CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from and the benefit of U.S. Provisional Application No. 63/352,157, entitled “SYSTEMS AND METHODS FOR CONTROLLING OPERATION OF A CHILLER,” filed June 14, 2022, which is herein incorporated by reference in its entirety for all purposes.

BACKGROUND

[0002] 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.

[0003] A heating, ventilation, air conditioning, and refrigeration (HVAC&R) system may 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 HVAC&R system (e.g., vapor compression system). The HVAC&R system may place the working fluid in a heat exchange relationship with a conditioning fluid (e.g., water) to heat and/or cool the conditioning fluid and may then deliver the conditioning fluid to various destinations to be utilized. For example, the HVAC&R system may include a heat pump system (e.g., heat pump vapor compression system) that includes one or more heat exchangers each configured to receive a working fluid and a respective additional fluid and to place the working fluid in a heat exchange relationship with the additional fluid. The heat pump system may include one or more compressors configured to pressurize the working fluid and circulate the working fluid through a working fluid circuit (e.g., vapor compression circuit). It is now recognized that improved systems and methods for controlling and/or initiating operation of HVAC&R systems are desired. SUMMARY

[0004] 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.

[0005] In an embodiment, a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes a vapor compression system having a vapor compression circuit comprising a compressor system configured to direct a working fluid through the vapor compression circuit to provide a heat exchange relationship between the working fluid and a cooling fluid, a conditioning fluid, or both. The HVAC system further includes a controller having a memory and processing circuitry, where the memory includes instructions stored thereon that, when executed by the processing circuitry, cause the processing circuitry to receive a signal to initiate operation of the vapor compression system, receive sensor data indicative of operating conditions of the vapor compression system, determine an expected lift of the compressor system based on the operating conditions of the vapor compression system, compare the expected lift of the compressor system to a threshold value, and control operation of the vapor compression system based on the comparison of the expected lift with the threshold value.

[0006] In another embodiment, a heating, ventilation, air conditioning, and refrigeration (HVAC&R) system includes a vapor compression system having a plurality of vapor compression circuits, where each vapor compression circuit comprises a compressor configured to direct a working fluid through the vapor compression circuit to establish a heat exchange relationship between the working fluid and a conditioning fluid. The HVAC&R system further includes a controller comprising a memory and processing circuitry, where the memory comprises instructions stored thereon that, when executed by the processing circuitry, cause the processing circuitry to receive a signal to initiate operation of the vapor compression system, receive sensor data indicative of operating conditions of the vapor compression system, and determine an expected lift of the respective compressor of each vapor compression circuit based on the operating conditions of the vapor compression system. The instructions, when executed, further cause the processing circuitry to compare the expected lift to a threshold value and control operation of the vapor compression system based on comparison of the expected lift with the threshold value.

[0007] In another embodiment, a tangible, non-transitory, computer-readable medium includes instructions executable by processing circuitry of a vapor compression system that, when executed by the processing circuitry, cause the processing circuitry to receive a signal to initiate operation of the vapor compression system, receive sensor data indicative of operating conditions of the vapor compression system, determine an expected lift of each compressor of one or more compressors of the vapor compression system based on the operating conditions of the vapor compression system, and determine a respective lower frequency limit for each compressor of the one or more compressors based on the expected lift. The instructions, when executed, further cause the processing circuitry to compare the respective lower frequency limit of each compressor of the one or more compressors to a threshold value, and control operation of the vapor compression system based on comparison of the respective lower frequency limit of each compressor of the one or more compressors with the threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Various aspects of this disclosure may be better understood upon reading the following detailed description and upon reference to the drawings in which:

[0009] FIG. 1 is a perspective view of an embodiment of a building utilizing a heating, ventilating, air conditioning, and refrigeration (HVAC&R) system in a commercial setting, in accordance with an aspect of the present disclosure;

[0010] FIG. 2 is a perspective view of an embodiment of a vapor compression system, in accordance with an aspect of the present disclosure;

[0011] FIG. 3 is a schematic of an embodiment of a vapor compression system, in accordance with an aspect of the present disclosure;

[0012] FIG. 4 is a schematic of an embodiment of a vapor compression system, in accordance with an aspect of the present disclosure; [0013] FIG. 5 is a schematic of an embodiment of a vapor compression system having three vapor compression circuits, in accordance with an aspect of the present disclosure;

[0014] FIG. 6 is a schematic of an embodiment of an HVAC&R system including a heat pump system in an open loop configuration, in accordance with an aspect of the present disclosure;

[0015] FIG. 7 is a flow diagram of an embodiment of a method for controlling startup of a vapor compression system, in accordance with an aspect of the present disclosure; and

[0016] FIG. 8 is a flow diagram of an embodiment of a method for controlling startup of a vapor compression system, in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION

[0017] 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.

[0018] 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 there may 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. [0019] 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.

[0020] As briefly discussed above, a heating, ventilation, air conditioning, and 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, heat pump system) that transfers thermal energy between a working fluid (e.g., refrigerant, heat transfer fluid), and a fluid to be conditioned (e.g., air, water, or brine). The vapor compression system may include one or more vapor compression circuits (e.g., heat pumps) that each may include a condenser and an evaporator that are fluidly coupled to one another via one or more conduits (e.g., vapor compression circuit, refrigeration circuit). In certain embodiments, the vapor compression system may be an open loop system, as described in greater detail below. Further, each vapor compression circuit may include a compressor configured to pressurize and circulate the working fluid through the circuit and, thus, enable the transfer of thermal energy between the working fluid and the fluid to be conditioned via the condenser and/or the evaporator.

[0021] 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 vapor compression circuits, each having a respective compressor configured to achieve a desired lift (e.g., pressure differential) of the working fluid directed through the respective vapor compression circuit. The lift or “head” of the compressor may be defined as the work or productivity of the compressor 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).

[0022] Some HVAC&R systems include various components configured to enable adjustment of compressor operation, such as compressor speed, compressor flow rate, and so forth. For example, an HVAC&R system may include a variable frequency drive (VFD) or variable speed drive (VSD) configured to adjust compressor speed, a flow reduction device (FRD) (e g., prerotation vane [PRV] systems, inlet guide vanes, and/or a variable geometry diffuser [VGD]) configured to adjust flow of working fluid through the compressor, and/or a hot gas bypass valve configured to enable bypass and/or recirculation of the working fluid through the compressor. Control of VSDs, PRVs, VGDs, hot gas bypass valves, and so forth may be based on data or feedback indicative of one or more operating conditions of the HVAC&R system, such as temperature and pressure data of the working fluid at the suction inlet and/or discharge outlet of the compressor, temperature and/or pressure data of the working fluid at the evaporator and condenser, temperature and/or pressure data of a fluid to be conditioned, PRV and/or VGD position data, hot gas bypass valve position data, temperature and/or pressure data of another fluid (e.g., cooling fluid, conditioning fluid), and so forth. The data from the sensors may be utilized to determine whether the HVAC&R system is operating to adequately satisfy a load demand (e.g., cooling demands, lift demands) of the HVAC&R system and/or whether operation of the one or more components is to be adjusted (e.g., to achieve or maintain operation of the HVAC&R system within various design conditions, to more desirably satisfy the load demand, and so forth). [0023] Traditional HVAC&R systems employing a vapor compression system (e.g., heat pump system) may initiate operation of the HVAC&R system without adequately considering the starting conditions of the HVAC&R system. In doing so, traditional systems may be susceptible to initiating operation of the HVAC&R systems and/or operating the HVAC&R systems with operating conditions that are more likely to lead to surging of the one or more compressors employed by the HVAC&R system, thereby increasing wear and degradation to components of the HVAC&R systems and decreasing an efficiency of the HVAC&R system. HVAC&R systems having multiple vapor compression circuits may be particularly susceptible to conditions associated with surge at startup. For example, multiple vapor compression circuits arranged in a series counterflow arrangement may have greater temperature differences (e.g., greater than 20 degrees, greater than 30 degrees) between the conditioning fluid (e.g., water) directed through the evaporators of the vapor compression system and the cooling fluid (e.g., water) directed through the condensers of the vapor compression system. Accordingly, present embodiments are directed to systems and methods for evaluating startup conditions of a vapor compression system. The systems and methods may be utilized to enable or block startup of the vapor compression system based on evaluation of various operating parameters and/or conditions of the vapor compression system at startup. In this way, the present techniques may be utilized to avoid operation of vapor compression systems in surge conditions. The disclosed techniques may be implemented in many types of HVAC&R systems, including vapor compression systems having multiple vapor compression circuits (e.g., arranged in a series counterflow arrangement), vapor compression systems having a single vapor compression circuit, vapor compression systems having an open loop cycle associated with a customer process, and the like.

[0024] 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.

[0025] 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, and the control panel 40 may be configured to control various components of the vapor compression system 14, as discussed in greater detail below.

[0026] Some examples of fluids that may be used as working fluids in the vapor compression system 14 are hydrofluorocarbon (HFC) based refrigerants, for example, R-410A, R-407, R-134a, hydrofluoro olefin (HFO), "natural" refrigerants like ammonia (NH3), R-717, carbon dioxide (CO2), R-744, or hydrocarbon based refrigerants, water vapor, or any other suitable working fluid. Tn 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.

[0027] In some embodiments, as shown in FIG. 3, the vapor compression system 14 may use one or more of a pre-rotation vane system (PRV) 31, a variable geometry diffuser (VGD) 33, a hot gas bypass valve 35, 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 PRV 31 and the VGD 33 are types of flow reduction devices (FRDs) utilized to control the flow of a working fluid or heat transfer fluid (e g., refrigerant) through the compressor 32, thereby enabling the vapor compression system 14 to increase or decrease the capacity of the vapor compression system 14 based on load demands. Each of the PRV 31 and the VGD 33 may be coupled to an actuator which may be communicatively coupled to the control panel 40. The control panel 40 may be configured to provide signals to the actuators of the PRV 31 and the VGD 33 to open the PRV 31 and/or the VGD 33 to increase the flow of a heat transfer fluid (e.g., refrigerant) through the compressor 32, thereby increasing the operating (e.g., cooling) capacity of the vapor compression system 14. The control panel 40 may also provide signals to the actuators to close the PRV 31 and/or the VGD 33, thereby decreasing the capacity of the vapor compression system 14. The hot gas bypass valve 35 may be configured to direct heat transfer fluid vapor from a discharge outlet of the compressor 32 to a suction inlet of the compressor 32, as discussed in greater detail below.

[0028] 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.

[0029] 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, 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.

[0030] The liquid working fluid delivered to the evaporator 38 may absorb heat from a conditioning fluid (e.g., water), which may or may not be the same cooling fluid used in the condenser 34. That is, the liquid working fluid in the evaporator 38 enters into a heat exchange relationship with the conditioning fluid to chill the temperature of the conditioning fluid in the evaporator 38. Thus, the liquid working fluid in the evaporator 38 may undergo a phase change as a result of the heat exchange relationship from the liquid working fluid to a working fluid vapor. As shown in the illustrated embodiment of FIG. 3, the evaporator 38 may include a tube bundle 58 having a supply line 60S and a return line 60R connected to a cooling load 62. The conditioning 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 conditioning 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.

[0031] 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.

[0032] 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 expansion device 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.

[0033] It should be appreciated that any of the features described herein may be incorporated with 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 vapor compression circuits arranged in a series counterflow arrangement. However, it should be appreciated that the systems and methods described herein may be incorporated with other embodiments of the vapor compression system 14 and HVAC&R system 10, including vapor compression systems 14 having one vapor compression circuit and/or having multiple vapor compression circuits arranged in other configurations.

[0034] With the preceding in mind, FIG. 5 is a schematic of an embodiment of a vapor compression system 100 (e.g., HVAC&R system) having multiple vapor compression circuits (e g , heat pumps). The multiple vapor compression circuits may be arranged in series relative to a flow of conditioning fluid and/or cooling fluid directed through respective components of the multiple vapor compression circuits. For example, the vapor compression system 100 may include a first vapor compression circuit 102, a second vapor compression circuit 104, and a third vapor compression circuit 106, in accordance with aspects of the present disclosure. It should be appreciated that the vapor compression system 100 and/or components thereof may be implemented with any of the systems described above, in accordance with the present techniques. For example, the vapor compression system 100 may correspond to the vapor compression system 14 of FIG. 3.

[0035] In the illustrated embodiment, each vapor compression circuit 102, 104, 106 of the vapor compression system 100 is configured to direct a respective working fluid (e g., refrigerant) from a respective evaporator, through a respective compressor, through a respective condenser, and then back to the evaporator to circulate the working fluid through the respective vapor compression circuit. Additionally, the vapor compression circuits 102, 104, 106 are arranged in a series counterflow arrangement relative to flows of cooling fluid and conditioning fluid (e.g., fluid to be conditioned, another cooling fluid) directed through the vapor compression system 100 (e.g., through each of the vapor compression circuits 102, 104, 106). For example, a conditioning fluid (e.g., water, air) may sequentially (e.g., serially) flow through the evaporators of the vapor compression circuits 102, 104, 106 to transfer heat to the working fluid directed through each vapor compression circuit 102, 104, 106, thereby cooling the conditioning fluid (e.g., in a cooling mode of the vapor compression system 100). In some embodiments, the evaporators of the vapor compression circuits 102, 104, 106 may each be configured to adjust the temperature of the conditioning fluid by five to ten degrees (e.g., degrees Centigrade). In such embodiments, the conditioning fluid may decrease in temperature by approximately fifteen to thirty degrees as the conditioning fluid is directed through the vapor compression system 100 (e.g., through the vapor compression circuits 102, 104, 106). Similarly, a cooling fluid (e.g., water, air) may sequentially (e.g., serially) flow through the condensers of the vapor compression circuits 102, 104, 106. However, as shown in the illustrated embodiment, the cooling fluid may flow through the condensers of the vapor compression circuits 102, 104, 106 in a sequential order opposite a corresponding sequential order of the evaporators through which the conditioning fluid flows. In this way, the vapor compression circuits 102, 104, 106 may be arranged in a series counterflow arrangement. As the cooling fluid passes through each of the condensers, the respective working fluid of each vapor compression circuit may transfer heat to the cooling fluid, thereby cooling the respective working fluid within each vapor compression circuit before directing the respective working fluid back to the respective evaporator.

[0036] The first vapor compression circuit 102 may include a compressor 108 (e.g., first compressor, first compressor system), a condenser 110 (e.g., first condenser), an evaporator 112 (e.g., first evaporator), an expansion valve 114 (e.g., first expansion valve), and a hot gas bypass valve 116 (e.g., first hot gas bypass valve). The compressor 108 may also include pre-rotation vanes (PRV) 118 (e.g., PRV system, first PRV) and a variable geometry diffuser (VGD) 120 (e.g., first VGD). In some embodiments, the first compressor 108 may include either the PRV 118 or the VGD 120. As will be appreciated, the PRV 118 may be adjustable guide vanes disposed at or adjacent an inlet (e.g., suction side) of the compressor 108 and are configured to control and/or adjust flow of working fluid entering the compressor 108 (e.g., by inducing a swirling flow or motion of the working fluid). The VGD 120 may be configured to adjust a size of the diffuser passage gap of the compressor 108 (e.g., downstream of an impeller of the first compressor 108) to adjust and/or control flow of working fluid through the first compressor 108. Operation of the PRV 118 and/or the VGD 120 may be adjusted to control operation of the vapor compression system 100 (e.g., the first vapor compression circuit 102, 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 108.

[0037] The first vapor compression circuit 102 also includes a motor 122 (e.g., first motor) configured to drive rotation of the first compressor 108 and a variable speed drive (VSD) 124 configured to control operation of the motor 122. As described above, the VSD 124 may convert alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source into power having a variable voltage and frequency to drive the motor 122. In this way, the VSD 124 may operate the motor 122 to drive the compressor 108 at different speeds (e.g., based on a load demand of the vapor compression system 100) to enable more efficient operation of the vapor compression system 100. That is, based on the demands of the system, the speed of the compressor 108 may be increased or decreased to operate the compressor 108 at a lower frequency limit that corresponds to a desired lift while avoiding surge conditions. The first compression circuit 102 may also include the hot gas bypass valve 116. In the illustrated embodiment, the hot gas bypass valve 116 is configured to direct compressed working fluid from a discharge outlet of the first compressor 108 to a suction inlet of the first compressor 108. However, in some embodiments, the hot gas bypass valve 116 may be configured to direct compressed working fluid from the discharge outlet of the first compressor 108 to a location (e.g., along the first vapor compression circuit 102) downstream of the expansion valve 114 and upstream of the evaporator 112. Further, the PRV 118, the VGD 120, the hot gas bypass valve 116, and/or the VSD 124 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 first compressor 108 (e.g., based on a load or cooling demand of the vapor compression system 100). [0038] The vapor compression system 100 also includes various components associated with the second vapor compression circuit 104. For example, the second vapor compression circuit 104 may include a compressor 126 (e.g., second compressor, second compressor system), a condenser 128 (e.g., second condenser), an evaporator 130 (e.g., second evaporator), an expansion valve 132 (e.g., second expansion valve), and a hot gas bypass valve 134 (e.g., second hot gas bypass valve). The compressor 126 may also include pre-rotation vanes (PRV) 136 (e.g., second PRV system, second PRV) and a variable geometry diffuser (VGD) 138 (e.g., second VGD). In some embodiments, the second compressor 126 may include either the PRV 136 or the VGD 138. Similar to the PRV 118 of the first vapor compression circuit 102, the PRV 136 may be adjustable guide vanes disposed at or adjacent an inlet (e.g., suction side) of the compressor 126 and are configured to control and/or adjust flow of working fluid entering the compressor 126 (e.g., by inducing a swirling flow or motion of the working fluid). The VGD 138 may be configured to adjust a size of the diffuser passage gap of the compressor 126 (e g., downstream of an impeller of the second compressor 126) to adjust and/or control flow of working fluid through the second compressor 126. Operation of the PRV 136 and/or the VGD 138 may be adjusted to control operation of the vapor compression system 100 (e.g., the second vapor compression circuit 104) and/or to avoid occurrences of stall and/or surge in the second compressor 126.

[0039] The second vapor compression circuit 104 also includes a motor 140 (e.g., second motor) configured to drive rotation of the second compressor 126 and a variable speed drive (VSD) 142 configured to control operation of the motor 140. As described above, the VSD 142 may convert alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source into power having a variable voltage and frequency to drive the motor 140. In this way, the VSD 142 may operate the motor 140 to drive the compressor 126 at different speeds (e.g., based on a load demand of the vapor compression system 100) to enable more efficient operation of the vapor compression system 100. That is, based on the demands of the system, the speed of the second compressor 126 may be increased or decreased to operate the compressor 126 at a lower frequency limit that corresponds to a desired lift while avoiding surge conditions. The second vapor compression circuit 104 may also include the hot gas bypass valve 134. In the illustrated embodiment, the hot gas bypass valve 134 is configured to direct compressed working fluid from a discharge outlet of the second compressor 126 to a suction inlet of the second compressor 126. However, in some embodiments, the hot gas bypass valve 134 may be configured to direct compressed working fluid from the discharge outlet of the second compressor 126 to a location (e.g., along the second vapor compression circuit 104) downstream of the expansion valve 132 and upstream of the evaporator 130. Further, the PRV 136, the VGD 138, the hot gas bypass valve 134, and/or the VSD 142 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 second compressor 126 (e g., based on a load or cooling demand of the vapor compression system 100).

[0040] The third vapor compression circuit 106 may include a compressor 144 (e.g., third compressor, third compressor system), a condenser 146 (e.g., third condenser), an evaporator 148 (e.g., third evaporator), an expansion valve 150 (e.g., third expansion valve), and a hot gas bypass valve 152 (e.g., third hot gas bypass valve). The compressor 144 may also include pre-rotation vanes (PRV) 154 (e.g., third PRV system, third PRV) and a variable geometry diffuser (VGD) 156 (e.g., third VGD). In some embodiments, the third compressor 144 may include either the PRV 154 or the VGD 156. Similar to the PRV 118 of the first vapor compression circuit 102, the PRV 154 may be adjustable guide vanes disposed at or adjacent an inlet (e.g., suction side) of the compressor 144 and are configured to control and/or adjust flow of working fluid entering the compressor 144 (e.g., by inducing a swirling flow or motion of the working fluid). The VGD 156 may be configured to adjust a size of the diffuser passage gap of the compressor 144 (e.g., downstream of an impeller of the third compressor 144) to adjust and/or control flow of working fluid through the third compressor 144. Operation of the PRV 154 and/or the VGD 156 may be adjusted to control operation of the vapor compression system 100 (e.g., the second vapor compression circuit 104) and/or to avoid occurrences of stall and/or surge in the third compressor 144.

[0041] The third compression circuit 106 also includes a motor 158 (e.g., third motor) configured to drive rotation of the third compressor 144 and a variable speed drive (VSD) 160 configured to control operation of the motor 158. As described above, the VSD 160 may convert alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source into power having a variable voltage and frequency to drive the motor 158. In this way, the VSD 160 may operate the motor 158 to drive the compressor 144 at different speeds (e.g., based on a load demand of the vapor compression system 100) to enable more efficient operation of the vapor compression system 100. That is, based on the demands of the system, the speed of the third compressor 144 may be increased or decreased to operate the compressor 144 at a lower frequency limit that corresponds to a desired lift while avoiding surge conditions. The third compression circuit 106 may also include the hot gas bypass valve 152. In the illustrated embodiment, the hot gas bypass valve 152 is configured to direct compressed working fluid from a discharge outlet of the third compressor 144 to a suction inlet of the third compressor 144. However, in some embodiments, the hot gas bypass valve 152 may be configured to direct compressed working fluid from the discharge outlet of the third compressor 144 to a location (e.g., along the third vapor compression circuit 106) downstream of the expansion valve 150 and upstream of the evaporator 148. Further, as discussed in greater detail below, the PRV 154, the VGD 156, the hot gas bypass valve 152, and/or the VSD 160 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 third compressor 144 (e g., based on a load or cooling demand of the vapor compression system 100).

[0042] It should be noted that the techniques discussed herein may be implemented in any suitable embodiment of the vapor compression system 100 having any number of vapor compression circuits (e.g., 1, 2, 4, 5, or more). For example, the present techniques may be utilized in embodiments of the vapor compression system 100 including chiller systems, heat pump systems, and/or other types of HVAC&R systems. Further, in some embodiments, the techniques discussed herein may be employed by vapor compression systems having fewer or more components than the vapor compression system 100 described above. For example, though each of the vapor compression circuits 102, 104, 106 is described above as having a corresponding VSD configured to control operation of the respective motor that drives the compressor within the respective vapor compression circuit, in some embodiments, one of the vapor compression circuits 102, 104, 106 may be associated with a corresponding VSD, and other vapor compression circuits 102, 104, 106 may include a fixed speed motor configured to operate at a fixed speed to drive the corresponding compressor. Similarly, in some embodiments, one or more of the vapor compression circuits 102, 104, 106 may not include one or more of the PRV, VGD, or a hot gas bypass valve discussed above. Further still, in certain embodiments, one or more of the vapor compression circuits 102, 104, 106 may be omitted. For example, the presently disclosed techniques may be employed in a vapor compression circuit, which may include one or more compressors, one or more evaporators, and one or more condensers.

[0043] Each vapor compression circuit 102, 104, 106 of the vapor compression system 100 directs a respective working fluid (e.g., refrigerant) from the corresponding compressor 108, 126, 144 to the corresponding condenser 110, 128, 146 within each vapor compression circuit 102, 104, 106. Each condenser 110, 128, 146 is configured to transfer heat (e.g., thermal energy) from the working fluid to a cooling fluid (e.g., water, air) in order to cool and/or condense the working fluid within each vapor compression circuit 102, 104, 106. Thereafter, the working fluid within each vapor compression circuit 102, 104, 106 is directed through the respective expansion valve 114, 132, 150 and to the respective evaporator 112, 130, 148 of each vapor compression circuit 102, 104, 106. The evaporators 112, 130, 148 may be fluidly coupled in series relative to a flow of conditioning fluid directed through the evaporators 112, 130, 148. The conditioning fluid (e g., water) may also be directed to a load 172 (e.g., cooling load) to provide cooling to the load 172. To this end, each evaporator 112, 130, 148 may enable transfer of heat (e.g., thermal energy) from the conditioning fluid to the working fluid, thereby heating the working fluid within each evaporator 112, 130, 148 and cooling the conditioning fluid directed therethrough. For example, each evaporator 112, 130, 148 may place the working fluid in a heat exchange relationship with the conditioning fluid (e.g., water) that is circulated through the load 172 to provide cooling. In some embodiments, each evaporator 112, 130, 148 may be configured to decrease a temperature of the conditioning fluid by five to ten degrees (e.g., degrees Centigrade). Accordingly, in some embodiments, the temperature of the conditioning fluid may decrease by approximately fifteen to thirty degrees as the conditioning fluid is successively directed through the evaporators 112, 130, 148 of the vapor compression system 100. It should be appreciated that embodiments of the present disclosure also include the vapor compression system 100 as a heat pump (e.g., chiller heat pump) configured to operate to provide heating to the load 172. Thus, the heat transfer within the condensers 110, 128, 146 and evaporators 112, 130, 148 discussed above may be reversed in some embodiments.

[0044] As noted above, the vapor compression circuits 102, 104, 106 are configured in series counterflow arrangement. Accordingly, the condensers 110, 128, 146 may be fluidly coupled in series relative to a direction of cooling fluid directed therethrough The condensers 110, 128, 146 are also fluidly coupled to a cooling tower 170, which may be configured to reject heat from the cooling fluid to another fluid flow (e.g., airflow). As shown in the illustrated embodiment, cooling fluid from the cooling tower 170 may be directed to the third condenser 146 of the third vapor compression circuit 106, whereby the working fluid of the third vapor compression circuit 106 may transfer heat to the cooling fluid. Thereafter, the cooling fluid may be directed to the second condenser 128 of the second vapor compression circuit 104, whereby the working fluid of the second vapor compression circuit 104 may transfer heat to the cooling fluid. The cooling fluid may then be directed to the first condenser 110 of the first vapor compression circuit 102, and heat may be transferred from the working fluid of the first vapor compression circuit 102 to the cooling fluid before the cooling fluid is directed back to the cooling tower 170 to reject the heat absorbed from the working fluids of the vapor compression circuits 102, 104, 106. The cooling fluid may then be directed back to the third condenser 146 continue the cycle.

[0045] Similarly, the evaporators 112, 130, 148 may be fluidly coupled in series relative to a direction of conditioning fluid directed therethrough. The evaporators 112, 130, 148 are also fluidly coupled to the load 172. Notably, the vapor compression system 100 is configured to direct the conditioning fluid through each of the evaporators 112, 130, 148 in a direction (e.g., sequential order) opposite to a flow direction (e.g., a sequential order) of the cooling fluid directed through the condensers 110, 128, 146 from the cooling tower 170. For example, conditioning fluid may first be directed from the load 172 to the first evaporator 112 of the first vapor compression circuit 102, whereby the working fluid within the first evaporator 112 may receive heat from the conditioning fluid to cool the conditioning fluid. Thereafter, the conditioning fluid may be directed to the second evaporator 130 of the second vapor compression circuit 104 to transfer heat to the working fluid of the second vapor compression circuit 104 to further cool the conditioning fluid. The conditioning fluid may then be directed to the third evaporator 148 of the third vapor compression circuit 106 to transfer heat to the working fluid within the third evaporator 148 before being directed back to the load 172 to provide cooling to the load 172. As noted above, in some embodiments, the vapor compression system 100 may operate as a heat pump configured to provide heating to a building (e.g., the load 172). Additionally, it should be noted that the vapor compression system 100 illustrated in FIG. 5 may be referred to as a closed loop system in which working fluid is directed within each vapor compression circuit 102, 104, 106 from a respective compressor to a respective condenser to a respective evaporator and back to the respective compressor within each vapor compression circuit 102, 104, 106.

[0046] In certain embodiments, the HVAC&R system 100 may correspond to heat pump system having an open loop cycle in fluid communication with a customer process. For example, FIG. 6 is a schematic of an embodiment of the HVAC&R system 100 including a heat pump system 250 (e.g., mechanical vapor compression system). In the illustrated embodiment, the heat pump system 250 is configured as an open (e.g., open loop) heat pump system 250. The open heat pump system 250 may include at least a portion of a vapor compression circuit 252 having a heat exchanger 254 (e.g., an evaporator 254), a first compressor 256, a second compressor 258, and an expansion valve 260. Similar to the compressors 108, 126, 144 of FIG. 5, the first compressor 256 may include pre-rotation vanes (PRY) 264 (e.g., PRV system) and a variable geometry diffuser (VGD) 266. In some embodiments, the first compressor 256 may include either the PRV 264 or the VGD 266. As will be appreciated, the PRV 264 may be adjustable guide vanes disposed at or adjacent an inlet (e.g., suction side) of the compressor 256 and are configured to control and/or adjust flow of working fluid (e.g., steam) entering the compressor 256 (e.g., by inducing a swirling flow or motion of the working fluid). The VGD 266 may be configured to adjust a size of the diffuser passage gap of the compressor 256 (e.g., downstream of an impeller of the first compressor 256) to adjust and/or control flow of working fluid through the first compressor 256. Operation of the PRV 264 and/or the VGD 266 may be adjusted to control operation of the heat pump system 250 (e.g., the vapor compression circuit 252, based on a load demand or cooling load of the heat pump system 250) and/or to avoid occurrences of stall and/or surge in the first compressor 256.

[0047] The first compressor 256 is coupled to a motor 268 (e.g., first motor) configured to drive rotation of the first compressor 256 and a variable speed drive (VSD) 270 configured to control operation of the motor 268. As described above, the VSD 270 may convert alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source into power having a variable voltage and frequency to drive the motor 268. In this way, the VSD 270 may operate the motor 268 to drive the compressor 256 at different speeds (e.g., based on a load demand of the heat pump system 250, load demand of the customer process 262) to enable more efficient operation of the heat pump system 250. That is, based on the demands of the system, the speed of the compressor 256 may be increased or decreased to operate the compressor 256 at a lower frequency limit that corresponds to a desired lift while avoiding surge conditions.

[0048] The second compressor 258 may also include pre-rotation vanes (PRV) 272 (e.g., second PRV system) and a variable geometry diffuser (VGD) 274. In some embodiments, the second compressor 256 may include either the PRV 272 or the VGD 274. Similar to the PRV 264 of the first compressor 256, the PRV 272 may be adjustable guide vanes disposed at or adjacent an inlet (e.g., suction side) of the compressor 258 and are configured to control and/or adjust flow of working fluid entering the compressor 258 (e.g., by inducing a swirling flow or motion of the working fluid). The VGD 274 may be configured to adjust a size of the diffuser passage gap of the compressor 258 (e.g., downstream of an impeller of the second compressor 258) to adjust and/or control flow of working fluid through the second compressor 258. Operation of the PRV 272 and/or the VGD 274 may be adjusted to control operation of the heat pump system 250 (e g., the vapor compression circuit 252) and/or to avoid occurrences of stall and/or surge in the second compressor 258. The second compressor 258 is also coupled to a motor 276 (e.g., second motor) configured to drive rotation of the second compressor 258 and a variable speed drive (VSD) 278 configured to control operation of the motor 276. As described above, the VSD 278 may convert alternating current (AC) power having a particular fixed line voltage and fixed line frequency from an AC power source into power having a variable voltage and frequency to drive the motor 276. In this way, the VSD 278 may operate the motor 276 to drive the compressor 258 at different speeds (e g., based on a load demand of the heat pump system 250, load demand of the customer process 262) to enable more efficient operation of the heat pump system 250. That is, based on the demands of the system, the speed of the second compressor 258 may be increased or decreased to operate the compressor 258 at a lower frequency limit that corresponds to a desired lift while avoiding surge conditions.

[0049] The open heat pump system 250 (e.g., the vapor compression circuit 252) is configured to circulate a working fluid (e.g., water, refrigerant, steam) to cool and/or heat one or more fluids and/or to provide thermal energy to a customer process 262 (e.g., client process). For example, the customer process 262 may receive compressed working fluid (e.g., steam) from the first and second compressors 256, 258, and the heat provided by the compressed working fluid may be utilized by the customer process 262 (e.g., industrial process, HVAC&R process, heating load, cooling load, district heating system, etc.) to satisfy a heating demand and/or a thermal load (e.g., heat a fluid) of the customer process 262, thereby cooling the working fluid. Tn turn, as the working fluid exchanges heat with the customer process 262, the working fluid may condense before being returned to the vapor compression circuit 252. In certain embodiments, the customer process 262 may also include an additional heat exchanger (e.g., boiler) configured to provide additional fluid (e.g., steam, air, oil, process fluid) and/or thermal energy to the customer process 262. Thus, in certain embodiments, the condensed steam returned to the vapor compression circuit 252 may originate from the additional heat exchanger of the customer process 262 rather than originating from the first and second compressors 256, 258, thereby resulting in an open loop cycle.

[0050] As illustrated in FIG. 6, working fluid (e.g., condensed steam, liquid water) returned from the customer process 262 may be directed toward the expansion valve 260 before being directed to the evaporator 254 to exchange heat with a fluid (e g., cooling fluid) 280 circulating through the evaporator 254. For example, the expansion valve 260 may decrease the pressure of the working fluid, thereby further decreasing the temperature of the working fluid before the working fluid is directed through the evaporator 254. The cooled, condensed working fluid may then exchange heat with a conditioning fluid 280 directed through the evaporator 254, thereby cooling the conditioning fluid 280. For example, the evaporator 254 may enable transfer of heat (e.g., thermal energy) from the conditioning fluid 280 to the working fluid, thereby heating the working fluid within the evaporator 254 and cooling the conditioning fluid 280 directed therethrough. As the working fluid receives heat from the conditioning fluid 280, the working fluid may transition to a working fluid vapor, which may be returned to the compressors 256, 258 for compression before being directed through the heat pump system 250 and toward the customer process 262. In certain embodiments, the heat pump system 250 may also include an isolation valve 282 configured to control a flow of the compressed working fluid (e.g., steam) toward the customer process 262.

[0051] In certain embodiments, the heat pump system 250 may be configured to operate with a cascade system that includes an additional heat exchanger (e.g., a condenser). The cascade system may provide additional heat exchange capabilities, thereby enabling adjustment of operating parameters of the working fluid directed through the heat pump system 250. For example, in certain embodiments, operation of the cascade system may be initiated prior to initiating operation of the heat pump system 250, thereby enabling working fluid directed through the cascade system to increase to a threshold temperature before operation of the heat pump system 250 is initiated. In this way, potential surge conditions may be avoided, thereby decreasing wear and degradation on the heat pump system 250.

[0052] Referring to FIGS. 5 and 6, components of the vapor compression system 100, the vapor compression circuits 102, 104, 106, and/or the heat pump system 250 and the vapor compression circuit 252 may be controlled via a controller 200 (e.g., control system, automation controller). In some embodiments, the controller 200 may be an embodiment of the control panel 40 of FIGS. 3 and 4. For example, the controller 200 may include an interface 202 (e.g., user interface, display, interface board), processing circuitry 204 (e.g., one or more microprocessors), a memory 206, and an analog to digital (A/D) converter 208. For example, the memory 206 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 that, when executed (e.g., by processing circuitry 204), enable control of operation of the vapor compression system 100. The processing circuitry 204 may be configured to execute such instructions stored on the memory 206. In some embodiments, the processing circuitry 204 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.

[0053] The controller 200 is configured to control operation of the vapor compression system 100 and/or the heat pump system 250 (e.g., control operation of one or more components of the vapor compression circuits 102, 104, 106, control operation of one or more components of the vapor compression circuit 252) to enable improved operation of the vapor compression system 100 or the heat pump system 250. For example, the controller 200 may be configured to coordinate operation of the compressors 108, 126, 144, 256, 258 of each of the vapor compression circuits 102, 104, 106, 252 and other components of the vapor compression circuits 102, 104, 106, 252 based on operating conditions of the vapor compression system 100 or the heat pump system 250 and/or a load of the vapor compression system 100 or the heat pump system 250. To this end, the controller 200 may be configured to output control signals to control operation (e.g., a respective position) of the PRVs 118, 136, 154, 264, 272, operation (e g., a respective position) of the VGDs 120, 138, 156, 266, 274, operation (e.g., a position) of the hot gas bypass valves 116, 134, 152, operation of the motors 122, 140, 158, 268, 276, and/or operation ofthe VSDs 124, 142, 160, 270, 278 associated with each of the compressors 108, 126, 144, 256, 258, respectively. As noted above, in some embodiments, the controller 200 may regulate operation of one or more components of the vapor compression system 100 and/or the heat pump system 250 based on the operating conditions of the vapor compression system 100 or the heat pump system 250, a load of the vapor compression system 100 or the heat pump system 250 (e.g., thermal demand of the customer process 262), or other suitable data. In accordance with present techniques, the controller 200 is also configured to enable or block operation of the vapor compression system 100 or the heat pump system 250 during desired startup of the vapor compression system 100 or the heat pump system 250 (e.g., after non-operation of the vapor compression system 100, after nonoperation of the heat pump system 250). In particular, the controller 200 is configured to enable or block startup of the vapor compression system 100 or the heat pump system 250 based on detected operating conditions of the vapor compression system 100 or the heat pump system 250. In this way, the controller 200 is configured to mitigate or avoid operation of the vapor compression system 100 or the heat pump system 250 in surge conditions (e.g., conditions that may cause surge in one or more of the compressors 108, 126, 144, 256, 258).

[0054] To this end, the controller 200 may be configured to control operation of the vapor compression system 100 and/or the heat pump system 250 based on feedback received from one or more sensors 210 of the vapor compression system 100 or the heat pump system 250. The sensors 210 may be configured to detect one or more operating conditions (e.g., operating parameters) of the vapor compression system 100 or the heat pump system 250 and provide feedback indicative of the operating conditions to the controller 200. The sensors 210 may include any suitable sensor configured to detect an operating parameter of the vapor compression system 100, the heat pump system 250, and/or the vapor compression circuits 102, 104, 106, 252 such as pressure sensors, temperature sensors, position sensors, voltage sensors, current sensors, flow rate sensors, speed sensors, and so forth.

[0055] In the illustrated embodiments of FIGS. 5 and 6, one or more sensors 210 are disposed at a respective inlet (e.g., suction side) of each of the compressors 108, 126, 144, 256, 258, a respective outlet (e.g., discharge side) of each of the compressors 108, 126, 144, 256, 258, a respective inlet of each of the condensers 110, 128, 146 (e.g., working fluid outlet, conditioning fluid outlet), a respective outlet of each of the condensers 110, 128, 146 (e g., working fluid outlet, conditioning fluid outlet), a respective inlet of each of the evaporators 112, 130, 148, 254 (e.g., working fluid outlet, cooling fluid outlet), and a respective outlet of each of the evaporators 112, 130, 148, 254 (e.g., working fluid outlet, cooling fluid outlet). Additionally, one of the sensors 210 may be positioned proximate the isolation valve 282 to detect a pressure of the working fluid directed toward the customer process 262. In certain embodiments, one or more sensors 210 may be disposed at an inlet of a heat exchanger of a cascade system associated with the heat pump system 250 and/or an outlet of the heat exchanger of the cascade system associated with the heat pump system 250. However, other embodiments of the vapor compression system 100 or the heat pump system 250 may include sensors 210 positioned at additional or alternative locations along the vapor compression circuits 102, 104, 106 within the vapor compression system 100, additional or alternative locations along the vapor compression circuit 252 within the heat pump system 250, or other suitable locations.

[0056] The sensors 210 may be configured to collect (e.g., measure, detect) data related to the working fluid, the conditioning fluid circulated by the evaporators 112, 130, 148, the cooling fluid circulated by the condensers 110, 128, 146, the conditioning fluid 280 circulated by the evaporator 254 and/or a conditioning fluid circulated by a heat exchanger of a cascade system associated with the heat pump system 250. For example, one or more of the sensors 210 may detect temperatures, pressures, flow rates, or other operating parameters of the working fluid within each vapor compression circuit 102, 104, 106, 252, the conditioning fluid directed through each vapor compression circuit 102, 104, 106, the cooling fluid directed through each vapor compression circuit 102, 104, 106, the conditioning fluid directed through a heat exchanger of a cascade system associated with the heat pump system 250, and/or the conditioning fluid 280 directed through the evaporator 254. Further, one or more sensors 210 may be associated with the PRVs 118, 136, 154, 264, 272 the VGDs 120, 138, 156, 266, 274 and/or the hot gas bypass valves 116, 134, 152. For example, sensors 210 may be configured to detect and transmit data indicative of positions of the PRVs 118, 136, 154, 264, 272 the VGDs 120, 138, 156, 266, 274 and/or the hot gas bypass valves 116, 134, 152. The vapor compression system 100 and/or the heat pump system 250 may also include one or more sensors 210 associated with the motors 122, 140, 158, 268, 276 and the VSDs 124, 142, 160, 270, 278, and the sensors 210 may be configured to detect and transmit data indicative of respective operating parameters of the motors 122, 140, 158, 268, 276 and the VSDs 124, 142, 160, 270, 278 (e.g., current, voltage, frequency, speed, position, and so forth). It should be noted that the vapor compression system 100 and/or the heat pump system 250 may include fewer or more sensors 210 than those illustrated in FIGS. 5 and 6, and additional or alternative sensors 210 may be configured to detect one or more operating parameters and transmit data indicative of the operating parameters to the controller 200 for use in controlling operation of the vapor compression circuits 102, 104, 106, 252 and/or other components of the vapor compression system 100 or the heat pump system 250.

[0057] As discussed above, the PRVs 118, 136, 154, 264, 272 and/or the VGDs 120, 138, 156, 266, 274 may be operated as flow reduction devices (FRDs) configured to control or otherwise adjust flow of working fluid through a respective compressor (e g., compressors 108, 126, 144, 256, 258). One or more of the PRVs 118, 136, 154, 264, 272 and the VGDs 120, 138, 156, 266, 274 may be coupled to a respective actuator, each of which may be communicatively coupled to the controller 200. The actuators may be configured to operate based on control signals received from the controller 200. For example, the actuators may operate to adjust respective positions of the PRVs 118, 136, 154, 264, 272 and/or the VGDs 120, 138, 156, 266, 274. In some embodiments, the controller 200 may instruct one or more actuators to adjust one or more of the PRVs 118, 136, 154, 264, 272 toward an open position and/or to adjust one or more of the VGDs 120, 138, 156, 266, 274 toward an open position. In this way, the controller 200 may control the vapor compression system 100 and/or the heat pump system 250 to increase flow of working fluid directed through one or more of the vapor compression circuits 102, 104, 106, 252, thereby increasing a capacity (e.g., operating capacity) of the vapor compression system 100 or the heat pump system 250. Similarly, the controller 200 may instruct one or more actuators to adjust one or more of the PRVs 118, 136, 154, 264, 272 toward a closed position and/or to adjust one or more of the VGDs 120, 138, 156, 266, 274 toward a closed position in order to decrease flow of working fluid directed through one or more of the vapor compression circuits 102, 104, 106, 252 thereby decreasing the capacity of the vapor compression system 100 or the heat pump system 250.

[0058] As discussed in greater detail below, the controller 200 may be configured to operate the vapor compression circuits 102, 104, 106, 252 and other components of the vapor compression system 100 or the heat pump system 250 to enable improved operation of the vapor compression system 100 or the heat pump system 250. For example, the controller 200 is configured to enable or block operation of the vapor compression circuits 102, 104, 106, 252 based on detected operating conditions of the vapor compression system 100 or the heat pump system 250. In particular, the controller 200 is configured to analyze detected operating conditions (e.g., startup conditions) of the vapor compression system 100 or the heat pump system 250 to determine whether operation of the vapor compression system 100 or the heat pump system 250 in the detected operating conditions may result in surge and/or stall of one or more of the compressors 108, 126, 144, 256, 258. Based on a determination that the detected operating conditions are associated with an unacceptable potential for surge and/or stall, the controller 200 may block startup of the vapor compression system 100 or the heat pump system 250 (e.g., one or more of the vapor compression circuits 102, 104, 106, 252). Thus, utilizing the present techniques disclosed herein, the controller 200 may limit or block operation of the vapor compression system 100 or the heat pump system 250 during undesirable operating conditions.

[0059] As will be appreciated, operation and performance of the compressors 108, 126, 144, 256, 258 may be expressed and/or defined in terms of a head factor (Q) and a flow factor (0). The head factor is generally indicative of a pressure ratio or differential between discharge pressure and suction pressure of the compressor 108, 126, 144, 256, 258, and the flow factor is generally indicative of a flow rate (e.g., mass flow rate) of fluid directed through the compressor 108, 126, 144, 256, 258. During operation at a particular speed (e.g., rotational speed), an operating point of the compressor 108, 126, 144, 256, 258 may be generally expressed in terms of corresponding head factor and flow factor values associated with the compressor 108, 126, 144, 256, 258 at the particular speed. Indeed, at the particular operating speed, each compressor 108, 126, 144, 256, 258 may be configured to operate at various operating points, where each operating point is expressly defined by particular corresponding head factor and flow factor values. The various corresponding head factor and flow factor values associated with the compressor 108, 126, 144, 256, 258 may be based on particular design characteristics of the compressor 108, 126, 144, 256, 258. Additionally, compressor operating points may be adjusted and/or achieved via operational adjustment of the compressor 108, 126, 144, 256, 258. For example, a speed of the compressor 108, 126, 144, 256, 258 and/or positions of the PRV 118, 136, 154, 264, 272 and/or VGD 120, 138, 156, 266, 274 may be adjusted to adjust and/or achieve a particular operating point (e.g., corresponding head factor and flow factor values) of the compressor 108, 126, 144, 256, 258. However, it is desirable to avoid operation of the compressors 108, 126, 144, 256, 258 at certain operating values of head factor and/or flow factor in order to avoid undesirable operating conditions or occurrences, such as surge.

[0060] In accordance with present techniques, the controller 200 is configured to control operation of the vapor compression circuits 102, 104, 106, 252 in a manner that avoids surge conditions and/or avoids an unacceptable potential for surge in one or more of the compressors 108, 126, 144, 256, 258. More particularly, in accordance with the present techniques, the controller 200 is configured to detect operating conditions of the vapor compression system 100 or the heat pump system 250 (e.g., temperature and/or pressure data of the conditioning and/or cooling fluid directed through the vapor compression circuits 102, 104, 106, 252, temperature and/or pressure data of the working fluid directed through the vapor compression circuits 102, 104, 106, 252) and limit operation of one or more of the compressors 108, 126, 144, 256, 258 based on a determination that the detected operating conditions correspond to surge conditions or correspond to an unacceptable potential for surge. For example, the present techniques may be utilized prior to startup of the vapor compression system 100 or the heat pump system 250, and initial operation of the vapor compression system 100 or the heat pump system 250 may be blocked based on a determination that detected startup conditions may result in surge within the vapor compression system 100 or the heat pump system 250. Thus, present embodiments enable improved operation of the vapor compression system 100 or the heat pump system 250 as compared to traditional systems by limiting operation (e g., startup) of the vapor compression system 100 or the heat pump system 250 during undesirable operating conditions (e.g., surge conditions), thereby limiting potential wear and degradation that may occur during surge conditions. Indeed, as discussed in greater detail below, the controller 200 may be configured to limit operation (e.g., startup) of the vapor compression system 100 or the heat pump system 250 until the starting operating conditions enable the vapor compression system 100 or the heat pump system 250 to operate without surge and/or without an unacceptable potential for surge.

[0061] With the preceding in mind, FIG. 7 illustrates a flow chart of an embodiment of a method 600 (e.g., capacity control scheme, control logic) for controlling operation (e g., controlling startup) of the vapor compression system 100 and/or the heat pump system 250. That is, the method 600 may be utilized to coordinate (e.g., initialize and/or block) startup of the vapor compression system 100 and/or the heat pump system 250. For example, the controller 200 (e.g., a single controller, control system, the processing circuitry 204) may be configured to implement and/or execute the method 600 to control various components of the vapor compression system 100 or the heat pump system 250. In other embodiments, the method 600 may be implemented by another controller (e.g., a dedicated controller of the vapor compression system 100, dedicated controller of the heat pump system 250), more than one controller, or other suitable control system. It should also be noted that additional steps may be performed with respect to the method 600. Moreover, certain steps of the depicted method 600 may be removed, modified, and/or performed in a different order.

[0062] As mentioned above, the method 600 may be implemented to limit and/or block startup of the vapor compression system 100 or the heat pump system 250 when detected starting conditions (e.g., starting operating conditions) of the vapor compression system 100 or the heat pump system 250 may result in surging in one or more of the compressors 108, 126, 144, 256, 258. In some embodiments, an inlet and/or outlet temperature of the evaporator 112, 130, 148 (e.g., conditioning fluid temperature) and an inlet and/or outlet temperature of the condenser 110, 128, 146 (e.g., cooling fluid temperature) within each vapor compression circuit 102, 104, 106 may be monitored and evaluated (e.g., prior to startup of the vapor compression system 100) to assess the starting operating conditions of the vapor compression system 100. Similarly, an inlet and/or outlet temperature of the evaporator 254 and an inlet and/or outlet temperature of a heat exchanger of a cascade system associated with the heat pump system 250 may be monitored and evaluated (e.g., prior to startup of the heat pump system 250) to assess the starting operating conditions of the heat pump system 250. For example, the inlet and/or outlet temperature of the evaporator 112, 130, 148, and the inlet and/or outlet temperature of the condenser 110, 128, 146 may be representative of the operating conditions of the vapor compression system 100 at startup, while the inlet and/or outlet temperature of the evaporator 254 and the inlet and/or outlet temperature of the heat exchanger of the cascade system associated with the heat pump system 250 may be representative of the operating conditions of the heat pump system 250 at startup. In some embodiments, the inlet and/or outlet temperature of the evaporators 112, 130, 148, 254 may be a temperature of the conditioning fluid conditioned via the evaporator 112, 130, 148, 254, and the inlet and/or outlet temperature of the condenser 1 10, 128, 146 or the heat exchanger of the cascade system may be a temperature of the cooling fluid directed through the condenser 110, 128, 146 or the heat exchanger. As will be appreciated, the inlet and/or outlet temperature of the evaporator 112, 130, 148, 254 and the inlet and/or outlet temperature of the condenser 110, 128, 146 or heat exchanger may be measured or detected by one of the sensors 210 described above.

[0063] As noted above, in some embodiments, the controller 200 may be configured to operate the vapor compression system 100 or the heat pump system 250 based on temperature conditions. For example, the difference between the inlet and/or outlet temperature of the evaporator 112, 130, 148 and the inlet and/or outlet temperature of the condenser 110, 128, 146 may correspond to the expected lift of the respective vapor compression circuit 102, 104, 106. Similarly, the difference between the inlet and/or outlet temperature of the evaporator 254 and the inlet and/or outlet temperature of the heat exchanger of the cascade system associated with the heat pump system 250 may correspond to the expected lift of the heat pump system 250 (e.g., expected lift of the vapor compression circuit 252). Accordingly, the present techniques discussed herein utilize the difference between the inlet and/or outlet temperature of the evaporator 112, 130, 148, 254 and the inlet and/or outlet temperature of the condenser 110, 128, 146 or heat exchanger to coordinate startup of the vapor compression system 100 or the heat pump system 250, as described in greater detail below. It should be noted that at startup, the inlet temperature of the evaporator 112, 130, 148, 254 may be substantially similar (e.g., within 1%) to the outlet temperature of the evaporator 112, 130, 148, 254 and the inlet temperature of the condenser 110, 128, 146 or heat exchanger of the cascade system may be substantially similar (e.g., within 1%) to the outlet temperature of the condenser 110, 128, 146 or heat exchanger of the cascade system. Thus, in certain embodiments, the controller 200 may be configured to utilize either the inlet or outlet temperature of the evaporator 112, 130, 148, 254 and either the inlet or outlet temperature of the condenser 110, 128, 146 or the heat exchanger of the cascade system to perform the techniques discussed herein.

[0064] Additionally, in certain embodiments, the controller 200 may be configured to utilize pressure values in combination with or in lieu of the temperature values obtained from the sensors 210. For example, in certain embodiments, inlet and/or outlet temperatures of a condenser may not be attainable (e g., embodiments in which the heat pump system 250 is not associated with a cascade system, embodiments in which the sensors 210 associated with the inlet and/or outlet of the condenser 110, 128, 146 or heat exchanger of the cascade system are inoperable). Accordingly, the controller 200 may be configured to utilize pressure values at the suction inlet and discharge outlet of the compressors 108, 126, 144, 256, 258 to determine the expected lift. That is, the pressure ratio between the suction inlet and discharge outlet (e.g., process side) of a particular compressor 108, 126, 144, 256, 258 may be utilized to determine the expected lift of the corresponding compressor. In certain embodiments, the sensor 210 associated with the isolation valve 282 in the heat pump system 250 may be configured to collect data indicative of the discharge pressure (e.g., process side pressure) of the compressors 256, 258. Additionally, in certain embodiments, the controller 200 may utilize temperature values (e.g., inlet and/or outlet temperature of the evaporator 112, 130, 148, 254) to calculate a saturated discharge temperature of the evaporator 112, 130, 148, 254, which may be used to calculate an expected pressure at the suction inlet of the compressor 108, 126, 144, 256, 258. In turn, the pressure value of the discharge side (e.g., process side) of the compressor 108, 126, 144, 256, 258 may be compared to the expected pressure at the suction inlet of the compressor 108, 126, 144, 256, 258 to establish a pressure ratio between the suction inlet and the discharge outlet of the compressor 108, 126, 144, 256, 258. The pressure ratio may then be used to determine the expected lift of the compressor 108, 126, 144, 256, 258.

[0065] In the illustrated embodiment, the method 600 begins with the vapor compression system 100 or the heat pump system 250 (e.g., the controller 200) receiving a signal to initiate startup of the vapor compression system 100 or the heat pump system 250, as indicated by block 602. For example, the vapor compression system 100 or the heat pump system 250 may receive the signal based on user input, based on a change in environmental conditions, based on a call for conditioning, and/or any other suitable input. During normal startup, in some instances, the controller 200 may be configured to initiate operation of each of the vapor compression circuits 102, 104, 106 or the vapor compression circuit 252 at a reduced capacity to satisfy the load demands of the vapor compression system 100 or the heat pump system 250 while facilitating more efficient operation. For example, the VSDs 124, 142, 160, 270, 278 associated with the compressors 108, 126, 144, 256, 258, respectively, may be configured to operate at a reduced speed (e.g., 10% of an upper speed limit), and the positions of the PRVs 118, 136, 154, 264, 272 and/or the VGDs 120, 138, 156, 266, 274 may be associated with a reduced flow rate (e.g., 10% PRV open, 10% VGD open) through the compressors 108, 126, 144, 256, 258. During operation, as the load demand increases, the controller 200 may progressively increase the speed of the VSDs 124, 142, 160, 270, 278 and/or adjust the position of the PRVs 118, 136, 154, 264, 272 and/or the VGDs 120, 138, 156, 266, 274 towards an open position (e.g., fully open position) to increase the capacity of the vapor compression system 100 or the heat pump system 250.

[0066] At block 604, the controller 200 may determine the expected lift of each of the vapor compression circuits 102, 104, 106, 252 based on the starting operating conditions of the vapor compression system 100 or the heat pump system 250. For example, the controller 200 may receive signals from the sensors 210 indicative of the inlet and/or outlet temperature of the evaporator 112, 130, 148, 254 and the inlet and/or outlet temperature of the condenser 110, 128, 146 or the heat exchanger of the cascade system associated with the heat pump system 250. As noted above, the difference between the inlet and/or outlet temperature of the evaporator 112, 130, 148, and the inlet and/or outlet temperature of the condenser 110, 128, 146 within each vapor compression circuit 102, 104, 106, may correspond to the lift (e.g., demanded lift) that each compressor 108, 126, 144, is expected to achieve based on the conditioning fluid and cooling fluid temperatures. Similarly, the difference between the inlet and/or outlet temperature of the evaporator 254 and the inlet and/or outlet temperature of the heat exchanger of the cascade system associated with the heat pump system 250 may correspond to the lift (e.g., demanded lift) that the compressor 256, 258 is expected to achieve based on the conditioning fluid and cooling fluid temperatures. Additionally, as noted above, pressure values between the suction inlet and the discharge outlet of the compressor 108, 126, 144, 256, 258 may be utilized in combination with or in lieu of the temperature values to determine the expected lift.

[0067] Based on the operating conditions prior to startup of the vapor compression system 100 or the heat pump system 250, the controller 200 may determine that the expected lift at startup of one or more of the compressors 108, 126, 144, 256, 258 may cause the compressor 108, 126, 144, 256, 258 to experience surge conditions. For example, at block 606, the controller 200 may compare the expected lift (e.g., difference between an inlet and/or outlet temperature of an evaporator and inlet and/or outlet temperature of a condenser in a corresponding vapor compression circuit) to a threshold value (e g., upper limit of lift). As noted above, at startup, each of the vapor compression circuits 102, 104, 106, 252 may be configured to operate at a reduced capacity. Thus, the threshold value may correspond to an upper limit of lift that each compressor 108, 126, 144, 256, 258 is capable of achieving when operating at the reduced capacity at startup (e.g., with VSD operating at 10% of an upper frequency limit, position of PRV and/or VGD 10% open) without experiencing surge conditions. In other words, the threshold value may be based on expected or desired positions of the PRVs 118, 136, 154, 264, 272 and/or the VGDs 120, 138, 156, 266, 274 and/or expected or desired speeds of the VSDs 124, 142, 160, 270, 278. In some embodiments, each of the compressors 108, 126, 144, 256, 258 may be associated with a different threshold value based on the physical and/or structural characteristics (e.g., manufacturing specifications) of the respective compressor 108, 126, 144, 256, 258, and/or a position of the vapor compression circuits 102, 104, 106, 252 relative to one another. Further, it should be noted that the threshold value may be selected from a plurality of threshold values that are empirically determined based on various data (e.g., empirical data), including but not limited to values for any of the parameters discussed above (e.g., cooling fluid temperatures, conditioning fluid temperatures). The threshold value may be selected based on a desired safety factor and/or acceptable potential for surge.

[0068J Based on a determination (e.g., via the controller 200) that the expected lift of one or more of compressors 108, 126, 144, 256, 258 does not exceed (e.g., is equal to or less than) the corresponding threshold value (e.g., upper limit of lift) associated with the compressor 108, 126, 144, 256, 258, the method 600 may proceed to block 608, and the controller 200 may initiate operation of the vapor compression system 100 or the heat pump system 250 (e.g., the vapor compression circuit 102, 104, 106 having the compressor 108, 126, 144 for which the expected lift does not exceed the threshold value, the vapor compression circuit 252 having the compressor 256, 258 for which the expected lift does not exceed the threshold value).

[0069] Based on a determination (e.g., via the controller 200) that the expected lift of one of the compressors 108, 126, 144, 256, 258 does exceed the corresponding threshold value associated with the compressor 108, 126, 144, 256, 258, the method 600 may proceed to block 610, and the controller 200 may block operation of the vapor compression system 100 or the heat pump system (e.g., the vapor compression circuit 102, 104, 106 having the compressor 108, 126, 144 for which the expected lift exceeds the threshold value, the vapor compression circuit 252 having the compressor 256, 258 for which the expected lift exceeds the threshold value).

[0070] Additionally, based on a determination that the expected lift of the compressor 108, 126, 144, 256, 258 exceeds the threshold value, at block 612, the controller 200 may output (e.g., send) a notification to a user indicating that one or more of the compressors 108, 126, 144, 256, 258 of the vapor compression system 100 or the heat pump system 250 is susceptible to surging if the corresponding compressor 108, 126, 144, 256, 258 and/or vapor compression system 100 or heat pump system 250 is started in the existing conditions. In some embodiments, the notification may be displayed on the interface 202 of the controller 200 and may include an alert or warning message notifying the user of the potential for surge if operation of the vapor compression system 100 or heat pump system 250 is started. The notification may additionally or alternatively be sent to a computing device associated with the user to inform the user of the potential for surge In some embodiments, the notification may include a recommendation for enabling a decrease in the expected lift for one or more of the compressors 108, 126, 144, 256, 258. For example, the recommendation may include a suggestion to increase the conditioning fluid temperature (e.g., directed through the evaporators 112, 130, 148, 254) and/or decrease the cooling fluid temperature (e.g., directed through the condensers 110, 128, 146) in one or more of the vapor compression circuits 102, 104, 106, 252. In this way, the expected lift (e.g., difference between inlet and/or outlet temperature of a respective evaporator and inlet and/or outlet temperature of a respective condenser or heat exchanger) may be decreased. The controller 200 may continue to compare the expected lift (e.g., based on additional or updated values of detected operating parameters) to the threshold value, and upon satisfying the threshold value, the controller 200 may initiate operation of the vapor compression system 100 or the heat pump system 250.

[0071] FIG. 8 is a flow chart of an embodiment of a method 700 for controlling operation (e.g., controlling startup) of the vapor compression system 100 or the heat pump system 250. That is, the method 700 may be utilized to coordinate startup of the vapor compression system 100 or the heat pump system 250. For example, the controller 200 may be configured to implement and/or execute the method 700 to control various components of the vapor compression system 100 or the heat pump system 250. In other embodiments, the method 700 may be implemented by another controller (e g., a dedicated controller of the vapor compression system 100, dedicated controller of the heat pump system 250), more than one controller, or other suitable control system. It should also be noted that additional steps may be performed with respect to the method 700. Moreover, certain steps of the depicted method 700 may be removed, modified, and/or performed in a different order.

[0072] The method 700 may be implemented to block startup of the vapor compression system

100 or the heat pump system 250 based on a determination that detected starting conditions of the vapor compression system 100 or the heat pump system 250 may result in surging in one or more of the compressors 108, 126, 144, 256, 258 (e.g., may result in an unacceptable risk of surge). Thus, similar to the blocks 602 and 604 of the method 600, at blocks 702 and 704, the controller 200 may receive a signal to initiate startup of the vapor compression system 100 or the heat pump system 250 and may determine the expected lift of each of the compressors 108, 126, 144, 256, 258 based on the starting conditions.

[0073] Utilizing the expected lift determined in block 704, the method may proceed to block 706 and determine a lower limit of frequency (e.g., lower frequency set point, Hzmin) to apply via the VSDs 124, 142, 160, 270, 278 to achieve the expected lift. That is, in some embodiments, the controller 200 may control the VSDs 124, 142, 160, 270, 278 to adjust the frequency of electrical power supplied to the motors 122, 140, 158, 268, 276 of the compressors 108, 126, 144, 256, 258, respectively, without reducing the frequency below a lower frequency set point in order to avoid occurrence of a surge condition in one or more of the compressors 108, 126, 144, 256, 258. Accordingly, the lower frequency set point may be determined based on characteristics and/or starting operating parameters of the vapor compression circuits 102, 104, 106, 252. The lower frequency limit for each compressor 108, 126, 144, 256, 258 may be calculated according to techniques described in EP2751430, which is hereby incorporated by reference in its entirety, and may be indicative of respective rotational speeds (e.g., lower speed limit) at which the compressors 108, 126, 144, 256, 258 may operate while avoiding or substantially avoiding surge conditions. Indeed, the lower frequency limit may be calculated based on expected or desired positions of the PRVs 118, 136, 154, 264, 272 and/or the VGDs 120, 138, 156, 266, 274, temperatures of the cooling fluid and/or conditioning fluid directed through the vapor compression circuit 102, 104, 106, 252, and so forth. It should be noted that the following discussion is described in the context of the vapor compression system 100 or the heat pump system 250 receiving electrical power with a frequency of 50Hz from a power source (e.g., utility grid, power grid). However, it should be appreciated that the vapor compression system 100 or the heat pump system 250 may receive electrical power from a power source at any suitable frequency (e.g., 48Hz, 60Hz).

[0074] At block 708, the controller 200 may compare the lower frequency set point for each compressor 108, 126, 144, 256, 258 to a threshold value to determine whether initiating operation of the vapor compression system 100 or the heat pump system 250 may result in the occurrence of surge conditions in one or more of the compressors 108, 126, 144, 256, 258. In some embodiments, the threshold value may correspond to an upper limit frequency (e.g., 50Hz) of a power source that supplies power to the VSDs 124, 142, 160, 270, 278 associated with each compressor 108, 126, 144, 256, 258, respectively. However, it should be noted that in some embodiments, the threshold value may be adjusted (e.g., multiplied) by a ratio value (e g., safety factor value, constant) to reduce a likelihood of occurrence of surge conditions. In some embodiments, the ratio value may be 0.96 or another suitable value. Accordingly, while the power source configured to supply power to the VSDs 124, 142, 160, 270, 278 may operate at 50Hz, the threshold value (e.g., based on the supplied power and the ratio value) may be set at 48Hz to limit the potential for surge conditions.

[0075] Based on a determination (e.g., via the controller 200) that the determined lower frequency set point for each of the compressors 108, 126, 144, 256, 258 does not exceed the threshold value, the method 700 may proceed to block 710, and the controller 200 may initiate operation of the vapor compression system 100 or the heat pump system 250 (e.g., the vapor compression circuit 102, 104, 106 having the compressor 108, 126, 144 for which the determined lower frequency set point does not exceed the threshold value, the vapor compression circuit having the compressor 256, 258 for which the determined lower frequency set point does not exceed the threshold value).

[0076] Based on a determination (e.g., via the controller 200) that the determined lower frequency set point (e.g., calculated based on detected operating conditions and/or calculated expected lift) does exceed the threshold value, the method 700 may proceed to block 712 and block operation (e.g., stay startup) of the vapor compression system 100 or the heat pump system 250 (e g , the vapor compression circuit 102, 104, 106 having the compressor 108, 126, 144 for which the determined lower frequency set point exceeds the threshold value, the vapor compression circuit having the compressor 256, 258 for which the determined lower frequency exceeds the threshold value).

[0077] At block 714, the controller 200 may determine an amount of adjustment to one or more operating parameters of the vapor compression system 100 or the heat pump system 250 that may enable operation of the vapor compression system 100 or the heat pump system 250. For example, increasing the conditioning fluid temperature at the evaporator 112, 130, 148, 254 and/or decreasing the cooling fluid temperature at the condenser 110, 128, 146 or the heat exchanger of the cascade system associated with the heat pump system 250 may decrease the expected lift that a respective compressor is expected to achieve. As the expected lift decreases, the lower limit frequency that may achieve the expected lift may also decrease. Thus, upon determining that the lower frequency set point exceeds the threshold value, the controller 200 may be configured to determine an amount by which the expected lift of one or more of the compressors 108, 126, 144, 256, 258 should decrease (e g., by increasing the temperature of the conditioning fluid in the evaporator 112, 130, 148, 254 and/or decreasing the temperature of the cooling fluid in the condenser 110, 128, 146 or the heat exchanger of the cascade system associated with the heat pump system 250).

[0078] For example, based on detected operating conditions (e.g., prior to startup of the vapor compression system 100), the controller 200 may determine that the lower frequency set point of the compressor 108 is 55Hz (which exceeds a threshold value of 50Hz or 48Hz, for example). Using Equation (1) below, the controller 200 may determine an amount of adjustment to apply to the expected lift to enable startup of the vapor compression system 100. percentage adjustment to expected lift = (1 - (Threshold value/Hzmin)) * 100 (1)

Thus, using the example above, upon determining that the expected lift of the compressor 108 corresponds to a lower frequency set point (e g., Hzmin) of 55Hz, the controller 200 may divide the threshold value (e.g., 48Hz) by the lower frequency set point to yield a ratio of 0.87. The ratio value may then be subtracted from 1 and multiplied by 100 to determine the amount of adjustment needed to apply to the expected lift (e g., 13 percent). [0079] Similar to block 612 of the method 600, at block 716, the controller 200 may output a notification to a user indicating that one or more of the compressors 108, 126, 144, 256, 258 of the vapor compression system 100 or the heat pump system 250 is susceptible to surging if started in the current conditions. In some embodiments, the notification may be displayed on the interface 202 of the controller 200 and may include an alert or warning message notifying the user of the potential for surge. Further, the notification may include an indication of an amount of adjustment to apply to the calculated expected lift of one of the compressors 108, 126, 144, 256, 258 to enable operation of the vapor compression system 100 or the heat pump system 250. That is, using the example above, the notification may include an indication to reduce the expected lift of the first vapor compression circuit 102 by 13 percent (e.g., (1- (48Hz/55Hz) * 100). As noted above, in certain embodiments, the expected lift of the compressor 108, 126, 144 may be determined based on the difference between the inlet and/or outlet temperature of conditioning fluid at the evaporator 112, 130, 148, and the inlet and/or outlet temperature of cooling fluid at the condenser 110, 128, 146 of a respective vapor compression circuit 102, 104, 106, while the expected lift of the compressor 256, 258 may be determined based on the difference between the inlet and/or outlet temperature of the conditioning fluid 280 at the evaporator 254, and the inlet and/or outlet temperature of cooling fluid at the heat exchanger of the cascade system associated with the heat pump system 250. Alternatively, the expected lift may be determined based on a pressure ratio between the suction pressure of the compressor 108, 126, 144, 256, 258 and the discharge pressure of the compressor 108, 126, 144, 256, 258. Additionally, in certain embodiments, the inlet and/or outlet temperature of the evaporator 112, 130, 148, 254 may be utilized to determine an expected suction pressure of the compressor 108, 126, 144, 256, 258, which may be compared to the discharge pressure of the compressor 108, 126, 144, 256, 258 to determine the pressure ratio, thereby enabling a determination of the expected lift of the compressor 108, 126, 144, 256, 258.

[0080] Accordingly, the notification may include a recommendation to increase the conditioning fluid temperature at the evaporator 112, 130, 148, 254, decrease the cooling fluid temperature at the condenser 110, 128, 146 of one of the vapor compression circuits 102, 104, 106, and/or decrease the conditioning fluid temperature of the heat exchanger of the cascade system associated with the heat pump system 250 in order to adjust (e.g., reduce) the expected lift of the corresponding compressor 108, 126, 144, 256, 258, thereby enabling the compressor 108, 126, 144, 256, 258 to start with reduced potential for surge.

[0081] As the expected lift is reduced (e.g., by increasing cooling fluid temperature and/or decreasing conditioning fluid inlet temperature), the controller 200 may continually monitor the lower frequency set point of each compressor 108, 126, 144, 256, 258 based on the expected lift as determined based on the starting conditions. Upon determining that the lower frequency set point associated with each compressor 108, 126, 144, 256, 258 is below the threshold value, the method 700 may proceed to block 710 and the controller 200 may initiate operation of the vapor compression system 100 or the heat pump system 250.

[0082] The present disclosure may provide one or more technical effects useful in the operation of an HVAC&R system. For example, the HVAC&R system may include a vapor compression system having multiple vapor compression circuits (e.g., vapor compression stages) in a series counterflow arrangement, a heat pump system having an open loop vapor compression circuit, and/or a vapor compression system having a single vapor compression circuit. In certain embodiments, the vapor compression system and/or heat pump system may have multiple compressors, each configured to operate with a VSD, and the vapor compression system and/or heat pump system may be configured to control each of the VSDs to operate the compressors at variable speeds based on demands of the vapor compression system or the heat pump system. Further, the vapor compression system and heat pump system discussed herein may include flow reduction devices configured to further control the operating parameters of the compressors. The vapor compression system or heat pump system may utilize various methods to control the FRDs and the speed of the variable speed compressor based on calculated parameters and/or feedback provided by sensors of the vapor compression system or heat pump system. By monitoring the operating conditions of the vapor compression system and/or heat pump system, head values (e.g., lift values) for each compressor may be determined, which may be used to limit operation (e.g., limit startup) of the vapor compression system or heat pump system during surge conditions. If the expected lift (e.g., head) based on the operating conditions of the vapor compression system or heat pump system exceeds specified threshold values, then a notification may be sent to inform a user that the system is susceptible to surge. Further, the notification may include a recommendation to adjust one or more operating parameters of the vapor compression system or heat pump system to enable operation of the vapor compression system or the heat pump system. Further still, the expected head value may be used to determine a lower frequency limit for each of the compressors in the vapor compression system or heat pump system, and the lower frequency limit may also be compared to threshold values to determine whether the system is susceptible to surge. In this way, an amount of adjustment to one or more operating parameters of the vapor compression system or heat pump system may be calculated and sent to the user to enable operation of the vapor compression system or heat pump system. The techniques discussed herein enable more efficient operation (e.g., increased isentropic efficiency) of the vapor compression system or heat pump system by limiting operating of the vapor compression system or heat pump system when the operating conditions are indicative of potential surge conditions. In doing so, operation, maintenance, and longevity of the vapor compression system or heat pump system may be improved. The technical effects and technical problems in the specification are examples and are not limiting. It should be noted that the embodiments described in the specification may have other technical effect and can solve other problems.

[0083] 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.

[0084] 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.

[0085] 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).