Making sense of Sun Control Window Film

August 14, 2012 1:39 PM

Should Solar/Sun Control Window Film be applied to these windows? I'm trying and failing to make sense of the specifications/numbers...

The windows belong to a high rise apartment in sometimes-chilly San Francisco. UV damage and color fading are concerns, as there is dark carpeting, a piano, some leather furniture, and art. Losing heat is a concern, as most windows face North towards the Golden Gate Bridge.

I have tried to research each of the values but have found it difficult- especially when the labels don't match up. I realize that there are qualities of materials in the unit that will affect their durability...

I'm looking for guidance as to the efficacy of this film on these windows- is it a huge improvement, or maybe not worth the expense? Thank you so much.


The windows in question are Solarban 60 (2) Clear + Clear. Specs:

Transmittance
19% Ultra Violet
70% Visible
33% Total Solar Energy

Reflectance
11% Visible Light
29% Total Solar Energy

U-Value
0.29 Winter Nighttime
0.27 Summer Daytime

Other
0.44 Shading Coefficient
0.38 Solar Heat Gain Coefficient
1.85 LSG (Light to Solar Grain)


Qualities of Clear Sun Control Film that may be purchased and installed:

62% Visible Light Transmitted
44% Total Solar Energy Rejected
50% Total Solar Energy Rejected - On 60degree angle
97% Infrared rejected
13% Visible Light Reflected Int.
15% Visible Light Reflected Ext.
99.9% UV Rejected
22% Glare Reduction
0.56 Solar Heat Grain Coefficient
0.47 U Value
1.1 Luminous Efficacy

posted by maya to home & garden (6 answers total)

I installed the r50s solar control window tint film from Tap Plastics on my single story house with single pane windows in San Jose. It made a substantial difference. While it did not stop the room from heating up on sunny days, it did slow the heating up substantially. For a week or so we had half a window covered, and you could clearly tell a difference in heat transmission from the sun between the two parts.

The film can be scuffed when cleaning. Wash/clean with soft clothes and minimize the amount of chemicals applied.

The film can be scratched (say by a chain hanging and holding a stained glass) and there is no repairing it (you would have to remove it and reinstall).

The film is unnoticed when the windows are closed. When open, you can see that the light transmitted through the film is less than the open air.
posted by fief at 2:14 PM on August 14, 2012 [1 favorite]

Thank you fief- personal experiences with film are also helpful in making the decision!
posted by maya at 2:26 PM on August 14, 2012

Direct sunlight has a broad spectrum that extends into the IR. It's this infrared light that brings heat into the house, increasing AC bills in summer. That's why a lot of window films advertize how well they block the IR. In your list of names, solar heat gain coefficient, IR rejected, total solar energy rejected all refer to getting rid of IR light.
In terms of engineering and light spectra, it's hard to block a lot of the IR without also blocking the reds; the ideal film would let through all the visible and block all the IR, so they advertize the high ratio of light to solar gain (LSG).
In my opinion, you don't care about that.

Your north-facing windows get very little direct sunlight (only dawn and dusk near midsummer) so you're generally only getting light from the sky. The sky is blue because it reflects short wavelengths (blue colors and UV) much better than it reflects the longer wavelengths (yellow-red and IR) of the sunlight. You will not get much heating (IR) from north-facing windows.

If I'm reading you right, though, you're worried the film would cut down on what cozy warmth you do get? Through a north-facing window, that's not much heat. Or concerned about how a large window is bad insulation and haises your heating bills, is there a chance the window film could help with that? In short no, window film will do only negligible things for the insulating value of the glass. They like to say it does (U-value) but personally I'm not a believer. A window is a big hole in the wall of fiberflass batting no matter how you dress it up, and a little film won't change that.

In my opinion, neither IR nor insulation should be one of your criteria for choosing a film. (In fact, you may prefer a film that doesn't block IR if you are hoping for a little bit of solar gain, though I don't think it'll matter.)

You didn't say anything about glare and brightness. Given that you're looking north, away from direct light, the main reason I could imagine you wanting sunglasses (yes, this whole thing is basically just like choosing a pair of sunglasses for your house) is that there's glarey reflections off neighboring windows. If you're not trying to reduce the overall brightness, you don't need a very dark tint. As fief just said, it's surprising how much tint there can be - that film reduces visible light by 50% - and you don't notice that it's dimmer without a clear glass to compare to. But you don't seem to need much glare reduction, so I'd look for a low visible light rejection or high visible transmissivity.

The one thing you said you did want was UV protection. Be sure you get that.

Looking at the list of product names, you either want "99.9% UV Rejected", or you look at some of the tinted films (you probably want >75% transmission) and confirm that they also block UV (which almost all do). Your requirements aren't very stringent, you've probably got a lot of options from various different companies.
posted by aimedwander at 2:38 PM on August 14, 2012 [1 favorite]

When I moved into my new house, I was told if I put any window film on my windows, it would void all warranties because it could mess with the gas layer in double-paned windows. I went ahead and did it anyway with no problems 6 years on, but I mention it to say you might see if your high rise association would have an issue with your installing it. Although, I'm generally a bigger fan of begging forgiveness rather than asking permission!
posted by cecic at 6:14 PM on August 14, 2012

Thoughts on installation;

The Tap Plastics videos were useful. The supplies they recommend are good.

Get a snap-off blade knife rather than a typical utility knife. You will want to snap off the tip regularly (at least every window) and it lets you get closer to the window edge than a typical utility knife.

I installed film on four double windows (each window being 2x3ish). We did an acceptable but not great job on the first (the problems were with the cutting of the edges). We had to scrap one piece.

I did not find their film removal goo to be particularly useful. I did find a four inch blade scrapper (replaceable sharp blades rather than just a squared edge as is often found on scrappers) to be essential.
posted by fief at 10:33 AM on August 15, 2012

If this happens, it will be a professional installation, and with the approval of the management. Cecic is correct, warranties are voided- one of the quotes included information on adding insurance by 3M at about 5% of the total cost of the project.

There is no glare or any problem with brightness. The loss of heat could be a concern, but 80-85% of the windows are North-facing. Issues of art damage and fading are the biggest concerns.

Thanks guys!
posted by maya at 12:22 PM on August 15, 2012