# Thermal and Energy-Efficiency Assessment of Hybrid CLT-glass Facade Elements
## 6 Thermal Numerical Analyses of the Hybrid CLT-glass Component Level
### Expected Thermal Performance Indicators  
Based on EN ISO 10077-2:2017 [55] provisions, the thermal calculation for the system in Figure 13 should be conventionally carried out based on:  
* Relative Humidity= 50%,
* External condition: \(T_{out}\)= 0 \({}^{\circ}\)C, film coefficient (timber and glass) = 23 W/m\({}^{2}\)K, \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Component**} & \multicolumn{2}{c}{**Interposed Cavity**} \\ \cline{2-5}  & **Glass** & **EVASAFE** & **Timber** & **Rubber** & **Air** \\ \hline Conductivity \(\lambda\) (W/mK) & 0.8 & 0.19 & 0.3 & 0.1 & 0.028 \\ Emissivity \(\varepsilon\) (\(-\)) & 0.95 & / & 0.7 & / & / \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Input thermal properties in use for FE modelling in ABAQUS. Figure 13: Reference FE model for the thermal assessment of full-size CLT–glass facade elements: (a) global assembly (1/4 th the geometry) and (b) a detailed view with hidden mesh (ABAQUS). Internal condition: \(T_{int}\)= 20 \({}^{\circ}\)C, film coefficient (timber and glass) = 8.02 W/m\({}^{2}\)K.  
This recommended thermal scenario was found to be representative of real field measurements from the Live-Lab facility (see Section 3). The major FE outcomes from the above thermal boundaries are presented in Table 8, where a significant improvement in the expected \(U\)-value from Section 5 can be found (with \(U=2.42\) W/m\({}^{2}\)K in Table 6). If the nominal geometry of the load-bearing components is described with accuracy, the local estimates of temperature distributions can further support the thermal performance assessment (and possible optimization) of the reference CLT-glass system in Figure 13. Figure 14, in this regard, shows a typical temperature distribution in glass and the adjacent portion of frame (corner joint). \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Double Laminated Glass with EVSAFE** \\ \hline \(U\) (W/m\({}^{2}\)K) & 1.826 \\ \(\Psi\) (W/mK) & 0.5285 \\ \(T_{max}\) (\({}^{\circ}\)C) & 16.60 \\ \(T_{min}\) (\({}^{\circ}\)C) & 9.15 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Numerical thermal performance assessment of the CLT–glass facade element under an imposed \(\Delta T=20\)\({}^{\circ}\)C (detailed FE model, ABAQUS). \(T_{max}\) and \(T_{min}\) values are calculated in the cavity. Figure 14: Numerical thermal performance assessment of a full-size CLT–glass facade element (ABAQUS). Expected distribution of temperature (**a**) in the internal glass panel (external side with CP\(n\) = 1, 2, and 3 diagonal distances corresponding to 50 mm, 90 mm, and 150 mm, respectively from the corner) and (**b**) in the timber frame with (**c**) a detail of the corner joint (front view). All the legend values are given in \({}^{\circ}\)C.  
According to Figure 14a,b, the temperature rapidly changes in the area of glass in contact with timber, thereby affecting the key performance indicators. Figure 14c, moreover, demonstrates the qualitative correlation of this detailed FE estimation with the thermographic acquisitions from the Live-Lab facility. Even more attention, however, should be paid to the temperature distribution in the frame cross-section (CLT members and purlins) given that the hybrid CLT-glass design concept is based on direct frictional contact between the two materials. The latter is emphasized in Figure 15a (timber members), while Figure 15b offers a more detailed representation of temperatures according to glass thickness and different locations. As long as the glass components are in contact with the frame in Figure 15a, the temperature distribution at the glass edges corresponds to the \"Glass edge\" plot in Figure 15b. In the same figure, moreover, the CP1, CP2, and CP3 control points are still representative of temperature distributions in the thickness of the glass panel. According to the contour plot in Figure 14a, however, these CP_n_ values are selected on the diagonal of the panel at a distance of 50 mm, 90 mm, and 150 mm from the corner.