Injection cooling of screw compressors

Abstract

A liquid injection expansion valve permits liquid refrigerant at high pressure, bled from the condenser, to be injected into the working chamber between the screws and intermediate of the suction and discharge sides of a helical rotary screw compressor for cooling the refrigerant working fluid and the captured oil. A solenoid valve limits bleeding of liquid refrigerant from the condenser at high compressor loads. A thermostat sensing the temperature of the screw compressor discharge, modulates the liquid injection expansion valve downstream of the liquid injection solenoid valve. A compressor unloader slide valve may port oil and the liquid refrigerant into the working chamber. The condenser may be positioned at a height considerably above that of the screw compressor to increase the head of the bled liquid refrigerant to a pressure higher than the screw compressor discharge pressure. System oil pressure may be supplied to a fluid pressure operated, direct acting, on-off control valve upstream of the liquid injection expansion valve and within the bleed line, under control of a solenoid valve which is responsive to the temperature of the oil leaving the oil pump, where such temperature is proportional to compressor loading.

What is claimed is:  .[.1. In a closed loop refrigeration system including, in order: a screw compressor, a condenser, and an evaporator, and having a refrigerant circulating therebetween, the improvement comprising: 
     
        injection passage means..]. 12. The refrigeration system as claimed in claim .[.11,.]. .Iadd.34 .Iaddend.wherein said valve comprises an on-off valve, and wherein a thermostat responsive to compressor discharge temperature is operatively coupled to said on-off valve for controlling 
     
     
        the operation of the same. 13. The refrigeration system as claimed in claim .[.11,.]. .Iadd.34 .Iaddend.further comprising: a variable flow valve within said bleed line, and a thermostat responsive to compressor discharge temperature operatively coupled to said variable flow valve to 
     
     
        modulate flow of liquid refrigerant through said bleed line. 14. The refrigeration system as claimed in claim .[.5,.]. .Iadd.35 .Iaddend.further comprising: a reciprocating slide valve for variably opening the working chamber to the suction side of the screw compressor, injection passage means carried by said slide valve, and wherein, said means for coupling one end of said bleed line to said compressor working chamber comprises means operatively coupling said bleed line to said slide 
     
     
        valve injection passage means. 15. The refrigeration system as claimed in claim 14, wherein said valve comprises an on-off valve and wherein a thermostat responsive to the compressor discharge temperature is operatively coupled to said on-off valve for controlling operation of the 
     
     
        same. 16. The refrigeration system as claimed in claim 14, further comprising a variable flow valve positioned within said bleed line, and a thermostat responsive to compressor discharge temperature operatively coupled to said variable flow valve for modulating the flow of liquid refrigerant through said bleed line.  .[.17. The refrigeration system as claimed in claim 2, wherein said valve comprises a variable position valve and wherein said means responsive to compressor load comprises means responsive to the temperature of the compressor discharge for modulating said valve..]. .[.18. The refrigeration system as claimed in claim 17, further comprising means responsive to the condensing temperature of the 
     
     
        refrigerant working fluid for additionally modulating said valve..]. 19. The refrigeration system as claimed in claim .[.18,.]. .Iadd.41 .Iaddend.wherein said valve .Iadd.means .Iaddend.comprises a movable valve member normally biased to valve closed position, and means responsive to the temperature of the compressor discharge .[.tending to operate.]. .Iadd.operates .Iaddend.in opposition to said bias, and further means responsive to the condensing .[.temperature.]. .Iadd.pressure .Iaddend.of the refrigerant working fluid .Iadd.acts .Iaddend.on said movable valve element tending to maintain said valve element in valve closed position. 
     
     
          . The refrigeration system as claimed in claim 19, wherein said valve .Iadd.means .Iaddend.comprises a tubular valve housing, annular means defines a fixed valve seat, a movable valve stem is concentrically positioned within said valve seat and includes an enlarged portion closing off said passage defined by the valve seat and said valve stem, a coil spring concentrically carried by said valve stem biases said valve to closed position, a diaphragm operatively contacts said valve stem at one end and defines with said valve casing, a first closed chamber and a second closed chamber on opposite sides thereof, a bulb is positioned in heat conducting relationship to the compressor outlet and is coupled to said first chamber by capillary means, said chamber, said capillary means and said bulb carry a thermo-expansive fluid, means fluid connects said second chamber directly to said compressor at its discharge side, whereby, said diaphragm is responsive to pressure differentials between said chambers and acts directly on said valve stem to open the valve 
     
     
        .Iadd.means .Iaddend.against the bias of said concentric coil spring. 21. In a refrigeration system including a helical rotary screw compressor, a condenser, and an evaporator, in that order, within a closed loop, with refrigerant circulating therebetween, and wherein said screw compressor includes a compressor housing defining with a pair of intermeshed screws rotatably mounted therein, a compressor working chamber and having a capacity control slide valve movable within the rotor housing and away from a fixed valve stop downstream of the compressor intake port for variably opening the compressor working chamber to said intake port, the improvement comprising: means carried by said slide valve for injecting liquid refrigerant bled from the refrigeration system downstream of the condenser into said screw compressor working chamber intermediate of the suction and discharge sides of the same and downstream of said fixed stop, 
     
     
        for limiting the discharge temperature of the refrigerant gas. 22. The refrigeration system as claimed in claim 21, wherein: hydraulic motor means effects movement of said slide valve and includes a slidable piston, rod means couples said piston at one end and said slide valve at the other, said rod means includes conduit means for feeding said liquid refrigerant, said slide valve includes means coupled to said conduit means defining a liquid refrigerant chamber, and at least one passage extends through a wall of said slide valve and fluid connects said liquid refrigerant chamber to said working chamber downstream of said fixed valve 
     
     
        stop. 23. The refrigeration system as claimed in claim 22, wherein; said rod means comprises a plurality of concentric tubes, said slide valve includes wall means defining a cavity concentrically surrounding said rod means, said cavity is separated by wall means intermediate of the axial ends of said cavity to form upstream and downstream closed chambers extending transversely across said cavity, and wherein first conduit means carried by said tubes means is fluid connected to a source of pressurized oil and to said first chamber, and has a passage opening up into the working chamber downstream of said fixed stop, said tubes further include second conduit means fluid coupled to said bled liquid refrigerant and to said second chamber and fluid passage means fluid coupled to said second chamber, and porting into said working chamber downstream of said first passage, whereby liquid refrigerant is injected into said working chamber downstream of the point of injection of said lubricating oil regardless of 
     
     
        the position of said capacity control slide valve. 24. The refrigeration system as claimed in claim 22, wherein; said hydraulic motor includes a piston mechanically coupled to said slider valve by a piston rod extending therebetween, said rod extends the full length of said slide valve and axially through the center of the same, partition means define first and second axially spaced fluid sealed chambers within said slide valve, fluid passage means is carried by said shaft and extends the length of the same, plug means carried by said shaft separate said passage means at said partition means, and means fluid couple one of said fluid passages to a .[.course.]. .Iadd.source .Iaddend.of lubricating oil, and the other of said passages on the opposite side of said plug to said bled liquid refrigerant and further passage means associated with each chamber fluid couple respective portions of said shaft passage to said chambers and said chambers to said screw compressor working chamber downstream of said fixed 
     
     
        valve stop. 25. In a refrigeration system including, in order, a screw compressor, a condenser, and an evaporator in a closed loop with refrigeration circulating therebetween, a port opening up into said working chamber of the screw compressor intermediate of the suction and discharge sides of said compressor, a bleed line fluid coupled to said loop downstream of the condenser and to said port, a compressor discharge temperature responsive liquid injection expansion valve positioned within said bleed line for modulating the flow of liquid refrigerant through said bleed line to said port, and on-off valve means within said bleed line upstream of said expansion valve, the improvement comprising: an external source of fluid pressure, and wherein said on-off valve comprises a direct acting fluid pressure operated, valve positioned within said bleed line upstream of said liquid expansion valve, and said system further includes means responsive to compressor load for coupling said fluid pressure 
     
     
        operated valve to said external source. 26. The refrigeration system as claimed in claim 25, wherein said external source of said fluid pressure comprises the compressor oil system, said pressure responsive on-off valve, is fluid coupled to said system oil pressure by an oil line including a solenoid valve therein, and said means responsive to compressor load for controlling the flow of fluid pressure from said source to said valve comprises a thermostat in heat receiving position with respect to said compressor discharge and means operatively coupling 
     
     
        said thermostat to said solenoid valve. 27. The refrigeration system as claimed in claim 26, wherein said thermostat comprises a thermal expansion bulb, fixed to said conduit coupling the discharge side of the compressor to the intake side of the condenser, and said means operatively coupling said thermostat to said solenoid valve comprises an electrical circuit including said solenoid valve and normally open thermostat contacts, remote from said thermal expansive bulb and responsive to expansion of 
     
     
        temperature responsive material carried by said bulb. 28. The refrigeration system as claimed in claim 26, further comprising a by-pass line coupled to the oil pressure supply line intermediate of the solenoid valve and the fluid pressure operated valve and acting as an oil return, and fluid restriction means carried with said by-pass line to limit flow therethrough and to insure the continued operation of said on-off valve in 
     
     
        response to energization of said solenoid valve. 29. The refrigeration system as claimed in claim 27, further comprising a by-pass line coupled to the oil pressure supply line intermediate of the solenoid valve and the fluid pressure operated valve and acting as an oil return, and fluid restriction means carried with said by-pass line to limit flow therethrough and to insure the continued operation of said on-off valve in response to energization of said solenoid valve. .Iadd. 30. In a closed loop refrigeration system including, in order, a screw compressor, a condenser, and an evaporator, a refrigerant circulating therebetween, means for bleeding high pressure liquid refrigerant from said system and injecting said liquid refrigerant into said screw compressor working chamber intermediate of the suction and discharge sides of the compressor for limiting the discharge temperature of the refrigerant gas, in response to compressor load and comprising means responsive to at least compressor discharge temperature for injecting liquid refrigerant in direct proportion to compressor load, and wherein, said means for bleeding and injecting liquid refrigerant comprises a bleed line coupled at one end to said compressor working chamber and coupled at the other end to said system intermediate of said condenser and said evaporator, and wherein a valve responsive to compressor load is positioned within said line for controlling the flow of liquid refrigerant therethrough and a thermostat is provided for sensing the temperature of said compressor discharge and means operatively couples said thermostat to said valve for controlling operation of the same, the improvement wherein: said condenser is located at a height, considerably above that of the screw compressor and said bleed line leading from said condenser to said screw compressor is ported to said compressor working chamber in the vicinity of the discharge side of the same, such that the liquid refrigerant injected into the compressor working chamber under control of said valve is at or above the compressor discharge pressure. .Iaddend..Iadd. 31. In a closed loop refrigeration system including, in order, a screw compressor, a condenser, and an evaporator, and having a refrigerant circulating therebetween, and further comprising an oil separator at the discharge end of the screw compressor to separate oil from the refrigerant working fluid, means for bleeding high pressure liquid refrigerant from said system and injecting said liquid refrigerant into said screw compressor working chamber intermediate of the suction and discharge sides of the compressor for limiting the discharge temperature of the refrigerant gas in response to compressor load and comprising means responsive to at least compressor discharge temperature for injecting liquid refrigerant in direct proportion to compressor load, and wherein, said means for bleeding and injecting liquid refrigerant comprises a bleed line coupled at one end to said compressor working chamber and coupled at the other end to said system intermediate of said condenser and said evaporator, and wherein a valve responsive to compressor load is positioned within said line for controlling the flow of liquid refrigerant therethrough and a thermostat is provided for sensing the temperature of said separated oil and means operatively couples said thermostat to said valve for controlling operation of the same, the improvement wherein:   said condenser is located at a height, considerably above that of said screw compressor, and said bleed line leading from said condenser to said screw compressor is ported to said compressor working chamber in the vicinity of the discharge side of the same, such that the liquid refrigerant injected into the compressor working chamber under control of said valve is at or above the compressor discharge pressure. .Iaddend..Iadd. 32. In a closed loop refrigeration system including, in order, a screw compressor, a condenser, and an evaporator, and having a refrigerant circulating therebetween, and further comprising an oil separator at the discharge end of the screw compressor to separate oil from the refrigerant working fluid, means for bleeding high pressure liquid refrigerant from said system and injecting said liquid refrigerant into said screw compressor working chamber intermediate of the suction and discharge sides of the compressor for limiting the discharge temperature of the refrigerant gas in response to compressor load and comprising means responsive to at least compressor discharge temperature for injecting liquid refrigerant in direct proportion to compressor load, and wherein, said means for bleeding and injecting liquid refrigerant comprises a bleed line coupled at one end to said compressor working chamber and coupled at the other end to said system intermediate of said condenser and said evaporator, and wherein an on-off valve responsive to compressor load is positioned within said line for controlling the flow of liquid refrigerant therethrough and a thermostat is provided for sensing the temperature of said separated oil and means operatively couples said thermostat to said valve for controlling operation of the same, the improvement wherein:   said condenser is located at a height, considerably above that of said screw compressor, and said bleed line leading from said condenser to said screw compressor is ported to said compressor working chamber in the vicinity of the discharge side of the same, such that the liquid refrigerant injected into the compressor working chamber under control of said valve is at or above the compressor discharge pressure, said valve comprising an on-off valve and said thermostat being operatively coupled to said on-off valve for controlling operation of the same. .Iaddend..Iadd. 33. In a closed loop refrigeration system including, in order, a screw compressor, a condenser, and an evaporator, and having a refrigerant circulating therebetween, means for bleeding high pressure liquid refrigerant from said system and injecting said liquid refrigerant into said screw compressor working chamber intermediate of the suction and discharge sides of the compressor for limiting the discharge temperature of the refrigerant gas, means responsive to compressor load for controlling said bleeding and injection means and including means responsive to at least compressor discharge temperature for injecting liquid refrigerant in direct proportion to compressor load, said means for bleeding and injecting refrigerant comprising a bleed line coupled at least at one end to said compressor working chamber and coupled at the other end to said system intermediate of said condenser and said evaporator, and a valve responsive to compressor load being positioned within said line for controlling the flow of liquid refrigerant therethrough, the improvement comprising:   a reciprocating slide valve for variably opening the working chamber to the suction side of the screw compressor, injection passage means carried by said slide valve, and wherein, said means for coupling one end of the bleed line to said compressor working chamber comprises means operatively coupling said bleed line to said slide valve injection passage means. .Iaddend..Iadd. 34. In a closed loop refrigeration system including, in order: a screw compressor, a condenser, and an evaporator, and having a refrigerant circulating therebetween, means for bleeding high pressure liquid refrigerant from said system and injecting said liquid refrigerant into said screw compressor working chamber intermediate of the suction and discharge sides of the compressor for limiting the discharge temperature of the refrigerant gas, including means responsive to at least compressor discharge temperature for injecting liquid refrigerant in direct proportion to compressor load, a bleed line coupled at one end to said compressor working chamber and coupled at the other end to said system intermediate of said condenser and said evaporator, and a valve responsive to compressor load positioned within said line for controlling the flow of liquid refrigerant therethrough, the improvement wherein:   an oil separator is positioned at the discharge end of the screw compressor to separate oil from the refrigerant working fluid, said means responsive to compressor load for controlling the flow of liquid refrigerant through said bleed line comprises a thermostat for sensing the temperature of the separated oil and means operatively coupling said thermostat to said valve for controlling operation of the same, and wherein a reciprocating slide valve is operatively mounted on said compressor for opening the working chamber to the suction side of the screw compressor, injection passage means is carried by the slide valve, and wherein said means for coupling one end of the bleed line to said compressor working chamber comprises means operatively coupling said bleed line to said slide valve injection passage means. .Iaddend. .Iadd. 35. A method of operating a refrigeration plant comprising: a refrigerant flow circuit including a compressor of the screw rotor type, a condenser and an evaporator; means for circulating oil and for injecting said oil into the compression chambers of said compressor; an oil separator provided in said circuit between the outlet of said compressor and the inlet of said condenser; and means for introducing liquid refrigerant into a circuit portion between the inlet of the compressor and the inlet of said oil separator;   comprising controlling the introduction of the liquid refrigerant into said circuit portion such that the temperature in the oil separator is kept at a level only slightly above the liquefaction temperature of the refrigerant at the pressure prevailing in the oil separator but is prevented from falling to said liquefaction temperature. .Iaddend..Iadd. 36. The method as defined in claim 35 comprising controlling the introduction of said liquid refrigerant into the compression chambers of said compressor. .Iaddend..Iadd. 37. A refrigeration plant comprising:   a refrigerant flow circuit including a compressor of the screw rotor type, a condenser and an evaporator;   means for circulating oil and for injecting said oil into the compression chambers of said compressor;   an oil separator provided in said circuit between the outlet of said compressor and the inlet of said condenser;   means for introducing liquid refrigerant into a circuit portion between the inlet of the compressor and the inlet of said oil separator;   means responsive to at least one parameter indicative of the difference between the temperature in the oil separator and the temperature in the condenser;   adjustable means for varying the quantity of liquid refrigerant introduced into said circuit portion; and   means connecting said responsive means with said adjustable means to control said adjustable means such that said temperature difference is kept small but is prevented from dropping down to zero. .Iaddend..Iadd.   
     
     
             The plant according to claim 37, wherein said liquid refrigerant is introduced into the compression chambers of said compressor and said adjustable means comprises a valve means coupled in the path of said liquid refrigerant to said compressor, said valve means being opened to increase the quantity of said liquid refrigerant introduced into said compressor. .Iaddend.