Plumbing Suggestions for Solar Bypass?

[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.

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
- This is the diagram: http://i1172.photobucket.com/albums/...olPlumbing.jpg

Anyone have any suggestions based on experience?

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

[mas985]

Is it one big loop or multiple smaller loops? Hopefully the later as that will be more efficient and have much less head loss.

If it is the former, then you will have a problem with efficiency and will only be able to push a very small amount of water through the loop.

Do you have filter pressure readings for each of the valve positions?

[shep377]

You are quite correct about the friction loss... however it is one big loop about 800' long. I can calculate friction loss numbers (same as fire hose I would expect). My intent was only to send a very small amount of water through the loop - like a garden hose trickle. It can remain in the line longer and absorb more heat with no problems. I just need to be sure that water is in fact flowing through the loop at all.

I don't have filter pressure readings for each valve position because I don't have this all hooked up yet. It is only circulating (skimmer->pump->filter->return).

My intent is to somehow have a visual indicator that there is water flowing through the loop. I just don't know what to put in.

Thanks!
Josh

[mas985]

You will know when water is flowing through the hose because the filter pressure will increase due to the extra head loss. A little pressure rise will result in little water going through the hose while a large pressure rise will result in more water going through the hose. If you want exact flow rates, that will be a little tricky but possible to calculate. If you want a visual indicator, then plumb a flow meter on the feed pipe to the hose. But choose one on the lower end of the scale because there will probably be little water flowing through the hose. But even with a bypass fully open, there will still be a trickle through the hose because there will always be a pressure differential between the input and output of the hose albeit a small one with the bypass fully open.

Also one thing to keep in mind is that the heat transfer efficiency from the cement to the hose is proportional to the flow rate through the hose. The higher the flow, the more heat that will be extracted from the cement. The lower the flow rate, the lower the heat transfer.

For example 1 GPM through a 1000' of 0.5" hose is going to be 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 arranged in multiple parallel loops much like a solar panel.

To get a pressure rise of only 6 PSI, the flow rate through the hose would need to be less than 0.6 GPM.

[shep377]

Excellent... so some experimentation with the valve and the pressure readings at the filter will give me some indication.

My filter is currently running about 12PSI (sorry I am quite new to this). If I gate back the main line a bit, forcing more water through the solar loop in the concrete, then it will go up. If I gate it back more, forcing more water through, it will go up more. What are safe limits to this? How high can (should?) this pressure go? I know I don't want to force all the water from a 1.5" line through a .5" line - it will put a HUGE amount of work on the pump I would expect.

I am also told I should backwash when the PSI climbs about 5PSI higher then normal... is this also correct?

Cheers
Josh

[mas985]

Pumps actually work less with higher pressures. Flow rates go down, energy use goes down, but slower, so efficiency (gallons/watt-hr) goes down as well. A pump has a maximum head/pressure that it can produce but if the flow rate is not high enough in the plumbing, it cannot produce the pressure. So even if you redirected all of the flow through the tube, there would still be some flow rate through the tube (~ 5 GPM) and the pressure will be limited to less than 26 PSI. But the turnover rate for the pool would increase to 70 hours!