Patent Publication Number: US-2023152016-A1

Title: Cooling system and method of operating a cooling system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/884,725, which was filed on Aug. 9, 2019 and is incorporated herein by reference. 
    
    
     BACKGROUND 
     The disclosure relates to a compressor and method of protecting a compressor during operation. More particularly, this disclosure relates to a compressor in a cooling system, such as a cooling unit in a building. 
     A typical cooling system includes an evaporator, a compressor, a condenser, and an expansion valve. In the evaporator, heat is transferred from air in the environment to be cooled to a refrigerant to cool the air as the refrigerant evaporates (e.g., enters the vapor phase). The vapor refrigerant is then compressed (pressurized) in the compressor. The high-pressure gaseous refrigerant is then condensed in a condenser. As the vapor refrigerant condenses (e.g., enters the liquid phase), it transfers heat to air outside of the environment to be cooled. Finally, the liquid refrigerant is passed through an expansion valve to reduce its pressure. As the pressure is reduced, some of the liquid flashes to vapor creating a saturated fluid consisting of both vapor and liquid refrigerant. The low pressure refrigerant fluid flows back to the evaporator. 
     Occasionally, less than all of the liquid refrigerant may evaporate in the evaporator, leaving liquid refrigerant in the refrigerant stream that subsequently enters the compressor. Liquid can interfere with compressor operation and lifetime. 
     SUMMARY 
     A cooling system according to an exemplary embodiment of this disclosure, among other possible things includes a compressor operable to compress refrigerant, an accumulator upstream from the compressor. The accumulator is operable to collect liquid from the refrigerant. A sensor is located upstream from the accumulator. The sensor is operable to detect information including a temperature and a pressure of the refrigerant. The controller is in communication with the sensor. The controller is operable to determine a rate of accumulation of liquid in the accumulator based on the information from the sensor. 
     In a further example of the foregoing, the controller includes an integrator. The controller is operable to determine an amount of time to reach a maximum liquid capacity of the accumulator via the integrator. 
     In a further example of any of the foregoing, the integrator is an asymmetrical integrator. 
     In a further example of any of the foregoing, the controller is operable to determine a rate of vaporization of the liquid in the accumulator. 
     In a further example of any of the foregoing, the sensor is operable to detect a flowrate of the refrigerant. 
     In a further example of any of the foregoing, the sensor is a first sensor, and the system further includes a second sensor downstream from the compressor and is in communication with the controller. The second sensor is operable to determine a temperature and pressure of the refrigerant. 
     In a further example of any of the foregoing, the controller is operable to detect a superheat condition of the refrigerant based on information from at least one of the first and second sensors. 
     In a further example of any of the foregoing, the controller is operable to detect a failure mode of the cooling system based on information from at least one of the first and second sensors. 
     In a further example of any of the foregoing, the refrigerant flows past the sensor and to the accumulator in a conduit. The conduit is less than 12 inches (30.48 cm) in length. 
     In a further example of any of the foregoing, the compressor is a high-side rotary compressor. 
     A method of operating a cooling system according to an exemplary embodiment of this disclosure, among other possible things includes detecting a temperature and a pressure of refrigerant upstream of an accumulator. The accumulator is operable to collect liquid in the refrigerant and is upstream of a compressor. The method also includes determining a rate of accumulation of liquid in an accumulator based on the detected temperature and pressure. 
     In a further example of the foregoing, the method includes determining an amount of time to reach a maximum liquid capacity of the accumulator based on the rate of accumulation of liquid. 
     In a further example of any of the foregoing, a rate of vaporization of liquid in the accumulator is determined. 
     In a further example of any of the foregoing, an amount of time to reach a maximum liquid capacity of the accumulator based on the rate of accumulation of liquid and the rate of vaporization of liquid is determined. 
     In a further example of any of the foregoing, a failure mode of the cooling system based is detected based on the detected temperature and pressure. 
     In a further example of any of the foregoing, a second temperature and a second pressure are detected of the refrigerant downstream from the compressor. 
     In a further example of any of the foregoing, the method includes determining whether the accumulator is empty based at least in part on the second temperature and the second pressure. 
     In a further example of any of the foregoing, a resolution process is performed if the accumulator is empty. 
     In a further example of any of the foregoing, a control command is implemented to shut down the compressor if the accumulator reaches a maximum liquid capacity. 
     In a further example of any of the foregoing, the the compressor is a high-side rotary compressor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    schematically shows a cooling system. 
         FIG.  2    shows a saturation curve for an example refrigerant. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    shows cooling system  20 . The cooling system  20  includes an evaporator  22 , a compressor  24 , a condenser  26 , and an expansion valve  28 . Refrigerant  30  is configured to flow through conduits  31  that joins the various components of the cooling system  20 . As refrigerant  30  flows through the evaporator  22 , heat is transferred from air in the environment to the refrigerant  30  causing the refrigerant  30  to evaporate (e.g., enters the vapor phase). The vapor refrigerant  30  is then compressed (pressurized) in the compressor  24 . The high-pressure vapor refrigerant  30  is then condensed in the condenser  26 . As the vapor refrigerant  30  flows through the condenser (e.g., enters the liquid phase), a condenser fan operates to blow ambient outdoor air across the condenser causing heat transfer between the refrigerant  30  and the air outside. Finally, the warm liquid refrigerant  30  is passed through an expansion valve  28  to reduce its pressure, and the low pressure refrigerant fluid flows back to the evaporator  28 . 
     The compressor  24  can be any known type of compressor. For instance, the compressor  24  can be a scroll compressor or a rotary compressor. The compressor  24  can be either a high-side compressor or a low-side compressor. In a particular example, the compressor  24  is a high-side rotary compressor. 
     In one example, the cooling unit  20  is part of an air conditioner for a building, such as a residential building. In this example, the environment to be cooled is the interior of the residential building. 
     As the cooling unit  20  operates, occasionally, less than all of the liquid refrigerant  30  evaporates in the evaporator  22 , leaving liquid mixed with vapor in the refrigerant  30  as it enters the compressor  24 . An accumulator  32  is arranged between the evaporator  22  and the compressor  24 . The accumulator  32  separates liquid from the refrigerant  30  and collects it within the accumulator  32  to substantially eliminate liquid in the refrigerant  30  as it enters the compressor  24 . Liquid may impede the operation of the compressor  24  and/or decrease its operational lifetime. 
     In one operating scenario, such as during installation or repair of the cooling system  20 , a service technician may need to add a large amount of refrigerant  30  to the system  20  while it is operating. This is known as a “charging mode.” In one example, the refrigerant is added to the system at a vapor service valve  35 . At the vapor service valve  35 , refrigerant  30  in the conduit  31  is typically mostly or all vapor during normal system  20  operation. The accumulator  32  has a finite capacity for liquid storage. If the accumulator  32  overflows, liquid could enter the compressor  24 . A system and method for operating the cooling system  20  and/or the compressor  24  so as to minimize the amount of liquid entering the compressor  24 , or prevent liquid from entering the compressor  24  to protect the compressor  24  is discussed below. 
     A sensor  34  is arranged upstream from the accumulator  32 . The sensor  34  is configured to measure the temperature and pressure of refrigerant  30  before it enters the accumulator  32 . The sensor  34  can include any known type of pressure and temperature sensor. In one example, the sensor  34  is arranged so that the conduit  31  that separates the accumulator  32  from the sensor  34  is less than 12 inches (30.48 cm) in length. 
     The sensor  34  may also sense other characteristics of the refrigerant  30  flow, such as its flowrate. In this example, the sensor  34  includes any known type of flowrate sensor. 
     A controller  36  is operably connected with the sensor  34 . In one embodiment, the controller  36  may be wired to the sensor  34 . In another embodiment, the controller  36  may communicate with the sensor  34  wirelessly. The controller  36  includes processors or other devices that are programmed so that the controller  36  is operable to analyze data from the sensor  34 . In particular, the controller  36  is operable to determine the amount of liquid in the refrigerant  30  based on the measured temperature and pressure from the sensor  34  and known phase characteristics of the refrigerant  30 . 
     For each refrigerant, there exists a saturation curve, which is a pressure/temperature relationship that corresponds to the phases of the refrigerant.  FIG.  2    shows a saturation curve for an example refrigerant. For any given temperature, there is a corresponding pressure at which the refrigerant exists in a state that may include a mixture of liquid and vapor phases, as represented by the curve in  FIG.  2   . At higher pressures, the refrigerant is entirely liquid. At lower pressures, the refrigerant is entirely vapor. This is also known as a “superheated” condition. Based on the saturation curve for the particular refrigerant  30 , the temperature and pressure information from the sensor  34 , the controller  36  can determine whether liquid may be present in the refrigerant  30  stream, e.g., what phase the refrigerant  30  is in. The controller  36  is also operable to estimate an amount of liquid in the refrigerant  30  stream (if any) based on experimental data that is pre-programmed into the controller. The controller  36  is also operable to estimate a rate of accumulation of liquid in the accumulator  32 , and, relatedly, an estimated amount of liquid in the accumulator  32 , by analyzing the amount of liquid in the refrigerant  30  and the flowrate of the refrigerant  30 , which can also be measured by the sensor  34  as discussed above. 
     The controller  36  is pre-programmed with a maximum liquid capacity of the accumulator  32 . The programmed maximum liquid capacity of the accumulator  32  may be less than the total volume of the accumulator  32  in order to avoid overflow of the accumulator  32 . The controller  36  is operable to compare the amount of liquid in the accumulator  32  with the maximum liquid capacity. For instance, if the controller  36  determines that the amount of liquid in the accumulator  32  is at the maximum liquid capacity of the accumulator  32 , the controller  36  can implement a control command to shut down the compressor  24 . The control command can be sent directly to the compressor  24 , or to a master controller for the cooling system  20 . 
     The controller  36  also includes an integrator  38 . The integrator  38  can be a hardware device programmed to perform an integrating function, or in another example, the controller  36  itself can be programmed to perform an integrating function. Based on the amount of liquid in the refrigerant  30  and the flowrate of the refrigerant  30 , the controller  36  is operable to estimate (via the integrator  38 ) an amount of liquid in the accumulator  32 . 
     The amount of liquid in the accumulator  32  corresponds to an amount of time that the cooling system  20  can run before reaching the maximum capacity of the accumulator  32 , e.g., without overflowing the accumulator  32 . In other words, the controller  36  can determine how long it would take to fill the accumulator  32  to its maximum liquid capacity by comparing the actual fill level of the accumulator  32  at a given time as determined by the accumulator  32  with the maximum capacity of the accumulator  32  to determine a difference, and then dividing the difference by the rate of accumulation (liquid flowrate into the accumulator  32 ). If the cooling system  20  runtime exceeds the amount of time that the cooling system  20  can run without overflowing the accumulator  32 , the controller  36  implements a control command to shut down the compressor  24 . The control command can be sent directly to the compressor  24 , or to a master controller for the cooling system  20 . 
     If the cooling system  20  is in the charging mode, discussed above, liquid refrigerant can be added to the system very rapidly such that the liquid accumulator  32  would be quickly filled to capacity. As discussed above, the controller  36  is operable to send a command to shut down the compressor  24  if the accumulator  32  is at maximum liquid capacity. In this example, the command is particularly important to protect the compressor  24  because in the charging mode, there is an increased amount of liquid refrigerant  30  in the system  20  which could enter the compressor  24 . 
     In some examples, the integrator  38  is an asymmetrical integrator. As the cooling system  20  runs, liquid in the accumulator  32  can vaporize. For instance, vaporization can occur during cooling system  20  downtime, or when conditions upstream of the accumulator  32  at sensor  34  are operating in superheat conditions (e.g, the refrigerant  30  is all vapor, as was discussed above). In this example, the integrator  38  is “asymmetrical” because the criteria for integrating up (e.g., measuring accumulation of liquid in the accumulator  32 ) may be different from the criteria for integrating down (e.g., measuring vaporization of liquid from the accumulator  32 ). 
     In a more particular example, superheated vapor refrigerant  30  passes through the accumulator  32 , causing the liquid in the accumulator  32  to boil because the superheated vapor adds heat to the liquid refrigerant  30  in the accumulator  32 , which causes at least some of the refrigerant  30  to vaporize according to the saturation curve. Therefore, the amount of liquid in the accumulator  32  will be reduced. The rate of vaporization can be determined based on data from the sensor  34 , the known phase characteristics of the refrigerant  30 , and/or pre-programmed experimental data, as discussed above. The asymmetrical integrator  38  is operable to take into account vaporization of refrigerant  30  in the accumulator when determining how long the cooling system  20  can operate without overflowing the accumulator  32 . That is, the asymmetrical integrator  38  takes into account the rate of liquid entering the accumulator  32  from the refrigerant  30  entering the accumulator  32 , and the rate of liquid leaving the accumulator  32 . 
     In one example, a second sensor  40  is arranged near an outlet of the compressor  24  and is operable to detect information about the temperature, pressure, and/or flowrate of the refrigerant  30  as it exits the compressor  24 . In general, the conditions of the refrigerant  30  at the sensor  34  and at the sensor  40  are related. For instance, if the refrigerant  30  increases in amount of superheat at the sensor  34  over time (e.g., the amount the temperature of the refrigerant  30  exceeds the saturation temperature of the refrigerant  30  at a given pressure), the amount of superheat at the sensor  40  will increase over time also, though the rates of increase may differ. The second sensor  40  is operably connected to the controller  36  to provide additional information about the refrigerant  30  to the controller  36 . In one embodiment, the controller  36  may be wired to the second sensor  40 . In another embodiment, the controller  36  may communicate with the second sensor  34  wirelessly. For instance, when the compressor  24  is running in superheat conditions (e.g., the refrigerant is superheated at the sensor  34  and at the sensor  40 ), there is substantially no liquid entering the accumulator  32 . The controller  36  (via the integrator  38 ) can determine the amount of time the compressor  24  runs at superheat conditions and take the time into account when determining the amount of liquid in the accumulator  32  and the amount of time the cooling system  20  can run without overflowing the accumulator  32 , as discussed above. 
     Furthermore, the controller  36  is operable to perform a resolution process when the accumulator  32  is empty. As the cooling system  20  runs, inaccuracies due to time delays in data transmission and changing conditions can build up and compound on one another, causing the time determinations discussed above to become imprecise. The resolution process resets the integrator  38  according to a known condition, e.g., the emptiness of the accumulator  32 , so that previous compounded inaccuracies are reduced from the controller  36  time determinations. 
     In another example, the controller  36  is operable to detect certain failures within the cooling system  20  based on the information from one or both of the sensors  34 ,  40 . One example of such a failure is failure of the expansion valve  28 . If the expansion valve  28  is too open, the pressure of the liquid refrigerant  30  may not be sufficiently reduced so that all of the refrigerant  30  evaporates in the evaporator  22 . In this failure mode, there will thus be accumulation of liquid in the accumulator  32  which exceeds normal accumulation levels in the normal operating mode for the cooling system  20  discussed above. In turn, the time that the cooling system  20  can run without overflow of the accumulator  32 , as determined by the controller  36 , will be reduced. In one example, the controller  36  is pre-programmed with a predetermined time and/or accumulation rate that indicates a failure mode. When a failure mode is detected, the controller  36  is operable to implement a control command to shut down the compressor  24  (as was discussed above). 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.