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Posted by Jeff on August 3, 2006, 10:48 am
 
Zombie Wolf wrote:

You are thinking of a concrete bock, which weighs about 40lbs, a
cinderblock weighs less.

But there's a lot of reasons not to rely on masonry storeage. "Since
masonry conducts heat slowly, only a small portion of the wall stores
heat. It will take approximately 5 hours for heat to pass through an 8
inch concrete wall".  (The Passive Solar Energy Book, Edward Mazria).
That's part of the reason why they recommend 9 times the surface area
(the area that light strikes) of masonry storeage as that of the  area
of windows.

   A drum of water will have a much smaller thermal lag due to
convective flow of water.

    So, it is not just about mass and specific heat. It's about design.

    If you were going pure passive, I would think out the heat store
carefully.


the front step, the lower of the two tiers,

But the real question is what temperature does the structure stabilize
at? Nick has already run those calculations, and it ain't warm. And none
of that heat is available to be used elsewhere.

   Jeff



Posted by Gary on August 2, 2006, 11:52 pm
 
Zombie Wolf wrote:

My point was to put any thermal mass that is used INSIDE the shop so that when
it loses heat, the heat goes to the shop not through the R1 glazing to the
outside world.
What you are proposing is effectively a high thermal mass greenhouse.  If you
look at the references on green house design they spend lots of design effort,
innovation, and money on thermal shades and shutters to keep the heat they
gained during the day from escaping to the outside at night.  Why would you want
to saddle yourself with that problem if you don't have to?
Here is a concept you might find interesting:
http://www.builditsolar.com/Experimental/ShurcliffPart1/PolySpace.htm


There is no need to build thermal mass into the collector.  It will perform
better if it has low thermal mass.  The heat you put into thermal mass in the
collector has a high conductance path to the outside, and thats where the heat
will go.

The masonry in the structure will not make the

The idea of the collector is not to store heat. The collector has low mass, and
will start producing hot air or water almost immediately.  You can do what you
want with that hot fluid -- directly heat the shop space, or direct it over the
inside the shop thermal mass to save the heat for later.

Heat rises, in case you havent

I don't know where you got the idea of a greenhouse glazing roof?  The collector
that I think would work well for Randy's situation is 6 inches thick and
vertical -- built right on the wall.  Air enters the bottom from the shop, heats
up in the collector and rises out the top back into the shop.  This vertical
wall collector can be protected either with a modest overhang, or by just
closing the vents from the collector to the shop.  The vertical orientation does
most of the work for you, in that vertical surfaces only receive about 1/3 of
the radiation of surfaces tilted at latitude during the summer.  They collect
well in the winter and poorly in the summer.

A Trombe wall would also be an option for Randy.  This being a vertical masonary
wall around 8+- inches thick that is glazed on the outside surface.  The idea is
that the sun warms the masonary starting in the morning -- the heat takes
several hours to work its way through the wall and starts warming the room on
the other side in the late morning.  It continues to warm the room a ways into
the evening.  This is often incorporated along with direct gain to provide some
evening heating after the direct gain stops.  Unless Randy works at night, I
don't see much advantage to this approach for this situation.  You also pay a
price in efficiency -- the instrumented Trombe walls that I have read about do
poorly -- in the 20% efficiency area.  They are also slow to get going in the
morning, which seems just the opposite of what you would want in a shop?



Gary

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









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