Modeling of secondary loop refrigeration systems in supermarket applications

Today\u27s supermarket refrigeration systems predominantly use the direct expansion vapor compression cycle to provide cooling to refrigeration and freezer display cases. Next to the environmental concerns of global warming and ozone depletion associated with leakage of the currently used CFC and HCFC refrigerants from these systems, there is also a concern for the rising cost of purchasing suitable alternative refrigerants as those currently used are phased-out. Many of the refrigeration challenges faced by supermarkets may be suitably addressed through the implementation of a secondary loop system. Secondary loop refrigeration will dramatically reduce or eliminate the direct harmful impact of refrigerant leakage to the environment; however, consideration must also be given to the indirect environmental impact of using secondary loop systems. This document provides a discussion on the challenges faced by supermarket refrigeration systems and discusses the advantages and disadvantages of implementing secondary loop refrigeration. Finally, this document presents the results of an extensive effort to numerically model both direct expansion and secondary loop refrigeration systems, and presents a case study in which the performance of a secondary loop refrigeration system is compared to that of a direct expansion system in a supermarket. The simulated results indicate that an ammonia/HFE 7100 secondary loop system will require 15% less energy to deliver the same cooling capacity as an HCFC-22 direct expansion system