2 chillers in series

[giovanni]

I was just wondering if 2 units in series is as good as one main unit. Here is the situation. On a trane 200 ton unit with 2 screw compresssors, one of the compressors blew. To keep the ice from melting in the rink a 125 ton unit with 2 screw compressors was connected in series with the 200 ton unit, which is operating with only one compressor at this time.
In this situation would just the main (200 ton unit fully working (after repair) give better results than the 2 units working now in series. Just curious. Thanks in advance

[Lowrider]

Are they really in series or parallel?

It's more usual to put them parallel. If there's a good management system that will adjust setpoint or current limit of both machines it will keep the leaving water steady!

Why was the screw blown? What type of screw? CHHN?

[Triggerman]

Howdy!

The most efficient system I've ever seen was two 2000 ton Trane centrifugals in series. The base machine ran at 100% capacity 24/7 and the downstream machine trimmed out the load. It works great because it keeps the base chiller fully loaded.

Hope this helps,
Ben

[giovanni]

Thanks for the response guys. My mistake they are parallel. The screw blew due to a short in the compressor it went straight to ground. The error was loss of phase. Im not sure of the compressor manufacturer, but the unit is a Trane RTAA200.

Right now they are both only running at 50% capacity. A service tech is coming Monday to check is out... Thanks again guys

[Triggerman]

The RTAA series is the finest air-cooled chiller ever made IMNSHO. The RTAA200 has two CHHx compressors @100t each and they are all manufactured by Trane in their Pueblo, CO facility. Good luck on the repair.

Ben

[Lowrider]

The RTAA is one of the better chillers!

You say it was blown because of phase loss?

I would like to know what the tech finds!

[giovanni]

The tech found that it shorted internally and went straight to ground. The plan is to eventually change the compressor. They temporarily connnected a 125 ton 2 screw unit in parallel and added and addtional pump for the glycol. So far all is working ok.. just waiting to see what happens this weekend when the outside temp jumps to 85-90 F.

[US Iceman]

What caused the ground short? If it was internal how did he find it?

[Lowrider]

What caused the ground short? If it was internal how did he find it?

Did he open it? Did an acid test?

[BOAB]

Having Worked For Trane For 3 Years We Do Not Do Acid Tests

[giovanni]

this is a rental unit and they determined that it was a dead short in the compressor. The error code it showed was "Loss of Phase." They in turn connected a second chiller (in parallel) which is now working fantastically. WE actually have better ice than before

[Lowrider]

I work for Trane and we do acid tests annually.

Did it trip on HP? or was there a power failure?

[US Iceman]

Help me out here guys, but if the motor failed due to a loss of phase would there even be any noticeable acid content?

The phase loss would almost be an instantaneous failure, so there might not be sufficient running time to actually develop acid content.

Do these chillers have power monitoring for phase loss, voltage imbalance, etc.?

[Lowrider]

RTAA's measure amps and inbalance between them.

If it was acid before the burn out it would explain why!

Phase loss is also displayed after a HP trip!

[US Iceman]

If it was acid before the burn out it would explain why!

Sure, then the problem may have started from something else and not an electrical failure. I'm just trying to understand what caused the fault.

If it was not due to electrical failure, then this points to air/water in the system and possibly high discharge pressures/temperatures. Sort of what I would call a precursor to a running burnout.

[Lowrider]

That's why I asked if it tripped on HP!

Phase loss will occour if it trips on hp, one of the phase's fails or if one of the motorrelais doesn't work correct!

[Dan]

Help me out here guys, but if the motor failed due to a loss of phase would there even be any noticeable acid content?

The phase loss would almost be an instantaneous failure, so there might not be sufficient running time to actually develop acid content.

The worst burnouts are from phase losses. The other two windings cook over a very long period of time as they try to keep the motor running. If you look at a stator that had a phase loss the lost phase is pristine. It's the other windings that are black.

[Triggerman]

Before we further this conversation, let's look at a couple of things. Domestic chillers are the basis for my experience and the comments to follow.

RTAA chillers are availble in a large variety of configurations. There are larger and smaller frame models. The RTAA200 we have been discussing is a large frame. Within the large frames there different controller package generations. Within each controller package there are options for protecting the compressors. For instance: if fully protected, the newer controls package can detect a loss of phase and shut the compressor(s) down within 1/4 of a cycle to prevent phase-loss damage.

The complete unit model number (a string of numbers and letters seeming to extend forever) is required to reveal the exact controls package and the options installed to protect the chiller. Even with that info, there is still no way to know until you dive into the configuration. This Spring, I performed an annual maintenance on an RTAA chiller and found almost all of the features turned off in the configuration!

Just my two cents worth.

Ben

[giovanni]

There was no power loss in the area or any problems with electric supply from power company that we know of. After the error code was displayed the service tech that arrived on scene reset the unit and the compressor ran for only a 1/2 hr and shut down again with the same error code for phase loss.. Thought that might help.. I could also give you the complete string of numbers you mentioned previously