Patent Publication Number: US-11656004-B2

Title: Cooling system with flexible evaporating temperature

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/939,262 filed Jul. 27, 2020, by Shitong Zha, and entitled “COOLING SYSTEM WITH FLEXIBLE EVAPORATING TEMPERATURE,” which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to a cooling system (e.g., a refrigeration system and/or an air conditioning system). 
     BACKGROUND 
     Cooling systems may cycle a refrigerant to cool various spaces. For example, a system may cycle refrigerant to cool spaces near or around low side heat exchangers. 
     SUMMARY 
     Cooling systems (e.g., refrigeration systems and/or air conditioning systems) may cycle a refrigerant to cool various spaces. For example, a system may cycle refrigerant to cool spaces near or around low side heat exchangers. One refrigerant that has seen increasing use in cooling systems is carbon dioxide, due to its environmentally friendly properties relative to other conventional refrigerants. One drawback of carbon dioxide refrigerant, however, is that carbon dioxide refrigerant is difficult to use and manage in extreme temperatures. For example, cooling systems that use carbon dioxide refrigerant tend to operate more inefficiently in high ambient heat than cooling systems that use other refrigerants. It may be more difficult to regulate the pressure of the carbon dioxide refrigerant and to remove heat from the carbon dioxide refrigerant in high ambient heat. 
     This disclosure contemplates a cooling system that implements various processes to improve efficiency in high ambient temperatures. First, the system can flood one or more low side heat exchangers in the system. Second, the system can direct a portion of vapor refrigerant from a low side heat exchanger to a flash tank rather than to a compressor. Third, the system can transfer heat from refrigerant at a compressor suction to refrigerant at the discharge of a high side heat exchanger. By using one or more of these processes, the system improves the efficiency of operation during high ambient temperatures in certain embodiments. Certain embodiments are described below. 
     According to an embodiment, an apparatus includes a high side heat exchanger, a first ejector, a flash tank, a first low side heat exchanger, a first separator, a second low side heat exchanger, a second separator, an accumulator, a first valve, a second valve, and a compressor. The high side heat exchanger removes heat from a refrigerant. The first ejector receives refrigerant from the high side heat exchanger. The flash tank stores refrigerant. The first ejector directs refrigerant from the high side heat exchanger to the flash tank. The first low side heat exchanger uses refrigerant from the flash tank to cool a first space. The first separator receives refrigerant from the first low side heat exchanger. The refrigerant from the first low side heat exchanger includes a first liquid portion and a first vapor portion. The second low side heat exchanger uses refrigerant from the flash tank to cool a second space. The second separator receives refrigerant from the second low side heat exchanger. The refrigerant from the second low side heat exchanger includes a second liquid portion and a second vapor portion. The accumulator receives the first liquid portion and the second liquid portion. The accumulator separates refrigerant within the accumulator into a third liquid portion and a third vapor portion. The first valve can open to direct the first vapor portion to the first ejector. The first ejector directs the first vapor portion to the flash tank. The first valve can close to direct the first vapor portion to the accumulator. The second valve can open to direct the second vapor portion to the first ejector. The first ejector directs the second vapor portion to the flash tank. The second valve can close to direct the second vapor portion to the accumulator. The compressor compresses the third vapor portion from the accumulator. 
     According to another embodiment, a method includes removing, by a high side heat exchanger, heat from a refrigerant, receiving, by a first ejector, refrigerant from the high side heat exchanger, and storing, by a flash tank, refrigerant. The method also includes directing, by the first ejector, refrigerant from the high side heat exchanger to the flash tank, using, by a first low side heat exchanger, refrigerant from the flash tank to cool a first space, and receiving, by a first separator, refrigerant from the first low side heat exchanger. The refrigerant from the first low side heat exchanger includes a first liquid portion and a first vapor portion. The method further includes using, by a second low side heat exchanger, refrigerant from the flash tank to cool a second space, and receiving, by a second separator, refrigerant from the second low side heat exchanger. The refrigerant from the second low side heat exchanger includes a second liquid portion and a second vapor portion. The method also includes receiving, by an accumulator, the first liquid portion and the second liquid portion and during a first mode of operation, opening a first valve to direct the first vapor portion to the first ejector, directing, by the first ejector, the first vapor portion to the flash tank, and closing a second valve to direct the second vapor portion to the accumulator. The method further includes, during a second mode of operation, closing the first valve further to direct the first vapor portion to the accumulator, opening the second valve to direct the second vapor portion to the first ejector, and directing, by the first ejector, the second vapor portion to the flash tank. The method further includes separating, by the accumulator, refrigerant within the accumulator into a third liquid portion and a third vapor portion and compressing, by a compressor, the third vapor portion from the accumulator. 
     According to another embodiment, a system includes a high side heat exchanger, a first ejector, a flash tank, a first low side heat exchanger, a first separator, a second low side heat exchanger, a second separator, an accumulator, a first valve, a second valve, and a compressor. The high side heat exchanger removes heat from a refrigerant. The first ejector receives refrigerant from the high side heat exchanger. The flash tank stores refrigerant. The first ejector directs refrigerant from the high side heat exchanger to the flash tank. The first low side heat exchanger uses refrigerant from the flash tank to cool a first space. The first separator receives refrigerant from the first low side heat exchanger. The refrigerant from the first low side heat exchanger includes a first liquid portion and a first vapor portion. The second low side heat exchanger uses refrigerant from the flash tank to cool a second space. The second separator receives refrigerant from the second low side heat exchanger. The refrigerant from the second low side heat exchanger includes a second liquid portion and a second vapor portion. The accumulator receives the first liquid portion and the second liquid portion and separates refrigerant within the accumulator into a third liquid portion and a third vapor portion. During a first mode of operation, the first valve opens to direct the first vapor portion to the first ejector, the first ejector further directs the first vapor portion to the flash tank, and the second valve closes to direct the second vapor portion to the accumulator. During a second mode of operation, the first valve further closes to direct the first vapor portion to the accumulator, the second valve further opens to direct the second vapor portion to the first ejector, and the first ejector further directs the second vapor portion to the flash tank. The compressor compresses the third vapor portion from the accumulator. 
     Certain embodiments provide one or more technical advantages. For example, an embodiment improves the efficiency of a carbon dioxide cooling system during high ambient temperatures. Certain embodiments may include none, some, or all of the above technical advantages. One or more other technical advantages may be readily apparent to one skilled in the art from the figures, descriptions, and claims included herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    illustrates an example cooling system; 
         FIG.  2    illustrates an example cooling system; and 
         FIG.  3    is a flowchart illustrating a method of operating an example cooling system. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure and its advantages are best understood by referring to  FIGS.  1  through  3    of the drawings, like numerals being used for like and corresponding parts of the various drawings. 
     Cooling systems (e.g., refrigeration systems and/or air conditioning systems) may cycle a refrigerant to cool various spaces. For example, a system may cycle refrigerant to cool spaces near or around low side heat exchangers. One refrigerant that has seen increasing use in cooling systems is carbon dioxide, due to its environmentally friendly properties relative to other conventional refrigerants. One drawback of carbon dioxide refrigerant, however, is that carbon dioxide refrigerant is difficult to use and manage in extreme temperatures. For example, cooling systems that use carbon dioxide refrigerant tend to operate more inefficiently in high ambient heat than cooling systems that use other refrigerants. It may be more difficult to regulate the pressure of the carbon dioxide refrigerant and to remove heat from the carbon dioxide refrigerant in high ambient heat. 
     This disclosure contemplates a cooling system that implements various processes to improve efficiency in high ambient temperatures. First, the system can flood one or more low side heat exchangers in the system. Second, the system can direct a portion of vapor refrigerant from a low side heat exchanger to a flash tank rather than to a compressor. Third, the system can transfer heat from refrigerant at a compressor suction to refrigerant at the discharge of a high side heat exchanger. By using one or more of these processes, the system improves the efficiency of operation during high ambient temperatures in certain embodiments. The cooling system will be described using  FIGS.  1  through  3   . 
       FIG.  1    illustrates an example cooling system  100 . As shown in  FIG.  1   , system  100  includes a high side heat exchanger  102 , a flash tank  104 , one or more valves  106 , one or more low side heat exchangers  108 , one or more compressors  110 , and an oil separator  112 . Generally, system  100  cycles a refrigerant (e.g., carbon dioxide refrigerant) to cool one or more spaces. This disclosure contemplates cooling system  100  or any cooling system described herein including any number of low side heat exchangers. Additionally, the cooling systems described herein may be implemented for any suitable cooling application (e.g., a refrigeration system, an air conditioning system, etc.). 
     High side heat exchanger  102  removes heat from a refrigerant. When heat is removed from the refrigerant, the refrigerant is cooled. This disclosure contemplates high side heat exchanger  102  being operated as a condenser and/or a gas cooler. When operating as a condenser, high side heat exchanger  102  cools the refrigerant such that the state of the refrigerant changes from a gas to a liquid. When operating as a gas cooler, high side heat exchanger  102  cools gaseous refrigerant and the refrigerant remains a gas. In certain configurations, high side heat exchanger  102  is positioned such that heat removed from the refrigerant may be discharged into the air. For example, high side heat exchanger  102  may be positioned on a rooftop so that heat removed from the refrigerant may be discharged into the air. As another example, high side heat exchanger  102  may be positioned external to a building and/or on the side of a building. This disclosure contemplates any suitable refrigerant (e.g., carbon dioxide) being used in any of the disclosed cooling systems. 
     Flash tank  104  stores refrigerant received from high side heat exchanger  102 . This disclosure contemplates flash tank  104  storing refrigerant in any state such as, for example, a liquid state and/or a gaseous state. Refrigerant leaving flash tank  104  is fed to low side heat exchangers  108 . In some embodiments, a flash gas and/or a gaseous refrigerant is released from flash tank  104 . By releasing flash gas, the pressure within flash tank  104  may be reduced. 
     One or more valves  106  control a flow of refrigerant from flash tank  104  to one or more low side heat exchangers  108 . For example, when valve  106  is opened, refrigerant flows through valve  106 . When valve  106  is closed, refrigerant stops flowing through valve  106 . In certain embodiments, valve  106  can be opened to varying degrees to adjust the amount of flow of refrigerant. For example, valve  106  may be opened more to increase the flow of refrigerant. As another example, valve  106  may be opened less to decrease the flow of refrigerant. 
     In certain embodiments, valves  106  are expansion valves that cool the refrigerant flowing through the expansion valves. Valves  106  may receive refrigerant from any component of system  100  such as for example high side heat exchanger  102  and/or flash tank  104 . Valves  106  reduce the pressure and therefore the temperature of the refrigerant. Valves  106  reduce pressure from the refrigerant flowing into the valve  106 . The temperature of the refrigerant may then drop as pressure is reduced. As a result, refrigerant entering valves  106  may be cooler when leaving valves  106 . 
     Low side heat exchangers  108  use refrigerant from flash tank  104  and/or valves  106  to cool spaces proximate low side heat exchangers  108 . For example, if system  100  were a refrigeration system, system  100  may include a low temperature portion and a medium temperature portion. The low temperature portion operates at a lower temperature than the medium temperature portion. In some refrigeration systems, the low temperature portion may be a freezer system and the medium temperature system may be a regular refrigeration system. In a grocery store setting, the low temperature portion may include freezers used to hold frozen foods, and the medium temperature portion may include refrigerated shelves used to hold produce. Refrigerant flows from flash tank  104  to both the low temperature and medium temperature portions of the refrigeration system. For example, the refrigerant flows to low side heat exchangers  108  that are set to cool spaces to different temperatures. When the refrigerant reaches low side heat exchangers  108 , the refrigerant removes heat from the air around low side heat exchangers  108 . As a result, the air is cooled. The cooled air may then be circulated such as, for example, by a fan to cool a space such as, for example, a freezer and/or a refrigerated shelf. As refrigerant passes through low side heat exchangers  108 , the refrigerant may change from a liquid state to a gaseous state as it absorbs heat. This disclosure contemplates including any number of low side heat exchangers  108  in any of the disclosed cooling systems. 
     As another example, if system  100  were an air conditioning system, system  100  may include one or more low side heat exchangers  108  that cool different zones of a structure or space to different temperatures. As with the refrigeration system, the refrigerant flowing through low side heat exchangers  108  may absorb heat from the surrounding air to cool the air. This air may then be circulated (e.g., by a fan) to cool a zone or space. 
     In the example of  FIG.  1   , system  100  includes valves  106 A and  106 B and low side heat exchangers  108 A and  108 B. Valve  106 A controls a flow of refrigerant from flash tank  104  to low side heat exchanger  108 A. Valve  106 B controls a flow of refrigerant from flash tank  104  to low side heat exchanger  108 B. System  100  may include any suitable number of valves  106  and low side heat exchangers  108 . 
     Refrigerant flows from low side heat exchangers  108  to one or more compressors  110 . This disclosure contemplates the disclosed cooling systems including any number of compressors  110 . Compressors  110  compress refrigerant to increase the pressure of the refrigerant. As a result, the heat in the refrigerant may become concentrated and the refrigerant may become a high-pressure gas. The compressors  110  may be arranged in any suitable arrangement (e.g., in series and/or parallel). 
     Oil separator  112  receives refrigerant from compressor(s)  110 . Oil separator  112  separates oil that may have mixed with the refrigerant. The oil may have mixed with the refrigerant in compressor(s)  110 . By separating the oil from the refrigerant, oil separator  112  protects other components of system  100  from being clogged and/or damaged by the oil. Oil separator  112  may collect the separated oil. The oil may then be removed from oil separator  112  and added back to compressor(s)  110 . Certain embodiments do not include oil separator  112 . In these embodiments, refrigerant from compressor(s)  110  flows directly to high side heat exchanger  102 . 
     As discussed previously, system  100  may cycle a carbon dioxide refrigerant to cool spaces. Although carbon dioxide has several environmentally friendly properties, carbon dioxide refrigerant may be difficult to use and manage in extreme temperatures. For example, cooling systems that use carbon dioxide refrigerant tend to operate more inefficiently in high ambient heat than cooling systems that use other refrigerants. It may be more difficult to regulate the pressure of the carbon dioxide refrigerant and to remove heat from the carbon dioxide refrigerant in high ambient heat. 
     This disclosure contemplates a cooling system that implements various processes to improve efficiency in high ambient temperatures. First, the system can flood one or more low side heat exchangers in the system. Second, the system can direct a portion of vapor refrigerant from a low side heat exchanger to a flash tank rather than to a compressor. Third, the system can transfer heat from refrigerant at a compressor suction to refrigerant at the discharge of a high side heat exchanger. By using one or more of these processes, the system improves the efficiency of operation during high ambient temperatures in certain embodiments. Embodiments of the cooling system are described below using  FIGS.  2 - 3   . These figures illustrate embodiments that include a certain number of valves  106 , low side heat exchangers  108 , and compressors  110  for clarity and readability. However, this disclosure contemplates these embodiments including any suitable number of valves  106 , low side heat exchangers  108 , and compressors  110 . 
       FIG.  2    illustrates an example cooling system  200 . As seen in  FIG.  2   , system  200  includes a high side heat exchanger  102 , a flash tank  104 , one or more valves  106 , one or more low side heat exchangers  108 , one or more compressors  110 , an oil separator  112 , a heat exchanger  202 , one or more ejectors  204 , one or more separators  206 , one or more valves  208 , one or more valves  210 , an accumulator  212 , and a valve  214 . Generally, system  200  implements one or more modifications and/or processes to system  100  that may improve the efficiency of using carbon dioxide refrigerant in high ambient temperatures. These modifications and/or processes may be activated individually or in combination to improve the efficiency of system  200 . 
     Various components of system  200  operate similarly as they did in system  100 . For example, high side heat exchanger  102  removes heat from a refrigerant. Flash tank  104  stores a refrigerant. Valves  106  control a flow of refrigerant from flash tank  104  to low side heat exchangers  108 . Low side heat exchangers  108  use refrigerant to cool a space proximate low side heat exchangers  108 . Compressors  110  compress a refrigerant. Oil separator  112  separates an oil from a refrigerant and directs that refrigerant to high side heat exchanger  102 . 
     The first process implemented by system  200  to improve the efficiency of using carbon dioxide refrigerant in high ambient temperatures is to flood low side heat exchangers  108 . In certain embodiments, valves  106  may be opened such that the flow of refrigerant from flash tank  104  to low side heat exchangers  108  is greater than the amount of refrigerant that low side heat exchangers  108  can evaporate. As a result, the discharge from low side heat exchangers  108  includes both a vapor portion and a liquid portion. This disclosure contemplates any suitable number of low side heat exchangers  108  in system  200  operating in the flooded condition. For example, some low side heat exchangers  108  may be operating in a flooded condition while other low side heat exchangers  108  are not operating in the flooded condition. In certain embodiments, by flooding one or more low side heat exchangers  108 , an efficiency gain of over 8% can be achieved. 
     Separators  206  receive the discharge from low side heat exchangers  108 . In the example of  FIG.  2   , separator  206 A receives the discharge from low side heat exchangers  108 A and separator  206 B receives the discharge from low side heat exchangers  108 B. As discussed previously, when low side heat exchangers  108  are operating in the flooded condition, the discharge from low side heat exchangers  108  includes both a vapor portion and a liquid portion. Separators  206  separate the liquid portion from the vapor portion. Specifically, the liquid portion sinks to the bottom of separator  206  while the vapor portion rises to the top of separator  206 . In the example of  FIG.  2   , separator  206 A receives a liquid portion  218 A and a vapor portion  220 A from low side heat exchanger  108 A, and separator  206 B receives a liquid portion  218 B and a vapor portion  220 B from low side heat exchanger  108 B. Separators  206  may direct the liquid portion  218  and the vapor portion  220  to different sections of system  200  in certain embodiments. 
     Valves  208  and valves  210  control a flow of refrigerant from separators  206 . Valves  208  may be check valves that control a flow of refrigerant from separators  206  to accumulator  212 . Check valves may not open to direct refrigerant from separators  206  to accumulator  212  until a pressure of that refrigerant exceeds an internal threshold of the check valve. Valves  210  may be solenoid valves that control a flow of vapor portions  220  from separators  206  to ejector  204 B. In the example of  FIG.  2   , valve  208 A controls a flow of refrigerant from separators  206 A to accumulator  212  and valve  208 B controls a flow of refrigerant from separator  206 B to accumulator  212 . Additionally, valve  210 A controls a flow of vapor portion  220 A from separator  206 A to ejector  204 B and valve  210 B controls a flow of vapor portion  220 B from separator  206 B to ejector  204 B. 
     Accumulator  212  receives refrigerant from separators  206 . Accumulator  212  separates the refrigerant into a liquid portion  215  and a vapor portion  216 . Generally, liquid portion  215  collects at the bottom of accumulator  212  and vapor portion  216  rises to the top of accumulator  212 . By separating liquid portion  215  from vapor portion  216 , accumulator  212  is able to prevent liquid portion  215  from reaching certain components of system  200 , such as, for example, compressor  110 . As seen in  FIG.  2   , accumulator  212  includes a U-shaped pipe that has an entry point above the level of liquid portion  215 . As a result, vapor portion  216  is able to enter the U-shaped pipe and be discharged towards compressor  110 . On the other hand, liquid portion  215  is not able to enter the U-shaped pipe unless the level of liquid portion  215  rises above the entry of the U-shaped pipe. 
     In certain embodiments, accumulator  212  includes an additional pipe with an entry positioned in liquid portion  215 . The entry of this pipe is below the entry of the U-shaped pipe. The pipe directs the liquid portion  215  to an ejector  204 A. Ejector  204 A then directs the liquid portion  215  to flash tank  104 . In this manner, the level of liquid portion  215  may be controlled such that the level of liquid portion  215  does not rise above the entry of the U-shaped pipe. 
     In certain embodiments, accumulator  212  receives a flash gas from flash tank  104 . Valve  214  may be opened to direct a flash gas from flash tank  104  to accumulator  212 . In this manner, the internal pressure of flash tank  104  may be reduced. The flash gas mixes with vapor portion  216  and is discharged by accumulator  212  towards compressor  110 . 
     The second process implemented by system  200  to improve the efficiency of using carbon dioxide refrigerant in high ambient temperatures is to direct vapor portions  220  to an ejector  204 B. In certain embodiments, different low side heat exchangers  108  may cool respective spaces to different temperatures. System  200  may direct the vapor portion  220  associated with the low side heat exchanger  108  that is cooling a space to the colder or coldest temperature to ejector  204 B while directing the vapor portions  220  of the other low side heat exchangers  108  to accumulator  212 . Using the example of  FIG.  2   , if low side heat exchanger  108 A is cooling a space to a colder temperature than low side heat exchanger  108 B, then valve  210 A may be opened and valve  210 B may be closed. As a result, vapor portion  220 A is directed through valve  210 A to ejector  204 B (while liquid portion  218 A is directed through valve  208 A to accumulator  212 ). Ejector  204 B then directs vapor portion  220 A to flash tank  104 . Additionally, because valve  210 B is closed, vapor portion  220 B is directed from separator  206 B to accumulator  212  (along with liquid portion  218 B). If an operator of system  200  subsequently changes the temperature settings of low side heat exchanger  108 A or  108 B such that low side heat exchanger  108 B is cooling a space to a colder temperature than low side heat exchanger  108 A, then valve  210 B may be opened and valve  210 A may be closed. As a result, vapor portion  220 B from separator  206 B is directed through valve  210 B to ejector  204 B (while liquid portion  218 B is directed through valve  208 B to accumulator  212 ). Ejector  204 B then directs vapor portion  220 B to flash tank  104 . Additionally, vapor portion  220 A from separator  206 A is directed to accumulator  212  through valve  208 A (along with liquid portion  218 A). In embodiments that include more than two low side heat exchangers  108 , system  200  may direct the vapor portion  220  of the low side heat exchanger  108  operating at the lowest temperature to ejector  204 B. By closing and opening various valves  210 , system  200  allows for low side heat exchangers  108  to be adjusted on the fly while maintaining efficiency gains. For example, temperature controls may be adjusted to change the amount of cooling provided by each low side heat exchanger  108 . System  200  may open and close certain valves  210  to maintain efficiency gains in response to these adjustments. In particular embodiments, by directing vapor portion  220  to ejector  204 B, an efficiency gain of 18% or more may be achieved. 
     Ejector  204 B receives refrigerant from high side heat exchanger  102  and/or separators  206  and directs that refrigerant to flash tank  104 . Certain embodiments include an additional ejector  204 A that receives refrigerant from high side heat exchanger  102  and accumulator  212  and directs that refrigerant to flash tank  104 . In some embodiments, when ejector  204 A is active and directing refrigerant to flash tank  104 , ejector  204 B is inactive. As a result, when ejector  204 A is needed (e.g., to lower the level of liquid portion  215  in accumulator  212 ), ejector  204 B shuts off while ejector  204 A is activated. When ejector  204 A is no longer needed, ejector  204 A is shut off and ejector  204 B is activated. Generally, ejector  204  ejects and/or directs refrigerant to flash tank  104 . In some systems, the pressure of the ejected refrigerant is controlled and/or adjusted by the pressure of the refrigerant entering ejector  204  and the shape of ejector  204 . 
     The third process implemented by system  200  to improve the efficiency of using carbon dioxide refrigerant in high ambient temperatures is to subcool the refrigerant from accumulator  212  using heat exchanger  202 . As seen in  FIG.  2   , heat exchanger  202  receives refrigerant from high side heat exchanger  102  and accumulator  212 . When activated, heat exchanger  202  transfers heat from the refrigerant from accumulator  212  to the refrigerant from high side heat exchanger  102 . Heat exchanger  202  then discharges the refrigerant from high side heat exchanger  102  to one or more ejectors  204  and flash tank  104 . Heat exchanger  202  also directs the refrigerant from accumulator  212  to compressor  110 . As a result of this heat transfer, the refrigerant entering compressor  110  is subcooled, which in certain embodiments, results in an efficiency gain of more than 7%. 
     In summary, system  200  implements three different processes to improve the efficiency of using carbon dioxide refrigerant in high ambient temperatures. First, system  200  may operate one or more low side heat exchangers  108  in a flooded configuration. Second, system  200  may direct vapor portion  220  of certain low side heat exchangers  108  to an ejector  204 B. Third, system  200  may use a heat exchanger  202  to subcool refrigerant entering compressor  110 . Each of these processes may be activated individually or in combination to achieve varying efficiency gains. In certain instances, none of these processes may be activated in system  200 . In certain embodiments, when all three processes are activated, an efficiency gain of 37% or more is achieved. This disclosure contemplates that none, one, two, or three of these processes may be active at one time. 
       FIG.  3    is a flowchart illustrating a method  300  of operating an example cooling system  200 . Generally, various components of system  200  perform the steps of method  300 . In particular embodiments, by performing method  300 , the efficiency of system  200  is improved. 
     A high side heat exchanger  102  begins by removing heat from a refrigerant in step  302 . In step  304 , an ejector  204 B receives refrigerant from the high side heat exchanger  102 . Flash tank  104  stores refrigerant in step  306 . In step  308 , the ejector  204 B directs refrigerant from the high side heat exchanger  102  to the flash tank  104 . Low side heat exchanger  108 A uses refrigerant from the flash tank  104  to cool a first space in step  310 . In step  312 , separator  206 A receives refrigerant from low side heat exchanger  108 A. Low side heat exchanger  108 B uses refrigerant from the flash tank  104  to cool a second space in step  314 . In step  316 , separator  206 B receives refrigerant from low side heat exchanger  108 B. As described previously, the refrigerant in separator  206 A and  206 B includes a liquid portion  218  and a vapor portion  220 . In step  318 , an accumulator  212  receives a liquid portion  218 A from separator  206 A and a liquid portion  218 B from separator  220 B. 
     In step  320 , system  200  determines whether the first space cooled by low side heat exchanger  108 A is cooler than the second space cooled by low side heat exchanger  108 B. In other words, system  200  determines which low side heat exchanger  108  is operating at the cooler temperature. If low side heat exchanger  108 A is operating with a cooler temperature, then in step  322 , a valve  210 A is opened to direct a vapor portion  220 A to ejector  204 B. Then, in step  324 , a valve  210 B is closed to direct vapor portion  220 B to accumulator  212 . If low side heat exchanger  108 B is operating at a cooler temperature than low side heat exchanger  108 A, then in step  326 , valve  210 B is opened to direct vapor portion  220 B to ejector  204 B. In step  328 , valve  210 A is closed to direct vapor portion  220 A to accumulator  212 . In particular embodiments, system  200  may switch between these two different modes of operation depending on the operating temperature of low side heat exchangers  108 A and  108 B. When the operating temperature of a low side heat exchanger  108  becomes lower than the other low side heat exchanger  108 , then system  200  may open and/or close certain valves  210  to direct vapor portions  220  to ejector  204 B. In step  330 , one or more compressors  110 , compress a vapor portion  216  from accumulator  212 . 
     Modifications, additions, or omissions may be made to method  300  depicted in  FIG.  3   . Method  300  may include more, fewer, or other steps. For example, steps may be performed in parallel or in any suitable order. While discussed as system  200  (or components thereof) performing the steps, any suitable component of system  200  may perform one or more steps of the method. 
     Modifications, additions, or omissions may be made to the systems and apparatuses described herein without departing from the scope of the disclosure. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. Additionally, operations of the systems and apparatuses may be performed using any suitable logic comprising software, hardware, and/or other logic. As used in this document, “each” refers to each member of a set or each member of a subset of a set. 
     This disclosure may refer to a refrigerant being from a particular component of a system (e.g., the refrigerant from the high side heat exchanger, the refrigerant from the flash tank, etc.). When such terminology is used, this disclosure is not limiting the described refrigerant to being directly from the particular component. This disclosure contemplates refrigerant being from a particular component (e.g., the high side heat exchanger) even though there may be other intervening components between the particular component and the destination of the refrigerant. For example, the flash tank receives a refrigerant from the accumulator even though there is an ejector between the flash tank and the accumulator. 
     Although the present disclosure includes several embodiments, a myriad of changes, variations, alterations, transformations, and modifications may be suggested to one skilled in the art, and it is intended that the present disclosure encompass such changes, variations, alterations, transformations, and modifications as fall within the scope of the appended claims.