REFRIGERANT CIRCUIT

Abstract

The invention includes a refrigerant circuit for a cooling operation and a heat pump operation. The refrigerant circuit has a high pressure area and a low pressure area, including at least one heat source/heat sink, a compressor, an expansion device, at least one thermal interior space module, and an internal heat exchanger. The internal heat exchanger has a high pressure side part and a low pressure side part, wherein the high pressure side part is disposed between the expansion device and the heat source/heat sink. The invention also includes at least one metering device through which the high pressure side part of the internal heat exchanger is operable during the heat pump operation at a medium pressure level intermediate a pressure level in the high pressure area and a pressure level in the low pressure area of the refrigerant circuit.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of German Patent Application No. DE 10 2011 109 506.7 filed Aug. 5, 2011, the entire disclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The invention involves a refrigerant circuit for a vehicle, and more particularly a refrigerant circuit for a vehicle configured to optimize performance of an internal heat exchanger during a cooling operation and a heat pump operation.

BACKGROUND OF THE INVENTION

DE 103 09 779 A1 discloses a double-loop air conditioner in which refrigerant is heated in a heat pump or through a compression of the refrigerant, and is then released to a condenser in an interior space module (hereinafter referred to as the heat register) for heating an inflow of air into an interior space. In addition, heat can be taken from a refrigerant circuit of a motor and directed to the refrigerant through a heat transfer device, or an inflow of air into the interior space may be heated in a conventional heating device via a heating core through which the refrigerant flows. In a cooling device, heat is removed from the inflow of air into the interior by a condenser, which in this operation works as an evaporator. The heat given off to a cooling material is thereupon released to the environment through another condenser.

DE 101 58 104 B4 discloses an air conditioner that has a refrigerant circuit in which heat in a heat pump process is taken from an outside air. The heat is released for heating an interior space inflow of air under high pressure through a condenser, which functions in a heating unit as a gas cooler or as a condenser.

It is known that a refrigerant circuit that is appropriate for both cooling and heat pump operation has a high and low pressure area. Such a refrigerant circuit includes at least one heat source or heat sink, such as a gas cooler or condenser and/or a glycol heat exchanger, as well as a compressor, an expansion module, at least a thermal interior space module and a refrigerant storage area.

In addition, an internal heat exchanger is provided, which has a high pressure side part and a low pressure side part, whereby the high pressure side part of the internal heat exchanger in the heat pump lies between the expansion module and the gas cooler. The low pressure side of the internal heat exchanger is arranged on a suction side of the compressor.

A disadvantage of the refrigerant circuit is that no heat exchange with the low pressure side part of the internal heat exchanger in the heat pump operation can occur without significant technical effort since the internal heat exchanger in the heat pump is disposed in the low pressure area of the refrigerant circuit. The internal heat exchanger is relatively inactive in the heat pump operation.

Further, the heat pump contains an excessive amount of the refrigerant since a filling amount is determined according to the air conditioner operation. As a result, suctioning of the refrigerant into the compressor is unavoidable, thereby decreasing an efficiency of the compressor.

Accordingly, it would be desirable to produce a refrigerant circuit for a vehicle configured to optimize performance of an internal heat exchanger during a cooling operation and a heat pump operation.

SUMMARY OF THE INVENTION

In concordance and agreement with the present invention, a refrigerant circuit for a vehicle configured to optimize performance of an internal heat exchanger during a cooling operation and a heat pump operation, has surprisingly been discovered.

In one embodiment, a refrigerant circuit for a vehicle, comprises: a compressor configured to compress a refrigerant; an internal heat exchanger in fluid communication with the compressor to receive the refrigerant therein, the internal heat exchanger including a high pressure side part and a low pressure side part, wherein the high pressure side part is in fluid communication with at least one additional heat exchanger; and at least one metering device configured to control a pressure level of the refrigerant, the at least one metering device in fluid communication with the internal heat exchanger, wherein the at least one metering device permits the high pressure side part of the internal heat exchanger to receive the refrigerant during a heat pump operation of the refrigerant circuit between a pressure level at which the refrigerant exits the compressor and a pressure level at which the refrigerant enters the compressor.

In another embodiment, the refrigerant circuit for a vehicle, comprises; a compressor configured to compress a refrigerant; an internal heat exchanger in fluid communication with the compressor to receive the refrigerant therein, the internal heat exchanger including a high pressure side part and a low pressure side part, wherein the high pressure side part is in fluid communication with a condenser/gas cooler and a heat exchanger/chiller; and at least one controllable expansion device configured to control a pressure level of the refrigerant, the at least one controllable expansion device in fluid communication with the internal heat exchanger, wherein the at least one controllable expansion device permits the high pressure side part of the internal heat exchanger to receive the refrigerant during a heat pump operation of the refrigerant circuit between a pressure level at which the refrigerant exits the compressor and a pressure level at which the refrigerant enters the compressor.

In yet another embodiment, the refrigerant circuit for a vehicle, comprising: a compressor configured to compress a refrigerant; an internal heat exchanger in fluid communication with the compressor to receive the refrigerant therein, the internal heat exchanger including a high pressure side part and a low pressure side part, wherein the high pressure side part is in fluid communication with a condenser/gas cooler and a heat exchanger/chiller; a first controllable expansion device configured to decrease a pressure level of the refrigerant, the first controllable expansion device in fluid communication with the internal heat exchanger and the condenser/gas cooler, wherein the first controllable expansion device permits the high pressure side part of the internal heat exchanger to receive the refrigerant during a heat pump operation of the refrigerant circuit between a pressure level at which the refrigerant exits the compressor and a pressure level at which the refrigerant enters the compressor; and a second controllable expansion device configured to decrease a pressure level of the refrigerant, the second controllable expansion device in fluid communication with the internal heat exchanger and the heat exchanger/chiller, wherein the second controllable expansion device permits the high pressure side part of the internal heat exchanger to receive the refrigerant during the heat pump operation of the refrigerant circuit between the pressure level at which the refrigerant exits the compressor and the pressure level at which the refrigerant enters the compressor.

It is an objective of the invention to simplify a refrigerant circuit to assure an active operation of an internal heat exchanger during a heat pump operation. A further objective is to correspondingly store unnecessary refrigerant in various operating conditions of the cooling and heating operation, and thus to optimally adjust a level of circulating refrigerant.

In certain embodiments, active operation of the internal heat exchanger is assured by relieving a stress of the refrigerant after the internal heat exchanger. A refrigerant storage area downstream from the internal heat exchanger in a heat pump is also supplied with standing refrigerant under high pressure. However, the storage area is too large based on a density of the refrigerant. Therefore, a sufficient buildup of pressure on the high pressure side may not be obtained.

According to the invention, the refrigerant circuit includes a metering device through which the high pressure side part of the internal heat exchanger in the heat pump is driven to a medium pressure level, which lies between the high and low pressure level of the refrigerant circuit.

A loss of pressure of the high pressure side of the inner heat exchanger to the heat source causes a pressure level of the stress-relieved two-phase refrigerant to be above that of the downstream heat source. In extreme cases, an area of the medium pressure level can be increased or decreased to correspond to the high pressure or low pressure level.

Because of the high specific heat of the two-phase refrigerant and the constant temperature, the internal heat exchanger can be used actively to superheat the refrigerant in the heat pump that flows through the low pressure side part of the internal heat exchanger. Accordingly, operation of the compressor is assured, and a suctioning of the refrigerant into the compressor is avoided.

The configuration and function of the refrigerant circuit can be employed regardless of the refrigerant used. At times, differences occur in particular pressure circumstances for low pressure, medium pressure, and high pressure levels.

In addition, wiring can be implemented independent of a drive design of the particular vehicle, be it conventional, hybrid, electric, etc., and thus independent of a type of the compressor.

In an advantageous embodiment, a metering device configured to drive the high pressure part of the internal heat exchanger to the medium pressure level is a damper. The damper is disposed downstream of the high pressure side of the internal heat exchanger during the heat pump operation, preferably downstream of a refrigerant storage area.

The damper is configured to produce a loss of pressure only in a direction of the flow of the refrigerant in the heat pump, dependent on a narrowing of a cross-section of the damper. In the air conditioner, the cross-section is maximized in an opposite direction of the flow of the refrigerant. A medium pressure level is adjusted by an expansion valve in the heat pump. The expansion valve is relieved to low pressure by a decrease of pressure created by the damper after the refrigerant flows through the internal heat exchanger.

Preferentially, the metering device for achieving the medium pressure level is configured as a conduit adjustment of a conduit disposed between the heat source or heat sink and the expansion valve. The refrigerant storage area and high pressure side part of the internal heat exchanger are also disposed between the heat source or heat sink and the expansion valve.

A cross-section of the conduit and a conduit guidance or bends in the conduit can be calculated for each vehicle, so that no noticeable loss of pressure occurs during the cooling operation, while a defined loss of pressure during the heat pump operation can be obtained for the heating operation.

In particular, the cross-section of the conduit is smaller than prior art. Accordingly, material for the conduits, and thus a cost and a weight can be minimized. A minimized conduit cross-section also results in a reduction in the amount for filling and a reduced need for refrigerant over the prior art.

According to the invention, in addition to the controllable expansion device, which is disposed in the flow direction in the heat pump upstream of the high pressure side part of the internal heat exchanger, at least one additional controllable expansion device can be employed. The additional controllable expansion device is disposed in the flow direction downstream of the high pressure side part of the heat exchanger and downstream of the refrigerant storage area, yet upstream of the heat source. The additional controllable expansion device, which initially is at a medium pressure level, can be decreased to a low pressure level.

In another advantageous embodiment, in addition to a condenser as a heat source or heat sink in the refrigerant circuit, an additional heat exchanger, in particular an external heat exchanger, can be provided as an additional heat source or heat sink for transferring heat between the motor and the refrigerant circuit. The additional external heat exchanger can be configured as a water-glycol heat exchanger (i.e. a chiller). The additional heat exchanger can be located in the refrigerant circuit either parallel or serial to the condenser. In both configurations, the conduit to the condenser and the conduit to the additional heat exchanger branch from the conduit originating from the high pressure side part of the internal heat exchanger. In an advantageous embodiment, the two branches can be combined together via one controllable expansion device. The refrigerant stream flow to one of the branches can be determined by control of the expansion device by which switch valves are replaced. Additionally, the controllable adjustment of the medium pressure level in the internal heat exchanger and the refrigerant storage area is assured for both of the branches.

By disposing the controllable expansion device in the heat pump downstream of the refrigerant storage area, the pressure level in the refrigerant storage area—and according to the wiring variant in the internal heat exchanger as well—can be flexible in a manner that optimizes the amount of refrigerant available in the refrigerant circuit.

Furthermore, the invention involves a method for operating an air conditioner including a refrigerant circuit as described hereinabove, whereby at least one additional controllable expansion device is employed in addition to the controllable expansion device disposed in the flow direction in the heat pump upstream of the high pressure side part of the internal heat exchanger. The additional controllable expansion device is disposed in the flow direction downstream of the high pressure side part of the heat exchanger and downstream the refrigerant storage area, yet upstream of the heat source.

According to the invention, the expansion devices are controlled and defined during operation. In particular, in the heat pump, the expansion devices are controlled to work individually, in which particular expansion devices work individually, and any other expansion devices are opened fully. In another application, all the expansion devices can be operated in combination with each other. In such case, the expansion devices are opened in interaction with one another in order to obtain a desired pressure level. Preferentially, the expansion devices can be operated alternately, as needed in combination, or individually.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as other objects and advantages of the invention, will become readily apparent to those skilled in the art from reading the following detailed description of a preferred embodiment of the invention when considered in the light of the accompanying drawings in which:

FIG. 1 is a schematic flow diagram of a refrigerant circuit according to an embodiment of the invention, showing a cooling operation thereof;

FIG. 1A is a schematic flow diagram of the refrigerant circuit illustrated in FIG. 1, showing a heat pump operation thereof;

FIG. 2 is a schematic flow diagram of a refrigerant circuit according to another embodiment of the invention, wherein the refrigerant circuit includes a conduit having an adjustable cross-section;

FIG. 3 is a schematic flow diagram of a refrigerant circuit according to another embodiment of the invention, wherein the refrigerant circuit includes controllable expansion devices and serial connection of a plurality of heat exchangers; and

FIG. 4 is a schematic flow diagram of a refrigerant circuit according to another embodiment of the invention, wherein the refrigerant circuit includes controllable expansion devices and parallel connection of a plurality of heat exchangers.

DETAILED DESCRIPTION of EXEMPLARY EMBODIMENTS OF THE INVENTION

The following detailed description and appended drawings describe and illustrate various exemplary embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner. Equivalent components or components with equivalent effect are shown in the following examples of embodiments with the same reference list number.

FIGS. 1 and IA show a schematic presentation of a refrigerant circuit 10 of a vehicle air conditioner according to the present invention. The refrigerant circuit 10 is suitable for both a cooling operation, illustrated in FIG. 1, and a heat pump operation, illustrated in FIG. 1A. During the cooling operation shown in FIG. 1, a refrigerant under high pressure flows out of a compressor 12 through a valve 14, through a condenser/gas cooler 26, and through a metering device 22. As a non-limiting example, the valve 14 is a 3-2 way valve and the metering device 22 is a damper. However, it would be understood to employ two separate controllable shutoff valves.

The metering device 22 is configured to decrease pressure only during the heat pump operation. On the other hand, during the cooling operation, the metering device 22 produces no or minimal pressure loss. The refrigerant flows through a refrigerant storage area 24 and a high pressure side part of an internal heat exchanger 20 at a high pressure level HD. The pressure level of the refrigerant is decreased from the high pressure level HD to a low pressure level ND at a main expansion valve 18. A shutoff valve 32 is in an open position, permitting the refrigerant at the low pressure level ND to flow through the evaporator 34 and then through a low pressure side part of an interior heat exchange 30. From the internal heat exchanger 30 the refrigerant flows to the compressor 12 to be compressed to the high pressure level HD. Because of a configuration of the metering device 22, no change in the pressure level of the refrigerant results from flowing through the metering device 22 during the cooling operation.

Conversely, during the heat pump operation shown in FIG. 1A, the refrigerant flows from the compressor 12 through the valve 14, through a heat register 16 to the main expansion valve 18. The refrigerant is at the high pressure level HD up to the main expansion valve 18. At the main expansion valve 18, the pressure level of the refrigerant is decreased to a medium pressure level MD. The refrigerant then flows from the main expansion valve 18 through the high pressure side of the internal heat exchanger 20. Thereafter, the refrigerant flows through the refrigerant storage area 24 to the metering device 22. The metering device 22 decreases a pressure level of the refrigerant from the medium pressure level MD to the low pressure level ND in the flow direction of the heat pump. At the low pressure level ND, the refrigerant flows through the condenser/gas cooler 26 operating as an evaporator. A shutoff valve 28 is in an open position, permitting the refrigerant at the low pressure level ND to flow to the low pressure side of the internal heat exchanger 30. The refrigerant flows through the low pressure side of the internal heat exchanger 30 and into the compressor 12. At the compressor 12, the refrigerant is once again compressed to the high pressure level HD.

According to the invention, during the heat pump operation, the refrigerant that flows through the high pressure side of the internal heat exchanger 20 is at the medium level pressure level MD, producing a potential heat exchange with the low pressure part of the internal heat exchanger 20. An advantage of the invention is that the refrigerant flowing through the low pressure part of the internal heat exchanger 30 is heated or superheated before entry into the compressor 12. A suction of a fluid refrigerant into the compressor 12 is militated against by the superheating of the refrigerant. Accordingly, effective operation of the compressor 12 is maintained.

FIG. 2 shows the refrigerant circuit 10 of a vehicle air conditioner according to another embodiment of the invention. During the heat pump operation, the medium pressure level MD of the refrigerant is assured by a metering device 36. As a non-limiting example, the metering device 36 is a conduit located between the main expansion valve 18 and the gas cooler 26. An adjustment of a cross-section of the conduit 36 controls a pressure of the refrigerant. The cross section of the conduit 36 is shown only schematically in FIG. 2. The cross section of the conduit 36 is configured in such a manner to produce a loss of pressure during the heat pump operation, but not during the cooling operation. This can be achieved on the basis of the different conditions of the refrigerant during the heat pump operation and the cooling operation. To ensure the affect, a technical conduit analysis can be conducted separately for each vehicle, in particular, as a function of conduit guidance or existing bends.

In another advantageous embodiment shown in FIG. 3, the refrigerant circuit 10 includes, in addition to the condenser/gas cooler 26, at least one chiller 38 for heat exchange with the refrigerant circuit 10, such as that of a vehicle motor. Additional heat sources might also be represented by an exhaust system or by various refrigerant circuits of a partially or fully electric vehicle.

In addition to the main expansion valve 18, metering devices 40, 42 are contemplated to guarantee the medium pressure level MD in the high pressure part of the internal heat exchanger 20. Hence, the flow of the refrigerant can be guided either through the glycol heat exchanger/chiller 38, the condenser/gas cooler 26, or a combination thereof. As a non-limiting example, the metering devices 40, 42 are additional controllable expansion devices 40, 42. In a pass-through position of the metering devices 40, 42, the medium pressure level MD during the heat pump operation is decreased to the low pressure level ND in order to be able to accept energy in the glycol heat exchanger/chiller 38 and/or the gas cooler 26. In this manner, the refrigerant circuit shown in FIG. 3 is advantageous because the refrigerant flowing into the high pressure side of the internal heat exchanger 20 is at the medium pressure level MD and can be used for superheating the refrigerant on the suction side of the compressor 12.

In addition, the pressure level of the refrigerant in the refrigerant storage area 24 can be so adjusted by the defined setting of the controllable main expansion valve 18 and of the other metering devices 40, 42 that as a result the storage of the refrigerant is assured at a density that guarantees both efficient heating and an effective and reliable operation of the compressor 12.

FIG. 4 shows an embodiment of the refrigerant circuit 10 that, in its function, essentially corresponds to the refrigerant circuit 10 shown in FIG. 3. As a distinction over FIG. 3, a connection conduit is employed which connects a flow channel through the condenser/gas cooler 26 to a flow channel through the glycol heat exchanger/chiller 38 via a shutoff valve 44 downstream of the condenser/gas cooler 26 and the glycol heat exchanger/chiller 38. Accordingly, the condenser/gas cooler 26 and the glycol heat exchanger/chiller 38 shown in FIG. 4 are connected and operate in parallel, while the condenser/gas cooler 26 and the glycol heat exchanger/chiller 38 shown in FIG. 3 are connected and operate in series.

From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, make various changes and modifications to the invention to adapt it to various usages and conditions.

LIST OF REFERENCE NUMERALS

• 10 Refrigerant circuit
• 12 Compressor
• 14 Three-two way valve
• 16 Heat register
• 18 Controllable main expansion device
• 20 Internal heat exchanger (high pressure)
• 22 Damper
• 24 Refrigerant storage area
• 26 Condenser/gas cooler
• 28 Shutoff valve
• 30 Internal heat exchanger (low pressure)
• 32 Shutoff valve
• 34 Evaporator
• 36 Conduit cross-section
• 38 Glycol heat exchanger/chiller
• 40 Controllable main expansion device
• 42 Controllable main expansion device
• 44 Shutoff valve
• ND Low pressure level
• MD Medium pressure level
• HD High pressure level

Claims

1. A refrigerant circuit for a vehicle, comprising: a compressor configured to compress a refrigerant;an internal heat exchanger in fluid communication with the compressor to receive the refrigerant therein, the internal heat exchanger including a high pressure side part and a low pressure side part, wherein the high pressure side part is in fluid communication with at least one additional heat exchanger; andat least one metering device configured to control a pressure level of the refrigerant, the at least one metering device in fluid communication with the internal heat exchanger, wherein the at least one metering device permits the high pressure side part of the internal heat exchanger to receive the refrigerant during a heat pump operation of the refrigerant circuit between a pressure level at which the refrigerant exits the compressor and a pressure level at which the refrigerant enters the compressor.

2. The refrigerant circuit of claim 1, wherein the high pressure side part of the internal heat exchanger is in fluid communication with an expansion device.

3. The refrigerant circuit of claim 1, wherein the at least one metering device is configured to decrease the pressure level of the refrigerant during the heat pump operation of the refrigerant circuit and maintain the pressure level of the refrigerant during a cooling operation thereof.

4. The refrigerant circuit of claim 1, wherein the at least one metering device is at least one of a damper, a conduit, and a controllable expansion device.

5. The refrigerant circuit of claim 4, wherein the conduit has a cross-section which facilitates a decrease in the pressure level of the refrigerant during the heat pump operation of the refrigerant circuit and maintains the pressure level of the refrigerant during a cooling operation thereof.

6. The refrigerant circuit of claim 1, wherein the high pressure side part of the internal heat exchanger during the heat pump operation of the refrigerant circuit is upstream of the at least one metering device.

7. The refrigerant circuit of claim 1, wherein the at least one additional heat exchanger is at least one of a condenser/gas cooler and a glycol heat exchanger/chiller.

8. The refrigerant circuit of claim 1, further comprising a refrigerant storage area disposed between the internal heat exchanger and the at least one additional heat exchanger.

9. The refrigerant circuit of claim 8, wherein the refrigerant storage area during the heat pump operation of the refrigerant circuit is downstream of the high pressure side part of the internal heat exchanger.

10. The refrigerant circuit of claim 1, wherein the at least one additional heat exchanger is operable with at least one of water, air, exhaust gas, electronics, heat storage, solar heat, and solar energy.

11. A refrigerant circuit for a vehicle, comprising: a compressor configured to compress a refrigerant;an internal heat exchanger in fluid communication with the compressor to receive the refrigerant therein, the internal heat exchanger including a high pressure side part and a low pressure side part, wherein the high pressure side part is in fluid communication with a condenser/gas cooler and a heat exchanger/chiller; andat least one controllable expansion device configured to control a pressure level of the refrigerant, the at least one controllable expansion device in fluid communication with the internal heat exchanger, wherein the at least one controllable expansion device permits the high pressure side part of the internal heat exchanger to receive the refrigerant during a heat pump operation of the refrigerant circuit between a pressure level at which the refrigerant exits the compressor and a pressure level at which the refrigerant enters the compressor.

12. The refrigerant circuit of claim 11, wherein the high pressure side part of the internal heat exchanger is in fluid communication with an additional expansion device.

13. The refrigerant circuit of claim 11, wherein the at least one controllable expansion device is configured to decrease the pressure level of the refrigerant during the heat pump operation of the refrigerant circuit and maintain the pressure level of the refrigerant during a cooling operation thereof.

14. The refrigerant circuit of claim 11, wherein the high pressure side part of the internal heat exchanger during the heat pump operation of the refrigerant circuit is upstream of the at least one controllable expansion device.

15. The refrigerant circuit of claim 11, wherein the at least one controllable expansion device is disposed between the internal heat exchanger and at least one of the condenser/gas cooler and the heat exchanger/chiller.

16. The refrigerant circuit of claim 11, further comprising a refrigerant storage area disposed between the internal heat exchanger and at least one of the condenser/gas cooler and the heat exchanger/chiller.

17. The refrigerant circuit of claim 11, wherein the condenser/gas cooler and the heat exchanger/chiller are connected in one of parallel and series.

18. The refrigerant circuit of claim 11, wherein the heat exchanger/chiller is in heat exchange relationship with a motor refrigerant circuit.

19. A refrigerant circuit for a vehicle, comprising: a compressor configured to compress a refrigerant;an internal heat exchanger in fluid communication with the compressor to receive the refrigerant therein, the internal heat exchanger including a high pressure side part and a low pressure side part, wherein the high pressure side part is in fluid communication with a condenser/gas cooler and a heat exchanger/chiller;a first controllable expansion device configured to decrease a pressure level of the refrigerant, the first controllable expansion device in fluid communication with the internal heat exchanger and the condenser/gas cooler, wherein the first controllable expansion device permits the high pressure side part of the internal heat exchanger to receive the refrigerant during a heat pump operation of the refrigerant circuit between a pressure level at which the refrigerant exits the compressor and a pressure level at which the refrigerant enters the compressor; anda second controllable expansion device configured to decrease a pressure level of the refrigerant, the second controllable expansion device in fluid communication with the internal heat exchanger and the heat exchanger/chiller, wherein the second controllable expansion device permits the high pressure side part of the internal heat exchanger to receive the refrigerant during the heat pump operation of the refrigerant circuit between the pressure level at which the refrigerant exits the compressor and the pressure level at which the refrigerant enters the compressor.

20. The refrigerant circuit of claim 19, wherein the second controllable expansion device and the first controllable expansion device can be operated at least one of individually, alternatingly, synchronously, and any combination thereof.