Energy and exergy analyses of a modified combined cooling, heating, and power system using supercritical CO2

• A modified combined cooling, heating and power system (CCHP) is proposed using supercritical CO2.
• A more practical performance metric is introduced in order to quantify system thermal efficiency.
• The ratio of COP between the new CCHP cycle and the transcritical CO2 ejector cycle increases from 1.29 to 2.43.
• The extraction turbine is helpful to gain more refrigeration.
• The exergy efficiency of the modified CCHP with extraction turbine is higher than that of CCHP with no-extraction turbine.

In aim to reduce the greenhouse-gas emissions and improve the low-grade heat efficiency, a modified CCHP (combined cooling, heating, and power) system is proposed using supercritical CO2. This cycle combines a Brayton cycle and a transcritical ejector refrigeration cycle by adding an extraction turbine. A mathematical model is developed to simulate the modified CCHP system. Parametric analysis and exergy analysis are conducted to investigate the effects of key thermodynamic parameters on the performance and exergy destruction. Due to the difficulties in the thermal efficiency evaluation for CCHP system, a more practical performance metric is introduced in order to quantify system performance. The results indicate that both higher extraction rate and extraction pressure are helpful to gain more refrigeration. For the conditions considered, the exergy efficiency of the modified CCHP with the extraction turbine is higher than that of the CCHP with the no-extraction turbine from 10.4% to 22.5%. Furthermore, there is a large increase in the turbine power output and the exergy efficiency with increased turbine inlet temperature. It reveals that a rise of heat source quality benefits the system performance.