|Filter Grade||EU Grade||Efficiency/Arrestance||Filter Types||Typical Applications|
|G3||EU3||80-90% Arrestance||Panel Filters||Medium level pre-filtration. Simple ventilation for garages & factories.|
|G4||EU4||90% Arrestance||Pleated Panel Filters,
|Higher level pre-filtration. Air-conditioning of paint booths & kitchens.|
|M5 (F5)||EU5||40-60% Efficiency||Bag Filters||Air-conditioning of restaurants, gyms, shops & workshops.|
|M6 (F6)||EU6||60-80% Efficiency|
|F7||EU7||80-90% Efficiency||Bag Filters,
Pleat Pack Filters
|Air-conditioning of schools, offices, theatres, computer rooms & spray booths.|
|F8||EU8||90-95% Efficiency||Bag Filters,
Pleat Pack Filters
|Air-conditioning of clean rooms, pharmaceutical, animal health & laboratories.|
|H10||EU10||> 95% Efficiency @ 0.3 µm||HEPA Filters||Highly effective against bacteria & smokes. Used in operating theatres, pill production, electronics & sterilisation applications.|
|H13||EU13||> 99.997% Efficiency @ 0.3 µm||HEPA Filters||Highest air quality applications. Used in sterile areas, class 1000 clean rooms, bacteriological, animal health & isolation.|
In the past air filtration systems in offices and schools were designed primarily to protect the HVAC equipment and reduce the need for equipment cleaning.
In recent years the focus has been on the issue of indoor air quality and the effects of airborne contaminants resulting in higher absenteeism and increased sickness. This has meant building and facility managers have felt increasing ethical and legal pressures to provide improved quality indoor air for their occupants. Air filtration systems now aim to capture as many as the suspended airborne contaminants as possible.
Air filters are graded according to their ability to remove particles from the airstream. Facility Managers should balance air filtration efficiency with the operating cost of powering the system.
Pressure drop is an important consideration, it is the measurement (in Pascals or inches wg) of the decrease in airflow (i.e. resistance) through the filter. Pressure drop is affected by the filter efficiency, dust loading and fan velocity. The higher the grade, the higher the pressure drop across the surface of the filter. Additionally, as the filter becomes loaded with particulate, the pressure drop increases resulting in decreased airflow.
It may appear that higher grade filters have higher operating costs, however most buildings operate variable flow systems with fans operating at less than 100% volume and the difference between medium and fine grades will be less at lower volumes and airflows.
It is more important that air filters be selected based on building location, occupancy, air quality issues and type of system in operation. G4 grade pleated panels along with F7 grade 85% efficiency bag filters, recommended for the school environment, both have clean filter pressure drops of <70 Pa, which can be handled by most existing air handling systems.
More expensive HEPA filters are very high efficiency filters, from 95% at 0.3 microns to 99.9999% at 0.12 microns. HEPAs are widely used to control allergens and microbes in hospitals & laboratories along with sensitive manufacturing.
All filters need replacing. Filter life depends on the amount of particulate being captured. Inner city polluted areas will saturate filters far quicker than the cleaner air countryside. As filters become contaminated they actually filter better, as the airways through become increasingly constricted. There is a limit though, all filters have a final recommended pressure drop for replacement. Failure to follow this may result in filter blow-out, causing damage to the system. As a general rule-of thumb filters should be regularly checked and replaced every 6-12 months.