Solar Pool Heater Plumbing Quesiton

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C

crokett

Well-known member
Jul 17, 2007
677
Hillsborough, NC
We have some passive solar heating panels. They are about 20' long and each section consists of 1.5" piping at each end with lots of 1/8" ID tubing running between them. Each section is about 2' wide. I have 4 sections connected together to create a panel that is 20' long by about 65" wide. Here's the best picture I could find. It shows 2 sections, I have 4.

6860-a-sq_3.jpg



I built a roof over the pool deck and last week had help getting the panels up on the roof and installed. I had them plumbed at ground level last summer. The line from the pool pump came in the top corner one end. The return went back to the pool at the bottom corner at the same end. Today I learned from my help that something fell out of one of the sections while we were putting them back together. He is not really a plumber and forgot to say something. It was at the end where I had the intake and return plumbed. Believe it or not I did find the part laying out there today, and it is a baffle. I -think- the baffle was there so that water would flow through the top half from one end to the other, then into the bottom half then flow back through the bottom half go back to the pool. Without the baffle I think water will just go straight through to the return. I think. So does it go between the halves at the end I have the intake and return? As an example, in the above pic water would flow in at the top, go to the far end of the top panel, then return through the bottom panel.
 
First, you want to feed the panels from the pool on the bottom and return from the top. Ideally, you would remove ALL the baffles and you would feed the panels on the lower far end and return the water to the pool from the close top end. So all the water is running through all the little tubes in parallel.

Each section usually has one baffle that forces the water to go one way in half the panel and return in the other half. With multiple panels and assuming you want to keep the plumb just on one end and not like I described above, I would think you would at the most just want 1 baffle so that water travels out in half and back in the other half, but I am not sure you could put the baffle at the intersection of 2 panels?
 
Why do I want to feed the panels from the bottom instead of the top? I haven't done the plumbing yet. I can switch the cap and the hookup to the PVC easily enough on the bottom section. I can also leave the baffle out and set it up to do everything in parallel.
 
Because then the air is forced out the top of the panels. Feeding from the top can trap air in portions of your panels.

I would highly suggest removing all baffles and feeding the panels on thy bottom of the far end and returning the water from the top of the near end. That is the least head loss in the plumbing and most efficient heating.
 
I had not thought of the air issue. I will do it that way, thanks. That then begs the question, should I plumb in an air bleed valve on the side that returns to to the pool? Sounds like I should. I will check to see if the rest of the baffles are removed.
 
I can't tell you the fluid dynamics science, but if you can, you do want them flowing vertically, in parallel, entry on bottom, return to pool from the top opposite corner of the entry. You want the top return to have the shorter pipe run if you can.

One key concept is that for maximum efficiency, you want to maintain the maximum temperature differential between the water and the heat. The vertical, parallel runs does that, extracting the maximum potential heat.

Sent from my Nexus 4 using Tapatalk
 
If the panels are below the water level of the pool you don't need an air bleed (vacuum release) valve. However, if the panels are above the water level of the pool you should have a vacuum release valve. This will also allow the panels to drain down when the pump is off which slightly extends their lifetime.
 
ok. The panels are about 12' higher than the pump. Should the valve go down by the pump or up by the panel? Also, until the lines reach the panel they are more or less going to be at the same height - they will be hung off the bottom of the deck joists.
 

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I would put the valve at the panels, opposite (far end) of where the water enters the panels. If water enters the panels on the lower right of the array, I would put the valve on the lower left.

I defer to Isaac, if he has any disagreement with what I just said.

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I would agree that this is a good place, as mentioned above there is debate on the topic. Traditionally the placement would be at then highest point, however if the pressure is marginal at that point then air may sucked into the system, this is particularly a problem with variable speed pumps since people often tune them for minimal functional flow, therefore locating the vacuum breaker a little lower near the feed point of the panels makes for a good compromise since it still prevents excessive negative pressure before draining yet insures a slight positive operating pressure if there is flow in the system. Others may suggest lower to the ground on the feed side for priming reasons, with only 12 ft of lift from the pump anywhere mid way up or higher on the feed side should be ok in reality though.

Ike
 
Thanks. I appreciate the consult. I also plan to plumb in a hose bib as a drain on both the line out and the line in from the panels. I will put those back at the pump since it is the lowest point. I am also planning on adding blocking under the joists to pitch the lines so that they are pitched down back towards the pump. This will help drain things out in the winter.
 
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