Increasing window thermal efficiency.
drystone
| Posted in Energy, Heating & Insulation on
On my last trip to Seattle I was told about a plastic film which could be applied to window glass. It had no effect on the transparency but added to the thermal efficiency of double glazing.
Does anyone have a name for this product and can comment on its effectiveness?
Replies
3M and others make them. Google window films. No personal experience with them.
Rich
It typically voids all window manufacturer's warranties. I've replaced a lot of glass that 'stress cracked' after having film applied. Most film companies have a warranty, but it usually doesn't cover the entire cost.
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My brother puts some kind of plastic window film on his windows every year. Looks AWFUL!! Can't see properly through the windows, etc...but he says does significantly improve thermal efficiency.I'm not saying all products are like this, but whatever he uses...I'd rather just not put windows in the house than have those eyesores in my way.-Carleton
That film your brother uses does not improve the themal effeciency of the window, instead it seals the window from drafts, which improves the infiltration rate. (Less draft = less heat loss)
Thanks to all for your help, I'll see if the products are available in the UK.
One idea out of Mother Earth News does work, but is butt ugly.
Bubble wrap, the small bubble type, that is.
Just mist the glass with a spray bottle of water and stick the bubble wrap directly to it.
DW did just that to the windows in her studio. I measured the temperature at the center of lite before the fix and after. Average of around 5 degrees better with the bubble wrap. These are new Semco double hungs and the bubble wrap was applied only to the glass.
It cuts down on light but she was more interested in saving $$ on the propane heating cost than the amount of light she gave up. It was kind of like all the windows were frosted like a shower enclosure.
Next winter she will reuse to same bubble wrap and is adding insulated drapes.
Believe me, as a single income family, I appreciate her conservation efforts, ugly or not.
Just call it privacy glass. :)
That IS improving the thermal efficiency. There are two thermal characteristics of windows ... conductive and convective ... OK ... 3 ... solar/light transmission.
The film I'm thinking about does not go directly on the glass, but on the casing using double-sided tape and then you use a hair dryer to shrink the plastic and make it tight.
Now, I'll grant you that the r-value will increase slightly, but the biggest benefit is reducing drafts.
No experience with film applied directly to glass. Window tint will decrease solar gain, not to sure about heat loss.
What else you want to argue about? :)
You are referring to cheap plastic storm windows. My guess is they will double your R-value ... not quite ... but close. And likely reduce infiltration. The problem is that they may begin to fail after a short time (e.g. 1-2 months). They effectively place another pane of glass on your window. So why doesn't everyone do it? Aesthetically, they aren't very nice ... from both the exterior and from a interior view standpoint. They take work to put on. They are inexpensive, cheap, and tacky ... but affective ... asuming they are applied correctly.
You want the film by 3M, installed by their certified installers not the DIY kind or other knockoffs.
I've had it applied to single pane glass and it does help there, though I think more with fending off summer heat than keeping in winter cold. It also helps protect furniture, drapes, and floors from the damaging effects of the UV.
I know that on one house I had done, it has been there ten years and you still can't tell it is there by looking at it.
You do have to warn painters not to use a razor knife to clean the glass with though, or it won't be there any more.
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In the late 80s, I spent a year as a project manager at a big window company near Pittsburgh, called Traco. They make aluminum-framed windows, commercial and residential. Very interesting company, but working there really sucked, thus the one year.
They are basic in IG, in other words, they have automated glazing lines for making insulated glass units. You would be surprised at the number of window companies that don't do IG, but instead buy it from someone like Cardinal.
One of the IG types built in their plants at the time I was there used a film suspended in the cavity of a two-thickness-of-glass unit. Called "heat mirror," it requires a special doubled spacer surround, and a carefully controlled oven to treat the unit after assembled, so as to shrink the film drum-tight.
Other than a little tiny by-design hole in the film, near an upper corner of the lite, the film is practically invisible. The hole is there for pressure equalization.
I don't find anything about this type IG unit at Traco's website today, but a lot of good info about the films, available coatings, and available inert gas fills can be found here
I am doing a house design right now for a guy who wants a lot of glass in his new house, because of a combination of southern exposure and drop-dead mountain views at his site. He likes all things Canadian, and we get a lot of building products shipping into upstate NY from Ontario and Quebec.
He will use windows made by an Ottawa manufacturer called Thermotech. They make an entire line of windows all using pultruded fiberglass frames. Frames like that are seen in Marvin's all-Ultrex window products, and a very common patio door product, the Andersen Frenchwood hinged patio door product line, has a frame in which all the weather-side components are pultruded glass.
Thermotech offers a large array of glazing assemblies for their windows, the array of available combinations including triple-glazed and double-glazed IG, with a cafeteria-style selection of coatings. They will custom-configure your window types per elevation of house, to deal with heat loss, solar gain, and more.
If you go here you can see quite a bit of detail about their various combinations of glazing.
For comparison purposes, if you may not be used to comparing thermal transmittance values ("u") to thermal resistance values ("R"), just get out your calculator, and use it to get the inverse of u-value to get the R. Thus done, a u = 0.25 calculates to R = 4 by doing 1 / u.
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Gene--
Thanks for that info; I'm in the process of designing a replacement window-wall for an A-frame chalet and have been looking for sources of electro-, photo-, or thermo-chromic IG panels. Do you know of any other suppliers?
Dinosaur
How now, Mighty Sauron, that thou art not broughtlow by this? For thine evil pales before that whichfoolish men call Justice....
I'm a BIG proponent of Heat Mirror glass. I've used it on my own house. I've recommended it a LOT. I've seen it used on a lot of commercial projects. In spite of the ease and economy of low-e coated glass, I still like the Heat Mirror. Superior thermal performance.
Trouble is ... availability and curretly the cost. Due to it's special mfg needs, there are only a handfull of fabricators in the country. We lost a couple in the NW back in the 90s. Now the cost is high which is too bad IMO. I've seen if fabricated into double films, triple, even quadruple for super low u-values.
I've bought it tinted and mirrored for maximum solar control (in addition to adjusting the low-e coating value).
"have a name for this product"
Missed that Q
I think it is called solarfilm
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It is solar film ... primarily for reducing solar loads, not cooling/heating loads. While it may reduce the U-value ... it would be small. If you have a solar problem, then it might be worthwhile ... if not find another alternative (replace the glass). Other hints that this can cause thermal stress cracking ... for double glazing (i.e. standard hermetically sealed insulated glass units). I've heard there are films for insulated glass, but don't know. Other films specifically cannot be applied to double glazing.