Efficient and Affordable Solar Pool Heating Solutions

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In summary: I'm assuming you're using water in the pool.)In summary, my longtime friend moved recently and his new place has an in-ground pool. He's a bit of an Engineering nerd, so he decided to build a solar heater from scratch. He's got some ideas down, but he's looking for feedback from others who are more experienced. Some of the ideas he has are that he uses black hose to absorb heat, that he makes a control box to open and shut the water, and that he exchanges heat directly on the pump. However, he's not sure if any of these are the best ideas. He also plans to paint the plywood black. My suggestion is to either paint
  • #1
DaveC426913
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My longtime friend moved recently and his new place has an in-ground pool. He's a bit* of an Engineering nerd he has decided to build a solar heater from scratch. Him being a neophyte at the art of pool science though, I felt it my duty - despite being someone who never got his own custom exchanger working - to share my wisdom.

*a lot

Some ideas I'm pretty sure of, some less so. But it's got my curiosity up. Looking for feedback.

In descending order of confidence:

4. His heat exchanger core is 50' of black garden hose. Obviously, thinner, more conductive tubing would be better. I would go with 1/4" copper tubing myself. Greater surface area per unit volume, better thermal conductivity. We all agree, but it's out of budget for now.

3. He intends to secure his heat exchange array to a large sheet of plywood.

Truth be told, we both agree that it would be good to have a heat sink (something more heat absorbent than plywood), and embed the array in a 1/2" or so of conductive substrate of some sort. (Heat exchange by direct conduction will be far more efficient than heat exchange via radiation from a reflective surface). However, such a solution is also not in the budget at this time, so plywood back it is.

He intends to paint the plywood black. My suggestion is to paint it silver, or better yet, line it with tinfoil. Failing an actual heat sink, you don't want your backing to absorb rays, you want it to reflect rays back to the hose.

2. They are using black hose, to absorb heat. I suggested clear hose would actually let more solar radiation in. Upon reflection though, I recanted. Clear hose will also let much of that same solar radiation right back out the other side. Even with a reflector, much radiation will never make it into the system.

1. They are making what I consider and excessively complex setup that takes cold water into the array and recirculates it - in a secondary loop off the main plumbing, and powered its own secondary pump - within the heat exchanger until it has reached a certain temperature, then releases it back into the pool.

Being a nerd with an electronics bent, he has constructed a control box from an arduino, a temperature probe and an actuator valve, that automagically opens and shuts when the water temp reaches the desired values. I am impressed to say I have seen it working, and - for this reason alone, I'd like to see his solution functional - however, I don't think he is gaining anything with his secondary loop.

Water running continuously through the system will draw heat from the solar array just as efficiently, no matter how fast it flows. (In fact, the faster the better, to a point) i.e. even if a single pass raises the temp by, say, only one degree, it will be made up for by the sheer throughput. Heat transferred is heat transferred, whether it be in 5 gallons of throughput or 50. Matter of fact, 50 is better - the higher he raises the temp., the more heat loss from the system.

0. Finally, something I've been toying with on my own: exchanging heat directly on the pump. It puts out a lot of waste heat. I'm thinking a coil of pipe off the main line, running through some sort of liquid-filled bag or pillow**, draped *directly* over the pump should transfer some heat, and do so with little fuss and muss.

** self-contained fluid-(prob'ly water)-filled bag acts as the substrate/heat sink. Form-fits to pump, with flexible copper pipe running in one corner, winding around lots of times, and out another. i.e. Fluid contents of bag are static, and not part of pool water.
 
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  • #2
If the hose orientation is fixed, you can use a clear hose and paint the lower side black. Paint at the inner surface is probably even more effective but I don't know how to get that reliably and without fancy chemicals.

The secondary cycle looks odd, unless there is a reason to not mix water running through the hose with pool water (e.g. some additives used in the heating circuit).

If the whole thing is efficient, the thermal power of the pump should not be a large contribution, but if it can be included easily, why not.
 
  • #3
mfb said:
If the hose orientation is fixed, you can use a clear hose and paint the lower side black. Paint at the inner surface is probably even more effective but I don't know how to get that reliably and without fancy chemicals.
I rejected the clear hose though because, even with reflecting from the backing, solar energy is lost. Any light that passes out of the hose is lost heat. (And since I can see something other than utter black, light is escaping)

mfb said:
The secondary cycle looks odd, unless there is a reason to not mix water running through the hose with pool water (e.g. some additives used in the heating circuit).
Sorry. Their secondary cycle is not isolated. They are heating pool water directly, after bringing it into the heat exchanger. The switches let hot water out nd cold water in.

I may have obfuscated that by mentioning my own system, in item 0.
 
  • #4
DaveC426913 said:
I rejected the clear hose though because, even with reflecting from the backing, solar energy is lost. Any light that passes out of the hose is lost heat. (And since I can see something other than utter black, light is escaping)
A completely clear hose is certainly not a good option. But a clear upper side and a black lower side could be more effective than all black. You can some absorption directly in the water, and everything else still gets absorbed at the black side. Reflection at the clear surface might be higher.
DaveC426913 said:
Sorry. Their secondary cycle is not isolated. They are heating pool water directly, after bringing it into the heat exchanger. The switches let hot water out nd cold water in.
Then that concept makes even less sense.
 
  • #5
mfb said:
DaveC426913 said:
Their secondary cycle is not isolated. They are heating pool water directly, after bringing it into the heat exchanger. The switches let hot water out and cold water in.
Then that concept makes even less sense.
Why? I mean beyond than the reasons I stated in the OP item 1?
 
  • #6
Well, I would see some advantages of a separate second circuit, but I don't see any advantages of such a messy system that just makes everything more complicated and reduces the efficiency.
 
  • #7
mfb said:
and reduces the efficiency.
This is what I'm interested in.

I'm not sure his logic is sound re: efficiency of the recirculating phase, as opposed to just once-through. Looking for confirmation (not that I'm going to tell him. He's pretty happy).
 
  • #8
Sure, a higher water temperature in the system will decrease the efficiency.
 
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  • #10
rbelli1 said:
heat transfer is proportional to temperature difference. More difference == more heat transferred.
Yes. Indeed, that is the basis for my argument.
 
  • #11
Forget about heat transfer from the pump motor. Even if the pump was wasting 500W to heat (which it does not), that would only be 3,400 BTU, which is enough to raise 12,000 gallons of water 1.3˚F per day at 8 hours of pump run time, and that assumes a perfect heat transfer.

As for the flow rate, we tell people with commercial pool heating panels all the time that more flow is better, as heat exchange (efficiency) increases as Delta T increases.
 
  • #12
I forgot to mention... Don't let copper touch pool water. It will corrode in no time.
 
  • #13
Jason Szumlanski said:
Forget about heat transfer from the pump motor. Even if the pump was wasting 500W to heat (which it does not), that would only be 3,400 BTU, which is enough to raise 12,000 gallons of water 1.3˚F per day at 8 hours of pump run time, and that assumes a perfect heat transfer.
I should have provided some numbers.
Again, this relates to my pool, not my friend's
My pool is only 3,000 gallons. And I only need to heat it up a degree or two (C). It spends much of the summer just a degree or two below tolerable temp for my delicate nether regions.

Funny thing about pump-heating - my hot tub does it that way. It does not have a heater, all it has is a couple of coils around the pump. And it reaches 105F. (Sure, it's 1/10th the volume, and has a lid, but still...)
 
  • #14
Fair Anne would NOT be happy with an ugly coil of pipe.

Science wise It'd sure work better to collect heat over area larger than the surface of the pipe and conduct it into the water without a plastic pipe wall in the way..

Most impressive solar pool heater i ever saw was much simpler.
The guy built a decorative structure with a shed roof to provide a shady area adjacent the pool. He put his Tiki bar, a small fridge, lights, and and some lounge chairs under it.
The roof he made from corrugated aluminum painted black
and covered that with a piece UV resistant plastic sheet made for greenhouses.
At the high end of shed roof between it and the plastic sheet he put a "header", just a piece of PVC pipe with holes drilled to distribute water into the corrugations ,
and collected the warmed water at bottom with a plain old rain gutter that drained right back into the pool. He plumbed the header into the pool pump, also with PVC.

That gave him tremendous area to collect heat with great thermal conduction right into the water. The plastic sheet prevents evaporation and keeps out the bird droppings.
And he got a nice looking conversation starter not an ugly coil of pipe.

Just a thought, one that seems to make sense from a heat transfer point of view.old jim
 
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  • #15
Here's a similar collector sans cover and Tiki bar
http://www.builditsolar.com/Projects/PoolHeating/OpenFlow/OpenFlowCollector.htm
OpenFl10.jpg


half as long twice as wide and six feet taller would make it aesthetic and dual purpose.

upload_2016-8-30_18-15-53.png


old jim
 

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1. How does a solar heat exchanger work on a pool?

A solar heat exchanger uses the sun's energy to heat the water in a pool. It works by circulating pool water through a series of tubes or panels that are exposed to the sun's rays, which then heats the water as it passes through. The heated water is then returned to the pool, raising its overall temperature.

2. Can a solar heat exchanger be used on any type of pool?

Yes, a solar heat exchanger can be used on both above-ground and in-ground pools. The size and type of the exchanger may vary depending on the size and shape of the pool, but it can be adapted for use on most pools.

3. How much does a solar heat exchanger cost?

The cost of a solar heat exchanger can vary depending on the size and type of the exchanger, as well as the specific needs of the pool. On average, a solar heat exchanger can cost anywhere from $3,000 to $7,000, including installation. However, the long-term cost savings on energy bills make it a worthwhile investment for many pool owners.

4. How long does it take for a solar heat exchanger to heat a pool?

The time it takes for a solar heat exchanger to heat a pool can vary depending on factors such as the size of the pool, the amount of sun exposure, and the temperature of the water. On average, a solar heat exchanger can raise the temperature of a pool by 1-2 degrees per day, so it may take a few days to significantly increase the overall temperature of the pool.

5. What are the benefits of using a solar heat exchanger on a pool?

There are several benefits to using a solar heat exchanger on a pool. Firstly, it is a more environmentally-friendly option as it uses renewable energy from the sun. It also helps to reduce energy costs as it lessens the reliance on traditional heating methods. Additionally, a solar heat exchanger can extend the pool season, allowing for more time to enjoy the pool in warmer water temperatures.

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