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HVAC Glossary Terms
Chapter 2: Glossary Terms
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Business
01/03/2012

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Term
Automatic Expansion Valve (AEV)
Definition
Metering device that maintains a constant evaporator pressure
Term
Bubble Point
Definition
For blended refrigerants, the temperature used to calculate condenser subcooling
Term
Bulb Pressure
Definition
Pressure that facilitates the opening of the thermostatic expansion valve
Term
Capillary Tube
Definition
A fixed bore metering device
Term
Compression
Definition
The portion of the compression process in which the refrigerant is compressed
Term
Compressor
Definition
The component of an air conditioning system that pumps refrigerant through the system by increasing the pressure of the vapor refrigerant
Term
Condenser
Definition
A heat transfer surface in an air conditioning system that rejects heat
Term
Condenser Saturation Temperature
Definition
The temperature at which system refrigerant will condense in the condenser; this temperature corresponds to the high side pressure in the system on a pressure/temperature chart
Term
Condensing Medium
Definition
The medium, usually air or water that absorbs the heat that is rejected by the system condenser
Term
Critically Charged System
Definition
A system that requires an exact quantity of refrigerant; all of the refrigerant is moving through the system at all times
Term
Cylinder
Definition
The component part of a reciprocating compressor that houses the piston
Term
Dehumidifying
Definition
The process of removing humidity from the air
Term
Desuperheating
Definition
The process by which the discharge refrigerant from the compressor is cooled down to the condenser saturation temperature
Term
Dew Point
Definition
The temperature at which air reaches 100% humidity; for blended refrigerants, the temperature used to calculate evaporator superheat
Term
Discharge
Definition
The portion of the compression process when the refrigerant is discharged from the compressor
Term
Discharge Line
Definition
The refrigerant line that carries the discharge refrigerant from the compressor to the condenser
Term
Discharge Pressure
Definition
The pressure of the refrigerant in the high-pressure side of the air conditioning system; also referred to as the high-side or head pressure
Term
Dry Type Evaporator
Definition
An evaporator that is designed to have all of the refrigerant boil off into a vapor before leaving the coil
Term
Evaporator
Definition
The component part of an air conditioning system that is responsible for absorbing heat from the space to be cooled
Term
Evaporator Pressure
Definition
The pressure that corresponds to the temperature at which refrigerant vaporizes in the evaporator on a pressure/ temperature chart
Term
Externally Equalized TEV
Definition
A thermostatic expansion valve that measures the evaporator pressure at the outlet of the coil
Term
Fixed-Bore Metering Device
Definition
A metering device that does not open or close in response to changes in the load on the system; examples of the fixed bore metering device are the capillary tube and the piston
Term
Flash Gas
Definition
The process by which some of the liquid refrigerant instantly vaporizes upon entering the evaporator
Term
Internally Equalized TEV
Definition
A thermostatic expansion valve that measures the evaporator pressure at the inlet of the coil
Term
Liquid Line
Definition
The refrigerant carrying line that connects the condenser to the metering device
Term
Metering Device
Definition
The component of an air conditioning system that controls the flow of refrigerant to the evaporator
Term
Outside Ambient Temperature
Definition
The temperature of the air that surrounds the outdoor coil of an air conditioning system
Term
Piston
Definition
The component part of the reciprocating compressor that moves back and forth within the cylinder to compress or expand the refrigerant in the cylinder
Term
Pressure/Temperature Chart
Definition
Shows the relationship that exists between the temperatures and pressures of saturated refrigerants
Term
Psig
Definition
Pounds per square inch gauge; pressure readings taken from gauge manifold
Term
Reexpansion
Definition
In a reciprocating compressor, the process by which the refrigerant trapped in the cylinder at the end or a cycle in expanded to reduce the pressure in the cylinder
Term
Repeating Cycle
Definition
A process than can repeat itself indefinitely without depleting resources
Term
Return Air
Definition
Air that is brought from the conditioned space to the evaporator
Term
Saturated
Definition
Refrigerant that is a mixture of liquid and vapor; saturated refrigerants follow a pressure/temperature relationship
Term
Spring Pressure
Definition
One of the closing pressures on the thermostatic expansion valve; also the opening pressure on the automatic expansion valve
Term
Subcooling
Definition
The process by which the refrigerant in the condenser is cooled below the condenser saturation temperature
Term
Suction
Definition
In a reciprocating compressor; the process by which refrigerant in the suction line is pulled into the compression chamber prior to being compressed
Term
Suction Line
Definition
The refrigerant carrying line that connects the outlet of the evaporator to the compressor
Term
Suction Pressure
Definition
The pressure of the low side of the system; also called low-side or back pressure
Term
Suction Valve
Definition
The component part of a reciprocating compressor that opens to pull refrigerant from the evaporator into the compressor for compression
Term
Superheat
Definition
The process by which vapor refrigerant is heated above its evaporator saturation temperature
Term
Supple Air
Definition
The air that is returned to the conditioned space after it has passed through the evaporator
Term
Thermal Bulb
Definition
TEV component that senses the temperature at the outlet of the evaporator and converts this temperature the valveā€™s opening pressure
Term
Thermostatic Expansion Valve (TEV)
Definition
Metering device designed to maintain a constant evaporator superheat
Term
Total System Charge
Definition
The amount of refrigerant a system contains
Term
Transmission Line
Definition
The small diameter tube that connects the thermal bulb to the body of a thermostatic expansion valve
Term
Discharge Valve
Definition
The component part of a reciprocating compressor that opens to discharge refrigerant from the compreesor into the discharge line