A shell placed in suction line for separating liquid refrigerant entrained in suction gas.

Air Changes

The amount of air leakage is sometimes computed by assuming a certain number of air changers per hour for each room, the number of changes assumed being dependent upon the type, use and location of the room.

Air Cooler, Forced Circulation

A factory-made encased assembly of elements by which heat is transferred from air to evaporating refrigerant.

Ambient Air

Generally speaking, the air surrounding an object. In a domestic or commercial refrigerating system having an air-cooled condenser, the temperature of the air entering the condenser.

Back Pressure

Loose terminology for suction pressure of refrigeration vapor in a system.

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British Thermal Unit (BTU)

Heat required to produce a temperature rise of 1 degree Fahrenheit in 1 lb. of water. The mean BTU is 1/180 of the energy required to heat water from 32°F. to 212°F.

Change of Air

Introduction of new, cleansed or recirculated air to conditioned space, measured by the number of complete changes per unit time.


To apply refrigeration moderately, as to meats, without freezing.

Chilling Room

Room where animal carcasses are cooled after dressing prior to cold storage.

Comfort Air Conditioning

The simultaneous control of all, or at least the first three, of the following factors affecting the physical and chemical conditions of the atmosphere within a structure for the purpose of human comfort; temperature, humidity, motion, distribution, dust, bacteria, odors, toxic gasses and ionization, most of which affect in greater or lesser degree human health or comfort.

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Comfort Cooling

Refrigeration for comfort as opposed to refrigeration for storage or manufacture.

Defrosting Cycle

A refrigeration cycle which permits cooling unit to defrost during off period.


The conservation of water vapor from air by cooling below the dew point or removal of water vapor from air by chemical or physical methods.


The removal of water vapor from air by the use of absorbing materials. (2) The removal of water from stored goods.

Dew Point

Temperature at which condensation starts if moist air is cooled at constant pressure with no loss or gain of moisture during the cooling process.

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Differential (of a control)

The difference between cut-in and cutout temperature or pressure.

Dry Bulb Temperature

Temperature measured by ordinary thermometer (term used only to distinguish from wet-bulb temperature).


A conduit or tube used for conveying air or other gas.


The part of a system in which refrigerant liquid is vaporizing to produce refrigerant.

External Equalizer

In a thermostatic expansion valve, a tube connection from the chamber containing the evaporation pressure actuated element of the valve to the outlet or the evaporator coil. A device to compensate for excessive pressure drop throughout the coil.

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Flash Gas

The gas resulting from the instantaneous evaporation of refrigerant in a pressure-reducing device to cool the refrigerant to the evaporations temperature obtained at the reduced pressure.

Flooded System

System in which only part of the refrigerant passing over the heat transfer surface is evaporated, and the portion not evaporated is separated from the vapor and recirculated. In commercial systems, one controlled by a float valve.

Frost Back

The flooding of liquid from an evaporator into the suction line accompanied by frost formation in suction line in most cases.

Head Pressure

Operating pressure measured in the discharge line at the outlet from the compressor.

Heat Exchanger

Apparatus in which heat is exchanged from one fluid to another through a partition.

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Heat, Latent

Heat characterized by change of state of the substance concerned, for a given pressure and always at a constant temperature for a pure substance, i.e., heat of vaporization or fusion.

High Side

Parts of refrigerating system under condenser pressure.


Air flowing inward as through a wall, leak, etc.

Liquid Line

The tube or pipe carrying the refrigerant liquid from the condenser or receiver of a refrigerating system to a pressure reducing device.

Low Side

Parts of a refrigerating system under evaporator pressure.

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Pressure Drop

Loss in pressure, as from one end of a refrigerant line to the other, due to friction, etc.

Refrigerating System

A combination of inter-connected refrigerant-containing parts in which a refrigerant is circulated for the purpose of extracting heat.


Production of CO₂ and the heat by ripening of perishables in storage.

Return Air

Air returned from conditioned or refrigerated space.

Sensible Heat

Heat which is associated with a change in temperature; specific heat x change of temperature; in contrast to a heat interchange in which a change of state (latent heat) occurs.

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Specific Heat

Energy per unit of mass required to produce one degree rise in temperature, usually BTU per lb. degree F. numerically equal to cal. per gram degree C.

Standard Air

Air weighing 0.075 lb. per cu. ft. which is closely air at 68°F. dry bulb and 50% relative humidity at barometric pressure of 29.92 in. of mercury of approximately dry air at 70°F. at the same pressure.

Suction line

The tube or pipe which carries the refrigerant vapor from the evaporator to the compressor inlet.


Temperature of vapor above its saturation temperature at that pressure.

Temperature, Wet-Bulb

Equilibrium temperature of water evaporating into air when the latent heat of vaporization is supplied by the sensible heat of air.

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Thermal Valve

A valve controlled by a thermally responsive element, for example, a thermostatic expansion valve which is usually responsive to suction or evaporator temperature.


The distance air will carry, measured along the axis of an air stream from the supply opening to the position, is the stream at which air motion reduces to 50 fpm.

Ton of Refrigeration

A rate of heat interchange of 12,000 BTU per hour; 200 BTU per min.

Unit Cooler

Adapted from unit heater to cover any cooling element of condensed physical proportions and large surface generally equipped with fan.

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