Scroll compressor

[AastroGuru]

I heard scroll compressors of smaller cubic capacity say 90 cc can have performance more than 170cc Piston compressor. Is it so?

What is the logic behind that?

Also i heard piston compressors are better than scroll compressors at lesser speeds. Why and how?

[sendhilkmar]

In general, scroll has high volumetric efficiency say 97% + than the reciprocating compressor whreas the 65 to 70% is the voulmetric efficiency. So for the same capacity the displacement of Scroll is approx. 30 % smaller than Pisto type.
The efficiency of scroll is alwas better than piston compressors as it has lesser moving parts than recips. Infact variable speed scrolls are widely used in comfort Ac application.

[Sandro Baptista]

In general, scroll has high volumetric efficiency say 97% + than the reciprocating compressor whreas the 65 to 70% is the voulmetric efficiency. So for the same capacity the displacement of Scroll is approx. 30 % smaller than Pisto type.

On the piston compressors The volumetric efficiency it depends of the pressure ratio and politropic exponent of the vapor refrigerant and the dead volume.
If you are talking about a single stage for AC I would say that the volumetric efficiency will be around 85%.