Auto-cascade heat pump system and control method thereof

Abstract

The invention provides an auto-cascade heat pump system and a control method thereof.The auto-cascade heat pump system comprises an air supplementing and enthalpy increasing compressor, an indoor side heat exchanger, an outdoor side heat exchanger, a separator, a condensation evaporator and a flow path switching valve which form auto-cascade circulation; the flow path switching valve has a first flow path state corresponding to a heating mode and a second flow path state corresponding to a cooling mode, and the flow path switching valve further comprises a rectifying valve set which is configured to be in the first flow path state or the second flow path state. And the refrigerant entering the rectifying valve group through one of the first port and the second port can enter the separator through the fourth port, at least partially flows to the third port and finally flows out of the rectifying valve group through the other one of the first port and the second port. According to the invention, the number of parts in the system is reduced, so that the fault rate and the system construction cost are reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of air conditioning, and particularly relates to a self-cascade heat pump system and a control method thereof. Background Art

[0002] Traditional heating methods such as coal burning have caused people's concerns due to problems such as high pollution, low efficiency, and non-renewability of coal. Although great progress has been made in replacing traditional heating technologies with air source heat pump technology, the heat pump equipment still mainly uses low-temperature heat pumps, and usually the output temperature is lower than 55°C. During the process of using heat pump technology to transform a coal-fired heating system, in order to match the indoor terminal equipment in the original heating system, hot water with a higher temperature must be output. However, applying the currently widely used vapor compression air source heat pump to cold regions will have the following defects: attenuation of heating capacity, reduction of heating efficiency, increase in the exhaust temperature of the compressor resulting in the heat pump being unable to operate or the reduction of operation reliability, and low outlet air temperature seriously affecting the comfort of the indoor environment. Therefore, if the heat pump technology is to be applied to cold regions, it is necessary to overcome the adverse effects of the low-temperature environment on its performance.

[0003] Due to the compressor being restricted by the evaporation pressure and the condensation pressure, it is difficult to achieve low-temperature production at normal temperature using a single refrigerant. Therefore, a cascade system or a multi-stage compression cycle is often used. The cascade system combines a high-temperature refrigerant cycle and a low-temperature refrigerant cycle through an evaporative condenser to achieve the function of producing a low-temperature environment. However, the cascade system has a complex structure and a high equipment cost, while the self-cascade system usually has characteristics such as a simple structure and simple control.

[0004] The self-cascade technology can achieve a larger operating temperature difference using a single compressor and has now been widely applied to various low-temperature equipment such as low-temperature storage boxes, low-temperature constant temperature baths, vacuum freeze dryers, natural gas liquefaction devices, and various high-temperature equipment such as heat pump water heaters and heating heat pumps. This technology is an effective way to achieve large-temperature-difference heating of high-temperature heat pumps. However, since most of the existing self-cascade heat pump systems adopt a single operating mode (that is, only having a heating operating mode and not having a refrigeration operating mode), such as Figure 1As shown in the figure, a self - cascading heat pump system in the related art is shown. It includes a compressor 1, an indoor heat exchanger 2, an outdoor heat exchanger 3, a separator 4, a condensation evaporator 5, and two electronic expansion valves (the first electronic expansion valve 61 and the second electronic expansion valve 62), which are controllably connected through pipelines, so as to achieve the purpose of efficiently heating the indoor environment space in a low - temperature environment through the indoor heat exchanger 3. However, when the outdoor heat exchanger 3 is frosted, the low - temperature heat - exchange performance of the heat pump system drops severely, which will lead to the deterioration of the heating performance and operating conditions, and is not conducive to the long - term use of the heat pump. Both the reliability and comfort are relatively poor. In view of the above - mentioned deficiencies, the self - cascading heating system usually needs to add another set of electric defrosting equipment, which not only consumes a large amount of defrosting energy, but also has a poor operating effect. And this type of self - cascading heating unit can only achieve heating and cannot be used for refrigeration output in hot seasons.

[0005] In order to enable the self - cascading heat pump system to have a dual - operation mode (that is, to have both refrigeration and heating modes), in the related art, Figure 1 a corresponding four - way valve is set in the self - cascading heat pump system shown, and corresponding solenoid valves and separators are set for the refrigeration mode and the heating mode to ensure that the flow direction of the refrigerant in each component of the heat pump system can adapt to different operating modes. This makes the components of the self - cascading heat pump system more, the pipeline layout and control logic relatively complex, and the components used in the system construction are also relatively more, resulting in a relatively high construction cost of the system and also increasing the system failure rate. Summary of the Invention

[0006] Therefore, the present invention provides a self - cascading heat pump system and its control method, which can overcome the technical problems in the related art that the self - cascading heat pump system with refrigeration and heating operation modes has more components, higher system construction cost and higher failure rate.

[0007] To solve the above problems, the present invention provides a self - cascading heat pump system, including a compressor, an indoor heat exchanger, an outdoor heat exchanger, a separator, a condensation - evaporator, and a flow - path switching valve. The compressor is an air - augmented enthalpy compressor. The condensation - evaporator has a first heat - exchange pipeline and a second heat - exchange pipeline that can exchange heat with each other. The first end of the first heat - exchange pipeline is connected to the liquid outlet pipe of the separator through a first throttling element, and the second end is connected to the suction port of the compressor. The first end of the second heat - exchange pipeline is connected to the gas outlet pipe of the separator. The flow - path switching valve has a first flow - path state corresponding to the heating mode and a second flow - path state corresponding to the cooling mode. In the first flow - path state, the exhaust port of the compressor is connected to the first port of the indoor heat exchanger, and the suction port is connected to the first port of the outdoor heat exchanger. In the second flow - path state, the exhaust port of the compressor is connected to the first port of the outdoor heat exchanger, and the suction port is connected to the first port of the indoor heat exchanger. The system further includes an air - augmented throttling pipeline. The first end of the air - augmented throttling pipeline is connected to the gas outlet pipe of the separator, and the second end is connected to the air - augmented port of the air - augmented enthalpy compressor. The self - cascading heat pump system further includes a rectifying valve group. The rectifying valve group has a first port connected to the second port of the outdoor heat exchanger, a second port connected to the second port of the indoor heat exchanger, a third port connected to the second heat - exchange pipeline through a second throttling element, and a fourth port connected to the inlet pipe of the separator. The rectifying valve group is configured such that, regardless of whether the flow - path switching valve is in the first flow - path state or the second flow - path state, the refrigerant entering the rectifying valve group through one of the first port and the second port can enter the separator through the fourth port, and at least partially flow to the third port and finally flow out of the rectifying valve group through the other of the first port and the second port.

[0008] In some embodiments, the rectifying valve group includes a first check valve, a second check valve, a third check valve, and a fourth check valve. The first check valve is on the pipeline between the first port and the fourth port, and its one - way conduction direction is from the first port to the fourth port. The second check valve is on the pipeline between the second port and the fourth port, and its one - way conduction direction is from the second port to the fourth port. The third check valve is on the pipeline between the first port and the third port, and its one - way conduction direction is from the third port to the first port. The fourth check valve is on the pipeline between the second port and the third port, and its one - way conduction direction is from the third port to the second port.

[0009] In some embodiments, a third throttling element is connected in series on the air - augmented throttling pipeline.

[0010] In some embodiments, the flow path switching valve is a four-way valve. The four-way valve has ports D, C, S, and E. Port D is communicated with the exhaust port of the compressor, port C is communicated with the first port of the indoor heat exchanger, port S is communicated with the suction port of the compressor, and port E is communicated with the first port of the outdoor heat exchanger. When the flow path switching valve is in the first flow path state, port D is communicated with port C, and port S is communicated with port E. When the flow path switching valve is in the second flow path state, port D is communicated with port E, and port C is communicated with port S.

[0011] The present invention also provides a self-cascade heat pump system, which includes a compressor, an indoor heat exchanger, an outdoor heat exchanger, a separator, a condensation evaporator, and a flow path switching valve. The compressor is a gas-injected enhanced enthalpy compressor. The condensation evaporator has a first heat exchange pipeline and a second heat exchange pipeline that can exchange heat with each other. The first end of the first heat exchange pipeline is communicated with the liquid outlet pipe of the separator through a first throttling element, and the second end is communicated with the gas injection port of the gas-injected enhanced enthalpy compressor. The first end of the second heat exchange pipeline is communicated with the gas outlet pipe of the separator. The flow path switching valve has a first flow path state corresponding to the heating mode and a second flow path state corresponding to the cooling mode. In the first flow path state, the exhaust port of the compressor is communicated with the first port of the indoor heat exchanger, and the suction port is communicated with the first port of the outdoor heat exchanger. In the second flow path state, the exhaust port of the compressor is communicated with the first port of the outdoor heat exchanger, and the suction port is communicated with the first port of the indoor heat exchanger. The self-cascade heat pump system further includes a rectifying valve group. The rectifying valve group has a first port communicated with the second port of the outdoor heat exchanger, a second port communicated with the second port of the indoor heat exchanger, a third port communicated with the second heat exchange pipeline through a second throttling element, and a fourth port communicated with the intake pipe of the separator. The rectifying valve group is configured such that no matter whether the flow path switching valve is in the first flow path state or the second flow path state, the refrigerant entering the rectifying valve group through one of the first port and the second port can enter the separator through the fourth port, and at least partially flow to the third port and finally flow out of the rectifying valve group through the other of the first port and the second port.

[0012] In some embodiments, the rectifying valve group includes a first one-way valve, a second one-way valve, a third one-way valve, and a fourth one-way valve. The first one-way valve is on the pipeline between the first port and the fourth port, and its one-way conduction direction is from the first port to the fourth port. The second one-way valve is on the pipeline between the second port and the fourth port, and its one-way conduction direction is from the second port to the fourth port. The third one-way valve is on the pipeline between the first port and the third port, and its one-way conduction direction is from the third port to the first port. The fourth one-way valve is on the pipeline between the second port and the third port, and its one-way conduction direction is from the third port to the second port.

[0013] In some embodiments, the flow path switching valve is a four-way valve. The four-way valve has a D port, a C port, an S port, and an E port. The D port is connected to the exhaust port of the compressor. The C port is connected to the first port of the indoor heat exchanger. The S port is connected to the suction port of the compressor. The E port is connected to the first port of the outdoor heat exchanger. When the flow path switching valve is in the first flow path state, the D port is connected to the C port, and the S port is connected to the E port. When the flow path switching valve is in the second flow path state, the D port is connected to the E port, and the C port is connected to the S port.

[0014] The present invention also provides a control method for controlling the above-mentioned auto-cascade heat pump system, including the following steps:

[0015] Obtain a working instruction;

[0016] When the working instruction is to run the heating mode, control the flow path switching valve to be in the first flow path state; or

[0017] When the working instruction is to run the cooling mode, control the flow path switching valve to be in the second flow path state; or,

[0018] When the working instruction is a shutdown instruction, control the first throttling element to be completely closed and the second throttling element to be completely opened.

[0019] In some embodiments, during the process that the flow path switching valve is in the first flow path state, when a defrosting instruction is received as the working instruction, control the operation mode of the system to switch to the cooling mode.

[0020] In some embodiments, during the process that the auto-cascade heat pump system runs in the heating mode:

[0021] When it is detected that the outdoor ambient temperature gradually decreases, the opening degree of the first throttling element 61 is reduced to increase its flow resistance, so that the amount of high-temperature refrigerant liquid stored in the separator 4 gradually increases, and the gas content of the high-temperature refrigerant sucked by the compressor 1 is reduced, so that the content of the low-temperature refrigerant in the gas-phase mixed refrigerant compressed by the compressor 1 increases; or,

[0022] When it is detected that the outdoor ambient temperature gradually rises, the opening degree of the first throttling element 61 is increased to reduce its flow resistance, so that the amount of high-temperature refrigerant liquid stored in the separator 4 gradually decreases, and the gas content of the high-temperature refrigerant sucked by the compressor 1 is increased, so that the content of the low-temperature refrigerant in the gas-phase mixed refrigerant compressed by the compressor 1 is reduced.

[0023] In some embodiments, when the opening degree of the first throttling element 61 is adjusted to the target opening degree, the opening degree of the second throttling element 62 is further adjusted.

[0024] In some embodiments, when the outdoor ambient temperature gradually decreases and the auto-cascade heat pump system operates in the heating mode, the change amount of the opening degree of the second throttling element 62 is 10% to 90% of the change amount of the opening degree of the first throttling element 61; or,

[0025] When the outdoor ambient temperature gradually rises and the auto-cascade heat pump system operates in the heating mode, the change amount of the opening degree of the second throttling element 62 is 90% to 150% of the change amount of the opening degree of the first throttling element 61.

[0026] An auto-cascade heat pump system and its control method provided by the present invention have the following beneficial effects:

[0027] On the one hand, by arranging a flow path switching valve and a rectifying valve group in the system, the single-heating-mode auto-cascade heat pump system in the prior art can also have a refrigeration mode, so that the auto-cascade heat pump system can refrigerate the indoor environment, and can defrost efficiently by operating the refrigeration mode when the outdoor heat exchanger frosts due to the operation of the auto-cascade heat pump system in the heating mode, without separately configuring a defrosting device (such as an electric heating device) for the outdoor heat exchanger, simplifying the system components and reducing the cost; on the other hand, the rectifying valve group in the present invention is configured such that the refrigerant entering it enters the same separator whether the flow path switching valve is in the first flow path state or the second flow path state, thereby ensuring that the flow direction of the refrigerant in the condensation evaporator and the pipeline connected thereto remains unidirectional and consistent in both the heating mode and the refrigeration mode of the system, and it is possible to avoid separately setting different separators for different operating modes of the system, reducing the number of components in the system, thereby reducing the failure rate and the system construction cost. Description of the Drawings

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. The drawings in the following description are merely exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can be obtained by extending the provided drawings.

[0029] Figure 1 is a schematic diagram of the principle of a self-cascade heat pump system in the related art. The self-cascade heat pump system shown in the figure only has a heating mode;

[0030] Figure 2 is a schematic diagram of the principle of a self-cascade heat pump system in an embodiment of the present invention. The heat pump system shown in the figure uses medium-pressure gas injection, and the flow path switching valve in the figure is in the first flow path state;

[0031] Figure 3 is a schematic diagram of the principle of a self-cascade heat pump system in another embodiment of the present invention. The heat pump system shown in the figure uses both low-pressure suction and medium-pressure gas injection at the same time, and the flow path switching valve in the figure is in the first flow path state.

[0032] The reference numerals are:

[0033] 1. Compressor; 2. Indoor heat exchanger; 3. Outdoor heat exchanger; 4. Separator; 5. Condensing evaporator; 61. First throttling element; 62. Second throttling element; 71. First check valve; 72. Second check valve; 73. Third check valve; 74. Fourth check valve; 8. Third throttling element; 9. Flow path switching valve; a1. First port; a2. Second port; a3. Third port; a4. Fourth port. Specific embodiments

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The description of at least one exemplary embodiment below is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0035] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by orientation words such as "front, rear, upper, lower, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom", etc. is usually based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description. Without contrary explanation, these orientation words do not indicate and imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation on the protection scope of the present invention; the orientation words "inside, outside" refer to the inside and outside relative to the contour of each component itself.

[0036] For the convenience of description, spatial relative terms such as "above...", "over...", "on the upper surface of...", "upper" etc. can be used here to describe the spatial positional relationship between a device or feature shown in the drawings and other devices or features. It should be understood that the spatial relative terms are intended to include different orientations in use or operation in addition to the orientation described in the drawings for the device. For example, if the device in the drawing is inverted, the device described as "above other devices or structures" or "over other devices or structures" will then be positioned as "below other devices or structures" or "under other devices or structures". Thus, the exemplary term "above..." can include both the orientations of "above..." and "below...". The device can also be positioned in other different ways (rotated 90° or in other orientations), and corresponding interpretations should be made for the spatial relative descriptions used here.

[0037] In addition, it should be noted that using words such as "first", "second", etc. to limit components is only for the convenience of differentiating the corresponding components. Without additional statement, the above words have no special meaning. Therefore, it should not be construed as a limitation on the protection scope of the present invention.

[0038] See Figure 2 and Figure 3 As shown, according to an embodiment of the present invention, a self - cascading heat pump system is provided. Specifically, see Figure 3As shown in the figure, it includes a compressor 1, an indoor heat exchanger 2, an outdoor heat exchanger 3, a separator 4, a condensation evaporator 5, and a flow path switching valve 9. The compressor 1 is an air-increasing enthalpy compressor. The condensation evaporator 5 has a first heat exchange pipeline (not labeled in the figure) and a second heat exchange pipeline (not labeled in the figure) that can exchange heat with each other. The first end of the first heat exchange pipeline is connected to the liquid outlet pipe of the separator 4 through a first throttling element 61 (specifically, it can be an electronic expansion valve), and the second end is connected to the suction port of the compressor 1. The first end of the second heat exchange pipeline is connected to the gas outlet pipe of the separator 4. The flow path switching valve 9 has a first flow path state corresponding to the heating mode and a second flow path state corresponding to the cooling mode. It can be understood that the flow path switching valve 9 can be controlled to switch between the first flow path state and the second flow path state. In the first flow path state, the exhaust port of the compressor 1 is connected to the first port of the indoor heat exchanger 2, and the suction port is connected to the first port of the outdoor heat exchanger 3. In the second flow path state, the exhaust port of the compressor 1 is connected to the first port of the outdoor heat exchanger 3, and the suction port is connected to the first port of the indoor heat exchanger 2. The auto-cascade heat pump system further includes an air-increasing throttling pipeline (not labeled in the figure). The first end of the air-increasing throttling pipeline is connected to the gas outlet pipe of the separator 4, and the second end is connected to the air-increasing port of the air-increasing enthalpy compressor. The auto-cascade heat pump system further includes a rectifying valve group. The rectifying valve group has a first port a1 connected to the second port of the outdoor heat exchanger 3, a second port a2 connected to the second port of the indoor heat exchanger 2, a third port a3 connected to the second heat exchange pipeline through a second throttling element 62 (specifically, it can be an electronic expansion valve), and a fourth port a4 connected to the inlet pipe of the separator 4. The rectifying valve group is configured such that regardless of whether the flow path switching valve 9 is in the first flow path state or the second flow path state, the refrigerant entering the rectifying valve group through one of the first port a1 and the second port a2 can enter the separator 4 through the fourth port a4, and at least partially flow to the third port a3 and finally flow out of the rectifying valve group through the other of the first port a1 and the second port a2. It can be understood that for the auto-cascade heat pump system, the aforementioned refrigerant is formed by mixing a first refrigerant and a second refrigerant with two different boiling points in a required proportion. After the refrigerant enters the separator 4, due to the different boiling points of the two refrigerants, the mixed refrigerant is separated into gaseous and liquid refrigerants in the separator 4. Among them, the liquid refrigerant contains more high-boiling refrigerant (the first refrigerant, high-temperature type refrigerant), and the gaseous refrigerant contains more low-boiling refrigerant (the second refrigerant, low-temperature type refrigerant). In the condensation evaporator 5, the liquid refrigerant flows in the first heat exchange pipeline, and the gaseous refrigerant flows in the second heat exchange pipeline.The liquid refrigerant transfers the cooling capacity to the gaseous refrigerant to achieve self-cascade and improve the system energy efficiency, while the gaseous refrigerant transfers its heat to the liquid refrigerant, so that the liquid refrigerant vaporizes and enters the compressor 1 after vaporization, effectively avoiding liquid carry-over during compressor suction.

[0039] In this technical solution, on the one hand, by setting a flow path switching valve 9 and a rectifying valve group in the system, the single-heating-mode self-cascade heat pump system in the prior art can also have a refrigeration mode, enabling the self-cascade heat pump system to cool the indoor environment and efficiently defrost by operating the refrigeration mode when the outdoor heat exchanger 3 frosts during the operation of the heating mode of the self-cascade heat pump system, without separately configuring a defrosting device (such as an electric heating device) for the outdoor heat exchanger 3, simplifying the system components and reducing costs; on the other hand, the rectifying valve group in the present invention is configured such that the refrigerant entering it enters the same separator 4 whether the flow path switching valve 9 is in the first flow path state or the second flow path state, thereby ensuring that the flow direction of the refrigerant in the condensation evaporator and the pipelines connected thereto remains unidirectional and consistent in both the heating mode and the refrigeration mode of the system, and it is not necessary to correspondingly set different separators 4 for different operating modes of the system, reducing the number of components in the system, thereby reducing the failure rate and the system construction cost.

[0040] In addition, in this technical solution, by introducing a part of the high-pressure gaseous refrigerant in the outlet pipe of the separator 4 into the gas injection port of the compressor through the gas injection throttling pipeline, the energy efficiency of the compressor 1 can be further improved.

[0041] In some embodiments, the rectifying valve group includes a first one-way valve 71, a second one-way valve 72, a third one-way valve 73, and a fourth one-way valve 74. The first one-way valve 71 is on the pipeline between the first port a1 and the fourth port a4, and its one-way conduction direction is from the first port a1 to the fourth port a4. The second one-way valve 72 is on the pipeline between the second port a2 and the fourth port a4, and its one-way conduction direction is from the second port a2 to the fourth port a4. The third one-way valve 73 is on the pipeline between the first port a1 and the third port a3, and its one-way conduction direction is from the third port a3 to the first port a1. The fourth one-way valve 74 is on the pipeline between the second port a2 and the third port a3, and its one-way conduction direction is from the third port a3 to the second port a2. It can be understood that the aforementioned first one-way valve 71, second one-way valve 72, third one-way valve 73, and fourth one-way valve 74 together form a bridge rectifying valve group.

[0042] In this technical solution, a bridge rectifier valve group is formed by four check valves. Since the on-off of the check valve depends on the refrigerant pressure difference at both ends to achieve its on-off, there is no need to control the electrical control logic of the system. Therefore, it can greatly reduce the difficulty of the electrical control design of the system, simplify the control logic, and further reduce the failure rate of the system. Additionally, it is worth mentioning that since the bridge rectifier valve group formed by four check valves in this application can restrict the one-way flow of the refrigerant, each throttling element in this system does not need to be equipped with a two-way throttling element, which can also reduce the system construction cost.

[0043] In some embodiments, the flow path switching valve 9 is a four-way valve. The four-way valve has a D port, a C port, an S port, and an E port. The D port is communicated with the exhaust port of the compressor 1, the C port is communicated with the first port of the indoor heat exchanger 2, the S port is communicated with the suction port of the compressor 1, and the E port is communicated with the first port of the outdoor heat exchanger 3. When the flow path switching valve 9 is in the first flow path state, the D port is communicated with the C port, and the S port is communicated with the E port. When the flow path switching valve 9 is in the second flow path state, the D port is communicated with the E port, and the C port is communicated with the S port.

[0044] In this technical solution, using a common four-way valve in the air-conditioning design field as the flow path switching valve 9 of the present invention can further reduce the system design difficulty and the system construction cost.

[0045] Taking Figure 3 as an example, when the auto-cascade heat pump system of the present invention operates in the refrigeration mode, the four-way valve usually remains energized so that DE and CS are conducted (that is, in the second flow path state, the D port is communicated with the E port, and the C port is communicated with the S port). The refrigerant circulation flow path is: compressor 1 exhaust port → four-way valve DE → outdoor heat exchanger 3 → first check valve 71 → separator 4 → (liquid refrigerant → first throttling element 61 → condensation evaporator 5 (in the first heat exchange pipeline) → compressor 1 suction port) / (gaseous refrigerant → condensation evaporator 5 (in the second heat exchange pipeline) → second throttling element 62 → fourth check valve 74 → indoor heat exchanger 2 → four-way valve CS → compressor 1 suction port / gaseous refrigerant → third throttling element 8 → compressor 1 gas supply port), and the second check valve 72 and the third check valve 73 are reversely cut off.

[0046] When the self - cascading heat pump system of the present invention operates in the heating mode, the four - way valve usually remains de - energized, making DC and ES conduct (i.e., in the first flow path state, the D port is connected to the C port, and the E port is connected to the S port). The circulating flow path of the refrigerant is: compressor 1 exhaust port → four - way valve DC → indoor heat exchanger 2 → second check valve 72 → separator 4 → (liquid refrigerant → first throttle element 61 → condensation - evaporation heat exchanger 5 → compressor 1 suction port) / (gaseous refrigerant → condensation - evaporation heat exchanger 5 → second throttle element 62 → third check valve 73 → outdoor heat exchanger 3 → four - way valve ES → compressor 1 suction port / gaseous refrigerant → third throttle element 8 → compressor 1 gas - make - up port), and the first check valve 71 and the fourth check valve 74 are reversely closed.

[0047] It can be understood that whether the system operates in the heating mode or the cooling mode, the refrigerant flow directions in the first throttle element 61, the second throttle element 62, and the third throttle element 8 are all consistent (no need for two - way), and the refrigerant inlet and gas - liquid outlet directions of the separator 4 are also consistent. This enables the number of system components in the present invention to be fewer, and only one - way components need to be selected, reducing the component cost.

[0048] In order to control the gas - make - up amount and reduce the amount of refrigerant entering the heat exchanger due to gas - make - up, in some embodiments, a third throttle element 8 is connected in series on the gas - make - up throttle pipeline, and the aforementioned third throttle element 8 can specifically be a capillary tube.

[0049] For specific reference, see Figure 2As shown, in another embodiment, the present invention further provides a self-cascade heat pump system, including a compressor 1, an indoor heat exchanger 2, an outdoor heat exchanger 3, a separator 4, a condensation-evaporation heat exchanger 5, and a flow path switching valve 9. The compressor 1 is an air-increasing enthalpy compressor. Inside the condensation-evaporation heat exchanger 5, there are a first heat exchange pipeline (not labeled in the figure) and a second heat exchange pipeline (not labeled in the figure) that can exchange heat with each other. The first end of the first heat exchange pipeline is connected to the liquid outlet pipe of the separator 4 through a first throttling element 61 (specifically, an electronic expansion valve) and the second end is connected to the air-increasing port of the air-increasing enthalpy compressor. The first end of the second heat exchange pipeline is connected to the gas outlet pipe of the separator 4. The flow path switching valve 9 has a first flow path state corresponding to the heating mode and a second flow path state corresponding to the cooling mode. It can be understood that the flow path switching valve 9 can be controlled to switch between the first flow path state and the second flow path state. In the first flow path state, the exhaust port of the compressor 1 is connected to the first port of the indoor heat exchanger 2, and the suction port is connected to the first port of the outdoor heat exchanger 3. In the second flow path state, the exhaust port of the compressor 1 is connected to the first port of the outdoor heat exchanger 3, and the suction port is connected to the first port of the indoor heat exchanger 2. The self-cascade heat pump system further includes a rectifying valve group. The rectifying valve group has a first port a1 connected to the second port of the outdoor heat exchanger 3, a second port a2 connected to the second port of the indoor heat exchanger 2, a third port a3 connected to the second heat exchange pipeline through a second throttling element 62 (specifically, an electronic expansion valve), and a fourth port a4 connected to the intake pipe of the separator 4. The rectifying valve group is configured such that, regardless of whether the flow path switching valve 9 is in the first flow path state or the second flow path state, the refrigerant entering the rectifying valve group through one of the first port a1 and the second port a2 can enter the separator 4 through the fourth port a4, and at least partially flow to the third port a3 and finally flow out of the rectifying valve group through the other of the first port a1 and the second port a2. It can be understood that for the self-cascade heat pump system, the aforementioned refrigerant is formed by mixing a first refrigerant and a second refrigerant with two different boiling points in a required proportion. After the refrigerant enters the separator 4, due to the different boiling points of the two refrigerants, the mixed refrigerant is separated into a gaseous refrigerant and a liquid refrigerant in the separator 4. The liquid refrigerant contains more high-boiling refrigerant (the first refrigerant, high-temperature type refrigerant), and the gaseous refrigerant contains more low-boiling refrigerant (the second refrigerant, low-temperature type refrigerant). Inside the condensation-evaporation heat exchanger 5, the liquid refrigerant flows in the first heat exchange pipeline, and the gaseous refrigerant flows in the second heat exchange pipeline. The liquid refrigerant conducts cold to the gaseous refrigerant to achieve self-cascade and improve the system energy efficiency, while the gaseous refrigerant conducts its heat to the liquid refrigerant, so that the liquid refrigerant vaporizes and enters the compressor 1.Effectively avoid liquid carryover in the compressor suction.

[0050] On the one hand, by setting a flow path switching valve 9 and a rectifying valve group in the system, the single-heating-mode auto-cascade heat pump system in the prior art can also have a refrigeration mode, enabling the auto-cascade heat pump system to cool the indoor environment and efficiently defrost by operating the refrigeration mode when the outdoor heat exchanger 3 frosts during the operation of the heating mode, eliminating the need to separately configure a defrosting device (such as an electric heating device) for the outdoor heat exchanger 3, simplifying system components and reducing costs. On the other hand, the rectifying valve group in the present invention is configured such that the refrigerant entering it, regardless of whether the flow path switching valve 9 is in the first flow path state or the second flow path state, enters the same separator 4, thus ensuring that the flow direction of the refrigerant in the condensation evaporator and the pipelines connected thereto remains unidirectional and consistent in both the heating mode and the refrigeration mode of the system. There is no need to correspondingly set different separators 4 for different operating modes of the system, reducing the number of components in the system, thereby reducing the failure rate and the system construction cost.

[0051] In some embodiments, the rectifying valve group includes a first check valve 71, a second check valve 72, a third check valve 73, and a fourth check valve 74. The first check valve 71 is on the pipeline between the first port a1 and the fourth port a4, and its one-way conduction direction is from the first port a1 to the fourth port a4. The second check valve 72 is on the pipeline between the second port a2 and the fourth port a4, and its one-way conduction direction is from the second port a2 to the fourth port a4. The third check valve 73 is on the pipeline between the first port a1 and the third port a3, and its one-way conduction direction is from the third port a3 to the first port a1. The fourth check valve 74 is on the pipeline between the second port a2 and the third port a3, and its one-way conduction direction is from the third port a3 to the second port a2. It can be understood that the aforementioned first check valve 71, second check valve 72, third check valve 73, and fourth check valve 74 together form a bridge rectifying valve group.

[0052] In this technical solution, a bridge rectifying valve group is formed by four check valves. Since the conduction of the check valve is achieved by the refrigerant pressure difference at both ends, there is no need to control the electrical control logic of the system. Therefore, it can greatly reduce the difficulty of the electrical control design of the system, simplify the control logic, and further reduce the failure rate of the system. Additionally, it is worth mentioning that since the bridge rectifying valve group formed by four check valves in this application can restrict the one-way flow of the refrigerant, each throttling element in this system does not need to be configured with a two-way throttling element, which can also reduce the system construction cost.

[0053] In some embodiments, the flow path switching valve 9 is a four-way valve. The four-way valve has ports D, C, S, and E. Port D is connected to the exhaust port of the compressor 1, port C is connected to the first port of the indoor heat exchanger 2, port S is connected to the suction port of the compressor 1, and port E is connected to the first port of the outdoor heat exchanger 3. When the flow path switching valve 9 is in the first flow path state, port D is connected to port C, and port S is connected to port E. When the flow path switching valve 9 is in the second flow path state, port D is connected to port E, and port C is connected to port S.

[0054] In this technical solution, a common four-way valve in the air-conditioning design field is used as the flow path switching valve 9 of the present invention, which can further reduce the system design difficulty and system construction cost.

[0055] Take Figure 2 As an example, when the auto-cascade heat pump system of the present invention operates in the cooling mode, the four-way valve usually remains energized so that DE and CS are conducted (that is, in the second flow path state, port D is connected to port E, and port C is connected to port S). The refrigerant circulation flow path is: compressor 1 exhaust port → four-way valve DE → outdoor heat exchanger 3 → first check valve 71 → separator 4 → (liquid refrigerant → first throttling element 61 → condensation-evaporation heat exchanger 5 (first heat exchange pipeline therein) → compressor 1 make-up gas port) / (gaseous refrigerant → condensation-evaporation heat exchanger 5 (second heat exchange pipeline therein) → second throttling element 62 → fourth check valve 74 → indoor heat exchanger 2 → four-way valve CS → compressor 1 suction port), and the second check valve 72 and the third check valve 73 are reversely blocked.

[0056] When the auto-cascade heat pump system of the present invention operates in the heating mode, the four-way valve usually remains de-energized, so that DC and ES are conducted (that is, in the first flow path state, port D is connected to port C, and port E is connected to port S). The refrigerant circulation flow path is: compressor 1 exhaust port → four-way valve DC → indoor heat exchanger 2 → second check valve 72 → separator 4 → (liquid refrigerant → first throttling element 61 → condensation-evaporation heat exchanger 5 → compressor 1 make-up gas port) / (gaseous refrigerant → condensation-evaporation heat exchanger 5 → second throttling element 62 → third check valve 73 → outdoor heat exchanger 3 → four-way valve ES → compressor 1 suction port), and the first check valve 71 and the fourth check valve 74 are reversely blocked.

[0057] According to an embodiment of the present invention, there is also provided a control method for controlling the above-mentioned auto-cascade heat pump system, including the following steps:

[0058] Obtain a working instruction;

[0059] When the working instruction is to operate in the heating mode, control the flow path switching valve 9 to be in the first flow path state; or

[0060] When the working instruction is to run the refrigeration mode, control the flow path switching valve 9 to be in the second flow path state; or,

[0061] When the working instruction is a shutdown instruction, control the first throttling element 61 to be completely closed and the second throttling element 62 to be completely opened. Specifically, when the system shuts down, affected by the rising temperature of the external air, the liquid refrigerant in the heat exchanger (the indoor heat exchanger 2 and / or the outdoor heat exchanger 3) will be heated, raised in temperature and pressure, and vaporized, and return to the separator 4 through the second check valve 72 or the first check valve 71. After this part of the gas enters the separator 4, it will squeeze the liquid space in the separator, so that the liquid refrigerant in the separator 4 may enter the condensation evaporator 5 through the first throttling element 61, and even enter the suction port or the make-up gas port of the compressor 1, which is likely to cause liquid slugging during compressor startup. The foregoing technical solution of the present invention can prevent this phenomenon from occurring, that is, after the system shuts down, the first throttling element 61 is completely closed and the second throttling element 62 is completely opened, preventing the separated and stored liquid refrigerant in the separator 4 from being extruded from the separator 4 and entering the condensation evaporator 5 and then overflowing to the suction port or the make-up gas port of the compressor 1, but allowing the squeezed liquid refrigerant to enter the condensation evaporator 5 from the refrigerant gas outlet pipe of the separator, and then enter the indoor heat exchanger 2 or the outdoor heat exchanger 3 through the second throttling element 62 for storage, thus ensuring the startup safety of the heat pump unit.

[0062] It should be particularly noted that when the auto-cascade heat pump system of the present invention switches between the refrigeration mode and the heating mode, only the energization and de-energization of the aforementioned flow path switching valve 9 need to be controlled, and the system can be stably in the corresponding target operation mode through the switching of its flow path state and the automatic action of the refrigerant pressure difference before and after each check valve after the switching, and the control is very simple.

[0063] In some embodiments, during the process that the flow path switching valve 9 is in the first flow path state, when a defrosting instruction is received as the working instruction, control the operation mode of the system to switch to the refrigeration mode, so as to achieve the purpose of efficient and stable defrosting of the outdoor heat exchanger 3.

[0064] In some embodiments, during the operation of the auto-cascade heat pump system in the heating mode:

[0065] When it is detected that the outdoor ambient temperature gradually decreases, reduce the opening degree of the first throttling element 61 to increase its flow resistance, so that the liquid of the high-temperature type refrigerant stored in the separator 4 gradually increases, and reduce the gas content of the high-temperature type refrigerant inhaled by the compressor 1, so that the content of the low-temperature type refrigerant in the gas-phase mixed refrigerant compressed by the compressor 1 increases, so as to ensure the operation of the compressor 1 to match the low-temperature working condition; or,

[0066] When it is detected that the outdoor ambient temperature is gradually rising, the opening degree of the first throttling element 61 is increased to reduce its flow resistance, so that the amount of the high-temperature type refrigerant liquid stored in the separator 4 is gradually reduced, and the gas content of the high-temperature type refrigerant sucked into the compressor 1 is increased, thereby reducing the content of the low-temperature type refrigerant in the gas-phase mixed refrigerant compressed by the compressor 1.

[0067] In some embodiments, when the opening degree of the first throttling element 61 is adjusted to the target opening degree, the opening degree of the second throttling element 62 is then adjusted to prevent the coupling problem of the two when the first throttling element 61 and the second throttling element 62 are adjusted synchronously, thereby reducing the adjustment difficulty of the throttling element and simplifying the system control logic.

[0068] In some embodiments, when the outdoor ambient temperature is gradually decreasing and the auto-cascade heat pump system is operating in the heating mode, the change amount of the opening degree of the second throttling element 62 is 10% - 90% of the change amount of the opening degree of the first throttling element 61 to increase the amount of the high-temperature type refrigerant entering the compressor 1; or, when the outdoor ambient temperature is gradually rising and the auto-cascade heat pump system is operating in the heating mode, the change amount of the opening degree of the second throttling element 62 is 90% - 150% of the change amount of the opening degree of the first throttling element 61 to reduce the amount of the high-temperature type refrigerant entering the compressor 1.

[0069] It is easy for those skilled in the art to understand that, on the premise of no conflict, the advantageous technical features of the above various modes can be freely combined and superimposed.

[0070] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention. The above is only the preferred implementation manner of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can still be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A self-cascade heat pump system, characterized in that: The invention comprises a compressor (1), an indoor heat exchanger (2), an outdoor heat exchanger (3), a separator (4), a condenser evaporator (5), and a flow path switching valve (9); the compressor (1) is an air-supplying enthalpy-increasing compressor; the condenser evaporator (5) has a first heat exchange pipeline and a second heat exchange pipeline capable of exchanging heat with each other; the first end of the first heat exchange pipeline is connected to the liquid outlet pipe of the separator (4) through a first throttling element (61); the second end of the first heat exchange pipeline is connected to the air inlet of the compressor (1); the first end of the second heat exchange pipeline is connected to the separator (4) through a first throttling element (61); The flow path switching valve (9) has a first flow path state corresponding to a heating mode and a second flow path state corresponding to a cooling mode. In the first flow path state, the exhaust port of the compressor (1) is connected to the first port of the indoor heat exchanger (2), and the air intake port is connected to the first port of the outdoor heat exchanger (3). In the second flow path state, the exhaust port of the compressor (1) is connected to the first port of the outdoor heat exchanger (3), and the air intake port is connected to the first port of the indoor heat exchanger (2). The self-cascade heat pump system further comprises an air supply throttling pipeline, wherein the first end of the air supply throttling pipeline is connected to the air outlet pipe of the separator (4), and the second end of the air supply throttling pipeline is connected to the air supply port of the air supply enthalpy increasing compressor. The self-cascade heat pump system further comprises a rectifying valve group, wherein the rectifying valve group has a first port (a1) connected to the second port of the outdoor heat exchanger (3), a second port (a2) connected to the second port of the indoor heat exchanger (2), and a third port (a3) ​​connected to the second heat exchange pipeline through a second throttling element (62). 3) and a fourth port (a4) connected to the air inlet pipe of the separator (4), the rectifying valve group is configured so that no matter whether the flow path switching valve (9) is in the first flow path state or the second flow path state, the refrigerant entering the rectifying valve group through one of the first port (a1) and the second port (a2) can enter the separator (4) through the fourth port (a4), at least partially flow to the third port (a3), and finally flow out of the rectifying valve group through the other of the first port (a1) and the second port (a2).

2. The self-cascade heat pump system according to claim 1, characterized in that: The rectifying valve group comprises a first one-way valve (71), a second one-way valve (72), a third one-way valve (73) and a fourth one-way valve (74); the first one-way valve (71) is located on the pipeline between the first port (a1) and the fourth port (a4), and its one-way conduction direction is from the first port (a1) to the fourth port (a4); the second one-way valve (72) is located on the pipeline between the second port (a2) and the fourth port (a4), and its one-way conduction direction is from the second port (a2) to the fourth port (a4); the third one-way valve (73) is located on the pipeline between the first port (a1) and the third port (a3), and its one-way conduction direction is from the third port (a3) ​​to the first port (a1); and the fourth one-way valve (74) is located on the pipeline between the second port (a2) and the third port (a3), and its one-way conduction direction is from the third port (a3) ​​to the second port (a2).

3. The self-cascade heat pump system according to claim 1, characterized in that: The flow path switching valve (9) is a four-way valve, and the four-way valve has a D port, a C port, an S port and an E port. The D port is connected to the exhaust port of the compressor (1), the C port is connected to the first port of the indoor heat exchanger (2), the S port is connected to the intake port of the compressor (1), and the E port is connected to the first port of the outdoor heat exchanger (3). When the flow path switching valve (9) is in the first flow path state, the D port is connected to the C port, and the S port is connected to the E port. When the flow path switching valve (9) is in the second flow path state, the D port is connected to the E port, and the C port is connected to the S port. And / or, a third throttling element (8) is connected in series to the air supply throttling pipeline.

4. A self-cascade heat pump system, characterized in that: The invention comprises a compressor (1), an indoor heat exchanger (2), an outdoor heat exchanger (3), a separator (4), a condenser evaporator (5), and a flow path switching valve (9). The compressor (1) is an air-supply and reheat-increasing compressor. The condenser evaporator (5) has a first heat exchange pipeline and a second heat exchange pipeline capable of exchanging heat with each other. The first end of the first heat exchange pipeline is connected to the liquid outlet pipe of the separator (4) through a first throttling element (61), and the second end is connected to the air supply port of the air-supply and reheat-increasing compressor. The first end of the second heat exchange pipeline is connected to the air outlet pipe of the separator (4). The flow path switching valve (9) has a first flow path state corresponding to a heating mode and a second flow path state corresponding to a cooling mode. In the first flow path state, the exhaust port of the compressor (1) is connected to the first port of the indoor heat exchanger (2), and the air intake port is connected to the first port of the outdoor heat exchanger (3). In the second flow path state, the exhaust port of the compressor (1) is connected to the outdoor The self-cascade heat pump system further comprises a rectifying valve group, the rectifying valve group comprising a first port (a1) connected to the second port of the outdoor heat exchanger (3), a second port (a2) connected to the second port of the indoor heat exchanger (2), a third port (a3) ​​connected to the second heat exchange pipeline via a second throttling element (62), and a fourth port (a4) connected to the intake pipe of the separator (4). The rectifying valve group is configured such that, regardless of whether the flow path switching valve (9) is in the first flow path state or the second flow path state, the refrigerant entering the rectifying valve group via one of the first port (a1) and the second port (a2) can enter the separator (4) via the fourth port (a4), flow at least partially to the third port (a3), and finally flow out of the rectifying valve group via the other of the first port (a1) and the second port (a2).

5. The self-cascade heat pump system according to claim 4, characterized in that: The rectifying valve group comprises a first one-way valve (71), a second one-way valve (72), a third one-way valve (73) and a fourth one-way valve (74); the first one-way valve (71) is located on the pipeline between the first port (a1) and the fourth port (a4), and its one-way conduction direction is from the first port (a1) to the fourth port (a4); the second one-way valve (72) is located on the pipeline between the second port (a2) and the fourth port (a4), and its one-way conduction direction is from the second port (a2) to the fourth port (a4); the third one-way valve (73) is located on the pipeline between the first port (a1) and the third port (a3), and its one-way conduction direction is from the third port (a3) ​​to the first port (a1); and the fourth one-way valve (74) is located on the pipeline between the second port (a2) and the third port (a3), and its one-way conduction direction is from the third port (a3) ​​to the second port (a2).

6. The self-cascade heat pump system according to claim 4, characterized in that: The flow path switching valve (9) is a four-way valve having a D port, a C port, an S port and an E port. The D port is connected to the exhaust port of the compressor (1), the C port is connected to the first port of the indoor heat exchanger (2), the S port is connected to the intake port of the compressor (1), and the E port is connected to the first port of the outdoor heat exchanger (3). When the flow path switching valve (9) is in the first flow path state, the D port is connected to the C port, and the S port is connected to the E port. When the flow path switching valve (9) is in the second flow path state, the D port is connected to the E port, and the C port is connected to the S port.

7. A control method for controlling the self-cascade heat pump system according to any one of claims 1 to 6, characterized in that: The steps include: Obtain work orders; When the working instruction is to operate in a heating mode, the flow path switching valve (9) is controlled to be in the first flow path state; or When the working instruction is to operate in a refrigeration mode, controlling the flow path switching valve (9) to be in the second flow path state; or, When the working instruction is a shutdown instruction, the first throttling element (61) is controlled to be fully closed and the second throttling element (62) is controlled to be fully opened.

8. The control method according to claim 7, characterized in that: When the flow path switching valve (9) is in the first flow path state, when the working instruction received is a defrosting instruction, the operating mode of the system is controlled to switch to a refrigeration mode.

9. The control method according to claim 7, characterized in that: During the operation of the heating mode of the self-cascade heat pump system: When it is detected that the outdoor ambient temperature is gradually decreasing, the opening of the first throttling element (61) is reduced to increase its flow resistance, so that the high-temperature refrigerant liquid stored in the separator (4) gradually increases, reducing the gas content of the high-temperature refrigerant sucked into the compressor (1), thereby increasing the content of the low-temperature refrigerant in the gas-phase mixed refrigerant compressed by the compressor (1); or, When it is detected that the outdoor ambient temperature is gradually rising, the opening of the first throttling element (61) is increased to reduce its flow resistance, so that the high-temperature refrigerant liquid stored in the separator (4) is gradually reduced, and the gas content of the high-temperature refrigerant sucked into the compressor (1) is increased, thereby reducing the low-temperature refrigerant content in the gas phase mixed refrigerant compressed by the compressor (1).

10. The control method according to claim 9, characterized in that: When the opening of the first throttling element (61) is adjusted to a target opening, the opening of the second throttling element (62) is adjusted.

11. The control method according to claim 10, characterized in that: When the outdoor ambient temperature gradually decreases and the cascade heat pump system operates in a heating mode, the opening change of the second throttling element (62) is 10% to 90% of the opening change of the first throttling element (61); or, When the outdoor ambient temperature gradually rises and the cascade heat pump system operates in a heating mode, the opening change of the second throttling element (62) is 90% to 150% of the opening change of the first throttling element (61).

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