AIR CONDITIONING UNIT, OPERATABLE WITH CARBON DIOXIDE, FOR VEHICLES AND METHOD FOR OPERATING THE AIR CONDITIONING UNIT

Abstract

An air conditioning unit for vehicles with work-doing expansion of the carbon dioxide is provided, the air conditioning unit including a combined refrigeration and heat pump circuit, wherein the air conditioning unit is switchably configured to change a flow direction of a refrigerant for switchable operation from the refrigeration circuit to the heat pump circuit. A method for operating the air conditioning unit is also provided.

Description

DRAWINGS

The above, as well as other advantages of the present disclosure, will become readily apparent to those skilled in the art from the following detailed description, particularly when considered in the light of the drawings described herein.

FIG. 1 is a schematic representation of an air conditioning unit with an expansion-compression machine;

FIG. 2 depicts two high-pressure/enthalpy diagrams A, B for an air conditioning unit with a first compressor stage A and an additional second compressor stage B;

FIG. 3 is a schematic representation of the air conditioning unit with an expansion-compression machine according to the invention in the refrigeration circuit;

FIG. 4 is a schematic representation of the air conditioning unit with an expansion-compression machine according to the invention in the heat pump circuit;

FIG. 5 is a schematic representation of the air conditioning unit to FIG. 1 with an inner heat exchanger (IHX);

FIG. 6 is a coefficient of performance (COP)/gas cooler outlet temperature diagram for an air conditioning unit; and

FIG. 7 is a high-pressure gas cooler outlet temperature diagram for the air conditioning unit.

Claims

1. An air conditioning unit comprising: a combined refrigeration and heat pump circuit, wherein the air conditioning unit is switchably configured to change a flow direction of a refrigerant for switchable operation from the refrigeration circuit to the heat pump circuit, the refrigeration and heat pump circuit further comprising: at least a main compressor adapted for a compression of the refrigerant from a low pressure to a medium pressure in a first compression stage;a first external heat exchanger in fluid communication with the main compressor;a subsidiary compressor in fluid communication with the first external heat exchanger and adapted for a compression of the refrigerant from the medium pressure to a high pressure in a second compression stage, an inlet and an outlet of the subsidiary compressor exchanged depending on the refrigeration and heat pump circuit desired;a second external heat exchanger in fluid communication with the subsidiary compressor, wherein different pressure levels are assigned to the external heat exchangers depending on the refrigeration and heat pump circuit desired;an expansion machine in fluid communication with the second external heat exchanger, wherein the expansion machine and the subsidiary compressor form an expansion-compression machine, an inlet and an outlet of the expansion machine exchanged depending on the refrigeration and heat pump circuit desired, and wherein an assigned volume/density ratio of the compression to the expansion within the expansion-compression machine is prespecified; andan internal heat exchanger providing fluid communication between the expansion machine and the main compressor.

2. The air conditioning unit of claim 1, wherein the air conditioning unit includes at least one of a second expansion-compression machine and a second expansion machine.

3. The air conditioning unit of claim 1, wherein the internal heat exchanger is an evaporator in the refrigeration circuit and is a heater in the heat pump circuit.

4. The air conditioning unit of claim 1, wherein the internal heat exchanger is an evaporator in the refrigeration circuit and the heat pump circuit, the heat pump circuit further including a heater disposed parallel to the internal heat exchanger.

5. The air conditioning unit of claim 1, wherein the expansion compression machine is adapted to operate in at least one of the following manners: the expansion machine is adapted to work at a full pressure and the subsidiary compressor, in addition to the displacing work, is adapted to be loaded with a volume changing work;the expansion machine is adapted to be loaded with a displacing work and a volume changing work, and the subsidiary compressor is adapted to work at the full pressure;both the expansion machine and the subsidiary compressor are adapted to work at the full pressure; andboth the expansion machine and the subsidiary compressor are adapted to be loaded with displacing work and volume changing work.

6. The air conditioning unit of claim 1, wherein a density/area ratio at the expansion-compression machine is from about 0.4 to about 0.675, the ratio providing an expansion-compression machine with a volumetric efficiency λ=1.

7. The air conditioning unit of claim 1, wherein the subsidiary compressor and the expansion machine are configured as one of a rotating displacement machine and an oscillating displacement machine.

8. The air conditioning unit of claim 7, wherein the rotating displacement machine is a rotary piston machine with one of an inner shaft and two-shaft toothed gear machines, each having opposite directions of rotation according to a pregiven direction of flow of the refrigerant, wherein the expansion machine and the subsidiary compressor at different ambient temperatures are switchably configured with respect to the refrigerant flow direction and are provided for switchable operation between the refrigeration circuit and the heat pump circuit, and wherein the density/area ratio between the expansion machine and the subsidiary compressor is specified as desired.

9. The air conditioning unit of claim 1, wherein the main compressor and the subsidiary compressor include feeding lines having controllable valves wherein a circuit-related flow passage of the main compressor and the subsidiary compressor are adjustable, and wherein the valves are in communication with a control device.

10. The air conditioning unit of claim 9, wherein the heat pump circuit is provided with at least one additional subsidiary compression stage in the expansion-compression machine, the stage used for at least a supercritical operation.

11. The air conditioning unit of claim 9, wherein the heat pump circuit is provided with at least one additional subsidiary expansion stage in the expansion-compression machine, the subsidiary expansion stage used for at least a supercritical operation, whereby both expansion-compression machines form at least one of a series and parallel circuit.

12. The air conditioning unit of claim 9, wherein the heat pump circuit is provided with additional throttling cross-sections that are parallel to at least one of an expansion stage and a subsidiary compressor stage in the expansion-compression machine, which are used for at least a supercritical operation.

13. The air conditioning unit of claim 1, including an inner heat exchanger (IHX) integrated into a line train between the main compressor and the internal heat exchanger; and integrated into a line train between the second external heat exchanger and the expansion machine.

14. A method for operating an air conditioning unit having a main compressor, a first external heat exchanger, a subsidiary compressor, a second external heat exchanger, an expansion machine, and an internal heat exchanger in communication with each other and forming a refrigeration circuit and a heat pump circuit, the method comprising at least one of: operating the refrigeration circuit, wherein the operation include the steps of: 1) compressing the carbon dioxide by means of the drive of the main compressor;2) passing the compressed carbon dioxide through the first external heat exchanger, which works as a medium-pressure gas cooler releasing heat;3) passing the carbon dioxide through the subsidiary compressor, which is driven by the expansion machine and, in the second compression stage, works as a compressor;4) passing the carbon dioxide through the second external heat exchanger, which works as a high-pressure gas cooler;5) passing the carbon dioxide through the expansion machine, where the work-doing expansion occurs which is directly used to drive the subsidiary compressor; and6) passing the carbon dioxide through the integrated internal heat exchanger, which works as evaporator; andoperating the heat pump circuit, wherein the operation includes the steps of: 1) compressing the carbon dioxide by means of the drive of the main compressor;2) passing the compressed carbon dioxide through the internal heat exchanger in opposite direction compared to a direction of flow through the refrigeration circuit, wherein the internal heat exchanger operates as a heater;3) passing the carbon dioxide through the expansion machine in opposite direction compared to the direction of flow through the refrigeration circuit, whereby inlet and outlet are exchanged and also in the expansion machine an expansion occurs, which is directly used work-doing to drive the subsidiary compressor;4) passing the carbon dioxide through the second external heat exchanger, which works as a medium-pressure evaporator;5) passing the carbon dioxide through the subsidiary compressor, which works as a precompressor for a first stage in a two-phase region; and6) passing the carbon dioxide through the external heat exchanger, which works as low-pressure evaporator and also takes heat from the environment.

15. The method of claim 14, wherein the inlet and the outlet of the expansion machine, because of a changed direction of the carbon dioxide flow, the two external heat exchangers in both the refrigeration and heat pump circuits work at different pressure levels, wherein the first external heat exchanger, in the refrigeration circuit works as a medium-pressure gas cooler which releases heat to an environment, and in the heat pump circuit works as a medium-pressure evaporator which takes heat from the environment, and wherein the second external heat exchanger, in the refrigeration circuit works as a high-pressure gas cooler which releases heat to the environment, and in the heat pump circuit works as a low-pressure evaporator which takes heat from the environment.

16. The method of claim 14, wherein a change of a ratio of an outlet density to an inlet density of the carbon dioxide in the subsidiary compressor is from about 1.0 to about 1.3.

17. The method of claim 16, wherein a volume/density ratio between compression and expansion is from about 0.40 to about 0.8 for a supercritical operation at a gas cooler outlet temperature of between about 30° C. to about 70° C., wherein values for an expansion-compression machine with a volumetric efficiency of λ=1, or corrected for an adapted expansion-compression machine with a volumetric efficiency different from λ=1, are provided.

18. The method of claim 17, wherein the volume/density ratio of the supercritical operation is adjusted in a subcritical refrigeration mode.

19. The method of claim 14, wherein the second compressor stage is also operated in a two-phase region.

20. The method of claim 14, wherein the subsidiary compressor of the expansion-compression machine is alternately operated as a compressor or as an expansion machine at the exchange of the inlet and outlet of the expansion-compression machine, and wherein the expansion machine of the expansion-compression machine is alternately operated as a compressor or as an expansion machine, the expansion machine being one of a combined toothed gear machine, a rotating machine, and an oscillating machines, wherein the volume/density ratio is adjusted such that the refrigeration circuit or the heat pump circuit is selected as desired.