A comprehensive analysis of the intervention of a fresh air ventilation system on indoor air quality in classrooms

ABSTRACT

Adequate classroom air quality is vital to student health and learning outcomes. Prolonged periods of air conditioner use in enclosed classrooms may result in poor air quality. However, opening classroom windows may expose students to air pollutants if the outdoor air quality is poor. This study investigated CO2 and PM2.5 concentrations in 86 classrooms installed with air conditioners in elementary and middle schools in southern Taiwan, each additionally installed with a fresh air ventilation system equipped with an E11-class filter. Enclosed air-conditioned classrooms generally have a CO2 concentration greater than 2500 ppm;occasionally, this figure reaches 3500 ppm. With the installed air ventilation system operating, mean classroom CO2 concentration decreased to 1084 ± 203 ppm, and the median CO2 concentration decreased to 1120 ppm. However, the CO2 concentrations of over half the classrooms remained higher than the concentration advised by the World Health Organization (1000 ppm). This high CO2 concentration was a result of the short distance (1.5–2 m) between the indoor air outlet and the recirculated air inlet resulting in a shortened circuit of air travel. Also, the initial filter installed over the indoor air outlet of the system reduced air penetration into the classroom. When the ventilation system was manually activated without activating the air conditioners, the median PM2.5 concentration measured at the indoor air outlet and the median classroom PM2.5 concentration were 2 μg/m3 and 20 μg/m3, respectively. This implied the presence of other sources of PM2.5 in classrooms, particularly ceiling and wall-mounted fans. The activation of these fans spread dust onto classroom furniture. Overall, fresh air ventilation systems providing filtered air improve classroom ventilation efficiency and indoor air quality by reducing CO2 and PM2.5 concentrations, but the cleanliness of fans and furniture must be maintained.