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Impacts of Temperature Variation on Energy Demand in Buildings |
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In the residential and commercial sectors, heating and cooling account for more than 40 percent of end-use energy demand. As a result, energy consumption in those sectors can vary significantly from year to year, depending on yearly average temperatures. In long-term energy forecasting, an average of the heating and cooling degree-days data for the previous 30 years is ordinarily used as a proxy for “normal” weather [97]. Both heating and cooling degree-days have shown a slight warming trend since 1973 (Figure 21), although no warming trend is evident from an examination of the long-term data since 1930. The direction of year-to-year fluctuations in U.S. average heating degree-days and in U.S. average cooling-degree days do not appear to be correlated; however, both the lowest yearly average for heating degree-days and the highest yearly average for cooling degree-days were recorded in 1998. The coldest winter over the 1973-2003 period (1978) was 11 percent colder than the average, and the warmest winter (1998) was 12 percent warmer than the average. The coolest summer (1976) was 16 percent cooler than the average, and the warmest summer (1998) was 15 percent warmer than the average. The AEO2005 reference case uses the 30-year average of heating and cooling degree-days from the National Oceanic and Atmospheric Administration at the State level, adjusted for State population forecasts through 2025, to represent future temperatures (previous AEOs used Census division forecasts). As a result of State population shifts, population-weighted heating degree-days are projected to decline by 3.2 percent, and population-weighted cooling degree-days are projected to increase by 4.1 percent from 2003 to 2025, relative to the weather normal average assumed in 2005, because the population is projected to shift to States with warmer climates. To estimate the possible impact of warmer or colder weather on energy use in the residential and commercial sectors, two alternative cases were examined: a warmer case assuming above-average temperatures and a cooler case assuming below-average temperatures throughout the projection period. For this analysis, it was assumed that State-level heating and cooling degree-days would reach the average of the five warmest or coolest levels that have occurred over the past 30 years by 2025. It was also assumed that warmer winters would coincide with warmer summers, and vice versa. Figures 22 and 23 show the projected trends in heating and cooling degree-days from 2005 to 2025 in the reference, warmer, and cooler cases. Compared with the reference case forecast, heating degree-days are projected to be 11 percent higher in the cooler case and 12 percent lower in the warmer case by 2025, and cooling degree-days are projected to be 17 percent higher in the warmer case and 16 percent lower in the cooler case. The impacts of the assumptions in the warmer and cooler weather cases on projected energy consumption in the residential and commercial sectors are mixed, because warmer winters reduce demand for space heating (generally fossil fuels) and warmer summers increase demand for space cooling (generally electricity), whereas colder winters and summers do the opposite. Figure 24 shows the impacts of the two cases on electricity consumption (including conversion losses) and direct fossil fuel consumption. Given that fossil-fuel-fired space heating is the largest use of energy in the two buildings sectors, it is not surprising that the cumulative change in the two weather cases is greatest for fossil fuels. The cumulative change in fossil fuel consumption in the buildings sector in the warmer and colder cases represents 2.4 and 1.9 percent, respectively, of the cumulative amount of fossil fuels used in the buildings sector from 2006 through 2025. For electricity, the cumulative change is 0.2 percent of the cumulative amount of electricity (including conversion losses) used in the buildings sector in both cases between 2006 and 2025. The much lower change for electricity is due to the fact that much less of the electricity load is temperature dependent—only 16 percent, compared with 62 percent for fossil fuels. For example, many of the major end-use services that are not temperature dependent, such as lighting, refrigeration, and office equipment, are powered almost exclusively by electricity. Changes in projected energy demand in the warmer and cooler cases also affect the projections of energy prices. Relative to the AEO2005 reference case, average residential and commercial electricity prices in the cooler case are 0.7 percent and 0.5 percent lower over the projection period, respectively, as summer peak demand is reduced by decreases in air conditioning use. In the warmer case, average electricity prices to residential and commercial customers over the period from 2006 to 2025 are 0.8 percent and 0.9 percent higher, respectively, as summer peak load is increased. The changes in electricity demand are not evenly distributed throughout the year; there is a much greater change in peak demand than there is in total demand. This also affects the amount of electric generating capacity needed, which is based on an assumed reserve over the peak demand. In the warmer case, peak demand in 2025 is 4.8 percent higher than in the reference case, resulting in a 3.5-percent increase in overall electricity generation capacity, although total demand in 2025 is only 0.5 percent higher than in the reference case. As a result, higher average electricity prices are projected, due to the increased costs of capacity without an equal increase in generation. The incremental cost is spread over relatively few additional kilowatthours. In the colder case, projected peak demand in 2025 is 4.4 percent lower than in the reference case, and total capacity is 3.2 percent lower, although total demand is only 0.7 percent lower. In this case, total costs are lower due to fewer new capacity additions, but total demand is again almost the same, and average prices are lower. Because changes in annual energy demand vary depending on season and fuel type in the two weather cases, it follows that changes in energy expenditures will vary as well. As shown in Figure 24, demand for fossil fuel and electricity change in opposite directions relative to the reference case in the two temperature sensitivity cases. Figure 25 shows the changes in projected present value of expenditures for electricity and fossil fuels in the residential and commercial sectors in the warmer and colder cases. The present value of commercial electricity expenditures changes the most, but the difference, as a percentage of current commercial electricity expenditures, reaches only 1.3 percent over the present value of all future expenditures on electricity in the sector. The present value of residential energy expenditures increases by $2.3 billion in the cooler case, meaning that consumers could expect to pay more money for their household energy use over the projection period. In the warmer case, the present value of residential energy expenditures decreases by $1.6 billion, reflecting the larger heating requirements relative to cooling requirements in the sector. In summary, average yearly temperatures that are warmer or cooler than expected would have mixed impacts on energy consumption and expenditures in the residential and commercial sectors if the changes were directionally the same in the heating and cooling seasons. Warmer summer temperatures would increase demand for air conditioning, and warmer winter temperatures would decrease demand for heating. Because space heating accounts for more energy use than air conditioning on the basis of sales volumes, heating fuels tend to be more affected by changes in temperature than do cooling fuels; however, given the relatively high delivered price of electricity compared to fossil fuels, changes in energy consumption tend to affect electricity more on the basis of total expenditures. The projections in the warmer and cooler weather cases show that energy consumption and expenditures are sensitive to changes in temperature. It should be noted, however, that the changes projected are relatively small relative to the sector totals. Accordingly, in the colder case, cumulative carbon dioxide emissions from 2003 to 2025 are projected to be only 0.1 percent higher than in the reference case, and in the warmer case they are projected to be only 0.2 percent lower than in the reference case.
[97] A degree-day is defined as the difference between the average daily temperature (in degrees Fahrenheit) and 65. Averages above 65 degrees Fahrenheit count as cooling degree-days, and averages below 65 degrees Fahrenheit count as heating degree-days. For example, if the average temperature on a given day is 40 degrees Fahrenheit, then 25 heating degree-days are counted
Contact: John Cymbalsky |
