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Window film further info


lizzie

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I have been researching the external window film to try and deal with my overheating problems.

 

The very nice people in Bognor Regis said it would be fine for my Internorm laminated windows and gave me a quote.  I asked a more local supplier for a quote too.  He asked exact spec of glass before going any further, looked at spec and then said he would advise against fitting flim as chances of glass cracking were very high.

 

I went back to BR ppl and they still said was OK but I pressed them and they went to film manufacturer who ran a thermal test on my glass spec.

 

Result back today, film not suitable for my glass.  I am glad I pressed on this.  If I had just taken the it will be fine route and window glass cracked would be a big mess, there is a small possibility -subject to further tests - of some silvered slightly mirrored film being able to be used but I cannot contemplate that in my location.

 

My windows glass is very thick triple glazed laminated both sides.  If anyone else has this spec be very careful about sticking film on. Get thermal rests run before installing film.

 

Back to square one on my overheating problems now...praying for a change in the weather!

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Our window film supplier did the same, as our glazing is a mix of 4-20-4-20-4 and 6-16-4-16-6, all Saint-Gobain Planitherm double low e coated, argon filled glazing.  There was a fair bit of confusion initially, as the glass manufacturer assumed that the film was going to be internal (which is clearly going to cause a potential problem) and said no, when challenged, and convinced that the film was external, they came back and said it was fine.  The suppliers thermal analysis software had already said it was fine, it only ended up going back to Saint-Gobain  because Munster wanted confirmation from them with regard to any impact on the warranty.

 

I believe a lot of the concern stems from the clear issues that are involved if fitting a heat reflective film on the inside of a low e coated glazing unit, as that is clearly going to cause the unit to overheat, by reflecting heat back and forth in the inter-pane void.  An external film removes that risk completely, and is no different to having a low e outward facing coating on the glazing itself (something that is now available, I believe).

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This is an external film and the problem is with our Internorm glass spec which is laminated internally and externally.  We have never considered an internal film as we knew that would cause problems.  They are quoting on an external film so we don't have any confusion on that - unless all are singing from different song sheets ......... and I will go back and check with them again but it clearly states external film -  the spec is very clear, its the same film from the company that Peter used.

 

We have been through the detail of the glass and it is deemed not suitable for the particular type of film because it is not toughened glass and is very thick and has a fairly high solar absorption rate which makes them say they think it is likely to crack. 2 separate film suppliers (different films too) have now come back with the same answer for external film on our windows. I think if you have laminated only on one pane then the problem goes away.

 

I don't understand the glass spec but this is it.

 

We have triple 48mm coated clear glass

 

22b.2(laminated)/16Ar/4/18Ar/b22.2(laminated. (O.5w/M2k, 35db) (3GW-JL)

 

They tell me broadly there are 2 different categories of non reflecting film - transmitting, which is pointless - and absorbing which the one we are looking at - and then there is reflective, the mirrored finish that we can't have.

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I can see the concern if you have laminated safety glass, rather than toughened.  Ours use toughened 6mm safety glass for the outer panes of the glazing that needs it, so there isn't the concern of delamination.

 

It's still a bit odd, though, as one effect of external heat reflective films is to make the glazing units a lot cooler in hot weather.  A lot of heat is reflected before it reaches the surface of the outer pane, with the consequence that all three panes of glass in the unit run a great deal cooler.  Before we fitted the external heat reflective film, the inner pane of our glazing could get quite hot, well over 30 deg C at times.  Now it sits at close to room temperature, even in really bright sun.

 

I wonder if Internorm have understood that the almost clear external films are very strongly heat reflective, or whether they believe that only the mirrored films are?

 

We have both types, the silvered finish stuff for privacy and the faintly tinted stuff where we just need to reflect out heat.  Both have near-identical performance and the glazing units for both sit at the same sort of temperature in bright sun.

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The film suppliers say the almost clear film is absorbing not reflecting. The silvered stuff is reflective and our glass would be ok with that but we would have the planners down on us like a ton of bricks.  We are on a ridge and would be reflecting clear across the valley.  It is a definite no no we even had to ensure non reflective roof covering.

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46 minutes ago, lizzie said:

The film suppliers say the almost clear film is absorbing not reflecting. The silvered stuff is reflective and our glass would be ok with that but we would have the planners down on us like a ton of bricks.  We are on a ridge and would be reflecting clear across the valley.  It is a definite no no we even had to ensure non reflective roof covering.

 

 

Not sure about that, as the slightly tinted film we have stays cool on the outside and is stated in the spec as reflecting 60% of the sun's heat, not absorbing it.  The glass is definitely cooler on the windows to which it is fitted than it is on the windows that don't have it.

 

It's not "light reflective", it's "heat reflective" so doesn't look at all shiny from the outside.  It just decreases the emissivity of the outer pane, so allowing more long wavelength radiation to be reflected away from the glazing unit, rather than pass through it and heat it up.

 

By way of evidence that the 3M Prestige films (the non-light reflective stuff) reflect back a significant amount of long wavelength radiation (heat),  I've attached the data sheets.  The clearest film is the Prestige 90, and it's worth noting that it reflects back 36% of the total solar energy (all wavelengths, so heat light and UV), and reflects back 97% of infrared (heat), yet allows through ~90% of visible light, so appears to be almost completely transparent.

 

Prestige_Series 90 exterior.pdf

 

Prestige_Series 70 exterior.pdf

 

Prestige_Series 40 exterior.pdf

Edited by JSHarris
Edited to add data sheets
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From your link they are clearly stating that the Sun-X film reflects 59% of all solar energy, yet allows through 77% of visible light. 

 

I can't see what bit of "reflects 59% of all solar energy" Internorm are reading as if the stuff absorbs solar energy.  The glass absorbs practically all the incident solar energy without the film, so the film gives a very significant reduction to the temperature of the glazing..

 

When we were looking around I did prefer the look of the 3M Prestige range, especially the almost transparent one, Prestige 90.  You can't really tell this is on the windows at all, yet if reduces the heat getting in a great deal.  The main snag with the 3M Prestige film is that it's a bit expensive.

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Cost has not been a factor, until quote comes in no idea on price and I only have one quote as other supplier declined to quote as risk factor too high (not sure what their product was) . I have not found a supplier of the 3M range.  @JSHarrisDo you have one you could suggest to me please.  

 

thank you for your valuable input as always

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1 hour ago, lizzie said:

Cost has not been a factor, until quote comes in no idea on price and I only have one quote as other supplier declined to quote as risk factor too high (not sure what their product was) . I have not found a supplier of the 3M range.  @JSHarrisDo you have one you could suggest to me please.  

 

thank you for your valuable input as always

 

have you tried contacting 3M themselves?

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