Solar Install - Pressure question

[Jon123]

Hi all... The previous homeowner had 4 "SunHeater" 2' x 20' panels they left behind, but not hooked up. The system is plumbed for them, so I figured I'd try getting them going again.

I did a quick test with a garden hose to see if they were leaking, and the water was going through them without leaking out anywhere (of course, this is with basically no pressure).

In the future I planned to switch over to a solution from Hot Sun (h2otsun.com), but until I get the rest of the pool figured out, I thought these may be a good interim solution to give a small boost to the pool temp. To be clear, I'm not expecting much from these, I'm hoping for maybe 2-3°F. At 160sqft, it's very undersized. Is this a reasonable expectation?

I have a flat roof and I've been reading over the h2otsun documentation for tips. I think I have the mounting part figured out (ballast), and largely the way it will be laid out on the roof and where/how I'll add a vacuum relief.

Hot Sun's main point is that the thing that causes most failures is problems with too much pressure in the panels.
I know very little about pressure right now, but I'm willing to learn a bit...

The panels would be on the roof, 14ft above the surface of the pool.
The pump and other equipment are at ground level, so maybe 6-12 inches above the surface of the pool at most.

In the attached photo you can see the lines going up to the roof. There is a diverter valve I can use to change the flow going up to them.
I plan to add a clear check valve to the return.

I suppose my question here is how do I know/manage the pressure in the panels? Given my setup, are there any concerns?
The pressure gauge on the filter was showing 14psi yesterday under normal operation.
Thank you!

 

[jblizzle]

I think I have seen than you only want to see about 3-4psi increase at the most. You likely will not want to divert all the flow through the panels so will want a bypass or just not turn the 3 way valve all the way. You know you have enough flow if the panels feel cool to the touch.

You will also want a VRV and check valves right after the filter and on the solar return pipe.

 

[atttech-2]

I did a Hot sun install, at the lower part of the system where the water enters the panels at the roof you want no more than 5 psi. The filter pressure has a relationship to the the panel pressure but it is biased on pipe size and amount of lift before it enters the panels and the amount of panels. That being the case if your filter is normally 14 psi you can't just assume that with they system on you want to shoot for 19 psi. In my system my filter pressure jumps 9 to 10 psi even though I only have about 5psi at the panels when priming and that falls to around 3 once the system is fully primed. The best thing to do is buy a pressure gauge that can read from 0 to 15psi and measure the pressure at the roof where the water first enters the system. That location is also often a good place for the VRV so you can use the threaded port for the VRV to atach the pressure gauge while testing.

Edit: forgot to add a couple things you asked about.
To manage the pressure you can try using the 3-way as Jason mentioned, but you will have to try to get it in the same position every time. Easy to do if the valve is automated less so if you are manually setting it. If you want a set it and forget it option connect the solar supply and returns together with a valve. You then slowly divert some of the flow away from the panels until you get the pressure you desire, leave the valve in that position all the time. Yet another more expensive options (at least up front) is a VS pump since you can dial in the flow rate by varying the speed of the pump.

Rule of thumb on heating is in order to get 10F increase you want a system that is about 100% or slightly higher the size of the surface area of the pool, so if you are around 25% and I am guessing that you are with 160sqft, I think 2-3F is reasonable, of course with regular use of a a cover that could easily be 8-13. One added benefit we have noticed is that you don't have to heat the whole pool for it to feel generally warmer. We spend much of our time in the shallow end, on the sun shelf, or in front of a return and the warm water tends to stay on the surface unless we have a ton of kids over. I would liken it to standing in front of a heater or near a stove when your house is cold it's only when you get to moving around you notice other areas are cold.

 

[jblizzle]

Just going to point out that the pentair 3 way valves have external pins to set stops so you can get the position the same every time.

 

[Jon123]

Thanks for the replies!

We got everything put up there this weekend. Photo attached here.
I have a few more things to do finish securing it, but it's largely done.
Ignore the water in the photo. The supply line wasn't welded for some reason so it blew open as soon as I turned it on to test. Welded it and it's working well now.

PSI at the filter rose about 4-5 psi. It hadn't even occurred to me to use the threaded VRV port to check pressure. I have the pressure gauge, just waiting for a bushing so I can test it at the panels.

I'm seeing a very small number of air bubbles coming out in to the pool when running through the solar. I'm not sure where it's coming from yet.

Today is my first real test day. It's been mostly sunny. After about 4 hours I see ~1°F rise in temp, I don't entirely trust this thermometer and the cover is on so I can't get to my other one right now (next investment is a reel to make that easier. With the indoor pool we have a thermal cover which is heavy and not fun to remove by hand). A feel test of the water leaving the jets tells me it's definitely working though.

 

[Jon123]

I don't think my 3 way valve has the pins... It does "click" as you turn it though, so I suppose I could probably figure it out that way if I pay attention. We'll see once I measure the pressure at the panels.

 

[Rocket J Squirrel]

I'm seeing a very small number of air bubbles coming out in to the pool when running through the solar. I'm not sure where it's coming from yet.

This is normal. When the solar turns off, the VRV allows air into the panels. When the solar restarts, that air returns to the pool. It should only last a few minutes. If you're seeing continuous air, that's a problem.

 

[jblizzle]

I don't think my 3 way valve has the pins... It does "click" as you turn it though, so I suppose I could probably figure it out that way if I pay attention. We'll see once I measure the pressure at the panels.

Yeah, that is not a Pentair with the pins on the handle.

 

[Jon123]

This is normal. When the solar turns off, the VRV allows air into the panels. When the solar restarts, that air returns to the pool. It should only last a few minutes. If you're seeing continuous air, that's a problem.

I see the bubbles when the VRV activates (lots of air at first of course), but while running I see some very small bubbles still. When it first started up I noticed it more, but even after running a while I'm seem a few of them popping out. I'll try to get a video of them for reference.

Previous owner never had a check valve on the solar return line, I got that in today and will probably install it tonight.

I also saw a manual for these panels today which scared me a bit - it shows a very strange arrangement for them.. I'm not sure if this matches the panels I have, going to get up on the roof today to confirm model numbers.



UPDATE: Pretty sure this is a different kit/model than the ones I have.

 

[Jon123]

Video of the bubbles here: solar-bubbles.mp4
Excuse the dirt and stains here - the pool is very old, and the heater has started dumping some rust out recently.

After 6 hours running today we have about a 2°F rise in temp. It's been cloudy the later part of the day. On a sunny day I'd expect we'll get a bit more out of it, but no matter I'm calling this a win as it should mitigate most/all of the nightly loss during the summer. It will be interesting to see how much it helps with the temp during the spring/early summer when it's difficult to get the water temp to budge without the heater.

 

[borjis]

I had a top of the line solar industries panel set at my last home. 100% coverage.
On a clear sunny summer day the return side would show 8 degrees higher coming back into the pool.
It raised pressure about 5 psi if I recall correctly.