Re: Radiation from Concrete

Discussion in 'Home Power and Microgeneration' started by Neon John, Nov 27, 2008.

  1. Neon John

    Neon John Guest

    On Wed, 26 Nov 2008 22:15:22 +0000, Tim Jackson <> wrote:


    >Radiated energy from a surface is proportional to the emissivity of the
    >surface and the fourth power of the *absolute* temperature. The most
    >emissive surface is a black body. You can find the theory in any
    >physics textbook.
    >
    >You can reduce the emissivity to about 10% or so by painting the surface
    >white, and to about 1% by applying a mirror finish.


    According to the emissivity table that came with my Wahl instrument, gloss
    paint is below 1%, depending on pigment (color doesn't matter much) and mirror
    surfaces such as glass and chrome are in the 0.01 to 0.001 range.

    >
    >Radiation is a surface effect. Adding stuff inside a material that is
    >in conductive contact with the bulk of it will have no effect at all on
    >radiation. Glass beaded paint is certainly highly reflective, and I
    >believe the idea of the ceramic beads is that they have low emissivity /
    >high reflectivity in the near infra-red where most of this radiation
    >occurs. So the theory is good but the practice is dubious. The amount
    >of heat loss through radiation with only a few degrees of differential
    >at normal temperatures is small.


    Not really. Radiation emission certainly is NOT a surface effect. Glass hot
    enough to glow is a simple illustration that one can easily visualize. The
    paint very well may be transparent or partially so to the wavelength involved.

    If these ceramic pellets/discs are hollow, radiation certainly takes place at
    the surface/space interface.

    Does this product work? No idea? Could it work in theory? Absolutely. A
    couple of quick questions you can ask them are a) what is the NASA patent
    number b) what is the NASA technology transfer contract number. c) who is the
    NASA contract administrator and d) what is the article number (normally a NASA
    tech briefs article) for the substance. All this information is easily and
    readily available if they really are NASA technology partners, as NASA refers
    to companies who license their technology.

    At the second stage of evaluation, ask for independent lab test results. I'm
    not sure but I believe that NASA requires such testing before a product can be
    tagged with the NASA logo and the "technology partner" moniker applied.

    I CAN tell you that ceramic coatings CAN do wonders. A common use is on
    racing engine exhaust headers. A few micron coating turns the headers from an
    engine compartment scorching heater to something that you can touch for short
    periods. There is almost no radiant OR conducted heat.
    >
    >However radiation is a two way street. Whatever you do to reduce heat
    >loss through radiation also proportionately reduces the heat absorption
    >from the sun or anything else hot, as emissivity is the inverse of
    >reflectivity.


    Absolutely false. Asymetrical emissivity/absorptive materials have been
    commercially available for decades. Most common use I know of is on thermal
    solar collectors. Even some finishes are asymetrical. black chrome comes to
    mind. Omega engineering has this info conveniently tabulated for your handy
    reference.

    >
    >The majority of heat loss through a wall is through conduction and
    >convection, and evaporation in wet weather (a.k.a. wind-chill).


    May or may not be true but with a concrete wall, if it's cold, it doesn't
    matter how warm the room is, one can still be uncomfortable because of
    radiative losses from the body to the walls. Most anyone who's been in a
    concrete block building in the winter recognizes the effect, if not the cause.
    >
    >If you really want to check, I have developed an instrument for directly
    >measuring the heat flow though walls, doors, ceilings etc. I note from
    >this that the flow though my single glazed windows reverses when they
    >are exposed to the weakest sunshine, and even in hazy bright conditions.


    Since this instrument has been an off-the-shelf item for decades, I can just
    imagine what kind of crap you've "improved on".

    Back to the OP: It looks like enough of this stuff to treat a gallon of paint
    is about $10. I suggest getting some, painting a square of surface in a room
    and then compare it on a cold or very hot day. Simply standing in front of
    the painted square vs another area will let you feel the difference. Cheap
    enough experiment.

    BTW, glass microspheres are widely used to reduce the weight of composite
    resins. I cant get to the site right now for some reason but AirCraft Spruce
    sells the beads in gallon buckets for very little money. You might buy some
    of them and give them a test alongside this magic stuff.

    John



    --
    John De Armond
    See my website for my current email address
    http://www.neon-john.com
    http://www.johndearmond.com <-- best little blog on the net!
    Tellico Plains, Occupied TN
    The profligate use of energy is the sign of a healthy, expanding civilization.
    Conservation is a leap backward toward the caves.
    Neon John, Nov 27, 2008
    #1
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  2. Neon John

    Neon John Guest

    On Thu, 27 Nov 2008 09:39:53 +0000, Tim Jackson <> wrote:


    >Oh true, I can read test books too. But *exterior* surfaces won't stay
    >that way for long in practice. I'm talking about actual building
    >surfaces and worst case after a few years of weathering and bird shit.
    >I'd refer you to,
    >www.omega.com/literature/transactions/volume1/emissivity.html
    >which would correct me the other way if anything.


    That's nice, Tim. I'm glad you can read "test books". Now if you only had
    some field experience. I do. In the past I did full scale energy audits and
    not just the electrical ones I do now. I have 4 or 5 (I'll be glad to provide
    an inventory for you if it would be a teaching moment) professional IR
    pyrometers (not the dime store optic-less, fixed emissivity stuff like HF
    sells) including one with a chilled mirror cassegranian telescope that lets me
    look at individual splices and connections on transmission lines. It looks
    like a large barrel rifle and has gotten the attention of the cops more than
    once. I no longer own an IR pyro camera (too much money tied up in not enough
    business but now that the price has dropped to the low 4 digit range, I may
    get another.

    One thing you quickly learn is that emissivity guides are just that - guides.
    I calibrate my instruments by placing a foil thermocouple on the surface to be
    measured and set the emissivity until the pyrometer agrees or the camera
    profile agrees.

    Your BS about outdoors is just that since this kind of coating is used
    indoors. It would be idiotic to place the stuff on an outer surface where
    pollution and chalking would defeat it in months. Well, considering with whom
    I'm debating...


    >
    >>> Radiation is a surface effect. Adding stuff inside a material that is
    >>> in conductive contact with the bulk of it will have no effect at all on
    >>> radiation.

    >>
    >> Not really. Radiation emission certainly is NOT a surface effect. Glass hot
    >> enough to glow is a simple illustration that one can easily visualize. The
    >> paint very well may be transparent or partially so to the wavelength involved.
    >>

    >I admit I did mean opaque materials. Paints and walls are generally
    >designed to be opaque, otherwise they are called varnishes and windows.
    > I know we can create exotic materials and situations in the lab that
    >don't fit my simple model.


    They are opaque to visible spectrum but not to IR. Do a little research on
    how places like the Smithsonian use IR to detect painting on the same canvas
    underneath the obvious visible painting. MANY paints are perfectly
    transparent to IR. Again, you'd know that if you'd either done your homework
    or had some experience.

    With my vintage early 90s B&W IR camera, I could see right through the paint
    on a customer's oil painting. I detected more than one forgery by seeing the
    underlying image where the forger had re-used the canvas so as to have
    period-correct canvas. The forger could scrape off the old paint but not
    enough that it would not show up under IR.

    >
    >>> However radiation is a two way street. Whatever you do to reduce heat
    >>> loss through radiation also proportionately reduces the heat absorption
    >>>from the sun or anything else hot, as emissivity is the inverse of
    >>> reflectivity.

    >>
    >> Absolutely false. Asymetrical emissivity/absorptive materials have been
    >> commercially available for decades. Most common use I know of is on thermal
    >> solar collectors. Even some finishes are asymetrical. black chrome comes to
    >> mind. Omega engineering has this info conveniently tabulated for your handy
    >> reference.
    >>

    >On CONCRETE? We are losing the plot a bit here aren't we?
    >If you paint concrete white you lose heat absorption during the day.
    >Are you disputing that? Few building materials are seriously asymmetric.


    But we're talking about coatings to minimize the radiation of concrete, aren't
    we?

    >
    >What is important is that in daytime we are talking about incoming
    >radiation in the near infrared and emission in the far infrared. Many
    >materials have emissivity which varies with wavelength.
    >
    >But this is not really the question here. We are talking about heat
    >radiated from the surface of the wall, heat received by the surface of
    >the wall from the ambient environment, and heat received from the sun.


    No we're not. We're talking about keeping it out of the conditioned spaces.
    It matters little if the blocks get hot if the radiative and conductive
    processes are stopped at the last millimeter by wall treatment.

    >My conclusion is that whatever you save (if anything) by applying a
    >coating, it is always a percentage of what you are losing by conduction
    >through the wall, so the better insulator the wall, the less advantage.
    >And almost always it will be cheaper and easier to improve the wall's
    >insulation.


    That's probably true as far as it goes. Going farther, one can use multiple
    barriers - insulation, an aluminum radiation barrier, perhaps sheet rock and
    (if it proves out) a ceramic or microsphere coating. One would want to do a
    cost-analysis, something that would not be simple. there is software to
    automate the process.


    >The radiated heat from the body is around 100W according to Wikipedia.
    >The corresponding received radiation from an environment at freezing
    >would be about 60W. This is independent of the air temperature.


    If that's what Wikipedia says then it is wrong as usual. The ASHRAE
    handbook's standard human, used for sizing HVAC and modeling same, sets the
    total emission, including nonsensible (latent) heat in exhaled and sweat
    evaporated moisture at 100 watts. the distribution of the heat doesn't matter
    much for HVAC purposes because it all has to be eliminated to maintain
    comfort. It DOES matter when discussing radiant heat transfer. Still
    puzzling why you drew this into the conversation other than for obfuscation.

    John
    --
    John De Armond
    See my website for my current email address
    http://www.neon-john.com
    http://www.johndearmond.com <-- best little blog on the net!
    Tellico Plains, Occupied TN
    Better to pass boldly into that other world in the full glory of some passion
    than fade and wither dismally with age. -Joyce
    Neon John, Nov 28, 2008
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  3. Neon John

    Neon John Guest

    On Thu, 27 Nov 2008 06:04:06 -0800 (PST), AC Me <>
    wrote:

    <please edit your replies. Thank you.>

    >
    >Thanks for all the info so far guys.


    Jackson's developed a well-deserved rep for bullsh*tting in areas where he
    knows little. Take what he says with a grain of salt.

    >
    >I guess I should clarify.
    >I am currently constructing my own home. I have decided that I want
    >the energy usage of the structure to be better than required by the
    >construction codes. Here in Ireland the codes, or building
    >regulations, require certain maximum 'u' values for each part of the
    >building fabric, or a maximum overall 'u' value.
    >I have decided that those parts of the structure that cannot easily be
    >improved afterwards should have the best insulation I can manage right
    >now. This means the floor in particular.


    I know I'm taking a big risk of tromping on my dick trying to advise about
    another country's standards so.. What is "u" value. It is like our "R"
    value? How is it measured/calculated.

    >So I am putting in three layers of under-floor insulation. The first
    >layer will be about 1" thick. On top of this will be a layer about 2
    >and 3/8" thick through which will be running ducting for domestic hot
    >and cold water and also the boiler return pipes which will allow the
    >possible future installation of boilers behind open fires or with
    >certain stoves. Then there will be a 2" layer on insulation on top of
    >which will be underfloor heating pipes. A 1" or 2" strip of insulation
    >will also be around the periphery of each room.


    OK, let me make sure I understand this. You're going to have a slab of
    concrete on top of a vapor barrier. On top of that will be 1" of something
    (specify please). then a 2+" air space. Then 2" of more insulation (again,
    please specify) and then some kind of flooring with hydronic radiant floor
    heating.

    Several questions.

    - what will the flooring be?
    - I don't see a radiation barrier in there (presumably why you asked about the
    paint.
    - What constitutes the walls of the air/utility space?

    I've never been there, but from friends who live in Ireland, I'm told that air
    conditioning is rarely needed. True? If so then we need to concentrate on
    heating.

    I don't agree with this layout. Any heat loss from the utility space, if
    directed properly upward, contributes to room comfort and therefore is not
    wasted. NO need for any insulation above the utility spaces.

    You must concentrate on stopping the heat from flowing down. MY first layer
    of insulation next to the utility space would be an infrared barrier - plain
    old paper-backed aluminum foil or whatever equivalent is available over there.
    Aluminum is about the 3rd best reflector of long wavelength IR behind gold and
    copper. If you can afford copper foil, go for it :)

    Under the foil you require a conduction barrier. Fiberglass batting,
    styrofoam, rigid foam and similar products all do that. If the materials are
    in contact, there won't be any convection. Since this is a floor and you
    don't want to raise it too far above the ground, I'd go with the highest "R"
    (or "u") value per unit thickness I could find. Probably rigid foam. At the
    same time, make sure it's a product with a life rating similar to that of your
    house. It'd be a bitch to have to rip up the floor to replace foam that is
    undergoing "reversion" or return to the monomer state (translate: gooey mess.

    Under THAT I'd place another radiant barrier and perhaps a second vapor
    barrier, for in the event the first one gets punctured. Another thin layer of
    insulation and the vapor barrier that is against the soil (preferably on a
    layer of sand to be gentle to the plastic vapor barrier) and you're done.

    This is overkill but that's what you asked for. Very little heat is lost
    downward through the floor even when the floor is a concrete slab resting on a
    vapor barrier and then just dirt and embedded with hydronic heating tubes.

    I have a friend whom I helped install a radiant slab system in his shop. A
    second friend pretty much copied the first setup except that he put a layer of
    styrofoam under the slab as recommended. Both have the same wood burning
    water boiler.

    I've measured and calculated the energy usage and am amazed that they are
    essentially the same, within the limits of measuring noise. I sat and thought
    and calculated a bit and now I think that I understand.

    Dry earth is a good insulator. Not great but good. In the installation with
    the slab against the dirt, the dirt is quickly dried by the 180 deg water
    flowing through the pipes. The pipes are about 1/3 the slab thickness from
    the bottom so the bottom gets much hotter than the top. Once the soil dries
    out, its insulating qualities aren't that much different than a similar
    thickness of fiberglass batting. In both cases, fairly conductive material
    (clay in one case and glass in the other) entrap air in little pockets. The
    air does the insulating. The pockets are too small for convection to set up
    so it's only the thermal conduction that matters. The actual volume of solids
    (clay or glass) in either case is small.

    I'd go with a layer of insulation, a radiant barrier and be done with the
    floor. The ceiling is where you need to spend all your effort and dollars.

    Something else you might want to consider is embedding small water tubing in
    the walls. I was once at a DuPont facility on other work and was shown an
    experimental room. All surfaces including the ceiling had electrical elements
    embedded in the sheet rock. That was the most comfortable room I think that I
    have ever been in. Absolutely no drafts, no chills and no hot spots.

    They were experimenting with the concept with an eye toward developing polymer
    sheeting that could be placed between layers of sheet rock and carry the
    water. It never came to market, probably because of cost but it damn sure
    worked.

    The engineers explained that the wall radiation was primarily to stop
    convection drafts by maintaining the same temperature floor to ceiling. The
    floor elements supplied the bulk of the heat while the ceiling elements
    prevented head chills, especially on bald guys :) I forget the number but
    some ungodly amount of body heat, >50%, is lost through an exposed scalp so
    that was an important element.

    Years ago when electricity was practically free (too cheap to meter :) there
    was a product called Ceil Heat. In this product, resistance wires were run in
    parallel rows about an inch apart on special ceiling sheet rock. Then a thin
    layer of sheet rock was placed over it. The surface got barely warm to the
    touch but it was quite comfortable heat.

    It failed when electrical prices ran up in the 70s because, given the almost
    free nature of electricity, they had neglected a radiant heat barrier between
    the sheet rock and the ceiling joists. Lots of heat got conducted into the
    attic.

    My grandmother owned a Ceil-heated house and I've owned one. Her's was in the
    cheap days and it was wonderful. Mine hit me with an August electric bill of
    over $100 in 1976! and that just to take the chill off. Of course, I found
    that the contractor hadn't installed any insulation in the house. (government
    built for the poor that I bought on repo.)

    I would love to explore that kind of heat, perhaps using water instead of
    electricity, again, using proper insulation.

    >As an aside, I also intend to 'bury' temperature sensors in the
    >building fabric during construction so that the 'performance' of the
    >building can be monitored afterwards.


    Good idea. Suggest welded bare Type T (copper constantine) because both
    metals are corrosion-resistant. Dipped in RTV and then embedded in the
    concrete or whatever, they'll last a lifetime. Type T also generates a decent
    voltage, in case you want to build your own readout or data acq.

    Stay away from thermistors. They drift over time. Platinum RTDs are the
    Cadillac (Rolls?) of temperature sensors but unless you go with a very high
    dollar unit, the bonding between the platinum and the base metal wire will
    likely fail in a few years. We had a rash of failures in nuclear plant
    (non-safety areas - the Class 1A stuff was the highest of zoot :) sensors a
    couple of decades ago.

    Copper RTDs have kinda fallen out of favor for some reason but they work, are
    durable and are even something you could build at home. I'd still stick with
    Type T bare thermocouples though.

    John



    --
    John De Armond
    See my website for my current email address
    http://www.neon-john.com
    http://www.johndearmond.com <-- best little blog on the net!
    Tellico Plains, Occupied TN
    I like you ... you remind me of me when I was young and stupid.
    Neon John, Nov 28, 2008
    #3
  4. Neon John

    daestrom Guest

    AC Me wrote:
    > On Nov 28, 11:36 am, Tim Jackson <> wrote:

    <snip>
    >
    > I had planned to use 1-Wire thermometers (Dallas Semiconductor, now
    > Maxim) DS18S20. http://www.maxim-ic.com/quick_view2.cfm/qv_pk/2816
    >


    I've installed several (about a dozen) of these around my house and utility
    equipment. Been working for about 3 years now. But I never buried them in
    concrete or someplace where they couldn't be replaced.

    Use them on furnace (forced hot air), water heating, ambient temperature,
    etc...

    Was using a USB interface from Dallas, but they are hard to come by now
    (DS9490R). You could use a serial interface like the DS9097U, but I don't
    think it supports parasitic power mode so you would need a separate power
    source.

    daestrom
    daestrom, Nov 29, 2008
    #4
  5. Neon John

    daestrom Guest

    AC Me wrote:
    > On Nov 28, 1:08 am, Neon John <> wrote:

    <snip>
    >
    > Ah, but the biggest problem here, the one that pretty much all the
    > building regs
    > are designed to overcome (with the solutions to all other problems
    > bolted-on) is
    > ....WATER.....WATER and more WATER. It sometimes seems as if it never
    > stops raining (there's the old joke - it only rained twice last week,
    > once for three
    > days and once for four days :)).
    > It's wet, wet, wet. Our soil might get dry, or dryish, sometimes (god,
    > I hope it's
    > sometime soon :)).


    We have similar issues in update New York. The water table during parts of
    the year can actually be above the basement floor. Drainage tile around the
    perimeter leading to a catch basin and sump pumps are the norm around here.
    I lucked out in my particular location (near top of hill) in that I ran the
    drain piping downhill away from the foundation so I don't need the sump
    pump. But still, the soil surrounding the basement is moist most of the
    year 'round.

    Basement floors and walls below grade in new contruction around here are
    often insulated with about 2 inches (50 mm) of foam board. Along with
    barriers for the moisture problem.

    daestrom
    daestrom, Nov 29, 2008
    #5
  6. Neon John

    Mike Guest

    On Fri, 28 Nov 2008 11:44:11 +0000, Tim Jackson
    <> wrote:

    >I would think you could get a better ROI investing in lowering your
    >flue gas temperatures than on fine-tuning insulation. Traditional
    >boilers blow some 30% of their power input up the chimney. I know mine
    >does. Open or closed solid-fuel fireplaces are worse.


    You probably would, but insulation is nearly always the cheapest fuel.


    --
    Mike, Dec 4, 2008
    #6
  7. Neon John

    Mike Guest

    On Thu, 27 Nov 2008 06:04:06 -0800 (PST), AC Me
    <> wrote:

    >I guess I should clarify.
    >I am currently constructing my own home. I have decided that I want
    >the energy usage of the structure to be better than required by the
    >construction codes. Here in Ireland the codes, or building
    >regulations, require certain maximum 'u' values for each part of the
    >building fabric, or a maximum overall 'u' value.
    >I have decided that those parts of the structure that cannot easily be
    >improved afterwards should have the best insulation I can manage right
    >now. This means the floor in particular.


    >So I am putting in three layers of under-floor insulation. The first
    >layer will be about 1" thick. On top of this will be a layer about 2
    >and 3/8" thick through which will be running ducting for domestic hot
    >and cold water and also the boiler return pipes which will allow the
    >possible future installation of boilers behind open fires or with
    >certain stoves. Then there will be a 2" layer on insulation on top of
    >which will be underfloor heating pipes. A 1" or 2" strip of insulation
    >will also be around the periphery of each room.
    >However, as the periphery insulation is only 1" to 2" thick, this
    >creates a 'cold bridge' that would result in an energy loss that would
    >be higher than I would like. One possible solution might be to make
    >use of the aforementioned 'insulating paint', applying this to the
    >peripheral insulation.



    The 'insulating paint' is snake oil. End of.

    The thickness and number of layers of the insulation means *nothing*
    and your total of 5 3/8" is quite frankly bugger all in modern terms
    particularly when you are running UFH pipes 'somewhere through the
    middle' You might end up warming the earth to the same extent as your
    house.


    You should also be optimising the insulation in *all* areas not just
    the floor and installing it **AT CONSTRUCTION TIME** not later!

    4 inch slabs of rigid PIR (rigid polyisocyanurate) like
    celotex/kingspan/xtratherm) are a basic starting point. 6 inches are
    better, 8 inches better still but insulation needs optimising for the
    installation and cost. Only ever rely on conventional insulation
    technologies, a number of self builders in the UK have seriously under
    insulated homes because they installed insulation approved by a bunch
    of cowboys. So forget completely **ALL** thin insulations like tri
    iso 9 /10 etc in the walls or roof - or anywhere! (and the snake oil
    paint above!)

    Can I suggest you pay a visit to the CAT bookshop at
    <http://www.cat.org.uk> or amazon or similar and buy "The Whole House
    Book" It's £35 quid well spent.


    From xtratherm download (free)

    <http://www.xtratherm.com/products/literature/Xtratherm%20-%20The%20Guide.pdf>


    From Celotex download (free)

    "Underfloor heating"

    <http://www.celotex.co.uk/downloads.asp?i=26>


    "Concrete slab floors"

    <http://www.celotex.co.uk/downloads.asp?i=23>


    The U value calculator is free at

    <http://www.celotex.co.uk/Other-Resources/U-value-Calculator>

    (xtratherm also have one on their website)


    For your exposed pipes - use Armaflex, nothing else comes close!

    "Armaflex Application Manual"

    <http://www.armacell.com/www/armacell/armacell.nsf/ansHTMLSeitenLookUp/UK-TI_Frame?OpenDocument>


    Design for maximum solar gain, maximum internal thermal mass, minimum
    air ingress, controlled ventilation, optimise insulation and burn all
    fuel as efficiently as possible.

    Depending on building occupancy levels ****ZERO**** fuel burn for
    heating at your latitude and with typical exposure conditions *is*
    possible.

    This shows one such project but many more have been built since.

    <http://www2.rgu.ac.uk/subj/search/Research/SustainableHousing/Sust-H-Design/Publications/zeroleaflet.htm>


    A good starting point is to take the last two versions of building
    regs, together with the current ones, work out the progression in U
    value and project it 30 years into the future. Then build to that
    level as a minimum.


    --
    Mike, Dec 4, 2008
    #7
  8. Tim Jackson <> wrote:
    > Mike wrote:
    >> Only ever rely on conventional insulation
    >> technologies, a number of self builders in the UK have seriously under
    >> insulated homes because they installed insulation approved by a bunch
    >> of cowboys. So forget completely **ALL** thin insulations
    > >

    > True. Especially "multiple-reflector" insulation quilting.
    >
    > I was doing some electronics repairs in a quilting factory when I saw
    > one of the machines making this stuff, and idly picked up a product
    > label. It claimed an insulation equivalent to 6" of glass-wool in a 1"
    > sheet. R-value claimed 6 ?C.m?/W. Well I could walk around the back of
    > the machine and see what was going into it, and didn't believe it.


    So what was this product? Layers of silvered plastic or something
    spacecraft looking?
    Cydrome Leader, Dec 6, 2008
    #8
  9. Neon John

    daestrom Guest

    Tim Jackson wrote:
    > Cydrome Leader wrote:
    >> Tim Jackson <> wrote:
    >>> Mike wrote:
    >>>> Only ever rely on conventional insulation
    >>>> technologies, a number of self builders in the UK have seriously
    >>>> under insulated homes because they installed insulation approved
    >>>> by a bunch of cowboys. So forget completely **ALL** thin
    >>>> insulations
    >>> True. Especially "multiple-reflector" insulation quilting.
    >>>
    >>> I was doing some electronics repairs in a quilting factory when I
    >>> saw one of the machines making this stuff, and idly picked up a
    >>> product label. It claimed an insulation equivalent to 6" of
    >>> glass-wool in a 1" sheet. R-value claimed 6 ?C.m?/W. Well I could
    >>> walk around the back of the machine and see what was going into it,
    >>> and didn't believe it.

    >>
    >> So what was this product? Layers of silvered plastic or something
    >> spacecraft looking?

    >
    > Sheets of aluminised Mylar film interspersed with layers of thin
    > polyethylene foam and polyester fibre, about a dozen layers in all,
    > sewn to make a quilt with about a 1" loft.
    >
    >


    Ah... I think I see what they were doing. A good IR reflector like
    aluminized Mylar would have some over-all R value. So they figured N layers
    should have an R/N overall R value probably. But radiant barriers in series
    don't 'add up' like conduction layers. Of course the foam/fibre in between
    is not IR transparent, so about the only true insulative effect is the 1"
    air trapped in the foam/fibre and the low emissivity IR surface on the
    outside.

    Here in the states there is a product that is simply a thin metalized film.
    It's purported to be useful in attics where it can lower your A/C bills.
    But government testing points out that it is only effective if installed on
    the rafters *above* the attic insulation so there is an air gap (you say,
    there must be an IR transparent layer). And more importantly, it must be
    face down so that dust doesn't settle on the surface. A thin layer of dust
    on any IR barrier can ruin its low emissivity. Then you're back to a
    'typical' emissivity > 0.8 again.

    daestrom

    > Tim
    daestrom, Dec 7, 2008
    #9
    1. Advertising

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