Posted by nicksanspam on August 17, 2005, 5:54 am
That way, you can have the window gain during the day (with warm air
circulating between the house and the sunspace) without much window
heat loss at night, when the sunspace gets cold.
This is an architectural issue in how people enjoy views and use space.
We like views, and it's natural to put windows on living spaces that
are warm 24-hours a day, but that wastes energy at night, when views are
less interesting and windows are often covered with shades. So why not
put the windows and views on sunspaces and occupy them during the day and
move back into the 24-hour heated space at night? People rarely do that.
I'm not sure why. It is more complex, with an extra wall. Maybe the extra
cost and complexity isn't worth the energy savings, for most people. Or
maybe they just don't think about the energy savings.
You need to rotate your house.
Fertile solar air heater territory...
Warm air rises. Fans can help. You might store heat in a low-e massy
ceiling or some fin-tubes under a low-e ceiling in the living space.
Here's my plan for a 1-hour lecture at the PA Renewable Energy Festival,
http://www.paenergyfest.com , on 9/23/05:
How to heat houses with sunspaces
Houses need several times more heat energy than electrical energy, and
solar heat can be a hundred times cheaper than solar electricity, not
counting valuable floorspace. Ohm's law applies to both...
Sunspaces with lots of thermal mass cost a lot and collect solar heat
inefficiently. Low-mass sunspaces get cold and lose little heat to the
outdoors at night. Windows to living spaces lose heat all night and on
cloudy days. How often do we need to look out windows at night?
A sunspace can be a simple air heater, eg polycarbonate "solar siding."
People can use deeper sunspaces, with shading and venting for comfort.
A lean-to greenhouse made with double-curved 1x3s can cost less than
a dollar per square foot.
A small sunspace that collects little heat compared to what a house needs
doesn't need thermal storage. A larger one might store heat in a ceiling,
as in the excellent Barra system, virtually unknown in the US.
Posted by Anthony Matonak on August 17, 2005, 12:18 am
It would be possible to install something automated. Perhaps some kind
of insulated window shutters or roll-down cover with a motor drive. It
could be triggered automatically either with a timer, daylight sensor or
differential thermostat and could include a manual switch to open/close
it when desired.
Posted by Gary on August 17, 2005, 12:43 am
Anthony Matonak wrote:
We did look into those roll-up exterior shutters that are insulated.
They seem nice, and they offer motorized operation. I think they
would also do a better job of stopping the summer heat gain, since
they catch the sun before it gets inside the glass. But, they are
kind of pricey ($00+ per window times 3 windows). Thats a lot more
than the $0 a window for the homemade aluminized mylar shades, and
I'm just not sure its worth it.
I know some people hate pulling blinds up and down, and end up just
leaving them up, but the manual thing is OK with us -- we already have
the duofold type shades on the windows, and use them each night.
Maybe there is another shade/shutter option out there we have missed?
Posted by Cosmopolite on August 17, 2005, 1:21 am
My parents have " Rollshutters " on their house, non insulated, and
they work really well, but I agree with you that these units are too pricey.
I plan to use 1 in. styrofoam with vinyl glued to the outside and
alum. foil on inside ( our problem is winter ), vinyl channel track for
sides and the " Rollshutter " idea of a strap type system on inside to
operate them. I feel that motorizing them would be a big headache in the
long run. The shutters will run vertically and they can be held at any
position , from bottom, thereby acting as curtains also.
Posted by nicksanspam on August 17, 2005, 5:31 am
That does seem possible, but nobody seems to make a practical standard
commercial product like that. I've looked hard, and the ones I've seen
seem to be very expensive or have low R-values (eg 4 vs 20, including
an unspecified window--windows can be R8 by themselves) or leak lots of
air around the edges.
Shurcliff's Shutters and Shades book describes a 5-layer aluminized Mylar
shade that opens up with spaces between layers as it rolls down. This
would have a high R-value, but it's no longer being made.
The best homemade shade I've seen (in a Washington's Crossing PA barn
conversion by Harrison Frakur) had a U-shaped layer of aluminized Mylar
with one horizontal edge permanently attached near the top of a window
and the other edge on a motorized roller near the top of the window, with
a roller-weight riding freely in the bottom of the film U. The roller
extended sideways into grooves on each side of the window. When dusk fell,
a photosensor would turn on the roller motor which lowered the film. You
could still see dimly out of the window. This might have been about R10,
with 4 reflective surfaces.