Water Cooled Fridge from main water tank

[StevenJMorgan]

Hi All.

I have a Isotherm watercooled fridge that currently has its own sea cock for water intake and drains out through a T in the galley sink.

So - its currently sea water cooled - not ideal, have to unblock regularly from sea life and salt crystals.

I'm thinking of cooling it from my main 200l fresh water tank which is in the keel below the sole. Idea is a T off water 'out' and returning back to tank through T in filler pipe. Has anyone done this and what are the pro's and cons _ we don't drink out of main water tank.

Also the fridge has a small anode - should I remove this and cap off for fresh water use.

Any ideas greatly received

Thanks

 

[PuffTheMagicDragon]

Interesting idea but I think that it will ultimately depend on the temperature of the water that is surrounding your keel and the temperature gradient between your fresh water tank and the sea itself. In other words, seeing that the sea water is currently (presumably) sufficient to cool your condenser, will the heat build up inside the fresh water tank or will it be able to dissipate to the exterior?

Compare with the following system.

TAMSEN II is a 170' (52metre) steel-hulled sailing yacht displacing 435 gross tons, currently in build at Perini Navi yard in Italy. The galley on the main deck has walk-in freezers and refrigerators. Instead of using sea-water as the medium for the condenser heat exchange, there is a tank in the keel filled with a glycol-based antifreeze solution. Heat from the refrigeration and air-conditioning system is exchanged with the antifreeze; the heat is then dissipated through the keel to the seawater. This limits the number of through-hull fittings and keeps seawater away from the condensers (Source: Professional BoatBuilder # 108, August -September 2007)

Not knowing your boat it is difficult to say but I think that, <u>provided that you can find a way of dissipating the heat build-up in the fresh water tank to the surrounding sea</u> the system could work. Otherwise you could soon be able to offer a tea-service to your neighbours!

Perhaps it is possible to build a dedicated tank directly into the keel? This could solve the heat-transfer situation. On the other hand, it might not be so efficient if your boat is built in FRP

 

[thalassa]

Keel-cooling is a feature often found on Dutch built steel yachts, even older traditional yachts. Normally for cooling inboard diesels, but it is done for fridges too. Two types : 1) boat keel is a box section and fresh water is simply circulated through the box keel (sailboats) 2) Freshwater is circulated through two external pipes, parallel to the keel (motorboats).
I've also seen freshwater piping running through the inner aft section of a fin keel to cool an engine. As you are based in a warmer climate, one of these solutions may be insufficient to cool an inboard diesel, but may be sufficient for a fridge. Some mathematics may be involved...

 

[jeremyshaw]

Lots of people do this in the Caribbean and pronounce it a great success. I have been meaning to convert my own boat, but have not yet done so.

You appear to be in the United Arab Emirates, so the seawater will be not dissimilar tin temperature to the freshwater tank. Therefore I doubt there is much difference in efficiency. In cold waters obviously sea water would be more efficient. Even in hot climes water cooling is regarded as more efficient than air cooling.

I have not heard reports of the fresh water tank getting warm. It goes up by a degree or two. And in any case, is that a problem? In the Caribbean we drink chilled water, and a lot of the water we take from the freshwater tank is then heated, so if it starts a tad warmer that can only be a good thing. Unless you have a tiny fresh water tank it's a huge potential heat sink.

You need to think about the circulation routes, and might need to install a check valve if you are going to tap into existing piping.

No idea about the anode I'm afraid. Can't see why it would be affected though.

 

[StevenJMorgan]

Thanks for the replies.

Water here is hot at this time of year like 30 oC plus! My fresh water tank is actually in the keel above the ballast and seems to maintan a very similar temp to the sea water. I think I will take some temp readings then set it up, let it run for a week and take a further set of readings.

Tank is 200 L so should be enough water. Problem I guess comes when running the tank down!

Cheers

 

[jeremyshaw]

I would be very interested to see what readings you get. This subject comes up now and again and the answers are either "you'll get a hot tank" or "loads of people do it". No one has yet given actual observations of temperature changes. Be particularly interesting when the tank gets low, as you say. So do post your findings!

 

[Anonymous]

Sea water down the sink is a bit of a pig's ear. Could you not at least T it into the sink drain? There should be no accumulation of salt as sea water is nowhere near saturated with NaCl. A couple of pounds on fittings an a couple of hours labour might give you a system that is both unobtrusive, and works.

The success of your proposal will depend on the thermal resistance between the water tank and the sea water. If the tank is well-sheathed then the thermal resistance will be quite high and the water will get hot. At a certain temperature, the performance of the Isotherm will drop off - your manual should tell you the inlet water temperature range it has been designed for.

Aside from this, any increase in tank water temperature will increase the electrolytic corrosion in your tank. This may or may not be an issue but don't assume that stainless tanks are immune, they are not.

It is a bit of a long-shot, I think. Purpose designed keel-cooler systems are available.

 

[ccscott49]

I would stick with the system you have, put an inline strainer in the system to stop critters.
I dont understand why you are getting salt crystals? You are not boiling the water?? There may well be a basic problem here, with the installation.
I would look at a booster pump to get more water through the sytem, if the water is getting so hot to leave salt crystals behind. The system pump should not let this happen.

I've been investigating and have never heard of this before and neither has a bunch of my friends, including those running air conditioning.

 

[Anonymous]

If the water is going into the sink itself then it will splash around leaving crystals, so by T-ing into the waste outlet this is avoided and it also allows the system to work when the sink is being use. Can't think who would have installed it to go into the sink /forums/images/graemlins/confused.gif

As for marine life, we have two Cruise Air air conditioners and there isn't a single in-line filter - it all goes through and I haven't had a blockage yet. Though unless one was sure, one would fit a stainer as you suggest; they are cheap and easy to obtain. The stainless steel mesh sort would be adequate.

 

[ccscott49]

In the original post, he says it's "teed" in to the galley sink.

 

[Anonymous]

Yes, so it does....for some reason I read that as discharging into the bowl. Can't see why it should get clogged with either salt or marine life. My aircon pipes are only 15mm, as are my watermaker lines and we never have any problems.

As you said, there should be no need to alter the system and you'd want to delve to find out what is causing the problem. Maybe a build-up of fat or other obstruction in the sink outlet? A kink in the outlet pipe? It might be problematic with some sinks when sailing, when heeled on that side, of course. The Nauticat 42 requires the two vanity basin outlets to be turned off when sailing (when heeled on that side).

 

[StevenJMorgan]

Current system has proper dedicated sea cock for the inlet through a filter and then into pump - outlet is T'd into sink waste in a proper fashion. Not quite sure where the idea of draining into the sink came from - that would be absolute rubbish and would last an nanno second on my boat where everything has to be correct or i can't rest.

This whole idea of cooling from the main water tank came into my head the other day when replacing all the cooling pipes to the fridge. Interestingly I threw away the old pipes this evening and the outlet / discharge was very heavy and full of shell so maybe this was the problem.

I still think I'll try the fresh water idea though cause I like experimenting, and I'll take readings before and after and let you all know. It might be a while till i get round to it though.

Thanks for the replies guys.

Fridge coolant draining into sink ............. Tut!

 

[Anonymous]

[ QUOTE ]
....that would be absolute rubbish and would last an nanno second on my boat where everything has to be correct or i can't rest.

[/ QUOTE ] In that case I should drop the idea of using the water tank as the coolant reservoir for the fridge. Aside from the issues I have already mentioned, what happens when you use your water up and the tank is nearly empty? I got the impression that you were trying to do a bodge on the cheap. There are professional systems designed to do the job.