Copper and heat exchanger

[Jimbo]

Howdy folks,
as I have posted before I live near Canberra where the winters are cold! At the moment it is 2.8 degrees outside and while the North American members probably don't think that is cold we all know that any fish we want to grow do think it is cold. At the moment this cold is putting a complete hold on further work on the system with the exception of my plan for heating the water.
So I have been planning , mostly in my head, a heater for my fish tank (4500l buried almost completely), which is completely solar powered.
I have a couple of old solar hot water panels, about 25 years old but still working until removed from a roof about a month ago, given to me by a mate.
I have also managed to find a 12V pump (Davies Craig EBP) which will run quite well from a 10w solar panel (also in stock) Might need to add an ATA maximiser to ensure proper pumping.
My plan is to use a glycol solution and heat exchange mechanism so that I don't have to worry about the panel freezing and also to minimise the contact the fish water has with whatever might come off the pipes in the panel.
At this stage it is fairly straightforward- make a stand for the Panel, hook up the PV panel, run the plumbing from the heater panel to the tank.
As the pump would only run when the sun shines I don't expect to lose any heat back to the panel at night.
Only one remaining problem- what to make the heat exchanger out of. My initial plan was to simply buy a coil of the 13mm soft copper pipe, which I used when I plumbed the hot water panels on the roof of my house into the heat exchange unit for home water heating, and join it into the loop with compression fittings.
Now the big question is how do I/we determine how likely it is that the copper from the coil will damage the fish. Everything I have read about copper toxicity talks about COPPER SULPHATE which is very soluble in water.
I know that Doug Basberg painted his copper heat exchanger pipes which are in the fish tank. He has had so much trouble that it seems very hard to pin down the source of his fish deaths and so who knows if it is copper toxicity.
My gut feeling is that copper pipes simply sitting in the water should NOT release significant copper into the water. I have also considered having the coil coated with something- perhaps chrome or powder coated - don't want to use paint as that is a whole new can of worms re toxicity.
Has anyone any hard evidence that metallic copper simply sitting in water will dissolve into the water in any significant concentrations?
Is it possible to buy test kits to check for copper in water?
Just had a thought- s**** metal merchants- aluminium or stainless steel pipe- would be easy to bend the aluminium and almost impossible with the SS. SS would be inert but perhaps unobtainable- what do people think about aluminium?
Must be a very sensitive filter on this forum- the bleeped out word was s****metal or recyclying?

[njh]

I would forget the heat exchanger, just wash your panels out and run the tank water directly through them. Put a small air gap on the outlet side so that when the circulating pump turns off, the water unsyphons back out of the panels (so that they can't freeze). Allowing the panels to dry out will help control biofilm (also the high temperatures).

My own experience is that copper will not dissolve in appreciable concentrations unless there is a galvanic cell somewhere. Mixing copper and iron pipes is bad news, but that is bad news for drinking water too! Putting chrome on the copper may make things worse if there are any scratches.

[Jimbo]

I have been running a little experiment with a length of copper pipe left to sit in plain rain water. And unfortunately copper does come from the pipe and into the water. After 5 days of exposure a length of 13mm pipe about 3 metres long sitting in 60 litres of water at a pH of about 7.3 produces a reading of about 5ppm of copper. As the hot water panels are also copper I reckon the copper concentration could become a problem so I am still thinking of making a heat exchanger of some sort.
So a question for Murray- how thick a coat of fibreglass do you reckon I could put over a coil of copper pipe and still be able to transfer the heat into the tank water? I would envisage dropping the whole FBG coated coil into the tank with plumbing connections of PVC or something similar.
A second question for Murray- do you reckon the FBG coating would be waterproof enough to achieve the isolation of the copper that I need?
The other ways I have thought about include painting the pipe- problem of finding a non toxic paint. Or powdercoating the pipe - possible similar problem and high cost. Or maybe even chrome plate- a whole new can of worms!

[Murray]

Hi Jimbo,
I do not believe there is an effective way of coating copper pipe for our purposes. FG is an insulator and if you applied enough to the copper pipe to seal it, then the heat transfer properties would be lost.
The only answer in my mind is a heat exchanger coil or grid of stainless steel in the fish tank water.
Or a copper pipe grid under the tank, like underfloor heating.
I am sure I posted some photos of an under tank copper grid I glassed onto the bottom of one of my tanks for a bloke here in Brisbane. Can't find the post..... Can somebody help ? some one who is better at using the search........ or I will just have to dig up the photo's again.....

[sillyoldfart]

I noticed you had a copper pipe heating system attached to the bottom of a tank in one of another thread Murray.

Two questions.

(1) How efficiently does this transfer (presumably) heated water through the fibeglass into the tank? (Edited)

(2) Does the heat have a detrimental and degradable effect on the fibreglass of the tank itself?

[Murray]

The heat transfer through the base of the tank would not be all that good, but it would be good enough I believe. Heat up to 100 deg C would not harm FG over time although more than that would start a slow breakdown. Personally I feel that a stainless steel tube grid heat exchanger inside the tank would be the better option. Stainless is not the greatest metal for heat transfer, but it is a clean stable metal and it would work the best of the options commonly avbl.
That is my belief and I reckon that is the way I will go well before next winter.

I have just installed one of those instant gas HWS for my house. The solar system died during the heavy frosts a couple of weeks ago. I reckon that if i can pick up an old second hand gas HWS from some where, a bit of plumbing magic and a really effective tank heater will appear.
Having it thermostatically controlled is a bit of a problem. Anyone got any ides how that might be done.

[GaryD]

Hi,

Having walked on a couple of hot tin roofs in my time, I'm inclined to try the simple trickle heaters that NJH described several weeks ago in this forum.

Aside from being easier to build, they are likely to be more effective that heat exchangers of any kind that I can visualise.

Gary

[Jimbo]

Thanks Murray for the info -Looks like I might have to start frequenting the metal recycling places looking for stainless steel tubing. That will be fun to bend and form into something usable. Another possibility might be aluminium tubing- quite easy to bend- just have to find a supply.
No disrespect intended for the simpler systems suggested by njh- but small and unobtrusive is what I am looking for- and I have almost all the bits needed to make a system such as I have been planning.
BTW the picture of the copper coil under the FBG tank was on the other forum
http://www.backyardaquaponics.com/fo...ht=copper#8145

[Murray]

Hi Jimbo, yes I did post that there last year sometime when I actually built the tank, but I thought I had put the same photo up on here a few weeks ago, anyway, here it is again.

I have several more pix from different angles if you want me to post them up.

On the stainless tube, I plan on using straight tube and use pre made bends. They are avbl from stainless suppliers. There is a mob here in Brissie that supplies them, when I find out cost etc I will post the info up.
Need to have access to a MIG welder and buy a small roll of stainless wire for it. I am told by a welder mate this will work fine. I am going to give it a go anyway.

[fishfood]

Bending ss tube is easy if you get the soft stuff i have bent 1/2 using a slow turning lathe Heres some 1/4 i bent around a broom handle for my still er [water purifier]