## 5 Discussion  
As underlined by the performed simulations, the installation of multiple DSFs in existing buildings leads to a general improvement in the energy performance with regard to both consumption and comfort. Intense heating and cooling savings are expected when comparing the building's original state and the Multi-Storey configuration. The annual heating and cooling consumption, in fact, can be cut down, respectively, to 52-57% and 65-68% for the considered year. Similar but less intense trends, especially regarding the heating requirement, were estimated for the other DSFs. The presence of horizontal or vertical partitions and the subdivision of the cavity into multiple chambers, in fact, causes a higher heating requirement and, even if they are associated with slightly better cooling needs (a reduction of 63-74% for the Shaft-Box and 68-79% for the Box-Window), the global annual energy is higher than when the Multi-Storey option is considered. The air channel increases the natural ventilation of the occupied spaces, thus reducing their temperature and, at the same time, creates a more effective barrier against heat loss throughout the building envelope during the wintertime. Finally, the two Corridor DSF versions exhibit negligible differences, underlining that the system performance is not affected by the air grills' location but is influenced by their dimensions. Figure 17: Comfort rates for a typical winter week according to the 2070 climatic file. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Configuration** & **Mean** & **Minimum** & **Maximum** \\  & **Temperature** & **Temperature** & **Temperature** \\ \hline Original State & 20.13 & 19.15 & 20.92 \\ MS-DSF & 21.72 (+7.9\%) & 19.88 (+3.8\%) & 25.61 (+22.4\%) \\ SB-DSF & 20.56 (+2.1\%) & 19.45 (+1.6\%) & 22.11 (+5.7\%) \\ C-DSF & 20.86 (+3.6\%) & 19.65 (+2.6\%) & 22.65 (+8.3\%) \\ BW-DSF & 20.59 (+2.3\%) & 19.49 (+1.8\%) & 21.98 (+5.1\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Indoor operative mean, minimum and maximum temperature expected for a typical winter week in 2050. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Configuration** & **Mean** & **Minimum** & **Maximum** \\  & **Temperature** & **Temperature** & **Temperature** \\ \hline Original State & 20.48 & 18.94 & 25.67 \\ MS-DSF & 20.74 (+1.3\%) & 19.14 (+1.1\%) & 24.27 (\(-\)5.5\%) \\ SB-DSF & 20.17 (\(-\)1.5\%) & 19.01 (+0.4\%) & 27.72 (+8.0\%) \\ C-DSF & 20.36 (\(-\)0.6\%) & 19.12 (+1.0\%) & 21.95 (\(-\)14.5\%) \\ BW-DSF & 20.18 (\(-\)1.5\%) & 19.01 (+0.4\%) & 21.64 (\(-\)15.7\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Indoor operative mean, minimum and maximum temperature expected for a typical winter week in 2070. The analysis of the expected thermal comfort conditions provides a few challenging aspects that should be considered in the case of DSFs. The implementation of an additional insulation layer represented by the Double-Skin Facade reduces heat transfer and ensures more stable indoor temperature fluctuations. This improvement becomes particularly noticeable during extreme meteorological conditions, such as hot summers and cold winters. As a main consequence of more uniform indoor temperatures, the discomfort conditions last longer because heat dissipation occurs slowly. For this reason, the summer comfort rate evaluation highlights higher discomfort, reaching the worst comfort categories, predicted for DSF solutions when compared to the original building state. Among the investigated options, the Multi-Storey configuration exhibits slightly better values than the others, decreasing from Category II, or 21% of the time, to 7% for 2030 and from 39% to 33% for 2070, respectively, for the existing configuration and the retrofitting one. The analysis of the indoor operative temperature confirms the above-mentioned considerations.