Solar, and SWG

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carnivalday

carnivalday

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Oct 25, 2017
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Ocala, FL
Okay, Ive got an equipment question, and Im not even sure what Im asking, but here goes. In reading up on solar heating, and what my system is (7 4 x 10 panels), Im finally getting to understand how it works. It appears the optimum rate for solar is 3-5 gallons per minute thru the panels. So I went to the Jandy calculator, and running my 1.65 pump at 1400 RPM gives me 31.5 gallons/minute, which I figure is close enough to what I need for solar (7 panels x 4 gpm = 28 gpm). So I went outside and turned on my solar, and set my pump to 1400 RPM....and the SWG turned off. So Im figuring the RPM is too low to run both the SWG and the solar. I played with the RPMs and when I got to 1800, the SWG kicked back on. So I figure thats were I need to be....except when I figure my Solar on 1800 RPMs, Ive got about 40 gpm, which seems way too high to efficiently run my solar. So Im not even sure Im figuring any of this correctly, can someone interpret this mess?
 
In general, you want about 0.1 GPM/sq-ft and your panels are 280 sq-ft so 28 GPM total is sufficient. A little higher flow rate should not be an issue for the panels. Heat transfer rates are related to flow rate, the higher the better. But some panels cannot handle high pressure so you need to keep an eye on that.

What is the panel brand/model?

What is the filter pressure?

How high are the panels relative to the filter gauge?
 
Okay, the panels are Eco Spark. Filter pressure, do you mean what the little guage reads when the pump is running? and how high, Ive got a single story house, so they dont seem to high. Would a picture help?
 
Looks like the gauge is about at 5 (is that psi?). Also have a lot of little bubbles coming out of the return closest to the pump. RPM right now is at 1800.
 
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If the filter pressure is 5 PSI, then the pressure at the top of a one story house would be most likely below 0 PSI so there is no excess pressure in the panels to worry about. But are you getting any air coming out of the pool returns? Do you know if there is a vacuum release valve installed and where it might be?
 
carnivalday said:
So I went to the Jandy calculator, and running my 1.65 pump at 1400 RPM gives me 31.5 gallons/minute, which I figure is close enough to what I need for solar (7 panels x 4 gpm = 28 gpm). So I went outside and turned on my solar, and set my pump to 1400 RPM....and the SWG turned off. So Im figuring the RPM is too low to run both the SWG and the solar. I played with the RPMs and when I got to 1800, the SWG kicked back on.
Click to expand...
What Jandy calculator?

I don't think that your numbers are accurate.

At lower RPMs, your flow is probably zero or close to zero.

You should increase the RPM until you feel good flow from the returns and the SWG flow switch comes on.
 
mas985 said:
If the filter pressure is 5 PSI, then the pressure at the top of a one story house would be most likely below 0 PSI so there is no excess pressure in the panels to worry about. But are you getting any air coming out of the pool returns? Do you know if there is a vacuum release valve installed and where it might be?
Click to expand...

Yes, I was getting bubbles out of the pool return closest to the pump when I had the Solar turned on. I turned it off, and the bubbles stopped. I have no clue what a vacuum release valve is, unless its that little doohicky on the top of the pump that I open up when I want to clean the cartridge.
 
For what it's worth, this is exactly why I installed a FlowVis flow meter with my solar system. I got the optimum flow rate for my panels directly from the manufacturer (I figured they'd know best) and dialed in my VS pump's RPM by simply watching my FlowVis. My panels need 40GPM, which requires about 2200RPM, which also happens to make my SWG happy. The "normal filter mode" (when the panels are not active) is about 1400RPM, based on the minimum my SWG requires.

For me, not having to try to figure out how to do all the calculations and measurements (head, height, volume, pressure, etc), and then constantly wondering if I got it all right, was worth the cost of the FlowVis. And it's turned out to be useful for other purposes, too. I got good value out of its purchase. And because I'm confident my system is as efficient as possible, in that I'm not using more pump energy than I absolutely have to, and my pool is heated as cost-effectively as possible, I expect the FlowVis will pay for itself at some point in time. If you're interested in installing one, it might be easier and cheaper than you think. FlowVis offers a model that fits into existing check valves. So if you have a check valve, and it's the right brand, a FlowVis is a very easy DIY install.
 
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JamesW said:
What Jandy calculator?

I don't think that your numbers are accurate.

At lower RPMs, your flow is probably zero or close to zero.

You should increase the RPM until you feel good flow from the returns and the SWG flow switch comes on.
Click to expand...

This is the Jandy calculator that I was using.

Pool Pump Savings Calculator | Jandy

Learn how much you can save by using a Jandy Pro Series variable-speed pump.
www.jandy.com www.jandy.com

Let me know if Im doing something wrong here. Thanks.
 
Dirk, I did get my optimum flow rate on my panels from the manufacturer. I looked it up online. It seems to me that my optimum flow rate for my solar panels is so low that I cant run the SWG at the same time. Im just hoping I can bump up my RPM rate high enough that makes the SWG happy without overloading the solar panels.

Actually, Mark eased my mind a bit in saying that the psi for up on the roof is probably low enough that I may be able to comfortably raise the RPM on my pump without worrying about too much pressure flowing thru my solar panels.
 

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That calculator doesn't take into account the resistance of the system when determining the flow rate.

As long as the SWG is activated, the flow is probably good enough. Maybe go slightly higher for a margin of error.
 
carnivalday said:
Yes, I was getting bubbles out of the pool return closest to the pump when I had the Solar turned on. I turned it off, and the bubbles stopped. I have no clue what a vacuum release valve is, unless its that little doohicky on the top of the pump that I open up when I want to clean the cartridge.
Click to expand...
My guess is there is a VRV installed and because the pressure is so low, it is not stopping the air from entering the solar system. You might increase the RPM until the filter gauge reads 8-10 PSI and see if the bubbles stop.
 
Dirk said:
For what it's worth, this is exactly why I installed a FlowVis flow meter with my solar system. I got the optimum flow rate for my panels directly from the manufacturer (I figured they'd know best) and dialed in my VS pump's RPM by simply watching my FlowVis. My panels need 40GPM, which requires about 2200RPM, which also happens to make my SWG happy. The "normal filter mode" (when the panels are not active) is about 1400RPM, based on the minimum my SWG requires.

For me, not having to try to figure out how to do all the calculations and measurements (head, height, volume, pressure, etc), and then constantly wondering if I got it all right, was worth the cost of the FlowVis. And it's turned out to be useful for other purposes, too. I got good value out of its purchase. And because I'm confident my system is as efficient as possible, in that I'm not using more pump energy than I absolutely have to, and my pool is heated as cost-effectively as possible, I expect the FlowVis will pay for itself at some point in time. If you're interested in installing one, it might be easier and cheaper than you think. FlowVis offers a model that fits into existing check valves. So if you have a check valve, and it's the right brand, a FlowVis is a very easy DIY install.
Click to expand...

This sounds like a very interesting toy. Ill have to look into it. Of course, the DIY part is laughable, but maybe I can get it installed.
 
Carnival, I think you missed what James is telling you. That Jandy calculation doesn't account for everything the pump is pushing against, which actually is changing in your system: the filter, the pipes, etc, is one resistance, then a second amount of resistance when the solar valve brings the panels online. You've got your panels' flow requirement, but you have no idea what your total system's resistance is to accurately calculate the actual flow. James is steering you how to come up with that based on pressure and height (math), which is fine, but at best it's going to be a guesstimate. And he's right, as long as you err high, (but not higher than your panels can handle), then the heat exchange at the panels will be fine. Higher is better than lower, in that regard. But there is a point of diminishing returns. You won't lose heat exchange by running the flow (and RPMs) higher, but you'll be wasting electricity if the flow is higher than needed, and that translates to a dollar figure. That's where my FlowVis comes in: I'm sure I have enough flow, but I'm not running any more RPMs than I need to.

Heck, some solar installers guess at the RPMs, then stick their hand in front of a return. If flow is good, and it feels slightly warmer than the pool, they call it a day (and frankly, that's not the worst way to figure this out).
 
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mas985 said:
My guess is there is a VRV installed and because the pressure is so low, it is not stopping the air from entering the solar system. You might increase the RPM until the filter gauge reads 8-10 PSI and see if the bubbles stop.
Click to expand...

I increased the RPMs to 2200, which was 8 psi, and the bubbles stopped. Brilliant!
 
carnivalday said:
This sounds like a very interesting toy. Ill have to look into it. Of course, the DIY part is laughable, but maybe I can get it installed.
Click to expand...
If you need to cut pipe and glue it in, yes, that can be a bit daunting. But if you have the right kind of check valve, it's unscrewing six screws, swapping out the check valve's guts with the FlowVis, and tightening six screws. That's it.

Do you know what a check valve looks like? If you have one, post a pic of it.
 
Thanks, Dirk, I did actually misunderstand what James said. I think I can run the RPMs a little bit high without harming anything. I increased the RPMs to 2200 and 8PSI from Mark's post, and that stopped the bubbles...well, just a very few, very very few. I wont be running the solar much for the time being, but I did want to understand it better, and I think I do now. I will check out that FloVis, sounds like something I really need. Thanks.
 
Dirk said:
If you need to cut pipe and glue it in, yes, that can be a bit daunting. But if you have the right kind of check valve, it's unscrewing six screws, swapping out the check valve's guts with the FlowVis, and tightening six screws. That's it.

Do you know what a check valve looks like? If you have one, post a pic of it.
Click to expand...

I dont. I barely know what a hose looks like.
 

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