Refrigeration System with Refrigerant Charge Control

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.

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.

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.

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.

is a schematic diagram of an example implementation of a refrigeration systemaccording to the present disclosure. In example aspects, refrigeration systemincludes 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 systemoperates with a natural refrigerant (e.g., carbon dioxide (CO) or ammonia) and legendinshows the relative states of the refrigerant (with arrows in the figures showing refrigerant flow direction) in particular portions of the system(applicable to other systems shown in the figures as well). However, alternative implementations of refrigeration system(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(and other refrigeration systems according to the present disclosure) can be referred to as a COrefrigeration system, the present disclosure contemplates that the disclosed refrigeration systems can be designed to operate with refrigerants other than CO.