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jema

Fun Solar - solar water heating article

Just have to say what a great article Smile

I played along similar but less suphisticated lines as a kid, and got good results. I can see this article inpiring me over the summer.
sean

That is a top article Very Happy Very Happy
onejohndog

dont know if this is where i need to do this but the article on solar water has prompted me to respond as this is just up my street.
i have an allotment , with a shed with a pitched roof and was wondering if it would be possible to use a couple of old radiators to do the same job as the copper pipe system as i have some available and some double glazing panels. i thought if the radiators were painted matt black, they would perform the same function.
Treacodactyl

Welcome onejohndog.

Would the shed be able to cope with the weight of two full rads? I would have thought they would produce some heat and I'm tempted to have a go if I can get hold of an old one. Smile
judyofthewoods

Flat radiators are often used in DIY solar panels, but are only suited for indirect systems (most are anyway)as you will probably get rust in the water, and maybe even residues of antifreeze.
dougal

Single panel radiators could be used, but, as I understand it, the more collector area warming the smallest *volume* of water gives the greatest temperature rise. And a rad hold more water than a couple of feet of pipe...
But a black painted rad inside a carefully-oriented insulated glazed box (somewhat like a 'cold frame') will get quite hot in the sunshine.

What are you hoping to achieve by heating in the shed? Just heating a (not too well insulated) tankful of water will give a slow release of the heat... But most of the solar benefit comes in the summer. Precious little in winter, when I guess it'd be most welcome.
Note that the demo "fun" system doesn't worry about freezing... or summer boiling. A pumped "drainback" system is controllable and more practically robust than the simpler "fun" thermosyphon.

For a "thermosyphon" you need the heat input (collector panel) LOW and your hw tank ABOVE it - hot water rises! So don't put the collector on the roof! (Unless you can add a pump - theoretically run on solar electricity?)
judyofthewoods

there is a way to have a solar collector on the roof without a pump - an in-line batch collector, a flat tank (preferably s/s) of about 4" depth which is just plumbed into a spur from the incoming line. The water is used directly from the tank, but requires a certain amount of organisation about when to use it, perhaps draining it into an insulated indoor tank just before its likely to cool down again. It would probably need a pressure relief valve, but otherwise very simple. The insulated, glased casing and blackened surface still apply.
cab

I can see how a radiator used in this fashion might work on my allotment. I can't see a reason to do it. Whereas in my farden, the pipe system might be a lot of fun. Again, not really useful, but fun. Although I wonder whether having such a set of pipes in summer could be useful to create a warmer plate; let it heat up during the day, wrap it in something to insulate it, and then unwrap it in the evening to keep barbecue food warm?
jema

I have been racking my brains for a practical application to playing with this Confused So keep the ideas coming.
judyofthewoods

A while ago I lent someone an article I had cut out from an old magazine, but sadly it disapeared where all thing lent disapear to - a black hole Evil or Very Mad . It was about a couple who built an earth sheltered house with an unusual slant to it, literally. They also grew vegetables all year round, even in the depth of winter with earth sheltered frames, which were using water filled barrels to capture solar heat and slowly radiate the heat back to the plants. It may have been 'Country Journal', January 1981 or thereabouts. Does anyone have back copies and could scan the article? I would be sooo happy. The concept was so brillian, that I think it would be great to post it on the forum. If I remember rightly, the whole frame was the 'solar panel', i.e. the blackened collector was inside an insulated box which also happened to be the growing frame. The earth would have been the buffer or additional heat store. These barels were lying on the ground rather than standing up, and there may have been a chain of them, like a giant pipe at the back of the frame.
Jonnyboy

Great article, I think there must be loads of practical applications if you think laterally.

I could install one on the hill above my house and have a gravity fed warm shower. Or just use it for washing up, running the washing machine even?
tahir

Jonnyboy wrote:
running the washing machine even?


That's a good idea.
Res

This is a brill article and future project for the allotment shed. Hot water for washing, filling padling pool, sounds to good to be true!

Will go well with my manure powered shed Razz
Rikki

Fun Solar - solar water heating article

I'm about to build a solar panel (posh term is collector) to preheat my domestic hot water. The CAT in Wales do a good booklet for anyone planning one. Rads do work, but the ideal is to have thin copper pipes with "wings" on. The thinner, the pipe the better, so 8mm copper - only the fittings are more expensive and they are more prone to frost damage, so I'm going to use 15mm. I have a roof above a first floor utility room about 6m squ. which will give more than enough energy in summer - so I've included a blind to pull over it on really hot days.

The key purchase has been the hot water cylinder. Initially I toyed with 2 or even 3 100 litre cylinders linked one above the other, but Albion now make two-coil cylinders. Mine cost 350. It holds 250 litres so will "store" plenty of energy. The lower coil will be connected to the solar panel, so on a hot day all 250 l heat up to boiling. (yes, there has to be a venting system to cope, and a blender to mix it with cold water). On colder days the condensing boiler will heat up just the top half - enough for a bath. But the real advantage is that on even moderately sunny days - like spring and autumn - the water is pre-heated, so the boiler only has to raise it a few degrees rather than 30+.

If anyone has already done this I'd love to hear your views. The new cylinder is sitting in the lounge having been delivered last week, and I'm starting work on the plumbing next month. (I'm a teacher so will have a long summer holiday to get it done.)

p.s. I don't seem to be able to find the original article these replies refer to.
Treacodactyl

Try here:

http://www.downsizer.net/Projects/Sustainable_Building%10Energy_Efficiency/Fun_solar_-_solar_water_heating/

Let us know how you get on.
Rikki

Cheers
dougal

Re: Fun Solar - solar water heating article

Rikki wrote:
...The thinner, the pipe the better, so 8mm copper - only the fittings are more expensive and they are more prone to frost damage, so I'm going to use 15mm. I have a roof above a first floor utility room about 6m squ. which will give more than enough energy in summer - so I've included a blind to pull over it on really hot days.
The key purchase has been the hot water cylinder. ... two-coil cylinders. ...so on a hot day all 250 l heat up to boiling. (yes, there has to be a venting system to cope, and a blender to mix it with cold water). On colder days the condensing boiler will heat up just the top half - enough for a bath. But the real advantage is that on even moderately sunny days - like spring and autumn - the water is pre-heated, so the boiler only has to raise it a few degrees rather than 30+..

A few points from my limited, and mostly theoretical experience.

IMHO really large dual-coil tank is the right way to go. Dual coil for the reasons you have given, and large to help absorb the bounty of good days, and to store enough to tide you through the less good days in summer. So the better insulated the tank the better.

Not so keen on the blender though. But I am in a hard water area. The hotter your tank water gets, the more of a scale problem you will have. And scale + thermostatic blender = trouble. Also, the hotter the tank water, the (massively) more the heat loss will be (heat flow proprtional to temperature difference to the fourth power?). Back to insulation! So storing *more* water at a lower (ready to use) temperature has its advantages.

Freeezing/boiling. To my mind these extremes are sorted most neatly (for a DIY flat plate system) by a "drain back" arrangement - where the collector is empty of 'water' *unless* the pump is running. So once the tank is hot enough, the pump just shuts off. Similarly, at night in winter the 'water' is relatively snug inside the house, not in the collector - where it possibly requires occasional pump activity (and heat loss) to keep it from freezing.

I've said 'water' (in quotes) because running an anti-freeze solution has other advantages, like a higher boiling point and higher specific heat (more heat carried at the same temperature).

Not knowing how effective your collector(s) may prove, or how "good" the solar coil in the tank will prove, you *might* think about splitting your collector into (say) four sections - each plumbed back inside, and valved. In that way, you could choose (change) whether the collectors were in series or parallel - which will determine the "output temperature" (and influence the flowrate). Again thinking T^4, you need a decent temperature to get good heat transfer into the tank.
I'm thinking that for summer you might want a parallel arrangement, to avoid boiling - while in winter a series arrangement should give a higher output temperature, resulting in more of your heat being transferred into the cylinder. (The alternative, probably rather more expensive alternative is a modulating pump.)
Remember we are talking about the "output temperature" having to be usefully above that of the bottom part of the tank...
One reason evacuated tubes are good (albeit expensive) is that they can produce an adequately high output temperature, even from a dull and cool autumn day.
Generally flat plate collectors, giving lower output temperatures than tubes, have a shorter useful season.
So, again to extend the season (at the sacrifice of midsummer efficency), the collector angle to the vertical would be optimised for mid-seasons rather than summer (and regard anything in winter as a pleasant surprise!)

And insulate! The collectors and pipes. Its not so much about maximising the summer performance (which may be briefly excessive), but in getting useful output in the "shoulder seasons".
15mm seems quite big for the collector pipework. Volume in the pipe is proportional to cross section area, so radius^2. 15mm (diameter) is going to have around 3x the water volume of 8mm... And the greater the volume of water you are heating in the collector, the *less* the temperature rise...
Rikki

1. Blender. I'm also in a hard water area and hadn't thought of the problems with the termostatic blender. Are the magnetic scale reducers any good? I've got one on the cold feed to my loft cistern but only put it on at Christmas so don't know if it's doing any good yet. However I still think, for safety reasons, one needs to avoid getting 90 deg water coming out of the taps.

2. ...more water... . That's why I went for the largest cylinder (250 litres) with the thickest insulation, and will wrap it round with spare duvets and sleeping blankets. But there are two problems with having yet more water stored: (a) price of a second cylinder, and (b) weight. The one I've got will be over a third of a ton when full.

3. Drain back. If I was putting the collector above the cylinder this would be a really neat solution. (I might even redesign my whole project around this idea.) BUT it requires a pump with sensors, whereas my system will work by the thermosyphonic method mentioned in the lead article. It means, however, that I'm faced with the twin problems we've all had to worry about: excess heat and freezing.

Excess heat: I'm going to have a thermostat connected to an electric valve that will simply dump excess hot water into the drain so that the whole system doesn't go above boiling point. (unless someone has a better solution)

Freezing: I'm told using normal CH inhibitor acts as an anti freeze (too what temp?) but on really cold days I'll have valves on the flow and return pipes, and drain down the collectors (returning the water to the header tank)

Thermosyphonic: this only works if the pipes are all monotonic increasing i.e. there must not be any downward slopes between the collector and the coil in the HW cylinder.

4. Collector design. Great ideas - thanks. What are "evacuated tubes" and can I make them myself? Looking at the lead article, I notice that he's used 15mm pipes for the risers, but 22mm for the footer and header, but then has reducers down to 15mm again for the flow and return pipes. Does anyone else have experience of what works best. I have to lead my flow and return pipes 3m horizontally (with a slight rise, of course)between the collector and the cylinder so was going to use 22mm or even 28mm for these.
dougal

Rikki wrote:
... hard water ... Are the magnetic scale reducers any good?
There is no scientific explanation for how they might work.
There's a lot of mumbo-jumbo. Much of it from the salesmen. The rest from their customers.
Shall I just say, I'm sceptical.

Quote:
... for safety reasons, one needs to avoid getting 90 deg water coming out of the taps.
That would be a nice problem to have! But its very unlikely to be one you are faced with often...

Quote:
Drain back... requires a pump with sensors, whereas my system will work by the thermosyphonic method mentioned in the lead article. It means, however, that I'm faced with the twin problems we've all had to worry about: excess heat and freezing.
However it will tend to self limit as it depends on the temperature difference between the tank and collector. As your tank heats up, so a higher collector temperature is needed to get any circulation and heat transfer. But the higher the collector temperature, the higher the heat losses from it will be.
Which is why *seriously* well insulated collectors are needed, and why cheap flat plates (with inevitable high losses) are thermally outperformed by evacuated tubes - which will give a much longer working season, for that very reason.

Quote:
What are "evacuated tubes" and can I make them myself?
No, I wouldn't expect you to be able to!
The basic idea is to surround the heat collector (and its water circulating pipe) with a clear glass "thermos flask" to insulate it.
Designs get even more advanced. I'm impressed with the UK-made Thermomax tubes, which have a "heat pipe" (not a water pipe) in the 'flask' that just plugs in to the manifold containing the 'water'. This allows the heat pipe to self limit the maximum temperature, and individual 'flasks' can be replaced should they ever be damaged.
http://www.thermomax-group.com/PRODUCTS/SOLAR/technologyT.htm (link is to the frame, not the whole page...)
Because evacuated tubes can, (and do) produce very high *temperature* outputs (yes at lowish flowrates) their heat can be effectively transferred into your tank. Its important to distinguish heat and temperature... and remember that temperature difference vastly effects heat transfer rate.

A simple, and hopefully cheap, system doesn't have to do much to pay back. It may be the most cost-effective renewable energy system available. But, its not going to give you anywhere as long a working season as a more advanced design...
What matters for a *practical* system in the UK, as opposed to a "fun" one, is how much it works, not just how well it can work on a hot sunny day. The real tests are dull mild conditions and cold, bright days - and they aren't going to boil your cylinder!

Get on with it! Have fun! And, if it helps with the tinkering, remember that you don't *have* to have the tank's "solar" coil connected to anything. You can disconnect while you tinker or rebuild. Its going to be a bonus! (Which also means its not essential.)
Get the tank installed to the rest of the system. And then start to have the fun!


Hint: you are going to be checking a lot of temperatures, so a robust truly "instant-read" thermometer is going to be an important toy, sorry TOOL! You may even care to check out "non-contact" ones... (Maplin's do them...)
Rikki

More useful advice - thanks.

I think I'll write up my plan and post it on the site.

I take your point about fun vs practical, and don't expect to get hot water from it in the winter, but any temperature rise from the solar coil reduces the amount the boiler has to do and so saves fuel.

Given that I'm going to use 8mm risers with fins soldered on, and that the collector is below the tank but horizontally 3m away, will using 22mm for the flow and return counteract the advantage of using narrow pipes in the risers? I suppose that if the flow is slower the collector will heat up more.

Your quite right about sorting the main plumbing first and then playing with the solar bit - it'll give me years of fun.
Rikki

Thermomax tubes look interesting, but will cost. Shocked puke_r

Your main point seems to be about insulating. most designs cover the collector with glass (lets UV in but doesn't let IR out) but the lead article suggests triple-layer plastic roof sheets. Thoughts Question Maybe use doubleglazing units over the collector.
dougal

Rikki wrote:
Thermomax tubes look interesting, but will cost. Shocked puke_r
Evacuated tubes, and a pressurised circuit, is the 'proper' way to go for a long useful season. Flat plate collectors are cheaper, DIY-able (much cheaper), but much less efficient - especially on 'poor' days.

Your main point seems to be about insulating. most designs cover the collector with glass (lets UV in but doesn't let IR out) but the lead article suggests triple-layer plastic roof sheets. Thoughts Question Maybe use doubleglazing units over the collector.[/quote]Building your collector(s) around the availability of second-hand (scrap?) double glazing is the cheap/effective way to go.
There's a tradeoff between insulation (preventing heat getting out) and transmission (allowing solar radiation in). And then there's the question of longevity and the action of UV...
You can buy the plastic fairly cheaply. So its accessible and great for a "fun" project...
Treacodactyl

I thought I'd bump this thread up after the INEBG programme last night.
dougal

Allowing me to reiterate Very Happy that flat plate collectors are potentially DIY constructable, but that evacuated tubes are much more efficient, but the collectors need to be bought in.

The Thermomax tubes are very highly regarded (and self limit) but those offered by Navitron (broadly similar but not self-limiting) are massively cheaper.
Evacuated tubes should be installed in a pressurised circuit, using metal (NOT plastic, because of the possible temperatures and pressures) pipework. Hence evacuated tubes are advanced DIY or pro plumbing for installation.

Rather than replace one's hot water tank, one can replace the immersion heater with a solar coil, for about 100 from Navitron. While this is unlikely to be super-efficient (one would prefer the solar coil right at the bottom of the tank) this would be a way of doing a solar thermal install without touching the existing tank or plumbing.

There is some 'armoured', insulated, flexible metal piping made specifically for solar installs. It'd be ideal for DIY installation of evacuated tubes.
Anyone got a link for it?
Treacodactyl

What is an 'Evacuated tube' and how does it work in simple terms?
dougal

Treacodactyl wrote:
What is an 'Evacuated tube' and how does it work in simple terms?

Its a long Thermos flask around the actual collector.
It would be surrounded or backed by a focussing reflector to increase the collection area.
The Thermos flask dramatically reduces the heat loss from the collector, making the solar harvest more efficient.
The better ones use a heat pipe to deliver the heat to the manifold.
Not least, the heat pipe means that, should one tube fail or be damaged, while that tube may not gather much heat, it won't lose the heat gathered by the other tubes - and its much more easily replaced.

Have a look at the diagrams on Navitron's own page...
http://www.navitron.org.uk/solar_collector_panel.htm
Lozzie

Extremely interesting. I am thinking about the swimming pool at the children's school - the cost of heating which is making life very uncomfortable for the School Treasurer ...
ken69

Dougal....

http://www.google.co.uk/search?sourceid=navclient&ie=UTF-8&rls=GEUA,GEUA:2005-36,GEUA:en&q=flexible+metal+pipes+for+solar+installs
dougal

Ken, I may be missing the obvious, but that Google search doesn't seem to 'home in' on anything useful.

I believe that there is stuff somewhat like this, but rather more attractively priced...
And even as a single (rather than twin) pipe...
http://www.s104321353.websitehome.co.uk/secon/pages/system/flexipipe.html
ken69

dougal wrote:
Ken, I may be missing the obvious, but that Google search doesn't seem to 'home in' on anything useful.

I believe that there is stuff somewhat like this, but rather more attractively priced...
And even as a single (rather than twin) pipe...
http://www.s104321353.websitehome.co.uk/secon/pages/system/flexipipe.html


That's Google for you Dougal. Very Happy

Just bought two 22mm 'armoured flexible pipes ' for my own solar panel thermosyphon project. The sought used on sinks. About 8inches long and only really for short awkward spots, and permits easy dis-connection from the cylinder. Cost 2 each.
dougal

ken69 wrote:
... About 8inches long and only really for short awkward spots, and permits easy dis-connection from the cylinder. Cost 2 each.

Well that's about 10/metre before insulating it... Shocked and you need about 2 metres of pipe for every metre distance between your tank and solar collector panel...
ken69

Yes Dougal, they are connectors rather than the full Monty.
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