## 4 Conclusions  
This paper presented the methodology applied as the initial step of an overall evaluation and materials selection process of the most suitable PCM to be implemented as TES in two innovative compact systems aimed to provide heating, cooling, and domestic hot water (DHW) in residential buildings in the Mediterranean and Continental regions in a more efficient way. A qualitative decision matrix was used in the pre-screening process to assess the potential of the most promising PCM candidates, by assigning a score to a few relevant properties and calculating a total score based on a weighted average of the scores obtained by the single properties of each PCM. The melting enthalpy and temperature range, availability, cost, and maximum allowed working temperature (for the CON concept), were considered as relevant properties in the decision matrix. A sensitivity analysis was also performed to check the robustness of the selection matrix and the influence that variations in the values assigned to the different weights might have on the results. For the MED system, which requires a PCM with phase change temperature around 4 \({}^{\circ}\)C, given the initial information available, RT4, A3, RT3 HC_1, and PureTemp 4 were the most promising options out of a total of ten PCM candidates assessed using the decision matrix. A detailed experimental characterization based on DSC and TGA analysis showed that save OM 03 was unacceptable. Regarding the CON system, for which the desired phase change temperature should be between 60 \({}^{\circ}\)C and 65 \({}^{\circ}\)C, given the initial information available, RT64 HC, PureTemp 63, and THP5860 were the most promising PCM candidates out of a total of nine PCM assessed using the decision matrix. The detailed experimental characterization based on DSC, thermal cycling, and TGA analysis confirmed that these PCMs were suitable options for the CON system. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Position**} & \multicolumn{2}{c}{**Scenario 1**} & \multicolumn{2}{c}{**Scenario 2**} \\ \cline{2-5}  & **Commercial** & **Frequency** & **Commercial Name/Composition** & **Frequency** \\ \hline
1 st & savE OM 03 & 49/49 (100\%) & savE OM 03 & 49/49 (100\%) \\
2 nd & RT4 & 47/49 (95.9\%) & RT4 & 45/49 (91.8\%) \\
3 rd & A3 & 23/49 (46.9\%) & Caprylic acid + lauric acid (9:1 by mol) & 28/49 (57.1\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Ranking of the best three PCM candidates and frequency distribution for the MED system. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Position**} & \multicolumn{2}{c}{**Scenario 1**} & \multicolumn{2}{c}{**Scenario 2**} \\ \cline{2-5}  & **Commercial Name/Composition** & **Frequency** & **Commercial Name/Composition** & **Frequency** \\ \hline
1 st & RT64 HC & 172/180 (95.6\%) & RT64 HC & 172/180 (95.6\%) \\
2 nd & PureTemp 63 & 135/180 (75.0\%) & PureTemp 63 & 150/180 (83.3\%) \\
3 rd & THP5860 & 109/180 (60.6\%) & THP5860 & 111/180 (61.7\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Ranking of the best three PCM candidates and frequency distribution for the CON system. It is also important to highlight that the selection process described in this study should be viewed as an initial step in an overall evaluation/materials selection process for the described applications. Since transportation costs and any other potential additional costs were not taken into consideration in the decision matrix, the results presented here could be different, although they can still serve as the basis for deeper analysis for any specific location and characteristics of the building where either the MED or the CON HYBUILD solution is intended to be implemented. Moreover, a further assessment of the actual thermophysical evaluation of the attained materials, as well as investigating the transient performance of the system and the role of the material selected are crucial steps to ensure the good performance of the entire system. Conceptualization, G.Z. and L.F.C. ; methodology, G.Z.