Here’s a rundown of the test standard that we use for our pleated cartridge filters:
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. Why? Well, 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. ASHRAE 52.2 was actually designed to test flat disposable HVAC filters, so the resulting data needs to be taken with a grain of salt. Yes, this filter will achieve 99.99% at 0.5 microns, but not right out of the box. It takes a couple of hours or days for the efficiency to peak and level off, where it will remain for the next 2000-3000 hours. So 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.
The first table on the right is a MERV 11 80/20 Blend Filter. The chart and tables below that are the same ASHRAE 52.2 test, except they include test data from one of our MERV 15 NANO filters. Note the huge increase in submicron efficiency on the initial loading (column 1). The 4th item down 96.3% at 0.7-1.0 microns corresponds to the 42.52% at 0.84 (mean) microns from the last table. Also note that both filters approach or exceed 99.99% by the 5th loading. To put this into perspective, with this size filter (250 sq. ft.), the 5th loading peaks at about 1.75 lbs of dust.
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! In practice 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. When reviewing MERV data, just be sure to check the the test velocity. Again, it must be a minimum of 118 fpm. We have seen “MERV” efficiency claims from one manufacturer that came from tests using a much lower velocity.
-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.
-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 between manufacturers, use the above charts. If you need efficiency for other calculations, such as EPA emissions, use our published 99.99% figure.
-When comparing MERV test results pay close attention to the reported pressure drop. All of our filters are tested to a final pressure drop of 4.0″ wg. This is where they display their peak efficiencies of 99.99%+. This is not, however, the pressure drop or efficiency that is used when we report the MERV values. By definition, MERV values must be the minimum reported value…this nearly always occurs after the initial loading, which is typically under 1.0″ wg. All Wynn filters come with MERV values reported as the minimum efficiency.
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 efficiency than the 80/20 Blend or NANO filter can provide, please give us a call. We build MERV 16 TetraTex membrane filters on a special order basis. We also have a warehouse full of HEPA filters in stock, right here in Warwick, PA!
We have been in this business for a long, long time. Our goal is the same as it has always been…to give every customer the very best product at the very best price. We truly appreciate your business.