A simple stylized diagram of the refrigeration cycle :
01). Condensing coil
02). Expansion valve
03). Evaporator coil
04). Compressor
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| A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressor. |
Capillary expansion valve connection to evaporator inlet. Notice frost formation.
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| Capillary expansion valve connection to evaporator inlet. Notice frost formation. |
In the refrigeration cycle a heat pump transfers heat from a lower-temperature heat source onto a higher-temperature heat sink. Heat would naturally flow in the opposite direction. This is the most common type of air conditioning. A refrigerator works in much the same way , as it pumps the heat out of the interior and into the room in which it stands.
This cycle takes advantage of the way phase changes work , where latent heat is released at a constant temperature during a liquid/gas phase change and where varying the pressure of a pure substance also varies its condensation/boiling point.
The most common refrigeration cycle uses an electric motor to drive a compressor. In an automobile the compressor is driven by a belt over a pulley , the belt being driven by the engine's crankshaft (similar to the driving of the pulleys for the alternator , power steering , etc.. ). Whether in a car or building , both use electric fan motors for air circulation. Since evaporation occurs when heat is absorbed , and condensation occurs when heat is released , air conditioners use a compressor to cause pressure changes between two compartments and actively condense and pump a refrigerant around. A refrigerant is pumped into the evaporator coil , located in the compartment to be cooled , where the low pressure causes the refrigerant to evaporate into a vapor , taking heat with it. At the opposite side of the cycle is the condenser , which is located out side of the cooled compartment , where the refrigerant vapor is compressed and forced through another heat exchange coil , condensing the refrigerant into a liquid , thus rejecting the heat previously absorbed from the cooled space.
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| A modern R-134a refrigeration compressor |
By placing the condenser (where the heat is rejected) inside a compartment and the evaporator (which absorbs heat) in the ambient environment (such as outside) or merely running a normal air conditioner's refrigerant in the opposite direction , the overall effect is the opposite , and the compartment is heated. This is usually called a heat pump and is capable of heating a home to comfortable temperatures (25°C ; 70°F) , even when the outside air is below the freezing point of water (0°C ; 32°F).
Cylinder unloaders are a method of load control used mainly in commercial air conditioning systems. On a semi-hermetic (or open) compressor , the heads can be fitted with unloaders which remove a portion of the load from the compressor so that it can run better when full cooling is not needed. Unloaders can be electrical or mechanical.