US20130298594A1

US20130298594A1 - Thermodynamic system provided with a plurality of compressors

Info

Publication number: US20130298594A1
Application number: US13/993,847
Authority: US
Inventors: Patrice Bonnefoi; Fabien GALL
Original assignee: Danfoss Commercial Compressors SA
Current assignee: Danfoss Commercial Compressors SA
Priority date: 2010-12-13
Filing date: 2011-11-28
Publication date: 2013-11-14
Also published as: DE112011104357T5; WO2012080611A1; FR2968731A1; CN103261690A; FR2968731B1; CN103261690B

Abstract

The thermodynamic system includes a circuit for circulating a refrigerant including a compression device including a first and a second compressors each including a sealed enclosure including a low-pressure portion containing a motor and an oil pan positioned at the bottom of the enclosure, and a refrigerant intake opening leading into the low-pressure portion, a refrigerant dispensing device arranged to connect an evaporator to the intake opening of the first compressor, an oil level equalization conduit putting the oil pans of the first and second compressors in communication, a connecting device putting the low-pressure portion of the first compressor in communication with the intake opening of the second compressor, and control means arranged to control the starting and stopping of the first and second compressors according to four control modes.

Description

The present invention relates to a thermodynamic system provided with a plurality of compressors.
A thermodynamic system, and more particularly a refrigeration system, comprises, in a known manner:
a circuit for circulating a refrigerant successively including a condenser, an expander, an evaporator and a compression device connected in series, the compression device comprising at least one first compressor and one second compressor mounted in parallel, each compressor comprising an enclosure including a low-pressure portion containing a motor and an oil pan positioned at the bottom of the enclosure on the one hand, and a refrigerant intake opening leading into the low-pressure portion on the other hand, and
a refrigerant dispensing device comprising a dispensing conduit connected to the evaporator, a first bypass conduit putting the dispensing conduit in communication with the intake opening of the first compressor, and a second bypass conduit putting the dispensing conduit in communication with the intake opening of the second compressor.
In order to ensure proper operation and reliability of such a refrigeration system, it is necessary to balance the oil levels in the oil pans of the two compressors. This balancing of the oil levels is advantageously obtained by connecting the oil pans of the two compressors using an oil level equalization conduit favoring the transfer of oil between the two compressors, and connecting the low-pressure portions of the two compressors by means of a pressure equalization conduit favoring the transfer of refrigerant between the two compressors.
Such a refrigeration system has the drawback of requiring a complex dispensing device and a pressure equalization conduit due to the parallel assembly of the first and second compressors.
Document U.S. Pat. No. 3,785,169 describes a refrigeration system comprising:
a circuit for circulating a refrigerant successively including a condenser, an expander, an evaporator and a compression device connected in series, the compression device comprising at least one first compressor and one second compressor, each compressor comprising an enclosure including a low-pressure portion containing a motor and an oil pan positioned in the bottom of the enclosure on the one hand, and a refrigerant intake opening leading into the low-pressure portion on the other hand,
a refrigerant dispensing device arranged to connect the evaporator to the intake opening of the first compressor,
an oil level equalization conduit putting the oil pans of the first and second compressors in communication,
a connecting device putting the low-pressure portion of the first compressor in communication with the intake opening of the second compressor, such that all of the refrigerant penetrating the low-pressure portion of the second compressor comes from the low-pressure portion of the first compressor, and
control means arranged to control the starting and stopping of the first and second compressors.
Such an assembly of the first and second compressors makes it possible to ensure satisfactory balancing of the oil levels in each compressor, without needing to provide a pressure equalization conduit between the latter and a complex dispensing device. This results in obtaining a refrigeration system with a simpler and more cost-effective structure.
However, such a refrigeration system has the drawback of only having two capacity stages, due to the fact that the control means are arranged necessarily to control the starting of the first compressor under operating conditions of the system.
This results in a refrigeration system that may be relatively ineffective under certain operating conditions.
The present invention aims to resolve this drawback.
The technical problem at the base of the invention therefore consists of providing a thermodynamic system, and in particular a refrigeration system, that has a simple and cost-effective structure, while preserving satisfactory efficiency irrespective of the operating conditions of the refrigeration system.
To that end, the present invention relates to a thermodynamic system of the aforementioned type, characterized in that the control means are arranged to control the starting and stopping of the first and second compressors according to:
a first control mode, in which the control means control the starting of the first and second compressors,
a second control mode, in which the control means control the starting of the first compressor and the stopping of the second compressor,
a third control mode, in which the control means control the stopping of the first compressor and the starting of the second compressor, and
a fourth control mode, in which the control means control the stopping of the first and second compressors,
and in that the oil level equalization conduit includes a portion turned toward the first compressor side and protruding inside the enclosure of said first compressor, said end portion including an end wall extending transversely to the longitudinal direction of said end portion and an opening formed above the end wall such that, when the oil level in the oil pan of the first compressor extends above the upper level of said end wall, oil flows through said opening toward the second compressor.
In the case where at least one of the first and second compressors is a variable-capacity compressor, or in the case where the first and second compressors are fixed-capacity compressors and have a capacity ratio comprised between 1.5 and 3, controlling the starting and stopping of the first and second compressors according to the third control mode makes it possible to obtain an additional capacity stage, which makes it possible to improve the efficiency of the compression system under certain operating conditions thereof. For example, when the first compressor is a variable-capacity compressor and the second compressor is a fixed-capacity compressor larger than the maximum capacity of the first compressor, it is possible, using this third control mode, to obtain an intermediate capacity between that obtained with the first compressor at maximum capacity and the second compressor stopped and that obtained with the first compressor at minimum capacity and the second compressor running.
The control of the starting and stopping of the first and second compressors according to the third control mode also makes it possible to favor the use of the second compressor when the latter has better efficiency than the first compressor for given operating conditions, for example when the first and second compressors are scroll compressors and the second compressor has a different compression ratio from the first compressor, or the second compressor has at least one bypass valve associated with the bypass passage formed in the plate of the fixed volute and arranged to put a discharge chamber in communication with an intermediate compression chamber defined by the scrolls of the fixed and moving volutes.
Controlling the starting and stopping of the first and second compressors according to the third control mode also makes it possible to favor the use of the second compressor during cycle inversions so as to provide better protection for the system against liquid “blows.”
Furthermore, the configuration of the end portion of the oil level equalization conduit turned toward the first compressor, and more particularly the arrangement of an opening above the end wall of the end portion, allows the flow of oil from the first compressor toward the second compressor when the quantity of oil in the first compressor exceeds a predetermined value, and prevents or at least limits such a flow of oil when the quantity of oil in the first compressor is below a predetermined value. These arrangements thus make it possible to ensure the presence of a minimum quantity of oil in the first compressor when the second compressor is running.
Advantageously, the thermodynamic system is a refrigeration system, and advantageously a reversible refrigeration system.
When the first and second compressors are fixed-capacity compressors, the capacity ratio between the first and second compressors is preferably comprised between 1.5 and 2.5, and advantageously between 1.7 and 2.3. Given the value range from which the capacity ratio can be chosen, one of the first and second compressors necessarily has a so-called “higher” capacity and the other compressor has a so-called “lower” capacity, one or the other of the first and second compressors being able to have a higher or lower capacity. The capacity ratio then refers to the ratio of the upper capacity to the lower capacity.
Advantageously, the first compressor includes a connecting opening leading into the low-pressure portion of the first compressor, the connecting device putting the connecting opening of the first compressor in communication with the intake opening of the second compressor.
Advantageously, the oil level equalization conduit is arranged and sized such that, when the system is in the overheated steady state, an upper portion of the flow cross-section of the equalization conduit is situated above the oil levels in the oil pans of the first and second compressors so as simultaneously to allow the transfer of oil and refrigerant between the first and second compressors.
The overheated steady state refers to a steady state of the thermodynamic system in which the suction temperature of the refrigerant at the intake opening of the first compressor is higher than the saturation temperature of the refrigerant at the suction pressure of the refrigerant at said intake opening, i.e., a permanent state in which the refrigerant at the intake opening of the first compressor has no refrigerant in liquid form (the latter may, however, include oil droplets).
Such a configuration of the oil level equalization conduit ensures a transfer of oil between the enclosures of the first and second compressors, as well as a limitation of the pressure deviations between the latter. Such a configuration also makes it possible to reduce the flow speed of the refrigerant at the end of the connecting device turned toward the first compressor side, and therefore to decrease the quantity of oil driven toward the second compressor by means of said connecting device.
Preferably, the oil level equalization conduit is substantially horizontal and includes two ends positioned substantially at the same altitude, said altitude being predetermined so as to ensure a minimal oil level in each compressor.
Preferably, the opening extends over at least one portion of the side wall of said end portion. This results in a reduction of the speed of the refrigerant at the free surface of the oil pan, and therefore a limitation of the quantity of oil driven by the first compressor toward the second compressor when the second compressor is running.
Preferably, the end portion of the oil level equalization conduit turned toward the first compressor side includes an oil return opening formed in the lower part of said end portion situated below the upper level of the end wall. These arrangements ensure a return of oil toward the oil pan of the first compressor when the second compressor is stopped, and thereby prevent oil storage beyond a predetermined level inside the enclosure of the second compressor.
According to a first alternative of the invention, one of the first and second compressors is a variable-capacity compressor, and the other of the first and second compressors is a fixed-capacity compressor.
According to this first alternative of the invention, the thermodynamic system comprises controlling means arranged to modulate the capacity of the variable-capacity compressor, preferably continuously, between a minimum capacity value and a maximum capacity value.
Preferably, the first compressor is the variable-capacity compressor. According to one embodiment, the second fixed-capacity compressor has a higher capacity than the maximum capacity of the first compressor.
Advantageously, the motor of the variable-capacity compressor is a variable-speed motor. In this case, the controlling means are arranged to modulate the speed of the motor of the variable-capacity compressor between a minimum speed and a maximum speed.
According to a second alternative of the invention, the first and second compressors are fixed-capacity compressors, the capacity of the first compressor being larger than that of the second compressor.
According to one embodiment, the compression device comprises a third compressor mounted in series with the first compressor and upstream therefrom, the dispensing device comprising a first dispensing conduit putting the evaporator in communication with the intake opening of the third compressor, and the second dispensing conduit putting the low-pressure portion of the third compressor in communication with the intake opening of the first compressor such that all of the refrigerant penetrating the low-pressure portion of the first compressor comes from the low-pressure portion of the third compressor.
According to one embodiment, the compression device comprises a fourth compressor mounted in parallel with the second compressor, the connecting device comprising a connecting conduit connected to the low-pressure portion of the first compressor, a first bypass conduit putting the connecting conduit in communication with the intake opening of the second compressor, and a second bypass conduit putting the connecting conduit in communication with the intake opening of the fourth compressor.
The connecting conduit and the bypass conduits for example have a substantially identical flow cross-section.
According to another embodiment, the connecting device comprises a connecting conduit putting the low-pressure portion of the first compressor in communication with the intake opening of the second compressor.
Advantageously, the oil level equalization conduit has a flow cross-section of approximately 0.5 to 1 times the flow cross-section of the connecting conduit.
Advantageously, the end of the connecting conduit turned toward the first compressor protrudes inside the enclosure of the first compressor.
Preferably, each compressor is a scroll refrigeration compressor. Preferably, the first compressor comprises a fixed volute and a moving volute following an orbital movement, a body on which the moving volute bears, an intermediate casing fixed on the body and inside which the motor is mounted, and at least one oil return conduit extending at least partially over the outer wall of the intermediate casing, the oil return conduit including a first end leading, preferably sealably, into the body, and a second end leading near the oil pan. These arrangements make it possible to further limit the quantity of oil driven from the first compressor toward the second compressor through the connecting device.
According to one embodiment of the invention, at least the first compressor comprises first deflecting means positioned in the enclosure of said first compressor and whereof at least one portion is positioned across from the intake opening of said first compressor, the deflecting means being arranged to orient at least a portion of the refrigerant penetrating the low-pressure portion of the first compressor along at least one portion of the inner wall of the sealed enclosure of said first compressor. These arrangements make it possible to increase the journey of the refrigerant inside the first compressor, and therefore the separation of the oil/refrigerant mixture in the enclosure of the first compressor. This results in limiting the quantity of oil driven from the first compressor toward the second compressor.
Preferably, the first deflecting means include a sintered plate fastened on the inner wall of the sealed enclosure so as to define a refrigerant circulation passage therewith.
According to one embodiment of the invention, at least the first compressor comprises second deflecting means positioned in the enclosure of said first compressor and whereof at least one portion is positioned across from the end of the connecting device turned toward the first compressor side, the deflecting means being arranged to orient the refrigerant penetrating the low-pressure portion of the first compressor following an ascending, then descending movement before the flow thereof through the connecting device. These arrangements make it possible to reduce the speed of the refrigerant inside the enclosure of the first compressor, and therefore to improve the separation of the oil/refrigerant mixture in the enclosure of the first compressor. This results in still further limiting the quantity of oil driven from the first compressor toward the second compressor.

In any case, the invention will be well understood using the following description in reference to the appended diagrammatic drawing showing, as non-limiting examples, several embodiments of this thermodynamic system.

FIG. 1 is a diagrammatic view of a thermodynamic system according to a first alternative embodiment of the invention.

FIG. 2 is a partial diagrammatic view of the thermodynamic system of FIG. 1.

FIG. 3 is a partial cross-sectional diagrammatic view of the thermodynamic system of FIG. 1.

FIGS. 4 a and 4 b are respectively perspective and top views of an end portion of the connecting device of a thermodynamic system according to a second alternative embodiment of the invention.

FIG. 5 is a partial cross-sectional diagrammatic view of the thermodynamic system according to a third alternative embodiment of the invention.

FIG. 6 is a transverse cross-sectional view of the first compressor of the thermodynamic system of FIG. 5.

FIG. 7 is a diagrammatic view of a thermodynamic system according to a fourth alternative embodiment of the invention.

FIG. 8 is a perspective view of the deflecting means equipping the first compressor of the thermodynamic system of FIG. 7.

FIG. 9 is a diagrammatic view of a thermodynamic system according to a fifth alternative embodiment of the invention.

FIG. 10 is a diagrammatic view of a thermodynamic system according to a sixth alternative embodiment of the invention.

FIG. 11 is a diagrammatic view of a thermodynamic system according to a seventh alternative embodiment of the invention.

FIG. 1 diagrammatically shows the main components of a thermodynamic system 1 according to the invention, and more particularly of a refrigeration system.
The refrigeration system 1 comprises a circuit 2 for circulating refrigerant successively including a condenser 3, an expander 4, an evaporator 5 and a compression device 6 connected in series.
The compression device 6 comprises a first variable-capacity compressor 7 and a second fixed-capacity compressor 8. Each compressor 7, 8 is advantageously a scroll refrigeration compressor. Each compressor 7, 8 comprises a sealed enclosure 9 including a low-pressure portion 11 containing the motor 12 and an oil pan 13 positioned at the bottom of the sealed enclosure, and a high-pressure portion 14, positioned above the low-pressure portion 11, containing a compression stage.
The sealed enclosure 9 of each compressor also includes a refrigerant intake opening 15 leading into an upper portion of the low-pressure portion 11, an equalization opening 16 leading into the oil pan 13, and a discharge opening 17 leading into the high-pressure portion 14.
The sealed enclosure 9 of the first compressor 7 also comprises a connecting opening 18 leading into an upper portion of the low-pressure portion 11 of the first compressor.
The refrigeration system 1 also comprises a refrigerant dispensing device. The dispensing device comprises a dispensing conduit 19 putting the evaporator 5 in communication with the intake opening 15 of the first compressor 7.
The refrigeration system 1 also comprises an oil level equalization conduit 21 connecting the equalization openings 16 of the two compressors and thereby putting the oil pans 13 of the first and second compressors 7, 8 in communication.
The refrigeration system 1 also comprises a connecting device including a connecting conduit 22 connecting the connecting opening 18 of the first compressor with the intake opening 15 of the second compressor and thereby putting the low-pressure portions 11 of the first and second compressors in communication, such that all of the refrigerant penetrating the low-pressure portion of the second compressor comes from the low-pressure portion of the first compressor. The end of the connecting conduit 22 turned toward the first compressor side preferably protrudes inside the sealed enclosure of the first compressor 7. The connecting conduit 22 is preferably generally S-shaped.
The refrigeration system 1 also comprises a refrigerant discharge device 24. The discharge device 24 comprises a discharge conduit 25 connected to the condenser 3, the first bypass conduit 26 putting the discharge conduit 25 in communication with the discharge opening 17 of the first compressor 7, the second bypass conduit 27 putting the discharge conduit 25 in communication with the discharge opening 17 of the second compressor 8.
The refrigeration system 1 also comprises control means 28 arranged to control the starting and stopping of the first and second compressors, and controlling means 29 arranged to modulate the speed of the motor 12 of the first compressor 7 between a minimum speed and a maximum speed.
The control means 28 are preferably arranged to control the starting and stopping of the first compressors according to four control modes, i.e.:
a first control mode, in which the control means control the starting of the first and second compressors,
a second control mode, in which the control means control the starting of the first compressor and the stopping of the second compressor,
a third control mode, in which the control means control the stopping of the first compressor and the starting of the second compressor, and
a fourth control mode, in which the control means control the stopping of the first and second compressors.
When the control means control the starting and stopping of the first and second compressors according to the second control mode, all of the refrigerant penetrating the low-pressure portion 11 of the first compressor 7 is suctioned in the high-pressure portion 14 of the first compressor so as to be compressed in the compression stage thereof, whereas when the control means control the starting and stopping of the first and second compressors according to the third control mode, all of the refrigerant penetrating the low-pressure portion 11 of the first compressor 7 is suctioned in the low-pressure portion 11 of the second compressor 8 by means of the connecting conduit 22 so as to be compressed in the compression stage of the second compressor 8.
When the control means control the starting and stopping of the first and second compressors according to the first control mode, a first portion of the refrigerant penetrating the low-pressure portion 11 of the first compressor 7 is suctioned in the high-pressure portion 14 of the first compressor so as to be compressed in the compression stage thereof and a second portion of the refrigerant penetrating the low-pressure portion 11 of the first compressor 7 is suctioned in the low-pressure portion 11 of the second compressor 8 by means of the connecting conduit 22 so as to be compressed in the compression stage of the second compressor.
According to one alternative embodiment of the refrigeration system shown in FIGS. 4 a and 4 b, the oil level equalization conduit 21 includes an end portion 31 turned toward the side of the first compressor 7 and protruding inside the enclosure 9 of the first compressor. The end portion 31 includes an end wall 32 extending transversely to the longitudinal direction of the end portion 31 and an opening 33 formed above the end wall 32 such that, when the oil level in the oil pan 13 of the first compressor 7 extends above the upper level of the end wall 32, oil flows through the opening 33 toward the second compressor. Preferably, the opening 33 extends over a portion of the side wall 34 of the end portion 31.
The end portion 31 also includes an oil return opening 35 formed in the lower portion of the end portion 31 situated below the upper level of the end wall 32. This position of the oil return opening 35 ensures a return of oil toward the oil pan 13 of the first compressor 7 when the second compressor 8 is stopped, and thereby avoids oil being stored beyond a predetermined level inside the enclosure of the second compressor.
According to one alternative embodiment of the refrigeration system shown in FIGS. 5 and 6, the first compressor 7 comprises first deflecting means positioned in the enclosure 9 of the first compressor 7 and whereof a portion is positioned across from the intake opening 15 of the first compressor, the deflecting means being arranged to orient at least one portion of the refrigerant penetrating the low-pressure portion 11 of the first compressor 7 along at least one portion of the inner wall of the sealed enclosure 9 of the first compressor. Preferably, the first deflecting means include a sintered plate 40 fixed on the inner wall of the sealed enclosure 9 so as to define a refrigerant circulation passage 41 therewith.
According to one alternative embodiment of the refrigeration system shown in FIG. 7, the first compressor comprises deflecting means positioned in the enclosure 9 of the first compressor 7 and whereof at least one portion is positioned across from the end of the connecting device turned toward the first compressor side, the deflecting means being arranged to orient the refrigerant penetrating the low-pressure portion of the first compressor in an ascending, then descending movement before it flows through the connecting device. Preferably, as shown in FIG. 8, the deflecting means include a plate 42 fastened on the inner wall of the sealed enclosure 9.
According to another alternative embodiment of the refrigeration system shown in FIG. 9, the first compressor comprises a fixed volute 43 and a moving volute 44 following an orbital movement, a body 45 on which the moving volute bears, an intermediate casing 46 fixed on the body 45 and inside which the motor 12 is mounted, and an oil return conduit 47 extending on the outer wall of the intermediate casing, the oil return conduit including a first end leading, preferably sealably, into the body, and a second end leading near the oil pan 13 of the first compressor.
According to another alternative embodiment of the refrigeration system shown in FIG. 10, the compression device 6 comprises a third compressor 48 mounted in series with the first compressor 7 and upstream therefrom, the dispensing device comprising a first dispensing conduit 19 a putting the evaporator 5 in communication with the intake opening 15 of the third compressor 48, and a second dispensing conduit 19 b putting the low-pressure portion of the third compressor 48 in communication with the intake opening 15 of the first compressor 7 such that all of the refrigerant penetrating the low-pressure portion of the first compressor 7 comes from the low-pressure portion of the third compressor 48. According to this alternative embodiment, the refrigeration system also comprises an oil level equalization conduit 21′ putting the oil pans 13 of the first and third compressors in communication, and the discharge device 24 also comprises a third bypass conduit 49 putting the discharge conduit 25 in communication with the discharge opening 17 of the third compressor 48.
According to another alternative embodiment of the refrigeration system shown in FIG. 11, the compression device 6 comprises a fourth compressor 50 mounted in parallel with the second compressor 8, the connecting device comprising a connecting conduit 22 a connected to the low-pressure portion of the first compressor 7, a first bypass conduit 22 b putting the connecting conduit 22 a in communication with the intake opening 15 of the second compressor 8, and a second bypass conduit 22c putting the connecting conduit 22 a in communication with the intake opening 15 of the fourth compressor 50. According to this alternative embodiment, the refrigeration system also comprises an oil level equalization device putting the oil pans 13 of the first, third and fourth compressors in communication. The oil level equalization device comprises the oil level equalization conduit 22 and a bypass conduit 51 putting the oil level equalization conduit 22 in communication with the oil pan 13 of the fourth compressor 50.
The discharge device 24 also comprises a third bypass conduit 52 putting the discharge conduit 25 in communication with the discharge opening 17 of the fourth compressor 50.
It should be noted that the control means 28 are arranged to control the starting and stopping of the third and/or fourth compressors.
The invention is of course not limited solely to the embodiments of this thermodynamic system described above as examples, but on the contrary encompasses all alternative embodiments.

Claims

1. A thermodynamic system, comprising:

a circuit for circulating a refrigerant successively including a condenser, an expander, an evaporator and a compression device connected in series, the compression device comprising at least one first compressor and one second compressor mounted in parallel, each compressor comprising a sealed enclosure including on the one hand a low-pressure portion containing a motor and an oil pan positioned at the bottom of the enclosure, and on the other hand a refrigerant intake opening leading into the low-pressure portion, and

a refrigerant dispensing device arranged to connect the evaporator to an intake opening of the first compressor,

an oil level equalization conduit putting the oil pans of the first and second compressors in communication,

a connecting device putting the low-pressure portion of the first compressor in communication with the intake opening of the second compressor, such that all of the refrigerant penetrating the low-pressure portion of the second compressor comes from the low-pressure portion of the first compressor, and

control means arranged to control the starting and stopping of the first and second compressors,

wherein the control means are arranged to control the starting and stopping of the first and second compressors according to:

a first control mode, in which the control means control the starting of the first and second compressors,

a second control mode, in which the control means control the starting of the first compressor and the stopping of the second compressor,

a third control mode, in which the control means control the stopping of the first compressor and the starting of the second compressor, and

a fourth control mode, in which the control means control the stopping of the first and second compressors,

and the oil level equalization conduit includes an end portion turned toward the first compressor side and protruding inside the sealed enclosure of said first compressor, said end portion including an end wall extending transversely to the longitudinal direction of said end portion and an opening formed above the end wall such that, when the oil level in the oil pan of the first compressor extends above the upper level of said end wall, oil flows through said opening toward the second compressor.

2. The thermodynamic system according to claim 1, wherein at least one of the first and second compressors is a variable-capacity compressor, or wherein the first and second compressors are fixed-capacity compressors and have a capacity ratio comprised between 1.5 and 3.

3. The thermodynamic system according to claim 1, wherein the oil level equalization conduit is arranged and sized such that, when the system is in the overheated steady state, an upper portion of the flow cross-section of the equalization conduit is situated above the oil levels in the oil pans of the first and second compressors so as simultaneously to allow the transfer of oil and refrigerant between the first and second compressors.

4. The thermodynamic system according to claim 1, wherein the end portion of the oil level equalization conduit turned toward the first compressor side includes an oil return opening formed in a lower part of said end portion situated below the upper level of the end wall.

5. The thermodynamic system according to claim 1, wherein one of the first and second compressors is a variable-capacity compressor, and the other of the first and second compressors is a fixed-capacity compressor.

6. The thermodynamic system according to claim 5, wherein the thermodynamic system comprises controlling means arranged to modulate the capacity of the variable-capacity compressor between a minimum capacity value and a maximum capacity value.

7. The thermodynamic system according to claim 1, wherein the first and second compressors are fixed-capacity compressors, the capacity of the first compressor being larger than that of the second compressor.

8. The thermodynamic system according to claim 1, wherein the compression device comprises a third compressor mounted in series with the first compressor and upstream therefrom, the dispensing device comprising a first dispensing conduit putting the evaporator in communication with the intake opening of the third compressor, and the second dispensing conduit putting the low-pressure portion of the third compressor in communication with the intake opening of the first compressor such that all of the refrigerant penetrating the low-pressure portion of the first compressor comes from the low-pressure portion of the third compressor.

9. The thermodynamic system according to claim 1, wherein the compression device comprises a fourth compressor mounted in parallel with the second compressor, the connecting device comprising a connecting conduit connected to the low-pressure portion of the first compressor, a first bypass conduit putting the connecting conduit in communication with the intake opening of the second compressor, and a second bypass conduit putting the connecting conduit in communication with the intake opening of the fourth compressor.

10. The thermodynamic system according to claim 1, wherein the connecting device comprises a connecting conduit putting the low-pressure portion of the first compressor in communication with the intake opening of the second compressor.

11. The thermodynamic system according to claim 10, wherein the end of the connecting conduit turned toward the first compressor protrudes inside the enclosure of the first compressor.

12. The thermodynamic system according to claim 1, wherein each compressor is a scroll refrigeration compressor.

13. The thermodynamic system according to claim 12, wherein the first compressor comprises a fixed volute and a moving volute following an orbital movement, a body on which the moving volute bears, an intermediate casing fixed on the body and inside which the motor is mounted, and at least one oil return conduit extending at least partially over the outer wall of the intermediate casing, the oil return conduit including a first end turned toward the body and inserted in an opening formed in the body, and a second end leading near the oil pan.

14. The thermodynamic system according to claim 1, wherein at least the first compressor comprises first deflecting means positioned in the sealed enclosure of said first compressor and whereof at least one portion is positioned across from the intake opening of said first compressor, the first deflecting means being arranged to orient at least a portion of the refrigerant penetrating the low-pressure portion of the first compressor along at least one portion of the inner wall of the sealed enclosure of said first compressor.

15. The thermodynamic system according to claim 1, wherein at least the first compressor comprises second deflecting means positioned in the sealed enclosure of said first compressor and whereof at least one portion is positioned across from the end of the connecting device turned toward the first compressor side, the second deflecting means being arranged to orient the refrigerant penetrating the low-pressure portion of the first compressor following an ascending, then descending movement before the flow thereof through the connecting device.