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Green Building Bible, Fourth Edition
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    • CommentAuthorjamesingram
    • CommentTimeApr 4th 2021 edited
     
  1.  
    Thanks for sharing the link!

    He concludes that for a U value lower than about 0.1 W/m2K, the embodied energy in manufacturing the insulation will outweigh the energy savings from adding more insulation, with variation about local climate, base data, insulation type etc

    What is missing for me is that the energy embodied in the insulation might come from carbon (eg polyurethane or mineral wool, shipped to site in a truck) but the energy to heat the house will increasingly be renewable, as the house will stand late into the 21st Century and maybe the 22nd.

    So if there's a choice of adding more layers of carbon-intensive insulation, or cranking up the renewably-powered heatpump another notch, it might be better to insulate less now and do more heating in future.

    Heresy! :shocked:
    • CommentAuthorGarethC
    • CommentTimeApr 4th 2021
     
    An increasingly green grid, plus the option of heat pumps, does change the equation, doesn't it (actually I've always thought this, so maybe I'm using this argument to justify my own opinion).

    Many argue to 'insulate, insulate, insulate," but surely the appropriate course must increasingly be "insulate to the extent appropriate, then install a green heating and hot water system,"?
    • CommentAuthortony
    • CommentTimeApr 4th 2021
     
    Insulate to the point that heating is no longer needed changes the economics and a no brainer on other considerations

    A cultural mindset shift is necessary for that to become mainstream.
    •  
      CommentAuthordjh
    • CommentTimeApr 4th 2021
     
    I'm not convinced by the article. It seems to be deliberately politicised and maybe careless too.

    He starts off by making his major claims:
    - “We just need houses to be more efficient”, I was told.
    - Will eliminating carbon emissions from housing ‘help’ to address climate change?: Yes.
    - Will eliminating carbon emissions from housing have any ‘significant’ effect on climate change?: No.
    then he does a bait and switch and says he will instead discuss
    - I’m going to explore an even simpler take on this issue: In summary, “Thermodynamics says no”.

    There's then a long rambling post essentially saying that there are practical limits to how much insulation is sensible - but isn't that fairly obvious? If you weren't already convinced, I'm not sure his blog would persuade you.

    And he totally ignores the most interesting part of his claims, which is that domestic energy consumption is not significant. (There's a helpful graph at https://en.wikipedia.org/wiki/World_energy_consumption#By_sector that tends to support the assertion, BTW)

    He starts with a formula: Tm = [ 1 ÷ Um ] × λm

    That's a strange way to write Tm = λm / Um but I suspect he does it because it's a way of rewriting Tm = Rm × λm where Rm is the thermal resistance. Of course, he doesn't want to say that because that graph IS a straight line.

    More fundamentally, he's discussing energy usage so why isn't energy (or power) on the left hand side of the equation? I'm not disagreeing with his point; it just seems very poorly explained.

    Then in the next section, he says: "Polystyrene and polyurethane are rigid blocks, that can be laid flat on top of ceilings or screwed upright to walls. Wool materials (even when woven into square ‘batts’), and flaky cellulose, can’t easily do that. Therefore the physical restrictions on how we use insulators as building materials constrains the choices over how they are used far more than their ecological performance."

    Which is true (and makes me feel smug sitting here with straw alongside me and newspaper over my head :bigsmile:, until I think about the EPS and concrete underneath me :cry:) but isn't really relevant IMHO. Yes there are different techniques used to employ different materials but there are sensible techniques for using most insulants in most situations. And yes, there are exceptions - EPS underfloor rather than straw bales, for example.

    Also in that section he claims "The average UK home uses 10kW-h/day" and links to a source page that carefully explains "These figures don’t include heating. If your home uses electric heating, then the figures would obviously be much higher.". So that 10 kWh/day number is nonsensical to use in a discussion about thermal insulation.

    And then under "Etot = EEIm,u + [ Um × 3600 × 24 × DDr × L ]" he comes to the amazing conclusion that a different level of insulation is optimal in different places, exactly as PH says! Remarkable! Holy reinvention, Batman. And even Scottish national regs are more strict than English - who'd a thunk it!

    In doing so, though, he ignores other things like the extra embodied energy of a central heating system that isn't needed in a PH or better. And he ignores the fact that the appropriate base temperature for degree days is itself a dependent variable of the amount of insulation. So he gets a pretty graph that is approximately the right shape, but just happens to be wrong.
    •  
      CommentAuthordjh
    • CommentTimeApr 4th 2021
     
    Posted By: WillInAberdeenWhat is missing for me is that the energy embodied in the insulation might come from carbon (eg polyurethane or mineral wool, shipped to site in a truck) but the energy to heat the house will increasingly be renewable, as the house will stand late into the 21st Century and maybe the 22nd.

    Agreed but as well as improvements in generation technology, one would hope there would also be improvements in the production and recycling of components.

    As Tony says, a cultural change is needed. More use of timber, less of concrete and brick (to illustrate).
    • CommentAuthorMike1
    • CommentTimeApr 4th 2021
     
    Yes, there is a limit to how for it's worth going, but there are several flaw in the article.

    Passivhaus effectively defined the limit for energy efficiency as the point when a conventional heating system is no longer required. In addition to reducing the in-use carbon emissions, this also makes the bills much more affordable without, in theory, increasing the build cost (eliminating the heating system pays for the additional insulation & airtightness) - i.e. the affordability of energy & fuel poverty are also major problems that Passivhaus addresses.

    The author of the paper doesn't seem to understand the Passivhaus approach, lumping in with Building Regs' U-value targets, and saying that the rules should prescribe in detail how architects and planners should go about achieving energy efficient buildings; the flexible PHPP approach to Passivhaus is a strength, not a weakness.

    While Insulation is a major factor, it's also not the only factor to consider in evaluating embodied energy. For a Passivhaus, the embodied energy of the heating system, and of the energy supply infrastructure that would otherwise supply the building with additional electricity / gas, are also eliminated - factors not considered in the article. A little ironic as the paper the author quotes (on measures backfiring / Jevons’ Paradox) specifically mentions the need to consider the appropriate 'system boundary' when evaluating such situations.

    However I don't think any of us would disagree on the benefits of non-technological alternatives mentioned - turning down the thermostat, putting a jumper on, and turning off household gadgets. That's a whole different challenge.
    • CommentAuthorjms452
    • CommentTimeApr 4th 2021
     
    Awesome & comprehensive analysis Dave - pretty much saves me reading the article and any subsequent irritation :bigsmile:
    • CommentAuthorjms452
    • CommentTimeApr 4th 2021
     
    I've gone and looked at it now :devil:

    His source data seems a bit weird, for one he gives the embodied energy of EPS as higher than PU when I had always understood that it was lower.? Also a very high GWP of EPS...?
    •  
      CommentAuthordjh
    • CommentTimeApr 4th 2021
     
    Posted By: jms452His source data seems a bit weird, for one he gives the embodied energy of EPS as higher than PU when I had always understood that it was lower.? Also a very high GWP of EPS...?

    Yes, I noticed that but didn't bother to investigate. Perhaps he was using old data before EPS was made with 'green'er blowing gases?
  2.  
    I'm glad this brought up some interesting challenges to the blogs writers thinking.
    Im left thinking, though insulation is still key to many improvement in the building sector the time will come when we need to widen our horizons , keep up with change and realise other factors willstart to play a greater role and need bringing into the formula.
    The whole 'rebound effect' always rears it's head worryingly in the energy efficiency debate. Let get the build stock improved first , then worry about that :-)
  3.  
    If the optimal thickness of insulation is a balance between the carbon it takes to manufacture the insulation, vs the carbon to make the heat which the insulation conserves,

    Then it follows that renewably-heated houses should have less insulation than fossil-heated houses. And heatpump houses should have less insulation than electric-resistance houses.

    Looking at the whole lifecycle of the house, maybe 100years, most of that lifetime will lie after 2050, by when all heating should be zero carbon. Lifecycle analysis would say that it's not clever to clad a house in carbon-intensive insulation, to conserve heat which will be carbon-free for most of the lifetime of the building.

    Heresy upon heresy!
  4.  
    Also interesting that the EROEI of the cellulose-derived insulation came out poor compared to the mineral wool, because you need many kg of cellulose to get the same insulation value as few kg of mineral wool.
    •  
      CommentAuthordjh
    • CommentTimeApr 6th 2021
     
    Posted By: WillInAberdeenAlso interesting that the EROEI of the cellulose-derived insulation came out poor compared to the mineral wool, because you need many kg of cellulose to get the same insulation value as few kg of mineral wool.

    Did they count the original energy in the production of the newspaper or denim jeans in the cost of the cellulose, or just the cost of re/up/whatever/cycling it?
    •  
      CommentAuthordjh
    • CommentTimeApr 6th 2021 edited
     
    Posted By: WillInAberdeenLooking at the whole lifecycle of the house, maybe 100years, most of that lifetime will lie after 2050, by when all heating should be zero carbon. Lifecycle analysis would say that it's not clever to clad a house in carbon-intensive insulation, to conserve heat which will be carbon-free for most of the lifetime of the building.

    Energy too cheap to meter! :bigsmile: Now where have I heard that before? Methinks the reality will be somewhat different and that the carbon content of the electricity generating and distributing machines will not go to zero for a very long time.

    Maybe Elon Musk et al have it right and we need to move manufacturing off-planet? Mine the asteroids!
    • CommentAuthorShevek
    • CommentTimeApr 6th 2021 edited
     
    Posted By: WillInAberdeenSo if there's a choice of adding more layers of carbon-intensive insulation, or cranking up the renewably-powered heatpump another notch, it might be better to insulate less now and do more heating in future.

    Heresy!


    Or you take it as an opportunity to insulate with insulation that doesn't bring more plastic into the world.

    This was a real dilemma for me when I retrofitted a home in London. We used graphite-enhanced EPS external wall insulation, but if I did again I'd do it in wood fibre and accept the lower u-value.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 6th 2021
     
    Posted By: WillInAberdeenAlso interesting that the EROEI of the cellulose-derived insulation came out poor compared to the mineral wool, because you need many kg of cellulose to get the same insulation value as few kg of mineral wool.
    What's 'per kg' got to do with it? 'Many kg' of a dense insulant requiring small input (embodied) energy would have better EROEI than 'a few kg' of lightweight hi-tech high-embodied insulant giving the same Uvalue.
  5.  
    The blogger cited his source data as
    https://doi.org/10.1016/j.enbuild.2017.12.009
    Title: A comparison of the environmental impacts of differentcategories of insulation materials
    Journal of Energy and
    Buildings

    Looks solid but no idea if it is.

    The embodied energy in MJ per kg for the cellulose and the mineral wool were similar, you just need a lot more kg of the cellulose to get the same U value.

    Edit to add: "cellulose" apparently includes woodfibre, which is wet-formed and dried
  6.  
    Posted By: djhEnergy too cheap to meter!


    Sorry - where did anyone mention anything about cost?


    Who knows if heating energy will be cheap or expensive throughout the lifetime of the house. But I'm presuming that you have heard about "Net Zero"? It's the national goal, by 2050, if I recall...! :bigsmile:
    •  
      CommentAuthordjh
    • CommentTimeApr 6th 2021
     
    Posted By: WillInAberdeenSorry - where did anyone mention anything about cost?

    Sorry, I've added a smiley to indicate that I was saying it tongue in cheek, referring to your assertion that energy will be carbon-free (and thus free in carbon terms, not cost terms; I thought that would be understood in context). The point is that so-called 'carbon free' energy isn't, because of the [carbon] cost of whatever produces it.
  7.  
    :bigsmile: me too!
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