Dryer based on the principle of carbon dioxide heat pump

Abstract

The present invention discloses a dryer based on the principle of a carbon dioxide heat pump, comprising a carbon dioxide heat pump heating system, including a variable frequency compressor, an evaporator and a heating circuit; an air drying heat exchange system, including a drying chamber, a drying fan and a first heat exchange circuit; an auxiliary heat exchange system, including an auxiliary heat exchanger, a heat exchange fan and a second heat exchange circuit, the heating circuit and the first heat exchange circuit respectively exchange heat in an air cooler and an evaporator; a control system, including a controller, a humidity sensor and a plurality of temperature sensors, the controller is respectively connected to the variable frequency compressor and the heat exchange fan for control, and is respectively connected to the humidity sensor and the plurality of temperature sensors for signal signals; the controller can control the variable frequency compressor and the heat exchange fan to perform work based on parameter information fed back by each sensor, so as to maintain a constant temperature in the drying chamber, adopts PID closed-loop control, is more efficient and reasonable in temperature control, and has a higher energy utilization rate.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide heat pump equipment technology, and in particular to a dryer based on the principle of carbon dioxide heat pump. Background Technology

[0002] A dryer is a mechanical device that uses heat energy to reduce the moisture content of materials. It is used to dry objects such as grains, clothing, and fruits. Traditional dryers sometimes use electric heating structures or heat conduction drying methods to dry the drying chamber, which have low heat energy utilization rates.

[0003] Chinese invention patent application CN105910421A discloses a dryer based on the principle of a carbon dioxide heat pump. It dehumidifies and heats air, then fills the drying chamber with the heated, dry air to dry the items being dried. The specification of this application discloses four specific embodiments. Embodiment 1 has the following drawback: due to the continuous work of the compressor, the temperature inside the drying chamber is constantly rising. This solution does not provide a technical means to maintain a constant temperature inside the drying chamber, making it impossible to keep the temperature within a constant drying temperature range. When the temperature inside the drying chamber reaches the set temperature, the system must be shut down to prevent overheating and scalding of the items being dried. Embodiments 2 and 3 have the same drawback as Embodiment 1. Although Embodiments 2 and 3 incorporate a regenerator in the circuit from the compressor outlet to the heater inlet and to the compressor return port, the purpose of the regenerator is to ensure that the refrigerant is preheated before entering the compressor. The refrigerant absorbs some heat, reducing the temperature difference between the compressor inlet and outlet. However, because some heat is absorbed by the refrigerant entering the heater, the temperature rise time in the drying chamber is prolonged, which slows down the drying time and reduces the drying efficiency. As the compressor continues to work, the problem of uncontrollable drying chamber temperature still exists. The technical solution described in Example 4 has the following drawback: it solves the above technical problems by adding an auxiliary cooler and an auxiliary heater. However, since the auxiliary cooler and auxiliary heater are always connected in series in the air circuit, when the drying chamber temperature is lower than the set temperature, the air circuit needs to supplement heat through the auxiliary heater, while the heat is released on the other side, resulting in energy loss. The energy utilization rate is low and the energy consumption is huge, making the temperature control of the drying chamber of the whole system not very reasonable and efficient. Summary of the Invention

[0004] To address the aforementioned technical problems, the purpose of this invention is to provide a dryer based on the principle of a carbon dioxide heat pump that offers more efficient and reasonable temperature control and higher energy utilization.

[0005] To achieve the objectives of the invention described above, the present invention adopts the following technical solution:

[0006] A dryer based on the principle of a carbon dioxide heat pump includes:

[0007] A carbon dioxide heat pump heating system includes a variable frequency compressor, an air cooler, an electronic expansion valve, and an evaporator. The variable frequency compressor, air cooler, electronic expansion valve, and evaporator are connected in series through refrigerant pipelines to form a heating circuit for circulating carbon dioxide refrigerant.

[0008] An air drying heat exchange system includes a drying chamber for drying the object to be dried and a drying fan. The drying chamber and the drying fan are connected in series through an air duct to form a first heat exchange loop for circulating drying air. The first heat exchange loop exchanges heat with the heating loop on the side of the air cooler and the side of the evaporator, respectively.

[0009] An auxiliary heat exchange system includes an auxiliary heat exchanger and a heat exchange fan. The auxiliary heat exchanger is connected in a first heat exchange loop from the outlet of the drying chamber to the evaporator. The heat exchange fan is connected in parallel with the auxiliary heat exchanger through an air duct to form a second heat exchange loop.

[0010] The control system includes a controller, a first temperature sensor and a humidity sensor disposed in the drying chamber, and a fourth temperature sensor disposed on the first heat exchange circuit and adjacent to the evaporator. The controller is connected to the variable frequency compressor and is signal-connected to the first temperature sensor, the humidity sensor, and the fourth temperature sensor, respectively. The controller can adjust the operating frequency of the variable frequency compressor based on the comparison result between the measured temperature value sent by the first temperature sensor and its internally preset first set temperature value. The controller can control the heat exchange fan to start and adjust its operating frequency based on the comparison result between the measured humidity value sent by the humidity sensor, the measured temperature value sent by the fourth temperature sensor, and its internally preset set humidity value and second set temperature value.

[0011] In the above technical solution, preferably, the control system further includes an eighth temperature sensor disposed on the heating circuit and near the outlet of the air cooler, and a second temperature sensor disposed on the first heat exchange circuit and near the inlet of the drying chamber. The controller is controlled and connected to the electronic expansion valve, and the controller is signal-connected to the second temperature sensor and the eighth temperature sensor respectively. The controller can adjust the flow rate of the electronic expansion valve based on the comparison result between the measured temperature value sent by the second temperature sensor and the measured temperature value sent by the eighth temperature sensor.

[0012] In the above technical solution, preferably, the controller is connected to the drying fan control, and the controller can adjust the operating frequency of the drying fan based on the comparison result of the measured temperature value sent by the first temperature sensor and the measured temperature value sent by the eighth temperature sensor.

[0013] In the above technical solution, preferably, the control system further includes a fifth temperature sensor and a first pressure sensor disposed on the outlet side of the variable frequency compressor, and a second pressure sensor disposed on the inlet side of the variable frequency compressor. The controller is signal-connected to the fifth temperature sensor, the sixth temperature sensor, the first pressure sensor, and the second pressure sensor respectively. The controller can adjust the operating frequency of the variable frequency compressor based on the comparison result between the measured temperature value sent by the fifth temperature sensor and its internally preset temperature warning value, and the ratio between the measured pressure value sent by the first pressure sensor and the measured pressure value sent by the second pressure sensor.

[0014] In the above technical solution, preferably, the heat exchange fan has a first operating frequency, a second operating frequency, and a third operating frequency. The first operating frequency is lower than the second operating frequency, and the second operating frequency is lower than the third operating frequency. When the measured temperature value of the fourth temperature sensor is 35°C and the measured humidity value of the humidity sensor is above 60%, the heat exchange fan starts working and operates at the first operating frequency. When the measured temperature value of the fourth temperature sensor is 35°C and the measured humidity value of the humidity sensor is below 40%, the heat exchange fan operates at the second operating frequency. When the measured temperature value of the fourth temperature sensor is 40°C, the heat exchange fan operates at the third operating frequency.

[0015] In the above technical solution, preferably, the control system further includes a sixth temperature sensor disposed on the side of the outlet of the variable frequency compressor and a seventh temperature sensor disposed on the side of the heating circuit and adjacent to the evaporator, and the controller is signal-connected to the sixth temperature sensor and the seventh temperature sensor respectively.

[0016] In the above technical solution, preferably, the initial speed of the variable frequency compressor satisfies the following formula:

[0017] FreqCS=(FreqCmax-FreqCmin)*0.6-AT*50FreqCs;

[0018] FreqC = FreqCS;

[0019] FreqCmin≤FreqCS≤FreqCmin;

[0020] Where FreqCS is the initial speed, FreqCmin is the minimum speed of the variable frequency compressor, FreqCmax is the maximum speed of the variable frequency compressor, FreqC is the actual speed of the variable frequency compressor, and AT is the ambient temperature.

[0021] In the above technical solution, preferably, the variable frequency compressor changes frequency according to a set time interval, and the frequency change amplitude and the frequency relationship before and after the frequency change satisfy the following formula:

[0022] ΔFreqC=(T x -T1)*((FreqCmax-FreqCmin) / 1000)*3;

[0023] ΔFreqC≤((FreqCmax-FreqCmin) / 8;

[0024] FreqC = pFreqC + ΔFreqC;

[0025] ΔT=|T x -T1|;

[0026] ΔT≤10;

[0027] t = (15 - ΔT) * 2 * 1000;

[0028] Wherein, ΔFreqC is the calculated speed difference for each frequency conversion, Tx is the first set temperature value, T1 is the measured temperature value of the first temperature sensor, FreqCmin is the minimum speed of the variable frequency compressor, FreqCmax is the maximum speed of the variable frequency compressor, FreqC is the actual speed of the variable frequency compressor, pFreqC is the speed during the previous frequency conversion, ΔT is the absolute value of the temperature difference, and t is the time interval between each frequency conversion in milliseconds.

[0029] In the above technical solution, preferably, the initial opening degree of the electronic expansion valve and the ambient temperature satisfy the following formula:

[0030] StepF = 4 * AT + 150;

[0031] StepF ≤ StepFmax;

[0032] Where StepF is the actual opening degree of the electronic expansion valve, StepFmax is the maximum opening degree of the electronic expansion valve, and AT is the ambient temperature.

[0033] In the above technical solution, preferably, the controller has a preset superheat setting, and the relationship between the superheat setting and the ambient temperature satisfies the following formula:

[0034] When AT≥25, SetovHotT=3;

[0035] When AT≥15, SetovHotT=2;

[0036] When AT≥0, SetovHotT=1;

[0037] When AT ≥ -10, SetovHotT = 0;

[0038] At other ambient temperatures, SetovHotT = -1;

[0039] Where AT represents the ambient temperature and SetovHotT represents the set superheat.

[0040] In the above technical solution, preferably, the actual opening degree of the electronic expansion valve is controlled according to the difference between the set superheat degree and the actual superheat degree, which satisfies the following relationship:

[0041] ΔovHotT=T8–T2;

[0042] If pStepF≤100, then we have;

[0043] ΔovHotT–SetovHotT>1.5, StepF=pStepF-3;

[0044] ΔovHotT–SetovHotT>0.8, StepF=pStepF-2;

[0045] ΔovHotT–SetovHotT>0.5, StepF=pStepF-1;

[0046] ΔovHotT–SetovHotT>-0.5, StepF=pStepF-0;

[0047] ΔovHotT–SetovHotT>-1, StepF=pStepF+2;

[0048] ΔovHotT–SetovHotT≤-1, StepF=pStepF+5;

[0049] If pStepF > 100, then we have;

[0050] ΔovHotT–SetovHotT>8, StepF=pStepF-15;

[0051] ΔovHotT–SetovHotT>5, StepF=pStepF-10;

[0052] ΔovHotT–SetovHotT>2, StepF=pStepF-5;

[0053] ΔovHotT–SetovHotT>0.5, StepF=pStepF-2;

[0054] ΔovHotT–SetovHotT>-0.3, StepF=pStepF-0;

[0055] ΔovHotT–SetovHotT>-1.3, StepF=pStepF+2;

[0056] ΔovHotT–SetovHotT>-2, StepF=pStepF+5;

[0057] ΔovHotT–SetovHotT≤-2, StepF=pStepF+10;

[0058] Wherein, ΔovHotT is the actual superheat, SetovHotT is the set superheat, pStepF is the opening degree of the previous electronic expansion valve, StepF is the actual opening degree of the electronic expansion valve, T2 is the measured temperature value of the second temperature sensor, and T8 is the measured temperature value of the eighth temperature sensor.

[0059] In the above technical solution, preferably, the initial rotational speed of the drying fan satisfies the following relationship:

[0060] FreqS = 0.5FreqFmax;

[0061] FreqFmin = 0.4FreqFmax;

[0062] Where FreqS is the initial speed of the drying fan, FreqFmax is the maximum fan speed, and FreqFmin is the minimum fan speed.

[0063] In the above technical solution, preferably, the actual rotational speed of the drying fan satisfies the following relationship:

[0064] If T8 > T1, then we have;

[0065] ΔT = T8 - T1, ΔT ≤ 40;

[0066] FreqF=((FreqFmax*0.6) / 40)*ΔT+FreqFmin;

[0067] If T8 ≤ T1, then we have;

[0068] ΔT = T1 - T8, ΔT ≤ 5;

[0069] FreqF=pFreqF-((FreqFmax*0.6) / 25), FreqF≥FreqFmin;

[0070] Where FreqF is the actual rotational speed of the drying fan, pFreqF is the rotational speed of the drying fan in the previous cycle, FreqFmax is the maximum fan speed, FreqFmin is the minimum fan speed, T1 is the measured temperature value of the first temperature sensor, and T8 is the measured temperature value of the eighth temperature sensor.

[0071] This invention establishes an air drying heat exchange system, an auxiliary heat exchange system, and a control system. The controller adjusts the operating frequency of the variable frequency compressor based on a comparison between the measured temperature value sent by a first temperature sensor and its internally preset first set temperature value. The controller also controls the operation and adjusts the operating frequency of the heat exchange fan based on a comparison between the measured humidity value sent by a humidity sensor, the measured temperature value sent by a fourth temperature sensor, and its internally preset set humidity value and second set temperature value. Thus, when the drying chamber temperature is lower than the set temperature, the heat output is increased by increasing the operating frequency of the variable frequency compressor. When the drying chamber temperature and humidity reach or exceed the set standards, the temperature inside the drying chamber is kept constant by turning on and adjusting the frequency of the heat exchange fan. Because the variable frequency compressor and the heat exchange fan each employ PID closed-loop control, temperature control is more efficient and rational, and energy utilization is higher. Attached Figure Description

[0072] Figure 1 This is a schematic diagram of the structure of the present invention;

[0073] The components include: 1. Carbon dioxide heat pump heating system; 11. Variable frequency compressor; 12. Air cooler; 13. Electronic expansion valve; 14. Evaporator; 15. Heating circuit;

[0074] 2. Air drying heat exchange system; 21. Drying chamber; 22. Drying fan; 23. First heat exchange circuit;

[0075] 3. Auxiliary heat exchange system; 31. Auxiliary heat exchanger; 32. Heat exchange fan; 33. Second heat exchange loop;

[0076] 4. Control system; 41. Controller;

[0077] T1, First temperature sensor; T2, Second temperature sensor; T3, Third temperature sensor; T4, Fourth temperature sensor; T5, Fifth temperature sensor; T6, Sixth temperature sensor; T7, Seventh temperature sensor; T8, Eighth temperature sensor; P1, First pressure sensor; P2, Second pressure sensor; W1, Humidity sensor. Detailed Implementation

[0078] To explain in detail the technical content, structural features, objectives, and effects of the invention, the following will provide a detailed description in conjunction with the embodiments and accompanying drawings.

[0079] Carbon dioxide heat pumps are considered an ideal application area for convective hot air dryers. The items to be dried can be grains, clothing, fruits, etc. In a dual-effect process, the cooling capacity is used to dehumidify the humid air, while the heating capacity is used to reheat the cold air. Simultaneously, the carbon dioxide heat pump can heat the air to a relatively high temperature, and with the assistance of frequency converter regulation, it can dry items over a wide temperature range. Because the air circulation is closed, excess heat is discharged to the outside through the auxiliary heat exchanger 31.

[0080] like Figure 1 As shown, the dryer based on the principle of carbon dioxide heat pump includes a carbon dioxide heat pump heating system 1, an air drying heat exchange system 2, an auxiliary heat exchange system 3, and a control system 4.

[0081] The carbon dioxide heat pump heating system 1 includes a variable frequency compressor 11, an air cooler 12, an electronic expansion valve 13, and an evaporator 14. The variable frequency compressor 11, air cooler 12, electronic expansion valve 13, and evaporator 14 are connected in series via refrigerant pipelines to form a heating loop 15 for circulating carbon dioxide refrigerant. Specifically, the entire carbon dioxide heat pump heating system 1 is designed as a transcritical carbon dioxide heat pump system. The variable frequency compressor 11 is a Panasonic C-CV303HOT variable frequency compressor, and the air cooler 12 is a microchannel air cooler. Low-temperature, low-pressure carbon dioxide vapor is drawn in from the evaporator 14, undergoes bipolar compression to become high-temperature, high-pressure vapor, and enters the microchannel air cooler for heat exchange. After passing through the air cooler 12, it becomes medium-temperature, high-pressure gas, and after being throttled by the electronic expansion valve 13, it becomes low-temperature, low-pressure liquid and enters the evaporator 14 for heat exchange, thus completing the cycle.

[0082] The air drying heat exchange system 2 includes a drying chamber 21 for drying the object to be dried and a drying fan 22. The drying chamber 21 and the drying fan 22 are connected in series via an air duct to form a first heat exchange loop 23 for circulating dry air. The first heat exchange loop 23 exchanges heat with the heating loop 15 on the side of the air cooler 12 and the side of the evaporator 14, respectively. Specifically, the drying chamber 21 is a drum drying chamber. Air enters the air cooler 12 through the drying fan 22 and exchanges heat with the carbon dioxide refrigerant to form high-temperature air that enters the drying chamber 21. The drying chamber 21 is rotated by a drum motor, and the object to be dried inside comes into full contact with the high-temperature air. The humid air discharged enters the evaporator 14, leaving moisture on the fins of the evaporator 14 and then being discharged, forming dry, low-temperature air that is then circulated and heated again.

[0083] The auxiliary heat exchange system 3 includes an auxiliary heat exchanger 31 and a heat exchange fan 32. The auxiliary heat exchanger 31 is connected to the first heat exchange circuit 23, which leads from the outlet of the drying chamber 21 to the evaporator 14. The heat exchange fan 32 and the auxiliary heat exchanger 31 are connected in parallel through an air pipeline to form a second heat exchange circuit 33.

[0084] The control system 4 includes a controller 41, a first temperature sensor T1 and a humidity sensor W1 installed in the drying chamber 21, and a fourth temperature sensor T4 installed on the first heat exchange circuit 23 and near the evaporator 14. The controller 41 is connected to the variable frequency compressor 11 for control. The controller 41 is also connected to the first temperature sensor T1, the humidity sensor W1, and the fourth temperature sensor T4 for signal transmission. The controller 41 can adjust the operating frequency of the variable frequency compressor 11 based on the comparison between the measured temperature value sent by the first temperature sensor T1 and its internally preset first set temperature value. The controller 41 can also control the heat exchange fan 32 to start and adjust its operating frequency based on the comparison between the measured humidity value sent by the humidity sensor W1, the measured temperature value sent by the fourth temperature sensor T4, and its internally preset set humidity value and second set temperature value.

[0085] The controller 41 is connected to the variable frequency drive board of the variable frequency compressor 11. The PID closed-loop control of the variable frequency compressor 11 is achieved by using the difference between the first set temperature value inside the controller 41 and the measured temperature value sent by the first temperature sensor T1 as the target value for adjustment. Specifically, when the first set temperature value T... x When the measured temperature value of the first temperature sensor T1 is greater than or equal to the measured temperature value, the controller 41 controls the variable frequency compressor 11 to increase its operating frequency, thereby increasing the heat output of the carbon dioxide heat pump heating system 1, causing the temperature of the drying chamber 21 to gradually rise until it reaches the first set temperature value; when the measured temperature value of the first temperature sensor T1 exceeds the first set temperature value T... x When this happens, controller 41 controls the variable frequency compressor 11 to reduce its operating frequency.

[0086] Specifically, after startup, the compressor runs at its initial speed for 1 minute. The initial speed is determined using the following algorithm:

[0087] FreqCS=(FreqCmax-FreqCmin)*0.6-AT*50FreqCs;

[0088] FreqC = FreqCS;

[0089] FreqCS represents the initial calculated speed, with a calculation range of FreqCmin ≤ FreqCS ≤ FreqCmin. FreqCmin is the minimum speed using the DC inverter compressor, FreqCmax is the maximum speed using the DC compressor, and FreqC is the actual speed assigned to the DC compressor. All speed units involved in the algorithm are in rpm (revolutions per minute). AT represents the ambient temperature at startup.

[0090] One minute later, the compressor enters its normal inverter operation phase, using the measured temperature value of the first sensor T1 and the first set temperature value T. x The algorithm control is implemented as follows:

[0091] ΔFreqC=(T x -T1)*((FreqCmax-FreqCmin) / 1000)*3;

[0092] The time interval for this calculation is 500ms, and ΔFreqC can have positive or negative values;

[0093] If the calculation result is outside the range (ΔFreqC≤((FreqCmax-FreqCmin) / 8);

[0094] If it is within the specified range, then it is controlled within that range.

[0095] FreqC = pFreqC + ΔFreqC;

[0096] The time interval for this calculation and assignment is calculated as follows:

[0097] ΔT=|T x -T1|, where ΔT is the absolute value, neither positive nor negative. If the calculation result exceeds the range (ΔT≤10), it will be kept within the range.

[0098] t = (15 - ΔT) * 2 * 1000;

[0099] Where ΔFreqC is the calculated speed difference for each frequency conversion, pFreqC is the speed at the previous frequency conversion, ΔT is the absolute value of the temperature difference, and t is the time interval between each frequency conversion in milliseconds.

[0100] To further increase the heat output of the carbon dioxide heat pump heating system 1 and enable the temperature inside the drying chamber 21 to reach the first set temperature as quickly as possible, the control system 4 also includes an eighth temperature sensor T8 located on the heating circuit 15 near the outlet of the air cooler 12, and a second temperature sensor T2 located on the first heat exchange circuit 23 near the inlet of the drying chamber 21. The controller 41 is connected to the electronic expansion valve 13, and the controller 41 is also connected to the second temperature sensor T2 and the eighth temperature sensor T8 via signals. The controller 41 can adjust the flow rate of the electronic expansion valve 13 based on the comparison between the measured temperature value sent by the second temperature sensor T2 and the measured temperature value sent by the eighth temperature sensor T8. In other words, the PID closed-loop control of the electronic expansion valve 13 is achieved by using the difference between the measured temperature values ​​of the second temperature sensor T2 and the eighth temperature sensor T8 as the target value for adjustment. Specifically, when the measured temperature value of the second temperature sensor T2 is greater than or equal to the measured temperature value of the eighth temperature sensor T8, the controller 41 controls the electronic expansion valve 13 to increase the flow rate, thereby increasing the intake volume of the variable frequency compressor 11, thus increasing its outlet pressure and outlet temperature, and thus increasing the output of the variable frequency compressor 11; when the measured temperature value of the second temperature sensor T2 is less than the measured temperature value of the eighth temperature sensor T8, the controller 41 controls the electronic expansion valve 13 to decrease the flow rate, thereby decreasing the intake volume of the variable frequency compressor 11, thus decreasing its outlet pressure and outlet temperature, and thus decreasing the output of the variable frequency compressor 11.

[0101] Specifically, the closed-loop control principle in this part is as follows: the difference between temperature T8 and temperature T2 is referred to as the actual superheat ΔT at the air cooler outlet. This actual superheat is compared with the set superheat T. If ΔT - T is greater than 0, it indicates that temperature T8 is too high, and the opening of the electronic expansion valve needs to be reduced. When ΔT - T is less than 0, it indicates that temperature T8 is too low, and the opening of the electronic expansion valve needs to be increased. In the actual system, T8 is the air cooler outlet temperature, and T2 is the temperature of the air entering the drying chamber. When the opening of the electronic expansion valve increases, the refrigerant flow rate at the air cooler outlet is larger, and less heat is transferred from the air cooler to the air. Therefore, the air cooler outlet temperature is relatively higher than the air inlet temperature in the drying chamber. When the opening of the electronic expansion valve decreases, the refrigerant flow rate at the air cooler outlet decreases, and the refrigerant accumulates in the air cooler, resulting in more efficient heat transfer to the air. This reduces the temperature difference between the air cooler outlet temperature and the air in the drying chamber. The control algorithm is as follows. The target value is the set superheat, which is achieved by adjusting the valve to bring the actual superheat closer to the set superheat. However, the set superheat varies depending on the ambient temperature and the system's power output, requiring specific testing to determine. The algorithm described below is based on a 20-horsepower unit.

[0102] After power-on, the electronic expansion valve is first reset and opened to the maximum StepF = StepFmax, where StepF is the actual opening degree of the electronic expansion valve and StepFmax is the maximum opening degree of the electronic expansion valve.

[0103] After reset, the electronic expansion valve actuates to the initial opening degree. The relationship between the initial opening degree and the ambient temperature satisfies the following formula: StepF=4*AT+150; StepF≤StepFmax, where AT is the ambient temperature.

[0104] After maintaining the initial opening for 3 minutes, the electronic expansion valve automatically adjusts. Before automatically adjusting according to the superheat algorithm, it needs to determine the system's exhaust pressure. If the system's exhaust pressure is less than 8 MPa, the electronic expansion valve decreases its position by 15 steps every 30 seconds until the exhaust pressure is greater than 8 MPa, or the valve opening reaches the set minimum value. Once the exhaust pressure exceeds 8 MPa, the electronic expansion valve controls according to the superheat, checking and acting once every 30 seconds.

[0105] First, determine the ambient temperature and then determine the different superheat settings (SetovHotT).

[0106] AT≥25:SetovHotT=3;

[0107] AT≥15:SetovHotT=2;

[0108] AT≥0:SetovHotT=1;

[0109] AT≥-10:SetovHotT=0;

[0110] Other: SetovHotT = -1;

[0111] Then calculate the required valve opening, where pStepF is the valve opening of the previous operation and ΔovHotT is the actual superheat.

[0112] ΔovHotT=T8–T2;

[0113] If pStepF≤100;

[0114] ΔovHotT–SetovHotT>1.5: StepF=pStepF-3;

[0115] ΔovHotT–SetovHotT>0.8: StepF=pStepF-2;

[0116] ΔovHotT–SetovHotT>0.5: StepF=pStepF-1;

[0117] ΔovHotT – SetovHotT > -0.5: StepF = pStepF - 0;

[0118] ΔovHotT – SetovHotT > -1: StepF = pStepF + 2;

[0119] ΔovHotT – SetovHotT ≤ -1: StepF = pStepF + 5;

[0120] If pStepF > 100;

[0121] ΔovHotT – SetovHotT > 8: StepF = pStepF - 15;

[0122] ΔovHotT – SetovHotT > 5: StepF = pStepF - 10;

[0123] ΔovHotT – SetovHotT > 2: StepF = pStepF - 5;

[0124] ΔovHotT – SetovHotT > 0.5: StepF = pStepF - 2;

[0125] ΔovHotT – SetovHotT > -0.3: StepF = pStepF - 0;

[0126] ΔovHotT – SetovHotT > -1.3: StepF = pStepF + 2;

[0127] ΔovHotT – SetovHotT > -2: StepF = pStepF + 5;

[0128] ΔovHotT – SetovHotT ≤ -2: StepF = pStepF + 10.

[0129] Based on the above, to ensure that the outlet temperature of the variable frequency compressor 11 is not too high and to guarantee the safety and reliability of the system, the control system 4 also includes a fifth temperature sensor T5 and a first pressure sensor P1 located on the outlet side of the variable frequency compressor 11, and a second pressure sensor P2 located on the inlet side of the variable frequency compressor 11. The controller 41 is connected to the fifth temperature sensor T5, the sixth temperature sensor T6, the first pressure sensor P1, and the second pressure sensor P2 respectively. The controller 41 can adjust the operating frequency of the variable frequency compressor 11 based on the comparison between the measured temperature value sent by the fifth temperature sensor T5 and its internally preset temperature warning value, and the ratio between the measured pressure value sent by the first pressure sensor P1 and the measured pressure value sent by the second pressure sensor P2. That is, when the outlet temperature of the variable frequency compressor 11 is too high, and when the ratio of the outlet pressure to the inlet pressure of the variable frequency compressor 11 is too large, considering the stability and safety of the system, the controller 41 controls the variable frequency compressor 11 to appropriately reduce its operating frequency, so that the system returns to normal.

[0130] The controller 41 is connected to the variable frequency drive board of the drying fan 22. The controller 41 adjusts the operating frequency of the drying fan 22 based on the comparison between the measured temperature value sent by the first temperature sensor T1 and the measured temperature value sent by the eighth temperature sensor T8. In other words, the PID closed-loop control of the drying fan 22 is achieved by using the difference between the measured temperature values ​​of the first temperature sensor T1 and the eighth temperature sensor T8 as the target value for adjustment. Specifically, when the measured temperature value of the first temperature sensor T1 is less than the measured temperature value of the eighth temperature sensor T8, the controller 41 controls the drying fan 22 to increase its operating frequency, resulting in more dry air entering the drying chamber 21, faster heating, and higher drying efficiency; when the measured temperature value of the first temperature sensor T1 is greater than or equal to the measured temperature value of the eighth temperature sensor T8, the controller 41 controls the drying fan 22 to decrease its operating frequency, resulting in less dry air entering the drying chamber 21 and maintaining a constant temperature within the drying chamber 21.

[0131] After startup, the dryer fan maintains its initial speed, FreqS = 0.5FreqFmax, where FreqS is the initial fan speed, FreqFmax is the maximum fan speed, and the minimum fan speed is FreqFmin = 0.4FreqFmax. All speed units are in rpm. After maintaining the initial fan speed for 3 minutes, automatic adjustment begins, with each adjustment interval being 1 minute.

[0132] If T8 > T1, then we have;

[0133] ΔT = T8 - T1, ΔT ≤ 40;

[0134] FreqF=((FreqFmax*0.6) / 40)*ΔT+FreqFmin;

[0135] If T8 ≤ T1, then we have;

[0136] ΔT = T1 - T8, ΔT ≤ 5;

[0137] FreqF = pFreqF - ((FreqFmax*0.6) / 25), FreqF ≥ FreqFmin, where FreqF is the actual speed of the drying fan and pFreqF is the previous fan speed.

[0138] The humid air discharged from the drying chamber 21 will also exchange heat with the auxiliary heat exchanger 31 under certain conditions, releasing some heat which is carried away by the auxiliary heat exchanger 31, thereby cooling down. Specifically, the heat exchange fan 32 has a first operating frequency, a second operating frequency, and a third operating frequency. The first operating frequency is lower than the second operating frequency, and the second operating frequency is lower than the third operating frequency. That is to say, the heat exchange fan 32 has three levels: low, medium, and high, corresponding to the first, second, and third operating frequencies, respectively. When the measured temperature value of the fourth temperature sensor T4 is 35℃ and the measured humidity value of the humidity sensor W1 is above 60%, the heat exchange fan 32 starts working and operates at the first operating frequency; when the measured temperature value of the fourth temperature sensor T4 is 35℃ and the measured humidity value of the humidity sensor W1 is below 40%, the heat exchange fan 32 operates at the second operating frequency; and when the measured temperature value of the fourth temperature sensor T4 is 40℃, the heat exchange fan 32 operates at the third operating frequency. This ensures that the temperature inside the drying chamber 21 remains at the set temperature, maintaining a constant drying temperature and improving the drying effect.

[0139] In this example, the first heat exchange loop 23 of the air drying heat exchange system 2 is closed. The maximum inlet temperature of the air-side drying chamber 21 is designed to be 60℃, which can be monitored in real time by the second temperature sensor T2. The maximum inlet temperature of the air-side evaporator 14 is 40℃. Assuming the entire system is an ideal system and energy loss is not considered, after continuous heating cycles and sufficient heat exchange, the following formula applies:

[0140] ① When auxiliary heat exchange system 3 does not participate in the circulation:

[0141] Q1 = Q c +Q4;

[0142] Q2 = Q1 - Q w -Q s ;

[0143] Q2 = Q3;

[0144] Q4 = Q3 - Qe ;

[0145] After conversion, we get: Q = Q w +Q s ;

[0146] In the above formula, Q represents the work done by the compressor; Q e Evaporator 14 absorbs heat from the first heat exchange loop 23 (air loop); Q c The heat transferred from the air cooler 12 to the first heat exchange circuit 23 (air circuit); Q w Q represents the heat absorbed by the dried substance. s Q1 is the heat absorbed by the drying chamber 21; Q2 is the heat carried by the air at the outlet of the air cooler 12; Q3 is the heat carried by the air at the outlet of the auxiliary heat exchanger 31; Q4 is the heat carried by the air at the outlet of the evaporator 14; Q5 is the heat carried away by the auxiliary heat exchanger 31.

[0147] ② In reality, since heat transfer is not without temperature difference, some heat loss is inevitable. However, as the variable frequency compressor 11 continues to work, the temperature of the drying chamber 21 and the object being dried will continue to rise. The control system 4 must ensure a constant temperature for the drying chamber 21 and the object being dried, and the air drying heat exchange system 2 must also remain stable. Therefore, when the temperature reaches a certain level, the auxiliary heat exchanger 31 needs to be turned on, resulting in the following formula:

[0148] Q3 = Q2 - Q5;

[0149] Q = Q w +Q s +Q5;

[0150] This allows for the adjustment of the heat exchanged by the auxiliary heat exchanger 31, ensuring that the air drying heat exchange system 2 remains in a balanced state.

[0151] When the air drying heat exchange system 2 operates stably at the set temperature in the drying chamber 21 for a certain period of time (the time varies for different drying materials), and the humidity parameter drops to a certain set value, the system will automatically shut down.

[0152] The entire control system 4 is a multi-coupled system with multiple variable frequency control sources. The above control approach is implemented in a decoupled manner. The variable frequency compressor 11, electronic expansion valve 13, drying fan 22, and heat exchange fan 32 all have corresponding variables for PID control and adjustment. At the same time, the inlet and outlet pressure parameters and exhaust temperature parameters of the variable frequency compressor 11 are used as system reliability parameters to ensure system stability. Since the temperature on the air side of the system (i.e., the first heat exchange loop 23) is relatively high during heat exchange in the evaporator 14, the defrosting process does not need to be considered. Therefore, in this control, the suction temperature of the variable frequency compressor 11 (based on the measured value of the sixth temperature sensor T6) and the coil temperature on the evaporator 14 side of the heating loop 15 (based on the measured value of the seventh temperature sensor T7) are not included in the closed-loop control of the control system 4. The controller 41 is connected to the sixth temperature sensor T6 and the seventh temperature sensor T7 respectively, and only reads the temperature information of each temperature sensor for user reference.

[0153] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A dryer based on the principle of carbon dioxide heat pump, characterized in that: include: A carbon dioxide heat pump heating system (1) comprises a variable frequency compressor (11), an air cooler (12), an electronic expansion valve (13) and an evaporator (14), wherein the variable frequency compressor (11), the air cooler (12), the electronic expansion valve (13) and the evaporator (14) are sequentially connected in series through a refrigerant pipeline to form a heating circuit (15) for circulating a carbon dioxide refrigerant; An air drying heat exchange system (2) comprises a drying chamber (21) for drying dried objects and a drying fan (22), wherein the drying chamber (21) and the drying fan (22) are connected in series via an air pipeline to form a first heat exchange circuit (23) for circulating drying air, and the first heat exchange circuit (23) and the heating circuit (15) perform heat exchange on the side of the air cooler (12) and the side of the evaporator (14), respectively. An auxiliary heat exchange system (3) comprises an auxiliary heat exchanger (31) and a heat exchange fan (32), wherein the auxiliary heat exchanger (31) is connected to a first heat exchange circuit (23) from the outlet of the drying chamber (21) to the evaporator (14), and the heat exchange fan (32) and the auxiliary heat exchanger (31) are connected in parallel via an air pipeline to form a second heat exchange circuit (33); A control system (4), comprising a controller (41), a first temperature sensor (T1) and a humidity sensor (W1) arranged in the drying chamber (21), a fourth temperature sensor (T4) arranged on the first heat exchange circuit (23) and adjacent to the evaporator (14), an eighth temperature sensor (T8) arranged on the heat supply circuit (15) and adjacent to the outlet of the air cooler (12), a second temperature sensor (T2) arranged on the first heat exchange circuit (23) and adjacent to the inlet of the drying chamber (21), a fifth temperature sensor (T5) and a first pressure sensor arranged on the air outlet of the variable frequency compressor (11), and a second temperature sensor (T5) and a first pressure sensor arranged on the air inlet of the variable frequency compressor (11). a second pressure sensor, a sixth temperature sensor (T6) arranged on the air outlet side of the variable frequency compressor (11), and a seventh temperature sensor (T7) arranged on the heating circuit (15) and adjacent to the evaporator (14); the controller (41) is respectively connected to the variable frequency compressor (11), the electronic expansion valve (13), and the drying fan (22); the controller (41) is connected to the first temperature sensor (T1), the second temperature sensor (T2), the fourth temperature sensor (T4), the fifth temperature sensor (T5), the sixth temperature sensor (T6), the seventh temperature sensor (T7), and the eighth temperature sensor (T8) , the humidity sensor (W1), the first pressure sensor and the second pressure sensor are respectively connected by signals, the controller (41) can adjust the operating frequency of the variable frequency compressor (11) based on the comparison result of the measured temperature value sent by the first temperature sensor (T1) and the first set temperature value preset internally, and can jointly adjust the operating frequency of the variable frequency compressor (11) based on the comparison result of the measured temperature value sent by the fifth temperature sensor (T5) and the temperature warning value preset internally, and the ratio of the measured pressure value sent by the first pressure sensor to the measured pressure value sent by the second pressure sensor, the controller (41) can adjust the operating frequency of the variable frequency compressor (11) based on the measured humidity value sent by the humidity sensor (W1), The measured temperature value sent by the fourth temperature sensor (T4) is compared with the internal preset set humidity value and the second set temperature value to control the start of the heat exchange fan (32) and adjust the operating frequency of the heat exchange fan (32). The controller (41) can adjust the flow rate of the electronic expansion valve (13) based on the comparison result between the measured temperature value sent by the second temperature sensor (T2) and the measured temperature value sent by the eighth temperature sensor (T8). The controller (41) can adjust the operating frequency of the drying fan (22) based on the comparison result between the measured temperature value sent by the first temperature sensor (T1) and the measured temperature value sent by the eighth temperature sensor (T8).

2. The dryer based on the carbon dioxide heat pump principle according to claim 1 is characterized in that: The heat exchange fan (32) has a first operating frequency, a second operating frequency and a third operating frequency, wherein the first operating frequency is less than the second operating frequency, and the second operating frequency is less than the third operating frequency. When the actual temperature value measured by the fourth temperature sensor (T4) is 35°C and the actual humidity value measured by the humidity sensor (W1) is greater than 60%, the heat exchange fan (32) is turned on and operates at the first operating frequency; when the actual temperature value measured by the fourth temperature sensor (T4) is 35°C and the actual humidity value measured by the humidity sensor (W1) is less than 40%, the heat exchange fan (32) is at the second operating frequency; when the actual temperature value measured by the fourth temperature sensor (T4) is 40°C, the heat exchange fan (32) is at the third operating frequency.

3. The dryer based on the carbon dioxide heat pump principle according to claim 1 is characterized in that: The initial speed of the variable frequency compressor satisfies the following formula: FreqCS=(Fre qCmax-FreqCmin)*0.6-AT*50FreqCs; FreqC=FreqCS; FreqCmin≤FreqCS≤FreqCmin; Among them, FreqCS is the initial speed, FreqCmin is the minimum speed of the variable frequency compressor, FreqCmax is the maximum speed of the variable frequency compressor, FreqC is the actual speed of the variable frequency compressor, and AT is the ambient temperature.

4. The dryer based on the carbon dioxide heat pump principle according to claim 3 is characterized in that: The variable frequency compressor changes frequency at a set time interval, and its frequency conversion amplitude value and the frequency relationship before and after the frequency conversion satisfy the following formula: ΔFreqC=(T x -T1)*((FreqCmax-FreqCmin) / 1000)*3; ΔFreqC≤((FreqCmax-FreqCmin) / 8; FreqC=pFreqC+ΔFreqC; ΔT=|T x -T1|; ΔT≤10; t = (15-ΔT)*2*1000; Among them, ΔFreqC is the calculated speed difference of each frequency conversion, T x is the first set temperature value, T1 is the measured temperature value of the first temperature sensor, FreqCmin is the minimum speed of the variable frequency compressor, FreqCmax is the maximum speed of the variable frequency compressor, FreqC is the actual speed of the variable frequency compressor, pFreqC is the speed at the previous frequency conversion, ΔT is the absolute value of the temperature difference, and t is the time interval between each frequency conversion, in milliseconds.

5. The dryer based on the carbon dioxide heat pump principle according to claim 1 is characterized in that: The relationship between the initial opening degree of the electronic expansion valve and the ambient temperature satisfies the following formula: StepF = 4*AT+150; StepF≤StepFmax; Among them, StepF is the actual opening of the electronic expansion valve, StepFmax is the maximum opening of the electronic expansion valve, and AT is the ambient temperature.

6. The dryer based on the carbon dioxide heat pump principle according to claim 5 is characterized in that: The controller is preset with a set superheat, and the relationship between the set superheat and the ambient temperature satisfies the following relationship: When AT≥25, SetovHotT=3; When AT≥15, SetovHotT=2; When AT≥0, SetovHotT=1; When AT≥-10, SetovHotT=0; At other ambient temperatures, SetovHotT = -1; Among them, AT is the ambient temperature and SetovHotT is the set superheat.

7. The dryer based on the carbon dioxide heat pump principle according to claim 6 is characterized in that: The actual opening of the electronic expansion valve is controlled according to the difference between the set superheat and the actual superheat, which satisfies the following relationship: ΔovHotT = T8–T2; If, pSt epF≤100, then; ΔovHotT–SetovHotT>1.5, St epF=pS t epF-3; ΔovHotT–SetovHotT>0.8, St epF=pS t epF-2; ΔovHotT–SetovHotT>0.5, St epF=pS t epF-1; ΔovHot T–S etovHotT>-0.5, St epF=pSt epF-0; ΔovHot T–S etovHotT>-1, St epF=pSt epF+2; ΔovHot T–S etovHotT≤-1, St epF=pSt epF+5; If, pSt epF>100, then; ΔovHot T–S etovHotT>8, S tepF=pSt epF-15; ΔovHot T–S etovHotT>5, S tepF=pSt epF-10; ΔovHotT–SetovHotT>2, St epF=pSt epF-5; ΔovHotT–SetovHotT>0.5, St epF=pS t epF-2; ΔovHot T–S etovHotT>-0.3, St epF=pSt epF-0; ΔovHot T–S etovHotT>-1.3, St epF=pSt epF+2; ΔovHot T–S etovHotT>-2, St epF=pSt epF+5; ΔovHot T–S etovHotT≤-2, St epF=pSt epF+10; Among them, ΔovHot T is the actual superheat, SetovHot T is the set superheat, pS t epF is the opening of the previous electronic expansion valve, StepF is the actual opening of the electronic expansion valve, T2 is the measured temperature value of the second temperature sensor, and T8 is the measured temperature value of the eighth temperature sensor.

8. The dryer based on the carbon dioxide heat pump principle according to claim 1 is characterized in that: The initial speed of the drying fan satisfies the following relationship: FreqS=0.5FreqFmax; FreqFmin=0.4FreqFmax; Among them, FreqS is the initial speed of the drying fan, FreqFmax is the maximum fan speed, and FreqFmin is the minimum fan speed.

9. The dryer based on the carbon dioxide heat pump principle according to claim 8 is characterized in that: The actual speed of the drying fan satisfies the following relationship: If T8>T1, then; ΔT=T8-T1, ΔT≤40; FreqF=((FreqFmax*0.6) / 40)*ΔT+FreqFmin; If T8≤T1, then; ΔT=T1-T8, ΔT≤5; FreqF=pFreqF-((FreqFmax*0.6) / 25), FreqF≥Fre qFmin; Among them, FreqF is the actual speed of the drying fan, pFreqF is the speed of the previous drying fan, FreqFmax is the maximum fan speed, FreqFmin is the minimum fan speed, T1 is the measured temperature value of the first temperature sensor, and T8 is the measured temperature value of the eighth temperature sensor.

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