## 3 Results and Discussion
### Thermal Comfort and Indoor Air Quality Analysis  
The measured data were analysed in terms of thermal comfort according to two of the main standards used by the scientific community, as set out in Section 2.2: the steady-state standard EN ISO 7730 [31] (Figure 5a) and adaptive ASHRAE Standard 55 [34] (Figure 5b). Both models evaluate whether the temperatures measured inside the classrooms stabilise within the comfort range or can be classed as overheating or undercooling situations.  
With both standards, the poorest results are observed in case 2 (located in southern Spain), primarily due to a high-intensity use of natural ventilation through windows during hours with low outdoor temperatures, and a low-intensity use of heating. Specifically, according to the steady-state standard, the percentage of undercooling hours in case 2 ranges from 50 to 60%, reflecting an overestimation in relation to the adaptive standard, where it is significantly lower (between 30 and 35%). In southern Spain, comfort issues stem exclusively from temperatures below the comfort band as, thanks to natural ventilation, there are no overheating issues during peak temperature or occupation hours. However, overheating issues do arise in classroom 4.2 in northern Italy (approximately 10% of overheating hours) as a result of more intense heating usage and inadequate dissipation of internal loads due to insufficient ventilation towards late morning.  
Secondly, IAQ was analysed using measured CO\({}_{2}\) levels in classrooms, as defined in Section 2.3. The results are presented in Figure 6, where blue indicates the percentage of hours with optimal air quality (CO\({}_{2}\)\(<\) 750 ppm); yellow indicates good air quality (750 ppm \(<\) CO\({}_{2}\)\(<\) 1200 ppm); and red indicates poor air quality (CO\({}_{2}\)\(>\) 1200 ppm). In southern Spain, air quality was optimal for more than 80% of the hours, while poor air quality occurred in less than 2% of the hours in two classrooms. By contrast, in northern Italy, in case 3, air quality was optimal for only 5-25% of the hours, with classroom 3.2 showing around 5%  
Figure 5: Thermal comfort analysis according to (**a**) EN ISO 7730 and (**b**) ASHRAE Standard 55.  
of hours with poor air quality. In case 4, although air quality was slightly worse than in southern Spain according to the results, optimal air quality values ranged from 50 to 70% of the hours.  
According to the analysis of thermal comfort and IAQ, the best balance between both environmental conditions, with very good comfort conditions (combining moderate ventilation with heating usage) and very acceptable IAQ conditions, was found in classroom 4.1. In the case studies in southern Spain, there may be overventilation early in the morning, as maintaining good air quality instead of optimal air quality could potentially improve thermal comfort conditions.  
In comparison with other similar studies, the results obtained in this work are slightly better, since both [PERSON] et al. [17] and [PERSON] et al. [18] found, in northern and southern Spain, respectively, unacceptable IAQ for approximately 30% of the occupied hours. In addition, poor thermal comfort was detected in up to 47% of the hours. However, it should be noted that both studies referenced above cover longer measurement periods, including summer months, with more unfavourable external conditions. In the case of [PERSON] et al. [26], focused on mild periods, poor air quality was found between 3 and 30% of the occupied hours, depending on the school.