Having used both single and twin rotor machines, each has a place. In GENERAL, the single rotor machines do better on high evaporator temps or lower pressure ratio jobs and the power is better than a twin rotor.

A twin rotor machine will typically do better on a low temp evaporator of higher pressure ratios.

I certainly hope that the single rotor machines have the star seals and bearing problems solved which I suffered through.

As for twin rotor machines, I have seen a pair of small Fricks that had close to 90,000 hours on them...R22 service, evap condenser on a large cooler. The only repairs were on the oil pumps and each had a shaft seal.

Seen plenty with 50,000 hours plus in a well designed system.

It all boils down to the fact that you can put the best compressor built in a poor system and it will not do well. Put a poorly built compressor in a well designed system and it will do OK, maybe not well though. So for the best, design your system properly and use a well proven compressor.

For the money, I'll still stick to a twin rotor machine...be it GEA, Frick, Mycom or Howden. I tend to shy away from the other brands.

Ken