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Old 08-27-14, 05:09 PM   #21
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Originally Posted by ICanHas View Post
The radiant heat transfer is dependent on the temperature difference and I think emissivity, reflectance and transparency. If you could somehow use radiant barrier on the roof, I speculate it woulId be an order of magnitude more effective. Maybe I'll test this out in my with the shield inside vs outside the windshield. I wonder why roof materials are usually black.
There was a study in florida years ago that measured identical houses, some with black shingles and some with the same shingles painted white. The cooling load with white shingles was 40% lower. I have no idea of the rest of the study as I have been watching these for 30 years. I do believe it was in a magazine called "Home Energy".

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Old 08-28-14, 12:13 AM   #22
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Instead of goretex maybe try tyvek. I believe the label has thinsulate printed on it.
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Old 08-28-14, 01:56 AM   #23
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The thermal performance quoted is only possible in the correct construction which is usually a 1" batton either side of it to create an air gap. This makes the minimum thickness of the insulation construction 2"+.
So when you say "batton" you mean the same thing as a spacer?

I'm really curious about 'air-space' requirements for various insulations, and what the rationale for a particular requirement is. I know that air is a good insulator. I also know that if the air space is too large, air currents can begin 'self pumping' and seriously reduce the effectiveness. Some folks have said it has to do with the wavelength of heat, but I did a calculation of the wavelength of unfra-red light, and the length of a wavelength is 700 nanometers (nm) to 1 mm, so it is very, very small.

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Whilst I could use it in my loft(attic) conversion I,m currently doing I decided to stick with polyurethane foam with foil on both sides. Using 4 layers of various thicknesses adding up to 150mm (6") which means 8 layers of foil so u guess it is multi foil in a way.
So will your configuration have air gaps, between layers?

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AC will be interested in your results as to how you get on with dig multi foil.
Yeah, me too. I went shopping yesterday at my local fabric warehouse, looking for some kind of very thin microfiber filler material, that was not dense and felted or closely woven. There weren't very many choices. But I did find almost exactly what I wanted, and it was fine, thin lambs wool filler material. Pretty gorgeous stuff, really (All the ladies at the fabric store kept saying, "you're going to do what!?"). So I bought enough to make a ten layer test piece that is 18" x 18".

I'm in the midst of a construction project myself (power tools and building debris are ruling my existence), so hopefully I'll be able to have my sample within a week.

Best,

-AC
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Old 08-28-14, 10:11 AM   #24
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NOTE: I have moved this post over from 3/4" foam board insulation help, as it is a better fit for this thread.

* * *

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...I'm not a big fan of using multiple layers of radiant barrier. A least here on Earth. Air can easily short circuit multiple layers though the process of conduction and convection. Here on Earth I would limit it two a maximum of two layers...
Exeric,

Being an earthling myself, I can certainly understand your preference for earthly solutions.

However, it is very interesting to note that not everyone is so smug about insulation.

For instance, in the UK, they have taken the lessons of NASA more seriously than here in the Motherland.

I came across THIS interesting Multi Layer Insulation that is for sale right now.

It is tested and sold as having an R rating of 2.71.

You gotta understand that this is 2.71 metric, which is not the same as our USA R-value.

I'm sure that someone smarter than myself could convert in a more straight forward way than me, but here's how I do it:

2.71 watts/m2-K is the R-value

If you invert that value you get .369 m2-K/watt which is the U-value in metric.

HERE is an amazingly useful converter for converting most things to and from metric.


Looking at the yellow ellipse on the left is the closest value I can find to .369 m2-K/watt.

Looking at the yellow ellipse on the right, you see the R-value equivalent, which is R-15.30

That is a whole different ball game, no?

But if you look at the detailed specs on the bottom of the next page you will find this chart:


You see that this 19-layer wonder stuff is 13.5 mm thick, which works out to:

13.5mm/25.4mm per inch = .55 inches

So in reality, the material actually has the following R-value:

15.3/.55 = R27.7 per inch.

That is the R-value in the UK, not in space, by the way.

So, you may not like this product, but you can't deny the principle.

* * *



I just found a much simpler way to convert R-value from Metric to Imperial:

1 R value = 0.17611 m[sup]2[/sup] kelvins/watt

So, you take what ever metric R value, like 2.71 from the illustration above, and devide it by 0.17611

So 2.71/0.17611 = 15.39 (even more than I came up with)

But you still need to level it out on a per inch basis, so

15.39/.55 = 27.98 per inch


-AC
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Old 08-28-14, 12:44 PM   #25
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You might like this unit converter w w w (dot) digitaldutch (dot) com/unitconverter

regards,
Zwerius
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Old 08-28-14, 02:15 PM   #26
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You might like this unit converter w w w (dot) digitaldutch (dot) com/unitconverter

regards,
Zwerius
Yes, you're right, this converter is very complete.

Thanks,

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Old 08-29-14, 02:30 PM   #27
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AC, I should explain a little better my rationale for down rating multiple layers of radiant barrier in air. When I installed my radiant barrier below the roof of my house it still got very warm up there. Much more warm than the standard formula you offered would indicate. Also, there was a reduced effectiveness at the point where the corners of my hip roof concentrated the heat. But the interesting thing was that you didn't feel any heat radiating directly from the radiant barrier. But if you touched it, it was hot! That's where the air transmissability of heat comes in. Even though a radiant barrier does not radiate heat it does get hot. And that heat will also heat air because air has a much bigger emmisivity than a vacuum. It is the reason that in space the side of an object facing the sun can be hundreds of degrees hotter than the side shaded from the sun. I have more knowledge on this particular subject than you. So I'm not a troll. I don't butt in on other subjects that you are much more knowledge about than me. You are just letting your ego get the better of you by calling me a troll. EDIT: I should add that insulating materials invariably have a higher emmisivity than a vacuum. So installing insulation between layers is not a solution. It's the touching of molecules to a radiant barrier that conducts (conductivity?) heat away. Of course, some molecules conduct heat better than others, but there isn't any molecules that conduct heat less than no molecules.

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Old 08-29-14, 04:30 PM   #28
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Originally Posted by AC_Hacker View Post
So when you say "batton" you mean the same thing as a spacer?

I'm really curious about 'air-space' requirements for various insulations, and what the rationale for a particular requirement is. I know that air is a good insulator. I also know that if the air space is too large, air currents can begin 'self pumping' and seriously reduce the effectiveness. Some folks have said it has to do with the wavelength of heat, but I did a calculation of the wavelength of unfra-red light, and the length of a wavelength is 700 nanometers (nm) to 1 mm, so it is very, very small.



So will your configuration have air gaps, between layers?



Yeah, me too. I went shopping yesterday at my local fabric warehouse, looking for some kind of very thin microfiber filler material, that was not dense and felted or closely woven. There weren't very many choices. But I did find almost exactly what I wanted, and it was fine, thin lambs wool filler material. Pretty gorgeous stuff, really (All the ladies at the fabric store kept saying, "you're going to do what!?"). So I bought enough to make a ten layer test piece that is 18" x 18".

I'm in the midst of a construction project myself (power tools and building debris are ruling my existence), so hopefully I'll be able to have my sample within a week.

Best,

-AC
AC
If you download the data sheet from the page you linked to a couple of posts back you will see what I mean about the insulation value in various constructions.
It looks like there multifoil is only a radiant barrier and still requires a more conventional type of insulation to tasked care of conduction.

Battons are just 2x1" lengths of timber used as spacers and so on.
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Old 08-29-14, 06:53 PM   #29
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Quote:
Originally Posted by Ormston View Post
AC
If you download the data sheet from the page you linked to a couple of posts back you will see what I mean about the insulation value in various constructions.

It looks like there multifoil is only a radiant barrier and still requires a more conventional type of insulation to tasked care of conduction.

Battons are just 2x1" lengths of timber used as spacers and so on.
OK, I think I'm seeing how this goes...

When UK vendors are describing insulation values and say, "up to", they assume a cumulative R-value that includes all of the insulative layers summed up, given unspecified, but generally understood building practices.

I'm assuming that this is common practice in the UK, and everyone expects this to be interpreted in terms of cumulative R-value, and would be able to shift their expatiations accordingly.

In the US, it is the practice to cite R-value as pertaining to the insulating material only. I think this is because of 'fair labeling laws' or something.

So a cultural adjustment is called for here.

When I look at this Fixing Instruction:


I do see that the multi layer insulation has a resistance value of 1.52, for the 40 mm thickness, which would equate to:

(1.52 / 0.17611) / (40mm / 25.4) = R 5.39 per inch, in US terms.

Hmmmm..... not at all so good as I thought.

And PIR, which I think is similar to what we refer to as "Poly Iso", come out in the example as:

(2.174 / 0.17611) / (50 / 25.4) = 6.27 per inch. in US terms. Pretty much standard.

OK, it isn't looking like quite the miracle material I had thought it to be.

-AC
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Old 08-30-14, 02:44 PM   #30
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So, does this mean I'm not a troll? Just want to know if disrespect without apology to someone who offers genuine knowledge on a particular subject should be considered Ok on this forum. Like I said, I try to not butt in where my expertise is inadequate (not always successfully) but if I continue to try to follow those ethics then I expect you to say the honorable thing here.

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