Filtration Efficiency of 80/20 Blend Filters

We get occasional calls about our posted 99.99% efficiency, as it compares to the ASHRAE 52.2 test standard.

The chart below shows the Particle Size Efficiency of a filter made from our 80/20 blend, based on the ASHRAE 52.2 test standard.  The numbers just below the chart (beginning with 0.35) are the particle size “geometric mean”, in microns. 

As you can see, these filters test very well, but the results do not indicate the 99.99% at 0.5 micron rating that we have given to our 80/20 blend.  This is because the ASHRAE 52.2 test standard is not designed for round pleated cartridge filters.  More importantly, it is not designed for cleanable filters.  It was actually designed to test flat disposable HVAC filters, so the resulting data needs to be taken with a grain of salt.  The ASHRAE 52.2 test does not give a true indication of what a user should expect to see from their dust collection filter…it can only tell you what the filter will do when it is brand new.   

Background info and further explanation: 

-ASHRAE 52.2 requires a minimum face velocity of 118 fpm.  This equates to over 1100 cfm on our Farr style filters!  We never push these filters past about 750 cfm, and normally run them at about 500 cfm, so the 52.2 test pushes them way beyond their intended flow rating.  ASHRAE 52.2 gives all cartridge filters (not just ours) an unfairly low indication of the true as-installed efficiency. 

-ASHRAE 52.2 does not allow the filters to be loaded then cleaned.  It simply injects dust until the desired pressure is achieved, then plots the efficiency at that pressure.  The “Loadings” are data points taken at 30 grams, 25%, 50%, 75%, and 100% of full pressure, they are not “loadings and cleanings” as has been suggested elsewhere.  As a result, the efficiency numbers are representative of a brand new filter, before its first cleaning.  This is only marginally useful to the person designing a dust collector.  His filter will only be “new” for an hour or two, so what happens after that?  ASHRAE 52.2 does not tell you.

So...the 52.2 standard allows an “apples-to-apples” test between suppliers, which is good, but it does not give a true indication of what the filter will do in actual use.  If you need data for an “apples-to-apples” comparison, use the above chart.  If you need efficiency for other calculations, such as EPA emissions, use our published 99.99% figure.

We hope this information proves useful, and please do not hesitate to call the office if there are any questions.  If you are looking for a cartridge filter with a higher MERV efficiency than the 80/20 Blend, please see our Torit page and our Cartridge Filter page for the NANO series Nanofiber filters with a MERV 15 rating.  Also, our dedicated Nanofiber filter page can be found Here.

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