Systems and methods for controlling capacity of a compressor system

Abstract

A compressor system (400) for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system (10) includes a low stage compressor (402) having a first pre-rotation vane (PRV) (406) and a first variable geometry diffuser (VGD) (408) configured to operate to regulate a capacity of the low stage compressor (402), wherein a first operational linkage for the low stage compressor (402) causes a first position of the first VGD (406) to be dependent upon a second position of the first PRV (408). The compressor system (400) also includes a high stage compressor (404) having a second PRV (410) and a second VGD (412) configured to operate to regulate a capacity of the high stage compressor (404), wherein a second operational linkage for the high stage compressor (404) causes a third position of the second PRV (410) to be dependent upon a fourth position of the second VGD (412).

Description

SYSTEMS AND METHODS FOR CONTROLLING CAPACITY OF A COMPRESSOR SYSTEMBACKGROUND

[0001] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

[0002] Chiller systems, or vapor compression systems, utilize a working fluid (e.g., a refrigerant) that changes phases between vapor, liquid, and combinations thereof in response to exposure to different temperatures and pressures within components of the chiller system. The chiller system may place the working fluid in a heat exchange relationship with a cooling fluid (e g., water) and may deliver the cooling fluid to conditioning equipment and / or a conditioned environment serviced by the chiller system. In such applications, the cooling fluid may be directed through downstream equipment, such as air handlers, to condition other fluids, such as air in a building. The chiller system may include one or more compressors configured to pressurize the working fluid and circulate the working fluid through a working fluid circuit. Unfortunately, implementation of multiple compressors and / or multistage compressors and the various components thereof in a chiller system increases the complexity of controlling the chiller system efficiently.SUMMARY

[0003] A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below.

[0004] In one embodiment, a compressor system for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes a low stage compressor having a first pre-rotationvane (PRV) and a first variable geometry diffuser (VGD) configured to operate to regulate a capacity of the low stage compressor, wherein a first operational linkage for the low stage compressor causes a first position of the first VGD to be dependent upon a second position of the first PRV. The compressor system also includes a high stage compressor having a second PRV and a second VGD configured to operate to regulate a capacity of the high stage compressor, wherein a second operational linkage for the high stage compressor causes a third position of the second PRV to be dependent upon a fourth position of the second VGD.

[0005] In another embodiment, a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes a vapor compression system having a working fluid circuit configured to circulate a working fluid therethrough, and a compressor system having a compressor configured to pressurize and direct the working fluid through the working fluid circuit, wherein the compressor includes a pre-rotation vane (PRV) adjustable between a fully open position and a first fully closed position and a variable geometry diffuser (VGD) adjustable between a maximum allowed open position and a second fully closed position. The HVAC&R system also includes a controller having a memory and processing circuitry, wherein the memory stores instructions that, when executed by the processing circuitry, cause the processing circuitry to link a first position of the PRV and a second position of the VGD, wherein the second position of the VGD is dependent upon the first position of the PRV.

[0006] In another embodiment, a vapor compression system for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes a working fluid circuit configured to circulate a working fluid therethrough, a first compressor configured to pressurize and direct the working fluid through the working fluid circuit, a second compressor configured to pressurize and direct the working fluid through the working fluid circuit, wherein the first compressor and the second compressor are arranged in series relative to a direction of the working fluid through the working fluid circuit, and a double bundle condenser positioned along the working fluid circuit and configured to receive the working fluid from the first compressor, the second compressor, or both. The vapor compression system also includes an economizer positioned downstream of the double bundle condenser and upstream of the second compressor relative to the direction of the working fluid through the working fluid circuit, wherein the economizer is configured to separate the working fluid received from the double bundle condenser into a liquid working fluid and avaporous working fluid, and an evaporator positioned downstream of the double bundle condenser and upstream of the first compressor relative to the direction of the working fluid through the working fluid circuit, wherein the evaporator is configured to receive the working fluid from the double bundle condenser and the liquid working fluid from the economizer, and wherein the first compressor is configured to achieve a target leaving water temperature of the evaporator or the double bundle condenser and the second compressor is configured to achieve a target saturated temperature in the economizer.BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

[0008] FIG. l is a perspective view of an embodiment of a building that may utilize a heating, ventilating, air conditioning, and / or refrigeration (HVAC&R) system in a commercial setting, in accordance with an aspect of the present disclosure;

[0009] FIG. 2 is a perspective view of an embodiment of a vapor compression system, in accordance with an aspect of the present disclosure;

[0010] FIG. 3 is a schematic of an embodiment of a vapor compression system, in accordance with an aspect of the present disclosure;

[0011] FIG. 4 is a schematic of an embodiment of a vapor compression system, in accordance with an aspect of the present disclosure;

[0012] FIG. 5 is a schematic of an embodiment of a vapor compression system, in accordance with an aspect of the present disclosure;

[0013] FIG. 6 is a schematic of an embodiment of a vapor compression system operating in a cooling mode, in accordance with an aspect of the present disclosure;

[0014] FIG. 7 is a schematic of an embodiment of a vapor compression system operating in a heating mode, in accordance with an aspect of the present disclosure;

[0015] FIG. 8 is a schematic of an embodiment of a vapor compression system operating in a simultaneous heating and cooling mode, in accordance with an aspect of the present disclosure;

[0016] FIG. 9 is a schematic of an embodiment of a vapor compression system, illustrating working fluid flow through a hot gas bypass valve, in accordance with an aspect of the present disclosure;

[0017] FIG. 10 is a schematic of an embodiment of a vapor compression system having a double bundle condenser, in accordance with an aspect of the present disclosure;

[0018] FIG. 11 is a graphical representation of an embodiment of an operational linkage between pre-rotation vane (PRV) position and variable geometry diffuser (VGD) position in a low stage compressor, in accordance with an aspect of the present disclosure; and

[0019] FIG. 12 is a graphical representation of an embodiment of an operational linkage between PRV position and VGD position in a high stage compressor, in accordance with an aspect of the present disclosure.DETAILED DESCRIPTION

[0020] One or more specific embodiments of the present disclosure will be described below. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0021] When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” and “the” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that theremay be additional elements other than the listed elements. Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0022] As used herein, the terms “approximately,” “generally,” “substantially,” and so forth, are intended to convey that the property value being described may be within a relatively small range of the property value, as those of ordinary skill would understand. For example, when a property value is described as being “approximately” equal to (or, for example, “substantially similar” to) a given value, this is intended to convey that the property value may be within + / - 5%, within + / - 4%, within + / - 3%, within + / - 2%, within + / - 1%, or even closer, of the given value. Similarly, when a given feature is described as being “substantially parallel” to another feature, “generally perpendicular” to another feature, and so forth, this is intended to convey that the given feature is within + / - 5%, within + / - 4%, within + / - 3%, within + / - 2%, within + / - 1%, or even closer, to having the described nature, such as being parallel to another feature, being perpendicular to another feature, and so forth. Mathematical terms, such as “parallel” and “perpendicular,” should not be rigidly interpreted in a strict mathematical sense, but should instead be interpreted as one of ordinary skill in the art would interpret such terms. For example, one of ordinary skill in the art would understand that two lines that are substantially parallel to each other are parallel to a substantial degree, but may have minor deviation from exactly parallel.

[0023] As briefly discussed above, a heating, ventilation, air conditioning, and / or refrigeration (HVAC&R) system may be used to thermally regulate a space within a building, home, or other suitable structure. For example, the HVAC&R system may include a vapor compression system (e.g., a chiller system, vapor compression circuit) that transfers thermal energy between a working fluid (e.g., refrigerant, heat transfer fluid), and a fluid to be conditioned (e.g., air, water, brine). The vapor compression system may include a first heat exchanger (e.g., a condenser) and a second heat exchanger (e.g., an evaporator) that are fluidly coupled to one another via one or more conduits (e.g., vapor compression circuit, refrigerant circuit, working fluid circuit). A compressor may be used to pressurize and circulate the working fluid through the one or more conduits and, thus, enable the transfer of thermal energy between the working fluid and the fluid to be conditioned via the condenser and the evaporator.

[0024] Compressors (e.g., centrifugal compressors) may be designed for certain operating conditions, which may include one or more characteristics or parameters of the working fluid (e.g., refrigerant). For example, compressors may be designed and / or selected for implementation in the HVAC&R system based on working fluid flow (e.g., flow rate), working fluid temperature and pressure conditions at a suction inlet of the compressor, and / or working fluid temperature and pressure conditions at a discharge outlet of the compressor. In some applications, the HVAC&R system may utilize multiple compressors (e.g., a compressor system) to achieve a desired lift (e.g., pressure differential) of the working fluid directed through the vapor compression fluid circuit. The lift or “head” of the compressor or compressor system may be defined as the work or productivity of the compressor or compressor system and may be expressed as a difference in compressor discharge pressure and compressor suction pressure. Operation of each compressor may be controlled to enable operation within various design conditions (e.g., parameters) and / or to avoid undesired operation or operating conditions (e.g., compressor surge, compressor stall).

[0025] Design conditions for a centrifugal compressor may be at least partially defined by parameters of a working fluid flow through the compressor, as well as temperature and pressure conditions at suction (e.g., inlet) and discharge (e.g., outlet) of the centrifugal compressor. The compressor may operate continuously at conditions that are close to the design conditions, or the operating environment may deviate widely from design conditions during extended periods of time. Compressors used in HVAC&R systems may be subject to wide variations in operating conditions. For example, the working fluid flow through the compressor may depend on a demand of a cooling load, while pressure conditions, such as a condensing pressure, may depend on ambient temperature conditions.

[0026] When operating conditions deviate from the design conditions, a centrifugal compressor may encounter instabilities, such as surge or stall, during operation. Stall or stalling is a local flow separation in one or more components of the compressor, and may be characterized by discharge pressure disturbances at certain frequencies that are less than a rotational frequency of an impeller of the compressor. Surge or surging is a transient phenomenon having oscillations in pressures and flow and can result in complete flow reversal through the compressor. When surging, a compressor may be unable to deliver working fluid flow at desired pressure conditions. Furthermore, surging can cause excessive noise and / or vibrations in both the rotating andstationary components of the compressor, which may result in compressor damage, wear, and / or degradation. Various devices and control parameters can be used to adjust the compressor operation to desired flow and pressure conditions while avoiding compressor surging. One way to reduce the flow of working fluid through a centrifugal compressor is to reduce the speed of the compressor. Variable speeds of the compressor may be enabled by a turbine drive or an electric motor with electrical power supplied via a variable speed drive (VSD). When available, speed reduction can be used to a limited extent to avoid surge but may not completely avoid instances of surge. When speed reduction is not possible or available, another solution is to use a flow reduction device (“FRD”), such as pre-rotation vanes (“PRV”) and / or a variable geometry diffuser (“VGD”), to reduce the flow of working fluid through the compressor.

[0027] For example, pre-rotation vanes (“PRV”) or inlet guide vanes may be disposed at an inlet of a respective compressor and may be configured to control the flow of working fluid into the compressor (e.g., from an evaporator). In certain cases, an actuator may be used to control the opening and closing of the PRVs to adjust an amount of working fluid flowing into the compressor, thereby adjusting an operating capacity of the system. Variable geometry diffusers (“VGD”) may be disposed at an outlet of the compressor and may be utilized for stall avoidance, surge avoidance, and / or noise reduction associated with such conditions. In certain cases, a VGD may be utilized to control a flow of working fluid out of the compressor. For example, a VGD may include a diffuser ring configured to move into and out of a diffuser passage, which may also correspond to the outlet or discharge flow path (e.g., diffuser) for the compressed working fluid discharged by the compressor. The VGD can be adjusted to a fully open position, in which the diffuser ring is completely removed from the outlet flow path to enable an upper threshold amount of working fluid flow, and to a partially or fully closed position, in which the diffuser ring occupies or extends within at least a portion of the outlet flow path, thereby restricting the working fluid flow. For example, when a stall condition is detected, an actuator may transition the VGD toward a partially or fully closed position until the stall condition is rectified, thereby avoiding or mitigating surge conditions.

[0028] Traditionally, PRVs are used to adjust a capacity of a compressor, while VGDs are generally controlled based on stall voltages. Depending on their availability on the compressor, the settings of aforementioned devices, such as the variable speed drive, pre-rotation vanes, and / orvariable geometry diffuser may be managed by stability control algorithms (e.g., control logic) intended to keep the compressor in stable operation and out of surge at desired operating conditions, while enhancing efficiency. However, such control logic may not enable the compressor to achieve certain lift demands when a flow rate of the working fluid through the compressor is below a threshold value (e.g., at low flow rates).

[0029] In HVAC&R systems including a variable speed motor, the stability control algorithms are used in conjunction with the variable speed drive. Adaptive capacity control logic utilizing system operating parameters and compressor FRD position information can be used, for example, to operate the compressor at a faster speed when a surge is detected while stability control algorithms are in a surge reacting state. Past performance parameters can be mapped and stored in memory to avoid future surge conditions by the adaptive capacity control logic. A description of an exemplary adaptive capacity control process is provided in U.S. Patent No. 4,608,833, which is hereby incorporated by reference.

[0030] Some HVAC&R systems employing multiple compressors or compression stages (e.g., low pressure compressor, medium pressure compressor, high pressure compressor, first stage compressor, second stage compressor, third stage compressor) may have respective capacity regulation components or flow reduction devices (FRDs) associated with each compressor (e.g., VSD, PRV systems, inlet guide vanes, VGD). Some systems utilizing various capacity regulation components or flow reduction devices may be configured to operate the various components utilizing a common control scheme. For example, in systems having variable speed compressors, each of the multiple VSDs may be operated according to a common frequency set point. Unfortunately, incorporation of multiple capacity regulation components in systems having multiple compressors (e.g., one VSD associated with each compressor, one PRV system and one VGD associated with each compressor) increases costs associated with manufacture, operation, and / or maintenance of HVAC&R systems and increases the complexity of controlling the various capacity regulation components. Accordingly, present embodiments are directed to a vapor compression system having multiple compressors (e.g., one or more of a low pressure compressor, a medium pressure compressor, and / or a high pressure compressor, a first stage compressor, a second stage compressor, a third stage compressor, a low stage compressor, a high stage compressor) configured to operate in conjunction with one another with increased efficiency andreduced energy consumption to satisfy load and / or cooling demands. More specifically, embodiments of the present disclosure are directed to a control scheme (e.g., adaptive control logic) for a vapor compression system having multiple compressors that enables coordinated operation of the multiple compressors to satisfy a load demand of the vapor compression system, while reducing energy consumption and maintaining operation of the vapor compression system within desired operating conditions (e.g., avoiding surge and / or stall conditions).

[0031] Turning now to the drawings, FIG. 1 is a perspective view of an embodiment of an environment for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system 10 in a building 12 for a typical commercial setting. The HVAC&R system 10 may include a vapor compression system 14 (e.g., a chiller) that supplies a chilled liquid, which may be used to cool the building 12. The HVAC&R system 10 may also include a boiler 16 to supply warm liquid to heat the building 12 and an air distribution system which circulates air through the building 12. The air distribution system can also include an air return duct 18, an air supply duct 20, and / or an air handler 22. In some embodiments, the air handler 22 may include a heat exchanger that is connected to the boiler 16 and the vapor compression system 14 by conduits 24. The heat exchanger in the air handler 22 may receive either heated liquid from the boiler 16 or chilled liquid from the vapor compression system 14, depending on the mode of operation of the HVAC&R system 10. The HVAC&R system 10 is shown with a separate air handler on each floor of building 12, but in other embodiments, the HVAC&R system 10 may include air handlers 22 and / or other components that may be shared between or among floors.

[0032] FIGS. 2 and 3 illustrate embodiments of the vapor compression system 14 that can be used in the HVAC&R system 10. The vapor compression system 14 may circulate a working fluid through a circuit starting with a compressor 32. The circuit may also include a condenser 34, an expansion valve(s) or device(s) 36, and a liquid chiller or an evaporator 38. The vapor compression system 14 may further include a control panel 40 that has an analog to digital (A / D) converter 42, a microprocessor 44, a non-volatile memory 46, and / or an interface board 48.

[0033] Some examples of fluids that may be used as working fluids in the vapor compression system 14 are hydrofluorocarbon (HFC) based working fluids, for example, R-410A, R-407, R- 134a, hydrofluoro olefin (HFO), "natural" working fluids like ammonia (NH3), R-717, carbondioxide (CO2), R-744, or hydrocarbon based working fluids, water vapor, or any other suitable working fluid. In some embodiments, the vapor compression system 14 may be configured to efficiently utilize working fluids having a normal boiling point of about 19 degrees Celsius (66 degrees Fahrenheit) at one atmosphere of pressure, also referred to as low pressure working fluids, versus a medium pressure working fluid, such as R-134a. As used herein, "normal boiling point" may refer to a boiling point temperature measured at one atmosphere of pressure.

[0034] In some embodiments, the vapor compression system 14 may use one or more of a variable speed drive (VSDs) 52, a motor 50, the compressor 32, the condenser 34, the expansion valve or device 36, and / or the evaporator 38. The motor 50 may drive the compressor 32 and may be powered by a variable speed drive (VSD) 52. The VSD 52 receives alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source, and provides power having a variable voltage and frequency to the motor 50. In other embodiments, the motor 50 may be powered directly from an AC or direct current (DC) power source. The motor 50 may include any type of motor that can be powered by a VSD or directly from an AC or DC power source, such as a switched reluctance motor, an induction motor, an electronically commutated permanent magnet motor, or another suitable motor.

[0035] The compressor 32 compresses a working fluid vapor and delivers the vapor to the condenser 34 through a discharge passage. In some embodiments, the compressor 32 may be a centrifugal compressor. The working fluid vapor delivered by the compressor 32 to the condenser 34 may transfer heat to a cooling fluid (e.g., water or air) in the condenser 34. The working fluid vapor may condense to a working fluid liquid in the condenser 34 as a result of thermal heat transfer with the cooling fluid. The liquid working fluid from the condenser 34 may flow through the expansion device 36 to the evaporator 38. In the illustrated embodiment of FIG. 3, the condenser 34 is water cooled and includes a tube bundle 54 connected to a cooling tower 56, which supplies the cooling fluid to the condenser 34.

[0036] The liquid working fluid delivered to the evaporator 38 may absorb heat from another cooling fluid, which may or may not be the same cooling fluid used in the condenser 34. The liquid working fluid in the evaporator 38 may undergo a phase change from the liquid working fluid to a working fluid vapor. As shown in the illustrated embodiment of FIG. 3, the evaporator38 may include a tube bundle 58 having a supply line 60S and a return line 60R connected to a cooling load 62. The cooling fluid of the evaporator 38 (e.g., water, ethylene glycol, calcium chloride brine, sodium chloride brine, or any other suitable fluid) enters the evaporator 38 via return line 60R and exits the evaporator 38 via supply line 60S. The evaporator 38 may reduce the temperature of the cooling fluid in the tube bundle 58 via thermal heat transfer with the working fluid. The tube bundle 58 in the evaporator 38 can include a plurality of tubes and / or a plurality of tube bundles. In any case, the vapor working fluid exits the evaporator 38 and returns to the compressor 32 by a suction line to complete the cycle.

[0037] FIG. 4 is a schematic of the vapor compression system 14 with an intermediate circuit 64 incorporated between condenser 34 and the expansion device 36. The intermediate circuit 64 may have an inlet line 68 that is directly fluidly connected to the condenser 34. In other embodiments, the inlet line 68 may be indirectly fluidly coupled to the condenser 34. As shown in the illustrated embodiment of FIG. 4, the inlet line 68 includes a first expansion device 66 positioned upstream of an intermediate vessel 70. In some embodiments, the intermediate vessel 70 may be a flash tank (e.g., a flash intercooler, an economizer, etc ). In other embodiments, the intermediate vessel 70 may be configured as a heat exchanger or a “surface economizer.” In the illustrated embodiment of FIG. 4, the intermediate vessel 70 is used as a flash tank, and the first expansion device 66 is configured to lower the pressure of (e.g., expand) the liquid working fluid received from the condenser 34. During the expansion process, a portion of the liquid may vaporize, and thus, the intermediate vessel 70 may be used to separate the vapor from the liquid received from the first expansion device 66.

[0038] Additionally, the intermediate vessel 70 may provide for further expansion of the liquid working fluid because of a pressure drop experienced by the liquid working fluid when entering the intermediate vessel 70 (e.g., due to a rapid increase in volume experienced when entering the intermediate vessel 70). The vapor in the intermediate vessel 70 may be drawn by the compressor 32 through a suction line 74 of the compressor 32. In other embodiments, the vapor in the intermediate vessel 70 may be drawn to an intermediate stage of the compressor 32 (e.g., not the suction stage). The liquid that collects in the intermediate vessel 70 may be at a lower enthalpy than the liquid working fluid exiting the condenser 34 because of the expansion in the expansiondevice 66 and / or the intermediate vessel 70. The liquid from intermediate vessel 70 may then flow in line 72 through a second expansion device 36 to the evaporator 38.

[0039] It should be appreciated that any of the features described herein may be incorporated with embodiments of the vapor compression system 14 or any other suitable HVAC&R systems. For example, the present techniques may be incorporated with any HVAC&R system having an economizer, such as the intermediate vessel 70, and a compressor, such as the compressor 32. The discussion below describes the present techniques incorporated with embodiments of the vapor compression system 14 having multiple compressors 32. For example, vapor compression system 14 may include one compressor 32 that is a low pressure compressor or first stage compressor and another compressor 32 that is a high pressure compressor or second stage compressor. However, it should be appreciated that the techniques described herein may be incorporated with other embodiments of the compressor 32, the vapor compression system 14, and the HVAC&R system 10.

[0040] FIG. 5 is a schematic view of an embodiment of a vapor compression system 100 (e.g., vapor compression system 14, chiller, chiller heat pump system) having a compressor system 400 (e.g., multi-stage compressor system) in accordance with aspects of the present disclosure. It should be appreciated that the compressor system 400 and / or components thereof may be implemented with any of the systems described above, in accordance with the present techniques. Further, it should be appreciated that the compressor system 400 may be utilized in systems configured to utilize variable speed compressors. For example, the compressor system 400 may include one or more compressors, with each compressor coupled to a respective variable speed drive, thereby enabling the variable speed drive to modulate a speed of the compressor to regulate certain operating parameters of the compressor system 400 (e.g., amount of work done by the compressor system 400, amount of lift achieved by the compressor system 400, regulate an evaporator leaving water temperature, regulate an economizer saturated temperature) based on certain operating conditions of the vapor compression system 100.

[0041] In the illustrated embodiment, the vapor compression system 100 is configured to direct a working fluid (e.g., vaporous working fluid) along a working fluid circuit 101 from an evaporator 102 (e.g., evaporator 38) to the compressor system 400. The compressor system 400 may includea first compressor 402 (e.g., low stage compressor, first stage compressor) and a second compressor 404 (e.g., high stage compressor, second stage compressor). More specifically, the first and second compressors 402, 404 may be arranged in series relative to a flow of working fluid through the compressor system 400 (e.g., along the working fluid circuit 101). The compressor system 400 is configured to pressurize (e.g., lift) the working fluid to a desired pressure and direct the working fluid through the vapor compression system 100 (e.g., based on a cooling demand and / or heating demand of the vapor compression system 100). For example, the first compressor 402 may receive working fluid from the evaporator 102, pressurize the working fluid by a first amount (e.g., first lift), and direct the working fluid to the second compressor 404. The second compressor 404 may further pressurize the working fluid by a second amount (e.g., second lift) and discharge the working fluid toward a condenser 104 (e.g., condenser 34) of the vapor compression system 100. In certain embodiments, the condenser 104 may be a double bundle condenser (DBC) having two circuits (e.g., bundles) that exchange heat with a working fluid vapor or a two-phase working fluid, separate subcoolers (e.g., drain legs), and separate water boxes as described in greater detail below. It should be appreciated that, in certain embodiments, the first compressor 402 and / or the second compressor 404 may be independently configured to satisfy a conditioning demand (e.g., cooling load, heating load) on the compressor system 400. For example, in certain embodiments and / or under certain operating conditions (e.g., when the conditioning demand is below a threshold value), the first compressor 402 may be configured to pressurize (e.g., lift) the working fluid to a desired pressure that may satisfy the conditioning demand on the compressor system 400 (e.g., without operation of the second compressor 404). In such embodiments, the first compressor 402 may be configured to direct the working fluid directly toward the condenser 104 (e.g., without flowing through the second compressor 404), as discussed in greater detail below.

[0042] The first compressor 402 may include pre-rotation vanes (PRV) 406 (e.g., PRV system) and a variable geometry diffuser (VGD) 408. As will be appreciated, the PRV 406 may be adjustable guide vanes disposed at or adjacent an inlet (e.g., suction side) of the first compressor 402 and are configured to control and / or adjust flow of working fluid entering the first compressor 402 (e.g., by inducing a swirling flow or motion of the working fluid). The VGD 408 may be configured to adjust a size of a diffuser passage or gap of the first compressor 402 (e.g., downstream of an impeller of the first compressor 402) to adjust and / or control flow of workingfluid through the first compressor 402. Operation of the PRV 406 and the VGD 408 may be adjusted to control operation of the vapor compression system 100 (e.g., based on a load demand or cooling load of the vapor compression system 100) and / or to avoid occurrences of stall and / or surge in the first compressor 402.

[0043] The second compressor 404 may also include pre-rotation vanes (PRV) 410 (e.g., PRV system) and a variable geometry diffuser (VGD) 412. As will be appreciated, the PRV 410 may be adjustable guide vanes disposed at or adjacent an inlet (e.g., suction side) of the second compressor 404 and are configured to control and / or adjust flow of working fluid entering the second compressor 404 (e.g., by inducing a swirling flow or motion of the working fluid). The VGD 412 may be configured to adjust a size of a diffuser passage or gap of the second compressor 404 (e.g., downstream of an impeller of the second compressor 404) to adjust and / or control flow of working fluid through the second compressor 404. Operation of the PRV 410 and the VGD 412 may be adjusted to control operation of the vapor compression system 100 (e.g., based on a load demand or cooling load of the vapor compression system 100) and / or to avoid occurrences of stall and / or surge in the second compressor 404.

[0044] The compressor system 400 includes a motor system 414 having one or more motors 416 configured to drive rotation of the first and second compressors 402, 404. In certain embodiments, each of the one or more motors 416 of the motor system 414 may be coupled to a variable speed drive (VSD) 418, and the VSD 418 may be configured to control operation (e.g., rotation, control a speed) of the motors 416, and thus, the compressors 402, 404. For example, each VSD 418 may convert alternating current (AC) power having a particular fixed lined voltage and fixed line frequency to drive the motors 416 of the motor system 414. In this way, each VSD 418 may operate the respective motor 416 coupled thereto to drive each of the compressors 402, 404 of the compressor system 400 at different speeds (e.g., based on a load demand of the vapor compression system 14) to enable more efficient operation of the vapor compression system 14. That is, based on the demands of the system, the speed of the first compressor 402 and / or the second compressor 404 may be increased or decreased to operate the compressors 402, 404 at a lower frequency limit that corresponds to a desired lift while avoiding surge conditions. In certain embodiments, each of the VSDs 418 coupled to a respective motor 416 may be configured to drive each of the motors 416, and thus, each of the compressors 402, 404 at the same speed, while inother embodiments, the VSDs 418 may be configured to drive each of the compressors 402, 404 at different speeds (e.g., independently). It should be appreciated that in certain embodiments, one or more of the capacity regulation components and / or FRDs discussed above may be omitted. For example, in certain embodiments, the compressor 402 may not include the PRV 406, the VGD 408, and / or the VSD 418. Similarly, in certain embodiments, the compressor 404 may not include the PRV 410, the VGD 412, and / or the VSD 418.

[0045] In certain embodiments, the vapor compression system 100 may include a hot gas bypass valve 420 disposed along a hot gas bypass circuit 421 of the vapor compression system 100. In the illustrated embodiment, the hot gas bypass valve 420 is configured to direct compressed working fluid from a discharge outlet of the second compressor 404 (e.g., compressed working fluid from the condenser 104 that has not yet been condensed) to a suction inlet of the first compressor 402. However, in certain embodiments, the hot gas bypass valve 420 may be configured to direct compressed working fluid from the discharge outlet of the second compressor 404 to a location along the working fluid circuit 101 of the vapor compression system 100, such as downstream of an expansion valve 106 (e.g., expansion valve 36) of the vapor compression system 100 and / or upstream of the evaporator 102. Additionally, in certain embodiments, the hot gas bypass valve 420 may be configured to direct compressed working fluid from a discharge outlet of the first compressor 402 to a suction inlet of the first compressor 402 or from a discharge outlet of the second compressor 404 to a suction inlet of the second compressor 404. Further, as discussed in greater detail below, the PRVs 406, 410, the VGDs 408, 412, the VSDs 418, and the hot gas bypass valve 420 may be operated or controlled to adjust a flow rate and / or a pressure differential (e.g., lift, head) of working fluid directed through the compressor system 400 (e.g., based on a load or cooling demand of the vapor compression system 100). In certain embodiments, each of the aforementioned devices may be operated and / or controlled to achieve certain target temperatures. For example, components associated with the first compressor 402 (e.g., PRV 406, VGD 408, VSD 418) may be operated or controlled to achieve a target evaporator leaving water temperature, while components associated with the second compressor 404 (e.g., PRV 410, VGD 412, VSD 418) may be operated or controlled to achieve a target economizer saturated temperature in the economizer 70, as discussed in greater detail below.

[0046] In certain embodiments, each of the compressors 402, 404 (e.g., each of the compressor stage) may include a stall detector 422 (e.g., stall voltage detection circuitry). The stall detector 422 may be a stall pressure transducer disposed at a respective outlet of the first compressor 402 and / or the second compressor 404. For example, a stall detector 422A may be configured to detect (e g., sense, measure, record) pressure pulsations at the outlet of the first compressor 402 and a stall detector 422B may be configured to detect pressure pulsations at the outlet of the second compressor 404. Each of the stall detectors 422A, 422B may then output a stall voltage signal (e g., a DC stall voltage signal) to a controller, thereby enabling the controller to modify a position of the VGDs 408, 412 based on the output stall voltage signal. The stall voltage signal may be indicative of a magnitude of the stall noise present at the compressors 402, 404. In certain embodiments, a position of the VGD 408, 412 of each compressor 402, 404, respectively, may be adjusted to control (e g., reduce, rectify, or eliminate) the stall noise. For example, upon detecting that a stall voltage signal detected by the stall detector 422A is above a threshold value, the controller may begin to adjust the position of the VGD 408 of the first compressor 402 from the maximum allowed open position to the fully closed position until the stall noise is rectified. Once the stall noise is rectified, the VGD 408 is maintained in the same position for a predetermined amount of time (e.g., a preset wait period). After the predetermined amount of time has passed, the controller may adjust (e.g., pulse, open in discrete steps or increments) the position of the VGD 408 toward the maximum allowed open position until the stall noise is detected again, or the maximum allowed open position is reached.

[0047] The vapor compression system 100 directs working fluid discharged by the compressor system 400 (e.g., discharged by the first compressor 402 and / or the second compressor 404) to the condenser 104. The condenser 104 is configured to transfer heat (e.g., thermal energy) from the working fluid to a conditioning or cooling fluid (e.g., water, air) in order to cool and / or condense the working fluid. Thereafter, the working fluid is directed through the expansion valve 106 and to the evaporator 102. The evaporator 102 may be fluidly coupled to a cooling load 108 (e.g., cooling load 62), and the evaporator 102 may enable transfer of heat (e.g., thermal energy) from the cooling load (e.g., cooling fluid, water) to the working fluid, thereby heating the working fluid and cooling the cooling load 108. For example, the evaporator 102 may place the working fluid in a heat exchange relationship with a cooling fluid (e.g., water) that is circulated through the cooling load 108 to provide cooling. However, it should be appreciated that embodiments of thepresent disclosure also include the vapor compression system 100 as a heat pump (e.g., chiller heat pump) configured to operate to provide heating to a load. Additionally, in certain embodiments, the condenser 104 may be fluidly coupled to an economizer 110 (e.g., flash tank 70) of the vapor compression system 100, and the economizer 110 may be configured to separate working fluid received from the condenser 104 into vaporous working fluid and liquid working fluid. For example, working fluid may be directed out of the condenser 104 and toward an expansion device 112 (e.g., valve 66) disposed upstream of the economizer 110 . The valve 112 may be configured to decrease the pressure of (e.g., expand) the liquid working fluid received from the condenser 104. During the expansion process, a portion of the liquid may vaporize, and thus, the economizer 110 may be used to separate the vapor from the liquid received from the valve 112.

[0048] In certain embodiments, the economizer 110 may provide for further expansion of the liquid working fluid due to the pressure drop experienced by the liquid working fluid when entering the economizer 110 (e.g., due to a rapid increase in volume experienced when entering the economizer 110). The vaporous working fluid in the economizer 110 may be drawn by the compressor system 400 to be recirculated along the working fluid circuit 101. For example, in the illustrated embodiment, the vaporous working fluid in the economizer 110 is drawn through a suction line 113 to the second compressor 404. In certain embodiments, one or more valves 114 (e.g., level control valves) may be disposed along the suction line 113 to control aspects of the economizer 110, as discussed in greater detail below. It should be appreciated that, in other embodiments, the vaporous working fluid may be directed toward a suction inlet of the first compressor 402 and / or to another location along the working fluid circuit 101. The liquid working fluid that collects within the economizer 110 may be at a lower enthalpy than the liquid working fluid exiting the condenser 104 because of the expansion in the valve 112 and / or the economizer 110. In certain embodiments, the liquid working fluid within the economizer 110 may be directed along a discharge line 115 toward the evaporator 102. One or more valves 116 (e.g., level control valves) may be disposed along the discharge line 115 to control aspects of the economizer 110 and / or the evaporator 102, as discussed in greater detail below. It should be appreciated that, while the discharge line 115 is illustrated as discharging liquid working fluid from the economizer 110 to the evaporator 102 downstream of the expansion valve 106, in other embodiments, the discharge line 115 may discharge the liquid working fluid from the economizer 110 upstream of theexpansion valve 106, thereby enabling further expansion of the liquid working fluid before the liquid working fluid is directed toward the evaporator 102.

[0049] Additionally, or alternatively, and as mentioned above, the condenser 104 may correspond to a double bundle condenser (DBC) which includes two circuits (e.g., bundles) that exchange heat with a working fluid vapor or two-phase refrigerant, thereby enabling the vapor compression system to operate in various modes to satisfy conditioning demands (e.g., cooling mode, heating mode, simultaneous heating and cooling mode). For example, the condenser 104 may include a first circuit 120 (e.g., condenser rejection circuit, condenser cooling circuit) and a second circuit 122 (e.g., condenser heating circuit). The working fluid may be directed through the condenser 104 (e.g., across tubes of the first circuit 120 and / or across tubes of the second circuit 122), thereby enabling the working fluid to exchange heat with one or more additional fluids (e.g., cooling fluid, conditioning fluids) circulated through the tubes of the first and second circuits 120, 122. For example, the first circuit 120 may be configured to circulate a cooling fluid to and from a cooling tower 124. In certain embodiments, the first circuit 120 (e.g., condenser rejection circuit) may correspond to an open-loop circuit for utilization with the cooling tower 124. As the cooling fluid is directed through the tubes of the first circuit 120, working fluid directed across the tubes of the first circuit 120, which may be at a greater temperature than the cooling fluid directed through the tubes, may deposit heat to the cooling fluid, thereby cooling the working fluid and heating the cooling fluid. The cooling fluid may be directed back to the cooling tower 124 to deposit the heat received from the working fluid. Thereafter, the cooled working fluid may be directed through a subcooler 126 of the first circuit 120 to be further cooled before being discharged along the working fluid circuit 101 toward the expansion valve 106 via a drain leg 121 of the first circuit 120.

[0050] The second circuit 122 may be configured to circulate a conditioning fluid (e.g., heating fluid) to and from a heating load 128. In certain embodiments, the second circuit 122 (e.g., condenser heating circuit) may correspond to a closed-loop circuit to increase heating capacity and / or for building heating use. As the conditioning fluid is directed through the tubes of the second circuit 122, working fluid directed across the tubes of the second circuit 122, which may be at a greater temperature than the conditioning fluid directed through the tubes, may deposit heat to the conditioning fluid, thereby cooling the working fluid and heating the conditioning fluid. Theheated conditioning fluid may be directed toward the heating load 128 to satisfy heating demands associated with the heating load 128. Thereafter, the cooled working fluid may be directed through a subcooler 130 of the second circuit 122 to be further cooled before being discharged toward the economizer 110 of the vapor compression system 100 via a drain leg 123 of the second circuit 122. In certain embodiments, each of the first circuit 120 and the second circuit 122 may include a dedicated water box configured to facilitate the flow of fluid (e.g., working fluid, conditioning fluid, cooling fluid) through the condenser 104. For example, the first circuit 120 may include a first water box configured to distribute the incoming cooling fluid flow (e.g., fluid flow from the cooling tower 124) amongst heat exchange tubes of the first circuit 120. Similarly, the second circuit 122 may include a second water box configured to distribute the incoming conditioning fluid flow (e.g., fluid flow from the heating load 128) amongst heat exchange tubes of the second circuit 122.

[0051] In certain embodiments, one or more of the valves 106, 112, 114, and / or 116 may be operated and / or modulated to control aspects of various components of the vapor compression system 100. For example, in certain embodiments, the expansion valve 106 may correspond to condenser liquid level control valve (CLLCV) and / or an economizer bypass valve (EBV) that enables working fluid discharged from the condenser 104 (e.g., discharged from the first circuit 120) to bypass the economizer 110 and be directed toward the evaporator 102. Depending on a mode of operation of the vapor compression system 100, the economizer bypass valve 106 may be operated to control a liquid level within the condenser 104 (e.g., liquid level within the subcooler 126), as discussed in greater detail below. In certain embodiments, the valve 112 may correspond to a subcooler liquid level control valve (SLCV) configured to control a liquid level within the subcooler 126 and / or 130. It should be appreciated that, in certain embodiments, multiple valves 112 may be employed, where each valve 112 is fluidly coupled to a respective subcooler 126, 130 of the condenser 104. For example, in certain embodiments, the vapor compression system 100 may include a low stage subcooler liquid level control valve 112 (LSSLCV) and a high stage subcooler liquid level control valve 112 (HSSLCV). The LSSLCV may be fluidly coupled to the subcooler 126 of the first circuit 120 and configured to control a liquid level within the subcooler 126, while the HSSLCV may be fluidly coupled to the subcooler 130 of the second circuit 122 and configured to control a liquid level within the subcooler 130, as discussed in greater detail below. In certain embodiments, the valve 114 may correspond to apressure control valve (PCV) configured to control or modulate a pressure of the economizer 110. For example, the valve 114 may be configured to transition toward an open position to enable gas (e.g., vaporous working fluid) from the economizer 110 to be directed to a suction inlet of the second compressor 404. In certain embodiments, the valve 116 may correspond to an economizer level control valve (ELCV) configured to control a liquid level within the economizer 110, as discussed in greater detail below.

[0052] As mentioned above, in certain embodiments, components of the compressor system 400 and / or the vapor compression system 100 may be controlled via a controller 430 (e.g., control system, automation controller), which may correspond to the control panel 40 of FIGS. 3 and 4 or any other suitable controller (e.g., a compressor controller). For example, the controller 430 may include an interface board 432, processing circuitry 434 (e.g., one or more microprocessors), a memory 436, an analog to digital (A / D) converter 438, and a stall voltage detection board 439. The AD converter 438 may be configured to receive input signals from various components of the vapor compression system 100 that indicate the performance of the vapor compression system 100. For example, the input signals received by the controller 430 may include a temperature of a leaving chilled liquid (e.g., conditioning fluid) from the evaporator 102, working fluid pressures in the evaporator 102, the condenser 104 (e.g., pressures in the first circuit 120 and / or second circuit 122 of the condenser 104), and the economizer 110, an acoustic or sound pressure measurement in the discharge passages of the compressors 402, 404, saturated temperatures at the suction inlet and discharge outlet of the compressors 402, 404, the pressure at the suction inlet of the compressors 402, 404, saturated temperatures at the suction inlet and discharge outlet of the economizer 110, liquid levels within the condenser 104 (e.g., liquid levels within the subcoolers 126, 130), and / or liquid levels within the economizer 110.

[0053] The stall voltage detection board 439 may be configured to receive the DC stall voltage signals from the stall detectors 422A, 422B of the compressors 402, 404, respectively. The stall voltage detection board 439 may be further configured to convert the DC stall voltage signals to AC stall voltage signals. An AC stall voltage signal may further represent the magnitude of stall noise experienced by a compressor, for example, the compressors 402, 404. The stall voltage detection board 439 may be further coupled to the controller 430 to transmit the AC stall voltage signals.

[0054] The memory 436 may include volatile memory, such as random-access memory (RAM), and / or non-volatile memory, such as read-only memory (ROM), optical drives, hard disc drives, solid-state drives, or any other non-transitory computer-readable medium storing instructions (e.g., control algorithms) that, when executed, control operation of the compressor system 400 and / or the vapor compression system 100. For example, the controller 430 may utilize various control algorithms (e.g., stored in the memory 436) to determine when and / or how to adjust the speed of the VSDs 418, the positions of the PRVs 406, 410 and / or the VGDs 408, 412, and or the positions (e.g., degree of opening) of the valves 106, 112, 114, 116 in response to particular compressor conditions to maintain a required capacity of each of the compressors 402, 404. Further, the controller 430 may use the control algorithms to achieve various target temperatures and / or pressures in the components employed by the vapor compression system 100. For example, the control algorithms stored in the memory 436 may be utilized by the processing circuitry 434 to control operation of the first compressor 402 to achieve a target evaporator leaving water temperature and / or to control operation of the second compressor 404 to achieve a target economizer saturated temperature, as discussed in greater detail below. The memory 436 may also be configured to store various threshold values required for maintaining system efficiency and stability, as discussed in greater detail below. The processing circuitry 434 may be configured to execute such instructions. In certain embodiments, the processing circuitry 434 may include one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), one or more general purpose processors, or any combination thereof.

[0055] The controller 430 is configured to control operation of the compressor system 400 (e.g., control operation of one or more components of the compressor system 400, control operation of one or more components of the vapor compression system 100) to enable more efficient operation of the vapor compression system 100, to improve operation during turndown (e.g., reduce turndown capacity, decrease turndown capacity), and / or to increase an operating envelope of the compressor system 400. In particular, the controller 430 is configured to coordinate (e.g., balance) operation of the first compressor 402 and the second compressor 404, each of which may include one or more capacity regulation components or flow reduction devices (e g., PRVs 406, 410, VGDs 408, 412, VSDs 418) to achieve more efficient operation of the compressor system 400 (e.g., operation with isentropic efficiency). In certain embodiments, the controller 430 may be configured to control operation of each of the compressors 402, 404 (e.g.,via one or more control algorithms), the condenser 104, the evaporator 102, and / or the valves 106, 112, 114, 116 to achieve a desired capacity and / or to achieve target conditions (e.g., temperature, pressure, liquid levels) in components employed by the vapor compression system 100. For example, the controller 430 may be configured to control the first compressor 402 according to a first control algorithm to achieve a target evaporator leaving water temperature in the evaporator 102 and / or the condenser 104. In certain embodiments, the controller 430 may be configured to control the second compressor 404 according to a second control algorithm to achieve a target economizer saturated temperature in the economizer 110. In certain embodiments, the controller 430 may employ a third algorithm to balance operation of the first and second compressors 402, 404 to achieve the aforementioned target temperatures while minimizing the occurrence of surge and / or stall.

[0056] It should be appreciated that while the controller 430 is described above as being configured to control the first compressor 402 to achieve a target evaporator leaving water temperature and to control the second compressor 404 to achieve a target economizer saturated temperature, in certain embodiments, one or more of the control algorithms may be overridden based on load demands of the compressor system 400. For example, under certain operating conditions and / or load demands, each of the compressors 402, 404 may be operating near an upper limit threshold of the respective compressor 402, 404, such that the motors 416 are operating near an upper limit frequency. In such situations, it may be difficult to achieve a target economizer saturated temperature while ensuring that load demands are satisfied. As such, in certain embodiments, the first control algorithm that operates to achieve a target leaving water temperature may override the second control algorithm that operates to achieve a target economizer saturated temperature, thereby ensuring that customer demands are met while enabling greater efficiency (e.g., during turndown, in situations in which one or more of the compressors 402, 404 is not operating near an upper limit threshold). That is, in certain embodiments, the compressor system 400 (e.g., the controller 430, the high stage compressor 404) may operate according to a priority scheme that prioritizes satisfying customer demands over achieving the target economizer saturated temperature.

[0057] Further, one or more of the control algorithms employed by the controller 430 to control the respective compressors 402, 404 may provide a linkage (e.g., digital linkage) between aposition of the PRV 406 and the VGD 408 of the first compressor 402 and / or a linkage between a position of the PRV 410 and the VGD 412 of the second compressor 404. In certain embodiments, the control algorithms that provide a linkage between PRV and VGD positions of the first and second compressors 402, 404 may operate independently of the control algorithms utilized to achieve target operating temperatures and / or pressures within components of the vapor compression system 100 (e.g., target leaving water temperature, target economizer or flash tank saturated temperature). In this way, a complexity associated with regulating operation of compressor systems having various capacity regulation devices may be simplified, thereby reducing costs associated with the maintenance and operation of such systems. For example, by linking a position of the VGD based on a position of the PRV and / or by linking a position of the PRV based on a position of the VGD to operate a compressor, degrees of freedom (e.g., PRV / VGD position, VSD frequency) associated with the regulation and / or operation of the compressor system 400 may be decreased, thereby increasing efficiency and reducing costs. To this end, the controller 430 may be configured to output control signals to control operation (e.g., respective positions) of the PRVs 406, 410, operation (e.g., respective positions) of the VGDs 408, 412, operation of the motor system 414, operation of the VSDs 418, and / or operation (e.g., a respective position) of the hot gas bypass valve 420. In certain embodiments, the controller 430 may regulate operation of one or more components of the compressor system 400 based on operating conditions of the vapor compression system 100 and / or a load of the vapor compression system 100 (e.g., a respective load on each of the compressors 402, 404), or other suitable data.

[0058] In certain embodiments, the controller 430 may be configured to control operation of the compressor system 400 based on feedback received from one or more sensors 440 of the vapor compression system 100. The sensors 440 may be configured to detect one or more operating conditions (e.g., operating parameters) of the vapor compression system 100 and provide feedback indicative of the operating conditions to the controller 430. The sensors 440 may include any suitable sensor configured to detect an operating parameter of the vapor compression system 100 and / or the compressor system 400, such as pressure sensors, temperature sensors, position sensors, voltage sensors, current sensors, flow rate sensors, speed sensors, and so forth. In certain embodiments, one or more sensors 440 may be disposed at a respective inlet (e.g., suction side) of each of the compressors 402, 404, a respective outlet (e.g., discharge side) of each of the compressors 402, 404, an outlet of the condenser 104 (e.g., working fluid outlet, cooling fluidoutlet), an outlet of the evaporator 102 (e g., working fluid outlet, cooling fluid outlet), an inlet of the economizer 110, and / or at an outlet of the economizer 110. However, other embodiments of the vapor compression system 100 may include sensors 440 positioned at additional or alternative locations along the vapor compression system 100 (e.g., along the working fluid circuit 101) and / or within the compressor system 400.

[0059] The sensors 440 may be configured to collect (e.g., measure, detect) data related to the working fluid, a cooling or conditioning fluid circulated through the evaporator 102, and / or a cooling or conditioning fluid circulated through the condenser 104. For example, one or more of the sensors 440 may detect temperatures, pressures, flow rates, or other operating parameters of the working fluid, a conditioning fluid, or a cooling fluid. Further, one or more sensors 440 may be associated with the PRVs 406, 410, the VGDs 408, 412, the VSDs 418, and / or the hot gas bypass valve 420. For example, the sensors 440 may be configured to detect and transmit data indicative of respective positions of the PRVs 406, 410, the VGDs 408, 412, and / or the hot gas bypass valve 420. The vapor compression system 100 may also include one or more sensors 440 associated with the motor system 414 (e.g., each of the motors 416 of the motor system 414, each of the VSDs 418), and the sensors 440 may be configured to detect and transmit data indicative of respective operating parameters of the motor system 414, such as a speed or frequency associated with each of the compressors 402, 404. Further still, the vapor compression system 100 may include one or more sensors 440 configured to detect and transmit data indicative of respective operating parameters of the vapor compression system 100 (e.g., a liquid level within the condenser 104, liquid level within the subcoolers 126, 130, liquid level within the evaporator 102, liquid level within the economizer 110). It should be noted that the vapor compression system 100 may include fewer or more sensors 440 than those illustrated in FIG. 5, and additional or alternative sensors 440 may be configured to detect one or more operating parameters and transmit data indicative of the operating parameters to the controller 430 for use in operating the compressor system 400 and / or other components of the vapor compression system 100.

[0060] FIGS. 6-9 are schematic views of embodiments of the vapor compression system 100 (e g., chiller, chiller heat pump system) having the compressor system 400. In particular, FIGS. 6-9 illustrate various working fluid flow paths of the working fluid through the vapor compression system 100 based on an operating mode of the vapor compression system 100. For example, FIG.6 illustrates a flow path of working fluid through the vapor compression system 100 during a cooling mode, FIG. 7 illustrates a flow path of working fluid through the vapor compression system 100 during a heating mode, FIG. 8 illustrates a flow path of working fluid through the vapor compression system 100 during a simultaneous heating and cooling mode, and FIG. 9 illustrates a flow path of working fluid through the hot gas bypass valve 420 of the vapor compression system 100.

[0061] Turning now to FIG. 6, a flow path of working fluid through the vapor compression system 100 during a cooling mode of the vapor compression system 100 is shown. In the cooling mode, the working fluid flows through the evaporator 102, the first compressor 402 (e.g., low stage compressor), across the first circuit 120 (e.g., condenser rejection circuit) and corresponding subcooler 126 within the condenser 104 , the expansion valve 106 (e.g., economizer bypass valve), and back to the evaporator 102. As shown in the illustrated embodiment, in the cooling mode, fluids (e.g., a conditioning fluid, a cooling fluid, water) are directed through the evaporator 102 (e.g., to and from the cooling load 108) and through the first circuit 120 (e.g., condenser rejection circuit) of the condenser 104 (e.g., to and from the cooling tower 124). Fluid does not flow through the second circuit 122 (e.g., condenser heating circuit) of the condenser 104 (e.g., to and from the heating load 128). As noted above, the first circuit 120 in the double bundle condenser 104 may correspond to or include an open-loop circuit for utilization with the cooling tower 124.

[0062] FIG. 7 illustrates a flow path of working fluid through an embodiment of the vapor compression system 100 during a heating mode. In the heating mode, the working fluid flows through the evaporator 102, the first compressor 402 (e.g., low stage compressor), the second compressor 404 (e.g., the high stage compressor), across the second circuit 122 (e.g., condenser heating circuit) and corresponding subcooler 130 within the condenser 104, the valve(s) 112 (e.g., one or more subcooler level control valves (SLCV, LSSLCV, HSSLCV)) disposed upstream of the economizer 110 (e.g., flash tank), the economizer 110, the valve 116 (e.g., ELCV) downstream of the economizer 110, and back to the evaporator 102. Additionally, the valve 114 (e.g., a pressure control valve (PCV)) is opened for gas (e.g., vaporous working fluid) from the economizer 110 to be directed to a suction inlet of the second compressor 404. The first circuit 120 (e.g., condenser rejection circuit) and / or corresponding subcooler 126 may not be operative because a heat rejection fluid (e.g., water) may not be directed therethrough in the heating mode.In the heating mode, fluids (e.g., a conditioning fluid, a cooling fluid, water) may be directed through the evaporator 102 (e.g., to and from a fluid source) and through the second circuit 122 (e.g., condenser heating circuit) of the condenser 104 (e.g., to and from the heating load 128). As noted above, the second circuit 122 in the double bundle condenser 104 may correspond to or include a closed-loop bundle to increase heating capacity and / or for building heating use.

[0063] FIG. 8 illustrates a flow path of working fluid through an embodiment of the vapor compression system 100 during a simultaneous heating and cooling mode (e.g., double bundle condenser 104 (DBC) operation). In the simultaneous heating and cooling (SHC) mode, the working fluid flows through the evaporator 102, the first compressor 402 (e.g., low stage compressor), the second compressor 404 (e.g., the high stage compressor). As the working fluid is directed into the condenser 104, the working fluid circuit 101 may bifurcate to direct (e.g., simultaneously direct) the working fluid across the first circuit 120 (e.g., condenser rejection circuit) and corresponding subcooler 126 within the condenser 104 and across the second circuit 122 (e.g., condenser heating circuit ) and corresponding subcooler 130 within the condenser 104. Thereafter, the working fluid may be discharged from the condenser 104 and may flow through the valve(s) 112 (e.g., one or more subcooler level control valves (SLCV, LSSLCV, HSSLCV)) disposed upstream of the economizer 110, the economizer 110, the valve 116 (e.g., ELCV) downstream of the economizer 110, and back to the evaporator 102. Similar to FIG. 7, the valve 114 (e.g., a PCV) may also be opened for gas (e.g., vaporous working fluid) from the economizer 110 to be directed toward the suction inlet of the second compressor 404. In certain embodiments, the subcooler 126 associated with the first circuit 120 (e.g., condenser rejection circuit) may be inoperative based on a position of the valve(s) 112. For example, a subcooler LCV (e.g., valve 112) fluidly coupled to the subcooler 126 associated with the first circuit 120 may be moved toward a fully closed position or a partially closed position, thereby limiting a flow of working fluid into subcooler 126 of the first circuit 120 despite the first circuit 120 having a fluid (e.g., water) flow therethrough. In the SHC mode, fluids (e.g., a conditioning fluid, a cooling fluid, water) are directed through the evaporator 102 (e.g., to and from the cooling load 108), the first circuit 120 (e.g., to and from the cooling tower 124), and the second circuit (e.g., to and from the heating load 128). FIG. 9 illustrates a flow path of working fluid along the hot gas bypass circuit 421 and through the hot gas bypass valve 420.

[0064] In FIGS. 6-9, when the first compressor 402 (e g., low stage compressor) is inoperative (e.g., in idle mode, in standby mode, not running), a low stage subcooler level control valve (LSSLCV) (e.g., valve 112 associated with the subcooler 126) may ramp to a standby position set by the controller 430 (e.g., will be progressively or incrementally adjusted toward a default position, which may correspond to 30 percent open). A control algorithm may track a process variable (e.g., subcooler liquid level probe in the subcooler 126 of the condenser 104) and a control variable for bumpless transfer (e.g., seamless transfer, smooth transition). When the first compressor 402 is operative, the LSSLCV may react to the control variable from the control algorithm. The liquid level set point is adjustable via the controller 430. When the first compressor 402 and the second compressor 404 are running, the LSSLCV will ramp toward a fully closed (0%) position.

[0065] When the second compressor 404 is inoperative (e.g., in idle mode, in standby mode, not running) and start is disabled, a high stage (e.g., two stage) subcooler level control valve (HSSLCV) (e.g., valve 112 associated with the subcooler 130) may ramp to a standby position (e.g., will be progressively or incrementally adjusted toward a default position, which may correspond to 0 percent open or fully closed). The control algorithm may track a process variable (e.g., subcooler liquid level probe in subcooler 130 of the condenser 104) and control variable for bumpless transfer (e.g., seamless transfer, smooth transition). When the second compressor 404 is inoperative and start is enabled, the HSSLCV may ramp toward a fully closed position (e g., 0 percent open). The control algorithm may track the process variable and control variable for bumpless transfer. When the first and second compressors 402, 404 are operative, the HSSLCV may react to the control variable from the control algorithm. The liquid level set point may be adjustable via the controller 430.

[0066] As noted above, the vapor compression system 100 of FIGS. 6-9 may also include an economizer (e.g., flash tank) level control valve (ELCV) (e.g., valve 116). When the second compressor 404 is inoperative (e.g., idle mode, standby mode, not running) and start is disabled, the ELCV 116 may ramp to a standby position (e.g., will be progressively or incrementally adjusted toward a default position, which may correspond to 0% open or fully closed). The control algorithm may track the process variable (e.g., economizer liquid level probe in the economizer 110) and control variable for bumpless transfer (e.g., seamless transfer, smooth transition). Whenthe second compressor 404 is inoperative and start is enabled, the ELCV 116 may ramp closed or toward a fully closed position (e.g., 0 percent open). The control algorithm may track the process variable and control variable for bumpless transfer. When the first and second compressors 402, 404 are operative, the ELCV 116 may react to the control variable from the control algorithm. The liquid level set point may be adjustable via the controller 430.

[0067] In certain embodiments, the vapor compression system 100 may correspond to a heatrecovery vapor compression system integrated with a boiler. For example, FIG. 10 is a schematic of an embodiment of the vapor compression system 100 (e.g., chiller, chiller heat pump system) configured and / or arranged as a heat-recovery chiller that is integrated with a boiler 500. In the illustrated embodiment, the vapor compression system 100 includes the double bundle condenser 104 (DBC) configured to operate to provide heating, cooling, or both (e.g., simultaneous heating and cooling) based on customer and / or load demands. For example, the double bundle condenser 104 may include the first circuit 120 (e.g., first volume, condenser rejection circuit) coupled to the cooling tower 124, and the second circuit 122 (e.g., second volume, condenser heating circuit) coupled to the heating load 128. As shown in the illustrated embodiment, conditioning fluid (e.g., heating fluid) heated by the working fluid in the second circuit 122 and directed from the second circuit 122 toward the heating load 128 may first be directed through a heat exchanger 502 that is fluidly coupled to the boiler 500. The heat exchanger 502 may be configured to place the conditioning fluid in an additional heat exchange relationship with an additional fluid received from the boiler 500, whereby the additional fluid deposits heat to the conditioning fluid to further heat the conditioning fluid. Thereafter, the conditioning fluid may be directed through the heating load 128 to satisfy heating demands of the vapor compression system 100. In certain embodiments, one or more pumps 504 may be employed to bias the various fluids (e.g., conditioning fluid, cooling fluid, heating fluid) through components of the vapor compression system 100 (e.g., through the evaporator 102, through the first and / or second circuits 120, 122 of the condenser 104, through the heat exchanger 502). Additionally, in certain embodiments, a cooling tower bypass valve 506 may be employed, whereby the cooling tower bypass valve 506 is configured to enable a flow of cooling fluid to bypass the cooling tower 124.

[0068] In FIGS. 6-10, to enable operation with the first circuit 120 (e.g., condenser rejection circuit) active, while still providing adequate subcooling, the condenser level control (e.g.,condenser liquid level control, subcooler liquid level control) may be modified. For example, the economizer bypass valve 106 may be adjusted (e.g., actuated) to regulate the condenser liquid level, and the valve(s) 112 (e.g., subcooler liquid level control valve (SLCV)) feeding the economizer 110 (e.g., flash tank) with liquid may be closed. Operation of the economizer bypass valve 106 may focus on condenser liquid level control in the condenser 104, and a liquid level set point may be different from two stage operation, as discussed in greater detail below. Other situations may also be regulated by the economizer bypass valve 106. For example, there is a potential situation in which greater than a threshold amount of liquid working fluid migrates into the economizer 110 (e.g., flash tank), such that the valve 116 (e.g., ELCV) draining the economizer 110 may bleed to ensure a threshold amount of working fluid is present within the evaporator 102. Additionally, there is a potential situation in which the evaporator 102 is too large with a small temperature difference (e.g., 5 °F). In such cases, the economizer bypass valve 106 may direct some amount of working fluid into the evaporator 102 while the condenser liquid level is still above a threshold amount (e.g., 20 percent).

[0069] To switch from low stage mode (e.g., operation of the first compressor 402 alone) to two stage (e.g., high stage) operation (e.g., both the first compressor 402 and the second compressor 404 operative), the working fluid may be directed through the economizer 110. For example, low stage operation enables the working fluid to flow through the economizer bypass valve 106, as discussed above, while two stage operation enables the working fluid to flow through the economizer 110 via valves feeding (e.g., valve(s) 112) and / or draining (e.g., valve 116) the economizer 110. When the system lift or head is above the first compressor 402 operation limit (e.g., above a threshold amount of lift that may not be achieved by first compressor 402 alone), the vapor compression system 100 may be switched to two stage operation. The switch control may correspond to the controller 430 opening the valve(s) 112 feeding the economizer 110 to pull (e.g., draw) the working fluid liquid level in the economizer 110 while the economizer bypass valve 106 regulates the condenser liquid level. At the same time, the economizer draining valve (e.g., ELCV 116) can build the economizer 110 liquid level. The high stage startup may implement start holds or other strategies to regulate the high stage, as discussed in greater detail below. The switch control from two-stage operation (e.g., first and second compressor 402, 404 operation) to low stage operation (e.g., first compressor 402 operation alone) involves a switch from the valves feeding and / or draining the economizer 110 (e.g., valve(s) 112 and 116) to the economizer bypassvalve 106 with a period of both valves regulating. A baffle may be disposed between the switches to limit frequency switches in between.

[0070] The high stage capacity control may be modified to support a new economizer 110 saturation temperature set point when operating both first compressor 402 and the second compressor 404. A PID controller (e.g., controller 430) may be utilized to drive the economizer 110 saturation temperature to a set point. For example, when the measured economizer 110 saturation temperature is greater than the set point, the PID controller may cause the second compressor 404 to load (e.g., subject to load limits on motor current, discharge pressure, etc.). When the measured economizer 110 saturation temperature is below the set point, the PID controller may cause the second compressor 404 to unload. There may be multiple methods for defining the economizer 110 saturation temperature set point. For example, an operator may choose to manually set the economizer 110 saturation temperature set point (Tsat.econ.target.manuai ), where the set point is bounded by various controls, parameters, limits, and / or inputs (e.g., default = 85.0 °F, minimum = 40.0 °F, maximum = 160 °F, precision = 0.1 °F). Alternatively, the vapor compression system 100 may automatically determine (e.g., calculate) the economizer 110 saturation temperature set point Tsat econ target auto) using equation (1) and equation (2) below, where all pressures are absolute and not gauge pressure.Pecon.target.abs - Pevap.abs ' Pcond.abs (I)In equation (1) above, Pecon.target.abs may correspond to the target absolute pressure in the economizer 110, which may be a function of the absolute pressure in the evaporator 102 (peVap.abs) and the absolute pressure in the condenser 104 (Pcond.abs) - In equation (2), the Tsat econ offse tmay be an operator configurable offset variable bounded by various controls, parameters, limits, and / or inputs (e.g., default = 0 °F, minimum = -40.0 °F, maximum = +40.0 °F, precision = 0.1 °F).

[0071] To find balance between responsiveness while reducing or limiting sensitivity to noise in the calculated set point, or large step changes in the manual set point, the control may implement an active economizer 110 saturation temperature set point (Tsat econ target active'), which mayapply a rate limit to the set point to effectively ramp the set point at a controlled rate. The vapor compression system 100 may determine the active economizer 110 saturation temperature set point using equation (3) below:The ramp rate Tsatecon :argetrateMmit') may be an operator configurable variable bounded by various controls, parameters, limits, and / or inputs (e.g., default = 0.05 °F / s, minimum = 0.01 °F / s, maximum = 1.0 °F / s, precision = 0.01 °F / s). Notably, during the high stage startup or high stage shutdown, an alternate strategy may be utilized that implements startup holds or other strategies to regulate the high stage (e.g., regulate the second compressor 404). Further, it should be appreciated that in situations in which a control design is impacted, override controls may be applied to the economizer 110 saturation temperature set point. For example, if one stage (e.g., first compressor 402 or second compressor 404) is approaching surge or choke, or if one stage is reaching a motor current limit, it may be advantageous to shift load to or from the high stage (e.g., to or from the second compressor 404). In such cases, it may be beneficial to apply override controls to the economizer 110 saturation temperature set point to drive the desired loading and / or unloading of the second compressor 404.

[0072] In certain embodiments, surge map control may be implemented for each compression stage (e.g., for the first compressor 402 or low stage compressor and for the second compressor 404 or the high stage compressor). For example, for each stage, the working fluid suction speed of sound (asuc) and isentropic head (A / is) may be estimated using estimates of suction pressure and discharge pressure for each stage. For the first compressor 402, the suction and discharge pressures may be estimated by the pressure in the evaporator 102 and discharge pressure of the first compressor 402, respectively. For the second compressor 404, suction and discharge pressures may be estimated by the discharge pressure of the first compressor 402 and discharge pressure of the second compressor 404, respectively.

[0073] For each working fluid available for operation, calculation methods may be defined to calculate the suction speed of sound and the isentropic head. For example, equations (4) and (5) may be employed to calculate a suction speed of sound and isentropic head.Using the values from equations (4) and (5), a lift (e.g., omega, fl) on a respective compressor (e.g., first or low stage compressor 402, second or high stage compressor 404) may be calculated using equation (6) below.Additionally, a control device (e.g., PRV position, VGD position) may be utilized to define surge Mach. For example, equation (7) illustrates a relationship between control device positions and the surge mach (SurgeMach) number for a particular compressor.SurgeMach = A ■ £lB(7)In equation (7) above, A is a function of a control device position, such as a PRV position or a VGD position, and B is also a function of a control device position, such as a PRV position or a VGD position. Values for A and B may be determined utilizing piecewise linear interpolation tables as a function of the control device position.

[0074] Upon determining the SurgeMach number using equation (7) above, an estimated antisurge minimum frequency (ASMF) may be calculated using equation (8) below. The ASMF may correspond to a minimum (e.g., lower limit) frequency that may be used to operate a particular compressor while avoiding undesirable conditions such as stall or surge.SurgeMach-aASMF[HZVSD] =sucTT-Dtip-GearRatlo-SlipFactor-60 (8)In equation (8) above, Dtipcorresponds to an impeller tip diameter (e.g., in meters), the GearRatio variable corresponds to a ratio of high speed to low speed shaft speed, and the SlipFactor corresponds to an estimate of the motor shaft speed correction accounting for slip (e.g., 0.9915). In certain embodiments, correction factors may be applied to the ASMF to facilitate and / or increase adjustability and / or flexibility during operation of the vapor compression system 100. Forexample, equation (9) illustrates an ASMF multiplier and an ASMF offset, both of which may correspond to operator-configurable parameters, being applied to the ASMF.ASMFactiVe =ASMF■ASMFmultiplier +A FM Fof fset (9)In certain embodiments, each of the ASMF multiplier and ASMF offset may be bounded by various controls, parameters, limits, and / or inputs. For example, the ASMF multiplier may be bounded by a default value of 1.0, a minimum value of 0.900, a maximum value of 1.100, and a precision value of 0.001. Similarly, the ASMF offset may be bounded by a default value of 0.0, a minimum value of -10.00, a maximum value of +10.00, and a precision value of 0.01.

[0075] In certain embodiments, control logic may be utilized to simplify the control of the flow reduction devices employed by the compressor system 400. For example, in traditional systems, the VGD moves based on a resultant stall signal, and processes through a sequence of stall reacting, stall waiting, and probing. Present embodiments provide a linkage (e.g., digital linkage, correlation, operational correlation) between the PRV command position and the VGD command position for a given stage (e.g., given compressor). In this way, control of a compressor system (e.g., compressor system 400) or vapor compression system (e.g., vapor compression system 100) having multiple compressors each with various flow reduction devices (PRVs, VGDs) may be simplified by removing free control parameters and mitigating and / or avoiding unstable processes induced by VGD probing action.

[0076] In certain embodiments, the linkage may be enabled for one or both stages (e.g., for both the first compressor 402 and the second compressor 404). For example, FIG. 11 is a graphical representation of a linkage for the first compressor 402 (e.g., low stage compressor) in which the position (e.g., degree of opening) of the VGD 408 is dependent upon the position (e.g., degree of opening) of the PRV 406 of the first compressor 402, and FIG. 12 is a graphical representation of a linkage for the second compressor 404 (e.g., a high stage compressor) in which the position (e.g., degree of opening) of the PRV 410 is dependent upon the position (e.g., degree of opening) of the VGD 412 of the second compressor 404. It should be appreciated that, by linking the PRV 406 and VGD 408 positions for the first compressor 402 and / or by linking the PRV 410 and the VGD 412 positions for the second compressor 404, the operational envelope of the first compressor 402 and / or second compressor 404 may be increased relative to systems that do not include the linkagedisclosed herein. Additionally, linking the PRV and VGD positions of the respective compressors 402, 404 may significantly increase the turndown capabilities of a particular stage, thereby enabling the stage to achieve a desired target evaporator leaving water temperature at reduced flow rates (e.g., compared to systems that do not utilize the linkages disclosed herein). That is, linking the PRV and VGD positions of the respective compressors 402, 404 may improve, decrease, or reduce a turndown capacity of the respective compressors 402, 404.

[0077] For example, in FIG. 11, the position of the PRV 406 of the first compressor 402 is represented on the X-axis and the position of the VGD 408 of the first compressor 402 is represented on the Y-axis. Thus, the position of the VGD 408 of the first compressor 402 is a function of the position of the PRV 406 in the first compressor 402. FIG. 11 further illustrates data derived from a number of tests that were performed to determine a position at which to link the VGD 408 position and the PRV 406 position of the first compressor 402. Based on empirical data, linking the PRV 406 position and the VGD 408 position in the first compressor 402 such that the VGD 408 begins to open once the PRV 406 reaches seventy percent open enables the operation envelope of the compressor system 400 (e.g., operation envelope of the first compressor 402) to be increased significantly, and further increases the turndown capabilities of the first compressor 402.

[0078] In FIG. 12, the position of the VGD 412 of the second compressor 404 is represented on the X-axis and the position of the PRV 410 of the second compressor 404 is represented on the Y-axis. Thus, the position of the PRV 410 of the second compressor 404 is a function of the position of the VGD 412 in the second compressor 404. FIG. 12 further illustrates that the linkage in the second compressor 404 may set a midpoint at 5 percent, such that when the VGD 412 position is less than 5 percent open, the PRV 410 position is linearly linked to the VGD 412 position. After the VGD 412 is opened beyond 5 percent open, the PRV 410 position may be opened to 100 percent (e.g., fully open position) with a variable VGD 412 position. In this way, the operation envelope and the turn down capabilities of the second compressor 404 may be increased while minimizing the occurrence of stall and / or surge.

[0079] Present embodiments are directed toward increasing an operating envelope of a compressor system having a high stage compressor and a low stage compressor and / or improving(e g., reducing) a turndown capacity of the compressor system. Additionally, present embodiments are directed toward minimizing undesirable operating conditions including surge and / or stall. For example, present embodiments may employ one or more control algorithms (e.g., control programs, proportional-integral-derivative (PID) control loop) to control each of the compressors of the compressor system. In certain embodiments, the control algorithms may be utilized to control various components of the vapor compression system or compressor system (e.g., flow reduction devices, PRVs, VGDs, VSDs, expansion valves, valves, level control valves, heat exchangers), thereby enabling the compressor system to satisfy heating and / or cooling demands while minimizing surge and / or stall. The control algorithms may also be utilized to regulate operation of each of the stages of the compressor system. For example, the low stage compressor, which is the compressor operating between the evaporator and economizer pressure, may be operated to achieve a target evaporator leaving water temperature. The high stage compressor, which is the compressor operating between the economizer pressure and the condenser pressure, may be operated to achieve a target economizer saturated temperature. That is, the various components associated with the high stage compressor and the low stage compressor (e.g., PRVs, VGDs, VSDs) may be operated to achieve the aforementioned targets temperatures.

[0080] In certain embodiments, a stage balance control (e.g., two stage balance control) may be utilized to provide balance between the low stage compressor and the high stage compressor. The stage balance control may be associated with economizer saturated temperature and may use an equal stage pressure ratio that includes override controls to limit the VSD frequency, motor current, and motor torque of a respective compressor employed by the compressor system (e.g., high stage compressor, low stage compressor). Surge mapping may also be employed for each of the low stage and high stage compressors.

[0081] In certain embodiments, the capacity control algorithm for the low stage compressor may utilize the VSD frequency and VGD associated with the low stage compressor and / or the VSD frequency and the PRV associated with the low stage compressor. Such systems discussed above may be designed for high lift heat pump conditions.

[0082] While only certain features and embodiments have been illustrated and described, many modifications and changes may occur to those skilled in the art, such as variations in sizes,dimensions, structures, shapes and proportions of the various elements, values of parameters, such as temperatures and pressures, mounting arrangements, use of materials, colors, orientations, and so forth, without materially departing from the novel teachings and advantages of the subject matter recited in the claims. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.

[0083] Furthermore, in an effort to provide a concise description of the exemplary embodiments, all features of an actual implementation may not have been described, such as those unrelated to the presently contemplated best mode, or those unrelated to enablement. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation specific decisions may be made. Such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure, without undue experimentation.

[0084] The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as “means for [perform]ing [a function]...” or “step for [perform]ing [a function]...”, it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is intended that such elements are not to be interpreted under 35 U.S.C. 112(f).

Claims

CLAIMS:

1. A compressor system for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system, wherein the compressor system comprises: a low stage compressor comprising a first pre-rotation vane (PRV) and a first variable geometry diffuser (VGD) configured to operate to regulate a capacity of the low stage compressor, wherein a first operational linkage for the low stage compressor causes a first position of the first VGD to be dependent upon a second position of the first PRV; and a high stage compressor comprising a second PRV and a second VGD configured to operate to regulate a capacity of the high stage compressor, wherein a second operational linkage for the high stage compressor causes a third position of the second PRV to be dependent upon a fourth position of the second VGD.

2. The compressor system of claim 1, wherein the first operational linkage and the second operational linkage are independent of one another.

3. The compressor system of claim 1, wherein the first operational linkage and the second operational linkage are configured to increase an operating envelope of the low stage compressor, the high stage compressor, or both.

4. The compressor system of claim 1, wherein the first operational linkage and the second operational linkage are configured to reduce a turndown capacity of the low stage compressor, the high stage compressor, or both.

5. The compressor system of claim 1, wherein the low stage compressor is configured to achieve a target leaving water temperature of an evaporator or a condenser of the HVAC&R system.

6. The compressor system of claim 1, wherein the high stage compressor is configured to achieve a target economizer saturated temperature of an economizer of the HVAC&R system.

7. The compressor system of claim 1, wherein the low stage compressor comprises a first variable speed drive (VSD) configured to control a speed of the low stage compressor, and the high stage compressor comprises a second variable speed drive (VSD) configured to control a speed of the high stage compressor.

8. The compressor system of claim 7, wherein the speed of the low stage compressor controlled by the first VSD is independent of the speed of the high stage compressor controlled by the second VSD.

9. The compressor system of claim 1, wherein the first PRV is adjustable between a first fully closed position and a fully open position, the first VGD is adjustable between a second fully closed position and a maximum allowed open position, and the first position of the first VGD corresponds to the second fully closed position based on the second position of the first PRV being less than seventy percent open.

10. The compressor system of claim 9, wherein the first operational linkage is configured to progressively increase a degree of opening of the first VGD from the second fully closed position to the maximum allowed open position based on the second position of the first PRV being greater than seventy percent open.

11. A heating, ventilation, air conditioning, and refrigeration (HVAC&R) system comprising: a vapor compression system, comprising: a working fluid circuit configured to circulate a working fluid therethrough; and a compressor system comprising a compressor configured to pressurize and direct the working fluid through the working fluid circuit, wherein the compressor comprises a prerotation vane (PRV) adjustable between a fully open position and a first fully closed position and a variable geometry diffuser (VGD) adjustable between a maximum allowed open position and a second fully closed position; and a controller comprising a memory and processing circuitry, wherein the memory stores instructions that, when executed by the processing circuitry, cause the processing circuitry to linka first position of the PRV and a second position of the VGD, wherein the second position of the VGD is dependent upon the first position of the PRV.

12. The HVAC&R system of claim 11, wherein the compressor is a low stage compressor, and wherein the compressor system comprises a high stage compressor configured to pressurize and direct the working fluid through the working fluid circuit, wherein the high stage compressor comprises a second pre-rotation vane (PRV) adjustable between a second fully open position and a third fully closed position and a second variable geometry diffuser (VGD) adjustable between a second maximum allowed open position and a fourth fully closed position.

13. The HVAC&R system of claim 12, wherein the instructions are configured to cause the processing circuitry to link a third position of the second PRV associated with the high stage compressor and a fourth position of the second VGD associated with the high stage compressor, wherein the third position of the second PRV is dependent upon the fourth position of the second VGD.

14. The HVAC&R system of claim 12, comprising an evaporator positioned upstream of the low stage compressor relative to a direction of the working fluid through the working fluid circuit and a condenser positioned downstream of the low stage compressor and the high stage compressor relative to the direction of the working fluid through the working fluid circuit, wherein the controller is configured to operate the low stage compressor to achieve a target leaving water temperature of the evaporator or the condenser.

15. The HVAC&R system of claim 12, comprising an economizer positioned downstream of a condenser of the HVAC&R system and upstream of the high stage compressor relative to a direction of the working fluid through the working fluid circuit, wherein the controller is configured to operate the high stage compressor to achieve a target economizer saturated temperature of the economizer.

16. A vapor compression system for a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system, the vapor compression system comprising:a working fluid circuit configured to circulate a working fluid therethrough; a first compressor configured to pressurize and direct the working fluid through the working fluid circuit; a second compressor configured to pressurize and direct the working fluid through the working fluid circuit, wherein the first compressor and the second compressor are arranged in series relative to a direction of the working fluid through the working fluid circuit; a double bundle condenser positioned along the working fluid circuit and configured to receive the working fluid from the first compressor, the second compressor, or both; an economizer positioned downstream of the double bundle condenser and upstream of the second compressor relative to the direction of the working fluid through the working fluid circuit, wherein the economizer is configured to separate the working fluid received from the double bundle condenser into a liquid working fluid and a vaporous working fluid; and an evaporator positioned downstream of the double bundle condenser and upstream of the first compressor relative to the direction of the working fluid through the working fluid circuit, wherein the evaporator is configured to receive the working fluid from the double bundle condenser and the liquid working fluid from the economizer, and wherein the first compressor is configured to achieve a target leaving water temperature of the evaporator or the double bundle condenser and the second compressor is configured to achieve a target saturated temperature in the economizer.

17. The vapor compression system of claim 16, comprising: one or more sensors configured to collect sensor data indicative of one or more operating parameters of the vapor compression system; and a controller comprising a memory and processing circuitry, wherein the memory stores instructions that, when executed, cause the processing circuitry to balance operation of the first compressor and the second compressor based on the sensor data from the one or more sensors.

18. The vapor compression system of claim 17, wherein the double bundle condenser comprises: a condenser rejection circuit fluidly coupled to a cooling tower, wherein the condenser rejection circuit comprises a first subcooler; anda condenser heating circuit coupled to a heating load, wherein the condenser heating circuit comprises a second subcooler, separate from the first subcooler.

19. The vapor compression system of claim 18, comprising: one or more subcooler liquid level control valves configured to control a liquid level in the first subcooler, the second subcooler, or both; an economizer liquid level control valve configured to control a liquid level of the economizer; and an economizer bypass valve configured to cause working fluid discharged from the double bundle condenser to bypass the economizer.

20. The vapor compression system of claim 19, wherein the one or more operating parameters comprise the liquid level of the first subcooler, the liquid level of the second subcooler, the liquid level of the economizer, or any combination thereof, and wherein the controller is configured to control a position of the one or more subcooler liquid level control valves, a position of the economizer liquid level control valve, a position of the economizer bypass valve, or any combination thereof based on the liquid level of the first subcooler, the liquid level of the second subcooler, the liquid level of the economizer, or any combination thereof.

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