A variable speed drive (or frequency converter) controls electric motors via the power supply. This way the motors only run at precisely the speed necessary to obtain the desired effect. Today, a huge amount of motors are running with full speed when they are switched on, irrespective of the need, which wastes a lot of energy.
Danfoss variable speed drives are used in many different applications in buildings, in the industry and in public systems. In buildings, the variable speed drives can typically save 40% energy in pump and fan applications. Pay-back time is usually 1-2 years. In the industry, variable speed drives typically save 15% of the energy consumption. For example, variable speed drives are used to control huge cranes and conveyor belts or to pump waste water from the cities to water purifying plants. Pay-back time varies from 1 to 6 years – dependent on the size of the application and variable speed drive.
Sources: 1) Danfoss (2010) and 2) IMS Research (2008): ”The World Market for Low Voltage AC & DC Motor Drives 2009" and ”The World Market for AC Induction Motors 2008”.