Solar Diverter Valve...backflow?

[DanL]

Hi,
New to this forum and totally new to pools. Do have liquid pumping system experience though.
I made a drawing of the pool system in the house we just bought. The question I have is related to shutdown and drainage of the solar panels.
With the solar system off, I opened the two drain valves shown in the drawing and let the panels drain. Then I closed the two manual ball valves to isolate the panels from any flow. When I turned on the main pump (solar diverter valve in the "off" position i.e. no flow to the panels), drain valve 2 in the drawing leaked water. I assume that leakage is because the solar diverter valve gate has an opening to allow the panels to drain when the solar system shuts off. Is that correct? Should that backflow device allow flow both ways or just one-way out of the panels?
Any other comments or hints on the system appreciated.

Another question please. What pump speeds would be good for running 1.no solar, 2.with solar and 3.spa only? Thanks.

 

[pooldv]

Welcome to TFP and congrats on the new pool!

Yes, the 3way solar valve #2 should have a small drain hole to allow the panels to drain down. If it is a true solar valve then it should have a flapper to only allow flow out of the panels but not back to the panels. But, sometimes people will use a regular 3way valve and drill a small hole instead which will allow flow each way.

I run my Intellifo pump to 1100 rpm for skimming, filtering and making chlorine with the SWG. There usually isn't much watt difference between 900 and 1200 rpm. Do you have SWG, saltwater chlorine generator? Or a puck dispenser?

I run 1950 rpm for solar but I only have 5 panels so you might need a higher rpm. You want about 10 gpm per panel. On a hot day you want enough flow for the panels to feel cool to the touch and the water from the returns should not feel too hot. The more flow through the panels the more heating efficiency you get.

I don't have a spa attached to my pool, maybe try 2500 and see how the flow is and raise it 100 rpm at a time if needed.

You can add your pool info to your sig. More here on what to add and how to do it, Pool School - Read This BEFORE You Post

 

[DanL]

Thank you for the thorough response. I will read the Intro information and add a sig and pool info.
I'm sure I'll have more questions as I learn about water chemistry, etc.
Thanks again.

 

[MarianParoo]

Again, welcome!

 

[xyz]

Solar panels do well with low pressure, as they are hot, flexible, thin walled pipes, made of materials not intended to hold high pressure at elevated temperatures.

So so this will be easy to calculate once we ge the info we need:

1) flow rate vs pressure drop across the panels. We can probably look that up if you have the brand.
2) height of the bottom of the array from the pump
3) height of the top,of the array from the pump.
4) GPM vs efficiency for the panels.

Assuming you are all 2" PVC, I think we can probably ignore that flow friction loss.

So get this info and we can dial your system in.

 

[DanL]

Solar panels do well with low pressure, as they are hot, flexible, thin walled pipes, made of materials not intended to hold high pressure at elevated temperatures.

So so this will be easy to calculate once we ge the info we need:

1) flow rate vs pressure drop across the panels. We can probably look that up if you have the brand.
2) height of the bottom of the array from the pump
3) height of the top,of the array from the pump.
4) GPM vs efficiency for the panels.

Assuming you are all 2" PVC, I think we can probably ignore that flow friction loss.

So get this info and we can dial your system in.

xyz...just saw your response. Thank you.

All 2" pipe.
1. Brand is Aquatherm Ecosun 4' x 12' panels x 10 (480sqft) model 16204-12
2. Bottom feed header approx. 11 ft above pump
3. Top collector approx. 17ft above pump
4 GPM vs efficiency: Here is some info I found:
Specifications link: ECOSUN® Solar Pool Heater Specifications
"unprecedented FSEC performance rating of 1,100 Btus per square foot per day"

Specs recommend max of 35psi at 140F. So could I just run with no panels and check pressure, then run with panels to see any increase in P. Should be almost imperceptible with 10 panels in parallel. Then set the solar mode pump speed so the P gauge on the filter is maybe 25psi? That would be total backpressure due to filter, panels and all downstream plumbing and would keep panel pressure well below the specified 35psi max at 140F.
Thanks much.

 

[xyz]

Ok, you will lose 4.3 psi getting up to 10', and another 3 getting to the top of your array.

so, measure pressure anywhere you want and we will know the pressure elsewhere (approximately). At 50 GPM (5 GPM per panel x 10), you will lose 1.2 psi per 100ft of your 2" pipe. The lower the pressure on the panel the better. Once you achieve your desired flow rate.

So figure out what RPM you need to get 50 GPM out of your pump, check the pressure somewhere in the feed line, and report back. this is a non trivial calculation, since back pressure effects flow rate, and flow rate effects back pressure.

So... what you may want to do is replace one of your check valve covers with a flow meter. Then you can dial in the flow rate you want, and then check to make sure you are not over pressuring your system (which I doubt will happen, given the info you have provided).

TFTestkits.net

 

[DanL]

xyz...your comments are all very educational for me....thank you.
Attached is a marked up pump curve for the Intelliflo 4.
My solar panels are now off (isolated). The pool guy has the pump set for daily recirc at 2700rpm. The P gauge on the filter reads 16 psig (brand new gauge). That P represents total system backpressure on the pump. Looking at the pump curve attached.....convert the 16 psig to ft head (h=P/0.433 for water) and you get 37. I'm not sure about whether this is a dynamic or static conversion factor, but assume 37ft head. Interpolating a 2700RPM curve between the shown pump RPM curves, the indicated flow rate is just over 100GPM!
I lowered the RPM to 2100, and the pressure dropped to 10psig. On the pump curve that plots out at about 70GPM.
I don't know what the settings were when the solar panels were being used. I need to check the program to see what pump RPM was set for solar mode and check the pressures with the solar panels in the circuit.
As I re-learn about all this (I was a chem e long ago....), I realize that I'm likely better off taking care of all the pool stuff myself, and having only basic water chemistry care done when I'm gone.
How does the above look to you? Close to being correct, or way off?

 

[DanL]

xyz...your comments are all very educational for me....thank you.....
.... The pool guy has the pump set for daily recirc at 2700rpm. ..... the indicated flow rate is just over 100GPM!
....I lowered the RPM to 2100, and the pressure dropped to 10psig. On the pump curve that plots out at about 70GPM.....

So for a 15,000G pool, 70GPM for 5hrs. pumps 21,000G. That's about 1.5 turnovers. XYZ, your thoughts on all this???? Thanks.

 

[pooldv]

Turn over is not an important factor for residential pools. It is only important in public, regulated, pools. More here about pump run time, Pool School - Determine Pump Run Time

 

[xyz]

pooldv beat me to it. That link will help you understand that you are probably using more run time and a higher power setting than you need.

Ok, so you saw how lowering the pressure saves you a lot of money, and will have less chance of over pressuring your system. I'd suggest you take another look at 50 GPM. If you can still get enough pressure to overcome the height, you will minimize pressure on your array, and still get the recommended mid-level flow through your array.

 

[DanL]

Thanks guys,
Lowered the RPM to 1800. P=7.5psig. From pump curve, that's just a bit over 60Gpm. Pump watts=360. Water flow from the spa to pool very slow and vacuum moving way too slow. Diverted more water to vac from skimmer. Beginning to question how close the pump curve flow rates are. Will likely buy a flowmeter when I return in late Jan just to satisfy my curiosity. This is starting to become yet another hobby for me....like a big tech toy...ha. And I haven't even delved into water chem yet.
Great forum.

 

[xyz]

You are measuring pressure at the middle of your system, so your PSI estimate is low. Basically, since you are measuring at your filter, the pressure losses after that are not being measured.

I higly recommend a flow meter (I'm designing one into my solar installation), because with a centrifugal pump, flow and pressure are highly coupled. But if you measure flow, you know you are getting the flow you want, and yet no need to waste pump energy to get more than you need.

Also, I recommend you have your automation bypass your solar array when vacuuming. OR, partially bypass your array when vaccuming, if you need more suction.

If you have a suction side floor cleaner, consider a robot (many suggest Maytronics, and I like my DX6). It uses less power, makes it easier to dial in your filtering, and it cleans and scrubs the waterline well. I run mine every day, and usually only have to empty it once or twice a week.

 

[DanL]

You are measuring pressure at the middle of your system, so your PSI estimate is low.....

Hmmmm....the P gauge is on the filter container, between the pump and filter. So it is measuring pressure right after the pump. That should be the total system back pressure.

.....Also, I recommend you have your automation bypass your solar array when vacuuming.....

The pool has a Hayward Poolvergneugen Pool Cleaner. It runs constantly when the pump is running, so I need to run solar and vacuuming at the same time (solar is on auto valves, vacuum is not). The water return is thru the skimmer and the vacuum - floor drain and spa drain are closed during circulation. At 2100RPM, the PoolCleaner worked fine. At 1800RPM, it is very slow, even when skimmer flow was reduced in order to pull more water through the vacuum.
The vacuum does a great job on the bottom and walls. Anything it collects goes into an in-line basket strainer in front of the pump.
The pump seems to have plenty of capacity....at 2700RPM it was feeding the solar array (all flow thru panels) and operating the vacuum and skimmer. I do need to get a flowmeter...
Will be back in late Jan...will update then.

 

[xyz]

So there is loss between your pump and your filter. That loss increases non-linearly with flow rate. Before I re plumbed it, I was losing, estimated 4 psi between my pump and filter.

Anyway, it sounds like your system is such that you need to run it near 2100. You don't have much of a choice, it sounds like. So when your existing vac breaks, switch to a robot and then ALL your suction goes toward skimming, AND you can run your pump slower to save power. Better skimming, better cleaning, and less pressure on your panels.

Till then, it sounds like you found the sweet spot for your current setup!

how many additional degrees of heat do you get? Sounds like a cool (warm!) setup.

How do do you control the solar valve?

 

[DanL]

So there is loss between your pump and your filter. That loss increases non-linearly with flow rate. Before I re plumbed it, I was losing, estimated 4 psi between my pump and filter.
The pump to filter pipe is 90elbow off pump, 2ft pipe, then 90elbow directly into filter. Very short and direct.

Anyway, it sounds like your system is such that you need to run it near 2100. You don't have much of a choice, it sounds like. So when your existing vac breaks, switch to a robot and then ALL your suction goes toward skimming, AND you can run your pump slower to save power. Better skimming, better cleaning, and less pressure on your panels.
The vac is a robot, unless I misunderstand the term. It's a Hayward Pool Cleaner...roams the bottom and sides. The vac hose goes into a built-in return fitting that feeds separately back to the pump. The surface skimmer also feeds back separately. The two can be balanced with a valve at the pump station. See the attached system diagram link in my signature line.

Till then, it sounds like you found the sweet spot for your current setup! Maybe, but it would be cool to have a flow meter to play even more....

how many additional degrees of heat do you get? Sounds like a cool (warm!) setup. On Nov 12, it was mostly sunny and 76F. Pool was 85F. Pump was likely at 2700RPM then. General experience is that its easy to get 10deg over air temp with 5hrs run time 11pm-4pm if covered at night.

How do do you control the solar valve? Solar valve is automatic. Operation controlled by setting minimum air temp for it to come on, and target water temp for it to shut off. Heating modes are solar off, solar on, or solar preferred (heater comes on if solar alone can't hit target water T).

Thanks much.