Comparison study of conventional and advanced exergy analysis on cascade high temperature heat pump system based on experiment

Abstract

Cascade high temperature heat pump (CHTHP) has shown remarkable application potential for industrial waste heat recovery owing to its superiority of large temperature lift. Great efforts have been made to optimize the performance of CHTHP by means of conventional exergy analysis (CEA), which was not qualified to uncover the thermodynamic interactions among components. Thus, advanced exergy analysis (AEA) has been adopted to comparatively evaluate the relationships of reversibility among the CHTHP components. Herein, both CEA and AEA were based on the experiment results from a prototype which could realize maximum temperature lift of 100 °C.The CEA results show that total exergy efficiency is 43.23%, while AEA results indicate that endogenous part accounts for 98.27% of the total exergy destruction and 67.69% of it is avoidable. The AEA reveals that the highest improvement priority belongs to low temperature compressor (LTCOM), followed by cascade heat exchanger (CHE) and high temperature compressor (HTCOM) and that low temperature expansion valve (LTEV) and high temperature expansion valve (HTEV) has no improvement potential which is different from the results of CEA theory. Conclusively, AEA can give more detailed guidance about the potential for improvement.

Keywords

• Cascade high temperature heat pump
• Advanced exergy analysis
• Low grade waste heat
• Exergy destruction
• Improvement potential