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poor man's trombe wall - Page 2

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Posted by nicksanspam on September 21, 2008, 8:36 am
vmpolesov@gmail.com wrote:

... 75 ft^2.

They might store overnight heat. Does the room get very cold by morning,
after an average day?

Inefficient ones. Trombe walls lose lots of heat back through the glazing
at night.

It might be more interesting to turn some of the windows into air heaters
that lose little heat at night by pushing in a tight-fitting piece of dark-
painted foil-foamboard insulation with an air gap at the top.

Or make a "heat storage counter" a 4'x2'x30" tall box with insulation on
4 sides and a 4'x30" glazed south wall (eg discarded windows) south of
a light-colored floor with lots of 2-liter water or soda bottles inside
the box stacked in a horizontal hexagonal pattern.

Water can store 2-3X more heat by volume than masonry (about 4.4 Btu/F for
a 4" diam x 1' tall 2-liter bottle, vs 5 Btu/F for an 8"x8"x16" hollow
concrete block), and glazing can make the box warmer than the room temp,
so the water can store more heat.

In December in Seattle, 420 Btu/ft^2 of sun hits a south wall. If a window
passes 80% of that and each of N layers of box glazing passes 90% of that
and adds R1 to the box and 336x0.9^N = 24h(T-70)1ft^2/N, with lots of water
in a 70 F room, the box temp T = 70+14N0.9^N on an average day, eg 82.6,
92.7, 100.6, and 106.7 F with N = 1 to 4 layers of glazing.


Posted by vmpolesov on September 22, 2008, 5:36 am

I like this idea better.  Cheap, simple, one-trip-to-the-store type of
project and no heavy lifting required. Would I put holes or air gap at
both the top and bottom to get some convection ailflow going (I think
I have seen this called a 'thermal siphon').  Thank you for this idea.

This is suprising to me.  Hollow cinder blocks I can believe, but how
about a solid block?  Of course there I suspect the issue is the whole
block never reaches temperature.

Posted by nicksanspam on September 22, 2008, 9:10 am

A 3' tall window might have a 3" gap between the foamboard and the window,
with a slot at the top but no slot at the bottom, so warm air can rise out
of the top slot during the day, with no airflow at night. With more thought,
we can make a foamboard insert with a flow organizer at the top that lets
cool room air flow down between a screen and the cool glass and lets solar-
warmed air rise up and out in another gap north of the screen.

We might let room air flow through the box on a cool day. This could work
well with phase-change materials.

Concrete stores about 25 Btu/F-ft^3, so 8x8x16" would store about 15 Btu/F.


Posted by RicodJour on September 21, 2008, 1:58 pm
 On Sep 20, 7:24pm, vmpole...@gmail.com wrote:



Posted by Jeff on September 21, 2008, 3:27 pm
 vmpolesov@gmail.com wrote:

This looks like adding mass to even out temperature swings. You will
have the same amount of solar gain with or without.

333.3 lbs at .3BTU/lb = 100BTU/F or 2K BTUs for 20F.

   Not much.

   Now lets look at 60SF of R1 glazing at say 40F temp change inside to
outside. That's 2400 BTU/hr, 28K overnight. 14K for R2 glazing.

   The best thing you can do is minimize loss through the windows.


    I know this is not

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