Fundamentals Of Filtration Terms To Help You Understand Our Technology Better

Activated Carbon FiltersIt is composite carbon material to remove gases and odors from the air. Gas adsorption filters…
AdsorptionThe trapping of gaseous or vapor contaminants by physical and chemical processes on the surface of a solid filter medium.
AerosolFine liquid or solid particles suspended in air. For example Fog or Smoke. They can be microscopic and less than 1 micron in size. They can chemical or biological and composed of many parts.
AHU*Air Handling Unit
A system comprising of a fan and ductwork in which a filter is placed e.g. heat exchangers, humidifier, etc.
Air Change RateThe number of times per hour the room air volume will pass through the air cleaner or air purifier. A typical air change rate for a well-selected HEPA system would be about 5 Air Changes per hour. ACR can be calculated by dividing the Air Volume Flow Rate M3/hr of the air cleaning unit by the volume of the room in M3.
Air CleanerThe air cleaner typically uses HEPA class filtration to remove ultra-fine airborne particles from the air in a room that may be bacteria or virus and cause infection or chemically toxic when inhaled. It would be used in industrial applications. 2000 and 6000 models are of this type.
Air FilterA device designed to remove suspended particles from air flowing through it.
Air FlowThe volume of air passing through the filter in unit time.
Air ImageComputer presentation software that enables real-time display of particle counter results demonstrating air cleaning performance of air purifiers
Air PurifierThe air purifier uses typically uses HEPA class filtration to remove ultra-fine airborne particles from the air in a room but also has molecular filtration to remove odors and selected noxious gases and fully clean the air. It would be used in office, light industrial and residential applications. City M 300 and 800 Models are of this type.
Air Quality IndexAn index published usually on a daily basis to advise on how much airborne pollution is being monitored and what effect this will have on public health. Commonly experienced outdoor problem pollutants are PM2.5 fine combustion particulates, Nitrogen oxides (NOx), Ozone and Sulphur oxides (SOx).
Others that may be experienced are Volatile Organic Compounds VOC’s. Carbon monoxide. The Clean Air Act and WHO guidelines give information on concentration limits for each pollutant.
Air Volume Flow RateThe Air Volume Flow Rate for an Air Cleaner is usually given in Metres3/Hour although Cubic Feet per minute CFM is sometimes used for older unit measurements or units manufactured in the USA
Airborne ParticlesAirborne particles include smoke, smog, bacteria, household dust, pet dander, mold spores, dust mite debris, and pollen. These particles range in size between 0.3 to 100 microns. Considering that the average diameter of a human hair is 50 microns, these particles are so small that most pass through ordinary furnace filters and return to the air in your home. This can negatively impact your indoor air quality.
AllergenAirborne contaminant that can induce an extreme reaction in a person who has an allergy to that substance. Typical Allergens are pollen, animal hair, skin particles, and bed-mites and can be inhaled or just have skin contact. Anti-Histamines are the usual medication.
AllergyAllergies are an abnormally high sensitivity to certain substances, such as pollen, certain foods or microorganisms. Common indications of an allergy may include sneezing, itching and skin rashes.
ArrestanceA measure of the ability of a filter to remove a standardized test dust from the air passing through it under given operating conditions. Expressed as a weight percentage.
ASHRAEAmerican Society of Heating, Refrigeration and Air Conditioning Engineers who produce comprehensive guidance on air cleaning plant
ASHRAE*American Society of Heating, Refrigerating, and Air-Conditioning Engineers
An industry organization who produce an efficiency standard.
AsthmaA respiratory complaint that can be serious in young and older people and is the result of allergens sometimes airborne causing irritation and swelling in the respiratory system. In extreme cases, it can lead to an increased chance of mortality.
BacteriaSingle-celled organisms that quickly multiply through cell division. Harmful bacteria called pathogens can cause disease, others can be beneficial to humans, animals, and plants.
Bag/Pocket FiltersAn extended surface filter in which the medium is formed into pockets or bags which may be self-supporting or supported by the air flow through them.
Burst PressureAn air flow rate, which exceeds the filter’s maximum pressure and causes it to burst.
Carbon Monoxide (CO)Carbon monoxide is a highly toxic gas that is colorless, odorless and tasteless. It is created by the incomplete burning of natural gas or any other material containing carbon, including gasoline, kerosene oil, propane, coal and wood.
Changeable Filter SystemA filter, which can be recharged with new media panels without having to change the entire frame or housing. Changeable Filter System…
Chemical EmissionChemical emissions are gases or particulates that have been released into the air.
CleanroomA cleanroom is an environment, typically used in manufacturing or scientific research, that has a low level of environmental pollutants such as dust, airborne microbes, aerosol particles and chemical vapours. A cleanroom has a controlled level of contamination that is specified by the number of particles per cubic meter at a specified particle size. Such environments usually require HEPA or ULPA levels of filtration.
CoalescerA filter which removes smaller water droplets from the air.
Coarse DustParticles which are larger than 10 μm and easily visible by naked eye.
Combustion PollutantCombustion pollutants are byproducts of the combustion or burning process. Burning fuels such as coal, oil, gas, and wood produces many pollutants, such as sulfur dioxide, nitrogen oxides and particulates. Combustion also produces airborne emissions and solid waste such as ash and sludge.
Combustion PollutantCombustion pollutants are byproducts of the combustion or burning process. Burning fuels such as coal, oil, gas, and wood produces many pollutants, such as sulfur dioxide, nitrogen oxides and particulates. Combustion also produces airborne emissions and solid waste such as ash and sludge.
Compact FiltersAn extended surface filter in which the medium is pleated (typically into a 2 or 4 V-design) to create a larger filtration area in order to provide a high dust holding capacity.
Concentration(Airborne Particles)Measured in number of particles per cubic Metre of air. For smaller particles of 0.3 to 0.5 micron diameter concentration may vary from less than 1 million per M3 to 1000 million (1billion) in parts of the underground system in central London. A thousand times variation is surprising when the particles are invisible to the unaided human eye.
Deep PleatMedia that has been folded into higher pleating formations using metal separators so that high dust holding capacities can be achieved.
DHC*Dust Holding Capacity – Amount of loading dust retained by the filter up to the final pressure drop.
DiffuserA mechanical device that is designed to distribute the air in a uni-directional way.
DownstreamRoute taken by air after filtration.
Droplet nucleiAirborne particles of about 1 to 4 microns that are the residue after evaporation of expelled droplets. They can carry airborne infection that can be transmitted if they land on eyes or are inhaled by a non-infected person or animal.
DustHousehold dust is composed of a wide variety of particles including dead skin from humans and pets, finely ground plant and insect parts, minute particles of sand and soil, and fabric fibers. Daily activities can stir up dust into the air. Dust can trigger allergic reactions in sensitive people, and can cause sneezing, runny nose and itchy/watering eyes.
Dust Mite DebrisDust mite debris is made up of the excrement and fragments of dust mites.
Dust MitesDust mites are tiny microscopic creatures related to ticks and spiders. Dust mites feed on skin flakes and can be found throughout the home, in mattresses, pillows, carpets and furniture. They produce airborne particles that can trigger allergic reactions or asthma episodes when inhaled by people who are sensitive to them.
EfficiencyThe ratio of the number of particles retained (by the filter) to the number entering it expressed in a percentage.
Electrostatic ChargeStoryThe electrostatic charge of Filtrete air filters acts like a magnet to attract and capture particles that can pass through fiberglass filters or other non-charged pleated filters. A Filtrete filter with electrostatically charged fibers performs better than non-electrostatic filters. The actual effectiveness of an air filter in allergen reduction depends on a variety of factors including the amount of air that the filter processes, the nature of the allergens and the rate at which the allergens are being introduced into the home. Electrostatic filters are most effective when new and clean.
Electrostatic FilterFiltration system using electrically charged plates and an electrically charged thread that will give a charge to the passing particles so these will be attracted by the plates.
Electrostatic PrecipitatorAn air cleaning device that uses an electrical charge to attract airborne dust out of the airstream onto plates. High maintenance, energy and running costs, safety issues and unwanted ozone are reasons why this type of air cleaning device is best avoided.
Energy EfficiencyMinimum use of energy to produce the required clean air is very important. Air purifiers and air cleaners are outstanding in this regard. Typically they use less energy than some light bulbs and they can save energy by supplementing or even replacing some existing ventilation systems.
EPAThe Environmental Protection Agency is responsible in the USA for the regulation and prevention of polluting hazardous wastes, toxic chemicals in both air and water.
EUROVENTTrade association which regulates the HVAC industry through independent testing of manufacturers of filters and other HVAC parts against their claims.
Exhaust AirAir leaving a building.
Face VelocityAir flow rate divided by the face area of the filter expressed in meters/second.
Fibre LossSee Shedding.
Filter AreaThe effective area of media through which the air can pass.
Filter ClassA term indicating a range of filter performance characteristics measured according to procedures in EN 779 or EN 1822.
Filter FramesThe outside section of filter which the media connects to. Available in a variety of different materials to suit each differing application.
Filter HousingsDedicated units to secure the filter in place. Filter housings…
Final FilterThe last filter in a multi-stage filtration system.
Final Pressure DropThe pressure drop up to which the filtration performance is measured for classification purposes. Also the point at which it is recommended to replace the filter.
Fine DustParticles which are between 1 and 10 μm, and hardly visible.
Fine Dust FiltersUsed to separate: PM2.5, soot, cement dust, spores and larger bacteria. Fine dust filters serve either as final filters for HVAC and similar applications, or as prefilters for EPA, HEPA or ULPA filters in ultra-clean environments. Fine dust filters typically feature either a mini-pleated media in variety of frame styles, or are formed into pockets in a bag filter.
Forced Air SystemA forced air system is a heating and cooling system in which air is blown by a fan through air channels or ducts to rooms.
FormaldehydeFormaldehyde is a volatile organic compound (VOC). Potential sources in the home include pressed wood products such as particleboard or fiberboard, smoking, and glues and adhesives
Gas Adsorption FiltersUsed to separate: Gases including volatile organic compounds, odors, and nitrous oxides. Gas adsorption filters typically use an activated carbon media to remove gaseous pollutants from an air flow. This could be to create a pleasant environment by removing odors, or to protect people from noxious gases and prevent sick building syndrome in built-up areas. Activated carbon filters are available in a variety of formats, including combined particle and gas filtration elements that can be installed in standard HVAC housings.
GasketA lip which runs around the front of the filter frame to ensure that no air (and its contaminants) escapes around the side of the filter within the AHU.
Glass Fibre MediaA media made from glass fibre. Possesses low electrostatic charge and is subject to the danger of downstream filter fibre discharge, but has certain applications.
Grease FiltersFilters typically used within kitchens to maintain hygiene standards. Also often a health and safety requirement, these filters collect grease and are usually available in permanent or washable formats.
HEPAHEPA stands for High Efficiency Particulate Air. This is a rating system used by the Department of Energy to denote an air cleaner or filter that is 99.97% efficient or better at removing 0.3 micron-sized particles from the air passing through it.
HEPAFilterHigh Efficiency Particulate Air filter. HEPA filters are made from pleated paper, usually fibreglass. In Europe HEPA filter classification is given by EN1822:2009 the test standard used by filter manufacturers. E10 to U17. The filter is tested to Most Penetrating MPPS
HEPA*High Efficiency Particulate Air A filter with an MPPS of between 85 – 99.995% and rated in the H- class, by EN1822. Also known as absolute filters.
High Efficiency FiltersUsed to separate: Tiny contaminants, such as germs, viruses, carbon black and radioactive particles. EPA, HEPA and ULPA filters can remove up to 99.99999% of particles 0.4 μm in diameter. These high efficiency filters are used to protect people – in applications such as biotechnology and pharmaceutical research, or processes – in the fields such as nanotechnology and microelectronics. High efficiency filters come in a number of shapes and sizes, from sprace-saving panels to high-capacity, deep-pleated filters.
HistamineIs a biological substance produced as part of an allergic reaction that can cause swelling of body parts and restricted airways. It causes irritation, eye watering and running nose. Hay fever is a common manifestation of histamine in action.
HVACHeating, Ventilation and Air Conditioning
IAQ*Indoor Air Quality – The content of interior air.
IncinerableA filter which can be completely destroyed by incineration. Incinerable filters are commonly used for applications which handle hazardous materials that must be destroyed.
Indoor Air Quality (IAQ)People are a main source of larger bio-particles and gas odours. There are also aerosols and VOC’s off-gassing from many materials and products used by people in buildings. A City Check test kit can be used to determine a wide range of indoor sourced molecular contaminants
IrritantAn irritant is a substance that, when breathed in, irritates the airways and can trigger asthma symptoms. Common examples include strong perfumes, cigarette smoke, and fumes from harsh cleaning fluids.
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LCC*Life Cycle Cost The total cost incurred over a filter’s life time. This not only includes the purchase price and installation cost, but also the energy used to drive the fan, disposal and its associated costs. In many cases, a filter with a higher initial purchase price may have a lower LCC than an inferior filter because it places less demand on the fan or simply last longer. We can provide a personalised calculation of the LCC of your installation free-of-charge, please contact us for further information.
LouverA filter which acts as a barrier against water by stopping and then draining liquid away from an application.
Mechanical Air FiltrationThe most effective method of air filtration used by that involves physical removal of the airborne particles from the cleaned airstream. Other methods such as ultra violet light radiation do not remove particles and these can cause subsequent dust deposits with the problems that entails.
Mechanical FiltrationA method of filtration which relies upon the gaps between the fibres of the media being smaller than the particles needed to be stopped.
MediaThe material through which the air passes during filtration.
Media Pads and RollsFilter media which is to be inserted into a filter frame. Typically supplied in either reel form or cut-to-size.
MicronA micron is one thousandth of a millimetre and is used to measure the size of dust. Particles below 10 microns in diameter cannot be seen unaided by the human eye. A human hair is about 50 microns in diameter.
Microparticle Performance Rating (MPR)The 3M MPR (Microparticle Performance Rating) reports a filter’s ability to capture tiny particles between 0.3 and 1 micron in size.
MicroparticlesMicroparticles are tiny airborne particles measuring between 0.3 and 1.0 micron. These include fine dust, smoke, smog, bacteria and some pet dander and pollen particles.
MigrationMovement of collected dust in the filter media in the direction of the air flow.
Mini PleatMedia that has been folded into smaller formations so it possesses excellent filtration characteristics.
Mold SporesMold spores are generated from mold, which is a fungus that grows in humid conditions. These spores can produce allergic reactions.
Molecular FilterAn air cleaning device that permits air to pass through but stops molecular contaminants and certain contaminant gases.
Most Penetrating Particle Size MPPSThe particle size that penetrates a filter medium at minimum particle stopping efficiency.
MPPS*Most Penetrating Particle Size – The maximum particle diameter which will penetrate through the filter medium.
Negative IonsCharged molecules that are found in certain environments and are sometimes attributed to a feeling of stimulation when inhaled. However they are also produced by Ozone and this can be unhealthy.
Non-electrostatic FiltersNon-electrostatic filters include 3-month pleated, washable and fiberglass filters that do not have electrostatically charged fibers. Filtrete 1″ and 4″ residential filters with electrostatically charged fibers have been proven to perform better than 1″ and 4″ residential non-electrostatic filters
OffGassingThe production of gases from the chemical aging of a material over time. Commonly measured contaminants are Aldehydes and VOC’s. See VOC’s Below
Operating TemperatureThe temperature in which a filter is able to operate.
Outdoor AirAir which has yet to go through any kind of application.
OzoneOzone is a form of oxygen often produced by ultra violet light radiation and is highly unstable and reactive. It can be unhealthy when inhaled and so sources that produce Ozone are best avoided.
Paint Spray FiltersUsed to separate: All types of contaminants, including water, dust, fine particles and paint overspray. A flawless finish, free from imperfections can only be achieved in an environment that’s free from imperfections too. Paint spray filters remove the contaminants that can ruin your work.
Panel FiltersFilters consisting of flat or pleated media packs surrounded by a frame (usually cardboard, plastic or metal).
Parasitic CystsParasitic cysts are egg-like sacs formed by the larva of a parasite. Sometimes found in unfiltered tap water, parasitic cysts can cause serious gastrointestinal infection and illness if consumed.
Particle CounterInstrument used to count numbers of airborne particles in and give a concentration. Some instruments are capable of measuring a range of particle sizes and thereby give a distribution profile at a given time.
Particulate Air FilterAn air cleaning device that permits air to pass through but stops airborne particles.
PathogenAn organism that has the ability to cause infection and disease that can in the extreme cases be fatal.
Pet DanderPet dander is made up of shed animal skin cells and dried saliva. It is extremely lightweight and tiny (approximately 2.5 microns in size) and can stay airborne for hours before settling on surfaces. Pet dander can be problematic for people sensitive to pet dander. If they are allergic to dander, it can worsen breathing problems.
Pleated/PleatsFilter media which is formed into homogenous shapes.
PM 2.5In air cleaning using filtration PM2.5 can be regarded as airborne Particulate Matter 2.5 microns and below in size. In city areas with traffic it mainly comprises fine combustion particulate that is extremely damaging to health when inhaled.
PollenPollen is made up of light, dry protein particles from trees, grasses, flowers and weeds. It is carried by the wind and can a potent stimulator of allergic reactions.
Power Generation FiltersUsed to separate: All types of contaminants, including sea salt, water, dust, sand and fine particles. Power generation air filters protect equipment like gas turbines from airborne contaminants that can cause fouling or damage. With clean intake air, turbine performance is improved and downtime for cleaning or repair is significantly reduced.
PrefiltersUsed to separate: Corase dust like insects, textile fibers, hair, sand, airborne ash, and pollen. Prefilters are typically the first stage in a filter system and protect higher-quality, fine dust filters from becoming clogged or damaged by corase dust. Prefilters come in a variety of shapes and sizes; from rolls of filter media, which provide a cost effective first filter stage, to pleated panel filters that pack large filters areas into a compact frame.
Pressure DropThe difference in pressure between two points immediately upstream and downstream of a filter carrying an air flow. Also known as the resistance or differential pressure.
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RadonRadon is a colorless, odorless gas that seeps up from the earth. It is created by the natural decay of uranium in the earth, and exists naturally in many locations. Radon may present a serious health risk when it accumulates in basements or crawl spaces beneath homes.
Recirculation AirAir which has been through an application or AHU, and is to be re-used.
Relative HumidityThe level of humidity in which a filter can operate. Expressed as a percentage of the maximum amount of water vapour that could be present if the vapour were at its saturation conditions.
Safe Change SystemA filter housing that is sealed to allow the filters to be changed inside a protective system which eliminates the opportunity for any of the captured particles to be released into the surrounding environment. Particularly used in the filtration of harmful, toxic and radioactive substances in nuclear, biological and chemical applications. NSC Safe Change System…
SealantA material used to seal the gaps within a filter, e.g. when attaching the media to a frame.
SedimentSediment is solid material that settles to the bottom of a liquid. In unfiltered tap water, sediment can be composed of soil, silt, sand and minerals
Service LifeThe length of time before a filter reaches the recommended final resistance and must be changed or cleaned.
SheddingThe release of previously collected particles or fibres from the filter into the downstream air flow.
Sick Building SyndromeA condition frequently attributed to buildings and is due to build up of indoor sourced air pollutants and poor ventilation. Air purifiers can be used to tackle these problems economically at point of need.
SmogSmog is the most visible form of air pollution. It is a brownish-yellow, hazy cloud caused when heat and sunlight react with various pollutants emitted from industry, cars, pesticides and oil-based home products. The word “smog” is a combination of the words smoke and fog.
SmokeSmoke can be generated by cigarettes, cigars, wood burning stoves and fireplaces. In addition to several known carcinogens, smoke can contain fine particles composed of wood tars, gases, soot and ashes. While it can cause the typical allergic reaction like sneezing and runny nose, exposure to smoke can also cause burning eyes, bronchitis and even trigger asthma attacks to people who are sensitive.
SporeA reproductive form of microorganism that remains dormant until it finds the right environmental conditions of warmth, moisture and a food source to activate
Suspended MatterParticles smaller than 1 µm and invisible to the naked eye.
Synthetic MediaA media made from a polymer material. Used for is electrostatic characteristics and the vast array of differing materials available.
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ULPA*Ultra Low Penetration Air – Filters with an efficiency greater then 99,9995 % for MPPS.
ULPACATS*ULPA Computer Aided Test System A highly specialised method of testing the effectiveness of ULPA filters. A test aerosol, like DEHS is emitted into the up stream air flow to measure the amount of particles still present downstream, once it has passed through the filter by using laser particle counters on both sides.
Ultra Violet light (UVC)Ultra Violet light can be used to sterilise deposited bio-particles on surfaces and biofilms but cannot remove airborne particles from a moving airstream. The energy required to irradiate and sterilize particles in a moving building ventilation airstream makes this technology currently uneconomic and therefore ineffective to use for this purpose.
Uni-directional FlowA controlled air flow in a specified direction and continuous velocity in approximately parallel, low turbulent streamlines (also see Laminar Flow above).
VirusAn infectious organism that exists as a microscopic particle until it finds a host cell
Volatile Organic Compound (VOC)A VOC is a compound that vaporizes at room temperature. Common sources that may emit VOCs into indoor air include cleaning and maintenance products, and building and furniture materials. In sufficient quantities, VOCs can cause eye, nose and throat irritations, headaches, dizziness, visual disorders and memory impairment. Some VOCs are known to cause cancer in animals, and some are suspected of causing, or are known to cause, cancer in humans. At present, not much is known about what health effects occur at the levels of VOCs typically found in public and commercial buildings
World Health OrganisationWorldwide Health Body that gives a true international view on health issues that is usually less biased than some national bodies.
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