GE PSH23SGNAFBS Series, Technical Service Manual

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Phases of Refrigeration
The compressor is the heart of any refrigeration system. It serves as a pump to circulate the refrigerant
and create pressure within the system. When the compressor is operating, one side of the system is at
high pressure and the other side is at low pressure. This difference in pressure creates a temperature
difference that allows heat to be removed from inside the cabinet and transferred to the outside of the
cabinet.
The 3 phases of the refrigeration system are:
•
Compression
•
Condensation – occurs on the “high side” of the system
•••••
Evaporation – occurs on the “low side” of the system
Compression
While the compressor is operating, refrigerant vapor is discharged into the condenser. A capillary (small
diameter tube) is connected to the outlet of the condenser. The capillary tube restricts the amount of
refrigerant that leaves the condenser. As the compressor continues to pump refrigerant into the
condenser, this restriction causes pressure to build in the condenser. Typical operating pressure in the
condenser in the inverter compressor system is 85 to 90 psig in an ambient temperature of 75 °F.
Condensation
The compressed refrigerant vapor entering the condenser is warmer than the temperature of the room.
As the refrigerant travels though the condenser, the heat from the high-pressure vapor is transferred to
the condenser, which transfers heat to the surrounding air (by convection). As heat is removed from the
high-pressure vapor, it begins to condense into a high-pressure liquid. This high-pressure liquid
refrigerant flows to the end of the condenser and is forced into the capillary tube.
Evaporation
High-pressure liquid refrigerant travels through the capillary and exits at a very high rate of speed into the
much-larger tubing of the evaporator. Low pressure in the evaporator, caused by the suction of the
compressor (typically 0 to 5 psig in the inverter compressor) causes the liquid refrigerant to vaporize.
Approximately 30% of the refrigerant will vaporize immediately upon exiting the capillary. The remaining
refrigerant will vaporize as it travels through the evaporator. As the refrigerant vaporizes, it absorbs
heat. Heat inside the cabinet is transferred (by convection) to the evaporator because the evaporator
temperature is lower than the cabinet air temperature. Refrigerant exiting the evaporator should have
completely vaporized so that only vapor is returned to the compressor through the suction line.
However, under certain conditions some refrigerant may remain in liquid form as it exits the evaporator.
The mixture of refrigerant (vapor and liquid) is known as “refrigerant quality.” Refrigerant that has a
higher ratio of vapor to liquid has a higher quality. Completely vaporized refrigerant has a quality rating of
100%. Refrigeration that is completely liquid has a quality rating of 0%. Refrigerant that is exiting the
evaporator should have a quality rating of 100%. Refrigerant that is exiting the condenser should have a
quality rating of 0%. Refrigerant quality is an important part of refrigeration system efficiency.
Principals of Refrigeration