## 3 Results
### Discussion  
In general, the results presented are consistent with the main observations other studies have made. In particular, the relevance of ventilation as a fundamental risk control strategy [38] is further highlighted. Considering that the airborne infection risk is larger indoors, particularly in poorly ventilated rooms, naturally ventilated buildings are a \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multicolumn{1}{c}{} & \multicolumn{6}{c}{**Reduction in \(R_{\mathbf{o}}\) with Dynamic Ventilation Rates**} \\ \hline \hline \(\mathbf{ACH_{low}\) [\(\mathbf{h^{-1}}\)]} & \multicolumn{3}{c}{**0.3 (7.63)**} & \multicolumn{3}{c}{**1 (4.32)**} & \\ \hline \hline \(\mathbf{ACH_{high}\) [\(\mathbf{h^{-1}}\)]} & \multicolumn{2}{c}{**6**} & \multicolumn{3}{c}{**10**} & \multicolumn{3}{c}{**6**} & \multicolumn{3}{c}{**10**} \\ \hline \hline \(\mathbf{t_{high}\) [\(\mathbf{min}\)]} & \multicolumn{2}{c}{**5**} & **10** & **5** & **10** & **5** & **10** & **5** & **10** \\ \hline \hline \(\mathbf{t_{low}\) [\(\mathbf{min}\)]} & \multicolumn{2}{c}{} & & & & & & & \\ \hline \(10\) & 68.5\% & 75.6\% & 77.5\% & 83.2\% & 51.6\% & 60.6\% & 64.2\% & 72.3\% \\  & (2.40) & (1.86) & (1.72) & (1.28) & (2.09) & (1.70) & (1.55) & (1.20) \\ \(15\) & 63.2\% & 71.5\% & 72.5\% & 79.6\% & 45.6\% & 55.3\% & 57.8\% & 67.1\% \\  & (2.80) & (2.18) & (2.10) & (1.56) & (2.35) & (1.93) & (1.82) & (1.42) \\ \(20\) & 59.1\% & 67.6\% & 68.3\% & 76.0\% & 41.0\% & 50.7\% & 52.5\% & 62.3\% \\  & (3.12) & (2.47) & (2.42) & (1.83) & (2.55) & (2.13) & (2.05) & (1.63) \\ \(25\) & 55.9\% & 64.2\% & 64.8\% & 72.5\% & 37.6\% & 46.6\% & 48.4\% & 57.6\% \\  & (3.36) & (2.73) & (2.69) & (2.10) & (2.70) & (2.31) & (2.23) & (1.83) \\ \(30\) & 52.7\% & 61.3\% & 60.9\% & 69.6\% & 34.1\% & 43.3\% & 43.7\% & 54.0\% \\  & (3.61) & (2.95) & (2.98) & (2.32) & (2.85) & (2.44) & (2.43) & (1.99) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Reduction of the basic reproduction number with periodical ventilation regimes. \(\mathbf{ACH_{low}}\) and \(\mathbf{ACH_{high}}\) are the basal and the high ventilation rates. \(t_{\mathrm{low}}\) and \(t_{\mathrm{high}}\) are the duration of each ventilation stage (alternating times with \(\mathbf{ACH_{low}}\) and \(\mathbf{ACH_{high}}\), respectively). The percentages of reduction are referred to the basal situation, with a constant \(\mathbf{ACH_{low}}\) ventilation rate. The basic reproduction number for the basal situation is indicated between parenthesis next to the basal ventilation rate value. The basic reproduction number for each situation is detailed below each percentage result. major concern. Given that schools are commonly naturally ventilated [39], they entail an interesting and complex case of study. There are two main aspects that need to be considered when analysing IAQ in a school classroom. On the one hand, the ventilation rates that the room can attain should be determined. These can be influenced by the ventilation configuration (i.e. which windows and doors are open) and by the environmental conditions. On the other hand, it is important to assess the impact that the ventilation rates can have on the airborne risk of infection and on thermal comfort. We have assessed the potential ventilation rates that the studied room can attain via the tracer gas method using CO\({}_{2}\), a popular strategy in the context of the COVID-19 pandemic. A large increase in the ventilation rate was observed when comparing unilateral and crossed ventilation schemes. This is consistent with the results presented in [40; 41], where a similar procedure was used. The tracer gas method was also used to estimate the ventilation rates during normal operation of the selected classroom for five months. This method has been recently used by several authors, see for instance [40; 41; 42; 43]. From the computed ventilation rates, it is concluded that the classroom can be well ventilated, which is consistent with the results of the control tests.