View Full Version : Superheat debate

07-04-2003, 07:54 AM
Recently someone told me that superheat was controlled by the compressor. I disagreed with him. I said superheat was controlled by heat load of the evaporator.

Can someone please elaborate on this?

Or is superheat controlled by the entire system as a whole?

07-04-2003, 11:20 AM
hi Zolar,

in my opinion whatevr you are thinking , that the superheat is the

function of the heat load acting on the evaporator is correct.

even then lets see here if some one gets into some different views.

have a nice time.



07-04-2003, 02:28 PM
In the case of a cap tube, float, or restrictor (passive) type expansion device or refrigerant control, I would consider the statement regarding the "Load" to be accurate. Even in the case of a thermostatic expansion valve, the actual superheat will increase with increased load (higher S.S.T.) and vice versa, though to a lesser extent, I think.

I would say that the statement, "The compressor controls superheat (or controls anything for that matter)", is incorrect. The compressor is selected in consideration of the design criteria of a system, design superheat being a part of those considerations.


09-04-2003, 04:44 PM
Superheat is controled by the amount of ***** boiling in the evap compared to how much enters the evap. Superheat is influenced by the compressors ability to pump ***** out, the valves ability to add ***** to the evap and the heat load boiling the *****. Change any one of those the superheat will change. I would say the easiest factor to change would by the heat load.

In summary superheat is a system parameter. One thing alone could not control superheat. (TEV goes a long way in controling superheat, but does can't control SH completly.)

08-02-2008, 10:23 PM
Although not incorrect it is fascinating that when discussing superheat everyone assumes we are talking about superheat at a certain point in a refrigeration system, namely at a point between the evaporator outlet and the compressor inlet. Generally this is the point of most interest for superheat but depending on the system, type of control methodology and numerous other things superheated vapour can and is at numerous points in the system. It is very interesting to measure the superheat at compressor discharge as well as compressor suction and this is often controlled by liquid injection or oil cooling in the case of a screw compressor. It is all affected by the suction inlet temperature.
Anywayback to the point the superheat at the outlet of the evaporator in a conventional DX system using a Thermal expansion valve is controlled by the expansion valve. If the expansion valve has been sized incorrectly or not set up correctly or the system is not running correctly due to loads of different reasons the valve often hunts and cannot maintain the desired superheat, but if all is well the valve will modulate to maintain the desired superheat regardless of what the compressor is doing.

The MG Pony
08-02-2008, 10:57 PM
5 years old, think we got a record for oldest necrothread!

Interesting comment non the less.