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# Efficiency

## The measure of usefulness.

Efficiency is the measure of "usefulness" of an operation, process or machine - and can be expressed on the generic form

μ = Wo / Wi    (1)

where

μ = efficiency

Wo = output from the operation - can be work, power, produced products ...

Wi = input to the operation - can work, power, input products ...

Efficiency can be expressed as a percentage or as a per-unit decimal fraction of 1.

### Example - Efficiency of an Electric Motor

The input power to an electric motor is 2000 W. The output power to the shaft is 1800 W. The efficiency of the motor can be calculated as

μ = (1800 W) / (2000 W)

= 0.9

= 90%

### Example - Efficiency of a Wind Mill

The teoretical energy potential for a wind mill is 300 kWh at given conditions. The power produced is 70 kWh. The efficiency of the wind mill can be calculated as

μ = (70 kWh) / (300 kWh)

= 0.23

= 23%

## Related Topics

• ### Basics

Basic engineering data. SI-system, unit converters, physical constants, drawing scales and more.

## Related Documents

• ### Air Conditioner Efficiency

The ratio between heat removed and power (watt) used - EER and SEER.
• ### Boiler - Efficiency

Combustion gross and net calorific value.
• ### Carnot Efficiency

The efficiency of the Carnot cycle.
• ### Combustion Efficiency and Excess Air

Optimizing boilers efficiency is important to minimize fuel consumption and unwanted excess to the environment.
• ### Cooling and Heating - Performance and Efficiency Terminology

Performance and efficiency terminology related to heat pumps and air condition systems.
• ### Cooling Tower Efficiency

Maximum cooling tower efficiency is limited by the cooling air wet-bulb temperature.
• ### Efficiency in Pumps or Fans

The overall pump and fan efficiency is the ratio power gained by the fluid to the shaft power supplied.
• ### Electric Motors - Efficiency

Calculate electric motor efficiency.
• ### Heat Recovery Efficiency

Classification of heat recovery efficiencies - temperature efficiency, moisture efficiency and enthalpy efficiency - online heat exchanger efficiency calculator.

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## Citation

• The Engineering ToolBox (2011). Efficiency. [online] Available at: https://www.engineeringtoolbox.com/efficiency-d_1768.html [Accessed Day Month Year].

Modify the access date according your visit.

4.19.9

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