## 4 Discussion
### Indoor Environmental Quality
Figure 4 reveals that the building maintained relative humidity within the Category 1 range for over 91.6% of the monitored period (from November 2023 to September 2024) and fell within the Category 2 range for the remaining 8.3% (in October 2023). EN 15251 sets a CO\({}_{2}\) concentration limit of 800 parts per million (ppm) for Category 1 and 1200 ppm for Category 3. These limits are based on the idea that higher CO\({}_{2}\) levels can negatively impact occupants' comfort and potentially their cognitive performance. In this study, although the educational building lacked a mechanical ventilation system, the CO\({}_{2}\) levels measured in this building fell within the more stringent Category 1 limits (800 ppm) for 50% of the year, specifically from May to October. The relatively favorable IAQ observed during these months is likely attributable to the natural ventilation provided by opening windows. For 33% of the year (November to March), the CO\({}_{2}\) levels were within the less strict Category 3 limits (1200 ppm), indicating acceptable, though perhaps not optimal, ventilation. However, during April and May, the CO\({}_{2}\) concentrations exceeded even the Category 3 limit, as shown in Figure 5. This exceedance suggests inadequate ventilation during these two months, leading to a poorer IAQ and potential discomfort for the occupants. In terms of acoustic comfort, EN 15251 specifies recommended sound levels in the range of 30-40 dB. However, our measurements, as detailed in Table 2 and illustrated in Figure 5, reveal that this recommended threshold was consistently exceeded throughout the entire year. This persistent exceedance likely stems from a combination of factors. These include the building's proximity to an intensely circulated road, noise generated by occupants (conversations, movement, and the use of personal laptops), and, maybe the most significant, ongoing rehabilitation work near the building during the measurement period. The illuminance requirements for classrooms, according to EN 12464-1, are 500 lx. EN 15,251 further specifies daylight factor criteria for lighting comfort: >5% on average for Category 1 and >2% for Category 3. Our findings (Figure 4) showed that the 500 lx target was not achieved in any month. Despite the classrooms having large windows (three 2.10 m \(\times\) 2.50 m windows each), students frequently used the window blinds to block direct sunlight, resulting in lighting conditions that, based on EN 15251's criteria for adjustable shading devices, aligned with Category 3 comfort. The field investigation carried out in Romania by [PERSON] et al. [34] focused on measuring environmental parameters like CO2, noise levels, and thermal comfort. Their results were similar to ours, indicating variations in CO2 levels throughout the day and average temperatures around 23 \({}^{\circ}\)C. It was observed there, as well as in this research, that the sound levels exceeded the established threshold limits. Yet another study performed in Romania [33] revealed concerning results during winter. These findings indicated that the CO2 levels often exceeded the recommended threshold, reaching as high as 3.600 ppm, while indoor temperatures typically failed to achieve the minimum comfort level of 19 \({}^{\circ}\)C.  
The monitored educational building generally met the thermal comfort criteria during the heating season, suggesting effective temperature regulation mechanisms. However, a comprehensive analysis of the full academic year revealed significant seasonal variations in the IEQ parameters, highlighting several areas for improvement. During the summer months, elevated temperatures were consistently observed, likely due to increased solar radiation and insufficient passive or active cooling strategies. The building's orientation and glazing characteristics may have contributed to solar heat gain [57]. Fluctuating CO2 concentrations, which intermittently exceeded the recommended limits, were primarily associated with periods of high occupancy and inadequate ventilation.