Optimal design method for absorption heat pump cycles based on energy-utilization diagram

Optimization for energy systems is considered at three levels: synthesis (configuration), design (component characteristics), and operation. The objective of this paper is to propose a method to perform design/operation optimization efficiently based on an energy-utilization diagram (EUD) for performance improvement. Before optimization, this paper evaluates the system performance and margins for improvement of two absorption heat pumps, including an absorber heat exchanger (AHX) and a solution heat exchanger (SHX). Then, 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. The operating points are adjusted to make the temperature gradients at 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, which presents both exergy destruction and margin for improvement at the components comprehensively, as well as operating properties of working fluids.