Thermo-economic analysis of a novel organic Rankine cycle integrated cascaded vapor compression–absorption system

Abstract

Integration of thermal systems improves the energy efficiency and reduces the carbon emissions. In this paper, a novel trigeneration system, which integrates the organic Rankine cycle and vapor compression–absorption cascade refrigeration cycle is proposed. The cascade refrigeration system combines the advantages of the conventional stand-alone vapor compression system and vapor absorption refrigeration system. The energetic and rational efficiencies of the proposed system, with n-pentane as an ORC working fluid, are calculated as 79.02% and 46.7%, respectively. Effects of variation in different operating parameters as well as organic working fluid on energetic and exergetic efficiencies have been studied. The coefficient of structural bond analysis demonstrates that the evaporator and cascade condenser operating temperature significantly affects the system performance. The proposed trigeneration system powered by waste heat is independent of the grid supply; however, a stand-alone vapor compression refrigeration system requires about 19.15 kWe to meet the equivalent cooling demand. The decision of selection between the stand-alone system and the proposed trigeneration system is influenced by the compressor capacity of stand-alone vapor compression refrigeration system, cost of unit electricity, compressor runtime, cost of organic Rankine cycle power block, and cost of vapor absorption system. Based on the condition of equality of the annualized cost of the stand-alone system and proposed trigeneration system, a methodology for selection between these two configurations, called selection diagram, is also presented in this paper. The selection diagram gives quick suggestion about the optimal configuration at the initial design stage. The economic analysis reveals that the simple payback period and breakeven point for the proposed hybrid system are 6.2 years and 4.9 years, respectively.