Variable Speed Screw Hz

[750 Valve]

Just wanted to get peoples experiences with "overclocking" a semi hermetic screw compressor above its rated Hz, or any semi hermetic compressor for that matter (although I doubt you'd do it to a recip).

Have you ever seen a semi hermetic screw compressor running above 60Hz? Do you guys in the UK frequently run them up at 60Hz? Any issues encountered, oil, disch temps

I have been discussing this with a manufacturer which claims to have run comps as high as 75Hz if the drive and motor will allow it to.

I am contemplating running up to 60Hz, thats up from 50Hz which is our normal line supply, but had it mentioned to me we may even be able to go higher, what do you guys think?

[Coolest Sparky]

I have seen screws running up to 75 hz, but they are Bitzer open direct drive. Never had any problems.

[750 Valve]

Thats the type I'm talking about, except the HSK semi screws. Cheers, thanks for the info.

[JFK]

Bitzer semi hermetic screw, HS 53 & HS 64 series can run up to 75Hz, for HS 74 series can run up to 67Hz
The minimum is 20Hz. As standard, you set in between 25Hz to 60 Hz is pretty safe.

[JFK]

the range of speed in Hz for semi hermetic screw compressor is depend on it's motor size, for example Bitzer semi hermetic screw HS series ( HSK or HSN ) up to 60 HP nominal can run up to 75Hz, for above 60HP, the higher range is up to 67Hz or 4000 rpm.

I also know Bitzer even have hermetic screw about 15HP nominal size with special motor can run up from 20 to 87Hz, specially design for train a/c application

[750 Valve]

Thanks for the info JFK, we're running between 30hz and 60hz but if needed we have the cond capacity and motor capacity to run to 75hz, we do not require it though.

[Andy]

Thanks for the info JFK, we're running between 30hz and 60hz but if needed we have the cond capacity and motor capacity to run to 75hz, we do not require it though.

Sounds good to me. I have a number of HSN and OSN screws and a Howden all running at these speeds.

Kind Regards Andy D