Can I use a plastic loft-type cold water tank for my solar water heater?

I've made the first stage, i.e. the copper tube, about 3 metres of it in a "snake" pattern. This will be mounted on a south-facing wall. Can I feed the hot water (on thermo-syphon principle) into a black plastic cold water tank as used in the loft? Or will this plastic release toxins when containing hot water?
NB: The tank will be mounted initially on outside wall, above the copper tube "snake".
Or maybe you have suggestions for alternative tank suitable for hot water?
The cold water tank I'm looking at (on the B&Q web site) is the Titan Wizard 25/15 Rectangular Water Tank KM15 Black.
MM
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For 3 metres of copper tube (15/22mm?) you are wasting your money and time
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On Sat, 21 Jun 2008 12:42:34 -0700 (PDT), cynic

How about double the length?
MM
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Such tanks are unsuitable for hot water, they soften and collapse, possibly inflicting nasty burns. People have even died this way
I hope your description of your solar system is quite inaccurate, as its not going to achieve much as described.
NT
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wrote:

Such tanks are unsuitable for hot water, they soften and collapse, possibly inflicting nasty burns. People have even died this way
I hope your description of your solar system is quite inaccurate, as its not going to achieve much as described.
NT
Agreed. You might pick up more heat direct into the tank than from the coil. The tank won't release toxins, but it will become brittle because of the UV.
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On Sat, 21 Jun 2008 13:38:22 -0700 (PDT), snipped-for-privacy@care2.com wrote:

What kind of (metal? plastic?) tank would you therefore recommend?
As long as my thermo-syphon domestic solar water heater can produce 15 litres hand-hot water for washing up and 5 litres for my daily ablutions, that's all I'll want from it! I know I can get half a bucketful of really hot water just from a garden hose in the sun. And even if I only got a kettleful for shaving from my contraption, that's one kettle for which I don't need to use electricity or burn oil to heat.
MM
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Right - 3m copper pipe in the sun isnt going to get you much though. Add it to a tank of colder water with no circulation and forget it. Sounds like you'd be better off with a hosepipe pancake collector. Make it a decent size and you wont need a tank at all. The hose can store several litres, and since you need lower temp you can dilute the hot at point of use, thus will require less than 15 litres in the collector.
The pancake collector would get hot enough to self sterilise, and will be flushed regularly. Your tank approach would be right in the bacterial breeding zone, and never get flushed out.
NT
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On Sun, 22 Jun 2008 06:07:57 -0700 (PDT), snipped-for-privacy@care2.com wrote:

I will have to see. If it isn't adequate, I'll add another 3m. Only 6.74 from B & Q and I take my pipe cutter with me so that the bus driver lets me on the bus with it.

The circulation is automatic, on the thermo-syphon principle, like a car radiator. Many old cars had no water pump.

Surely it gets flushed each time I empty it to use the hot water and it is replenished with cold?
MM
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If you spent your 13.48 on garden hosepipe you'd get way more heat. Cover it with polythene to give reasonable stagnation temp, lengthen the season and make it heat faster.

Yes, but it never circulates as well as pumped.

yes, but only if you empty both tank and pipe fully. I'm not sure how you're going to achieve that.
Freecycle might get you free hose. Almost any colour works, green, yellow etc. Using copper wont help.
NT
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On Sun, 22 Jun 2008 15:03:14 -0700 (PDT), snipped-for-privacy@care2.com wrote:

3m of copper tube and a holding tank are far neater and more compact than 30 metres of garden hose. And I don't relish the thought of 30 metres of hose with polythene over it practially hiding the entire lawn.

It circulated well enough for the systems which relied on the thermo-syphon principle. An oft-demonstrated example of the KISS principle.

Why "fully"? Surely if you have a bowl of hot water and you pour cold into it, excess water spills over, then the temperature of the water - ALL the water - falls? Else, why did pouring cold water into overheated car radiators stop them from boiling over and allowing the journey to proceed? My "spill over" will be achieved by the simple expediency of turning on a tap and waiting for a few moments...

Green! Yellow! It HAS to be black this year! (I have to think of the garden's feng shui, too.)
MM
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Since youre determined not to learn anything, lets hope something else gets you before the bugs in the water.
NT
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On Mon, 23 Jun 2008 17:40:29 -0700 (PDT), snipped-for-privacy@care2.com wrote:

No wonder you call yourself meow!
MM
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On Sat, 21 Jun 2008 17:47:37 +0100, MM wrote:

Not long enough unless soldered along all its length (not spots here and there) to some other form of collector plate a couple of square metres in area, even then the spacing would be to high to have effcient transfer of collected energy into the water.

With your very poor collector it's not likely to get hot enough to deform, that would be the major risk. Deformation resulting in a split or collapse of the tank.
I can't find that Titan Wizard KM15 tank anywhere other than on the B&Q site. It's not a Titan Tanks product as far as I can tell. You need to find out its specified temperature range.
--
Cheers
Dave.




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wrote:

yes :) This might be a start:
http://www.wiki.diyfaq.org.uk/index.php?title=Solar_Thermal
NT
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On Sat, 21 Jun 2008 22:03:57 +0100 (BST), "Dave Liquorice"

As an experiment I took one black plastic builder's bucket (3 gall size) and filled it with 12 litres of cold water from the tap. I stuck in my (German) Tauchsieder (1200W) and switched it on for 15 minutes. I measured the amount of electricity consumed with my Tschibo meter at 0.035 (3 pence) and the temperature of the water had increased to *beyond* hand-hot. That is, I could just about dip my fingers in, but not for more than a second. The bucket did not deform at all. I doubt whether another 15 minutes (when the water would be VERY hot) would make any difference. Now I appreciate that a builder's bucket is not the same as a loft tank, and is probably far sturdier, especially in the rim. So what I'm looking for is either an even larger builder's bucket, or a tank made from the same kind of material. I could, of course, just use two (or three) builder's buckets connected together.
MM
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On Sun, 22 Jun 2008 10:45:43 +0100, MM wrote:

So probably not much above 60C or 70C a decent solar collector is perfectly capable of boil it's circulating water. Plastics do not soften in a linear manner.
http://news.bbc.co.uk/1/hi/england/cornwall/3035606.stm http://news.bbc.co.uk/1/hi/england/somerset/7175037.stm
Cold water storage tanks are not designed to hold hot water.
--
Cheers
Dave.




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On Sun, 22 Jun 2008 11:26:40 +0100 (BST), "Dave Liquorice"

I don't need it to boil. Just to get hot. I've just popped out the back and run the tap after 2 hours in the (today, not very hot) sun (no collector tank yet!) and the water is already warm, despite today's strong winds. This is even before I construct the insulated box and paint the pipes black.

So this must exclude plastic (i.e. non-metal) as a material, yes? I've now stuck an advert in Freecycle for an old loft galvanised tank. (My old one in Bucks would have been ideal.)
MM
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MM wrote: <>

You might not need it to boil - but what are you doing to prevent it boiling?
Why are you persisting with trying to use a cold water tank? (I have never seen a loft galvanised HOT water tank.) Galvanised tanks are rather unusual these days - given that most new loft tanks are plastic. So you are likely to be offered a heap of junk.
Having a hot open tank in your loft (or pretty much anywhere else) is a bad idea as there will be lots and lots of water vapour leading to condensation and consequent problems.
The obvious thing to try would be a hot water cylinder.
--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
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wrote:

Add cold water.

I just need * a tank * ! I don't care what it's made from,or what its original use may have been. All it needs to do is hold hot water at a temperature of around hand-hot for a decent shower or for washing dishes.

But I might be offered a perfectly usable one! My old tank in Bucks wasn't leaking when I replaced it with a black plastic one. I only replaced it because it *may* have started leaking (it was 47 years old). So even if I get hold of a tank with a minor leak that I can easily repair, the tank will be good for years at what I want to use it for.

It's not going to be mounted inside the house. The tank will be painted black and mounted outside, against the house wall, above the collector. (This is only for summer use.)

Yes, I might put another advert in Freecycle.
MM
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MM wrote:

But the point both Dave and I were making is that a tank (whatever sort) not suitable for boiling water must not be allowed to boil. Which you could do manually - but what if you just happen to miss the temperature going past the critical point?
Designed systems have mechanisms to avoid accidental scalding. Take care.
--
Rod

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