Patent Publication Number: US-11656012-B2

Title: Cooling system with vertical alignment

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/782,618 filed Feb. 5, 2020, by Shitong Zha, and entitled “COOLING SYSTEM WITH VERTICAL ALIGNMENT,” which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to a cooling system. 
     BACKGROUND 
     Cooling systems may cycle a refrigerant (e.g., carbon dioxide refrigerant) to cool various spaces. 
     SUMMARY 
     Cooling systems may cycle a refrigerant (e.g., carbon dioxide refrigerant) to cool various spaces. These systems typically include a compressor to compress refrigerant and a high side heat exchanger that removes heat from the compressed refrigerant. When the compressor compresses the refrigerant, oil that coats certain components of the compressor may mix with and be discharged with the refrigerant. 
     When these systems are installed in tall buildings (e.g., high-rises), the high side heat exchanger may be installed on the roof of the building while the compressor is installed on a lower floor of the building. As a result, a significant vertical separation may exist between the compressor and the high side heat exchanger. If refrigerant from the compressor were directed to the high side heat exchanger, the oil that mixed with the refrigerant discharged by the compressor may not be able to overcome the vertical separation and, as a result, the oil may flow backwards to the compressor. To avoid this oil return issue, conventional systems use a separate water cooling system that cycles water that absorbs heat from the refrigerant discharged by the compressor. The water is then pumped to the high side heat exchanger on the roof so that the absorbed heat can be removed. The cooled refrigerant is cycled back to the rest of the cooling system, bypassing the high side heat exchanger. The water cooling system, however, increases the overall energy consumption, size, and cost of the cooling system. 
     This disclosure contemplates an unconventional cooling system that uses P-traps to address the oil return issues that result from a vertical separation between the compressor and the high side heat exchanger. Generally, the vertical piping that carries the refrigerant from the compressor to the high side heat exchanger includes P-traps installed at various heights to capture oil in the refrigerant and to prevent that oil from flowing back to the compressor. As oil collects in the P-traps, the refrigerant begins to push the oil upwards until the oil reaches the high side heat exchanger. Multiple piping of different sizes may be used depending on a discharge pressure of the compressor. When the discharge pressure is higher, a larger piping may be used direct the oil and refrigerant to the high side heat exchanger. Certain embodiments of the cooling system are described below. 
     According to an embodiment, a system includes a high side heat exchanger, a flash tank, a first low side heat exchanger, a second low side heat exchanger, a first compressor, a second compressor, first piping, second piping, a first valve, and a second valve. The high side heat exchanger removes heat from a refrigerant. The flash tank stores the refrigerant. The first low side heat exchanger uses the refrigerant to cool a space proximate the first low side heat exchanger. The second low side heat exchanger uses the refrigerant to cool a space proximate the second low side heat exchanger. The first compressor compresses refrigerant from the first low side heat exchanger. The second compressor compresses refrigerant from the second low side heat exchanger and the first compressor. The high side heat exchanger is positioned vertically above the second compressor. The first piping directs refrigerant from the second compressor to the high side heat exchanger. The first piping includes a first p-trap positioned vertically above the second compressor and vertically below the high side heat exchanger and a second p-trap positioned vertically above the first p-trap and vertically below the high side heat exchanger. The second piping directs refrigerant from the second compressor to the high side heat exchanger. The second piping is larger than the first piping. The second piping includes a third p-trap positioned vertically above the second compressor and vertically below the high side heat exchanger and a fourth p-trap positioned vertically above the first p-trap and vertically below the high side heat exchanger. The first valve controls a flow of refrigerant and oil from the second compressor to the first piping. The second valve controls a flow of refrigerant and oil from the second compressor to the second piping. 
     According to another embodiment, a method includes removing, by a high side heat exchanger, heat from a refrigerant and storing, by a flash tank, the refrigerant. The method also includes using, by a first low side heat exchanger, the refrigerant to cool a space proximate the first low side heat exchanger and using, by a second low side heat exchanger, the refrigerant to cool a space proximate the second low side heat exchanger. The method further includes compressing, by a first compressor, refrigerant from the first low side heat exchanger and compressing, by a second compressor, refrigerant from the second low side heat exchanger and the first compressor. The high side heat exchanger is positioned vertically above the second compressor. The method also includes directing, by first piping, refrigerant from the second compressor to the high side heat exchanger. The first piping includes a first p-trap positioned vertically above the second compressor and vertically below the high side heat exchanger and a second p-trap positioned vertically above the first p-trap and vertically below the high side heat exchanger. The method further includes directing, by second piping, refrigerant from the second compressor to the high side heat exchanger. The second piping is larger than the first piping. The second piping includes a third p-trap positioned vertically above the second compressor and vertically below the high side heat exchanger and a fourth p-trap positioned vertically above the first p-trap and vertically below the high side heat exchanger. The method also includes controlling, by a first valve, a flow of refrigerant and oil from the second compressor to the first piping and controlling, by a second valve, a flow of refrigerant and oil from the second compressor to the second piping. 
     According to yet another embodiment, a system includes a high side heat exchanger, a flash tank, a first low side heat exchanger, a second low side heat exchanger, a first compressor, a second compressor, first piping, second piping, and a valve. The high side heat exchanger removes heat from a refrigerant. The flash tank stores the refrigerant. The first low side heat exchanger uses the refrigerant to cool a space proximate the first low side heat exchanger. The second low side heat exchanger uses the refrigerant to cool a space proximate the second low side heat exchanger. The first compressor compresses refrigerant from the first low side heat exchanger. The second compressor compresses refrigerant from the second low side heat exchanger and the first compressor. The high side heat exchanger is positioned vertically above the second compressor. The first piping directs refrigerant from the second compressor to the high side heat exchanger. The first piping includes a first p-trap positioned vertically above the second compressor and vertically below the high side heat exchanger and a second p-trap positioned vertically above the first p-trap and vertically below the high side heat exchanger. The second piping directs refrigerant from the second compressor to the high side heat exchanger. The second piping is larger than the first piping. The second piping includes a third p-trap positioned vertically above the second compressor and vertically below the high side heat exchanger and a fourth p-trap positioned vertically above the first p-trap and vertically below the high side heat exchanger. The valve controls a flow of refrigerant and oil from the second compressor to the second piping. 
     Certain embodiments provide one or more technical advantages. For example, an embodiment uses P-traps to prevent oil from flowing back to a compressor when there is a vertical separation between the compressor and a high side heat exchanger. As another example, an embodiment reduces energy consumption, size, and cost relative to a cooling system that uses a separate water cooling system to overcome a vertical separation between a compressor and a high side heat exchanger. 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: 
         FIGS.  1 A- 1 B  illustrate an example cooling system; 
         FIGS.  2 A- 2 B  illustrate example cooling systems; 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 A through  3    of the drawings, like numerals being used for like and corresponding parts of the various drawings. 
     Cooling systems may cycle a refrigerant (e.g., carbon dioxide refrigerant) to cool various spaces. These systems typically include a compressor to compress refrigerant and a high side heat exchanger that removes heat from the compressed refrigerant. When the compressor compresses the refrigerant, oil that coats certain components of the compressor may mix with and be discharged with the refrigerant. 
     When these systems are installed in tall buildings (e.g., high-rises), the high side heat exchanger may be installed on the roof of the building while the compressor is installed on a lower floor of the building. As a result, a significant vertical separation may exist between the compressor and the high side heat exchanger. If refrigerant from the compressor were directed to the high side heat exchanger, the oil that mixed with the refrigerant discharged by the compressor may not be able to overcome the vertical separation and, as a result, the oil may flow backwards to the compressor. To avoid this oil return issue, conventional systems use a separate water cooling system that cycles water that absorbs heat from the refrigerant discharged by the compressor. The water is then pumped to the high side heat exchanger on the roof so that the absorbed heat can be removed. The cooled refrigerant is cycled back to the rest of the cooling system, bypassing the high side heat exchanger. The water cooling system, however, increases the overall energy consumption, size, and cost of the cooling system. 
     This disclosure contemplates an unconventional cooling system that uses P-traps to address the oil return issues that result from a vertical separation between the compressor and the high side heat exchanger. Generally, the vertical piping that carries the refrigerant from the compressor to the high side heat exchanger includes P-traps installed at various heights to capture oil in the refrigerant and to prevent that oil from flowing back to the compressor. As oil collects in the P-traps, the refrigerant begins to push the oil upwards until the oil reaches the high side heat exchanger. Multiple piping of different sizes may be used depending on a discharge pressure of the compressor. When the discharge pressure is higher, a larger piping may be used direct the oil and refrigerant to the high side heat exchanger. In this manner, the P-traps prevent oil from flowing back to the compressor when there is a vertical separation between the compressor and the high side heat exchanger. Additionally, the cooling system reduces energy consumption, size, and cost relative to a cooling system that uses a separate water cooling system to overcome the vertical separation between the compressor and the high side heat exchanger. The cooling system will be described using  FIGS.  1 A through  3   .  FIGS.  1 A- 1 B  will describe an existing cooling system.  FIGS.  2 A- 2 B and  3    describe the cooling system that uses P-traps. 
       FIG.  1 A  illustrates an example cooling system  100 . As shown in  FIG.  1 A , system  100  includes a high side heat exchanger  102 , a flash tank  104 , a low temperature low side heat exchanger  106 , a medium temperature low side heat exchanger  108 , a low temperature compressor  110 , a medium temperature compressor  112 , a valve  114 , and an oil separator  116 . Generally, system  100  cycles a refrigerant to cool spaces proximate the low side heat exchangers  106  and  108 . Cooling system  100  or any cooling system described herein may include any number of low side heat exchangers, whether low temperature or medium temperature. 
     High side heat exchanger  102  removes heat from a refrigerant. When heat is removed from the refrigerant, the refrigerant is cooled. High side heat exchanger  102  may be 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. 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 temperature low side heat exchanger  106  and medium temperature low side heat exchanger  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. 
     System  100  includes 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 temperature low side heat exchanger  106  and medium temperature low side heat exchanger  108 . 
     When the refrigerant reaches low temperature low side heat exchanger  106  or medium temperature low side heat exchanger  108 , the refrigerant removes heat from the air around low temperature low side heat exchanger  106  or medium temperature low side heat exchanger  108 . For example, the refrigerant cools metallic components (e.g., metallic coils, plates, and/or tubes) of low temperature low side heat exchanger  106  and medium temperature low side heat exchanger  108  as the refrigerant passes through low temperature low side heat exchanger  106  and medium temperature low side heat exchanger  108 . These metallic components may then cool the air around them. 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 temperature low side heat exchanger  106  and medium temperature low side heat exchanger  108 , the refrigerant may change from a liquid state to a gaseous state as it absorbs heat. Any number of low temperature low side heat exchangers  106  and medium temperature low side heat exchangers  108  may be included in any of the disclosed cooling systems. 
     Refrigerant flows from low temperature low side heat exchanger  106  and medium temperature low side heat exchanger  108  to compressors  110  and  112 . The disclosed cooling systems may include any number of low temperature compressors  110  and medium temperature compressors  112 . Both the low temperature compressor  110  and medium temperature compressor  112  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. Low temperature compressor  110  compresses refrigerant from low temperature low side heat exchanger  106  and sends the compressed refrigerant to medium temperature compressor  112 . Medium temperature compressor  112  compresses a mixture of the refrigerant from low temperature compressor  110  and medium temperature low side heat exchanger  108 . When the compressors  110  and  112  compress the refrigerant, oil that coats certain components of compressors  110  and  112  may mix with and be discharged with the refrigerant. 
     Valve  114  controls a flow of flash gas from flash tank  104 . When valve  114  is closed, flash tank  104  may not discharge flash gas through valve  114 . When valve  114  is opened, flash tank  104  may discharge flash gas through valve  114 . In this manner, valve  114  may also control an internal pressure of flash tank  104 . Valve  114  directs flash gas to medium temperature compressor  112 . Medium temperature compressor  112  compresses the flash gas along with refrigerant from low temperature compressor  110  and medium temperature low side heat exchanger  108 . 
       FIG.  1 B  illustrates example cooling system  100  installed in a tall building  120 . As seen in  FIG.  1 B , high side heat exchanger  102  is positioned on the roof of the building  120 . Rack  122 , which includes the other components of system  100  such as compressors  110  and  112 , is positioned on a lower level of building  120 . Thus, a significant vertical separation exists between high side heat exchanger  102  and compressors  110  and  112 . If refrigerant from compressors  110  and/or  112  were directed to high side heat exchanger  102 , the oil that mixed with the refrigerant discharged by the compressors  110  and/or  112  may not be able to overcome the vertical separation and, as a result, the oil may flow backwards to the compressor  112 . To avoid this oil return issue, a separate water cooling system  124  is installed so that the refrigerant need not be directed to high side heat exchanger  102 . Water cooling system  124  cycles water that absorbs heat from the refrigerant discharged by compressor  112 . The water is then pumped to high side heat exchanger  102  on the roof so that the absorbed heat can be removed. The water is then cycled back down from high side heat exchanger  102  to absorb more heat from the refrigerant. The cooled refrigerant is cycled back to the rest of the cooling system, bypassing the high side heat exchanger  102 . Water cooling system  124 , however, increases the overall energy consumption, size, and cost of the cooling system. 
     This disclosure contemplates an unconventional cooling system that uses P-traps to address the oil return issues that result from a vertical separation between the compressor  112  and the high side heat exchanger  102 . Generally, the vertical piping that carries the refrigerant from the compressor  112  to the high side heat exchanger  102  includes P-traps installed at various heights to capture oil in the refrigerant and to prevent that oil from flowing back to the compressor  112 . As oil collects in the P-traps, the refrigerant begins to push the oil upwards until the oil reaches the high side heat exchanger  102 . Multiple piping of different sizes may be used depending on a discharge pressure of the compressor  112 . When the discharge pressure is higher, a larger piping may be used direct the oil and refrigerant to the high side heat exchanger  102 . In this manner, the P-traps prevent oil from flowing back to the compressor  112  when there is a vertical separation between the compressor  112  and the high side heat exchanger  102 . Additionally, the cooling system reduces energy consumption, size, and cost relative to a cooling system that uses a separate water cooling system  124  to overcome the vertical separation between the compressor  112  and the high side heat exchanger  102 . Embodiments of the cooling system are described below using  FIGS.  2 A- 2 B and  3   . These figures illustrate embodiments that include a certain number of low side heat exchangers and compressors for clarity and readability. These embodiments may include any suitable number of low side heat exchangers and compressors. 
       FIGS.  2 A- 2 B  illustrate example cooling systems  200 . Generally, cooling system  200  includes P-traps installed in the vertical piping used to direct refrigerant from compressor  112  to high side heat exchanger  102 . The P-traps collect oil and prevent that oil from flowing back to compressor  112 . 
       FIG.  2 A  illustrates an example cooling system  200 A. As seen in  FIG.  2 A , system  200 A includes a high side heat exchanger  102 , a flash tank  104 , a low temperature low side heat exchanger  106 , a medium temperature low side heat exchanger  108 , a low temperature compressor  110 , a medium temperature compressor  112 , valve  114 , piping  202 A and  202 B, valves  206 A and  206 B, and sensor  208 . There may be a significant vertical separation between high side heat exchanger  102  and medium temperature compressor  112 . For example, high side heat exchanger  102  may be installed on the roof of a building such that high side heat exchanger  102  is over 50 feet higher than medium temperature compressor  112 . To overcome the issues associated with directing refrigerant up this vertical separation (e.g., oil flowing back to compressor  112 ), system  200 A uses piping  202  that includes P-traps to collect oil and to prevent that oil from flowing back to medium temperature compressor  112 . As oil collects in the P-traps, the refrigerant may begin pushing the oil up piping  202  until the oil reaches high side heat exchanger  102 . In this manner, the oil is prevented from flowing downwards back to compressor  112 . As a result, system  200 A does not need to use a separate water cooling system, which reduces energy consumption, size, and cost in certain embodiments. 
     Several components of system  200 A operate similarly as they did in system  100 . For example, high side heat exchanger  102  removes heat from a refrigerant. Flash tank  104  stores the refrigerant. Low temperature low side heat exchanger  106  and medium temperature low side heat exchanger  108  use refrigerant to cool spaces proximate low temperature low side heat exchanger  106  and medium temperature low side heat exchanger  108 . Low temperature compressor  110  compresses refrigerant from low temperature low side heat exchanger  106 . Medium temperature compressor  112  compresses refrigerant from low temperature compressor  110 , medium temperature low side heat exchanger  108 , and flash tank  104 . Valve  114  controls the flow of refrigerant, as a flash gas, from flash tank  104  to medium temperature compressor  112 . 
     Piping  202 A and  202 B direct refrigerant from medium temperature compressor  112  to high side heat exchanger  102 . The structure of piping  202 A and  202 B allows piping  202 A and  202 B to carry refrigerant up the vertical separation to high side heat exchanger  102  without allowing oil to flow back to medium temperature compressor  112 . Although system  200 A is illustrated with only two piping  202 A and  202 B, system  200 A (and any system described herein) may include any suitable number of piping (e.g., three, four, five, etc.). 
     As seen in  FIG.  2 A , piping  202 A and  202 B includes P-traps  204  installed at various heights on piping  202 A and  202 B. P-trap  204 A is installed on piping  202 A at a lower height than P-traps  204 B and  204 C. P-trap  204 B is installed on piping  202 A at a lower height than P-traps  204 C. P-trap  204 D is installed on piping  202 B at a lower height than P-traps  204 E and  204 F. P-trap  204 E is installed on piping  202 B at a lower height than P-trap  204 F. Each P-trap  204  may be positioned ten to twenty feet vertically above or below the next or preceding P-trap  204 . In other words, there may be a P-trap  204  positioned every ten to twenty feet of piping  202 . Each piping  202  described herein may include any suitable number of P-traps  204 . The greater the vertical separation between high side heat exchanger  102  and compressor  112 , the more P-traps  204  are positioned on piping  202 . 
     Refrigerant flowing from medium temperature compressor  112  to high side heat exchanger  102  through one of piping  202 A and  202 B will flow through P-traps  204 A-C or P-traps  204 D-F enroute to high side heat exchanger  102 . As the refrigerant, which is a vapor, flows through piping  202 A or  202 B, oil in the refrigerant may begin to flow back towards medium temperature compressor  112 . P-traps  204 A-F collect the oil before the oil reaches medium temperature compressor  112 . As a result, P-traps  204 A-F prevent oil from flowing back to medium temperature compressor  112 . As more refrigerant is sent through piping  202 A or  202 B, more oil collects in P-traps  204 A-F. 
     As more oil collects in P-traps  204 A-F, the refrigerant flowing through piping  202 A or  202 B will begin pushing the oil in these P-traps  204 A-F upwards until the oil reaches the next P-trap  204  and/or until the oil reaches high side heat exchanger  102 . For example, as refrigerant flows through piping  202 A, oil will begin collecting in P-trap  204 A. As the level of oil in P-trap  204 A increases, the refrigerant in piping  202 A will begin pushing that oil upwards until that oil reaches and is collected by P-trap  204 B. As the level of oil in P-trap  204 B increases, the refrigerant in piping  202 A will begin pushing that oil upwards. This process continues until that oil reaches and is collected by P-trap  204 C. As the level of oil in P-trap  204 C increases the refrigerant in piping  202 A will begin pushing that oil upwards until that oil reaches high side heat exchanger  102 . In this manner, oil is kept flowing in system  200 A in the same direction as the refrigerant. 
     Valves  206 A and  206 B control a flow of refrigerant and/or oil through piping  202 A and  202 B, respectively. When valve  206 A is open, valve  206 A allows refrigerant and/or oil to flow through piping  202 A. When valve  206 A is closed, valve  206 A prevents refrigerant and/or oil from flowing through piping  202 A. Similarly, when valve  206 B is open, valve  206 B allows refrigerant and/or oil to flow through piping  202 B. When valve  206 B is closed, valve  206 B prevents refrigerant and/or oil from flowing through piping  202 B. 
     In certain embodiments, piping  202 A and  202 B may be different sizes. For example, piping  202 A may be ⅞ of an inch in diameter and piping  202 B may be 1 and ⅛ inches in diameter. The smaller size of piping  202 A may result in refrigerant and/or oil flowing through piping  202 A to maintain a higher velocity and experience a smaller pressure drop than refrigerant and/or oil flowing through piping  202 B. Valves  206 A and  206 B can be controlled to send refrigerant and/or oil from compressor  112  through differently sized piping  202 A and  202 B depending on the discharge pressure and/or capacity of compressor  112 . For example, sensor  208  may be a pressure sensor that detects a discharge pressure and/or capacity of compressor  112 . When the discharge pressure and/or capacity is below a first threshold (e.g., 40%), valve  206 A may be opened and valve  206 B may be closed such that refrigerant and/or oil from compressor  112  is directed through the smaller piping  202 A. In this manner, the smaller piping  202 A is used to maintain sufficient velocity and pressure to push oil up piping  202 A when the discharge pressure and/or capacity of compressor  112  is low. When the discharge pressure and/or capacity of compressor  112  is between the first threshold (e.g., 40%) and a second threshold (e.g., 70%) that is higher than the first threshold, valve  206 A may be closed and valve  206 B may be open such that refrigerant and/or oil from compressor  112  is directed through larger piping  202 B. In this manner, the larger piping  202 B is used when the discharge pressure and/or capacity of compressor  112  are high enough such that the refrigerant discharged from compressor  112  can push oil up piping  202 B. When the discharge pressure and/or capacity of compressor  112  is above the second threshold (e.g., 70%), both valves  206 A and  206 B may be open such that refrigerant and/or oil from compressor  112  is directed through both piping  202 A and  202 B. In this manner, both piping  202 A and  202 B are used when the discharge pressure and/or capacity of compressor  112  necessitates additional piping  202  to handle the refrigerant discharge of compressor  112 . 
       FIG.  2 B  illustrates an example cooling system  200 B. Generally, in system  200 B, piping  202 A and  202 B are the same size and valve  206 A is removed such that refrigerant and/or oil from compressor  112  is always directed through at least piping  202 A. 
     Several components of system  200 B operate similarly as they did in system  200 A. High side heat exchanger  102  removes heat from a refrigerant. Flash tank  104  stores the refrigerant. Low temperature low side heat exchangers  106  and medium temperature low side heat exchanger  108  use refrigerant to cool spaces proximate low temperature low side heat exchanger  106  and medium temperature low side heat exchanger  108 . Low temperature compressor  110  compresses refrigerant from low temperature low side heat exchanger  106 . Medium temperature compressor  112  compresses refrigerant from low temperature compressor  110 , medium temperature low side heat exchanger  108 , and flash tank  104 . Valve  114  controls the flow of refrigerant, as a flash gas, from flash tank  104  to medium temperature compressor  112 . Piping  202 A and  202 B direct refrigerant from medium temperature compressor  112  to high side heat exchanger  102 . P-traps  204 A-F collect oil and prevent that oil from flowing back to medium temperature compressor  112 . Valve  206 B controls a flow of oil and/or refrigerant through piping  202 B. Sensor  208  is a pressure sensor that detects a discharge pressure of medium temperature compressor  112 . 
     As discussed above, in system  200 B, piping  202 A and  202 B are the same size. Additionally, valve  206 A is removed such that refrigerant and/or oil from compressor  112  is always directed at least through piping  202 A. Similar to system  200 A, valve  206 B may open or closed depending on a discharge pressure and/or capacity of compressor  112  detected by sensor  208 . For example, when the discharge pressure and/or capacity falls below a threshold (e.g., 60%), valve  206 B is closed such that refrigerant and/or oil from compressor  112  is directed through piping  202 A but not piping  202 B. In this manner, only one piping  202 A is used when the discharge pressure and/or capacity of compressor  112  is lower. When the discharge pressure and/or capacity exceeds the threshold (e.g., 60%), valve  206 B is opened such that refrigerant and/or oil from compressor  112  is directed through both piping  202 A and piping  202 B. In this manner, the amount of available piping  202  effectively doubles when the discharge pressure and/or capacity of compressor  112  is higher. 
       FIG.  3    is a flow chart illustrating a method  300  of operating an example cooling system  200 . Generally, various components of systems  200 A and  200 B perform the steps of method  300 . In particular embodiments, performing method  300  reduces the energy consumption, size, and cost of cooling systems  200 A and  200 B relative to cooling systems that use a water cooling system. 
     In step  302 , high side heat exchanger  102  removes heat from a refrigerant. Flash tank  104  stores the refrigerant in step  304 . In step  306 , low temperature low side heat exchanger  106  uses the refrigerant to cool a space. In step  308 , medium temperature low side heat exchanger  108  uses the refrigerant to cool a space. Low temperature compressor  110  compresses the refrigerant from low temperature low side heat exchanger  106  in step  310 . In step  312 , medium temperature compressor  112  compresses the refrigerant from low temperature compressor  110 , medium temperature low side heat exchanger  108 , and flash tank  104 . In step  314 , sensor  208  detects a discharge pressure of medium temperature compressor  112 . 
     In step  316 , it is determined whether the detected discharge pressure exceeds a first threshold. If the discharge pressure does not exceed the first threshold, then a first valve  206 A opens in step  318 , a second valve  206 B closes in step  320 , and piping  202 A directs refrigerant to high side heat exchanger  102  in step  322 . If the discharge pressure does exceed the first threshold, then it is determined in step  324  whether the discharge pressure exceeds a second threshold that is higher than the first threshold. If the discharge pressure does not exceed the second threshold, then the second valve  206 B opens in step  326 , the first valve  206 A closes in step  328 , and piping  202 B directs refrigerant to high side heat exchanger  102  in step  330 . If the discharge pressure exceeds the second threshold, then the second valve  206 B is opened in step  332 , the first valve  206 A is opened in step  334 , and piping  202 A and  202 B direct refrigerant to the high side heat exchanger  102  in step  336 . 
     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 systems  200 A and  200 B (or components thereof) performing the steps, any suitable component of systems  200 A and  200 B 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 medium temperature compressor, the refrigerant from the low temperature compressor, 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 low temperature low side heat exchanger) even though there may be other intervening components between the particular component and the destination of the refrigerant. For example, the medium temperature compressor receives a refrigerant from the low temperature low side heat exchanger even though there is a low temperature compressor between the low temperature low side heat exchanger and the medium temperature compressor. 
     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.