SYSTEMS AND METHODS FOR DETERMINING THE START-UP PRESSURE RATIO FOR DYNAMIC COMPRESSORS

Abstract

A control device for a system with an evaporator, a condenser, and a dynamic compressor includes a processor and a memory that stores instructions programming the processor to determine a first heat transfer fluid temperature at a first heat transfer fluid path of the evaporator, to determine a first pressure at a first working fluid path based on the first heat transfer fluid temperature, to determine a second heat transfer fluid temperature at a second heat transfer fluid path of the condenser, to determine a second pressure at a second working fluid path based on the second heat transfer fluid temperature, to calculate a compressor pressure ratio from the first and second pressures, to determine a compressor speed setpoint based on the pressure ratio, and to operate the compressor at the speed setpoint to compress a working fluid until a condition is met.

Description

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Patent Application No. 17 / 804,317, filed May 27, 2022, the entire disclosure of which is hereby incorporated by reference in its entirety. TECHNICAL FIELD OF DISCLOSURE

[0002] The technical field of the disclosure relates generally to control systems and more particularly to control systems for dynamic compressors. TECHNICAL BACKGROUND

[0003] Dynamic compressors, including centrifugal compressors, are widely used in the process industry and in heating, ventilation, and air conditioning (HVAC) systems. The compressor is operatively connected to a prime mover via a shaft carrying one or more compression stages. The prime mover rotates the compression stage(s) via the shaft at a speed and load condition selected to compress a refrigerant to a specified demand. The prime mover speed and load can be controlled to allow the compressor to operate under a wide range of conditions. The compressor's operating range is limited by regions of surge at low flow rates and by regions of choke at high flow rates.Knowing the exact operating point of the system can help avoid compressor operation in surge or throttle mode and minimize the duration of the compressor start-up routine.

[0004] The operating point of a dynamic compressor is determined in part by the compressor speed, which can be controlled by the user, and by the pressure ratio across 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 prior to a startup routine because a discharge check valve downstream of the dynamic compressor prevents high-pressure refrigerant from flowing from a condenser to the compressor pressure sensor to be measured. Therefore, there is a need for a system and method for determining the pressure ratio across the dynamic compressor at startup without the use of pressure measurements.

[0005] This section is intended to introduce the reader to various aspects of the prior art that may be related to various aspects of the disclosure described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information that will facilitate a better understanding of the various aspects of the present disclosure. Accordingly, these statements are to be construed in this spirit and not as an admission of prior art. SUMMARY

[0006] One aspect of the disclosure relates to a system having 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 thereto. The condenser includes a second working fluid path and a second heat transfer fluid path thermally coupled thereto. 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 in the first heat transfer fluid path of the evaporator and a second temperature sensor positioned in the second heat transfer fluid path of the condenser.The system also includes a controller connected to the dynamic compressor, including a processor and a memory. The memory stores instructions that program the processor to receive a command to start operation of the compressor, receive a first heat transfer fluid temperature from the first temperature sensor, determine a first pressure at 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 at 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 and second pressures, determine a speed setpoint of the dynamic compressor based on the pressure ratio, and operate the dynamic compressor at, orto operate at the speed setpoint to compress the working fluid until a condition is met.

[0007] Another aspect of the present disclosure relates to a control device for a system having an evaporator, a condenser, and a dynamic compressor fluidly coupled therebetween. The control device includes a processor and a memory.The memory stores instructions that program the processor to receive a command to begin operation of the dynamic compressor, determine a first heat transfer fluid temperature at a first heat transfer fluid path of the evaporator, determine a first pressure at a first working fluid path of the evaporator based on the first heat transfer fluid temperature, determine a second heat transfer fluid temperature at a second heat transfer fluid path of the condenser, determine a second pressure at 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 and second pressures, determine a speed setpoint of the dynamic compressor based on the pressure ratio, and operate the dynamic compressor at, orto operate at the speed setpoint to compress a working fluid until a condition is met.

[0008] There are various refinements to the features mentioned in connection with the above-mentioned aspects of the present disclosure. Additional features may also be included in the above-mentioned aspects of the present disclosure. These refinements and additional features may occur individually or in any combination. For example, various features discussed below with respect to any of the illustrative embodiments of the present disclosure may be included individually or in any combination in any of the above-described aspects of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a perspective view of an assembled dynamic compressor. Fig. 2 shows a sectional view of the dynamic compressor from Fig. 1 along line 2-2, with the external line removed. Fig. Figure 3 shows a schematic view of an exemplary HVAC system in which the Fig. 1 and Fig. 2 dynamic compressors can be installed. Fig. Figure 4 shows a block diagram of a control system for the Fig. 1 and Fig. 2 dynamic compressor shown. Fig. 5 shows an operating map of the Fig. 1 and Fig. 2 shown dynamic compressor. Fig. 6 shows a method for determining a starting pressure ratio of the Fig. 1 and Fig. 2 shown dynamic compressor. Fig. Figure 7 shows a map of predetermined operating points of the Fig. 1 and Fig. 2 shown dynamic compressor. Fig. 8A shows a first part of a flowchart of an exemplary control algorithm for performing a start-up routine of the Fig. 1 and Fig. 2 shown dynamic compressor. Fig. 8B shows a second part of the Fig. 8A shown flowchart.

[0009] Corresponding reference numerals indicate corresponding parts in the drawings. DETAILED DESCRIPTION

[0010] For brevity, examples are described for a centrifugal compressor. However, the methods and systems described here 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 a safe operating envelope during a startup routine. A compressor startup pressure ratio, which represents the pressure rise between the inlet and outlet of the compressor, can be estimated using temperature measurements from other cycle components. The estimated pressure ratio can then be used to determine a speed setpoint within the compressor's safe operating envelope.

[0011] Fig. Figure 1 shows a two-stage refrigerant compressor, generally indicated at 100. The dynamic compressor 100 is operable to compress a working fluid (e.g., a refrigerant) and includes a compressor housing 102 defining at least one sealed cavity in which each stage of refrigerant compression is performed. The dynamic compressor 100 includes a first refrigerant inlet 110 for introducing refrigerant vapor into a first compressor stage (in Fig. 1 not labeled), a first refrigerant outlet or refrigerant outlet 114, a refrigerant transfer line 112 for transferring compressed or compressed refrigerant from the first compressor stage to a second compressor stage (in Fig. 1 not labeled), a second refrigerant inlet 118 for introducing refrigerant vapor into the second compressor stage, and a second refrigerant outlet 120. The refrigerant transfer line 112 is operatively connected at opposite ends to the first refrigerant outlet 114 and the second refrigerant inlet 118, respectively. The second refrigerant outlet 120 supplies compressed refrigerant from the second compressor stage to a refrigeration system in which the compressor 100 is integrated ( Fig. 3).

[0012] Referring to Fig. 2, the compressor housing 102 encloses the first compressor stage 124 and the second compressor stage 126 at opposite ends of the compressor 100. The first compressor stage 124 includes a first compression mechanism 106 configured to impart kinetic energy to the refrigerant entering via the first refrigerant inlet 110. In some embodiments, the first compression mechanism 106 is an impeller. The kinetic energy imparted to the refrigerant by the first compression mechanism 106 is converted into increased refrigerant pressure as the refrigerant's velocity is slowed as it is transferred into a sealed cavity (e.g., a diffuser) formed in the volute 132. The first compressor stage 124 additionally includes a first variable inlet guide vane (VID).variable inlet guide vane (VIGV) 134 disposed upstream of the first compression mechanism 106 in the first refrigerant inlet 110. The first VIGV 134 includes a plurality of guide vanes whose position can be controlled to introduce a pre-swirl 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 impart kinetic energy to the refrigerant transferred from the first compressor stage 124 and entering via the second refrigerant inlet 118. In some embodiments, the second compression mechanism 116 is an impeller. The kinetic energy imparted to the refrigerant by the second compression mechanism 116 is converted into increased refrigerant pressure as the velocity of the refrigerant is slowed during transfer into a sealed cavity (e.g., a diffuser) formed in the diffuser 132. The compressed refrigerant exits the second compressor stage 126 via the second refrigerant outlet 120 (in Fig. 2 (not shown). The second compressor stage 126 additionally includes a second variable inlet guide vane (VIGV) 136 disposed upstream of the second compression mechanism 116 in the second refrigerant inlet 118. The second VIGV 136 includes a plurality of guide vanes whose position can be controlled to introduce a pre-swirl into the gaseous refrigerant entering the second refrigerant inlet 118.

[0014] The first compression mechanism 106 and the second compression mechanism 116 are connected at opposite ends of a shaft 104. The shaft 104 is operatively connected to a prime mover 108 positioned between the first compression mechanism 106 and the second compression mechanism 116 such that the first compression mechanism 106 and the second compression mechanism 116 are rotated at a speed selected to compress the refrigerant to a preselected pressure available at the second refrigerant outlet 120 (in Fig. 2 not shown). Any suitable prime mover may be incorporated into the compressor 100, including, but not limited to, an electric prime mover.

[0015] Fig. Figure 3 shows a schematic diagram of a first example of an HVAC system 300 in which the dynamic compressor 100 of the Fig. 1 and Fig. 2 can be installed. The system 300 has a single, closed refrigerant circuit comprising the compressor 100, a condenser 320, a first expansion device 330, and an evaporator 340. The refrigerant enters the dynamic compressor 100 at the first refrigerant inlet 110 as a low-pressure, low-temperature gas. The dynamic compressor 100 adds kinetic energy to the refrigerant and converts this into a pressure increase, and the refrigerant leaves the dynamic compressor 100 at the 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 111.Outlet pressure sensor 121 disposed near the second refrigerant outlet 120 to measure the refrigerant pressure downstream of the dynamic compressor 100.

[0016] The refrigerant then enters a second working fluid path 322 of the condenser 320, which is fluidly coupled to the second compressor stage 126 downstream thereof. The condenser 320 further includes a second heat transfer fluid path 324 thermally coupled to the second working fluid path 322. The second heat transfer fluid path 324 is configured to allow flow of a heat transfer fluid and may be part of a secondary fluid loop (not shown). The heat transfer fluid may be water, glycol, refrigerant, air, or another suitable heat transfer fluid that enables the HVAC system 300 to function as described herein.The second working fluid path 322 and the second heat transfer fluid path 324 enable the condenser 320 to function as a heat exchanger, with the heat transfer fluid absorbing heat from the refrigerant to convert the refrigerant gas into a high-pressure, high-temperature liquid. The heat transfer fluid can then release heat to an external space (not shown).

[0017] The second working fluid path 322 of the condenser 320 is fluidly coupled to the first expansion device 330, which reduces the pressure of the refrigerant. In some embodiments, the pressure may be reduced until the current temperature of the liquid refrigerant reaches the boiling temperature at that pressure, and the refrigerant becomes a two-phase mixture as a portion of the liquid refrigerant boils and becomes a gas. The first expansion device 330 may be a fixed nozzle, a thermal expansion valve, an electronic expansion valve, or any type of expansion device that enables 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 the evaporator 340, which receives low-pressure, low-temperature liquid refrigerant or a two-phase mixture of liquid and gas refrigerant at its inlet. The evaporator 340 further includes a first heat transfer fluid path 344 thermally coupled to the first working fluid path 342. The first heat transfer fluid path 344 is configured to permit the flow of a heat transfer fluid and may be part of a tertiary fluid loop (not shown). The heat transfer fluid may be water, glycol, refrigerant, or other suitable heat transfer fluid that enables the HVAC system 300 to function as described herein. The first working fluid path 342 and the first heat transfer fluid path 344 allow the evaporator 340 to function as a heat exchanger.The heat transfer fluid in the first heat transfer fluid path 344 can absorb heat from a conditioned interior or from an additional fluid circuit (not shown). The refrigerant in the first working fluid path 342 absorbs heat from the first heat transfer fluid path 344 to change its phase from a liquid to a gas. The first working fluid path 342 of the evaporator 340 is fluidly coupled to the first refrigerant inlet 110 upstream thereof, and the cycle begins again.

[0019] The system 300 includes a first temperature sensor 360 positioned within the first heat transfer fluid path 344 of the evaporator 340. In the Fig. 3, the first temperature sensor 360 is positioned near an exit of the first heat transfer fluid path 344 of the evaporator 340, but the first temperature sensor 360 may be positioned at any suitable location upstream, for example and without limitation near an inlet of the first heat transfer fluid path 344 of the evaporator 340 or within the first heat transfer fluid path 344 itself. The system 300 further includes a second temperature sensor 380 positioned within the second heat transfer fluid path 324 of the condenser 320. In the embodiment shown in Fig. 3, the second temperature sensor 380 is positioned near an exit of the second heat transfer fluid path 324 of the condenser 320, but the second temperature sensor 380 may be positioned at any suitable location, for example and without limitation near an inlet of the second heat transfer fluid path 324 of the condenser 320 or within the second heat transfer fluid path 324 itself. The first and second temperature sensors 360, 380 may be thermocouples, thermistors, resistance temperature detectors (RTDs), or any other suitable type of temperature sensor.

[0020] Fig. 4 shows an embodiment of the system 300 with the dynamic compressor 100. The compressor 100 includes a compressor housing 102, at least one compression mechanism 106, 116, a prime mover 108, a speed sensor 317, pressure sensors 111, 121, and a controller 410. In the present embodiment, the dynamic compressor 100 is a two-stage centrifugal compressor, and the compression mechanism includes the first compression mechanism 106 and the second compression mechanism 116, each of which may be an impeller. In other embodiments, the dynamic compressor 100 may be an axial compressor, and each of the first and second compression mechanisms 106, 116 may be an axial rotor.The speed sensor 317 measures the speed of the dynamic compressor 100, and the pressure sensors 111, 121 measure the pressure at the first refrigerant inlet 110 and the second refrigerant outlet 120, respectively, as shown in FIG. Fig. 3. The dynamic compressor 100 may include additional pressure sensors for measuring the pressure at various points along the compressor flow path. Additional sensors may be installed in the compressor 100 to provide data about its operation, including, but not limited to, temperature sensors, flow sensors, current sensors, voltage sensors, angular rate sensors, and any other suitable sensors. The dynamic compressor 100 is not limited to a particular design in the system 300 and may be similar to the one with reference to Fig. 1 and Fig. 2 or be constructed in another manner. The system 300 further includes an unloading device 301, a variable frequency drive (VFD) 316, and a user interface 315.

[0021] A controller 410 is operatively connected to the dynamic compressor 100 to control its operation based at least in part on the measured parameters described above. The controller 410 includes a processor 420 and a memory 430. The memory 430 stores a map 700 (see, e.g., Fig. 7) of a plurality of predetermined operating points 50 of the dynamic compressor 100, which may be stored in any suitable data structure, such as a table, a matrix, or the like. Additionally stored in memory 430 are instructions that program the processor 420 to determine a starting pressure ratio PR of the dynamic compressor 100. The map 700 of predetermined operating points 50 and a method 600 for determining the starting pressure ratio PR of the dynamic compressor 100 are explained in more detail below.

[0022] The system 300 includes an interface for connecting the controller 410 to the VFD 316 and an engine interface 313 for connecting the VFD 316 to the engine 108. In certain embodiments, the VFD 316 operates under the control of the controller 410. In other 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 control device 410 is operatively coupled via the unloading interface 314 to the unloading device 301, which unloads and / or reduces the load on the dynamic compressor 100 during the start-up routine and the shutdown routines, during detected surge events, and when otherwise instructed by the control device 410. In the 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 discharge 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 discharge device 301, such as a position of each VIGV.

[0024] The system 300 further includes a user interface 315 configured to output (e.g., display) and / or receive (e.g., from a user) information associated with the system 300. In some embodiments, the user interface 315 is configured to receive activation and / or deactivation input from a user to activate and deactivate (e.g., turn on and off) or otherwise enable operation of the system 300. Furthermore, in some embodiments, the user interface 315 is configured to output information associated with one or more operating characteristics of the system 300, including, for example and without limitation, warning indicators such as severity warnings, occurrence warnings, fault warnings, engine speed warnings, and any other suitable information.

[0025] The user interface 315 may include any suitable input devices and output devices that enable the user interface 315 to function as described herein. For example, the user interface 315 may include input devices including, but not limited to, a keyboard, a mouse, a touchscreen, one or more joysticks, one or more throttles, buttons, switches, and / or other input devices. In addition, the user interface 315 may include output devices, such as, but not limited to, a display (e.g., a liquid crystal display (LCD) or an organic light-emitting diode (OLED) display), speakers, indicator lights, instruments, and / or other output devices. In addition, the user interface 315 may be part of another component, e.g., a system controller (not shown).Other embodiments do not include a user interface 315.

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

[0027] The controller 410 may generally comprise any suitable computer and / or other processing unit, including any suitable combination of computers, processing units, and / or the like, that may be communicatively coupled to one another and that may operate independently or in conjunction with one another (e.g., the controller 410 may form, in whole or in part, a control network). The controller 410 may comprise one or more modules or devices, one or more of which are enclosed within the system 300, or it may be located remotely from the system 300. The controller 410 may be part of the dynamic compressor 100 or separate and may be part of a system controller in an HVAC system. The controller 410 and / or components of the controller 410 may be integrated or incorporated into other components of the system 300.The controller 410 may include one or more processors 420 and associated memory device(s) 430 configured to perform a variety of 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 a controller, a microcontroller, a microcomputer, a programmable logic controller (PLC), an application-specific integrated circuit, and other programmable circuits. Furthermore, the storage device(s) 430 of the controller 410 may generally be or include one or more storage elements, including, but not limited to, a computer-readable medium (e.g., random access memory (RAM)), a computer-readable non-volatile medium (e.g., flash memory), a floppy disk, a compact disc read-only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD), and / or other suitable storage elements.This storage device(s) 430 may generally be configured to store suitable computer-readable instructions that, when implemented by the processor(s) 420, configure or cause the controller 410 to perform various functions described herein, including, but not limited to, controlling the system 300, controlling the operation of the engine 108, receiving inputs from the user interface 315, providing output to a user via the user interface 315, controlling the unloading device 301, and / or various other suitable computer-implemented functions.

[0029] In Fig. 5 shows an operating map 500 of the dynamic centrifugal compressor 100. The operating map 500 graphically represents the performance of a compressor in terms of flow, heads, and speed. The operating map 500 shows the head compared to the inlet mass flow rate as a percentage of their values ​​at the design point of the dynamic compressor 100. The head is the ratio of the outlet pressure to the inlet pressure. The inlet mass flow rate is a measure of the amount of a working fluid, e.g., a refrigerant, flowing through the compression mechanisms 106, 116. The operating map 500 shows a plurality of compressor speed lines 507.In this example, there are five speed lines 507 ranging from 70% design speed to 110% design speed, with each line separated by a 10% difference. Although these specific speed lines are shown in this example, any number of speed lines can be shown for any compressor type at any different percentage of the compressor's design speed.

[0030] A surge limit line 504 indicates the minimum flow before a surge occurs in the surge region 506 (i.e., to the left of the surge limit line 504). A surge control line 503 roughly indicates the minimum flow below which the compressor 100 can safely operate without the risk of entering surge. The surge control line 503 is defined by a surge margin 505 from the surge limit line 504. By operating to the right of the surge control line 503, the dynamic compressor 100 should avoid surging. Similarly, the throttle line 501 indicates that operation to the right of it will be at throttled flow.

[0031] A first operating point 509 of the dynamic compressor 100 is represented in the operating map 500 as the intersection of a speed line, an inlet mass flow value, and a pressure ratio value. For example, the first operating point 509 in the operating map 500 is at 112% inlet mass flow, 90% head, and 100% speed, although any number of operating points may be displayed for each compressor type. The operating point defines the current operating parameters of the dynamic compressor 100, and the operating map 500 indicates how close the current operating point is to operating in an unstable state (e.g., surge) or an inefficient state (e.g., throttling).

[0032] Instructions are stored in memory 430 that program processor 420 to determine a starting pressure ratio PR of dynamic compressor 100. An example method 600 is shown in Fig. 6. The processor 420 receives 602 a command to begin operation, or to start up, the dynamic compressor 100. In some embodiments, the command may be initiated by a user, by an automatic command, or by another suitable means. The processor 420 is further programmed to determine 604 a first heat transfer fluid temperature T 1,htf at the first heat transfer fluid path 344 of the evaporator 340 and 608 a second heat transfer fluid temperature T 2,htf at the second heat transfer fluid path 324 of the condenser 320. In some embodiments, determining 604 the first heat transfer fluid temperature T 1,htf receiving the first heat transfer fluid temperature T 1,htf from the first temperature sensor 360, and determining 608 the second heat transfer fluid temperature T 2,htfcomprises receiving the second heat transfer fluid temperature T 2,htf from the second temperature sensor 380.

[0033] The processor 420 is additionally programmed to determine a first pressure P1 at the first working fluid path 342 of the evaporator 340 based on the first heat transfer fluid temperature T 1,htf to determine 606, and a second pressure P2 at the second working fluid path 322 of the condenser 320 based on the second heat transfer fluid temperature T 2,htf to determine 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 determining a first or second working fluid saturation temperature T 1,wf , T 2,wf based on the first or second heat transfer fluid temperature T 1,htf , T 2,htf, and calculating the first or second pressure P1, P2 as a function of the first or second working fluid saturation temperature T 1,wf , T 2,wf using an empirical equation of the working fluid. For example, in embodiments where the refrigerant is R134a, the refrigerant pressure P can be calculated as a function of the working fluid saturation temperature T wf can be calculated using the formula: P=0.01165⋅Twf2−0.12869⋅Twf+35.63

[0034] In some embodiments, the first and second working fluid saturation temperatures T 1,wf , T 2,wf estimated based on other system parameters. Such embodiments are discussed in more detail below.

[0035] In further embodiments, determining the first pressure P1 includes receiving a first pressure value corresponding to the first working fluid saturation temperature T 1,wffrom a data table for the working fluid stored in memory, and determining the second pressure P2 includes retrieving a second pressure value corresponding to the second working fluid saturation temperature T 2,wf from the data table for the working fluid. The data table may contain experimental data, simulated data, or any other suitable type of data.

[0036] 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 as the second pressure P2 divided by the first pressure P1: PRest=P2P1

[0037] The processor 420 is then programmed to generate a speed setpoint N based on the pressure ratio PR setof the dynamic compressor 100 614. With reference to Fig. 5 the speed setpoint N set be selected such that the operating point of the dynamic compressor 100 lies between the surge control line 503 and the throttle line 501 to avoid operation under unstable or inefficient conditions. For example, the processor 420 may set a surge speed N surge and a throttle speed N choke corresponding to the pressure ratio PR and determine that the speed setpoint N set a value between the pumping speed N surge and the throttle speed N choke In some embodiments, the speed setpoint N set be calculated as: Nset=Nsurge+k⋅(Nchoke−Nsurge) where k is a scaling factor between zero and one. In some embodiments, k may be 0.5, so that the speed setpoint N setexactly in the middle between the pumping speed N surge and the throttle speed N choke In further embodiments, k can be less than 0.5, so that the speed setpoint N set closer to the pumping speed N surge than at the throttle speed N choke In still further embodiments, k may be greater than 0.5, so that the speed setpoint N set closer to the throttle speed N choke than at the pumping speed N surge lies.

[0038] In some embodiments, the processor 420 may determine the pumping speed N surge and the throttle speed N choke according to the pressure ratio PR using the map 700 of the predetermined operating points 50 stored in the memory 430. Fig. For example, Figure 7 shows a representative representation of a map 700 of predetermined operating points 50 stored in memory 430. Each predetermined operating point 50 is represented 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 a range up to and including points along the machine surge line 720 and the machine throttle line 730. The map 700 does not include any points above the surge line 720 or below the throttle line 730 because points above the surge line 720 or below the throttle line 730 are to be avoided and thus do not represent "operating points."In other embodiments, predetermined operating points may be included above the surge line 720 or below the throttle line 730.

[0039] In map 700, the predetermined operating points 50 range between 10% and 35% speed and between 5% and 50% pressure ratio, with each point separated by 5% on both axes. Although these particular predetermined operating points 50 are shown in this example, any number of operating points at any values ​​and with any resolution may be shown for any compressor type. The values ​​for speed, pressure ratio, inlet mass flow rate, and VIGV position of each predetermined operating point 50 may be generated by simulating the operation of the dynamic compressor 100 on a computer, by testing the dynamic compressor 100 in a controlled environment, by a combination of simulation and testing, or by any other suitable method for predetermining the values ​​for speed, pressure ratio, inlet mass flow rate, and VIGV position of each predetermined operating point 50.

[0040] The predetermined operating points 50, which are retrieved from the characteristic map 700, can themselves indicate the throttle speed or the surge speed of the dynamic compressor 100 at the starting pressure ratio PR. At a starting pressure ratio PR = 25% head, the surge speed N is surge for example 15% of the design speed and the throttle speed N choke 30% of the design speed. The scaling factor k can be selected so that the speed setpoint N set on the dashed line 760 between the pumping speed N surge and the throttle speed N choke For example, k can be chosen so that the speed setpoint N set at 25% design speed, as in Fig. 7. In further embodiments, the predetermined operating points 50 retrieved from the map 700 can be used to graphically or numerically determine the throttle speed or the surge speed at the starting pressure ratio PR, e.g., by interpolation. In further embodiments, the predetermined operating points 50 that are closest to the surge speed and the throttle speed can be retrieved.

[0041] The processor 420 is further programmed to control the dynamic compressor 100 with the speed setpoint N set operates 616 to compress the working fluid until a condition is met. In some embodiments, the processor 420 operates 616 the dynamic compressor 100 at the speed setpoint N setuntil a predetermined start-up time expires. The predetermined start-up time may be, for example and without limitation, 1 minute, 2 minutes, or another suitable duration. In further embodiments, the processor 420 is further programmed to measure a measured pressure ratio PR meas of the dynamic compressor 100 and the dynamic compressor 100 with the speed setpoint N set operates until the measured pressure ratio PR meas the estimated pressure ratio PR est exceeds.

[0042] The measured pressure ratio PR meas can be calculated from measured pressure values. For example, instructions may be stored in memory 430 that program processor 420 to calculate a value of a first measured pressure P 1,meas of the working fluid upstream of the dynamic compressor 100. The first measured pressure P 1,meascan be obtained from the inlet pressure sensor 111 located near the first refrigerant inlet 110. Similarly, the memory 430 can store additional instructions that program the processor 420 to obtain a value of a second measured pressure P 2,meas of the working fluid downstream of the dynamic compressor 100. The second measured pressure P 2,meas can be obtained from the outlet pressure sensor 121 located near the second refrigerant outlet 120.

[0043] In such embodiments, the memory 430 stores further instructions that program the processor 420 to calculate a measured pressure ratio PR meas based on the first and second measured pressures P 1,meas , P 2,meas The measured pressure ratio PR meas can be considered as the second measured pressure P 2,meas divided by the first pressure P 1,meas be calculated: PRmeas=P2,measP1,meas In further embodiments, the processor 420 is programmed to control the dynamic compressor 100 with the speed setpoint N set operates 616 to compress the working fluid until the measured pressure ratio PR meas the estimated pressure ratio PR est or the predetermined start-up time expires.

[0044] The Fig. 8A and Fig. 8B (together Fig. 8) show an exemplary control algorithm 800 for calculating the start-up pressure ratio PR of the dynamic compressor according to the method 600. After receiving 802 the command to start up the dynamic compressor 100, the processor 420 calculates 804 the first working fluid saturation temperature T 1,wf on the first working fluid path 342 of the evaporator 340. In the illustrated embodiment, the first working fluid saturation temperature T 1,wfat the first working fluid path 342 as the difference between the first heat transfer fluid temperature T measured at the first heat transfer fluid path 344 1,htf and a first temperature offset T e calculated: T1,wf=T1,htf−Te

[0045] The first temperature offset T e takes into account the temperature difference between the saturated refrigerant in the first working fluid path 342 and the heat transfer fluid exiting the first heat transfer fluid path 344. The first temperature offset T e may be, for example, and without limitation, 5 degrees F, 10 degrees F, or any other suitable temperature offset.

[0046] Similarly, the second heat transfer fluid temperature T 2,htf, which is measured at the second heat transfer fluid path 324 of the condenser 320, a temperature offset is added to account for the temperature difference between the saturated refrigerant in the second working fluid path 322 and the heat transfer fluid exiting the second heat transfer fluid path 324. In the Fig. 8, the processor 420 determines 806 what type of heat transfer fluid is used in the second heat transfer fluid path 324 of the condenser 320 and calculates 808, 810 the second working fluid saturation temperature T 2,wf in the second working fluid path 322 accordingly. If the processor 420 determines that the heat transfer fluid is water, the second working fluid saturation temperature T 2,wfat the second working fluid path 322 are calculated 808 as the sum of the second heat transfer fluid temperature T measured at the second heat transfer fluid path 324 2,htf and a second temperature offset T cw : T2,wf=T2,htf+Tcw

[0047] The second temperature offset T cw may be, for example and without limitation, 5 degrees F, 10 degrees F, 20 degrees F, or another suitable temperature offset. If the processor 420 determines that the heat transfer fluid is air, the second working fluid saturation temperature T 2,wf at the second working fluid path 322 are calculated 810 as the sum of the second heat transfer fluid temperature T measured at the second heat transfer fluid path 324 2,htf and a second temperature offset T ca : T2,wf=T2,htf+Tca

[0048] The second predetermined temperature offset T camay be, for example and without limitation, 10 degrees F, 20 degrees F, or any other suitable temperature offset.

[0049] In the Fig. 8, the processor 420 is further programmed to determine the first and second pressures P1, P2 based on the first and second working fluid saturation temperatures T 1,wf , T 2,wf determined 812 and the estimated pressure ratio PR est as the second pressure P2 divided by the first pressure P1 is calculated 814. The processor 420 then determines 816 the surge and throttle speeds N surge , N choke of the dynamic compressor 100 at the estimated pressure ratio PR est and calculates 818 the speed setpoint N set of the dynamic compressor 100 as a value between the surge and throttle speeds N surge , N choke .

[0050] The processor 420 is then programmed to control the dynamic compressor 100 with the speed setpoint N set starts 820 and starts a startup timer. The startup timer can have a startup time t start which indicates the time that has elapsed since the start of operation of the dynamic compressor 100. The processor 420 determines 822 whether the start-up time t start a start-up completion time t1 has been reached, and if so, it also determines that the start-up is complete and starts based on the measured pressure ratio PR meas with the operation of the dynamic compressor 100. In the illustrated embodiment, the start-up termination time t1 is one minute, but the start-up termination time t1 may be any suitable period of time, for example and without limitation, 30 seconds, 90 seconds, or two minutes. If the processor 420 determines 822 that the start-up time t starthas not yet reached the start-up completion time t1, the processor 420 also determines 826 which of the estimated pressure ratios PR est and the measured pressure ratio PR meas is greater. The processor 420 then determines 828 the pumping and throttling speeds N surge , N choke , which corresponds to the larger of the two pressure ratios PR est , PR meas and calculates 830 the speed setpoint N set of the dynamic compressor 100 as a value between the surge and throttle speeds N surge , N choke new. The processor 420 sets 832 the speed of the dynamic compressor 100 to the newly calculated speed setpoint N set , and the processor 420 determines 822 again whether the start-up time t start the start-up termination time t1 has been reached and proceeds with the following steps described above.

[0051] The technical advantages of the systems described here are as follows: (1) existing system instruments can be used to determine a safe operating range for a dynamic compressor during its start-up routine, (2) compressor reliability can be improved by limiting the time the compressor spends outside the safe operating range.

[0052] The terms "about," "substantially," "mainly," and "approximately," when used herein in connection with ranges of dimensions, concentrations, temperatures, or other physical or chemical properties or characteristics, are intended to cover variations that may occur at the upper and / or lower limits of the ranges of properties or characteristics, including, for example, variations resulting from rounding, methods of measurement, or other statistical variations.

[0053] When introducing elements of the present disclosure or its embodiment(s), the articles "a," "an," "an," "the," "the," and "said" are intended to mean that there is one or more of the elements. The terms "comprising," "including," "containing," and "having" are intended to be all-inclusive and mean that there may be additional elements in addition to those listed. The use of terms indicating a particular orientation (e.g., "top," "bottom," "side," etc.) is for convenience of description and does not require a particular orientation of the described subject matter.

[0054] Since various changes could be made in the above constructions and methods without departing from the scope of the disclosure, all matter contained in the above description and shown in the accompanying drawings is to be regarded as illustrative and not in a limiting sense. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 17 / 804 317

[0001]

Claims

[1] System, with: an evaporator having a first working fluid path and a first heat transfer fluid path thermally coupled thereto; a condenser having a second working fluid path and a second heat transfer fluid path thermally coupled thereto; 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 operable to compress a working fluid; a first temperature sensor positioned in the first heat transfer fluid path of the evaporator; a second temperature sensor positioned in the second heat transfer fluid path of the condenser; a control device connected to the dynamic compressor, the control device comprising a processor and a memory, the memory storing instructions that program the processor to: Receiving a command to start operation of the dynamic compressor; Receiving a first heat transfer fluid temperature from the first temperature sensor; Determining a first pressure in the first working fluid path of the evaporator based on the first heat transfer fluid temperature; Receiving a second heat transfer fluid temperature from the second temperature sensor; Determining a second pressure in the second working fluid path of the condenser based on the second heat transfer fluid temperature; Determining a pressure ratio of the dynamic compressor from the first and second pressures; Determining a speed setpoint of the dynamic compressor based on the pressure ratio; and Operating the dynamic compressor at the speed setpoint to compress the working fluid until a condition is met. [2] The system of claim 1, wherein operating the dynamic compressor at the speed setpoint until a condition is met comprises operating the dynamic compressor at the speed setpoint until a predetermined start-up time expires. [3] The system of claim 1 or claim 2, wherein determining the first pressure comprises: Determining a first working fluid saturation temperature at the first heat transfer 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 equation for the working fluid; and wherein determining the second pressure comprises: Determining a second working fluid saturation temperature at the second heat transfer 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 working fluid equation. [4] The system of claim 1 or claim 2, wherein determining the first pressure comprises: Determining a first working fluid saturation temperature at the first working fluid path of the evaporator based on the first heat transfer fluid temperature; and Retrieving a first pressure value corresponding to the first working fluid saturation temperature from a working fluid data table stored in the memory, and wherein determining the second pressure comprises: Determining a second working saturated fluid temperature at the second working fluid path of the condenser based on the second heat transfer fluid temperature; and Retrieving a second pressure value corresponding to the second working fluid saturation temperature from the working fluid data table. [5] The system of claim 1 or claim 2, wherein determining the pressure ratio comprises calculating an estimated pressure ratio as the second pressure divided by the first pressure. [6] The system of claim 1 or claim 2, wherein the pressure ratio is an estimated pressure ratio, and wherein the memory stores further instructions programming the processor to: Receiving a value of a first measured pressure of the working fluid upstream of the dynamic compressor; Receiving a value of a second measured pressure of the working fluid downstream of the dynamic compressor; and Determining a measured pressure ratio based on the first and second measured pressures. [7] The system of claim 6, wherein operating the dynamic compressor at the speed setpoint until the condition is met comprises operating the dynamic compressor at the speed setpoint until the measured pressure ratio exceeds the estimated pressure ratio. [8] The system of claim 6, wherein operating the dynamic compressor at the speed setpoint comprises operating the dynamic compressor at the speed setpoint until a first of the measured pressure ratio exceeding the estimated pressure ratio or a predetermined ramp-up time elapses. [9] The system of any one of claims 1 to 8, wherein determining the speed setpoint of the dynamic compressor comprises: Determining a pumping speed corresponding to the pressure ratio; Determining a throttle speed corresponding to the pressure ratio; and Determine that the speed setpoint is a value between the surge speed and the throttle speed. [10] A system according to any one of claims 1 to 9, wherein the dynamic compressor is a centrifugal compressor. [11] A control device for a system, the system comprising an evaporator, a condenser and a dynamic compressor fluidly coupled therebetween, the control device comprising: a processor; and a memory, the memory storing instructions that program the processor to: Receiving a command to start operation of the dynamic compressor; Determining a first heat transfer fluid temperature at a first heat transfer fluid path of the evaporator; Determining a first pressure at a first working fluid path of the evaporator based on the first heat transfer fluid temperature; Determining a second heat transfer fluid temperature at a second heat transfer fluid path of the condenser; Determining a second pressure at a second working fluid path of the condenser based on the second heat transfer fluid temperature; Calculating a pressure ratio of the dynamic compressor from the first and second pressures; Determining a speed setpoint of the dynamic compressor based on the pressure ratio; and Operating the dynamic compressor at the speed setpoint to compress a working fluid until a condition is met. [12] The controller of claim 11, wherein determining the first heat transfer fluid temperature comprises receiving the first heat transfer fluid temperature from a first temperature sensor on the first heat transfer fluid path of the evaporator, and wherein determining the second heat transfer fluid temperature comprises receiving the second heat transfer fluid temperature from a second temperature sensor on the second heat transfer fluid path of the condenser. [13] A control device according to claim 11 or claim 12, wherein determining the first pressure comprises: Determining a first working fluid saturation temperature at 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 equation of the working fluid; and wherein determining the second pressure comprises: Determining a second working fluid saturation temperature at 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 second working fluid saturation temperature using the empirical working fluid equation. [14] The controller of claim 13, wherein determining the first working fluid saturation temperature comprises subtracting a first temperature offset from the first heat transfer fluid temperature, and wherein determining the second working fluid saturation temperature comprises adding a second temperature offset to the second heat transfer fluid temperature. [15] A control device according to claim 11 or claim 12, wherein determining the first pressure comprises: Determining a first working fluid saturation temperature at 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 working fluid data table stored in memory, and wherein determining the second pressure comprises: Determining a second working fluid saturation temperature at 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 working fluid data table. [16] A control device according to any one of claims 11 to 15, wherein determining the pressure ratio comprises calculating an estimated pressure ratio as the second pressure divided by the first pressure. [17] A control device according to any one of claims 11 to 15, wherein the pressure ratio is an estimated pressure ratio, and wherein the memory stores further instructions programming the processor to: Receiving a value of a first measured pressure of the working fluid upstream of the dynamic compressor; Receiving a value of a second measured pressure of the working fluid downstream of the dynamic compressor; and Determining a measured pressure ratio based on the first and second measured pressures. [18] The control device of claim 17, wherein operating the dynamic compressor at the speed setpoint until the condition is met comprises operating the dynamic compressor at the speed setpoint until the measured pressure ratio exceeds the estimated pressure ratio. [19] The controller of claim 17, wherein operating the dynamic compressor at the speed setpoint comprises operating the dynamic compressor at the speed setpoint until the first of the measured pressure ratio exceeding the estimated pressure ratio or a predetermined start-up time elapses. [20] Control device according to one of claims 11 to 19, wherein determining the speed setpoint of the dynamic compressor comprises: Determining a pumping speed corresponding to the pressure ratio; Determining a throttle speed corresponding to the pressure ratio; and Determine that the speed setpoint is a value between the surge speed and the throttle speed.

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