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NFRC & glass coatings

Guest metint

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Very educational websites and, though they speak in terms of glass, the information is the basis for decision making when it comes to 'glazing' energy efficiency, which can easily include a film product placed on the interior surface.

May it stand as a contribution to those who care to know what is important when helping a consumer select a solar control product.

Make your own conclusions as to where it is important in your own effort to bring in the bread and butter.

The info below and the site links were found after typing in infrared rejection into Google search:


Coating reflects almost half of the incident solar radiation back outside while still allowing copious quantities of daylight to enter. Thus the window does not appear tinted. It's as bright as a pane of clear uncoated glass.

There are two numbers which all window manufacturers use to tell how good their windows are in admitting both solar heat and light. The visible transmittance, sometimes called VT, or Tv, gives the fraction of incident light that is admitted. Look for this number to be high, ideally above 0.6 to 0.8 (or 60% to 80%). The other number is called the solar heat gain coefficient, SHGC.

Look for this number to be as low as possible for hot climate applications, ideally below 0.4 (or 40%). By keeping VT high and SHGC low, you can be sure that adequate daylight will be admitted while still blocking significant quantities of solar radiant heat gain.? Both VT and SHGC numbers can be found on the energy efficiency label developed by the National Fenestration Rating Council for U.S. windows.


There is a way to make the high solar gain type of low-e glass appropriate for hot climates. Instead of making the outer glass pane clear to all solar radiation, it is possible to tint the glass a special way so that it absorbs the unwanted and unused infrared part of the solar spectrum. This would be a mistake for single-pane glass, however, since the hot glass would radiate and conduct much of its heat to the interior. If the absorbing pane is the outer one of a double pane glazing system, however, the northern, cold climate, low-e coating is effective at reducing the transfer of heat from the hot outer lite of tinted glass to the inner pane. Few residential window manufacturers may be using this technique for blocking solar gain currently.

The more common way to achieve the same effect is by reflecting rather than absorbing the unwanted solar infrared radiation. This is done with a special coating that is also a low-e coating, but a specially designed one for hot climates. The new low solar gain low-e coating blocks some of the solar radiation incident on it, by reflection, and is quite effective in hot climates like Florida's. There are various trade names for this hot climate insulated glass. The common feature is a solar heat gain coefficient (SHGC) lower than the visible transmittance (VT).


Pages 8 & 9 clearly indicate the need for a NIR absorbing product not to be located on the interior surface of a building?s glazing unit, especially in warmer or hot climates.

It's 20 pages of very good information that can easily stand for glazing performance with film applied as well.?


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Admittedly... I have approached the topic attempting to point out sour grapes in a sour grapes fashion...

The organization below is the source for accurate energy performance in terms of glazing for structures.


The number recognized by NFRC as the most accurate measure of a glazing unit's performance is, solar heat gain coefficient (SHGC). Few if any other numbers are recognized as accurate by the NFRC as a true or accurate measure of solar performance (This also includes, but is not limited to, TSER... total solar energy rejected).

Architects, ESCO's, savvy builders, energy engineers, window mfg.'s, all use SHGC and this is the direction window film is going and need go in order to be recognized as a viable energy saving product for use in glazing units.

Do your film parameter sheets state SHGC... if they do... great.... if they don't, you should encourage your supplier to make that number available on those sheets for future use in the sales of solar window film product.

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Guest vclimber

Thank ME, a lot to read, but good stuff. Nice contribution. :dunno

I have a pile of film hand sample cards that are minus the SHGC:


Solar Zone


Huper Optik



I'm sure there are more and maybe some of these could be outdated as Mfg's change their marketing materials. But in the event that you lose or do not have the solar heat gain coefficient (SHGC), you can use this formula to determine it:


The TSER is the mathematical equivalent but as some of the information gathered by ME suggests, the NFRC prefers to recognize one over the other. It is nice to know that so that you can highlight certain parameters with customers who are trained to identify the standards set for by the NFRC or other organizations. However, one would want to exercise caution when dealing with the average consumer too. Explaining the finer points of IR, SHGC, U-value, SC, TSER, and the like can cause information overload and could lose you a sale. So sometimes a very simple, yet informative presentation, and perhaps a BTU demonstration along with a nice product sample will help the customer appreciate what window film can do and what it looks like once it is placed on the window.

As long as we are discussing organizations that affect architectual film. There is another organization that film mfg's & retailers have ignored for decades. This group is called the "Home Owners & Promperty Managers", they go by various names but they have one thing in common. That is, they enforce a thing called Covenants, Conditions, & Restrictions. (CC&R's) Many of these CC&R's include restrictions against reflective window film in newer developments. So if a homeower were to apply a film that was in violation of the CC&R's, they would have to remove it or be fined. So in this situation, the VLT and more importantly, the Exterior Visible Light Reflectance (VLR) are the most important parameters to the above mentioned organization.

So we the windowfilm professional have a fine balance that we have to maintain and with the assistance of our mfg's and distributors providing us with up to date and the most complete information about their products, we can move forward and sell these products to the consumer in an ethical manner thus providing a product, a service, and a living for all who are involved.

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Someone who can speak eloquently... :dunno Vclimber

What I got from the read was what I have always believed and spoke of and that is putting a high heat absorbing film on the interior of the glass in hot climates isn't the best approach. Seems that for those sun-belt regions a spectrally selective or a semi- to highly reflective film would do well.

Makes selling film a little more complicated than just saying it'll do the job. All factors must be taken into consideration as far as what will truly perform well for the region.

In those communities that have regulated reflective out need only be reeducated in knowing there are spectrally selective products that can work for their community standards. Or and also enlightened to the fact that reflective does not always translate into mirror tint... they should regulate according to VLR rather than a blanket, 'Nothing reflective'.

Thanks for your input as well... On the SHGC / parameter sheet issue... I am sure future printing would take this into consideration, however in the interim, many manufacturer's have made SHGC available via their web sites and now your addition of a simple mathematics will have to do until then. :thumb

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