Development of a demand defrost controller. Final report

Abstract

Tile purpose of this project was to develop and commercialize a demand defrost controlle, (hat initiates defrosts of refrigeration systems only when required. The standard method of control is a time clock that usually defrosts too often, which wastes energy. The controller developed by this project uses an algorithm based on the temperature difference between the discharge and return of the display case air curtain along with several time settings to defrost only when needed. This controller was field tested in a supermarket where it controlled defrost of the lowtemperature display cases. According to test results the controller could reduce annual energy consumption by 20,000 and 62,000 kWh for hot gas and electric defrost, respectively. The controller saves electJ'ic demand as well as energy, is adaptable to ambient air conditions, and provides valuable savings throughout the year. The savings are greatest for lowtemperature systems that use the most energy. A less tangible benefit of the demand controller is the improvement in food quality that results from fewer defrosts.