CN115183499A

CN115183499A - Heat pump type drying system and defrosting method for same

Info

Publication number: CN115183499A
Application number: CN202210706306.3A
Authority: CN
Inventors: 王策; 李伟
Original assignee: Qingdao Haier Air Conditioner Gen Corp Ltd; Qingdao Haier Air Conditioning Electric Co Ltd; Haier Smart Home Co Ltd
Current assignee: Qingdao Haier Air Conditioner Gen Corp Ltd; Qingdao Haier Air Conditioning Electric Co Ltd; Haier Smart Home Co Ltd
Priority date: 2022-06-21
Filing date: 2022-06-21
Publication date: 2022-10-14
Anticipated expiration: 2042-06-21

Abstract

The invention relates to a heat pump drying system and a defrosting method for the same. This heat pump-type drying system includes: a refrigeration main loop which comprises a compressor, a condenser, an expansion device and an evaporator, wherein the bottom of the evaporator is provided with a bottom coil which is provided with an inlet end connected with the expansion device and an outlet end connected with an air suction port of the compressor, a first electromagnetic valve is arranged between the inlet end and the expansion device, and a second electromagnetic valve is arranged in the bottom coil; a defrosting bypass pipe having a first end connected to the discharge port of the compressor and a second end connected to the inlet port, the defrosting bypass pipe being provided with a third solenoid valve; and a capillary line configured to be arranged in the bottom coil in parallel with the second solenoid valve, and when the heat pump type drying system enters the defrosting mode, the first solenoid valve and the second solenoid valve are in a closed state, and the third solenoid valve is in an open state. The heat pump type drying system can prevent the compressor from being started and stopped frequently while defrosting is carried out.

Description

Heat pump type drying system and defrosting method for same

Technical Field

The invention relates to the technical field of refrigeration, in particular to a heat pump type drying system and a defrosting method for the same.

Background

The drying system is an equipment combination for drying materials with high water content by utilizing heat energy. The drying system can be divided into various types such as an electric heating type, a gas type, a fuel oil type, a coal type, a heat pump type and the like according to different heat energy generation forms. Compared with the traditional fuel type drying system, the heat pump type drying system has the advantages of energy conservation, high efficiency, environmental friendliness, low operating cost and the like, so that the heat pump type drying system is widely applied to various fields of tobacco processing, grain storage, metallurgy and chemical engineering and the like.

In the tobacco processing process, the heat pump type drying system can realize precision adjustment on the temperature and the humidity in the curing barn, so that the tobacco curing efficiency is effectively improved, and the tobacco quality is ensured. A heat pump drying system in the prior art generally includes a compressor, a condenser, an expansion device and an evaporator connected in sequence by refrigerant pipes to form a refrigeration circuit for allowing a refrigerant to flow therein. Wherein the condenser is generally disposed within the heating chamber adjacent to the curing barn for delivering drying air into the curing barn; the evaporator is generally disposed outside the heating chamber to exchange heat with the external environment, thereby ensuring the evaporation efficiency of the refrigerant in the evaporator. However, in the low temperature condition, the dry bulb temperature of the external environment is low, so that the surface of the evaporator (especially the bottom of the evaporator) is easy to frost.

In order to solve the technical problem that an evaporator of a heat pump type drying system is easy to frost under a low-temperature working condition, a technical scheme for defrosting the evaporator by using high-temperature gas of a compressor has been developed in the prior art. For example, chinese utility model patent CN215898848U discloses an air source heat pump drying unit and tobacco flue-curing house. The air source heat pump drying unit comprises a compressor, a condenser, a throttling element and a cold evaporator which are sequentially connected through pipelines. The outlet end of the compressor is connected with a bypass pipeline. The other end of the bypass pipeline is connected into a pipeline between the throttling element and the inlet end of the evaporator. A bypass electromagnetic valve for controlling the on-off of the pipeline is arranged on the bypass pipeline. When the exhaust pressure of the compressor is detected to reach the preset pressure, the bypass electromagnetic valve is opened, so that part of high-temperature gaseous refrigerant is discharged from the compressor and then directly enters the bypass pipeline without passing through the condenser. The part of the refrigerant enters the evaporator after passing through the bypass pipeline, so that the high-temperature refrigerant of the compressor is utilized to defrost the evaporator, and defrosting without stopping the machine is realized. However, the high-temperature gaseous refrigerant is condensed into a liquid refrigerant after heat exchange in the evaporator and flows into a gas-liquid separator in the refrigeration circuit, and cannot be directly sucked by the compressor in a gaseous form for recompression, so that the suction pressure of the compressor is too low, and frequent start and stop are caused.

Therefore, there is a need in the art for a new solution to the above problems.

Disclosure of Invention

The invention provides a heat pump type drying system, aiming at solving the technical problem that in the prior art, when defrosting is carried out under a low-temperature working condition, a compressor is frequently started and stopped due to the fact that the suction pressure is too small. The heat pump type drying system includes: the refrigeration main loop comprises a compressor, a condenser, an expansion device and an evaporator which are sequentially connected through refrigerant pipelines, wherein a bottom coil is arranged at the bottom of the evaporator, the bottom coil is provided with an inlet end connected with the expansion device and an outlet end connected with an air suction port of the compressor, an openable and closable first electromagnetic valve is arranged between the inlet end and the expansion device, and an openable and closable second electromagnetic valve is arranged in the bottom coil; the defrosting bypass pipe is provided with a first end connected with the exhaust port of the compressor and a second end connected with the inlet end, and the defrosting bypass pipe is also provided with a third electromagnetic valve capable of being opened and closed; and a capillary line configured to be disposed in the bottom coil in parallel with the second solenoid valve, and when the heat pump drying system enters a defrost mode, the first and second solenoid valves are in a closed state and the third solenoid valve is in an open state.

The heat pump type drying system comprises a refrigeration main loop, a defrosting bypass pipe and a capillary pipeline. The refrigeration main loop comprises a compressor, a condenser, an expansion device and an evaporator which are sequentially connected through a refrigerant pipeline so as to form a refrigerant loop allowing a refrigerant to circularly flow in the refrigeration main loop. The bottom of the evaporator is provided with a bottom coil having an inlet end connected to the expansion device and an outlet end connected to the suction port of the compressor, and a first electromagnetic valve is provided between the inlet end and the expansion device and is openable and closable. The bottom coil is also provided with a second electromagnetic valve which can be opened and closed. It should be noted that the evaporator is formed by combining a plurality of spaced coils, and the bottom coil at the bottom of the evaporator is most likely to generate frosting due to insufficient air supply, low evaporation temperature, and the like. Therefore, the invention takes the bottom coil as the main object of defrosting of the evaporator, and can obviously improve the pertinence of defrosting. The first electromagnetic valve and the second electromagnetic valve are arranged, so that the on-off of the refrigerant in the bottom coil pipe can be conveniently controlled. The defrosting by-pass pipe is provided with a first end connected with the exhaust port of the compressor and a second end connected with the inlet end of the bottom coil pipe, and the defrosting by-pass pipe is also provided with a third electromagnetic valve capable of being opened and closed so as to control the on-off of the refrigerant in the defrosting by-pass pipe. The capillary tubing is configured to be disposed in the bottom coil in parallel with the second solenoid valve. When the heat pump type drying system enters a defrosting mode, the first electromagnetic valve and the second electromagnetic valve are closed, so that the liquid refrigerant after being decompressed and expanded by the expansion device can not enter the bottom coil from the inlet end. Meanwhile, the third solenoid valve is opened, so that a part of high-temperature and high-pressure gaseous refrigerant discharged from the exhaust port of the compressor flows into the bottom coil pipe through the defrosting bypass pipe, and the bottom coil pipe is defrosted. In this process, the high-temperature and high-pressure gaseous refrigerant is condensed into a medium-temperature and high-pressure liquid refrigerant. Then, the medium-temperature high-pressure liquid refrigerant flows into the capillary tube, and is decompressed and expanded into a low-temperature low-pressure liquid refrigerant. Then, the low-temperature low-pressure liquid refrigerant continues to flow in the bottom coil between the second solenoid valve and the outlet end, thereby being evaporated into a low-temperature low-pressure gaseous refrigerant. Finally, the low-temperature and low-pressure gaseous refrigerant is sucked into the compressor again from the air suction port along the refrigerant pipeline, so that the compressor is ensured to have moderate suction pressure, the compressor is prevented from being started and stopped frequently due to too low suction pressure, the service life of the compressor is prolonged, and the running stability of the whole heat pump type drying system is improved.

In a preferred technical solution of the above heat pump type drying system, the bottom coil includes a first flow path, a second flow path, a third flow path, and a fourth flow path that are connected end to end in sequence, ends of the first flow path and the fourth flow path are the inlet end and the outlet end, respectively, and the second electromagnetic valve and the capillary line are arranged in parallel between the second flow path and the third flow path. Through the arrangement, the bottom coil pipe can have a simple structure. In addition, the second electromagnetic valve and the capillary pipeline are arranged between the second flow path and the third flow path in parallel, so that the liquid refrigerant flowing in from the capillary pipeline can be completely evaporated into the gaseous refrigerant in the fourth flow path, and the compressor can be ensured to have moderate suction pressure.

In a preferred embodiment of the heat pump drying system, the refrigerant pipeline includes an exhaust pipe located between the exhaust port and the condenser, the exhaust pipe has a first inner diameter, and the defrosting bypass pipe has a second inner diameter, where the first inner diameter is larger than the second inner diameter. The first inner diameter of the exhaust pipe is set to be larger than the second inner diameter of the defrosting bypass pipe, so that the resistance of the high-temperature and high-pressure gaseous refrigerant discharged from the exhaust port of the compressor when flowing in the exhaust pipe is smaller than the resistance of the high-temperature and high-pressure gaseous refrigerant when flowing in the defrosting bypass pipe, and the distribution proportion of the high-temperature and high-pressure gaseous refrigerant between the exhaust pipe and the defrosting bypass pipe can be conveniently adjusted by adjusting the opening degree of the expansion device.

In order to solve the technical problem that the compressor is frequently started and stopped due to the fact that the suction pressure is too small when the heat pump type drying system defrosts under the low-temperature working condition in the prior art, the invention also provides a defrosting method for the heat pump type drying system, wherein the defrosting method is executed in the heat pump type drying system according to any one of the above items, and comprises the following steps:

and when the condition that the heat pump type drying system enters the defrosting mode is met, controlling a first electromagnetic valve and a second electromagnetic valve of the heat pump type drying system to be closed, and controlling a third electromagnetic valve to be opened. When the condition that the heat pump type drying system enters the defrosting mode is met, the first electromagnetic valve and the second electromagnetic valve are controlled to be closed, and the third electromagnetic valve is controlled to be opened, so that the high-temperature and high-pressure gaseous refrigerant discharged from the air outlet of the compressor can flow into the bottom coil pipe through the defrosting bypass pipe, and the bottom coil pipe is defrosted conveniently. In addition, through the capillary pipeline arranged on the defrosting bypass pipe, part of the refrigerant used for defrosting the bottom coil pipe can be converted into low-temperature and low-pressure gas refrigerant, so that the compressor is ensured to have moderate suction pressure, and the compressor is prevented from being started and stopped frequently.

In the above defrosting method for a heat pump drying system, the defrosting method further comprises:

detecting the temperature of the external environment;

comparing the measured temperature of the external environment with a preset temperature;

when the temperature of the external environment is lower than the preset temperature, detecting the temperature of a coil of an evaporator of the heat pump type drying system, and determining the difference value of the temperature of the external environment minus the temperature of the coil;

comparing the difference value with a first preset difference value;

and when the difference is greater than or equal to the first preset difference, the condition for entering the defrosting mode is met. When the temperature of the external environment is lower than the preset temperature, the temperature of the external environment is lower, and the evaporator has a risk of frosting. Accordingly, a coil temperature of an evaporator of a heat pump drying system is sensed and a difference between an outside ambient temperature minus the coil temperature is determined. When the difference is larger than or equal to the first preset difference, the temperature of the coil is lower, the possibility of frosting of the evaporator is higher, and the condition of entering the defrosting mode is met.

In the above defrosting method for a heat pump drying system, after "controlling a first solenoid valve and a second solenoid valve of the heat pump drying system to be closed, and controlling a third solenoid valve to be opened", the defrosting method includes:

after a first preset time period, re-detecting the temperature of the external environment and the temperature of the coil;

determining a current temperature of the external environment minus the coil temperature;

comparing the current difference value with the first preset difference value and the second preset difference value;

adjusting an opening degree of an expansion device of the heat pump type drying system based on the comparison result,

wherein the second preset difference is smaller than the first preset difference. Through foretell setting, can accurate control refrigerant distribution ratio between refrigeration major loop and defrosting bypass pipe, improve the availability factor of refrigerant.

In the defrosting method for the heat pump drying system, when the current difference is greater than the second preset difference and smaller than the first preset difference, the current opening degree of the expansion device is maintained. When the current difference is greater than the second preset difference and less than the first preset difference, it indicates that there is a moderate difference between the temperature of the external environment and the temperature of the coil of the evaporator, so that the current opening of the expansion device is maintained.

In the defrosting method for the heat pump type drying system, when the current difference value is greater than the second preset difference value and smaller than the first preset difference value, the expansion device is controlled to reduce the first opening. When the current difference is greater than the second preset difference and less than the first preset difference, it indicates that there is a moderate difference between the temperature of the external environment and the temperature of the coil of the evaporator, so the expansion device can be controlled to reduce the first opening properly to ensure the heating efficiency.

In the defrosting method for the heat pump drying system, when the current difference is greater than or equal to the first preset difference, the expansion device is controlled to reduce a second opening degree, wherein the second opening degree is greater than the first opening degree. When the current difference is greater than or equal to the first preset difference, the difference between the temperature of the external environment and the temperature of the coil of the evaporator is larger, namely the temperature of the coil of the evaporator is lower, the evaporator has a larger frosting risk, and therefore the expansion device is controlled to reduce the second opening, so that more refrigerants flow to the defrosting bypass pipe to defrost the evaporator better.

In the defrosting method for the heat pump type drying system, when the current difference is smaller than or equal to the second preset difference and is kept for the second preset time period, the current opening degree of the expansion device is kept, the third electromagnetic valve is controlled to be closed, and the first electromagnetic valve and the second electromagnetic valve are controlled to be opened. When the current difference is smaller than or equal to the second preset difference and the second preset time period is kept, the temperature of the coil of the evaporator is already high, and the possibility of frosting of the evaporator is low. Therefore, the current opening degree of the expansion device is maintained, the third electromagnetic valve is controlled to be closed, and the first electromagnetic valve and the second electromagnetic valve are controlled to be opened, so that the liquid refrigerant passing through the expansion device can flow into the bottom coil pipe to participate in the circulation of the refrigeration main loop, and the utilization efficiency of the refrigerant is ensured.

Drawings

Preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a refrigeration circuit of a heat pump drying system according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of an evaporator of a heat pump drying system according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a first refrigerant flow path of an embodiment of a bottom coil of a heat pump drying system of the present invention;

FIG. 4 is a schematic diagram of a second refrigerant flow path of an embodiment of a bottom coil of a heat pump drying system of the present invention;

FIG. 5 is a schematic flow diagram of a defrost method for a heat pump drying system of the present invention;

FIG. 6 is a schematic flow diagram of a first embodiment of a defrost method for a heat pump drying system of the present invention;

fig. 7 is a schematic flow chart of a defrosting method for a heat pump type drying system according to a second embodiment of the present invention.

List of reference numbers:

1. a heat pump type drying system; 10. a refrigeration primary circuit; 11. a compressor; 11a, a first compressor; 11b, a second compressor; 111. an exhaust port; 112. an air suction port; 12. a condenser; 13. an expansion device; 13a, a first expansion device; 13b, a second expansion device; 14. an evaporator; 141. a bottom coil; 1411. an inlet end; 1412. an outlet end; 1413. a first flow path; 1414. a second flow path; 1415. a third flow path; 1416. a fourth flow path; 142. a coil pipe; 15. a refrigerant pipeline; 151. an exhaust pipe; 152. a high pressure liquid pipe; 153. a low pressure liquid pipe; 154. an air intake duct; 16. a first solenoid valve; 17. a second solenoid valve; 20. a defrosting bypass pipe; 21. a first end; 22. a second end; 23. a third solenoid valve; 30. a capillary channel.

Detailed Description

Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only for explaining the technical principle of the present invention, and are not intended to limit the scope of the present invention.

It should be noted that in the description of the present invention, the terms of direction or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, which are only for convenience of description, and do not indicate or imply that the device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

Furthermore, it should be noted that, in the description of the present invention, unless otherwise explicitly specified or limited, the terms "disposed" and "connected" are to be interpreted broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; either directly or indirectly through intervening media, or through the communication between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In order to solve the technical problem that in the prior art, when the heat pump type drying system is defrosted under a low-temperature working condition, the compressor is frequently started and stopped due to the fact that the suction pressure is too small, the invention provides a heat pump type drying system 1. The heat pump type drying system 1 includes: a refrigeration main circuit 10, the refrigeration main circuit 10 includes a compressor 11, a condenser 12, an expansion device 13 and an evaporator 14 which are connected in sequence through a refrigerant pipeline 15, a bottom coil 141 is arranged at the bottom of the evaporator 14, the bottom coil 141 is provided with an inlet end 1411 connected with the expansion device 13 and an outlet end 1412 connected with a suction port 112 of the compressor 11, an openable and closable first electromagnetic valve 16 is arranged between the inlet end 1411 and the expansion device 13, and an openable and closable second electromagnetic valve 17 is arranged in the bottom coil 141; a defrosting bypass pipe 20, the defrosting bypass pipe 20 having a first end 21 connected to the discharge port 1111 of the compressor 11 and a second end 22 connected to the inlet port 1411, the defrosting bypass pipe 20 being further provided with a third solenoid valve 23 that can be opened and closed; and a capillary line 30, the capillary line 30 configured to be arranged in the bottom coil 141 in parallel with the second solenoid valve 17, when the heat pump type drying system 1 enters the defrosting mode, the first solenoid valve 16 and the second solenoid valve 17 are in a closed state, and the third solenoid valve 23 is in an open state.

Fig. 1 is a schematic structural diagram of an embodiment of a refrigeration circuit of a heat pump drying system according to the present invention. As shown in FIG. 1, in one or more embodiments, a heat pump drying system 1 of the present invention includes components such as a refrigeration main circuit 10, a defrost bypass 20, and a capillary line 30. In one or more embodiments, heat pump dryer system 1 is configured to deliver drying air into a curing barn (not shown) for placing tobacco therein, thereby adjusting the temperature and humidity within the curing barn to dry the tobacco. Alternatively, the heat pump drying system 1 may be configured to deliver the drying air to other predetermined spaces according to actual needs.

As shown in fig. 1, the main refrigeration circuit 10 includes a compressor 11, a condenser 12, an expansion device 13, and an evaporator 14, which are connected in series by a refrigerant line 15 to form a circuit for allowing a refrigerant to circulate therethrough. The refrigerant includes, but is not limited to, R410a, R32a, and the like. In one or more embodiments, the compressor 11 includes a first compressor 11a and a second compressor 11b connected in parallel with each other. Each of the first compressor 11a and the second compressor 11b is a constant frequency compressor to reduce component costs. The first compressor 11a and the second compressor 11b may be alternately started and stopped. That is, when one of the first and

second compressors

11a and 11b is turned on, the other of the first and

second compressors

11a and 11b is turned off. Through foretell setting, can effectively avoid single compressor frequently surely to open and stop to the life of extension compressor. In addition, when the heating demand is large, the first compressor 11a and the second compressor 11b can also be simultaneously turned on to provide a large amount of heating in a short time. Alternatively, each of the first and

second compressors

11a and 11b may be an inverter compressor, or one of the first and

second compressors

11a and 11b may be a fixed frequency compressor and the other may be an inverter compressor. The first compressor 11a and the second compressor 11b may be a piston compressor, a screw compressor, a turbo compressor, or the like. Alternatively, the number of compressors 11 may be provided in other suitable numbers, more or less than 2, such as 1, 3, etc.

With continued reference to fig. 1, the first compressor 11b has an exhaust port 111 and a suction port 112. The exhaust port 111 communicates with an inlet end (not shown) of the condenser 12 through an exhaust pipe 151. The exhaust pipe 151 has a first inner diameter. The first inner diameter is 12.7mm. Alternatively, the first inner diameter may be set to other suitable values greater or less than 12.7mm. The condenser 12 includes, but is not limited to, a finned coil heat exchanger and a plate heat exchanger, and is provided with a corresponding fan. The outlet end (not shown) of the condenser 12 communicates with the corresponding expansion device 13 (i.e., the first expansion device 13 a) through a high-pressure liquid pipe 152. The first expansion device 13a may be, but is not limited to, an electronic expansion valve, a thermostatic expansion valve, or the like. The first expansion device 13a communicates with the evaporator 14 through a low pressure liquid pipe 153. The evaporator 14 communicates with the suction port 112 of the first compressor 11a through a suction pipe 154. The first compressor 11a, the condenser 12, the first expansion device 13a and the evaporator 14 together form a refrigeration circuit. In addition, the second compressor 11b, the condenser 12, the second expansion device 13b and the evaporator 14 together form another refrigeration circuit independent from the above refrigeration circuit.

Fig. 2 is a schematic structural diagram of an embodiment of an evaporator of the heat pump drying system of the present invention. As shown in FIG. 2, in one or more embodiments, the evaporator 14 is a finned coil heat exchanger. The evaporator 14 has a plurality of coils 142 spaced apart from one another. Each coil 142 has an inlet (not shown) in communication with the first expansion device 13a through a distributor tube or other distribution device (not shown) and an outlet (not shown) in communication with the suction port 112 of the first compressor 11a through a header (not shown). At the bottom of the evaporator 14 is a bottom coil 141. The bottom coil 141 has opposite inlet 1411 and outlet ends 1412. Wherein the inlet end 1411 communicates with the first expansion device 13a and the outlet end 1412 communicates with the suction port 112 of the first compressor 11 a. An openable and closable first solenoid valve 16 is further provided between the inlet end 1411 and the first expansion device 13a, and an openable and closable second solenoid valve 17 is further provided in the bottom coil 141. It can be understood that when the first solenoid valve 16 and the second solenoid valve 17 are simultaneously opened, the low-pressure liquid refrigerant expanded and decompressed by the first expansion device 13a can flow into the bottom coil 141 from the inlet end 1411 and be evaporated into a low-temperature and low-pressure gas refrigerant in the bottom coil 141. At this point, the bottom coil 141 functions the same as any other coil 142 in the evaporator 14.

As shown in FIG. 1, in one or more embodiments, the defrost bypass 20 has opposing first and second ends 21, 22. Wherein the first end 21 communicates with the exhaust port 111 of the first compressor 11 a. In one or more embodiments, the first end 21 is positioned on the discharge tube 151 between the first compressor 11a and the condenser 12. The second end 22 communicates with the inlet end 1411 of the bottom coil 141 of the evaporator 14. Further, an openable and closable third solenoid valve 23 is provided in the defrosting bypass pipe 20. That is, the third solenoid valve 23 is located between the first end 21 and the second end 22. It can be understood that when the third solenoid valve 23 is opened, a portion of the high-temperature and high-pressure gaseous refrigerant discharged from the discharge port 111 of the first compressor 11a may flow into the defrosting bypass pipe 20 from the first end 21 and further into the bottom coil 141, thereby defrosting the same. The defrost bypass line 20 has a second inner diameter, and the second inner diameter is smaller than the first inner diameter of the vent line 151. The second inner diameter includes, but is not limited to, 9.52mm, 7mm, etc. With the above arrangement, when the third solenoid valve 23 is opened, the distribution ratio of the refrigerant between the refrigeration main circuit 10 and the defrost bypass 20 can be easily controlled by adjusting the opening degree of the first solenoid valve 13 a.

As shown in fig. 1, the capillary line 30 is disposed in the bottom coil 141 and is connected in parallel with the second solenoid valve 17. Fig. 3 is a schematic view of a first refrigerant flow path of the embodiment of the bottom coil of the heat pump type drying system of the present invention; fig. 4 is a schematic diagram of a second refrigerant flow path of the bottom coil of the heat pump drying system according to the embodiment of the present invention. In one or more embodiments, as shown in fig. 3 and 4, the bottom coil 141 has a first flow path 1413, a second flow path 1414, a third flow path 1415, and a fourth flow path 1416 in end-to-end sequence to form a serpentine coil. The first flow path 1413 terminates at an inlet end 1411 of the bottom coil 141 and the fourth flow path 1416 terminates at an outlet end 1412 of the bottom coil 141. The capillary line 30 and the second solenoid valve 17 are arranged in parallel with each other between the second flow path 1414 and the third flow path 1415. It should be noted that, when the heat pump type drying system 1 of the present invention does not need to perform defrosting, the first solenoid valve 16 and the second solenoid valve 17 are opened, and the third solenoid valve 23 is closed, the refrigerant flows in the direction indicated by the arrow in fig. 3. As described above, the bottom coil 141 evaporates the liquid refrigerant sent from the first expansion device 13a into a low-temperature low-pressure gas refrigerant together with the other coils 142 in the evaporator 14. When the heat pump type drying system 1 of the present invention needs to be defrosted, the first solenoid valve 16 and the second solenoid valve 17 are closed, and the third solenoid valve 23 is opened, and the refrigerant flows in the direction indicated by the arrow in fig. 1 and 4. Since the first solenoid valve 16 is closed, the liquid refrigerant expanded and decompressed by the first expansion device 13a cannot enter the bottom coil 141. Accordingly, since the third solenoid valve 23 is opened, a portion of the high-temperature and high-pressure gas refrigerant discharged from the discharge port 111 of the first compressor 11a can enter the foot coil 141 along the defrost bypass 20. Then, the high-temperature and high-pressure gaseous refrigerant flows through the first flow passage 1413 and the second flow passage 1414 in this order, and the underfloor coil 141 is heated and defrosted. In this process, the high-temperature and high-pressure gaseous refrigerant is condensed into a low-temperature and high-pressure liquid refrigerant. Then, the part of the low-temperature and high-pressure liquid refrigerant flows to the capillary tube 30 and is expanded and reduced to a low-temperature and low-pressure liquid refrigerant in the capillary tube 30 by being blocked by the second solenoid valve 17. This part of the low-temperature low-pressure liquid refrigerant is evaporated into a low-temperature low-pressure gas refrigerant in the third flow passage 1415 and the fourth flow passage 1416, and is sucked again into the suction port 112 by the first compressor 11a to enter the next refrigeration cycle.

The defrosting method for the heat pump drying system 1 according to the present invention will be described in detail with reference to the above-mentioned embodiment of the heat pump drying system 1.

FIG. 5 is a flow chart of the defrosting method for the heat pump drying system according to the present invention. As shown in fig. 5, when the condition for the heat pump type drying system 1 to enter the defrosting mode is satisfied, the first solenoid valve 16 and the second solenoid valve 17 of the heat pump type drying system 1 are controlled to be closed, and the third solenoid valve 23 is controlled to be opened (step S1). With the above arrangement, when the condition for entering the defrost mode is satisfied, a portion of the high-temperature and high-pressure gaseous refrigerant discharged from the discharge port 111 of the compressor 11 can be delivered to the bottom coil 141 of the evaporator 14 through the defrost bypass pipe for defrosting. In addition, the liquid refrigerant condensed in the bottom coil 141 can flow through the capillary tube 30 to expand and reduce the pressure, and then continue to evaporate into a low-temperature and low-pressure gaseous refrigerant, so that the compressor 11 is ensured to have sufficient suction pressure, and frequent start and stop caused by insufficient suction pressure are prevented.

Fig. 6 is a schematic flow chart of a defrosting method for a heat pump type drying system according to a first embodiment of the present invention. As shown in fig. 6, in one or more embodiments, when the defrosting method for the heat pump type drying system 1 of the present invention is started, step S10 of detecting the temperature of the external environment is first performed. The temperature of the external environment may be detected by a temperature sensor arranged in the external environment. Next, step S11 is executed to determine whether the temperature of the external environment is less than a preset temperature. In one or more embodiments, the preset temperature is 3 ℃ (degrees celsius). Alternatively, the preset temperature may be set to other suitable temperatures higher or lower than 3 ℃, such as 2 ℃, 4 ℃, and the like. If the result of the determination is negative, it means that the temperature of the external environment is high at this time, and the evaporator 14 is less likely to frost. Therefore, step S10 may be repeatedly executed to continuously detect the temperature of the external environment. If the determination result is yes, it means that the temperature of the external environment is low at this time, and the evaporator 14 may be frosted. However, whether the evaporator 14 is frosted or frosted with a high probability also needs to be determined after further detection of the coil temperature of the evaporator 14. Accordingly, the defrost method proceeds to step S12, where the coil temperature of evaporator 14 of heat pump dryer system 1 is sensed and the difference between the outside ambient temperature minus the coil temperature is determined. The coil temperature of the evaporator 14 can be measured by a temperature sensor disposed on the evaporator 14. The type, number and arrangement position of the temperature sensors can be adjusted according to actual needs. Next, the defrosting method proceeds to step S13, and determines whether the difference is greater than or equal to a first preset difference. In one or more embodiments, the first predetermined difference is 3 ℃. Alternatively, the first preset difference may also be set to other suitable temperatures higher or lower than 3 ℃, such as 2 ℃, 4 ℃ and the like. If the determination result is yes, it is described that the temperature of the external environment is low, but the coil temperature is still high, and the evaporator 14 is less likely to be frosted, so that the step S10 may be repeatedly executed to continuously detect the temperature of the external environment. If the determination result is negative, it indicates that the temperature of the external environment is low, the coil temperature is also low, and the evaporator 14 is likely to be frosted. Therefore, step S14 is executed, i.e. the first solenoid valve 16 and the second solenoid valve 17 of the heat pump type drying system 1 are controlled to be closed, and the third solenoid valve 23 is controlled to be opened, thereby defrosting the evaporator 14.

With continued reference to fig. 6, after step S14 is completed, the defrost method proceeds to step S15, and the outside environment temperature and the coil temperature are re-detected after a first preset time period. In one or more embodiments, the first preset time period is 5s (seconds). Alternatively, the first preset time period may be set to other suitable times longer or shorter than 5s, such as 4s, 6s, etc. Next, step S16 is performed to determine the difference between the current outside ambient temperature minus the coil temperature. Then, it is judged whether or not the current difference is equal to or larger than a first preset difference (step S17). If the determination result is yes, which indicates that the coil temperature is still low, step S18 is executed to control the expansion device 13 to decrease the second opening degree. It is to be noted that the "expansion device 13" referred to herein refers only to the first expansion device 13a in the same refrigeration circuit as the defrost bypass 20, and does not include the second expansion device 13b in a different refrigeration circuit from the defrost bypass 20. In one or more embodiments, the second opening is 50 steps. Alternatively, the second opening degree may be set to other suitable number of steps larger or smaller than 50 steps. By decreasing the expansion device by the second opening degree, the amount of the refrigerant flowing into the defrost bypass pipe 20 can be increased accordingly, thereby improving the defrost efficiency. When step S18 is completed, the defrosting method repeatedly executes step S15, that is, after the first preset time period, the temperature of the external environment and the temperature of the coil are re-detected.

With continued reference to fig. 6, after the step S17 is executed, when the determination result is negative, a step S19 is executed, that is, it is determined whether the current difference is greater than a second preset difference and smaller than a first preset difference. In one or more embodiments, the second predetermined difference is 0 ℃. Alternatively, the second predetermined difference may be set to other suitable values higher or lower than 0 ℃, such as 0.5 ℃, -1 ℃, etc. When the judgment result is yes, which indicates that the coil temperature has started to decrease at this time, step S20 is executed, in which the current opening degree of the expansion device 13 is maintained, so that defrosting of the evaporator 14 is continued. After step S20, the defrosting method repeats step S15, that is, after the first preset time period, the temperature of the external environment and the temperature of the coil are re-detected.

With continued reference to fig. 6, after step S19 is executed, when the determination result is no, which indicates that the current difference is less than or equal to the second preset difference, step S21 is executed to obtain the duration. Next, it is determined whether the duration is less than a second preset time period (step S22). In one or more embodiments, the second preset time period is 5min (minutes). Alternatively, the second preset time period may also be set to other suitable times longer or shorter than 5 min. When the interpretation result is yes, step S20 is performed, i.e., the current opening degree of the expansion device 13 is maintained. After step S20 is completed, step S15 is repeatedly executed, that is, after the first preset time period elapses, the temperature of the external environment and the temperature of the coil are re-detected. When the judgment result is negative, the coil temperature is already high and the duration is long, the current opening degree of the expansion device 13 is kept, the third electromagnetic valve 23 is controlled to be closed, and the first electromagnetic valve 16 and the second electromagnetic valve 17 are controlled to be opened. When step S23 is completed, the defrosting process is ended.

Fig. 7 is a schematic flow chart of a defrosting method for a heat pump type drying system according to a second embodiment of the present invention. As shown in fig. 7, in one or more embodiments, in the defrosting method for the heat pump type drying system 1 of the present invention, after step S19 is completed, if the determination result is yes, step S24 of controlling the expansion device 13 to decrease the first opening degree is performed, wherein the second opening degree is greater than the first opening degree. In one or more embodiments, the first opening is 5 steps. Alternatively, the first opening degree may be set to other suitable number of steps larger or smaller than 5 steps, such as 4 steps, 6 steps, or the like. By appropriately decreasing the opening degree of the expansion device 13, the amount of refrigerant flowing into the defrost bypass pipe 20 can be appropriately increased, thereby improving defrost efficiency. It should be noted that the parts not mentioned in the second embodiment may be configured the same as the first embodiment, and are not described herein again.

So far, the technical solutions of the present invention have been described in connection with the preferred embodiments shown in the drawings, but it is apparent to those skilled in the art that the scope of the present invention is not limited to these specific embodiments. Equivalent changes or substitutions of related technical features can be made by those skilled in the art without departing from the principle of the invention, and the technical scheme after the changes or substitutions can fall into the protection scope of the invention.

Claims

1. A heat pump drying system, comprising:

the refrigeration main loop comprises a compressor, a condenser, an expansion device and an evaporator which are sequentially connected through refrigerant pipelines, wherein a bottom coil is arranged at the bottom of the evaporator, the bottom coil is provided with an inlet end connected with the expansion device and an outlet end connected with an air suction port of the compressor, an openable and closable first electromagnetic valve is arranged between the inlet end and the expansion device, and an openable and closable second electromagnetic valve is arranged in the bottom coil;

the defrosting bypass pipe is provided with a first end connected with the exhaust port of the compressor and a second end connected with the inlet end, and the defrosting bypass pipe is also provided with a third electromagnetic valve capable of being opened and closed; and

a capillary line configured to be arranged in the bottom coil in parallel with the second solenoid valve to each other, and

when the heat pump type drying system enters a defrosting mode, the first electromagnetic valve and the second electromagnetic valve are in a closed state, and the third electromagnetic valve is in an open state.

2. A heat pump drying system according to claim 1, wherein said bottom coil comprises a first flow path, a second flow path, a third flow path, and a fourth flow path connected end to end, said first flow path and said fourth flow path terminating in said inlet end and said outlet end, respectively, said second solenoid valve and said capillary line being arranged in parallel with each other between said second flow path and said third flow path.

3. A heat pump drying system according to claim 1, wherein the refrigerant line comprises an exhaust duct between the exhaust outlet and the condenser, the exhaust duct having a first inner diameter and the defrost bypass duct having a second inner diameter, wherein the first inner diameter is larger than the second inner diameter.

4. A defrosting method for a heat pump drying system, wherein the defrosting method is performed in the heat pump drying system according to any one of claims 1 to 3, and comprises:

and when the condition that the heat pump type drying system enters the defrosting mode is met, controlling a first electromagnetic valve and a second electromagnetic valve of the heat pump type drying system to be closed, and controlling a third electromagnetic valve to be opened.

5. A defrost method for a heat pump drying system, said defrost method further comprising:

detecting the temperature of the external environment;

comparing the difference value with a first preset difference value;

and when the difference is greater than or equal to the first preset difference, the condition for entering the defrosting mode is met.

6. A defrosting method for a heat pump drying system according to claim 5, wherein after "controlling the first and second solenoid valves of the heat pump drying system to be closed and controlling the third solenoid valve to be opened", the defrosting method comprises:

wherein the second preset difference is smaller than the first preset difference.

7. A defrost method for a heat pump drying system according to claim 6,

and when the current difference value is larger than the second preset difference value and smaller than the first preset difference value, keeping the current opening degree of the expansion device.

8. A defrost method for a heat pump drying system according to claim 6, wherein said expansion device is controlled to decrease by a first opening degree when said difference is greater than said second predetermined difference and less than said first predetermined difference.

9. A defrost method for a heat pump drying system according to claim 8, wherein said expansion device is controlled to decrease a second opening when said difference is greater than or equal to said first predetermined difference, wherein said second opening is greater than said first opening.

10. A defrost method for a heat pump drying system according to claim 6,

and when the current difference is smaller than or equal to the second preset difference and is kept for a second preset time period, keeping the current opening degree of the expansion device, controlling the third electromagnetic valve to be closed, and controlling the first electromagnetic valve and the second electromagnetic valve to be opened.