Saleswoman says that there’s argon in the space between the windows, and that it’s 6 times denser than air. I doubt that, but if it’s true, wouldn’t the increased density mean that it’s a worse insulator than a less dense medium? Meaning that I’ll lose more heat through that window in the winter than if the space were filled with just air? I had the feeling she was trying to talk “scientific” to make a sale, but it only made me more skeptical. Dopers?
The higher density dampens convection currents. There’s no way argon is six times denser than air though, it’s more like 25%.
I would think a denser material would insulate better, which would be why exterior walls tend to be filled with insulation rather than left hollow. How far wrong am I?
Reasonably far. If density were the thing, cast iron walls would offer good insulation. They don’t.
Air is a very good insulator, provided it is not allowed to circulate. Insulation inside walls (e.g. batts of fiberglass) work by trapping lots of air which can’t circulate.
But we try to fill them with the least dense material possible - foam, expanded pellets or light, fibrous stuff. It’s not the denser solid that’s doing the insulating, it’s the little trapped pockets of air/gas. The insulation material just stops them moving around and transferring heat via convection.
Actually closer to 38% - 1.78 g/L vs 1.29 g/L
Density in-and-of-itself doesn’t matter. The only thing that matters is how well the medium attenuates the transfer of heat.
Heat is transferred via conduction, convection, and radiation. So all else being equal,
- The lower its thermal conductivity is, the better.
- The lower its convection coefficient is, the better.
- If it is a fluid, then the less it is allowed to move or circulate, the better.
- The better it attenuates heat los via radiation, the better.
Googling argon “six times denser” makes it appear that every window manufacturer and home improvement site in the world believes it is 6 times denser than air. Where do they get that? Looking at their properties, I can’t find any number of argon’s that is six times the corresponding number for air.
Sulfur hexafluoride is also used in windows and it’s about 5.14 times as dense as air. I wonder if that’s where the argon myth came from.
Density is not a criterion for insulation. Here is an article that compares Argon with some other gases for insulation properties -
cite
Although its a different insulation application, the underlying reasoning is the same
Ok, then my related question is this: wouldn’t it be best of all to have a vacuum between the panes? I presume you can’t do this because the panes would tend to bend in toward the center and possibly eventually crack if the vacuum is strong enough. But what if the glass had little columns placed every so often between the panes, or even without them what if the vacuum was not total. Wouldn’t that tiny bit of air - or whatever - be a better insulator than filling the space with some gas?
I’m sure that’s been experimented with, but the latest thing I saw was a triple pane. Two panes of glass and a center ‘pane’ of some type of plastic. After the window is assembled it’s put into an oven so the plastic shrinks and pulls tight so it’s nearly invisible. The plastic is also coated with various types of metals to reflect heat and/or light. The idea behind this is that any air currents that do manage to set themselves up will have to get set up on one side of the film, transfer to the other side of the film, create a current on that side and then transfer heat to the far side of the glass (into the house in summer, out of the house in winter). That’s a lot more work for your furnace to do in winter and should, keep the windows warmer (and the opposite in summer). That’s all on top of the metal coating on the film to reflect heat/light.
Pressure?
Re vacuums, I think they’re the best insulators, so they’re used in vacuum flasks. People wouldn’t accept little bits of glass supports in their windows, though.
One of the best insulators is an aerogel. There is so little actual solid material it makes essentially no difference to the final result, and it traps the gas in pores so small that there is no circulation. Even better, there are aerogels that can support a vacuum. So you can create a sandwich around an aerogel and evacuate it. This produces an astonishingly good insulator. However the downside is that the best we can do is produce aerogels that look like their nickname - solid smoke. Creating an aerogel with a very tightly controlled structure could make one that was transparent. That would revolutionise window technology. As it is, you can get translucent panels for building. Would be great for skylights.
Here is an article from 2009 on vacuum windows that were expected to make it to market in 2011-2012. The panes were only 1/4 millimeter apart and had little “pillars” to keep the panes separated that the company said were visible to only about 50% of people when viewed at a high angle. No idea if they hit the market. This company only makes glass to supply window manufactures so it’s up to those companies to use it.