CN115654823A - Thermodynamic system for refrigeration house, steam defrosting method of thermodynamic system and refrigeration house - Google Patents

Abstract

The invention provides a thermodynamic system for a refrigeration house, a steam defrosting method of the thermodynamic system and the refrigeration house. Wherein, thermodynamic system for the freezer includes: a refrigeration system circulation loop and a water system circulation loop; the refrigerating system circulation loop is provided with an evaporator and a condenser; the water system circulation loop is provided with a water tank, the water tank and the condenser form a first circulation loop, and the water tank and the evaporator form a second circulation loop; the first circulation loop absorbs the heat of the condenser by using the water in the water tank; the second circulating water path utilizes water in the water tank to generate steam to defrost the evaporator. When the refrigeration house is used for refrigerating, the water in the water tank is utilized to exchange heat with the refrigerant in the condenser, so that the temperature of the condenser is reduced, and the heat exchange effect is improved; meanwhile, the condensation heat is utilized to heat the water, so that the condition that the water is converted into steam is reduced; during defrosting, water in the water tank is converted into steam, the steam is introduced into the evaporator to be defrosted, defrosting can be performed uniformly, the defrosting effect is good, and energy is saved.

Description

A thermal system for cold storage and its steam defrosting method and cold storage

technical field

The invention belongs to the technical field of cold storage, and in particular relates to a thermal system for cold storage, a steam defrosting method thereof, and the cold storage.

Background technique

At present, the defrosting methods used by evaporators mainly include the following types: 1. Heat fluoride defrosting; 2. Water defrosting; 3. Electric heating defrosting. Hot fluorinated frost is to introduce the high-temperature and high-pressure gaseous refrigerant discharged from the compressor into the evaporator, and the gaseous refrigerant releases heat in the evaporator to melt the frost layer on the evaporator. However, when the ambient temperature is lower than 18°C, the discharge temperature of the compressor is low, resulting in a low temperature of the gaseous refrigerant entering the evaporator, which cannot normalize the frost layer on the evaporator, which will lead to blockage of the evaporator and wind. The channel circulation is not smooth, which will affect the cooling effect and increase the compressor load; therefore, simply using hot fluorinated defrosting method will prolong the defrosting time, increase power consumption, and affect the life of the compressor. And water defrost will appear if there is water in the evaporator, cooling again will cause the frost layer on the evaporator to become an ice layer, thus affecting the cooling effect; electric heating defrosting is a commonly used defrosting method However, the energy consumption of defrosting by electric heating is high, and the storage temperature fluctuates greatly during defrosting.

Contents of the invention

In view of this, the present invention provides a thermal system for cold storage, a steam defrosting method thereof, and a cold storage to solve the problem of frosting of the evaporator.

In order to solve the above technical problems, the first aspect of the present invention provides a thermal system for cold storage, the thermal system includes a refrigeration system circulation loop and a water system circulation loop;

The circulation loop of the refrigeration system is equipped with an evaporator and a condenser;

The circulation circuit of the water system is provided with a water tank, the water tank and the condenser constitute the first circulation circuit, and the evaporator constitutes the second circulation circuit;

The first circulation loop utilizes the water in the water tank to absorb the heat of the condenser;

The second circulating water circuit utilizes the water in the water tank to generate steam to defrost the evaporator.

Further optionally, a first control valve is provided on the first circulating circuit; a second control valve is provided on the second circulating water circuit.

Further optionally, the thermal system for cold storage also includes:

The filter is arranged on the first circulation circuit pipeline between the water outlet of the condenser and the water tank, and the filter is used to filter out impurities in the condensed water.

Further optionally, the evaporator is preset with a steam pipe for defrosting, and the steam generated by the water in the water tank is passed into the steam pipe for defrosting.

Further optionally, the thermal system is also provided with a gas-liquid mixing pump and a heating device;

The first circulation loop and the second circulation loop are provided with a shared branch, and the water tank and the gas-liquid mixing pump are arranged on the shared branch;

The first circulation circuit includes a condenser fluidly connected by water, a water tank, a gas-liquid mixing pump and a first control valve;

The second circulation loop includes a water tank connected by water fluid, a gas-liquid mixing pump, a second control valve, and an evaporator;

The water tank is provided with a first inlet WA, a second inlet WB and a fluid outlet WC, wherein the fluid outlet WC communicates with the inlet of the gas-liquid mixing pump through the first circulation loop, and the first inlet WA communicates with the condenser outlet through the first circulation loop , the second inlet WB communicates with the evaporator outlet through the second circulation loop;

The condenser is provided with a first inlet CA and a first outlet CA, a second inlet CB and a second outlet CB, wherein the first inlet CA and the first outlet CA are connected to the refrigeration system circulation circuit, and the second inlet CB and the second outlet CB is connected to the first circulation circuit of the water system; inside the condenser, a refrigerant flow path is formed between the first inlet CA and the first outlet CA, and a water flow path is formed between the second inlet CB and the second outlet CB;

The evaporator is provided with a first inlet EA and a first outlet EA, a second inlet EB and a second outlet EB, wherein the first inlet EA and the first outlet EA are connected to the circulation circuit of the refrigeration system, and the second inlet EB and the second outlet EB is connected to the second circulation loop of the water system; inside the evaporator, a refrigerant flow path is formed between the first inlet EA and the first outlet EA, and a water flow path is formed between the second inlet EB and the second outlet EB;

The heating device is set in the water tank or on the common branch or on the side of the second inlet EB of the evaporator of the second circulation loop;

When the cold storage is refrigerated, the water in the water tank is sent to the condenser to cool the condenser, and then returns to the water tank; when the evaporator defrosts, the condensed water in the water tank is heated to convert it into steam and then passed into the evaporator for further cooling. defrost.

The second aspect of the present invention provides a steam defrosting method using the thermal system of the cold storage in the first aspect. The steam defrosting method includes:

When the cold storage is refrigerated, the water in the water tank is sent to the condenser to cool the condenser, and the condensed water that cools the condenser is collected and returned to the water tank; when it is determined that the evaporator needs to be defrosted, the water in the water tank is converted into After the steam is passed into the evaporator for defrosting.

Further optionally, water is sent to the condenser to cool the condenser, and the condensed water that cools the condenser is collected; when it is determined that the evaporator needs to be defrosted, the condensed water is converted into steam and then passed into the evaporator Perform defrosting, including:

Control the pump body and the first control valve to open, and control the heating device and the second control valve to close, so as to pump the water in the water tank into the condenser, and use the water to absorb the condensation heat generated by the condenser;

Determine whether to defrost the evaporator;

If necessary, close the first control valve and the pump body, and control the heating device to convert the water inside it into steam, open the second control valve, and pass the steam into the evaporator for defrosting.

Further optionally, judging whether to defrost the evaporator includes:

Obtain the cooling running time, and determine whether the cooling running time is greater than or equal to the first preset time;

If yes, it is deemed necessary to defrost the evaporator.

Further optionally, the heating device is controlled to convert the water inside it into steam, and the second control valve is opened to pass steam into the evaporator for defrosting, including:

Obtain the defrosting heating time, and judge whether the defrosting heating time is greater than or equal to the second preset time;

If so, open the second control valve and pass the generated steam into the evaporator for defrosting;

Obtaining the duration of steam introduction, and judging whether the duration of steam introduction is greater than or equal to the third preset duration;

If so, close the second control valve and the heating device, and open the first control valve and the pump body.

The third aspect of the present invention provides a cold storage, which is equipped with any thermal system of the first aspect or the steam defrosting method of any one of the second aspect.

After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

The present invention utilizes the refrigerant in the condenser to exchange heat with the water in the water tank during refrigeration in the cold storage, thereby lowering the temperature of the condenser and improving the heat exchange effect, and at the same time using the heat of condensation to raise the temperature of the water and reducing the conditions for water to turn into steam , when defrosting, steam is passed into the evaporator to defrost, which can defrost evenly, has good defrosting effect and saves energy.

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Description of drawings

The accompanying drawings, as a part of the present invention, are used to provide a further understanding of the present invention, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute improper limitations to the present invention. Apparently, the drawings in the following description are only some embodiments, and those skilled in the art can also obtain other drawings according to these drawings without creative efforts. In the attached picture:

Fig. 1 shows a schematic structural diagram of a thermal system for cold storage according to an embodiment of the present invention.

Fig. 2 shows a schematic structural diagram of an evaporator according to an embodiment of the present invention.

Fig. 3 shows a schematic diagram of a steam defrosting method for a thermal system for cold storage according to an embodiment of the present invention.

Fig. 4 shows a schematic diagram of a steam defrosting method for a thermal system for cold storage according to an embodiment of the present invention.

Among them: 1-compressor; 2-condenser; 3-first control valve; 4-second control valve; 5-heating device; 6-gas-liquid mixing pump; 7-water tank; 8-throttling device-filter ; 10-evaporator; 11-fin; 12-hot copper tube; 13-steam pipe jack.

It should be noted that these drawings and text descriptions are not intended to limit the concept scope of the present invention in any way, but illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments.

Detailed ways

In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "inner", "outer" and the like are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description. It is not intended to indicate or imply that the referred device or element must have a particular orientation, be constructed in a particular orientation, and operate in a particular orientation, and thus should not be construed as limiting the invention.

In the description of the present invention, it should be noted that unless otherwise specified and limited, the terms "installation", "connection", "connection", "contact", and "communication" should be understood in a broad sense, for example, it can be Fixed connection, detachable connection, or integral connection; mechanical connection or electrical connection; direct connection or indirect connection through an intermediary. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention in specific situations.

When the refrigeration unit is working normally, as time goes by, due to the low temperature of the working environment where the evaporator is located, it will cause frost on its surface. This will greatly reduce the cooling effect of the unit. At this stage, the commonly used defrosting methods for cold storage evaporators generally include: thermal fluoride defrosting; water defrosting; electric heating defrosting. Hot fluorinated frost is to introduce the high-temperature and high-pressure gaseous refrigerant discharged from the compressor into the evaporator, and the gaseous refrigerant releases heat in the evaporator to melt the frost layer on the evaporator. However, when the ambient temperature is lower than 18°C, the discharge temperature of the compressor is low, resulting in a low temperature of the gaseous refrigerant entering the evaporator, which cannot normalize the frost layer on the evaporator, which will lead to blockage of the evaporator and wind. The channel circulation is not smooth, which will affect the cooling effect and increase the compressor load; therefore, simply using hot fluorinated defrosting method will prolong the defrosting time, increase power consumption, and affect the life of the compressor. And water defrost will appear if there is water in the evaporator, cooling again will cause the frost layer on the evaporator to become an ice layer, thus affecting the cooling effect; electric heating defrosting is a commonly used defrosting method However, the energy consumption of defrosting by electric heating is high, and the storage temperature fluctuates greatly during defrosting.

Therefore, the first aspect of this embodiment provides a thermal system for cold storage. Combined with Figure 1, a thermal system for cold storage, the thermal system includes a refrigeration system circulation loop and a water system circulation loop;

The refrigeration system circulation loop is provided with an evaporator 10 and a condenser 2;

The water system circulation loop is provided with a water tank 7, the water tank 7 forms a first circulation loop with the condenser 2, and forms a second circulation loop with the evaporator 10;

The first circulation loop utilizes the water in the water tank 7 to absorb the heat of the condenser 2;

The second circulating water circuit utilizes the water in the water tank 7 to generate steam to defrost the evaporator 10 .

For ease of control, preferably, a first control valve 3 is provided on the first circulation circuit; a second control valve 4 is provided on the second circulation water circuit; specifically, the first control valve 3 and the second control valve 4 are preferably electromagnetic valve.

Further optionally, the thermal system for cold storage further includes: a filter 9, which is arranged on the first circulation circuit pipeline between the water outlet of the condenser 2 and the water tank 7, and is used for filtering out impurities in the condensed water.

Specifically, no water pipes are arranged on the condenser 2, and the water in the water tank can be directly sprayed on the condenser 2. Further, a container with a water outlet can be arranged under the condenser 2 to discharge the collected condensed water. , into the water tank 7 after the filter 9. The water in the water tank 7 can be recycled like this. Since the water is sprayed directly on the condenser, the condensed water is then recovered. There will be dust and other impurities on the condenser. If it is not filtered, the condensed water will bring it into the water tank and enter the cycle. Damage to the pump body may result. Secondly, after impurities enter the heating device, impurities may be deposited at the bottom of the heating device.

Further optionally, the evaporator 10 is preset with a steam pipe for defrosting, and the steam generated by the water in the water tank 7 is passed into the steam pipe for defrosting.

Specifically, the evaporator 10 is preferably a fin, and heat exchange copper tubes 12 are arranged inside the fins, and the heat exchange copper tubes 12 are used for circulating refrigerant so that the cold storage can be normally refrigerated; Steam pipe sockets 13, these steam hole sockets 13 are used to arrange steam pipelines in the evaporator 10, and the steam pipelines are used to pass through steam to defrost the evaporator, so that the steam can be used to defrost evenly and defrost The effect is better, so as to ensure the cooling effect of the unit.

Further optionally, the thermal system is also provided with a gas-liquid mixing pump 6 and a heating device 5;

The first circulation loop and the second circulation loop are provided with a shared branch, and the water tank 7 and the gas-liquid mixing pump 6 are arranged on the shared branch;

The first circulation loop includes a condenser 2, a water tank 7, a gas-liquid mixing pump 6 and a first control valve fluidly connected by water;

The second circulation loop includes a water tank 7 fluidly connected by water, a gas-liquid mixing pump 6, a second control valve, and an evaporator 10;

The first circulation loop and the second circulation loop are provided with a shared branch, and the water tank 7 and the gas-liquid mixing pump 6 are arranged on the shared branch;

The water tank is provided with a first inlet WA, a second inlet WB and a fluid outlet WC, wherein the fluid outlet WC communicates with the inlet of the gas-liquid mixing pump 6 through the first circulation circuit, and the first inlet WA and the outlet of the condenser 2 pass through the first circulation The loop is connected, and the second inlet WB is connected with the outlet of the evaporator 10 through the second circulation loop;

The condenser 2 is provided with a first inlet CA and a first outlet CA, a second inlet CB and a second outlet CB, wherein the first inlet CA and the first outlet CA are connected to the refrigeration system circulation circuit, the second inlet CB and the second The outlet CB is connected to the first circulation circuit of the water system; inside the condenser 2, a refrigerant flow path is formed between the first inlet CA and the first outlet CA, and a water flow path is formed between the second inlet CB and the second outlet CB ;

The evaporator 10 is provided with a first inlet EA and a first outlet EA, a second inlet EB and a second outlet EB, wherein the first inlet EA and the first outlet EA are connected to the refrigeration system circulation circuit, and the second inlet EB and the second The outlet EB is connected to the second circulation loop of the water system; inside the evaporator 10, a refrigerant flow path is formed between the first inlet EA and the first outlet EA, and a water flow path is formed between the second inlet EB and the second outlet EB ;

The heating device 5 is arranged in the water tank or on the common branch or on the side of the second inlet EB of the evaporator 10 of the second circulation loop; in this embodiment, the heating device 5 is preferably arranged on the common branch;

When the cold storage is refrigerated, the water in the water tank is sent to the condenser 2 to cool the condenser 2, and then returns to the water tank; when the evaporator 10 defrosts, the condensed water in the water tank is heated to convert it into steam and then enter the evaporation Defrost in the device 10.

In this embodiment, when the cold storage is refrigerated, the refrigerant in the condenser 2 is used to exchange heat with the water in the water tank, thereby reducing the temperature of the condenser 2 and improving the heat exchange effect. The condition of the steam is that when defrosting, the steam is passed into the evaporator 10 to make it defrost, the defrosting can be uniform, the defrosting effect is good and energy saving.

In this embodiment, preferably, the gas-liquid mixing pump 6 is connected to the condenser 2 through the heating device 5 , that is, the water pumped out by the gas-liquid mixing pump 6 passes through the heating device 5 before being pumped into the condenser 2 . The water pumped in by the gas-liquid mixing pump 6 exchanges heat with the refrigerant in the condenser 2, which can reduce the temperature of the condenser 2, thereby improving its heat exchange effect. At the same time, the heat of condensation is used to raise the temperature of water, which can reduce the adjustment of turning water into steam, thereby reducing the energy consumption required for steam defrosting. The heating device 5 heats the water inside it into steam, passes the steam into the steam pipeline in the evaporator 10, and uses the steam to defrost the frost layer in the evaporator, so that the defrosting can be uniform and the defrosting effect is better.

In addition, the single pump body is divided into a water pump and an air pump. In this embodiment, if a single pump body is to be used, both of the above two pumps need to be used, which makes the system more complicated. Therefore, the gas-liquid mixing pump is preferred in this embodiment.

The second aspect of this embodiment provides a steam defrosting method used in the thermal system for cold storage in the first aspect. The steam defrosting method includes steps S1-S2, wherein:

S1, when the cold storage is cooling, the water in the water tank is sent to the condenser to cool the condenser, and the condensed water from the cooling condenser is collected and returned to the water tank;

S2, when it is determined that the evaporator needs to be defrosted, the water in the water tank is converted into steam and then passed into the evaporator for defrosting.

The steam defrosting method of this embodiment uses the refrigerant in the condenser 2 to exchange heat with the water in the water tank during the refrigeration of the cold storage, thereby reducing the temperature of the condenser 2 and improving the heat exchange effect. At the same time, the condensation heat is used to make the water Heating up reduces the conditions for water to turn into steam. When defrosting, steam is passed into the evaporator 10 to make it defrost. The defrosting can be uniform, the defrosting effect is good and energy saving.

Optionally, in conjunction with Fig. 3, the steam defrosting method sends water to the condenser to cool the condenser when the refrigerator is refrigerated, and collects the condensed water that cools the condenser; when it is determined that the evaporator needs to be defrosted , convert the condensed water into steam and pass it into the evaporator for defrosting, including steps A1-A3, wherein:

A1, when the cold storage is cooling, both the control pump body and the first control valve are turned on, and the heating device and the second control valve are turned off, so as to pump the water in the water tank into the condenser, and use the water to absorb the condensation heat generated by the condenser;

A2, judge whether it is necessary to defrost the evaporator; if necessary, execute S3;

A3, close the first control valve and the pump body, and control the heating device to convert the water inside it into steam, open the second control valve, and let the steam flow into the evaporator for defrosting.

In the steam defrosting method of this embodiment, when the unit is cooling normally, the compressor 1 compresses the refrigerant into a high-temperature and high-pressure gaseous refrigerant, and then the refrigerant enters the condenser 2 for heat exchange. At the same time, the first control valve 3 and the gas-liquid mixing pump 6 are opened, and the condensed water in the water tank 7 is pumped to the condenser 2 to absorb the condensation heat generated by it, so as to improve the heat exchange effect of the condenser 2, and then the condensed water passes through the filter 9 flows back in the water tank 7. After heat exchange, the high-temperature and high-pressure refrigerant becomes a low-temperature and high-pressure refrigerant, which is throttled by the electronic expansion valve 8 to become a low-temperature and low-pressure refrigerant, and then evaporates and absorbs heat through the evaporator 10 to become a low-pressure and high-temperature refrigerant and flows back into the compressor 1 . In addition, during the cooling process, it is necessary to judge whether it is necessary to defrost the evaporator 10. If necessary, the first control valve 3 and the pump body 6 are closed, and the heating device 5 starts to heat the condensed water therein, so that the condensed water becomes steam. Then open the second control valve 4 to feed steam into the evaporator 10 for steam defrosting; if not needed, continue to pump the condensed water to the condenser 2 to exchange heat with the refrigerant in the condenser 2 .

Further optionally, with reference to FIG. 4, step A2 includes A21-A22, wherein:

A21, obtain the cooling running time, and determine whether the cooling running time is greater than or equal to the first preset time; if so,

A22, it is considered that the evaporator needs to be defrosted.

Generally, the defrosting will start after 8 hours of refrigeration operation. In this embodiment, the first preset duration is preferably 8 hours. Specifically, time is counted from when the unit starts to run, and the time when the unit defrost starts is set as t1, and the unit is second. Judging the timing time t≥t1-T, T is the defrosting heating time, calculated by T=CmΔT/ηP, where C is the specific heat of water, m is the quality of water, ΔT is the changing temperature, η is the heating efficiency, η is taken as The value is generally 90%-98%, and P is the heating power; if the conditions are met, then close the first control valve 3 and the gas-liquid mixing pump 6, and the heating device 5 starts to heat the condensed water therein. If the condition is not satisfied, the condensed water will continue to be pumped to the condenser 2 for heat exchange.

After the unit has satisfied the condition t≥t1-T, it is judged that t≥t1, if the condition is met, the second control valve 4 and the gas-liquid mixing pump 6 are opened, and the high-temperature steam in the heating device 5 is pressed into the evaporator through the gas-liquid mixing pump 6 In the steam pipe reserved in 10, the defrosting is carried out through the heat exchange between the steam pipe and the fins and the heat radiation with the heat exchange copper pipe 12. If the condition is not met, then keep the second control valve 4 and the gas-liquid mixing pump 6 closed.

Further optionally, in step S3, the heating device is controlled to convert the water inside it into steam, and the second control valve is opened to pass steam into the evaporator for defrosting, including steps A31-A34, wherein:

A31, obtain the defrosting heating time, and judge whether the defrosting heating time is greater than or equal to the second preset time; if so, execute A32;

A32, open the second control valve, and pass the generated steam into the evaporator for defrosting;

A33, obtain the duration of steam introduction, and judge whether the duration of steam introduction is greater than or equal to the third preset duration; if so, execute A34;

A34, close the second control valve and heating device, open the first control valve and pump body.

Generally, the duration of steaming is 5min-13min, that is, the value range of the third preset duration is 5min-13min; the defrosting heating duration is T, and its calculation formula is T=CmΔT/ηP, and the second preset duration is greater than or equal to T . Specifically, set the defrosting end time of the unit as t2, and t2>t1. It is judged that t≥t2, if the condition is satisfied, the second control valve 4 is closed, the first control valve 3 is opened, the heating device 5 stops working, and the defrosting ends. If the conditions are not met, continue to defrost.

The third aspect of this embodiment provides a cold storage, including the thermal system according to any one of the first aspect or the steam defrosting method according to any one of the second aspect.

The thermodynamic system for cold storage and its steam defrosting method and cold storage provided in this embodiment use a condenser to exchange heat between refrigerant and water. On the one hand, the heat exchange effect is improved, and on the other hand, the water for steam defrosting can be preheated. Reduce the conditions for water to be converted into steam, that is, reuse the heat generated by the condenser, so as to save more energy; through the arrangement of pipes in the evaporator, the steam can defrost evenly when defrosting.

The device embodiments described above are only illustrative, and the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in One place, or it can be distributed to multiple network elements. Part or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. It can be understood and implemented by those skilled in the art without any creative effort.

Through the above description of the implementations, those skilled in the art can clearly understand that each implementation can be implemented by means of software plus a necessary general hardware platform, and of course also by hardware. Based on this understanding, the essence of the above technical solution or the part that contributes to the prior art can be embodied in the form of software products, and the computer software products can be stored in computer-readable storage media, such as ROM/RAM, magnetic discs, optical discs, etc., including several instructions to make a computer device (which may be a personal computer, server, or network device, etc.) execute the methods described in various embodiments or some parts of the embodiments.

The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with the technology of this patent Without departing from the scope of the technical solution of the present invention, personnel can use the technical content of the above prompts to make some changes or modify them into equivalent embodiments with equivalent changes. In essence, any simple modifications, equivalent changes and modifications made to the above embodiments still fall within the scope of the solutions of the present invention.

Claims (10)

1. A thermal system for cold storage, characterized in that: the thermal system includes a refrigeration system circulation loop and a water system circulation loop; The circulation loop of the refrigeration system is provided with an evaporator and a condenser; The water system circulation loop is provided with a water tank, the water tank and the condenser form a first circulation loop, and the evaporator forms a second circulation loop; The first circulation loop utilizes the water in the water tank to absorb the heat of the condenser; The second circulating water circuit utilizes the water in the water tank to generate steam to defrost the evaporator. 2 . The thermal system for cold storage according to claim 1 , wherein a first control valve is provided on the first circulation circuit; a second control valve is provided on the second circulation water circuit. 3 . 3. The thermal system for cold storage according to claim 2, wherein the thermal system for cold storage further comprises: A filter is arranged on the first circulation loop pipeline between the water outlet of the condenser and the water tank, and the filter is used to filter out impurities in the condensed water. 4. The thermal system for cold storage according to claim 2, wherein a steam pipe for defrosting is preset on the evaporator, and the steam generated by the water in the water tank is passed into the steam pipe for defrosting . 5. The thermal system for cold storage according to any one of claims 2-4, characterized in that: The thermal system is also provided with a gas-liquid mixing pump and a heating device; The first circulation loop and the second circulation loop are provided with a common branch, and the water tank and the gas-liquid mixing pump are arranged on the common branch; The first circulation loop includes a condenser fluidly connected by water, a water tank, a gas-liquid mixing pump and a first control valve; The second circulation loop includes a water tank fluidly connected by water, a gas-liquid mixing pump, a second control valve, and an evaporator; The water tank is provided with a first inlet WA, a second inlet WB and a fluid outlet WC, wherein the fluid outlet WC communicates with the inlet of the gas-liquid mixing pump through the first circulation circuit, and the first inlet WA communicates with the condenser The outlet of the evaporator is communicated through the first circulation loop, and the second inlet WB is communicated with the outlet of the evaporator through the second circulation loop; The condenser is provided with a first inlet CA and a first outlet CA, a second inlet CB and a second outlet CB, wherein the first inlet CA and the first outlet CA are connected to the refrigeration system circulation circuit, the second inlet CB and the second outlet The second outlet CB is connected to the first circulation circuit of the water system; inside the condenser, a refrigerant flow path is formed between the first inlet CA and the first outlet CA, and between the second inlet CB and the second outlet CB form a water flow path; The evaporator is provided with a first inlet EA and a first outlet EA, a second inlet EB and a second outlet EB, wherein the first inlet EA and the first outlet EA are connected to the circulation circuit of the refrigeration system, and the second inlet EB and the second outlet The second outlet EB is connected to the second circulation loop of the water system; inside the evaporator, a refrigerant flow path is formed between the first inlet EA and the first outlet EA, and between the second inlet EB and the second outlet EB form a water flow path; The heating device is arranged in the water tank or on the common branch or on the side of the second inlet EB of the evaporator of the second circulation loop; When the cold storage is refrigerated, the water in the water tank is sent to the condenser to cool the condenser, and then returns to the water tank; when the evaporator is defrosted, the condensed water in the heated water tank is converted into The steam is then passed into the evaporator for defrosting. 6. A steam defrosting method for the thermal system of the cold storage according to any one of claims 2-5, characterized in that, the defrosting method comprises: When the cold storage is refrigerated, the water in the water tank is sent to the condenser to cool the condenser, and the condensed water that cools the condenser is collected and returned to the water tank; when it is determined that the evaporator needs to be During frost, the water in the water tank is converted into steam and then passed into the evaporator for defrosting. 7. The steam defrosting method according to claim 6, wherein water is delivered to the condenser to cool the condenser, and the condensed water for cooling the condenser is collected; When the evaporator is defrosting, the condensed water is converted into steam and then passed into the evaporator for defrosting, including: Control the pump body and the first control valve to open, and control the heating device and the second control valve to close, so as to pump the water in the water tank into the condenser, and use the water to absorb the condensation heat generated by the condenser; Determine whether to defrost the evaporator; If necessary, close the first control valve and the pump body, control the heating device to convert the water inside it into steam, open the second control valve, and pass steam into the inside of the evaporator for defrosting. 8. The steam defrosting method according to claim 7, wherein judging whether to defrost the evaporator comprises: Obtain the cooling running time, and judge whether the cooling running time is greater than or equal to the first preset time; If so, it is deemed necessary to defrost the evaporator. 9. The steam defrosting method according to claim 8, characterized in that the heating device is controlled to convert the water inside it into steam, and the second control valve is opened to pass steam into the inside of the evaporator for defrosting ,include: Acquiring the defrosting heating time, and judging whether the defrosting heating time is greater than or equal to the second preset time; If so, open the second control valve, and pass the generated steam into the inside of the evaporator for defrosting; Obtaining the duration of steam introduction, and judging whether the duration of steam introduction is greater than or equal to a third preset duration; If so, close the second control valve and the heating device, and open the first control valve and the pump body. 10. A cold store, which is provided with any one of the thermal systems of claims 1-5 or the steam defrosting method of any one of claims 6-9.

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