Solar hot water

[Smelly]

Lady Muck inspired me to some idle surfing while I was drinking my morning coffee and I came across this which has sent me into a bit of a tiz...

 

I reckon...

 

I can get my hands on quite a few fridge matrices, and plan to use either two freezer shelves (bigger bore) or two plain fridge matrices fastened to the back of a sheet of 2mm stainless steel with the heat transfer gunge you use to fasten CPU's to heat sinks, the other side of the stainless being sprayed black. I don't know how big it will be yet. Looking at the matrices I might use a couple more to get coverage of the roof space (there's enough stainless!).

 

The roof's got quite a steep camber so I'll cut all the bracing off the matrices and gently bend 'em; by fastening one side to the roof then standing on the other side of the sheet of stainless covering them; or have a triangular set up that compensates for the camber.

 

Via a bleed point on the roof, the feed and return will drop through the roof via a couple of bulkhead fittings, one to one side of the calorifier coil, via 10mm white PEX pipe, the other to a pump. The pump I'm thinking about using is a cheap (hopefully) generic diesel lift pump, with a variable resistor to reduce the flow as much as reasonably possible.

 

Below the pump I'll put a T port valve in so's I can use the pump to draw coolant into the system with the pump.

 

For an expansion tank I'd use one from this place.

 

Apart from the pump, I can lay my hands on everything rerquired by said plan. The fella in the link above reckons in a not entirely un temperate climate it'll do a decent job when it's sunny, i.e when I don't want to run the engine because of the solar panel. The roof's hot enough today to shave, although not wash up.

 

Questions...

 

Does a lift pump need diesel in it to lubricate it? If not can anyone suggest a cheapish (less than 50 quid) generic one. If so, alternatives?

Would I be better to insulate from, or fasten it to, the roof ( a big bit of metal that gets searingly hot when I need to; and have the energy availabe to, use this system)

How much current does an electric lift pump draw? Ideally it would be less than 1.2A as that's the excess energy managment max off my solar panel controller (and it's 14A (ish) 180 watt panel).

Should I have got on with putting my ammeter in instead of posting this?

Am I mad?

 

Answers onna postcard pleez!

 

Ta

[Justme]

Mad idea but what about

 

Fitting gutters to the sides of the roof & then pumping water onto the roof via a central pipe with feed holes so the water flows over the roof gathering the heat directly from the steel work collected into the gutters & piped via gravity into you insulated storage tank? Would have a secondary function of cooling the interior of the boat as well.

 

Thought about this whilst I was sat on top of a static caravan roof in the sun trying to paint the edges with roof sealer. The roof that was in the sun was to hot to touch.

 

Justme

[Hobson]

Sire Smelly,

 

this looks really interesting. I can't see why it won't work, the tagged link seems pretty explanatory and he seemed happy with the end result.

 

there are a couple of issues:

 

1. storing the water once heated, keeping it warm for a period of time

2. obviously only useful in direct sunlight, something we get for maybe a third of the year?

 

- Hobs

[Roger Gunkel]

One of the problems with most of these DIY and to some extent flat plate solar water heaters is that they give quite good results on hot Summer days, but then so does a black plastic bag filled with water. As Hobson also said, you also need to store the hot water although you could construct a roof mounted storage tank and transfer the water to it with a convection loop. You could then take water from it via a gravity feed and top up with a small pump.

 

The trouble is, that most people want to have hot water available in the morning so the storage would need to be highly efficient, cloudy days would give you nothing worthwhile and short winter days not enough time to heat worth while ammounts. You could perhaps put the matrix behind double glazed sealed units for less heat loss on colder days, but there would also be the problem of freezing in the Winter.

 

I have also been looking long and hard at solar water heating and concluded that unless you just want warm water on hot Summer days, the only effective system would be using evacuated tubes. I have been looking at that as a possible system, but still WIP because of the size of easily available units.

 

Roger

[Gibbo]

The last diesel lift pump I looked at used quite a lot of power. I think was about 3 or 4 Amps. A 12 volt circulation pump uses much less. About the figure you're aiming for. Yes I know they're expensive.

 

Contrary to popular belief the "gunge" for mounting heatsinks to processors (heat sink compound) is an attrocious conductor of heat. It just happens to be better than the air which would otherwise be in there. People who put too much of this stuff on soon learn this when their processor overheats. The idea of the stuff is to put the barest minimum on to exclude the air. Not to have loads of it "cos it's great at conducting heat". If you mounted pipes onto a plate using that stuff I'd be surprised if any heat got transferred at all.

 

Gibbo

Edited August 17, 2008 by Gibbo

[Smelly]

Well, storage is via the stated calorier, the fella reckons that he could heat calorifier type amounts of water using his system... I'm not in a rush

 

Gibbo, best bit of advice I've heard... yet!

 

Justme; I was remembering my burned feet when I was painting the roof earleir this year as I was drafting this, I hope you did'n't stand on yours...

[Justme]

Justme; I was remembering my burned feet when I was painting the roof earleir this year as I was drafting this, I hope you did'n't stand on yours...

 

No was crawling about using spreader boards. Not that its rely needed. Dismantled one (static caravan) for a friend & the roof is made like a wing with arches & cross braces. Each part is very thin but together they make a strong shape. I could hang on one roof truss & bounce up & down & still not break it & it was only 1" x 1" just well braced. The trusses are only about 12-18" apart.

 

 

Justme

[tidal]

I have used a similar set up here on the roof of a static caravan and used a greenhouse irrigation pump which conveniently had both an interval timer and a timeclock for on and off and was powered by 12v through a mains supply

(well it was until I got the wind genny going). I got the pump locally and cannot find one on the net just now but will try again in the morning

 

It worked remarkably well..........only one trouble. That is in Spain....and even here I had to have it as a standalone system (with cross-over taps) so I could drain it down over the winter

 

I don't know how effective the system would be there, or how much heat losses would be.

 

As the guy in the link demonstrates it does work and I for one would be fascinated to hear how effective such a system is there if you get it functioning.

[Smelly]

The last diesel lift pump I looked at used quite a lot of power. I think was about 3 or 4 Amps. A 12 volt circulation pump uses much less. About the figure you're aiming for. Yes I know they're expensive.

 

Contrary to popular belief the "gunge" for mounting heatsinks to processors (heat sink compound) is an attrocious conductor of heat. It just happens to be better than the air which would otherwise be in there. People who put too much of this stuff on soon learn this when their processor overheats. The idea of the stuff is to put the barest minimum on to exclude the air. Not to have loads of it "cos it's great at conducting heat". If you mounted pipes onto a plate using that stuff I'd be surprised if any heat got transferred at all.

 

Gibbo

 

Well the heat transfer gunge might be rubbish, but will I be able to solder instead? Brazing's past my skill level. On a different note if a circ' pump's the way to go then I won't argue, but think I they're expensive for what they are, see your boat painting thread for reasons.

 

Can anyone recommend any suppliers?

 

 

Your hopefully

 

Dan

 

Oh, you've juat explained why an editing station I built back in the days had issues! Gone are those days...

[twocvbloke]

I think the fridge matrices would make an ideal solar panel, as the smaller bore pipe plus the grills attached to them would be an effective heat transfer setup, all you'd need to do is place them in a box with a window and paint everything inside matt black, and that'll pick up lots of sunshine...

 

It's just the water connections you need to make that's the, erm, "fun" part...

 

But there must be some small-bore to normal bore (I ain't no plumber, I couldn't tell you the sizes of the pipes!!!) connector, they appear on some radiator systems where smallbore pipe is used...

 

Don't forget the insulation though, heating water then losing the heat defeats the purpose of free heat...

[Smelly]

I think the fridge matrices would make an ideal solar panel, as the smaller bore pipe plus the grills attached to them would be an effective heat transfer setup, all you'd need to do is place them in a box with a window and paint everything inside matt black, and that'll pick up lots of sunshine...

 

It's just the water connections you need to make that's the, erm, "fun" part...

 

But there must be some small-bore to normal bore (I ain't no plumber, I couldn't tell you the sizes of the pipes!!!) connector, they appear on some radiator systems where smallbore pipe is used...

 

Don't forget the insulation though, heating water then losing the heat defeats the purpose of free heat...

 

I was thinking of using gas pipe for the small bore stuff...

 

Tidal, I only need it on the sunny days, when it's as it is today there's a good argument for running the engine.

 

optimism...

[stuart]

Can anyone recommend any suppliers?

 

 

Not really, I've got a Jabsco circulation pump on my central heating on the boat - works great take about 0.5Amps but did cost about £80 at the time - really expensive for what they are.

 

Have you seen this:

 

http://cgi.ebay.co.uk/12V-WATER-CIRCULATIO...id=p3286.c0.m14

 

£45 ?

[magnetman]

I was thinking of making solar collectors using polycarbonate roofing sheets. They have multiple channels for the coolant and are nice and thin and would bend to the shape of the roof and are easily available from DIY stores. Only tricky bit is sealing pipes to each edge for in and output of liquid. It could be done I reckon.

[Trilby Tim]

I reckon that should work, or at least in summer anyway. You're planning on fixing the matrices to the underside of the steel sheet and painting the topside black, right? I'm sure it would work, but I reckon it would be more efficient to put the matrices on top of the sheet and enclose with a sheet of glass, on the other hand your solution is definitely neater. You rely on very good thermal contact between the plate (any reason for stainless?) and the matrix though. Also you want to minimise heat losses from the back surface of the plate, so insulating the plate from the roof of the boat would be a good idea, and not having any air gap so that all the heat from the plate goes into the pipes. You could fill the space between the roof and the panel with foam filler to achieve that. 2 part polyurethane foams like this are much the same as what's used as spray foam insulation and much better than the 1 part aerosol can from the DIY store. Are you running your hot water direct through the panel or running an antifreeze type coolant through it to heat the calorifier?

 

Mad idea but what about

Fitting gutters to the sides of the roof & then pumping water onto the roof via a central pipe with feed holes so the water flows over the roof gathering the heat directly from the steel work collected into the gutters & piped via gravity into you insulated storage tank? Would have a secondary function of cooling the interior of the boat as well.

Thought about this whilst I was sat on top of a static caravan roof in the sun trying to paint the edges with roof sealer. The roof that was in the sun was to hot to touch.

Justme

Would work to some extent, the problem is that you'd evaporate a lot of water from the large surface area of the roof. And the evaporation would cool it down (same principle as a fridge). So it would be a good way to cool the roof, but not such a good way to heat water.

[Smelly]

Not really, I've got a Jabsco circulation pump on my central heating on the boat - works great take about 0.5Amps but did cost about £80 at the time - really expensive for what they are.

 

Have you seen this:

 

http://cgi.ebay.co.uk/12V-WATER-CIRCULATIO...id=p3286.c0.m14

 

£45 ?

 

13l per minute is quite as lot... would I be able to "turn it down" do you think? From some rather extensive reading, most of the "authorities" seem to think the lower the flow rate the better. In all fairness, if I spent the money on a Jabsco, for the sakes of turning it down (edit) or a low flow (if poss, I've installed one for a mate and you couldn't with that unit) it's probably be worth it

 

however this is only 2 and a bit litres a minute... I wonder what the max head is?

 

Where's TomandSophie when you need 'em?

 

I can see how the polycarb would possibly work nicely, but instinctively that's an awful lot of water for an exchange sytem, probably ok for direct tho, and for my purposes the camber of the roof would mean I'd need to "hinge" it.

 

In the cold light of day I'm thinking that using the available stainless would be a bad idea. Although it'd be brilliant for catching heat, at least if painted, it wouldn't take advantage of the greenhouse effect, where you catch the lower freq light radiated back from whatever is absorbing the heat, I can get sheets of 2mm transparent acrylic from my local builders merch that'd be flexi enough to bend to the roof's camber and simply fit it into a groove in a profiled frame. Oh dear, that's another tenner on the budget... shame!

 

Tim, you posted while I was typing.

 

Like minds!

 

For the sakes of the budget instead of using 2 part foam, I'd probably use car floor mats, such as you get from Tesco for a couple of quid. this is, mainly, an experiment so I don't want to chuck loads of cash at it, if it works then it works!

 

Then again, clicking your linky (oooh err!) makes me think another tenner's not going to break the Bank.

 

I'll be using the last spare coil on my calorifier so antifreeze is the way forward; plus I won't need to drain it down in the winter, I might even be able to take advantage of those rare sunny days!

 

thought! Why can't I leave the matrices under the stainless with a sheet of acrylic over the top of that with a bit of an air gap to prevent conduction? neater, but would it get as hot? i'm leaning toward over the top.

 

Final edit... I only need it in the summer as during the winter i'll be burning dinosaurs to charge the batteries when the sun's not shining and the spare energy from that will heat the water, either by engine or genny/immersion. Also, the other calorifier is plumbed into the fire so hot water in't winter's not really a problem.

Edited August 18, 2008 by Smelly

[Smelly]

This is as much thinking out loud but...

 

I've been thinking most of the pumps I can see are too fast flowing, however if they were run intermittently it wouldn't matter so I wonder whether there's some form of control I could get...

 

I've been looking for eber/webasto control panels but they seem to be room thermostatic as well. there's got to be some kind of control gear I could pick up that's adjustable on/off. i don't know what it'd be called so searching could take ages, but I'll bet there's someone out there who knows...

 

Wahey!

 

and again

Edited August 18, 2008 by Smelly

[Smelly]

One last note on the pipework bores... Next time you're down the boozer have a look at the beer pipes, it's all mini plumbing kit... Looks like floplast junior.

 

Starting to think I can't do this on the cheap, pump, expansion tank and double glazed roof box come to about £150. It'll be next year of a job.

Edited August 18, 2008 by Smelly

[Smelly]

and finally, if I bought Stuart's suggested pump, how would I reduce from 20 to 10mm?

[Trilby Tim]

Not sure there'd be much point in acrylic over the top and the pipes underneath. As I understand it the glass/plastic over the top creates a mini greenhouse for the pipes, so they need to be inside the greenhouse, if they're underneath I'm not sure that doesn't defeat the point. I not sure on the pump, but I really suspect that a fuel pump requires fuel flowing through it to lubricate it and protect it from corrosion. I doubt it will last long pumping water (although I'm not sure on that).

I don't think the head it will pump to matters as long as you fill the system manually. Once the system is full then the pump just needs to circulate the fluid, it doesn't matter how high the high point is, it's a closed loop, so the fluid goes down as far as it goes up.

If you need to reduce the flow rate of your pump then having a timer switch on it should do that, so for example have it set to be on for one minute, off for 5. Would also reduce it's power consumption. From what I remember of GCSE electronics I think you can use two 555 timer chips to control that, one set as an astable and one as a monostable. The astable gives a pulse every 5 minutes (for example) and then the monostable counts how long to stay on for (there's probably better ways of doing it than that, that's just the way I happen to remember). Then you need a relay to switch the pump. If you wanted to be really flash you could wire in a thermistor in the solar panel so it pumps for longer the hotter the panel is, or even doesn't pump at all if the panel is below a certain temperature.

[Smelly]

thermistor... that's what it's called cheers Tim.

 

back to maplins then.

 

Tim if you follow the links in my last post I've found the kit!

 

looking at the thermistors at maplins I've just fallen off the end of my somewhat limited electronics knowledge. I think I'll leave it alone and switch it in when it's needed. unless, of course someone would be generous enough to give me some idiot proof instructions how to do it.

 

Now I come to think of it I guess it'd be across the pot controlling the length of the pulse and would need to be matched to the resistance of said pot at a given temp range, probably 70 - 110 farenheit.

[GSer]

If you still struggle for a pump, i used an old second hand Aldi boiler pump and header tank for a similar project (not boats though) i found it in an old scrapped caravan

 

Paul

[Chris Pink]

How about a small solar panel connected to a pump with no battery so that the pump pumps more when the sun is brighter?

[tidal]

after much searching of spanish websites (not something you want to do if you like to retain your sanity) and not finding the damned pump unit I phoned up the guy who bought the caravan and ancillary gear from me and asked him to look at the thing's name for me. It is an econoagua unit made by a company in Seville. and the diagrams show that it is designed to water pot plants etc.

 

Nothing I can find on the net ties in with this so I doubt that they are widespread. If it is of any use at all it was a pulse type pump simlar to those that used to be used in domestic heating systems but much smaller.

 

Sorry I cannot help further at this time

[Trilby Tim]

The maplins kit is the monostable half of the circuit, you still need an astable to provide the trigger pulse. Astables go on/off/on/off/on/off continuously, you can change the frequency, but they're always on for 50% of the time, off for 50% of the time. Monostables are off until triggered and then on for a fixed period of time before turning back off. So if you use the astable turning off to trigger the monostable to start timing you can control the percentage of the time that it's on for. The book you link to would probably give you the detail you need. A thermistor is a resistor that varys it's resistance with temperature, so you'd replace one of the fixed value resistors that's used to set the monostable's time delay with the thermistor.

[Smelly]

The maplins kit is the monostable half of the circuit, you still need an astable to provide the trigger pulse. Astables go on/off/on/off/on/off continuously, you can change the frequency, but they're always on for 50% of the time, off for 50% of the time. Monostables are off until triggered and then on for a fixed period of time before turning back off. So if you use the astable turning off to trigger the monostable to start timing you can control the percentage of the time that it's on for. The book you link to would probably give you the detail you need. A thermistor is a resistor that varys it's resistance with temperature, so you'd replace one of the fixed value resistors that's used to set the monostable's time delay with the thermistor.

 

Sorry I thought I'd modifed that link but it didn't seem to have worked, they stock an astable switching kit as well with a modifiable period and frequency. they've got a thermistor of matching resistance so it's looking feasible to get flash. I don't know how I'd stage the resistance so I get the correct results yet though...

 

Interestingly they do a temp sensing switch as well so that's that one sorted! On at about 2o deg C would be about right I'd thunk... This will be cheaper than buying solar panels (cheers Chris) but just as elegant a solution methinks!

 

I really want to build this NOW but we're going away on Saturday so I'll have to wait. It'll be next year before I see any results...

 

Tidal cheers for the help but I think I've cracked it!

 

You never know, maybe Bagpuss will get her nice warm wash during the summer now without an age running the engine!

 

edit... but I'm going to run out of roof space for firewood if I'm not careful

Edited August 18, 2008 by Smelly