Brochure

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Static pressure: Pressure exerted in all directions
by a fluid or gas at rest. For fluids in motion,
measured perpendicular to the direction of flow.
Steam trap: Steam boiler accessory that removes
air and condensate from steam lines, and heating
units.
Subcooling: Process of cooling of a substance such
as a refrigerant to a temperature that is lower than
the saturated temperature of the substance at a
particular pressure.
Superheat: Sensible heat that is added to a sub-
stance after the substance has turned to vapor.
Supply air: A conditioned mixture of return air, and
outside air delivered to a space.
Time-weighted average concentration (TWA):
Refers to concentrations of airborne materials
which have been weighted for a certain time
duration, usually eight hours.
(TLV) threshold limit value: A time-weighted
average concentration under which most people
can work consistently for eight hours a day, day
after day, without suffering harmful effects. The
American Conference of Governmental Industrial
Hygienists publishes a table of these values and
accompanying precautions annually.
Ton: A unit of measure for cooling capacity. One
ton=12,000 BTUs per hour.
Unit ventilator: A fan-coil unit package device
for applications in which the use of outdoor- and
return-air mixing is intended to satisfy tempering
requirements, and ventilation needs.
Unitary system: Air conditioning system that has
all components enclosed in one cabinet.
Variable air volume system (VAV): Air distri-
bution system in which the air flow rate in the
building spaces is varied by mixing dampers,
but the temperature of the supply air remains
constant.
Ventilation rate: The rate at which indoor air
enters and leaves a building. Expressed in one of
two ways: the number of changes of outdoor air
per unit of time (air changes per hour, or “ach”) or
the rate at which a volume of outdoor air enters
per unit of time (cubic feet per minute, or “cfm”).
Volatile organic compounds (VOCs): Compounds
that vaporize (become a gas) at room tempera-
ture. Common sources which may emit VOCs into
indoor air include housekeeping and maintenance
products, and building and furnishing materials.
In sufficient quantities, VOCs can cause eye, nose,
and throat irritations, headaches, dizziness, visual
disorders, memory impairment; some are known
to cause cancer in animals; some are suspected of
causing, or are known to cause, cancer in humans.
Wet-bulb temperature: The lowest air tempera-
ture that can be reached through evaporation at
a specific air saturation point. Wet bulb and dry
bulb temperatures will be identical at 100 % air
saturation.
Zone: The occupied space or group of spaces
within a building which has its heating or cooling
controlled by a single thermostat.
Sources
From http://www.epa.gov/iaq/glossary.html
Used with permission from Heating, Ventilating,
and Air Conditioning, 3rd Edition, Swanson, Don,
American Technical Publishers, 2004.
From U.S. EPA, “Building Air Quality: A Guide for
Building Owners and Facility Managers,” 1991.