## 3 Results and Discussion
### Simulation Results and Comparison with Conventional Glazing Solutions  
The innovative solution (here referred as AER-DGU) was compared with commercially available glazing systems, which were considered in this study as benchmarks:  
* an argon (90%) filled double glazing embodying a low-e (Magnetron Sputter Vacuum Deposition) coating (here referred as LOW-E DGU);
* an argon (90%) filled triple glazing embodying two low-e (Magnetron Sputter Vacuum Deposition) coatings (here referred as LOW-E TGU). Their main features and energy performance parameters are reported in Table 5. \begin{table}
\begin{tabular}{c c c c} \hline \hline \(\mathbf{\tau_{\rm e}}\) [-] & \(\mathbf{\alpha_{\rm e}}\) [-] & \(\mathbf{q_{\rm i}}\) [-] & \(\mathbf{g}\) [-] \\ \hline
0.62 [18] & 0.19 [18] & 0.08 & 0.70 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Solar properties of the aerogel DGU. As a first comparison, it can be observed that the U-value of the aerogel window is comparable to that of the low-e glazing (aerogel system U-value 10% lower than LOW-E-DGU), while the LOW-E-TGU U-value is 30% lower than the one of the aerogel sample. Nevertheless, while the aerogel and the LOW-E-DGU glazing have about the same thickness (24-26 mm), the LOW-E-TGU thickness is 10 mm more (36 mm). The g-value of the aerogel sample (0.70) is higher than both the LOW-E systems: +0.15 with respect to DGU and + 0.26 with respect to TGU. The light transmittance \(\tau_{\
u}\) of the aerogel glazing unit is 0.69; it is comparable to the one of a triple glazing window (LOW-E-TGU shows a value of 0.66). It is lower than the \(\tau_{\
u}\) of the LOW-E-DGU, equal to 0.76 (-0.07). The lighting behavior of the monolithic solution is intermediate between the one of the conventional solutions chosen for the comparison, but the g-value is significantly higher and the thickness lower, especially when compared to the triple glazing unit. Simulations were carried out in order to show the influence of the glazing typology on building energy performance: ideal energy use was calculated to meet the zone loads, which means 100% efficiency for heating, cooling, and ventilation systems. The relative performance of the aerogel glazing was assessed by looking at the differences in the annual energy demand for heating, cooling, and lighting. Tables 6 and 7 (for the window-to-wall ratio WWR1 = 50 % and WWR2 = 100 %, respectively) show the energy loads (by considering the 2 nd floor of the building) for the three typologies of glazing units at the four considered climate conditions. In winter, aerogel glazing outperforms conventional solutions in all the examined climate conditions: when compared to low-e double glazing (Figure 4) and to low-e triple glazing (WWR1), it guarantees heating load reduction of about 5% and 1%, respectively, in Helsinki, of about 9% and 7%, respectively, in Turin, and of about 8% and 5 %, respectively, in Paris. For hot climate (Rome), the heating energy demands are very low for all the glazing systems. When considering a higher window-to-wall ratio (WWR2 = 100%) the benefits slightly increase (Figure 4): for moderate climate conditions (Turin), a reduction of 15% is obtained with respect to low-e DGU, whereas it is about 7% and 12% lower in Helsinki and Paris, respectively. Results are consistent with U and g values of the windows: the heating energy savings due to the innovative solution are higher in Turin, characterized by higher solar radiation, especially in winter time. The higher solar factor increases, indeed, the heat gain from aerogel windows. At the same time, the high value of the solar factor for the aerogel glazing increases the energy demand for cooling in moderate and hot climates: when compared to low-e double glazing and to low-e triple glazing (WWR1), it is 4% and 7% higher, respectively, in Turin, 11% for both in Paris, and about 4% and 6 % in Rome. The cooling energy demand increase is higher when considering a higher window-to-wall ratio (WWR2 = 100%, Figure 4).