# Ventilation Strategies to Ensure Thermal Comfort for Users in School Buildings: A Critical Review
## 5 Conclusions  
This study has presented a critical review which analyzed the ventilation strategies most commonly used in schools to both guarantee indoor air quality and ensure the thermal comfort of students. After an initial selection of 277 articles and a final selection of 19, a total of nine strategies were identified in five different climates according to [PERSON]'s classification, grouped by natural, mechanical, or hybrid ventilation. This highlighted the low number of studies which focus on ensuring both thermal comfort and air quality in schools. It is also important to highlight the geographical concentration of the analyzed studies, with most of them being located in Europe. Most of the 80 studies analyzed initially address only one of these aspects, neglecting the other, particularly thermal comfort. Most studies focus on ensuring air quality even when this means sacrificing thermal comfort. This trend has been particularly pronounced since the COVID-19 pandemic, when the focus of studies shifted to air quality in order to prevent airborne disease transmission, irrespective of the thermal comfort of the occupants. Therefore, a clear lack of studies has been identified in this area. Within natural ventilation, the most employed strategies in studies considering air quality and thermal comfort are: user-dependent natural ventilation (with permanently open windows or with irregular window opening patterns); user-dependent natural ventilation according to established window opening patterns; user-independent natural ventilation with parameter control through sensors (CO\({}_{2}\) or temperature sensors); and user-independent natural ventilation using a windcatcher and stack ventilation. Mechanical ventilation strategies can be summarized as ventilation with constant airflow or ventilation with variable airflow, with the latter based on CO\({}_{2}\) or temperature measurements. There are no additional categories of mixed ventilation strategies. Natural ventilation strategies are the most used in all climates: 73% in the continental climate, 68% in the Mediterranean climate, 66% in the oceanic climate, 100% in the semi-arid climate, and 63% in the tropical climate. However, only in 17% of the cases analyzed in the selected works are optimal average temperature and air quality conditions achieved with these strategies in summer. None are achieved in winter, highlighting a clear need for the implementation of hybrid or mixed systems in school spaces. Regarding the analysis of results obtained with the different strategies, it must first be noted that the lack of data prevents us from determining whether some strategies are better than others for the simultaneous promotion of thermal comfort and air quality. After a comparison of the strategies that have sufficient data on temperature and CO\({}_{2}\), it is concluded that there are almost no studies where both comfort conditions and CO\({}_{2}\) values are ensured simultaneously; in most cases, one of the two variables is compromised. Only two studies, one in summer and one in winter, have been found to show suitable values for both parameters. It is also worth noting a greater wealth of data in winter, which may seem surprising, as some schools are heated by radiators but rarely have cooling. Therefore, summer could be more critical due to the high temperatures in some of the countries studied, including Spain, Italy, and Portugal. However, in the rest of European countries, winter is the most critical season, as they have milder summers. These issues warrant further investigation in future studies, as they represent a relevant area of interest with direct implications for indoor air quality (IAQ) and thermal comfort (TC). Therefore, it is essential to conduct new studies testing different ventilation strategies in educational buildings to simultaneously ensure thermal comfort and air quality. This review serves as a guide to the protocols used in the various studies analyzed. **Author Contributions:** Conceptualization, R.S.