HK1142392A - Transcritical refrigerant vapor compression system with charge management - Google Patents

Description

Transcritical refrigerant vapor compression system with capacity control

[ technical field ] A method for producing a semiconductor device

[0001] The present invention relates generally to refrigerant vapor compression systems, and more particularly to refrigerant charge management in refrigerant vapor compression systems operating in a transcritical cycle.

[ background of the invention ]

[0002] Refrigerant vapor compression systems are known in the art and are commonly used to condition air to be supplied to climate controlled comfort zones within a residence, office building, hospital, school, restaurant or other facility. Refrigerant vapor compression systems are also commonly used in refrigerating air supplied to display cases, merchandis, freezer compartments, cold rooms or other perishable/frozen product storage areas in commercial establishments.

[0003] Refrigerant vapor compression systems are also commonly used in transport refrigeration systems for refrigerating air supplied to a temperature controlled cargo space of a truck, trailer, container or the like for transporting perishable/frozen goods by truck, rail, ship or intermodal. Refrigerant vapor compression systems used in conjunction with transport refrigeration systems are typically subjected to more severe operating conditions due to the wide range of operating load conditions and the wide range of outdoor environmental conditions under which the refrigerant vapor compression system must operate in order to maintain the product within the cargo space at a desired temperature. The desired temperature at which the cargo needs to be controlled can also vary widely depending on the nature of the cargo being held. Refrigerant vapor compression systems must not only have sufficient capacity and refrigerant charge to rapidly reduce the temperature of the product loaded into the cargo space at ambient temperature, but must also operate efficiently at lower excess refrigerant charge loads while maintaining a steady product temperature during transport. In addition, transport refrigerant vapor compression systems are subject to shock and movement not encountered by stationary refrigerant vapor compression systems. As such, the use of a conventional refrigerant collection canister in the suction line upstream of the compressor suction inlet to store additional refrigerant liquid would be subject to sloshing during movement, which could result in refrigerant liquid being undesirably carried through the suction line into the compressor via the suction inlet thereon.

[0004] Traditionally, most of these refrigerant vapor compression systems operate at subcritical refrigerant pressures and typically include a compressor, a condenser, an evaporator, and an expansion device (typically an expansion valve) disposed upstream with respect to refrigerant flow of the evaporator and downstream of the condenser. These basic refrigerant system components are interconnected in a closed refrigerant circuit by refrigerant lines, arranged in accordance with known refrigerant vapor compression cycles, and operated in a subcritical pressure range for the particular refrigerant in use. Refrigerant vapor compression systems operating in the subcritical range are commonly charged with fluorocarbon refrigerants such as, but not limited to, chlorofluorocarbons (HCFCs), such as R22, and more commonly Hydrofluorocarbons (HFCs), such as R134a, R410A, R404A, and R407C.

[0005] In the current market there is a great interest in "natural" refrigerants, such as carbon dioxide, for use in air conditioning and transport refrigeration systems to replace HFC refrigerants. However, because carbon dioxide has a relatively low critical temperature, most refrigerant vapor compression systems charged with carbon dioxide as the refrigerant are designed to operate at transcritical pressures. In refrigerant vapor compression systems operating in a subcritical cycle, both the condenser and the evaporator heat exchangers operate at refrigerant temperatures and pressures at the critical point of the refrigerant. However, in refrigerant vapor compression systems operating in a transcritical cycle, the heat rejection heat exchanger (which is a gas cooler rather than a condenser) operates at refrigerant temperatures and pressures above the critical point of the refrigerant, while the evaporator operates at refrigerant temperatures and pressures in the subcritical range. Thus, for a refrigerant vapor compression system operating in a transcritical cycle, the difference between the refrigerant pressure in the gas cooler and the refrigerant pressure in the evaporator is characteristically substantially greater than the difference between the refrigerant pressure in the condenser and the refrigerant pressure in the evaporator of a refrigerant vapor compression system operating in a subcritical cycle.

[0006] It is also common practice to incorporate an economizer into the refrigerant circuit for increasing the capacity of the refrigerant vapor compression system. For example, in some systems, a refrigerant-to-refrigerant heat exchanger is incorporated into the refrigerant circuit as an economizer. A first portion of the refrigerant exiting the condenser passes through a first pass of the heat exchanger to exchange heat with a second portion of the refrigerant passing through a second pass of the heat exchanger. The second portion of refrigerant typically constitutes the portion of refrigerant leaving the condenser that is diverted through an expansion device, wherein the portion of refrigerant is expanded to a lower pressure and temperature vapor or vapor/liquid mixture refrigerant before passing through the second pass of the economizer refrigerant-refrigerant heat exchanger. Having traversed the second pass of the economizer heat exchanger, a second portion of refrigerant is introduced therefrom into an intermediate pressure change stage of the compression process. The refrigerant in the primary refrigerant circuit passes through the first pass of the refrigerant-to-refrigerant economizer heat exchanger and is thus further cooled before traversing the main expansion device of the system before entering the evaporator. U.S. patent No. 6,058,729 discloses a subcritical refrigerant vapor compression system for a transport refrigeration unit incorporating a refrigerant-to-refrigerant heat exchanger in the refrigerant circuit as an economizer. 6,694,750 discloses a subcritical refrigeration system including a first refrigerant-to-refrigerant heat exchanger economizer and a second refrigerant-to-refrigerant heat exchanger economizer arranged in series in the refrigerant circuit between the condenser and the evaporator.

[0007] In some systems, a flash tank economizer is incorporated into the refrigerant circuit between the condenser and the evaporator. In this case, the refrigerant exiting the condenser is expanded through an expansion device, such as a thermostatic expansion valve or an electronic expansion valve, before entering the flash tank, wherein the expanded refrigerant separates into a liquid refrigerant component and a vapor refrigerant component. The vapor component of the refrigerant is thereby introduced from the flash tank into an intermediate pressure stage of the compression process. The liquid component of the refrigerant is directed from the flash tank through a main expansion valve of the system before entering the evaporator. 5,174,123 discloses a subcritical vapor compression system incorporating a flash tank economizer in the refrigerant circuit between the condenser and the evaporator. 6,385,980 discloses a transcritical refrigerant vapor compression system incorporating a flash tank economizer into the refrigerant circuit between the gas cooler and the evaporator.

[ summary of the invention ]

[0008] A transcritical refrigerant vapor compression system with improved refrigerant charge management includes a compression device, a refrigerant heat rejection heat exchanger, a refrigerant heat absorption heat exchanger, and a refrigerant-to-refrigerant heat exchanger economizer and flash tank disposed in serial refrigerant flow relationship in a primary refrigerant circuit intermediate the refrigerant heat rejection heat exchanger and the refrigerant heat absorption heat exchanger. A primary expansion valve is disposed in the refrigerant circuit upstream of and operatively associated with the refrigerant heat absorption heat exchanger, and a secondary expansion valve is disposed in the refrigerant circuit upstream of and operatively associated with the flash tank. A refrigerant vapor bypass line establishes refrigerant vapor flow communication between the flash tank and a suction pressure portion of the primary refrigerant circuit downstream of the refrigerant heat absorption heat exchanger. A bypass flow control valve having an open position and a closed position is disposed on the refrigerant vapor bypass line for controlling the flow of refrigerant vapor through the refrigerant vapor bypass line.

[0009] The refrigerant-to-refrigerant heat exchanger has a first refrigerant pass disposed in the primary refrigerant circuit downstream of the refrigerant-cooling heat exchanger and upstream of the primary expansion device, and a second bypass disposed in an economizer circuit refrigerant line extending in refrigerant flow communication from the primary refrigerant circuit to an intermediate pressure stage of the compression device. An economizer circuit expansion device is disposed in the economizer circuit refrigerant line upstream with respect to refrigerant flow of the second refrigerant pass of the refrigerant-to-refrigerant heat exchanger economizer. The economizer circuit expansion device may comprise an electronic expansion valve or a thermostatic expansion valve.

[0010] In one embodiment, the bypass flow control valve may comprise a two-position solenoid valve, a pulse width modulated solenoid valve, or an electronic expansion valve. In one embodiment, the primary expansion valve may comprise an electronic expansion valve or a thermostatic expansion valve. In one embodiment, the secondary expansion valve may comprise an electronic expansion valve or a fixed orifice expansion valve.

[0011] In one embodiment, the compression device may be a single compressor having at least a first compression stage and a second compression stage. In one embodiment, the compression device may be a first compressor and a second compressor disposed in the refrigerant circuit in continuous refrigerant flow communication, with the discharge outlet of the first compressor being in refrigerant flow communication with the suction inlet of the second compressor. Whether in a single compressor arrangement or a multiple compressor arrangement, each compressor may be a scroll compressor, a reciprocating compressor, or a screw compressor.

[ description of the drawings ]

[0012] For a further understanding of the invention, reference will be made to the following detailed description of the invention, which is to be read in connection with the accompanying drawings, wherein:

[0013] FIG. 1 is a schematic diagram illustrating an exemplary embodiment of a refrigerant vapor compression system according to the present invention;

[0014] fig. 2 is a chart showing the pressure-enthalpy relationship for an exemplary embodiment of the refrigerant vapor compression system of the present invention operating in a transcritical cycle as shown in fig. 1.

[0015] FIG. 3 is a graph showing pressure-enthalpy relationship for a prior art refrigerant vapor compression system operating in a transcritical cycle; and

[0016] fig. 4 is a graph showing pressure-enthalpy relationship for a prior art refrigerant vapor compression system operating in a transcritical cycle with a single flash tank economizer.

[ detailed description ] embodiments

[0017] Referring now to fig. 1, an exemplary embodiment of a transcritical refrigerant vapor compressor system 10 suitable for use in a transport refrigeration system for refrigerating air supplied to a temperature controlled cargo space of a truck, trailer, container or the like transporting perishable frozen goods is depicted. The refrigerant vapor compression system 10 is also suitable for use in conditioning air to be supplied to a climate controlled comfort zone within a residence, office building, hospital, school, restaurant or other facility. Refrigerant vapor compression systems may also be used to refrigerate air supplied to display cases, merchandis, freezer compartments, refrigerated rooms, or other perishable frozen product storage areas in commercial establishments.

[0018] The transcritical refrigerant vapor compression system 10 includes a multistage compression device 20, a refrigerant heat rejection heat exchanger 40 (also referred to herein as a gas cooler), a refrigerant heat absorption heat exchanger 50 (also referred to herein as an evaporator), and a primary expansion device 55, such as, for example, an electronic expansion valve or thermostatic expansion valve operating in conjunction with the evaporator 50, and various refrigerant lines 2, 4 and 6 connecting the aforementioned components in the primary refrigerant circuit. The compression device 20 serves to compress and circulate refrigerant in the main refrigerant circuit, as will be discussed in more detail below. The compression device 20 may comprise a single, multi-stage refrigerant compressor, such as a reciprocating compressor, having a first compression stage 20a and a second compression stage 20b, or a single compressor, such as a scroll compressor or a screw compressor, adapted in a conventional manner for injecting refrigerant through an injection port into an intermediate pressure point of a compression chamber of the compressor, whereby the first compression stage 20a is located upstream of the intermediate pressure point and the second compression stage 20b is located downstream of the intermediate pressure point. The first compression stage 20a and the second compression stage 20b are disposed in a continuous refrigerant flow relationship with the refrigerant leaving the first compression stage passing directly to the second compression stage for further compression. The compression device 20 may also include a pair of compressors 20a and 20b connected in continuous refrigerant flow relationship in the main refrigerant circuit by a refrigerant line connecting the discharge outlet of the first compressor 20a in refrigerant flow communication with the suction inlet of the second compressor 20 b. The compressors 20a and 20b may be scroll compressors, screw compressors, reciprocating compressors, rotary compressors or any other type of compressor or combination of any such compressors.

[0019] The refrigerant heat rejection heat exchanger 40 may include a finned tube heat exchanger 42 through which hot refrigerant at high pressure passes in heat exchange relationship with a cooling medium (most commonly ambient air drawn through the heat exchanger 42 by a condenser fan 44). The finned tube heat exchanger 42 may comprise, for example, a finned round tube heat exchange coil or a finned flat plate microchannel tube heat exchanger.

[0020] Additionally, the refrigerant vapor compression system 10 of the present invention includes a refrigerant-to-refrigerant heat exchanger economizer 60 and a flash tank 70 disposed in serial refrigerant flow relationship with respect to refrigerant flow downstream of the gas cooler 40 in the refrigerant line 4 of the primary refrigerant circuit and upstream with respect to refrigerant flow of the evaporator 50. The refrigerant-to-refrigerant heat exchanger economizer 60 is disposed in refrigerant line 4 of the primary refrigerant circuit downstream with respect to refrigerant flow of the gas cooler 40 and upstream with respect to refrigerant flow of the flash tank 70. Additionally, a secondary expansion device 75, such as, for example, an electronic expansion valve or a fixed orifice device, is disposed in the primary refrigerant circuit between the refrigerant-to-refrigerant heat exchanger economizer 60 and the flash tank 70.

[0021] The refrigerant-to-refrigerant heat exchanger economizer 60 includes a first refrigerant pass 62 and a second refrigerant pass 64 arranged in heat transfer relationship. A first refrigerant passage 62 is provided in the refrigerant line 4 and forms part of the main refrigerant circuit. A second refrigerant pass 64 is disposed in the refrigerant line 12 and forms part of the economizer circuit. The economizer circuit refrigerant line 12 is connected in refrigerant flow communication with an intermediate pressure stage of the compression process. In the exemplary embodiment shown in fig. 1, the economizer circuit refrigerant line 12 is connected to refrigerant line 4 of the main refrigerant circuit upstream with respect to refrigerant flow of the first pass 62 of the refrigerant-to-refrigerant heat exchange economizer 60 and establishes refrigerant flow. Alternatively, the economizer circuit refrigerant line may be connected to refrigerant line 4 of the main circuit downstream with respect to refrigerant flow in the first pass 62 of the refrigerant-to-refrigerant heat exchange economizer 60. The first refrigerant pass 62 and the second refrigerant pass 64 of the refrigerant-to-refrigerant heat exchanger economizer 60 may be optionally arranged in a laminar flow heat exchange relationship or a convective heat exchange relationship. The refrigerant-to-refrigerant heat exchanger 60 may be a brazed plate heat exchanger, a tube-in-tube heat exchanger, a tube-on-tube heat exchanger, or a shell-and-tube heat exchanger.

[0022] An economizer circuit expansion device 65 is disposed on the economizer circuit refrigerant line 12 upstream with respect to refrigerant flow in the second pass 64 of the refrigerant-to-refrigerant heat exchanger economizer 60. The economizer circuit expansion device 65 meters the flow of refrigerant through the refrigerant line 12 and the second pass 64 of the refrigerant-to-refrigerant heat exchanger economizer 60 in heat exchange relationship with refrigerant passing through the first pass of the heat exchanger economizer 60 to maintain a desired level of superheat in the refrigerant vapor leaving the second pass 64 of the heat exchanger economizer 60 to ensure that no liquid is present therein. The expansion valve 65 may be an electronic expansion valve, for example, as shown in fig. 1-3, in which case the expansion valve 65 meters refrigerant flow in response to a signal from the controller 100 to maintain a desired refrigerant temperature or pressure in the refrigerant line 12. The expansion device 65 may also be a thermostatic expansion valve, in which case the expansion valve 65 meters refrigerant flow in response to an indication of refrigerant temperature or pressure sensed by a sensing device (not shown), which may be a conventional thermal element such as a bulb or thermocouple mounted to the refrigerant line 12 downstream of the second pass of the heat exchanger economizer 60. The refrigerant vapor passing through the economizer circuit refrigerant line 12 is injected into the compression device 20 at an intermediate pressure end of the compression process. For example, if the compression device 20 is a multi-stage reciprocating compressor, the refrigerant line 12 directs refrigerant vapor directly into an intermediate pressure stage of the reciprocating compressor between the first compression stage 20a and the second compression stage 20 b. If the compression device 20 is a single scroll compressor or a single screw compressor, the refrigerant line 12 introduces refrigerant vapor at an intermediate pressure of the compression process into an injection port of the compression device opening into a compression chamber of the compression device. If the compression device 20 is a pair of compressors 20a, 20b connected in series (e.g., a pair of scroll compressors, or screw compressors, or reciprocating compressors), or a single reciprocating compressor having a first bank of cylinders and a second bank of cylinders, the second economizer circuit refrigerant line 12 directs refrigerant vapor into a refrigerant line connecting the discharge outlet of the first compressor 20a in refrigerant flow communication with the suction inlet of the second compressor 20 b.

[0023] A flash tank 70 is disposed in refrigerant line 4 of the primary refrigerant circuit downstream with respect to refrigerant flow of the first pass 62 of the refrigerant-to-refrigerant heat exchanger economizer 60 and upstream with respect to refrigerant flow of the evaporator 50 for receiving refrigerant flowing through refrigerant line 4. A secondary expansion device 75 is disposed in refrigerant line 4 of the primary refrigerant circuit downstream with respect to refrigerant flow of the first refrigerant pass 62 of the refrigerant-to-refrigerant heat exchanger economizer 60 and upstream with respect to refrigerant flow of the inlet of the flash tank 70. As it traverses the secondary expansion device 75, the high pressure refrigerant vapor passing through refrigerant line 4 is expanded to a subcritical pressure and temperature before the refrigerant passes to the flash tank 70. The secondary expansion device 75 may be an electronic expansion valve, as shown in fig. 1, in which case the secondary expansion valve 75 meters refrigerant flow in response to a signal from the controller 100 to maintain a desired refrigerant pressure in the refrigerant line 4 upstream with respect to refrigerant flow of the secondary expansion device 75. The secondary expansion device 75 could also be simply a fixed orifice expansion device, in which case the refrigerant pressure in refrigerant line 4 upstream with respect to refrigerant flow of the secondary expansion device 75 would fluctuate depending on ambient conditions, and refrigerant flow would be essentially metered depending on the magnitude of the pressure differential across the fixed orifice.

[0024] The flash tank 70 defines a separation chamber 72 into which expanded refrigerant flows at subcritical pressure and separates into a liquid refrigerant portion collected in a lower portion of the flash tank 70 and a vapor portion collected in an upper portion of the flash tank 70 above the liquid level within the flash tank 70. As such, the flash tank 70 functions as a receiver for storing liquid refrigerant whenever the refrigerant vapor compression system is operating at a capacity that does not require a full charge of refrigerant for the system.

[0025] Additionally, the refrigerant vapor compression system includes a refrigerant line 14, the refrigerant line 14 establishing refrigerant flow communication between the flash tank 70 of the primary refrigerant circuit and refrigerant line 6 at a point downstream with respect to refrigerant flow of the outlet of the evaporator 50 and upstream with respect to refrigerant flow of the suction inlet of the compression device 20.

[0026] Refrigerant vapor collecting in the portion of the flash tank 70 above the liquid level therein passes from the flash tank 70 through refrigerant line 14 to enter the primary refrigerant circuit to return to the compression device 20. A flow control valve 85 is disposed in refrigerant line 14 to restrict the flow of refrigerant vapor through refrigerant line 14 to maintain the separation chamber 72 of the flash tank 70 at a refrigerant pressure above the suction pressure, if necessary. In one embodiment, the flow control valve 85 comprises a solenoid valve having a first open position and a second closed position, such as, for example and without limitation, a pulse width modulated solenoid valve. In one embodiment, the flow control valve 85 may comprise an electronic expansion valve.

[0027] From there, liquid refrigerant collecting in the lower portion of the flash tank economizer 70 passes through refrigerant line 4 and traverses a main refrigerant circuit expansion valve 55, which main refrigerant circuit expansion valve 55 may be an electronic expansion valve or a conventional thermostatic expansion valve, disposed in refrigerant line 4 upstream with respect to refrigerant flow of the evaporator 50. As this liquid refrigerant traverses the first expansion device 55, it expands to a lower pressure and temperature before entering the evaporator 50. As the liquid refrigerant passes through the evaporator 50, it flows in heat exchange relationship with the thermal medium, whereby the liquid refrigerant is vaporized and typically superheated, while the thermal medium is cooled. In one embodiment, the evaporator 50 constitutes a finned tube coil heat exchanger 52, such as a finned round tube heat exchanger or a finned flat plate microchannel tube heat exchanger. The heated fluid flowing in heat exchange relationship with the refrigerant in the evaporator 50 can be air drawn from a climate controlled environment, such as a perishable/frozen goods storage area associated with a transport refrigeration unit or a food display or storage area of a commercial establishment, or a building comfort area associated with an air conditioning system that is to be cooled and typically also dehumidified, by an associated fan 54, and the drawn air is thereby returned to the climate controlled environment. The low pressure refrigerant vapor leaving the evaporator 50 returns through refrigerant line 6 to the suction inlet of the compression device 20.

[0028] In conventional practice, the primary expansion valve 55 meters the flow of refrigerant through refrigerant line 4 to maintain a desired level of superheat in the refrigerant vapor leaving the evaporator 50 and passing through refrigerant line 6 to ensure that no liquid is present in the refrigerant leaving the evaporator. As previously indicated, the primary expansion valve 55 may be an electronic expansion valve, in which case the expansion valve 55 meters refrigerant flow in response to a signal from the controller 100 to maintain a desired suction temperature or suction pressure in the refrigerant line 6 on the suction side of the compression device 20. The primary expansion device 55 may also be a thermostatic expansion valve, in which case the expansion valve 55 meters refrigerant flow in response to signals indicative of refrigerant temperature or pressure sensed by a sensing device, which may be a conventional thermal element such as a bulb or thermocouple mounted to the refrigerant line 6 near the evaporator outlet.

[0029] In the exemplary embodiment of the refrigerant vapor compression system 10 illustrated in fig. 1, the operation of the refrigerant vapor compression system is controlled by a control system comprising a controller 100, the controller 100 operating in association with a flow control valve 85 disposed in refrigerant line 14 and an economizer circuit expansion device 65 disposed in refrigerant line 12. The controller 100 may also control the operation of the electronic expansion valves 55 and 65, the compression device 20, and the fans 44 and 54. Conventionally, in addition to monitoring environmental conditions, the controller 100 may also monitor various operating parameters via various sensors that are operatively associated with the controller 100 and disposed at selected locations throughout the system. For example, in the exemplary embodiment illustrated in fig. 1, a pressure sensor 102 may be operatively disposed in association with the flash tank 70 to sense a pressure within the flash tank 70, a temperature sensor 103 and a pressure sensor 104 may be configured to sense a refrigerant suction temperature and a pressure, respectively, and a temperature sensor 105 and a pressure sensor 106 may be configured to sense a refrigerant discharge temperature and a pressure, respectively. The pressure sensors 102, 104, 106 may be conventional pressure sensors such as, for example, pressure transducers, while the temperature sensors 103 and 105 may be conventional temperature sensors such as, for example, thermocouples or thermistors.

[0030] The refrigerant vapor compression system of the present invention is particularly suited for operation in a transcritical cycle with a lower critical point refrigerant such as carbon dioxide, but may also be operated in a subcritical cycle with a conventional higher critical point refrigerant. When the refrigerant vapor compression system 10 is operating in the economized mode, the controller 100 controls the economizer circuit expansion device 65 to meter the flow of refrigerant vapor from refrigerant line 4 through the economizer circuit refrigerant line 12 in response to system operating conditions and capacity demand. When the system is operating in the non-economized mode, the controller 100 closes the economizer circuit expansion valve 65 so that all of the refrigerant passing from the gas cooler 40 through refrigerant line 4 passes through the secondary expansion device 75 and thence into the flash tank 70. In either the economized or non-economized mode, the controller 100 controls the primary expansion valve 55 to meter the correct amount of refrigerant liquid exiting the flash tank 70 in response to a sensed system operating parameter (e.g., compressor discharge temperature) to match the refrigerant capacity demand of the system.

[0031] In addition, the controller 100 controls the positioning of the flow control valve 85 disposed in the refrigerant line 14 to restrict the flow of refrigerant vapor from the flash tank 70 in response to the sensed pressure within the separation chamber flash tank 70 to maintain the desired subcritical flash tank pressure. Because the ratio of refrigerant liquid to refrigerant vapor present in the flash tank will depend on the subcritical pressure level within the separation chamber, the flash tank pressure may be controlled by positioning the flow control valve 85 to produce a selected refrigerant quality when expanded. If the flow control valve 85 is continuously closed, the pressure in the flash tank will rise to the upper limit of the gas cooler pressure. If the flow control valve 85 is continuously open, the pressure within the flash tank 70 will drop to a lower pressure, but above the suction pressure. When the flow control valve is fully open, the actual pressure differential between the pressure in the flash tank and the suction pressure will be controlled by the size of the orifice in the particular flow control valve used. Controlled discharge of refrigerant vapor from the flash tank 70 to suction pressure through refrigerant line 14 is necessary to maintain low pressure in the flash tank. Thus, the controller 100 can also continuously cycle the flow control valve 85 between open and closed positions to selectively control flash tank pressure. This manipulation of the primary expansion valve 55 and the flow control valve 85 provides the controller 100 with the ability to effectively manage refrigerant charge across a wide range of operating conditions (even when the refrigerant vapor compression system 10 is operating in transcritical mode). Additionally, separating the refrigerant in the flash tank 70 into liquid and vapor phases and passing only liquid refrigerant through the evaporator while diverting vapor refrigerant to a point downstream of the evaporator improves heat exchange efficiency in the evaporator.

[0032] A comparison of the pressure to enthalpy relationship shown in fig. 2, which is representative of the characteristic pressure enthalpy relationship of the refrigerant vapor compression system 10 of fig. 1, with either of the pressure enthalpy relationships shown in fig. 3 or fig. 4, which are representative of conventional refrigerant vapor compression systems, illustrates the capacity improvement associated with the refrigerant vapor compression system of the present invention. Figure 3 illustrates the characteristic pressure enthalpy relationship for conventional prior art transcritical refrigerant vapor compression with a single refrigerant-refrigerant heat exchange economizer. Fig. 4 illustrates the characteristic pressure enthalpy relationship for conventional prior art transcritical refrigerant vapor compression with a single flash tank economizer. In each of fig. 2-4, AB represents the gas heat rejection process in the gas cooler 40 and DE represents the gas heat absorption process in the evaporator 50. In fig. 2, KG represents the process in the refrigerant-refrigerant heat exchange economizer circuit and MN represents the process in the flash tank-suction evaporator bypass circuit. In fig. 3, KG represents the process within the refrigerant-refrigerant heat exchange economizer circuit. In fig. 4, JL represents the process within the flash tank economizer circuit. The evaporator line DE in fig. 1 is longer than the individual refrigerant lines associated with any of the prior art single economizer systems, indicating the increased evaporator efficiency associated with the refrigerant vapor compression system of the present invention.

[0033] Those skilled in the art will recognize that many changes may be made to the specific exemplary embodiments described herein. While the present invention has been particularly shown and described with reference to the exemplary embodiments shown in the drawings, it will be understood by those skilled in the art that various minor changes may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims (20)

1. A refrigerant vapor compression system comprising:

a primary refrigerant circuit including a refrigerant compression device, a refrigerant cooling heat exchanger for passing refrigerant received from the compression device at high pressure in heat exchange relationship with a cold medium, a refrigerant heating heat exchanger for passing refrigerant at low pressure in heat exchange relationship with a hot medium, and a primary expansion device disposed in the primary refrigerant circuit downstream of the refrigerant cooling heat exchanger and upstream of the refrigerant heating heat exchanger.

A refrigerant-to-refrigerant heat exchanger economizer having a first refrigerant pass disposed in the primary refrigerant circuit downstream of said refrigerant cooling heat exchanger and upstream of said primary expansion device and a second bypass disposed in the economizer circuit refrigerant line;

a flash tank disposed in the primary refrigerant circuit downstream of the first refrigerant pass of the refrigerant-to-refrigerant heat exchanger and upstream of the primary expansion device, the flash tank defining a separation chamber with liquid refrigerant collecting in a lower portion of the separation chamber and vapor refrigerant in a portion of the separation chamber above the liquid refrigerant;

a secondary expansion device disposed in the primary refrigerant circuit operatively associated with and upstream of the flash tank;

a refrigerant vapor bypass line establishing refrigerant flow communication between an upper portion of the separation chamber of the flash tank and a suction pressure portion of the primary refrigerant circuit downstream of the refrigerant heat absorption heat exchanger; and

a bypass flow control valve disposed in the evaporator bypass line, the bypass flow control valve having a first open position at which refrigerant vapor can pass through the evaporator bypass line and a second closed position at which refrigerant vapor is blocked from passing through the evaporator bypass line.

2. A refrigerant vapor compression system as recited in claim 1 wherein said flow control valve comprises a solenoid valve having a first open position and a second closed position.

3. A refrigerant vapor compression system as recited in claim 1 wherein said flow control valve comprises a pulse width modulated solenoid valve.

4. A refrigerant vapor compression system as recited in claim 1 wherein said flow control valve comprises an electronic expansion valve.

5. A refrigerant vapor compression system as recited in claim 1 wherein said primary expansion device comprises an electronic expansion valve.

6. A refrigerant vapor compression system as recited in claim 1 wherein said primary expansion device comprises a thermostatic expansion valve.

7. A refrigerant vapor compression system as recited in claim 1 wherein said secondary expansion device comprises an electronic expansion valve.

8. A refrigerant vapor compression system as recited in claim 1 wherein said secondary expansion device comprises a fixed orifice expansion valve.

9. A refrigerant vapor compression system as recited in claim 1 wherein said economizer circuit refrigerant line extends in refrigerant flow communication from said main refrigerant circuit to an intermediate pressure stage of said compression device.

10. A refrigerant vapor compression system as recited in claim 9 wherein said system further comprises an economizer circuit expansion device disposed in said economizer circuit refrigerant line upstream with respect to refrigerant flow in said second refrigerant pass of said refrigerant-to-refrigerant heat exchanger economizer.

11. A refrigerant vapor compression system as recited in claim 10 wherein said economizer circuit expansion device comprises an electronic expansion valve.

12. A refrigerant vapor compression system as recited in claim 10 wherein said economizer circuit expansion device comprises a thermostatic expansion valve.

13. A refrigerant vapor compression system as recited in claim 1 wherein said compression device comprises a single compressor having at least two compression stages.

14. A refrigerant vapor compression system as recited in claim 1 wherein said compression device comprises at least two compressors disposed in the refrigerant circuit in serial relationship with respect to refrigerant flow.

15. A refrigerant vapor compression system as recited in claim 1 wherein said compression device comprises a scroll compressor.

16. A refrigerant vapor compression system as recited in claim 1 wherein said compression device comprises a reciprocating compressor.

17. A refrigerant vapor compression system as recited in claim 1 wherein said compression device comprises a screw compressor.

18. A refrigerant vapor compression system as recited in claim 1 wherein said system is incorporated into a transport refrigeration system for conditioning a temperature controlled cargo storage area.

19. A refrigerant vapor compression system as recited in claim 18 wherein said system operates in a transcritical cycle.

20. A refrigerant vapor compression system as recited in claim 19 wherein said refrigerant comprises carbon dioxide.