Analysis of three commonly used test methods for filtration efficiency1

Three test methods for filtration efficiency (gravimetric method, colorimetric method and atmospheric dust counting method)“Filtration efficiency”It is the ratio of the amount of dust captured to the dust content of the original air: The actual meaning and specific value of filter efficiency vary greatly from test to test. When determining the filtration efficiency, the valley is full of pits“quantity”The meaning of , and the efficiency values ​​measured and calculated from it are also varied. In engineering, to save time and to reduce misunderstandings, several methods of expressing efficiency specifications by code names have emerged. Test method: Gravimetric method Arrestance: The test dust source is standard dust with large particle size and high concentration. The main components of the dust are the screened and specified areas of floating dust, and then mixed with a specified amount of fine carbon black and short fibers. Most countries prescribe the use of Arizona desert“road dust”(Arizona Road Dust), the Chinese standard once stipulated the use of dust from a village on the Loess Plateau, and the Japanese standard stipulated the use of Japanese-derived dust.“Off East Asian Clay”. measured“quantity”is the dust weight. The filter is installed in the standard test wind tunnel, and the upper wind side continuously emits dust. At regular intervals, measure the weight of dust passing through the filter or the amount of dust collected on the filter, thereby obtaining the filtration efficiency of the filter calculated by the weight of dust at this stage. The final weighted efficiency is the weighted average of the efficiency of each test stage according to the amount of dust generated. The conditions for the termination of the gravimetric test are: the agreed final resistance value, or when the efficiency drops significantly. here so-called“convention”Refers to the agreement between the customer and the tester, or the tester's own regulations. Obviously, different conditions for terminating the test will lead to different weighting efficiency values. When the test is terminated, the weight of the filter to accommodate the test dust is called“Dust holding capacity”. The gravimetric method is used to measure low-efficiency filters, which are typically used for pre-filtration in central air-conditioning systems. The gravimetric test is a destructive test and cannot be used for the daily product performance inspection of the manufacturer. Relevant standards: American ANSI/ASHRAE 52.1-1992, European EN779-1993, China GB12218-89. Atmospheric dust counting method: The dust source is the natural atmosphere.“atmospheric dust”. dusty“quantity”is the total number of particles greater than or equal to a certain particle size. The instruments for measuring dust are ordinary optical or laser dust particle counters. The efficiency value is the initial efficiency of the new filter. Name Explanation A, B, C, D Classification of airborne molecular pollutants in integrated circuit manufacturing. A stands for Acids, B for Bases, C for Condensables, and D for Dopants. Absolute Filter, Absolute Filter In the early days, a foreign company used the trade name of a high-efficiency filter with a partition, which corresponds to a filtration efficiency of 99.97% (0.3mm DOP). AC fine (Air Cleaner Test Dust, fine), AC fine ash The standard dust specified by the United States for the performance test of filtration and dust removal equipment is common to all countries except China and Japan. The dust is taken from the Arizona desert area, commonly known as Arizona Road Dust. Adding a specified amount of short fibers and carbon black to AC fine ash becomes the ASHRAE standard dust commonly used in filter testing. The International Organization for Standardization ISO stipulates that AC fine ash is used to measure the filtration effect of automobile filters. Aerosol, aerosol is a relatively stable suspension system formed by solid or liquid particles and gas. Internationally, most people who engage in filtration theory participate in the activities of the Aerosol Society, but those who engage in filtration applications prefer to get together in the HVAC industry. AFI (Air Filter Institute), American Air Filter Institute The test methods of filtration efficiency, gravimetric method and colorimetric method, were first used by AFI, and some people call it AFI efficiency. If you see“AFI efficiency”, you have to judge whether it is the weight efficiency (Arrestance) or the colorimetric efficiency (Dust-spot). AHU (Air Handling Unit), central air conditioner Colorimetric Dust-spot: The test bench and test dust are the same as those used in the gravimetric method. dust“quantity”It is the light flux of the high-efficiency filter paper at the sampling point. Sampling before and after the filter, there is high-efficiency filter paper on the sampling head. Obviously, the pollution degree of the high-efficiency filter paper at the sampling point before and after the filter will be different. In the test, after each period of dust emission test, measure the light flux of the high-efficiency filter paper at the sampling points before and after the filter under the condition of no dust emission.“Filtration efficiency”. The final colorimetric efficiency is the weighted average of the efficiency values ​​of each stage in the whole process of the test according to the amount of dust generated. The conditions for terminating the test are similar to those of the gravimetric method: the agreed final resistance value, or when the efficiency drops significantly. Colorimetry is used to measure general ventilation filters with high efficiency, and most filters in air conditioning systems belong to this type of filter. Colorimetry used to be a common test method abroad, and this method was gradually replaced by counting method. Strict colorimetry is a destructive test. Relevant standards: American ANSI/ASHRAE 52.1-1992, European EN 779-1993. Central air conditioning is the most common place to see air filters: Air Filter, when used in central air conditioning and clean rooms, it is called an air filter; when used in piston engines and small air compressors, it is called an air filter .​​

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