Plumbing Help! Redirecting a trickle of water... for solar

[shep377]

I am now trying to get my solar system plumbed and running. I put about 1000' of tubing into my stamped concrete deck (which gets very hot in the sun) with the intent of claiming some of the heat for the water, while cooling the concrete down a little. I have the in and out of this big loop running back to my return lines. What I want is to run a slow flow of water through this loop to do the heat exchange.

I am trying to figure out valve positions so that some water will be:
1. Branched off the return lines
2. Forced through the solar system loop
3. Merged back into the return lines and on into the pool

The trouble is that this is a closed loop in that I cannot "see" anything happening. I was trying to get a piece of clear pipe or a flow meter or something so I can see how much water I am forcing through the smaller loop and make sure it is not too much. I am using 1.5" PVC for the main pool plumbing and 1/2" for the solar loops. I thought I could put in a restriction by partially closing a ball valve which would force some water through the solar loop. There will be a TON of friction loss in the loop, but I only want a trickle so it heats up... How can I be sure it's flowing through it?!?

A picture is worth a thousand words...

- Open valve --A-- to allow flow in solar loop
- Partially close valve --B-- to force some water through that loop

Anyone have any suggestions based on experience?

Cheers! (BTW, great forum. Fun stuff - this is all like a giant mechano set fr adults!)
Shep

 

[Bama Rambler]

Re: Plumbing Help! Redirecting a trickle of water... for sol

Welcome to TFP.

You could either put a flow meter in the loop after valve "A" or right before it returns to the return piping. Either place will tell you if there's flow through the loop.

 

[jblizzle]

Re: Plumbing Help! Redirecting a trickle of water... for sol

Just an FYI, you will get more heat transfer with higher flows rates than a trickle. The exiting water will not feel as warm but there will be a lot more water heated a little which ultimately will add more heat to the pool.

Posted with Tapatalk ... sorry if I sound short ... hate typing on phone

 

[mas985]

Re: Plumbing Help! Redirecting a trickle of water... for sol

As I posted in the other forum, you cannot expect much flow rate through 1000' of 0.5" tubing. Only 1 GPM will have an extra 33.3' head loss and a 14 PSI filter pressure rise. That is going reduce the overall flow rate of the pump significantly and depending on the pump, may not even be possible. Not only that but 1 GPM through the hose will not extract much heat at all so it may be pointless. Ideally, the hose should be arranged in multiple parallel loops much like a solar panel.

 

[shep377]

Re: Plumbing Help! Redirecting a trickle of water... for sol

Well that's not good. Perhaps I just cut the loop out of the system and cap it off... ? It has to do something I would think...

From what I looked up, friction loss in .5" pipe running 1 GPM per 100' (I have 600') is about 1.1 feet of water column... convert at 0.43197 PSI per foot... I could flow 1GPM through it with about a 2.85PSI rise on my filter head pressure. (I got this by saying 1 x 1.1 x 0.43197 x 6 = 2.85)

So I might be able to push 1.5 gal/min through this and collect some heat... the question is, how much do I want to increase the pressure on my filter pump? I am currently running at 12PSI as a standard. If I adjust the main value (forcing water through the loop) until the pressure on my filter is about 15-16, then I will be getting just over 1 GPM through the solar loop. (Don't know if it is safer to go further or not...) then at what pressure do I know to backwash? (I run at 12, backwash when it gets to be about 17).

Am I getting any benefit from heating up 60 gal of water an hour for 6 hours every day? I imagine the water would come out a fair amount hotter... say 10-20deg.

...I am sure in all this my ignorance is showing through.

Thanks everyone.

 

[mas985]

Re: Plumbing Help! Redirecting a trickle of water... for sol

If you are using PVC pipe tables, it will give you an optimistic value. 1/2" PVC pipe is actually 0.622" ID but black poly pipe is closer to 0.5" ID. Using the Darcy-Weisbach hydraulics equation, for 600' @ 1 GPM, I get 20' of head loss and 8.6 PSI rise. That is still fairly high pressure rise and 1 GPM is still not going to gain you much.

As for acceptable pressure on the pump, the higher the pressure, the lower the flow rate and the lower the overall efficiency (gallons pumped per watt-hr). So it is just a matter of what you are willing to tolerate vs the heat gain which will probably not be much. But since you have already gone to the trouble, you might as well use it. If nothing else, it might reduce the temperature of the concrete a little. But I wouldn't bother with more than 3-4 PSI rise.

 

[shep377]

Re: Plumbing Help! Redirecting a trickle of water... for sol

So I now have reality to try and force into the theory of all this!

I have the solar piping hooked up under the deck. If I open the valve, the water comes out at 1.5gal/min, with no other restriction on the return lines - so the filter pressure remains exactly the same. No additional load on the pump means no real increase in electricity use (please don't correct me - I'm in my happy place on this one). A thermometer under the stream shows 105deg - fairly constant over a 5 hour window on a sunny day. Even if it is not hot out, sun on the concrete seems to be constant. I put an old garden hose timer valve onto the line, and set it that it automatically opens every day from 1pm-6pm when the concrete is hottest.

A visit to a fluid mixing temperature calculator online shows that mixing (1.5gal/min x 60mins x 5hours = ) 450 gal of water at 105deg into 20800gal at 80deg will move the entire body of water temp up by 0.5deg (52941176470603 deg F to be exact ).

Summary: I am getting 1/2 a degree a day and there will be some resultant cooling of the concrete deck for the feet.

I know it's not optimal, and I certainly could have done it better, but not bad for not knowing anything about it...

I'm happy.