Posted By: fostertomEver ingenious

Yes, just something you have to get used to

Keep trying Tom

I agree - Keith, you could lock the other one?

Do you mean you've read and understood what I said, Biff?

Can't you therefore say what in particular is wrong with it, instead of dismissing out of hand? You put time and trouble into your spreadsheet calc, which I always felt must contain a flaw, but as a black-box, wasn't able to crit constructively. I put time and trouble into a simple (maybe simplistic) paper calc, which anyone can examine and crit. Funcrusher did so, and I answered his criticism, but that wasn't responded to. You didn't at all.

Primarily I was pointing out that even the boffins amongst us were saying that radiant transfer is proportional to the fourth power of the temp difference, which indeed would give the steeply-diminishing transfer that you suggest.
But that's wrong - transfer is proportional to the difference between the two fourth powers of the the two abs temps - and that comes out almost linear.
Not the fourth power of the difference, but the difference between two fourth powers.

That means that the temp drop across a multifoil is near-evenly distributed from layer to layer, so every layer plays a near-equal role (whatever that is). Not that only the first (and last?) layers do anything and the interior ones have exponentially diminishing effect, which is your suggestion.

Of course, as with any insulation, every additional layer (or increment in thickness) gives diminishing benefit. That's not the kind of diminishing return you're talking about - yours is another kind, that's far steeper.

Posted By: biffvernonWhy did my coffee get cold?

Why did the Actis twin-shack not? The Actis experiment may have been sound, or deliberately or accidentally biased. Ditto for your coffee pot. The Actis experiment (and much much more evidence) suggests that there's something important, possibly radical or involving key factors not yet understood, that's worth open-minded non-partisan investigation. Working from 'first principles' (aka schoolboy physics, like mine) you've convinced yourself it's all eco-bollocks. Me, the opposite. Let the debate continue - but no stonewalling, however jocular ... please!

So if I've done my sums right the Total R-Value for the product and two air gaps is..

0.92 + 2 x ( 0.16 + 0.487) = 2.214 m^2K/W

U-Value = 0.45 W/M^2K

So additional insulation required to meet building regs in most cases.

Posted By: CWatters•0.487 m^2K/W resistance of an unventilated air cavity (min 15 mm) adjacent to the product.

Hmm, http://www.learn.londonmet.ac.uk/packages/clear/thermal/buildings/building_fabric/elements/cavities_and_air_spaces.html has

Air cavity Placement Thickness of air layer (mm) Thermal resistance (m2K/W)
Vertical 10- 20 0.14
20- 50 0.17
Horizontal- heat flow from bottom to top 10- 50 0.17
Horizontal- heat flow from top to bottom 10- 50 0.21

So even the most favourable orientation is less than half what the BBA cert says, in their view.

Anybody any idea who is right, and why whoever is wrong is wrong?

But are usually brought low by Occam's razor.

Nice post- agree with every word of that.

Posted By: fostertomstranger confoundments have happened, with predictable regularity, throughout science's history

Posted By: biffvernonBut are usually brought low by Occam's razor

The old shaver needs sharpening, from over-use. From http://en.wikipedia.org/wiki/Occam%27s_razor :
".... taken today as a heuristic maxim (rule of thumb) that advises economy, parsimony, or simplicity, often or especially in scientific theories. Here the same caveat applies to confounding topicality with mere simplicity. (A superficially simple phenomenon may have a complex mechanism behind it. A simple explanation would be simplistic if it failed to capture all the essential and relevant parts. Instead, one should choose the simplest explanation that explains the most data.)"

The last bit seems a fine description of heat flow, and multifoils in particular. Superficially simple, but complex mechanisms emerging - danger of hanging onto old simplicisms, in the face of mounting 'aberant' evidence.

Posted By: fostertom
What about the fact that most multifoils - the through-stitched ones - are very far from airtight? Explanations involving superior airtightness don't stand up. In my sample of Actis, the stitch holes are easy to measure and total up - their area is equivalent to a 86mm diam hole for every square meter! It's easy as anything to blow/suck air through it, by mouth. The imperforate spot-welded types are a different matter, but they're relatively new on the market.

I'm not sure that lots of little holes 'is equivalent' to one big hole. It's easy to blow/such air through glass fibre, sheeps wool etc. but that doesn't mean that they are no good for insulation.

Posted By: Saintwhat other product in any other often less critical application, so shrouded in controversy, villified by all but a valiant possibly misguided few and technically totally unsupported by its manufacturers would any of us truthfully purchase as a solution in any other walk of life?

Well, if you happen to have 'insider' knowledge and/or hard-won understanding, you may well see tye advantages of going against conventional wisdom, which is almost by definition unreliable and ripe for change - surely history repeatedly shows that!

However, I wouldn't currently specify multifoils except possibly in tandem with Cellotex etc, as Thinsulex-certified. That's not because I've become unconvinced, but because as you say multifoils are currently 'unsupported by the manufacturers'; specifically as far as I'm concerned by Paul Mitton, boffin of Euroform (Xfoil) who's giving his MF baby a rest while otherwise busy, having been made MD of Euroform after SIG bought it for £8m. When and if SIG, Actis etc decide to re-engage with the temporary restraint-of-trade victors, then we'll see.

Posted By: Saintit is the only insulation that defies "standard" testing on the basis that common insulations manufactured by global players are tested

MFs happen to do badly under the bad-science regime of the hotbox. Aerogel happens to do unnaturally well, so the anomaly that it is escapes attention. Aerogel and MFs, also the carbon-black in 'Platinum' EPS, are all pl;aying a different thermal game that the hotbox specifically sets out to eliminate, as 'experimental error'.

The fundamental notion of conventional insulation thinking, embodied in the hotbox methodology, is that insulant materials are all attempts to get as close as possible to the theoretical ideal thermal conductivity of still air - 0.025w/mK - see http://en.wikipedia.org/wiki/Thermal_conductivity . In real life air is much more 'conductive' than that, due to radiant and convective transfer. Insulants set out to minimise convection as far as possible, and largely ignore internal radiation. So you'd expect the best of insulants to get close to 0.025 but not beat it. So how come aerogel gets 0.004 to 0.4? and even PIRs can beat 0.025. Everyone loves aerogels but the'yre just as much of a challenge to conventional insulation thinking, and to the hotbox, as is MF. The hotbox results for aerogel, that we're happy to believe, are just as unreliable as those for MF.

Posted By: Johanvapour barrier on the inside and OSB/breather membrane on the outside ... no pressure driven air movement within the mineral wool

True - that's the kind of separate air movemrnt protection that is necessary - same is necessary for stitched MF. However, Mark's alerting us, as well as to pressure-driven air, also to wind-washing (you've covered that) and convection in the airgaps within the airsealed void (you'd prob be getting that).

<blockquote><cite>Posted By: fostertom</cite
The fundamental notion of conventional insulation thinking, embodied in the hotbox methodology, is that insulant materials are all attempts to get as close as possible to the theoretical ideal thermal conductivity of still air - 0.025w/mK - see http://en.wikipedia.org/wiki/Thermal_conductivity . In real life air is much more 'conductive' than that, due to radiant and convective transfer. Insulants set out to minimise convection as far as possible, and largely ignore internal radiation. So you'd expect the best of insulants to get close to 0.025 but not beat it. So how come aerogel gets 0.004 to 0.4? and even PIRs can beat 0.025. Everyone loves aerogels but the'yre just as much of a challenge to conventional insulation thinking, and to the hotbox, as is MF. The hotbox results for aerogel, that we're happy to believe, are just as unreliable as those for MF.</blockquote>

Tom you seem to be saying that still air is the optimal insulation and that all other insulants strive to achieve the same thermal performance?.
Still air however is equally subject to the 3 forms of thermal transport i.e. conduction, convection and to a greater or lesser part, depending on ambient, radiation. Hence its relatively average thermal conductivity 0.025W/mK. Removing air as in a vacuum panel sees that thermal conductivity improve to 0.05W/mk. Replacing air with say argon improves the thermal conductivity by 35% or so.
If you follow those logical arguments then there are no surprises in seeing PIR beat 0.025W/mK due to the blowing agent used and hence the reduction in conduction and convection in the cell gas nor indeed aerogel where the mass of the material is so little that conduction is dramatically reduced and the nano sized cell sizes significantly reduce convection.
There is no magic or trickery in obtaining these results just science and as I’ve indicated previously the performance is proven in many other applications.
As an example recently a 100mm exhaust was wrapped in just 30mm aerogel. The aim to achieve a touch temperature of less than 70 degC on the outside of the 30mm. The exhaust runs at 550 degC. The calculation estimated 67degC it achieved 68 degC. Conversely a similar application but this time for cryogenics. Again it matched the calculated performance. Can you ever imagine MF appearing let alone performing in a serious insulation application?

Posted By: SaintStill air however is equally subject to the 3 forms of thermal transport i.e. conduction, convection and to a greater or lesser part, depending on ambient, radiation

Yes

Posted By: SaintHence its relatively average thermal conductivity 0.025W/mK

No, I think - correct me if wrong, but isn't 0.025 the strictly-conduction-only figure for still air, with convection and radiation stripped out?

Posted By: Saintthere are no surprises in seeing PIR beat 0.025W/mK due to the blowing agent used

That has been the 'explanation' for PIRs beating the 0.025 holy grail of still air, but aerogels can offer no such excuse. as they're full of ordinary air, not exotic blowing agent.

Posted By: Saintaerogel where the mass of the material is so little that conduction is dramatically reduced

True - that is, conduction through the solid paths of the aerogel, which is fabulously contorted so as to make those path lengths very long

Posted By: Saintand the nano sized cell sizes significantly reduce convection

Maybe, but those nano sized cells do nothing to reduce the dominant conduction through the air that fills them. So far you've described an ordinary average air-filled conventional insulation, albeit with its solids and voids divided on a much more nano scale than say foamed plastic. However, aerogel has one more trick up its sleeve that changes that (as does the carbon black in Platinum EPS) - and the role of internal radiant transfer is key to that.

Posted By: SaintCan you ever imagine MF appearing let alone performing in a serious insulation application?

Yes indeed, no one challenges the efficacy of MFs in cryogenics and spacecraft, for which they were originally developed.

Thanks Saint - will look at that about aerogel.

Posted By: SaintAs far as I'm aware 0.025W/mk is the thermal conductivity for air including all forms of thermal transport

Hm, would that apply to all the gasses listed in http://en.wikipedia.org/wiki/List_of_thermal_conductivities ? I doubt it. Isn't 'still' air meant to denote 'no convection'? Can anyone answer that?

Copied from http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=5380&page=1#Item_30
It refers to PUR insulation but the %age of internal transfer effected by radiation is relevant to the MF debate.

Posted By: CWattersThis paper says that the conductivity of PU insulation depends on three modes.. conduction in the cell gas mixture, conduction in the solid polymer and radiation between cell walls.

http://lsta.lt/files/events/28_jarfelt.pdf

Page 5 has a diagram showing how each of those three contributes to the overall thermal conductivity at different foam densities. It suggests the vast majority is by conduction through the gas, followed by conduction through the foam and lastly radaition between cell walls appears to account for only about 4.5% of the total heat loss.

Haven't read thro it yet, but one thing jumps out:

"It suggests the vast majority is by conduction through the gas, followed by conduction through the foam and lastly radaition between cell walls appears to account for only about 4.5% of the total heat loss."

'Only 4.5%' would be assuming steady-state in the calcs, or under test in the artificial steady-state conditions of the hotbox. In the real-world of dynamically-varying micro-conditions, it's a different matter - radiation becomes the dominant mode of transfer:

This thread, Aug 19th 2007

Posted By: fostertomImagine a fresh temperature wavefront working its way slowly through a conductor, on the way to establishing a new equilibrium temperature gradient. The wavefront reaches a cavity - an entrained bubble, or the airspace between fibres. There will be a lag before the wavefront works its way by conduction around the edge of the cavity and warms the far shore. However the commencement of radiant heat transfer across the cavity is instantaneous, and will do the bulk of the warming of the far shore, long before the conductive temperature wavefront gets there. In other words, in other-than-steady-state conditions, radiation suddenly becomes the main method of transmission.

Composites that are configured specifically to resist radiant transfer (multifoils, or Cellotex with chrome-plated bubble interiors) therefore score highly, in dynamically varying temperature conditions, compared with dumb aero bars composed of average mud-coloured building materials which have relatively high emissivity.

Or, in story form!: www.greenbuildingforum.co.uk/forum/index2.php?DATEIN=tpc_wlpssdlpg_1142805843&showpage=120