Green Building Forum - Best glazing

Best glazing

williamd — Thu, 23 Feb 2012 12:19:27 +0000

In a recent magazine article Tim Pullen suggested that argon filled double glazing should be used in south facing windows because a) it has the same U value as standard triple glazing, b) it is cheaper than 3G, c) it is easier to fit than 3G and d) solar gain is greater than 3G.

However in a recent newspaper article Jeff Howell indicated that his industry sources tell him that argon leaks out within a few months of installation.

Does anyone have experience of argon leaking. Are some makes of glass better than others. Is there any alternative to argon that has proved itself, is reasonably priced and is good for solar gain/insulation.

Best glazing

tony — Thu, 23 Feb 2012 12:37:37 +0000

Why compare dg with to 3g without?

It is better to use 3g preferably gas filled and south facing I use a more expensive gas filling, low iron glass, low e coating.

Do you mean best?

dg in any form is certainly not the best.

Best glazing

Joiner — Thu, 23 Feb 2012 13:49:23 +0000

You won't know if the gas has leaked unless you've got a super-duper mega-bucks meter, which you'll also need to check the CONCENTRATION of gas - unless you see condensation on the inside of the unit! Although I guess you could always compare the temp drop across the unit under identical conditions to those pertaining at the time of fitting.

Best glazing

pmagowan — Thu, 23 Feb 2012 14:27:45 +0000

A thermal imaging camera will often show it up (or so I am lead to believe).

Best glazing

Joiner — Thu, 23 Feb 2012 15:10:25 +0000

Still expensive. And how often are you going to hire one to check on the existence and concentration of the gas?

Covered here, where we all learnt a thing or two...

http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=6511&page=1

Best glazing

pmagowan — Thu, 23 Feb 2012 17:13:50 +0000

That is a very interesting post. I read all of it. I am getting my 3G panes on monday, Krypton filled with soft coat low-e. I will be getting out my torch!

Best glazing

Cav8andrew — Thu, 23 Feb 2012 17:22:16 +0000

pm, do you know what method of gas filling was used? There seem to be two types, immersion tank and a form of injection. Still trying to get my head around which system would be the more foolproof/provable, quite like the idea of the immersion method but that's purely a instinctive feeling.

Best glazing

pmagowan — Thu, 23 Feb 2012 17:27:24 +0000

I have a feeling that immersion was the method being used for my units. I think I read about it somewhere in the manufacturers literature. I cant be sure and so I will check the labels, look for holes and shine a torch on them.

Best glazing

Joiner — Thu, 23 Feb 2012 17:29:19 +0000

Incidentally, the fill holes (if that's the method used) can sometimes be hidden away in the corners.

The "provable" bit is going to be a toss-up. With the fill holes at least you have an indication that something's been done, otherwise you're totally dependant on the labels.

Best glazing

fostertom — Thu, 23 Feb 2012 17:30:30 +0000

Posted By: williamdsuggested that argon filled double glazing should be used in south facing windows because a) it has the same U value as standard triple glazing, b) it is cheaper than 3G, c) it is easier to fit than 3G and d) solar gain is greater than 3G.

a) Argon fill (rather than air) is cheap and is the minimum spec for both 2G and 3G, so 3G has higher U value.
b) From continental sources, 3G being industry standard is same or cheaper than 2G.
c) ?
d) only applicable if the window in question really 'sees' a great deal of low-angle winter direct sun, what with orientation, shading by the building, horizon (adjacent buildings, trees) obstructing low-angle sun. If winter direct sun is obstructed, then no solar gain is available, so go for max U value.

Regardless of argon (or more expensive gasses) leaking or not, 3G shd be the standard option in 95% of cases.

Both these articles sound like the usual propaganda used to obscure the UK window industry's abysmal standards.

Best glazing

pmagowan — Thu, 23 Feb 2012 17:31:07 +0000

I will be thorough!

Best glazing

Cav8andrew — Thu, 23 Feb 2012 17:35:48 +0000

Good point Joiner, makes you want to actually go to the factory and see your actual units manufactured.

Best glazing

MarkBennett — Thu, 23 Feb 2012 17:46:31 +0000

Posted By: fostertomd) only applicable if the window in question really 'sees' a great deal of low-angle winter direct sun, what with orientation, shading by the building, horizon (adjacent buildings, trees) obstructing low-angle sun. If winter direct sun is obstructed, then no solar gain is available, so go for max U value

I'm inclined to agree. Usually there is a trade-off between u-value and solar gain. For our proposed house the glazing difference is negligible between the two glazing types. I will probably go for the higher u-value over the higher solar gain.

My reasoning is that the U-value works all day and night, while the solar gain is only relevant for a part of the day as a result the solar gain is likely to encourage slightly wider temperature swings. My SE facing windows are large and mainly bedroom windows, where i don't want to risk overheating, so a smaller temperature swing is more desirable.

Best glazing

Monty Gerhardy — Thu, 23 Feb 2012 22:52:27 +0000

Posted By: Cav8andrewpm, do you know what method of gas filling was used? There seem to be two types, immersion tank and a form of injection. Still trying to get my head around which system would be the more foolproof/provable, quite like the idea of the immersion method but that's purely a instinctive feeling.

Just ensure that the supplier has BS EN 1279-3 (and -2) certification in place. 1279-3 allows for leakage rates of no more then 1% per annum. With well made units I would expect the actual leakage to be at most 50% of that figure. You'd be daft buying from anybody who doesn't have the certification in place as its mandatory now.

Monty

Best glazing

Joiner — Fri, 24 Feb 2012 10:38:07 +0000

Agree Monty, but it's still just a piece of paper and the process is still subject to human fallibility.

What's needed is a simple technique like the one Megacycles gave us in Gusty's thread to check for a low-e coating.

Something for the boffins on here to get their heads around?

Best glazing

Jonti — Fri, 24 Feb 2012 11:25:39 +0000

Posted By: Monty Gerhardy
Posted By: Cav8andrewpm, do you know what method of gas filling was used? There seem to be two types, immersion tank and a form of injection. Still trying to get my head around which system would be the more foolproof/provable, quite like the idea of the immersion method but that's purely a instinctive feeling.

Just ensure that the supplier has BS EN 1279-3 (and -2) certification in place. 1279-3 allows for leakage rates of no more then 1% per annum. With well made units I would expect the actual leakage to be at most 50% of that figure. You'd be daft buying from anybody who doesn't have the certification in place as its mandatory now.

Monty

BS EN 1279-3 shows that the producer can manufacture to a specific standard but does it mean that ALL their units are at this standard? Is it not the case that pieces are often specifically made for the test (either officially or not) but general production does not necessarily meet the same standard?

Jonti

Best glazing

Joiner — Fri, 24 Feb 2012 11:47:03 +0000

BS EN 1279-3 is just one of the standards you should be looking for. Typically, you can be fairly confident if the manufacturer has something like this lot here...

http://www.theomegagroup.co.uk/accreditations.php

... It's the: "BS EN 1279-6:2002 - Glass in building. Insulating glass units. Factory production control and periodic tests." ...that's probably the most important one because it addresses the issue I referred to.

My point was specific. Fallibility in terms of human error, I ought also to have mentioned machine malfunction. The point being that at the end of the day there's a lot of trust involved, but at least with the production procedures in place to ensure standards are adhered to your level of confidence can be higher.

Best glazing

pmagowan — Fri, 24 Feb 2012 12:17:14 +0000

I suppose the best way of checking a window is with the temperature compared to a known window. You could use a thermal camera. It would only be obvious if there was a significant difference in u value.

Best glazing

gustyturbine — Fri, 24 Feb 2012 12:36:58 +0000

When I started asking questions I was told that nearly all odern windows are filled using the bath system. Leakage is another question. As joiner mentioned, condensation is a give away on warm days etc.
Good luck as it can become a bit of a nightmare,
Gusty.

Best glazing

Joiner — Fri, 24 Feb 2012 14:23:13 +0000

Is ignorance REALLY bliss in this case?

Best glazing

Megacycles — Fri, 24 Feb 2012 20:38:53 +0000

If the graph appears it shows, according to the Swedish study it was taken from, that only glazing with a U-value <1.4 is likely to produce daytime external condensation (I think the dotted line is the steeper curve). 2G 16mm air fill is around 1.4U, with argon around 0.2 less so the former will rarely produce external condensation caused by radiative overnight cooling. This fits in with the observations from window fitters who report complaints from customers whose windows condense externally only started when argon became available!

Local conditions will strongly influence the chance of external condensation so its far from a definitive test but I commonly see it here in autumn , and occasionally through spring/summer, claimed U value 1.2.
It rarely extends above the bottom half of the glass though, I wonder if the argon fill is low ,say 50%, how the gasses distribute within glazing. Does argon sit at the bottom so U value increases toward the top or does Brownian motion keep it all well mixed?

Best glazing

Monty Gerhardy — Fri, 24 Feb 2012 20:57:40 +0000

The external condensation is a result of the temperature of the outer pane falling below the due point. The lower the temperature of the glass the greater the incidence of external condensation. In other words you will get it even more freqently with triple-glazing using glass of Ug 0.7 or less.

Monty

Best glazing

djh — Sat, 25 Feb 2012 20:43:32 +0000

Posted By: MegacyclesI wonder if the argon fill is low ,say 50%, how the gasses distribute within glazing. Does argon sit at the bottom so U value increases toward the top or does Brownian motion keep it all well mixed?

I don't know about Brownian motion but I'd guess that there's enough convection created by whatever light passes through the window to keep the gas well enough stirred. But that's a WAG; I claim no expertise.

Best glazing

tony — Sat, 25 Feb 2012 22:21:47 +0000

They will be totally mixed

Best glazing

Ed Davies — Sat, 25 Feb 2012 23:19:14 +0000

I think Tony is right. Perhaps it's worth explaining why.

When you have a mixture of gases each behaves nearly independently. Collisions between atoms/molecules of the different gases will equalise the temperatures but the pressures and densities are separate and, in the absence of mixing, will also reduce with altitude at the different rates appropriate to the densities of each. Over the height of a window this difference will be tiny so the ratio between densities and pressures at the top and bottom will be nearly identical. Any tiny amount of convection or other forced movement will result in the gases mixing completely removing even this small effect. The denser gases will tend to be held up by the lighter gases.

In much the same way, all the longer-lifetime gases in the atmosphere are well mixed despite being of different molecular weights. The percentage of oxygen in the atmosphere at the top of Everest is about the same as that at sea level despite Oâ‚‚ molecules being heavier than Nâ‚‚ molecules. It's the absolute amount of oxygen available, not the proportion, which makes breathing high up a problem.

Best glazing

fostertom — Sun, 26 Feb 2012 10:29:28 +0000

Are all gasses miscible in this way?

Best glazing

Ed Davies — Sun, 26 Feb 2012 10:59:57 +0000

Yes, I think so. AIUI, gasses don't have bonds between adjacent molecules - each molecule just flies around whereever until it collides with another molecule or the edges. (In some cases, like Argon, each â€œmoleculeâ€ consists of just one atom.)

Liquids do have bonds of sorts between adjacent molecules but they keep making and breaking those bonds as they move around. Surface tension is where there are bonds left over at the edges which wrap round a bit. I think miscibility is to do with the nature of these bonds - Tony?

Solids have bonds between adjacent atoms/molecules which are static.

Best glazing

tony — Sun, 26 Feb 2012 14:54:20 +0000

mixing of gasses is mostly to do with temperature but even at very low temperatures they mix well

Possible exception is for very a heavy gas like Radon which can sink in still coolish air -- in the atmosphere it mixes well.

In a dg unit I would expect perfect mixing