High Amps on Chiller Compressor Motor

[MFJewell]

I am experiencing an issue with one of the chillers at my facility and am looking for some insight. The unit is a 1974 vintage Carrier 17DA unit. It is nominally 5000 tons (holds 15,000 pounds of R-134A).

We took it down for maintenance and have been experiencing 100+ amps higher draw on the motor after the maintenance. Both the evaporator and condenser were opened, cleaned, and eddy current performed. We removed the charge from the unit, dried it out and put it back in. Motor was not touched.

Before the maintenance, the unit had the following parameters: Chilled water flow of 8300-9000 gpm, 3800 to 4000 tons, 360-390 amps, guide vanes at 28-36%.
After the maintenance, the unit had the following parameters: Chilled water flow of 5800-6300 gpm, 3000 to 3300 tons, 450-485 amps, guide vanes at 41-49%.

We ran the unit in single pass and still had high amps. Put it back to double pass and confirmed the chilled water flow meter is correct, Sub-cooler level is good, hot gas bypass is full closed, evap dP is good. We have no abnormal noise or vibration from the motor and it megged good. I believe all of this seems to point towards an overcharge or refrigerant in the unit. Anyone with experience similar to this and have feedback on what to check next?

 

[lukaiENG]

What voltage are you getting at the chiller/components? perhaps the integrity of the electrical connection was compromised leading to low voltage/high current?

 

[MFJewell]

My plant electrician is out this week, so not sure of the voltage.

 

[willard3]

Could very well be low voltage

 

[MFJewell]

Motor checked out good.

We pulled almost 1800 pounds of refrigerant out of the machine and still couldn't make tonnage (limiting on suction pressure). Put about 400 pounds back in to get suction pressure up, but still can't make tonnage (limiting on amps). Starting to suspect I may have an issue with the compressor.

 

[BronYrAur]

a 1974 chiller running 134A?

 

[willard3]

I'm with BronYrAUR, your 40yr old chiller was not designed to use R134a and is down on performance. Probably designed for R11 or R12.

Check pressure enthalpy diagrams for 134a as opposed to original refrigerant.

 

[MFJewell]

It was converted by Carrier (along with two of our other units) to run 134A about 10-15 years ago. The performance guarantee was 4900 tons. We regularly get 4400-4800 tons from the converted machines. This particular unit was making as much as 4700 before this loss of performance.

 

[HVAC68]

Both the condenser and cooler flow rates are down from the earlier numbers. Any reason why this is so ? Low suction ? High discharge ?


HVAC68

 

[MFJewell]

Controls are set-up to meet chilled water leaving temp. The unit backs off when it gets high amps though. If the amps weren't going high, the unit would continue to load up and the CVs for both condenser water and chilled water would open further.

Suction and discharge pressures are nearly the same as before (34-35 and 100-115).

 

[Antifed]

Not sure if this document would be useful to you (in case you don't have it).

 

[MFJewell]

I have that one and the original one from when the unit was installed.

 

[LittleInch]

This may sound stupid, but have you actually, really checked that the motor is going the right way around??

Mixing up a phase can have this consequence.

but does sound like something not right with the compressor.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MFJewell]

Confirmed that the motor is turning in the correct direction.

 

[LittleInch]

Well more power for less flow but the same DP makes it look like the compressor, but can you confirm how this unit works?

Is it all on the guide vanes or is there a VFD in the way?

The operating instruction give different versions, but it looks to me like the guide vanes work to control flow based on ? and motor amps?

But chiller water flow is based on outlet temp? on a separate control circuit?


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MFJewell]

No VFD. As stated above, the unit is set-up to meet a chilled water leaving temp demand. Guide vanes will go more open as needed to meet that temp and make tonnage. Chilled water valve typically goes 100% open, condenser water valve typically 36-38%.

One other item we haven't fully investigated is the potential of bypassing water. This unit can be run in single or double pass. Depending on valve position, there is a chance we could be bypassing water back to the header. In doing so, the discharge flow is is missing some and it makes it look like the unit is short on tonnage.

Testing the valves and opening the compressor and next on the agenda come October.

 

[LittleInch]

Yes but what activates / controls the guide vanes?? You said the unit "backs off" due to high amps. I assume that was the guide vanes closing to reduce load (flowrate) going through the compressor and then the chiller control valves controlled on exit temperature?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MFJewell]

Correct, except that the condenser and chilled water control valves are pretty much constant throughout the range of operation.

 

[MFJewell]

Found the problem, an incorrectly ranged flowmeter based on logic changes during the annual (set to 15,000 gpm rather than 25,000). We ended up using an ultrasonic meter on the pipe, ran the unit and saw the discrepancy. Reranged the meter to the correct setting and the unit performs as expected.

 

[LittleInch]

Thanks for getting back to us all on an update. Doesn't happen very often but yes, re ranging the flow transmitters would do it!

So instead of what you thought was "Chilled water flow of 5800-6300 gpm" what do you now think it was??

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.