## 5 Conclusions  
The research describes the principles, simulation, implementation, and monitoring of two different scenarios of natural cross ventilation applied to a school building affected by a subtropical climate. The findings are summarized in the following points:  
* Two different ventilation control algorithms, the SNVP and DNVP, were developed by the contribution of the software simulation to guarantee an acceptable IAQ, according to the most-accepted standards. * For this case study simulation, the SNVP provides a 2.16% WWeqR to maintain CO2 below 800 ppm for a typical winter day in a subtropical climate, with 2.6 m/s wind and a northeast direction, when the occupancy is twenty-one students. * The simulation of the DNVP anticipates that any WWeqR below 2.16% can maintain CO2 below 800 ppm if it increases the WWeqR to remove the unwanted CO2. * The simulations, run in _DesignbuilderTM_, obtain a different grade of validation for the SNVP. The results, with a steady 2.16% WWeqR, shown in Figure 9, are similar to the monitored results in Figure 12. However, the accuracy of the simulated DNVP is reduced because of a lack of accuracy in the opening management. The DNVP simulation describes double the WWeqR modifications compared to the DNVP monitoring. The implementation of manual proceedings applied by the building staff seem to be less effective than mechanical controls. This may be considered in future studies. * According to the results obtained in the monitoring process, the application of the SNVP maintains the CO2 concentration under 800 ppm during 100% of the operational time when the WWeqR was 2.16%, but failed during part of the study when the DNVP was applied. That suggests the need to implement better WWeqR controls to increase the efficiency of the protocols, as described in the simulation process. * The CO2 limits proposed by RITE, 500 ppm, were only achieved for 15.52% of the time with the maximum WWeqR applied, which demonstrates the inadequacy of the natural ventilation to fulfil the standard. * When the DNVP is used with a WWeqR below 2.16%, it can partially maintain CO2 under the required limits for those standards different to RITE. The analysis demonstrates compliance for 48.28% to 65.52% of the monitored time if the WWeqR is between 0.23 and 1.07, and a compliance for 48.28% to 74.14% of the monitored time if the WWeqR is between 1.07 and 1.82. * During the monitoring process, the TC was also monitored to demonstrate the adequacy of the natural ventilation protocols with the adaptive TC described in the UNE-EN 16798 [27], for category III with a \(\pm 4\)\({}^{\circ}\)C of adaptation. The application of the DNVP on a mild winter day achieved 100% TC during the full monitoring period. For schools in colder climatic zones, the TC could be compromised, if the rest of the conditions remain the same. However, passive-design principles could be used. * Future versions of these ventilation protocols may include temperature sensors to improve the WW\({}_{\text{eq}}\)R control. Therefore, it could lead to an increase in energy efficiency to become nearly zero-energy buildings by means of passive-design techniques. Conceptualization, methodology, software, validation, formal analysis, investigation, data curation, writing--original draft preparation, and visualization, A.S.C. ; supervision, project administration, writing--review and editing, S.G.M. and J.M.A.M. All authors have read and agreed to the published version of the manuscript. This work has been funded by the Research Center for Technology, Energy and Sustainability (CITES) at the University of Huelva (Spain). Not applicable. Data Availability Statement: Data are contained within the article. The authors declare no conflicts of interest. The Transient Mass Balance Equation. As briefly described in Section 2.3, the _DesignBuilderTM_ CO\({}_{2}\) prediction is based on the calculation provided by _EnergyPlusTM_ in the Engineering Reference, Section 2.5 [47].