Went with an unorthodox solar heater arrangement and don't think it's working optimally

[Dirrby]

Leave the panels like you have them but replumb the supply to both panels at the bottom and the return is from the top of both panels. Make sure those valves in the middle of the panel manifold are shut. That should work better than what you have going right now and won't require a lot of extra work or material.

 

[Dirrby]

Like this. I think its worth a shot

 

[toddrhodes]

Those diagrams are

Like this. I think its worth a shot

That would definitely be a shortcut and not require nearly as much moving and re-plumbing, and it seems to be similar in concept to the diagram from @Dirk where it's basically in parallel. I think the *ideal* routing of that would have me tilt each panel upward slightly in the middle, so the output is the high point, and then run lines out to the far corners of the panels which would be the corresponding low entry point. I attached the PDF I got from Fafco support which kinda led me to the path I chose, but I just overthought it, it would appear. And that's totally fine - it's why I asked and I can't say thanks enough for all the input.

Now, to start, I am going to replumb per your diagram - the cold water going in the inside bottom on each panel, close each shutoff valve on the panels (which Fafco themselves says is needed in one of the configs in the attachment), and the return coming from the inside top manifold exits on each panel. I'll orient the panels so at least the exits are the highest points and make them as equal as I can get. Then, if I'm feeling froggy down the line, I'll run a line to the end of each panel for the input water.

Either way, it seems like we're on the same page and again, thank you both for your guidance!

Todd

 

[Dirk]

Not on the same page, at all. Had I seen the Solar Bear diagrams before I would have approached this in an entirely different way. Those panels, based on the Fafco diagrams, work nothing like the panels I know about. And I'm guessing just about everything I described and advised is incorrect, or not applicable. The built-in solar valves are performing a function completely unknown to me, and unlike anything I've worked with or studied.

So I'd advise assembling your system exactly as depicted in those diagrams, and don't deviate from them or mix and match advice from me with Fafco's. Sorry if I created any additional confusion for you... Good luck!

 

[toddrhodes]

Not on the same page, at all. Had I seen the Solar Bear diagrams before I would have approached this in an entirely different way. Those panels, based on the Fafco diagrams, work nothing like the panels I know about. And I'm guessing just about everything I described and advised is incorrect, or not applicable. The built-in solar valves are performing a function completely unknown to me, and unlike anything I've worked with or studied.

So I'd advise assembling your system exactly as depicted in those diagrams, and don't deviate from them or mix and match advice from me with Fafco's. Sorry if I created any additional confusion for you... Good luck!

That's my bad for not trying to attach it earlier - not all forums can attach files and I didn't realize this one could.

That said - I'm nothing if not inquisitive, and I've at least got some results so far and tools to measure, so I will at least try the parallel/T-method and work with the valves to see how it performs.

It's honestly not a huge deal - this has all been incredibly informative and I still believe much of what has been shared here will still apply to my panels, even if there are some caveats as well.

For science!

Todd

 

[Dirk]

For science!

For sure!

My bad, too. I should have asked about the panel brand and model. Post pics of whatever you come up with and that might help the next guy with similar questions.

 

[toddrhodes]

Just wanted to update this - since switching it around, basically making a "T" on each input and output, and running them essentially in parallel, with a diverter valve on the outlet so I can turn off one panel or another (in case of a leak) or give one panel more priority than another - it seems to be working MUCH better. I can't say that it's running at its most optimum, frankly I'm not even sure how to discern that, but with some sunny weather lately, I've been able to measure temps coming back into the pool as high as 12-15* higher than ambient or pool water temp. After it's run through what's been baked in the panels for a bit, it settles in around 5-6* above the water temp level.

Panels are now mounted so they both point "up" toward the output side, to make it the highest point I can. Input water goes in at ground level through a T to each inlet. Outputs are on top, to a T, then off to the SWCG.

Long and short of it is - we enjoyed our pool all last week, in Northern Indiana, with 80+ degree water temps. What's funny is that even with south-facing sun, I don't know that the panels are placed optimally to catch as much sun as they could, but I'm limited in that regard to where I can put them. For now, I have no plans to change anything else - they're working, and that's great to me.

I did end up needing to open the valve on the panels all the way, and throttle down the input valve to about 80% flow (that feeds both panels) to keep everything happy and that seems to give me the best temps coming out of them. They are generally "on" during the part of the pump schedule that it runs about 1500 RPM. Ultimately, I would prefer to feed them from an opposite end / diagonal to the outputs, but that's a whole lot of pipe for what I can't guess is a huge improvement. Maybe if I get bored one of these weekends

 

[Dirk]

I can't say that it's running at its most optimum, frankly I'm not even sure how to discern that, but with some sunny weather lately, I've been able to measure temps coming back into the pool as high as 12-15* higher than ambient or pool water temp. After it's run through what's been baked in the panels for a bit, it settles in around 5-6* above the water temp level.

I don't exactly have a great track record steering you in the right direction, but I'll share anyway, for what it's worth. It might seem counterintuitive, but the hotter the water is coming out of the returns, the less efficient the heating is, believe it or not. The temperature of the water at the returns coming from a properly optimized heater should feel just slightly warmer than the pool. 12-15° is not that. It should be more like a few degrees. The other clue is when you mentioned 1500 RPM. That's probably low. This has to do with the physics of heating a pool (which I only barely understand). A large volume of slightly warmer water will heat a pool better, and faster, than a small volume of very hot water. If your flow rate is low (like it might be at 1500 RPM), then the water in the solar panels has more time to heat. That's why it feels warmer at the return. But it's the volume of warm water that better heats a pool, not the temperature. So you up the RPMs, which ups the flow rate, which will lower the output temperature, but warm your pool better because there's more water moving. It's something to do with physics of heat exchange. Maybe @mas985 can explain it better.

I need to run my pump at about 2200 RPM to get the optimal flow through my panels. I determined what the optimal flow should be based on the manufacturer's recommendation (I figure they would know). I verified that 2200RPM produces the correct flow rate by installing a flow meter (FlowVis) and adjusting my variable speed pump's RPM until the FlowVis indicated the correct rate. Which for my eight panels is 40 GPM (gallons per minute).

That all said, if your pool is warm and it feels good, then none of that matters!

even with south-facing sun, I don't know that the panels are placed optimally to catch as much sun as they could, but I'm limited in that regard to where I can put them.

I was told by the solar installers that sold me my panels that solar water heating panels are not anywhere near as sensitive about their angle to the sun than electricity producing PV panes are. The latter have to be pointed directly at the sun for maximum output. But the former just needs to be in the sun, not necessarily pointing just so. Your panels are probably just fine where they are. Mine face North! I saved the South side for my PV panels...

 

[toddrhodes]

I don't exactly have a great track record steering you in the right direction, but I'll share anyway, for what it's worth. It might seem counterintuitive, but the hotter the water is coming out of the returns, the less efficient the heating is, believe it or not. The temperature of the water at the returns coming from a properly optimized heater should feel just slightly warmer than the pool. 12-15° is not that. It should be more like a few degrees. The other clue is when you mentioned 1500 RPM. That's probably low. This has to do with the physics of heating a pool (which I only barely understand). A large volume of slightly warmer water will heat a pool better, and faster, than a small volume of very hot water. If your flow rate is low (like it might be at 1500 RPM), then the water in the solar panels has more time to heat. That's why it feels warmer at the return. But it's the volume of warm water that better heats a pool, not the temperature. So you up the RPMs, which ups the flow rate, which will lower the output temperature, but warm your pool better because there's more water moving. It's something to do with physics of heat exchange. Maybe @mas985 can explain it better.

I need to run my pump at about 2200 RPM to get the optimal flow through my panels. I determined what the optimal flow should be based on the manufacturer's recommendation (I figure they would know). I verified that 2200RPM produces the correct flow rate by installing a flow meter (FlowVis) and adjusting my variable speed pump's RPM until the FlowVis indicated the correct rate. Which for my eight panels is 40 GPM (gallons per minute).

That all said, if your pool is warm and it feels good, then none of that matters!


I was told by the solar installers that sold me my panels that solar water heating panels are not anywhere near as sensitive about their angle to the sun then electricity producing PV panes are. The latter have to be pointed directly at the sun for maximum output. But the former just needs to be in the sun, not necessarily pointing just so. Your panels are probably just fine where they are. Mine face North! I saved the South side for my PV panels...

Great information Dirk, thank you. For what it's worth, that 12-15* delta was basically the first "batch" of water that had cooked in the panels for a bit out in the sun, before I turned it on. Once that volume is exchanged out of the panels and it's exchanging water more normally, the temp delta is about 5-6 degrees. But what you say makes sense. Unfortunately my pump isn't truly variable speed, just "multi speed" with 4 options - 1k, 1.5k, 2.5k, and 3k. It does most of its cycle at 1k or 1.5k to save on energy. So far, as you say, it's heated sufficiently that we were able to use it in early-mid May in northern Indiana. I'll take it!

But I also appreciate any opportunity to learn more, so thanks for taking the time on that!

 

[mknauss]

Unfortunately my pump isn't truly variable speed,

The pump has 4 speeds you can save. But each one can be adjusted for what rpm you wish to run the pump.
Read the manual.

 

[toddrhodes]

The pump has 4 speeds you can save. But each one can be adjusted for what rpm you wish to run the pump.
Read the manual.

I've read the manual 4-5 times. Guess which section I did not pay any mind to? The one titled "Custom schedules." Because I hadn't really needed that yet, and therein is where the speed settings are. How about that - thanks for the tip.

 

[Dirk]

Theoretically, the more water you pump through a solar panel the better it will heat your pool. There are [at least] two limits that determine just how high you should go:

1. The cost. At some point, the cost of running your pool pump is not worth the added amount of heat produced. So 3000RPM might make your pool 1° warmer than running the pump at 2500RPM, but the cost in electricity each month to get that wouldn't be worth that 1 degree. (Just example numbers, I have no idea what they would actually be).

2. The pressure. Your solar panels can only take so much. Your filter and other plumbing as well. The higher you run the pump, the sooner you'll either wear something out, or blow it up!

Generally speaking, a typical solar panel works best at 3-5 GPM. Unfortunately I don't know how to calculate that without a flow meter. Which is why I bought a FlowVis, because just the time it would take me to figure out the calculations was worth more to me than the hundred bucks! Not only did the 'Vis help me tune my solar heater, but I use if for checking on my filter, fine tuning my pool vac, and maintaining flow for my SWG. So for me it was a good investment.

I do know that that general rule applies to each panel. And you multiply that by the number of panels. So for me, I have 8 panels and I run them each at 5 GPM (as per the manufacturer), so I have to multiply 5 x 8. That's how I got to 40 GPM for my system. So for your setup, you'd multiply by 2: 6-10 GPM total.

I always turn to these guys when it comes to solar know-how. This article doesn't really help with figuring out how to achieve 3-5 GPM, but it does explain about pressure limits. And it seems pressure is of greatest concern when panels are lower than the pool (I just learned that just now, reading the article). You might want to give it a read, though it's pretty dry, and long!

Solar Pool Ideal Flow Rate / Hot Sun Solar

The ideal flow and pressure for a solar pool heater. An expert mechanical analysis.

www.h2otsun.com

 

[Dirk]

I do know that that general rule applies to each panel. And you multiply that by the number of panels. So for me, I have 8 panels and I run them each at 5 GPM (as per the manufacturer), so I have to multiply 5 x 8. That's how I got to 40 GPM for my system. So for your setup, you'd multiply by 2: 6-10 GPM total.

I may have misspoke (again!). My math is 5 x 8 because my panels are plumbed in parallel. That 40 GPM gets split evenly to the eight panels because they all share the same supply and return manifolds, so they each get a 1/8 portion of that 40: the 5 GPM they want.

If your panels are connected in series, one after the other, then I think you wouldn't multiply by two. You'd want your total flow to be 3-5 GPM. Sorry, I lost track of your plumbing scheme, as to how you're now running them, in parallel or in series. Plus yours have that adjustment valve that I can't quite wrap my head around. But I think you get the gist of what to look out for...

 

[mas985]

So you up the RPMs, which ups the flow rate, which will lower the output temperature, but warm your pool better because there's more water moving. It's something to do with physics of heat exchange. Maybe @mas985 can explain it better.

It has to do with heat loss. The warmer the water, the more heat is lost to the "cooler" surrounding environment and doesn't make it to the pool. Heat transfer in solar panels can be broken down into several components:

Solar heat gain
Convection (air) heat gain/loss
Conduction (roof) heat gain/loss
Radiation heat gain/loss (surrounding buildings, trees, sky)

The first is always a heat gain but the last three can be either heat gain or loss depending on the temperature differences between the surrounding objects and the water/panel. Heat transfers from warmer object to cooler ones. But the sky is almost always at a lower temperature. If you take an IR thermometer and point it at the sky, it is usually >30F cooler than the air. Right now, our air temp is 73F and I just took a measurement of 13F at the sky. Big temperature difference so radiation accounts for most of the heat loss from solar panels (and the pool too).

 

[Dirk]

The warmer the water, the more heat is lost to the "cooler" surrounding environment and doesn't make it to the pool.

Make perfect sense! Thank you!!