# Thermal and Energy-Efficiency Assessment of Hybrid CLT-glass Facade Elements
## 6 Thermal Numerical Analyses of the Hybrid CLT-glass Component Level
### Methods and Assumptions  
A refined numerical study was dedicated to the thermal analysis of the facade elements only. Taking advantage of the double symmetry of the reference CLT-glass panel in Figures 2 and 4, the corresponding Finite Element (FE) model was described in ABAQUS [54], which primarily focused on \(\frac{1}{4}\)th the nominal module (with appropriate boundary conditions). The final FE assembly (see Figure 13) consisted of a set of 8-node heat transfer solid elements (DC3D8 type from ABAQUS library) comprising:  
* Two double laminated glass sections (10 + 10 mm glass layers with a middle 1.6 mm thick EVASAFE bond);
* The interposed air cavity (\(s\)= 12.8 mm the thickness);
* The linear rubber edge trim allowing the glass panels to keep their position under ordinary thermo-mechanical loads,
* The CLT frame members (\(90\times 160\) mm their cross-section); \begin{table}
\begin{tabular}{c c c c c} \hline
**Parameter** & **Symbol** & **Unit** & **Fagade Element** & **Door** \\ \hline Total heat transfer coefficient & \(U\) & (W/m\({}^{2}\)K) & 2.42 & 0.43 \\ Degree of transmission of solar energy through glazing & \(g_{\perp}\) & - & 0.64 & 0 \\ Opening surface & \(A_{w}\) & (m\({}^{2}\)) & 9.82 & 1.78 \\ Proportion of glazing & 1-\(f_{\mathrm{P}}\) & - & 0.8 & 0.7 \\ Panel & \(f_{\mathrm{P}}\) & - & 0 & 0 \\ Frame surface & \(A_{\mathrm{d}}\) & (m\({}^{2}\)) & 1.964 & 0.534 \\ Glazing surface & \(A_{\mathrm{g}}\) & (m\({}^{2}\)) & 7.856 & 1.246 \\ Panel surface & \(A_{\mathrm{P}}\) & (m\({}^{2}\)) & 0 & 0 \\ External glazing heat transfer coefficient & \(U_{\mathrm{gl}}\) & W/m\({}^{2}\)K & 5.15 & 1 \\ Degree of transmission of solar energy through glazing & \(S_{\perp 1}\) & - & 0.80 & 0.00 \\ Internal glazing heat transfer coefficient & \(U_{\mathrm{g}2}\) & (W/m\({}^{2}\)K) & 5.15 & - \\ Degree of transmission of solar energy through glazing & \(S_{\perp 2}\) & - & 0.80 & - \\ Heat transfer coefficient of the frame & \(U_{\mathrm{f}}\) & (W/m\({}^{2}\)K) & 1.8 & - \\ Heat transfer coefficient of glass & \(U_{\mathrm{g}}\) & (W/m\({}^{2}\)K) & 2.51 & 0.18 \\ Heat transfer coefficient of the panel & \(U_{\mathrm{P}}\) & (W/m\({}^{2}\)K) & 0 & 0 \\ Glazing perimeter & \(I_{\mathrm{g}}\) & (m) & 11.54 & 0 \\ Linear thermal bridge (glass edge) & \(\psi_{\mathrm{g}}\) & (W/mK) & 0.05 & 0.05 \\ Panel perimeter & \(I_{\mathrm{p}}\) & (m) & 0 & 0 \\ Linear thermal bridge (panel edge) & \(\psi_{\mathrm{P}}\) & (W/mK) & 0 & 0 \\ Opening inclination (to horizontal) & \(\alpha\) & (deg) & 90 & 90 \\ Internal surface resistance & \(R_{\mathrm{si}}\) & (m\({}^{2}\)K/W) & 0.13 & - \\ External surface resistance & \(R_{\mathrm{se}}\) & (m\({}^{2}\)K/W) & 0.04 & - \\ Air cavity resistance & \(R_{\mathrm{se}}\) & (m\({}^{2}\)K/W) & 0.18 & - \\ \hline \end{tabular}
\end{table} 
Table 6: Calculation of the thermo–physical parameters for the facade and door openings. * Additional timber purlins, providing a linear slot for the positioning of the glass panels and thus being responsible for the activation of the frictional mechanisms along the CLT-glass edges in contact. Similar to Section 5, the thermal performance of the CLT-glass facade panel was first assessed by evaluating a few key performance indicators, such as the overall heat transfer coefficient \(U\) and the corresponding linear thermal transmittance (\(\Psi\)-value). Further advantages of the detailed FE model were then represented according to the availability of a series of local estimations of temperature values that are primarily involved in the thermal characterization of facade systems, such as the expected temperature under an imposed thermal gradient \(\Delta T\) (for condensation risk assessment) and the minimum surface temperature on glass surfaces, as well as the relevant temperature data that are directly involved in the definition of the overall thermal comfort (i.e., \(f_{\text{Rsi}}\) from Equation (1)).