Abstract
In order to utilize the medium-and-low grade energy sources more efficiently, a new combined cooling, heating and power system using CO2 working fluid is proposed in this paper. The system is coupled by supercritical CO2 Brayton cycle and transcritical CO2 refrigeration cycle, and is characterized by the clever arrangement of some heat exchangers which could recover overall waste heat to generate useful heating capacity. Firstly detailed mathematical models are established to investigate the thermodynamic and exergoeconomic performance of the system. Under the preliminary design conditions with 170 °C heat source, the system could achieve values of 115.49%, 41.37% and 16.84$‧GJ−1 in thermal efficiency, exergy efficiency, and cost of unit product exergy respectively. Then comprehensive parameter analysis are conducted and reveal that within some certain ranges, the decrease of turbine inlet pressure and the increase of turbine inlet temperature, turbine outlet pressure, evaporation pressure and ratio of CO2 mass flow rates would lead to higher exergy efficiency and lower unit product exergy cost. Afterwards multi-objective optimizations performed under two operation modes demonstrate the everlasting high-efficiency of the system at different modes. Finally a performance comparison with a similar system in the literature further proves the superiority of the proposed system.
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