Scroll compressor on a VFD?

[marinechiller]

Been lurking on here for years, and usually find good answers to my questions. But haven't been able to find a discussion on using a VFD to control a scroll compressor. My plant has a system with four 5hp Copeland scrolls running two evaporators to chill seawater and I have a spare VFD. Anyone have a reason not to try running one unit on a VFD? Currently we control temperature by chilling to just below the target and then heating (oil-fired boilers) to our target temperature. This is to keep the temp at 5.5 degrees C +/- 0.2 degrees. Our chillers are currently on/off controlled and the temp swing is too great without the boilers running.

[smilies]

I would contact Copeland and see what they say. Copeland does have a Digital Scroll out, maybe some bearing difference between the two.

[SteinarN]

Copeland scrolls runs fine on a VFD. I think the limits is 35 to 75 Hz, maybe dependent on supply voltage. A phone to a suplier should confirm this.

[Peter_1]

What a waste of energy, cooling and then reheating it to achiev a correct proces temperature.
We've done something similar and control it also within 0.2°C.

Cool as you say a small vessel like you do... 1 tot 2°C below desired proces temperature.
Install in the return line to the vessel a servo controlled 3 way valve which bypasses some warmer return water back to the colder outlet of the boiler.
You use this way the warmer return water to reheat a little bit.
The control signal comes from the outlet of the small vessel and this signal comes into a PID controller.
These valves with controller are available by Siemens/Staeffa Controls, Honeywell, .... and aren't not that expensive.

I think you can control your scroll from 35 Hz to 60 Hz, depends on the make.

Smilies suggested the digital scroll which is a very good alternative. But the compressors are in the machine I suppose.

I should invest the money in the 3 way valve instead of the VFD.

[marinechiller]

I agree on the waste of energy for controls. The price of oil is finally driving us to fix this. The 3 way valve sounds like a great solution. We have a spare VFD but with the price of oil and power, it's about time we did it right.