DIY solar pool heater

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Re: DIY solar pool heater

Postby rob_hi » Tue Nov 10, 2009 2:32 pm

Thanks for all the feedback. I'm well acquainted with poly pipe, and have a roll or two lying around. I have a farm and have laid a fair few km of the stuff underground.

I will give it a whirl.

The pool's indoors and has a heat-pump, but it's costing too many KWhs to heat on its own. Time to put some of that wasted heat out there to use.

thanks everyone.
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Re: DIY solar pool heater

Postby peters-place » Wed Nov 11, 2009 5:07 pm

Check out your local Bunnings in the swimming pool area. They sell components for pool heating. While you might not want to use any or all of the components they sell, it's worthwhile checking it out and getting a complete installation guide from them. Then you can substitute your own components for the bits you don't want to buy. The company which supplies these parts can also be contacted directly for more info.
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Re: DIY solar pool heater

Postby timetaxi » Fri Nov 13, 2009 8:09 pm

Remember that you're trying to heat a lot of water a little bit, unlike a domestic water heater where you need to heat a little bit of water a lot. You'll do this most efficiently by keeping the piping relatively cool so it doesn't radiate too much of the heat it absorbs. This means that you will get a good result from a higher flow rate which removes as much of the heat as possible.

This suggests that you need large pipes (maybe 25mm) to the array and a network of smaller pipes in parallel to do the absorption. This also cuts down the friction head in the system which means less energy will be used doing the pumping. Because the water goes up (to the roof or whatever) and back down, static head will not be an issue - most pump manufacturers have tables of friction head for different pipe sizes in their literature. Try for about 10 degC gain from input to output as a starting point. I'd use 20mm headers with 12 mm tubes and heaps of plastic tees. Cable ties make great clamps. Try to sit the absorbers on some sort of insulation - plywood perhaps, or styrene foam sheet if you can. Glass over the top is less significant if the tubes don't get very hot.

A coil of tube works too, all the rest is just to increase efficiency...
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Re: DIY solar pool heater

Postby SR76 » Tue Nov 24, 2009 12:26 am

You see a heap of poly pipe on rooftops here in Perth. Best thing for pools.

If looks are important there are professionals who might be able to do a neater job than many I've seen around here, though.

As I just mentioned in other threads - used to be available in black only but now some companies are offering different colours to blend with tiles or colorbond roofing.
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Re: DIY solar pool heater

Postby scar59 » Sat Nov 28, 2009 9:45 pm

I saw on youtube where the guy on "greenpower science" used the polly pipe method to heat water feeding into his hot water system in his house. That way you only need to half heat your hot water, regardless whether you use electricity or gas. I think that is a simple and brilliant idea.
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Re: DIY solar pool heater

Postby Inspector » Wed Mar 31, 2010 7:34 pm

Glad I found this thread...

Familyman, it looks like I am planning a similar setup to you; a 1000L outdoor spa next to the garage, and I plan to use sun to heat it rather than the 10A (approx) pump/heater inside the spa. I was thinking a "pond pump" (as used in water fountains/features) would be adequate but the height of the water from the top of the spa to the garage roof would be up to 2m, and probably too much "load" for the spare little pond pump I have.
When I first installed the (second-hand) spa, I used to run it off a timer for 4-6hrs a day (until I got the next electricity bill!), so now I only turn it on when I plan to use it, calculating the time it needs to heat up from current temperature (which tends to be about 20-25 degrees average for summer and under 10 degrees in winter), knowing the heater increases temperature about 3 degrees an hour. So in winter, it needs to be on the day before to heat up to about 37 degrees. In summer it's usually only turned on a couple of hours before we go in to let the filter do it's work, as it's usually nicer to get in it just to cool down!

We tend to use it more in winter, and because it takes so much longer to heat up in winter, it uses alot more electricity. I did work out the cost once to be about $2.50 each time we heated it up to use it. We are currently on a flat-rate for electricity but that will change in the next couple of months when we install solar-pv and have to upgrade to TOU metering. The "peak" rate is about two and a half times the "flat" rate (not that it would be heating much during peak time; we tend to heat it either overnight or from very early in the morning). Thus, I want to try and heat it us much as possible (for free, without having to use the filter/heat pump for long periods).

When my solar hot water tank (roof-mount) sprung a leak last year, I was considering salvaging the old solar panels from it and using them to heat the spa. Unfortunately we couldn't afford to replace the whole 27-year-old system as we weren't elligible for the government hot water rebate (as we already owned a solar hot water system) so I just had the tank replaced, and will replace the panels when they finally die (probably soon, knowing my luck!).

In the meantime, I'll go with poly pipe, even though the spa is "ozone" (not chlorine) as it's cheaper than copper pipe. Unless of course the solar hot water panels die sooner rather than later :)

Thinking about physically installing the pipe, I was originally going to install it on a removable frame which would lay across the spa cover, and have each end of the poly pipe poke under the middle of the cover, intake sitting in the bottom of the spa (connected to the pond pump), and outlet sitting near the top (or vice-versa). While that short distance might be OK for the little pond pump, it would probably become too much of a hassle continually moving it all the time, plus place stress on connections and likely prematurely damage the heating system overall, due to moving it all the time.

After reading this thread, it makes so much more sense going back to the roof-mount system (the garage is less than 2m away from the spa, and will have about 5 square meters of spare roof space left-over after the solar-pv panels go on it). Because of the extra distance involved going from the spa to the garage roof (about 2m vertically I guess, as the spa ground level is approx 600mm higher than the garage ground level), I was wondering what size pump I'd need to use? What size pumps are used in "split" solar hot water systems? Would that be about the same size I'd need for circulating the heated water through the poly pipes for the spa?

Any other issues I'd need to be aware of? Would the "hydrogen peroxide" which is used in "ozone" spas be nasty for the poly pipe?
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Re: DIY solar pool heater

Postby Helipos » Wed Mar 31, 2010 11:24 pm

Since you live on a farm, run the poly straight down hill and then on the return leg put most of your heating coils and a simple convection current form and will push the water around once there is a sufficient density gradient.

My Aunt & Uncle use it to great effect in their pool.

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Re: DIY solar pool heater

Postby PeterM » Sat Jun 12, 2010 9:22 pm

Inspector wrote:Because of the extra distance involved going from the spa to the garage roof (about 2m vertically I guess, as the spa ground level is approx 600mm higher than the garage ground level), I was wondering what size pump I'd need to use? What size pumps are used in "split" solar hot water systems? Would that be about the same size I'd need for circulating the heated water through the poly pipes for the spa?

I guess you have solved all your issues by now. But I thought it worth mentioning that so long as you keep all the pipes full of water all the time, the vertical distance of the roof is unimportant. What goes up comes down! Only thing important is friction in the pipes, and there are tables for that so you can work out the pressure drop and so the size of the pump required.
But I have been told that commercial installations dump all the water each night. The load on the roof is high, and this helps. Doing that means you need a pump that can overcome the static lift and the pipe friction.
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Re: DIY solar pool heater

Postby Inspector » Sat Jun 12, 2010 9:36 pm

Thanks for the tips, Peter.

I haven't progressed with that project any further, mainly due to the fact the solar-pv panels were installed on that far end of the garage roof to avoid shading issues from a neighbour's two dead palm trees. Once the tree (trunks) are removed, I'll be able to have the panels moved to make room for the water-heating tubes, but at this rate it'll be NEXT winter...
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Re: DIY solar pool heater

Postby zzsstt » Sun Aug 01, 2010 7:21 pm

PeterM wrote:I thought it worth mentioning that so long as you keep all the pipes full of water all the time, the vertical distance of the roof is unimportant. What goes up comes down! Only thing important is friction in the pipes, and there are tables for that so you can work out the pressure drop and so the size of the pump required.
But I have been told that commercial installations dump all the water each night. The load on the roof is high, and this helps. Doing that means you need a pump that can overcome the static lift and the pipe friction.


(I'm aware this thread has not seen action for a while, but I've only just read it!).

The vertical distance is important. Unless you pump enough water through the pipe to keep positive pressure throughout its length, which normally means far too much flow for water heating, you actually end up with negative pressure at the highest point - the water is trying to run out of the pipe faster than you are pumping it in. Most poly pipe is NOT designed for use in a "suction" situation, and therefore can and will collapse, especially when softened by heat.

You could avoid this problem by using a tap at the return end of the pipe to limit flow and create positive pressure at all points, but it is easier to do what commercial systems do and have an automatic vacuum release valve at the highest point. The water is pumped up to that high point and then can run back down, sucking in air if required. Adding such a valve of course also means the system becomes self draining when it is switched off - assuming you don't fit a non return valve at the pump! To make this work, the high point must be the start of the return line, after the heat absorbing section (small pipes, panels, whatever), so the rate of flow through the heating section is controlled by the pump speed. If the heating portion is after the high point, with a vacuum release system the water will rush through under gravity, probably far too fast to be effectively heated. Without a vacuum release the entire system is likely to go though a "fill - vacuum - collapse - refill" cycle until the pipe fails!

Pipe friction is a factor of rate of flow. It would seem unlikely that you would ever desire a flow rate high enough to make friction an issue, so the only real concern is the static head to which you are pumping. Select a pump that will flow a suitable rate at the pressure (static head) required. A variable speed pump will allow the system to be tuned to flow the right amount of water to get good heat gain, but a tap after the pump will also reduce the flow! Theoretically the pipe is absorbing much the same amount of energy regardless of the flow rate, so pumping faster will heat more water to a lower temperature, and pumping slower will heat less water to a higher temperature. The total energy added to the pool will be much the same, but the faster pump will use more power to move the water.

It is wise to note that a very slow pump MAY return small volumes of very HOT water. A local mineworker told me that there was a case when an "emergency safety shower" actually caused serious scalding when a worker tried to wash after a chemical spill. It was a sunny day, and the supply water ran through a long unburied length of poly pipe. The guy rushed in to the shower, hit the lever and was deluged with a large quantity of very hot water that had been heating up in that pipe all day. If the return is combined with fresh pool water (i.e. plumbed to the filter return line) this is probably not an issue, but if the heating return goes to the pool in such a ways that a bather can be exposed directly to the heated water, it might be worth considering.
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