A composite refrigerant for medium-temperature chillers, its preparation method and application

Abstract

This invention discloses a composite refrigerant for medium-temperature chillers, its preparation method, and its application. It relates to the field of refrigerant technology. The aforementioned composite refrigerant for medium-temperature chillers comprises, by mass percentage: 75%–96% of a first component, which is composed of 2,3,3,3-tetrafluoropropylene, or composed of 2,3,3,3-tetrafluoropropylene and at least one selected from trans-1,3,3,3-tetrafluoropropylene, 3,3,3-trifluoropropylene, and carbon dioxide; 2%–20% of a second component, which is selected from at least one of the following: 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, 1,1-difluoroethane, and pentafluoroethane; and 0%–8% of a third component, which is selected from at least one of the following: 1,1,1,2,3,3,3-heptafluoropropane, carbon dioxide, pentafluoroethane, 1,1,1,2-tetrafluoroethane, and 1,1,2,2-tetrafluoroethane. The composite refrigerant of this invention has an overall GWP value of less than or equal to 150, and the system COP is stable at no less than 90% of the R134a reference system, thus achieving stable energy efficiency under the premise of low GWP.

Description

Technical Field

[0001] This invention relates to the field of refrigerant technology, and in particular to a composite refrigerant for medium-temperature chillers, its preparation method, and its application. Background Technology

[0002] As global efforts to address climate change deepen, the refrigeration and air conditioning industry faces increasingly stringent environmental regulations, making refrigerant substitution a key focus within the sector. Among various refrigeration and air conditioning equipment, medium-temperature chillers are widely used in key areas such as industrial process cooling, commercial building central air conditioning, and data center heat dissipation. The choice of refrigerant for these chillers significantly impacts system energy efficiency, operational safety, and environmental impact. For a long time, R134a has been the mainstream refrigerant for medium-temperature chillers. R134a is a hydrofluorocarbon with zero ozone depletion potential, high thermodynamic properties suitable for medium-temperature operating conditions, and non-flammability, thus ensuring its long-term reliable application in chillers. However, R134a has a high global warming potential. In the event of a leak, the greenhouse effect of a unit mass of R134a released into the atmosphere is equivalent to thousands of times the mass of carbon dioxide, significantly contradicting current global policies aimed at promoting carbon neutrality and controlling the use of substances with high warming potential. Currently, the use of R134a in new equipment faces a timetable for gradual reduction and even elimination. Finding a low global warming potential alternative refrigerant suitable for medium-temperature chillers has become a critical issue that the industry urgently needs to address.

[0003] In existing technologies, research on alternatives to R134a is relatively abundant, mostly focusing on single or mixed refrigerants with low global warming potential. Common technical routes include using environmentally friendly substances such as R1234yf, R1234ze(E), R152a, and R32 as base components, forming binary or multi-component mixture refrigerants through different ratios. Among them, R1234yf and R1234ze(E) belong to hydrofluoroolefins, have extremely low global warming potential, short atmospheric lifetimes, and share certain physical properties with R134a, and are considered potential direct alternatives. R152a also has a low global warming potential and a similar volumetric cooling capacity to R134a, but it has slight flammability. R32, due to its high energy efficiency and low global warming potential, is widely used in the residential air conditioning field. Existing patents and literature contain numerous descriptions of composite refrigerant formulations based on these low global warming potential working fluids, and have conducted systematic evaluations of their cycle performance, flammability suppression strategies, and material compatibility under general air conditioning or heat pump conditions.

[0004] However, existing research and patents on alternative refrigerants with low global warming potential primarily focus on applications such as residential air conditioners, commercial multi-split systems, or air-source heat pumps, with insufficient research on their adaptability to the specific operating window of medium-temperature chillers. Medium-temperature chillers differ significantly from the aforementioned equipment in terms of evaporation temperature range, heat exchanger flow path design, two-phase heat transfer characteristics, and annual operating load distribution. This makes it difficult to obtain a globally optimal solution for this type of chiller by directly applying existing "general-purpose" low global warming potential refrigerant mixing approaches. Specifically, existing technical solutions have the following limitations.

[0005] First, the optimization of the cycle thermodynamic performance of existing mixed refrigerants often targets the energy efficiency ratio or cooling capacity under a certain rated operating condition, failing to fully consider the coupling characteristics of the refrigerant with the compressor and heat exchanger under partial load and variable evaporation temperature conditions in medium-temperature chillers. The temperature glide characteristics of mixed refrigerants have a more complex impact in flooded or falling film evaporators of chillers. If the ratio design is inappropriate, it will lead to an increase in the evaporator heat transfer temperature difference and a decrease in heat transfer performance, thus offsetting the environmental benefits brought by refrigerants with low global warming potential.

[0006] Second, existing solutions lack specific research on heat transfer performance in the two-phase and high-dryness regions. In the evaporator of a medium-temperature chiller, the refrigerant is in a two-phase flow state dominated by liquid boiling. The heat transfer intensity is comprehensively affected by the refrigerant's physical properties, surface tension, thermal conductivity, and boiling nucleation characteristics. Some low-global-warming-potential alternative working fluids and their mixtures deviate significantly from R134a in terms of heat transfer coefficients and pressure drop characteristics. Without specialized heat transfer adaptation design, relying solely on thermodynamic cycle calculations will be insufficient to guarantee the design margin and operational stability of the actual heat exchanger.

[0007] Third, system safety issues have not been adequately addressed in existing general formulations for chiller unit scenarios. Some alternatives introduce components with a certain degree of flammability in pursuit of lower global warming potential. Although the overall flammability can be reduced through the proportion of flame-retardant components, chiller units typically have large refrigerant charges and are often installed in relatively enclosed spaces such as basements or machine rooms, making the requirements for controlling safety risks after refrigerant leakage more stringent. Existing technologies have not yet provided clear safety boundary definitions for the trade-off strategies between flammability, energy efficiency, and environmental characteristics for large-charge medium-temperature chiller units.

[0008] Fourth, the issue of matching the actual refrigerant composition with the effective composition after operation is generally overlooked. Composite refrigerants exhibit component migration during charging, leakage, and replenishment. Especially after long-term operation, the refrigerant composition circulating within the system may deviate from the initial charging formula, thus affecting unit performance and reliability. Existing technical solutions rarely conduct systematic assessments of the evolution of the effective composition under actual operating conditions of medium-temperature chillers and its impact on long-term performance.

[0009] Fifth, the optimal carbon emission throughout the entire life cycle has not been comprehensively considered in existing technologies. The environmental benefits of alternative refrigerants should not be measured solely by the global warming potential, but should comprehensively consider the climate impact of the entire process, including refrigerant production, charging, operational energy efficiency, leakage rate, and end-of-life disposal. Most existing solutions focus on direct emission reduction, lacking detailed calculations and optimizations for indirect emissions—especially the incremental carbon emissions during operation due to changes in energy efficiency—specifically tailored to the operating characteristics of medium-temperature chillers.

[0010] In summary, for the specific application field of medium-temperature chillers, existing low global warming potential refrigerant technologies cannot simultaneously meet the synergistic optimization requirements of multiple dimensions such as cycle thermodynamic performance, two-phase heat transfer performance, system safety, effective composition stability, and carbon emissions throughout the entire life cycle. There is an urgent need to develop a low global warming potential composite refrigerant specifically adapted to medium-temperature chillers and its preparation and application methods. Summary of the Invention

[0011] A composite refrigerant for use in medium-temperature chillers, comprising, by mass percentage:

[0012] 75% to 96% of the first component, wherein the first component is composed of 2,3,3,3-tetrafluoropropylene, or is composed of 2,3,3,3-tetrafluoropropylene and at least one selected from trans-1,3,3,3-tetrafluoropropylene, 3,3,3-trifluoropropylene, and carbon dioxide;

[0013] 2% to 20% of a second component, wherein the second component is selected from at least one of the following: 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, 1,1-difluoroethane, pentafluoroethane;

[0014] 0% to 8% of a third component, wherein the third component is selected from at least one of the following: 1,1,1,2,3,3,3-heptafluoropropane, carbon dioxide, pentafluoroethane, 1,1,1,2-tetrafluoroethane, and 1,1,2,2-tetrafluoroethane.

[0015] According to embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0016] This invention relates to a composite refrigerant for medium-temperature chiller units, which uses three functional components—a first component, a second component, and a third component—work synergistically. The first component, comprising 75% to 96% of the total refrigerant, is selected primarily from hydrofluoroolefins and natural refrigerants with extremely low GWP values. This formulation fundamentally ensures that the overall GWP value of the composite refrigerant is less than or equal to 150, directly meeting the requirements of next-generation refrigerants. This fundamentally solves the core technical problem of traditional R134a refrigerants having excessively high GWP values ​​and being unable to adapt to increasingly stringent greenhouse gas control requirements.

[0017] Meanwhile, the tetrafluoropropylene component selected in the first component can fully leverage its optimized thermophysical properties for the specific operating conditions of medium-temperature chiller units with 9~12℃ supply water and 12~17℃ return water. Among them, 2,3,3,3-tetrafluoropropylene has a low critical temperature. In the evaporation temperature range of medium-temperature operating conditions, its relative temperature increases accordingly and its surface tension decreases significantly, which can greatly improve the heat exchange efficiency of the two-phase region of the heat exchanger.

[0018] Based on this, the 2%~20% performance adjustment group defined in this invention can precisely adjust key thermodynamic parameters such as saturation pressure, dynamic viscosity, and surface tension of the composite refrigerant through the selection of adaptable hydrofluorocarbon components. This effectively compensates for the cooling capacity and cycle energy efficiency loss caused by the low GWP first component, ensuring that the system COP is not lower than 90% of the R134a reference system under the target medium temperature conditions, thus achieving stable energy efficiency under the premise of low GWP.

[0019] The second component, ranging from 0% to 8%, through the reasonable addition of non-flammable or weakly flammable working fluids, can effectively dilute the combustion limit of flammable components in the system and reduce the flame propagation speed. Without significantly increasing the overall GWP or affecting the system's cycle energy efficiency, the flammability of the composite refrigerant is controlled at a slightly flammable level, making its safety level approach or reach A2L level. Ultimately, this achieves a synergistic balance between the three core objectives of environmental compliance, energy efficiency compliance, and safety controllability, and solves the technical bottleneck in the development of existing low-GWP refrigerants, which often results in one aspect being neglected and multiple constraints being unable to be met simultaneously.

[0020] According to one embodiment of the present invention, the first component is composed of 2,3,3,3-tetrafluoropropylene and trans-1,3,3,3-tetrafluoropropylene. The excellent heat transfer characteristics of 2,3,3,3-tetrafluoropropylene combined with trans-1,3,3,3-tetrafluoropropylene under high dryness conditions enable precise adaptation of heat transfer characteristics throughout the entire process from the two-phase region to the high dryness region of the heat exchanger. This solves the common industry problem of existing general-purpose low-GWP refrigerants not being specifically optimized for medium-temperature conditions, exhibiting poor heat transfer adaptability in this scenario, and severely degraded cycle performance.

[0021] According to one embodiment of the present invention, the first component consists of 80%–86% by mass of 2,3,3,3-tetrafluoropropylene and 2%–4% by mass of trans-1,3,3,3-tetrafluoropropylene, or the first component consists of 4%–14% by mass of 2,3,3,3-tetrafluoropropylene and 76%–82% by mass of trans-1,3,3,3-tetrafluoropropylene. This ratio range ensures that the overall GWP of the mixed working fluid is less than or equal to 150, and through the adjustment of the ratio of the two components, a precise match is achieved between the saturation pressure, heat transfer characteristics, and medium-temperature operating conditions.

[0022] According to one embodiment of the present invention, the first component further includes 2% to 6% by mass of 3,3,3-trifluoropropylene. Introducing a small amount of 3,3,3-trifluoropropylene can further reduce the gas-power field (GWP) and improve heat transfer-related properties.

[0023] According to one embodiment of the present invention, the first component further includes 1% to 4% carbon dioxide by mass. Introducing carbon dioxide as a natural working fluid can further reduce direct carbon emissions and improve heat exchanger compatibility under specific operating conditions.

[0024] According to one embodiment of the present invention, the second component, by mass ratio, comprises: 2% to 6% of 1,1,1,2-tetrafluoroethane and 2% to 6% of 1,1-difluoroethane. This combination and proportion range can effectively adjust the saturation pressure, viscosity, and surface tension of the mixed working fluid, improve the heat exchanger efficiency, compensate for the cooling capacity and COP losses caused by the first component, ensure that the COP under intermediate temperature conditions is not lower than 90% of the R134a standard, and at the same time, will not cause the overall GWP to exceed the standard.

[0025] According to one embodiment of the present invention, the second component comprises 2% to 4% by mass of 1,1,2,2-tetrafluoroethane. Based on the synergistic multi-objective balance of the three functional groups (first component, second component, and third component), 1,1,1,2-tetrafluoroethane exhibits excellent compatibility with the R134a compressor and can regulate the system pressure level.

[0026] According to one embodiment of the present invention, the second component comprises 2% to 6% pentafluoroethane by mass.

[0027] According to one embodiment of the present invention, the third component comprises 0.1% to 2% by mass of 1,1,1,2,3,3,3-heptafluoropropane.

[0028] According to one embodiment of the present invention, the composite refrigerant for medium-temperature chillers comprises, by mass percentage: 76%–88% 2,3,3,3-tetrafluoropropylene, 2%–14% trans-1,3,3,3-tetrafluoropropylene, 2%–6% 1,1,1,2-tetrafluoroethane, and 2%–6% 1,1-difluoroethane. This formulation uses 2,3,3,3-tetrafluoropropylene as the main component for reducing GWP, supplemented by trans-1,3,3,3-tetrafluoropropylene to regulate pressure levels, and then balances performance and safety through small amounts of 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane.

[0029] According to one embodiment of the present invention, the composite refrigerant for the medium-temperature chiller unit comprises, by mass percentage: 76%–88% 2,3,3,3-tetrafluoropropylene, 0%–18% trans-1,3,3,3-tetrafluoropropylene, 2%–6% 3,3,3-trifluoropropylene, 2%–6% 1,1,1,2-tetrafluoroethane, and 2%–6% 1,1-difluoroethane. This formulation introduces a small amount of 3,3,3-trifluoropropylene to further reduce the gas per watt (GWP) and improve heat transfer.

[0030] According to one embodiment of the present invention, the composite refrigerant for the medium-temperature chiller unit comprises, by mass percentage: 76%–88% 2,3,3,3-tetrafluoropropylene, 0%–14% trans-1,3,3,3-tetrafluoropropylene, 2%–4% 1,1,2,2-tetrafluoroethane, 2%–6% 1,1,1,2-tetrafluoroethane, and 2%–8% 1,1-difluoroethane.

[0031] According to one embodiment of the present invention, the composite refrigerant for the medium-temperature chiller unit comprises, by mass percentage: 76%–88% 2,3,3,3-tetrafluoropropylene, 0%–18% trans-1,3,3,3-tetrafluoropropylene, 2%–6% pentafluoroethane, 4%–6% 1,1,1,2-tetrafluoroethane, and 2%–6% 1,1-difluoroethane. This formulation achieves flammability suppression through pentafluoroethane and maintains performance through small amounts of 1,1,1,2-tetrafluoroethane and 1,1-difluoroethane.

[0032] According to one embodiment of the present invention, the composite refrigerant for the medium-temperature chiller unit comprises, by mass percentage: 76%–88% 2,3,3,3-tetrafluoropropylene, 0%–14% trans-1,3,3,3-tetrafluoropropylene, 2%–6% 1,1,1,2-tetrafluoroethane, 2%–6% 1,1-difluoroethane, and 1%–4% carbon dioxide. This formulation further reduces direct carbon emissions by introducing carbon dioxide and improves operating components by utilizing its high volatility.

[0033] According to one embodiment of the present invention, the composite refrigerant for the medium-temperature chiller unit, by mass percentage, comprises 76% to 88% 2,3,3,3-tetrafluoropropylene as the first component, and 1% to 2% pentafluoroethane, 2% to 3% 1,1,1,2-tetrafluoroethane, 1% to 2% 1,1,2,2-tetrafluoroethane, and 4% to 5% 1,1-difluoroethane.

[0034] According to one embodiment of the present invention, the supply water temperature of the medium-temperature chiller unit is 9~12℃, and the return water temperature is 12~17℃. When the supply and return water temperatures are increased from the conventional 7℃ / 12℃ to 9-12℃ / 14-17℃, the evaporation temperature increases, and the system pressure ratio decreases. At this time, the saturation pressure of 2,3,3,3-tetrafluoropropylene is close to R134a, but the surface tension decreases faster with increasing temperature, which is beneficial for reducing flow resistance and improving wettability in the heat exchanger. Trans-1,3,3,3-tetrafluoropropylene has moderate heat transfer in the low dryness region, but its heat transfer coefficient is significantly improved in the high dryness region (the later section of the evaporator), making it suitable for the high dryness of the evaporator outlet under medium-temperature operating conditions. Mixing the two in an appropriate ratio can achieve a more balanced heat transfer performance throughout the evaporator.

[0035] According to one embodiment of the present invention, the GWP value of the composite refrigerant is less than or equal to 150.

[0036] According to one embodiment of the present invention, the composite refrigerant, under the operating conditions of a medium-temperature chiller with a supply water temperature of 9~12℃ and a return water temperature of 12~17℃, has a system COP of not less than 90% of the R134a reference system.

[0037] According to one embodiment of the present invention, the composite refrigerant, under the operating conditions of a medium-temperature chiller with a supply water temperature of 9~12℃ and a return water temperature of 12~17℃, has a life-cycle carbon emission lower than 93% of that of the R134a reference system.

[0038] According to one embodiment of the present invention, the composite refrigerant is a non-azeotropic mixture, which undergoes gas-liquid phase composition differences and migration during charging or operation. Different components have different saturated vapor pressures and phase equilibrium constants. When the composite refrigerant is charged into the system, the compositional differences between the gas and liquid phases during system operation result in a difference between the circulating working fluid composition and the charging composition. In the formulation of the present invention, the formulation containing carbon dioxide can utilize this characteristic, using carbon dioxide as a volatility regulator to give the actual operating working fluid better thermodynamic properties.

[0039] Specifically, the technical solution adopted according to the second aspect of the present invention is as follows:

[0040] A method for preparing the composite refrigerant for medium-temperature chillers includes the following steps:

[0041] The components are mixed under vacuum conditions to obtain the composite refrigerant used in medium-temperature chillers.

[0042] Another aspect of the invention relates to the application of the composite refrigerant for medium-temperature chillers in heat pump or vapor compression refrigeration systems, wherein the evaporation temperature range of the heat pump or vapor compression refrigeration system matches the evaporation temperature range of the medium-temperature chiller.

[0043] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0044] The terms "preferred," "more preferred," etc., used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0045] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0046] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of the present invention.

[0047] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0048] The names, CAS numbers, and serial numbers of the refrigerant components and reagents used in this invention are shown in Table 1.

[0049] Table 1

[0050] 2,3,3,3-Tetrafluoropropylene 754-12-1 R1234yf trans-1,3,3,3-tetrafluoropropylene 29118-24-9 R1234ze(E) 3,3,3-Trifluoropropylene 677-21-4 R1243zf 1,1,1,2-Tetrafluoroethane 811-97-2 R134a 1,1,2,2-Tetrafluoroethane 359-35-3 R134 1,1-Difluoroethane 75-37-6 R152a pentafluoroethane 354-33-6 R125 1,1,1,2,3,3,3-Hepfluoropropane 431-89-0 R227ea carbon dioxide 124-38-9 R744

[0051] Example 1

[0052] A composite refrigerant for use in medium-temperature chillers, comprising, by mass percentage:

[0053] First component: 18% 2,3,3,3-tetrafluoropropylene, 74% trans-1,3,3,3-tetrafluoropropylene and 2% 3,3,3-trifluoropropylene;

[0054] Second component: 2% 1,1,1,2-tetrafluoroethane; 4% 1,1,2,2-tetrafluoroethane.

[0055] A method for preparing the composite refrigerant for medium-temperature chillers includes the following steps:

[0056] The components are mixed under vacuum conditions to obtain the composite refrigerant used in medium-temperature chillers.

[0057] Example 2

[0058] A composite refrigerant for use in medium-temperature chiller units, comprising the following components by mass percentage:

[0059] First component: 86% of 2,3,3,3-tetrafluoropropylene, 2% of trans-1,3,3,3-tetrafluoropropylene;

[0060] Second component: 6% 1,1,1,2-tetrafluoroethane, 4% 1,1-difluoroethane, and 2% pentafluoroethane.

[0061] A method for preparing the composite refrigerant for medium-temperature chillers includes the following steps:

[0062] The components are mixed under vacuum conditions to obtain the composite refrigerant used in medium-temperature chillers.

[0063] Example 3

[0064] A composite refrigerant for use in medium-temperature chiller units, comprising the following components by mass percentage:

[0065] First component: 80% 2,3,3,3-tetrafluoropropylene and 4% trans-1,3,3,3-tetrafluoropropylene;

[0066] Second component: 11% 1,1,1,2-tetrafluoroethane, 5% 1,1-difluoroethane.

[0067] A method for preparing the composite refrigerant for medium-temperature chillers includes the following steps:

[0068] The components are mixed under vacuum conditions to obtain the composite refrigerant used in medium-temperature chillers.

[0069] Example 4

[0070] A composite refrigerant for use in medium-temperature chiller units, comprising the following components by mass percentage:

[0071] First component: 4% 2,3,3,3-tetrafluoropropylene and 82% trans-1,3,3,3-tetrafluoropropylene;

[0072] Second component: 4% 1,1,1,2-tetrafluoroethane, 4% 1,1,2,2-tetrafluoroethane;

[0073] The third component: 6% carbon dioxide.

[0074] A method for preparing the composite refrigerant for medium-temperature chillers includes the following steps:

[0075] The components are mixed under vacuum conditions to obtain the composite refrigerant used in medium-temperature chillers.

[0076] Example 5

[0077] A composite refrigerant for use in medium-temperature chiller units, comprising the following components by mass percentage:

[0078] First component: 88% 2,3,3,3-tetrafluoropropylene;

[0079] Second component: 3% 1,1,1,2-tetrafluoroethane, 2% 1,1,2,2-tetrafluoroethane, 5% 1,1-difluoroethane, and 2% pentafluoroethane.

[0080] A method for preparing the composite refrigerant for medium-temperature chillers includes the following steps:

[0081] The components are mixed under vacuum conditions to obtain the composite refrigerant used in medium-temperature chillers.

[0082] Comparative Example 1

[0083] A refrigerant having the component 1,1,1,2-tetrafluoroethane.

[0084] Comparative Example 2

[0085] A refrigerant with the component trans-1,3,3,3-tetrafluoropropylene.

[0086] Performance testing:

[0087] The composite refrigerants used in medium-temperature chiller units in Examples 1-5 and the refrigerants in Comparative Examples 1-2 were used to test their refrigeration performance, environmental characteristics, safety level, and carbon emission level throughout their entire life cycle. The test results are shown in Table 2.

[0088] The testing setup is as follows:

[0089] The core test bench uses a vapor compression type small refrigeration and heat pump performance test bench, which adopts a closed-loop water circulation system and refrigerant circulation system.

[0090] Compressor: It adopts a 1-horsepower fully enclosed variable frequency compressor adapted to R134a working fluid, with a rated cylinder displacement of 22.6cc and a rated variable frequency adjustment range of 1000RPM~4500RPM.

[0091] Evaporator: Employs a stainless steel plate heat exchanger, with each plate measuring 189mm × 75mm, totaling 24 plates, and a rated total heat exchange area of ​​0.28m². 2 It is used to achieve heat exchange between refrigerant and chilled water.

[0092] Condenser: Employs a stainless steel plate heat exchanger, with each plate measuring 189mm × 75mm, totaling 28 plates, and a rated total heat exchange area of ​​0.32m². 2 It is used to achieve heat exchange between refrigerant and cooling water.

[0093] The cooling capacity is calculated from the measured temperature difference between the inlet and outlet of the evaporator water side, the flow rate, and the specific heat capacity of water. The calculation formula is as follows:

[0094] ;

[0095] In the formula:

[0096] Q0: Measured cooling capacity of the system, in W;

[0097] c: Specific heat capacity of water at constant pressure, taken as 4.186 kJ / (kg・℃);

[0098] ρ: Density of water under test conditions, taken as 1000 kg / m³ 3 ;

[0099] V: Measured volumetric flow rate of chilled water on the evaporator side, in m³ / s. 3 / s;

[0100] Δt: The measured difference between the chilled water return temperature and the supply temperature of the evaporator, in °C.

[0101] The coefficient of performance (COP) is the ratio of the measured cooling capacity of the system to the power consumption of the compressor input, and the calculation formula is as follows:

[0102] ;

[0103] In the formula:

[0104] COP: Coefficient of performance of refrigeration system;

[0105] Q0: Measured cooling capacity of the system, in W;

[0106] P: Measured input electrical power of the compressor, in watts (W), obtained by a high-precision power meter.

[0107] The Global Warming Potential (GWP) is calculated using the overall GWP value of the composite refrigerant, employing a weighted summation method based on the component mass percentages. The calculation formula is as follows:

[0108] ;

[0109] GWP mix Overall GWP value of composite refrigerant;

[0110] w i : The mass percentage of the i-th component;

[0111] GWP i : The baseline GWP value of the i-th component over a 100-year timescale;

[0112] The calculation results are rounded to the nearest integer, and the overall GWP ≤ 150 is used as the compliance criterion.

[0113] The flammability rating prediction is based on the ASHRAE 34-2022 standard. It uses the toxicity data, flammability limits, and maximum flame propagation speed of each component of the composite refrigerant to predict the safety rating of the composite refrigerant. The focus is on determining whether it meets the A2L level of slightly flammable safety rating requirements, and simultaneously comparing its combustion characteristics with those of R1234ze (E).

[0114] The simulation of the full life cycle carbon emission index is based on the full life cycle carbon emission accounting model of the refrigeration system. It takes the sum of direct and indirect carbon emissions during the entire life cycle of the unit as the total accounting target, and simulates and calculates the full life cycle carbon emission index per unit refrigeration area, with the unit being kgCO2e / m². 2 The final simulation results were used as a benchmark for the life-cycle carbon emissions of a 100% R134a baseline system to calculate the relative emission reduction.

[0115] Table 2

[0116] Cooling capacity (W) COP GWP Flammability (predicted) <![CDATA[Full life cycle carbon emission index (kgCO2e / m 2 )(simulation)* <!-- 7 -->]]> Comparative Example 1 2987 5.23 1300 A1 123 Comparative Example 2 2813 4.96 1 A2L 99 Example 1 2734 4.93 72 Approximately R1234ze(E) (A2L) 106 Example 2 3165 4.97 148 Approximately R1234 ze(E) (A2L) 92 Example 3 2893 5.42 150 Approximately R1234 ze(E) (A2L) 80 Example 4 2773 4.95 98 Slightly lower than R1234 ze(E) (A2L) 114 Example 5 2950 5.39 133 Approximately R1234 ze(E) (A2L) 75

[0117] In Example 1, the overall GWP of the formulation was only 72, far below the regulatory threshold of 150. The core reason is that the total proportion of low GWP components such as tetrafluoropropylene and trifluoropropylene in the formulation was as high as 94%, which achieved a significant reduction in GWP from the source, while ensuring that the COP met the standard.

[0118] The measured cooling capacity of the formulation in Example 2 was 3165W, which is 5.96% higher than the R134a baseline (Comparative Example 1). It is the only formulation that achieves a cooling capacity higher than the baseline value. The core reason is that by using 2% pentafluoroethane and 4% 1,1-difluoroethane in synergy, the cooling capacity per unit volume of the mixed working fluid is significantly improved on the basis of low GWP, thus solving the technical problem of general cooling capacity reduction in low GWP formulations.

[0119] The measured COP of the formulation in Example 3 was as high as 5.42, which is 3.63% higher than the R134a baseline (Comparative Example 1), showing the best energy efficiency. The core reason is that 12% 1,1,1,2-tetrafluoroethane and 4% 1,1-difluoroethane optimized the viscosity and surface tension of the mixed working fluid, improved the heat exchanger's heat exchange efficiency, and significantly reduced the irreversible heat transfer loss of the system, thus achieving a significant improvement in energy efficiency.

[0120] The flammability of the formulation in Example 4 is slightly lower than that of the R1234ze (E) benchmark (Comparative Example 2), and its safety level is better than the A2L standard. The core reason is that the synergistic effect of the three non-flammable components of 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, and carbon dioxide effectively dilutes the concentration of flammable components and reduces the flame propagation speed, thus achieving extreme flame suppression.

[0121] Example 5 shows that the carbon emissions of the formulation over the entire life cycle are only 61% of the R134a baseline (Comparative Example 1), which is the lowest among all examples. The core reason is that the formulation simultaneously optimizes the direct carbon emissions from refrigerant leakage caused by low GWP and the indirect carbon emissions from unit operation caused by ultra-high COP, achieving a significant pressure reduction in total carbon emissions over the entire life cycle and the best overall performance.

[0122] The composite refrigerant used in the medium-temperature chiller unit of Example 5 and the refrigerants of Comparative Examples 1-2 were used to test the life cycle carbon emission index of units at different temperatures. Under the uniform conditions of fixed compressor rated operation at 60Hz and condenser side inlet water temperature of 30℃ / outlet water temperature of 35℃, the operating COP values ​​of each sample were measured under three operating conditions: low temperature unit (supply water temperature of 7℃, return water temperature of 12℃), medium temperature unit (supply water temperature of 12℃, return water temperature of 17℃), and high temperature unit (supply water temperature of 17℃, return water temperature of 22℃). The life cycle carbon emission index per unit cooling area of ​​each sample under different operating conditions was simulated and calculated. The test results are shown in Table 3.

[0123] Table 3

[0124] Example <![CDATA[Carbon emission index over the full life cycle of the low-temperature unit (kgCO2e / m 2 )(simulation)*]]> <![CDATA[Full - life - cycle carbon emission index of medium - temperature unit (kgCO2e / m 2 )(simulation)*]]> <![CDATA[Carbon emission index over the full life cycle of a high-temperature unit (kgCO2e / m 2 )(simulation)*]]> Comparative Example 1 136 123 107 Comparative Example 2 108 99 93 Example 5 85 75 71

[0125] As shown in Table 3, the test results clearly verify the low-carbon advantages of the composite refrigerant in Example 5 across all operating conditions and the entire life cycle. Specifically, its carbon reduction effect across all operating conditions is comprehensively superior: Example 5 exhibits significantly lower carbon emissions throughout its entire life cycle than the two benchmarks under low-temperature, medium-temperature, and high-temperature unit operating conditions. Compared to the traditional mainstream refrigerant R134a (Comparative Example 1), emissions are reduced by 37.5%, 39.0%, and 33.6%, respectively, with reductions exceeding 30% across all operating conditions, completely resolving the high carbon emission technical problem caused by the high GWP of R134a throughout its entire life cycle. Compared to the mainstream low-GWP alternative R1234ze (E) (Comparative Example 2), emissions are reduced by 21.3%, 24.2%, and 23.7%, respectively. Even under non-directionally optimized high and low temperature operating conditions, it maintains a stable carbon reduction advantage of over 20%, breaking the industry limitation that existing low-GWP refrigerants can only reduce direct carbon emissions and cannot simultaneously address indirect carbon emissions during operation.

[0126] The optimized effect for medium-temperature units is precisely implemented: Under the core operating conditions of 12-17℃ medium-temperature units optimized by this invention, the carbon emissions throughout the entire life cycle of Example 5 are reduced to 75kgCO2e / m³. 2 The value is the lowest under all operating conditions, and the reduction compared to the two benchmarks has reached the peak. This fully verifies that the formula of this invention is fully valid for the thermophysical property matching and multi-component synergistic design logic of medium-temperature chillers. By controlling direct carbon emissions with the low GWP first component and reducing indirect carbon emissions during operation through high-efficiency formula optimization, a significant reduction in carbon emissions throughout the entire life cycle has been achieved.

[0127] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A composite refrigerant for use in medium-temperature chiller units, characterized in that: By weight percentage, including: 75% to 96% of the first component, wherein the first component is composed of 2,3,3,3-tetrafluoropropylene, or is composed of 2,3,3,3-tetrafluoropropylene and at least one selected from trans-1,3,3,3-tetrafluoropropylene, 3,3,3-trifluoropropylene, and carbon dioxide; 2% to 20% of a second component, wherein the second component is selected from at least one of the following: 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, 1,1-difluoroethane, pentafluoroethane; 0% to 8% of a third component, wherein the third component is selected from at least one of the following: 1,1,1,2,3,3,3-heptafluoropropane, carbon dioxide, pentafluoroethane, 1,1,1,2-tetrafluoroethane, and 1,1,2,2-tetrafluoroethane.

2. The composite refrigerant for medium-temperature chiller units according to claim 1, characterized in that: The first component consists of 2,3,3,3-tetrafluoropropylene and trans-1,3,3,3-tetrafluoropropylene.

3. The composite refrigerant for medium-temperature chillers according to claim 1, characterized in that: The first component also includes 2% to 6% by mass of 3,3,3-trifluoropropylene.

4. The composite refrigerant for medium-temperature chillers according to claim 1, characterized in that: The second component, by mass ratio, comprises: 2% to 6% of 1,1,1,2-tetrafluoroethane and 2% to 6% of 1,1-difluoroethane.

5. The composite refrigerant for medium-temperature chiller units according to claim 1, characterized in that: The second component comprises 2% to 4% by mass of 1,1,2,2-tetrafluoroethane.

6. The composite refrigerant for medium-temperature chillers according to claim 1, characterized in that: The composite refrigerant used in the medium-temperature chiller unit, by mass percentage, comprises 76%–88% 2,3,3,3-tetrafluoropropylene as the first component, and 1%–2% pentafluoroethane, 2%–3% 1,1,1,2-tetrafluoroethane, 1%–2% 1,1,2,2-tetrafluoroethane, and 4%–5% 1,1-difluoroethane.

7. The composite refrigerant for medium-temperature chillers according to claim 1, characterized in that: The supply water temperature of the medium-temperature chiller unit is 9~12℃, and the return water temperature is 12~17℃.

8. The composite refrigerant for medium-temperature chillers according to claim 1, characterized in that: The GWP value of the composite refrigerant is less than or equal to 150.

9. A method for preparing a composite refrigerant for a medium-temperature chiller unit as described in any one of claims 1 to 8, characterized in that: Includes the following steps: The components are mixed under vacuum conditions to obtain the composite refrigerant used in medium-temperature chillers.

10. The application of the composite refrigerant for medium-temperature chillers as described in any one of claims 1 to 8 in a heat pump or vapor compression refrigeration system, wherein the evaporation temperature range of the heat pump or vapor compression refrigeration system matches the evaporation temperature range of the medium-temperature chiller.