Primary filters
Illustrated Guide to Ventilation (BG 2/2009), compiled by Kevin Pennycook and published by BSRIA in 2009, states : ‘Primary filters (Grade G1 to G4) have an average arrestance ranging from 50 – 90%. Average arrestance is the amount of dust retained as a percentage of the total load (a ratio). Primary filters can arrest particles down to 5 um but have a minimal effect on particles below 1 μm. Air velocity through primary filters is an average of 2 m/s, and the pressure drop rises from 10-60 Pa when clean to 125-250 Pa when dirty. These filters can be permanent and cleanable (made of foam or metal mesh) or disposable (made of a glass or synthetic media). Primary filters are mainly used to protect ventilation and air conditioning equipment (if building use does not require filtered air), or as pre-filters to extend the operating life of fine filters installed further downstream.’
--BSRIA
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