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solar pool heating


euro

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hi , we are looking to add some free heat to our pool to hopefully extend the period of use / comfort and i wondered if anyone has experience of using the off the shelf and fairly inexpensive plastic pipe / mat systems for this ?

do they work ?

much warmer ?

do they leak ?

etc
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Hi Euro,  Ok pool heating to extend the season. Either side of the nice warm summers are the cool bits we want to have as extended swim times. the problem being black mat types require the warm sun to heat the water. 

If you want reliable at the flick of a switch heating the an air source heat pump would be a better option as they are capable of working to low external temp will give you more output for the electricity you put in so for 1kw put in you should get 3-4kw in cool weather.

The other option for solar are evacuated tubes as these can work with the available light rather than heat to warm the water but you'll need extra space facing the right direction and angle.

Don't leave out the basics, a good solar cover (clear) will get the maximum warmth from the sun and save heat by reducing evaporation which is where the majority of heat is lost.

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Hi Euro,

Yes they do work to extend your season but as teapot says they do rely on sunshine. We have had polypropylene solar heating for 12 yrs on our pool with no problems and usually open the pool for early April and close end Sept - typical temperatures at end of seasons months are 26 deg C. We are based in the southern Charente so I would think north of the Loire you may have a bit of a problem.

Avoid HPDM rubber as they perish after a few years, and the cheap chinese ones aren't a lot of good. As with most things you get what you pay for and the same goes for Heat pumps. The ratio of kW in to kW out varies with ambient temp and humidity so take manufacturers figures with a pinch of salt !

You can always combine solar with heat pumps to get free heat when available.

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Halfblind, can you give some idea as to the area of pool and heat collector area please.

I don't want to seem as though I am pushing heat pumps and as you say you need to be careful of manufacturers stats but pumps used in the Scandinavian countries and UK are able to produce the goods at lower temperatures than units produced for warmer climates that are invariably the cheaper end of the market.

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We bought one in the UK 4-5 years ago, when the exchange rate was very friendly. It's a couple of kms of rubber tubing and works very well. It does suffer from the occasional leak where the tubing is joined to the manifolds, but it's no big deal fixing them. We have to turn it off in summer or the water gets too hot and pool chemistry becomes a nightmare not to mention the water becoming a "delightful" green colour. They are certainly a winner in the shoulder part of the season. They are also easier, to install, and cheaper than heat pumps or solar panels and your heat is free.One thing to bear in mind though is your pump big enough to pump both pool and solar mat, ours was fine but I don't know what you would do if the pump wasn't up to the job.

Regards

W

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[quote user="Théière"]

Halfblind, can you give some idea as to the area of pool and heat collector area please.

I don't want to seem as though I am pushing heat pumps and as you say you need to be careful of manufacturers stats but pumps used in the Scandinavian countries and UK are able to produce the goods at lower temperatures than units produced for warmer climates that are invariably the cheaper end of the market.

[/quote]

The solar panel area is 50% of the pools surface area. They are manufactured by a company in the USA who have been in the business for 35 yrs and also make product for other companies via branding. Website http://www.solarindustries.com/

Declaration of Interest:- Since I tried the product out back in 1999/2000 I have become involved with importing and installing the product in to France, only in a small way as I have other "irons in the fire" and mainly in the South West of France. Customers seem pleased though and some have asked for another system when they have moved house. I use controllers on my systems so do not suffer from overheating in summer.

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Thanks halfblind, yes I know of the company and it explains your results.  Considerably better than black EPDM mats as you can utilise the existing pump in most cases as the headloss is low compared to Wilko who needed a bigger pump with the result that more energy is being used so more cost for a pump and electricity although the initial outlay maybe cheaper.  A two speed or variable speed pump is the ideal addition as it has the extra umph when the heating system is on but can save you a lot as you can reduce the pump flow/speed when the heating is not in use, coupled to the fact the pumps are nearly twice as efficient as a regular pump. Of course Wilko is so much further south which helps [:)]

Euro you don't say where abouts you are in France and that will make a big difference too. 

Declaration of interest:- Since I tried the product in 2011 I have become involved in the importation and installation of the most efficient variable speed pump currently available (up 94% efficient) [:D]

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That will be Theiere, yes your English is as bad as my reading but no offence.  My quip at the bottom of the post was not trying to sell stuff it was a tongue in cheek response to Halfblind's.  I am trying to pass on information and as such your pump was powerful enough which would also mean that when the heating is not being used the pump is pumping too fast for maximum efficiency and best filtration, forcing water through a filter is a waste of energy and results in channelling of filter media leading to poor water quality hence the two speed pump or variable speed pump. Sorry if I am ahead with the technology side but that is my forte, it's why I can run my system pump using only 160watts.  
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Hi

sorry i forgot to say we are in lot et garonne (47) the pool has full sun virtually all day with a little dappled shade from a tree.

i was thinking about the solar collector being mounted on my barn roof which sits adjacent to the pool facing south and is generally red hot.

perhaps the idea of free "heating " is ambitious for a big pool , i have made a few enquiries with suppliers of the epdm etc smartpool / mats etc and surprised to learn how costly it is at over £1000 to supply !

i had envisaged pricing in the region of a few hundred at most as its little more than pvc drainpipes !

giving a little more thought to a heatpump ................

Euro
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Ok, here is a related question - I have fitted ten solar panels to heat a pool I take care of. They are on a dedicated circuit with an outlet and return in opposite corners of the pool, with a dedicated pump operated by a sensor that fires it up when sunlight is warming the panels.

The panels themselves are replacements for older ones that had been left when the place was abandoned - leaking, weeds growing through them etc.

My question is this - they are arranged in two rows of five panels and I have the option to plumb the two banks in different ways. Firstly, and how it was done originally, the output from the pump splits through a "T" and the two banks flow in parallel, with the flows merging through another "T" and into the pool.

Alternatively, I could plumb the two banks in series. This strikes me as better, as the water will go through twice the surface area, so should collect more heat on its passage.

Any problems or thoughts?

I also plan to fit a thermostat to switch it off when the water temperature reaches a determined level.
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Running them in parallel is best as it reduces the headloss on the system so it is easier for the pump to circulate (less electricty by way of load) as each panel is fed individually rather than a long long path.  Each panel will get the same solar gain and all those gains added together will be more than the diminishing returns of a series circuit where the panels are pre heating ready for the next panel and by the end the panels are not managing to add any more heat.

Did I make that at all understandable?[8-)]

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[quote user="euro"]Hi

sorry i forgot to say we are in lot et garonne (47) the pool has full sun virtually all day with a little dappled shade from a tree.

i was thinking about the solar collector being mounted on my barn roof which sits adjacent to the pool facing south and is generally red hot.

perhaps the idea of free "heating " is ambitious for a big pool , i have made a few enquiries with suppliers of the epdm etc smartpool / mats etc and surprised to learn how costly it is at over £1000 to supply !

i had envisaged pricing in the region of a few hundred at most as its little more than pvc drainpipes !

giving a little more thought to a heatpump ................

Euro[/quote]

For a quality system you will be paying around the same as for a heat pump (installed price); DIY a little cheaper.

What you will avoid is electricity costs and maintenance and noise.

As you are in the Lot et Garonne I would go for solar, but then I am biased ;)

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[quote user="Théière"]

Running them in parallel is best as it reduces the headloss on the system so it is easier for the pump to circulate (less electricty by way of load) as each panel is fed individually rather than a long long path.  Each panel will get the same solar gain and all those gains added together will be more than the diminishing returns of a series circuit where the panels are pre heating ready for the next panel and by the end the panels are not managing to add any more heat.

Did I make that at all understandable?[8-)]

[/quote]

Teapot is right, you may have to put a throttle valve in to the feed of one of the lines to balance the flow through the 2 arrays. You don't need a flow valve just feel the panels on a sunny day when water is flowing, they should be cool showing that the heat is going into the water, if one array is warmer then the other needs throttling back a little to balance the flow.

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Can I just say something which has gone unsaid at this point.

That a SOLAR MAT system like this (which is what you've all been talking about)

[IMG]http://i1277.photobucket.com/albums/y495/TeknosAchat/AUT_2593.jpg[/IMG]

 

Will ALWAYS UNDERPERFORM and be generally more expensive to install and to maintain than a SOLAR PANEL system of evacuated tubes like this

[IMG]http://i1277.photobucket.com/albums/y495/TeknosAchat/SolarPanels.jpg[/IMG]

 

There reason is that the SOLAR MAT only absorbs energy and transfers it when the sun is shining, is generally uncontrolled in terms of flow rates and will be a constant worry from leaks created by expansion of the material. Whereas the Evac. Tubes, are precisely controlled, no more expensive and produce 80% more heat for a given area partly because they can still operate on overcast days as well as sunny ones and for many other highly technical reasons.

O

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Getting back to the original question which was an inexpensive option.

No doubt about it, evacuated tubes and heat pumps are most efficient but an arm an a leg with payback more than 10 years probably.

I had a look HERE and while I found the mathematics quite challenging (and it's for a system in Uruguay so you have to turn the dates and angles upside down) but with the help of a friend who conveniently has a doctorate in pure mathematics it can be boiled down as:

It's complicated

There are many variables

The outcome?  You need a collector which is at minimum half the surface area of the pool and at max 100% the surface area, outside these limits you get little benefit or diminishing returns.

In most of France, you can expect a pool temperature rise of between 1 and 3 deg C in the 'shoulder' periods of the year.

If I had a pool I would firstly get a cover because as said previously, evaporation and wind blowing across the surface account for big losses then I would try getting lots of cheap plastic tube and joints, paint them black, connect then up  and put a pump on it, total outlay possibly a few hundred euros but what a good experiment [geek]

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[quote user="Pierre ZFP"]Getting back to the original question which was an inexpensive option.
No doubt about it, evacuated tubes and heat pumps are most efficient but an arm an a leg with payback more than 10 years probably.  Payback based on what? If it's too cold you don't use the pool, or the extra €500 pw rental income? The cost of a pure electrical heater vs heat pump vs solar?  8 weeks more income @ €500 pw is payback in 12months-18 months for solar, electrical cost is higher but more reliable turnkey solution.
Evacuated tube solar will produce hot water even when it's snowing so can be used for hot water supplementation or under floor heating so more benefits to that system.

I had a look HERE and while I found the mathematics quite challenging (and it's for a system in Uruguay so you have to turn the dates and angles upside down) but with the help of a friend who conveniently has a doctorate in pure mathematics it can be boiled down as:

It's complicated
There are many variables

The outcome?  You need a collector which is at minimum half the surface area of the pool and at max 100% the surface area, outside these limits you get little benefit or diminishing returns.

In most of France, you can expect a pool temperature rise of between 1 and 3 deg C in the 'shoulder' periods of the year.

If I had a pool I would firstly get a cover because as said previously, evaporation and wind blowing across the surface account for big losses then I would try getting lots of cheap plastic tube and joints, paint them black, connect then up  and put a pump on it, total outlay possibly a few hundred euros but what a good experiment [geek] That would work well in summer when you don't need it but in shoulder season with the occasional "good day" not a practical solution and black pipe is already available but you would really need a bigger collector area just like flat plate (mats) already have. 
[/quote]

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This argument about panel types isn't so simple as one is always better than the other or more economical.  It depends on how you will use them and the usual weather where you live.  [url=http://www.troublefreepool.com/solar-panel-technology-comparisons-t9648.html]This thread[/url] shows a technical comparison of different panel technologies (add 13% to all evacuated tube values in the table for the most efficient tubes now available).

[url=http://eosweb.larc.nasa.gov/cgi-bin/sse/retscreen.cgi?email=rets%40nrcan.gc.ca&step=1&lat=48.8742&lon=2.3470&submit=Submit]This link[/url] shows the solar insolation in Paris, France.  (submit your own location using [url=http://eosweb.larc.nasa.gov/sse/RETScreen/]this link[/url] but you need to enter latitude/longitude since the geographic map link doesn't work).  Your summer sun is similar to my August sun.  I have black flat mat panels and they heat our pool to 88ºF adding 15ºF-20ºF to the water temp compared to no solar or cover.

[url=http://www.troublefreepool.com/what-does-it-cost-to-run-a-pool-heater-anyway-t18542.html#p151853]This post[/url] shows the situation with my pool.  Note that without a pool cover and no solar or gas heating, the pool water temperature will get to slightly above the average day/night air temperature (it gets higher in more humid environments where there is less heat loss from evaporation so the sun's heating is a net positive).  A pool cover can increase the temp by 10-15ºF (my cover is an electric safety cover so while it eliminates evaporation, it is not as insulating against conductive losses so raises temps by around 5-8ºF).  The solar system adds another 10-15ºF on top of that.

So what's the bottom line here?  If you are only going to be swimming when the weather is somewhat warm with mostly clear sunny skies most days with little wind, then a black flat mat should work well for you and will be far less expensive up-front cost.  If you instead intend to swim during the time of year when the days are partly or mostly cloudy or there is cold wind, then glazed panels or evacuated tubes would cost more up-front, but save more energy when in use.

In the U.S., the glazed panels cost around 3 times as much as the black flat mats (for the same gross area of panel) while the evacuated tubes cost around 2 times that of the glazed panels so 6 times that of the black flat mats.  With that sort of price differential, the payback time is longer unless one would otherwise be using gas heating extensively during cloudier or cooler days.  Some argue that you need less surface area with the more efficient panels, but then you get slower heating on sunny days which may or may not be important depending on your situation.

On a sunny day where the daytime air temperature is warm and close to the pool water temperature, then the black flat mat panels are the most efficient at around 80% or so.  However, with a 10ºF or higher air vs. water temperature difference, the glazed panels start to become more efficient (probably at a higher temp difference since the table does not account for heat exchanger losses since you normally cannot pump pool water directly into the glazed or evacuated tube panels).  At a 20ºF or higher air vs. water temp difference, the evacuated tube panels start to become more efficient.

Now it's for cloudy/overcast days where the situation shifts even more.  Technically, if the air and water temps are the same, then the flat black mat is still the most efficient though the total amount of heating is lower for all panels (about 1/3rd) due to less sunlight.  However, if there is even the smallest temperature difference between air and water, the glazed and evacuated tube panels start to shine.  With a 27ºF temperature difference between air and water, the flat black mat doesn't heat at all, the glazed panel is 51% efficient, and the best evacuated tube is 48% efficient.  With an 85ºF temperature difference between air and water, the glazed panels don't heat at all while the evacuated tubes are at more than 20% efficiency.

If you want to use the system for domestic hot water heating, then hands-down the evacuated tube is most efficient (except in hot summer) since the temperature difference is much greater since domestic hot water is in the 120-140ºF range compared to a pool in the 80-90ºF range.
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Hi Richard, I have carefully read through the links you gave me last time we discussed this and after a long consideration agree that black mats are ok for low temperature raises of a high volume of water in reasonable weather conditions although I believe your weather conditions are more favorable.  The rubber mats are cheapest for a reason, you'll be buying them over and over compared to others so whole of life costs are not as good as they first appear.  The better Fafco and polypropylene mats will last longer but cost more and the estimated cost of evacuated tubes has dropped considerably form the x2 of the links you gave which may not be the case in the US but is certainly true in Europe in fact the cost is only around 25% -30% more than the mats and evacuated tubes will works all year round so can provide hot water and underfloor heating when the pool is up to temperature or closed for the season thus the payback is much quicker.

Other than that I will agree to disagree on the matter [:)]

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I had better help here so that we don't go out of sorts with price differences US/Europe/UK etc. and get all hot about what is and what's not better.

The only sensible way to view 'value for money' in the matter is 'whole of life cost' with respect to the LOCE (levelised cost of energy). That is the cost of the installation over its lifetime, including the initial installation as well as replacement cost when the equipment has worn out as well as energy consumption and maintenance.

Now assume the following :

  1. Pool is 10 x 5 x1.5m with a good thermal bubble cover
  2. Pool is open to be used 180 days per year from say May till September
  3. Life span of the test is 20 years
  4. all other parameters are equal, and prices include TVA

So using manufacturers recommendations I find the following:

  • Solar mats are €0.92/kWhr
  • Flat plate collectors are €0.35/kWhr
  • Evac. tubes are €0.33/kWhr
  • Heat pump is €1.18/kWhr ( as one would expect!)

These are calculated using current pricing averages as well as recommendations.

So for rentability, the evacuated tube system is NO QUESTION the most cost efficient of all systems, however all three solar systems do not guarantee consistant heat delivery of the heat pump which for some is an issue to be considered. But as is plainly on view, a pool owner has to pay 3.5 times the price for the privilege of that assurance when choosing a heat pump.

O

 

Note: LOCE is defined as "the initial capital, discount rate, as well as the costs of continuous operation, fuel, and maintenance. This type of calculation assists policy makers, researchers and others to guide discussions and decision making." Wikipedia ed.

 

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For glazed panels and evacuated tubes, one must include not only the price of the panels, but that of the heat exchanger system since pool water is not supposed to go directly through these panels (which to me is ironic since chlorinated tap water has a higher active chlorine level than pools with cyanuric acid in them -- perhaps the issue is to avoid the risk of higher chlorine from excessive shocking or low pH from improper maintenance).  I presume one was looking at complete system costs including any differences in installation labor.

If the purchase price of the glazed panels and evacuated tubes has really come way down to be closer to black flat mat, then I'll certainly be looking at those when I eventually replace my panels (they are currently 9 years old and going strong -- no leaks).  9 years ago in the U.S., these other alternatives would have added tens of thousands of dollars to the system.  Our roughly $1500 per year in gas heating if completely eliminated would have taken 10 years or so to pay back.  It sounds like the economics have drastically changed since then.  I also wish that we had insulated the pool and piping -- the pool builder didn't think that was necessary, but I don't think he understood how we wanted the pool warm for pool water therapy (88ºF) and that we would be using it not just for 5 months but for a 7-8 month season.

Another consideration that was touched upon earlier is the increase in pump electricity costs if the panel has a lot of head (pressure) resistance to flow.  My Fafco panels at 4 GPM per panel (48 GPM for 12 panels) has 2 feet of head (0.87 PSI), but far worse is the loss from very long runs to/from the panels and between them, though they are at least 2" pipe (would be better to be larger, say 2.5").  At least with my variable speed pump I have cut my pump electricity costs in half, mostly from running the pump slower when the solar isn't on as well as tuning the rate when the solar is on -- my pump electricity costs went from around $1500 to $750 per year.

By the way, our marginal electricity rate is high (I live in California) at around $0.33/kWh while the equivalent cost for gas is only $0.05/kWh.  That makes a heat pump less economical than in areas with lower electric rates.

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Interesting Richard, I don't see a problem with the heat exchanger as it's a one off purchase but the plus points of evacuated tubes against mats is as you say the extra electricity required to overcome the increased headloss of pushing water around mats vs the much easier push of water through the heat exchanger so re couping that extra outlay would be easy. Of course the position of each individual setup will be different but out of interest how long and high are the pipe runs to the panels.

I can't supply any info at present but I have spent a long time developing and engineering the lowest possible headloss for my setup (without solar) together with the most efficient hydraulics possible (the work continues with major additions in the spring) from my flow rate information at given setups this year I expect to be able to save 85% of the energy consumed for a standard pool setup but with improved water quality. I don't know of any other pool builder who can offer that so with heating, reducing the cost of the additional water flow is a major point in considering which heating option to use.

The rough cost of electricity is €0.12 = USD 0.16 although there are a couple of different tariffs available.

 

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