Finned tubing

[chibear]

I am setting up thermal storage for in a 1500 gal tank, heated by solar panels (and possibly a wood boiler later), and to be used as a preheat for domestic hot water and radiant floor heating. I have been playing with different ideas for heat exchangers inside the tank. Flexible copper tubing is the easiest to obtain and used by several people on this board. I have read, though, that finned tubing has 9X the heat transfer of plain tubing. I have so far been able to locate only one North American supplier at http://www.fintube.com/soldered.htm I was first of all wondering if anyone knows of any other suppliers. Locally some finned tubing is sold with aluminum plates attached to a copper tubing. It isn't all that expensive. My question is if I were to submerse this copper-aluminum construction would I have to worry about electrolysis between the two dissimilar metals and thus premature failure??

[Aelric]

the aluminum finned copper tubing should be fine, just if it is going to be used for hot water in your house (showers, sink, etc) I would make sure there is no lead used anywhere on it.  Lead poisoning is bad news.  But so long as its lead free and rinsed out a few times and no other toxic chemicals/metals in it, it should be fine.

If you are on the other hand just using it for radiant floor heating not for showering or any other direct human or pet contact, then it really wouldn't matter as much, even an old radiator (leak free of course) would be alright, just don't want to have toxic chem's used where people will be exposed.

[weldingrodd]

Did you try the Thomas Register looking for heat exchanger parts or .A large plumbing supplier might have a line on finned tubing there are lot of domestic hot water units in boilers that use them.

I would go to   www.thomasregister.com  Its sort of like industries google search.Has local or national sections etc.

[Hank]

Copper is significantly more "Noble" then aluminum.

Simply put, the aluminum will corrode in a water environment (galvanic corrosion).

Have you considered using radiators (auto or air-conditioning) as potential heat exchangers. Another thought is if you can get your hands on "tankless" heater coils. These are used in domestic hot water oil furnaces to provide hot water. They in fact are heat exchangers made of finned copper tubes. Might find these at your local scrap iron yard.

Enjoy,

Hank

[farmerfrank]

Finned tubing may have 9X better heat transfer properties when conducting to or from air. When used in a water to water scenario I would suspect little if any difference as water is an excellent heat transfer medium. Personally I would go with a few extra feet of large copper pipe as a restriction in flow is much more counterproductive than a slightly more efficent coil that is of a smaller diameter.Also remember that water layer temperature wise so try to return in the bottom of your storage and draw hot off the top...just like a domestic hot water heater.

[whatsnext]

I agree with Frank. There is no point whatsoever in having finned tubing in the water.

John......

[RP]

Also,  put your copper coils in the bottom of the tank where the water is cooler to get better heat transfer.  Heat flow is dependent on temperature difference so you'll move more BTUs into cooler tank water.

rp

[TomW]

RP;

Excellent point that is probably not obvious to everyone!

Cheers.

TomW

[farmerfrank]

Actually if the tank is the resevoir for the panel collected water and the coils are used to pick up the heat for the domestic water,then the coils should exit the top of the storage tank...where its warmer.

[Seth]

bottom to top .... sigh

Depending if u want it cooler durrng the summer, or hotter durring the winter.....