Solar Pool Heating

[jedi127]

I am from New Zealand and new to this forum. I have tried to follow comments on home made solar pool heating using 1/2" black alkathene pipe. Maybe answers to my questions have already been covered, if so perhaps someone could point me in the right direction.

I won't be using the existing pool pump as I want to keep the pool heating entirely separate from the filtration system. The pool heating will have it's own pump.

I have an area on an adjacent fence available to me facing the sun about 75% of the pool area.

My dilema is the age old question of having either a few long lengths, or a larger quantity of shorter lengths, to gain maximum efficiency. And the trade off of water volume versus water temperature. Obviously all commercial solar heaters seem to use multiple small tubes (around 1/4") running between two manifolds. Presumably the multiple smaller tubes offer more surface area to the sun than the larger 1/2" pipe. But can that be offset by using a longer length of the larger pipe before it passes into a manifold?

The height of my fence is around 8' and I can go around 32 feet in length. So I was thing of making 4 coils 8' in diameter, then joining them up with one inlet manifold & one outlet manifold. I'm not sure how many feet in length each coil would be. Perhaps this length would be wasted with the water having already reached it's maximum temperature part way along. So instead of 4 coils 8' in diameter, I could make 16 coils of 4' in diameter, which would cover the same area.

Any help would be appreciated.

[wooferhound]

I'm using 80 feet of 1.5 inch black ABS plastic pipe. At a flow rate of 15 gallons a minute, I get almost a 2 degree rise in temprature in one pass through the system.

More info about my system here . . .

http://www.fieldlines.com/story/2003/7/8/19177/93125

[gatu]

You are not needing a very big temperature rise for each pass, so you can avoid radiative losses by keeping rise low. Your 1/2 inch pipes will keep pumping load lower than pushing the same volume through 1/4 inch. I would suggest coils in parallel, connected onto a larger diameter pipe. The higher the flow rate the greater the solar efficiency, but the higher the pumping energy. Multiple parallel systems, however are more like a large diameter pipe, and so offer reduced drag.