Alternating airflow heat pump dehumidification and drying device and control method thereof

Abstract

This invention provides an alternating airflow heat pump dehumidification and drying device and its control method, relating to the field of agricultural product drying technology. It includes a drying bed and a heat pump device. The drying bed comprises at least two drying chambers, upper and lower, each chamber containing at least multiple layers of thick material arranged from top to bottom. The thick material layers and airflow channels are alternately arranged, with airflow blocking structures alternately installed at the front and rear ends of the airflow channels. A ventilation fan is provided on the side wall of the drying bed. The heat pump device includes a compressor, a throttling valve, condenser-evaporator A, condenser-evaporator B, condenser-evaporator C, and condenser-evaporator D, and corresponding reversing valves A, B, and C. In this invention, the drying bed is a multi-layered alternating airflow thick material layer, with the material layers and airflow channels arranged alternately. The heat pump device includes four sets of condenser-evaporators and corresponding reversing valves, enabling alternating airflow dehumidification and drying of the thick material layer.

Description

Technical Field

[0001] This invention relates to the field of agricultural product drying technology, and in particular to an alternating airflow thick-layer heat pump dehumidification and drying device and its control method. Background Art

[0002] Drying agricultural products is a crucial step in their storage, value-added processing, and pre-processing, and is an important component of agricultural product processing. Currently, thin-layer drying is commonly used, where agricultural products are spread flat on a tray and airflow passes over them. However, thin-layer drying equipment is bulky and has low volume utilization. To improve equipment utilization and reduce size, materials can be piled to a certain thickness (usually over 5cm), with airflow passing through the bed. Thick-layer drying, however, suffers from poor material uniformity along the thickness direction. For example, a 35cm thick grain bed results in a moisture difference of approximately 4% after drying. To improve the uniformity of thick-layer drying, some existing technologies propose thick-layer drying methods based on alternating airflow. By switching airflow temperature and direction, heat utilization is improved, leading to better product drying quality.

[0003] Heat pump drying, as an emerging drying method, has been widely adopted due to its advantages such as energy saving, environmental protection, intelligent control, and good drying effect. Depending on the method of handling the hot and humid air in the drying room, it can be divided into dehumidification heat pumps and exhaust heat pumps. Using dehumidification heat pumps results in the loss of a large amount of high-quality heat energy, wasting energy and hindering energy conservation and environmental protection. Dehumidification heat pumps mostly employ closed-loop dehumidification methods, where the operating conditions of the evaporator and condenser are interconnected and change in real time during the drying process, potentially leading to poor dehumidification effect and reliability. Regarding the control strategy of heat pump dehumidification systems, some existing technologies disclose dehumidification control methods that intelligently adjust the drying moisture load according to the current drying stage of the material, dynamically matching the moisture load with the actual capacity. Other existing technologies disclose control methods for dehumidification heat pumps that adjust the airflow through the evaporator based on 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] To address the problems of thick-layer drying and alternating airflow control in existing technologies, this invention proposes the following technical solution:

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

[0007] The drying bed and heat pump unit; wherein the drying bed includes at least two drying chambers, upper and lower, and each drying chamber includes at least multiple layers of thick material arranged from top to bottom, such as an even number of layers of thick material, such as four layers of thick material; obviously, multiple layers of thick material arranged in this way can be arranged in parallel in the drying chamber, for example, three can be arranged in parallel through material drawers.

[0008] The thick material layer and airflow channels are arranged alternately, and airflow blocking structures are set alternately at the front and rear ends of the airflow channels. This ensures that after the airflow enters the airflow channel from the inlet, it must pass through the thick material layer and then flow out of the airflow channel from the adjacent airflow channel, thus achieving the mixing of airflow and material. The thick material layer and airflow channels in the upper and lower drying chambers are arranged in a symmetrical structure (e.g., rotational symmetry, that is, the airflow direction in the upper and lower drying chambers is opposite). Ventilation fans are provided on the side walls of the drying bed.

[0009] In this invention, the airflow channel, the front end, and the rear end of the thick material layer refer to the direction in which the airflow enters as the front end and the direction in which it exits as the rear end. For example, an airflow blocking structure can be set at the front end of the uppermost and / or lowermost thick material layer and connected to the upper and / or lower wall of the drying chamber. Then, at every other airflow channel, an airflow blocking device can be set at the front end of the airflow channel, and at the rear end of the spaced airflow channels, airflow blocking devices can be set at intervals, alternating with the front airflow blocking devices. This achieves a semi-closed state for each airflow channel, with each airflow channel having only one function: airflow entry or exit.

[0010] The airflow channels with airflow inflow function and the airflow channels with airflow outflow function are separated from each other, and the airflow enters from the front end of the airflow channel with airflow inflow function and exits from the rear end of the airflow channel with airflow outflow function; the airflow inlet of the airflow channel is on the same side, and the airflow outlet of the airflow channel is on the other side.

[0011] The heat pump unit includes a compressor, a throttling 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 condenser-evaporator B, and temperature and humidity sensors T2, W2, and T4 are installed on both sides of condenser-evaporator C.

[0013] Furthermore, when the device is in forward flow operation, the compressor outlet is sequentially connected to 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, and reversing valve A, finally returning to the compressor inlet.

[0014] Furthermore, when the device is running in reverse flow, the compressor outlet is sequentially connected to 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 back to the compressor inlet.

[0015] During operation, condenser-evaporator A and condenser-evaporator D can be switched off by reversing valves B and C to reduce the superheat of the compressor intake air and improve the system dehumidification efficiency.

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

[0017] Furthermore, the present invention also provides a control method for the above-mentioned device, comprising:

[0018] Step S1: Start the device and collect the temperatures T1, T2, T3, T4, humidity W1, W2, and compressor inlet and outlet pressures P1 and P2; set the target supply air temperature Tset, the maximum permissible humidity Wset, the condenser heat exchange temperature difference ΔTcon, the dehumidifying evaporator heat exchange temperature difference ΔTvap, the dehumidifying cooling temperature difference ΔTw, and the switching cycle t.

[0019] Step S2: Control the direction of the reversing valves A, B, and C, as well as the fan direction of the condenser-evaporator A, B, C, and D, so that the system is in the forward 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 maximum permissible humidity Wset, and adjust the ventilation fan speed accordingly; when Tg>Tset or Wg>Wset, increase the fan speed to increase the ventilation volume, and vice versa.

[0021] Step S4: Based on the target drying temperature Tset and the condenser heat exchange temperature difference ΔTcon, obtain the target condensing temperature Tcon, where Tcon = Tset + ΔTcon. Calculate the target discharge pressure Pcon using the target condensing temperature Tcon and the refrigerant properties. Detect the compressor discharge pressure P2, compare the target discharge pressure Pcon with the actual discharge pressure P2, and adjust the compressor frequency accordingly. When P2 > Pcon, decrease the compressor frequency; otherwise, increase the compressor frequency.

[0022] Step S5: Calculate the return air dew point temperature Tw based on the return air temperature Tb and humidity Wb. Then, based on the heat exchange temperature difference ΔTvap of the dehumidifier evaporator, obtain the target evaporation temperature Tvap, where Tvap = Tw - ΔTvap. Calculate the target intake pressure Pvap using the target evaporation temperature Tvap and refrigerant properties. Monitor the compressor intake pressure P1, compare the target intake pressure Pvap with the actual discharge pressure P1, and adjust the throttle valve opening accordingly. When P1 > Pvap, decrease the throttle valve opening; otherwise, increase it.

[0023] Step S6: Based on the dew point temperature Tw and the dehumidification cooling temperature difference ΔTw, obtain the target dehumidification airflow temperature Tdc, where Tdc = Tw - ΔTw. Detect the outlet airflow temperature Td of the dehumidifier evaporator, compare the target dehumidification temperature Tdc with the actual dehumidification temperature Td, and adjust the dehumidifier evaporator fan speed accordingly. When Td > Tdc, decrease the dehumidifier evaporator fan speed; conversely, increase the dehumidifier evaporator fan speed.

[0024] Step S7: When the switching cycle is reached, control the reversing valves A, B, and C, as well as the condenser-evaporator A, B, C, and D to make the system be in the counter-current direction, and execute steps S3-S6.

[0025] Step S8: Repeat steps S2-S7 until drying is complete.

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

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

[0028] Furthermore, the heat exchange temperature differences ΔTcon and ΔTvap are taken as 5-50℃.

[0029] The device and its 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 material to be dried and the thickness of the material layer (1). By switching the reversing valve and regulating the direction / flow of the condenser evaporator fan, the alternating airflow drying of the thick material layer is realized, thereby improving the drying uniformity and the energy efficiency of the drying system.

[0030] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following:

[0031] Compared to thin-layer drying (where material thickness is typically around 3cm, and gas is usually passed over the surface for drying), thick-layer drying effectively improves the volume utilization of the equipment. To enhance the drying uniformity in the thickness / width direction of the material layer, a multi-layer alternating airflow bed is employed. To adapt to alternating airflow dehumidification and drying, the heat pump system is equipped with two condensers and two evaporators, which can be switched according to the airflow direction. Because of the two evaporators, the initial moisture content can be adjusted during dehumidification by regulating the gas flow rate of the dehumidifying evaporator.

[0032] Compared with existing heat pump drying equipment, the device of the present invention has the following advantages: (1) It is equipped with two sets of evaporators, and the dehumidification effect is adjusted in real time according to the working air volume of the evaporator during the drying process to ensure the dehumidification efficiency of the system. (2) It adopts heat pump alternating airflow switching, the equipment is small in size, and it can achieve uniform drying of thick materials. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

[0035] Figure 2 This is a schematic diagram of the reverse flow operation of the device of the present invention;

[0036] Wherein: 1-thick material layer, 2-airflow channel, 3-ventilation fan, 4-compressor, 5-reversing valve A, 6-reversing valve B, 7-condenser-evaporator A, 8-condenser-evaporator B, 8-throttle valve, 10-condenser-evaporator C, 11-reversing valve C, 12-condenser-evaporator D. Detailed Implementation

[0037] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0038] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0039] In this embodiment of the invention, the terms "image" and "picture" may sometimes be used interchangeably. It should be noted that, without emphasizing the difference, their intended meanings are consistent. Similarly, the terms "of," "corresponding," and "corresponding" may sometimes be used interchangeably. It should be noted that, without emphasizing the difference, their intended meanings are consistent.

[0040] In this embodiment of the invention, sometimes a subscript such as W1 may be mistakenly written as a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0041] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0042] Example 1

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

[0044] This invention provides an alternating airflow heat pump drying system and control method, wherein the drying system includes a drying bed and a heat pump system.

[0045] The drying bed consists of four thick material layers 1 on each side, with an airflow partition between the upper and lower material layers to allow airflow to circulate within the bed. Each layer has three material trays, and the thickness of the thick material layer 1 is 10cm. Above and below the thick material layers are airflow channels 2, each 10cm wide. The entire bed is filled with 500kg of semi-dried tomatoes. A 30-50cm wide circulating airflow channel is provided on the right side of the material layer, and a heat pump system is installed on the left side. Ventilation vents and a ventilation fan 3 are located on the left wall.

[0046] The heat pump unit includes a compressor 4, a throttling valve 9, condenser-evaporator A 7, condenser-evaporator B 8, condenser-evaporator C10, condenser-evaporator D 12, and corresponding reversing valves A 5, B 6, and C 11. By switching the reversing valves, the fan direction and flow rate of condenser-evaporator A7, B8, C10, and D 12 are controlled, achieving 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 20-horsepower variable frequency compressor, the throttle valve 9 is a Sanhua electronic expansion valve, the fans on the condenser evaporator B 8 and condenser evaporator C 10 are frequency-controlled, and a water collection tank is installed at the bottom so that condensate can be drawn out of the equipment during operation.

[0048] Temperature and humidity sensors T1, W1, and T3 are installed on both sides of condenser-evaporator B8, and temperature and humidity sensors T2, W2, and T4 are installed on both sides of condenser-evaporator C10. The compressor 4's inlet pressure P1, inlet temperature T1, and exhaust pressure P2 are also measured. These parameters are used for dehumidification control of the heat pump system. By switching the reversing valve and adjusting the condenser-evaporator fan direction / flow rate, alternating airflow drying of the thick material layer is achieved, thereby improving drying uniformity and the energy efficiency of the drying system.

[0049] When the system operates in forward flow mode, the outlet of compressor 4 is sequentially connected to reversing valve A5, reversing valve B6, condenser-evaporator A7, reversing valve B6, condenser-evaporator B8, throttle valve 9, condenser-evaporator C10, reversing valve C11, condenser-evaporator D12, reversing valve C11, and reversing valve A5, finally returning to the inlet of compressor 4. At this time, condenser-evaporator A7 and condenser-evaporator B8 act as condensers in the heat pump system, with their fans in blowing mode; condenser-evaporator C10 acts as a dehumidifying evaporator in the heat pump system, and condenser-evaporator D12 acts as a superheating evaporator in the heat pump system, with its fans in suction mode. When operating in reverse flow mode, 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 operates in reverse flow, the reversing valve and condenser-evaporator fan states are switched. The compressor 4 outlet is sequentially connected to reversing valve A4, reversing valve C11, condenser-evaporator D12, reversing valve C11, condenser-evaporator C10, throttle valve 9, condenser-evaporator B8, reversing valve B6, condenser-evaporator A7, reversing valve B6, and reversing valve A5, finally returning to the compressor 4 inlet. At this time, condenser-evaporator C10 and condenser-evaporator D12 act as condensers in the heat pump system, with their fans in blowing mode; condenser-evaporator B8 acts as a dehumidifying evaporator in the heat pump system, and condenser-evaporator A7 acts as a superheating evaporator in the heat pump system, with their fans in suction mode. During 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 selected is R314a.

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

[0053] S1: Start the device.

[0054] S2: Temperatures T1, T2, T3, and T4, humidity W1 and W2, and compressor inlet and outlet pressures P1 and P2 are collected by primary instruments.

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

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

[0057] S5: Control the direction of the fans of reversing valves A (5), B (6), and C (11), and evaporators A (7), B (8), C (10), and D (12) to make the system in the forward flow direction, that is, the upper 4 layers of air flow from left to right and the lower 4 layers of air flow from right to left. Evaporators A (7) and B (8) are condensers of the heat pump system, evaporator C (10) is a dehumidifying evaporator, and 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 permissible humidity Wset, and adjust the speed of the ventilation fan (3). The specific adjustment method is that the speed of the heat exchange fan is adjusted by the frequency converter and PID control is adopted. When Tg>Tset or Wg>Wset, the fan speed is increased to increase the air exchange volume, and vice versa. The PID control parameters are set during the commissioning process according to the material and equipment performance.

[0060] S7: Detect the compressor discharge pressure P2, compare the target discharge pressure Pcon with the actual discharge pressure P2, and adjust the compressor (4) frequency. The specific adjustment method is to reduce the compressor frequency when P2>Pcon, and increase the compressor frequency when P2>Pcon.

[0061] The target condensing temperature Tcon is obtained from the target supply air temperature Tset and the condenser heat exchange temperature difference ΔTcon, where Tcon = Tset + ΔTcon.

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

[0063] S8: Monitor the compressor intake pressure P1, compare the target intake pressure Pvap with the actual exhaust pressure P1, and adjust the opening of the throttle valve (9). The specific adjustment method is as follows: when P1>Pvap, reduce the opening of the throttle valve, and vice versa.

[0064] Based on the return air temperature Tb and return air humidity Wb, the return air dew point temperature Tw is calculated using thermodynamics, and the target evaporation temperature Tvap is obtained, where Tvap = Tw - ΔTvap, and ΔTvap is the heat exchange temperature difference of the dehumidifier evaporator.

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

[0066] S9: Detect the outlet airflow temperature Td of the dehumidifier evaporator, compare it with the target dehumidification temperature Tdc and the actual dehumidification temperature Td, and adjust the dehumidifier evaporator fan speed accordingly. The fan speed is controlled by a frequency converter using PID regulation. When Td > Tdc, the dehumidifier evaporator fan speed is reduced; conversely, when Td > Tdc, the dehumidifier evaporator fan speed is increased.

[0067] Based on the dew point temperature Tw and the dehumidification and cooling temperature difference ΔTw, the target dehumidification airflow temperature Tdc is obtained, where Tdc = Tw - ΔTw.

[0068] S10: After running for 30 minutes, control the direction of the fans of reversing valves A (5), B (6), and C (11), and evaporators A (7), B (8), C (10), and D (12) so that the system is in a counter-current direction, that is, the upper 4 layers of air flow from right to left and the lower 4 layers of air flow from left to right. Evaporators C (10) and D (12) are condensers of the heat pump system, evaporator B (8) is a dehumidifying evaporator, and 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 S5-S9 process.

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

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

[0073] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An alternating airflow heat pump dehumidification and drying device, comprising a drying bed and a heat pump unit, wherein; The drying bed includes at least two drying chambers, upper and lower. Each drying chamber includes at least multiple layers of thick material arranged from top to bottom. The thick material layers and airflow channels are arranged alternately, and airflow blocking structures are alternately set at the front and rear ends of the airflow channels. This allows the airflow to enter the airflow channel from the inlet located at the front end of the thick material layer, pass through the thick material layer, and then exit the airflow channel from the outlet located at the rear end of the thick material layer of the adjacent airflow channel. The arrangement of the thick material layers and airflow channels in the upper and lower drying chambers is symmetrical, and ventilation fans are provided on the side walls of the drying bed. The heat pump unit 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. Temperature sensor T1 and humidity sensor W1 are installed on condenser-evaporator B near the drying bed, and temperature sensor T3 is installed near the heat pump unit. Temperature sensor T2 and humidity sensor W2 are installed on condenser-evaporator C near the drying bed, and temperature sensor T4 is installed near the heat pump unit. When the unit is running in forward flow, the compressor outlet is connected in sequence to 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, and finally back to the compressor inlet. When the unit is running in reverse flow, the compressor outlet is connected in sequence to 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 back to the compressor inlet.

2. The drying apparatus according to claim 1, characterized in that, The compressor is a variable frequency compressor; the throttling valve is an electronic expansion valve; the fans of condenser-evaporator B and condenser-evaporator C are variable frequency fans.

3. A control method for the drying apparatus according to any one of claims 1-2, characterized in that, include: Step S1: Start the device and collect the temperatures T1, T2, T3, and T4, humidity W1 and W2, and compressor inlet and outlet pressures P1 and P2. Set the target supply air temperature Tset, the maximum permissible humidity Wset, the condenser heat exchange temperature difference ΔTcon, the dehumidifying evaporator heat exchange temperature difference ΔTvap, the dehumidifying cooling temperature difference ΔTw, and the switching cycle t. Step S2: Control the direction of the reversing valves A, B, and C, as well as the fan direction of the condenser-evaporator A, B, C, and D, so that the system is in the forward flow direction; Step S3: Detect the supply air temperature Tg and supply air humidity Wg, compare them with the target supply air temperature Tset and the maximum permissible humidity Wset, and adjust the ventilation fan speed accordingly. Step S4: Based on the target drying temperature Tset and the condenser heat exchange temperature difference ΔTcon, obtain the target condensing temperature Tcon, Tcon = Tset + ΔTcon. Calculate the target discharge pressure Pcon using the target condensing temperature Tcon and the refrigerant properties. Detect the compressor discharge pressure P2, compare the target discharge pressure Pcon with the actual discharge pressure P2, and adjust the compressor frequency accordingly. Step S5: Calculate the return air dew point temperature Tw based on the return air temperature Tb and humidity Wb. Then, based on the heat exchange temperature difference ΔTvap of the dehumidifier evaporator, obtain the target evaporation temperature Tvap, where Tvap = Tw - ΔTvap. Calculate the target intake pressure Pvap using the target evaporation temperature Tvap and refrigerant properties. Monitor the compressor intake pressure P1, compare the target intake pressure Pvap with the actual discharge pressure P1, and adjust the throttle valve opening accordingly. Step S6: Based on the dew point temperature Tw and the dehumidification cooling temperature difference ΔTw, obtain the target dehumidification airflow temperature Tdc, where Tdc = Tw - ΔTw. Detect the outlet airflow temperature Td of the dehumidifier evaporator, compare the target dehumidification temperature Tdc with the actual dehumidification temperature Td, and adjust the fan speed of the dehumidifier evaporator accordingly. Step S7: When the switching cycle is reached, control the reversing valves A, B, and C, as well as the condenser-evaporator A, B, C, and D to make the system be in the counter-current direction, and execute steps S3-S6. Step S8: Repeat steps S2-S7 until drying is complete.

4. The method according to claim 3, characterized in that, The target drying temperature Tset is set to 50-100℃.

5. The method according to claim 3, characterized in that, The dehumidification and cooling temperature difference △Tw is taken as 5-50℃.

6. The method according to claim 3, characterized in that, The heat exchange temperature difference ΔTcon and ΔTvap are taken as 5-50℃.

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