Measuring filtration efficiency

• By: Craig Booth
• On: 01/10/2009 16:41:16
• In: Uncategorised
• Comments: 0 Add

Let me recommend that you read David Sellers of Facility Dynamics Engineering, and his excellent series of posts (start here) on evaluating modern, extended surface air filters as against traditional technology.

He also gets on to talking about particle count testing of filters, and reminds me of this important point when thinking about filter efficiency:

To give you a feel for what your typical filter is up against, here is a plot of atmospheric particle count by weight and size that I developed from a couple of industry resources.

Basically, the graph says that there are zillions of little tiny particles in the air all around us, but they are so small that they don’t contribute much to the total weight of the particles suspended in the air. So, that means, in a general sense, that eliminating the big stuff; i.e. the stuff that tends to be pretty easy to filter out, really won’t eliminate much of the fine stuff that is really our target. A low efficiency filter does great job of catching the occasional “boulder” that is in the air stream, but by and large, doesn’t do much to stop the “pebbles” that comprise the bulk of the contaminants its exposed to.

In the old days the filter classification systems were effectively set up so that every filter could be described as >95% efficient. The question was always 'against what challenge?' - house bricks or combustion products?