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Absorption chillers:
refrigeration equipment that generates chilled water via a chemically driven process using water and a desiccant salt as refrigerant; comprised of four major components: a generator, condenser, absorber, and evaporator; operating energy is input as heat.
Air:
a mixture of gases (including oxygen, nitrogen, argon, carbon dioxide, and water vapor) and suspended solid and liquid materials.
Air changes:
the number of times per hour that a volume of air equal to room volume is replaced; one air change per hour (ACH) represents the supply and return of air equal to the volume of the room in question once every hour.
Air conditioning:
a process that simultaneously controls the temperature, moisture content, distribution, and quality of air.
Air filter:
a device designed to remove contaminants and pollutants from air passing through the device.
Air handling unit:
an assembly of air-conditioning components that normally includes a fan, a filter, heating and cooling coils, and control elements.
Air-water HVAC system:
a category of central HVAC systems that distribute conditioning effect by means of heated or chilled water and heated or cooled air.
All-air HVAC system:
a category of central HVAC systems that distribute conditioning effect solely by means of heated or cooled air.
All-water HVAC system:
a category of central HVAC systems that distribute conditioning effect solely by means of heated or chilled water.
ASHRAE:
the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.; the primary professional organization in North America involved with HVAC systems design; developer of many HVAC system standards and guidelines.
Axial fan:
a fan, usually with a propeller-type design, that moves air along a consistent axis without substantial change in direction; occasionally used in air handling units and commonly used for return and exhaust air applications.
Balance point temperature:
that outside air temperature at which a particular building will be in thermal equilibrium, requiring neither heating nor cooling to support thermal comfort.
Boiler:
equipment designed to heat water or generate steam.
British thermal unit: (Btu)
a measure of thermal energy (heat); quantity of energy required to raise the temperature of one pound of water by one degree Fahrenheit.
Central HVAC system:
a system that produces a heating or cooling effect in a central location for subsequent distribution to satellite spaces that require conditioning; see also all-air, all-water, and air-water HVAC systems.
Centrifugal:
a particular type of fluid moving device that imparts energy to the fluid by high velocity rotary motion through a channel, fluids enter the device along one axis and exit along another axis; see also centrifugal chiller, centrifugal fan, centrifugal pump.
Centrifugal chiller:
a vapor compression chiller that utilizes a centrifugal compressor; most commonly used in systems with cooling capacities of from 80 to 10,000 tons.
Centrifugal fan:
a fan that utilizes a centrifugal air flow design; most common fan design for air handling unit applications.
Centrifugal pump:
a pump that utilizes a centrifugal water flow design; most common pump design for general purpose HVAC applications (chilled water, condenser water, hot water).
Chiller:
equipment designed to produce chilled water; see also vapor compression chiller (centrifugal, reciprocating) and absorption chiller.
Coefficient of performance:
an efficiency measure for cooling source equipment; the ratio of cooling effect (output) to energy input -- with cooling effect and energy input in consistent units.
Coil:
a liquid-to-air heat exchanger consisting of tubes through which the liquid flows and multiple fins (attached to the tubes) across which the air flows; an electric resistance element used to heat air or water.
Combustion:
an oxidation process that releases heat; on-site combustion is a common heat source for buildings.
Comfort:
an expression of satisfaction with a particular environment; see also thermal comfort.
Commissioning:
a systematic process to verify that building components and systems function as intended and required; systems may need to be re-commissioned at intervals during a building's life cycle.
Compressor:
a device designed to compress (increase the density) of a compressible fluid; a component used to compress refrigerant; a component used to compress air.
Condenser:
a device designed to condense a refrigerant; an air-to-refrigerant or water-to-refrigerant heat exchanger; part of a vapor compression or absorption refrigeration cycle.
Control:
a means of regulating the operation of a device or system; equipment or systems designed to regulate the operation of an HVAC system.
Cooling:
a process that removes sensible and/or latent heat from a material or space.
Cooling load:
the magnitude of heat removal required to maintain a building at appropriate thermal conditions.
Cooling tower:
equipment designed to reject heat from a refrigeration cycle to the outside environment through an open cycle evaporative process; an exterior heat rejection unit in a water-cooled refrigeration system.
Damper:
a device designed to regulate the flow of air in a distribution system.
Dehumidifier:
equipment designed to remove moisture from the air; in the generally used sense of this term, a freestanding moisture removal device.
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