WO2016027116A1

WO2016027116A1 - Improved direct expansion evaporator based chiller system

Info

Publication number: WO2016027116A1
Application number: PCT/IB2014/001842
Authority: WO
Inventors: Charbel RAHHAL; Richard G. Lord; Jack Leon Esformes
Original assignee: Carrier Corporation
Priority date: 2014-08-21
Filing date: 2014-08-21
Publication date: 2016-02-25
Also published as: EP3183514A1; CN106662365A; CN106662365B; ES2886603T3; EP3183514B1; US20170268808A1

Abstract

A chiller system is provided including a vapor compression circuit consisting of a fluidly coupled compressor, condenser, expansion valve, and evaporator. A refrigerant circulates through the vapor compression circuit. The evaporator is a direct exchange heat exchanger. Refrigerant provided at an outlet of the evaporator is a two-phase mixture including liquid refrigerant and vapor refrigerant. The vapor refrigerant comprises less than or equal to 85% of the two-phase mixture. A refrigerant to refrigerant heat exchanger is fluidly coupled to the circuit. The refrigerant to refrigerant heat exchanger is configured to convert the vapor refrigerant provided at the outlet of the evaporator into a superheated vapor.

Description

IMPROVED DIRECT EXPANSION EVAPORATOR BASED CHILLER SYSTEM

BACKGROUND OF THE INVENTION

[001] The invention relates generally to air conditioning and refrigeration systems and, more particularly, to an air conditioning and refrigeration system that enables the use of immiscible oil.

[002] In a vapor compression system, refrigerant vapor from an evaporator is drawn in by a compressor, which then delivers the compressed refrigerant to a condenser (or a gas cooler for transcritical applications). In the condenser, heat is exchanged between a secondary fluid, such as air or water, and the refrigerant. From the condenser, the refrigerant, typically in a liquid state passes to an expansion device, where the refrigerant is expanded to a lower pressure and temperature before being provided to the evaporator. In air conditioning applications, heat is exchanged within the evaporator between the refrigerant and air or another secondary fluid, such as water, glycol, or brine for example, to condition the indoor air of a space.

[003] Since the refrigerant compressor necessarily involves moving parts, it is typically required to provide lubrication to these parts by means of lubricating oil that is mixed with or entrained in the refrigerant passing through the compressor. Although the lubricant is normally not useful within the system other than in the compressor, its presence in low concentrations in the system does not generally detract from the flow, heat transfer, and properties of the refrigerant as it passes through the system in a conventional vapor compression cycle. [004] Various types of heat exchangers, such as direct expansion and flooded heat exchangers for example, may be used as evaporators in HVAC systems. In a flooded heat exchanger, the refrigerant typically surrounds the exterior of the tubes positioned within a shell and the secondary fluid to be cooled, such as water for example, flows through the tubes. By immersing the tubes of a flooded heat exchanger within the "boiling" liquid refrigerant, only a very small approach temperature (.5°K - 1.5°K) between the refrigerant and the chilled secondary fluid is required, thereby improving heat transfer efficiency. In a direct expansion heat exchanger, the refrigerant is expanded within the tubes while the chilled second fluid is circulated through the shell. The typical approach temperature in a direct expansion heat exchanger is between 4°K and 6°K to ensure vapor phase at compressor suction.

[005] Due to environmental global warming potential concerns, new types of refrigerants are being considered for use in air conditioning applications. These new refrigerants include refrigerants that result in the coexistence of vapor and liquid phases through the compression process or refrigerants that have lower discharge gas temperatures and higher miscibility with lubricants compared to conventional refrigerants. Examples of these new refrigerants include, but are not limited to Hydrofluoroolefins (HFOs), and blends of HFOs and Hydrofluorocarbons (HFCs), or other refrigerants and/or refrigerant blends commonly referred to as "wet refrigerants" that have similar properties.

[006] Due to their higher miscibility, these new "wet refrigerants" tend to absorb significant amounts of oil making the viscosity requirements of the oil-refrigerant mixture difficult to achieve. Use of immiscible oil, which does not mix with these refrigerants will improve the viscosity of the oil; however, at the same time use of immiscible oil significantly and permanently reduces the performance of air conditioning and refrigeration systems that employ modern flooded type evaporators. Use of direct exchange evaporators instead of flooded evaporators may allow the use of immiscible oils in a refrigeration system. In such instances, the oil return is driven by the velocity of refrigerant through the heat exchanger tubes.

BRIEF DESCRIPTION OF THE INVENTION [007] According to an aspect of the invention, a chiller system is provided including a vapor compression circuit consisting of a fluidly coupled compressor, condenser, expansion valve, and evaporator. A refrigerant circulates through the vapor compression circuit. The evaporator is a direct exchange heat exchanger. Refrigerant provided at an outlet of the evaporator is a two-phase mixture including liquid refrigerant and vapor refrigerant. The vapor refrigerant comprises less than or equal to 85% of the two-phase mixture. A refrigerant to refrigerant heat exchanger is fluidly coupled to the circuit. The refrigerant to refrigerant heat exchanger is configured to convert the refrigerant provided at the outlet of the evaporator into a superheated vapor. [008] In addition to one or more of the features described above, or as an alternative, in further embodiments the refrigerant has a low global warming potential.

[009] In addition to one or more of the features described above, or as an alternative, in further embodiments, the refrigerant includes at least one of a Hydrofluoroolefin (HFO) and an HFO blend.

[0010] In addition to one or more of the features described above, or as an alternative, in further embodiments the chiller system includes a lubrication system having an oil separator arranged generally downstream from the compressor. The oil separator is configured to supply oil separated from the refrigerant to one or more moving components of the compressor. [0011] In addition to one or more of the features described above, or as an alternative, in further embodiments the oil is an immiscible oil.

[0012] According to another embodiment of the invention, a chiller system is provided including a vapor compression circuit consisting of a fluidly coupled compressor, condenser, expansion valve, and evaporator. A refrigerant circulates through the vapor compression circuit. The evaporator is a direct exchange heat exchanger. Refrigerant provided at an outlet of the evaporator is a two-phase mixture including liquid refrigerant and vapor refrigerant. The vapor refrigerant comprises less than or equal to 85% of the two-phase mixture. An efficiency circuit includes a separator configured to separate the two-phase mixture of refrigerant into liquid refrigerant and vapor refrigerant. The efficiency circuit is operably coupled to the outlet of the evaporator and is configured to recirculate liquid refrigerant from the separator through the evaporator to improve the efficiency of the evaporator and chiller system.

[0013] In addition to one or more of the features described above, or as an alternative, in further embodiments the refrigerant has a low global warming potential.

[0014] In addition to one or more of the features described above, or as an alternative, in further embodiments, the refrigerant includes at least one of a Hydrofluoroolefin (HFO) and an HFO blend. [0015] In addition to one or more of the features described above, or as an alternative, in further embodiments the chiller system includes a lubrication system having an oil separator arranged generally downstream from the compressor. The oil separator is configured to supply oil separated from the refrigerant to one or more moving components of the compressor.

[0016] In addition to one or more of the features described above, or as an alternative, in further embodiments the oil is an immiscible oil.

[0017] In addition to one or more of the features described above, or as an alternative, in further embodiments the separator is operably coupled to the compressor and is configured to supply a refrigerant vapor thereto.

[0018] In addition to one or more of the features described above, or as an alternative, in further embodiments the efficiency circuit further includes an ejector having a first inlet and a second inlet. The ejector is positioned generally downstream from the condenser and upstream from the separator.

[0019] In addition to one or more of the features described above, or as an alternative, in further embodiments a first outlet of the separator is operably coupled to the second inlet of the ejector and is configured to supply liquid refrigerant thereto.

[0020] In addition to one or more of the features described above, or as an alternative, in further embodiments the separator is arranged generally downstream from the evaporator and upstream from the compressor.

[0021] In addition to one or more of the features described above, or as an alternative, in further embodiments the ejector is positioned generally upstream from the expansion device.

[0022] In addition to one or more of the features described above, or as an alternative, in further embodiments the outlet of the evaporator is operably coupled to the second inlet of the ejector.

[0023] In addition to one or more of the features described above, or as an alternative, in further embodiments the separator is arranged generally downstream of the ejector and generally upstream from the expansion device. [0024] In addition to one or more of the features described above, or as an alternative, in further embodiments the chiller system includes a refrigerant to refrigerant heat exchanger fluidly coupled to the vapor compression circuit and the efficiency circuit. The refrigerant to refrigerant heat exchanger is configured to convert the vapor refrigerant provided from an outlet of the separator into a superheated vapor.

[0025] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

[0027] FIG. 1 is a schematic diagram of a chiller refrigeration system according to an embodiment of the invention; [0028] FIG. 2 is a cross-sectional view of an evaporator of the chiller refrigeration system of FIG. 1 according to an embodiment of the invention;

[0029] FIG. 3 is a schematic diagram of another chiller refrigeration system according to an embodiment of the invention;

[0030] FIG. 4 is a schematic diagram of another chiller refrigeration system according to an embodiment of the invention; and

[0031] FIG. 5 is a schematic diagram of another chiller refrigeration system according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0032] Referring now to the FIGS., an improved chiller refrigeration system 20 configured for use with either a miscible or immiscible oil is illustrated. A refrigerant R is configured to circulate through the chiller system 20 such that the refrigerant R absorbs heat when evaporated at a low temperature and pressure and releases heat when condensed at a higher temperature and pressure. In one embodiment, the refrigerant has a low global warming potential, such as a Hydrofluoroolefin (HFO) or an HFO blend refrigerant for example. Within this chiller system 20, the refrigerant R flows in a counterclockwise direction as indicated by the arrows. The compressor 25 receives refrigerant vapor from the evaporator 40 and compresses it to a higher temperature and pressure, with the relatively hot vapor then passing to the condenser 30 where it is cooled and condensed to a liquid state by a heat exchange relationship with a cooling medium, such as air or water for example. The liquid refrigerant R then passes from the condenser 30 to an expansion valve 35, wherein the refrigerant R is expanded to a low temperature two phase liquid/vapor state as it passes to the evaporator 40. After the addition of heat in the evaporator 40, low pressure vapor then returns to the compressor 25 where the cycle is repeated. Together the compressor 25, condenser 30, expansion device 35 and evaporator 40 form a vapor compression circuit. [0033] In the illustrated embodiments of the chiller system 20, the evaporator 40 is a direct expansion heat exchanger. As illustrated in FIG. 2, the evaporator 40 includes a connected first shell 100a and second shell 100b, and a coupled first plurality of tubes 105a and second plurality of tubes 105b, arranged within each of the shells 100a, 100b, respectively. However, embodiments having any number of shells 100a, 100b are within the scope of the invention. In embodiments where the evaporator 40 includes multiple shells, such as shell 100a and 100b for example, the shells are fluidly coupled to one another and the tubes 105 a, 105b within each respective shell 105 a, 105 are fluidly coupled. A plurality of large baffles 107 and small baffles 109 generally receive and support the tubes 105 a, 105b to maintain the position of the tubes 105a, 105b along the length of the shell 100a, 100b. In one embodiment, the large baffle 107 is configured to receive each of the plurality of tubes 105a, 105b within a shell 100a, 100b and the small baffle 109 is configured to receive only a portion, such as a central portion for example, of the plurality of tubes 105a, 105b within a shell 100a, 100b.

[0034] The refrigerant of the chiller system 20 is configured to pass from an inlet header

110, through the one or more plurality of tubes 105b, 105a, and out an outlet header 115.

Similarly, a heating medium, such as water for example, is pumped into the interior 120 of the shell 100 via an inlet 125, through the one or more shells 100a, 100b, and out an outlet 130. In the illustrated, non-limiting embodiment, the heating medium is configured to flow from the second shell 100b to the first shell 100a, and the refrigerant is configured to flow from the first plurality of tubes 105 a to the second plurality of tubes 105b. The illustrated and described evaporator 40 has a counter flow configuration to maximize the heat transfer between the heating medium and the refrigerant. The refrigerant provided at the outlet header 115 of the evaporator 40 may be a two-phase mixture including both liquid and vapor refrigerant. In one embodiment, 85 percent or less of the two-phase mixture is vaporized refrigerant.

[0035] Referring again to FIG. 1, the system 20 includes an additional heat exchanger 45 configured to receive a first flow of refrigerant and a second flow of refrigerant. The heat exchanger 45 may be positioned within the system 20 such that the first flow of refrigerant is provided from the outlet of the condenser 30. In the illustrated, non-limiting embodiment, the first flow of refrigerant is configured to pass through the heat exchanger 45 before being supplied to the expansion valve 35. The second flow of refrigerant within the heat exchanger 45 is generally provided from the outlet of the evaporator 40. The second flow of refrigerant is configured to pass through the heat exchanger 45 before being supplied to the compressor 25. By arranging the warm liquid refrigerant from the condenser 30 in a heat transfer relationship with the refrigerant vapor or two-phase mixture exiting the evaporator 40, heat from the first flow of refrigerant transfers to the second flow of refrigerant. As a result, the second flow of refrigerant supplied from the heat exchanger 45 to the compressor 25 is generally a superheated vapor.

[0036] A lubrication system, illustrated schematically at 50, may be integrated into the chiller system 20. Because lubricant may become entrained in the refrigerant as it passes through the compressor 25, an oil separator 55 is positioned directly downstream from the compressor 20. In one embodiment, the oil separator 55 is integrally formed with an outlet of the compressor 25. The refrigerant separated by the oil separator 55 is provided to the condenser 30, and the lubricant isolated by the oil separator 55 is recirculated to the moving portions (not shown) of the compressor 25, such as to the rotating bearings for example, where the lubricant becomes entrained in the refrigerant R and the lubricant cycle is repeated. [0037] In another embodiment, illustrated in FIG. 3, the chiller system 20 additionally includes a circuit 58 configured to recirculate liquid refrigerant of the two-phase mixture provide at the outlet 115 of the evaporator 40 to improve the efficiency of the chiller system 20. The circuit 58 includes a flash gas refrigerant separator 60 configured to separate the liquid and vapor phases of the refrigerant. In the illustrated, non-limiting embodiment, the separator 60 is arranged generally downstream from the expansion device 35 and upstream from the evaporator 40 such that the two-phase refrigerant passes from the expansion device 35 into the separator 60. A pump 65 is configured to draw the liquid refrigerant from a first outlet 66 of the separator 60 and supply it to the evaporator 40. The outlet of the evaporator 40 is also connected to the separator 60 and configured to supply a two-phase refrigerant mixture thereto. Within the separator 60, the liquid refrigerant is separated from the liquid and vapor mixture and recirculated through the evaporator 40 repeatedly until it is vaporized. A second outlet 68 of the separator 60 is operably coupled to the compressor 25 such that the separated vaporized refrigerant is supplied directly thereto. In such instances, the vaporized refrigerant bypasses the evaporator 40. In embodiments where the chiller system 20 includes a refrigerant to refrigerant heat exchanger 45, the vaporized refrigerant from the separator 60 may pass through the heat exchanger 45 before being supplied to the compressor 25.

[0038] Referring now to FIG. 4, in another embodiment of the chiller system 20, the flash gas separator 60 is positioned generally downstream from the evaporator 40 and generally upstream from the compressor 25 relative to the flow of refrigerant. In such embodiments, the additional circuit 58 of the chiller system 20 also includes an ejector 70 arranged within the refrigerant flow path between the condenser 30 and the expansion valve 35. Refrigerant from the condenser 30 is provided to a first inlet 72 of the ejector 70. As the refrigerant flows through the ejector 70, the flow is accelerated and the pressure of the flow is decreased, such that the refrigerant supplied to the expansion device 35 is generally a liquid-vapor mixture.

[0039] After the refrigerant passes through the evaporator 40, the refrigerant passes to the flash gas separator 60 for separation into a liquid refrigerant and a vapor refrigerant. A first outlet 66 of the separator 60 is fluidly connected to a second inlet 74 of the ejector 70. The high velocity and pressure reduction of the refrigerant flow through the first inlet 72 of the ejector 70 draws the liquid refrigerant from the separator 60 into the ejector 70 through the second inlet 74. Therefore any liquid refrigerant provided at the outlet 115 of the evaporator 40 will repeatedly cycle through the circuit 58 and the evaporator 40 until being vaporized. A second outlet 68 of the separator 60 is configured to supply the vaporized refrigerant within the separator 60 to the compressor 25. In embodiments where the chiller system 20 includes a refrigerant to refrigerant heat exchanger 45, the liquid refrigerant from the condenser 30 may pass through the heat exchanger 45 as the first flow of refrigerant before being supplied to the ejector 70 and the vaporized refrigerant provided at the second outlet 68 of the separator 60 may pass through the heat exchanger 45 as the second flow of refrigerant before being supplied to the compressor 25.

[0040] In another embodiment, illustrated in FIG. 5, the flash gas separator 60 is positioned generally downstream from the condenser 30 and generally upstream from the expansion device 35 relative to the flow of refrigerant. In such embodiments of the circuit 58, the ejector 70 is arranged generally downstream from the condenser 30 and generally upstream from the separator 60 relative to the flow of refrigerant. Refrigerant from the condenser 30 is provided to the first inlet 72 of the ejector 70 and refrigerant from the outlet 115 of the evaporator 40 is provided to the second inlet 74 of the ejector 70. A liquid-vapor refrigerant mixture is supplied from the ejector 70 to the separator 60 where it is divided into liquid refrigerant and vapor refrigerant. The liquid refrigerant within the separator 60 is provided to the expansion device 35 via a first outlet 66 in the separator 60. After passing through the expansion device 35 and the evaporator 40, the refrigerant is provided to the second inlet 74 of the ejector 70. As previously described, the high velocity and pressure reduction of the refrigerant flow through the ejector 70 draws the mixture of two phase refrigerant from the evaporator 40 through the second inlet 74 of the ejector 70. The refrigerant then returns to the separator 60, where it is separated into liquid refrigerant and vapor refrigerant. Consequently, the liquid refrigerant provided at the outlet 115 of the evaporator 40 will continue to cycle through circuit 58 and the evaporator 40 until it is entirely vaporized. The vapor compression cycle further benefits from this configuration in that the placement of the ejector 70 reduces the compression ratio of the compressor 25, thereby increasing the system coefficient of performance.

[0041] A second outlet 68 of the separator 60 is configured to supply the vaporized refrigerant to the compressor 25. In such instances, the vaporized refrigerant bypasses the expansion device 35 and the evaporator 40. In embodiments where the chiller system 20 includes a refrigerant to refrigerant heat exchanger 45, the liquid refrigerant from the condenser 30 may pass through the heat exchanger 45 as the first flow of refrigerant before being supplied to the ejector 70 and the vaporized refrigerant provided at the second outlet 68 of the separator 60 may pass through the heat exchanger 45 as the second flow of refrigerant before being supplied to the compressor 25.

[0042] The various embodiments of a chiller system 20 described herein have an efficiency or performance level at least equal to conventional systems that include a flooded evaporator. In addition, the chiller system 20 is compatible with immiscible oil, which reduces the amount of oil needed by the system and therefore the cost. As a result, the design of the lubrication system 50 may be simplified.

[0043] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.

Claims

CLAIMS:

1. A chiller system comprising: a vapor compression circuit including a compressor, a condenser, an expansion valve, and an evaporator fluidly coupled and having a refrigerant circulating there through, the evaporator being a direct exchange heat exchanger such that the refrigerant provided at an outlet of the evaporator is a two-phase mixture of liquid refrigerant and vapor refrigerant, and the vapor refrigerant comprises less than or equal to about 85% of the two-phase mixture; and a refrigerant to refrigerant heat exchanger fluidly coupled to the circuit, the refrigerant to refrigerant heat exchanger being configured to convert the vapor refrigerant provided at the outlet of the evaporator into a superheated vapor.

2. The chiller system according to claim 1, wherein the refrigerant has a low global warming potential.

3. The chiller system according to claim 2, wherein the refrigerant includes at least one of a Hydrofluoroolefin (HFO) or an HFO blend.

4. The chiller system according to claim 1, further comprising a lubrication system including an oil separator arranged generally downstream from the compressor, the oil separator being configured to supply oil separated from the refrigerant to one or more moving components of the compressor.

5. The chiller system according to claim 4, wherein the oil is an immiscible oil.

6. A chiller system comprising: a vapor compression circuit including a compressor, a condenser, an expansion valve, and an evaporator fluidly coupled and having a refrigerant circulating there through, the evaporator being a direct exchange heat exchanger such that the refrigerant provided at an outlet of the evaporator is a two-phase mixture of liquid refrigerant and vapor refrigerant, and the vapor refrigerant comprises less than or equal to about 85% of the two-phase mixture; and an efficiency circuit including a separator configured to separate the two-phase mixture into liquid refrigerant and vapor refrigerant, the efficiency circuit being operably coupled to the outlet of the evaporator and configured to recirculate liquid refrigerant from the separator through the evaporator to improve the efficiency of the chiller system.

7. The chiller system according to claim 6, wherein the refrigerant has a low global warming potential.

8. The chiller system according to claim 7, wherein the refrigerant includes an HFO.

9. The chiller system according to claim 6, further comprising a lubrication system including an oil separator arranged generally downstream from the compressor, the oil separator being configured to supply oil separated from the refrigerant to one or more moving components of the compressor.

10. The chiller system according to claim 9, wherein the oil is immiscible oil.

11. The chiller system according to claim 6, wherein the separator is operably coupled to the compressor and is configured to supply vapor refrigerant thereto.

12. The chiller system according to claim 11, wherein the efficiency circuit further includes an ejector having a first inlet and a second inlet, the ejector being positioned generally downstream from the condenser and upstream from the separator.

13. The chiller system according to claim 12, wherein a first outlet of the separator is operably coupled to the second inlet of the ejector and is configured to supply liquid refrigerant thereto.

14. The chiller system according to claim 13, wherein the separator is arranged generally downstream from the evaporator and upstream from the compressor.

15. The chiller system according to claim 14, wherein the ejector is positioned generally upstream from the expansion device.

16. The chiller system according to claim 12, wherein the outlet of the evaporator is operably coupled to the second inlet of the ejector.

17. The chiller system according to claim 16, wherein the separator is arranged generally downstream of the ejector and generally upstream from the expansion device.

18. The chiller system according to claim 6, further comprising: a refrigerant to refrigerant heat exchanger fluidly coupled to the vapor compression circuit and the efficiency circuit, the refrigerant to refrigerant heat exchanger being configured to convert the vapor refrigerant provided from an outlet of the separator into a superheated vapor.