Window Films for UV protection

[Jeremy Harris]

I've just been out and taken a thermal image of the glazing.  Not ideal, as it's warm and overcast, with no direct sun, but the contrast between the glass and the patches of heat reflective film is marked:

The cooler thing at the far left is a stainless steel mailbox.

[Gone West]

That's interesting. Do you have any data for the 3M Prestige film?

[Jeremy Harris]

Not yet, the chap is sending me all the details next week, together with a thermal analysis of both systems when applied to our glazing.  The warranty is longer on the 3M stuff (12 years IIRC) as it doesn't need edge sealing.  Apparently the Sentinel Plus does need edge sealing, as it uses a metal sputtered internal film layer and this can corrode unless the edges are sealed after fitting.  The 3M stuff has no metal coating, it's a multi-layer construction, that presumably relies on mixing film layers with differing refractive indices to get the performance.  It's also more expensive.

As soon as I have some more details I'll post them here, but based on the thermal image above I doubt that there's any significant practical difference between either film.  The chap was saying that the almost clear version of the 3M film is very nearly as good thermally as the medium tint, as it really only reflects IR, and allows a fair bit of visible light through.  Our choice will probably come down to the privacy enhancement, given the similarity in IR reflectance.

Both of these films block around 95% plus of UV, which may be a consideration in some applications (although I think that triple glazing probably blocks a great deal of UV on its own).

What I found interesting in the thermal image is that the plain glass was allowing the thermal imaging camera to read the room temperature from inside, so there was virtually no IR reflection from it at all from outside in (which fits with the spec for the glazing).  You can also see how the floor inside the hall has warmed up, with the lower part of the glazing seemingly warmer than the upper part which is looking at the temperature of the wall to the rear of the hall.  You can just make out the thermal reflection of me holding the tablet with the Seek Thermal camera up to the right of the door handle, and also the thermal reflection of the post and rail fence behind, so there is some IR reflection from the standard glazing, but not a great deal.

[Jeremy Harris]

We have the film fitted, the guys left about half an hour or so ago.  My first impressions are that the reduction in solar gain through the gable is absolutely massive.  It's not been a particularly hot day, but the difference when you open the front door and feel the heat of the sun, compared with standing in the sunlit area of the hall with the glazed door closed is enormous.  You literally don't feel any heat from the sun coming through the glazing at all.  By this time of day, in weather like this, both the floor cooling and the MVHR cooling would be running (floor cooling comes on at 22.5 deg C, MVHR cooling comes on at 23 deg C).  Neither have come on yet, and now it's well past 4pm I don't think they will.

The stainless steel Sentinel film does make the entrance hall very slightly darker, but that's partly due to me having got used to it being very bright in there.  It's far from gloomy, but the reduction in visible light is noticeable.  The impact on privacy is high, at least in daylight.  This film is a very effective "one-way mirror", and prevents anyone seeing in from outside almost completely.  I think this may take some getting used to, as from inside you can still see out very clearly.

The 3M film in the bedroom hasn't really had a chance to show any effect, as it was fitted after the sun had shifted around away from that wall, but it has very little impact on the light level in the room, but also provide less privacy.  I should know tomorrow morning how effective it is at blocking solar gain, but if it performs as the thermal images of the samples suggest, then it should be equally as good as the front gable.

In terms of external appearance, I'm a bit surprised to find that I prefer the reflective look of the stainless steel Sentinel film over the plane glass.  To me it enhances the appearance of what is a fairly prominent feature at the front of the house; not something I was expecting.

It's early days, and it will take some time to assess how this film performs over a range of weather conditions, but right now I'm very pleased with it, it seems to perform far better than I expected and has shown that I was mistaken in thinking that the gable glazing wasn't a major contributor to the over-heating problem.  I was considering just the area of floor that was being heated by the sun coming in through this glazing, and what this film has shown is that it significantly reduces the temperature of the inner glass pane - this is now near-room temperature, and much cooler than the inner pane on the windows that don't have the film applied.  Clearly there must have been quite a lot of heat being conducted and radiated from the inner glass panes of this glazed area, and that was contributing a lot more heat than I had thought was coming from this area.

If the weather is cooperative I'll try and take some photos tomorrow - the camera batter was flat when I tried earlier and I don't have a charger over here.

The cost was a bit less than the price Peter Starck quoted for his gable glazing, but still quite costly.  It took three chaps around 4 hours to do the 5 fixed panes and the glazed door in the gable, plus the two panes in the bedroom window, and they hired a scaffold tower locally for the day that added to the cost.  Having seen the process I don't think I'd want to attempt to DIY it, as the job is made massively easier with the proper film roll holder, dispenser and cutting/slitting machine they use.  Plus there is no way that you could do a large window on your own, it really needs two people just to handle the film.

 

[jack]

7 minutes ago, JSHarris said:

... but right now I'm very pleased with it, it seems to perform far better than I expected and has shown that I was mistaken in thinking that the gable glazing wasn't a major contributor to the over-heating problem.  I was considering just the area of floor that was being heated by the sun coming in through this glazing, and what this film has shown is that it significantly reduces the temperature of the inner glass pane - this is now near-room temperature, and much cooler than the inner pane on the windows that don't have the film applied.  Clearly there must have been quite a lot of heat being conducted and radiated from the inner glass panes of this glazed area, and that was contributing a lot more heat than I had thought was coming from this area.

Very interesting.  It's pleasing to perhaps have identified another potential contributor (on top of your local microclimate) for the apparently very different performances of our houses in warmer weather, given the similarity in construction type and window performance.

As you know, overheating isn't something we've yet experienced to any great degree.  I was showing a friend of mine around yesterday and we noted how the overhangs to the south on many of the windows completely shade them through the middle of the day.  We then have external blinds that come down in the afternoon to the west, and then trees to the northwest shade us for the rest of the evening.      

As a comparison, when I got back from a walk this morning at about 9, the house was a little warmer than I like, especially upstairs.  Since it was still cool despite the sun, I cracked some windows upstairs.  The house cooled down fairly quickly and has remained cool all day.  

On the flipside, I believe we need quite a bit more heating in the winter than you, so it's swings and roundabouts.  It'll be interesting to see whether this film changes the balance for you (ie, less cooling required in summer, but more heating required in winter).

[Gone West]

That's interesting Jeremy, we are hoping to have ours installed this month so I'm hoping it will be as effective. Will report back when it's completed.

[Gone West]

Had our window film installed today. Had to wait a couple of days for the wind to die down a bit. It's not easy to see the difference between glazing with the film and without. I'll have to wait till this evening to see what the effect is on solar gain.

[Moira Niedzwiecka]

We had heat film fitted to the large display windows of our south facing office.

We actually didn't notice any difference to the temperature & ended up have an awning fitted instead.

 

[Gone West]

17 hours ago, Moira Niedzwiecka said:

We had heat film fitted to the large display windows of our south facing office.

We actually didn't notice any difference to the temperature & ended up have an awning fitted instead.

 

 

There are many different internal and external window films for different applications and it sound as if the specification was wrong in that case. I worked in an all glass building built in the late sixties that was single glazed. It overheated in the summer and they fitted a mirrored film which even back then made a huge difference. The film I have had fitted has made a big difference to the amount of solar gain and glare in my sitting room.

[Nickfromwales]

On 23 July 2016 at 15:55, Moira Niedzwiecka said:

We had heat film fitted to the large display windows of our south facing office.

We actually didn't notice any difference to the temperature & ended up have an awning fitted instead.

 

 

Can you give details of which make / type of film you went with please?