The United States is the second-largest single consumer of energy in the world. The U.S. Department of Energy categorizes national energy use in four broad sectors: transportation, residential, commercial, and industrial.US Dept. of Energy, "Annual Energy Report" (July 2006), Energy Flow diagram Energy usage in transportation and residential sectors (about half of U.S. energy consumption) is largely controlled by individual domestic consumers. Commercial and industrial energy expenditures are determined by businesses entities and other facility managers. National energy policy has a significant effect on energy usage across all four sectors.
Transportation The transportation sector includes all vehicles used for personal or freight transportation. Of the energy used in this sector, approximately 65% is consumed by gasoline-powered vehicles, primarily personally owned. Diesel-powered transport (trains, merchant ships, heavy trucks, etc.) consumes about 20%, and air traffic consumes most of the remaining 15%.US Dept. of Energy, "Annual Energy Outlook" (February 2006), Table A2 The two oil supply crisis of the 1970s spurred the creation, in 1975, of the federal Corporate Average Fuel Economy (CAFE) program, which required auto manufacturers to meet progressively higher fleet fuel economy targets.
The 1980s saw dramatic improvements in fuel economy, mostly the result of reductions in vehicle size and weight which originated in the late 1970s, along with the transition to front wheel drive. These gains eroded somewhat after 1990 due to the growing popularity of sport utility vehicles, pickup trucks and minivans, which fall under the more lenient "light truck" CAFE standard.
In addition to the CAFE program, the U.S. government has tried to encourage better vehicle efficiency through tax policy. Since 2002, taxpayers have been eligible for income tax credits for gas/electric hybrid vehicles. A "gas-guzzler" tax has been assessed on manufacturers since 1978 for cars with exceptionally poor fuel economy. While this tax remains in effect, it generates very little revenue as overall fuel economy has improved.
Another focus in gasoline conservation is reducing the number of miles driven. An estimated 40% of American automobile use is associated with daily commuting. Many urban areas offer subsidized public transportation to reduce commuting traffic, and encourage carpooling by providing designated high-occupancy vehicle lanes and lower tolls for cars with multiple riders. Remote work is also a viable alternative to commuting for some jobs.
Fuel economy-maximizing behaviors also help reduce fuel consumption. Among the most effective are moderate driving, as opposed to aggressive driving, driving at lower speeds, using cruise control, and turning off a vehicle's engine at stops rather than idling. A vehicle's gas mileage decreases rapidly with increasing highway speeds, normally above 55 miles per hour (though the exact number varies by vehicle), because aerodynamic forces are proportionally related to the square of an object's speed (when the speed is doubled, drag quadruples). According to the U.S. Department of Energy (DOE), as a rule of thumb, each one drives over is similar to paying an additional $0.30 per gallon for gas. The exact speed at which a vehicle achieves its highest efficiency varies based on the vehicle's drag coefficient, frontal area, surrounding air speed, and the efficiency and gearing of a vehicle's drive train and transmission.
Residential sector The residential sector is all private residences, including single-family homes, apartments, manufactured homes and dormitories. Energy use in this sector varies significantly across the country, due to regional climate differences and different regulation. On average, about half of the energy used in U.S. homes is expended on space conditioning (i.e. heating and cooling).
The efficiency of furnaces and air conditioners has increased steadily since the energy crises of the 1970s. The 1987 National Appliance Energy Conservation Act authorized the Department of Energy to set minimum efficiency standards for space conditioning equipment and other appliances each year, based on what is "technologically feasible and economically justified". Beyond these minimum standards, the Environmental Protection Agency (EPA) awards the Energy Star designation to appliances that exceed industry efficiency averages by an EPA-specified percentage.
Despite technological improvements, many American lifestyle changes have put higher demands on heating and cooling resources. The average size of homes built in the United States has increased from in 1970 to in 2005. The single-person household has become more common, as has central air conditioning: 23% of households had central air conditioning in 1978, that figure rose to 55% by 2001.
As furnace efficiency gets higher, appropriate matching of equipment size to distribution system capacity and building load becomes more critical to optimizing equipment ability to maximize efficient operation. Installing much lower output high-efficiency replacement equipment offers opportunity for comfort and savings gains, but improving the building envelope through air sealing and adding more insulation, advanced windows, etc., should be explored concurrently or before replacement equipment design stage. The passive house approach produces superinsulated buildings that approach zero net energy consumption. Improving the building envelope can also be cheaper than replacing a furnace or air conditioner.
Even lower cost improvements include weatherization, which is frequently subsidized by utilities or state and federal tax credits, as are programmable thermostats. Consumers have also been urged to adopt a wider indoor temperature range (e.g. in the winter, in the summer).
One underutilized, but potentially very powerful means to reduce household energy consumption is to provide real-time feedback to homeowners so they can effectively alter their energy using behavior. Low-cost energy feedback displays, such as the Energy Detective or Wattvision, have become available. A study of a similar device deployed in 500 homes in Ontario, Canada, by Hydro One showed an average 6.5% drop in total electricity use when compared with a similarly sized control group.ChartwellHydroOneMonitoringProgram.pdf Another technique is to ask homeowners to conserve energy in real time at times of peak demand, when relatively dirty power plants would otherwise need to be turned on.
Standby power used by consumer electronics and appliances while they are turned off accounts for an estimated 5 to 10% of household electricity consumption, adding an estimated $3 billion to annual energy costs in the US. "In the average home, 75% of the electricity used to power home electronics is consumed while the products are turned off."home_office.html
Home energy consumption averages +Home energy consumption averagesUS Dept. of Energy, "Buildings Energy Data Book " (2011)SectorPercentageNotesHome heating systems 28.9% Home cooling systems 14.0% Water heating 12.9% Lighting 9.0% Home electronics 7.1% Refrigerators and freezers 5.9% Clothing and dish washers 4.5% includes clothes dryers, does not include hot waterCookings 3.7% Computers 2.2% Other 4.4% includes small electrics, heating elements, motors, pool and hot tub heaters, outdoor grills, and natural gas outdoor lightingNon end-user energy expenditure 5.4%
Energy usage in some homes may vary widely from these averages. Milder regions such as the Southern U.S. and Pacific Coast of the US need far less energy for space conditioning than New York City or Chicago. Air conditioning energy use can be quite high in hot-arid regions (Southwest) and hot-humid zones (Southeast) In milder climates such as San Diego, lighting energy may easily consume up to 40% of total energy. Certain appliances such as a waterbed, hot tub, or pre-1990 refrigerator, use significant amounts of electricity.
Recent trends in home entertainment equipment can make a large difference in household energy use. For instance a 50-inch LCD television, average on-time of six hours a day, may draw 300 watts less than a similarly sized plasma system. In most residences no single appliance dominates, and any conservation efforts must be directed to numerous areas in order to achieve substantial energy savings. Ground, air and water source heat pump systems, solar heating systems and evaporative coolers are among the more energy efficient, environmentally clean, and cost-effective space conditioning and domestic hot water systems available (Environmental Protection Agency), and can achieve reductions in energy consumptions of up to 69%.
Building practices Current practices in building design, construction, and retrofitting result in homes that are profoundly more energy conserving than average new homes. This includes insulation and energy-efficient windows and lighting.
Modern methods construct homes such that minimal resources are used to cooling and heating the house in summer and winter respectively can significantly reduce energy costs.
Commercial sector The commercial sector consists of retail stores, offices (business and government), restaurants, schools and other workplaces. Energy in this sector has the same basic end uses as the residential sector, in slightly different proportions. Space conditioning is again the single biggest consumption area, but it represents only about 30% of the energy use of commercial buildings. Lighting, at 25%, plays a much larger role than it does in the residential sector. Lighting is also generally the most wasteful component of commercial use. Several case studies indicate that more efficient lighting and elimination of over-illumination can reduce lighting energy by approximately fifty percent in many commercial buildings.
Commercial buildings can greatly increase energy efficiency by thoughtful design, with today's building stock being very poor examples of the potential of systematic (not expensive) energy efficient design.Steffy, 1997 Commercial buildings often have professional management, allowing centralized control and coordination of energy conservation efforts. As a result, fluorescent lighting (about four times as efficient as incandescent) is the standard for most commercial space, although it may produce certain adverse health effects.Susan L. Burks, Managing your Migraine, Humana Press, New Jersey (1994) Cambridge Handbook of Psychology, Health and Medicine, edited by Andrew Baum, Robert West, John Weinman, Stanton Newman, Chris McManus, Cambridge University Press (1997) L. Pijnenburg, M. Camps and G. Jongmans-Liedekerken, Looking closer at assimilation lighting, Venlo, GGD, Noord-Limburg (1991)Igor Knez, "Effects of colour of light on nonvisual psychological processes", Journal of Environmental Psychology, Volume 21, Issue 2, June 2001, pages 201–208