Multi-Objective Evaluation Strategy Based on Data Envelopment Analysis for Working Fluid Selection in the Organic Rankine Cycle

Currently, in Chinese industry substantial amounts of low-grade waste heat are underutilized. Effectively harnessing these low-temperature waste heat sources is instrumental in promoting energy conservation and emission reduction objectives. The organic Rankine cycle (ORC) serves as an effective method for utilizing low-grade waste heat. The selection of a suitable working fluid is a pivotal aspect of the design of an ORC system. There are many kinds of working fluid and they have complex molecular structures, which increases the difficulty of screening working fluids. A novel approach is proposed based on data envelopment analysis (DEA) for multi-objective evaluation of working fluids. This method takes into account the thermodynamic performance of the working fluid in the ORC (thermal efficiency, net power output, exergy efficiency), economic aspects (investment cost, exergy loss cost), and environmental considerations (exergy environmental factors, CO2 emission reduction). DEA offers a distinct advantage by objectively balancing these conflicting objectives through data-driven optimization, eliminating the need for subjective weight assignment and enabling simultaneous evaluation of thermodynamic, economic, and environmental metrics in working fluid selection. A total of 62 different working fluids were evaluated in the integrated technology. Heptane working fluid screened out by DEA was compared with working fluid R245fa, a fluid commonly used in existing literatures. The exergy loss of the Heptane working fluid is reduced by 5.02%, the thermal efficiency is increased by 0.24%, and the net output work is increased by 2.04%. The proposed evaluation method introduces a novel perspective for the efficient screening of working fluids in the ORC system for low-temperature waste heat power generation.