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AFEAS and the U.S. Department of Energy (DOE) have co-funded three studies using a systems
approach to determine the overall contribution of CFC alternatives to global warming. The first
study, which was conducted in 1991, focused on those technical options that could be
implemented by the year 2000 in each of the major CFC application areas - refrigeration, air
conditioning, insulation, and solvent cleaning. The time frame was defined by the CFC phaseout
schedule under the 1990 version of the Montreal Protocol.
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Figure 1. Radiative forcing of greenhouse gases (in
Kg of CO2 from a refrigerator/freezer
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The second study, conducted in 1993/94, evaluated the energy and global warming impacts of
next generation fluorocarbons as well as not-in-kind (NIK)/non-fluorocarbon technologies that
could be developed or improved to replace CFCs and HCFCs. A third study, initiated in 1996,
focuses on insulation, refrigeration, and air conditioning technologies that can be commercialized
during the phaseout of HCFCs.
The AFEAS/DOE studies assessed the direct contribution of greenhouse gases used to make or
operate the systems and the indirect contribution of the carbon dioxide emissions resulting from
the energy required to run the systems over their normal lives. Both must be taken into account
when determining the total global warming impact of a system. The sum of the direct and
indirect emissions of greenhouse gases represents the "total equivalent warming impact" (TEWI)
of the technologies being compared. The calculated TEWI is sensitive to assumptions of the
system lifetime, emission losses, and the integration time horizon chosen to calculate global
warming potential (GWP) values as well as the source and consumption of energy.
The upper graph of Figure 1 illustrates the release of the refrigerant, blowing agent, and CO2 from
energy use associated with a household refrigerator. The effects of the CO2 build up as
electricity is used during the lifetime of the appliance, and then drop off sharply and decay in
time. The release of the blowing agent is indicated by a sharp peak when the refrigerator is removed
from service after 20 years of use and assumed to be crushed upon disposal. A narrow region below
the curve for the blowing agent represents the effects of the refrigerant, also assumed to be
released at the end of the service life. The global warming effects of the refrigerator are represented
by the area under the curves from time zero for a designated number of years. Both the blowing
agent and the refrigerant are completely accounted for within 100 years; the CO2 resulting from use of
the refrigerator will continue to contribute to global warming even 500 years later.
The lower graph in Figure 1 represents the effects
from the release of a single kilogram of CO2. The
total equivalent warming impact, or TEWI, for a
system is the area under the curves in Figure 1a out to a certain number of years (typically 100
years) divided by the area under the curve in Figure 1b for the same number of years. The number
of years chosen is referred to as the integration time horizon, or ITH. A very long ITH accounts
for all of the global warming impacts, but could put too little emphasis on short-term effects.
Short ITHs also lack balance in that they understate the significant long-term effects of CO2
emissions.
Results of the AFEAS/DOE studies show that, where data are available for comparison, it is
essential to analyze the direct and indirect contributions of all alternatives to be able to choose the
most environmentally acceptable option. The main conclusions from the studies follow.
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The use of non-fluorocarbon and NIK technologies may expand in already established niche
markets, and other NIK technologies may find new market applications. But it appears
unlikely that conventional and HFC technologies can be displaced to any large degree in the
foreseeable future. |
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The studies showed that energy efficiency is a powerful tool to mitigate future potential
climate change. In most applications, HFCs are the most efficient and safest available
technology. |
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In many applications, NIK technologies will need to compete with the demonstrated
continuing improvements in efficiency, emissions control, and product reclamation of
conventional refrigeration, air conditioning, insulating, and cleaning/drying technologies. |
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