Posted by nicksanspam on November 18, 2005, 8:00 pm
That's a radiation conductance.
Which you add to the convection conductance, which typically brings
the combined R-value of the foil down to something between 1 and 10.
For the foil radiation alone. But you have to add the convective
conductance Hc for the foil to its radiation conductance EeffHr.
Then take the reciprocal, then add the insulation's R-value.
No. Add the insulation's R-value to the foil's R-value...
It's valuable on either side, but people don't like foil walls,
and the foil would weather badly outdoors, and wind would raise
its convection loss.
Posted by Dennis on November 19, 2005, 1:16 am
OK. Looks like I got it figured out.
Now as far as window insulation goes, what about packing peanuts
between the panes?
Posted by nicksanspam on November 19, 2005, 7:50 am
Sounds rather permanent. The Zomeworks Beadwall system moved small
styrofoam beads into and out of a window cavity with a vacuum cleaner.
It worked well, but the beads required lots of storage space and they
wouldn't flow well through fittings, so each window cavity required
a separate store and vacuum cleaner. And the multiple vacs required
an electrical sequencer to avoid blowing fuses.
"Replacement foam insulation" (filling the space between two glazings
with soap bubble foam at night) seems more practical. It's being applied
to greenhouses now. In one system, a shop vac pushes air through a 100'x2"
pipe with some holes in a 10% detergent solution near the ground, making
bubbles rise to the top of a 100' long quonset-shaped greenhouse. When
the bubbles reach the top, the vac automatically turns off until they
recede, then starts again for a few seconds every hour or so to replenish
them during the night. The bubble system turns off at dawn and a small
blower inflates the space between the 2 plastic glazings with air.
Posted by Anthony Matonak on November 19, 2005, 9:59 am
As I recall, I've heard reports that there were other issues with
the beadwall system. For instance, the foam beads would break down
This might be fine for a greenhouse but I question it's usefullness
in a house. For instance, how clear and streak free are the windows
when the foam goes away? How do you insure that the window cavities
are sealed well enough that they don't ever leak in some hard to
detect fashion and cause damage to the structure? With a bubble foam
system, how do you design the windows so that they can open?
How about this for a possible solution. There are double pane windows
being sold now that have window shades or blinds inbetween the panes.
Mostly, this means that they never get dusty and you won't find the
cat has hung himself from them. Air is a pretty good insulator except
when there is some kind of circulation going on. A cellular shade
could be produced using thin mylar or paper such that it folds up
into a small space at the top or bottom of the window cavity and yet
can unfold to fill the entire space with small air-filled pockets.
One or more layers of aluminum coatings could be added as well to
help cut down on radiant loss.
Posted by nicksanspam on November 19, 2005, 12:33 pm
Not exactly. They tended to clump if never cycled.
IIRC, cycling once a month would fix that.
Moreso than my $00 500 ft^2 cloudy plastic film sunspace :-)
I'd probably make the "windows" with 2 layers of 0.020" clear polycarbonate
from a 48" roll, over plastic 2x4s, with lots of silicone caulk.
You don't. A few plain windows might do that.
Even tiny circulations.
It could be...
Good idea. Scheme 18.7 on page 168 of Bill Shurcliff's 1980 Brick House book
"Thermal Shutters and Shades" describes 5 sheets of metallized Mylar with
springy spacers that unfold when it's rolled down. Scheme 18.8 on page 170
describes an interesting self-inflating Mylar shade. Alas, these are no longer
being made. Perhaps they can be recreated with an iron or a $18 -RS1 hot
roller for plastic film seam-sealing from Hillas at (800) 952 7274.
Symphony "energy track" shades with tracks on each side to reduce air leaks
are fairly expensive and low performing. They (877) 966-3689 say their room
darkening shade has a R-value of 3.2, when used with an R1.8 window :-) This
increases to R4.8 with side tracks. A 3'x6' shade costs $70 with the tracks.
Tiny cold soap bubbles can have the same R-value as fiberglass. A 6" window
might transmit 80% of the sun during the day and become an R20 wall at night.