US20060083626A1

US20060083626A1 - Compressor and hermetic housing with minimal housing ports

Info

Publication number: US20060083626A1
Application number: US11/247,340
Authority: US
Inventors: Dan Manole
Original assignee: Tecumseh Products Co
Current assignee: Tecumseh Products Co
Priority date: 2004-10-19
Filing date: 2005-10-11
Publication date: 2006-04-20
Also published as: CA2523719A1

Abstract

A vapor compression system having a multi-stage compressor with a minimal number of ports located in the hermetically sealed compressor housing. A working fluid at suction pressure enters the compressor housing through a first port and is compressed to an intermediate pressure. The intermediate pressure refrigerant flows from the first stage compressor mechanism to the second stage compressor mechanism where it is compressed to a discharge pressure and discharged through a second port. The intermediate pressure refrigerant is in thermal communication with a heat exchange medium which is introduced into the compressor housing through a third port in the housing.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a hermetically sealed compressor for a vapor compression system and, more particularly, to a compressor housing having a minimal number of housing ports.
2. Description of the Related Art
A vapor compression system typically includes at least a compressor, a first heat exchanger, an expansion device, and a second heat exchanger fluidly linked in serial order. Other components such as accumulators, flash tanks, and the like are also well-known and may be employed with the vapor compression system, but are not essential for the operation of the vapor compression system.
One known type of vapor compression system is a transcritical vapor compression system wherein the refrigerant is compressed to a supercritical pressure and is returned to the compressor at a subcritical pressure. When the refrigerant is at a supercritical pressure, the liquid and vapor phases of the refrigerant are indistinguishable and the first heat exchanger is typically referred to as a gas cooler instead of a condenser. After cooling the refrigerant in the gas cooler, the pressure of the refrigerant is reduced to a subcritical pressure by the expansion device and the low pressure liquid is communicated to the evaporator where the refrigerant is converted to a vapor.
When carbon dioxide is used as a refrigerant, the vapor compression system is typically operated as a transcritical system and generally requires the use of a discharge pressure that is considerably higher than the discharge pressure used with conventional refrigerants in a subcritical system.
To provide the relatively high discharge pressures required in a transcritical system, the compressor in a transcritical vapor compression system is often a multi-stage compressor. The use of multi-stage compressors, such as a two-stage compressor, is known and such compressors typically include first and second stage compressor mechanisms mounted at opposite ends of a drive motor. The drive motor is drivingly linked to each of the first and second stage compressor mechanisms by a common drive shaft. In general, the drive shaft is coupled to the first and second stage compressor mechanisms in a manner that the first and second stage compressor mechanisms are out of phase with respect to one another and/or at different points in the compression cycle. To provide a relatively high pressure differential between the suction and discharge pressures, the compressor mechanisms may be arranged in series. Multi-stage compressor assemblies also often include an intercooler wherein intermediate pressure refrigerant is cooled by ambient air in a heat exchanger after being compressed by a first compressor mechanism before being returned to the compressor assembly for compression to the discharge pressure in a second compressor mechanism.
FIG. 1 provides a schematic illustration of a known vapor compression system 10 that includes gas cooler 12, expansion device 14, evaporator 16, and two-stage compressor 18 connected in series by a plurality of conduits 19. Compressor 18 includes first stage compressor mechanism 20 and second stage compressor mechanism 22 arranged in series and mounted in the compressor housing schematically represented by dashed line 24. During operation of the two-stage compressor 18, suction pressure refrigerant enters housing 24 through first port 26 and flows into first stage compressor mechanism 20 where it is compressed to an intermediate pressure. The intermediate pressure refrigerant then exits compressor 18 through second port 28 and enters intercooler 30 where it is cooled. By cooling the intermediate pressure refrigerant, the efficiency and capacity of second stage compressor mechanism 22 are typically increased. The cooled intermediate pressure refrigerant is then returned to the compressor assembly through third port 32 into second stage compressor mechanism 22. The intermediate pressure refrigerant is then compressed to discharge pressure and discharged from compressor 18 through fourth port 34.
A problem with the foregoing compressor mechanism is that the compressor housing requires as many as four or more ports, each of which include an opening in the compressor housing which requires a seal, thereby increasing the cost of the compressor and the number of locations on the compressor housing at which a fluid leak could potentially occur.
What is needed is a compressor and for transcritical vapor compression systems which is an improvement over the foregoing.

SUMMARY OF THE INVENTION

The present invention provides a multi-stage compressor having a reduced number of ports located in the compressor housing. The intermediate pressure refrigerant is cooled between the first and second compressor stages by a flash gas which is introduced into the compressor housing through a single port in the housing. Alternatively, a heat pipe or other heat transfer device may be inserted through a single port in the housing of the compressor assembly to provide a thermal exchange with the intermediate pressure refrigerant.
The invention comprises, in one form thereof, a compressor assembly operable in a vapor compression system defining a fluid circuit for circulating a vapor. The compressor assembly includes a hermetically sealed housing with a first and second compressor mechanism being disposed in the housing. The first and second compressor mechanisms are operable to compress the vapor in two stages, wherein the first compressor mechanism compresses the vapor from a suction pressure to an intermediate pressure and the second compressor mechanism compresses the vapor from the intermediate pressure to a discharge pressure. The housing defines first, second, and third ports. The first and second ports are in fluid communication with the fluid circuit wherein suction pressure vapor is communicated from the fluid circuit to the compressor assembly through the first port and discharge pressure vapor is communicated from the compressor assembly to the fluid circuit through the second port. The third port defines a passage for a heat exchange medium wherein thermal energy is transferable between the heat exchange medium and the compressor assembly. Further, all vapor circulating within the circuit and all heat exchange mediums communicated through the housing are communicated through one of the first, second, and third ports.
The invention comprises, in another form thereof, a transcritical vapor compression system having a compressor assembly, a first heat exchanger, an expansion device and a second heat exchanger serially disposed in a fluid circuit circulating a refrigerant. The compressor assembly includes a hermetically sealed housing with a first and second compressor mechanism being disposed in the housing. The first and second compressor mechanisms are operable to compress the refrigerant in two stages, wherein the first compressor mechanism compresses the refrigerant from a suction pressure to an intermediate pressure and the second compressor mechanism compresses the refrigerant from the intermediate pressure to a discharge pressure. The housing defines first, second, and third ports. The first and second ports are in fluid communication with the fluid circuit wherein suction pressure refrigerant is communicated from the fluid circuit to the compressor assembly through the first port and discharge pressure refrigerant is communicated from the compressor assembly to the fluid circuit through the second port. The third port defines a passage for a heat exchange medium wherein thermal energy is transferable between the heat exchange medium and the compressor assembly. Further, all refrigerant circulating within the circuit and all heat exchange mediums communicated through the housing are communicated through one of the first, second, and third ports.
The invention comprises, in a further form thereof, a method of compressing a refrigerant. The method includes hermetically sealing a first compressor mechanism and a second compressor mechanism in a housing. The method also includes forming first, second, and third ports in the housing and introducing the refrigerant into the housing through the first port. The method further includes compressing the refrigerant in the first compressor mechanism from a suction pressure to an intermediate pressure; and compressing the refrigerant in the second compressor mechanism from the intermediate pressure to a discharge pressure. The method includes discharging the refrigerant from the housing through the second port. The method also includes communicating a thermal exchange medium through the third port; exchanging thermal energy between the intermediate pressure refrigerant and the thermal exchange medium; and wherein all refrigerant and thermal exchange medium communicated through the housing is communicated through one of the first, second, and third ports.
An advantage of the present invention is that same provides a multi-stage compressor mechanism wherein intermediate pressure refrigerant may be cooled without requiring an intercooler and the two housing ports associated with the use of an intercooler. The elimination of the intercooler is beneficial because it may simplify the manufacture of the compressor assembly.
The reduction in the number of ports required in the hermetically sealed housing is also beneficial because each of the ports of the housing must be properly sealed to ensure that the housing provides a hermetically sealed enclosure and an increase in the number of ports in the housing increases the chances that one of such ports may later develop a leak and may also increase the initial cost of manufacturing the compressor assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a schematic view of a prior art vapor compression system;
FIG. 2 is a schematic view of a first embodiment of a vapor compression system having a compressor in accordance with the present invention;
FIG. 3 is a schematic view of a second embodiment of a vapor compression system having a compressor in accordance with the present invention; and
FIG. 4 is a schematic view of a third embodiment of a vapor compression system having a compressor in accordance with the present invention.
Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplifications set out herein illustrate embodiments of the invention, the embodiments disclosed below are not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise forms disclosed.

DETAILED DESCRIPTION

Referring to FIG. 2, vapor compression system 40 is a closed loop fluid circuit through which a working fluid is circulated. Vapor compression system 40 has operably disposed therein, in serial order, first heat exchanger 42, expansion device 44, second heat exchanger 46, and compressor assembly 48. In the illustrated vapor compression system 40, the working fluid is carbon dioxide and vapor compression system 40 is a transcritical system. Consequently, first heat exchanger 42 is a gas cooler wherein the carbon dioxide within gas cooler 42 is at a supercritical pressure while the carbon dioxide within second heat exchanger or evaporator 46 is at a subcritical pressure. The components of vapor compression system 40 are fluidly connected by a plurality of conduits 49. Although a charge of carbon dioxide flows through the fluid circuit in the illustrated embodiments, other refrigerants may alternatively be employed with the present invention.
The use of carbon dioxide as the refrigerant requires vapor compression system 40 to operate as a transcritical vapor compression system, wherein the high pressure side of the system is at a pressure substantially greater than a vapor compression system using a conventional refrigerant in a subcritical system. During operation of vapor compression system 40, carbon dioxide is conveyed to compressor assembly 48 from evaporator 46 at a relatively low suction pressure. The compression of the carbon dioxide increases its temperature and pressure to a higher discharge temperature and pressure which, in the illustrated systems employing carbon dioxide as the refrigerant, will be a supercritical pressure. The discharged refrigerant is then conveyed to gas cooler 42 where the refrigerant is cooled. The high pressure refrigerant exhausted from gas cooler 42 is then delivered to expansion device 44 where the pressure of the refrigerant is reduced. The relatively low pressure refrigerant is then conveyed to evaporator 46. When employing carbon dioxide as the refrigerant, the carbon dioxide will be reduced to a subcritical pressure by the expansion device 44. The relatively low pressure refrigerant will enter evaporator 46 including liquid phase refrigerant wherein thermal energy is transferred to the low pressure refrigerant and liquid phase refrigerant within evaporator 46 is converted to a vapor or gaseous state. The low pressure refrigerant vapor is then returned to compressor assembly 48 and the cycle is repeated.
Such a vapor compression system may be used in various applications that are well known in the art. For example, gas cooler 42 can be used to provide heat for heating air in a heat pump application, or heating water in a water heater application. In other applications, evaporator 46 may be used for cooling purposes such as in an air conditioning or refrigeration applications.
Compressor assembly 48 in vapor compression system 40 is a hermetically sealed multi-stage compressor having at least two compressor mechanisms. The compressor assembly may include any suitable type of compressor mechanism including rotary, scroll and reciprocating piston compressors. Compressor assembly 48 is schematically illustrated in FIG. 2 having a hermetically sealed housing represented by line 50. Compressor assembly 48 is a two-stage compressor including first stage compressor mechanism 52 and second stage compressor mechanism 54. Housing 50 defines interior plenum 51 in which first and second stage compressor mechanisms 52 and 54 are located. Compressor mechanisms 52 and 54 may be mounted on opposite ends of a common drive shaft driven by an electric motor (not shown) located within housing 50. The compressor mechanisms 52 and 54 are advantageously mounted out of phase from one another or at different points in the compression cycle to provide a more balanced load on the motor.
Compressor assembly 48 may be a low side compressor in which interior plenum 51 is filled with suction pressure refrigerant. The suction pressure refrigerant is at a lower temperature than the compressed refrigerant and facilitates the cooling of the motor. The present invention is not limited to low side compressors, however, and alternative embodiments may employ a variety of configurations including high side compressor designs wherein the motor cavity is filled with discharge pressure refrigerant.
During operation of compressor assembly 48, suction pressure refrigerant is compressed in first stage compressor mechanism 52 to an intermediate pressure. The intermediate pressure refrigerant passes through conduit 56 located within housing 50 and fluidly linking first stage compressor mechanism 52 and second stage compressor mechanism 54. The intermediate pressure refrigerant is cooled while in conduit 56 by means which will be described further hereinbelow. The cooled, intermediate pressure refrigerant is then compressed in second stage compressor mechanism 54 to a higher, discharge pressure.
Cooling the intermediate pressure refrigerant in a two-stage compressor assembly between first stage compressor mechanism 52 and second stage compressor mechanism 54 improves the efficiency and capacity of the second stage compressor mechanism and thus compressor assembly 48. In the present invention, the lack of an intercooler 30 (FIG. 1) external of the compressor mechanism 52 eliminates the need for one of the ports in compressor housing 50 while still providing means for cooling the intermediate pressure refrigerant. The elimination of one port in compressor housing 50 is advantageous in that the number of connections between compressor assembly 48 and the fluid circuit of vapor compression system 40 are reduced. Further, by using alternative means, described below, to cool the intermediate pressure refrigerant while same passes between first stage compressor mechanism 52 and second stage compressor mechanism 54, an intercooler 30 (FIG. 1) is not necessary, thereby reducing the number of components of vapor compression system 40.
Compressor housing 50 is provided with three ports 58, 60, and 62. First and second ports 58 and 60 provide passages through which refrigerant gas is communicated to and from compressor assembly 48 to the vapor compression circuit. The suction pressure refrigerant enters compressor housing 50 through first port 58 formed in the housing and is directed into first stage compressor mechanism 52. The discharge pressure gas compressed by second stage compressor mechanism 54 is discharged from compressor housing 50 through port 60. Third port 62 defines a passage through which a heat exchange medium enters compressor housing 50 to cool the intermediate pressure gas passing from first stage compressor mechanism 52 to second stage compressor mechanism 54.
Referring to FIG. 2, a means of transferring thermal energy between a heat exchange medium and compressor assembly 48 is illustrated. As discussed above, discharge pressure refrigerant is exhausted from compressor assembly 48 and is conveyed to gas cooler 42. In gas cooler 42, heat is transferred from the high pressure refrigerant to ambient air or other heat exchange medium. The temperature of high pressure refrigerant in gas cooler 42 is thereby reduced. The refrigerant then passes through expansion device 44 where the pressure of the refrigerant is reduced resulting in a mixture of vapor and liquid phase refrigerant.
In the embodiment of FIG. 1, a portion of the low pressure, vapor phase refrigerant exiting the expansion device 44 is diverted as a flash gas to compressor assembly 48 where it provides a heat exchange medium for cooling the compressor assembly including intermediate pressure refrigerant. Conduit 64 defines a fluid passage for the flash gas having a first end of conduit 64 fluidly linked to the vapor compression system fluid circuit at a location between expansion device 44 and evaporator 46. The second end of conduit 64 is in fluid communication with interior plenum 51 of compressor housing 50 via third port 62. A valve 66 may be operably positioned along conduit 64 to control the flow of flash gas through conduit 64.
In alternative embodiments, conduit 64 may divert refrigerant from another location in vapor compression system 40 to compressor assembly 48. For example, the flash gas may be diverted from a location downstream of evaporator 46. Conduit 64 may also include an expansion device to further reduce the pressure, and consequently the temperature, of the flash gas which is conveyed to the compressor assembly 48. The use of an expansion device also allows refrigerant to be diverted from a location upstream of expansion device 44 to provide the flash gas entering compressor assembly 48 through third port 62.
The relatively low pressure and temperature flash gas is conveyed by conduit 64 provides a heat exchange medium for cooling the intermediate pressure refrigerant in conduit 56. The flash gas enters compressor assembly 48 through third port 62 and fills interior plenum 51 of compressor housing 50, surrounding conduit 56. As the intermediate pressure refrigerant flows through conduit 56, heat is transferred from the intermediate pressure refrigerant to the flash gas in interior plenum 51, thus reducing the temperature of the intermediate pressure refrigerant prior to entering second stage compressor mechanism 54. In this embodiment, compressor assembly 48 is a low side compressor with low pressure gas filling interior plenum 51.
Referring to the embodiment illustrated in FIG. 3, the vapor compression system includes compressor assembly 70 having a hermetically sealed housing 74 and a thermal exchange device 72.
As with the previous embodiment shown in FIG. 2 and described above, first stage compressor mechanism 52 and second stage compressor mechanism 54 are positioned within interior plenum 76 of housing 74 and are fluidly linked by conduit 78. Suction pressure refrigerant enters compressor housing 74 through first port 80 and is compressed to an intermediate pressure in first stage compressor mechanism 52. The intermediate pressure refrigerant flows through conduit 78 into second stage compressor mechanism 54 where it is compressed to a discharge pressure and discharged to gas cooler 42 through second port 82. Heating or cooling device 72 is mounted in third port 84 formed compressor housing 74 so as to exchange thermal energy between the interior and exterior of housing 74. For example, device 72 may be a heat pipe that cools the interior of the compressor assembly 48, including the intermediate pressure refrigerant in conduit 78.
Conduit 78 is provided with a second passage 86 extending substantially, for example, perpendicularly to conduit 78. Passage 86 is closed at the internal end and the opposite end sealingly engages the internal surface of compressor housing 74 in surrounding relationship of third port 84 such that the intermediate pressure refrigerant in conduit 78 does not leak into interior plenum 76. Sleeve 88 is sealingly mounted in third port 84 and extends into passage 86 with a portion of sleeve 88 being in communication with conduit 78. Heating or cooling device 72 is positioned within sleeve 88. As intermediate pressure refrigerant flows along conduit 78 from first stage compressor mechanism 52 toward second stage compressor mechanism 54, a thermal exchange occurs between heating and cooling device 72 and the intermediate pressure refrigerant to modify the temperature of the refrigerant and thus control the efficiency of compressor assembly 70. Device 72 may be in the form of a heat pipe, for example, or the like.
The heat transfer device 72 may be a heat pipe, thermosyphon or other suitable device. Heat pipes and thermosyphons are commonly used to provide a heat transfer device within laptop computers, for example, and are well known to those of ordinary skill in the art. Heat pipes and tubular thermosyphons may take the form of an elongate tube having a sealed interior volume. A fluid is provided within the sealed interior volume and provides a heat transfer medium. One end of the device functions as an evaporator and at this end of the device liquid phase working fluid is evaporated thereby providing a cooling effect. The vaporized working fluid migrates to the opposite end of the device where it is condensed and returns to a liquid phase thereby exhausting thermal energy to the surrounding environment. The condensed liquid phase working fluid returns to the evaporator end of the device either by means of gravity or through a wicking effect provided by a porous media located within the interior volume.
FIG. 4 illustrates a third embodiment of the present invention. In this embodiment, compressor assembly 90 includes a heating or cooling device 92 extending through compressor housing 94 and which transfers thermal energy between the interior and exterior of housing 94. Suction pressure refrigerant enters compressor housing 94 through first port 96 and is compressed to an intermediate pressure in first stage compressor mechanism 52. The intermediate pressure flows through conduit 95 into second stage compressor mechanism 54 where it is compressed to a discharge pressure and discharged through second port 98. Heating or cooling device 92 is mounted in third port 100 formed in compressor housing 94 and is in thermal communication with the intermediate pressure refrigerant in conduit 95.
Conduit 95 is provided with a second passage 102 extending substantially perpendicularly to, for example, conduit 95. Passage 102 is closed at the internal end and the opposite end sealingly engages the internal surface of compressor housing 94 in surrounding relationship to third port 100 such that the intermediate pressure refrigerant in conduit 95 does not leak into interior plenum 104 defined by housing 94. Openings 106 extend in a direction substantially parallel, for example, to conduit 95 and are formed near the internal end of passage 102. Openings 106 are in fluid communication with oil located in interior plenum 104.
A first sleeve 108 is mounted in passage 102 in thermal communication with openings 106. A second sleeve 110 is positioned adjacent first sleeve 108 with one end sealingly mounted in third port 100 such that a portion of second sleeve 110 is in communication with conduit 95. Wall 112 is located in passage 102 to prevent fluid communication between the oil passing through openings 106 and intermediate pressure refrigerant flowing through conduit 95. Sleeves 108 and 110 are concentrically positioned to receive heating or cooling device 92. Device 72 may be in the form of a heat pipe, for example, or the like.
As intermediate pressure refrigerant flows along conduit 95 from first stage compressor mechanism 52 toward second stage compressor mechanism 54, a thermal exchange occurs between heating and cooling device 92 and the intermediate pressure refrigerant to alter the temperature of the refrigerant. In addition, oil flows through openings 106 and around sleeve 108 so that a thermal exchange may occur between the oil and heating and cooling device 92 to control the temperature thereof and thus the efficiency of compressor assembly 90.
While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.

Claims

1. A compressor assembly operable in a vapor compression system defining a fluid circuit for circulating a vapor, said compressor assembly comprising:

a hermetically sealed housing;

a first compressor mechanism disposed within said housing;

a second compressor mechanism disposed within said housing, wherein said first and second compressor mechanisms are operable to compress the vapor in two stages wherein said first compressor mechanism compresses the vapor from a suction pressure to an intermediate pressure and said second compressor mechanism compresses the vapor from the intermediate pressure to a discharge pressure; and

wherein said housing defines first, second and third ports, said first and second ports in fluid communication with said fluid circuit wherein suction pressure vapor is communicated from the fluid circuit to said compressor assembly through said first port and discharge pressure vapor is communicated from said compressor assembly to the fluid circuit through said second port, said third port defining a passage for a heat exchange medium, wherein thermal energy is transferable between the heat exchange medium and said compressor assembly, and wherein all superheated or wet vapors circulating within the circuit and all heat exchange mediums communicated through said housing are communicated through one of said first, second and third ports.

2. The compressor assembly of claim 1 wherein the heat exchange medium is a flash gas and said third port is in communication with an interior plenum defined by said housing, said first and second compressor mechanisms disposed within said interior plenum.

3. The compressor assembly of claim 1 wherein said interior plenum of said housing is at suction pressure.

4. The compressor assembly of claim 1 wherein said compressor assembly defines a flow path between said first compressor mechanism and said second compressor mechanism for intermediate pressure vapor and the heat exchange medium transfers thermal energy with the intermediate pressure vapor.

5. The compressor assembly of claim 4 wherein the heat exchange medium is a flash gas and said third port is in communication with an interior plenum defined by said housing, said first and second compressor mechanisms disposed within said interior plenum.

6. The compressor assembly of claim 1 further comprising a heat transfer device extending through said third port.

7. The compressor assembly of claim 6 wherein said heat transfer device is a heat pipe.

8. The compressor assembly of claim 1 wherein said third port is in communication with a sleeve, said housing defining an interior plenum, said sleeve extending within said plenum and defining an elongate volume in communication with said third port and sealingly separated from said plenum.

9. The compressor assembly of claim 8 further comprising a heat transfer device extending through said third port and partially disposed within said sleeve.

10. A transcritical vapor compression system comprising:

a compressor assembly, a first heat exchanger, an expansion device and a second heat exchanger serially disposed in a fluid circuit circulating a refrigerant; said compressor assembly comprising:

a hermetically sealed housing;

a first compressor mechanism disposed within said housing;

a second compressor mechanism disposed within said housing, wherein said first and second compressor mechanisms are operable to compress the refrigerant in two stages wherein said first compressor mechanism compresses the refrigerant from a suction pressure to an intermediate pressure and said second compressor mechanism compresses the refrigerant from the intermediate pressure to a discharge pressure; and

wherein said housing defines first, second and third ports, said first and second ports in fluid communication with said fluid circuit wherein suction pressure refrigerant is communicated from the fluid circuit to said compressor assembly through said first port and discharge pressure refrigerant is communicated from said compressor assembly to the fluid circuit through said second port, said third port defining a passage for a heat exchange medium, wherein thermal energy is transferable between the heat exchange medium and said compressor assembly, and wherein all refrigerant circulating within said vapor compression system and all heat exchange mediums communicated through said housing are communicated through one of said first, second and third ports.

11. The compressor assembly of claim 10 wherein the heat exchange medium is a flash gas and said third port is in communication with an interior plenum defined by said housing, said first and second compressor mechanisms disposed within said interior plenum, the flash gas comprising relatively low pressure refrigerant diverted from said fluid circuit from a location between said expansion device and said compressor assembly.

12. The compressor assembly of claim 10 wherein said compressor assembly defines a flow path between said first compressor mechanism and said second compressor mechanism for intermediate pressure refrigerant and the heat exchange medium transfers thermal energy with the intermediate pressure refrigerant.

13. The compressor assembly of claim 12 wherein the heat exchange medium is a flash gas and said third port is in communication with an interior plenum defined by said housing, said first and second compressor mechanisms disposed within said interior plenum, the flash gas comprising relatively low pressure refrigerant diverted from said fluid circuit from a location between said expansion device and said compressor assembly.

14. The compressor assembly of claim 10 further comprising a heat transfer device extending through said third port.

15. The compressor assembly of claim 10 wherein the refrigerant comprises carbon dioxide.

16. A method of compressing a refrigerant, said method comprising:

hermetically sealing a first compressor mechanism and a second compressor mechanism in a housing;

forming first, second and third ports in said housing;

introducing the refrigerant into said housing through said first port;

compressing the refrigerant in the first compressor mechanism from a suction pressure to an intermediate pressure;

compressing the refrigerant in the second compressor mechanism from the intermediate pressure to a discharge pressure;

discharging the refrigerant from the housing through said second port;

communicating a thermal exchange medium through said third port;

exchanging thermal energy between the intermediate pressure refrigerant and the thermal exchange medium; and

wherein all refrigerant and thermal exchange medium communicating through said housing is communicated through one of said first, second and third ports.

17. The method of claim 16 wherein said step of communicating a heat exchange medium through said third port comprises introducing a flash gas into said housing through said third port.

18. The method of claim 17 wherein said refrigerant comprises carbon dioxide and the discharge pressure exceeds the critical pressure of the refrigerant.

19. The method of claim 16 wherein communicating a heat exchange medium through said third port comprises extending a heat pipe through said third pipe.