CN106855353A - Heat pump drying equipment and drying means with dehumidification type Yu hydrofuge type handoff functionality - Google Patents

Abstract

The invention discloses a heat pump drying equipment and a material drying method with the function of switching between dehumidification type and dehumidification type, including a heat pump system and a drying workshop. The drying workshop is equipped with a heat pump main machine room, a return air duct and a drying room ;The top of the return air duct is higher than the drying chamber, and the right side of the drying chamber is provided with an air outlet connected with the return air duct; into the heat pump main room; there is an internal circulation damper between the exhaust room and the heat pump main room, and an exhaust damper is set on the side wall of the exhaust room; there is a fresh air duct in the heat pump main room, and the intersection of the fresh air duct and the dehumidification air duct There is a heat recovery device, and an inner fresh air damper is installed on the fresh air duct. The heat pump drying equipment with the function of switching between the dehumidification type and the dehumidification type of the present invention has a compact structure, cooperates with the drying method, can select the optimal operation mode according to the specific situation, integrates the advantages of each mode, and reduces the disadvantages of each mode through mode switching. impact, low energy consumption and high drying efficiency.

Description

Heat pump drying equipment with switching function between dehumidification type and dehumidification type and drying method

technical field

The invention relates to a heat pump drying device, in particular to a special device and a drying method suitable for dehydration and drying of agricultural by-products and the like.

Background technique

At present, heat pump drying equipment has broad development prospects in the field of drying equipment, especially in the field of drying where the drying temperature is below 75°C. As the country pays more and more attention to energy conservation and environmental protection, the application of heat pump drying equipment has attracted more and more attention.

Heat pump drying equipment is a special equipment for material drying. The heat pump system provides heat supply for the drying equipment, and sends the heated airflow into the drying chamber. The high-temperature dry airflow takes away the water vapor in the material, so as to achieve the purpose of drying. When using circulating air, as the high-temperature airflow continues to take away water vapor, the temperature of the airflow will gradually decrease, the humidity will increase, and the dehydration ability of the material will gradually decrease; when the airflow humidity reaches the set humidity target, a part of the heat in the drying room will be discharged. Humid air, while introducing dry air in the environment, continues the dehydration drying process.

At present, heat pump drying equipment is mainly divided into two types, namely hot air dehumidification type and evaporator dehumidification type. The hot air dehumidification type heat pump drying equipment uses the exhausted hot and humid air to introduce the external dry air to achieve the purpose of drying.

The evaporator dehumidification drying equipment uses the cooling capacity of the evaporator to treat the exhaust air below the dew point temperature and condense condensed water to achieve the purpose of drying materials.

The above two types of drying equipment have their own characteristics, and their advantages and disadvantages are also obvious. The hot air dehumidification mode is greatly affected by the state of the cold air outside, and the efficiency is relatively low when the outside world is colder; the evaporator dehumidification type is greatly affected by the characteristics of the material. Energy efficiency is very low.

At present, there is a lack of a heat pump drying equipment that can maximize strengths and avoid weaknesses, and integrates two types of drying equipment.

Contents of the invention

The purpose of the present invention is to provide a heat pump drying device capable of switching between the evaporator dehumidification type drying device and the hot air dehumidification type heat pump drying device.

In order to achieve the above object, the heat pump drying equipment with switching function between dehumidification type and dehumidification type of the present invention includes a heat pump system and a drying workshop, and the drying workshop is provided with a heat pump main engine room, a return air duct and a utility In the drying room for materials; the top of the return air duct is higher than the drying room and extends to the right. There is an air outlet on the right side of the drying room, and the air outlet is connected with the return air duct;

The bottom side of the heat pump main room is equipped with a damper for the heat pump main room, and the heat pump main room is connected with an exhaust room upward; the return air duct is provided with a dehumidifying air duct at the top, and the other end of the dehumidifying air duct extends into the exhaust room and is closed. Extending downwards into the lower part of the heat pump main room;

The heat pump system includes a compressor, a condenser, a throttling device and an evaporator connected through a refrigerant pipeline circulation, the compressor, the throttling device and the evaporator form a heat pump main unit, the heat pump main unit is located in the heat pump main unit room, and the top of the heat pump main unit is A heat pump evaporator fan with an upward air outlet direction is provided; the evaporator is adjacent to the lower opening of the dehumidification air duct; the condenser is located between the bottom of the return air duct and the drying workshop; the dehumidification air duct is separated by two The right end opening of each humid air duct is respectively equipped with a humid exhaust fan;

There is an internal circulation damper between the exhaust chamber and the heat pump main engine room, and an exhaust damper is arranged on the side wall of the exhaust chamber;

The heat pump main engine room is provided with a fresh air duct, and the two ends of the fresh air duct are respectively opened on the opposite side walls of the heat pump main room, and the two ends of the fresh air duct are respectively provided with outdoor fresh air dampers; The wet air ducts are all in the shape of a cross, and the intersection of the fresh air duct and each humid air duct is equipped with a heat recovery device. The shell side or tube side of each heat recovery unit is connected with the fresh air duct. The tube side or shell side is connected with the dehumidification air duct;

The fresh air duct of the drying room is installed on the fresh air duct between the two rows of wet air ducts, and the fresh air damper of the drying room is located between the fresh air duct and the return air duct;

The return air duct below the fresh air duct is equipped with a circulation fan with the air outlet direction facing downward, and the circulation fan is located above the condenser;

With the direction pointing to the fresh air damper of the drying chamber as inward, the fresh air ducts outside the two rows of wet air ducts are respectively provided with inner fresh air dampers, and the inner fresh air dampers are located between the fresh air duct and the return air duct.

There are more than two dampers in the heat pump main engine room arranged side by side at intervals; two exhaust dampers are arranged symmetrically on opposite side walls of the exhaust chamber.

A humidity sensor and a temperature sensor are arranged in the return air duct.

The purpose of the present invention is also to provide a drying method for drying materials using the above-mentioned heat pump drying equipment.

In order to achieve the above object, the method of drying materials using the above-mentioned heat pump drying equipment with the function of switching between dehumidification type and dehumidification type according to the present invention is carried out in the following steps:

The first step is to run in simple mode; open the damper of the heat pump main engine room, the internal circulation damper, the exhaust damper, the heat pump evaporation fan, the compressor and the circulating fan, and close the dehumidification fan, the internal fresh air damper, the drying room fresh air damper and the outdoor fresh air throttle;

At this time, under the action of the heat pump evaporating fan, the outdoor air enters the heat pump main room through the damper of the heat pump main room to exchange heat with the evaporator, and the cold generated by the evaporator is discharged through the internal circulation damper and the exhaust damper; Under the action, the circulating air enters the drying room through the condenser downwards, and the circulating air is heated when passing through the condenser, and the heated circulating air has a drying effect on the materials in the drying room; the water vapor generated during the drying process of the materials is absorbed The circulating air is taken away, and the circulating air returns to the circulating fan through the return air duct, so that the materials are continuously dried during the circulating process;

During the operation of the simple mode, when the material is continuously dried, the water vapor generated continuously enters the circulating air; the higher the relative humidity of the circulating air, the lower the drying effect; when the relative humidity in the return air duct is higher than the first When switching humidity, turn to the second step, that is, the evaporator dehumidification mode; the first switching humidity is greater than 50% and less than or equal to 80%, and the specific value is determined by the staff according to the operating conditions;

Close the internal circulation damper and exhaust damper, open the inner fresh air damper and dehumidification fan, and enter the second step;

The second step is to operate in the dehumidification mode of the evaporator; at this time, under the action of the dehumidification fan, part of the return air in the return air duct enters the dehumidification duct, and the other part of the return air still directly returns to the circulation fan; enters The circulating air of the humidity exhaust air duct is discharged into the heat pump main engine room from the lower opening of the humidity exhaust air duct after passing through the heat recovery device, and is sent to the top of the heat pump main engine room by the heat pump evaporating fan after passing through the evaporator, and enters the fresh air through the inner fresh air damper. The air duct enters the return air duct through the fresh air damper of the drying room, merges with the circulating air that has not entered the dehumidification air duct, and then is sent to the drying room through the circulating fan and condenser, and the circulating air is heated at the condenser. And produce drying effect on the materials in the drying chamber; the circulating air re-enters the return air duct through the air outlet on the right side of the drying chamber to form a circulation;

When the relative humidity in the return air duct is lower than the second switching humidity, switch to the hot air dehumidification drying mode; the second switching humidity is greater than or equal to 10 and less than or equal to 50%, and the specific value is determined by the staff according to the operating conditions;

Open the outdoor fresh air damper, internal circulation damper and exhaust air damper, close the inner fresh air damper, and enter the third step;

The third step is to operate in the hot air dehumidification and drying mode; at this time, under the action of the dehumidification fan, part of the return air in the return air duct enters the dehumidification air duct as dehumidification air, and the other part of the return air is still directly returned to the circulation fan; under the suction of the circulation fan, the outdoor fresh air enters the fresh air duct from the outdoor fresh air door, and exchanges heat with the exhaust air when passing through the heat recovery device. After absorbing the heat in the exhaust air, it passes The fresh air door of the drying room enters the return air duct, and after being combined with the circulating air that has not entered the dehumidifying air duct, it is sent into the drying room through the circulating fan and the condenser. The materials in the drying chamber produce drying effect; the air flows through the air outlet on the right side of the drying chamber and enters the return air duct again, so as to run continuously;

During the continuous operation of the third step, the hot and humid air flow in the dehumidification air duct provides heat for the evaporator when passing through the evaporator to realize waste heat utilization; The outdoor air at the damper is sucked into the main engine room of the heat pump, takes away the cold generated by the evaporator, and then is discharged by the internal circulation damper and the exhaust damper;

When the relative humidity in the return air duct is higher than the first switching humidity, turn to the second step, that is, the evaporator dehumidification mode;

The fourth step is to turn off the fans, air doors and compressors of the heat pump system after the drying degree of the materials reaches the standard, and transport the materials out of the drying chamber to stop the drying process of the materials.

The present invention designs a heat pump drying equipment with switching function between dehumidification type and dehumidification type and the corresponding drying method. The mutual switching between the hot air dehumidification type and the evaporator dehumidification type can be realized by using the mutual conversion of the damper. Choose the appropriate drying mode for different drying needs, and combine the advantages of the two drying modes to improve drying efficiency and reduce drying costs.

The simple mode has the advantages of simple operation and faster temperature rise of hot air (because in the simple mode, neither fresh air is introduced into the drying room nor the circulating air is cooled through the evaporator, so the temperature rises faster). The disadvantage of this mode is that the heat pump system is greatly affected by the external ambient temperature. When the external temperature is low, the temperature at the evaporator is very low, thereby reducing the operating efficiency of the heat pump system.

The advantage of the evaporator dehumidification mode is that the heat pump system is less affected by the ambient temperature and is more adaptable to low temperature environments. In this mode, the high-temperature dehumidifying air (the airflow in the dehumidifying air duct) is used to heat the evaporator, which greatly improves the temperature at the evaporator, increases the evaporation pressure, and improves the operating efficiency of the heat pump system. Since the temperature at the evaporator is basically not affected by the outside air temperature, the dehumidification mode of the evaporator has the advantages of high efficiency of the heat pump system and low degree of environmental influence. The disadvantage of the evaporator dehumidification mode is that when the humidity of the dehumidification air is low, due to the low dew point temperature of the dehumidification air, it may still not reach the dew point temperature after passing through the heat recovery device and the evaporator, or it may just reach the dew point temperature. When passing through the evaporator, the condensed moisture is very little, and the dehumidifying air returns to the drying room again, which cannot reduce the air humidity in the drying room (or the effect is very small), while the dehumidifying air passes through the evaporator to cool down and then returns to the drying room. The process of heating up through the heater is an ineffective process, not only the dehumidification effect is not obvious but also consumes a lot of energy.

The advantage of the hot air dehumidification drying mode is to use the humidity difference between the external dry air and the humid air in the drying room to accelerate the drying process. Under the conditions of high external air temperature and low humidity, the drying efficiency is high and the energy consumption is small. At the same time, in this mode, the waste heat contained in the dehumidification wind has been recycled in two stages, and the waste heat utilization rate is relatively high. The first stage of waste heat utilization is in the heat recovery device, the exhaust air heats the outdoor fresh air passing through the fresh air duct; the second stage waste heat utilization is to heat the evaporator when the exhaust air passes through the evaporator, which improves the operation of the heat pump system Efficiency (higher than simple mode and lower than evaporator dehumidification mode), making the heat pump system less affected by ambient temperature than simple mode.

The disadvantage of the hot air dehumidification drying mode is that when the humidity difference between the outside air and the air in the drying room is small, a large amount of hot air needs to be discharged, which wastes energy and the drying efficiency is low; when the external environment temperature is low, the fresh air and the air in the drying room The temperature difference is large, and the fresh air heat load is large.

The heat pump drying equipment of the present invention with the function of switching between dehumidification type and dehumidification type has a compact structure. With the drying method of the present invention, various operating modes can be realized, and the optimal operating mode can be selected according to specific operating conditions. It has the advantages of reducing the influence of the shortcomings of each mode through mode switching, the overall energy consumption is low, and the drying efficiency is high.

Description of drawings

Fig. 1 is a schematic structural diagram of the present invention in a simple mode;

Fig. 2 is the right view diagram of Fig. 1;

Fig. 3 is a top view schematic diagram of Fig. 1;

Fig. 4 is a structural schematic diagram of the present invention under the evaporator dehumidification mode;

Fig. 5 is a schematic right view of Fig. 4;

Figure 6 is a schematic top view of Figure 4;

Fig. 7 is a schematic structural view of the present invention in the hot air dehumidification drying mode;

Fig. 8 is a schematic right view of Fig. 7;

FIG. 9 is a schematic top view of FIG. 7 .

detailed description

The direction indicated by the arrow in each view is the airflow direction at that place.

As shown in Figures 1 to 9, the heat pump drying equipment with the switching function of dehumidification type and dehumidification type of the present invention includes a heat pump system and a drying workshop 1, and a heat pump host room 3 is arranged in the drying workshop 1 from left to right. , the return air duct 12 and the drying chamber 9 for holding materials; the top of the return air duct 12 is higher than the drying chamber 9 and extends to the right, and the right side of the drying chamber 9 is provided with an air outlet, and the air outlet and the return 12 air ducts are connected;

Heat pump host room 3 bottom side is provided with heat pump host room damper 16, and heat pump host room 3 is connected with exhaust room 31 upward; The other end extends into the exhaust chamber 31 and extends downward into the lower part of the heat pump host chamber 3;

The heat pump system includes a compressor, a condenser 8, a throttling device and an evaporator 5 that are circulated through a refrigerant pipeline 7 (preferably a copper pipe). In the host room 3, the top of the heat pump host is provided with a heat pump evaporating fan 2 with an upward air outlet direction; the evaporator 5 is adjacent to the lower end opening of the humidity exhaust air duct 14; Between the drying workshop 1; the said dehumidification air duct 14 is provided with two intervals, and the right end opening of each dehumidification air duct 14 is respectively provided with a dehumidification fan 13;

An internal circulation damper 17 is provided between the exhaust chamber 31 and the heat pump host chamber 3, and an exhaust damper 18 is provided on the side wall of the exhaust chamber 31;

The heat pump host room is provided with a fresh air duct 22, and the two ends of the fresh air duct 22 are respectively opened on the opposite side walls of the heat pump host room 3, and the two ends of the fresh air duct 22 are respectively provided with an outdoor fresh air damper 21; 22 and each of the dehumidifying air ducts 14 are in the shape of a cross, and the intersection of the fresh air duct 22 and each dehumidifying air duct 14 is provided with a heat recovery device 15, and the shell side or tube side of each heat recovery device 15 It communicates with the fresh air duct 22, and the tube side or shell side of each heat recovery unit 15 communicates with the humidity exhaust duct 14;

The fresh air duct 22 between the two rows of wet air ducts 14 is provided with a drying chamber fresh air damper 20, and the drying chamber fresh air damper 20 is located between the fresh air duct 22 and the return air duct 12;

The return air duct 12 below the fresh air duct 22 is provided with a circulation fan 6 with the air outlet direction facing downward, and the circulation fan 6 is located above the condenser 8;

With the direction pointing to the fresh air damper 20 of the drying chamber as inward, the fresh air duct 22 outside the two rows of wet air ducts 14 is respectively provided with an inner fresh air damper 19, and the inner fresh air damper 19 is located between the fresh air duct 22 and the return air duct 12. between.

Wherein, the heat pump system is a conventional technology in the field, and the compressor and throttling device are not shown in the figure. The throttling device can be a capillary tube or an expansion valve, both of which are conventional techniques in the art.

Two or more dampers 16 of the heat pump main engine room are arranged side by side at intervals; two exhaust dampers 18 are symmetrically arranged on opposite side walls of the exhaust chamber 31 .

The return air duct 12 is provided with a humidity sensor and a temperature sensor. Both the humidity sensor and the temperature sensor are conventional devices, not shown in the figure.

During operation, the material 11 to be dried is contained in the material loading device 10 and sent into the drying chamber 9 .

The present invention also discloses a method for drying materials by using the above-mentioned heat pump drying equipment with the function of switching between dehumidification type and dehumidification type, which is carried out in sequence according to the following steps:

The first step is to operate in simple mode; open the damper 16 of the heat pump host room, the internal circulation damper 17, the exhaust damper 18, the heat pump evaporation fan 2, the compressor and the circulation fan 6 of the heat pump host, and close the dehumidification fan 13 and the internal fresh air damper 19. Drying room fresh air damper 20 and outdoor fresh air damper 21;

At this time, under the action of the heat pump evaporator fan 2, the outdoor air enters the heat pump main room 3 through the heat pump main room damper 16 to exchange heat with the evaporator 5, and the cold generated by the evaporator 5 passes through the internal circulation damper 17 and the exhaust damper. 18 discharge; under the action of the circulating fan 6, the circulating air enters the drying chamber 9 through the condenser 8 downwards, and the circulating air is heated when passing through the condenser 8, and the heated circulating air produces a drying effect on the material in the drying chamber 9. Drying effect; the water vapor generated during the material drying process is taken away by the circulating air, and the circulating air returns to the circulating fan 6 through the return air duct 12, so that the material is continuously dried during the circulating process;

During the operation of the simple mode, when the material is continuously dried, the water vapor generated continuously enters the circulating air; the higher the relative humidity of the circulating air, the lower the drying effect; when the relative humidity in the return air duct 12 is higher than When switching the humidity for the first time, turn to the second step, that is, the dehumidification mode of the evaporator 5; the first switching humidity is greater than 50% and less than or equal to 80%, and the specific value is determined by the staff according to the operating conditions; when drying a certain material , the staff observes the change of the relative humidity of the circulating air. When the relative humidity of the circulating air changes from a rapid increase to a slow increase or basically no longer changes, it means that the drying effect is too low when the circulating air reaches the relative humidity under this working condition. , the relative humidity when the relative humidity of the circulating air rises slowly or basically does not change is set as the first switching humidity.

Close the internal circulation damper 17 and the exhaust damper 18, open the inner fresh air damper 19 and the dehumidification blower 13, and enter the second step;

The second step is to operate according to the dehumidification mode of the evaporator 5; at this time, under the action of the dehumidification blower 13, a part of the return air in the return air duct 12 enters the dehumidification air duct 14, and the other part of the return air is still directly returned to the There are 6 circulating fans; the circulating air that enters the dehumidifying air duct 14 passes through the heat recovery device 15 and is discharged into the heat pump main engine room 3 from the lower opening of the dehumidifying air duct 14, and is sent to the heat pump by the heat pump evaporating fan 2 after passing through the evaporator 5 The top of the host room 3, and enters the fresh air duct 22 through the inner fresh air damper 19, and then enters the return air duct 12 through the fresh air damper 20 of the drying room, and merges with the circulating air that has not entered the dehumidification air duct 14, and passes through the circulating fan 6 And the condenser 8 is sent into the drying chamber 9, the circulating air is heated at the condenser 8, and has a drying effect on the materials in the drying chamber 9; the circulating air re-enters through the air outlet on the right side of the drying chamber 9 The return air duct 12 forms a circulation;

During the continuous operation of the second step, the temperature of the circulating air with high humidity decreases when passing through the evaporator 5, and condensed water is condensed at the evaporator 5 to realize dehumidification; the dehumidified air passes through the heat pump evaporating fan 2 and the fresh air damper 19. The fresh air duct 22 and the fresh air damper 20 of the drying chamber re-enter the return air duct 12, and mix with the return air that has not passed through the dehumidification air duct 14, reducing the overall humidity of the return air, thereby allowing the circulating air to recover and absorb materials ability to retain moisture. The advantage of the dehumidification mode of the evaporator 5 is that the cooling capacity generated by the evaporator 5 itself is used to remove the moisture in the air in the drying chamber 9, and a part of the circulating air with a higher temperature is used to take away the cooling capacity of the evaporator 5, so the heat pump system The working efficiency is high, and the heat pump system is very little affected by the external ambient temperature, which solves the problem of low efficiency of the heat pump system when the ambient temperature is low. The disadvantage of the dehumidification mode of the evaporator 5 is: when the humidity of the circulating air (humidity exhausting air) is low, the temperature of the dew point of the dehumidification air may not reach below the dew point temperature after passing through the heat recovery unit 15 and the evaporator 5, or It has just reached the dew point temperature. At this time, when passing through the evaporator 5, the condensed moisture is very little, and the dehumidifying wind returns to the drying chamber 9 again, which cannot reduce the air humidity in the drying chamber 9 (or the effect is very small). small), and the process of dehumidifying air cooling through the evaporator 5 and then heating up through the heater is an ineffective process, not only the dehumidification effect is not obvious but also consumes a lot of energy.

When the relative humidity in the return air duct 12 is lower than the second switching humidity, switch to the hot air dehumidification drying mode; the second switching humidity is greater than or equal to 10 and less than or equal to 50%, and the specific value is determined by the staff according to the operating conditions ;

When drying a certain material, the staff observes the condensed water at 5 places of the evaporator. When the second step just starts to run, a large amount of condensed water will inevitably be produced at the evaporator 5 place. When no more condensed water is generated at the evaporator 5 , or the amount of condensed water generated is very small, the corresponding relative humidity value of the circulating air is set as the second switching humidity.

Open the outdoor fresh air damper 21, the internal circulation damper 17 and the exhaust damper 18, close the inner fresh air damper 19, and enter the third step;

The third step is to operate according to the hot air dehumidification and drying mode; at this time, under the action of the dehumidification blower 13, a part of the return air in the return air duct 12 enters the dehumidification air duct 14 as the dehumidification wind, and the other part of the return air Then it still directly flows back to the circulating fan 6; under the suction of the circulating fan 6, the outdoor fresh air enters the fresh air duct 22 from the outdoor fresh air damper 21, and exchanges heat with the dehumidifying air when passing through the heat recovery device 15, and absorbs After dehumidifying the heat in the dehumidifying air, it enters the return air duct 12 through the fresh air door 20 of the drying chamber, merges with the circulating air that has not entered the dehumidifying air duct 14, and is sent to the drying chamber 9 through the circulating fan 6 and the condenser 8 , the converging air is heated at the condenser 8, and has a drying effect on the materials in the drying chamber 9; the air flows through the air outlet on the right side of the drying chamber 9 and re-enters the return air duct 12, thereby continuously run;

During the continuous operation of the third step, when the hot and humid air flow in the dehumidification air duct 14 passes through the evaporator 5, it provides heat for the evaporator 5 to realize waste heat utilization; The air flow inside and the outdoor air at the damper 16 of the heat pump main engine room are sucked into the heat pump main engine room 3, and the cold generated by the evaporator 5 is taken away, and then discharged by the internal circulation damper 17 and the exhaust damper 18;

When the relative humidity in the return air duct 12 is higher than the first switching humidity, turn to the second step, that is, the dehumidification mode of the evaporator 5;

The fourth step is to turn off the fans, dampers and compressors of the heat pump system after the staff confirms that the drying degree of the materials reaches the standard, and transport the materials out of the drying chamber 9 to stop the drying process of the materials.

The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced without departing from it. Any modifications or partial replacements within the spirit and scope of the present invention shall fall within the scope of the claims of the present invention.

Claims (4)

1. The heat pump drying equipment with dehumidification type and dehumidification type switching function is characterized in that it includes a heat pump system and a drying workshop. The drying workshop is equipped with a heat pump main engine room, a return air duct and a A drying room for storing materials; the top of the return air duct is higher than the drying room and extends to the right. There is an air outlet on the right side of the drying room, and the air outlet is connected to the return air duct; The bottom side of the heat pump main room is equipped with a damper for the heat pump main room, and the heat pump main room is connected with an exhaust room upward; the return air duct is provided with a dehumidifying air duct at the top, and the other end of the dehumidifying air duct extends into the exhaust room and is closed. Extending downwards into the lower part of the heat pump main room; The heat pump system includes a compressor, a condenser, a throttling device and an evaporator connected through a refrigerant pipeline circulation, the compressor, the throttling device and the evaporator form a heat pump main unit, the heat pump main unit is located in the heat pump main unit room, and the top of the heat pump main unit is A heat pump evaporator fan with an upward air outlet direction is provided; the evaporator is adjacent to the lower opening of the dehumidification air duct; the condenser is located between the bottom of the return air duct and the drying workshop; the dehumidification air duct is separated by two The right end opening of each humid air duct is respectively equipped with a humid exhaust fan; There is an internal circulation damper between the exhaust chamber and the heat pump main engine room, and an exhaust damper is arranged on the side wall of the exhaust chamber; The heat pump main engine room is provided with a fresh air duct, and the two ends of the fresh air duct are respectively opened on the opposite side walls of the heat pump main room, and the two ends of the fresh air duct are respectively provided with outdoor fresh air dampers; The wet air ducts are all in the shape of a cross, and the intersection of the fresh air duct and each humid air duct is equipped with a heat recovery device. The shell side or tube side of each heat recovery unit is connected with the fresh air duct. The tube side or shell side is connected with the dehumidification air duct; The fresh air duct of the drying room is installed on the fresh air duct between the two rows of wet air ducts, and the fresh air damper of the drying room is located between the fresh air duct and the return air duct; The return air duct below the fresh air duct is equipped with a circulation fan with the air outlet direction facing downward, and the circulation fan is located above the condenser; With the direction pointing to the fresh air damper of the drying chamber as inward, the fresh air ducts outside the two rows of wet air ducts are respectively provided with inner fresh air dampers, and the inner fresh air dampers are located between the fresh air duct and the return air duct. 2. The heat pump drying equipment with switching function between dehumidification type and dehumidification type according to claim 1, characterized in that: there are more than two dampers in the main engine room of the heat pump arranged side by side; There are two symmetrically arranged on the opposite side walls. 3. The heat pump drying equipment with switching function between dehumidification type and dehumidification type according to claim 1 or 2, characterized in that a humidity sensor and a temperature sensor are arranged in the return air duct. 4. The method for drying materials by using the heat pump drying equipment with the switching function of dehumidification type and dehumidification type described in claim 3, characterized in that the following steps are carried out in sequence: The first step is to run in simple mode; open the damper of the heat pump main engine room, the internal circulation damper, the exhaust damper, the heat pump evaporation fan, the compressor and the circulating fan, and close the dehumidification fan, the internal fresh air damper, the drying room fresh air damper and the outdoor fresh air throttle; At this time, under the action of the heat pump evaporating fan, the outdoor air enters the heat pump main room through the damper of the heat pump main room to exchange heat with the evaporator, and the cold generated by the evaporator is discharged through the internal circulation damper and the exhaust damper; Under the action, the circulating air enters the drying room through the condenser downwards, and the circulating air is heated when passing through the condenser, and the heated circulating air has a drying effect on the materials in the drying room; the water vapor generated during the drying process of the materials is absorbed The circulating air is taken away, and the circulating air returns to the circulating fan through the return air duct, so that the materials are continuously dried during the circulating process; During the operation of the simple mode, when the material is continuously dried, the water vapor generated continuously enters the circulating air; the higher the relative humidity of the circulating air, the lower the drying effect; when the relative humidity in the return air duct is higher than the first When switching humidity, turn to the second step, that is, the evaporator dehumidification mode; the first switching humidity is greater than 50% and less than or equal to 80%, and the specific value is determined by the staff according to the operating conditions; Close the internal circulation damper and exhaust damper, open the inner fresh air damper and dehumidification fan, and enter the second step; The second step is to operate in the dehumidification mode of the evaporator; at this time, under the action of the dehumidification fan, part of the return air in the return air duct enters the dehumidification duct, and the other part of the return air still directly returns to the circulation fan; enters The circulating air of the humidity exhaust air duct is discharged into the heat pump main engine room from the lower opening of the humidity exhaust air duct after passing through the heat recovery device, and is sent to the top of the heat pump main engine room by the heat pump evaporating fan after passing through the evaporator, and enters the fresh air through the inner fresh air damper. The air duct enters the return air duct through the fresh air damper of the drying room, merges with the circulating air that has not entered the dehumidification air duct, and then is sent to the drying room through the circulating fan and condenser, and the circulating air is heated at the condenser. And produce drying effect on the materials in the drying chamber; the circulating air re-enters the return air duct through the air outlet on the right side of the drying chamber to form a circulation; When the relative humidity in the return air duct is lower than the second switching humidity, switch to the hot air dehumidification drying mode; the second switching humidity is greater than or equal to 10 and less than or equal to 50%, and the specific value is determined by the staff according to the operating conditions; Open the outdoor fresh air damper, internal circulation damper and exhaust air damper, close the inner fresh air damper, and enter the third step; The third step is to operate in the hot air dehumidification and drying mode; at this time, under the action of the dehumidification fan, part of the return air in the return air duct enters the dehumidification air duct as dehumidification air, and the other part of the return air is still directly returned to the circulation fan; under the suction of the circulation fan, the outdoor fresh air enters the fresh air duct from the outdoor fresh air door, and exchanges heat with the exhaust air when passing through the heat recovery device. After absorbing the heat in the exhaust air, it passes The fresh air door of the drying room enters the return air duct, and after being combined with the circulating air that has not entered the dehumidifying air duct, it is sent into the drying room through the circulating fan and the condenser. The materials in the drying chamber are dried; the air flows through the air outlet on the right side of the drying chamber and enters the return air duct again, so as to run continuously; During the continuous operation of the third step, the hot and humid air flow in the dehumidification air duct provides heat for the evaporator when passing through the evaporator to realize waste heat utilization; The outdoor air at the damper is sucked into the main engine room of the heat pump, takes away the cold generated by the evaporator, and then is discharged by the internal circulation damper and the exhaust damper; When the relative humidity in the return air duct is higher than the first switching humidity, turn to the second step, that is, the evaporator dehumidification mode; The fourth step is to turn off the fans, air doors and compressors of the heat pump system after the drying degree of the materials reaches the standard, and transport the materials out of the drying chamber to stop the drying process of the materials.