Bitzer Screw Unloaders

[Joel404a]

Hi, I am monitoring a couple low and medium temp hill phoenix racks. Both have Bitzer screw compressors with two unloaders on each compressor staging capacity at 50%, 75%, and 100%. I have had great success in removing unloaders from capacity control on Carlyle screws because of their inefficiencies. I don't know much about the Bitzers yet and was wondering if anybody had any experience or data on Bitzer screw unloaders and efficiencies?

Bitzer HSN5343-25 Low temp
Bitzer HSK5343-30 Med temp

[Magoo]

generally the unloaders open a bypass port on the screw length. Disconnect power to each solenoid coil will keep compressor fully loaded. Ramp speed up and down with a VSD would be more efficient, minimum hertz for oil flow is around 30 Hertz

[GPD]

Quoting Magoo. Unloaders simply creates by-pass which means you spend power in compressing and then you by-pass what you compressed ... very poor efficiency. VSD is the way.

[THE DUDE]

Hi Joel404a
Do you not need capacity control for you application? It would be interesting to see the difference between running a lower SST due to less staging VS the Parasitic losses of utilizing the Unloaders.