Comprehensive Performance Evaluation Method of Working Fluids For High Temperature Heat Pump Based on Multi-Objective Optimization

Abstract

The working fluid has garnered significant attention as a critical factor influencing the efficiency of high-temperature heat pumps. A novel approach for assessing the efficacy of working fluids through the utilization of a multi-objective optimization is proposed. This method offers significant advantages in enhancing the screening efficiency of mixtures. This study utilizes eight pure refrigerants as the initial fluid set and evaluates 560 binary mixtures with a 5% composition variation. The NSGA-II algorithm is combined with the theoretical heat pump cycle model to obtain Pareto optimal solutions regarding the mixtures, with the coefficient of performance and volumetric heating capacity as the objective functions. Then the evaluation of the optimal solutions is conducted by considering their flammability, toxicity, environmental performance, and temperature glide properties. Subsequently, a comprehensive performance index is derived. The evaluation reveals the dominant solution set for each pure refrigerant. For instance, the blend R1233zd(E)/R142b(0.65/0.35) is established as a superior alternative when compared to R600a and R600. The mixture R601a/R600(0.4/0.6) is recognized to exhibit more favorable performance than R1233zd(E). In addition, various cycle configurations have been investigated, including the basic cycle, internal heat exchanger cycle, and vapor injection cycle. The optimal fluids corresponding to these cycles are R142b/R1233zd(E)(0.85/0.15), R245fa/R601(0.2/0.8), and R600a/R601(0.6/0.4), respectively, based on the specified operating conditions. This approach replaces the previous qualitative comparison-based decision making methods, offering high efficiency and practicality.

Keywords: high temperature heat pump, multi-objective optimization, working fluid, comprehensive evaluation