## 3 Results and Discussion
### General Results of ACH and CO\({}_{2}\)
Figure 14 shows the hourly evolution of CO\({}_{2}\) for all simulated scenarios throughout the year. An analysis was conducted regarding the average hourly CO\({}_{2}\) concentrations in the church's naive by day of the week. This examination of the pollutant behaviour can, first, eliminate extreme events such as the spikes observed in some days of October and, second, give a visual aid in the comprehension of CO\({}_{2}\) extraction patterns. The values shown in Figure 15 are the hourly average for the entire year. The only simulation that shows a relevant difference is Sim_4, as the number of occupants is significantly larger compared to those in the other scenarios. Sunday peak values average 370 ppm above outdoor concentrations, corresponding to the IDA 2 category. All other simulations do not show a significant variation considering the 350 ppm threshold that separates IDA 1 from IDA 2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{4}{c}{**ACH Variation Compared to Sim_02**} \\ \hline
**Month** & **Sim\_1** & **Sim\_2** & **Sim\_3.1** & **Sim\_3.2** & **Sim\_4** \\ \hline January & \(-48\%\) & 0\% & 5\% & 3 & 0\% \\ February & \(-47\%\) & 0\% & 5\% & 3 & 0\% \\ March & \(-47\%\) & 18\% & 8\% & 3 & 0\% \\ April & \(-42\%\) & 53\% & 8\% & 3 & 0\% \\ May & \(-44\%\) & 70\% & 13\% & 4 & 0\% \\ June & \(-47\%\) & 26\% & 9\% & 4 & 0\% \\ July & \(-55\%\) & 0\% & 9\% & 3 & 0\% \\ August & \(-57\%\) & 0\% & 9\% & 3 & 0\% \\ September & \(-57\%\) & 22\% & 9\% & 3 & 0\% \\ October & \(-42\%\) & 55\% & 10\% & 4 & 0\% \\ November & \(-46\%\) & 44\% & 6\% & 3 & 0\% \\ December & \(-49\%\) & 24\% & 5\% & 2 & 0\% \\ Average & \(-48\%\) & 26\% & 8\% & 3 & 0\% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Ventilation rate comparison to the current ventilation performance, by month. Figure 14: Average daily \(\Delta\)CO\({}_{2}\) (ppm) by simulation. Figure 13: Average seasonal \(\Delta\)CO\({}_{2}\) (ppm) by simulation. As shown in Figure 15, the highest values are seen in Sim_4 for the larger number of occupants during the open hours. This increase compared to Sim_02 is responsible for the passage of the IDA category from 1 to 2. It is relevant to mention the good IAQ attributed to IDA classes 1, 2 and even 3. Although a more in-depth analysis will be made, the monthly average \(\Delta\)CO\({}_{2}\) concentration, displayed in Table 6, shows the higher values of Sim_4. Considering a seasonal analysis of the average hourly CO\({}_{2}\) by day type (see Figure 16), it is possible to evaluate the proximity of the results during the Wintertime for all simulations, excluding Sim_1 and Sim_4. Sim_1 has no occupants and, therefore, a constant \(\Delta\)CO\({}_{2}\) concentration. Therefore, no comparison or analysis is made. All other ventilation strategies show similar results in terms of this pollutant. The reason for this is the fact that mass service is the main source for CO\({}_{2}\) emissions, and after this period, when the church is closed, the building is ventilated by air infiltration. As the infiltration parameters of the spans, walls and roof are the same in all simulations, the infiltration rates are also the same. This means that CO\({}_{2}\) concentrations can only be controlled by ventilation rates attributed to the open-door period. Sim_3.1 presents the lowest CO\({}_{2}\) concentrations in the Winter and Summer seasons, with maximum average values of 139 for both seasons. These values occur during Sunday mass. During the Spring and Autumn seasons, Sim_2 presents the lowest results, as the seasonal opening of the bell towers causes an increase in ventilation rates during the open-door period. A comparison was made between Sim_02 and the other simulations in order to better understand the effects of increasing the ACH of the church on the CO\({}_{2}\) concentration. Sim_2 shows a reduction in the CO\({}_{2}\) concentration of 28% and 23% for the Spring and Autumn seasons, respectively, and a reduction of 18% for the whole year. For the Winter