What is energy efficient?

Answer 1

It's a device that can convert energy of one form into another efficiently. Like a lightbulb for example, an energy efficient one would use less electricity but still produce as much light as one that is less efficient. It's a measure of what you get out versus what you put in.

Answer 2

AnswerEnergy efficiency measures the per cent rate, or ratio, at which a device converts an energy source into a desired resulting energy. Consider the common household light bulb. It converts electricity into three categories of energies: visible light (the desired resulting energy); invisible light (including infrared); and heat. Only the visible light is useful to people in common lighting applications, and is therefore considered the desired type of energy. The energy efficiency of the light bulb, therefore, describes ratio of visible energy generated to the electrical energy consumed.

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Energy Efficiency = desired resulting energy / consumed source energy

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An automobile engine converts chemical potential energy (typically gasoline) into mechanical energy through a controlled internal combustion. Some of the converted energy is lost directly to heat, some is lost to friction (which turns into heat), some energy is lost to acoustic (sound) energy, and some source energy is lost because the motor did not completely burn all of the fuel, and let the unburned fuel escape with the exhaust. The proportion of the generated useful mechanical energy compared to the amount of potential chemical energy (the volume of gasoline) the engine consumed is the energy efficiency. Even here, the "useful" mechanical energy requires further analysis. An automobile engine diverts some of its mechanical energy to drive the cam shaft, the alternator, and various pumps, vacuums, fans, and compressors. The useful mechanical energy is what remains to drive the wheels after servicing all these ancillary mechanical energy consuming devices.

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Energy efficiency is often misunderstood. It does NOT describe how much energy is consumed - quite the opposite - it describes how much useful energy is generated. A 25 Watt incandescent light bulb consumes exactly the same amount of electrical energy, and creates exactly the same amount of resulting energy, as a 25 Watt compact fluorescent light bulb. The difference is the 25 Watt compact fluorescent light bulb generates more useful visible light than its incandescent counterpart. The left-over energy is usually considered to be wasted, and it is therefore more costly to achieve the same desired effect.

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Practicing energy efficiencies can lead to surprising results. For example, a 100 W incandescent light bulb is no more wasteful than a 25W compact fluorescent light bulb on a cold winter's night, because the "wasted" thermal energy is required to heat the house anyway. In effect, less house heating energy is required because the "wasted" energy from the incandescent light bulb partially heated the house already, and the end result is nearly energy neutral. By contrast, using an incandescent light bulb instead of a compact fluorescent light bulb in the summer while the air conditioning is running is doubly wasteful - not only will the incandescent light draw more electricity to produce the same amount of light, but the air conditioner will also consume even more electricity again to rid the house of the wasted heat the incandescent light bulb generated.

AnswerRefers to programs that are aimed at reducing the energy used by specific end-use devices and systems, typically without affecting the services provided. Such savings are generally achieved by substituting technically more advanced equipment to produce the same level of end-use services (eg lighting, heating, motor drive) with less electricity.

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A good place to start is www.energyefficientnation.org to get the information and tools you need to be energy efficient.