## 6 Results and Analysis
Nevertheless, the system's capacity to reliably control the concentration of CO2 highlights its efficacy. The findings of System 2 demonstrated even more noteworthy outcomes, as it successfully maintained carbon dioxide (CO2) levels below 1000 parts per million (ppm) for 99% of the duration of occupancy. This outcome serves as a strong indicator of the system's exceptional control of air quality. The temperature within the enclosed space reached a maximum of 26 \({}^{\circ}\)C, a value that falls within the allowed range for creating appropriate educational settings. The third system, despite maintaining air quality levels below 1000 ppm for 65% of the time, did not employ its boost mode. The utilization of this function during periods of rest has the potential to significantly improve its effectiveness of removing pollutants. Significantly, this classroom, characterized by the presence of two external walls, showed a lower maximum temperature of 25.2 \({}^{\circ}\)C in contrast to the preceding two systems. System 4 consistently demonstrated exceptional air quality, as seen by its ability to consistently control carbon dioxide (CO2) levels below 1000 parts per million (ppm) during its operation. The classroom, experiencing reduced solar heat gain, had a temperature of 25.3 \({}^{\circ}\)C, which is beneficial for creating a comfortable learning environment. In general, it can be observed that all four systems demonstrated satisfactory performance by successfully delivering fresh air and ensuring the maintenance of suitable indoor conditions. The notable disparity in air quality and temperature regulation between the ventilated and non-ventilated classroom serves to emphasize the effectiveness of these systems and emphasizes the pressing necessity for their implementation in educational settings. The present investigation not only showcases the efficacy of these systems in upholding ideal learning settings but also provides significant data to the domain of indoor environmental quality in educational structures. The analysis of carbon dioxide (CO2) concentrations in different ventilation systems, in comparison to a situation without any ventilation, provides valuable findings regarding their efficacy in controlling indoor air quality (see Figure 8). Without adequate ventilation, carbon dioxide (CO2) levels experience substantial variations, ranging from a minimum of 440 parts per million (ppm) during nighttime to a maximum of 7036 ppm. Consequently, the average CO2 concentration calculated only for the occupation period (8:00-18:00) in this situation amounts to 1296 ppm. System 1 demonstrates a notable enhancement with a more favorable concentration of 697 ppm (46% reduction compared to with no ventilation). System 2 demonstrates superior performance compared to the other systems, as it effectively achieves a harmonious equilibrium between the lowest maximum concentration of 1495 ppm and an appropriate average concentration of 636 ppm (50.9% reduction compared to with no ventilation). Moreover, System 2 constantly maintains outstanding air quality throughout its operation. System 3, however, is less efficient than System 2 and demonstrates a notable reduction in the maximum concentration of CO2 to 2072 ppm and maintains an average level of 753 ppm (41.8% reduction compared to with no ventilation). Finally, System 4 demonstrates strong performance by maintaining a maximum carbon dioxide (CO2) level of 3234 parts per million (ppm) (the system shut down at that moment) and an average level of 673 ppm, thereby preserving favorable air quality for a significant duration. In general, it can be observed that each ventilation system exhibits a notable improvement in air quality when compared to that with the absence of ventilation. Figure 8: Long-term analysis of CO\({}_{2}\) levels for the heat recovery ventilation units (11 March 2023 to 11 April 2023).