Carbon dioxide internal defrosting system

Abstract

The utility model discloses a carbon dioxide internal defrosting system which comprises a carbon dioxide circulation loop and an internal defrosting liquid return pipeline, the carbon dioxide circulation loop and the internal defrosting liquid return pipeline are formed by connecting pipelines, the carbon dioxide circulation loop conducts compression refrigeration circulation, and the internal defrosting liquid return pipeline conducts low-temperature defrosting circulation. The internal defrosting liquid return pipeline further comprises a second electromagnetic valve, a third electromagnetic valve and a check valve on the basis of the carbon dioxide circulation loop, the second electromagnetic valve is arranged on the connecting pipeline and connected with the electronic expansion valve in parallel, and a liquid return pipeline connected with the carbon dioxide liquid storage device through the third electromagnetic valve and the check valve is arranged at an outlet of the low-temperature air cooler. The device does not consume electric energy, and is energy-saving and environment-friendly; no risk exists in long-time defrosting, and safety and reliability are achieved; and the defrosting time is short, the defrosting heating area is large, and the defrosting efficiency is high.

Description

TECHNICAL FIELD

[0001] The utility model relates to refrigeration heating technical field, concretely is a kind of carbon dioxide internal defrosting system. BACKGROUND

[0002] Carbon dioxide is a kind of natural refrigerant, green environmental protection, leakage or non-recovery cannot pollute environment;With good thermodynamic characteristics, high thermal conductivity coefficient;Unit volume refrigerating capacity is high, equipment size can be significantly reduced, save material;Low viscosity, good compatibility with lubricating oil;Source is extensive, cheap, can greatly reduce refrigerant replacement cost.

[0003] Carbon dioxide circulation system will include evaporator to provide cold source, and evaporator will be frost under the influence of ambient temperature and humidity, the influence on evaporator is huge.Frost can reduce the heat transfer effect of evaporator, reduce air flow area, store frozen oil, make refrigerant performance decline.Low temperature freezer-18 ℃ to-35 ℃ quick freezer, commonly used defrosting mode has electric defrosting and water defrosting, salt solution defrosting and so on.Electric defrosting high temperature of electric heating pipe, power consumption is large, not energy-saving;Water defrosting has splashing water, water leakage, icing, ice accumulation and other shortcomings;Salt solution defrosting needs additional heat exchange pipe, so that cold air machine becomes huge and cumbersome, reduces refrigeration heat transfer area, also needs to prevent salt solution dilution and freeze.

[0004] Therefore, a new defrosting mode needs to be designed to solve the problems encountered by electric defrosting, water defrosting and salt solution defrosting in low temperature environment. Utility model content

[0005] The utility model aims at solving the problem of defrosting evaporator in carbon dioxide circulation system in low temperature environment, avoiding the shortcomings of existing electric defrosting, water defrosting and salt solution defrosting, and providing a carbon dioxide internal defrosting system which does not consume electric energy, is energy-saving and environmentally friendly, has no risk in long-time defrosting, is safe and reliable, has short defrosting time, large defrosting heating area and high defrosting efficiency.

[0006] To achieve the above object, the utility model provides the following technical scheme:

[0007] The carbon dioxide internal defrosting system comprises a carbon dioxide circulation loop formed by pipeline connection, and an internal defrosting return liquid pipeline, wherein the carbon dioxide circulation loop performs a compression refrigeration cycle, and the internal defrosting return liquid pipeline performs a low-temperature defrosting cycle; the carbon dioxide circulation loop comprises, in sequence, a carbon dioxide compressor set, an oil separator, a condenser, a carbon dioxide liquid accumulator, a carbon dioxide refrigeration pump, and a heat regenerator, wherein the heat regenerator is connected with a low-temperature cold air machine and the carbon dioxide compressor set respectively; the output end of the carbon dioxide refrigeration pump is connected with a first inlet of the heat regenerator through a first straight-through stop valve pipeline, and is connected with an inlet of the low-temperature cold air machine through a second straight-through stop valve pipeline; a connecting pipeline between the second straight-through stop valve and the inlet of the low-temperature cold air machine is communicated with a first outlet of the heat regenerator; an electronic expansion valve is arranged on the connecting pipeline; an outlet of the low-temperature cold air machine is connected with a second inlet of the heat regenerator through a first electromagnetic valve and a third straight-through stop valve pipeline; and a second outlet of the heat regenerator is connected with the carbon dioxide compressor set through a pipeline.

[0008] In the scheme, the evaporator is the low-temperature cold air machine, which evaporates the internal carbon dioxide through the heat dissipation structure such as the coil pipe and the fin, and reduces the ambient temperature; since the surface temperature is low, the low-temperature cold air machine is easy to frost, and the scheme adds some components on the basis of the carbon dioxide circulation loop, forms the internal defrosting return liquid pipeline through the pipeline connection, controls the opening and closing of the pipeline by the electromagnetic valve, opens the complete carbon dioxide circulation loop in the normal carbon dioxide compression cycle, closes part of the carbon dioxide circulation loop in the defrosting, and opens the internal defrosting return liquid pipeline to connect the carbon dioxide circulation loop; in the defrosting, the condensing pressure of the condenser is adjusted to increase the pressure of the carbon dioxide liquid stored in the carbon dioxide liquid accumulator, the high-pressure carbon dioxide liquid is discharged by the carbon dioxide refrigeration pump, and the defrosting is performed in the low-temperature cold air machine through the second straight-through stop valve pipeline and the second electromagnetic valve; the 5 DEG C or so carbon dioxide liquid exchanges heat with the coil pipe and the fin of the low-temperature cold air machine to melt the frost, and returns to the carbon dioxide liquid accumulator through the third electromagnetic valve, the check valve and the pipeline.

[0009] As the preferred scheme of the utility model, the carbon dioxide liquid accumulator is provided with a gas return pipeline connected with the gas inlet of the condenser.

[0010] In a preferred embodiment of this invention, the condenser is equipped with a carbon dioxide heat exchange tube and a medium heat exchange tube. The medium heat exchange tube is a fluorine heat exchange tube, an ammonia heat exchange tube, or a water heat exchange tube. The medium heat exchange tube is connected to an external fluorine system, an ammonia system, or a chiller unit. The pressure of the carbon dioxide receiver is adjusted by regulating the fluorine system, the ammonia system, or the chiller unit. This condenser overlaps with external systems, such as a fluorine system, an ammonia system, and a chiller unit, allowing for primary heat exchange with the high-temperature, high-pressure carbon dioxide gas discharged from the carbon dioxide compressor unit in the carbon dioxide circulation loop, resulting in subcooled, high-pressure carbon dioxide liquid. By adjusting the operating states of the fluorine system, the ammonia system, and the chiller unit, the conversion rate of the subcooled, high-pressure carbon dioxide liquid can be changed, thereby adjusting the pressure of the carbon dioxide receiver.

[0011] As a preferred embodiment of this invention, the carbon dioxide refrigeration pump is provided in two sets, which are connected in parallel. This parallel configuration of the carbon dioxide refrigeration pumps allows them to be used alternately or simultaneously.

[0012] As a preferred embodiment of this utility model, when the compression refrigeration cycle is started, in the carbon dioxide circulation loop, the carbon dioxide compressor unit, condenser, carbon dioxide refrigeration pump, and low-temperature air cooler are operating. The first direct-acting shut-off valve, the second direct-acting shut-off valve, the electronic expansion valve, the first solenoid valve, and the third direct-acting shut-off valve are open, while the second solenoid valve, the third solenoid valve, and the check valve are closed. The compression cycle of the carbon dioxide system in this embodiment is as follows: high-temperature, high-pressure carbon dioxide gas is discharged from the carbon dioxide compressor unit, goes to the oil separator for gas-oil separation, and then is cooled at the condenser through pipelines, undergoing a heat exchange with fluorine, ammonia, or water to obtain subcooled high-pressure carbon dioxide liquid; it then goes through pipelines to the carbon dioxide storage tank, where the low-temperature, high-pressure carbon dioxide liquid is pumped out by the carbon dioxide refrigeration pump, passes through the second direct-acting shut-off valve to the electronic expansion valve for throttling and expansion, resulting in low-temperature, low-pressure two-phase carbon dioxide; it then undergoes heat exchange with the environment in the low-temperature air cooler to obtain low-temperature, low-pressure carbon dioxide gas; it then goes through the first solenoid valve, the third direct-acting shut-off valve, and pipelines to the regenerator for heat exchange; finally, it returns to the carbon dioxide compressor unit through pipelines, completing a single compression and refrigeration cycle.

[0013] As a preferred embodiment of this utility model, when the low-temperature defrosting cycle starts, the carbon dioxide compressor unit, condenser, and carbon dioxide refrigeration pump operate in the internal defrosting return pipeline, while the low-temperature air cooler stops. The second direct-connect valve, second solenoid valve, third solenoid valve, and check valve are opened, while the first direct-connect valve, electronic expansion valve, first solenoid valve, and third direct-connect valve are closed. The low-temperature defrosting cycle process of this embodiment is as follows: at the start of defrosting, the electronic expansion valve, low-temperature air cooler, and first solenoid valve are closed to stop refrigeration, while the second solenoid valve, third solenoid valve, and check valve are opened. The condensing pressure of the condenser is adjusted to increase the pressure of the carbon dioxide liquid in the carbon dioxide receiver; the high-pressure carbon dioxide liquid is pumped out by the carbon dioxide refrigeration pump; it passes through the second direct-connect valve pipeline and the second solenoid valve to the low-temperature air cooler for defrosting. The carbon dioxide liquid at approximately 5°C exchanges heat with the coils and fins of the low-temperature air cooler, melting the frost; it then returns to the carbon dioxide receiver through the third solenoid valve, check valve, and pipeline.

[0014] In a preferred embodiment of this invention, after the low-temperature defrosting cycle is completed, the second solenoid valve closes, and the low-temperature air cooler turns on its fan to evaporate the remaining liquid carbon dioxide in the air cooler. In this embodiment, after defrosting is complete, the second solenoid valve is closed and the fan of the low-temperature air cooler is turned on, causing the remaining liquid carbon dioxide in the evaporator of the low-temperature air cooler to evaporate, while simultaneously reducing the pressure in the carbon dioxide reservoir.

[0015] In a preferred embodiment of this invention, after the remaining liquid carbon dioxide in the low-temperature air cooler has evaporated, the third solenoid valve closes, and the fan of the low-temperature air cooler shuts off. In this embodiment, after evaporation, the third solenoid valve and the fan of the low-temperature air cooler are shut off; then, when needed, the electronic expansion valve and the carbon dioxide refrigeration pump can be activated, and the fan of the low-temperature air cooler can be started simultaneously, allowing the system to resume cooling.

[0016] In this scheme, the defrosting signal of the carbon dioxide internal defrosting system can be: (1) human triggering; (2) simultaneously satisfying four conditions: the cold storage temperature is lower than the set value, the return air temperature of the low temperature air cooler return pipe is lower than the set value, the overheating of the low temperature air cooler return pipe is lower than the set value for a period of time, and the shortest running time of the low temperature air cooler; (3) video recognition judgment, and at the same time the running current reaches the defrosting set value.

[0017] In this scheme, the signal for the completion of defrosting of the carbon dioxide internal defrosting system can be: (1) human triggering; (2) simultaneously meeting the two conditions of the low temperature air cooler fin temperature being higher than the set value and the defrosting time; (3) video recognition judgment that the air cooler return air side has reached a frost-free state.

[0018] The video recognition and judgment in this solution utilizes cases with different frost thicknesses, lighting, and angles to enable the surveillance camera to automatically identify whether frost has formed. If the frost formation meets the standard, a defrosting signal is output; if the defrosting process is deemed complete, a defrosting termination signal is output.

[0019] The technical effects and advantages of this utility model are as follows: This utility model is a novel defrosting method, which is different from the traditional defrosting method. Compared with electric defrosting, this system has the advantages of not consuming electricity, being energy-saving and environmentally friendly; having no risk during long-term defrosting, being safe and reliable; having short defrosting time, large defrosting heating area, and high defrosting efficiency.

[0020] Compared to water defrosting, this invention requires less investment, defrosting does not require the addition of an extra medium, and there is no need to install a separate defrosting system circuit; it can remove the oil deposited in the evaporator without reducing the efficiency of the evaporator; if the water flow is not properly adjusted, water splashing may cause ice to form on the fan or inside the evaporator; if defrosting is not thorough, it will lead to more severe frost formation, while this system does not have such problems.

[0021] Compared to defrosting with salt solutions, this invention does not cause corrosion damage to pipes and evaporators, and requires no special treatment of the defrosting medium; it eliminates the need for additional heat exchange tubes or reduction of refrigerant heat exchange tubes, as defrosting and refrigeration share a single set of heat exchange tubes, resulting in a large defrosting area; it is green, environmentally friendly, and does not pollute the environment; and it eliminates the need to treat residual salt solutions and impurities on the evaporator surface, reducing costs.

[0022] Compared to hot gas defrosting, this invention is an inside-out defrosting method, unlike the external defrosting of hot gas defrosting. Hot gas defrosting exhausts at a temperature of 30~50℃ and is sent into the low-temperature air cooler, resulting in a temperature difference of 50~90℃. The heat exchange tubes of the low-temperature air cooler are prone to thermal fatigue, and hot gas defrosting has a significant impact on the low-temperature air cooler. This invention does not require a complex control system and sensors, thus avoiding increased equipment cost and maintenance difficulty. It does not cause system pressure increases or refrigerant flow changes due to defrosting, exhibiting strong stability and preventing safety accidents caused by refrigerant leakage or metal thermal fatigue damage. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a pipe connection structure according to the present invention.

[0024] In the diagram: 1. Carbon dioxide compressor unit; 2. Oil separator; 3. Condenser.

[0025] 4. Carbon dioxide receiver 5. Carbon dioxide refrigeration pump 6. Regenerator

[0026] 7. Low-temperature air cooler; 8. First straight-through shut-off valve; 9. Second straight-through shut-off valve.

[0027] 10. Connecting pipe; 11. Electronic expansion valve; 12. First solenoid valve

[0028] 13. Third straight-through shut-off valve; 14. Second solenoid valve; 15. Third solenoid valve

[0029] 16. Check valve 17. Liquid return pipe 18. Gas return pipe. Detailed Implementation

[0030] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present utility model. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments.

[0031] Reference Figure 1 ,

[0032] A carbon dioxide internal defrosting system includes a carbon dioxide circulation loop formed by pipe connections and an internal defrosting return pipeline. The carbon dioxide circulation loop performs a compression refrigeration cycle, and the internal defrosting return pipeline performs a low-temperature defrosting cycle. The carbon dioxide circulation loop includes a carbon dioxide compressor unit 1, an oil separator 2, a condenser 3, a carbon dioxide receiver 4, a carbon dioxide refrigeration pump 5, and a regenerator 6 connected in sequence. The regenerator 6 is connected to a low-temperature air cooler 7 and the carbon dioxide compressor unit 1, respectively. The output end of the carbon dioxide refrigeration pump 5 is connected to the first inlet of the regenerator 6 through a first straight-through shut-off valve 8 and to the inlet of the low-temperature air cooler 7 through a second straight-through shut-off valve 9. One outlet connects to the second straight-through shut-off valve 9 and the inlet of the low-temperature air cooler 7 via a connecting pipe 10. An electronic expansion valve 11 is installed on the connecting pipe 10. The outlet of the low-temperature air cooler 7 is connected to the second inlet of the regenerator 6 via a pipe through the first solenoid valve 12 and the third straight-through shut-off valve 13. The second outlet of the regenerator 6 is connected to the carbon dioxide compressor unit 1 via a pipe. The internal defrosting return liquid pipeline, based on the carbon dioxide circulation loop, also includes a second solenoid valve 14, a third solenoid valve 15, and a check valve 16. The second solenoid valve 14 is installed on the connecting pipe 10 and is connected in parallel with the electronic expansion valve 11. The outlet of the low-temperature air cooler 7 is provided with a return liquid pipeline 17 that connects to the carbon dioxide reservoir 4 via the third solenoid valve 15 and the check valve 16.

[0033] The carbon dioxide storage tank 4 is equipped with a return gas pipe 18 that connects to the gas inlet of the condenser 3.

[0034] The condenser 3 is equipped with a carbon dioxide heat exchange tube and a medium heat exchange tube. The medium heat exchange tube is a fluorine heat exchange tube, an ammonia heat exchange tube, or a water heat exchange tube. The medium heat exchange tube is connected to an external fluorine system, an ammonia system, or a chiller unit. The pressure of the carbon dioxide receiver 3 is adjusted by regulating the fluorine system, the ammonia system, or the chiller unit.

[0035] Two sets of carbon dioxide refrigeration pumps 5 are provided, and the two sets of carbon dioxide refrigeration pumps 5 are connected in parallel.

[0036] When the compression refrigeration cycle starts, in the carbon dioxide circulation loop, the carbon dioxide compressor unit 1, condenser 3, external fluorine system or ammonia system or chiller unit, carbon dioxide refrigeration pump 5, and low temperature air cooler 7 are running. The first straight-through shut-off valve 8, the second straight-through shut-off valve 9, the electronic expansion valve 11, the first solenoid valve 12, and the third straight-through shut-off valve 13 are open, while the second solenoid valve 14, the third solenoid valve 15, and the check valve 16 are closed.

[0037] When the low-temperature defrosting cycle starts, in the internal defrosting return pipeline, the carbon dioxide compressor unit 1, condenser 3, and carbon dioxide refrigeration pump 5 are running, the low-temperature air cooler 7 is stopped, the second direct-connection shut-off valve 9, the second solenoid valve 14, the third solenoid valve 15, and the check valve 16 are open, and the first direct-connection shut-off valve 8, the electronic expansion valve 11, the first solenoid valve 12, and the third direct-connection shut-off valve 13 are closed.

[0038] After the low-temperature defrosting cycle is completed, the second solenoid valve 14 closes, and the low-temperature air cooler 7 turns on to evaporate the remaining carbon dioxide liquid in the low-temperature air cooler 7.

[0039] After the remaining liquid carbon dioxide in the low-temperature air cooler 7 has evaporated, the third solenoid valve 15 closes, and the low-temperature air cooler 7 shuts down.

[0040] Specific usage process:

[0041] This solution uses an external system superimposed on the condenser, such as a fluorine system, an ammonia system, and a chiller unit, to regulate the liquid carbon dioxide pressure in the carbon dioxide receiver. The pressure is controlled at 40~45 bar and the temperature at 6~11℃. When the pressure is higher than this range, the intermediate temperature circulation system is started. When the pressure is lower than this range, the intermediate temperature circulation system is stopped and the carbon dioxide compressor is started. The entire circulation system is designed to have a pressure of 52 bar.

[0042] The compression cycle of the carbon dioxide system in this scheme is as follows: High-temperature, high-pressure carbon dioxide gas is discharged from the carbon dioxide compressor unit 1, and then undergoes gas-oil separation in the oil separator 2. After cooling in the condenser 3 through pipelines, it exchanges heat with fluorine, ammonia, or water to obtain subcooled high-pressure carbon dioxide liquid. The subcooled high-pressure carbon dioxide liquid passes through pipelines to the carbon dioxide storage tank 4, where the carbon dioxide refrigeration pump 5 pumps out the low-temperature, high-pressure carbon dioxide liquid. The liquid passes through the second direct-flow shut-off valve 9 to the electronic expansion valve 11 for throttling and expansion, resulting in low-temperature, low-pressure two-phase carbon dioxide, which then enters the low-temperature air cooler 7. In the low-temperature air cooler 7, it exchanges heat with the environment to obtain low-temperature, low-pressure carbon dioxide gas. The low-temperature, low-pressure carbon dioxide gas passes through the first solenoid valve 12, the third direct-flow shut-off valve 13, and pipelines to the regenerator 6 for heat exchange. Finally, it returns to the carbon dioxide compressor unit 1 through pipelines, completing a single compression and refrigeration cycle.

[0043] The low-temperature defrosting cycle is as follows: When defrosting begins, the electronic expansion valve 11, the low-temperature air cooler 7, and the first solenoid valve 12 are closed to stop refrigeration, and the second solenoid valve 14, the third solenoid valve 15, and the check valve 16 are opened. The condensing pressure of the condenser 3 is adjusted to increase the pressure of the carbon dioxide liquid in the carbon dioxide receiver 4. The high-pressure carbon dioxide liquid is pumped out by the carbon dioxide refrigeration pump 5 and flows through the second straight-through shut-off valve 9 and the second solenoid valve 14 to the low-temperature air cooler 7 for defrosting. The carbon dioxide liquid at about 5°C exchanges heat with the coils and fins of the low-temperature air cooler 7 to melt the frost, and then returns to the carbon dioxide receiver 4 through the third solenoid valve 14, the check valve 15, and the pipeline.

[0044] After defrosting is complete, close the second solenoid valve 14 and turn on the fan of the low-temperature air cooler 7 to evaporate the remaining carbon dioxide liquid in the evaporator of the low-temperature air cooler 7, while reducing the pressure in the carbon dioxide reservoir 4.

[0045] After evaporation is complete, turn off the third solenoid valve 15 and the fan of the low-temperature air cooler 7; then, when needed, the electronic expansion valve 11 and the carbon dioxide refrigeration pump 5 can be turned on, and the fan of the low-temperature air cooler 7 can be started at the same time, and the system will cool down again.

[0046] Then, by adjusting the high-temperature side of the cascading system (such as a fluorine system, an ammonia system, or a chiller unit), the pressure of the carbon dioxide receiver 4 is reduced to complete a single defrosting cycle.

[0047] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A carbon dioxide internal defrosting system, characterized in that: The carbon dioxide internal defrosting system includes a carbon dioxide circulation loop formed by pipe connections and an internal defrosting return liquid pipeline. The carbon dioxide circulation loop performs a compression refrigeration cycle, and the internal defrosting return liquid pipeline performs a low-temperature defrosting cycle. The carbon dioxide circulation loop includes a carbon dioxide compressor unit, an oil separator, a condenser, a carbon dioxide liquid receiver, a carbon dioxide refrigeration pump, and a regenerator connected in sequence. The regenerator is connected to a low-temperature air cooler and a carbon dioxide compressor unit. The output end of the carbon dioxide refrigeration pump is connected to the first inlet of the regenerator through a first straight-through shut-off valve pipe and to the inlet of the low-temperature air cooler through a second straight-through shut-off valve pipe. The first outlet of the regenerator is connected to the connecting pipe between the second straight-through shut-off valve and the inlet of the low-temperature air cooler. An electronic expansion valve is provided on the connecting pipe. The outlet of the low-temperature air cooler is connected to the second inlet of the regenerator through a first solenoid valve and a third straight-through shut-off valve pipe. The second outlet of the regenerator is connected to the carbon dioxide compressor unit. The internal defrosting return pipeline, based on the carbon dioxide circulation loop, also includes a second solenoid valve, a third solenoid valve, and a check valve. The second solenoid valve is located on the connecting pipeline and is connected in parallel with the electronic expansion valve. The outlet of the low-temperature air cooler is provided with a return pipeline that connects to the carbon dioxide reservoir through the third solenoid valve and the check valve.

2. The carbon dioxide internal defrosting system according to claim 1, characterized in that: The carbon dioxide storage tank is equipped with a return gas pipe connected to the gas inlet of the condenser.

3. The carbon dioxide internal defrosting system according to claim 1, characterized in that: The condenser is equipped with a carbon dioxide heat exchange tube and a medium heat exchange tube. The medium heat exchange tube is a fluorine heat exchange tube, an ammonia heat exchange tube, or a water heat exchange tube. The medium heat exchange tube is connected to an external fluorine system, an ammonia system, or a chiller unit. The pressure of the carbon dioxide reservoir is adjusted by regulating the fluorine system, the ammonia system, or the chiller unit.

4. The carbon dioxide internal defrosting system according to claim 1, characterized in that: The carbon dioxide refrigeration pump is provided in two sets, which are connected in parallel.

5. A carbon dioxide internal defrosting system according to claim 1, characterized in that: When the compression refrigeration cycle is started, in the carbon dioxide circulation loop, the carbon dioxide compressor unit, condenser, carbon dioxide refrigeration pump, and low-temperature cold air blower are running, and the first straight-through shut-off valve, the second straight-through shut-off valve, the electronic expansion valve, the first solenoid valve, and the third straight-through shut-off valve are open, while the second solenoid valve, the third solenoid valve, and the check valve are closed.

6. The carbon dioxide internal defrosting system according to claim 1, characterized in that: When the low-temperature defrosting cycle is started, the carbon dioxide compressor unit, condenser, and carbon dioxide refrigeration pump operate in the internal defrosting return pipeline, the low-temperature air cooler stops, the second direct-connection shut-off valve, the second solenoid valve, the third solenoid valve, and the check valve open, and the first direct-connection shut-off valve, the electronic expansion valve, the first solenoid valve, and the third direct-connection shut-off valve close.

7. A carbon dioxide internal defrosting system according to claim 6, characterized in that: After the low-temperature defrosting cycle is completed, the second solenoid valve closes, and the low-temperature air cooler turns on its fan to evaporate the remaining liquid carbon dioxide in the low-temperature air cooler.

8. A carbon dioxide internal defrosting system according to claim 7, characterized in that: After the remaining liquid carbon dioxide in the low-temperature air cooler has evaporated, the third solenoid valve closes, and the low-temperature air cooler shuts down.

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