Refrigerator Water Cooled to Fresh Water Tank

[Palarran]

This exact idea has been discussed before. I'll try to find the thread. In my opinion the way to do it correctly is to remove the tube in tube condenser coil and run a new condenser coil directly into the tank. It would entail cutting a hole in the tank. But, then you wouldn't have to have a water pump at all. Another way to to it is use an air cooled condenser and use the water tank as a de-superheater. Then, you would have a fan on the air cooled condenser coil that would be engaged if head pressure rises too high.

My concern would mostly be around always having 110 degree water coming out of the tap and if algae would grow to fast.

[Palarran]

I think this was it:
http://www.cruisersforum.com/forums/...tem-18439.html

[kiltym]

Originally Posted by Palarran

I think this was it:
http://www.cruisersforum.com/forums/...tem-18439.html

Yup, this is a thread about putting the condenser coil into the tank. I read through all that earlier today.

I guess I am looking at an easier solution by just using the water and a pump since everything is already in place for this.


I don't want 110 degree water either, especially since we are drinking it. This is also my concern, and why I am looking for info. The algae, for us anyway, is not a big concern as we are pretty regularly using the water since we live on the boat and have a good filter system in place. The water in the tank I would think is about 80 since we are in the Caribbean. A 30 degree temp rise is too much for me to consider, 5 degrees, I could probably deal with. The question is how do I know before I do it .

[captain465]

Why not use the keel cooler, but mounted in the water tank? This would keep the two systems isolated from one another, yet still give you the advantage of a "no pump" system...the main advantage of the keel cooler. There would be no difference in the amount of heat the water in the tank would have to accept. It would be wise, however, to calculate the ability of the water in the tank (+/- 25 Gallons) to absorb the heat.
I will testify to the benifits of the keel cooler........no pump, strainer, hoses to maintain, plus power usage savings.

[Sailmonkey]

Originally Posted by Larry

Might get a coil of soft plumbing copper place it in the bottom of the fresh water tank - presto freshwater heatexchanger with no cross contamination.
Cheers
Larry

Originally Posted by kiltym

This is true, but it entails a bunch of other issues, like cutting a hole in the tank, somehow attaching it so it doesnt move around in the tank, length of copper tubing that the refrigerant can move through, etc, etc. There have been other threads and people that have done this as well.

Using the water is easy. Two tee fittings from the already existing hoses.... Thats why I am curious about it. There has been some talk, but no people that have real experience with how it works.

I think that what was meant by this is to use the coil of copper to run some water in. Keeps the refrigerant seperate from the cooling water seperate from the drinking water. Also if the water tank is ever run dry the closed cooling loop may be able to continue to operate the reefer, but at a reduced capacity.

[JimJohnston]

our caliber 40 has two water tanks and the previous owner arranged to have the frigoboat fridge/freezer combination to pump water from the 70 gallon tank. We haven't used the water for drinking at all (in fact I plan on flushing it and changing it in the near future for fear of algae contamination). the system has worked well as a heat sink and has pretty well been maintenance free, which is a bonus. However, we did have to replace the condenser and evaporator pan when they failed recently. But it wasn't salt water corrosion that did it!

Cruising in the Bahamas was not a problem even though the water around us was close to body temperature. The heat dissipated quickly enough not be an issue.

[svcambria]

I'll chip in as someone who actually does run fresh water from the tank to the compressor to cool it. I have two systems, one an Adler-Barbour Supercold combined air and water cool to an evaporator box, and a home-made water-cooled system to a holding plate. In the winter I just run the AB and in the summer (Mexico) I run both, and both are plumbed to draw and return cooling water from an 80 gallon steel tank, which is under a salon seat and next to the hull.
Theoretically, the heat "mined" from the ice box should be removed from the cabin altogether, but dumping it into the water tank has had no noticeable effect on the water temp in the tank or the air temp in the cabin. Equilibrium with its surroundings seems easy to achieve; the fresh water has never seemed warm (warmer than ambient air temperature). I have run these with as little as 10 gallons in the tank.
An argument can be made that corrosion in the water-cooled condenser could corrupt the fresh water. This is certainly possible but apparently not very likely. The fresh water doesn't have the caustic properties of sea water, and I have been using this arrangement for about eight years with no problem. (One non-discussed benefit is that I can run it in the yard as well.) Someday it might happen; I assume I would taste it in the water, but in any event before I drank too much of it I would notice that my compressor(s) weren't working, and investigate why.
Science alert! An AB Supercold unit is designed to remove up to 650 Btu per hour. That amount of heat if entirely put into the water would raise 650 pounds of water by one degree F. A 55 gallon tank has (55 gallons)*(8.3 pounds/gallon) = 456 pounds of water; a 'fridge running full out will raise the water temp by 650 Btu per hour/456 pounds of water = approx. 1.4 degrees F per hour. Your water tank if warmer than its surroundings is shedding heat as well. Science alert over.
Now to roll up the shirt sleeves to arm-waive a bit - how long would an unisulated hot water tank stay hotter than its surroundings? Common-sense answer - not very long.
FWIW, I use March magnetic pumps and a sea-strainer to circulate and clean the water. A poly. water filter would probably be better, and someday I will be motivated enough to change filter housings...

Michael

[Palarran]

Well, that's about as good as it gets. Thanks for the input Michael.

[jkleins]

I think one question that we haven't addressed is that the whole purpose of having water cooled refrigeration is that the water is hopefully a little cooler then the air temp and will be more effective at removing the heat from the refer and will take the heat out of the boat reducing the inside boat temperature.

If you drive up the water temp and just recirculate the water you may find that the efficiency goes down to the point that you are better off with an air cooled unit since you avoid the energy costs of the pump.

Since the tanks are located in the boat and the heat that they dissipate stays in the boat you haven't done anything that an air cooled unit couldn't do cheaper and maybe more effectively.

Jim

Edit: I guess it was being addressed as I was writing. :-)

[jkleins]

Originally Posted by svcambria

...
Theoretically, the heat "mined" from the ice box should be removed from the cabin altogether, but dumping it into the water tank has had no noticeable effect on the water temp in the tank or the air temp in the cabin. ...

While it may seem like that it has to have been increased by the same amount of energy that is removed (650 BTU's) per hour. I guess that is what I was trying to get at. That 650 BTU's has to go somewhere and the question is "is it more efficient to just blow that out into the air or pump it into the water and have it transfer to the air?"

I think only the engineers that know the actual efficiencies of the units can tell us for sure. I know the guy I worked with (Sea Frost) felt his units were efficient enough that you couldn't run the pump for what you were losing by going to air rather then water. I think if you aren't even removing the heat from your boat you have even less reason to use water cooling at all.

Jim

[svcambria]

Water is soooo much more efficient at moving heat:

Overall Heat Transfer Coefficients for some common Fluids and Heat Exchanger Surfaces

so even when water and air temps are the same (which in the tropics is most of the time) water will continue to remove copious quantities of heat where air won't.

The devil is always in the details; does the amp draw of a water pump justify its use?

Series 893 Pumps

Model 893-07, uses 1 amp when running.
A Danfoss 50 uses 5 to 7 amps per hour:

http://de.refrignet.danfoss.com/Tech..._ed100e502.pdf

If the compressor is using 6 amps and you cut down the run time by 16 per cent or more with a water pump (not a difficult threshold to meet), you are better off...
Only your mechanical engineer knows for sure...

Michael

[JimJohnston]

I just did a quick test: the freezer and pump are both currently running and the current draw measured on the link interface is around 4 amps. There are some instruments and leds on at the moment too with a total load of 4.8 A. The freezer is at 20F. We are currently on the Chesapeake where a few days ago we opened the freezer to warm the cabin!

[MarcW]

Check out OZEfridge www.ozefridge.com.au, we have one but have yet to hook up the fresh water cooling.
The system requires around 50L tank of fresh water to add additonal cooling to a sytem.
We have yet to get to the tropics will hook it up then.
System run well no issues.

[kiltym]

Wow!

Thanks Michael and Jim. Just the information I was looking for.

I can't say thanks enough for being willing to post your experiences and thoughts. There is a lot of theory about it, which I have looked into, but was also wanting some actual information from people who did it. Thanks again.

Certainly there are some "drawbacks" that people have brought up, but I guess as with everything on our boats, everything is a bit of a compromise. I am glad though that this does seem like a viable option for me, and others, that might be looking to do something like this. I do agree water transfer is far better then air transfer when in the tropics, even though some experts disagree.

All the suggestions for other systems, that's great, but if I had unlimited money, and the ability to move and re-arrange everything, I would have taken that approach from the beginning (and probably gone with a keel-cooler, water and no pump is a nice combo). The idea here is I want to work with what I have already, and try to improve it without breaking the bank, or my back.....

Thanks again, and I hope everyone gets a great sail in this week!

[kiltym]

Originally Posted by JimJohnston

I just did a quick test: the freezer and pump are both currently running and the current draw measured on the link interface is around 4 amps. There are some instruments and leds on at the moment too with a total load of 4.8 A. The freezer is at 20F. We are currently on the Chesapeake where a few days ago we opened the freezer to warm the cabin!

I assume you have a Danfoss 35 compressor on your Frigoboat? Those numbers seem low for a 50....?