The primary filter is mainly used to filter dust particles with particle size of 5um and above.
The filtration efficiency of the primary filter is measured by weighing method which is named as arrestance.
The weighing method adopts the high concentration of artificial dust (the particle size is larger than that of atmospheric dust, and its components are dust, carbon black and short fiber, which are composed by a certain ratio). The efficiency is calculated after the dust weight of the air flow is measured before and after the filter.
It is generally used to measure the low efficiency filter used as the pre filter in the central air-conditioning system, namely the primary efficiency filter.
Relevant standards of weighing method：
● American standard: ANSI/ASHRAE52.1-1992
● British standard: EN779-1993
● Chinese standard: GB12218-1989.
As for the test dust source, it is generally the standard dust with large particle size and high concentration.
The filtering efficiency of the air filter is the ratio of the amount of dust captured to the amount of dust in the original air.
The filtration efficiency of the primary filter is equal to: 1 minus the ratio of dust content in the downstream air to that in the upstream air.
The filter is installed in the standard test wind tunnel with intermittent dust generation at the windward end. At regular intervals, measure the weight of dust passing through the filter (the amount of dust collected on the filter) to obtain the filter efficiency calculated by the weight of dust at this stage.
The final weighing efficiency is the weighted average of the efficiency of each test stage according to the amount of dust generated.
When the test is terminated, the weight of the test dust contained in the filter is called "dust holding capacity".
The test termination conditions of the weighing method are: the final resistance value agreed with the customer, or the final resistance value specified by the tester himself, or when the efficiency drops significantly.
Obviously, different final resistance values will lead to different weighing efficiency values.
The weighing method is a destructive test and cannot be used for the daily product performance inspection of the manufacturer.
