There is one thing that I am intrigued by here and still don't feel that anyone has addressed and that is the need to move to a higher particle size. It was stated in the proposed standard that if we need to assess the efficiency of a finer filter F7+ we should look at the 1 micron data rather than the 0.4 micron data.
Thinking about this this afternoon I did some analysis on data generated on three bag filters (rated F7, F8 and F9) tested some time ago. The elements were tested with both KCl and DEHS aerosol for fractional efficiency before and after IPA vapour discharge to the TC142 protocol from 2013. The particle size channels were set as per ASHRAE 52.2 (not EN779) The data that I have showed a very nice and very significant relationship between the efficiencies at 2.57 microns, 1.14 microns and 0.47 microns.
The issue I see here is that as you use a larger particle size, the efficiency range F7-F9 narrows significantly (so at 0.47 microns you cover a range of efficiency 35% to around 85%, a range of 50%, for the 3 elements but at 1.14 microns the range is now only 60% to 96%, a range of 36%) making the discrimination of efficiency ratings much harder to discriminate at 1 and 2.5 micron than at 0.4 microns making it much harder to effectively differentiate between good and bad filters commercially.
Thoughts?
No comments:
Post a Comment