Major Food Distributor Upgrades To Big Savings With VFDs

This cool solution has led to improved system control, lowered monthly electrical bills and less wear and tear on equipment.

Variable speed drives from Control Techniques, an Emerson Industrial Automation business, have helped slash energy bills by $2000 per month for a U.S. distribution center owned by one of the largest players in the food-service industry. The facility stores massive quantities of foodstuffs in freezer- and cooler-boxes ready for regional distribution. Prior to the upgrade work, each freezer- and cooler-box had been controlled by a circuit with its own compressor, condenser and evaporator(s)—which were controlled by individual mechanical thermostats and defrost-time-clocks.

The defrost performance of the evaporators on the freezers presented a problem: While all of the evaporators needed to be defrosted at the same time, the individual mechanical defrost clocks on the freezer-condensing units wouldn’t remain synchronized once set. Key Mechanical, the distribution center’s refrigeration contractor, approached Emerson for help with finding a solution.

Working alongside Emerson Retail Solutions, an Emerson Climate Technologies company, Control Techniques proposed new control systems for the circuits on the freezer- and cooler-boxes. The solution involved the installation of 21 Commander HSK variable frequency drives (VFDs) from Control Techniques, two Einstein E2 RX400 refrigeration controllers from Emerson Retail Solutions and Copeland (semi hermetic/ scroll) compressors from Emerson Climate Technologies.

Upgrading to this new system has allowed the distribution center to control the speed of each Copeland compressor, as well as the speed of the condenser- and evaporator-fan motors. The RX400 controllers are programmed to control temperature, defrost cycles and frequency drive output for floating head pressure, floating suction pressure and evaporator fan motor speed during the normal refrigeration cycle. Of the 21 HSK drives, seven control the Copeland compressors, seven control the condensers and seven control the evaporators. 

The retrofit led to a reduction in electricity consumption of 250,676 kWhr per year—translating into that associated welcome reduction of $2000 on the site’s monthly power bill. These savings were possible due to a reduction in fan-motor energy consumption as a result of improved fan management and a reduction in compressor-energy consumption due to decreased compression ratios. Downtime was also slashed, and overall equipment life extended in light of better temperature control and defrosts-management and reduced compressor cycling.

According to Dan Wilson, Project Manager at Key Mechanical, other than this successful drive retrofit, the only other solution available to his distribution-center customer would have involved replacing an entire piece of the plant—an option that would clearly have been a much larger capital expense.MT 

Control Techniques Americas LLC
Minneapolis, MN