Abstract:
An improved refrigeration system utilizing a subcooler/economizer is provided. The refrigeration system comprises a compressor, a condenser, a refrigeration case, and an evaporator for cooling the refrigeration case. The refrigeration system may further include a subcooler. A modulating evaporator pressure regulator valve is located downstream of the evaporator, on the return line between the subcooler and the compressor. The valve controls the suction gas pressure of the compressor which, in turn, controls the liquid temperature of the refrigerant entering the evaporators. The modulation of the pressure regulator valve is dependent on the dew point of the store and/or the temperature of the liquid entering the evaporators.

Description:
This application claims the benefit of U.S. Provisional Application Ser. No. 60/157,330, filed on Oct. 1, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to refrigeration and air conditioning systems, and more particularly, to an improved system utilizing a modulating valve in conjunction with a subcooler/economizer for controlling the temperature of a refrigerant in the system. The present invention finds particular application in conjunction with supermarket food refrigeration systems, and it will be described with particular reference thereto. However, it is to be appreciated that the present invention is also amenable to other like applications. 
     2. Discussion of the Art 
     Commercial refrigeration and air conditioning systems frequently employ multiple evaporators to meet specific cooling needs. Often the evaporators and their associated expansion valves are remotely located relative to other components of the refrigeration system in order to cool refrigeration cases. As a result, lines, conduits, or piping leading to the remotely located evaporators cover great distances and decrease the overall efficiency of the refrigeration system. With the increasingly high cost of energy, it is generally desirable to increase the efficiency of commercial refrigeration systems. 
     One method of combating the inefficiencies associated with remotely located refrigeration cases is to use subcooling. Subcooling the liquid refrigerant of a refrigeration system increases the refrigerant effect, or the quantity of heat absorbed in the refrigerated space per unit mass, without increasing energy input to the compressors. Thus, subcooling increases the efficiency of the system and reduces the power requirements of the system per unit of refrigerating capacity. 
     Even with subcooling, inefficiencies may still exist. For example, pipes running from the condenser to the evaporators are often not insulated due to the remote location of the evaporators. As a result the refrigerant flowing through these pipes is often below the dew point and causes sweating or condensation of water on the pipes. As is well known, sweating decreases the efficiency rating of the refrigeration system. 
     Therefore, it is desirable to provide an improved refrigeration system with controlled subcooling for overcoming these problems and others. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to an improved refrigeration system utilizing a modulating valve in conjunction with a subcooler/economizer for controlling the temperature of a refrigerant in the system. 
     In accordance with one aspect of the present invention, the refrigeration system comprises a compressor, a condenser, one or more refrigeration cases, and an evaporator for cooling the refrigeration cases. The compressor is interconnected to the condenser, the condenser is interconnected to the evaporator, and the evaporator is interconnected to the compressor in a closed loop. 
     The refrigeration system further includes a subcooler operatively disposed downstream of the condenser and upstream of the evaporator. The subcooler includes an expansion valve for expanding a first portion of the condensed refrigerant exiting the condenser and using the expanded refrigerant for subcooling a second portion of remaining unexpanded refrigerant exiting the condenser. The unexpanded refrigerant flows to the evaporator after subcooling. The subcooler also has a return line in parallel with the evaporator for returning the expanded refrigerant to the compressor after subcooling. 
     A modulating evaporator pressure regulator valve is located on the return line. The modulating valve controls a suction gas pressure to the compressor which controls the liquid temperature of the refrigerant entering the evaporators. The modulation of the valve occurs in response to a dew point in the ambient environment or store and/or the temperature of the liquid entering the evaporators which efficiently cools the refrigeration cases to a desired temperature while preventing line sweating. 
     In accordance with another aspect of the present invention, the modulating valve modulates in response to the ambient temperature in the store. 
     In accordance with another aspect of the present invention, the modulating valve modulates in response to the temperature of the expanded refrigerant entering the subcooler. 
     In accordance with another aspect of the present invention, the subcooler is removed. 
     A primary advantage of the present invention is the provision of a refrigeration system that allows for a smaller compressor without reducing the refrigeration capacity of the system. 
     Another advantage of the present invention is the provision of a refrigeration system that can be operated remotely. 
     A further advantage of the present invention is the provision of a refrigeration system that allows for smaller, less expensive refrigeration lines. 
     Another advantage of the present invention is the provision of a refrigeration system that does not require insulated lines, yet limits sweating of the lines. 
     Still another advantage of the present invention is the provision of a refrigeration system that requires less refrigerant in the system. 
     Further advantages and benefits of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The structure, operation and advantages of presently preferred embodiments of this invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings. Of course, the drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention. 
     FIG. 1 is a schematic diagram of a refrigeration system having a subcooler in accordance with the present invention. 
     FIG. 2 is a schematic diagram of a refrigeration system without a subcooler in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, a refrigeration system according to a preferred embodiment of the present invention is generally indicated by reference numeral  10 . The refrigeration system  10  comprises a compressor  12 , a condenser  14 , a subcooler  16 , one or more refrigeration cases  18 , and an evaporator  20  for cooling the refrigeration cases  18 . 
     The refrigerant output of the compressor  12  flows via line, passage, conduit, or piping  22  to the condenser  14 , the refrigerant output of the condenser  14  flows via line  24  to the subcooler  16 , the refrigerant output of the subcooler  16  generally flows via line  26  to the evaporator  20 , and the refrigerant output of the evaporator  20  flows via line  28  to the compressor  12 . The line  26  flowing to the evaporator  20  is often lengthy and not insulated allowing remote placement of the evaporator  20  and the refrigeration cases  18  relative to the remaining components of the refrigeration system. 
     A portion of the refrigerant flowing through line  24  is diverted by bleed line  30 . An expansion valve  32  is disposed in bleed line  30  for expanding the portion of refrigerant passing therethrough. The expanded refrigerant is used to subcool the remaining refrigerant flowing through the subcooler  16  and into the evaporator  20  via line  26 . A return line  36 , in parallel with the evaporator  20 , is used for returning the expanded refrigerant to the compressor  12  after subcooling. The expansion valve  32  operates in response to the temperature of the expanded refrigerant exiting the subcooler  16  in the return line  36  as measured by return line sensor  38 . 
     A modulating evaporator pressure regulator valve  40  is disposed in return line  36 . The modulating valve  40  selectively controls return suction gas pressure to the compressor  12  and thereby controls the liquid temperature of the refrigerant entering the evaporator  20 . More specifically, the modulating valve  40  modulates the flow of refrigerant therethrough. Modulation occurs via valve controller  40 ′, in response to the dew point of the store, or ambient environment that surrounds the line  26 , as measured by sensor  42 , and/or the temperature of the liquid refrigerant entering the evaporator  20 , as measured by evaporator inlet sensor  44 . Modulating the flow of refrigerant allows the system  10  to efficiently cool the refrigeration cases  18  to a desired temperature while preventing line sweating in line  26  connected to the evaporator  20 . 
     In order to prevent line sweating in a refrigeration system, the temperature of the liquid refrigerant running through the line  26  to the evaporator  20  must be kept above the dew point temperature in the store. When the dew point temperature is high as a result of high humidity, the temperature of the liquid refrigerant must be kept relatively high to prevent line sweating. In prior art systems, the temperature of the liquid refrigerant was constant and, therefore, had to be set for a high dew point in order to prevent line sweating under high humidity. As a result, the prior art refrigeration systems avoided line sweating but were inefficient on lower humidity days, or undesirable sweating occurred on higher humidity days. Ideally, the temperature of the liquid refrigerant should be as low as possible without dipping below the dew point temperature. 
     The modulating valve  40  of the present invention operates to adjust the temperature of the liquid refrigerant entering the evaporator  20 . When the humidity is relatively high, the controller  40 ′ throttles toward a closed position which causes the temperature of the liquid refrigerant to rise and stay above the dew point. When the humidity is relatively low, the modulating valve is throttled toward an open position allowing for maximum subcooling and causing the temperature of the liquid refrigerant to lower. Under these operating conditions, the system  10  advantageously prevents line sweating and runs more efficiently. 
     Besides the system described above, the modulating valve  40  is capable of operating in response to various types of sensors in different locations of the refrigerant system. For instance, the modulating valve controller can also respond to the temperature in the refrigeration cases  18 . In this alternative, the refrigeration case sensor  42  monitors the temperature in the refrigeration cases and provides feedback data or information via line  42 ′ to the valve controller  40 ′ so that the valve is modulated in response thereto. 
     In another alternative, the valve controller can also receive a signal relating to the temperature of the refrigerant returning to the compressor via the line  28 , as measured by sensor  46 . A feedback signal is provided to the controller  40 ′ as indicated by line  46 ′. In yet another alternative, the temperature of the refrigerant entering the subcooler  16 , as measured by a subcooler sensor  48 , is conveyed to the controller  40 ′ through line  48 ′ to modulate the valve. It is to be appreciated that the valve  40  can modulate in response to a combination of measurements taken by the above disclosed sensors  42 - 48 , however, the present invention uses the information from sensor  42  to control the modulating valve, and may also use additional data from one or more of the sensors  44 ,  46 , and  48 . The number of sensors used and the location of the sensors may vary. All such combinations and locations are to be considered within the scope of the present invention. 
     The location of the modulating valve  40  in the system  10  may also be varied. For example, the modulating valve  60  can be positioned in the line  28  between the evaporator  20  and the compressor  12 . The modulating valve  40  or  60  continues to selectively control the suction gas pressure to the compressor  12  thereby controlling the liquid temperature of the refrigerant entering the evaporator  20 . The sensors are used in generally the same manner as described above to provide feedback/response signals to the modulating valve controller. 
     With reference to FIG. 2, a refrigeration system according to another preferred embodiment of the present invention is generally indicated by reference numeral  100 . The components of the system  100  are generally the same as the components of the system  10  of the first preferred embodiment and, accordingly, like reference characters are used to represent like elements. Notably, the systems  10 ,  100  are substantially similar except that the subcooler  16  and its expansion valve  32  have been removed in the embodiment of FIG.  2 . 
     Without the subcooler  16  and the expansion valve  32 , bleed line  30  and return line  36  (FIG. 1) are replaced by a single line  102  (FIG. 2) disposed in parallel relation with the evaporator  20 . The modulating evaporator pressure regulator valve is disposed on the single line  102 . As described in detail above, the modulating valve selectively controls suction gas pressure of the compressor  12  and thereby controls the liquid temperature of the refrigerant entering the evaporator  20 . Again, modulation occurs in response the dew point of the store as measured by sensor  42 , and possible in conjunction with one or more of the temperature of the refrigerator case as measured by sensor  44 , the temperature of the refrigerant returning to the compressor as monitored by sensor  46 , or the subcooler sensor  48 . Modulating the flow of refrigerant allows the system  100  to efficiently cool the refrigeration cases  18  to a desired temperature while preventing line sweating in line  26  connected to the evaporator  20 . 
     Alternative sensors and measurements can be used as described above. Again, one skilled in the art will appreciate that the valve  40  can modulate in response to any combination of measurements taken by the above disclosed sensors  42 - 46  and the number of sensors used and the precise location of the sensors may vary. All such combinations and locations are to be considered within the scope of the present invention. 
     As in the preferred embodiment of FIG. 1, the location of the modulating valve  40  in the system  100  may be varied. The modulating valve  60  can alternatively be positioned in the line  28  between the evaporator  20  and the compressor  12 . In this alternate arrangement, the modulating valve  60  continues to selectively control the suction gas pressure to the compressor  12  thereby controlling the liquid temperature of the refrigerant entering the evaporator  20 . The sensors are used in the same manner as described previously. 
     The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.