Walk-In Cooler Controllers

In almost all coolers and freezers—small or large—air is cooled by forced-circulation evaporators that contain propeller fans powered by fractional-horsepower motors. These fans typically run continuously, even though, on average, full airflow is only required about half of the time. In the most common applications (those that use single-phase power), motors for the fans are usually shaded-pole or permanent-split-capacitor types, both of which are very inefficient.

Controllers are currently available that slow these fans when full-speed operation is unnecessary. They do this simply and inexpensively by taking advantage of a basic principle of motor operation: The lower the voltage that’s applied to a motor, the less rotational force it produces and the slower the motor speed. Reducing the operating speed also reduces the energy consumption of the fan. In addition, the motor produces less heat at slower speeds, which means that the compressor has less heat to remove from the refrigerated compartment. Anecdotal evidence also suggests that product quality in walk-in coolers can be improved. Because less air is circulated when the fan speed is reduced, items such as flowers, produce, or meat do not dehydrate as much.

In field tests for controllers from one manufacturer, documented savings varied from 10 percent to 60 percent of overall refrigeration energy, and some users reported payback periods as short as one year. Savings vary widely, however, as they are dependent primarily on duty cycle, evaporator motor power, and local utility rates.

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