Refrigeration machine having a cascade type refrigeration system using parallel expansion devices for adjustable expansion

Abstract

A cascade-type refrigeration system having a first refrigeration stage defining a first fluid circuit and including a first expansion device, and a second refrigeration stage defining a second fluid circuit fluidly separated from the first fluid circuit and including a second expansion device. The second expansion device includes a first capillary tube and a second capillary tube arranged in parallel flow, and a second stage valve in fluid communication with the second capillary tube for selectively controlling the flow of the second refrigerant through the second capillary tube in response to at least one operating condition of the refrigeration system without blocking the flow of the second refrigerant through the first capillary tube. The refrigeration system further includes at least one inter-stage heat exchanger in heat transfer communication with the first and second fluid circuits for exchanging heat between the first refrigerant and the second refrigerant.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 325,877, filed April 8, 2022, the contents of which are incorporated by reference herein as if set forth in their entirety.

[0002] FIELD OF THEINVENTION The present invention relates generally to refrigeration equipment such as high performance laboratory freezers, and more specifically to the refrigeration system of such freezers that includes cascaded stages with adjustable expansion within the stages to achieve ultra-low temperature set points inside the cabinet. [Background technology]

[0003] Refrigeration systems are known for use with laboratory freezers of a type known as "high performance freezers" (the designation "high performance" typically depends on the specific limits of peak temperature change allowed within the freezers) and are used to cool their interior storage spaces to relatively low temperatures, such as, for example, about -20°C or lower. In one example, these high performance freezers are used to store blood and / or plasma. In so-called ultra-low temperature ("ULT") freezers, which cool the cabinet interior to low temperatures, such as -20°C to -90°C, cascaded refrigeration systems are used that include multiple refrigeration stages coupled in series to cool the cabinet interior to these ultra-low temperature set points. For example, various designs including variable speed and fixed speed compressors are used with ULT freezers in the refrigeration stages.

[0004] The initial pulldown from ambient temperature to the low temperature set point used in the ULT refrigerator tends to be a time-consuming process, sometimes taking several hours. Similarly, restoring the temperature set point after a door opening, power loss, or similar event can also generally be a time-consuming process. When storing temperature-sensitive items such as blood and plasma or other biological samples, it is important to maintain the temperature of the stored items near the low temperature set point while minimizing temperature spikes caused by these events. Although refrigeration systems associated with ULT refrigerators are typically configured to perform optimally in the worst operating conditions, such conditions (high ambient temperatures, frequent door openings, etc.) do not exist in all environments. For example, a refrigeration system designed to operate in a lower temperature range (e.g., -60°C to -90°C) effectively achieves minimized temperature spikes or non-uniformities in the internal heat exchangers as well as the cabinet interior at an operating set point temperature of, for example, -80°C. However, the same conventional refrigeration systems operating at widely different set point temperatures (e.g., -50°C) will encounter higher levels of temperature spikes and non-uniformities within the heat exchangers and cabinets, and may be difficult to respond to effectively and efficiently to minimize these higher levels of temperature spikes or non-uniformities. Thus, conventional refrigeration systems of ULT chillers often do not perform in an optimal and energy-efficient manner over a wide range of operating temperatures, e.g., from about -20°C to about -90°C. Considering these design parameters, it is desirable to further improve the performance and energy efficiency of ULT chillers and their associated cascaded refrigeration systems.

[0005] Thus, a need exists for further improvements in refrigeration systems for use with laboratory freezers that address these and other deficiencies of known designs. Summary of the Invention

[0006] According to one embodiment of the invention, a cascade refrigeration system includes a first and a second refrigeration stage. The first refrigeration stage includes a first fluid circuit for circulating a first refrigerant, a first compressor, a condenser, and a first expansion device in fluid communication with the first fluid circuit. The second refrigeration stage includes a second fluid circuit for circulating a second refrigerant. The second refrigeration stage is fluidly separated from the first fluid circuit and includes a second compressor, a second expansion device, and an evaporator in fluid communication with the second fluid circuit. The refrigeration system further includes at least one heat exchanger in heat transfer communication with the first and second fluid circuits for exchanging heat between the first and second refrigerants. The first and second refrigeration stages thus define at least a portion of a cascade cooling arrangement. The second expansion device of the second fluid circuit further includes a first capillary tube and a second capillary tube arranged in co-flow, and a second stage valve in fluid communication with the second capillary tube for selectively controlling the flow of the second refrigerant through the second capillary tube in response to at least one operating condition of the refrigeration system without blocking the flow of the second refrigerant through the first capillary tube to provide an adjustable or variable amount of expansion of the refrigerant.

[0007] According to one aspect of the invention, the first fluid circuit includes a first fluid line in fluid communication with the outlet of the first condenser and the first inlet of at least one interstage heat exchanger. The first fluid line includes a first expansion device. The first fluid circuit further includes a first suction line in fluid communication with the first outlet of the at least one interstage heat exchanger and the inlet of the first compressor, and a first heat exchanger defined by a portion of the first fluid line or a portion of the first expansion device in heat transfer communication with a portion of the first suction line, thereby exchanging heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line. According to a further aspect, the second fluid circuit includes a second fluid line in fluid communication with the second outlet of the at least one interstage heat exchanger and the inlet of the evaporator. The second fluid line includes a second expansion device. The second fluid line also includes a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor, and a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device in heat transfer communication with a portion of the second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

[0008] In another aspect of the invention, the second fluid circuit includes a second fluid line in fluid communication with the second outlet of the at least one interstage heat exchanger and the inlet of the evaporator. The second fluid line includes a second expansion device. The second fluid line also includes a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor, and a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device in heat transfer communication with a portion of the second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

[0009] According to one aspect of the invention, the first expansion device comprises an electronic expansion valve. In another aspect, the second stage valve comprises a solenoid valve. In yet another aspect, the second stage valve comprises an electronic expansion valve.

[0010] According to one aspect of the invention, the first expansion device includes a third capillary and a fourth capillary in a co-flow arrangement, and a first stage valve for selectively controlling the flow of the first refrigerant through the fourth capillary in response to at least one operating condition of the refrigeration system without blocking the flow of the first refrigerant through the third capillary. According to a further aspect, the first fluid circuit includes a first fluid line in fluid communication with an outlet of the first condenser and a first inlet of the at least one interstage heat exchanger. The first fluid line includes a first expansion device. The first fluid line also includes a first suction line in fluid communication with the first outlet of the at least one interstage heat exchanger and the inlet of the first compressor, and a first heat exchanger defined by a portion of the first suction line in heat transfer communication with a portion of the first fluid line or a portion of the first expansion device, thereby exchanging heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line.

[0011] According to one embodiment, the second fluid circuit includes a second fluid line in fluid communication with the second outlet of the at least one interstage heat exchanger and the inlet of the evaporator. The second fluid line includes a second expansion device. The second fluid line also includes a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor, and a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device in heat transfer communication with a portion of the second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

[0012] According to one aspect of the invention, the first stage valve is a solenoid valve. According to another aspect, the first stage valve is an electronic expansion valve. According to yet another aspect, the second stage valve is an electronic expansion valve. According to one aspect, the second stage valve comprises a solenoid valve.

[0013] According to one aspect of the invention, a refrigeration system is associated with a cabinet having a refrigerated interior, and first and second refrigeration stages operate to cool the cabinet to a temperature set point in the range of -20°C to -90°C.

[0014] According to another embodiment of the invention, a refrigerator includes a cabinet interior and a cabinet having a door providing access to the cabinet interior. The refrigerator also includes a cascaded refrigeration system having first and second refrigeration stages. The first refrigeration stage includes a first fluid circuit for circulating a first refrigerant, a first compressor, a condenser, and a first expansion device in fluid communication with the first fluid circuit. The second refrigeration stage includes a second fluid circuit for circulating a second refrigerant. The second refrigeration stage is fluidly separated from the first fluid circuit and includes a second compressor, a second expansion device, and an evaporator in fluid communication with the second fluid circuit. The refrigeration system further includes at least one heat exchanger in heat transfer communication with the first and second fluid circuits for exchanging heat between the first and second refrigerants. Thus, the first and second refrigeration stages define at least a portion of a cascaded cooling arrangement. The second expansion device of the second fluid circuit further includes a first capillary tube and a second capillary tube arranged in co-flow and a second stage valve in fluid communication with the second capillary tube for selectively controlling the flow of the second refrigerant through the second capillary tube in response to at least one operating condition of the refrigeration system without blocking the flow of the second refrigerant through the first capillary tube to provide an adjustable or variable amount of expansion of the refrigerant. The refrigerator of the present invention achieves improved operating performance as compared to refrigerators known in the art.

[0015] According to one aspect of the invention, the first fluid circuit includes a first fluid line in fluid communication with the outlet of the first condenser and the first inlet of at least one interstage heat exchanger. The first fluid line includes a first expansion device. The first fluid circuit also includes a first suction line in fluid communication with the first outlet of the at least one interstage heat exchanger and the inlet of the first compressor, and a first heat exchanger defined by a portion of the first fluid line in heat transfer communication with a portion of the first suction line or a portion of the first expansion device, thereby exchanging heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line. According to a further aspect, the second fluid circuit includes a second fluid line in fluid communication with the second outlet of the at least one interstage heat exchanger and the inlet of the evaporator. The second fluid line includes a second expansion device. The second fluid circuit also includes a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor, and a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device in heat transfer communication with a portion of the second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

[0016] According to another aspect, the second fluid circuit includes a second fluid line in fluid communication with the second outlet of the at least one interstage heat exchanger and the inlet of the evaporator. The second fluid line includes a second expansion device. The second fluid circuit also includes a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor, and a second heat exchanger defined by a portion of the second fluid line or the second expansion device in heat transfer communication with a portion of the second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

[0017] According to one embodiment, the first expansion device is an electronic expansion valve. According to another embodiment, the second stage valve is a solenoid valve.

[0018] According to one aspect of the invention, the first expansion device includes a third capillary tube and a fourth capillary tube arranged in parallel flow, and a first stage valve for selectively controlling the flow of the first refrigerant through the fourth capillary tube in response to at least one operating condition of the refrigeration system without blocking the flow of the first refrigerant through the third capillary tube.

[0019] According to another aspect of the invention, the first fluid circuit includes a first fluid line in fluid communication with the outlet of the first condenser and the first inlet of at least one interstage heat exchanger. The first fluid line includes a first expansion device. The first fluid circuit also includes a first suction line in fluid communication with the first outlet of the at least one interstage heat exchanger and the inlet of the first compressor, and a first heat exchanger defined by a portion of the first suction line in heat transfer communication with a portion of the first fluid line or a portion of the first expansion device, thereby exchanging heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line. According to a further aspect, the second fluid circuit includes a second fluid line in fluid communication with the second outlet of the at least one interstage heat exchanger and the inlet of the evaporator. The second fluid line includes a second expansion device. The second fluid line also includes a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor, and a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device in heat transfer communication with a portion of the second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

[0020] According to one aspect, the first stage valve is a solenoid valve. According to another aspect, the first and second refrigeration stages operate to cool the cabinet interior to a temperature set point in the range of -20°C to -90°C.

[0021] These and other objects and advantages of the present invention will become more apparent through the following detailed description taken in conjunction with the drawings herein. [Brief description of the drawings]

[0022] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the general description of the invention provided above and the detailed description of the embodiments provided below, explain the principles of the invention. [Figure 1] FIG. 1 is a perspective view of a refrigerator including a cabinet and a deck configured to include a cascade refrigeration system for cooling the cabinet to cryogenic temperatures, according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of an exemplary cascade refrigeration system for cooling the refrigerator cabinet of FIG. 1. [Diagram 3] FIG. 3 is a simplified schematic diagram of the main elements of the first and second refrigeration stages of the cascade refrigeration system of FIG. 2 according to a first embodiment having a parallel capillary tube as the expansion device of one of the refrigeration stages. [Figure 4] FIG. 3 is a simplified schematic diagram of the main elements of the first and second refrigeration stages of the cascade refrigeration system of FIG. 2 according to a second embodiment having parallel capillaries as expansion devices in both refrigeration stages. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] With reference to the figures, an exemplary high performance laboratory freezer 10 according to an embodiment of the present invention is illustrated. While the terms "high performance laboratory freezer" and "freezer" are used throughout the specification, it will be understood that the present invention encompasses any type of cooling device, including, for example, any type of refrigerator or freezer. As shown in FIG. 1, the freezer 10 includes a cabinet 12 for storing items requiring cooling, for example, to a temperature of about -20°C or below. In this regard, the freezer 10 may be considered, for example, a very low temperature ("ULT") freezer designed to operate in a temperature range of about -20°C to about -90°C. The cabinet 12 includes a cabinet housing 14 defining a generally rectangular cross-section and a door 16 providing access to a refrigerated interior 18 of the cabinet 12 through a cabinet opening. The refrigerated cabinet interior 18 is configured to receive a product to be kept at a low temperature, such as, for example, blood or other biological samples or drugs. Cabinet 12 is mounted atop a deck 20 that is configured to contain a refrigeration system 22 (FIG. 2) of refrigerator 10, as described in more detail below.

[0024] An exemplary refrigeration system 22 of the present invention includes first and second cascaded refrigeration stages, each of which includes one or more expansion devices that provide an adjustable or variable amount of refrigerant expansion to enable each of the heat exchangers in the refrigeration stages to operate at an optimized temperature when cooling the cabinet interior 18 to a temperature setpoint. As described in more detail below, in one embodiment, the second refrigeration stage includes a pair of capillaries (e.g., first and second capillaries) arranged in parallel flow and a valve that controls refrigerant flow to one of the capillaries to provide adjustable refrigerant expansion. More specifically, refrigerant flows freely through the first capillary while a valve is provided to selectively control refrigerant flow through the second capillary in response to at least one operating condition of the refrigeration system without blocking refrigerant flow through the first capillary. In this regard, operation of the refrigeration system 22, in the context of a ULT chiller, provides a variable amount of refrigerant expansion at the very low operating temperature of the second refrigeration stage. Thus, the refrigerator 10 of the following embodiments provides optimal performance (including minimized energy consumption and minimized peak temperature change over time) over a range of operating conditions, not just worst case operating conditions.

[0025] One example of a detailed schematic layout of a cascade refrigeration system 22 for use with an embodiment of the chiller 10 of the present invention is shown with reference to Figure 2. As shown in this schematic layout, the refrigeration system 22 comprises a first refrigeration stage 24 and a second refrigeration stage 26 that define a first fluid circuit 28 and a second fluid circuit 30, respectively. The first fluid circuit 28 and the second fluid circuit 30 are provided for circulating a first refrigerant 32 and a second refrigerant 34, respectively. The first refrigeration stage 24 transfers energy (e.g., heat) from the first refrigerant 32 to the surrounding environment 36, while the second refrigerant 34 of the second refrigeration stage 26 receives thermal energy from the cabinet interior 18. With the first fluid circuit 28 and the second fluid circuit 30 fluidly isolated from each other but in thermal communication with each other via the interstage heat exchanger 38, heat is transferred from the second refrigerant 34 to the first refrigerant 32 through the interstage heat exchanger 38, which is in fluid communication with the first refrigeration stage 24 and the second refrigeration stage 26 of the refrigeration system 22.

[0026] The first refrigeration stage 24 includes, in order, a first compressor 40, a condenser 42, a first expansion device 44, and an interstage heat exchanger 38. A blower 46 directs filtered ambient air across the condenser 42 to facilitate the transfer of heat from the first refrigerant 32 to the ambient environment 36. The second refrigeration stage 26 also includes, in order, a second compressor 48, an interstage heat exchanger 38, a second expansion device 50, and an evaporator 52. The evaporator 52 is in thermal communication with the cabinet interior 18 of the cabinet 12 such that heat is transferred from the cabinet interior 18 to the second refrigerant 34 circulating through the evaporator 52, thereby cooling the cabinet interior 18. Each of first refrigeration stage 24 and second refrigeration stage 26 may include various other additional components as are known, such as, for example, an oil separator, attemperator, filter dryer, and / or suction accumulator, etc. The performance of these various additional elements in refrigeration system 22 will not be described as they will be well understood by those skilled in the art of refrigeration.

[0027] 2, during operation, the second refrigerant 34 receives heat from the cabinet interior 18 through the evaporator 52 and flows from the evaporator 52 to the second compressor 48, as indicated by the arrows. From the second compressor 48, the compressed second refrigerant 34 flows into an interstage heat exchanger 38 that is in thermal communication with the first refrigeration stage 24 and the second refrigeration stage 26. The second refrigerant 34 enters the interstage heat exchanger 38 in gas form to transfer heat to the first refrigerant 32 as the second refrigerant 34 condenses. In this regard, the flow of the first refrigerant 32 may be counter-current to the second refrigerant 34, for example, to maximize the rate of heat transfer. In one specific, non-limiting example, the heat exchanger 38 is in the form of a brazed plate heat exchanger oriented vertically within the deck 20 of the chiller 10 and designed to maximize the amount of turbulence of the first and second refrigerants 32, 34 within the interstage heat exchanger 38, thereby maximizing heat transfer from the condensing second refrigerant 34 to the evaporating first refrigerant 32. Other suitable types or configurations of heat exchangers are possible as well. As the process described above is repeated to cool the cabinet interior 18 of the chiller 10, the second refrigerant 34 exits the interstage heat exchanger 38 in liquid form, flows through the second expansion device 50, and then returns to the evaporator 52.

[0028] With continued reference to FIG. 2, during operation, the first refrigerant 32 flows through the first refrigeration stage 24. Specifically, the first refrigerant 32 receives thermal energy from the second refrigerant 34 flowing through the interstage heat exchanger 38 as described above, and then exits the interstage heat exchanger 38 in gas form to the first compressor 40. The compressed first refrigerant 32 flows from the first compressor 40 to the condenser 42. The first refrigerant 32 in the condenser 42 transfers heat to the surrounding environment 36 as the first refrigerant 32 condenses before flowing in liquid form to the first expansion device 44, where the first refrigerant 32 undergoes a pressure drop. The first refrigerant 32 again flows in liquid form from the first expansion device 44 to the interstage heat exchanger 38.

[0029] With continued reference to FIG. 2, at least one of the first compressor 40 or the second compressor 48 of this embodiment of the refrigeration system 22 is a variable speed compressor. In a specific embodiment, the first compressor 40 and the second compressor 48 may have different maximum capacities. For example, but not limited to, the second compressor 48 may have a maximum capacity that is less than the maximum capacity of the first compressor 40. Alternatively, the maximum capacities of the first compressor 40 and the second compressor 48 may be substantially equal. Furthermore, operation of the system 22 may be designed such that in a steady state mode, one or both compressors 40, 48 operate at or below their maximum capacity, which may be desirable, for example, to maximize the life of the compressors 40, 48. In other embodiments, the first compressor 40 and / or the second compressor 48 are fixed speed compressors. To this end, the use of adjustable expansion in the refrigeration stages 24, 26 allows for variation of operating parameters to improve efficiency, even with fixed speed compressors.

[0030] As shown in FIG. 2, the refrigeration system 22 also includes an exemplary controller 54 operably coupled to each of the first compressor 40 and the second compressor 48 for independently controlling each of the compressors 40, 48. While this embodiment illustrates a single controller 54, one of ordinary skill in the art will readily recognize that the system 22 may instead have any other number of controllers. An exemplary interface 56 is operably coupled to the controller 54 to enable a user to interact with the controller 54. Such interaction may include, for example, selecting among different operating modes of the system 22. The controller 54 also includes a plurality of sensors S1-S2 configured to sense different properties of the first refrigerant 32 and the second refrigerant 34 along the first fluid circuit 28 and the second fluid circuit 30 of the first refrigeration stage 24 and / or the second refrigeration stage 26. 11 is operatively coupled to

[0031] As shown in FIG. 2, the first fluid circuit 28 includes a suction pressure sensor S1 configured to measure the suction pressure generated by the first compressor 40, and a suction temperature sensor S2 configured to measure the temperature of the refrigerant 32 entering the first compressor 40. The first fluid circuit 28 further includes a liquid temperature sensor S3 operatively disposed in series between the condenser 42 and the expansion device 44 and configured to measure the temperature of the liquid refrigerant 32 exiting the condenser 42. The interstage heat exchanger 38 includes at least a temperature sensor S4 for measuring an operating temperature of the interstage heat exchanger 38. The temperature sensor S4 may be located on an exterior surface of the heat exchanger 38. For example, the temperature sensor S4 may be located on the exterior surface near the middle of the heat exchanger 38, or alternatively, on a lower portion of the exterior surface of the heat exchanger 38. The first fluid circuit also includes a temperature sensor S4 configured to measure the temperature of the refrigerant at the outlet of the heat exchanger 38. 11 Includes.

[0032] The second fluid circuit 30 also includes a suction pressure sensor S5 configured to measure the suction pressure generated by the second compressor 48, and a suction temperature sensor S6 configured to measure the temperature of the refrigerant 34 entering the second compressor 48. The second fluid circuit 30 further includes a liquid temperature sensor S7 operatively disposed in series between the interstage heat exchanger 38 and the expansion device 50 and configured to measure the temperature of the refrigerant 32 exiting the interstage heat exchanger 38. The second fluid circuit also includes at least an evaporator inlet temperature sensor S8 and an evaporator outlet temperature sensor S9 configured to measure the temperature of the refrigerant 34 entering and exiting the evaporator 52, respectively. The cabinet interior 18 includes at least a cabinet temperature probe S1 configured to measure the temperature of the cabinet interior 18. 10 The refrigeration system also includes an ambient air temperature sensor (not shown) for measuring the temperature of the ambient air surrounding the system 22, as well as various other sensors for detecting operating parameters of the refrigerator 10, such as, for example, a door 16 open sensor (not shown). As will be described in more detail below, sensors S1-S 11The sensors are configured to generate respective signals indicative of selected operating conditions of the refrigerator 10 to the controller 54 such that, in turn, in response to the signals generated by the sensors, the controller 54 can generate respective control signals for various operations of the system 22.

[0033] Having described the detailed structural layout of the refrigeration system 22 for use with embodiments of the chiller 10 of the present invention, reference is now made to Figure 3, which illustrates a specific embodiment that enables the chiller 10 to perform optimally. The cascade refrigeration system 22 is again shown, but with only the core equipment elements for ease of illustration. It will be understood that additional equipment consistent with that shown in Figure 2 and described above will also typically be included in this embodiment.

[0034] 3, the refrigeration system 22 again includes a first refrigeration stage 24 including, in order, a first compressor 40, a condenser 42, a first expansion device 44, and an interstage heat exchanger 38 to define a first fluid circuit 28 through which a first refrigerant 32 flows. More specifically, the first fluid circuit 28 is defined by a first fluid line 66 for conveying the refrigerant 32 from an outlet of the condenser 42 to a first inlet 68 of the interstage heat exchanger 38, as indicated by the arrows, and a first suction line 70 for conveying the refrigerant 32 from a first outlet 72 of the interstage heat exchanger 38 to an inlet of the first compressor 40. A fluid line 71 is provided from the outlet of the first compressor 40 to the inlet of the condenser 42 to convey the refrigerant 32 back to the condenser 42. As shown, first expansion device 44 is disposed along a first fluid line 66 and first compressor 40 is disposed along a first suction line 70 .

[0035] The refrigeration system 22 also includes a second refrigeration stage 26 having, in order, a second expansion device 50, an evaporator 52, a second compressor 48, and an interstage heat exchanger 38 to define a second fluid circuit 30 through which a second refrigerant 34 flows. The second fluid circuit 30 is defined by a second fluid line 74 for conveying the refrigerant 34 from a second outlet 76 of the interstage heat exchanger 38 to the evaporator 52, as indicated by the arrows, and a second suction line 78 for conveying the refrigerant 34 from the evaporator 52 back to a second inlet 80 to the interstage heat exchanger 38. As shown, the second expansion device 50 is disposed along the second fluid line 74 and the second compressor 48 is disposed along the second suction line 78. The second fluid line 74 may be temporarily branched into multiple fluid lines arranged in parallel flow to accommodate components of the expansion device 50, for reasons that will become more apparent below.

[0036] To enable each of the heat exchange elements (e.g., the condenser 42, the interstage heat exchanger 38, and the evaporator 52) to operate at a respective optimized temperature for the current operating conditions of the chiller 10, the first expansion device 44 and the second expansion device 50 are provided in this embodiment as adjustable expansion devices. In that regard, the first expansion device 44 is in the form of an electronic expansion valve ("EEV") 58. The second expansion device 50 is defined by a first capillary tube 60 and a second capillary tube 62 arranged in parallel flow with a valve 64 positioned upstream of the second capillary tube 62 for selectively controlling the flow of the second refrigerant 34 through the second capillary tube 62. More specifically, the valve 64 is positioned to control only the flow of the second refrigerant 34 through the second capillary tube 62. Thus, the second refrigerant 34 is free to flow from the interstage heat exchanger 38 through the first capillary tube 60 regardless of the operational state of the valve 64 (e.g., whether the valve 64 is open or closed). When the valve 64 is open, the second refrigerant 34, in addition to flowing through the first capillary tube 60, also flows through the second capillary tube 62. To this end, the second fluid line 74 branches into parallel flow fluid lines to accommodate the first capillary tube 60 and the second capillary tube 62, but the parallel flow fluid lines recombine into a single fluid line to direct a single flow of refrigerant 34 into the evaporator 52. The adjustable expansion provided by these elements in both refrigeration stages 24, 26 (in combination with setting the speeds of the first compressor 40 and the second compressor 48, if such elements are variable speed compressors) serves to set the temperature of the refrigerant flowing through each of the heat exchange elements in a manner that can be controlled to be optimized for the current cabinet interior 18 setpoint temperature or other current operating conditions in the chiller 10, such as, for example, ambient temperature. In another embodiment, the parallel flow fluid lines from the first capillary tube 60 and the second capillary tube 62 each flow into the evaporator 52 without recombining. The length of the second fluid line 74 from the second outlet 76 to the second capillary tube 62 can be longer than the length of the second fluid line 74 from the second capillary tube 62 to the evaporator 52.The length of the second fluid line 74 from the second outlet 76 to the first capillary tube 60 may be longer than the length of the second fluid line 74 from the first capillary tube 60 to the evaporator 52 .

[0037] The electronic expansion valve 58 forming the first expansion device 44 in this embodiment may be of any known commercial design capable of controlling the flow of refrigerant into the interstage heat exchanger 38. In that regard, the electronic expansion valve 58 is capable of reliably regulating the expansion and flow of the refrigerant in the operating temperature range of the first refrigerant 32 used in the first refrigeration stage 24 of the cascade refrigeration system 22. In contrast, the second expansion device 50 of the second refrigeration stage 26 is provided by two capillary tubes 60, 62 and a valve 64 arranged in parallel flow. Each capillary tube 60, 62 may have the same or different lengths and cross-sectional sizes, whereby an adjustable amount of expansion of the refrigerant 34 is provided by selectively flowing the refrigerant 34 through one or both of the capillary tubes 60, 62 through the operation of the valve 64. In that regard, the valve 64 is a solenoid valve capable of operating in the low temperature region of the second refrigeration stage 26.

[0038] As an example, at a predetermined temperature set point, such as a high temperature set point (e.g., −50° C.), the valve 64 is opened to increase the mass flow rate of the refrigerant 34 through the evaporator 52. In this regard, the flow of the refrigerant 34 through the first capillary tube 60 and the second capillary tube 62 increases the mass flow rate of the refrigerant 34 through the evaporator 52 and raises the temperature of the evaporator 52, which also improves system efficiency and reduces the variation of temperature peaks in the cabinet interior 18. To this end, the increase in the mass flow rate of the refrigerant 34 through the evaporator 52 minimizes extreme cold spots in the cabinet interior 18 and reduces the variation of temperature peaks in the cabinet interior across different ambient conditions. The valve 64 may be similar to, for example, a Type EVU solenoid valve available from Danfoss LLC, Baltimore, Maryland. Operation of the valve 64 may be manual or responsive to at least one operating condition of the refrigeration system 22. Thus, the valve 64 may be in a normally closed position and may be powered open upon receiving an appropriate signal.

[0039] The operation of the valve 64 may be based on current operating conditions and instructions from the main controller 54. In one embodiment, the controller 54 controls the cabinet temperature probe S 10 The valve 64 is operated in response to the actual temperature of the cabinet interior 18 as measured by, for example, a cabinet temperature probe S 10 If the temperature inside the cabinet 18 measured by the cabinet temperature probe S is greater than -55°C, the controller operates to open the valve 64. 10 If the temperature of the cabinet interior 18 measured by is lower than -55°C, the controller 54 operates to close the valve 64. In another embodiment, the second stage valve 64 is controlled by a set point at the beginning of the steady state cycle. For example, the valve 64 is closed if the set point is lower than -60°C, and the valve 64 is opened if the set point is higher than -60°C. In another embodiment, the solenoid valve 64 is controlled by the superheat of the evaporator 52 (e.g., the second stage valve 64 is opened if the superheat of the evaporator 52 is greater than a threshold). To this end, further control of the temperature of the cabinet interior 18 can be achieved, for example, by varying the speed of the compressor 48. This adjustable expansion of the refrigerant provided to at least the second refrigeration stage 26 sets the temperature of the refrigerant 34 flowing through the evaporator 52 to minimize energy consumption as well as fluctuations in peak temperature around the set point of the cabinet interior 18. These temperatures also optimize temperature pull down and recovery times by causing their operation to occur more quickly than if the refrigerant in the evaporator 52 had a different operating temperature.

[0040] Both the diverter valve 64 and the capillary tubes 60, 62 continue to reliably operate throughout the entire operating temperature range of the second refrigeration stage 26. For example, the range of cabinet temperatures and set points typically encountered in a ULT chiller is approximately -20°C to -90°C. Note that while the adjustment of the set point is generally referred to in this description as the set point temperature of the cabinet interior 18, the set point may also refer to setting the temperature of one or more heat exchangers within the chiller 10. Conventional ULT chiller refrigeration systems are typically set such that the operating temperatures of the heat exchange elements perform optimally in the worst case operating conditions (e.g., optimally cooling to a set point temperature of -80°C or lower at an ambient outside temperature of 20°C, and reliably operating within an ambient temperature range of 10°C to 35°C). To this end, typically one or both compressors and expansion devices are specifically tuned for this one use case or operating condition, meaning that whenever the ULT chiller operates at other operating conditions, performance is not optimized because the heat exchange devices are at temperatures that are not adapted for maximum energy efficiency and heat transfer at the other operating conditions. However, the adjustable expansion provided by the electronic expansion valve 58 and by the capillary tubes 60, 62 alone or in combination with the various speeds of the compressors 40, 48 allows more precise control options for setting the operating temperatures of the heat exchange elements, including the condenser 42, the interstage heat exchanger 38, and the evaporator 52. Thus, optimized temperature settings for each of these heat exchange elements can be provided in response to the operating conditions measured by various sensors in communication with the main controller 54.

[0041] To further optimize the performance and efficiency of the refrigeration system 22, the first refrigeration stage 24 and the second refrigeration stage 26 may each include a heat exchanger 82, 84, respectively. Depending on the system configuration, the heat exchangers 82, 84 may be in the form of a liquid line to suction line heat exchanger ("LLSLHX") or a capillary tube to suction line heat exchanger ("CTSLHX"). In the parallel capillary configuration described above with respect to FIG. 3, typically the capillary not associated with a solenoid valve (e.g., the first capillary 60) includes a heat exchanger in the form of a CTSLHX. If the expansion device does not include a capillary, the heat exchanger is in the form of a LLSLHX.

[0042] 3, the heat exchanger 82 is in the form of a LLSLHX. As an example, the heat exchanger 82 of the first refrigeration stage 24 forms part of the first fluid circuit 28, in which a section 86 of the first fluid line 66 is arranged in heat transfer communication with a section 88 of the first suction line 70 to transfer heat from the refrigerant 32 flowing through the first fluid line 66 to the refrigerant 32 flowing through the first suction line 70. As shown, the section 86 of the first fluid line 66 forming part of the heat exchanger 82 is located upstream of the first expansion device 44 to subcool the hot refrigerant 32 before it enters the first expansion device 44 and ultimately the interstage heat exchanger 38. Subcooling the refrigerant 32 improves the operation of the first expansion device 44 and the interstage heat exchanger 38, and thus the efficiency of the system. A section 88 of the first suction line 70, which forms part of the heat exchanger 82, is located upstream of the first compressor 40 for heating the refrigerant 32 before it enters the first compressor 40. More specifically, heating the refrigerant 32 improves system reliability by vaporizing any liquid droplets that accumulate within the first suction line 70.

[0043] With continued reference to FIG. 3, the heat exchanger 84 of the second refrigeration stage 26 is in the form of a CTSLHX. In that regard, the heat exchanger 84 forms part of the second fluid circuit 30, in which a portion or the entirety of the first capillary tube 60 is disposed in heat transfer communication with the section 90 of the second suction line 78 to transfer heat from the refrigerant 34 flowing through the first capillary tube 60 to the refrigerant 34 flowing through the second suction line 78. In some embodiments, the second capillary tube 62 is separate from the heat exchanger 84. Separating the second capillary tube from the heat exchanger 84 can increase the energy efficiency of the system. For example, the refrigerant 34 flowing through the first capillary tube 60 cools the refrigerant flowing through the section 90 of the second suction line 78, while the refrigerant flowing through the second capillary tube 62 retains its temperature as the refrigerant flows to the evaporator. In some embodiments, the heat exchanger 84 may be defined by a portion or the entirety of the first capillary 60 that is arranged in heat transfer communication with a section 90 of the second suction line 78 to transfer heat from the refrigerant 34 flowing through the first capillary 60 to the refrigerant 34 flowing through the second suction line 78, while the second capillary 62 is isolated from heat transfer communication with the section 90 of the second suction line 78. The section 90 of the second suction line 78 that forms part of the heat exchanger 84 is also located upstream of the second compressor 48 to heat the refrigerant 34 before it enters the compressor 48. Heating the refrigerant 34 before it enters the compressor 48 can maximize the amount of gas, rather than liquid, that flows into the compressor. Increasing the amount of gas, rather than liquid, that flows into the compressor can improve the reliability of the compressor. This can also reduce or eliminate condensation on the compressor shell. In another embodiment, the heat exchanger 84 may be defined by a portion or the entirety of the second capillary tube 62 disposed in heat transfer communication with a section 90 of the second suction line 78 to transfer heat from the refrigerant 34 flowing through the second capillary tube 62 to the refrigerant 34 flowing through the second suction line 78. In yet another embodiment, the heat exchanger 84 may be a LLSLHX defined by a portion of the second fluid line 74 disposed in heat transfer communication with the section 90 of the second suction line 78.The second capillary 62 being in heat transfer communication with the section 90 of the second inlet line 78 may allow for easier manufacture. For example, it may be easier to have only the second capillary 62 in heat transfer communication than to have both the first capillary 60 and the second capillary 62. Although the capillary and liquid line may each achieve the same heat transfer rate, the capillary may achieve the heat transfer rate over a shorter tube length than the liquid line. The capillary may provide a faster pulldown of the temperature of the heat exchanger 84 than the liquid line.

[0044] To provide one example of the operation of the refrigeration system 22 described above with respect to Figures 1-3, in a first operating state, the chiller 10 is tasked with setting the cabinet interior 18 to -86°C when the ambient temperature surrounding the cabinet 12 is 20°C. In this state, the controller 54 operates the electronic expansion valve 58 of the first refrigeration stage 24 by actively controlling the superheat of the refrigerant 32 in the interstage heat exchanger 38, and also operates the second stage valve 64 to close and allow the refrigerant 34 to flow only through the first capillary tube 60 into the second refrigeration stage 26. The second stage valve 64 is connected to a cabinet temperature probe S. 10 The refrigeration stage 42 controls the temperature of the evaporator 52 in response to the temperature of the cabinet interior 18 measured by the refrigeration controller 46. This adjustable amount of expansion of the refrigerant provided to the first refrigeration stage 24 and the second refrigeration stage 26 sets the temperatures of the refrigerants 32, 34 flowing through the condenser 42, the interstage heat exchanger 38, and the evaporator 52, respectively, to minimize energy consumption and allowable peak temperature fluctuations about the set point of the cabinet interior 18. These temperatures also optimize temperature pull-down and recovery times by allowing their operation to occur more quickly than would be the case with different operating temperatures in the heat exchange elements.

[0045] Now assume that the chiller 10 changes mode to a second operating state to set the cabinet interior 18 to -50°C with the ambient temperature reduced to 10°C. To compensate for these operational differences, the controller 54 then adjusts the operation of the compressors 40, 48 (e.g., variable speed compressors) and the first and second expansion devices 44, 50. Compared to the first operating state, the electronic expansion valve 58 adjusts to the same superheat set point while the second stage valve 64 is open. Adjusting the expansion and / or compression of the refrigerant changes the operating temperatures of the refrigerant 32, 34 delivered to the condenser 42, the interstage heat exchanger 38, and the evaporator 52. These new operating temperatures are adapted for more energy-efficient performance and heat transfer for the second operating state than if the temperatures were repeated from the first operating state. Furthermore, adjustable expansion is reliably enabled by selective use of the first capillary 60 and the second capillary 62 of the second refrigeration stage 26 to improve performance of the refrigerator 10 under a plurality of different operating conditions.

[0046] In summary, the use of adjustable refrigerant expansion in chiller 10 according to embodiments of the present invention allows for a wider range of optimal performance operating set points (e.g., in one example, −20° C. to −90° C.). At any set point within this wider range, chiller 10 functions to maintain consistently low evaporator 52 (and other heat exchanger) temperature profile non-uniformity, i.e., minimized spikes, over the operating cycle. By virtue of the low level of temperature non-uniformity achieved, fluctuations in cabinet interior 18 temperature peaks are also minimized. This results in improved or minimized energy consumption at all set points, improving the operational stability and reliability of chiller 10. Thus, chiller 10 of the present invention provides several technical advantages and benefits over conventional designs.

[0047] In an alternative embodiment of the refrigeration system 22 described above with respect to FIGS. 1-3, the second stage valve 64 may instead be an electronic expansion valve. In that regard, the controller 54 is configured to operate the electronic expansion valve between a fully closed position and a fully open position in the same manner as the second stage valve 64 described above. Additionally, the controller 54 is configured to operate the electronic expansion valve to precisely control the flow of refrigerant 34 through the second capillary tube 62, thereby controlling the load in smaller increments. The controller 54 may be configured to operate the electronic expansion valve in this manner, and in response to the temperature of the heat exchanger 84 measured by the temperature sensor S4, such as during pulldown. The controller is configured to precisely adjust the electronic expansion valve in response to the temperature difference between the evaporator inlet temperature measured by the temperature sensor S8 and the evaporator outlet temperature measured by the temperature sensor S9, once steady state operation is achieved. To this end, the electronic expansion valve may be throttled anywhere between a fully open position and a fully closed position to accommodate the demands of the system 22. As a result, the flow and expansion of the refrigerant 34 within the second refrigeration stage 26 is more precisely controlled, resulting in, for example, reduced energy consumption and more precise response to changes in load experienced by the chiller 10. In this embodiment, the first refrigeration stage 24 may include a fluid line-to-suction line heat exchanger 82 disposed such that a section 86 of the first fluid line 66 is in heat transfer communication with a section 88 of the first suction line 70. Additionally, the second refrigeration stage 26a may also include a capillary-to-suction line heat exchanger 84 disposed such that a portion or all of the first capillary 60 is in heat transfer communication with a section 90 of the second suction line 78.

[0048] In another alternative embodiment of the refrigeration system 22 described above with respect to Figures 1-3, the second stage valve 64 and the second capillary tube 62 may be replaced with a single electronic expansion valve. In that regard, the controller 54 is configured to operate the electronic expansion valve between fully closed and fully open positions in the same manner as the second stage 64 described above. Additionally, the controller 54 is configured to operate the electronic expansion valve to precisely control the flow of refrigerant 34 through the second capillary tube 62, thereby controlling the load in smaller increments. The controller 54 may be configured to operate the electronic expansion valve in this manner, and in response to the temperature of the heat exchanger 84 measured by the temperature sensor S4, such as during pulldown. The controller is configured to precisely adjust the electronic expansion valve in response to the temperature difference between the evaporator inlet temperature measured by the temperature sensor S8 and the evaporator outlet temperature measured by the temperature sensor S9, once steady state operation is achieved. To this end, the electronic expansion valve may be throttled anywhere between a fully open and a fully closed position to accommodate the demands of the system 22. As a result, the flow and expansion of the refrigerant 34 in the second refrigeration stage 26 may be more precisely controlled, resulting in, for example, reduced energy consumption and more precise response to changes in the load experienced by the chiller 10. In this embodiment, the first refrigeration stage 24 may include a liquid line-to-suction line heat exchanger 82, in which a section 86 of the first fluid line 66 is disposed in heat transfer communication with a section 88 of the first suction line 70. Additionally, the second refrigeration stage 26a may also include a capillary-to-suction line heat exchanger 84, in which a portion or the entirety of the first capillary 60 is disposed in heat transfer communication with a section 90 of the second suction line 78.

[0049] In another alternative embodiment of the refrigeration system 22 described above with respect to Figures 1-3, the second stage valve 64 and the second capillary tube 62 are replaced with a single electronic expansion valve, and the first capillary tube 60 is also replaced with a single electronic expansion valve. In that regard, the two electronic expansion valves are arranged in parallel flow. The controller 54 is configured to operate each electronic expansion valve to control the superheat of the evaporator 52. More specifically, the controller 54 is configured to operate each electronic expansion valve between a fully closed position and a fully open position in the same manner as the second stage valve 64 described above. Additionally, the controller 54 may be configured to operate one or both electronic expansion valves in this manner and in response to the temperature of the heat exchanger 84 measured by the temperature sensor S4, such as during pulldown. The controller is configured to precisely adjust each electronic expansion valve in response to the temperature difference between the evaporator inlet temperature measured by the temperature sensor S8 and the evaporator outlet temperature measured by the temperature sensor S9 once steady state operation is achieved. To this end, each electronic expansion valve may be throttled anywhere between a fully open and a fully closed position to accommodate the demands of the system 22. As a result, the flow and expansion of the refrigerant 34 in the second refrigeration stage 26 may be more precisely controlled, resulting in, for example, reduced energy consumption and more precise response to changes in the load experienced by the chiller 10. In this embodiment, the first refrigeration stage 24 may include a fluid line-to-suction line heat exchanger 82, in which a section 86 of the first fluid line 66 is disposed in heat transfer communication with a section 88 of the first suction line 70. Additionally, the second refrigeration stage 26a may also include a fluid line-to-suction line heat exchanger, in which a section of the second fluid line 74 is disposed in heat transfer communication with a section of the second suction line 78.

[0050] 4, where like numerals represent like features, there is shown details of a second embodiment of a refrigeration system 22a that may be used with chiller 10, in accordance with another embodiment of the present invention. The primary difference between refrigeration system 22a of this embodiment and refrigeration system 22 of the previously described embodiment is the configuration of the first refrigeration stage 24a. In that regard, refrigeration system 22a includes a first cascaded refrigeration stage 24a and a second cascaded refrigeration stage 26a in a similar configuration to the previously described embodiment, with many of the same elements (first compressor 40a, condenser 42a, interstage heat exchanger 38a, second compressor 48a, and evaporator 52a) having the same reference numerals and will not be described further herein. The second fluid circuit 30a is similar to the second fluid circuit 30 described above with respect to Figures 1-3 and includes a second expansion device 50a defined by a first capillary tube 60a and a second capillary tube 62a arranged in parallel flow with a valve 64a positioned upstream of the second capillary tube 62a to selectively control the flow of the second refrigerant 34a through the second capillary tube 62a. As in the embodiment described above with respect to Figure 3, the valve 64a is positioned to control only the flow of the second refrigerant 34a through the second capillary tube 62a. Thus, the second refrigerant 34a is free to flow from the interstage heat exchanger 38a through the first capillary tube 60a regardless of the operational state of the valve 64a (e.g., whether the valve 64a is open or closed). The second refrigeration stage 26a also includes a heat exchanger 84a in the form of a CTSLHX. In one embodiment, the heat exchanger 84a may be a LLSLHX defined by a portion of the second fluid line 74a disposed in heat transfer communication with a section 90a of the second suction line 78a.

[0051] The first fluid circuit 28a is defined by a first fluid line 66a for conveying the refrigerant 32a from the condenser 42a to a first inlet 68a of the interstage heat exchanger 38a, and a first suction line 70a for conveying the refrigerant 32a from a first outlet 72a of the interstage heat exchanger 38a to an inlet of the first compressor 40a, as indicated by the arrows. A fluid line 71a is provided from the outlet of the first compressor 40a to the inlet of the condenser 42a for conveying the refrigerant 32a back to the condenser 42a. As shown, the first expansion device 44a is disposed along the first fluid line 66a, and the second compressor 40a is disposed along the first suction line 70a. More specifically, the first fluid line 66a temporarily branches into multiple fluid lines arranged in parallel flow to accommodate the components of the expansion device 44a.

[0052] The parallel flow arrangement of the first fluid line 66a may be similar to the parallel flow arrangement of the second fluid line 74a of the second fluid circuit 30a. In that regard, the first expansion device 44a is defined by a parallel flow arranged first capillary tube 92 and a second capillary tube 94 with a valve 96 positioned upstream of the second capillary tube 94 to selectively control the flow of the first refrigerant 32a through the second capillary tube 94. More specifically, the valve 96 is positioned to control only the flow of the first refrigerant 32a through the second capillary tube 94. As a result, the first refrigerant 32a is free to flow from the condenser 42a through the first capillary tube 92 regardless of the operational state of the valve 96 (e.g., whether the valve 96 is open or closed). When the valve 96 is open, the first refrigerant 32a, in addition to flowing through the first capillary tube 92, also flows through the second capillary tube 94. To this end, the first fluid line 66a branches into a parallel flow fluid line to accommodate the first capillary tube 92 and the second capillary tube 94, but the parallel flow fluid lines recombine into a single fluid line 66a to direct a single flow of refrigerant 32a into the first inlet 68a of the interstage heat exchanger 38a.

[0053] The adjustable expansion provided by the parallel capillary arrangement in both refrigeration stages 24a, 26a (in combination with setting the speeds of the first compressor 40a and second compressor 48a, if such elements are variable speed compressors) serves to set the temperature of the refrigerant 32a, 34a flowing through each of the heat exchange elements (e.g., the condenser 42a, the interstage heat exchanger 38a, and the evaporator 52a) in a manner that can be controlled to be optimized for the current cabinet interior 18 setpoint temperature or other current operating conditions in the chiller 10.

[0054] To further optimize the performance, efficiency, and pulldown time of the refrigeration system 22a, the first refrigeration stage 24a also includes a heat exchanger 82a in the form of a CTSLHX. In that regard, the heat exchanger 82a forms part of the first fluid circuit 28a, in which a portion or all of the first capillary tube 92 is disposed in heat transfer communication with a section 98 of the first suction line 70a to transfer heat from the refrigerant 32a flowing through the first capillary tube 92 to the refrigerant 32a flowing through the first suction line 70a. To improve cycle efficiency, the section 98 of the first suction line 70a forming part of the heat exchanger 82a is located upstream of the first compressor 40a to heat the refrigerant 32a before it enters the compressor 40a. In one embodiment, the heat exchanger 82a may be a LLSLHX defined by a portion of the first fluid line 66a disposed in heat transfer communication with the section 98a of the first suction line 70a.

[0055] The present invention has been illustrated by the description of several exemplary embodiments, and while these embodiments have been described in detail, it is not the intention of the applicant to limit or in any way limit the scope of the appended claims to such details. Additional advantages and modifications will be readily apparent to those skilled in the art. Thus, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Thus, departures may be made from such details without departing from the general inventive concept.

Claims

1. 1. A refrigeration system comprising: a first refrigeration stage defining a first fluid circuit for circulating a first refrigerant, A first capacitor; A first compressor; and a first refrigeration stage having a first expansion device in fluid communication with the first fluid circuit; a second refrigeration stage defining a second fluid circuit, fluidly separated from the first fluid circuit, for circulating a second refrigerant, A second capacitor; A second compressor; and a second expansion device in fluid communication with the second fluid circuit, a first capillary and a second capillary arranged in parallel flow; a second stage valve in fluid communication with the second capillary tube for selectively controlling the flow of the second refrigerant through the second capillary tube in response to at least one operating condition of the refrigeration system without blocking the flow of the second refrigerant through the first capillary tube; a second refrigeration stage having a second expansion device including at least one interstage heat exchanger in heat transfer communication with the first and second fluid circuits for exchanging heat between the first refrigerant and the second refrigerant; The first and second refrigeration stages are configured in a cascade cooling arrangement.

2. The first fluid circuit comprises: a first fluid line in fluid communication with an outlet of the first condenser and a first inlet of the at least one interstage heat exchanger, the first fluid line including the first expansion device; a first suction line in fluid communication with a first outlet of the at least one interstage heat exchanger and an inlet of the first compressor; 10. The refrigeration system of claim 1, further comprising: a first heat exchanger defined by a portion of the first fluid line or a portion of the first expansion device in heat transfer communication with a portion of the first suction line, thereby exchanging heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line.

3. The second fluid circuit comprises: a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of an evaporator, the second fluid line including the second expansion device; a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor; 10. The refrigeration system of claim 1, further comprising: a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device in heat transfer communication with a portion of a second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

4. The second fluid circuit comprises: a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of an evaporator, the second fluid line including the second expansion device; a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor; 3. The refrigeration system of claim 2, further comprising a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device in heat transfer communication with a portion of a second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

5. The refrigeration system of claim 1 , wherein the first expansion device comprises an electronic expansion valve.

6. The refrigeration system of claim 1 , wherein the second stage valve comprises a solenoid valve.

7. 10. The refrigeration system of claim 1, wherein the second stage valve comprises an electronic expansion valve.

8. The first expansion device comprises: a third capillary and a fourth capillary in a parallel flow arrangement; 10. The refrigeration system of claim 1, further comprising: a first stage valve for selectively controlling the flow of the first refrigerant through the fourth capillary tube in response to at least one operating condition of the refrigeration system without blocking the flow of the first refrigerant through the third capillary tube.

9. The first fluid circuit comprises: a first fluid line in fluid communication with an outlet of the first condenser and a first inlet of the at least one interstage heat exchanger, the first fluid line including the first expansion device; a first suction line in fluid communication with a first outlet of the at least one interstage heat exchanger and an inlet of the first compressor; 10. The refrigeration system of claim 8, further comprising: a first heat exchanger defined by a portion of the first suction line in heat transfer communication with a portion of the first fluid line or a portion of the first expansion device, thereby exchanging heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line.

10. The second fluid circuit comprises: a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of an evaporator, the second fluid line including the second expansion device; a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor; 10. The refrigeration system of claim 9, further comprising: a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device in heat transfer communication with a portion of a second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

11. 9. The refrigeration system of claim 8, wherein the first stage valve is a solenoid valve.

12. 9. The refrigeration system of claim 8, wherein the first stage valve is an electronic expansion valve.

13. 9. The refrigeration system of claim 8, wherein the second stage valve is an electronic expansion valve.

14. 9. The refrigeration system of claim 8, wherein the second stage valve comprises a solenoid valve.

15. 10. The refrigeration system of claim 1, wherein the refrigeration system is associated with a cabinet having a refrigerated interior, and the first refrigeration stage and the second refrigeration stage operate to cool the cabinet to a temperature set point in the range of -20°C to -90°C.

16. A refrigerator, comprising: a cabinet having a cabinet interior and a door providing access to the cabinet interior; 1. A cascade-type refrigeration system, comprising: a first refrigeration stage defining a first fluid circuit for circulating a first refrigerant, A first capacitor; A first compressor; and a first refrigeration stage having a first expansion device in fluid communication with the first fluid circuit; a second refrigeration stage defining a second fluid circuit, fluidly separated from the first fluid circuit, for circulating a second refrigerant, A second capacitor; A second compressor; and a second expansion device in fluid communication with the second fluid circuit, a first capillary and a second capillary arranged in parallel flow; a second stage valve in fluid communication with the second capillary tube for selectively controlling the flow of the second refrigerant through the second capillary tube in response to at least one operating condition of the refrigeration system without blocking the flow of the second refrigerant through the first capillary tube; a second refrigeration stage having a second expansion device and at least one interstage heat exchanger in heat transfer communication with the first and second fluid circuits for exchanging heat between the first refrigerant and the second refrigerant; The first and second refrigeration stages are configured in a cascade cooling arrangement.

17. The first fluid circuit comprises: a first fluid line in fluid communication with an outlet of the first condenser and a first inlet of the at least one interstage heat exchanger, the first fluid line including the first expansion device; a first suction line in fluid communication with a first outlet of the at least one interstage heat exchanger and an inlet of the first compressor; 17. The refrigerator of claim 16, further comprising: a first heat exchanger defined by a portion of the first fluid line in heat transfer communication with a portion of the first suction line or a portion of the first expansion device, thereby exchanging heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line.

18. The second fluid circuit comprises: a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of an evaporator, the second fluid line including the second expansion device; a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor; 17. The refrigerator of claim 16, further comprising a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device in heat transfer communication with a portion of a second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

19. The second fluid circuit comprises: a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of an evaporator, the second fluid line including the second expansion device; a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor; 18. The refrigerator of claim 17, further comprising: a second heat exchanger defined by a portion of a second fluid line or the second expansion device in heat transfer communication with a portion of a second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

20. The first expansion device comprises: a third capillary and a fourth capillary in a parallel flow arrangement; 17. The refrigerator of claim 16, further comprising: a first stage valve for selectively controlling the flow of the first refrigerant through the fourth capillary tube in response to at least one operating condition of the refrigeration system without blocking the flow of the first refrigerant through the third capillary tube.

21. The first fluid circuit comprises: a first fluid line in fluid communication with an outlet of the first condenser and a first inlet of the at least one interstage heat exchanger, the first fluid line including the first expansion device; a first suction line in fluid communication with a first outlet of the at least one interstage heat exchanger and an inlet of the first compressor; 21. The refrigerator of claim 20, further comprising a first heat exchanger defined by a portion of the first suction line in heat transfer communication with a portion of the first fluid line or a portion of the first expansion device, thereby exchanging heat between the first refrigerant flowing through the first fluid line and the first refrigerant flowing through the first suction line.

22. The second fluid circuit comprises: a second fluid line in fluid communication with a second outlet of the at least one interstage heat exchanger and an inlet of an evaporator, the second fluid line including the second expansion device; a second suction line in fluid communication with the outlet of the evaporator and the inlet of the second compressor; 22. The refrigerator of claim 21, further comprising a second heat exchanger defined by a portion of the second fluid line or a portion of the second expansion device in heat transfer communication with a portion of a second suction line, thereby exchanging heat between the second refrigerant flowing through the second fluid line and the second refrigerant flowing through the second suction line.

Images