Energy Services Bulletin June 2013 - Technology spotlight: Evaporator fan controllers reduce energy use

Technology spotlight: Evaporator fan controllers reduce energy use

By operating fans at low speed when cooling isn’t needed, and at high speed only when the system is actively cooling the refrigerator, the EC motor controller introduces much less heat into the refrigerator. (Photo by Energy Control Equipment, Inc.)

The small and inconspicuous evaporator fans in walk-in coolers and freezers don’t usually get much attention, but they can have a surprising effect on energy bills because they typically run 24/7 and generate heat that adds to the cooling load. Controlling evaporator fans so they run at full speed only when necessary can reduce refrigeration bills by 25 to 35 percent.

Fans waste energy

For a small piece of equipment, evaporator fan motors in refrigeration units are big energy wasters because:

They are very inefficient. Evaporator fan motors are usually single-phase motors of the shaded-pole type (10 to 40 percent efficient) or permanent-split-capacitor motors (30 to 60 percent efficient).
They run 24/7. Evaporator fans provide air circulation when the compressor is on and the evaporator is cooling the walk-in unit. Even when the compressor is off, some air circulation is desirable so the cool air is distributed evenly. The fan can operate at a slower speed and still provide adequate circulation.
They generate excess heat. Any heat generated by the motors adds to the cooling load so the compressor has to work harder. Energy savings from reducing fan use is essentially doubled because the compressor will also run less.

Monitor compressor, turn fan down

When the compressor is not running, the controller turns the fan down to a lower speed to save energy. Two companies currently manufacture these controllers: Energy Control Equipment Inc., and Functional Devices, Inc.

Energy Control Equipment offers the Frigitek ECM I and ECM III controllers for electronically commutated permanent magnet (ECPM motors)—also referred to as ECMs or EC motors—because this technology saves energy and has few service issues. Because most coolers do not have ECPM motors, Energy Control Equipment also sells ECPM motors and the controllers to go with them.

This strategy addresses all three modes of energy waste:

ECPM motors are much more efficient than typical single-phase motors. ECPM motors are generally 75 to 85 percent efficient, providing significant energy savings just with the motor change.
Reduce the full-speed run time of the fans. The fans still operate 24/7, but they run at low speed most of the time. When the compressor is on—usually less than 40 percent of the time—the fans run at full speed. At low speed, the motors use only about 10 percent of the energy as at full speed. This also reduces product shrinkage due to excessive evaporation.
Reduce the cooling load. With more efficient, variable-speed motors, the fans add significantly less to the cooling load so the compressor does not have to work so hard, which also saves energy and maintenance.

Functional Devices Inc. manufactures the EFC4045T controller, which can also control shaded-pole or permanent-split-capacitor motors. Although average savings are between 25 and 35 percent of the cooler’s total energy use, the actual savings may vary as much as 10 to 60 percent. Simple paybacks generally range from one to three years.

Motor type, run-time key to energy savings

The amount of energy saved by installing a controller depends on:
• The kind of motor being replaced
• The current run-time of the compressor. The less the compressor runs (the more oversized it is for the load), the more energy your customer can save. The evaporator fan can run at low speed more often when the controller is installed. Making other efficiency improvements, such as improving the walk-in doors, seals and shell, will actually increase the effectiveness of the controller, since they will make the compressor run less.

When to use a controller

Controllers offer a quick, easy, inexpensive and usually cost-effective way to save energy. After achieving success with this measure, your customers may be willing to look at lighting, HVAC or other efficiency measures. Keep incentive programs simple and straightforward to encourage your customers to participate. For help calculating potential savings for different applications, or advice on how to structure an incentive program, call Western’s Energy Experts hotline at 800-769-3756.