# Ventilation Strategies to Ensure Thermal Comfort for Users in School Buildings: A Critical Review
## 4 Discussion  
This article investigates different ventilation strategies in educational centers and their ability to simultaneously guarantee air quality and hygothermal comfort conditions. The 19 articles selected were used as the starting point for an analysis of the conditions monitored in different seasons and climates for each of the ventilation strategies considered. The protocols used in each study have been analyzed and a detailed study carried out for the measurements and conditions in place. The results obtained show the main parameters conditioning thermal comfort and air quality-temperature, humidity, and CO\({}_{2}\). Due to the volume of data obtained from the available literature, establishing an equivalent comparison in the different climatic zones is a difficult task. This is not only because of the lack of measurement data, but also because the differences in protocols (spot measurements versus continuous measurements, measurements only during occupied time versus measurements throughout the day) hamper comparison of the different results. Furthermore, hygothermal sensitivity levels vary in the different climatic zones. However, a trend can be identified between the different climates and ventilation strategies. Therefore, this study does not aim to establish an optimal protocol and ventilation conditions to ensure thermal comfort and air quality but to create a guide which can be used for the purposes of reference and comparison in any future studies. In addition to the results presented, this review reveals key trends and patterns that warrant further reflection. Natural ventilation is by far the most widely implemented strategy across all climates, likely due to its low cost and ease of implementation. However, the high dependence on user behavior--especially in strategies without predefined window opening schedules--makes it an unreliable solution for ensuring consistent indoor environmental quality. Mechanical ventilation, on the other hand, though less frequently studied, offers greater control but often lacks thermal treatment or heat recovery elements, which limits its effectiveness in colder climates. Hybrid ventilation strategies, although least represented in the literature, have shown promising results in achieving both acceptable CO\({}_{2}\) levels and thermal comfort, particularly when sensor-based control is involved. These findings suggest that automation and mixed-mode systems could be a direction for future development, especially in regions where outdoor conditions vary widely or where user behavior cannot be easily regulated. The results of the measured variables--temperature, humidity, and carbon dioxide--are shown in Tables 10 and 11, detailing average, maximum, and minimum values. Only winter and summer results are analyzed, as these are the most extreme seasons in terms of thermal comfort. As the tables show, not all studies measured all variables. In Table 10, summer results, temperature values of between 23 and 26 \({}^{\circ}\)C, humidity between 45% and 60%, and CO\({}_{2}\) levels below 800 ppm are highlighted in green following the comfort parameters of the UNE EN ISO 7730:2006 [56] standard and air quality parameters according to UNE EN 16798-1 [57]. In Table 11, winter results, temperature values of between 20 and 24 \({}^{\circ}\)C, humidity between 40% and 50%, and CO\({}_{2}\) levels below 800 ppm are highlighted in green. As observed in Table 12, there are few strategies that achieve optimal temperature and CO\({}_{2}\) values to ensure thermal comfort and air quality. It should be stressed that the lack of data collection in many studies complicates the analysis of the different strategies. There are three cases worth highlighting, as they achieve an average temperature of between 23 and 25 \({}^{\circ}\)C and average CO\({}_{2}\) values below 800 ppm. These three strategies were implemented in the same study by [PERSON] et al. [38].