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Air filter
An air cleaning device that removes particulate contamination from an airstream by straining, impingement, interception, electrostatic attraction or absorption.
Air Filtration
The process of removing particulate
material from an air stream.
Air
Handler
The blower, filter, cooling
coil, and housing parts of an HVAC system.
Aerosol
Particles in a gas suspension.
Arrestance
A measure of the ability of an
air-filtration device to remove synthetic dust from the air. The
percentage weight of ASHRAE dust caught by the filter compared to the
total weight of dust fed into the filter throughout the filter test.
ASHRAE
American Society of Heating,
Refrigerating and Air Conditioning Engineers
ASHRAE
52.1
Test standard for filters that
measures pressure drop, arrestance, dust
spot efficiency, and dust holding
capacity.
ASHRAE
52.2
Test standard that measures
the fractional particle size efficiency of a filter
and assigns a MERV depending on the particle size
efficiency in three different particle size ranges.
Atmospheric
Dust Spot Efficiency Test
ASHRAE
52.1 Standard test method that measures the ability of a filter to
remove the staining portion of the atmospheric dust from the test air.
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Bacteria
Single-celled microorganisms
ranging from harmless and beneficial to intensely virulent and lethal.
Range in size from ~0.2 microns to ~2 microns.
Bioaersols
Airborne microbial
contaminants, such as a viruses, bacteria,
fungus, algae, or protozoa, or particulate
material associated with one of these microorganisms.
Blower
(Fan)
An air handling device (fan)
for moving air under pressure in an air handler.
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CFM (Cubic Feet per Minute)
Unit of measure of the volume
rate of airflow.
Cooling
Coils
A cooling element through
which treated gas or liquid is passed, exchanging thermal energy with
the air surrounding it for purposes of heating or cooling.
Commercial Airflows
The airflow (between 300 and 500 FPM)
at which most non-residential, non-HEPA HVAC systems are designed to
operate.
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Dander
Skin cells or organic matter from cats, dogs, mice,
dust mites, cockroaches or other animals.
Diffusion
Filter collection mechanism that occurs when the random
(Brownian) motion of a particle causes that particle to contact a fiber.
See also Inertial Impaction, Interception,
and Electrostatic Attraction.
DOP
Dioctlyphthalate (diethylhexylphosphate), an oily
liquid used in aerosol form as a challenge for efficiency and leak
testing HEPA filters.
Duct
Round or rectangular conduit through which air is
carried from a central air conditioning system to various spaces in the
building.
Dust
An aerosol of particles of any solid material, usually
with particulate size less than 100 microns.
Dust Holding
Capacity (DHC)
Amount of dust a filter can hold until a specified pressure
drop is reached. Provides information about the expected life of the
filter.
Dust Spot Efficiency
See atmospheric
dust spot efficiency test.
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Efficiency
The ability of a filter to remove particulate
material from an air stream. Expressed as a percentage.
Electronic Air Cleaner (EAC)
A device that uses the principle of electrical
attraction, like a magnet, to collect airborne pollutants. As particles
in the air stream approach the unit, a pre-charging section on the EAC
gives them a positive charge. The charged particles then pass between a
series of alternating plates, or electrodes. One of the series of plates
has a positive charge and the other has the opposite charge. The plates
with the positive charge repel and deflect the particles to the
oppositely charged plates, where they are attracted and collected.
Electrostatic
Attraction
Filter collection mechanism in which particles are
attracted to and retained on fibers using electrostatic
forces. See also inertial impaction,
interception, and diffusion.
Electrostatic Forces
Also called Coulombic forces, hold almost everything
together. Electrostatic Forces work in much the same way as magnetic
forces –
like forces repel and unlike forces attract.
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Face Area
The area of an air filter perpendicular to the flow of
air through it.
Face Velocity
Velocity of the air as it approaches the filter face.
See also media velocity.
Filter
Medium
The
part of an air filter that provides filtration. Materials include
non-woven synthetic fibers, acrylics, activated carbon, aluminum mesh,
electrostatic fabric, paper, polyurethane foam, polyester and
poly/cotton composites. Also known as filter media.
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HEPA (High
Efficiency Particulate Air) Filter
A specialized mechanical
filter capable of removing 99.97% of particulates
0.3 microns in diameter as defined in AS 4260 and EN 1822.
HVAC
Heating, ventilating and air conditioning systems used
to regulate indoor air comfort.
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Inertial
Impaction
Filter collection mechanism that occurs when a particle
traveling in the air stream deviates from the air stream's normal path
around the fiber and instead (because of particle inertia), collides
with a fiber. See also, interception,
diffusion, and electrostatic
attraction.
Interception
Filter collection mechanism that occurs when a large
particle, because of its size, collides with a fiber in the filter.
See also inertial impaction, diffusion,
and electrostatic attraction.
Ionization Electrode
A thin metal component that when electrified, can
generate negative or positive ions.
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Laminar Airflow
Streamlined airflow in which the entire body of air
within a designated space moves with uniform velocity in one direction
along parallel flow lines. In the context of a building's air space, the
smooth, non-turbulent flow of air through the air
handlers.
Legionnaire's
Disease
Legionnaires Disease (and Pontiac Fever) is caused by
the Legionella pneumonia, which means "lung-loving."
Outbreaks have occurred after persons have breathed mists that come from
a water source (e.g., air conditioning cooling towers) contaminated with
Legionella bacteria. Persons may be exposed to these mists in
homes, workplaces, hospitals, or public places.
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Manometer
Instrument for measuring the pressure of gases, vapors
and liquids.
Mechanical Filter
A device consisting of a flat or pleated mat of fibers
that remove particles from the air passing through them by impaction,
interception and diffusion
Media
See Filter Media.
Media Velocity
Velocity of the air as it moves through the filter
media. The airflow (in CFM) divided by the effective media
area in ft2. See also face
velocity.
MERV (Minimum Efficiency
Reporting Value)
A numerical system of rating filters based on a minimum
particle size efficiency. A rating of 1 is least
efficient; a 16 is the most efficient. See also ASHRAE
52.2.
Micron
One millionth of a meter. A micron is also known as a
micrometer (µm).
Mold
A fungus that grows on damp decaying organic matter. It
is characterized by a fuzzy mat surface.
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Negative Ion Generator
An ion generator that can be used for air cleaning
purposes by applying static charges to remove particles from indoor air.
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Outside Air
Air taken from outdoors and not previously circulated
through the HVAC system. See also recirculated
air and supply air.
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Particulates
Small airborne particles found in indoor and outdoor
environments. These particles include fibrous materials, solid-state
semi-volatile organic compounds, and biological materials.
Pathogen
Any microorganism or substance that causes disease,
including bacteria, viruses,
fungi, mold, spores, pollens, etc. Pathogens range
in size from less than one to several microns in size.
Penetration
A measure, in percent, of the material passing through
a filter. Mathematically penetration is 100 - Efficiency
(percent). If a filter is 98% efficient, its penetration is 2% (100 -
98). Contrast with efficiency.
Polarization
The phenomenon that occurs to atoms and molecules that
are subjected to an electric field where the positive and negative
charges within the atom or molecule are pulled in opposite directions.
PPM
Parts per million.
Pressure Drop
A measure of a filter's resistance
to airflow through it. The difference between the static
pressure upstream and downstream of the filters. Resistance is
measured in inches w.g. in the Inch-Pound system of measurement or
Pascals in the SI system. The greater the pressure drop, the
greater the resistance to air flow through the filter. 1 in. w.g.=
248.8 Pascals (Pa).
PSE (Particle Size Efficiency)
As
used in the ASHRAE 52.2
test, indicates the filter’s ability to remove airborne particles of
differing sizes between 0.3 and 10 microns in diameter.
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Recirculated Air
Air that has been taken from the space, reconditioned
(temperature, humidity and cleanliness adjusted as necessary) and
returned to the space. See also outside air
and supply air.
Resistance (to Airflow)
See pressure drop.
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Sick
Building Syndrome
(SBS)
A
phenomenon in which building occupants experience a variety of health
and/or comfort effects linked to time spent in a particular building,
but where no specific illness or causative agent can be identified.
Symptoms in sufferers often include headaches, eye irritation, and
respiratory irritation. Alternatively, a set of symptoms that affect
some number of building occupants during the time they spend in the
building and diminish or go away altogether during periods when they
leave the building.
SMPS (Scanning Mobility Particle Sizer)
An
instrument for measuring high-resolution size distributions of ultrafine
particles. An SMPS consists of two main parts, the electrostatic
classifier and the condensation particle counter.
Static Pressure
The
force exerted in all directions within an air handling system. Think of
it as the pressure attempting to burst the duct.
Supply Air
A mixture of recirculated
air and outside air that has been
conditioned and delivered to the space. Supply air can be 100% outside
air and 100% recirculated air. See also recirculated
air and outside air.
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Total
Pressure
The sum of the static
pressure and velocity pressure. Air
handling systems are designed with a specific total pressure so the blower
can be sized properly. See also static
pressure and velocity pressure.
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ULPA
(Ultra Low Penetration Air) Filter
Filters
in this category typically have efficiencies of 99.999% on 0.1 micron DOP
particles.
UVGI
(Ultraviolet Germicidal Irradiation)
Many microbes can be killed or neutralized by exposure
to ultraviolet light at wavelengths at or near 2537 Angstroms.
Irradiation at this wavelength damages their molecular structure by
altering DNA and RNA. Various types of UVGI lamps can be mounted within
HVAC systems to lend a germicidal effect.
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Velocity
Pressure
The
pressure caused by the velocity of air moving in the direction of
flow. See also static
pressure and total pressure.
Virus
The smallest microbes that range in size from 0.01 to
0.3 microns.
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wg or Water Gauge
Common unit of measure used to measure pressure and pressure
drop within an HVAC system.
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