Ok, what I have is the same concept: Go to LeisureLiving.com and look at their FantaSea pools for the decking.

It's not concrete, it's a hollow plastic panel, 4'x2' and about 1" thick. It's hollow and has to be completely supported along all four edges (but not in the middle). There's about a 1" intake at one end and an output at the other end. The water snakes through it and that's how my solar deck works.

But I think a clever person could design an in-ground system using these panels. They come in gray as well as brown...You'd need a shallow trench 1' 6" wide to support the panels on concrete. You'd need cross pieces every 4 feet and room for the connecting hoses. And you'd need very good drainage of this trench.

But if you want to embed piping in concrete I suggest you check out installers of in-floor heating. A flexible tube is buried in the concrete near the surface to heat it. I can't think of any reason why that wouldn't work in a deck to absorb heat rather than emit it.

But you'd have to be VERY careful with you site prep to avoid damaging the piping if there's any settling. And you'd have to be VERY careful with your winterizing to get all the water and antifreeze in.