A material with a high resistance to vapor movement, such as foil, plastic film, or specially coated paper, that is used to control condensation or prevent migration of moisture.
Vapor migration
The natural movement of water vapor from regions of higher vapor pressure to regions of lower vapor pressure.
Vapor pressure
The pressure at which a liquid and its vapor are in equilibrium at a definite temperature.
Vapor-tight luminaire
A luminaire constructed so that a specified vapor or gas cannot enter its enclosure Ñ usually water vapor.
Vara
A measurement or unit of length, usually 31 to 33 inches and predominantly South American or Spanish.
Variable
Subject to change.
Variable air volume system (vav)
A mechanical HVAC system capable of serving multiple zones which controls the temperature maintained in a zone by controlling the amount of heated or cooled air supplied to the zone.
