Hybrid working fluid heat pump system and control method

Abstract

The embodiment of the application discloses a kind of mixed working medium heat pump systems and control method, in mixed working medium heat pump system, the first pressure of mixed working medium that compressor exports is detected by first pressure sensor, the second pressure of mixed working medium that evaporator exports is detected by second pressure sensor, the opening of first expansion valve is controlled according to the first pressure and the dew point pressure of mixed working medium by controller, and the opening of second expansion valve is controlled according to the second pressure and the bubble point pressure of mixed working medium, since first expansion valve is set after condenser, second expansion valve is set before evaporator, can be adjusted by the opening of first expansion valve Condensation pressure of condenser is equal to dew point pressure, the evaporation pressure of evaporator is adjusted by the opening of second expansion valve equal to bubble point pressure, so that condensation pressure and evaporation pressure reach ideal state simultaneously, mixed working medium is completely liquefied in condenser, completely gasified in evaporator, so that heat pump system reaches optimal performance state.

Description

Technical Field

[0001] The present invention relates to the field of heat pump technology, and in particular to a mixed working fluid heat pump system and control method. Background Technology

[0002] With the implementation of the national dual-carbon emission reduction strategy, the application scenarios of heat pumps have expanded from home appliances to buildings, agriculture, industry and other scenarios. In many application scenarios, the temperature variation range of heat source and heat sink is large. Non-azeotropic working fluids can be selected according to the application scenario to meet the needs of large temperature range, and are widely used as cold and heat transfer media in heat pump systems.

[0003] A heat pump system typically includes a condenser and an evaporator. The optimal operating condition for a heat pump system is that the working fluid mixture is completely liquefied after passing through the condenser and completely vaporized after passing through the evaporator. Complete liquefaction and complete condensation are closely related to the condensing pressure and evaporating pressure. However, traditional heat pump systems use a single-stage expansion valve. When the condensing pressure is adjusted by the single-stage expansion valve to achieve complete liquefaction of the working fluid mixture, the evaporating pressure may deviate from the ideal evaporating pressure. When the evaporating pressure is adjusted by the single-stage expansion valve to achieve complete vaporization of the working fluid mixture, the condensing pressure may deviate from the ideal condensing pressure. It is difficult to make the condensing pressure and evaporating pressure reach the ideal state at the same time, causing the heat pump system to fail to achieve optimal performance. Summary of the Invention

[0004] This invention provides a mixed working fluid heat pump system and control method to solve the problem that existing mixed working fluid heat pump systems cannot simultaneously achieve ideal condensation pressure and evaporation pressure, thus affecting the performance of the heat pump system.

[0005] In a first aspect, embodiments of the present invention provide a mixed working fluid heat pump system, characterized in that it includes a compressor, a condenser, a first expansion valve, a liquid receiver, a second expansion valve, and an evaporator connected in sequence to form a mixed working fluid circulation loop;

[0006] The condenser is equipped with a first pressure sensor at the mixed working fluid input end, and the first pressure sensor is used to detect the first pressure of the mixed working fluid output by the compressor.

[0007] The evaporator is equipped with a second pressure sensor at the output end of the mixed working fluid. The second pressure sensor is used to detect the second pressure of the mixed working fluid output by the evaporator, and also includes:

[0008] A controller is configured to receive the first pressure and the second pressure, and control the opening of the first expansion valve according to the first pressure and the dew point pressure of the mixed working fluid, and control the opening of the second expansion valve according to the second pressure and the bubble point pressure of the mixed working fluid, wherein the dew point pressure indicates that the mixed working fluid is completely liquefied and the bubble point pressure indicates that the mixed working fluid is completely vaporized.

[0009] Optionally, the condenser includes an inlet water temperature sensor, which is electrically connected to the controller and is used to detect the inlet water temperature of the condenser.

[0010] The controller determines the dew point pressure of the mixed working fluid based on the inlet water temperature.

[0011] Optionally, the evaporator includes an inlet air temperature sensor, which is electrically connected to the controller and is used to detect the inlet air temperature of the evaporator.

[0012] The controller determines the bubble point pressure of the mixed working fluid based on the inlet air temperature.

[0013] Optionally, a third pressure sensor electrically connected to the controller is also included. The third pressure sensor is disposed at the mixed working fluid output end of the reservoir and is used to detect the third pressure of the mixed working fluid output by the first expansion valve.

[0014] Optionally, it also includes a regenerator, the mixed working fluid output end of the liquid receiver is connected to the second expansion valve through the regenerator, the mixed working fluid output end of the evaporator is connected to the mixed working fluid input end of the compressor through the regenerator, and the second pressure sensor is disposed between the regenerator and the compressor.

[0015] Optionally, it also includes a gas-liquid separator, through which the regenerator is connected to the compressor.

[0016] In a second aspect, embodiments of the present invention provide a control method for a mixed working fluid heat pump system, applied to the mixed working fluid heat pump system described in the first aspect, comprising:

[0017] The first pressure of the mixed working fluid output by the compressor is detected by the first pressure sensor;

[0018] The second pressure of the mixed working fluid output by the evaporator is detected by a second pressure sensor;

[0019] The opening degree of the first expansion valve is controlled according to the first pressure and the dew point pressure of the mixed working fluid, wherein the dew point pressure indicates that the mixed working fluid is completely liquefied.

[0020] The opening degree of the second expansion valve is controlled according to the second pressure and the bubble point pressure of the mixed working fluid, wherein the bubble point pressure indicates that the mixed working fluid is completely vaporized.

[0021] Optionally, controlling the opening degree of the first expansion valve based on the first pressure and the dew point pressure of the mixed working fluid includes:

[0022] Determine whether the first pressure is within the pressure range of the dew point pressure;

[0023] If the first pressure is less than or equal to the lower limit of the pressure range of the dew point pressure, reduce the opening of the first expansion valve and return to the step of determining whether the first pressure is within the pressure range of the dew point pressure.

[0024] If the first pressure is greater than or equal to the upper limit of the pressure range of the dew point pressure, increase the opening of the first expansion valve and return to the step of determining whether the first pressure is within the pressure range of the dew point pressure.

[0025] If the first pressure is within the pressure range of the dew point pressure, control the first expansion valve to maintain its current opening.

[0026] Optionally, controlling the opening degree of the second expansion valve based on the second pressure and the bubble point pressure of the mixed working fluid includes:

[0027] Determine whether the second pressure is within the pressure range of the bubble point pressure;

[0028] If the second pressure is less than or equal to the lower limit of the pressure range of the bubble point pressure, increase the opening of the second expansion valve and return to the step of determining whether the second pressure is within the pressure range of the bubble point pressure;

[0029] If the second pressure is greater than or equal to the upper limit of the pressure range of the bubble point pressure, reduce the opening of the second expansion valve and return to the step of determining whether the second pressure is within the pressure range of the bubble point pressure.

[0030] If the second pressure is within the pressure range of the bubble point pressure, control the second expansion valve to maintain the current opening.

[0031] Optionally, before determining whether the second pressure is within the pressure range of the bubble point pressure, the method further includes:

[0032] Receive the third pressure from the third pressure sensor;

[0033] When the third pressure is within the preset pressure range, the step of determining whether the second pressure is within the pressure range of the bubble point pressure is performed.

[0034] The mixed refrigerant heat pump system of this invention includes a compressor, a condenser, a first expansion valve, a receiver, a second expansion valve, and an evaporator connected in sequence to form a mixed refrigerant circulation loop. A first pressure sensor detects the first pressure of the mixed refrigerant output by the compressor, and a second pressure sensor detects the second pressure of the mixed refrigerant output by the evaporator. The controller controls the opening of the first expansion valve based on the first pressure and the dew point pressure of the mixed refrigerant, and controls the opening of the second expansion valve based on the second pressure and the bubble point pressure of the mixed refrigerant. Because a first expansion valve is located after the condenser and a second expansion valve is located before the evaporator, the opening of the first expansion valve can be used to adjust the condensing pressure of the condenser to equal the dew point pressure, and the opening of the second expansion valve can be used to adjust the evaporating pressure of the evaporator to equal the bubble point pressure. This allows the condensing pressure and evaporating pressure to simultaneously reach ideal states, ensuring that the mixed refrigerant is completely liquefied in the condenser and completely vaporized in the evaporator, thus achieving optimal performance of the heat pump system. Attached Figure Description

[0035] Figure 1 A schematic diagram of a mixed working fluid heat pump system provided in one embodiment of the present invention;

[0036] Figure 2 A schematic diagram of a mixed working fluid heat pump system provided for another embodiment of the present invention;

[0037] Figure 3 A schematic diagram of a mixed working fluid heat pump system provided in another embodiment of the present invention;

[0038] Figure 4 A schematic diagram of a mixed working fluid heat pump system provided in another embodiment of the present invention;

[0039] Figure 5 This is a flowchart of a control method for a mixed working fluid heat pump system provided in one embodiment of the present invention;

[0040] Figure 6 This is a flowchart of a mixed working fluid heat pump system control method provided in another embodiment of the present invention. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0042] Figure 1This is a schematic diagram of a mixed working fluid heat pump system provided in an embodiment of the present invention. In this embodiment, the mixed working fluid heat pump system refers to a heat pump system using two or more working fluids with different boiling points. Injecting two or more working fluids with different boiling points into the mixed working fluid heat pump system forms a non-azeotropic mixed working fluid heat pump system. For example... Figure 1 As shown, the mixed refrigerant heat pump system of this embodiment includes a compressor 1, a condenser 2, a first expansion valve 3, a liquid receiver 4, a second expansion valve 5, and an evaporator 6 connected in sequence to form a mixed refrigerant circulation loop. It also includes a controller 9. The mixed refrigerant circulation process in the mixed refrigerant heat pump system is as follows:

[0043] The mixed working fluid is first compressed in compressor 1 to form a high-temperature, high-pressure gas. The high-temperature, high-pressure gaseous mixed working fluid discharged from compressor 1 is input into condenser 2. Condenser 2 absorbs cold energy and releases heat. The high-temperature, high-pressure gaseous mixed working fluid undergoes heat exchange in condenser 2, absorbing cold energy and releasing heat. The high-temperature, high-pressure gaseous mixed working fluid condenses in condenser 2 to form a low-temperature liquid mixed working fluid. The low-temperature liquid mixed working fluid flowing out of condenser 2 enters liquid receiver 4 after passing through first expansion valve 3. The low-temperature liquid mixed working fluid in liquid receiver 4 enters evaporator 6 after passing through second expansion valve 5. Evaporator 6 absorbs heat and releases cold energy. In evaporator 6, the low-temperature liquid mixed working fluid absorbs heat and vaporizes, enabling evaporator 6 to provide cooling. The low-temperature liquid mixed working fluid vaporizes to form a low-temperature gaseous mixed working fluid. This low-temperature gaseous mixed working fluid flows out of evaporator 6 and is input into compressor 1, thus forming a mixed working fluid circulation loop.

[0044] like Figure 1 As shown, in this embodiment, the condenser 2 is equipped with a first pressure sensor 7 at the mixed working fluid input end. The first pressure sensor 7 is used to detect the first pressure of the high-temperature and high-pressure mixed working fluid output by the compressor 1. The evaporator 6 is equipped with a second pressure sensor 8 at the mixed working fluid output end. The second pressure sensor 8 is used to detect the second pressure of the low-temperature gaseous mixed working fluid output by the evaporator 6. The controller 9 is used to receive the first pressure and the second pressure, and to control the opening of the first expansion valve 3 according to the first pressure and the dew point pressure of the mixed working fluid, and to control the opening of the second expansion valve 5 according to the second pressure and the bubble point pressure of the mixed working fluid. The dew point pressure represents the complete liquefaction of the mixed working fluid, and the bubble point pressure represents the complete vaporization of the mixed working fluid.

[0045] In this embodiment of the invention, when the first pressure is not within the dew point pressure range, the condensing pressure of the condenser 2 can be adjusted to the dew point pressure range through the first expansion valve 3, so that the mixed working fluid is completely liquefied in the condenser 2. When the second pressure is not within the bubble point pressure range, the evaporating pressure of the evaporator 6 can be adjusted to the bubble point pressure range through the second expansion valve 5, so that the mixed working fluid is completely liquefied in the evaporator 6. That is, this embodiment of the invention can achieve the ideal state of condensing pressure and evaporating pressure at the same time, the mixed working fluid is completely liquefied in the condenser and completely vaporized in the evaporator, and the heat pump system reaches the optimal performance state.

[0046] In one optional embodiment, the condenser 2 includes an inlet water temperature sensor electrically connected to the controller 9. The inlet water temperature sensor detects the inlet water temperature of the condenser 2, and the controller 9 determines the dew point pressure of the mixed working fluid based on the inlet water temperature. Taking water as the heat exchange medium in the condenser 2 as an example, the inlet water temperature of the condenser 2 can be detected by the inlet water temperature sensor, and the dew point pressure of the mixed working fluid can be determined based on the inlet water temperature. In one embodiment, a dew point pressure lookup table can be pre-configured, which includes the matching relationship between inlet water temperature and dew point pressure. The dew point pressure corresponding to the inlet water temperature can be found through the dew point pressure lookup table.

[0047] Similarly, in an optional embodiment, the evaporator 6 includes an inlet air temperature sensor, which is electrically connected to the controller 9. The inlet air temperature sensor is used to detect the inlet air temperature of the evaporator 6. The controller 9 determines the bubble point pressure of the mixed working fluid based on the inlet air temperature. Since the evaporator 6 needs to exchange heat with the outside, taking air as the heat exchange medium as an example, the low-temperature liquid mixed working fluid exchanges heat with the air around the radiator when it passes through the radiator. After the temperature of the mixed working fluid rises to the boiling point, it vaporizes to form a low-temperature gaseous mixed working fluid. The inlet air temperature of the evaporator 6 can be detected by the inlet air temperature sensor, and the bubble point pressure of the mixed working fluid can be determined by the inlet air temperature. In one embodiment, a bubble point pressure lookup table can be pre-configured. The bubble point pressure lookup table includes the matching relationship between the inlet air temperature and the bubble point pressure. The bubble point pressure corresponding to the inlet air temperature can be found through the bubble point pressure lookup table.

[0048] Of course, the calculation functions for the dew point pressure and bubble point pressure of the mixed working fluid can also be pre-configured in the controller. The detected inlet water temperature is input into the dew point pressure calculation function to obtain the dew point pressure, and the inlet air temperature is input into the bubble point pressure calculation function to obtain the bubble point pressure.

[0049] In this embodiment, the dew point pressure is determined by the inlet water temperature of the condenser, and the bubble point pressure is calculated by the inlet air temperature of the evaporator. The dew point pressure can be dynamically adjusted in real time according to the inlet water temperature of the condenser, and the bubble point pressure can be dynamically adjusted according to the inlet air temperature of the evaporator, so that the mixed working fluid can be completely liquefied and vaporized according to the external ambient temperature of the condenser and evaporator.

[0050] like Figure 2 As shown, in an optional embodiment, the mixed working fluid heat pump system may further include a third pressure sensor 10 electrically connected to the controller 9. The third pressure sensor 10 is located at the mixed working fluid output end of the reservoir 4. The third pressure sensor 10 is used to detect the third pressure of the mixed working fluid output by the first expansion valve 3. The controller 9 can determine whether the first pressure after adjustment by the first expansion valve 3 is within the dew point pressure range and is in a stable state through the third pressure. For example, if the first pressure is within the dew point pressure range and the third pressure is maintained within the preset pressure range within a preset time, it can be determined that the first pressure has been adjusted to the dew point pressure range and is in a stable state. The second expansion valve 5 can be adjusted based on the third pressure. In this embodiment, the third pressure of the mixed working fluid output by the first expansion valve 3 is detected by the third pressure sensor 10 to determine whether the first pressure has been adjusted to the dew point pressure range and is in a stable state, so as to trigger the adjustment of the second expansion valve 5 and provide a pressure reference for the adjustment of the second expansion valve 5. This avoids the need to repeatedly adjust the second expansion valve 5 when the first pressure has not been adjusted to a stable state, thereby improving the adjustment efficiency of the second expansion valve 5.

[0051] like Figure 3 As shown, in an optional embodiment, the mixed working fluid heat pump system may further include a regenerator 11. The mixed working fluid output end of the liquid receiver 4 is connected to the second expansion valve 5 through the regenerator 11, and the mixed working fluid output end of the evaporator 6 is connected to the mixed working fluid input end of the compressor 1 through the regenerator 11. A second pressure sensor 8 is disposed between the regenerator 11 and the compressor 1. The regenerator 11 is used to further cool the mixed working fluid output from the liquid receiver 4. Specifically, when the liquid mixed working fluid flowing out of the condenser 2 passes through the first expansion valve 3, a gaseous flash will occur, meaning that after passing through the first expansion valve 3, there is a gas-liquid two-state mixed working fluid. If the gas-liquid two-state mixed working fluid enters the second expansion valve 5, it will cause gas blockage in the second expansion valve 5. In this embodiment, since the boiling point of the mixed working fluid is low, the low-temperature gaseous mixed working fluid flowing out of the evaporator 6 enters the regenerator 11 after flowing out of the evaporator 6. In the regenerator 11, it exchanges heat with the gas-liquid two-state mixed working fluid flowing out of the liquid storage tank 4, thereby further cooling the gas-liquid two-state mixed working fluid flowing out of the liquid storage tank 4 in the regenerator 11. The gaseous mixed working fluid is cooled into a liquid mixed working fluid in the regenerator 11, ensuring that the fluid flowing into the second expansion valve 5 is a pure liquid mixed working fluid, thus avoiding gas blockage in the second expansion valve 5.

[0052] like Figure 4 As shown, the mixed working fluid heat pump system of this embodiment may further include a gas-liquid separator 12. The regenerator 11 is connected to the compressor 1 through the gas-liquid separator 12. That is, the low-temperature gaseous mixed working fluid output by the evaporator 6 may contain liquid mixed working fluid before entering the compressor 1 after passing through the regenerator 11. In order to ensure that the gaseous mixed working fluid enters the compressor 1, the gaseous mixed working fluid and the liquid mixed working fluid can be separated by the gas-liquid separator 12 so that the mixed working fluid entering the compressor 1 is pure gaseous mixed working fluid.

[0053] Figure 5 This is a flowchart illustrating a control method for a mixed-working-refrigerant heat pump system according to an embodiment of the present invention. This control method is applied to control a mixed-working-refrigerant heat pump system, and can be implemented by a controller within the system. Figure 5 As shown, the mixed working fluid heat pump system control method of this embodiment of the invention may specifically include the following steps:

[0054] S501, The first pressure of the mixed working fluid output by the compressor is detected by the first pressure sensor.

[0055] like Figure 1 As shown, the mixed working fluid heat pump system of this embodiment includes a compressor 1, a condenser 2, a first expansion valve 3, a liquid receiver 4, a second expansion valve 5, and an evaporator 6 connected in sequence to form a mixed working fluid circulation loop. A first pressure sensor 7 is provided at the mixed working fluid input end of the condenser 2, which is used to detect the first pressure of the high-temperature and high-pressure mixed working fluid output by the compressor 1. A second pressure sensor 8 is provided at the mixed working fluid output end of the evaporator 6, which is used to detect the second pressure of the low-temperature gaseous mixed working fluid output by the evaporator 6.

[0056] The controller 9 can detect the first pressure of the mixed working fluid output by the compressor 1 through the first pressure sensor.

[0057] S502, The second pressure of the mixed working fluid output by the evaporator is detected by the second pressure sensor.

[0058] Similarly, the controller 9 can detect the second pressure of the low-temperature gaseous working fluid output by the evaporator 6 through the second pressure sensor.

[0059] S503. The opening degree of the first expansion valve is controlled according to the first pressure and the dew point pressure of the mixed working fluid, where the dew point pressure indicates that the mixed working fluid is completely liquefied.

[0060] In one embodiment, a dew point pressure range can be set according to the dew point pressure. If the first pressure is within the dew point pressure range, the first expansion valve maintains its current opening. If the first pressure is less than or equal to the lower limit of the dew point pressure range, the opening of the first expansion valve is reduced. If the first pressure is greater than or equal to the upper limit of the dew point pressure range, the opening of the first expansion valve is increased, so that the first pressure is within the dew point pressure range, ensuring that the mixed working fluid is completely liquefied in the condenser.

[0061] S504. The opening degree of the second expansion valve is controlled according to the second pressure and the bubble point pressure of the mixed working fluid. The bubble point pressure represents the complete vaporization of the mixed working fluid.

[0062] In one embodiment, a bubble point pressure range can be set according to the bubble point pressure. If the second pressure is within the bubble point pressure range, the second expansion valve maintains its current opening. If the second pressure is less than or equal to the lower limit of the bubble point pressure range, the opening of the second expansion valve is increased. If the second pressure is greater than or equal to the upper limit of the bubble point pressure range, the opening of the second expansion valve is decreased, so that the second pressure is within the bubble point pressure range, ensuring that the mixed working fluid is completely vaporized in the evaporator.

[0063] The mixed refrigerant heat pump system of this embodiment includes a first expansion valve and a second expansion valve. A first pressure sensor detects the first pressure of the mixed refrigerant output by the compressor, and a second pressure sensor detects the second pressure of the mixed refrigerant output by the evaporator. The opening of the first expansion valve is controlled according to the first pressure and the dew point pressure of the mixed refrigerant, and the opening of the second expansion valve is controlled according to the second pressure and the bubble point pressure of the mixed refrigerant. Since the first expansion valve is set after the condenser and the second expansion valve is set before the evaporator, the condensing pressure of the condenser can be adjusted to equal the dew point pressure by adjusting the opening of the first expansion valve, and the evaporating pressure of the evaporator can be adjusted to equal the bubble point pressure by adjusting the opening of the second expansion valve. This allows the condensing pressure and evaporating pressure to reach their ideal states simultaneously, so that the mixed refrigerant is completely liquefied in the condenser and completely vaporized in the evaporator, enabling the heat pump system to reach its optimal performance state.

[0064] Figure 6 A flowchart of a control method for a mixed working fluid heat pump system, as provided in another embodiment of the present invention, is shown below. Figure 6 As shown, the mixed working fluid heat pump system control method of this embodiment of the invention may specifically include the following steps:

[0065] S601, The first pressure of the mixed working fluid output by the compressor is detected by the first pressure sensor.

[0066] S602, The second pressure of the mixed working fluid output by the evaporator is detected by the second pressure sensor.

[0067] S603. Determine whether the first pressure is within the pressure range of the dew point pressure.

[0068] In an optional embodiment, the inlet water temperature of the condenser can also be detected by an inlet water temperature sensor, and the dew point pressure can be determined by the inlet water temperature. For example, a dew point pressure lookup table can be pre-configured, which includes the matching relationship between inlet water temperature and dew point pressure. The dew point pressure corresponding to the inlet water temperature can be found by looking up the dew point pressure in the dew point pressure lookup table.

[0069] After determining the dew point pressure, the dew point pressure range can be set according to the dew point pressure. For example, assuming the dew point pressure is Pc, the set dew point pressure is [Pc-0.02, Pc+0.02]. Further determine whether the first pressure is within the pressure range of the dew point pressure. If yes, execute S604; if no, execute S605 and S606.

[0070] S604, Control the first expansion valve to maintain the current opening.

[0071] If the first pressure is within the dew point pressure range, and the current condensing pressure of the condenser is within the dew point pressure range, the high-temperature and high-pressure gaseous working fluid can be completely liquefied in the condenser under the current pressure, without the need to adjust the opening of the first expansion.

[0072] S605. If the first pressure is less than or equal to the lower limit of the pressure range of the dew point pressure, reduce the opening of the first expansion valve.

[0073] If the first pressure is less than or equal to the lower limit of the dew point pressure, it is determined that the current condensing pressure of the condenser is too low, which is not conducive to the condensation of the mixed working fluid. The opening of the first expansion valve can be reduced to increase the first pressure, and then return to execute S603.

[0074] S606. If the first pressure is greater than or equal to the upper limit of the pressure range of the dew point pressure, increase the opening degree of the first expansion valve.

[0075] If the first pressure is greater than or equal to the upper limit of the dew point pressure, it is determined that the current condensing pressure of the condenser is too high, which is not conducive to the condensation of the mixed working fluid. The opening of the first expansion valve can be increased to reduce the first pressure, and then return to execute S603.

[0076] S607. Determine whether the second pressure is within the pressure range of the bubble point pressure.

[0077] like Figure 4As shown, in an optional embodiment, the mixed working fluid heat pump system may further include a third pressure sensor 10 electrically connected to the controller 9. The third pressure sensor 10 is located at the mixed working fluid output end of the reservoir 4. The third pressure sensor 10 is used to detect the third pressure of the mixed working fluid output by the first expansion valve 3. Before adjusting the second pressure through the second expansion valve 5, the third pressure can be received from the third pressure sensor. If the first pressure is adjusted to the dew point pressure range, and if the third pressure is within the preset pressure range, it indicates that the first pressure is within the dew point pressure range and is in a relatively stable state. The second expansion valve 5 can then be adjusted. For example, the second expansion valve 5 can be adjusted based on the third pressure. This realizes the adjustment of the second expansion valve 5 by detecting the third pressure and provides a pressure reference for the adjustment of the second expansion valve 5, avoiding the need to repeatedly adjust the second expansion valve 5 before the first pressure is adjusted to a stable state, thus improving the adjustment efficiency of the second expansion valve 5.

[0078] In an optional embodiment, the inlet air temperature of the evaporator can be detected by an inlet air temperature sensor, and the bubble point pressure of the mixed working fluid can be determined by the inlet air temperature. For example, a bubble point pressure lookup table can be pre-configured, which includes the matching relationship between inlet air temperature and bubble point pressure. The bubble point pressure corresponding to the inlet air temperature can be found by looking up the bubble point pressure in the bubble point pressure lookup table.

[0079] After determining the bubble point pressure, the bubble point pressure range can be set according to the bubble point pressure. For example, assuming the bubble point pressure is Pe, the set bubble point pressure is [Pe-0.005, Pe+0.005]. Further determine whether the second pressure is within the pressure range of the bubble point pressure. If yes, execute S608; if no, execute S609 and S610.

[0080] S608, Control the second expansion valve to maintain the current opening.

[0081] If the second pressure is within the bubble point pressure range, and the current evaporation pressure of the evaporator is determined to be within the bubble point pressure range, the low-temperature liquid mixed working fluid can be completely vaporized in the evaporator under the current pressure, without the need to adjust the opening of the second expansion.

[0082] S609. If the second pressure is less than or equal to the lower limit of the pressure range of the bubble point pressure, increase the opening degree of the second expansion valve.

[0083] If the second pressure is less than or equal to the lower limit of the bubble point pressure, it is determined that the current evaporation pressure of the evaporator is too low, which is not conducive to the evaporation and vaporization of the mixed working fluid. The opening of the second expansion valve can be increased to raise the second pressure, and then return to execute S607.

[0084] S610. If the second pressure is greater than the upper limit of the pressure range of the bubble point pressure, reduce the opening degree of the second expansion valve.

[0085] If the second pressure is greater than or equal to the upper limit of the bubble point pressure, it is determined that the current evaporation pressure of the evaporator is too high, which is not conducive to the evaporation and vaporization of the mixed working fluid. The opening of the second expansion valve can be reduced to lower the second pressure and return to S607.

[0086] In this embodiment, after receiving the first pressure and the second pressure, if the first pressure is less than or equal to the lower limit of the dew point pressure range, the opening of the first expansion valve is reduced; if the first pressure is greater than or equal to the upper limit of the dew point pressure range, the opening of the first expansion valve is increased. This continues until the first pressure is within the dew point pressure range, at which point the opening of the first expansion valve is maintained, ensuring that the condensing pressure of the condenser is within the dew point pressure range. Similarly, if the second pressure is less than or equal to the lower limit of the bubble point pressure range, the opening of the first expansion valve is increased; if the second pressure is greater than or equal to the upper limit of the bubble point pressure range, the opening of the second expansion valve is reduced. This continues until the second pressure is within the bubble point pressure range, at which point the opening of the second expansion valve is maintained, ensuring that the evaporating pressure of the evaporator is within the bubble point pressure range. This achieves the goal of adjusting the condensing pressure of the condenser to equal the dew point pressure via the first expansion valve and adjusting the evaporating pressure of the evaporator to equal the bubble point pressure via the second expansion valve. Both the condensing and evaporating pressures simultaneously reach ideal states, resulting in complete liquefaction of the mixed working fluid in the condenser and complete vaporization in the evaporator, thus enabling the heat pump system to achieve optimal performance.

[0087] Based on the above description of the implementation methods, those skilled in the art can clearly understand that the present invention can be implemented using software and necessary general-purpose hardware, and of course, it can also be implemented using hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause the controller to execute the mixed working fluid heat pump system control method described in the various embodiments of the present invention.

[0088] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A mixed working fluid heat pump system, characterized in that, It includes a compressor (1), a condenser (2), a first expansion valve (3), a liquid receiver (4), a second expansion valve (5), and an evaporator (6) that are connected in sequence to form a mixed working fluid circulation loop; The condenser (2) is provided with a first pressure sensor (7) at the mixed working fluid input end. The first pressure sensor (7) is used to detect the first pressure of the mixed working fluid output by the compressor (1). The evaporator (6) is equipped with a second pressure sensor (8) at the mixed working fluid output end. The second pressure sensor (8) is used to detect the second pressure of the mixed working fluid output by the evaporator (6), and also includes: A controller (9) is configured to receive the first pressure and the second pressure, and control the opening of the first expansion valve (3) according to the first pressure and the dew point pressure of the mixed working fluid, and control the opening of the second expansion valve (5) according to the second pressure and the bubble point pressure of the mixed working fluid, wherein the dew point pressure indicates that the mixed working fluid is completely liquefied and the bubble point pressure indicates that the mixed working fluid is completely vaporized.

2. The mixed working fluid heat pump system according to claim 1, characterized in that, The condenser (2) includes an inlet water temperature sensor, which is electrically connected to the controller (9) and is used to detect the inlet water temperature of the condenser (2). The controller (9) determines the dew point pressure of the mixed working fluid based on the inlet water temperature.

3. The mixed working fluid heat pump system according to claim 1, characterized in that, The evaporator (6) includes an inlet air temperature sensor, which is electrically connected to the controller (9). The inlet air temperature sensor is used to detect the inlet air temperature of the evaporator (6). The controller (9) determines the bubble point pressure of the mixed working fluid based on the inlet air temperature.

4. The mixed working fluid heat pump system according to claim 1, characterized in that, It also includes a third pressure sensor (10) electrically connected to the controller (9), the third pressure sensor (10) being disposed at the mixed working fluid output end of the reservoir (4), the third pressure sensor (10) being used to detect the third pressure of the mixed working fluid output by the first expansion valve (3).

5. The mixed working fluid heat pump system according to any one of claims 1-4, characterized in that, It also includes a regenerator (11), the mixed working fluid output end of the liquid receiver (4) is connected to the second expansion valve (5) through the regenerator (11), the mixed working fluid output end of the evaporator (6) is connected to the mixed working fluid input end of the compressor (1) through the regenerator (11), and the second pressure sensor (8) is disposed between the regenerator (11) and the compressor (1).

6. The mixed working fluid heat pump system according to claim 5, characterized in that, It also includes a gas-liquid separator (12), through which the regenerator (11) is connected to the compressor (1).

7. A control method for a mixed working fluid heat pump system, characterized in that, The mixed working fluid heat pump system according to any one of claims 1-6 comprises: The first pressure of the mixed working fluid output by the compressor is detected by the first pressure sensor; The second pressure of the mixed working fluid output by the evaporator is detected by a second pressure sensor; The opening degree of the first expansion valve is controlled according to the first pressure and the dew point pressure of the mixed working fluid, wherein the dew point pressure indicates that the mixed working fluid is completely liquefied. The opening degree of the second expansion valve is controlled according to the second pressure and the bubble point pressure of the mixed working fluid, wherein the bubble point pressure indicates that the mixed working fluid is completely vaporized.

8. The control method for a mixed working fluid heat pump system according to claim 7, characterized in that, Controlling the opening degree of the first expansion valve based on the first pressure and the dew point pressure of the mixed working fluid includes: Determine whether the first pressure is within the pressure range of the dew point pressure; If the first pressure is less than or equal to the lower limit of the pressure range of the dew point pressure, reduce the opening of the first expansion valve and return to the step of determining whether the first pressure is within the pressure range of the dew point pressure. If the first pressure is greater than or equal to the upper limit of the pressure range of the dew point pressure, increase the opening of the first expansion valve and return to the step of determining whether the first pressure is within the pressure range of the dew point pressure. If the first pressure is within the pressure range of the dew point pressure, control the first expansion valve to maintain its current opening.

9. The control method for a mixed working fluid heat pump system according to claim 7, characterized in that, Controlling the opening degree of the second expansion valve based on the second pressure and the bubble point pressure of the mixed working fluid includes: Determine whether the second pressure is within the pressure range of the bubble point pressure; If the second pressure is less than or equal to the lower limit of the pressure range of the bubble point pressure, increase the opening of the second expansion valve and return to the step of determining whether the second pressure is within the pressure range of the bubble point pressure; If the second pressure is greater than or equal to the upper limit of the pressure range of the bubble point pressure, reduce the opening of the second expansion valve and return to the step of determining whether the second pressure is within the pressure range of the bubble point pressure. If the second pressure is within the pressure range of the bubble point pressure, control the second expansion valve to maintain the current opening.

10. The control method for a mixed working fluid heat pump system according to claim 9, characterized in that, Before determining whether the second pressure is within the pressure range of the bubble point pressure, the process also includes: Receive the third pressure from the third pressure sensor; When the third pressure is within the preset pressure range, the step of determining whether the second pressure is within the pressure range of the bubble point pressure is performed.

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