Help! My Windows Are Melting My Grass!

[Ben]

Actually they're not melting my grass, but I ran into this on reddit, and did not know it was a thing that energy efficient windows, when reflecting the sun, can melt artificial turf, ruin car paint, and melt vinyl siding. It was of interest to me because this time of year, when I take the dog out for pre-bedtime business, the setting sun is directly in line with my office window, with the back patio in between. When I walk through that line, heat hits my head and it feels like I'm an ant under a magnifying glass.

I did not know this was common and that there are films specifically designed to stop it, which I am now considering putting on that window.

https://windowfilmforturf.com/pages/what-causes-vinyl-siding-to-melt#:~:text=Melted%20Vinyl%20Siding,-Experts%20call%20the&text=Energy%20efficient%20windows%20can%20melt,here%20is%20much%20the%20same.

[WLJ]

Can't speak to the effectiveness of the flims but this may be of some related interest
From 2013

'Walkie-Talkie' skyscraper melts Jaguar car parts
https://www.bbc.com/news/uk-england-london-23930675

No more Walkie Scorchie! London skyscraper which melted cars by reflecting sunlight is fitted with shading
https://www.dailymail.co.uk/news/article-2786723/London-skyscraper-Walkie-Talkie-melted-cars-reflecting-sunlight-fitted-shading.html

[Brad Johnson]

Go with a Fresnel lens and make the most of it. Everyone needs their own personal Death Ray.

Brad

[HankB]

When an entire building is curved, it acts like a huge concave mirror and can indeed damage whatever lies near the focus.

Individual windows acting as individual mirrors? Well, sure, but a flat mirror won't give you any more light on a surface than the original source. Necessarily LESS, of course.

Color me skeptical when it comes to individual flat windows being sufficiently concave to act as solar concentrators. A quick search shows that vacuum insulated glass has pillars every couple of inches between the 2 layers of glass to support the glazing against atmospheric pressure, limiting the concavity.

[Ben]

When an entire building is curved, it acts like a huge concave mirror and can indeed damage whatever lies near the focus.

Individual windows acting as individual mirrors? Well, sure, but a flat mirror won't give you any more light on a surface than the original source. Necessarily LESS, of course.

Color me skeptical when it comes to individual flat windows being sufficiently concave to act as solar concentrators. A quick search shows that vacuum insulated glass has pillars every couple of inches between the 2 layers of glass to support the glazing against atmospheric pressure, limiting the concavity.

Sorry, personal experience says you're wrong. My window is flat, and it is HOT when I get between it and the sun when the angle is right. There are a ton of articles on this.

[HankB]

Sorry, personal experience says you're wrong. My window is flat, and it is HOT when I get between it and the sun when the angle is right. There are a ton of articles on this.

For a FLAT window -

If you get between your window and the sun, your window is shaded by your shadow, and won't reflect any direct sunlight.

If you position yourself so that you're in both direct sunlight and whatever fraction of sunlight the window reflects, you'll note a modest increase of insolation. (Note the spelling.)

If you position yourself so that you're shaded from direct sunlight but in whatever fraction of sunlight the window reflects, you'll note some insolation, but necessarily LESS than from direct sunlight.

If a LOT of windows are reflecting sunlight to the SAME area . . . that's a solar concentrator. Don't stand there.

[Kingcreek]

We went with window tint on big windows for our greatroom, west and south with sliding glass doors on the north.
Only problem we have is the damn birds. 3 different breeds have been beating the bell out of them and making a mess for about 8 weeks. We did it 3 or 4 years ago but this year has been terrible.

[Ben]

you'll note some insolation, but necessarily LESS than from direct sunlight.

Again, single flat double pane window and more - much more - heat than direct sunlight.

Understanding the Problem
The Science Behind the Reflection
Low-E windows, designed for energy efficiency, inadvertently create hot spots due to their reflective properties. These windows can act as magnifying glasses, focusing the sun's rays onto a small area, which can significantly increase the temperature of the surface it hits.

The Impact on Different Surfaces
Siding: Various types of siding, particularly vinyl, are susceptible to warping and melting when exposed to high temperatures.
Artificial Turf: Synthetic materials in artificial turf can melt or deform, altering the appearance and functionality of the landscaping.
Other Surfaces: Concentrated reflections can also affect automobiles, patio furniture, and other outdoor items.

Reports show the coating used on the windows to reflect the sun, combined with a concave effect in some windows, magnifies and intensifies the beam up to 200 degrees Fahrenheit. The problem is worse in late fall, winter and early spring due to the low angle of the sun.

Problems with low-e windows have been reported across the country. The beams have melted vinyl siding, plastic and paneling on cars and garbage cans. Reflections from the windows burned people at a pool at the Vdara hotel, a high-rise in Las Vegas. The windows on a London skyscraper were blamed for melting part of a Jaguar XJ. The Consumer Product Safety Commission said beams from sunroom roofs have started fires on cedar shingles in at least four homes.

[HankB]

Again, single flat double pane window and more - much more - heat than direct sunlight.

A simple flat reflector won't focus light.

Reflections from the windows burned people at a pool at the Vdara hotel, a high-rise in Las Vegas.

The wall of windows at the Vdara hotel is not flat. Overlapping reflections from MANY windows concentrate sunlight.

The windows on a London skyscraper were blamed for melting part of a Jaguar XJ.

The wall of windows at the London skyscraper is not flat. Overlapping reflections from MANY windows concentrate sunlight.

[Ben]

It's single Low-E windows melting siding and starting fires. I already told you I personally experienced the heat effect and that there are literally dozens of articles on it you can find with a simple google search.

https://apnews.com/article/business-fires-8a4779a964566e84ac73d97aa32b517b
https://abc7ny.com/7-on-your-side-consumer-low-e-windows-emission/2264513/
https://www.fireengineering.com/fire-prevention-protection/the-dangers-of-sunflight-reflected-off-energy-efficient-windows/

[Ben]

Just now took the thermo out to get window readings. One showed 264F, and once I got it lined up (difficult without going blind) I hit 381F. This was at 845PM.