## 4 Results of the Optimizations
### Distributed Generation Solution
Moving from the economic towards the environmental optimal solution, the number of the DHN pipelines increase, as well as the size of the HPs and the ST panels installed. The size of the CCs remains quite constant while the size of ICEs, of ABSs, of PV panels and of TSs adopted decreases. The sizes of the components related to the environmental optimal solution do not follow this trend, because the size of the components is free of penalty. Figure 8 shows the Pareto front of the distributed generation solutions, and is compared with the isolated solutions and conventional solution. It can be clearly seen that, with the exception of the environmental optimal solutions, all the other optimal solutions dominate the conventional solution and allow both the objective functions to be improve. However, the distributed generation solution does not lead to a significant improvement of the economic objective function, compared with the Isolated Solutions (less than 1%). Figure 7: Superstructure of the distributed generation solution. Table 10 shows the economic and environmental results of the optimizations. Moving from the economic to the environmental optimum the operation cost increase by about 80%, resulting from a significant increase of the bought electricity cost and a reduction of the natural gas cost and sold electricity income. The maintenance cost decreases noticeably, while the investment cost increases significantly. The environmental optimal solutions are characterized by a noticeable reduction of the total annual emissions, but a raise in total annual cost. Table 11 shows the total optimal annual energy magnitudes for the different solutions. Moving from the economic towards the environmental optimal solution, it can be noted that the electricity produced by the ICEs decreases significantly. On the other hand, the electricity bought from the grid increases to feed electric components, such as CCs and HPs. In the economic optimal solution, the thermal energy produced by ICEs satisfies almost completely the demand, while it decreases significantly in the environmental optimal solution and is partially replaced by the thermal production of HPs and ST panels. As far as the cooling energy balance is concerned, the production of the \begin{table}
\begin{tabular}{l c c c c c} \hline  & **Environmental** & **90\% Env.** & **60\% Env.** & **30\% Env.** & **Economic** \\  & **Optimization** & **Optimization.** & **Optimization.** & **Optimization.** \\ \hline CHP natural gas cost (k/y) & 389 & 643 & 994 & 1296 & 1614 \\ BOI natural gas cost (k/y) & 0 & 0 & 0 & 0 & 0 \\ Buought electricity cost (k/y) & 1603 & 1030 & 446 & 130 & 21 \\ Sold electricity income (k/y) & 76 & 82 & 126 & 264 & 539 \\ Photovoltaic incentive (k/y) & 0 & 0 & 30 & 58 & 67 \\ Operating cost (k/y) & 1917 & 1591 & 1284 & 1105 & 1028 \\ Maintenance cost (k/y) & 37 & 57 & 84 & 107 & 132 \\ Annual investment cost (k/y) & 1519 & 410 & 378 & 381 & 397 \\ Total investment cost (k/y) & 17,422 & 4403 & 3968 & 4050 & 4178 \\
**Total annual cost (k/y)** & **3472** & **2058** & **1746** & **1593** & **1558** \\
**Reduction wet conv. solution** & **-3244\%** & **21.52\%** & **33.42\%** & **39.23\%** & **40.59\%** \\ Electricity emissions (t/y) & 3358 & 2157 & 934 & 273 & 44 \\ Sold electricity emissions (t/y) & 269 & 292 & 456 & 972 & 1981 \\ Natural gas emissions (t/y) & 1710 & 2885 & 4461 & 5818 & 7244 \\
**Total annual emissions (t/y)** & **4699** & **4750** & **4940** & **5120** & **5307** \\
**Reduction wet conv. solution** & **27.68\%** & **26.89\%** & **23.97\%** & **21.20\%** & **18.33\%** \\ \hline \end{tabular}
\end{table} 
Table 10: Total economic and environmental results of the optimizations—distributed generation solutions. Figure 8: Pareto front of the optimal distributed generation solutions, including the points representing isolated solutions (with and without TS) and the conventional solution. CCs is quite constant, while ABSs and HPs have opposite trends, moving from economic towards environmental optimum.