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poor performance and condensation - Page 2

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Posted by Solar Flare on April 9, 2006, 4:34 pm
 
Where the liquid can get in it should be sealed (allowing for
different thermal coefficients)

The vent should be somewhere else.



Posted by Gary on April 8, 2006, 6:39 pm
 
Tom wrote:

Hi Tom,


If I am reading your numbers correctly, you are getting a 12F temperature rise
from inlet to outlet at 1gpm flow in full sun?

A panel operating at 60% efficiency in full sun might be expected to collet:

Qout = (40 sqft) (250 BTU/hr-sqft) (0.6 efic) = 6000 BTU/hr or 100 BTU/min

This would heat 1 gpm (8.2 lb/min) by:

dT = Q/W*Cp = (100 BTU/min)/((8.2lb/min)(1.0 BTU/lb-F) = 12.2F

So, to this rough check, the panel's performance seems to be roughly what one
might expect.  Did you actually measure the 1gpm, or?

SJC's explanation seems plausable to me.
I guess the first thing I would want to do is make sure there are no leaks in
the absorber plate or manifolds by pressure testing them.  Then you could
concentrate on trying to find where the air leak in the case is?

Gary

--


Gary

www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects









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Posted by Tom on April 8, 2006, 7:00 pm
 Gary wrote:

Hi Gary,

Thanks for the reply. Yes, I sampled the water leaving the bottom of the
tank and the water returning to the tank at one GPM as indicated by an
inline flow meter. I have doublechecked the flow meter for accuracy and
it seems to be pretty much on the money.

You calculations may indicate that my system is undersized for my 75 gal
tank and for my water usage here at the house. Perhaps now that I have
the panel running to a suitable level of performance I should think of
adding another collector to boost overall daily temp gain.

Back to the drawing board.

Thanks again. All I have been getting from the manufacturer is that this
panel should be making 160 degree water in the dead of the night in
Greenland and I must be screwing it up to not be getting that kind of
performance (excuse the "slight" exageration). It's good to have some
input that lets me know that I might just be getting al out of the
system that I can get now that the condensation issue seems to be at
least identified.

Knowledge is good!

Posted by SJC on April 8, 2006, 8:28 pm
 

  I would say that if you are getting 25,000 BTUs per day with that one
collector, you are doing pretty good. With over 600 pounds of water
in a 75 gallon tank, 25,000 BTUs you can take your tank up more that
40 degrees F. Your efficiency will drop as the water gets hotter, so
even 60% efficiency seems pretty optimistic. If you take a look at
the Sunearth Imperial they spec maybe 50% at 35F above ambient.
http://www.sunearthinc.com/imperial_series_flat_plate.htm
You may have gotten the moisture out and if you reseal it that could
be it. The question is, how did the moisture get in there during =
shipping
without a leak?

Posted by Solar Flare on April 8, 2006, 10:07 pm
 Drill a very small vent hole in the bottom where the liquid should run
to. The breathing that happens should stop you condensation problems
and not affect the performance.

Warranty? I don't believe in them anyway. Most are just a rip-off
selling hype.




house in

support

condensation

BTU/min

roughly

  I would say that if you are getting 25,000 BTUs per day with that
one
collector, you are doing pretty good. With over 600 pounds of water
in a 75 gallon tank, 25,000 BTUs you can take your tank up more that
40 degrees F. Your efficiency will drop as the water gets hotter, so
even 60% efficiency seems pretty optimistic. If you take a look at
the Sunearth Imperial they spec maybe 50% at 35F above ambient.
http://www.sunearthinc.com/imperial_series_flat_plate.htm
You may have gotten the moisture out and if you reseal it that could
be it. The question is, how did the moisture get in there during
shipping
without a leak?



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