## 6 Results and Analysis
The investigation of the researched ventilation systems, which lack integrated humidity management, uncovers notable difficulty in upholding ideal indoor humidity levels, particularly in winter when the exterior air is cold and dry. The introduction of outside air into classrooms through these systems may result in a notable decrease in interior humidity levels, which could potentially give rise to perceptions of discomfort and health-related concerns. The phenomenon is particularly accentuated when airflows are increased, as ventilation systems have the potential to severely dry the indoor air. The data obtained from the systems highlight this particular risk (see Figure 9). System 1 shows an average humidity level of 30.87%, which is closely trailed by System 3 at 30.76% and System 2 at 30.43%. The observed results exhibit a proximity to the lower threshold of permissible indoor humidity, suggesting a modest yet constant decrease in moisture levels. System 4 exhibits a little improvement, as it consistently sustains an average humidity level of 33.45%. Although this value is closer to the target range, it still resides towards the lower end. On the other hand, the room without ventilation has a comparatively elevated average humidity level of 35.04%. This can be attributed to the absence of external air circulation and the inherent moisture produced within the space. Figure 9: Long-term analysis of humidity levels for the heat recovery ventilation units (11 March 2023 to 11 April 2023). The analysis of the ventilated and non-ventilated scenarios indicates that ventilation plays a vital role in maintaining the air quality. However, it is important to note that the implementation of ventilation systems can mistakenly result in decreased humidity levels. The concern is notably apparent in systems lacking the means for controlling humidity levels. To address this issue, the implementation of humidifiers in conjunction with ventilation systems could be a feasible approach, aiding in the maintenance of a balanced and pleasant interior environment. The data unequivocally demonstrate that although ventilation systems are efficient for controlling air quality, they do require supplementary measures, such as humidification, to guarantee comprehensive indoor environmental quality. The Predicted Mean Vote (PMV) index is a widely recognized method for calculating thermal comfort in indoor environments. Developed by [PERSON] in the 1970s, the PMV model estimates the average thermal sensation of a large group of people. It is based on the heat balance of the human body and incorporates six key factors: air temperature, mean radiant temperature, air velocity, humidity, clothing insulation, and metabolic rate. The PMV index serves to forecast the mean rating of a large number of people on a seven-point scale measuring the thermal feeling, which spans from \(-3\) (indicating chilly) to \(+3\) (indicating hot), while a rating of \(0\) signifies a state of neutral thermal comfort. The inclusion of this scale in the PMV model is crucial as it allows for the measurement of the subjective aspect of thermal comfort, recognizing that different individuals may have varying responses to identical environmental conditions. In our study, assessing the thermal comfort in classrooms equipped with different ventilation systems, we employed the Testo 400 IAQ and Comfort Kit to measure the Predicted Mean Vote (PMV) index. The evaluation of thermal comfort using the Predicted Mean Vote (PMV) index for the four different ventilation systems provides valuable insights regarding their efficacy in sustaining a pleasant indoor environment. System 1 showed a PMV satisfaction percentage of 79.6%, whereas the PMV values ranged from \(-0.5\) to \(+0.5\). This finding suggests that a significant proportion of individuals reported a thermal sensation that was close to neutral, a state that is generally regarded as comfortable in the context of indoor environments (see Figure 10).