Air filters are devices that use filtration, adhesion or charge trapping to remove airborne particles, gases contaminants and microorganisms. They can be used everywhere in our lives. They are used in clean rooms for the production of medical masks, electronic products, semiconductors, etc. And those closely related to our lives are filters for air conditioning, filters for purifiers, fresh air units for HVAC systems, primary return air conditioning units and so on. How to grade and select these filters to ensure our health?
Classification of Air Filters
There are many different types of air filters, involving many international and national standards, each with its own classification and testing methods, which has caused trouble to manufacturers and users.
In the process of communication with customers, when we mentioned the grade of air filters, people said that it was more common to see F, H and U grades, which shows that the filtration efficiency grading of air filters in engineering is still following the European standard grading. With EN 779 being replaced by ISO 16890 and EN 1822-2, EN 1822-3, EN 1822-4 and EN 1822-5 being replaced by ISO 29463, the internationalization process of the air filter industry will be faster.
Test of Air filters
The acceleration of the internationalization process also means the intensification of competition, local protection no longer exists, and enterprises in the industry are on the same competitive platform, then the enterprises with good products and services will have more opportunities.
Throughout the grading of air filters in various standards, the efficiency is used as the basis for grading, with gravimetric efficiency, fractional efficiency, particulate matter efficiency and MPPS efficiency, etc.
There are two main categories of air filters test system:
One is for filters for general ventilation, class F9 and below, including filters for HVAC systems, air filters of road vehicle and etc. Test aerosols including A2 dust, KCl and DEHS, measuring devices are electronic balances and particle counters. Test index including gravimetric efficiency, particulate matter efficiency (ePM1.0, ePM2.5, ePM10.0), air flow - resistance curve, capacity - resistance curve, capacity - gravimetric efficiency curve, etc.
The other is for high efficiency filters (EPA, HEPA and ULPA), i.e. filters with a filtration efficiency of 95% or more, these filters are mainly used in clean rooms, nuclear industry etc. Test aerosols are oil aerosols such as DEHS, PAO, paraffin oil etc. The measuring device is particle counter, which tests the filtration efficiency at MPPS and detect the leakage of class H14 filters and above.
In addition to the above dust or particulate filtration efficiency and resistance tests, photo catalytic filters and activated carbon filters with filtration requirements for gaseous pollutants also require testing of gas filtration performance such as efficiency, capacity and desorption, etc.
While air filters for general ventilation and gas filters for general occasions can be controlled product quality through sampling inspection. HEPA and ULPA filters and filters for special occasions need to be tested individually to ensure that each filter is intact and meet the standard.
Settings of Air filter
There are many types and grades of filters, which is because various types and grades of filters have their own uses. Coarse filters are mainly used for filtering fugitive dust, pollen, fibres, etc. with particle size >5μm; medium and fine filters are mainly used for filtering dust and microorganisms with particle size 0.1~10.0μm; sub-HEPA EPA filters are used for filtering air microorganisms, cigarette smoke, etc. with particle size 0.1~1.0μm; HEPA and ULPA filters can filter all particulate matter and air microorganisms. In practice, the filters are configured according to the specific use. Generally, in order to extend the life of the main filter and improve the filtration effect, coarse and medium efficiency filters will be configured at the front end as pre-filters. Photo catalytic filters and activated carbon filters are also configured to treat gaseous pollutants.
Whether the performance indicators of the air filters meet the standard requirements and whether the different levels and types of filters are reasonably set up in the system is a matter of whether the whole system can protect our health, both of which are equally important.
