## 6 Numerical Results
### Thermoeconomic Analysis
Finally, the next step deals with translating the exergy unit costs to economic unit costs by means of the economic data. Table 5 shows the average annual unit costs required for producing heating, DHW and cogenerated electricity (referred per unit of energy). The annual cost for the whole building and the cost for each dwelling are also shown. These costs are calculated considering the acquisition costs of Table 1 and the unit price of electricity and natural gas; nevertheless, a deeper analysis can be undertaken if life-cycle analysis (LCA) is carried out. Indeed, the cost of environmental impact is calculated in the same way but instead of considering the economic values, the whole life impact is taken into account (through an eco-indicator), from the cradle to the grave. Finally, Table 6 shows the savings obtained with cogenerated electricity (which corresponds to the by-product obtained simultaneously when heating demand is being covered). This value is obtained by subtracting the cost of cogenerated electricity from the cost of direct purchase from the grid. Although the cogeneration engines present a relatively reduced working time (1477 h per year for both engines), they still save an important amount of money. After all, the electricity purchased from the grid with a price of 22.33 c/kWh is replaced by the cogenerated electricity at a unit cost of 11.37 c/kWh. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{2}{c}{**Eco. Savings [f/year]**} \\ \hline
**Purchasing from Grid** & 6737 \\
**Cost of Cogenerating** & 3512 \\
**Saving during a Year** & 3226 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Savings with self-produced electricity when covering heating demand. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{4}{c}{**Costs of Products [c/kWhen]**} \\ \hline  & \(\text{c}_{\text{P}}^{e}\) & \(\text{c}_{\text{P}}^{z}\) & \(\text{\textc}\)/year & \(\text{\textc}\)/dwelling \\ \hline
**Heat** & 6.16 & 1.27 & 45.174 \(\text{\textc}\) & 257 \(\text{\textc}\) \\
**DHW** & 5.16 & 2.09 & 23.278 \(\text{\textc}\) & 132 \(\text{\textc}\) \\
**Elec. (by-Product)** & 6.68 & 4.69 & 14.516 \(\text{\textc}\) & 82 \(\text{\textc}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Unit costs of system products and annual total costs. According to the results, the micro-cogeneration engines are more efficient than boilers, since they have higher exergy efficiency, as they produce simultaneously heat and electricity. Therefore, if only exergetic cost is considered, producing heat with cogeneration would always be more beneficial because there are less irreversibilities. However, cogeneration requires a relatively high investment, if we compare its purchase cost with the cost of buying a boiler with the same heating power. Nevertheless, the annual savings obtained with electricity cogenerated are 3226 \(\epsilon\), as shown in Table 6.  
On the other hand, one cannot forget that the electricity demand can also be fulfilled by the production of the PV panels, and that option should also be considered. After all, the best configuration and the best control that minimizes the energy consumption needs to be analyzed, but that is beyond the scope of this work.