The European standard EN779 is leading for testing and classification of air filters in the air conditioning. In 2012, a new version of the EN779 was adopted by the CEN with some changes on the previous revision of 2002. The changes relate mainly to the F7, F8 and F9 filters.

The test methods for classifying the filters are, in the 2012 revision, the same. The G-class filters (coarse filters) are classified by measuring the retention of a test dust in a test rig. The filter is mounted in an air duct, after which the test dust is blown through the filter. The percentage (Am) of dust that is retained by the filter, determines the filter class.

For the (M- and) -F class filters they use the atomised aerosol DEHS (Diethylhexyl sebacate) as a test substance. The filters are mounted in the same test rig as the coarse filters. The 0.4 micron particles of the DEHS aerosol are measured before and after the filter. The percentage (Em) of captured 0,4 micron particles, determines the filter class.

Minimum efficiency

An addition to the EN779: 2002 is the minimum efficiency for F7, F8 and F9 filters. In the 2002 version, the test results showed only the average efficiency over the full lifetime of the filter. This resulted in filters with an average efficiency of 85%, but an initial efficiency of < 10%. These filters met the requirements of the EN779:2002, but functioned poorly in real life.  For this reason it was decided to set a minimum efficiency for the fine filters in the 2012 revision. The F7, F8 and F9 filters must meet a minimum efficiency of respectively 35%, 55% and 70% of 0.4 micron DEHS particles. Electrostatic discharge

In the 2012 version of EN779, the F7, F8 and F9 filters also meet the minimum efficiency after removing the electrostatic charge from the media. This is done by the liquid isopropanol. The filter media is immersed in the fluid for 2 minutes, dried for 24 hours and cleaned with purified air. The media is placed in the test rig and tested according to the same procedure as before. The efficiency is measured and should be above the minimum requirements. The efficiency of the discharged media is shown on any test certificate.

Filter classes

The classification of the G-class filters remain unchanged. The F5 and F6 filters are classified as M5 and M6, otherwise nothing is changed. Efficiency is still calculated in a test rig with the DEHS aerosol. The minimum efficiency of the M-class filters is not measured.