Case Studies / Energy Management

Variable Speed Drives Help U.S. Foodservice Distributor Slash Energy Bills

Variable speed drives from Control Techniques, an Eden Prairie, Minn.-based manufacturer of AC and DC variable speed drives, servos and power conversion Emerson roof condensortechnologies and division of Emerson Industrial Automation, helped a U.S. foodservice distributor slash energy bills by more than $2,000 a month, reduce downtime and extend equipment life.

The facility stores massive quantities of foodstuffs in freezers and cooler boxes ready for regional distribution. Prior to Emerson’s upgrade work, each freezer and cooler box was controlled by a circuit with its own compressor, condenser and evaporator. These were in turn controlled by individual mechanical thermostats and defrost time clocks.

The customer experienced an issue with the defrost performance of the evaporators on the freezers. All of the evaporators needed to be defrosted at the same time, but the freezer condensing units had individual mechanical defrost clocks that would not remain synchronized once set.

Key Mechanical, the customer’s refrigeration contractor headquartered in Livermore, Calif., approached Emerson for help with finding a solution.

Working alongside Emerson Retail Solutions, an Emerson Climate Technologies company, Control Techniques and Key Mechanical 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 from Control Techniques and two Einstein E2 RX400 refrigeration controllers from Emerson Retail Solutions controlling existing Copeland semi-hermetic compressors from Emerson Climate Technologies.

The new system enabled the customer to control the speed of each Copeland compressor, as well as 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.

Installation of the new variable speed drives reduced electricity consumption by 250,676 kWhr per year, providing a savings of more than $2,000 a month on the customer’s energy bill. Energy savings were possible due to reduced fan motor energy consumption as a result of improved fan management, and a reduction in compressor energy consumption due to reduced compression ratios. Additional energy savings include decreased downtime, extended overall equipment life due to better temperature control and defrost management and reduced compressor cycling.

“The only option for the customer, other than a drive retrofit was replacing all the rooftop equipment for the plant, which would obviously have been a much larger capital expense,” says Ron Kvinge, branch manager for Key Mechanical Portland. “The solution suggested by Key Mechanical resulted in better control of the freezer/cooler systems, major energy savings and less wear and tear on equipment.”

“Without Emerson’s proprietary suction and head pressure controller technology, the energy and cost savings for our customer could not have been achieved,” says David Yankaskas, regional sales manager for Control Techniques. “From the perspective of day-to-day operations, controlling the HSK drives through the two Einstein RX400 controllers is obviously much simpler than having to program and monitor all 21 of them individually. Overall, the Emerson/Key Mechanical solution is functioning extremely well and is saving the customer over $2,000 dollars a month.”

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