Control of airborne particle concentrations in a meeting room with stand-alone air cleaners: influence of type, airflow rate, flow pattern and position in the room

The objective of this study is to assess the ability to mitigate the airborne particle concentration in a mechanically ventilated meeting room with stand-alone air cleaners (ACs) as function of the amount and type of devices, the total airflow rate, the location(s) of the device(s) in the room and their flow pattern. Six commercially available ACs, selected to be representative of the French market, are included in the study, each featuring distinct airflow patterns for both air inlet and outlet. The intrinsic performances of the ACs have been measured according to the French standard (NF B 44-200, 2016). Their filtration efficiencies are close to 100%, as expected with HEPA filter, the airflow rates targeted for this study, 80, 200 and 400 m³/h corresponding to respectively 1, 2.5 and 5 volume per hour (vol/h), are attained. Nevertheless, the airflow rate is 20 to 50% lower than values declared by the manufacturers. The sound power level as well as the operating power of the air cleaners have also been measured. 
Numerical 3D simulation (CFD) was used to assess 66 configurations of ACs in the room. The airflow pattern, the air velocity, the particle concentration as function of time and at different locations in the room at breathing zone were calculated. The cleaning efficiency represented by the particle concentration after 16 minutes AC operating divided by the initial concentration was determined. When the AC is placed in a corner behind a wall (a common placement), the performance is lower compared to other locations in the room. As the total airflow rate increases, the cleaning efficiency increases (C16/C0 decreases). The differences in particle concentrations across the room when an AC is used are weak at 5 vol/h but become larger at 2.5 vol/h. Airborne particle concentrations within the room are more homogeneous with the ceiling-type ACs. Also, most of the studied ACs have sound power levels exceeding 50 dB(A) above 200 m³/h, which can lead to noise nuisance for occupants. 9 of the 66 simulated configurations were also assessed through experimental measurements of airborne particle concentrations using low-cost particle sensors (0.3 to 5 µm range).