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Old 06-16-2016, 07:06 PM   #1
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Thoughts about cooling the refrigerator compressor itself using sea water?

I have a 10 cubic foot apartment sized fridge non frost free. The compressor gets very hot. The condenser coils run a lot cooler. The compressor sits under the fridge and of course a lot of heat wafts up and is absorbed by the fridge body, and it can heat up the cabin. It can be hot enough you could burn yourself touching it maybe is 140*F.

I have been thinking, I would like to cool the compressor. I have some 1/4 inch copper tubing.
How about wrapping copper coils around the compressor and have a small pump moving sea water through that.

Anyone know of an idea?
A small cheap aquarium water pump could move the water.
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Old 06-16-2016, 09:50 PM   #2
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Nice idea, but probably not practical. Do you really want another potential source for a leak. Also, there is the cost in power consumption when running off batteries. Think 1 or 2 muffin fans circulating air around the compressor while it's running would be far more realistic with a significantly lower energy cost.

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Old 06-17-2016, 06:32 AM   #3
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Put a DC computer fan behind the compressor and blow the heat into the cabin and out from under the box.

Plan B could be what was done in the 1920's , relocate the compressor on top or away from the fridge box.
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Old 06-17-2016, 07:33 AM   #4
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Nice idea, but probably not practical. Do you really want another potential source for a leak. Also, there is the cost in power consumption when running off batteries. Think 1 or 2 muffin fans circulating air around the compressor while it's running would be far more realistic with a significantly lower energy cost.

Ted
I don't think it's a terrible idea...

The thermal capacity of water is about 14 times better than air, so won't take much water to circulate to dissipate the coil heat, and not have to remove the same heat from the cabin air.

Depends on where the water comes in and goes out that might be a risk, plus the heat exchanger at the fridge.

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Old 06-17-2016, 08:43 AM   #5
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How do you plan to bond the copper tubing to the compressor can?

Could be buzzy when running if not a solid mechanical and thermal connection.

My experience with sea water and small tubes/pumps is not too good, they clog easy; plan for a good strainer on the intake side.
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Old 06-17-2016, 09:03 AM   #6
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I wondered about bonding the tubing. That could be done by soldering it to the compressor steel shell, with a lot of effort as in remove compressor.

Other idea is simply coil the tube into a hat and sit that on top the compressor.
That would transfer rising heat into the copper coils. Copper is a very good heat conductor.

I could tap off the head supply line. That intake has a strainer. Finding a reasonably priced little water pump maybe a problem. External small aquarium pump or maybe use a Tsunami bait well pump. 500 gph and works in salt water
https://www.amazon.com/Attwood-Corpo...bait+well+pump

I already use an 800 gph Tsunami pump for my Cruisair 16k heat pump, works very well. wonder if I could tee off its output? It could tee off at the pump or tee off after the cruisair condensing coil. wonder iff a tee would give it enough water flow to the fridge. I dont think it needs much to work. That clear plastic hard tubing for fridge water lines could be run to the fridge.

That pump is 15 feet away from the fridge. The outflow from the fridge coil could just exit the sink drain or even a 1/4 inch hole in the hull side.
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Old 06-17-2016, 11:02 AM   #7
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Yeah, bonding a tubing manifold to a curved surface is a hassle. Soldering would take so much heat likely that would destroy the compressor. And all paint would have to be removed too.

The "hat" would be real buzzy when running, and the heat transfer path would be: comp/to air/to copper/to water, not very efficient (30+ year mechanical engineering/heat transfer here.) If you could flatten the tubing a bit and band-clamp it to the non-tapered section of the can, fighting chance.

Maybe find a scrapped-out compressor can and and use the top half as a manifold that you JB weld to the top dome of the compressor. A couple of bulkhead barb fittings at either end for water in/out. I just scrapped one out last month when I turned my old 'fridge into a dock box, but its gone now, sorry.

I like your idea of tapping off existing pump and going to the sink drain. Good luck with this, I bet your yard is going to hell like mine 'cause I'd rather mess around on the boat!
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Old 06-17-2016, 11:25 AM   #8
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Is there a substance, that effectively transfers heat better than air such that you could saturate the areas of the copper tubing to the steel compressor shell?

Clamping or tie down the copper tubing with copper wires is good idea.
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Old 06-17-2016, 11:49 AM   #9
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Yeah, I've used it on photo-lithography equipment. It was epoxy filled with silver, real spendy/space-grade stuff.

The problem is keeping coefficients of thermal expansion of all the various materials close enough that it won't unbond under all the heating/cooling cycles of a 'fridge compressor can.

Maybe a home brew of epoxy and aluminum filings/powder. Aluminum has good heat transfer properties and would strengthen the epoxy resin. Build a masking tape/cardboard dam around the coil and pour it on. Keep the bond line thin as practical to minimize thermal expansion/fatigue issues.

There is thermal grease, used to bed power transistors to heat sinks. Sticky icky stuff, good with a thin bond line, no good if thick heat transfer path. Don't know how you'd keep it from running all over the floor when hot.
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Old 06-17-2016, 12:08 PM   #10
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Go to radio shack and buy a computer fan ,they are 120 volt ,12,&24 volt units. Tie in to wiring harness and cool comp. Water coil ,pump ,line distance will be a factor as well as how to bond tubing to shell. It's not rocket science. Just move more air than what's there.
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Old 06-17-2016, 12:16 PM   #11
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Good idea but try a source other than Radio Shack, they've been out of business for a year or two now.
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Old 06-17-2016, 12:18 PM   #12
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Still have one in marathon.
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Old 06-17-2016, 12:23 PM   #13
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Still have one in marathon.

Holy crap you're right! 3 local stores closed at the same time suddenly and I ASSumed the chain went under.

My bad, carry on and thanks for that information too.
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Old 07-09-2016, 06:57 AM   #14
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Save the effort. Cooling the compressor shell would be like wrapping the tailpipe of your car to cool the engine. If it's an air-cooled condenser, insure that the condenser has a free path to and from, make sure it's not recirculating reject heat and possibly introduce cool ambient air to the inlet side- anything to reduce the temps at the condenser. The condenser is where the heat transfer takes place, the refrigerant that circulates through the compressor is also removing heat from the windings. The windings of the compressor aren't the primary source of heat, the evaporator is. Read up on refrigerant theory and the refrigerant circuit, that will help make sense of what's going on in the equipment, and give you some insight into how to best improve the efficiency and reduce the load. If cooling the compressor shell was helpful, you'd probably see more attention to that in system design.
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Old 07-09-2016, 08:26 AM   #15
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You are Needlessly. Refrigerator compressors run hot! Often too hot to touch. Messing around with sea water pumps tubing etc would almost cost more than another small fridge

My suggestion would be put AC in the boat or at least some high volume fans and ventilation
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Old 07-09-2016, 10:01 AM   #16
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Here is a tidbit of wisdom passed to me....ACR is another of my weak spots so I thought I would just pass this along....

Quoted from post #14

"The windings of the compressor aren't the primary source of heat, the evaporator is."

Uh, the evaporator is where heat is removed from the space to be cooled. Refrigerant leaving the evaporator is generally cold compared to any other part of the circuit. There is no increase in sensible heat across the evaporator. The refrigerant leaving the evaporator is much cooler than when it enters. That is why an evaporator often frosts or freezes, the only heat is sees is the latent heat required to change the liquid entering to gas.

The compressor windings are hot and in a hermetic system use the incoming cold suction gas for cooling. The highest temperature is at the compressor discharge. The refrigerant is heated by compression so that the hot high pressure gas is more easily converted to liquid in the condenser by removal of the "latent heat of condensation."

"Read up on refrigerant theory and the refrigerant circuit, that will help make sense of what's going on in the equipment ..."

This last tidbit is edited by psn for general consumption....."good advice for all troubleshooting or repairing systems"....
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Old 07-09-2016, 10:26 AM   #17
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Compressor is designed to tolerate the heat. Heat is created by the motor, churning of the oil, and most of all the heat of compression. Heat is transfered to the discharging refrigerant, that's how heat leaves the unit. You could wrap the compressor in insulation and it probably still would not overheat. In fact some heat pump compressors are wrapped in insulation to avoid cold starts in winter.

If your complaint is heat being rejected from fridge into cabin, maybe you can set up one or two computer fans and some exterior vents to circ outside air and get the heat out that way. If running AC in cabin, just don't worry about the heat.

If your concern is poor circulation around the condensing coils, then fans or strategically placed vent holes in cabinetry can do wonders.

No way would I want copper piping circ'ing sea water in the cabin just for a fridge. Have to run a pump continuously and lots of new leak sources.
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Old 07-09-2016, 10:36 AM   #18
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Why split units make more sense, the condenser can be located in non living space,
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Old 07-09-2016, 10:46 AM   #19
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Why split units make more sense, the condenser can be located in non living space,

Yes. I really like my split units-- I have two Danfoss compressors tucked away in the generator room, and they are keel cooled. The other nice thing is how quite the system is with the compressors not in the living space, plus no cooling fan helps with the noise.
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Old 07-09-2016, 10:48 AM   #20
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My new self contained units are so quiet and low energy that the only complaint is the air flow noise. You cannot hear (notice) the compressors except for a quick hum that lasts less than a second.

To me having a single unit versus a split unit....I can have it at a good, non-marine air conditioner shop in a couple hours to be troubleshoot and repaired.

Too many places the marine A/C repair guys/shops are few and far between...and worse....not all that competent like so many other marine trades.
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