Technoeconomic Optimization of Turbocompression Cooling Systems

Low grade waste heat streams with temperatures near 100°C are abundant, presenting a significant opportunity to reduce primary energy consumption across the world. For example, thermally activated cooling systems can utilize waste heat to meet air conditioning loads. Recently, a turbocompression cooling system (TCCS) that utilizes low grade waste heat from power plants was investigated to improve the economic viability of dry air cooling systems. The TCCS utilizes Rankine and vapor-compression cycles that are directly coupled through a high efficiency centrifugal turbine and a compressor. In this paper, a coupled thermodynamic, heat transfer, and economic model for a TCCS is applied to utilizing low grade engine coolant waste heat to meet cargo ship cooling load requirements while minimizing the payback period for a particular operational scenario. The results of this study show that with a constant heat input of 2 MW, the liquid coupled turbocompression cooling system provided 642 kW of cooling with a payback period of 2 years and 6 months, and the total cost of the heat exchangers made up more than 84% of the total system cost. In addition, a sensitivity analysis showed that the effectiveness of the power cycle heat exchangers have a stronger influence on the payback period than the cooling cycle heat exchangers.