cast iron radiators as in-tank HXs?

[pybyr]

I'm going to use a flat plate HX for my system, so this question is more food for thought for other possibilities, but I'm not recalling whether it's been discussed before-

People have built all sorts of copper &/or PEX coils, manifolds & tube arrangements, etc., for in-tank heat exchangers for heat storage.

Has anyone tried or considered simply putting some good old fashioned cast iron radiators (ones built for a HW system, so that they have inlets and outlets) right into the tank?

Cast iron will experience initial corrosion, but usually that self-ceases near the surface, and a relatively closed tank should become at least partially oxygen depleted from the heating.

Interested in peoples' reactions to this

 

[tom in maine]

That's a new one!

Somebody's gonna be pissed if it doesn't work or corrodes, getting it into the tank intact is one thing, taking it out is quite another.

I suspect the thermal lag of the iron will be a major issue, but it might be fun to try. I guess.

 

[pybyr]

Thanks Tom-- this struck me as something that could perhaps be an option for some who do DIY tanks and who'd like to try a different approach to save $ on the coils. If it works (and I'm in concept-mode on this- I cannot vouch for whether or how well it works), and if someone were able to scrounge up some appropriate Rads. at no or low cost, then it could be another mode of getting lowest possible cost DIY storage. If the radiators didn't work, they could be disconnected and allowed to fill with tank water, as "reefs" in the tank.

It does seem that it would be essential to make sure that any fittings and hardware (including the through-rods and nuts, inlet & outlet fittings, etc., are iron, not steel, as steel will just keep on rusting (unlike iron).

If anyone knows of someone having tried this- or if someone tries this, please share results.

 

[tom in maine]

Hey Trevor,
As much as I like to try new things, please don't ask me to help put these in your tank!

Have Fun!!

 

[Jim K in PA]

Trevor, a farmer friend of mine did that with WVO when he was making bio-diesel. He submerged an old CI radiator into the tank of WVO to heat it. He supplied hot water from his OWB ( :roll: ) and ran it through the rad to heat the WVO. It worked very well. I see no reason other than logistics that it would not work (big/heavy). I think you are correct that after initial corrosion and O2 depletion, continued corrosion would not be a major issue. As Tom says, it may not be as rapid an initial transfer as a FP, but once up to temp it should work fine. The size and surface area as well as total mass of the radiator will affect transfer rates and ramp up times.

 

[Gooserider]

There has been discussion of the concept before - look for some of the CI rad threads, especially a fairly early one where Eric Johnson was posting a lot about his experiences with them - but I don't recollect anybody actually doing it...

The potential issue that I see as a possible problem is how to position the rad in the tank to get stratification... Coils can be run top to bottom and because of the linear way water flows through them, you can get some pretty good stratification on them, but a CI rad gets to be a pretty much uniform temperature over it's entire surface... Aside from the obvious question about heat distribution, you'd have the secondary challenge of how to position it mechanically in the tank if the answer to the first question was anything other than standing on the bottom...

Gooserider

 

[deerefanatic]

Please don't waste the CI rads in your tanks.... The belong in your HOUSE!! and if you have some you don't want, I'LL TAKE EM! LOL!!

Actually, it might work ok..... But I'm still stickin' with copper. (If I ever get it done.... )

 

[Eric Johnson]

I've always thought it was a great idea. I haven't tried it, but you won't find a cheaper hx, and I think you could easily design a tank around them, or get some strong friends to help get them into the tank. As to stratification, I think you could easily stack a few ci rads in the tank and then pipe it so that the ones on top served as output units, the lower ones--input, etc.

 

[pjcassidy]

I've got a drawing from MEN for a wood burner with CI radiators as collectors from the heated air to the water storage tanks.

http://www.motherearthnews.com/multimedia/image-gallery.aspx?id=66496&seq=1

Pages 3 and 4 show some more drawings.

Patrick