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U Values for Opaque Windows - different to clear?


Adam2

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Well that was a surprise! Changing a window currently U for the 3G glazed element is 0.7. Why on earth would changing it to be opaque result in this changing to 1.2? I struggle to believe that a coating on glass can have such an impact but it has been stated by a supplier and this is what is in their quote so I thought I would check in here with others. Really appreciate your views before I go back and challenge them ?

 

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That's a big drop, are you sure it's still triple? That's a double glazed Ug value in all honesty. 

 

Triple glazed, has the opaque glass in the centre, it doesn't have any coatings on it and the value for the glass is generally not massively impacted. It can go from a 0.5Ug to a 0.6 but generally it's the decimal place that will change (i.e. 0.52Ug to 0.55Ug  for example) as well as the LT value, G Value changing but not a drop like that unless it's went to double.

Edited by craig
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I would need to see the glass specification sheet, what coatings they have used, spacers and gas used. Sounds wrong to me, satin finish is a "modern" alternative to patterned glass but it shouldn't impact the value by the value mentioned.

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Thanks @craig I'm going back to them asking them to check and if they maintain it is 1.2 will ask for more detail on glass spec - though I'm expecting it to be the same glass spec as before (U0.7) with just the satin coat on the middle pane

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  • 2 weeks later...

Well after further discussion the supplier is adamant that the 3G windows will be negatively impacted by the satin coat as this means that the necessary energy efficiency related coating cannot be applied hence the change from 0.7 to 1.2. I struggle to accept this but there are only a few opaque windows so probably not worth any more energy on that with them. When I mentioned others quotes has the same U value for opaque units he questioned if they really did so seems they are pretty convinced on the subject. When I get the time will try and get info from a glass manufacturer. Ultimately they will be 3G so hopefully it is just a spec/interpretation issue. They did suggest krypton gas to improve U values but at a cost....

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8 hours ago, craig said:

You got the specs? I can run it through Calumen / gaurdian configurators.

 

Thanks - this is an opaque one

1500 mm x 1350 mm, Consisting of a Top Hung Window.
ODC77
Colours: 76 7M16 Matt Anthracite grey Pré-ano
Glazing: 1 x (4mm Clear Tgh/4mm Satin Tgh/4mm Clear
Softcoat Tgh {W/E Spacer, Argon Filled} Triple Glazed) U g =1.2
W/(m 2 K)

 

and this is a clear one for comparison

4476 mm x 1850 mm, Consisting of a Tilt before Turn Window
and three Fixed Fields.
ODC77
Colours: 76 7M16 Matt Anthracite grey Pré-ano
Glazing: 4 x (4mm Clear Tgh/4mm Clear Tgh VTE/4mm Clear
Tgh VTE {Blk Warm Edge, Argon Filled} Triple Glazed) U g =0.7
W/(m 2 K)

 

ODC77 is a high insulating window system that meets elevated requirements regarding thermal insulation, stability
and security. Anticipating on the thermal requirements, the insulation value (Uf) for the HI+ variant of this system goes
down to 1.7 W/m²K for a standard opening window. The unique concept of the system makes it perfectly suitable for
triple glazing and ODC77 even achieved the Swiss Minergie® component label.

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On 21/08/2019 at 09:41, Adam2 said:

(4mm Clear Tgh/4mm Clear Tgh VTE/4mm Clear Tgh VTE {Blk Warm Edge, Argon Filled} Triple Glazed) U g =0.7 W/(m 2 K)

 

I don't understand, have I missed something? I thought the only difference was that the centre pane was either clear or satin. Why has one got softcoat and are the spacers the same?

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I've just checked the spec for the one window we have with an obscured glass centre pane.  It's exactly the same as all the others, no difference in Ug, and has two low e coated panes. 

 

Looking at the orientation of the glass, it looks to me as if it's the flat face of the obscured glass that has the coating, which makes sense.  I did this check using a laser pointer held at an angle and looking at the relative brightness of the row of internal reflections.  Our windows are mainly 4 - 20 - 4 - 20 - 4, and Ug is stated as being 0.55 W/m².K

 

I can't see any reason why obscured glass cannot be low e coated on its flat face, as it's no different to any other pane in that respect.

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47 minutes ago, PeterStarck said:
7 hours ago, Adam2 said:

(4mm Clear Tgh/4mm Satin Tgh/4mm Clear Softcoat Tgh {W/E Spacer, Argon Filled} Triple Glazed) U g =1.2 W/(m 2 K)

 

7 hours ago, Adam2 said:

(4mm Clear Tgh/4mm Clear Tgh VTE/4mm Clear Tgh VTE {Blk Warm Edge, Argon Filled} Triple Glazed) U g =0.7 W/(m 2 K)

I don't understand, have I missed something? I thought the only difference was that the centre pane was either clear or satin. Why has one got softcoat and are the spacers the same?

Warm Edge = W/E but something I can check with them. TBH softcoat I would expect to be in all units when I get their revised spec and pricing will check all have exactly the same detail or at least that I understand why it might differ. Also no idea on "VTE"

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7 hours ago, Adam2 said:

 

Thanks - this is an opaque one

1500 mm x 1350 mm, Consisting of a Top Hung Window.
ODC77
Colours: 76 7M16 Matt Anthracite grey Pré-ano
Glazing: 1 x (4mm Clear Tgh/4mm Satin Tgh/4mm Clear
Softcoat Tgh {W/E Spacer, Argon Filled} Triple Glazed) U g =1.2
W/(m 2 K)

 

and this is a clear one for comparison

4476 mm x 1850 mm, Consisting of a Tilt before Turn Window
and three Fixed Fields.
ODC77
Colours: 76 7M16 Matt Anthracite grey Pré-ano
Glazing: 4 x (4mm Clear Tgh/4mm Clear Tgh VTE/4mm Clear
Tgh VTE {Blk Warm Edge, Argon Filled} Triple Glazed) U g =0.7
W/(m 2 K)

 

ODC77 is a high insulating window system that meets elevated requirements regarding thermal insulation, stability
and security. Anticipating on the thermal requirements, the insulation value (Uf) for the HI+ variant of this system goes
down to 1.7 W/m²K for a standard opening window. The unique concept of the system makes it perfectly suitable for
triple glazing and ODC77 even achieved the Swiss Minergie® component label.

 

Ask them for the datasheet(s) from the glass supplier if possible.

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22 minutes ago, JSHarris said:

I can't see any reason why obscured glass cannot be low e coated on its flat face, as it's no different to any other pane in that respect.

Indeed, maybe no reason but certainly Ideal Combi refused me a low-e/opaque combination saying either/or, so perhaps is worth people being alert to checking their chosen supplier does work with it.

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