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Mobile air cleaners (MACs) have been proposed as a supplementary solution to combat the spread of respiratory aerosols in school classrooms. To determine which, where and how to use MACs, seven small- and medium-sized MACs were selected and assessed for different settings and configurations by 1) a decay test for determining the clean air delivery rate (CADR), and 2) a perception test with a panel of subjects, together with physical measurements, of noise and air movement. The findings show that to achieve the desired CADR (appr. 1000 m3/h for 30 students per classroom), the key factors are the induced airflow pattern and the location of the MACs. MACs with an upward air supply toward the occupied zone showed much higher CADR (max. 775–1332 m3/h) than those with a horizontal air supply (max. 219–333 m3/h). Moreover, using multiple devices simultaneously was crucial when the room size was increased, and combining mechanical ventilation could improve aerosol removal. Achieving a sufficient CADR would always lead to a noise level above the limit of 35 dB(A), yet sometimes the rating of the panel was more than 50% acceptable. The air velocities mostly fulfilled the requirement (<0.2 m/s), which aligned with the positive panel assessment. Hence, the evaluation by a panel of subjects can help to optimize the use of MACs in a classroom.
Mobile air cleaners (MACs) have been proposed as a supplementary solution to combat the spread of respiratory aerosols in school classrooms. To determine which, where and how to use MACs, seven small- and medium-sized MACs were selected and assessed for different settings and configurations by 1) a decay test for determining the clean air delivery rate (CADR), and 2) a perception test with a panel of subjects, together with physical measurements, of noise and air movement. The findings show that to achieve the desired CADR (appr. 1000 m3/h for 30 students per classroom), the key factors are the induced airflow pattern and the location of the MACs. MACs with an upward air supply toward the occupied zone showed much higher CADR (max. 775–1332 m3/h) than those with a horizontal air supply (max. 219–333 m3/h). Moreover, using multiple devices simultaneously was crucial when the room size was increased, and combining mechanical ventilation could improve aerosol removal. Achieving a sufficient CADR would always lead to a noise level above the limit of 35 dB(A), yet sometimes the rating of the panel was more than 50% acceptable. The air velocities mostly fulfilled the requirement (<0.2 m/s), which aligned with the positive panel assessment. Hence, the evaluation by a panel of subjects can help to optimize the use of MACs in a classroom.
The connection form of pipelines has an important impact on the comprehensive performance evaluation of fresh air systems. The most used PVC fresh air pipeline material in the market was selected for experimental research in this paper, and the deposition rates of particles of different pipeline connection form of 45?, 90? bend, and straight tee were all tested and compared. The purification effect of the pipeline connection form of the highest deposition rate is tested and studied. The results showed that the particle deposition rates were the highest in the connection form of straight tee, with deposition rates of 47.61, 18.06, and 8.13% for PM10, PM2.5, and PM1.0, respectively. As the particle size increases, the deposition rate of particles also gradually increases. The larger the inlet velocity, the greater the deposition rate. The particle concentration on the outlet of the pipeline in the connection forms of straight tee was significantly decreased after adding the purification equipment, and the deposition rates of PM10, PM2.5, and PM1.0 decreased by 45.01, 68.89, and 77.48%. Therefore, the use of pipeline elbows should be reduced, and purification equipment should be installed in the process of using, which will reduce the deposition of particles in the fresh air systems.
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