Comparison of CO_2-Glycol-Ammonia Cascade to Trans-Critical CO_2 and Ammonia-CO_2 Cascade Systems

摘要

With the need to use low GWP / ODP refrigerants as a result of environmental factors, including newlegislation, carbon dioxide has returned to the fore as an industrial refrigerant – particularly for freezer andcold storage applications. Typical system types include trans-critical CO_2 and ammonia cascade systems. Avariation that uses cooled glycol from ammonia package chillers to condense the carbon dioxide within asubcritical system has been developed and installed in industrial cold storage applications. The system takesadvantage of equipment already being installed for chilled storage on site in order to avoid trans-criticaloperation of the CO_2 system.This paper describes the CO_2-glycol-ammonia cascade system and presents examples of installed systems. Thepaper then compares trans-critical CO_2, ammonia-CO_2 cascade and CO_2-glycol-ammonia cascade systems,and concludes with recommendations in terms of efficiency and capital cost.