| Passive Design
Radiant Barriers
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Spacecraft
are subject to temperature extremes that range from 400o F above
zero to 400o below zero. Protecting astronauts from these
extreme temperatures was a prime concern for NASA spacecraft
designers.
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| NASA researchers
sought after a temperature control technology for the Apollo
spacecraft that would provide a barrier which was both lightweight
and flexible and had sufficient durability to withstand the rigors
of space. After considerable effort, a process technology was
developed that permitted producing plastic films coated with a
thin layer of aluminum. |
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These thin “metallized” plastics were
utilized in virtually all spacecraft from then on. With this technology,
the temperature in manned spacecraft could be controlled to permit a
comfortable working environment. The
radiant barrier was a useful temperature controller in space, so the earth
applications possible, such as in insulating homes and office buildings,
soon followed. |
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Savings
Since
everyone's home and lifestyle are different, it is difficult to precisely
calculate savings from attic radiant barriers. However, it's reasonable to
expect that an attic radiant barrier can save a minimum of 8-12 percent of
your annual cooling costs in the Southeast.
Savings from an attic radiant barrier depend on the amount of heat the
roof and attic contribute to your home's cooling load. ("Cooling
load" is the total amount of heat your air conditioner must remove to
maintain comfortable indoor temperatures.) In general, the more energy
efficient the rest of your home is, the larger the percentage of energy
you save from an attic radiant barrier because the roof and attic make up
a larger portion of the cooling load.
Figure
2 shows a breakdown of cooling loads in a typical 1500-square-foot
Central Florida home. The attic (including heat gains to the duct
system) accounts for 22 percent of the total cooling load. In this
house, an attic radiant barrier could save 8-12 percent on the annual
air-conditioning costs.
Although
not as significant, heating savings may also accrue from the use of
radiant barriers. |
A
radiant barrier is a layer of aluminum foil placed in an airspace to block
radiant heat transfer between a heat-radiating surface (such as a hot
roof) and a heat-absorbing surface (such as conventional attic
insulation). Figure 1 illustrates the locations in which a radiant
barrier may be installed in an attic. Only locations 1 and 2 are
recommended for sheet radiant barriers because dust will accumulate on the
radiant barrier if it is installed at location 3.
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Thursday August 28, 2008 - 09:04 PM
