CLASSIFICATION OF AIR FILTERS IN TERMS OF EFFICIENCY
3 basic criteria are important for air filters. These criteria are filter dust holding efficiency, dust holding capacity by weight, service life, and filter initial resistance, respectively.
Filter test standards primarily ensure that filters can be compared with each other. According to the European standard, air filters can be grouped into two separate groups, the first of which is the EN 779 standard applied for filter groups with G and F efficiency, and the second is the EN 1822 standard, which determines the efficiency of Hepa filters.
EN 779:2012 standard determines and classifies coarse filters with G efficiency only according to their weight average dust holding values. Accordingly, the average dust holding values of G type coarse filters are as follows.
The efficiency of medium and fine filters is determined by testing, counting the particles in the 0.2 – 3 micron size range at the filter inlet and outlet and proportioning them to each other. However, for classification, 0.4 micron, which is the average size of the particles used in the test, is used, therefore the efficiency of filters with F efficiency is expressed in terms of the average efficiency of the particle at 0.4 microns.
TABLE-3.7 Classification of air filters according to EN 779:2012 standard
Filter Class
Final Pressure Loss Pa
Average Test Powder Retention % (Am)
Average yield (Em) at 0.4 µm particle size
Minimum Yield at 0.4 μm particle size
G1
250
50 < Am < 65
-
-
G2
250
65 < Am < 80
-
-
G3
250
80 < Am < 90
-
-
G4
250
90 < am
-
-
M5
450
-
40 < Em < 60
-
M6
450
-
60 < Em < 80
-
F7
450
-
80 < Em < 90
35
F8
450
-
90 < Em < 95
55
F9
450
-
95 < Em
70
Note: Synthetic powder and atmospheric dust used in EN 779 tests may differ in characteristic from each other. Therefore, there may be differences between test results and operational performance and filter service life. In addition, electrostatic loss of charge and fiber breaks of the filter material may adversely affect the overall dust holding efficiency.
Hepa filters are tested according to the EN1822 test method and their efficiency is determined. According to this method, the efficiency of the filters is determined according to the particle size that will give the minimum efficiency, in other words, they are tested according to the particle size that gives the lowest efficiency value at a certain air speed for a certain filter paper. The particle size that exceeds this particle size the most is called the Most Penerating Particle Size (MPSS). After determining the efficiency of the filter paper, the filter efficiency should be determined in two ways, first for the entire filter construction with the filter frames and gasket, and then pointwise by scanning the entire filter surface area. The efficiency value should be calculated using the obtained permeability value. The tested filter should be scanned using the movable aerosol feed nozzle and measuring tips. Multiple point efficiency values to be determined here will be entered into the chart to be added to the test report. In order to make the correct classification for the efficiency, the efficiency of the point and the entire filter must be in accordance with the values shown in the table.
TABLE-3.8 HEPA filter classification table according to EN 1822 standard
Filter Class
Yield in MPPS (%)
MPPS (%) Permeability
Total Yield
Regional Yield
Total Yield
Regional Yield
E10
> 85
-
15
-
E11
> 95
-
5
-
E12
> 99.5
-
0.5
-
H13
> 99.95
99.75
0.05
0.25
H14
> 99.995
99,975
0.005
0.025
U15
> 99.9995
99,9975
0.0005
0.0025
U16
> 99.99995
99.99975
0.00005
0.00025
U17
> 99.9999995
99.9999
0.000005
0.00001 Notes: Local efficiency values are not required for filters with E10, E11 and E12 efficiency. For filters with H13 and H14 efficiency, a smoke leak test can be performed as an alternative to the standard screening test.