WO2012037021A2

WO2012037021A2 - Compressor having an oil management system

Info

Publication number: WO2012037021A2
Application number: PCT/US2011/051201
Authority: WO
Inventors: Satheesh Kulankara; William L. Kopko; Paul Nemit, Jr.; Shahebaz Malik
Original assignee: Johnson Controls Technology Company
Priority date: 2010-09-14
Filing date: 2011-09-12
Publication date: 2012-03-22
Also published as: WO2012037021A3

Abstract

A vapor compression system including a compressor, a condenser, an expansion device and an evaporator connected in a closed refrigerant loop. The compressor has a high pressure discharge, a low pressure inlet and a port having an intermediate pressure greater than the low pressure inlet and less than the high pressure discharge. A fluid moving device is arranged and positioned to receive intermediate pressure refrigerant and oil mixture from the port to urge flow of a mixture of oil and refrigerant from the evaporator to the low pressure inlet of the compressor.

Description

COMPRESSOR HAVING AN OIL MANAGEMENT SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The application claims priority from and the benefit of U.S. Provisional Application No. 61/382,517, entitled REFRIGERATION SYSTEM WITH SCREW COMPRESSOR HAVING A DEDICATED EDUCTOR PORT, filed September 14, 2010, which is hereby incorporated by reference.

BACKGROUND

[0002] The application generally relates to positive-displacement compressors used with vapor compression systems. The application relates more specifically to controlling the flow of refrigerant oil for a screw compressor.

[0003] In a rotary screw compressor, intake and compression can be accomplished by two tightly-meshing, rotating, helically lobed rotors that alternately draw lower pressure gas into the meshing threads and compress the gas to a higher discharge pressure. Oil is injected into the screw compressor for lubrication of internal moving parts as well as for sealing internal refrigerant leakage paths. A portion of the oil used in the compressor leaves through the discharge port of the compressor mixed with the higher pressure refrigerant. In typical refrigeration systems, an oil separator is installed in the discharge line to separate this oil from the refrigerant. The oil that is separated from the refrigerant in the oil separator is returned to the compressor, completing the main oil flow loop. Typical oil separators that are used in refrigeration systems have oil separation efficiencies that can be greater than 99 percent, but are not perfect. An oil separator operating at greater than 99 percent efficiency separates more than 99 percent of the oil that flows out of the compressor from the mixed refrigerant oil flow. The remaining oil (typically less than one percent) continues to flow with the refrigerant to the other components of the refrigeration system and eventually reaches the evaporator.

[0004] In the evaporator of a refrigeration system, the fluid to be cooled flows on one side and the relatively low pressure refrigerant flows on the other side. The evaporation of the refrigerant on one side cools the fluid on the other side. Evaporators used in refrigeration system can be broadly classified into two types: direct expansion (DX) and shell side evaporators. In a DX evaporator, refrigerant flows inside tubes or within narrow channels. Examples of DX evaporators are plate heat exchangers and shell and tube heat exchangers where the refrigerant flows inside the tubes. Shell side evaporators include flooded, falling film and hybrid falling film evaporators where the refrigerant is on the outer surface of the tube and the fluid to be cooled flows inside the tubes.

[0005] In a refrigeration system with a DX type evaporator, the oil that is mixed with the refrigerant flows along with the evaporated refrigerant to the suction side of the compressor. The refrigerant piping in such systems are sized and designed to ensure that the oil will flow back to the compressor. In such cases, no other devices are needed to return oil to the compressor.

[0006] In a refrigeration system with shell side evaporators, the refrigerant evaporates and flows back to the compressor suction through refrigerant lines. However, due to the nature of shell side evaporator design, the oil tends to remain in the evaporator, not flowing with the refrigerant. In such cases, an additional device may be needed to return oil to the compressor.

[0007] One such device that has been used in refrigeration systems to return oil from shell side evaporators is an eductor. Eductors operate by drawing or aspirating in an educted fluid, refrigerant and oil mixture in this case, into a high velocity stream of driving fluid. A description of eductor operation described in Applicant's U.S. Patent No. 5,086,621 is incorporated by reference in its entirety and illustrated in FIG. 1. FIG. 1 shows a basic vapor compression based refrigeration system that uses a screw compressor. In this system, the evaporated refrigerant from evaporator 138 flows into a screw compressor 132 through a piping line 20. Compressor 132 compresses the refrigerant gas from a low pressure to a high pressure and discharges the refrigerant mixed with oil through a piping line 21 to an oil separator 3. The oil separator 3 separates most of the oil from the refrigerant oil mixture. The remainder of the oil, along with the high pressure refrigerant, flows through a piping line 22 into a condenser 134. The oil that is separated by the oil separator flows through oil return piping line 27 back to compressor 132. The high pressure refrigerant gas condenses in the condenser into liquid refrigerant, transferring thermal energy to the cooling medium 156, such as a cooling tower. The oil that enters the condenser mixes with the liquid refrigerant and flows through piping line 23 to an expansion valve 136. The refrigerant oil mixture expands through the expansion valve where a portion of the refrigerant vaporizes and cools the remaining refrigerant oil mixture. The cooled refrigerant and oil mixture, consisting of liquid and vapor phases, flows through piping 24 to the evaporator 138. In the evaporator, the liquid refrigerant part of the mixture evaporates and cools a fluid to be chilled or cooling load 162. The evaporated refrigerant flows out of the evaporator 138 through piping 20 completing the refrigerant flow loop. The evaporation of refrigerant in evaporator 138 results in an oil rich refrigerant and oil mixture in the evaporator. This oil rich mixture is pumped back to the suction side of the compressor using eductor 6.

[0008] The flow of oil rich refrigerant and oil mixture to the eductor 6 is driven by the high pressure refrigerant gas. In prior art, the high pressure refrigerant gas is obtained from the high pressure side of the refrigeration system downstream of the oil separator 3, such as through piping 28. The high pressure refrigerant gas in the prior art is obtained from a convenient location such as the high pressure discharge side of the compressor 132, with the high pressure refrigerant flowing through piping 21 or 22 or from condenser 134 as described in U.S. Patent No. 5,086,621. The refrigerant and oil mixture that is drawn from piping 29 of evaporator 138 by eductor 6 flows through piping 30 to the low pressure suction side of the compressor 132. The flow of refrigerant and oil mixture from eductor 6 is fed into a location such as piping 20, or a dedicated port on the low pressure side of compressor 132 determined by overall system design. Since the high pressure gas is obtained from the discharge side of the screw compressor 132, there usually will be some amount of oil mixed with the refrigerant. The use of high pressure refrigerant gas from the discharge side of a compressor results in a loss in efficiency and capacity for the refrigerant system.

[0009] It is well known to those skilled in the art that for the eductor 6 to function in a manner that results in a desired flow of refrigerant oil mixture from the evaporator 138, the pressure of the high pressure refrigerant that is used to drive the flow must be maintained within a relatively narrow range for a given suction pressure. Due to the need for a relatively narrow range of driving pressures, it is difficult to design an eductor for refrigerant systems that operates properly when subjected to a wide range of discharge pressures in the prior art. Refrigerant systems that experience a wide range of discharge pressures include air cooled chiller systems where the discharge pressure depends on the ambient temperature.

[0010] Therefore what is needed is a vapor compression system having an oil management system operable over a wide range of compressor pressures.

SUMMARY

[0011] The present invention is directed to a vapor compression system including a compressor, a condenser, an expansion device and an evaporator connected in a closed refrigerant loop. The compressor has a high pressure discharge, a low pressure inlet and a port having an intermediate pressure greater than the low pressure inlet and less than the high pressure discharge. A fluid moving device is arranged and positioned to receive intermediate pressure refrigerant and oil mixture from the port to urge flow of a mixture of oil and refrigerant from the evaporator to the low pressure inlet of the compressor.

[0012] The present invention is also directed to a vapor compression system including a compressor, a condenser, a first expansion device, an intermediate vessel and an evaporator connected in a closed refrigerant loop. The compressor as a high pressure discharge, a low pressure inlet and a port having an intermediate pressure greater than the low pressure inlet and less than the high pressure discharge. The intermediate vessel is positioned downstream of the condenser and the first expansion device for receiving oil and refrigerant from the condenser. They intermediate vessel cools and directs flow of oil and refrigerant to the port of the compressor and directs flow of oil and refrigerant to the evaporator. A fluid moving device is arranged and positioned to receive intermediate pressure refrigerant and oil mixture from at least one of the port of the compressor and the intermediate vessel to urge flow of a mixture of oil and refrigerant from the evaporator to the low pressure inlet of the compressor.

[0013] The present invention is further directed to a vapor compression system including a compressor, a condenser, a first expansion device, an intermediate vessel and an evaporator connected in a closed refrigerant loop. He compressor has a high pressure discharge, a low pressure inlet and a port having an intermediate pressure greater than the low pressure inlet and less than the high pressure discharge. The intermediate vessel is positioned downstream of the condenser and the first expansion device for receiving oil and refrigerant from the condenser. The intermediate vessel cools and directs flow of oil and refrigerant to the port of the compressor and directs flow of oil and refrigerant to the evaporator. A fluid moving device is arranged and positioned to receive intermediate pressure refrigerant and oil mixture from at least one of the port of the compressor and the intermediate vessel to urge flow of a mixture of oil and refrigerant from the evaporator to the low pressure inlet of the compressor. The port of the compressor is in fluid communication with piping connecting the intermediate vessel and the compressor, and the port of the compressor is in fluid communication with the fluid moving device and the evaporator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 shows a prior art vapor compression system.

[0015] FIG. 2 shows an exemplary embodiment of a heating, ventilation and air conditioning system.

[0016] FIG. 3 shows an isometric view of an exemplary vapor compressor system.

[0017] FIGS. 4-5 show exemplary embodiments of a vapor compression system.

[0018] FIGS. 6-8 show alternate embodiments of vapor compression systems.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0019] FIG. 2 shows an exemplary environment for a heating, ventilation and air conditioning (HVAC) system 100 in a building 112 for a typical commercial setting. System 100 can include a vapor compression system 114 that can supply a chilled liquid which may be used to cool building 12. System 100 can include a boiler 116 to supply heated liquid that may be used to heat building 112, and an air distribution system which circulates air through building 112. The air distribution system can also include an air return duct 118, an air supply duct 120 and an air handler 122. Air handler 122 can include a heat exchanger that is connected to boiler 116 and vapor compression system 1 14 by conduits 124. The heat exchanger in air handler 122 may receive either heated liquid from boiler 116 or chilled liquid from vapor compression system 114, depending on the mode of operation of system 100. System 100 is shown with a separate air handler on each floor of building 1 12, but it is appreciated that the components may be shared between or among floors.

[0020] FIGS. 3-5 show an exemplary vapor compression system 114 that can be used in HVAC system 100. Vapor compression system 114 can circulate a refrigerant through a circuit starting with compressor 132 and including a condenser 134, expansion valve(s) or device(s) 136, and an evaporator or liquid chiller 138. Vapor compression system 114 can also include a control panel 140 that can include an analog to digital (A/D) converter 142, a microprocessor 144, a non-volatile memory 146, and an interface board 148. Some examples of fluids that may be used as refrigerants in vapor compression system 1 14 are hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-407, R-134a, hydrofluoro olefin (HFO), "natural" refrigerants like ammonia (NH₃), R-717, carbon dioxide (C0₂), R-744, or hydrocarbon based refrigerants, water vapor or any other suitable type of refrigerant. In an exemplary embodiment, vapor compression system 114 may use one or more of each of variable speed drives (VSDs) 152, motors 150, compressors 132, condensers 134, expansion valves 136 and/or evaporators 138.

[0021] Motor 150 used with compressor 132 can be powered by a variable speed drive (VSD) 152 or can be powered directly from an alternating current (AC) or direct current (DC) power source. VSD 152, 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 motor 150. Motor 150 can include any type of electric motor that can be powered by a VSD or directly from an AC or DC power source. Motor 150 can be any other suitable motor type, for example, a switched reluctance motor, an induction motor, or an electronically commutated permanent magnet motor. In an alternate exemplary embodiment, other drive mechanisms such as steam or gas turbines or engines and associated components can be used to drive compressor 132. [0022] Compressor 132 compresses a refrigerant vapor and delivers the vapor to condenser 134 through a discharge passage. Compressor 132 can be a screw compressor in one exemplary embodiment. The refrigerant vapor delivered by compressor 132 to condenser 134 transfers heat to a fluid, for example, water or air. The refrigerant vapor condenses to a refrigerant liquid in condenser 134 as a result of the heat transfer with the fluid. The liquid refrigerant from condenser 134 flows through expansion device 136 to evaporator 138. In the exemplary embodiment shown in FIG. 4, condenser 134 is water cooled and includes a tube bundle 154 connected to a cooling tower 156. In another embodiment, the condenser can be air cooled.

[0023] The liquid refrigerant delivered to evaporator 138 absorbs heat from another fluid, which may or may not be the same type of fluid used for condenser 134, and undergoes a phase change to a refrigerant vapor. In the exemplary embodiment shown in FIG. 4, evaporator 138 includes a tube bundle having a supply line 160S and a return line 160R connected to a cooling load or fluid to be chilled 162. A process fluid, for example, water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable liquid, enters evaporator 138 via return line 160R and exits evaporator 138 via supply line 160S. Evaporator 138 chills the temperature of the process fluid in the tubes. The tube bundle in evaporator 138 can include a plurality of tubes and a plurality of tube bundles. The vapor refrigerant exits evaporator 138 and returns to compressor 132 by a suction line to complete the cycle.

[0024] FIG. 5, which is similar to FIG. 4, shows the vapor compression system 114 with an intermediate circuit 164 incorporated between condenser 134 and expansion device 136. Intermediate circuit 164 has an inlet line 168 that can be either connected directly to or can be in fluid communication with condenser 134. As shown, inlet line 168 includes an expansion device 166 positioned upstream of an intermediate vessel 170. Intermediate vessel 170 can be a flash tank, also referred to as a flash intercooler, in an exemplary embodiment. In an alternate exemplary embodiment, intermediate vessel 170 can be configured as a heat exchanger or a "surface economizer." In the configuration shown in FIG. 5, i.e., the intermediate vessel 170 is used as a flash tank, a first expansion device 166 operates to lower the pressure of the liquid received from condenser 134. During the expansion process, a portion of the liquid vaporizes. Intermediate vessel 170 may be used to separate the vapor from the liquid received from first expansion device 166 and may also permit further expansion of the liquid. The vapor may be drawn by compressor 132 from intermediate vessel 170 through a line 174 to the suction inlet, a port at a pressure intermediate between suction and discharge or an intermediate stage of compression. The liquid that collects in the intermediate vessel 170 is at a lower enthalpy from the expansion process. The liquid from intermediate vessel 170 flows in line 172 through a second expansion device 136 to evaporator 138.

[0025] As shown in FIG. 6, one embodiment of the disclosure provides at least a port, such as port 5 on a screw compressor 132 to provide refrigerant gas at an intermediate pressure less than the discharge pressure, but greater than the suction pressure to act as the driving flow for eductor 6. The intermediate pressure port 5 could be a dedicated port for providing driving flow for eductor 6 or a multi-purpose port 5 that would be used for other purposes within the refrigeration system in addition to providing driving flow for eductor 6. An example of a multi-purpose port would be an economizer port on the compressor that provides an economizer feature in the refrigeration system, as will be discussed in further detail below. An advantage of providing an intermediate pressure port over using a high pressure discharge refrigerant as in conventional systems is that the variations in pressure at the intermediate pressure port will be reduced, in comparison to pressure variations associated with high pressure discharge refrigerant, making it possible to design an eductor to obtain the desired refrigerant oil mixture flow rate from the evaporator over a wide range of operating conditions for the refrigeration system. It should be understood that the driving intermediate pressure refrigerant gas from the dedicated port would have some oil mixed with it and that the term intermediate pressure refrigerant gas is used for simplicity. Another advantage of the present disclosure over known art is that the use of intermediate pressure refrigerant gas, rather than high pressure discharge gas to drive the eductor improves the efficiency of the refrigeration system.

[0026] FIG. 6 further shows an embodiment with a dedicated intermediate pressure port 6, in which the evaporated refrigerant from evaporator 138 flows into screw compressor 132 through piping line 20. Compressor 132 compresses the refrigerant gas to a greater pressure and discharges the refrigerant mixed with oil through piping line 21 to an oil separator 3. Oil separator 3 separates most of the oil from the refrigerant oil mixture. The remainder of the oil, along with the relatively greater or high pressure refrigerant, flows through piping line 22 into condenser 134, which can be air cooled or liquid cooled, such as by water or other suitable liquid. The oil that is separated by the oil separator flows through oil return piping line 27 back to compressor 132. The greater or relatively higher pressure refrigerant gas condenses in condenser 134 into liquid refrigerant, transferring thermal energy to air flowing across condenser coils (in an air cooled condenser). The oil that enters condenser 134 mixes with the liquid refrigerant and flows through piping line 23 to an expansion device 136, such as a valve. The refrigerant oil mixture expands through the expansion valve where a portion of the refrigerant vaporizes and cools the remaining refrigerant oil mixture. The cooled refrigerant and oil mixture, consisting of liquid and vapor phases, flows through piping 24 to the evaporator 138. In the evaporator, the liquid refrigerant portion of the mixture evaporates and cools the fluid to be chilled 162. The evaporated refrigerant flows out of evaporator 138 through piping 20, completing the refrigerant flow loop. The evaporation of refrigerant in evaporator 138 results in an oil rich refrigerant and oil mixture in the evaporator. This oil rich mixture is pumped back to the suction side of the compressor using eductor 6. [0027] The flow of oil rich refrigerant and oil mixture from the evaporator 138 to eductor 6 is driven by the intermediate pressure refrigerant gas obtained through a dedicated intermediate pressure port on compressor 132 as previously discussed. The refrigerant and oil mixture that is drawn from evaporator 138 by eductor 6 flows to the low pressure suction side of the compressor 132. The flow of refrigerant and oil mixture from eductor 6 is fed into a location such as piping 20, or a dedicated port, such as port 5 on the low pressure side of compressor 132 determined by overall refrigeration system design. Since the intermediate pressure gas is obtained from the screw compressor 132, there usually will be some amount of oil mixed with the refrigerant. The use of the intermediate pressure refrigerant gas results in a reduction in efficiency loss for the refrigerant system as compared to known refrigerant systems that use high pressure discharge gas with eductor 6.

[0028] FIG. 7 shows an alternate embodiment of an economized refrigeration system with a flash tank economizer and a screw compressor with a dedicated intermediate pressure port. In the system in FIG. 7, screw compressor 132 has two intermediate pressure ports 5A, 5B arranged between the suction pressure and discharge pressure. The pressure of these two intermediate ports 5A, 5B has a comparatively reduced pressure level, serving as an economizer port (port 5B), while the other port (port 5A) serves as a dedicated port for providing intermediate pressure refrigerant gas for driving the eductor. In one embodiment, the intermediate pressures associated with ports 5A, 5B may be the same, while in another embodiment, the pressures associated with ports 5A, 5B may be different from each other. In this system, the evaporated refrigerant from evaporator 138 flows into screw compressor 132 through piping or piping line 20. The compressor 132 compresses the refrigerant gas to a relatively greater or high pressure and discharges the refrigerant mixed with oil through piping or piping line 21 to an oil separator 3. The oil separator 3 separates most of the oil from the refrigerant oil mixture. The remainder of the oil, along with the high pressure refrigerant, flows through piping line 22 into an air cooled condenser 134. The oil that is separated by the oil separator flows through oil return piping line 27 back to compressor 132. The relatively greater or high pressure refrigerant gas condenses in condenser 134 into liquid refrigerant, transferring thermal energy to air flowing across condenser coils (in an air cooled condenser). The oil that enters condenser 134 mixes with the liquid refrigerant and flows through piping line 23 to an expansion device 166, such as a valve. The expansion device or valve can be a fixed expansion device or a variable expansion device. Applicants' co-pending patent applications include Appl. No. 61/230,393 titled REFRIGERANT CONTROL SYSTEM AND METHOD, filed July 30, 2010 and Appl. No. 61/382,858 titled SYSTEM AND METHOD FOR CONTROLLING AN ECONOMIZER CIRCUIT, filed September 14, 2010, which are each incorporated by reference in their entirety herein and further disclose details related to controls for these expansion devices.

[0029] It is to be understood that terms such as piping, piping line, line and the like can be used interchangeably.

[0030] As further shown in FIG. 7, the refrigerant oil mixture expands through the expansion valve into an intermediate vessel 170, such as an economizer 170, including a flash tank economizer, where a portion of the refrigerant vaporizes and cools the remaining refrigerant oil mixture. The cooled refrigerant and oil mixture, which may include liquid and vapor phases, flows through piping 24 through another expansion device 136 to the evaporator 138. The refrigerant that evaporated during expansion through expansion device 166 is directed to flow through piping 31 to economizer port 5B on screw compressor 132. Piping line 31 could have an arrangement of flow control devices, such as valves or devices 8, 9 and 10, such as a shut-off valve, a check valve and throttling valve, respectively, as shown in a serial arrangement, although in another embodiment a parallel arrangement of flow control devices may be used, to modulate the flow of refrigerant to economizer port 5B. In one embodiment, piping 31 , also referred to as the economizer line, can have an arrangement of valves that open or close without a modulating feature to control the flow from economizer 170 to economizer port 5B of compressor 132. In evaporator 138, the liquid refrigerant portion of the mixture evaporates and cools the fluid to be chilled 162. The evaporated refrigerant flows out of evaporator 138 through piping 20, completing the refrigerant flow loop. The evaporation of refrigerant in evaporator 138 results in an oil rich refrigerant and oil mixture in the evaporator. This oil rich mixture is pumped back to the suction side of compressor 132 using eductor 6.

[0031] FIG. 8 shows another embodiment of an economized refrigeration system with a flash tank economizer and a screw compressor with a multipurpose intermediate pressure port 5C. As further shown in FIG. 8, the screw compressor 132 has one intermediate pressure port 5C between the suction pressure and discharge pressure of the screw compressor, which port 5C acting both as an economizer port and as a source of intermediate pressure refrigerant gas for driving the eductor flow. In this system, the evaporated refrigerant from evaporator 138 flows into screw compressor 132 through piping line 20. The compressor 132 compresses the refrigerant gas to a relatively greater or high pressure and discharges the refrigerant mixed with oil through piping line 21 to an oil separator 3. The oil separator 3 separates most of the oil from the refrigerant oil mixture. The remainder of the oil, along with the relatively greater or high pressure refrigerant, flows through piping line 22 into condenser 134, which can be air cooled, or liquid cooled, such as with water. The oil that is separated by the oil separator flows through oil return piping line 27 back to compressor 132. The relatively greater or high pressure refrigerant gas condenses in the condenser into liquid refrigerant, transferring thermal energy to air flowing across condenser coils (for air cooled condensers). The oil that enters condenser 138 mixes with the liquid refrigerant and flows through piping line 23 to an expansion valve 166. Expansion valve 166 can be fixed expansion device or a variable expansion device. The refrigerant oil mixture expands through the expansion valve into intermediate vessel 170, such as a flash tank economizer, where a portion of the refrigerant vaporizes and cools the remaining refrigerant oil mixture. The cooled refrigerant and oil mixture, including liquid and vapor phases, flows through piping 24 through another expansion device 136, such as an expansion valve, to the evaporator 138. The refrigerant that evaporated during expansion through intermediate vessel 170 or economizer flows through piping 31 toward the economizer port 5C on the screw compressor 132.

[0032] Piping line 31 or economizer line could have a series of valves or control devices 8, 9 and 10 to modulate the flow of refrigerant toward the economizer port 5C. The piping 31 or economizer line also could have a series of valves that open or close without a modulating feature to control the flow to economizer port 5C of compressor 132 as previously discussed. In evaporator 138, the liquid refrigerant portion of the mixture evaporates and cools the fluid to be chilled 162. The evaporated refrigerant flows out of the evaporator 138 through piping 20, completing the refrigerant flow loop. The evaporation of refrigerant in evaporator 138 results in an oil rich refrigerant and oil mixture in the evaporator. This oil rich mixture is pumped back to the suction side of the compressor 132 using eductor 6.

[0033] As further shown in FIG. 8, the flow of oil rich refrigerant and oil mixture from evaporator 138 to eductor 6 is driven by the intermediate pressure refrigerant gas obtained from the multi-purpose intermediate pressure port 5C on compressor 132. The intermediate pressure refrigerant gas could be tapped directly from compressor 132 or from a convenient point in piping line 31 or economizer line between flow control device 10 and the compressor 132. The refrigerant and oil mixture that is drawn from evaporator 138 by eductor 6 flows to the low pressure suction side of the compressor 132. The flow of refrigerant and oil mixture from eductor 6 is fed into a location such as piping 20, or a dedicated port on the low pressure side of compressor 132, determined by overall refrigeration system design. Since the intermediate pressure gas is obtained from the screw compressor 132, there usually will be some amount of oil mixed with the refrigerant. The use of the intermediate pressure refrigerant gas results in a reduction in efficiency loss for the refrigerant system, as compared to a system based on prior art utilizing high pressure discharge gas from the compressor.

[0034] The disclosed system includes several advantages over known systems. First, the disclosed system provides the ability to increase system efficiency by making use of intermediate pressure refrigerant gas to drive eductor flow from the evaporator, as compared to using high pressure refrigerant gas from the discharge side employed in conventional systems. Second, the disclosed system provides improved oil return from evaporator. The dedicated or multi-purpose intermediate pressure port on the compressor provides a source of intermediate pressure refrigerant gas, providing reduced variation in pressure. This reduction in pressure variation improves eductor operation and oil return from the evaporator, minimizing the risk of damaging the compressor from loss of oil. Improved oil return from the evaporator also improves evaporator and system capacity. Third, the disclosed system is less expensive than known system constructions. The system cost to incorporate a dedicated or multi-purpose port on the compressor is relatively low compared to other means of obtaining reliable oil return from the evaporator.

[0035] While only certain features and embodiments of the invention have been shown and described, many modifications and changes may occur to those skilled in the art (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters (e.g., temperatures, pressures, etc.), mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described (i.e., those unrelated to the presently contemplated best mode of carrying out the invention, or those unrelated to enabling the claimed invention). It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.

Claims

WHAT IS CLAIMED IS:

1. A vapor compression system comprising:

a compressor, a condenser, an expansion device and an evaporator connected in a closed refrigerant loop, the compressor having a high pressure discharge, a low pressure inlet and a port having an intermediate pressure greater than the low pressure inlet and less than the high pressure discharge; and

a fluid moving device arranged and positioned to receive intermediate pressure refrigerant and oil mixture from the port to urge flow of a mixture of oil and refrigerant from the evaporator to the low pressure inlet of the compressor.

2. The system of Claim 1 , wherein the fluid moving device is an eductor.

3. The system of Claim 1 , wherein the compressor is a screw compressor.

4. The system of Claim 1 , wherein the condenser is a direct expansion type condenser.

5. The system of Claim 1 , wherein the condenser is a shell side type condenser.

6. The system of Claim 1 , including an oil separator to receive a mixture of oil and refrigerant from the high pressure discharge of the compressor, the oil separator separating and returning an amount of oil to the compressor, a mixture of the remaining oil and high pressure refrigerant flowing from the oil separator to the condenser.

7. The system of Claim 1 , wherein the condenser is air cooled.

8. The system of Claim 1 , wherein the condenser is water cooled.

9. A vapor compression system comprising:

a compressor, a condenser, a first expansion device, an intermediate vessel and an evaporator connected in a closed refrigerant loop, the compressor having a high pressure discharge, a low pressure inlet and a port having an intermediate pressure greater than the low pressure inlet and less than the high pressure discharge;

the intermediate vessel downstream of the condenser and the first expansion device for receiving oil and refrigerant from the condenser, the intermediate vessel to cool and direct flow of oil and refrigerant to the port of the compressor and direct flow of oil and refrigerant to the evaporator; and

a fluid moving device arranged and positioned to receive intermediate pressure refrigerant and oil mixture from at least one of the port of the compressor and the intermediate vessel to urge flow of a mixture of oil and refrigerant from the evaporator to the low pressure inlet of the compressor.

10. The system of Claim 9, wherein the intermediate vessel is an economizer.

1 . The system of Claim 9, wherein a second expansion device is positioned between the intermediate vessel and the evaporator.

12. The system of Claim 9, wherein the port of the compressor is in fluid communication with piping connecting the intermediate vessel and the compressor, and the port of the compressor is in fluid communication with the fluid moving device and the evaporator.

13. The system of Claim 12, wherein piping connecting the intermediate vessel and the compressor comprises a plurality of flow control devices to modulate the flow of refrigerant through the piping.

14. The system of Claim 13, wherein the plurality of flow control devices are arranged serially.

15. The system of Claim 13, wherein the plurality of flow control devices are arranged in parallel.

16. The system of Claim 12, wherein piping connecting the intermediate vessel and the compressor comprises a plurality of flow control devices that operate without a modulating feature to control the flow of refrigerant through the piping.

17. The system of Claim 11 , wherein the second expansion device is a fixed expansion device.

18. The system of Claim 11 , wherein the second expansion valve is a variable expansion device.

19. A vapor compression system comprising:

a fluid moving device arranged and positioned to receive intermediate pressure refrigerant and oil mixture from at least one of the port of the compressor and the intermediate vessel to urge flow of a mixture of oil and refrigerant from the evaporator to the low pressure inlet of the compressor;

wherein the port of the compressor is in fluid communication with piping connecting the intermediate vessel and the compressor, and the port of the compressor is in fluid communication with the fluid moving device and the evaporator.

20. The system of Claim 19, wherein a second expansion device is positioned between the intermediate vessel and the evaporator.