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Million Housing Units

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At the same time that the number of housing units was increasing, the size of housing units in the United States also became increasingly larger, resulting in an increased demand for energy-consuming activities, such as heating, airconditioning, and lighting. The percentage of smaller housing units, those with four or fewer rooms (excluding bathrooms), decreased from 35 percent to 30 percent (Figure 2.3). At the other end of the scale, the percentage of larger housing units, those with seven or more rooms, increased from 22 percent in 1978 to 29 percent in 1997.

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RECS Survey Year Note: The number of housing units was obtained from data from the U.S. Bureau of the Census. Current Population Survey (CPS). For general information about the CPS, see http://www.bls.census.gov/pcs/cpsmain.htm.

Sources: Energy Information Administration; 1978 through 1997 Residential Energy Consumption Surveys.

Energy Consumption

Although the number of housing units in all four U.S. Census regions increased over the 1978-1997 period, the distribution of those same housing units across the Nation also changed (Figure 2.2).

Energy consumption can be expressed as the amount of energy consumed within the housing unit (site energy) or it can include the energy consumed in generating and

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The total amount of site energy consumed by American housing units in 1997 was 10.2 quadrillion Btu (Figure 2.4). In 1978, 10.6 quadrillion Btu had been consumed. (Those totals are not statistically different.) Over this 19-year period, the total Btu consumption first decreased by 19 percent over the 1978-1982 period, then reversed course and increased by 19 percent over the 1984-1997 period.

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.

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Figure 2.4. Total U.S. Residential Site Energy Consumption, 1978-1997

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Quadrillion Site Bti

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Suures: Energy Informa un Adrriristraton 1978 through 1997 Residential Energy Corsirans.teys

On a per-housing unit basis, site energy consumption was 27 percent lower in 1997 than in 1978, dropping from 138 million Btu per housing unit to 101 million Btu per housing unit (Figure 2.5). All of this decrease occurred in the 19781987 period. Btu consumption per housing unit in 1997 was unchanged from the 1987 estimate.

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).

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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.

Figure 2.6a. Percent of Total U.S. Residential Site Energy Consumption by Fuel, 1978, 1987, and 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.

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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).

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Natural Gas

LPG

Primary Electricity

Fuel OIV Kerosene

• 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

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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 2.96). 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

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.

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