# Parametric Analysis of a Polygeneration System with CO\({}_{2}\) Working Fluid
## 3 Results and Discussion
### Discussion  
In this work, a novel polygeneration system with CO\({}_{2}\) as the only working fluid was studied. This system is able to produce significant amounts of electricity, heating and refrigeration. Moreover, it has a relatively high performance. In nominal operating conditions (Section 3.1), the energy efficiency was 78.07% and the exergy efficiency was 26.29%. The values of the exergy efficiency are similar to those found in the literature, for example, 28.8% exergy efficiency was found in [18], and 22.5% was found in [19]. The exergy efficiency in [18] is a bit higher than in the present work but the energy efficiency was only 53%, which is much lower than the 78% found in the present study. Moreover, the parametric study (Section 3.2) and Table 4 indicate that the maximum possible exergy efficiency of the present system is 30.19%, so the suggested configuration is a highly efficient system. Moreover, previous studies [21; 22] found energy efficiencies close to 45%, which is lower than those found in the present study. With regard to the exergy efficiency, some studies indicate relatively high values but it depends on the definition of exergy efficiency used in each case. The examined system is a configuration that can operate with various heat inputs such as fuel, biomass, or solar energy. In particular, concentrating solar power is needed in order \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Parameters** & \multicolumn{3}{c}{**Energy Efficiency**} & \multicolumn{2}{c}{**Energy Efficiency**} \\
**Symbol** & **Min** & **Max** & **Min** & **Max** & **Min** & **Max** \\ \hline TIT (\({}^{\circ}\)C) & 400 & 1000 & 70.76\% & 80.15\% & 15.01\% & 29.60\% \\ P\({}_{\text{high}}\) (bar) & 110 & 230 & 72.10\% & 78.88\% & 8.69\% & 28.38\% \\ P\({}_{\text{med}}\) (bar) & 75 & 125 & 67.51\% & 117.10\% & 14.36\% & 30.19\% \\ T\({}_{\text{hex}}\) (\(-\)) & 0.00 & 0.96 & 75.39\% & 88.92\% & 17.92\% & 28.36\% \\ T\({}_{\text{ref}}\) (\({}^{\circ}\)C) & \(-35\) & 10 & 75.69\% & 83.03\% & 12.67\% & 27.16\% \\ T\({}_{\text{hr}}\) (\({}^{\circ}\)C) & 20 & 45 & 74.42\% & 79.48\% & 24.86\% & 27.57\% \\ T\({}_{\text{heat,high}}\) (\({}^{\circ}\)C) & 45 & 115 & 65.63\% & 95.83\% & 24.63\% & 26.50\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The impact of the examined parameters on the energy and exergy efficiencies. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter (Par)** &
\begin{tabular}{c} \(\frac{\text{Parameter}-\text{T}_{\text{medit}}}{\text{Parameter}-\text{T}_{ \text{medit}}}\) \\ \hline \(\frac{\text{Parameter}-\text{T}_{\text{medit}}}{\text{Parameter}-\text{T}_{ \text{medit}}}\) \\ \hline \(\frac{\text{Parameter}-\text{T}_{\text{medit}}}{\text{Parameter}-\text{T}_{ \text{medit}}}\) \\ \hline TIT & 14.03\% & 64.75\% & Positive trend & Positive trend \\ P\({}_{\text{high}}\) & 14.47\% & 124.83\% & Positive trend & Positive trend \\ P\({}_{\text{med}}\) & 107.98\% & 102.36\% & Positive trend & Negative trend \\ T\({}_{\text{hex}}\) & 16.25\% & 37.23\% & Negative trend & Positive trend \\ T\({}_{\text{ref}}\) & 1.04\% & 6.12\% & Maximum point & Positive trend \\ T\({}_{\text{hr}}\) & 9.07\% & 14.43\% & Negative trend & Positive trend \\ T\({}_{\text{heat,high}}\) & 44.21\% & 8.13\% & Negative trend & Maximum point \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Ratios of the efficiency difference to the parameter range (sensitivity analysis). to achieve high values of the turbine inlet temperature and maybe solar tower or solar dishes. Moreover, the temperature levels of the heating and the refrigeration production can be varied in great ranges something that makes possible the use of the present system in various applications such as industries, buildings, hotels, hospitals, etc. In the future, the present system could be optimized and examined in a specific application in steady-state or dynamic mode. Moreover, different heat sources can be studied and more specifically, the combination of solar energy and biomass can be investigated.