Energy $aver$ of America
1- INTRODUCTION
The obligation to insulate a house or a building has
became an indisputable reality. The energy crisis has put the costs of
oil, gas and electricity so high that a good insulation will bring
significant economies. It pays to
insulate.
Sufficient insulation, properly installed, is still one of the most
cost-effective ways available to reduce energy consumption, control
rising fuel and electricity costs and provide a comfortable living
environment all year long. It is a simple installation procedure. Armed
with some guidelines and a few basic tools, even a novice
do-it-yourselfer can insulate like a pro.
The purpose of insulation is basically twofold. It must
KEEP THE HEAT IN
throughout
our long winter and
KEEP THE HEAT OUT during our
sweltering summer. (
It's a
simple matter of Heat Containment )
Keep in mind, you will only do the job once. Take your
time to do it properly. Patience is rewarded when it comes to
installing your insulation and vapor barrier. Install the right
product today and it will keep working well into the next century.
An efficient insulation system is essential to maintain a comfortable
and healthy environment in the building and also to maintain the
efficiency of the heating / cooling system. The choice of good
insulation material is very important and should be done carefully. It
is not an expense but an investment considering it daily pays you back
with important energy savings. Once you have made a choice, it is
difficult to come back later to improve your insulation without costly
expenses.
It is very important to consider that you have to keep the insulation
system in very good condition. A failing system without the proper
elements installed at the right place could increase the risk of having
moisture or water in it. Some
insulation products absorbing moisture can easily loose up to 50% of
its thermal efficiency.
2-FUNCTION AND ELEMENTS OF A GOOD INSULATION SYSTEM
When installed correctly, insulation reduces heat transfer through the
envelope of a building. Whenever there is a temperature difference,
heat flows naturally from a warmer to a cooler space. To
maintain comfort in the winter, the heat lost must be replaced by your
heating system. In the summer, the heat gained must be removed by your
air conditioner. (
It's a simple matter of Heat Containment )
Heat moves across empty wall cavities or between roofs
and attic floors by
radiation,
conduction and convection. A reflective
insulation reduces heat transfer by radiation to a very low level,
and most products also reduce heat transfer by convection.
Mass insulations
reduce the convection part to a low level and slow down the conduction mode.
However, reflective reduction is achieved by absorption of heat rather
than reflecting it. Both types involve placing a solid material between
the warm and the cool regions to reduce heat flow across the insulation
region.
The benefits of insulating all cavities within the
building envelope are many. A few Are:
1. It supports the individual and national economic and energy
conservation goals,
2. Provides a much more livable structure.
Well-insulated buildings, where effects of moisture condensation and
air movement are minimized, require less maintenance, plus they
deteriorate move slowly. Various forms of thermal insulation exist and
one of the better
ones is the reflective system.
The building envelope consists of five main elements
which are : the weather barrier, the air barrier, the insulation, the
vapor barrier and the interior finish. These must fulfill the following
critical functions :
_ Provide the minimum thermal insulation as required by the building
code applicable.
_ Restrict the flow of house air through the building envelope. _
Restrict the passage of interior water vapor by diffusion into the
exterior shell.
_ Allow moisture trapped within the exterior shell to breath to the
outside.
_ Provide the minimum fire retardant, flame spread and smoke
development ratings.
3-VAPOR BARRIER AND CONDENSATION
Why is a vapor retardant necessary? During the heating months, humidity
contained in the inside air is much higher than in the outside air. The
inside air loaded with moisture will naturally move toward colder
surfaces such as ceilings and exterior walls. If water vapor penetrates
the wall or ceiling and condenses on cold surfaces, it may cause
discoloration, mildew, or even structural damage. This will also
decrease significantly the thermal resistance of this assembly.
Therefore it’s vital to install a vapor retardant between the inside
air and the insulation. Humid air can go through any hole, gap or crack
in the vapor retardant. It is very important to install an efficient
and solid barrier and to take the time to be sure warm inside air stays
where it should, inside in winter, outside in summer.
The insulating capability of fibrous and rigid insulation comes mostly
from the dry air cells in it and not from the material itself. For
example, fiberglass insulates 30 times more than glass by itself. It's
because of the air trapped in the fiberglass. That shows all the
importance of an efficient vapor barrier preventing the moisture to
migrate and condense in the insulation and lowered dramatically its
thermal efficiency. * For more details on condensation and dew point;
see "Physics of foil".
4-REFLECTIVE INSULATION BASICS
It is not rare in construction to find some materials
or methods that, for some reason, had been forgotten. The principle of
reflectivity to prevent heat transfer through radiation has been used
since the dawn of time. Romans were already using it during Antiquity.
To understand the principles of reflective insulation, we need to
understand well how heat is transferred and the basic modes of energy
transmission.
HOW HEAT IS TRANSFERRED
Since 50%
to 70%
of the energy used in the average home in North America is for heating
and cooling. It makes sense to use thermal insulation to reduce the
energy consumed and increase comfort and save money.
The performance of any thermal insulation system depends on how well it
reduces heat flow. Heat moves from warm locations to cool locations in
three ways:
A· By radiation from surface to surface through an air space,
B· By conduction through solid or fluid materials,
C· By convection which involves the physical movement of the air.
BASIC MODES OF HEAT TRANSMISSION
A. RADIATION from heat source is transmitted through air or vacuum to a
cold surface at 186,000 miles per second.
B. CONDUCTION through a solid material is caused by fast moving
molecules on the hot side colliding with and transferring energy to
slower moving molecules on the cold side.
C. CONVECTION occurs when air or fluid moves. Warm air rises and cold
air falls to create a convection loop. The moving air infiltrates or
leaves your building during this process.
Modern construction these days demands high performance insulation
systems that have the capability to prevent heat loss by conduction,
convection and radiation. The systems must also stop air infiltration
and be 100% vapor barrier.
How is it possible to create a thin insulation that
would meet the criteria?
The principle is simple:
1. Air that does not move is one of the best insulation against heat
transfer by convection.
2. Reflecting colors act like a mirror and reflects exterior energy
toward the exterior and interior energy toward the interior.
The principle of reflective insulation is the result of studies done on
different kind of insulation worldwide. It had been shown that there
was an undeveloped market to fulfill. Therefore, it was appropriate to
innovate and bring a new multi-purpose product to give end users a new
solution.
It is as simple
as that, just like a survival blanket. The technique is based on those
two essential elements; trapped air against heat transfer by conduction
and a good reflector (like aluminum) against heat transfer by radiation.
Reflective insulation is a combination of aluminum foil and air spaces
to provide reflective cavities which have low values of radiant energy
emission (emittance). These cavities may have low emittance surfaces
(foil) or encapsulated air spates within the layers of foil such as the
bubble pack product.
Reflective insulation has been used in both residential and commercial
applications for over forty years. These products provide a proven,
reliable alternative or supplement to mass insulations.
Reflective insulation effectiveness depends on its ability to reduce
each of the three modes of heat transfer. For example, a typical
multi-layer reflective insulation divides a cavity into a set of
smaller air spaces with parallel high reflectance and low emittance
surfaces (A good insulation technique.). For a cavity, the cell
dimensions are designed to minimize air movement and reduce convection.
The low emittance of the facing surfaces minimizes direct radiative
heat transfer across the cells. See "Physics of
foil".
The reflectivity being function of the surface finish, it is obtained
from a thin sheet of 99% pure aluminum. Also, the aluminum is so thin
that it does not retain the energy in its mass. The ability of the foil
to reflect the energy and not conduct it in its mass allows the people
to quickly feel comfortable inside their home. This will also allow to
bring back the temperature to a comfortable degree much faster when
thermostats are lowered at night. Another way to save energy.
To obtain maximum efficiency, it is always better to have, on each side
of the reflector a trapped air space (minimum of 16mm). It is essential
to seal all the seams with a vapor barrier tape to insure perfect
tightness.
Radiation is also heat loss.
Authorities
agree that
65% to 80% of all energy that goes from the warm side to the cold side
of a wall assembly, summer and winter, is radiant heat;
depending upon the direction of
the heat flow (because of the varying
role convection plays in the transfer of heat across buildings spaces).
Of the remainder of the heat transfer, convection is responsible for
15% to 28%, and conduction is responsible for between 3% and 7% (see
document "Physics of foil".).
And more, the air volume facing the aluminum foil restricts the heat
loss by conduction considering that stagnant air is a better insulation
on that account than any solid material.
Reflective insulation materials work on a different concept than
conventional thermal insulation like foam or mineral wool. In order to
understand reflective insulation capabilities, one must be aware that
the radiant heat rays of the sun do not become heat until they strike
an object such as a home or everything that is in it. Thus, radiant
heat rays must be kept out in warm weather; while in the cold weather,
warmth must be kept in.
Conventional thermal insulation does not stop those heat rays; but
rather, will absorb them and transfer heat.
Thus, mineral wool and other
thermal insulation will only « slow down »
the transfer
of heat. Reflective products,
on the other hand,
stop approximately
70 %
of all radiant heat by reflecting up to 97% of the radiant heat rays.
What this means is that only 30% of
this heat remains, in some cases to
be handled by conventional thermal insulation used in conjunction with
the reflective insulation products.
The end result is that reflective insulation products are installed in
conjunction with conventional insulation, the optimum energy can be
experienced.
For reflective insulation materials, if air spaces are left out in the
construction plan, the reflective insulation material will still
provide excellent vapor barrier and air-infiltration benefits, but will
give a lower RÂ value, and system performance will be affected.
Since there are built in air spaces inside walls and roofs, it makes
sense that installing a material capable of reflecting large
percentages of radiant heat it would thus provide a highly effective
insulating material.
However, by creating a space which is bounded by at least one surface
which is highly reflective of heat rays (as aluminum foil), a
reflective space is created which can effectively stop the transfer of
a majority of the heat.
Experts agree that as far as the rate of heat transfer is concerned, it
makes only little difference whether the reflective surface is on the
cooler or warmer side of the space.
5-R-VALUE
R values are commonly used to show the thermal value of insulating
material.
But it is important to know that R-value is just a measure of heat
transfer by conduction and does not apply for other heat transfer ways. The
R-value has no utility to measure the capability of a material to
reflect the energy. Even
if reflective insulation materials have a
respectable R Value, their first quality is to stop heat transfer
through radiation. Those products can stop up to 97% of heat transfer
through radiation and provide an excellent temperature control method.
R-value is a measure of resistance to direct conduction of heat, and is
a good measure of the effectiveness of mass insulation. The greater the
mass, the higher the R-value, therefore the more effective most
insulating materials become.
Properly installed foil
insulation,
however reflects 97% of the radiant heat to which it is exposed, a
factor not matched by common mass insulation, nor measured directly by
R values.
Therefore, while reflectivity remains constant, this insulation
provides a secondary benefit of resistance to conduction (lost of heat
through absorption) to varying degrees of effectiveness depending on
whether its placement would be affected by Down, Up or Side Heat Flow.
That is why this product has three R-values.
Thermal resistance measurements have
been made
according to the most recent test revisions using a calibrated hot box
operated in accordance with ASTM C 976. Analysis of results was done in
accordance in ASTM C 236
revised to ASTM C 1224. The R-values observed are highly
dependent
on method of installation.
Once
again, it is very important to understand that the benefits brought by
reflective insulation materials can go way beyond the R values
indicated in this chart.