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camfilapc.com US Pharmacopeia 10 As the filters are cleaned, emission levels will fluctuate because the shock of compressed air that cleans them also allows some dust to pass through the filter media. The pressure drop will increase when cleaning is paused and decrease when it restarts. The frequency of cleaning affects the pressure drop in the system, and the compressed air used for cleaning is the main driver of energy consump- tion. Filters with inherently greater pressure drop consume more energy because they require more pulsing/ compressed air, and thus more elec- tricity is needed for the fan's motor to overcome the higher static pressure in the system. The tests use calcium carbonate dust, and section 6.1 of the standard spec- ifies its properties, including particle size, bulk density, and moisture con- tent. By using a standardized material, the test results are applicable across all industries. Measuring performance parameters Emissions. The tests used in Standard 199 measure not only the initial emis- sions, but emissions over the duration of testing, an approach that is more meaningful to manufacturers than others. Emissions are measured in milligrams per cubic meter of air. Pressure drop. The more dust a filter can hold and the better it can release the dust, the less frequently it will need cleaning. That, in turn, helps the system maintain a low pressure drop throughout the filter's service life. Compressed air usage. How much air the system consumes varies according to how self-cleaning the filter is. The better the cleaning characteristics, the less compressed air the system needs. Energy consumption. Pressure drop and compressed air usage largely de- termine how much energy you con- sume running the system. A filter with a low pressure drop—in conjunction with a variable-frequency drive, as is specified for the test rig in Standard 199—will reduce electricity usage and extend the filter's service life. Pulsing less frequently also cuts energy con- sumption because it conserves com- pressed air. Emission reading. It's important to know how much dust penetrates the filters and reaches the outlet. The emissions undergo photometric mea- surement in accordance with 40 CFR Part 50 and are categorized by particu- late mass (PM): This full-scale test rig, built in accordance with Standard 199 specifications, includes a cartridge dust collector with four high-effi- ciency filters.