20 percent during 1979–2003, while primary energy use per square foot decreased by 6 percent. The difference between on-site and primary-energy-use growth rates was due to growing electrification, which engendered sizable generating, transmitting, and distributing losses.
Factors that have affected energy use in buildings over the last several decades include increased electrification, population shifts to milder climates, growing penetration of appliances and electronics, larger home sizes, smaller households, growing household incomes, and dramatic improvements in the energy efficiency of appliances and other equipment. The last item is a key factor in the decline in energy intensity of buildings over the past 30 years. For example, the average electricity use of new refrigerators sold in 2007 was 71 percent less than that of new refrigerators sold in 1977 (AHAM, 2008), despite their becoming larger and having more features.
Significant energy efficiency gains have also been made in lighting. Sales and use of compact fluorescent lamps, which consume about 75 percent less electricity per unit of light output than incandescent lamps consume, have greatly increased in the past decade. In commercial buildings, energy-efficient fluorescent lighting fixtures containing T8 fluorescent lamps and high-frequency electronic lamp ballasts use 15–30 percent less energy per unit of light output than do older fixtures with T12 lamps and electromagnetic ballasts. These devices also have been used increasingly in recent years, as periodic surveys by the EIA attest. However, a large fraction of commercial buildings still have not embraced common energy efficiency measures such as energy management and control systems.
The adoption of ENERGY STAR®-labeled products has also grown substantially in recent years. For example, the construction and certification of ENERGY STAR® new homes increased from about 57,000 in 2001 to 189,000 in 2006, or 11.4 percent of all new homes built that year.
Many studies, whether on the local, regional, national, or global levels, have estimated the potential for improved energy efficiency in buildings.3 For the most part, these efforts evaluate the quantity of savings that could be realistically