AIR FILTRATION TECHNICAL SECTION - General

GLOSSARY OF COMMON AIR FILTER TERMS

Absorption – a process by which a liquid or gas is taken into a porous substance and is held there.

Adsorption – a process by which gases chemically react with a solid surface and become entrained (held) there.

Agglomeration – the process in which particles of a smaller size bind together and behave as a larger particle.

Air – the mixture of gases and particulate matter found in our atmosphere. It is composed of 78% nitrogen, 21% oxygen and 1% other gases and particulate matter.

Air change – a measure of the volume of air moving into and out of a space as a function of time.

Air conditioning – the process in which the physical conditions of the air within a space is maintained to a desired quality by controlling its temperature, humidity, cleanliness and motion simultaneously.

Air filter – a device for removing particulate matter from an airstream.

Air flow – the quantity of air that passes through a given area at a stated velocity.

Aerosol – a suspension of a solid or a liquid particle in the air.

Arrestance - a measure (expressed as a percentage) of the ability of a filter to remove a synthetic test dust from the air. The test dust used in this application was designed to simulate the typical composition of dust found in an HVAC system.

AS1324 - Australian Standard "Air filters for use in general ventilation and airconditioning.  The standard by which air filters should be tested in Australia. Unfortunately, no independent NATA certified laboratories exists that are certified to test to this standard.  As such, AS1324 is not an adequate way of determining a filters performance.  All filters should be tested independently to either the American standard ASHRAE 52.1 or 52.2 or the European Standard EN779.  It should also be noted, that according to AS1324 a filter media is not required to undergo a fire resistance test, as is the case in Europe and America as well as more of the rest of the world (see our short video filter Media Fire Classification Demonstration Video to see how this affects a filters characteristics)

ASHRAE – American Society of Heating, Refrigeration, and Air-Conditioning Engineers.

ASHRAE 52.1 - The ASHRAE testing method for air filters that classifies filters according to average performance data.  Results of ASHRAE 52.1 and EN779 (see below) are equivalent, and their classifications can be considered as the same. See Air Filter Ratings and Test Methods Around the World for further information.

ASHRAE 52.2 - The ASHRAE testing method for air filters that classifies filters according to minimum performance data.  Results of ASHRAE 52.2 are expressed as Minimum Efficiency Reporting Value (MERV) ratings.  This is widely considered to be the best method for assessing filtration performance as it is based upon minimum performance not average performance (as is the case for ASHRAE 52.1 and EN779). See Air Filter Ratings and Test Methods Around the World for further information.

Bacterium – single celled organism ranging from beneficial to harmless to deleterious to lethal to human health.

Bacteria – plural form of bacterium

Brownian Movement – the irregular movement of particles suspended in either an aerosol or fluid. The irregular movement is caused by the impaction of the small particles with other particles and molecules present.

CFM – Cubic Feet per Minute. 1 CFM = 0.471947 litres per second (l/s)= 0.000472 metres cubed per second (m 3/s) = 1.699011 metres cubed per hour (m 3/h)

Clean room– a confined space in which the concentrations and size of airborne particles are carefully controlled.

Contaminant – an unwanted substance that may reduce the quality of the air.

Denier – a measurement of weight of a given length of fibres. Denier can be used to indicate the thickness of fibres with specific gravity.

Differential pressure – the resistance of a device to the flow of a fluid through it. The pressure drop of a filter is a measure of the resistance the filter has to the air flow through it. Differential pressure is directly proportional to the air velocity at which it is measured.

Diffusion media – filter media that is constructed to create an even flow of air through it. Commonly used in paint spray booths (see Peregrine Industries Filter Training Manual (industrial applications) – Paint Spray Booths for further information).

DIN – the German Institute for Standardization (Deutsches Institut fur Normung e. V.). This Institute establishes standards for testing and classifying filters.

DOP – Dioctlyphthalate (diethylhexylphosphate). An oily liquid used in aerosol form for leak testing of HEPA filters.

Dust Holding Capacity – a measurement of the quantity (in grams) of AHSRAE arrestance test dust that a filter will hold when it is at its final tested pressure.

Dust Spot Efficiency – a measurement (in percentage) of the ability of a filter to remove the staining portion of atmospheric dust from the test airstream. Officially titled ASHRAE atmospheric dust spot efficiency.

Electronic Air Cleaner – a two-staged electrically powered filter. In the first stage the particles are electrically charged, and in the second they are removed from the airstream.

Electrostatic precipitators - an electronic air cleaner that uses a strong electric field (50 to 100 kV) to charge the dust laden air as it passes through. This causes the particles to be attracted to oppositely charged collection plates so that they can be removed from the airstream. These devices are primarily used for stack gas cleaning, and frequently produce ozone in the process.

Electrostatic filters – a mechanical filter where collection efficiency is assisted by the development of an electrostatic charge on the media by other means than a continuous external power source. The electrostatic charge may be imposed on the fibres as the air flows through the media, or it may be imposed on the media at the time of manufacture.

EN 779 - The Eurovent (European testing authority)testing method for air filters that classifies filters according to average performance data.  Results of ASHRAE 52.1 and EN779 (see below) are equivalent, and their classifications can be considered as the same. See Air Filter Ratings and Test Methods Around the World for further information.

Eurovent  - European authority that certifies the performance ratings of air-conditioning and refrigeration products according to European and international standards.

Exhaust filtration - a filtration system used on the exhaust air to prevent or limit the emissions produced by equipment or process.

Exhaust air – air that is removed from a space and not returned.

Face area – the area of a filter through which the air enters through.

Face Velocity – the velocity at which the air is traveling as it enters the filter.

Filter, air - a device used to remove airborne contaminants from an airstream.

Filter media – the material used in a filter that makes up the filter element.

FPM – feet per minute. Used to measure velocity. 1 FPM = 0.00508 metres per second (m/s).

Gas – is any material that exists as a state of matter that will expand to fill the container in which it is placed.

Housing/Holding frame – the device used to hold the filter in place during its service life.

Header frame – the part of the face of a pocket or bag filter used to secure the filter to the holding frame.

HEPA – High Efficiency Particulate Air filter.  A HEPA filter must achieve a minimum efficiency of 99.97% to 0.3 micron particles to be called a HEPA as per ASHRAE standards.  Unfortunately in Australia we commonly refer to any filter with an efficiency of greater than 85% as a HEPA filter which was correct under EN1822 but this has been revised to change the old H10, H11 and H12 classes to be F10, F11 and F12.  This change would then clear up the use of the term HEPA for these classes of filters.

IAQ – Indoor Air Quality.

Impingement – the process by which particles are removed from the airstream by their inertia causing them to impact upon a filter’s fibre or other collection surface.

Inches of water gauge (in.w.g.) – a unit of measurement of pressure. 1 in.w.g. = 249.082 pascals (Pa).

Inertia – the property of matter whereby it continues in its current state of rest or in a straight line along its current path until acted upon by an external force.

Inorganic – compounds whose composition do not contain carbon.

Interception – the process by which a particle is removed from the airstream as it follows the air path around a fibre. As the particle comes in contact with the fibre it remains “stuck” there due to the van der Waals forces acting upon it until a greater force acts to break the attractive bonds between the fibre and the particle.

Laminar flow - the uniform flow of air in straight, non-turbulent, fashion in one direction through a space.

Laser Particle Counter – a device used to measure the size and quantity of airborne particles within an airstream.

Litre (l) – a unit of measure used to measure volume. 1 l = 0.001 cubic metre (m 3)

Magnehelic – a propriety brand name of an instrument used to measure resistance.

Make-up air – the air supplied to a building to replace the exhausted air.

Manometre – instrument used to measure the pressure of gases and vapours.

Media area – Gross: the total area of media used in the production of a filter. Net: the total area of useable media in an air filter.

Media velocity – the velocity at which the air is travelling when is enters the air filter media.

Membrane filter – a solid continuous film of material that has microscopic pores of controlled size.

Microbe – a microscopic single-celled organism.

Micron (micrometre) - one millionth of a metre ( mm). Equal to 1/25,400 th of an inch.

Mould – a fungus that grows on damp decaying organic matter.

Odour – a gas which stimulates the olfactory senses.

Organic – molecules that contain one or more carbon atoms.

Ozone – a gas with molecules consisting of three oxygen atoms (O 3). Ozone is a know toxin that has adverse effects on the Human respiratory system.

Pascal – a unit of measurement used to quantify pressure. 1Pa = 0.00401in.w.g. = 9.869 x 10 6 Atmospheres.

Penetration – a measurement (in percentage) of the material of concern that passes through the air filter.

Pressure Drop – the resistance of a device to the flow of air through it. This pressure drop is a measure of the resistance to airflow of the device (measured in Pascals).

Rated filter capacity – the specific quantity of air that is recommended by an air filter manufacturer to be handled by the air filter.

Recirculated air – air that has been taken from the space, reconditioned, and returned back into the space.

Resistance – a measurement of the force required to push air through an air filter at a given air velocity. Measured in Pascals.

SBS – Sick Building Syndrome.

Smog – a mixture of gases and aerosols generated from a variety of sources. Smogs are harmful to the Human respiratory system.

Smoke – an aerosol of particles caused by the incomplete combustion of a substance.

SULPA – Super Ultra Low Penetration Air filter.

Supply air – a mixture of recirculated and outside air which has been conditioned and delivered into the space. This can be 100% recirculated air, or 100% outside air, or any mixture of the two.

Tackifier – a substance applied to a filter media that has an adhesive quality to it. It can assist the air filter media in keeping the dust particles entrapped within the air filter.

ULPA – Ultra Low Penetration Air filter.

Van der Waals forces – the weak electrostatic forces of attraction between molecules.

Ventilation – the introduction of outdoor air into a building by mechanical means.

Visible particle size – any particle of a size that it can be seen with the naked eye. Any non-light emitting particle of a size greater than 100 mm is visible to the naked eye. Particles smaller than 100 mm that are light emitting (light that is of a wavelength that is detectable to the human eye), or have high reflective properties can be detected by the human eye under certain conditions.

Virus – a microscopic particle composed of nucleic acid (either DNA or RNA) encased in a protein. Viruses replicate by entering a cell, releasing their nucleic acid, and thus taking over the control of the cell. It can manufacture (replicate) itself and then invade more cells. In doing this the cells it invades are usually killed.

VOC – Volatile Organic Compound.

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