Sungrabber solar panel flow rate calculation

[TRHOD12]

Al,

thanks for your thoughts.

I FINALLY got a couple of rainless days, and got the system hooked up last night and was able to give it a test run before dark.

When I fully closed the bypass valve, my pressure only increased by 2psi. That didn't seem like a very big jump. I had contacted the solar panel company, who said if the rise in pressure was greater that 8psi from normal operating pressure, it would be hard on the pump.

SO, still not sure about how to get the 1-4gpm optimal flow.

1 thing I thought about doing was opening the return line from the solar panel and putting a 5gal bucket under it. Turn on the pump and pump water for 1 minute and measure how much water was pumped out of the panels. This should probably work, shouldn't it?? Then if I am over the 1-4gpm, just close the bypass valve about 1/2way and do the test again. Sound like a plan??

[CarlD]

It should, but really what you want is the maximum flow through the panels without straining the pump or risking damaging the panels (which usually isn't a problem).

Here's a tip: If you think you need to slow down the water in the panels so it heats up more, that's wrong. All you are doing is preventing the movement of heat energy. Remember: It's all about HEAT transfer, not temperature. You want to maximize BTU output from your panels, not degrees and the more water you can safely move through the panels, the better! (There are some physical limits, such as cavitation of the water, but you'll never see them)

If the water from the panels is flowing very strongly (and not crossing that 8psi limit) and the water from the panels is only slightly warmer than the pool, it's working and working well! If your pool is 75 and your panels are putting out 77deg, don't worry. When the water is 77, the panels will be 79 deg as they are EFFICIENTLY transferring heat energy to your water!

I find that when the flow is too high, it's obvious because the skimmer and the main return just don't seem to be working too well. If I cut the flow to the panels and the skimmer and return improve, I know I had too much flow to the panels. You want to get it where the pool's plumbing is working well AND there is an ample flow through the panels.

[Poconos]

Ted,
The method you propose for measuring the flow will be close. The flow rate you measure will probably be a little on the high side because the panel outlet is now at zero pressure as opposed to something when it's connected on the other side of the bypass valve, but close enough. I think Carl said what I said but in simpler terms. Since your pressure only increased 2 psi with the bypass closed, that's good. Indicates little flow resistance in the panel. Even if you run that way you're toally OK. 8 psi rise? No.
Al

[CarlD]

Simple! That's me!

[mas985]

Based upon your other post, you have about 200 sq-ft of panels. I usually use a rule of thumb of about 1 GPM per 10 sq-ft of panels so in your case that would be 20 GPM total. That is the upper end of the range they gave you.

You said that you have a 1 HP Hayward pump. Is that a 1 HP Superpump?

Also, what is the actual pressure reading with and without solar?

How high are the panels installed?

Do you have separate suction lines coming to the pump?

What size is the pipe for the solar panels?

2 PSI rise could be reasonable for your setup but it depends on the answers to the above questions. However, forcing all of the water through the panels may not be necessary given you only need 20 GPM.

[TRHOD12]

Based upon your other post, you have about 200 sq-ft of panels. I usually use a rule of thumb of about 1 GPM per 10 sq-ft of panels so in your case that would be 20 GPM total. That is the upper end of the range they gave you.

You said that you have a 1 HP Hayward pump. Is that a 1 HP Superpump?

Yes it is a Hayward superpump 1HP pump.

Also, what is the actual pressure reading with and without solar?

[I]Pressure reading w/o panel is 20psi, with panels on (bypass valve fully closed) reading is 20psi. When I close the bypass valve the pressure will rapidly bump up to 25psi for a split second, then goes back down to 22psi[/I][

How high are the panels installed?

1 story house. The inlet line runs all the way up to the peak of the roof, then back down the south facing slow and ties into the panel at the bottom. The top of the return line from the panels is at the peak of the roof, and flows down the roof and back into the return line after the filter.

Do you have separate suction lines coming to the pump?

No, I have this plumbed in as follows. I put a T in the return line after the filter. This is the inlet to the solar panels. Approx 6" after the T on the return line from the filter, I installed the bypass valve. The return from the panels ties into the return line going to the pool approx 6" below the bypass valve.

What size is the pipe for the solar panels?

Headers are 1 1/2", all the plumbing I did was with 1 1/2" schedule 40 pvc.
2 PSI rise could be reasonable for your setup but it depends on the answers to the above questions. However, forcing all of the water through the panels may not be necessary given you only need 20 GPM.

Carl and Al, I get what you are saying now. Thanks.

[mas985]

20 PSI is really high for a 1 HP Superpump even with 1 1/2" plumbing. I would have expected much lower pressure. That is 50' of head for just the return side.

Are you sure the gauge is operating properly? Does it go to zero with the pump off?

Also, how long are the runs from pool to the equipment?

Anyway it sounds like the panels will not fully prime unless the bypass is closed so you may need to operate that way. You might try to slowly close the valve until you hear the panels starting to prime and air coming out of the returns. This would be the minimum required flow setting but it probably wouldn't hurt anything to have all the water going through the panels.