Site (point-of-use) measure of energy consumption reflects the use of electricity, natural gas, propane, and/or fuel oil by an appliance at the site where the appliance is operated, based on specified test procedures.
Source (extended site) measure of energy consumption includes, in addition to site energy use, the energy losses that occur in the fuel supply chains for an appliance. For appliances powered by electricity, source energy consumption would include losses in the generation, transmission, and distribution of the generated electricity. For appliances fueled by natural gas, propane, or oil, etc., source energy consumption would include the fuel losses experienced in the transportation and distribution of the fuel.
Full-fuel-cycle measure of energy consumption includes, in addition to site energy use, the energy consumed in the extraction, processing, and transportation of primary fuels such as coal, oil, and natural gas; energy losses in thermal combustion in power-generation plants; and energy losses in transmission and distribution to homes and commercial buildings.
How Site Energy Measurement Fails to Capture the Full Impact of Energy Use
Although the site measure of energy consumption allows easy comparison of the operating efficiency of one appliance over another in isolation, it gives only a partial picture of total energy use because it omits the energy needed to mine, process, and transport the primary fuel to a generating plant; the energy used at the generating plant; and the energy used in delivering electricity or fuel to the site of operation of an appliance. For example, based on their site energy consumption, an electric storage water heater might operate with 90 percent efficiency and a natural gas water heater with 70 percent efficiency. But for the electric storage water heater, energy losses of about 70 to 75 percent occur in acquiring the primary fuel and in the generation, transmission, and distribution of the electricity, yielding an overall energy efficiency for the electric storage water heater of about 27 percent. This figure is much lower than the gas-fired storage water heater's overall energy efficiency of about 64 percent, when full-fuel-cycle energy consumption is the measure employed (Jaramillo et al., 2007, 2008). In general, energy losses in heating applications with electric resistance heaters are greater than in heating applications with natural gas when the measure is full-fuel-cycle energy use (Review of Site [Point-of-Use] and Full-Fuel-Cycle Measurement Approaches to DOE/EERE Building Appliance Energy-Efficient Standards page 6). Therefore, full-fuel-cycle measurement provides consumers with more complete information on energy use and environmental impacts especially greenhouse gas emissions.
- National Academy of Sciences report "Review of Site (Point-of-Use) and Full-Fuel-Cycle Measurement Approaches to DOE/EERE Building Appliance Energy Efficient Standards" May 15, 2009
Resources and Tools
Direct Use of Natural Gas: Natural Gas Results in Less Total Energy Consumption and Fewer Carbon Emissions. This American Gas Foundation study found that increased direct use of natural gas in R&C applications can increase the productivity of available energy supplies, reduce overall energy cost, and reduce related CO2 emissions. The energy efficiency advantage of using natural gas directly in homes and businesses stems from the fact that natural gas retains about 90 percent of its usable energy from the point of production to the burner tip in the home.
AGA-NRDC Joint Statement on Full-Fuel-Cycle Measurement for Energy Efficiency Standards. AGA has released a joint statement with the Natural Resources Defense Council (NRDC) supporting the recommendations of the National Academies that the Department of Energy (DOE) move toward the use of a “full-fuel-cycle” measurement of energy consumption for assessment of national and environmental impacts, especially levels of greenhouse gas emissions.