Moeller displays `cool’ drives

Birmingham – To show energy savings possibilities offered by ac variable frequency drives, Moeller Electric produced an eye catching demonstration here at the Drives & Controls exhibition of its Optidrives running an industrial fridge.

The 2,700 litre fridge, shown in the photo, has a 3kW cooling capacity and is powered by a 1kW compressor and two condenser motors rated at 125W each. Working in tandem, two Optidrives set the optimum efficient running of the motors while maintaining temperature between 0°C and 2°C.

A temperature rise to 2°C signals the drives to start up the compressor and condenser motors via individual PID control loops. However, unlike conventional refrigerators, the motors don’t run at full speed.

Instead the system monitors the compressor’s suction pressure and keeps it at 3.5 bar by varying the speed of the motor. If the pressure drops below 3.5 bar the motor increases speed; if it rises above the set level the motor slows down and may even stop. Similarly the condenser motors maintain 18 bar condensing pressure with motor speed control.

The demonstration system displays energy consumption and saving data and compares the data to conventional continuous motor operation. Moeller claims the variable frequency drives for this application save 23% of the cost of the electricity when contrasted with standard full speed motors.

To encourage energy conservation in the U.K. the government introduced the so-called `Climate Change Levy’ which charges an additional $0.68 for each kWh consumed by manufacturers. To balance the surcharge, the government also introduced Enhanced Capital Allowances (ECAs) which allows companies to `write off’ 100% of the cost of energy-saving equipment such as ac drives.

Control Engineering Daily News DeskMichael Babb, editor, Control Engineering Europe mbabb@reedbusiness.com

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