One of the UK’s major producers of ready meals is saving 25 percent a year on its cooling costs by employing a single 55 kW ABB HVAC variable-speed drive (VSD).  Saladworks of Leicester supplies 135 different ready-meal products to four of the UK’s major retailers.

A major part of its process is chilling the finished products, for which Saladworks employs two refrigeration circuits, each with a duty and a standby glycol pump and a condenser.  The company asked an ABB UK Drives Alliance member to recommend ways to reduce its energy use.

Paul Hampton, Engineering Manager for the plant, says: “We knew that variable-speed drives could save us money by cutting our energy use and this was confirmed by a more analytical review.  A site wide appraisal then identified glycol pumps that could save considerable energy savings. We look for a payback of under a year and these applications met that criterion.”

An ABB drive was selected on one glycol pump in each refrigeration circuit, one of 55 kW, the other of 11 kW. The circuits are in constant operation, with the VSD controlled pump motor running 98 percent of the time. The direct-on-line pump is run for the other two percent of the time to ensure it remains in running order ready to take over the load if the main pump suffers a breakdown.

The ACH550 controlled pump motor is operated at 40 Hz, producing a saving of 25 percent of the original energy usage, which equated to a payback time of less than a year, meeting Saladworks pay-back time.

Saladworks has the option of running it at 43 to 44 Hz as temperatures increase in the summer.  A feedback loop from a temperature sensor to the drive is used to ensure the chillers can maintain a temperature of less than five degrees Celsius. Using the drives has the added benefit of causing less stress on the motors, reducing the maintenance  requirement.

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