Farming, Saturday, March 30, 1996
RADIANT BARRIER
INSULATION
Kenneth Kephart
Associate Professor
Animal Science
Eileen Wheeler
Assistant Professor
Agricultural And
Biological Engineering
Protecting pigs from the ele
ments is a major reason for keep
ing them in an environmentally
controlled facility.
Part of the comfort we provide
comes in the form of addol heat
during the winter months; another
byway of increased ventilation
rates during the summer.
Both modifications require
energy and cost money. To minim
ize our energy expenditure and to
make the building more comfort
able and efficient, we insulate it.
Conventional insulation
includes ball (fiberglass), rigid
(polystyrene, etc.) and blown-in
(cellulose). Another, less conven
tional form, is radiant barrier
insulation.
It isn’t new. And despite the fact
that it has seen little use by the
livestock industry, manufacturers
periodically “re-introduce” the
product as a new technology that
we’re ignoring.
Radiant barrier insulation func
tions and performs differently than
conventional forms. The purpose
of this article is to clarify what
radiant barrier insulation docs, and
in regard to livestock housing,
what it docs not do.
Heat Losses During
Winter Months
Heal losses from livestock facil-
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hies occur by three methods: con
duction, convection, and radiation.
Conduction is the transfer of
heat between two materials that
touch. Sit down on a cold metal
seat at a football game and heat
flows from your backside to the
seat From a heated livestock
building, heat is conducted
through the walls from the inside
to the exterior surface. Heat is also
transferred from building mater
ials, such as floors and lower side
walls, to the surrounding earth.
Convection is the transfer of
heat by movement of a fluid such
as air or water. Convection can be
natural as when wanned air rises,
or forced, as with a fan. From a
bam, heat losses by convection
occur from wind, infiltration, and
the ventilation system. Radiation
is the transfer of beat energy (emit
ted and absorbed) between two
surfaces that do not touch.
In a room with a hot wood stove,
you feel the heat on the side of your
body facing the stove even though
you might be a considerable dis
tance away. The hotter, closer, and
larger the surface, the mote intense
the thermal radiation.
With our livestock building,
heal will radiate from the relatively
warm walls or roof to anything in
direct view of that surface. When
radiation strikes an object, it can
bounce back (reflect); it can pass
through (transmit); or it can be
retained as heat (absorb).
Now, how docs heat from inside
the building get outside? By these
three methods combined. For
simplicity, let’s say our bam is an
unheated gestation bam full of
sows in the winter. As the sows lie
on the floor, heat from their bodies
is conducted through the concrete
into the cooler earth below. Heat
from their bodies is also conducted
to the air molecules that actually
touch the sow. These warmed air
molecules rise and set up convec
tion currents within the room.
Both conduction and convec
tion warm the air inside the facili
ty, which warms the side walls and
ceiling by the same means. Finally,
the ventilation system will remove
warm, moist air by natural or
mechanical convection.
In addition, sows and warm
objects in the room radiate heat in
all directions. Little if any radia
tion will be transmitted to the out
side. For most materials in a bam,
only a small amount of radiant heat
will be reflected, so the radiation
(from the sows) tends to be
absorbed by building surfaces.
This thermal radiation, together
with conduction and convection,
will warm the side walls and ceil
ing. Some heat from the walls and
ceiling will be radiated back into
the room. The rest will be trans
ferred to the outside surface by
conduction.
Heat Gains
During Summer Months
In hot weather, the situation is
more or less in reverse. Higher
temperatures outdoors warm the
bam by the same three methods.
Also, the sun’s radiant energy is
much more intense in the summer.
That warms most of the roof and
sidewalls. This heat can be then be
transferred into the building.
Stopping Heat
Transfer With
Insulation
Actually, insulation doesn’t
stop heat transfer, it just slows it
down. (Higher R values mean a
higher “resistance” to heat
transfer.)
Consider our sow facility during
the winter. The inside wall surface
is warm. That heat will be con
ducted through the wall materials
to the outside surface and lost to
the outdoors by a combination of
conduction, convection, and
radiation.
How ftst will heat loss occur?
That depends on several things, the
most important of which is
insulation.
How Docs A
Radiant Barrier
Fit Into This Mess?
Radiant barriers are used to
reflect thermal radiation. In winter,
you want to reflect the radiant
energy back into the building, and
in summer you want to reflect the
sun’s radiant energy back out of
the building.
Radiant barriers are usually
made of aluminum, because of its
excellent thermal reflective prop
erties. They often look like heavy
aluminum foil; in fact, they’re two
aluminized sheets separated by a
porous material or thin layer of air
bubbles.
When they come out of the box,
radiant barriers do a good job of
reflecting radiation. Most of the
heat radiating from a cow or a sow
or the sun will bounce back when it
hits the barrier. But for that reflec
tance to be maximized, the surface
must stay clean and shiny.
Radiant barriers (even those
with air bubbles, commonly called
Bubble Pack) arc not too effective
at slopping heat transfer associated
with conduction. Because of this,
radiant barriers must be installed
so that little if anything touches
one or both sides of the radiant
barrier.
Keeping one side “open”
reduces heat transfer by conduc
tion and enables the radiant barrier
to reflect thermal radiation. In fact,
they work best if they’re installed
inside wall or ceiling panels adja
cent to a thin (less than 2-inch)
airspace. This keeps dust and dirt
from accumulating and also
reduces heat transfer from convec
tive currents.
Should Radiant
Barriers Be Used
In Livestock Facilities?
When used alone, radiant bar-
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riers permits lot ofheat transfer by
conduction. Unfortunately, some
distributors may tell you other
wise. When they do. they’re ignor
ing research studies by several
institutions between 198 S and
1992. These studies showed the
following:
•Radiation barriers by them-
little resistance to heat
flow (an effective R value of 0 for
foil alone, to 1 for Bubble Pack).
• When installed adjacent to a
dead air space of a six-inch wall
section, they increase the average
R value of the entire wall section
by about 1.9.
• The reflective properties aie
significantly reduced when the
material is covered with dust or a
small amount of condensation.
• Broilers grew faster when in a
facility insulated with six inches of
Fiberglass compared to those in an
identical building insulated with
radiant barrier bubble pack. The
house with radiant barrier required
more heating fuel (2,700 extra gal
lons over 10 flocks).
In addition, condensation
formed on the ceiling under the
eaves, and after 31 months the
reflectance of the radiant barrier
was reduced by approximately 33
percent.
So, using a radiant barrier as the
only insulating material is not wise
in regard to operating cost or ani
mal comfort.
What about using radiant barrier
in addition to conventional insula
tion? To be effective, the radiant
barrier should be installed next to a
narrow air space inside the ceiling
and wall panels. That is no easy
task, but let’s assume it could be
done without altering wall or insu
lation thickness.
Typical cost of radiant barrier is
about $.30/square foot. If we
installed fibciglass in a six-inch
side wall, the R value of the entire
wall would be approximately 20.5.
Adding the radiant barrier
(inside the wall, next to an air
space) would increase the R value
(Turn to Page C 5)
SIDE BARS CAN
BE VERTICAL OR
HORIZONTAL