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Solar Barn Version 2 - Page 3

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Posted by Gary on May 21, 2004, 7:18 pm
Bert Menkveld wrote:

Hi Bert,

Its actually not as good as a window, but then windows are $0 and up a
square foot, and are not always desirable.

I guess I would agree with the two points above -- the scheme is best
suited for a buiding (workshop etc.) that is only used during the day
time.  But, there are millions of these.  I'm guessing there might be
10,000 of them around the Bozeman area (pop 40000)

I did run simulations for all of the winter months using the NREL TMY
weather for Billings, MT.  For every month, the collector is a net
gainer of heat even with the large losses at night.  It gets better in
the "shoulder" months, where we still do quite a bit of heating here.
But, I agree, the losses at night are large.

Will do.

To me, the things that were most appealing about the concept is that it
is SO simple, and it is SO easy to do.

I think that for a person who is a homeowner, rancher, mechanic ... that
spending    multiple days of effort on buiding a solar heater for his
workshop/barn is unlikely.  But, if its only an afternoon project and
only costs a couple hundred dollars, that might be another story???

I am also really interested in the radiant heat aspect.  Would this help
make up for the fact that the barn/workshop will start off at a low
temperature in the morning??

I guess I am wondering if from a "solar specialist" point of view the
first design is more appealing, but from an actual getting some built
point of view, maybe the 2nd design would be more successful??

Thanks -- Gary

Posted by Ecnerwal on May 21, 2004, 4:19 pm

In my opinion, version 2 is highly inferior to version 1.

- losses from non-insulated wall while sun not shining - nigh onto 75%
of the time during heating season. Even with your lightly insulated
barn, this is a huge difference. With a better insulated structure the
difference just increases. Might as well put in windows and get the

-inefficient collection of heat, as reflected in high collector
temperatures (which increase collector loss to the outside, which means
less heat is getting to the building). I'm not convinced that your BTU/$
is actually better for version 2 than for version 1. Given limited south
wall space, even if the cost per BTU delivered is somewhat lower, the
larger input of version 1 may be a better deal.

-both of the above mean less heat in the building. Cost savings does not
seem huge. Going to movable insulation generally costs more than fixed
insulation, and has been largely proven not to work in practice. The
humans get tired of bothering with it, it wears out and no longer works
right, is not cost effective to repair (anyone want some old "Window
Quilts"?), etc.

- cooking of the unvented collector, unwanted heat gain in summer.
Stagnation can be an impressive effect. You should soon have summertime
results to see for yourself.

- the advantages of radiant heating (over convective) are strongly
affected by distance from the radiant source. In a typical
radiant-heat-floor installation, the source is always close. A hot south
wall will have relatively little 'comfort" effect on the north end of
the barn. There will also be a "one-side" effect, most familar as
roasting your front and freezing your backside when standing around a
fire in the cold; this probably will not enhance percieved comfort.

If you want some radiant effect, you can get that (as well as mixing the
convectively heated air better) by ducting the hot air (from version 1)
across the ceiling to the north side of the barn - the heated ducts will
act in a moderate radiant fashion. They will also reduce efficiency
somewhat by restricting the airflow, but if overall comfort is improved,
that might be fine. A PV panel and DC duct-booster fan might compensate
for the added duct restriction, but add further cost and a small amount
of complexity as well.

-you can do a lot better than R4 for a garage door.

-According to your photos, there's room on the second floor for more
collectors ;-)

Cats, Coffee, Chocolate...vices to live by

Posted by Gary on May 21, 2004, 8:00 pm
 Ecnerwal wrote:

Putting in a wall of windows is not really an option for most barn
owners both for cost and use of the wall reasons?  If you put in some
windows (always nice), this collector can still easily be used on the
rest of the wall.

But, I agree its not well suited to buildings where the nightime
temperature is important.

My impression (without precise measurements) is that version 1 is more
thermally efficient.  But, version two at half the material cost and
1/6th the labor costs might be a lot more appealing to the busy barn owner?
If you value the labor at $0 per hour, cost ratio is:

        ($50 + 4*$0) / ($00 + 24*$0) = 230/780 =  1/3

There is also the mental thing that three day tasks probably don't get
done, but half day tasks might?

Yes, I agree, its hard to come up with a good movable insulation scheme.
And, it should really be automatic.

I did set up the test panel today with an extra layer of glazing and
isulation on the back side.  I put a thermocouple in, and will check it
when the weather gets warmer.

I wish I could figure out a simple way to test the radiant heat aspect
of the version 2 collector.

OK, OK -- maybe :-) -- I'm not to hot for more work 10 ft off the
ground, and my siding is not ideal for the version 2 collector.

Thanks -- Gary

Posted by John on May 21, 2004, 7:43 pm
 Why not a standard wall with an exterior of this


and it would still have a finished appearance

: Hi,
: I reported earlier on the solar heater for my garage/barn when it was
: built in February (with quite a bit of help from this group :-).  I have
: added a short update based on the past few months of service that
: suggest changing a couple things. The changes are listed at:
: http://users.montanadsl.net/~reysa/   -- then choose the "Simple Solar
: Barn Heater" link -- the update is all the way at the bottom.
: I have been thinking about a different version of the
: garage/barn/workshop heater that is quite a bit simplier yet, and have
: built some test panels that use the new concept. It basically eliminates
: the separate absorber, the collector framework, and the vents through
: the garage wall.  The new concept is described in way too much detail
: at: http://users.montanadsl.net/~reysa/ , then choose "Simpler Yet Solar
: Barn Heater" link (its about a 280k pdf).
: I would be very interested in any comments on the new concept (or the
: old one).
: Gary

Posted by Gary on May 22, 2004, 11:43 pm
 John wrote:

Hi John,
Interesting product -- I wish they would provide a little more detail on
the web site about how its built and what it costs -- I'm guessing it
might be a bit more than $ per ft^2?


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