Energy Efficiency
The utilization of energy for human purposes is a defining characteristic of industrial society. The conversion of energy from one form to another and the efficient production of mechanical work for heat energy has been studied and improved for centuries. The science of thermodynamics deals with the relationship between heat and work and is based on two fundamental laws of nature, the first and second laws of thermodynamics. The utilization of energy and the conservation of critical, nonrenewable energy resources are controlled by these laws and the technological improvements in the design of energy systems.
The First Law of Thermodynamics states the principle of conservation of energy: energy can be neither created nor destroyed by ordinary chemical or physical means, but it can be converted from one form to another. Stated another way, in a closed system, the total amount of energy is constant. An interesting example of energy conversion is the incandescent light bulb. In the incandescent light bulb, electrical energy is used to heat a wire (the bulb filament) until it is hot enough to glow. The bulb works satisfactorily except that the great majority (95%) of the electrical energy supplied to the bulb is converted to heat rather than light. The incandescent bulb is not very efficient as a source of light. In contrast, a fluorescent bulb uses electrical energy to excite atoms in a gas, causing them to give off light in the process at least four times more efficiently than the incandescent bulb. Both light sources, however, conform to the First Law in that no energy is lost and the total amount of heat and light energy produced is equal to the amount of electrical energy flowing to the bulb.
The Second Law of Thermodynamics states that whenever heat is used to do work, some heat is lost to the surrounding environment. The complete conversion of heat into work is not possible. This is not the result of inefficient engineering design or implementation but, rather, a fundamental and theoretical thermodynamic limitation. The maximum, theoretically possible efficiency for converting heat into work depends solely on the operating temperatures of the heat engine and is given by the equations: E = 1 - T2/T1. T1 is the absolute temperature at which heat energy is supplied and T2 is the absolute temperature at which heat energy is exhausted.
The maximum possible thermodynamic efficiency of a four-cycle internal combustion engine is about 54%; for a diesel engine, the limit is about 56%; and for a steam engine, the limit is about 32%. The actual efficiency of real engines, which suffer from mechanical inefficiencies and parasitic losses (eg. friction, drag, etc.) is significantly lower than these levels. Although thermodynamic principles limit maximum efficiency, substantial improvements in energy utilization can be obtained through further development of existing equipment such as power plants, refrigerators, and automobiles and the development of new energy sources such as solar and geothermal.
Experts have estimated the efficiency of other common energy systems. The most efficient of these appear to be electric power generating plants (33% efficient) and steel plants (23% efficient). Among the least efficient systems are those for heating water (1.5–3%), for heating homes and buildings (2.5–9%), and refrigeration and air-conditioning systems (4–5%). It has been estimated that about 85% of the energy available in the United States is lost due to inefficiency.
The predominance of low efficiency systems reflects the fact that such systems were invented and developed when energy costs were low and there was little customer demand for energy efficiency. It made more sense then to build appliances that were inexpensive rather than efficient because the cost to operate them was so low. Since the 1973 oil embargo by the Organization of Petroleum Exporting Countries (OPEC), that philosophy has been carefully reexamined. Experts began to point out that more expensive appliances could be designed and built if they were also more efficient. The additional cost to the manufacturer, industry and homeowner could usually be recovered within a few years because of the savings in fuel costs.
The concept of energy efficiency suggests a new way of looking at energy systems and that is the examination of the total lifetime energy use and cost of the system. Consider the common light bulb. The total cost of using a light bulb includes both its initial price and the cost of operating it throughout its lifetime. When energy was cheap, this second factor was small. There was little motivation to make a bulb that was more efficient when the life-cycle savings for its operation was minimal.
But as the cost of energy rises, that argument no longer holds true. An inefficient light bulb costs more and more to operate as the cost of electricity rises. Eventually, it makes sense to invent and produce more efficient light bulbs. Even if these bulbs cost more to buy, they pay back that cost in long-term operating savings.
Thus, consumers might balk at spending $25 for a fluorescent light bulb unless they knew that the bulb would last ten times as long as an incandescent bulb that costs $3.75. Similar arguments can and have been used to justify the higher initial cost of energy-saving refrigerators, solar-heating systems, household insulation, improved internal combustion engines and other energy-efficient systems and appliances.
Governmental agencies, utilities, and industries are gradually beginning to appreciate the importance of increasing energy efficiency. The 1990 amendments to the Clean Air Act encourage industries and utilities to adopt more efficient equipment and procedures. Certain leaders in the energy field, such as Pacific Gas and Electric and Southern California Edison have already implemented significant energy efficiency programs.
Resources
Books
Miller, G. T., Jr. Energy and Environment: The Four Energy Crises. 2nd edition. Belmont, CA: Wadsworth Publishing Company, 1980.
Sears, F. W. and M. W. Zemansky. University Physics. 2nd edition. Reading, MA: Addison-Wesley Publishing, 1957.
Other
Council on Environmental Quality. Environmental Quality, 21st annual report. Washington, DC: U. S. Government Printing Office, 1990.
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