In 1991, the manufacturing sector, on average, consumed more energy per value of shipments than in either 1988 or 1985, showing an increase in purchased energy intensity of four percent from 1988 to 1991. This increased energy requirement is a function of a myriad of internal and external factors. Among the numerous internal factors that could influence energy intensity are changes in manufacturers' internal mix of products produced during these years, and changes in the technologies and processes used to produce them. Economic conditions represent one of the most influential external factors. At one time, cost control had been cited as one of the most common business incentives for investing in projects to manage energy usage. Now however, this stimulus has been lessened due to the steady decline in energy prices (Figure ES1), the end of the 1991 Persian Gulf War, and the continuing weakness of the Organization of Petroleum Exporting Countries (OPEC).
Changes in Energy Intensity in the Manufacturing Sector, 1985-1991 presents statistics about changes in energy consumption per constant dollar of value of shipments. The report is based on the 1991 Manufacturing Energy Consumption Survey (MECS), and is the third publication associated with that survey. The 1991 MECS is the third survey conducted, with earlier surveys gathering information on 1985 and 1988 energy consumption patterns. The information in this report continues the data series on changes in energy intensity based on information collected by the two earlier surveys.
Past manufacturing surveys did not collect information relating to the potential causes of changes in energy efficiency. The 1991 survey, however, provides a cross-sectional view of the energy-management activities and general technologies in existence at manufacturing establishments, and it estimates the effects of changes in product mix (structural shift). With the completion of the 1994 survey, trends relating those factors to energy efficiency may begin to be revealed.
In this report, energy intensity is defined as the ratio of energy consumption per unit of output. Output is measured as the constant dollar of value of shipments and receipts, and two measures of energy consumption are presented in British thermal units (Btu): Offsite-Produced Energy and Total Inputs of Energy. A decrease in energy intensity from one period to another suggests an increase in energy efficiency, and vice versa.
Energy efficiency can be defined and measured in various ways. Certain concepts of energy efficiency, especially those limited to equipment efficiencies, cannot be measured over time using changes in energy-intensity ratios. While improved energy efficiency will tend to reduce energy intensity, it is also true that a change in energy intensity can be due to factors unrelated to energy efficiency. For this report, energy intensity is used as a surrogate measure for energy efficiency, based on industry knowledge and current methodological analyses.
Data for the MECS were collected on an establishment-by-establishment basis and reported based on the Standard Industry Classification (SIC) system. For more information on SIC, see Chapter 2.
