HK1142664B - Refrigerant vapor compression system and method of transcritical operation - Google Patents

Description

Refrigerant vapor compression system and transcritical operation method

Technical Field

The present invention relates generally to refrigerant vapor compression systems, and in particular, to improving both efficiency and capacity and improving refrigerant charge management in a refrigerant vapor compression system under transcritical cycle operation.

Background

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, merchandisers, freezer compartments, refrigerated compartments or other perishable/frozen product storage areas in commercial establishments.

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 to rapidly reduce the temperature of the product loaded into the cargo space at ambient temperatures, but must also operate efficiently at lower loads while maintaining a stable 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.

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

In today's 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, most refrigerant vapor compression systems charged with carbon dioxide as the refrigerant are designed to operate in a transcritical pressure regime due to the low critical temperature of carbon dioxide. In a subcritical cycle operating refrigerant vapor compression system, both the condenser and the evaporator are operated at refrigeration temperatures and pressures below the refrigerant critical point. However, in a refrigerant vapor compression system operating in a transcritical cycle, the heat rejection heat exchanger is a gas refrigerator rather than a condenser, operating at a refrigeration temperature and pressure in excess of the refrigerant critical point, while the evaporator operates at a refrigeration temperature and pressure in the subcritical range. Thus, for a refrigerant vapor compression system operating in a transcritical cycle, the difference between the refrigerant pressure within the gas refrigerator and the refrigerant pressure within the evaporator is characteristically substantially greater than the difference between the refrigerant pressure within the condenser and the refrigerant pressure within the evaporator of a refrigerant vapor compression system operating in a subcritical cycle.

It is also common practice to incorporate an economizer into the refrigerant circuit to increase 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. 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 as an economizer into the refrigerant circuit. The disclosed system also includes a Suction Modulation Valve (SMV) for regulating refrigerant flow to the compressor suction inlet and an unloading circuit for intermediate pressure-suction pressure for compressor capacity control. U.S. patent No. 7,114,349 discloses a refrigerant vapor compression system having a conventional economizer and a Liquid-suction Heat Exchanger (Liquid-suction Heat Exchanger) disposed in the refrigerant circuit downstream with respect to refrigerant flow of the condenser and upstream with respect to refrigerant flow of the evaporator. The conventional heat exchanger can be operated as an economical heat exchanger or as a liquid suction type heat exchanger, although by various bypass lines and on/off operations of various solenoid valves associated with the bypass lines.

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 disposed in series in the refrigerant circuit between the condenser and the evaporator. The refrigerant passes from the condenser, through the primary refrigerant circuit to the evaporator, successively through the first pass of the first refrigerant-to-refrigerant heat exchanger, and thence through the first pass of the second refrigerant-to-refrigerant heat exchanger, before traversing the expansion valve of the single evaporator in the primary refrigerant circuit and before entering the evaporator. A second portion of the refrigerant passing from the condenser is diverted from the primary refrigerant circuit and passed through the secondary expansion valve, and thence through the first refrigerant-to-refrigerant heat exchanger second pass, prior to being injected into the high pressure stage of the compression process. Before being injected into the low-pressure phase of the compression process, a third portion of the refrigerant passing from the condenser is diverted from the main refrigerant circuit and passed through another secondary expansion valve, and thence through the second pass of the second refrigerant-to-refrigerant heat exchanger.

In some systems, a flash tank economizer is incorporated into the refrigerant circuit between the condenser and the evaporator. In this case, the refrigerant leaving the condenser is expanded by an expansion device (e.g., a thermostatic expansion valve or an electronic expansion valve) before entering the flash tank, where the expanded refrigerant separates into a liquid refrigerant component and a vapor refrigerant component. The vapor refrigerant component is thereby introduced from the flash tank to an intermediate pressure stage of the compression process. The liquid component of the refrigerant is directed from the flash tank through a system main expansion valve before entering the evaporator. 5,174,123 discloses a subcritical vapor compression system incorporating a flash tank in the refrigerant circuit between the condenser and the evaporator. 6,385,980 discloses a transcritical vapor compression system incorporating a flash tank economizer between a gas chiller and an evaporator in a refrigerant circuit.

Disclosure of Invention

As one aspect of the invention, a refrigerant vapor compression system is provided having a primary refrigerant circuit including a refrigerant compression device, a refrigerant cooling heat exchanger disposed downstream of the compression device, a refrigerant heating heat exchanger disposed downstream of the refrigerant cooling heat exchanger, a primary expansion device disposed in the refrigerant circuit downstream of the refrigerant cooling heat exchanger and upstream of the refrigerant heating heat exchanger, and a flash tank disposed in the refrigerant circuit downstream of the refrigerant heat rejection heat exchanger and upstream of the primary expansion device. The flash tank defines a separation chamber with liquid refrigerant collecting in a lower portion of the separation chamber and gaseous refrigerant collecting in a portion of the separation chamber above the refrigerant liquid. A secondary expansion device is disposed in the refrigerant circuit upstream of and operatively associated with the flash tank. A refrigerant vapor injection line establishes refrigerant flow communication between an upper portion of the separation chamber and an intermediate pressure stage of the compression device and a suction pressure portion of the main refrigerant circuit. A refrigerant liquid injection line establishes refrigerant flow communication between a lower portion of the separation chamber and an intermediate pressure stage of the compression device and a suction pressure portion of the main refrigerant circuit. A bypass line may be provided between an intermediate pressure stage of the compression device and a suction pressure portion of the main refrigerant circuit.

The refrigerant vapor compression system may include a control system for selectively directing refrigerant vapor from the flash tank through the refrigerant vapor injection line for injection into the main refrigerant circuit or into the suction portion of the main refrigerant circuit at an intermediate pressure stage of the compression device and selectively directing refrigerant liquid from the flash tank through the refrigerant liquid injection line for injection into the main refrigerant circuit or into the suction portion of the main refrigerant circuit at an intermediate pressure stage of the compression device. The control system may also, alternatively or in conjunction with the above, direct refrigerant from an intermediate pressure stage of the compression device into the suction portion of the main refrigerant circuit. In one embodiment, the compression device may be a single compressor having at least a first lower pressure compression stage and a second higher pressure compression stage. In one embodiment, the compression device may be a first compressor and a second compressor disposed in the refrigerant circuit in a continuous refrigerant flow relationship with the discharge outlet of the first compressor in refrigerant flow communication with the suction inlet of the second compressor. In either a single compressor arrangement or a dual compressor arrangement, each compressor may be a scroll compressor, a reciprocating compressor, or a screw compressor.

In one embodiment, the control system includes a controller and a plurality of flow control valves operatively associated with the refrigerant vapor injection line and/or the refrigerant liquid injection line. A controller selectively controls the positioning of each of the plurality of flow control valves between its respective open or closed position. The plurality of flow control valves may include a first flow control valve disposed on an upstream portion of the refrigerant vapor injection line, a second flow control valve disposed on an upstream portion of the refrigerant liquid injection line, a third flow control valve disposed upstream of the intermediate pressure stage of the compression device with respect to refrigerant flow and downstream of the first and second flow control valves, and a fourth flow control valve disposed upstream of the suction pressure portion of the main refrigerant line with respect to refrigerant flow and downstream of the first and second flow control valves with respect to refrigerant flow. In one embodiment, the compressor unload bypass line forms a downstream extension of both the refrigerant vapor injection line and the refrigerant liquid injection line, and the third and fourth flow control valves are disposed on the compressor unload bypass line. In one embodiment, each of the first, second, third and fourth flow control valves comprises a solenoid valve having a first open position and a second closed position. A suction modulation valve operatively controlled by the controller may be disposed in the refrigerant circuit downstream of the refrigerant heating heat exchanger and upstream of the compression device.

As another aspect of the invention, a method is provided for a refrigerant vapor compression system operating in a transcritical cycle, the method including the steps of: compressing the refrigerant to a supercritical state in a two-stage compression process; passing a supercritical pressure refrigerant through a cold medium in heat exchange relationship therewith; expanding the refrigerant in the supercritical state to a subcritical pressure in a first expansion step to form a first expanded refrigerant comprising refrigerant vapor and refrigerant liquid; separating the first expanded refrigerant into a refrigerant vapor portion and a refrigerant liquid portion; expanding at least a portion of the refrigerant liquid portion to a lower pressure in a second expansion step to a second expanded refrigerant comprising refrigerant liquid; evaporating the second expanded refrigerant; selectively passing a portion of the first expanded refrigerant vapor portion to an intermediate stage of a compression process or to a suction pressure portion of a refrigerant vapor compression system; selectively passing a portion of the liquid portion of the refrigerant to an intermediate stage of the compression process or to a suction pressure portion of the refrigerant vapor compression system. In one embodiment, the method further comprises the step of selectively bypassing refrigerant from an intermediate stage of the compression process into a suction pressure portion of the refrigerant vapor compression system.

In a first mode of operation, the method comprises the steps of: selectively passing a portion of the refrigerant vapor portion to an intermediate pressure stage of the compression process; and selectively blocking passage of the refrigerant liquid portion into an intermediate pressure stage of the compression process or into a suction pressure portion of the refrigerant vapor compression system. In a second mode of operation, the method comprises the steps of: selectively passing a portion of the refrigerant vapor portion to an intermediate pressure stage of the compression process; and simultaneously selectively passing a portion of the liquid portion of the refrigerant to an intermediate pressure stage of the compression process. In a third mode of operation, the method comprises the steps of: selectively passing a portion of the refrigerant vapor portion into a suction pressure portion of the refrigerant vapor compression system; and simultaneously selectively passing a portion of the refrigerant liquid portion into a suction pressure portion of the refrigerant vapor compression system. In a fourth mode of operation, the method comprises the steps of: the subcritical pressure of the flash tank is controlled and the refrigerant is separated into refrigerant vapor and refrigerant liquid at the pressure by selectively passing a portion of the refrigerant vapor portion into a suction pressure portion of the refrigerant vapor compression system.

Drawings

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:

FIG. 1 is a schematic diagram illustrating a first exemplary embodiment of a refrigerant vapor compression system in accordance with the present invention; and

figure 2 is a schematic illustrating a second embodiment of a refrigerant vapor compression system according to the present invention.

Detailed Description

Referring now to fig. 1 and 2, there is depicted an exemplary embodiment of a refrigerant vapor compression system 10, the system 10 being suitable for use in a transport refrigeration system for refrigerating air or other gaseous environments within a truck, trailer, container or device for transporting perishable/frozen goods. The refrigerant vapor compression system 10 is also suitable for supplying conditioned air to a comfort climate controlled area of a residence, office building, hospital, school, restaurant or other setting. The refrigerant vapor compression system may also be used to refrigerate air supplied to a perishable/frozen item storage area in a display case, merchandiser, freezer, or other commercial establishment.

The refrigerant vapor compression system 10 is particularly suited for operation in a transcritical cycle using a low critical point temperature refrigerant, such as for example, but not limited to, carbon dioxide. However, it is to be understood that: the refrigerant vapor compression system 10 may also be operated in a subcritical cycle using high critical point refrigerants such as conventional hydrochlorofluorocarbons and hydrochlorocarbons. The refrigerant vapor compression system 10 includes a multi-stage compression device 20, a refrigerant heat rejection heat exchanger 40, a refrigerant heat absorption heat exchanger 50 (also referred to herein as an evaporator), and a primary expansion valve 55, such as, for example, an electronic expansion valve or a thermostatic expansion valve, operatively associated with the evaporator 50, with refrigeration lines 2, 4 and 6 connecting the above in a primary refrigerant circuit.

In a refrigerant vapor compression system operating in a transcritical cycle, the refrigerant heat rejection heat exchanger 40 constitutes a gas refrigerator through which supercritical refrigerant passes in heat exchange relationship with a cold medium, such as, for example, but not limited to, ambient air or water, and which may also be referred to herein as a gas refrigerator. In a refrigerant vapor compression system operating in a subcritical cycle, the refrigerant heat rejection heat exchanger 40 will constitute a refrigerant condensing heat exchanger through which hot, high pressure refrigerant passes in heat exchange relationship with a refrigerant medium. In the depicted embodiment, the refrigerant heat rejection heat exchanger 40 comprises a fin-tube heat exchanger 42, such as, for example, a fin-shaped round tube heat exchange coil or a fin-shaped mini-channel flat tube heat exchanger (mini-channel heat exchanger), through which refrigerant passes in heat exchange relationship with ambient air, and the ambient air is drawn through the fin-tube heat exchanger 42 by a fan 44 associated with the gas chiller 40.

The refrigerant heat absorption heat exchanger 50 functions as an evaporator wherein a refrigerant liquid passes through the heat exchanger in heat exchange relationship with a fluid to be cooled, most commonly air, which is drawn from and returned to the temperature controlled environment 200, such as: a refrigerated transport truck, trailer or container, or a cargo compartment of a perishable/frozen product storage area of a display case, merchandiser, freezer or other commercial establishment, or a comfort climate controlled area within a residence, office building, hospital, school, restaurant or other facility. In the depicted embodiment, the refrigerant heat absorption heat exchanger 50 includes a fin-tube heat exchanger 52 through which refrigerant passes in heat exchange relationship with air, and to which air is drawn from and returned to the refrigerated cargo compartment 200 by an evaporator fan 54 associated with the evaporator 50. The finned tube heat exchanger 52 may comprise, for example, a finned round tube heat exchange coil or a finned microchannel flat tube heat exchanger.

The compression device 20 is used to compress and circulate refrigerant through the main refrigerant line, as will be discussed in further detail below. The compression device 20 may comprise a single multi-stage refrigerant compressor, such as, for example, a scroll compressor, a screw compressor, or a reciprocating compressor, disposed on the main refrigeration line and having a first compression stage 20a and a second compression stage 20 b. The first and second compression stages are arranged in series with the refrigerant flow such that the refrigerant flow leaving the first compression stage passes directly to the second compression stage for further compression. Alternatively, the compression device 20 may include a pair of independent compressors 20a and 20b connected in serial refrigerant flow relationship to the main refrigeration circuit, with the discharge outlet port of the first compressor 20a being connected in refrigerant flow communication through the refrigeration circuit to the suction inlet port of the second compressor 20 b. In a separate compressor embodiment, the compressors 20a and 20b may be scroll compressors, screw compressors, reciprocating compressors, rotary compressors or other types of compressors or any combination of such compressors. In the exemplary embodiment depicted in fig. 2, the compressor 20 is a scroll compressor having a suction inlet 22, a discharge outlet 24, and a port 26, the port 26 opening directly to an intermediate pressure stage of the compressor compression chamber.

Additionally, the refrigerant vapor compression system 10 of the present invention includes a flash tank economizer 70 disposed in the refrigeration line 4 between downstream of the gas chiller 40 and upstream of the evaporator 50 of the main refrigerant circuit with respect to refrigerant flow. A secondary expansion device 65 is disposed on the refrigeration line 4 in operative association with the flash tank economizer 70 and upstream of the flash tank economizer 70. The secondary expansion device 65 may be an electronic expansion valve, such as that depicted in fig. 1 and 2, or a fixed orifice expansion device (fixed orifice expansion device). The refrigerant traversing the secondary expansion device 65 expands to a sufficiently low pressure to form a mixture of gaseous refrigerant and liquid refrigerant. The flash tank economizer 70 defines a separation chamber 72 with liquid refrigerant collecting in a lower portion of the separation chamber and gaseous refrigerant collecting in a portion of the separation chamber 72 above the liquid refrigerant.

Liquid refrigerant collecting in the lower portion of the flash tank economizer 70 passes thereby through refrigerant line 4 and traverses the main refrigerant circuit expansion valve 55, with the expansion valve 55 being disposed upstream with respect to refrigerant flow of the evaporator 50. As this liquid refrigerant traverses the first expansion valve, 55, it expands to a lower pressure and temperature before entering the evaporator 50. The evaporator 50 constitutes a refrigerant evaporating heat exchanger through which expanded refrigerant passes in heat exchange relationship with the air to be cooled, whereby the refrigerant is evaporated and typically superheated. Conventionally, the primary expansion valve 55 measures the flow of refrigerant through the refrigerant line 4 to maintain a desired level of superheat during the time that the refrigerant vapor exits the evaporator 50 to ensure that no liquid is present in the refrigerant exiting the evaporator. The low pressure refrigerant vapor leaving the evaporator 50 returns through refrigerant line 6 to either the first compression stage of the compression device 20 in the embodiment depicted in fig. 1 or to the suction port of the first compressor 20a or to the suction inlet 22 of the scroll compressor 20 in the embodiment depicted in fig. 2.

The refrigerant vapor compression system 10 further includes a refrigerant vapor injection line 14 and a refrigerant liquid injection line 18. The refrigerant vapor injection line 14 establishes refrigerant flow communication between an upper portion of the separation chamber 72 of the flash tank economizer 70 and an intermediate stage of the compression process and between an upper portion of the separation chamber 72 and a suction pressure portion of the refrigerant circuit. The refrigerant liquid injection line 18 normally establishes refrigerant flow communication between the lower portion of the separation chamber of the flash tank 70 and an intermediate stage of the compression process and between the lower portion of the separation chamber and the suction pressure portion of the refrigerant circuit by virtue of the liquid-conducting refrigerant line 4 connecting downstream of the flash tank 70 and upstream of the main expansion valve 55.

In the exemplary embodiment of the refrigerant vapor compression system 10 depicted in fig. 1, the injection of refrigerant vapor or refrigerant liquid into an intermediate pressure stage of the compression process will be accomplished by causing the injection of refrigerant vapor or refrigerant liquid into the refrigerant passing from the first compression stage 20a to the second compression stage 20b of a single compressor or from the discharge outlet of the first compressor 20a to the suction inlet of the second compressor 20 b. In the exemplary embodiment of the refrigerant vapor compression system 10 depicted in fig. 2, injection of refrigerant vapor or refrigerant liquid into the intermediate pressure stage of the compression process will be accomplished by injecting refrigerant vapor or refrigerant liquid into the compression chambers of the scroll compressor 20 through the intermediate pressure port 26.

The refrigerant vapor compression system 10 may also include a compressor unload bypass line 16 establishing refrigerant flow communication between an intermediate pressure stage of the compression device 20 and a suction pressure portion of the refrigerant circuit, which, as noted previously, constitutes the refrigeration line 6 extending between the outlet of the evaporator 50 and the suction inlet of the compression device 20. In the exemplary embodiment depicted in fig. 1 and 2, an upstream portion of the refrigerant vapor injection line 14 and an upstream portion of the refrigerant liquid injection line 18 are both open in fluid communication with the compressor unload bypass line 16, and the compressor unload bypass line 16 forms a downstream extension of both the refrigerant vapor injection line 14 and the refrigerant liquid injection line 18.

As depicted in fig. 1 and 2, the refrigerant vapor compression system 10 may include an operatively associated control system for selectively directing refrigerant vapor from the flash tank 70 through the refrigerant vapor injection line 14 or directing refrigerant liquid from the flash tank 70 through the refrigerant liquid injection line 18 for injection into the main refrigerant circuit or into the refrigerant line 6 at an intermediate pressure stage of the compression process, wherein the intermediate pressure stage is between the first or first compressor 20a and the second or second compressor 20b, with the refrigerant line 6 forming the main refrigerant circuit suction. In one embodiment of the refrigerant vapor compression system 10, the control system includes a controller 100 and a plurality of flow control devices operatively associated with the refrigerant vapor injection line 14 and/or the refrigerant liquid injection line 18. In operation, the controller 100 selectively controls each of the plurality of flow control devices to be positioned between their respective open and closed positions to selectively direct refrigerant flow through the refrigerant vapor injection line 14 and the refrigerant liquid injection line 18.

In the embodiment depicted in fig. 1 and 2, the control means includes a first flow control valve 73 disposed in an upstream portion of the refrigerant vapor injection line 14, a second flow control device 93 disposed in the compressor unload bypass line 16 at a location intermediate the first flow control device and the intermediate pressure stage of the compression process, a third flow control device 53 disposed in an upstream portion of the refrigerant liquid injection line 18, and a fourth flow control device 83 disposed in the compressor unload bypass line 16 at a location intermediate the third flow control device and the refrigerant line 6. Each of the flow control devices 53, 73, 83, 93 described above may include a flow control valve selectively positionable between an open position wherein refrigerant flow is permitted through the refrigerant line with the flow control valve incorporated therein and a closed position wherein refrigerant flow is blocked through the refrigerant line with the flow control valve incorporated therein. In one embodiment, each flow control valve comprises a two position solenoid valve of the positionable type selectively positionable between a first open position and a second closed position under the control of the controller 100.

The controller 100 not only controls the operation of the various flow control valves 53, 73, 83, 93 to selectively direct refrigerant flow through the refrigerant vapor injection line 14 and the refrigerant liquid injection line 18, but also controls 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 monitors various operating parameters via various sensors operatively associated with the controller 100 and disposed at selected locations throughout the system. For example, in the exemplary embodiment depicted in fig. 1 and 2, a pressure sensor 102 is provided in operative association with the flash tank 70 to sense the pressure within the flash tank 70, a temperature sensor 103 and a pressure sensor 104 are provided to sense the refrigerant suction temperature and pressure, respectively, and a temperature sensor 105 and a pressure sensor 106 are provided to sense the refrigerant discharge temperature and pressure, respectively. The pressure sensors 102, 104, 106 may be conventional pressure sensors, such as for example pressure transducers, and the temperature sensors 103 and 105 may be conventional temperature sensors, such as for example thermocouples or thermistors.

A Suction Modulation Valve (SMV)23 may be disposed on refrigerant line 6 between the outlet of evaporator 50 and the suction inlet of compression device 20. In the exemplary embodiment depicted in fig. 1 and 2, the suction modulation valve 23 is positioned on the refrigerant circuit 6 between the outlet of the evaporator 50 and the intersection of the compressor unload bypass line 16 and the refrigerant line 6. Such as flow control valves 53, 73, 83, 93, the operation of the suction modulation valve 23 is controlled by a controller 100. When it is desired to increase or decrease the flow of refrigerant through the refrigerant circuit 6 to the suction inlet of the compression device 20, the controller 100 modulates the suction modulation valve 23 to control the refrigeration capacity of the refrigeration system 10. In one embodiment, the suction modulation valve 23 comprises a pulse width modulated solenoid valve.

In the embodiment depicted in fig. 2, the refrigerant vapor compression system 10 includes a discharge pressure-suction pressure heat exchanger 60. The heat exchanger 60 includes a first pass 62 disposed on the refrigerant circuit 4 of the main refrigerant circuit between the gas refrigerator 40 and the secondary expansion device 65, and a second pass 64 disposed on the refrigerant line 6 downstream of the evaporator 50 of the main refrigerant circuit and in heat exchange relationship with the first pass 62. The high pressure refrigerant vapor having traversed the gas refrigerator 40 passes through the first passage 62 in heat exchange relationship with the suction pressure refrigerant vapor having traversed the evaporator 50. In this manner, the high pressure refrigerant vapor passing through refrigerant line 4 is further cooled and the low pressure refrigerant vapor passing through refrigerant line 6 is thereby heated. This additional refrigeration reduces the enthalpy of the high pressure refrigerant before it is expanded through the secondary expansion device 65. Thus, the ratio between the refrigerant vapor and the refrigerant liquid collected in the flash tank 70 after expansion is reduced, which results in less refrigerant vapor being injected into the compression chambers of the scroll compressor 20 through the injection ports 26. This definition of the quality of the refrigerant collected in the flash tank 70 reduces the power requirements of the scroll compressor. In addition, the further heating of the low pressure refrigerant vapor ensures that any liquid remaining therein is evaporated and the refrigerant vapor is superheated prior to passing to the first compression stage or first compressor 20a of the compression device 20.

The refrigerant vapor compression system 10 may be operated in a selected mode of operation depending upon load requirements and ambient conditions. The controller 100 determines the desired mode of operation based on ambient conditions and various sensed system controls and then positions the various flow control valves accordingly. To operate the refrigerant vapor compression system 10 in its standard non-economized mode, i.e., a standard cycle, the controller 100 closes each of the flow control valves 53, 73, 83 and 93 whereby refrigerant can only circulate through the main refrigerant circuit, i.e., from the discharge outlet of the compression device 20a through refrigerant lines 2, 4 and 6, sequentially across the gas refrigerator 40, the secondary expansion device 65, the flash tank 70 (which serves only as a receiver in the standard mode), the main expansion valve 55, the evaporator 50 and the suction modulation valve 23 and back to the suction inlet of the compression device 20 a.

In this non-economized mode, in response to the pressure sensed by the sensor 102, the controller 100 controls the pressure within the flash tank 70 by selectively opening the flow control valves 73 and 83 to direct refrigerant vapor from the flash tank 70 through the refrigerant vapor injection line 14 and the compressor unload bypass line 16 into the refrigerant line 6 while keeping the flow control valves 53 and 93 closed. Also in this non-economized mode, the controller 100 responds to the high discharge temperature sensed by the temperature sensor 105 by directing a small amount of liquid through the refrigerant line 18 and through a portion of the compressor unload bypass line 16 into the refrigerant line 6 to desuperheat the refrigerant suction flow by intermittently opening the valve 53 in conjunction with the above valve configuration.

The controller 100 may operate the refrigerant vapor compression system 10 in the economized mode by closing the flow control valves 53 and 83 and opening the flow control valves 73 and 93 whereby refrigerant is circulated not only through the primary refrigerant circuit, but also through the refrigerant vapor injection line to an intermediate pressure stage of the compression device 20 a. Refrigerant passing through the primary refrigerant circuit passes from the discharge outlet of the compression device 20a through refrigerant lines 2, 4 and 6, sequentially traversing the gas refrigerator 40, the secondary expansion device 65, the flash tank 70 (which functions as an economizer and receiver in the economized mode), the primary expansion valve 55, the evaporator 50 and the suction modulation valve 23 and returning to the suction inlet of the compression device 20 a. With the flow control valves 73 and 93 open, refrigerant vapor passes from the flash tank 70 through the refrigerant vapor injection line 14 and a portion of the compressor bypass line 16 into an intermediate pressure stage of the compression device 20, thereby increasing the economizer cycle to standard cycle operation.

In this economized cycle, the controller 100 responds to either a high discharge temperature sensed by temperature sensor 105 or a high discharge pressure sensed by pressure sensor 106 by selectively opening flow control valves 53, 73 and 93 while keeping flow control valve 83 closed to direct refrigerant vapor through refrigerant line 14 and refrigerant liquid through refrigerant line 18 while entering and passing through a portion of the compressor unload bypass line 16 into an intermediate pressure stage of the compression device 20 a.

In addition, the controller 100 may unload the compression device 20 in any mode of operation by closing the flow control valves 53 and 73 and opening both flow control valves 83 and 93 on the compressor unload bypass line 16. With both flow control valves 83 and 93 open, refrigerant flow from the intermediate stage of the compression process passes through the compressor unload bypass line, into refrigerant line 6, and directly back to the suction side of the compression device, thereby bypassing the second compression stage or second compressor 20a, thereby unloading the compression device 20. This unloading of the compressor 20 can be accomplished via the compressor unload bypass line 16 in response to a high compressor refrigerant discharge temperature or for capacity reduction or compressor power reduction. The controller 100 may also modulate the suction modulation valve 23 if additional capacity needs to be released.

Those skilled in the art will recognize that many changes may be made to the specific exemplary embodiments described herein. For example, the refrigerant vapor compression system may also be operated in a subcritical cycle mode, rather than the transcritical cycle mode described above. While the present invention has been particularly shown and described with reference to exemplary embodiments as illustrated in the drawings, those skilled in the art will understand that: various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.

Claims (42)

1. A refrigerant vapor compression system comprising:

a primary refrigerant circuit including a refrigerant compression device, a refrigerant heat rejection heat exchanger downstream of the compression device, a refrigerant heat absorption heat exchanger downstream of the refrigerant heat rejection heat exchanger, and a primary expansion device disposed in the primary refrigerant circuit downstream of the refrigerant heat rejection heat exchanger and upstream of the refrigerant heat absorption heat exchanger;

a flash tank disposed in the primary refrigerant circuit downstream of the refrigerant heat rejection 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 gaseous refrigerant collecting in a portion of the separation chamber above the liquid refrigerant;

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

a refrigerant vapor injection line establishing refrigerant flow communication between an upper portion of the separation chamber and an intermediate pressure stage of the compression device and a suction pressure portion of the primary refrigerant circuit; and

a refrigerant liquid injection line establishing refrigerant flow communication between a lower portion of the separation chamber and an intermediate pressure stage of the compression device and a suction pressure portion of the primary refrigerant circuit,

wherein the suction pressure portion of the primary refrigerant circuit is the portion extending between the outlet of the refrigerant heat absorption heat exchanger and the suction inlet of the compression device.

2. A refrigerant vapor compression system as recited in claim 1 further comprising a control system for selectively directing refrigerant vapor from said flash tank through said refrigerant vapor injection line for injection into the main refrigerant circuit at an intermediate pressure stage of the compression process or into a suction pressure portion of the main refrigerant circuit and for selectively directing refrigerant liquid from said flash tank through said refrigerant liquid injection line for injection into the main refrigerant circuit at an intermediate pressure stage of the compression process or into a suction pressure portion of the main refrigerant circuit.

3. A refrigerant vapor compression system as recited in claim 2 wherein said control system comprises a plurality of flow control valves operatively associated with said refrigerant vapor injection line and/or said refrigerant liquid injection line and a controller selectively controlling the positioning of each of said plurality of flow control valves between its respective open and closed positions.

4. A refrigerant vapor compression system as recited in claim 3 wherein said plurality of flow control valves comprises:

a first flow control valve disposed on an upstream portion of the refrigerant vapor injection line;

a third flow rate control valve provided on an upstream portion of the refrigerant liquid injection line;

a second flow control valve disposed upstream of the intermediate pressure stage of the compression device with respect to refrigerant flow and downstream of the first and third flow control valves with respect to refrigerant flow; and

a fourth flow control valve disposed upstream with respect to refrigerant flow of the suction pressure portion of the main refrigerant circuit and downstream with respect to refrigerant flow of the first and third flow control valves.

5. A refrigerant vapor compression system as recited in claim 4 wherein each of said first, second, third and fourth flow control valves comprises a solenoid valve having a first open position and a second closed position.

6. A refrigerant vapor compression system as recited in claim 1 further comprising a compressor unload bypass line establishing refrigerant flow communication between an intermediate pressure stage of said compression device and a suction pressure portion of said main refrigerant circuit.

7. A refrigerant vapor compression system as recited in claim 6 wherein said compressor unload bypass line forms a downstream extension of said refrigerant vapor injection line and a downstream extension of said refrigerant liquid injection line.

8. A refrigerant vapor compression system as recited in claim 7 further comprising:

a first flow control valve disposed on an upstream portion of the refrigerant vapor injection line;

a third flow rate control valve provided on an upstream portion of the refrigerant liquid injection line;

a second flow control valve disposed in the compressor unload bypass line upstream of the intermediate pressure stage of the compression device with respect to refrigerant flow; and

a fourth flow control valve disposed on the compressor unload bypass line at a location between the third flow control valve and the suction pressure portion of the main refrigerant circuit.

9. A refrigerant vapor compression system as recited in claim 8 wherein each of said first, second, third and fourth flow control valves comprises a solenoid valve having a first open position and a second closed position.

10. A refrigerant vapor compression system as recited in claim 3 further comprising a suction modulation valve operatively controlled by said controller and disposed in said main refrigerant circuit downstream of said refrigerant heat absorption heat exchanger and upstream of said compression device.

11. A refrigerant vapor compression system as recited in claim 1 wherein said system operates in a transcritical cycle.

12. A refrigerant vapor compression system as recited in claim 1 wherein the refrigerant comprises carbon dioxide.

13. A refrigerant vapor compression system as recited in claim 1 wherein said compression device comprises a single compressor having at least a first lower pressure compression stage and a second higher pressure compression stage.

14. A refrigerant vapor compression system as recited in claim 1 wherein said compression device comprises a first compressor and a second compressor disposed in continuous refrigerant flow relationship in said primary refrigerant circuit with a discharge outlet of said first compressor in refrigerant flow communication with a suction inlet of said second compressor.

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 13 further comprising a refrigerant-to-refrigerant heat exchanger having a first refrigerant pass disposed in heat exchange relationship with a second refrigerant pass, said first refrigerant pass disposed on said primary refrigerant circuit between said refrigerant heat rejection heat exchanger and said secondary expansion device, and said second refrigerant pass disposed on said primary refrigerant circuit between a refrigerant heat absorption heat exchanger and said compression device (20).

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 compression device comprises a reciprocating compressor.

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

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

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

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

23. A method of operating a refrigerant vapor compression system in a transcritical cycle, comprising the steps of:

compressing the refrigerant to a supercritical state in a two-stage compression process;

passing a supercritical pressure refrigerant in heat exchange relationship with a cold medium;

expanding the refrigerant in the supercritical state to a subcritical pressure in a first expansion step to form a first expanded refrigerant comprising refrigerant vapor and refrigerant liquid;

separating the first expanded refrigerant into a refrigerant vapor portion and a refrigerant liquid portion;

expanding at least a portion of the refrigerant liquid portion to a lower pressure in a second expansion step to a second expanded refrigerant comprising refrigerant liquid;

evaporating the second expanded refrigerant;

selectively directing a portion of the refrigerant vapor portion to an intermediate stage of the compression process or to a suction pressure portion of the refrigerant vapor compression system; and

selectively directing a portion of the liquid portion of the refrigerant to an intermediate stage of the compression process or to a suction pressure portion of the refrigerant vapor compression system,

wherein the refrigerant circuit of the refrigerant vapor compression system includes a refrigerant heat absorption heat exchanger and a compression device, the suction pressure portion being the portion of the refrigerant circuit extending between an outlet of the refrigerant heat absorption heat exchanger and a suction inlet of the compression device.

24. The method as recited in claim 23 further comprising the step of controlling the pressure of the supercritical pressure refrigerant passing in heat exchange relationship with the cold medium to a desired pressure by selectively controlling the flow of the supercritical pressure refrigerant expanded in said first expansion step.

25. The method as recited in claim 23, wherein the method further comprises, in the first mode of operation, the steps of:

selectively passing a portion of the refrigerant vapor portion to an intermediate pressure stage of the compression process; and

selectively blocking passage of the refrigerant liquid portion into an intermediate pressure stage of the compression process or into the suction pressure portion of the refrigerant vapor compression system.

26. The method of claim 23, further comprising, in the second mode of operation, the steps of:

selectively passing a portion of the refrigerant vapor portion to an intermediate pressure stage of the compression process; and

while selectively passing a portion of the liquid portion of the refrigerant to an intermediate pressure stage of the compression process.

27. The method of claim 23, further comprising, in the third mode of operation, the steps of:

selectively passing a portion of the refrigerant vapor portion into a suction pressure portion of the refrigerant vapor compression system; and

while selectively passing a portion of the refrigerant liquid portion into a suction pressure portion of the refrigerant vapor compression system.

28. The method as recited in claim 23 further comprising the step of controlling said subcritical pressure within said flash tank during a fourth mode of operation by selectively passing a portion of the refrigerant vapor portion into a suction pressure portion of the refrigerant vapor compression system.

29. A refrigerant vapor compression system for use in conjunction with a transport refrigeration system comprising:

a primary refrigerant circuit including a refrigerant compression device, a refrigerant heat rejection heat exchanger disposed downstream of the compression device, a refrigerant heat absorption heat exchanger disposed downstream of the refrigerant heat rejection heat exchanger, and a primary expansion device disposed in the primary refrigerant circuit downstream of the refrigerant heat rejection heat exchanger and upstream of the refrigerant heat absorption heat exchanger;

a flash tank disposed in the primary refrigerant circuit downstream of the refrigerant heat rejection 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 gaseous refrigerant collecting in a portion of the separation chamber above the liquid refrigerant;

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

a refrigerant vapor injection line establishing refrigerant flow communication between an upper portion of the separation chamber and an intermediate pressure stage of the compression device and a suction pressure portion of the primary refrigerant circuit; and

a refrigerant liquid injection line establishing refrigerant flow communication between a lower portion of the separation chamber and an intermediate pressure stage of the compression device and a suction pressure portion of the primary refrigerant circuit,

wherein the suction pressure portion of the primary refrigerant circuit is the portion extending between the outlet of the refrigerant heat absorption heat exchanger and the suction inlet of the compression device.

30. A refrigerant vapor compression system as recited in claim 29 further comprising a control system for selectively directing refrigerant vapor from said flash tank through said refrigerant vapor injection line for injection into the main refrigerant circuit at an intermediate pressure stage of the compression process or into the suction pressure portion of the main refrigerant circuit and for selectively directing refrigerant liquid from said flash tank through said refrigerant liquid injection line for injection into the main refrigerant circuit at an intermediate pressure stage of the compression process or into the suction pressure portion of the main refrigerant circuit.

31. A refrigerant vapor compression system as recited in claim 30 wherein said control system comprises a plurality of flow control valves operatively associated with said refrigerant vapor injection line and/or said refrigerant liquid injection line and a controller selectively controlling the positioning of each of said plurality of flow control valves between its respective open and closed positions.

32. A refrigerant vapor compression system as recited in claim 30 further comprising a compressor unload bypass line establishing refrigerant flow communication between an intermediate pressure stage of said compression device and a suction pressure portion of said main refrigerant circuit.

33. A refrigerant vapor compression system as recited in claim 32 wherein said compressor unload bypass line forms a downstream extension of said refrigerant vapor injection line and a downstream extension of said refrigerant liquid injection line.

34. A refrigerant vapor compression system as recited in claim 33 further comprising:

a first flow control valve disposed on an upstream portion of the refrigerant vapor injection line;

a third flow rate control valve provided on an upstream portion of the refrigerant liquid injection line;

a second flow control valve disposed in the compressor unload bypass line upstream of the intermediate pressure stage of the compression device with respect to refrigerant flow; and

a fourth flow control valve disposed on the compressor unload bypass line at a location between the third flow control valve and the suction pressure portion of the main refrigerant circuit.

35. A refrigerant vapor compression system as recited in claim 34 wherein each of said first, second, third and fourth flow control valves comprises a solenoid valve having a first open position and a second closed position.

36. A refrigerant vapor compression system as recited in claim 31 further comprising a suction modulation valve operatively controlled by said controller and disposed in said primary refrigerant circuit downstream of said refrigerant heat absorption heat exchanger and upstream of said compression device.

37. A refrigerant vapor compression system as recited in claim 30 wherein said system operates in a transcritical cycle.

38. A refrigerant vapor compression system as recited in claim 37 wherein the refrigerant comprises carbon dioxide.

39. A refrigerant vapor compression system as recited in claim 30 wherein said compression device comprises a scroll compressor.

40. A refrigerant vapor compression system as recited in claim 30 further comprising a refrigerant-to-refrigerant heat exchanger having a first refrigerant pass disposed in heat exchange relationship with a second refrigerant pass, said first refrigerant pass being disposed on said primary refrigerant circuit between said refrigerant heat rejection heat exchanger and said secondary expansion device, and said second refrigerant pass being disposed on said primary refrigerant circuit between a refrigerant heat absorption heat exchanger and said compression device (20).

41. A refrigerant vapor compression system as recited in claim 30 wherein said compression device comprises a screw compressor.

42. A refrigerant vapor compression system as recited in claim 30 wherein said compression device comprises a reciprocating compressor.