WO2008112568A2

WO2008112568A2 - Compressor with multiple inlets

Info

Publication number: WO2008112568A2
Application number: PCT/US2008/056273
Authority: WO
Inventors: Holger Tychsen
Original assignee: Johnson Controls Technology Company
Priority date: 2007-03-09
Filing date: 2008-03-07
Publication date: 2008-09-18
Also published as: WO2008112549A3; WO2008112569A2; WO2008112554A1; WO2008112549A2; WO2008112566A3; WO2008112566A2; WO2008112568A3; WO2008112594A2; WO2008112591A2; WO2008112572A1; WO2008112593A1; WO2008112591A3; WO2008112569A3; WO2008112594A3

Abstract

A compressor is provided having a compression device configured to compress a vapor in an inlet volume from a first pressure to a second pressure higher than the first pressure. A first inlet provides vapor at the first pressure to the inlet volume of the compression device. A second inlet provides vapor to the inlet volume of the compression device at an intermediate pressure between the first pressure and the second pressure. The compression device includes an outlet to discharge vapor at the second pressure from a discharge chamber of the compression device. A valve is positioned near the second inlet and is configured to provide a variable flow of intermediate pressure vapor to the inlet volume from the second inlet.

Description

COMPRESSOR

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from and the benefit of U.S. Provisional Application No. 60/894,052, entitled SYSTEMS AND METHODS OF USING CO2 IN REFRIGERATION AND AIR CONDITIONING APPLICATIONS, filed March 9, 2007 and U.S. Provisional Application No. 60/917,175, entitled SYSTEMS AND METHODS OF USING NATURAL REFRIGERANTS, filed May 10, 2007, which are hereby incorporated by reference.

BACKGROUND

[0002] The application generally relates to compressors. The application relates more specifically to screw compressors having a variable inlet opening to receive intermediate pressure vapor.

[0003] Rotary screw compressors that are utilized for compressing a refrigerant vapor or other fluid conventionally include a pair of rotors having intermeshing lands and grooves helically disposed about the periphery of the rotors. A working fluid enters the compressor from an inlet port and enters the grooves between the rotors. The rotation of the rotors forms a somewhat chevron-shaped compression chamber in which the working fluid is received. The chamber diminishes in volume as the chamber is moved toward an outlet in the compressor. The working fluid is discharged when the crest of the rotor lands defining the leading edge of a compression chamber pass an edge of the discharge ports in the discharge casings of the compressors.

[0004] One technique that can be used to improve the operating performance of a compressor is to provide an intermediate pressure vapor, i.e., a vapor that has a pressure between the suction pressure of the compressor and the discharge pressure of the compressor, to the suction inlet of the compressor. The addition of the intermediate pressure vapor can raise the pressure of the vapor provided to the compressor, which can then reduce the amount of work required by the compressor to reach the discharge pressure. Another technique that can be used to improve the operating performance of the compressor is to provide a fixed amount of intermediate pressure vapor directly into the compression chamber of the compressor. The insertion of the intermediate pressure vapor into the compression chamber raises the pressure in the compression chamber and reduces the amount of work required by the compressor to reach the discharge pressure.

SUMMARY

[0005] The present invention relates to a compressor having a compression device, a first inlet, a second inlet, an outlet and a valve. The compression device is configured to compress a vapor in an inlet volume from a first pressure to a second pressure higher than the first pressure. The first inlet provides vapor at the first pressure to the inlet volume of the compression device. The outlet discharges vapor at the second pressure from a compression chamber of the compression device. The second inlet provides vapor to the inlet volume of the compression device at an intermediate pressure between the first pressure and the second pressure. The valve is configured and disposed to provide a variable flow of intermediate pressure vapor to the inlet volume via the second inlet.

[0006] The present invention also relates to a vapor compression system having a compressor, a first heat exchanger, a vessel and a second heat exchanger connected in a closed loop. The compressor has a compression device, a first inlet, a second inlet, an outlet and a valve. The compression device is configured to compress a vapor in an inlet volume from a first pressure to a second pressure higher than the first pressure. The first inlet provides vapor at the first pressure to the inlet volume of the compression device. The outlet discharges vapor at the second pressure from a compression chamber of the compression device. The second inlet provides vapor at an intermediate pressure between the first pressure and the second pressure to the inlet volume of the compression device. The valve is configured and disposed to provide a variable flow of intermediate pressure vapor to the inlet volume via the second inlet.

[0007] The present invention further relates to compressor having a compression device, a first inlet, a second inlet, an outlet and a valve. The compression device is configured to compress a vapor in an inlet volume from a first pressure to a second pressure higher than the first pressure. The first inlet provides vapor at the first pressure to the inlet volume of the compression device. The outlet discharges vapor at the second pressure from a compression chamber of the compression device. The second inlet provides vapor to the inlet volume of the compression device at an intermediate pressure between the first pressure and the second pressure. The third inlet provides vapor at the first pressure to the inlet volume of the compression device. The third inlet being fluidly connected to the first inlet. The valve is disposed between the first inlet and the third inlet and is configured to provide a variable flow of first pressure vapor to the inlet volume via the third inlet.

BRIEF DESCRIPTION OF THE FIGURES

[0008] FIGS. 1 through 3 show exemplary environments using systems that can incorporate a screw compressor.

[0009] FIG. 4 shows an elevational view of an exemplary screw compressor that is part of a packaged unit.

[0010] FIG. 5 shows a cross section of an exemplary screw compressor.

[0011] FIG. 6 schematically shows an exemplary embodiment of a vapor compression system.

[0012] FIG. 7 shows a cross section of a vapor inlet to an exemplary embodiment of a screw compressor.

[0013] FIG. 8 shows a plan view of the vapor inlet and rotors of FIG. 7.

[0014] FIG. 9 shows a cross section of the vapor inlet of another exemplary embodiment of a screw compressor.

[0015] FIG. 10 shows a plan view of the vapor inlet and rotors of FlG. 9.

[0016] FTGS. 1 1 and HA show cross sections of the vapor inlet of a further exemplary embodiment of a screw compressor.

[0017] FIG. 12 shows a plan view of the vapor inlet and rotors of FIG. 1 1.

[0018] FIG. 13 shows a cross section of the vapor inlet of yet another exemplary embodiment of a screw compressor. [0019] FIG. 14 shows a plan view of the vapor inlet and rotors of FIG. 13.

[0020] FIG. 15 shows a cross section of the vapor inlet of an exemplary embodiment of a screw compressor.

[0021] FIG. 16 shows a plan view of the suction inlet and rotors of FIG. 15.

[0022] FIG. 17 shows a cross section of the vapor inlet of another exemplary embodiment of a screw compressor.

[0023] FIG. 18 shows a plan view of the suction inlet and rotors of FIG. 17.

[0024] FIG. 19 shows a volume - rotor angle curve for an exemplary embodiment of a screw compressor.

[0025] FIG. 20 shows a pressure - volume curve showing different opening positions for an intermediate inlet.

[0026] FIG. 21 shows a pressure - enthalpy curve for a refrigerant used in a transcritical vapor compression system.

[0027] FIGS. 22 and 23 show exemplary embodiments of a vapor compression system that can provide an intermediate pressure to an intermediate inlet.

[0028] FIGS. 24 and 25 show corresponding pressure - enthalpy curves for the refrigerant in the vapor compression systems of FIGS. 22 and 23.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0029] FIGS. 1 through 3 show several exemplary environments that can use a screw compressor in a refrigeration system or a heating, ventilation, and air conditioning (HVAC) system. FIG. 1 shows an environment for an exemplary multistage refrigeration system 10 that can incorporate a screw compressor. Multistage refrigeration system 10 can provide both refrigeration and freezing capacity for a supermarket 12 in a commercial setting. The multistage refrigeration system 10 can have evaporators incorporated into refrigerated cases or displays 14 and freezer cases or displays 16 that are accessible by a person shopping in supermarket 12. According to an exemplary embodiment, refrigerated cases or displays 14 can be used to keep produce or dairy products at a preselected temperature and can be operated at a temperature between about 2 deg C and about 7 deg C. According to an exemplary embodiment, freezer cases or displays 16 can be used to keep frozen items at a preselected temperature and can be operated at a temperature between about -20 deg C and about -30 deg C. Multistage refrigeration system 10 can have an evaporator 18 in a freezer storage area 20 of supermarket 12 and can have an evaporator 22 in a refrigerated storage area 24 of supermarket 12. According to an exemplary embodiment, freezer storage area 20 can be used to store items to be subsequently placed in freezer cases or displays 16 at a preselected temperature and can be operated at a temperature between about -20 deg C and about -30 deg C. According to an exemplary embodiment, refrigerated storage area 24 can be used to store items to be subsequently placed in refrigerated cases or displays 14 at a preselected temperature and can be operated at a temperature between about 2 deg C and about 7 deg C.

[0030] FIG. 2 depicts multistage refrigeration system 10 supplying freezing capacity to a plate freezer 28 in a factory or industrial setting 26. Plate freezer 28 may have horizontal or vertical plates 30 to freeze flat products, such as pastries, fish fillets, and beef patties, as well as irregular-shaped vegetables that are packaged in brick-shaped containers, such as asparagus, cauliflower, spinach, and broccoli. The product may be firmly pressed between metal plates 30 that are cooled to subfreezing temperatures by internally circulating refrigerant from the second stage system through thin channels within plates 30. A high rate of heat transfer can be obtained between the product and plates 30. According to an exemplary embodiment, plate freezers 28 provide cooling temperatures of between about -20 deg C and about -50 deg C or colder and can be used when rapid freezing is desired to retain product flavor and freshness.

[0031] FIG. 3 shows an exemplary environment for an HVAC system 32 in a building 34 for a typical commercial setting. System 32 can include a screw compressor incorporated into a rooftop unit 36 that can supply a chilled liquid that may be used to cool building 34. System 32 can also include a boiler 38 to supply a heated liquid that may be used to heat building 34, and an air distribution system that circulates air through building 34. The air distribution system can include an air return duct 40, an air supply duct 42 and an air handler 44. Air handler 44 can include a heat exchanger that is connected to boiler 38 and rooftop unit 36 by conduits 46. The heat exchanger in air handler 44 may receive either heated liquid from boiler 38 or chilled liquid from rooftop unit 36 depending on the mode of operation of system 32. System 32 is shown with a separate air handler on each floor of building 34, but it will be appreciated that these components may be shared between or among floors.

[0032] FIG. 4 shows an exemplary embodiment of a screw compressor in a packaged unit. The packaged unit includes a screw compressor 50, a motor 52 to drive screw compressor 50, a control panel 54 to provide control instructions to equipment included in the packaged unit such as motor 52. An oil separator 56 can be provided to remove entrained oil (used to lubricate the rotors of screw compressor 50) from the discharge vapor before providing the discharge vapor to its intended application.

[0033] FIG. 5 shows a rotary screw compressor 60 having a housing 62 that can define a pair of parallel intersecting rotor chambers or bores in which are mounted intermeshing rotors. Each rotor can include a plurality of elongated spiral lands 64 and grooves 66 which extend from an inlet face 68 of the rotor to a discharge face 70. When mounted in an intermeshing relationship, each intermeshing land and groove forms a continuous pocket in which a fluid is compressed as the rotors are rotated and as the fluid passes from inlet face 69 to discharge face 70 of the rotors. A fluid, e.g., a refrigerant vapor, enters compressor 60 through an inlet 74 in housing 62 and after the fluid is compressed, the fluid is discharged through a discharge opening 76,

[0034] Each of the rotors can be supported by appropriate shafts in bearings mounted within housing 62. As shown in FIG. 5, a drive shaft 78 can be connected to one of the rotors and extend outwardly of housing 62. Drive shaft 78 can be connected to an appropriate drive source, such as a motor (not shown). The drive shaft 78 can be rotatably supported within bearing assemblies mounted within bearing bores formed in housing 62. Positioned centrally beneath the bores and having an axis generally parallel with respect thereto is a longitudinally extending secondary bore or recess 80. Slidably mounted within secondary bore 80 is a slide valve assembly 82 (shown in the fully open position in FIG. 5) which can be used to control the output capacity of the compressor by diverting vapor from the compression chamber.

[0035] FIG. 6 schematically shows an exemplary vapor compression system. Vapor compression system 100 can circulate a refrigerant through a compressor 101 driven by a motor 52, a condenser or gas cooler 102, an expansion device 104, an evaporator 106, an intermediate circuit 108 and a control panel 54. Intermediate circuit 108 can have an intermediate vessel 109, an inlet line 1 10, an economizer expansion valve 112, a first outlet line 1 14, and a second outlet line 1 16. Some examples of fluids that may be used as refrigerants in vapor compression system 100 are hydrofluorocarbon (HFC) based refrigerants (e.g., R-410A), carbon dioxide (CO₂;

R-744), and any other suitable type of refrigerant.

[0036] Motor 52 used with compressor 101 can be powered by a variable speed drive (VSD) 122 or can be powered directly from an alternating current (AC) or direct current (DC) power source. Variable speed drive 122, if used, receives AC power having a particular fixed line voltage and fixed line frequency from the AC power source and provides power having a variable voltage and frequency to the motor. Motor 52 can be any type of electric motor that can be powered by a VSD or directly from an AC or DC power source. For example, motor 52 can be a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or any other suitable motor type. In an alternate embodiment, other drive mechanisms such as steam or gas turbines or engines and associated components can be used to drive motor 52.

[0037] Vapor compression system 100 can be operated either sub-critically, i.e., the discharge pressure from compressor 101 is below the critical pressure for the refrigerant being circulated in vapor compression system 100 or transcritically, i.e., the discharge pressure from compressor 101 is above the critical pressure for the refrigerant being circulated in vapor compression system 100, e.g., 73 bar at 31 deg C for carbon dioxide. During transcritical operation, vapor compression system 100 can be operated partly below (sub-critical) and partly above (supercritical) the critical pressure of the circulating refrigerant. For both sub-criticai and transcritical operation of vapor compression system 100, compressor 101 compresses a refrigerant vapor and delivers the compressed vapor to condenser or gas cooler 102 through a discharge line. Compressor 101 can be a screw compressor, reciprocating compressor, rotary compressor, scroll compressor, or any other suitable type of positive displacement compressor. The refrigerant vapor delivered by compressor 101 to condenser or gas cooler 102 transfers heat to a fluid, e.g., water or air.

[0038] During sub-critical operation of vapor compression system 100, the refrigerant vapor condenses to a refrigerant liquid in condenser 102 as a result of the heat transfer with the fluid. The liquid refrigerant from condenser 102 can then flow to intermediate circuit 108. In contrast, during transcritical operation of vapor compression system 100, the refrigerant vapor can only be cooled in gas cooler 102 (which can operate as a condenser in low ambient temperatures) as a result of the heat transfer with the fluid before flowing to intermediate circuit 108. The cooling of the refrigerant in gas cooler 102 can also gradually increase the density of the refrigerant. During transcritical operation, the refrigerant vapor will be maintained as a single- phase refrigerant (vapor) through gas cooler 102 and is first converted into the liquid phase and vapor phase refrigerant when it is expanded by an expansion device.

[0039] Intermediate circuit 108 is incorporated in the main refrigerant circuit between the condenser or gas cooler 102 and the expansion device 104. Intermediate circuit 108 has an inlet line 1 10 that can be either connected directly to or can be in fluid communication with condenser or gas cooler 102. Inlet line 1 10 has an expansion valve 1 12 upstream of intermediate vessel 109. Intermediate vessel 109 can be a heat exchanger in one embodiment and can be a flash tank in another embodiment. Expansion valve 112 operates to lower the pressure of the liquid refrigerant from condenser 102 (if vapor compression system 100 is operating sub- critically) or to expand vapor refrigerant from gas cooler 102 into liquid refrigerant and vapor refrigerant (if vapor compression system 100 is operating transcritically). Downstream of expansion valve 112, liquid refrigerant and vapor refrigerant can enter intermediate vessel 109. In one embodiment, intermediate vessel 109 can be a flash tank and vapor refrigerant can collect in the top or upper portion of the flash tank and liquid refrigerant can settle in the bottom or lower portion of the flash tank.

[0040] The liquid refrigerant in intermediate vessel 109 then flows through first outlet line 1 14 to expansion device 104. Second outlet line 116 can return the vapor refrigerant in intermediate vessel 109 to a port in compressor 101 that is in fluid communication with the inlet volume of compressor 101. In another embodiment, when vapor compression system 100 is operating subcritically, a third outlet line 118 can be connected to intermediate vessel 109 and can return the vapor refrigerant in intermediate vessel 109 to a port in fluid communication with the compression chamber or cycle of compressor 101. According to an exemplary embodiment, intermediate circuit 108 can operate in a similar manner to that described above with respect to FIG. 6, except that instead of receiving the entire amount of refrigerant from condenser or gas cooler 102, as shown in FIG. 6, intermediate circuit 108 receives only a portion of the refrigerant from condenser or gas cooler 102 and the remaining refrigerant proceeds directly to expansion device 104.

[0041] The liquid refrigerant from intermediate vessel 109 can flow through expansion device 104 to evaporator 106. The liquid refrigerant delivered to evaporator 106 absorbs heat from a fluid, e.g., air or water and undergoes a phase change to a refrigerant vapor. The vapor refrigerant exits evaporator 106 and returns to compressor 101 by a suction line to complete the cycle.

[0042] FIGS. 7 and 8 show an exemplary embodiment of a screw compressor that can receive refrigerant vapor for compression from an evaporator and an intermediate pressure source. Screw compressor 120 can have a suction inlet 122 (shown stippled in FIGS. 7 and 8) to receive refrigerant vapor at a low pressure, i.e., a suction pressure, such as may be provided by evaporator 106 (shown in FIG. 6). The refrigerant vapor entering suction inlet 122 flows into an inlet volume or swept volume of screw compressor 120 as defined by the pocket between the lands and grooves of a pair of rotors 124. The inlet volume of refrigerant vapor can then be compressed as the pocket is reduced in size as it travels to the discharge end of screw compressor 120 by the rotation of rotors 124. Once the pocket reaches the discharge end of screw compressor 120, the compressed refrigerant vapor exits screw compressor through discharge outlet 126.

[0043] Screw compressor 120 can also have an intermediate inlet 128 (shown stippled in FIGS. 7 and 8) to receive refrigerant vapor at an intermediate pressure, i.e., a pressure between suction pressure and discharge pressure, such as may be provided by intermediate vessel 109 (shown in FIG. 6). The refrigerant vapor entering intermediate inlet 128 can also flow into the inlet volume or swept volume and contribute to filling the inlet volume with refrigerant vapor. A valve 130 can be used to regulate the amount of refrigerant vapor that can be provided by suction inlet 122 and intermediate inlet 128. Valve 130 can include a valve body 132 that may slide in a corresponding channel 134. Channel 134 can be positioned above rotors 124 in the inlet portion or the filling cycle of rotors 124, i.e., from a cusp position of rotors 124 to a top of rotor position. A centerline of channel 134 can be located between the centerlines of rotors 124 or in a vertical plane with the centerline of one of rotors 124. In another exemplary embodiment, a second valve 130 can be located near the rotors 124 to provide a second passageway from intermediate inlet 128 to the inlet volume.

[0044] Channel 134 can be in fluid communication with suction inlet 122, intermediate inlet 128 and the inlet volume. The position of the valve body 132 in channel 134 can be used to regulate the amount of refrigerant vapor provided to the inlet volume by both suction inlet 122 and intermediate inlet 128. Valve 130 can use an axial mover 136 to slide valve body 132 in channel 134. In one embodiment, axial mover 136 can be operated either electrically or hydraulically. In another embodiment, axial mover 136 can be an electric motor.

[0045] The movement of valve body 132 to the right in FIGS. 7 and 8 can be used to reduce the amount refrigerant vapor provided to the inlet volume by intermediate inlet 128 (and correspondingly increase the amount provided by suction inlet 122) until intermediate inlet 128 is fluidly disconnected from the inlet volume and suction inlet 122 is providing the entire inlet volume. The movement of valve body 132 to the left in FIGS. 7 and 8 can be used to reduce the amount of refrigerant vapor provided to the inlet volume by suction inlet 122 (and correspondingly increase the amount provided by intermediate inlet 128) until a minimum contribution position for suction inlet 122 has been reached. The minimum contribution position for suction inlet 122 corresponds to the minimum amount of refrigerant vapor that suction inlet 122 can contribute to the inlet volume. In one embodiment, the minimum amount of refrigerant vapor that suction inlet 122 can contribute to the inlet volume can range from about 60% of the inlet volume to about 95% of the inlet volume.

[0046] FIGS. 9 and 10 show another exemplary embodiment of a screw compressor similar to FIGS. 7 and 8 except that a different valve is used to regulate flow from suction inlet 122 and intermediate inlet 128. Screw compressor 138 is similar to screw compressor 120 except that valve 140 is used in place of valve 130. Valve 140 can be used to regulate the amount of refrigerant vapor that can be provided by suction inlet 122 and intermediate inlet 128. Valve 140 can include a valve body 142 that may slide in a corresponding channel 144. Valve body 142 can have a corresponding aperture 146 that is in fluid communication with intermediate inlet 128 and is also in fluid communication with channel 144 and/or the inlet volume. Channel 144 can be positioned above rotors 124 in the inlet portion or the filling cycle of rotors 124. A centerline of channel 144 can be located between the centerlines of rotors 124 or in a vertical plane with the centerline of one of rotors 124. In another embodiment, a second valve 140 can be located near the rotors 124 to provide a second passageway from intermediate inlet 128 to the inlet volume.

[0047] Channel 144 can be in fluid communication with suction inlet 122, intermediate inlet 128 and the inlet volume. The position of the valve body 142 (and aperture 146) in channel 144 can be used to regulate the amount of refrigerant vapor provided to the inlet volume by both suction inlet 122 and intermediate inlet 128. Valve 140 can use axial mover 136 to slide valve body 142 in channel 144.

[0048] The movement of valve body 142 (and aperture 146) to the right in FIGS. 9 and 10 can be used to reduce the amount refrigerant vapor provided to the inlet volume by intermediate inlet 128 (and correspondingly increase the amount provided by suction inlet 122) until intermediate inlet 128 is fluidly disconnected from the inlet volume and suction inlet 122 is providing the entire inlet volume. In another embodiment, the movement of valve body 142 (and aperture 146) to fluidly disconnect intermediate inlet 128 from the inlet volume can result in aperture 146 being moved to a position such that aperture 146 can provide a fluid connection between intermediate inlet 128 and a compression chamber for compressor 138. The movement of valve body 142 (and aperture 146) to the left in FIGS. 9 and 10 can be used to reduce the amount refrigerant vapor provided to the inlet volume by suction inlet 122 (and correspondingly increase the amount provided by intermediate inlet 128) until a minimum contribution position for suction inlet 122 has been reached. The minimum contribution position for suction inlet 122 corresponds to the minimum amount of refrigerant vapor that suction inlet 122 can contribute to the inlet volume. In one embodiment, the minimum amount of refrigerant vapor that suction inlet 122 can contribute to the inlet volume can range from about 60% of the inlet volume to about 95% of the inlet volume.

[0049] FIGS. 1 1 , HA and 12 show another exemplary embodiment of a screw compressor similar to FIGS. 7 and S except that multiple valves can be used to regulate flow from suction inlet 122 and intermediate inlet 128. Screw compressor 148 is similar to screw compressor 120 except that valves 150, 151 are operated independently of one another and are used in place of valve 130. Valves 150, 151 can be used to regulate the amount of refrigerant vapor that can be provided by suction inlet 122 and intermediate inlet 128. Valve 150 can include a first valve body 152 that may slide in a corresponding channel 154. Valve 151 can include a second valve body 156 that may slide in channel 154. Channel 154 can be positioned above rotors 124 in the inlet portion or the filling cycle of rotors 124. A centerline of channel 154 can be located between the centerlines of rotors 124 or in a vertical plane with the centerline of one of rotors 124. In another embodiment, a second set of valves 150, 151 can be located near the rotors 124 to provide a second passageway from intermediate inlet 128 to the inlet volume.

[0050] Channel 154 can be in fluid communication with suction inlet 122, intermediate inlet 128 and the inlet volume. The position of the first valve body 152 and second valve body 156 in channel 154 can be used to regulate the amount of refrigerant vapor provided to the inlet volume by both suction inlet 122 and intermediate inlet 128. Valves 150, 151 can use corresponding axial movers 136 to slide first valve body 152 and second valve body 156 in channel 154.

[0051] The movement of first valve body 152 to the right in FIGS. 1 1 and 12 can be used to increase the corresponding amount of refrigerant vapor provided to the inlet volume (and correspondingly decrease the amount provided by intermediate inlet 128) until intermediate inlet 128 is fluidly disconnected from the inlet volume and suction inlet 122 is providing the entire inlet volume. In an exemplary embodiment, the length of first valve body 152 can be substantially equal to the length between two (2) tips of rotor 124. The movement of second valve body 156 to the left can be used in tandem with first valve body 152 to reduce the amount of refrigerant vapor provided by intermediate inlet 128. If first valve body 152 is not moving while second valve body 56 is moving to the left, then the corresponding amount provided by suction inlet 122 can remain the same. In another embodiment, second valve body 156 can come into contact with first valve body 152 to fluidly disconnect intermediate inlet 128 from the inlet volume.

[0052] The movement of first valve body 152 to the left in FIGS. 11 and 12 can be used to reduce the amount refrigerant vapor provided to the inlet volume by suction inlet 122 until a minimum contribution position for suction inlet 122 has been reached. Depending on the position of second valve body 156, the amount provided by intermediate inlet 128 to the inlet volume may be increased. The minimum contribution position for suction inlet 122 corresponds to the minimum amount of refrigerant vapor that suction inlet 122 can contribute to the inlet volume. In one embodiment, the minimum amount of refrigerant vapor that suction inlet 122 can contribute to the inlet volume can range from about 60% of the inlet volume to about 95% of the inlet volume. In another embodiment shown in FIG. HA, when first valve body 152 is positioned in channel 154 to fluidly disconnect the inlet volume from the intermediate inlet 128, the second valve body 152 may be positioned to enable intermediate inlet 128 to be in fluid communication with the compression chamber of compressor 148.

[0053] FIGS. 13 and 14 show another exemplary embodiment of a screw compressor similar to FIGS. 7 and 8 except that a valve to regulate flow from suction inlet 122 and intermediate inlet 128 is shown in the cusp position between rotors 124. Screw compressor 158 is similar to screw compressor 120 except that valve 160 is used in place of valve 130. Valve 160 can be used to regulate the amount of refrigerant vapor that can be provided by suction inlet 122 and intermediate inlet 128. Valve 160 can include a valve body 162 that may slide in a corresponding channel 164. Channel 164 can be positioned substantially centrally above rotors 124 in the inlet portion or the filling cycle of rotors 124.

[0054] Channel 164 can be in fluid communication with suction inlet 122, intermediate inlet 128 and the inlet volume. The position of the valve body 162 in channel 164 can be used to regulate the amount of refrigerant vapor provided to the inlet volume by both suction inlet 122 and intermediate inlet 128. Valve 160 can use axial mover 136 to slide valve body 162 in channel 164. [0055] The movement of valve body 162 to the right in FIGS. 13 and 14 can be used to decrease the amount refrigerant vapor provided to the inlet volume by intermediate inlet 128 (and correspondingly increase the amount provided by suction inlet 122) until intermediate inlet 128 is fluidly disconnected from the inlet volume. The movement of valve body 162 to the left in FIGS. 13 and 14 can be used to reduce the amount refrigerant vapor provided to the inlet volume by suction inlet 122 (and correspondingly increase the amount provided by intermediate inlet 128) until a minimum contribution position for suction inlet 122 has been reached. The minimum contribution position for suction inlet 122 corresponds to the minimum amount of refrigerant vapor that suction inlet 122 can contribute to the inlet volume. In one embodiment, the minimum amount of refrigerant vapor that suction inlet 122 can contribute to the inlet volume can range from about 60% of the inlet volume to about 95% of the inlet volume.

[0056] FIGS. 15 and 16 show another exemplary embodiment of a screw compressor similar to FIGS. 7 and 8 except that a different valve is used to regulate flow from suction inlet 122 and intermediate inlet 128 has an open connection to the inlet volume. Screw compressor 168 is similar to screw compressor 120 except that valve 170 is used in place of valve 130 and port 172 provides a direct connection between intermediate inlet 128 and the inlet volume. Valve 170 can be used to regulate the amount of refrigerant vapor that can be provided by suction inlet 122 through a secondary suction inlet 174 to the inlet volume. Valve 170 can include a valve body 176 that can be used to control the flow of refrigerant vapor. Valve 170 and port 172 can be positioned above rotors 124 in the inlet portion or the filling cycle of rotors 124. A second port 172 can be located near rotors 124 to provide a second passageway from intermediate inlet 128 to the inlet volume and a second valve 170 can provide a second set of passageways from secondary suction inlet 174 and intermediate inlet 128 to the inlet volume. Valve 170 can use axial mover 136 to move valve body 176.

[0057] The movement of valve body 176 to an open position in valve 170 permits refrigerant vapor to flow into the inlet volume from secondary suction inlet 174. The movement of valve body 176 to the closed position prevents flow into the inlet volume from secondary suction inlet 174 and intermediate inlet 128. In one embodiment, the position of valve body 176 in valve 170 can be varied between the open position and the closed position to provide a variable amount of refrigerant vapor into the inlet volume. When valve 170 is in the closed position, suction inlet 122 is in a minimum contribution position. The minimum contribution position for suction inlet 122 corresponds to the minimum amount of refrigerant vapor that suction inlet 122 can contribute to the inlet volume. In one embodiment, the amount of refrigerant vapor that suction inlet 122 can contribute to the inlet volume can be about 60% of the inlet volume. In another embodiment, a valve may be disposed in port 172 to regulate flow of refrigerant vapor through port 172.

[0058] FIGS. 17 and 18 show another exemplary embodiment of a screw compressor similar to FIGS. 7 and 8 except that a valve to regulate flow from suction inlet 122 and intermediate inlet 128 is shown in the cusp position between rotors 124. Screw compressor 178 is similar to screw compressor 120 except that valve 180 is used in place of valve 130. Valve 180 can be used to regulate the amount of refrigerant vapor that can be provided by suction inlet 122 and intermediate inlet 128. Valve 180 can include a valve body 182 that may slide in a corresponding channel 184. Channel 184 can be positioned substantially centrally above rotors 124 in the inlet portion or the filling cycle of rotors 124.

[0059] Channel 184 can be in fluid communication with suction inlet 122, intermediate inlet 128 and the inlet volume. The position of the valve body 182 in channel 184 can be used to regulate the amount of refrigerant vapor provided to the inlet volume by both suction inlet 122 and intermediate inlet 128. Valve 180 can use axial mover 136 to slide valve body 182 in channel 184.

[0060] As shown in FIGS. 17 and 18, valve body 182 can be positioned to the far left to fluidly disconnect suction inlet 122 from the inlet volume. Since suction inlet 122 is fluidly disconnected when valve body 182 is positioned in the far left position, intermediate inlet 128 provides the entire inlet volume. As valve body 182 is moved to the right in channel 184, indicated by position 182A, the amount of the inlet volume contributed by suction inlet 122 increases and the amount inlet volume contributed by intermediate inlet 128 decreases. Once valve body 182 is positioned to the far right position, as indicated by position 182B, intermediate inlet 128 is fluidly disconnected from the inlet volume and suction inlet 122 is providing the entire inlet volume.

[0061] The intermediate inlet can be used when the compressors of FIGS. 7 through 18 are being operated transcritically to control the capacity of the compressors and to improve the operating efficiency of the compressors. The capacity of the compressors can be controlled by controlling the amount of intermediate pressure refrigerant vapor being provided to the inlet volume. The providing of more intermediate pressure refrigerant into the inlet volume results in more refrigerant being available to provide capacity for the system. The positioning of the valve for the intermediate inlet can be controlled based on the transcritical temperature of the refrigerant. The use of the intermediate port can be used to lower the pressure of a transcritical refrigerant vapor to a point below the critical point of the refrigerant to permit the transcritical refrigerant vapor to be converted to a refrigerant vapor and a refrigerant liquid. In one embodiment, the intermediate inlet 128 can be closed when the compressors of FIGS. 7 through 18 are being operated sub-critically and the inlet volume can be provided by suction inlet 122. In another embodiment, the compressors of FIGS. 7 through 18 can be used in the vapor compression cycle of FIG. 6.

[0062] While intermediate inlet 128 has been shown above rotors 124 with a radial inlet in FIGS. 7 through 18, intermediate inlet 128 can be positioned in different locations in the compressor housing, In an exemplary embodiment, intermediate inlet 128 can be positioned tangentially to the axes of rotors 124 and have a radial inlet. In another exemplary embodiment, intermediate inlet 128 can be positioned at an angle to the axes of rotors 124 and have a radial inlet. In a further exemplary embodiment, intermediate inlet can be positioned in the axial inlet portion of the rotors 124. In an exemplary embodiment, the shape of valve body used to regulate the flow of refrigerant vapor through suction inlet 122 and intermediate inlet 128 can correspond to the shape and helix angles of the tips of rotors 124. In another exemplary embodiment, the valve body can have a length corresponding to the length between two tips of the rotors and correspond to the distance between where the valve body closes the suction inlet 122 and where the valve body opens the intermediate inlet 128. [0063] FIG. 19 shows a volume — rotor angle curve that can be applied to the screw compressors of FIGS. 7 through 18. The curve shows the process of filling the inlet volume or swept volume of a screw compressor with refrigerant vapor and then compressing and discharging the refrigerant vapor from the compressor. The process starts with no inlet volume and the inlet volume (which can be filled with refrigerant vapor from the suction inlet) develops through rotation of the rotors. Depending on the operation of the compressor, the suction inlet may be closed and the intermediate inlet opened somewhere in range A. If the suction inlet is closed before the full inlet volume has been provided, then the intermediate inlet can be opened in range A and closed at the end of range A. However, if the suction inlet is not closed in range A, then the intermediate inlet may be opened and closed in range B to provide refrigerant vapor to the compression chamber. Range C indicates the range where an intermediate pressure port to the compression chamber may be located during compression. Finally, range D indicates the placement of a specific intermediate pressure port, e.g., a conventional economizer port, to the compression chamber.

[0064] FIG. 20 shows a pressure - volume curve showing different opening positions for intermediate inlet in the compressors of FIGS. 7 through 18. The curves shows the process of filling the inlet volume or swept volume of a screw compressor with refrigerant vapor and then compressing and discharging the refrigerant vapor from the compressor. The process begins at point 1 where the suction inlet is opened to begin filing the inlet volume. At point 2, the suction inlet can be closed and the intermediate inlet opened. At point 3, the inlet volume is entirely filled and the compression process begins. The compression process is completed at point 4 and the discharge process starts. The discharge process is completed at point 5 and the process can begin again at point 1. Curve A shows the pressure-volume curve for a compressor where the intermediate inlet is not opened and the suction inlet provides the entire inlet volume. Curve B shows the pressure-volume curve for a compressor where suction inlet is closed at 50% inlet volume and the intermediate inlet is opened. Curve C shows the pressure-volume curve for a compressor where suction inlet is closed at 60% inlet volume and the intermediate inlet is opened. Curve D shows the pressure-volume curve for a compressor where suction inlet is closed at 90% inlet volume and the intermediate inlet is opened. [0065] FIG. 21 shows a pressure - enthalpy curve for a refrigerant used in the transcritical vapor compression system of FlG. 6. The process begins in the evaporator at point 200 where low temperature, low pressure liquid refrigerant absorbs heat and undergoes a phase change to vapor refrigerant at point 201. The vapor refrigerant is then partially compressed by the compressor to point 207 and mixed with the vapor refrigerant from the intermediate vessel at point 205. The vapor refrigerant is then compressed and discharged as high pressure, high temperature refrigerant at point 202. The vapor refrigerant is then cooled in a gas cooler at point 203. The vapor refrigerant is then expanded in the expansion device and the intermediate vessel to obtain a mixture of refrigerant vapor and refrigerant liquid at point 204. The refrigerant vapor from point 204 is provided to the intermediate inlet of the compressor at point 205. The refrigerant liquid from point 204 is provided to another expansion device at point 206 and the refrigerant liquid is expanded to a low temperature, low pressure refrigerant that is provided to the evaporator at point 200.

[0066] FIGS. 22 and 23 show exemplary embodiments of a vapor compression system that can provide an intermediate pressure refrigerant vapor to an intermediate inlet of the compressor. In vapor compression system 210, a compressor 212 compresses a refrigerant vapor and delivers the compressed vapor to a condenser 214. Compressor 212 can be a compressor from FIGS. 7 through 18. The refrigerant vapor delivered by compressor 212 to condenser 214 transfers heat to a fluid, e.g., air, and condenses to a refrigerant liquid. The liquid refrigerant from condenser 214 can then flow to a vessel 216. From vessel 216, a portion of the liquid refrigerant flows through a first expansion device 218 into evaporator 220 and a portion of the liquid refrigerant flows through a second expansion device 222 into evaporator 224. The liquid refrigerant entering evaporator 220 can absorb heat from a fluid and undergo a phase change to a refrigerant vapor. The vapor refrigerant exits evaporator 220 at a first pressure and first temperature and can be provided to the suction inlet of compressor 212. The liquid refrigerant entering evaporator 224 can absorb heat from a fluid and undergo a phase change to a refrigerant vapor. The vapor refrigerant exits evaporator 224 at a second pressure greater than the first pressure and a second temperature greater than the first temperature and can be provided to the intermediate inlet of compressor 212. FIG. 23 is similar to FIG. 22 except that an expansion device 226 is located between condenser 214 and vessel 216 and that refrigerant vapor from vessel 216 can be provided to an economizer port on compressor 212.

[0067] FIGS. 24 and 25 show pressure - enthalpy curves for a refrigerant used in the vapor compression systems of FIGS. 22 and 23. In FIG. 24, which corresponds to the vapor compression system of FIG. 22, the process begins at point 250 in evaporator 220 where liquid refrigerant absorbs heat and undergoes a phase change to vapor refrigerant at point 251. The vapor refrigerant is then compressed by compressor 212 until point 252. The partial compressed refrigerant vapor is mixed with the refrigerant vapor from evaporator 224 at point 253. From point 253, the refrigerant is compressed unti! discharged by compressor 212 at point 254. The vapor refrigerant then transfers heat and is condensed into a refrigerant liquid at point 255. From point 255, a portion of the liquid refrigerant is expanded in expansion device 218 and provided to evaporator 220 at point 250 and another portion of the liquid refrigerant is expanded in expansion device 222 and provided to evaporator 224 at point 256. The liquid refrigerant in evaporator 224 then absorbs heat and undergoes a phase change to vapor refrigerant that is provided to compressor 212 at point 253.

[0068] FIG. 25, which corresponds to the vapor compression system of FIG. 23, is similar to FIG. 23 except that from point 255, the liquid refrigerant is expanded in expansion 226 and provided to vessel 216 at point 257. From vessel 216, refrigerant vapor is provided to compressor 212 and mixed at point 258 with partial compressed refrigerant vapor from point 259. From point 258, the refrigerant is compressed in compressor 212 and discharged to condenser 214 at point 254. The liquid refrigerant from vessel 216 can then be expanded by expansion devices 218 and 222 and provided to evaporators 220 and 224 at points 250 and 256, respectively.

[0069] The vapor compression systems of FIGS. 22 and 23 show embodiments of subcritical uses for the compressors of FIGS 7 through 18. The use of two different evaporating temperatures in the systems of FIGS. 22 and 23 (as shown in FIGS. 24 and 25) can provide the corresponding suction pressure for the suction inlet and the corresponding intermediate pressure for the intermediate inlet. The vapor compression systems of FIGS. 22 and 23 may be used in a multistage refrigeration system such as the one shown in FIG. 1. [0070] While several embodiments have been shown controlling the suction inlet contribution to the inlet volume and the intermediate inlet contribution to the inlet volume in a screw compressor, it is to be understood that similar valve configurations can be used with any positive displacement compressor, e.g., reciprocating compressor, rotary compressor and scroll compressor, having a intermediate pressure port on the suction to achieve similar results.

[0071] In another embodiment, by using variable speed drive 122 (FlG. 6) with motor 52 (FIG. 6), the output capacity of the compressors can be further controlled by adjusting the speed of the compressor. The speed of the compressor can be increased to increase the output capacity of the compressor up to the maximum output capacity. Conversely, the speed of the compressor can be decreased to decrease the output capacity of the compressor to the minimum output capacity,

[0072] While only certain features and embodiments of the invention have been illustrated and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re- sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the invention, or those unrelated to enabling the claimed invention). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.

Claims

WHAT IS CLAIMED IS:

1. A compressor comprising: a compression device configured to compress a vapor in an inlet volume from a first pressure to a second pressure higher than the first pressure; a first inlet to provide vapor at the first pressure to the inlet volume of the compression device; an outlet to discharge vapor at the second pressure from a compression chamber of the compression device; a second inlet to provide vapor to the inlet volume of the compression device at an intermediate pressure between the first pressure and the second pressure; and a valve configured and disposed to provide a variable flow of intermediate pressure vapor to the inlet volume via the second inlet.

2. The compressor of claim 1, wherein the valve comprises: a channel disposed between the second inlet and the inlet volume; and a valve element slidably disposed in the channel to regulate flow of intermediate pressure vapor between the second inlet and the inlet volume.

3. The compressor of claim 2, wherein the valve element is positionable to fluidly disconnect the second inlet from the inlet volume.

4. The compressor of claim 2, wherein the valve element is positionable to decrease flow of first pressure vapor from the first inlet to the inlet volume.

5. The compressor of claim 2, wherein a position of the valve element in the channel determines a respective contribution of vapor from the first inlet and the second inlet to the inlet volume.

6. The compressor of claim 2, wherein the valve further comprises an axial mover to slide the valve element in the channel.

7. The compressor of claim 6 wherein the axial mover is operated electrically or hydraulically.

8. The compressor of claim 6, wherein the axial mover comprises a motor.

9. The compressor of claim 2, wherein the valve element comprises an aperture, the aperture in the valve element being positionable between the second inlet and the inlet volume to provide fluid communication between the second inlet and the inlet volume.

10. The compressor of claim 2, further comprises a second valve, the second valve comprises a second valve element slidably disposed in the channel.

1 1. The compressor of claim 10, wherein the second valve element is positionable in the channel to regulate flow of first pressure vapor from the first inlet to the inlet volume.

12. The compressor of claim 1, wherein the compressor further comprises a third inlet to provide vapor at a second intermediate pressure between the first pressure and the second pressure to the compression chamber of the compression device.

13. The compressor of claim 1, wherein the first inlet is configured to provide less than all of the vapor for the inlet volume.

14. The compressor of claim 1, wherein the compression device comprises a pair of rotors.

15. The compressor of claim 14, wherein the valve is disposed above one rotor of the pair of rotors.

16. The compressor of claim 14, wherein the valve is disposed between the pair of rotors.

17. The compressor of claim 14, wherein the compressor further comprises: a third inlet to provide vapor at an intermediate pressure between the first pressure and the second pressure to the inlet volume of the compression device; a second valve configured and disposed to regulate a volume of intermediate pressure vapor provided to the inlet volume via the third inlet; and wherein the valve is disposed above one rotor of the pair of rotors and the second valve is disposed above the other rotor of the pair of rotors.

18. The compressor of claim 1, wherein the valve comprises: a channel disposed between the first inlet and the second inlet and the inlet volume; a valve element slidably disposed in the channel to concurrently regulate flow of intermediate pressure vapor between the second inlet and the inlet volume and flow of first pressure vapor between the first inlet and the inlet volume, the valve element being positionable to fluidly disconnect the second inlet and the inlet volume and being positionable to fluidly disconnect the first inlet and the inlet volume; and wherein a position of the valve element in the channel determines a respective contribution of vapor from the first inlet and the second inlet to the inlet volume.

19. The compressor of claim I₅ further comprises: a motor connected to the compression device, the motor being configured to drive the compression device; and a variable speed drive connected to the motor, the variable speed drive being configured to provide a variable voltage and variable frequency signals to the motor to vary the speed of the motor.

20. The compressor of claim 1, wherein the compression device is configured to compress the vapor above a critical point for the vapor.

21. A vapor compression system comprising: a compressor, a first heat exchanger, a vessel and a second heat exchanger connected in a closed loop; the compressor comprising: a compression device configured to compress a vapor in an inlet volume from a first pressure to a second pressure higher than the first pressure; a first inlet to provide vapor at the first pressure to the inlet volume of the compression device; an outlet to discharge vapor at the second pressure from a compression chamber of the compression device; a second inlet to provide vapor at an intermediate pressure between the first pressure and the second pressure to the inlet volume of the compression device; and a valve configured and disposed to provide a variable flow of intermediate pressure vapor to the inlet volume via the second inlet.

22. The system of claim 21 , wherein the compression device is configured to compress the vapor above a critical point for the vapor.

23. The system of claim 22, wherein the intermediate vessel and the second inlet are configured and disposed to lower the intermediate pressure vapor to a pressure below the critical point for the vapor.

24. The system of claim 23, wherein the first heat exchanger is a gas cooler.

25. The system of claim 21, wherein the vapor is carbon dioxide.

26. The system of claim 21, wherein the compression device is configured to operate in a subcritical region for the vapor.

27. The system of claim 26, further comprising a third heat exchanger disposed in parallel with the second heat exchanger, the second heat exchanger and the third heat exchanger being configured to convert a liquid into a vapor.

28. The system of claim 27, wherein the second heat exchanger provides vapor to the first inlet and the third heat exchanger provides vapor to the second inlet.

29. The system of claim 28, wherein the compressor comprises a third inlet to provide vapor at a second intermediate pressure between the first pressure and the second pressure to the compression chamber of the compression device.

30. The system of claim 29, wherein the third inlet is in fluid communication with vapor in the vessel.

31. The system of claim 29, wherein the valve comprises: a channel disposed between the second inlet and the inlet volume; a valve element slidably disposed in the channel to regulate flow of intermediate pressure vapor between the second inlet and the inlet volume.

32. The system of claim 31, wherein the valve element being disposed to fluidly disconnect the second inlet and the inlet volume.

33. The system of claim 32, wherein the valve element is configured and disposed to fluidly connect the second inlet and the compression chamber of the compression device.

34. A compressor comprising: a compression device configured to compress a vapor in an inlet volume from a first pressure to a second pressure higher than the first pressure; a first inlet to provide vapor at the first pressure to the inlet volume of the compression device; an outlet to discharge vapor at the second pressure from a compression chamber of the compression device; a second inlet to provide vapor to the inlet volume of the compression device at an intermediate pressure between the first pressure and the second pressure; a third inlet to provide vapor at the first pressure to the inlet volume of the compression device, the third inlet being fluidly connected to the first inlet; and a valve disposed between the first inlet and the third inlet, the valve being configured to provide a variable flow of first pressure vapor to the inlet volume via the third inlet.

35. The system of claim 34, wherein the second inlet continually provides vapor at the intermediate pressure to the inlet volume.