A cryogenic-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles

Abstract

The present invention discloses a low-temperature-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles, which includes a compressor, a four-way valve, an outdoor heat exchanger, a first regenerator, a first dryer filter, a second dryer filter, an indoor heat exchanger, and a gas-liquid separator that are sequentially connected through pipelines; a second regenerator is further provided between the first and second dryer filters, and a one-way expansion valve is respectively arranged on the high-pressure side and the medium-pressure side of the second regenerator; the outlet of the medium-pressure side of the second regenerator is connected to the gas supplement port of the compressor. The quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles disclosed by the present invention can achieve ultra-low temperature operation of the carbon dioxide heat pump through the quasi-two-stage compression-intermediate gas supplement design, improve the energy efficiency ratio, broaden the application ambient temperature range of the heat pump, increase the circulation volume and reduce the exhaust temperature through intermediate gas supplement during the heating process, and reduce the dryness at the inlet of the evaporator through the first regenerator during the refrigeration process, so that the quasi-two-stage compression carbon dioxide heat pump operates efficiently under all working conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of rail vehicle air conditioners, and in particular to a low-temperature-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles. Background Art

[0002] The existing carbon dioxide heat pump air conditioner for rail vehicles includes a compressor, a four-way valve, an outdoor heat exchanger, a first regenerator, a first drying filter, a second drying filter, an indoor heat exchanger, and a gas-liquid separator connected in sequence through pipelines. However, for the existing rail carbon dioxide heat pump air conditioner, the heating effect is poor in a low-temperature environment. Summary of the Invention

[0003] The present invention provides a low-temperature-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles to solve the above problems.

[0004] The technical means adopted by the present invention are as follows:

[0005] A low-temperature-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles includes a compressor, a four-way valve, an outdoor heat exchanger, a first regenerator, a first drying filter, a second drying filter, an indoor heat exchanger, and a second regenerator;

[0006] The exhaust port of the compressor is connected to the first valve port of the four-way valve through a pipeline, the second valve port of the four-way valve is connected to the first interface of the outdoor heat exchanger through a pipeline, the second interface of the outdoor heat exchanger is connected to the first interface of the high-pressure side of the first regenerator through a pipeline, the second interface of the high-pressure side and the first interface of the high-pressure side of the first regenerator are respectively connected to the first interface of the first drying filter through pipelines, the second interface of the first drying filter is connected to the first interface of the second drying filter and the first interface of the high-pressure side of the second regenerator through pipelines, the second interface of the high-pressure side of the second regenerator is connected to the first interface of the second drying filter through a pipeline, the second interface of the second drying filter is connected to the first interface of the indoor heat exchanger through a pipeline, the second interface of the indoor heat exchanger is connected to the third valve port of the four-way valve through a pipeline, the fourth valve port of the four-way valve is connected to the first interface of the low-pressure side of the first regenerator through a pipeline, and the second interface of the low-pressure side of the first regenerator is connected to the intake port of the compressor through a pipeline;

[0007] The first interface of the medium-pressure side of the second regenerator is connected to the second interface of the high-pressure side of the second regenerator through a pipeline, and the second interface of the medium-pressure side of the second regenerator is connected to the gas supplement port of the compressor through a pipeline;

[0008] A second check valve and a first check valve are respectively provided on the pipelines connecting the second interface on the high-pressure side and the first interface on the high-pressure side of the first regenerator to the first interface of the first dryer filter;

[0009] A first one-way electronic expansion valve and a second one-way electronic expansion valve are respectively provided on the two pipelines connecting the second interface of the first dryer filter to the first interface of the second dryer filter and the first interface on the high-pressure side of the second regenerator;

[0010] A third one-way electronic expansion valve is provided on the pipeline connecting the first interface on the medium-pressure side of the second regenerator to the second interface on the high-pressure side of the second regenerator.

[0011] Further, it also includes the gas-liquid separator provided on the pipeline connecting the fourth valve port of the four-way valve to the first interface on the low-pressure side of the first regenerator.

[0012] Further, it also includes a high-pressure pressure transmitter, a high-pressure pressure switch, a first stop valve, and a safety valve provided on the pipeline connecting the exhaust port of the compressor to the first valve port of the four-way valve;

[0013] A low-pressure pressure switch, a low-pressure pressure transmitter, and a second stop valve provided on the pipeline connecting the intake port of the compressor to the second interface on the low-pressure side of the first regenerator; and,

[0014] A medium-pressure pressure transmitter provided on the pipeline connecting the second interface on the medium-pressure side of the second regenerator to the gas replenishing port of the compressor.

[0015] Further, it also includes a first pipeline temperature sensor, a second pipeline temperature sensor, and a third pipeline temperature sensor;

[0016] The first pipeline temperature sensor is provided on the pipeline connecting the second interface of the outdoor heat exchanger to the first interface on the high-pressure side of the first regenerator;

[0017] The second pipeline temperature sensor is provided on the pipeline connecting the second interface on the low-pressure side of the first regenerator to the intake port of the compressor;

[0018] The third pipeline temperature sensor is provided on the pipeline connecting the second interface on the medium-pressure side of the second regenerator to the gas replenishing port of the compressor.

[0019] Further, an exhaust shock-absorbing pipe and a suction shock-absorbing pipe are respectively provided at the exhaust port and the intake port of the compressor.

[0020] Further, a discharge temperature switch is also provided at the exhaust port of the compressor.

[0021] Further, it further includes a first blower and a second blower which are correspondingly arranged with the outdoor heat exchanger and the indoor heat exchanger.

[0022] Further, the outdoor heat exchanger is a copper tube-aluminum fin heat exchanger; the first blower is an axial flow blower; both the first regenerator and the second regenerator are plate heat exchangers; the indoor heat exchanger is a copper tube-aluminum fin heat exchanger; the second blower is a centrifugal blower.

[0023] Compared with the prior art, the low-temperature resistant quasi-binary compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles disclosed by the present invention has the following beneficial effects: for the existing rail carbon dioxide heat pump air conditioner, the heating effect is poor in a low-temperature environment. The low-temperature resistant quasi-binary compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles disclosed by the present invention can realize the ultra-low temperature operation of the carbon dioxide heat pump through the quasi-binary compression-intermediate gas injection design, improve the energy efficiency ratio, and broaden the application ambient temperature range of the carbon dioxide heat pump.

[0024] During the heating process, the circulation volume is increased and the exhaust temperature is reduced through intermediate gas injection. During the refrigeration process, the dryness at the inlet of the evaporator is reduced through the first regenerator, so that the quasi-binary compression carbon dioxide heat pump operates efficiently under all working conditions. Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the low-temperature resistant quasi-binary compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles disclosed by the present invention;

[0026] Figure 2 It is a refrigerant flow direction diagram of the refrigeration process of the low-temperature resistant quasi-binary compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles disclosed by the present invention;

[0027] Figure 3 It is a refrigerant flow direction diagram of the heating process of the low-temperature resistant quasi-binary compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles disclosed by the present invention;

[0028] In the figure: 1. Compressor; 2. Four-way valve; 3. Outdoor heat exchanger; 4. First regenerator; 5. First drying filter; 6. Second drying filter; 7. Indoor heat exchanger; 8. Second regenerator; 9. First check valve; 10. Second check valve; 11. First one-way electronic expansion valve; 12. Second one-way electronic expansion valve; 13. Third one-way electronic expansion valve; 14. Gas-liquid separator; 15. High-pressure pressure transmitter; 16. High-pressure pressure switch; 17. First stop valve; 18. Safety valve; 19. Low-pressure pressure switch; 20. Low-pressure pressure transmitter; 21. Second stop valve; 22. Medium-pressure pressure transmitter; 23. First pipeline temperature sensor; 24. Second pipeline temperature sensor; 25. Third pipeline temperature sensor; 26. Exhaust shock-absorbing pipe; 27. Suction shock-absorbing pipe; 28. Discharge temperature switch; 29. First blower; 30. Second blower. Detailed implementation mode

[0029] As Figure 1 described, the low-temperature resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles disclosed by the present invention includes a compressor 1, a four-way valve 2, an outdoor heat exchanger 3, a first regenerator 4, a first dryer filter 5, a second dryer filter 6, an indoor heat exchanger 7, and a second regenerator 8;

[0030] The exhaust port of the compressor 1 is connected to the first valve port A of the four-way valve 2 through a pipeline, the second valve port B of the four-way valve 2 is connected to the first interface of the outdoor heat exchanger 3 through a pipeline, the second interface of the outdoor heat exchanger 3 is connected to the first interface of the high-pressure side of the first regenerator 4 through a pipeline, the second interface and the first interface of the high-pressure side of the first regenerator 4 are respectively connected to the first interface of the first dryer filter 5 through pipelines, the second interface of the first dryer filter 5 is respectively connected to the first interface of the second dryer filter 6 and the first interface of the high-pressure side of the second regenerator 8 through pipelines, the second interface of the high-pressure side of the second regenerator 8 is connected to the first interface of the second dryer filter 6 through a pipeline, the second interface of the second dryer filter 6 is connected to the first interface of the indoor heat exchanger 7 through a pipeline, the second interface of the indoor heat exchanger 7 is connected to the third valve port C of the four-way valve 2 through a pipeline, the fourth valve port D of the four-way valve 2 is connected to the first interface of the low-pressure side of the first regenerator 4 through a pipeline, and the second interface of the low-pressure side of the first regenerator 4 is connected to the intake port of the compressor 1 through a pipeline;

[0031] The first interface of the medium-pressure side of the second regenerator 8 is connected to the second interface of the high-pressure side of the second regenerator 8 through a pipeline, and the second interface of the medium-pressure side of the second regenerator 8 is connected to the gas replenishing port of the compressor 1 through a pipeline;

[0032] A second one-way valve 10 and a first one-way valve 9 are respectively arranged on the pipelines connecting the second interface and the first interface of the high-pressure side of the first regenerator 4 to the first interface of the first dryer filter 5;

[0033] A first one-way electronic expansion valve 11 and a second one-way electronic expansion valve 12 are respectively arranged on the two pipelines connecting the second interface of the first dryer filter 5 to the first interface of the second dryer filter 6 and the first interface of the high-pressure side of the second regenerator 8;

[0034] A third one-way electronic expansion valve 13 is arranged on the pipeline connecting the first interface of the medium-pressure side of the second regenerator 8 to the second interface of the high-pressure side of the second regenerator 8;

[0035] Further, it further includes a gas-liquid separator 14 disposed on the pipeline connecting the fourth valve port D of the four-way valve 2 and the first interface on the low-pressure side of the first regenerator 4.

[0036] Further, it further includes a high-pressure pressure transmitter 15, a high-pressure pressure switch 16, a first stop valve 17, and a safety valve 18 disposed on the pipeline connecting the exhaust port of the compressor 1 and the first valve port A of the four-way valve 2;

[0037] a low-pressure pressure switch 19, a low-pressure pressure transmitter 20, and a second stop valve 21 disposed on the pipeline connecting the intake port of the compressor 1 and the second interface on the low-pressure side of the first regenerator 4; and,

[0038] a medium-pressure pressure transmitter 22 disposed on the pipeline connecting the second interface on the medium-pressure side of the second regenerator 8 and the gas replenishing port of the compressor 1.

[0039] Further, it further includes a first pipeline temperature sensor 23, a second pipeline temperature sensor 24, and a third pipeline temperature sensor 25;

[0040] The first pipeline temperature sensor 23 is disposed on the pipeline connecting the second interface of the outdoor heat exchanger 3 and the first interface on the high-pressure side of the first regenerator 4;

[0041] The second pipeline temperature sensor 24 is disposed on the pipeline connecting the second interface on the low-pressure side of the first regenerator 4 and the intake port of the compressor 1;

[0042] The third pipeline temperature sensor 25 is disposed on the pipeline connecting the second interface on the medium-pressure side of the second regenerator 8 and the gas replenishing port of the compressor 1.

[0043] Further, an exhaust shock-absorbing pipe 26 and a suction shock-absorbing pipe 27 are respectively provided at the exhaust port and the intake port of the compressor 1.

[0044] Further, a discharge temperature switch 28 is further provided at the exhaust port of the compressor 1.

[0045] Further, it further includes a first fan 29 and a second fan 30 correspondingly arranged with the outdoor heat exchanger 3 and the indoor heat exchanger 7.

[0046] Further, the outdoor heat exchanger 3 is a copper tube-aluminum fin heat exchanger; the first fan 29 is an axial flow fan; the first regenerator 4 and the second regenerator 8 are both plate heat exchangers; the indoor heat exchanger 7 is a copper tube-aluminum fin heat exchanger; the second fan 30 is a centrifugal fan.

[0047] The low-temperature resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner disclosed by the present invention can realize refrigeration cycle, heating cycle and heating defrosting functions. The specific working processes of each function are as follows:

[0048] Refrigeration cycle:

[0049] In the following description process, according to the flow direction of the refrigerant, the first interface and the second interface of each component are sequentially referred to as the intake port and the outlet port;

[0050] As Figure 2 shown, in the low-temperature resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner system disclosed by the present invention, the compressor is the power source for the entire circulation process. During the refrigeration process, it cooperates with the first one-way electronic expansion valve to establish the system pressure difference, and during the heating process, it cooperates with the second one-way electronic expansion valve to establish the system pressure difference. The compressor is a variable-frequency compressor, which can adapt to a wide range of heating and refrigeration demands. The compressor has three ports: the suction port, the discharge port, and the gas replenishing port. The discharge port of the compressor is connected to the first valve port of the four-way valve through a pipeline, and an exhaust shock absorber pipe is provided on this pipeline. The suction port of the compressor is connected to the low-pressure side outlet of the first regenerator through a pipeline, and a suction shock absorber pipe is provided on this pipeline; both the exhaust shock absorber pipe and the suction shock absorber pipe are corrugated hoses, and their main function is to absorb the vibration of the compressor and prevent the amplitude from being transmitted to the system pipeline.

[0051] The four-way valve is a refrigeration and heating switching valve. During refrigeration, AB is connected (the first valve port and the second valve port are connected), and CD is connected (the third valve port and the fourth valve port are connected); during heating, AC is connected (the first valve port and the third valve port are connected), and BD is connected (the second valve port and the fourth valve port are connected).

[0052] The second valve port of the four-way valve is connected to the intake port of the outdoor heat exchanger through a pipeline. In this embodiment, the outdoor heat exchanger is a small-diameter copper tube-aluminum fin heat exchanger with an outer diameter of 5 mm, which has small air resistance and high heat exchange efficiency. The first fan used for the outdoor heat exchanger is an axial flow fan with a large air volume.

[0053] During the refrigeration process, the refrigerant (R744) is discharged from the discharge port of the compressor, enters the inlet A (the first valve port) of the four-way valve through the exhaust shock absorber pipe, flows through the B port (the second valve port) of the four-way valve, enters the outdoor heat exchanger. The first fan and the outdoor heat exchanger are in a countercurrent form, and the two cooperate to forcibly cool the refrigerant (R744), and then the refrigerant (R744) enters the high-pressure side of the first regenerator.

[0054] The first regenerator uses a plate heat exchanger, which is a wall-type heat exchanger. The heat exchanger is formed by laminating a series of corrugated heat exchange fins. The refrigerant flow channels are located between two adjacent heat exchange fins. On both sides of the same heat exchange fin, there are a heat source and a cold source refrigerant respectively. The high-pressure side inlet is connected to the outlet of the outdoor heat exchanger, the high-pressure side outlet is connected to the inlet of the second one-way valve, the low-pressure side inlet is connected to the outlet of the indoor heat exchanger, and the low-pressure side outlet is connected to the inlet of the compressor suction shock absorber pipe. In this embodiment, the first regenerator has a total of 30 heat exchange fins with an outer dimension of 191X77 mm 2 , and the number of heat exchange fins and the volume of the regenerator can be set according to requirements.

[0055] The refrigerant (R744) flows out of the outdoor heat exchanger, passes through the high-pressure side of the first regenerator, then passes through the second one-way valve, and enters the first drying filter; the main function of the drying filter is to filter impurities in the pipeline to prevent the electronic expansion valve from being blocked. At the same time, it can adsorb moisture in the refrigerant to purify the refrigerant. The drying filter is a two-way filter element with low resistance.

[0056] During the refrigeration process, the second one-way electronic expansion valve and the third one-way electronic expansion valve are closed. The refrigerant enters the first one-way electronic expansion valve after passing through the first drying filter. The electronic expansion valve has a built-in throttling orifice, which plays a role in throttling and reducing pressure. After the refrigerant passes through the first one-way electronic expansion valve, the high-pressure and low-temperature liquid refrigerant expands into a low-temperature and low-pressure gas-liquid mixed refrigerant, and then passes through the second drying filter. In this embodiment, the first one-way electronic expansion valve, the second one-way electronic expansion valve, and the third one-way electronic expansion valve are all one-way expansions.

[0057] The second drying filter is the same as the first drying filter, which is a two-way filter element with very low resistance. Its main function is to filter impurities in the pipeline during the heating process to prevent the electronic expansion valve from being blocked. At the same time, it can adsorb moisture in the refrigerant to purify the refrigerant.

[0058] The low-temperature and low-pressure gas-liquid mixed refrigerant flows out of the second drying filter and enters the indoor heat exchanger. By cooperating with the second fan, it exchanges heat with the indoor air, takes away the heat of the indoor humid air, and liquefies the water vapor in the indoor humid air into condensed water, playing a role in dehumidification and cooling. In this embodiment, the indoor heat exchanger is a copper tube-aluminum fin heat exchanger with an outer diameter of 7.94 mm. The fins have a hydrophilic coating, which is conducive to the precipitation of condensed water. The second fan is an EC fan (centrifugal fan), which can meet the different ventilation volume requirements of the user side and can also achieve various heat load and humidity load adjustment requirements. The second fan and the indoor heat exchanger are in a parallel flow type.

[0059] The refrigerant flows out of the indoor heat exchanger, passes through the third and fourth ports of the four-way valve, and enters the gas-liquid separator. In this embodiment, the volume of the gas-liquid separator is 2L, which is mainly used to store the refrigerant that has not participated in the cycle during the heating operation to prevent liquid slugging of the compressor.

[0060] The refrigerator passes through the gas-liquid separator and becomes 100% saturated steam. Then it enters the low-pressure side of the first regenerator. The low-pressure side refrigerant and the high-pressure side refrigerant enter the first regenerator for inter-wall heat exchange. The plate heat exchanger has high heat exchange efficiency. On the one hand, it reduces the dryness of the refrigerant after the valve, and on the other hand, it superheats the refrigerant at the evaporator outlet to improve the energy efficiency ratio. The high-pressure side refrigerant and the low-pressure side refrigerant in the first regenerator are in countercurrent form.

[0061] The refrigerant flows out from the low-pressure side outlet of the first regenerator into the suction shock absorber pipe, and then enters the compressor to complete the entire refrigeration cycle.

[0062] In the low-temperature-resistant rail vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air-conditioning system disclosed by the present invention, a high-pressure side branch is provided between the exhaust shock absorber pipe and the first valve port of the four-way valve, the high-pressure side branch has a first stop valve, a high-pressure pressure transmitter, a high-pressure pressure switch, and a safety valve, and a low-pressure side branch is provided between the intake shock absorber pipe and the low-pressure side outlet of the first regenerator, the low-pressure side branch has a second stop valve, a low-pressure pressure transmitter, and a low-pressure pressure switch.

[0063] The main function of the first stop valve is to facilitate maintenance and inspection. The high-pressure switch, high-pressure pressure sensor, and safety valve can be replaced without draining the refrigerant. The first stop valve has three ports: inlet, outlet, and charging port. The inlet is connected to the main pipeline, and the outlet is connected to the high-pressure switch, high-pressure pressure transmitter, and safety valve. When the valve stem of the first stop valve is opened, the inlet and outlet of the first stop valve are connected, and the charging port is connected to the atmosphere, but not to the inlet and outlet. When the valve stem of the first stop valve is closed, the inlet and outlet of the stop valve are not connected, and the charging port is connected to the inlet.

[0064] In this embodiment, the safety valve is a reset relief valve with an operating value of 14 MPa ± 0.2 MPa and a reset value of 12 MPa ± 0.2 MPa; the high-pressure pressure switch is of the normally closed type, with an operating value of 12.5 ± 0.5 MPa and a reset value of 9 MPa ± 1 MPa; the high-pressure pressure transmitter is of the current type, outputting 4 - 20 mA, corresponding to a pressure range of 0 - 16 MPa, which is a linear correspondence. The function of the safety valve is to achieve the third-level pressure protection. The characteristic of carbon dioxide refrigerant is that it operates under a high pressure in a transcritical cycle. Under the same working conditions, the high-pressure is 5 times that of R407c refrigerant, up to 10 MPa. Considering safety, three-level protection is designed on the high-pressure side: the first level is achieved by the cooperation of the high-pressure pressure transmitter and the electronic expansion valve. The high-pressure pressure threshold is set at 12 MPa. When the high-pressure pressure detected by the high-pressure pressure transmitter is greater than 12 MPa for 1 s, the opening of the electronic expansion valve will increase to control the pressure within 12 MPa; the second-level pressure protection is the high-pressure pressure switch. When the first-level pressure protection fails due to force majeure, the high-pressure switch will stop the compressor when the high-pressure is greater than 12.5 MPa. The specific principle is that there is a normally closed bimetallic structure inside the high-pressure pressure switch. When the pressure exceeds the operating value, the bimetallic sheet disconnects to achieve circuit disconnection. The air-conditioning controller receives a high-level signal and changes it to a low-level signal to control the compressor to stop, ensuring that the air conditioner stops and the pressure of the pipeline system returns to normal; the third-level pressure protection is the safety valve. When both the first-level pressure protection and the second-level pressure protection fail due to force majeure and the high-pressure is still rising, when the high-pressure exceeds the operating value of the safety valve, the safety valve will open, discharging carbon dioxide to the outside to reduce the pressure and protect the compressor.

[0065] The main function of the second stop valve is to facilitate maintenance. Without emptying the refrigerant, the low-pressure pressure switch and the low-pressure pressure sensor can be replaced. The second stop valve has three ports: an inlet, an outlet, and a charging port. The inlet is connected to the main pipeline, and the outlet is connected to the low-pressure pressure switch and the low-pressure pressure sensor. When the valve stem of the second stop valve is opened, the inlet and outlet of the second stop valve are connected, and the charging port is connected to the atmosphere, but the charging port is not connected to the inlet and the outlet. When the valve stem of the second stop valve is closed, the inlet and outlet of the second stop valve are not connected, and the charging port is connected to the inlet.

[0066] In this embodiment, the low-pressure pressure switch is of the normally open type, with an operating value of 2.5 ± 0.2 MPa and a reset value of 3.5 MPa ± 0.2 Mpa; the low-pressure pressure transmitter is of the current type, with an output of 4 - 20 mA, corresponding to a pressure range of 0 - 16 MPa, which is a linear correspondence; the refrigerant charge is 1.8 Kg; two-stage protection is designed on the low-pressure side: the first stage is achieved by the cooperation of the low-pressure pressure transmitter and the electronic expansion valve. The low-pressure pressure threshold is set at 3.3 MPa. When the low-pressure pressure transmitter detects that the low-pressure is less than 3.3 MPa for 1 s, the opening of the electronic expansion valve will increase to control the pressure above 3.3 MPa; the second-stage pressure protection is the low-pressure pressure switch. When the first-stage pressure protection fails due to force majeure, the low-pressure switch will stop the compressor when the low-pressure is less than 2.5 MPa. The specific principle is that there is a normally open bimetallic strip structure inside the low-pressure pressure switch. When the pressure is lower than the operating value, the bimetallic strip disconnects to open the circuit, and the air-conditioning controller receives a high-level signal that changes to a low-level signal to control the compressor to stop, ensuring that the air conditioner stops and the pipeline system pressure returns to normal. At the same time, a pipeline temperature sensor is attached to the outlet of the outdoor heat exchanger. The optimal system high pressure is calculated through the value of this temperature sensor, and then the opening of the first one-way electronic expansion valve is adjusted to ensure the efficient operation of the system. A discharge temperature switch is installed at the compressor exhaust port, with a set value of 120 °C. When the exhaust temperature exceeds the operating value, the compressor stops. When the exhaust temperature drops below 90 °C, the compressor resumes normal control.

[0067] Heating cycle:

[0068] As Figure 3 shown, during the heating process, the refrigerant (R744) is discharged from the compressor exhaust port, enters the four-way valve inlet (the first valve port) through the exhaust shock absorber pipe, flows through the C port (the third valve port) of the four-way valve, and enters the indoor heat exchanger. The second fan and the indoor heat exchanger are in a countercurrent form, and the two cooperate to forcibly cool the refrigerant (R744). Then the refrigerant (R744) enters the second dryer filter.

[0069] During the heating process, the first one-way electronic expansion valve is closed, and the refrigerant flows out of the second dryer filter in two paths. One path enters the high-pressure side of the second regenerator, and the other path enters the third one-way electronic expansion valve.

[0070] In this embodiment, the second regenerator has a total of 15 heat exchange fins, with an outer shape of 191X77 mm 2 , which is divided into a high-pressure side and a medium-pressure side. The number of heat exchange fins and the volume of the regenerator can be set according to needs. The refrigerant on the high-pressure side is cooled twice by the refrigerant on the medium-pressure side, and the refrigerant on the medium-pressure side is superheated by the refrigerant on the high-pressure side to form supplementary gas and enter the compressor supplementary gas pipe. The fluids on both sides inside the second regenerator are in countercurrent.

[0071] The refrigerant is throttled and depressurized into medium-pressure wet steam through the third one-way electronic expansion valve. In addition, the third one-way electronic expansion valve has two functions: first, controlling the air supply flow rate; second, controlling the air supply superheat through the cooperation of the intermediate pressure transmitter and the third pipeline temperature sensor. In this application, the second regenerator can increase the circulation flow rate and the circulation energy efficiency ratio, so it is also called an economizer.

[0072] The compressor has two-stage compression inside. The low-temperature and low-pressure refrigerant gas enters from the air intake port, and is compressed by the first stage of the compressor to discharge the medium-pressure and medium-temperature refrigerant gas into the compressor cavity. At this time, the refrigerant entering from the air supply port is mixed with the compressor cavity, and is compressed by the second stage of the compressor and discharged to the compressor exhaust port.

[0073] The main refrigerant flows out from the high-pressure side of the second heat exchanger and enters the second one-way electronic expansion valve. The second one-way electronic expansion valve is a main throttle valve, which has the same function as the first one-way electronic expansion valve in the refrigeration cycle. The refrigerant is throttled and reduced in pressure to low-temperature and low-pressure wet steam through the second one-way electronic expansion valve.

[0074] The refrigerant flows out of the second one-way electronic expansion valve and enters the first drying filter. The first drying filter and the second drying filter protect the three one-way electronic expansion valves in the system to prevent impurities from entering the electronic expansion valves and causing system damage.

[0075] The refrigerant flows out of the first filter drier and enters the first one-way valve. In the heating cycle, the first regenerator is short-circuited and does not work. The refrigerant flows out of the first one-way valve and enters the outdoor heat exchanger. The first fan cooperates with the outdoor heat exchanger for forced heat exchange, and the refrigerant changes from low-temperature and low-pressure wet steam to low-pressure superheated steam.

[0076] The refrigerant flows out from the outdoor heat exchanger outlet, enters the four-way valve B port (the second valve port), then flows out from the four-way valve D port (the fourth valve port) and enters the gas-liquid separator.

[0077] In the heating cycle, the gas-liquid separator can store the remaining refrigerant that does not participate in the cycle in the piping system to prevent the refrigerant from migrating and forming liquid hammer.

[0078] The refrigerant flows out of the gas-liquid separator and enters the low-pressure side of the first reheater. At this time, because the high-pressure side of the first reheater is short-circuited, the first reheater does not work, which is equivalent to a section of the pipeline; the refrigerant flows out of the low-pressure side of the first reheater, enters the suction shock absorber pipe, and then enters the compressor suction port to form a cycle; the second pipeline temperature sensor is attached to the compressor suction port pipeline. In the heating cycle, the second pipeline temperature sensor and the low-pressure pressure transmitter cooperate with the second one-way electronic expansion valve to control the suction superheat, and the suction superheat is 4K. The compressor cavity is attached with a heating belt for preheating the heating cycle.

[0079] Heating and defrosting:

[0080] When the ambient temperature is between -5°C and 5°C and the humidity is relatively high, the outdoor heat exchanger is particularly prone to frosting. After a long time, the heat transfer of the outdoor heat exchanger deteriorates, seriously affecting the heat pump heating, so defrosting is required.

[0081] The low-temperature resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air-conditioning system for rail vehicles disclosed in the present invention uses the readings of the low-pressure pressure transmitter and the second pipeline temperature sensor as the defrosting judgment conditions. Specifically, the reading of the low-pressure pressure transmitter is denoted as Pl, and the reading of the second pipeline temperature sensor is denoted as T2. The defrosting judgment conditions are:

[0082] (1) Pl < 3.5 MPa;

[0083] (2) 0.0612 * Pl 5 - 0.9466 * Pl 4 + 6.0791 * Pl 3 - 21.643 * Pl 2 + 55.273 * Pl - 78.923 - T2 > -3;

[0084] When the above conditions are simultaneously met, the cycle enters the heating defrosting

[0085] The heating defrosting is the refrigeration cycle, but the fan A does not work.

[0086] Denote the reading of the first pipeline temperature sensor as T1. When T1 > 5°C, the defrosting is exited. The cycle resumes normal control.

[0087] As described above, only the preferred specific implementation manners of the present invention are provided, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A low-temperature resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles, characterized in that: It includes a compressor, a four-way valve, an outdoor heat exchanger, a first regenerator, a first dryer filter, a second dryer filter, an indoor heat exchanger, and a second regenerator; The exhaust port of the compressor is connected to the first valve port of the four-way valve through a pipeline. The second valve port of the four-way valve is connected to the first interface of the outdoor heat exchanger through a pipeline. The second interface of the outdoor heat exchanger is connected to the first interface of the high-pressure side of the first regenerator through a pipeline. The second interface of the high-pressure side and the first interface of the high-pressure side of the first regenerator are respectively connected to the first interface of the first dryer filter through pipelines. The second interface of the first dryer filter is respectively connected to the first interface of the second dryer filter and the first interface of the high-pressure side of the second regenerator through pipelines. The second interface of the high-pressure side of the second regenerator is connected to the first interface of the second dryer filter through a pipeline. The second interface of the second dryer filter is connected to the first interface of the indoor heat exchanger through a pipeline. The second interface of the indoor heat exchanger is connected to the third valve port of the four-way valve through a pipeline. The fourth valve port of the four-way valve is connected to the first interface of the low-pressure side of the first regenerator through a pipeline. The second interface of the low-pressure side of the first regenerator is connected to the intake port of the compressor through a pipeline; The first interface of the medium-pressure side of the second regenerator is connected to the second interface of the high-pressure side of the second regenerator through a pipeline. The second interface of the medium-pressure side of the second regenerator is connected to the gas replenishing port of the compressor through a pipeline; A second check valve and a first check valve are respectively provided on the pipelines connecting the second interface of the high-pressure side and the first interface of the high-pressure side of the first regenerator to the first interface of the first dryer filter; A first one-way electronic expansion valve and a second one-way electronic expansion valve are respectively provided on the two pipelines connecting the second interface of the first dryer filter to the first interface of the second dryer filter and the first interface of the high-pressure side of the second regenerator; A third one-way electronic expansion valve is provided on the pipeline connecting the first interface of the medium-pressure side of the second regenerator to the second interface of the high-pressure side of the second regenerator.

2. The cryogenic-resistant quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner for rail vehicles according to claim 1, characterized in that: It also includes a gas-liquid separator provided on the pipeline connecting the fourth valve port of the four-way valve to the first interface of the low-pressure side of the first regenerator.

3. The cryogenic-resistant orbit vehicle quasi-binary compression variable-frequency carbon dioxide heat pump air conditioner according to claim 1, wherein: It also includes a high-pressure pressure transmitter, a high-pressure pressure switch, a first stop valve, and a safety valve provided on the pipeline connecting the exhaust port of the compressor to the first valve port of the four-way valve; A low-pressure pressure switch, a low-pressure pressure transmitter, and a second stop valve provided on the pipeline connecting the intake port of the compressor to the second interface of the low-pressure side of the first regenerator; and, A medium-pressure pressure transmitter provided on the pipeline connecting the second interface of the medium-pressure side of the second regenerator to the gas replenishing port of the compressor.

4. The cryogenic-resistant orbiting vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner according to claim 1, characterized in that: It also includes a first pipeline temperature sensor, a second pipeline temperature sensor, and a third pipeline temperature sensor; The first pipeline temperature sensor is provided on the pipeline connecting the second interface of the outdoor heat exchanger to the first interface of the high-pressure side of the first regenerator; The second pipeline temperature sensor is provided on the pipeline connecting the second interface of the low-pressure side of the first regenerator to the intake port of the compressor; The third pipeline temperature sensor is arranged on the pipeline connecting the second interface on the medium-pressure side of the second regenerator and the gas supplement port of the compressor.

5. The cryogenic-resistant orbit vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner according to any one of claims 1 to 4, characterized in that: An exhaust shock-absorbing pipe and a suction shock-absorbing pipe are respectively arranged at the exhaust port and the intake port of the compressor.

6. The cryogenic-resistant orbit vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner according to claim 5, characterized in that: A discharge temperature switch is also arranged at the exhaust port of the compressor.

7. The cryogenic-resistant orbiting vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner according to claim 6, characterized in that: It further includes a first fan and a second fan which are correspondingly arranged with the outdoor heat exchanger and the indoor heat exchanger.

8. The cryogenic-resistant orbit vehicle quasi-two-stage compression variable-frequency carbon dioxide heat pump air conditioner according to claim 7, characterized in that: The outdoor heat exchanger is a copper tube-aluminum fin heat exchanger; the first fan is an axial flow fan; both the first regenerator and the second regenerator are plate heat exchangers; the indoor heat exchanger is a copper tube-aluminum fin heat exchanger; the second fan is a centrifugal fan.

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