Dynamic performance comparison of different cascade waste heat recovery systems for internal combustion engine in combined cooling, heating and power

Abstract The internal combustion engine is an important prime mover in combined cooling, heating and power systems. However, approximately 30–40% of the input energy is discharged by exhaust; thus, it is significant to recover the exhaust waste heat. Cascade energy-utilisation systems have high efficiencies for exhaust recovery with a large temperature drop. However, waste heat-recovery systems usually work under different conditions and therefore, it is meaningful to study the dynamic performance of cascade systems. In this work, by developing a model library of common components in thermodynamic systems, dynamic simulation models of three cascade systems are established: an electric-cooling cogeneration system (ECCS), a double-effect absorption refrigeration system, and a double-stage organic Rankine cycle. The dynamic response speed and off-design performance of each system are analysed and compared. The results indicate that all the cascade systems respond considerably more slowly than any single-stage cycle, and the ECCS achieves the best off-design performance because both its upper and lower stages (high-temperature organic Rankine cycle and absorption refrigeration) exhibit perfect working condition adaptability, especially the lower stage. Furthermore, the structure of the ECCS is more beneficial for the lower stage to maintain satisfactory off-design performance.