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stmbtwle

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Reply with quote  #31 
With air and water temps within a couple degrees, probably not much. Even sitting in the sun, a small-car radiator by itself isn't going to capture much heat; which is why the collector box. It's kinda like a funnel. Here in Florida, though, I might get good results by simply putting the radiator in my attic (hmm something to try). I use a small storage because this IS an experiment and I don't want to wait all day for results.

I'm using a small "solar" pump, which puts about 1 gpm (~4lpm) through the system.  By reducing the flow I can get higher output temperatures, but at reduced volume, so I think it's a zero gain proposition. 

As storage temperature (input to the collector) increases so does the overall collector temp (and the output temp) which makes sense as the actual energy.

I'm going to try a screen in the thing and see if I get any improvement.  If I set it up properly should be able to get some reference temps, then put in the screen and try again in a few minutes.

I like the concept as it's a whole lot easier to build than a water-tube collector, but I'm not sure the integrated system is the way to go.  I'm still worried about stagnation temps wrecking the fans, and it doesn't lend itself well to expansion.  I think an ordinary air collector with a separate or attached "radiator box" might be better.  Additional collectors could simply be ducted to the box.  One could use any design collector.

Any of you air-collector guys want to try that?

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Willie, Tampa Bay

paolometeo

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Reply with quote  #32 

Dear  Willie, Dan, Budwyzer

I followed your discussion with much interest . I thought that it should be better to give you more details about ARETHA prototype working in Milan. So I send you two more detailed sketches about ARETHA size. Furthermore I want to show  you a graph made by data collected three days ago.  Now ARETHA works with a 5 m2 collector surface and a radiator belonging to a 98 kW (131 HP) car (power at the wheels). Only one of the two fan is working. The pump run 24 h a day because we do not want to overheat the tank, but in normal conditions the automatic system switch off the pump when temperature difference between air and water drops below  a fixed threshold. In the graph you can see:

The solar irradiance measured on the collector plane by a Kypp&Zonen CMP radiometer ;

The water temperature in the 950 liter tank (the fast decrease during the night is due to the running pump);

The external air temperature, close to the collector (in the shadow of the back);

The temperature difference between internal air and water inside the radiator.

 

In similar situation we have computed the energy added to  the water after one clear sky day: it is about 11 kWh.

 Thank-you for your attention

Paolo
Diapositiva3.PNG  Diapositiva4.PNG 

GR_20140515.png 


stmbtwle

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Reply with quote  #33 

Paolo,
Thanks for the comeback, I was wondering when we were going to hear from you again...  Your collector is very similar to what I had understood, and built in a much smaller scale.  I have a few questions though:

How do you have the airflow set up?  is it down along the glazing and up along the backplate?

As the radiator looks to occupy the depth of the collector, I guess it takes its intake from the sides.  Is this correct?

Do you think adding a divider/absorber or screen would help?

I'm very impressed with your concept.  You get a big high power collector at low cost/labor.  What are you planning to use it for? 

Thank you for the info.


Thought:  A second radiator unit mounted remotely could be used to heat a home...


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

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Reply with quote  #34 
Quote:
How do you have the airflow set up?  is it down along the glazing and up along the backplate?


The fan sucks the air, so the airflow goes from the back to the glaze.

Quote:
As the radiator looks to occupy the depth of the collector, I guess it takes its intake from the sides.  Is this correct?  Do you think adding a divider/absorber or screen would help?

Yes, correct. We still have some problems to push air till the edge of the box. Temperature difference between the box center and the outermost point is still too high. Of course, changing the geometry can improve the air mixing inside the box. But we want to preserve the building simplicity.

Quote:

I'm very impressed with your concept.  You get a big high power collector at low cost/labor.  What are you planning to use it for? 


We plan to optimize the geometry and to issue a detailed description of how to build one ARETHA with very cheap materials. A big collector, as this one (5 sqm and 950 liter tank) can be useful, for instance, for heating greenhouses by night or providing hot water to the washing machines of an Hospital somewhere in Developing Countries.
stmbtwle

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Reply with quote  #35 
It looked like it was intended for "developing countries", and my guess was hospitals.  I commend your research, they need all the help they can get!   Just out of curiosity what radiator are you using?  My guess would be a Toyota Corolla, just about the most common car on the planet.

Just finished a quick test with a screen today:  

Screen:           1 layer "solar" screen.  (twin "standard" screen might be better, and easier to come by)
Collector size:  2'x4'  effective area    .675 sq m
pump:             just over 1 gpm          4 Lpm
Water storage:    6.3 US gal (53#)      24 L  
fans                2 @ 40 cfm (rated)      2.264 cu meter/min
radiator           Oil cooler 10" x 14"      .09 sq m
Glazing            6.0mm twinwall

Test without screen (empty box):

Start:  1232 EDT     Water temp 86F / 30C
Stop:   1302                            97F /  36.1C        + 11F / 6.1C      581 btu  .17 kwh

With screen divider:

Start    1310 EDT    Water temp 86F / 30C
Stop     1340                           99F /  37.2 C        + 13 / 7.2 C       687 btu  .20 kwh     + 106 btu / .03 kwh   + 17.6%

Difference with screen nearly 18%

Admittedly this is a small collector and a short test, but it's something to think about...





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

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Reply with quote  #36 
What do you mean with "Screen" ? Is it the glaze? If it is, I wonder that it is so thin (0.6 mm)
stmbtwle

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Reply with quote  #37 
Paolometeo,

My glazing is 6.0mm twinwall, not 0.6mm.  Sorry about the typo.

The "screen" is a divider made of black fiberglass window screen down the middle of the collector box, midway between the glazing and the back of the collector. My fan discharges in front of the screen, and the air has to go through the screen, picking up more heat in the process (same concept as Scott's screen collector http://www.simplysolar.supporttopics.com/post/double-layer-screen-solar-hot-air-collector-the-reference-standard-6086944?&trail=10). I used a single layer of "solar" screen, but two layers of "standard" screen are thought to be better. You'll find lots of discussion in the air collector section. I'll try to draw up a diagram for you.

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

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Reply with quote  #38 
More pix for those interested:

http://s71.photobucket.com/user/stmbtwle/library/Solar%20collector


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

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Reply with quote  #39 
Very interesting pictures, thank-you Willie! Have you considered to measure the efficiency of the whole device? I mean, energy stored in water divided by solar energy falling down.
Paolo
stmbtwle

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Reply with quote  #40 
I would, but I simply don't (yet) have the equipment to do that.  I rather doubt it is anywhere near as efficient as a straight water collector; I think its advantage is cost and ease of construction. 

From Build-it-Solar: "Of course, efficiency is not the only important characteristic of a collector.  Its durability and price are also of great importance.  A collector that is 5% more efficient, but 30% more expensive than another is not a good deal"

I want to build a couple more units so I can do some side-by-side comparisons of some ideas I have.

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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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