Patent Publication Number: US-2009228152-A1

Title: Chiller Adaptation for Cold Weather Use

Description:
CROSS REFERENCE OF RELATED APPLICATIONS 
     This patent claims the priority benefit under 35 U.S.C. §119(e) of U.S. provisional patent application Ser. No. 61/033,615 (2008P0385US01), submitted on Mar. 4, 2008; the content of which is hereby incorporated by reference for all purposes. 
    
    
     FIELD OF INVENTION 
     This invention relates to refrigeration systems, in particular, cold water chillers for medical equipment that need to operate at low ambient temperatures. 
     BACKGROUND 
     Industrial chillers are used for controlled cooling of products, mechanisms and factory machinery in a wide range of industries, including the hospital industry, which requires around the clock reliability for equipment operation. During extremely cold temperatures in the winter, several installations experience chiller failures, due to colder than expected North American ambient temperatures. Replacement of chillers is a major expense and undertaking. In general, chillers are expensive devices and when purchased require cranes and other large machinery to lift and situation them into position. Another challenge involving industrial chillers is that complicated wiring and plumbing accompany the installations for chiller operation. 
     Therefore, there is a need for a less expensive and minimally business impacting solution to modify existing chillers for reliable operation in low ambient temperatures. 
     SUMMARY 
     It is one objective of the invention to provide, a chiller refrigeration system comprising: an evaporator for heating a refrigerant; a compressor for removing vapor from the evaporator; a condenser for dissipating a heat held in the vapor and converting the vapor to a pressurized liquid refrigerant; a head pressure control valve for selectively bypassing the pressurized liquid refrigerant around the condenser back to a first or second receiver for storing the pressurized liquid refrigerant; a check valve for preventing pressurized liquid refrigerant from migrating backwards to a low pressure point; a pressure relief valve for controlling a pressure in a system; and a thermal expansion valve for controlling a rate at which the refrigerant flows to the evaporator. 
     It is another objective of the invention to provide, a chiller service kit comprising: a second receiver for storing a large volume of a pressurized liquid refrigerant to flood a condenser at all ambient conditions; a head pressure control valve for selectively bypassing pressurized liquid refrigerant around the condenser back to a first or the second receiver; a check valve for preventing pressurized liquid refrigerant from migrating backwards to a low pressure point; and a pressure relief valve for controlling a pressure in a system. 
     It is another objective of the invention to provide, a method to optimize a chiller refrigeration system, the method comprising steps of: providing a second receiver for storing a large volume of a pressurized liquid refrigerant to flood a condenser at all ambient conditions; selectively bypassing pressurized liquid refrigerant around the condenser to the second receiver using a head pressure control valve during low ambient temperatures; providing a pressure relief valve for controlling pressure in the chiller refrigeration system; and providing a check valve for preventing a refrigerant from migrating backwards to a low pressure point in the chiller refrigeration system. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a schematic diagram of the refrigeration system. 
         FIG. 2  shows a block diagram of the refrigeration system. 
         FIG. 3  shows an electrical diagram of the refrigerated parts. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIGS. 1 and 2 , the refrigeration system  10  comprises the evaporator  20  where the refrigerant R134 or R22 boils or evaporates at a temperature sufficiently low to absorb heat from a space or from a medium that is being cooled. The evaporating temperature is determined, for any given refrigerant, by the pressure maintained in the evaporator  20 , therefore, the higher the pressure, the higher the boiling point; the lower the pressure, the lower the boiling point. 
     The refrigeration system  10  also comprises a compressor  30  that removes vapor from the evaporator  20  as vapor is created. The rate at which vapor is removed is adequately rapid to sustain the desired pressure in the evaporator  20 . The vapor is then compressed and transferred to the condenser  40 . The condenser  40  dissipates heat held in the hot vaporized refrigerant to a circulating coolant, usually ambient air; however, others skilled in the art may also use water. The refrigerant is condensed to a liquid and is returned to the first receiver  45  and made ready for another refrigeration cycle. 
     Located before the evaporator  20  is a thermal expansion valve  50  which controls the rate at which liquid refrigerant can flow to the evaporator  20 . This is accomplished by use of a temperature sensing device that causes the thermal expansion valve  50  to open or close as temperature changes in the evaporator  20 . The thermal expansion valve  50  acutely decreases the pressure of the liquid refrigerant passing through it, thereby substantially reducing the pressure and temperature of the refrigerant in evaporator  20 . Once the evaporator  20  reaches the pressure and temperature lower than the medium to be cooled, effective heat transfer begins. Refrigerant leaving the evaporator  20  is in a superheated vapor state and is then pulled by the compressor  30  and discharged to the condenser  40  for another refrigeration cycle to begin. 
     In the evaporator  20 , the vapor compression and expansion refrigeration process as described above depends upon a refrigerant, which absorbs heat at a relatively low temperature. In the condenser  40 , by action of mechanical work of the compressor  30 , the refrigerant is compressed and raised to an adequately high temperature to permit the dissipation of this heat to the surrounding ambient air. Therefore, the refrigeration system  10  uses the refrigerant as a heat transfer fluid that absorbs heat from the medium that is to be cooled, and releases the recovered heat in another location. 
     Refrigeration system  10  also comprises a second receiver  60  located before the evaporator  20  and compressor  30 . The second receiver  60  is approximately three times larger in volume than the first receiver  45  (shown in  FIG. 2 ). The second receiver  60  is sized large enough to equal the volume of the condensor  40  and associated piping. Sufficient refrigerant is then available to flood condensor  40  under all ambient conditions, in particular, extremely low ambient temperatures. The second receiver  60  is heated and insulated to maintain a temperature and pressure, which will allow normal chiller operation at low ambient temperatures. The second receiver  60  insures that there is always a ready supply of liquid refrigerant available for the compressor  30  to work on and run at start up. The refrigeration system  10  also comprises a pressure controlled valve  70  to selectively bypass pressurized refrigerant gas around the condenser  40  back to the second receiver  60  when the ambient air is too cold to sustain continuous compressor  30  operation. In cold ambient temperatures refrigerant migrates to the coldest or lowest pressure point in the system, i.e. condenser  40 , which is exposed to ambient air. Pressure control valve  70  bypasses refrigerant to the second receiver  60  and makes it available to run the refrigeration cycle and maintain overall liquid refrigerant pressures in the refrigeration system  10  under cold ambient conditions. 
     The refrigeration system  10  also comprises check valve  80 . Check valve  80  prevents refrigerant from migrating backwards to the low pressure point in the system. The refrigeration system  10  also comprises a pressure relief valve  90  which serves as system safety device. 
     In  FIG. 3 , components of the refrigeration system  10  are shown in electrical configuration. An additional temperature controller  100  and DC contactor  130  are added to the refrigeration system  10  to regulate temperature of the second receiver  60 . The second receiver  60  is equipped with a temperature sensor  150  which relays sensed temperature to the temperature controller  100 . After processing the input received from the temperature sensor  150 , the temperature controller  100  then sends a signal to the DC contactor  130 . The blanket heaters  160  are then activated or alternatively disengaged to maintain pre-set temperature and pressure points. An AC power supply  120  supplies power to the DC contactor  130  and the temperature controller  100  is powered by a DC power supply  110 . R.C suppressor  140  suppresses any inductive spikes that may be created across the temperature controller  100  when active. Instructions will be provided to correctly install the second heated receiver tank  60 , pressure control valve  70 , check valve  80 , and pressure relief valve  90  and other necessary devices to make the refrigeration system  10  function properly. The instructions also cover other related maintenance items that are required to enable a chiller system to provide peek performance at extreme low ambient temperatures. 
     While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the true spirit and scope of the present invention.