Environmental effects on indoor air quality and data-driven natural ventilation strategies for advanced energy management: Evidence from a classroom living-lab study

As renovated low-energy buildings become increasingly airtight, maintaining a balance between indoor air quality and energy performance represents a growing operational challenge, particularly in naturally ventilated educational spaces. This study examines how occupancy and outdoor environmental conditions influence indoor air quality (IAQ) and opportunities for data-driven natural ventilation within a classroom living-lab setting. Continuous measurements of PM10, PM2.5, CO2, temperature, and humidity were used to characterize pollutant dynamics during occupancy and nonoccupancy, with attention to seasonal infiltration and building-operation factors. Over the five-month campaign, CO2 levels exceeded 1,000 ppm only 0.8-2% of the time, while particulate matter exceedances reached 24-32% during the heating season and 9-13% outside the heating season, indicating limited need for mechanical ventilation under current local conditions. Long-term measurements revealed pronounced winter increases in particulate matter driven by outdoor infiltration. These findings underscore the importance of establishing a location-specific IAQ baseline for energy-efficient, concentration-based natural ventilation control. Integrating real-time CO2, PM10, and PM2.5 data enables adaptive window-opening strategies that maintain IAQ without unnecessary heating losses or energy demand, and also provides a foundation for future multidimensional, multiparameter, application-oriented ventilation strategies. The study supports more informed decisions on natural versus mechanical ventilation and contributes to advanced energy management and environmentally responsive building operation.