Abstract:
An air conditioning system includes a condenser and an evaporator configured to remove thermal energy from a water flow through the evaporator via a refrigerant flow through the evaporator. A refrigerant conduit is configured to convey a refrigerant flow through the evaporator and the condenser. An ice storage tank is fluidly connected to the refrigerant conduit such that the refrigerant flow is flowable through the ice storage tank to transfer thermal energy between the refrigerant flow and a volume of frozen water disposed in the ice storage tank.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to air conditioning systems. More specifically, the subject disclosure relates ice storage systems for air conditioning systems. 
         [0002]    Ice storage is used in air conditioning systems, for example, chiller systems, to take advantage of the large energy content of a volume of frozen water. A traditional ice storage system for an air conditioning system  100  is shown in  FIG. 1 . In the air conditioning system  100 , refrigerant is circulated in a refrigerant loop  102  which flows the refrigerant through a typical refrigerant cycle including a compressor  104 , a condenser  106 , an expansion valve  108 , and an evaporator  110 . A brine loop  112  also passes through the evaporator  110  such that the evaporator  110  acts as a brine cooler during operation of the air conditioning system  100 . The brine loop  112  passes through an ice storage tank  114 , typically with one or more valves  116  to direct the brine flow, a typical brine is an ethylene glycol solution, through the brine loop  112 . 
         [0003]    Such a system operates in many different modes depending on cooling requirements. In brine cooling mode, also called vapor compression mode, the chiller  100  operates as a conventional chiller. The valves  116  are closed and/or opened so that the brine flow bypasses the ice storage tank  114  and flows through the evaporator  110 . In this mode, the evaporator  110  cools the brine flow to about 7 degrees Celsius and the brine is flowed to a chiller  118  to cool a desired space. When the system  100  is operating in ice storage mode, such as when there is not a need to cool the desired space, the air conditioning system  100  flows the brine not to the chiller  118 , but to the ice storage tank  114 . During this mode, the brine is cooled to −5 degrees to −10 degrees Celsius by the evaporator  110  and freezes water in the ice storage tank  114  thus storing cooling energy in the ice storage tank  114 . During operation of the air conditioning system  100  in ice cooling mode, the refrigerant loop  102  is not operating. Brine is circulated through the ice storage tank  114  to cool the brine flow which is then flowed to the chiller  118  to cool the desired space. 
         [0004]    Use of the ice storage tank  114  in conjunction with the chiller  118  allows a size of the chiller  118  and allows the air conditioning system  100  to take advantage of lower nighttime electricity costs by using ice storage mode. 
         [0005]    Circulation of brine through the ice storage tank  114 , however, reduces thermal efficiency of the air conditioning system  100  versus a system utilizing water routed through the chiller  118 , since brine has poor heat transfer characteristics when compared to water. Further, inclusion of the brine loop  112  makes the air conditioning system  100  layout complicated due to the valves  116  and other components required to direct the brine flow through the system when operating in the various modes. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0006]    According to one aspect of the invention, an air conditioning system includes a condenser and an evaporator configured to remove thermal energy from a water flow through the evaporator via a refrigerant flow through the evaporator. A refrigerant conduit is configured to convey a refrigerant flow through the evaporator and the condenser. An ice storage tank is fluidly connected to the refrigerant conduit such that the refrigerant flow is flowable through the ice storage tank to transfer thermal energy between the refrigerant flow and a volume of frozen water disposed in the ice storage tank. 
         [0007]    According to another aspect of the invention, a method of operating an air conditioning system includes urging a refrigerant flow along a refrigerant pathway and through a compressor. The refrigerant flow is conveyed through a condenser disposed along the refrigerant pathway and at least a portion of the refrigerant flow is flowed through an ice storage tank via an ice tank pathway. A volume of water disposed in the ice storage tank is frozen via the refrigerant flow thus storing cooling energy in the ice storage tank. 
         [0008]    According to yet another aspect of the invention, a method of operating an air conditioning system includes conveying a refrigerant flow through a refrigerant conduit to an ice storage tank, the ice storage tank containing a volume of frozen water therein. Thermal energy is transferred from the refrigerant flow to the volume of frozen water, thereby cooling the refrigerant flow. The refrigerant flow is urged from the ice storage tank to an evaporator and a water flow is conveyed to the evaporator via a water pathway. Thermal energy is transferred from the water flow to the refrigerant flow via the evaporator, thereby cooling the water flow. The water flow is conveyed to a chiller to cool a desired space via the chiller. 
         [0009]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    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: 
           [0011]      FIG. 1  is a schematic diagram of a typical air conditioning system including ice storage; 
           [0012]      FIG. 2  is a schematic of an embodiment of an improved air conditioning system; 
           [0013]      FIG. 3  is a schematic of an embodiment of an air conditioning system operating in vapor compression mode; 
           [0014]      FIG. 4  is a schematic of an embodiment of an air conditioning system operating in ice storage mode; 
           [0015]      FIG. 5  is a schematic of an embodiment of an air conditioning system operating in ice cooling mode; and 
           [0016]      FIG. 6  is a schematic of an embodiment of an air conditioning system operating an alternative cooling mode; 
       
    
    
       [0017]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Shown in  FIG. 2  is an improved air conditioning system  200 . In the air conditioning system  200 , refrigerant is circulated in a refrigerant pathway  202  which flows the refrigerant through a typical refrigerant cycle including a compressor  204 , a condenser  206 , an expansion valve  208 , and an evaporator  210 . A direct-expansion ice storage tank  212  is connected to the refrigerant conduit  202  via an ice tank pathway  214 . The ice tank pathway  214  is connected to the refrigerant conduit  202  by one or more control valves  216 . A refrigerant pump  218  may be located along the ice tank conduit  214 . The evaporator  210  cools a flow of water which is circulated through a water pathway  220  through the evaporator  210  and to a chiller  222  which cools a desired space  224  via the flow of water. While the ice storage tank  212  is shown in  FIG. 2  to be located outside of the chiller  222 , in some embodiments the ice storage tank  212  may be disposed internal to the chiller  222 . As will be explained in more detail below, the air conditioning system  200  eliminates the brine loop of the prior art resulting in a more efficient and less complex operation of the air conditioning system  200  versus that of the prior art. 
         [0019]    The air conditioning system  200  operates in a variety of modes depending on cooling requirements of the space  224 . Shown in  FIG. 3  is operation of the air conditioning system  200  in vapor compression, or water cooling mode. In this mode, the refrigerant flow (as shown by the dashed lines in  FIG. 3 ) is circulated through the refrigerant pathway  202  as in a traditional air conditioning system. In this mode, the refrigerant flow passing through the evaporator  210  absorbs thermal energy from the water flow passing through the evaporator  210 . 
         [0020]    Illustrated in  FIG. 4  is operation of the air conditioning system  200  in ice storage mode. At times where it is advantageous to do so, such as off-peak hours where electricity cost is reduced and/or cooling needs are lower, the system can be operated in ice storage mode to freeze water, or other phase change material, in the ice storage tank  212  thus “storing” an amount of cooling energy in the ice storage tank  212  for use at a later time. In ice storage mode, a control valve  216  is opened between the refrigerant pathway  202  and the ice tank pathway  214  and the expansion valve  208  is closed. This diverts the refrigerant flow from the condenser  206  through the control valve  216  and through the ice storage tank  212  via the ice tank pathway  214 . As the refrigerant flow (shown again by the dashed lines in  FIG. 4 ) passes through the ice storage tank  212  at about −3 to −7 degrees Celsius, the water in the ice storage tank  212  is frozen. The refrigerant flow leaving the ice storage tank  212  is returned to the compressor  204 . In some embodiments, the refrigerant flow bypasses the evaporator  210  when the system  200  is operating in ice storage mode. 
         [0021]    The stored cooling energy in the ice storage tank  212  is utilized when the system  200  is operated in ice cooling mode illustrated in  FIG. 5 . In this mode, the compressor  204 , condenser  206  an expansion valve  208  are all turned “off”. As such, the refrigerant (shown by dashed lines in  FIG. 5 ) is circulated between the evaporator and the ice storage tank  212 . The refrigerant flow naturally seeks the lowest temperature portion of the system  200 , which in this mode is the ice storage tank  212 , so it is not necessary to pump the refrigerant to the ice storage tank  212 . The refrigerant flows through the ice storage tank  212  where it is cooled, changing the phase from gas to liquid and pumped in liquid phase from the ice storage tank  212  via the refrigerant pump  218 . The cooled refrigerant then flows through the evaporator  210  where thermal energy from the water flowing through the water pathway  220  is absorbed by the refrigerant flow thereby cooling the water flow. The water flow is then circulated to the chiller  222  via the water pathway  220 . The refrigerant is evaporated while absorbing a heat from water and in gas phase flow from the evaporator  210  bypasses the compressor  204 , condenser  206  and expansion valve  208  via a bypass pathway  226  and returns to the ice storage tank  212 . 
         [0022]    The system  200  can also be operated in a dual water cooling and ice cooling mode. In this mode, as shown in  FIG. 6 , the compressor  204 , condenser  206  and expansion valve  208  are turned “on”, but the valve  216  is closed. Refrigerant (shown as the dashed lines in  FIG. 6 ) circulates through both the refrigerant pathway  202  and the ice tank pathway  214 , with a portion of the refrigerant bypassing the compressor  204  and flowing to the ice storage tank  212  via the bypass pathway  226 . The refrigerant portion flowing through the ice storage tank  212  is cooled by the ice stored therein while the refrigerant portion flowing into the compressor  204  is cooled via the compressor  204 , condenser  206  and expansion valve  208 . 
         [0023]    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.