# Thermal and Energy-Efficiency Assessment of Hybrid CLT-glass Facade Elements
## 5 Full-Size Numerical Analysis of the Live-Lab Facility
### Preliminary Energy Efficiency Assessment  
First, besides the simplified geometrical description of the envelope details for the full-sized numerical model of the Live-Lab prototype, the required energy for heating and cooling the facility was calculated (see Figure 11).  
The expected cooling energy was found to reach the highest values from April to September, with Q\({}_{\text{C}}\) = 260-650 kWh. Similarly, the maximum energy required for heating was expected from November to February, with Q\({}_{\text{H}}\) = 300-460 kWh. The annual energy for heating and cooling was thus estimated as Q\({}_{\text{H,nd}}\) = 1906 kWh/year and Q\({}_{\text{c,nd}}\) = 3155 kWh/year, respectively, with a relatively higher cooling consumption. Significant energy losses, as expected, were observed to derive especially from the linear thermal bridges due to the different properties of the materials used, as well as from relevant geometrical variations (Figure 8).  
The energy estimates in Figure 11 refer to the floor area of the building prototype. The maximum requirements per year/square meter were found to be \(\approx\)128 kWh/m\({}^{2}\) year and \(\approx\)210 kWh/m\({}^{2}\) year for heating and cooling, respectively.  
The above estimates are related both to the geometrical aspects of the facility and to climatic conditions. Following Figure 10 and the data previously reported in Tables 1 and 2, the shape factor \(f_{0}\) of the building was also calculated using the most common index in professional practice. The latter is commonly defined as the ratio between the envelope surface (\(A\)) and the inner heated volume (\(V_{c}\)) of a given building, which for the Live-Lab mock-up facility is  
\[f_{0}=\frac{A}{V_{c}}=\frac{71.4m^{2}}{46.49m^{3}}=1.54~{}m^{-1}. \tag{2}\]  
Figure 11: Calculation of required heating and cooling energy (EnCert-HR).  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline  & & & & & & & & & & & \\ \cline{2-13}  & **Jan** & **Feb** & **Mar** & **Apr** & **May** & **Jun** & **Jul** & **Aug** & **Sep** & **Oct** & **Nov** & **Dec** \\ \hline Temperature (\({}^{\circ}\)C) & 1.0 & 2.9 & 7.1 & 11.7 & 16.8 & 20.3 & 21.9 & 21.3 & 16.3 & 11.4 & 6.5 & 1.4 \\ Relative humidity (\%) & 81.0 & 74.0 & 68.0 & 67.0 & 66.0 & 67.0 & 67.0 & 69.0 & 76.0 & 80.0 & 83.0 & 85.0 \\ \hline \end{tabular}
\end{table}
Table 3: Reference meteorological data for Zagreb city (average Live-Lab outdoor records).  
The research in [49; 50] notes that the above shape factor can affect the energy demands of a given building, especially one with wide glass surfaces and complex architectural geometries and irregular facades. The parametric study described in [49] for five building examples (Nordic climate conditions) with imposed \(f_{0}\) values in the range from 1 to 1.7, for example, resulted in up to +10%-20% energy demand variations for higher shape factors. Accordingly, this aspect should be further assessed in future developments of the Live-Lab facility. Given the value in Equation (2), additional relevant geometrical characteristics are represented by  
* Net volume \(V\)= 31.33 m\({}^{3}\);
* Gross floor area \(A_{floor}\)= 14.95 m\({}^{2}\).  
Thus resulting in a glass-to-floor-area ratio of \(\approx\)1.14.  
The examined 3D prototype is characterized by a compact regular shape/size that cannot represent a real building configuration but can still efficiently support research aimed at the optimization of the hybrid CLT-glass facade concept, working towards the definition of generalized design recommendations. A notable intrinsic feature of the CLT-glass design concept is the relatively large glass-to-floor-area ratio (with \(\approx\)0.2-0.25 as the conventional value; see [49]) for the facade elements directly exposed to external environmental events.