Comparative analysis of low temperature industrial refrigeration systems

This paper compares the energy performance and economics of a direct two-stage ammonia system to an ammonia-carbon dioxide cascade system for low temperature (below -40 degrees C) applications. Component and system models are developed for both the direct ammonia and the ammonia-carbon dioxide cascade options. These models provide the basis for quantifying the relative operating costs for both systems on annual and life-cycle bases. The analysis shows that the ammonia-carbon dioxide cascade system option using a shell-and-tube cascade condenser offers the potential for increased energy efficiency when compared to a direct two-stage ammonia system when operating with evaporating temperatures that are below -46.2 degrees C. For the cascade system option, the analysis shows that a shell-and-tube cascade heat exchanger with design approach temperature of 5.6 degrees C provides the optimal balance of system performance with capital cost. (C) 2012 Elsevier Ltd and IIR. All rights reserved.