# Ventilation Strategies to Ensure Thermal Comfort for Users in School Buildings: A Critical Review
## 3 Results
This means that mechanical ventilation has its own intake and mechanical extraction, with a controlled airflow and number of renewals, while, in parallel, the windows are opened, either manually by the users or mechanically. This ventilation is also referred to in some of the studies as mixed or mixed-mode. Figure 4: Distribution of the articles analyzed according to year of publication. Figure 5: Classification of articles according to the country in which the study was conducted. \begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt}} \hline \hline
1. & User-dependent natural ventilation: operation relies entirely on occupant behavior; users decide when to manually open or close windows, without a specific pattern. \\ V: No need for automation systems or technical maintenance. \\ D: High uncertainty in performance; can be ineffective during extreme weather or when users misjudge the need for ventilation. \\ \hline
1.a. With permanently open windows: windows remain open continuously, regardless of outdoor conditions or occupancy levels. \\ \hline
1.b. With irregular window opening patterns: windows are opened sporadically, based on the user’s perception (e.g., feeling warm or detecting odors). \\ \hline
2. & User-dependent natural ventilation according to established window opening patterns: users follow predefined window opening schedules or rules, based on time of day. \\ V: Greater predictability and potentially improved performance if users are educated. \\ D: Still relies on consistent user behavior; may not respond in real time to changing conditions. \\ \hline
3. & User-independent natural ventilation with parameter control through sensors: ventilation is automatically triggered based on indoor environmental parameters. \\ V: Reliable performance; responsive to real-time indoor air quality; reduces reliance on occupant behavior. \\ D: Requires sensor calibration and maintenance; may have higher initial installation costs. \\ \hline
3.a. CO\({}_{2}\) sensors: ventilation activates when indoor CO\({}_{2}\) levels exceed a threshold, indicating occupancy and air quality deterioration. \\ \hline
3.b. Temperature sensors: ventilation responds to indoor temperature levels to maintain thermal comfort. \\ \hline
4. & User-independent natural ventilation based on wind and thermal gradient: utilizes natural forces such as wind pressure and stack effect to drive airflow through building openings or passive devices. \\ V: Energy-free operation; can be highly effective if well-designed. \\ D: Highly climate-dependent; performance varies with external conditions; complex to design for year-round effectiveness. \\ \hline
4.a. Windcatcher: architectural elements (typically towers) capture wind and channel it into indoor spaces, facilitating cross or downward airflow. \\ \hline
4.b. Stack ventilation: warm indoor air rises and exits through high-level openings, drawing in cooler outside air through lower openings. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Classification of different ventilation strategies. Additionally, as shown in Table 5, the various existing climates have been grouped into five categories: tropical, semi-arid, oceanic, Mediterranean, and continental. Figure 6 presents a list of the types of strategies used according to the climate, referencing the five groups previously shown in Table 5. As shown in Figure 6, natural ventilation is one of the ventilation strategies most widely used in schools, accounting for more than 50% of the total strategies used in all cases, irrespective of climate. In some cases, such as the semi-arid climate, this figure can even reach 100%. An analysis of natural