Over the past two decades, the sources of the site energy consumed in U.S. housing units changed (Figure 2.6a). Over that period, the percentage of site energy provided by electricity increased from 23 percent of all site energy consumed in 1978 to 35 percent in 1997. In contrast, the site energy provided by fuel oil/kerosene (some housing units use either fuel oil or kerosene; some use both) decreased from 21 percent in 1978 to 10 percent in 1997. The percentage of site energy provided by natural gas, 52 percent in 1997, and LPG, 4 percent in 1997, were statistically unchanged from the 1978 levels. Over the 1978-1997 period, the percentage of total primary energy provided by primary electricity increased from 48 percent of all energy consumed to 61 percent. In contrast, the percentage of primary energy provided by both natural gas and fuel oil/kerosene decreased. The percentage of total primary energy consumption of natural gas decreased from 36 percent in 1978 to 30 percent in 1997; the primary energy consumption of fuel oil/kerosene decreased from 14 percent in 1978 to 6 percent in 1997. The end-use consumption of site energy in U.S. housing units has also changed over the 1978-1997 period. The percentage of Btu consumed for space heating decreased and the Btu consumed in operating appliances increased (Figure 2.7). Energy consumption for space heating decreased from 66 percent of all site Btu in 1978 to 51 percent in 1997. Figure 2.7. Percent of Total U.S. Residential Site Energy Consumption by End Use, 1978, 1987, and 1997 Space Heating A/C Water Heating Appliances and Lighting * The difference between the 1978 and 1997 estimates is statistically significant at the 95-percent confidence level Sources Energy Information Administration, 1978, 1987 and 1997 Residential Energy Consumption Surveys Btu consumption for appliances and lighting increased from 17 percent of all site Btu in 1978 to 27 percent in 1997. Over the same 19-year period, the proportion of Btu consumed for cooling remained unchanged. The proportion of Btu consumed for water heating increased from 15 percent in 1978 to 19 percent in 1997. As noted earlier, site energy consumption per housing unit has decreased by 27 percent since 1978. In 1978, an average 138 million Btu were consumed; in 1997, an average 101 million Btu were consumed. Virtually all of that decrease was the result of a 44-percent decrease in site Btu consumption for space heating (Figure 2.8). In 1978, an average of 91 million Btu was consumed for space heating (66 percent of all the Btu consumed); in 1997, an average of 51 million Btu was consumed for space heating (51 percent of all the Btu consumed). • The difference between the 1978 and 1997 estimates is statistically significant at the 95-percent confidence level. Sources: Energy Information Administration; 1978, 1987, and 1997 Residential Energy Consumption Surveys. Energy Information Administration Primary and Site Energy Primary energy is the sum of the energy directly consumed by end users (site energy) and the energy consumed in the production and delivery of energy products. Electricity, of the major energy sources, has the greatest disparity between primary and site energy-a vastly greater amount of energy is used to generate and transmit electricity than to produce and distribute the other major sources. In 1997, steam-electricity utility plants, which were the largest source of electricity generation, were estimated to have used approximately 3.02 Btu of fossil-fuel energy to generate 1 Btu of electricity. Thus, in keeping with EIA policy, primary energy, as measured in this report, is the sum of site energy and electricity losses. The choice of expressing energy consumption data as site energy or primary energy (or site electricity or primary electricity, when that energy source alone is considered) depends on how the data are used. Site energy and site electricity reflect the amount actually consumed within the housing unit. Primary energy and primary electricity data are useful to policymakers, energy analysts, and others, who are concerned with environmental issues, such as carbon emissions from energy sources. The consumption data presented in previous RECS have been expressed as site energy and site electricity. Primary electricity data are presented in the tables in the Total Consumption section of the 1997 RECS Detailed Data Tables (Chapter 4 of this report). Energy Information Administration Over the past two decades, the sources of the site energy consumed in U.S. housing units changed (Figure 2.6a). Over that period, the percentage of site energy provided by electricity increased from 23 percent of all site energy consumed in 1978 to 35 percent in 1997. In contrast, the site energy provided by fuel oil/kerosene (some housing units use either fuel oil or kerosene; some use both) decreased from 21 percent in 1978 to 10 percent in 1997. The percentage of site energy provided by natural gas, 52 percent in 1997, and LPG, 4 percent in 1997, were statistically unchanged from the 1978 levels. Over the 1978-1997 period, the percentage of total primary energy provided by primary electricity increased from 48 percent of all energy consumed to 61 percent. In contrast, the percentage of primary energy provided by both natural gas and fuel oil/kerosene decreased. The percentage of total primary energy consumption of natural gas decreased from 36 percent in 1978 to 30 percent in 1997; the primary energy consumption of fuel oil/kerosene decreased from 14 percent in 1978 to 6 percent in 1997. The end-use consumption of site energy in U.S. housing units has also changed over the 1978-1997 period. The percentage of Btu consumed for space heating decreased and the Btu consumed in operating appliances increased (Figure 2.7). Energy consumption for space heating decreased from 66 percent of all site Btu in 1978 to 51 percent in 1997. Figure 2.7. Percent of Total U.S. Residential Site Energy Consumption by End Use, 1978, 1987, and 1997 Percent of Total Site Btu • The difference between the 1978 and 1997 estimates is statistically significant at the 95-percent confidence level. Sources: Energy Information Administration; 1978, 1987, and 1997 Residential Energy Consumption Surveys. As noted earlier, site energy consumption per housing unit has decreased by 27 percent since 1978. In 1978, an average 138 million Btu were consumed; in 1997, an average 101 million Btu were consumed. Virtually all of that decrease was the result of a 44-percent decrease in site Btu consumption for space heating (Figure 2.8). In 1978, an average of 91 million Btu was consumed for space heating (66 percent of all the Btu consumed); in 1997, an average of 51 million Btu was consumed for space heating (51 percent of all the Btu consumed). Energy Information Administration In addition to an overall decrease in site energy consumption for space heating, the source of the space heating Btu changed substantially after 1978 (Figure 2.9a). While the percent of all space heating Btu from natural gas increased from 61 percent in 1978 to 70 percent in 1997, the percent provided by fuel oil/kerosene dropped from 30 percent in 1978 to 18 percent in 1997. The distribution of total energy consumption for space heating by fuel is not very different when primary electricity, rather than site electricity, is compared to the other fuels (Figure 2.9b). One noteworthy difference is that, in 1997 primary electricity accounted for a larger share of space heating Btu (20 percent) than did fuel oil/kerosene (15 percent). When site electricity is considered, the reverse is the case (Figure 2.9a) with site electricity accounting for 8 percent of space-heating Btu and fuel oil/kerosene accounting for 18 percent. Also noteworthy is the finding Main Heating Fuel • The difference between the 1978 and 1997 estimates is statistically significant at the 95-percent confidence level. Sources. Energy information Administration; 1978, 1987, and 1997 Residential Energy Consumption Surveys. Figure 2.9b. Percent of U.S. Residential SpaceHeating Primary Energy Consumption by Main Heating Fuel, 1978, 1987, and 1997 Percent of Space Heat Primary Btu 1978 1987 1997 75 61 60 55 50 25 20 16 15 26 19 15 3 4 4 Primary Electricity • The difference between the 1978 and 1997 estimates is statistically significant at the 95-percent confidence level Sources Energy Information Administration, 1978, 1987 and 1997 Residential Energy Consumption Surveys. On a per-housing unit basis, the decrease in site Btu. consumption for space-heating occurred regardless of the main heating fuel used (Figure 2.10). On a percentage basis, the largest decrease in space heating energy consumption occurred in those housing units whose main heating fuel was electricity. In those housing units, site Btu consumption decreased by 60 percent, from 32 million Btu per housing unit in 1978 to 13 million Btu in 1997. Btu consumption in housing units where natural gas or fuel oil/kerosene was the main heating fuel decreased by 34 percent and 33 percent, respectively, over the 1978-1997 period. Btu consumption in housing units where LPG was the main heating fuel decreased by 21 percent over the same period. Energy Information Administration |