Yes, I see ... interesting. But still v hard to belive those pores are that small.
How small wd they need to be? Of the order of a few mollecules, I'd think.
How small are they actually?
I wait with a little scepticism.

@fostertom, The pores need to be small enough to affect the number of collisions with each other that the gas molecules make, which is characterised by the mean free path. According to http://www.uccs.edu/~tchriste/courses/PHYS549/549lectures/gasses.html the mean free path of air at room temperature and pressure is 6.7 x 10-6 cm = 6.7 x 10-8 m = 6.7 x 10 nm = 67 nm. The radius of atoms is about a thousand times smaller (Oxygen radius 60 pm and Nitrogen 65 pm according to http://en.wikipedia.org/wiki/Atomic_radius) and the molecular size of N2 and O2 is about four times that as I understand it.

The size of the pores in an aerogel can vary a lot, depending on what it was made from and how it was made. In silica aerogels they typically vary from around 1 nm to 100 nm http://eande.lbl.gov/ECS/aerogels/sa-pore.html with a mean of 20 nm http://eande.lbl.gov/ECS/aerogels/sa-physical.html

The whole idea of nanomaterials is that they have interesting structure at these sort of scales. Aerogels, zeolites (used in fuel cells etc), nanotubes, DNA structures, membranes in desalination filters, integrated circuits.

I picked up on the foil insulation sort of late of.
Most of the info is completely off base. I also noticed the Irish test. I don't know the exact parameters of their test, but it was bogus too.
I'm attaching a paper I give to individuals and architects that are interested in reflective insulation

George Himmeger 224 SOUTH St TROY, IL 62294 CELL 618 698 8393 HM 618 667 4222 e-m rbisys@juno.com

Information and opinions by George Himmeger : The chart data enclosed is taken from a mechanical engineering handbook along with
opinions from thirty years field experience

EXPLORING THE LEGITIMACY OF CLAIMS OF CHARACTERISTICS, TEST PROCEDURES AND “R” RATINGS FOR THERMAL INSULATIONS USING MECHANICAL ENGINEERING HAND BOOK DATA AND FORMULA

Fiber glass FG - Radiant Barriers RB

Confusion about the performance of various insulation materials is not a recent phenomenon. Some of the confusion comes from the fact that various materials control heat energy transfer according to the specific physical properties of the materials and their assembly for use. Another problem is that large manufacturers, with government sanction, literally control the methods used to test their product and competing products. This has been an ongoing fight for over fifty years in this country. Some products, commonly used here, are not allowed in other countries because of low performance and serious health issues. The most common testing problems are:

(1) The tests do not reflect actual “installed summer / winter conditions”, which can reveal up to fifty percent difference in performance compared to “accepted tests”.
(2) Most tests favor conductivity resistance and limit the effects of radiant energy. Most homes have about 12-15% conductive surfaces, about 7% is convection and air spaces accounting for up to 80% radiant energy gain or loss.
(3) Some tests do not reveal the serious performance degradation from condensation, actually storing and increasing heat flow, and how it affects the interior humidity levels.
(4) Some tests do not reveal possible mold and other problems.
(5) Some tests, or labeling, do not reveal the health problems due to toxic chemicals. This information is classified as proprietary information and given only to the government.
(6) The tests or labels do not reveal the ratio of material to air volume This ratio can be as low as 1% mass to 99% air volume allowing radiant energy to travel through like an open door, plus air infiltration. The exception to this is radiant barriers which rely on the air space to perform efficiently. If insulation tests were performed with the best interest of the consumer at heart, there would probably be only two insulations available to the consumer.
(7) The other subject ignored by the bulk insulation manufacturers is the approximate 80% heat gain/loss in buildings through radiant heat, infrared energy. This can be expected because most bulk insulations are only about 10 – 20% efficient in rejecting radiant energy, compared to about 97% for radiant barriers.
(8) The “R” factor for bulk insulations are based on the reciprocal of a “u” factor, a conductive test ( for a material that is about 99% air spaces?). The efficiency of RBS are based on a “k” factor. You cannot obtain a “R” value from a “k” factor.
The independent, non competitive, method presented here is based on long established data of energy exchange between two surfaces, ceiling/floor, at a given Delta T” (temperature difference between two surfaces) and will tell you what amount of heat energy is radiated into and out of the home summer and winter. This method depends on no tests and incorporates the characteristics of the insulation, building materials and the effects of any climate condition. It can be performed by anyone with a thermometer. Conventional “R” factor calculations cannot tell you this, due to the problems mentioned above and that the calculations are usually for material only. With “R” factors you can calculate for one set of condidtions and then find out the calculations had no reference to what is actually going on in the structure.

The common denominator for all insulations is; what is the temperature of the drywall and the floor it is radiating to? This “in situ” method incorporates all the variables because the drywall temperature determines your heating / cooling costs. You can use either Btu calculations or temperature calculations. You can see why the manufacturer of low efficiency insulation will not want to use this method. The drywall emission rate, about 90%+, is used in the following chart because that is the most commonly used material. The source of this information, and the following chart, is from an emissivity chart and formula of a mechanical engineering handbook. You may not be familiar with this source of information. It is a manual of materials charts, characteristics, formulas and numerous other factors used by engineers to manufacture most every thing you use. For many professional engineers it is the engineer’s “bible”.

THE HUMAN FACTOR The average person believes that the air temperature is the dominant factor in comfort. This might be true if it wasn’t for the energy radiating into and out of the building with its effects. It is this energy ratio between the interior surfaces and the surface of the body that ultimately determines the comfort factor and energy consumption.
For maximum energy savings you want the lowest rate of absorption and re-radiation of energy. Lower is better. The determining factors of any insulation’s performance are:
1 The rate of absorption and re-emittance ( radiating ) of energy. From the “bible” we see that wood (cellulose), and glass (fiberglass) is about 90%+ efficient in absorbing and re radiating energy. Base foam materials are about 20% efficient. Aluminum foil about .03%.
2 Other than the basic material and its construction features, moisture, either from humidity or condensations can cause substantial energy flow. Using the ratio or 5% increase per 1% of moisture by weight, data published by the National Bureau of Standards shows that fiberglass and cellulose can increase energy flow about 45 / 72% due to moisture in an uninhabited structure. Even the relative humidity can account for a dramatic increase in energy flow. Increased humidity levels in an inhabited structure can cause even more energy lose / gain along with the 1,000+ btu used to convert vapor to liquid. Since radiant barriers do not cause condensation and are superior vapor barriers, the interior humidity levels can be lower than with other insulations.
3 The low quality of installation can also be a detriment to the effectiveness of insulation.
The following chart shows Btu transfer for various ceiling temperatures. Calculations for infiltration, doors and windows are separate as they will be the same for any insulation installed. To increase the envelope efficiency even more, Insulation Specialists has developed a simple method of installing RB to reduce to about 1% the conductivity surfaces of studs and ceiling joists from the normal 12-15 % surface area. In summer you can measure the drywall temperature which can reach up to 110 degs on a 95 deg day with the lower efficiency insulations and no roof shading. If the floor temperature is 75 degs the ceiling, using temperature figures, will radiate about 99 degs/sf/hr. The 110 deg ceiling temperature is about 25 degrees hotter than a winter radiant heat system, causing the air conditioner to run continuously to try to compensate. Without the air conditioner the interior temperature could exceed 100 degs. If the RB is 110 degs it will radiate about 2-3 degs /sf/hr. In a properly designed ranch home the interior temperature, with RB, will be about 80-81 degs without air-conditioning. The humidity levels can also be lower as the RB does not cause condensation which can be forced into the home by the high temperatures in the structure as with some of the lower efficiency materials. Question; if the indoor temperature can be hotter inside than outside without the air-conditioned, how can the manufacturer claim their material is insulation?
As you use the chart keep in mind these two questions;
1 If bulk insulations are about 99% airspaces and radiant energy travels through space at about the speed of light, and the base material absorbs and re-radiates the energy at about an 80-90 percent efficiency, how can a manufacturer claim their material is an insulator? More importantly how can an “R” value be assigned to them ?
2 If the function of a RB is to reflect energy, how can an “R” factor be assigned to it? How can the government and the manufacturers of bulk insulations legitimately force the use of “R” factors in evaluating radiant barriers? More importantly, why?
3 Why has the US Senate interfered with, at least twice, the governments fair trade polices, including FTC regulations, when it comes to insulations? Regulations which would have provided for a fair playing field. Answer: Over $100,000,000,000.00 tax revenue per year due to the excessive use of energy.
Because of this and other reasons the American home owners is using up to two to three times the amount of energy to heat a cool a home than what should be used.
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 difference this method can be used foe 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.

Myth: Dust adversely affects the RB performance. A: Dust has little or no effect on a horizontally installed RB with airspace both sides. The top surface could be painted black and the bottom surface might emit 1 or 2 extra Btus. Most ceiling installations have one or more layers, so any increase in heat flow is doubtful. There is little or no dust on vertical installations. Even with dust present the RB is superior to other materials. These comments never reveal the test material type or test method or actual performance differences.
Myth: Holes adversely affect the RB performance. A: Some RBs are manufactured with vapor escape holes. I know of no laboratory tests showing an increase in heat flow, particularly in multi layer installations. Obviously you don’t want large holes, these should be repaired.
Myth: RBs are not as efficient on up heat (winter) as summer. A: The engineering handbook does not make such a distinction. The mechanics of up heat vs down conductive heat flow are different; therefore any given material may exhibit slight differences for winter. However these comments never note that the RB is still superior to other materials.
Myth: Aluminum corrodes. A: Pure aluminum, such as the 99.9% pure foil used in RB, does not corrode under normal atmospheric conditions.
A light, invisible, oxidation does occur preventing any further oxidation. You would not want to breathe the fumes that could cause severe corrosion. Corrosion can and does occur in some unfinished alloy aluminum because of the dissimilar metals used for alloying the metal.
Myth: RB loses its insulation values over time. A: Since RBs do not corrode, the answer is self evident. I know of installations over 30 years old that work just fine.
Myth: You can’t use RB in very cold climates: A When Perry and other scientists went to the poles they use aluminum foil to insulate the structures. The Navy SEALS used multi-layer foil (mfg’d to mil spec HH I 1252) in 1964 in the Artic buildings where the mineral wool was failing. RB are used quite extensively and exclusively, in severely cold conditions, such as, cryogenics and space platforms.
Myth: RB are not very efficient in attic add-on application. If the application is not proper then this is a true statement. However, the retrofit tests so far conducted are not the most effect application method. I have found that a double layer installation directly over the existing material can reduce a/c run time 50% or more. Why test the most inefficient method?

Seems the system wants to conserve space.
Just string out the numbers under the a-d and a-d sections and it will read ok.
The first a-d is summer the second winter.
Remember this is a BTU/hr/sf

You would think that if multifoil was so great it would be used by the Australian Antarctic Building System to insulate their 3.6m x 6m modules, where space saving would be highly valued, instead they use 150mm of foam.
This means a lose of 5m3 of internal space to insulation for each module. I think they would have chosen mf if it was any good, but they didnt....

What are you doing Colin? Biting your tongue?

"Sounds to me that AANBUS is thoroughly obsolete and inadequate - well below current temperate-climate spec - I doubt it was ever conceived in any cutting-edge spirit! "


Tom, when these modules were first conceived in the 1980s, we had already been putting satellites and spacecraft out into the most hostile eniviroments for many many years.
Im sure that australian scientists at the time were well aware of the harsh ondititions they needed too design against and the existing knowledge regarding energy conservation in extreme conditions.

Posted By: bot de paille... with a 150mm thick `M' grade polystyrene foam core. The insulation has a U value of 0.2 w/m2k. The panel is bolted to girts which in turn are fixed to the steel framework lined with two layers of plasterboard. The airspace and plasterboard would reduce the coefficient to approx. 0.15 w/m2k

How is that cutting-edge? It's just a damn good uprate of conventional 1980s temperate-climate practice, but is no kind of a from-scratch anything's-possible scientific solution for the situation.

Posted By: marktimeWhat are you doing Colin? Biting your tongue?

No, had to rush off to the docs before I could finish.

Posted By: rbisysThe primary mode of heat transfer in a building is "radiant energy". up to 80%.

I believe this is absolute nonsense, as Colin said.

Please supply a reference to an independent peer-reviewed explanation if you expect anybody to take your assertion seriously. Please don't refer to anything you have written yourself.

djh quote "I believe this is absolute nonsense, as Colin said.
Please supply a reference to an independent peer-reviewed explanation if you expect anybody to take your assertion seriously. Please don't refer to anything you have written yourself. "

This is so well established and documented that I am surprised that you are not aware of it.
The misinformation that conductivity and convection currents are authored by the bulk insulation manufacturers. This is the only way they can convince you that they have a viable product.

What's wrong with what I've written? You think perhaps I'am not being truthful or have trouble communicating what I wish to tell? If you want to really know what's happening in your walls and ceilings, find it on the internet. Visit some of the radiant barrier web sites.

Which independent peer review study would like? One from the bulk insulation manufacturers or how about one from a university or gov lab which is funded by a bulk insulation manufacturer.

For instance, the DOE web site says that RB are not as efficient on up heat as down heat. Well that doesn't jibe with mechanical engineering handbooks. The government has a vested interest in you using the least efficient insulation material as does the utility company.

One other thing, your stranded, in the cold, on the side of a mountain, No one can get to you for several days. What are you going to keep your self warm with, aluminum foil or batt insulation?

How do you get a peer review from your competitors?

Credibility? How about implying that doubling your ceiling batt insulation from 6" to 12" will save you up to 30% on energy. Now that's interesting because the increase in deficiency, not savings, is only about 7.6%. How does that equate, especially since 75 - 80%* of the energy saved is in the first 3"? * This does not mean you're saving this amount. You could be saving only about 20 - 25%. Since the insulation mfgrs imply that that their materials SLOW DOWN HEAT FLOW, one must ask, just how much? Slowing down IS NOT the same as rejection as in reflection.

Be careful what you call nonsense.

Posted By: fostertomheat flux alters instantaneously, as soon as delta-t changes

Not quite right but it is a lot faster than conductance. Temperatures can be integrated over a time period/distance quite simply. It is how we can capture a pulse of light on video. Varying temperature difference with respect to time can be thought of as being 'thermally damped', changing with the characteristics of the material they are passing through. So a vacuum has no damping and a perfect insulator will have 100% damping, everything else is in-between. As far as buildings are concerned the two major heat loss parameters are the insulation properties and convection unless specifically designed to take advantage of radiative forcing. Hence a standard black roof tile will allow more solar (radiative) energy to be captured than a tin foil roof. The shiny tin foil roof will be a lot closer to the ambient air temperature but will also re-emit any stored energy at a lower rate (giving the impression of insulation because of the smaller initial temperature differences).

When we insulate a building we are actually using trapped air to insulate and we try and combine this with a material that conducts very little heat, hence we do not use copper wool to trap air but a animal/mineral/vegetable that has all the properties we need to trap air. Double/triple glazing presents us with a challenge here as we need a material that is transparent and tough enough. Hence we can replace the air with another gas (vacuum would be better but limits size) that has a lower thermal conductivity (and often convects less/has a lower SHC). This is why some gas filled windows can have a smaller gap and still be of comparable performance.

Posted By: rbisysYou think perhaps I'am not being truthful or have trouble communicating what I wish to tell?

Yes, that's exactly what I think.

Posted By: rbisysWhich independent peer review study would like?

Any you care to choose.

"Vacuum"

I'm not taking sides here, but a vacuum flask more or less eliminates bulk conduction/convection and so the surfaces are silvered to combat radiative transfer which would otherwise dominate AFAIK.

Rgds

Damon

Posted By: SteamyTeaNot quite right but it is a lot faster than conductance

How do you mean, ST? Surely you don't mean the difference between 'instantaneous' and 'speed of light'?

Posted By: CWattersI don't really support this idea of cold fronts

I agree - I shouldn't do it. So I'll restate the example and hope you can support:
"For example, one end of a conductive couple may rise in temp but the resultant 'hot front' takes calculable time (a decrement phenomenon) to propagate to the the cooler end of the couple. Until it does, the cool end doesn't 'know' it's about to start receiving more heat flux, to establish a new (increased flow) equilibrium and/or to fill the 'hole'.
Whereas by radiant transfer, heat flux alters instantaneously, as soon as delta-t changes...."

Posted By: CWattersRadaition requires a transparent medium which can be the "air" in a bubble in the insulation

and much smaller pores too, down to nano-size, which most materials (other than crystaline) are riddled with.

Posted By: CWattersIf the cold front takes time to propagate then both walls of that bubble are at the same temperature until the cold front "gets there". eg There is no increase in radaition until the cold front arrives. No?

No! The hot front is propagating through the 'solid', by conduction, yes, until it reaches the near 'shore' of a bubble (or nano-pore). That shore is thereby raised in temp, and it takes a while for conducted heat to work its way round the 'shoreline' to warm up the the far shore by conduction. Before then, the far shore has already been bombarded with radiation immediately, from the hot near shore, so the job's two thirds done, by radiation, before the conducted hot front gets there, in fact the latter may stop in its tracks as the delta-t that's driving it gets 'filled in'.

Posted By: CWattersRadaition requires a transparent medium to propagate through so presumably you have to establish a gap/cavity for it to radiate across

No need to creat a macroscale cavity - most materials are riddled with micro-scale pores already. Start to think micro - that's the operative scale for this.