## 3 Results and Discussion
### General Results of ACH and CO\({}_{2}\)
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{7}{c}{\(\Delta\)CO\({}_{2}\) Concentration (ppm)} \\ \hline
**Month** & **Sim\_02** & **Sim\_1** & **Sim\_2** & **Sim\_3.1** & **Sim\_3.2** & **Sim\_4** \\ \hline January & 36 & 0 & 36 & 31 & 34 & 65 \\ February & 37 & 0 & 37 & 32 & 34 & 66 \\ March & 45 & 0 & 38 & 38 & 41 & 81 \\ April & 54 & 0 & 37 & 44 & 49 & 97 \\ May & 53 & 0 & 33 & 39 & 47 & 96 \\ June & 57 & 0 & 47 & 46 & 51 & 103 \\ July & 51 & 0 & 51 & 41 & 47 & 96 \\ August & 49 & 0 & 49 & 38 & 45 & 89 \\ September & 62 & 0 & 56 & 50 & 56 & 112 \\ October & 77 & 0 & 54 & 64 & 72 & 139 \\ November & 52 & 0 & 36 & 45 & 49 & 93 \\ December & 39 & 0 & 31 & 34 & 36 & 70 \\ Average & 51 & 0 & 42 & 42 & 47 & 92 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Monthly average \(\Delta\)CO\({}_{2}\) concentration (ppm), by month. Figure 15: Average \(\Delta\)CO\({}_{2}\) (ppm) for each simulation by day. and Summer seasons, since the ventilation strategies are the same for Sim_02 and Sim_2, no significant variations were obtained, as can be seen in Figure 17 with the weekly average values of the CO\({}_{2}\) concentration. Figure 16: Average \(\Delta\)CO\({}_{2}\) (ppm) for each simulation by day type for all seasons. Figure 17: Comparison of the average hourly CO\({}_{2}\) concentration by day of the week between Sim_02 and Sim_2. Sim_3.1 shows an annual average decrease in the CO\({}_{2}\) concentration of 18% (Figure 18). The average Sunday peak of 144 ppm, immediately after the service, is relatively lower compared to the 205 ppm obtained for Sim_02. During the weekdays, when mass takes place, the difference in the CO\({}_{2}\) concentration between Sim_3.1 and Sim_02 is about 33 ppm, and at the moment when the church opens each day, a difference of 2 to 5 ppm was found. Sim_3.2 shows an annual average decrease in the CO\({}_{2}\) concentration of 8%. The average Sunday peak of 160 ppm, immediately after the service, is relatively lower compared to the 205 ppm for the same period in Sim_02. During the weekdays, when mass takes place, the CO\({}_{2}\) concentration difference between the two simulations is about 33 ppm, and no difference was found when the church doors were opened (Figure 19). Sim_4 showed an annual average increase in the CO\({}_{2}\) concentration of 80% (Figure 20). The Sunday average peak is 338 ppm, immediately after the mass service. During the weekdays, when mass takes place, the difference in the CO\({}_{2}\) concentration between the two simulations is about 135 ppm, and unlike the simulations previously examined, a difference was found at the moment the doors of the church are opened each day, i.e., the ventilation by infiltration during the closed hours is no longer able to remove as much used air. A difference of about 25 ppm was recorded just before the church doors opened on Wednesday, Thursday and Friday. On the remaining days of the week, Sunday, Monday and Saturday, there is a longer period before the doors open when no occupants are releasing CO\({}_{2}\). Figure 19: Comparison of the average hourly CO\({}_{2}\) concentration by day of the week between Sim_02 and Sim_3.2. Figure 20: Comparison of the average hourly CO\({}_{2}\) concentration by day of the week between Sim_02 and Sim_4. Table 7 shows the percentage difference of the monthly average CO\({}_{2}\) concentration compared to the current ventilation strategy of the Sao Cristovao church (Sim_02). An important conclusion is that there is no need to change the ventilation strategy. Sim_02, the current ventilation strategy, was found to be highly capable of maintaining low levels of the analysed pollutant. The increase in ventilation rates is associated with an increase in air velocity both around the occupants, reducing the thermal sensation of people inside, and around the artwork on display, potentially increasing the deposition of other pollutants and promoting abrasion.