Sungrabber solar panel flow rate calculation

Ok, I am not the sharpest knife in the draw, but I need some help understanding this.

In the installation instructions it states:

The solar system works best at flow rate of 1-4 gpm. To regulate flow, simply document the pressure on the pressure gauge of the filter with the by-pass valve open and the pump running. Then throttle the by-pass ball valve closed until the pressure on the filter gauge has increased more than the originally documented........Additional fine tuning may be required.

Ok, how am I supposed to figure out the pressure increase on the filter gauge vs gpm flow thru the panels????

I have 1 1/2" pool lines, a 1 hp hayward pump.

Thanks for any insight you might have.

TRHOD

Simple answer is you can't calculate anything based on the vague setup information they gave you. With any kind of heat exchanger you get the maximum heat transfer at the maximum temperature differential. In the extreme limits, no flow would be a hot panel and at full flow a panel at pool water temperature. In the first case you get 0 BTU transferred to the pool because the flow is zero. The last case would result in the maximum BTU transfer to the pool but may restrict the flow unnecessarily. A BTU is the amount of heat needed to raise one pound of water one degree F. I would set the bypass valve to divert enough flow to the panel to result in a few degree F rise at the solar panel outlet in full sun. Nothing critical about this. Just using some numbers as an example with no idea how close they are, if no flow results in a panel temperature of 150 deg F and the water is at 75 deg F, you have a 75 deg differential. So what if the outlet is now 80 deg F. You still have a 70 deg differential so the efficiency penalty isn't much at all and you still maintain a good flow. From a pressure rise standpoint, see what the rise is with the bypass fully closed and that will give you an idea of the flow resistance the panel adds to the system. The lower the resistance the more flow you can put through the panel without taking a significant flow hit. It's all voodoo and whatever works best.
I know I rambled but I hope this helps.
Al

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??

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.

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

Simple! That's me!;)

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.

Quote:

---

Originally Posted by 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?

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.

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.

Doesn't sound high to me. I have a Hayward 1 hp Superpump 2 spd and 20lbs is perfectly normal for 8 years now. When it hits 25 lbs I have to backwash. Since my solar panels are on a "Y" connection with the return, I don't see much of a change in pressure when they are on. My pump is only about 5' from the pool, and my return line is maybe 10' long and rises no more than 4' above the pump, plus another foot to the solar panels. I have 240 sq feet of panels.

The reason I think it is high is because 20 PSI is about 49' of return head (adjusted for filter gauge height of 3') and if you assume another 5' of suction head, which is probably on the low side, results in 54' of total head loss. That pump puts out about 34 GPM @ 54' of head so the plumbing would be the equivalent of almost 800' of 1.5" pipe! To me it seems like a lot of head loss for such little flow rate. Also, the operating point is on the far left of the head curve which is far from optimum. If true, then there is something in the plumbing which is causing a lot of heat loss.

Quote:

---

Originally Posted by 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?
Yes, the gauge is working. It goes to zero when pump is off, and I can see pressure changes when I back wash, turn on the solar panel lines, etc

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

I'll try and give you my best guess estimate. The pool is 18X36. I have a skimmer line that I would say is 66-75', I have a wall drain I would say is 35'. My return line is a single line, and I would say it is 25-35'.

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.

---

The panels DO prime. Actually, I have additional shut off valves going TO the solar panels, AND a shut off valve coming FROM the panels. When I open the shutoff valve TO the panels I can hear water moving thru the pipes and can see bubbles in the pool(air pushed out of panels before the water starts flowing), even before I turn the bypass valve on. So the panels are priming. As I start to turn the bypass valve, when I get it fully closed I will get a short bump in pressure from about 20-21 psi up to 25psi, the it rapidly returns to about 21-22psi.

Today we had a partly sunny day, and I saw a 4-5 degree raise in the pool temp. It seems to me that it is working, but is it working to its full potential.

One other side note that I can't figure out. When I start up the solar panels (open valves and flow water thru the panels) I have several glued joints that will leak. These are glued joints on the plumbing going TO the panels, and not the panels themselves) These are Drip leaks, not stream shooting leaks. When I go back out to the pool to shut the panels down at night, there are NO leaks and the concrete below the filter/pump, etc is dry.

Why would the plumbing leak upon startup, but stop leaking thru out the day as water, pressure, and heat are applied to these joints???? This one is blowing my mind. I would think the heat, pressure, and water would cause the leak to get worse. This has happend the last 2 days I have run the panels. (keep in mind these are the only 2 days I have had the panels installed to run them)

BLessings,

If the panels are only leaking when they are first turned on, then it could be the VRV. Sometimes they will let a bit of water through before shutting off. However, if you still see the water dripping after several hours of operation, then it is likely a very small leak somewhere. Just trace it back to it's origin to make sure.

As for priming the panels. After all the air as stopped coming out of the returns with the bypass open (i.e. bypassing water around the panels), if you then close the bypass, is there any more air that is forced out of the panels? If not, then they are probably fully priming even when the bypass is on. However, if you get more air out, then the panels may not be fully priming.

The leak is NOT from the panels, it is from the plumbing (abs sch 40) glued fittings going TO the panels, but NOT the actual panels.

The glued fittings will leak when I start moving water thru the pipes, but as the day goes on, the leaks will stop. This doesn't make sense to me.

Why???

If the leak is small enough and the pipe heats up, it could be that it is expanding enough close off the leak. There is PVC epoxy that can be used on the outside to seal small leaks.

Mark,

I'll look for that PCV epoxy.

Thanks for all your time on this and the other "winterizing solar panel" threads.


Blessings,