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Goldilocks and Bubble Wrap Windows

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Posted by Jeff Thies on December 13, 2005, 12:08 pm
 
   I've decided to bubble wrap most of my windows. Most are in shade or
partial shade.

    But like Goldilocks, I'm unsure of which size to go. 3/16, 5/16, or
1/2"?

   3/16 may be too small (large % of space between bubbles) and 1/2 may
be too large (is there such a  thing?). I'm thinking two (bubble to
bubble) layers of 5/16. Ideas? Caveats?

   I hope this is On Topic here, thought this was better than
alt.home.repair. Another group?

   Cheers,
Jeff

Posted by Anthony Matonak on December 13, 2005, 12:30 pm
 
Jeff Thies wrote:

I'm no expert but the mirrored bubble wrap the sell in hardware stores
around here for attic insulation uses the small bubbles. The problem,
as I see it, for the large bubbles is that they may be large enough to
support internal air circulation loops.

Anthony

Posted by phatty mo on December 13, 2005, 3:41 pm
 Anthony Matonak wrote:

They also used to use "mirrored" (conductive,anti-static) bubble-bags to
ship hard-drives and PC components in. I recall seeing a sheet of this
stuff somewhere,so i'm sure they sell it by the roll.
I'd think the mirrored coating would be a benefit.
The bubbles were the small size,and closely spaced,and they had a layer
on each side.(unlike the usual bubblewrap)

Not a bad idea,really.

Posted by Gary on December 13, 2005, 3:26 pm
 Jeff Thies wrote:

Hi Jeff,

The bubbles on my window bubble wrap are 1 inch diameter, and are about 0.3
inches
tall (measured perpendicular to the plane of the bubble wrap).  The
channels between the bubbles are quite small.  They seem to work fine, but
Anthony may be right circulation in larger bubbles.

I did have a go at measuring how effective the bubble wrap is.  I reported the
results in a message here a while back -- the message is pasted in below.
I think you could get some idea by putting up pieces of all sizes, and then
measuring the temperature of the inside skin of the bubble wrap.  Seems
like the one with the warmest inside temp is "just right".

I think you may have trouble with the 2nd layer of bubble wrap if you use
plain water to hold the wrap to the window.  The water holds up one layer
just barely -- I don't think it will do 2.  Sometimes I have to go back
and respray some small areas that separate even with only one layer.
If you work out a way to get two layers to stick, please let us know
how it works.
Some pictures of mine here:
http://www.builditsolar.com/Projects/Conservation/bubblewrap.htm

Here is the old message with the performance test:
October 24, 2004

Hi,
I have tried the greenhouse style bubble wrap insulation to cut the
heat loss on a few of my windows, and thought I would pass along some
results and measurements.

The bubble wrap insulation I bought is intended for reducing heat loss
in the winter season in greenhouses.  I got it from Charlie's
Greenhouse in Seattle (via the Internet).  It actually looks pretty
much like regular bubble wrap, but is supposed to last longer in this
application.

They suggest that you put it up by wetting the windows, and then
applying the bubble side of the bubble wrap to the wet surface.
I found that using a spray bottle (like an old Windex bottle) to wet
the glass works well and goes fast.  I tried plain water, and water
with a bit of Glycerin in it -- both seem to work fine.  I have not
had any of the bubble wrap come off.  A razor knife cuts it to size
easily and quickly.  You can take it down at the end of winter, and
reuse it for several years.

I used the bubble wrap on windows that we don't need the view out of,
but we still want the light.

I attempted to measure the change in heat loss as follows:

I used two identical, side by side windows.  My windows are double
pane, but not sure if they are low e or not (anyone know how to
tell?).  I put the bubble wrap on one of them, and let it dry for a
day.  I shut the heat vent in this room, so the inside air temperature
would be more consistent.  I measured the inside ambient air
temperature, the temperature on the inside surface of the glass, and
on the inside surface of the bubble wrap, and the outside ambient
temperature.
I used a Raytek IR temperature scanner with a small piece of tape on
the surface where I took the temperature measurements (to keep it from
getting confused by the non 0.95 surface emissivity).  I also measured
the same temperatures with a low mass, surface type thermocouple.
This was all done with no sun on windows.

The TC and IR measurements were close, and showed the same differences.

Troom          67F     (room temperature)
Tbubblewrap    60.5F   (inside surface of bubble wrap)
Tglass         55.3F   (inside surface of glass)

If you assume that the airfilm next to the inside surface of the glass
or bubble wrap has an R of 0.65, then knowing the inside surface
temperature, and the room temperature you can calculate the heat flow
with and without the bubble wrap:

Qnobubble = (67F - 55.3F)/ R0.65 = 18 BTU/hr-ft^2 out of the room

Qbubble = (67F - 60.5F)/0.65 =  10 BTU/hr-ft^2 out of the room

This amounts to an  (18-10)/18 = 45% reduction in heat loss.

I was expecting that (at best) it would go from about R2 for the
double pane to about R3 for the double pane plus bubble wrap -- this
would give a 33% reduction in heat flow.  So, maybe bubble wrap is a
little better than just adding one extra layer of glazing?  Or, my
measurements could be off a little?  Or, maybe my thinking is off a
little :-)?

Does the low emissivity of Polyethylene in the IR play any role here?

Any ideas on how to do a better job of measuring the improvement?

At any rate, if the heat loss reduction numbers above are anywhere
near correct, the payoff period for insulating with bubble wrap in a
cold climate is really short -- weeks.

Gary
--


Gary

www.BuildItSolar.com
gary@BuildItSolar.com
"Build It Yourself" Solar Projects










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Posted by Jeff Thies on December 14, 2005, 4:32 am
   >>   I've decided to bubble wrap most of my windows. Most are in shade or

<snip>

   Thanks for the information below. I did look at your article on build
it solar also...

   It looks like the greenhouse bubbles may be more optimized for heat
loss. I've been looking around for a while (1' perforated) is very
common, but not what I wanted.

<URL: http://uline.com  />

has s-2504 5/16" 24" * 188' for $5 US. That's a packaging product. It's
also cheap enough to tape several layers together and still give a bunch
to friends... I imagine a simple frame made out of 1/2" polyiso with the
  bubblewrap taped on each side could be whomped up for take downs.

It's hard to argue with your spray and go though!

(I've bought some of the metalized for windows I don't need light from.)

   Cheers,
Jeff


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