Multi-objective optimization screening method for high-temperature heat pump with large temperature rise and low gwp mixed refrigerant

Abstract

The application discloses a multi-target optimization screening method for a high-temperature heat pump low-GWP mixed refrigerant with a large temperature rise, and steps are as follows: a candidate pure refrigerant library is constructed; a high-temperature heat pump system thermodynamic model is constructed, and system heating performance coefficient, unit volume heating capacity and comprehensive temperature glide matching degree of the model are calculated; the NSGA-III algorithm is adopted to perform collaborative optimization on combinations of pure refrigerants in the candidate pure refrigerant library and mass fractions of components, so that a Pareto optimal solution set of the mixed refrigerant is obtained; total equivalent greenhouse effect and total investment cost of each candidate solution in the Pareto optimal solution set are calculated; the TOPSIS method is adopted to comprehensively evaluate the Pareto optimal solution set, so that comprehensive closeness degrees of each solution are obtained, and the one with the highest comprehensive closeness degree is selected as a final screening result. The method fully considers temperature glide characteristics of the non-azeotropic mixed refrigerant in evaporation and condensation processes, and solves the problem of insufficient matching of the screened mixed refrigerant with temperature change processes of a heat source and a heat sink side.

Description

Technical Field

[0001] This invention belongs to the technical field of refrigerant screening methods, specifically relating to a multi-objective optimization screening method for mixed refrigerants with low global warming potential (GWP) in high-temperature heat pumps. Background Technology

[0002] High-temperature heat pump systems typically operate under conditions of significant temperature rise, and the thermophysical properties of the refrigerant directly affect the system's cycle performance and heat exchange process. Therefore, selecting suitable refrigerants for the operating conditions of high-temperature heat pumps is an important technical approach to improving system performance.

[0003] With the development of refrigerants with low global warming potential (GWP), low GWP refrigerant blends have gradually become an important research direction for high-temperature heat pump working fluids. Existing methods for screening low GWP refrigerant blends typically use pure low GWP refrigerants as the base component. By constructing binary or ternary refrigerant blend systems and combining them with thermodynamic cycle models to calculate performance parameters such as COP and VHC under different mixing ratios, the optimal blend working fluid is determined based on the evaluation results. This type of method can utilize the complementary thermophysical properties between different components to improve the performance deficiencies of single refrigerants and enhance the cycle performance of blended refrigerants.

[0004] However, existing low-GWP mixed refrigerant screening methods mainly rely on cycle performance indicators such as COP and VHC for evaluation, without fully considering the temperature glide characteristics of non-azeotropic mixed refrigerants during evaporation and condensation. This may result in the screened mixed refrigerants having insufficient matching with the temperature change process of the heat source and heat sink, increasing irreversible losses in the heat exchange process and limiting their application in high-temperature-rise heat pumps.

[0005] Therefore, there is an urgent need to propose a multi-objective optimization screening method for low-GWP mixed refrigerants for high-temperature rise heat pumps, so as to improve the accuracy and engineering applicability of mixed refrigerant screening. Summary of the Invention

[0006] The purpose of this invention is to provide a multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature heat pumps, which solves the problem that existing screening methods do not fully consider the temperature glide characteristics of non-azeotropic mixed refrigerants during evaporation and condensation, resulting in insufficient matching between the screened mixed refrigerants and the temperature change processes of the heat source and heat sink.

[0007] The technical solution adopted in this invention is a multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature heat pumps, the steps of which are as follows: Step 1: Construct a library of candidate pure refrigerants; Step 2: Construct a thermodynamic model of the high-temperature heat pump system and calculate the system heating performance coefficient, heating capacity per unit volume, and overall temperature glide matching degree of the model. Step 3: The NSGA-III algorithm is used to combine pure refrigerants in the candidate pure refrigerant library and perform synergistic optimization of the mass fraction of the components to obtain the Pareto optimal solution set of the mixed refrigerants; Step 4: Calculate the total equivalent greenhouse effect and total system investment cost for each candidate solution in the Pareto optimal solution set; Step 5: Use the TOPSIS method to comprehensively evaluate the Pareto optimal solution set, obtain the comprehensive closeness of each solution, and select the one with the highest comprehensive closeness as the final screening result.

[0008] The invention is further characterized by: In step 1, the refrigerants in the candidate pure refrigerant library must cover hydrofluoroolefin refrigerants, hydrochlorofluoroolefin refrigerants, and hydrocarbon refrigerants.

[0009] In step 2, the thermodynamic model of the high-temperature heat pump system includes a compressor, the compressor outlet is connected to the condenser inlet, the condenser outlet is connected to the first inlet of the regenerator, the first outlet of the regenerator is connected to the evaporator inlet through an expansion valve, the evaporator outlet is connected to the second inlet of the regenerator, and the second outlet of the regenerator is connected to the compressor inlet.

[0010] In step 2, the expression for the system's coefficient of performance (COP) is: (1) (2) In equations (1) to (2), m This is the mass flow rate of the refrigerant, expressed in kg / s. h 1 and h 2 represents the specific enthalpy of the refrigerant at the compressor inlet and outlet, respectively, in kJ / kg; h 2s Enthalpy is the specific enthalpy at the compressor outlet after isentropic compression, expressed in kJ / kg. The isentropic efficiency of the compressor; This refers to the input power of the compressor; Provides heating for the system; This is the system's heating performance coefficient.

[0011] In step 2, the expression for the heat output per unit volume is: (3) In equation (3), The density of the refrigerant at the compressor inlet is expressed in kg / m³. 3 ;h 3 represents the specific enthalpy of the refrigerant at the condenser outlet, expressed in kJ / kg; Heat output per unit volume.

[0012] In step 2, the expression for the overall temperature glide matching degree is: (4) In equation (4), To achieve comprehensive temperature glide matching; This refers to the flow loss through the evaporator; This refers to the flow loss through the condenser; Loss due to the pinch point on the heat sink side of the condenser; The heat source side pinch loss of the evaporator; in, (5) (6) In equations (5) to (6), The value of the user-side fluid flowing into the evaporator; The value of the fluid flowing out of the evaporator on the user side; The refrigerant flow rate at the evaporator; The refrigerant flow rate into the evaporator; The refrigerant flow rate into the condenser; The refrigerant flow rate at the condenser; The value of the fluid flowing out of the condenser on the user side; The value of the fluid flowing into the condenser on the user side; (7) (8) In equations (7) to (8), The heat absorbed by the evaporator from the heat source side is measured in kW. The ambient temperature is expressed in Kelvin (K). The temperature of the heat source fluid when it enters the evaporator, in K; The temperature of the heat source fluid when it leaves the evaporator, in K; This represents the minimum pinch temperature difference of the heat exchanger, expressed in Kelvin (K). The heat released by the condenser to the heat sink side is measured in kW. This is the temperature of the fluid leaving the condenser on the heat sink side, in Kelvin (K). This is the temperature of the fluid entering the condenser on the heat sink side, expressed in Kelvin (K).

[0013] In step 3, the optimization objectives of the NSGA-III algorithm are: maximizing the system's coefficient of performance (COP), maximizing the volumetric heating capacity (VHC), and maximizing the overall temperature glide matching degree. minimize; The constraint of the NSGA-III algorithm is: evaporation pressure P e ≥0.2MPa, condensing pressure P c ≤3MPa, compressor discharge temperature T dis ≤180 ℃; The parameters for the NSGA-III algorithm optimization process are set as follows: population size 68, number of iterations 300, crossover probability 1.0, mutation probability 0.4, and variable length 0.1.

[0014] In step 4, the expression for the total equivalent greenhouse effect is: (9) (10) In equations (9) to (10), The total equivalent greenhouse effect; The total equivalent greenhouse effect of direct emissions; The total equivalent greenhouse effect of indirect emissions; The global warming potential is for a mixed refrigerant. The annual leakage rate of the mixed refrigerant is taken as 5%; The equipment's service life is set at 15 years. This refers to the mixed refrigerant charge, expressed in kg / s. The mixed refrigerant recovery coefficient is set to 0.7. Annual electricity consumption; The indirect CO2 emission factor is 0.581 kg CO2 / kWh. The first in the mixed refrigerant k The mass fraction of a pure refrigerant component; The first in the mixed refrigerant k The global warming potential of a single refrigerant; N is the total number of components in a mixed refrigerant.

[0015] In step 4, the expression for the total system investment cost is: (11) (12) (13) (14) In equations (11) to (14), Total system investment cost; Costs include capital investment and maintenance. Operating investment costs; For the first high-temperature heat pump system b Investment costs of major equipment; The maintenance factor is set to 1.06. This is the capital recovery factor; For interest rates; B This represents the total number of devices in a high-temperature heat pump system. The annual operating time of the equipment; The electricity price is set at $0.09 / kWh. The main equipment includes condensers, evaporators, regenerators, compressors, and expansion valves. The investment costs of the main equipment are as follows: (15) (16) (17) (18) (19) In equations (15) to (19), The capital cost of the condenser; This is the effective heat transfer area of ​​the condenser. The capital cost of the evaporator; The effective heat transfer area of ​​the evaporator; The capital cost of the regenerator; The effective heat transfer area of ​​the regenerator; The capital cost of the compressor; This refers to the input power of the compressor; The capital cost of the expansion valve; The effective heat transfer areas of the condenser, evaporator, and regenerator are all obtained from formula (20), that is: (20) In equation (20), Q Heat exchange is measured in kW. U Δ is the heat transfer coefficient, in units of kW / (m²·K); A is the effective heat transfer area; Δ t mt is the logarithmic mean temperature difference; Logarithmic mean temperature difference Δ t The expression for mt is: (twenty one) In equation (21), The inlet temperature of the hot fluid; The outlet temperature of the hot fluid; This refers to the inlet temperature of the cold fluid. This is the outlet temperature of the cold fluid.

[0016] In step 5, the evaluation indicators for comprehensively evaluating the Pareto optimal solution set using the TOPSIS method are: system coefficient of performance (COP), volumetric heating capacity (VHC), total equivalent greenhouse effect (TEWI), and total system investment cost. Z total Among them, the system heating performance coefficient (COP) and volumetric heating capacity (VHC) are extremely large indicators, while the total equivalent greenhouse effect (TEWI) and total system investment cost are also considered. Z total It is a very small indicator; The weights of the indicators used to comprehensively evaluate the Pareto optimal solution set using the TOPSIS method are set according to different engineering application scenarios, specifically as follows: Different engineering application scenarios include engineering application scenarios with equal weighting benchmarks, engineering application scenarios prioritizing performance, engineering application scenarios prioritizing economy, engineering application scenarios prioritizing environment, and engineering application scenarios with comprehensive balance. Engineering application scenarios for equal-weighted benchmarks: COP=0.25, VHC=0.25, TEWI=0.25. Z total=0.25; Performance-priority engineering applications: COP=0.35, VHC=0.25, TEWI=0.20 Z total=0.20; Economically viable engineering application scenarios: COP=0.20, VHC=0.15, TEWI=0.25. Z total=0.40; Environmentally-oriented engineering application scenarios: COP=0.20, VHC=0.15, TEWI=0.40. Z total=0.25; Comprehensive and balanced engineering application scenarios: COP=0.25, VHC=0.20, TEWI=0.30. Z total=0.25.

[0017] The beneficial effects of this invention are: (1) The method of the present invention optimizes the comprehensive temperature glide matching degree, the heating capacity per unit volume, and the system heating performance coefficient as optimization objectives of the NSGA-III algorithm (multi-objective optimization algorithm), so that the thermodynamic cycle performance of the mixed refrigerant and the temperature matching characteristics of the heat exchanger can be evaluated simultaneously during the screening process. This effectively avoids the problem of insufficient matching between the screened mixed refrigerant and the temperature change process of the heat source and heat sink side due to screening based solely on cycle performance indicators such as the system heating performance coefficient and the heating capacity per unit volume, and reduces irreversible losses in the heat exchange process. (2) When using the TOPSIS method (approximation ideal solution ranking method) for evaluation, the method of the present invention introduces the total equivalent greenhouse effect to replace the static GWP, and links the operating energy efficiency of the high temperature heat pump system with the environmental load of the life cycle; at the same time, it incorporates the total investment cost of the system, including the capital recovery coefficient and the operating electricity cost, to form a comprehensive scoring system covering multiple dimensions of thermodynamics, environment and economy. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the high-temperature heat pump system structure in the method of the present invention; Figure 2 This is a comparison diagram of the three-dimensional Pareto fronts of pure, binary, and ternary mixed working fluids obtained in Example 7 of the present invention; Figure 3 This is a graph showing the relationship between TEWI, GWP, and COP of candidate pure refrigerants in the Pareto optimal solution set in Embodiment 7 of the present invention. Figure 4 The candidate pure refrigerants in the Pareto optimal solution set of Embodiment 7 of the present invention Z total Relationship diagram with COP; Figure 5 This is a heat map showing the comprehensive proximity results of the mixed refrigerant under the weighting scheme in the equal-weight benchmark engineering application scenario of Embodiment 7 of the present invention. Figure 6 This is a radar chart showing the overall proximity of the top five mixed refrigerants under the weighting schemes of five engineering application scenarios in Embodiment 7 of the present invention.

[0019] In the diagram, 1-1. Compressor, 1-2. Condenser, 1-3. Regenerator, 1-4. Expansion valve, 1-5. Evaporator. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0021] Example 1 The present invention provides a multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature heat pumps, comprising the following steps: Step 1: Construct a candidate pure refrigerant library. The refrigerants in the candidate pure refrigerant library must cover hydrofluoroolefin refrigerants, hydrochlorofluoroolefin refrigerants, and hydrocarbon refrigerants. Step 2: Construct a thermodynamic model of the high-temperature heat pump system and calculate the system heating performance coefficient, heating capacity per unit volume, and overall temperature glide matching degree of the high-temperature heat pump system thermodynamic model; A thermodynamic model of a high-temperature heat pump system is used to simulate the refrigerant cycle process and to evaluate the performance of low-GWP mixed refrigerants. Step 3: The NSGA-III algorithm is used to combine pure refrigerants in the candidate pure refrigerant library and to perform synergistic optimization of the mass fraction of components in the combined refrigerant to obtain the Pareto optimal solution set of the mixed refrigerant. Step 4: Calculate the total equivalent greenhouse effect and total system investment cost for each candidate solution in the Pareto optimal solution set; Step 5: Use the TOPSIS method to comprehensively evaluate each solution in the Pareto optimal solution set, obtain the comprehensive similarity of each solution in the Pareto optimal solution set, sort each solution according to the comprehensive similarity from high to low, obtain the comprehensive ranking of each solution, and select the solution with the highest comprehensive similarity as the final screening result.

[0022] Example 2 Based on Example 1, in step 2, the thermodynamic model of the high-temperature heat pump system includes a compressor 1-1, the outlet of the compressor 1-1 is connected to the inlet of the condenser 1-2, the outlet of the condenser 1-2 is connected to the first inlet of the regenerator 1-3, the first outlet of the regenerator 1-3 is connected to the inlet of the evaporator 1-5 through the expansion valve 1-4, the outlet of the evaporator 1-5 is connected to the second inlet of the regenerator 1-3, and the second outlet of the regenerator 1-3 is connected to the inlet of the compressor 1-1.

[0023] The refrigerant cycle is as follows: low-pressure superheated vapor (i.e., refrigerant at state point 1 at the compressor inlet) is compressed to a high-pressure, high-temperature state (i.e., refrigerant at state point 2 at the compressor outlet), condenses into a subcooled liquid in the condenser (i.e., refrigerant at state point 3 at the condenser outlet), is further cooled by the regenerator (i.e., refrigerant at state point 4 at the regenerator outlet), expands through the expansion valve into a low-temperature two-phase state (i.e., refrigerant at state point 5 at the expansion valve outlet), absorbs heat in the evaporator to form superheated vapor (i.e., refrigerant at state point 6 at the evaporator outlet), and then returns to the compressor suction port after being reheated by the regenerator.

[0024] The input parameters for the thermodynamic model of a high-temperature heat pump system include: minimum pinch temperature difference between the evaporator and condenser, isentropic efficiency of the compressor, regenerative efficiency of the regenerator (IHX), system heating capacity, heat source inlet temperature, heat source outlet temperature, heat sink inlet temperature, heat sink outlet temperature, and superheat.

[0025] Example 3 Based on Example 2, in step 2, the expression for the system's heating performance coefficient is: (1) (2) In equations (1) to (2), m This is the mass flow rate of the refrigerant, expressed in kg / s. h 1 and h 2 represents the specific enthalpy of the refrigerant at the compressor inlet and outlet, respectively, in kJ / kg; h 2s Enthalpy is the specific enthalpy at the compressor outlet after isentropic compression, expressed in kJ / kg. The isentropic efficiency of the compressor; This refers to the input power of the compressor; Provides heating for the system; This is the system's heating performance coefficient.

[0026] The expression for heat output per unit volume is: (3) In equation (3), The density of the refrigerant at the compressor inlet is expressed in kg / m³. 3 ; h 3 represents the specific enthalpy of the refrigerant at the condenser outlet, expressed in kJ / kg; Heat output per unit volume.

[0027] The expression for the overall temperature glide matching degree is: (4) In equation (4), To achieve comprehensive temperature glide matching; This refers to the flow loss through the evaporator; This refers to the flow loss through the condenser; Loss due to the pinch point on the heat sink side of the condenser; The heat source side pinch loss of the evaporator; in, (5) (6) In equations (5) to (6), The value of the user-side fluid flowing into the evaporator; The value of the fluid flowing out of the evaporator on the user side; The refrigerant flow rate at the evaporator (the refrigerant flow rate at state point 6); The refrigerant flow rate into the evaporator is the refrigerant flow rate (the refrigerant flow rate at state point 5). The refrigerant flow rate into the condenser is the refrigerant flow rate (the refrigerant flow rate at state point 2). The refrigerant flow rate at the condenser (the refrigerant flow rate at state point 3); The value of the fluid flowing out of the condenser on the user side; The value of the fluid flowing into the condenser on the user side; The reduction in the vortex value of the fluid on the heat source side is calculated using the following formula:

[0028] The formula for calculating the increase in the sludge value of the fluid on the heat sink side is as follows:

[0029] In the formula, h 5 and h 6 represents the specific enthalpy of the refrigerant at the evaporator inlet and outlet, respectively, in kJ / kg. This is the temperature of the heat source fluid when it enters the evaporator (heat source inlet temperature), in Kelvin (K). The temperature of the heat source fluid when it leaves the evaporator (heat source outlet temperature), in K; The temperature of the fluid leaving the condenser on the heat sink side (heat sink outlet temperature), in K; The temperature of the fluid entering the condenser on the heat sink side (heat sink inlet temperature), in K; The value of ∠j at any state point j E j The expression is:

[0030] In the formula, h j State point j Specific enthalpy, expressed in kJ / kg; State point j Specific entropy, in kJ / (kg·K); h0 is the specific enthalpy under ambient conditions, in kJ / kg; T0 is the specific entropy under environmental conditions, expressed in kJ / (kg·K); T0 is the ambient temperature, expressed in K. m This is the mass flow rate of the refrigerant, expressed in kg / s. When calculating the value of σ at any state point j, the ambient temperature is T0 = 293.15 K and the atmospheric pressure is P0 = 101.325 kPa. The distribution of state points is as follows: refrigerant at compressor inlet is state point 1, refrigerant at compressor outlet is state point 2, refrigerant at condenser outlet is state point 3, refrigerant at regenerator outlet is state point 4, refrigerant at expansion valve outlet is state point 5, and refrigerant at evaporator outlet is state point 6. (7) (8) In equations (7) to (8), The heat absorbed by the evaporator from the heat source side is measured in kW. The ambient temperature is expressed in Kelvin (K). This is the temperature of the heat source fluid when it enters the evaporator (heat source inlet temperature), in Kelvin (K). The temperature of the heat source fluid when it leaves the evaporator (heat source outlet temperature), in K; This represents the minimum pinch-point temperature difference between the evaporator and the condenser, expressed in Kelvin (K). The heat released by the condenser to the heat sink side is measured in kW. The temperature of the fluid leaving the condenser on the heat sink side (heat sink outlet temperature), in K; The temperature of the fluid entering the condenser on the heat sink side (heat sink inlet temperature) is expressed in K.

[0031] Example 4 Based on Example 3, in step 3, the optimization objectives of the NSGA-III algorithm are: maximizing the system's coefficient of performance (COP), maximizing the volumetric heating capacity (VHC), and maximizing the overall temperature glide matching degree. minimize; The constraint of the NSGA-III algorithm is: evaporation pressure P e ≥0.2MPa, condensing pressure P c ≤3MPa, compressor discharge temperature T dis ≤180 ℃; The parameters for the NSGA-III algorithm optimization process are set as follows: population size 68, number of iterations 300, crossover probability 1.0, mutation probability 0.4, and variable length 0.1.

[0032] The NSGA-III algorithm optimization process includes: (1) Randomly generate an initial population based on the combination method of the candidate pure refrigerants (e.g., binary mixture, ternary mixture); (2) Using the thermodynamic model of the high-temperature heat pump system established in step 2, calculate the system heating performance coefficient (COP), volumetric heating capacity (VHC), and overall temperature glide matching degree for each individual component. ; (3) Select dominant individuals based on non-dominant ranking and reference point association strategies; (4) Generate new candidate solutions through crossover and mutation operations; (5) After multiple iterations, the set of non-dominated solutions that satisfy the constraints is obtained, which is the Pareto optimal solution set of the mixed refrigerant.

[0033] Example 5 Based on Example 4, in step 4, the expression for the total equivalent greenhouse effect is: (9) (10) In equations (9) to (10), The total equivalent greenhouse effect; The total equivalent greenhouse effect of direct emissions; The total equivalent greenhouse effect of indirect emissions; The global warming potential (GWP) is for the mixed refrigerant. The annual leakage rate of the mixed refrigerant is taken as 5%; The equipment's service life is set at 15 years. This refers to the mixed refrigerant charge, expressed in kg. The mixed refrigerant recovery coefficient is set to 0.7. Annual electricity consumption; The indirect CO2 emission factor is 0.581 kg CO2 / kWh. The first in the mixed refrigerant k The mass fraction of a pure refrigerant component; The first in the mixed refrigerant k Global warming potential of a single pure refrigerant; N This represents the total number of components in the mixed refrigerant; in, m r = m ×240 E annual = W com ×3600 (kWh).

[0034] The expression for the total system investment cost is: (11) (12) (13) (14) In equations (11) to (14), Total system investment cost; Costs include capital investment and maintenance. Operating investment costs; For the first high-temperature heat pump system b Investment costs of major equipment; The maintenance factor is set to 1.06. This is the capital recovery factor; For interest rates; B This represents the total number of devices in a high-temperature heat pump system. The annual operating time of the equipment; The electricity price is set at $0.09 / kWh. This includes the capital cost of the main equipment, the capital cost of additional equipment, and installation labor costs. The sum of the capital cost of additional equipment and installation labor costs accounts for 15% of the capital cost of the main equipment. The main equipment includes condensers, evaporators, regenerators, compressors, and expansion valves. The investment costs of the main equipment are as follows: (15) (16) (17) (18) (19) In equations (15) to (19), The capital cost of the condenser; This is the effective heat transfer area of ​​the condenser. The capital cost of the evaporator; The effective heat transfer area of ​​the evaporator; The capital cost of the regenerator; The effective heat transfer area of ​​the regenerator; The capital cost of the compressor; This refers to the input power of the compressor; The capital cost of the expansion valve; The effective heat transfer areas of the condenser, evaporator, and regenerator are all obtained from formula (20), that is: (20) In equation (20), QThe heat exchange capacity is expressed in kW; U is the heat transfer coefficient, expressed in kW / (m²·K), with the heat transfer coefficients of the evaporator, condenser, and regenerator being 0.05, 0.04, and 0.18, respectively; A is the effective heat transfer area; Δ t mt is the logarithmic mean temperature difference; Logarithmic mean temperature difference Δ t The expression for mt is: (twenty one) In equation (21), The inlet temperature of the hot fluid; The outlet temperature of the hot fluid; This refers to the inlet temperature of the cold fluid. This is the outlet temperature of the cold fluid.

[0035] Example 6 Based on Example 5, in step 5, the evaluation indicators for comprehensively evaluating the Pareto optimal solution set using the TOPSIS method are: system heating performance coefficient (COP), volumetric heating capacity (VHC), total equivalent greenhouse effect (TEWI), and total system investment cost. Z total Among them, the system heating performance coefficient (COP) and volumetric heating capacity (VHC) are extremely large indicators (positive indicators), while the total equivalent greenhouse effect (TEWI) and total system investment cost are also considered. Z total It is a very small indicator (negative indicator); The weights of the indicators used to comprehensively evaluate the Pareto optimal solution set using the TOPSIS method are set according to different engineering application scenarios, specifically as follows: Different engineering application scenarios include engineering application scenarios with equal weighting benchmarks, engineering application scenarios prioritizing performance, engineering application scenarios prioritizing economy, engineering application scenarios prioritizing environment, and engineering application scenarios with comprehensive balance. Engineering application scenarios for equal-weighted benchmarks: COP=0.25, VHC=0.25, TEWI=0.25. Z total=0.25; Performance-priority engineering applications: COP=0.35, VHC=0.25, TEWI=0.20 Z total=0.20; Economically viable engineering application scenarios: COP=0.20, VHC=0.15, TEWI=0.25. Z total=0.40; Environmentally-oriented engineering application scenarios: COP=0.20, VHC=0.15, TEWI=0.40. Z total=0.25; Comprehensive and balanced engineering application scenarios: COP=0.25, VHC=0.20, TEWI=0.30. Z total=0.25.

[0036] Example 7 This embodiment uses the method of Embodiment 6, wherein the candidate refrigerants in the candidate pure refrigerant library include R600, R150, R600a, R290, R1123, R1216, R1224yd(Z), R1233zd(E), R1234yf, R1234ze(E), R1234ze(Z), R123, R21, R601a, R1243zf, R1336mzz(Z), R152a, R161, R40, R41, R170 and RE170, and the GWP of each refrigerant used is ≤200; The thermophysical properties and environmental indicators of each refrigerant are shown in Table 1; Table 1

[0037] The specific input parameters for the thermodynamic model of the high-temperature heat pump system are as follows: minimum pinch temperature difference between the evaporator and condenser is 5 ℃, compressor isentropic efficiency is 80%, regenerator (IHX) regeneration efficiency is 0.2, system heating capacity is 42 kW, heat source inlet temperature is 25 ℃, heat source outlet temperature is 15 ℃, heat sink inlet temperature is 100 ℃, heat sink outlet temperature is 110 ℃, and superheat is 5 ℃.

[0038] This embodiment optimizes binary and ternary mixed refrigerants respectively, with ternary mixed refrigerants being the main screening target.

[0039] The NSGA-III algorithm is used to perform co-optimization on the combination of pure refrigerants in the candidate pure refrigerant library and the mass fraction of components in the combined refrigerants, to obtain the Pareto optimal solution set of the mixed refrigerants, as detailed below. Figure 2 As shown, the Pareto optimal solution set of ternary mixed refrigerants (a combination of three pure refrigerants) has a wider coverage range and better potential for comprehensive performance optimization. Its performance boundary is significantly better than that of binary mixed refrigerants (a combination of two pure refrigerants) and pure refrigerants (single-component refrigerants). Its theoretical maximum COP reaches 2.45, and its maximum VHC reaches 2523 kJ / m³. π glide,overall As low as 1.37.

[0040] The total equivalent greenhouse effect for each candidate solution in the Pareto optimal solution set for mixed refrigerants The relationship between Global Warming Potential (GWP) and Coefficient of Performance (COP) of a system is as follows: Figure 3 As shown, the total equivalent greenhouse effect (TEWI) decreases significantly with the increase of the system's coefficient of performance (COP). When the COP increases from approximately 1.9 to 2.4, the TEWI decreases by about 25%, indicating that improving the system's cycle energy efficiency can significantly reduce the lifecycle carbon emissions generated by electricity consumption during operation. In contrast, the GWP of different candidate refrigerants shows a more obvious discrete distribution within the same COP range, and some low-GWP refrigerants do not exhibit lower TEWIs. This indicates that using GWP alone is insufficient to comprehensively characterize the lifecycle environmental performance of high-temperature heat pump systems. Therefore, this invention uses the total equivalent greenhouse effect... As an environmental assessment indicator; Total system investment cost for each candidate solution in the Pareto optimal solution set for mixed refrigerants Z total The relationship between the system's coefficient of performance (COP) and the system's heating performance is as follows: Figure 4 As shown, with the increase of COP, Z total Overall, the trend is downward, but within the same COP range, different candidate refrigerants... Z total Significant differences still exist, indicating that COP cannot fully characterize system economy. Therefore, this invention will... Z total It should be included in the comprehensive evaluation as an economic evaluation indicator; Under the weighting scheme of the equal-weighted benchmark engineering application scenario, the comprehensive ranking of each solution obtained in step 5 is as follows: Figure 5 As shown, the combination of pure refrigerants R600, R290, and R40 yielded the highest overall similarity, thus it was chosen as the preferred result for this scenario, with mass fractions of R600, R290, and R40 of 31%, 3%, and 66%, respectively. like Figure 6 As shown, the overall closeness of the ternary mixed refrigerant obtained by screening the combination of R600, R290 and R40 remained the highest under the weighted schemes of the five engineering application scenarios, which verified the stability of the formula under different decision preferences and provided a repeatable and verifiable decision basis for the selection of working fluid in clean heating projects with large temperature rise.

Claims

1. A multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature heat pumps, characterized in that, The steps are as follows: Step 1: Construct a library of candidate pure refrigerants; Step 2: Construct a thermodynamic model of the high-temperature heat pump system and calculate the system heating performance coefficient, heating capacity per unit volume, and overall temperature glide matching degree of the model. Step 3: The NSGA-III algorithm is used to combine pure refrigerants in the candidate pure refrigerant library and perform synergistic optimization of the mass fraction of the components to obtain the Pareto optimal solution set of the mixed refrigerants; Step 4: Calculate the total equivalent greenhouse effect and total system investment cost for each candidate solution in the Pareto optimal solution set; Step 5: Use the TOPSIS method to comprehensively evaluate the Pareto optimal solution set, obtain the comprehensive closeness of each solution, and select the one with the highest comprehensive closeness as the final screening result.

2. The multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature rise heat pumps according to claim 1, characterized in that, In step 1, the refrigerants in the candidate pure refrigerant library must cover hydrofluoroolefin refrigerants, hydrochlorofluoroolefin refrigerants, and hydrocarbon refrigerants.

3. The multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature rise heat pumps according to claim 1, characterized in that, In step 2, the thermodynamic model of the high-temperature heat pump system includes a compressor (1-1), the outlet of the compressor (1-1) is connected to the inlet of the condenser (1-2), the outlet of the condenser (1-2) is connected to the first inlet of the regenerator (1-3), the first outlet of the regenerator (1-3) is connected to the inlet of the evaporator (1-5) through the expansion valve (1-4), the outlet of the evaporator (1-5) is connected to the second inlet of the regenerator (1-3), and the second outlet of the regenerator (1-3) is connected to the inlet of the compressor (1-1).

4. The multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature rise heat pumps according to claim 3, characterized in that, In step 2, the expression for the system's coefficient of performance (COP) is: （1） （2） In equations (1) to (2), m This is the mass flow rate of the refrigerant, expressed in kg / s. h 1 and h 2 represents the specific enthalpy of the refrigerant at the compressor inlet and outlet, respectively, in kJ / kg; h 2s Enthalpy is the specific enthalpy at the compressor outlet after isentropic compression, expressed in kJ / kg. The isentropic efficiency of the compressor; This refers to the input power of the compressor; Provides heating for the system; This is the system's heating performance coefficient.

5. The multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature rise heat pumps according to claim 4, characterized in that, In step 2, the expression for the heat output per unit volume is: （3） In equation (3), The density of the refrigerant at the compressor inlet is expressed in kg / m³. 3 ; h 3 represents the specific enthalpy of the refrigerant at the condenser outlet, expressed in kJ / kg; Heat output per unit volume.

6. The multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature rise heat pumps according to claim 5, characterized in that, In step 2, the expression for the overall temperature glide matching degree is: （4） In equation (4), To achieve comprehensive temperature glide matching; This refers to the flow loss through the evaporator; This refers to the flow loss through the condenser; Loss due to the pinch point on the heat sink side of the condenser; For the pinch point loss on the heat source side of the evaporator; in, （5） （6） In equations (5) to (6), The value of the user-side fluid flowing into the evaporator; The value of the fluid flowing out of the evaporator on the user side; The refrigerant flow rate at the evaporator is [value missing]. The refrigerant flow rate into the evaporator; The refrigerant flow rate into the condenser; The refrigerant flow rate at the condenser; The value of the fluid flowing out of the condenser on the user side; The value of the fluid flowing into the condenser on the user side; （7） （8） In equations (7) to (8), The heat absorbed by the evaporator from the heat source side is measured in kW. The ambient temperature is expressed in Kelvin (K). The temperature of the heat source fluid when it enters the evaporator, in K; The temperature of the heat source fluid when it leaves the evaporator, in K; This represents the minimum pinch-point temperature difference between the evaporator and the condenser, expressed in K. The heat released by the condenser to the heat sink side is measured in kW. This is the temperature of the fluid leaving the condenser on the heat sink side, in Kelvin (K). This is the temperature of the fluid entering the condenser on the heat sink side, expressed in Kelvin (K).

7. The multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature heat pumps according to claim 1, characterized in that, In step 3, the optimization objectives of the NSGA-III algorithm are: maximizing the system's coefficient of performance (COP), maximizing the volumetric heating capacity (VHC), and maximizing the overall temperature glide matching degree. minimize; The constraint of the NSGA-III algorithm is: evaporation pressure P e ≥0.2MPa, condensing pressure P c ≤3MPa, compressor discharge temperature T dis ≤180 ℃; The parameters for the NSGA-III algorithm optimization process are set as follows: population size 68, number of iterations 300, crossover probability 1.0, mutation probability 0.4, and variable length 0.

1.

8. The multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature rise heat pumps according to claim 6, characterized in that, In step 4, the expression for the total equivalent greenhouse effect is: （9） （10） In equations (9) to (10), The total equivalent greenhouse effect; The total equivalent greenhouse effect of direct emissions; The total equivalent greenhouse effect of indirect emissions; The global warming potential value for the mixed refrigerant; The annual leakage rate of the mixed refrigerant; For the service life of the equipment; This refers to the mixed refrigerant charge, expressed in kg / s. The system refrigerant recovery coefficient; Annual electricity consumption; This is the indirect emission factor for CO2; The first in the mixed refrigerant k The mass fraction of a pure refrigerant component; The first in the mixed refrigerant k The global warming potential of a single refrigerant; N is the total number of components in a mixed refrigerant.

9. The multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature heat pumps according to claim 8, characterized in that, In step 4, the expression for the total system investment cost is: （11） （12） （13） （14） In equations (11) to (14), Total system investment cost; Costs include capital investment and maintenance. Operating investment costs; For the first high-temperature heat pump system b Investment costs of major equipment; For maintenance factor; This is the capital recovery factor; For interest rates; B This represents the total number of devices in a high-temperature heat pump system. The annual operating time of the equipment; Electricity price; The main equipment includes condensers, evaporators, regenerators, compressors, and expansion valves. The investment costs of the main equipment are as follows: （15） （16） （17） （18） （19） In equations (15) to (19), The capital cost of the condenser; This is the effective heat transfer area of ​​the condenser. The capital cost of the evaporator; The effective heat transfer area of ​​the evaporator; The capital cost of the regenerator; The effective heat transfer area of ​​the regenerator; The capital cost of the compressor; This refers to the input power of the compressor; The capital cost of the expansion valve; The effective heat transfer areas of the condenser, evaporator, and regenerator are all obtained from formula (20), that is: （20） In equation (20), Q is the heat exchange capacity in kW; U is the heat transfer coefficient in kW / (m²·K); A is the effective heat transfer area; Δ t mt is the logarithmic mean temperature difference; Logarithmic mean temperature difference Δ t The expression for mt is: （21） In equation (21), The inlet temperature of the hot fluid; The outlet temperature of the hot fluid; This refers to the inlet temperature of the cold fluid. This is the outlet temperature of the cold fluid.

10. The multi-objective optimization screening method for low-GWP mixed refrigerants in high-temperature rise heat pumps according to claim 9, characterized in that, In step 5, the evaluation indicators for comprehensively evaluating the Pareto optimal solution set using the TOPSIS method are: system coefficient of performance (COP), volumetric heating capacity (VHC), total equivalent greenhouse effect (TEWI), and total system investment cost. Z total Among them, the system heating performance coefficient (COP) and volumetric heating capacity (VHC) are extremely large indicators, while the total equivalent greenhouse effect (TEWI) and total system investment cost are also considered. Z total It is a very small indicator; The weights of the indicators used to comprehensively evaluate the Pareto optimal solution set using the TOPSIS method are set according to different engineering application scenarios, specifically as follows: Different engineering application scenarios include engineering application scenarios with equal weighting benchmarks, engineering application scenarios prioritizing performance, engineering application scenarios prioritizing economy, engineering application scenarios prioritizing environment, and engineering application scenarios with comprehensive balance. Engineering application scenarios for equal-weighted benchmarks: COP=0.25, VHC=0.25, TEWI=0.

25. Z total=0.25; Performance-priority engineering applications: COP=0.35, VHC=0.25, TEWI=0.20 Z total=0.20; Economically viable engineering application scenarios: COP=0.20, VHC=0.15, TEWI=0.

25. Z total=0.40; Environmentally-oriented engineering application scenarios: COP=0.20, VHC=0.15, TEWI=0.

40. Z total=0.25; Comprehensive and balanced engineering application scenarios: COP=0.25, VHC=0.20, TEWI=0.

30. Z total=0.25.

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