while the cost associated with the product is calculated using Equation (17). \[c_{F,K}=\frac{\dot{C}_{F,K}}{\dot{E}_{I,K}} \tag{16}\]  
\[c_{P,K}=\frac{\dot{C}_{P,K}}{\dot{E}_{P,K}} \tag{17}\] \begin{table}
\begin{tabular}{c c c} \hline \hline
**Economic Constants** & **Value** & **Reference** \\ \hline Interest rate \(\left(i_{eff}\right)\) & 5\% & [37] \\ Nominal scaling ratio \(\left(r_{n}\right)\) & 5\% & [24; 31] \\ Project lifetime \(\left(n\right)\) & 20 years & [6; 31] \\ Annual Hours of Operation \(\left(\tau\right)\) & 7446 h & [37] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters considered in the thermoeconomic modeling. The cost rates of exergy destruction and exergy loss are fundamental values for the thermoeconomic optimization of the systems under study. The costs of exergy destruction for a component of the system are not involved in the cost balances, so it is usually associated with a hidden cost. The costs associated with the destruction and loss of exergy is calculated through Equations (18) and (19) [34]. \[\dot{C}_{D,K} =c_{F,K}\dot{E}_{D,k} \tag{18}\] \[\dot{C}_{L,K} =c_{F,K}\dot{E}_{L,k} \tag{19}\]  
In these equations, it is assumed that the average fuel exergy cost remains constant with a variable amount of exergy destruction or exergy lost. Thus, it could be assumed that this is the specific exergy cost of the product, and not of the fuel that remains constant. On the other hand, the relative cost difference for a system component (\(r_{K}\)) is calculated by means of Equation (20) and determines the increase in the unit exergy cost between the product and the fuel in relation to the unit cost of the input [34].