[Greenbuilding] [BULK] Re: Radiant barriers under Radiant Underfloor Heating
Lawrence Lile
LLile at projsolco.com
Thu Oct 18 11:32:57 EDT 2007
Blue Man Group's grease paint is good for at least R60, because they got
it from NASA too. ;-)
In 1980 a buddy of mine built an insulation test machine to test another
"radiant barrier" product, which claimed that they could achieve huge
R-values with an inch or two of a special blown-in attic insulation
called Fire-Guard. The insulation test box proved it was all hokus
pocus and the insulation turned out to be vermiculite. It was fireproof
at least. They are long out of business and other people are using the
name for other things. I thought this test box was a great thing to have
around and wished I still had it for these kinds of arguments. I am
pretty skeptical of radiant barrier claims in general, the thinner they
are the more skeptical I am.
Lawrence Lile, PE, LEED AP
Project Solutions Engineering
-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of John
Straube
Sent: Thursday, October 18, 2007 10:13 AM
To: Keith Winston
Cc: Greenbuilder list
Subject: [BULK] Re: [Greenbuilding] Radiant barriers under Radiant
Underfloor Heating
Importance: Low
Yeah, this NASA and conspiracy stuff drives me crazy. The reason NASA
uses radiant barriers is that they work in space. In space, there is no
air. Hence, no convection, no conduction and radiation rules. If you
build on the surface of the planet or within about 50 000 ft of sea
level, then radiant barriers follow the rules of other insulation.
BTW. I am involved in a major project to investigate R-values in real
walls under the temperature differences that walls really experience.
While badly installed batt insulation under large temperature
differences can loose 30-40%+ of its rated Rvalue, this is hardly a
conspiracy.
Keith Winston wrote:
> NASA uses radiant barriers?!! I thought they used ceramic paints, like
> Supertherm, etc? 2 coats of paint and you've got R-30! And, I've heard
> recently (from the ceramic paint people) that the use of R-values was
> actually a plot by fiberglass manufacturers, and it doesn't actually
> measure anything meaningful (for if it did, everyone would have
painted
> themselves with ceramic paint, like Blue Man Group -- then we could
live
> on the sun!).
>
> Building science? We don't need no stinkin' building science!
>
> Keith
>
>
> John Straube wrote:
>> Hi there
>> One of the radiant barrier products I tested under concrete slabs was
a bubble foil. The tiny air gaps that are formed by the bubble and
between the bubble and the lower surface (the concrete is liquid and
fills the top voids) do increase the R value of a pure reflective film.
A pure reflective film i unlikely to provide R0.1 when sandwiched
between EPS and concrete and less when on faced polyiso or extruded.
The bubble sheet likely adds about R0.5 if laid on top of EPS and a
little less on sand.
>> My analysis is that the radiant foils do very little to no good under
radiant slabs. Given that there costs in my experience range from 25 to
$1 per square foot, they are the most expensive insulation any ever
specifies for buildings (at a cost of 5 to 20 times that of foam per
Rvalue) and darn expensive vapor barriers (at a cost 3 to 10 times that
of poly sheets).
>> But they are shiny, and they have good marketing, and are used by
NASA. Those attributes seem to sell a lot.
>>
>> Sorry for the cranky cynicism, but I have been answering radiant
barrier questions and refuting rediculous claims for more than 10 years.
>>
>> John
>>
>>
>>
>> Philip Proefrock wrote:
>>
>>> I should have been more specific with my question. I'm not talking
about
>>> using a reflective foil in place of rigid insulation, but using it
on top of
>>> the insulation and under the concrete in place of a plain poly
layer. I am
>>> specifically interested in whether it makes sense to include the
foil (in a
>>> configuration where there is an air space between the foil and the
slab) in
>>> addition to the rigid insulation and other appropriate measures, or
whether
>>> it doesn't provide enough benefit to justify the extra cost.
>>>
>>> A lot of those excerpts cited in the link Chris provided seemed to
be
>>> addressing instances when foil-bubble insulation was being
*substituted* for
>>> other insulation (which, I completely agree, would be foolish).
>>>
>>> Philip Proefrock, LEED-AP
>>>
>>> Luckenbach|Ziegelman Architects
>>> 255 E Liberty Suite 277
>>> Ann Arbor, MI 48104
>>> 734.997.9444
>>> 734.997.7004 Fax
>>> PProefrock at LZArch.com
>>>
>>>
>>> -----Original Message-----
>>> From: Chris Green <pojeros at telus.net>
>>> Subject: Re: [Greenbuilding] Hydronic Radiant Underfloor Heating
>>>
>>>
>>>> What about foil insulation with "bubble-wrap facing" that holds the
foil
>>>> film itself 1/8" - 1/4" away from the surface of the concrete? Do
those
>>>> provide better performace as radiant reflectors, or are those no
better
>>>>
>>> than
>>>
>>>> face foil radiant barriers?
>>>>
>>>>
>>> The following page discusses those bubble wrap layers.
>>> http://www.healthyheating.com/Page%2055/Page_55_o_bldg_sys.htm
>>>
>>> Oh, this link from the above page is funny:
>>> http://www.therightfoot.net/mystuff/whatever/swf/bubblewrap.swf
>>> "..must have...more..." :-)
>>>
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>>>
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>>
>
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--
Dr John Straube, P.Eng.
Associate Professor
Dept of Civil Engineering & School of Architecture
University of Waterloo
Waterloo, ON Canada
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