Multiobjective optimization based on mixed refrigerants and different two-stage vapor injection systems

Vapor injection two stage cycles proved to be an effective method for heat pumps to cope with extreme conditions. COP (coefficient of performance) and volumetric heating capacity usually contradictory as two important indicators. It is necessary to provide system designers a variety of solutions to select to adapt different working conditions. This paper proposed a method to obtain the Pareto front of COP and volumetric heating capacity by exhaustive method and non-dominated sorting. This paper sets a series of equivalent conditions and range conditions to evaluate the performance of different combinations. Variables include system form, types of mixed refrigerants, mixed refrigerants components, ratio of injection. The results show that IHX (internal heat exchanger) and ternary refrigerants have advantages under the set conditions. An example and an extended case study were used to illustrate the application method of a series of optimization schemes in the Pareto front. The method proposed in this paper is not limited to the set working conditions and can be applied to other working conditions. At the same time, the Pareto front is not limited to one solution, and the system designer can select the best solution according to the actual needs from a series of solutions.