Frequently Asked
Question and Answers
1) Do aluminum heat reflectors work for home owners?
They claim R-4 and are on ebay
and home stores for $5 to $9 and up per 4ft x 8ft.panel?
Answer- No. It isn't illegal to claim a test shows
some R value because that is not a claim
about the product, but about
a test result. The values reported to the government are never this high for such thin
materials, especially Aluminum
which has 200
times the thermal conductivity of ceramics. They simply trap air. That is
why they are almost always
attached to inexpensive open cell thin foams for
vertical uses. The combination dampens
the peak heat spots and fills
in the cold spots. When
less variation is present, there is less heat lost in a building.
From THAT point of view they
do work, but the point is that the claims made by the
manufacturer do not mean what
the home owner may think that
they mean, and that is poor quality assurance.
2) Can't R values be calculated from the conductivity of a material instead of tests?
Answer - Not very accurately. The idea of R
values began because science could not separate the radiative
component outside from the other components that exist on the outside of a material and
it’s environment.
All materials
have capacities to absorb heat.
This results from mass. Mass can
also ‘reflect’ heat which results
from it's density, surface finish and temperature
change and wetness or wind currents relative to the other surfaces.
In ways
similar to reflection it can radiate heat
at various wavelengths and velocities. The
only simple way to
combine everything into one single non-dimensional
unit was to make some simple assumptions.
Because of heat
reflection, the expected temperature a given distance
from a hot body is not always the inverse square root of the unit
distances. (1/d^2). When near a reflecting body, the measured temperature shows a near field effect where a zone of
constant temperature heat surrounds the radiating
material. That is the only difference between “reflected” heat and
radiated heat, and it is only noticed near the heat
source, not the reflector. That is the temperature change is noticed.
The infrared waves can be measured at the reflector
surface as emissivity or infrared. These are waves about 1 micro-
meter in
wavelegth. The spherical ceramics have millions of tiny spheres this same size
that react to this radiation. It would pass right
through ordinary insulation. Even state studies like
Florida State’s have concluded that any radiant barrier will increase R
values form 19 to 30. But for higher temperature
differences such as colder climates, a better barrier is needed as infrared
radiation becomes more difficult to stop by the fourth power of the temperature differences.
3) You have read the literature and can see
that the heat barriers claim to reflect 90 percent of the radiated heat that
hits them, then
how do you explain that?
Answer- Reflection mostly happens when a radiated heat
'ray' hits a surface at an angle.
Snell’s law explains what happens next, but it depends
if the surface is partly transparent to the ray.
If it is, more of the ray as a percentage is reflected
if it enters at a right angle from matter below.
If it is not, more of the ray is often absorbed, even
if the first surface is reflective, if the first surface
does not permit some transmittance to the second
surface. Heat follows laws of optics and sound.
This can happen near large warmly radiating I-beams in steel frame buildings and where thin reflective barrier
is draped like a curtain on the ceiling between bays
and other support members. This use of
a polished surface
is also good for visible light reflection, which is
probably the most valid reason for its
use in barns and industrial buildings.
It is not really intended for residential use because
the silvery surface will grow old and rough in an attic space where it
would degrade by moisture, mildew and exposure instead of hanging downward from the
ceiling, trapping air and
reflecting radiation
from the thick slab below and heavy steel I-beams. Our product’s silvery
surface is encapsulated by
a heat transmitting first surface layer.
4) So are 'R values' just the results of tests of heat passing
through material?
Answer:
No, they are based on very old (1920 bureau of
standards hot plate tests at 68 deg. F) research
that showed that a
single pane of glass at has an R value of .9434, and half inch plaster and tile has an R
value of 3.33 and 12 inch of
sawdust is 40 and so on. These are total R
values. Then 1/R times the
temperature differential should give the BTU's
required for partitions of one square foot under these same conditions. A btu is about as much heat as comes from
burning a match. It may be confused with BTU which is
shorthand for 1000 btu’s. One major complaint has been that
multiplying temperature differential by 1/R gives BTUs but ignores specific heat. Of course, some people know that
it takes 0.17
BTUs to heat air one degree, but the standard for one degree
change is water. These days, if a material
has an R value, it just means
it absorbs and re-radiates heat. Newer materials such as paints and additives
do not fit into the
same conceptual framework,
or lack of it. When Joseph Black first distinguished between Q (BTUs
heat flux) in 1760
and Temperature, he
failed to give a framework for comparing heat flux that results in temperature
changes in different
materials. Hence converting
to or from air temperature results in non-linear and unpredictable estimates
and does
nothing to account for
conditions such as instability and/or boiling caused by reverse heat fluxes
that exist wherever
changes in the emissivity of
materials interface with high Q values. One BTU of flux is supposed to raise
one pound
of water by one degree
Fahrenheit. The science is built around boiler technology ,not the heating of
air and wood
and insulation foam found in
building materials these 243 years later.
You can see why people
prefer more simple but less accurate metrics. It also allows them to size their
furnace
or boiler, since they will
need 5.88 times more heat to make the system work. The bonus is, it sounds
efficient and
even economical when in fact
it is not, but that is good for business. The truth is that we simply don’t
know if we
should divide by 5.88 before
putting in the temperature values or after. The results are not the same, but
that is
consistent with the talk
about ‘non-linearity’. What we mean is that you must know the entire system’s
composition
when radiation is used,
including the source and medium if water or gas. Thus, it seems best to divide
after finding
the net heat flux if we know
we are dealing with air radiation. Since the newest measurement technology-
heat flux
meters – can only measure
flux across a small distance, we still don’t know all the answers to these old
questions.
Even the manufacturers of
these science class radiometers don’t know what values to assign to their
indications of
energy. Grays? joules?
joules per second? BTU’s? Your guess is as good as mine. If you use F=MA and
you know the
mass, you can assume the air
coming from the black plate is at the speed of sound. It’s a complex
calculation involving
the coefficient of friction,
but if anyone out there wants to take a stab at it, write to us and let us see
the results.
READ NEW RADIOMETER EXPERIMENT RESULTS PAGE
Up to 16 RPM can be stopped on this radiometer by two radiant scrims black behind
white coated. The white must be non-organic based or sand. This is without wrapping
the foil around the bulb of the radiometer, allowing ambient light to circumvent the barrier.
[300 watts of light bulbs behind a 1/8 inch white glass diffuser lens ; distance = 2 feet.] The air
that the radiation is reflected into has too low a specific heat – some solid matter must interact and
diffuse the reflected infrared radiation to be effective, and this may result in convection.
Over the years, R value has come to mean about 3 or 4
per inch of thickness for most insulation
products, with closed
cell foams having a little better than that when new.
The best way is to test a one
inch thickness is by finding the
change in temperature of two surfaces and knowing the
amount of heat put into a hotplate, calculate the equivalent
total R value on
your stovetop. A brick should have an R value of about 2 (per sq.ft) for a 4
inch brick, but anything
will work as long as you use it as a standard. A’ K
value’ is the part of the R value due to convection and radiation
which are always present when a surface interacts with
air. Other
brands of barriers work by introducing a low K value
to the surface receiving or
radiating heat.
Since the colder side contrasts with the cold air, radiation is drawn that way.
This is an advantage because
the convection is not as violent as it would be on the lighter, lower density
warm air side,
but also a disadvantage because a thin layer of warm air forms near the metal, causing some condensation.
Of course radiation barrier
materials work best if they can be on both such surfaces. When dealing with reflective
horizontal surfaces, you cannot use only R values.
You can however easily look at the measured
temperatures as a
hot plates cools. The
reason is that the heat source interacts with the insulation materials in ways
that makes
outwards heat flow or flow toward cooler areas the
most dominant flow. Just as the sun’s radiation is pulled away
from the source by the cold of space, it strikes the
earth and the earth then radiates at a frequency that heats up
the air around the earth. Even light photons can
change to a much longer wavelength wave after being scattered
by the atmosphere. Water in the soil absorbs infrared
and re-radiates it. The water responds well because the
vibrational motion and twisting of the hydrogen to
oxygen bonds is what is absorbing the infrared energy.
Carbon dioxide, a greenhouse gas, reflects back the
soil’s re-radiated heat because it finds molecules that do respond by
absorbing
the water’s special infrared radiation wavelength. Since
moist air is lighter than dry air, it rises up and is cooled by expansion,
keeping the atmosphere in a condition to pass it’s
longer wave infrared through the dry air layers. The condensation after
cooling we get as rain. The carbon dioxide bonds strongly
absorb some wavelengths of infrared (short ones ) and transmit
others (longer ones). If the frequency matches some
transition of a charged particle or thermal phonon (an electronic rotational,
vibrational or quantum energy transition in the atoms or the
bonds) it is absorbed, otherwise it may penetrate deeply or
be reflected if the surface is mirror like.
ALL INSULATION tries to reflect, and then scatter or
change infrared radiation. It does this by converting from radiative transfer to
diffusion. At present surface
‘emissivity’ is used as a heuristic or a ‘rule of thumb’ concept not related to
temperature. The higher
RELATIVE energy of the waves thus penetrate more
deeply in a colder medium but that is not the same as saying higher
frequencies by themselves penetrate deeper. Emissivity
assumes that what doesn’t bounce off must be absorbed, and
that is not exactly the whole story. But since
re-radiation is low from the FIRST
SURFACE of low emissivity materials,
that assumption is convenient for most discussion
purposes.
The really important differences have to do with how
very cold surfaces pull radiation into their dense core, well
beyond the surface penetration of ordinary infrared
waves. This is called more specular versus diffuse radiation
transfer. Concrete and human body radiation are
identical in wavelength (1/100,000 of a meter). This does mean
real consequences for human comfort when radiation
barrier type insulation is used in cold weather situations.
It can deprive the human environment of this
wavelength of heat if not properly engineered by retaining cold air
in layers of foam sometimes attached to the reflective
film. While nothing cannot change the total energy absorbed
at a given wavelength, various factors change the
frequency distribution to a more comfortable profile. Assuming long wave
infrared on a clear day is fairly independent of
temperatures from zero to 30 degrees centigrade, it is about 96 W/m2.
Now, average conduction of
heat into the top surface is about 57 W/m2, assuming a soil density of 2.7 kg/m3
and specific
heat of 0.84 kJ/(kg.K)
The difference is a little more than half reflection, with latent heat the
remaining 43 percent.
That means 23 percent of
long infrared is reflected by soil. When the heat is in the soil, diffusivity
is used to model the
‘cooling’ because no heat is
being input and then specific heat becomes the controlling factor, more than
the radiation
and temperature difference
and other factors considered as ‘conductive’ versus heat ‘diffusivity’ or
cooling mode transfer.
Actually at 32 deg Fahrenheit there is
107 Watts per square meter but at 59 degrees Fahrenheit there is only 92 Watts.
This is due to
the effect of specular radiation mode versus warmer, more active molecular
motion mode , more ‘diffuse’
(but not diffusive), more scattered heat. Wein’s law would
indicate that for the falling temperatures, there is more longer
waves, however
frequencies must then decrease. The longer IR waves have more penetration power
because they do not
match the usual energy
levels of most materials. So, the sun’s filtered heat through the air’s
molecular bonds redistributes the
sun’s profile by
scattering and reflection, yet absorbs only selectively. The deep soil is at
constant volume, or contained, and
thus air there has a much
lower specific heat or ability to
retain heat, also making diffusivity or diffusion derived methods
an imperative.
Such air at 32 F has 716 Joules/Kg per degree K versus the normal 1000 J/Kg*K.
So sand and aerated soils
are better insulators than R values indicate. Another good example if you have an infrared non-contact thermometer, is to
measure the temperature of a thin .001” emergency blanket when it is taped to a cold window, about 35 degrees.
It will show almost room temperature( 65F). However, a mercury thermometer will show that surface to be about 55F.
Low thalpance materials will show an infrared reading of about 55F on both it’s shiny side or white side. This is due to the more specular
narrow columnated beam sent out by the non-contact unit interacting with the specular, less diffuse reflections of the
uncoated blanket. The same will happen if a spot of Supertherm paint is applied, that area will then measure a much lower
temperature, on that same false reading 65F surface. This works best in the presence of morning sunlight with snow. In shade,
temperature differentials of 3 degrees are more common under the same conditions.
5)
Why do some
insulating materials block radiation and other do not?
Answer:
Let’s say that we have two square
foot of iron to be heated 21.7
degree centigrade.
The iron weighs 10 pounds.
It is an I-beam one foot
long or a cooking pot on a stove. We know that then 1/R times the temperature differential
should give the BTU's required for partitions of one
square foot. It would take 216 BTU’s to do the job based on
the specific heat of iron.
So the R value is just 216 divided by 46.8 degrees Fahrenheit. The R value is 4.6 to balance the equation
so to speak.
We also know that the K value for iron or brick is
0.15. That is heat loss due only to
radiation and convection,
not conduction. Combining this information to show the
system total U value we get .0886. Then 1/.0886 equivalent
required heat input is already up to R-11.28. This is now heat input(U), not heat
required U=1/R. The conducted
portion of 4.6 is only 40 percent of the total losses
assuming the I-Beam contacts some other surface for 1 square
foot and this surface is holding steady at the starting
temperature before heating up the I-beam.
Because most of the heat is lost by convection and
radiation to the air by the second square foot, the surfaces of
those materials with less that R6.6 per inch thickness
cannot stop this radiation. It takes a
very high insulation
R value, but this value may be a fairly thin
membrane. A system may be dominated by
convection and radiation, like
a brick wall would be when it’s windy and raining
outside. This can raise the
radiated/convected K factor by
3.8 times normal, depending on whether heat is being
supplied (conducted) or it is passively cooling off (diffusivity).
That is why the combination of special materials that achieve a very high waterproof insulation value through
external reflection,
scattered internal reflection and low re-radiation can be more than just
important. This can
only be done by combining
the vacuum sputtering of just the right amount of metal on plastic with high
gloss
finishes and Compton
scattering ceramics. Other materials do something about the convected heat when
they
are horizontal but they will
not do as much if applied to the warm side airspace of a vertical brick wall,
just where
our product is at it’s very best application advantages.
Only Thermcoating shows heat containment and isolation of the warm side from the cold side
even though the tested material is only a few square inches and the metal radiating body is
about 2 square feet.
Graph of Thermcoat hot plate tests and other similar products. Higher lines are all The Thermcoat tests.
Observable Hotplate Test
(Left) Aluminum foil with crystals
1800X
(Above)
Sputtered Aluminum with plastic coating. The crystals are imperfections that are now covered.
They would conduct 5 to 10 times more heat if left exposed than the surrounding smooth areas.
They would also allow speedy corrosion and oxidation to begin.
The plastic is transparent to a wide range of infrared frequencies.
(Left) Fine Ceramic 1450X
6) Do you have any advice
for anyone who wants to bag mineral or glass fibers and wants to buy
low cancer risk materials to work with?
We believe that putting
fibers in to a heat sealed bag to form
a pillow is better than letting
fibers loose in a ceiling or
wall structure. It is too easy for
rodents and rats to access such materials.
The research is difficult to
read and keep up with. A recent study
found that very similar fibers may
produce different results,
but as many as 160 rats per 1000 developed cancer after exposure to thin
fibers. There was some correlation with early
irritation and later health problems.
Of course, it is
the thin fibers that are
most likely to get into the air through wall spaces or when someone wants to
make a repair on any part of
a wall or ceiling. Our advice is to
wear protective masks and wash
up well all clothes and body
parts after heat sealing any fibers. Do
this work outside where fibers left
lying around can biodegrade
early. We will bag or seal. Email your requirements. In summer 2003 Cabot
has announced it will begin
making aerogel beads at affordable prices. For vertical walls we recommend
using
them or else vapor expanded
polystyrene and third choice extruded polystyrene. For horizontal walls we
recommend using Argon, available at any gas welding supply store.
See the physics of heat page for more information. 
Sealing Wand/Iron
7) Do you have any
calculations for earth burm walls?
I have an idea of using snow
as insulation combined with earth burm structures, especially if you design for
it before
building the burm. Remember
that polystyrene and polyurethane foams have poor weathering characteristics,
but having said that, I’ll
assume you have a pit to catch snow. I also assume you don’t want to keep
shoveling show into
the pit every day. The
average winter day in Boston is 6 degrees centigrade above zero (freezing) so
snow will slowly melt.
So, to offset variations in
weekly weather, we can try to block out 6 degrees centigrade and possibly use
extruded foam as
movable covering insulation
material if the weather stays warm for too many days.
Tests show extruded foam
panels absorb no water all all, but expanded Styrofoam does absorb water.
Shock models show the
promise of low thalpance materials best. Three inches of Styrofoam at 2.0 lbf
per cubic
foot would have a 35 minute
shock half time, Polyurethane foam 3.3 hours and paraffin wax 17.8 hours to
reach half it’s
ultimate stable temperature.
In this case we want
the cold to penetrate the top layer of that foot wide earth wall so that the
snow barrier can act
as insulation against losses
below the frost point. It’s a bit tricky. But, at one foot depth average soil
has a diffusivity of
.00000048 square meters per
second, and thus one foot deep it varies only 1.35 degrees Fahrenheit on an
average diurnal
(daily) time basis. It takes
10 hours for this thermal shock to penetrate to the one foot depth. Whenever
temperatures are
below the freezing mark, you
will save money on fuel bills. The well should not be very deep, because frost
penetrates
during the non-snow covered
winter. It does not have to be very deep to get the benefits of snow
insulation, but at least
1 foot wide and 8 inches
deep to give 1 hour shock value half time.
There is a difference
between an extreme thermal shock and a gentle sine wave change. The shock uses
the square of the
distance in centimeters
while the sine wave change uses only the distance in centimeters. These models
are both diffusivity
derived models. The first
model, the shock model tells you how long it takes at that depth from the
heated surface before it
reaches half of whatever temperature
it will eventually reach at some future time, assuming the heat source stays
constant.
The second model, or sine
wave, tells you how many seconds pass before that heat flux or cold snap peaks
at that depth.
The Wave model is very slow
variation- 24 hours peak to peak. (.001 inch =.00254 cm)
T Seconds T Seconds Equivalent
Radiation-instant Variation –24 hour cycle Thickness
Shock model Wave model To Damp 24 hr.
cm *cm* factor cm * factor Cycle to 6 deg.
C
Polystyrene fm 41 874 16.3
Air 4.78 186 14.0
Argon 5.56 195 13.3
Polyurethane fm 226 1,172 7.25
Soil average 217 1,197 2.18
Snow average 8.875 1,422 1.84
Parrafin 1103.0 2,622 1.00
A Word About Special R
Values
Caution is advised when considering
the hybrid R values too. Today, those firms that wish to be supportive of
insulation that has poor shock
characteristics (like ‘paint
additives’) would sell the buyer a ‘Mass enhanced R value’ or an ‘Effective R
value’. They reason that as the temperature
difference
across the wall is reversed, the heat flow is also reversed. Actually, unless
there is extreme differences, the flow of heat is always
taking place in
all directions as well as in several other ‘degrees of freedom’ that depend on
the shape of the molecules or atoms conducting the heat.
As you can see
from the table above, the reversed flow some try to champion is also delayed and at a very
small depth, here .012 inches to 16.3 times
.012 or .195 inches (a fifth
of an inch) . There, two thirds of the original Tambient – Tinitial temperature
variation has already been diffused by the
diffusivity i.e.
conductivity/(specific heat* density) ratio of an intended insulating
material or thermal barrier covering even the most mediocre
insulation. Furthermore,
careful reading of their analysis shows that the ‘changed’ R value only is
valid when the outside temperature crosses over
the inside temperature, or
when there is some doubtful equipment efficiency factored in, as if the same
effect would not be there if we did not know
about delayed onset of peak
air conditioning equipment demand times. So, Caveat Emptor: Buyer Beware.
Then too R-value does not
indicate if such value was obtained in vertical and/or horizontal positions. It’s
not that the horizontal value is always better
either, because a vertical
test can allow radiated heat that strikes the first surface and is converted by
convection into warm rising air to go up and out
the cold box cold air supply
side drain or simply collect undetected. Any value that is added in or onto a
test probably means the test itself was biased.
There simply is no single
test value that truly indicates a system’s ability to block all forms of heat
in all installation situations and conditions.
As we attempt to show on
these pages, calculation done right is foolproof . This air convects and either
contains heat or rejects
it out of the measured
areas. A science text book gives linear values for glass batting to be 1.7
times that of air which is .000057
calories/cm * sec*C.
If air was really R-6 as
some internet sites claims, then other insulation values become higher, none of
which would be due to radiated heat
blocking or reflection. But
again, in vertical spaces, air alone cannot insulate per inch more than
conservatively R-0.9, meaning glass
wool would then also have
inferred by this comparison a much lower actual R value . A lot depends on what
the
accepted values for air
really are and at what temperature and composition. Since water is not tested
in standard fixtures but the BTU makes
water the basis for
comparison, it is a confusing metric to
use a decision tool and is best left to the realm of math where it suits
generalities best.