Energy Efficiency

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ENERGY EFFICIENCY provides an immediate answer to an energy crisis because it can significantly reduce energy consumption, which further decreases greenhouse gas emissions. For example, during the first energy crisis during the 1970s, popular energy-efficiency measures included fuel-efficient cars and well-insulated buildings. With climate change considerations, the technological solutions to improve energy efficiency are much more diverse and more widely supported than the solutions from the end of the 20th century. To evaluate the performance of energy-efficient devices, products, and engineeringsystem solutions, an index called energy efficiency can be used. The definition of energy efficiency as an index depends on the thermodynamic system under consideration. In general, energy efficiency is defined as a desired output divided by a required input, and it represents a ratio of energy or work output to energy or work input for a particular ther-modynamic system.

For systems that convert energy or work from one form to another, the values of energy efficiency are between zero and one. The maximum value is one, because the useful output cannot be larger than the costly input according to the First Law of Thermodynamics. For heat pumps that are transferring energy between outdoor and indoor environments, the efficiency is called Coefficient of Performance (COP) and can be larger than one. Adoption of energy efficient devices in households is enabled by the U.S. Energy Star and the European Union Energy Label to distinguish devices that produce more useful output for the same input as devices without these certifications. These marketing efforts are aimed at the faster adoption of energy-efficient technologies. Even though energy-effi cient technological improvements are welcomed, they are not always adopted in the marketplace because of associated costs. In general, energy-efficient products cost more, but over their lifetime, they save energy and make their up-front investment worthwhile. This phenomenon is called the energy-efficiency gap, and can significantly slow or prevent adoption of these innovations. This gap can be bridged with appropriate government policies and economic incentives to stimulate technology invention, innovation, diffusion, and use of energy-efficient technologies.

SEE ALSO: Policy, International; Policy, U.S.; Technology.

BIBLIOGRAPHY. Frank Kreith and D. Yogi, Goswami Handbook of Energy Efficiency and Renewable Energy (CRC, 2007); G.G. Rajan, Optimizing Energy Efficiencies in Industry (McGraw-Hill Professional, 2002); U.S. Department of Energy Efficiency and Renewable Energy Web site, www. eere.energy.gov.

Jelena Srebric Pennsylvania State University

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