Energy Matters Forums

[danneva]

Heat is lost from your pool in three ways: through evaporation, radiating heat to the atmosphere and by loss to the ground for in-ground pools or through the walls for above ground pools. While there is little that can be done about the last of three heat losses, the others can be minimized through the use of a solar pool cover. A solar pool cover acts to reduce evaporation, trap heat in the pool water and keep leaves and other debris out of the pool.

[solarexpert12]

The idea of a solar pool heater is much the same as any solar water heater. The only big difference is that instead of using a tank to hold hot water until you need it, a pool circulates water continuously which means that you have to alter the design such that the water is heated as fast as possible.

In order to heat the water as fast a possible, you want to expose as much surface area of the water to the sun as possible because the more surface area, the more energy it will absorb.

Building the solar pool heater itself is pretty simple and straightforward. You can use 500 feet of 10mm black irrigation piping and a couple of valves and some interconnecting piping.

All you have to do is coil the piping nice and tight around itself and flat. You can use a little bit of hardware to secure the coiling so that it holds form. You want to make sure that you have easy access to both ends of the piping because these will be where you route the water in and out of your pool heater.

[sealbasher]

I recently brought home from work 3 coils (made them up in workshop) of 1/2" swagelok staInless steel tubing. 6m lengths tightly wound were only about 300mm in length. I fitted 2 of the coils in the flue of my Chiminea wood fire and the 3rd coil was actually in the fire box. They were all linked up with swagelok fittings and the inlet and outlet poked out the top of flue. I got the fire going and was disappointed that my 15C water only came out at 30-38C with fire raging. This was at a flowrate of 9l/min. Plan was to heat my swimming pool. The other problem i had was leakage, no matter how tight my fittings were done up the heat must have expanded the joints and small leakage resulted. My pool is ~50,000liters so would take too long at this rate, and overall uneffective. Has anyone else tried this with copper? I still would like to experiment more with this....

[zzsstt]

At 9L/minute in 1/2" pipe water is travelling at about 1.2m/second, so in a 6m coil it is only exposed to the heat for 5 seconds. In a 0.5" pipe, as opposed to a very narrow (high surface area to volume) heat exchanger, gaining possibly 25C in 5 seconds is not bad going!

Remember you can heat a small amount of water to a high temperature and then dilute it, or a large amount of water by a small amount. It is not completely safe to have a jet of 70C water going in to your pool - people get scalded! The same warnings apply to the system in general - if the pump stalls, the water boils and sends steam and boiling water everywhere.... unlike an "official" pool water heater your's probably has no sensors to detect pump failure and instantly dowse the fire (given that you can't just turn off the gas!). Again for making sure the water is flowing before you light the fire - otherwise the first water in the pipe boils and comes out as steam!

The leakage problem should not happen. Presumably the joins are not exposed to direct heat? If the joins are in the fire then there may be problems, but as long as they are outside they shouldn't get much above the water temperature?

Then, of course, it comes to energy. The specific heat capacity of water is 4.2J/g/C (roughly), so to raise 50,000L by 5C would take:

4.2 * 1000 * 50,000 * 5 = 1050megajoules

At 70% burning efficiency, hardwood generates about 10megajoule/kilo (Wiki). If your heat exchanger was 100% efficient, and could convert all that energy, and your chiminea could burn the wood at 70% efficiency, you'd still need to burn 105kg of hardwood to heat your pool by 5C.......

[Tracker]

At 70% burning efficiency, hardwood generates about 10megajoule/kilo (Wiki). If your heat exchanger was 100% efficient, and could convert all that energy, and your chiminea could burn the wood at 70% efficiency, you'd still need to burn 105kg of hardwood to heat your pool by 5C.......

Now, does that not bring you back to earth with a thump.

It makes it pretty clear that only solar, could be considered as energy efficient.. Sounds like the old roll of polly-pipe on the pergola is the answer.
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