Subject: A larger polytope solar structure

From: [email-masked] (Nick Pine)
Date: 24 May 1996 06:54:15 -0400

We could add more floor space to a pyramid treehouse with another horizontal 
telephone pole at the peak extending it in the east-west direction. The sunny 
vertical face would be glazed again, with four tensile supports running north
and south, and it might still be 24' tall at the peak, using three telephone
poles this time, and some flexible membrane walls, eg aluminized tarps (what
would the neighbors say? :-) This inexpensive 100% solar heated structure
would have 1152 ft^2 of basement floor on grade, with walls sloping upward
and inward, and two smaller floors above. 

(Try looking at this with a non-proportional "typewriter" font like Courier.)

A vertical wall elevation:    

        24'     ........30'...... <--chainsaw mortise and tenon joint, with
              .                  .            steel plates and bolts thru
     16'    ............42'..........         flattened sides?
          . <-glazed area: 384 ft^2-> .   
   8'   ................54'..............     
      .     <-glazed area: 480 ft^2->     .    
........................66'.......................

>From  above:

   ---          ........*........     * rope or cable or pole
              . .               . .         
            .   .               .   .      
   24'    * 216 *    720 ft^2   * 216 *   
        .  ft^2 .               . ft^2  .
      .         .               .         .    
.........pole..........pole........pole...........
                 .             .
                  .           .
                   .         .
                    *       *
                     .     .
                      .   .
                       . .
                        .

                    sun
>From  the east:
                              .   
                    sun     t . t    
                          t   ..8'.t 
                        t     .       t 
                      t       .....16'...t
                    t         . SC          t
             .....t.....pool?.........24'......t......

The upper floors might be cable-supported...

                                   16'
    ................................................................       
                    .               .               . 
     2' ?           .               .               . 
                    .               .               . 
    ---                             .
 
We could glaze the whole thing with polyethylene film and recycle the lower
16' of the south face every three years (less often with a summer shadecloth
awning hanging from the south support cables) in a couple of hours, at a
materials cost of $50. The solar closet could be in the walk-out basement,
sitting inside the poly film near the vertical wall, with a single layer of
clear polycarbonate plastic over the sunny side of a strawbale room, and
an air gap between the plastic and the strawbales. The lower 16' of the
vertical face of this structure might gather about a million Btu (300 kWh)
of sun on an average winter day, if it has a reflecting surface in front.
The second floor would have an exposed surface area of 384 ft^2 for the R1
wall, and more for the sloped walls. Suppose we lined the plastic pillows of
the sloped walls and ceiling with sheepskins (or fiberglass or polystyrene
beads, or leaves, or something...) so the main heat loss from the second
floor were thru the R1 vertical glazing.

On a freezing day, when it's 72 F (20 C) inside, the middle floor might
need 24(72-32)384/R1=370K Btu (110 kWh) to stay warm, which the room's
own glazing could supply on an average winter day, with some sun, in
the coldest month, where I live.

How much water is needed to store heat for 5 days without sun? Each 55 gal
drum full of water can store about 25K Btu (7.5 kWh) as it cools from 130 F
to 80 F, so we might need 384K/7.5K = 50 drums, or 500 5 gallon plastic
paint pails with lids or a 10 year supply of Pepsi (recall the Arkansas
solar supermarket whose thermal mass is its inventory of canned goods, etc)
or water in recycled 2 liter soda bottles. Each drum is about 3' tall and
2' in diameter, so we might use a 10'x10'x6' tall (id) room to hold the
drums in two 5x5 layers. It might be made with 12 large $25 straw bales,
each 4' x 4' x 8', and four smaller bales, darkened and glazed on the sunny
side, with an air space under the glazing, and a couple of plastic film
one-way dampers to keep the heat inside at night. 

Wool bales would also do, with dark wool on the sunny side. Regardless of
sweater prices, wool can be inexpensive: I take my neighbor's wool to market
when he thinks it's worth the effort, and it sometimes brings 6 cents per
pound, if the fleece is short or tangled or dark-colored or dirty. They
send it off to make felt washers, in huge bales. When he slaughters a sheep,
my neighbor burns the sheepskin. 

The 1993 ASHRAE HOF says a few shorn mature basement sheep might produce
2.4 Btu/hr-lb of sensible heat at 68 F (1.5 W/kg at 20 C :-) This drops to
1 Btu/hr-lb with a fleece length of 2.4" (6 cm.) Lambs less than 2 weeks
old produce a total heat of 10.5 Btu/hr-lb at an air temperature of 46 F.
We could heat this barn with an R1 wall in the dead of winter with 67 shorn
100 lb sheep, if there were no sun. Or 0 sheep, and 1 sun.

Nick