CN114992889A - Cascade heat pump system and control method thereof - Google Patents
Cascade heat pump system and control method thereof Download PDFInfo
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- CN114992889A CN114992889A CN202210579892.XA CN202210579892A CN114992889A CN 114992889 A CN114992889 A CN 114992889A CN 202210579892 A CN202210579892 A CN 202210579892A CN 114992889 A CN114992889 A CN 114992889A
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- 238000000034 method Methods 0.000 title claims abstract description 42
- 239000003507 refrigerant Substances 0.000 claims abstract description 285
- 238000001704 evaporation Methods 0.000 claims description 37
- 230000008020 evaporation Effects 0.000 claims description 33
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims description 19
- 229910052731 fluorine Inorganic materials 0.000 claims description 19
- 239000011737 fluorine Substances 0.000 claims description 19
- 238000005265 energy consumption Methods 0.000 abstract description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 5
- 238000000926 separation method Methods 0.000 description 5
- 238000006243 chemical reaction Methods 0.000 description 2
- 230000005494 condensation Effects 0.000 description 2
- 238000009833 condensation Methods 0.000 description 2
- 238000006467 substitution reaction Methods 0.000 description 2
- LVGUZGTVOIAKKC-UHFFFAOYSA-N 1,1,1,2-tetrafluoroethane Chemical compound FCC(F)(F)F LVGUZGTVOIAKKC-UHFFFAOYSA-N 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000003889 chemical engineering Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000004134 energy conservation Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000004753 textile Substances 0.000 description 1
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B7/00—Compression machines, plants or systems, with cascade operation, i.e. with two or more circuits, the heat from the condenser of one circuit being absorbed by the evaporator of the next circuit
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B41/00—Fluid-circulation arrangements
- F25B41/20—Disposition of valves, e.g. of on-off valves or flow control valves
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B41/00—Fluid-circulation arrangements
- F25B41/40—Fluid line arrangements
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B49/00—Arrangement or mounting of control or safety devices
- F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
- Y02B30/70—Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Thermal Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Compression-Type Refrigeration Machines With Reversible Cycles (AREA)
Abstract
The invention relates to the technical field of cascade heat pumps, in particular to a cascade heat pump system and a control method thereof, and aims to solve the problem that the existing cascade heat pump system is easily influenced by the ambient temperature and has a narrow operation range. Therefore, the cascade heat pump system comprises a high-pressure refrigerant circulation loop, a first low-pressure refrigerant circulation loop, a second low-pressure refrigerant circulation loop and a bypass branch, wherein the first low-pressure refrigerant circulation loop, the second low-pressure refrigerant circulation loop and the bypass branch can selectively run; based on the above, the cascade heat pump system of the invention controls the operation states of the first low-pressure refrigerant circulation loop and the second low-pressure refrigerant circulation loop according to the acquired environment temperature, so as to effectively reduce the operation energy consumption of the cascade heat pump system; the running state of the bypass branch is controlled according to the obtained running parameters of the high-pressure refrigerant circulating loop, so that the high-pressure refrigerant circulating loop can be effectively ensured to run all the time by controlling the on-off state of the bypass branch, and the running range of the cascade heat pump system is effectively expanded.
Description
Technical Field
The invention relates to the technical field of cascade heat pumps, and particularly provides a cascade heat pump system and a control method thereof.
Background
With the popularization of policies of energy conservation and emission reduction, industries such as food processing, textile, chemical engineering and the like use high-temperature heat pump systems to carry out high-temperature heating treatment in more and more application occasions. The industrial heating demand is strong, and the application requirements of the high-temperature heat pump system are higher and higher. First, the final heating temperature of the high temperature heat pump system is typically greater than 70 ℃ or even over 90 ℃. Secondly, the application environment temperature of the heating system is from-30 ℃ to 35 ℃, and the span is even larger, and high-temperature hot water or hot air needs to be supplied in both winter and summer.
The high temperature hot water used in industry is high, which results in that the common heat pump system cannot meet the actual heating requirement, and the technology of using the cascade heat pump system to provide high temperature hot water is mature. The cascade heat pump system generally comprises a high-pressure refrigerant circulation loop and a low-pressure refrigerant circulation loop, wherein the high-pressure refrigerant circulation loop and the low-pressure refrigerant circulation loop exchange heat through a shared intermediate heat exchanger to achieve the purpose of providing high-temperature hot water. However, the existing cascade heat pump system is limited by the ambient temperature, and cannot operate when the ambient temperature is higher or lower, that is, the existing cascade heat pump system has a narrow operation range, and cannot always provide hot water for users, which brings inconvenience to the users.
Accordingly, there is a need in the art for a new cascade heat pump system and a control method thereof to solve the above technical problems.
Disclosure of Invention
The present invention is directed to solve the above-mentioned technical problem, that is, to solve the problem that the existing cascade heat pump system is easily affected by the ambient temperature and has a narrow operation range.
In a first aspect, the present invention provides a method for controlling a cascade heat pump system, the cascade heat pump system includes a high-pressure refrigerant circulation loop, a first low-pressure refrigerant circulation loop, a second low-pressure refrigerant circulation loop, and a bypass branch,
the high-pressure refrigerant circulating loop is provided with a first compressor, a first heat exchanger, a first throttling component and an intermediate heat exchanger, the first low-pressure refrigerant circulating loop is provided with a second compressor, the intermediate heat exchanger, a second throttling component and a second heat exchanger, the second low-pressure refrigerant circulating loop is provided with a fluorine pump, a second heat exchanger and the intermediate heat exchanger, two ends of the fluorine pump are connected with the first low-pressure refrigerant circulating loop, two ends of the second compressor are connected with the second low-pressure refrigerant circulating loop, the first low-pressure refrigerant circulating loop and the second low-pressure refrigerant circulating loop are arranged to be capable of selectively exchanging heat with the high-pressure refrigerant circulating loop through the intermediate heat exchanger,
a first end of the bypass branch is connected between a connection point of the fluorine pump and the first low-pressure refrigerant circulation loop and the second heat exchanger, a second end of the bypass branch is connected between the second compressor and the intermediate heat exchanger, a control valve is arranged on the bypass branch and can control the on-off state of the bypass branch,
the control method comprises the following steps:
acquiring the ambient temperature of the cascade heat pump system;
controlling the running states of the first low-pressure refrigerant circulating loop and the second low-pressure refrigerant circulating loop according to the environment temperature;
acquiring operation parameters of the high-pressure refrigerant circulation loop;
and controlling the running state of the bypass branch according to the running parameters of the high-pressure refrigerant circulating loop.
In a preferred embodiment of the control method, the step of controlling the operating states of the first low-pressure refrigerant circulation circuit and the second low-pressure refrigerant circulation circuit according to the ambient temperature includes:
and if the ambient temperature is greater than or equal to a preset ambient temperature, controlling the first low-pressure refrigerant circulation loop not to operate, and controlling the second low-pressure refrigerant circulation loop to operate.
In a preferred embodiment of the above control method, the step of controlling the operating states of the first low-pressure refrigerant circulation circuit and the second low-pressure refrigerant circulation circuit according to the ambient temperature further includes:
and if the environment temperature is lower than the preset environment temperature, controlling the first low-pressure refrigerant circulation loop to operate, and controlling the second low-pressure refrigerant circulation loop not to operate.
In a preferred technical scheme of the control method, the step of acquiring the operating parameters of the high-pressure refrigerant circulation loop specifically comprises the following steps:
acquiring the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature of the intermediate heat exchanger;
the step of controlling the operation state of the bypass branch according to the operation parameters of the high-pressure refrigerant circulation loop specifically comprises the following steps:
and controlling the running state of the bypass branch according to the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature.
In a preferred technical solution of the above control method, the step of controlling the operating state of the bypass branch according to the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature specifically includes:
calculating the difference value between the maximum refrigerant evaporation temperature and the current refrigerant evaporation temperature, and recording the difference value as a first difference value;
if the first difference is smaller than a first preset difference, controlling the bypass branch to operate; and/or the like, and/or,
and if the first difference value is greater than or equal to the first preset difference value, controlling the bypass branch circuit not to operate.
In a preferred technical scheme of the control method, the step of acquiring the operating parameters of the high-pressure refrigerant circulation loop specifically comprises the following steps:
acquiring the current suction pressure and the maximum suction pressure of the first compressor;
the step of controlling the operation state of the bypass branch according to the operation parameters of the high-pressure refrigerant circulation loop specifically comprises the following steps:
and controlling the running state of the bypass branch according to the current suction pressure and the maximum suction pressure.
In a preferred embodiment of the above control method, the step of "controlling the operation state of the bypass branch according to the current suction pressure and the maximum suction pressure" specifically includes:
calculating the difference value between the maximum suction pressure and the current suction pressure, and recording as a second difference value;
if the second difference is smaller than a second preset difference, controlling the bypass branch to operate; and/or the like and/or,
and if the second difference is greater than or equal to the second preset difference, controlling the bypass branch not to operate.
In a preferred embodiment of the above control method, when the first low-pressure refrigerant circulation circuit is operated and the bypass branch circuit is not operated, the control method further includes:
acquiring the temperature of a refrigerant at an outlet of the second heat exchanger;
and further controlling the running state of the bypass branch according to the temperature of the refrigerant at the outlet of the second heat exchanger.
In a preferred technical solution of the above control method, the step of further controlling the operating state of the bypass branch according to the temperature of the refrigerant at the outlet of the second heat exchanger specifically includes:
if the temperature of the refrigerant at the outlet of the second heat exchanger is less than or equal to the preset temperature of the refrigerant, controlling the bypass branch to operate; and/or the like and/or,
and if the temperature of the refrigerant at the outlet of the second heat exchanger is greater than the preset temperature of the refrigerant, controlling the bypass branch not to operate.
In another aspect, the present invention further provides a cascade heat pump system comprising a controller, the controller being capable of executing the control method according to any one of the above preferred embodiments.
Under the condition of adopting the technical scheme, the cascade heat pump system can control the running states of the first low-pressure refrigerant circulating loop and the second low-pressure refrigerant circulating loop according to the acquired environmental temperature so as to effectively reduce the running energy consumption of the cascade heat pump system; the operation state of the bypass branch can be controlled according to the obtained operation parameters of the high-pressure refrigerant circulation loop, so that the high-pressure refrigerant circulation loop can be ensured to operate all the time by controlling the on-off state of the bypass branch, the operation range of the cascade heat pump system is effectively expanded, and the use requirements of users are met.
Drawings
Preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:
fig. 1 is a schematic view of the overall structure of the cascade heat pump system of the present invention;
FIG. 2 is a flow chart of the main steps of the control method of the present invention;
FIG. 3 is a flowchart illustrating the detailed steps of a first preferred embodiment of the control method of the present invention;
FIG. 4 is a flow chart of the specific steps of a second preferred embodiment of the control method of the present invention;
reference numerals are as follows:
1. a high pressure refrigerant circulation loop; 11. a first compressor; 12. a first heat exchanger; 13. a first throttle member; 14. an intermediate heat exchanger;
2. a first low-pressure refrigerant circulation loop; 21. a second compressor; 22. a second throttling member; 23. a second heat exchanger; 24. a first check valve; 25. a second one-way valve;
3. a second low-pressure refrigerant circulation loop; 31. a fluorine pump; 32. a third check valve;
4. a bypass branch; 41. a control valve;
5. and a heat exchange water path.
Detailed Description
Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only for explaining the technical principle of the present invention, and are not intended to limit the scope of the present invention. And can be adjusted as needed by those skilled in the art to suit particular applications. For example, the cascade heat pump system described in the present invention may be a domestic cascade heat pump system, and may also be an industrial cascade heat pump system, which are not limited, and those skilled in the art may set the application of the cascade heat pump system according to the actual use requirement. Such changes in the application are within the scope of the present invention without departing from the basic concept thereof.
It should be noted that, in the description of the preferred embodiments, unless explicitly stated or limited otherwise, the terms "first", "second", and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. Furthermore, the terms "connected" and "connecting" should be interpreted broadly, such as mechanically or electrically, directly or indirectly through intervening media, or internally to both elements, and thus should not be interpreted as limiting the scope of the present invention. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
Further, it should be noted that in the description of the present invention, although the steps of the control method of the present invention are described in a specific order in the present application, the order is not limited, and those skilled in the art may perform the steps in a different order without departing from the basic principle of the present invention.
Based on the problem that the existing cascade heat pump system is easily affected by the ambient temperature and has a narrow operation range, the invention provides a novel cascade heat pump system and a control method thereof, aiming at expanding the operation range of the cascade heat pump system by selectively operating a first low-pressure refrigerant circulation loop, a second low-pressure refrigerant circulation loop and a bypass branch circuit, and further effectively ensuring that a high-pressure refrigerant circulation loop always operates to meet the use requirements of users.
Referring first to fig. 1, fig. 1 is a schematic view of the overall structure of the cascade heat pump system of the present invention. As shown in fig. 1, the cascade heat pump system of the present invention includes a high-pressure refrigerant circulation loop 1, a first low-pressure refrigerant circulation loop 2, and a second low-pressure refrigerant circulation loop 3, wherein the high-pressure refrigerant circulation loop 1 is provided with a first compressor 11, a first heat exchanger 12, a first throttling member 13, and an intermediate heat exchanger 14, the first low-pressure refrigerant circulation loop 2 is provided with a second compressor 21, an intermediate heat exchanger 14, a second throttling member 22, and a second heat exchanger 23, the second low-pressure refrigerant circulation loop 3 is provided with a fluorine pump 31, a second heat exchanger 23, and an intermediate heat exchanger 14, and the first low-pressure refrigerant circulation loop 2 and the second low-pressure refrigerant circulation loop 3 are configured to selectively exchange heat with the high-pressure refrigerant circulation loop 1 through the intermediate heat exchanger 14.
Based on the structure, the cascade heat pump system disclosed by the invention effectively ensures that the high-pressure refrigerant circulation loop 1 runs all the time by selectively running the first low-pressure refrigerant circulation loop 2 and the second low-pressure refrigerant circulation loop 3, so that the running range of the cascade heat pump system can be effectively expanded, the running energy consumption of the cascade heat pump system can be effectively reduced, and the use experience of a user is improved.
It should be noted that the present invention does not limit the specific types of the refrigerants flowing in the high-pressure refrigerant circulation circuit 1, the first low-pressure refrigerant circulation circuit 2, and the second low-pressure refrigerant circulation circuit 3, and those skilled in the art can set the types according to actual situations. In a specific embodiment, the refrigerant in the high-pressure refrigerant circuit 1 is the refrigerant R134a, and the refrigerants in the first low-pressure refrigerant circuit 2 and the second low-pressure refrigerant circuit 3 are the refrigerant R410A.
In addition, it should be noted that the present invention does not limit the specific structure of the intermediate heat exchanger 14, and the intermediate heat exchanger may be a shell-and-tube heat exchanger or a plate heat exchanger, and those skilled in the art can set the intermediate heat exchanger according to the actual situation. In the present embodiment, the intermediate heat exchanger 14 is preferably a plate heat exchanger, so as to effectively improve the heat exchange efficiency of the refrigerant in the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 in the intermediate heat exchanger 14.
Preferably, the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 are connected to simplify the structure of the cascade heat pump system. As shown in fig. 1, two ends of the fluorine pump 31 are connected to the first low-pressure refrigerant circulation circuit 2, and two ends of the second compressor 21 are connected to the second low-pressure refrigerant circulation circuit 3; specifically, a first end of the fluorine pump 31 is connected between the second throttling member 22 and the second heat exchanger 23, and a second end of the fluorine pump 31 is connected between the intermediate heat exchanger 14 and the second throttling member 22. The intermediate heat exchanger 14 includes a first heat exchange channel and a second heat exchange channel, and the second heat exchanger 23 includes a first heat exchange tube, wherein the refrigerant in the high-pressure refrigerant circulation loop 1 flows through the first heat exchange channel, and the refrigerant in the first low-pressure refrigerant circulation loop 2 and the refrigerant in the second low-pressure refrigerant circulation loop 3 flow through the second heat exchange channel and the first heat exchange tube, so as to achieve the purpose of heat exchange.
It should be noted that the present invention does not set any limit to the specific structures and specific models of the first compressor 11, the second compressor 21, the fluorine pump 31, the first throttle member 13, the second throttle member 22, the first heat exchanger 12 and the second heat exchanger 23; the first compressor 11 and the second compressor 21 may be frequency conversion compressors or fixed frequency compressors, and preferably, the first compressor 11 and the second compressor 21 are frequency conversion compressors so as to control the operation state of the cascade heat pump system; the fluorine pump 31 can be a fluorine-lined centrifugal pump, a fluorine-lined magnetic pump or a fluorine-lined self-priming pump; the first throttling component 13 and the second throttling component 22 can be electronic expansion valves, capillary tubes or thermal expansion valves; the first heat exchanger 12 and the second heat exchanger 23 may be plate heat exchangers or shell and tube heat exchangers, which are not restrictive and can be set by those skilled in the art according to the actual situation.
In addition, it should be noted that the present invention also does not limit the source of the heat source of the second heat exchanger 23, and it may be an air source or a ground source, which are not restrictive, as long as the purpose of exchanging heat with the second heat exchanger 23 can be achieved, and those skilled in the art can set the purpose according to actual situations. In the preferred embodiment, the heat source of the second heat exchanger 23 is an air source, so as to further reduce the energy consumption of the cascade heat pump system and improve the operation energy efficiency; specifically, the cascade heat pump system further includes a heat exchange fan (not shown in the figure), and the heat exchange fan is disposed near the second heat exchanger 23 to improve the heat exchange effect between the air and the refrigerant in the second heat exchanger 23.
Further, in the preferred embodiment, the cascade heat pump system further includes a bypass branch 4, a first end of the bypass branch 4 is connected between a connection point of the fluorine pump 31 and the first low-pressure refrigerant circulation loop 2 and the second heat exchanger 23, a second end of the bypass branch 4 is connected between the second compressor 21 and the intermediate heat exchanger 14, and the bypass branch 4 is arranged to further expand an operation range of the cascade heat pump system, thereby effectively ensuring that the high-pressure refrigerant circulation loop 1 can always operate, and meeting actual requirements of users. It should be noted that the present invention does not limit the specific connection position of the first end and the second end of the bypass branch 4, and the person skilled in the art can set the connection position according to practical situations.
Preferably, the bypass branch 4 is provided with a control valve 41, and the control valve 41 is configured to control an on/off state and a refrigerant flowing direction of the bypass branch 4. It should be noted that the present invention does not limit the specific structure and type of the control valve 41, and those skilled in the art can set the control valve according to the actual situation.
As a specific embodiment, the control valve 41 is a reversing control valve configured to control, by reversing, not only the refrigerant flowing through the bypass branch 4 to flow from the second end of the bypass branch 4 to the first end of the bypass branch 4, but also the refrigerant flowing through the bypass branch 4 to flow from the first end of the bypass branch 4 to the second end of the bypass branch 4.
Specifically, the reversing control valve is configured to enable the refrigerant flowing in the first low-pressure refrigerant circulation circuit 2 to flow from the second end of the bypass branch 4 to the first end of the bypass branch 4 when the first low-pressure refrigerant circulation circuit 2 operates and the second low-pressure refrigerant circulation circuit 3 does not operate. After the refrigerant in the first low-pressure refrigerant circulation loop 2 is discharged from the exhaust port of the second compressor 21, a part of the refrigerant enters the bypass branch 4 through the second end of the bypass branch 4, and the other part of the refrigerant enters the intermediate heat exchanger 14 to exchange heat with the refrigerant in the high-pressure refrigerant circulation loop 1, and then the refrigerant is throttled and depressurized by the second throttling component 22, then the refrigerant is converged with the refrigerant flowing out of the first end of the bypass branch 4, enters the second heat exchanger 23, and then returns to the second compressor 21 from the air inlet of the second compressor 21.
In addition, the reversing control valve is also configured to enable the refrigerant flowing in the second low-pressure refrigerant circulation loop 3 to flow from the first end of the bypass branch 4 to the second end of the bypass branch 4 when the first low-pressure refrigerant circulation loop 2 is not operated and the second low-pressure refrigerant circulation loop 3 is operated. Specifically, a part of the refrigerant circulated by the fluorine pump 31 enters the bypass branch 4 through the first end of the bypass branch 4, and the other part of the refrigerant enters the second heat exchanger 23 to be evaporated and absorb heat and then joins with the refrigerant flowing out of the second end of the bypass branch 4, and then enters the intermediate heat exchanger 14 to exchange heat with the refrigerant in the high-pressure refrigerant circulation loop 1, and the refrigerant after heat exchange enters the fluorine pump 31 again to participate in circulation.
In addition, when the first low-pressure refrigerant circulation loop 2 and the second low-pressure refrigerant circulation loop 3 both operate, a person skilled in the art can control the flow direction of the refrigerant in the bypass branch 4 by controlling the direction of the reversing control valve, which is not limited by the present invention.
Preferably, the first low-pressure refrigerant circulation circuit 2 is further provided with a first check valve 24, the first check valve 24 is disposed between the second compressor 21 and the second end of the bypass branch 4, the first check valve 24 is configured to only allow the refrigerant to flow from one side of the exhaust port of the second compressor 21 to the second end of the bypass branch 4 and one side of the intermediate heat exchanger 14, and the first check valve 24 can effectively ensure that the refrigerant flowing out of the second end of the bypass branch 4 cannot flow back into the second compressor 21 when the first low-pressure refrigerant circulation circuit 2 is not operated and the second low-pressure refrigerant circulation circuit 3 is operated.
Further, the first low-pressure refrigerant circulation circuit 2 is further provided with a second check valve 25, the second check valve 25 is arranged between the first end of the bypass branch 4 and a connection point of the fluorine pump 31 and the first low-pressure refrigerant circulation circuit 2, the second check valve 25 is set to allow only the refrigerant to flow from one side of the connection point of the fluorine pump 31 and the first low-pressure refrigerant circulation circuit 2 to the first end of the bypass branch 4 and one side of the second heat exchanger 23, and the second check valve 25 can effectively ensure that the refrigerant flowing out of the first end of the bypass branch 4 cannot flow back to the fluorine pump 31 when the first low-pressure refrigerant circulation circuit 2 operates and the second low-pressure refrigerant circulation circuit 3 does not operate.
Further preferably, the second low-pressure refrigerant circulation circuit 3 is further provided with a third check valve 32, the third check valve 32 is disposed between the second heat exchanger 23 and the intermediate heat exchanger 14, specifically, the third check valve 32 is disposed in parallel with the second compressor 21, and the third check valve 32 is disposed to allow the refrigerant to flow from one side of the second heat exchanger 23 to one side of the intermediate heat exchanger 14.
It should be noted that the present invention does not limit the specific structure and model of the first check valve 24, the second check valve 25 and the third check valve 32, and those skilled in the art can set them according to the actual situation.
In addition, in the preferred embodiment, the cascade heat pump system further includes a heat exchange water path 5, and a part of the heat exchange water path 5 is disposed in the first heat exchanger 12 to exchange heat with the refrigerant in the high-pressure refrigerant circulation circuit 1. It should be noted that the present invention does not limit the specific structure of the heat exchange water path 5, and those skilled in the art can set the structure according to actual situations.
Further, the high-pressure refrigerant circulation loop 1 is further provided with a first air separation device (not shown in the figure), and the first air separation device is arranged at an air inlet of the first compressor 11. The first low-pressure refrigerant circulation circuit 2 is further provided with a second air separation device (not shown in the figure), which is disposed at an air inlet of the second compressor 21. The first air distribution device and the second air distribution device are arranged, so that the problem of liquid impact of the first compressor 11 and the second compressor 21 can be effectively avoided, and the service lives of the first compressor 11 and the second compressor 21 are effectively guaranteed. It should be noted that, the present invention does not limit the specific structure of the first gas separation device and the second gas separation device at all, and those skilled in the art can set the structure according to the actual situation.
Further, the cascade heat pump system further includes a temperature sensor, a pressure sensor and a controller, the temperature sensor is configured to detect an ambient temperature, a current refrigerant evaporation temperature of the intermediate heat exchanger 14 and a refrigerant temperature at an outlet of the second heat exchanger 23, and the pressure sensor is configured to detect a current suction pressure of the first compressor 11. It should be noted that, the present invention does not limit the specific structure, model, number and position of the temperature sensor and the pressure sensor, and those skilled in the art can set the temperature sensor and the pressure sensor according to the actual situation.
The controller may control an operation state of the cascade heat pump system, for example, the controller may control operation states of the first low-pressure refrigerant circulation circuit 2, the second low-pressure refrigerant circulation circuit 3, and the bypass branch 4, and the controller may further obtain detection results of the temperature sensor and the pressure sensor, and the like, which are not limited. It can be understood by those skilled in the art that the present invention does not limit the specific structure and type of the controller, and the controller may be the original controller of the cascade heat pump system, or may be a controller separately configured to execute the control method of the present invention, and those skilled in the art can set the structure and type of the controller according to the actual use requirement.
Referring first to fig. 2, fig. 2 is a flow chart of main steps of the control method of the present invention. As shown in fig. 2, based on the cascade heat pump system described in the above embodiment, the control method of the present invention mainly includes the following steps:
s1: acquiring the ambient temperature of the cascade heat pump system;
s2: controlling the running states of the first low-pressure refrigerant circulating loop and the second low-pressure refrigerant circulating loop according to the ambient temperature;
s3: acquiring operation parameters of a high-pressure refrigerant circulation loop;
s4: and controlling the running state of the bypass branch according to the running parameters of the high-pressure refrigerant circulating loop.
First, in step S1, the controller obtains an ambient temperature of the cascade heat pump system detected by the temperature sensor; of course, the present invention does not limit the specific time and manner for acquiring the ambient temperature, and the controller may acquire the ambient temperature in real time or at certain time intervals, which is not restrictive, and may be set by a person skilled in the art according to actual conditions. Preferably, the controller acquires the ambient temperature in real time, so that the operating state of the cascade heat pump system can be timely and effectively adjusted, the operating energy efficiency of the cascade heat pump system is effectively improved, and the operating range of the cascade heat pump system is expanded.
Next, in step S2, the controller controls the operation states of the first low-pressure refrigerant circuit 2 and the second low-pressure refrigerant circuit 3 according to the ambient temperature.
It should be noted that, the present invention does not limit the specific control logic of step S2, and the controller may control the on/off states of the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 according to the ambient temperature, and may also control the operation speeds of the refrigerants in the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3, which are not restrictive, and may be set by a person skilled in the art according to actual situations.
Further, in step S3, the controller obtains an operation parameter of the high-pressure refrigerant circulation loop 1; of course, the present invention does not limit any specific parameter type of the obtained operation parameter of the high-pressure refrigerant circulation loop 1, and the specific parameter type may be the operation frequency of the first compressor 11, or the discharge pressure or the suction pressure of the first compressor 11, which is not restrictive, and the person skilled in the art may set the operation parameter according to the actual situation.
Next, in step S4, the controller controls the operation state of the bypass branch 4 according to the operation parameters of the high-pressure refrigerant circuit 1.
It should be noted that, the present invention does not limit the specific control logic of step S4, the controller may control the on/off state of the bypass branch 4 according to the operation parameter of the high-pressure refrigerant circulation loop 1, or may control the operation state of the bypass branch 4 by controlling the opening of the control valve 41 according to the operation parameter of the high-pressure refrigerant circulation loop 1, which is not restrictive, and the skilled person may set the control logic according to the actual situation.
In addition, it should be noted that, in the present invention, the specific execution sequence of step S1 and step S3 is not limited at all, and may be executed simultaneously, or may be executed sequentially without any sequence, which is set by a person skilled in the art according to the actual situation.
Referring next to fig. 3, fig. 3 is a flowchart illustrating specific steps of the first preferred embodiment of the control method according to the present invention. As shown in fig. 3, based on the cascade heat pump system described in the above embodiment, the control method of the first preferred embodiment of the present invention includes the following steps:
s101: acquiring the ambient temperature of the cascade heat pump system;
s102: if the ambient temperature is greater than or equal to the preset ambient temperature, controlling the first low-pressure refrigerant circulation loop not to operate, and controlling the second low-pressure refrigerant circulation loop to operate;
s103: if the ambient temperature is lower than the preset ambient temperature, controlling the first low-pressure refrigerant circulation loop to operate, and controlling the second low-pressure refrigerant circulation loop not to operate;
s104: acquiring the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature of the intermediate heat exchanger;
s105: calculating the difference value between the maximum refrigerant evaporation temperature and the current refrigerant evaporation temperature, and recording as a first difference value;
s106: if the first difference is smaller than a first preset difference, controlling the bypass branch to operate;
s107: and if the first difference is greater than or equal to a first preset difference, controlling the bypass branch circuit not to operate.
Firstly, in step S101, the controller obtains an ambient temperature of the cascade heat pump system detected by the temperature sensor; of course, the present invention does not limit the specific time and manner for acquiring the ambient temperature, and the controller may acquire the ambient temperature in real time or at certain time intervals, which is not restrictive, and may be set by a person skilled in the art according to actual conditions. Preferably, the controller acquires the ambient temperature in real time, so that the operating state of the cascade heat pump system can be timely and effectively adjusted, the operating energy efficiency of the cascade heat pump system is effectively improved, and the operating range of the cascade heat pump system is expanded.
Then, the controller controls the operation states of the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 according to the ambient temperature.
It should be noted that, the present invention does not limit the specific control logic of the above steps, the controller may control the on/off states of the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 according to the ambient temperature, and may also control the operation speeds of the refrigerants in the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3, which are not restrictive, and may be set by a person skilled in the art according to actual situations.
Preferably, in step S102, if the ambient temperature is greater than or equal to the preset ambient temperature, the controller controls the first low-pressure refrigerant circulation circuit 2 not to operate and controls the second low-pressure refrigerant circulation circuit 3 to operate, so as to effectively reduce the operation energy consumption of the cascade heat pump system.
Further, in step S103, if the ambient temperature is less than the preset ambient temperature, the controller controls the first low-pressure refrigerant circulation loop 2 to operate and controls the second low-pressure refrigerant circulation loop 3 not to operate, so as to effectively ensure that the heat exchange capacity of the intermediate heat exchanger 14 can enable the high-pressure refrigerant circulation loop 1 to operate normally, thereby meeting the user demand.
It should be noted that, the specific setting value of the preset ambient temperature is not limited in the present invention, and those skilled in the art may set the setting value according to the actual operation condition of the cascade heat pump system, or obtain the setting value according to the actual use requirement of the user, which is not limited in this respect.
Further preferably, in step S104, the controller obtains the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature of the intermediate heat exchanger 14 detected by the temperature sensor. It should be noted that, the present invention does not limit the specific time and manner for obtaining the evaporation temperature of the current refrigerant, and those skilled in the art can set the time and manner according to the actual situation.
Then, the controller controls the running state of the bypass branch 4 according to the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature; of course, the present invention does not limit the specific control logic of this step, for example, the controller may compare the current refrigerant evaporating temperature with the maximum refrigerant evaporating temperature, and control the operation state of the bypass branch 4 according to the comparison result.
Preferably, in step S105, the controller calculates a difference between the maximum refrigerant evaporation temperature and the current refrigerant evaporation temperature, and records the difference as a first difference.
Then, the controller controls the operation state of the bypass branch 4 according to the first difference. Specifically, in step S106, if the first difference is smaller than the first preset difference, which indicates that the current refrigerant evaporation temperature is close to the maximum refrigerant evaporation temperature, and the first compressor 11 is shut down due to an excessively high intake temperature, thereby preventing the high-pressure refrigerant circulation circuit 1 from operating, the controller controls the bypass branch 4 to operate, so as to reduce the refrigerant evaporation temperature of the intermediate heat exchanger 14 by reducing the refrigerant condensation temperature of the intermediate heat exchanger 14, thereby effectively ensuring that the high-pressure refrigerant circulation circuit 1 can operate normally.
Further, in step S107, if the first difference is greater than or equal to the first preset difference, which indicates that the difference between the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature is relatively large, and the current refrigerant evaporation temperature does not cause the shutdown of the first compressor 11 due to the excessively high intake air temperature, thereby causing the problem that the high-pressure refrigerant circulation loop 1 does not operate, the controller controls the bypass branch 4 not to operate, so as to improve the operating efficiency of the cascade heat pump system.
It should be noted that, the present invention does not limit any specific setting value of the first preset difference, and a person skilled in the art may set the first preset difference according to the actual operating condition of the cascade heat pump system, or may obtain the first preset difference according to the actual use requirement of the user, which is not restrictive; preferably, the first preset difference is 1 ℃, so as to ensure the high-efficiency operation of the high-pressure refrigerant circulation loop 1 to the maximum extent.
In addition, it should be noted that, the specific execution order of step S101 and step S104 is not limited in any way, and the steps may be executed simultaneously or sequentially without any order, and those skilled in the art will set themselves according to the actual situation.
Referring next to fig. 4, fig. 4 is a flowchart illustrating specific steps of a second preferred embodiment of the control method according to the present invention. As shown in fig. 4, based on the cascade heat pump system described in the above embodiment, the control method of the second preferred embodiment of the present invention includes the following steps:
s201: acquiring the ambient temperature of the cascade heat pump system;
s202: if the ambient temperature is greater than or equal to the preset ambient temperature, controlling the first low-pressure refrigerant circulation loop not to operate, and controlling the second low-pressure refrigerant circulation loop to operate;
s203: if the ambient temperature is lower than the preset ambient temperature, controlling the first low-pressure refrigerant circulation loop to operate, and controlling the second low-pressure refrigerant circulation loop not to operate;
s204: acquiring the current suction pressure and the maximum suction pressure of a first compressor;
s205: calculating the difference between the maximum suction pressure and the current suction pressure, and recording the difference as a second difference;
s206: if the second difference is smaller than a second preset difference, controlling the bypass branch to operate;
s207: and if the second difference is greater than or equal to a second preset difference, controlling the bypass branch circuit not to operate.
Firstly, in step S201, the controller obtains an ambient temperature of the cascade heat pump system detected by the temperature sensor; of course, the present invention does not limit the specific time and manner for acquiring the ambient temperature, and the controller may acquire the ambient temperature in real time or at certain time intervals, which is not restrictive, and may be set by a person skilled in the art according to actual conditions. Preferably, the controller acquires the ambient temperature in real time, so that the operating state of the cascade heat pump system can be timely and effectively adjusted, the operating energy efficiency of the cascade heat pump system is effectively improved, and the operating range of the cascade heat pump system is expanded.
Then, the controller controls the operation states of the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 according to the ambient temperature.
It should be noted that, the present invention does not limit the specific control logic of the above steps, the controller may control the on/off states of the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3 according to the ambient temperature, and may also control the operation speeds of the refrigerants in the first low-pressure refrigerant circulation circuit 2 and the second low-pressure refrigerant circulation circuit 3, which are not restrictive, and may be set by a person skilled in the art according to actual situations.
Preferably, in step S202, if the ambient temperature is greater than or equal to the preset ambient temperature, the controller controls the first low-pressure refrigerant circulation circuit 2 not to operate and controls the second low-pressure refrigerant circulation circuit 3 to operate, so as to effectively reduce the operation energy consumption of the cascade heat pump system.
Further, in step S203, if the ambient temperature is less than the preset ambient temperature, the controller controls the first low-pressure refrigerant circulation loop 2 to operate and controls the second low-pressure refrigerant circulation loop 3 not to operate, so as to effectively ensure that the heat exchange amount of the intermediate heat exchanger 14 can enable the high-pressure refrigerant circulation loop 1 to operate normally, so as to meet the use requirement of the user.
It should be noted that, the specific setting value of the preset ambient temperature is not limited in the present invention, and those skilled in the art may set the setting value according to the actual operation condition of the cascade heat pump system, or obtain the setting value according to the actual use requirement of the user, which is not limited in this respect.
Further preferably, in step S204, the controller obtains the current suction pressure and the maximum suction pressure of the first compressor 11 detected by the pressure sensor. It should be noted that the present invention does not limit the specific timing and manner of obtaining the current suction pressure, and those skilled in the art can set the timing and manner according to the actual situation.
Then, the controller controls the running state of the bypass branch 4 according to the current suction pressure and the maximum suction pressure; of course, the present invention does not limit the specific control logic of this step, for example, the controller may compare the current suction pressure with the maximum suction pressure and control the operation state of the bypass branch 4 according to the comparison result.
Preferably, in step S205, the controller calculates a difference between the maximum suction pressure and the current suction pressure, which is recorded as a second difference.
Then, the controller controls the operation state of the bypass branch 4 according to the second difference. Specifically, in step S206, if the second difference is smaller than the second preset difference, which indicates that the current suction pressure is close to the maximum suction pressure at this time, and the first compressor 11 is shut down due to too high suction pressure, so that the high-pressure refrigerant circulation circuit 1 does not operate, the controller controls the bypass branch 4 to operate, so as to reduce the refrigerant evaporation temperature of the intermediate heat exchanger 14 by reducing the refrigerant condensation temperature of the intermediate heat exchanger 14, further reduce the suction pressure of the first compressor 11, and ensure that the high-pressure refrigerant circulation circuit 1 can operate normally.
Further, in step S207, if the second difference is greater than or equal to the second preset difference, which indicates that the current suction pressure is different from the maximum suction pressure at this time, and the first compressor 11 can normally operate, the controller controls the bypass branch 4 not to operate, so as to improve the operating efficiency of the cascade heat pump system.
It should be noted that, the specific setting value of the second preset difference is not limited in the present invention, and those skilled in the art may set the second preset difference according to the actual operating condition of the cascade heat pump system, or obtain the second preset difference according to the actual using requirement of the user, which is not limited.
In addition, it should be noted that, the specific execution sequence of step S201 and step S204 is not limited in any way, and the steps may be executed simultaneously or sequentially without any order, and those skilled in the art will set themselves according to the actual situation.
In addition, under the condition that the first low-pressure refrigerant circulation loop 1 is operated and the bypass branch 4 is not operated, that is, under the condition that the first low-pressure refrigerant circulation loop 1 is operated and the first difference is greater than or equal to the first preset difference or the second difference is greater than or equal to the second preset difference, the control method of the invention further comprises the steps of obtaining the temperature of the refrigerant at the outlet of the second heat exchanger 23, and further controlling the operation state of the bypass branch 4 according to the temperature of the refrigerant at the outlet of the second heat exchanger 23, so as to effectively avoid the problems of frost formation and even frost cracking of the second heat exchanger 23.
It should be noted that, the present invention does not set any limitation to the specific acquisition time and acquisition mode of the temperature of the refrigerant at the outlet of the second heat exchanger 23, nor to the specific control logic of the above steps, and those skilled in the art can set the acquisition time and acquisition mode according to the actual situation.
Preferably, if the temperature of the refrigerant at the outlet of the second heat exchanger 23 is less than or equal to the preset temperature of the refrigerant, the controller controls the bypass branch 4 to operate, so that the refrigerant flowing out of the exhaust port of the second compressor 21 directly enters the second heat exchanger 23 through the bypass branch 4, and further the problem that the second heat exchanger 23 is frosted or even frozen due to too low temperature is effectively avoided.
Further, if the temperature of the refrigerant at the outlet of the second heat exchanger 23 is greater than the preset temperature of the refrigerant, the controller controls the bypass branch 4 not to operate, so as to effectively ensure the operation energy efficiency of the cascade heat pump system.
It should be noted that, the specific set value of the preset refrigerant temperature is not limited in the present invention, and those skilled in the art can set the preset value according to the actual operation condition of the cascade heat pump system.
So far, the technical solutions of the present invention have been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of the present invention is obviously not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can fall into the protection scope of the invention.
Claims (10)
1. A control method of a cascade heat pump system is characterized in that the cascade heat pump system comprises a high-pressure refrigerant circulation loop, a first low-pressure refrigerant circulation loop, a second low-pressure refrigerant circulation loop and a bypass branch,
the high-pressure refrigerant circulating loop is provided with a first compressor, a first heat exchanger, a first throttling component and an intermediate heat exchanger, the first low-pressure refrigerant circulating loop is provided with a second compressor, the intermediate heat exchanger, a second throttling component and a second heat exchanger, the second low-pressure refrigerant circulating loop is provided with a fluorine pump, a second heat exchanger and the intermediate heat exchanger, two ends of the fluorine pump are connected with the first low-pressure refrigerant circulating loop, two ends of the second compressor are connected with the second low-pressure refrigerant circulating loop, the first low-pressure refrigerant circulating loop and the second low-pressure refrigerant circulating loop are arranged to be capable of selectively exchanging heat with the high-pressure refrigerant circulating loop through the intermediate heat exchanger,
a first end of the bypass branch is connected between a connection point of the fluorine pump and the first low-pressure refrigerant circulation loop and the second heat exchanger, a second end of the bypass branch is connected between the second compressor and the intermediate heat exchanger, a control valve is arranged on the bypass branch and can control the on-off state of the bypass branch,
the control method comprises the following steps:
acquiring the ambient temperature of the cascade heat pump system;
controlling the running states of the first low-pressure refrigerant circulating loop and the second low-pressure refrigerant circulating loop according to the environment temperature;
acquiring operation parameters of the high-pressure refrigerant circulation loop;
and controlling the running state of the bypass branch according to the running parameters of the high-pressure refrigerant circulating loop.
2. The control method according to claim 1, wherein the step of controlling the operation states of the first and second low-pressure refrigerant circulation circuits according to the ambient temperature includes:
and if the ambient temperature is greater than or equal to a preset ambient temperature, controlling the first low-pressure refrigerant circulation loop not to operate, and controlling the second low-pressure refrigerant circulation loop to operate.
3. The control method as claimed in claim 2, wherein the step of controlling the operation states of the first and second low-pressure refrigerant circulation circuits according to the ambient temperature further comprises:
and if the environment temperature is lower than the preset environment temperature, controlling the first low-pressure refrigerant circulation loop to operate, and controlling the second low-pressure refrigerant circulation loop not to operate.
4. The control method according to claim 3, wherein the step of obtaining the operating parameters of the high-pressure refrigerant circulation circuit specifically comprises:
acquiring the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature of the intermediate heat exchanger;
the step of controlling the operation state of the bypass branch according to the operation parameters of the high-pressure refrigerant circulation loop specifically comprises the following steps:
and controlling the running state of the bypass branch according to the current refrigerant evaporation temperature and the maximum refrigerant evaporation temperature.
5. The control method according to claim 4, wherein the step of controlling the operation state of the bypass branch according to the current refrigerant evaporating temperature and the maximum refrigerant evaporating temperature specifically comprises:
calculating the difference value between the maximum refrigerant evaporation temperature and the current refrigerant evaporation temperature, and recording the difference value as a first difference value;
if the first difference is smaller than a first preset difference, controlling the bypass branch to operate; and/or the like and/or,
and if the first difference value is greater than or equal to the first preset difference value, controlling the bypass branch circuit not to operate.
6. The control method according to claim 3, wherein the step of obtaining the operation parameter of the high-pressure refrigerant circulation loop comprises:
acquiring the current suction pressure and the maximum suction pressure of the first compressor;
the step of controlling the operation state of the bypass branch according to the operation parameters of the high-pressure refrigerant circulation loop specifically comprises the following steps:
and controlling the running state of the bypass branch according to the current suction pressure and the maximum suction pressure.
7. The control method according to claim 6, wherein the step of controlling the operating state of the bypass branch according to the current suction pressure and the maximum suction pressure specifically comprises:
calculating the difference value between the maximum suction pressure and the current suction pressure, and recording as a second difference value;
if the second difference is smaller than a second preset difference, controlling the bypass branch to operate; and/or the like, and/or,
and if the second difference is greater than or equal to the second preset difference, controlling the bypass branch not to operate.
8. The control method according to any one of claims 5 or 7, wherein in a case where the first low-pressure refrigerant circulation circuit is operated and the bypass branch is not operated, the control method further comprises:
acquiring the temperature of a refrigerant at an outlet of the second heat exchanger;
and further controlling the running state of the bypass branch according to the temperature of the refrigerant at the outlet of the second heat exchanger.
9. The control method according to claim 8, wherein the step of further controlling the operating state of the bypass branch according to the temperature of the refrigerant at the outlet of the second heat exchanger specifically comprises:
if the temperature of the refrigerant at the outlet of the second heat exchanger is less than or equal to the preset temperature of the refrigerant, controlling the bypass branch to operate; and/or the like and/or,
and if the temperature of the refrigerant at the outlet of the second heat exchanger is greater than the preset temperature of the refrigerant, controlling the bypass branch not to operate.
10. A cascade heat pump system characterized in that it comprises a controller capable of performing the control method of any one of claims 1 to 9.
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