Air filter refers to air filter device, generally used for clean workshop, clean factory room, laboratory and clean room, or for electronic mechanical communication equipment and other dust. There are primary filter, medium filter, filter and sub-filter models. Various models have different standards and use efficiency.

For a variety of reasons, in the past decade, all the professional laboratories and filter manufacturers in the country rarely carry out filter dust capacity test. At present, JG/T22-1999 "Air Filter performance Test method for General Ventilation", the industry standard is being revised, and the dust capacity test method is one of the key contents of the revision.

Dust capacity of air filter

Combined with JG/T22-1999, American ANSI/ASHRAe 52.1-1992, European EN779:2002, Japanese JISB9908: 2001 and other four representative standards in the air filter performance test methods of the definition of dust capacity and test methods are introduced and compared, to help the revision of the national standard.

1. Introduction of dust capacity in national standards

In JG/T22-1999, the dust capacity is defined as the total amount of artificial dust intercepted by the test filter before reaching the test termination conditions, which is calculated by multiplied by the total dust mass of the artificial dust by the average weight efficiency of the test filter. The test method of dust capacity is: Through hair send a certain amount of artificial dust to dust device equipped with subjects filters filter (usually) at the end of the filter and standard test duct, until send after artificial dust, remove the subjects filters and filter at the end, weighing respectively, it is concluded that the quality variation, to calculate the efficiency of the filter weight subjects, Repeat the above steps until the test filter reaches the final resistance value, and then calculate the average weight efficiency of the whole test process, and finally get the dust capacity of the test filter by multiplying the average weight efficiency by the total amount of dust.

The definition of dust capacity and the test method of dust capacity in EN779:2002 are almost the same as those in JG/T22-1999. ANSI/ASHRAE52.1-1992 differs from JG/T22-1999 only in terms of the dust capacity test termination conditions, and other contents are consistent; Jisb9908:2001 is similar to JG/T22-1999 except for the termination conditions and calculation methods of dust capacity test. Therefore, there are some differences in the test termination conditions and calculation methods among the standard dust capacity test methods.

2. Termination conditions of dust capacity test

According to the actual situation, the test terminations of the four criteria are based on the final resistance, and JG/T22-1999 and EN779:2002 only use this criterion, while ANSI/ASHRAE52.1-1992 and JISB9908: In 2001, the reduction of weight efficiency was also used to judge whether the test was terminated.

2.1. Take the final resistance as the termination condition of the test

For most filters, the resistance is generally only up and not down. In this case, the final resistance can be directly used to judge whether the dust capacity test is terminated. At this time, the amount of dust capacity is closely related to the final resistance. The higher the final resistance is, the greater the dust capacity value will be obtained.

The final resistance is mainly determined in two cases: 1) 2 times the initial resistance; 2) Recommended by the manufacturer zhongjian South. Filter because of its structure and different types, some initial resistance is very low, at this time if 2 times the initial resistance as the final resistance, for these filters is obviously unfair; If the final resistance is recommended only by the manufacturer, it is likely to cause the final resistance of the same level of filter of different manufacturers is not the same, so that the dust capacity of each manufacturer is not comparable, which will bring trouble to consumers in the selection of filters. Therefore, in order to make the dust capacity index of zhongjian Southern filter more reasonable and standardized, the final resistance value can be considered to be unified. One level of filter corresponds to one or a certain range of final resistance value. After analysis and summary, some suggestions for final resistance are given.

2.2. The reduction of weight efficiency shall be taken as the termination condition of the test

For the low efficiency filter made of fluffy coarse fiber material, because the filter material is sparse, the dust particles are more coarse, the filter resistance increases to a certain value, the dust layer is penetrated and the dust particles bounce off from the dust layer, secondary dust, resulting in the filter resistance does not rise but fall. In this case, the termination condition of the test must be determined by a reduction in weight efficiency, i.e., conditions B) and C) in ANSI/ASHRAe52.1-1992 or B) in JISB9908:2001, which is not specified in JG/T22-1999 and EN779:2002. Obviously, JG/T22-1999, as a national standard, is not perfect in this area, so it is necessary to add this area in the revision.

2.3. The conditions for the termination of the test stipulated in most European and American standards are:

When the resistance reaches 2 times or more of the initial resistance; When the instantaneous filtration efficiency is less than 85% of the maximum efficiency value. Most air filters will not occur efficiency reduction phenomenon, only the fluffy crude fiber (≥10mm) made of G3 and a small number of G4 air filters may occur this situation, the reason is that the gap between the fiber is too large, can not hold dust.

The problem arises when the termination condition is "twice or more of the initial resistance". The higher the resistance, the more dust in the air filter, the greater the dust capacity. It is not fair to prescribe twice as much. The initial resistance is low and the air filter has to suffer. So the client and the experimenter have to terminate the conditions of the trial. If the conditions for stopping the test are not clear, the dust volume data are meaningless.

The European standard eurovent4/9 specifies a termination resistance of 450Pa, which is well above 2 times the initial resistance. The Chinese standard does not require dust testing of "medium effect" air filters. The test Dust specified in the European and American standards is Ashrae artificial Dust, which is mainly composed of Arizona Road Dust from a specific location in the Desert region of Arizona, USA, mixed with a specified proportion of fine carbon black and staple fibers. Japan has its own "road dust," which has physical and chemical properties similar to those of American dust.

3. Calculation method of dust capacity of air filter

According to JG/T22-1999, ASHRAE52.1-1992 and EN779:2002, the calculation method of dust capacity is the same. The product value of the total mass of artificial dust and the average weight efficiency of the tested filter is recorded as dust capacity. JISB9908:2001 is obtained by directly weighing the test filter or the end filter.

According to the standard calculation methods such as JG/T22-1999, ASHRAE52.1-1992 and EN779:2002, the average weight efficiency must be calculated in order to obtain the value of dust capacity. However, the average weight efficiency is only used for the grading evaluation of coarse efficiency filters, and it has no practical significance for medium efficiency and filters. The calculation method of JISB9908:2001 is simple and convenient, and can more directly reflect the dust capacity of the filter.

Therefore, the calculation method of JISB9908:2001 can be considered in the revision of the standard. The weight of the tested filter before and after the test can be directly weighed, and the difference between them is taken as the value of dust capacity. The application of air filter in air conditioning and ventilation system is more and more, the service life is one of the indicators that people care about when choosing air filter. But in practice, it is difficult to predict the service life of air filters, so the dust capacity is usually used to evaluate it. The dust capacity can only be qualitative but not quantitative reflection of the actual dust weight of the air filter. At the same time, only when the test conditions and methods are the same, the life of different filters can be evaluated according to the dust capacity data.