efficiency
before the clean room end high efficiency (hepa) filter, the filter with the efficiency of not less than f8 should be protected; the ultra-high efficiency (ulpa) filter can be used with the f9~h11 filter. the central air conditioner itself should be protected by a filter with an efficiency specification of not less than f5. in the sand-free, low-pollution areas, there is no protection grade filter in front of the f7 filter; in the central air conditioning system of the city, g3~f6 are common primary filters.
what level of efficiency filters should be installed to protect the latter level of filters, which requires designers and field engineers to consider the use of environment, spare parts costs, operating energy consumption, maintenance costs and other factors before deciding.
reasonable determination of filter efficiency at all levels
in general, the last stage filter determines the degree of air purification. all levels of filters at the upper end play a protective role, which protects the filter at the lower end to extend its service life, or protects the air conditioning system to ensure its normal operation. in air conditioning design, the efficiency of the last filter should be determined according to the user's cleanliness requirements. then, the protective filter should be selected. if this filter also needs to be protected, a filter should be added at its upper end.
the efficiency of filters at all levels should be properly matched. if the efficiency difference between two adjacent filters is too large, the former one can not protect the latter one; if the difference between two filters is not too big, the burden of the latter one is too small. high efficiency (hepa) filters at the end of the clean room should be protected by filters with efficiency specifications not less than f8, and filters of f9~h11 can be used before ultra-high efficiency (ulpa) filters. the central air conditioner itself should be protected by filters with efficiency specifications of not less than f5. no protective filter can be installed before f7 filter in areas without sand and low pollution. in urban central air-conditioning system, g3-f6 is a common primary filter.
what level of efficiency filters should be installed to protect the latter level of filters, which requires designers and field engineers to consider the use of environment, spare parts costs, operating energy consumption, maintenance costs and other factors before deciding.
test methods for general ventilation filters
1、measurement of low efficiency filter with artificial dust weighing method（eu1-eu4）；
2、measurement of high efficiency filter with laser particle counter（eu5-eu9）；3、using laser particle counter to determine the size of dust particles and the number of particles in different sizes of upstream and downstream；4、particle size range（0.2-5.0um）；
5、the dust source is polydisperse liquid aerosol（dehs：hexyl sebacic acid two hexa）。scanning principle of laser particle technology
mpps efficiency
the efficiency of air filter varies with the particle size of dust. at a certain particle size, the efficiency is the lowest, that is, the penetration rate is the highest, which is called the most easily penetrated particle size (mpps). the mpps point varies with filtration material and filtration speed. for high efficiency (hepa) and ultra high efficiency (ulpa) air filters, mpps is usually between 0.1-0.25um.
in addition to normal penetration of the filter material, dust may also leak from the damaged material or the poor seal of the filter element and the outer frame. a hepa/ulpa filter with a high efficiency is not always qualified. the total efficiency and point-by-point efficiency of the high efficiency and ultra-efficient filters used in the unidirectional flow clean room end must be achieved. specified value. the traditional sodium flame method, oil mist method, dop method and other total efficiency test methods, as well as smoke or variable air volume leak detection methods are not sensitive enough and accurate, and can not meet the increasingly demanding requirements.
in 1999, the european standards commission (cen) formulated and promulgated the en1822 standard, which is the latest standard for scanning, testing and grading hepa/ulpa filters based on mpps efficiency.
(1) under the air velocity of the filter to be measured, the grading and counting efficiency of the filter material under different particle sizes was tested by using the condensate nodule particle counting (cnc) or laser particle counting equipment, and the mpps of the filter material was determined.
（2）under the prescribed surface wind speed (generally 0.45m/s), the outlet surface of the filter is scanned to test the mpps efficiency point by point.
(3) the total mpps efficiency of the filter is calculated based on the pointwise mpps efficiency.
（4）according to mpps total efficiency and pointwise efficiency, we can judge whether the filter reaches the required level.
dop, dehs, paraffin oil and other organic liquids are easy to produce high concentrations of artificial aerosols, so they are often used to test hepa/ulpa filters.
performance and efficiency testing equipment
smoke visual measurement
through smoke trail experiment, we can observe the leakage of high efficiency filter visually.
energy consumption test
by testing the initial resistance of the air filter under different air volume, the energy consumption in the life cycle of the filter is judged.
automatic efficiency scanning of laser particle counter
through block scanning of the air outlet surface of the high efficiency filter at about 20 mm position, the local filtration efficiency is obtained and the overall efficiency is judged.