Brit boffins brew nanotech self-cleaning glass

Re: Question

I think it's cr*p phrasing but does actually make sense. On a sunny day heat mainly enters windows via radiation, but leaves by conduction and convection. We get round the heat loss by double-glazing etc., but the amount of heat entering is largely fixed. With this glass they're saying that when it's cold it's transparent to IR, hence all the available radiation passes through, however when it's warm it's reflective so the heat remains outside. "escaping" is an unfortunate word to use.

Re: Question

As I recall, the radiation from the sun arrives at the outside of your window with a lot of energy in the short-wavelength part of the infra-red spectrum. This goes straight through ordinary glass and I expect this stuff too. The re-radiated heat is of course coming from a much cooler system so the infra-red is of the long wavelength variety and this doesn't go through ordinary glass at all well - which is why greenhouses work.

So they are saying (rather badly) that this is something that acts like ordinary glass and keeps heat in when its cold, but lets the heat escape when its hot.

Re: Question

I think it's all to do with vanadium dioxide's anomalous reflectivity:

Natural metamaterial looks cooler when heated

A special coating that can hide its own temperature from thermal cameras has been developed by researchers from the US. The technology relies on the temperature-dependant reflective properties of vanadium oxide, a material that undergoes extreme electronic changes at a specific temperature. When heated from room temperature to 80 °C, the material's thermal radiation rises normally up until 74 °C, before suddenly appearing to drop to around 20 °C colder than in reality. The rather surprising result could have potential military applications, including camouflage, be used in communication systems and help with future metamaterial research.

http://physicsworld.com/cws/article/news/2013/oct/25/natural-metamaterial-looks-cooler-when-heated

They don't discuss the new windows here as they don't need cleaning. The sentence seems clear to me.

It's currently estimated - as in right now - if you install standard windows on a skyscraper, the costs of cleaning them over the next 5 years is the same as it will cost you for their installation.

I infer from this that paying more for glass that does not need cleaning and saves on your energy bills, when it becomes available, is a long-term investment that may cost you less in the long run. Obviously the cost of the self-cleaning glass is an important aspect of this calculation.

Re: Cleaing Costs for Skyscapers?

Maybe having opening windows 80 storeys above ground isn't a good idea ?

Re: Cleaing Costs for Skyscapers?

They are not real windows. They are bolted to a simple structure, not properly framed. More like tiles.

The cost (and more importantly weight) of replacing the lattice which carries the glass panels with proper framing for something like the Gerkin or the Shard will be astronomical. It is much cheaper to put rails around the top, crane on them and get a couple of madmen to clean it (I get nausea from the mere thought of looking down from the cleaner platform).

Re: Cleaing Costs for Skyscapers?

"I'm sure those who build these things have very good reasons for it, but I've never understood why skyscraper windows have to be cleaned from the outside. Surely some sort of mechanism could be included in the frame to allow the whole panel to rotate 180 degrees, so that the outside side is reachable from someone on the inside?"

They MUST be cleaned from the outside because of pressure differential. Think of a skyscraper, especially high up, as like an airplane. There's a positive pressure inside the building versus the outside. So skyscraper exteriors above a certain elevation are hermetically sealed to contain the pressure. The last thing you want to do is break a window at 1000 feet up. It'll cause quite an air blast. I recall a story once of a Toronto guy ramming a skyscraper window (about 25 stories up), breaking it thanks partly to the pressure differential, and falling to his death.

Self Cleaning Glass

We have SCG on our Conservatory Roof (circa 2007) We have had it cleaned by the window cleaner twice in that time (and not for any real reason). IIRC it added about £3 - 4K to the total cost instead of plastic.

Not sure how good it is to be honest as I rarely take any notice of it but I do know it doesn't collect algae like the plastic roofs and i have never noticed a large amount of water marks.

@Rol

"Self cleaning glass has seemingly been available for many years, as I distinctly remember the news about a coating that basically Teflon's your windows.

I must also assume it is bloody expensive and only practical for luxury liner's portholes and other hard to reach places, as I have never heard of it since."

The difference is that this isn't simply a coating, various kinds of which have indeed been around for a while and hit the news every now and then, but the actual structure of the glass itself. Coatings can wear off, but unless someone starts sanding your windows down this is likely to be a lot longer lasting, as well as not involving any toxic materials and so on. While they do discuss a coating as well, that's actually an entirely separate thing and it probably doesn't help their case by mixing the two up; the nano-structures are what make the glass self-cleaning while the coating just helps block IR radiation, and either could be used independently.

Re: Odd I seem to recall Pilkington doing this a few years ago using Titanium Oxide

TiO2 is a proven technology for self cleaning glass, and advertised as such by all the makers of TiO2. Easy to apply to the glass during manufacture. Also applied to glass bottles during manufacture to increase their resilience to bottling line handling.

Seems to me that this is just like lasers - a solution looking for a problem. And a department wishing to big up its "nano-" credentials. Any sensible builder should avoid such "ground breaking technology" like the plague.

Re: What about Bird Shit?

This is where the titanium dioxide acts as a catalyst on current SCG, oxidising the organic products and then waiting on the rain to wash off the loosened guano.

The ultra-hydrophobic vanadium oxide coating may make the bird muck bounce off like that anti-peeing paint. So it never sticks. Look out below!

Re: George Formby hangs up his bucket and sponge

I'm sure it will be more entertaining than continuing to practice his cleaning on a lampost at the corner of the street...

Re: Limited lifetime.

Until they malfunction and fall 1,000 feet to the street below. If you've seen a tower crane collapse, you've got a decent idea of what'll happen; a whole lotta ugly.

Re: This glass for solar panels?

"The best place to put them is a desert, but deserts are typically hot, dry and dusty, and water in a desert is an expensive commodity. Desert panels need to be washed, and if this glass means they could use less water to wash them just as well, that's a big advantage."

Being dry and dusty would that not mean they just need to be blown clean? I'd have thought the dust blowing about in a desert is not likely to be sticky stuff.

The adaptive thermal barrier might be helpful but IIRC there are existing coatings/techniques which are cheaper because it doesn't really need to be smart to keep the panels warm during cold periods.

Rain is actually the enemy of glass since it picks up contaminants and becomes slightly acidic. Over time, this etches the glass and reduces transparency.