Green Building Bible, Fourth Edition |
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Posted By: WatchIthttp://www.communities.gov.uk/publications/planningandbuilding/determination451238" rel="nofollow" >http://www.communities.gov.uk/publications/planningandbuilding/determination451238
well well...the debate takes another twist (against in-situ testing).
31. More recent theoretical research by Professor Philip Eames of Loughborough University2, carried out for the Department after your full plans application was made, lends support to BRE’s conclusions. Professor Eames calculated the U-value of a typical roof construction insulated with multi-foil and compared it with the U-value of the same roof insulated with mineral wool – in effect modelling the comparative tests carried out by TRADA and CIM. To do the calculations, Professor Eames assumed values for reflectivity (which is independent of thickness) and thermal resistance (which is dependent on thickness) corresponding to bright aluminium foil and foam layers respectively.
To determine the best possible system performance that could be achieved using the best materials currently available, he repeated the calculations for multi-foil comprising polished silver foil and aerogel layers. The predicted U-values were:
•
200mm mineral wool (no reflective backing): 0.17 to 0.19 W/m2K
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100mm mineral wool (no reflective backing): 0.33 to 0.34 W/m2K
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Multi-foil – typical (aluminium foil and foam): 0.35 to 0.50 W/m2K
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Multi-foil – best possible (silver foil and aerogel): 0.23 to 0.27 W/m2K
Professor Eames therefore calculated that the predicted thermal performance of typical multi-foil material is worse than that of 100mm of mineral wool insulation; and even if made from silver foil and aerogel, it is worse than that of 200mm of mineral wool insulation.
Posted By: WatchItWe don't all know this test method is "deeply flawed" TomIn what way isn't it?
Posted By: WatchItThe report that made my mind up on multifoil claims was the NPL hotbox testing where they compared Triso to glasswool and Celotex, testing them all in the hotbox. We don't all know this test method is "deeply flawed" Tom...I for one believe this is by far the fairest test method we have.Simply allowing temp to vary in a slow and steady way within the hotbox bears no resemblance to real-world rapid micro-variation and reversal of temps. That is still equiv to steady-state, as far as MFs' operating principle is concerned. And that is what the NPL settle-this-once-and-for-all testers did, as their sop to the MF manufs' insistence that testing should be done under dynamically varying conditions. The NPL testers didn't bother to check out their silly methodology with the MF manufs - and why should they, as their paymasters' hidden brief was to run MFs out of town.
Posted By: CWattersthe manufacturers haven't been able to convince the world there is a differenceThe Confed of Multifoil Manuf did indeed convince the European testing over-body that there is a difference and as a result a programme to build 13 v expensive dynamically-varying test rigs across Europe was put in hand. But for reasons I don't have info on, that decision was reversed. Conventional insulants would also have got tested, under real-world dynamically varying conditiions, and the results wd have been v interesting - and embarassing. The leading lights of the CMM effort seem to have accepted defeat (for now). For that reason I'm not now recommending or specifying MFs, because MF manufs' wholehearted tech backing isn't there at present
Posted By: WatchItloads of industry professionals that don't want to accept they have been taken for a rideCertainly the old scientists who have safeguarded BRE's 50yr development and application of hotbox methodology - and the entire conventional insulation industry.
Posted By: WatchItan airtight materialone of the standard red herrings - most MFs are peppered with stitch holes so none of thelr performance can be attributed to airtightness.
Posted By: biffvernonAnd still the physics is ignoredand you in particular Biff have consistently stonewalled alternative interpretations of physics that have been offered. 'Stonewalled' means not disputed - just ignored.
Posted By: WatchItits common senseThe last resort of the 'ay oop' conservative.
Posted By: WatchItthe effect of a few stitched holesGet a sample of MF and tot up the area per m2 of the stitch holes - as far as I remember it's equiv to a 80mm diam hole. How much larger than that wd become significant? Tho there are imperforate MFs now, the ones that took part in those old comparative tests were as leaky as a sieve. So let's drop that 'due to airtightness' myth.
Posted By: Paul in Montrealhttp://www.astm.org/DIGITAL_LIBRARY/STP/SOURCE_PAGES/STP1116.htm" >http://www.astm.org/DIGITAL_LIBRARY/STP/SOURCE_PAGES/STP1116.htm
"Brings together the latest research data on thermal insulation materials.
Posted By: djhBefore everybody gets too excited, note that it was the latest research data in 1991 when it was published!It may be old, but the problems that Tom claims are being ignored are right there in the research back then - even a paper on transient response of insulation and ways to solve the energy and radiation equations in changing conditions simultaneously. Everything he claims is not taken into account is right there in the papers. This is not rocket science! Even papers on the aging of foam-based insulation (recent discussions here about that too). There's a particularly interesting paper about insulation in attics in both unfaced and foil-faced configurations that correlate actual test house measurements with the physics used to describe them - and yet we still see people claim here that in "real world" situations everything is somehow different or doesn't apply.