Inverters keep cool to save energy

IBL Cold Stores in Knowsley, Liverpool, spent three years researching power consumption within its refrigeration units and identifying ways in which to save energy without losing efficiency. The company elected to install Yaskawa variable speed drives to its chillers and saved 28% on its power consumption. That figure has been independently verified by a consultant working under the auspices of the Department of the Environment, Transport and the Regions' "Energy Efficiency Best Practice" programme.

The Yaskawa AC inverters were recommended by the Japanese manufacturer's UK drives partner FPT Fenner through its local branch. The Blackburn headquartered specialist distributor has supported the Yaskawa drives for a number of years. IBL Cold Stores engineer, Mr Jim Smith, identified it was possible to run the motors at lower speed without loss of performance within the chillers. He then called in FPT Fenner's engineers to assist in designing the system and supply the drive. Not only has energy been saved, but all the moving parts have increased lifetimes and vibration has been lowered, reducing the chance of refrigerant gas leaks as a result.

Previously the motors had been operated using star delta starters with the motors running 24 hours a day protecting £40-50 million worth of food. The common method of store temperature control is to use a "pump down" system. That is, when the temperature needs to drop it is lowered to a point below that required. A thermostat then switches off a solenoid valve which controls the feed of refrigerant to the air coolers. This in turn creates a reduction in pressure at the compressor, which once detected by a pressure sensor switches off the compressor motor. By using the Yaskawa inverter, the motor can be controlled to run more slowly at low demand times, enabling a more consistent pressure to be maintained while retaining more accurate control over the refrigerant flow and hence the temperature within the chillers.

There are nearly 40 30kW motors used in IBL's refrigeration units. By fitting Yaskawa 616 P5 variable torque energy saving flux vector inverters and given that IBL's electricity bills have been as high as £100,000 a year, the savings are substantial.

The Yaskawa 616 Varispeed P5 inverters were designed specifically for fan and pump applications. The inverters range from 0.4kW right up to 600kW. The P5 has a 12 pulse option built in and there are DC reactors to reduce harmonics. Automatic energy saving functions with timers, together with "hours run" counters, are standard.
The 616 range provides excellent acceleration/deceleration control and smooth operation with the sensorless flux vector version being high torque at very low speeds. Standard features include automatic tuning to any AC induction motor and user friendly programming via a detachable digital operator keypad.

Mr Jim Smith, senior engineer at IBL said, "We have been able not only to save energy, but also improve the performance of our plant while reducing maintenance. We have also witnessed a reduction in breakdowns".
IBL was honoured for its work in energy reduction with the presentation of the Envirenergy Award from Scottish Power that is the parent company of Manweb, IBL's regional electricity company.

Released April 2000