System and method for determining the startup pressure ratio of a dynamic compressor

Abstract

A controller of a system having an evaporator, a condenser, and a dynamic compressor includes a processor and a memory. The memory stores instructions that cause the processor to determine a first heat transfer fluid temperature in a first heat transfer fluid path of the evaporator, determine a first pressure in a first working fluid path based on the first heat transfer fluid temperature, determine a second heat transfer fluid temperature in a second heat transfer fluid path of the condenser, determine a second pressure in a second working fluid path based on the second heat transfer fluid temperature, calculate a pressure ratio of the compressor from the first pressure and the second pressure, determine a speed setpoint of the compressor based on the pressure ratio, and operate the compressor at the speed setpoint to compress the working fluid until conditions are met.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority to U.S. Patent Application No. 17 / 804,317, filed on May 27, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] The field of the present disclosure generally relates to control systems, and more specifically to control systems for dynamic compressors.

Background Art

[0003] Dynamic compressors, including centrifugal compressors, are commonly used in process industries, heating, ventilation, and air conditioning (HVAC) systems. The compressor is operably connected to a motor via a shaft that supports one or more compression stages. The motor rotates the compression stages via the shaft at a selected rotational speed and load condition to compress the refrigerant to a specified demand. The motor speed and load can be controlled to operate the compressor under a wide range of operating conditions. The operating range of the compressor is limited by the surge region at low flow rates and the choke region at high flow rates. Knowing the exact operating point of the system can help avoid the compressor operating in surge or choke and minimize the duration of the compressor startup routine.

[0004] The operating point of a dynamic compressor is partially determined by the speed of the compressor that the user can control and by the overall pressure ratio of the compressor, which is a function of the compressor speed and load conditions. However, it is difficult to accurately measure the pressure ratio of a dynamic compressor before the startup routine because a discharge check valve downstream of the dynamic compressor prevents high - pressure refrigerant from flowing from the condenser to the compressor pressure sensor being measured. Thus, there is a need for a system and method for determining the overall pressure ratio of a dynamic compressor at startup without using pressure measurement.

[0005] This section is intended to introduce the reader to various aspects of technologies that may be relevant to the various aspects of the present disclosure described below and / or claimed. This discussion is believed to be useful in providing the reader with background information to better understand the various aspects of the present disclosure. Accordingly, it should be understood that these descriptions are to be read from this perspective and are not to be taken as an admission of prior art.

Summary of the Invention

[0006] One aspect of the present disclosure relates to a system including an evaporator, a condenser, and a dynamic compressor operable to compress a working fluid. The evaporator includes a first working fluid path and a first heat transfer fluid path thermally coupled to the first working fluid path. The condenser includes a second working fluid path and a second heat transfer fluid path thermally coupled to the second working fluid path. The dynamic compressor is fluidly coupled to the first working fluid path of the evaporator and the second working fluid path of the condenser. The system further includes a first temperature sensor positioned within the first heat transfer fluid path of the evaporator and a second temperature sensor positioned within the second heat transfer fluid path of the condenser. The system further includes a controller including a processor and a memory connected to the dynamic compressor. The memory stores instructions for causing the processor to receive a command to initiate operation of the compressor, receive a first heat transfer fluid temperature from the first temperature sensor, determine a first pressure in the first working fluid path of the evaporator based on the first heat transfer fluid temperature, receive a second heat transfer fluid temperature from the second temperature sensor, determine a second pressure in the second working fluid path of the condenser based on the second heat transfer fluid temperature, determine a pressure ratio of the dynamic compressor from the first pressure and the second pressure, determine a speed setpoint of the dynamic compressor based on the pressure ratio, and operate the dynamic compressor at the speed setpoint to compress the working fluid until conditions are met.

[0007] Another aspect of the present disclosure relates to a controller for a system including an evaporator, a condenser, and a dynamic compressor fluidly coupled between the evaporator and the condenser. The controller includes a processor and a memory. The memory stores instructions for causing the processor to receive a command to start operation of the dynamic compressor, determine a first heat transfer fluid temperature in a first heat transfer fluid path of the evaporator, determine a first pressure in a first working fluid path of the evaporator based on the first heat transfer fluid temperature, determine a second heat transfer fluid temperature in a second heat transfer fluid path of the condenser, determine a second pressure in a second working fluid path of the condenser based on the second heat transfer fluid temperature, calculate a pressure ratio of the dynamic compressor from the first pressure and the second pressure, determine a speed setpoint of the dynamic compressor based on the pressure ratio, and operate the dynamic compressor at the speed setpoint to compress the working fluid until conditions are met.

[0008] The features described in connection with the above aspect of the present disclosure have various improvements. Further features may be incorporated into the above aspect of the present disclosure. These improvements and additional features can exist individually or in any combination. For example, the various features discussed below in connection with any of the illustrated embodiments of the present disclosure can be incorporated into any of the above aspects of the present disclosure, either alone or in any combination.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

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Figure 8B

DETAILED DESCRIPTION OF THE INVENTION

[0010] For the sake of brevity, an example regarding a centrifugal compressor will be described. However, the methods and systems described herein can be applied to any suitable dynamic compressor. The operation of a dynamic compressor can be improved by limiting the time the compressor spends outside the safe operating range during the startup routine. The startup pressure ratio of the compressor represents the pressure rise between the inlet and the outlet of the compressor and can be estimated using temperature measurements from other cycle components. Next, the estimated pressure ratio can be used to determine a speed setpoint within the safe operating range of the compressor.

[0011] Referring to FIG. 1, a two-stage refrigerant compressor is generally indicated at 100. The dynamic compressor 100 is operable to compress a working fluid (e.g., refrigerant) and includes a compressor housing 102 that forms at least one sealed cavity in which refrigerant compression for each stage is carried out. The dynamic compressor 100 includes a first refrigerant inlet 110 for introducing refrigerant vapor into a first compressor stage (not labeled in FIG. 1), a first refrigerant outlet 114, a refrigerant transfer conduit 112 for transferring compressed refrigerant from the first compressor stage to a second compressor stage (not labeled in FIG. 1), a second refrigerant inlet 118 for introducing refrigerant vapor into the second compressor stage, and a second refrigerant outlet 120. The refrigerant transfer conduit 112 is operably connected at opposite ends to the first refrigerant outlet 114 and the second refrigerant inlet 118, respectively. The second refrigerant outlet 120 sends the compressed refrigerant from the second compressor stage to a cooling system in which the compressor 100 is incorporated (FIG. 3).

[0012] Referring to FIG. 2, the compressor housing 102 surrounds a first compressor stage 124 and a second compressor stage 126 at opposite ends of the compressor 100. The first compressor stage 124 includes a first compression mechanism 106 configured to add kinetic energy to the refrigerant flowing in through the first refrigerant inlet 110. In some embodiments, the first compression mechanism 106 is an impeller. The kinetic energy imparted by the first compression mechanism 106 to the refrigerant is converted into an increase in refrigerant pressure as the refrigerant velocity slows when transferred to a sealed cavity (e.g., diffuser) formed within the volute 132. The first compressor stage 124 further includes a first variable inlet guide vane (VIGV) 134 disposed upstream of the first compression mechanism 106 at the first refrigerant inlet 110. The first VIGV 134 includes a plurality of vanes whose positions can be controlled to introduce pre-whirl into the gaseous refrigerant entering the first refrigerant inlet 110.

[0013] Similarly, the second compressor stage 126 includes a second compression mechanism 116 configured to add kinetic energy to the refrigerant transferred from the first compressor stage 124 and flowing in through the second refrigerant inlet 118. In some embodiments, the second compression mechanism 116 is an impeller. The kinetic energy imparted by the second compression mechanism 116 to the refrigerant is converted into an increase in refrigerant pressure as the velocity of the refrigerant slows as it moves into a sealed cavity (e.g., a diffuser) formed within the volute 132. The compressed refrigerant is discharged from the second compressor stage 126 via a second refrigerant outlet 120 (not shown in FIG. 2). The second compressor stage 126 further includes a second variable inlet guide vane (VIGV) 136 disposed upstream of the second compression mechanism 116 at the second refrigerant inlet 118. The second VIGV 136 includes a plurality of vanes whose positions can be controlled to introduce pre-rotation into the gaseous refrigerant entering the second refrigerant inlet 118.

[0014] The first compression mechanism 106 and the second compression mechanism 116 are connected to opposite ends of the shaft 104. The shaft 104 is operably connected to a motor 108 positioned between the first compression mechanism 106 and the second compression mechanism 116, and the first compression mechanism 106 and the second compression mechanism 116 rotate at a selected rotational speed to compress the refrigerant exiting the second refrigerant outlet 120 (not shown in FIG. 2) to a predetermined pressure. The compressor 100 can incorporate any suitable motor, including but not limited to an electric motor.

[0015] FIG. 3 is a schematic diagram of a first example of an HVAC system 300 to which the dynamic compressor 100 of FIGS. 1 and 2 can be attached. The system 300 has a single closed refrigerant loop that includes a compressor 100, a condenser 320, a first expansion device 330, and an evaporator 340. Refrigerant enters the dynamic compressor 100 from a first refrigerant inlet 110 as a low-pressure, low-temperature gas. The dynamic compressor 100 adds kinetic energy to the refrigerant and converts it into a pressure increase, and the refrigerant exits the dynamic compressor 100 from a second refrigerant outlet 120 as a high-pressure, high-temperature gas. The dynamic compressor 100 may include at least one inlet pressure sensor 111 disposed near the first refrigerant inlet 110 to measure the refrigerant pressure upstream of the dynamic compressor 100, and at least one outlet pressure sensor 121 disposed near the second refrigerant outlet 120 to measure the refrigerant pressure downstream of the dynamic compressor 100.

[0016] Next, the refrigerant enters a second working fluid path 322 of the condenser 320 that is fluidly coupled to a second compressor stage 126 downstream of the condenser 320. The condenser 320 further includes a second heat transfer fluid path 324 that is thermally coupled to the second working fluid path 322. The second heat transfer fluid path 324 is configured such that a heat transfer fluid flows through the second heat transfer fluid path 324 and may form part of a secondary fluid loop (not shown). The heat transfer fluid may be water, glycol, refrigerant, air, or any suitable heat transfer fluid that enables the HVAC system 300 to function as described herein. By the second working fluid path 322 and the second heat transfer fluid path 324, the condenser 320 functions as a heat exchanger, and the heat transfer fluid absorbs heat from the refrigerant and converts the refrigerant gas into a high-pressure high-temperature liquid. Next, the heat transfer fluid may release the heat to an external space (not shown).

[0017] The second working fluid path 322 of the condenser 320 is fluidly coupled to a first expansion device 330 that reduces the pressure of the refrigerant. In some embodiments, the pressure is reduced until the current temperature of the liquid refrigerant reaches the boiling point temperature at that pressure, and when a portion of the liquid refrigerant boils and turns to gas, the refrigerant becomes a two-phase mixture. The first expansion device 330 may be a fixed orifice, a thermal expansion valve, an electronic expansion valve, or any type of expansion device that allows the HVAC system 300 to function as described herein.

[0018] The first expansion device 330 is fluidly coupled to a first working fluid path 342 of an evaporator 340 that receives a low-pressure, low-temperature liquid refrigerant or a two-phase mixture of liquid and gaseous refrigerant at the inlet of the evaporator 340. The evaporator 340 further includes a first heat transfer fluid path 344 that is thermally coupled to the first working fluid path 342. The first heat transfer fluid path 344 is configured to allow a heat transfer fluid to pass through the first heat transfer fluid path 344 and may form part of a tertiary fluid loop (not shown). The heat transfer fluid may be water, glycol, refrigerant, or any suitable heat transfer fluid that allows the HVAC system 300 to function as described herein. By the first working fluid path 342 and the first heat transfer fluid path 344, the evaporator 340 functions as a heat exchanger. The heat transfer fluid in the first heat transfer fluid path 344 may absorb heat from a conditioned interior space or an additional fluid loop (not shown). The refrigerant in the first working fluid path 342 absorbs heat from the first heat transfer fluid path 344 and undergoes a phase change from liquid to gas. The first working fluid path 342 of the evaporator 340 is fluidly coupled to a first refrigerant inlet 110 upstream of the first working fluid path 342, and the cycle starts again.

[0019] System 300 includes a first temperature sensor 360 positioned within a first heat transfer fluid path 344 of evaporator 340. In the embodiment shown in FIG. 3, the first temperature sensor 360 is positioned near the outlet of the first heat transfer fluid path 344 of evaporator 340, although the first temperature sensor 360 can be positioned at any suitable location upstream, such as, but not limited to, near the inlet of the first heat transfer fluid path 344 of evaporator 340, or within the first heat transfer fluid path 344 itself. System 300 further includes a second temperature sensor 380 positioned within a second heat transfer fluid path 324 of condenser 320. In the embodiment shown in FIG. 3, the second temperature sensor 380 is positioned near the outlet of the second heat transfer fluid path 324 of condenser 320, although the second temperature sensor 380 can be positioned at any suitable location, such as, but not limited to, near the inlet of the second heat transfer fluid path 324 of condenser 320, or within the second heat transfer fluid path 324 itself. The first temperature sensor 360 and the second temperature sensor 380 may be a thermocouple, a thermistor, a resistance temperature detector (RTD), or any other suitable type of temperature sensor.

[0020] FIG. 4 shows an exemplary embodiment of a system 300 that includes a dynamic compressor 100. The compressor 100 includes a compressor housing 102, at least one compression mechanism 106, 116, a motor 108, a speed sensor 317, pressure sensors 111, 121, and a controller 410. In this embodiment, the dynamic compressor 100 is a two-stage centrifugal compressor, and the compression mechanisms include a first compression mechanism 106 and a second compression mechanism 116, and each mechanism may be an impeller. In other embodiments, the dynamic compressor 100 is an axial flow compressor, and the first compression mechanism 106 and the second compression mechanism 116 may each be an axial flow rotor. The speed sensor 317 measures the rotational speed of the dynamic compressor 100, and the pressure sensors 111, 121 measure the pressures at the first refrigerant inlet 110 and the second refrigerant outlet 120, respectively, as shown in FIG. 3. The dynamic compressor 100 may include additional pressure sensors for measuring pressures at various points along the compressor flow path. Additional sensors may be attached to the compressor 100 to provide data regarding its operation, and the additional sensors include, but are not limited to, temperature sensors, flow rate sensors, current sensors, voltage sensors, rotational speed sensors, and other suitable sensors. The dynamic compressor 100 is not limited to a specific configuration within the system 300 and may be configured similarly to or differently from the dynamic compressor 100 described with respect to FIGS. 1 and 2. The system 300 further includes an unloader device 301, a variable frequency drive (VFD) 316, and a user interface 315.

[0021] The controller 410 is operably connected to the dynamic compressor 100 and controls its operation, at least in part, based on the above-mentioned measurement parameters. The controller 410 includes a processor 420 and a memory 430. The memory 430 stores a map 700 (see FIG. 7) of a plurality of predetermined operating points 50 of the dynamic compressor 100. This map can be stored in any suitable data structure such as a table or a matrix. The memory 430 further stores instructions for programming the processor 420 to determine the startup pressure ratio PR of the dynamic compressor 100. The map 700 of the predetermined operating points 50 and the method 600 for determining the startup pressure ratio PR of the dynamic compressor 100 will be described in more detail below.

[0022] The system 300 includes an interface for connecting the controller 410 to the VFD 316 and a motor interface 313 for connecting the VFD 316 to the motor 108. In certain embodiments, the VFD 316 operates under the control of the controller 410. In further embodiments, the VFD 316 is part of the controller 410. The system 300 further includes an unloading interface 314 for connecting the controller 410 to the unloading device 301.

[0023] The controller 410 is operably coupled to the unloading device 301 via the unloading interface 314, and the unloading interface 314 removes and / or reduces the load of the dynamic compressor 100 during startup and shutdown routines, during detected surge events, and when instructed by the controller 410. In an exemplary embodiment, the unloading device 301 is a variable inlet guide vane (VIGV) at the inlet of each impeller stage (FIG. 2). In other embodiments, the unloading device 301 may be a variable diffuser or a bypass valve. The controller 410 is configured to control at least one operating parameter of the unloading device 301, such as the position of each VIGV.

[0024] System 300 further includes a user interface 315 configured to output (e.g., display) and / or receive information associated with the system 300 (e.g., from a user). In some embodiments, the user interface 315 is configured to receive activation and / or deactivation inputs from the user to activate and deactivate (i.e., turn on and off) the system 300 or enable the operation of the system 300. Further, in some embodiments, the user interface 315 is configured to output information related to one or more operating characteristics of the system 300, which information includes, for example, warning indicators such as severity alerts, occurrence alerts, fault alerts, motor speed alerts, etc., and other suitable information, but is not limited thereto.

[0025] The user interface 315 can include any suitable input and output devices that enable the user interface 315 to function as described herein. For example, the user interface 315 can include input devices including, but not limited to, a keyboard, mouse, touch screen, joystick, throttle, button, switch, and / or other input devices. Further, the user interface 315 can include output devices including, but not limited to, a display (e.g., a liquid crystal display (LCD) or an organic light emitting diode (OLED) display), speaker, indicator light, meter, and / or other output devices. Further, the user interface 315 can be part of another component such as a system controller (not shown). In other embodiments, the user interface 315 is not included.

[0026] The controller 410 is generally configured to control the operation of the dynamic compressor 100. The controller 410 controls its operation either through programming and instructions from another device or controller, or is integrated with the system 300 through a system controller. In some embodiments, for example, the controller 410 receives user input from the user interface 315 and controls one or more components of the system 300 in response to such user input. For example, the controller 410 can control the motor 108 based on user input received from the user interface 315. In some embodiments, the system 300 can be controlled by a remote control interface. For example, the system 300 can include a communication interface (not shown) configured for connection to a wireless control interface that enables remote control and activation of the system 300. The wireless control interface can be embodied in a portable computing device such as a tablet or smartphone.

[0027] Controller 410 can generally include any suitable computer and / or other processing units, including, for example, computers that are communicatively connected to each other and can operate independently or in connection with each other, and / or any suitable combination such as a processing unit (e.g., Controller 410 can form all or part of a controller network). Controller 410 includes one or more modules or devices, one or more of which are housed within System 300 or located remotely from System 300. Controller 410 may be part of the dynamic compressor 100, may be separate, or may be part of a system controller within the HVAC system. Controller 410 and / or components of Controller 410 may be integrated or incorporated within other components of System 300. Controller 410 includes one or more processors 420 and associated memory devices 430 configured to perform various computer-implemented functions (e.g., the calculations, determinations, and functions disclosed herein).

[0028] As used herein, the term "processor" refers not only to integrated circuits, but also to controllers, microcontrollers, microcomputers, programmable logic controllers (PLCs), application specific integrated circuits, and other programmable circuits. Further, the memory device 430 of the controller 410 generally includes, but is not limited to, computer-readable media (e.g., random access memory (RAM)), computer-readable non-volatile media (e.g., flash memory), floppy disks, compact disk read-only memory (CD-ROM), magneto-optical disks (MOD), digital versatile disks (DVD), and / or other suitable memory elements, or can include memory elements. Such a memory device 430 is generally configured to store appropriate computer-readable instructions that, when implemented by the processor 420, cause the controller 410 to perform various functions described herein, including, but not limited to, control of the system 300, control of the operation of the motor 108, receipt of input from the user interface 315, provision of output to the operator via the user interface 315, control of the unloading device 301, and / or various other suitable computer-implemented functions.

[0029] Referring to FIG. 5, an operating envelope or operating map 500 of an exemplary dynamic centrifugal compressor 100 is shown. The operating map 500 graphically displays the performance of the compressor in terms of flow rate, head, and speed. The operating map 500 shows the head versus inlet mass flow rate at the design point of the dynamic compressor 100 as a percentage of those values. The head is the total pressure ratio of the outlet pressure and the inlet pressure. The inlet mass flow rate is a measure of the amount of working fluid, such as refrigerant, flowing through the compression mechanisms 106, 116. A plurality of compressor speed lines 507 are shown on the operating map 500. In this example, there are five speed lines 507 in the range from 70% to 110% of the design speed, and each line is separated by a 10% difference. In this example, these specific speed lines are shown, but any number of speed lines can be shown at any different percentage of the compressor's design speed for any type of compressor.

[0030] The surge limit line 504 indicates the minimum flow rate before surge occurs in the surge region 506 (i.e., to the left of the surge limit line 504). The surge control line 503 roughly indicates the minimum flow rate at which the compressor 100 can operate safely without the risk of falling into surge. The surge control line 503 is defined by a surge margin 505 from the surge limit line 504. By operating on the right side of the surge control line 503, the dynamic compressor 100 avoids surge. Similarly, the choke line 501 indicates that the dynamic compressor 100 operates at choke flow by operating on its right side.

[0031] The first operating point 509 of the dynamic compressor 100 is shown on the operating map 500 as the intersection of a speed line, an inlet mass flow rate value, and a pressure ratio value. For example, the first operating point 509 shown on the operating map 500 is an inlet mass flow rate of 112%, a head of 90%, and a speed of 100%, but any number of operating points can be shown for any type of compressor. The operating point defines the current operating parameters of the dynamic compressor 100, and the operating map 500 shows how close the current operating point is to operating in an unstable state (i.e., surge) or an inefficient state (i.e., choke).

[0032] The memory 430 stores instructions for programming the processor 420 to determine the startup pressure ratio PR of the dynamic compressor 100. An example of the method 600 is shown in FIG. 6. The processor 420 receives a command to start the operation of the dynamic compressor 100 (602). In some embodiments, the command can be initiated by a user, an automatic command, or other suitable means. The processor 420 determines the first heat transfer fluid temperature T 1,htf in the first heat transfer fluid path 344 of the evaporator 340 (604), and is further programmed to determine the second heat transfer fluid temperature T 2,htf in the second heat transfer fluid path 324 of the condenser 320 (608). In some embodiments, determining the first heat transfer fluid temperature T 1,htf (604) includes receiving the first heat transfer fluid temperature T 1,htf from the first temperature sensor 360, and determining the second heat transfer fluid temperature T 2,htf (608) includes receiving the second heat transfer fluid temperature T 2,htf from the second temperature sensor 380.

[0033] Based on the first heat transfer fluid temperature T 1,htf , the processor 420 determines the first pressure P1 in the first working fluid path 342 of the evaporator 340 (606), and is further programmed to determine the second pressure P2 in the second working fluid path 322 of the condenser 320 based on the second heat transfer fluid temperature T 2,htf (610). In some embodiments, determining the first and second pressures P1, P2 based on the first and second heat transfer fluid temperatures T 1,htf , T 2,htf includes determining the first or second working fluid saturation temperature T 1,htf , T 2,htf based on the first or second heat transfer fluid temperature T 1,htf , T 2,htf , and using the empirical formula of the working fluid to determine the first or second pressure P1, P2 from the first or second working fluid saturation temperature T 1,wf , T 2,wf , T 1,wf , T 2,wfincluding calculating as a function of, for example, in an embodiment where the refrigerant is R134a, the refrigerant pressure P can be calculated as a function of the working fluid saturation temperature T using the following equation wf as a function. P = 0.01165·T wf 2 - 0.12869·T wf + 35.63 In some embodiments, the first and second working fluid saturation temperatures T 1,wf , T 2,wf are estimated based on other system parameters. Such embodiments will be described in more detail below.

[0034] In a further embodiment, determining the first pressure P1 includes receiving a first pressure value corresponding to the first working fluid saturation temperature T 1,wf from a data table of the working fluid stored in memory, and determining the second pressure P2 includes obtaining a second pressure value corresponding to the second working fluid saturation temperature T 2,wf from the data table of the working fluid. The data table can include experimental data, simulated data, or other suitable types of data.

[0035] The processor 420 is further programmed to determine (612) the pressure ratio PR of the dynamic compressor 100 from the first and second pressures P1, P2. In some embodiments, the pressure ratio PR is determined by calculating an estimated pressure ratio PR est by dividing the second pressure P2 by the first pressure P1. PR est = P2 / P1

[0036] Next, the processor 420 is programmed to determine (614) the speed setpoint N set of the dynamic compressor 100 based on the pressure ratio PR. Referring to FIG. 5, the speed setpoint N setis selected such that the operating point of the dynamic compressor 100 lies between the surge control line 503 and the choke line 501, and it is possible to avoid operating in an unstable state or an inefficient state. For example, the processor 420 may determine the surge speed N surge corresponding to the pressure ratio PR and the choke speed N choke , and determine that the speed setpoint N set is a value between the surge speed N surge and the choke speed N choke . In some embodiments, the speed setpoint N set can be calculated as follows. N set = N surge + k · (N choke - N surge ) Here, k is a scaling factor between 0 and 1. In some embodiments, k can be 0.5, and the speed setpoint N set is exactly in the middle between the surge speed N surge and the choke speed N choke . In further embodiments, k can be less than 0.5, and the speed setpoint N set is closer to the surge speed N choke than to the choke speed N surge . In still other embodiments, k can be greater than 0.5, and the speed setpoint N set is closer to the choke speed N surge than to the surge speed N choke .

[0037] In some embodiments, the processor 420 uses a map 700 of predetermined operating points 50 stored in the memory 430 to determine the surge speed N surge corresponding to the pressure ratio PR and the choke speed N chokecan be determined. For example, FIG. 7 is a representative diagram of a map 700 of predetermined operating points 50 stored in the memory 430. Each predetermined operating point 50 is shown as the intersection of a compressor speed value and a compressor pressure ratio value. An inlet mass flow rate is also defined for each predetermined operating point 50. The map 700 includes predetermined operating points 50 in the range up to the points along the mechanical surge line 720 and the mechanical choke line 730. The map 700 does not include points above the surge line 720 or below the choke line 730. This is because points above the surge line 720 or below the choke line 730 should be avoided and are not "operating points". In other embodiments, predetermined operating points above the surge line 720 or below the choke line 730 may be included.

[0038] In the map 700, the predetermined operating points 50 are in the range where the speed is from 10% to 35% and the pressure ratio is from 5% to 50%, and each point is 5% apart on both axes. In this example, these specific predetermined operating points 50 are shown, but for any type of compressor, any number of operating points can be shown at any values and any resolution. The values of the speed, pressure ratio, inlet mass flow rate, and VIGV position for each predetermined operating point 50 can be obtained by simulating the operation of the dynamic compressor 100 on a computer, testing the dynamic compressor 100 in a controlled environment, combining simulation and testing, or by other suitable methods for pre-determining the values of the speed, pressure ratio, inlet mass flow rate, and VIGV position for each predetermined operating point 50.

[0039] The predetermined operating point 50 obtained from the map 700 can itself indicate the choke speed or the surge speed of the dynamic compressor 100 at the startup pressure ratio PR. For example, at the startup pressure ratio PR = 25% head, the surge speed N surge is 15% of the design speed, and the choke speed N choke is 30% of the design speed. The scaling factor k is such that the speed setpoint N set is the surge speed N surge and the choke speed N chokeIt can be selected to be located on the dashed line 760 between. For example, as shown in FIG. 7, the speed setpoint N set k can be selected such that is 25% of the design speed. In a further embodiment, a predetermined operating point 50 obtained from the map 700 can be used to determine, for example, by interpolation, the choke speed or the surge speed at the starting pressure ratio PR graphically or numerically. In a further embodiment, a predetermined operating point 50 closest to the surge speed and the choke speed can be obtained.

[0040] The processor 420 is further programmed to operate the dynamic compressor 100 at the speed setpoint N set until the conditions are met (616). In some embodiments, the processor 420 operates the dynamic compressor 100 at the speed setpoint N set until a predetermined startup time has elapsed. The predetermined startup time can be, for example, but not limited to, 1 minute, 2 minutes, or other suitable period. In a further embodiment, the processor 420 determines the measured pressure ratio PR meas of the dynamic compressor 100, and the measured pressure ratio PR meas is greater than the estimated pressure ratio PR est until the dynamic compressor 100 is further programmed to operate at the speed setpoint N set .

[0041] The measured pressure ratio PR meas can be calculated using the measured pressure value. For example, the memory 430 may store instructions for programming the processor 420 to receive the value of the first measured pressure P 1,meas of the working fluid upstream of the dynamic compressor 100. The first measured pressure P 1,meas may be obtained from an inlet pressure sensor 111 disposed near the first refrigerant inlet 110. Similarly, the memory 430 may store additional instructions for programming the processor 420 to receive the value of the second measured pressure P 2,meas of the working fluid downstream of the dynamic compressor 100. The second measured pressure P 2,measmay be obtained from an outlet pressure sensor 121 disposed near the second refrigerant outlet 120.

[0042] In such an embodiment, the memory 430 may store additional instructions for programming the processor 420 to determine a measured pressure ratio PR 1,meas , P 2,meas based on the first and second measured pressures P meas . The measured pressure ratio PR meas can be calculated as the second measured pressure P 2,meas divided by the first pressure P 1,meas . PR meas = P 2,meas / P 1,meas In a further embodiment, the processor 420 operates the dynamic compressor 100 at a speed set point N meas to compress the working fluid (616) until the measured pressure ratio PR est exceeds the estimated pressure ratio PR set or a predetermined startup time has elapsed.

[0043] Figures 8A and 8B (collectively Figure 8) illustrate an exemplary control algorithm 800 for calculating the startup pressure ratio PR of a dynamic compressor according to method 600. After receiving a command to start operation of the dynamic compressor 100 (802), the processor 420 calculates the first working fluid saturation temperature T 1,wf in the first working fluid path 342 of the evaporator 340 (804). In the illustrated embodiment, the first working fluid saturation temperature T 1,wf in the first working fluid path 342 is calculated as the difference between the first heat transfer fluid temperature T 1,htf measured in the first heat transfer fluid path 344 and the first temperature offset T e . T 1,wf = T 1,htf - T e The first temperature offset T erepresents the temperature difference between the saturated refrigerant in the first working fluid path 342 and the heat transfer fluid discharged from the first heat transfer fluid path 344. The first temperature offset T e may be, for example, but not limited to, 5°F, 10°F, or other suitable temperature offsets.

[0044] Similarly, to account for the temperature difference between the saturated refrigerant in the second working fluid path 322 and the heat transfer fluid discharged from the second heat transfer fluid path 324, a temperature offset may be added to the second heat transfer fluid temperature T 2,htf measured in the second heat transfer fluid path 324 of the condenser 320. In the exemplary control algorithm 800 shown in FIG. 8, the processor 420 determines (806) the type of heat transfer fluid used in the second heat transfer fluid path 324 of the condenser 320 and, accordingly, calculates (808, 810) the second working fluid saturation temperature T 2,wf in the second working fluid path 322. When the processor 420 determines that the heat transfer fluid is water, the second working fluid saturation temperature T 2,wf in the second working fluid path 322 is calculated (808) as the sum of the second heat transfer fluid temperature T 2,htf measured in the second heat transfer fluid path 324 and the second temperature offset T cw . T 2,wf = T 2,htf + T cw The second temperature offset T cw may be, for example, but not limited to, 5°F, 10°F, 20°F, or other suitable temperature offsets. When the processor 420 determines that the heat transfer fluid is air, the second working fluid saturation temperature T 2,wf in the second working fluid path 322 is calculated (810) as the sum of the second heat transfer fluid temperature T 2,htf measured in the second heat transfer fluid path 324 and the second temperature offset T ca . T 2,wf = T 2,htf + T ca The second predetermined temperature offset T cais, for example, but not limited to, 10°F, 20°F, or other suitable temperature offsets.

[0045] In the exemplary control algorithm 800 shown in FIG. 8, the processor 420 determines (812) the first and second operating fluid saturation temperatures T 1,wf , T 2,wf and based thereon determines the first and second pressures P1, P2, and is further programmed to calculate (814) an estimated pressure ratio PR as the value obtained by dividing the second pressure P2 by the first pressure P1. The processor 420 then determines (816) the surge speed N est and the choke speed N est of the dynamic compressor 100 at the estimated pressure ratio PR surge and calculates (818) a speed setpoint N choke of the dynamic compressor 100 as a value between the surge speed N set and the choke speed N surge . choke

[0046] Next, the processor 420 is programmed to start the dynamic compressor 100 at the speed setpoint N set and start a startup timer (820). The startup timer can measure a startup time t start indicating the time elapsed since the start of operation of the dynamic compressor 100. The processor 420 determines (822) whether the startup time t start has reached a startup completion time t1, and if so, also determines (824) that startup has been completed, and starts the operation of the dynamic compressor 100 based on the measured pressure ratio PR meas . In the illustrated embodiment, the startup completion time t1 is 1 minute, but the startup completion time t1 can be any suitable time, for example, but not limited to, 30 seconds, 90 seconds, or 2 minutes, etc. If the processor 420 determines (822) that the startup time t start has not yet reached the startup completion time t1, the processor 420 also determines (826) which of the estimated pressure ratio PR est and the measured pressure ratio PR meas is greater. Next, the processor 420 also determines (826) which of the two pressure ratios PRest and PR meas The surge speed N corresponding to the larger one among them surge and the choke speed N choke are determined (828), and the speed setpoint N of the dynamic compressor 100 set is recalculated (830) as a value between the surge speed N surge and the choke speed N choke . The processor 420 sets the speed of the dynamic compressor 100 to the recalculated speed setpoint N set (832), and the processor 420 determines again (822) whether the startup time t start has reached the startup completion time t1, and proceeds to the following procedure.

[0047] The technical advantages of the system described in this specification are as follows. (1) Using existing system instrumentation, a safe operating range can be determined during the startup routine of a dynamic compressor. (2) By limiting the time the compressor spends outside the safe operating range, the reliability of the compressor is improved.

[0048] In this specification, the terms "about", "substantially", "essentially", and "approximately" when used in connection with ranges of dimensions, concentrations, temperatures, or other physical or chemical properties or characteristics are intended to cover variations that may exist at the upper and / or lower limits of the range of the property or characteristic, including variations resulting from, for example, rounding, measurement methods, or other statistical fluctuations.

[0049] When introducing elements of the present disclosure or its embodiments, the articles "a," "an," "the," and "said" shall be taken to mean that an element can be one or more. The terms "comprising," "including," "containing," and "having" are intended to be inclusive and shall be taken to mean that additional elements other than the recited elements may exist. The use of terms indicating a particular orientation (such as "top," "bottom," "side," etc.) is for convenience of explanation and does not require a particular orientation of the item being described.

[0050] Since various changes can be made to the above-described configurations and methods without departing from the scope of the present disclosure, all matters included in the above description and shown in the accompanying drawings shall be construed as illustrative rather than in a limiting sense.

Claims

1. A system, the system comprising: An evaporator having a first working fluid path and a first heat transfer fluid path thermally coupled to the first working fluid path; A condenser having a second working fluid path and a second heat transfer fluid path thermally coupled to the second working fluid path; A dynamic compressor fluidly coupled to the first working fluid path of the evaporator and the second working fluid path of the condenser, the dynamic compressor being operable to compress a working fluid; A first temperature sensor positioned within the first heat transfer fluid path of the evaporator; A second temperature sensor positioned within the second heat transfer fluid path of the condenser; A controller connected to the dynamic compressor, the controller including a processor and a memory, the memory storing instructions for causing the processor to: Receive a command to start operation of the dynamic compressor; Receive a first heat transfer fluid temperature from the first temperature sensor; Determine a first pressure in the first working fluid path of the evaporator based on the first heat transfer fluid temperature; Receive a second heat transfer fluid temperature from the second temperature sensor; Determine a second pressure in the second working fluid path of the condenser based on the second heat transfer fluid temperature; Determine a pressure ratio of the dynamic compressor from the first pressure and the second pressure; Determine a speed setpoint of the dynamic compressor based on the pressure ratio; and Operate the dynamic compressor at the speed setpoint to compress the working fluid until conditions are met. The system.

2. Operating the dynamic compressor at the speed setpoint until conditions are met includes operating the dynamic compressor at the speed setpoint until a predetermined startup time has elapsed, the system of claim 1.

3. Determining the first pressure includes: Determining a first working fluid saturation temperature in the first working fluid path of the evaporator based on the first heat transfer fluid temperature; and Calculating the first pressure as a function of the first working fluid saturation temperature using an empirical formula of the working fluid. Determining the second pressure includes: ​ Determining a second working fluid saturation temperature in the second working fluid path of the condenser based on the second heat transfer fluid temperature, and Calculating the second pressure as a function of the saturation temperature of the second working fluid using the empirical formula of the working fluid, the system according to claim 1 or 2.

4. Determining the first pressure includes Determining a first working fluid saturation temperature in the first working fluid path of the evaporator based on the first heat transfer fluid temperature, and Obtaining a first pressure value corresponding to the first working fluid saturation temperature from the data table of the working fluid stored in the memory, Determining the second pressure includes Determining a second working saturated fluid temperature in the second working fluid path of the condenser based on the second heat transfer fluid temperature, and Obtaining a second pressure value corresponding to the second working fluid saturation temperature from the data table of the working fluid, the system according to claim 1 or 2.

5. Determining the pressure ratio includes calculating an estimated pressure ratio as a value obtained by dividing the second pressure by the first pressure, the system according to claim 1 or 2.

6. The pressure ratio is an estimated pressure ratio, and the memory stores further instructions for programming the processor to Receive a value of a first measured pressure of the working fluid upstream of the dynamic compressor, Receive a value of a second measured pressure of the working fluid downstream of the dynamic compressor, and Determine a measured pressure ratio based on the first measured pressure and the second measured pressure, the system according to claim 1 or 2.

7. Operating the dynamic compressor at the speed set point until the condition is met includes Operating the dynamic compressor at the speed set point until the measured pressure ratio exceeds the estimated pressure ratio, the system according to claim 6.

8. Operating the dynamic compressor at the speed set point includes Operating the dynamic compressor at the speed set point until a first point in time when the measured pressure ratio exceeds the estimated pressure ratio or until a predetermined startup time has elapsed, the system according to claim 6.

9. Determining the speed set point of the dynamic compressor includes Determining a surge speed corresponding to the pressure ratio, Determining a choke velocity corresponding to the pressure ratio, and Determining that the speed setpoint is a value between the surge velocity and the choke velocity, the system according to any one of claims 1 to 8. **Claim 10** The system according to any one of claims 1 to 9, wherein the dynamic compressor is a centrifugal compressor. **Claim 11** A controller of a system, the system includes an evaporator, a condenser, and a dynamic compressor fluidly coupled between the evaporator and the condenser, the controller includes a processor and a memory, and the memory causes the processor to Receive a command to start the operation of the dynamic compressor, Determine a first heat transfer fluid temperature in a first heat transfer fluid path of the evaporator, Based on the first heat transfer fluid temperature, determine a first pressure in a first working fluid path of the evaporator, Determine a second heat transfer fluid temperature in a second heat transfer fluid path of the condenser, Based on the second heat transfer fluid temperature, determine a second pressure in a second working fluid path of the condenser, Calculate a pressure ratio of the dynamic compressor from the first pressure and the second pressure, Based on the pressure ratio, determine a speed setpoint of the dynamic compressor, and Program instructions are stored to cause the dynamic compressor to operate at the speed setpoint to compress the working fluid until the conditions are met. Controller. **Claim 12** Determining the first heat transfer fluid temperature includes receiving the first heat transfer fluid temperature from a first temperature sensor in the first heat transfer fluid path of the evaporator, Determining the second heat transfer fluid temperature includes receiving the second heat transfer fluid temperature from a second temperature sensor in the second heat transfer fluid path of the condenser, the controller according to claim 11. **Claim 13** Determining the first pressure includes Based on the first heat transfer fluid temperature, determining a first working fluid saturation temperature in the first working fluid path of the evaporator, and Using an empirical formula of the working fluid to calculate the first pressure as a function of the first working fluid saturation temperature, Determining the second pressure includes Determining a second working fluid saturation temperature in a second working fluid path of the condenser based on the second heat transfer fluid temperature, and Calculating the second pressure as a function of the second working fluid saturation temperature using the empirical formula of the working fluid, the controller according to claim 11 or 12.

14. Determining the first working fluid saturation temperature includes subtracting a first temperature offset from the first heat transfer fluid temperature, Determining the second working fluid saturation temperature includes adding a second temperature offset to the second heat transfer fluid temperature, the controller according to claim 13.

15. Determining the first pressure is Determining a first working fluid saturation temperature in a first working fluid path of the evaporator based on the first heat transfer fluid temperature, and Receiving a first pressure value corresponding to the first working fluid saturation temperature from a data table of the working fluid stored in the memory, Determining the second pressure is Determining a second working fluid saturation temperature in the second working fluid path of the condenser based on the second heat transfer fluid temperature, and Receiving a second pressure value corresponding to the second working fluid saturation temperature from the data table of the working fluid, the controller according to claim 11 or 12.

16. Determining the pressure ratio includes calculating an estimated pressure ratio as a value obtained by dividing the second pressure by the first pressure, the controller according to any one of claims 11 to 15.

17. The pressure ratio is an estimated pressure ratio, and the memory causes the processor to Receive a value of a first measured pressure of the working fluid upstream of the dynamic compressor, Receive a value of a second measured pressure of the working fluid downstream of the dynamic compressor, and Determine a measured pressure ratio based on the first measured pressure and the second measured pressure, and further instructions are stored to program the controller according to any one of claims 11 to 15.

18. Operating the dynamic compressor at the speed set point until the condition is met is Operating the dynamic compressor at the speed set point until the measured pressure ratio exceeds the estimated pressure ratio, the controller according to claim 17.

19. Operating the dynamic compressor at the speed set point comprises The controller according to claim 17, comprising operating the dynamic compressor at the speed set point until a first time point when the measured pressure ratio exceeds the estimated pressure ratio or until a predetermined startup time has elapsed.

20. Determining the speed set point of the dynamic compressor comprises Determining a surge speed corresponding to the pressure ratio, Determining a choke speed corresponding to the pressure ratio, and Determining that the speed set point is a value between the surge speed and the choke speed, the controller according to any one of claims 11 to 19.

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