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Posted by Tommy on August 20, 2008, 2:08 pm
Thanks Morris. I was vague I guess. I was just thinking of making a wall
unit that may hold heat for some amount of time after the sun was gone.
No DHW needed, just a self contained unit closed loop with
thermosiphoning. The inner back side of unit could be tiled flat black.
Is any of this practical?


Posted by Morris Dovey on August 20, 2008, 5:25 pm
Tommy wrote:

(caught in a time crunch...)

A collector is almost certainly practical. Thermosiphoning is certainly
possible. The details of the design and the performance amd the cost
trade-offs all need to be worked out.

I'm going to be busy all afternoon - and will try to be more helpful
this evening. In the meanwhile you might provide a bit of info that'll
help others help you: how old are you? How much math and physics have
you had? Where are you wanting to use the collector (theres a lot of
difference between northern Minnesota and southern Florida!) What skills
and tools can you bring to bear on the construction? Tell about your
weather (typical and worst case) during the heating season, etc.

Meanwhile, feel welcome to browse my web site for ideas (and there's
some info about my background there, too.)

http://www.iedu.com/mrd/mrd_res1.html  (my background - dull)
http://www.iedu.com/DeSoto/solar.html  (solar starting point)
http://www.iedu.com/DeSoto/Projects/   (some of what I do)

You'd do well to explore http://www.builditsolar.com  to look over Gary's
  website - there's a wealth of DIY info there/

More later...

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by Morris Dovey on August 21, 2008, 12:46 am
 Morris Dovey wrote:

Ok - here are a few design factors to consider...

# Losses are what rob panels of efficiency and spoil performance. These
include thermal conduction, reflection of incoming energy, re-radiation
of captured energy, and airflow inhibitions (which can exaggerate losses).

# Absorber design strategy can play a major role in determining panel
efficiency and performance. To illustrate:

The most common strategy is to present a front-facing flat surface that
is heated by transfer of energy from impinging photons. Nearly all
reflection from the surface will be directed back toward the glazing, as
will most of the re-radiated energy.

My own strategy has been to use low-mass aluminum ribbons formed and
arranged in such a way that an absolute minimum (less than 1/2 of 1%) of
reflected energy is directed toward the glazing - and to position these
ribbons in such a way that not only do they absorb on both 'front' and
'back', but so that the energy re-radiated from each ribbon is mostly
directed toward a neighboring ribbon instead of the environment.

# Transfer of energy from the absorber to the air inside the collector
can be managed. As air is heated it becomes more viscous. You can
improve airflow and heat transfer by minimizing the amount of contact
between the warmest air and internal surfaces. Note that an absorber
with a single flat surface is the worst case scenario because air at the
surface becomes more and more hot and gooey as it attempts to slide upward.

My strategy was to break the flat surface into horizontal ribbons so as
to limit the amount of time any given "piece" of air could be in close
proximity to the surface. It's a PIA and it's costly to build, but it
works ever so much better.

# Airflow within the panel is more important than you might guess. It's
an important part of helping the panel run cooler.

I've had a lot of good help from the folks here on alt.solar.thermal -
I'd suggest not being bashful about asking specific questions and taking
the time to think about the answers you get. There have been times when
the answer to a question I asked led me to think about something else
that was more important still...

I hope this helps to get you started. <g>

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

Posted by Tommy on August 21, 2008, 2:39 pm
  Morris I'm 43. I'm not a math wizard not even close.  I have just an
H.S. education. joined the Navy.  I rebuilt weapons support equipment on
the USS Nimitz for about 3, and a half years. Worked 11 years as an
maintance mechanic for Dart Container plastics co. Worked for an OEM
brake pad co. Akebono LLC as a maintance mechanic. Presently working for
Omnicare Medical systems as a maintance mechanic. Allot of experience
with liquid to liquid heat exchangers, hydraulics, electrical,
pneumatic's, new machine setup,  industrial jet printers, ac & dc
servo's, mill work"metal", welding"mig, tig", sweat fitting, most
plumbing, machine heating , and cooling "natural gas, electric heaters
all types, and anti-freeze, glycol, freon", some PLC's and allot of
metal & Lexan fabrication.

 Also auto body work, carpentry, farming, and most any auto mechanic
work. Love building offroad Jeeps.

Anyway I'm located in south central Ky, I already have long, lat, and
winter degree angle figures printout somewhere. I have only have one
panel location on my home right now, which is a south-south west
position. Panel can be up to 8'Hx8'W.

Morris you have been around, impressive background. You must be in your
early sixty's.


Posted by Morris Dovey on August 21, 2008, 6:01 pm
 Tommy wrote:

Wow! You have a whole pile of experience that I really wish /I/ had! I
was about to make a list, but it would've come out just repeating yours.
I wish you were closer - but then I'd probably be a pest...

Now I can see how you might prefer a fluid-based system, and I'd like to
encourage you to think of air as a fluid in the context of solar energy
collection. I'm partial to air for collection because it appears to
offer advantages for passive systems - but I think that liquids might
offer major advantages for heat storage.

It helps me to know something about who I'm talking to. On usenet it's
hard to know if I'm talking to is a grade-schooler working on a science
fair project or a physics professor. Everybody seems to know things I
don't, but I've always figured that works in my favor by providing
opportunity to learn new and interesting stuff.

It's been a while since I visited your area - I have memories of warm
hospitality and beautiful country...

An 8x8 should produce enough heat to reward you well for tackling
the project.

Early sixties would be good - I'll take it. <g> Most of the rest was a
matter of being lucky enough to be in the right place when there was a
problem I could help solve. When I've done well, it's hardly ever been
all by myself. Strange how that works...

Morris Dovey
DeSoto Solar
DeSoto, Iowa USA

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