Solar 'geothermal' Tank Heating
Posted 26 April 2014 - 01:48 PM
The outdoor tank is now plumbed into solar heating and underground temperature stabilisation.
Schematic included here:
Solar Geothermal Sketch (II).jpg 27.92KB 5 downloads
The solar heater is very simple, made from Bunnings reticulation piping, and then put in a box with a clear polycarbonate cover. It's pumped by a solar fountain pump, so that it won't run unless it supplies heated water.
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It's unlikely to overheat the tank, as the poly-pipe ground coils will absorb big temperature differences.
Today is overcast so it's going very slowly, but the water coming down is still half a degree warmer than the water going up.
The tank slipped to 20C last week when the night-time temp was in the single figures, and the solar panel wasn't yet running, but is sitting steadily at 22C now. We'll see how far into the winter it will get before I have to put in the electric heater.
Here's the tank concerned.
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Posted 26 April 2014 - 03:00 PM
Posted 26 April 2014 - 03:30 PM
And thanks Malawiman, the proof will be in the pudding as they say...
I had a trial run a week ago, and it raised the temp 2C in one afternoon (it doesn't get the sun until 11am), but it had a leak and had to be pulled down for rebuilding. Hopefully now it will be mostly set and forget.
Posted 26 April 2014 - 03:58 PM
I am interested to see how it goes myself.
The reason I actually thought of Ruperts experiment was that he had used plastic as well, to ill effect. He was pushing the temps much hard though, by using the electric controller.
I will be watching with interest!
Posted 03 September 2014 - 07:36 AM
Well.... winter has been and gone - officially at least.
Here's how the experiment went. The home-made solar panel worked of sorts, it just wasn't big enough at first and my workmanship was not sufficient to make it completely air-tight.
If the joints suck in air then the panel empties overnight, then the little solar powered pump couldn't get the water up and over the height of the roof in the morning. I got over this by re-routing the canister filter flow to help it along and that worked well. The panel was too small however and in June I had to install a 200W heater to provide a 'floor' temp of 20C. Not bad considering we're talking a 770L tank outside in the winter - and it was still thermostat 'off' much more than it was on.
Then mid-winter all of a sudden it couldn't keep up on the cold nights. I realised eventually that the ground temperature had dropped below 20C as well (2.5m down in the ground) and I had to divert the flow from the ground coils, then that was fine too. At the same time I rebuilt the panel (again), this time out of all PVC painted black and then that worked better too.
Now it's early spring and the electric heater seems not to run at all anymore, the tank is maintaining about 21.5C.
Have I saved money? No, not yet. Has it cost me a lot to set up? No, just a a fair bit of time and effort to set up and learn from my mistakes. Next winter, touch wood, I’ll just be to just plonk it back on the roof and away it will go. Maybe start a bit earlier in the season so that the ground might start from a warmer state.
The next project might be a tank rack in the shed, in which case there will definitely be a similar larger set-up on the roof. It will be easier in fact, because the water won’t have to rise so high.
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