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
VANEAXIAL: A type of fan completely contained
in a section of round duct.
VAPOR: A substance in gas form, particularly
one near equilibrium with its condensed phase
and which does not follow the ideal gas laws;
in general, any gas below its critical temperature.
VAPOR BARRIER: A moisture-impervious layer applied
to the surfaces enclosing a humid space to prevent
moisture travel to a point where it may condense
due to lower temperature.
VAPOR PRESSURE: Vapor pressure denotes the lowest
absolute pressure that a given liquid at a given
temperature will remain liquid before evaporating
into its gaseous form or state.
VARIABLE AIR VOLUME (VAV): A supply air system
that holds the supply air temperature constant
but varies supply air flow to compensate for the
thermal loads in the space.
VARIABLE AIR VOLUME BOX: the terminal device
of a VAV system that controls the volume of conditioned
air admitted from the air supply.
VARIABLE VOLUME VARIABLE TEMPERATURE: an HVAC
system that combines variable air volume with
variable temperature to provide greater low-load
airflow to the conditioned space than that provided
by standard VAV systems.
VEHICLE: Any contaminated inanimate material,
such as water or food, through which microorganisms
can be transported or dispersed to a susceptible
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VELOCITY: A vector quantity which denotes, at
once, the time rate and the direction of a linear
VELOCITY, OUTLET: The average discharge velocity
of primary air being discharged from the outlet,
normally measured in the plane of the opening.
VELOCITY PRESSURE: The pressure produced by the
movement of air, such as the wind, or the air
coming from a fan.
VELOCITY, TERMINAL: The highest sustained air
stream velocity existing in the mixed air path
at the end of the throw.
VENTILATION: The process of supplying and removing
air by natural or mechanical means to and from
any space. Such air may or may not be conditioned.
VENITLATION CONTROL: an air pollutant strategy
that uses ventilation to remove and/or dilute
pollutants to levels at which they do not present
a threat to health and comfort.
VENTILATION EFFECTIVENESS: a measure of the fraction
or percentage of outdoor air that reaches the
occupied zone of a specified area; an evaluation
of air delivery to occupants, regardless of the
effectiveness of contaminant removal.
VENTILATION EFFICIENCY: an evaluation of the
pollutant removal capacity of a ventilation system,
as defined by the local mean age of air in the
exhaust divided by the mean age of air in the
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VENTILATION RATE: the rate of intake of outdoor
air into indoor spaces.
VENILATION STANDARD: a specification for the
minimum rate of input of outdoor air into indoor
VIRUS: An infectious agent that contains either
RNA or DNA in its core surrounded by a protein
shell, is able to alternate between intracellular
and extracellular states, and replicates only
when present in living cells.
VOC: Volatile Organic Compound Any
organic chemical reacting with atmospheric ozone.
This designation is not a reflection or indication
of human health effects.
VOLATILE FUMES: The fumes from substances such
as gasoline or alcohol; usually very flammable.
VOLATILITY: the tendency of a molecule to exist
in a gaseous state.
VOLUME: Cubic feet per pound of dry air in the
air-water vapor mixture as used in pschrometrics.
VOLUME, SPECIFIC: The volume of a substance per
unit mass; the reciprocal of density.
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