Subject: Re: Today's high, in the solar attic

From: [email-masked] (Nick Pine)
Date: 24 Oct 1995 07:36:13 -0400

Andrew McKegney  <[email-masked]> wrote:
 
>If your attic has any wood , paper or non-fireproofed wood fibers in it 
>you could create a problem for yourself.

It has all that stuff. Wide pine floorboards, cedar shingles on the north
side, dacron ropes around the rafters, holding up the second floor, etc.

>If these materials are exposed to high temperatures for long periods of time,
>they develop phyric (?) compounds that can eaisly catch fire.

I wonder how high these high temperatures have to be? It seems unlikely to me
that the attic will catch fire, since it has little insulation. That would be
interesting, tho. A pyric victory, in solar air heater design. I'd worry more
if this were a concentrating system. Howard Reichmuth, P.E., says he almost
melted a pair of good rubber boots, by accidentally standing in the line
focus of his parabolic concentrating greenhouse, 20 years ago. His advice:
"Don't stand in the focus!" 

The attic will have some cooling, eventually, in the form of blowing some
of the warm air down to the rest of the stone house, to store heat in the
stone walls, surrounded by foam insulation on the outside.

>This is why the idea of building solar panels of wood went up in flames.
>Literally.

Sounds like suburban folklore to me. Altho I could imagine that happening in
a well-insulated, stagnated, liquid solar collector, if the pump failed. That
kind of collector is expensive and goes on the roof, in the wind and the snow,
with antifreeze and heat exchangers and complicated control panels. I'm not
very interested in those things. If I insulated it _really_ well, perhaps
my attic could use some 180 F passive vent openers to open the doors under the
turbine vents, if the temperature gets too high up there. Solar Components
121 Valley Street/Manchester, NH 03103-6211 $56 #13040 Solarvents are said to
start opening at 188 F and be fully open at 212 F, altho the last one I tried
20 years ago didn't work very well. Perhaps you are not supposed to boil them
long in a pot full of water on the stove. Jade Mountain (800) 442-1972 sells
$54 #FC115 Thermofor vents, and Steve Troy says they work well, lifting 15
pounds 15", but the catalog says "select a temperature between 55-85 degrees." 

BTW, I've decided to hang a $70, 32' x 16' layer of 80% greenhouse shadecloth
on top of the transparent part of the attic next summer, using a couple of
pulleys and ropes. This should make the attic a lot cooler, and make the
clear, corrugated, polycarbonate glazing last a lot longer. It won't interfere
with the view that much. I had it hanging over the whole south front wall
of the house this summer, and the worst part was the moire pattern it made
as I looked through the screened part of the windows from the inside. From
the outside, it just looked black. A new look in houses. Trendy, perhaps.

>Better consult your local fire department before you go much further.

I don't think they know much about this sort of thing. I gave them a copy
of my solar closet paper a while ago, and suggested that they modify their
firehouse accordingly. The firehouse has a very nice white stucco south-facing
wall, with no windows, but I don't see any changes yet. I suspect they don't
even know about Ohm's law for heatflow. The south wall of the Ursinus College
building next to the firehouse is completely shaded by big evergreens close 
to the wall, and it has a lovely porch upstairs that is crying out to be
glazed in, after the evergreens are cut down, but that hasn't happened either.
I guess Ursinus College doesn't know much about Ohm's law for heatflow either. 

>A point to consider. Unless you have something to store the heat in, 
>you'd be better off installing a skylight directly into the living space. 

Sounds like a good idea for daylighting, perhaps with a reflective sunscoop,
aimed south, but I'd think one would want a large amount of vertical glazing
to collect low-angle winter sun, and one needs some way to avoid having all
the house heat disappear out the glazing at night, or during periods of
cloudy weather.

>The mass in the living space will absorb some of the heat...

Indeed it will. We should build more stone houses, surrounded by polyurethane
foam. There was one described in a recent Mother Earth News, built by two
brothers with wheelbarrows--13 million pounds of rocks, including the stone
roof, but they forgot the foam on the outside. Concrete furniture also helps,
in ordinary houses. 

>Remember maximize the insulation before trying to use the insolation!

Perhaps someone should tell David Boyer about that. His 2,000 ft^2 commercial
greenhouse in Sassamansville, PA is doing fine at the moment, with a single
layer of R0.7 polyethylene greenhouse film surrounding a lot of poinsettias,
which are sitting on top of 200 55 gallon drums full of water. He doesn't seem
worried about fire, either. I think he understands Ohm's law for heatflow.

Thank you for your concern, Andy.

Nick