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issue: June 2009 APPLIANCE Magazine

Appliance Engineer - Motor Technology
Efficient Refrigeration


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An EC motor designed for commercial refrigeration applications is said to use 15% less power at rated speed than a conventional PSC motor.

The ARKTIC 142 fractional-horsepower motor from Morrill Motors Inc. (Erwin, TN, U.S.; www.morrillmotors.com) has been especially designed for refrigeration applications that require a ¾, ½, 1/3, or 1/5 horsepower motor, such as walk-in coolers and freezers, parallel racks, and condenser units. According to Tim Neal, director of marketing, the Arktic 142 offers a high-energy-efficiency solution for compliance with demanding new appliance regulations. “With an emphasis on quick integration into existing equipment designs, the 142 makes our reliable, field-proven ECM technology a high-efficiency alternative for heavy-duty refrigeration applications,” Neal says.

The electronically commutated motor (ECM) reportedly uses 15% less power at rated speed than a conventional permanent split capacitor (PSC) motor, thus providing an answer to tougher efficiency standards for appliances. According to Morrill Motors, beginning in 2008, California Title 20 appliance regulations require that evaporator boxes in all new walk-in coolers and freezers use high-efficiency motors. This standard has gone nationwide this year. “The efficiency issue isn’t going away any time soon, and businesses should expect more regulations in the future,” says Neal. “Going forward, conservation is going to be a key issue in foodservice. Motors are the heart of what runs refrigeration equipment, so they have become a prime target for cutting consumption.”

The efficiency of the Arktic 142 is due partly to its brushless dc design, which, Neal says, is inherently more efficient over a wide speed range than a PSC design. The other factor is the motor's permanent-magnet rotor, which, unlike a PSC with its conventional rotor, does not require current to be induced across the air gap between the rotor and stator—a characteristic that causes efficiency losses in the form of heat. “In refrigeration, PSC motors create a double inefficiency because their heat losses actively fight the cooling process,” noted Neal. “For every unit of cooling a PSC motor creates, it contributes a half-unit of heat back into the system. Extra heat forces a longer cooling cycle, which means higher electric bills, and more wear and tear on every component in the system.”

Unlike a PSC motor, an ECM also decreases power use and heat dramatically as the motor speed slows. The Arktic 142 becomes even more efficient when equipment runs at lower speeds. The 142 is capable of running at one, two, or three preset speeds. In applications such as a parallel rack unit that is used to keep refrigeration compressors from overheating, one method for improving performance is to implement variable-capacity operation, explains Morrill Motors. In variable-capacity equipment, coolant flow and operating temperatures can be raised or lowered to match the exact needs of the refrigeration system.

Variable capacity is achieved by wiring several multiple-speed fans in a series, so that some of the fans only operate under heavy-load conditions. The minimal operation uses less power overall, and decreases heat contribution from the fans. For example, when a grocery store is closed, equipment can run more slowly to maintain appropriate food temperatures without overcooling. In addition to cutting power use, reduced cooling helps avoid the need for a defrost cycle, and keeps temperature and humidity more constant, which yields fresher, longer-lasting food.

The Arktic 142 allows engineers to develop both single-speed and multiple-speed equipment with ease, thanks to the programmability of ECM technology. Speed settings are determined by commands that are saved inside of the ECM, and design engineers can modify motor settings in-house with the firm’s special tool called the ECM Toolbox. Programmability allows manufacturers to skip a lengthy specification process and decreases inventory, because the same motor can be reprogrammed for a variety of system configurations, or be installed in different equipment altogether.

The Arktic 142 also features BlaKBox Diagnostics, a built-in data recorder that provides feedback from equipment in the field. Like a flight recorder on an airplane, BlaKBox provides information that is key to diagnosing existing equipment, improving product reliability, and developing future refrigeration technologies.

 

Read more about motor technology online:

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