## 2 Materials and Methods
### CFD Model Setup
#### 2.5.1 Mesh Sensitivity  
The domain was discretized using an orthogonal grid, as depicted in Figure 5, which also shows the sensor locations. Given the relatively simple geometry, a block-based tetrahedral mesh was employed to improve the overall mesh quality. The grid was refined near the solid surfaces (building walls) and at the inlet and outlet, with the spacing between grid lines gradually increasing as they moved away from these surfaces. All inflation ratios of the mesh were maintained at 1.15. A mesh sensitivity analysis was conducted to assess the independence of the numerical solution from the mesh size, utilizing coarse, medium, and fine grids with 0.2, 0.8, and 2.2 million cells, respectively. The temperature recorded by one of the experimental measurement sensors (sensor number 66) was selected as the control parameter for this analysis.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Outdoor**} & \multicolumn{3}{c}{**Centre of the Room**} & \multicolumn{3}{c}{**South-East Wall**} & \multicolumn{3}{c}{**North-West Wall**} \\ \cline{2-11}  & **Max.** & **Avg.** & **Min.** & **Max.** & **Avg.** & **Min.** & **Max.** & **Avg.** & **Min.** & **Max.** & **Avg.** & **Min.** \\ \hline Temp. [\({}^{\circ}\)C] & 39 & 27.7 & 16.2 & 32.4 & 28.4 & 23.9 & 32.1 & 28.7 & 24.1 & 34.3 & 28.6 & 23.8 \\ \hline \multirow{2}{*}{Date} & 31/7/20 & \multirow{2}{*}{-} & 1/9/20 & 31.7/20 & \multirow{2}{*}{-} & 1/9/20 & 31/7/20 & \multirow{2}{*}{-} & 1/9/20 & 25/7/20 & \multirow{2}{*}{-} & 1/9/20 \\  & 15:45 & & 06:45 & 12:35 & & 8.35 & 12:35 & & 8.35 & 10:35 & & 9.05 \\ \hline Humidity [\%gkl] & 91 & 58.4 & 25 & 70.4 & 58.9 & 44.8 & 71.6 & 61.2 & 48.1 & 71.9 & 59.6 & 43.6 \\ \hline \multirow{2}{*}{Date} & 9/8/20 & \multirow{2}{*}{-} & 9/8/20 & \multirow{2}{*}{-} & 9/8/20 & \multirow{2}{*}{-} & 2/8/20 & \multirow{2}{*}{15/8/20} & \multirow{2}{*}{-} & 26/7/20 & 29/7/20 & \multirow{2}{*}{-} & 16/7/20 \\  & 15:00 & & 13/8/20 & & 3.35 & & 15:05 & 6:05 & & 18:35 & 2:34 & & 10:34 \\ \hline Dew point [\({}^{\circ}\)C] & 24.4 & 18.2 & 10.7 & 23.9 & 19.5 & 14.9 & 24.5 & 20.4 & 16.1 & 24.5 & 19.9 & 15.2 \\ \hline \multirow{2}{*}{Date} & 31/7/20 & \multirow{2}{*}{-} & 5/8/20 & \multirow{2}{*}{-} & 5/8/20 & \multirow{2}{*}{-} & 26/7/20 & \multirow{2}{*}{2/8/20} & \multirow{2}{*}{-} & 26/7/20 & 3/8/20 & \multirow{2}{*}{-} & 5/8/20 \\  & 23:00 & & 14:45 & 22:05 & & 5:33 & 21:35 & & 6:35 & 00:05 & & 00:05 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Outdoor and indoor environmental conditions during the period from 24 July 2020 to 15 September 2020.  
GCI can be expressed as follows [27]:  
* Equation (1) provides the value of the convergence order \(p\): \[p=\frac{\frac{ln\left[\varphi_{average}-\varphi_{center}\right]}{\varphi_{ line}-\varphi_{average}}}{ln(r)}\] (1) where \(\varphi_{center}\), \(\varphi_{average}\), and \(\varphi_{fine}\) are, respectively, the average temperatures for the course, medium, and fine meshes.
* The mesh refinement ratio \"\(r\)\" can be calculated as shown in Equation (2) [28]. \[r=\left(\frac{N_{fine}}{N_{medium}}\right)^{1/D}\] (2) where \(N\) is the number of cells and \(D\) is the size of a single cell.
* \(GCI\) is calculated using Equations (3) and (4): \[GCI=\frac{\epsilon}{r^{p}-1}\] (3) \[\epsilon=\left|\frac{\varphi_{fine}-\varphi_{medium}}{\varphi_{fine}}\right|\] (4)  
\begin{table}
\begin{tabular}{c c c c} \hline  & **Mesh A** & **Mesh B** & **Mesh C** \\ \hline
**Number of cells [-]** & \(\sim\)800,000 & \(\sim\)200,000 & \(\sim\)2,200,000 \\
**Cell spacing [m]** & 0.1 & 0.2 & 0.05 \\ \(\Delta\%\) temperature [-] & 3.15 & 15.72 & - \\
**GCI [\%]** & 0.1 & - & 0.05 \\ \hline \end{tabular}
\end{table}
Table 4: Mesh sensitivity test.  
Figure 5: Domain mesh and sensor locations.  
As shown in Table 4, all _CGI_ values are below 1%, which confirms that the numerical results are independent of the grid [28].