Five Tips for Selecting Cartridge Dust Collector Filters - #1

#1 Understand the different measures of filter efficiency and how to apply them.

There are two methods that dust collector filter manufacturers typically use to express filter efficiency. Gravimetric analysis is based on particle capture by weight: For example, filter efficiency might be stated as 99.995 percent on particles of 0.5 μm or larger by weight. Filter efficiency may also be expressed as a Minimum Efficiency Reporting Value or MERV, based on a scale from 1 to 16, with MERV 16 being the highest efficiency.

The MERV scale was developed for the HVAC filter market and does not take into account the way a dust collector operates (i.e., it pulse-cleans filters periodically when a dust cake builds up). Though MERV and gravimetric efficiency ratings are useful tools for comparing filters, you should not rely on these measures alone to determine efficiency. It is more relevant to make sure you are satisfying OSHA or EPA requirements for filter performance – OSHA if you are discharging the air and recirculating it indoors downstream of the collector, the EPA if you are discharging the air outside or into the environment.

Mass density efficiency, defined as the weight per unit volume of air, is the best predictor of a filter’s OSHA compliance. For example, OSHA might require that emissions will not exceed 5 milligrams per cubic meter at the discharge of the dust collector. Similarly, the EPA doesn’t care about percentage efficiency claims: They want to know that emissions will be at or below required thresholds, typically stated as grains per cubic foot or milligrams per cubic meter.

Concerned about which efficiency measure(s) to use? If so, you are not alone. But there is a way to cut through the confusion and make sure your bases are covered: Require your filter supplier to provide a written guarantee of performance stating that the filters you select will satisfy applicable OSHA or EPA requirements. It is worth noting here that ASHRAE is developing a new standard specifically for measuring performance of dust collector filters. Finalization of that standard, however, is at least a couple of years away.

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This first tip is an excerpt from the white paper "Five Tips for Selecting Cartridge Dust Collecting Filters" by Rick Kreczmer of Camfil APC. The full article can be downloaded here.