Bubble wrap window insulation testing
I have a large amount of glass in my 1965 home. I had read a question here that talked about window quilts and that eventually led me to the idea of covering windows with bubble wrap.
Much of my glass including large sliding doors etc are all bare aluminum frames without thermal breaks or insulation. The idea of adding a semi-clear covering that admits light and I can apply over the glass and frame is pretty appealing.
Of course replacing the windows is a huge expense. Some have single pane and others are double pane from 1965.
(Apparently greenhouse owners have been doing this for years.)
My question is, how would one best measure the value of this concept? I have read some r value estimates but I am suspicious. When I use my temperature gun on a piece of tape attached to the bubble wrap and a similar window without, the temp difference is only about 3-4 degrees. But my sense, based on how the room feels, is there is a lot more to this concept.
I can see how convective losses are reduced, radiative losses and gains are the same except when the sun is shining? Conductive losses are reduced? R value just seems too simple.
Any thoughts?
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My guess is that there's a reason that this hasn't been done before. I'm not sure if the bubble wrap would provide any advantages to the clear plastic sheets that are sold in hardware stores for this purpose??? The clear sheet would have less visual distortion than the bubble wrap and likely is easier to seal against the window frame. The seal is going to be an important factor in it's performance. The other factor is maintaining a properly sized air gap between the plastic and glass to get the R-value. The gap with the bubble wrap will be variable as it's thickness varies. It's not clear to me how that would affect things, but you would probably want to make sure none of the bubble wrap is in direct contact with the glass in order to avoid thermal conduction.
Mark, have you checked window film? Might be worth it and not so much work as an annual installation of that stuff?
Just a thought.
Joe W
Daniel,
Well if it werent for the greenhouse people I wouldn't have tried it. But. If anybody has a lot of single pane glass to deal with in the winter it's them.
The wrap is 1/2 inch thick and each bubble stops the convection inherent in a single sheet that covers the whole window. The way you install it is to wet the glass and apply the wrap bubble-first to the glass. You can do a second layer the same way.
Here's a pic.
This is an interesting question and one that would be good to know the answer. I know the clear film will not have convection issues if the gap to the glass is sized appropriately. It makes sense that the bubble wrap wouldn't have that issue either if directly in contact with the glass. However, there is then a potential issue of conduction depending on the properties of the plastic, which I don't know.
You might be able to get a better sense of the value of the bubble wrap if you can get temp readings inside, outside and in-between the glass and bubblewrap. I believe a single pane has an R-value of around 1. The better the R-value of the bubble wrap, the more closely the in-between reading will be to the outside temp. If it does little, the temp ought to be closer to the inside temp (measured right next to the bubble wrap as there is likely to be a draft and thus a temp gradiant from the window to the interior of the room.) You would want to make the measurements when the temps are fairly steady and there's no direct sunlight hitting it. Speaking of which, solar heat gain is another factor that hasn't been discussed. No idea how well the plastic transmits the solar heat gain. This could be an important consideration if there is direct sunlight on the glass. My guess is that it would transmit pretty well, but it might not. I don't know what the answer is for that.
Joe w - Thanks for the tip. I applied some yesterday in comparison. For sure putting up the clear poly (3m) is harder than adding the bubble wrap. See pic on next post.
Daniel - Here are two single pane glass "windows".One with poly from 3m with a 1-1/4 space and one with the 1/2 bubble. I put tape on them at chest height and at the bottom to keep the temp gun from getting confused.
It's 20 degrees outside. The top tapes measure 57.4 for the poly, 55 for the bubble. The bottom tape measures 52 for the poly and 51.5 for the bubble. The sheetrock between is 61.5 at the bottom and 63.5 at the top tape height. (All studs no insulation).
Glass at chest high is 47.5.
So there is 2 degrees difference in the room's temp from low to high per the adjacent sheetrock measurement.
5.4 for the poly, net 3.4
3.5 for the bubble, net 1.5. (I think this is because there is still a continuous space between the bubbles.)
Difference to glass only is - 10.5 for poly, 7.5 for bubble.
Note the bubble is less than half the air gap thickness of the poly.
It's difficult to tell via text where each measurement is made etc. I'm not following it very well, but it sounds like measurements were being made vertically. The temps that I think you need are horizontal through the door.
A more simplified attempt to make a comparison between the poly and bubble wrap could be to measure the temp on the inside(heated side) of each material. If one is warmer than the other, it is loosing less heat then the other.
The bottom line is that bubble wrap isn't likely to hurt the situation unless it's blocking solar heat gain. It may even do a little better than the poly sheet, but I sure like the view a lot better through the poly! If you don't care about the view, you might consider some rigid polyiso insulation instead. I know that'll give you more thermal protection! It could even be made into a thermal shutter/door so that it can be opened during times when there would be solar heat gain or occupied and some light and/or views are desired. I have a number of homemade thermal shutters in my house and really like them.
Hi Mark,
I did some testing on the insulating value of bubblewrap on windows -- its described here: http://www.builditsolar.com/Projects/Conservation/bubblewrap.htm
The result was that it has about the same R value as adding a pane of glass.
I do plan to do a bit more on this during the winter.
One reason that you may not be getting good readings on the IR gun is that it sees through the poly -- that is, the poly is nearly transparent to the IR. I use this on collector testing to be able to see through the glazing to the collector absorber with an IR camera. Putting some painters tape where you intend to take readings is a least a partial solution, but only good when the sun is not shining on it.
The interest in this topic just amazes me -- for the last couple days the page refferred above has gotten over 3000 visitors a day. I guess its just so simple it really appeals to people.
For your sliding glass door, you might consider this: http://www.builditsolar.com/Projects/Conservation/Slider/SlidingDoor.htm
We just leave it up all year -- it insulates well and does not get in the way.
Gary
Gary, nice work on the testing. I don't have any argument with your math but the end result feels right. What I mean is that the impact on the room was substantial. It always felt that there was more to it than R value. I have since moved and used all my bubble wrap for packing, (still does that well too :) )
One note, when I removed in the spring I noticed there were bubble wrap patterns on my windows whenever they were steamed up etc. Maybe using distilled water, especially in hard water areas, would help.
I am looking in to the Indow product for a similar use in my new home.
Bubble wrap definitely works, but almost any circa 1965 single pane window in reasonably OK shape can be upgraded with exterior low-E storm windows. Unlike replacement windows it's usually cost-effective in short-years, and often outperforms a code-min replacement window (for a LOT less money up front.)
See: http://www.ornl.gov/sci/buildings/2010/Session%20PDFs/22_New.pdf