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stmbtwle

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Reply with quote  #51 
The lower air flow does give higher air temps inside the collector, but the object is to get all that heat into the water. To do that I need to move the hot air through the heat exchanger, and that means airflow (and fans). I don't doubt that a larger radiator or multiple radiators (2, 6, 10?) would be better, but would also increase complexity and cost, which IMO is not in the spirit of the thing.

So far, it appears that increasing airflow increases transfer... more to come.

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Willie, Tampa Bay

stmbtwle

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Reply with quote  #52 
Finally got the side-by-side test with the ARETHA collector with, and without the fans. Both collectors are identical black-box type with no collector other than the box itself. Both have 10" x 12" heat exchangers (oil coolers) mounted in the top of the collector. Both have identical pumps (about 4 lpm). ONE collector has two 120mm computer fans to force air through the heat exchanger. Otherwise they are identical.

Both collectors were fastened to the same frame and set up facing roughly due west into the afternoon sun. The pumps were connected to separate containers with 1 gal of water. Both pumps and the fans powered from a 12v battery.

Test started @ 16:45. Water starting temp 93F. Ambient air temp 95F. Weather cloudy.

Pump output temp difference was less than I could measure, so I had to measure the cumulative difference over an hour.

Start temps: air 95 F, Water 93F.

After 1 hour:
Collector w/ fans: air temp 120F, water 118F
Collector w/o fans: air temp 153F, water 106F.

Observation: The collector with fans runs cooler, yet transfers more heat to the water (output).

Conclusion: Fans are required in this type of collector for it to run efficiently.

I am not going to run this test again. Further experiment will address fan size and absorber types.

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Willie, Tampa Bay
solardan1959

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Reply with quote  #53 
Another video on the ARETHA idea.


The more I see it, the more it seems reasonable,  Willie, have you thought about the minimum size box needed to generate the heat needed to heat the radiator?

Dan


stmbtwle

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Reply with quote  #54 
Hi Dan sorry about the delay...

No I haven't considered the "minimum size needed".  Paleo's collector is about 5 sq meters (50 sq ft).  I don't think you could physically get an auto radiator into anything much smaller than 4x8ft which is about 3 sq meters.  Of course it depends on the size of the radiator. To save space I used an oil cooler and computer fan in my smaller collectors.

In reality though it's like an air collector.  Size "required" is dictated by how much heat you need.  The more heat you want to take out of the system, the bigger the collector needs to be.  Temperature is dependent on input (sun) vs output (pump), the radiator is just the "middle man".  The bigger the pump, the faster you circulate the water, the more heat you can take out of the system, and the cooler the collector will run.  Just like using a big blower with an air collector. 

IMO the storage is the key, not the collector.

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mattie

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Reply with quote  #55 
A lot like Russel Benoy's greenhouse setup apart from the plants  http://www.builditsolar.com/Projects/Sunspace/GreenhouseHX/HeatPumpEnergyStorage.pdf
stmbtwle

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Reply with quote  #56 
Yes very similar, and the concept is the same.  The only "real" difference is the Aretha is a dedicated collector.

Here's another from BIS using (you guessed it, a radiator): Low-Cost Active Heat Storage pdf ....

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

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Reply with quote  #57 
the fans help with heat transfer but you could use low power computer fans and get as good results.
A thermosyphon could work well with proper box design, just provide a channel for the cool air to return to the bottom of the box to get circular flow.
_____
1\   1
1 1  1
1 1  1
1 1  1
1___1

where the backslash is the radiator but at a more horizontal slant.
You would still need to pump the water, but the water would cool the air and it would drop through the rear channel and help push the hot air back to the top.
stmbtwle

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Reply with quote  #58 
That's pretty much how it works, and I DO use computer fans.

Thermosyphon works but not that well, I've tried it. Fans make for better heat transfer in a side-by-side test. They also allow more flexibility in mounting.

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Willie, Tampa Bay
involute reflection

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Reply with quote  #59 
stmbtwle

looking at your pictures it appears that there is no center divider between front and back, by having a longer channel it would increase air flow, from what I've read here  screen would improve performance also.
involute reflection

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Reply with quote  #60 
another thought, base board heaters have copper pipe with many aluminum fins, I don't know if you can remove the heater from inside them, but if you could they would make good collectors for this type project as they could be connected end to end to fit even very long boxes and would sit happily at the top of a thermosyphon box (or fan assisted if needed).
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