Evaporator-fan controllers operate by cutting the voltage to the motor by almost 80 percent (from between 110 and 115 volts to 20 volts in typical single-phase applications). This reduces the motor’s speed—usually from about 1,600 to 400 rpm. The lower speed is considered to be the bare minimum required to provide defrosting and prevent air in the cooler from stratifying into layers of higher and lower temperature.
There are two manufacturers that produce evaporator-fan controllers. One of them, Energy Control Equipment Inc., produces a controller called the Frigitek that can be used in either coolers or walk-in freezers (Figure 1). The Frigitek reduces fan speed in response to a signal from the thermostat to stop the flow of refrigerant. For single-phase power applications, the Frigitek is available in configurations that can handle from 3.5 to 25.0 amps and from 115 to 480 volts (V). These units also have a field-adjustable low-speed setting to accommodate unique application requirements. For three-phase power applications, one available configuration uses a master control unit that can handle 480 V and motors of up to 20 horsepower. Additional power units are added for multiple evaporators.
Figure 1: The Frigitek evaporator-fan controller
This unit is for single-phase applications.
For single-phase controllers, Frigitek’s prices start at about $500. Three-phase applications are considerably more expensive, particularly if fans from multiple evaporators are to be controlled. Installation costs for single-phase units are typically about $100 per unit, but they will vary depending on the region, the number of fans controlled, and the installer.
The second manufacturer, Functional Devices Inc., produces the ECT4045T, an enclosed, two-speed electronically commutated motor (ECM)/shaded-pole-motor phase controller with temperature differential input of 120 or 240 volts alternating current (VAC) for use in walk-in coolers. Check with manufacturers for current pricing.