Electronic stepper valves improve on mechanical pressure regulators

Store Equipment & Design, August, 2000 by Marc Sandofsky

As the refrigeration industry moves away from mechanical controls and toward electronic, the problem remains as how to best integrate them into systems. To that end, manufacturers are banding together to provide integrated solutions which can take maximum advantage of the new controls' capabilities.

One example of this is Emerson Electric Companies' Alco Controls of St. Louis, Mo., and CPC of Kennesaw, Ga. Alco developed the Electronic Stepper Regulator (ESR) to replace mechanical pressure regulators such as the ORIT, SORIT, and SPORT valves. The ESR is being combined now with CPC's ESR board and Einstein rack controller to provide an integrated regulator system. The ESR board provides precise and accurate system control by modulating a single plunger moved by a stepper motor. In this way, system performance is maximized.

Stepper-driven valves have a number of advantages over mechanical regulators, such as very low internal and external leakage, very little pressure drop (0.5 PSI with the valves 100% open), no orifices to clog, and no required seasonal adjustment. Those advantages provide users with three important benefits:

* More consistent product temperatures as the ESRs modulate to maintain case temperatures within [ or -]1/2[degrees] of the set point.

* Higher product quality and longer shelf life due to faster defrost and quicker recovery.

* Substantially lower energy consumption by ensuring that racks operate at optimum suction pressures.

When Alco's ESR is coupled with CPC's ESR-8 board and Einstein rack controller, a low-cost, high-performance alternative to mechanical suction regulators is created. The new arrangement provides remote temperature adjustments to minimize service calls, increased efficiency by ensuring higher suction pressures, reduced equipment stress, remote diagnostics, and alarms on high temperature, sensor or valve failure so that immediate action can be taken.

With the Einstein operating the ESR valves, the need to make adjustments to compensate for seasonal temperature changes is eliminated. By comparison, mechanical ESRs require different summer and winter setpoints since higher liquid sub-cooling and lower case loads in the winter cause higher evaporator pressure settings. This difference can be 2-3 psi, or 4-6% in energy use. Combining the ESR board and ESR valve optimizes the performance of the refrigeration system according to ambient temperatures.

When placed in a system, 1 ESR board can control up to 8 Stepper valves. Algorithms developed by CPC ensure that the lead circuit valve is always 100% open in order to raise suction pressures. This allows the compressor to operate at the highest suction pressure and lowest compression ratio so energy use is reduced," explained Abtar Singh, research manager for CPC. "For every 1 psi of suction pressure increase, energy use is reduced by roughly 2%. With electronic valves, suction pressured can be raised by up to 5 psi. That equates to about 10% savings."

CPC points out that since there is virtually no additional cost for ESRs vs. mechanical valves, and since operating and maintenance costs are lower for ESRs, there is an immediate return on investment. CPC calculates that in a store with four 50 hp racks and an energy cost of 10 cents per kWh, savings of $18 per day will be achieved, or $6,570 per year. And that's only the savings from optimizing the suction pressure. Additional savings can result from maintenance workers making fewer trips to the stores to changes valve settings since this task can be done remotely.

Mike Noble, business unit leader for regulators and electronic products for Alco, sees a number of other applications for the Stepper valve technology in the years ahead. "ESRs are only the tip of the iceberg. For example, in mechanical sub-cooling today, two different expansion valves and two-solenoid valves are required. A single Stepper expansion valve could replace the four other valves."

Noble points out that the slow, steady operation of the Stepper is more conducive to proper system operation. "Mechanical valves go directly from open to shut. Stepper valves open gradually, over 16 seconds, so system shock is eliminated."

Noble notes that the demand for electronic valves has been limited until recently because conversion costs have been very high and supermarkets have been reluctant to pay the premium. "Now that racks are being controlled electronically, it costs no more to go with electronic valves than mechanical, so they're starting to make a significant impact in the marketplace."