Patent Publication Number: US-10767911-B2

Title: Cooling system

Description:
TECHNICAL FIELD 
     This disclosure relates generally to a cooling system, such as a refrigeration system. 
     BACKGROUND 
     Cooling systems are used to cool spaces, such as residential dwellings, commercial buildings, and/or refrigeration units. These systems cycle a refrigerant (also referred to as charge) that is used to cool the spaces. 
     SUMMARY OF THE DISCLOSURE 
     This disclosure contemplates an unconventional cooling system that efficiently handles refrigerant from a low temperature load when a medium temperature load is not in use. The system directs refrigerant from the discharge of a low temperature compressor to a flash tank instead of to a suction of a medium temperature compressor. The refrigerant then mixes with the refrigerant in the flash tank. The flash tank discharges liquid refrigerant back to the low temperature load and gaseous refrigerant (also referred to as a flash gas) to a parallel compressor. On its way to the parallel compressor, a heat exchanger may transfer heat from a refrigerant from a high side heat exchanger to the flash gas. Certain embodiments will be described below. 
     According to an embodiment, an apparatus includes a flash tank, a load, a first compressor, a heat exchanger, and a second compressor. The flash tank stores a refrigerant and releases the refrigerant as a flash gas. The load uses the refrigerant to remove heat from a space proximate the load. The first compressor compresses the refrigerant from the load and directs the refrigerant to the flash tank. The heat exchanger transfers heat from the refrigerant from a high side heat exchanger to the refrigerant released from the flash tank as the flash gas. The second compressor compresses the refrigerant released from the flash tank as the flash gas. 
     According to another embodiment, a method includes storing a refrigerant in a flash tank and releasing the refrigerant from the flash tank as a flash gas. The method also includes using the refrigerant to remove heat from a space proximate a load and compressing, using a first compressor, the refrigerant from the load. The method further includes directing the refrigerant from the first compressor to the flash tank and transferring, using a heat exchanger, heat from the refrigerant from a high side heat exchanger to the refrigerant released from the flash tank as the flash gas. The method also includes compressing, using a second compressor, the refrigerant released from the flash tank as the flash gas. 
     According to yet another embodiment, a system includes a high side heat exchanger, a flash tank, a load, a first compressor, a heat exchanger, and a second compressor. The high side heat exchanger removes heat from a refrigerant. The flash tank stores the refrigerant and releases the refrigerant as a flash gas. The load uses the refrigerant to remove heat from a space proximate the load. The first compressor compresses the refrigerant from the load and directs the refrigerant to the flash tank. The heat exchanger transfers heat from the refrigerant from the high side heat exchanger to the refrigerant released from the flash tank as the flash gas. The second compressor compresses the refrigerant released from the flash tank as the flash gas. 
     Certain embodiments provide one or more technical advantages. For example, an embodiment operates a low temperature load and no medium temperature load without needing a desuperheater, thus reducing cost and space requirements. Additionally, the embodiment improves efficiency by operating a low temperature compressor and a parallel compressor. As another example, an embodiment may further improve efficiency by including an optional desuperheater at a low temperature compressor discharge. 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. 1A-1B  illustrate portions of an example cooling system; 
         FIG. 2  illustrates portions of an example cooling system; and 
         FIG. 3  is a flowchart illustrating a method for operating the cooling system of  FIG. 2 . 
     
    
    
     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 are used to cool spaces, such as residential dwellings, commercial buildings, and/or refrigeration units. These systems cycle a refrigerant (also referred to as charge) that is used to cool the spaces. In existing refrigeration systems, such as ones in grocery stores, refrigerant is cycled through various cooling cases to keep food cold. Generally, these refrigeration systems use two types of loads known as medium temperature loads and low temperature loads. The medium temperature loads may be produce shelves that keep a space cooled above freezing temperatures (e.g., above 32 degrees Fahrenheit), and the low temperature loads may be freezer cases that keep a space cooled below freezing temperatures (e.g., at or below 32 degrees Fahrenheit). 
     Refrigerant from these two types of loads are directed to their respective compressors (e.g., a low temperature compressor and a medium temperature compressor). The discharge from the low temperature compressor is then directed to the medium temperature compressor. The refrigerant from the medium temperature load mixes with and cools the refrigerant from the low temperature compressor before the mixture enters the medium temperature compressor. 
     In some installations however (such as those shown in  FIGS. 1A and 1B ), the medium temperature loads are sometimes shut off and/or removed from the system. When that happens, the medium temperature compressor may not operate appropriately or efficiently due to the absence of the refrigerant from the medium temperature load, which causes the refrigerant entering the medium temperature compressor being too hot or too high pressure. To protect against the medium temperature compressor malfunctioning, additional piping and equipment (e.g., a desuperheater) is added to the system to cool the refrigerant entering the medium temperature compressor. This additional piping and equipment increase the cost of the system as well as the space requirements for installing the system. 
     This disclosure contemplates an unconventional cooling system that efficiently handles refrigerant from a low temperature load when a medium temperature load is not in use. The system directs refrigerant from the discharge of a low temperature compressor to a flash tank instead of to a suction of a medium temperature compressor. The refrigerant then mixes with the refrigerant in the flash tank. The flash tank discharges liquid refrigerant back to the low temperature load and gaseous refrigerant (also referred to as a flash gas) to a parallel compressor. On its way to the parallel compressor, a heat exchanger may transfer heat from a refrigerant from a high side heat exchanger to the flash gas. The cooling system will be described in more detail using  FIGS. 2 and 3 . 
       FIG. 1A  illustrates portions of an example cooling system  100 , such as one found in a grocery store. As seen in  FIG. 1A , system  100  includes a high side heat exchanger  105 , a flash tank  110 , a medium temperature load  115 , a low temperature load  120 , a low temperature compressor  125 , and a medium temperature compressor  130 . 
     High side heat exchanger  105  may remove heat from a refrigerant. When heat is removed from the refrigerant, the refrigerant is cooled. This disclosure contemplates high side heat exchanger  105  being operated as a condenser, a fluid cooler, and/or a gas cooler. When operating as a condenser, high side heat exchanger  105  cools the refrigerant such that the state of the refrigerant changes from a gas to a liquid. When operating as a fluid cooler, high side heat exchanger  105  cools liquid refrigerant and the refrigerant remains a liquid. When operating as a gas cooler, high side heat exchanger  105  cools gaseous refrigerant and the refrigerant remains a gas. In certain configurations, high side heat exchanger  105  is positioned such that heat removed from the refrigerant may be discharged into the air. For example, high side heat exchanger  105  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  105  may be positioned external to a building and/or on the side of a building. 
     Flash tank  110  may store refrigerant received from high side heat exchanger  105 . This disclosure contemplates flash tank  110  storing refrigerant in any state such as, for example, a liquid state and/or a gaseous state. Refrigerant leaving flash tank  110  is fed to low temperature load  120  and medium temperature load  115 . In some embodiments, a flash gas and/or a gaseous refrigerant is released from flash tank  110 . By releasing flash gas, the pressure within flash tank  110  may be reduced. 
     System  100  may include a low temperature portion and a medium temperature portion. The low temperature portion may operate 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. As seen in  FIG. 1A , system  100  includes a medium temperature load  115  and a low temperature load  120 . Each of these loads is used to cool a particular space. For example, medium temperature load  115  may be a produce shelf in a grocery store and low temperature load  120  may be a freezer case. Generally, low temperature load  120  keeps a space cooled to freezing temperatures (e.g., below 32 degrees Fahrenheit) and medium temperature load  115  keeps a space cooled above freezing temperatures (e.g., above 32 degrees Fahrenheit). 
     Refrigerant may flow from flash tank  110  to both the low temperature and medium temperature portions of the refrigeration system. For example, the refrigerant may flow to low temperature load  120  and medium temperature load  115 . When the refrigerant reaches low temperature load  120  or medium temperature load  115 , the refrigerant removes heat from the air around low temperature load  120  or medium temperature load  115 . 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 temperature load  120  and medium temperature load  115 , the refrigerant may change from a liquid state to a gaseous state as it absorbs heat. 
     Refrigerant may flow from low temperature load  120  and medium temperature load  115  to compressors  125  and  130 . This disclosure contemplates system  100  including any number of low temperature compressors  125  and medium temperature compressors  130 . The low temperature compressor  125  and medium temperature compressor  130  may be configured 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  125  may compress refrigerant from low temperature load  120  and send the compressed refrigerant to medium temperature compressor  130 . Medium temperature compressor  130  may compress refrigerant from low temperature compressor  125  and medium temperature load  115 . The refrigerant from low temperature compressor  125  mixes with and is cooled by the refrigerant from medium temperature load  115  before entering medium temperature compressor  130 . Medium temperature compressor  130  may then send the compressed refrigerant to high side heat exchanger  105 . 
     In some installations, medium temperature load  115  is sometimes shut down and/or removed from system  100 . As a result, the refrigerant from low temperature compressor  125  is not cooled by the refrigerant from medium temperature load  115  before it enters medium temperature compressor  130 . Thus, the refrigerant entering medium temperature compressor  130  may be too hot, which may cause medium temperature compressor  130  to operate inefficiently and/or malfunction. In these instances, to protect medium temperature compressor  130 , additional piping and/or equipment is added to system  100  to cool the refrigerant from low temperature compressor  125 . This additional piping and equipment increases both the cost of system  100  and the space occupied by system  100 . 
       FIG. 1B  illustrates system  100  with medium temperature load  115  removed and additional piping and/or equipment installed. As seen in  FIG. 1B , system  100  includes a desuperheater  135 , a flash gas bypass valve  140  controlling a flash gas bypass line, and a liquid injection valve  145  controlling a liquid injection line. Each of these additional components operate to cool the refrigerant from low temperature compressor  125  before it enters medium temperature compressor  130 . Each of these components increase the cost of system  100  and the space occupied by system  100 . 
     Desuperheater  135  operates similarly to a heatsink. Desuperheater  135  absorbs heat from the refrigerant from low temperature compressor  125  and discharges that absorbed heat away from system  100 , for example into the atmosphere. Desuperheater  135  may include metallic components that transfer and/or conduct heat away from the refrigerant from low temperature compressor  125 . Desuperheater  135  may include a fan that circulates air to expel heat absorbed from the refrigerant from low temperature compressor  125 . In this manner, desuperheater  135  cools the refrigerant from low temperature compressor  125 . 
     The flash gas bypass line and the liquid injection line direct cool refrigerant from flash tank  110  to mix with the refrigerant from low temperature compressor  125  before it enters medium temperature compressor  130 . The flash gas bypass line directs flash gas (e.g., refrigerant in a gaseous state) from flash tank  110  to mix with the refrigerant from low temperature compressor  125 . The liquid injection line directs liquid refrigerant from flash tank  110  to mix with the refrigerant from low temperature compressor  125 . Both lines operate to cool the refrigerant from low temperature compressor  125 . 
     Flash gas bypass valve  140  and liquid injection valve  145  control the flow of refrigerant through the flash gas bypass line and the liquid injection line respectively. System  100  may include a controller that opens and closes flash gas bypass valve  140  based on a pressure of the refrigerant in flash tank  110  and opens and closes liquid injection valve  145  based on a temperature of the refrigerant at the suction of medium temperature compressor  130 . For example, if the pressure of the refrigerant in flash tank  110  is too high, the controller may open flash gas bypass valve  140  to direct flash gas to mix with the refrigerant from low temperature compressor  125 . If the refrigerant at the suction of medium temperature compressor  130  is too hot, then the controller may open liquid injection valve  145  to direct liquid refrigerant from flash tank  110  to mix with the refrigerant from low temperature compressor  125 . 
       FIG. 2  illustrates portions of an example cooling system  200 . As shown in  FIG. 2 , system  200  includes a high side heat exchanger  105 , a flash tank  110 , a low temperature load  120 , a low temperature compressor  125 , a heat exchanger  205 , and a parallel compressor  210 . In particular embodiments, system  200  reduces costs by eliminating the additional piping and/or equipment present in cooling system  100 . In some embodiments, system  200  takes up less space than system  100  by eliminating certain piping and equipment. 
     High side heat exchanger  105 , flash tank  110 , low temperature load  120 , and low temperature compressor  125  operate similarly to these components in system  100 . For example, high side heat exchange  105  removes heat from a refrigerant. Flash tank  110  stores the refrigerant as both a liquid and a flash gas. Flash tank  110  releases liquid refrigerant to low temperature load  120  and releases flash gas to heat exchanger  205 . Low temperature load  120  uses the refrigerant to remove heat from a space  202  proximate low temperature load  120 . Low temperature compressor  125  compresses the refrigerant from low temperature load  120 . 
     System  200  eliminates certain piping and equipment from system  100  by reconfiguring the discharge of low temperature compressor  125  and flash tank  110 . As illustrated in  FIG. 2 , low temperature compressor  125  directs compressed refrigerant to flash tank  110 . The refrigerant then mixes and is cooled by the refrigerant in flash tank  110 . The discharge of flash gas from flash tank  110  is directed through heat exchanger  205  to parallel compressor  210  and then to high side heat exchanger  105 . 
     Heat exchanger  205  transfers heat from the refrigerant from high side heat exchanger  105  to the flash gas discharged by flash tank  110 . Heat exchanger  205  may include any heat conducting surfaces such as plates, fins, and/or tubes. As heat exchanger  205  transfers heat from the refrigerant from high side heat exchanger  105  to the flash gas from flash tank  110 , the refrigerant from high side heat exchanger  105  is cooled and the flash gas is heated. In this manner, the efficiency of system  200  is improved because more liquid refrigerant enters flash tank  110  from heat exchanger  205 . Additionally, the flash gas from flash tank  110  is heated sufficiently so that parallel compressor  210  may efficiently compress the flash gas. 
     Parallel compressor  210  receives the flash gas from heat exchanger  205  and compresses the flash gas. By compressing the flash gas, parallel compressor  210  concentrates the heat within the flash gas. Parallel compressor  210  then directs the compressed flash gas to high side heat exchanger  105 . High side heat exchanger  105  may then remove the concentrated heat from the compressed flash gas. Though this disclosure describes heat exchanger  205 , parallel compressor  210 , and high side heat exchanger  105  operating on a flash gas, it is understood that the flash gas is a term for the refrigerant when it is in a gaseous state. 
     In this manner, system  200  is able to operate efficiently and safely without a medium temperature load, a desuperheater, a flash gas bypass line, and a liquid injection line. 
     In particular embodiments, system  200  includes an oil separator  215  between parallel compressor  210  and high side heat exchanger  105 . The oil separator  215  operates to separate an oil from the refrigerant before the refrigerant enters high side heat exchanger  105 . The oil may be introduced by certain components of parallel compressor  210  and/or low temperature compressor  125 . By separating out the oil, the efficiency of high side heat exchanger  105  is maintained. If the oil separator  215  is not present, then the oil may clog high side heat exchanger  105  and load  120 , which may reduce the heat transfer efficiency of system  200 , high side heat exchanger  105 , and/or load  120 . 
     In some embodiments, a desuperheater  220  may be added between low temperature compressor  125  and flash tank  110 . The desuperheater  220  may cool the refrigerant from low temperature compressor  125  before it enters flash tank  110 . This desuperheater  220  may reduce the energy consumption of system  200  by about 2% to 5%. 
       FIG. 3  is a flow chart illustrating a method  300  for operating cooling system  200  in  FIG. 2 . In particular embodiments, the various components of system  200  perform method  300 . By performing method  300 , system  200  may operate efficiently and safely even though a medium temperature load, a desuperheater, a flash gas bypass line, and a liquid injection line are eliminated. 
     A high side heat exchanger may remove heat from a refrigerant in step  305 . A flash tank stores the refrigerant in step  310 . In step  315 , a load such as a low temperature load uses the refrigerant to remove heat from a space. A compressor such as a low temperature compressor then compresses the refrigerant in step  320 . 
     The compressor can direct the refrigerant to a flash tank in step  325 . In step  330 , the flash tank releases the refrigerant as a flash gas. The flash gas is then directed to a heat exchanger that transfers heat from the refrigerant from a high side heat exchanger to the refrigerant released from the flash tank as the flash gas in step  335 . The heat exchanger then directs the refrigerant to a parallel compressor that compresses the refrigerant released from the flash tank as the flash gas in step  340 . In this manner, the refrigerant from the low temperature compressor mixes and is cooled by the refrigerant in the flash tank. The heated refrigerant in the flash tank can then be discharged to a parallel compressor to be compressed before being directed to the high side heat exchanger. 
     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  100  (or components thereof) performing the steps, any suitable component of system  100  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. 
     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.