Air Filters Glossary
Activated Carbon Filters
Utilise a composite carbon material to remove gases and odours from the air.
AHU
(Air Handling Unit) A system comprising of a fan and ductwork in which a filter(s)
is placed.
Air Flow
The volume of air passing through the filter
Air Filter
A device designed to remove suspended particles from air flowing through it.
Arrestance
A measure of the ability of a filter to remove a standardised test dust from the
air passing through it under given operating conditions. Expressed as a weight percentage.
Bag/Pocket Filters
An 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.
Baffle
Plate or vane used to direct or control movement of fluid or air within a confined
area.
BS EN 13779:2007
British Standard in Ventilation and room-conditioning for non-residential buildings
BSI
British Standards Institution relating to the provision of standards across management
systems, business improvements and regulatory approval.
Chemisorption
Removal of gases from an airstream by the chemical reaction of gas with an impregnant
on the surface of or distributed throughout the filter.
Compact Flters
An 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.
Deep Pleat
Media 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.
Dust Holding Capacity
The amount of dust held by a filter to its recommended final pressure drop.
Efficiency
The ratio of the number of particles retained (by the filter) to the number entering
it expressed in a percentage.
Electrostatic Filter
Filtration 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.
Eurovent Certification
A pan European scheme that guarantees participating companies air filter performance
to EN779, using a system of continuous monitoring and testing.
Face Velocity
Air flow rate divided by the face area of a the filter expressed in meters/second.
FETA
Federation of Environmental Trade Associations – UK body that represents the interests
of manufacturers, suppliers, installers and contractors within the heat pump, controls,
ventilating, refrigeration and air conditioning industry
Filter Area
The effective area of media through which the air can pass.
Filter Class
A term indicating a range of filter performance characteristics measured according
to procedures in EN 779 or EN 1822.
Filter Housings
Dedicated units to secure the filter in place.
Final Pressure Drop
The 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.
Gasket
A 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 Media
A 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 Filters
Filters 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.
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.
HEVAC
Heating, Ventilation and Air Conditioning Manufacturers Association.
IAQ
(Indoor Air Quality) The content of interior air.
ISO
International Organisation for Standardisation
LEV
Local Exhaust Ventilation. HSG54 – relates to guidance on the maintenance, examination
and testing of LEV, commonly used to control the release of hazardous airborne substances
in the work environment.
Magnehelic
Trade name for a diaphragm-activated gauge that measures resistance to air.
Media Pads and Rolls
Filter media which is to be inserted into a filter frame. Typically supplied in
either reel form or cut-to-size.
Mini Pleat
Media that has been folded into smaller formations so it possesses excellent filtration
characteristics.
MPPS
(Most Penetrating Particle Size) The maximum particle diameter which will penetrate
through the filter medium.
OEMs
Original Equipment Manufacturers
Panel Filters
Filters consisting of flat or pleated media packs surrounded by a frame (usually
cardboard, plastic or metal).
Pleated/Pleats
Filter media which is formed into homogenous shapes.
PPI
Pores per Inch. A measurement of the porosity of foam materials.
Pre-filter
Used in multi-stage applications to remove larger particles. Pre-filters often protect
the more efficient filters found in the next stage and extend their life time.
Pressure drop - final
Pressure drop up to which the filtration performance is measured for classification
purposes.
Pressure drop - initial
Pressure drop of the clean filter operating at its test air flow rate.
Safe Change System
A 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.
Synthetic Media
A media made from a polymer material. Used for is electrostatic characteristics
and the vast array of differing materials available.
ULPA
(Ultra Low Penetration Air) Filters with an efficiency greater then 99,9995 % for
MPPS.
