Heat Exchanger

[Araucaria]

If I can find the money, I'm hoping to do a combined "warm the pool and heat the hot water" solar installation. It will be flat panel collectors, filled with an antifreeze (for winter use) and it will need a heat exchanger to warm the pool - rather than pool water circulating directly through the panels.

I understand there's an issue about the temperature of the transfer medium (antifreeze etc) in the heat exchanger - some (all?) will only cope with water temperatures up to 90 degrees, possibly because they are designed to use heated water from the domestic boiler rather than from solar panels. I understand that water/antifreeze mix in the solar panels can get to 130 or 140 degrees (as it's under pressure).

Are there heat exchangers specifically for this use? I believe the unions with the pool water system have to be capable of withstanding a high temperature too - I have a vague memory of having heard horror stories of the unions melting or burning. Any advice would be gratefully received.

[Théière]

Cannot help with your questions but unless you have a very large panel array and an insulated pool your losses will be = to your heat gains except in summer when you don't need to heat the pool anyway. If it is a liner pool you do have to watch the temperature.

[Araucaria]

[quote user="Théière"]Cannot help with your questions but unless you have a very large panel array and an insulated pool your losses will be = to your heat gains except in summer when you don't need to heat the pool anyway. If it is a liner pool you do have to watch the temperature.[/quote]

Thanks Teapot.

Do you know what the science is that underlies "your losses will be = to your heat gains"? I've seen suggestions that the array needs to be half the pool surface area, but I don't know how that rule of thumb is arrived at either. I'm not trying to heat the pool in winter - just extend the period I can use it by 4 to 6 weeks either side of full summer.

It's not a liner pool, though.

And if anyone knows about higher temperature heat exchangers?

[Théière]

You are spot on "A"

I had some calculations done earlier this year by one manufacturer and even they were surprised by the losses and the fact that half the pool area was required. New pools in the UK have to comply (should) with the building regs for thermal efficiency,  the pool is a massive heat loss radiator especially without wall and floor insulation. You would need a very good quality thermal cover as well.

I have a copy of the BRe report on swimming pools, if you email me I will attach a copy

And from Thermapool worth reading through the info on their site.

[Araucaria]

Hmm.

I've looked at the BRE report (easily found on the web), and it is purely a paper exercise (that's to say, with no actual experimental results) prepared for a group of pool manufacturers/constructors/installers.

It assumes an outside temperature of 10 degrees and that the pool is to be heated to 29 degrees for 12 months of the year. Naturally the figures will look rather scary. But I can see it would have been nice if I had had the hole in the ground insulated before the pool went in four years ago. Regrettably I didn't.

Common sense, not always the best guide, tells me that if I put some heat into a pool it will get warmer. If I try to keep the heat in (with a cover) it will stay warmer than if I don't. In any event I'm prepared to give it a try - the solar panels will certainly give me domestic hot water at other times (winter, high summer), so the results won't be too depressing whatever they may be.

[AnOther]

[quote user="Araucaria"]Common sense, not always the best guide, tells me that if I put some heat into a pool it will get warmer.[/quote]But only of course if you are putting in more than you are losing, hence the need for a decent area of collector (the 50% of pool area commonly suggested) and flow management.

It's all highly experimental for the DIYer but I'm sure someone could come up with a rough and ready formula on which to form the basis of a plan.

[Théière]

It sounds like "A" will do that, unfortunately I binned my info as the cost/benefit didn't stack up in any way and an uninsulated pool may increase fro 14 deg to 18 deg but I still wouldn't go in that! [:-))]

Maybe "A" is made of tougher stuff (Scandinavian perhaps, maybe they enjoy being beaten with birch twigs, who knows) [:)]

"It assumes an outside temperature of 10 degrees and that the pool is to be heated to 29 degrees for 12 months of the year. Naturally the figures will look rather scary. But I can see it would have been nice if I had had the hole in the ground insulated before the pool went in four years ago. Regrettably I didn't".

A real world situation for the UK and they installed into a local school at Woodmansterne who could not afford to keep their pool open, now they can.

 

[Poolguy]

[quote user="Araucaria"]If I can find the money, I'm hoping to do a combined "warm the pool and heat the hot water" solar installation. It will be flat panel collectors, filled with an antifreeze (for winter use) and it will need a heat exchanger to warm the pool - rather than pool water circulating directly through the panels.

I understand there's an issue about the temperature of the transfer medium (antifreeze etc) in the heat exchanger - some (all?) will only cope with water temperatures up to 90 degrees, possibly because they are designed to use heated water from the domestic boiler rather than from solar panels. I understand that water/antifreeze mix in the solar panels can get to 130 or 140 degrees (as it's under pressure).

Are there heat exchangers specifically for this use? I believe the unions with the pool water system have to be capable of withstanding a high temperature too - I have a vague memory of having heard horror stories of the unions melting or burning. Any advice would be gratefully received.
[/quote]

 

Araucaria

This is a noble endeavour and certainly doable. I've been working on this concept for a few years so that a solar installation can be used all year round and its capabilities maximised; The secret I have discovered is to mount the pool heat exchanger inside the Accumulator and then you can avoid all the problems with over heating and also direct the heat any where you want it. A schematic might look like this;

                    [IMG]http://i584.photobucket.com/albums/ss285/andrewhenderson/HousePoolSolarAkvatermV41-1.jpg[/IMG]

You will see in this diagram that you can add pool heating, domestic hot water and even heat you home (to some extent) all is possible and its the safest and most robust design we have found to date. All other options are fraught with problems and overload complications I fear. If you want more discussion on this idea then email me and I'd be happy to elaborate. Tell me why would you want to use flat solar panels then rather than tubes?

Cheers

Andrew

 

 

[Dog]

To heat the pool we used three tough hose pipes coiled and painted black under glass.

Cheap as chips and easily drained before freezing conditions.

In Crete I noticed the latest simple and cheap solar water is provided by a large black plastic tank with indented panels.

[Jonzjob]

Dog, if that's anything like Cyprus then the tanks are there just for storing water. In Cyprus a lot of people have to buy and store their water that way because of their water shortage. They also lock the lids shut so that the neighbours don't syphon it off!!

[Araucaria]

Hi Poolguy

your last question first (but it explains a bit more). It will be flat plate collectors because the solar panels will be quite close to the ground, as the roof of a purpose-built shed near the pool, which will also contain the pool machinery. I found the buried local technique too inaccessible (and the lid didn't open far enough either). The grandchildren would have a very good chance of breaking the evacuated tubes if we went for those instead. The roof starts about 70cm from the ground. Which is, in fact, just about the present height of the grandchildren.

To give you an idea, this is what the shed looks like at present:

[IMG]http://i585.photobucket.com/albums/ss293/Vanman15/skeleton.jpg[/IMG]

and whatever other faults it may have, it faces due south and gets unobstructed sunshine all day - when the sun is shining, that is.

Regrettably, the purpose built shed won't be very close to the house - there really wasn't a lot of choice as to where to put it as the garden isn't all that big, and it is a funny shape to boot. I suppose it would be possible to put an accumulator in the shed, but we already have a ballon with an extra serpentine for the solar input, and that's in the house.

I did wonder whether a possible solution was to route the heated water from the solar panels to the ballon first, and then to the heat exchanger for the pool last of all just before it came back to the collectors. I supposed that there wasn't much chance of the water temperature exceeding 90 degrees after going quite a long way through underground pipes and heating our hot water on the way. But this might give a bit of a problem with the control mechanisms. And it also might not heat our pool very much!

[Jonzjob]

Why can't you fit them at ground level?

[IMG]http://i47.photobucket.com/albums/f180/Jonzjob/Tubes2.jpg[/IMG]

They will withstand 30mm hailstones and one bloke on the Navitron forum actually hurled a football a load of times at his ground level setup to make sure that it was safe for his son to play football near them! They are made from the same glass as Pyrex dishes and the only delicate part is the vacuum nipple at the bottom and you have to e a bit careful not to knock it when you are fitting the tubes in the rack. your setup looks ideal for tubes and because they are more efficient than a flat panel in anything less than wall to wall sunshine you don't need such a large area of them.

I could really do with another 10 tubes for the optimum for our 9.5 X 4.5 metre pool, but space says no, but they still put extra heat into he water. I don't have figures as to the heat output/input to the pool. For me life is too short for that, but in comparison to our neighbours in the same situation, but no heating our water is warmer. It took a while to set the controller for the optimum, but I'm getting there now.

Just as a matter of interest. We also have 4 sq M of 20 + year old flat panels, also at ground level, that heat our water and as soon as the sun is out we get all of the hot water we need. That wouldn't be anywhere near enough to heat a pool, but it does us for the water thank you very much!!

[IMG]http://i47.photobucket.com/albums/f180/Jonzjob/Johns/29solar.jpg[/IMG]

[Araucaria]

[quote user="Jonzjob"]Why can't you fit them at ground level?

They will withstand 30mm hailstones and one bloke on the Navitron forum actually hurled a football a load of times at his ground level setup to make sure that it was safe for his son to play football near them!

[/quote]

You haven't met our grandchildren and ....... a handy supply of rocks?

You're living a bit further south than us, but I am certainly curious to know which months you can use your pool with the extra heating you have. It would give us some very rough idea what our 10 m2 panels might do.

If we can find a heat exchanger that's suitable, that is........

[Poolguy]

Araucaria

I think that you'l find that a flat panel is far more suseptable to rocks than a tube system. At least with tube is it happen that one or two get broken for what ever reason then you just replace the glass bits at about €25 ea, and the system continues untroubled during and after,  whereas a flat panel glass pane is broken then the whole panel is finished.

As I said before, the heat echanger is no real problem. I can show you more if you want to contact me.

Andrew

 

[Jonzjob]

It sounds as if you could well do with an electric cattle prod for your grandchildren Araucaria? If they are going to be throwing rocks around then a very sharp word sounds to be in order whatever type of heating system you use. [:'(][:-))]

[gyn_paul]

I know this sounds a silly question, but if you have a goodly array of tubes - sufficient to heat the pool up quickly in a spell of good weather,... what happens to the heat/to the tubes when you think the pool has reached its optimum temperature?

p

[AnOther]

Err, turn off the flow of water through it maybe [Www]

[gyn_paul]

[quote user="AnOther"]Err, turn off the flow of water through it maybe [Www]
[/quote]

nooooo. you lummuck... what happens in the tubes I mean !  Do they just get hotter and hotter?

[Poolguy]

[quote user="gyn_paul"]

I know this sounds a silly question, but if you have a goodly array of tubes - sufficient to heat the pool up quickly in a spell of good weather,... what happens to the heat/to the tubes when you think the pool has reached its optimum temperature?

p

[/quote]

Its not Silly Gyn, au contraire its very insightful and I think the critical factor in good Solar system design. Typically heating systems are designed for the spring warm up and the autumn end of season to help with water temps sometimes in their teens°c. But that means heat is not needed during the hottest part of the year - summer, but with solar you cannot turn it off, it just keeps producing heat. That is to say that the panel will continue to produce heat and if the circulation is turned off the panel will reach stagnation which is up to 250°c. This is the max possible no matter what the radiation and will not hurt the panels but is very bad for the pump which can melt the impeller if the fluid (vapour) arriving is too hot.

Consequently, several fail-safes should be design in, but also important is some sort of heat dump - a harmless place to put the heat, which is not needed. Its usually the pool but no one wants a pool to be heated into the 30's so you can leave to cover off at night to let it cool down or have somewhere else to loose the heat., Many systems are size on the small side to minimise this issue but that sort of defeats the purpose in my opinion.

Andrew

[Jonzjob]

I have put some caravan awning rail across the top box on my tubes and just slide a cotton canvas cover over the tubes. The covers are secured at the bottom with bungy cord.

Works a treat and they are covered through the winter too to stop the pump running for no reason because there just isn't enough sunshine to heat anything..

[Araucaria]

[quote user="Jonzjob"]I have put some caravan awning rail across the top box on my tubes and just slide a cotton canvas cover over the tubes. The covers are secured at the bottom with bungy cord.

Works a treat and they are covered through the winter too to stop the pump running for no reason because there just isn't enough sunshine to heat anything..

[/quote]

That sounds like a very simple and practical idea - and as we've not yet installed the panels it can be custom-designed for our roof.

But - winter - pump running for no reason? Doesn't the controller only turn the pump on when there is a sufficiently large temperature difference between the input and output probes? I'm certainly hoping to get some water heating in winter - we're at about 500m here and we often get clear cold but sunny winter days.

[Jonzjob]

As you can see,my setup is at ground level and it only feeds heat to the pool. We have another 4 flat panels that have been here, also at ground level, almost since the house was built in 1982.

[IMG]http://i47.photobucket.com/albums/f180/Jonzjob/Johns/Navitroncover.jpg[/IMG]

[IMG]http://i47.photobucket.com/albums/f180/Jonzjob/Johns/Navitroncover1.jpg[/IMG]

The cover was part of a small awning for our caravan that we used when we were 'on route' so to speak, but apart from being slightly short, which doesn't matter, was just the job and works a treat!!

Edit :- Our controller is set to switch the pump on when the panel temp reaches 20 deg C above the water temp and off again at 10 above. That happens quite a lot during the winter. It is also set to run the pump for 5 mins in the hour if the temp drops to 5 deg and 20/hour at 2 deg. So it's a built in anti freeze..