Estimating added winding superheat in hermetic compressors.
Hermetic compressors A good idea but hungry on refrigerant vapour to cool the electricals.
Now many have heard me go on about the pressure enthalpy charts. They can be used very loosely to predict winding superheat on the refrigerant , and this is no means accurate but as a guide.
The theoretical discharge port temperature is derived from adiabatic compression lines but it predicts this from given vapour entering temperatures to the compressor. What we don't see is the extra energy added to the already superheated vapour by the electrical motor in the atmosphere of the dome prior to inlet for compression.
You can sort if predict it , but its best done with a system balanced and with ideal evaporator design superheats. Using the difference between the vapour entering temperature , referenced back to the actual real discharge pipe temperature we can estimate the added K to the gas by the motor. Now this is not to be taken as literal , yet it is a guide to future problems.
If you understand the charts , you might get the idea , where we estimate the vapour entering temperature prior to compression by the given discharge pipe temperature as close to the compressor as possible. If you know the real vapour entering temp to the compressor. then it becomes a sort of take one from the other. I have shown an example of a AC unit system on R22 with around an estimated 15K of winding superheat added to the refrigerant after entering the compressor pulling down to 4.c S.E.T. at 40.c condensing temp and a vapour entering temperature of 15.c
Hermetics have bigger condensers due to this added heat, And why i always say that using a hermetic compressor for a freezer system is not the best option. Keeping hermetics well tuned and with low vapour entering temperatures by lower superheat really helps.
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