WHAT IS SUPERHEAT?
Superheat is the term used to describe the difference between the vapour point (i.e. the temperature at which the refrigerant evaporates at a given pressure) and the actual temperature of the refrigerant exiting the evaporator coil.
The correct superheat temperature is decisive for the refrigerating process. This can be only achieved with the correct setting of the expansion valve: Expansion valves regulate the amount of supercooled liquid refrigerant to be injected into the evaporator distributor in accordance with the superheating of the refrigerant vapour at the evaporator outlet.
In each case, only so much refrigerant can be injected as is required - or can be evaporated - under the respective operating conditions while utilising the heat-transfer surface of the evaporator.
Incorrectly set expansion valves result either in too high or too low a superheating.
The required refrigerated space temperature is not reached or is only reached with an increased expenditure of energy.
Under certain circumstances, the cooling system itself can become damaged. If the superheating is insufficient, drops of liquid, for example, can be carried over into the suction line, which can then cause damage to the compressor.
On the other hand, excessive superheating reduces the performance of the evaporator because the heat exchanger surface is not completely utilised. If the intake vapour temperatures are too high, the compressor is frequently subjected to increased wear and tear. It is therefore important to correctly match the evaporator performance and the size of the expansion valve, the nozzle used and the setting of the expansion valves to one another.
|The ideal evaporator performance is reached at a superheating
ratio of 0.65. This is calculated from the difference of the evaporation temperature t0 to the superheating temperature t0h in relationship to the difference between the air inlet temperature into
the evaporator tL1 and the evaporation temperature t0.
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