System, controller, and method for controlling a co2 refrigeration system

Abstract

A method of controlling a CO2 refrigeration system includes obtaining a target outlet pressure of refrigerant from a gas cooler / condenser, a measurement of a pressure of a flash tank, and an opening percentage of a bypass valve (BGV). Whether to reduce the pressure of the flash tank is determined based at least in part on the pressure of the flash tank and the opening percentage of the BGV. When the controller determines to reduce the pressure of the flash tank, the target outlet pressure is increased by an amount.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 615,936, filed on December 29, 2023, which is incorporated herein by reference in its entirety. Background Technology

[0003] This application generally relates to the control of refrigeration systems. More specifically, this application relates to systems, controllers, and methods for controlling CO2 refrigeration systems.

[0004] Known CO2 refrigeration systems typically employ a dual-mode control architecture, changing the control mode depending on whether the system is operating in subcritical or transcritical mode. Mode switching is usually based on the user's selection of a threshold temperature. In some systems, the threshold temperature is the critical temperature of the refrigerant (CO2). Subcritical mode is used when the refrigerant temperature at the gas cooler / condenser outlet is below the critical temperature, and transcritical mode is used when the refrigerant temperature at the gas cooler / condenser outlet is at or above the critical temperature. Such a dual-mode control scheme can cause the system itself to switch back and forth between modes, even when the ambient conditions around the unit remain unchanged, particularly in areas where operating conditions are near the critical temperature. Mode switching is usually based on the user's selection of a threshold temperature. For at least some heat recovery applications, the unit can operate only in transcritical mode to increase heat generation even at low ambient temperatures and low gas cooler outlet CO2 temperatures.

[0005] Furthermore, at least some known systems attempt to use high-pressure valves (HPVs) to control the pressure at the outlet of a gas cooler / condenser to a target pressure determined based on the temperature of the refrigerant at the outlet, regulated by one or more fans. Changing pressure causes a change in the refrigerant temperature at the outlet, which may cause the system to change its pressure target to one determined based on the new temperature, again causing a temperature change. The fans will then attempt to regulate the temperature, leading to pressure changes. This "tail-chasing" is typically observed when the heat transfer performance of the gas cooler / condenser is reduced or its size is insufficient, and the temperature of the refrigerant at the outlet does not follow the temperature of the air input to the gas cooler / condenser.

[0006] In subcritical mode, the subcooling at the gas cooler outlet becomes a control objective in some systems. This typically involves altering the control algorithm used for the gas cooler pressure control valve, as this valve is now used as a subcooling control valve. This is also the main reason why a two-mode control approach is often employed in CO2 systems. To avoid instability in subcooling control, a minimum condensing pressure limit is usually applied to operate the system at a condensing temperature much higher than the inlet air temperature. Therefore, the system operates at lower efficiency to maintain stability.

[0007] This background section is intended to introduce the reader to various aspects of the art that may relate to the aspects of this disclosure described below and / or claimed. This discussion is intended to help provide the reader with background information to facilitate a better understanding of the various aspects of this disclosure. Therefore, it should be understood that these statements are to be read in this context and not as an admission of prior art. Summary of the Invention

[0008] One aspect of this disclosure is a CO2 refrigeration system including a compressor, a gas cooler / condenser, a flash tank, a bypass valve (BGV), and a controller. The gas cooler / condenser receives refrigerant discharged from the compressor and outputs a refrigerant flow. The gas cooler / condenser can operate as a gas cooler when the CO2 refrigeration system operates in transcritical mode, and as a condenser when the CO2 refrigeration system operates in subcritical mode. A flash tank is connected to receive refrigerant output from the gas cooler / condenser. The BGV, located between the flash tank and the suction side of the compressor, controls the refrigerant flow from the flash tank to the suction side of the compressor. The controller includes a processor and a memory. The processor is configured via instructions stored in memory to perform the following steps: obtaining a target outlet pressure of the refrigerant from the gas cooler / condenser, a measurement of the flash tank pressure, and the percentage of the BGV open; determining whether to reduce the flash tank pressure based at least in part on the flash tank pressure and the BGV open percentage; and increasing the target outlet pressure by a certain amount when the controller determines to reduce the flash tank pressure.

[0009] Another aspect of this disclosure is a controller for a CO2 refrigeration system, the CO2 refrigeration system comprising: a compressor; a gas cooler / condenser that receives refrigerant discharged from the compressor and outputs a refrigerant flow; a flash tank connected to receive refrigerant output from the gas cooler / condenser; and a bypass valve (BGV) located between the flash tank and the suction side of the compressor for controlling the refrigerant flow from the flash tank to the suction side of the compressor. The controller includes a processor and a memory. The processor is configured, via instructions stored in the memory, to perform the following steps: obtaining a target outlet pressure of the refrigerant from the gas cooler / condenser, a measurement of the pressure of the flash tank, and the percentage of opening of the BGV; determining whether to reduce the pressure of the flash tank based at least in part on the pressure of the flash tank and the percentage of opening of the BGV; and increasing the target outlet pressure by a certain amount when the controller determines to reduce the pressure of the flash tank.

[0010] Another aspect of this disclosure is a method for controlling a CO2 refrigeration system, the CO2 refrigeration system comprising: a compressor; a gas cooler / condenser that receives refrigerant discharged from the compressor and outputs a refrigerant flow; a flash tank connected to receive refrigerant output from the gas cooler / condenser; and a bypass valve (BGV) located between the flash tank and the suction side of the compressor for controlling the refrigerant flow from the flash tank to the suction side of the compressor. The method includes: obtaining a target outlet pressure of the refrigerant from the gas cooler / condenser, a measurement of the pressure of the flash tank, and a percentage opening of the BGV; determining whether to reduce the pressure of the flash tank based at least in part on the pressure of the flash tank and the percentage opening of the BGV; and increasing the target outlet pressure by a certain amount when the controller determines to reduce the pressure of the flash tank.

[0011] Various improvements exist regarding the features indicated in the foregoing aspects. Other features may also be incorporated into the foregoing aspects. These improvements and additional features may exist individually or in any combination. For example, the various features discussed below with respect to any embodiment of the illustrated embodiments may be incorporated individually or in any combination into any of the foregoing aspects. Attached Figure Description

[0012] The accompanying figures below illustrate various aspects of this disclosure.

[0013] Figure 1 This is a schematic diagram of an example CO2 refrigeration system.

[0014] Figure 2 It is used for Figure 1A flowchart of the existing technology control algorithm for controlling the gas cooler of a CO2 refrigeration system.

[0015] Figure 3 This disclosure is for the purpose of Figure 1 A flowchart of an example control algorithm for a CO2 refrigeration system.

[0016] Figure 4 It is used in Figure 1 An example controller used in a CO2 refrigeration system.

[0017] Figure 5 This disclosure is for the purpose of Figure 1 The flowchart shows another example of a control algorithm for a CO2 refrigeration system.

[0018] Figure 6 This disclosure is for the purpose of controlling Figure 1 The flow diagram of an example control algorithm for a CO2 refrigeration system.

[0019] Figure 7 It is based on Figure 6 The algorithm operates at an ambient temperature of approximately 60°F. Figure 1 A graph showing the system's fan speed percentage, HPV on percentage, refrigerant outlet pressure from the refrigerant stream in the gas cooler / condenser, and target outlet pressure.

[0020] Figure 8 It is based on Figure 6 The algorithm operates at an ambient temperature of approximately 20°F. Figure 1 A graph showing the system's fan speed percentage, HPV on percentage, refrigerant outlet pressure from the refrigerant stream in the gas cooler / condenser, and target outlet pressure.

[0021] Figure 9 This disclosure is for the purpose of controlling Figure 1 The flow diagram of an example control algorithm for a CO2 refrigeration system.

[0022] Figure 10 Is using Figure 9 The graph shows the various operational characteristics of an example system operating over a period of time for two regional versions of the algorithm.

[0023] Figure 11 This disclosure is for the purpose of controlling Figure 1 A flow diagram of an example control algorithm for a CO2 refrigeration system that keeps the BGV off where possible.

[0024] Figure 12 Is using including Figure 11 The algorithm controls and adjusts the operation. Figure 1The system's various operational characteristics are represented by graphs.

[0025] Throughout the accompanying drawings, corresponding reference numerals indicate the corresponding parts. Detailed Implementation

[0026] Example embodiments will now be described more fully with reference to the accompanying drawings. For convenience, embodiments will be described with respect to CO2 rack systems using multiple compressors operating in parallel. However, the systems, controllers, and methods of this disclosure can be applied to any suitable CO2 refrigeration system, including condenser units and systems incorporating condenser units.

[0027] Reference Figure 1 An example CO2 refrigeration system 10 is shown. Example system 10 is a medium-temperature, pressurized, cryogenic CO2 refrigeration system, but other embodiments may include any other suitable CO2 refrigeration system. System 10 includes a cryogenic compressor rack 12 with compressors 13, 14 and a medium-temperature compressor rack 16 with compressors 17, 18, 19. Compressors 13, 14, 17, 18, 19 may be fixed-capacity compressors or variable-capacity compressors. For example, each compressor rack 12, 16 may include at least one variable-capacity compressor and at least one fixed-capacity compressor. The compressors in each rack may be connected via suitable suction and discharge manifolds. The cryogenic compressor rack 12 may be connected in series with the medium-temperature compressor rack 16 such that refrigerant discharged from the cryogenic compressor rack 12 is received on the suction side of the medium-temperature compressor rack 16. The number of compressors shown is merely an example; other embodiments may include more or fewer compressors in each rack, including only one cryogenic compressor and one medium-temperature compressor.

[0028] Refrigerant (e.g., CO2) discharged from the intermediate-temperature compressor rack 16 is received / introduced to the gas cooler / condenser 20. As described further in detail below, the refrigeration system 10 can operate in subcritical or transcritical mode. In transcritical mode, the gas cooler / condenser 20 functions as a gas cooler. In subcritical mode, the gas cooler / condenser 20 functions as a condenser. For simplicity, the gas cooler / condenser 20 may sometimes be referred to herein as a gas cooler or a condenser, without limiting the gas cooler / condenser 20 to only being able to operate as a gas cooler or condenser or currently operating as a gas cooler or condenser.

[0029] Fan 27 provides airflow into gas cooler / condenser 20. The fan includes a motor 28 controlled by speed controller 29. Speed ​​controller 29 controls the speed of motor 28 in response to commands from system controller 50, thereby controlling the airflow into gas cooler / condenser 20. In other embodiments, speed controller 29 is integrated into system controller 50. In various embodiments, fan 27 is a component of gas cooler / condenser 20.

[0030] The refrigerant output from the gas cooler / condenser 20 is received by a liquid receiver 21 (sometimes referred to as a flash tank). The liquid receiver 21 is connected to a first discharge line 22, which guides gaseous refrigerant from the liquid receiver 21 back to the suction side of the intermediate-temperature compressor frame 16. The liquid receiver 21 is also connected to a second discharge line 23, which guides liquid refrigerant from the liquid receiver 21 to the evaporators 24, 26.

[0031] Refrigerant, guided from liquid receiver 21 via second discharge line 23, is received by low-temperature evaporator 24 and medium-temperature evaporator 26. Low-temperature evaporator 24 may include, for example, a grocery store freezer or a frozen food container. Medium-temperature evaporator 26 may include, for example, a dairy container or a meat container.

[0032] The refrigerant from the low-temperature evaporator 24 is then discharged to the suction side of the low-temperature compressor frame 12. The refrigerant from the medium-temperature evaporator 26 is then discharged to the suction side of the medium-temperature compressor frame 16. The refrigeration cycle then restarts.

[0033] The refrigeration system 10 may include various valves controlled by various associated controllers to monitor and regulate various temperatures and pressures within the refrigeration system 10, thereby maintaining efficient and desired operation.

[0034] Specifically, the refrigeration system 10 includes a high-pressure valve (HPV) 30 and a bypass gas valve (BGV) 40. For example... Figure 1 As shown, HPV 30 is connected between the output of the gas cooler / condenser 20 and the liquid receiver 21. BGV 40 is located on the first discharge line 22 between the liquid receiver 21 and the suction side of the intermediate-temperature compressor frame 16. As described in further detail below, HPV 30 and BGV 40 are regulated and controlled to maintain certain system operating conditions for efficient and desired operation. For example, HPV 30 controls the flow of refrigerant from the gas cooler / condenser 20 to the liquid receiver 21. BGV 40 controls the flow of refrigerant from the liquid receiver 21 to the suction side of the intermediate-temperature compressor frame 16. HPV 30 and BGV 40 may include associated stepper motors, for example, for variable adjustment of valve opening.

[0035] The low-temperature evaporator 24 and the medium-temperature evaporator 26 each include associated expansion valves (EV) 42 and 44.

[0036] The refrigeration system 10 includes various controllers that monitor operating and environmental conditions, including temperature and pressure, and control various system components according to a programmed control strategy. Specifically, the system controller 50 controls compressor racks 12 and 16 by activating, deactivating, and regulating compressors 13, 14, 17, 18, and 19 of compressor racks 12 and 16. The system controller 50 also controls the gas cooler / condenser 20 by activating, deactivating, and regulating the fan of the gas cooler / condenser 20. The system controller 50 can be any suitable controller, including a processor and memory storing appropriate instructions executable by the processor to program the processor to operate according to this disclosure. The system controller 50 may include a user interface (e.g., a touchscreen or display screen) and user input devices (e.g., a keyboard) for communicating with the user. For example, the system controller 50 may output system parameters such as system operating temperature or pressure and / or system setpoint to the user. Furthermore, the system controller 50 may receive user input that modifies the system setpoint or control algorithm.

[0037] The refrigeration system 10 includes a valve controller 60 programmed to control HPV 30 and BGV 40. Although illustrated as separate components, in some embodiments, some or all of the functions of the valve controller may be included in a system controller 50, and actions attributable to the valve controller 60 may be performed by the system controller 50, and / or the system controller may be communicatively coupled to the valve controller 60 to control HPV and / or BGV by instructing the valve controller 60. The valve controller 60 is connected to various temperature and pressure sensors to monitor system and environmental conditions. Specifically, the valve controller 60 is connected to a refrigerant temperature sensor 62, which senses the outlet temperature of the refrigerant leaving the gas cooler / condenser 20. The valve controller 60 is also connected to a refrigerant pressure sensor 64, which senses the outlet pressure of the refrigerant leaving the gas cooler / condenser 20. Although Figure 1Separate pressure and temperature sensors are shown, but alternatively, a single combined refrigerant pressure and temperature sensor can be used to sense both the pressure and temperature of the refrigerant leaving the gas cooler / condenser 20. Valve controller 60 is also connected to temperature sensor 66, which senses the temperature of the airflow entering the gas cooler / condenser 20 from fan 27; this airflow temperature is sometimes referred to as the inlet air temperature. In other embodiments, temperature sensor 66 senses the outdoor ambient temperature, which may be the temperature of the air to be directly or indirectly input to the gas cooler / condenser. Valve controller 60 is also connected to liquid receiver pressure sensor 68, which senses the pressure of the refrigerant within liquid receiver 21 (sometimes also referred to as flash tank pressure). As discussed in further detail below, valve controller 60 controls the openings of HPV 30 and BGV 40 to maintain efficient and desired operation of the refrigeration system 10 in both subcritical and transcritical modes.

[0038] Valve controller 60 can be any suitable controller with appropriate programming for controlling HPV 30 and BGV 40 according to this disclosure. Furthermore, valve controller 60 may include a user interface (e.g., a touchscreen or display screen) and user input devices (e.g., a keyboard) for communicating with the user. For example, valve controller 60 may output system parameters such as system operating temperature or pressure and / or system setpoints to the user. Additionally, valve controller 60 may receive user input that modifies the system setpoint or control algorithm.

[0039] The refrigeration system 10 also includes a housing controller 70, 80 for controlling the low-temperature evaporator 24 and the medium-temperature evaporator 26, and their associated expansion valves 42, 44. For example, the housing controller 70, 80 can activate, deactivate, and regulate the evaporator fans of the evaporators 24, 26. The housing controller can also regulate the expansion valves 42, 44. The housing controller 70, 80 can be any suitable controller with appropriate programming according to this disclosure. Furthermore, the housing controller can be implemented as part of the system controller 50. Additionally, the housing controller 70, 80 can include a user interface (e.g., a touchscreen or display screen) and user input devices (e.g., a keyboard) for communicating with the user. For example, the housing controller 70, 80 can output system parameters such as system operating temperature or pressure and / or system setpoints to the user. Furthermore, the housing controller 70, 80 can receive user input that modifies the system setpoint or control algorithm.

[0040] Figure 1Each controller shown is operable to communicate with each other. For example, system controller 50 can adjust the operation or setpoint of valve controller 60 and box controllers 70, 80. Furthermore, if a local sensor of valve controller 60 fails, valve controller 60 can communicate with system controller 50 or box controllers 70, 80 to adjust its operation accordingly. For example, if local temperature sensor 66 of valve controller 60 fails, valve controller 60 can communicate with system controller 50 or box controllers 70, 80 to receive inlet air temperature data or ambient air temperature data from a temperature sensor connected to or accessible by system controller 50 or box controllers 70, 80. Moreover, as described above, valve controllers and box controllers 70, 80 can be implemented wholly or partially within system controller 50 (as hardware, software, or both), and system controller 50 can perform functions attributed herein to other controllers. In some implementations, system controller 50 performs some or all of the actions of other controllers by directing valve controller 60 and / or box controller 70, 80 to perform operations.

[0041] In addition, remote computer 90 can be connected to system controller 50, allowing remote users to log in to system controller 50 and monitor, control, or regulate the operation of any controller among the controllers including system controller 50, valve controller 60, and box controllers 70 and 80.

[0042] Furthermore, system controller 50 can communicate with building automation system (BAS) 95. BAS 95 can connect to additional temperature and pressure sensors and can monitor and store additional temperature and pressure data, which can be accessed by system controller 50 and / or valve controller 60 in the event of sensor failure. Remote computer 90 can also connect to BAS 95, allowing remote users to log in to BAS 95 and monitor, control, or regulate the operation of any controller, including system controller 50, valve controller 60, and box controllers 70 and 80.

[0043] Reference Figure 2A prior art control algorithm 200 for regulating HPV 30 is shown. Control algorithm 200 can be executed by valve controller 60. Alternatively, control algorithm 200 can be executed by system controller 50, which can output appropriate control signals to valve controller 60 or directly to HPV 30. During operation using control algorithm 200, fan speed is controlled by speed controller 29 using non-feedback control based on air inlet temperature or other criteria. Control algorithm 200 begins at 202. At 204, valve controller 60 receives pressure and temperature values ​​from connected pressure sensors 64, 68 and temperature sensors 62, 66. Specifically, valve controller 60 receives data indicating the pressure and temperature of the refrigerant leaving gas cooler / condenser 20, ambient air temperature, and pressure within liquid receiver 21. In this prior art example, sensor 66 is an outdoor ambient temperature sensor.

[0044] At position 206, valve controller 60 determines whether refrigeration system 10 is operating in subcritical or transcritical mode. For example, valve controller 60 may compare the current system or operating conditions with a specific system or operating condition setpoint. As an example, valve controller 60 may compare the current ambient air temperature with a temperature setpoint to determine whether refrigeration system 10 is in subcritical or transcritical mode. When the air temperature is above the temperature setpoint, valve controller 60 may determine that refrigeration system 10 is in transcritical mode. When the air temperature is below the temperature setpoint, valve controller 60 may determine that refrigeration system 10 is in subcritical mode. For example, the temperature setpoint could be 14 degrees Celsius. As another example, valve controller 60 may compare the current air temperature with a temperature setpoint minus a predetermined hysteresis value. In this case, for example, the temperature setpoint could be 21 degrees Celsius, and the hysteresis value could be 7 degrees Celsius. Both the temperature setpoint and the hysteresis value can be user-configurable. Alternatively, valve controller 60 may determine this by comparing the current temperature and / or pressure of the refrigerant leaving gas cooler / condenser 20 with a temperature or pressure setpoint. Alternatively, the valve controller 60 can combine the pressure and / or temperature of the refrigerant leaving the gas cooler / condenser 20 to assess the air temperature in order to determine whether the refrigeration system 10 is operating in subcritical or transcritical mode.

[0045] At point 208, when the refrigeration system 10 is in subcritical mode, valve controller 60 proceeds to point 210. At point 210, valve controller 60 calculates the current subcooling temperature based on the temperature and pressure of the refrigerant leaving the gas cooler / condenser 20. Specifically, based on the temperature and pressure of the refrigerant leaving the gas cooler / condenser 20, valve controller 60 can determine the critical point of the refrigerant. Valve controller 60 can then compare the critical point of the refrigerant with the current temperature of the refrigerant leaving the gas cooler / condenser 20. Valve controller 60 can determine the subcooling temperature value as the difference between the critical point of the refrigerant and the current temperature of the refrigerant leaving the gas cooler / condenser 20.

[0046] At 212, valve controller 60 compares the subcooling temperature with the subcooling temperature setpoint and determines the difference between the two values. For example, the subcooling temperature setpoint could be 10 degrees Celsius.

[0047] At 214, valve controller 60 adjusts HPV 30 based on this comparison. Specifically, valve controller 60 adjusts HPV 30 to drive the current subcooling temperature value toward the subcooling temperature setpoint. Valve controller 60 can appropriately adjust HPV 30 using PID control algorithms, PI control algorithms, fuzzy logic, or neural network-type control systems / algorithms. After adjusting HPV 30, the valve controller loops back to 204.

[0048] At 208, when the refrigeration system 10 is in transcritical mode, valve controller 60 proceeds to 216. At 216, valve controller 60 determines a pressure setpoint. For example, valve controller 60 may refer to a lookup table that includes pressure setpoints indexed based on system or environmental operating conditions. For example, the lookup table may include pressure setpoints indexed based on ambient air temperature. Thus, valve controller 60 can determine the current ambient air temperature and access the lookup table to determine the corresponding pressure setpoint. If the current ambient air temperature is between table entries, valve controller 60 can insert a pressure setpoint based on the most recent table entry. The lookup table may be stored in or accessible by valve controller 60. For example, the lookup table may be stored at system controller 50, and valve controller 60 may query system controller 50 to obtain the pressure setpoint. Alternatively, the lookup table may include pressure setpoints indexed based on the temperature or pressure of the refrigerant exiting gas cooler / condenser 20 or another system or environmental operating temperature or pressure.

[0049] Lookup tables can be dedicated to and optimized for specific models, sizes, or types of compressors or other system components. For example, system controller 50 can query individual compressors 13, 14, 17, 18, 19 in compressor racks 12, 16, or system controller 50 itself, to identify compressors present in refrigeration system 10. The most suitable lookup table can be determined based on the identified compressors included in refrigeration system 10, or an installation-specific lookup table can be generated. For example, each compressor 13, 14, 17, 18, 19 may include a separate compressor controller and / or non-volatile memory with sufficient identification information to identify the compressor's model, size, or type. This identification information can be used to determine the most suitable lookup table. Specific lookup tables can be pre-generated based on field data or experimental data and / or modeling data corresponding to the operation of each compressor model, size, type, etc. Furthermore, a model of a specific compressor can be generated based on field data and / or experimental data and then inserted into other similar compressors.

[0050] Alternatively, valve controller 60 can calculate the pressure setpoint as a function of inlet air temperature. Alternatively, valve controller 60 can determine the pressure setpoint based on other system or environmental data, such as the temperature or pressure of the refrigerant leaving gas cooler / condenser 20.

[0051] At 218, valve controller 60 compares the pressure of the refrigerant leaving gas cooler / condenser 20 with a determined pressure setpoint. At 220, valve controller 60 then controls HPV 30 based on this comparison. Specifically, valve controller 60 adjusts HPV 30 to drive the current pressure value toward the determined pressure setpoint. Valve controller 60 can appropriately adjust HPV 30 using PID control algorithms, PI control algorithms, fuzzy logic, or neural network-type control systems / algorithms. After adjusting HPV 30, the valve controller loops back to 204.

[0052] Figure 3 This disclosure pertains to the control of CO2 refrigeration systems (e.g., Figure 1 The flow diagram of the control algorithm 300 in system 10 is shown below. In this example, temperature sensor 66 is an inlet air temperature sensor that senses the temperature of the airflow entering the gas cooler / condenser 20 from fan 27. In the example embodiment, control algorithm 300 will be described as being executed by system controller 50. In other embodiments, control algorithm 300 may be executed by valve controller 60 and speed controller 29.

[0053] At 302, controller 50 receives the inlet air temperature from temperature sensor 66. At 304, controller 50 receives the outlet pressure of the refrigerant in the refrigerant stream from gas cooler / condenser from pressure sensor 64, and controller 50 receives the outlet temperature of the refrigerant in the refrigerant stream from gas cooler / condenser from temperature sensor 62.

[0054] At 310, controller 50 determines a target outlet pressure (also known as an outlet pressure setpoint) based on the received inlet air temperature. The target outlet pressure can be determined by calculation using an equation with the inlet air temperature as input. Any equation relating the inlet air temperature to the desired outlet pressure can be used. In an example implementation, this equation is a fifth-order polynomial equation. In other implementations, controller 50 uses a lookup table stored in controller 50's memory to determine the target outlet pressure. The lookup table can include a specific target outlet pressure for a particular inlet air temperature. Controller 50 can access the lookup table to determine the target outlet pressure corresponding to the inlet air temperature. If the received inlet air temperature falls between table entries, controller 50 can insert the target outlet pressure based on the most recent table entry. The lookup table can be dedicated to a particular model, size, or type of compressor or other system component and optimized for that specific model, size, or type of compressor or other system component. For example, system controller 50 can query the individual compressors 13, 14, 17, 18, 19 in compressor racks 12, 16 or system controller 50 to identify compressors present in refrigeration system 10, and can determine the most suitable lookup table based on the identified compressors included in refrigeration system 10, or can generate installation-specific lookup tables. For example, each compressor 13, 14, 17, 18, 19 may include a separate compressor controller and / or non-volatile memory with sufficient identification information to identify the compressor's model, size, or type. The identification information can be used to determine the most suitable lookup table. In other embodiments, a user or installer can identify the device to controller 50, select a specific lookup table to use, modify an existing table, or create a unique table. Specific lookup tables can be pre-generated based on field data or experimental data and / or modeling data corresponding to the operation of each compressor model, size, type, etc. Furthermore, a model of a specific compressor can be generated based on field data and / or experimental data and then inserted into other similar compressors.

[0055] In some implementations, controller 50 determines the target outlet pressure by determining the saturation pressure of the refrigerant at a calculated temperature, which is the sum of the inlet air temperature and a preset temperature difference. In one example, the preset temperature difference is approximately eleven degrees Fahrenheit. In other implementations, other preset temperature differences may be used. Controller 50 determines the saturation pressure at the calculated temperature using equations, lookup tables, or any other suitable technique.

[0056] In some implementations, controller 50 determines the target outlet pressure based on the received outlet temperature. The target outlet pressure can be determined by calculating subcooling with the outlet temperature as input. Any equation relating the outlet temperature to the desired outlet pressure can be used. In other implementations, controller 50 uses a lookup table, similar to that discussed above, stored in controller 50's memory and including a specific target outlet pressure for a given outlet temperature, to determine the target outlet pressure.

[0057] For CO2, 1070 pounds per square inch (PSIA) is the critical pressure for the fluid, and the target outlet pressure should be avoided when setting it near this pressure. Therefore, controller 50 is configured to determine the target outlet pressure to avoid a target outlet pressure that is 1070 PSIA plus or minus a preset pressure difference. In one example, the preset pressure difference is ±30 PSIA. In other implementations, the preset pressure difference can be any other suitable value and can be user / installer configurable. If the calculated target outlet pressure falls within a prohibited pressure range, controller 50 can round the target outlet pressure (up or down) to a value outside the range of 1070 PSIA plus or minus the preset pressure difference.

[0058] In the pressure target setting described above, the compressor operating envelope limit on the minimum discharge pressure can also be incorporated into the lookup table, or the maximum value of the lower limit pressure and the recommended discharge pressure can be used to ensure that the compressor does not operate outside its envelope.

[0059] At 310, controller 50 determines the target outlet temperature based on the received inlet air temperature. In an example implementation, if the inlet air temperature is greater than or equal to a preset temperature threshold, the controller determines the target outlet temperature as the sum of the inlet air temperature and a preset first air temperature difference. Typically, when the pressure target is above the critical pressure, the temperature difference can be set to zero or near zero to provide 100% fan speed output. When the pressure target is below the critical pressure, the maximum subcooling or minimum temperature target at the gas cooler outlet is determined by the saturated liquid enthalpy at the liquid receiver pressure, or, as a simple implementation, can be calculated as the average of the saturation temperature at the gas cooler pressure and the saturation temperature at the liquid receiver pressure. In an example implementation, the preset temperature threshold is seventy-seven degrees Fahrenheit. Other implementations may use any other suitable temperature threshold. If the inlet air temperature is less than the preset temperature threshold, controller 50 sets the target outlet temperature as the saturation temperature of the refrigerant at the target outlet pressure determined above, minus a preset second air temperature difference.

[0060] After setting the target outlet pressure and target outlet temperature, at 312, controller 50 controls HPV 30 to move the outlet pressure of the refrigerant in the refrigerant stream from the gas cooler / condenser 20 toward the target outlet pressure. At 314, controller 50 controls fan 27 to move the outlet temperature of the refrigerant in the refrigerant stream from the gas cooler / condenser 20 toward the target outlet temperature by selectively increasing or decreasing the speed of motor 28. The speed of the fan motor can be directly set / controlled by controller 50, or controller 50 can command speed controller 29 to control the fan motor to 100%. In the example embodiment, if the inlet air temperature is higher than or equal to a preset temperature threshold, the controller sets the speed of motor 28 of fan 27 to 100%.

[0061] Therefore, when the CO2 refrigeration system operates in transcritical mode and when the CO2 refrigeration system operates in subcritical mode, the controller 50 of this disclosure controls the HPV 30 and the fan 27 based on the inlet air temperature. That is, the controller 50 uses both the HPV 30 and the fan 27 together to control the system, based on the inlet air temperature, without needing to determine whether the system is in transcritical or subcritical mode, and without needing two different control schemes for the two different modes.

[0062] The control techniques described herein avoid the artificial lower limit of gas cooler condensing temperature under low ambient conditions, as found in at least some known systems, thereby improving system efficiency under such conditions. In some known system controllers, a lower limit of 15°C (59°F) is set for the gas cooler condensing temperature to prevent system instability, regardless of how low the ambient (or inlet) air temperature is. This reduces system efficiency because it operates the system at pressures above the required condensing pressure. In the currently applied system, the HPV is regulated to bring the outlet pressure sensor reading to its target. A fan speed controller is used to bring the outlet temperature sensor reading to its target. When both sensors are controlled to their targets, the subcooling requirement is automatically met without the artificial lower limit found in other known systems. Therefore, the system of this disclosure can operate at a lower condensing pressure under low ambient conditions, thereby improving system efficiency.

[0063] The optimal gas cooler pressure at a given gas cooler outlet temperature can also be maintained using the control scheme described herein. Although the gas cooler / condenser outlet pressure target is not set directly from the gas cooler / condenser outlet temperature reading during transcritical operation as is done in some known systems, the implementation of this disclosure will still satisfy the optimal gas cooler pressure at a given gas cooler outlet temperature for CO2 transcritical operation when both the pressure and temperature targets are met during steady-state operation.

[0064] Figure 4 This is an example configuration of a computing device 400 used as a controller in a CO2 refrigeration system 10 (e.g., as a control system 50, valve controller 60, speed controller, etc.). The computing device 400 includes a processor 402, a memory 404, a media output unit 406, an input device 410, and a communication interface 412. Other embodiments include different components, additional components, and / or no components. Figure 4 All the components shown.

[0065] Processor 402 is configured to execute instructions. In some embodiments, the executable instructions are stored in memory 404. Processor 402 may include one or more processing units (e.g., in a multi-core configuration). Memory 404 is any means that allows storage and retrieval of information such as executable instructions and / or other data. Memory 404 may include one or more computer-readable media.

[0066] Media output component 406 is configured to present information to user 408. Media output component 406 is any component capable of transmitting information to user 408. In some embodiments, media output component 406 includes output adapters such as video adapters and / or audio adapters. The output adapters are operatively connected to processor 402 and are operatively connected to output devices such as display devices (e.g., liquid crystal display (LCD), organic light-emitting diode (OLED) display, cathode ray tube (CRT), "electronic ink" display, one or more light-emitting diodes (LEDs)) or audio output devices (e.g., speakers or headphones).

[0067] The computing device 400 includes or is connected to an input device 410 for receiving input from a user 408. An input device is any means that allows the computing device 400 to receive analog and / or digital commands, instructions, or other inputs from the user 408, including visual, audio, touch, button presses, stylus taps, etc. Input device 410 may include, for example, a variable resistor, input dial, keyboard / keyboard, pointing device, mouse, stylus, touch-sensitive panel (e.g., touchpad or touchscreen), gyroscope, accelerometer, position detector, or audio input device. A single component such as a touchscreen may serve as an output device for both media output component 406 and input device 410.

[0068] Communication interface 412 enables computing device 400 to communicate with remote devices and systems, such as sensors 62, 64, 66, valve controller 60, speed controller 29, compressor racks 16, 12, remote computing device 90, BAS 95, etc. Communication interface 412 can be a wired or wireless communication interface that allows the computing device to communicate directly or via a network with remote devices and systems. Wireless communication interface 412 may include radio frequency (RF) transceivers, Bluetooth® adapters, Wi-Fi transceivers, ZigBee® transceivers, near field communication (NFC) transceivers, infrared (IR) transceivers, and / or any other devices and communication protocols for wireless communication (Bluetooth is a registered trademark of the Bluetooth Special Interest Group of Kirkland, Washington; ZigBee is a registered trademark of the ZigBee Consortium of San Ramon, California). Wired communication interface 412 can use any suitable wired communication protocol for direct communication, including but not limited to USB, RS232, I2C, SPI, analog, and proprietary I / O protocols. In some implementations, the wired network interface 412 includes a wired network adapter that allows a computing device to be coupled to a network such as the Internet, a local area network (LAN), a wide area network (WAN), a mesh network, and / or any other network to communicate with remote devices and systems via the network.

[0069] Figure 5 This disclosure pertains to the control of CO2 refrigeration systems (e.g., Figure 1 The flow diagram of the control algorithm 500 of system 10 is shown. In this algorithm, the CO2 outlet temperature target is set using the gas cooler inlet air temperature reading. The gas cooler pressure target can be set by using the desired subcooling to determine the subcritical pressure target, and the target for the transcritical case can be set using the optimal pressure for COP correlation. Critical pressure is avoided in both cases. Valve controller 60 uses only feedback pressure control to control HPV 30, and speed controller 29 uses only feedback temperature control to control fan 27.

[0070] As mentioned above, at least some existing CO2 systems attempt to operate both fan 27 and HPV 30 independently, which can lead to thermodynamic instability because the gas cooler / condenser temperature and pressure affect each other and cannot operate independently. This problem is amplified under low ambient temperature conditions. Furthermore, under low ambient conditions, this regulation can cause the gas cooler / condenser temperature and pressure to drop below the minimum condensing pressure of the system compressor. See below for further details. Figure 1 System 10 describes a method for controlling a CO2 refrigeration system to address low ambient temperature conditions. This method can be applied to any suitable CO2 refrigeration system and can be used in conjunction with methods 300 and 500 described above or with any other suitable control method.

[0071] Figure 6 This disclosure pertains to the control of CO2 refrigeration systems (e.g., Figure 1 The flow diagram of an example control algorithm 600 for system 10 is shown below. In the example implementation, control algorithm 600 will be described as being executed by system controller 50. In other implementations, control algorithm 600 may be executed by valve controller 60 and speed controller 29. In this example, temperature sensor 66 is an inlet air temperature sensor that senses the temperature of the airflow entering the gas cooler / condenser 20 from fan 27.

[0072] At 602, controller 50 receives inlet air temperature (also known as supply air temperature) from temperature sensor 66, outlet pressure of refrigerant in the refrigerant stream from gas cooler / condenser from pressure sensor 64, and outlet temperature of refrigerant in the refrigerant stream from gas cooler / condenser from temperature sensor 62.

[0073] At 604, controller 50 determines whether the inlet air temperature is less than the minimum condensing saturation temperature of the system compressor. The minimum condensing saturation temperature is a temperature threshold below which the supply air temperature is considered a low ambient temperature condition. In the example embodiment, the minimum condensing saturation temperature is calculated based on the minimum condensing pressure from the compressor envelope. In other embodiments, a fixed temperature may be used instead of the minimum condensing saturation temperature, which can be retrieved from a lookup table or calculated / determined by any other suitable method.

[0074] If the inlet air temperature is not less than the minimum condensing saturation temperature (i.e., greater than or equal to the minimum condensing saturation temperature), then at 606, controller 50 operates system 10 according to its standard operation. Therefore, for example, when used in conjunction with control algorithm 300, controller 50 will control HPV 30 to move the outlet pressure of the refrigerant in the refrigerant stream from gas cooler / condenser 20 toward the target outlet pressure. In this embodiment, when the inlet air temperature is greater than the minimum condensing saturation temperature, controller 50 commands speed controller 29 to control fan motor 28 to 100%, thus making HPV 30 the only variable to be controlled, and fan operation ensures subcooling. This operation in Figure 7 The curve is shown in graph 700. In graph 700, the fan speed percentage 702 is constant at 100%, and the HPV opening percentage 704 is controlled to move the refrigerant outlet pressure 706 in the refrigerant stream from the gas cooler / condenser 20 toward the target outlet pressure 708. When the data for graph 700 was collected, the ambient temperature around the system 10 was 60°F.

[0075] If the inlet air temperature is lower than the minimum condensing saturation temperature, a low ambient condition exists, and at 608 the controller determines whether the pressure setpoint of the liquid receiver 21 is greater than the minimum condensing pressure of the compressor envelope. If the pressure setpoint of the liquid receiver 21 is not greater than the minimum condensing pressure, at 606 the controller 50 operates the system 10 according to its standard operation. If the pressure setpoint of the liquid receiver 21 is greater than the minimum condensing pressure, at 610 the controller 50 opens the HPV 30 to 100%, which allows the liquid receiver 21 to maintain a sufficient liquid level to supply the evaporator for refrigeration, and the fan speed is the only variable that needs to be controlled. The controller 50 then begins to control the speed of the fan 27 (by controlling the fan motor 28 using the speed controller 29) to control the outlet pressure of the refrigerant in the refrigerant flow toward the target pressure. This operation... Figure 8The curve is shown in graph 800. In graph 800, the HPV opening percentage 704 is constant at 100%, and the fan speed percentage 702 is controlled to move the refrigerant outlet pressure 706 in the refrigerant stream from the gas cooler / condenser 20 toward the target outlet pressure 708. When the data for graph 800 was collected, the ambient temperature around the system 10 was 20°F.

[0076] In another implementation similar to control algorithm 600, the fan speed percentage is controlled to attempt to move the refrigerant outlet pressure in the refrigerant flow from the gas cooler / condenser toward a target outlet pressure, which is set slightly above the minimum point of the compressor envelope (e.g., 40 bar and (580 psia) in the example system). Setting the target of slightly above the minimum point of the gas cooler / condenser outlet pressure causes the fan to adjust only when the target gas cooler / condenser pressure for HPV is set to the minimum point of the compressor envelope; otherwise, the fan will operate at 100%.

[0077] In this embodiment, the fan will operate at 100% speed when the gas cooler / condenser outlet pressure is higher than the pressure at the lowest point of the compressor envelope, because its target is set slightly above the pressure at the lowest point of the compressor envelope, and this target will never be reached as long as the HPV is controlled to regulate the gas cooler / condenser outlet pressure to the pressure target at the lowest point of the compressor envelope. These conditions typically exist when the ambient temperature is not low. In some embodiments, these conditions exist when the ambient temperature is approximately 41.5°F or higher.

[0078] When the target gas cooler / condenser outlet pressure is less than the target fan pressure (which is slightly above the pressure at the lowest point of the compressor envelope), the HPV will open to 100%, and the fan speed percentage will vary as needed to attempt to move the refrigerant outlet pressure in the refrigerant stream from the gas cooler / condenser toward its target outlet pressure, which is slightly above the lowest point of the compressor envelope. In an example system, the lowest point of the compressor envelope is 40 bar, and the target gas cooler / condenser pressure for the fan is 41 bar.

[0079] Figure 9 This disclosure pertains to the control of CO2 refrigeration systems (e.g., Figure 1The flow diagram of an example control algorithm 900 for system 10 is shown below. In the example implementation, control algorithm 900 will be described as being executed by system controller 50. In other implementations, control algorithm 900 may be executed by valve controller 60 and speed controller 29. Control algorithm 900 may be executed using one or more aspects of other control algorithms discussed above.

[0080] At 902, controller 50 receives, for example, a measurement of the outlet pressure of the refrigerant leaving gas cooler / condenser 20 from refrigerant pressure sensor 64. At 904, controller 50 determines, based on the measurement, whether the outlet pressure exceeds or equals a pressure threshold. The pressure threshold is a pressure higher than the minimum outlet pressure of the refrigerant from gas cooler / condenser 20. The minimum outlet pressure may be the minimum pressure of the compressor (i.e., the lowest point pressure of the compressor envelope). In some embodiments, the pressure threshold is equal to the minimum outlet pressure of the refrigerant from gas cooler / condenser 20 plus a predetermined amount. Alternatively, the pressure threshold may be equal to the minimum outlet pressure of the refrigerant from gas cooler / condenser 20 plus a determined, calculated, or variable amount. The pressure threshold is configurable (e.g., user-selectable, selectable by the manufacturer / installer, etc.). In one example embodiment, the pressure threshold is approximately 650 PSIA.

[0081] If the outlet pressure exceeds or equals a pressure threshold, at 906, controller 50 operates fan 27 at a fixed first speed threshold. The first speed threshold is a threshold indicating that fan 27 should operate at approximately full speed / 100% speed. As used herein, full speed or 100% speed is the maximum fan speed used in operation, which is not always (but sometimes is) the maximum speed at which the fan can operate. Therefore, in some embodiments, the first speed threshold is 100% speed. In other embodiments, the first speed threshold is any other suitable speed close to 100% (e.g., 101%, 99%, 98%, 97%, 96%, 95%, etc.). If the outlet pressure is less than the pressure threshold, at 908, controller 50 variably controls the speed of fan 27 to control the outlet pressure toward a target outlet pressure. The target outlet pressure can be set by any suitable method, including those discussed above.

[0082] In algorithm 900, the control of HPV 30 and the control objectives of HPV 30 are determined based on the speed of fan 27. A speed threshold is used to define two or three operating regions, which are an upper region and a lower region in an implementation with two regions, and an upper region, a lower region, and a transition region in an implementation with three operating regions. In an implementation with three operating regions, the transition region serves as a transition (in both directions) between operations in the upper region and operations in the lower region. Figure 9 The illustrated implementation uses three zones. In operation, the different operating zones typically correspond to different relative ambient temperatures for system operation. That is, the system is typically in the upper operating zone when the ambient temperature is normal / warm for a particular system. A lower operating zone occurs when the ambient temperature around the system is low for that particular system. The ambient temperature during operation in the lower operating zone can be at or below approximately 41.5°F.

[0083] At 910, the controller obtains a measurement of the fan speed, for example, from the speed controller 29, from the speed of the fan 27 as recently commanded, or from a speed sensor coupled to the fan 27. At 912, the controller determines whether the fan speed is greater than or equal to a first speed threshold. If at 912 the controller 50 determines that the fan speed is greater than or equal to the first speed threshold, it is in the upper operating region, and at 914 the controller 50 variably controls the HPV 30 to control the outlet pressure toward the target outlet pressure. It should be noted that this variable control of the HPV 30 occurs at 914 when the fan 27 operates at a fixed first speed threshold at 906.

[0084] If at 912 the controller 50 determines that the fan speed is not higher than or equal to a first speed threshold, then at 916 the controller 50 determines whether the fan speed is less than a second speed threshold. In an example implementation, the second speed threshold is less than the first speed threshold, thus participating in the definition of the transition region and the lower operating region. In one example, the second speed threshold is approximately 90% speed. In other examples, the second speed threshold is any other suitable speed, such as approximately 91%, 92%, 93%, 89%, 88%, etc. If at 916 the controller 50 determines that the fan speed is not less than the second speed threshold, it is in the transition region, and at 918 the controller maintains HPV 30 at a fixed open percentage. In an example, the fixed open percentage is 100% open. In other implementations, the fixed open percentage is the current open percentage of HPV 30 before the determination at 916 or any other suitable fixed open percentage. Because the fan speed is less than the first speed threshold at that point, at 918 the controller 50 maintains HPV 30 in the fixed open position while at 908 the speed of fan 27 is variably controlled to control the outlet pressure toward the target outlet pressure.

[0085] If at 916 the controller 50 determines that the fan speed is less than a second speed threshold, it is in the lower operating region, and at 920 the controller variably controls HPV 30 (e.g., controls the percentage of HPV 30 that is open) to control the flash tank pressure of the liquid receiver / flash tank 21 toward the target flash tank pressure. Because the fan speed is less than a first speed threshold at this point, the controller 50 variably controls HPV to control the flash tank pressure toward the target flash tank pressure, while at 908 the speed of the fan 27 variably controls the outlet pressure toward the target outlet pressure. In some embodiments, when the controller 50 variably controls HPV 30 to control the flash tank pressure toward the target flash tank pressure, the control of HPV 30 is slowed down. For example, the magnitude of HPV regulation that the controller would otherwise perform can be reduced. In some embodiments, the regulation is reduced by half. Alternatively, the regulation can be reduced by 10%, 25%, 33%, 60%, or any other suitable reduction to slow the opening / closing of HPV 30. In some implementations, the target flash tank pressure is the flash tank setpoint (set by any suitable method) minus an adjustment amount. In some implementations, the adjustment amount is approximately 0.5 bar, while other implementations use any other suitable adjustment amount. By controlling the flash tank pressure to an amount below the setpoint, the controller 50 can completely shut down the BGV 40 under certain operating conditions, which can improve system efficiency and stability.

[0086] Implementations with only two operating regions do not include a transition region. In fact, such implementations do not include a second speed threshold, but this can be achieved by considering that the second speed threshold is equal to the first speed threshold. Figure 9 Visualization. Therefore, if the controller determines at 912 that the fan speed is not greater than or equal to the first speed threshold, then the fan speed must be less than the second speed threshold (which is also the first speed threshold), and the algorithm proceeds directly to variably controlling the HPV opening percentage at 920 to regulate the flash tank pressure. Similarly, in practice, the second speed threshold is not used at all in such an implementation, and Figure 9 Steps 916 and 918 are removed, and step 920 is directly connected to the negative answer at step 912.

[0087] Figure 10 Graph 1000 shows various operating characteristics of the actual system operating over a period of time using two versions of Algorithm 900 in different regions. As can be seen, the system begins operating in the upper operating region, where the fan speed (Fan Speed ​​%) is maintained at 100% from t0 to t1, and the ambient air temperature (air supply temperature) decreases from approximately 50°F to approximately 41.5°F. During this time period, the HPV opening percentage (HPV %) is controlled to drive the outlet pressure (GCO pressure) toward the target outlet pressure (GC pressure SP). At approximately time t1, the outlet pressure drops below a pressure threshold of approximately 650 PSIA, and the fan speed is now variably controlled to drive the outlet pressure toward the target outlet pressure. After time t1, the system is in the lower operating region. Because the fan speed has decreased from the first speed threshold (100% in this example), controller 50 controls the HPV opening percentage to bring the flash tank pressure (FT pressure) to the target pressure, which is an amount below the flash tank setpoint (FT SP) (e.g., 0.5 bar). As can be seen, at approximately time t2, BGV 40 is completely shut off and remains so until after time t3 (discussed below). During the time interval from t1 to t3, the entire system remains stable, and the compressor speed (compressor (Comp) speed %) remains stable while the ambient air temperature (air supply temperature) decreases from approximately 41°F to almost 20°F. At approximately time t3, the outlet pressure has increased to the pressure threshold of approximately 650 PSIA. At this point, the system returns to the upper operating range. The fan speed is then controlled to a fixed speed of 100%, and the HPV opening percentage is controlled to variably control the outlet pressure to the target outlet pressure.

[0088] Many known CO2 control systems utilize HPV to regulate the gas cooler / condenser outlet pressure to the outlet pressure setpoint. In such systems, the pressure in the flash tank is typically regulated to the flash tank setpoint by BGV. The operation of these control elements is usually independent of each other. In such systems, when the flash tank pressure rises above the setpoint, the BGV opens to relieve that pressure. When the BGV is open, the mass flow from the evaporator is diverted to the compressor's suction line / inlet. This reduces capacity and efficiency, causing the suction pressure to rise and the compressor to increase its speed. Therefore, keeping the BGV closed or near closed is desirable for system capacity, efficiency, and stability.

[0089] Figure 11 This disclosure pertains to the control of CO2 refrigeration systems (e.g., Figure 1 The flow diagram of the example control algorithm 1100 (system 10) and, where possible, keeps BGV 40 closed. In the example implementation, control algorithm 1100 will be described as being executed by system controller 50. In other implementations, control algorithm 1100 may be executed by valve controller 60. Control algorithm 1100 may be executed using one or more aspects of other control algorithms discussed above.

[0090] Typically, Algorithm 1100 uses the pressure setpoint of the refrigerant exiting the gas cooler / condenser 20 as a variable to control the flash tank pressure. Where appropriate and depending on operating conditions, increasing the outlet pressure setpoint of the gas cooler / condenser 20 will result in a decrease in the flash tank pressure and may lead to a reduction in the amount by which the BGV 40 opens; or decreasing the outlet pressure setpoint of the gas cooler / condenser 20 will result in an increase in the flash tank pressure and may lead to an increase in the amount by which the BGV 40 opens (if any).

[0091] Algorithm 1100 is executed when the system is otherwise controlled according to any other suitable control scheme, including those discussed herein, wherein (or over a period of time) the HPV 30 is controlled to regulate the outlet pressure of the refrigerant leaving the gas cooler / condenser 20 to a target outlet pressure (i.e., the outlet pressure setpoint). At 1102, the controller 50 obtains the flash tank pressure, the outlet pressure setpoint of the refrigerant leaving the gas cooler / condenser 20, and the percentage of time the BGV 40 is open. These values ​​can be obtained from sensors, from previous commands, retrieved from memory, or by any suitable method for obtaining the values.

[0092] At 1104, controller 50 compares the flash tank pressure with a first limit. In the example implementation, the first limit is a pre-alarm limit, which is a pressure exceeding the desired level but not high enough to warrant an alarm. The first limit can be a target flash tank pressure (i.e., the flash tank setpoint), a flash tank pressure a certain amount above the target flash tank pressure, or any other suitable limit value.

[0093] If the flash tank pressure exceeds the first limit, at 1106, controller 50 checks whether the percentage of BGV 40 open exceeds the BGV limit. The BGV limit is the maximum amount by which the BGV is expected to open. In some embodiments, the BGV limit may be approximately equal to the percentage of BGV 40 closed. That is, in such embodiments, if BGV 40 is fully open, its open percentage is greater than the limit. In other embodiments, the BGV limit is a certain amount greater than full closure, such as 10%, 20%, 30%, 40%, etc. If the percentage of BGV 40 not open exceeds the BGV limit, the algorithm proceeds to 1110 and continues normal regulation. If the percentage of BGV 40 open exceeds the BGV limit, at 1108, controller 50 increases the outlet pressure setpoint of cooler / condenser 20. Typically, the increase will be relatively small, such as 5 PSIA, 10 PSIA, 15 PSIA, 20 PSIA, 25 PSIA, 50 PSIA, etc. In some implementations, the increase is less than one hundred PSIA. In some implementations, the increase is less than five percent or ten percent of the current (not yet increased) outlet pressure setpoint. When HPV 30 is controlled to regulate the outlet pressure of the refrigerant leaving the gas cooler / condenser 20 to the outlet pressure setpoint, an increase in the outlet pressure setpoint will cause HPV 30 to close more to increase the outlet pressure. This change also has the effect of reducing the flash tank pressure. In some implementations, the increase in the outlet pressure setpoint is repeated until the flash tank pressure is equal to or below the first limit or the BGV 40 opening is equal to or below the BGV limit, and then at 1110 the algorithm returns to normal system regulation. That is, algorithm 1100 can cycle back from 1108 to 1102. In some implementations, an increase in the outlet pressure setpoint occurs once at 1108, and at 1110 the system returns to normal system regulation. In such an implementation, normal adjustment may include periodically (e.g., once per second, once per minute, once every thirty minutes, once per hour, whenever a certain control event occurs, once per control cycle, once per other control cycle, etc.) returning to 1102 and repeating algorithm 1100.

[0094] If the flash tank pressure is not greater than the first limit, at 1112, controller 50 checks if the flash tank pressure is less than the second limit. The second limit is less than the first limit. Therefore, the first limit can be referred to as the upper limit, and the second limit can be referred to as the lower limit. The second limit is typically the minimum desired flash tank pressure. In some embodiments, the second limit is 90 percent of the flash tank pressure setpoint. In other embodiments, the second limit is 95 percent of the flash tank pressure setpoint, 85 percent of the flash tank pressure setpoint, a fixed amount below the flash tank pressure setpoint (e.g., 25 PSIA below the setpoint, 50 PSIA below the setpoint, etc.), or a fixed pressure. If the flash tank pressure is not less than the second limit, the algorithm returns to normal adjustment at 1110. If the flash tank pressure is less than the second limit, at 1114, controller 50 determines whether BGV 40 is closed (i.e., whether the percentage of BGV 40 open is essentially zero percent). If BGV 40 is not closed, the algorithm proceeds to 1110 and continues normal adjustment. If BGV 40 is closed, controller 50 lowers the outlet pressure setpoint of cooler / condenser 20 at 1116. Similar to the increase at 1108, the decrease will typically be relatively small, such as five PSIA, ten PSIA, fifteen PSIA, twenty PSIA, twenty-five PSIA, fifty PSIA, etc. In some embodiments, the decrease is less than one hundred PSIA. In some embodiments, the decrease is less than five percent or less than ten percent of the current (not yet decreased) outlet pressure setpoint. The amount by which the outlet pressure setpoint is lowered at 1116 can be the same amount or a different amount than the amount by which the outlet pressure setpoint is increased at 1108. When HPV 30 is controlled to regulate the outlet pressure of the refrigerant leaving gas cooler / condenser 20 to the outlet pressure setpoint, the decrease in the outlet pressure setpoint will cause HPV 30 to open more to lower the outlet pressure. This change also has the effect of increasing the flash tank pressure. In some implementations, the outlet pressure setpoint is repeatedly lowered until the flash tank pressure equals or exceeds the second limit or BGV 40 is opened, then the algorithm returns to normal system regulation at 1110. That is, algorithm 1100 can cycle back from 1116 to 1102. In some implementations, an outlet pressure setpoint lowering occurs once at 1116, and the system returns to normal system regulation at 1110. In such implementations, normal regulation may include periodically (e.g., once per second, once per minute, once every thirty minutes, once per hour, whenever a certain control event occurs, once per control cycle, once per other control cycle, etc.) returning to 1102 and repeating algorithm 1100.

[0095] Figure 12This is graph 1200 showing various operating characteristics of an example system operating using control regulation including algorithm 1100. At time t0, the system operates with the flash tank pressure well below the flash tank setpoint, and BGV 40 is fully closed (i.e., the BGV opening percentage is 0%). After time t0, the flash tank pressure begins to rise. At time t1, the flash tank pressure has climbed above the flash tank setpoint, and controller 50 has begun to open BGV 40 to reduce the pressure. At this point, the flash tank pressure is above the first limit, and BGV 40 is open beyond the BGV limit. Therefore, controller 50 increases the outlet pressure setpoint of gas cooler / condenser 20, which causes the flash tank pressure to decrease after t1. As the flash tank pressure decreases, controller 50 reduces the opening percentage of BGV 40 to regulate the flash tank pressure toward the flash tank setpoint. At time t2, the flash tank pressure has again risen above the first limit, and BGV 40 is open beyond the BGV limit. Therefore, controller 50 increases the outlet pressure setpoint of gas cooler / condenser 20, which causes the flash tank pressure to decrease after t2. As the flash tank pressure decreases, controller 50 again reduces the opening percentage of BGV 40 to adjust the flash tank pressure toward the flash tank setpoint.

[0096] The foregoing provides a detailed description of exemplary embodiments of systems and methods for controlling CO2 refrigeration systems. The system is not limited to the specific embodiments described herein, but rather its components can be used independently and separately from other components described herein. For example, the controllers and processors described herein can also be used in combination with other systems and methods, and are not limited to practice using only systems as described herein.

[0097] This written description discloses the invention using examples including the best mode and also enables any person skilled in the art to practice the invention, including making and using any device or system and performing any incorporated method. The scope of the patent is defined by the claims and may include other examples that would occur to a person skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if such other examples comprise equivalent structural elements that do not substantially differ from the literal language of the claims.

[0098] As used herein, when used in conjunction with ranges of size, concentration, temperature or other physical or chemical properties or characteristics, the terms “about,” “approximately,” “substantially,” and “approximately” are intended to cover variations that may exist within the upper and / or lower limits of the range of properties or characteristics, including variations caused, for example, by rounding, measurement methods, or other statistical changes.

[0099] When elements or embodiments thereof are incorporated into this disclosure, the articles “a,” “an,” “the,” and “described” are intended to mean the presence of one or more elements. The terms “comprising,” “including,” “containing,” and “having” are intended to be inclusive and mean that additional elements may be present in addition to the listed elements. The use of terms indicating a particular orientation (e.g., “top,” “bottom,” “side,” etc.) is for ease of description and does not require any particular orientation of the described object.

[0100] Since various changes can be made to the above structures and methods without departing from the scope of this disclosure, all content contained in the above description and shown in the accompanying drawings is intended to be illustrative rather than restrictive.

Claims

1. A CO2 refrigeration system, comprising: compressor; A gas cooler / condenser that receives refrigerant discharged from the compressor and outputs a refrigerant stream, wherein the gas cooler / condenser can operate as a gas cooler when the CO2 refrigeration system operates in transcritical mode and as a condenser when the CO2 refrigeration system operates in subcritical mode. A flash tank, which is connected to receive refrigerant output from the gas cooler / condenser; A bypass valve (BGV) is located between the flash tank and the suction side of the compressor, and is used to control the refrigerant flow from the flash tank to the suction side of the compressor; as well as The controller has a processor and a memory, the processor being configured to perform the following steps via instructions stored in the memory: Obtain the target outlet pressure of the refrigerant from the gas cooler / condenser, the pressure of the flash tank, and the percentage of the BGV open; Whether to reduce the pressure of the flash tank is determined at least in part based on the pressure of the flash tank and the percentage of the BGV open; as well as When the controller determines to reduce the pressure of the flash tank, it increases the target outlet pressure by a certain amount.

2. The CO2 refrigeration system according to claim 1, wherein, The processor is configured to determine to reduce the pressure of the flash tank when the pressure of the flash tank exceeds a first limit and the opening percentage of the BGV exceeds the BGV limit.

3. The CO2 refrigeration system according to claim 2, wherein, The first limit includes the flash tank pressure setpoint.

4. The CO2 refrigeration system according to claim 2, wherein, The processor is configured to repeat the following steps: obtaining, determining whether to reduce the pressure of the flash tank, and increasing the target outlet pressure by the amount until the flash tank pressure does not exceed the first limit or the opening percentage of the BGV does not exceed the BGV limit.

5. The CO2 refrigeration system according to any of the preceding claims, wherein, The processor is configured to perform the following steps via instructions stored in the memory: Whether to increase the pressure of the flash tank is determined at least in part based on the pressure of the flash tank and the percentage of the BGV open; and When the controller determines to increase the pressure of the flash tank, it reduces the target outlet pressure by the amount.

6. The CO2 refrigeration system according to claim 5, wherein, The processor is configured to determine to increase the pressure of the flash tank when the pressure of the flash tank is below a second limit lower than the first limit and the opening percentage of the BGV indicates that the BGV is closed.

7. The CO2 refrigeration system according to claim 6, wherein, The processor is configured to repeat the following steps: obtaining, determining whether to increase the pressure of the flash tank, and reducing the target outlet pressure by the amount until the flash tank pressure is not less than the second limit or the BGV opening percentage does not indicate that the BGV is closed.

8. A controller for a CO2 refrigeration system, the CO2 refrigeration system comprising: compressor; A gas cooler / condenser that receives refrigerant discharged from the compressor and outputs a refrigerant stream; A flash tank, which is connected to receive refrigerant output from the gas cooler / condenser; and a bypass valve (BGV) located between the flash tank and the suction side of the compressor for controlling the refrigerant flow from the flash tank to the suction side of the compressor, the controller comprising: Processor; and The processor is configured to perform the following steps via instructions stored in the memory: Obtain the target outlet pressure of the refrigerant from the gas cooler / condenser, the pressure of the flash tank, and the percentage of the BGV open; The determination of whether to reduce the pressure of the flash tank is based at least in part on the pressure of the flash tank and the percentage of the BGV open; and When the controller determines to reduce the pressure of the flash tank, it increases the target outlet pressure by a certain amount.

9. The controller according to claim 8, wherein, The processor is configured via instructions stored in the memory to determine to reduce the pressure of the flash tank when the pressure of the flash tank exceeds a first limit and the opening percentage of the BGV exceeds the BGV limit.

10. The controller according to claim 9, wherein, The first limit includes the flash tank pressure setpoint.

11. The controller according to claim 9, wherein, The processor is configured, via instructions stored in the memory, to repeat the following steps: obtaining, determining whether to reduce the pressure of the flash tank, and increasing the target outlet pressure by the amount until the flash tank pressure does not exceed the first limit or the opening percentage of the BGV does not exceed the BGV limit.

12. The controller according to any one of claims 8 to 11, wherein, The processor is configured to perform the following steps via instructions stored in the memory: Whether to increase the pressure of the flash tank is determined at least in part based on the pressure of the flash tank and the percentage of the BGV open; and When the controller determines to increase the pressure of the flash tank, it reduces the target outlet pressure by the amount.

13. The controller according to claim 12, wherein, The processor is configured, via instructions stored in the memory, to determine to increase the pressure of the flash tank when the pressure of the flash tank is below a second limit lower than the first limit and the opening percentage of the BGV indicates that the BGV is closed.

14. The controller system according to claim 13, wherein, The processor is configured, via instructions stored in the memory, to repeat the following steps: obtaining, determining whether to increase the pressure of the flash tank, and reducing the target outlet pressure by the amount until the flash tank pressure is not less than the second limit or the BGV opening percentage does not indicate that the BGV is closed.

15. A method for controlling a CO2 refrigeration system, the CO2 refrigeration system comprising: compressor; A gas cooler / condenser that receives refrigerant discharged from the compressor and outputs a refrigerant stream; A flash tank, which is connected to receive refrigerant output from the gas cooler / condenser; and a bypass valve (BGV) located between the flash tank and the suction side of the compressor for controlling the refrigerant flow from the flash tank to the suction side of the compressor, the method comprising: Obtain the target outlet pressure of the refrigerant from the gas cooler / condenser, the pressure of the flash tank, and the percentage of the BGV open; The determination of whether to reduce the pressure of the flash tank is based at least in part on the pressure of the flash tank and the percentage of the BGV open; and When the controller determines to reduce the pressure of the flash tank, it increases the target outlet pressure by a certain amount.

16. The method according to claim 15, wherein, Determining whether to reduce the pressure of the flash tank includes: determining to reduce the pressure of the flash tank when the pressure of the flash tank exceeds a first limit and the opening percentage of the BGV exceeds the BGV limit.

17. The method of claim 16, further comprising repeating the steps of: obtaining, determining whether to reduce the pressure of the flash tank, and increasing the target outlet pressure by the amount until the flash tank pressure does not exceed the first limit or the opening percentage of the BGV does not exceed the BGV limit.

18. The method according to any one of claims 15 to 17, further comprising: Whether to increase the pressure of the flash tank is determined at least in part based on the pressure of the flash tank and the percentage of the BGV open. as well as When the controller determines to increase the pressure of the flash tank, it reduces the target outlet pressure by the amount.

19. The method according to claim 18, wherein, Determining whether to increase the pressure of the flash tank includes: determining to increase the pressure of the flash tank when the pressure of the flash tank is below a second limit lower than the first limit and the BGV opening percentage indicates that the BGV is closed.

20. The method of claim 19, further comprising repeating the steps of: obtaining, determining whether to increase the pressure of the flash tank, and reducing the target outlet pressure by the amount until the flash tank pressure is not less than the second limit or the open percentage of the BGV does not indicate that the BGV is closed.

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