Grocery Medium Temperature Display Case Defrost Control

Evaluate a demand defrost control technology for a grocery medium temperature display case application.

In supermarkets and grocery stores, the refrigeration system operates continuously to maintain proper food product temperatures within the refrigerated display cases. The most important constituent of the cooling load of these display cases, and particularly of open cases, is the infiltration of warm and moist air from the neighboring space. When this moist air contacts the evaporator coil, which has a surface temperature below the dew point temperature of the air, formation of frost on the coil is inevitable. The coil then requires defrosting to maintain system performance and product temperature within the cases. However, conventional defrost processes add to the energy usage of the refrigeration system. In this context, conventional defrost refers to off-cycle defrosts that are initiated on a preset time cycle, normally every six to eight hours, and terminated when either the evaporator temperature reaches a predetermined temperature or the defrost cycle reaches a predetermined duration, whichever takes place first. Demand defrost technologies—technologies that can detect ice on the evaporator coil and then optimally initiate and terminate defrosts—have the potential to greatly improve the efficiency of the defrost cycle. According to the manufacturer, demand defrost technology is an ice-sensing component consisting of a line-array of light-emitting diodes (LEDs) and light detectors attached to the evaporator tubes. This component can detect all forms of water (e.g., dew, condensation, and frost) that are in contact with the probe’s surface by the optical opacity and refraction index. That is, the detector senses frost build up as an occlusion of the LED light—which causes the component to initiate a defrost—and the absence of frost as the light expected from the LED—which causes the component to terminate the defrost Aligned with its mandate to validate the benefits of emerging energy technologies, SCE undertook an investigation to determine the potential energy and demand reduction possible with demand defrost technology—and to determine if the technology offered performance comparable to conventional technology.