Aluminized Mylar Window Treatment
Gary
We have large, east facing windows that gain way to much heat on
summer mornings. They also lose way to much heat in the winter.
The windows are lightly tinted, and during the heavy sunshine period,
we lower a set of the cellular blinds to reduce heat gain, but my
feeling is that there is still a lot of heat gain.
We are thinking about adding a 2nd shade between the window and the
existing shade. The 2nd shade would be a roll up type, and would be
made from aluminized mylar -- reflective on both sides.
My hope is that in the summer, the highly reflective surface will
reflect most of the light of all wavelengths right back out the glass.
And, while it won't be as effective as blocking the light outside
the window, it might be pretty good.
Dr. Shurcliff's book on on "Thermal Shutter and Shades" says the
aluminum foil can be very effective in the winter as long as it has
some air film space on each side. He says:
"Foil flanked on both faces with a thick region of still air is worth
R 2.7!! (exclamation points are mine).
This high performance, he says, is due to the foils ability to reflect
IR radiated from heated objects back into the room on the inside
surface, and the fact that it radiates almost no energy on the outside
surface due to its low emissivity.
I plan to install wood strips on the sides of the window frame that
the edges of the foil will lightly rest against for a seal, and to
have a slightly weighted bar along the bottom where the shade rests on
the window sill to seal the bottom.
This all seems like a pretty nice, and inexpensive way to go.
Has anyone tried this?
Does anyone see any down side?
--
Gary
www.BuildItSolar.com
ga...@BuildItSolar.com
"Build It Yourself" Solar Projects
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dances_wit...@yahoo.com
seconds you spent looking out the window.. Divide by 168x60x60.
Then tell me if you shouldn't just put R-10 fiberglass over the windows
Gary
view.
I'd never give up the daytime view, and putting R10 panels in and out
each night is too much work.
nicks...@ece.villanova.edu
>I'd never give up the daytime view, and putting R10 panels in and out
>each night is too much work.
How often do you look out at night? How about an insulated wall between
the low-mass sunspace with lots of south windows and the living space?
Nick
Anthony Matonak
> dances_wit...@yahoo.com wrote:
>
>> Here's an idea. During a week (=168 hours), keep a log of how many
>> seconds you spent looking out the window.. Divide by 168x60x60.
>>
>> Then tell me if you shouldn't just put R-10 fiberglass over the windows
>>
> Actually we look out the windows all the time -- its a great mountain view.
> I'd never give up the daytime view, and putting R10 panels in and out
> each night is too much work.
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.
Anthony
Gary
> Gary <ga...@builditsolar.com> wrote:
>
>
>>I'd never give up the daytime view, and putting R10 panels in and out
>>each night is too much work.
>
>
> How often do you look out at night?
Rarely -- it would be easy to give up the night view.
How about an insulated wall between
> the low-mass sunspace with lots of south windows and the living space?
I'm a bit lost here.
Could you explain that in more detail.
My offending big windows face just a touch north of east. They get
too much summer sun (7am->11am), but basically zero winter sun (this
is due to the mountains to the east, and the lower and more southerly
winter sun). The way my house is built, the south exposure is hard to
take advantage of -- the garage takes up half of it, and the way the
rooms are arranged makes it hard to use the other half even if I was
willing to do major wall surgery (which I am :-)). I have made some
use of the garage part of the south exposure with this:
http://www.builditsolar.com/Projects/SpaceHeating/garcol.htm
But, I am hard put to find any way other than active collectors on the
south roof (which I am thinking seriously about) to use the rest of
the south exposure.
From a passive solar point of view the house design stinks, and I
would not have built the house this way, but it is the way it is, and
aside from the bad solar design we like it a lot.
I guess one possibility would be to build a low mass sunspace south
from the half south wall of the house not used by the garage, but
getting the heat from the sunspace to where its needed, and providing
some type of heat storage seem like difficult problems?
If there is a better way, especially one that would allow more solar
gain without the complexity of an active collector system, I'm all ears.
The aluminized mylar window shades seem like an easy way to 1) cut
down on the unwanted solar gain in the summer, and 2) reduce the heat
loss in the winter.
Gary
Gary
Hi Anthony,
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 ($800+ per window times 3 windows). Thats a lot more
than the $50 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?
Gary
Cosmopolite
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.
nicks...@ece.villanova.edu
>It would be possible to install something automated. Perhaps some kind
>of insulated window shutters or roll-down cover with a motor drive...
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.
Nick
nicks...@ece.villanova.edu
>>>I'd never give up the daytime view, and putting R10 panels in and out
>>>each night is too much work...
>> How often do you look out at night?
>Rarely -- it would be easy to give up the night view.
>How about an insulated wall between the low-mass sunspace with lots
>of south windows, and the living space?
>I'm a bit lost here. Could you explain that in more detail.
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.
>My offending big windows face just a touch north of east.
You need to rotate your house.
>...the south exposure is hard to take advantage of --
>the garage takes up half of it...
Fertile solar air heater territory...
>...the way the rooms are arranged makes it hard to use the other half
>even if I was willing to do major wall surgery (which I am :-).
Good...
>I have made some use of the garage part of the south exposure with this:
http://www.builditsolar.com/Projects/SpaceHeating/garcol.htm
Good...
>But, I am hard put to find any way other than active collectors on the
>south roof (which I am thinking seriously about) to use the rest of
>the south exposure.
Bad...
>I guess one possibility would be to build a low mass sunspace south
>from the half south wall of the house not used by the garage, but
>getting the heat from the sunspace to where its needed, and providing
>some type of heat storage seem like difficult problems?
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.
Nick
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.
webs...@cox.net
Gary wrote:
> Hi,
>
> We have large, east facing windows that gain way to much heat on
> summer mornings.
I used to have a Texas house with 6 upstairs windows that gained heat
in the PM. The room was about 5 degrees warmer than the rest of the
house.
I bought the cheapest pull-down shades I could get, and removed the
shade material. Then I bought this reflector material--think
re-inforced aluminum foil--and -remade the sheets with that. I mounted
the shades as usual, and was able to raise or lower them at will, for
keeping cool, gaining heat, or looking out.
The rooms were then about 5 degrees cooler than the rest of the house.
The thermostat was far away, at the other end of the house. This isn't
scientific I guess, but it was obvious that it worked.
So I used the foil to in the garage, by sticky-taping a layer of it to
the inside of the big garage doors, which also faced mostly west. I
don't have numbers, but the garage went from "oven preheat" to "Hey, I
can work here."
Fortunately for me, some trees blocked the view of the upstairs window
from the street, so the HOA wasn't upset about the foil-in-the-window
thing, and I had other blinds inside, so it didn't look trashy there
either.
Now I'm in Arizona, and the HOA and builders won't let you do a @^%#
thing for energy efficiency.
Anyway, the foil idea worked very well for me.