Centrifugal chiller showing high cond. pressure in Stndby 1

[Centravac]

I work with low pressure Centrifugal chiller (Trane) that is showing that it has exceeded the high condenser pressure. It has been in standby for last couple of months. It could be a sensor problem. but is there any other explanation for this. Thanks in advance.

 

[imok2]

I believe you have air in your system. Start the purge unit and get rid of the air, if you try to start the chiller it will probably go off on hi head. Watch out not to rupture the bursting disk(also a source of leaks)

 

[Centravac]

Yes. I was thinking about that but our purge pump out rate is zero. I was considering that the Purge could have gone bad. I will look for that but want to make sure that I know all the possible causes.

 

[Centravac]

Imok 2. Can you explain how does the bursting (rupture) disk rupture? I want to understand the concept. Also, if the area temperature around the chiller gets too high, wouldn't that also cause the high condenser pressure?

 

[chilled]

If you plan on learning centrifugal chiller service proceedures on the internet, do us one favour; Be totally upfront with the service mechanic when he is eventually called in to repair the original problem plus the additional problems created. Nothing is more frustrating than trying to troubleshoot a machine that has been monkeyed with.

 

[imok2]

The rupture disk is there to protect the chiller from excessive pressure and on low pressure systems the busrting pressure is determined by the chiller mfg and refrigerant used.

 

[Keith53]

Quote "that is showing that it has exceeded the high condenser pressure..."

I'm assuming you mean it has stored a fault condition, in this case an incedence of high condensor pressure.

If so, this can be caused by several things, but not realy mean there is a fault in the chiller.

-If condensor pump stopped or failed while chiller was running, then chiller should have shut down on flow switch. However flow switches are prone to failure, and chiller could then shut down on high condensor pressure due to high water temps. If this is the case, there is noting wrong with the chiller, but there is with the pump....Same can happen when basin water get's too low.

- If however there is air in the chiller, it will also cause it to indicate high condensor temps.

Not sure what refrigerant you are running, but R-11 will rupture the disc at around 116 degrees F....You might be running R-123.....Most discs are designed to rupture at 15 PSIG

Please post what type refrigerant you are using, the ambient temp in chiller room, and the pressure presently indicated in condensor while shut down.

Hopefully you have kept good operating logs. If so, you can review them and look for increasing trends in condensor pressure VS cond sat temp....If you see increase there, then tubes are very dirty or you have an air leak....Also look to see if comp discharge temps have increased over time....On L/P chiller you should be running about 118 degrees F comp discharge.

 

[Keith53]

Oh, ....Also describe if chiller chilled water sys has xconnect valves to hot water heating sys....Sometimes if so equipped, the valves can leak and cause high temps in idle chiller....If they get high enuff it will blow the disc and you will lose complete charge.

 

[HVAC68]

Also check the condenser tubes for fouling. Time to clean them ?
How about the inlet water temperature to the condenser ? As per design ? or has it gone up due to some other reason (Cooling tower related - like fan not working) ?

HVAC68

 

[Keith53]

Yes, check to see if tower fan is operating, and also VFD drive if so equipped.....Also good time to check operation of tower cold water basin by-pass valve to hot basin.

 

[Centravac]

We have two chillers. One is always running, while other is in standby. This particular chiller has been in standby since May 2007. The high condenser pressure trip is at 1 inHg Vacuum. Refrigerant is R-113. Area temperature fluctuates between 85 F to 96 F. Since there is no water to the condenser as it is not running, inlet water temp would be irrelevant. We do not have cooling towers. Water is drawn directly from the river and hence it fluctuates between 35 F to 85 F from winter to summer. Also, some one asked if chiller chilled water sys has Xconnect valves to hot water system and the answer is no.
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Microprocessor shows the condenser pressure that is direct convert of condenser refrigerant temp to Pressure (No Pressure elemet). The trip comes from a separate pressure element in the condenser. When the high condenser pressure alarm came in, the microprocessor was shown Ref Cond temp to be 86.9 F (-6.6 lbs) but when the pressure was measured from the pressure gauge, it was about 0.5 inHg vacuum (-0.25 lbs). Hope this clarifies.
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Also, we have verified that the purge is working and there is no air in the machine.

 

[chilled]

There is air in the machine.

 

[absrbrtek]

Air in the machine.

 

[Drivewizard]

How did you verify purge is working? What type of purge is it. Recip, purifier, etc.

 

[Centravac]

It is purifier. We did the functional test (as stated in the Vendor manual) to verify that the purge runs at 18 F and stops at 22 F. Verified that air was bleeding out. Also, verified that the chiller refrigirant is condensing in the purge unit and going back to the condenser of the chiller. We had a extra unit on site so we replaced it. Now the suction temperature is in negatives and staying there and the chiller is loosing vacuum. Also the line from purge evaporator coil to compressor is freezing. Chiller is not running.

 

[Drivewizard]

You need to pull the refrig and pressurize with nitrogen to find leaks. Your Purge can't keep up with the air leaking in.
Did I understand you correctly, did you put a whole new purge unit on. If so, maybe the restrictor is plugged in pump-out line,or there is so much air that pumpout never shuts off. Regardless, you need to find leaks and repair. Good luck.