CO2 heat pump system and control method thereof

Abstract

The invention relates to the technical field of air conditioners, in particular to a CO2 heat pump system and a control method thereof. The problem that the capacity and the energy efficiency of a heat pump system with an ejector are reduced when the heat pump system deviates from the design working condition is solved. In order to achieve the purpose, the CO2 heat pump system is provided with an ejector set, the ejector set comprises at least two ejectors connected in parallel, at least one ejector can be independently connected and disconnected, an exhaust port of a compressor communicates with a first port of an outdoor heat exchanger, and a second port of the outdoor heat exchanger communicates with inlets of all the ejectors; outlets of all the ejectors are communicated with an inlet of the gas-liquid separator, an exhaust port of the gas-liquid separator is communicated with an air suction port of the compressor, a liquid outlet of the gas-liquid separator is communicated with a first port of the first throttling element, a second port of the first throttling element is communicated with a first port of the first indoor heat exchanger, and the first port of the first indoor heat exchanger is communicated with ejection ports of all the ejectors. According to the CO2 heat pump system, the on-off state of each ejector is changed to adapt to various operation conditions, and the energy efficiency of the CO2 heat pump system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of air conditioners, and particularly relates to a CO2 heat pump system and a control method thereof. Background Art

[0002] As a new type of environmentally friendly refrigerant, CO2 (carbon dioxide) has currently become a research hotspot in the heat pump industry. The advantages and disadvantages of a heat pump system using CO2 as a refrigerant are equally obvious. Its advantages are that the heating performance is generally better than that of traditional heat pumps, and the disadvantages are that the large system pressure difference causes large expansion work loss in the system, resulting in poor refrigeration energy efficiency, which severely restricts the popularization and application of CO2 in the air conditioning field.

[0003] To solve the above problems, using ejectors, compression-expansion integrated machines, and vortex tubes are relatively common solutions at present. Among them, the ejector has an absolute advantage in terms of maturity and cost performance and is the current mainstream solution. However, the ejector has the problem of poor variable load capacity. In terms of flow regulation, it can be regarded as a capillary tube, that is, after being designed according to a certain working condition, its flow range has been determined. Therefore, when adjusting under a wide range of variable working conditions, the ability and energy efficiency of the heat pump system will drop significantly when deviating from the designed working condition.

[0004] Correspondingly, a new technical solution is needed in this field to solve the above problems. Summary of the Invention

[0005] To solve at least one of the above problems in the prior art, that is, to solve the problem that the ability and energy efficiency of a heat pump system with an ejector decrease when deviating from the designed working condition, the present application provides a CO2 heat pump system. The CO2 heat pump system includes a compressor, an outdoor heat exchanger, an ejector group, a gas-liquid separator, a first throttling element, and a first indoor heat exchanger. The ejector group includes at least two ejectors connected in parallel, and at least one of the ejectors can be independently turned on and off. The exhaust port of the compressor is communicated with the first port of the outdoor heat exchanger, the second port of the outdoor heat exchanger is communicated with the inlets of all the ejectors, the outlets of all the ejectors are communicated with the inlet of the gas-liquid separator, the exhaust port of the gas-liquid separator is communicated with the suction port of the compressor, the liquid discharge port of the gas-liquid separator is communicated with the first port of the first throttling element, the second port of the first throttling element is communicated with the first port of the first indoor heat exchanger, and the first port of the first indoor heat exchanger is communicated with the injection ports of all the ejectors.

[0006] According to the above technical solution, by setting the ejector group, it is possible to adapt to various operating conditions by changing the on-off state of each ejector in the ejector group, which is beneficial to improving the refrigeration capacity and energy efficiency of the CO2 heat pump system and ensuring the stable operation of the system.

[0007] In the preferred technical solution of the above CO2 heat pump system, a on-off valve is provided on the outlet pipeline of each ejector.

[0008] In the above technical solution, by setting the on-off valve, the on-off of each ejector can be controlled through the on-off valve.

[0009] In the preferred technical solution of the above CO2 heat pump system, the CO2 heat pump system further includes a throttle opening valve. One end of the throttle opening valve is communicated with the second port of the outdoor heat exchanger, and the other end is communicated with the inlets of all the ejectors.

[0010] In the above technical solution, by setting the throttle opening valve, the refrigerant flow rate into the ejector group can be controlled, and the flow control accuracy can be improved.

[0011] In the preferred technical solution of the above CO2 heat pump system, the rated flow rates of at least two ejectors in the ejector group are different.

[0012] By setting ejectors with different rated flow rates, it is beneficial to improve the adaptability of the heat pump system to different working conditions and further improve the system energy efficiency.

[0013] In the second aspect of this proposal, a control method for a CO2 heat pump system is further provided, which is characterized in that the CO2 heat pump system includes a compressor, an outdoor heat exchanger, an ejector group, a gas-liquid separator, a first throttling element, and a first indoor heat exchanger. The ejector group includes at least two ejectors connected in parallel, and at least one of the ejectors can be independently turned on and off. The exhaust port of the compressor is communicated with the first port of the outdoor heat exchanger, the second port of the outdoor heat exchanger is communicated with the inlets of all the ejectors, the outlets of all the ejectors are communicated with the inlet of the gas-liquid separator, the exhaust port of the gas-liquid separator is communicated with the suction port of the compressor, the liquid discharge port of the gas-liquid separator is communicated with the first port of the first throttling element, the second port of the first throttling element is communicated with the first port of the first indoor heat exchanger, and the first port of the first indoor heat exchanger is communicated with the injection ports of all the ejectors.

[0014] The control method includes:

[0015] Determine the load of the CO2 heat pump system;

[0016] Based on the magnitude of the load, control the on-off state of each ejector in the ejector group.

[0017] In the control method of this application, by controlling the on-off state of each ejector in the ejector group based on the load magnitude, automatic adaptation to various operating conditions can be achieved, which is beneficial to improving the refrigeration capacity and energy efficiency of the CO2 heat pump system and ensuring the stable operation of the system.

[0018] In the preferred technical solution of the control method of the above CO2 heat pump system, the CO2 heat pump system further includes an opening degree regulating valve, one end of the opening degree regulating valve is communicated with the second port of the outdoor heat exchanger, and the other end is communicated with the inlets of all the ejectors.

[0019] The control method further includes:

[0020] Based on the magnitude of the load, control the opening degree of the opening degree regulating valve.

[0021] The above control method can further control the refrigerant flow rate entering the ejector group by controlling the opening degree of the opening degree regulating valve, and further improve the operating energy efficiency.

[0022] In the preferred technical solution of the control method of the above CO2 heat pump system, the ejector group includes a first ejector and a second ejector, the rated flow rate of the first ejector is greater than the rated flow rate of the second ejector, and the step of "based on the magnitude of the load, control the opening and closing states of each ejector in the ejector group and the opening degree of the opening degree regulating valve" further includes:

[0023] When the load is a low load, control the second ejector to be separately communicated, and control the opening degree regulating valve to be opened to a preset opening degree, where the preset opening degree is determined based on the corresponding relationship between the load and the preset opening degree;

[0024] When the load is a rated load, control the first ejector to be separately communicated, and control the opening degree regulating valve to be fully opened;

[0025] When the load is a large load, control the first ejector to be communicated and the second ejector to be communicated, and control the opening degree regulating valve to be fully opened.

[0026] In the preferred technical solution of the control method of the above CO2 heat pump system, the ejector group includes a first ejector, a second ejector and a third ejector, the rated flow rates of the first ejector, the second ejector and the third ejector decrease in sequence, and the step of "based on the magnitude of the load, control the opening and closing states of each ejector in the ejector group" further includes:

[0027] When the load is a low load, control the second ejector or the third ejector to be separately communicated;

[0028] When the load is a rated load, control the first ejector to be separately communicated;

[0029] When the load is a large load, control the first ejector to be communicated, and at least one of the second ejector and the third ejector to be communicated.

[0030] The above control method can improve the adaptability of the heat pump system to different operating conditions and further enhance the system energy efficiency by setting three ejectors with different rated flows.

[0031] In the preferred technical solution of the control method for the above CO2 heat pump system, the control method further includes:

[0032] Obtaining the temperature difference between the inlet and outlet of the first indoor heat exchanger;

[0033] Based on the temperature difference between the inlet and outlet, controlling the frequency of the compressor.

[0034] The above control method can achieve a small-range adjustment of the refrigerant flow rate and improve the control accuracy by controlling the frequency of the compressor based on the temperature difference between the inlet and outlet of the first indoor heat exchanger.

[0035] In the preferred technical solution of the control method for the above CO2 heat pump system, the step of "determining the load of the CO2 heat pump system" further includes:

[0036] Obtaining the outdoor ambient temperature and the set temperature;

[0037] Calculating the difference between the outdoor ambient temperature and the set temperature;

[0038] Based on the difference, determining the load of the CO2 heat pump system; or

[0039] Obtaining the indoor ambient temperature and the set temperature;

[0040] Calculating the difference between the indoor ambient temperature and the set temperature;

[0041] Based on the difference, determining the load of the CO2 heat pump system. Brief Description of the Drawings

[0042] The present application will be described below with reference to the drawings. In the drawings:

[0043] Figure 1 is the system diagram of the CO2 heat pump system in the first embodiment of the present application;

[0044] Figure 2 is the system diagram of the CO2 heat pump system in the second embodiment of the present application;

[0045] Figure 3 is the flow chart of the control method for the CO2 heat pump system of the present application;

[0046] Figure 4 is the logic diagram of the control method for the CO2 heat pump system of the present application.

[0047] List of Reference Numerals

[0048] 1. Compressor; 2. Four-way valve; 3. Outdoor heat exchanger; 4. Injector group; 41. First injector; 42. Second injector; 43. Third injector; 44. On-off valve; 5. Gas-liquid separator; 6. First throttling element; 7. First indoor heat exchanger; 8. Second indoor heat exchanger; 9. Opening regulating valve; 10. Regenerator. Specific embodiments

[0049] The preferred embodiments of the present application will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principle of the present application and are not intended to limit the protection scope of the present application. For example, although the regenerator is introduced in combination with the drawings, the setting of the regenerator is not necessary. Those skilled in the art can adjust it according to needs to adapt to specific application scenarios. For example, in some embodiments, the setting of the regenerator can also be omitted.

[0050] It should be noted that the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. It should also be noted that in the description of the present application, unless otherwise clearly specified and limited, the terms "connected", "linked", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0051] First, refer to Figure 1 , and describe the CO2 heat pump system of the present application.

[0052] As Figure 1 shown, in order to solve the problem that the capacity and energy efficiency of a heat pump system with an injector decrease when deviating from the design conditions, the CO2 heat pump system (hereinafter sometimes simply referred to as the heat pump system or the system) of the present application includes a compressor 1, an outdoor heat exchanger 3, an injector group 4, a gas-liquid separator 5, a first throttling element 6, and a first indoor heat exchanger 7. The injector group 4 includes at least two injectors connected in parallel, and at least one injector can be independently turned on and off. The exhaust port of the compressor 1 is communicated with the first port of the outdoor heat exchanger 3, the second port of the outdoor heat exchanger 3 is communicated with the inlets of all the injectors, the outlets of all the injectors are communicated with the inlet of the gas-liquid separator 5, the exhaust port of the gas-liquid separator 5 is communicated with the suction port of the compressor 1, the liquid discharge port of the gas-liquid separator 5 is communicated with the first port of the first throttling element 6, the second port of the first throttling element 6 is communicated with the first port of the first indoor heat exchanger 7, and the first port of the first indoor heat exchanger 7 is communicated with the injection ports of all the injectors.

[0053] When the CO2 heat pump system is operating, the refrigerant discharged from the compressor 1 first enters the outdoor heat exchanger 3 to exchange heat with the outdoor air. After heat exchange, the refrigerant enters the ejector group 4, is ejected through the ejector group 4 and enters the gas-liquid separator 5. The gaseous refrigerant entering the gas-liquid separator 5 returns to the compressor 1 through the exhaust port, and the liquid refrigerant flows through the drain port to the first throttling element 6 for throttling and pressure reduction. The refrigerant after throttling and pressure reduction enters the first indoor heat exchanger 7 to exchange heat with the indoor air, and the refrigerant after heat exchange returns to the ejector group 4 through the injection port to continue participating in the cycle. When the system load changes, by adjusting the on-off of the ejectors with independent on-off functions in the ejector group 4, the refrigerant flow rate of the ejector group 4 can be adapted to the current working conditions.

[0054] In the above technical solution, by setting the ejector group 4, the adaptation to various operating conditions can be achieved by changing the on-off of each ejector in the ejector group 4, which is beneficial to improving the refrigeration capacity and energy efficiency of the CO2 heat pump system and ensuring the stable operation of the system.

[0055] The following refers to Figure 1 to introduce the first preferred embodiment of the present application.

[0056] As Figure 1 shown, in the first preferred embodiment of the present application, the CO2 heat pump system includes a compressor 1, a four-way valve 2, an outdoor heat exchanger 3, an ejector group 4, a gas-liquid separator 5, a first throttling element 6, a first indoor heat exchanger 7, a second indoor heat exchanger 8 and a regenerator 10.

[0057] The four-way valve 2 has four interfaces a, b, c, and d. The exhaust port of the compressor 1 is connected to the interface a of the four-way valve 2. The interface b of the four-way valve 2 is connected to the first port of the outdoor heat exchanger 3. The second port of the outdoor heat exchanger 3 is connected to the first port of the regenerator 10 ( Figure 1 the upper left port in Figure 1 ). The second port of the regenerator 10 ( Figure 1 the lower left port in Figure 1 ) is connected to the inlet of the ejector group 4, and an opening regulating valve 9 is provided on the pipeline between the second port of the regenerator 10 and the inlet of the ejector group 4. The opening regulating valve 9 is preferably an electronic expansion valve. The outlet of the ejector group 4 is connected to the first port of the second indoor heat exchanger 8 ( Figure 1 the left port in Figure 1The upper right port in ) is communicated with the suction port of the compressor 1. Wherein, a first heat exchange flow path is formed between the first port and the second port of the regenerator 10, and a second heat exchange flow path is formed between the third port and the fourth port of the regenerator 10. Heat exchange can be carried out between the first heat exchange flow path and the second heat exchange flow path.

[0058] Continue to refer to Figure 1 , the liquid discharge port of the gas-liquid separator 5 is communicated with the first port of the first throttling element 6 ( Figure 1 The right port in ), the second port of the first throttling element 6 ( Figure 1 The left port in ) is communicated with the first port of the first indoor heat exchanger 7 ( Figure 1 The right port in ), the second port of the first indoor heat exchanger 7 ( Figure 1 The left port in ) is communicated with the injection port of the injector group 4.

[0059] Preferably, the injector group 4 includes a first injector 41 and a second injector 42. The inlets, outlets and injection ports of the two injectors are all converged to the same pipeline. Wherein, on-off valves 44 are respectively arranged on the outlet pipelines of the first injector 41 and the second injector 42. The on-off valve 44 is an electromagnetic valve in this embodiment. More preferably, the rated flow rates of the first injector 41 and the second injector 42 are different. For example, the rated flow rate of the first injector 41 is greater than that of the second injector 42, and the rated flow rate of the first injector 41 is adapted to the design working conditions.

[0060] In this way, during operation, the refrigerant discharged by the compressor 1 passes through the interfaces a and b of the four-way valve 2 and then enters the outdoor heat exchanger 3 to exchange heat with outdoor air. The heat-exchanged refrigerant enters the first heat exchange flow path of the regenerator 10 and exchanges heat with the refrigerant in the second heat exchange flow path. The refrigerant discharged from the regenerator 10 passes through the opening degree regulating valve 9 and then enters the injector group 4, is ejected by the injector group 4 and enters the second indoor heat exchanger 8 to conduct a primary heat exchange with indoor air. The refrigerant discharged from the second indoor heat exchanger 8 enters the gas-liquid separator 5. The refrigerant entering the gas-liquid separator 5 is divided into two paths. Among them, the gaseous refrigerant is discharged through the exhaust port and flows through the interfaces d, c of the four-way valve 2 and the second heat exchange flow path of the refluxer and then returns to the compressor 1. The liquid refrigerant flows through the liquid discharge port to the first throttling element 6 for throttling and pressure reduction. The throttled and pressure-reduced refrigerant enters the first indoor heat exchanger 7 to conduct a secondary heat exchange with indoor air, and the heat-exchanged refrigerant returns to the injector group 4 through the injection port to continue to participate in the cycle.

[0061] When the system load changes, the flow rate into the ejector group 4 is adjusted by controlling the on / off states of the first ejector 41 and the second ejector 42 in the ejector group 4, as well as the opening degree of the opening degree regulating valve 9. For example, when the system load is small, the opening degree regulating valve 9 can be adjusted, the second ejector 42 can be opened, and the first ejector 41 can be closed to match the current refrigerant flow rate. When the system load is at the design condition, the opening degree regulating valve 9 can be controlled to be fully open, the second ejector 42 can be closed, and the first ejector 41 can be opened to enable the system to operate at the design condition. When the system load is large, the opening degree regulating valve 9 can be controlled to be fully open, and the first ejector 41 and the second ejector 42 can be opened simultaneously to meet the demand for the current refrigerant flow rate.

[0062] In the above technical solution, by adopting the combination of the ejector group 4 and the opening degree regulating valve 9, the adaptation to the current operating condition is achieved. The on / off valve 44 is provided, and the on / off of each ejector can be controlled through the on / off valve 44. By providing the opening degree regulating valve 9, the refrigerant flow rate into the ejector group 4 can be controlled, improving the flow rate control accuracy. By providing ejectors with different rated flow rates, it is beneficial to improve the adaptability of the heat pump system to different operating conditions and further improve the system energy efficiency.

[0063] Next, with reference to Figure 2 , the second preferred embodiment of the present application will be introduced.

[0064] As Figure 2 shown, the biggest difference between the second embodiment and the first embodiment is that the opening degree regulating valve 9 is omitted, and at the same time, the number of ejectors in the ejector group 4 is adjusted. Specifically, the second port of the regenerator 10 is directly connected to the ejector group 4 through a pipeline. The ejector group 4 includes a first ejector 41, a second ejector 42, and a third ejector 43. Among them, preferably, the rated flow rates of the first ejector 41, the second ejector 42, and the third ejector 43 decrease in sequence. Among them, the rated flow rate of the first ejector 41 is adapted to the design condition, the rated flow rate of the second ejector 42 is about 40% of that of the first ejector 41, and the rated flow rate of the third ejector 43 is about 20% of that of the third ejector 43.

[0065] In this way, when the system load changes, the matching with the corresponding operating condition can be achieved by changing the opening and closing states of the three ejectors in the ejector group 4. For example, when the system load is small, the second ejector 42 or the third ejector 43 can be opened, and the other ejectors can be closed to match the current refrigerant flow rate. When the system load is at the design condition, the first ejector 41 can be opened, and the other two ejectors can be closed to enable the system to operate at the design condition. When the system load is large, when the first ejector 41 is opened, the second ejector 42 and / or the third ejector 43 can be opened to meet the demand for the current refrigerant flow rate.

[0066] In the above technical solution, by changing the opening and closing of the three ejectors in the ejector group 4, the matching of the current operating conditions can be achieved, and the variable load capacity of the system can be improved.

[0067] It should be noted that the above preferred implementation manners are only used to illustrate the principle of the present application, and are not intended to limit the protection scope of the present application. Without departing from the principle of the present application, those skilled in the art can adjust the above settings so that the present application can be applied to more specific application scenarios.

[0068] For example, although the above implementation manner is described in combination with all ejectors being independently openable and closable, this is only a relatively preferred implementation manner, and as long as at least one ejector can be independently opened and closed.

[0069] In an alternative implementation manner, it is not necessary to provide the on-off valve 44 on the outlet pipeline of each ejector. Those skilled in the art can also set the on-off valve 44 at other positions, such as on the inlet pipeline of the ejector, etc. In addition, in addition to the solenoid valve, the on-off valve 44 can also adopt other electronically controlled valves such as expansion valves.

[0070] Again, in another alternative implementation manner, in the above two implementation manners, the introduction is made by taking the rated flow rate of each ejector being different as an example, but this is only exemplary, and those skilled in the art can select based on specific application scenarios. For example, the rated flow rate of each ejector can be set to be the same, or the flow rates of some of the ejectors can be set to be the same, and the flow rates of some of the ejectors can be different.

[0071] Again, the specific composition structure of the above heat pump system is only exemplary, and is not intended to limit the protection scope of the present application. Those skilled in the art can adjust the specific composition of the heat pump system, add or delete some of the above components. For example, the second indoor heat exchanger 8 or the regenerator 10 can be removed, etc.

[0072] Of course, the above alternative implementation manners can be used in cross combination with each other, and between the alternative implementation manners and the preferred implementation manners, so as to combine new implementation manners to be applicable to more specific application scenarios.

[0073] Next, with reference to Figure 3 , the control method of the CO2 heat pump system of the present application will be introduced.

[0074] As Figure 3 shown, corresponding to the above CO2 heat pump system, the control method of the present application includes:

[0075] S101. Determine the load of the CO2 heat pump system. For example, determine the magnitude of the current load of the heat pump system by obtaining the operating parameters or environmental parameters of the current heat pump system, etc.

[0076] S103. Based on the magnitude of the load, control the on / off states of each ejector in the ejector group. For example, when the load is small, adapt to the current operating condition by turning on some ejectors in the ejector group. When the load is large, match the current operating condition by turning on all ejectors in the ejector group.

[0077] The control method of the present application can achieve automatic adaptation to various operating conditions by controlling the on / off states of each ejector in the ejector group based on the magnitude of the load, which is beneficial to improving the refrigeration capacity and energy efficiency of the CO2 heat pump system and ensuring the stable operation of the system.

[0078] In one embodiment, the step of "determine the load of the CO2 heat pump system" further includes: obtaining the outdoor ambient temperature and the set temperature; calculating the difference between the outdoor ambient temperature and the set temperature; and determining the load of the CO2 heat pump system based on the difference.

[0079] For example, when the heat pump system is operating, obtain the outdoor ambient temperature through a temperature sensor set outdoors, obtain the user's set temperature through the controller of the heat pump system, and then calculate the difference between the two. When the difference is large, it proves that the load of the system is large at this time and a larger refrigerant flow rate is required to quickly reduce the indoor temperature to the set temperature. When the difference is small, it proves that the load of the system is small at this time and only a very small refrigerant flow rate is required to stabilize the indoor temperature at the set temperature.

[0080] In an alternative embodiment, obtain the indoor ambient temperature and the set temperature; calculate the difference between the indoor ambient temperature and the set temperature; and determine the load of the CO2 heat pump system based on the difference.

[0081] For example, obtain the indoor ambient temperature through a temperature sensor set indoors, obtain the user's set temperature through the controller of the heat pump system, and then calculate the difference between the two. When the difference is large, it proves that the current indoor temperature is far from the set temperature and a larger refrigerant flow rate is required to quickly reduce the indoor temperature to the set temperature, that is, the system load is large. When the difference is small, it proves that the current indoor temperature is far from the set temperature and only a very small refrigerant flow rate is required to stabilize the indoor temperature at the set temperature, and the system load is small at this time.

[0082] Preferably, in the present application, the system load can be divided into three ranges, namely high load, rated load, and low load. Among them, the rated load is the case when the refrigerant flow rate matches the rated flow rate (or the rated flow rate range) of the ejector, the high load is the case when the refrigerant flow rate is greater than the rated flow rate of the ejector (or the maximum value of the rated flow rate range), and the low load is the case when the refrigerant flow rate is less than the rated flow rate of the ejector (or the minimum value of the rated flow rate range).

[0083] Of course, the specific segmentation method of the system load is not restrictive, and those skilled in the art can adjust it based on the specific application scenario. For example, it can be divided into high load or low load, or the above three ranges can be further divided, etc.

[0084] In one implementation manner, corresponding to Figure 1 the heat pump system provided with the opening degree regulating valve shown in the first implementation manner, the control method further includes: controlling the opening degree of the opening degree regulating valve based on the magnitude of the load.

[0085] For example, when the load is small, the opening degree of the corresponding opening degree regulating valve is reduced to provide an appropriate refrigerant flow rate for the ejector group at the rear end. When the load is large, the opening degree of the corresponding opening degree regulating valve is increased to provide an appropriate refrigerant flow rate for the ejector group at the rear end.

[0086] The above control method can further control the refrigerant flow rate entering the ejector group by controlling the opening degree of the opening degree regulating valve, thereby further improving the operation energy efficiency.

[0087] Of course, when the opening degree regulating valve is not provided, the above control method can also be omitted.

[0088] Furthermore, in the case where the opening degree regulating valve is provided, the step of "controlling the opening and closing state of each ejector in the ejector group and the opening degree of the opening degree regulating valve based on the magnitude of the load" further includes: when the load is low, controlling the second ejector to be separately connected, and controlling the opening degree regulating valve to be opened to a preset opening degree, where the preset opening degree is determined based on the corresponding relationship between the load and the preset opening degree; when the load is the rated load, controlling the first ejector to be separately connected, and controlling the opening degree regulating valve to be fully opened; when the load is high, controlling the first ejector and the second ejector to be connected, and controlling the opening degree regulating valve to be fully opened.

[0089] For example, when the load is low and the required refrigerant flow rate is small at this time, controlling the second ejector with a smaller rated flow rate to be separately connected can adapt to the current operating condition. And control the opening degree regulating valve to open to a preset opening degree to match the current required refrigerant flow rate. The preset opening degree can be determined through experiments or based on experience. For example, at the flow rate required for each load, by adjusting the opening degree of the opening degree regulating valve, the refrigerant flow rate after passing through the opening degree regulating valve can be made to match the required flow rate. When the load is the rated load, it is adapted to the design condition of the system at this time. At this time, control the first ejector to be separately connected and control the opening degree regulating valve to be fully open. When the load is high, the required refrigerant volume is large at this time. Control the first ejector and the second ejector to be connected, and control the opening degree regulating valve to be fully open. The refrigerant volume required for the current condition is adapted through the two ejectors.

[0090] In one implementation, corresponding to Figure 2 the heat pump system of the second implementation manner without an opening degree regulating valve and with three ejectors, the step of "controlling the opening and closing states of each ejector in the ejector group based on the load size" further includes: when the load is low, controlling the second ejector or the third ejector to be separately connected; when the load is the rated load, controlling the first ejector to be separately connected; when the load is high, controlling the first ejector to be connected and at least one of the second ejector and the third ejector to be connected.

[0091] For example, when the load is low and the required refrigerant flow rate is small at this time, controlling the second ejector or the third ejector with a smaller rated flow rate to be separately connected can adapt to the current operating condition. When the load is the rated load, it is adapted to the design condition of the system at this time. At this time, control the first ejector to be separately connected so that the system operates at the design condition with the highest efficiency. When the load is high, the required refrigerant volume is large at this time. While controlling the first ejector to be connected, based on the specific refrigerant flow rate requirement, control the second ejector and / or the third ejector to be connected. The refrigerant volume required for the current condition is adapted by opening two or even three ejectors.

[0092] In one implementation, the control method further includes: obtaining the temperature difference between the inlet and outlet of the first indoor heat exchanger; controlling the frequency of the compressor based on the temperature difference between the inlet and outlet.

[0093] For example, the temperature difference between the inlet and outlet of the first indoor heat exchanger can reflect the heat exchange situation of the refrigerant in the first indoor heat exchanger, and further reflect whether the size of the refrigerant flow rate is adapted to the current operating condition. When the temperature difference between the inlet and outlet is too large, it proves that the refrigerant flow rate is small. On the contrary, when the temperature difference between the inlet and outlet is small, the refrigerant flow rate is large. Whether the refrigerant flow rate is large or small, it does not match the refrigerant flow rate requirement of the current condition. At this time, by controlling the compressor to increase or decrease the frequency, the regulation of the refrigerant flow rate is achieved.

[0094] In the above control method, by controlling the frequency of the compressor based on the temperature difference between the inlet and outlet of the first indoor heat exchanger, small-range adjustment of the refrigerant flow rate can be achieved, improving the control accuracy.

[0095] Of course, the method of controlling the compressor frequency based on the temperature difference between the inlet and outlet is not necessary, and those skilled in the art can choose whether to set this control step according to requirements.

[0096] It should be noted that when the heat pump system is set in the Figure 1 first embodiment shown, by controlling the compressor frequency, the opening degree of the opening degree regulating valve, and the opening and closing of the two ejectors, different degrees of adjustment of the refrigerant flow rate can be achieved simultaneously. Among them, small-range adjustment of the refrigerant flow rate can be achieved by controlling the compressor frequency, intermediate-range flow rate adjustment can be achieved by controlling the opening degree of the opening degree regulating valve, and large-range flow rate adjustment can be achieved by the opening and closing of the ejectors. The superposition of the three adjustment methods can achieve a more stable and accurate control effect.

[0097] When the heat pump system is set corresponding to the Figure 2 second embodiment shown, due to the specific flow rate range relationship between the three ejectors, when the opening degree regulating valve is omitted, only the superposition of the compressor frequency control and the control of the ejector group can also achieve small, medium, and large-range adjustment of the refrigerant flow rate, achieving a more stable and accurate adjustment effect.

[0098] Next, with reference to Figure 4 , a possible working process of the CO2 heat pump system of the present application will be introduced.

[0099] As Figure 4 shown, in a possible working process:

[0100] S201, during the operation of the CO2 heat pump system, first obtain the outdoor ambient temperature To and the set temperature Ts, and then execute S202.

[0101] S202, calculate the difference △T1 = To - Ts between the outdoor ambient temperature and the set temperature, and then execute S203.

[0102] S203, determine whether △T1 < T1 holds? If it holds, execute S204, otherwise if it does not hold, execute S205.

[0103] S204, control the second ejector to be separately connected, and open the opening degree regulating valve to a preset opening degree, and then execute S208.

[0104] S205, determine whether △T1 ≥ T2 holds? If it holds, execute S206, otherwise if it does not hold, execute S207.

[0105] S206, control the first injector and the second injector to be connected simultaneously, and open the opening degree regulating valve to the fully open state, then execute S208.

[0106] S207, control the first injector to be connected separately, and control the opening degree regulating valve to the fully open state, then execute S208.

[0107] S208, obtain the inlet temperature T1i and the outlet temperature T1o of the first indoor heat exchanger, then execute S209.

[0108] S209, calculate the temperature difference △T2 = T1i - T1o between the inlet and outlet of the first indoor heat exchanger, then execute S210.

[0109] S210, determine whether △T2≥T3 holds? If it holds, execute S211, otherwise if it does not hold, execute S212.

[0110] S211, control the compressor frequency to increase.

[0111] S212, control the compressor frequency to decrease.

[0112] In the above embodiments, although each step is described in the above order, those skilled in the art can understand that in order to achieve the effects of this embodiment, different steps do not have to be executed in such an order. They can be executed simultaneously (in parallel) or in a reversed order, and these simple changes are within the protection scope of this application.

[0113] In addition, those skilled in the art can understand that although some of the embodiments described herein include certain features included in other embodiments rather than other features, the combination of the features of different embodiments means that it is within the scope of this application and forms different embodiments. For example, in the claims of this application, any of the claimed embodiments can be used in any combination.

[0114] It should be noted that although the detailed steps of the method of this application are described in detail above, on the premise of not deviating from the basic principles of this application, those skilled in the art can combine, split and change the order of the above steps. The technical solutions modified in this way do not change the basic concept of this application, so they also fall within the protection scope of this application.

[0115] So far, the technical solutions of this application have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of this application is obviously not limited to these specific embodiments. Without departing from the principle of this application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of this application.

Claims

1. A CO2 heat pump system, characterized in that, The CO2 heat pump system includes a compressor, an outdoor heat exchanger, an ejector group, a gas-liquid separator, a first throttling element, and a first indoor heat exchanger. The ejector group includes at least two ejectors connected in parallel, and at least one of the ejectors can be independently turned on and off. The exhaust port of the compressor is communicated with the first port of the outdoor heat exchanger, the second port of the outdoor heat exchanger is communicated with the inlets of all the ejectors, the outlets of all the ejectors are communicated with the inlet of the gas-liquid separator, the exhaust port of the gas-liquid separator is communicated with the suction port of the compressor, the liquid discharge port of the gas-liquid separator is communicated with the first port of the first throttling element, the second port of the first throttling element is communicated with the first port of the first indoor heat exchanger, and the first port of the first indoor heat exchanger is communicated with the injection ports of all the ejectors.

2. The CO2 heat pump system according to claim 1, characterized in that, A on-off valve is provided on the outlet pipeline of each ejector.

3. The CO2 heat pump system according to claim 1, wherein, The CO2 heat pump system further includes an opening adjustment valve. One end of the opening adjustment valve is communicated with the second port of the outdoor heat exchanger, and the other end is communicated with the inlets of all the ejectors.

4. The CO2 heat pump system according to claim 1, characterized in that, The rated flow rates of at least two of the ejectors in the ejector group are different.

5. A control method for a CO2 heat pump system, characterized in that, The CO2 heat pump system includes a compressor, an outdoor heat exchanger, an ejector group, a gas-liquid separator, a first throttling element, and a first indoor heat exchanger. The ejector group includes at least two ejectors connected in parallel, and at least one of the ejectors can be independently turned on and off. The exhaust port of the compressor is communicated with the first port of the outdoor heat exchanger, the second port of the outdoor heat exchanger is communicated with the inlets of all the ejectors, the outlets of all the ejectors are communicated with the inlet of the gas-liquid separator, the exhaust port of the gas-liquid separator is communicated with the suction port of the compressor, the liquid discharge port of the gas-liquid separator is communicated with the first port of the first throttling element, the second port of the first throttling element is communicated with the first port of the first indoor heat exchanger, and the first port of the first indoor heat exchanger is communicated with the injection ports of all the ejectors. The control method includes: Determining the load of the CO2 heat pump system; Based on the magnitude of the load, controlling the on-off states of each ejector in the ejector group.

6. The control method of the CO2 heat pump system according to claim 5, characterized in that, The CO2 heat pump system further includes an opening adjustment valve. One end of the opening adjustment valve is communicated with the second port of the outdoor heat exchanger, and the other end is communicated with the inlets of all the ejectors. The control method further includes: Based on the magnitude of the load, controlling the opening degree of the opening adjustment valve.

7. The control method of the CO2 heat pump system according to claim 6, characterized in that, The ejector group includes a first ejector and a second ejector. The rated flow rate of the first ejector is greater than that of the second ejector. The step of "controlling the opening and closing states of each ejector in the ejector group and the opening degree of the opening adjustment valve based on the magnitude of the load" further includes: When the load is a low load, controlling the second ejector to be independently connected, and controlling the opening adjustment valve to be opened to a preset opening degree, where the preset opening degree is determined based on the corresponding relationship between the load and the preset opening degree; When the load is the rated load, control the first ejector to be separately connected, and control the opening degree regulating valve to be fully open; When the load is a large load, control the first ejector to be connected and the second ejector to be connected, and control the opening degree regulating valve to be fully open.

8. The control method of the CO2 heat pump system according to claim 5, characterized in that, The ejector group includes a first ejector, a second ejector, and a third ejector. The rated flow rates of the first ejector, the second ejector, and the third ejector decrease in sequence. The step of "controlling the opening and closing states of each ejector in the ejector group based on the magnitude of the load" further includes: When the load is a low load, control the second ejector or the third ejector to be separately connected; When the load is the rated load, control the first ejector to be separately connected; When the load is a large load, control the first ejector to be connected, and at least one of the second ejector and the third ejector to be connected.

9. The control method of the CO2 heat pump system according to claim 5, characterized in that, The control method further includes: Obtain the temperature difference between the inlet and outlet of the first indoor heat exchanger; Based on the temperature difference between the inlet and outlet, control the frequency of the compressor.

10. The control method of the CO2 heat pump system according to claim 6, characterized in that, The step of "determining the load of the CO2 heat pump system" further includes: Obtain the outdoor ambient temperature and the set temperature; Calculate the difference between the outdoor ambient temperature and the set temperature; Based on the difference, determine the load of the CO2 heat pump system; or Obtain the indoor ambient temperature and the set temperature; Calculate the difference between the indoor ambient temperature and the set temperature; Based on the difference, determine the load of the CO2 heat pump system.

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