Published on EGEE 401: Energy in a Changing World (https://www.e-education.psu.edu/egee401)

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Energy Efficiency

Energy efficiency is the amount of useful energy you get from any type of system. It is calculated as the useful energy output divided by the total energy input.

A light bulb converts electricity to light and heat. Typically, the light is the "useful" output and the heat is a byproduct. Consider this, only five to eight percent of the energy used by a standard incandescent light bulb is converted to light, the rest is dissipated as heat. An incandescent bulb is actually a space heater that throws off a little light!

About 20% of the energy contained in gasoline is used to propel a vehicle with a combustion engine. On the other hand, cars with electric motors are able to convert around 60% of the electricity they get from the grid to power at the wheels. (source: fueleconomy.gov) [1]

The energy efficiency measure (useful output/total input) can be helpfully applied to many products and systems. However, units of measure must be handled carefully. The electricity a light bulb uses is measured in watts; the light it produces is measured in lumens. To simplify, many industries have adopted standard measures to simplify efficiency comparisons between related products. Lamps, for example, are often compared on the basis of lumens/Watt, called luminous efficacy.

Similarly, the efficiency air conditioning units is regulated by the U.S. Department of Energy (DOE) using the Seasonal Energy Efficiency Ratio or "SEER" rating system. The SEER rating is BTUs (total cooling output) divided by Watt hours (total electric input). The higher the rating, the more efficient the unit is. For more details, see the Air-Conditioning, Heating and Refrigeration Institute [2].

The US Government has simplified energy efficiency shopping for customers with the ENERGY STAR [3] rating system, a joint program of the U.S. Environmental Protection Agency and the U.S. Department of Energy that awards Energy Star status to highly efficient products. If you'd like more information, visit the Energy Star [4] website or read through How Energy Star Works [5].

"Energy Efficiency"

A word about the words "energy efficiency"...

The term "energy efficiency" is also used with a more broadly scoped meaning, such as this previously published definition from the World Energy Council, "energy efficiency improvements refer to a reduction in the energy used for a given service (heating, lighting, etc.) or level of activity. The reduction in the energy consumption is usually associated with technological changes, but not always, since it can also result from better organization and management or improved economic conditions in the sector ('non-technical factors')."

In this sense, a programmable thermostat may help with "energy efficiency." Simple steps such as remembering to turn off the lights is a non-technical behavior that can also improve energy efficiency. These are examples of energy efficiency in its broader meaning, related to the smarter use of energy for a specific purpose.


Source URL: https://www.e-education.psu.edu/egee401/content/p2_p9.html

Links
[1] http://www.fueleconomy.gov/feg/evtech.shtml
[2] http://www.ahrinet.org/site/588/Homeowners/Save-Energy/Seasonal-Energy-Efficiency-Ratio
[3] http://www.energystar.gov/index.cfm?c=about.ab_index
[4] http://www.energystar.gov/
[5] http://home.howstuffworks.com/home-improvement/construction/green/energy-star.htm