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Green Building Bible, Fourth Edition
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  1.  
    I dont see what the big mystery is, the gap is acting like double glazing in that its holding air as an insulating layer.
    The reason 25mm is optimal is because anything over 25mm and the insulating effects start to be diminished by convection currents transporting heat across the air void.

    It doesnt matter why the air gaps helps, it just needs to be taken in account when using whatever method to measure the effectiveness of MF.

    All this debate could be resolved very quickly by talking to those engineers on the forum link.
    And looking at where MF is used in the real world. I can tell you that the Actis factory isnt insulated with MF.
  2.  
    Mike, Paul has answered very well (and I quite like the foil / low-e coating comparison). This isn't a personal debate, rather an attempt at the truth.

    Of course air gaps contribute to the overall effect but using air gaps to promote mutifoils is like building a straw-bale wall, tacking multifoil on to it and saying "Look at this low u_value wall I've built. Aren't multifoils wonderful!".
    • CommentAuthorMike George
    • CommentTimeNov 2nd 2010 edited
     
    No Biff, Paul did not answer the question I asked you. Its quite obvious that no matter how many times I ask it, I will not get a straight answer.

    Instead of answering you keep using straw man arguments while insinuating that I believe foil to have some magical properties - I do not. And I don't know who you are quoting in inverted commas above but it certainly isn't me.

    WHAT I SAID WAS THAT HOT BOX TESTING INDICATES AN OPTIMUM AIR GAP WHICH NEEDS TO BE INSTALLED FOR REAL LIFE PERFORMANCE TO COME ANYWHERE NEAR THAT IN THE LABORATORY.

    Now if you disagree with that then you are also disagreeing with the long established method of measuring heatloss, and also the laws of Physics which undermine it.

    I'm assuming therefore that you don't disagree, and that there is therefore an optimum air space. I repeat I am not using the optimum air space to say 'Aren't multifoils wonderful'

    10/1 says I don't get a Yes/No answer. Anyone like the odds?
  3.  
    Posted By: Mike GeorgeNo Biff, Paul did not answer the question I asked you. Its quite obvious that no matter how many times I ask it, I will not get a straight answer.
    Mike, with respect, Biff said he agreed with me. Seems like a straight answer to me. I don't know why you're flogging this dead horse - everyone agrees that there is an optimum sized airgap before convection losses overcome the extra insulating effect of the air itself. Just the same as there's an optimum spacing in glazing units, also revealed by thermal modelling and hotbox testing.

    Paul in Montreal.
  4.  
    Exactly so.

    Funnily enough, the air-gap recommended for use with multifoils tends to be a bit on the big size. I don't understand that as there seems to be a real danger that convection will negate the air's low conductivity. With double glazed windows it's usually assumed that the gap needs to be less than about 20mm and many units are made at 16mm, as anything extra does not add much and the convection risks increase.
    • CommentAuthorMike George
    • CommentTimeNov 2nd 2010 edited
     
    Posted By: Paul in MontrealMike, with respect, Biff said he agreed with me. Seems like a straight answer to me. I don't know why you're flogging this dead horse - everyone agrees that there is an optimum sized airgap before convection losses overcome the extra insulating effect of the air itself. Just the same as there's an optimum spacing in glazing units, also revealed by thermal modelling and hotbox testing.

    Paul in Montreal.


    Now that Paul, finally, IS the straight answer I was looking for, the bit about everyone agreeing that there is an optimum sized airgap and that it applies to foil applications. I note you have said as much previously, but Biff hasn't acknowleged that, at least until now. Shame we had to go through all this straw man crap before getting to the point. So no more flogging the dead horse.

    I'm going away now to design a smiley for banging my head aginst a brick wall.
  5.  
    Still bonkers. There is an optimum sized air-gap - as big as possible without allowing convection (see my previous post). It applies in all situations. Nothing special about foil applications. No idea what you think I haven't acknowledged when I've agreed with everything Paul has said :confused:
    •  
      CommentAuthorfostertom
    • CommentTimeNov 3rd 2010
     
    Posted By: biffvernonthe air-gap recommended for use with multifoils tends to be a bit on the big size
    No it's not - the air gap you get from following recommendations is less than zero:
    Posted By: fostertomthe air gap will unavoidably be 25-30 = -5mm - the (30 thick) MF will be compressed 5mm and in intimate contact with both adjoining surfaces
    • CommentAuthorcvhorie
    • CommentTimeNov 10th 2010
     
    As a simple DIYer, this discussion is useful on the level of testing standards. Has anyone done a thorough finite element analysis (or similar) on this material, then compared the results against reality?

    However in the next few weeks, I shall be buying insulation materials for internal wall insulation for a solid brick wall house in the UK. Actis claims that their installed system Triso-super 10 (ca 70mm thick) is as effective as ca 210m thick of mineral wool (+ plasterboard). The saving of space is considerable, even better than Aerogel. I realise that the mechanisms of thermal transmission are very different, so the comparative test methods must evaluate the overall heat loss reduction rather than measuring the effect of separate elements of the system.

    Can you point me towards an independent judgement on this claim or more generally a comparison between foil and volume fill heat reduction materials?
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 10th 2010
     
    Posted By: cvhoriethen compared the results against rea


    Think the trouble here is that no one can agree what 'reality' is.
    • CommentAuthorCWatters
    • CommentTimeNov 10th 2010
     
    Posted By: cvhorie The saving of space is considerable, even better than Aerogel.


    How can that be? Aerogel holds the world record as the best thermal insulator. Perhaps someone should tell NASA :-)

    http://en.wikipedia.org/wiki/Aerogel

    "Silica aerogel holds 15 entries in Guinness World Records for material properties, including best insulator"

    http://www.sti.nasa.gov/tto/Spinoff2008/ch_9.html

    "Aerogels have unsurpassed thermal insulation values (providing three times more insulation than the best fiberglass"

    It might appear transparent but it's also virtually opaque to infra red.
    • CommentAuthorMike George
    • CommentTimeNov 10th 2010 edited
     
    Posted By: cvhorieAs a simple DIYer, this discussion is useful on the level of testing standards. Has anyone done a thorough finite element analysis (or similar) on this material, then compared the results against reality?


    I did some research comparing PUR, Mineral wool and multifoil a while back using Thermal simulation analysis and posted the initial results on this thread -the multifoil performed favourably, and was not in agreement with the NPL report. Unfortunately, the charts have since been removed [not by me!]. The research was never written up completely though because of the lack of for key information about the material composition of multifoil. Dont want a legal writ slapped on me. I also sent the results to NPL as part of a report - I did not receive so much as an acknowledgment.
    • CommentAuthorcvhorie
    • CommentTimeNov 10th 2010
     
    Aerogel vs Triso thickness
    All my information is derivative. On the Greenspec webpage, Insulation materials introduction, is a chart showing insulation to achieve U = 0.2.
    210mm for rock wool (Actis says Triso insulation is equivalent to 210mm mineral wool)
    75mm for Aerogel

    Actis say that 2 wood battens 25mm thick are needed + thickness of compressed Triso, ca 10mm = 60 mm

    So the Triso system is thinner. For my situation, insulation applied to a solid brick wall, these numbers need 12.5mm plasterboard added.

    Perhaps you cannot find 25mm wood battens in space. Or NASA don't like the French. Or perhaps they were measuring something else.
  6.  
    Posted By: cvhorie(Actis says Triso insulation is equivalent to 210mm mineral wool)
    It's one thing to say something, another thing to back it up. I could say I'm a rocket scientist ... but I can't back it up. None of the accreditation bodies will give a certificate that backs up that claim so I'd be wary. Aerogel is at least proven. I'd be especially way of a claim that says 75mm of insulation compressed into 10mm has anything like the same thermal properties of the original material. Why don't they make it 10mm thick in the 1st place?

    Paul in Montreal.
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 11th 2010 edited
     
    Paul
    Think we did that one http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6367&page=3#Item_24


    The National Physics Laboratory did a test on Multifoil, you can download the report (may need to log in). I consider the NPL to be a reliable testing body. http://www.npl.co.uk/content/ConPublication/3991

    After, admittedly a brief scan of the article, most of the points raised on this thread seem to be answered.

    One thing that keeps cropping up is the difference between steady state and a dynamic system when testing. This thermal inertia effect does have an influence when comparing results and thought experiments but can be calculated using:
    Thermal Inertia = (Thermal Conductivity.Density.Specific Heat Capacity)^0.5.
    Start breaking down the units and it all starts to fall into place, though I find the concept of time in an equation a bit tricky to understand still sometimes.
    • CommentAuthormands
    • CommentTimeJan 9th 2011
     
    A multifoil isn't particularly insulation at all, it's a reflector!
    • CommentAuthorCWatters
    • CommentTimeJan 9th 2011 edited
     
    Posted By: mandsA multifoil isn't particularly insulation at all, it's a reflector!


    I guess you just couldn't face reading nearly 800 comments :-)
  7.  
    Posted By: CWatters I guess you just couldn't face reading nearly 800 comments :-)
    I have avoided this thread because the 800 comments would take a few hours to digest, would somebody mind giving me an overview in a few sentences please?
  8.  
    Posted By: Viking Housewould somebody mind giving me an overview in a few sentences please?
    No! The rest of us had to suffer reading through all 800 ...


    ... ok then. Some people, Fostertom being one, think that multifoil works in some kind of magical way that defies regular testing. Some of us are not so sure. Some of us (me for example) posted links to detailed papers which go through the mathematics of how foils work in practice. Fostertom has said he'd read these, but hasn't yet and keeps postulating all sorts of stuff about micro-dynamics. Real-world physics already takes into account all this stuff. Some people postulate that multifoils work well because they help airtightness, compared to fibre insulation or badly fitted foam boards. At the end of the day, the stuff is overpriced for what it delivers. May as well go aerogel and get something that is known to work well in thin-ish layers.

    Hope I didn't offend anyone!

    Paul in Montreal.
    • CommentAuthorJoiner
    • CommentTimeJan 10th 2011
     
    And Tom is on holiday for (I think) two weeks, in case anyone wonders why he doesn't respond.
    • CommentAuthorCWatters
    • CommentTimeJan 10th 2011 edited
     
    As far as English Building Control regulations are concerned...

    a) The government has stated to LABC that "the only appropriate methods for measuring the thermal performance of materials and products are the “hot-box”...

    http://www.communities.gov.uk/documents/planningandbuilding/pdf/divlettermultifoil.pdf

    b) Not all multifoil products have been tested and shown to achieve the required performance using the Hot Box method so not all should be accepted by LBCO.

    c) Hot box tests carried out by the National Physical Laboratory showed that some products failed to live up to manufacturers claims by a factor of three.

    d) Tests carried out by the BRE in 2005 showed that "Hot Box testing" gave similar results to the test method preferred by some multifoil manufacturers ("in-situ testing") and that both test methods showed that the multifoils tested failed to achieve the manufacturers claims.

    e) Some muiltifoil products have been Hot Box tested and the results used to support roof designs that incorporate a combination of conventional and multi foil insulation to achieve the required u-values.
  9.  
    Thanks Paul and Colin!
    •  
      CommentAuthorfostertom
    • CommentTimeJan 24th 2011
     
    Posted By: JoinerTom is on holiday for (I think) two weeks
    Yes, it was soooo boring, I completely forgot to take Paul's learned papers with me!
    Actually, it's more that I'm waiting opportunity to ask my boffin colleague what it all means, because I think I've spotted a few flaws and assumptions, along with the valuable understanding in the papers.
    • CommentAuthorrbisys
    • CommentTimeNov 3rd 2011
     
    Greetings,

    I skipped 25 pages too. Since I was a reflective insulation contractor for over 30 yrs I've heard most of the arguments presented here.
    There is a tendency to refer to both reflective insulation sys (RIS) and radiant barriers (RB) as if they are the same. They are not. RB are open air systems such as installing a reflective sheet over existing attic insulation. The foil is exposed to open air space, such as attic. I do not recommend attaching to the rafters. RIS are usually 2 or 3 sheets of reflective material installed in stud area that is bound by interior/exterior sheathing. In attics, between the joists above drywall. I mention this because I run into people quoting RB tests when the subject is RIS.

    Here is what I have found about my sips house which I retrofitted the ceiling with a furred out RBI sys with new drywall. This is also true for new houses where the owner has followed my recommendations for a multi layer RBI sys. About 4 yrs ago our power was out for 6 1/2 days due to a tornado. The house is ranch style with no shade and a dark roof. The day temps were 95 + degs. The interior temp never got above 80 degs.

    Winter our gas furnace operates about 6-7 minutes and is off for about 15-20 mins, depending on exterior temps. This I feel puts to rest that RBI is not effective in winter as other materials argument to rest, because my neighbors furnaces run all the time at night and pretty regular during the day.
    Our utility company has told me to my face, twice, that they do not make any money on my houses. They have killed a lot of RBI sys sales over the years.

    If properly installed as I recommend the btu/sf/hr on a 95+ deg day is about TWO. And that is a sys that insulates the studs and joists. This according to Marks Mechanical Engineering Handbook.

    My experience with RB over existing is about a 50% reduction in ac run time. I do not quote savings as that is a variable determined by the occupants life style. How ever there is a definite increase in summer comfort as less energy is RADIATING to the occupants.
    • CommentAuthorrbisys
    • CommentTimeNov 3rd 2011
     
    Greetings,
    In the above comments I inadvertently used the RBI designation in the 2nd and 3rd paragraphs. Should have used RI ( radiant insulation)or RIS (radiant insulation sys).
  10.  
    Hi rbisys,
    can you give a run down of the total thickness of your RI system , and the component parts?

    Your retro fit consisted of adding your RI system to the existing SIPs panels in the roof?
    • CommentAuthorrbisys
    • CommentTimeNov 4th 2011
     
    Greetings,

    The retrofit consisted of:
    Attaching 2"x3"x1/2" osb pcs 16"c/c along the rafter line over drywall. Used 2 1/2 " finish nails from Harbor Frt.
    Attaching single layer reflective foil, perforated, to the pads. Foil is overlapped at seams 2" and then folded over and stapled.
    Attaching across the rafter line 7/8" steel furring strips. Used 2 3/8" ring shank nails. Could use drywall screws. Fasteners should go into rafter at least 1".
    Drywall.
    Check fifoil.com for product info. Foils must be perforated.

    If you are retrofitting a cathedral ceiling use above or run 2x2 across the rafter line and install 2 layer RI between the 2x2s.
    Attach a single layer to bottom of 2x2 and the 7/8" furring strips across the 2x2.
    Ck fifoil.com for two layer material.

    I'm installing alum soffit and fascia on my house now and next spring I will attach 1 1/2" x 1/2" furring strips over the T 1-11 exterior walls and a perforated foil, then steel siding.

    When foil is installed on the exterior in this manner it becomes the dominate insulator, therefore, most if not all condensation stops in the wall along with mold growth.

    Here is a chart from an article I wrote.
    In summer you can determine the temperature of your ceiling drywall by taping a thermometer to the drywall surface.
    This chart is based on a 75 deg floor temperature. The chart can be validated by using the emissivity data and formula from Mark’s Mechanical Engineering Handbook. FG values are for insulation between joists and include joist heat transfer. The RB value is for the joists surfaces covered with the RB and a furring strip to separate the RB from the drywall. “A” is the dry wall temperature. “B” represents the Btu’s radiated for the FG installation. “C” represents the Btu’s radiated for the RB installation. “D” the Btu difference between the FG and RB.
    Although the mechanics for side walls will be slightly different this method can be used for approximate comparisons.

    Summer Winter
    “A” “B” “C” “D” “A” “B” “C” “D”
    150 88 5 83 75 0 0 0
    140 75 4 71 70 5 .3 5
    130 61 3 58 60 14 1 13
    120 49 3 48 50 22 1 21
    *110 37 2 35 40 31 2 29
    100 26 1 25 *30 38 2 36
    90 15 1 14 20 45 3 42
    80 5 .3 5 10 52 3 49
    75 0 0 0 0 58 3 55

    The 110 deg is high lighted to represent a 95 deg day. The 30 line is highlighted to show the similarities of the summer winter conditions. Note the jump when the temperature gets down to zero degs. Because of the rapid drop off in FG efficiency as the material thickness is increased it is difficult to extrapolate the RB and FG data for “R” value comparison. Compared to the advertised “R” value for FG the RB “R” factor could exceed “R”100 value by a considerable amount, and it is impossible to have a “R” value of 100 much less 100 plus. Data from Marks Mech. Eng. Handbook

    For those of you who think cellulose is superior consider the results of a retrofitted house by the NBS, in 1977.
    The amount of moisture in the wall cellulose was about 15% by weight. Using a common used factor of 5% increase of heat flow for every 1% of moisture by weight we get 75% increase.

    Any one wanting the info I have send an e-m to rbisys@juno.com and I'll send it to you.

    By the way, I live in the St. Louis, Mo area and we get plenty of temperature variations, over 100 and below zero.

    Hope this helps.
    • CommentAuthorrbisys
    • CommentTimeNov 4th 2011
     
    Greetings,
    The chart did not reproduce very well.
    These are 4 digit units, so count over 4 digits and move the rt hand 4 digits over to the right.
    •  
      CommentAuthorfostertom
    • CommentTimeNov 4th 2011
     
    rbisys, you can edit your prev posts - better than posting amendment instructions!
    • CommentAuthorrbisys
    • CommentTimeNov 4th 2011
     
    Greetings Fostertom,
    There's an inverse problem with my knowledge of RB and computers.
    Can you help me out here? Thanks.
   
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