Atty. Dkt. No.: 26427-0005-PCT

REFRIGERATION SYSTEM

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims 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 present invention relates to a systems and methods of lubrication in refrigeration systems. The application relates more specifically to systems and methods of recovering lubricant, particularly an immiscible lubricant, that is entrained in liquid refrigerant, and returning the recovered lubricant to a compressor in the refrigeration or chiller system.

[0003] Chillers and refrigeration systems typically employ gas compressors to compress refrigerant gas from a vapor state to a liquid state. In many cases, a relatively small amount of lubricant used by the system compressor, such as for bearing lubrication or cooling or sealing purposes, may become entrained in the compressed refrigerant gas discharged from the compressor. Although some of the entrained lubricant is separated from the refrigerant gas, a portion of the lubricant may remain entrained in the refrigerant gas and subsequently flow to the system condenser. At the condenser, the lubricant mixes with liquid refrigerant created by the heat exchange process occurring within the condenser. The mixed stream of lubricant and liquid refrigerant exits the condenser and flows through the system's expansion device and into the system evaporator.

SUMMARY

[0004] The present invention relates to a system including a compressor, a condenser, an expansion device and an evaporator connected in a closed refrigeration loop with a

Atty. Dkt. No.: 26427-0005-PCT

refrigerant being circulated in the closed loop. The evaporator has a mixture of liquid refrigerant and lubricant disposed in the evaporator. A collection vessel is arranged to receive the mixture. The collection vessel further includes a heating element arranged to heat the mixture to evaporate the liquid refrigerant, wherein refrigerant in a gaseous phase exits the vessel and the lubricant is drained from the vessel.

[0005] The present invention also relates to a system including a first valve configured to control a flow of a mixture including liquid refrigerant and lubricant from an evaporator through a first flow path. A collection vessel is arranged to receive the mixture from the first flow path. The collection vessel includes a pumping device configured to circulate the mixture by generation of fluid pressure resulting from thermal expansion, A second valve is arranged to return the evaporated liquid refrigerant to the evaporator through a second flow path. A third valve is arranged to return lubricant into the compressor through a third flow path. The gas refrigerant exits the collection vessel through the second flow path and the lubricant returned from the evaporator exits the collection vessel via a drain pipe to the compressor.

[0006] The present invention further relates to a method of recovering lubricant for a compressor lubrication system of a refrigeration system. The method includes circulating a refrigerant in a closed refrigeration loop connecting a compressor, a condenser, an expansion device and an evaporator; providing in the evaporator a mixture of liquid refrigerant and lubricant; receiving the mixture in a collection vessel with a heating element; heating the mixture to evaporate the liquid refrigerant; exhausting the refrigerant in a gaseous phase from the collection vessel; and draining the lubricant from the collection vessel.

BRIEF DESCRIPTION OF THE FIGURES

|0007] FIGS. 1 and 2 show exemplary embodiments of environments incorporating a refrigeration system.

[0008] FIG. 3 shows a perspective view of an exemplary embodiment of a refrigeration system.

Atty. Dkt. No.: 26427-0005-PCT

[0009] FIG. 4 shows a front view of the refrigeration system shown in FIG. 3.

[0010] FIG. 5 schematically illustrates an exemplary embodiment of a multistage refrigeration system.

[0011] FIG. 6 is a schematic illustration of an exemplary embodiment of an immiscible lubricant return system in accordance with embodiments of the application.

[0012] FIG. 7 is a schematic illustration of an exemplary embodiment of an immiscible lubricant return system in accordance with embodiments of the application.

[0013] FIG. 8 is a schematic illustration of yet another exemplary embodiment of an immiscible lubricant return system in accordance with embodiments of the application;

[0014] FIG. 9 schematically illustrates still another exemplary embodiment of an immiscible lubricant return system in accordance with embodiments of the application.

[0015] FIG. 10 schematically illustrates another exemplary embodiment of an immiscible lubricant return system in accordance with embodiments of the application; and

[0016] FIG. 11 schematically illustrates one more exemplary embodiment of an immiscible lubricant return system in accordance with embodiments of the application.

[0017] FIG. 12 illustrates a floating funnel for use with the immiscible lubricant return system.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0018] FIGS. 1 and 2 illustrate several exemplary applications for a multistage refrigeration system (also referred to as a cascade refrigeration system or a multi-pressure refrigeration system). Multistage refrigeration systems can include a first stage system (also referred to as a high side system) and a second stage system (also referred to as a low side system) that are interconnected by a heat exchanger and can be used to provide different levels of cooling capacity and/or achieve low temperatures that are difficult to achieve with a single vapor compression cycle.

Atty. Dkt. No.: 26427-0005-PCT

[0019] FIG. 1 shows a multistage refrigeration system 10 that can provide both refrigeration and freezing capacity for a supermarket 12 in a commercial setting. The second stage system of 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, and 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. The second stage system of 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, and 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.

[0020] FIG. 2 shows the use of a multistage refrigeration system 10 as 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 may 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. Once the product is frozen between plates 30, the product may be difficult to remove from plate freezer 28

Atty. Dkt. No.: 26427-0005-PCT

because the product may be frozen to plates 30. A defrost system that warms plates 30 but does not thaw the product between plates 30 is used to assist in the removal of the product from between plates 30. FIGS. 1 and 2 illustrate exemplary applications only and multistage refrigeration systems are used in many other environments as well.

[0021J FIGS. 3 through 5 illustrate a multistage refrigeration system (shown schematically in FIG. 5). The multistage refrigeration system can include a first stage system 32 and a second stage system 34 that are interconnected by a heat exchanger 36. Heat exchanger 36 can be a plate heat exchanger, a shell and tube heat exchanger, a plate and shell heat exchanger or any other suitable type of heat exchanger. First stage system 32 can be a vapor compression system that circulates a refrigerant through a compressor 38, a condenser 40, a receiver 42 (optional), an expansion device 44, and an evaporator 46 that is incorporated into heat exchanger 36. Some examples of fluids that may be used as refrigerants in first stage system 32 are carbon dioxide (CO2; for example, R-744), nitrous oxide (N2O; for example, R -744A), ammonia (NH3; for example, R-717), hydro fluorocarbon (HFC) based refrigerants (for example, R-410A, R- 407C, R-404A, R-134a), other low global warming potential (GWP) refrigerants, and any other suitable type of refrigerant.

[0022] Second stage system 34 can be a vapor compression system that circulates a refrigerant through a compressor 48, a condenser 50 that is incorporated into heat exchanger 36, a receiver or separator 52, a pump 54, and a first expansion device 56 and a first evaporator 58 that can be in parallel with a second valve 60 and second evaporator 62, According to another exemplary embodiment, second stage system can be operated with only first expansion device 56 and first evaporator 58. According to still another exemplary embodiment, second stage system 34 can be operated as a volatile system by removing compressor 48, first expansion device 56 and first evaporator 58. Some examples of refrigerants that may be used in second stage system 34 are carbon dioxide (CO2; R-744), nitrous oxide (N2O; R-744 A), or mixtures of carbon dioxide and nitrous oxide, or hydrocarbon based refrigerants (for example, R- 170). The refrigerant in the second stage can be the same or different than the refrigerant in the first stage. When

Atty. Dkt. No.: 26427-0005-PCT

second stage system 34 is operated as a volatile system, the refrigerant circulating through the system can be replaced with a glycol solution or a brine solution,

[0023] In first stage system 32, when operated sub-critically, that is, below the critical pressure for the refrigerant being circulated in first stage system 32, compressor 38 compresses a refrigerant vapor and delivers the compressed vapor to condenser 40 through a discharge line. Compressor 38 can be a screw compressor, reciprocating compressor, centrifugal compressor, rotary compressor, swing link compressor, scroll compressor, turbine compressor, or any other suitable type of compressor. Within condenser 104, the compressed vapor transfers heat to a fluid, for example, water from a cooling tower, and as a result condenses from a vapor phase refrigerant to a liquid phase refrigerant. The condensed refrigerant exiting condenser 40 can be stored in receiver 42 before flowing through expansion device 44 to evaporator 46 in heat exchanger 36.

[0024] The condensed liquid refrigerant enters evaporator 46 and absorbs heat from fluid being circulated in condenser 50 in heat exchanger 36 by second stage system 34. The absorbed heat causes the liquid phase refrigerant to evaporate into a vapor phase refrigerant. The vapor refrigerant exits evaporator 46 exits and returns to compressor 38 by a suction line to complete the cycle.

[0025] First stage system 32 can be operated as a transcritical or supercritical system. During transcritical operation, first stage system 32 can be operated partly below (sub- critical) and partly above (supercritical) the critical pressure of the refrigerant circulated in first stage system 32. The discharge pressure of compressor 38 (or high side pressure) can be greater than the critical pressure of the refrigerant, for example, 73 bar at 31 deg C for carbon dioxide. Furthermore, during transcritical operation, the refrigerant is maintained as a single phase refrigerant (vapor phase) in the high pressure side of first stage system 32 and is first converted into the liquid phase when it is expanded in expansion device 44. When operated as a transcritical system, the refrigerant from compressor 38 flows to a gas cooler (which can operate as a condenser in low ambient temperatures permitting the system to operate sub-critical) that cools the refrigerant by heat exchange with another fluid. The cooling of the refrigerant gradually increases the

Atty. Dkt, No.: 26427-0005-PCT

density of the refrigerant. During transcritical operation of first stage system 32, the high side pressure can be modulated to control capacity or to optimize the coefficient of performance by regulating the refrigerant charge and/or by regulating the total internal high side volume of refrigerant.

[0026] In second stage system 34, compressor 48 compresses a refrigerant vapor and delivers the compressed vapor to condenser 50 through a discharge line. Compressor 48 can be a screw compressor, reciprocating compressor, centrifugal compressor, rotary compressor, swing link compressor, scroll compressor, turbine compressor, or any other suitable type of compressor. The vapor refrigerant enters condenser 50 and transfers heat to the fluid being circulated in evaporator 46. in heat exchanger 36 enters into a heat exchange relationship with the fluid being circulated in evaporator 46 by first stage system 32, and undergoes a phase change to a refrigerant liquid as a result. The liquid phase refrigerant exits condenser 50 and flows to receiver 52. From receiver 52, the refrigerant is circulated to a first expansion device 56 and first evaporator 58 and then to a valve 60 and a second evaporator 62 by pump 54.

[0027] In first evaporator 58, the liquid refrigerant from first expansion device 56 enters into a heat exchange relationship with a cooling load, for example, a fluid, and undergoes a phase change to a refrigerant vapor as a result. The refrigerant vapor exits first evaporator 58 and returns to compressor 48 to complete the cycle. In second evaporator 62, the liquid refrigerant from valve 60 absorbs heat from a cooling load, for example, a fluid, and may undergo a phase change to a refrigerant vapor. However, according to one exemplary embodiment, the amount of refrigerant liquid provided to second evaporator 62 may exceed the heat exchange capabilities of the cooling load, causing less than all of the liquid refrigerant to undergo a phase change. Thus, the refrigerant exiting second evaporator 62 may be a mixture of refrigerant vapor and refrigerant liquid. The refrigerant fluid exiting second evaporator 62, regardless of the phase, returns to receiver 52. Receiver 52 can also have a connection to the discharge line from compressor 48 to provide refrigerant vapor from receiver 52 to the discharge line and subsequently to condenser 50 in heat exchanger 36.

Atty. Dkt. No.: 26427-0005-PCT

[0028] Compressor 38 of first stage system 32 and compressor 48 of second stage system 34 can each be driven by a motor or drive mechanism. The motor used with compressor 38 or compressor 48 can be powered by a variable speed drive (VSD) or can be powered directly from an alternating current (AC) or direct current (DC) power source. The VSD, 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. The motor used with compressor 38 or compressor 48 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, the motor used with compressor 38 or compressor 48 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 the motor used with compressor 38 or compressor 48.

[0029] Referring next to FIG. 6, evaporator 46, which also may function as a receiver, receives a mixture of liquid refrigerant and lubricant from a condenser that accumulates in the bottom portion of evaporator 46. In the embodiments illustrated in FIGS. 6 through 12, the lubricant used in the compressor is an immiscible oil or lubricant mixed with the liquid refrigerant that has a lower density than the liquid refrigerant. For example, according to exemplary embodiments, the lubricant may be a synthetic petroleum such as poly-alpha-olefin that is immiscible in a carbon dioxide refrigerant. It should be understood that the mixture of refrigerant and lubricant that is drawn from the evaporator might alternately be drawn from a low pressure receiver or a pump separator, to supply the mixture refrigerant lubricant mixture to the lubricant collection vessel or thermopump vessel. By thermopump, what is meant is a pumping device that can circulate a fluid by generation of fluid pressure resulting from thermal expansion. In the following discussion of FIGS. 6 through 10, the term evaporator includes a low pressure receiver or a pump separator, and these terms are used interchangeably. The terms oil and lubricant may be used interchangeably throughout the specification, and include synthetic petroleum lubricants.

Atty. Dkt. No.: 26427-0005-PCT

[0030] As a liquid level 79 rises in receiver 46, a measurement of the level is determined by a liquid level sensor 66. A controller 84 receives a signal from level sensor 66. An outlet 69 is disposed in a wall of receiver 46 at a predetermined height Ho- Level sensor 66 determines the actual liquid level H _A , which represents the level of liquid in receiver 46. The combination of liquid refrigerant and compressor lubricant can be estimated, based on historical data or other calculations, such as a ratio. For example, if the liquid in the receiver is typically comprised of about 80 percent refrigerant and 20 percent lubricant, the top 20 percent of the liquid level will be lubricant, because of the relative densities and immiscible properties of the lubricant and the refrigerant.

[0031] When height H _A is greater than predetermined height H ₀ , the surface layer of the liquid mixture in receiver 46 will be substantially composed of lubricant. Because the lubricant is immiscible and is less dense than the refrigerant, the liquid mixture will generally separate into two layers, a bottom layer containing primarily refrigerant and a top layer containing primarily lubricant. The predetermined height Ho is measured by level sensor 66 and set using a predetermined ratio of H _A to Ho. For example, before the level of the refrigerant layer rises above height H ₀ , controller 84 senses the desired ratio and opens an inlet solenoid valve 72 to permit the top layer of primarily immiscible lubricant to drain into an oil collector vessel 70. Oil collection vessel 70 includes a heat source 75, which according to exemplary embodiments may include a coil circulating a heated fluid or vapor, such as oil from a compressor crankcase or condenser water from an external cooling tower. As the liquid in oil collection vessel 70 is heated, the refrigerant contained in the liquid is vaporized. A solenoid valve SO is opened by controller 84 upon sensing a predetermined liquid level or pressure within oil collection vessel 70. When solenoid valve 80 is opened, refrigerant gas is returned to receiver 46 via a conduit 67 and return inlet 68. When the liquid level within oil collection vessel 70 reaches a predetermined level, a solenoid valve 82 is opened creating fluid communication with the suction line of the compressor lubrication system to return the lubricant to an oil reservoir (not shown) located within the compressor. A back-pressure control valve 76 is connected in parallel with refrigerant return solenoid valve 80 to allow

Atty. Dkt. No.: 26427-0005-PCT

excess pressure to be released from vessel 70 by automatically returning a portion of the vaporized refrigerant to receiver 46, via conduits 63 and 67.

[0032] Referring next to FIG. 7 an alternate embodiment of the oil return system employs a floating funnel 90 disposed on the surface of the liquid mixture of refrigerant and lubricant. The lubricant, which is less dense than the liquid refrigerant, rises to the surface of the liquid mixture to form a top layer containing primarily lubricant and a bottom layer containing primarily refrigerant. Floating funnel 90 is fluidly connected to oil collection vessel 70 through a drain line 71 exiting the bottom receiver 46. Funnel 90 includes a buoyant float ring 94 that floats substantially even with or above the liquid level. Float ring 94 encircles a wide opening 93 connected to a tapered sidewal! 97 that tapers radially inward to a narrow conical outlet 96. Conical outlet 96 is fluidly connected to a flexible line 92 connected to drain line 71 , which exits the bottom of receiver 46. Apertures 95 (FIG. 12) are spaced around the top periphery of funnel 90 and allow liquid to be drawn into funnel 90 and drained into conical orifice 96 at the bottom of funnel 90.

[0033] FIG. 12 shows a diagram of floating funnel 90. Reference numeral 98 generally indicates the flow path for draining the lubricant, which separates from the refrigerant to create a top layer of liquid within reservoir 46, through funnel 90 to send the lubricant to oil collection vessel 70. The lubricant enters funnel 90 through apertures 95 disposed below float ring 94. Tapered sidewalls 97 contain the lubricant within funnel 90 and direct the lubricant toward conical outlet 96. The lubricant exits conical outlet to flow through drain 71 (FIG. 7) to oil collection vessel 70.

[0034] FIG. 7 illustrates a solenoid valve 72 that controls the flow of fluid through drain line 71. Solenoid valve 72 remains closed until the level of the liquid inside receiver 46 reaches a predetermined height to ensure that a minimum depth of lubricant has separated to liquid surface. When a controller 84 senses a threshold minimum depth of liquid inside receiver 46, controller 84 opens solenoid valve 72 allowing the surface liquid, which is primarily lubricant, to drain through flexible hose 92 and outlet 71 into oil collection vessel 70. Heat source 75 is disposed within oil collection vessel 70 to provide

Atty. Dkt. No.: 26427-0005-PCT

heat for vaporizing the refrigerant. Solenoid valves 72 and 80, which can be controlled by a controller, open and close to vent the vapor refrigerant back into receiver 46. Solenoid valve 82 (FIG. 6) may be opened to return lubricant to the compressor lubricant system.

[0035] FIG. 8 illustrates an alternate embodiment of an oil return system. Four solenoid drain valves 72a, 72b, 72c, and 72d are shown in the exemplary embodiment, although more or less solenoid valves may be used for selectively draining the immiscible lubricant from receiver 46. Drain valves 72a, 72b, 72c, and 72d are spaced apart to align with discrete levels within receiver 46. Level sensor 66 indicates the level of the liquid within receiver 46. Controller 84 is in electronic communication with level sensor 66 and receives a level indicating signal and determines which of the four drain valves 72a, 72b, 72c, or 72d is submerged in the liquid and located nearest to the surface of the liquid within receiver 46. Controller 84 opens the nearest submerged drain valve 72a, 72b, 72c, or 72d to drain the top layer of liquid, which is primarily lubricant, to oil collection vessel 70. In oil collection vessel 70, the liquid is collected and heated by heat source 75. The application of heat causes the refrigerant mixed with the lubricant to boil into a vapor that rises within oil collection vessel 70 and escapes through solenoid valve 80 to return to receiver 46. The lubricant, which may mostly remain in the liquid phase, is returned to the compressor oil reservoir through solenoid valve 82. For simplicity, a controller is not shown in all of the figures, but it is understood that the solenoid valves are operated by a controller, through relay logic, programmable logic and/or microprocessor-based controls.

[0036J FIG. 9 illustrates an alternate embodiment of an oil return system that is similar to the embodiment shown in FIG. 6, and incorporates a thermopump vessel 74. Thermopump vessel 74 is located within oil collection vessel 70 and collects the recovered lubricant and sends the lubricant to a compressor discharge line 77 through conduit 81. Receiver 46, which may function as an evaporator, receives a mixture of liquid refrigerant and lubricant from a condenser. The mixture accumulates in the bottom portion of receiver 46. In the exemplary embodiments shown in FIGS. 6-12, the

Atty. Dkt. No.: 26427-0005-PCT

lubricant used in the compressor is an immiscible oil or lubricant in the liquid refrigerant, and has a lower density than the liquid refrigerant, such that the immiscible lubricant floats on the liquid refrigerant. For example, poly-alpha-olefin is synthetic petroleum that is immiscible in CO2 refrigerant.

[0037] As liquid level 79 rises in receiver 46, a measurement of the level is determined by liquid level sensor 66. Controller 84 receives a signal from level sensor 66. Outlet 69 is disposed in a wall of receiver 46 at predetermined height H ₀ . Level sensor 66 determines the actual liquid level H _A , which represents the level of liquid in receiver 46. The combination of liquid refrigerant and compressor lubricant can be estimated, based on historical data or other calculations, such as a ratio. For example, if the liquid in the receiver is typically comprised of about 80 percent refrigerant and 20 percent lubricant, the top 20 percent of the liquid level will be lubricant, because of the relative densities and immiscible properties of the lubricant and the refrigerant.

[0038] When height H _A is greater than predetermined height Ho, the surface layer of the liquid mixture in receiver 46 will be substantially composed of lubricant. Because the lubricant is immiscible and is less dense than the refrigerant, the liquid mixture will generally separate into two layers, a bottom layer containing primarily refrigerant and a top layer containing primarily lubricant. The predetermined height Ho is measured by level sensor 66 and set using a predetermined ratio of H _A to H ₀ . For example, before the level of the refrigerant layer rises above height Ho, controller 84 senses the desired ratio and opens an inlet solenoid valve 72 to permit the top layer of primarily immiscible lubricant to drain into an oil collector vessel 70.

[0039] Conduit 71 is connected at one end to evaporator 46 and at the opposite end to thermopump vessel 74, which is connected to a controller 84, to control the flow of the refrigerant and lubricant mixture entering thermopump vessel 74 from receiver 46. Thermopump vessel 74 receives the mixture of liquid refrigerant and lubricant from receiver 46 via conduit 71. Oil collection vessel 70 receives lubricant through an inlet conduit 91. The lubricant received via inlet conduit 91 collects directly in oil collection vessel 70. Inlet conduit 91 is connected to a lubricant separator 96, which provides

Atty Dkt. No.: 26427-0005-PCT

lubricant at a temperature higher than the refrigerant and lubricant mixture received from evaporator 46, Lubricant separator 96 receives a mixture of lubricant and vapor from compressor 100 through a discharge conduit 77. Lubricant separator 96 separates a portion of the miscible lubricant from the refrigerant vapor and lubricant mixture discharged by the compressor. For example, according to exemplary embodiments, baffle plates 96a and 96b may be inserted in the flow path of the vapor and lubricant mixture to separate the lubricant from the vapor. Separated lubricant 78 flows from lubricant separator 96 through inlet conduit 91 into oil collection vessel 70. The lubricant collects in the bottom of oil collection vessel 70 to a level such that a thermopump vessel within oil collection vessel 74 is at least partially submerged in the lubricant received from lubricant separator 96.

[0040] Thermopump vessel 74 accumulates refrigerant and lubricant mixture 78, The filling and evacuation of thermopump vessel 74 is controlled by level sensors 86 and 88. Control panel 84 senses a first liquid level signal from first level sensor 86, and a second liquid level signal from second liquid level sensor 88, Liquid level sensors 86 and 88 are located at different heights within thermopump 74. First level sensor 86 senses a low liquid level in the thermopump vessel 74, and is disposed beneath second liquid level sensor 88, which senses a high liquid level within the thermopump vessel 74. Controller 84 controls inlet solenoid valve 72 and thermopump vessel outlet solenoid valve 80 to open and close both valves 72 and 80 at approximately the same time. A thermostat (not shown) in controller 84 starts thermopump vessel 74 once the compressor discharge vapor temperature reaches a predetermined temperature. The predetermined input may be preset in the controller 84, either manually or automatically through an algorithm programmed into the controller.

[0041] When the liquid level drops below first level sensor 86, control panel 84 activates inlet solenoid 72 and outlet solenoid valve 80. Outlet solenoid valve 80 opens in the conduit connection to the compressor discharge side, decreasing the pressure in the thermopump vessel slightly. At approximately the same time, inlet solenoid valve 72 opens and the liquid refrigerant/ lubricant mixture starts flowing into thermopump vessel

Atty. Dkt. No.: 26427-0005-PCT

74. When second level sensor 88 senses that liquid refrigerant and lubricant mixture 79 has reached the second level, inlet solenoid valve 72 and outlet solenoid valve 80 are both closed by control panel 84. When the valves 72 and 80 are both closed, pressure within thermopump74 begins to rise due to the heat transferred from the lubricant in oil collection vessel 70 to the liquid contained within thermopump 74. When the temperature within thermopump 74 reaches a predetermined temperature, controller 84 opens outlet solenoid valve 80 allowing the liquid refrigerant and lubricant mixture to flow through conduit 81 into compressor discharge line 77 for re-introduction into oil separator 96 for separation and handling. According to other exemplary embodiments, the pressurized refrigerant and lubricant mixture from the thermopump may be discharged under pressure directly back into the oil collection vessel to be collected with the separated oil received from the oil separator. Whenever thermopump 74 stops, for example, when the compressor is operating below a predetermined capacity level, controller 84 evacuates the thermopump vessel.

[0042] Thermopump vessel 74 provides a reservoir for liquid refrigerant and lubricant mixture. Thermopump vessel 74 is a liquid-tight enclosure and may optionally include cooling fins on two or more of the vessel walls to improve heat transfer properties. Control cables 84a, 84b, 84c, 84d, 84e, 84f, and 84g interconnect controller 84 with the various devices for communication of sensor signals and operating signals. Controller 84 operates inlet solenoid valve 72 and outlet solenoid valve 80, in response to the liquid level signals received from first and second liquid level sensors 86 and 88. According to another exemplary embodiment, other signals and sensors may be input to and output by controller 84, for example, compressor discharge pressure, oil collection vessel pressure, and other operating parameters, as required to operate the oil return.

[0043] Four solenoid drain valves 72a, 72b, 72c, and 72d are shown in the exemplary embodiment, although more or less solenoid valves may be used for selectively draining the immiscible lubricant from receiver 46. Drain valves 72a, 72b, 72c, and 72d are spaced apart to align with discrete levels within receiver 46. A level sensor 66 (see, for example, FIG. 6) indicates the level of the liquid within receiver 46. Controller 84 is in

ARy. Dkt. No.: 26427-0005-PCT

electronic communication with level sensor 66 (see, for example, FIG. 6) and receives a level indicating signal and determines which of the four drain valves 72a, 72b, 72c, or 72d is submerged in the liquid and located nearest to the surface of the liquid within receiver 46. Controller 84 opens the nearest submerged drain valve 72a, 72b, 72c, or 72d to drain the top layer of liquid, which is primarily lubricant, to oil collection vessel 70. In oil collection vessel 70, the liquid is collected and heated by heat source 75. The heat causes the refrigerant mixed with the lubricant to boil into a vapor that rises within oil collection vessel 70 and escapes through solenoid valve 80 to return to receiver 46., The lubricant, which may mostly remain in the liquid phase, is returned to the compressor oil reservoir through conduit 81.

[0044] Referring next to FIG. 10, another embodiment of the oil return system, similar in principle with that of FIG. 8, wherein the system also includes a thermopump vessel 74 for returning recovered lubricant from receiver 46 back to the compressor discharge conduit 77. Four solenoid drain valves 72a, 72b, 72c, and 72d are shown in the exemplary embodiment, although more or less solenoid valves may be used for selectively draining the immiscible lubricant from receiver 46. Drain valves 72a, 72b, 72c, and 72d are spaced apart to align with discrete levels within receiver 46. A level sensor 66 indicates the level of the liquid within receiver 46. Controller 84 is in electronic communication with level sensor 66 and receives a level indicating signal and determines which of the four drain valves 72a, 72b, 72c, or 72d is submerged in the liquid and located nearest to the surface of the liquid within receiver 46. Controller 84 opens the nearest submerged drain valve 72a, 72b, 72c, or 72d to drain the top layer of liquid, which is primarily lubricant, to oil collection vessel 70. In oil collection vessel 70, the liquid is collected and heated by heat source 75. The heat causes the refrigerant mixed with the lubricant to boil into a vapor that rises within oil collection vessel 70 and escapes through solenoid valve 80 to return to receiver 46., The lubricant, which may mostly remain in the liquid phase, is returned to the compressor oil reservoir through conduit 81.

Arty. Dkt. No.: 26427-0005-PCT

[0045] Conduit 71 is connected at one end to evaporator 46 and at the opposite end to thermopump vessel 74, which is connected to a controller 84, to control the flow of the refrigerant and lubricant mixture entering thermopump vessel 74 from receiver 46. Thermopump vessel 74 receives the mixture of liquid refrigerant and lubricant from receiver 46 via conduit 71. Oil collection vessel 70 receives lubricant through an inlet conduit 91. The lubricant received via inlet conduit 91 collects directly in oil collection vessel 70. Inlet conduit 91 is connected to a lubricant separator 96, which provides lubricant at a temperature higher than the refrigerant and lubricant mixture received from evaporator 46. Lubricant separator 96 receives a mixture of lubricant and vapor from compressor 100 through a discharge conduit 77. Lubricant separator 96 separates a portion of the miscible lubricant from the refrigerant vapor and lubricant mixture discharged by the compressor. For example, according to an exemplary embodiment, baffle plates 96a and 96b may be inserted in the flow path of the vapor and lubricant mixture to separate the lubricant from the vapor. Separated lubricant 78 flows from lubricant separator 96 through inlet conduit 91 into oil collection vessel 70. The lubricant collects in the bottom of oil collection vessel 70 to a level such that a thermopump vessel within oil collection vessel 74 is at least partially submerged in the lubricant received from lubricant separator 96.

[0046] Thermopump vessel 74 accumulates refrigerant/ lubricant mixture 78, as discussed above. The filling and evacuation of thermopump vessel 74 is controlled by two level sensors 86 and 88. Control panel 84 senses a first liquid level signal from a first level sensor 86, and a second liquid level signal from a second liquid level sensor 88. The liquid level sensors 86 and 88 are located at different heights within thermopump 74. First level sensor 86 senses a low liquid level in the thermopump vessel 74, and is disposed beneath second liquid level sensor 88, which senses a high liquid level within the thermopump vessel 74.. Controller 84 controls inlet solenoid valve 72 and thermopump vessel outlet solenoid valve 80 to open and close both valves 72 and 80 simultaneously. A thermostat (not shown) in controller 84 starts thermopump vessel 74 once the compressor discharge vapor temperature reaches a predetermined temperature.

Atty. Dkt. No.: 26427-0005-PCT

The predetermined input may be preset in the controller 84, either manually or automatically through an algorithm programmed into the controller.

[0047] When the liquid level drops below first level sensor 86, control panel 84 activates inlet solenoid 72 and outlet solenoid valve 80. Outlet solenoid valve 80 opens in the conduit connection to the compressor discharge side, decreasing the pressure in the thermopump vessel slightly. At the same time, inlet solenoid valve 72 opens and the liquid refrigerant/ lubricant mixture starts flowing into thermopump vessel 74. When second level sensor 88 senses that liquid refrigerant/ lubricant mixture 79 has reached the second level, inlet solenoid valve 72 and outlet solenoid valve 80 are both closed by control panel 84. When the valves 72 and 80 are both closed, pressure within thermopump74 begins to rise due to the heat transferred from the lubricant in oil collection vessel 70 to the liquid contained within thermopump 74, When the temperature within thermopump 74 reaches a predetermined temperature, controller 84 opens outlet solenoid valve 80 allowing the liquid refrigerant and lubricant mixture to flow through conduit 81 into compressor discharge line 77 for re-introduction into oil separator 96 for separation and handling. According to other exemplary embodiments, the pressurized refrigerant and lubricant mixture from the thermopump may be discharged under pressure directly back into the oil collection vessel to be collected with the separated oil received from the oil separator. Whenever thermopump 74 stops, for example, when the compressor is operating below a predetermined capacity level, controller 84 evacuates the thermopump vessel.

[0048] FIG. 1 1 illustrates another embodiment of an immiscible oil return system in which floating funnel 90 is configured in receiver 46. Thermopump vessel 74 is incorporated into oil collection vessel 70 to return recovered lubricant from receiver 46 to discharge line 77 of the compressor. Floating funnel 90 is fluidly connected to oil collection vessel 70 through a drain line 71 exiting receiver 46. Funnel 90 includes a buoyant float ring 94 that floats substantially even with or above the liquid level. Float ring 94 encircles a wide opening 93 connected to a tapered sidewall 97 that tapers radially inward to a narrow conical outlet 96. Conical outlet 96 is fluidly connected to a

Atty. Dkt. No.: 26427-0005-PCT

flexible line 92 connected to drain line 71, which exits the bottom of receiver 46. Apertures 95 are spaced around the top periphery of funnel 90 and allow liquid to be drawn into funnel 90 and drained into conical orifice 96 at the bottom of funnel 90.

[0049] Solenoid valve 72a remains closed until the level of the liquid inside receiver 46 reaches a predetermined height to ensure that a minimum depth of lubricant has separated to liquid surface. When a controller 84 senses a threshold minimum depth of liquid inside receiver 46, controller 84 opens solenoid valve 72a allowing the surface liquid, which is primarily lubricant, is drained through flexible hose 92 and outlet 71.

[0050] Conduit 71 is connected at one end to evaporator 46 and at the opposite end to thermopump vessel 74, which is connected to a controller 84, to control the flow of the refrigerant and lubricant mixture entering thermopump vessel 74 from receiver 46. Thermopump vessel 74 receives the mixture of liquid refrigerant and lubricant from receiver 46 via conduit 71. Oil collection vessel 70 receives lubricant through an inlet conduit 91. The lubricant received via inlet conduit 91 collects directly in oil collection vessel 70. Inlet conduit 91 is connected to a lubricant separator 96, which provides lubricant at a temperature higher than the refrigerant and lubricant mixture received from evaporator 46. Lubricant separator 96 receives a mixture of lubricant and vapor from compressor 100 through a discharge conduit 77. Lubricant separator 96 separates a portion of the miscible lubricant from the refrigerant vapor and lubricant mixture discharged by the compressor. For example, according to exemplary embodiments, baffle plates 96a and 96b may be inserted in the flow path of the vapor and lubricant mixture to separate the lubricant from the vapor. Separated lubricant 78 flows from lubricant separator 96 through inlet conduit 91 into oil collection vessel 70. The lubricant collects in the bottom of oil collection vessel 70 to a level such that a thermopump vessel within oil collection vessel 74 is at least partially submerged in the lubricant received from lubricant separator 96.

[0051 J Thermopump vessel 74 accumulates refrigerant/ lubricant mixture 78, as discussed above. The filling and evacuation of thermopump vessel 74 is controlled by two level sensors 86 and 88. Control panel 84 senses a first liquid level signal from a

Atty. Dkt. No.: 26427-0005-PCT

first level sensor 86, and a second liquid level signal from a second liquid level sensor 88. The liquid level sensors 86 and 88 are located at different heights within thermopump 74. First level sensor 86 senses a low liquid level in the thermopump vessel 74, and is disposed beneath second liquid level sensor 88, which senses a high liquid level within the thermopump vessel 74. Controller 84 controls inlet solenoid valve 72 and thermopump vessel outlet solenoid valve 80 to open and close both valves 72 and 80 simultaneously. A thermostat (not shown) in controller 84 starts thermopump vessel 74 once the compressor discharge vapor temperature reaches a predetermined temperature. The predetermined input may be preset in the controller 84, either manually or automatically through an algorithm programmed into the controller.

[0052] When the liquid level drops below first level sensor 86, control panel 84 activates inlet solenoid 72 and outlet solenoid valve 80. Outlet solenoid valve 80 opens in the conduit connection to the compressor discharge side, decreasing the pressure in the thermopump vessel slightly. At the same time, inlet solenoid valve 72 opens and the liquid refrigerant/ lubricant mixture starts flowing into thermopump vessel 74. When second level sensor 88 senses that liquid refrigerant/ lubricant mixture 79 has reached the second level, inlet solenoid valve 72 and outlet solenoid valve 80 are both closed by control panel 84. When the valves 72 and 80 are both closed, pressure within thermopump74 begins to rise due to the heat transferred from the lubricant in oil collection vessel 70 to the liquid contained within thermopump 74. When the temperature within thermopump 74 reaches a predetermined temperature, controller 84 opens outlet solenoid valve 80 allowing the liquid refrigerant and lubricant mixture to flow through conduit 81 into compressor discharge line 77 for re-introduction into oil separator 96 for separation and handling. According to other exemplary embodiments, the pressurized refrigerant and lubricant mixture from the thermopump may be discharged under pressure directly back into the oil collection vessel to be collected with the separated oil received from the oil separator. Whenever thermopump 74 stops, for example, when the compressor is operating below a predetermined capacity level, controller 84 evacuates the thermopump vessel.

Atty. Dkt. No.: 26427^0005-PCT

[0053] Unless otherwise indicated, the valves described in the specification and drawings refer to solenoid valves, however, other automatic valves that are controllable between the open and closed positions are considered to be within the scope of the appended claims.

[0054] While only certain features and embodiments of the invention have been illustrated and described herein, many modifications and changes may occur to those skilled in the art (for example, variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (for example, 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 (that is, 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.