Patent Publication Number: US-10330369-B2

Title: Control system for a refrigerated merchandiser

Description:
BACKGROUND 
     The present invention relates to refrigerated merchandisers, and more particularly to a control system for refrigerated merchandisers. 
     Refrigerated merchandisers are used by grocers to store and display food items in a product display area that must be kept within a predetermined temperature range. These merchandisers generally include a case that is conditioned by a refrigeration system that has a compressor, a condenser, and at least one evaporator connected in series with each other. At low operating temperatures, frost often forms on the evaporator, especially near the air inlet to the heat exchanger. Such frost formation can damage the evaporator and necessitate relatively frequent and thorough defrost cycles. 
     Both open and closed merchandisers require regular defrost cycles to maintain the coil sufficiently free of ice build-up such that it can perform to its intended purpose and capacity. However, the defrost cycles add heat to the product display area, which shortens product shelf life and increases the refrigeration load needed to cool product to the desired temperature. It is common for existing medium temperature merchandisers to have four to eight defrost cycles within a 24 hour period. For existing low temperature merchandisers, it is common to have one to four defrost cycles within a 24 hour period. 
     SUMMARY 
     The invention provides, in one aspect, a refrigerated merchandiser including a case that defines a product display area and that has an air outlet and an air passageway in fluid communication with the product display area via the outlet to direct an airflow into the product display area to condition product supported in the product display area. The merchandiser also includes at least a portion of a refrigeration system that has an evaporator disposed in the case within the air passageway to refrigerate the airflow. A control system is in communication with and programmed to control the refrigeration system so that the product display area is maintained within a predetermined temperature range. The control system is further programmed to vary the temperature of the refrigerated airflow through the outlet above an airflow temperature threshold between about 35 degrees Fahrenheit and 41 degrees Fahrenheit at least once during a predetermined time period to avoid formation of frost on the evaporator while maintaining the product display area within the predetermined temperature range. 
     In another aspect, the invention provides a refrigerated merchandiser including a case that defines a product display area and that has an air outlet and an air passageway in fluid communication with the product display area via the outlet to direct an airflow into the product display area to condition product supported in the product display area. The merchandiser also includes at least a portion of a refrigeration system that has an evaporator disposed in the case within the air passageway to refrigerate the airflow, and a compressor that is in fluid communication with the evaporator. The evaporator has a coil with a hydrophobic coating. A control system is in communication with and programmed to control the evaporator within a predetermined evaporating temperature range to condition the product display area within a predetermined temperature range. The control system also is programmed to selectively cycle the compressor between an on state and an off state at least once during a predetermined time period to avoid formation of frost on the coil while maintaining the product display area within the predetermined temperature range. 
     In another aspect, the invention provides a method of controlling a refrigerated merchandiser that includes a case defining a product display area. The case has an air outlet and an air passageway in fluid communication with the product display area via the outlet to direct an airflow into the product display area. The method includes continuously operating an evaporator disposed in the merchandiser within a predetermined evaporating temperature range, refrigerating the airflow using the evaporator to condition the product display area within a predetermined temperature range, cycling a compressor between an on state and an off state to avoid formation of frost on the evaporator, and maintaining the temperature of product supported in the product display area within the predetermined product temperature range when the compressor is in the on state and in the off state. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of a refrigerated merchandiser embodying the present invention. 
         FIG. 2  is a schematic view of a refrigeration system for the refrigerated merchandiser of  FIG. 1 . 
     
    
    
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     DETAILED DESCRIPTION 
       FIG. 1  shows one construction of a refrigerated merchandiser  10  that may be located in a supermarket or a convenience store or other retail setting (not shown) for presenting fresh food, beverages, and other food product (not shown) to consumers. The illustrated refrigerated merchandiser  10  includes a case  15  having a base  20 , a rear wall  25 , and a canopy  30 . The area partially enclosed by the base  20 , the rear wall  25 , and the canopy  30  defines a product display area  35  that stores food product in the case  15  (e.g., on shelves  37 ) and that is accessible by customers through an opening  40  adjacent the front of the case  15 . In the illustrated construction, the merchandiser  10  is a self-contained upright merchandiser with an open front. In some constructions, the merchandiser  10  may include one or more doors positioned over the opening  40  to provide access to the product display area  35 . In other constructions, the merchandiser  10  can include a self-contained horizontal merchandiser with an open or enclosed top. 
     The illustrated base  20  is disposed substantially below the product display area  35  and can be supported by a floor or support surface (not shown) of the retail setting. The base  20  includes an air inlet  45  located adjacent a lower portion of the opening  40 . The air inlet  45  is positioned to receive surrounding air from within and adjacent the product display area  35  in a substantially vertical direction to direct the surrounding air into the base  20 . 
     The canopy  30  is disposed substantially above the product display area  40  and defines an upper portion of the product display area  40  that has an air outlet  50 . The case  15  defines an air passageway  55  that provides fluid communication between the inlet  45  and the outlet  50 . As illustrated, the air passageway  55  conducts air substantially horizontally through the base  20  from the inlet  45 , substantially vertically along the rear wall  35 , and substantially horizontally through the canopy  30  to the outlet  50 . A fan  60  is coupled to the case  15  to generate an airflow (denoted by arrows  65 ) within the air passageway  55 , although the fan  60  can be located anywhere within the air passageway  55 . The outlet  50  is positioned to discharge the airflow  65  from the air passageway  55  into the product display area  40  adjacent the opening  40  in the form of an air curtain  70 . As will be appreciated, the merchandiser  10  can include additional air curtains (not shown) depending on desired temperature(s) for the product supported in the product display area  35  and airflow characteristics of the merchandiser  10 . 
     With reference to  FIGS. 1 and 2 , a refrigeration system  75  circulating a heat transfer fluid or refrigerant is in communication with the merchandiser  10  (or plural merchandisers  10 ) to refrigerate product supported in the product display area  35 . In particular, the refrigeration system  75  includes a refrigeration circuit  80  that is defined by an evaporator  85 , a compressor  90  (e.g., one compressor  90  or several compressors  90  in an assembly), a condenser  95 , and a receiver  100 . The evaporator  85  (e.g., microchannel or round tube plate-fin) is fluidly coupled with the compressor  90  via a suction line  105  to deliver evaporated refrigerant from the evaporator  85  to the compressor  90 , and is fluidly coupled with the condenser  95  via an inlet line  110  to receive cooled, condensed refrigerant from the condenser  95 . An expansion valve  115  is disposed in the inlet line  110  to create a pressure differential and to control the pressure of the refrigerant fluid delivered to the evaporator  85 . The expansion valve  115  can include any valve configuration (e.g., thermostatic expansion valve  115 , etc.). A second valve  120  (e.g., solenoid valve, etc.) is connected to the suction line  105  downstream of the evaporator  85  to control refrigerant flow from the evaporator  85  through the compressor  90  and within the refrigeration circuit  80  more generally. 
     The evaporator  85  is disposed in the passageway  55  and includes one or more coils  125  in heat exchange relationship with the refrigerant to refrigerate the airflow  65  within the passageway  55 . The air curtain  70  generated by the airflow  65 , among other things, helps to maintain the air temperature in the product display area  35  within a predetermined temperature range so that product can be maintained close to or at a desired temperature. For example, the illustrated merchandiser  10  is a medium temperature merchandiser (e.g., a reach-in refrigerated food merchandiser) in which the product display area  35  is maintained within a temperature range of approximately 32 degrees Fahrenheit to 41 degrees Fahrenheit. In other constructions, the merchandiser  10  can be a low temperature merchandiser (e.g., a reach-in frozen food merchandiser) in which the product display area  35  is maintained within a temperature range generally below 32 degrees Fahrenheit. 
     The evaporator  85  also includes a hydrophobic or super-hydrophobic coating (e.g., ECRA-SH or ECRA-SHM), manufactured by ProMek Anti-Corrosion Australia Pty, with its business located at Unit 25, 17-21 Bowden Street, Alexandria NSW 2015, Australia) that is applied to the coil  125 . Generally, the hydrophobic coating is thin and non-porous, and can be formed of a water-based, self-etching epoxy resin or other suitable materials. The hydrophobic coating acts as a barrier for the evaporator  85  to repel water from the coil  125  to minimize or prevent corrosion and frost from forming on the coil  125 . 
     With reference to  FIG. 2 , a discharge line  130  fluidly connects the compressor  90  to the condenser  95  to direct refrigerant to the condenser  95  for cooling. The condenser  95  is coupled to the compressor  90  and the evaporator  85 , and includes a series of looped conduits  135  to facilitate heat transfer between the refrigerant and the surrounding environment. Refrigerant in the evaporator  85  absorbs heat, decreasing the temperature of the airflow  65  passing over the evaporator  85 . The heated or gaseous refrigerant then exits the evaporator  85  and is directed to the compressor  90 . The refrigerated airflow  65  exiting the evaporator  85  is directed toward the product display area  35  via the passageway  55  and the outlet  50  to maintain product in the product display area  35  at desired conditions. The condenser  95  can be located on a rooftop or in other suitable areas of the retail setting to discharge heat energy to the surrounding atmosphere. 
     With reference to  FIGS. 1 and 2 , the merchandiser  10  and the refrigeration system  75  can be controlled by a control system  140 , which evaluates the status of and controls the merchandiser  10  and/or the refrigeration system  75  and its components to maintain product display area  35  within the predetermined temperature range. The control system  140  can be located in any suitable location on, adjacent, or even remote from the merchandiser  10 , and can be connected to one of more sensors (not shown) in the merchandiser  10  and/or the refrigeration system  75 . 
     More specifically, the control system  140  selectively controls the merchandiser and the refrigeration components in response to the desired and/or sensed operating parameters. In some constructions, the control system  140  maintains the temperature of the product display area  35  within the predetermined temperature range based on a signal indicative of airflow temperature at the outlet  50  using a sensor  145  by adjusting operation of the refrigeration system  75  accordingly. Other signals indicative of the product display area temperature (e.g., evaporating temperature of the evaporator  85 , environmental conditions surrounding the case  15 , etc.) also can be used by the control system  140  to control the merchandiser  10  and the refrigeration system  75 . 
     The control system  140  is in electrical communication with the evaporator  85 , the compressor  90 , the expansion valve  115 , and the suction line valve  120  to control refrigerant flow and refrigerant temperatures within the refrigeration system  75 . More specifically, the control system  140  is programmed to control refrigerant flow between the condenser  95  and the evaporator  85  via the expansion valve  115 , which in part determines the evaporating temperature at which the evaporator  85  cools the airflow  65 . For example, in the illustrated medium temperature merchandiser  10 , the control system  140  controls the evaporator  85  within a predetermined evaporating temperature range between about 13 degrees Fahrenheit and 33 degrees Fahrenheit, although other evaporating temperature ranges are possible and considered herein. 
     The control system  140  also selectively cycles the compressor  90  between an on state in which refrigerant is compressed prior to being discharged to the condenser  95 , and an off state in which refrigerant flows through the compressor  90  without being compressed. The control system  140  is further programmed to selectively cycle the suction line valve  120  between an open position and a closed position to control refrigerant flow from the evaporator  85  to the compressor  90 . In the open position, the suction line valve  120  permits refrigerant flow from the evaporator  85  to the compressor  90 . In the closed position, the suction line valve  120  inhibits refrigerant flow to the compressor  90 . 
     In operation, the control system  140  controls the refrigeration system  75  so that the airflow  65  discharged through the outlet  50  is maintained at a first predetermined temperature set point so that the product display area  35  can be maintained within the predetermined temperature range. The first predetermined temperature set point can be a single temperature (e.g., 33 degrees Fahrenheit), or a range of temperatures (e.g., between 23 degrees Fahrenheit and 35 degrees Fahrenheit). 
     The control system  140  selectively increases the temperature of the refrigerated airflow  65  above a second predetermined temperature set point or airflow temperature threshold (e.g., above a temperature between about 35 degrees Fahrenheit and 41 degrees Fahrenheit) during normal operation of the merchandiser  10  (i.e., not during a defrost cycle) to avoid formation of frost on the evaporator  85  while still maintaining the product display area  35  within the predetermined temperature range. For example, the airflow temperature threshold can be approximately 37 degrees Fahrenheit, or another suitable temperature based on the desired cooling characteristics for the merchandiser  10 . 
     More specifically, the control system  140  employs cyclic off-cycle control of the refrigeration system  75  to increase the airflow temperature above the airflow temperature threshold. Cyclic off-cycle control encompasses operating the evaporator  85  within the predetermined evaporating temperature range while selectively and cyclically varying the compressor  90  between the on state and the off state during a predetermined time period. The predetermined time period can be relatively short (e.g., 30 minutes, 1 hour, etc.) or relatively long (e.g., 12 hours, 24 hours, etc.). 
     The control system  140  also selectively employs suction stop control of the suction line valve  120  to balance the refrigerant evaporating temperature within the evaporator  85  while still maintaining the evaporating temperature within the predetermined evaporating temperature range. More specifically, the suction line valve  120  is closed when the compressor  90  is in the off state such that refrigerant downstream of the valve  120  will be essentially at a compressor operating suction pressure. Refrigerant pressure upstream of the valve  120  generally rises to a pressure that is approximately equal to the pressure temperature equivalent of return air flowing through the passageway  55 . Moreover, use of a suction line valve  120  as opposed to other valves (e.g., a liquid line solenoid valve) minimizes cooling that can be caused by liquid refrigerant entering the evaporator  85  from the liquid line during the off state (i.e., the pump-down cooling effect associated with use of liquid line valves). 
     When control system  140  employs cyclic off-cycle control, the temperature of the airflow  65  goes above the airflow temperature threshold at some point, possibly only briefly, during the predetermined time period without increasing the temperature of the product display area  35  above the predetermined temperature range. Generally, the airflow temperature threshold is higher than the first predetermined temperature set point, although in circumstances where the first predetermined temperature set point encompasses a range of temperatures, the airflow temperature threshold can be a temperature near the higher end of that range. 
     For example, the control system  140  can cycle or adjust the temperature of the refrigerated airflow  65  above the airflow temperature threshold at least once, and two or more times if desired, during a predetermined time period to ensure that frost does not form on the evaporator coil  125 . Cyclic frequency depends, for the most part, on the design parameters for the merchandiser  10  (e.g., type of merchandiser  10 , evaporator coil size relative to the operating evaporating temperature, etc.). For example, cyclic off-cycle control can be employed between four times per predetermined time period (e.g., 1 hour) and twelve times per time period. Alternatively, cyclic off cycle control can be employed fewer than four times per predetermined time period or more than twelve times per time period. 
     The hydrophobic coating on the evaporator coil  125  and the control system  140  cooperate to provide a merchandiser that can be operated continuously or substantially without a defrost cycle. Stated another way, the control system  140  selectively cycles the compressor  90  between the on state and the off state one or more times during the predetermined period and balances the refrigerant temperature within the evaporator  85  to ensure no frost builds up on the coil  125  while maintaining the evaporating temperature within the predetermined evaporating temperature range and keeping the product display area within the predetermined temperature range over the entire predetermined time period. The control system  140  continuously operates the evaporator  85  within the predetermined evaporating temperature range for the entire predetermined time period regardless of whether the compressor  90  is in the on state or the off state. In this manner, the merchandiser  10  can be operated for significant periods of time (e.g., days, weeks) without a defrost cycle and without significant (if any) frost buildup on the coil  125 . 
     Various features and advantages of the invention are set forth in the following claims.