Two-stage compression heat pump and control method thereof

Abstract

The invention relates to the field of heat pumps, in particular to a two-stage compression heat pump and a control method thereof, and aims to solve the problem that an existing two-stage compression heat pump cannot switch refrigeration and heating. In order to achieve the purpose, an air outlet of an air inlet pipeline of the two-stage compression heat pump can communicate with a first compressor or communicate with a second compressor through an electromagnetic valve, the first compressor can communicate with an air outlet pipeline or the second compressor through a valve body, and the second compressor communicates with the air outlet pipeline; the air outlet pipeline communicates with an outer port of the first connecting pipe, an inner port of the first connecting pipe can communicate with an inner port of the second connecting pipe or the third connecting pipe, and an outer port of the second connecting pipe, the condenser, the throttling valve, the air side heat exchanger and an outer port of the third connecting pipe communicate in sequence. The inner port of the fourth connecting pipe can be connected with the inner port of the second connecting pipe or the third connecting pipe, and the outer port of the fourth connecting pipe is communicated with the air inlet pipeline. According to the invention, switching of series-parallel connection and switching of refrigeration and heating can be realized.

Description

Technical Field

[0001] The present invention relates to the field of heat pumps, and particularly provides a two-stage compression heat pump and a control method thereof. Background Art

[0002] Compared with ordinary heat pumps, two-stage compression heat pumps can provide a higher water outlet temperature (≥60°C) at ultra-low ambient temperatures (ambient temperature below -20°C), and have a small attenuation of heating capacity (the capacity can be maintained without attenuation when operating at -30°C). In order to balance the relatively high annual operating energy efficiency of the heat pump and the refrigeration demand, two-stage heat pumps can usually switch between single-compressor operation, two-compressor series operation, and two-compressor parallel operation modes to adapt to the energy-saving performance under different working conditions, but they cannot switch between refrigeration and heating modes. Existing two-stage compression heat pumps use an oil equalizing valve for oil equalization, or a capillary tube is set for oil return, but these oil return methods make it inconvenient for the two-stage compression heat pump to return oil in some modes. In order to ensure the reliability of the operation of the heat pump system, the oil return problem in each mode needs to be focused on. In addition, on the basis of being able to achieve single-machine operation and series-parallel operation, it is also necessary to consider how to keep the system at a relatively high energy efficiency while ensuring the comfort of users, so as to reduce the energy consumption of the two-stage compression heat pump.

[0003] Correspondingly, a new technical solution is needed in this field to solve the above problems. Summary of the Invention

[0004] The present invention aims to solve the above technical problems, that is, to solve the problem that existing two-stage compression heat pumps cannot switch between refrigeration and heating. For this purpose, the present invention provides a two-stage compression heat pump, including: an intake pipeline and an exhaust pipeline, the air outlet of the intake pipeline can be connected to the air inlet of the first compressor or to the air inlet of the second compressor through a solenoid valve, the air outlet of the first compressor can be connected to the exhaust pipeline or the air inlet of the second compressor through a valve body, and the air outlet of the second compressor is connected to the exhaust pipeline; a four-way valve, on which a first connecting pipe, a second connecting pipe, a third connecting pipe, and a fourth connecting pipe are provided, the exhaust pipeline is connected to the outer port of the first connecting pipe, the inner port of the first connecting pipe can be connected to the inner port of the second connecting pipe or the third connecting pipe, the outer port of the second connecting pipe, a condenser, a throttle valve, an air-side heat exchanger, and the outer port of the third connecting pipe are connected in sequence, the inner port of the fourth connecting pipe can be connected to the inner port of the second connecting pipe or the third connecting pipe, and the outer port of the fourth connecting pipe is connected to the air inlet of the intake pipeline.

[0005] In the above specific embodiment of the two-stage compression heat pump, the two-stage compression heat pump further includes: a check valve, which is arranged between the air outlet of the first compressor and the exhaust pipeline, and limits the gas flow direction to only flow from the air outlet of the first compressor to the exhaust pipeline.

[0006] In the above specific embodiment of the two-stage compression heat pump, the two-stage compression heat pump further includes: an oil separator disposed on the outlet gas pipeline; an oil return pipeline, one end of the oil return pipeline is connected to the oil separator, and the other end is respectively connected to the first compressor and the second compressor through a first oil return capillary and a second oil return capillary.

[0007] In the above specific embodiment of the two-stage compression heat pump, the second oil return capillary is connected to the oil return port of the second compressor through a solenoid valve; or the second oil return capillary is connected to the oil return port of the second compressor.

[0008] In the above specific embodiment of the two-stage compression heat pump, the two-stage compression heat pump further includes: an oil equalizing pipeline, one end of the oil equalizing pipeline is connected to the first compressor, and the other end is connected to the second compressor, and an oil equalizing valve is provided on the oil equalizing pipeline.

[0009] A control method for a two-stage compression heat pump, used to control the two-stage compression heat pump in any one of the above, includes the following steps: running in a dual-machine mode after starting up; judging whether the actual operating frequencies of the first compressor and the second compressor are less than or equal to their minimum operating frequencies, and selecting to switch to a single-machine mode or maintain the dual-machine mode according to the judgment result.

[0010] In the above specific embodiment of the control method of the two-stage compression heat pump, if it is selected to switch to the single-machine mode, then compare the cumulative operating durations of the first compressor and the second compressor, and select the first compressor or the second compressor to work according to the comparison result.

[0011] In the above specific embodiment of the control method of the two-stage compression heat pump, the control method further includes the following steps: after switching to the single-machine mode of operation, judge whether the actual operating frequency of the corresponding compressor is greater than or equal to its maximum operating frequency, and select to maintain the single-machine mode or switch to the dual-machine mode according to the judgment result.

[0012] In the above specific embodiment of the control method of the two-stage compression heat pump, "running in a dual-machine mode after starting up" is specifically: during heating, after starting up, judge whether the actual ambient temperature Ta is greater than or equal to the set temperature T0, and run in a dual-machine parallel mode or a dual-machine series mode according to the judgment result; and / or during cooling, run in a dual-machine parallel mode after starting up.

[0013] In the above specific embodiment of the control method of the two-stage compression heat pump, "judging whether the actual ambient temperature Ta is greater than or equal to the set temperature T0, and running in a dual-machine parallel mode or a dual-machine series mode according to the judgment result" is specifically: if the actual ambient temperature Ta is greater than or equal to the set temperature T0, then run in a dual-machine parallel mode; if the actual ambient temperature Ta is less than the set temperature T0, then run in a dual-machine series mode.

[0014] In the case of adopting the above technical solution, the present invention can achieve single-machine operation, series-parallel switching, and refrigeration-heating switching, and the structure of the pipeline is simple and easy to implement; in the oil return solution of the present invention, no matter which working mode the two-stage compression heat pump is in, an oil return path can be provided for it, improving the stability and reliability of the system. In the present invention, running in the dual-machine mode after startup can enable the two-stage compression heat pump to meet the user's needs as soon as possible; the method of detecting the actual operating frequency of the compressor to determine whether to maintain dual-machine operation can reduce energy consumption while meeting the user's needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings, in which:

[0016] Figure 1 is a schematic structural diagram of a two-stage compression heat pump in the present invention, which shows the connection structure in the dual-machine series heating mode;

[0017] Figure 2 is a main step flowchart of the control method of the two-stage compression heat pump in the present invention;

[0018] Figure 3 is a step flowchart of a possible implementation manner of the control method of the two-stage compression heat pump in the heating mode;

[0019] Figure 4 is a step flowchart of a possible implementation manner of the control method of the two-stage compression heat pump in the refrigeration mode;

[0020] Figure 5 is a schematic structural diagram of the second connection manner of the second oil return capillary in the present invention.

[0021] In the figure: 1, intake pipeline; 2, outlet pipeline; 3, first compressor; 4, valve body; 41, first intake port; 42, first outlet port; 43, second outlet port; 5, second compressor; 6, four-way valve; 61, first connecting pipe; 62, second connecting pipe; 63, third connecting pipe; 64, fourth connecting pipe; 7, condenser; 8, throttle valve; 9, air-side heat exchanger; 10, solenoid valve; 11, check valve; 12, oil separator; 13, oil return pipeline; 14, first oil return capillary; 15, second oil return capillary; 16, oil equalizing pipeline; 17, oil equalizing valve. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principle of the present invention and are not used to limit the protection scope of the present invention. Those skilled in the art can make adjustments according to needs to adapt to specific application scenarios.

[0023] It should be noted that in the description of the present invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the drawings. This is only for convenience of description and does not indicate or imply that the relevant devices or components must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In addition, ordinal numbers such as "first", "second", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0024] In addition, it should also be noted that in the description of the present invention, unless otherwise clearly specified and defined, the terms "installation" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] Furthermore, in order to more clearly show the core technical solutions of the present invention, the description below omits the description of the well-known structures of devices such as compressors and four-way valves. However, this omission is only for convenience of description and does not mean that devices such as compressors and four-way valves can do without these well-known structures.

[0026] As Figure 1 shown, the present invention provides a two-stage compression heat pump, including: an intake pipeline 1 and an exhaust pipeline 2. The air outlet of the intake pipeline 1 can be communicated with the air inlet of the first compressor 3 or, through a solenoid valve 10, with the air inlet of the second compressor 5. The air outlet of the first compressor 3 can be communicated with the exhaust pipeline 2 or the air inlet of the second compressor 5 through a valve body 4. The air outlet of the second compressor 5 is communicated with the exhaust pipeline 2. The valve body 4 can be a three-way valve or composed of two solenoid valves. One solenoid valve is used to control the on-off between the first compressor 3 and the exhaust pipeline 2, and the other solenoid valve is used to control the on-off between the first compressor 3 and the air inlet of the second compressor 5. As Figure 1 and Figure 5As shown in the figure, when the valve body 4 is a three-way valve, it is provided with a first air inlet 41, a first air outlet 42 and a second air outlet 43. The air outlet of the first compressor 3 is communicated with the first air inlet 41, and the first air inlet 41 can be communicated with the first air outlet 42 or the second air outlet 43. The first air outlet 42 is communicated with the air outlet pipeline 2. The four-way valve 6 is provided with a first connecting pipe 61, a second connecting pipe 62, a third connecting pipe 63 and a fourth connecting pipe 64. The air outlet pipeline 2 is communicated with the outer port of the first connecting pipe 61. The inner port of the first connecting pipe 61 can be communicated with the inner port of the second connecting pipe 62 or the inner port of the third connecting pipe 63. The outer ports of the second connecting pipe 62, the condenser 7, the throttle valve 8, the air-side heat exchanger 9 and the outer port of the third connecting pipe 63 are communicated in sequence. The inner port of the fourth connecting pipe 64 can be connected with the inner port of the second connecting pipe 62 or the inner port of the third connecting pipe 63, and the outer port of the fourth connecting pipe 64 is communicated with the air inlet of the air inlet pipeline 1.

[0027] The two-stage compression heat pump has 7 common working modes, namely: series heating of two compressors, independent heating of the first compressor 3, independent heating of the second compressor 5, parallel heating of two compressors, independent refrigeration of the first compressor 3, independent refrigeration of the second compressor 5, and parallel refrigeration of two compressors. The pipeline structure in this embodiment can also achieve series refrigeration of two compressors.

[0028] When the two compressors are in series heating, the solenoid valve 10 is closed. The first air inlet 41 is communicated with the second air outlet 43. The inner port of the first connecting pipe 61 is communicated with the inner port of the second connecting pipe 62. The inner port of the third connecting pipe 63 is communicated with the inner port of the fourth connecting pipe 64. The refrigerant in the air inlet pipeline 1 sequentially passes through the first compressor 3, the first air inlet 41, the second air outlet 43, the second compressor 5, the air outlet pipeline 2, the first connecting pipe 61, the second connecting pipe 62, the condenser 7, the throttle valve 8, the air-side heat exchanger 9, the third connecting pipe 63, the fourth connecting pipe 64, and then enters the air inlet pipeline 1 again.

[0029] When the first compressor 3 is independently heating, the second compressor 5 and the solenoid valve 10 are closed. The first air inlet 41 is communicated with the first air outlet 42. The inner port of the first connecting pipe 61 is communicated with the inner port of the second connecting pipe 62. The inner port of the third connecting pipe 63 is communicated with the inner port of the fourth connecting pipe 64. The refrigerant in the air inlet pipeline 1 sequentially passes through the first compressor 3, the first air inlet 41, the first air outlet 42, the air outlet pipeline 2, the first connecting pipe 61, the second connecting pipe 62, the condenser 7, the throttle valve 8, the air-side heat exchanger 9, the third connecting pipe 63, the fourth connecting pipe 64, and then enters the air inlet pipeline 1 again.

[0030] When the second compressor 5 operates in heating mode alone, the first compressor 3 is turned off, the solenoid valve 10 is opened, the inner port of the first connecting pipe 61 communicates with the inner port of the second connecting pipe 62, and the inner port of the third connecting pipe 63 communicates with the inner port of the fourth connecting pipe 64. The refrigerant in the intake pipe 1 sequentially passes through the solenoid valve 10, the second compressor 5, the outlet pipe 2, the first connecting pipe 61, the second connecting pipe 62, the condenser 7, the throttle valve 8, the air-side heat exchanger 9, the third connecting pipe 63, the fourth connecting pipe 64, and then re-enters the intake pipe 1.

[0031] When the two compressors operate in parallel for heating, the first intake port 41 communicates with the first outlet port 42, the solenoid valve 10 is opened, the inner port of the first connecting pipe 61 communicates with the inner port of the second connecting pipe 62, and the inner port of the third connecting pipe 63 communicates with the inner port of the fourth connecting pipe 64. The refrigerant in the intake pipe 1 is divided into two paths. One path enters the first compressor 3 and then flows into the outlet pipe 2, and the other path passes through the solenoid valve 10, enters the second compressor 5, and then flows into the outlet pipe 2. Then they jointly flow through the first connecting pipe 61, the second connecting pipe 62, the condenser 7, the throttle valve 8, the air-side heat exchanger 9, the third connecting pipe 63, the fourth connecting pipe 64, and then re-enters the intake pipe 1.

[0032] When the first compressor 3 operates in cooling mode alone, the second compressor 5 and the solenoid valve 10 are turned off, the first intake port 41 communicates with the first outlet port 42, the inner port of the first connecting pipe 61 communicates with the inner port of the third connecting pipe 63, and the inner port of the second connecting pipe 62 communicates with the inner port of the fourth connecting pipe 64. The refrigerant in the intake pipe 1 sequentially passes through the first compressor 3, the first intake port 41, the first outlet port 42, the outlet pipe 2, the first connecting pipe 61, the third connecting pipe 63, the air-side heat exchanger 9, the throttle valve 8, the condenser 7, the second connecting pipe 62, the fourth connecting pipe 64, and then re-enters the intake pipe 1.

[0033] When the second compressor 5 operates in cooling mode alone, the first compressor 3 is turned off, the solenoid valve 10 is opened, the inner port of the first connecting pipe 61 communicates with the inner port of the third connecting pipe 63, and the inner port of the second connecting pipe 62 communicates with the inner port of the fourth connecting pipe 64. The refrigerant in the intake pipe 1 sequentially passes through the solenoid valve 10, the second compressor 5, the outlet pipe 2, the first connecting pipe 61, the third connecting pipe 63, the air-side heat exchanger 9, the throttle valve 8, the condenser 7, the second connecting pipe 62, the fourth connecting pipe 64, and then re-enters the intake pipe 1.

[0034] When two compressors are connected in parallel for refrigeration, the first intake port 41 is in communication with the first outlet port 42, the solenoid valve 10 is opened, the inner port of the first connecting pipe 61 is in communication with the inner port of the third connecting pipe 63, and the inner port of the second connecting pipe 62 is in communication with the inner port of the fourth connecting pipe 64. The refrigerant in the intake pipeline 1 is divided into two paths. One path enters the first compressor 3 and then flows into the outlet pipeline 2, and the other path passes through the solenoid valve 10, enters the second compressor 5, and then flows into the outlet pipeline 2. Then they jointly flow through the first connecting pipe 61, the third connecting pipe 63, the air-side heat exchanger 9, the throttle valve 8, the condenser 7, the second connecting pipe 62, the fourth connecting pipe 64, and then enter the intake pipeline 1 again.

[0035] In this embodiment, in order to be able to switch between refrigeration and heating under the condition of realizing single-machine operation and series-parallel switching of two compressors, the design of the pipeline structure is optimized. Through the cooperation of the valve body 4, the four-way valve 6 and other valves, single-machine operation, series-parallel switching, and refrigeration-heating switching can be realized, and the structure of the pipeline is simple and easy to implement. The solenoid valve 10 is arranged between the outlet of the intake pipeline 1 and the second compressor 5, which can prevent refrigerant from flowing into the second compressor 5 when only the first compressor 3 is working.

[0036] Furthermore, in order to prevent the refrigerant flowing out of the second compressor 5 from flowing back to the first compressor 3 when the two compressors are connected in parallel, the two-stage compression heat pump further includes: a check valve 11. The check valve 11 is arranged between the outlet of the first compressor 3 and the outlet pipeline 2, and the gas flow direction is limited to only flow from the outlet of the first compressor 3 to the outlet pipeline 2. As Figure 1 shown, the check valve 11 is arranged between the first outlet port 42 and the outlet pipeline 2, and the gas flow direction is limited to only flow from the first outlet port 42 to the outlet pipeline 2.

[0037] Furthermore, in order to ensure the reliability of the operation of the heat pump system, the two-stage compression heat pump further includes: an oil separator 12. The oil separator 12 is arranged on the outlet pipeline 2 and is used to separate the refrigeration oil in the high-pressure steam discharged by the first compressor 3 and / or the second compressor 5; an oil return pipeline 13. One end of the oil return pipeline 13 is connected to the oil separator 12, and the other end is respectively connected to the first compressor 3 and the second compressor 5 through a first oil return capillary 14 and a second oil return capillary 15.

[0038] The refrigerating oil separated by the oil separator 12 can return to the first compressor 3 through the first oil return capillary 14, or can return to the second compressor through the second oil return capillary 15. In this way, no matter which working mode the two-stage compression heat pump is in, an oil return path can be provided for it, and the oil return speed can also be adjusted by adjusting the lengths of the two oil return capillaries to balance the oil amounts of the first compressor 3 and the second compressor 5, so that the oil return amounts of the first compressor 3 and the second compressor 5 reach a suitable ratio. Compared with the oil return methods that only use one oil return capillary or only use an oil equalizing valve in the prior art, the oil return scheme in this embodiment improves the stability and reliability of the whole system, and also helps to extend the service life of the compressor.

[0039] Furthermore, there are two ways to set the second oil return capillary 15. The first way: the second oil return capillary 15 is connected to the oil return port of the second compressor 5 through the solenoid valve 10; the second way: the second oil return capillary 15 is connected to the oil return port of the second compressor 5.

[0040] The connection method of the first second oil return capillary 15 is as Figure 1 shown, the second oil return capillary 15 is connected to the solenoid valve 10 and then to the oil return port of the second compressor 5.

[0041] The oil return path during the series heating of the two compressors is: the oil in the oil separator 12 flows into the oil return pipeline 13, is sucked into the first compressor 3 through the first oil return capillary 14 and the second oil return capillary 15, and then enters the oil separator 12 after passing through the second compressor 5 to complete the oil circuit cycle.

[0042] The oil return path when the first compressor 3 operates alone for heating and refrigeration is: the oil in the oil separator 12 flows into the oil return pipeline 13, is sucked into the first compressor 3 through the first oil return capillary 14 and the second oil return capillary 15, and then enters the oil separator 12 after passing through the check valve 11 to complete the oil circuit cycle.

[0043] The oil return path when the second compressor 5 operates alone for heating and refrigeration is: the oil in the oil separator 12 flows into the oil return pipeline 13, is sucked into the second compressor 5 through the second oil return capillary 15 and the solenoid valve 10, and then enters the oil separator 12 to complete the oil circuit cycle.

[0044] The oil return path during the parallel heating and refrigeration of the two compressors is: the oil in the oil separator 12 flows into the oil return pipeline 13, a part of the oil is sucked into the first compressor 3 through the first oil return capillary 14 and then enters the oil separator 12 after passing through the check valve 11 to complete the oil circuit cycle; another part of the oil is sucked into the second compressor 5 through the second oil return capillary 15 and the solenoid valve 10, and then enters the oil separator 12 to complete the oil circuit cycle.

[0045] The connection method of the second second oil return capillary 15 is as follows Figure 5 As shown, the second oil return capillary 15 is arranged between the solenoid valve 10 and the second compressor 5, and the second oil return capillary 15 is connected to the oil return port of the second compressor 5.

[0046] The oil return path during the combined heating of the two compressors in series is as follows: The oil in the oil separator 12 flows into the oil return pipeline 13. A part of the oil is sucked into the first compressor 3 through the first oil return capillary 14, flows out of the first compressor 3 and then is sucked into the second oil return capillary 15, and finally enters the oil separator 12; Another part of the oil is sucked into the second compressor 5 through the second oil return capillary 15, and then enters the oil separator 12 to complete the oil circuit cycle.

[0047] The oil return path when the first compressor 3 operates independently for heating and refrigeration is as follows: The oil in the oil separator 12 flows into the oil return pipeline 13, is sucked into the first compressor 3 through the first oil return capillary 14, and then enters the oil separator 12 through the check valve to complete the oil circuit cycle.

[0048] The oil return path when the second compressor 5 operates independently for heating and refrigeration is as follows: The oil in the oil separator 12 flows into the oil return pipeline 13, is sucked into the second compressor 5 through the second oil return capillary 15, and then enters the oil separator 12 to complete the oil circuit cycle.

[0049] The oil return path when the two compressors operate in parallel for heating and refrigeration is as follows: The oil in the oil separator 12 flows into the oil return pipeline 13. A part of the oil is sucked into the first compressor 3 through the first oil return capillary 14, and then enters the oil separator 12 through the check valve to complete the oil circuit cycle; Another part of the oil is sucked into the second compressor 5 through the second oil return capillary 15, and then enters the oil separator 12 to complete the oil circuit cycle.

[0050] Furthermore, the two-stage compression heat pump further includes: an oil equalizing pipeline 16. One end of the oil equalizing pipeline 16 is connected to the first compressor 3, and the other end is connected to the second compressor 5. An oil equalizing valve 17 is arranged on the oil equalizing pipeline 16. In the two-stage compression heat pump, the setting of the double oil return capillary can balance the oil amounts of the first compressor 3 and the second compressor 5 to a great extent. However, the oil amount distribution between the first compressor 3 and the second compressor 5 may still be uneven due to various factors. To further balance the oil amounts between the two compressors, an oil equalizing valve 17 and an oil equalizing pipeline 16 are arranged between the two compressors. The oil equalizing valve 17 can adjust the flow of oil between the two compressors as needed to ensure that they both obtain an appropriate amount of lubricating oil, thereby maintaining normal operation, preventing damage or unstable operation of any compressor due to lack of oil, and at the same time avoiding problems such as efficiency reduction or other issues caused by excessive oil. Since the oil equalizing valve 17 ensures the uniform distribution of the lubricating oil, it helps to improve the stability and reliability of the entire system, and also helps to extend the service life of the compressor.

[0051] The single - machine mode includes two modes: the first compressor 3 runs alone and the second compressor 5 runs alone; the dual - machine mode includes two modes: the first compressor 3 and the second compressor 5 run in series and the first compressor 3 and the second compressor 5 run in parallel. Among them, when the first compressor 3 and the second compressor 5 run in series, it is a two - stage compression. The refrigerant is initially compressed when passing through the first compressor 3 and is compressed for the second time when passing through the second compressor 5.

[0052] A control method for a two - stage compression heat pump is used to control the above - mentioned two - stage compression heat pump. As Figure 2 shown, it includes the following steps: After starting up, run in the dual - machine mode; judge whether the actual operating frequencies of the first compressor 3 and the second compressor 5 are less than or equal to their minimum operating frequencies, and select to switch to the single - machine mode or maintain the dual - machine mode according to the judgment result.

[0053] In this embodiment, running in the dual - machine mode after starting up can enable the two - stage compression heat pump to meet the user's needs as soon as possible; during the operation of the heat pump, if the load decreases, the operating frequency of the compressor will also decrease accordingly. When the operating frequency of the compressor decreases to a certain extent, only the single - machine mode can meet the user's needs. If the dual - machine mode is still running, it may cause the compressor to stop running, and the energy consumption of the dual - machine mode is greater than that of the single - machine mode. In order to prevent the compressor from stopping running and reduce energy consumption while meeting the user's needs, after running in the dual - machine mode, the actual operating frequency of the compressor is detected to judge whether it is necessary to maintain the dual - machine operation.

[0054] Specifically: If the actual operating frequencies of both the first compressor 3 and the second compressor 5 are less than or equal to their minimum operating frequencies, it means that the load is small and only the single - machine mode can meet the user's needs, then switch to the single - machine mode; if the actual operating frequency of the first compressor 3 and / or the second compressor 5 is greater than its minimum operating frequency, then maintain the dual - machine mode.

[0055] The actual operating frequency of the first compressor 3 is fd1, the minimum operating frequency of the first compressor 3 is f11, and the maximum operating frequency of the first compressor 3 is f12; the actual operating frequency of the second compressor 5 is fd2, the minimum operating frequency of the second compressor 5 is f21, and the maximum operating frequency of the second compressor 5 is f22. It should be noted that f11 and f21 can be the same or different. Similarly, f12 and f22 can be the same or different. In the actual application process, the values of f11, f12, f21, and f22 can be determined according to the specific operating conditions of the compressor.

[0056] Further, if the single - machine mode is selected for switching, the cumulative operation durations of the first compressor 3 and the second compressor 5 are compared, and the first compressor 3 or the second compressor 5 is selected for operation according to the comparison result. In this embodiment, selection based on the cumulative operation time of the compressor can prevent a certain compressor from being damaged due to long - term use. Specifically, if the cumulative operation duration of the first compressor 3 is less than or equal to that of the second compressor 5, the first compressor 3 is selected for operation; if the cumulative operation duration of the first compressor 3 is greater than that of the second compressor 5, the second compressor 5 is selected for operation.

[0057] Starting from the commissioning of the two - stage compression heat pump, the operation durations of the first compressor 3 and the second compressor 5 are cumulatively calculated. Each time when switching to the single - machine mode, the compressor with the shorter operation duration is selected. This can prevent the operation times of the first compressor 3 and the second compressor 5 from differing too much, and avoid the situation where one compressor is damaged due to excessive use while the other compressor has hardly been used.

[0058] After selecting to switch to the single - machine mode, which compressor to select for operation can be considered according to the actual situation. It can be selected based on the cumulative operation time of the compressor, or based on the volume size of the compressor, or the single - machine mode can be set to default to operate the first compressor 3 or the second compressor 5.

[0059] Further, after operating in the single - machine mode, it may occur that the load increases and then the operation frequency increases. After the operation frequency increases to a certain extent, it may lead to problems such as compressor damage and a decrease in refrigeration or heating efficiency, and it cannot meet the user's needs as soon as possible. Therefore, the control method further includes the following steps: after switching to the single - machine mode for operation, it is judged whether the actual operation frequency of the corresponding compressor is greater than or equal to its maximum operation frequency, and the single - machine mode is maintained or switched to the two - machine mode according to the judgment result. Specifically, if the actual operation frequency of the corresponding compressor is greater than or equal to its maximum operation frequency, the two - machine mode is switched; if the actual operation frequency of the corresponding compressor is less than its maximum operation frequency, the single - machine mode is maintained.

[0060] If the first compressor 3 operates alone, it is judged whether the actual operation frequency fd1 of the first compressor 3 is greater than or equal to its maximum operation frequency f12; if so, the two - machine mode is switched, and it can be switched to two - machine parallel or two - machine series; if not, the first compressor 3 continues to operate alone. If the second compressor 5 operates alone, it is judged whether the actual operation frequency fd2 of the second compressor 5 is greater than or equal to its maximum operation frequency f22; if so, the two - machine mode is switched, and it can be switched to two - machine parallel or two - machine series; if not, the second compressor 5 continues to operate alone.

[0061] Further, "run in dual - machine mode after startup" specifically means: during heating, after startup, determine whether the actual ambient temperature Ta is greater than or equal to the set temperature T0, and run in dual - machine parallel mode or dual - machine series mode according to the judgment result; and / or during cooling, run in dual - machine parallel mode after startup. The value range of T0 is: - 5 ≤ T0 ≤ 0 °C. Before making the judgment, the actual ambient temperature Ta can be obtained through a temperature sensor.

[0062] When the two - stage compression heat pump is in a low - temperature environment, since series heating can provide a higher pressure ratio and a higher water outlet temperature compared to parallel heating, it is possible to determine whether to run in dual - machine parallel mode or dual - machine series mode based on the temperature. Specifically: if the actual ambient temperature Ta is greater than or equal to the set temperature T0, run in dual - machine parallel mode; if the actual ambient temperature Ta is less than the set temperature T0, run in dual - machine series mode. In the case of cooling, generally, there is no need to increase the pressure ratio in series, so the parallel mode is selected after startup.

[0063] Further, when running in dual - machine series mode, before proceeding to the next step, determine again whether the actual ambient temperature Ta is greater than or equal to the set temperature T0, and select to maintain the dual - machine series mode or switch to dual - machine parallel mode according to the comparison result. Specifically: if the actual ambient temperature Ta is greater than or equal to the set temperature T0, switch to dual - machine parallel mode; if the actual ambient temperature Ta is less than the set temperature T0, maintain the dual - machine series mode. When running in dual - machine series mode, it is also possible to directly judge the operating frequency without making another temperature judgment, but judging the temperature first can ensure that the series mode is maintained when the actual ambient temperature Ta is less than the set temperature T0.

[0064] As Figure 3 shown, in the heating mode, in a possible operating process:

[0065] S201: Obtain the actual ambient temperature Ta.

[0066] S202: Determine whether the actual ambient temperature Ta is greater than or equal to the set temperature T0; if not, execute S203; if so, execute S204.

[0067] S203: Run in dual - machine series mode; then execute S201.

[0068] S204: Run in dual - machine parallel mode; then execute S205.

[0069] S205: Determine whether the actual operating frequency fd1 of the first compressor is less than or equal to its minimum operating frequency f11 and whether the actual operating frequency fd2 of the second compressor is less than or equal to its minimum operating frequency f21; if so, execute S206; if not, execute S204.

[0070] S206: Compare whether the cumulative operation duration t1 of the first compressor is less than or equal to the cumulative operation duration t2 of the second compressor; if so, execute S207; if not, execute S208.

[0071] S207: The first compressor 3 operates; then execute S209.

[0072] S208: The second compressor 5 operates; then execute S210.

[0073] S209: Determine whether the actual operation frequency fd1 of the first compressor 3 is greater than or equal to its maximum operation frequency f12; if so, execute S204; if not, execute S207.

[0074] S210: Determine whether the actual operation frequency fd2 of the second compressor 5 is greater than or equal to its maximum operation frequency f22; if so, execute S204; if not, execute S208.

[0075] As Figure 4 shown, in the refrigeration mode, in a possible operation process:

[0076] S301: Operate in the dual-compressor parallel refrigeration mode.

[0077] S302: Determine whether the actual operation frequency fd1 of the first compressor is less than or equal to its minimum operation frequency f11 and whether the actual operation frequency fd2 of the second compressor is less than or equal to its minimum operation frequency f21; if so, execute S303; if not, execute S301.

[0078] S303: Compare whether the cumulative operation duration t1 of the first compressor is less than or equal to the cumulative operation duration t2 of the second compressor; if so, execute S304; if not, execute S305.

[0079] S304: The first compressor 3 operates; then execute S306.

[0080] S305: The second compressor 5 operates; then execute S307.

[0081] S306: Determine whether the actual operation frequency fd1 of the first compressor 3 is greater than or equal to its maximum operation frequency f12; if so, execute S301; if not, execute S304.

[0082] S307: Determine whether the actual operation frequency fd2 of the second compressor 5 is greater than or equal to its maximum operation frequency f22; if so, execute S301; if not, execute S305.

[0083] Those skilled in the art will understand that although some of the embodiments described herein include certain features included in other embodiments rather than other features, the combination of features of different embodiments is meant to be within the scope of this application and forms different embodiments. For example, in the claims of this application, any of the claimed embodiments can be used in any combination.

[0084] So far, the technical solution of the present invention has been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

Claims

1. A two-stage compression heat pump, characterized in that, Comprising: An intake pipeline and an exhaust pipeline. The air outlet of the intake pipeline can be connected to the air inlet of the first compressor or, through a solenoid valve, to the air inlet of the second compressor. The air outlet of the first compressor can be connected to the exhaust pipeline or the air inlet of the second compressor through a valve body. The air outlet of the second compressor is connected to the exhaust pipeline; A four-way valve. The four-way valve is provided with a first connecting pipe, a second connecting pipe, a third connecting pipe, and a fourth connecting pipe. The exhaust pipeline is connected to the outer port of the first connecting pipe. The inner port of the first connecting pipe can be connected to the inner port of the second connecting pipe or the inner port of the third connecting pipe. The outer ports of the second connecting pipe, the condenser, the throttle valve, the air-side heat exchanger, and the third connecting pipe are connected in sequence, The inner port of the fourth connecting pipe can be connected to the inner port of the second connecting pipe or the inner port of the third connecting pipe, and the outer port of the fourth connecting pipe is connected to the air inlet of the intake pipeline.

2. The two-stage compression heat pump according to claim 1, wherein The two-stage compression heat pump further comprises: a check valve, which is arranged between the air outlet of the first compressor and the exhaust pipeline, restricting the gas flow direction to only flow from the air outlet of the first compressor to the exhaust pipeline.

3. The two-stage compression heat pump according to claim 1, characterized in that, The two-stage compression heat pump further comprises: An oil separator, which is arranged on the exhaust pipeline; An oil return pipeline. One end of the oil return pipeline is connected to the oil separator, and the other end is respectively connected to the first compressor and the second compressor through a first oil return capillary and a second oil return capillary.

4. The two-stage compression heat pump according to claim 3, wherein The second oil return capillary is connected to the oil return port of the second compressor through the solenoid valve; or The second oil return capillary is connected to the oil return port of the second compressor.

5. The two-stage compression heat pump according to claim 1, wherein, The two-stage compression heat pump further comprises: An oil equalizing pipeline. One end of the oil equalizing pipeline is connected to the first compressor, and the other end is connected to the second compressor. An oil equalizing valve is arranged on the oil equalizing pipeline.

6. A control method for a two-stage compression heat pump, which is used to control the two-stage compression heat pump described in any one of claims 1-5, characterized in that, Including the following steps: After starting up, operate in the dual-compressor mode; Judge whether the actual operating frequencies of the first compressor and the second compressor are less than or equal to their minimum operating frequencies, and select to switch to the single-compressor mode or maintain the dual-compressor mode according to the judgment result.

7. The control method of the two-stage compression heat pump according to claim 6, wherein If it is selected to switch to the single-compressor mode, compare the cumulative operating durations of the first compressor and the second compressor, and select the first compressor or the second compressor to work according to the comparison result.

8. The control method of the two-stage compression heat pump according to claim 6 or 7, characterized in that The control method further comprises the following steps: After switching to the single-compressor mode for operation, judge whether the actual operating frequency of the corresponding compressor is greater than or equal to its maximum operating frequency, and select to maintain the single-compressor mode or switch to the dual-compressor mode according to the judgment result.

9. The control method of the two-stage compression heat pump according to any one of claims 6-8, characterized in that, The "After starting up, operate in the dual-compressor mode" is specifically: During heating, after starting up, judge whether the actual ambient temperature Ta is greater than or equal to the set temperature T0, and operate in the dual-compressor parallel mode or the dual-compressor series mode according to the judgment result; and / or During cooling, operate in the dual-compressor parallel mode after starting up.

10. The control method of the two-stage compression heat pump according to claim 9, characterized in that, The statement "judge whether the actual ambient temperature Ta is greater than or equal to the set temperature T0, and operate in the dual-machine parallel mode or the dual-machine series mode according to the judgment result" specifically means: If the actual ambient temperature Ta is greater than or equal to the set temperature T0, operate in the dual-machine parallel mode; If the actual ambient temperature Ta is less than the set temperature T0, operate in the dual-machine series mode.

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