19-07-2012, 03:54 PM
Refrigeration Basics 101
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Basics
Refrigeration is the removal of heat from a material or space, so that it’s temperature is lower than that of it’s surroundings.
When refrigerant absorbs the unwanted heat, this raises the refrigerant’s temperature (“Saturation Temperature”) so that it changes from a liquid to a gas — it evaporates. The system then uses condensation to release the heat and change the refrigerant back into a liquid. This is called “Latent Heat”.
This cycle is based on the physical principle, that a liquid extracts heat from the surrounding area as it expands (boils) into a gas.
To accomplish this, the refrigerant is pumped through a closed looped pipe system.
The closed looped pipe system stops the refrigerant from becoming contaminated and controls its stream. The refrigerant will be both a vapor and a liquid in the loop.
The Refrigeration Cycle
There are four main components in a refrigeration system:
The Compressor
The Condensing Coil
The Metering Device
The Evaporator
Two different pressures exist in the refrigeration cycle. The evaporator or low pressure, in the "low side" and the condenser, or high pressure, in the "high side". These pressure areas are divided by the other two components. On one end, is the metering device which controls the refrigerant flow, and on the other end, is the compressor.
The Compressor
The compressor is the heart of the system. The compressor does just what it’s name is. It compresses the low pressure refrigerant vapor from the evaporator and compresses it into a high pressure vapor.
The inlet to the compressor is called the “Suction Line”. It brings the low pressure vapor into the compressor.
After the compressor compresses the refrigerant into a high pressure Vapor, it removes it to the outlet called the “Discharge Line”.
Metering Devices
Metering devices regulate how much liquid refrigerant enters the evaporator .
Common used metering devices are, small thin copper tubes referred to as “cap tubes”, thermally controller diaphragm valves called “TXV’s” (thermal expansion valves) and single opening “orifices”.
The metering device tries to maintain a preset temperature difference or “super heat”, between the inlet and outlet openings of the evaporator.
As the metering devices regulates the amount of refrigerant going into the evaporator, the device lets small amounts of refrigerant out into the line and looses the high pressure it has behind it.
Now we have a low pressure, cooler liquid refrigerant entering the evaporative coil (pressure went down – so temperature goes down).
Basic Refrigeration Cycle
Starting at the compressor;
Low pressure vapor refrigerant is compressed and discharged out of the compressor.
The refrigerant at this point is a high temperature, high pressure, “superheated” vapor.
The high pressure refrigerant flows to the condenser by way of the "Discharge Line".
The condenser changes the high pressure refrigerant from a high temperature vapor to a low temperature, high pressure liquid and leaves through the "Liquid Line".
The high pressure refrigerant then flows through a filter dryer to the Thermal Expansion valve or TXV.
The TXV meters the correct amount of liquid refrigerant into the evaporator.
As the TXV meters the refrigerant, the high pressure liquid changes to a low pressure, low temperature, saturated liquid/vapor.
This saturated liquid/vapor enters the evaporator and is changed to a low pressure, dry vapor.
The low pressure, dry vapor is then returned to the compressor in the "Suction line".
The cycle then starts over.