Impact of filter class and airflow control on the indoor airborne particles in a nursery school

This study focuses on the impact of filtration efficiency level and airflow control, based on CO2, on indoor air quality described by particle concentration in an urban low energy consumption nursery school during an autumn and a winter period. Measurements of indoor and outdoor particle concentrations have been carried out by using three different filter efficiency configurations in the school equipped with a balanced ventilation system with heat recovery. The tested filters are respectively classed G4, M5 and F7 according to NF EN 779 (2012). Some simulations were conducted to replicate the measurement configuration of the school equipped with G4+F7 filter configuration and to serve as a basis for the simulations with airflow control. The simulations were carried out using CONTAM multi-zone simulation tool. Measured particle concentration values have been used for the calculation of the filtration efficiency and the indoors to outdoors particle concentration ratio (I/O), the simulations boundary condition and simulations validations. The measurement results show that the efficiency on the finest particles (diameters lower than 1 μm) with G4 filter is very low, near zero, while with the G4+M5 and G4+F7 configurations the efficiency is slowly and considerably increased, at respectively about 20 to 50% and 82 to 90%, depending on the measurement day and particle diameters. For particles of diameter less than 1µm, the I/O ratio decreases as the filtration efficiency increases. But for larger particles, the I/O ratio is higher and increases when the particle size considered increases and is higher when children are present in the classrooms. 
The aim of the control of airflow based on CO2 levels is to optimize indoor air quality and energy consumption by automatically adjusting airflow according to real-time needs in the classrooms. This can help to maintain acceptable CO2 levels and reduce airborne particle concentrations, creating a healthier environment for kindergarten occupants. Simulations using CONTAM validated the model, showing that reducing airflow by 41% increased peak CO2 by 25% and 0.4/2.5 μm particles by 19-35%, while demand-controlled ventilation based on CO2 maintained CO2 levels below threshold with only a 5.7% airflow increase, reducing 2.5 μm particles by 12.4%. 
This research provides useful data for optimising indoor air quality in urban nursery schools using appropriate filters and intelligent control of airflow according to CO2 levels.