What is the dust holding capacity of an air filter?

The use of air filters continues to rise in both the industrial and residential sectors.
The type of air filter used varies from field to field.
I believe that most air filter users are unfamiliar with the term "dust holding capacity" and only know that the higher the dust holding capacity of an air filter, the longer its service life.
In the process of using an air filter, the dust-holding capacity of the filter reaches saturation, which means that it reaches the end of its service life.
So how is the dust capacity of an air filter calculated? How do you ensure that it lasts effectively during use? Here is a brief introduction.


What is the dust holding capacity of a filter: The dust holding capacity refers to the maximum allowable dust accumulation of a filter, when the dust accumulation exceeds this value, the filter resistance will become larger and the filtration efficiency will decrease.
Therefore, the dust holding capacity of a filter is generally defined as the amount of dust that accumulates when the resistance reaches a specified value (generally two times the initial resistance) due to dust accumulation under the action of a certain air volume.


The increase in resistance after dust accumulation in the filter is related to the size of the solid dust particles.
After the dust has been deposited on the filter, the effect on its efficiency is very complex and depends on the nature of the filter material, and the nature and size of the dust particles at a certain wind speed.
For example, the general fiber material composition of the air filter paper, because the filter media after the accumulation of dust increased the contact retention effect of the filter, but also because of the role of the charge of the dust particles so that other dust particles in the dust particles have been blocked on the accumulation, thereby improving the filter efficiency of the filter; but when the dust accumulation to a certain limit, the accumulation of dust will be scattered, or because the pressure difference between the two sides of the filter media is too large, through the filter media, resulting in a serious filter efficiency The efficiency of the filter will drop.


Based on the parameters of the rated dust capacity of the air filter, the service life of the air filter can be calculated.
The service life of an air filter is generally based on the time it takes to reach the rated dust capacity.


The service life of an air filter is related to the amount of dust generated by indoor dust sources, the dust particles carried by people, and the concentration of atmospheric dust particles.


The dust-holding capacity of an air filter is the weight of a specific amount of artificial dust that can be held under specific test conditions.
By "specific", we mean:

1. a standard test wind tunnel and associated test and measurement equipment

2. standard artificial dust which is significantly larger than the actual atmospheric dust particles

3. the test methods and calculations specified in the standard, or agreed upon between the client and the tester

4. the conditions for termination of the test as agreed between the client and the test party.



Only if the test conditions are the same can a rough estimate of which air filter will last longer than the other be made based on the dust capacity of the air filter. There is no direct correlation between the "dust capacity" and the actual weight of dust held by the air filter, and isolated "dust capacity" figures have no meaning for the user.
For example, an air filter with a test capacity of 600g may hold 2.5kg of atmospheric dust at the end of its life; another with a capacity of 900g may only hold 1.5kg of dust when it reaches you.

When evaluating air filter products for general ventilation, air filter manufacturers and specialist test laboratories carry out destructive dust generation tests on air filters, the main purpose of which is to assess the average efficiency of the air filter throughout the test.
The dust holding capacity is one figure in a set of data obtained by such a test.
If a laboratory has carried out dust generation tests on a large batch of air filters, the tester can use the dust capacity data from one batch to compare the relevant air filters.
It is difficult for an outsider to understand the actual meaning of those dust tolerances.


Most standards specify test termination conditions: 1) when the resistance reaches twice the initial resistance or higher; 2) when the instantaneous filtration efficiency falls below 85% of the maximum efficiency value.
Most air filters do not reduce efficiency, only fluffy coarse fibers (≥ 10mm) made of G3 or less and a small number of G4 air filters may appear in this case, the reason is that the gap between the fibers is too large, and can not pocket dust.
The problem arises when the termination condition is "twice the initial resistance or higher".
The higher the resistance, the more dust there is in the air filter and the greater the dust capacity.

It is not fair to stipulate that the initial resistance is two times as high as the initial resistance, so the air filter has to suffer.
So the commissioner and the tester have to terminate the conditions of the test.
The Eurovent 4/9 standard specifies an end-of-test resistance of 450 Pa, which is much higher than the initial resistance of 2 times.

The test dust specified in the standard is Ashrae artificial dust, which is mainly composed of floating dust from a specific location in the desert (Arizona Road Dust), mixed with a specified proportion of fine carbon black and short fibers.