## 3 Results and Discussion
### General Results of ACH and CO\({}_{2}\)  
The first and last simulations, Sim_02 and Sim_4, have the same span opening/closing schedule, and the ACH values are also the same (Figure 10). What differs is the CO\({}_{2}\) concentrations, as the number of occupants are different for the two simulations. Sim_1, which represents the closed status for the entire year, will not be referenced as much as the other simulation because it is a hypothetical scenario in which some standards do not apply, as there are no occupants. This simulation can provide an important basis for future work studying the effects of the COVID-19 pandemic and its impact on the artwork housed in the Sao Cristovao church. Sim_2, which represents the highest peaks in ventilation rates due to the opening of the bell towers in Spring and Autumn, is the strategy with the highest seasonal average ACH. The average ACH for Summer and Winter are the same as in Sim_02. In comparison with the current ventilation behaviour, an increase of 28% in ACH is achieved when strategy Sim_2 is in place. Sim_3.1 and Sim_3.2, the two cross-ventilation strategies implemented in CONTAM, show good results. Sim_3.1, having the second-greatest ACH average of all the simulations, ensures an acceptable IAQ by all standards. On a monthly average, Sim_3.1 has a 5% increase in ventilation capacity compared to Sim_3.1. The seasonal average ACH is displayed in Figure 11.  
Figure 11: Average seasonal ACH for each simulation. Figure 10: Average daily ACH for each simulation. During Winter and Summer, Sim_02, Sim_3.1 and Sim_4 have the same ventilation characteristics and, therefore, ACH values. Sim_2 has the largest amount of fresh air entering the church during the Spring and Autumn, compared to the other simulations. Sim_3.2 shows the ventilation capabilities of the church if the correct pathways are available for the air to move through. If the two small windows are open in a small room, during the mass time, very similar results are achieved compared to those in Sim_3.1, where windows and doors on opposite sides of the church need to remain open for the duration of the mass service. A monthly analysis of the results, as shown in Figure 12, can display the far superior ventilation capability of the Sim_2 strategy and the small variations between Sim_02 and the remaining simulations, apart from Sim_1. An interesting and relevant comparison is the one where all simulations are studied against the current ventilation strategy of the church. For this purpose, Table 5 is presented. Sim_1 shows circa \(-48\%\) of the fresh air circulation in the church. Sim_2, although only applicable during a limited period of the year, shows a significant increase in ACH values. With this strategy implemented, new studies should be made regarding the air velocity and trajectory near the artworks displayed inside the church in a conservation effort, which is not the aim of this study. Although both Sim_3.1 and Sim_3.2 also increase the ventilation rates throughout the year, the first has a more significant effect, as the direction of the wind tends to follow a north-south trajectory, and the windows opened are also larger. Sim_4, which has the same ventilation performance as Sim_02, is compared hereafter in terms of the CO2 concentration analysis. Seasonally, the CO2 indoor/outdoor deferential was examined. During Winter, all simulations showed the highest ACH values leading to low CO2 concentrations, apart from Sim_2, where the lowest concentration was found in the Spring, as shown in Figure 13. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Church Open/Closed Period** & **Sim_02** & **Sim_1** & **Sim_2** & **Sim_3.1** & **Sim_3.2** & **Sim_4** \\ \hline Open doors & 0.75 & - & 1.04 & 0.85 & 0.79 & 0.75 \\ Closed doors & 0.15 & 0.15 & 0.15 & 0.15 & 0.15 & 0.15 \\ All year & 0.30 & 0.15 & 0.37 & 0.32 & 0.31 & 0.30 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Average ACH value by church status, for each simulation. Figure 12: Average monthly ACH for each simulation.