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From: John De Armond
Newsgroups: sci.engr.heat-vent-ac,,,,misc.rural,misc.consumers.frugal-living
Subject: Re: A 16' cube
Message-ID: <>
Date: Wed, 07 Mar 2001 16:40:06 -0500

Zentuck wrote:
> "Jeepers!" wrote:
> >
> >  What the hell did he say?
> He basically explained how much energy is available to use.  Then
> explained the best ways to use it.  Provided the numbers involved so
> that the person wishing to do the project can do a cost benefit
> analysis.  By providing such a detailed post the builder can assess the
> finished product and see if it is working at a reasonable efficiency.
> Such a detailed post is a wonderful resource given freely by an engineer
> that understands what is involved and how to quantify the project.
> For me it is refreshing to see detailed answers that can be evaluated
> and checked.  While I do find much value in the posts that have a less
> technical nature they can not compare to this stuff.
> I thought it was clear and concise.  But hey I like numbers that can be
> crunched!

Yes, but with all the assumptions, it was little more than an
academic exercise in GIGO.  For someone who's going to actually try
to heat with solar, a more practical-oriented answer would be much
more useful.  Instructions for how to make a few simple measurements
along with advice on what steps to take to constrain the unknowns
would be really handy.

Following my own advice, here's what I did back in '74 to heat my
1200 sq ft house cuz I was a student too poor to afford utility

Right in the midst of the post-arab oil embargo hysteria, TVA had
published tons of documents on solar heat.  One I found particularly
useful was on how to fabricate a solar collector using (mostly)
ordinary building materials.  The collector consisted of a frame of
1 or 2X4  pressure treated boards wrapped around a sheet of metal
corrugated roofing.  The roofing is painted flat black (fancier
coatings were also listed in the paper but flat black paint is cheap
and works well.  Behind the roofing are bats of fiberglass
insulation.  Over the top is either glass or heavy plastic (I used
salvage glass).  Along the top of the roofing is a length of copper
tubing drilled with holes so that water would spray into the grooves
of the roofing.  AT the bottom is a gutter to collect the water.
The water is heated by being in direct contact with the black

I made a rough measure of the collection efficiency by simply
measuring the flow and temperature rise of water flowing through a
collector.  Then using TVA's published insolation numbers for this
area, computed what I'd need on the worst case day I wanted the
system to work.  based on that, I built sufficient collectors and
installed them in my large rural back yard facing south.  These
would have fit on my roof but I'd have had to build a mount to angle
them due south.

For heat storage, I buried a 2000 gal septic tank in the back yard
and insulated it with several inches of styrofoam board that I
picked up salvage.  No detailed computations done here - the 2k
gallon tank and the styrofoam were what I could find salvage.  To
heat the house I modified a large condenser coil by converting it to
once-thru flow.  copper tubing headers were soldered on each end
after all the elbows were removed.  This was mounted in the same
duct work that served my homemade wood burning central furnace.  A
solar cell, a mechanical time clock, some platinum RTD thermal
sensors (from the boneyard at TVA where I worked) and some discrete
logic/analog controls (no microprocessors yet.) drained the
collectors when the sun went down and/or when the outlet water
temperature dropped below the temperature of the water in the septic
tank.  This prevented freezing and prevented diluting the hot water
with cooler water.  I interconnected this control system with the
wood fired furnace control system so that if the water temperature
in the septic tank dropped below about 80 degrees, the furnace was
automatically lighted and took over heating.  I later installed
water coils in the furnace to heat the water in addition to heating
air.  The furnace fired only very seldom - a cord of wood lasted all
winter plus.

This was a case of "turn it on and see if it worked".  It did.  I
like to take that approach first and only if it doesn't work do the
formal engineering analysis.  I ended up adding a few more
collectors as I could afford them.  Total cost?  I'm going to
estimate under $500 plus a lot of (fun) work plus the favor I owed a
friend for borrowing his back hoe.  Figure 30 years of inflation and
with some clever scrounging, this system could still easily be built
for under $2k.

I believe that the system is still mostly in place but is not now
being used.  I talked to the current owners of the house a couple of
years ago.  They're still using the furnace but they've removed most
of the collectors to install a pool.  It probably served this house
for 20+ years though.

This 'back of the match book' approach probably wouldn't work in
Minnesota but it worked fine here in the Sunny Mid South.


From: John De Armond
Newsgroups: sci.engr.heat-vent-ac,,,,misc.rural,misc.consumers.frugal-living
Message-ID: <>
Subject: Re: A 16' cube
Date: Thu, 08 Mar 2001 01:05:33 -0500

Zentuck wrote:
> Neon John wrote:
> >
> > Zentuck wrote:
> >
> > > What color was the insulation?  This is a real question, I really want
> > > to know if the insulation you used was yellow or pink?
> > >
> > > BTW, Man o man I loved your post too!
> >
> > Pink.
> >
> > Well heck, they do make the stuff right up the road :-)
> >
> > John
> John,
> Did you have trouble with outgassing of the insulation?  I was told
> years, perhaps decades, ago that the pink insulation would outgas and
> fog the glass or plastic.  Word was that the problem would exist as long
> as the insulation was in place.  Every commercial panel I installed or
> had any dealings with had yellow insulation.
> So did you notice a problem and if so how bad was it?

I put the insulation BEHIND the corrugated metal.  The metal is
RTVed to the wood frame to make it water-tight so the insulation is
not in the heated space.  It simply insulated the back side of the
metal.  I did not attempt to insulate the wooden sides.

I imagine the pink stuff would offgas.  I used it to insulate the
walls of an annealing kiln for my glass shop (after stripping the
backing off, of course) and it smoked like HELL the first couple
hours of operation.  When it quits smoking, the fiberglass is just
slightly on the grey side of white.  The glass is stiff so it
obviously has some sort of coating, probably to make it less itchy.
When I need fiberglass insulation for a project now, I buy the stuff
in the pink plastic stocking.  Inside the pink plastic is pure white
fiberglass wool without any apparent coating.

From: John De Armond
Newsgroups: sci.engr.heat-vent-ac,,,,misc.rural,misc.consumers.frugal-living
Subject: Re: A 16' cube
Message-ID: <>
Date: Thu, 08 Mar 2001 01:06:35 -0500

Sechler wrote:
> "Neon John" <> wrote in message
> >
> > This was a case of "turn it on and see if it worked".  It did.  I
> > like to take that approach first and only if it doesn't work do the
> > formal engineering analysis.
> IMHO, a little preliminary engineering analysis with reasonable assumptions
> helps one determine a starting point, an order of magnitude, from which a
> prototype can be built, tested, and expanded upon.  I'm sure the TVA's
> documents listed "rule of thumbs" that were based on previous engineering
> analysis and testing.
> Joe

Oh, absolutely. TVA spent $millions of tax dollars on this stuff.
Which meant I didn't have to re-invent the wheel.


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