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What Is Evaporator Superheat?
Superheat is a common term that most HVAC/R professionals encounter every day.
There are different types of superheat, and each of them is equally important for understanding the actual conditions of a refrigeration system. These include evaporator superheat, compressor superheat, and discharge superheat.
In this article, we will talk about Evaporator Superheat.
How is Superheat Measured?
Evaporator superheat is measured at the outlet of the evaporator, and it basically tells us if the refrigerant is boiling at a satisfactory rate. It is controlled by the metering device of the system, commonly known as the expansion valve.
To measure evaporator superheat, you need a thermistor, a pressure gauge, and a pressure-temperature chart.
Typical evaporator superheat values are:
- Air conditioning: 12°F to 15°F
- Medium temperature refrigeration: 8°F to 10°F
- Low temperature refrigeration: 6°F to 8°F
My evaporator superheat is low. What is happening?
A low evaporator superheat indicates that the refrigerant is not absorbing the appropriate amount of heat prior to exiting the evaporator and will result in liquid entering the compressor. This term is commonly known in the industry as liquid floodback.
Compressors are not made to pump liquid, so any large amounts of liquid entering the compressor will likely result in a catastrophic failure.
Causes for low evaporator superheat include iced-up or dirty coils and oversized/poorly adjusted expansion valves.
My evaporator superheat is high. What is happening?
A high evaporator superheat indicates that the refrigerant is boiling too soon in the evaporator. This means that the vapor is gaining too much heat, which will result in higher suction and discharge temperatures.
Excessive heat will cause the oil in the compressor to break down and eventually lose lubrication capacity, among other critical issues, such as the cut-out of internal protector devices due to insufficient cooling.
Causes for high evaporator superheat include undersized/poorly adjusted expansion valves, low refrigerant charge, liquid line restriction, and excessive load.
Contact Us
If you have any further questions about evaporator superheat, or if you have any other questions regarding refrigeration, you can contact the Refrigeration Support Team for further advice. Alternatively, you can contact your local branch for support.