Display Cases Gain Demand-Defrost Option

June 5, 2000
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Display case defrost is one of the toughest challenges faced by contractors and service technicians. Supermarket cases run 24 hrs a day, seven days a week, 52 weeks a year - and almost always under the eyes of impulse buyers.

Case defrost requires the use of electric heaters or hot refrigerant gas, resulting in an added heat load that can increase compressor running time and energy use.

Two established defrost technologies are electric and reverse-cycle hot gas. The latter has been favored for some time because of its use of waste heat. However, the refrigeration equipment must later remove any added heat to fixtures in the case.

Now an approach is being used to tip the scale back to electric from reverse-cycle hot gas defrost. It is called "smart defrost," and is designed to offset the higher operating costs of defrosting. With demand defrost, a cycle is started only when required, or "on demand."

How Smart Defrost Works

As developed by Palo Alto, CA-based Electric Power Research Institute (EPRI), the defrost controller takes a different approach from conventional demand defrost systems.

Instead of measuring ice buildup or other indicators, it relies on the history of defrost cycling in each refrigerated case. A proprietary algorithm predicts when the next defrost cycle is needed by analyzing past defrost patterns.

According to the developers, generally no additional hardware is needed and software is easily installed.

The technology has been undergoing field testing in supermarkets. The control algorithm is available as a software addition to the Johnson Controls/Encore 2100 direct digital control system. A stand-alone unitary version replaces the standard mechanical timer controls used in most supermarkets.

For more information, contact EPRI, 3412 Hillview Ave., Palo Alto, CA 94304; 972-869-9773;

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