confused about solar panels (or mats)

[matt4x4]

Hi Farmgirl,
I think I explained this to you last year....
First off, there's no difference between IG and AG panels, when looking at the kit, the difference lies purely in the accessories they soak you another 100 dollars for when getting the IG panel, however, panel costruction and operation normally does not differ.

edit...
Ok, after trying to get the make of my panels, I came across some info regarding certain companies and different construction between IG and AG - Sunheater by smartpool, does things a bit differently, they use open manifolds on both ends, thus utilizing each panel in a one directional flow, essentially the panels all get tied together in parallel on one end to feed and the output sides all get tied together to collect back to the pool - this should make each panel's efficiency pretty much equal seeing that the water on the input side is the same temp for each panel.
Here are their instructions for both the AG and IG panels - hope this helps some........it sounds like your 4th panel is like thse IG from this Company...

http://www.smartpool.com/website/sun...%20English.pdf aboveground

http://www.smartpool.com/website/sun...%20English.pdf inground

end edit

When looking at the split manifold panel, there is a header manifold at each end of the panel, the 2 oposing headers are different internally.
One header has a SOLID block in the middle, this is the input/output header, water flows in and gets forced up half the panel because the block will not allow water straight through, once it reaches the other side of the panel, it enders into the open header (which should have caps on either end), this header does NOT have any blockage in it, the water from half the panel fills this header and pushes down the panel in the opposite direction, going back to the input/output header. Now the water reaches the input/output header on the previously dry half, and flows out the pipe, this pipe either gets connected back to your pool return or to the input/output header of the next panel and the process repeats itself.

Air pockets play a big part in the functionality of these panels, if air gets trapped in the open header, it may render a portion of that panel useless, the only way to get rid of trapped air is to place purge valves at each panel's highest point, depending on how the panels are mounted, this can mean several valves.

The most efficient way I found when mounting panels on a roof is side to side, feeding at the very bottom, with a checkvalve (automatic one way valve) in line to stop gravity from draining the panels backwards when not under pressure, this will allow the air to travel upwards working itself up and out of the panels naturally, once the air is purged from the panels, it will stay purged since there is a check valve at the input on the bottom.
Thihs method also only requires one air bleeder valve at the top where your panel meets your return line going back to the pool - this bleeder will automatically purge any air that makes it to the top of the panel, but not allow any air back into the system.

I think I drew a diagram last year, but can't find it on my PC.