Increasing energy prices, tighter energy efficiency legislation, and interest in energy conservation have created a strong demand for efficient refrigerated appliances. In response, suppliers have started to offer a range of solutions to save energy in applications such as refrigerated display cases, bottle coolers, walk-in coolers, and refrigerated vending machines. Possibly the easiest and most widely adopted energy-efficiency improvement is the substitution of electronically commutated (ECM) evaporator and condenser fan motors for their wasteful traditional motor counterparts.

Although ECM motors have been available for some time, their use in the fractional horsepower range was limited to premium applications because of complex and costly, fully featured electronic controls. In more recent years though, ECM motor manufacturers have developed simpler, energy-efficient solutions that can now cost-effectively replace traditionally inefficient induction motors as standard products.

Wellington Drive Technologies Ltd., a supplier of energy-saving ECM motors, developed and manufactures the ECR series; a range of ECM motors specifically designed to replace inefficient shaded-pole and PSC induction motors in commercial refrigeration applications.

In January 2009, Wellington launched two products as part of the ECR series: the ECR83/93 for display cases, bottle coolers, and vending machines; and the ECR85/95 for walk-in coolers. These complement the ECR92 UltraSynch motor released in 2008, and the long-established ECR80/90 and 81/91 motors. The ECR85/95 in particular was designed as a solution to help satisfy the requirements of the Energy Independence and Security Act of 2007 (Sec 312), which stated that, among other energy-saving improvements, all walk-in coolers and freezers installed in the U.S. after Jan. 1, 2009, shall use either electronically commutated or three-phase motors as evaporator fan motors of under 1 HP and less than 460 V.

ECM technology

The ECR83/93 was designed as a low-cost solution for display cases and vending machines.

ECM motors are brushless DC motors in which the direction of the electric current in the motor is switched (commutated) using electronic controllers. Apart from energy efficiency, ECM motors have several other key advantages over traditional shaded-pole and PSC motors. ECM motors can have independent speed control, which enables better control of air-flow in a refrigeration application. Additionally, this independent control allows for many air-flow requirements to be accommodated by a single motor (reducing the number of motor variants a refrigeration OEM needs to carry). With long-life ball bearings and little heat rejected into the motor (operating at much higher efficiency points than traditional motors), the ECR series of electronically commutated motors has high reliability and design life longer than most AC motors.

The UltraSynch technology deployed in the ECR92 was chosen by Vendo de Mexico for the majority of its bottle coolers and was selected by Hill Phoenix for the company’s high-efficiency display cases. UltraSynch technology enables motors to maintain absolutely constant speed across wide input voltage ranges (185 V to 250 V and 90 V to 140 V). This is achieved by on-board electronics and software that measure the AC supply many times each second and lock the motor speed to the AC supply frequency. In countries with large voltage fluctuations in the power supply, UltraSync can lengthen motor life up to three times.

UltraSync technology also eliminates beat-frequency noise in multi-motor installations, such as refrigerated display cases. Beat-frequency noise often occurs in the most sensitive part of the human hearing spectrum — an irritation to retailers and shoppers alike. In addition, the speed of the ECR92 UltraSynch motor is precisely fixed and remains stable over the life of the motor. This means that, from the spare parts standpoint, if an ECR92 UltraSynch motor has to be replaced, the replacement will run at exactly the same speed as the original, and the fan will deliver the same flow. This removes the possibility of problems with replacements, or the need to hold inventory of expensive motors set for different speeds.

Another characteristic of the Wellington ECR motor is Timed Reverse, a software feature that automatically reverses condenser fans for a preset time during compressor off periods. This helps keep condenser fins and coils cleaner and more efficient and, with no relays needed, saves cost.

Mechanically, the ECR series is very different from a traditional motor. The motors use distributed windings as opposed to the more traditional stamped lamination and wound slot geometries that consume more steel and copper (and drive up cost). The distributed winding does not concentrate flux at stator poles as a traditional motor geometry does. The distributed winding therefore almost completely eliminates cogging, the largest driver for torque ripple and in-turn motor derived vibration. It therefore almost eliminates motor-derived noise.

Energy savings

Enlarge this picture Fig. 1. Energy cost comparison between ECR85/95 and shaded-pole motor.

The main element that sets ECR motors apart from induction motors used in refrigerated equipment is their energy saving capability. In particular, the smaller size ECR motors, such as the ECR83/93 (6 W to 12 W output power) for display cases, bottle coolers, and vending machines, feature efficiency ratings up to 65 percent, much higher than the typical 18 percent efficiency of comparable shaded-pole motors. Another widely used type of refrigeration motor, the PSC induction motor, has full-load efficiency levels up to 50 percent, but in most cases operate at less than full load, which reduces the efficiency of the motor to only 15 percent to 40 percent when installed in a refrigerator. The higher efficiency of the ECR motor is due to the precise control of motor current and yields high direct energy savings when compared to both shaded pole and PSC induction motors.

In addition, because of their higher efficiency, ECR motors run cool. They generate and release very little heat inside the refrigerators, which means that the compressor has to run less time to maintain a constant low temperature, allowing further energy savings. Extensive comparative tests of ECR motors and a range of shaded-pole products have shown that ECR motors typically use 70 percent less energy than comparable shaded-pole motors in display cases, bottle coolers and vending machines, which results in payback periods of less than one year.

Larger ECR motors like the ECR85/95 (1/15 HP output power) for walk-in coolers’ evaporators have efficiency rates greater than 70 percent; while shaded-pole motors in this range are typically 25 percent to 30 percent efficient, and PSC induction motors are 40 percent to 45 percent efficient. In the case of shaded-pole motors, 70 percent to 75 percent of the energy used by the motors is released as waste heat inside the walk-in cooler, and that waste heat must be removed by the system’s condensing unit. This means that ECR85/95’s cool operation not only reduces direct energy consumption, but also yields additional energy savings at the condensing unit level. On average, for every two watts saved in the evaporator with ECR, an additional watt is saved at the condensing unit level, for a total saving of three watts. In terms of cost, this means savings of approximately $163/year/motor (with price of electricity 0.12 $/kWh), and payback periods of less than one year. (See Fig. 1.)

Motor design

Enlarge this picture Fig. 2. CAD illustration of the ECR83/93. High moisture and dust resistance were achieved by potting the fully integrated electronic control board, enclosing the motor in a plastic body, and sealing the shaft and end shield.

Shaded-pole motors have very simple and inexpensive designs, and while PSC induction motors provide better efficiency, they also come at higher cost due to the addition of a capacitor and more complex windings. Electronically commutated motors are undoubtedly the most expensive motor type to manufacture, mainly because of the cost of the electronic controller. But in commercial refrigeration applications electronically commutated motors are often the most cost-effective solution due to their significant energy cost savings.

Wellington ECR motors have a relatively short payback period, usually less than one year. This results from both energy cost savings and the advantages of the company’s proprietary motor design. ECR motors are built using a large number of polymer components that typically cut the motors’ steel content by 80 percent, and the copper content by 30 percent. Furthermore, the ECR motors are compact compared to induction motors, providing additional material and cost savings. (The ECR83/93 is the same size as 5 W shaded pole motor, but delivers 6 W to 12 W.)

At the electronics level, ECR motors have simpler control boards than most ECM motors including only the features required in specific refrigeration applications. Most appliance OEMs only need a more efficient drop-in replacement for the traditional motors they already use. Therefore, fully featured, variable-speed control is currently of little value in these applications and only serves to drive up cost. In time, as the value of some of these features can be measured, other ECM capabilities can be justified. Finally, because one ECR motor can match the performance of a wide range of induction motors, switching to ECR allows users to significantly reduce inventory.

In addition to cost and efficiency, two other features were considered key aspects during the design of the ECR series: ease of replacement of induction motors, and moisture resistance.

The main design challenge that Wellington engineers faced during development was fitting the electronic control inside the motor while maintaining the length of the motor within induction motor standards. Initially, this led to the design of integrated fan-motor solutions, but those required adjustments at the application level. The development of the ECR platform allowed Wellington engineers to match the external design of common shaded-pole motors while having a fully enclosed electronic control and even, as in the case of the ECR83/93, to reduce the motor length. For ease of substitution, ECR motors were also designed with the same mounting options traditionally found in refrigeration motors, along with standard fan blades, wall rings, guard grilles, brackets, and plugs. Recently, the addition of plastic accessories has helped to create an even lower cost solution for display cases, bottle coolers, and vending machines.

To deliver a drop-in replacement product, Wellington also conducted extensive airflow tests of induction motors in several refrigeration applications and designed its products to easily match induction motor airflow performance. In particular, the ECR83 speed (230 V, 50/60 Hz, 6 W to 12 W output power) was set at 1,300 RPM, while the ECR93 model (115 V, 60 Hz, 6 W to 12 W) was set at 1,550 RPM: the most common speed settings for display cases applications. The ECR85 (230 V, 50/60 Hz, 1/15 HP) runs at 1,350 RPM, while the ECR95 (115 V, 60 Hz, 1/15 HP) runs at 1,550 RPM, again the most common speed settings for walk in coolers and freezers. Notwithstanding their standard product characteristics, ECR motors can be customized to a degree only available with ECM motors, including user-defined speed settings and reversibility.

And, because refrigeration motors operate in a dusty and humid environment, the ECR motors were designed with an IP44 enclosure rating, with optional IP55 degree of protection for even higher reliability. High moisture and dust resistance were achieved by potting the fully integrated electronic control board, enclosing the motor in a plastic body and sealing the shaft and end shield. (See Fig. 2.)

Conclusion
While there are a number of approaches to cutting energy costs in commercial refrigeration applications, testing performed with OEMs showed that, in most cases, ECR motors deliver top or very competitive kWh savings for each additional dollar of investment, delivering high ROI with a relatively small initial investment. ECR motors, often in combination with another technology, can also allow refrigerated equipment to qualify for ENERGY STAR and other energy efficiency labeling programs.

For more information, email:
Marta Di Domizio: marta.didomizio@wdtl.com
David Mc Shane: david.mcshane@wdtl.com