Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




  1.  
    Time marches on, and tempered evacuated glazing (from China?) is now apparently available in Canada:

    http://vacuumglass.ca/
    • CommentAuthorringi
    • CommentTimeJun 15th 2017
     
    These come into their own if listed building control will not let you change the windows, hence stopping you using normal double glazing.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 15th 2017
     
    Wow! the void gap is only 0.2mm, overall unit thickness 0.44inch. 'normal vacuum glass' 0.62w/m2k, other options a bit better.

    First, this revolutionises glazing for Listed Buildings - near-PH with no effort!
    Second, for real PHs, this plus an extra single glass should be good enough; phenomenal Uvalues with multiple.
    •  
      CommentAuthordjh
    • CommentTimeJun 15th 2017 edited
     
    https://www.pilkington.com/en-gb/uk/products/product-categories/thermal-insulation/pilkington-spacia

    "Proven solution; installed successfully in the UK and used in Japan for over a decade"

    edit: "samples are available however, since they are rather expensive, we ask for details about your project"
  2.  
    NSG Spacia is not (or was not) available tempered.

    Tempered evacuated glazing has many more potential uses.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 15th 2017
     
    Bizarre - the Pilks product gives centre-pane U = 1.1, and compares it to 4/16/4 U = 1.7 - which sounds like the old days (it's only K-glass not soft-coat).
    Anyway, 1.1 centre-pane is not impressive - esp compared to the Canadian one's 0.62.
  3.  
    I think they might have a lower temperature offgassing process. The old high-temperature process would start to anneal the glass and destroy soft low-e coatings.

    Either that and/or they are using glass with a high critical temperature and heat resistant soft coatings.

    It's possible they might have a better spacer material. It doesn't appear to say.
    •  
      CommentAuthordjh
    • CommentTimeJun 15th 2017
     
    Tom, where are you reading the 0.62?
  4.  
    I acquired a sample of this vacuum glass when I was investigating slim-line double glazing in 2012. The sides/edges are made from glass so very unlikely to 'off-gas', spacers are visible in the wrong light. There is a slightly unsightly plug on each pane which is used to extract the air to make the vacuum. Overall I feel it is a very well engineered product. Its shortcomings seems to be 1) cost £500/m2 (2012) 2) its made in Japan and then shipped by sea, so you need to be patient, and make sure you don't make a mistake over sizing.
    I do however feel it might be more reliable in the long term than other (UK made) slim line double glazing products which rely on expensive inert gases, and appear to use sealant for edge spacers, which I suspect will off-gas over time.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 16th 2017
     
    Posted By: djhwhere are you reading the 0.62?
    Converted it from Murican.
  5.  
    Why would there be a difference in the U-value of the Japanese product compared with the Pilkinton product if they're both Vacuum Glass?
  6.  
    The Japanese product is the Pilkington product. The new one is Chinese.

    I notice that the figures they're quoting are for 11mm overall glass. Since the glass is thicker, that might mean fewer spacers could be used as the glass would bend less under atmospheric pressure. A fairer comparison would be between the 6mm versions.
    •  
      CommentAuthorfostertom
    • CommentTimeJun 17th 2017 edited
     
    yeah, the older Pilks product that ActivePassive is talking about is 6.2mm thick, centre U=1.1 or 0.9, prob uses old fashioned hard-coat K-glass (Pilks, like Dunlop and other UK household names, now a Japanese co).

    The new Chinese one is 11mm thick, basic version centre U=0.62
    and amazingly down to 0.23 for 18mm thick laminated, quite opaqeuish solar control glass - prob uses soft-coat glass
    The ability to use soft-coat maybe for heat-process reasons that passivhausfan mentions 2 above.
  7.  
    I emailed Icesun (and sent them the URL of this discussion, so they might possibly weigh in), to ask what the U-value of the 6mm product was.

    Somewhat confusingly they said that the thinnest available was 8.4mm, but they might have meant that the thinnest available tempered was 8.4mm, which would make sense as I asked specifically about tempered versions, and 3mm tempered glass is rather rare in any case.

    This is the performance they quoted me in metric units for the tempered 8.4mm version that seems most useful to me in a UK climate:

    # 3 Central U Value 0.5 W/m2.K, VT 62%, SHGC 0.48

    That seems better than what's stated on their website in American units. I am not sure why? Maybe they used American climate modelling conventions for the American units and some other conventions for the metric ones? I don't know.

    They can do a higher SHGC, but only by omitting the low-e coating, which strikes me as pointless.

    I really think if this turns out to be a reliable product, the architectural possibilities are very exciting, especially in heritage and traditional domestic architecture applications, although it would require modifications to the design of sashes and casements to take full advantage because of the high edge conduction that all evacuated glazing suffers from.

    You really need the edge to be lost in insulation so that the path for heat transfer is lengthened.
    •  
      CommentAuthordjh
    • CommentTimeJun 17th 2017
     
    Posted By: passivhausfanThey can do a higher SHGC

    In the figures I saw quoted earlier for vacuum glazing the SHGC was notably high, so I'm surprised that this is so low, and especially surprised that it is below the PH minimum allowed?

    You really need the edge to be lost in insulation so that the path for heat transfer is lengthened.

    Agreed but that will need some extra careful design if the glazing is to be replaceable.
  8.  
    Chinese vacuum glass manufacturer:
    http://landglass.en.made-in-china.com/product/kSvJcgnCsfRm/China-Landvac-China-Supplier-Sound-Insulation-Vacuum-Gorilla-Glass-for-Car-Front-Glass.html
    U value of 0.48, or 0.42 for the triple glazed version, more here: http://www.landglass.net/News/Group-News/Safety-Vacuum-Glass-Sets-New-S.html
    possibly the same one as in the http://vacuumglass.ca/ reference above?
    •  
      CommentAuthordjh
    • CommentTimeJun 19th 2017
     
    Exactly the sort of stuff I'd want to see a PHI certificate for before I touched it. What exactly is "Sound Insulation Vacuum Gorilla Glass For Car Front Glass"?
  9.  
    Somebody is now selling Landvac in the UK:

    https://www.grosvenorrestoration.co.uk/services/double-glazed-sash-windows-re-glazing/

    I suspect they haven't actually done a job with it yet as they don't seem to have any pictures?
  10.  
    Another brand:

    https://www.agc-yourglass.com/be/en/brands/fineo

    This one has no visible evacuation port and a U-value of 0.7, but it looks like it's only available as annealed glass, not tempered.
    •  
      CommentAuthordjh
    • CommentTimeSep 10th 2020
     
    Hmm, their datasheet claims: "U-value does not change when used in inclined or roof glazing".

    How do they manage that then? Especially since the increase for rooflights is applied by regulation AIUI, to offset the silly rule that rooflights have to be tested in a vertical orientation.

    They do say that laminated safety glazing is available.
  11.  
    That is an inherent property of vacuum glazing: no convection.
    • CommentAuthortony
    • CommentTimeSep 10th 2020
     
    And another inherent property - destined to fail 🙁
    •  
      CommentAuthordjh
    • CommentTimeSep 10th 2020
     
    Posted By: passivhausfanThat is an inherent property of vacuum glazing: no convection.

    Can you explain how that works then, or point to an explanation? For normal glazing, the U-value is less (better) in a vertical orientation, when I would expect convection to be greater. And this is formalised in building regs. Is there an exception in building regs for vacuum glazing?
  12.  
    Dunno about regs, but for conventional filled DG in a horizontal orientation, there will be many little convection cells in the filler gas, carrying heat directly across the unit in the shortest possible direction. In vertical orientation, there will be fewer convection cells, carrying heat mainly up towards the top edge of the glazing and cold down towards the bottom edge, with fewer cross overs, so U should indeed be better (lower) in a vertical orientation. Likewise for the surface resistance of the room air that is in contact with the glazing, and the outside air if there's no wind.

    Same way, heat transfer is more effective from horizontal UFH than from vertical radiators, if area and flow temperature were to be equal. And wide/low radiators give off more heat than narrow/tall ones.

    Vacuum glazing -> no convection between the glass, only radiation.

    In conventional DG filled with noble gas, the partial pressure of air between the glass is ~zero. For vacuum glazing, the same. So no good reason why a vacuum would be lost any earlier than an argon fill might be lost.
  13.  
    Posted By: WillInAberdeenIn conventional DG filled with noble gas, the partial pressure of air between the glass is ~zero. For vacuum glazing, the same. So no good reason why a vacuum would be lost any earlier than an argon fill might be lost.

    The usual problem with DG units failing is a failure of the sealing around the edges. Once this fails through pin holes or standing in moisture (through not having spacers between the DG unit and frame) then gas exchange can happen and water vapour can enter the unit causing misting and a loss of argon causing a degradation of insulative value. The argon gas in a DG unit is at 1 bar (absolute not gauge pressure)- the same as the air - so the pressure to exchange gas is just the daily variation in atmospheric pressure. With a vacuum unit the internal pressure will be close to zero absolute pressure so there is a suction into the unit driven by the 1 bar pressure on the outside thus a very small failure in the seal between the panes of glass will result in a (quick) failure of the unit.
    There will also be diffusion of the air through seal at a rate depending upon the material used to make the seal and the pressure difference each side of the material. Given the very small gap between the panes very little air diffusion will be needed to get a failure:
  14.  
    An evacuated glazing unit needs a very hard vacuum; even a tiny amount of air will ruin it; it's not the same sort of thing as having some air in an argon fill.
    • CommentAuthorjeffguest
    • CommentTimeJun 3rd 2021
     
    I found a UK company who are making Heritage windows and doors with LandVac glass. Looks like they have done quite a few jobs with it and they have managed to conceal the plug - sounds like a win-win.
    https://www.gowercroft.co.uk/heritage-windows-and-doors/" target="_blank" >www.gowercroft.co.uk
  15.  
    Looks nice. Their website mentioned they using the pilkington spacia glass - was mentioned in the 2007 original post of this thread - is that some kind of record for GBF? :bigsmile:

    Edit: they have a 10 year guarantee.

    Posted By: Peter_in_HungaryThe usual problem with DG units failing is a failure of the sealing around the edges
    the two panes in the spacia glass unit are actually welded together (IE not sealed with a sealant or bead) at the edges, across the 0.2mm cavity. Welds are generally much more reliable than seals.

    Posted By: Peter_in_HungaryThe argon gas in a DG unit is at 1 bar (absolute not gauge pressure)- the same as the air - so the pressure to exchange gas is just the daily variation in atmospheric pressure. With a vacuum unit the internal pressure will be close to zero absolute pressure so there is a suction into the unit driven by the 1 bar pressure on the outside thus a very small failure in the seal between the panes of glass will result in a (quick) failure of the unit.
    Perhaps I wasn't clear what a ’partial pressure' means? The partial pressure of argon etc inside a conventional DG unit is 1bar, and in the outside air the partial pressure of argon is nearly zero, so there is 1 bar of partial pressure trying to make the argon escape. Likewise the partial pressure of nitrogen+oxygen+watervapour outside the unit is 1bar, and inside it is zero, so there is another separate 1bar of pressure, trying to force air into the unit. The N2/O2 molecules 'think' that the inside of a DG unit is a very high vacuum, which they really ought to rush in and fill, and the argon 'thinks' the same about the outside air.

    The seal of a conventional DG unit has to resist two completely separate pressures, each of 1bar, in opposite directions but not cancelling each other out. If there were a tiny hole, the pressures would not cancel each other out, instead there would be 1bar worth of partial pressure forcing air in through the hole, and another 1bar worth of partial pressure forcing argon outward.


    By comparison, vacuum panels only have to deal with a single 1-bar pressure difference, not two at once. There is a net (mechanical) pressure difference, which squashes the panes together, so the spacia ones have tiny spacers every 20mm.
    • CommentAuthorjms452
    • CommentTimeJun 4th 2021 edited
     
    Posted By: WillInAberdeenThe seal of a conventional DG unit has to resist two completely separate pressures, each of 1bar, in opposite directions but not cancelling each other out. If there were a tiny hole, the pressures would not cancel each other out, instead there would be 1bar worth of partial pressure forcing air in through the hole, and another 1bar worth of partial pressure forcing argon outward.


    By comparison, vacuum panels only have to deal with a single 1-bar pressure difference, not two at once. There is a net (mechanical) pressure difference, which squashes the panes together, so the spacia ones have tiny spacers every 20mm.


    This is all 'correct' but for the benefit of the less physics savy 'partial pressure' and 'pressure' are totally different things and the life of a DG unit 'resisting two partial pressures is not harder than the life of a vacuum unit resisting a bulk pressure difference

    Partial pressure drives diffusion and doesn't typically apply a bulk force. In the argon fill case there are essentially no forces on the DG unit due to these partial pressures. This is why gas fill is so ubiquitous - it's quite 'easy' from a mechanical integrity perspective.

    Bulk pressure differences exert bulk forces and drive bulk flow so in the vacuum glazing case the unit is experiencing 100000N/m2 crushing it. This is why vacuum 'fill' is so niche - it's horrible from a mechanical integrity perspective.

    edited for typo
  16.  
    Indeed - the partial pressures make the argon leak out and the air leak in and are essentially the same problem for vacuum glazing as for DG or 3G, which some folks are finding counter-intuitive. They thought vacuum would be more likely to leak than argon, but not so.

    The total mechanical pressure squashes the panes together. Worth looking at the Spacia website, they have solved this by including a grid of teeny tiny spacers every 20mm across the panes to keep them 0.2mm apart. The very narrow spacing works with vacuum but not argon, and allows the unit to be welded up shut, rather than the elastomer seals you get with DG.

    They have been selling them since at least the start of this thread in 2007 (!) so have enough confidence in their reliability to offer a 10year guarantee, so AFAICS they are at least as reliable as DG/3G and probably better. If the welds last for 10years they will probably last for 100, there's no perishable components.

    I imagine the niche-ness is something to do with the price, and that is something to do with the number of manufacturers able to do this....!
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press