CN-121252282-B - Cascade high-temperature heat pump system based on low GWP mixed working medium and performance optimization method

Abstract

The invention discloses an overlapping high-temperature heat pump system based on a low GWP mixed working medium and a performance optimization method, wherein the system comprises a high-temperature-level cycle and a low-temperature-level cycle, the high-temperature-level cycle adopts a first non-azeotropic mixed working medium (R1233 zd (E)/R1234 ze (Z)), and the low-temperature-level cycle adopts a second non-azeotropic mixed working medium (R1234 ze (E)/R245 fa). During optimization, a thermodynamic model is built based on a Peng-Robinson state equation and van der Waalsco volume mixing rule, and then a Pareto optimal solution set is generated by a non-dominant sorting genetic algorithm-II with the aim of maximizing COP, minimizing the compressor pressure ratio and minimizing the system GWP, and finally the optimal proportion of working media is screened out by a TOPSIS method, so that the method is suitable for industrial waste heat recovery and other high-temperature heat pump application scenes. The invention discloses a cascade high-temperature heat pump system based on a low GWP mixed working medium and a performance optimization method, which aim to solve the technical problem that the cascade high-temperature heat pump is difficult to balance in high efficiency and low environmental influence.

Inventors

• LI XIAOHUA
• LI SHENGNAN
• Kong Cuifeng
• ZENG ZHI
• TAN JIAWANG
• LIU XIANGLONG
• LI WENJING
• ZENG LIPING
• WANG PING
• CHEN WEI

Assignees

• 湖南工程学院

Dates

Publication Date

20260508

Application Date

20251119

Claims (5)

1. 1. The performance optimization method of the cascade high-temperature heat pump system based on the low GWP mixed working medium is characterized in that the cascade high-temperature heat pump system comprises a high-temperature level cycle and a low-temperature level cycle, and an intermediate heat exchanger connected with the high-temperature level cycle and the low-temperature level cycle, wherein the high-temperature level cycle adopts a first non-azeotropic mixed working medium, the low-temperature level cycle adopts a second non-azeotropic mixed working medium, and the optimization method comprises the following steps: S1, constructing a thermodynamic model, namely, based on a Peng-Robinson state equation and van der Waalsco volume mixing rule, constructing a thermodynamic model of the cascade high-temperature heat pump system, and calculating thermodynamic parameters and core performance indexes of the thermodynamic model, wherein the thermodynamic parameters comprise pressure, temperature, enthalpy and molar volume of working media, and the core performance indexes comprise coefficient of performance (COP), compressor pressure ratio, total Global Warming Potential (GWP) of the system and exhaust temperature of a compressor; S2, setting multi-objective optimization and constraint, namely, taking performance parameters such as COP maximization, compressor pressure ratio minimization and GWP minimization as objective functions, taking the conditions that the exhaust temperature of the compressor is not higher than a preset temperature threshold value and the compressor pressure ratio is not higher than a preset pressure ratio threshold value as constraint conditions, and determining the mass fraction of a first component in the first non-azeotropic mixed working medium and the mass fraction of a second component in the second non-azeotropic mixed working medium as optimization variables, wherein the first non-azeotropic mixed working medium is a combination of R1233zd (E) and R1234ze (Z), the second non-azeotropic mixed working medium is a combination of R1234ze (E) and R245fa, and the first component is R1233zd (E) and the second component is R1234ze (E); S3, optimizing an NSGA-II algorithm, namely, calculating an optimization target value corresponding to each group of optimization variables based on the thermodynamic model by taking the optimization variables as input, and performing iterative optimization through non-dominant sequencing, crowding calculation and elite retention strategies to generate a Pareto optimal solution set; and S4, screening an optimal solution, namely comprehensively evaluating the Pareto optimal solution set by adopting a TOPSIS method, calculating the closeness between each candidate solution and a positive ideal solution based on a preset weight distribution rule, and screening out a candidate solution with the maximum closeness as an optimal solution, wherein the optimal solution corresponds to the optimal mass ratio of the first non-azeotropic mixed working medium to the second non-azeotropic mixed working medium.
2. 2. The method for optimizing performance of a cascade high-temperature heat pump system based on a low-GWP mixed working medium according to claim 1, wherein in the step S2, the value range of an optimization variable is that the mass fraction of a first component in the first non-azeotropic mixed working medium is 0.3-0.9, and the mass fraction of a second component in the second non-azeotropic mixed working medium is 0.2-0.6.
3. 3. The performance optimization method of the cascade high-temperature heat pump system based on the low-GWP mixed working medium according to claim 2 is characterized in that in the step S3, parameters of the NSGA-II algorithm are set to be 100 individuals in population scale, the iteration number is 60 generations, the crossover probability is 0.8-0.9, the variation probability is 0.01-0.03, and in the iteration process, when the average COP variation of the optimal solution sets of 10 successive generations of Pareto is smaller than 0.01, the judgment algorithm converges.
4. 4. The method for optimizing performance of the cascade high-temperature heat pump system based on the low-GWP mixed working medium according to claim 3, wherein in the step S4, the preset weight distribution rule is an index set with the maximum COP, the minimum pressure ratio, the minimum GWP and the lowest exhaust temperature, wherein the coefficient of performance COP weight is 0.5, the compressor pressure ratio weight is 0.2, the total GWP weight of the system is 0.2, and the compressor exhaust temperature weight is 0.1.
5. 5. The method for optimizing performance of a cascade high-temperature heat pump system based on a low-GWP mixed working medium according to claim 4, wherein the performance index corresponding to the optimal solution screened in the step S4 is that the system COP is more than or equal to 4.1, the compressor pressure ratio is less than or equal to 3.3, the total GWP of the system is less than or equal to 220, the exhaust temperature of the compressor is less than or equal to 116 ℃, the optimal mass ratio of the first non-azeotropic mixed working medium is R1233zd (E): R1234ze (Z) =0.62:0.38, and the optimal mass ratio of the second non-azeotropic mixed working medium is R1234ze (E): R245 fa=0.45:0.55.

Description

Cascade high-temperature heat pump system based on low GWP mixed working medium and performance optimization method Technical Field The invention relates to the technical field of heat pumps, in particular to a cascade high-temperature heat pump system based on a low GWP (global warming potential) mixed working medium and a performance optimization method. Background The cascade high-temperature heat pump can effectively enlarge the working temperature range of the heat pump by virtue of the cascade energy utilization characteristics of high-temperature and low-temperature-level circulation, realizes the efficient recovery of industrial waste heat and waste heat, has irreplaceable application value in the fields of industrial waste heat recovery, food processing and drying, medicine sterilization and the like, and has the core advantages of simple structure, high safety and strong environmental adaptability, and can meet the high-temperature heating requirements under multiple scenes. However, with the gradual implementation of global environmental protection regulations such as basic and additive amendments (Ke-Gao), traditional refrigerants with high global warming potential values (global warming potential, GWP) (such as R134a and R245 fa) are gradually limited or eliminated due to obvious influence on climate change, and a cascade high-temperature heat pump faces the core technical bottlenecks of 'high efficiency and low environmental influence' which are difficult to balance, on one hand, the environmental protection performance of new generation low-GWP pure working media (such as R1234yf and R1234ze (E)), but when the traditional working media are directly replaced, the heating quantity and the coefficient of performance (COP) of the system are generally reduced, the energy efficiency requirement of high-temperature heating is difficult to meet, on the other hand, the traditional mixed working media are researched into multi-focus single-cycle optimization, the precise proportioning design is not carried out aiming at the wide-temperature-area operation characteristics of the cascade high-temperature heat pump, and the problems of high-efficiency (caused by the compressor pressure ratio and the high-efficiency of the GWP) are lacked, the system is easy to occur, the pressure ratio is invalid (the compressor is caused, the exhaust temperature exceeds standard (influences are influenced by the service life of the equipment), Yong losses are large, and the like are solved. In addition, in the design of the traditional cascade heat pump system, the temperature sliding characteristic of the non-azeotropic mixed working medium is often ignored, so that the high-temperature and low-temperature-level cycle matching performance is poor, the heat transfer temperature difference of the intermediate heat exchanger is overlarge, the energy loss is further aggravated, and the cascade energy utilization advantage of the cascade cycle is difficult to fully develop. In summary, it is highly desirable to develop a system performance optimization scheme that adapts to the working conditions of a cascade high-temperature heat pump, and combines low GWP, high COP and safe operation, so as to break through the limitation of the prior art. Disclosure of Invention The invention aims to provide a cascade high-temperature heat pump system based on a low-Global Warming Potential (GWP) mixed working medium and a performance optimization method, which are used for improving the technical direction of energy efficiency and environmental friendliness of the system through thermodynamic modeling and a multi-objective optimization algorithm, are particularly suitable for industrial and civil scenes requiring high-temperature heating, such as industrial waste heat recovery, food processing and drying, medicine sterilization and the like, and are particularly suitable for the adoption of the low-Global Warming Potential (GWP) non-azeotropic mixed working medium. In order to achieve the aim, the invention provides an overlapping type high-temperature heat pump system based on a low GWP mixed working medium, which comprises a high-temperature level circulation, a low-temperature level circulation and an intermediate heat exchanger for connecting the high-temperature level circulation and the low-temperature level circulation, The high-temperature-level circulation adopts R1233zd (E)/R1234 ze (Z) non-azeotropic mixed working medium, and the mass ratio of R1233zd (E) to R1234ze (Z) is 0.62:0.38; The low-temperature-level circulation adopts R1234ze (E)/R245 fa non-azeotropic mixed working medium, and the mass ratio of R1234ze (E) to R245fa is 0.45:0.55; the heat transfer temperature difference of the intermediate heat exchanger is 5K, and energy exchange between low-temperature-level working medium condensation heat release and high-temperature-level working medium evaporation heat absorption is realized. Preferably, the high-temperature-s