Subject: Thermally Activated Shutters: A Solar-Heated House Design

From: [email-masked] (Catherine woodgold)
Date: Wed, 21 Aug 1996 19:02:46 GMT

Summary:  Thermal expansion in a bar of metal is used to open and
close shutters, which insulate glazing at night and on dark, cloudy
days.  No electrically operated parts are required.  No human
intervention is required.  The shutters automatically open
whenever the sun is shining strongly enough, and close at other
times.  The sun's rays heat a roomful of black metal cans of
water, which are then used to heat the house.

Two thermal expansion bars, one in the solar closet and
one in a test airspace exposed to the glazing, experience
differential thermal expansion.  When the sun shines, the
test bar (bar #1) becomes longer than the solar closet bar.  This
activates levers, which extend first northwards, then
up, then southwards, successively magnifying the motion of the thermal
expansion bars by leverage from an imperceptible difference
in length to a 1-inch motion which is used to open the shutters.

Disclaimer:  This is just an idea.  It isn't thoroughly
thought out or tested.  End of disclaimer.

A double-glazed glass window, 36 feet long and 8 feet high, is
used.  Reflectors below and above the window approximately
double the amount of sunshine entering the window.  The window
is not used on a human-occupied room;  it is on a solar closet
filled with cans of water, painted black to absorb the sun's rays.

At night the window is insulated by a set of shutters, composed
of lightweight insulation 2 inches thick.  There are 8 shutters
which are 3 feet wide and 7.5 feet tall, and 2 shutters, at the
east and west ends of the window, which are 6 feet wide and
7.5 feet tall.  The window side of the shutters is composed
of a furry black material, which is designed to absorb the sun's
heat when the shutter is open, and to seal firmly against
the window when the shutter is closed, insulating the window
and preventing air currents from occurring in any space
between window and shutter.

The bottom 6 inches of the window is not used to collect
energy.  It is used as a test area, to determine automatically
whether the sun is shining strongly enough for it to be worthwhile
opening the shutters.  This test area contains 2 inches
of insulation on its top, bottom and north side;  inside this
insulation is a 2-inch-high, 2-inch-wide airspace which contacts
the glazing.  Inside the test area is a 36-foot-long thermal
expansion bar.  It is shaped like an I-beam but is only
1 inch wide.  This thermal expansion bar is made of materials
which maximize strength, rigidity, and thermal expansivity, and
minimize thermal mass.  It might be made of copper.  (I don't
know enough about various materials to choose one.)  Any commonly-used
metal would probably suffice.  The bar is painted black with the
same paint as the cans of water.  It is centred in the 2 by 2 inch
space, and held in place by 17 2 by 2 inch pieces of wood, spaced
one per 2 feet, with holes the right shape for the bar to pass
through easily.

4 inches to the north of the thermal expansion bar (TEB) is a
second TEB.  This TEB is in the same airspace as the solar closet,
as opposed to the first TEB (TEB #1) which is insulated off
>from  the solar closet but exposed to the glazing.
The western ends of both bars are firmly attached to the wall.
The eastern ends of the bars are attached to Lever # 1, which
extends 6 feet northwards into the solar closet.
(For this purpose, TEB #1 first passes through a hole in
some insulation;  its eastern 2 inches are in the solar closet
airspace.)

If TEB #1 is significantly warmer than TEB #2, it is also longer
by thermal expansion.  Therefore lever #1 feels a force tending
to move its northern end westward.  Lever #1 has no fulcrum;  only
the two TEB's and lever #2 are attached to it.
 
Lever #2 is attached at its bottom to the north end of
lever #1, and extends
upwards 7.75 feet.  It is attached to a fixed fulcrum 6 inches
above its bottom end.  When its bottom is pushed westward by
lever #1, its top end tends to move eastward.
 
Lever #3 is attached to lever #2 at the top northeast corner
of the solar closet.  It has a fulcrum 6 inches south of that
point.  The fulcrum is held stationary.  When its north end
is moved eastward by lever #2, its south end moves westward
and automatically operates the shutter-opening bar.

The shutter-opening bar runs along the top
of the shutters, 2 inches north of the glazing.
It has 1-inch protrusions which are attached to the shutters themselves
(or to 1-inch-long protrusions from the shutters) in such
a way that when it is moved westward one inch, the shutters
open.   (I admit I haven't quite figured out how this works,
but I'm convinced a simple geometry will accomplish the purpose.)
Moving it in the opposite direction closes the shutters.
When lever #3 moves further than is necessary to open or close
the shutters, the extra motion is absorbed by a spring which
forms the attachment between lever #3 and the shutter-opening
bar.  Another, much weaker, spring, attached to a little
lever on the shutter-opening bar, causes the shutters to
spring suddenly into open or closed position, rather than
opening gradually.
 
When in open position, the 6-foot-wide shutters are flat against
the east and west walls.  The other shutters are back-to-back
in pairs.  Half the shutters open westwards, half eastwards.
Thus, for most of the window, 6-foot-wide sections of window
are bared, and incoming sunshine is obstructed only by pairs of
open shutters (  :-)  which extend 3 feet into the room and have
a combined width of 4 inches.  At the ends of the window, 9-foot-wide
sections of window are unobstructed.
For almost all of the winter day,
at least half of the sunshine goes deep into the room and warms
the cans of water.  At noon, almost no sunshine is stopped by
the shutters.  The sunshine which does shine on the shutters
warms them, due to the black heat-absorbing material, and
warm air is generated which circulates by convection and
warms the cans of water.  Note that it's preferable to have the
sun shine directly on the cans.
 
Remarks:
A material expanding when warmed presumably only expands
an imperceptible amount, especially if differences of only a
few degrees exist.  However, it expands with tremendous
strength.   Magnifying the motion with levers creates a
much weaker force;  but since the original force is large,
the expanded force is presumably strong enough to move lightweight
shutters which are balanced on well-oiled hinges.  I don't
know how much magnification of the force is required;  the
above lever dimensions are just guesses.  But any required
magnification is theoretically possible to obtain.
 
On a cold night, TEB #1 becomes very cold.  It therefore acts
through the levers to press the shutters firmly against the window,
improving the seal and insulating well.

Cathy                                   TISSATAAFL
There is no frigate like the 'net 
To take us lands away; 
Nor any coursers like a pulse 
Of prancing packetry..

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From: Carlos Portela <[email-masked]>
Date: Thu, 22 Aug 1996 23:34:27 -0700

Catherine,

Regarding using expanding metal to open vents,
metal probably cannot expand enough.

What you need is a solar vent opener.  These are
very reliable and have been used successfully
for many years in greenhouses and coldframes.
They look like a thin shock absorber.
I believe they have a parafin-like compound
which expands and pushes a piston -- all this
sealed, of course (no mess).  They are available
>from  greenhouse supply companies, and renewable
energy dealers such as Jade Mountain.
For more info, see this web page at the
Jade Mountain web site:
http://www.indra.com/jade-mtn/fans.html

Sincerely,

Carlos Portela
-- 
3-D Software
P.O. Box 220, Mapleton OR  97453  USA
[email-masked]
http://www.teleport.com/~solar3d

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From: [email-masked]
Date: Sat, 24 Aug 1996 01:27:30 GMT

>>differential thermal expansion. 

	Consider using an automotive "automatic" choke actuator.
-- 
Regards,
Derald Martin

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From: [email-masked] (Catherine woodgold)
Date: Mon, 26 Aug 1996 20:09:53 GMT

Carlos said,

>metal probably cannot expand enough.

When I made that design, I used my intuition to guess how much
metal would expand.

I find in S. Baer's Sunspots that copper and aluminum both expand
roughly 0.00001 (per degree F, I think it is).

So, with the design I gave, with a 1 degree temperature difference
the shutter-opening bar would move something like 60 times as far
as I said I needed it to.

The 36-foot-long bars I specified would expand by about
0.004 inches per degree.  The levers I described multiply the
motion by about 7000 times.  That's too much.  Suppose the
levers are modified to multiply by only about 100.  Then it would
be easy to obtain the 1-inch motion of the shutter-opening bar.

Suppose the doors are light and well-hinged enough that the
shutter-opening bar requires only one pound of force (over
one inch, moving slowly) to open or close the shutters.
Then the thermal expansion bars must be able to take 100
times that force ... 100 pounds.  It's easy to make a metal
bar that does this.

Likely there are cheaper designs, but my design is certainly
possible and not very expensive.  I think it can be modified so
the heat falling on the test bar is also collected.

S. Baer (Sunspots) describes some designs using the motion of a volatile
fluid from one container to another, to open and close shutters.
They're probably better.  I wouldn't use freon or anything that's
bad for the ozone layer.  Maybe alcohol.

I'm hoping to design something that opens and closes windows,
built mostly from materials I find around my house.  I'm not
sure I'll succeed.  I reckon that there are probably several
months in the year here where the house can be heated simply
by opening the windows whenever it's warmer outside than inside.
Vice versa for cooling in summer.  Oh, yes.  Rubber bands.
Identical sets of rubber bands, outside and inside.  They contract
when heated.  Ought to be able to close a lightweight window
that way.  Just have to make sure it seals well enough, when
closed, to make it worthwhile.  (even a poorly sealing version
can be useful in weather where the average outdoor temperature
is only slightly different from the desired average indoor
temperature.  E.g. suppose it's warmer outside for 8 hours
every day.)

Cathy                                   TISSATAAFL
There cannot be a crisis today; my schedule is already full.  :-)

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From: Philip Griffiths <[email-masked]>
Date: Tue, 27 Aug 1996 09:57:33 +0100

> >>differential thermal expansion.

The material for this is called a "memory metal".

regards

-- 
----------------------------------------------------
Dr Philip Griffiths,     PROBE, University of Ulster
TEL:+44 (0)1232 368238              Northern Ireland
FAX:+44 (0)1232 368239 E-MAIL [email-masked] 
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