Comparing efficiency projections 

Realized improvements in energy efficiency generally rely on a combination of technology and economics [47]. The figure below illustrates the role of technology assumptions in the AEO2010 projections for energy efficiency in the residential and commercial buildings sector. Projected energy consumption in the Reference case is compared with projections in the Best Available Technology, High Technology, and 2009 Technology cases and an estimate based on an assumption of no change in efficiency for building shells and equipment (the cases are defined in Appendix E). 

figure data

With the exception of the constant efficiency estimate, the rate at which existing equipment stocks are replaced in each of the cases is governed by the rate of stock turnover. The constant efficiency estimate assumes no stock turnover and no change in efficiency from the 2009 existing stock. The 2009 Technology case assumes a normal rate of stock turnover, but limits new equipment choices to what is available in 2009. Comparing the two projections, energy consumption in 2035 is 1.2 quadrillion Btu lower in the 2009 Technology case. The difference— about 4.5 percent—shows the effect of stock turnover even absent any technology improvements. 

In the Best Available Technology case, with new construction materials and replacement equipment limited to the most energy-efficient available, energy consumption in the buildings sector in 2035 is 8.6 percent lower than the 2009 level and 23 percent lower than in the Reference case, even though total floorspace grows by more than 50 percent. Even in 2035, however, not every piece of equipment or every building shell reaches the maximum efficiency that could be achieved as a result of technology improvements, because some long-lived equipment and building shells installed before 2009 still have not been replaced at that point. Surpassing the efficiency levels projected in the Best Available Technology case would require policies designed to increase the rate of stock turnover—for example, by incentivizing or mandating retrofits of existing buildings and replacement of equipment with the most efficient models available.