DIY swimming pool experimental solar heating

[Jackie]

Just a few things I have been playing with from time to time over the last few years. Any comments welcome.

 

1/ An open solar trough in concrete of 10 square metres was tried. The pool water was pumped into the trough and ran back into the pool at about 23 litres/minute. The trough, painted black, produced a temperature rise of 3 degrees Celsius in sunlight at most times of the year. This was not developed further as the water in the trough became mucky with leaves and worms and bugs falling into it. Further the black paint, several different types tried, was degraded by the action of the pool chemicals, salt and chlorine, and needed repainting each year. Black tiles instead of paint could have been tried with better filtering of debris and might be worth investigating further. As an alternative a shallow tank made of glass fibre with black resin could be tried though the action of pool chemicals might be a problem and concrete with tiles would be a cheaper option I think.

 

2/ After initial promising experiment with uPVC water pipe, grey 100mm, 184 metres of such pipe was layed out in a zig zag pattern in our field and raised about 6cms above the ground. 100mm pipes give a larger surface area than smaller bore tubes and are about the cheapest here from an agricultural supplier. Pipes running roughly East and West so the sun was broadside on at- the solar maximum thus making a 90 degree angle with the maximum surface area possible. Pipes were painted in Sika Resin coloured black with a powder additive and later on over coated with a light coat of mat black spray paint. Results in Spring, when the pool temperature was low at 21 degrees, were promising giving a rise of 6 to 7 degrees Celsius at between 30 and 36 litres/minute. Results now at the end of July with the pool at 30 degrees are less promising giving only a 3 to 4 degree rise at the same flow rate. The top coat of mat black spray produced little benefit which is surprising as the Sika resin has a glossy finish until it has been weathered for some time. The black spray paint, Go-On, must have some unwanted significant reflectivity. 

 

3/ Metal fins, sprayed black, have been glued to the pipe using Araldite. My feeling is that the contact area between the fin and the pipe is too small to be very effective in the transfer of heat to the water in the pipe and Araldite, even in a very thin layer, is not a good thermal conductor and is expensive even for the small quantity needed. On the other hand the plastic of the pipe is also not a good thermal conductor either!

 

4/ Metal plates, 1mm thickness in steel, sprayed black and suggested by Jackie, have been tied under and between the pipes. These get very hot in the sun and a temperature gradient can be detected getting colder the closer one comes to the plastic pipe which indicates to me that heat is being transferred though maybe not very efficiently. Aluminium plates would be better but also more expensive I think. I do not have a point contact digital thermometer which would be needed to investigate this fully.

 

5/ 50mm uPVC pipes embeded in a layer of black painted concrete have been tried in an area equal to the original solar trough but performance was not as good only producing a 2 and not a 3 degree rise in temperature at about the same flow rate of 23 litre/minute with the water remaining clean as this was a closed system.

 

Conclusions open to debate and comment I hope:

 

The pipes in the field work and work reasonably well when the pool temperature is low, less so when the pool temperature is high. Would like to increase the efficiency of this system and black metal plates between the pipes might be the solution, only a few have been fitted so far. An alternative would be to extend the pipe system as 184 metres of pipe gives an effective heat collecting surface area of less than one third of the total area of the pipe surface. Say about 18 square metres currently. Most "Experts" suggest a minimum of at least half the pool surface area (50 metres squared in  our case) is needed. A lower reflectivity mat black paint would be of benefit for the pipes, something like Blackboard paint with an ability to withstand weather. Sika resin is a bit glossy and rather pricey but it does weather well.

 

The open trough is the simplest system and worthy of further experiment. Rather a permanent fixture however and some heavy labour needed to produce it. 25 square metres of trough would rather dominate a small garden though this is less than the space taken by the pipes but not a problem for us having a field to play with!

 

The concrete was disappointing and might have been better with added graphite or slag ash to increase the thermal conductivity. However slow to repond but with some heat storage after the sun had set. Might be worthy of more experiments. 

 

With all solar heating systems for a swimming pool there must be an optimum flow rate for each individual system. My feeling is that the important figure for each system must be the flow rate multiplied by the temperature rise obtained. If the product of these two is plotted for different flow rates a maximum product would indicate the optimum flow rate for a particular system.

 

So you might think I should have better things to do but my pool is currently at 30 degrees and the system cost a lot less than a commercial one! I look forward to any and all comments, photos are available........................................John

 

[Maricopa]

How about covering the open trough with glass?  That should make it even more thermally efficient AND prevent stuff getting in there.[geek]

[Uffcat]

It sounds like an interesting concept to me!

We have a friend living in Almeria (admittedly a lot hotter there) who has made a fabulous (and simple) heating system which he says extends their use of the pool by a month either side of the season.  It involves nothing more than a couple of hundred metres of black irrigation tubing coiled up like one of those old-fashioned licquorice sweets and a small pump. The water is pumped from the pool into one end of the black pipe, goes all around the coil and back into the pool.  The coil lies on top of his carport so is not obtrusive either.  He says it raises the temperature of the water by about 5 degrees.  It appears to work so well I'm still trying to work out where I could place a similar setup here, I like the idea of the warmer water very much.  Perhaps you could fill your trough with thin black tubing as it would solve the paint peeling problem and also the bits problem.

[Jackie]

Thanks for the suggestions. I did think of putting glass over the solar trough but in fact this might not help that much as the trough and water were horizontal of course and the light would strike the glass at an angle so much would be lost by reflection also rather a lot of glass, 25 square metres needed. Swimming pools need a small rise in temperature at a high flow rate so re-radiation from the solar collector would be minimal therefore glazing would add little to the performance. In solar heating for a house hot water supply  glazing would be helpful as we would be dealing with a low volume of water raised to a much higher temperature and re-radiation would be a significant loss or so wiser heads than mine have suggested.

I have tried the coiled tube in a glazed box and laid out on the lawn but the pump I am using is the same as the one for the pool circulation and flow rate in a small diameter tube is limited and I don't want the cost of a separate pump using extra electricity. Others have used the black water supply tube sold by bricos but again the bore is small and flow rate a problem.

Someone has suggested an open plastic gutter type trough system with plastic glazing but the plastic sheet would have a limited life due to UV radiation. For sure the open concrete trough worked and is relatively cheap and is not unpleasant to look at. Tiles would overcome the paint problem though external quality would have to be used as ordinary tiles for house floors might be damaged by freezing in winter I think. I may add some more metal plates between the pipes and see if there is a significant increase in performance. They are clear of the gound and painted white underneath to cut down re-radiation from the underside. Brico charge a lot for sheet metal so maybe I should find a scrap merchant. Having got the pool to a good temperature I would like to keep it there for as long as possible. Look forward to any more suggestions though..............John

 

 

[Phil & Pat]

John,

Have sent you a PM.

Phil.

[buckdendave]

The coiled black tube (it's polyethylene by the way) comes in a range of sizes all the way up to about 180mm outside diameter.  If you have tried 25mm then consider 32mm or 50mm or 63mm or whatever (probably available from a farm supply depot).  Of course the disadvantage is that the cost also increases with diameter, and it's a bit of a beast to handle at the larger sizes.  However you should get the flow rate you desire using a standard pool pump.

Dave

[Jackie]

Hi and thanks for the information. I suppose if it is already black it would save the problem of painting it but one wonders about the effects of UV as a coat of paint would offer some protection. It would have to be just over 260 metres ( if I were starting again) of 100mm OD tube to get the minimum surface area recommended for a pool of 50sq/m and that is a bit of a guess as I am assuming only a bit less than a third of the surface area of a pipe as being active in collecting energy and that may be optimistic. Can it be glued like uPVC, others suggest not, or are all the fittings compression type? Only a certain percentage of the output of our pool pump passes through the tubes I have already in service, say 20% at a guess.

I did note today that our new Bricomarche store in St Maixent L'Ecole has galvanised corrugated metal sheet at a reasonable price which could be painted, black topside and white underside, and installed under the existing pipes. Corrugated sheet could also be used in an unglazed trickle system where evaporation loss would much less than from the pool's surface but then we have the problem of finding a paint that will withstand both salt and chlorine and the only corrugated plastic/ fibre sheet I have seen of a dark colour is red.  Food for thought..............................................John

[Poolguy]

Blimey.........!

What a lot of trouble you re going to, to invent something which is already very advanced and accessable.

Evacuated tube solar panels will heat your pool and not consume your back yard or your time and money in the way its doing at the moment.

But I guess you are more interested in Doing it yourself than getting the result... n'est  pas.

Andrew

 

[Jonzjob]

Encore Blimey. I think that I can find all sorts to do including swimming in our pool. Half of the cash you have spent could have heated your pool and used 25% of the area of it, I would have thought?

Then again if you really want to re-invent the wheel then who am I to argue [:D][:)][:D]

[Brier]

For an alternative DIY solution try the following link:

http://www.chauffepiscine.com/index.htm

[buckdendave]

You can join black polyethylene by compression fittings or electrofusion (it's a welding method with a resistance wire built into the fittings - a bit specialised unless you want to get all the information from the manufacturers).  Black PE will last for many years if it's to a French or European Norm and made by a well known maker.  However that amount of pipe would be quite expensive and take up a lot of space.  It might be easier to get similar results with some manifolds and a lot of small diameter pipe (running in parallel).

Dave

[Jackie]

Well Véronica looks nice. From what I have read feeding tubes in parallel has some advantages and is certainly more space efficient however using the 100mm grey plastic pipe that I have used doing this would result in a much greater cost as off-the-shelf T junctions or clip and glue side entry thingys are expensive compared with the cost of 4m sections of pipe. The point about 100mm is that it is cheap for the active area you get compared with smaller sizes. Drag factor is low so lends itself to serpentine layout without expensive fittings used in parallel pipe systems and not that much pressure is needed to drive a reasonable flow of water through it so part of the output of the existing pool pump can be used and no other pump is needed. I accept that serpentine layout follows the law of diminishing returns by the way but I lack the expertise and tools to create the manifolds used in parallel fed sytems and as I have said buying off-the-shelf to make one up is not cheap.

On the negative side a lot of space is needed but as I am fortunate to have a field not used for anything else so not a problem for me. (The space taken by the pipes gives me less to mow and only needs spraying with Glyphos three or four times a year, less if I used Sodium Chlorate.) The pipes hold a lot of water which is lost on draining in winter. This is not a problem as it is only done once a year and is less that the amount we pump out of the pool in winter due to rain. (We don't drain the pool in winter and run the pump on those few nights that freezing might be possible). The pipes need painting and the Sika resin I have used is expensive but the resin seems to have a long life and takes colouring agent easily. Pipe I painted 3 years ago still looks good.

Evacuated tubes are good for small size, high efficiency and solar heating for house hot water I think. From what I have read use for pool heating using the two glass tube type and selective coating might be ok for pools but what a cost! Those that use metal tubes inside would worry me for a salt water pool use but no doubt someone will set me straight on this. Experimenting with my system continues to give me a lot of fun, keeps me off the streets and out from under Jackie's feet and I guess I have not spent more than 500 euros altogether so far if that!...........John

[Poolguy]

Jackie

If you are happy with the experimentation, then let me not divert you.

BUT if you want to know how to heat your pool from the sun then contact me, because you are not making good decisions up to now.

TO further your research let me tell you that the evacuated tube solar system provides the most kw/euro by far than anything else on the market today including what your are now experimenting with. Its been researched extensively and the results are conclusive so even though you are spending small amounts, so is the benefit to your pool. The evac Tube will provide real temperature increase they do not need to be maintained or drained in winter unlike your 'wet system'.

Andrew

 

 

[Jackie]

Having looked at your web site I see that the system you sell is based on what I believe to be a rack of heat pipes with a pump/controller passing non-freezing fluid in a loop through a chamber containing the hot end of the heat pipes and then through a heat exchanger with pool water being pumped through the heat exchanger and back to the pool. As such I am sure that the system is most efficient but at what initial cost? If I read your info aright then for a 50 sq/m pool I would need a heat pipe panel or panels of about 12 sq/m, would that not cost a lot more than 500 euros even if I fitted it myself? I note that another firm who supply in France based on the same Navitron System charge 2400 Euros for their cheapest swimming pool complete kit and 3950 Euros for one of our pool size and that would buy a hell of a lot of plastic pipe! For another 500 Euros I could almost triple the collector area, still got a lot of field left, not that I am going to just now as there are other cheap options to try though I would agree less efficient but more fun!............................................John

PS The domestic hot water system based on the same technique does look interesting however but I wonder about the payback time.

PPS Have just tried re-painting some of the pipe with non-reflective black board paint with promising results but do not yet know of its weathering properties however none has washed off yet and time will tell.

[Jonzjob]

It would cost you more than 500€,

BUT IT WORKS!!![:D]

[IMG]http://i47.photobucket.com/albums/f180/Jonzjob/50tubes.jpg[/IMG]

A nice balmy 30 deg today thank you [8-|].

[Théière]

Hey Jonzjob, whats that made from? All your evacuated beer bottles. [:)][:D][:P][;-)]

[Jonzjob]

Na TP ( hey that reminds me of Telak Paku, the beach club just behind R.A.F. Changi, Singapore, in 1967. Directly behind the flight line of 205 Sqdn Shackeltons. Once the 17 hour patrol was airbourne we were in for a pint of Tiger or two?? Well maybe three but who counts in those situations?)

My beer bottles have no beer in them after use, but the above babies are a vacume (is that 2 'u's?) and even I can't give claim to getting that much from a beer bottle. Besides which the bottles are green [B]!

That was a close all I think! I wonder if I got away with the description??[8-)]

Those tubes are much more effective than any home made contraption lke a beer bottle or ??????? (Quit while you are ahead John!)