Fears about warming the globe may change the way we chill our foods. Concern about global warming, as expressed in the President's Climate Change Action Plan of 1993, is the latest motivation for
putting future American refrigerators and freezers on a strict energy diet. A
current national goal is to design an environmentally sound
refrigerator-freezer by 1998 that uses half as much energy as 1993 models.
Interest in designing a more energy-efficient refrigerator is not new. It first
became a goal almost 20 years ago. In the 1970s, the United States was relying
on increasingly unstable supplies of imported oil for fuel, and energy prices
began to rise. Utilities balked at building additional power plants because of
rising costs and investment risks. As a result, a premium was placed on
developing energy-efficient appliances, culminating in the passage of the
National Appliance Energy Conservation Act of 1987. In the late 1980s,
refrigerator design was again a target of engineers because of the need to
change the refrigerant and insulation used. The reason: the Montreal Protocol
called for the phasing out of substances containing chlorofluorocarbons (CFCs)
by the year 2000 because they were thought to be destroying the earth's
stratospheric ozone layer. Ozone shields humans from solar rays that can cause
skin cancer and cataracts. Among the CFCs to be phased out are common
refrigerants like R-12 and the refrigerator insulation blowing agent R-11.
Today, the ozone-friendly refrigerant R-134a has been designated to replace
CFC-containing refrigerants in new refrigerators because of its lack of
chlorine, the main chemical element causing ozone depletion. However, it may become a target for future phaseout because it contributes to global
warming, although much less so than CFCs. In that event, its likely replacement
will be a hydrocarbon such as isobutane or propane. These natural refrigerants
will have to be "engineered around" in a new refrigerator design because they
are flammable. Thus, their widespread use may slow global warming but raise the
risk of house fires.
Brooks Lunger, a guest user at ORNL's Buildings Technology Center from DuPont,
checks instrumentation on test refrigerators.
The goal of the Department of Energy's Refrigeration Systems Program, in which ORNL's Buildings Technology Center (BTC) plays a large role, is to develop and market advanced refrigeration systems to reduce the projected energy consumption in U.S. buildings by 10% in 2010. There are several reasons for the current energy reduction goal. They include saving money, reducing reliance on imported oil, and helping utilities avoid risky capital investments in new power plants to meet escalating demands for electricity during certain times of day.
The most compelling reason to curb demand for electricity is to slow global
warming. Fossil fuels used for electricity production are a large source of
atmospheric carbon dioxide, a greenhouse gas that may alter the climate. Energy
use in buildings accounts for 36% of carbon dioxide emissions produced in the
United States, suggesting that buildings may have a significant impact on
outdoor as well as indoor environments.
Among the researchers who have led the more recent developments in BTC's $1-million-a-year refrigeration research program are Van Baxter, Phil Fairchild, Steve Fischer, Patrick Hughes, Keith Rice, Jim Sand, John Tomlinson, and Ed Vineyard, all of the Energy Division, and Tom Kollie, Ron Graves, and Ken Wilkes, all of the Metals and Ceramics Division. Several of these researchers have been influential in their fields.
In three of the past five years, Sand and Vineyard have won American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) technical paper awards; the award recognizes the best papers presented at the annual meetings of the international organization. Vineyard has participated on technical panels for ASHRAE, the Super Efficient Refrigerator Program of the Consortium for Energy Efficiency, the Association of Home Appliance Manufacturers (AHAM), and the United Nations Environment Programme (which in 1991 and 1994 produced Technical Progress on Protecting the Ozone Layer, to which he contributed a chapter). Sand is a member of an advisory committee for the Materials Compatibility and Lubricant Research program of the Air-Conditioning and Refrigeration Institute (ARI), which sponsors research aimed at solving the equipment problems resulting from the use of alternative refrigerants. He also was a panelist for a February 10, 1994, video conference on CFC refrigerant recovery and replacement, which was broadcast by satellite to a wide regional audience in the Southeast.
Baxter was the recipient of ASHRAE's 1982 Willis H. Carrier Award. Fairchild, who helped establish ORNL's research program on CFC alternative refrigerants, is an adviser to ARI's Research and Technology Committee; in 1987 he gave testimony at U.S. Senate Joint Subcommittee Hearings on Stratospheric Ozone Protection and Substitutes for Ozone-Depleting Chemicals. These and other ORNL researchers have also helped steer the refrigeration industry in a new direction through their work as influential members of ASHRAE's Refrigeration Technical Advisory Committee.
In one project, ORNL engineers worked with engineers from Amana, a refrigerator manufacturer, to develop a more efficient refrigerator-freezer. To help them, they used a computer model of a refrigerator developed in 1977 by Arthur D. Little, Inc., under an ORNL subcontract. Amana performed field tests of different models of refrigerators to determine which ones were most efficient. ORNL provided technical guidance and expertise for all this work.
The engineers focused on vapor-compression refrigeration. In this device, a refrigerant under low pressure is evaporated in a coiled pipe called an evaporator. To get energy to evaporate, the refrigerant pulls heat away from the refrigerator compartment, chilling it to the desired temperature. A compressor draws away the evaporated refrigerant, compresses the vapor, and passes it to a condenser, where it gives off the heat it had absorbed to the kitchen air. The increased pressure and loss of heat forces the refrigerant to condense into a liquid. The liquid refrigerant is expanded to the lower pressure, reducing its temperature, and then is returned to the evaporator. Throughout these cycles, a thermostat regulates the temperature inside the refrigerator by switching the compressor on and off.
To design a more efficient refrigerator, Amana and ORNL engineers decided to increase the insulation thickness in the refrigerator's walls from 1/2 inch to 2 inches, install an anti-sweat switch, move the fan to a better location, improve compressor efficiency, and increase heat exchanger areas. They elected to have two evaporators instead of one—one evaporator for maintaining freezer temperature at 0-5°F and the other for holding the refrigerator at 40°F for fresh food. Because electric heaters are used for defrosting, they decided to save additional energy by setting the refrigerator-freezer for automatic defrost every 4 days instead of every 18 hours.
The collaborating engineers showed that refrigerator efficiency could be increased by these changes. Although these changes would raise the cost of the appliance, they argued that the difference could be made up by reduced long-term operational costs through decreased use of electricity.
Amana built and sold a more efficient refrigerator that incorporated these
changes. "Its major features were a delayed defrost, increased insulation, and
a dual evaporator," says Sand. "But it was on the market for only a few years
because it had some moisture problems in the fresh food compartment."
In a November 17, 1994, letter to DOE officials, Tom Wilbanks, corporate fellow in ORNL's Energy Division, wrote: "Quite clearly, the ADEPT project is viewed as a major success in India—a model of bilateral cooperation. Besides leading to a new joint venture between Amana and Voltas, it is credited with encouraging Whirlpool's entry into the Indian market (purchasing Frigidaire's share in Kelvinator-India). The results of ORNL's tests of five Indian home refrigerators have led directly to a decision by the Bureau of Indian Standards to [tighten] the voluntary efficiency standard for Indian refrigerators. . . . In addition, the Indian Institute of Technology (IIT) has added an environmental chamber to its refrigeration R&D lab as a direct result of [an IIT professor's] participation in the April 1994 workshop in Oak Ridge and his observation of ORNL's testing approaches."
A related project in the late 1970s that was an unusually big success was
the development of a more efficient refrigerator compressor by engineers from
industry. ORNL was technical monitor for this project with Columbus Products,
which later became White Westinghouse and then Americold Compressor Company. In
1981, the subcontractor, by incorporating design changes to the motor, suction
muffler, and compressor valve assembly, developed a compressor that uses 44%
less energy than conventional units of the same size. The compressor is part of
product lines of Americold Compressor and Frigidaire. This compressor
technology has helped reduce annual refrigerator energy use from 1500 kilowatt
hours (kwh) to 900 kwh per year in 1990. Between 1980 and 1990, according to
DOE, the energy-efficient refrigerator compressors saved U.S. consumers
$6 billion in energy costs. The more efficient compressor is one of three
achievements cited as "notable successes" in DOE's 1991 Refrigeration Systems
Program Summary report, and it was recently awarded a DOE Pioneer Award.
An improved microprocessor controller that modulates the compressor capacity to meet changing refrigeration loads accounted for about half of the efficiency gain. The remaining improvement came from further refinements developed by manufacturers sponsored by the Electric Power Research Institute. In addition to cost savings, the reduced energy consumption by supermarkets avoided the emission of almost 10 million metric tons of carbon.
During this time, DOE's Roof Research Facility at ORNL was dedicated as a national user facility to help industry develop longer-lasting energy-efficient roofs. Soon after, this facility became concerned with developing and testing CFC-free roof insulations. It added a room with apparatus for evaluating the energy performance of CFC-free insulations and CFC-free refrigerants for refrigerators, air conditioners, and heat pumps.
Ed Vineyard checks instrument readings during a test of chlorine-free
refrigerant mixtures and alternatives to the coolant HCFC-22.
In 1993, the user facility was renamed the Buildings Technology Center. Researchers from industry used this center not only for roof research but also for development of more-efficient appliances. Just as ORNL's early refrigeration researchers had collaborated with industrial firms through subcontracts, the Laboratory's current researchers became involved with the refrigeration industry through collaborative agreements and CRADAs. The focus of these agreements has been energy-efficient, environmentally acceptable refrigerators and other refrigeration equipment.
The problem is that CFCs contribute not only to ozone depletion but also to
global warming. In fact, their contribution to global warming is second only to
that of carbon dioxide, which accounts for 80% of greenhouse gas emissions in
the United States. However, replacing CFCs with ozone-friendly compounds such
as hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) would still
affect global warming. HCFCs and HFCs are also greenhouse gases, but their
direct impact on global warming is much smaller than that of CFCs. However,
widespread use of some CFC alternatives in refrigeration systems would result
in larger consumption of electricity from fossil fuel plants. Thus, emissions
of carbon dioxide would increase, speeding up global warming. Clearly, the
substitute refrigerants would have an indirect impact (energy-related) as well
as a direct impact (emission-related) on global warming. The combined effect is
called the total equivalent warming impact (TEWI).
Under the CRADA, ORNL evaluated the relative performance, subsequent carbon
dioxide emissions, and net global climate change potential of CFC alternatives
in building energy-related applications. ORNL investigated alternative
refrigerants; insulation materials and systems; and advanced refrigeration,
air-conditioning, and heating technologies. Consortium members contributed
technical expertise on refrigerant alternatives. The CRADA was extended and a
second report was issued in December 1994. The extension focused on
investigating several alternative technologies to fluorocarbon-based
vapor-compression refrigeration.
The ORNL researchers had tested numerous alternative refrigerants supplied by DuPont and Pennwalt using the Laboratory's Alternative Refrigerants Calorimeter Facility. In examining each refrigerant, they measured its energy performance (the electrical energy required to operate the appliance using the refrigerant) and its refrigeration capacity (the ability of the fluid to absorb heat—a measure of the cooling output). The ratio of the refrigeration capacity to the electrical energy input is the coefficient of performance (COP). The alternative refrigerants that have the highest COPs were considered the best candidates for future refrigerators.
Charlie Hardin (now retired) sets up a breadboard refrigeration loop to test heat transfer performance of zeotropic mixture alternatives to HCFC-22.
Vineyard, Sand, and others have used a computer model of a detailed refrigerator system to evaluate the energy savings for several design modifications of a refrigerator using an alternative refrigerant such as HFC R-134a. The design options included use of a more efficient compressor, increased evaporator and condenser size, door gaskets to reduce energy losses, improved cabinet and door insulation, and high-efficiency fan motors. Laboratory refrigerator prototypes were built and tested to verify the model's analytical results experimentally. The modeled and experimental results were generally in agreement. The differences observed guided the researchers in improving the model.
Partly as a result of the influence of ORNL researchers Sand and Vineyard on AHAM's Refrigeration Technical Advisory Committee, the refrigeration industry adopted R-134a as the refrigerant of the future.
"Just as you must switch from an internal combustion engine to a diesel engine if you want to use diesel fuel instead of gasoline," Sand says, "we found that the refrigerator design had to be changed to use R-134a as a refrigerant."
"It is not easy to change from a refrigerant used for 40 years," Vineyard says. "To use 134a, the refrigerator had to be redesigned in a short time because after 1995 it will be illegal to build a refrigerator that uses only R-12 because this refrigerant will be phased out."
"We faced several complications in the rush to redesign the refrigerator for the new refrigerant," Sand says. "For example, we learned that the conventionally used lubricating oil is not compatible with 134a. So we tried a different oil. But we found out that this oil dissolves insulation for the compressor motor, causing it to burn out. So we tried a different oil, but it plugged up the expansion valve. As you can see, the ripple effect of one change necessitates a cascade of changes that jacks up the cost of the refrigerator."
Because of these problems, DOE and the Air-Conditioning and Refrigeration Technology Institute are jointly funding research to determine the compatibility of structural materials and lubricants with refrigerants being considered as replacements for restricted CFC compounds.
"Some environmentalists complain that the refrigeration industry is slow to manufacture environmentally sound refrigerators," Sand says, "but the reason for the delay is that it takes time to develop and test a system that accommodates a change in refrigerants. If enough time is not taken to conduct tests, a financial disaster could occur. Recently, a leading manufacturer of refrigerators lost almost a billion dollars replacing damaged refrigerators. For these new models, the company had decided to use a new compressor design. But the new compressors failed in consumers' homes after a few weeks of operation, so the company lost a considerable amount of money."
HFCs such as R-134a have been favored over CFCs because they are less of a threat to the ozone layer. However, HFCs have since fallen into disfavor in some quarters because they are greenhouse gases that have long atmospheric lifetimes. R-134a absorbs infrared radiation emitted by the earth's surface in the spectrum not absorbed by other gases.
"The ultimate refrigerant of the future," Sand says, "could be hydrocarbons
like isobutane or propane if HFCs fall victim to global warming concerns.
Hydrocarbons are 4 to 5% more efficient than R-12, they don't destroy the ozone
layer, and they don't contribute to global warming. Isobutane is a propellant
used to replace CFCs in spray cans, and propane is found in crude petroleum and
natural gas. European refrigerator manufacturers are now switching to
hydrocarbons."
Two types of vacuum insulation being developed and tested at ORNL are powder evacuated panels (PEPs) and an insulation that contains fibrous glass. Because the insulating value of these materials is several times greater than current refrigerator insulation, they could save $10 to $20 a year in electricity per unit. But vacuum insulations are more costly than foam insulation.
In vacuum insulations, powder or fiber is sealed in evacuated envelopes. "Vacuum insulations," says Wilkes, "are like boxes of coffee grounds packed in vacuum except the grounds are insulating powders or fibers and the packages are made of plastic or steel sheets."
In 1981 Arthur D. Little, Inc., and ORNL looked into developing vacuum insulations for refrigerators, ovens, and mobile homes to improve energy efficiency. At ORNL, David McElroy made laboratory measurements of properties and performance of materials in vacuum insulations. He determined the insulating value of the fine powders and the ability of evacuated envelopes of different materials to support the load of the atmosphere without collapsing.
For vacuum insulations, durability is a key issue. If they are not durable, they develop holes and air leaks in, destroying the vacuum. In addition, air molecules can diffuse through plastic envelopes, even if they have no holes. In some Japanese refrigerators, vacuum insulations have been known to lose their vacuum in a year. They must be made durable for 15 to 20 years, the expected lifetime of refrigerators.
Evacuated panels contain fibrous glass or ceramic or metallic powders. Vacuum insulation jackets are made of plastic sheets or steel foils. They will be embedded in foam in the refrigerator door and wall. From the outside in, the refrigerator of the future may consist of a steel skin, vacuum insulation panels about 1 inch thick, about 1 to 2 inches of insulating foam blown with a non-ozone-depleting chemical instead of a chlorine-containing agent, and a plastic inner wall. The foam will give the steel wall structural rigidity.
Currently, ORNL researchers are evaluating vacuum insulations under CRADAs with PPG, Aladdin Industries, DuPont, VacuPanel, and the AHAM, which represents all major refrigerator manufacturers ranging from Amana to General Electric to Whirlpool. The goal of the research is to develop fillers and vacuum envelopes that offer increased thermal resistivity and longer lifetimes while decreasing cost.
The refrigerator firms have proposed changes and sent their best components and improved versions to ORNL for testing. ORNL tests units containing the best components from the different companies. ORNL then gives participants test results and suggests changes to further improve component and refrigerator design.
A new CRADA is being negotiated between ORNL and an undisclosed large refrigerator manufacturer. The goal is to develop the most energy-efficient unit using advanced door gaskets (with better seals to reduce energy losses), improved defrost, advanced insulation, and a different evaporator-compressor-condenser cycle.
Bill Miller inspects a facility for testing heat exchanger designs for advanced heat pump systems.
ORNL also manages a program for DOE that has guided industry in producing
more-efficient heating and cooling equipment. A new technology that doubles the
efficiency of gas heating—a gas-fired heat pump called the GAX system—has
been developed. ORNL engineers are working with a leading company and gas
utilities to market this technology (see the following article).
"DOE is focusing more on helping vendors sell their efficient appliances than on developing new ones," Sand says. "This is the softer side of DOE. It is selling the sizzle rather than the steak."
"The DOE sticker will be on future appliances to lend credibility to vendors' claims that energy savings from a product will eventually pay for its initial cost," Vineyard says. "Because DOE has name recognition and a reputation for energy expertise, appliance vendors want DOE's name on their efficient products to help them sell. DOE wants to help the vendors because it knows that convincing consumers to replace yesterday's inefficient appliances with today's more efficient ones will save energy."
The DOE sticker will also be useful to salesmen and customers. It will help them identify the high-efficiency appliances for which some electric utilities give rebates.
The refrigerator of the future will likely also bear a DOE sticker because
it will use half as much energy as today's refrigerator. Saving energy benefits
many groups. Consumers enjoy lower electricity bills and may use their savings
to buy other products, stimulating the economy. Commercial and industrial firms
using more-efficient refrigeration equipment may use their savings to hire more
workers. Electric utilities may be able to avoid building new power plants. The
nation has less of a need to rely on imported oil for electricity production.
And, environmentalists and policymakers have less concern that refrigerators
will contribute to thinning of the ozone layer and to global warming. In short,
the refrigerator of the future will be environmentally acceptable. It is hoped
that it will keep our food cold without making the globe too warm.
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