Ultralow-temperature heat pump taking oil-free carbon dioxide as refrigerant

Abstract

The utility model discloses an ultralow-temperature heat pump taking oil-free carbon dioxide as a refrigerant. The ultralow-temperature heat pump comprises a storage tank, a supercharger, a first air energy main machine, a second air energy main machine and a secondary refrigerant heat exchanger, a second port of the first air energy host is connected with the supercharger through a first branch pipeline; a second port of the second air energy main machine is connected with a supercharger through a second branch pipeline. An outlet of the supercharger is connected with the secondary refrigerant heat exchanger and the first air energy main machine. An outlet of the secondary refrigerant heat exchanger is connected with the first air energy main machine, the second air energy main machine and the supercharger. And a first pressure sensor, a second pressure sensor, a third pressure sensor and a fourth pressure sensor are respectively arranged between the secondary refrigerant heat exchanger and the supercharger, between the supercharger and the secondary refrigerant heat exchanger, and between the first branch pipeline and the second branch pipeline. According to the utility model, the pressure change in the pipeline can be detected, and the pressure at the corresponding position can be kept stable through adjustment.

Description

Technical Field

[0001] This utility model relates to the field of heat pump technology, specifically to an ultra-low temperature heat pump using oil-free carbon dioxide as a refrigerant. Background Technology

[0002] Artificial refrigeration methods mainly include phase change refrigeration, gas expansion refrigeration, vortex tube refrigeration, and thermoelectric refrigeration, each with its own characteristics. Artificial heating mainly involves two methods: one is the traditional heat pump method, which uses electric auxiliary heating in low-temperature environments, but this method has low energy efficiency in low-temperature heating environments; the second is heat pump heating, where a refrigerant absorbs low-grade heat energy from the environment, increases its enthalpy, and vaporizes into a low-temperature gaseous refrigerant. This refrigerant is then isentropically compressed by a compressor into a refrigerant with high-grade heat energy, which then releases heat energy to the refrigerant, thus raising the refrigerant's temperature.

[0003] Many existing technologies also include heat pump (air conditioning) systems for cooling and heating. For example, CN116772321A discloses an air-source central air conditioning refrigerant circulation system and its cooling and heating method. Specifically, this air-source central air conditioning refrigerant circulation system includes: a storage tank, a booster compressor, a first air-source evaporator, a second air-source evaporator, and a refrigerant heat exchanger; the first and second air-source evaporators are located in a single air-source heat pump unit; the outlet of the storage tank is connected via pipes to the first port of the first air-source evaporator, the first port of the second air-source evaporator, and the low-pressure inlet of the booster compressor; a first return pipe connects the second port of the first air-source evaporator and the first port of the second air-source evaporator; and in the second... A second return pipe is also connected between the second port of the two air-source evaporators and the first port of the first air-source evaporator; the second ports of the first and second air-source evaporators are respectively connected to the low-pressure inlet of the booster compressor via pipes; the high-pressure outlet of the booster compressor is respectively connected to the inlet of the storage tank, the inlet of the refrigerant heat exchanger, and the second port of the first air-source evaporator via pipes, and a first expansion valve is provided at the inlet of the refrigerant heat exchanger; the first port of the first air-source evaporator is connected to the inlet of the refrigerant heat exchanger via a pipe; the outlet of the refrigerant heat exchanger is respectively connected to the first port of the first air-source evaporator, the first port of the second air-source evaporator, and the low-pressure inlet of the booster compressor via pipes.

[0004] However, the aforementioned air-source central air conditioning refrigerant circulation system still has some drawbacks. For example, pressure fluctuations at the inlet of the booster compressor can easily affect the system stability during carbon dioxide circulation and shorten the booster compressor's service life. Furthermore, carbon dioxide pressure fluctuations before the refrigerant heat exchanger inlet can also affect the stability of the refrigerant temperature during heat exchange, thus requiring further improvement in both system stability and refrigerant temperature stability. Utility Model Content

[0005] To address the problems existing in the prior art, the purpose of this utility model is to provide an ultra-low temperature heat pump using oil-free carbon dioxide as a refrigerant. By installing a first, second, third, and fourth pressure sensor on the corresponding pipeline, it can instantly detect changes in the pressure of carbon dioxide in the pipeline. This allows for timely adjustment of the carbon dioxide mass in the system through a storage tank and by adjusting the speed of the booster compressor to maintain the pressure at the booster compressor inlet, the inlet of the refrigerant heat exchanger, and the second port of the first or second air source heat pump at a set value during the corresponding heating and cooling modes. This results in more stable overall system operation, a longer booster compressor lifespan, and a more stable refrigerant temperature.

[0006] To achieve the above objectives, the technical solution of this utility model is as follows:

[0007] An ultra-low temperature heat pump using oil-free carbon dioxide as refrigerant includes a storage tank, a booster compressor, a first air source heat pump, a second air source heat pump, and a refrigerant heat exchanger.

[0008] The storage tank is used to store carbon dioxide; the outlet of the storage tank is connected to the inlet of the booster compressor via a pipe, and the inlet is connected to the outlet of the booster compressor via a pipe.

[0009] A first return pipe is connected between the second port of the first air source heat pump and the first port of the second air source heat pump; a second return pipe is also connected between the second port of the second air source heat pump and the first port of the first air source heat pump.

[0010] The second port of the first air source heat pump unit is connected to the inlet of the booster compressor via a first pipe; the second port of the second air source heat pump unit is connected to the inlet of the booster compressor via a second pipe, and the second port of the second air source heat pump unit is also connected to the inlet of the refrigerant heat exchanger via a pipe.

[0011] The outlet of the booster is connected via pipes to the inlet of the refrigerant heat exchanger and the first port of the first air source heat pump unit. An expansion valve for cooling mode and a proportional valve for heating mode are respectively installed at the inlet and outlet of the refrigerant heat exchanger. Gaseous carbon dioxide is pressurized by the booster and transformed into supercritical high-temperature superfluid carbon dioxide. In cooling mode, the high-temperature superfluid carbon dioxide can be sequentially input into the first and second air source heat pump units to cool down to room-temperature superfluid carbon dioxide. In heating mode, the high-temperature superfluid carbon dioxide can be input into the refrigerant heat exchanger to release heat.

[0012] The outlet of the refrigerant heat exchanger is connected via pipes to the first port of the first air source heat pump, the first port of the second air source heat pump, and the inlet of the booster compressor, respectively. In cooling mode, room-temperature superfluid carbon dioxide expands through the expansion valve to become low-temperature carbon dioxide. The low-temperature carbon dioxide absorbs heat from the refrigerant in the refrigerant heat exchanger, becomes gaseous carbon dioxide, and is then input into the inlet of the booster compressor, thus achieving circulation. In heating mode, high-temperature superfluid carbon dioxide releases heat to the refrigerant in the refrigerant heat exchanger and can then be input into the first or second air source heat pump. After running for a certain period of time, it switches to the air source heat pump first. The fan of one air source heat pump is in the off state while the fan of the other air source heat pump is in the on state, or high-temperature superfluid carbon dioxide releases heat to the refrigerant in the refrigerant heat exchanger and can be simultaneously input into the first air source heat pump and the second air source heat pump; when the fan of the first air source heat pump or the second air source heat pump is in the off state, carbon dioxide can defrost the surface of the heat exchanger; when the fan of the first air source heat pump or the second air source heat pump is in the on state, the carbon dioxide is depressurized and cooled to below the ambient temperature, and then absorbs heat from the air and heats up to become gaseous carbon dioxide. The gaseous carbon dioxide is input into the inlet of the booster to realize circulation;

[0013] A first pressure sensor is installed on the pipe between the outlet of the refrigerant heat exchanger and the inlet of the booster compressor to measure the carbon dioxide pressure at the inlet of the booster compressor in cooling mode.

[0014] A second pressure sensor is installed on the pipe between the outlet of the booster and the inlet of the refrigerant heat exchanger to measure the carbon dioxide pressure at the inlet of the refrigerant heat exchanger.

[0015] A third pressure sensor is installed on the first branch pipe to measure the carbon dioxide pressure at the second port of the first air source heat pump unit during heating mode.

[0016] A fourth pressure sensor is installed on the second branch pipe to measure the carbon dioxide pressure at the second port of the second air source heat pump unit during heating mode.

[0017] It also includes the following technical solutions:

[0018] Furthermore, a first electric ball valve and a second electric ball valve are respectively installed at the inlet and outlet of the storage tank to control the mass flow rate of carbon dioxide, while maintaining the carbon dioxide pressure at the inlet of the booster compressor at a set value, and maintaining the carbon dioxide pressure at the inlet of the refrigerant heat exchanger at a set value.

[0019] Furthermore, in heating mode, the carbon dioxide pressure setting at the inlet of the booster compressor is between 0.5 MPa and 4 MPa, and the carbon dioxide pressure setting at the inlet of the refrigerant heat exchanger is between 7.5 MPa and 13 MPa; in cooling mode, the carbon dioxide pressure setting at the inlet of the booster compressor is between 0.5 MPa and 5.5 MPa, and the carbon dioxide pressure setting at the inlet of the refrigerant heat exchanger is between 7.5 MPa and 13 MPa.

[0020] Furthermore, a third electric ball valve is installed on the first branch pipe; a fourth electric ball valve is installed on the second branch pipe; a fifth electric ball valve and a sixth electric ball valve are respectively installed on the first return pipe and the second return pipe; a seventh electric ball valve is installed on the pipe between the outlet of the booster compressor and the inlet of the refrigerant heat exchanger; an eighth electric ball valve is installed on the pipe between the outlet of the refrigerant heat exchanger and the first port of the first air source heat pump; a ninth electric ball valve is installed on the pipe between the outlet of the refrigerant heat exchanger and the first port of the second air source heat pump; a tenth electric ball valve is installed on the pipe between the outlet of the refrigerant heat exchanger and the inlet of the booster compressor; an eleventh electric ball valve is installed on the pipe between the outlet of the booster compressor and the first port of the first air source heat pump; and a twelfth electric ball valve is installed on the pipe between the second port of the second air source heat pump and the inlet of the refrigerant heat exchanger.

[0021] Furthermore, the number of the refrigerant heat exchangers is one or at least two arranged in parallel; the expansion valve and the proportional valve are correspondingly provided at the inlet and outlet of each of the refrigerant heat exchangers.

[0022] Furthermore, the carbon dioxide stored in the storage tank is pure carbon dioxide without additives.

[0023] The beneficial effects of this utility model are as follows:

[0024] (i) The carbon dioxide refrigerant in this invention is a supercritical fluid before entering the inlet of the heat exchanger, which can greatly reduce the frictional resistance when high-pressure carbon dioxide flows, thereby effectively reducing the energy consumption of the booster.

[0025] (II) By installing a first pressure sensor, a second pressure sensor, a third pressure sensor, and a fourth pressure sensor on the corresponding pipeline, this utility model can detect the pressure change of carbon dioxide in the pipeline in real time. Thus, in the corresponding heating and cooling modes, it can adjust the mass of carbon dioxide in the system through the storage tank and adjust the speed of the booster to keep the pressure at the inlet of the booster, the inlet of the refrigerant heat exchanger, and the second port of the first air source heat pump or the second air source heat pump at the set value. This makes the overall operation of the system more stable, the booster has a longer lifespan, and the temperature of the refrigerant is more stable.

[0026] (III) In heating mode, this utility model adopts a series dual air source heat pump structure. During operation, one air source heat pump uses the waste heat of carbon dioxide refrigerant for defrosting, while the other air source heat pump can absorb heat from the air to increase the enthalpy of the carbon dioxide refrigerant and vaporize it. After operating for a period of time, the order of carbon dioxide flow into the two air source heat pumps is switched, so that one air source heat pump is always in a heating state absorbing heat from the air. Because it can always ensure that one air source heat pump is in normal heating operation, the normal operation of the heating function can be guaranteed while defrosting is achieved, and the phenomenon of the system stopping heating during defrosting will not occur, that is, the thermal stability of the system is improved. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the frame of an ultra-low temperature heat pump using oil-free carbon dioxide as a refrigerant, according to this utility model.

[0028] Figure 2 This is a schematic diagram of the operating principle of an oil-free carbon dioxide-based ultra-low temperature heat pump in cooling mode according to this utility model.

[0029] Figure 3 This is the first operating principle diagram of an oil-free carbon dioxide-based ultra-low temperature heat pump in heating mode according to this utility model.

[0030] Figure 4 yes Figure 3 The diagram shows the operating principle after switching between the two air source heat pump units.

[0031] Figure label:

[0032] 1. Storage tank; 2. Booster compressor; 3. First air source heat pump unit; 31. First port of the first air source heat pump unit; 32. Second port of the first air source heat pump unit; 4. Second air source heat pump unit; 41. First port of the second air source heat pump unit; 42. Second port of the second air source heat pump unit; 5. Refrigerant heat exchanger; 6. First return pipe; 7. Second return pipe; 8. Expansion valve; 9. Proportional valve; 10. First pressure sensor; 11. Second pressure sensor; 12. Third pressure sensor; 13. Fourth pressure sensor; 14. First electric ball valve; 15. Second electric ball valve; 16. Third electric ball valve; 17. Fourth electric ball valve; 18. Fifth electric ball valve; 19. Sixth electric ball valve; 20. Seventh electric ball valve; 21. Eighth electric ball valve; 22. Ninth electric ball valve; 23. Tenth electric ball valve; 24. Eleventh electric ball valve; 25. Twelfth electric ball valve; 26. First branch pipe; 27. Second branch pipe. Detailed Implementation

[0033] The utility model will be further described below with reference to the accompanying drawings and specific embodiments. The following description is merely exemplary and does not limit the scope of protection of the utility model. Example 1:

[0034] refer to Figure 1 An ultra-low temperature heat pump using oil-free carbon dioxide as refrigerant includes: a storage tank 1, a booster 2, a first air source heat pump 3, a second air source heat pump 4, and a refrigerant heat exchanger 5.

[0035] The storage tank 1 is used to store carbon dioxide and provide carbon dioxide refrigerant for the heat pump. Furthermore, the refrigerant used in the following description is exemplified using carbon dioxide. In this heat pump, the two air source heat pump units serve as the outdoor units, while the refrigerant heat exchanger 5 serves as the indoor unit. Both the first air source heat pump unit 3 and the second air source heat pump unit 4 include an adjustable fan, and correspondingly, ambient air temperature probes, refrigerant pressure sensors, and refrigerant temperature sensors are installed on the air source heat pump units. However, since these are all existing technologies, they will not be described in detail here.

[0036] The refrigerant heat exchanger 5 is equipped with a heat exchanger, pressure sensor, and temperature sensor, etc. The refrigerant transfers heat to the refrigerant through the tube walls of the heat exchanger. Pressure sensors are also installed at the inlet and outlet of the booster compressor 2.

[0037] Carbon dioxide is a new type of natural working fluid. In terms of its environmental impact, it is the most environmentally friendly working fluid for cooling and heating, second only to water and air. In addition, carbon dioxide also has excellent safety and chemical stability.

[0038] The outlet of storage tank 1 is connected to the inlet of booster 2 via a pipe, and the inlet is connected to the outlet of booster 2 via a pipe for outputting carbon dioxide.

[0039] A first return pipe 6 connects the second port 32 of the first air source heat pump unit 3 and the first port 41 of the second air source heat pump unit 4 to transport carbon dioxide output from the first air source heat pump unit 3 to the second air source heat pump unit 4. A second return pipe 7 connects the second port 42 of the second air source heat pump unit 3 and the first port 31 of the first air source heat pump unit 4 to transport carbon dioxide output from the second air source heat pump unit 4 to the first air source heat pump unit 3. Therefore, the first return pipe 6 and the second return pipe 7 are mainly used for the mutual flow of carbon dioxide between the two air source heat pump units, so that the waste heat of the carbon dioxide can be used to defrost the air source heat pump unit that enters first.

[0040] The second port 32 of the first air source heat pump is connected to the inlet of the booster compressor 2 via the first branch pipe 26; the second port 42 of the second air source heat pump is connected to the inlet of the booster compressor 2 via the second branch pipe 27, and the second port 42 of the second air source heat pump is also connected to the inlet of the refrigerant heat exchanger 5 via a pipe. Therefore, with the above arrangement, carbon dioxide can be correspondingly input into the booster compressor 2, the storage tank 1, and the refrigerant heat exchanger 5.

[0041] The outlet of the booster compressor 2 is connected via pipes to the inlet of the refrigerant heat exchanger 5 and the first port 31 of the first air source heat pump unit. An expansion valve 8 for cooling mode and a proportional valve 9 for heating mode are respectively installed at the inlet and outlet of the refrigerant heat exchanger 5. Gaseous carbon dioxide is pressurized by the booster compressor 2 and transformed into supercritical high-temperature superfluid carbon dioxide. In cooling mode, the high-temperature superfluid carbon dioxide can be sequentially input into the first air source heat pump unit 3 and the second air source heat pump unit 5 to cool down into room-temperature superfluid carbon dioxide. In heating mode, the high-temperature superfluid carbon dioxide can be input into the refrigerant heat exchanger 5 via the expansion valve 8 to release heat. Therefore, the carbon dioxide output route of the booster compressor 2 is different in different modes.

[0042] The outlet of the refrigerant heat exchanger 5 is connected via pipes to the first port 31 of the first air source heat pump, the first port 41 of the second air source heat pump, and the inlet of the booster compressor 2. In cooling mode, room-temperature superfluid carbon dioxide expands through the expansion valve 8 to become low-temperature carbon dioxide. The low-temperature carbon dioxide absorbs heat from the refrigerant in the refrigerant heat exchanger 5, becomes gaseous carbon dioxide, and is then input into the inlet of the booster compressor 2, thus achieving circulation. In heating mode, high-temperature superfluid carbon dioxide releases heat to the refrigerant in the refrigerant heat exchanger 5 and can then be input into the first air source heat pump 3 or the second air source heat pump 2. After running for a certain period of time, the air source heat pump 4 switches, with the fan of the first air source heat pump 3 being in the off state and the fan of the other air source heat pump 4 being in the on state. When the fan of the first air source heat pump 3 or the second air source heat pump 4 is in the off state, carbon dioxide can use waste heat to defrost the surface of the heat exchanger. When the fan of the first air source heat pump 3 or the second air source heat pump 4 is in the on state, the carbon dioxide is depressurized and cooled to below the ambient temperature. Then, it absorbs heat from the air and heats up to become gaseous carbon dioxide. The gaseous carbon dioxide is input to the inlet of the booster 2 to achieve circulation.

[0043] Therefore, the output carbon dioxide can be input into two air source heat pumps. The input order of the two air source heat pumps is not limited in heating mode, as long as the carbon dioxide is input into the two air source heat pumps in sequence and the fan of the first air source heat pump is turned off while the fan of the other air source heat pump is turned on.

[0044] A first pressure sensor 10 is installed on the pipe between the outlet of the refrigerant heat exchanger 5 and the inlet of the booster compressor 2 to measure the carbon dioxide pressure at the inlet of the booster compressor 2 in cooling mode; a second pressure sensor 11 is installed on the pipe between the outlet of the booster compressor 2 and the inlet of the refrigerant heat exchanger 5 to measure the carbon dioxide pressure at the inlet of the refrigerant heat exchanger 5; a third pressure sensor 12 is installed on the first branch pipe 26 to measure the carbon dioxide pressure at the second port 32 of the first air source heat pump in heating mode; and a fourth pressure sensor 13 is installed on the second branch pipe 27 to measure the carbon dioxide pressure at the second port 42 of the second air source heat pump in heating mode.

[0045] Preferably, a first electric ball valve 14 and a second electric ball valve 15 are respectively provided at the inlet and outlet of the storage tank 1 to control the mass flow rate of carbon dioxide, while maintaining the carbon dioxide pressure at the inlet of the booster 2 at a set value, and maintaining the carbon dioxide pressure at the inlet of the refrigerant heat exchanger 5 at a set value.

[0046] In heating mode, the carbon dioxide pressure setting at the inlet of the booster compressor 2 is between 0.5 MPa and 4 MPa, and the carbon dioxide pressure setting at the inlet of the refrigerant heat exchanger 5 is between 7.5 MPa and 13 MPa; in cooling mode, the carbon dioxide pressure setting at the inlet of the booster compressor 2 is between 0.5 MPa and 5.5 MPa, and the carbon dioxide pressure setting at the inlet of the refrigerant heat exchanger 5 is between 7.5 MPa and 13 MPa.

[0047] A third electric ball valve 16 is also installed on the first branch pipe 26.

[0048] A fourth electric ball valve 17 is also installed on the second branch pipe 27.

[0049] A fifth electric ball valve 18 and a sixth electric ball valve 19 are respectively installed on the first return pipe 6 and the second return pipe 7. In heating mode, carbon dioxide can enter the second air source heat pump 4 after passing through the first air source heat pump 3 and the fifth electric ball valve 18, or it can enter the first air source heat pump 3 after passing through the second air source heat pump 4 and the sixth electric ball valve 19. In cooling mode, refrigerant can enter the second air source heat pump 4 after passing through the first air source heat pump 3 and the fifth electric ball valve 18.

[0050] A seventh electric ball valve 20 is installed on the pipeline between the outlet of the booster 2 and the inlet of the refrigerant heat exchanger 5.

[0051] An eighth electric ball valve 21 is installed on the pipe between the outlet of the refrigerant heat exchanger 5 and the first port 31 of the first air source heat pump; a ninth electric ball valve 22 is installed on the pipe between the outlet of the refrigerant heat exchanger 5 and the first port 41 of the second air source heat pump; and a tenth electric ball valve 23 is installed on the pipe between the outlet of the refrigerant heat exchanger 5 and the inlet of the booster compressor 2.

[0052] An eleventh electric ball valve 24 is installed on the pipe between the outlet of the booster 2 and the first port 31 of the first air source unit.

[0053] A twelfth electric ball valve 25 is installed on the pipe between the second port 42 of the second air source heat pump and the inlet of the refrigerant heat exchanger 5.

[0054] Therefore, each of the above-mentioned electric ball valves can control the switch on the corresponding pipeline.

[0055] Preferably, the number of refrigerant heat exchangers 5 can be one or at least two arranged in parallel. That is, the number of refrigerant heat exchangers 5 can be one, two, three or four, etc. The refrigerant heat exchangers 5 are arranged in parallel so that people can increase or decrease the number of refrigerant heat exchangers 5 at any time to increase or decrease the cooling capacity or heating capacity.

[0056] In this embodiment, the number of refrigerant heat exchangers 5 is selected as two.

[0057] To prevent refrigerant backflow from affecting operation, this oil-free carbon dioxide-based cryogenic heat pump is also equipped with a one-way valve (not shown in the diagram). It is specifically located at the inlet of storage tank 1 and the outlet of booster compressor 2. See [link to diagram]. Figure 1 The location shown will not be described in detail here.

[0058] In this application, the carbon dioxide stored in storage tank 1 is pure carbon dioxide without additives, which allows the carbon dioxide circulation system to be unaffected by the carbonization of additives at high temperatures, thus ensuring the stability of the heat pump and resolving various malfunctions caused by poor oil return in oil-containing refrigerants.

[0059] Regarding the use of refrigerant, the refrigerant on the refrigerant heat exchanger 5 can be a gaseous refrigerant or a liquid refrigerant. For example, the gaseous refrigerant is air, nitrogen or argon, and the liquid refrigerant is water, brine, ethylene glycol or propylene glycol solution. Example 2:

[0060] refer to Figures 2-4 This utility model also provides a cooling and heating method for an ultra-low temperature heat pump using oil-free carbon dioxide as a refrigerant, which employs the aforementioned ultra-low temperature heat pump using oil-free carbon dioxide as a refrigerant and includes the following steps:

[0061] (a) Startup Mode:

[0062] S101, the refrigerant heat exchanger 5 is shut down, and the booster compressor 2 is set to a fixed speed;

[0063] S102. During startup mode operation, when the carbon dioxide pressure sensed by the first pressure sensor 10, the second pressure sensor 11, the third pressure sensor 12, and the fourth pressure sensor 13 is lower than the set value, the first electric ball valve 14 is opened to input carbon dioxide from the storage tank 1 to the inlet of the booster 2; when the carbon dioxide pressure sensed by the second pressure sensor 11 is higher than the set value, the second electric ball valve 15 is opened to recover carbon dioxide from the storage tank 1; when the carbon dioxide pressure sensed by the first pressure sensor 10, the second pressure sensor 11, the third pressure sensor 12, and the fourth pressure sensor 13 reaches the set value, the startup mode is completed, i.e., carbon dioxide refrigerant balance is achieved; the first electric ball valve 14 and the second electric ball valve 15 are closed.

[0064] S103. After the start-up mode is completed, the refrigerant heat exchanger 5 will turn on either the cooling or heating mode.

[0065] (ii) Cooling mode:

[0066] like Figure 2As shown, in S201, the fans of the first air source heat pump 3 and the second air source heat pump 4 are both in the open state. In addition, after being pressurized by the booster 2, the carbon dioxide is transformed into high-temperature superfluid carbon dioxide. The high-temperature superfluid carbon dioxide first enters the first air source heat pump 3 and the second air source heat pump 4 in sequence, and is transformed into room temperature superfluid carbon dioxide by releasing heat into the ambient air. After being output from the second port 42 of the second air source heat pump, the room temperature superfluid carbon dioxide passes through the second pressure sensor 11 and the expansion valve 8 for throttling expansion and cooling before entering the refrigerant heat exchanger 5. Therefore, at this time, the eleventh electric ball valve 24, the fifth electric ball valve 18 and the twelfth electric ball valve 25 are open.

[0067] S202. The cooled carbon dioxide enters the refrigerant heat exchanger 5 and absorbs heat from the refrigerant through the outer surface of the refrigerant heat exchanger 5, becoming gaseous carbon dioxide. The refrigerant releases heat to the carbon dioxide to achieve cooling.

[0068] S203. The carbon dioxide gas discharged through the refrigerant heat exchanger 5 is input to the inlet of the booster 2 via the first pressure sensor 10, and is boosted by the booster 2 into high-temperature superfluid carbon dioxide, thereby realizing the carbon dioxide refrigeration cycle; therefore, the tenth electric ball valve 23 is open at this time.

[0069] S204. During the refrigeration cycle, the carbon dioxide pressure sensed by the first pressure sensor 10 can be maintained at a set value by adjusting the speed of the booster compressor 2 or adjusting the first electric ball valve 14; the carbon dioxide pressure sensed by the second pressure sensor 11 can be maintained at a set value by adjusting the speed of the booster compressor 2 or the second electric ball valve 15.

[0070] S205. Repeat steps S201-S204 above;

[0071] (III) Heating Mode:

[0072] S301. The carbon dioxide after passing through the booster 2 is transformed into high-temperature superfluid carbon dioxide, which enters the refrigerant heat exchanger 5 through the expansion valve 8. The high-temperature superfluid carbon dioxide releases heat to the refrigerant through the surface of the refrigerant heat exchanger 5 to complete the heating of the refrigerant.

[0073] S302. When the ambient temperature is greater than 2℃, the carbon dioxide that has completed the heat release in the refrigerant heat exchanger 5 simultaneously enters the first air source heat pump 3 and the second air source heat pump 4. After the first air source heat pump 3 and the second air source heat pump 4 are depressurized and cooled, they absorb heat from the air and become gaseous carbon dioxide. Then, they pass through the third pressure sensor 12 and the fourth pressure sensor 13 respectively and enter the inlet of the booster 2 to complete the cycle.

[0074] S303, such as Figure 3 and Figure 4 As shown, when the ambient temperature is below 2°C, the carbon dioxide that has released heat in the refrigerant heat exchanger 5 sequentially enters the first air source heat pump 3 and the second air source heat pump 4, or sequentially enters the second air source heat pump 4 and the first air source heat pump 3 (specifically through the first return pipe 6 with the fifth electric ball valve 18 and the second return pipe 7 with the sixth electric ball valve 19). In the first air source heat pump, the waste heat of the carbon dioxide can be used to defrost its evaporator, and at this time the fan of the air source heat pump is in the off state. Then, after the carbon dioxide flows into the second air source heat pump, it is depressurized to become carbon dioxide below the ambient temperature. Then, the carbon dioxide absorbs the air heat of the air source heat pump and becomes gaseous carbon dioxide. At this time, the fan of the second air source heat pump is in the on state. Then, the gaseous carbon dioxide is discharged and enters the inlet of the booster 2 after passing through the third pressure sensor 12 or the fourth pressure sensor 13. Of course, depending on the flow direction of the carbon dioxide, the fourth electric ball valve 17 and the third electric ball valve 16 also need to be opened accordingly.

[0075] After running for a period of time, for example, after the air source heat pump unit has been in use for 20-120 minutes, the order in which the carbon dioxide that releases heat in the refrigerant heat exchanger 5 enters the two air source heat pump units is switched, and the on / off mode of the fans of the two air source heat pump units is also switched accordingly. That is to say, if the carbon dioxide first enters the first air source heat pump unit 3 and the second air source heat pump unit 4 in sequence, the fan of the first air source heat pump unit 3 is off and the fan of the second air source heat pump unit 4 is on. After running for a period of time, it is necessary to switch the carbon dioxide to enter the second air source heat pump unit 4 and the first air source heat pump unit 3 in sequence. At this time, the fan of the first air source heat pump unit 3 is on and the fan of the second air source heat pump unit 4 is off, thereby realizing the switching of defrosting and heat absorption vaporization functions, ensuring that the two air source heat pump units can obtain effective defrosting effect, while the heating capacity remains stable during defrosting.

[0076] S304. During the heating cycle of carbon dioxide, the carbon dioxide pressure sensed by the third pressure sensor 12 or the fourth pressure sensor 13 can be maintained at a set value by adjusting the speed of the booster compressor 2 or adjusting the first electric ball valve 14; the carbon dioxide pressure sensed by the second pressure sensor 11 can be maintained at a set value by adjusting the speed of the booster compressor 2 or the second electric ball valve 15. Specifically, when carbon dioxide passes through the third pressure sensor 12, the carbon dioxide pressure sensed by the third pressure sensor 12 can be maintained at a set value by adjusting the speed of the booster compressor 2 or adjusting the first electric ball valve 14. Similarly, when carbon dioxide passes through the fourth pressure sensor 13, the carbon dioxide pressure sensed by the fourth pressure sensor 13 can be maintained at a set value by adjusting the speed of the booster compressor 2 or adjusting the first electric ball valve 14.

[0077] S305. Repeat steps S301-S304 above.

[0078] More specifically, adjusting the speed of the booster 2 as described above can correspondingly increase or decrease the amount of refrigerant circulating, while adjusting the first electric ball valve 15 and the second electric ball valve 16 can correspondingly output and recover carbon dioxide.

[0079] In addition, in step S201 of the cooling mode, the flow rate of superfluid carbon dioxide in the refrigerant heat exchanger 5 can be controlled by adjusting the expansion valve 8; in step S301 of the heating mode, the flow rate of superfluid carbon dioxide entering the refrigerant heat exchanger 5 can be controlled by adjusting the proportional valve 9.

[0080] Therefore, regarding the operation of the various electric ball valves mentioned above, during operation, when the corresponding pipeline is needed, the electric ball valve on that pipeline will be opened, while other electric ball valves that are not needed will be closed accordingly to avoid affecting the flow of carbon dioxide. In addition, the usage of each valve has already been partially reflected in the description above, so it will not be elaborated on here.

[0081] In summary, by installing a first pressure sensor 10, a second pressure sensor 11, a third pressure sensor 12, and a fourth pressure sensor 13 on the corresponding pipes, this utility model can instantly detect changes in the pressure of carbon dioxide in the pipes. This allows for timely adjustment of the carbon dioxide mass in the system via the storage tank 1 and by adjusting the speed of the booster 2 to maintain the pressure at the inlet of the booster 2, the inlet of the refrigerant heat exchanger 5, and the second port 31 of the first air source heat pump or the second port 44 of the second air source heat pump at the set values ​​during the corresponding heating and cooling modes. This results in more stable overall system operation, a longer lifespan for the booster 2, and a more stable temperature for the refrigerant.

[0082] This utility model is not limited to the above-described embodiments. If any modifications or variations to this utility model do not depart from the spirit and scope of this utility model, and if such modifications and variations fall within the scope of the claims and equivalent technologies of this utility model, then this utility model also intends to include such modifications and variations.

Claims

1. An ultra-low temperature heat pump using oil-free carbon dioxide as refrigerant, characterized in that: Includes storage tanks, booster compressors, a first air source heat pump, a second air source heat pump, and a refrigerant heat exchanger; The storage tank is used to store carbon dioxide; the outlet of the storage tank is connected to the inlet of the booster compressor via a pipe, and the inlet is connected to the outlet of the booster compressor via a pipe. A first return pipe is connected between the second port of the first air source heat pump and the first port of the second air source heat pump; a second return pipe is also connected between the second port of the second air source heat pump and the first port of the first air source heat pump. The second port of the first air source heat pump unit is connected to the inlet of the booster compressor via a first pipe; the second port of the second air source heat pump unit is connected to the inlet of the booster compressor via a second pipe, and the second port of the second air source heat pump unit is also connected to the inlet of the refrigerant heat exchanger via a pipe. The outlet of the booster is connected via pipes to the inlet of the refrigerant heat exchanger and the first port of the first air source heat pump unit. An expansion valve for cooling mode and a proportional valve for heating mode are respectively installed at the inlet and outlet of the refrigerant heat exchanger. Gaseous carbon dioxide is pressurized by the booster and transformed into supercritical high-temperature superfluid carbon dioxide. In cooling mode, the high-temperature superfluid carbon dioxide can be sequentially input into the first and second air source heat pump units to cool down to room-temperature superfluid carbon dioxide. In heating mode, the high-temperature superfluid carbon dioxide can be input into the refrigerant heat exchanger to release heat. The outlet of the refrigerant heat exchanger is connected via pipes to the first port of the first air source heat pump, the first port of the second air source heat pump, and the inlet of the booster compressor, respectively. In cooling mode, room-temperature superfluid carbon dioxide expands through the expansion valve to become low-temperature carbon dioxide. The low-temperature carbon dioxide absorbs heat from the refrigerant in the refrigerant heat exchanger, becomes gaseous carbon dioxide, and is then input into the inlet of the booster compressor, thus achieving circulation. In heating mode, high-temperature superfluid carbon dioxide releases heat to the refrigerant in the refrigerant heat exchanger and can then be input into the first or second air source heat pump. After running for a certain period of time, it switches to the air source heat pump first. The fan of one air source heat pump is in the off state while the fan of the other air source heat pump is in the on state, or high-temperature superfluid carbon dioxide releases heat to the refrigerant in the refrigerant heat exchanger and can be simultaneously input into the first air source heat pump and the second air source heat pump; when the fan of the first air source heat pump or the second air source heat pump is in the off state, carbon dioxide can defrost the surface of the heat exchanger; when the fan of the first air source heat pump or the second air source heat pump is in the on state, the carbon dioxide is depressurized and cooled to below the ambient temperature, and then absorbs heat from the air and heats up to become gaseous carbon dioxide. The gaseous carbon dioxide is input into the inlet of the booster to realize circulation; A first pressure sensor is installed on the pipe between the outlet of the refrigerant heat exchanger and the inlet of the booster compressor to measure the carbon dioxide pressure at the inlet of the booster compressor in cooling mode. A second pressure sensor is installed on the pipe between the outlet of the booster and the inlet of the refrigerant heat exchanger to measure the carbon dioxide pressure at the inlet of the refrigerant heat exchanger. A third pressure sensor is installed on the first branch pipe to measure the carbon dioxide pressure at the second port of the first air source heat pump unit during heating mode. A fourth pressure sensor is installed on the second branch pipe to measure the carbon dioxide pressure at the second port of the second air source heat pump unit during heating mode.

2. The ultra-low temperature heat pump using oil-free carbon dioxide as refrigerant according to claim 1, characterized in that: A first electric ball valve and a second electric ball valve are respectively installed at the inlet and outlet of the storage tank to control the mass flow rate of carbon dioxide, while maintaining a stable carbon dioxide pressure at the inlet of the booster and at the inlet of the refrigerant heat exchanger.

3. The ultra-low temperature heat pump using oil-free carbon dioxide as refrigerant according to claim 2, characterized in that: In heating mode, the carbon dioxide pressure setting at the inlet of the booster compressor is between 0.5 MPa and 4 MPa, and the carbon dioxide pressure setting at the inlet of the refrigerant heat exchanger is between 7.5 MPa and 13 MPa; in cooling mode, the carbon dioxide pressure setting at the inlet of the booster compressor is between 0.5 MPa and 5.5 MPa, and the carbon dioxide pressure setting at the inlet of the refrigerant heat exchanger is between 7.5 MPa and 13 MPa.

4. The ultra-low temperature heat pump using oil-free carbon dioxide as refrigerant according to claim 2, characterized in that: A third electric ball valve is also installed on the first branch pipe; A fourth electric ball valve is also installed on the second branch pipe; A fifth electric ball valve and a sixth electric ball valve are respectively installed on the first return pipe and the second return pipe; A seventh electric ball valve is installed on the pipeline between the outlet of the booster and the inlet of the refrigerant heat exchanger; An eighth electric ball valve is installed on the pipe between the outlet of the refrigerant heat exchanger and the first port of the first air source heat pump. A ninth electric ball valve is installed on the pipe between the outlet of the refrigerant heat exchanger and the first port of the second air source heat pump. A tenth electric ball valve is installed on the pipeline between the outlet of the refrigerant heat exchanger and the inlet of the booster; An eleventh electric ball valve is installed on the pipe between the outlet of the booster and the first port of the first air source heat pump unit; A twelfth electric ball valve is installed on the pipe between the second port of the second air source heat pump and the inlet of the refrigerant heat exchanger.

5. The ultra-low temperature heat pump using oil-free carbon dioxide as refrigerant according to claim 1, characterized in that: The number of the refrigerant heat exchangers is one or at least two arranged in parallel; the expansion valve and the proportional valve are respectively provided at the inlet and outlet of each refrigerant heat exchanger.

6. The ultra-low temperature heat pump using oil-free carbon dioxide as refrigerant according to claim 1, characterized in that: The carbon dioxide stored in the storage tank is pure carbon dioxide without any additives.

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