Over the last decade, there have been substantial changes made to the design of these products, largely due to environmental and energy regulations. Industry and government have worked together to minimize cumulative regulatory burden, while at the same time significantly improving the environmental and energy aspects of refrigerator-freezers. This article will focus on the environmental concerns associated with the foam blowing agents.
Polyurethane foam insulation has been used in refrigerator-freezer applications for more than 30 years. As foaming techniques and formulations have improved, it has helped considerably to enhance the efficiency of these appliances by significantly reducing thermal losses. In addition, it has also helped to reduce weight by providing good structural support so that less steel is required.
The process of applying the polyurethane foam requires the use of a low thermal conductivity blowing agent to facilitate the flow and expansion of the chemicals as they are injected into the refrigerator-freezer casing. For many years, the almost universal blowing agent used in refrigerator-freezer applications was CFC-11. Because CFCs were linked to stratospheric ozone depletion, the decision to replace them in all products worldwide was made under the Montreal Protocol in the late 1980s. The phaseout of ozone depleting substances (ODS) in the U.S. is regulated under the Clean Air Act by the EPA. Its Significant New Alternatives Program (SNAP) approves chemicals that can be used to replace ODS.
During 1994, most manufacturers of refrigerator-freezers in the U.S. converted to foams using HCFC-141b as the blowing agent. Some conversions were also made to HCFC-22, but to a much lesser extent. Although HCFCs are an ODS, their ozone depleting potential is significantly less than CFCs, so they were identified as the best transition blowing agent on a path leading to the total phaseout of all ozone depleting substances with emphasis on improved energy efficiency. These HCFC conversions were considered interim solutions until energy-efficient zero ODS options could be developed and implemented.
The SNAP list of approved replacements considers all CFC and HCFC alternatives relative to their ozone depletion, toxicity, flammability, energy efficiency, and global warming potential, among other factors. Under the Clean Air Act regulations, HCFC-141b can no longer be produced for use in the U.S. after Jan. 1, 2003.
Anticipation of this phaseout date led to intensive industry research to investigate alternatives. AHAM's Appliance Research Consortium (ARC) has funded several projects to investigate alternatives. The leading alternatives that have been identified include HFC-245fa, HFC-134a, and cyclopentane, which is a hydrocarbon (HC).
Cyclopentane and isopentane/cyclopentane blends are being used extensively in many parts of the world, but due to the flammability and volatile organic compound (VOC) concerns associated with the use of HCs in the U.S., the best alternatives for production in the U.S. were determined to be HFCs. HFCs have zero ozone depleting potential, but have higher global warming potential (GWP).
Investigation of the three leading alternatives to HCFC-141b led to the following general characterization of each:
Cyclopentane blown foams:
- Have the lowest foam material cost impact
- Require high capital cost for safety
in foam process equipment
- Increase refrigerator energy usage by about
6-10 percent versus HCFC-141b
- Are difficult and expensive to implement
in locations with VOC restrictions
HFC-134a blown foams:
- Have the next lowest foam material cost impact
- Require high pressure rated metering
and mixing equipment
- Increase refrigerator energy usage by 8-10 percent
HFC-245fa blown foams:
- Have the highest foam material cost impact
- Increase refrigerator energy usage
by 0-2 percent
- Require some revision to existing foam equipment
- Offer the best retention of
insulating characteristics over time
Even though HFCs have relatively high GWP, it has been shown that HFC-245fa has the lowest Total Environmental Warming Impact (TEWI), which is a measure of its contribution to global warming. The TEWI accounts for global warming due to both the direct greenhouse gas emissions from the product and the indirect greenhouse gas emissions from the power plant associated with the energy consumption of the product. The indirect effect accounts for more than 90 percent of the total warming impact from refrigerators in the U.S., which is dominated by power generation from fossil fuels.
HFC-245fa has the best TEWI of the three alternatives because of its better insulating/efficiency characteristics, which minimizes its indirect effect to global warming. In addition, ARC-sponsored research (in conjunction with the EPA) at the Technical University of Denmark has shown that most of the blowing agent remains in the foam even after it is shredded at end of life when refrigerator-freezers are decomissioned. This reduces the direct effect of the blowing agent since most of the chemical is not immediately emitted to the atmosphere. Additional research is currently being conducted to determine what happens to the foam blowing agent when it is buried in a landfill.
Research has also been sponsored by ARC, in conjunction with the Department of Energy, at Oak Ridge National Laboratories to investigate the aging characteristics of foam. The research shows that HFC-245fa retains its thermal conductivity better than the other alternatives, including HCFC-141b.
Most of the U.S. appliance industry will convert to an HFC blowing agent this year. The majority of the conversions will be to HFC-245fa, although at least one major manufacturer has converted to HFC-134a. In addition, some units will be built out of the U.S. using cyclopentane and exported to the U.S.
No manufacturers have announced plans to produce refrigerator-freezers using HCs within the U.S. Process safety and environmental regulatory issues will need to be resolved before hydrocarbon blowing agents can be implemented in the U.S. appliance plant locations, and plant layout are major factors to be considered for existing plants. Some European countries are trying to phase out the use of HFCs altogether, in favor of HCs. However, the U.S. feels it is important that the use of HFCs be retained as an option for the reasons discussed above.
In a joint announcement, the U.S. EPA, the United Nations Environment Program (UNEP), and the Alliance for Responsible Atmospheric Policy (ARAP) have announced responsible use principles for HFCs. The principles include: select HFCs for applications where they provide safety, environmental, technical, economic, or unique societal benefits; minimize HFC emissions to the lowest practical level during chemical manufacture and during use and disposal of equipment using cost-effective technology; engineer, operate, and maintain HFC-using systems to minimize emissions and maximize energy efficiency; and recover, recycle, reclaim and/or destroy used HFCs where technically and economically feasible.
AHAM supports the above Responsible Use Principles and is a member of ARAP. As long as HFCs are used responsibly, their use should be retained as an option worldwide. Continued improvement in energy efficiency is expected for HFCs as formulations and foam flow are optimized. In the future, we can expect to see more blowing agent blends developed to optimize cost and energy efficiency.
This whole transition away from CFCs and HCFCs will be essentially transparent to consumers. Refrigerator-freezers will continue to offer excellent quality, reliability, and value, while retaining all desired features. Household refrigerator-freezers consume less than 2 percent of all the energy consumed in the U.S. Nonetheless, manufacturers are committed to further reducing the energy and environmental impact of these appliances.
is the vice president of Engineering Services at the Association
of Home Appliance Manufacturers (AHAM).