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.

What are the options?

Evaporator fan controllers operate by cutting the voltage to the motor by almost 80%, which reduces the motor’s speed from about 1,600 to 400 rpm. The lower speed is the minimum speed required to provide defrosting and prevent air in the cooler from stratifying into layers of higher and lower temperature.

Figure 1 provides an overview of walk-in cooler options, including their features and expected savings.

Figure 1: Walk-in cooler control options

Several manufacturers offer evaporator fan controllers. The table below presents some of the options, including an overview of device features and manufacturer savings estimates. To learn more about these products, check out the US Department of Energy report Summary of Advanced WICF Control Technologies (PDF).
Figure 1: The Frigitek evaporator-fan controller

How to make the best choice

Selection factors Controllers don’t work for every application, so you should consider several factors before deciding to install one on your cooler (figure 2).

Figure 2: When to use an evaporator fan controller

Use our table to help determine whether a particular walk-in cooler is a good candidate for an evaporator fan controller.
Figure 2: When to use an evaporator fan controller

Cost-effective controllers Controller cost-effectiveness needs to be evaluated on a case-by-case basis. For coolers with three-phase fans—which are typically found in warehouses or distribution centers—cost-effectiveness calculations can be complicated. These calculations need to factor in the cost of installing conduit and wiring to reach multiple evaporator coils, and the number of master control and power units needed will vary by application. But because single-phase applications don’t have these issues, and the controllers for single-phase fans and their installation are relatively inexpensive and usually highly cost-effective, evaluations for their cost-effectiveness aren’t especially detailed or complicated. To help with determining cost-effectiveness, manufacturers offer tools that help evaluate the cost-effectiveness of their products in the context of a specific project.

Who are the manufacturers?

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