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Packaged air-conditioner:
a self-contained unit designed to provide control of air temperature, humidity, distribution, and quality; see also unitary air-conditioner.
Perimeter:
those portions of a building adjacent to exterior walls; thermal zones adjacent to the building exterior
Pipe:
a container for distribution of water or steam
Pressure:
a measure of the force exerted by a fluid; static pressure is a measure of the force exerted by a fluid at rest; velocity pressure is a measure of the force exerted by the momentum of a fluid in motion; total pressure is the sum of static and velocity pressures
Pump:
a device designed to impart energy (velocity and/or pressure) to water in an HVAC system; found in chilled water, hot water, and condenser water circuits; see also centrifugal pump
Psychrometric chart:
a graphic means of displaying multiple properties of moist air, used to plot air conditioning processes
Reciprocating:
a particular type of fluid moving device that imparts energy to the fluid by a positive displacement, piston-like action
Reciprocating chiller:
a vapor compression chiller that utilizes a reciprocating compressor; most commonly used in systems with cooling capacities up to approximately 200 tons
Refrigerant:
a heat transfer fluid employed by a refrigerating process, selected for its beneficial properties (stability, low viscosity, high thermal capacity, appropriate state change points).
Refrigeration:
a process whereby a heat sink is artificially established by action of some electro-mechanical device; equipment used to establish an artificial heat sink
Reheat HVAC system:
a central air-all HVAC system with a single supply air stream that is heated by a terminal device (reheat coil) at each zone to provide appropriate thermal conditions
Relative humidity:
a measure of moisture content in the air; the ratio of moisture contained by an air sample to the maximum amount of moisture the air could hold at the same temperature.
Space heating:
a process whereby sensible heat is introduced to a room or building
Static pressure:
the force exerted by a fluid not considering the energy equivalent of fluid velocity
System:
an assembly of components with a specific structure and intended function
Temperature:
a measure of the density of heat in a substance
Terminal box:
a device used to provide thermal control in an all-air central HVAC system and located adjacent to the zone being served; common types include reheat terminals, dual duct terminals, and variable volume terminals
Thermal comfort:
individually, an expression of satisfaction with the thermal environment; statistically, such expression of satisfaction from at least 80% of the occupants in a space
Ton:
a capacity measure for cooling equipment; equivalent to 12,000 British thermal units per hour
Tube:
a relatively small diameter pipe, usually of non-ferrous material
Unitary air-conditioner:
a self-contained unit designed to provide control of air temperature, humidity, distribution, and quality; see also packaged air-conditioner
Unit heater:
equipment designed to deliver heat to a space from an all-water heating system; a packaged unit consisting of a water or steam heating coil, a fan, and a housing
Valve:
a device designed to control water flow in a distribution system; common valve types include globe, gate, butterfly, and check
Vapor compression chiller:
refrigeration equipment that generates chilled water via a mechanically driven process using a specialized heat transfer fluid as refrigerant; comprised of four major components: a compressor, condenser, expansion valve, and evaporator; operating energy is input as mechanical motion.
Variable air volume (VAV) HVAC system: a central air-all HVAC system that utilizes a single supply air stream and a terminal device at each zone to provide appropriate thermal conditions through control of the quantity of air supplied to the zone
Ventilation:
a process whereby outdoor air is brought into a building as a means of maintaining acceptable indoor air quality, to control building pressurization, or to provide thermal comfort
Zone:
during design -- an area of a building that must be separately controlled if conditions conducive to thermal comfort are to be provided by an HVAC system; in existing buildings -- an area that is controlled from a single control point (thermostat)
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