Patent Publication Number: US-7216494-B2

Title: Supermarket refrigeration system and associated methods

Description:
RELATED APPLICATION 
   This application is based upon prior filed now abandoned provisional application Ser. No. 60/510,303 filed Oct. 10, 2003, and provisional application Ser. No. 60/513,713 filed Oct. 23, 2003 the entire disclosures of which are incorporated herein by reference in their entirety. 

   FIELD OF THE INVENTION 
   The invention relates to the field of refrigeration, and, more particularly to a refrigeration system and associated refrigeration methods for a supermarket. 
   BACKGROUND OF THE INVENTION 
   A typical supermarket includes a rack type refrigeration system wherein a plurality of individual refrigeration cases are placed throughout the supermarket. These cases display and store the supermarket goods requiring cold temperatures to prevent spoilage and/or melting. Each case may include a housing that also contains an expansion valve and evaporator. As the liquid refrigerant passes through the expansion valve, it cools and passes through the evaporator to extract heat therefrom. Fans blow air through the evaporator to extract heat from the air so that a flow of cool air is generated and directed toward the goods to be kept cool. 
   Each evaporator receives a flow of liquid refrigerant from a central equipment room that houses common refrigeration equipment. The refrigerant gas output from each evaporator is supplied to the input of a common compressor. A common condenser is connected downstream from the compressor to cool the heated compressed refrigerant from the compressor. A common high pressure receiver is connected downstream from the condenser to collect liquid refrigerant. The liquid refrigerant from the receiver is then supplied back to the evaporators. 
   This conventional type of supermarket refrigeration system requires considerable copper piping to supply the liquid refrigerant to the evaporators, and to return the refrigerant gas back to the compressor. Indeed, a typical supermarket may contain about eight miles of copper piping. Unfortunately, the piping for the return refrigerant gas may still be relatively cool and therefore cause moisture condensation along its outer surface. This moisture is typically collected, such as using drip pans, to avoid wet areas in the supermarket. These pipes are also of a relatively large diameter, for example, about 1⅝ inches. In other words, a considerable investment in piping, maintenance, and moisture control is needed for the conventional supermarket refrigeration system. 
   Another type of supermarket refrigeration uses self-contained refrigeration cases that include the expansion valve, evaporator, compressor and condenser. These do not require the extensive piping as described above for the rack type system. However, the heat released from the condenser into the interior of the supermarket needs to be removed by the supermarket air conditioning system. 
   Yet another supermarket refrigeration system is described in U.S. Pat. No. 5,440,894 to Schaeffer et al. The patent discloses a plurality of refrigeration cases connected to a distribution manifold and return manifold. The distribution manifold is connected to evaporators in the refrigeration cases. The evaporators are connected to a common suction header that connects to a number of multiplexed compressors that are connected to a condenser rack. 
   U.S. Pat. No. 4,748,820 to Shaw discloses a refrigeration system for multiple refrigeration cases in which each refrigeration case has a low-stage booster compressor and an evaporator. The low-stage booster compressor is connected to a manifold that is connected to high-stage compressors. The high-stage compressors are connected to an oil separator and the oil separator is connected to a condenser. The condenser is connected to a receiver that is connected to a liquid distribution manifold that is connected to the evaporator. 
   U.S. Pat. No. 5,042,268 to LaBrecque discloses a refrigeration system that operates evaporators in both moderate and low refrigerated cases in which respective compressors are associated with each type of evaporator. The compressors are connected downstream of the evaporators and upstream of the receiver. In addition, all the compressors are lubricated by an oil separator using dedicated oil lines. 
   Unfortunately, current supermarket refrigeration systems may be relatively complicated and expensive, especially where moisture control and/or separate oil lines are used. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing background, it is therefore an object of the present invention to provide a supermarket refrigeration system that is simpler and less expensive to install and operate. 
   This and other objects, features, and advantages in accordance with the present invention are provided by a supermarket refrigeration system that includes a plurality of supermarket refrigeration cases that can contain refrigerated goods therein. Each supermarket refrigeration case may include an evaporator and an associated compressor connected downstream therefrom. The system may further include a common condenser connected downstream from the compressors. A receiver may be connected downstream from the common condenser and upstream from the evaporators. A liquid header may extend throughout the supermarket and connect the receiver and evaporators. Similarly, a discharge header may extend throughout the supermarket to connect the compressors to the common condenser. An oil-bearing refrigerant mixture may circulate through a refrigerant circulation path defined by the evaporators, associated compressors, common condenser, receiver, liquid header, and discharge header. Moreover, the oil-bearing refrigerant mixture advantageously lubricates the compressors without undesired pooling and without an oil separator in the refrigerant circulation path. Accordingly, the present invention is simpler and less expensive to install and operate than supermarket refrigeration systems found today, especially those requiring extensive moisture control and/or separate oil lines. 
   The supermarket refrigeration system may include a common condenser located external from the supermarket. Each evaporator and associated compressor in the system may have matched capacities. In some embodiments, each supermarket refrigeration case may further include an insulated enclosure surrounding the compressor. Unused expansion drop connections may also be provided along the liquid header and the discharge header. 
   In accordance with another advantageous aspect of the invention, each case may further include a selectively operable defrost circuit to provide hot refrigerant mixture for defrosting the evaporator. The supermarket refrigeration system may further include a refrigerant defrost pump connected between the evaporator and the liquid header that operates with the defrost circuit. 
   The common condenser of the system may include a condenser heat exchanger and a plurality of selectively operable condenser fans associated therewith. In addition, the liquid header and the discharge header of the system may each comprise copper lines. 
   Another aspect of the invention relates to a method for operating the supermarket refrigeration system as described above. The method may include circulating the oil-bearing refrigerant mixture through a refrigerant circulation path defined by the evaporators, compressors, common condenser, receiver, liquid header, and discharge header so that the oil-bearing refrigerant mixture lubricates the compressors without undesired pooling and without an oil separator in the refrigerant circulation path. 
   Another aspect of the invention is directed to defrosting. The method may include selectively operating the defrost circuit of a supermarket refrigeration case to use hot refrigerant mixture for defrosting. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram of a supermarket refrigeration system in accordance with the present invention. 
       FIG. 2  is a schematic diagram of an alternative embodiment of a supermarket refrigeration case as may be used in the system shown in  FIG. 1 . 
       FIG. 3  is a schematic diagram of an alternative embodiment of a condenser and receiver as may be used in the system shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternate embodiments. 
   Referring now initially to  FIG. 1 , the basic components and interconnections of a supermarket refrigeration system  10  in accordance with the invention are now described. The supermarket refrigeration system  10  illustratively includes a plurality of supermarket refrigeration cases  22   a ,  22   b , which can contain refrigerated goods therein. Each supermarket refrigeration case  22   a ,  22   b  includes a respective evaporator  14   a ,  14   b  and an associated respective compressor  12   a ,  12   b  connected downstream therefrom. Although only two refrigeration cases  22   a ,  22   b  are shown in the illustrated system  10 , those of skill in the art will recognize that more than two such cases would be used in a typical supermarket  38 . 
   The illustrated supermarket refrigeration system  10  further includes a common condenser  18  connected downstream from the compressors  12   a ,  12   b . A receiver  20  is connected downstream from the common condenser  18  and upstream from the evaporators  14   a ,  14   b . A liquid header  30  extends throughout the supermarket  38  and connects the receiver  20  and evaporators  14   a ,  14   b . A discharge header  28  extends throughout the supermarket  38  to connect the compressors  12   a ,  12   b  to the common condenser  18 . 
   Moreover, an oil-bearing refrigerant mixture  19  circulates through a refrigerant circulation path defined by the evaporators  14   a ,  14   b , associated compressors  12   a ,  12   b , common condenser  18 , receiver  20 , liquid header  30 , and discharge header  28 . The oil-bearing refrigerant mixture  19  lubricates the compressors  12   a ,  12   b  without undesired pooling and without an oil separator in the refrigerant circulation path. Accordingly, the system  10  is simpler and less expensive to install and operate than other supermarket refrigeration systems. 
   The supermarket refrigeration system  10  illustratively includes the common condenser  18  located external from the supermarket  38 . Each evaporator  14   a ,  14   b  and associated compressor  12   a ,  12   b  can have matched capacities. Unused expansion drop connections  32   a ,  32   b  may be provided along the liquid header  30  and discharge header  28 . 
   In accordance with another advantageous aspect of the invention, each case  22   a ,  22   b  may further include a selectively operable defrost circuit  36   a ,  36   b  to provide hot oil-bearing refrigerant mixture  19  for defrosting. Each refrigeration case may also include a refrigerant defrost pump  68   a ,  68   b  connected between the respective evaporators  14   a ,  14   b  and the liquid header  30 . 
   The common condenser  18  may include a condenser heat exchanger  54  and a plurality of selectively operable condenser fans  56  associated therewith. In addition, the liquid header  30  and the discharge header  28  of refrigeration system  10  may each comprise copper lines as will be appreciated by those skilled in the art. 
   A method aspect of the invention is for operating the supermarket refrigeration system  10 . The method may include circulating an oil-bearing refrigerant mixture  19  through a refrigerant circulation path defined by the evaporators  14   a ,  14   b , compressors  12   a ,  12   b , common condenser  18 , receiver  20 , liquid header  30 , and discharge header  28 . The oil-bearing refrigerant mixture  19  may lubricate the compressors  12   a ,  12   b  without undesired pooling and without an oil separator in the refrigerant circulation path. 
   Another aspect of the invention is a method for defrosting a refrigeration case  22   a ,  22   b . The method includes selectively operating a defrost circuit  36   a ,  36   b  to use hot refrigerant mixture  19  for defrosting the respective case  22   a ,  22   b.    
   In supermarket refrigeration system  10 , a respective compressor  12   a ,  12   b  is provided at each refrigeration case  22   a ,  22   b  and is connected adjacent to its evaporator  14   a ,  14   b . The connection illustratively comprises a suction line  40   a ,  40   b  and a check valve  42   a ,  42   b . The check valve  42   a ,  42   b  can be gas powered. 
   Each compressor  12   a ,  12   b  can be a highly efficient state-of-the-art compressor whose capacity is matched to the capacity of evaporator  14   a ,  14   b . The matched capacity of compressor  12   a ,  12   b  and evaporator  14   a ,  14   b  reduces the suction line  40   a ,  40   b  inefficiencies brought on by suction line control valves. 
   Another advantage of locating the compressor  12   a ,  12   b  and evaporator  14   a ,  14   b  close together is that such a configuration can significantly reduce the suction line  40   a ,  40   b  pressure losses due to long runs of piping to increase the efficiency of refrigeration system  10 . As a result, the piping from the individual compressors  12   a ,  12   b  can be considerably smaller in diameter than a traditional supermarket refrigeration system. 
   In the illustrated refrigeration system  10 , the discharged oil-bearing refrigerant mixture  19  from each compressor  12   a ,  12   b  is relatively warm thereby substantially reducing the amount of condensation found in traditional supermarket refrigeration system. Each compressor  12   a ,  12   b  is connected to the common condenser  18  by the discharge header  28 . 
   In a preferred embodiment, the common condenser  18  is located outside the air-conditioned structure of supermarket  38  such as on the roof, behind the building, or in a mechanical room. Removing the condenser  18  from the air-conditioned interior of the supermarket  38  eliminates the heat dissipated by the condenser  18  from heating the air-conditioned space of the supermarket  38 . Therefore, the air conditioning system of supermarket  38  does not need to be sized to carry away the heat generated by common condenser  18  as when individual self-contained refrigeration cases are used. 
   The common condenser  18  receives heated oil-bearing refrigerant mixture  19  from each compressor  12   a ,  12   b  and cools it. The common condenser  18  is connected to the receiver  20  and the receiver collects the cooled oil-bearing refrigerant mixture  19  as will be appreciated by those skilled in the art. 
   Referring now additionally to  FIG. 2 , another embodiment of a supermarket refrigeration case  22   a ′ is now described. In this embodiment, the compressor  12   a ′ and evaporator  14   a ′ are both within one housing  34   a ′ that may be insulated. Respective lines  17   a ′,  16   a ′ to the liquid header and discharge header penetrate the housing  34   a ′ and connect to the high pressure side of refrigeration system  10 . The compressor  12   a ′ is also surrounded by an insulated enclosure  24   a ′ in this illustrated embodiment. The refrigerant suction line  40   a ′ is very short and is inside the housing  34   a ′, thus eliminating the need for long runs of exposed suction lines. As a result, the use of drain pans for catching condensate may be reduced. 
   Accordingly, the use of ¾″ and 1″ Armaflex insulation may be eliminated due to the location and reduction in size of suction line  40   a ′. Maintenance of saturated Armaflex, the liability and health department issues associated with the latter may be reduced. An optional hood  26   a ′ is also shown in the illustrated embodiment to control the airflow around the evaporator  14   a′.    
   The short suction lines  40   a ,  40   b ,  40   a ′ of the refrigeration system  10  also eliminate the need for an oil separator that is required by traditional supermarket refrigeration rack systems. Thus, the refrigeration system  10  does not need an oil separator whether refrigeration system  10  includes low temperature refrigeration cases, moderate temperature refrigeration cases or a combination of the two. 
   Referring again to  FIG. 1  and additionally to  FIG. 3 , the high pressure side of refrigeration system  10  includes the common condenser  18 , receiver  20 , pressure vessels, piping, and instrumentation specifically designed for this application. The common condenser  18  can be sized to accommodate all refrigeration cases  22   a ,  22   b  in the refrigeration system  10 . Further, the capacity of condenser  18  can be controlled to meet load conditions by cycling the condenser fans  44  ( FIG. 3 ). A common condenser  18  with multiple condenser fans  44  is an energy efficient way to condense oil-bearing refrigerant mixture  19 . 
   The receiver  20  is connected downstream of the common condenser  18 . The flow of oil-bearing refrigerant mixture  19  to the receiver  20  is controlled by valves  62   a – 62   h  as will be appreciated by those skilled in the art. The receiver  20  may have associated therewith the illustrated pump-out compressor  60 , filter drier  64 , and liquid level gauge  66 . 
   The refrigeration system  10  may include one discharge header  28  and one liquid header  30  to serve all compressors  12   a ,  12   b  and evaporators  14   a ,  14   b . The efficiency of the compressors  12   a ,  12   b  will not be penalized by discharging into a properly sized discharge header  28 . 
   As discussed briefly above, the discharge header  28  and the liquid header  30  can have expansion drop connections  32  by which additional equipment can easily be added. Accordingly, the discharge header  28  and liquid header  30  can also be evacuated and a new connection made at quick connect valves  31   a – 31   d  where additional refrigeration cases are to be located in refrigeration system  10 . Accordingly, the cost of relocating cases, adding cases, or remodels in general throughout the life of the supermarket  38  will be reduced. 
   During the refrigeration cycle when each refrigeration case  22   a ,  22   b  calls for cooling, liquid oil-bearing refrigerant mixture  19  flows from the liquid header  30  and into liquid supply lines  17   a ,  17   b . The liquid oil-bearing refrigerant mixture  19  flows through the liquid supply lines  17   a ,  17   b  and is controlled by the liquid solenoid valves  50   a ,  50   b.    
   Liquid oil-bearing refrigerant mixture  19  flows through the thermal expansion valve  46   a ,  46   b , and into the coil of evaporator  14   a ,  14   b . The evaporator fans  56   a ,  56   b  and compressor  12   a ,  12   b  are energized and the refrigeration system  10  produces cooling. The compressor  12  discharges heated oil-bearing refrigerant mixture  19  through discharge lines  16   a ,  16   b  to the discharge header  28 . This high pressure, high temperature oil-bearing refrigerant mixture  19  flows in the discharge header  28  to the common condenser  18 . 
   The oil-bearing refrigerant mixture  19  is condensed and the heat is dissipated. The oil-bearing refrigerant mixture  19 , now a liquid, is stored in the high pressure receiver  20  awaiting demand from the refrigeration cases  22   a ,  22   b.    
   Returning again briefly to  FIG. 2 , when the refrigeration temperatures are above freezing, the evaporator coils  54   a ′ remain clean by off cycle, or timed off, air defrost. In the off cycle mode, temperatures are satisfied, and liquid flow to the evaporator  14   a ′ is stopped by the liquid solenoid valve  50   a ′ and the compressor  12   a ′ lowers the pressure and automatically shuts off. The air temperature inside refrigeration case  22   a ′ is warm enough to defrost the evaporator coils  54   a ′ within a specified time frame. 
   Where refrigeration temperatures are below freezing, the evaporator coils  54   a ′ are defrosted by the defrost circuit  36   a ′. The defrost circuit  36   a ′ uses hot gas, which is heated oil-bearing refrigerant mixture  19 , circulating in the discharge header  28 . 
   The control system initiates the defrost cycle. The liquid solenoid valve  50   a ′ stops the oil-bearing refrigerant mixture  19  from flowing to the evaporator  14   a ′. The compressor  12   a ′ pumps down and shuts off and evaporator fans  56   a  ( FIG. 1 ) shut off. The hot gas solenoid valve  48   a ′ opens thereby allowing hot oil-bearing refrigerant mixture  19  to flow from discharge header  28  into evaporator coil  54   a ′. The hot oil-bearing refrigerant mixture  19  is generated by the other refrigerated cases connected to the discharge header  28 . 
   The flow of hot oil-bearing refrigerant mixture  19  is created by a refrigerant defrost pump  68   a ′ on the dump line  52   a ′. Also on the dump line  52   a ′ is a check valve  70   a ′. The heat from the oil-bearing refrigerant mixture  19  is dissipated in the evaporator coil  54   a ′. The ice melts, and the water is collected and directed down the drain line  59   a ′. The condensed oil-bearing refrigerant mixture  19  is pumped back through the dump line  52   a ′ by the refrigerant defrost pump  68   a ′ to the liquid header  30 . The condensed oil-bearing refrigerant mixture  19  is then available to serve as the oil-bearing refrigerant mixture  19  for the other refrigerated cases attached to the liquid header  30 . 
   The defrost circuit  36   a ′ can use termination sensors to end the defrost cycle. However, termination sensors are not required because when evaporator  14   a ′ is defrosted, the hot oil-bearing refrigerant mixture  19  will no longer condense and will stay in a vapor state. The refrigerant defrost pump  68   a ′ cannot pump vapor and this stops the flow of hot oil-bearing refrigerant mixture  19  through the dump line  52   a ′ and evaporator  14   a ′. Accordingly, when the flow of hot oil-bearing refrigerant mixture  19  is stopped in this manner, the refrigerated case  22   a ′ will not be exposed to unplanned heating due to a faulty control system or a failure of a termination switch. 
   By connecting to the discharge header  28 , a sufficient volume of the hot oil-bearing refrigerant mixture  19  will be available to properly defrost any low temperature evaporators in the refrigeration system  10 . With multiple evaporators connected to one discharge header  28 , the hot oil-bearing refrigerant mixture  19  is readily available. The discharge header  28  can also supply the hot oil-bearing refrigerant mixture  19  for the heat reclaim unit  58  ( FIG. 3 ) or hot water systems and/or reheat coils for humidity control. 
   This concept lends itself to meeting the temperature requirements of the food industry. The system  10  uses an evaporator and compressor located at individual refrigerated cases and connected to a common high side. The amount of Freon or other refrigerant used per store would reduce from 30% to 40% as well as the monthly consumption. Hot gas system Freon leaks, created by the expansion and contraction of the copper piping, also will be reduced. Both factors are a result of reducing the use of copper pipe. Equipment installation cost may be reduced 35% due to the elimination of the equipment room. Electrical installation costs will be reduced as well. 
   Independently cooled refrigerated cases according to the present invention will also significantly reduce food loss. For example, compressor failures will be isolated per refrigerated case compared to the failure of an entire section of refrigerated cases in a current supermarket refrigeration system. The compressor size differential liability is reduced on maintenance and servicing of the equipment. Finding and training qualified service technicians will become easier due to the systems simplicity. 
   Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.