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Engineering ToolBox > Filter Arrestance and Efficiency
Efficiency and arrestance are commonly used to describe air filters functionality.
The ability of a device to remove particulate or gaseous material from an airstream by measuring the concentration of the material upstream and downstream of the device.
The efficiency describes how well of 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 the ability of a filter to remove the staining portion of atmospheric dust from the 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
A measure of the ability if 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 that the filter will hold without exceeding the resistance 0.18 in W.G. for low-resistance filters, 0.50 in W.G. for medium-resistance filters and 1.0 in W.G. for high-resistance filters.
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