Variable Speed Drive on Centrifugal Chiller

[Jubaer]

Is theer any risk of damage of the compressor, if VFD is installed for Trane Brand Centrifugal Chiller? The VFD's shall be install only to reduce inrush current. 650 Ton Centrifugal Chiller with 134A refrigerant and model is CVGF-0013.

[KnewYork]

Trane sells VFDs with their chillers (at least in the U.S.) so they must believe it's O.K. York has been selling VFDs on centrifugal compressors for over 30 years. I believe the technology has been proven.

[Jubaer]

As I am suppling the VFD's and Chiller's are going to be supplied by another comapny, I was little bit confused, if there is any challenge to commission the VFD. I gues it should be like operating a fan motor through VFD, as our goal is to reduce the inrush current only.

[DDC_Dan]

You're going to feed an otherwise constant speed machine with a 3rd party VFD? Interesting. I wonder how the chiller's motor protection, etc. will react. Does Trane know about (and approve of) this installation?

650 tons.... That's a pretty hefty VFD.

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[KnewYork]

You're going to feed an otherwise constant speed machine with a 3rd party VFD? Interesting. I wonder how the chiller's motor protection, etc. will react. Does Trane know about (and approve of) this installation?

650 tons.... That's a pretty hefty VFD.

Putting third party VFDs on chillers is done frequently. Using it as a soft start only seems to be a waste of its potential, but there are many controls considerations that would have to be addressed to vary the speed while it's operating.

I would guess the VFD will be around 500 HP. Not that large considering York offers an 1100 HP and ABB makes low voltage drives to 7500 HP.

[DDC_Dan]

Putting third party VFDs on chillers is done frequently. Using it as a soft start only seems to be a waste of its potential, but there are many controls considerations that would have to be addressed to vary the speed while it's operating.

I would guess the VFD will be around 500 HP. Not that large considering York offers an 1100 HP and ABB makes low voltage drives to 7500 HP.

I guess I've lived a sheltered life, have never seen this done. Seems like a soft-starter would be more cost effective than a VFD.....

One of my customers has a total of 6 York YK's, 900-ish tons each. Two were ordered as VSD, four were not. They are on an energy-saving kick, and plan to have the rest factory retrofitted to VSD's. They are also installing VFD's on everything in sight - CHW and CW pumps, Tower fans, just to experiment with various strategies.

[Tech Rob]

Why are you doing this? Are you in an area where starting the chiller with a traditional Wye-Delta or Solid State Starter would have an adverse effect on the power grid or other loads in the building? Using a VFD as a starter, i.e. ramping up to 60HZ and keeping it there is less efficient than just starting with a conventional electro-mechanical starter.

I see no reason why it can't be done, but I am interested in knowing what you're trying to accomplish, because a VFD may not be the answer.

[KnewYork]

Using a VFD as a starter, i.e. ramping up to 60HZ and keeping it there is less efficient than just starting with a conventional electro-mechanical starter.

It is true that running a VFD at 60 Hz. consumes more than a conventional starter due to the losses in converting power from AC to DC and back to AC. I think if it were me, I'd fix the drive to run at 57-58 Hz. (IF I was going to employ the OP's strategy.)

A VFD running at 55 Hz. is consuming 77% of the HP of the motor at 60 Hz. Even at 57 Hz. the HP is 85% of the rated HP. I would think there would be very few times that the chiller would be unable to make capacity when running at 57 Hz. What do you think? Would that work for this application?

[Tech Rob]

It is true that running a VFD at 60 Hz. consumes more than a conventional starter due to the losses in converting power from AC to DC and back to AC. I think if it were me, I'd fix the drive to run at 57-58 Hz. (IF I was going to employ the OP's strategy.)

A VFD running at 55 Hz. is consuming 77% of the HP of the motor at 60 Hz. Even at 57 Hz. the HP is 85% of the rated HP. I would think there would be very few times that the chiller would be unable to make capacity when running at 57 Hz. What do you think? Would that work for this application?

You make a great point. 57 Hz is 95% of the motor's rated speed. 90% of the savings that are to be had with a VFD are in the 50-60 Hz range. I think if the chiller ended up a little short on tonnage, it might be able to make up the difference by opening the vanes up a few degrees more or by running the condenser water a few degrees colder.

[R123]

I too am interested in knowing why you would do this for low inrush instead of a wye delta or soft starter.

[KnewYork]

I too am interested in knowing why you would do this for low inrush instead of a wye delta or soft starter.

There is terrific inrush with both of those starters when compared with a VSD. A VSD never pulls more than FLA, not true with wye-delta or solid state starter.

[joegrind]

I could see a room for a big pissing match between manufacturer of unit ,drive ,installation contractor, and engineer if it's not selected properly Or fails to perform in anyway. All things being equal if you reduce the htz you may lose your lift, surges are tough on the bearings, stalls are tough on the whole machine!

[R123]

There is terrific inrush with both of those starters when compared with a VSD. A VSD never pulls more than FLA, not true with wye-delta or solid state starter.

I know that. Like Tech Rob's asking, why is the inrush a problem? Is there issues with the electrical system not being able to handle the inrush? A VFD is a HUGE expense.

[Jubaer]

Electricity is the problem. There is huge power failure and needs to be depend on own generaation. If the VFD is not used, then the Generator sytem needs higher capacity.

[joegrind]

As mentioned in previous posts, frequency drives are not new to chillers! When used properly they can do some amazing things I would just recommend that you consu lt with the manufacturer They may have accessory components that will lend it better for the application

[KnewYork]

I think one of the things that wasn't realized by the responders to this thread is that this chiller is not in the U.S. When Jubaer said the TRANE chiller had R134a in it I knew this chiller wasn't located in North America.

The concerns about consulting the manufacturer are unfounded. Jubaer is just replacing one starter with another type. He clearly stated he wants to run at 60 Hz. So what difference does it make if he replaces a wye-delta starter with a VFD? Many VFDs have been put on chillers without checking with the manufacturer of the chiller. It's done all the time. If Jubaer wished to vary the frequency while running then he would have to have a way of controlling speed and vane opening.

If the owner of the chiller isn't concerned about electrical costs past inrush then running at 60 Hz. Is fine. I think I would at least experiment with running at 55-57 Hz. as the upper limit. Money could be saved with little loss of capacity (if any).

[Tech Rob]

If the owner of the chiller isn't concerned about electrical costs past inrush then running at 60 Hz. Is fine. I think I would at least experiment with running at 55-57 Hz. as the upper limit. Money could be saved with little loss of capacity (if any).

Agreed.

[Jubaer]

Thanks KnewYork. My clients concern is just to reduce the inrush current. I am working with VFD's for FAN and PUMPS application long time but this is the first time with Chiller compressor. So just to check whether my step is ok or nor.

[joegrind]

Why do some of us even bother? There's a reason why I only posted 100 times in 10 years!

[joegrind]

I don't see where the OP clearly states it will be 60 hertz, Where is he located? What is the voltage and the cycles?