Suction & discharge cooled compressors

[Peter_1]

Most hermetic and semi-hermetic compressors are suction gas cooled and very few are discharge cooled. What's the advantage of the discharge cooled ones?
What AC brands use discharge cooled compressors?

[monkey spanners]

I think the discharge cooled ones are mostly rotary ones in air con applications. I think it helps reduce noise and oil carryover.

[al]

Hitachi use discharge cooling if i remember rightly?

[Peter_1]

And Daikin VRVII and III as well but what's the advantage?

[mad fridgie]

Ah ,this is a good question.
Think about the point of entry into the compression chamber (not the compressor), with a suction cooled system, refrigerant must pick up superheat, hence effecting the the possible refrigerant mass flow. So in theory a discharge cooled comp has to be more efficient, (well the compression part). This could also effect maximum discharge temp.
Do the windings transfer heat easier, because the discharge gas is more dense, and because the whole shell is hot, is heat dissipated more easily. Or because suction is cold, the winding do not become as hot in the first place. How does winding temp effect motor efficiency, or are any advantages or disavantages, accounted for in the motor design.

[al]

Also if the windings are at discharge temperature do you have fewer issues with windings to earth?

al

[Yuri B.]

How does the "discharge cooled" compressor differ in appearance from the normally cooled one ? Suction pipe on the top and the discharge pipe at the bottom ?