ClimaFoil.com
"Reducing your energy bill is our business"
Radiant barriers are installed in homes -- usually in attics -- primarily to
reduce summer heat gain and reduce cooling costs. The barriers consist of a
highly reflective material that reflects radiant heat rather than absorbing it.
They don't, however, reduce heat conduction like thermal insulation
materials.
How They Work
Heat travels from a warm area to a cool area by a combination of conduction,
convection, and radiation. Heat flows by conduction from a hotter location
within a material or assembly to a colder location, like the way a spoon placed
in a hot cup of coffee conducts heat through its handle to your hand. Heat
transfer by convection occurs when a liquid or gas -- air, for example -- is
heated, becomes less dense, and rises. As the liquid or gas cools, it becomes
denser and falls. Radiant heat travels in a straight line away from any surface
and heats anything solid that absorbs its energy.
Most common insulation materials work by slowing conductive heat flow and --
to a lesser extent -- convective heat flow. Radiant barriers and
reflective insulation systems
work by reducing radiant heat gain. To be effective, the reflective surface must
face an air space. Dust accumulation on the reflective surface will reduce its
reflective capability. The radiant barrier should be installed in a manner to
minimize dust accumulation on the reflective surface.
When the sun heats a roof, it's primarily the sun's radiant energy that makes
the roof hot. Much of this heat travels by conduction through the roofing
materials to the attic side of the roof. The hot roof material then radiates its
gained heat energy onto the cooler attic surfaces, including the air ducts and
the attic floor. A radiant barrier reduces the radiant heat transfer from the
underside of the roof to the other surfaces in the attic.
A radiant barrier works best when it is perpendicular to the radiant energy
striking it. Also, the greater the temperature difference between the sides of
the radiant barrier material, the greater the benefits a radiant barrier can
offer.
Radiant barriers are more effective in hot climates than in cool climates,
especially when cooling air ducts are located in the attic. Some studies show
that radiant barriers can reduce cooling costs 5% to 10% when used in a warm,
sunny climate. The reduced heat gain may even allow for a smaller air
conditioning system. In cool climates, however, it's usually more cost-effective
to install more thermal insulation than to add a radiant barrier.
http://energy.gov/energysaver/articles/radiant-barriers
(Source: U.S. Department of Energy)
