Abstract:

Optimization for energy systems is considered at three levels: synthesis (configuration), design (component characteristics), and operation. This paper aims to evaluate the system performance and margins for improvement of two absorption heat pump systems, including an absorber heat exchanger (AHX) and a solution heat exchanger (SHX), and perform their design/operation optimization efficiently based on an energy-utilization diagram (EUD) for performance improvement. Before optimization, exergy efficiency is higher in the SHX cycle, while the margin for improvement is larger in the AHX cycle. The optimization attempts to reduce exergy destruction in the components where dominant exergy destruction caused by heat transfer occurs. In the absorber, the operating points are adjusted to make the temperature slopes at the hot and cold sides coincide. The design parameters in other components are adjusted to improve the heat transfer performances. The distribution of exergy destruction of each component leads to improve exergy efficiency. After these improvements, exergy efficiency is higher in the AHX cycle. It is concluded that we could efficiently realize the design/operation optimization of thermodynamic systems using an EUD, because the diagram presents both exergy destruction and margin for improvement at the components comprehensively, as well as the operating properties of working fluids.

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