The performance of building ventilation systems and/or portable indoor air cleaners is greatly affected by the performance of the fibrous filters installed in them. The initial particle efficiency is generally used as a measure to evaluate the performance of the fibrous filters. However, with dust loading, the long-term performance of the filters might change, and the filters may become particle sources themselves and affect the performance of other systems. Previous studies on long-term performance were mainly based on theoretical analyses or laboratory experimental tests. This study investigates the long-term efficiency and pressure-drop change of various ventilation filters during real operation. No obvious efficiency decrease is observed, and it is inferred that the effect of dust loading on efficiency can be ignored. Secondary particle detachment is found to be possible in real applications, but its effect on the downstream concentration and indoor air can be made negligible with the use of an H-level filter. The pressure drop of the ventilation filter is also found to increase significantly.
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