Application of zeotropic refrigerants in large chillers.

Large commercial or industrial chiller systems conventionally are configured with the fluid to be cooled flowing inside tubes and refrigerant evaporating outside the tubes; either as flooded bundle or thermosyphon-type systems. In such systems, single-component or azeotropic refrigerants have historically been preferred. Such systems also have inventories of refrigerant measured in hundreds of kilograms, limiting the application of some low-GWP refrigerant options. The search continues for refrigerants having acceptable safety characteristics and low environmental impact, measured by low GWP and low/no production of persistent degradation products such as trifluoroacetic acid. This paper presents conceptual modelling and practical performance testing for using zeotropic refrigerant R-444A (GWP 92) and other fluids in such chiller application geometries. The consequences of the system composition shift are demonstrated.