###### Abstract  
Decentralized ventilation systems in schools are becoming more important due to the focus on indoor air quality and energy economy. The research aims to explore how these technologies affect classroom air quality, thermal comfort, and noise. The study examined four decentralized ventilation systems in a real-world school using field measurements and data analysis. This included measuring the CO\({}_{2}\), temperature, noise, and thermal comfort using the Predicted Mean Vote (PMV) index. All systems greatly improved the air quality, keeping CO\({}_{2}\) levels within suggested limits. They failed to control indoor humidity, often lowering it to below optimal levels. Noise surpassed the 35 dB(A) criteria at maximum operation but was acceptable at lower airflows. Noise and air drafts did not bother residents. The study found that decentralized ventilation systems improve air quality and are easy to adapt to, although they need humidity control and noise management at higher operational levels. indoor air quality; decentralized ventilation; school environment +
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a comprehensive review to assist future researchers in developing a standardized rating system and measurement protocols for the consistent evaluation of indoor environmental quality (IEQ) in educational facilities. While the thermal comfort in schools has been investigated frequently by using the well-known PMV-PPD model proposed by [PERSON] in the early 80s, the indoor air quality in schools concept remains a challenge today, due to different influencing factors, such as the type of indoor pollutants to be investigated, the school location (in a rural or urban environment), the most appropriate ventilation system, or the local climate. [PERSON] et al. [7] investigated the indoor air quality factors and natural ventilation in 454 primary Slovenian schools, by means of extended surveys, performed for one winter month (February 2020). The authors outlined the importance of the school micro location, such as the proximity to main roads or other polluting sources (industrial areas), on the IAQ level in classrooms. Concerning the importance of the natural ventilation, it has been shown that the lack of outdoor filtration and the strong dependence of the ventilation airflow on the meteorological factors (wind speed and direction and outdoor temperatures) make this system unreliable, and a mechanical ventilation system should be mandatory. Regarding the indoor air pollutants in educational buildings, the majority of scientists assumed that some of them could be considered less harmful than others. While the carbon dioxide (CO\({}_{2}\)) is considered a marker of human presence and a maximal indoor average concentration of 1000 ppm could be considered a threshold for \"un-ventilated\" air [8; 9; 10], larger concentrations (around 2000 ppm), frequently seen in poorly ventilated spaces, including classrooms, lead to a decrease in the cognitive and academic performance of pupils, as shown in a recent study [11]. Apart from CO\({}_{2}\), there are many other indoor pollutants in schools that could be harmful at elevated concentrations and with long-term exposure, taking into account that pupils spend around 8 to 12 h in the indoor school environments. It has been shown that TVOC (Total Volatile Organic Compounds), a category of pollutants released indoors by building materials, furnishings, acrylic paints, permanent markers, and some cleaning products [12], have measured concentrations markedly elevated compared to those in the outdoor air and lead to severe adverse health effects among school children [13; 14; 15; 16]. A toxic influence on pupils' health is also present as PAHs (Polycyclic Aromatic Hydrocarbons), transported to the indoor school environments via ventilation airflow, when schools are in the proximity of heavy road traffic [17].