low temp refriger superheat

[paulsref]

Hi, I have a question on superheat for low temp walk in freezer. when using negetive numbers what is the proper way to calculate the compressor and evap superheat. Example: I have a suction pressure temp at evap of -18 and temp at bulb is -12 do I have a 6degree superheat? If compressor suction temp is -18 and I have a pipe temp of +10 would that be a 28 degree superheat. Example at compressor: -25 and -5 om pipe ? would that be 20 degree superheat?? Thanks for all replys Paul

[Gary]

Correct... correct... and correct.

[Sandro Baptista]

Correct, correct and correct :). A part is useful superheat the rest is non useful superheat.

[paulsref]

Thank you all for the confirmation!! I sometimes second guess myself and it is nice to get confirmation that I am on the right track. Thanks again Paul

[D.D.KORANNE]

When temp measured at suction valve & tex outlet , it becomes total system superheat which has a bearing on discharge end temp of compressor . Neither high superheat nor total superheat is desireable

[Sandro Baptista]

Neither high superheat nor total superheat is desireable

I don't agree totally with you.
For R404A and R507 and other gases of this kind higher useful superheat is harmless (not exagerated superheat) - 20 K for instance - It is advantageous due to increased capacity and the discharge temperature are not very high.