The aim of this master’s thesis was to perform an integrated analysis of Indoor Air Quality (IAQ) and Thermal Comfort (TC) in two primary school classrooms: one with natural ventilation (U-NP) and the second with hybrid ventilation (U-HP). The study is based on continuous measurements of CO₂ concentration, air temperature, surface temperatures, and relative humidity in the period from May 30, 2025, to January 31, 2026. It was complemented by measurements of radon and PM2,5 concentrations, as well as calculations of Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) indices. The results were analysed separately for the non-heating and heating seasons. In the U-NP classroom, CO₂ concentrations were strongly dependent on occupancy and users’ ventilation habits. During two periods of the non-heating season, average values during class time reached 815 ± 266 ppm (May–June) and 1235 ± 1073 ppm (September–October), with peak values exceeding 5000 ppm. During the heating season, average values reached 1044 ± 499 ppm, with frequent exceedances of the Category III limit according to SIST EN 16798-1:2019. Time profiles show a rapid increase in CO₂ concentration after the beginning of classes, typically peaking towards the end of lessons. In the U-HP classroom, CO₂ concentration was lower and more stable during the non-heating season (774 ± 143 ppm, 685 ± 119 ppm), while in the heating season it increased (936 ± 411 ppm), with occasional exceedances of higher IAQ categories. Thermal comfort in U-HP was 70 % of the time in Category I, whereas U-NP achieved this level only 40 % of the time and fell into lower categories for the remaining 60 %. Radon concentration during class time was generally low (U-NP: up to 180 Bq/m³; U-HP: up to 343 Bq/m³), although values in U-HP may exceed the reference level. The highest concentration occurred before the start of ventilation and during unoccupied periods (weekends, holidays), particularly in U-HP. The results confirm that hybrid ventilation enables more stable indoor conditions when the ventilation system is properly designed and operated, while natural ventilation is highly dependent on user behaviour and external conditions. The findings provide a basis for optimising ventilation strategies in terms of timing and airflow rates to ensure adequate IAQ and thermal comfort simultaneously.
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