Oak Ridge National Laboratory
C. L. Kusik J. T. Dieckmann E. M. McMahon N. Hobday
Arthur D. Little, Inc.
Sponsored by the Alternative Fluorocarbons Environmental Acceptability Study (AFEAS) and the U. S. Department of Energy (DOE)
Chlorofluorocarbons (CFCs) have been the subject of worldwide attention due to the stratospheric ozone issue and the related landmark international agreement on control measures for ozone protection known as the Montreal Protocol. Review provisions of this Protocol have established the phaseout deadline for the controlled CFCs by the year 2000, except for a delay of 10 years for developing countries. Some European community and other countries are adopting even stricter timetables with phaseout ranging from 1995 to 1997. Research, engineering development, and manufacturing investment decisions are underway throughout the world to achieve an orderly transition from CFCs to suitable and environmentally acceptable chemical substitutes or alternative technologies within the timeframes cited.
In addition to their role in ozone depletion, CFCs are among the "greenhouse gases" in the atmosphere that contribute to future global warming. Figure 1.1 illustrates the proportional contribution of various greenhouse gases to calculated global warming.
As shown in Fig. 1.1, the contribution of CFCs to global warming in the last decade is second only to carbon dioxide (CO2). CFCs are much more potent on a per molecule basis than CO2 and some other greenhouse gases, even though the emissions of those gases are larger than CFC emissions by several orders of magnitude.
By simply replacing the CFCs with hydrochlorofluorocarbons (HCFCs) or hydrofluorocarbons (HFCs), the proportional global warming impact of these chemical emissions in the future would change as represented in Fig. 1.2.
However, CFCs (and their alternatives) function in energy-dependent systems or processes, and energy consumption in each of these specific applications can also affect CO2 emissions linked to electricity or fossil fuel use. The DIRECT chemical greenhouse gas emission effect must be seen therefore, not in isolation, but together with the INDIRECT energy-related CO2 emissions of the systems in which they are used.
It should be noted that new scientific data (WMO/UNEP, 1991) indicate that observed stratospheric ozone losses could be decreasing the global warming forcing by an amount that at least partially offsets that caused by the increased infrared trapping of CFCs. Although this indirect effect may decrease the GWPs of CFCs, it does not change the main conclusions of this study. Rather, the new information increases the importance of a systems analysis and the need to account for carbon dioxide emissions resulting from the energy requirements of a system.
For convenience in combining these effects, the DIRECT (chemical emission) effect is expressed as equivalent carbon dioxide, consistent with the Global Warming Potential (GWP) indexing approach of IPCC (explained further in Section 1.3). This equivalent CO2 DIRECT effect can readily be combined with the INDIRECT (energy-related) CO2 emissions. The combined or total effect is termed the Total Equivalent Warming Impact or TEWI.
This concept is illustrated in Fig. 1.3 for replacement of CFCs in a household refrigerator.
In this example, the TEWI--represented by the comparative area of the two "pies"--is reduced by 18% in the transition from CFCs to the HCFC and HFC alternatives. This improvement is due to the reduction in DIRECT (emission-related) impact from 20% to 2% combined with no change in INDIRECT (energy-related) impact. An evaluation of this combined impact for the various alternatives to CFCs in a number of specific end-use applications is the purpose of this study.
1.2 PURPOSE AND SCOPE
The primary objective of this study is to develop representative indications of the relative energy use, associated CO2 emissions, and total equivalent warming impact (TEWI) of viable options to replace CFCs in their major energy-related application areas. It was motivated, in part, by a concern that most attention to date has focused on the DIRECT global warming effect of CFC's and their alternatives, with inadequate attention being paid to the INDIRECT effect of the CO2 emissions arising from the differences in energy consumption by systems using different alternatives. The DIRECT and INDIRECT contributions are combined in this analysis to determine the TEWI of the various technical options. The study is international in scope and takes into account significant differences in present CFC end-use practices, sources of energy, and other societal factors between Europe, Japan, and North America.
Information developed in this report complements on-going studies to assess other environmental effects, safety, toxicology and costs. It will assist government, industry, and international policymakers in making sound decisions from the options available to meet future societal needs--in the developed and in the developing world--in view of the CFC phaseout.
This study should be considered an overview of key issues. It relied largely on readily available information and focused on first generation CFC replacement technologies. The study is not comprehensive in its coverage of all CFC applications, technical options, and geographic regions, nor is the level of analysis undertaken exhaustive or technically detailed. However, the study did adequately assess, in the judgment of knowledgeable experts, alternatives that could reasonably be expected to be available for commercialization over the next decade. Simplifications were necessary in order to complete the study within the time and budget available. Also, the shorter, simplified approach seems more suited to the rapidly changing CFC transition situation underway now than a more lengthy, exhaustive study.
The analysis addresses CFCs as well as alternative chemicals and technology alternatives in uses such as refrigeration, foam insulation, and metal and electronic cleaning and drying processes. The major refrigerant applications covered in the analysis include:
The major applications of foam insulation include:
The major applications of solvents include:
Table 1.1 lists the alternatives considered for each of these applications.
The study involved experts from industry, government, and academia around the world in the above applications to characterize existing CFC practices or baseline technology and to identify the technology options for the various applications and geographic regions. The focus of the technical analysis is on energy-use comparisons of the technology options and associated per lifetime equivalent CO2 emissions, together with estimated emissions of the refrigerant, blowing agent, or cleaning solvent, all on a per unit basis. Electricity end-uses of energy are referenced back to the power plant, with regionally specific proportions of various fossil and other source energy, for purposes of estimating CO2 emissions per unit of energy delivered. After extensive review of the findings to assure an objective and thorough evaluation, the report was made available to the Technology Options Assessment Panel of the United Nations Environment Programme (UNEP) for their use in the Montreal Protocol reassessment process, and to the global climate change Intergovernmental Negotiating Committee for the 1992 United Nations Conference on Environment and Development (UNCED).
1.3 GREENHOUSE WARMING POTENTIAL INDEX
Considerable uncertainty exists about the climate change responses to greenhouse gas emissions due to an incomplete understanding of sources and sinks of greenhouse gases, clouds, oceans, polar ice, and interactive climate feedback mechanisms. "Radiative forcing" (factors that can perturb the radiative balance of the Earth-atmosphere system) or direct heat trapping effect involves less uncertainty and is used by atmospheric scientists to assess relative impacts of different gases.
Many of the indices that have been used as measures of relative contributions of the various greenhouse gases are based on past concentration changes in the atmosphere. An index termed the Global Warming Potential (GWP) has been developed which provides a simplified means of describing the relative ability of each greenhouse gas emission to affect future radiative forcing and thereby global climate change. The GWP, as developed by atmospheric scientists follows from the concept of relative Ozone Depletion Potential (ODP). The ODP, an integral part of the Montreal Protocol process for protection of stratospheric ozone, has been adopted by the Intergovernmental Panel on Climate Change (IPCC) and by AFEAS. The GWPs used throughout this report are relative to carbon dioxide, consistent with the IPCC indexing approach.
Global Warming Potential Relative to Carbon Dioxide
The extent to which a greenhouse gas contributes to calculated global warming depends on the amount of it that is emitted, the length of time which elapses before it is purged from the atmosphere and the infrared energy absorption properties of the gas. In this report, for each application, the amounts of gases emitted have been calculated explicitly, from estimates of either DIRECT fluorocarbon emissions or the quantities of carbon dioxide associated with energy usages. The other important factors are parameterized in Global Warming Potentials (GWPs). GWPs enable chemical emissions to be converted to their equivalent emissions of carbon dioxide so that there is a common basis for comparing impacts.
Carbon dioxide, CFCs, HCFCs and HFCs are purged from the atmosphere at very different rates. This is illustrated in Fig. 1.4a which shows that 100 years after a single emission of a representative HFC, almost none remains in the atmosphere. After the same interval, however, 41% of an emission of carbon dioxide would remain and, even after 500 years, 19% survives (Maier-Reimer, 1987). Therefore, the potential for an emission of carbon dioxide or other longer-lived greenhouse gases to warm the atmosphere exists for more than 500 years.
The GWP of a gas is calculated from its energy absorbing properties together with the amount present in the atmosphere over a specified length of time (i.e., the area under the curve for an individual gas as shown in Fig. 1.4). The computation is referenced to the same set of values for carbon dioxide. The specified period of time is the Integration Time Horizon, as described in IPCC (1990). If the time horizon is set at 100 years, the whole of the potential effect of a short-lived HCFC or HFC would be counted, but a substantial part of the effect of carbon dioxide--the hatched area in Fig. 1.4b--would be excluded. Thus, the 100-year time horizon does not give a true measure of the equivalence between any other gas and carbon dioxide. The situation is worse at the 20 year time horizon when, although 71% of the effect from the HFC has been counted, substantially less than 10% of the effect of carbon dioxide is included.
This report uses GWPs at the 500-year time horizon as listed in Appendix Table A.1, but the Executive Summary and Section 14 also contain representative calculations at the 100-year integration time horizon (IT) to illustrate the effect of the ITH on the conclusions. These values represent the nearest approach to a true means of equating emissions of CFCs, HCFCs and HFCs to each other and to carbon dioxide. The effect of carbon dioxide after 500 years is highly uncertain and is neglected.
The general approach employed in all cases consisted of the following steps:
- for solvent these calculations were done on the bases of unit throughput
"Current Generation" and "Next Generation" Alternative Technologies
New systems, materials, and processes that represent potential CFC replacement technologies are being developed rapidly. Technology options already available or identified by the user industries as their primary development focus for first generation replacement of CFCs, whether fluorocarbon or not-in-kind (non-fluorocarbon) alternatives, were given first consideration with regard to quantitative analysis of their DIRECT and INDIRECT effects and their TEWI. These are referred to as "current generation" alternative technologies in this report and are distinguished from "next generation" alternative technologies.
The emerging or potential "next generation" alternative technologies have also been evaluated, where adequate information on such options was available, to provide a more complete picture of future possibilities. These "next generation" options are not likely to be sufficiently well developed or available in the time frame of the commercial transition away from CFCs in the 1990s.
The development and commercial implementation of cleaning system technology options (solvent, aqueous, and semi-aqueous) is occurring at a more accelerated pace; therefore, the technology categories are defined somewhat differently. Currently sold and manufactured machines for major user markets are defined as "baseline" technology. Technology developed and likely to be increasingly practiced is defined as "best available current technology."
1.5 MAJOR FINDINGS
The results of the quantitative analyses conducted for each of the applications are illustrated in a series of summary bar graph figures. These figures show the changes in TEWI of the various CFC alternatives relative to the baseline CFC technology for a range of refrigerant, insulation, and cleaning applications. The relative proportions of the DIRECT and INDIRECT effects on the TEWI for each of the various alternatives or technical options are also illustrated. Reference will be made to these figures as the major findings are highlighted and discussed below. The study findings are separated into major general findings and application-specific findings.
The major general findings that address all three major application areas include the following:
- Refrigerators/freezers show only 2-3% DIRECT impact with a variety of HFC refrigerants and HCFC foam blowing agents
- Open top equipment for batch electronic cleaning of electronic components may have as high as a 98% DIRECT impact
- Aqueous and semi-aqueous cleaning technologies are examples of NIK alternatives already in widespread use which exhibit a substantial reduction in TEWI relative to the baseline CFC cleaning technology (as shown in Fig. 1.7).
SPECIAL NOTE: Improper conclusions can be drawn by comparing the TEWI shown in Figs. 1.5, 1.6, 1.7, and 1.11 using 100 year GWP values with those shown using 500 year values. For example, the 500 year TEWI show a higher percentage indirect effect, not a higher indirect effect than is shown for the 100 year GWP values. The indirect effect has the same magnitude in each case, the percentage increases because the total effect is smaller using the 500 year GWP values.
Figures 1.8a-b, 1.9a-b, and 1.10 focus on the fluorocarbon (HCFC and HFC) alternatives and illustrate the relative importance of their INDIRECT (efficiency-related) and DIRECT (emissions-related) effects. Most of the "current generation" HCFC and HFC technologies are still being optimized and, thus, the currently available data are not likely to represent the lowest cost effective energy consumption or the lowest losses/emissions achievable. Accordingly, these illustrations focus on identifying opportunities for further future reductions in the TEWI.
- These applications represent important target opportunities for developing and demonstrating new technology options aiming at substantially no-release equipment that could work with the most efficient substitutes (in-kind or not-in-kind) available in the long term.
- Cleaning industries have generally identified and are already adopting or evaluating improved containment measures, technology to reduce energy consumption, and not-in-kind alternative options.
SPECIAL NOTE: The TEWI comparisons shown in Figs. 1.5, 1.6, 1.7, and 1.11 are valid only for different technology options within the same application. Different applications are combined on these figures only as a convenience in summarizing the results. It is important not to make comparisons between different applications; e.g., commercial roof insulation options should not be compared with household refrigerator insulation options with regard to TEWI differences.
1.6 APPLICATION SPECIFIC FINDINGS:
1.6.1. CFC Refrigerant Alternatives
- Early published test data indicate small penalties for substitutes, but recent industry data show near equal refrigerant performance as achievable
-- with new lubricants
-- with optimized engineering design
1.6.1.a For household refrigerators/freezers and building air-conditioning equipment dominated by INDIRECT (energy-related) effects:
- conventional vapor compression cycle technology with HCFC/HFCs or other suitable working fluids, or
- alternative cycles or processes
1.6.1.b The DIRECT (chemical-related) effect is a substantial proportion of the TEWI for automotive air conditioning and retail refrigeration HCFC/HFC applications (Fig. 1.8b).
- Further containment, new equipment design configurations and/or cycles/processes are longer term options for further reducing the TEWI for these applications.
1.6.2. CFC Blowing Agents or Insulation Alternatives
1.6.2.a For appliance insulation and residential/commercial wall insulation dominated by INDIRECT (energy-related) effects:
- improved thermal resistance foam and advanced manufacturing processes with HCFCs (or other suitable low-conductivity gases or blowing agents),
- thermal envelopes with higher insulation levels in buildings, or
- next-generation insulation materials such as evacuated panels for some applications.
1.6.2.b The most significant DIRECT impact from HCFC-blown foam is associated with commercial roofing and re-roofing (Fig. 1.9a-b).
1.6.3. CFC Alternatives for Metal and Electronic Cleaning and Drying
- use of control systems (e.g., "economizers") can reduce the distillation rates in the idling mode by 67%.
- use of heat pumps in low boiling solvent based systems that can reduce energy requirements by as much as 75%.
- use of closed loop systems and/or heat exchangers for aqueous or semi-aqueous cleaning with potential savings of approximately 30 to 35%.
- better control of emissions of solvents, especially in batch metal and electronic cleaning. With moderate increases in equipment costs, emissions from these systems can be reduced by 80% or more; reductions in excess of 90% are possible with more advanced systems. For example, systems are available to control solvent emissions from 0.5 kg/m for batch systems down to 0.02 kg/m of printed circuit boards cleaned.
- much of this technology can be retrofitted to existing equipment.
An estimate of the impacts of systems using the best available current technology is shown in Fig. 1.11. This figure shows that the TEWI for CFC-113 using the best available current technology is only about 20% of the TEWI for CFC-113 current practice (as shown in Fig. 1.7) and the TEWIs of the alternatives with BACT are even less. When widely adopted, the TEWI of solvent systems will be comparable or less than aqueous or semi-aqueous systems.
The potential changes in CO2 emissions related to energy use of CFC replacement technologies (i.e., the INDIRECT effects) were found to be relatively small due, in part, to the emphasis placed on energy efficiency by the user industries. Therefore, the ten-fold reduction in DIRECT effects resulting from replacing CFCs depicted in Fig. 1.2 will yield a substantial reduction in TEWI and, hence, in contributions to future global warming in the industrialized countries by the end of the 1990s. This conclusion assumes that the options considered in this study are available and otherwise acceptable for the CFC transition.
Effects of not-in-kind replacement technologies and improved conservation/containment and recovery of the replacement fluorocarbons should further reduce the DIRECT effects and provide added reductions in the TEWI. The IPCC report (1990) and industry estimates (Gidunal, 1991) suggest that the future demand for HCFCs and HFCs may only be 40% of that for CFCs (based on projections from demand in late 1980's), due to the effects of reduced emissions and use of non-nuorocarbon alternatives. If this occurs, a twenty-fold reduction in DIRECT effects from fluorocarbon applications could be realized.
There is ample evidence from the user industry inputs to this study that conservation efforts are receiving increased attention for controlling current CFC emissions. The improved containment and recovery practices and technological solutions generated by these efforts should be readily adopted for the alternative fluorocarbons. On the other hand, not-in-kind (NIK) alternative technologies are generally not receiving major research attention in the refrigeration, air conditioning and insulation user industries, for a variety of valid business, technical, and time-related reasons.
The potential importance of these NIK options in the longer-term is acknowledged. The study has included some examples; although many more are under development. These options should be considered more fully, but information and verifiable data on many of these options are fragmented and difficult to interpret and compile. It is also difficult to assure comparability of available data on developmental technology with commercial or near-commercial technology. Misleading or speculative conclusions could be reached, perhaps to the detriment of the new or unconventional technology. At a later stage, when these technologies reach a more mature state of development, further analysis should be attempted.
It was judged most important in this initial assessment to focus on "current generation" technology options and to reflect the thinking and planning of the user industries mainstream. The impacts of their preferred options represent the most likely outcome for the immediate CFC transition in the 1990s. The analysis and findings point out and highlight those applications in which the opportunities for NIK options may be the greatest, that is, in applications for which substantial HCFC/HFC DIRECT (emissions-related) effects remain. In the other applications in which the INDIRECT (energy-related) effects dominate, the NIK technologies would essentially have no significant TEWI advantage over fluorocarbon technologies unless they also offered lower energy use. A change of only 2 to 5% in efficiency would have a greater impact on TEWI than completely eliminating the direct (fluorocarbon-related) effect. NIK technologies would therefore have to be developed that are equal (or better) in energy efficiency and comparable in cost to the HCFC/HFC options to offer a TEWI reduction benefit in these applications.
Prior to the October, 1991 release of the UNEP/WMO Scientific Assessment Summary it was believed that replacing CFCs was the most important single near-term step that could be taken toward reducing future global warming impacts. However, since ozone depletion, linked to CFCs, appears to lead to a reduction in radiative forcing and hence the global warming impact of these gases, the net reduction to future global warming due to CFC elimination is uncertain. Because of the world's dependence on fossil fuels for primary energy needs and the predominant contribution of CO2 to future global warming forcing, energy efficiency will be critical in limiting CO2 emissions.
Finally, it is well recognized that the needs of the developing countries must be considered. The industrialized nations must be sensitive to the applicability, adaptability, and appropriateness of our technological solutions in those regions, where, for example, refrigeration needs are increasing dramatically. These global environmental issues such as ozone depletion and global warming require near complete participation worldwide if the solutions are to be effective. The energy and CFC replacement technology choices made by the developing nations will be crucial in determining how well we do overall in minimizing contributions to these issues.
* NOTE: Absorption chiller results shown in Fig. 1.5 are representative of peaking duty for direct-fired double-effect equipment and are not directly comparable to the adjacent results for baseload duty of the CFC and HCFC/HFC chillers.
CFCs and other gases do not include effect through depletion of stratospheric ozone. Changes in lifetime and variations of radiative forcing with concentration are neglected.
* The persistence of carbon dioxide has been estimated by explicitly integrating the box-diffusion model of Siegenthaler (1983).
2 The HCFC-225ca/cb GWP values used in this report have been calculated by Atmospheric and Environmental Research, Inc. (AER) and are based on rate constant measurements reported by M. J. Kurylo, et al; Geophysical Research Letter, Vol 18, No. 1, pages 5-7, January 1991, and the infrared energy absorption properties measured at ALLIED-SIGNAL Central Research Laboratory.
Source: IPCC "Climate Change," 1990, except for HCFC-225ca and HCFC-225cb (see Note a).
NOTE: The values presented in Table A.1 are under review by the Stratospheric Ozone Assessment Panel, which may lead to changes in GWP values. The revised values, where necessary, will be used to recalculate the direct energy contribution of the working fluids to the applications assessed in this report.