Shell and tube heat exchanger antifreeze device and air conditioning unit

Abstract

This application relates to an anti-freezing device for shell-and-tube heat exchangers and an air conditioning unit. The anti-freezing device includes a pressurization assembly connected to the shell-and-tube heat exchanger of the air conditioning unit. The pressurization assembly specifically includes a temperature sensing element, a liquid storage tank, a heating element, and a controller. The top of the liquid storage tank is connected to the shell-and-tube heat exchanger; the temperature sensing element is located in the refrigerant flow path of the air conditioning unit; the heating element is located inside the liquid storage tank; and the controller is connected to both the temperature sensing element and the heating element. By using a pressurization assembly connected to the shell-and-tube heat exchanger, this application increases the pressure of the gaseous refrigerant inside the shell-and-tube heat exchanger when there is a risk of freezing of the water. This causes the gaseous refrigerant to condense into a liquid and release heat, thereby heating the liquid refrigerant inside the shell and tubes. The heated liquid refrigerant then exchanges heat with the water inside the heat exchange tubes, effectively preventing the water inside the heat exchange tubes from freezing and solving the technical problem of easy freezing and cracking of the shell-and-tube heat exchanger when the unit is shut down in winter without drainage.

Description

Technical Field

[0001] This application relates to the field of air conditioning technology, and in particular to an antifreeze device for shell and tube heat exchangers and an air conditioning unit. Background Technology

[0002] Modular heating units, designed for low-temperature environments, offer flexible adjustments to the number of units in operation due to their modular design. They are widely used in northern winter heating systems, especially in temperatures as low as -25°C, providing stable heating and significant energy savings. However, a prominent technical issue arises during winter maintenance: when ambient temperatures drop below -5°C, prolonged shutdown of the equipment and failure to promptly drain the circulating water from the shell-and-tube heat exchanger can easily lead to freezing. Since ice is 9% larger than water, the expansion stress from freezing directly impacts the copper tubes of the heat exchanger. Combined with the increased brittleness of metal materials at low temperatures, this double effect can easily cause tube wall rupture. Such freezing cracks not only damage the heat exchanger itself but can also trigger refrigerant leaks, leading to a series of secondary malfunctions such as compressor liquid slugging and short circuits in the electrical control system, severely impacting the equipment's safety and lifespan.

[0003] Currently, the mainstream protective measures adopted in related technologies to address this problem have significant drawbacks: adding electric heating tape significantly increases equipment costs; using antifreeze instead of water reduces heat exchange efficiency and affects heating performance; and adding emergency backup power requires additional investment and poses maintenance risks. Therefore, how to effectively prevent shell-and-tube heat exchangers from freezing and cracking during winter shutdowns without draining water, without affecting the original performance of the equipment, has become a critical issue that urgently needs to be addressed. Summary of the Invention

[0004] This application provides an antifreeze device for shell-and-tube heat exchangers and an air conditioning unit to solve the technical problem of how to effectively prevent shell-and-tube heat exchangers from freezing and cracking when the equipment is shut down and not drained in winter without affecting the original performance of the equipment.

[0005] According to one aspect of the embodiments of this application, this application provides a shell-and-tube heat exchanger antifreeze device, applied in an air conditioning unit with a shell-and-tube heat exchanger. The shell-and-tube heat exchanger antifreeze device includes a pressurization component connected to the shell-and-tube heat exchanger of the air conditioning unit. The pressurization component specifically includes a temperature sensing element, a liquid storage tank, an electric heating element, and a controller, wherein: the top of the liquid storage tank is connected to the shell-and-tube heat exchanger; the temperature sensing element is disposed in the refrigerant flow path of the air conditioning unit; the electric heating element is disposed inside the liquid storage tank; and the controller is connected to the temperature sensing element and the electric heating element respectively.

[0006] Optionally, the pressurization component is used to increase the pressure of the gaseous refrigerant in the shell-and-tube heat exchanger when there is a risk of freezing of the water in the shell-and-tube heat exchanger. This causes the gaseous refrigerant in the shell-and-tube heat exchanger to condense into liquid and heat the liquid refrigerant in the shell and tubes. The heated liquid refrigerant then exchanges heat with the water in the heat exchange tubes to prevent the water in the heat exchange tubes from freezing. The liquid storage tank is used to store the liquid refrigerant. The temperature sensing element is used to detect the system refrigerant temperature of the air conditioning unit. The electric heating element is used to heat the liquid refrigerant in the liquid storage tank, causing the liquid refrigerant to evaporate into gaseous refrigerant, thereby increasing the pressure of the gaseous refrigerant in the liquid storage tank and increasing the pressure of the gaseous refrigerant in the shell-and-tube heat exchanger connected to the liquid storage tank. The controller is used to receive the system refrigerant temperature of the air conditioning unit detected by the temperature sensing element and, if it is determined based on the system refrigerant temperature that there is a risk of freezing of the water in the shell-and-tube heat exchanger, control the electric heating element to heat the liquid refrigerant in the liquid storage tank.

[0007] Optionally, the pressurization assembly also includes a level switch, wherein: the top of the liquid receiver is connected to the refrigerant flow path between the shell-and-tube heat exchanger and the throttle valve of the air conditioning unit; the inlet of the throttle valve is connected to the finned tube heat exchanger of the air conditioning unit; the installation height of the finned tube heat exchanger is higher than the installation height of the liquid receiver and the shell-and-tube heat exchanger; the level switch is located inside the liquid receiver and is used to detect the liquid level of the liquid refrigerant in the liquid receiver.

[0008] Optionally, the controller is connected to a level switch and a throttle valve respectively. The controller is used to obtain the liquid level height when it is determined that there is a risk of freezing of the water in the shell-and-tube heat exchanger, and to generate a heating control signal and send it to the heating element when it is determined that the liquid level height is higher than or equal to the set height of the heating element, so that the heating element heats the liquid refrigerant in the storage tank. Alternatively, the controller is used to control the throttle valve to open when it is determined that the liquid level height is lower than the set height of the heating element, so that the liquid refrigerant in the finned tube heat exchanger flows to the storage tank to raise the liquid level height, and to generate a throttle valve to close and send it to the throttle valve when it is determined that the liquid level height is higher than the set height of the heating element, and to generate a heating control signal and send it to the heating element, so that the heating element heats the liquid refrigerant in the storage tank.

[0009] Optionally, the controller is also used to determine whether there is a risk of freezing of the water in the shell and tube heat exchanger based on the system refrigerant temperature in the following manner: when the air conditioning unit is detected to be shut down, the drain pipe of the shell and tube heat exchanger is blocked, and the system refrigerant temperature is lower than a first preset temperature, it is determined that there is a risk of freezing of the water in the shell and tube heat exchanger.

[0010] Optionally, after the controller controls the heating element to heat the liquid refrigerant in the storage tank, the controller is further configured to: control the heating element to turn off when the system refrigerant temperature is detected to be higher than a second preset temperature, wherein the second preset temperature is higher than a first preset temperature.

[0011] Optionally, the device further includes a refrigerant return path and an electric valve, wherein: the inlet of the refrigerant return path is connected to the refrigerant side at the bottom of the shell-and-tube heat exchanger, the outlet of the refrigerant return path is connected to the bottom of the liquid storage tank, the installation height of the shell-and-tube heat exchanger is higher than the installation height of the liquid storage tank, and the refrigerant return path is used to supply liquid refrigerant in the shell-and-tube heat exchanger back to the liquid storage tank; the electric valve is installed in the refrigerant return path and is used to control the on / off state of the refrigerant return path.

[0012] Optionally, when the air conditioning unit is in cooling mode, the refrigerant in the liquid receiver tank and the refrigerant in the shell-and-tube heat exchanger are both low-pressure refrigerants. The ambient temperature of the environment where the liquid receiver tank is located is higher than the refrigerant temperature inside the liquid receiver tank. The liquid receiver tank is also used to: exchange heat between the refrigerant in the liquid receiver tank and the external environment, so that the remaining liquid refrigerant in the liquid receiver tank absorbs heat and evaporates into gaseous refrigerant, thereby increasing the internal pressure of the liquid receiver tank and forming a relatively high-pressure zone. This allows the remaining liquid refrigerant in the air conditioning unit to be stored in the shell-and-tube heat exchanger and the finned-tube heat exchanger, which belong to the relatively low-pressure zone, thereby increasing the amount of refrigerant liquid in the shell-and-tube heat exchanger and the finned-tube heat exchanger and increasing the subcooling of the refrigerant in the shell-and-tube heat exchanger and the finned-tube heat exchanger.

[0013] Optionally, when the air conditioning unit is in heating mode, the refrigerant in the liquid receiver tank and the refrigerant in the shell-and-tube heat exchanger are both high-pressure refrigerants. The ambient temperature of the environment where the liquid receiver tank is located is lower than the refrigerant temperature inside the liquid receiver tank. The liquid receiver tank is also used to: exchange heat between the refrigerant in the liquid receiver tank and the external environment, so that the remaining gaseous refrigerant in the liquid receiver tank releases heat and condenses into liquid refrigerant, thereby reducing the internal pressure of the liquid receiver tank and forming a relatively low-pressure zone. This allows some of the refrigerant in the shell-and-tube heat exchanger and finned-tube heat exchanger, which belong to the relatively high-pressure zone in the air conditioning unit, to flow back to the liquid receiver tank, thereby reducing the amount of refrigerant liquid in the shell-and-tube heat exchanger and finned-tube heat exchanger and reducing the subcooling of the refrigerant in the shell-and-tube heat exchanger and finned-tube heat exchanger.

[0014] Optionally, the liquid storage tank is wrapped with a heat insulation layer, and the heat insulation layer is provided with an openable and closable heat dissipation window. The controller is connected to the drive component of the heat dissipation window. The controller is also used to: control the heat dissipation window to open when the air conditioning unit is in cooling or heating mode, so as to enhance the heat exchange efficiency between the liquid storage tank and the external environment; and control the heat dissipation window to close when it is determined that the water in the shell and tube heat exchanger is at risk of freezing and enters the antifreeze mode, so as to reduce the heat loss in the liquid storage tank.

[0015] According to another aspect of the embodiments of this application, this application provides an air conditioning unit, including a compressor, a finned tube heat exchanger, a shell and tube heat exchanger, and an antifreeze device for the shell and tube heat exchanger as described above.

[0016] Compared with related technologies, the technical solutions provided in this application have the following advantages:

[0017] This application provides a shell-and-tube heat exchanger antifreeze device, which includes a pressurization assembly connected to the shell-and-tube heat exchanger of an air conditioning unit. The pressurization assembly specifically includes a temperature sensing element, a liquid receiver, an electric heating element, and a controller. The top of the liquid receiver is connected to the shell-and-tube heat exchanger. The temperature sensing element is installed in the refrigerant flow path of the air conditioning unit. The electric heating element is installed inside the liquid receiver. The controller is connected to the temperature sensing element and the electric heating element. This application, by setting up a pressurization component connected to the shell-and-tube heat exchanger, can specifically increase the pressure of the gaseous refrigerant inside the heat exchanger when there is a risk of freezing of the water inside. This causes the gaseous refrigerant to condense into liquid and release heat, thereby heating the liquid refrigerant inside the shell and tubes. The heated liquid refrigerant then exchanges heat with the water inside the heat exchange tubes, effectively preventing the water inside the heat exchange tubes from freezing. This fundamentally avoids the problem of heat exchange tube wall rupture caused by water freezing and expansion, and reduces the risk of secondary failures such as compressor liquid slugging and electrical control system short circuits caused by refrigerant leakage. At the same time, this device does not rely on traditional solutions such as electric heating tape, antifreeze replacement, or emergency backup power. While preventing freezing damage, it does not significantly increase equipment costs or reduce system energy efficiency, ensuring the safety and operating performance of the air conditioning unit in low-temperature environments. It solves the technical problem of how to effectively prevent the shell-and-tube heat exchanger from freezing and cracking when the unit is shut down and not drained in winter without affecting the original performance of the equipment. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0020] Figure 1 This is a simplified diagram of a conventional dual-purpose (cooling and heating) air conditioning unit system;

[0021] Figure 2 This is a schematic diagram of an optional shell-and-tube heat exchanger antifreeze device according to an embodiment of this application;

[0022] Figure 3 This is a schematic diagram of another optional shell-and-tube heat exchanger antifreeze device provided according to an embodiment of this application;

[0023] Figure 4 This is a schematic diagram of another optional shell-and-tube heat exchanger antifreeze device provided according to an embodiment of this application.

[0024] Reference numerals: 101, temperature sensing element; 102, liquid storage tank; 103, heating element; 104, liquid level switch; I, refrigerant return path; G, electric valve. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] In the following description, the use of suffixes such as "module," "part," or "unit" to denote elements is solely for the purpose of illustration and has no specific meaning in itself. Therefore, "module" and "part" may be used interchangeably.

[0027] Conventional dual-purpose air conditioning unit system such as Figure 1 As shown, the air conditioning unit operates as follows: When the flow direction of the four-way reversing valve is the solid line in the diagram, the air conditioning system is in heating mode. The finned tubes act as evaporators, exchanging heat with the low-temperature air in the environment and evaporating. The refrigerant is then compressed by the compressor, heated by water in the shell-and-tube heat exchanger, and condensed into a liquid. It then flows to the expansion valve for throttling and returns to the finned tube inlet. When the flow direction of the four-way reversing valve is the dashed line in the diagram, the system is in cooling mode. In this mode, the finned tubes become the condenser, and the shell-and-tube heat exchanger becomes the evaporator.

[0028] When the ambient temperature is below -5℃, if the equipment is shut down for an extended period and the circulating water in the shell-and-tube heat exchanger is not drained in time, the remaining water is highly susceptible to freezing. Since ice is 9% larger in volume than water, the expansion stress generated by freezing will directly act on the copper tubes of the heat exchanger. Furthermore, the increased brittleness of metal materials at low temperatures, combined with this effect, can easily lead to tube wall rupture. This freezing cracking not only damages the heat exchanger itself but may also cause refrigerant leakage, resulting in a series of secondary failures such as compressor liquid slugging and short circuits in the electrical control system, severely impacting the safety and service life of the equipment.

[0029] To address the problems mentioned in the background art, according to one aspect of the embodiments of this application, an embodiment of a shell-and-tube heat exchanger antifreeze device is provided, applied in an air conditioning unit with a shell-and-tube heat exchanger, such as... Figure 2 As shown, the antifreeze device for the shell-and-tube heat exchanger includes:

[0030] The pressurization component 1 is connected to the shell and tube heat exchanger of the air conditioning unit. It is used to increase the pressure of the gaseous refrigerant in the shell and tube heat exchanger when there is a risk of freezing of the water in the shell and tube heat exchanger. This causes the gaseous refrigerant in the shell and tube heat exchanger to condense into liquid and heat the liquid refrigerant in the shell and tube. The heated liquid refrigerant then exchanges heat with the water in the heat exchange tube to prevent the water in the heat exchange tube from freezing.

[0031] In this embodiment, the pressurization assembly refers to a combination of components that can increase the pressure of the gaseous refrigerant inside the shell-and-tube heat exchanger. Its core function is to induce a change in the refrigerant state through pressure regulation to achieve heating and antifreeze. A shell-and-tube heat exchanger is a common heat exchange device, consisting of a shell and internal heat exchange tubes. Energy transfer is achieved through heat exchange between the medium inside and outside the tubes. In air conditioning units, it can be used as a condenser or evaporator.

[0032] In this embodiment, when there is a risk of freezing of the water inside the shell-and-tube heat exchanger, the pressurization component connected to the shell-and-tube heat exchanger starts to operate. The pressurization component increases the pressure of the gaseous refrigerant inside the shell-and-tube heat exchanger in a specific manner. According to the physical properties of the refrigerant, the gaseous refrigerant condenses into a liquid when the pressure increases, releasing heat during this condensation process. The released heat is transferred to the liquid refrigerant inside the shell and tubes, raising its temperature. Subsequently, the heated liquid refrigerant exchanges heat with the water in the heat exchange tubes of the shell-and-tube heat exchanger, transferring heat to the water and thus maintaining the water temperature above the freezing point, preventing freezing. For example, in a northern winter, when the ambient temperature drops to -8°C, an air conditioning unit shuts down due to a malfunction, and the drain pipe of the shell-and-tube heat exchanger becomes blocked, resulting in residual water inside. At this time, the water inside the shell-and-tube heat exchanger is at risk of freezing. Upon detecting this situation, the pressurization component starts, increasing the pressure of the gaseous refrigerant inside the shell-and-tube heat exchanger through internal structural actions. The refrigerant, initially in a gaseous state, condenses into a liquid state under pressure, releasing heat and raising the temperature of the liquid refrigerant inside the shell and tube from 5°C to 12°C. The heated liquid refrigerant then exchanges heat with the water inside the heat exchange tube, maintaining the water temperature at 3°C ​​and effectively preventing the water from freezing.

[0033] This application, by setting up a pressurization component connected to the shell-and-tube heat exchanger, can specifically increase the pressure of the gaseous refrigerant inside the heat exchanger when there is a risk of freezing of the water inside. This causes the gaseous refrigerant to condense into liquid and release heat, thereby heating the liquid refrigerant inside the shell and tubes. The heated liquid refrigerant then exchanges heat with the water inside the heat exchange tubes, effectively preventing the water inside the heat exchange tubes from freezing. This fundamentally avoids the problem of heat exchange tube wall rupture caused by water freezing and expansion, and reduces the risk of secondary failures such as compressor liquid slugging and electrical control system short circuits caused by refrigerant leakage. At the same time, this device does not rely on traditional solutions such as electric heating tape, antifreeze replacement, or emergency backup power. While preventing freezing damage, it does not significantly increase equipment costs or reduce system energy efficiency, ensuring the safety and operating performance of the air conditioning unit in low-temperature environments. It solves the technical problem of how to effectively prevent the shell-and-tube heat exchanger from freezing and cracking when the unit is shut down and not drained in winter without affecting the original performance of the equipment.

[0034] The pressurization assembly, with the vertical liquid storage tank as its core component, will be explained in detail below.

[0035] In an optional embodiment, such as Figure 3 As shown, the pressurization assembly 1 includes a temperature sensing element 101, a liquid storage tank 102, an electric heating element 103, and a controller (not shown in the figure), wherein:

[0036] The top of the liquid storage tank 102 is connected to the shell and tube heat exchanger, and the liquid storage tank 102 is used to store liquid refrigerant.

[0037] The temperature sensing element 101 is installed in the refrigerant flow path of the air conditioning unit to detect the system refrigerant temperature of the air conditioning unit;

[0038] The electric heating element 103 is disposed inside the liquid storage tank 102 and is used to heat the liquid refrigerant in the liquid storage tank 102, so that the liquid refrigerant evaporates into gaseous refrigerant, thereby increasing the pressure of the gaseous refrigerant in the liquid storage tank 102 and increasing the pressure of the gaseous refrigerant in the shell and tube heat exchanger connected to the liquid storage tank 102.

[0039] The controller is connected to the temperature sensing element 101 and the heating element 103 respectively. It is used to receive the system refrigerant temperature of the air conditioning unit detected by the temperature sensing element 101, and to control the heating element 103 to heat the liquid refrigerant in the storage tank 102 when it is determined that there is a risk of freezing of the water in the shell and tube heat exchanger based on the system refrigerant temperature.

[0040] In this embodiment, the temperature sensing element is a device capable of detecting temperature, such as a temperature sensor, which can convert temperature signals into electrical signals and transmit them to the controller. The liquid storage tank is a container used to store liquid refrigerant and plays a role in regulating the amount of refrigerant and stabilizing the system operation. The heating element is a component that can convert electrical energy into heat energy, such as an electric heating tube, which can heat the liquid refrigerant in the liquid storage tank. The controller is a device that receives various signals and issues control commands according to preset logic, such as a microprocessor, which is the control core of the system.

[0041] In this embodiment, the top of the liquid storage tank is connected to the shell-and-tube heat exchanger, and the tank stores liquid refrigerant. A temperature sensing element is installed in the refrigerant flow path of the air conditioning unit to continuously monitor the system refrigerant temperature and transmit the detected temperature signal to the controller in real time. When the controller determines that there is a risk of freezing of the water in the shell-and-tube heat exchanger based on the received system refrigerant temperature, it sends a control command to the heating element. Upon receiving the command, the heating element starts working and heats the liquid refrigerant in the storage tank. The liquid refrigerant absorbs heat and evaporates into gaseous refrigerant, increasing the pressure inside the storage tank. Since the storage tank is connected to the shell-and-tube heat exchanger, the pressure of the gaseous refrigerant in the shell-and-tube heat exchanger also increases, which in turn causes the gaseous refrigerant to condense and release heat. The released heat then heats the liquid refrigerant in the shell-and-tube heat exchanger. The heated liquid refrigerant then exchanges heat with the water in the heat exchange tubes, thereby maintaining the water in the heat exchange tubes at a certain temperature and preventing it from freezing, thus achieving antifreeze protection for the water inside the shell and tubes. Specifically, for example, if the temperature sensor of an air conditioning unit detects that the system refrigerant temperature has dropped to -3°C, the controller, based on other conditions, determines that the water in the shell-and-tube heat exchanger is at risk of freezing. At this point, the controller sends a heating command to the heating element in the receiver tank, and the heating element begins to operate. Under the heating of the heating element, the liquid refrigerant in the receiver tank gradually evaporates, increasing the amount of gaseous refrigerant, and the pressure inside the receiver tank rises from 0.5 MPa to 0.8 MPa. Because the receiver tank is connected to the shell-and-tube heat exchanger, the pressure inside the heat exchanger also rises simultaneously, causing the gaseous refrigerant to condense and release heat, thus preventing the water from freezing.

[0042] In this embodiment, the temperature sensing element can be installed in any refrigerant flow path of the air conditioning unit to detect the refrigerant temperature of the entire system. Preferably, as follows... Figure 4 As shown, it can be installed in a liquid storage tank to directly detect the temperature of the refrigerant in the tank, or it can be installed in a shell-and-tube heat exchanger to directly detect the temperature of the refrigerant in the shell-and-tube heat exchanger.

[0043] This application achieves precise control of the antifreeze function of shell-and-tube heat exchangers by working in concert with a pressurization assembly consisting of a temperature sensing element, a liquid storage tank, an electric heating element, and a controller.

[0044] In this embodiment, a pressurization assembly consisting of a liquid storage tank, a phase change energy storage module, a heat-conducting sheet, and a pressure sensor can also be provided. During normal operation, the phase change energy storage module absorbs waste heat from the air conditioning system, such as exhaust heat from the compressor, storing the energy as latent heat of phase change. When a freezing risk is detected, the phase change material spontaneously solidifies and releases heat, which heats the refrigerant in the liquid storage tank through the heat-conducting sheet, causing it to evaporate and pressurize without requiring additional electrical energy input. The pressure sensor monitors the system pressure in real time, and when the pressure reaches a preset value, a one-way valve prevents excessive pressurization. In this way, this application can utilize the system's waste heat for energy storage, achieving zero-energy pressurization and overcoming the limitations of electric heating elements relying on external power sources, making it particularly suitable for scenarios without emergency power supplies.

[0045] In this embodiment, a pressurization assembly consisting of a miniature refrigerant circulation pump, a liquid storage tank, a check valve, and a temperature-pressure linkage controller can also be provided. When a freezing risk is detected, the controller starts the miniature refrigerant circulation pump, pressurizing the liquid refrigerant in the storage tank and pumping it into the gaseous refrigerant zone of the shell-and-tube heat exchanger. The liquid refrigerant evaporates rapidly in the high-pressure zone, directly increasing the total mass and pressure of the gaseous refrigerant in the shell-and-tube heat exchanger, causing the original gaseous refrigerant to condense and release heat. The check valve prevents the refrigerant from flowing backward. When the temperature inside the shell-and-tube heat exchanger rises back to a safe value, the circulation pump stops working. Thus, this application achieves pressurization through active refrigerant pumping, resulting in a faster response time, especially suitable for rapid cooling scenarios, and avoiding potential local overheating problems of the heating element.

[0046] In an optional embodiment, such as Figure 4 As shown, the pressurization assembly 1 also includes a level switch 104, wherein:

[0047] The top of the liquid storage tank 102 is connected to the refrigerant flow path between the shell and tube heat exchanger and the throttle valve of the air conditioning unit. The inlet of the throttle valve is connected to the finned tube heat exchanger of the air conditioning unit. The installation height of the finned tube heat exchanger is higher than that of the liquid storage tank 102 and the shell and tube heat exchanger.

[0048] The liquid level switch 104 is installed inside the liquid storage tank 102 and is used to detect the liquid level of the liquid refrigerant inside the liquid storage tank 102.

[0049] In an optional embodiment, the controller is connected to the level switch 104 and the throttle valve respectively. The controller is used to obtain the liquid level height when it is determined that there is a risk of freezing of the water in the shell-and-tube heat exchanger, and to generate a heating control signal and send it to the heating element 103 when it is determined that the liquid level height is higher than or equal to the set height of the heating element 103, so that the heating element 103 heats the liquid refrigerant in the storage tank. Alternatively, the controller is used to control the throttle valve to open when it is determined that the liquid level height is lower than the set height of the heating element 103, so that the liquid refrigerant in the finned tube heat exchanger flows to the storage tank 102 to raise the liquid level height, and to generate a throttle valve to close and send it to the throttle valve when it is determined that the liquid level height is higher than the set height of the heating element 103, and to generate a heating control signal and send it to the heating element 103, so that the heating element 103 heats the liquid refrigerant in the storage tank 102.

[0050] In this embodiment, the liquid level switch is a device for detecting the liquid level in a container, the throttle valve is a component in an air conditioning system used to control the refrigerant flow and reduce the refrigerant pressure, and the flow state of the refrigerant is changed by adjusting the opening degree. The finned tube heat exchanger is a heat exchanger composed of fins and tubes, and the heat exchange efficiency is improved by increasing the heat exchange area. It can be used as an evaporator or condenser in an air conditioning unit.

[0051] In the embodiments of this application, such as Figure 4As shown, the top of the storage tank is connected to the refrigerant flow path between the shell-and-tube heat exchanger and the expansion valve. The inlet of the expansion valve is connected to the finned-tube heat exchanger, and the installation height of the finned-tube heat exchanger is higher than that of the storage tank and the shell-and-tube heat exchanger. A level switch is installed inside the storage tank to detect the liquid refrigerant level. When the controller determines that there is a risk of freezing in the shell-and-tube heat exchanger, it will obtain the liquid level detected by the level switch. If the liquid level is higher than or equal to the set height of the heating element, the controller directly controls the heating element to heat the liquid refrigerant in the storage tank, thereby increasing the pressure of the gaseous refrigerant in the storage tank and the connected shell-and-tube heat exchanger, thus causing the gaseous refrigerant to condense and release heat to achieve antifreeze. If the liquid level is lower than the set height of the heating element, the controller first controls the expansion valve to open. Because the finned-tube heat exchanger is installed at a higher position, the liquid refrigerant inside it flows to the storage tank under gravity, causing the liquid level in the storage tank to rise. When the liquid level exceeds the set height of the heating element, the controller closes the throttle valve and controls the heating element to heat the liquid refrigerant, thus preventing freezing. Specifically, for example, if the controller determines that the water in the shell-and-tube heat exchanger is at risk of freezing, and the level switch detects a liquid level of 10cm in the storage tank while the set height of the heating element is 15cm, the liquid level is lower than the set height. The controller opens the throttle valve, allowing the liquid refrigerant in the finned tube heat exchanger to flow into the storage tank under gravity, gradually raising the liquid level to 18cm. Once the controller detects that the liquid level is higher than the set height of the heating element, it closes the throttle valve and controls the heating element to begin heating, ensuring the heating process proceeds smoothly.

[0052] This application avoids the situation where the heating element cannot heat effectively due to insufficient refrigerant in the storage tank by using a liquid level switch. At the same time, by cooperating with the throttle valve, the refrigerant is replenished, ensuring the continuity and reliability of the heating process. Furthermore, by setting the height difference between the finned tube heat exchanger and the storage tank, the refrigerant flow is achieved by gravity, eliminating the need for an additional power unit, reducing system cost and energy consumption, and further optimizing the performance of the antifreeze device.

[0053] In an optional embodiment, the controller is also configured to determine, based on the system refrigerant temperature, whether there is a risk of freezing of the water inside the shell-and-tube heat exchanger:

[0054] If the air conditioning unit is detected to be shut down, the drain pipe of the shell and tube heat exchanger is blocked, and the system refrigerant temperature is lower than the first preset temperature, it is determined that there is a risk of freezing of the water in the shell and tube heat exchanger.

[0055] In this embodiment, if the unit's water can be drained in time during winter, the freezing of the tubes during shutdown can be largely avoided. However, in extreme cases, if the unit is shut down and the water in the shell-and-tube heat exchanger cannot be drained in time due to special circumstances (such as severe weather or maintenance personnel not being able to arrive in time), the residual circulating water inside the shell-and-tube heat exchanger is very likely to freeze and expand. Therefore, the controller can comprehensively determine whether there is a risk of freezing of the water in the shell-and-tube heat exchanger based on the unit's operating status, the working status of the drain pipe of the shell-and-tube heat exchanger, and the temperature. Specifically, the controller first checks whether the air conditioning unit is in a shutdown state; if the unit is running, there is no need to perform an anti-freeze judgment. Secondly, it checks whether the drain pipe of the shell-and-tube heat exchanger is blocked; if the drainage is unobstructed, freezing can be avoided even if the unit is shut down. Finally, it obtains the system refrigerant temperature detected by the temperature sensing element. When the system refrigerant temperature is lower than a first preset temperature, combined with the first two conditions, the controller determines that there is a risk of freezing of the water in the shell-and-tube heat exchanger. This first preset temperature can be set according to actual needs. For example, if the first preset temperature is set to 2°C, and an air conditioning unit stops operating at night because heating is not required, the controller detects that the unit is in a stopped state. Simultaneously, the controller detects through relevant sensors that the drain pipe of the shell-and-tube heat exchanger is blocked due to impurities. The temperature sensing element detects that the system refrigerant temperature is 1°C, lower than the first preset temperature. Based on this information, the controller determines that the water in the shell-and-tube heat exchanger is at risk of freezing and initiates appropriate anti-freezing measures.

[0056] This application accurately and promptly identifies freezing threats to shell-and-tube heat exchangers, avoiding misjudgments or omissions. A freezing risk is only determined when all three conditions are met simultaneously: unit shutdown, drainage pipe blockage, and system refrigerant temperature below a first preset temperature. This improves the accuracy of anti-freeze control and reduces unnecessary energy consumption.

[0057] In an optional embodiment, after the controller controls the heating element to heat the liquid refrigerant in the storage tank, the controller is further configured to:

[0058] If the system refrigerant temperature is detected to be higher than the second preset temperature, the heating element is controlled to turn off, wherein the second preset temperature is higher than the first preset temperature.

[0059] In this embodiment, after the controller controls the heating element to heat the liquid refrigerant in the storage tank, the temperature sensing element continuously monitors the system refrigerant temperature and feeds the temperature signal back to the controller. When the controller detects that the system refrigerant temperature has risen above a second preset temperature, it indicates that the water in the shell-and-tube heat exchanger is no longer at risk of freezing. The controller then issues a command to shut down the heating element, stopping the heating process. Specifically, for example, the second preset temperature is set to 5°C. Under the heating action of the heating element, the system refrigerant temperature gradually increases. When the temperature sensing element detects that the system refrigerant temperature reaches 6°C, which is higher than the second preset temperature, the controller receives this signal and immediately shuts down the heating element, stopping the heating of the liquid refrigerant in the storage tank.

[0060] This application achieves automatic start-stop control of the heating element by setting a second preset temperature, avoiding energy waste caused by continuous heating of the heating element, and preventing adverse effects on the equipment caused by excessively high system refrigerant temperature, thereby improving the energy efficiency and safety of the system.

[0061] In an optional embodiment, such as Figure 4 As shown, the device also includes a refrigerant return path I and an electric valve G, wherein:

[0062] The inlet of refrigerant return flow path I is connected to the fluorine side at the bottom of the shell and tube heat exchanger, and the outlet of refrigerant return flow path I is connected to the bottom of the liquid storage tank 102. The installation height of the shell and tube heat exchanger is higher than the installation height of the liquid storage tank 102. Refrigerant return flow path I is used to supply the liquid refrigerant in the shell and tube heat exchanger to flow back to the liquid storage tank 102.

[0063] The electric valve G is installed in the refrigerant return flow path I and is used to control the opening and closing of the refrigerant return flow path I.

[0064] In the embodiments of this application, such as Figure 4 As shown, the refrigerant return path is a channel connecting the bottom refrigerant side of the shell-and-tube heat exchanger to the bottom of the receiver tank, used to guide the liquid refrigerant in the shell-and-tube heat exchanger back to the receiver tank. The electric valve can be opened or closed by the controller, thereby controlling the on / off state of the refrigerant return path.

[0065] In this embodiment, the inlet of the refrigerant return path is connected to the refrigerant side at the bottom of the shell-and-tube heat exchanger, and the outlet is connected to the bottom of the storage tank. The shell-and-tube heat exchanger is installed at a height higher than the storage tank. An electric valve is installed on the refrigerant return path to control its opening and closing. When it is necessary for the liquid refrigerant in the shell-and-tube heat exchanger to flow back to the storage tank, the controller opens the electric valve. Due to the height difference between the shell-and-tube heat exchanger and the storage tank, the liquid refrigerant in the shell-and-tube heat exchanger flows into the storage tank through the refrigerant return path under gravity. When refrigerant return is not required, the controller closes the electric valve, blocking the flow of refrigerant.

[0066] This application achieves controllable flow of liquid refrigerant between the shell-and-tube heat exchanger and the liquid storage tank by setting up a refrigerant return path and an electric valve. This facilitates the adjustment of the refrigerant quantity between the two according to system requirements, improves the system's refrigerant utilization rate and control flexibility, and reduces system energy consumption by using gravity to achieve refrigerant flow.

[0067] Air conditioning units typically need to operate in both cooling and heating modes. In heating mode, excessive refrigerant charge leads to severe liquid carryover at the finned tube outlet of the evaporator and excessive subcooling of the shell and tubes of the condenser, significantly reducing heat exchange efficiency. Conversely, insufficient refrigerant charge in cooling mode results in excessive superheat at the shell and tube outlet of the evaporator, reducing heat exchange efficiency and causing insufficient subcooling of the finned tubes, thus affecting cooling capacity. Furthermore, the evaporation temperature in heating mode is usually lower than that in cooling mode, and the refrigerant density is lower. This means that the required refrigerant charge for heating mode is lower than that for cooling mode. Related technologies often require refrigerant level monitoring, refrigerant subcooling monitoring, and active control to dynamically allocate refrigerant; however, these solutions all suffer from rapidly increasing costs or reduced energy efficiency. Therefore, this application provides a method for matching refrigerant charge amounts for cooling and heating without the need for control, which will be described in detail below.

[0068] In an optional embodiment, when the air conditioning unit is in cooling mode, the refrigerant in the liquid receiver 102 and the refrigerant in the shell-and-tube heat exchanger are both low-pressure refrigerants. The ambient temperature of the environment where the liquid receiver is located is higher than the refrigerant temperature inside the liquid receiver 102. The liquid receiver 102 is also used for:

[0069] The refrigerant in the liquid storage tank 102 exchanges heat with the external environment, causing the remaining liquid refrigerant in the liquid storage tank 102 to absorb heat and evaporate into gaseous refrigerant. This increases the internal pressure of the liquid storage tank 102 and forms a relatively high-pressure zone, so that the remaining liquid refrigerant in the air conditioning unit is stored in the shell-and-tube heat exchanger and finned-tube heat exchanger, which belong to the relatively low-pressure zone. This increases the amount of refrigerant liquid in the shell-and-tube heat exchanger and finned-tube heat exchanger and improves the subcooling of the refrigerant in the shell-and-tube heat exchanger and finned-tube heat exchanger.

[0070] In this embodiment, when the air conditioning unit is in cooling mode, both the refrigerant in the liquid receiver tank and the refrigerant in the shell-and-tube heat exchanger are low-pressure refrigerants, and the ambient temperature of the environment surrounding the liquid receiver tank is higher than the temperature of the refrigerant inside the tank. The refrigerant in the liquid receiver tank exchanges heat with the external environment. The remaining liquid refrigerant in the tank absorbs heat from the environment and evaporates into gaseous refrigerant, causing an increase in the internal pressure of the tank and creating a relatively high-pressure zone. Meanwhile, the shell-and-tube heat exchanger and the finned-tube heat exchanger are in a relatively low-pressure zone. Under the influence of the pressure difference, the remaining liquid refrigerant in the air conditioning unit is stored in the shell-and-tube and finned-tube heat exchangers, increasing the refrigerant volume and enhancing the subcooling of the refrigerant. Specifically, for example, in summer cooling mode, the ambient temperature is 35°C, and the refrigerant temperature inside the liquid receiver tank is 10°C. The liquid refrigerant in the tank absorbs heat from the environment and evaporates into gas, causing the pressure inside the tank to rise from 0.3 MPa to 0.4 MPa, creating a relatively high-pressure zone. The pressure inside shell-and-tube heat exchangers and finned tube heat exchangers is relatively low. Under the action of pressure difference, more liquid refrigerant in the system flows to the shell-and-tube heat exchangers and finned tube heat exchangers, increasing the refrigerant liquid volume in the shell-and-tube heat exchangers by 20% and increasing the refrigerant subcooling of the finned tube heat exchangers from 5°C to 8°C.

[0071] This application increases the refrigerant volume in the shell-and-tube heat exchanger and finned-tube heat exchanger under refrigeration conditions by utilizing the heat exchange and pressure difference between the liquid receiver and the external environment. This improves the subcooling of the refrigerant, enhances the refrigeration efficiency and capacity of the air conditioning unit, and optimizes the system performance under refrigeration conditions. It can match the required refrigerant charge amount for refrigeration conditions without the need for control.

[0072] In an optional embodiment, when the air conditioning unit is in heating mode, the refrigerant in the liquid receiver 102 and the refrigerant in the shell-and-tube heat exchanger are both high-pressure refrigerants. The ambient temperature of the environment where the liquid receiver 102 is located is lower than the refrigerant temperature inside the liquid receiver 102. The liquid receiver 102 is also used for:

[0073] The refrigerant in the liquid storage tank 102 exchanges heat with the external environment, causing the remaining gaseous refrigerant in the liquid storage tank 102 to release heat and condense into liquid refrigerant. This reduces the internal pressure of the liquid storage tank 102 and creates a relatively low-pressure zone, allowing some of the refrigerant in the shell-and-tube heat exchanger and finned-tube heat exchanger, which are in a relatively high-pressure zone in the air conditioning unit, to flow back into the liquid storage tank 102. This reduces the amount of refrigerant liquid in the shell-and-tube heat exchanger and finned-tube heat exchanger and lowers the subcooling of the refrigerant in the shell-and-tube heat exchanger and finned-tube heat exchanger.

[0074] In this embodiment, when the air conditioning unit is in heating mode, both the refrigerant in the liquid receiver tank and the refrigerant in the shell-and-tube heat exchanger are high-pressure refrigerants, and the ambient temperature of the environment surrounding the liquid receiver tank is lower than the temperature of the refrigerant inside the liquid receiver tank. The refrigerant in the liquid receiver tank exchanges heat with the external environment. The remaining gaseous refrigerant in the liquid receiver tank releases heat to the environment and condenses into liquid refrigerant, causing a decrease in the internal pressure of the liquid receiver tank, forming a relatively low-pressure area. Meanwhile, the shell-and-tube heat exchanger and the finned-tube heat exchanger are in a relatively high-pressure area. Under the influence of the pressure difference, some of the refrigerant in the shell-and-tube heat exchanger and the finned-tube heat exchanger flows back into the liquid receiver tank, reducing the amount of liquid refrigerant in both and simultaneously reducing the subcooling of the refrigerant. Specifically, for example, in winter heating mode, the ambient temperature is -5°C, and the temperature of the refrigerant inside the liquid receiver tank is 40°C. After the gaseous refrigerant in the liquid receiver tank releases heat to the environment and condenses into liquid, the pressure inside the liquid receiver tank drops from 1.5 MPa to 1.2 MPa, forming a relatively low-pressure area. The pressure inside the shell-and-tube heat exchanger and the finned tube heat exchanger is relatively high. Under the action of the pressure difference, some of the refrigerant flows back from the shell-and-tube heat exchanger and the finned tube heat exchanger to the liquid storage tank, which reduces the amount of refrigerant liquid in the shell-and-tube heat exchanger by 15% and reduces the refrigerant subcooling of the finned tube heat exchanger from 10°C to 6°C.

[0075] This application reduces the amount of refrigerant in the shell-and-tube and finned-tube heat exchangers under heating conditions by utilizing the heat exchange and pressure difference between the storage tank and the external environment. This reduces the subcooling of the refrigerant, avoids the problems of severe liquid carryover at the finned-tube outlet and decreased heat exchange efficiency of the shell-and-tube heat exchanger, optimizes the system performance under heating conditions, and can match the required refrigerant charge amount for heating conditions without control.

[0076] In an optional embodiment, the storage tank 102 is externally wrapped with a heat insulation layer, and the heat insulation layer is provided with an openable and closable heat dissipation window. The controller is connected to the drive component of the heat dissipation window, and the controller is further used for:

[0077] When the air conditioning unit is in cooling or heating mode, the heat dissipation window is opened to enhance the heat exchange efficiency between the liquid storage tank 102 and the external environment.

[0078] When it is determined that there is a risk of freezing in the water inside the shell and tube heat exchanger and the antifreeze mode is entered, the heat dissipation window is closed to reduce heat loss from the storage tank 102.

[0079] In related technologies, the outer shell of the liquid storage tank typically does not have an insulation layer. However, in this application, to improve the heating efficiency of the heating element in anti-freeze mode, an insulation material layer can be wrapped around the outside of the liquid storage tank, thereby reducing heat exchange between the liquid storage tank and the external environment when the heating element is turned on. Simultaneously, to improve the heat exchange efficiency between the refrigerant in the liquid storage tank and the external environment during cooling or heating conditions, an openable and closable window can be provided on the insulation layer, thereby adjusting the heat exchange efficiency between the liquid storage tank and the external environment during cooling or heating conditions.

[0080] In this embodiment, the liquid storage tank is externally wrapped with a heat insulation layer. The heat dissipation vents on the insulation layer are controlled to open and close by a drive component connected to a controller. When the air conditioning unit is in cooling or heating mode, the controller controls the drive component to open the heat dissipation vents, enhancing the heat exchange efficiency between the liquid storage tank and the external environment, thus facilitating the adjustment of the refrigerant quantity under the corresponding operating conditions. When it is determined that the water in the shell-and-tube heat exchanger is at risk of freezing and enters anti-freeze mode, the controller controls the drive component to close the heat dissipation vents, reducing heat loss from the liquid storage tank and ensuring the heating effect of the electric heating element.

[0081] This application incorporates an insulation layer with openable and closable heat dissipation windows. Opening the heat dissipation windows enhances heat exchange efficiency during cooling and heating operations, ensuring the liquid storage tank's ability to regulate the refrigerant volume. Closing the heat dissipation windows in antifreeze mode reduces heat loss and improves the heating efficiency of the electric heating elements, enabling the system to maintain good performance under different operating conditions and further optimizing the overall performance of the device.

[0082] According to another aspect of the embodiments of this application, this application provides an air conditioning unit, including a compressor, a finned tube heat exchanger, a shell and tube heat exchanger, and an antifreeze device for the shell and tube heat exchanger as described above.

[0083] In this embodiment, the compressor is responsible for compressing the refrigerant and driving its circulation within the system; the finned tube heat exchanger and shell-and-tube heat exchanger function as evaporators or condensers, respectively, depending on the operating conditions; the shell-and-tube heat exchanger antifreeze device functions when necessary to prevent the heat exchanger from freezing and cracking, and optimizes system performance under different operating conditions. All components work together to achieve the cooling and heating functions of the air conditioning unit and ensure its safe operation in low-temperature environments.

[0084] In this application, the controller mentioned above can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0085] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A shell-and-tube heat exchanger antifreeze device, applied in an air conditioning unit equipped with a shell-and-tube heat exchanger, characterized in that, The shell-and-tube heat exchanger antifreeze device includes a pressurization assembly connected to the shell-and-tube heat exchanger of the air conditioning unit. The pressurization assembly specifically includes a temperature sensing element, a liquid storage tank, a heating element, and a controller, wherein: The top of the storage tank is connected to the shell-and-tube heat exchanger; The temperature sensing element is disposed in the refrigerant flow path of the air conditioning unit; The heating element is disposed inside the liquid storage tank; The controller is connected to the temperature sensing element and the heating element respectively; The pressurization component is used to increase the pressure of the gaseous refrigerant in the shell-and-tube heat exchanger when there is a risk of freezing of the water in the shell-and-tube heat exchanger. This causes the gaseous refrigerant in the shell-and-tube heat exchanger to condense into liquid and heat the liquid refrigerant in the shell and tubes. The heated liquid refrigerant then exchanges heat with the water in the heat exchange tubes to prevent the water in the heat exchange tubes from freezing. The liquid storage tank is used to store the liquid refrigerant. The temperature sensing element is used to detect the system refrigerant temperature of the air conditioning unit. The electric heating element is used to heat the liquid refrigerant in the liquid storage tank, causing the liquid refrigerant to evaporate into gaseous refrigerant. This increases the pressure of the gaseous refrigerant in the liquid storage tank and also increases the pressure of the gaseous refrigerant in the shell-and-tube heat exchanger connected to the liquid storage tank. The controller is used to receive the system refrigerant temperature of the air conditioning unit detected by the temperature sensing element and, if it is determined based on the system refrigerant temperature that there is a risk of freezing of the water in the shell-and-tube heat exchanger, controls the electric heating element to heat the liquid refrigerant in the liquid storage tank.

2. The apparatus according to claim 1, characterized in that, The pressurization assembly also includes a level switch, wherein: The top of the liquid storage tank is connected to the refrigerant flow path between the shell-and-tube heat exchanger and the throttle valve of the air conditioning unit. The inlet of the throttle valve is connected to the finned tube heat exchanger of the air conditioning unit. The installation height of the finned tube heat exchanger is higher than that of the liquid storage tank and the shell-and-tube heat exchanger. The liquid level switch is installed inside the liquid storage tank and is used to detect the liquid level of the liquid refrigerant inside the liquid storage tank.

3. The apparatus according to claim 2, characterized in that, The controller is connected to the liquid level switch and the throttle valve respectively; The controller is used to obtain the liquid level height when it is determined that there is a risk of freezing in the water in the shell and tube heat exchanger, and to generate a heating control signal and send it to the heating element when it is determined that the liquid level height is higher than or equal to the set height of the heating element, so that the heating element heats the liquid refrigerant in the storage tank. or, The controller is configured to, when determining that the liquid level is lower than the set height of the heating element, control the throttle valve to open so that the liquid refrigerant in the finned tube heat exchanger flows to the storage tank to raise the liquid level; and when determining that the liquid level is higher than the set height of the heating element, generate a throttle valve closing signal and send it to the throttle valve, and generate a heating control signal and send it to the heating element so that the heating element heats the liquid refrigerant in the storage tank.

4. The apparatus according to any one of claims 1 to 3, characterized in that, The controller is also configured to determine, based on the system refrigerant temperature, whether there is a risk of freezing in the water inside the shell-and-tube heat exchanger: If the air conditioning unit is detected to be shut down, the drain pipe of the shell and tube heat exchanger is blocked, and the refrigerant temperature of the system is lower than the first preset temperature, it is determined that there is a risk of freezing of the water in the shell and tube heat exchanger.

5. The apparatus according to claim 4, characterized in that, After the controller controls the heating element to heat the liquid refrigerant in the storage tank, the controller is further configured to: If the system refrigerant temperature is detected to be higher than the second preset temperature, the heating element is controlled to turn off, wherein the second preset temperature is higher than the first preset temperature.

6. The apparatus according to claim 1, characterized in that, The device also includes a refrigerant return path and an electric valve, wherein: The inlet of the refrigerant return flow path is connected to the fluorine side at the bottom of the shell and tube heat exchanger, and the outlet of the refrigerant return flow path is connected to the bottom of the liquid storage tank. The installation height of the shell and tube heat exchanger is higher than the installation height of the liquid storage tank. The refrigerant return flow path is used to allow the liquid refrigerant in the shell and tube heat exchanger to flow back to the liquid storage tank. The electric valve is installed in the refrigerant return flow path and is used to control the opening and closing of the refrigerant return flow path.

7. The apparatus according to claim 2, characterized in that, When the air conditioning unit is in cooling mode, the refrigerant in the liquid receiver tank and the refrigerant in the shell-and-tube heat exchanger are both low-pressure refrigerants. The ambient temperature of the environment where the liquid receiver tank is located is higher than the refrigerant temperature inside the liquid receiver tank. The liquid receiver tank is also used for: The refrigerant in the storage tank exchanges heat with the external environment, causing the remaining liquid refrigerant in the storage tank to absorb heat and evaporate into gaseous refrigerant. This increases the internal pressure of the storage tank and creates a relatively high-pressure zone, allowing the remaining liquid refrigerant in the air conditioning unit to be stored in the shell-and-tube heat exchanger and the finned-tube heat exchanger, which belong to the relatively low-pressure zone. This increases the amount of refrigerant in the shell-and-tube heat exchanger and the finned-tube heat exchanger and enhances the subcooling of the refrigerant in the shell-and-tube heat exchanger and the finned-tube heat exchanger.

8. The apparatus according to claim 2, characterized in that, When the air conditioning unit is in heating mode, the refrigerant in the liquid receiver tank and the refrigerant in the shell-and-tube heat exchanger are both high-pressure refrigerants. The ambient temperature of the environment where the liquid receiver tank is located is lower than the refrigerant temperature inside the liquid receiver tank. The liquid receiver tank is also used for: The refrigerant in the storage tank exchanges heat with the external environment, causing the remaining gaseous refrigerant in the storage tank to release heat and condense into liquid refrigerant. This reduces the internal pressure of the storage tank and creates a relatively low-pressure zone, allowing some of the refrigerant in the shell-and-tube heat exchanger and the finned-tube heat exchanger, which are located in the relatively high-pressure zone of the air conditioning unit, to flow back into the storage tank. This reduces the amount of refrigerant in the shell-and-tube heat exchanger and the finned-tube heat exchanger, and also reduces the subcooling of the refrigerant in the shell-and-tube heat exchanger and the finned-tube heat exchanger.

9. The apparatus according to any one of claims 7 or 8, characterized in that, The storage tank is externally wrapped with a heat insulation layer, and the heat insulation layer is provided with an openable and closable heat dissipation window. The controller is connected to the drive component of the heat dissipation window, and the controller is also used for: When the air conditioning unit is in cooling or heating mode, the heat dissipation window is opened to enhance the heat exchange efficiency between the liquid storage tank and the external environment. When it is determined that the water in the shell and tube heat exchanger is at risk of freezing and enters antifreeze mode, the heat dissipation window is closed to reduce heat loss from the storage tank.

10. An air conditioning unit, comprising a compressor, a finned tube heat exchanger, a shell-and-tube heat exchanger, and a shell-and-tube heat exchanger antifreeze device as described in any one of claims 1 to 9.

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