HK1138059B - Economized refrigeration cycle with expander - Google Patents

Description

Economized refrigeration cycle with expander

[ technical field ] A method for producing a semiconductor device

The present invention relates generally to vapor compression systems and, more particularly, to refrigerant vapor compression systems equipped with an economizer cycle.

[ background of the invention ]

Refrigerant vapor compression systems are well known in the art and are commonly used to condition air (or other auxiliary media) to provide a climate controlled comfort zone in a residence, office building, hospital, school, restaurant or other location. Refrigerant vapor compression systems are also commonly used in transport refrigeration systems to provide refrigerated air to temperature controlled cargo spaces of trucks, trailers, containers and the like to transport perishable items, and if appropriate, in commercial refrigeration systems to provide refrigerated air to cold rooms, beverage coolers, milk boxes or temperature controlled spaces where freezers display perishable food items in a frozen or refrigerated state. Typically, these refrigerant vapor compression systems include a compressor, a condenser, an evaporator, and an expansion device. An expansion device, typically a fixed orifice, a capillary tube, a thermostatic expansion valve (TXV), or an electronic expansion valve (EXV), is typically disposed in the refrigerant line 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 accord with known refrigerant vapor compression cycles.

Most of these refrigerant vapor compression systems conventionally operate at subcritical refrigerant pressures. Refrigerant vapor compression systems operating in the subcritical range are typically flooded with fluorocarbon refrigerants such as, but not limited to, Hydrochlorofluorocarbons (HCFCs), such as R22, and more commonly chlorofluorocarbons (HFCs), such as R134a, R410A and R407C. Although chlorofluorocarbon (HFC) refrigerants are more environmentally friendly than the chlorine containing Hydrochlorofluorocarbon (HCFC) refrigerants that they replace, the "natural" refrigerants, such as carbon dioxide (also known as R744), are being diverted for use in air conditioning and transport refrigeration systems in place of the chlorofluorocarbon (HFC) refrigerants.

Because carbon dioxide has a low critical point, refrigerant vapor compression systems that are mostly filled with carbon dioxide as the refrigerant are designed to operate in a transcritical pressure regime. In a refrigerant vapor compression system operating in a transcritical cycle, the refrigerant discharged from the compressor is a vapor having a temperature and pressure in excess of the critical point of the refrigerant. As in conventional refrigerant vapor compression systems operating at subcritical points, refrigerant vapor compression systems operating in a transcritical cycle include a compression device, a heat rejection heat exchanger functioning as a gas cooler rather than a condenser, an evaporator and an expansion device consistent with known refrigerant vapor compression cycle arrangements. The expansion device is typically a thermostatic expansion valve (TXV) or an electronic expansion valve (EXV) disposed in the refrigerant line upstream of the evaporator in refrigerant flow and downstream of the gas cooler in refrigerant flow.

Refrigerant vapor compression systems utilizing a low critical point refrigerant, such as carbon dioxide, often utilize a two-stage compression system, either a pair of compressors disposed in series with respect to refrigerant flow or a single compressor having at least two compression stages. In order to improve the performance of Refrigerant systems and to control the temperature of the Refrigerant vapor discharged from the final stage of a compression system over a wide range of operating conditions, commonly referred to as the discharge pressure or high end pressure, it is known to equip such systems with an economizer cycle that includes a Refrigerant-to-Refrigerant (recuperator) economizer heat exchanger. An economizer heat exchanger is typically provided in the refrigerant circuit intermediate the gas cooler and the evaporator to further cool the refrigerant in the main circuit exiting the gas cooler, and an expanded (to intermediate pressure) portion of the refrigerant having traversed the economizer heat exchanger in heat transfer relationship with the refrigerant in the main circuit is returned to the compressor as make-up cooling fluid. Typically, refrigerant vapor returning to the compressor is injected into an intermediate stage of the compression process either through one or more injection ports into an intermediate pressure stage of the compression chamber(s) of a single compressor, or in the case of a multiple compressor system into a refrigerant line extending between the discharge port of an upstream compressor and the suction port of a downstream compressor. In addition, liquid refrigerant may be withdrawn from a location downstream of the heat rejection heat exchanger and returned to the compressor, typically through a separate injection port or ports to an intermediate stage of the compression process. It will be appreciated that the injection of vapor in the economizer cycle and liquid injection is likely to occur at different intermediate pressures in the compression process, particularly when the vapor and liquid are injected through separate lines.

For example, U.S. Pat. No. 6,571,576 discloses a refrigerant vapor compression system operating in a subcritical cycle and equipped with an economizer heat exchanger wherein vapor refrigerant and liquid refrigerant are returned to an intermediate stage of the compression process through one or more economizer injection ports provided in the compressor. To provide refrigerant vapor for injection into the compressor, liquid refrigerant is withdrawn from the refrigerant circuit at a location downstream of the condenser, expanded to an intermediate pressure and lower temperature by an expansion valve to form a refrigerant liquid/vapor mixture which is then passed through an economizer heat exchanger in heat exchange relationship with the main flow of refrigerant liquid. This refrigerant liquid/vapor mixture in the transverse economizer heat exchanger extracts heat from the main flow of refrigerant liquid, further cooling the liquid, thus evaporating any liquid components remaining in the two-phase mixture and generally further heating the vapor. The refrigerant vapor leaving the economizer heat exchanger is then injected into the compressor through an economizer injection port at an intermediate (between suction and discharge) pressure. In addition, liquid refrigerant is selectively withdrawn from the refrigerant circuit at a location downstream of the condenser and mixed with refrigerant vapor passing from the economizer to the compressor and injected into an intermediate pressure stage of the compression process along with refrigerant vapor passing through the same economizer injection ports.

U.S. patent application publication No. US2005/0044885 a1 discloses a transcritical cycle for a carbon dioxide refrigerant vapor compression system including a compressor, a gas cooler, a flash tank economizer, an evaporator, a first expansion valve upstream of the flash tank economizer, and a second expansion valve downstream of the flash tank economizer. The refrigerant from the gas cooler to the evaporator is expanded to a lower pressure by a first expansion valve before entering a flash tank economizer where the refrigerant is separated into a liquid component and a vapor component. The liquid refrigerant passes from the flash tank economizer through a second expansion valve and is further expanded in the second expansion valve before traversing the evaporator. The vapor refrigerant is returned to the compressor at some intermediate pressure.

Us patent No. 6,880,357 discloses a refrigerant cycle device using carbon dioxide as a refrigerant, which is equipped with an expander and an optional secondary expander disposed in the refrigerant circuit between an outdoor heat exchanger and an indoor heat exchange. High pressure refrigerant is taken from the refrigerant circuit and injected into an intermediate pressure stage of the expander. The energy recovered during the expansion process of the expander and the secondary expander can be used to drive a compressor or an electrical generator.

[ summary of the invention ]

It is a general object of the present invention to provide a refrigerant vapor compression system including an expander and an economizer cycle containing injection of vapor and/or liquid refrigerant at an intermediate pressure stage in the compression process.

It is an aspect of the object of the present invention to provide a refrigerant vapor compression system equipped with an expander and economizer cycle and providing vapor refrigerant and liquid refrigerant injection through common lines at intermediate pressure stages in the compression process.

A refrigerant vapor compression system of the present invention includes a compression device disposed in a refrigerant circuit to compress vapor from a suction pressure to a discharge pressure, a Heat rejecting Heat Exchanger disposed in the refrigerant circuit downstream of a refrigerant flow of the compression device, a Heat Accepting Heat Exchanger disposed in the refrigerant circuit downstream of the Heat rejecting Heat Exchanger and upstream of the compression device, an economizer Heat Exchanger disposed in the refrigerant circuit downstream of the refrigerant flow of the Heat rejecting Heat Exchanger and upstream of the Heat Accepting Heat Exchanger, and an expansion device disposed in the refrigerant circuit downstream of the economizer Heat Exchanger and upstream of the Heat Accepting Heat Exchanger. The economizer heat exchanger has a first pass and a second pass operatively connected in a heat transfer relationship.

An evaporator bypass line is provided for passing a portion of the refrigerant from the primary refrigerant circuit after having traversed the first pass of the economizer heat exchanger to exit the expansion device at an intermediate pressure during the expansion process, and thence through the second pass of the economizer heat exchanger and into the intermediate pressure port of the compression device. The economizer bypass line is an evaporator bypass line provided for passing a portion of refrigerant from the primary refrigerant circuit after having traversed the heat rejection heat exchanger and partially expanded in the expander into a position upstream of the second pass of the economizer heat exchanger with respect to refrigerant flow. An expansion valve disposed in the economizer bypass line is used to expand the refrigerant through the expansion valve to a lower pressure to provide the desired liquid injection. The economizer vapor injection and liquid injection can be performed as desired. This invention will be most beneficial for transcritical cycles, with the most pronounced being the benefit of using an expander as the expansion device.

In one embodiment of the invention, the expander device comprises a primary expander and a secondary expander. A main expander is operatively connected in the refrigerant circuit upstream with respect to refrigerant flow of the evaporator to expand a major portion of refrigerant flow having traversed the first pass of the economizer heat exchanger and circulated through the main refrigerant circuit. A secondary expander is operatively connected in the evaporator bypass line upstream with respect to refrigerant flow of the second pass of the economizer heat exchanger to expand a minor portion of the refrigerant flow having traversed the first pass of the economizer heat exchanger and circulated through the economizer circuit. In this embodiment, the economizer loop refrigerant can also flow upstream of the economizer heat exchanger.

In another embodiment of the invention, the expansion device comprises a single expander having a first stage of expansion for expanding refrigerant vapor having traversed the first pass of the economizer heat exchanger to a pressure intermediate the discharge pressure and the suction pressure, and a second stage of expansion for expanding refrigerant vapor having traversed the first pass of the economizer heat exchanger to a pressure near the suction pressure. In this embodiment, the evaporator bypass line communicates with the expansion device to receive the refrigerant flow at an intermediate pressure.

The compression device may consist of a first compressor having a discharge port connected by a refrigerant line in refrigerant flow communication to the suction port of the second compressor with an evaporator bypass line opening into the refrigerant line at a location between the discharge port of the first compressor and the suction port of the second compressor. The compression device may be a single compressor having a compression chamber (or chambers) with an evaporator bypass line leading into the compression chamber (or chambers) at an intermediate stage of the compression process.

[ description of the drawings ]

For a further understanding of these and other objects and advantages of the invention, reference will be made to the following detailed description of the invention, taken in conjunction with the accompanying drawings, in which:

figure 1 is a schematic diagram illustrating a first embodiment of a refrigerant vapor compression system of the present invention;

figure 2 is a schematic diagram illustrating a second embodiment of the refrigerant vapor compression system of the present invention;

FIG. 3 is a schematic diagram illustrating another arrangement of the embodiment of the refrigerant vapor compression system of the present invention depicted in FIG. 1; and

figure 4 is a schematic illustrating another arrangement of the embodiment of the refrigerant vapor compression system of the present invention depicted in figure 2.

[ detailed description ] according to the present embodiment

The present invention will be further described herein with reference to the embodiment of the refrigerant vapor compression system 10 depicted in fig. 1-2, which refrigerant vapor compression system 10 preferably operates in a transcritical cycle and is flooded with carbon dioxide or other related low critical point refrigerant. As with conventional systems, the Refrigerant vapor compression system 10 includes a compression device 20, a Refrigerant Heat rejection Heat Exchanger 30 (also referred to as a gas cooler), a Refrigerant Heat absorption Heat Exchanger (also referred to herein as an evaporator) 40, and a plurality of Refrigerant lines 70A, 70B, 70C and 70D connecting the elements of the basic Refrigerant circuit 70 as previously described. Although the refrigerant vapor compression system of the present invention is suitable, in part, for operating in a transcritical cycle with a low critical point refrigerant (e.g., carbon dioxide), it should be understood that the refrigerant vapor compression system described herein may also operate in a subcritical cycle when charged with a conventional refrigerant having a relatively high critical point temperature.

The compression device 20 is used to compress and circulate a refrigerant through the refrigerant circuit, details of which are discussed further below. In the embodiment depicted in fig. 1, the compression device 20 is a single refrigerant compressor having at least a first compression stage and a second compression stage (e.g., a screw compressor or a screw compressor having staged compression ports, or a reciprocating compressor having at least first and second banks of cylinders). In the embodiment depicted in fig. 2, the compression device 20 is a pair of compressors 20A and 20B, such as a pair of screw compressors, reciprocating compressors (or separate cylinders of a single reciprocating compressor), or rotary compressors in series, having a refrigerant line 22 connecting the discharge ports of a first compressor 20A, the first compressor 20A constituting a first compression stage, which is in refrigerant flow communication with the suction port of a second compressor 20B, the second compressor 20B constituting a second compression stage.

In a refrigerant vapor compression system operating in a transcritical cycle, the compressor discharge pressure is sufficiently high that the refrigerant vapor cannot condense as it traverses the heat rejection heat exchanger 30. Therefore, with respect to systems operating in a transcritical cycle, the heat rejection heat exchanger 30 functions as a refrigerant gas cooler rather than a refrigerant vapor condenser. The supercritical refrigerant vapor discharged from the single compressor 20 of the embodiment of fig. 1 or the second stage compressor 20B of the embodiment of fig. 2 into the refrigerant line 70A is cooled by heat exchange with a secondary cooling fluid and the ambient outdoor air is typically passed through the refrigerant carrying coils 34 by an air mover (e.g., one or more fans 32) operatively connected to the gas cooler 30. In a transcritical system, the refrigerant flow enters refrigerant line 70B from coil 34 of gas cooler 30 at a high pressure, lower temperature condition.

A majority of the refrigerant exiting the gas cooler 30 passes through refrigerant line 70B to the evaporator 40. To this end, the refrigerant traverses the expansion device 80 and expands to a lower (typically subcritical) pressure, whereby the refrigerant enters the evaporator 40 as a lower temperature, lower pressure liquid refrigerant, or more generally a liquid/vapor refrigerant mixture. In the refrigerant vapor compression system of the present invention, the expansion device 80 is an expander rather than a flow restrictor type expansion device such as an expansion valve, a capillary tube or a fixed orifice. The evaporator 40 constitutes a refrigerant heat absorption heat exchanger through which liquid refrigerant is passed in heat exchange relationship with a secondary fluid to be cooled and delivered to a conditioned environment, thereby heating the refrigerant and thereby evaporating the liquid component and superheating the vapor produced thereby. The secondary fluid that exchanges heat with the refrigerant in the evaporator 40 may be air that is passed through the evaporator refrigerant coils 44 by an air mover (e.g., one or more fans 42) to condition the air by cooling the air and condensing moisture in the air. The conditioned air may be used in a climate controlled environment, such as a comfort zone associated with an air management system or a perishable product storage zone associated with a transport refrigerant unit or a commercial refrigerant unit.

The refrigerant vapor compression system 10 of the present invention further includes an economizer heat exchanger 60 disposed in the refrigerant circuit 70 between the gas cooler 30 and the evaporator 40. In the embodiment of the system 10 depicted in fig. 1 and 2, the economizer heat exchanger 60 is a refrigerant-to-refrigerant heat exchanger wherein a first flow of refrigerant passes through a first pass 62 of the economizer heat exchanger 60 in heat exchange relationship with a second flow passing through a second pass 64 of the economizer heat exchanger 60. The first flow of refrigerant comprises the major portion of the high pressure refrigerant vapor passing through refrigerant line 70B while the second flow of refrigerant comprises the minor economizer loop portion of refrigerant passing through refrigerant line 70B.

As noted above, the refrigerant vapor compression system 10 of the present invention includes an expansion device 80 for expanding at least a major portion of the refrigerant passing therethrough. An expansion device 80 is disposed in refrigerant line 70C of the refrigerant circuit 70 downstream, with respect to refrigerant flow, of the economizer heat exchanger 60 and upstream of the evaporator 40. In the embodiment of the refrigerant vapor compression system 10 depicted in fig. 1, all of the refrigerant having traversed the heat exchanger coil 62 of the economizer heat exchanger 60 enters a single expander device 80. The first portion of the refrigerant, which constitutes the major portion of the refrigerant, traverses fully the expander 80 and is thus expanded to a lower subcritical pressure. A first portion of this refrigerant exits from the expander 80 into refrigerant line 70C and thereafter passes through the evaporator 40 as previously described.

In this embodiment, the second economized portion of refrigerant entering the expander device 80, which constitutes a minor portion of refrigerant, does not completely traverse the expander 80, but instead is discharged through line 70E after having been only partially expanded in the expander 80 to pass through the second pass 64 of the economizer heat exchanger 60 in heat exchange relationship with the first portion of refrigerant passing through the first pass 62 of the economizer heat exchanger 60. Having been partially expanded in the expander 80 to a lower pressure, which is intermediate the discharge pressure and the suction pressure, and a lower temperature, the second portion of the refrigerant passing through the second pass 64 of the economizer heat exchanger 60 is cooler than the higher temperature, higher pressure refrigerant passing through the first pass 62 of the economizer heat exchanger 60. Thus, the refrigerant flowing through the first pass 62 is cooled by rejecting heat to a second portion of the refrigerant flowing through the second pass 64, and the second portion of the refrigerant flowing through the second pass 64 is warmed by absorbing heat from the cooling of the refrigerant passing through the first pass 62 of the economizer heat exchanger 60.

In the embodiment of the refrigerant vapor compression system of the invention depicted in fig. 2, the expansion device comprises a primary expander 80 and a secondary expander 82. In this embodiment, the primary expander 80 may have only one stage of expansion, with the second stage of expansion being performed by the secondary expander 82. The portion of refrigerant that has traversed the first pass 62 of the economizer heat exchanger 60, which again constitutes a minor portion of refrigerant, passes from refrigerant line 70C to refrigerant line 70E at a location upstream of refrigerant flow of the main expander 80 and downstream of the economizer heat exchanger 60. The remaining major portion of the refrigerant that has traversed the first pass 62 of the economizer heat exchanger 60 continues through refrigerant line 70C to pass through the main expander 80, thereafter through the heat exchanger coil 44 of the evaporator 40, and then back to the suction of the compressor 20A through refrigerant line 70D. The diverted minor portion of the refrigerant flowing through refrigerant line 70E passes through a secondary expander 82 disposed in refrigerant line 70E and is expanded thereat to a lower intermediate pressure, lower intermediate temperature state prior to flowing through the second pass 64 of the economizer heat exchanger 60. Having been expanded to a lower pressure and temperature in the secondary expander 82, the diverted minor portion of the refrigerant passing through the second pass 64 of the economizer heat exchanger 60 is cooler than the higher temperature, higher pressure refrigerant passing through the first pass 62 of the economizer heat exchanger 60. Thus, the refrigerant flowing through the first pass 62 of the economizer heat exchanger 60 is cooled by rejecting heat to a minor portion of the refrigerant flowing through the second pass 64 of the economizer heat exchanger 60, and the minor portion of the refrigerant flowing through the second pass 64 of the economizer heat exchanger 60 is warmed by absorbing heat from the cooling of the refrigerant flowing through the first pass 62 of the economizer heat exchanger 60. It must be understood that in this embodiment, a minor, economizer portion of the refrigerant can also be designated to flow upstream of the economizer heat exchanger 60.

In any of the embodiments of the present invention, the second portion of the refrigerant that has traversed the second pass 64 of the economizer heat exchanger 60 flows through a section downstream of refrigerant line 70E and is returned to the compression device 20 at an intermediate pressure state during compression. If the compression device is a refrigerant compressor 20, such as a scroll compressor, screw compressor or multi-pass reciprocating compression, as depicted in fig. 1, refrigerant from the second pass 64 of the economizer heat exchanger 60 enters the compressor through at least one injection port opening at an intermediate pressure state of compression within the compressor 20. If the compression device 20 is a pair of compressors 20A and 20B connected in series in refrigerant flow relationship, as depicted in fig. 2, refrigerant having traversed the second pass 64 of the economizer heat exchanger 60 is injected into the refrigerant line 22 connected to the discharge of the first stage compressor 20A, which first stage compressor 20A is in refrigerant flow communication with the second stage compressor 20B. In the embodiments of fig. 1 and 2, a shut-off valve 74 may also be provided to disconnect the economizer circuit from the operating refrigerant circuit when needed.

Further, in another aspect of the invention, the portion of the refrigerant vapor from the gas cooler 30 passing through refrigerant line 70B to the first pass 62 of the economizer heat exchanger 60 is diverted through refrigerant line 70F to a section downstream of refrigerant line 70E to provide additional cooling to the compression process. Through refrigerant line 70F, the diverted flow of refrigerant traverses an expansion valve 50 disposed in refrigerant line 70F and is expanded to a lower pressure and lower temperature to generally form a liquid refrigerant or a liquid/vapor refrigerant mixture. The resulting lower pressure and lower temperature liquid refrigerant or liquid/vapor refrigerant mixture then enters a section downstream of refrigerant line 70E for return to the compression device 20. When the economizer loop is in operation, the shutoff valve 74 is open and refrigerant entering refrigerant line 70E from refrigerant line 70F will mix with refrigerant vapor that has traversed the second pass 64 of the economizer heat exchanger 60 before being returned to the compression device 20 as previously described.

The refrigerant vapor passing through the expansion valve 50 is expanded to a pressure below the compressor discharge pressure, but above the average refrigerant pressure present in the intermediate pressure stage of the refrigerant returning to the compression device 20 through refrigerant line 70E, the expansion valve 50 may be an electrostatic expansion valve (EXV) or a thermostatic expansion valve (TXV). Similarly, the portion of refrigerant diverted through the second pass 64 of the economizer heat exchanger 60 exits the expander 80 at a pressure below the compressor discharge pressure, or it exits the expander 80 expanded by the expander 82 to a pressure below the compressor discharge pressure, but above the average refrigerant pressure present in the intermediate pressure stage at which the refrigerant is returned to the compression device 20 through refrigerant line 70E.

It should be noted that the expansion valve 50 may be disposed upstream of the line 70E of the second pass 64 of the economizer heat exchanger 60 and upstream of the shutoff valve 74 but downstream of a point in the refrigerant cycle at which a minor economized portion of the refrigerant flow has been partially expanded. For example, in the embodiment of the refrigerant vapor compression system depicted in fig. 3, the expansion valve 50 may be disposed in refrigerant line 70G, with refrigerant line 70G providing a refrigerant flow path for the portion of the partially expanded refrigerant exiting the main expander 80 to pass out of refrigerant line 70E from a point upstream of the throttle valve 74 to reenter refrigerant line 70E at a point downstream of the second pass 64 of the economizer heat exchanger 60. The portion of refrigerant diverted from refrigerant line 70E bypasses the economizer heat exchanger 60 and is further expanded as it traverses the expansion valve 50 to provide liquid refrigerant or a liquid/vapor refrigerant mixture for injection into an intermediate pressure stage of a compression device as previously described. Alternatively, as in the embodiment of the refrigerant vapor compression system depicted in fig. 4, the expansion valve 50 may be disposed in refrigerant line 70G, with refrigerant line 70G providing a refrigerant flow path for the portion of the unexpanded refrigerant passing from refrigerant line 70C into refrigerant line 70E at a point upstream of the primary expander 80 to pass from refrigerant line 70E at a point upstream of both the throttle valve 74 and the secondary expander 82 to re-enter refrigerant line 70E at a point downstream of the second pass 64 of the economizer heat exchanger 60. This portion of refrigerant diverted from refrigerant line 70E bypasses both the secondary expander 82 and the economizer heat exchanger 60 and is further expanded as it traverses the expansion valve 50 to provide liquid refrigerant or a liquid/solid refrigerant mixture for injection at an intermediate pressure between the first and second compression stages 20A and 20B as previously described.

Liquid refrigerant flow through refrigerant line 70F and into a segment downstream of refrigerant line 70E to mix with refrigerant vapor passing through refrigerant line 70E from the second pass 64 of the economizer heat exchanger 60 when the shutoff valve 74 is open and to be injected as a liquid/vapor refrigerant mixture into an intermediate stage of the compression device 20 can be controlled by a controller 90 operatively connected to the expansion valve 50 disposed in refrigerant line 70F. The controller 90 is programmed in a conventional manner to control the opening of the expansion valve 50 to control the flow rate of refrigerant from refrigerant line 70B through refrigerant line 70F. The controller 90 may also be programmed to monitor the compressor discharge temperature, which is the refrigerant vapor temperature discharged into refrigerant line 70A from the discharge port of the second compression stage, and control the operation of the expansion valve 50 to provide sufficient liquid refrigerant flow into refrigerant line 70E to ensure that the compressor discharge temperature does not exceed a certain upper limit. The exhaust temperature may be measured, for example, by a temperature sensor 92. The controller 90 can also be operatively connected to the shut-off valve 74 to selectively open the valve when additional system capacity is required to meet the thermal load requirements within the conditioned space. The economized refrigerant flow may also assist in controlling the compressor discharge temperature such that the discharge temperature is below a certain limit.

In an embodiment of the invention, the controller 90 constitutes the main system controller and receives operational data relating to various system operating parameters as is conventional in practice provided by appropriate sensors (not shown), such as, for purposes of illustration and not limitation, refrigerant temperature and/or pressure at compressor discharge, at compressor suction, at evaporator exit and other desired locations. The controller 90 may also be programmed to control the operation of the expander 80 and the secondary expander 82 to react to selected system operating parameters. For example, the controller 90 can be programmed to control the speed of the expander 80 to adjust the refrigerant flow rate through refrigerant line 70C to the evaporator 40 to control the evaporator outlet temperature. The controller 90 can also be programmed to control the speed of the secondary expander 82 to adjust the refrigerant flow rate through refrigerant line 70E back to the injection port or ports in the intermediate stage of the compression device 20 as previously described. Alternatively, a flow control valve (not shown) operatively connected to and controlled by the controller 90 may be disposed in refrigerant line 70C either upstream or downstream of the main expander 80 to control the refrigerant flow rate through the main expander 80, and disposed in refrigerant line 70E to control the refrigerant flow rate through the second pass 64 of the economizer heat exchanger 60.

The use of a particular type of expander is not relevant to the present invention. The expanders 80 and 82 may be rotary vane expanders, helical expanders, screw expanders or other conventional expanders. The use of an expander in the refrigerant circuit rather than an expansion valve or a fixed orifice as the expansion device is advantageous because the energy generated by the expansion of the refrigerant through the expander can be easily recovered rather than wasted. For example, as shown in fig. 1, a generator G may be operatively connected to the expander 80, whereby energy recovered in the expander 80 is transferred to the generator G to generate electricity, which may be used to at least partially power the compression device 20, the auxiliary fluid moving device, or for other purposes. As shown in FIG. 2, for example, expander 80 may be operatively connected to assist in driving first stage compressor 20A and secondary expander 20B, so that the energy recovered during each expansion drives or assists in driving each compressor. Moreover, the expansion process in the expanders 80 and 82 is more thermodynamically efficient than a restrictor type expansion device (expansion valve, fixed orifice or capillary tube) because it follows an isentropic, rather than Isenthalpic, expansion line, the refrigerant passing through the expander will have a higher thermodynamic potential at the evaporator inlet, which results in an overall increase in system efficiency and cooling capacity.

While the present invention has been particularly shown and described with reference to the preferred forms as illustrated in the drawing, it will be understood by one skilled in the art 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 (19)

1. A refrigerant vapor compression system including a compression device disposed in a refrigerant circuit for compressing a refrigerant vapor from a suction pressure to a discharge pressure, a heat rejection heat exchanger disposed in the refrigerant circuit downstream with respect to refrigerant flow of the compression device, and a heat accepting heat exchanger disposed in the refrigerant circuit downstream with respect to refrigerant flow of the heat rejection heat exchanger and upstream with respect to refrigerant flow of the compression device, the refrigerant vapor compression system characterized by:

an economizer heat exchanger having first and second passages operatively connected in heat transfer relationship, the first passage being disposed in the refrigerant circuit downstream refrigerant flow of the heat rejection heat exchanger and upstream refrigerant flow of the heat accepting heat exchanger;

a main expander disposed in the refrigerant circuit downstream with respect to refrigerant flow of the first pass of the economizer heat exchanger and upstream with respect to refrigerant flow of the heat accepting heat exchanger;

an evaporator bypass line providing a refrigerant flow path for a portion of refrigerant from the refrigerant circuit after having traversed the first pass of the economizer heat exchanger and having been partially expanded to an intermediate pressure to pass through the second pass of the economizer heat exchanger and into an intermediate pressure stage of the compression device;

an economizer bypass line for passing a portion of the refrigerant from the refrigerant circuit into the evaporator bypass line at a location downstream of the refrigerant flow of the second pass of the economizer heat exchanger; and

a restrictor-type expansion device disposed in the economizer bypass line for expanding the refrigerant passing therethrough to a lower pressure to provide a liquid component of the refrigerant flow.

2. A refrigerant vapor compression system as recited in claim 1 wherein said refrigerant circuit operates at least in part in a transcritical cycle.

3. A refrigerant vapor compression system as recited in claim 1 wherein said refrigerant circuit operates at least in part in a subcritical cycle.

4. A refrigerant vapor compression system as recited in claim 1 wherein said restrictor-type expansion device is selected from the group consisting of a fixed orifice, a capillary tube, a thermostatic expansion valve, or an electronic expansion valve.

5. A refrigerant vapor compression system as recited in claim 1 wherein the refrigerant circulating through the refrigerant circuit of the refrigerant vapor compression system is carbon dioxide.

6. A refrigerant vapor compression system as recited in claim 1 wherein said economizer bypass line extends in refrigerant flow communication from a point in the refrigerant circuit upstream with respect to refrigerant flow of the first pass of the economizer heat exchanger and downstream with respect to refrigerant flow of the heat rejection heat exchanger to a point in the evaporator bypass line downstream with respect to the second pass of the economizer heat exchanger.

7. A refrigerant vapor compression system as recited in claim 1 wherein said economizer bypass line extends in refrigerant flow communication from a point in the refrigerant circuit downstream with respect to refrigerant flow of said first pass of said economizer heat exchanger and upstream with respect to refrigerant flow of said main expander to a point in said evaporator bypass line downstream with respect to said second pass of said economizer heat exchanger.

8. A refrigerant vapor compression system as recited in claim 1 wherein said evaporator bypass line extends from the intermediate expansion stage of said main expander in refrigerant flow communication through said second pass of said economizer heat exchanger and into an intermediate pressure stage of said compression device.

9. A refrigerant vapor compression system as recited in claim 8 wherein said economizer bypass line extends in refrigerant flow communication from a point in the refrigerant circuit upstream with respect to refrigerant flow of said second pass of said economizer heat exchanger and downstream with respect to refrigerant flow of said main expander to a point in said evaporator bypass line downstream with respect to said second pass of said economizer heat exchanger.

10. A refrigerant vapor compression system as recited in claim 1 wherein,

the evaporator bypass line extends in refrigerant flow communication through the second pass of the economizer heat exchanger from a point upstream with respect to refrigerant flow of the main expander and downstream with respect to refrigerant flow of the first pass of the economizer heat exchanger and into an intermediate pressure stage of the compression device; and

a secondary expander disposed in the evaporator bypass line upstream with respect to refrigerant flow of the second pass of the economizer heat exchanger.

11. A refrigerant vapor compression system as recited in claim 10 wherein said economizer bypass line extends in refrigerant flow communication from a point in the refrigerant circuit downstream with respect to refrigerant flow of the first pass of the economizer heat exchanger and upstream with respect to refrigerant flow of both the primary and secondary expanders to a point in the evaporator bypass line downstream with respect to the second pass of the economizer heat exchanger.

12. A refrigerant vapor compression system as recited in claim 10 wherein said primary expander is operatively connected in said refrigerant circuit upstream with respect to refrigerant flow of said heat accepting heat exchanger to expand a major portion of said refrigerant flow having traversed said first pass of said economizer heat exchanger, and said secondary expander is operatively connected in said evaporator bypass line upstream with respect to refrigerant flow of said second pass of said economizer heat exchanger to expand a minor portion of said refrigerant flow having traversed said first pass of said economizer heat exchanger.

13. A refrigerant vapor compression system as recited in claim 1 wherein said main expander comprises a single expander providing a first expansion process for expanding said refrigerant stream having traversed said first pass of said economizer heat exchanger to a pressure intermediate said discharge pressure and said suction pressure and a second expansion process for expanding said refrigerant stream having traversed said first pass of said economizer heat exchanger to a pressure near said suction pressure, said evaporator bypass line communicating with said single expander to receive refrigerant stream at said intermediate pressure.

14. A refrigerant vapor compression system as recited in claim 1 wherein said compression device comprises a first compressor and a second compressor, said first compressor having a discharge port connected in refrigerant flow communication to a suction port of said second compressor in refrigerant flow communication through a refrigerant line, said evaporator bypass line communicating with said refrigerant line at a location between said discharge port of said first compressor and said suction port of said second compressor.

15. A refrigerant vapor compression system as recited in claim 1 wherein said compression device comprises a single compressor having a compression chamber, said evaporator bypass line communicating with said compression chamber at an intermediate pressure stage.

16. A refrigerant vapor compression system as recited in claim 1 wherein a refrigerant flow control device is disposed in said evaporator bypass line.

17. A method of controlling refrigerant discharge temperature from a compression device in a refrigerant vapor compression system including a compression device disposed in a refrigerant circuit for compressing refrigerant vapor from a suction pressure to a discharge pressure, a heat rejection heat exchanger disposed in the refrigerant circuit downstream with respect to refrigerant flow of the compression device, a heat accepting heat exchanger disposed in the refrigerant circuit downstream with respect to refrigerant flow of the heat rejection heat exchanger and upstream with respect to refrigerant flow of the compression device, and an economizer heat exchanger having a first pass and a second pass disposed in heat exchange relationship, the first pass disposed in the refrigerant circuit upstream with respect to refrigerant flow of the heat accepting heat exchanger and downstream with respect to refrigerant flow of the heat rejection heat exchanger, the method comprising the steps of:

passing a major portion of the refrigerant having traversed the first pass of the economizer heat exchanger through an expander to be fully expanded to a first pressure that is approximately equal to the suction pressure;

passing a minor portion of the refrigerant passing through the refrigerant circuit through an expander to be partially expanded to a second pressure that is higher than the first pressure and intermediate the suction pressure and the discharge pressure; and

selectively passing the minor portion of the partially expanded refrigerant through the second pass of the economizer heat exchanger and thence into an intermediate pressure stage of the compression device.

18. The method as set forth in claim 17 further including the step of controlling the amount of refrigerant in said minor portion of the partially expanded refrigerant flow passing through said second pass of said economizer heat exchanger and thence into an intermediate pressure stage of said compression device.

19. The method as set forth in claim 17, further including the step of selectively injecting refrigerant liquid from said refrigerant circuit into an intermediate pressure stage of said compression device.