REFRIGERATION SYSTEM WITH REFRIGERANT CHARGE CONTROL

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of, and claims priority under 35 U.S.C. § 120 to, U.S. patent application Ser. No. 19/131,904, filed on May 21, 2025, which is a U.S. National Stage Application under 35 U.S.C. § 371 of International Application No. PCT/US2025/015281, filed Feb. 10, 2025, which claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 63/552,805, filed Feb. 13, 2024. The entire contents of all prior applications are incorporated by reference herein.

TECHNICAL FIELD

The present disclosure describes refrigeration systems and, more particularly, refrigeration systems with refrigerant charge control, including booster refrigeration systems capable of transcritical operation with a natural refrigerant.

BACKGROUND

Conventional refrigeration systems include a cycle having an evaporator, a compressor, a condenser, and an expansion valve. The refrigerant is compressed by the compressor to a high pressure, high temperature mode, after which a phase change is introduced in the condenser, in order to reject heat from the refrigerant. Thereafter, an expansion valve reduces the pressure and thereby reduces the temperature of the refrigerant. The low temperature refrigerant is then led through the evaporator in which it is utilized to cool the surroundings of the refrigerant, such as an interior space of the refrigerator. The refrigerant is thereafter after led to the compressor, and the cycle repeats. The refrigeration cycle contains a refrigerant, which can be a substance or a mixture of substances and may be a natural or synthetic refrigerant. Sometimes, such as in the case of a power shutdown of the refrigeration system, a refrigerant charge can be undesirably lost to an ambient environment. Conventionally, an auxiliary condensing unit is coupled in thermal communication with a refrigerant charge in the refrigeration system to maintain the refrigerant charge in a liquid state to avoid escape from the system.

SUMMARY

In an example implementation, a refrigeration system includes a first refrigeration subsystem including a first set of one or more first compressors operating at a first suction pressure to compress a refrigerant fluid, one or more first evaporators fluidly coupled to the one or more first compressors through a first suction conduit and configured to cool a first enclosed space, and one or more first expansion valves fluidly coupled to the one or more first evaporators; a second refrigeration subsystem including a second set of one or more second compressors operating at a second suction pressure different than the first suction pressure to compress the refrigerant fluid, one or more second evaporators fluidly coupled to the one or more second compressors through a second suction conduit configured to cool a second enclosed space, and one or more second expansion valves fluidly coupled to the one or more second evaporators; at least one gas cooler/condenser fluidly coupled to the first and second refrigeration subsystems and configured to cool a vapor phase of the refrigerant fluid from the one or more first compressors and the one or more second compressors to a liquid phase or mixed phase of the refrigerant fluid; a flash tank fluidly coupled to the at least one gas cooler/condenser; and at least one third compressor configured to pump down at least a portion of the refrigerant fluid to the flash tank. The at least one third compressor includes a suction side fluidly coupled to at least two of: the first suction conduit, the second suction conduit, or the flash tank, and a discharge side fluidly coupled to the at least one gas cooler/condenser.

In an aspect combinable with the example implementation, the suction side is fluidly coupled to the first suction conduit, the second suction conduit, and the flash tank.

Another aspect combinable with one, some, or all of the previous aspects includes a first branch conduit fluidly coupled between the first suction conduit and the at least one third compressor, a second branch conduit fluidly coupled between the second suction conduit and the at least one third compressor, and a third branch conduit fluidly coupled between the flash tank and the at least one third compressor.

In another aspect combinable with one, some, or all of the previous aspects, the first, second, and third branch conduits are fluidly coupled together upstream of the suction side.

In another aspect combinable with one, some, or all of the previous aspects, the discharge side includes a first discharge side and a second discharge side.

In another aspect combinable with one, some, or all of the previous aspects, the first discharge side is fluidly coupled to the at least one gas cooler/condenser, and the second discharge side is fluidly coupled to a bypass conduit that fluidly couples the flash tank to the first suction conduit.

In another aspect combinable with one, some, or all of the previous aspects, the at least one third compressor includes a first third compressor including a first suction side and a first discharge side; and a second third compressor including a second suction side and a second discharge side.

In another aspect combinable with one, some, or all of the previous aspects, the first suction side is fluidly coupled to the first suction conduit, and the second suction side is fluidly coupled to the second suction conduit.

In another aspect combinable with one, some, or all of the previous aspects, the first and second discharge sides are fluidly coupled to the at least one gas cooler/condenser.

In another aspect combinable with one, some, or all of the previous aspects, the first discharge side is fluidly coupled to the at least one gas cooler/condenser, and the second discharge side is fluidly coupled to a bypass conduit that fluidly couples the flash tank to the first suction conduit.

In another aspect combinable with one, some, or all of the previous aspects, the flash tank includes a high level sensor configured to measure a level of the liquid phase of the refrigerant fluid in the flash tank.

Another aspect combinable with one, some, or all of the previous aspects includes a control system communicably coupled to the at least one third compressor, one or more pressure transducers positioned in the refrigeration system, and one or more shut-off valves positioned in the refrigeration system.

In another aspect combinable with one, some, or all of the previous aspects, the control system is configured to perform operations including determining an event occurrence in the refrigeration system; and based on the determination of the event occurrence, operating the at least one third compressor to pump down the portion of the refrigerant fluid to the flash tank.

In another aspect combinable with one, some, or all of the previous aspects, the operations include receiving or identifying one or more fluid pressure values measured by the one or more pressure transducers; and based on the one or more fluid pressure values, adjusting at least one of the one or more shut-off valves between a closed position and an open position.

In another aspect combinable with one, some, or all of the previous aspects, the event occurrence includes a loss of main power to at least one of the first or second refrigeration subsystems.

In another aspect combinable with one, some, or all of the previous aspects, the operations include activating an uninterruptible power supply (UPS) electrically coupled to the at least one third compressor to provide power to the at least one third compressor.

In another aspect combinable with one, some, or all of the previous aspects, the UPS is not electrically coupled to the one or more first compressors or the one or more second compressors.

In another aspect combinable with one, some, or all of the previous aspects, the refrigerant fluid includes carbon dioxide.

In another aspect combinable with one, some, or all of the previous aspects, the first refrigeration subsystem includes a medium temperature (MT) refrigeration subsystem, and the second refrigeration subsystem includes a low temperature (LT) refrigeration subsystem.

In another aspect combinable with one, some, or all of the previous aspects, the MT subsystem including the one or more first evaporators is configured to cool the first enclosed space to a first temperature, and the LT subsystem including the one or more second evaporators is configured to cool the second enclosed space to a second temperature less than the first temperature.

Another aspect combinable with one, some, or all of the previous aspects includes an oil return assembly that includes a conduit fluidly coupled between the third compressor and a discharge conduit that fluidly couples the discharge side of the third compressor with the at least one gas cooler/condenser.

In another aspect combinable with one, some, or all of the previous aspects, the oil return assembly includes an integrated oil separator/reservoir positioned in the discharge conduit and fluidly coupled to the conduit; and an oil return valve fluidly coupled to the third compressor in the conduit.

In another example implementation, a method of operating a refrigeration system includes operating a first refrigeration subsystem of a refrigeration system to cool a first enclosed space, the first refrigeration subsystem including a first set of one or more first compressors operating at a first suction pressure to compress a refrigerant fluid and supply the refrigerant fluid through one or more first expansion valves and to one or more first evaporators fluidly coupled to the one or more first compressors through a first suction conduit to cool the first enclosed space; operating a second refrigeration subsystem of the refrigeration system to cool a second enclosed space, the second refrigeration subsystem including a second set of one or more second compressors operating at a second suction pressure to compress the refrigerant fluid and supply the refrigerant fluid through one or more second expansion valves and to one or more second evaporators fluidly coupled to the one or more second compressors through a second suction conduit to cool the second enclosed space; operating at least one gas cooler/condenser fluidly coupled to the first and second refrigeration subsystems to cool a vapor phase of the refrigerant fluid from the one or more first compressors and the one or more second compressors to a liquid phase or mixed phase of the refrigerant fluid; supplying the liquid phase or mixed phase of the refrigerant fluid to a flash tank fluidly coupled to the at least one gas cooler/condenser; based on an event occurrence, operating at least one third compressor to draw the portion of the refrigerant fluid through a suction side of the at least one third compressor that is fluidly coupled to at least two of: the first suction conduit, the second suction conduit, or the flash tank; pumping down at least a portion of the refrigerant fluid drawn through the suction side to the flash tank by; and discharging compressed refrigerant fluid from the at least one third compressor through a discharge side.

An aspect combinable with the example implementation includes operating the at least one third compressor to draw the portion of the refrigerant fluid through the suction side of the at least one third compressor that is fluidly coupled to the first suction conduit, the second suction conduit, and the flash tank.

Another aspect combinable with one, some, or all of the previous aspects includes operating the at least one third compressor to draw the portion of the refrigerant fluid through a first branch conduit fluidly coupled between the first suction conduit and the at least one third compressor, a second branch conduit fluidly coupled between the second suction conduit and the at least one third compressor, and a third branch conduit fluidly coupled between the flash tank and the at least one third compressor.

In another aspect combinable with one, some, or all of the previous aspects, the first, second, and third branch conduits are fluidly coupled together upstream of the suction side.

In another aspect combinable with one, some, or all of the previous aspects, the discharge side includes a first discharge side and a second discharge side.

Another aspect combinable with one, some, or all of the previous aspects includes discharging a portion of compressed refrigerant fluid from the first discharge side to the at least one gas cooler/condenser; and discharging another portion of compressed refrigerant fluid from the second discharge side to a bypass conduit that fluidly couples the flash tank to the first suction conduit.

In another aspect combinable with one, some, or all of the previous aspects, operating the at least one third compressor includes operating a first third compressor to draw refrigerant fluid through a first suction side and discharge compressed refrigerant fluid through a first discharge side; and operating a second third compressor to draw refrigerant fluid through a second suction side and discharge compressed refrigerant fluid through a second discharge side.

In another aspect combinable with one, some, or all of the previous aspects, operating the first third compressor to draw refrigerant fluid through the first suction side includes operating the first third compressor to draw refrigerant fluid to the first suction side from the first suction conduit, and operating the second third compressor to draw refrigerant fluid through the second suction side includes operating the second third compressor to draw refrigerant fluid to the second suction side from the second suction conduit.

Another aspect combinable with one, some, or all of the previous aspects includes discharging compressed refrigerant fluid from the first and second discharge sides to the at least one gas cooler/condenser.

Another aspect combinable with one, some, or all of the previous aspects includes discharging a portion of compressed refrigerant fluid from the first discharge side to the at least one gas cooler/condenser, and discharging another portion of compressed refrigerant fluid from the second discharge side to a bypass conduit that fluidly couples the flash tank to the first suction conduit.

Another aspect combinable with one, some, or all of the previous aspects includes determining, with a high level sensor positioned in the flash tank, a level of the liquid phase of the refrigerant fluid in the flash tank.

Another aspect combinable with one, some, or all of the previous aspects includes determining, with a control system communicably coupled to the first and second refrigeration subsystems, the event occurrence in the refrigeration system; and based on the determination of the event occurrence, activating, with the control system, the at least one third compressor.

Another aspect combinable with one, some, or all of the previous aspects includes determining one or more fluid pressure values with one or more pressure transducers positioned in the refrigeration system; and based on the one or more fluid pressure values, adjusting one or more shut-off valves positioned in the refrigeration system between a closed position and an open position.

In another aspect combinable with one, some, or all of the previous aspects, the event occurrence includes a loss of main power to at least one of the first or second refrigeration subsystems.

Another aspect combinable with one, some, or all of the previous aspects includes activating an uninterruptible power supply (UPS) electrically coupled to the at least one third compressor to provide power to the at least one third compressor.

In another aspect combinable with one, some, or all of the previous aspects, the UPS is not electrically coupled to the one or more first compressors or the one or more second compressors.

In another aspect combinable with one, some, or all of the previous aspects, the refrigerant fluid includes carbon dioxide.

In another aspect combinable with one, some, or all of the previous aspects, the first refrigeration subsystem includes a medium temperature (MT) refrigeration subsystem, and the second refrigeration subsystem includes a low temperature (LT) refrigeration subsystem.

Another aspect combinable with one, some, or all of the previous aspects includes cooling, with the MT subsystem including the one or more first evaporators, the first enclosed space to a first temperature; and cooling, with the LT subsystem including the one or more second evaporators, the second enclosed space to a second temperature less than the first temperature.

Another aspect combinable with one, some, or all of the previous aspects includes separating, with an integrated oil separator/reservoir of an oil return assembly, oil from the refrigerant fluid discharged from the third compressor; and transporting at least a portion of the separated oil to the third compressor through a conduit fluidly coupled between the third compressor and a discharge conduit that fluidly couples the discharge side of the third compressor with the at least one gas cooler/condenser.

Another aspect combinable with one, some, or all of the previous aspects includes storing the separated oil in the integrated oil separator/reservoir that is positioned in the discharge conduit and fluidly coupled to the conduit; and controlling the transporting of the portion of the separated oil with an oil return valve positioned in the conduit and fluidly coupled to the third compressor.

In another example implementation, a refrigeration system includes a first refrigeration subsystem including a first set of one or more first compressors operating at a first suction pressure to compress a refrigerant fluid, one or more first evaporators fluidly coupled to the one or more first compressors through a first suction conduit and configured to cool a first enclosed space, and one or more first expansion valves fluidly coupled to the one or more first evaporators; a second refrigeration subsystem including a second set of one or more second compressors operating at a second suction pressure different than the first suction pressure to compress the refrigerant fluid, one or more second evaporators fluidly coupled to the one or more second compressors through a second suction conduit configured to cool a second enclosed space, and one or more second expansion valves fluidly coupled to the one or more second evaporators; at least one gas cooler/condenser fluidly coupled to the first and second refrigeration subsystems and configured to cool a vapor phase of the refrigerant fluid from the one or more first compressors and the one or more second compressors to a liquid phase or mixed phase of the refrigerant fluid; a flash tank fluidly coupled to the at least one gas cooler/condenser; and at least one third compressor configured to pump down at least a portion of the refrigerant fluid to the flash tank. The at least one third compressor includes a suction side fluidly coupled only to the first suction conduit, and a discharge side fluidly coupled to the at least one gas cooler/condenser.

In another example implementation, a refrigeration system includes a first refrigeration subsystem including a first set of one or more first compressors operating at a first suction pressure to compress a refrigerant fluid, one or more first evaporators fluidly coupled to the one or more first compressors through a first suction conduit and configured to cool a first enclosed space, and one or more first expansion valves fluidly coupled to the one or more first evaporators; a second refrigeration subsystem including a second set of one or more second compressors operating at a second suction pressure different than the first suction pressure to compress the refrigerant fluid, one or more second evaporators fluidly coupled to the one or more second compressors through a second suction conduit configured to cool a second enclosed space, and one or more second expansion valves fluidly coupled to the one or more second evaporators; at least one gas cooler/condenser fluidly coupled to the first and second refrigeration subsystems and configured to cool a vapor phase of the refrigerant fluid from the one or more first compressors and the one or more second compressors to a liquid phase or mixed phase of the refrigerant fluid; a flash tank fluidly coupled to the at least one gas cooler/condenser; and at least one third compressor configured to pump down at least a portion of the refrigerant fluid to the flash tank. The at least one third compressor includes a suction side fluidly coupled only to the second suction conduit, and a discharge side fluidly coupled to the at least one gas cooler/condenser.

The details of one or more implementations of the subject matter described in this disclosure is set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-8 are schematic diagrams of example implementations of a refrigeration system according to the present disclosure.

FIGS. 9A and 9B are flowcharts of example methods for controlling a refrigeration system according to the present disclosure.

FIG. 10 is a graph that shows an example operation envelope for an external cooling compressor according to the present disclosure.

FIG. 11 shows a schematic drawing of a control system that can be used to control a refrigeration system according to the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of an example implementation of a refrigeration system 100 according to the present disclosure. In example aspects, refrigeration system 100 includes a booster refrigeration system with at least two compressor groups (each having one or more compressors) that operate at different pressure ranges (e.g., suction and discharge pressure differences). At least one of the two compressor groups can operate transcritically (e.g., in both subcritical and supercritical operation), while another compressor group operates subcritically. In some aspects, refrigeration system 100 operates with a natural refrigerant (e.g., carbon dioxide (CO₂) or ammonia) and legend 991 in FIG. 1 shows the relative states of the refrigerant (with arrows in the figures showing refrigerant flow direction) in particular portions of the system 100 (applicable to other systems shown in the figures as well). However, alternative implementations of refrigeration system 100 (and other refrigeration systems according to the present disclosure) may operate with a synthetic refrigerant (such as an HCFC or blended synthetic refrigerant). Thus, although refrigeration system 100 (and other refrigeration systems according to the present disclosure) can be referred to as a CO₂ refrigeration system 100, the present disclosure contemplates that the disclosed refrigeration systems can be designed to operate with refrigerants other than CO₂.

Generally, CO₂ refrigeration system 100 is a vapor compression refrigeration system, which circulates a refrigerant between an evaporator and a gas cooler/condenser to provide cooling to a temperature-controlled space (e.g., a refrigerator, a freezer, a temperature-controlled display case, etc.). The refrigerant (also referred to as CO₂ refrigerant) absorbs heat in the evaporator and rejects heat in the gas cooler/condenser as the CO₂ refrigerant flows through the refrigeration circuit.

Referring now to FIG. 1, the CO₂ refrigeration system 100 is shown, according to an exemplary implementation. CO₂ refrigeration system 100 and is shown to include a system of pipes, conduits, or other fluid channels (e.g., fluid conduits 1, 3, 5, 7, 9, 13, 23, 27, and 42) for transporting the CO₂ refrigerant between various components of CO₂ refrigeration system 100. The components of CO₂ refrigeration system 100 are shown to include a gas cooler/condenser 2, a high pressure valve 4, a flash tank (or receiver) 6, a gas bypass valve 8, a medium-temperature (“MT”) subsystem (comprising a compressor group of one or more MT compressors 14, one or more MT evaporators 12, and one or more expansion valves 11), and a low-temperature (“LT”) subsystem (comprising a compressor group of one or more LT compressors 24, one or more LT evaporators 22, and one or more expansion valves 21). The components of CO₂ refrigeration system 100 form a refrigeration circuit configured to circulate the CO₂ refrigerant and provide cooling for a temperature-controlled space (e.g., a refrigerator, a freezer, a refrigerated display case, etc.).

Gas cooler/condenser 2 can be a heat exchanger or other similar device for removing heat from the CO₂ refrigerant. Gas cooler/condenser 2 is shown receiving CO₂ vapor from fluid conduit 1. In example implementations, the CO₂ vapor in fluid conduit 1 can have a pressure within a range from approximately 45 bar to approximately 100 bar (e.g., about 640 psig to about 1420 psig), depending on ambient temperature and other operating conditions. In example implementations, gas cooler/condenser 2 can partially or fully condense CO₂ vapor into liquid CO₂ (e.g., if system operation is in a subcritical region). The condensation process can result in fully saturated CO₂ liquid or a liquid-vapor mixture (e.g., having a thermodynamic quality between 0 and 1). In other implementations, gas cooler/condenser 2 can cool the CO₂ vapor (e.g., by removing superheat) without condensing the CO₂ vapor into CO₂ liquid (e.g., if system operation is in a supercritical region). In example implementations, the cooling/condensation process is an isobaric process. Gas cooler/condenser 2 is shown outputting the cooled and/or condensed CO₂ refrigerant into fluid conduit 3.

In alternative implementations, refrigeration system 100 can include multiple gas coolers/condensers 2. In some aspects, each of the multiple gas coolers/condensers 2 are fluidly coupled to both fluid conduit 42 (through fluid conduit 1) and discharge 63 (through discharge conduit 29). Thus, refrigerant fluid flows from MT compressors 14 (and LT compressors 24), as well as EC compressor 26, to the one or more gas coolers/condensers 2 in combination. In alternative implementations, there can be separate gas coolers/condenser 2 for the MT and LT compressors 14 and 24 (for one set of gas coolers/condenser 2) and the EC compressor(s) 26 (for a fluidly separate, on the suction side, for a second set of gas coolers/condenser 2).

High pressure valve 4 can receive the cooled and/or condensed CO₂ refrigerant from fluid conduit 3 and can discharge the CO₂ refrigerant to fluid conduit 5. High pressure valve 4 can control the pressure of the CO₂ refrigerant in gas cooler/condenser 2 by controlling an amount of CO₂ refrigerant permitted to pass through high pressure valve 4. In example implementations, high pressure valve 4 is a high pressure thermal expansion valve (e.g., if the pressure in fluid conduit 3 is greater than the pressure in fluid conduit 5). In such implementations, high pressure valve 4 can allow the CO₂ refrigerant to expand to a lower pressure state.

The expansion process can be an isenthalpic and/or adiabatic expansion process, resulting in a flash evaporation of the high pressure CO₂ refrigerant to a lower pressure, lower temperature state. The expansion process can produce a liquid/vapor mixture (e.g., having a thermodynamic quality between 0 and 1). In example implementations, the CO₂ refrigerant expands to a pressure of approximately 38 bar (e.g., about 540 psig), which corresponds to a temperature of approximately 37° F. The CO₂ refrigerant then flows from fluid conduit 5 into flash tank 6. High pressure valve 4 can be operated automatically by controller 50, as described in greater detail with reference to FIG. 2A.

Flash tank 6 can collect the CO₂ refrigerant from fluid conduit 5. Flash tank 6 is shown to include a CO₂ liquid portion 16 and a CO₂ vapor portion 15 and can contain a partially saturated mixture of CO₂ liquid and CO₂ vapor. In example implementations, flash tank 6 separates the CO₂ liquid from the CO₂ vapor. The CO₂ liquid can exit flash tank 6 through fluid conduits (e.g., liquid lines) 9. Fluid conduits 9 can be liquid headers leading to MT subsystem and/or LT subsystem. The CO₂ vapor can exit flash tank 6 through fluid conduit 7. Fluid conduit 7 is shown leading the CO₂ vapor to a gas bypass valve 8 and to section conduit 13.

Still referring to FIG. 1, MT subsystem includes one or more expansion valves 11, one or more MT evaporators 12, and one or more MT compressors 14. In various implementations, any number of expansion valves 11, MT evaporators 12, and MT compressors 14 can be present. Expansion valves 11 can be electronic expansion valves or other similar expansion valves. Expansion valves 11 are shown receiving liquid CO₂ refrigerant from fluid conduit 9 and outputting the CO₂ refrigerant to MT evaporators 12. Expansion valves 11 can cause the CO₂ refrigerant to undergo a rapid drop in pressure, thereby expanding the CO₂ refrigerant to a lower pressure, lower temperature state. In example implementations, expansion valves 11 can expand the CO₂ refrigerant to a pressure of approximately 30 bar. The expansion process can be an isenthalpic and/or adiabatic expansion process.

MT evaporators 12 are shown receiving the cooled and expanded CO₂ refrigerant from expansion valves 11. In example implementations, MT evaporators 12 can be associated with particular enclosed spaces, such as display cases/devices (e.g., refrigerated cases if CO₂ refrigeration system 100 is implemented in a supermarket setting) or other enclosed spaces, such as human-occupiable living spaces (and reference numeral 12 can refer to an MT evaporator in combination with an enclosed space). MT evaporators 12 can be configured to facilitate the transfer of heat from the display cases/devices into the CO₂ refrigerant. The added heat can cause the CO₂ refrigerant to evaporate partially or completely. According to example implementations, the CO₂ refrigerant is fully evaporated in MT evaporators 12. In example implementations, the evaporation process can be an isobaric process. MT evaporators 12 are shown outputting the CO₂ refrigerant via suction line 13, leading to MT compressors 14.

MT compressors 14 can operate to compress the CO₂ refrigerant into a superheated vapor having a pressure within a range of approximately 45 bar to approximately 100 bar. The output pressure from MT compressors 14 can vary depending on ambient temperature and other operating conditions. In example implementations, MT compressors 14 operate in a transcritical mode. In operation, the CO₂ discharge gas exits MT compressors 14 and flows through fluid conduit 1 into gas cooler/condenser 2. In example implementations, an oil separator 31 is located along fluid conduit 1 and configured to separate oil from the CO₂ discharge gas exiting MT compressors 14. The separated oil can be collected within oil separator 31 and returned to MT compressors 14 and/or LT compressors 24. In some aspects, EC compressor 26 (or multiple EC compressors in some example implementations) also utilizes oil from the oil separator 31. However, a separate oil separator (not shown) can be used to separate oil from a CO₂ discharge gas exiting the EC compressor 26, which can be collected within the separate oil separator and returned to the EC compressor 26.

Still referring to FIG. 1, LT subsystem includes one or more expansion valves 21, one or more LT evaporators 22, and one or more LT compressors 24. In various implementations, any number of expansion valves 21, LT evaporators 22, and LT compressors 24 can be present. In example implementations, LT subsystem can be omitted and the CO₂ refrigeration system 100 can operate with a single compressor group (e.g., the MT subsystem).

Expansion valves 21 can be electronic expansion valves or other similar expansion valves. Expansion valves 21 are shown receiving liquid CO₂ refrigerant from fluid conduit 9 and outputting the CO₂ refrigerant to LT evaporators 22. Expansion valves 21 can cause the CO₂ refrigerant to undergo a rapid drop in pressure, thereby expanding the CO₂ refrigerant to a lower pressure, lower temperature state. The expansion process can be an isenthalpic and/or adiabatic expansion process. In example implementations, expansion valves 21 can expand the CO₂ refrigerant to a lower pressure than expansion valves 11, thereby resulting in a lower temperature CO₂ refrigerant. Accordingly, LT subsystem can be used in conjunction with a freezer system or other lower temperature display cases.

LT evaporators 22 are shown receiving the cooled and expanded CO₂ refrigerant from expansion valves 21. In example implementations, LT evaporators can be associated with particular enclosed spaces, such as display cases/devices (e.g., freezer or low temperature spaces if CO₂ refrigeration system 100 is implemented in a supermarket setting) or other enclosed spaces (and reference numeral 22 can refer to an LT evaporator in combination with an enclosed space). LT evaporators 22 can be configured to facilitate the transfer of heat from the display cases/devices into the CO₂ refrigerant. The added heat can cause the CO₂ refrigerant to evaporate partially or completely. In example implementations, the evaporation process can be an isobaric process. LT evaporators 22 are shown outputting the CO₂ refrigerant via suction line 23, leading to LT compressors 24.

LT compressors 24 can operate to compress the CO₂ refrigerant. In example implementations, LT compressors 24 can compress the CO₂ refrigerant to a pressure of approximately 30 bar (e.g., about 425 psig) having a saturation temperature of approximately 23° F. (e.g., about −5° C.). In example implementations, LT compressors 24 operate in a subcritical mode. LT compressors 24 are shown outputting the CO₂ refrigerant through discharge line 25. Discharge line 25 can be fluidly connected with the suction (e.g., upstream) side of MT compressors 14 (e.g., suction line 13).

Still referring to FIG. 1, CO₂ refrigeration system 100 is shown to include a gas bypass valve 8. Gas bypass valve 8 can receive the CO₂ vapor from fluid conduit 7 and output the CO₂ refrigerant to MT subsystem. In example implementations, gas bypass valve 8 is arranged in series with MT compressors 14. In other words, CO₂ vapor from flash tank 6 can pass through both gas bypass valve 8 and MT compressors 14. MT compressors 14 can compress the CO₂ vapor passing through gas bypass valve 8 from a low pressure state (e.g., approximately 30 bar or lower) to a high pressure state (e.g., 45-100 bar).

Gas bypass valve 8 can be operated by controller 50 to regulate or control the pressure within flash tank 6 (e.g., by adjusting an amount of CO₂ refrigerant permitted to pass through gas bypass valve 8). For example, gas bypass valve 8 can be adjusted (e.g., variably opened or closed) to adjust the mass flow rate, volume flow rate, or other flow rates of the CO₂ refrigerant through gas bypass valve 8. Gas bypass valve 8 can be opened and closed (e.g., manually, automatically, by a controller, etc.) as needed to regulate the pressure within flash tank 6.

In example implementations, gas bypass valve 8 includes a sensor for measuring a flow rate (e.g., mass flow, volume flow, etc.) of the CO₂ refrigerant through gas bypass valve 8. In other implementations, gas bypass valve 8 includes an indicator (e.g., a gauge, a dial, etc.) from which the position of gas bypass valve 8 can be determined. This position can be used to determine the flow rate of CO₂ refrigerant through gas bypass valve 8, as such quantities can be proportional or otherwise related.

In example implementations, gas bypass valve 8 can be a thermal expansion valve (e.g., if the pressure on the downstream side of gas bypass valve 8 is lower than the pressure in fluid conduit 7). According to one implementation, the pressure within flash tank 6 is regulated by gas bypass valve 8 to a pressure of approximately 38 bar, which corresponds to about 37° F. Advantageously, this pressure/temperature state can facilitate the use of copper tubing/piping for the downstream CO₂ lines of the system. Additionally, this pressure/temperature state can allow such copper tubing to operate in a substantially frost-free manner.

In example implementations, the CO₂ vapor that is bypassed through gas bypass valve 8 is mixed with the CO₂ refrigerant gas exiting MT evaporators 12 (e.g., via suction line 13). The bypassed CO₂ vapor can also mix with the discharge CO₂ refrigerant gas exiting LT compressors 24 (e.g., via discharge line 25). The combined CO₂ refrigerant gas can be provided to the suction side of MT compressors 14.

In example implementations, the pressure immediately downstream of gas bypass valve 8 (e.g., in suction line 13) is lower than the pressure immediately upstream of gas bypass valve 8 (e.g., in fluid conduit 7). Therefore, the CO₂ vapor passing through gas bypass valve 8 and MT compressors 14 can be expanded (e.g., when passing through gas bypass valve 8) and subsequently recompressed (e.g., by MT compressors 14). This expansion and recompression can occur without any intermediate transfers of heat to or from the CO₂ refrigerant, which can be characterized as an inefficient energy usage.

As shown in the example of FIG. 1, CO₂ refrigeration system 100 includes an external cooling (EC) compressor 26. EC compressor 26, in this example, is fluidly coupled (e.g., directly) on a branch conduit 27 to the flash tank 6 and the suction line 23. EC compressor 26, in this example, is fluidly coupled (e.g., directly) on a discharge side 29 to the fluid conduit 1 (and the gas cooler/condenser 2). In some aspects, EC compressor 26 can the same or similar to at least one of the MT compressors 14). Although only one EC compressor 26 is shown, any number of EC compressors can be present in this example (and reference to “a” component of the system can include reference to more than one of such component).

Therefore, in this example implementation, a suction 61 of the EC compressor 26 is fluidly coupled (e.g., directly, with no intervening pressure reducing valves or expansion valves) to the branch circuit 37 (i.e., the MT suction line 13), the suction line 27 (i.e., flash tank 6), and the branch circuit 39 (i.e., the LT suction line 23). Thus, in example aspects, a fluid pressure at the suction 61 is set by the fluid pressures at the MT suction line 13, flash tank 6, and the LT suction line 23 upon loss of power. The fluid pressure at the suction 61 may also differ from such fluid pressures (or a fluid pressure set by these three fluid pressure) based on conventional pipe and fitting friction loss between the MT suction line 13, flash tank 6, the LT suction line 23 and the suction 61. A pressure at a discharge 63 of the EC compressor 26 is set by operation of the EC compressor 26.

Generally, EC compressor 26 can be used to operate to preserve or control a refrigerant charge of the CO₂ refrigeration system 100 in case of loss of power to all or portions of the system 100 (such as the MT subsystem and LT subsystem). In a loss of power situation, a refrigerant charge (e.g., the volume or amount of CO₂ refrigerant enclosed within the vapor-compression cycle of the system 100) can escape the system 100 (and be lost, e.g., to an ambient environment, often undesirably so). In order to control (save) the CO₂ refrigerant charge (e.g., up to 100%) from being lost during such loss of power, the EC compressor 26 can be operated (e.g., on back up or emergency power) to maintain the CO₂ refrigerant charge at conditions (e.g., pressure/temperature) so that the refrigerant will not escape the system 100 through one or more relief valves in the system 100 (such as relief valves at fluidly coupled to flash tank 6, suction line 23, suction line 13, not shown here).

In some aspects, EC compressor 26, as well as one or more other components of the CO₂ refrigeration system 100 such as a controller 999, are electrically coupled to an uninterruptible power supply (UPS) 990 (e.g., generator, battery, or otherwise). UPS 990, therefore, can be operated to provide power to the EC compressor 26 and controller 999 during a power outage to operate these components (and others where required) to save the CO₂ refrigerant charge from escaping the system 100. In an example operation, upon a loss of power, the controller 999 operates to close the high-pressure valve 4 and the gas bypass valve 8. This allows the liquid portion 16 of the CO₂ refrigerant charge in the flash tank 6 and fluid conduit 9 up to the expansion valves 21 (which fail closed upon loss of power) to be enclosed therein without escape.

However, based on a pressure of the CO₂ vapor portion 15 in the flash tank 6, this portion of the refrigerant charge could escape through one or more relief valves on the flash tank 6 without operation of the EC compressor 26. For example, provided with power from the UPS 990, the EC compressor 26 operates to maintain a suction pressure at a suction inlet of the EC compressor 26 at or about a suction pressure of MT compressors 14 (e.g., pressure in suction line 13), and pressure in the flash tank 6 (e.g., pressure in fluid conduit 7). Based on the ECU compressor 26's operating envelope, the compressor suction can be expanded to LT suction to save 100% of the refrigerant system charge. Thus, during periods of UPS 990, the ECU compressor 26 operates (e.g., based on a pressure increase in the system 100 during loss of power) to pump down vapor refrigerant into a liquid state for complete storage in the flash tank 6 as the liquid portion 16. This can present loss of refrigerant vapor from the system 100 during loss of power situations.

As shown in this example, in a loss of power situation, a fluid circuit 35 is formed (e.g., by closing or opening one or more valves due to power failure) and includes the EC compressor 26, fluid conduit 1, the gas cooler/condenser 2, fluid conduit 3, bypass loop 43, flash tank 6, and branch conduit 27. Branch conduits 37 and 39 fluidly coupled the suctions 13 and 23, respectively, to the branch conduit 27 and are included in the fluid conduit 35. The bypass loop 43, as shown fluidly couples to fluid conduit 3 and bypasses high pressure valve 4 (which closes upon loss of power). The bypass loop 43 also fluidly couples at or near an inlet 41 of the flash tank 6 (downstream of the high pressure valve 4). In this example, a bypass shut-off valve 47 (e.g., solenoid valve) is fluidly coupled within the bypass loop 43. Bypass shut-off valve 47 opens upon loss of power (e.g., is a NO valve) and a pressure determination in the gas cooler/condenser 2 to allow CO₂ refrigerant liquid to be circulated into the flash tank 6 by the EC compressor 26 during loss of power.

As further shown in the example implementation of FIG. 1, shut-off valves 51a, 51b, and 51c are positioned in branch conduit 37, suction line 27, and branch conduit 39, respectively. During loss of power (and operation of the EC compressor 26 by the UPS 990), shut-off valves 51a, 51b, and 51c can open (e.g., by NO solenoid valves) to allow CO₂ refrigerant (vapor) to flow to the EC compressor 26 during emergency operation. During return of normal power (e.g., when the UPS 990 and EC compressor 26 are not operating), the shut-off valves 51a, 51b, and 51c can return to a closed state to allow flow of the CO₂ refrigerant normally through the CO₂ refrigeration system 100. Shut-off valves 51a, 51b & 51c and 47 can be any type of valve such as solenoid valve or Motorized ball valve or inlet pressure regulating valve or outlet pressure regulating valve or stepper valve or pulse valve or expansion type valve or ball valve.

In some aspects, the gas cooler/condenser 2 can also be electrically coupled to the UPS 990 so that it can be operated (e.g., one or more fans of the gas cooler/condenser 2 can be operated) during loss of power. Through operation, all or a portion of CO₂ refrigerant circulated to the gas cooler/condenser 2 can be condensed and returned to the flash tank 6 (through bypass loop 43). Alternatively, gas cooler/condenser 2 may not be electrically coupled to the UPS 990 such that condensation of at least some of the CO₂ refrigerant circulated to the gas cooler/condenser 2 by the EC compressor 26 occurs based on, e.g., ambient temperature conditions.

Control system 999 can be part of the CO₂ refrigeration system 100, and it can be part of a flow control system that controls the operations of the refrigeration system 100 (as well as other refrigeration systems 200 through 800) according to the present disclosure. A flow control system can include one or more flow pumps, fans, blowers, or otherwise to move fluid streams, one or more flow pipes through which the process streams are flowed and one or more valves to regulate the flow of streams through the pipes. Each of the configurations described herein can include at least one variable frequency drive (VFD) coupled to a respective pump that is capable of controlling at least one liquid flow rate. In some implementations, liquid flow rates are controlled by at least one flow control valve.

In example implementations, a flow control system can be operated manually. For example, an operator can set a flow rate for each pump or transfer device and set valve open or close positions to regulate the flow of the process streams through the pipes in the flow control system. Once the operator has set the flow rates and the valve open or close positions for all flow control systems distributed across the system, the flow control system can flow the streams under constant flow conditions, for example, constant volumetric rate or other flow conditions. To change the flow conditions, the operator can manually operate the flow control system, for example, by changing the pump flow rate or the valve open or close position.

In example implementations, a flow control system can be operated automatically. For example, the flow control system can be connected to a computer or control system (e.g., control system 999) to operate the flow control system. The control system can include a computer-readable medium storing instructions (such as flow control instructions and other instructions) executable by one or more processors to perform operations (such as flow control operations). An operator can set the flow rates and the valve open or close positions for all flow control systems distributed across the facility using the control system. In such implementations, the operator can manually change the flow conditions by providing inputs through the control system. Also, in such implementations, the control system can automatically (that is, without manual intervention) control one or more of the flow control systems, for example, using feedback systems connected to the control system. For example, a sensor (such as a pressure sensor, temperature sensor or other sensor) can be connected to a pipe through which a process stream flows. The sensor can monitor and provide a flow condition (such as a pressure, temperature, or other flow condition) of the process stream to the control system. In response to the flow condition exceeding a threshold (such as a threshold pressure value, a threshold temperature value, or other threshold value), the control system can automatically perform operations. For example, if the pressure or temperature in the pipe exceeds the threshold pressure value or the threshold temperature value, respectively, the control system can provide a signal to the pump to decrease a flow rate, a signal to open a valve to relieve the pressure, a signal to shut down process stream flow, or other signals.

According to the present disclosure, in some aspects, the control system 999 can represent, e.g., a building automation system that controls operations of the refrigeration system 100 (including EC compressor 26 and shut-off valves 51a-51c and valve 47), as well as other building systems (e.g., lighting, fire protection, etc.). In some aspects, the control system 999 can represent a dedicated control system (with, e.g., additional sub-controllers) for the refrigeration system 100, including EC compressor 26 and shut-off valves 51a-51c and valve 47 (by a sub-controller or the system 999, generally). In some aspects, the control system 999 can represent a dedicated controller for the EC compressor 26 and shut-off valves 51a-51c and valve 47; in other words, a controller that operates independently from other controllers for, e.g., the MT compressors 14, LT compressors 24, etc., and is supplied with power from UPS 990.

In an example sequence of operations for controlling the CO₂ refrigeration system 100, prior to a loss of power, certain relief valves and operating pressures can be set in the system 100. For example, an LT suction typical operating range can be −25 F to −15 F (181 psig to 221 psig), while an LT subsystem relief valve can be set to open at 30 bar (435 psig). An MT suction typical operating range can be +15 F to +25 F (375 psig to 441 psig), while an MT relief valve can be set to open at 45 bar (650 psig). A flash tank pressure can be 515 psig, while a flash tank relief valve can be set to open at 45 bar (650 psig) with a standstill pressure of 60 bar (870 psig).

As shown in FIG. 1, pressure transducers (or sensors) 53a, 53b, and 53c can be installed in the branch conduit 39, branch conduit 37, and branch conduit 27, respectively. As shown, shut-off valves (e.g., solenoid valves) 51a, 51b, and 51c are installed in branch conduit 37, branch conduit 27, and branch conduit 39, respectively. In this example, an LT suction control range can be between 300 psig (cut-out) and 375 psig (cut-in); an MT suction control range can be between 400 psig (cut-out) and 475 psig (cut-in); and a flash tank control range can be between 500 psig (cut-out) and 600 psig (cut-in). Here, the cut-in and cut-out ranges are given as examples, and this can be varied based on, e.g., the system design pressure. In some aspects, system design pressure can be out of range and can go as low as 12 bar (170 psig) and as high as 140 bar (2030 psig).

Upon loss of power, UPS 990 can supply power, e.g., to the EC compressor 26 and the control system 999 can determine the states of the shut-off valves 51a, 51b, and 51c. Shut-off valves 51a, 51b, and 51c can be opened based on the pressures measured by pressure transducers 53b, 53c, and 53a, respectively. As the EC compressor 26 operates, priority can be given to circulating refrigerant vapor from flash tank 6, then the refrigerant vapor from the branch conduit 37 (and suction conduit 13), and then the refrigerant vapor from the branch conduit 39 (and suction conduit 23), e.g., based on the percentage of CO₂. During operation of the EC compressor 26, and if gas cooler pressure (measured by pressure transducer 53d) is above a threshold pressure (e.g., about 108 bar), the bypass shut-off valve 47 can be opened to reduce the pressure in the gas cooler/condenser 2. Thus, the example implementation of the CO₂ refrigeration system 100 can pump down at least a portion of the CO₂ refrigerant charge to the volume of the system 100 encompassed by the flash tank 6 and fluid conduits (liquid lines) 9 that extend to the expansion valves 11 and 21 during a power outage.

In some aspects, the control system 999 (in combination with UPS 990), operates the EC compressor 26 and shut-off valves 51a-51c sequentially, based on, for example, the pressure measurements of pressure transducers 53a-53c (in comparison with cut-in and cut-out pressure values). Optionally, in some aspects, the control system 999 can give priority to the sequential opening of the shut-off valves 51a-51c so that the EC compressor 26 operates to pump down refrigerant fluid from the flash tank 6 (though suction conduit 27), the MT subsystem (through branch conduit 37), and the LT subsystem (through branch conduit 39), or some combination of these locations less than all three. In an example sequential operation, the solenoid valve 51b is opened first (e.g., based on flash tank cut-in pressure) while shut-off valves 51a and 51c remain closed until the flash tank cut-out pressure is achieved. Next, for example, after closure of valve 51b, shut-off valve 51a can be opened while valves 51b and 51c are closed and EC compressor 26 operates (and valve 51a is open) until the cut-out pressure for the MT subsystem is met. Next, after closure of valve 51a, shut-off valve 51c can be opened while valves 51a and 51b are closed and EC compressor 26 operates (and valve 51c is open) until the cut-out pressure for the LT subsystem is met.

In some aspects, alternatively, two or more of the shut-off valves 51a-51c can be opened simultaneously, and EC compressor 26 operates to pump down refrigerant fluid from at least two of the flash tank 6 (though suction conduit 27), the MT subsystem (through branch conduit 37), and the LT subsystem (through branch conduit 39) during a loss of power, refrigerant pump down operation. In such an operation, refrigerant fluid (e.g., CO₂ refrigerant) is circulated through EC compressor 26 (or multiple EC compressors) and compressed, cooled (and, in some aspects, condensed) in the gas cooler/condenser 2, and circulated (e.g., as a liquid phase) into flash tank 6 (and liquid line(s) 9)) for storage until main power is returned.

In some aspects, alternatively, the shut-off valve 51a can be an inlet pressure regulating valve, which regulates pressure in the MT subsystem. Shut-off valve 51a can be set to open at a set pressure (e.g., 625 psig) and maintain the MT subsystem pressure at 625 psig. If the pressure exceeds 625 psig, then shut-off valve 51a opens and releases refrigerant fluid (and thus the pressure) through suction conduit 27 and to the EC compressor 26 branch conduit 37. In such an operation, the refrigerant fluid from the branch circuit 37 is circulated through EC compressor 26 (or multiple EC compressors) and compressed, cooled (and, in some aspects condensed) in the gas cooler condenser 2. The cooled (or condensed) refrigerant fluid is circulated (e.g., as a liquid phase) into flash tank 6 (and liquid line(s) 9)) for storage until the main power is returned. In this example a flash tank control range can be between 500 psig (cut-out) and 600 psig (cut-in), and the MT subsystem pressure is maintained at a higher pressure than the flash tank 6, so that the refrigerant fluid can flow from the MT subsystem to suction conduit 27 through shut-off valve 51a (as an inlet pressure regulating valve) and through branch conduit 37 due to a pressure differential.

In some aspects, alternatively, the flash tank 6, the liquid line(s) 9 (up to expansion valves 11 and 21) can be rated for 60 bar (870 psig) (or 80 bar or 90 bar or 100 bar or 120 bar or 130 bar as examples). In this example, flash tank 6 and the liquid line(s) 9 (and other piping and fittings up to expansion valves 11 and 21) can be rated for 60 bar (870 psig). The shut-off valve 51b can be an inlet pressure regulating valve, which maintains a pressure (e.g., 840 psig) in the flash tank 6 and liquid line(s) 9 and releases the pressure when it exceeds 840 psig through suction conduit 27 (measured by pressure transducer 53c). In this example, the refrigerant fluid from suction conduit 27 is circulated through EC compressor 26 (or multiple EC compressors), compressed, cooled (and, in some aspects condensed) in the gas cooler condenser 2, and circulated (e.g., as a liquid phase) into flash tank 6 (and liquid line(s) 9)) for storage until the main power is returned. In this operation, the MT subsystem can be maintained at, e.g., 625 psi (cut-in) and 550 psi (cut-out).

In some aspects, alternatively, the flash tank 6, the liquid line(s) 9 (up to expansion valves 11 and 21) can be rated for 90 bar or 100 bar or 120 bar or 130 bar. In this example, these components can be rated for 90 bar (1305 psig), and the shut-off valve 51b can be an inlet pressure regulating valve, which maintains the pressure (e.g., at 1265 psig) in the flash tank 6 and liquid line(s) 9. The refrigerant fluid is released when the pressure exceeds 1265 psig through suction conduit 27.

The MT refrigeration sub system and LT subsystem can be rated for 60 bar (870 psig) or 45 bar (650 psig), and the shut-off valves 51a and 51c can be open to EC compressor 26. In this example, the MT subsystem, LT subsystem, and the EC compressor 26 are fluidly connected through the suction conduit 27 and branch conduits 37 and 39. Shut-off valves 51a and 51c are in an open position and the pressure in this section is maintained at 60 bar or 45 bar (e.g., as a defined set pressure). In this example, the shut-off valve 51b can be an inlet pressure regulating set to open at a certain pressure (e.g., 1265 psig) through the suction conduit 27 to the EC compressor 26. Based on the pressure setpoint (e.g., 840 psig cut-in and 780 cut-out pressure), refrigerant fluid from suction conduit 27 is circulated through EC compressor 26 (or multiple EC compressors) compressed, cooled (and, in some aspects, condensed) in the gas cooler condenser 2 and circulated (e.g., as a liquid phase) into flash tank 6 (and liquid line(s) 9)) for storage until the main power is returned. This cycle can continue until the power is returned.

FIG. 2 is a schematic diagram of another example implementation of a refrigeration system 200 according to the present disclosure. Generally, refrigeration system 200 (or CO₂ refrigeration system 200) is similar to the CO₂ refrigeration system 100, and the components shown and described with reference to FIG. 2 are the same (or similar) and operate the same (or similarly) as those same components shown in FIG. 1. However, in this example implementation, the CO₂ refrigeration system 200 does not include the branch conduit 27. Thus, as shown, branch conduit 37 fluidly couples the suction conduit 13 to the EC compressor 26, while branch conduit 39 fluidly couples the suction conduit 23 to the EC compressor 26. Discharge conduit 29 fluidly couples the discharge of EC compressor 26 to the fluid conduit 1 (and to the gas cooler/condenser 2).

In the example implementation of CO₂ refrigeration system 200, the refrigerant vapor in the flash tank 6 and suction conduit 13 can be consolidated and circulated to the EC compressor 26 during loss of power operations. In addition, the gas bypass valve 8 can be opened (e.g., fail open) during a power outage, so that this refrigerant vapor (in the flash tank 6 and MT compressors 14) can be circulated to the EC compressor 26. Refrigerant vapor in branch circuit 39 (e.g., from the LT compressors 24) can be circulated to the EC compressor 26 as described in FIG. 1.

In an example sequence of operations for controlling the CO₂ refrigeration system 200, prior to a loss of power, certain relief valves and operating pressures can be set in the system 200. For example, an LT suction typical operating range can be −25 F to −15 F (181 psig to 221 psig), while an LT subsystem relief valve can be set to open at 30 bar (435 psig). An MT suction typical operating range can be +15 F to +25 F (375 psig to 441 psig), while an MT relief valve can be set to open at 45 bar (650 psig). A flash tank pressure can be 515 psig, while a flash tank relief valve can be set to open at 45 bar (650 psig) with a standstill pressure of 60 bar (870 psig).

As shown in FIG. 2, pressure transducers 53a and 53b can be installed in the branch conduit 39 and branch conduit 37, respectively. As shown, shut-off valves (e.g., solenoid valves) 51a and 51c are installed in branch conduit 37 and branch conduit 39, respectively. In this example, an LT suction control range can be between 300 psig (cut-out) and 375 psig (cut-in); and an MT suction control range can be between 475 psig (cut-out) and 600 psig (cut-in).

Upon loss of power, UPS 990 can supply power, e.g., to the EC compressor 26 and the control system 999 can determine the states of the shut-off valves 51a and 51c. The gas bypass valve 8 is opened (or fails opened by loss of power). Shut-off valves 51a and 51c can be opened based on the pressures measured by pressure transducers 53b and 53a, respectively. As the EC compressor 26 operates, priority can be given to circulating refrigerant vapor from the combined flow path of the flash tank 6 and branch conduit 37 (and suction conduit 13), and then the refrigerant vapor from the branch conduit 39 (and suction conduit 23), e.g., based on the percentage of CO₂. During operation of the EC compressor 26, and if gas cooler pressure (measured by pressure transducer 53d) is above a threshold pressure (e.g., about 108 bar), the bypass shut-off valve 47 can be opened to reduce the pressure in the gas cooler/condenser 2. Thus, the example implementation of the CO₂ refrigeration system 200 can pump down at least a portion of the CO₂ refrigerant charge to the volume of the system 200 encompassed by the flash tank 6 and fluid conduits (liquid lines) 9 that extend to the expansion valves 11 and 21 during a power outage.

In an example, the flash tank 6 and liquid line(s) 9 can be rated for 90 bar or 100 bar, and MT subsystem and LT subsystem can be rated for 60 bar or 45 bar. During a power outage, the high pressure valve 4, flash gas bypass valve 7, and expansion valves 11 and 21 can be closed (e.g., as NC valves). The pressure of this section of the system 200 can be maintained under 90 bar. The MT subsystem and LT subsystem are fluidly coupled through branch conduit 37 and branch conduit 39 (respectively), and through shut-off valves 51a and 51c (respectively). Shut-off valves 51a and 51c can be solenoid valves, which open to EC compressor 26 based on pressure (read by sensors 53a and 53b) or it can be inlet pressure regulating valve opens when the pressure reaches its set point (say for example 58 bar in 60 bar system or 43 bar in the 45 bar system). In such operations, the refrigerant fluid from suction conduit 37 is circulated through EC compressor 26 (or multiple EC compressors), compressed, cooled (and, in some aspects condensed) in the gas cooler condenser 2, and circulated (e.g., as a liquid phase) into flash tank 6 (and liquid line(s) 9)) for storage until the main power is returned.

FIG. 3 is a schematic diagram of another example implementation of a refrigeration system 300 according to the present disclosure. Generally, refrigeration system 300 (or CO₂ refrigeration system 300) is similar to the CO₂ refrigeration system 100, and the components shown and described with reference to FIG. 3 are the same (or similar) and operate the same (or similarly) as those same components shown in FIG. 1. However, in this example implementation, the CO₂ refrigeration system 300 does not include the branch conduit 27, and dual EC compressor sets are used, as shown. For example, one or more MT-EC compressors 26a is fluidly coupled to suction conduit 13 and to fluid conduit 29, while one or more LT-EC compressors 26b is fluidly coupled to suction conduit 23 and to fluid conduit 29. Discharge conduit 29 fluidly couples the discharge of EC compressor 26 to the fluid conduit 1 (and to the gas cooler/condenser 2).

This example implementation of CO₂ refrigeration system 300 can be implemented, e.g., based on a cooling capacity or size of refrigerant charge of the system 300, as the dual compressor set design can be advantageous for larger systems. For example, the one or more MT-EC compressors 26a is operated to circulate refrigerant vapor from the flash tank 6 and MT subsystem, while the one or more LT-EC compressors 26b is operated to circulate refrigerant vapor from the LT subsystem. Both EC compressor sets (compressors 26a and 26b) can operate simultaneously (or in series) based on the pressure rise in the system 300.

In this example implementation, a suction 61a of the EC compressor 26a is fluidly coupled (e.g., directly, with no intervening pressure reducing valves or expansion valves) to the branch circuit 37 (i.e., the MT suction line 13). Thus, in example aspects, a fluid pressure at the suction 61a is set by the fluid pressure at the MT suction line 13 but may also differ from such fluid pressure based on conventional pipe and fitting friction loss between the MT suction line 13 and the suction 61a. Likewise, a suction 61b of the EC compressor 26b is fluidly coupled (e.g., directly, with no intervening pressure reducing valves or expansion valves) to the branch circuit 39 (i.e., the LT suction line 23). Thus, in example aspects, a fluid pressure at the suction 61b is set by the fluid pressure at the LT suction line 23 but may also differ from such fluid pressure based on conventional pipe and fitting friction loss between the LT suction line 23 and the suction 61. Pressures at discharge 63a of the EC compressor 26a and discharge 63b of the EC compressor 26b are set by operation of the EC compressor 26a and EC compressor 26B, respectively.

Thus, the example implementation of the CO₂ refrigeration system 300 can pump down all the CO₂ refrigerant charge to the volume of the system 300 encompassed by the flash tank 6 and fluid conduits (liquid lines) 9 that extend to the expansion valves 11 and 21 during a power outage, and the system design pressure can stay the same as conventional designs (e.g., without requiring a high pressure design on the LT subsystem). In some aspects, a capacity of the flash tank 6 in the CO₂ refrigeration system 300 can be increased on design so as to hold 100% of the refrigerant charge of the system 300. Generally, the example sequence of operations for CO₂ refrigeration system 300 is the same as or similar to the example sequence of operations for CO₂ refrigeration system 200.

Although CO₂ refrigeration system 300 is shown as having both EC compressor 26a and EC compressor 26b (with respective branch circuits 37 and 39), alternative implementations of the CO₂ refrigeration system 300 can include one or the other of EC compressors 26a, 26b. For example, in an alternative implementation, CO₂ refrigeration system 300 does not include branch circuit 39 (or pressure transducer 53a and shut-off valve 51c) and EC compressor 26b. Such an example implementation still includes branch circuit 37 (and pressure transducer 53b and shut-off valve 51a) and EC compressor 26a. In an alternative implementation, CO₂ refrigeration system 300 does not include branch circuit 37 (or pressure transducer 53b and shut-off valve 51a) and EC compressor 26a. Such an example implementation still includes branch circuit 39 (and pressure transducer 53a and shut-off valve 51c) and EC compressor 26b.

In an example, the flash tank 6 and liquid line(s) 9 are rated for 90 bar or 100 bar, and MT subsystem and LT subsystem are rated for 60 bar or 45 bar. During a power outage, the high pressure valve 4, flash gas bypass valve 7, and expansion valves 11 and 21 are closed. The pressure of this section of the system 300 can be maintained under 90 bar or 100 bar, and this section may never release the refrigerant charge subsequent to the power outage. The MT subsystem is fluidly coupled with gas cooler 2 through fluid conduit 29, EC compressor 26a, branch conduit 37, and shut-off valve 51a. The LT subsystem is fluidly coupled with gas cooler 2 through fluid conduit 29, EC compressor 26b, branch conduit 39, and shut-off valve 51c. The pressure (e.g., set pressure based on 45 bar or 60 bar) in the MT subsystem can be maintained by the EC compressor 26a. The pressure (e.g., set pressure based on 45 bar or 60 bar) in the LT subsystem can be maintained by the EC compressor 26b.

FIG. 4 is a schematic diagram of another example implementation of a refrigeration system 400 according to the present disclosure. Generally, refrigeration system 400 (or CO₂ refrigeration system 400) is similar to the CO₂ refrigeration system 300, and the components shown and described with reference to FIG. 4 are the same (or similar) and operate the same (or similarly) as those same components shown in FIG. 3. However, in this example implementation, the MT-EC compressor 26a discharges through discharge conduit 29a to the fluid conduit 1, while the LT-EC compressor 26b discharges through discharge conduit 29b to the fluid conduit 7 (e.g., between a vapor outlet 55 of the flash tank 6 and the gas bypass valve 8 in this example).

In the example implementation of CO₂ refrigeration system 400 (like the CO₂ refrigeration system 300), the refrigerant vapor in the flash tank 6 and suction conduit 13 can be consolidated and circulated to the EC compressor 26 during loss of power operations. In addition, the gas bypass valve 8 can be opened (e.g., fail open) during a power outage, so that this refrigerant vapor (in the flash tank 6 and MT compressors 14) can be circulated to the MT-EC compressor 26a. Refrigerant vapor in branch circuit 39 (e.g., from the LT compressors 24) can be circulated to the LT-EC compressor 26b as described in FIG. 3. Differently than the CO₂ system 300, however, in CO₂ system 400, once the refrigerant vapor in branch circuit 39 (e.g., from the LT compressors 24) is compressed by LT-EC compressor 26b, the compressed refrigerant vapor is circulated back to the MT-EC compressor 26a (through branch conduit 29b, fluid conduit 7, suction line 13, and branch conduit 37) for further compression and cooling through the gas cooler/condenser 2.

Thus, the example implementation of the CO₂ refrigeration system 400 can pump down all the CO₂ refrigerant charge to the volume of the system 400 encompassed by the flash tank 6 and fluid conduits (liquid lines) 9 that extend to the expansion valves 11 and 21 during a power outage, and the system design pressure can stay the same as conventional designs (e.g., without requiring a high pressure design on the LT subsystem). In some aspects, a capacity of the flash tank 6 in the CO₂ refrigeration system 400 can be increased on design so as to hold 100% of the refrigerant charge of the system 400. Generally, the example sequence of operations for CO₂ refrigeration system 400 is the same as or similar to the example sequence of operations for CO₂ refrigeration system 200 (and 300).

FIG. 5 is a schematic diagram of another example implementation of a refrigeration system 500 according to the present disclosure. Generally, refrigeration system 500 (or CO₂ refrigeration system 500) is the same as or similar to the CO₂ refrigeration system 100, and the components shown and described with reference to FIG. 5 are the same (or similar) and operate the same (or similarly) as those same components shown in FIG. 1. However, in this example implementation, a high (liquid) level sensor 57 is added to the flash tank 6. Generally, high level sensor 57 can be implemented in any of refrigeration systems 100, 200, 300, 400, 600, and 700 as well without departing from the scope of the present disclosure.

High level sensor 57 can be positioned in the flash tank 6 to measure a liquid level of liquid refrigerant 16 (e.g., CO₂ liquid) within the flash tank 6 during a loss of power pump down operation as described herein. The sensor 57 can be used, e.g., when the flash tank 6 is sized for liquid capacity that is less than (e.g., 85%) of a total refrigerant charge of the refrigeration system (in liquid form). In such cases, for instance, if the flash tank 6 is sized to handle less than a total refrigerant charge, then pumping down all the refrigerant charge (by EC compressor 26) to the flash tank 6 can cause issues (e.g., flooding the MT or LT compressors).

To mitigate such issues, the high level sensor 57 senses a liquid level of liquid refrigerant 16 in the flash tank 6. When the sensed liquid level is at a threshold or maximum level, the control system 999 (which can receive or identify such measurement) can stop operation of the EC compressor 26. While some refrigerant charge may escape the CO₂ refrigeration system 500, other issues (such as flooding) can be avoided.

An example sequence of operation of a refrigeration system that includes the high level sensor 57 can vary depending on the system design. For example, in an example sequence of operation of CO₂ refrigeration system 500, when the liquid refrigerant 16 level reaches the threshold limit, then the control system 999 can close the shut-off valves 51a and 51c. This may vent any charge that is left in the suction line 13 and the suction line 23. Shut-off valve 51b can remain open based on the pressure in the flash tank 6, so that the refrigerant vapor 15 in the flash tank 6 can keep recirculating through the EC compressor 26 and gas cooler/condenser 2 (until, e.g., all refrigerant charge is liquid or escaped).

In an example sequence of operation of CO₂ refrigeration system 200 with the addition of the high level sensor 57, when the liquid refrigerant 16 level reaches the threshold limit, then the control system 999 can close the shut-off valve 51c. This may vent any charge that is left in the suction line 23. Shut-off valve 51a can remain open based on the pressure in the flash tank 6, so that the refrigerant vapor 15 in the flash tank 6 can keep recirculating through the EC compressor 26 and gas cooler/condenser 2 (until, e.g., all refrigerant charge is liquid or escaped). A similar sequence of operations can also apply to CO₂ refrigeration system 300 and CO₂ refrigeration system 400.

FIG. 6 is a schematic diagram of another example implementation of a refrigeration system 600 according to the present disclosure. Generally, refrigeration system 600 (or CO₂ refrigeration system 600) is similar to the CO₂ refrigeration system 100, and the components shown and described with reference to FIG. 6 are the same (or similar) and operate the same (or similarly) as those same components shown in FIG. 1. However, in this example implementation, the discharge conduit from the EC compressor 26 is split into discharge conduit 29a that is fluidly coupled to fluid conduit 1 and discharge conduit 29b that is fluidly coupled to the fluid conduit 7 (e.g., between the vapor outlet 55 of the flash tank 6 and the gas bypass valve 8 in this example). As shown in this example, shut-off valve 51d (e.g., a solenoid valve) is positioned in discharge conduit 29a, while shut-off valve 51e (e.g., a solenoid valve) is positioned in discharge conduit 29b.

In an example sequence of operations for controlling the CO₂ refrigeration system 600, prior to a loss of power, certain relief valves and operating pressures can be set in the system 600. For example, an LT suction typical operating range can be −25 F to −15 F (181 psig to 221 psig), while an LT subsystem relief valve can be set to open at 30 bar (435 psig). An MT suction typical operating range can be +15 F to +25 F (375 psig to 441 psig), while an MT relief valve can be set to open at 45 bar (650 psig). A flash tank pressure can be 515 psig, while a flash tank relief valve can be set to open at 45 bar (650 psig) with a standstill pressure of 60 bar (870 psig).

As shown in FIG. 6, pressure transducers 53a, 53b, and 53c can be installed in the branch conduit 39, branch conduit 37, and branch conduit 27, respectively. As shown, shut-off valves (e.g., solenoid valves) 51a, 51b, and 51c are installed in branch conduit 37, branch conduit 27, and branch conduit 39, respectively. In this example, an LT suction control range can be between 300 psig (cut-out) and 375 psig (cut-in); an MT suction control range can be between 400 psig (cut-out) and 475 psig (cut-in); and a flash tank control range can be between 500 psig (cut-out) and 600 psig (cut-in).

Upon loss of power, UPS 990 can supply power, e.g., to the EC compressor 26 and the control system 999 can determine the states of the shut-off valves 51a, 51b, and 51c. Shut-off valves 51a, 51b, and 51c can be opened based on the pressures measured by pressure transducers 53b, 53c, and 53a, respectively. As the EC compressor 26 operates, priority can be given to circulating refrigerant vapor from flash tank 6, then the refrigerant vapor from the branch conduit 37 (and suction conduit 13), and then the refrigerant vapor from the branch conduit 39 (and suction conduit 23), e.g., based on the percentage of CO₂. During operation of the EC compressor 26, and if gas cooler pressure (measured by pressure transducer 53d) is above a threshold pressure (e.g., about 108 bar), the bypass shut-off valve 47 can be opened to reduce the pressure in the gas cooler/condenser 2. Furthermore, when the shut-off valve 51c is open, shut-off valves 51a, 51b, and 51d will be closed, and shut-off valve 51e will be open to discharge to the flash tank 6. Thus, the example implementation of the CO₂ refrigeration system 600 can pump down at least a portion of the CO₂ refrigerant charge to the volume of the system 600 encompassed by the flash tank 6 and fluid conduits (liquid lines) 9 that extend to the expansion valves 11 and 21 during a power outage.

FIG. 7 is a schematic diagram of another example implementation of a refrigeration system 700 according to the present disclosure. Generally, refrigeration system 700 (or CO₂ refrigeration system 700) is similar to the CO₂ refrigeration system 600, and the components shown and described with reference to FIG. 7 are the same (or similar) and operate the same (or similarly) as those same components shown in FIG. 6. However, in this example implementation, the CO₂ refrigeration system 700 does not include the branch conduit 27, which is included in FIG. 6 and CO₂ refrigeration system 600. Thus, as shown in FIG. 7, branch conduit 37 fluidly couples the suction conduit 13 to the EC compressor 26, while branch conduit 39 fluidly couples the suction conduit 23 to the EC compressor 26. Discharge conduit 29a fluidly couples the discharge of EC compressor 26 to the fluid conduit 1 (and to the gas cooler/condenser 2), while discharge conduit 29b is fluidly coupled to the fluid conduit 7 (e.g., between the vapor outlet 55 of the flash tank 6 and the gas bypass valve 8 in this example).

In the example implementation of CO₂ refrigeration system 700, the refrigerant vapor in the flash tank 6 and suction conduit 13 can be consolidated and circulated to the EC compressor 26 during loss of power operations. In addition, the gas bypass valve 8 can be opened (e.g., fail open) during a power outage, so that this refrigerant vapor (in the flash tank 6 and MT compressors 14) can be circulated to the EC compressor 26. Refrigerant vapor in branch circuit 39 (e.g., from the LT compressors 24) can be circulated to the EC compressor 26 as described in FIG. 1.

In an example sequence of operations for controlling the CO₂ refrigeration system 700, prior to a loss of power, certain relief valves and operating pressures can be set in the system 700. For example, an LT suction typical operating range can be −25 F to −15 F (181 psig to 221 psig), while an LT subsystem relief valve can be set to open at 30 bar (435 psig). An MT suction typical operating range can be +15 F to +25 F (375 psig to 441 psig), while an MT relief valve can be set to open at 45 bar (650 psig). A flash tank pressure can be 515 psig, while a flash tank relief valve can be set to open at 45 bar (650 psig) with a standstill pressure of 60 bar (870 psig).

As shown in FIG. 7, pressure transducers 53a and 53b can be installed in the branch conduit 39 and branch conduit 37, respectively. As shown, shut-off valves (e.g., solenoid valves) 51a and 51c are installed in branch conduit 37 and branch conduit 39, respectively. In this example, an LT suction control range can be between 300 psig (cut-out) and 375 psig (cut-in); and an MT suction control range can be between 475 psig (cut-out) and 600 psig (cut-in).

Upon loss of power, UPS 990 can supply power, e.g., to the EC compressor 26 and the control system 999 can determine the states of the shut-off valves 51a and 51c; the control system 999 determines which shut-off valve 51a or 51c to open based on the pressures measured by pressure transducers 53b and 53a, respectively. The gas bypass valve 8 is opened (or fails opened by loss of power).

As the EC compressor 26 operates, priority can be given to circulating refrigerant vapor from the combined flow path of the flash tank 6 and branch conduit 37 (and suction conduit 13), and then the refrigerant vapor from the branch conduit 39 (and suction conduit 23), e.g., based on the percentage of CO₂. During operation of the EC compressor 26, and if gas cooler pressure (measured by pressure transducer 53d) is above a threshold pressure (e.g., about 108 bar), the bypass shut-off valve 47 can be opened to reduce the pressure in the gas cooler/condenser 2. Furthermore, when the shut-off valve 51c is open, shut-off valves 51a and 51d will be closed, and shut-off valve 51e will be open to discharge to the flash tank 6. Thus, the example implementation of the CO₂ refrigeration system 700 can pump down at least a portion of the CO₂ refrigerant charge to the volume of the system 700 encompassed by the flash tank 6 and fluid conduits (liquid lines) 9 that extend to the expansion valves 11 and 21 during a power outage.

FIG. 8 is a schematic diagram of another example implementation of a refrigeration system 800 according to the present disclosure. Generally, refrigeration system 800 (or CO₂ refrigeration system 800) is similar to the CO₂ refrigeration system 100, and the components shown and described with reference to FIG. 8 are the same (or similar) and operate the same (or similarly) as those same components shown in FIG. 1. However, in this example implementation, the CO₂ refrigeration system 800 includes an oil return assembly 801 as shown. In some aspects, upon loss of power and operation of the EC compressor 26, oil 803 can be supplied to the EC compressor 26 with the oil return assembly 801. In some aspects, oil return assembly 801 can be implemented in one, some, or all of the refrigeration systems 100 through 700, even if not expressly shown in these figures.

In this example implementation, the oil sub-assembly includes a conduit 802 that fluidly couples the EC compressor 26 (e.g., at the bearings or other component of the compressor 26 or compressor motor) to an integrated oil separator/reservoir 806. As shown in this example, the integrated oil separator/reservoir 806 is fluidly coupled in discharge conduit 29 downstream of the EC compressor 26. In operation, the integrated oil separator/reservoir 806 removes all or a substantial portion of any oil 803 entrained in the compressed refrigerate in the discharge conduit 29 (with the oil separator portion) and stores the removed oil 803 in the reservoir portion of the integrated oil separator/reservoir 806.

In this example implementation, an oil return valve 804 is fluidly coupled within the conduit 802 between the integrated oil separator/reservoir 806 and the EC compressor 26. For example, the conduit 802 can fluidly couple the reservoir portion of the integrated oil separator/reservoir 806 to a portion of the EC compressor 26 in which an oil supply is needed (e.g., motor bearings or otherwise). Optionally, an oil pump 808 can also be installed in the conduit 802 between the integrated oil separator/reservoir 806 and the oil return valve 804 (or between the oil return valve 804 and the EC compressor 26.

In addition to the example operational sequence upon loss of power as described with reference to FIG. 1, the oil return valve 804 (e.g., as a normally open solenoid valve) can open upon loss of primary or main power. Alternatively, the oil return valve 804 (e.g., as a normally closed solenoid valve) can open with power provided by the UPS 990 upon loss of primary or main power.

Oil 803 is transported (e.g., gravity fed or forced circulation) from the reservoir portion of the integrated oil separator/reservoir 806 to the EC compressor 26 to feed oil to the compressor motor (and/or other compressor components) during operation. As the EC compressor 26 operates to recover (or save) refrigerant during the loss of power, oil that is entrained in the refrigerant as it leaves a discharge of the EC compressor 26 (into discharge conduit 29) is separated and removed from the refrigerant by the integrated oil separator/reservoir 806 and stored (at least transiently) as oil 803 in the reservoir portion of the integrated oil separator/reservoir 806. The stored oil 803 is recirculated back through conduit 802 to the EC compressor 26. In example implementations with multiple EC compressors (e.g., refrigeration systems 300 and 400), there can be multiple oil return assemblies 801 (e.g., a 1:1 ratio of refrigeration systems to oil sub-assemblies) or there can be a single oil sub-assembly that supplies oil to both (or all) of the EC compressors.

FIGS. 9A and 9B are flowcharts of example methods 900 and 950, respectively for controlling a refrigeration system according to the present disclosure. For example, turning to FIG. 9A, this flowchart shows a method 900 that can be implemented to control, e.g., refrigeration system 100 or refrigeration system 200. Method 900 can begin at step 902, which includes detecting a loss of main power (or other event, such as inoperation of one or both of the MT compressors 14 or LT compressors 24) to a refrigeration system. For example, method 900 may only be implemented, e.g., by the control system 999 and CO₂ refrigeration system 100 (or CO₂ refrigeration system 200) in the case of loss of main power. In some aspects, method 900 (and method 950) can end prior to completion of all (or even some) of the exemplary steps in the case of restoration of main power to the refrigeration system.

Method 900 can continue at step 904, which includes activating a UPS power to one or more EC compressors in the refrigeration system. For example, once main power is lost (and most of the components of CO₂ refrigeration system 100 are not supplied with power), the UPS 990 can supply electrical power to the EC compressor 26 (or compressors 26). Additionally, in some aspects, other components of the CO₂ refrigeration system 100 (such as one or more shut-off valves 51a-51c and shut-off bypass valve 47) can be supplied with power from the UPS 990.

Method 900 can continue at step 906, which includes determining one or more refrigerant pressures in the refrigeration system. For example, pressure transducers 53a-53c can measure refrigerant fluid pressures, which are transmitted to or otherwise exposed to control system 999.

Method 900 can continue at step 908, which includes a decision of whether one or more pressures (e.g., refrigerant pressures) on a suction side of one or more EC compressors in the refrigeration system is greater than a cut-in pressure value. For example, pressure transducer 53a can measure a pressure value in branch circuit 39, which can be compared to a cut-in value for the LT suction control (e.g., 375 psig). Pressure transducer 53b can measure a pressure value in branch circuit 37, which can be compared to a cut-in value for the MT suction control (e.g., 475 psig). Pressure transducer 53c can measure a pressure value in suction line 27, which can be compared to a cut-in value for the flash tank 6 (e.g., 600 psig). In the case of method 900 implemented in CO₂ refrigeration system 200, only pressure transducers 53a and 53b are present and determine pressure values in their respective branches shown in FIG. 2.

If none of the measured pressures are determined to be greater than the appropriate cut-in value, then method 900 can continue at step 910, which includes resetting a timer. Once the timer has expired, step 910 can revert back to step 906.

If at least one of the measured pressures is determined to be greater than the appropriate cut-in value, then method 900 can continue at step 912, which includes a decision of whether a pressure (e.g., refrigerant pressure) in a gas cooler (or condenser) of the refrigeration system is greater than a set point. If the determination is yes, then method 900 can continue at step 914, which includes opening a bypass shut off valve. For example, valve 47 can be opened to allow refrigerant liquid to circulate from the gas cooler/condenser 2 to the flash tank 6 based on a measured pressure from pressure transducer 53d.

In series or parallel with step 912 (and after a yes determination in step 908), method 900 can continue at step 916, which includes operating (and in some cases, activating) the one or more EC compressors to pump down a refrigerant fluid (e.g., all or a portion of a refrigerant charge) into a flash tank and/or liquid lines of the refrigeration system. For example, EC compressor 26 operates to draw refrigerant vapor from one or more of branch circuit 37, suction line 27, and branch circuit 39. In the case of method 900 implemented in CO₂ refrigeration system 200, EC compressor 26 operates to draw refrigerant vapor from one or both of branch circuit 37 and branch circuit 39.

Method 900 can continue at step 918, which includes a decision of whether the one or more pressures (e.g., refrigerant pressures) on the suction side of the one or more EC compressors in the refrigeration system is less than a cut-out pressure value. For example, pressure transducer 53a can measure the pressure value in branch circuit 39, which can be compared to a cut-out value for the LT suction control (e.g., 300 psig). Pressure transducer 53b can measure the pressure value in branch circuit 37, which can be compared to a cut-out value for the MT suction control (e.g., 400 psig). Pressure transducer 53c can measure the pressure value in suction line 27, which can be compared to a cut-out value for the flash tank 6 (e.g., 500 psig). In the case of method 900 implemented in CO₂ refrigeration system 200, only pressure transducers 53a and 53b are present and determine pressure values in their respective branches shown in FIG. 2.

If none of the measured pressures are determined to be less than the appropriate cut-out value, method 900 can revert to step 916. If all of the measured pressures are determined to be less than the appropriate cut-in value, then method 900 can continue at step 920, which includes a decision of whether the one or more pressures (e.g., refrigerant pressures) on the suction side of the EC compressors is greater than the cut-in pressure value (similar to step 908). If the decision is no, then method 900 reverts to step 916. If the decision is yes, then the one or more EC compressors is deactivated and method 900 reverts to step 910.

Turning to FIG. 9B, this flowchart shows a method 900 that can be implemented to control, e.g., refrigeration system 600 or refrigeration system 700. Method 950 can begin at step 952, which includes detecting a loss of main power (or other event, such as inoperation of one or both of the MT compressors 14 or LT compressors 24) to a refrigeration system. For example, method 950 may only be implemented, e.g., by the control system 999 and CO₂ refrigeration system 600 (or CO₂ refrigeration system 700) in the case of loss of main power.

Method 950 can continue at step 954, which includes activating a UPS power to one or more EC compressors in the refrigeration system. For example, once main power is lost (and most of the components of CO₂ refrigeration system 600 are not supplied with power), the UPS 990 can supply electrical power to the EC compressor 26 (or compressors 26). Additionally, in some aspects, other components of the CO₂ refrigeration system 600 (such as one or more shut-off valves 51a-51e and shut-off bypass valve 47) can be supplied with power from the UPS 990.

Method 950 can continue at step 956, which includes determining one or more refrigerant pressures in the refrigeration system. For example, pressure transducers 53a-53c can measure refrigerant fluid pressures, which are transmitted to or otherwise exposed to control system 999.

Method 950 can continue at step 958, which includes a decision of whether one or more pressures (e.g., refrigerant pressures) on a suction side of one or more EC compressors in the refrigeration system is greater than a cut-in pressure value. For example, pressure transducer 53a can measure a pressure value in branch circuit 39, which can be compared to a cut-in value for the LT suction control (e.g., 375 psig). Pressure transducer 53b can measure a pressure value in branch circuit 37, which can be compared to a cut-in value for the MT suction control (e.g., 475 psig). Pressure transducer 53c can measure a pressure value in suction line 27, which can be compared to a cut-in value for the flash tank 6 (e.g., 600 psig). In the case of method 900 implemented in CO₂ refrigeration system 700, only pressure transducers 53a and 53b are present and determine pressure values in their respective branches shown in FIG. 7.

If none of the measured pressures are determined to be greater than the appropriate cut-in value, then method 950 can continue at step 960, which includes resetting a timer. Once the timer has expired, step 960 can revert back to step 956.

If at least one of the measured pressures is determined to be greater than the appropriate cut-in value, then method 950 can continue at step 962, which includes a decision of whether a pressure (e.g., refrigerant pressure) in a gas cooler (or condenser) of the refrigeration system is greater than a set point. If the determination is yes, then method 950 can continue at step 964, which includes opening a bypass shut off valve. For example, valve 47 can be opened to allow refrigerant liquid to circulate from the gas cooler/condenser 2 to the flash tank 6 based on a measured pressure from pressure transducer 53d.

In series or parallel with step 962 (and after a yes determination in step 958), method 950 can continue at step 966, which includes operating (and in some cases activating) the one or more EC compressors to pump down a refrigerant fluid (e.g., all or a portion of a refrigerant charge) into a flash tank and/or liquid lines of the refrigeration system. For example, EC compressor 26 operates to draw refrigerant vapor from one or more of branch circuit 37, suction line 27, and branch circuit 39. In the case of method 950 implemented in CO₂ refrigeration system 700, EC compressor 26 operates to draw refrigerant vapor from one or both of branch circuit 37 and branch circuit 39.

Method 950 can continue at step 968, which includes adjusting one or more shut-off valves (if needed). For example, CO₂ refrigeration system 600 includes shut-off valves 51a-51e. If needed in step 968, control system 999 can open or check to make sure shut-off valve 51c is open, and if so, close shut-off valves 51a, 51b, and 51d. Shut-off valve 51e can be opened in step 968. In the case of CO2 refrigeration system 700, if needed in step 968, control system 999 can open or check to make sure shut-off valve 51c is open, and if so, close shut-off valves 51a and 51d (as is there is no valve 51b). Shut-off valve 51e can be opened in step 968 for system 700 as well.

Method 950 can continue at step 970, which includes a decision of whether the one or more pressures (e.g., refrigerant pressures) on the suction side of the one or more EC compressors in the refrigeration system is less than a cut-out pressure value. For example, pressure transducer 53a can measure the pressure value in branch circuit 39, which can be compared to a cut-out value for the LT suction control (e.g., 300 psig). Pressure transducer 53b can measure the pressure value in branch circuit 37, which can be compared to a cut-out value for the MT suction control (e.g., 400 psig). Pressure transducer 53c can measure the pressure value in suction line 27, which can be compared to a cut-out value for the flash tank 6 (e.g., 500 psig). In the case of method 950 implemented in CO2 refrigeration system 700, only pressure transducers 53a and 53b are present and determine pressure values in their respective branches shown in FIG. 7.

If none of the measured pressures are determined to be less than the appropriate cut-out value, method 950 can revert to step 966. If all of the measured pressures are determined to be less than the appropriate cut-in value, then method 950 can continue at step 972, which includes a decision of whether the one or more pressures (e.g., refrigerant pressures) on the suction side of the EC compressors is greater than the cut-in pressure value (similar to step 958). If the decision is no, then method 950 reverts to step 966. If the decision is yes, then the one or more EC compressors is deactivated and method 950 reverts to step 960.

FIG. 10 is a graph 1000 that shows an example operation envelope for an external cooling compressor according to the present disclosure. Graph 1000 shows a curve 1006 that represents an operation envelope of the EC compressor 26, which, in example aspects, is a CO₂ compressor, such as a reciprocating, screw, or scroll compressor. In example implementations, the EC compressor 26 has a suction temperature range of −20° C. to 11° C. (−4° F. to +51.8° F.) and a suction pressure range of 19 bar (275 psig) to 50 bar (725 psig). In graph 1000, the x-axis 1002 represents suction pressure (in bar) and the y-axis 1004 represents discharge pressure (in bar). Curve 1006 represents the operational discharge pressure range over the suction pressure range of 19 bar to 50 bar.

FIG. 11 shows a schematic drawing of a control system (or controller) 1100 that can be used to control a refrigeration system according to the present disclosure. Control system 1100 can be all or part of control system 999 that controls the operations of example implementations of refrigeration systems 100 through 800 according to the present disclosure.

Some or all of the example control system (or controller) 1100 can be implemented as cloud-based system and/or service, alone or in combination with other portions of the example control system 1100. The controller 1100 is intended to include various forms of digital computers, such as printed circuit boards (PCB), processors, digital circuitry, or otherwise. Additionally, the system can include portable storage media, such as, Universal Serial Bus (USB) flash drives. For example, the USB flash drives can store operating systems and other applications. The USB flash drives can include input/output components, such as a wireless transmitter or USB connector that can be inserted into a USB port of another computing device.

The controller 1100 includes a processor 1110, a memory 1120, a storage device 1130, and an input/output device 1140. Each of the components 1110, 1120, 1130, and 1140 are interconnected using a system bus 1150. The processor 1110 is capable of processing instructions for execution within the controller 1100. The processor can be designed using any of a number of architectures. For example, the processor 1110 can be a CISC (Complex Instruction Set Computers) processor, a RISC (Reduced Instruction Set Computer) processor, or a MISC (Minimal Instruction Set Computer) processor.

In one implementation, the processor 1110 is a single-threaded processor. In another implementation, the processor 1110 is a multi-threaded processor. The processor 1110 is capable of processing instructions stored in the memory 1120 or on the storage device 1130 to display graphical information for a user interface on the input/output device 1140.

The memory 1120 stores information within the control system 1100. In one implementation, the memory 1120 is a computer-readable medium. In one implementation, the memory 1120 is a volatile memory unit. In another implementation, the memory 1120 is a non-volatile memory unit.

The storage device 1130 is capable of providing mass storage for the controller 1100. In one implementation, the storage device 1130 is a computer-readable medium. In various different implementations, the storage device 1130 can be a floppy disk device, a hard disk device, an optical disk device, a tape device, flash memory, a solid state device (SSD), or a combination thereof.

The input/output device 1140 provides input/output operations for the controller 1100. In one implementation, the input/output device 1140 includes a keyboard and/or pointing device. In another implementation, the input/output device 1140 includes a display unit for displaying graphical user interfaces.

In example implementations, the processor 1110 is configured to execute a machine learning model (e.g., an artificial intelligence model) that employs multiple layers of models to generate an output for a received input. A deep neural network is a deep machine learning model that includes an output layer and one or more hidden layers that each apply a non-linear transformation to a received input to generate an output. In some cases, the neural network may be a recurrent neural network. A recurrent neural network is a neural network that receives an input sequence and generates an output sequence from the input sequence. In particular, a recurrent neural network uses some or all of the internal state of the network after processing a previous input in the input sequence to generate an output from the current input in the input sequence. The machine learning model executed by the processor 1110 can be, for example, a deep-learning neural network or a “very” deep learning neural network. For example, the machine learning model executed by the processor 1110 can be a convolutional neural network or a recurrent network. The machine learning model can have residual connections or dense connections.

In example implementations, the machine learning model executed by the processor 1110 is an ensemble of models that may include all or a subset of the architectures described above.

In example implementations, the machine learning model executed by the processor 1110 is a graph neural network (GNN). GNNs are a designed to process data that can be represented in a graph form and feature pairwise message passing to enable iterative updating of node representation of the graph data.

In example implementations, the machine learning model executed by the processor 1110 can be a feedforward auto-encoder neural network. For example, the machine learning model executed by the processor 1110 can be a three-layer auto-encoder neural network. The machine learning model executed by the processor 1110 may include an input layer, a hidden layer, and an output layer. In example implementations, the neural network has no recurrent connections between layers. Each layer of the neural network may be fully connected to the next, e.g., there may be no pruning between the layers. The neural network may include an optimizer for training the network and computing updated layer weights. In example implementations, the neural network may apply a mathematical transformation, e.g., a convolutional transformation or factor analysis to input data prior to feeding the input data to the network.

In example implementations, the machine learning model executed by the processor 1110 can be a supervised model. For example, for each input provided to the model during training, the machine learning model can be instructed as to what the correct output should be. The machine learning model executed by the processor 1110 can use batch training, e.g., training on a subset of examples before each adjustment, instead of the entire available set of examples. This may improve the efficiency of training the model and may improve the generalizability of the model. In example implementations, the machine learning model executed by the processor 1110 may be an unsupervised model. For example, the model may adjust itself based on mathematical distances between examples rather than based on feedback on its performance. In example implementations, the machine learning model executed by the processor 1110 can provide suggested additional data that could further improve the output of the machine learning model.

The features described can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The apparatus can be implemented in a computer program product tangibly embodied in an information carrier, for example, in a machine-readable storage device for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions of the described implementations by operating on input data and generating output. The described features can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. A computer program is a set of instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

Suitable processors for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and the sole processor or one of multiple processors of any kind of computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memories for storing instructions and data. Generally, a computer will also include, or be operatively coupled to communicate with, one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, solid state drives (SSDs), and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits).

To provide for interaction with a user, the features can be implemented on a computer having a display device such as a CRT (cathode ray tube) or LCD (liquid crystal display) or LED (light-emitting diode) monitor for displaying information to the user and a keyboard and a pointing device such as a mouse or a trackball by which the user can provide input to the computer. Additionally, such activities can be implemented via touchscreen flat-panel displays and other appropriate mechanisms.

The features can be implemented in a control system that includes a back-end component, such as a data server, or that includes a middleware component, such as an application server or an Internet server, or that includes a front-end component, such as a client computer having a graphical user interface or an Internet browser, or any combination of them. The components of the system can be connected by any form or medium of digital data communication such as a communication network. Examples of communication networks include a local area network (“LAN”), a wide area network (“WAN”), peer-to-peer networks (having ad-hoc or static members), grid computing infrastructures, and the Internet.

While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any inventions or of what can be claimed, but rather as descriptions of features specific to particular implementations of particular inventions. Certain features that are described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features can be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination can be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing can be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

A number of implementations have been described. Nevertheless, it will be understood that various modifications can be made without departing from the spirit and scope of the disclosure. For example, example operations, methods, or processes described herein can include more steps or fewer steps than those described. Further, the steps in such example operations, methods, or processes can be performed in different successions than that described or illustrated in the figures. Accordingly, other implementations are within the scope of the following claims.