Energy efficiency refers to any process by which the amount of useful energy obtained from some process is increased compared to the amount of energy put into that process. As a simple example, some automobiles can travel 40 mi (17 km) by burning a single gallon (liter) of gasoline, while others can travel only 20 mpg (8.5 km/l). The energy efficiency achieved by the first car is twice that achieved by the second car. In general, energy efficiency is measured in units such as mpg, lumens per watt, or some similar “output per input” unit.
History of energy concerns
Interest in energy efficiency is relatively new in the history of modern societies, although England’s eighteenth century search for coal was prompted by the de- cline of the country’s forest resources. For most of the past century, however, energy resources seemed to be infinite, for all practical purposes. Little concern was expressed about the danger of exhausting the world’s supplies of coal, oil, and natural gas, its major energy resources.
The turning point in that attitude came in the 1970s when the major oil-producing nations of the world suddenly placed severe limits on the amounts of petroleum that they shipped to the rest of the world. This oil embargo forced major oil users such as the United States, Japan, and the nations of Western Europe to face for the first time the danger of having insufficient petroleum products to meet their basic energy needs. Use of energy resources suddenly became a matter of national and international discussion.
Energy efficiency can be accomplished in a number of different ways. One of the most obvious is conservation; that is, simply using energy resources more careful- ly. For example, people might be encouraged to turn out lights in their home, to set their thermostats at lower temperatures, and to use bicycles rather than automobiles for transportation. Energy efficiency in today’s world also means more complex and sophisticated approaches to the way in which energy is used in industrial, commercial, and residential settings.
Energy efficiency in buildings
Approximately one-third of all the energy used in the United States goes to heat, cool, and light buildings. A number of technologies have been developed that im- prove the efficiency with which energy is used in buildings. Some of these changes are simple; higher grades of insulation are used in construction, and air leaks are plugged. Both of these changes reduce the amount of heated or air-conditioned air (depending on the season) lost from the building to the outside environment.
Other improvements involve the development of more efficient appliances and construction products. For example, the typical gas furnace in use in residential and commercial buildings in the 1970s was about 63% efficient. Today, gas furnaces with efficiencies of 97% are readily available and affordable. Double-glazed windows with improved insulating properties have also been developed. Such windows can save more than 10% of the energy lost by a building in a year.
Buildings can also be designed to save energy. For example, they can be oriented on a lot to take advantage of solar heating or cooling. Many commercial structures also have computerized systems that automatically ad- just heating and cooling schedules to provide a comfort- able environment for occupants only when and in portions of the building that are occupied.
Entirely new technologies can be used also. For example, many buildings now depend exclusively on more efficient fluorescent lighting systems than on less efficient incandescent lights. In some situations, this single change can produce a greater savings in energy use than any other modification. The increasing use of solar cells is another example of a new kind of technology that has the potential for making room and water heating much more efficient.
About one-third more of the energy used in the United States goes to moving people and goods from place to place. For more than two decades, governments have made serious efforts to convince people that they should use more energy-efficient means of transportation, such as bicycles or some form of mass transit (buses, trolleys, subways, light-rail systems, etc.). These efforts have had only limited success.
Another approach that has been more successful has been to encourage car manufacturers to increase the efficiency of automobile engines. In the 1970s, the average fuel efficiency of cars in the United States was 13 mpg
(5.5 km/l). Over the next decade, efficiency improved nearly twice over to 25 mpg (10.6 km/l). In other nations, similar improvements were made. Cars in Japan, for example, increased from an average efficiency of 23 mpg (9.8 km/l) in 1973 to 30 mpg (12.8 km/l) in 1985.
Yet, even more efficient automotive engines appear to be possible. Many authorities believe that efficiencies approaching 50 mpg (21 km/l) should be possible by the year 2001. As of 1987, at least three cars with fuel efficiencies of more than 50 mpg (21 km/l) were already in production (the Ford Escort, Honda City, and Suzuki Sprint). Experimental cars with efficiencies close to 100 mpg (42.5 km/l) were also being tested; the Toyota AXV has achieved 98 mpg (41.7 km/l) on test tracks, and the Renault VESTA has logged 124 mpg (52.7 km/l).
To a large extent, automobile manufacturers have been slow to produce cars that have the maximum possible efficiencies because they question whether consumers will pay higher purchase prices for these cars. Improvements continue to be made, however, at least partly because of the legislative pressure for progress in this direction.
Energy efficiency in industry
The final third of energy use in the United States occurs in a large variety of industrial operations such as producing steam, heating plants, and generating electric- ity for various operations. Improvements in the efficiency with which energy is used in industry also depends on two principal approaches: the development of more efficient devices and the invention of new kinds of technologies. More efficient motors are now available so that the same amount of work can be accomplished with a smaller amount of energy input. And, as an example of the use of new technologies, laser beam systems that can both heat and cut more efficiently than traditional tools are being given new applications. Industries are also finding ways to use computer systems to design and carry out functions within a plant more efficiently than traditional resource management methods.
One of the most successful approaches to improving energy efficiency in industry has been the development of cogeneration systems. Cogeneration refers to the process in which heat produced in an industrial operation (formerly regarded as “waste heat”) is used to generate electricity. The plant saves money through cogeneration because it does not have to buy electrical power from local utilities.
Other techniques for increasing energy efficiency
Many other approaches are available for increasing the efficiency with which energy is used in a society. Recycling has become much more popular in the United States over the past few decades at least partly because it provides a way of salvaging valuable resources such as glass, aluminum, and paper. Recycling is also an energy efficient practice because it reduces the cost of producing new products from raw materials. Another approach to energy efficiency is to make use of packaging materials that are produced with less energy. The debate still continues over whether paper or plastic bags are more energy efficient, but at least the debate indicates that people are increasingly aware of the choices that can be made about packaging materials.
Government policies and regulations
Most governmental bodies were relatively unconcerned about energy efficiency issues until the OPEC (Organization of Oil Exporting Countries) oil embargo of 1973-74. Following that event, however, they began to search for ways of encouraging corporations and private consumers to use energy more efficiently. One of the first of many laws that appeared over the next decade was the Energy Policy and Conservation Act of 1975. Among the provisions of that act were: a requirement that new appliances carry labels indicating the amount of energy they use, the creation of a federal technical and financial assistance program for energy conservation plans, and the establishment of the State Energy Conservation Program. A year later, the Energy Conservation and Production Act of 1976 provided for the development of national mandatory Building Energy Performance Standards and the creation of the Weatherization Assistance Program to fund energy-saving retrofits for low-income households. Both of these laws were later amended and updated.
In 1991, the U.S. Environmental Protection Agency (EPA) established two voluntary programs to prevent pollution and reduce energy costs. The Green Lights Partnership provided assistance in installing energy-efficient lighting, and the Energy Star Buildings Partnership used Green Lights as its first of five stages to improve all aspects of building efficiency. The World Trade Center and the Empire State Building in New York City and the Sears Tower in Chicago (four of the world’s tallest structures) joined the Energy Star Buildings Partnership as charter members and have reduced their energy costs by millions of dollars. The EPA also developed software with energy management aids for building operators who enlist in the partnership. By 1998, participating businesses had reduced their lighting costs by 40%, and whole- building upgrades had been completed in over 2.8 billion ft2 (0.3 billion m2) of building space. The EPA’s environ- mental interest in the success of these programs comes not only from conserving resources but from limiting carbon dioxide emissions that result from energizing industrial plants and commercial buildings and that cause changes in the world’s climate.