Solar heating a swimming pool

[Dengue]

Well, this does have a little bit to do with woodwork, as my solar heating array is on a timber backing, and supported at the optimal angle by a wooden frame. The array is 50m of 13mm irrigation pipe, laid in a spiral formation on a plywood backing 1m x 1m, and inclined at 25 - 45 degC for here in the tropics, depending on the month.

We get 5kWh per sqm of solar heating each day here in winter, so will probably need a couple of arrays.

What I need is a suitable pump, preferably submersible solar, that will pump water from my pool, through the array, and back into the pool. I am not sure if solar pumps can push water over 50m length, with a head of 1m above the pool deck. The pool is 2m at the deepest part, but I would be taking water out from the shallow end.

I know that you are all quite practical, so any helpful comments and suggestions please?

It would have been ideal if I could have got it to work as a siphon, but that is not the case. Something to do with hydrostatic pressure between intake and outlet in the pool being inadequate. ( not enough height?)
regards,
Jill

[The Bleeder]

Jill,

It's not that it has to push water through 50m. It's how much pressure/power is required to lift it 1m. Gravity usually takes over after that.

Check out some of the pool manufactures' sites.

Mine has to lift it nearly 3.5 meters to the top of the shed. Pool mob did the lot.

[arose62]

I'd guess you couldn't have any thermo-siphoning happening because you have a spiral layout. This would mean that half the time the heated water would be expected to go down (hot water rises).

Typically there is a (fairly) obvious bottom-to-top path through the solar collector for thermo-siphoning.

Cheers,
Andrew

[pawnhead]

I know nothing about solar pool heating, but I can't see that the head would make much difference at all until it gets to such a height that it creates a vacuum and crushes the irrigation line. That is of course if it's a closed system with no leaks. The water going down balances the water coming up, the only difference being the density. The hot water going down is slightly less dense so it would need a slight boost to bring it past a balance and give a bit of flow.
It's like an elevator with a counterweight. The elevator may be very heavy, but it's easy to lift because of the counterweight.

I'd try a cheap, small, in-line pond pump on the cold side, and see if it gets a reasonable flow going.

[Dengue]

Thanks for all your interesting replies. I took John's advice and tried a small 16W, 12 Volt submersible pool pump used for fountains ( from Bunnies, $40) with good results, although the array had to be primed first.

The flow rate was 1 litre / minute, just about right, the outlet temperature at midday on the last day of April was 8degC (36degC) more than the pool water at the intake to the pump (28degC). There wasn't much solar heat gain outside of 9.30am to 3.30pm, so I switched off the pump at3.30pm.

So with that flow rate heated 360 litres over that 6 hours of operation that day, with the water boosted from 4- 8 degC, depending on thetime of day, and the cloud cover.... Only trouble is, the pool holds 20,000 litres

Back to the drawing board and budget. Looks like it really needs about 5 of these panels to heat the pool by 1 degC, which is then lost overnight

regards,

Jill