Definition of superheat: "Superheat" is the number of temperature degrees to which a refrigerant gas is above its boiling point.
As long as you keep the scale consistent across various measurements, tables, standards, the temperature scale can be in Kelvin, Centigrade, or Farenheit - it doesn't matter.
As long as you keep the scale consistent across various measurements, tables, standards, the temperature scale can be in Kelvin, Centigrade, or Farenheit - it doesn't matter.
Superheated high pressure refrigerant gas exits the compressor where it is condensed to a liquid in the compressor/condenser unit outdoor condensing coil.
Superheat is determined by taking the low side pressure gauge reading, converting that pressure to temperature using a PT [pressure - temperture] chart [for the specific refrigerant involved], and then subtracting that temperature from the actual temperature measured (using an accurate thermometer or thermocouple) at the same point the pressure was taken.
Superheat gives an indication if the amount of refrigerant flowing into the evaporator is appropriate for the load. If the superheat is too high, then not enough refrigerant is being fed resulting in poor refrigeration and excess energy use. If the superheat is too low, then too much refrigerant is being fed possibly resulting in liquid getting back to the compressor and causing compressor damage. Emerson Climate Technologies (2005)
The damage referred to is "liquid slugging" - a compressor's valves are designed to pass gas, not liquid. Slamming a piston into liquid destroys the compressor.
For discussion of the refrigerant pressure / temperature chart shown above see REFRIGERANT PRESSURE READINGS
Danfoss (2005) TEV fitters notes provides details about where and how to measure superheat on HVACR equipment, from which we quote this excerpt:
Superheat is measured at the point where the bulb is located on the suction line and is the difference between the temperature at the bulb and the evaporating pressure/evapora- ting temperature at the same point. Superheat is measured in Kelvin (K) or °C and is used as a signal to regulate liquid injection through the expansion valve. - Danfoss (2005)
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