|| Non-HCFC Closed-Cell Foam Insulation
Closed-cell foam insulations are widely used
in building envelopes and appliances. Both polyisocyanurate board insulation and
polyurethane refrigerator insulation owe their high thermal resistance (R-value) primarily
to the low thermal conductivity of the gas used as a blowing agent to produce the foam.
Chlorofluorocarbons (CFCs) were formerly used
as blowing agents, but were banned from use by the Montreal Protocol, an international
plan to limit the production and ultimately the release of CFCs. Chlorofluorocarbons
contain chemicals that contribute to the destruction of the ozone layer, the barrier that
protects the earth from the sun's harmful ultraviolet radiation. Currently, foam
insulation is blown with hydrochlorofluorocarbons such as HCFC-141b, which are less
threatening to the earth's upper atmosphere, but still have ozone depletion
potential. Production of this chemical for use as a blowing agent is to cease by
January 1, 2003. Therefore, a new, non-ozone-depleting chemical is needed as a
replacement for CFCs and HCFCs.
the long-term thermal performance of foams blown with non-HCFC blowing agents
experimental methods and models that properly account for the aging characteristics
of complete foam insulation systems
Studies are underway to measure the aging characteristics
(the decrease in thermal performance as air components diffuse into the cells of the foam
and as the blowing agent gas diffuses out) of foam insulations blown with several
alternative blowing agents. One study has looked at the thermal conductivity and
aging characteristics of simulated refrigerator panels containing polyurethane foam blown
with third-generation blowing agents. Four companies that supply foam to the
refrigerator / freezer industry provided a set of 96 test panels containing polyurethane
foam blown with HCFC-141b and with three potential non-ozone-depleting replacements.
We have also been working on the development of a computational model for the aging of
foam insulation with semi-permeable surface skins, which will be used to predict the aging
characteristics of the refrigerator walls.
|Third generation blowing agents
compared to HCFC-141b
||Heat-flow meter apparatus for
testing homogeneous materials
Additional studies are underway to develop a
fundamental understanding of the aging processes. This includes development and
validation of mathematical models of aging and measurement of basic material properties
that control the aging process. Further research will continue to focus on
collecting and analyzing thermal performance data for foams blown with various alternative
blowing agents so that the best choice of a new blowing agent can be made.
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