Economized Refrigerant System With Flow Control

Field of the Invention

[0001] This invention relates generally to refrigerant vapor compression systems and, more particularly, to refrigerant vapor compression systems equipped with an economizer cycle.

Background of the Invention

[0002] Refrigerant vapor compression systems are well known in the art and commonly used for conditioning air (or other secondary media) to be supplied to a climate-controlled comfort zone within a residence, office building, hospital, school, restaurant or other facility. Refrigerant vapor compression systems are also commonly used in transport refrigeration for refrigerating air supplied to a temperature-controlled cargo space of a truck, trailer, container or the like for transporting perishable items, and in commercial refrigeration for cooling air supplied to a temperature-controlled space in a cold room, a beverage cooler, a diary case or a refrigerated merchandiser for displaying perishable foods item in a chilled or frozen state, as appropriate. Typically, these refrigerant vapor compression systems include: a compressor, a condenser, an evaporator; and an expansion device. Commonly, the expansion device, typically a fixed orifice, a capillary tube, a thermostatic expansion valve (TXV) or an electronic expansion valve (EXV), is disposed in the refrigerant line upstream, with respect to refrigerant flow, of the evaporator and downstream of the condenser. These basic refrigerant vapor compression system components are serially interconnected by refrigerant lines in a closed-loop refrigerant circuit, arranged in accord with known refrigerant vapor compression cycles.

[0003] To improve performance of the refrigerant vapor compression system and to control the temperature of the refrigerant vapor discharged from the final stage of the compressor over a wide range of operating conditions, it is known to equip such systems with an economizer cycle incorporating a refrigerant-to-refrigerant economizer heat exchanger. The economizer heat exchanger is generally disposed in the refrigerant circuit intermediate the condenser and the evaporator. In

operation, a portion of the refrigerant leaving the condenser is diverted from the primary refrigerant circuit, expanded to an intermediate pressure and then passed through the economizer heat exchanger in heat exchange relationship with the main portion of the refrigerant leaving the condenser. In this manner, any liquid in the economized expanded refrigerant flow is evaporated, and then the evaporated refrigerant is typically superheated, while the refrigerant passing through the primary refrigerant circuit from the condenser to the evaporator is further cooled. Typically, the expanded refrigerant vapor is injected into an intermediate stage in the compression process, either through an injection port or ports opening into an intermediate pressure stage of the compression chamber (or chambers) of a single compressor or, in the case of a multiple compressor system, into a refrigerant line extending between the discharge outlet of the upstream compressor and the suction inlet of the downstream compressor.

[0004] 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 opening into the compression chambers of a scroll compressor. To provide the refrigerant vapor for injection into the compressor, a portion of liquid refrigerant is taken from the primary refrigerant circuit at a location downstream of the condenser, expanded to an intermediate pressure and iower temperature by means of an expansion device, such as a valve, to form a refrigerant liquid/vapor mixture which is thereafter passed through the economizer heat exchanger in heat exchange relationship with the main flow of refrigerant liquid. In traversing the economizer heat exchanger, this refrigerant liquid/vapor mixture extracts heat from the main flow of refrigerant liquid, further cooling this liquid, thereby evaporating any remaining liquid component in the two-phase mixture and typically further heating the vapor. The refrigerant vapor leaving the economizer heat exchanger is then injected into the compressor through the economizer injection ports at the intermediate (between suction and discharge) pressure. Additionally, liquid refrigerant is selectively taken from the refrigerant circuit at a location downstream of the condenser and mixed into the refrigerant

vapor being passed from the economizer to the compressor and injected into an intermediate pressure stage of the compression chambers of the scroll compressor together with the refrigerant vapor through the same economizer injection ports. [0005] U.S. Pat. No. 7,114,349 discloses a refrigerant vapor compression system with a refrigerant-to-refrigerant heat exchanger interdisposed in the refrigerant circuit downstream of the condenser, with respect to refrigerant flow, and upstream of the evaporator, with respect to refrigerant flow. Through various bypass lines and manipulation of various open/closed solenoid valves associated with the bypass lines, the common heat exchanger may be operated either as an economizer heat exchanger or as a liquid-suction heat exchanger. When the system is operating with the refrigerant-to-refrigerant heat exchanger functioning as an economizer, refrigerant is passed from the primary refrigerant circuit through an economizer expansion device and thence through the refrigerant-to-refrigerant heat exchanger in heat exchange relationship with the remainder of the refrigerant passing through the primary refrigerant circuit from the condenser to the evaporator. After traversing the refrigerant-to-refrigerant heat exchanger, the expanded refrigerant is injected into an intermediate pressure stage of the compressor or returned to the primary refrigerant circuit at a point downstream, with respect to refrigerant flow, of the evaporator and upstream of the suction inlet of the compressor.

[0006] U.S. Pat. No. 6,058,729 discloses a subcritical refrigerant vapor compression system for a transport refrigeration unit incorporating a refrigerant- to-refrigerant heat exchanger into the refrigerant circuit as an economizer. The disclosed system also includes a suction modulation valve (SMV) for throttling refrigerant flow to the suction inlet of the compressor and an intermediate pressure-to-suction pressure unload circuit for compressor capacity control.

Summary of the Invention

[0007] The refrigerant vapor compression system of the invention includes a primary refrigerant circuit, an economizer circuit, a bypass line, a bypass flow control device, and an economizer/compressor unload flow control apparatus. The primary refrigerant circuit includes a refrigerant compression device, a refrigerant

heat rejection heat exchanger, a refrigerant heat absorption heat exchanger, and a primary expansion device interdisposed in the primary refrigerant circuit downstream of the refrigerant heat rejection heat exchanger and upstream of the refrigerant heat absorption heat exchanger. The economizer circuit includes an economizer refrigerant line extending in refrigerant flow communication between the economizer and an intermediate pressure stage of the compression device. [0008] A bypass line extends in refrigerant flow communication from the economizer refrigerant line to the primary refrigerant circuit at a location downstream, with respect to refrigerant flow, of the refrigerant heat absorption heat exchanger. A bypass flow control device is disposed in the bypass line. The bypass flow control device has a first open position whereat refrigerant may flow through the bypass line and a second closed position whereat refrigerant is blocked from flowing through the bypass line. In an embodiment, the bypass flow control device may comprise a solenoid valve having a first open position and a second closed position.

[0009] Additionally, a flow control apparatus disposed in the economizer refrigerant line provides a first flow path through the economizer refrigerant line in a first direction from the intermediate pressure stage of the compression device to the bypass line and a second flow path through the economizer refrigerant line in a second direction from the economizer into the intermediate pressure stage of the compression device. The first flow path has a first hydraulic resistance to refrigerant flow through the first flow path and the second flow path has a second hydraulic resistance to refrigerant flow through the second flow path, the first hydraulic resistance being different from the second hydraulic resistance. In an embodiment, the first hydraulic resistance is relatively lower and the second hydraulic resistance is relatively higher.

[0010] In an embodiment, flow control apparatus comprises a "fluid diode" device interdisposed in the economizer refrigerant line at a location intermediate the intermediate pressure stage of the compression device and the bypass line. The "fluid diode" device has different flow resistance depending on the direction of the flow through the "fluid diode". A check valve with two position openings is one embodiment of such a "fluid diode" device. The check valve is used to illustrate

this embodiment; however, other types of "fluid diodes" known in the art would fall within the scope of this invention. The check valve has a first position wherein refrigerant may flow therethrough in a first direction from the intermediate pressure stage of the compression device to the bypass line and a second flow path through the economizer refrigerant line in a second direction from the second refrigerant pass of the refrigerant-to-refrigerant heat exchanger into the intermediate pressure stage of the compression device. [0011] In an embodiment, the flow control apparatus comprises a first branch refrigerant line in refrigerant flow communication with the economizer refrigerant line, a second branch refrigerant line in refrigerant flow communication with the economizer refrigerant line and disposed in parallel with the first branch refrigerant line, and a check valve disposed in the first branch refrigerant line and having a first position wherein refrigerant may flow through the first branch refrigerant line and a second position wherein refrigerant flow through the first branch refrigerant line is blocked and refrigerant may flow through the second branch refrigerant line.

[0012] The economizer may be a heat exchanger economizer or a flash tank economizer. In an embodiment, the economizer comprises a refrigerant-to- refrigerant heat exchanger including a first refrigerant pass and a second refrigerant pass disposed in heat exchange relationship with said first refrigerant pass. The first refrigerant pass interdisposed in the primary refrigerant circuit and the second refrigerant pass interdisposed in the economizer refrigerant line. The economizer refrigerant line extends in fluid communication from the primary refrigerant circuit through the second refrigerant pass to an intermediate pressure stage of the compression device. In this embodiment, an economizer expansion device is interdisposed in the economizer refrigerant line upstream with respect to refrigerant flow of the second refrigerant pass of the refrigerant-to-refrigerant heat exchanger.

[0013] . The invention may be equally applied to flash tank type economized systems. In such systems, the control of the bypass flow and economizer vapor flow is accomplished in a similar fashion by controlling flow through the refrigerant economizer line. In such an embodiment, the flash tank economizer is

interdisposed in the primary refrigerant circuit downstream, with respect to refrigerant flow, of the refrigerant heat rejection heat exchanger and upstream, with respect to refrigerant flow, of the primary expansion device. The economizer refrigerant line extends in refrigerant vapor flow communication from the flash tank economizer to an intermediate pressure stage of the compression device and an economizer expansion device is interdisposed in the primary refrigerant circuit upstream with respect to refrigerant flow of the flash tank economizer.

Brief Description of the Drawings

[0014] 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 drawing, where:

[0015J FIG. 1 is a schematic diagram illustrating an exemplary embodiment of a refrigerant vapor compression system in accord with the invention; and [0016] FIG. 2 is a schematic diagram illustrating another exemplary embodiment of a refrigerant vapor compression system in accord with the invention.

Detailed Description of the Invention

[0017] The invention will be described further herein with respect to the exemplary embodiments of the refrigerant vapor compression system 20 depicted in FIGS. 1 -2. As in conventional systems, the refrigerant vapor compression system 20 includes a compression device 22, a heat rejection heat exchanger 24, an evaporator expansion device 26, and an evaporator 28, interconnected by various refrigerant lines 3, 5 and 7 in serial refrigerant flow communication in a conventional refrigeration cycle in a primary refrigerant circuit. The refrigerant vapor compression system 20 is suitable for use in a transport refrigeration system for refrigerating the air or other gaseous atmosphere within the temperature- controlled cargo space of a truck, trailer, container or the like for transporting perishable/frozen goods. The refrigerant vapor compression system 20 is also suitable for use in conditioning air to be supplied to a climate-controlled comfort zone within a residence, office building, hospital, school, restaurant or other facility. The refrigerant vapor compression system 20 could also be employed in

refrigerating air supplied to display cases, merchandisers, freezer cabinets, cold rooms or other perishable/frozen product storage areas in commercial establishments.

[0018] The compression device 22 may comprise a single refrigerant compressor having at least a first compression stage and a second compression stage, such as, for example, a scroll compressor, such as illustrated in FIG. 1, or a screw compressor having staged compression pockets, or a reciprocating compressor having at least a first bank and a second bank of cylinders, or a pair of compressors 22A and 22B connected in series refrigerant flow relationship as illustrated in FIG. 2, such as, for example, a pair of scroll compressors, screw compressors, centrifugal compressors, reciprocating compressors (or separate cylinders of a single reciprocating compressor) or rotary compressors, with the discharge outlet port of the upstream compressor connected in serial refrigerant flow communication with the suction inlet port of the downstream compressor. [0019] In the compression device 22, refrigerant vapor is compressed from a suction pressure at which the refrigerant vapor enters the suction inlet port of the compression device 22 to a discharge pressure, substantially higher than the suction pressure. The hot, high pressure refrigerant vapor passes from the discharge outlet port of the compression device 22 through refrigerant line 3 of the primary refrigerant circuit to and through the heat rejection heat exchanger 24. In the heat rejection heat exchanger 24, the hot, high pressure refrigerant passes in heat exchange relationship with a cooling medium to cool and, in a subcritical cycle, condense the refrigerant vapor. The heat rejection heat exchanger 24 may comprise, for example, a finned tube heat exchanger, such as for example a plate fin and round tube heat exchanger or a fin and minichannel flat tube heat exchanger, wherein the refrigerant passes through the heat exchanger tubes in heat exchange relationship with ambient (typically outdoor) air being drawn through the finned tube heat exchanger by an air mover, such as one or more fans (not shown) operatively associated with the heat rejection heat exchanger 24. [0020] The refrigerant leaving the heat rejection heat exchanger 24 passes through refrigerant line 5 of the primary refrigerant circuit to the evaporator 28. In doing so, the refrigerant traverses the evaporator expansion device 26 interdisposed in

refrigerant line 5 and expands to a lower temperature, lower pressure liquid refrigerant or more commonly a liquid/vapor refrigerant mixture, before entering the evaporator 28. The evaporator expansion device 26 may be a restriction type expansion device, such as a capillary tube or a fixed plate orifice, a thermostatic expansion valve or an electronic expansion valve. The evaporator 28 constitutes a refrigerant heat absorbing heat exchanger through which the liquid or liquid/vapor refrigerant mixture passes in heat exchange relationship with a secondary fluid to be cooled, and typically dehumidified, and delivered to a conditioned environment. The refrigerant is heated thereby evaporating the liquid component and typically superheating the resultant vapor. The secondary fluid, typically air to be supplied to a climate-controlled environment, in the conditioned, cooled and typically dehumidified, state. In an embodiment, the evaporator 28 may comprise a finned tube heat exchanger through which refrigerant passes in heat exchange relationship with air that may be drawn from and returned to a climate-controlled environment by the one or more fans (not shown) operatively associated with the evaporator 28. The finned tube heat exchanger may comprise, for example, a plate fin and round tube heat exchanger or a fin and minichannel flat tube heat exchanger. The refrigerant vapor leaving the evaporator 28 passes through the refrigerant line 7 of the primary refrigerant circuit to reenter the compression device 22 through the suction inlet port of the compression device. [0021] The refrigerant vapor compression system 20 further includes an economizer circuit comprising an economizer refrigerant line 9, an economizer heat exchanger 30 and an associated economizer expansion device 32 interdisposed in the economizer refrigerant line 9. The economizer heat exchanger 30 comprises a refrigerant-to-refrigerant heat exchanger having a first refrigerant pass 31 and a second refrigerant pass 33 disposed in heat exchange relationship. The first refrigerant pass 31 is interdisposed in refrigerant line 5 of the primary refrigerant circuit downstream, with respect to refrigerant flow, of the heat rejection heat exchanger 24 and upstream, with respect to refrigerant flow, of the evaporator expansion device 26. The second refrigerant pass 33 is interdisposed in the economizer refrigerant line 9 downstream, with respect to refrigerant flow, of the economizer expansion device 32. Refrigerant passing through the refrigerant

line 5 of the primary refrigerant circuit passes through the first refrigerant pass 31 of the economizer heat exchanger 30 in heat exchange relationship with a flow of refrigerant tapped off the refrigerant line 5 into the economizer refrigerant line 9 to pass through the second refrigerant pass 33 of the economizer heat exchanger 30. [00221 The economizer refrigerant line 9 establishes refrigerant flow communication between the refrigerant line 5 of the primary refrigerant circuit and an intermediate pressure stage of the compression process. The economizer refrigerant line 9 may tap a portion of refrigerant from the refrigerant line 5 at a location upstream with respect to refrigerant flow of the first refrigerant pass 31 of the economizer heat exchanger 30, as depicted in FIG. 1, or at a location downstream with respect to refrigerant flow of the first refrigerant pass 31 of the economizer heat exchanger 30, as depicted in FIG. 2. If the compression device 22 of the refrigerant vapor compression system 20 is a single compressor, such as a scroll compressor as illustrated in FIG. 1, the economizer refrigerant line 9 communicates in refrigerant flow communication via an injection port 25 that opens into an intermediate pressure stage of the compression chambers of the compressor 22. If the compression device 22 of the refrigerant vapor compression system 20 is a pair of compressors 22A and 22B, the economizer refrigerant line 9 communicates in refrigerant flow communication with a refrigerant line 11 connecting the outlet of the first compressor 22A with the inlet to the second compressor 22B as illustrated in FIG. 2.

[0023] The refrigerant vapor compression system 20 also includes a compressor unloading circuit comprising a bypass line 17, which establishes refrigerant flow communication between the economizer refrigerant line 9 and the suction refrigerant line 7 of the primary refrigerant circuit, and a flow control device such as valve 50 interdisposed in the bypass line 17. The flow control device 50 has at least a first open position and a second closed position. In an embodiment, the flow control device may comprise a two-position solenoid valve having a first open position and a second closed position. At its inlet, the bypass line 17 taps into the economizer refrigerant line 9 at a location downstream, with respect to refrigerant flow, of the second refrigerant pass 33 of the economizer heat exchanger 30 and upstream, with respect to refrigerant flow, of the terminus of the

economizer refrigerant line 9 at an intermediate compression stage of the compression device 22. At its outlet end, the refrigerant bypass line 17 taps into the refrigerant suction line 7 of the primary refrigerant circuit at a location downstream, with respect to refrigerant flow, of the outlet of the evaporator 28 and upstream, with respect to refrigerant flow, of the suction inlet port of the compression device 22. In this manner, the bypass line 17 provides a refrigerant flow path through which intermediate pressure refrigerant may pass from an intermediate pressure stage in the compression process into the primary refrigerant circuit, in a region thereof where the refrigerant is at suction pressure, in order to unload the compressor. As used in herein, the term "downstream portion" with reference to the economizer refrigerant line 9 refers to that part of the economizer refrigerant line 9 extending between the junction of the bypass line 17 with the economizer refrigerant line 9 and the terminus of the economizer refrigerant line 9 at an intermediate stage of the compression device 22, and the term "upstream portion" with reference to the economizer refrigerant line 9 refers to that part of the economizer refrigerant line 9 extending between refrigerant line 5 of the primary refrigerant circuit and the junction of the bypass line 17 with the economizer refrigerant line 9.

[0024] The refrigerant vapor compression system 20 further includes a check valve 40 interdisposed in a downstream portion of the economizer refrigerant line 9. The check valve 40 has a first position wherein the check valve opens to refrigerant vapor flow through the downstream portion of the economizer refrigerant line 9 in a direction from an intermediate stage of the compression process with the compression device 22, and a second position wherein the check valve 40 restricts refrigerant flow through the downstream portion of the economizer refrigerant line 9 in a direction from the upstream portion of the economizer refrigerant line 9 into an intermediate stage of the compression process within the compression device 22.

[0025] Referring now to FIG. 1, in the exemplary embodiment of the refrigerant vapor compression system 20 depicted therein, a flow metering device 42 is disposed in parallel flow arrangement with the check valve 40. For example, the flow metering device 42 and the check valve 40 may be interdisposed respectively

in parallel branches 9a and 9b of the downstream portion of the economizer refrigerant line 9 such as depicted in FIG. 1. In this embodiment, when the refrigerant vapor compression system 20 is operating in an economized mode without compressor unloading, the flow control device 50 in the bypass line 17 is closed and the flow of refrigerant from the upstream portion of the economizer refrigerant line 9 into the downstream portion of the economizer refrigerant line 9 sets the check valve 40 in branch line 9b in its second position, which, in this embodiment, completely closes the check valve. With the check valve 40 fully closed, refrigerant from the economizer passes from the upstream portion of the refrigerant line 9 through the flow metering device 42 in the branch 9b of the downstream portion of the economizer refrigerant line 9 to enter into an intermediate pressure stage of the compression process of the compression device 22. The flow metering device 42 may comprise, but is not limited to, a fixed flow area orifice. For example, in an embodiment, the flow metering function desired in the economized mode of operation may be provided by an appropriate sizing of the branch line 9a, whereby the branch line 9a itself provides the desired flow restriction thereby eliminating the need for a Fixed area orifice or other form of flow metering device 42 in the branch line 9a.

[0026] However, when the refrigerant vapor compression system 20 is operating with compressor unloading, the bypass flow control valve 50 in the bypass line 17 is open, whereby refrigerant vapor flows from an intermediate stage of the compression process of the compression device 22 through the branch 9a of the downstream portion of the economizer refrigerant line 9, setting the check valve 40 in its open position, and flowing into and through the bypass line 17 and thence the refrigerant line 7 of the primary refrigerant circuit to reenter the compression device 22 through the suction inlet port thereof. If the refrigerant vapor compression system 20 is operating in the economized mode when the compressor is unloaded, the refrigerant passing through the upstream portion of the economizer refrigerant line 9 passes into the bypass 17 and also passes therethrough into refrigerant line 7 of the primary refrigerant circuit to reenter the compression device 22 through the suction inlet port thereof.

[0027] Referring now to FIG. 2, in the exemplary embodiment of the refrigerant vapor compression system 20 depicted therein, the check valve 40 interdisposed in the downstream portion of the economizer refrigerant line 9 has a first full open position and a second partially open position. In this embodiment, when the refrigerant vapor compression system 20 is operating in a economized mode without compressor unloading, the flow control device 50 in the bypass line 17 is closed and the flow of refrigerant from the upstream portion of the economizer refrigerant line 9 into the downstream portion of the economizer refrigerant line 9 sets the check valve 40 in its second partially open position, which in this embodiment meters the refrigerant flow passing therethrough into an intermediate pressure stage of the compression process of the compression device 22. However, in this embodiment, when the refrigerant vapor compression system 20 is operating with compressor unloading, the bypass flow control device 50 in the bypass line 17 is open, whereby refrigerant vapor flows from an intermediate stage of the compression process of the compression device 22 through the downstream portion of the economizer refrigerant line 9, setting the check valve 40 in its first fully open position, and flowing into and through the bypass line 17 and thence the refrigerant line 7 of the primary refrigerant circuit to reenter the compression device 22 through the suction inlet port thereof. Again, if the refrigerant vapor compression system 20 is operating in the economized mode when the compressor is unloaded, the refrigerant passing through the upstream portion of the economizer refrigerant line 9 passes into the bypass line 17 and also passes therethrough into the refrigerant line 7 of the primary refrigerant circuit to reenter the compression device 22 through the suction inlet port thereof. [0028] In either embodiment of the invention, in the economized mode of operation without bypass, the portion of the refrigerant having traversed the second refrigerant pass 33 of the economizer heat exchanger 30 flows through the economizer refrigerant line 9 to return to the compression device 22 at an intermediate pressure state in the compression process. If the compression device is a single refrigerant compressor 22, such as for example a scroll compressor as illustrated in FIG. 1, or a screw compressor or a multi-bank reciprocating compressor, the refrigerant from the second refrigerant pass 33 of the economizer

heat exchanger 30 enters the compressor 22 through at least one injection port opening at an intermediate pressure state of compression process within the compressor 22. If, as depicted in Figure 2, the compression device is a pair of compressors 2OA and 2OB connected in series relationship, with respect to refrigerant flow, the refrigerant having traversed the second refrigerant pass 33 of the economizer heat exchanger 30 is injected into the refrigerant line 11 interconnecting the discharge outlet of the first stage compressor 2OA in refrigerant flow communication with the suction inlet of the second stage compressor 2OB.

[0029] The positioning of the bypass flow control device 50 may be controlled by a controller 80 operatively associated with the refrigerant vapor compression system 20. In an embodiment, the controller 80 may constitute the main system controller and may receive operating data regarding various system operating parameters as in conventional practice, such as for purposes of illustration but not limitation, the refrigerant temperature and/or pressure at the compressor discharge, at the compressor suction inlet, at the evaporator outlet, and other locations, as desired, provided by appropriately disposed sensors (not shown). If the primary expansion device 26 is an electronic expansion valve, the controller 80 may also control the operation of the primary expansion device in response to selected operating parameters. Similarly, if the economizer expansion device 32 is an electronic expansion valve, the controller 80 may also control the operation of the economizer expansion device in response to selected operating parameters. [0030] In prior art refrigerant vapor compression systems using a common portion of the economizer refrigerant line through which refrigerant passes in a first direction ihto an intermediate pressure stage of the compression device from the economizer heat exchanger, during an economized mode operation, but in a second direction from an intermediate pressure stage of the compression device to return to the suction inlet of the compression device, during an unload mode of operation, the refrigerant line can not be optimally sized for each of the flow control conditions. Typically, the optimal flow area of a refrigerant line for unloading the compression device is significantly larger, for example, by as much

as an order of magnitude, than the optimal flow area of a refrigerant line for injecting refrigerant into an intermediate pressure stage of the compression device. [0031] However, in the refrigerant vapor compression system 20 of the invention, a flow control apparatus is provided having a first flow path through the economizer refrigerant line in a first direction from the intermediate pressure stage of the compression device to the bypass line and a second flow path through the economizer refrigerant line in a second direction from the second refrigerant pass of the refrigerant-to-refrigerant economizer heat exchanger into the intermediate pressure stage of the compression device. The first flow path has a first hydraulic resistance to refrigerant flow through the first flow path and the second flow path has a second hydraulic resistance to refrigerant flow through the second flow path, with the first hydraulic resistance being different from the second hydraulic resistance. In an embodiment, the first hydraulic resistance is relatively lower and the second hydraulic resistance is relatively higher. Therefore, the flow area of each of these flow paths may be optimally sized for the respective refrigerant vapor flows therethrough, which may improve compressor efficiency by as much as 10%.

[0032] In the exemplary embodiment depicted in FIG. 1, in its open position, the check valve 40 provides a relatively lower hydraulic resistance to refrigerant flow through the branch refrigerant line 9b, while the flow restrictor 42 provides a relatively higher hydraulic resistance to refrigerant flow through the branch refrigerant line 9a. In the exemplary embodiment depicted in FIG. 2, The check valve 40 provides a relatively lower hydraulic resistance to refrigerant flow through the economizer refrigerant line 9 in the direction of flow from the intermediate pressure stage of the compression device 22 to the bypass line 17 and provides a relatively higher hydraulic resistance to refrigerant flow through the economizer refrigerant line 9 in the direction of flow from the economizer 30 into the port 25 opening into the intermediate stage of the compression device 22. [0033J The invention may be equally applied to flash tank type economized systems. In such systems, the control of the bypass flow and economizer vapor flow is accomplished in a similar fashion by controlling flow through the refrigerant economizer line. In such an embodiment, the flash tank economizer is

interdisposed in the primary refrigerant circuit downstream, with respect to refrigerant flow, of the refrigerant heat rejection heat exchanger and upstream, with respect to refrigerant flow, of the primary expansion device. The economizer refrigerant line extends in refrigerant vapor flow communication from the flash tank economizer to an intermediate pressure stage of the compression device and an economizer expansion device is interdisposed in the primary refrigerant circuit upstream, with respect to refrigerant flow, of the flash tank economizer. [0034] While the present invention has been particularly shown and described with reference to the exemplary embodiments as illustrated in the drawings, 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. For example, the check valve 40 of the Fig. 2 embodiment may be positioned externally or internally, in relation to the shell of the compression device 22. Also, the check valve 40 may be substituted by a solenoid valve that would be controlled by the controller 80.