A transcritical carbon dioxide heat pump air conditioning system and a control method thereof

Abstract

The application relates to a transcritical carbon dioxide heat pump air conditioning system and a control method thereof, which comprises a refrigerant loop and a bypass loop; the refrigerant loop comprises a compressor, a gas cooler, a first heat exchange channel of a regenerator, a throttling device, a plate heat exchanger and a second heat exchange channel of a heat exchanger of the regenerator which are sequentially connected; the bypass loop is connected in parallel to two ends of the first heat exchange channel of the regenerator, and an electromagnetic bypass valve is arranged on the bypass loop; during control, the change of the state of the regenerator and the optimization of the high pressure of system exhaust are completed through a control strategy in the system, so that the optimal performance is searched for under the premise of ensuring the safety of the system. Compared with the prior art, the regenerator bypass or access to the system is realized only by controlling a single valve, and a regenerator and high pressure control method suitable for the transcritical CO2 heat pump air conditioner is proposed in combination with the reliability of the compressor, so that the system can operate safely and has the maximum energy-saving potential.

Description

Technical Field

[0001] This invention relates to the field of heat pump technology, and in particular to a transcritical carbon dioxide heat pump air conditioning system and its control method. Background Technology

[0002] Currently, with the increasing severity of energy shortages and environmental degradation, people have begun to research more environmentally friendly and energy-efficient new technologies. Based on this, transcritical CO2 heat pump systems have been widely researched and applied. This is partly due to CO2's environmental friendliness and good thermal properties as a natural refrigerant, and partly due to the significant advantages of highly efficient and energy-saving heat pump technology in both residential and industrial heating.

[0003] However, compared to traditional cycles, transcritical CO2 cycles suffer from significant throttling losses due to their lower critical temperature and higher internal pressure. To improve the energy efficiency of transcritical CO2 systems, researchers have proposed various technologies, among which regenerators are a commonly used measure. However, studies show that the presence of a regenerator does not consistently improve system efficiency; in some operating conditions, it can even degrade system performance. Furthermore, due to the limited operating range of the compressor, the adverse effects of the regenerator are amplified, especially under conditions with high pressure ratios. The regenerator's increase in suction superheat causes a sharp rise in compressor discharge temperature, leading to coking of the compressor lubricating oil and affecting system reliability. Therefore, an optimal control scheme should be developed for the transcritical CO2 system based on the compressor's operating limits.

[0004] Patent CN 216644604 U discloses a transcritical carbon dioxide single- or two-stage compression hot water system. This system can intelligently switch between single- or two-stage transcritical operation under varying conditions. By using a given optimal high-pressure correlation and controlling the opening degree of the expansion valve, it improves the problem of excessively high exhaust temperature in transcritical carbon dioxide circulation. However, this technical solution requires the use of two carbon dioxide compressors, making the system very complex.

[0005] Patent CN 109579377 A discloses a method for controlling the electronic expansion valve in a transcritical carbon dioxide heat pump system. This invention uses a combination of adjusting the opening of the electronic expansion valve and changing the exhaust temperature to control the exhaust pressure. However, all the above inventions control the exhaust pressure by controlling the expansion valve, which is a technical solution that addresses the system control aspect. In actual operation, it is difficult to achieve precise and effective control of the system. Furthermore, the above solutions are suitable for carbon dioxide heat pump systems without a regenerator, but the exhaust temperature control effect is poor for systems with a regenerator. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing a transcritical carbon dioxide heat pump air conditioning system and its control method. This system achieves regenerator bypass or connection to the system by controlling only a single valve. In conjunction with the reliability of the compressor, a regenerator and high-pressure control method suitable for transcritical CO2 heat pump air conditioning is proposed to ensure that the system can achieve maximum energy-saving potential while operating safely.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] The first aspect of the present invention provides a transcritical carbon dioxide heat pump air conditioning system, including a refrigerant loop and a bypass loop;

[0009] The refrigerant loop includes a compressor, a gas cooler, a first heat exchange channel of a regenerator, a throttling device, a plate heat exchanger, and a second heat exchange channel of the regenerator connected in sequence. The second heat exchange channel of the regenerator is connected to the compressor to form a cycle.

[0010] Furthermore, the gas cooler is connected to the first inlet of the regenerator, and the throttling device is connected to the first outlet of the regenerator; the plate heat exchanger is connected to the second inlet of the regenerator, and the compressor is connected to the second outlet of the regenerator.

[0011] Furthermore, the bypass circuit is connected in parallel to both ends of the first heat exchange channel of the regenerator, and an electromagnetic bypass valve is provided on the bypass circuit;

[0012] Furthermore, an electromagnetic bypass valve is provided on the bypass circuit, one end of which is connected to the connecting pipe between the gas cooler and the regenerator, and the other end is connected to the connecting pipe between the regenerator and the throttling device.

[0013] Both the gas cooler and the plate heat exchanger are connected to the external cooling water flow path. By switching the external cooling water flow paths on both sides, the mode switching between external heating and cooling can be achieved.

[0014] The throttling device in this technical solution is one of a capillary tube, a throttling short tube, or an electronic expansion valve. In order to facilitate the realization of automated control, this technical solution preferably uses an electronic expansion valve.

[0015] Furthermore, a first temperature sensor is provided on the refrigerant pipeline at the outlet of the gas cooler to monitor the refrigerant temperature at the outlet of the gas cooler.

[0016] A second temperature sensor is installed on the compressor exhaust pipe to monitor the compressor exhaust temperature.

[0017] Furthermore, a first pressure sensor is provided on the compressor suction line to monitor the compressor suction pressure.

[0018] A second pressure sensor is installed on the compressor exhaust pipe to monitor the compressor exhaust pressure.

[0019] A second aspect of this invention provides a control method for a transcritical carbon dioxide heat pump air conditioning system. Considering the actual operating conditions of the system, the method utilizes internal control strategies to modify the regenerator state and optimize the system's exhaust pressure, thereby finding optimal performance while ensuring system safety.

[0020] Depending on the on / off state of the electromagnetic bypass valve, the refrigerant operating state in the transcritical CO2 heat pump air conditioner's regenerator bypass and control method of this invention can be divided into the following two scenarios:

[0021] 1. When the electromagnetic bypass valve is open, the working state of the refrigerant loop in the system is as follows: the high-temperature and high-pressure gas formed by the refrigerant after being compressed by the compressor is cooled by the gas cooler, and then all of it enters the throttling device through the electromagnetic bypass valve. In the throttling device, it is throttled to form a low-temperature gas-liquid two-phase refrigerant, and then enters the plate heat exchanger to absorb heat and become a low-temperature and low-pressure refrigerant gas. Finally, it enters the compressor again after passing through the regenerator.

[0022] 2. When the electromagnetic bypass valve is closed, the working state of the refrigerant loop in the system is as follows: the high-temperature and high-pressure gas formed by the refrigerant after being compressed by the compressor is cooled by the gas cooler and then flows into the regenerator. After being subcooled in the regenerator, the refrigerant enters the throttling device, where it is throttled to form a low-temperature gas-liquid two-phase refrigerant. Then it enters the plate heat exchanger to absorb heat and become a low-temperature and low-pressure refrigerant gas. Finally, it absorbs heat through the regenerator to become a superheated state and then re-enters the compressor.

[0023] The internal control strategy of the system in this invention is as follows:

[0024] Cooling mode

[0025] During summer cooling operation, the regenerator can significantly reduce CO2 throttling losses and improve system energy efficiency; therefore, it is connected to the system by default. The specific control flow inside the system is as follows:

[0026] When the system starts working, the compressor discharge pressure is first set to 8500 kPa, the electromagnetic bypass valve is closed, the regenerator is connected to the system, and the gas cooler outlet temperature, compressor discharge temperature, compressor suction pressure and compressor discharge pressure are monitored using the first temperature sensor, the second temperature sensor, the first pressure sensor and the second pressure sensor.

[0027] First, determine if the exhaust temperature exceeds the limit: when the system detects that the current exhaust temperature is less than the maximum allowable exhaust temperature, continue to judge the gas cooler outlet temperature; otherwise, the target exhaust pressure is the current exhaust pressure of the system minus 500 kPa.

[0028] When the gas cooler outlet temperature exceeds the critical value for the gas cooler outlet temperature in refrigeration mode, the regenerator operating status signal is set to 1, and the optimal exhaust pressure is calculated according to the first functional relationship. Otherwise, the regenerator operating status signal is set to 0, and the optimal exhaust pressure is calculated according to the second functional relationship. Then, the compressor exhaust pressure is checked. When the calculated optimal exhaust pressure is less than the maximum allowable exhaust pressure of the system and the ratio of the calculated optimal pressure value to the system's current suction pressure is less than the maximum allowable pressure ratio of the compressor, the exhaust pressure target value is the calculated optimal exhaust pressure value; otherwise, the exhaust pressure target value is the maximum allowable exhaust pressure of the compressor.

[0029] Finally, based on the target exhaust pressure value and the regenerator operating status signal after the judgment is completed, the exhaust pressure and the control result of the regenerator are output. When the final value of the regenerator operating status signal is 0, the electromagnetic bypass valve opens, and the regenerator is bypassed; when the final value of the regenerator operating status signal is 1, the electromagnetic bypass valve closes, and the regenerator is connected to the system to participate in the circulation.

[0030] Heating mode

[0031] In winter heating mode, due to the relatively high system operating pressure, the regenerator has a significant impact on the compressor discharge temperature. Therefore, the regenerator is defaulted to bypass mode, and its connection to the system is determined based on operational results. The specific control flow within the system is as follows:

[0032] When the system starts working, the compressor discharge pressure is first set to 8000 kPa, the electromagnetic bypass valve is opened, and the regenerator is bypassed. At the same time, the first temperature sensor, the second temperature sensor, the first pressure sensor, and the second pressure sensor are used to monitor the gas cooler outlet temperature, the compressor discharge temperature, the compressor suction pressure, and the compressor discharge pressure.

[0033] First, it is still necessary to determine whether the exhaust temperature exceeds the limit: when the system detects that the exhaust temperature is less than the maximum allowable exhaust temperature, the gas cooler outlet temperature is further judged; otherwise, the exhaust pressure target value is the current exhaust pressure of the system minus 500 kPa.

[0034] When the gas cooler outlet temperature exceeds the critical value for gas cooler outlet temperature in heating mode, the regenerator operating status signal is set to 1; otherwise, it is set to 0. When the regenerator operating status signal is set to 1, the system's ability to connect to the regenerator is determined by the exhaust temperature: if the difference between the compressor exhaust temperature and the upper limit of the exhaust temperature is greater than the given regenerative value, it indicates that the system's exhaust temperature has a reasonable margin, so the regenerator operating status signal is set to 1. Simultaneously, the optimal exhaust pressure is calculated based on the third function relationship, and the final exhaust pressure value is output after the system verifies the compressor exhaust pressure. If the exhaust temperature difference is less than the regenerative value, it indicates that connecting the regenerator will cause the system exhaust temperature to exceed the limit, so the regenerator operating status signal is set to 0. The optimal exhaust pressure is then calculated based on the fourth function relationship, and the final exhaust pressure value is output after the system verifies the compressor exhaust pressure.

[0035] The process for verifying the system's exhaust pressure is the same as the process for verifying the exhaust pressure during system cooling.

[0036] The relevant statements in the above control strategies will be explained in further detail:

[0037] Critical outlet temperature of the gas cooler: Previous practical experience and relevant literature data indicate that systems using regenerators do not consistently improve system performance at all operating points. Using the gas cooler outlet temperature as a criterion, a critical temperature value is always found. When the gas cooler outlet temperature exceeds this critical temperature value, the use of a regenerator helps improve system performance; conversely, below this value, system performance degrades. This critical temperature value is the critical outlet temperature of the gas cooler in this invention. Due to differences in cooling and heating modes within the same system, the critical outlet temperature of the gas cooler will also differ.

[0038] The system-defined regenerative temperature value: Compared to a system without a regenerative heater, using a regenerative heater increases the compressor's suction superheat. This increase in suction superheat leads to an increase in the compressor's discharge temperature, which can generally be approximated as an increase in discharge temperature by the same magnitude. The system-defined regenerative temperature value is the increase in compressor suction superheat after using a regenerative heater, which can be taken as 40K in this invention. This value is defined to determine whether the regenerative heater is bypassing the system by checking the system's discharge temperature. The specific determination principle is as follows: In the case of a system without a regenerative heater, if the difference between the maximum allowable discharge temperature of the system and the current system discharge temperature is greater than the system-defined regenerative temperature value, it indicates that the discharge temperature after using a regenerative heater is still below the maximum allowable discharge temperature of the system, meeting the system's safe operating conditions, and the regenerative heater can be connected to the system; conversely, if the difference is less than the maximum allowable discharge temperature of the system after using a regenerative heater, it indicates that the discharge temperature after using a regenerative heater has exceeded the maximum allowable discharge temperature of the system, not meeting the system's safe operating conditions, and the regenerative heater cannot be connected to the system.

[0039] Functional Relationship: Based on extensive experimental data and literature, a correlation formula can be fitted to determine the optimal exhaust pressure from the gas cooler outlet temperature and the system's optimal exhaust pressure. This is the aforementioned functional correlation formula. The functional correlation formula varies depending on whether a regenerator is used in the system and the control mode (cooling / heating). Therefore, in this invention, the first functional relationship is the correlation between the optimal exhaust pressure and the gas cooler outlet temperature when a regenerator is used in cooling mode; the second functional relationship is the correlation between the optimal exhaust pressure and the gas cooler outlet temperature when a regenerator is not used in cooling mode; the third functional relationship is the correlation between the optimal exhaust pressure and the gas cooler outlet temperature when a regenerator is used in heating mode; and the fourth functional relationship is the correlation between the optimal exhaust pressure and the gas cooler outlet temperature when a regenerator is not used in heating mode.

[0040] The regenerator bypass and control method for transcritical CO2 heat pump air conditioners in this invention has the following structural features and innovations:

[0041] A bypass circuit with an electromagnetic bypass valve is provided: the system regenerator can be bypassed or connected to the system using only a single electromagnetic bypass valve. The structure is simple and can avoid the performance degradation of the system using the regenerator at some operating points, which is conducive to improving the system performance at different operating points.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] 1. This technical solution takes into account that the use of a regenerator cannot always help improve system energy efficiency. A bypass circuit with an electromagnetic bypass valve is set in the system. The bypass of the regenerator is achieved by opening and closing a single electromagnetic bypass valve. Compared with the traditional system without a regenerator bypass structure, this technical solution is not only simple in structure, but also helps the system to continuously operate at the optimal energy efficiency point.

[0044] 2. This technical solution proposes a regenerator and high-pressure control method suitable for transcritical CO2 heat pump air conditioning, ensuring safe system operation. Through internal control strategies, the system is consistently operated at its optimal performance point under actual operating conditions, maximizing energy savings while maintaining safe operation. Compared to traditional solutions, this solution is more suitable for practical transcritical CO2 heat pump air conditioning systems due to its enhanced consideration of operational safety and reliability.

[0045] 3. This technical solution proposes separate regenerator and high-pressure control methods for cooling and heating modes. Based on the different operating limitations of the system in different modes, corresponding regenerator and high-pressure control signals are output, enabling the system to operate at its optimal energy efficiency point in the corresponding mode according to actual conditions. Furthermore, this technical solution proposes an approximate criterion for determining whether the regenerator should be connected to the system in heating mode. Compared to traditional solutions, this technical solution is more convenient and feasible while meeting the control requirements of different modes. Attached Figure Description

[0046] Figure 1 This is a schematic flowchart of Embodiment 1 of the transcritical CO2 heat pump air conditioning system of the present invention;

[0047] Figure 2 This is a schematic diagram of the process of the transcritical CO2 heat pump air conditioning system in cooling mode according to the present invention;

[0048] Figure 3 This is a schematic diagram of the process of the transcritical CO2 heat pump air conditioning system in heating mode according to the present invention;

[0049] Figure 4 This is a control flowchart of the transcritical CO2 heat pump air conditioning system in cooling mode according to the present invention;

[0050] Figure 5 This is a control flowchart of the transcritical CO2 heat pump air conditioning system in heating mode according to the present invention;

[0051] Figure 6 This is a schematic diagram of the process of Embodiment 2 of the transcritical CO2 heat pump air conditioning system in this invention;

[0052] In the diagram: 1-Compressor; 2-Gas cooler; 3-Solenoid bypass valve; 4-Throttling device; 5-Plate heat exchanger; 6-Regenerator; 7-16 Refrigerant connecting pipes; 17-20 Water connecting pipes; 21-First temperature sensor; 22-First pressure sensor; 23-Second temperature sensor; 24-Second pressure sensor; P dis : Compressor discharge pressure; Flag_IHX: Regenerator operating status signal; T gc,out : Gas cooler outlet temperature; P suc Compressor suction pressure; T dis Compressor discharge temperature; T dis,max The maximum allowable exhaust temperature of the system; T gc,out0 : Critical outlet temperature of the gas cooler in cooling mode; T gc,out1 : Critical value of gas cooler outlet temperature in heating mode; P opt : Optimal exhaust pressure of the system; f1~f4: Functional relationship; P dis,max The maximum required exhaust pressure of the system; Pr max P: The maximum allowable pressure ratio of the compressor. comp,max P: The maximum allowable discharge pressure of the compressor. dis` ΔT: The final exhaust pressure value output by the system. sh The system-given temperature regeneration value;

[0053] Further detailed explanations of the aforementioned terms are provided below:

[0054] Critical outlet temperature T of gas cooler 2 gc,out0 / T gc,out1 Previous practical experience and relevant literature data indicate that systems using regenerator 6 do not necessarily improve system performance at all operating points. Taking the outlet temperature T of gas cooler 2 as an example... gc,out As a criterion, it was found that there is always a critical temperature value, when the outlet temperature T of gas cooler 2... gc,out When the temperature exceeds this critical temperature value, using regenerator 6 helps improve system performance; conversely, when the temperature falls below this value, system performance will degrade. The critical temperature value here is the critical outlet temperature T of the gas cooler in this invention. gc,out0 / T gc,out1 .

[0055] The system provides a regenerative temperature value ΔT sh Compared to a system without a regenerator 6, using a regenerator 6 system will increase the suction superheat of compressor 1, and the increase in suction superheat will increase the discharge temperature T of compressor 1. dis The increase, generally speaking, can be approximated as causing the exhaust temperature T to rise. disThe same increase is achieved. The system provides a regenerative capacity value ΔT. sh This refers to the increase in superheat of the compressor 1's suction gas after the regenerator 6 is used; in this invention, 40K can be taken as the value. This value is defined to determine whether the regenerator 6 is bypassing the system by checking the system's exhaust temperature. Specifically, the determination principle is: when the system has no regenerator 6, when the maximum allowable exhaust temperature T of the system... dis,max With the system exhaust temperature T at this time dis The difference is greater than the given recoil value ΔT of the system. sh When this occurs, it indicates that the exhaust temperature T after the system uses regenerator 6 is... dis Still within the maximum allowable exhaust temperature T of the system dis,max The following conditions must be met for the system to operate safely before regenerator 6 can be connected to the system; otherwise, it indicates that the exhaust temperature T after using regenerator 6 will be insufficient. dis The exhaust temperature has exceeded the maximum allowable temperature T of the system. dis,max The system's safe operating conditions are not met, and the regenerator 6 cannot be connected to the system.

[0056] Functional relationships f1~f4: Based on a large amount of experimental data and literature, the outlet temperature T of gas cooler 2 can be used as a basis for calculation. gc,out and the system's optimal exhaust pressure P opt Fit a value based on the outlet temperature T of gas cooler 2 gc,out Determine the optimal exhaust pressure P opt The correlations are the functional correlations f1 to f4. Due to the presence or absence of the regenerator 6 in the system and the different control modes under cooling and heating conditions, functional correlations f1 to f4 also differ. Therefore, in this invention, the first functional relationship f1 represents the optimal exhaust pressure P when the regenerator 6 is used in cooling mode. opt With gas cooler 2 outlet temperature T gc,out The correlation between them; the second functional relationship f2 is the optimal exhaust pressure P when the regenerator 6 is not used in the cooling mode. opt With gas cooler 2 outlet temperature T gc,out The correlation between them; the third functional relationship f3 is the optimal exhaust pressure P when using regenerator 6 in heating mode. opt With gas cooler 2 outlet temperature T gc,out The correlation between them; the fourth functional relationship f4 is the optimal exhaust pressure P when the regenerator 6 is not used in the heating mode. opt With gas cooler 2 outlet temperature T gc,out The relationship between them. Detailed Implementation

[0057] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0058] Example 1

[0059] Combination Figures 1-5 The first embodiment will be described below. This embodiment describes a method for bypassing and controlling the regenerator of a transcritical CO2 heat pump air conditioner, the structure of which is as follows: Figure 1 As shown, the main structure includes a compressor 1, a gas cooler 2, an electromagnetic bypass valve 3, a throttling device 4, a plate heat exchanger 5, a regenerator 6, refrigerant connecting pipes 7-16, water connecting pipes 17-20, a first temperature sensor 21, a first pressure sensor 22, a second temperature sensor 23, and a second pressure sensor 24.

[0060] In this embodiment, compressor 1, connecting pipe 7, gas cooler 2, connecting pipes 8 and 9, regenerator 6, connecting pipes 10 and 13, throttling device 4, connecting pipe 14, plate heat exchanger 5, connecting pipe 15, regenerator 6, and connecting pipe 16 are connected in sequence to form a refrigerant loop. Simultaneously, a bypass circuit is connected in parallel on the high-pressure side of the regenerator 6 in this refrigerant loop. This bypass circuit consists of connecting pipe 11, electromagnetic bypass valve 3, and connecting pipe 12. One end of the bypass circuit is connected to the outlet connecting pipe 8 of gas cooler 2 via connecting pipe 11, and the other end is connected to the inlet pipe 13 of throttling device 4 via connecting pipe 12.

[0061] Based on the different switching states of electromagnetic bypass valve 3, the regenerator bypass and control method of the transcritical CO2 heat pump air conditioner of the present invention can be divided into the following two situations regarding the working state of the refrigerant inside the system:

[0062] 1. When the electromagnetic bypass valve 3 is open, the operating state of the refrigerant loop in the system is as follows: the refrigerant, after being compressed by the compressor 1, forms a high-temperature, high-pressure gas, which is then cooled by the gas cooler 2. Most of the refrigerant then enters the throttling device 4 through the electromagnetic bypass valve 3. A small portion of the refrigerant may flow into the throttling device 4 through the regenerator 6, but the heat exchange between the refrigerant fluids in the regenerator 6 is negligible at this time. The refrigerant fluid is throttled in the throttling device 4 to form a low-temperature gas-liquid two-phase refrigerant, which then enters the plate heat exchanger 5 to absorb heat and become a low-temperature, low-pressure refrigerant gas. Finally, it re-enters the compressor 1 through the regenerator 6.

[0063] 2. When the electromagnetic bypass valve 3 is closed, the working state of the refrigerant loop in the system is as follows: the refrigerant is compressed by the compressor 1 to form a high-temperature and high-pressure gas, which is then cooled by the gas cooler 2 and then flows into the regenerator 6. After being subcooled in the regenerator 6, the refrigerant enters the throttling device 4, where it is throttled to form a low-temperature gas-liquid two-phase refrigerant. Then it enters the plate heat exchanger 5 to absorb heat and become a low-temperature and low-pressure refrigerant gas. Finally, it is superheated by the regenerator 6 and then re-enters the compressor 1.

[0064] This invention discloses a regenerator bypass and control method for a transcritical CO2 heat pump air conditioner. Considering the actual operating conditions of the system, it optimizes the regenerator state and the system exhaust pressure through an internal control strategy, thereby finding optimal performance while ensuring system safety. The internal control strategy of this invention is as follows:

[0065] (a) When the system is cooling:

[0066] Under summer cooling conditions, regenerator 6 can significantly reduce CO2 throttling losses and improve system energy efficiency; therefore, it is connected to the system by default. The specific control flow inside the system is as follows:

[0067] When the system starts working, first set the discharge pressure P of compressor 1. dis The pressure is set to 8500 kPa, the electromagnetic bypass valve 3 is closed, the regenerator 6 is connected to the system, and the outlet temperature T of the gas cooler 2 is monitored using the first temperature sensor 21, the second temperature sensor 23, the first pressure sensor 22, and the second pressure sensor 24. gc,out Compressor 1 exhaust temperature T dis Compressor 1 suction pressure P suc Compressor 1 discharge pressure P dis Conduct monitoring;

[0068] First, determine the exhaust temperature T. dis Exceeding limits: When the system detects the exhaust temperature T at this time dis Less than the maximum allowable exhaust temperature T of the system dis,max At that time, continue to monitor the outlet temperature T of gas cooler 2. gc,out Make a judgment; otherwise, the target value of the exhaust pressure P. dis` That is, the current exhaust pressure P of the system. dis Subtract 500 kPa.

[0069] When the outlet temperature of gas cooler 2 is T gc,out The outlet temperature T of gas cooler 2 is greater than the critical value of T in cooling mode. gc,out0 At this time, the operating status signal Flag_IHX of the regenerator 6 is set to 1, and the optimal exhaust pressure P is calculated according to the first functional relationship f1. optOtherwise, set the operating status signal Flag_IHX of the regenerator 6 to 0, and calculate the optimal exhaust pressure P at this time according to the second function relationship f2. opt Then, the discharge pressure P of compressor 1 is measured. dis Verification was performed when the calculated optimal exhaust pressure P was... opt Less than the maximum allowable exhaust pressure P of the system dis,max And the calculated optimal high pressure value P opt With the system's current intake pressure P suc The ratio is less than the maximum allowable pressure ratio Pr of the compressor. max At that time, the target value of exhaust pressure P dis` The calculated optimal exhaust pressure value P opt Otherwise, the target value of the exhaust pressure P dis` The maximum allowable discharge pressure P of the compressor comp,max .

[0070] Finally, based on the target exhaust pressure P after the judgment is completed... dis` The operating status signal Flag_IHX of the regenerator 6 outputs the exhaust pressure and the control result of the regenerator 6. When the final value of the operating status signal Flag_IHX of the regenerator 6 is 0, the electromagnetic bypass valve 3 is opened, and the regenerator 6 is bypassed; when the final value of the operating status signal Flag_IHX of the regenerator 6 is 1, the electromagnetic bypass valve 3 is closed, and the regenerator 6 is connected to the system to participate in the circulation.

[0071] (a) Heating mode

[0072] In winter heating mode, due to the relatively high system operating pressure, the discharge temperature T of the regenerator 6 relative to the compressor 1 is... dis The impact is significant, therefore, regenerator 6 is assumed to be in bypass mode by default, and its connection to the system will be determined based on the operational results. The specific control flow within the system is as follows:

[0073] When the system starts working, first set the discharge pressure P of compressor 1. dis When the pressure is set to 8000 kPa, the electromagnetic bypass valve 3 opens, bypassing the regenerator 6. Simultaneously, the outlet temperature T of the gas cooler 2 is monitored using the first temperature sensor 21, the second temperature sensor 23, the first pressure sensor 22, and the second pressure sensor 24. gc,out Compressor 1 exhaust temperature T dis Compressor 1 suction pressure P suc Compressor 1 discharge pressure P dis Conduct monitoring;

[0074] First, it is still necessary to determine the exhaust temperature T. dis Exceeding limits: When the system detects the exhaust temperature T at this time disLess than the maximum allowable exhaust temperature T of the system dis,max At that time, continue to monitor the outlet temperature T of gas cooler 2. gc,out Make a judgment; otherwise, the target value of the exhaust pressure P. dis` That is, the current exhaust pressure P of the system. dis Subtract 500 kPa.

[0075] When the outlet temperature of gas cooler 2 is T gc,out The outlet temperature T of gas cooler 2 is greater than the critical value of T in heating mode. gc,out1 When the regenerator 6 operating status signal Flag_IHX is set to 1, otherwise, the regenerator 6 operating status signal Flag_IHX is set to 0. When the regenerator 6 operating status signal Flag_IHX is set to 1, the exhaust temperature T is then measured. dis Determine if the system can be connected to the regenerator 6: When the discharge temperature T of compressor 1 is at this time dis With upper limit of exhaust temperature T dis,max The difference is greater than the given recoil value ΔT sh When, it indicates the system's exhaust temperature T dis Since there is a reasonable margin, the operating status signal Flag_IHX of the regenerator 6 is set to 1. At the same time, the optimal exhaust pressure P is calculated according to the third function relationship f3. opt Then, the system controls the discharge pressure P of compressor 1. dis The final exhaust pressure value P of the verification output system dis` When the exhaust temperature difference is less than the regenerative value ΔT sh When this is the case, it indicates that connecting the regenerator 6 will cause the system exhaust temperature T to increase. dis Since the limit is exceeded, the operating status signal Flag_IHX of the regenerator 6 is set to 0. Then, the optimal exhaust pressure P at this time is calculated according to the fourth function relationship f4. opt Then, the system controls the discharge pressure P of compressor 1. dis The final exhaust pressure value P of the verification output system dis` .

[0076] The system controls the exhaust pressure P dis The verification process and the exhaust pressure P during system cooling were performed. dis The verification process is consistent.

[0077] Example 2

[0078] Combination Figure 6 The second embodiment will now be described. The structures, functions, and effects in the second embodiment that are not specifically described are the same as in the first embodiment; only the differences from the embodiments described above will be explained below.

[0079] This embodiment describes a regenerator bypass and control method for a transcritical CO2 heat pump air conditioner, the structure of which is as follows: Figure 6 As shown. In the second embodiment, compared to the first embodiment, the electromagnetic bypass valve 3 is placed on the low-pressure side of the system via connecting pipes 11 and 12. Connecting pipe 11 is connected to the intake pipe 9 of the compressor 1, and connecting pipe 12 is connected to the plate heat exchanger 5 via connecting pipe 10. The remaining structure is the same as the first embodiment.

[0080] Based on the different switching states of electromagnetic bypass valve 3, the regenerator bypass and control method of the transcritical CO2 heat pump air conditioner of the present invention can be divided into the following two situations regarding the working state of the refrigerant inside the system:

[0081] 1. When the electromagnetic bypass valve 3 is open, the working state of the refrigerant loop in the system is as follows: the refrigerant is compressed by the compressor 1 to form a high-temperature and high-pressure gas, which is then cooled by the gas cooler 2. After that, it enters the throttling device 4 through the regenerator 6. In the throttling device 4, it is throttled to form a low-temperature gas-liquid two-phase refrigerant. Then, it enters the plate heat exchanger 5 to absorb heat and become a low-temperature and low-pressure refrigerant gas. Finally, most of it re-enters the compressor 1 through the electromagnetic bypass valve 3. A small amount of refrigerant may flow into the compressor 1 through the regenerator 6, but the heat exchange of the refrigerant in the regenerator 6 can be ignored at this time.

[0082] 2. When the electromagnetic bypass valve 3 is closed, the working state of the refrigerant loop in the system is as follows: the refrigerant is compressed by the compressor 1 to form a high-temperature and high-pressure gas, which is then cooled by the gas cooler 2 and flows into the regenerator 6. After being subcooled in the regenerator 6, the refrigerant enters the throttling device 4, where it is throttled to form a low-temperature gas-liquid two-phase refrigerant. It then enters the plate heat exchanger 5 to absorb heat and become a low-temperature and low-pressure refrigerant gas. Finally, it passes through the regenerator 6 to become superheated and then re-enters the compressor 1.

[0083] The control strategy inside the system in this embodiment is the same as that in the first embodiment.

[0084] It should be stated that other arrangements based on the principles of this invention are also within the scope of protection of this invention.

[0085] The terms "first" and "second" are used in this document to define components. Those skilled in the art should understand that the use of these terms is solely for the purpose of distinguishing components in description. Unless otherwise stated, these terms have no special meaning.

[0086] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A control method for a transcritical carbon dioxide heat pump air conditioning system, characterized in that, Including refrigerant loop and bypass loop; The refrigerant loop includes a compressor, a gas cooler, a first heat exchange channel of a regenerator, a throttling device, a plate heat exchanger, and a second heat exchange channel of the regenerator connected in sequence. The second heat exchange channel of the regenerator is connected to the compressor to form a cycle. The bypass circuit is connected in parallel to both ends of the first heat exchange channel of the regenerator, and an electromagnetic bypass valve is provided on the bypass circuit; Both the gas cooler and the plate heat exchanger are connected to the external cooling water flow path. By switching the external cooling water flow paths on both sides, the mode switching between external heating and cooling can be realized. The control method for the transcritical carbon dioxide heat pump air conditioning system includes: In cooling mode, the electromagnetic bypass valve is initially closed. Based on the target exhaust pressure value and the regenerator operating status signal, it outputs the exhaust pressure and the control results of the regenerator: When the final value of the regenerator operating status signal is 0, the solenoid bypass valve opens and the regenerator is bypassed; when the final value of the regenerator operating status signal is 1, the solenoid bypass valve closes and the regenerator is connected to the system to participate in the circulation. In cooling mode, the target value of the exhaust pressure and the operating status signal of the regenerator are obtained in the following ways: First, determine if the exhaust temperature exceeds the limit: if the compressor exhaust temperature is less than the maximum allowable exhaust temperature of the system, continue to judge the gas cooler outlet temperature; otherwise, the target exhaust pressure is the current exhaust pressure of the system minus 500 kPa. When the outlet temperature of the gas cooler is greater than the critical value of the outlet temperature of the gas cooler in the refrigeration mode, the operating status signal of the regenerator is set to 1, and the optimal exhaust pressure at this time is calculated according to the first functional relationship; otherwise, the operating status signal of the regenerator is set to 0, and the optimal exhaust pressure at this time is calculated according to the second functional relationship. Then, the compressor discharge pressure is checked. When the calculated optimal discharge high pressure is less than the maximum allowable discharge pressure of the system, and the ratio of the calculated optimal high pressure value to the system's current suction pressure is less than the maximum allowable pressure ratio of the compressor, the discharge pressure target value is the calculated optimal discharge high pressure value; otherwise, the discharge pressure target value is the maximum allowable discharge pressure of the compressor. In heating mode, the electromagnetic bypass valve is initially in the open state, and the regenerator is in the bypass state. Based on the target value of the exhaust pressure after the judgment is completed and the regenerator operating status signal, the exhaust pressure and the control result of the regenerator are output: When the final value of the regenerator operating status signal is 0, the solenoid bypass valve opens and the regenerator is bypassed; when the final value of the regenerator operating status signal is 1, the solenoid bypass valve closes and the regenerator is connected to the system to participate in the circulation. In heating mode, the target value of the exhaust pressure and the regenerator operating status signal are obtained in the following ways: First, determine if the exhaust temperature exceeds the limit: when the system detects that the current exhaust temperature is less than the maximum allowable exhaust temperature, continue to judge the gas cooler outlet temperature; otherwise, the exhaust pressure target value is the current system exhaust pressure minus 500 kPa. When the gas cooler outlet temperature is greater than the critical value of the gas cooler outlet temperature in heating mode, the regenerator operating status signal is set to 1; otherwise, the regenerator operating status signal is set to 0. When the regenerator operating status signal is set to 1, the exhaust temperature is then used to determine whether the system can be connected to the regenerator. When the difference between the compressor discharge temperature and the upper limit of the discharge temperature is greater than the given regenerative value, the regenerator operating status signal is set to 1. At the same time, the optimal discharge pressure is calculated according to the third function relationship, and the final discharge pressure value of the system is output after the system verifies the compressor discharge pressure. When the discharge temperature difference is less than the regenerative value, the regenerator operating status signal is set to 0. The optimal discharge pressure is calculated according to the fourth function relationship, and the final discharge pressure value of the system is output after the system verifies the compressor discharge pressure. The regenerative capacity value is the increase in compressor suction superheat after the regenerator is used; The regenerative value is used to determine whether the regenerator is bypassed by checking the system exhaust temperature: when there is no regenerator in the system, if the difference between the maximum allowable exhaust temperature of the system and the current system exhaust temperature is greater than the given regenerative value of the system, the regenerator can be connected to the system; otherwise, the regenerator cannot be connected to the system. The first functional relationship is the correlation between the optimal exhaust pressure and the outlet temperature of the gas cooler when a regenerator is used in refrigeration mode; The second functional relationship is the correlation between the optimal exhaust pressure and the outlet temperature of the gas cooler when the regenerator is not used in the refrigeration mode; The third functional relationship is the correlation between the optimal exhaust pressure and the gas cooler outlet temperature when a regenerator is used in the heating mode. The fourth functional relationship is the correlation between the optimal exhaust pressure and the outlet temperature of the gas cooler when the regenerator is not used in the heating mode.

2. The control method for a transcritical carbon dioxide heat pump air conditioning system according to claim 1, characterized in that, A first temperature sensor is installed on the refrigerant pipeline at the outlet of the gas cooler to monitor the refrigerant temperature at the outlet of the gas cooler. A second temperature sensor is installed on the compressor exhaust pipe to monitor the compressor exhaust temperature.

3. The control method for a transcritical carbon dioxide heat pump air conditioning system according to claim 1, characterized in that, The compressor suction line is equipped with a first pressure sensor for monitoring the compressor suction pressure; A second pressure sensor is installed on the compressor exhaust pipe to monitor the compressor exhaust pressure.

4. A control method for a transcritical carbon dioxide heat pump air conditioning system as described in any one of claims 1 to 3, characterized in that, When the electromagnetic bypass valve is open, the refrigerant loop operates as follows: the refrigerant is compressed by the compressor to form a high-temperature, high-pressure gas, which is then cooled by the gas cooler. The main refrigerant fluid then enters the throttling device through the electromagnetic bypass valve. The refrigerant fluid is throttled in the throttling device to form a low-temperature gas-liquid two-phase refrigerant. It then enters the plate heat exchanger to absorb heat and become a low-temperature, low-pressure refrigerant gas. Finally, it re-enters the compressor after passing through the regenerator.

5. The control method for the transcritical carbon dioxide heat pump air conditioning system according to claim 4, characterized in that, When the electromagnetic bypass valve is closed, the refrigerant loop operates as follows: the refrigerant is compressed by the compressor to form a high-temperature, high-pressure gas, which is then cooled by the gas cooler and flows entirely into the regenerator. After being subcooled in the regenerator, the refrigerant enters the throttling device, where it is throttled to form a low-temperature gas-liquid two-phase refrigerant. It then enters the plate heat exchanger to absorb heat and become a low-temperature, low-pressure refrigerant gas. Finally, it absorbs heat through the regenerator to become superheated and re-enters the compressor.

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