US3795117A - Injection cooling of screw compressors - Google Patents

Injection cooling of screw compressors Download PDF

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Publication number
US3795117A
US3795117A US00285695A US3795117DA US3795117A US 3795117 A US3795117 A US 3795117A US 00285695 A US00285695 A US 00285695A US 3795117D A US3795117D A US 3795117DA US 3795117 A US3795117 A US 3795117A
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Prior art keywords
valve
compressor
oil
refrigeration system
discharge
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H Moody
C Hamilton
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Dunham Bush Inc
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Dunham Bush Inc
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B1/00—Compression machines, plants or systems with non-reversible cycle
    • F25B1/04—Compression machines, plants or systems with non-reversible cycle with compressor of rotary type
    • F25B1/047—Compression machines, plants or systems with non-reversible cycle with compressor of rotary type of screw type
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C29/00—Component parts, details or accessories of pumps or pumping installations, not provided for in groups F04C18/00 - F04C28/00
    • F04C29/04—Heating; Cooling; Heat insulation
    • F04C29/042—Heating; Cooling; Heat insulation by injecting a fluid
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B31/00—Compressor arrangements
    • F25B31/006—Cooling of compressor or motor
    • F25B31/008—Cooling of compressor or motor by injecting a liquid

Definitions

  • 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 consider ably 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 bleedline, 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.
  • compressors are pumps that are used to raise gases or refrigerant from one pressure level to a higher pressure level. In the process, the vapor or gas is superheated by the work of compression. Through thermodynamic relationships, operating temperatures can be predicted by applying isotropic r polytropic compression processes. With all types of compressors, the higher the compression ratio [compression ratio (discharge pressure/suction pressure) ⁇ the higher the discharge temperature that will be reached.
  • lubricating oil has been injected into the working chamber, that is, the space occupied by the intermeshed screws in a helical rotary screw compres- 501', for the dual purposes of lubricating the intermeshed screws and to provide the necessary seals between the rotating screws and the stationary housing.
  • the capacity of helical rotary screw compressors has been modified by incorporating a capacity control slide valve within the rotor housing and slidable parallel to the axis of the screw. Axial movement of the valve is programmed by a solid state, temperature initiated hydraulic actuated control arrangement.
  • the slide valve shifts longitudinally between limits with the slide valve in closed position and against a valve stop when the compressor is fully loaded, in which case all the gas flows through the rotor housing from the intake to the discharge side of the screw compressor. Unloading is achieved by moving the valve away from the valve stop to create an opening within the rotor housing through which the suction gas can return to the inlet port area before compression of the same.
  • Unloading is achieved by moving the valve away from the valve stop to create an opening within the rotor housing through which the suction gas can return to the inlet port area before compression of the same.
  • an object of the present invention to eliminate the necessity for a separate pump in liquid injection cooling of a screw compressor and to effect liquid injection cooling of a screw compressor without materially affecting the volumetric capacity of the compressor or increasing the horsepower required.
  • the objects of the present invention are met in conjunction with a screw compressor operating as a component within a refrigeration system wherein compressed gas is condensed to high pressure liquid within a condenser and expanded in an evaporator or chiller for cooling a refrigeration load, and then returned as a low pressure gas to the inlet side of the screw compressor.
  • the invention involves bleeding high pressure refrigerant liquid from the condenser and liquid injection expansion valve, with the solenoid valve being under control of a thermostat bulb sensitive to the temperature of the oil, preferably at the discharge side of the oil pump and downstream of the screw compressor.
  • the condenser is located at a height considerably above that of the screw compressor so that the gravity head acts in conjunction with the normal high pressure of the liquid refrigerant within the condenser to provide liquid refrigerant within the bleed line at a pressure considerably above the discharge gas pressure of the screw compressor so that the refrigerant may be injected into the screw compressor at the discharge side of the same or slightly upstream of the discharge side.
  • a helical rotary screw compressor employs a capacity control slide valve within the rotor housing movable away from a fixed valve stop for reducing the capacity of the compressor.
  • a chamber carried by the valve may be supplied'the bled liquid refrigerant which is ported into the working chamber, downstream of the end of the slide valve which contacts the stop when the compressor is fully loaded.
  • the liquid refrigerant chamber may be sealed from a second chamber of the capacity control slide valve which ports lubricating oil into the compressor working chamber; the refrigerant chamber preferably being downstream of the oil chamber.
  • Coaxial oil and liquid refrigerant lines may be coupled to the respective sealed chambers of the capacity control slide valve from opposite ends, or by means of concentric passags direct flow to the chambers of the slide valve or by means of parallel flow lines from the same end. 7 g
  • a thermal expansion valve within the bleed line and responsive to the temperature of the compressor discharge gas modulates the flow of liquid refrigerant through the bleed line to thecom pressor injection port.
  • An on-off valve is interposed in the bleed line downstream from the thermal expansion valve and is operatively coupled to an oil pressure line at the discharge side of the oil pressure pump. The valve is direct acting in response to system oil pressure.
  • the oil pressure line in turn, carries a solenoid operated valve which is responsive to the temperature of the oil at the discharge side of the pump which is representative of compressor load.
  • a by-pass oil line by-passes the oil pressure operated valve and carries a restriction or orifice between the valve and the sump.
  • FIG. 4 is yet another schematic view of an alternate embodiment of the liquid refrigerant injection cooling system of the present invention, as applied to a refrigeration system.
  • FIG. 5 is an enlarged sectional view of the liquid injection expansion valve employed in the liquid refrigerant injection cooling system of FIG. 1.
  • FIG. 6 is a schematic, sectional view of a portion of a helical rotary screw compressor of the type employed in the system of FIG. '1, employing a capacity control slide valve to port the liquid refrigerant to the working chamber of the compressor.
  • FIG. 6a is an enlarged sectional view of the slide valve forming a portion of the compressor of FIG. 6.
  • FIG. 7 is a sectional elevational view of a portion of a helical rotary screw compressor similar to that of FIG. 6 but illustrating an alternative mode of porting the liquid refrigerant to the screw compressor working chamber.
  • FIG. 8 is a perspective view of the refrigeration system of the rotary screw compressor type employing the improved liquid refrigerant injection cooling system of the present invention.
  • FIG. 9 is a schematic representation of the liquid injection cooling system of the present invention as applied to the refrigeration system of FIG. 8.
  • FIG. 1 illustrates in perspective view a refrigeration system incorporating a helical, rotary screw compressor which employs the liquid refrigerant injection oil cooling system of the present invention, in one form.
  • the principal components of the closed loop refrigeration system are: the helical, rotary screw compressor assembly 10; the condenser 12 which receives the compressor discharge through conduit 14; the chiller or evaporator 16, which is connected to the discharge end of the condenser 12 via conduit 18 and a filter drier 20 incorporated in conduit 18 intermediate of condenser 12 and chiller 16.
  • Conduit 22 connects the discharge end of the chiller to the intake or inlet side of the axial screw compressor 10.
  • Lubricating oil is circulated through the compressor assembly 10 and in fact mixes to a limited extent with the refrigerant working fluid, and is separated by oil separator 25 located after hermetic electric drive motor 24, at the downstream or discharge side of the screw compressor.
  • the separated oil enters oil sump 28 through pipe 27 and is pressurized by an oil pump (not shown) at one end, prior to being returned to the compressor assembly 10 after passage through an oil cleaner or filter 30.
  • the oil filter 30 receives oil from sump 28 through line 32 and discharges the same through a plurality of lines 34 at the discharge end of the oil filter 30.
  • the refrigerant working fluid which may comprise freon or the like, enters the right hand end of compressor assembly at 10, through inlet 22 in gaseous or vapor form at relatively low pressure and is compressed by the helical rotary screw compressor 26 for discharge over and across the hermetic motor windings (not shown) of the electric motor 24 and exits from oil separator 25.
  • the high pressure vapor discharge from the compressor passes through conduit 14 into the condenser 12 where the vapor is condensed by contact with tubes containing coolant such as water or air and is discharged therefrom through conduit 18 to filter drier 20.
  • the high pressure liquid refrigerant then expands within chiller 16 to cool the load consisting of water or other heat exchange fluid within the chiller or evaporator 16.
  • lubricating oil at a relatively low temperature leaves the oil filter 30 via lines 34 to various points along the compressor assembly for lubrication purposes or is employed as hydraulic motor fluid for one or more hydraulic motors such as that associated with compressor unloader 40, for instance, via line 42.
  • the present invention is directed to a liquid refrigerant injection system for limiting the discharge tempera ture of the compressor and thus the maximum temperature to which the system oil is subjected.
  • high pressure liquid refrigerant is bled from conduit 18 downstream of the filter drier as at 44 by a small diameter bleed tube or line 46 through shut off valve 48.
  • the liquid refrigerant passes through a solenoid valve 50 within bleed line 46 and flows to a liquid injection expansion valve 52 which modulates the flow of liquid refrigerant through the bleed line 46 and into the screw compressor 26, line 46 opening into the compressor working chamber intermediate of the discharge and suction sides of compressor 26.
  • a second manually operable shut off valve 54 is positioned within the bleed line 46 intermediate of the screw compressor 26 and the liquid injection expansion valve 52 to assist in isolating the injection system.
  • the liquid injection expansion valve 52 is of the modulating or variable flow type.
  • solenoid valve 50 may be a pilot operated, solenoid energized, two position valve such as that produced by ALCO Controls Corporation of St. Louis,v Missouri, a division of Emerson Electric Company, under the trade designation 230R8.
  • a thermostat bulb 60 may be filled with a temperature expansive material such as a liquid or gas, which operates a thermostat associated with the panel (not shown) causing the normally open contacts to close at a predetermined oil temperature which, in turn, closes the electrical circuit to the solenoid which is integral with valve assembly 50.
  • a temperature expansive material such as a liquid or gas
  • liquid injection expansion valve 52 which is nonelectrical in operation and which is coupled to a temperature expansion valve bulb 56 by a capillary tube 57.
  • the bulb and capillary tube carry a temperature expansive material which may be liquid, gas or part liquid and part gas and which expands in response to increased temperature to variably shift a movable valve element within valve 52 to modulate the flow of liquid refrigerant to the injection port of the screw compressor 26.
  • Essential to the operation of the expansion valve 52, is equalizing line 53 which couples the expansion valve 52 to the screw compressor 26 at the discharge side of the same.
  • the liquid injection expansion valve 52 consists essentially of a dumb bell shaped valve housing or casing 80 expanding at its upper ends and supporting a diaphragm 82 across the chamber 84 defined by that end of the valve housing, the diaphragm 82 exerting pressure on a movable valve stem 86 which is movable axially, being supported by a fixed guide member 88, the stem carrying a disc 90 which is movable therewith, within housing 80' and against which one end of a compression spring 92 abuts, the other end abutting against the fixed guide means 88.
  • valve stem 86 carries an enlarged diameter valve element 94, which is normally biased against an annular valve seat 96 preventing the liquid refrigerant in the bleed line 46 to pass through the horizontal inlet and discharge through the vertical outlet at the bottom of the casing.
  • Chamber 84 is divided by the diaphragm into an upper section 98 which is coupled by means of capillary tube 57 to the bulb 56.
  • the equalizing line 53 opens up into the valve casing 80 and being in fluid communication with the lower section 100 of working chamber 84 and acting on the bottom of the diaphragm 82 in opposition to the pressure exerted by the thermo-expansive material which additionally fills the upper chambers section 98 as well as the capillary tube 57 and bulb 56.
  • the temperature responsive bulb 56 is, operatively positioned with respect to the compressor discharge, that is, it is mounted on or adjacent to conduit 14 which couples the discharge side of the compressor to the inlet side of the condenser 12. Alternatively, it could sense oil temperature downstream of the oil separator 25, which is proportional to compressor load. However, this is only one of the parameters affecting the operating of the liquid injection expansion valve 52, the other being the pressure within equalizing line 53 which provides the valve 52 with a signal respresentative of condensing temperature and which acts on the opposite side of the diaphragm to the signal indicative of a compressor discharge temperature.
  • the compressive force acting on the valve stem 86 through the fixed disc 90 and thus on the diaphragm in the same direction as the force emanating from the equalizing line 53, is purposely set to assist in keeping the valve closed in conjunction with the force representative of condensing temperature from line 53.
  • the present invention is directed to a system in which it is desired to keep a fixed temperature differential between the condensing temperature and the compressor discharge temperature regardless of operating conditions ofthe helical rotary screw compressor. It is a characteristic of the oil separator 20 that it requires approximately a 35 temperature differential between the condensing temperature of the refrigerant and the discharge temperature of the refrigerant to operate efficiently.
  • valve 50 and bulb 60 insure that the temperature of the oil stays above 140 F.
  • the function of valve 52 is to maintain a 45 superheat temperature difference between the condensing temperature and the discharge temperature. This is accomplished by selecting a spring having the desired spring constant and providing a charge within the power assembly, that is, the temperature responsive material within bulb 56 capillary 57 and the upper power assembly chamber section 98 and acting on the diaphragm 82 in opposition to the spring 90. Only under these two conditions will the valve open to variably supply the liquid refrigerant to the working chamber of the compressor in an attempt to maintain the desired conditions.
  • a compressor inlet condition is defined as an inlet pressure and an inlet temperature with the inlet temperature being above the saturated vapor level, for instance, which in that case, the refrigerant vapor has suction superheat, but if it lies on the saturated vapor line, the suction gas does not have superheat.
  • the predicted discharge temperatures basically follow an isotropic line on the pressure and enthalpy diagram.
  • the temperature responsive bulb S6 is operatively positioned with respect to the compressor discharge, and in the illustrated embodiment it is mounted on or adjacent to conduit 14 which couples the discharge side of the compressor to the inlet side of the condenser 12. Alternatively, it could sense oil temperatures downstream of oil separator 25, which is proportional to compressor load. Compressor discharge temperature, modulated by condensing temperature therefor, controls the flow rate of liquid refrigerant through the liq uid injection expansion valve such that, in general, as the temperature of the compressor discharge increases, more liquid refrigerant is injected through the expansion valve which opens to a greater extent to increase the flow of liquid refrigerant to the screw compressor 26.
  • a sight glass 58 is placed in the bleed line 46 to visually ascertain the extent of refrigerant flow through that line.
  • the solenoid valve 50 is an electrically powered on-off valve, which is responsive to oil temperature, to permit initial flow of refrigerant to the axial screw compressor 26 to limit the maximum temperature of the working fluid being compressed and thus the temperature rise of the oil within the system.
  • thermostatic bulb 60 senses the temperature of the oil from sump.28 at the discharge end of the same as it passes through conduit 32 prior to entering oil filter 30 and signals the solenoid of the liquid injection solenoid valve 50 to open the valve in response to rise in oil temperature to a predetermined minimum value of say 140 as previously described.
  • liquid injection is not required by the machine during its off cycle or when the unit is running at low refrigeration loads, since at low loads, the discharge temperature of the compressor working fluid is at a point where additional cooling is not required; Since the temperature of the oil is'a function of the temperature of the discharge working fluid from the compressor, the oil temperature at the oil pump outlet is insufficient to turn the solenoid valve on. Assuming the load on the chiller or evaporator 16 increases to the point where the oil temperature reaches the'pr edetermined minimum level necessary to open the solenoid valve 50, liquid refrigerant flows through the bleed line 46, at slightly less than the discharge pressure from the compressor unit 10, to the liquid injection expansion valve 52.
  • the thermostat bulb 56 modulates the volume of liquid injection expansion valve 52 and only the amount of liquid refrigerant is injected into the compressor which is sufficient to maintain the gas discharge temperature within a predetermined range.
  • the discharge temperature of the working fluid increases and bulb 56 senses the demand for more liquid refrigerant to be injected into the screw compressor just upstream from the discharge side of the screws.
  • the expansion valve 52 opens wider to deliver more liquid refrigerant through bleed line 46 to the compressor 26, and conversely as the load within the evaporator or chiller falls off, the compressor discharge temperature decreases and the expansion valve will throttle back to reduce the supply of liquid refrigerant delivered to the compressor. ln the illustrated embodiment, it is not necessary to employ an external separate oil cooler.
  • shutoff valves 48 and 54 The precentage of oil in the refrigerant which is a liquid and at relatively high pressure in the condenser, is very small, from zero to three per cent or less and does not materially interfere with the liquid refrigerant which is injected through bleed line 46 just upstream from the discharge side of the screws. Some minor flashing or vaporization may occur intermediate of the liquid expansion valve and the port (not shown) within thescrew compressor 26, but most'of the'expansion and vaporization takes place within the space defined between the lobes of the screws which space captures the working fluid gas which is compressed as it moves from the intake side to the discharge side of the intermeshed screws.
  • the purpose of shutoff valves 48 and 54 is to isolate the bleed line components from the main components of the refrigeration system for maintenance purposes.
  • the thermostat which is responsive to the temperature of the oil at the oil pump discharge and which controls the on-off solenoid valve 50, is positioned to be responsive to the temperature of the oil, since the outside surface of the oil line heats up much quicker than the outside surface of the refrigerant discharge conduit 14 and therefore the change in the oil temperature conduit surface anticipates the subsequent increase in the temperature of refrigerant working fluid conduit exterior surface and effects liquid refrigerant 'truly limits the discharge temperatures at the heart of the compressor and by selecting the point of injection of the liquid refrigerant, cooling is achieved without materially affecting the volumetric capacity of the compressor. Injection occurs when the suction stroke has been completed and the compression stroke is well in process, and may in fact occur just at the point of full compression prior to discharge from the compressor.
  • the injection of liquid refrigerant during the compression stroke permits the heat required to vaporize the liquid refrigerant to remove a significant part of the heat generated in the compression process and thereby materially reducing the discharge temperature of the working fluid and, of course, the maximum temperature to which the oil is subjected.- Further, since the pressure level of the injected refrigerant is only slightly less than the discharge pressure of the working fluid, the horsepower requirement to raise the vaporized refrigerant to the full discharge pressure is minimum and the very small horsepower increase necessary to achieve this end does not seriously affect the overall efficiency of the compressor.
  • FIG. 2 there is illustrated schematically a refrigeration system similar to that of FIG. 1 which incorporates liquid refrigerant injection for oil cooling purposes and when the liquid injection system components are modified to some extent.
  • the screw compressor unit or assembly 110 comprises a screw compressor motor 124 for driving the screw compressor 126 which receives the gaseous or vaporous refrigerant working fluid through intake line 122 and compresses the same for discharge over the screw compressor motor 124, the high pressure vapors exiting from the screw compressor through discharge conduit 114.
  • the oil separator 125 is illustrated schematically, in this case, as being downstream of the screw compressor motor and upstream of a conventional water cooled condenser and positioned within line 114 intermediate of a screw compressor assembly 110 and condenser 112.
  • a liquid refrigerant bleed line 146 permits some of the high pressure liquid refrigerant to be bled to the screw compressor 126 for injection through an injection port 170 defined by the headed end of the arrow which lies intermediate of the suction and discharge sides of the screw compressor 126.
  • Refrigerant vapor returns from the chiller or evaporator 116 to the suction side of the screw compressor through line 122.
  • the simplified liquid refrigerant injection control system in this embodiment consists essentially of a thermostat in the form of a temperature sensitive bulb 156 which carries along with capillary 157, a temperature responsive material which upon expansion modulates the valve 152 to thereby variably increase the delivery of liquid refrigerant to the injection port 170 of screw compressor 126.
  • gualiai ng line 1 5 5 provides a second input to valve 152 responsive to condensing pressure.
  • FIG. 3 a further embodiment of the present invention is shown for a refrigeration system which is identical in most respects to the refrigeration system of FIG. 2. In this case, similar components are given similar numerical designations.
  • the bleed line 146 carries a solenoid operated on-off valve 150 similar to liquid injection solenoid valve 50 of the first embodiment and, in which case, the electric control line 157 provides electrical current to the solenoid under control of thermostat operated switch contacts at a control panel 171 intermediate a thermostat bulb 172 operatively associated with the discharge line 114 atthe discharge end of the screw compressor assembly 110.
  • Bulb 172 could alternatively be positioned so as to sense directly the temperature of the separated oil at or downstream of oil separator 125.
  • the thermostat bulb 172 carries a temperature responsive material such as a liquid or a gas along with capillary tube 173 which is coupled to the thermostat (not shown) within panel 171.
  • Switch contacts close the current through line 157 which includes the solenoid associated with valve 150 and which is powered from a source (not shown).
  • the solenoid valve 150 merely cycles on and off and the function of the thermostat is to either allow injection .of liquid refrigerant via port to the screw compressor 126 or prevent such injection of liquid refrigerant thereon. In this case, there is no modulation or variation in the rate of flow of refrigerant to the injection port 170 and, at high temperatures, liquid refrigerant is injected into the screw compressor while at low working fluid discharge temperatures, there is an absence of liquid injection.
  • the thermostat 172 bulb merely functions to signal the valve 150 to open or close and thus continually cycles the valve during operation of the system. Again, while the system is simplified, a possible detrimental effect is the fact that the cycling of the components may reduce the life of the same well below the design life of the major components of the machine, such as the screw compressor, etc.
  • FIG. 4 illustrates a fourth embodiment of the invention, again as applied to a refrigeration system essentially identical to that of FIGS. 2 and 3 and, in which case, the like components are given like numerical designations.
  • the condenser 112 rather than being positioned close to and at the same height as the other components of the refrigeration system, is positioned at a much greater height.
  • the refrigeration system may be one incorporated within a relatively tall building as, for instance, where the condenser 112 is positioned on the roof, perhaps some 10 or 15 stories above the screw compressor assembly 110, and the other components of the system which may well be in the basement of the same building.
  • the bleed line 174 creates a static pressure head relative to the injection port 176 which adds materially to the pressure of the liquid refrigerant emanating from condenser 112.
  • the combined pressure head of the liquid refriger ant within belled line 174 may be in excess of the discharge pressure of the screw compressor discharge working fluid.
  • the system employs a tempera ture sensitive bulb 156 carrying a temperature expansible material as does capillary 157 to modulate operation of valve 152 proportional to the temperature of the discharge gas, further modulated by the condensing pressure for the working fluid via equalizing line 153 i in similar fashion to the embodiment of FIGS. 1 and 2, the bulb 156 being operatively associated with the conduit 114 at the discharge side of the screw compressor assembly 110.
  • the valve 152 variably controls the flow of liquid refrigerant at high pressure which enters the screw compressor through the injection port 176, in this'case very close to the discharge side of the same.
  • the condenser may be a distinct height advantage over the other components of the system.
  • FIG. 6 illustrates an alternate embodiment of the present invention in which the liquid refrigerant is ported to the working chamber of the helical rotary screw compressor by means of a capacity control slide valve associated therewith.
  • the screw compressor may be, in general, identical to the compressor illustrated in FIG. 1 as at and including the hermetically sealed type and including from left to right, the screw compressor itself, as at 26, the hermetic drive motor 24 and terminating in an oil separator 25 which drains the oil to a sump (not shown) through an oil discharge passage 27, the compressed refrigerant working fluid exiting through an axial port 29 to gas discharge conduit 14.
  • the unloader 40 consists of a reciprocating capacity control slide valve 204 mounted within the rotor housing 202 and fixed at one end to an outer tubular shaft or rod 206 which is concentrically fixed to an inner shaft or rod 208, the slide valve 204 moving therewith at one end of both shafts 206 and 208 in response to shifting of piston 210 within cylinder 214 of the unloader hydraulic drive motor 212.
  • the inner shaft 208 sealably carries a fitting 216, closing off one end of tubular shaft 204, while the opposite end of the inner shaft is fixed to an end wall 218 of slide valve 204.
  • Concentric shafts or rods 206 and 208 are sealably and slidably carried by the compressor housing.
  • Valve 204 reciprocates between limits defined by casing end wall 219 and a valve stop 220 and, when moved to the position illustrated in FIG. 6, provides a relatively large opening 222 within the bottom of the rotor housing.
  • the working chamber 224 carries the intermeshed male and female screws or rotors 226 and 228.
  • the capacity control slide valve forms no part of the present invention as such, and, when in the closed position.
  • the present invention in the embodiment of FIG. 6 provides the means for supplying both oil to the working chamber 224 under high pressure for lubrication and sealing of the rotary screws and also for porting liquid refrigerant to the working chamber, the expansion of which achieves cooling of the screws, the working fluid and any oil in contact therewith.
  • a suitable passage 240 isformed between the inner and outer shafts 206 and 208 through which oil under pressure is delivered from flexible line 236 and the fitting or coupling means 238.
  • Passage 240 extends axially, FIG. 6a, and opens up into an oil chamber 242 defined by an end wall 244 of the slide valve 204 and a partition member 246 as well as spaced walls 248 and 250 at the top and bottom of the slide valve 204. Oil is ported directly to the working chamber 224 through one or more inclined passages 252, thus permitting the oil to reach the intermeshed screws intermediate of the suction and discharge sides of the compressor.
  • the present invention is directed to the employment in this embodiment of a second axial conduit, preferably by making the inner shaft 208 hollow, that is, providing it with a bore 254 and supplying by means of a second flexible conduit 256, liquid refrigerant via bleed line 46 and coupling means or fitting 216 to a liquid refrigerant chamber 260 defined by the right hand end wall 218 of the slide valve 204, upper and lower walls 248 and 250 and the partition 246, which spaces the same and sealably surrounds the internal shaft 208.
  • the bore 254 terminates near the right hand end, and one or more radial passages 266 permit delivery of the liquid refrigerant to chamber 260.
  • one or more oblique or inclined passages 268 downstream of the oil injection passages 252 open up into the working chamber 224 to insure liquid injection of the refrigerant at predetermined points in the compression cycle when the valve is fully closed and the compressor is working at maximum capacity.
  • the point of injection for the liquid refrigerant changes and shifts mechanically, however, because the capacity is reduced, the net effect is positive rather than negative in terms of compressor efficiency, etc.
  • FIG. 7 An alternative arrangement for delivering both oil to its injection port within the capacity control slide valve and the refrigerant to its injection port, is shown in FIG. 7. Again, the drawing shows a portion of a hermetic compressor similar to that of FIG. 6, and like elements are given like numerical designations.
  • the shaft 206 connects the piston 210 of the hydraulic motor 212 to the slide valve 204, is provided with a first bore section 270 which acts as a central oil passage, this bore section being provided with one or more radial openings 272 permitting the oil to enter the oil chamber 242 again defined by end wall 244, partition 246, a top wall 248, and a bottom wall 250.
  • Oil under pressure is delivered to shaft 206 through line 236 via fitting 238.
  • a plug 274 closes off the hollow shaft 206.
  • Extending coaxially therewith but in the opposite direction is a second bore section 276.
  • Shaft 206 protrudes through the right hand end wall 218 which forms with top and bottom walls 248 and 250 and the partition 246, a liquid refrigerant chamber 260.
  • a series of radial passages 282 permits the liquid refrigerant which enters through a flexible conduit 284 coupled to the outer end of shaft 206 by coupling means 286 to fill the chamber and to be injected through one or more inclined passages 268 which are ported to the working chamber 224 in similar manner to the embodiment of FIG. 6, downstream of oil passages 252.
  • the costruction is somewhat simplified in that the necessity for multiple concentric tubes or shafts is elimihated and the oil and refrigerant are essentially isolated from each other. Further, the natural introduction from opposite sides permits the injection passages of the oil to lie upstream of the refrigerant injection passages.
  • liquid refrigerant injection system in which refrigerant is injected through passages carried by the slide valve, is controlled identically to the manner set forth with respect to those systems illustrated in FIGS. 1-4 inclusive.
  • the injection of the liquid refrigerant which maintains lower operating temperatures for thecompressor. This is especially advantageous for refrigeration systems in which water is unavailable as a coolant, especially where water is normally employed as a liquid for an oil cooler incorporated within the oil system.
  • this system is particularly advantageous especially where the oil cooler may be dispensed with, eliminating all the problems and foul ups in terms of oil leakage and water requirements.
  • this system has application also to refrigeration systems in which an oil cooler is required to partially maintain the oil temperature within defined limits.
  • the methods involve bleeding high pressure refrigerant liquid downstream of the condensor and directing it through a temperature modulated expansion valve where it enters the screw compressor working chamber through a port which lies intermediate of the suction and discharge sides of the compressor.
  • a thermostat sensitive to the compressor discharge temperature for instance, variably controls the volume of bled liquid refrigerant through the expansion valve which operates in conjunction with a solenoid valve normally interposed in the bleed line downstream of the liquid injection expansion valve.
  • the solenoid valve may be controlled by a second thermostat which is sensitive to the temperature of the oil in the sump, and preferably at the discharge side of the oil pump.
  • the temperature varies with compressor load and the solenoid valve acts to ensure that liquid refrigerant flows through the bleed line to the liquid expansion valve only-during compressor operation and when the compressor is running above the minimum load condition.
  • the solenoid valve is often subjected to chattering which is detrimental to the component life, and is also undesirable due to the noise problem.
  • the pressure'differential across the bleed line is relatively small.
  • the flow in the liquid injection assembly constituted by the bleed line is modulated by three mechanisms; (1) the thermal expansion valve; (2) the port location which is the available differential between the liquid line; and (3) the point of the compression cycle of the screw compressor at which injection occurs. This differential in turn is effected by the operating conditions relative to the built in compression ratio of the screw compressor.
  • the liquid injection is shut off and the operating differential (P -P drops to some point below the built in ratio because the liquid pressure drops to, or below the port pressure.
  • the fourth mechanism comprises the injection port size; for instance if the port size drilled into the compressor is too small, the injection rate is restricted at high flow rates due to the AP in the port itself.
  • valve chattering a condition which is normally present when valve chattering occurs is the existence of a solid column of liquid downstream of the thermal expansion.
  • the effect of the solid column of liquid refrigerant feeding directly to the motor is to produce a water hammer" effect.
  • This pulsation combined with the operation of the pilot operated solenoid valve in the marginal AP range, is the basic cause of the liquid injection solenoid valve chattering.
  • Attempts have been made to minimize the valve chattering in the marginal AP ranges by such steps as moving the injection port towards-the suction side of the compressor to increase the AP from discharge pressure to the. injection port. While this minimizes the chances, it does not completely eliminate the possibility of operating with a solid column of liquid, however, the moving of the port may have a highly adverse effect on performance.
  • FIG. 8 illustrates in perspective view, a closed loop refrigeration system incorporating a rotary screw compressor which employs the improved liquid refrigerant injection cooling system of the present invention in an alternative form.
  • the principle components of the refrigeration system comprise; the axial, rotary screw compressor assembly 310 consisting of the axial screw compressor 326, the'electric drive motor 324 and oil separator 325 axially positioned in that order from the suction or intake side of the assembly as defined by conduit 322.
  • the refrigeration system further comprises a condenser 312 which receives the compressor discharge through conduit 314 and cools the same by water or other heat exchange medium passing therethrough.
  • conduit 318 which connects the condenser 312 to the evaporator or chiller 316, with the refrigerant passing through a filter dryer 320 incorporated within conduit 318 intermediate of condenser 312 and chiller 316.
  • the conduit 322 connects the discharge side of the chiller or evaporator 316 to the intake or suction side of the axial screw compressor 326.
  • Lubricating oil is circulated through the compressor assembly 310 and, in fact, mixes to a limited extent with the refrigerant working fluid during compression, but the lubricating oil is separated from the working fluid by oil separator 325 associated with the electric drive motor 324 at the downstream or discharge side of the screw compressor.
  • the separated oil accumulates with an oil sump 328 via pipe or passage 327 and is pressurized by the oil pump (not shown) within sump 328 prior to being returned to the compressor assembly 310 after passage through an oil cleaner or filter 330.
  • the oil filter 330 receives oil from sump 328through line 332 and discharges the same through a plurality of lines 334 indicated generally at 334 at the discharge side of the oil filter 330.
  • the refrigerant working fluid which may comprise Freon or the like, enters the compressor assembly 310 at the right hand end through inlet or .in-
  • conduit 322 take conduit 322 in gaseous or vapor form at relatively low pressure and is-copressed by the rotary screw compressor 326 to a relatively high pressure for discharge over and across the motor (not shown) of electric motor 324.
  • the refrigerant as a high pressure gas exits from the oil separate 325 and passed to the condenser 312 where it condenses, by contacting with a coolant such as water.
  • the high pressure liquid refrigerant then passes to the filter dryer 320 via conduit 318 and to the chiller or evaporator 316.
  • the high pressure liquid refrigerant expands within the evaporator 316 to cool the load which may consist of water or other heat exchange fluid within the evaporator 316, with the expansion, modulation and delivery of liquid refrigerant to the evaporator or chiller being suitably controlled by means 336 within line 318 intermediate of the filter dryer 320 and the intake side of the evaporator or chiller 316.
  • lubrieating oil at relatively low temperature leaves the oil filter 330 via lines 334 to various points along the compressor assembly 310 for either lubrication purposes or to be employed as a hydraulic motor fluid for hydraulic motors such as that associated with compressor unloader 340; oil passing to the unloader for instance via line 342.
  • the present invention is directed to an improvement in a liquid refrigerant injection system which limits the discharge temperature of the compressor working fluid and thus the maximum temperature to which the system oil is subjected.
  • high pressure liquid refrigerant is bled from conduit 318 downstream of the filter dryer 320 at a bleed or tap point 344 by a small diameter, bleed tube or bleed line 346 under control of a manually operated shut-off valve 348.
  • the liquid refrigerant is directed through bleed line 346 to a liquid injection expansion valve 352 which modulates the flow of liquid refrigerant to the screw compressor 326 and to an injection port (not shown) at the termination of line 346 which opens up into the screw compressor working chamber intermediate of the discharge and suction sides of the compressor 326.
  • a second manually operable shut-off valve 354 is positioned within the bleed line 346 intermediate of the screw compressor injection port and the liquid injection expansion valve 352 to isolate the injection system when acting in conjunction with shut-off valve 348.
  • the liquid injection expansion valve 352 is of the modulating or variable flow type and preferably, is nonelectrical in operation.
  • a thermostat bulb 356 is coupled, at one end of a capillary tube 357 and coupled at the other end directly to valve 352.
  • the bulb 356, and the capillary tube 357 carry a temperature expansive material which may be liquid, gas or part liquid and part gas but which expands in response to increased temperature to variably shift a movable valve element (not shown) within valve 352 and to thereby modulate the flowof liquid refrigerant within bleed line 346 to the injection port of 'the screw compressor 326.
  • An equalizing line 353 couples the expansion valve 352 to the compressor 326 at the discharge side of the compressor.
  • the liquid injection expansion valve 352 operates identically to that of the previous embodiments.
  • the temperature responsive bulb 356 is operatively positioned with respect to the compressor discharge
  • conduit 314 which couples the discharge side of the compressor to the inlet side of condenser 312 and lies adjacent to the compressor assembly 310.
  • the compressor discharge temperature therefore controls the flow rate of liquid refrigerant through the liquid injection expansion valve 352 such that, as the temperature of the compressor discharge increases, more liquid refrigerant is injected through the injection port associated with compressor 326 under control of the expansion valve 352 which opens to a greater extent.
  • bleed line 346 has positioned, downstream from the manual control valve 348 a fluid pressure operated direct acting, on-off valve 364 which is connected to oil sump 328 through supply line 368 and is prsx dwyvi h serum o ra l q 37 h by-pass line 370 couples the oil supply line 368 to the oil sump 328 through a fluid restriction or orifice 372 such that, when the oil passes througr the supply line 368 as a result of energization of solenoid valve 374, the valve 364 is maintained in open position.
  • solenoid valve 374 permits relief of the system pressure after the solenoid valve again closes to drain the line through restriction 372 back to the sump.
  • Energization of solenoid valve 374 occurs much in the same manner as that of the previous embodiments. That is, a thermal expansion bulb 360 or a thermostat bulb is filled with a temperature expansive material such as liquid or gas and which is coupled by capillary tube 362 to a panel not illustrated in FIG. 8 but illustrated in block form at 376 and FIG. 9, panel 376 including a thermostat (not shown) having normally open contacts but closing in response to expansion of the material filling bulb 360 and capillary 362 so as to close an electrical circuit to the solenoid associated with solenoid valve 374 through electrical line 378.
  • a thermal expansion bulb 360 or a thermostat bulb is filled with a temperature expansive material such as liquid or gas and which is coupled by capillary tube 362 to a panel not illustrated in FIG. 8 but illustrated in block form at 376 and FIG. 9, panel 376 including a thermostat (not shown) having normally
  • the solenoid valve therefore comprises an on-off valve permitting the selective application of high pressure oil to the direct acting fluid pressure operated valve 364 Upon application high pressure fluid, valve 364 moves from fully closed to fully opened position permitting the expansion valve 352 to modulate the flow of liquid refrigerant to the compressor injection port.
  • shut-off valve 364 which is responsive to compressor load is not pilot operated, and since it is not dependent upon a pressure drop across the valve to maintain the valve open, chattering due to minor changes in pressure differential is eliminated.
  • the solenoid valve 374 which is responsive to the oil temperature and indirectly the compressor load is open, the direct operating, fluid pressure responsive valve 364 is maintained in open position and high pressure refrigerant liquid is available to the compressor working chamber via the injection port to the extent that the modulation valve 352 varies the flow of same.
  • valve 364 Since the operation of valve 364 is independent of the controlled medium, that is the liquid refrigerant passing through the feed line, the operation will be unaffected by modulation of the liquid flow through line 346 and the elimination of the modulation effects in terms of valve 364 virtually eliminates the chances of valve chattering.
  • a closed loop refrigerationsystem including, in order: a screw compressor, a condenser, and an evaporator, and having a refrigerant circulating therebetween, the improvement comprising:
  • said means for bleeding and injecting 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.
  • valve comprises an on-off valve and wherein a thermostat responsive to the compressor discharge temperature is operatively coupled to said onoff valve for controlling operation of the same.
  • the refrigeration system as claimed in claim 5 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 to modulate flow of liquid refrigerant through said bleed line.
  • valve comprises an on-off valve, and wherein a thermostat responsive to compressor discharge temperature is operatively coupled to said onoff valve for controlling the operation of the same.
  • valve comprises an on-off valve and wherein a thermostat responsive to the compressor discharge temperature is operatively coupled to said onoff valve for controlling operation of the same.
  • 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.
  • 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.
  • valve comprises a movable valve member normally biased to valve closed position, and means responsive to the temperature of the compressor discharge tending to operate in opposition to said bias, and further means responsive to the condensing temperature of the refrigerant working fluid on said movable valve element tending to maintain said valve element in valve closed position.
  • valve 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 against the bias of said concentric coil spring.
  • 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.
  • 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.
  • 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
  • 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,
  • 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 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.
  • 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 onoff 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.
  • 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
  • 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.
  • 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.

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US3859814A (en) * 1973-10-03 1975-01-14 Vilter Manufacturing Corp Variable capacity rotary screw compressor
US4020642A (en) * 1973-11-19 1977-05-03 Hall-Thermotank Products Limited Compression systems and compressors
US3885402A (en) * 1974-01-14 1975-05-27 Dunham Bush Inc Optimized point of injection of liquid refrigerant in a helical screw rotary compressor for refrigeration use
DE2529331A1 (de) * 1974-07-26 1976-02-12 Dunham Bush Inc Schraubenkompressor
US4049410A (en) * 1974-07-29 1977-09-20 Allan Sinclair Miller Gas compressors
US4006603A (en) * 1975-06-13 1977-02-08 Vapor Corporation Air conditioning system for a railway vehicle
US4062199A (en) * 1975-06-24 1977-12-13 Kabushiki Kaisha Maekawa Seisakusho Refrigerating apparatus
FR2325832A1 (fr) * 1975-09-29 1977-04-22 Svenska Rotor Maskiner Ab Procede et dispositif de refroidissement de l'huile dans un systeme comportant un compresseur avec alimentation en huile
US4086072A (en) * 1976-01-29 1978-04-25 Dunham-Bush, Inc. Air source heat pump with multiple slide rotary screw compressor/expander
US4261180A (en) * 1978-01-06 1981-04-14 Hitachi, Ltd. Refrigerator
US4328684A (en) * 1978-04-10 1982-05-11 Hughes Aircraft Company Screw compressor-expander cryogenic system with magnetic coupling
US4291547A (en) * 1978-04-10 1981-09-29 Hughes Aircraft Company Screw compressor-expander cryogenic system
US4311021A (en) * 1978-04-10 1982-01-19 Hughes Aircraft Company Screw compressor-expander cryogenic system with mist lubrication
JPS56117056A (en) * 1980-02-22 1981-09-14 Hitachi Ltd Refrigerating cycle
US4275570A (en) * 1980-06-16 1981-06-30 Vilter Manufacturing Corporation Oil cooling means for refrigeration screw compressor
FR2491558A1 (fr) * 1980-10-03 1982-04-09 Dunham Bush Inc Systeme a gaz comprime a boucle fermee avec compresseur a vis lubrifie par huile pulverisee
US4515540A (en) * 1983-11-22 1985-05-07 Frick Company Variable liquid refrigerant injection port locator for screw compressor equipped with automatic variable volume ratio
US4553911A (en) * 1983-11-22 1985-11-19 Frick Company Method of coding the oil in screw compressors equipped with automatic variable volume ratio
US4573324A (en) * 1985-03-04 1986-03-04 American Standard Inc. Compressor motor housing as an economizer and motor cooler in a refrigeration system
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FR2198104A1 (enrdf_load_stackoverflow) 1974-03-29
ZA735392B (en) 1974-07-31
IT999535B (it) 1976-03-10
FR2198104B1 (enrdf_load_stackoverflow) 1976-11-19
AU5979173A (en) 1975-03-06
BR7306788D0 (pt) 1974-08-29
JPS4964950A (enrdf_load_stackoverflow) 1974-06-24
DE2343334A1 (de) 1974-03-14

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