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Fundamentals: DG vs TG windows southwest aspect

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1 to 14 of 14

  1.  
    • CommentAuthorchan
    • CommentTimeNov 2nd 2013
     
    As i understand it DG on a strait south aspect with clear view of sun would be optimum for winter solar gain.
    what wold be optimum for heating season with SouthWest unobstructed aspect 3g or 2g?

    As it stands we have kitchen dining and bedroom SW facing with single glassing and towards eve (12 till sunset) get massive amounts of Light/heat so worry that 3G might reduce this evening heat and loose beautiful afternoon and evening light compared to DG. We are in Northwest Ireland by coast.

    Münster joinery Dg 24mm u1.3
    VS
    TG 36mm u1.1

    I have actually ordered 3g but wonder should we change south west window to DG.
    Thanks
    • CommentAuthortony
    • CommentTimeNov 2nd 2013
     
    Definitely go 3g, use low iron glass to maximise solar gain and gas filling helps too.

    Make the windows slightly bigger to overcome the loss of light but this is small so only a few percent large.

    You will likely need to shade the windows externally even in the winter! To prevent overheating more especially if you are properly insulated.
    • CommentAuthorchan
    • CommentTimeNov 2nd 2013
     
    thanks tony
    this is a 1970s semi d with 50mm insulation in cavity probably will pump walls. window are relative large. so there is plenty light because the house backs SW over an estuary we get allot of light when sun is out also bounced off the water.
    my worry is that TG will reduce the afternoon/eve solar gain compared to if we got DG.
    or is the difference marginal compared to heat loss ?
    IE with SW aspect is it best to get TG over DG in all situations?

    windows are soft coat, low e, argon, pvc
    4/12/4/12/4
    thanks
  4.  
    Yes, difference relatively marginal. I think there have been threads here discussing the relative loss of gain between 2G and 3G, but I can't for the life of me think where. Anyone?
    • CommentAuthorEd Davies
    • CommentTimeNov 2nd 2013 edited
     
    Yes, I'd say very marginal.

    From the http://www.degreedays.net/ site the HDD to 18.5 °C for Malin Head in 2012 December was 377 so an average temperature difference of 12.16 °C giving the extra loss from going from 3G 1.1 to 2G 1.3 W/m²·K of 2.43 W/m².

    From PVGIS for Dungloe: input on a vertical panel facing 45° west of south for December is 28.9 kWh/m² giving an average of 38.8 W/m². I don't have any data on the transmission of those but looking at the simple Fresnel equation for the extra reflection from my calculator at http://edavies.me.uk/2008/10/fresnel/ says going from 2G to 3G drops the transmission from 85% to 78% so the loss in heat gain is 38.8 × (0.85-0.78) W/m² = 2.7 W/m².

    3G will also have a bit more glass so a bit more absorption on the way through. But that effect is, I think, small and helps a bit with reducing heat loss anyway.

    So, on the face of it, 2G is slightly better (by 0.27 W/m²) but the extra comfort from lack of drafts associated with 3G probably dominates anyway. Definitely not something to lose sleep over.
    • CommentAuthorchan
    • CommentTimeNov 3rd 2013
     
    wow thanks Ed,
    Thats a lot of calks, so in basic terms 2g could loose 18% light heat and 3G 25% heat light.
    in this % way i wonder over the heating season what the difference in heat lose being lost interior to exterior would be between 2G and 3G?
    Sounds like it might come down to aesthetics and how the glass looks transparency/colour tint/ perceived effect on views and natural lighting.
    wonder does anyone regret getting 3G because of how it affects views transparency increased feeling of being in a box?
    sales men hear say 1 in 4 houses are getting 3G but think more and more are getting 3G, cant say i see much about except new builds.
    Thanks
    • CommentAuthortony
    • CommentTimeNov 3rd 2013
     
    In central Europe 3g has become the norm 90% in new build and dg is as a consequence becoming increasingly more difficult to obtain.

    In the UK we are a good few years behind the times.
    •  
      CommentAuthorfostertom
    • CommentTimeNov 4th 2013
     
    2G can only kick in when the window in question actually does receive prolonged solar exposure in deep winter - that means v few windows qualify, because usually shaded by building/trees. The 2G argument requires v low horizons to SE/S/SW - otherwise it's just a trade con.
    • CommentAuthorchan
    • CommentTimeNov 4th 2013
     
    This is where I am unsure on what way to go as I have uninstructed SW view over water with no shading getting sun from 12 till sunset even yesterday day great amount of heat gain due to the low height of sun. And worry that i will miss that positive direct heat from sun through 3G.
    Thanks
    • CommentAuthorchan
    • CommentTimeNov 4th 2013
     
    Sw aspect
    •  
      CommentAuthorfostertom
    • CommentTimeNov 4th 2013 edited
     
    Wow! Where is it? If this is SW view, the window is prob either W or S unless diagonal to this terrace? The answer wd make a big difference.

    Needs careful custom consideration because potentially you'll get gain bigtime incl reflection off the water, great to exploit winter but the water makes it v hard to shade out overheating in summer. If the window is S, the usual big overhang won't intercept the reflected. If W, makes it even trickier - the sun will be lower but still powerful and the reflection will bounce in even better.

    Cmon team, no pat answers, let's discuss this unique, real situation.
    • CommentAuthorchan
    • CommentTimeNov 4th 2013
     
    Shot is looking west window faces Sw. I not worried about over heating.
    Thing is I have ordered 3G with Munster but can be adjusted as they have not made them yet but I if I change them to 2G should do it today or tomorrow. Hmmm.
    This is sligo
    • CommentAuthorchan
    • CommentTimeNov 4th 2013
     
    Yeh I would gues I get at least 30% extra light in winter bouncing off the water:cool::cool:
    • CommentAuthortony
    • CommentTimeNov 4th 2013
     
    go 3g and never have regrets

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