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12-10-2008, 12:04 AM #1
Poor performance provision freezer
Hi there. Im new to this forum, and hope you guys can help me out with a problem.
Onboard this ship we have a provision cooling/freezing system consisting of 2 evaporators (one freezer and one in the cooling room) and two compressors sharing a common liquid line. Each compressor has its own condenser. System is running on R404
Experiencing very low performance when running compressor 2. Suction pressure barely over 0 bar Head pressure around 12 bar. Freezer Evaporator temp is only -6C. Liquid is visible in sight glass wet indicator is OK.
No problems when running compressor #1. -21C temp head pressure 15bar and suction pressure 1bar
We recently needed to remove a lot of oil from comp2 as it fills up while comp1 is loosing oil when its running.
We removed almost 2 liters. Max volume in sight glass is about 1 liter.
After we removed oil from comp 2 we can see foaming inside the crankcase. Can all this be due to a faulty reed valve?
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12-10-2008, 08:38 AM #2
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Re: Poor performance provision freezer
If nobody has added any oil before, you now have compressors starved with oil. Expect more compressor damage if system continue to run that way.
What is oil level regulation method in that system?
What is superheat and subcooling when compressor 2 is in operation?
What is crankcase temperature of compressor 2?
Does compressor 2 have crankcase heater and is he OK?
What is evaporator air in and air out temperature when you measuring 0 bar suction?
Does both evaporator solenoids are open when you have this low pressure?
Describe control logic of compressors and evaporators solenoids activation.
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12-10-2008, 06:16 PM #3
Re: Poor performance provision freezer
are the two compressors sharing a common suction line to??
Ice
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12-10-2008, 08:59 PM #4
Re: Poor performance provision freezer
Hi.
There is no oil level control of the compressors.
Only one compressor is running at any time. The compressors share a common suction line.
Both solenoids are open. When running comp1 there are no problems. Same configuration running comp2 gives low suction pressure and reduced heat exchange in both evaps.
ChengTrit
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12-10-2008, 09:11 PM #5
Re: Poor performance provision freezer
Here is a schematic of the system
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12-10-2008, 09:37 PM #6
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Re: Poor performance provision freezer
From this blurred diagram, I think you have oil separators at every compressor. Is that correct?
If you have bad read valve then suction pressure would be elevated!
You could make pump down of both compressors and compare pressure equalization time to establish are the valves are OK!
Are both compressor of same model# and one of them is as redundancy? They newer work together?Last edited by nike123; 12-10-2008 at 10:02 PM.
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12-10-2008, 10:27 PM #7
Re: Poor performance provision freezer
If you can't fix it leave it that no one else will:rolleyes:
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12-10-2008, 10:58 PM #8
Re: Poor performance provision freezer
Yes that is correct.
chengtrit
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12-10-2008, 11:18 PM #9
Re: Poor performance provision freezer
No,there is only one common drier for both condensers.
chengtrit
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12-10-2008, 11:23 PM #10
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13-10-2008, 12:32 AM #11
Re: Poor performance provision freezer
The highlighted valve is a non-return valve.
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13-10-2008, 02:03 AM #12
Re: Poor performance provision freezer
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13-10-2008, 03:30 AM #13
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13-10-2008, 04:12 AM #14
Re: Poor performance provision freezer
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13-10-2008, 07:06 AM #15
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13-10-2008, 07:15 AM #16
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Re: Poor performance provision freezer
Last edited by nike123; 13-10-2008 at 07:40 AM.
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13-10-2008, 07:54 AM #17
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Re: Poor performance provision freezer
Ignore.....
Last edited by nike123; 13-10-2008 at 07:57 AM.
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13-10-2008, 03:11 PM #18
Re: Poor performance provision freezer
Or possibly the oil return line from separator1 is hooked up to comp2?
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13-10-2008, 03:39 PM #19
Re: Poor performance provision freezer
Or maybe some sort of oil equalization system has been added that is not on the diagram?
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13-10-2008, 05:01 PM #20
Re: Poor performance provision freezer
Looking at the diagram: When one compressor is running, what stops refrigerant from gathering in, and staying in, the inactive condenser?
It seems to me that when using one system, the inactive system should be completely isolated by closing the hand valves before the compressor and after the condenser.
You might try running each system with the opposite system manually isolated to see if this improves the performance.Last edited by Gary; 13-10-2008 at 05:08 PM.
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13-10-2008, 07:33 PM #21
Re: Poor performance provision freezer
i think there is a valve not closing properly.or staying open.if you are working whit one line,there has to be a by-pass or a regulator to prevent things like that to happen??? or am i wrong ??
something is not wright in the drawing....
Ice
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13-10-2008, 07:46 PM #22
Re: Poor performance provision freezer
After each condenser, there are two manual valves in series (?). It seems like one of these should be a check valve?
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13-10-2008, 07:52 PM #23
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13-10-2008, 09:08 PM #24
Re: Poor performance provision freezer
Gents,
it is quite normal for oil to migrate to the off compressor where this type of common suction line is employed.
I have even seen the oil migrate from the discharge lines, where a worn check valve was fitted.
Kind Regards AndyIf you can't fix it leave it that no one else will:rolleyes:
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14-10-2008, 04:22 PM #25
Re: Poor performance provision freezer
Thank you guys for all input regarding this problem.
We will keep the standby compressor and condenser isolated and observe the oil levels in each crankcase.
After 24 hrs running it seems OK so far.
ChengTrit
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