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 °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 °C. For the cascade system option, the analysis shows that a shell-and-tube cascade heat exchanger with design approach temperature of 5.6 °C provides the optimal balance of system performance with capital cost.