Subcooler and deep subcooler for refrigerating system and control method of subcooler and deep subcooler

Abstract

The invention discloses a subcooler and a deep subcooler for a refrigerating system and a control method of the subcooler and the deep subcooler, and belongs to the technical field of refrigeration. The deep subcooler comprises a subcooling heat exchange unit, an independent cold source loop and a pressure control valve; the supercooling heat exchange unit is connected between the high-pressure liquid reservoir and the throttling device in series, and the primary liquid refrigerant is deeply cooled to be equal to or close to the target value of the evaporation temperature through low-temperature cooling capacity provided by a low-pressure evaporation system or an independent cold source loop. The independent cold source is driven by a compressor with the minimum refrigerating capacity in the system, and an air return pipeline of the independent cold source is bridged with air return pipelines of other compressors of the system through an outlet pressure balance valve, so that the surplus refrigerating capacity is fully utilized. The evaporation pressure of a cold source loop is changed by monitoring the supercooled liquid temperature and feeding back and adjusting the opening degree of a pressure control valve, precise closed-loop control over the supercooled temperature is achieved, throttling flash gas can be remarkably reduced or even eliminated, the effective refrigerating capacity of unit refrigerant and the heat exchange efficiency of an evaporator are improved, and the system energy efficiency is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of refrigeration system technology, specifically to a subcooler and a deep subcooler for refrigeration systems and their control methods. Background Technology

[0002] In a conventional vapor compression refrigeration cycle, after the high-pressure condensed liquid refrigerant flows through the throttling device, a large amount of flash gas is generated because the temperature before throttling is higher than the saturation temperature corresponding to the pressure after throttling. This phenomenon stems from the inherent thermodynamic characteristic of "insufficient sensible heat, supplemented by latent heat": the throttling process is approximately an adiabatic isenthalpic process. The sensible heat of the liquid before throttling is insufficient to provide the enthalpy value required at the pressure after throttling. Some of the liquid must absorb latent heat through evaporation to make up for this enthalpy difference, thus forming flash gas (flash evaporation).

[0003] Flash gas cannot effectively participate in the entire refrigeration cycle through its latent heat of phase change; it can only exchange heat as sensible heat, directly causing three adverse effects: First, it reduces the effective cooling capacity per unit mass of refrigerant, as the flash gas flows through the evaporator as a gaseous phase and cannot utilize its latent heat of phase change for cooling. Second, it increases system flow resistance; the flow resistance of a two-phase flow (gas-liquid) is much greater than that of a single-phase liquid, resulting in an increase in the actual evaporation pressure of the evaporator. The compressor then needs to consume more effective work to maintain the entire refrigeration cycle. Third, it occupies a significant portion of the evaporator's effective heat exchange area; the flash gas requires a large portion of the evaporator's actual heat exchange area to pass through, reducing the evaporator's effective heat exchange efficiency and potentially leading to a decrease in the actual evaporation pressure, further increasing compression work. Ultimately, this results in a significant decrease in the system's coefficient of performance (COP).

[0004] To reduce flash gas emissions, various supercooling solutions have emerged in existing technologies, but all of them have significant technical limitations: (1) Conventional regenerative cycle subcooling: using return gas for subcooling, the degree of subcooling is limited by the return gas temperature. Usually, after subcooling, the liquid temperature is more than 8°C higher than the evaporation temperature, making it difficult to achieve deep subcooling. After throttling, there is still a large amount of flash gas. (2) Two-stage compression with intermediate cooling: It can only subcool the liquid refrigerant to about 5°C above the saturation temperature corresponding to the intermediate pressure. The subcooling depth is limited, and flash gas cannot be fundamentally suppressed. (3) Existing external subcooling units or economizers: Although they can provide additional cooling capacity, the subcooling temperature of the cold source is usually too high, which leads to a mismatch between the temperature of the subcooled liquid and the main system, resulting in high energy consumption. In addition, they lack precise closed-loop control and the subcooling effect is unstable.

[0005] In summary, existing technologies cannot eliminate flash gas at its source. Therefore, the industry urgently needs a subcooling device for refrigeration systems that can deeply subcool the primary liquid refrigerant in the main cycle to near or equal to the evaporation temperature, minimize or even completely eliminate flash gas, operate stably and controllably, and achieve optimal system energy efficiency. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a subcooler and a deep subcooler for a refrigeration system and a control method thereof, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, a specific embodiment of the present invention provides a deep subcooler for a refrigeration system. The refrigeration system includes a main compressor, an auxiliary compressor, a condenser, a high-pressure receiver, a subcooling heat exchange unit, a throttling device, an evaporator, and an outlet pressure control valve, connected sequentially via pipelines. It also includes a subcooling heat exchange unit having a primary side flow path and a secondary side flow path for mutual heat exchange. The primary side flow path is connected in series between the outlet of the high-pressure receiver and the inlet of the throttling device. The deep cooler has an independent cold source circuit for providing cooling capacity to the secondary side flow path of the subcooling heat exchange unit. This cold source circuit includes a dedicated subcooling auxiliary compressor and a pressure control valve, which is installed on the return gas pipeline of the independent cold source circuit or on the subcooling heat exchange unit, for regulating and stabilizing the evaporation pressure on the secondary side of the subcooling heat exchange unit at a saturation pressure 3°C lower than the evaporation pressure of the main refrigeration system. The subcooling heat exchange unit is configured to cool the primary liquid refrigerant flowing through its primary side flow path to a target temperature. This reduces the amount of flash gas generated by the primary liquid refrigerant after throttling by the throttling device to zero; the target temperature satisfy: In the formula, Temperature of the supercooled liquid, expressed in degrees Celsius (°C). The evaporation temperature of the evaporator in the main refrigeration system, expressed in degrees Celsius (°C).

[0008] According to another embodiment of this application, a subcooler and its control method for a refrigeration system are used to cool the primary liquid refrigerant of the main circulation to a temperature higher than the target temperature by utilizing the evaporation pressure of the main refrigeration system. The subcooled liquid at 3°C ​​reduces the dryness of the flash gas after throttling to ≤2%, thereby significantly improving the COP of the refrigeration system. Simultaneously, this invention provides technical support for replacing the complex and costly low-pressure circulating tank pump unit, enabling the direct expansion liquid supply system to completely replace the traditional low-pressure liquid supply method, thus facilitating the integrated factory prefabrication and assembly of refrigeration rooms.

[0009] In addition, the two types of subcoolers and deep subcoolers for refrigeration systems and their control methods proposed above in this application may also have the following additional technical features: In one embodiment of this application, the rated cooling capacity of the subcooling auxiliary compressor is less than or equal to the rated cooling capacity of the main compressor in the refrigeration system, and is preferably the compressor with the smallest rated cooling capacity in the refrigeration system.

[0010] In one embodiment of this application, when the device is configured as a deep subcooler, the heat transfer temperature difference... That is, the temperature of the liquid refrigerant after subcooling is 3°C higher than the evaporator evaporation temperature; that is, the evaporation temperature of the cold source circuit is 3°C lower than the evaporator evaporation temperature of the main system; the target temperature when the device is configured as a subcooler. The difference between the actual temperature and the temperature is 3°C, at which point the amount of flash gas generated reaches ≤2%; the actual temperature satisfy: In the formula, Temperature of the supercooled liquid, expressed in degrees Celsius (°C). The evaporation temperature of the evaporator in the main refrigeration system is expressed in degrees Celsius (°C).

[0011] In one embodiment of this application, the heat transfer temperature difference The range of values ​​is to Optimal heat transfer temperature difference for More preferably, the subcooling heat exchange unit is configured to have a preset heat exchange area, so as to achieve the desired heat transfer temperature difference. for Under the conditions specified, the primary liquid refrigerant is cooled to the target temperature. (To+3℃).

[0012] In one embodiment of this application, the subcooled heat exchange unit is one of a vertical or horizontal shell-and-tube heat exchanger, a plate heat exchanger, a coaxial heat exchanger, and a heat exchange tube inside a container.

[0013] In one embodiment of this application, the primary liquid refrigerant is any currently available refrigerant.

[0014] A refrigeration system comprising the aforementioned deep subcooler and subcooler.

[0015] A control method for the subcooler and the deep subcooler includes the following steps: S1: Set target temperature The target temperature of the deep supercooler satisfies: In the formula, This refers to the evaporation temperature of the evaporator, expressed in degrees Celsius (°C). The evaporation temperature of the main refrigeration system, in degrees Celsius (°C); The target temperature of the subcooler satisfies: + In the formula, The evaporation temperature of the evaporator is expressed in degrees Celsius (°C). This is the preset heat transfer temperature difference, expressed in degrees Celsius (°C). ; The evaporation temperature of the main refrigeration system; The evaporation temperature of the main refrigeration system, in degrees Celsius (°C); S2: When the device is configured as a subcooler, the refrigeration system is started, and the subcooling temperature is controlled by adjusting the liquid supply on the secondary side of the subcooling heat exchange unit; when the device is configured as a deep subcooler, an independent cold source circuit is started and the pressure control valve is used to control the secondary side evaporation temperature to always be 3°C lower than the evaporation temperature of the main refrigeration system. S3: Monitor the subcooling temperature of the primary liquid refrigerant flowing out of the primary side outlet of the subcooling heat exchange unit. ; S4: According to and The difference corresponds to adjusting the operating parameters to make... Stable to Or To+3℃; where, in subcooler mode, the secondary side liquid supply of the subcooling heat exchange unit is adjusted to ensure the subcooled liquid temperature. When the temperature is 3°C or lower than the evaporation temperature, the amount of flash gas formed is ≤2%. In deep subcooler mode, the opening of the pressure control valve is adjusted to control the evaporation pressure on the secondary side of the subcooling heat exchange unit to ensure that it is 3°C lower than the main refrigeration system, at which point the amount of flash gas formed is 0.

[0016] In one embodiment of this application, in step S1, the heat transfer temperature difference The range of values ​​is to Optimal heat transfer temperature difference for .

[0017] The advantages of this invention compared to existing technologies are: (1) Through an independent cold source circuit and a subcooling heat exchange unit, the primary liquid refrigerant of the main cycle is deeply subcooled to the target temperature (evaporation temperature plus a small heat transfer temperature difference), so that the liquid specific enthalpy before throttling is reduced to close to or equal to the saturated liquid specific enthalpy after throttling. According to the principle of adiabatic isenthalpy throttling, the dryness of flash gas after throttling can be reduced to 0, and flash gas can be completely eliminated.

[0018] (2) After the primary liquid in the refrigeration system is subcooled by the subcooler, the amount of flash gas generated after throttling can be greatly reduced. Taking typical operating conditions (condensing temperature 35℃, evaporating temperature -10℃) as an example: for R717 refrigerant, the flash gas dryness fraction drops from 16.07% to 0; for R507 refrigerant, it drops from 33.3% to 0; for R410A refrigerant, it drops from 33.84% to 0. This significantly improves the evaporator heat exchange efficiency and the system operating COP value is significantly improved.

[0019] (3) Use the compressor with the smallest rated cooling capacity in the system as a dedicated subcooling compressor to avoid wasting cooling capacity, realize energy cascade utilization, and optimize overall energy consumption.

[0020] (4) The secondary side evaporation pressure is precisely adjusted by the pressure control valve, thereby controlling the subcooling temperature, so that the subcooling effect is stable and reliable and can adapt to different working conditions.

[0021] (5) The heat transfer temperature difference ΔT of the heat exchange unit is preferably 3℃, which takes into account both economy and heat exchange area. It can be achieved by presetting the heat exchange area, with simple structure and controllable cost.

[0022] (6) The subcooling heat exchange unit can be in various forms (shell and tube type, plate type, sleeve type, internal heat exchange tube in container, etc.) to adapt to different installation spaces and heat exchange requirements, and has strong versatility.

[0023] Additional aspects and advantages of this application 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 this application. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a physical connection diagram of the system of the present invention; Figure 2 This is a schematic diagram of the supercooling / deep supercooling temperature control curve of the present invention; Figure 3 This is a schematic diagram of the subcooling heat exchange unit structure of the present invention; Figure 4 This is a schematic diagram of the cryogenic system framework of the present invention; Figure 5 This is a schematic diagram of the subcooling system framework of the present invention; Figure 6 This is a flowchart illustrating the installation process of the subcooler in the single-stage compression direct expansion liquid supply system of the present invention. Figure 7 This is a flowchart illustrating the installation process of the subcooler in the single-stage compression gravity liquid supply system of the present invention. Figure 8 This is a flowchart illustrating the installation process of the subcooler in the single-stage compression forced liquid supply system of the present invention. Figure 9 This is a flowchart illustrating the installation process of the subcooler in the two-stage compression forced liquid supply system of the present invention. Figure 10 This is a flowchart illustrating the installation process of the subcooler in the two-stage compression gravity liquid supply system of the present invention. Figure 11 This is a flowchart illustrating the installation process of the subcooler in the two-stage compression direct expansion liquid supply system of the present invention. Figure 12 This is a flowchart illustrating the installation process of the cryostat in the single-stage compression direct expansion liquid supply system of the present invention. Figure 13 This is a flowchart illustrating the installation process of the cryostat in the single-stage compression gravity fluid supply system of the present invention. Figure 14 This is a flowchart illustrating the installation process of the cryostat in the single-stage compression forced liquid supply system of the present invention. Figure 15 This is a flowchart illustrating the installation process of the cryostat in the two-stage compression forced liquid supply system of the present invention. Figure 16 This is a flowchart illustrating the installation process of the cryostat in the two-stage compression gravity fluid supply system of the present invention. Figure 17 This is a flowchart illustrating the installation process of the cryocooler in the two-stage compression direct expansion liquid supply system of the present invention.

[0026] Explanation of reference numerals in the attached figures: 1. Main compressor; 2. Auxiliary compressor; 3. Condenser; 4. High-pressure liquid receiver; 5. Subcooling heat exchange unit; 6. Throttling device; 7. Evaporator; 8. Pressure control valve. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The core of this invention revolves around the design concept of reducing or even eliminating the participation of throttling flash gas in the main loop refrigeration cycle. Throttling flash gas can only achieve heat exchange using a small amount of sensible heat, and cannot play the core refrigeration role of the latent heat of phase change of the refrigerant. However, it will occupy the effective heat exchange area of ​​the evaporator, increase the flow resistance of the system, and needlessly consume the effective compression power of the refrigeration compressor, which is a waste of work in the refrigeration cycle. Eliminating or reducing the generation of flash gas is equivalent to directly increasing the proportion of useful compression power of the refrigeration compressor, and significantly improving the COP value of the refrigeration system as a whole. This effect is particularly significant for halogenated hydrocarbon refrigerants.

[0029] This invention includes two independently implementable core forms: a subcooler and a deep subcooler. Both forms share the core subcooling heat exchange unit structure, but their key differences lie in the cold source configuration and control method. Each also has its applicable scenarios and advantages and disadvantages. Subcooler type: The evaporator system is connected in series with the existing refrigeration system. It does not require a separate cold source. Its advantages are that it is easy to install and modify and has low cost. Its disadvantage is that it can only significantly reduce the amount of flash gas generated, but a small amount of flash gas is still generated. Deep subcooler configuration: requires an independent cold source circuit. The advantage is that the amount of flash gas generated after throttling can be reduced to 0, completely eliminating the waste of flash gas. The disadvantage is that the system modification is relatively complex and the equipment cost is higher.

[0030] It should be noted that, based on the preset heat transfer temperature difference With different values ​​of , this invention can achieve three typical operating modes: when Pick At that time, the target temperature Equal to the evaporation temperature of evaporator 7 This is called "deep cooler mode," which theoretically can reduce the dryness of the flash gas after throttling to absolute zero, achieving a maximum energy efficiency improvement; when the device is configured as a subcooler, the following settings are made: When the temperature of the liquid refrigerant after subcooling is 3°C higher than the evaporation temperature of evaporator 7, the amount of flash gas can be significantly reduced with low-cost retrofitting; when the unit is configured as a deep subcooler, the setting is... This means the evaporation temperature of the cold source loop is 3°C lower than the evaporation temperature of the main system evaporator 7, balancing energy efficiency gains with equipment investment costs, and reducing the dryness of the flash gas to zero. Users can choose the appropriate option based on their actual energy efficiency requirements and equipment investment costs. The value can be adjusted, or the mode can be switched online via the control system.

[0031] All temperature-related parameters in this application, such as evaporation temperature... Target temperature Heat transfer temperature difference All of these are in the International System of Units (SI) for degrees Celsius (°C).

[0032] It should be further noted that the "main compressor" and "subcooling-specific compressor" in this application have corresponding application forms in different types of refrigeration systems. In a single-stage compression system, the "main compressor" refers to the main compressor of the system, while the "subcooling-specific auxiliary compressor" refers to the compressor configured in the independent cold source circuit. In a two-stage compression system, the "main compressor" can be further understood as the main high-pressure stage compressor and the main low-pressure stage compressor (or the main low-pressure stage compressor), while the "subcooling-specific compressor" can correspond to the auxiliary stage compressor configured in the independent cold source circuit. Regardless of whether the system is a single-stage or two-stage structure, the independent cold source circuit of this application can use the compressor with the smallest cooling capacity in the system as the subcooling-specific compressor to achieve energy cascade utilization and system energy efficiency improvement.

[0033] Example 1: System Composition and Core Working Principle like Figures 1 to 17 As shown in the figure, an embodiment of the present invention provides a subcooler and a deep subcooler for a refrigeration system, demonstrating a typical refrigeration system integrated with the device of the present invention. The basic main refrigeration circuit of the system is a general vapor compression cycle, and the subcooler and the deep subcooler are both connected in series in the main circuit. The system structure and principle of the two forms are described in detail below.

[0034] 1. Basic main refrigeration circuit hardware connection relationship All embodiments of this invention are based on the same basic main refrigeration circuit. The pipeline connection sequence is as follows: the exhaust ports of the main compressor 1 and auxiliary compressor 2 are connected to the inlet of the condenser 3; the liquid outlet of the condenser 3 is connected to the inlet of the high-pressure liquid receiver 4; the liquid outlet of the high-pressure liquid receiver 4 is connected to the inlet of the primary side flow path of the subcooling heat exchange unit 5; the outlet of the primary side flow path of the subcooling heat exchange unit 5 is connected to the inlet of the throttling device 6; the outlet of the throttling device 6 is connected to the inlet of the evaporator 7; and the outlet of the evaporator 7 is connected back to the suction ports of the main compressor 1 and auxiliary compressor 2, forming a closed loop.

[0035] The condenser 3 is one of the four core components of the refrigeration cycle. It is used to condense the high-temperature and high-pressure gaseous refrigerant discharged from the main compressor 1 and the auxiliary compressor 2 into high-pressure room-temperature liquid refrigerant, realizing the phase change of the refrigerant from gaseous to liquid. The high-pressure liquid receiver 4 is connected in series after the outlet of the condenser 3. It is used to temporarily store the condensed high-pressure liquid refrigerant, stabilize the system liquid supply, buffer load fluctuations, and ensure that the refrigerant entering the subcooling heat exchange unit 5 is pure liquid refrigerant without bubbles, thus ensuring stable subcooling effect.

[0036] 2. Subcooler configuration (without independent cold source) system structure and principle This design is a subcooler solution without an independent cold source. It is directly connected in series with the evaporator system of the existing refrigeration system, without the need for additional compressor equipment, and is suitable for low-cost energy-saving retrofitting of existing systems.

[0037] Core hardware: Only the subcooling heat exchange unit 5 is retained, which has a primary side flow path and a secondary side flow path for mutual heat exchange. The primary side flow path is connected in series between the outlet of the high-pressure liquid receiver 4 and the inlet of the throttling device 6. The secondary side flow path is connected to the low-pressure evaporation system of the refrigeration system, and directly uses the low-pressure evaporation cooling capacity of the main system to provide subcooling for the primary side liquid refrigerant.

[0038] Core working principle: The low-pressure cooling capacity of the main system, connected through the secondary side flow path, cools the high-pressure liquid refrigerant in the primary side flow path to the target temperature. +3℃ significantly reduces the specific enthalpy of the refrigerant before throttling, thereby significantly reducing the amount of flash gas generated after throttling; target temperature Satisfying the formula: + In the formula, This refers to the liquid subcooling temperature on the primary side of the refrigerant, expressed in degrees Celsius (°C). This is the operating evaporation temperature of evaporator 7, expressed in degrees Celsius (°C). The preset heat transfer temperature difference is expressed in degrees Celsius (°C), and is preferably defined in the form of a subcooler. This means that after subcooling, the temperature of the liquid refrigerant is 3°C higher than the evaporation temperature.

[0039] This configuration does not require modification of the core equipment of the main system; the modification can be completed simply by adding a subcooling heat exchange unit 5. It is easy to install and has a low cost, and can significantly reduce the dryness of flash gas. The disadvantage is that it is limited by the evaporation temperature of the main system and cannot achieve deep subcooling, so a small amount of flash gas is still generated.

[0040] 3. System composition and principle of deep subcooler (with independent cold source) This design features a deep subcooler with an independent cold source circuit, which can completely eliminate throttling and flashing gases, making it suitable for newly built high-standard refrigeration systems and high-requirement energy-saving renovation projects.

[0041] Core hardware: Based on the subcooling heat exchange unit 5, an independent cold source circuit and pressure control valve 8 are added; the independent cold source circuit includes a dedicated subcooling compressor, and the pressure control valve 8 is set on the return gas pipeline of the independent cold source circuit, or directly integrated into the subcooling heat exchange unit 5, to regulate the evaporation pressure on the secondary side of the subcooling heat exchange unit 5.

[0042] Hardware connection: The discharge port of the subcooled compressor can be connected to the condenser 3 shared by the main system. The condensed high-pressure liquid falls into the high-pressure liquid receiver for temporary storage. The liquid in the high-pressure liquid receiver flows through the cold circuit throttling device 6 to reduce pressure and become a low-temperature, low-pressure saturated refrigerant liquid. It enters the secondary flow path of the subcooled heat exchange unit 5 from the liquid supply port. In the secondary flow path, the refrigerant absorbs heat from the primary side and evaporates completely. The generated gas is discharged from the outlet, flows through the pressure control valve 8, and returns to the suction port of the subcooled compressor, forming an independent closed loop.

[0043] Core working principle: It provides low-temperature cooling capacity through an independent cold source circuit, which is not limited by the main system's operating conditions, and deeply cools the high-pressure liquid refrigerant in the primary side flow path to the target temperature. This reduces the refrigerant specific enthalpy before throttling to the saturated liquid specific enthalpy at the evaporation pressure after throttling. Based on the principle of adiabatic isenthalpic throttling, the dryness fraction of the flashing gas after throttling can be reduced to 0, completely eliminating flashing gas; target temperature. Satisfying the formula: Optimal configuration of the subcooling compressor: To achieve optimal economy, the rated cooling capacity of the subcooling compressor is less than or equal to the rated cooling capacity of the main compressor 1, and preferably the compressor with the smallest rated cooling capacity in the refrigeration system. Its core advantages are: subcooling load is usually much smaller than the main refrigeration load, and the cooling capacity of the smallest compressor is sufficient to meet the demand, avoiding energy waste from "overkill"; at the same time, it utilizes a "small cold source" with low marginal operating cost in the system to complete the deep subcooling task, achieving a significant improvement in the main system's energy efficiency with minimal additional energy consumption, conforming to the principle of energy cascade utilization; in the retrofitting of existing systems, the small compressor in the original system can be directly converted to a dedicated compressor, without the need for a new large main unit, and the retrofitting cost is controllable.

[0044] The core regulating function of pressure control valve 8: Pressure control valve 8 can be an integrated outlet pressure balancing valve or an assembled outlet pressure balancing valve (for higher control precision). Liquid supply control uses electronic expansion valves (for high control precision), thermostatic expansion valves, etc. It is a key actuator for achieving precise and stable subcooling temperature. Its regulation logic is based on the one-to-one correspondence between refrigerant saturation pressure and temperature: by changing the opening of pressure control valve 8, the evaporation pressure of the secondary side flow path of subcooling heat exchange unit 5 is directly changed. When the pressure decreases, the corresponding saturated evaporation temperature decreases synchronously, and when the pressure increases, the evaporation temperature increases synchronously. In essence, by adjusting the evaporation temperature of the secondary side cold source, the heat transfer temperature difference between it and the primary side liquid is changed, thereby precisely controlling the cooling intensity and outlet temperature of the primary side liquid.

[0045] This design can completely eliminate throttling flash gas and completely eliminate the wasted energy loss caused by flash gas, thus improving the COP of the main system. It is especially suitable for cryogenic refrigeration systems and halogenated hydrocarbon refrigerant systems. The disadvantage is that an independent cold source circuit needs to be added, the system modification is relatively complex, and the initial cost of the equipment is higher.

[0046] It should be further noted that the heat transfer temperature difference in this application Its value not only determines the target temperature of the liquid refrigerant after subcooling, but also corresponds to different equipment configurations and application scenarios. When When a smaller value is used (e.g., 1℃~3℃), the degree of supercooling is higher, and the flash gas after throttling approaches zero, but an independent cold source loop is required to achieve deep supercooling; when When a larger value is selected (e.g., 3℃~5℃), low-cost subcooling can be achieved by relying on the low-pressure cold source of the main system, significantly reducing the proportion of flash gas. Users can flexibly choose based on system type, energy efficiency targets, and investment costs. The value and the corresponding device form are not uniquely limited in this application.

[0047] Example 2: Detailed workflow of the control method This invention addresses two types of devices: subcoolers and deep subcoolers, and provides corresponding control methods for each. The core of both methods is closed-loop control based on temperature feedback, ensuring that the subcooling temperature remains stable at the target value. The following is a detailed description of each method, with the core steps of the control methods for the two types as follows: 1. Methods for controlling the shape of the subcooler S1: Set target temperature The target temperature satisfies: In the formula, The evaporation temperature of evaporator 7 is expressed in degrees Celsius (°C). The preset heat transfer temperature difference, in degrees Celsius (°C), is in subcooler configuration. The range of values ​​is to Preferred ; The supercooling temperature of a supercooled liquid is measured in degrees Celsius (°C). S2: Start the refrigeration system. The main refrigeration circuit is running normally. High-pressure liquid refrigerant flows out from the high-pressure liquid receiver 4 and enters the primary side of the subcooling heat exchange unit 5. The low-pressure cold source of the main system enters the secondary side of the subcooling heat exchange unit 5. S3: Monitor the temperature of the primary liquid refrigerant flowing out from the primary side outlet of subcooled heat exchange unit 5. ; S4: According to With the setting The difference is used to adjust the primary side liquid inlet flow rate and the secondary side low-pressure liquid supply flow rate of the subcooled heat exchange unit 5, thereby changing the heat exchange intensity between the primary and secondary sides. Stable to :like This increases the low-pressure liquid supply on the secondary side and decreases the liquid inlet on the primary side, thereby enhancing the heat exchange intensity and promoting... Decrease; if This reduces the low-pressure liquid supply on the secondary side and increases the liquid inlet on the primary side, thereby reducing the heat exchange intensity and promoting... Recovery.

[0048] 2. Methods for controlling the shape of deep subcoolers S1: Set target temperature The target temperature satisfies: In the formula, The evaporation temperature of evaporator 7 is expressed in degrees Celsius (°C). This refers to the temperature of the supercooled liquid, expressed in degrees Celsius (°C).

[0049] S2: Start the independent cold source circuit, the subcooling dedicated compressor runs normally, the entire subcooling dedicated circuit starts to work, the high-pressure liquid refrigerant from condenser 3 is throttled by the cold source circuit throttling device and becomes a low-temperature cold source to enter the secondary side of the subcooling heat exchange unit 5. S3: Monitor the temperature of the primary liquid refrigerant flowing out from the primary side outlet of subcooled heat exchange unit 5. ; S4: According to With the setting The difference is used to adjust the opening of pressure control valve 8 to control the evaporation pressure on the secondary side of subcooled heat exchange unit 5, so that... Stable to The specific adjustment logic is as follows: like This indicates insufficient subcooling. The controller commands an increase in the opening of pressure control valve 8. Increased opening leads to decreased secondary side return gas resistance, decreased secondary side evaporation pressure, decreased secondary side evaporation temperature, increased heat transfer temperature difference, and enhanced subcooling heat exchange capacity, thus promoting... Decline, trend ; like This indicates excessive subcooling. The controller commands a reduction in the opening of pressure control valve 8. A reduced opening leads to increased secondary side return gas resistance, increased secondary side evaporation pressure, increased secondary side evaporation temperature, decreased heat transfer temperature difference, and weakened subcooling heat exchange capacity, thus promoting... Rebound, trending .

[0050] The above adjustment process is carried out continuously and automatically, forming a negative feedback closed loop, which will ultimately... Precisely stabilized at Within a very small area, a stable and reliable deep supercooling effect is achieved. The control method in this application embodiment can be automatically controlled by a PLC controller or an industrial-grade industrial control computer. The control method of the controller can be implemented by simple programming by those skilled in the art, which is common knowledge in the art. Furthermore, this application is mainly used to protect mechanical structures, so the control method and circuit connection will not be explained in detail here.

[0051] Example 3: Specific implementation structure of subcooled heat exchange unit 5 (vertical shell and tube type) Reference Figure 3 This paper presents a specific and preferred embodiment of the subcooling heat exchange unit 5—a vertical fixed tube sheet shell and tube heat exchanger. This structure is suitable for both subcoolers and deep subcoolers, and only the heat exchange area needs to be adjusted according to the actual load.

[0052] Overall layout: The heat exchanger is installed vertically. The primary side flow path (main loop liquid) preferably runs through the shell side, while the secondary side flow path (low-pressure cold source / independent cold source) preferably runs through the tube side. The counter-flow arrangement is conducive to enhancing heat exchange, and the vertical structure helps the secondary side gas to rise and be discharged smoothly, avoiding liquid accumulation that affects the heat exchange effect.

[0053] Interface and Functionality: Primary side interface: A primary liquid inlet N2 is provided on the upper side wall of the shell, and a primary liquid outlet N3 is provided on the lower side wall; the primary liquid enters the shell side from N2, flows from top to bottom and is cooled, and flows out from N3 and connects to the subsequent throttling device 4.

[0054] Secondary side interface: A liquid supply port N4 is provided in the lower tube box for introducing a low-temperature refrigerant liquid cold source; an outlet N1 is provided at the top of the upper tube box for discharging the gas after heat absorption and evaporation; the secondary side fluid enters the tube side from N4, absorbs heat and evaporates from bottom to top, and flows out from N1.

[0055] Example of key design parameters: Design pressure: 2.0 MPa for both shell side (primary side) and tube side (secondary side); Design temperature: The shell side and tube side are both at the evaporation temperature of the main refrigeration system -6℃; Operating pressure: shell side approximately 1.4 MPa (corresponding to condensing pressure conditions), tube side approximately 0.26 MPa (corresponding to evaporating pressure conditions). Heat exchange tubes: High-quality seamless steel tubes with diameters of 10mm and 1mm are selected according to GB47012 requirements. Seamless steel pipes are arranged in an equilateral triangle pattern with four passes to improve flow rate and heat transfer coefficient. Main materials: The shell is made of Q245R steel plate or high-quality seamless steel pipe, the heat exchange tube is made of high-quality seamless steel pipe selected according to GB47012 requirements, and the forgings meet the relevant pressure vessel standards; Connection and Inspection: The heat exchange tubes and tube sheets are welded with strength. All A and B type welded joints are 100% radiographically inspected. After the equipment is manufactured, it undergoes water pressure and air tightness tests.

[0056] Heat exchange area determination: The heat exchange area ultimately determined by the above structural parameters (pipe diameter, pipe length, number of pipes) is based on the selected heat transfer temperature difference. Under these conditions, the primary liquid at the rated flow rate is cooled from the condensation temperature to the target temperature. It is derived from the required heat load calculation.

[0057] Pressure control valve 8 installation method: As a specific installation method, pressure control valve 8 is installed as a bridge between the suction pipe of the subcooled special compressor and the suction pipe of the main compressor.

[0058] Example 4: Complete Working Process Example (I) Examples of subcooler configuration and operation Take a conventional air conditioning refrigeration system using R410A refrigerant as an example: 1. Initial conditions and goal setting: System evaporation temperature condensation temperature 35℃; Selected subcooler mode for heat transfer temperature difference .

[0059] The controller calculates the target temperature: .

[0060] 2. System Operation and Adjustment: When the main refrigeration circuit is started, the main compressor 1 runs, and the outlet of the condenser 3 produces 35°C R410A saturated liquid, which enters the high-pressure liquid receiver 4 for stable liquid supply. The 35°C primary side liquid flows out from the high-pressure liquid reservoir 4 and enters the primary side (shell side) of the subcooled heat exchange unit 5 to exchange heat with the 5°C low-pressure cold source of the main system connected in the tube side. Initial temperature sensor measurement The controller initiates closed-loop control, increasing the low-pressure liquid supply to the secondary side, thereby enhancing heat exchange intensity. from Gradually decreasing.

[0061] 3. Stable operation: After a brief adjustment It stabilized at 8℃ (±0.5℃), at which point the primary side liquid achieved a subcooling of 27℃; After the subcooled liquid is throttled by the throttling device 6, the dryness of the flash gas is reduced from 33.84% under normal operating conditions to less than 5%, the heat exchange efficiency of the evaporator is significantly improved, the system COP is increased by more than 12%, and low-cost energy-saving renovation is achieved.

[0062] (II) Examples of Deep Subcooler Configuration and Operation Take a low-temperature cold storage system using R717 refrigerant as an example: 1. Initial conditions and goal setting: System evaporation temperature condensation temperature 35℃; Selected subcooler mode for heat transfer temperature difference .

[0063] The controller calculates the target temperature: .

[0064] The dedicated subcooling compressor is selected from the smallest compressor in the system with a rated cooling capacity of 50℃W.

[0065] 2. System Operation and Adjustment: When the main refrigeration circuit is started, the main compressor 1 runs, and the outlet of the condenser 3 produces 35°C R717 saturated liquid, which enters the high-pressure liquid receiver 4 for stable liquid supply. When the subcooling circuit is started, the subcooling compressor runs. After the condensate is throttled by the cold source circuit throttling device, it becomes a low-temperature refrigerant liquid of about -15°C and enters the secondary side (tube side) of the subcooling heat exchange unit 5. The primary side liquid at 35°C flows out from the high-pressure liquid reservoir 4 and enters the primary side (shell side) of the subcooled heat exchange unit 5 to exchange heat with the cold source in the tube side at approximately -10°C to -12°C. Initial temperature sensor measurement The controller initiates closed-loop control, increasing the opening of pressure control valve 8; Increasing the opening of pressure control valve 8 reduces the secondary side evaporation pressure from 0.29 MPa to 0.27 MPa, corresponding to a drop in evaporation temperature from -10℃ to -12℃, resulting in enhanced cooling capacity. from Gradually decreasing.

[0066] 3. Stable operation: After a brief adjustment It stabilized at -7℃ (±0.5℃), at which point the primary side liquid achieved a subcooling of up to 42℃ from 35℃ to -7℃; After the deep subcooled liquid is throttled by the throttling device 6, the dryness of the flash gas x approaches 0, and the almost pure liquid refrigerant enters the evaporator 7, completely eliminating the useless power loss caused by the flash gas, and the system COP is increased by more than 20%. Throughout the entire operation, regardless of how the cold storage load changes... The controller will recalculate in real time even for the slightest fluctuations. And by adjusting the opening of pressure control valve 8, Continuously track the target value to maintain optimal supercooling effect.

[0067] It should be noted that this embodiment uses R717 and R410A refrigerants as examples. This invention is applicable to all currently used refrigerants. Different refrigerants have different physical property parameters. When applying them, specific design calculations need to be performed according to their pressure-enthalpy diagrams, but the system composition and control logic remain completely unchanged. For halogenated hydrocarbon refrigerants, the COP improvement effect of eliminating flash gas in this invention is more significant.

[0068] Example 5: Other Implementation Methods and Variations This invention is not limited to the above embodiments. Those skilled in the art can make various modifications based on the concept of this invention, all of which fall within the protection scope of this invention. 1. Variations of subcooling heat exchange unit 5: It can be a plate heat exchanger (compact and efficient, suitable for space-constrained applications), a shell-and-tube heat exchanger (simple structure, easy to clean, suitable for small and medium-sized systems), or an integrated device with heat exchange tube bundles installed in a pressure vessel; the core is to have isolated primary and secondary flow paths to achieve heat exchange, and it can be adapted to both subcooler and deep subcooler forms.

[0069] 2. Variations of control valves and algorithms: The pressure control valve 8 can be an integrated outlet pressure balancing valve or a split outlet pressure balancing valve (high control accuracy); in addition to PID, advanced algorithms such as fuzzy control and adaptive control can also be used.

[0070] 3. Flexible application of values: exist The interval is adjustable. Except... In addition to the preferred value, 1℃, 2℃, 4℃, 5℃, etc. can be selected according to the specific circumstances of the project to balance the improvement in energy efficiency with the cost of equipment investment.

[0071] 4. Variation of independent cold source circuit: The exhaust of the subcooling compressor can be connected to the main system to share the condenser, or it can be configured with an independent condenser and throttling device to form a completely independent cold source cycle, without sharing any equipment with the main system, which is suitable for retrofit scenarios where it is not possible to share a condenser.

[0072] Example 6: Stand-alone modular equipment The subcooler and deep subcooler of the present invention can not only be integrated into newly designed refrigeration systems, but also serve as independent modular devices for energy-saving retrofits of existing refrigeration systems without requiring significant modifications to the original system.

[0073] Independent subcooler module: It includes an independent chassis, which integrates subcooling heat exchange unit 5, liquid supply regulating valve, temperature sensor and controller. The chassis has a pair of primary side interfaces (primary liquid inlet and primary liquid outlet) for connecting in series between the outlet of the high-pressure liquid receiver 4 and the inlet of the throttling device 6 of the existing refrigeration system; it also has a pair of secondary side interfaces for connecting to the low-pressure evaporation system of the existing system. The module has its own control unit and can operate independently, automatically adjusting the liquid supply to control the subcooling temperature.

[0074] Independent deep subcooler module: It includes an independent chassis or frame, and integrates a subcooling heat exchange unit 5, a dedicated subcooling compressor, a pressure control valve 8, a cold source circuit throttling device, a temperature sensor and a PLC controller. The chassis has a pair of primary side interfaces (primary liquid inlet and primary liquid outlet) for connecting in series with the outlet of the high-pressure liquid receiver 4 and the inlet of the throttling device 6 of the existing refrigeration system through pipelines. The module has a complete independent cold source circuit and control unit, which can operate independently. It can automatically adjust the subcooling temperature through the built-in temperature sensor and pressure control valve 8 to realize the deep subcooling transformation of the existing system.

[0075] All of the above independent modules can use shell-and-tube, plate, or coaxial heat exchangers as subcooling heat exchange units 5. Their system composition and control methods are exactly the same as the aforementioned integrated system, and can be flexibly selected according to the on-site installation space and modification requirements.

[0076] Obviously, the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. A subcooler and a deep subcooler for a refrigeration system, the refrigeration system comprising a main compressor (1), an auxiliary compressor (2), a condenser (3), a high-pressure liquid receiver (4), a subcooling heat exchange unit (5), a throttling device (6), an evaporator (7), and an outlet pressure control valve (8) connected sequentially by pipelines; characterized in that, Also includes: The subcooling heat exchange unit (5) has a primary side flow path and a secondary side flow path for mutual heat exchange. The primary side flow path is connected in series between the outlet of the high-pressure liquid reservoir (4) and the inlet of the throttling device (6). The cryogenic cooler has an independent cold source circuit, which is used to provide cooling capacity to the secondary side flow path of the subcooling heat exchange unit (5). The cold source circuit includes a dedicated subcooling auxiliary compressor and a pressure control valve (8), which is installed on the return gas pipeline of the independent cold source circuit or on the subcooling heat exchange unit (5) to regulate and stabilize the evaporation pressure of the secondary side of the subcooling heat exchange unit (5) at the saturation pressure corresponding to 3°C lower than the evaporation pressure of the main refrigeration system. The subcooling heat exchange unit (5) is configured to cool the primary liquid refrigerant flowing through its primary side path to a target temperature. This reduces the amount of flash gas generated by the liquid refrigerant after being throttled by the throttling device (6) to 0. The target temperature satisfy: In the formula, Temperature of the supercooled liquid, expressed in degrees Celsius (°C). The evaporation temperature of the evaporator (7) of the main refrigeration system is expressed in degrees Celsius (°C).

2. A subcooler and a deep subcooler for a refrigeration system according to claim 1, characterized in that, The rated cooling capacity of the subcooling auxiliary compressor is less than or equal to the rated cooling capacity of the main compressor (1) in the refrigeration system, and preferably is the compressor with the smallest rated cooling capacity in the refrigeration system.

3. A subcooler and a deep subcooler for a refrigeration system according to claim 1, characterized in that, When the device is configured as a deep subcooler, the heat transfer temperature difference That is, the temperature of the liquid refrigerant after subcooling is 3°C higher than the evaporation temperature of the evaporator (7); that is, the evaporation temperature of the cold source circuit is 3°C lower than the evaporation temperature of the main system evaporator (7); the target temperature when the device is configured as a subcooler. The temperature difference from the actual temperature is 3℃, at which point the amount of flash gas generated reaches ≤2%. The actual temperature satisfy: In the formula, Temperature of the supercooled liquid, expressed in degrees Celsius (°C). The evaporation temperature of the evaporator (7) of the main refrigeration system is expressed in degrees Celsius (°C).

4. A subcooler and a deep subcooler for a refrigeration system according to claim 1, characterized in that, Heat transfer temperature difference The range of values ​​is to Optimal heat transfer temperature difference for More preferably, the subcooling heat exchange unit (5) is configured to have a preset heat exchange area, so as to achieve the desired heat transfer temperature difference. for Under the conditions specified, the primary liquid refrigerant is cooled to the target temperature. (To+3℃).

5. A subcooler and a deep subcooler for a refrigeration system according to claim 1, characterized in that, The subcooled heat exchange unit (5) is a heat exchanger that is one of the following: vertical or horizontal shell and tube heat exchanger, plate heat exchanger, coaxial heat exchanger, and internal heat exchange tube in a container.

6. A subcooler and a deep subcooler for a refrigeration system according to claim 1, characterized in that, The primary liquid refrigerant is any currently used refrigerant.

7. A refrigeration system, characterized in that, Includes the deep subcooler and subcooler as described in any one of claims 1-6.

8. A control method for the subcooler and deep subcooler according to any one of claims 1-6, characterized in that, Includes the following steps: S1: Set target temperature The target temperature of the deep supercooler satisfies: In the formula, The evaporation temperature of the evaporator (7) is expressed in degrees Celsius (°C). The evaporation temperature of the main refrigeration system, in degrees Celsius (°C); The target temperature of the subcooler satisfies: + In the formula, The evaporation temperature of the evaporator (7) is expressed in degrees Celsius (°C). This is the preset heat transfer temperature difference, expressed in degrees Celsius (°C). ; The evaporation temperature of the main refrigeration system; The evaporation temperature of the main refrigeration system, in degrees Celsius (°C); S2: When the device is configured as a subcooler, start the refrigeration system and control the subcooling temperature by adjusting the secondary side liquid supply of the subcooling heat exchange unit (5); when the device is configured as a deep subcooler, start an independent cold source circuit and use the pressure control valve (8) to control the secondary side evaporation temperature to always be 3°C lower than the evaporation temperature of the main refrigeration system. S3: Monitor the subcooling temperature of the primary liquid refrigerant flowing out from the primary side outlet of the subcooling heat exchange unit (5). ; S4: According to and The difference corresponds to adjusting the operating parameters to make... Stable to Or To+3℃; wherein, in subcooler mode, the secondary side liquid supply of the subcooled heat exchange unit (5) is adjusted to ensure the subcooled liquid temperature. When the temperature is 3°C or lower than the evaporation temperature, the amount of flash gas formed is ≤2%. In the deep subcooler mode, the opening of the pressure control valve (8) is adjusted to control the evaporation pressure on the secondary side of the subcooling heat exchange unit (5) to ensure that it is 3°C lower than the main refrigeration system, at which point the amount of flash gas formed is 0.

9. The control method according to claim 8, characterized in that, In step S1, the heat transfer temperature difference The range of values ​​is to Optimal heat transfer temperature difference for .

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