A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
RADIANT TEMPERATURE ASYMMETRY: The difference
between the plane radiant temperature of the two
opposite sides of a small plane element.
RADIATION, THERMAL: The transmission of heat
through space by wave motion; the passage of heat
from one object to another without warming the
RADIUS OF DIFFUSION: The horizontal distance
in feet from the diffuser to a point where the
terminal velocity of 50 feet per minute occurs.
RASH: A skin swelling. Kinds of rashes are butterfly
rash, diaper rash, drug rash, heat rash.
REACTIVATION: the removal of adsorbates from
spent activated charcoal, which allows the carbon
to be reused; also called regeneration.
RECIPROCATING: In refrigeration, a type of compressor
which compresses refrigerant vapor by moving a
piston up and down in a cylinder.
RECIRCULATED AIR: the return air that has been
conditioned and returned to a given space.
REEINTRAINMENT: the attraction of contaminants
exhausted from a building into the supply air
stream by way outside air supply inlets or other
routes of outside air infiltration, such as leaks,
windows, doorways, elevators shafts, and stairways.
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REFRIGERANT: The fluid used for heat transfer
in a refrigerating system, which absorbs heat
at a low temperature and a low pressure of the
fluid and rejects heat at a higher temperature
and a higher pressure of fluid, usually involving
changes of state of the fluid.
REGISTER: A grille which is equipped with a damper
or control valve, and which directs air in a non-spreading
REHEAT: a coil placed after the cooling coil,
used to raise the air temperature; the process
of raising the cooled air temperature. Used mainly
with DX coil dehumidification.
RELATIVE HUMIDITY: The ratio of the quantity
of water vapor present in the air compared to
the quantity of water vapor present in saturated
air at the same temperature and barometric pressure.
RELATIVE RISK: the ratio of health impact incidence
among exposed individuals to incidence among unexposed
REPLACEMENT AIR: the air supplied to a space
to replace exhausted air; compensating air, make
RESERVOIR: the environmental substrate, or source,
of a particular organism. Reservoirs for indoor
biocontaminants include stagnant water, moist
surfaces, and dust collection sites.
RESET: A process of automatically adjusting the
control point of a given controller to compensate
for changes in outdoor temperature. The hot deck
control point is normally reset upward as the
outdoor temperature drops. The cold deck control
point is normally reset downward as the outdoor
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RESPIRABLE PARTICLES: Those particles in air
which penetrate into and are deposited in the
conciliated portion of the lung.
RESPIRABLE SIZE PARTICULATES: Particulates in
the size range that permits them to penetrate
deep into the lungs upon inhalation
RETURN: Any opening through which air is removed
from a conditioned space.
RETURN AIR: Air returned from conditioned or
REVERBERATION: The persistence of sound in an
enclosed space after the sound source has stopped.
In a reverberation room, it is characterized by
the decay or dying away the sound.
REVERBERATION TIME: The reverberation time of
an enclosed space is the number of seconds required,
or that would be required were the decay rate
to remain constant, for the sound pressure level
to decrease by 60 decibels.
RHINITIS: an inflammation of the mucous membrane
of the nose caused by an infection or exposure
to an allergen.
RISER SHAFT: A vertical shaft designed to house
electric cables, piping and ductwork.
ROOM CRITERIA CURVES (RC CURVES): Curves similar
to NC curves that represent a close approximation
to a well balanced, bland-sounding spectrum.
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ROOM DRY BULB: The actual temperature of the
conditioned room or space as measured with an
ROOM VELOCITY: The residual air velocity level
in the occupied zone of the conditioned space
(e.g. 65, 50, 35 fpm).
ROTAMETER: A flow meter, consisting of a precision-bored,
tapered, transparent tube with a solid float inside.
Used for calibrating instruments.
RTC: room temperature catalyst; a catalyst that
accelerates chemical reactions at room temperature
rather than at the usually required higher temperatures
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