## 4 Discussion
### The (Combined) Impact of Climate Change and Energy Retrofit  
To further analyse the impact of climate change and retrofit interventions on the risk of overheating, three parameters are defined (Figure 12). In un-retrofitted buildings, \(\Delta 1\) represents the increase in the number of overheating hours in future scenarios compared to the present scenario (e.g., overheating hours caused by climate change in un-retrofitted buildings). Similarly, \(\Delta 2\) represents the increase in the number of overheating hours for retrofitted buildings. In addition to that, \(\Delta 3\) depicts the increase in the number of overheating hours in the retrofitted case compared to un-retrofitted case for the same time period (i.e., impact of retrofit interventions on overheating hours). Table 8 shows the results for all these three parameters for Portici house-I and II. Figure 11: Thermal comfort state in the Livingroom of Portici house-I (**left**) and Portici house-II (**right**) according to adaptive thermal comfort model of EN15251. P = 2008–2018, F1 = 2041–2050, and F2 = 2091–2100; M1–4 refer to the climate models in Table 2.  
As a result of the significant temperature increase in the far future, \(\Delta\)1 and \(\Delta\)2 rise notably in both climate zones. In Portici house-I, \(\Delta\)1 is higher than \(\Delta\)2 in most climate scenarios, showing that the impact of climate change is more pronounced in un-retrofitted case than retrofitted one. The impact of retrofit on overheating hours is even more severe than climate since \(\Delta\)3 is always larger than \(\Delta\)1 or \(\Delta\)2 in all the climate scenarios. However, \(\Delta\)3 decreases slightly from present to F2. In climate zone II the results are slightly different and \(\Delta\)2 is higher than \(\Delta\)1 in all climatic projections for Portici house-II, implying that retrofitted buildings are more vulnerable to overheating under changing climatic conditions. Whether this discrepancy between the two reference buildings result from climate difference or building differences such as \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & \multicolumn{4}{c}{**P**} & \multicolumn{4}{c}{**F1**} & \multicolumn{4}{c}{**F2**} \\ \cline{3-10}  & & & **M1** & **M2** & **M3** & **M4** & **M1** & **M2** & **M3** & **M4** \\ \hline \multirow{3}{*}{Portici house I} & CIBSE-A & 1653.1 & 1707.6 & 1880.8 & 1789.9 & 1714.8 & 2051.8 & 2383.4 & 2264.1 & 2061.8 \\  & CIBSE-A & (28.8\%) & (29.8\%) & (32.8\%) & (31.2\%) & (29.9\%) & (35.8\%) & (41.6\%) & (39.5\%) & (35.9\%) \\  & EN15251 & 717.9 & 659.1 & 804.4 & 744.9 & 641 & 808.1 & 1301.4 & 1236.8 & 1060.6 \\  & EN15251 & (20.5\%) & (17.9\%) & (20.9\%) & (20.8\%) & (17.8\%) & (20.7\%) & (24.8\%) & (31.6\%) & (27.9\%) \\ \hline \multirow{3}{*}{Portici house II} & CIBSE-A & 343.8 & 543.4 & 1146.5 & 1019.3 & 721.6 & 1190.8 & 1919.5 & 1912.4 & 1553.9 \\  & (6.0\%) & (9.5\%) & (20.0\%) & (17.8\%) & (12.6\%) & (20.8\%) & (33.5\%) & (33.3\%) & (27.1\%) \\ \cline{1-1}  & EN15251 & 90.7 & 115.8 & 129.6 & 151.9 & 132.3 & 116.6 & 536.6 & 561.9 & 324.3 \\ \cline{1-1}  & EN15251 & (2.9\%) & (3.6\%) & (3.8\%) & (4.7\%) & (4.2\%) & (3.3\%) & (12.3\%) & (13.7\%) & (9.2\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Overheating hours/ratio of the retrofitted case, which is assessed with fixed operative temperature threshold (Method 1) and adaptive model (Method 2). P = 2008–2018, F1 = 2041–2050, and F2 = 2091–2100; M1–4 refer to the climate models in Table 2.