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Glossary: A

Absolute humidity
Amount of moisture in the air, indicated in grains per ft3.

Absolute pressure
Gauge pressure plus atmospheric pressure (14.7 psi).

Absolute temperature
Temperature measured from absolute zero.

Absolute zero temperature
Temperature at which all molecular motion ceases (-460F and -273C).

Absorbent
The ability to soak up another substance.

Absorber
A solution or surface that is capable of soaking up (taking in) anther substance or energy form.

Absorption
The process of taking or soaking up into a substance.

Absorption chiller
A chiller that uses a brine solution and water to provide refrigeration without the aid of a compressor.

Absorption refrigerator
Refrigerator that creates low temperatures by using the cooling effect formed when a refrigerant is absorbed by chemical substance.

Accessible hermetic
Assembly of motor and compressor inside a single bolted housing unit.

Accumulator
Storage tank that receives liquid refrigerant from the evaporator and prevents it from flowing into the suction line before vaporizing.

Acid condition in system
Condition in which refrigerant or oil in system is mixed with acidic fluids.

ACR tubing
Tubing used in air conditioning and refrigeration. Ends are sealed to keep tubing clean and dry.

Activated alumina
A chemical that is a form of aluminum oxide. It is used as a drier or desiccant.

Activated carbon
Specially processed carbon used as a filter-drier; commonly used to clean air.

Active solar heating system
A system in which solar energy is absorbed in a collector, stored, and distributed by an auxiliary circulating system.

Actuator
That portion of a regulating valve that converts mechanical fluid, thermal energy, or electrical energy into mechanical motion to open or close valve seats.

Adiabatic compression
Compressing refrigerant gas without removing or adding heat.

Adsorbent
Substance with the property to hold molecules of fluids without causing a chemical or physical change.

Adsorption
The adhesion of a thin layer of molecules of a gas or liquid to a solid object.

Aeration
Act of combining a substance with air.

Agitator
Device used to cause motion in confined fluid.

Air
An invisible, odorless, and tasteless mixture of gases that surrounds the earth.

Air break
An inverted opening placed in the chimney of a gas furnace to prevent back pressure from outside wind from reaching the furnace flame or pilot.

Air cleaner
Device used for removal of airborne impurities.

Air coil
Coil on some types of heat pumps used either as an evaporator or a condenser.

Air conditioner
Device used to control temperature, humidity, cleanliness, and movement of air in conditioned space.

Air conditioning
Control of the temperature, humidity, air movement, and cleaning of air in a confined space.

Air-cooled condenser
Heat of compression is transferred from condensing coils to surrounding air. This may be done either by convection or by a fan or blower.

Air cooler
Mechanism designed to lower temperature of air passing through it.

Air core solenoid
A solenoid that has a hollow core instead of a solid core.

Air curtain
A system in which a blower is activated when a door is opened to blow across the open area, preventing the transfer of air between outdoors and indoors.

Air defrosting
Evaporator defrosting that occurs as evaporator warms when the compressor is not running.

Air diffuser
Air distribution outlet or grille designed to direct airflow into desired patterns.

Air gap
The space between magnetic poles or between rotating and stationary assemblies in a motor or generator.

Air handler
Fan-blower, heat transfer coil, filter, and housing parts of a system.

Airtight
Sealed to prevent the passage of gas.

Air-to-air heat pump
A heat pump that uses outdoor air, as opposed to a geothermal heat pump.

Air vent
Valve used to remove air from the highest point of a coil or piping assembly.

Air washer
Device used to clean air while changing its humidity.

Alcohol brine
Water and alcohol solution that remains a liquid below 32F (0).

Algae
Low form of plant life, found floating free in water.

Allen-type screw
Screw with recessed, hex-shaped head.

Allen wrench
Hexagonal (6-point) tip used to fit socket head screws or setscrews.

Alternating current (ac)
Electric current in which direction of flow alternates (reverses). In 60-cycle (Hertz) current, direction of flow reverses every 1/20th of a second.

Altitude
The height at a point above a reference level, sea level, or the earth's surface.

Ambient compensator
An electronic device that provides a small amount of heat to the refrigeration compartment to ensure that the machinery continues to cycle when ambient temperatures are low.

Ambient temperature
Temperature of a fluid (usually air) that surrounds an object.

American Standard Pipe Thread
Type of screw thread commonly used on pipe and fittings to ensure a tight seal.

Ammeter
Electric meter used to measure current.

Ammonia
Chemical combination of nitrogen and hydrogen (NH3). Ammonia refrigerant is identified as R-117.

Amperage
Electron or current flow past a given point in a circuit.

Ampere
Unit of electric current equivalent to flow of one coulomb per second.

Ampere-turns
Term used to measure magnetic force. Represents product of amperes times number to turns in coil of electromagnet.

Amplifier
Electrical device that increases electron flow in a circuit.

Anemometer
Instrument for measuring the rate of airflow.

Angle valve
Type of globe valve design, having pipe openings at right angles to each other. Usually, one opening is in the horizontal plane and one is in the vertical plane.

Annealing
Cooling a metal slowly form a high temperature to make the metal soft.

Annual Fuel Utilization Efficiency (AFUE) rating
A rating system for furnaces that compares energy input and energy output.

Anode
Positive terminal of electrolytic cell.

Anticipator
A device used with a start-stop control to reduce the control differential.

Arcing
Band of sparks formed when an electrical discharge from a conductor jumps to another conductor.

ARI
Air-Conditioning and Refrigeration Institute.

Armature
Part of an electric motor, generator, or other device moved by magnetism.

Articulated connection rods
Short connecting rods in a compressor.

ASA
Formerly, abbreviation for American Standards Association. Now known as American National Standards Institute (ANSI).

Asbestos
Strong, fire-resistant, cancer-causing silicate.

ASME Code
Standard specifications issued by the American Society of Mechanical Engineers Boiler for the construction of boilers and pressure vessels.

Aspect ratio
Ratio of length to width of a rectangular air grille or duct.

Aspirating psychrometer
Device that draws a sample of air through it to measure the humidity.

Aspiration
Movement produced by suction.

ASTM Standards
Standards issued by the American Society for Testing and Materials.

Atmospheric Dust Spot Efficiency
Measurement of a device's ability to remove atmospheric air from test air.

Atmospheric pressure
Pressure that gases in air exert upon the earth (14.7 psi).

Atom
Smallest unit of an element that can exist alone or in combination.

Atomize
Process of changing a liquid to minute particles or a fine spray.

Auger
Device with a helical shaft that, when rotated, can be used to move material.

Automatic control
Valve action reached through self-operated or self-actuated means, not requiring manual adjustment.

Automatic defrost
System of removing ice and frost from evaporators automatically.

Automatic expansion valve (AEV)
Pressure-controlled valve that reduces high-pressure liquid refrigerant and low-pressure refrigerant.

Automatic ice cube maker
Refrigerating mechanism designed to automatically produce ice cubes in quantities.

Autotransformer
Transformer in which both primary and secondary coils have turns in common. Step-up or step-down of voltage is accomplished by taps on common winding.

Auxiliary evaporator
Small evaporator consisting of coils of tinned tubing below the shelves in a display case.

Azeotropic mixture
A liquid mixture having constant maximum and minimum boiling points. Refrigerants comprising the azeotropic mixture do not combine chemically, yet the mixture provides constant characteristics.

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