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    • CommentAuthordelprado
    • CommentTimeOct 2nd 2017
     
    The more I look into it, the more I think double glazing is the way to go - assuming I can get whole frame performance of 1.0 with double which I can with a supplier I am considering.

    Whats more, you can spend the money you save in not using triple to improve double to a level above triple from an acoustic perspctive without spending more money overall
  1.  
    I am in the same situation, trying to decide between double and triple glazing for a retrofit project; modern double glazing offers almost the same U values and better G values (solar transmittance). Probably going to end up with double glazing on all sides apart from north side where I might put triple glazing, only because solar gain on the north is not so important. Noise, where I live in a rural location is not an issue, so triple glazing's additional noise insulation isn't really a benefit.

    My only other comment about triple glazing is that having done a lot of thermal imaging surveys of homes, opening windows are more likely to sag over time because of the additional weight - something I see even when the triple glazing has been supplied by well known European names.
    • CommentAuthordelprado
    • CommentTimeOct 2nd 2017
     
    Triple glazing doesnt offer any benefit to noise.

    The key things from my detailed research on this basically equates to:

    1. Thick glass stops noise better

    2. Use acoustic pvc laminates.

    3. Use different thickness panes of glass (although laminates somewhat level out the frequency weaknesses of a pane of glass so this isnt as important either as conventional wisdom - and the thickner the glass the less natural weakness anyway - 25mm has no weakness!)

    4. Second Glazing beats everything when you have a 200mm air gap.

    A sensible buildup is something like 10mm plus laminate 0.76mm and 4mm x 2 in a double glazed unit and some iteration of that I will go with.
  2.  
    So your telling me I could have had double glazing with the same u value as my Argon filled 4 16 4 16 4 triple glazing. My windows are direct into the stone mullions so insulation depth between window and stone mullion is the same width as the glazing unit. Having walls over 600 mm wide a glazing unit of 50 mm is not significant. We have no opening windows but use a through the wall MHVR unit instead which also filters pollen.
    •  
      CommentAuthordjh
    • CommentTimeOct 2nd 2017
     
    Posted By: delpradoTriple glazing doesnt offer any benefit to noise.

    Not strictly true, since the extra mass of the third pane does reduce noise transmission, but certainly there are better ways to achieve noise reduction.

    A sensible buildup is something like 10mm plus laminate 0.76mm and 4mm x 2 in a double glazed unit and some iteration of that I will go with.

    I'm not quite sure what you mean here. Are you planning a normal 4+x+4 double-glazed unit plus a secondary glazed laminated unit with some unstated separation? That sounds quite reasonable. Are they fixed windows or opening? If opening, then do pay attention to the airtightness sealing since that will have a major effect on noise.

    A whole window U-value of 1.0 with double glazing is a very impressive spec. Who is selling that?
    •  
      CommentAuthordjh
    • CommentTimeOct 2nd 2017
     
    Posted By: ActivePassivemodern double glazing offers almost the same U values and better G values (solar transmittance)

    I don't believe that's true either - the U-value claim, I mean, I do agree about the g value. State of the art for triple glazing Ug is now about 0.5 and I don't think double glazing comes anywhere close to that.

    Whether it matters in your circumstance is an entirely different question of course.

    As regards sagging window sashes, I agree that triple-glazed are heavier so I think what's important to make sure is that the frame and sash are strong and rigid and that the hardware is good quality and has adjustable hinges. I'd be particularly wary of cheaper products and be very interested how PVC was reinforced.
    • CommentAuthortony
    • CommentTimeOct 2nd 2017
     
    +1 an urban myth propagated by the UK industry and is incorrect.

    Sound insulation is superb with 3g

    Quality is far higher if from Europe, better frames, much better ironmongery

    Mine will last 200 years I reckon, lots in the UK are done in after 25 years and finish up on landfill

    no sagging on my windows or snagging for that matter.
    • CommentAuthorgravelld
    • CommentTimeOct 2nd 2017
     
    Posted By: ActivePassivemodern double glazing offers almost the same U values
    Point me to the 2G with even Uw<1, let alone the really super duper windows?
  3.  
    Pilkington energiKare™ Advantage claims a Ug of 0.9; although I have seen a Ug of 0.8 claimed for it.

    Although I haven't got quotes yet, my choice may come down to cost. For a retrofit project, with a cavity wall whose outer leaf is 220mm, and windows set forward in the reveal, insulating the outer leaf reveal back across the cavity (with VIP) is likely to be a much better investment. No benefit in going for triple glazing if there is a massive thermal bridge all round the reveal.
  4.  
    What would the Uw be in a typical reasonable-spec uPVC or timber window with a Ug of 0.9?
    • CommentAuthorgravelld
    • CommentTimeOct 2nd 2017
     
    Posted By: ActivePassivePilkington energiKare™ Advantage claims a Ug of 0.9; although I have seen a Ug of 0.8 claimed for it.
    That's Ug.

    Posted By: ActivePassiveAlthough I haven't got quotes yet, my choice may come down to cost. For a retrofit project, with a cavity wall whose outer leaf is 220mm, and windows set forward in the reveal, insulating the outer leaf reveal back across the cavity (with VIP) is likely to be a much better investment. No benefit in going for triple glazing if there is a massive thermal bridge all round the reveal.
    I hear you. But unless the cavity is also 220mm (or thereabouts) then surely a retrofit will require EWI, in which case, windows go in the insulation layer.
  5.  
    Unfortunately there is almost no chance of getting planning for EWI, prominent position in rural AONB, greenbelt, conservation area village where all homes are stone or rubblestone, plus my walls are already 420mm thick. Not a big fan of IWI, although likely to apply tactically to north facing walls which have less window area.

    I am aware the Uw of a 0.9 Ug window will be higher, planning on butting internally insulated window reveals against the frame as an attempt to minimise losses and get Ug as close to Uw as possible. Will take pragmatic approach to 3D v. 2D - cost benefit comparison.
    •  
      CommentAuthordjh
    • CommentTimeOct 2nd 2017
     
    The energiKare does look to have an impressive Ug but it doesn't match good triple glazing. What does it cost, compared to the price of a triple-glazed unit?

    I don't know much about the practicalities of having a hard coat on the innermost surface. They do mention possible damage during cleaning and the need to clean off anything except water as potential issues, but that doesn't sound too bad. Still I haven't heard of any triple-glazed units with the same inner pane to increase their performance even further; perhaps there's no demand.

    As you say though, designing the frame and how it is mounted into the opening with insulation is likely to be most important. I don't know whether there are insulated frames for normal double glazed depth units?
    • CommentAuthorgravelld
    • CommentTimeOct 3rd 2017
     
    djh, are you referring to thermal breaks in the frame themselves or a break from the frame onto the fixings where mounted? Also, remember there are different approaches to this. Some alu-clad has the break between the alu and the timber, meaning no drainage gap, some have it in the timber itself. So maybe the former approach could be used if there's not enough depth in the timber frame itself.

    Actually - can you get alu clad for 2G in the same way you can get it for 3G?

    AP, just another thing - you've probably already thought of this, but the reason that 3G is chosen for Ph is because it hits the required performance level to make sure certain other undesirable things don't occur. For example, a level of downdraft that is considered (according to the studies Ph use) comfortable to stand next to occurs at a certain U. When you compromise performance you aren't compromising value (certainly not; it's inescapable that high quality 3G costs more than it saves) you're compromising comfort, while also perhaps paying an opportunity cost.

    But being in the same boat as you, I totally understand about the nominal costs.
  6.  
    Posted By: renewablejohnSo your telling me I could have had double glazing with the same u value as my Argon filled 4 16 4 16 4 triple glazing. My windows are direct into the stone mullions so insulation depth between window and stone mullion is the same width as the glazing unit. Having walls over 600 mm wide a glazing unit of 50 mm is not significant. We have no opening windows but use a through the wall MHVR unit instead which also filters pollen.


    Are your mullions internally insulated or left as exposed stone?

    We have them in our home and I'm always open to insulation suggestions. I've done one window with aerogel, but I'm not thrilled with how it looks.
  7.  
    Posted By: Pile-o-Stone
    Posted By: renewablejohnSo your telling me I could have had double glazing with the same u value as my Argon filled 4 16 4 16 4 triple glazing. My windows are direct into the stone mullions so insulation depth between window and stone mullion is the same width as the glazing unit. Having walls over 600 mm wide a glazing unit of 50 mm is not significant. We have no opening windows but use a through the wall MHVR unit instead which also filters pollen.


    Are your mullions internally insulated or left as exposed stone?

    We have them in our home and I'm always open to insulation suggestions. I've done one window with aerogel, but I'm not thrilled with how it looks.


    All mullions are exposed stone and look very impressive. Obviously inside of the wall is Lime plaster which breaths and keeps the walls dry. As the Scottish results showed heat loss through the stone walls is actually less than expected due to the thickness of the walls. The heat loss used to be through the wooden frames and single glaze (fridge) this has been radically reduced with the 3G glass sealed to the stone mullions.
    • CommentAuthordelprado
    • CommentTimeOct 3rd 2017
     
    I will reply properly when not on my phone but residence 9 windows with low e offer a u value of 1.0 for the whole window
    • CommentAuthorTimSmall
    • CommentTimeOct 4th 2017 edited
     
    Interesting - I had thought about getting some sealed units made up to that arrangement myself in the past, but wondered about the increased risk of condensation on the inner pane (because of the reduced glass surface temperature), and also damage to the coating when cleaning.

    Annoyingly Pilkington Spectrum doesn't allow you to play with the spec much - you can only specify a 16mm spacer (Ug = 0.95 W/m²·K), or 20mm spacer (Ug = 0.97 W/m²·K) - so declaring (the 16mm one I assume) as 0.9 W/m²·K seems a bit Volkswageny - presumably to 3 decimal places it's something like 0.947 W/m²·K to allow them to round it down to 0.9 W/m²K

    Also, this "energiKare Advantage" arrangement uses "Optitherm S1 Plus" glass as the other low-e pane, which has a pretty low g value compared to the low-e panes which are normally used, so the g value of these "super-double-glazed" windows ends up pretty low (lower than all my triple glazing) at g = 0.50 ... so it seems that the "higher solar gain == better with double glazing" doesn't apply to this.

    To get a feel for how much difference this extra low-e surface on the room-facing glass surface makes - without the extra K glass pane (so just a 4-16-4 argon with one "Optitherm S1 Plus"), you get a Ug = 1.05 at g = 0.56.

    Pilkington Spectrum doesn't allow you to model a triple glazed sealed unit with this arrangement unfortunately - it'd be interesting to see what you could get out of a triple glazed unit with the additional K glass inner.

    I wonder why they haven't used the newer higher-performance "K Glass A" instead of the original "K Glass".

    For the system I went with for my first floor, rear windows (Rehau Total70 with triple galzing - Ug = 0.62 W/m²·K and Uw = ~ 0.8 W/m²·K with a g = 0.61 ) was pretty cheap I thought and I'd go for that spec again I think.

    That was 2x low-e soft-coat panes (Planitherm Total+) as 4-16-4-16-4 with argon spacers. The good thing about this arrangment is that it uses the most commonly stocked glass types and spacers, so everyone should be able to fabricate it. The visible light transmission at 71% is 1% lower than the "energiKare Advantage".

    For a North-facing version, you can use three soft coat low-e panes (two facing each other) to push it down to Ug = 0.59 W/m²·K with g = 0.55

    If you have a profile which will take 4-18-4-18-4 - which I have elsewhere, then that drops further to:

    Ug = 0.57 W/m²·K with g = 0.61 (2x low-e)

    or:

    Ug = 0.54 W/m²·K with g = 0.55 (3x low-e)


    Still - interesting to have another option and maybe useful for upgrading existing North-facing double glazed units, or South facing where the extra solar gain isn't needed...

    Tim.
    • CommentAuthordelprado
    • CommentTimeOct 4th 2017
     
    "Interesting - I had thought about getting some sealed units made up to that arrangement myself in the past, but wondered about the increased risk of condensation on the inner pane (because of the reduced glass surface temperature), and also damage to the coating when cleaning."

    I discussed this with Residence 9 technical as I thought it was a benefit of triple glazing, but if the u value is the same then the glass temp is the same - there is no magic in triple - unless your point was based not on the "magic" but that the u value would be lower, in which case, surely, though, the double glazed u value is low enough that there is no risk of condensation, especially with swiss spacers, etc and the other features modern windows have?
    • CommentAuthorRex
    • CommentTimeOct 4th 2017
     
    This is an interesting thread, particularly regarding sagging.

    I have 3g, pultruded (made by Pro-Tec, now merged with someone else so no longer in existence) and am both happy and disappointed with them.

    The frames are strong and have very thin sightliness, as a result, the lower edge has sagged a little. Interestingly, those that have sagged are south facing, so receive more heat from the sun. North facing are all OK. But my frames are dark grey, so absorb more heat than white frames would.

    I don't think the sag is as a result of the weight because virtually all the weight is supported near the lower corners where it is transferred to the vertical part of the frames. I think that at almost 1 meter wide, it is just poor design.

    I'm also don't feel the hardware is correctly specced for the size of my windows, which are quite large. But I was not aware of this at the ordering stage. With everything I saw and the meetings with the rep. I (incorrectly) assumed that all would be hunky dory.

    Oh well, it's all a learning experience!
    • CommentAuthorowlman
    • CommentTimeOct 4th 2017 edited
     
    That's the critical issue Rex IMO. Modern timber design demands narrow frames, modern production techniques often produce corner joints that are not actually mortise and tenoned let alone wedged. Profiled tooling more often than not simply has a counter profile and the whole relies on the adhesive and maybe a screw for a rigid structure. This is not a good design for a frame that has to carry such weight. All of that before you start looking at the hardware. It's inevitable that once adhesives and seals "give" with time, the bottom leading corner will sag. Whether that sufficient to cause weather seals to become less efficient will depend on how much sag. It would be interesting to find out if top hung fares any better.
    If you compare to wide doors for instance which can have the similar weight issues the wedged and mortised rails are wide enough to provide support, especially the bottom one which can be up to 230mm wide on very large doors.
    • CommentAuthorTimSmall
    • CommentTimeOct 5th 2017 edited
     
    Posted By: delprado > increased risk of condensation on the inner pane (because of the reduced glass surface temperature)...

    I discussed this with Residence 9 technical as I thought it was a benefit of triple glazing, but if the u value is the same then the glass temp is the same


    This assumption seems reasonable at first consideration, but it only holds if the ratio of radiative vs. conductive heat exchange between the room and the inner pane is the same in both setups.

    This isn't the case with this arrangement - with a "conventional" triple glazed arrangement, there is no low-e coating facing into the room, but with the "energiKare Advantage" setup there is.

    This means that the interior pane exchanges less heat with the interior of the room by radiation than a "normal" sealed unit. This will necessarily drop the surface temperature of the inner pane.

    To think about it another way since the coating is on the room-side of the sealed unit, this means that the conductivity through the main part of the sealed unit (i.e. through everything except "surface 4") is identical. Given that, then the only possible way to reduce the total heat flow is to reduce the inner surface temperature of the glass.

    Don't just take my word for it tho, you could download some software like "Window" from LBNL and see what it says. I'm pretty sure that'd support modelling low-e inner surfaces, and it definitely has the Pilkington glass types in it's database.
    • CommentAuthorTimSmall
    • CommentTimeOct 5th 2017
     
    Found this on a document from Pilkington North America:

    "Note that while the addition of a low-e coating to #4 surface cuts the unwanted heat loss from the room it does
    inhibit the glass from being warmed by radiant heat. The net result is that the #4 surface glass temperature falls [...]"

    https://www.pilkington.com/resources/ats138dmultiplelowecoatingsinig20130115.pdf


    I'd expect there to be more condensation - particularly along the bottom edge of the inner pane. Whether this will be a hassle in practice depends on the interior humidity, the exterior climate. I'd probably run this through "Window" and possibly "Therm" too, to get a good feel for the difference I think.

    Getting a bit off topic, but putting a low-e coating on the outer surface would have the opposite effect - increasing the temperature of the outer surface of the outside-facing pane (surface #1), and this is how (some?) "anti-condenstation" coatings for triple glazed units work -

    https://www.pilkington.com/en-gb/uk/products/product-categories/special-applications/pilkington-anti-condensation-glass#overview

    They should also have the side-effect of dropping both the U and g values for the unit a bit.
  8.  
    When talking about 2g or 3g I get the picture but when talking about additional coatings on outside faces that need care cleaning or extra coating internally that give an improvement of less than 0.1Ug is it really worth the extra?
    • CommentAuthortony
    • CommentTimeOct 5th 2017
     
    I have never had any condensation on the inside of any of my windows even when it was -11C outside, reguaraly get on the outer pane as so little heat escapes to keep them warm enough to prevent this unusual phenomenon.
  9.  
    Posted By: tonyI have never had any condensation on the inside of any of my windows even when it was -11C outside, reguaraly get on the outer pane as so little heat escapes to keep them warm enough to prevent this unusual phenomenon.

    Ditto my 3g windows but I did get a small amount on the bottom edge at -22 outside despite having warm edge. (No mvhr, which might make a difference).
    •  
      CommentAuthordjh
    • CommentTimeOct 6th 2017
     
    Posted By: delpradoI will reply properly when not on my phone but residence 9 windows with low e offer a u value of 1.0 for the whole window

    Interesting looking windows for conservation applications; their brochures seem to be well produced and make the windows sound well-designed.

    I don't see a 1.0 U-value though. I didn't see any in their brochures; they seem to concentrate more on the 'authenticity' of the appearance. Their website says - http://www.residencecollection.co.uk/planning-and-conservation/ -

    "Attaining U-values of 0.8 with triple glazing, PassivHaus Standard, and 1.2 with double glazing"

    and checking with the PHI database to see that they are not certified rings my bullshit detector. I'd check the certificates of any specific product very carefully to see what it offers.
    • CommentAuthorgravelld
    • CommentTimeOct 6th 2017
     
    To be fair... if something isn't Ph certified I don't think that's a reason to doubt them, so much, is it? Rather, it's a reason to discount them because of the risk that you're being sold something that isn't as well tested... But if you're happy with the risk, and you've managed it well, that might be alright.
    •  
      CommentAuthordjh
    • CommentTimeOct 8th 2017
     
    Posted By: gravelldif something isn't Ph certified I don't think that's a reason to doubt them, so much, is it?

    Stating that something is PassivHaus Standard when it hasn't been tested against that standard is certainly a reason for me to doubt them. As to whether they're actually fit for delprado's purpose, that's a decision for him, but I would strongly recommend checking the actual product documentation as I suggested, since the marketing material clearly isn't totally open and honest.
    • CommentAuthorTimSmall
    • CommentTimeOct 9th 2017
     
    To be fair, they aren't saying that it's a ph certified component, just that its U value meets the ph standard (with the implication being for cool-temperate).

    I've seen quite a few manufacturers say this (including ones which do have certified components when referring to other non-certified products which they supply).

    BTW, do bits of the UK south coast now fall into the "warm temperate" climate zone? If so, then 1.0 W/m²K is OK.
   
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