Auto-cascade heat pump system, expansion valve control method, control device and controller

Abstract

The invention relates to an auto-cascade heat pump system, an expansion valve control method, an expansion valve control device and a controller, the system comprises a compressor, a condensing device, a gas-liquid separation device, an intermediate heat exchanger and an evaporation device which are sequentially and circularly connected, and further comprises a cooling device arranged in the gas-liquid separation device; and the first expansion valve is connected with an inlet of the cooling device and a liquid phase outlet of the gas-liquid separation device, an outlet of the cooling device is connected with an outlet of the evaporation device, and by means of the system, the heating capacity of the auto-cascade heat pump system can be enhanced.

Description

Technical Field

[0001] The present application relates to the technical field of heat pumps, and in particular, to a self-cascade heat pump system, an expansion valve control method, a control device, and a controller. Background Art

[0002] At present, in order to improve the hot water production capacity in a low-temperature environment, a self-cascade heat pump is usually used for heating. The existing cascade heat pump uses a bipolar cycle of a high-temperature stage and a low-temperature stage, and uses two refrigerants with different boiling points to increase the evaporation and condensation temperature difference, so as to achieve the purpose of producing high-temperature hot water in a cold environment.

[0003] The cascade heat pump system is complex and difficult to control. Therefore, azeotropic refrigerant mixtures are generally used to form a cold cycle of the self-cascade heat pump system through single-stage compression. The self-cascade heat pump system usually includes a compressor, a condenser, a gas-liquid separator, an intermediate heat exchanger, an expansion valve, and an evaporator. The compressor compresses the refrigerant mixture into a high-temperature and high-pressure gaseous refrigerant mixture. After the gaseous refrigerant mixture flows into the condenser, the high-boiling refrigerant condenses into a liquid state, and the low-boiling refrigerant is in a gaseous state and is preliminarily separated in the gas-liquid separator. Subsequently, the high-boiling refrigerant flows through the expansion valve and exchanges heat with the low-boiling refrigerant through the intermediate heat exchanger to cool the low-boiling refrigerant. Then, the low-boiling refrigerant flows through the expansion valve and absorbs heat from the low-temperature environment through the evaporator. After that, the low-boiling refrigerant and the high-boiling refrigerant return to the compressor again, thus forming a cycle of the self-cascade heat pump system.

[0004] However, the applicant found during the implementation process that due to the possible problem of insufficient subcooling degree of the condenser of the existing self-cascade heat pump system after long-term use, the separation of the high-boiling refrigerant and the low-boiling refrigerant in the gas-liquid separator is incomplete, thereby affecting the heating capacity of the self-cascade heat pump system. Summary of the Invention

[0005] Based on this, it is necessary to provide a self-cascade heat pump system, an expansion valve control method, a control device, and a controller that can enhance the heating capacity of the self-cascade heat pump system for the above technical problems.

[0006] In a first aspect, a self-cascade heat pump system is provided. The system includes a compressor, a condensation device, a gas-liquid separation device, an intermediate heat exchanger, and an evaporation device that are sequentially connected in a cycle, and further includes:

[0007] A cooling device disposed in the gas-liquid separation device;

[0008] A first expansion valve respectively connected to the inlet of the cooling device and the liquid phase outlet of the gas-liquid separation device, and the outlet of the cooling device is connected to the outlet of the evaporation device.

[0009] The above-mentioned self-cascade heat pump system includes a compressor, a condensation device, a gas-liquid separation device, an intermediate heat exchanger, and an evaporation device that are sequentially connected in a cycle; a cooling device is arranged in the gas-liquid separation device; a first expansion valve is respectively connected to the inlet of the cooling device and the liquid phase outlet of the gas-liquid separation device, and the outlet of the cooling device is connected to the outlet of the evaporation device. With the above structure, a self-cascade refrigeration cycle can be formed by single-stage compression. The cycle system has a simple structure and is convenient to control, realizing refrigeration and heating. And by arranging a cooling device in the gas-liquid separation device, a self-cooling cycle can be formed to achieve the purpose of full gas-liquid separation, so that the low-boiling refrigerant can absorb more heat in the evaporation device and release heat in the condensation device, enhancing the heating capacity.

[0010] In one embodiment, the liquid phase outlet includes a first liquid phase outlet and a second liquid phase outlet; the cooling device includes a cooling coil;

[0011] The first expansion valve is connected to the first liquid phase outlet, and the second liquid phase outlet is connected to the intermediate heat exchanger;

[0012] One end of the cooling coil is connected to the first expansion valve, and the other end is connected to the outlet of the evaporation device.

[0013] In one embodiment, the gas-liquid separation device is further provided with a mixed refrigerant inlet and a gas phase outlet;

[0014] The mixed refrigerant inlet communicates with the condensation device;

[0015] The two heat exchange channels of the intermediate heat exchanger respectively communicate with the gas phase outlet and the second liquid phase outlet, and a second expansion valve is arranged on the connecting pipeline between the intermediate heat exchanger and the second liquid phase outlet.

[0016] In one embodiment, the system further includes:

[0017] A first temperature detection device is arranged at the outlet of the condensation device for detecting the outlet temperature of the condensation device;

[0018] A first pressure detection device is arranged at the outlet of the condensation device for detecting the outlet pressure of the condensation device;

[0019] A controller is electrically connected to the first temperature detection device, the first pressure detection device and the first expansion valve respectively, and is used for controlling the opening or closing of the first expansion valve according to the outlet temperature of the condensation device and the outlet pressure of the condensation device.

[0020] In one embodiment, the liquid phase outlet includes a second liquid phase outlet; the system further includes a second temperature detection device and a second temperature detection device;

[0021] The second temperature detection device is arranged at the second liquid phase outlet for detecting the second liquid phase outlet temperature of the gas-liquid separation device;

[0022] A second pressure detection device is provided at the second liquid phase outlet for detecting the pressure at the second liquid phase outlet of the gas-liquid separation device;

[0023] A controller is electrically connected to the second temperature detection device and the second pressure detection device respectively. The controller is used to control the opening or closing of the first expansion valve according to the temperature and pressure at the second liquid phase outlet.

[0024] In a second aspect, an expansion valve control method is provided, which is applied to the self-cascade heat pump system as described above. The method includes:

[0025] Obtain the outlet temperature and outlet pressure of the condensation device, and determine the saturation temperature corresponding to the outlet pressure of the condensation device;

[0026] If the outlet temperature of the condensation device is less than the saturation temperature corresponding to the outlet pressure of the condensation device, control the first expansion valve to be normally closed;

[0027] If the outlet temperature of the condensation device is greater than or equal to the saturation temperature corresponding to the outlet pressure of the condensation device, control the first expansion valve to be normally open.

[0028] The above expansion valve control method controls the first expansion valve to be normally closed or normally open through the outlet temperature of the condensation device and the saturation temperature corresponding to the outlet pressure of the condensation device. In this way, it can be realized that the first expansion valve is opened when the degree of subcooling is insufficient, so that the refrigerant flows out from the liquid phase outlet, passes through the first expansion valve and enters the cooling device, and the refrigerant in the cooling device forms a self-cooling cycle, ensuring sufficient subcooling degree, thereby enhancing the heating capacity.

[0029] In one embodiment, the method further includes:

[0030] Obtain the temperature and pressure at the second liquid phase outlet of the gas-liquid separation device, and determine the saturation temperature corresponding to the pressure at the second liquid phase outlet;

[0031] If the temperature at the second liquid phase outlet is less than the saturation temperature corresponding to the pressure at the second liquid phase outlet, control the first expansion valve to be normally closed;

[0032] If the temperature at the second liquid phase outlet is greater than or equal to the saturation temperature corresponding to the pressure at the second liquid phase outlet, control the first expansion valve to reduce the preset opening degree, and control the first expansion valve to maintain operation for a preset time after reducing the opening degree.

[0033] In one embodiment, before controlling the first expansion valve to reduce the preset opening degree, it further includes:

[0034] Obtain the opening and closing state of the first expansion valve;

[0035] When in the open / closed state and used to represent that the first expansion valve is closed, control the first expansion valve to open.

[0036] In a third aspect, an expansion valve control device is provided, which is applied to the self-cascade heat pump system as described above. The control device includes:

[0037] A temperature determination module, configured to obtain the outlet temperature and outlet pressure of the condensation device, and determine the saturation temperature corresponding to the outlet pressure of the condensation device;

[0038] A normally closed control module, configured to control the first expansion valve to be normally closed if the outlet temperature of the condensation device is less than the saturation temperature corresponding to the outlet pressure of the condensation device;

[0039] A normally open control module, configured to control the first expansion valve to be normally open if the outlet temperature of the condensation device is greater than or equal to the saturation temperature corresponding to the outlet pressure of the condensation device.

[0040] In a fourth aspect, a controller is provided, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the steps of the method described above are implemented. Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0042] Figure 1 It is a schematic structural diagram of a self-cascade heat pump system in an embodiment;

[0043] Figure 2 It is a schematic structural diagram of a gas-liquid separation device in an embodiment;

[0044] Figure 3 It is a schematic flow diagram of an expansion valve control method in an embodiment;

[0045] Figure 4 It is a schematic flow diagram of an expansion valve control method in another embodiment;

[0046] Figure 5 It is a schematic flow diagram of an expansion valve control method in yet another embodiment;

[0047] Figure 6 It is a schematic block diagram of an expansion valve control device in an embodiment.

[0048] Reference Signs:

[0049] 110 - Compressor; 120 - Condensing device; 130 - Gas-liquid separation device; 140 - Intermediate heat exchanger; 150 - Evaporation device; 170 - Cooling device; 180 - First expansion valve; 190 - Second expansion valve; 131 - First liquid phase outlet; 132 - Second liquid phase outlet; 171 - Cooling coil; 1711 - One end of the cooling coil; 1712 - The other end of the cooling coil; 133 - Mixed refrigerant inlet; 134 - Gas phase outlet; 100 - Four-way valve; 160 - Gas-liquid separator. Detailed implementation mode

[0050] To facilitate the understanding of the present application, the present application will be described more comprehensively below with reference to the relevant drawings. Embodiments of the present application are shown in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present application more thorough and comprehensive.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the specification of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0052] It can be understood that the terms "first", "second", etc. used in this application can be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from another element.

[0053] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element or connected to the other element through an intermediate element. In addition, in the following embodiments, "connection", if there is a transmission of electrical signals or data between the connected objects, should be understood as "electrical connection", "communication connection", etc.

[0054] As used herein, the singular forms "a", "an" and "the" may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" or "having", etc. specify the presence of the stated features, wholes, steps, operations, components, parts or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts or combinations thereof.

[0055] As described in the background art, there is a problem of insufficient heating capacity in the self-cascade heat pump system in the prior art. After research by the applicant, it is found that the reason for this problem is that after the condenser of the self-cascade heat pump system is used for a long time, there may be a problem of insufficient subcooling degree, resulting in incomplete separation of the high-boiling refrigerant and the low-boiling refrigerant in the gas-liquid separator.

[0056] For the above reasons, the present invention provides a self-cascade heat pump system, an expansion valve control method, a control device and a controller that can enhance the heating capacity of the self-cascade heat pump system.

[0057] In an exemplary embodiment, as Figure 1 shown, a self-cascade heat pump system is provided. The system includes a compressor 110, a condensation device 120, a gas-liquid separation device 130, an intermediate heat exchanger 140, and an evaporation device 150 that are sequentially connected in a cycle, and further includes:

[0058] A cooling device 170, which is arranged in the gas-liquid separation device 130.

[0059] A first expansion valve 180, which is respectively connected to the inlet of the cooling device 170 and the liquid phase outlet of the gas-liquid separation device 130, and the outlet of the cooling device 170 is connected to the outlet of the evaporation device 150.

[0060] Among them, the cooling device 170 can be a device for cooling the liquid in the gas-liquid separation device 130. The cooling device 170 can be used for self-circulation cooling of the gas-liquid separation device 130 to reduce the temperature of the liquid in the gas-liquid separation device 130, so as to ensure sufficient subcooling degree. The gas-liquid separation device 130 can be a liquid storage tank or a gas-liquid separator. The first expansion valve 180 can be a common valve element in a refrigeration and heating system. The first expansion valve 180 can be used for throttling or controlling the refrigerant flow rate; the first expansion valve 180 can be an electronic expansion valve. The liquid phase outlet of the gas-liquid separation device 130 can be an outlet for the liquid refrigerant in the gas-liquid separation device 130 to flow out.

[0061] Exemplarily, the self-cascade heat pump system can include a compressor 110, a condensation device 120, a gas-liquid separation device 130, an intermediate heat exchanger 140, an evaporation device 150 that are sequentially connected in a cycle, a cooling device 170 arranged in the gas-liquid separation device 130, and a first expansion valve 180 that is respectively connected to the inlet of the cooling device 170 and the liquid phase outlet of the gas-liquid separation device 130; among them, the outlet of the cooling device 170 is connected to the outlet of the evaporation device 150, so as to return the liquid flowing in the cooling device 170 to the compressor 110.

[0062] In the specific implementation process, the compressor 110 can compress the mixed refrigerant into a high-temperature and high-pressure gaseous mixed refrigerant. After the gaseous mixed refrigerant flows into the condenser, the high-boiling refrigerant condenses into a liquid state, and the low-boiling refrigerant remains in a gaseous state and is preliminarily separated in the gas-liquid separator. When the supercooling degree of the liquid high-boiling refrigerant is insufficient, the first expansion valve 180 can be opened. After the liquid high-boiling refrigerant is cooled by the first expansion valve 180, it flows into the cooling device 170 in the gas-liquid separation device 130 again to cool the liquid high-boiling refrigerant, thereby forming a self-cooling cycle process. In this way, it can be ensured that the liquid high-boiling refrigerant has sufficient supercooling degree in the gas-liquid separation device 130.

[0063] Subsequently, the high-boiling refrigerant flows through another expansion valve and exchanges heat with the low-boiling refrigerant through the intermediate heat exchanger 140 to cool the low-boiling refrigerant. After heat exchange, the low-boiling refrigerant releases heat and becomes a liquid, and the high-boiling refrigerant absorbs heat and becomes a gas. Then the low-boiling refrigerant flows through another expansion valve and absorbs heat through the evaporation device 150 to achieve refrigeration. After the low-boiling refrigerant evaporates, it becomes a gas. Then the low-boiling refrigerant and the high-boiling refrigerant, both in a gaseous state, return to the compressor 110 after passing through another gas-liquid separator, thereby forming a cycle of a self-cascade heat pump system.

[0064] In this embodiment, the self-cascade heat pump system includes a compressor, a condensation device, a gas-liquid separation device, an intermediate heat exchanger, and an evaporation device that are sequentially connected in a cycle; a cooling device is arranged in the gas-liquid separation device; a first expansion valve is respectively connected to the inlet of the cooling device and the liquid phase outlet of the gas-liquid separation device, and the outlet of the cooling device is connected to the outlet of the evaporation device. With the above structure, a self-cascade refrigeration cycle can be formed through single-stage compression. The cycle system has a simple structure, is convenient to control, can achieve refrigeration and heating, and by arranging a cooling device in the gas-liquid separation device, a self-cooling cycle can be formed to achieve the purpose of full gas-liquid separation, so that the low-boiling refrigerant can absorb more heat in the evaporation device and release heat in the condensation device, enhancing the heating capacity.

[0065] In an exemplary embodiment, as Figure 1 、 2 shown, Figure 2 in, (a) is a sectional structure diagram of the gas-liquid separation device 130, and (b) is a front structure diagram of the gas-liquid separation device 130.

[0066] The liquid phase outlet includes a first liquid phase outlet 131 and a second liquid phase outlet 132; the cooling device 170 includes a cooling coil 171;

[0067] The first expansion valve 180 is connected to the first liquid phase outlet 131, and the second liquid phase outlet 132 is connected to the intermediate heat exchanger 140.

[0068] One end 1711 of the cooling coil 171 is connected to the first expansion valve 180, and the other end 1712 is connected to the outlet of the evaporation device 150.

[0069] Among them, the first liquid phase outlet 131 can be an outlet for realizing cooling reflux. The second liquid phase outlet 132 can be an outlet for the liquid high-boiling refrigerant to flow to the intermediate heat exchanger 140. One end of the cooling coil 170 can be the liquid inlet end, and the other end can be the liquid outlet end.

[0070] Exemplarily, the first liquid phase outlet 131 and the second liquid phase outlet 132 can be arranged below the bottom of the gas-liquid separation device 130 so that the liquid high-boiling refrigerant can easily flow out. The first expansion valve 180 is connected to the first liquid phase outlet 131 and is connected to the inlet of the cooling coil 170, so that the liquid high-boiling refrigerant flowing out from the first liquid phase outlet 131 is cooled by the first expansion valve 180 and then flows back into the cooling coil 170 in the gas-liquid separation device 130 to cool the liquid high-boiling refrigerant in the gas-liquid separation device 130, thereby forming a self-cooling circulation process. The outlet of the cooling coil 170 can be connected to the outlet of the evaporation device 150 so that the liquid high-boiling refrigerant flowing into the cooling coil 170 can flow back to the compressor.

[0071] In this embodiment, the first expansion valve is arranged to be connected to the first liquid phase outlet, and the second liquid phase outlet is connected to the intermediate heat exchanger; and a cooling coil is arranged, with one end connected to the first expansion valve and the other end connected to the outlet of the evaporation device. With this structure, the cooling circulation reflux of the gas-liquid separation device can be effectively realized. In the case of insufficient subcooling degree, the high-boiling refrigerant flowing out of the gas-liquid separation device is cooled by the first expansion valve and then further cooled by the cooling coil in the gas-liquid separation device. The cooling coil can more effectively cool the high-boiling refrigerant, thereby improving the heating capacity of the self-cascade heat pump system.

[0072] In an exemplary embodiment, as Figure 1 、 2 shown, the gas-liquid separation device 130 is further provided with a mixed refrigerant inlet 133 and a gas phase outlet 134;

[0073] The mixed refrigerant inlet 133 communicates with the condensing device 120.

[0074] The two heat exchange channels of the intermediate heat exchanger 140 communicate with the gas phase outlet 134 and the second liquid phase outlet 132 respectively, and a second expansion valve 190 is arranged on the pipeline connecting the intermediate heat exchanger 140 and the second liquid phase outlet 132.

[0075] Among them, the mixed refrigerant inlet 133 can be an inlet through which the mixed refrigerant flows in from the condensing device 120. The gas-phase outlet 134 can be an outlet through which the low-boiling refrigerant in the gas-liquid separation device 130 flows out. The heat exchange channel can be a channel for heat exchange between the liquid high-boiling refrigerant and the gaseous low-boiling refrigerant. In the heat exchange channel, the low-boiling refrigerant releases heat and turns into a liquid, and the high-boiling refrigerant absorbs heat and turns into a gas. The second expansion valve can be a common valve element in the refrigeration and heating system and can be used for throttling or controlling the refrigerant flow rate; the second expansion valve can be an electronic expansion valve.

[0076] Exemplarily, the mixed refrigerant inlet 133 can be arranged above the gas-liquid separation device 130, and the gas-phase outlet 134 can be arranged above the top of the gas-liquid separation device 130 so that the gaseous low-boiling refrigerant can fully flow to the intermediate heat exchanger 140.

[0077] The mixed refrigerant inlet 133 of the gas-liquid separation device 130 is connected to the outlet of the condensing device 120 so that the high-boiling refrigerant and the low-boiling refrigerant condensed by the condensing device 120 flow into the gas-liquid separation device 130, and the gas-liquid separation device 130 can separate the liquid high-boiling refrigerant and the gaseous low-boiling refrigerant.

[0078] The two heat exchange channels of the intermediate heat exchanger 140 are respectively connected to the gas-phase outlet 134 and the second liquid-phase outlet 132. The liquid high-boiling refrigerant flows out from the second liquid-phase outlet 132, flows through the second expansion valve and then into one heat exchange channel of the intermediate heat exchanger 140, and the gaseous low-boiling refrigerant flows into the other heat exchange channel of the intermediate heat exchanger 140 through the gas-phase outlet 134.

[0079] In this embodiment, the mixed refrigerant inlet is connected to the condensing device, and the two heat exchange channels of the intermediate heat exchanger are respectively connected to the gas-phase outlet and the second liquid-phase outlet, and a second expansion valve is arranged on the connecting pipeline between the intermediate heat exchanger and the second liquid-phase outlet. Through the above structure, it is possible to make the high-boiling refrigerant and the low-boiling refrigerant after gas-liquid separation and having sufficient subcooling degree fully flow into the intermediate heat exchanger for heat exchange, thereby improving the heating capacity.

[0080] In an exemplary embodiment, as Figure 1 shown, the auto-cascade heat pump system further includes a four-way valve 100 and a gas-liquid separator 160, including:

[0081] The outlet of the condensation device 120 is connected to the inlet of the gas-liquid separation device 130. The condensed mixed refrigerant flows into the gas-liquid separation device 130 for gas-liquid separation. The low-boiling-point gaseous refrigerant flows out from the upper part of the gas-liquid separation device 130, and the high-boiling-point liquid refrigerant flows out from the lower outlet of the gas-liquid separation device 130. A part of the high-boiling-point refrigerant liquid flows through the electronic expansion valve to be cooled and then flows into the cooling device 170 in the gas-liquid separation device 130 again to cool the liquid refrigerant. The cooled refrigerant flows into the gas-phase outlet of the intermediate heat exchanger 140, thus forming a self-cooling cycle process. A part of the high-boiling-point refrigerant liquid flows through the first expansion valve 180 to be cooled and then flows into the intermediate heat exchanger 140. The upper outlet of the gas-liquid separation device 130 is connected to the inlet of the intermediate heat exchanger 140, and the other lower outlet of the gas-liquid separation device 130 is connected to the inlet of the intermediate heat exchanger 140 through the second expansion valve 190. The low-boiling-point gaseous refrigerant flowing out from the upper part of the gas-liquid separation device 130 flows into the intermediate heat exchanger 140 and exchanges heat with the high-boiling-point liquid refrigerant. After heat exchange, the low-boiling-point gaseous refrigerant releases heat and becomes a liquid, and the high-boiling-point liquid refrigerant absorbs heat and becomes a gas. The liquid outlet of the intermediate heat exchanger 140 is connected to the inlet of the evaporation device 150 through the second expansion valve 190. The low-boiling-point liquid refrigerant flows through the second expansion valve 190 to be cooled twice and then flows into the evaporation device 150, absorbs heat in the evaporation device 150 and becomes a gaseous refrigerant, and is mixed with the high-boiling-point refrigerant. At this time, the refrigerant is in a gas-liquid mixed state. The outlet of the evaporation device 150 is connected to the inlet of the four-way valve 100, and the outlet of the four-way valve 100 is connected to the inlet of the gas-liquid separator 160. The mixed refrigerant flows through the four-way valve 100 and then flows into the gas-liquid separator 160 for gas-liquid separation. The outlet of the gas-liquid separator 160 is connected to the inlet of the compressor 110. The mixed refrigerant is compressed into a high-temperature and high-pressure refrigerant gas in the compressor 110. The outlet of the compressor 110 is connected to the inlet of the four-way valve 100, and the outlet of the four-way valve 100 is connected to the inlet of the condensation device 120. The mixed refrigerant gas is condensed into a refrigerant in a gas-liquid coexistence state in the condensation device 120 and then flows into the gas-liquid separation device 130 for gas-liquid separation, thus forming a system cycle.

[0082] In an exemplary embodiment, the system further includes:

[0083] A first temperature detection device, disposed at the outlet of the condensation device, for detecting the outlet temperature of the condensation device;

[0084] A first pressure detection device, disposed at the outlet of the condensation device, for detecting the outlet pressure of the condensation device;

[0085] A controller, electrically connected to the first temperature detection device, the first pressure detection device and the first expansion valve respectively, for controlling the opening or closing of the first expansion valve according to the outlet temperature and the outlet pressure of the condensation device.

[0086] Among them, the first temperature detection device can be used to detect the liquid temperature at the outlet. The first pressure detection device can be used to detect the liquid pressure at the outlet.

[0087] Exemplarily, a first temperature detection device and a first pressure detection device can be provided at the outlet of the condensing device, which are respectively used to detect the outlet temperature and the outlet pressure of the condensing device. The controller can be electrically connected to the first temperature detection device and the first pressure detection device respectively. The controller can obtain the outlet temperature of the condensing device and the outlet pressure of the condensing device. The controller can also obtain the saturation temperature corresponding to the outlet pressure of the condensing device according to the preset pressure-enthalpy diagram. Further, according to the outlet temperature of the condensing device and the saturation temperature corresponding to the outlet pressure of the condensing device, it can be determined whether the refrigerant flowing through the outlet of the condensing device has sufficient subcooling degree. For example, if the outlet temperature of the condensing device is lower than the saturation temperature corresponding to the outlet pressure of the condensing device, it can be considered that there is sufficient subcooling degree.

[0088] The controller is also electrically connected to the first expansion valve. In the case where the refrigerant flowing through the outlet of the condensing device does not have sufficient subcooling degree, the first expansion valve can be controlled to open, so that the liquid high-boiling refrigerant flows through the first expansion valve and cools down, and then flows into the cooling device in the gas-liquid separation device again to cool the liquid high-boiling refrigerant, thereby forming a self-cooling cycle process. In the case where the refrigerant flowing through the outlet of the condensing device has sufficient subcooling degree, the first expansion valve can be controlled to close.

[0089] In this embodiment, by providing a first temperature detection device, which is arranged at the outlet of the condensing device and is used to detect the outlet temperature of the condensing device; a first pressure detection device, which is arranged at the outlet of the condensing device and is used to detect the outlet pressure of the condensing device; and a controller, which is electrically connected to the first temperature detection device, the first pressure detection device and the first expansion valve respectively, and is used to control the opening or closing of the first expansion valve according to the outlet temperature of the condensing device and the outlet pressure of the condensing device, when the refrigerant does not have sufficient subcooling degree, the first expansion valve can be controlled to open, so as to improve the heating capacity of the self-cascade heat pump system.

[0090] In an exemplary embodiment, the liquid phase outlet includes a second liquid phase outlet; the system further includes a second temperature detection device and a second temperature detection device;

[0091] The second temperature detection device is arranged at the second liquid phase outlet and is used to detect the temperature of the second liquid phase outlet of the gas-liquid separation device.

[0092] The second pressure detection device is arranged at the second liquid phase outlet and is used to detect the pressure of the second liquid phase outlet of the gas-liquid separation device.

[0093] A controller is electrically connected to a second temperature detection device and a second pressure detection device respectively. The controller is used to control the opening or closing of the first expansion valve according to the second liquid-phase outlet temperature and the second liquid-phase outlet pressure.

[0094] Among them, the second temperature detection device can be used to detect the liquid temperature at the second liquid-phase outlet. The second pressure detection device can be used to detect the liquid pressure at the second liquid-phase outlet.

[0095] Exemplarily, a second temperature detection device and a second pressure detection device can be arranged at the second liquid-phase outlet, which are respectively used to detect the second liquid-phase outlet temperature and the second liquid-phase outlet pressure of the gas-liquid separation device. The controller can be respectively connected to the second temperature detection device and the second pressure detection device. The controller can obtain the second liquid-phase outlet temperature and the second liquid-phase outlet pressure at the second liquid-phase outlet. The controller can also obtain the saturation temperature corresponding to the second liquid-phase outlet pressure according to the preset pressure-enthalpy diagram. Further, it can be determined whether the refrigerant flowing through the second liquid-phase outlet has sufficient subcooling degree according to the second liquid-phase outlet temperature and the saturation temperature corresponding to the second liquid-phase outlet pressure.

[0096] The controller can also control the opening or closing of the first expansion valve according to the second liquid-phase outlet temperature and the second liquid-phase outlet pressure. For example, if the refrigerant flowing through the second liquid-phase outlet has sufficient subcooling degree, the first expansion valve can be controlled to close. At this time, it is still necessary to detect whether there is subcooling degree at the second liquid-phase outlet. If there is no subcooling degree, it is also necessary to detect whether the first expansion valve is open. If it is not open, the valve needs to be opened first, and then the opening degree of the first expansion valve is reduced according to the preset current value, and the preset time is run. Then, it is detected whether there is subcooling degree at the second liquid-phase outlet again. If there is still none, the opening degree of the first expansion valve is reduced again, and so on in a cycle. This control mode can be enabled when the use time of the condensing device is too long, the thermal resistance increases, and the equipment performance deteriorates and cannot reach a certain subcooling degree, so as to improve the performance of the self-cascade heat pump system under full operating conditions.

[0097] In this embodiment, by providing a second temperature detection device at the second liquid-phase outlet for detecting the second liquid-phase outlet temperature of the gas-liquid separation device, and a second pressure detection device is also provided at the second liquid-phase outlet for detecting the second liquid-phase outlet pressure of the gas-liquid separation device, and the controller controls the opening or closing of the first expansion valve according to the second liquid-phase outlet temperature and the second liquid-phase outlet pressure, it can ensure that the refrigerant flowing out of the second liquid-phase outlet has sufficient subcooling degree and improve the heating capacity of the self-cascade heat pump system under full operating conditions.

[0098] In an exemplary embodiment, as Figure 3 shown, a method for controlling an expansion valve is provided. Taking this method applied to a controller as the execution subject as an example for description, this method is applied to the self-cascade heat pump system as described above. This method includes S302 to S306, where:

[0099] S302, Obtain the outlet temperature and outlet pressure of the condensation device, and determine the saturation temperature corresponding to the outlet pressure of the condensation device;

[0100] S304, If the outlet temperature of the condensation device is less than the saturation temperature corresponding to the outlet pressure of the condensation device, then control the first expansion valve to be normally closed;

[0101] S306, If the outlet temperature of the condensation device is greater than or equal to the saturation temperature corresponding to the outlet pressure of the condensation device, then control the first expansion valve to be normally open.

[0102] Wherein, the outlet temperature of the condensation device may be the liquid temperature of the liquid high-boiling refrigerant flowing out of the outlet of the condensation device. The outlet pressure of the condensation device may be the liquid pressure of the outlet pressure of the condensation device.

[0103] Exemplarily, the controller may obtain the outlet temperature of the condensation device detected by the first temperature detection device and the outlet pressure of the condensation device detected by the first pressure detection device, and may obtain the saturation temperature corresponding to the outlet pressure of the condensation device according to a preset pressure-enthalpy diagram. The controller may compare the outlet temperature of the condensation device with the saturation temperature corresponding to the outlet pressure of the condensation device. If the outlet temperature of the condensation device is less than the saturation temperature corresponding to the outlet pressure of the condensation device, it may indicate that the liquid high-boiling refrigerant flowing out of the outlet of the condensation device has a degree of subcooling, and the controller may control the first expansion valve to be normally closed. If the outlet temperature of the condensation device is greater than or equal to the saturation temperature corresponding to the outlet pressure of the condensation device, it may indicate that the liquid high-boiling refrigerant flowing out of the outlet of the condensation device has no degree of subcooling, and the controller may control the first expansion valve to be normally open, so that after the liquid high-boiling refrigerant is cooled by passing through the first expansion valve, it flows back into the cooling device in the gas-liquid separation device again to cool the liquid high-boiling refrigerant, thereby forming a self-cooling cycle process to ensure that the circulating refrigerant has a degree of subcooling and improve the heating capacity of the self-cascade heat pump system.

[0104] In this embodiment, by the outlet temperature of the condensation device and the saturation temperature corresponding to the outlet pressure of the condensation device, control the first expansion valve to be normally closed or normally open. In this way, it is possible to realize that the first expansion valve is opened when the degree of subcooling is insufficient, so that the refrigerant flows out from the liquid phase outlet, passes through the first expansion valve and enters the cooling device to cool the refrigerant in the cooling device, forming a self-cooling cycle, ensuring a sufficient degree of subcooling, and thus enhancing the heating capacity.

[0105] In an exemplary embodiment, as Figure 4 shown, the method further includes S402 to S406, wherein:

[0106] S402, obtain the temperature and pressure at the second liquid phase outlet of the gas-liquid separation device, and determine the saturation temperature corresponding to the pressure at the second liquid phase outlet;

[0107] S404, if the temperature at the second liquid phase outlet is less than the saturation temperature corresponding to the pressure at the second liquid phase outlet, control the first expansion valve to be normally closed;

[0108] S406, if the temperature at the second liquid phase outlet is greater than or equal to the saturation temperature corresponding to the pressure at the second liquid phase outlet, control the first expansion valve to reduce the preset opening degree, and control the first expansion valve to maintain operation for a preset time after reducing the opening degree.

[0109] Among them, the temperature at the second liquid phase outlet can be the liquid temperature of the high-boiling refrigerant flowing out of the second liquid phase outlet. The pressure at the second liquid phase outlet can be the liquid pressure of the high-boiling refrigerant flowing out of the phase outlet. The preset opening degree can be controlled according to a preset current value.

[0110] Exemplarily, the controller can obtain the temperature at the second liquid phase outlet detected by the second temperature detection device and the pressure at the second liquid phase outlet detected by the second pressure detection device, and can obtain the saturation temperature corresponding to the pressure at the second liquid phase outlet according to a preset pressure-enthalpy diagram. If the temperature at the second liquid phase outlet is less than the saturation temperature corresponding to the pressure at the second liquid phase outlet, it can indicate that the liquid high-boiling refrigerant flowing out of the second liquid phase outlet has subcooling. The controller can control the first expansion valve to be normally closed. At this time, it is still necessary to detect whether there is subcooling at the second liquid phase outlet. If there is no subcooling, the controller reduces the opening degree of the first expansion valve according to the preset current value, operates for a preset time, and then detects whether there is subcooling at the second liquid phase outlet again. If there is still no subcooling, the opening degree of the first expansion valve is reduced again, and so on in a cycle. This control mode can be enabled when the condensation device has been used for too long, the thermal resistance increases, and the equipment performance deteriorates and cannot reach a certain subcooling degree, thereby improving the performance of the self-cascade heat pump system under full operating conditions.

[0111] In this embodiment, by obtaining the temperature and pressure at the second liquid phase outlet of the gas-liquid separation device and determining the saturation temperature corresponding to the pressure at the second liquid phase outlet; and by judging whether the temperature at the second liquid phase outlet is less than the saturation temperature corresponding to the pressure at the second liquid phase outlet, thereby controlling the opening and closing of the first expansion valve, it can ensure that the refrigerant flowing out of the second liquid phase outlet has sufficient subcooling and improve the heating capacity of the self-cascade heat pump system under full operating conditions.

[0112] In an exemplary embodiment, before controlling the first expansion valve to reduce the preset opening degree, it further includes:

[0113] Obtain the opening and closing state of the first expansion valve;

[0114] When the opening and closing state is used to represent that the first expansion valve is closed, control the first expansion valve to open.

[0115] Exemplarily, if there is no subcooling degree, the controller also needs to detect whether the first expansion valve is open. If it is not open, the valve needs to be opened first, and then the opening degree of the first expansion valve is reduced according to a preset current value and operated for a preset time, so as to improve the heating capacity of the auto-cascade heat pump system under full operating conditions.

[0116] In this embodiment, after confirming that there is no subcooling degree, it is necessary to first control the first expansion valve to open to ensure that the first expansion valve can realize the cooling cycle and improve the heating capacity of the auto-cascade heat pump system.

[0117] In an exemplary embodiment, as Figure 5 shown, a method for controlling an expansion valve is provided, which is applied to an auto-cascade heat pump system as Figure 1 shown. The method includes:

[0118] S501, detecting the outlet pressure P and the outlet temperature T of the condensing device 120, and obtaining the saturation temperature Tb corresponding to the outlet pressure P according to the pressure-enthalpy diagram.

[0119] S502, judging whether the outlet temperature T of the condensing device 120 is less than the saturation temperature Tb corresponding to the outlet pressure P of the condensing device 120.

[0120] If the outlet liquid of the condensing device 120 has sufficient subcooling degree, that is, the outlet temperature T of the condensing device 120 is lower than the saturation temperature Tb corresponding to the outlet pressure P of the condensing device 120, the high-boiling refrigerant can be fully condensed into liquid, and S503 can be executed at this time; if there is no subcooling degree, S505 is executed.

[0121] S503, closing the first expansion valve 180 in the self-cooling cycle.

[0122] S504, opening the first expansion valve 180 in the self-cooling cycle.

[0123] S505, detecting the second liquid phase outlet pressure P1 and the second liquid phase outlet temperature T1 of the lower part of the gas-liquid separation device 130, and obtaining the saturation temperature Tb1 corresponding to the second liquid phase outlet pressure P1 according to the pressure-enthalpy diagram.

[0124] S506, judging whether the second liquid phase outlet temperature T1 is less than the saturation temperature Tb1 corresponding to the second liquid phase outlet pressure P1.

[0125] If the lower part of the gas-liquid separation device 130 has subcooling degree at the second liquid phase outlet, that is, the second liquid phase outlet temperature T1 is lower than the saturation temperature Tb1 corresponding to the second liquid phase outlet pressure P1, then S507 is executed; if there is no subcooling degree, S508 is executed.

[0126] S507. Close the first expansion valve 180. At this time, it is still necessary to detect whether there is subcooling at the second liquid phase outlet, and return to S505.

[0127] S508. Detect whether the first expansion valve 180 is open. If it is not open, execute S509; if it is open, execute S510.

[0128] S509. Open the first expansion valve 180.

[0129] S510. Reduce the opening degree of the first expansion valve 180 according to a preset current value, and operate for a preset time T2. Return to S505, and then detect whether there is subcooling at the second liquid phase outlet. If there is still no subcooling, reduce the opening degree of the first expansion valve 180 again, and so on in a cycle.

[0130] In this embodiment, the above control method can be enabled when the use time of the condensing device is too long, the thermal resistance increases, and the equipment performance deteriorates and cannot reach a certain degree of subcooling, so as to improve the performance of the self-cascade heat pump system under full operating conditions.

[0131] It should be understood that although the steps in the flowcharts involved in the above-described embodiments are displayed in sequence according to the arrows, these steps do not necessarily have to be executed in the order indicated by the arrows. Unless otherwise clearly stated in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least some of the steps in the flowcharts involved in the above-described embodiments may include multiple steps or multiple stages. These steps or stages do not necessarily have to be executed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be executed alternately or alternately with at least some of the steps or stages in other steps or other steps.

[0132] Based on the same inventive concept, the embodiment of the present application also provides an expansion valve control device for implementing the above-mentioned expansion valve control method. The solution provided by this device to solve the problem is similar to the solution described in the above method. Therefore, the specific limitations in one or more of the following embodiments of the expansion valve control device can refer to the limitations on the expansion valve control method in the above text, and will not be repeated here.

[0133] In an exemplary embodiment, as Figure 6 shown, an expansion valve control device is provided, which is applied to the self-cascade heat pump system as described above. The control device includes: a temperature determination module 610, a normally closed control module 620, and a normally open control module 630, where:

[0134] A temperature determination module 610 is configured to obtain the outlet temperature and outlet pressure of the condensation device, and determine the saturation temperature corresponding to the outlet pressure of the condensation device.

[0135] A normally closed control module 620 is configured to control the first expansion valve to be normally closed if the outlet temperature of the condensation device is less than the saturation temperature corresponding to the outlet pressure of the condensation device.

[0136] A normally open control module 630 is configured to control the first expansion valve to be normally open if the outlet temperature of the condensation device is greater than or equal to the saturation temperature corresponding to the outlet pressure of the condensation device.

[0137] In an exemplary embodiment, the temperature determination module is further configured to obtain the second liquid phase outlet temperature and the second liquid phase outlet pressure of the gas-liquid separation device, and determine the saturation temperature corresponding to the second liquid phase outlet pressure. The normally closed control module is further configured to control the first expansion valve to be normally closed if the second liquid phase outlet temperature is less than the saturation temperature corresponding to the second liquid phase outlet pressure. The normally open control module is further configured to control the first expansion valve to reduce a preset opening degree and maintain operation for a preset time after reducing the opening degree if the second liquid phase outlet temperature is greater than or equal to the saturation temperature corresponding to the second liquid phase outlet pressure.

[0138] In an exemplary embodiment, the control device further includes an opening / closing state acquisition module.

[0139] The opening / closing state acquisition module is configured to acquire the opening / closing state of the first expansion valve. The normally open control module is further configured to control the first expansion valve to open in the case where the opening / closing state is used to characterize that the first expansion valve is closed.

[0140] Each module in the above expansion valve control device can be implemented in whole or in part by software, hardware, and their combination. The above modules can be embedded in or independent of a processor in a computer device in the form of hardware, or stored in a memory in the computer device in the form of software, so as to be called by the processor to execute the operations corresponding to the above respective modules.

[0141] In an exemplary embodiment, a controller is provided, including a memory and a processor. A computer program is stored in the memory, and when the processor executes the computer program, the steps in the above respective method embodiments are implemented.

[0142] In an exemplary embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps in the above respective method embodiments are implemented.

[0143] In an exemplary embodiment, a computer program product is provided, including a computer program. When the computer program is executed by a processor, the steps in the above respective method embodiments are implemented.

[0144] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, storage, database, or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memories. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, or optical memory, etc. Volatile memory can include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0145] In the description of this specification, the description with reference to terms such as "for example" and "exemplary" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic description of the above terms does not necessarily refer to the same embodiment or example.

[0146] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0147] The above-described embodiments only represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A self - cascading heat pump system, characterized in that, The system includes a compressor (110), a condensing device (120), a gas-liquid separation device (130), an intermediate heat exchanger (140), and an evaporation device (150) that are connected in a cyclic sequence. It further includes: A cooling device (170) disposed within the gas-liquid separation device (130); A first expansion valve (180) that is respectively connected to the inlet of the cooling device (170) and the liquid-phase outlet of the gas-liquid separation device (130), and the outlet of the cooling device (170) is connected to the outlet of the evaporation device (150).

2. The auto-cascade heat pump system according to claim 1, wherein, The liquid-phase outlet includes a first liquid-phase outlet (131) and a second liquid-phase outlet (132); the cooling device (170) includes a cooling coil (171); The first expansion valve (180) is connected to the first liquid-phase outlet (131), and the second liquid-phase outlet (132) is connected to the intermediate heat exchanger (140); One end (1711) of the cooling coil (171) is connected to the first expansion valve (180), and the other end (1712) is connected to the outlet of the evaporation device (150).

3. The self - cascading heat pump system according to claim 2, wherein The gas-liquid separation device (130) is further provided with a mixed refrigerant inlet (133) and a gas-phase outlet (134); The mixed refrigerant inlet (133) communicates with the condensing device (120); Two heat exchange channels of the intermediate heat exchanger (140) respectively communicate with the gas-phase outlet (134) and the second liquid-phase outlet (132), and a second expansion valve (190) (190190) is provided on the pipeline connecting the intermediate heat exchanger (140) and the second liquid-phase outlet (132).

4. The self - cascading heat pump system according to claim 1, characterized in that, The system further includes: A first temperature detection device disposed at the outlet of the condensing device (120) for detecting the outlet temperature of the condensing device (120); A first pressure detection device disposed at the outlet of the condensing device (120) for detecting the outlet pressure of the condensing device (120); A controller that is electrically connected to the first temperature detection device, the first pressure detection device, and the first expansion valve (180) respectively, and is used to control the opening or closing of the first expansion valve (180) according to the outlet temperature of the condensing device (120) and the outlet pressure of the condensing device (120).

5. The auto-cascade heat pump system according to claim 4, characterized in that, The liquid-phase outlet includes a second liquid-phase outlet (132); the system further includes a second temperature detection device and a second temperature detection device; The second temperature detection device is disposed at the second liquid-phase outlet (132) for detecting the second liquid-phase outlet temperature of the gas-liquid separation device (130); The second pressure detection device is disposed at the second liquid-phase outlet (132) for detecting the second liquid-phase outlet pressure of the gas-liquid separation device (130); The controller is electrically connected to the second temperature detection device and the second pressure detection device respectively, and the controller is used to control the opening or closing of the first expansion valve (180) according to the second liquid-phase outlet temperature and the second liquid-phase outlet pressure.

6. A method for controlling an expansion valve, characterized in that, Applied to the self - cascading heat pump system according to any one of claims 1 to 5, the method includes: Obtain the outlet temperature and outlet pressure of the condensation device (120), and determine the saturation temperature corresponding to the outlet pressure of the condensation device (120); If the outlet temperature of the condensation device (120) is less than the saturation temperature corresponding to the outlet pressure of the condensation device (120), control the first expansion valve (180) to be normally closed; If the outlet temperature of the condensation device (120) is greater than or equal to the saturation temperature corresponding to the outlet pressure of the condensation device (120), control the first expansion valve (180) to be normally open.

7. The method according to claim 6, characterized in that, The method further includes: Obtain the second liquid - phase outlet temperature and second liquid - phase outlet pressure of the gas - liquid separation device (130), and determine the saturation temperature corresponding to the second liquid - phase outlet pressure; If the second liquid - phase outlet temperature is less than the saturation temperature corresponding to the second liquid - phase outlet pressure, control the first expansion valve (180) to be normally closed; If the second liquid - phase outlet temperature is greater than or equal to the saturation temperature corresponding to the second liquid - phase outlet pressure, control the first expansion valve (180) to reduce a preset opening degree, and control the first expansion valve (180) to maintain operation for a preset time after reducing the opening degree.

8. The method according to claim 7, wherein Before controlling the first expansion valve (180) to reduce the preset opening degree, it further includes: Obtain the opening - closing state of the first expansion valve (180); In the case where the opening - closing state is used to represent that the first expansion valve (180) is closed, control the first expansion valve (180) to open.

9. An expansion valve control device, characterized in that, Applied to the self - cascading heat pump system according to any one of claims 1 to 5, the control device includes: A temperature determination module, configured to obtain the outlet temperature and outlet pressure of the condensation device (120), and determine the saturation temperature corresponding to the outlet pressure of the condensation device (120); A normally - closed control module, configured to control the first expansion valve (180) to be normally closed if the outlet temperature of the condensation device (120) is less than the saturation temperature corresponding to the outlet pressure of the condensation device (120); and is also configured to control the first expansion valve (180) to be normally closed if the second liquid - phase outlet temperature is less than the saturation temperature corresponding to the second liquid - phase outlet pressure; A normally - open control module, configured to control the first expansion valve (180) to be normally open if the outlet temperature of the condensation device (120) is greater than or equal to the saturation temperature corresponding to the outlet pressure of the condensation device (120); and is also configured to control the first expansion valve (180) to reduce a preset opening degree if the second liquid - phase outlet temperature is greater than or equal to the saturation temperature corresponding to the second liquid - phase outlet pressure, and control the first expansion valve (180) to maintain operation for a preset time after reducing the opening degree.

10. A controller, characterized in that, Comprising a memory and a processor, the memory stores a computer program, characterized in that when the processor executes the computer program, the steps of the method according to any one of claims 6 to 8 are implemented.

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