Hi there, I am trying to source triple glazed windows for a new build .I would also like to know anyone who has them fitted and if they are good as expected.
Many thanks

I bought mine in from Sweden - fully finished (painted) wooden frames, tripple glazing, argon filled, low e etc. Not much more than buying from the UK and they are stunning quality. Best bit is the sound proofing - good tripple glazing beats double every time. My advise though - look to our european neighbours as they are years ahead of our own domestic industry.

There are a few UK resellers, but I went direct and arranged my own shipping...

http://www.spfonster.se/ is their main web site... these were the ones I bought (as they look a bit similar to british style windows) http://www.spfonster.se/1C3BEC86-A57E-4A06-B725-8BD656003FFD.W5Doc

Posted By: fostertom
Note that by 'Scandinavian' I mean windows where frame and opening sash are flush on the outside ... - not designs based on the British 'stormproof' principle where the sash lips over the frame on the outside...

On an aesthetic note, I think flush looks much nicer than stormproof.

There's lots of emailed interest in the results of my 3G roundup - I've just sent out quote invites to 7 cos and there's 4 more I'm awaiting info from. So many of them try to talk me out of 3G "for the British market"! I will publish full details eventually, and keep you posted meanwhile.

Does anyone know why absolutely none of them can offer 2x16mm cavity 3G units, all settling for 2x12mm, whilst emphasising the importance of the full 16mm cavity in their 2G units? Does the 16mm optimum not apply when it's 3G?

So do triple glazed windows actually make sense in the UK climate? Reduced g values, increased costs, extra embodied energy. I'm certain there is no financial payback. Is there even a carbon one?

BFRC A rated double-glazed windows are already net contributors of heat energy over the course of a year. So what extra value does triple glazing add?

This gives pause for thought. Am I understanding right? In UK where extreme cold isn't usually the problem, we afford to can relax a little on maximising glazing U-value, and thereby benefit more from solar gains, which high U-value glazing keeps out?

In that case,

Posted By: Mike Georgesummer cooling requirements outweighing the energy saved by triple glazing during winter

seems wrong way round. In UK, max-U-value (triple) glazing, by resisting solar gain, wouldn't save so much energy in winter but would by same token reduce cooling requirements in summer.

Fostertom,

The focus of the student project was to simulate a typical dwelling to current building regs. Then explore possibilities of saving energy used to heat the building while maintaining comfort conditions, typically 18 -23 degrees C.

As the windows are the weakest thermal element, it would seem the obvious thing to do would be to reduce the u-value as much as possible. However, what seemed apparent when incorporating triple glazing was the effect this had on summertime overheating, especially in South and West facing rooms.

A limitation of this is that the students were not investigating reflective or other high-tech glazing options, they were merely attempting to reduce the u-value by trying to find the optimum glazing configuration. Perhaps high tech options would give greater favour to TG

Of course this is also always context dependent and shading measures can of course mitigate overheating, but this also has cost implications.

Regarding extreme temperatures, hotter summers and milder winters mean less heat is lost during winter and more overheating in summer yes? Last time I was in a conservatory in Summer it got pretty damn hot.

Mike,
It's all in the g-value (what did your students run in the simulation?). Typically double glazing has a higher g-value than triple and as a result is more prone to over heating. Triple has a lower g-value and thus cools the building in the summer, but as it can be a net-contributor during the winter you win under this condition also. Another way to look at it is that with triple glazing you can have larger windows and avoid over heating, whereas DG requires smaller. Of course as Tom notes, opening the windows always helps.
Also 18 -23 C is limited 25/26C is more typical (provided that it's less than 5% of the year).

All,
Ensuring that the windows are net-contributors are the important in reducing carbon emissions (in PH it is also peak load so U-value also plays a part, this may require triple glazing. The EE saved on heating systems offsets the EE from 3G.)

Thermal comfort is another issue, radiant temp and down drafts etc. Internal pane temp needs to be >16C (17C PH standard) under design day conditions. By addressing the comfort issue you can reduce service instalation costs (i.e. rads don't have to be under the window.)

PHfan,
I can only go off what I've seen but have no calcs of my own to say one way or another.

Mark

Mike,
In the USA they call it the Solar Heat Gain Co-efficient. Basically it's the proportion solar irradition transmitted through the glass; the more layers of glass, and the lower the emissivity of the low-E coating/s the lower the g-value. Say 64% for DG and 52% for 3G.

Mark

Tom,
Both. Low E reduces g-value (hence why they are also known as a selective surface). Triple reduces g-value due to the fact that glass isn't actually clear and thus impedes the flow of light.

Also I'm not arguing that we "need" 3G. (That's where this thread started, so I have tried to remain contextual.)

In a broader respect I was merely trying to point out aspects of a performance specification which can help to ensure that comfort is achieved (by my reckoning a good start to determining how well a window should perform). These comfort criteria, when combined with a given climate, determine the maximum permissable U-value. In order to offer a net-contribution to the winter space heating a window with a given U-value can support a minimum g-value (ideally this will be exceeded). By following this logic all arguements about whether 2G or 3G windows should be used is rendered meaningless. What ever glazing technology satisfies the requirements is adequate, once these conditions are satisfied further conservation measures can be contemplated. On this basis to satisfy the comfort condition where the internal pane temp is 16C (reasonable radiant temp and minimal down draft) when external temp is -14C a window with a U-value of 0.8w/m2K, g-value >50% is required. (A very good question is "What is max. U-value and min. g-value required for the various regions of the UK?" At this time it's a question that I'm currently trying to answer.)

Having had a look on the BFRC website I must say that it's clear as mud as to how they actually test the frames using the software i.e. what are the test conditions (degree days, external design temp, solar irradiance etc. Apparently the whole of the UK is one climatic zone; so whether your in Scotland (-10C, XX degree days) or Southern England (-5C, YYY degree days) you're meant to get the same solar radiation? The BFRC have used one big tar brush for us all. Not particularly useful when you trying to design buildings that are appropriate to climate!) As an example, an "A" rated window may perform in a satisfactory manner in London but "poorly" in Glasgow. I'd argue that greater regionalism is required from the BFRC.

Mark

Posted By: Mark SiddallLow E reduces g-value

Does it necessarily? Low E's not the same as solar control glass. Low E aims to minimise resistance to incoming high frequency solar radiation whilst maximising resistance to outgoing low frequency radiation. The better the low E coating, the greater the ratio between these factors. How much more resistive to incoming solar is a good low E coating, than plain glass?

Posted By: Mark SiddallTriple reduces g-value due to the fact that glass isn't actually clear and thus impedes the flow of light

How much more resistive, actually, is the third, non-coated layer of glass?

When extra-special low E coatings and/or 3G result in super-low U values, does that or does it not include the expectation of solar gain reducing nett seasonal heat loss, giving a lower 'effective' U value?
If yes, then the solar gain is already factored in, and the resultant U value is in fact substantially lower than say a gd 2G window, so why is it being said that the 2G window would do better by allowing more solar gain?
If no, and no expectation of solar gain is included, just the part of the low E coatings' performance that relates to outgoing radiation, then how come the U value is so affected by the coating's ratio of incoming to outgoing resistance?
Something doesn't add up here - I smell a falacy, or double-counting or something.

Also, if yes, it's so full of assumptions, whether the window actually sees the sun etc, as to be meaningless.

Yes, it does seem that the attempt to combine assumed solar gain with raw conductive/radiant outbound U-value, into one practically-useful equivalent-U-value, is doomed.

As you say, Mark, just what does it assume about how much direct sun the particular window sees, and therefore how much solar gain to set against the raw outbound loss? Does it assume low horizon, Isle of Wight, due S orientation, or Orkney, totally shaded, due N orientation? If it assumes Yorkshire (plain or Pennine?), suburban garden, E/W orientation, I wouldn't call that 'neutral', just 'less active than due S'. If it's said that at best a window can be a seasonal nett gainer of energy, and at worst something more lossy than generally quoted, then we're looking at an equivalent U-value ranging from say minus 0.5 (gain) to 2.0 (loss), for a window presently quoted as 1.2. That's so wildly misleading, that it looks more like DG-industry serving market hype than merely a failed attempt to be helpful - but it's presumably what the govt's hopes for carbon targets rest upon.

What we need is a whole-window raw U-value figure quantifying pure conductive/radiant loss with no assumption about solar gain; then we so-scientific designers do our sunpath studies and consult our regional data to determine just how much direct sun each individual window gets (which will depend as much on the vagaries of nearby buildings and trees, as on orientation) and therefore how much gain to set against the raw loss. Even then, it's no good saying that across the heating season the window is a nett gainer or whatever, if the building has no ability to store and even out that gain across the season - and how many can do that trick (yet)? In a lightweight fast response building, solar gain is nothing but an overheating problem, because it's unlikely to coincide, on a scale of hours, with heating need - quite the reverse, in fact.

So it seems to me that, unless your building is deliberately designed to store heat over an exceptionally long period, all talk of solar gain through windows should be ignored, maybe even prevented. Assumption of solar gain through windows, to arrive at a more favourable effective U-value is almost wholey misleading and counter-productive and should be banned - or at least members of this forum should know to ignore such marketing blandishments and demand the real, depressing U-value figures.

Meanwhile, don't pay extra for sophisticated coatings whose main feature is a highest-possible ratio between outgoing resistance and incoming receptivity. Unless the window in question definitely sees a lot of direct sun (during the heating season - forget summer), plus the building is designed to store and even out the gain, then solar gain is irrelevant, harmful even, so the incoming part of the coating's performance is irrelevant - only the outgoing part is useful. Presumably, for a window that sees little sun during the heating season, and so simply needs to maximise its raw outgoing resistance, then a coating that does just that (and hang its incoming receptivity) could be cheaply produced and do even better at that limited trick than an expensive dual-performance coating. Reserve the latter for genuine solar-gaining windows - and they will be few.

Perhaps this is where 3G, cheaply-coated raw outgoing-resistive windows would be used, in most parts of the building, where solar gain's not expected or welcomed. Then perhaps 2G, sophisticated dual-performance coated windows would be used where you really can welcome, capture and exploit solar gain.

Mark, thanks for the info on g-values. I have now found the g-value settings [hidden]in the software database.

Posted By: Mike Georgecheaply-coated raw outgoing-resistive

Is there such a coated glass? what's it called? Maybe just 3G plain glass wd do it.