Filter Arrestance and Efficiency

Air filter efficiency and arrestance

Efficiency and arrestance are commonly used to describe air filters functionality.

Air Filter Efficiency

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

μ_e = n_t / n_u = (n_u - n_d) / n_u (1)

where

μ_e = air filter efficiency

n_t = particles trapped

n_u = particles upstream

n_d = particles downstream

Air Filter Arrestance

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

μ_a = 1 - C_a / C_b (2)

where

μ_a = dust arrestance

C_a = dust concentration after filter

C_b = dust concentration before filter

• Particle Sizes - Sizes of airborne particle as dust, pollen bacteria, virus and many more

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