We have a lot to thank the humble air filter for, says Thomas Klamp.
The quality of the air we breathe has a profound impact on the quality of our lives and yet it is something we tend to take for granted. This is particularly surprising given that we spend up to 90 per cent of our lives indoors.

The health effects from indoor air pollutants can include irritation of the eyes, nose, and throat; headaches; dizziness and fatigue, and exposure to poor indoor air quality can result in more serious conditions such as asthma, hypersensitivity pneumonitis and humidifier fever.

The main barrier to these pollutants and the primary guardian of indoor air quality is the humble air filter. Air filtration is the most important procedure in a ventilation system and depending on the filtration requirements, there are different types and groups of filters.

Standard particulate filters are coarse and fine dust filters for removing contamination from the air in air conditioning and ventilation systems as well as in process technology.

Classification and testing of these filters is according to European standard EN 779:2002 'Particulate filters for general ventilation - Determination of the filtration performance'.

With standard FprEN779-2011 (final draft) there will be some changes to this standard to make the requirements on filters even tougher. The new filter group M with filter classes M5 and M6, for example, will replace the current filter classes F5 and F6. Furthermore an additional classification criteria, the new minimum efficiency requirement for F7, F8 and F9 filters will ensure that poorer quality filters will be not be acceptable in this sector of the market. This change will revolutionise the classification of fine dust filters.

While EN 779 classifies air filters by their average particle efficiency, the importance of energy efficiency leads to the EUROVENT 4/11 guideline 'Energy Efficiency Classification of Air Filters for General Ventilation Purposes'. This guideline defines a method of classifying air filters with regard to their level of energy efficient operation. Filter manufacturers who voluntarily take part in the EUROVENT Filter Certification program have to have annual tests on four randomly chosen fine dust filters. These tests are carried out by independent institutes to ensure customers' confidence in a high level of product quality.

High efficiency particulate filters are used for the most demanding requirements in terms of air purity and hygiene. They are critical in the separation of aerosols, toxic bacteria and particles from the air in ventilation systems in areas such as clean rooms or operating theatres as well as in research or production facilities. The testing and classification of efficient particulate air filters (EPA), high efficiency particulate air filters (HEPA), and ultra low penetration air filters (ULPA) is according to EN 1822. This standard defines a method for testing the filtration efficiency on the basis of particle counting using a liquid test aerosol thus allowing a uniform classification of high efficiency particulate filters to ensure a very high quality.

There is a great variety of air filters available for special applications and, as 85 per cent of the costs that are generated by an air filter arise from the energy used during the operation of the ventilation system, it is important to carefully select the design and material of the filter to guarantee a lower pressure drop and thus lower energy costs. TROX has, for example, developed a filter manufacturing technique that enables the optimisation of air filters to the customers' technical requirements with respect to filter performance, air flow rate and pressure loss.

Associated filter housings are also available for different installation situations. One example is the TROX ducted HEPA filter unit which can be used in areas that require pure air such as in the pharmaceutical industries.

This unit can be installed as a single unit or in a combination of four or more adjacent filter units. An important aspect of this filter unit is that the soiled filter elements can be easily removed from the casing and safely disposed of.

•Thomas Klamp is product manager - filter technology at TROX