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solarozq

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Posts: 19
Reply with quote  #1 
Before last winter I made an air heater which we used for several weeks. It was effective but as the weather became warmer I removed it. It was in storage for several months taking up quite a bit of space. This winter was very mild so we didn't use it. Rather than leave it sitting gathering dust I decided to turn it into a pool heater. I made a video describing the steps I took. In addition I made a second pool heater, they are both covered in the video. The new heaters use minimal power and seem to be locally raising the temperature of pool bottom (shallow end) by about 0.4C/day (without the pool filter pump running, and cover in place). The heaters have a temperature controller which only draws mA, the associate pump only runs when the heaters are up to temperature typically (in the spring) 40 seconds, 4 times an hour for approximately 4-5 hours a day.  Which equates to 13.3 min/day. As the associated pump is only 400 watts the total power use is negligible. The heaters have only been in service a little over a week.
The heaters contain approximately 175m of 13mm I.D. poly pipe which according to my calculations should have a capacity of 23.22 litres.  The run time is 40 seconds which appears to equate to 929 litres/pump. This seems awfully high for a small pump (however it is pumping against almost no head).  
Only time will tell what the long term effect will be but so far it's looking promising. 
If anyone is interested I will be happy to supply details not dealt with in the video 


Nov 2019 Update
With the cover on the pool, the pool bottom temperature slowly crept up to 30C. However with the cover removed the set up was not able to maintain this temperature, it is slowly dropping. It is late spring.
I re-positioned the panels to catch the sun longer for the summer sun.
I have ordered a second temperature controller such that either panel being up to temperature will start the heater feed pump . 
I had to raise the submersible pump such that the pool cleaner does not catch it.
The set up is generally going well.
Has anybody considered wash and waxing their water heater polycarbonate to keep it clean and protect it?

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stmbtwle

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Reply with quote  #2 
Nice setup, though I'd be worried about melting the tubing in the glazed unit, if the power ever fails.
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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
solarozq

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Posts: 19
Reply with quote  #3 
That's true but historically in this area power costs are pretty rare. Another source of concern may be gradual algae build up.
I already have one pump failure cover and will be buying another one.

I gave my numbers more thought.
No pump curve was supplied but based on 8000l/hr and an advertised 5m head the minimum flow should be something greater than 2.22 l/sec (as the head is much less than 5m).
That would suggest each pump session would heat a minimum of 88.88 litres of water by approx 19C. (The pool bottom temperature was 21C and the discharge about 40C). 
Based on the initial pumps of approx 4 pumps per hour for 5 hours/day that would give 1777.6 l/day heated by approx 19C. 
As the pool heats I can raise the pump start temperature to maintain the 19-20C differential. Summer weather (still a few months away) should cause the time between pumps to reduce and may increase the period of pumping slightly, this should give a gradually improving performance (for several months).  
The two heaters contain different amounts of poly pipe, the pump is controlled by the temperature of the smaller 75m unit, I noticed that by the end of the pump cycle it's temperature had fallen (stopping the pump) but the larger 100m heater discharge pipe was still at the full temperature.  
stmbtwle

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Reply with quote  #4 
Once installed the pump stats are pretty much meaningless except as an estimate. Try running the collector discharge into a bucket of known volume and timing it.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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