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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorbiffvernon
    • CommentTimeAug 21st 2007
     
    Tom was a little bit right on his last post. I know that most of the heat leave a domestic 'radiator' by convection, but bare skin, which is pretty sensitive, can detect the small proportion of heat that is radiated sideways. Tom's glass sheet trick is just to demonstrate that his skin really is feeling the radiated heat and not wafts of turbulant convection.

    But the radiator may be up at 50 degrees and more.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 21st 2007 edited
     
    Ta mate
    Posted By: biffvernonthe radiator may be up at 50 degrees and more
    And I'm at 37 degrees (core), say 32 skin surface (does anyone know?), a differential of 13-18 degrees, in same league as UK building calcs 0-21 degrees, therefore directly comparable.

    Johan, you're right that gross radiant emission from a (black) body, disregarding any return radiation from surrounding bodies, is proportional to 4th power of its absolute temp. But in practice, it's the nett radiant transfer between two bodies of only slightly dissimilar absolute temp (one emitting slightly more than the other), that we sense and buildings experience. Applying the 4th power law, www.greenbuildingforum.co.uk/forum/index2.php?DATEIN=tpc_tuzncnnui_1170338947 shows that the radiant transfer between two such bodies is, surprisingly simply, 'near enough' proportional to the simple first power of the temp difference between them, regardless of mean absolute temp of the system (the delta-t of radiator output calcs). With the important proviso that this 'near enough' approximation only holds good within a narrow range of absolute temp, e.g. 273K to 294K as experienced by UK buildings.

    Posted By: johanHow do the manufacturers derive a k/R-vaule for multifoil?
    That's the very key question, to which hangs a long and ornate tale. The answer is unexpected and revolutionary, not at all self-evident as your rhetorical tone implies. 17 European companies manufacture multifoils and, having just now reached agreement on protocol, the testing houses of 7 European countries are begining construction of between 13 and 20 very expensive test rigs. US, Canada, Australia have agreed to sit back and watch, for the time being. Multifoils will be tested against conventional insulants, Cellotex etc as well as mineral wool. Each rig has dozens of thermocouples recording at frequent time intervals, the 'like real life' dynamically varying test cycles will run over months, or a year. Under investigation will be actual energy loss, and old-fashioned slide-rule-era concepts like R-value won't get a look in. The huge data sets will be number-crunched to reveal the hidden patterns and the key determinant criteria, chaos-theory-style. Each insulant's performance will be shown to vary considerably, depending on the prevailing conditions. The days of single R-value rating for a given insulant are numbered; in future the expected heat-retention performance of any given insulant will be modelled, with local weather data, plugging in the key operative criteria that they're about to start deriving empirically. There will be big winners and embarassing big losers.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 21st 2007 edited
     
    Found it - from http://en.wikipedia.org/wiki/Paradigm_shift , about Thomas Kuhn's 1962 book The Structure of Scientific Revolutions:

    When enough significant anomalies have accrued against a current paradigm, the scientific discipline is thrown into a state of crisis, according to Kuhn. During this crisis, new ideas, perhaps ones previously discarded, are tried. Eventually a new paradigm is formed, which gains its own new followers, and an intellectual "battle" takes place between the followers of the new paradigm and the hold-outs of the old paradigm............Sometimes the convincing force is just time itself and the human toll it takes, Kuhn said, using a quote from Max Planck: "a new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it."

    Luckily, things change quicker than that these days!
  1.  
    Some very impressive and interesting science going on here. However, getting back to basics the Building Reg killed TRADA certificate for Actis was based on comparitive tests between MF and mineral wool over a winter period. During cold damp winters would the insulation value of the wool be severely reduced by additional conduction caused by damp air within the wool, thereby allowing another insulating product to match it for performance even if, technically, it might be inferior. In nice dry laboratory hot-box conditions the wool may perform quite differently.
    I have not seen any TRADA certificate type tests between MF and more airtight Kingspan type products reported; perhaps this would not produce the results wanted by MF manufacturers? Whatever results the old or new tests indicate obviously it is the performance in the field (or attic) that really counts and perhaps simple comparative tests may be a better way forward.
  2.  
    The temperature difference may be similar, but the absolute temperature is what controls radiation.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 21st 2007 edited
     
    Posted By: Charlie Duketests between MF and more airtight Kingspan type products
    The rough equivalence seems to be 30 multifoil gives whole-season heat loss equivalent to 200-250 min wool equivalent to 120 PUR. But all of them at an insulation value about 40% of what you'd expect from the min wool or PUR published U-values - in other words pathetic!
    • CommentAuthorbiffvernon
    • CommentTimeAug 21st 2007
     
    30 multifoil ?????
    •  
      CommentAuthorfostertom
    • CommentTimeAug 21st 2007
     
    Yes, nom 30, why not?
    • CommentAuthorbiffvernon
    • CommentTimeAug 22nd 2007
     
    nom ??????

    is that 30 mm thick or 30 layers of foil (as in vacuum cryogenic jackets)?
    • CommentAuthorJohan
    • CommentTimeAug 22nd 2007 edited
     
    Posted By: fostertom
    Posted By: johanHow do the manufacturers derive a k/R-vaule for multifoil?
    That's the very key question, to which hangs a long and ornate tale. The answer is unexpected and revolutionary, not at all self-evident as your rhetorical tone implies. 17 European companies manufacture multifoils and, having just now reached agreement on protocol, the testing houses of 7 European countries are begining construction of between 13 and 20 very expensive test rigs. US, Canada, Australia have agreed to sit back and watch, for the time being. Multifoils will be tested against conventional insulants, Cellotex etc as well as mineral wool. Each rig has dozens of thermocouples recording at frequent time intervals, the 'like real life' dynamically varying test cycles will run over months, or a year. Under investigation will be actual energy loss, and old-fashioned slide-rule-era concepts like R-value won't get a look in. The huge data sets will be number-crunched to reveal the hidden patterns and the key determinant criteria, chaos-theory-style. Each insulant's performance will be shown to vary considerably, depending on the prevailing conditions. The days of single R-value rating for a given insulant are numbered; in future the expected heat-retention performance of any given insulant will be modelled, with local weather data, plugging in the key operative criteria that they're about to start deriving empirically. There will be big winners and embarassing big losers.
    That's a long reply Tom! You are missing the point though. The multifoil manufacturers are quoting u-values in their documentation. How did they come up with them? Per definition it should be impossible as the u-value relates directly to the k/R-value which per definition only applies to conduction of heat and not radiation.

    The interesting thing with multifoil though is to look at which countries uses it. France, UK, Spain, etc. I find it hard to believe it's a coincidence that all countries where it gets truley cold in the winter like the Scandinavian countries, Canada, Germany, etc. all have discard it...

    Tom, all you need to do is prove Planck's law is flawed and I'll believe you... :wink:
    As long as there is no scientific evidence that it does work it's hard to believe. From biff's (and others) experiments it looks like it doesn't work particulary well for insulation of buildings.

    I'd imagine if you use IR heaters instead of radiators multifoil would work fantastic! :cool:
    •  
      CommentAuthorfostertom
    • CommentTimeAug 22nd 2007
     
    Posted By: JohanThat's a long reply Tom!
    That makes it my fault - it would be more accurate to say "I'm not managing to understand what you mean"
    • CommentAuthorJohan
    • CommentTimeAug 22nd 2007
     
    No Tom, I understand what you're saying but it doesn't answer the question I asked.
    • CommentAuthormoogaloo
    • CommentTimeAug 22nd 2007
     
    As entertaining as this is, I tire of the polerised replies on this subject. I think the simple answer is none of you know for sure how well Multifoils work.

    So maybe we need to ask the question as to what proof either view requires to change their mind?

    Is there any testing that will satisfy all? Will the current testing scheme cover that? If not what would you like to see?
    •  
      CommentAuthorfostertom
    • CommentTimeAug 22nd 2007 edited
     
    Posted By: JohanTom, a question for you. How do the manufacturers derive a k/R-vaule for multifoil? Per definition it should be impossible...
    Oh I see, sorry. Answer is, I don't know, must be some 'equivalent to' thing. It's certainly a much better figure than the useless R-value that everyone gets when testing multifoils 'by the book' in the current hotbox test. Multifoils don't pretend to perform well on conduction/convection alone, with radiation-within-the-pores carefully minimised by the way the test's set up.

    Under carefully created steady-state conditions, heat transfer through the body of an insulant happens overwhelmingly by conduction/convection within-the-pores. Multifoils perform pathetically at this, but conventional insulations have been developed over decades to do well in this artificial test environment, without any check, until now, about how that corresponds to real life.

    Under dynamically varying temperature conditions, like real life, the reverse is true. Then heat transfer through the body of an insulant happens overwhelmingly by radiation within-the-pores. Multifoils perform very well at this, but conventional insulations might as well have been custom-designed to facilitate, not resist radiant transfer. The swift radiant transfer within-the-pores continually evens-out the local temp differentials that drive conduction/convection, before the latter can get started.
    •  
      CommentAuthorfostertom
    • CommentTimeAug 22nd 2007
     
    Posted By: moogalooIs there any testing that will satisfy all? Will the current testing scheme cover that? If not what would you like to see?
    The new testing regime that's being set up at great expense is excellent but we'll have to wait 3-5yrs for final results, it seems! The multifoil manufacturers are delighted that the paradigm-change process (these are my words, not theirs) has now been taken out of the commercial arena of propaganda, manoevring and disinformation, and is now safely in the hands of scientists (who we all know are immune to personal turf-protection and commercial influence!). However, much sooner than 3-5yrs the lessons will be learned and the whole practice of heat-loss prevention will change, for the better. Thank you, CMM, for your persistence in enlightened self-interest!
    • CommentAuthorsparrow
    • CommentTimeSep 10th 2007
     
    Anyone with the patience and stamina left for this topic may find this interesting.
    •  
      CommentAuthorfostertom
    • CommentTimeSep 10th 2007
     
    Wow! I'll have to find an hour or two to absorb this. Thanks for honouring us with so much care.
  3.  
    At Interbuild last week both YBS & Actis stands expected MF to be allowed to be used at an R value of about 5 within the year, based on the tests mentioned above which are being commenced this comimng winter. The countries where the tests are being conducted range from Finland to Spain so there should be some extremes to record. We may see earlier than expected then if the claims for MF are correct, but still have to wait for the EEC to accept the methodology before building regs can change.
  4.  
    Charlie,

    is that "R value" you quote RSI or imperial? If it's RSI, that would be R28 (for us folks on the wrong side where things are still in imperial units for many things). For comparison polyisocyanurate foam board is around R7 per inch and wood is R1 per inch.

    Paul in Metrically Challenged Montreal
    • CommentAuthorSaint
    • CommentTimeNov 7th 2007
     
    Charlie, so the MF guys before commencing these extraordinary "never been done before " tests are already predicting and expecting to be allowed to quote R5 (coincidentally the equivalent to 200mm mineral wool with a lambda of 0.04W/mK). Haven't we all been here before?
    •  
      CommentAuthorfostertom
    • CommentTimeNov 8th 2007
     
    The MF guys have done more tests than you can imagine - in fact have created all the volume of base data that the testing houses of Europe have used, and provisionally verified, in agreeing the new protocols amongst themselves - protocols that will reveal very embarasing data about conventional insulations' performance. The MF guys already know very well how their stuff performs, and also know better than the conventional insulation manufacturers, how badly the conventional stuff performs, in real-life-like tests, that the other manufacturers aren't geared-up to do.
  5.  
    Tom
    Air leakage through building envelopes is the major issue as far as energy (heat and cool) conservation, insulation is the secondary issue. Thickness of insulation compensates for air leakage in a very expensive way. If multifoil can produce an 'airtight' sealed building envelope I believe it could be more effective than the 400mm of air permeable insulation required for the PassivHaus standard. The problem is maintaining the desired level of airtightness beyond the first season. Air leakage through building envelopes has been very good for insulation manufactures. It is in their interest to push the energy wasting nonsense of ‘breathing wall’. It is their best kept secret.

    Cheers

    Steve
    • CommentAuthorSaint
    • CommentTimeNov 8th 2007
     
    Steve, I very nearly agreed with you then, certainly air infiltration is of far greater importance than recognised in earlier times. However don't confuse airtightness with permeability. In normal constructions the structure has to be permeable to allow moisture vapour to escape without allowing it to condense within the structural elements and indeed some insulation materials. I know an ASMET house employs MHVC to get round this. Multifoils if installed properly do handle air infiltration well but then again other insulations of a non foil type installed properly with strict attention to airtightness will perform much better too.
    •  
      CommentAuthorfostertom
    • CommentTimeNov 8th 2007
     
    Posted By: steveleighAir leakage .... is the major issue .... , insulation is the secondary issue
    That only becomes true once insulation has reached a high standard - higher than current Bldg Regs require, but perfectly attainable nowadays, no point in going much further. It's 'insulation - problem solved - on to the next priority'.
    Posted By: steveleighThickness of insulation compensates for air leakage
    Airtightness is no kind of alternative to insulation (or insulation/thermal massiveness - massiveness can be a fair substitute for insulation, subject to getting the various factors right).
    Posted By: steveleighThe problem is maintaining the desired level of airtightness beyond the first season
    Just a matter of detailing - primarily not relying on sticky tape at all.
    Posted By: steveleighenergy wasting nonsense of ‘breathing wall
    'Breathing wall' means transparent to water vapour, says nothing either way about airtightness. A 'breathing wall' generally aims to be water vapour transparent but airtight.
  6.  
    Saint and Tom,
    I am not confused I am including air permeability and air infiltration when I use the term ‘air leakage’.

    Both of you are talking from the accepted view of all building boffins, that water vapour has got to be allowed to travel through building fabric! BUT WHY?

    This is not the case with a sealed system.

    Mark Brinkley said that the average house holds about ten tonnes of water within the building fabric. A sealed system is about being able to produce a dramatic reduction the water contained within the fabric and being able to have full control over it by MVHR.

    Its a simple theory. In a sealed system there is no pressure within the wall build-up, no water molecules will migrate through it. In affect it means all the construction contained within the skin becomes part of the interior and therefore the moisture content is easily controllable by MVHR. The external insulation and building structure is protected from external vapour pressure and remains at the same pressure as the interior of the building.

    In a breathing walls situation, if the external relative humidity is 100% then the heating system of a home is drawing water into the interior through the walls which is a huge waste of energy per household per year.

    A sealed system has been discussed in great detail by three of the world's biggest ventilation manufacturers, three local authorities, three major insulation manufacturers etc. all agree that with a sealed system on top of external insulation (wall and roof) in conjunction with an MVHR all water molecules within the envelope can be easily managed. A sealed system will only work if the seals on the exterior skin can be maintained airtight without relying on sticky tape hidden from view inside the wall/roof fabric.

    That is the basis I am working from. Its a completely different way of looking at the problem.

    Allowances for interior moisture generated from opening doors and windows can easily managed by an MVHR system.

    In a sealed system insulation becomes about 70% more effective so maybe about 100mm would be enough to meet Passiv Haus for a sealed airtight building.

    Also just launched my new website www.sustainconstruction.com with easily obtainable documents on it.

    Cheers

    Steve
    • CommentAuthorhowdytom
    • CommentTimeNov 8th 2007
     
    Steve,
    I have been given a quantity of industrial cold store panels 6m x 1m x 100mm they are plastic coated sheet steel some filled with rock-wool some with polystyrene bonded to the steel. In the cold store they were the walls and roof , with the joints (large tongue and groove) sealed with mastic. internal temp was a constant 5'c external was open to UK climate. When removed there was no sign of water ingress.
    If i installed them on top of the purl ins, sealed them all around and covered them with pan tiles (for looks/UV protection) then in theory the dew point would be within the insulant, I just don't understand how vapour can condense in that scenario ? any comments
    tom
  7.  
    Tom,

    A cold store panel is basically two impervious steel skins either side of the insulation which forms sealed 'warm-deck' system which is similar to the gridshell roof. You won't have any problems with the panels because they have been designed as an airtight sealed system which is the ultimate insulation solution. Imagine the energy and material savings that could be achieved if a sealed 'warm-deck' was applied to a full building envelope with an MVHR system providing fresh air and moisture control.

    What an ingenious use for old cold store panels. If you could find some way of sealing the ends you will have a great system. Maybe pot-rivet some end caps on and put some insulation under the eaves to prevent cold bridging.

    The performance of insulation should be phenomenal when there is no air infiltration or water vapour penetration.

    Cheers

    Steve
  8.  
    >with an MVHR all water molecules within the envelope can be easily managed

    That's it, it has to be managed. It doesn't just look after itself. That may be appropriate for industrial buildings like cold stores but it does not a healthy home make.
    • CommentAuthorsteveleigh
    • CommentTimeNov 9th 2007 edited
     
    Biff
    Managed indoor air also means constantly venting out all the many horrible compounds floating about in the air of a modern home to be replaced by fresh air. This can be achieved sustainably by MVHR in an airtight structure if the level of air leakage (via air infiltration and air permeability) is reduced to the point where the MVHR can be run on the most energy saving setting.

    The alternative is for everybody to live in a naturally vented home built with natural materials and kitted out with natural fixtures and fittings.

    By the way Biff are you a naturist? :bigsmile:
    Cheers

    Steve
    • CommentAuthorbiffvernon
    • CommentTimeNov 11th 2007
     
    >The alternative is for everybody to live in a naturally vented home built with natural materials and kitted out with natural fixtures and fittings.
    Is that a problem?
   
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