Alternating airflow heat pump dehumidification drying device and control method thereof

Abstract

The invention provides an alternating airflow heat pump dehumidification drying device and a control method thereof, and relates to the technical field of agricultural product drying, the alternating airflow heat pump dehumidification drying device comprises a drying bed and a heat pump device, the drying bed at least comprises an upper drying chamber and a lower drying chamber, and each drying chamber at least comprises multiple thick material layers arranged from top to bottom; the thick material layers and the airflow channels are alternately arranged, airflow blocking structures are alternately arranged at the front ends and the rear ends of the airflow channels, and ventilation fans are arranged on the side walls of the drying beds. The heat pump device comprises a compressor, a throttling valve, a condensation evaporator A, a condensation evaporator B, a condensation evaporator C, a condensation evaporator D, a corresponding reversing valve A, a corresponding reversing valve B and a corresponding reversing valve C. The drying bed is a plurality of alternating airflow thick material layers, the material layers and airflow channels are alternately arranged, the heat pump device comprises four sets of condensation evaporators and corresponding reversing valves, and alternating airflow dehumidification and drying of the thick material layers can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of drying agricultural products, and in particular to an alternating airflow thick layer heat pump dehumidification drying device and a control method thereof. Background Art

[0002] Drying of agricultural products is an important process for their storage value-added and deep processing pretreatment, and is an important part of agricultural product processing. At present, agricultural products are mostly dried in thin layers, that is, the agricultural products are spread flat on the tray, and the airflow passes through the materials. The thin layer drying equipment is large in size and has low volume utilization. In order to improve equipment utilization and reduce equipment size, the materials can be piled to a certain thickness (usually more than 5cm), and the airflow passes through the bed. Thick layer drying is adopted. The material uniformity of the thick bed in the direction of the bed thickness is poor. Taking a 35cm thick bed of grain as an example, the humidity difference is about 4% after drying. In order to improve the uniformity of thick bed drying, some existing technologies have proposed thick layer drying methods based on alternating airflow. By switching the airflow temperature and airflow direction, the heat utilization rate is improved to obtain better product drying quality.

[0003] As an emerging drying method, heat pump drying has the advantages of energy saving, environmental protection, intelligent control, and good drying effect, and has been widely promoted. According to the different ways of handling hot and humid air in the drying room, it can be divided into dehumidification heat pump and dehumidification heat pump. The use of dehumidification heat pump will lose a large amount of high-quality heat energy, waste energy, and is not conducive to energy saving and environmental protection. Dehumidification heat pumps mostly use closed dehumidification method. The operating conditions of the evaporator and condenser are interrelated and change in real time during the drying process, which may lead to poor dehumidification effect and dehumidification reliability. Regarding the control strategy of the heat pump dehumidification system, some existing technologies disclose dehumidification control methods. According to the current drying stage of the material, the drying wet load is intelligently adjusted to dynamically match the wet load with the actual capacity. Other existing technologies disclose control methods for dehumidification heat pumps. The air volume passing through the evaporator is adjusted according to the dew point temperature to improve the dehumidification effect.

[0004] However, there is currently a lack of matching heat pump control strategies for thick layer drying based on alternating airflow. Summary of the invention

[0005] In order to solve the problems of thick layer drying, alternating airflow control, etc. in the prior art, the present invention proposes the following technical solutions:

[0006] An alternating airflow heat pump dehumidification and drying device, comprising:

[0007] A drying bed and a heat pump device; wherein the drying bed comprises at least two upper and lower drying chambers, each drying chamber comprising at least multiple layers of thick material arranged from top to bottom, for example, an even number of layers of thick material arranged, for example, four layers of thick material arranged; obviously, multiple layers of thick material arranged in this way can be arranged in parallel in the drying chamber, for example, three layers can be arranged in parallel through a material bin.

[0008] Thick material layers and air flow channels are arranged alternately, and air flow blocking structures are alternately arranged at the front and rear ends of the air flow channels, so that after the air flow enters the air flow channel from the inlet, it needs to pass through the thick material layer, and then flow out of the air flow channel from the adjacent air flow channel to achieve mixed flow of air flow and material. The thick material layer and the air flow channel in the upper and lower drying chambers are arranged in a symmetrical structure (for example, rotational symmetry, that is, the flow direction of the airflow in the upper and lower drying chambers is opposite); a ventilation fan is provided on the side wall of the drying bed.

[0009] The front and rear ends of the airflow channel and the thick material layer in the present invention refer to the direction of airflow entering as the front end and the direction of airflow flowing out as the rear end. For example, an airflow blocking structure connected to the upper and / or lower wall of the drying chamber is provided at the front end of the uppermost thick material layer and / or the lowermost thick material layer, and then an airflow blocking device is provided at the front end of each airflow channel, and airflow blocking devices staggered with the front end airflow spacing devices are provided at intervals at the rear ends of the separated airflow channels, so that each airflow channel is in a semi-closed state and each airflow channel has only one function of airflow entering or flowing out.

[0010] The airflow channel with airflow inflow function and the airflow channel with airflow outflow function are spaced from each other, and the airflow enters from the front end of the airflow channel with airflow inflow function and flows out from the rear end of the airflow channel with airflow outflow function; the airflow inlets of the airflow channels are on the same side, and the airflow outlets of the airflow channels are on the other side.

[0011] The heat pump device includes a compressor, a throttle valve, a condenser-evaporator A, a condenser-evaporator B, a condenser-evaporator C, a condenser-evaporator D, and corresponding reversing valves A, B and C.

[0012] Furthermore, temperature and humidity sensors T1, W1 and T3 are installed on both sides of the condenser evaporator B, and temperature and humidity sensors T2, W2 and T4 are installed on both sides of the condenser evaporator C.

[0013] Furthermore, when the device is running in forward flow, the compressor outlet is connected in sequence to the reversing valve A, the reversing valve B, the condenser evaporator A, the reversing valve B, the condenser evaporator B, the throttle valve, the condenser evaporator C, the reversing valve C, the condenser evaporator D, the reversing valve C, the reversing valve A, and finally returns to the compressor inlet.

[0014] Furthermore, when the device operates in reverse flow, the compressor outlet is connected in sequence to the reversing valve A, the reversing valve C, the condenser evaporator D, the reversing valve C, the condenser evaporator C, the throttle valve, the condenser evaporator B, the reversing valve B, the condenser evaporator A, the reversing valve B, the reversing valve A, and finally returns to the compressor inlet.

[0015] During operation, the condenser evaporator A and the condenser evaporator D can be cut off through the reversing valve B and the reversing valve C to reduce the compressor intake air superheat and improve the system dehumidification efficiency.

[0016] Furthermore, the compressor adopts a variable frequency compressor; the throttle valve adopts an electronic expansion valve; and the fans of the condenser evaporator B and the condenser evaporator C are variable frequency fans.

[0017] At the same time, the present invention also provides a control method for the above device, comprising:

[0018] Step S1, start the device and collect temperatures T1, T2, T3, T4, humidity W1, W2, and compressor inlet and outlet pressures P1 and P2; set the target air supply temperature Tset, the maximum allowable humidity Wset, the condenser heat exchange temperature difference △Tcon, the dehumidification evaporator heat exchange temperature difference △Tvap, the dehumidification and cooling temperature difference △Tw and the switching period t;

[0019] Step S2, controlling the reversing valve A, the reversing valve B, the reversing valve C, and the fan directions of the condenser evaporator A, the condenser evaporator B, the condenser evaporator C, and the condenser evaporator D, so that the system is in a positive flow direction;

[0020] Step S3, detect the supply air temperature Tg and supply air humidity Wg, compare them with the target supply air temperature Tset and the permitted maximum humidity Wset, and adjust the ventilation fan speed; when Tg>Tset or Wg>Wset, increase the fan speed to increase the ventilation volume, otherwise reduce the ventilation volume.

[0021] Step S4: According to the target drying temperature Tset and the condenser heat exchange temperature difference △Tcon, the target condensing temperature Tcon is obtained, Tcon=Tset+△Tcon, and the target exhaust pressure Pcon is calculated using the target condensing temperature Tcon and the refrigerant properties; the compressor exhaust pressure P2 is detected, and the target exhaust pressure Pcon is compared with the actual exhaust pressure P2 to adjust the compressor frequency. When P2>Pcon, the compressor frequency is reduced, otherwise the compressor frequency is increased.

[0022] Step S5: Calculate the return air dew point temperature Tw based on the return air temperature Tb and humidity Wb, and then obtain the target evaporation temperature Tvap based on the heat exchange temperature difference △Tvap of the dehumidification evaporator, Tvap=Tw-△Tvap, and calculate the target intake pressure Pvap using the target evaporation temperature Tvap and the refrigerant properties; monitor the compressor intake pressure P1, compare the target intake pressure Pvap with the actual exhaust pressure P1, and adjust the throttle valve opening. When P1>Pvap, reduce the throttle valve opening, otherwise increase the throttle valve opening.

[0023] Step S6: According to the dew point temperature Tw and the dehumidification and cooling temperature difference △Tw, the target dehumidification air flow temperature Tdc is obtained, Tdc=Tw-△Tw. The dehumidification evaporator outlet air flow temperature Td is detected, and the target dehumidification temperature Tdc is compared with the actual dehumidification temperature Td, and the dehumidification evaporator fan speed is adjusted. When Td>Tdc, the dehumidification evaporator fan speed is reduced, otherwise the dehumidification evaporator fan speed is increased.

[0024] Step S7, when running to the switching cycle, control the reversing valve A, reversing valve B, reversing valve C, and condenser evaporator A, condenser evaporator B, condenser evaporator C, condenser evaporator D so that the system is in a countercurrent direction, and execute the process of steps S3-S6.

[0025] Step S8, repeat the process of steps S2-S7 until the drying is completed.

[0026] Furthermore, the target air supply temperature Tset is set to 50-100°C.

[0027] Furthermore, the dehumidification and cooling temperature difference △Tw is 5-50℃.

[0028] Furthermore, the heat exchange temperature differences ΔTcon and ΔTvap are 5-50°C.

[0029] The device and control method of the present invention change the air supply temperature Tg and the alternating airflow direction in real time based on the characteristics of the dried material and the thickness of the material layer (1). By switching the reversing valve and regulating the direction / flow rate of the condenser evaporator fan, alternating airflow drying of thick material layers is achieved, thereby achieving the purpose of improving drying uniformity and the energy efficiency of the drying system.

[0030] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0031] Compared with thin layer drying (the material thickness is generally about 3cm, and the gas is usually used to pass over the surface for drying), thick layer drying can effectively improve the volume utilization rate of the equipment. In order to improve the drying uniformity of the material layer thickness / width direction, a multi-layer alternating airflow bed method is adopted. In order to adapt to the alternating airflow dehumidification and drying, the heat pump system is equipped with two sets of condensers and two sets of evaporators, and the evaporators and condensers can be switched as the airflow direction changes. Since two sets of evaporators are set, the dehumidification evaporator gas volume can be adjusted during the dehumidification process to achieve the optimal initial wet effect.

[0032] Compared with the existing heat pump drying equipment, the device of the present invention has the following advantages: (1) Two sets of evaporators are provided, and the dehumidification effect is adjusted in real time according to the air volume of the working evaporator during the drying process to ensure the dehumidification efficiency of the system. (2) The heat pump alternating air flow switching is adopted, the equipment is small in size, and uniform drying of thick layers of materials can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 It is a schematic diagram of the positive flow operation of the device of the present invention;

[0035] Figure 2 It is a schematic diagram of the countercurrent operation of the device of the present invention;

[0036] Among them: 1-thick material layer, 2-air flow channel, 3-ventilation fan, 4-compressor, 5-reversing valve A, 6-reversing valve B, 7-condensing evaporator A, 8-condensing evaporator B, 8-throttle valve, 10-condensing evaporator C, 11-reversing valve C, 12-condensing evaporator D. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is described below in conjunction with the accompanying drawings.

[0038] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design described as "example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or it can be either of the two.

[0039] In the embodiments of the present invention, "image" and "picture" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same. "of", "corresponding" and "corresponding" can sometimes be used interchangeably. It should be noted that when the difference between them is not emphasized, the meanings they want to express are the same.

[0040] In the embodiments of the present invention, sometimes a subscript such as W1 may be mistakenly written as a non-subscript such as W1. When the difference is not emphasized, the meanings to be expressed are consistent.

[0041] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0042] Example 1

[0043] Reference Figure 1 , Figure 2 , the arrows in the figure represent the flow direction of air and refrigerant when the equipment is working.

[0044] The embodiment of the present invention provides an alternating airflow heat pump drying system and a control method. The drying system includes a drying bed layer and a heat pump system.

[0045] The drying bed is composed of 4 thick material layers 1 above and below, with airflow partitions between the upper and lower material layers, so that the airflow circulates in the bed. There are 3 material drawers in each layer, and the thickness of the thick material layer 1 is 10 cm. There are airflow channels 2 above and below the thick material layer, and the airflow channel is 10 cm. The entire bed is loaded with 500 kg of semi-dried tomatoes. A 30-50 cm wide circulating airflow channel is left on the right side of the material layer, a heat pump system is installed on the left side, and ventilation holes and ventilation fans 3 are provided on the left wall.

[0046] The heat pump device includes a compressor 4, a throttle valve 9, a condenser evaporator A 7, a condenser evaporator B 8, a condenser evaporator C 10, a condenser evaporator D 12, and corresponding reversing valves A 5, B 6, and C 11. By switching the reversing valves, the fan directions and flow rates of the condenser evaporator A 7, B 8, C 10, and D 12 are regulated to achieve alternating airflow drying of thick material layers, thereby improving drying uniformity and the energy efficiency of the drying system.

[0047] The compressor 4 is a 20HP variable frequency compressor, the throttle valve 9 is a Sanhua electronic expansion valve, the fans on the condenser evaporator B 8 and the condenser evaporator C 10 are variable frequency controlled, and a water tank is installed at the bottom, so that condensed water can be led out of the equipment during operation.

[0048] Temperature and humidity sensors T1, W1 and T3 are installed on both sides of the condenser evaporator B 8, temperature and humidity sensors T2, W2 and T4 are installed on both sides of the condenser evaporator C 10, and the intake pressure P1, intake temperature T1 and exhaust pressure P2 of the compressor 4 are obtained for the dehumidification control of the heat pump system. By switching the reversing valve and regulating the direction / flow rate of the condenser evaporator fan, alternating airflow drying of thick material layers is achieved to improve the drying uniformity and energy efficiency of the drying system.

[0049] When the system is in forward flow operation, the outlet of the compressor 4 is sequentially connected to the reversing valve A5, the reversing valve B6, the condenser evaporator A7, the reversing valve B6, the condenser evaporator B8, the throttle valve 9, the condenser evaporator C10, the reversing valve C11, the condenser evaporator D12, the reversing valve C11, the reversing valve A5, and finally returns to the inlet of the compressor 4. At this time, the condenser evaporator A7 and the condenser evaporator B8 are used as the condenser of the heat pump system, and the fan is in the blowing state; the condenser evaporator C10 is used as the dehumidification evaporator of the heat pump system, and the condenser evaporator D12 is used as the superheated evaporator of the heat pump system, and the fan is in the suction state. When running downstream, T1 is the supply air temperature Tg, W1 is the supply air humidity Wg, T2 is the return air temperature Tb, and W2 is the return air humidity Wb.

[0050] When the system is in reverse flow operation, the reversing valve and the condenser evaporator fan state are switched, and the outlet of the compressor 4 is connected to the reversing valve A4, the reversing valve C11, the condenser evaporator D12, the reversing valve C11, the condenser evaporator C10, the throttle valve 9, the condenser evaporator B8, the reversing valve B6, the condenser evaporator A7, the reversing valve B6, the reversing valve A5 in sequence, and finally returns to the inlet of the compressor 4. At this time, the condenser evaporator C10 and the condenser evaporator D12 are used as the condenser of the heat pump system, and the fan is in the blowing state; the condenser evaporator B8 is used as the dehumidification evaporator of the heat pump system, and the condenser evaporator A7 is used as the superheated evaporator of the heat pump system, and the fan is in the suction state. In reverse flow operation, T2 is the supply air temperature Tg, W2 is the supply air humidity Wg, T1 is the return air temperature Tb, and W1 is the return air humidity Wb.

[0051] The refrigerant used is R314a.

[0052] The drying system adopts the following control strategy:

[0053] S1: Start the device.

[0054] S2: The primary instrument collects temperatures T1, T2, T3, T4, humidity W1, W2, and compressor inlet and outlet pressures P1 and P2.

[0055] S3: Set the target supply air temperature Tset=80℃, the maximum allowable humidity Wset=30%, the condenser heat exchange temperature difference △Tcon=10℃, the dehumidification evaporator heat exchange temperature difference △Tvap=20℃, and the dehumidification and cooling temperature difference △Tw=15℃.

[0056] S4: Set the switching period t=30 minutes.

[0057] S5: Control the reversing valve A (5), reversing valve B (6), reversing valve C (11), and the fan directions of condenser evaporator A (7), condenser evaporator B (8), condenser evaporator C (10), and condenser evaporator D (12) so that the system is in the positive flow direction, that is, the upper 4 layers of air flow are from left to right, and the lower 4 layers of air flow are from right to left. Condenser evaporator A (7) and condenser evaporator B (8) are condensers of the heat pump system, condenser evaporator C (10) is a dehumidification evaporator, and condenser evaporator D (12) is a superheating evaporator.

[0058] At this time, the supply air temperature Tg=T1, the supply air humidity Wg=W1, the return air temperature Tb=T2, and the return air humidity Wb=W2.

[0059] S6: Detect the supply air temperature Tg and supply air humidity Wg, compare them with the target supply air temperature Tset and the maximum allowable humidity Wset, and adjust the speed of the ventilation fan (3). The specific adjustment method is that the heat exchange fan is adjusted by the inverter and PID control is adopted. When Tg>Tset or Wg>Wset, the fan speed is increased to increase the ventilation volume, and vice versa. The ventilation volume is reduced. The PID control parameters are set according to the material and equipment performance during the commissioning process.

[0060] S7: Detect the compressor exhaust pressure P2, compare the target exhaust pressure Pcon with the actual exhaust pressure P2, and adjust the compressor (4) frequency. The specific adjustment method is that when P2>Pcon, the compressor frequency is reduced, and vice versa, the compressor frequency is increased.

[0061] According to the target supply air temperature Tset and the condenser heat exchange temperature difference △Tcon, the target condensing temperature Tcon is obtained, Tcon=Tset+△Tcon.

[0062] The target exhaust pressure Pcon is calculated using the target condensing temperature Tcon and the properties of R314a.

[0063] S8: Monitor the compressor intake pressure P1, compare the target intake pressure Pvap and the actual exhaust pressure P1, and adjust the throttle valve (9) opening. The specific adjustment method is that when P1>Pvap, the throttle valve opening is reduced, otherwise the throttle valve opening is increased.

[0064] According to the return air temperature Tb and return air humidity Wb, the return air dew point temperature Tw is calculated using thermodynamic knowledge to obtain the target evaporation temperature Tvap, Tvap=Tw-△Tvap, where △Tvap is the heat exchange temperature difference of the dehumidification evaporator.

[0065] The target intake pressure Pvap is calculated using the target evaporation temperature Tvap and the properties of R314a.

[0066] S9: Detect the air flow temperature Td at the outlet of the dehumidification evaporator, compare the target dehumidification temperature Tdc with the actual dehumidification temperature Td, and adjust the fan speed of the dehumidification evaporator. The fan speed is controlled by a frequency converter and PID regulation is adopted. When Td>Tdc, the fan speed of the dehumidification evaporator is reduced, otherwise the fan speed of the dehumidification evaporator is increased.

[0067] According to the dew point temperature Tw and the dehumidification and cooling temperature difference △Tw, the target dehumidification air flow temperature Tdc is obtained, Tdc=Tw-△Tw.

[0068] S10: After running for 30 minutes, control the reversing valve A (5), reversing valve B (6), reversing valve C (11), and the fan directions of condenser evaporator A (7), condenser evaporator B (8), condenser evaporator C (10), and condenser evaporator D (12) so that the system is in a countercurrent direction, that is, the upper 4 layers of air flow are from right to left, and the lower 4 layers of air flow are from left to right. Condenser evaporator C (10) and condenser evaporator D (12) are condensers of the heat pump system, condenser evaporator B (8) is a dehumidification evaporator, and condenser evaporator A (7) is a superheating evaporator.

[0069] At this time, the supply air temperature Tg=T2, the supply air humidity Wg=W2, the return air temperature Tb=T1, and the return air humidity Wb=W1.

[0070] S11: Repeat the process from S5 to S9.

[0071] S12: After drying for 4 hours, the drying is terminated.

[0072] After 4 hours, the tomato slices can be dried to a relative humidity below 14%, and the drying uniformity is less than ±3%.

[0073] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An alternating airflow heat pump dehumidification and drying device, comprising a drying bed and a heat pump device, wherein; The drying bed comprises at least two upper and lower drying chambers, each of which comprises at least a plurality of thick material layers arranged from top to bottom; the thick material layers and the air flow channels are arranged alternately, and air flow blocking structures are alternately arranged at the front and rear ends of the air flow channels, so that the air flow enters the air flow channel from the air flow channel inlet located at the front end of the thick material layer, passes through the thick material layer, and then flows out of the air flow channel from the outlet of the adjacent air flow channel located at the rear end of the thick material layer. The thick material layers and the air flow channels in the upper and lower drying chambers are arranged in a symmetrical structure, and a ventilation fan is provided on the side wall of the drying bed; The heat pump device includes a compressor, a throttle valve, a condenser-evaporator A, a condenser-evaporator B, a condenser-evaporator C, a condenser-evaporator D, and corresponding reversing valves A, B and C.

2. The drying device according to claim 1, It is characterized in that Temperature and humidity sensors T1, W1 and T3 are installed on both sides of the condenser evaporator B, and temperature and humidity sensors T2, W2 and T4 are installed on both sides of the condenser evaporator C.

3. The drying device according to claim 1, It is characterized in that When the device is running in forward flow, the compressor outlet is connected to the reversing valve A, reversing valve B, condenser evaporator A, reversing valve B, condenser evaporator B, throttle valve, condenser evaporator C, reversing valve C, condenser evaporator D, reversing valve C, reversing valve A in sequence, and finally returns to the compressor inlet.

4. The drying device according to claim 1, It is characterized in that When the device is running in reverse flow, the compressor outlet is connected in sequence to the reversing valve A, reversing valve C, condenser evaporator D, reversing valve C, condenser evaporator C, throttle valve, condenser evaporator B, reversing valve B, condenser evaporator A, reversing valve B, reversing valve A, and finally returns to the compressor inlet.

5. The drying device according to claim 1, It is characterized in that The compressor adopts a variable frequency compressor; the throttle valve adopts an electronic expansion valve; the fans of the condenser evaporator B and the condenser evaporator C are variable frequency fans.

6. A control method for the drying device according to any one of claims 1 to 5, It is characterized in that include: Step S1, start the device and collect temperatures T1, T2, T3, T4, humidity W1, W2, and compressor inlet and outlet pressures P1 and P2; Set the target air supply temperature Tset, the maximum allowable humidity Wset, the condenser heat exchange temperature difference △Tcon, the dehumidification evaporator heat exchange temperature difference △Tvap, the dehumidification and cooling temperature difference △Tw and the switching period t; Step S2, controlling the reversing valve A, the reversing valve B, the reversing valve C, and the fan directions of the condenser evaporator A, the condenser evaporator B, the condenser evaporator C, and the condenser evaporator D, so that the system is in a positive flow direction; Step S3, detecting the supply air temperature Tg and the supply air humidity Wg, comparing them with the target supply air temperature Tset and the permitted maximum humidity Wset, and adjusting the ventilation fan speed; Step S4, according to the target drying temperature Tset and the condenser heat exchange temperature difference ΔTcon, obtain the target condensing temperature Tcon, Tcon=Tset+ΔTcon, and calculate the target exhaust pressure Pcon using the target condensing temperature Tcon and the refrigerant properties; detect the compressor exhaust pressure P2, compare the target exhaust pressure Pcon with the actual exhaust pressure P2, and adjust the compressor frequency; Step S5, calculate the return air dew point temperature Tw according to the return air temperature Tb and humidity Wb, and then obtain the target evaporation temperature Tvap based on the heat exchange temperature difference △Tvap of the dehumidification evaporator, Tvap=Tw-△Tvap, and calculate the target intake pressure Pvap using the target evaporation temperature Tvap and the refrigerant properties; monitor the compressor intake pressure P1, compare the target intake pressure Pvap with the actual exhaust pressure P1, and adjust the throttle valve opening; Step S6: Obtain the target dehumidification air flow temperature Tdc according to the dew point temperature Tw and the dehumidification and cooling temperature difference △Tw, where Tdc=Tw-△Tw. Detect the dehumidification evaporator outlet air flow temperature Td, compare the target dehumidification temperature Tdc with the actual dehumidification temperature Td, and adjust the dehumidification evaporator fan speed; Step S7, when the switching cycle is reached, control the reversing valve A, the reversing valve B, the reversing valve C, and the condenser evaporator A, the condenser evaporator B, the condenser evaporator C, and the condenser evaporator D so that the system is in a countercurrent direction, and execute the process of steps S3-S6; Step S8, repeat the process of steps S2-S7 until the drying is completed.

7. The method according to claim 6, It is characterized in that The target drying temperature Tset is set to 50-100°C.

8. The method according to claim 6, It is characterized in that The dehumidification and cooling temperature difference △Tw is 5-50℃.

9. The method according to claim 6, It is characterized in that The heat exchange temperature difference △Tcon and △Tvap is 5-50℃.

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