Abstract:
In one aspect, a refrigeration system is provided. The refrigeration system includes a refrigeration circuit configured to condition an air supply, a subcooling circuit configured to cool the refrigeration circuit, the subcooling circuit including a subcooling condenser, a subcooling heat exchanger, and at least one adsorption bed, and a heat generation system thermally coupled to the subcooling circuit.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    This invention was made with government support under contract number DE-AR0000183 awarded by the Department of Energy. The government has certain rights in the invention. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The subject matter disclosed herein relates to refrigeration systems and, more specifically, to transport refrigeration systems with an adsorption based subcooler. 
       BACKGROUND 
       [0003]    Truck trailers used to transport perishable and frozen goods include a refrigerated trailer pulled behind a track cab unit. The refrigerated trailer, which houses the perishable or frozen cargo, requires a refrigeration unit for maintaining a desired temperature environment within the interior volume of the container. The refrigeration unit must have sufficient refrigeration capacity to maintain the product stored within the trailer at the desired temperature over a wide range of ambient air temperatures and load conditions. Refrigerated trailers of this type are used to transport a wide variety of products, ranging for example from freshly picked produce to frozen seafood. 
         [0004]    One type of transport refrigeration system used in connection with truck trailers includes an electrically powered refrigeration unit operatively associated with the trailer. The refrigeration unit includes an engine driven electric generator, and the two are contained in a framework that is attached to the front wall of the trailer behind the truck cab. The refrigeration unit circulates air or another gas within the interior volume of the trailer to condition the cargo stored therein. The electric generator is driven by a diesel powered engine and is adapted to produce AC current at a selected voltage and frequency to power components of the refrigeration unit. 
         [0005]    It is desirable that truck/trailer refrigeration units operate efficiently over a wide range of refrigeration capacity demands. Further, the refrigeration units must be capable of providing sufficient increased refrigeration capacity during pull-down (i.e., rapid cool down) to reduce the temperature within the cargo box of the trailer down to the desired storage temperature when perishable product is loaded. However, in some known systems, the generator consumes large amounts of fuel to produce power for the refrigeration unit, especially during pull-down. Accordingly, it is desirable to provide supplemental cooling to the refrigeration unit to reduce the fuel consumption and/or size of the generator. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    In one aspect, a refrigeration system is provided. The refrigeration system includes a refrigeration circuit configured to condition an air supply, a subcooling circuit configured to cool the refrigeration circuit, the subcooling circuit including a subcooling condenser, a subcooling heat exchanger, and at least one adsorption bed, and a heat generation system thermally coupled to the subcooling circuit. 
         [0007]    In another aspect, a transportation refrigeration system for a cargo container is provided. The system includes a refrigeration circuit configured to condition a space in the cargo container, and a subcooling circuit having a first adsorption bed, a second adsorption bed, and a third adsorption bed, the subcooling circuit configured to provide cooling to the refrigeration circuit. The system further includes a generator electrically coupled to the refrigeration circuit, and a heat exchange circuit thermally coupled to the generator and the first, second, and third adsorption beds. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0009]      FIG. 1  is a schematic illustration of an exemplary refrigeration system. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0010]      FIG. 1  illustrates an exemplary refrigeration system  10  that generally includes a refrigeration circuit  100 , a subcooling or adsorption circuit  200 , a heat exchange circuit  300 , and a heat generation system  400  (e.g., an engine or generator  400 ). 
         [0011]    Refrigeration circuit  100  generally includes a compressor  112 , a condenser  114 , a heat exchanger  115 , an expansion device  116 , and an evaporator  118 . Condenser  114  is arranged to receive high pressure refrigerant or coolant in a vapor state from compressor  112  via a discharge line  120 . The refrigerant is condensed in condenser  114  and is supplied to evaporator  118  via a conduit line  122 . Typically, the refrigerant in condenser  114  is cooled using cooling water, air, or the like, which carries away the heat of condensation. Heat exchanger  115  functions as a subcooling heat exchanger for refrigeration circuit  100  and as an evaporator for adsorption circuit  200 . As such, a first refrigerant circulating within refrigeration circuit  100  is cooled within heat exchanger  115  by a second refrigerant circulating within adsorption circuit  200 . In one embodiment, the first refrigerant is R404A and the second refrigerant is ammonia. However, first and second refrigerants may be any suitable refrigerants that enable system  10  to function as described herein. 
         [0012]    Expansion device  116  (e.g., an expansion valve) is mounted within conduit line  122  and serves to throttle the liquid refrigerant down to a lower pressure and to regulate the flow of refrigerant through the system. Due to the expansion process, the temperature and pressure of the refrigerant is reduced prior to entering evaporator  118 . 
         [0013]    In evaporator  118 , the refrigerant is brought into heat transfer relationship with a substance to be cooled such as air. The refrigerant at the lower pressure absorbs heat from the substance being cooled and the refrigerant is subsequently vaporized. Saturated vapors are then drawn from evaporator  118  via compressor inlet line  124  and compressed to begin the cycle over again. 
         [0014]    In the exemplary embodiment, adsorption circuit  200  generally includes a condenser  202 , a receiver  204 , an expansion device  206  (e.g., expansion valve), heat exchanger  115 , and three adsorption cores or beds  208 ,  210 , and  212 . Although three adsorption beds are illustrated in  FIG. 1 , adsorption circuit  200  may have any suitable number of adsorption beds that enables system  10  to function as described herein. For example, circuit  200  may include two or five beds. 
         [0015]    Condenser  202  is arranged to receive the second refrigerant in a vapor state from adsorption beds  208 ,  210 ,  212  via a discharge line  214 . The refrigerant is condensed in condenser  202  and is supplied via line  216  to receiver  204  where the refrigerant may be stored until required. The refrigerant in condenser  202  is cooled using cooling water, air, or the like, which carries away the heat of condensation. Additionally, the heat of condensation may be stored in a thermal storage system (e.g., phase change material) for future use. Expansion device  206  is mounted within a conduit line  218  and serves to throttle the liquid refrigerant down to a lower pressure and to regulate flow of the refrigerant through the system. Due to the expansion process, the temperature and pressure of the second refrigerant is reduced prior to entering heat exchanger  115 . 
         [0016]    In heat exchanger  115 , the second refrigerant is brought into heat transfer relationship with the first refrigerant circulated through refrigeration circuit  100 . The second refrigerant at the lower pressure absorbs heat from the first refrigerant and the second refrigerant is subsequently vaporized. Refrigerant vapors are then drawn from heat exchanger  115  via respective bed inlet lines  220 ,  222 ,  224  of adsorption beds  208 ,  210 ,  212 . Valves  226 ,  228 , and  230  (e.g., two-way valves) are respectively disposed on bed inlet lines  220 ,  222 ,  224  to selectively supply refrigerant vapor to beds  208 ,  210 ,  212 . 
         [0017]    Adsorption beds  208 ,  210 ,  212  include an adsorbent (e.g., BaC12) and are configured to operate between an adsorption mode and a desorption mode. In the adsorption mode, the beds adsorb vapor refrigerant from heat exchanger  115 . The adsorption beds are subsequently regenerated by heating the adsorbent to desorb the vapor refrigerant. The desorbed refrigerant may then be supplied to condenser  202  to begin the cycle over again. As such, beds  208 ,  210 ,  212  include respective outlet lines  232 ,  234 , and  236  with respective valves  238 ,  240 , and  242  to selectively supply the refrigerant vapor to condenser  202 , as is described herein in more detail. 
         [0018]    Heat exchange circuit  300  generally includes an adsorber cooling circuit  302  and an adsorber heating circuit  304  each fluidly coupled to adsorption beds  208 ,  210 ,  212  via respective adsorber inlet lines  306 ,  308 ,  310  and adsorber outlet lines  312 ,  314 ,  316 . Adsorber inlet lines  306 ,  308 ,  310  include respective valves  318 ,  320 ,  322  (e.g., three-way valves) to selectively supply a third refrigerant to beds  208 ,  210 ,  212  from either cooling circuit  302  or heating circuit  304 . Similarly, adsorber outlet lines  312 ,  314 ,  316  include respective valves  324 ,  326 ,  328  (e.g., three-way valves) to selectively supply the third refrigerant from beds  208 ,  210 ,  212  to either cooling circuit  302  or heating circuit  304 , as described herein in more detail. The refrigerant in lines  306 ,  308 ,  310  is in indirect contact with the adsorbent such that heat transfer occurs therebetween. 
         [0019]    In the exemplary embodiment, cooling circuit  302  includes a heat exchanger  330 , a pump  332 , an inlet line  334 , and an outlet line  336 . Inlet line  334  is fluidly coupled to adsorber inlet lines  306 ,  308 ,  310 , and outlet line  336  is fluidly coupled to adsorber outlet lines  312 ,  314 ,  316 . The refrigerant in heat exchanger  330  is cooled using cooling air, water, or the like, and is selectively supplied by pump  332  and valves  318 ,  320 ,  322  to adsorption beds  208 ,  210 ,  212  that are operating in the adsorption mode. The refrigerant is heated in beds  208 ,  210 ,  212  by the heat of adsorption and is subsequently supplied via outlet line  336  back to heat exchanger  330  for subsequent cooling. 
         [0020]    Heating circuit  304  includes generator  400 , a pump  350 , an inlet line  352 , and an outlet line  354 . Inlet line  352  is fluidly coupled to adsorber inlet lines  306 ,  308 ,  310 , and outlet line  354  is fluidly coupled to adsorber outlet lines  312 ,  314 ,  316 . Generator  400  includes a radiator  402  and an engine coolant jacket  404 . The fluid in generator  400  is heated as it passes through jacket  404  and cooled as it passes through radiator  402 . The heated fluid is selectively supplied by pump  350  and valves  318 ,  320 ,  322  to adsorption beds  208 ,  210 ,  212  that are operating in the desorption mode. As such, the adsorbent is heated by the waste heat from generator  400 , which desorbs the second refrigerant, and the fluid is supplied via outlet line  354  back to generator  400  for heating. 
         [0021]    In the exemplary operation, when refrigeration system  10  requires supplemental subcooling, adsorption circuit  200  and heat exchange circuit  300  are activated. In the exemplary embodiment, adsorption bed  208  is operated in desorption mode and adsorption beds  210 ,  212  are operated in adsorption mode. As such, refrigerant may be supplied from receiver  204  to heat exchanger  115  to provide supplemental subcooling to refrigeration circuit  100  and then adsorbed on beds  210 ,  212 . However, adsorption beds  208 ,  210 ,  212  may be operated in various combinations depending on the subcooling requirement. For example, a single adsorption bed may be operated in adsorption mode if less supplemental cooling is required; all three adsorption beds may be operated in adsorption mode if more supplemental cooling is required; or the adsorption beds may be switched between adsorption mode and desorption mode to provide a constant supply of subcooling to refrigeration circuit  100  without need for storage in receiver  204  (i.e., a continuous operation mode). 
         [0022]    In this operation, the desorbing bed  208  requires heat from heating circuit  304  to facilitate the desorption process, and the adsorbing beds  210 ,  212  require cooling from cooling circuit  302  to facilitate the adsorption process. As such, valve  318  is opened to conduit  352  (closed to conduit  334 ) to supply heated fluid or refrigerant from generator  400  to bed  208  for desorption of refrigerant stored therein. Valves  320  and  322  are closed to conduit  352 , but are open to inlet conduit  334  to supply cooled fluid or refrigerant from heat exchanger  330  to beds  210 ,  212  to facilitate adsorption of refrigerant therein. 
         [0023]    Downstream of the adsorption beds, valve  324  is open to conduit  354  (closed to conduit  336 ) to return the cooled fluid or refrigerant to generator  400 . Valves  326 ,  328  are open to conduit  336  (closed to conduit  354 ) to return the fluid or refrigerant heated by the adsorption process to heat exchanger  330  for subsequent cooling. 
         [0024]    With adsorption bed  208  in desorbing mode and saturated with refrigerant, valve  226  is closed to prevent receipt of vapor refrigerant from heat exchanger  115 . Valve  238  is open to supply the desorbed refrigerant to receiver  204  for subsequent storage or to provide cooling in heat exchanger  115 . With adsorption beds  210 ,  212  in adsorbing mode and free of stored refrigerant, valves  228 ,  230  are open to receive vapor refrigerant from heat exchanger  115 . Valves  240 ,  242  are closed to conduits  234 ,  236 ,  214  while the refrigerant received through conduits  222 ,  224  is adsorbed in beds  210 ,  212 . 
         [0025]    When adsorption bed  208  is empty of refrigerant and/or when adsorption beds  210 ,  212  are saturated with refrigerant, the operation mode of the beds may be switched. As such, adsorption bed  208  may now be operated in adsorption mode while adsorption beds  210 ,  212  may be operated in desorption mode. 
         [0026]    In this mode, valve  318  is open to conduit  334  (closed to conduit  352 ) to supply cooled refrigerant from heat exchanger  330  to bed  208  to facilitate adsorption of refrigerant therein. Valves  320 ,  322  are open to conduit  352  (closed to conduit  334 ) to supply heated fluid or refrigerant from generator  400  to beds  210 ,  212  for desorption of refrigerant stored therein. 
         [0027]    Downstream of the adsorption beds, valve  324  is open to conduit  336  (closed to conduit  354 ) to return the refrigerant heated by the adsorption process to heat exchanger  330  for subsequent cooling. Valves  326 ,  328  are open to conduit  354  (closed to conduit  336 ) to return the cooled refrigerant to generator  400 . 
         [0028]    With adsorption beds  210 ,  212  in desorbing mode and saturated with refrigerant, valves  228 ,  230  are closed to prevent receipt of vapor refrigerant from heat exchanger  115 . Valves  240 ,  242  are opened to supply the desorbed refrigerant to receiver  204  for subsequent storage or to provide cooling heat exchanger  115 . With adsorption bed  208  in adsorbing mode, valve  226  is open to receive vapor refrigerant from heat exchanger  115 . Valve  238  is closed to conduit  232 ,  214  while the refrigerant received through conduit  220  is adsorbed in bed  208 . As such, the process may be repeated, and adsorption beds  208 ,  210 ,  212  may be alternated between adsorption/desorption modes to provide the desired cooling to refrigeration circuit  100 . Additionally, adsorption circuit  200  may be disconnected from refrigeration circuit  100  and function as a standalone heating/cooling system. 
         [0029]    The systems and methods described herein provide a transportation refrigeration system with a subcooling circuit. The subcooling circuit includes two or more adsorption beds that operate between an adsorption mode to store vapor refrigerant and a desorption mode to release the stored vapor refrigerant. The subcooling circuit utilizes waste heat from the refrigeration system generator to desorb the vapor refrigerant. The desorbed refrigerant is condensed, expanded, and supplied to a subcooling heat exchanger to subsequently provide additional cooling to refrigerant circulating in a primary refrigerant circuit. By utilizing waste heat of the generator in the subcooling circuit, the size and fuel consumption of the generator is reduced. 
         [0030]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.