## 3 Results
### Definition of Corrective Strategies Based on Simulations
Figure 12 shows that an increase in the ventilation of the church during the day improves the overall performance of the church from the point of view of CO2 concentration, although it worsens the situation in terms of relative humidity. Opening the doors has hardly any effect on the interior temperature. However, CO2 concentrations are above the maximum required at times when a large influx of visitors is reached, so this measure would only be effective if combined with a restriction on occupancy. The opening of the doors makes it possible to reach the extreme higher values of relative humidity that occur in Valencia during the study period with percentages close to 100%. At the same time, CO2 concentrations close to 800 ppm appear, which, although lower than those reached with regular use, are still high. As an alternative to the daytime opening, a study of the influence of temperature and ventilation during the night was performed. During the study period, the outdoor night temperature drops, although not to the necessary limits, and at the same time, the relative humidity drops. As can be seen in Figure 13, greater nighttime ventilation generates a greater reduction in CO2 concentrations after a religious event with many people. At the same time, it allows for an improvement in the indoor temperature. However, the relative humidity, as with the door open during the day, is more similar to the outdoor conditions. In this case, the decrease in the concentration of CO2 occurs more quickly, although at times when there is a greater influx of visitors, the concentrations are still around 800 ppm. This means that the viability of this proposal is also reliant on a restriction in visitor numbers, like the previous one. Figure 11: Comparison of indoor temperature, indoor relative temperature, and CO2 concentration with capacity limited to 5% of the maximum. Figure 12: Comparison of indoor temperature, indoor relative temperature, and CO2 concentration providing ventilation during day activities. Since all simulations indicate that the building does not have enough openings for natural ventilation to lower the temperature, humidity, and CO2 concentration levels, a calculation was made using mechanical ventilation. An indoor CO2 concentration below 500 ppm could be achieved by means of a ventilation system that provides a flow rate of 0.5 renovations/h. To achieve this ventilation rate, it would be necessary to install two centrifugal fans with a power of 245 W that operate at 900 revolutions per minute. The renewed air must be distributed through a network of ducts so that the air enters gradually. The air inlet should have a section of 0.24 M2 that could be divided into four bars of 0.50 \(\times\) 0.25 m\({}^{2}\) assuming a passage coefficient of 0.5. The size of these fans is small, at 565 \(\times\) 521 \(\times\) 508 mm. However, the main issue of installing them comes from the impact of the needed wall perforations and the position of the air conducts over the protected walls. To achieve a CO2 concentration below 500 ppm, it would be necessary to have the fans working for 7180 h/year, which would use 2297 kWh. Considering the average price per kWh of electricity in Spain in 2023, which stands at 0.13 kWh without including taxes, this implies an annual energy cost of EUR 298 plus taxes. If it were considered necessary to reduce humidity and temperature, it would be necessary to install a dehumidifying and conditioning machine. This equipment of considerable size would need to operate 40% of the year, with a consumption of 29,784 kWh, generating a significantly higher cost of EUR 3871 plus taxes.