Almost all coolers—small and large—are cooled by forced-circulation evaporators that contain propeller fans powered by fractional-horsepower motors. These fans run continuously, even though full airflow is only required about half of the time on average. Typically, they have shaded-pole or permanent-split-capacitor motors, both of which are inefficient.
There are controllers that slow these fans when full-speed operation is unnecessary. They do so 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. Because less air is circulated when the fan speed is reduced, items such as flowers, produce, and meat don’t dehydrate as much.
According to the Regional Technical Forum’s 2016 analysis of Walk-in Evaporator Fan ECM Motor Controllers, controllers can save 121 to 327 kilowatt-hours annually, depending on the temperature of the freezer and the wattage of the fan.
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