Solar heating the pool


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Old 10-23-19, 03:53 PM
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Solar heating the pool

Currently we have perhaps 30 hard plastic (expensive) panels (3 ft X 4 ft) up on the roof to heat our spa/pool. The panels are starting to leak and they are pretty far from the pool. The plumbing runs underground and to be honest - in the six years we have lived here we have only ever used the spa because the pool is always very cold (we can isolate the water flow to only heat the spa).

We have a neighbor who has designed/built a pool heating system which consists of 20 hard plastic boxes roughly 3 ft square, maybe 3-4 inches deep with a glass top. Inside each box is coiled 1/2" flexible copper tubing (I do not know the length of each coil). The pool water flows through the boxes. Her pool is a very similar size as ours and it gets so hot that at times she has to restrict flow to some of the boxes.

We are planning to install a system similar to our neighbor. Each box is going to cost around $250 US - most of the cost being the copper tubing.

- Is copper the best solution for what I have described ?
- I'm wondering if it is better to send the water serially through all 20 boxes or if there might be a more efficient arrangement.
- Is there a commercially available system at all similar to what I have described that I could review ?

Any thought appreciated.
 
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Old 10-23-19, 04:10 PM
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3 ft square, maybe 3-4 inches deep with a glass top. Inside each box is coiled 1/2" flexible copper tubing
That wouldn't be very much copper. Why don't you ask your neighbor how much copper they used ?

You could probably use a product like PEX instead of the copper. It would be less costly and easier to roll but it has a maximum working temperature of 200f. That could be a problem with intense sun.
 
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Old 10-23-19, 04:10 PM
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Copper is a good choice, especially if it's painted black. It conducts heat very well so it can soak up a lot of heat from inside the box. You could do similar with a coil of black poly pipe. It wouldn't be as efficient but would be less expensive.

Before determining serial or parallel flow through the heaters consider how you will pump the water and what results you want. The boxes in series will create a lot of resistance but the water exiting could be quite hot. If using your pool's filtration pump serial flow could cause enough resistance to hurt filtration but the hotter water could be better for the spa. Parallel flow would have much less resistance and the water exiting the heaters would not be as hot but would extract more heat from the panels.
 
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Old 10-23-19, 04:25 PM
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Thanks. The guy who built our neighbors system is coming back on Friday. We will have another look at her system together.

Obviously, the purpose of the tubing is to heat the water flowing through it. Do you think the PEX tubing would heat the water comparably to the copper ? I guess that would be the "thermal conductivity" ?

Aluminum would be much cheaper than copper as well but is only half as conductive.

Don't let me fool you. All this is greek to me and I'm just rapidly doing some research. But you know, now that I think about it, a couple years back the same guy stood on our roof and said a cheaper solution would be using black hosing.

Edit : I did just see this - "PEX is also negatively affected by UV rays and therefore cannot be used where sunlight is directly present." - which I think I had read a long time ago.
 
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Old 10-23-19, 04:37 PM
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Thank you both. My little fingers are going a mile a minute searching the internet.

I just found this site which looks very interesting (and somewhat similar to our neighbors system) - but I have to read it more slowly.

https://rimstar.org/renewnrg/diy_pex...thermal_dn.htm
 
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Old 01-01-20, 12:19 PM
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Happy New Year !

Well we have gone ahead with this project. On Friday (fingers crossed) we will have 18 silver aluminum boxes, roughly 2" deep by 2 ft or so square. The boxes will have coiled copper tubing (not sure of the diameter at this moment) which will be painted black. The boxes will have a glass cover and each box will have copper connectors such that if a box fails it can be removed from the 6 X 3 grid.

The 'grid' will sit on a flat section of the roof that is about 15 ft high. The boxes will sit on a metal base about 1 ft off the roof so that the copper connections and 1 1/2" PVC will sit under the boxes. We will also secure the whole thing using thin metal cabling which will run underneath (we can get really strong winds at times).

Today I drained the spa (into the pool) and timed how long it took to refill the spa from the main drain of the pool - without travelling to the roof. Took 19.5 minutes. I drained the spa and repeated the experiment sending the water to the roof (using our soon to be replaced plastic panels). Took 44 minutes. So at this point I'm not sure if all the bending and twisting in the current water path is restricting the flow, or if our 1hp pool pump doesn't have enough umph to move the water quickly to the roof. My next experiment will be to cut the 1 1/2" PVC near ground level and see what the times look like. There is a run of perhaps 40 ft our so PVC underground from the pool room to where the tubing goes up to the roof. At some point I know I will have to insulate at least the plumbing with the returning hot water.

Another question I have - there is a timer on the pump and to be honest, to date I just manually flip the switch to run the pump, but there is an unused dial/thermometer in the pool room. I don't understand how a single sensor (thermometer) can control turning off the pump if the water becomes too hot AND turn on the pump if the water is too cold. (I haven't played with it all all yet).

Any thoughts/comments on this project appreciated.
 
 

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