Air Filters - Arrestance and Efficiency
The mission of an air-filter is to remove particulate or gaseous materials from the air-stream and efficiency and arrestance are used to describe filter functionality.
Air Filter Efficiency
Efficiency describes how well an air filter removes microscopic particles - such as dust, dust mites, pollen, mold, bacteria, and smoke.
In the ASHRAE 52.1 Standard test method, efficiency is a measure of ability to remove the staining portion of atmospheric dust from test air - officially termed "Atmospheric Dust Spot Efficiency".
Air filter efficiency can be expressed as
μe = nt / nu
= (nu - nd) / nu (1)
where
μe = air filter efficiency
nt = particles trapped
nu = particles upstream
nd = particles downstream
Air Filter Arrestance
Arrestance is a measure of the ability of an air filtration device to remove synthetic dust from the air.
The arrestance describes how well an air filter removes larger particles - such as dirt, lint, hair, and dust. ASHRAE arrestance is a measure of the ability of a device to remove ASHRAE dust from test air.
The dust holding capacity of a filter is the amount by weight of standard dust the filter will hold without exceeding the resistance 0.18 in W.G. for low-resistance filters or 0.50 in W.G. for medium-resistance filters and 1.0 in W.G. for high-resistance filters.
Filter dust arrestance can be expressed as
μa = 1 - Ca / Cb (2)
where
μa = dust arrestance
Ca = dust concentration after filter
Cb = dust concentration before filter
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Related Documents
Particle Sizes
The size of dust particles, pollen, bacteria, virus and many more.
Porosity
Volume not occupied by solid material.
Ventilation Filters
Classification of air filters used in ventilation systems.