As proud as i might be of Canadian buidling products, as far as i know, the laws of physics are basically the same here as they are in the UK.

So, depending on the type of low-e in Arnold's windows the casements, would have a Uwindow,americas of either 1.65 or 1.54 W/m^2K . (This is based on a window size of 600x1500mm, North American temperature differences, 90% argon gas fill and Edgetech's SuperSpacer). So my guess at Uwindow,european would be no lower than 1.4 W/m^2K . In fact, the suppliers website suggests their best 2G casement is Uwindow,americas 1.6 W/m^2K

So i agree with the knowledgwable people on the forum, a 2G window with U 0.8 is unlikely, to say the least (at least until vacuum glazing is commercialized and maybe not even then)


As far as sound attenuation goes, i am at least equally skeptical. Canadian windows are typically 3mm glass. Only switching to 4mm glass when glass areas exceed 1.5m^2. (some USA windows start at 2.5mm!) Whereas UK windows start at 4mm. Thicker glass attenuates sound better than thinner glass. I work for a company that also makes a GRP window with polystyrene insulation in the frame, and i've not seen any independant reports that would lead us to believe that we offer superior sound attenuation to our PVC framed competition.

On the other hand my skepticism may be misplaced. As compelling as anecdotal evidence maybe, i need to see independantly measured data to be convinced that Canadian style insulated GRP window frames offer better sound attenuation than their UK PVC counterparts.


By the way, all of our in-house calculations show that the effect of filling otherwise hollow frames with polystyrene insulation, makes very little difference to Uwindow of a 2G window. However, in a 3G window the effect of filling otherwise hollow frames with polystyrene insulation, does make a difference to Uwindow.

Stephen T, what do you think of
Posted By: fostertom
Radiant transfer is proportional to the difference between two fourth powers, not the the fourth power of the difference. And over the narrow operating band say 253K to 313K, that works out close enough to proportional to the first power of the difference, just like conduction and convection.

So the U value difference you're finding must be due to something else - any ideas?


Went back and checked my textbooks and i think you are correct, its not radiation between the panes that accounts for the difference.
So i think the next most likely culprit is the roomside convection co-efficient
I'll try to track down some people more on top of this topic.....

Re: differences in Uwindow,european and Uwindow,americas

Looks like i was not only wrong about the difference being do radiation heat transfer, but also about the roomside convection coefficient. yikes.

After some discussions w/ more knowledgable people it seems that the roughly 10% difference in U is due to the difference in outside air temperature used to calculate Uglass. In North America we use -18C, i believe Europeans use ?0C?

It was explained to me that this means the temperature of the gases between the panes of glass are different in the each of the two approaches. Different interspace temperatures mean the gases have slightly different thermal properties. This means there are differences in the amount of heat transfer across the interspace by convection and conduction. And apparently this is enough to create the difference....

There can of course be differences in Uwindow, due to size differences. This is particularly true of windows where the glass insulaltes significantly better than the frame.

hope this helps

Posted By: fostertomTime for another 3G price/availability survey. Meanwhile, I'd like advice ...

I think it would be helpful to set a specification as there are huge variations in triple-glazed windows. To be more exact there are significant variations in the properties of both the glazing units and the framing materials.

As an example in order to get a window beneath the 0.8 PH benchmark many people, Rationel for example, are supplying glazing units with a 0.4 W/m/k u-value. What they negelect to mention is that such a unit will typically also have a low g value and relatively lowish light transmission. Another very significant issue with such glazing will be external condensation. It is a problem with glazing units at 1.2 and it is going to become even more prevalent with glazing units at 0.4

Another question that should be asked is why go to triple-glazing. What u-value are looking at and what sort of solar factor? On another thread I saw a reference to a Nordan window with a u-value of 1.2 for a double-glazed window. I spoke with one of their reps before Christmas and he told me that they could probably go even lower then that if the customer was prepared to pay extra for krypton and take a hit on the g-value and light transmission with coatings on both panes.

If you tell me what performance level are you looking to acheive I might be able to help with a specification ?

Monty

You draw it we'll make it! Seriously I think someone with the knowledge should tell a small time joinery manufacturer like me how to build a window! We are pre programed by tradition into making more of the same. Re-program me!

johnz, don't you think that quality 3G units properly installed shd last a gd long time? Just because the typical UK cheaply-fa'bd 2G unit bedded in mastic has limited/unknown life.

Another question is how long the gas filling stays in even the best of units - no one seems to know. Seems to me we can rely on multiple panes and their coatings, but only regard gas fillings as an initial performance bonu, if dead cheap, that may not last forever.

Doing it as 2x or 3x 1G - hard to imagine how that could be developed to be as cheap as 3G, reliable and not requiring constant condensation-wiping. Any ideas?

<blockquote><cite>Posted By: johnz</cite>Fostertoms, building regs/glazing situation .... which shows that even with relatively underperforming glazing elements, shortfalls can be made up elsewhere</blockquote>I'd say, in this more highly glazed case, glass performance is more important than wall/roof - makes the biggest difference to overall loss. It's cheap and easy to get to BldgRegs wall/roof min standard, and progressively harder to do significantly better. But BldgRegs window min standard is so very low, that it's cheap and easy to do twice as well, which has a big impact on overall loss, even tho of smaller area than the walls/roof.

Are you including some local wood working businesses?

That would be greener than importing, or can they not compete in this market?

Hi .. I'm new to the forum and fairly new to the whole issue of energy efficiency in construction .. but I've been reading and am learning fast. What brings me here is a building project due to start in a couple of months .. a garden room/entrance/WCcloakroom extension (5m x 6m single storey) which faces north-east and has mucho glass. I've really had to work on all the energy factors as I want to use the room all year round, and it will join our kitchen via a wide linking space (ie it won't be considered a conservatory for B regs). I have been working with an energy consultant and we now have the building better than B Regs. BUT, this relies on me being able to source windows with U-values of around PH levels. (I am not at all concerned with solar gain - there won't be any.) I want windows which will hang on to whatever heat we put in there - which will be via UFH wet system. So .. all you people who've been thinking about this and researching for years .. I've read your info from a year or so back .. where should I be directing my attention for prices now? I'd really value up-to-date advice.

Hello again ..

Another issue re my NE facing extension and 3G windows - 3 of which are floor to ceiling jobs. I'm debating what to go for re the glass - ie whether toughened or laminated.

We live in a fairly isolated position so security is an issue .. laminated is reckoned to be better from the security angle. But .. toughened is, well, tougher, and we have a lot of grass (quite rough) alongside two of the windows. One firm told me that stones flying from mowers accounts for a fair amount of their business in spring when the mowing season gets going. I'm inclined to go for toughened on the basis that 3G windows are more difficult to break through anyway (ie without worrying too much about the glass). What say you?

Also .. given that solar gain isn't going to be either an advantage or disadvantage .. what arrangement of glass and coatings do you think would be best? I've asked companies about this but got some confusing (or confused) responses. I'm not sure whether they're trying to sell their pet products and/or think that being female I won't understand anyway (I do get this sometimes). So - what glass/coatings arrangement do you think would best suit my situation?

Jo, what is the glass rebate depth of the window frames??

Posted By: howdytomif your alloy frames are a one piece extrusion, ie no thermal break,

then the alloy will still conduct the heat around any infill insulation.

you could drill 6mm holes then after foaming fit grommets

Thanks Tom,
The frames have a thermal break in, i believe, so maybe filling with something insulating would not be possible, or useful?
I am having trouble visualising it, I have never seen a window frame other than installed into a wall, so i don't understand how they are constructed.

peter

Roger .. I meant 4-16-4-16-4, of course! .. J

Ok Jo - 4-16-4-16-4 then, with the argon. Toughened.

2 upgrades worth thinking about: warm-edge spacers (generic term) especially if a vented dry-glazing system is used; maybe a low-E soft-coat rather than the normal hard coat.

Posted By: JoHello again ..
We live in a fairly isolated position so security is an issue ..

If your house is wood framed (i.e. not ICF or brick facade) then the window security is a moot point.
A crook with a cordless circular saw & recip saw can easily cut a hole through the wall.

-Ralph

Some criminals have no respect for the finer points of airtight construction....

J