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Paul_L
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Posted: 09 January 2018 at 5:22pm | IP Logged Quote Paul_L

Are there any experienced refrigeration techs out there?

My big 5 year old Freon compressor in the heat pump is popping the 50 amp circuit breaker instantly. It's a 6 ton R-410 Copeland scroll compressor with a locked rotor current of 149 A and a rating of 69,000 BTUs. I have found an exact replacement in Indiana for $750.

This compressor was always a little oversized. I had to monitor the suction and discharge temperatures closely to avoid the compressor's internal overpressure lockout. This resulted in relatively short operation cycles and a lot of repetitive starting and stopping.

The backyard heat exchanger field (100 feet by 60 feet with 6000 feet of 3/4" HDPE pipe buried 7 feet down) was not quite big enough. I knew this when I dug the hole back in 2012 but I couldn't make it any bigger.

Does anyone know if I can replace the compressor with a slightly smaller compressor without changing the size of the plate type heat exchangers or the thermal expansion valve?

I presume that if I reduce the compressor size I would have to determine the amount of refrigerant to load by creeping up on the amount of superheat generated by the evaporator. My guess would be to shoot for about 12F of superheat. I know that this would have to be done by charging with R-410 as a liquid because it is a misture of two other refrigerants with slightly different entropy curves.

Paul in NY



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chronic
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Posted: 10 January 2018 at 6:31pm | IP Logged Quote chronic

[ -- knowing zip about actual fridges -- ]
I guess it is running in extract-heat-from-field mode, but the field is very cold right ? Is it gulping liquid/emulsion freon instead of vapor, why is the current
high ? It makes me think a small bypass ie backflow might help ie so the compressed vapour would be fed back and precondition the intake mix a bit ?
[ I repeat, I know zip about fridges in general, apologies for sheer speculation ]
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palcal
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Posted: 10 January 2018 at 7:12pm | IP Logged Quote palcal

I am a refrigeration mechanic but worked mainly on domestic and small air conditioning. 69000 BTU would be about 3-4 HP compressor. If the 'new' compressor is not all that much smaller it should be OK, you may have to adjust the TX to get the correct superheat. If the 'new' compressor is a lot smaller you would have to change the TX and suffer a loss in heating capacity.
I have the opposite problem where I live the water out of our cold water taps is 30C (86F).
Paul.

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Paul_L
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Posted: 10 January 2018 at 10:49pm | IP Logged Quote Paul_L

Stuart, the breaker pops instantly, it isn't a case of the current being a little high. The compressor is a Copeland Scroll which is very tolerant of liquid ingestion. The compressor motor is definitely fried. That breaker tolerates the normal locked rotor current of 150 amperes on every startup.

Paul, the compressor is a 7 ton 5 hp monster. I'm just guessing that I can install a smaller compressor without changing the heat exchangers or TXV. I have found a 5 ton scroll compressor for $675 in Ohio. The labor involved in modifying the tubing to fit the smaller compressor and brazing the thing in is considerable. I kind of think that I will have to carefully flush the plate type exchangers and the TXV with a solvent to get rid of the crap from the cooked motor. I don't really want to start doing this unless I'm assured that it will work. An additional complication is that the thing also contains a reversing valve so it can pump heat both ways.

The alternative is to just replace the whole gizmo for about $2500 which will give me a different set of exchangers and a matched TXV (and a new cabinet).

Fortunately I have backup heat. Central Hudson Gas and Electric finally installed a natural gas main in my street two years ago and I immediately hooked up to it then I installed a 200,000 BTU Navian condensing water boiler. Five years ago I was stuck buying #2 fuel oil at $4.20 per gallon. Now I'm buying natural gas at the equivalent of $0.80 per gallon of oil.

Since then I really only need the heat pump for the summer cooling it provides.

This will, of course, throw the nearly finished control program into a cocked hat because the new heat pump will have much less capacity and I won't have to worry about over pressure conditions.

According to some government agency I am located 75 miles north of New York City on the 52F thermocline which means that at a depth of 7 feet the ground temperature varies from 62F in September to 42F in March. That makes it relatively easy to extract heat in the winter and dump heat in the summer.

Paul in NY





Edited by Paul_L on 10 January 2018 at 10:56pm
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palcal
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Posted: 11 January 2018 at 6:49am | IP Logged Quote palcal

Flushing the system is essential, the burnt gas and oil is acidic and will damage the new compressor.
Paul.

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palcal
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Posted: 11 January 2018 at 7:24am | IP Logged Quote palcal

Can you still get the Freon gas, they have been phased out in Australia. The latest Air Conditioners here use R32 a HFC refrigerant. What gas were you using R22?
Paul.

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Paul_L
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Posted: 11 January 2018 at 7:13pm | IP Logged Quote Paul_L

Paul -- it's a fairly modern compressor using R410A so that will be no problem.

I don't know how I will manage to flush it adequately. The plate type heat exchangers have a lot of tiny passages which are going to be a problem. Lots of nooks and crannys for junk to hide in.

Back in January of 2013 this thing had its reversing valve fail so I replaced it and a filter / dryer, flushed the system, pulled a 20 micron vacuum for 24 hours, and put it back to work.



After Installation of New Reversing Valve and Filter Dryer


Flushing and Evacuating


I found a lot of what seemed to be flux deposits in the old reversing valve. I suspect that a lot of this trash was still circulating in the system after flushing and may have contributed to the recent compressor failure.


Then again, it worked well for nearly five years after the system was opened up to replace the reversing valve so maybe it failed for some other reason.

Paul in NY
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palcal
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Posted: 11 January 2018 at 7:53pm | IP Logged Quote palcal

I would be looking at spending the $2,500 for a new system.
Paul

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Azure
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Posted: 11 January 2018 at 8:05pm | IP Logged Quote Azure

@Palcal (Paul)

If there was a section on TBS about air conditioning, compressors and such I am sure you would be flat out trying to respond to any sensible posts.

But then that would take you away from MM stuff, so that's not good.

Edited by Azure on 11 January 2018 at 8:05pm
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chronic
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Posted: 12 January 2018 at 8:24am | IP Logged Quote chronic

In general is HDPE used with refrigerants a lot ? I am wondering,
often plastics have plasiciser, stabilisers etc that slowly extract into
solvents

Edited by chronic on 12 January 2018 at 8:24am
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Paul_L
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Posted: 12 January 2018 at 1:43pm | IP Logged Quote Paul_L

@chronic -- The HDPE pipe is not suitable for use with refrigerants. The stainless steel plate type heat exchangers transfer heat to a water/alcohol or water/glycol mixture which circulates through the 6000 feet of HDPE pipe buried 7 feet down in the yard. Heat is dumped into the ground during the summer, and absorbed from the ground during the winter.

@azure -- I posted this here because I have been working on an MMBasic heat pump controller for about 2 years and have been discussing the controller with people here. This compressor failure will very likely change the operational requirements for the controller, depending on how I re-implement the heat pump. Then again, maybe I stuck it in a microprocessor forum because I'm very old and confused.

Paul in NY
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palcal
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Posted: 12 January 2018 at 4:27pm | IP Logged Quote palcal

@azure
Don't really know what you mean. I was a refrigeration mechanic for over 45 years but as I said not specifically in this field. If I am wrong on anything I have said please let me know.
Paul.

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