Abstract:
A method of controlling a refrigerated merchandiser. The method includes refrigerating a product display area of the merchandiser using a refrigerant, detecting a presence of an air-refrigerant mixture in the refrigerated merchandiser, activating a fan in response to detecting the presence of an air-refrigerant mixture, and at least partially evacuating an interior of the merchandiser in response to fan activation.

Description:
BACKGROUND 
       [0001]    The present invention relates to refrigerated merchandisers, and more particularly to a control system for refrigerated merchandisers that utilize hydrocarbon refrigerants. 
         [0002]    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. Typically, existing merchandisers use refrigerants such as R404a, R134a, or carbon dioxide. 
         [0003]    Some refrigeration systems utilize hydrocarbon-based refrigerant (e.g., propane) that has a higher tendency to be flammable relative to conventional refrigerants. There are ways to reduce the risk of the ignition of a hydrocarbon-based refrigerant such as using intrinsically safe electrical components, and quality control to minimize any potential for leaks. However, a flammable mixture of refrigerant and air may exist inside the merchandiser and an ignition source such as a static electrical discharge may occur, causing the air and refrigerant mixture to ignite. When there is no path for the energy released by the ignition to escape, which is especially common in sealed cases, the excessive internal pressure may cause the case to explode. 
       SUMMARY 
       [0004]    The invention provides a refrigerated merchandiser including a case defining a product display area and including a refrigeration circuit that circulates a hydrocarbon refrigerant operable to condition the product display area via heat exchange with air passing through an evaporator of the refrigeration circuit. A refrigerant leakage sensor is coupled to the case and is operable to determine the presence of gaseous refrigerant in the air, and a control unit is in communication with the sensor and responsive to a signal from the sensor indicative of gaseous refrigerant above a predetermined threshold to manage the risk of refrigerant ignition. A fan or blower is coupled to the merchandiser, for example, on the exterior of the case, to clear a flammable mixture of refrigerant gas and air from the case. 
         [0005]    In one construction, the invention provides a method of controlling a refrigerated merchandiser. The method includes refrigerating a product display area of the merchandiser using a refrigerant, detecting a presence of an air-refrigerant mixture in the refrigerated merchandiser, activating a fan in response to detecting the presence of an air-refrigerant mixture, and at least partially evacuating an interior of the merchandiser in response to fan activation. 
         [0006]    In another construction, the invention provides method of controlling a refrigerated merchandiser. The method includes refrigerating a product display area of the merchandiser using a refrigerant, detecting a presence of an air-refrigerant mixture in the refrigerated merchandiser, and initiating an action in response to the detected air-refrigerant mixture reaching a predetermined threshold relative to a lower flammability limit of the refrigerant. 
         [0007]    In another construction, the invention provides refrigerated merchandiser including a case that defines a product display area and a refrigeration system that has an evaporator coupled to the case and through which a hydrocarbon refrigerant is circulated to condition the product display area. The merchandiser also includes a sensor that is coupled to the case and configured to detect an air-refrigerant mixture within the merchandiser and to generate a signal indicative of the detected air-refrigerant mixture. A controller is programmed to initiate an action in response to the signal indicative of the air-refrigerant mixture reaching a predetermined threshold relative to a lower flammability limit of the refrigerant. 
         [0008]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic view of an exemplary multi-circuit refrigeration system including a plurality of refrigerated merchandisers. 
           [0010]      FIG. 2  is perspective view of one refrigerated merchandiser of  FIG. 1  embodying the invention. 
           [0011]      FIG. 3  is a schematic view of the refrigerated merchandiser of  FIG. 2  including a refrigeration system. 
           [0012]      FIG. 4  is another schematic view of the refrigerated merchandiser of  FIG. 2  the refrigeration system and a blower. 
           [0013]      FIG. 5  is a perspective view of a portion of the refrigerated merchandiser including the blower coupled to an exterior of the merchandiser. 
           [0014]      FIG. 6  is a schematic view of the refrigerated merchandiser illustrating a control system of the merchandiser. 
           [0015]      FIG. 7  is a flow chart illustrating an exemplary control process of the control system. 
           [0016]      FIG. 8  is flow chart illustrating another exemplary control process of the control system. 
       
    
    
       [0017]    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 
       [0018]      FIG. 1  illustrates an exemplary multi-circuit refrigeration system  10  that can be used in a commercial setting (e.g., a retail store, supermarket, or an industrial setting) or other settings that have temperature-controlled environments. The multi-circuit refrigeration system  10  includes a primary circuit  15  that circulates a first refrigerant, a plurality of secondary circuits  20  that circulates a second refrigerant (e.g., a hydrocarbon refrigerant such as propane), and a pump circuit  25  that circulates a third refrigerant in heat exchange relationship with the refrigerants in the primary circuit  15  and the secondary circuits  20 . Part or all of the primary circuit  15  can be located remote from the secondary refrigeration circuits  20 . 
         [0019]    The primary circuit  15  includes a primary compressor assembly  30  (e.g., one or more compressors), a primary condenser  35 , and a chiller  40  through which the first refrigerant (e.g., R134a) is circulated to withdraw heat from the third refrigerant. The primary circuit  15  also can include other components (e.g., a receiver or accumulator, an expansion valve, etc.). 
         [0020]    With reference to  FIGS. 1-3 , each secondary circuit  20  includes one or more merchandisers  45  that have an evaporator assembly  50  in fluid communication with a compressor  55  (e.g., one compressor , or several compressors in an assembly) and a condenser  60  that provides heat exchange between the secondary circuit  20  and the pump circuit  25 . The evaporator  50  is in heat exchange relationship with a product display area  65  of the merchandiser  45 , and is fluidly coupled to the compressor  55  via a suction line  70  to deliver evaporated second refrigerant from the evaporator  50  to the compressor  55 . The evaporator  50  is also fluidly coupled with the condenser  60  via an inlet line  75  to receive cooled (e.g., condensed) second refrigerant from the condenser  60 . A discharge line  80  fluidly connects the compressor  55  to the condenser  60  to direct the compressed second refrigerant to the condenser  60 , where heat from the second refrigerant can be transferred to the third refrigerant in the pump circuit  25 . As will be appreciated, the secondary circuit  20  can include other components (e.g., receiver or accumulator, an expansion valve, etc.). 
         [0021]    As shown in  FIG. 1 , the pump circuit  25  includes a pump  85  that circulates the third refrigerant (e.g., water) between the water chiller  40  of the primary circuit  15  and the condensers  60  of the secondary circuit  20 . As illustrated, the refrigeration system  10  also includes an outdoor heat exchanger  90  that is in communication with the pump circuit  25 . In some constructions, the heat exchanger  90  can be located on a rooftop of the commercial setting to discharge energy from the third refrigerant in the pump circuit  25  to the surrounding environment. The heat exchanger  90  is in fluid communication with the pump circuit  25  via an inlet line  93  and an outlet line  95 . A valve (not shown) can be coupled to the inlet line  93  and/or the outlet line  95  to control flow of refrigerant between the pump circuit  25  and the heat exchanger  90  based at least in part on the temperature of the surrounding environment. When the heat exchanger  90  is used to cool the third refrigerant, the primary circuit  15  can be shutdown, or the primary circuit  15  and the heat exchanger  90  can operate simultaneously to cool the third refrigerant. 
         [0022]    The merchandiser  45  can be a low or medium temperature merchandiser.  FIG. 2  shows that the merchandiser  45  is a horizontal merchandiser including a case  100 , although the merchandiser  45  can take other forms (e.g., a vertical merchandiser with an open or door-enclosed customer access). The case  100  has a base  105  and sidewalls  110 , a front wall  115 , and a rear wall  120  cooperatively defining the product display area  65  that supports food product. The case  100  also defines an interior area  125  (illustrated in  FIG. 3  below the product display area  65 ) that supports at least a portion of the secondary circuit  20 . As illustrated, lids or doors  130  are disposed over the product display area  65  to substantially enclose the product display area  65  and to selectively provide access (e.g., by sliding) to product supported in the product display area  65 . 
         [0023]    Referring to  FIG. 3 , the second refrigerant in the evaporator  50  absorbs heat from an airflow  135  passing over or through the evaporator  50 , which decreases the temperature of the airflow  135 . The refrigerated airflow  135  exiting the evaporator  50  is directed toward the product display area  65  to maintain product in the product display area  65  at desired conditions. The condenser  60  discharges heat from the second refrigerant to the third refrigerant in the pump circuit  25 . Air passing through or over the condenser  60  can be directed from the condenser  60  to the environment surrounding the merchandiser  45  using exhaust fans  137  that direct the air through an exhaust  140  coupled to the case  100 . The compressor  55  and the condenser  60  can be disposed in the refrigerated merchandiser  45  within an interior area  125  of the case  100 , or located remote from the case  100 . 
         [0024]    Hydrocarbon refrigerant are generally more flammable than conventional refrigerants. The flammability risk can be mitigated by reducing the refrigerant charge (i.e. the amount of second refrigerant) in the secondary circuits  20 , using intrinsically save electrical components, and/or quality control to minimize any potential for refrigerant leakage. When hydrocarbon refrigerant leaks from the circuit  20 , the leaked refrigerant mixes with air in the case  45  and can become flammable. As such, it is generally desirable to do at least one of the following: 1) Detect when a mixture of air and refrigerant is present in the merchandiser  45 ; 2) determine whether the air-refrigerant mixture has reached or exceeded a predetermined threshold (e.g., a percentage of a lower flammability limit at which the mixture becomes highly flammable); 3) determine the presence of an ignition source (e.g., static electricity, electrical power provided to components in the merchandiser  45 , etc.) in or surrounding or adjacent the merchandiser  45 ; and 4) clear the air-refrigerant mixture from the merchandiser  45 . 
         [0025]    To this end, and with reference to  FIGS. 4 and 5 , the merchandiser  45  includes a blower  145  that is coupled to the case  100  (e.g., on one of the side walls  110 , the front wall  115 , and the rear wall  120 ) to selectively direct air through the case  100 . As illustrated, the blower  145  is coupled to an exterior of the case  100  to avoid frosting the blower  145  in view of the substantially colder temperature in the case  100 , although in some circumstances the blower  145  can be coupled to an interior the case  100  or suitable other locations. The illustrated blower  145  operates at a relatively high speed (e.g., 20,000 to 30,000 RPMs) to introduce a large volume of ambient air into the case  100  over a relatively short period of time. Depending on how the blower  145  is connected to the merchandiser  45 , the blower  145  can be energized to draw ambient air into the case  100 , or the blower can push ambient air into the case  100 . 
         [0026]    With reference to  FIG. 5 , the blower  145  mounted to the case by a mounting bracket  147  and is in fluid communication with the interior of the merchandiser  45  via an inlet pipe  150 . As will be appreciated by one of ordinary skill in the art, the blower  145  is connected to a power source (e.g., one or more batteries, a powered connection via the merchandiser  45 , or another source of power). As shown in  FIG. 5 , a check valve  155  is coupled to the inlet pipe  150  downstream of the blower  145  (in the direction of airflow through the blower  145 ) to provide unidirectional ambient airflow into the case  100  when the blower  145  is activated. That is, the check valve  155  inhibits flow of refrigerated air into the blower  145 . 
         [0027]    With reference to  FIGS. 3 and 4 , the merchandiser  45  includes one or more sensors  160  (e.g., gas detector) that are mounted in the interior area  125  of the case  100  to detect the presence, if any, of leaked refrigerant within the merchandiser  45 . That is, the sensor  160  detects the presence of any second refrigerant that is mixed with air inside the merchandiser  45 . The sensor  160  can be coupled to the case  100  in any suitable location (e.g., on a wall of the case  100 , within the interior area  125 , adjacent one or more of the refrigeration components in the merchandiser  45 , adjacent or in the product display area  65 , etc.). 
         [0028]    The sensor  160  is operable to generate a signal indicative of the presence of second refrigerant in the merchandiser  45  and to communicate the signal to a control unit  165  that is in communication (e.g., wired, wireless, etc.) with the sensor  160 . With reference to  FIGS. 3 and 4 , the control unit  165  is disposed inside the merchandiser  45  (e.g., within the interior area  125 ), although the control unit  165  can be located remote from the merchandiser  45 . In response to the signal from the sensor  160 , the control unit  165  is programmed to control the secondary circuit  20  and electrically-powered or electronic components  170  of the merchandiser  45  to mitigate the risk of igniting the air-refrigerant mixture. For example, the electronic components  170  can include the compressor assembly  55 , pumps (not shown), light assemblies (not shown) within the merchandiser  45 , or other components of the merchandiser  45  that could provide a potential ignition source for the leaked refrigerant. As described in detail below, the control unit  165  controls the exhaust fans  137  and/or the blower  145  separately from the electronic components  170  so that the exhaust fans  137  or the blower  145 , or both, can operate when the electronic components  170  are shutdown or disabled to clear the flammable air-refrigerant mixture from the merchandiser  45 . 
         [0029]    With reference to  FIG. 6 , the control unit  165  is in communication with one or more spark-free alarm indicators  175  (e.g., lights, sound devices, etc.) to indicate one or more of the presence of refrigerant in the merchandiser  45 , a malfunctioning sensor  160 , and other parameters of the merchandiser  45 . For example, the alarm indicators  175  can be coupled to the case  100  within the product display area  65  to convey an alarm condition to people located adjacent the merchandiser  45 . Some or all of the alarm indicators  175  can also or alternatively be located remote from the merchandiser  45  (e.g., in a control room). 
         [0030]      FIG. 7  illustrates an exemplary control process that is programmed into the control unit  165  to control the merchandiser  45  and to indicate, as necessary, abnormal conditions associated with the merchandiser via the alarm indicators  175 . The control unit  165  determines whether the merchandiser  45  is powered on at step  200 . For example, the control unit  165  determines whether the secondary circuit  20  is circulating refrigerant and whether other components of the merchandiser  45  are operational and powered. If “No,” the control process again determines whether the merchandiser is powered on after a predetermined time has elapsed. If the control unit  165  determines the merchandiser  45  is on at step  200  (i.e. “Yes”), the control unit  165  determines at step  205  whether the sensor  160  is configured or present in the merchandiser  45 . If “No” at step  205 , the control unit  165  controls the merchandiser  45  based on normal operating conditions. In some constructions, the control process then returns to step  200  and repeats. 
         [0031]    If the sensor  160  is detected and installed for operation (i.e. “Yes” at step  205 ), the control process proceeds to step  215  to detect whether the sensor  160  has been configured for operation and that the sensor  160  is communicating with the control unit  165 . If “No” at step  215 , the control process determines whether a first predetermined time (e.g., 30 seconds) has elapsed at step  220 . If the first predetermined time has not elapsed (i.e. “No at step  220 ), the process returns to step  215  to again determine whether the sensor  160  has been configured. 
         [0032]    If the control unit  165  determines that the first predetermined time has elapsed and the sensor  160  is not configured properly, the control process proceeds to step  225  to de-energize the electrical/electronic components  170  of the merchandiser  45 . In some constructions, the control unit  165  also can concurrently or consecutively energize the fans  137  and/or the blower  145  at step  245  and activate the alarm indicators  175  at step  250  before returning to step  200  and repeating the control process. Generally, the control unit  165  initiates an alarm when an abnormal condition associated with the merchandiser  45  (e.g., detection of refrigerant in the air within the merchandiser  45 , a malfunctioning component such as the blower  145  or the sensor  160 , etc.) is detected, and the control unit  165  then operates the merchandiser  45  in a failsafe mode. 
         [0033]    In other constructions, the control process can proceed directly from step  225  to step  200  without energizing the fans  137  or the blower  145  and without activating the alarm indicators  175 . The electrical components  170  are de-energized or powered down to minimize the risk of igniting a flammable air-refrigerant mixture that may exist in the merchandiser  45 . The merchandiser  45  can be manually or automatically restarted at step  200  after the electrical components  170  have been de-energized, and in some cases after air in the case  100  has been cleared by the fans  137  or the blower  145 . 
         [0034]    Returning to step  215 , if the sensor  160  has been properly configured, the control process proceeds to step  230  to wait (e.g., 30 seconds, 60 seconds, 90 seconds, 5 minutes, etc.) until the sensor  160  is ready for use. When the sensor  160  is ready for use, the control process proceeds to step  235  to monitor data detected by the sensor  160 . In some constructions, the control process can be provided without steps  215  and/or  230 . That is, the control process can detect the presence of the sensor  160  at step  205  and, if the sensor  160  is detected, proceed directly to step  235 . 
         [0035]    At step  235 , the control process determines whether data detected by the sensor  160  is valid. Generally, sensor data is valid when the data is consistent or uniform relative to baseline data associated with the sensor  160  and/or the conditions in the merchandiser  45 . Stated another way, the sensor data is deemed invalid, for example, when a fault condition associated with the sensor  160  is detected by the control unit  165  (e.g., on the basis of data received or not received from the sensor  160 , the state of the sensor  160 , a disconnected or severed wire connected to or in the sensor  160 , etc.) after a period of time (e.g., 30 seconds, 60 seconds, etc.) has elapsed. Because the sensor  160 , in some constructions, can have complex circuitry and may include several components, determining whether sensed data is valid (i.e. indicative of the conditions in the merchandiser  45 ) can be useful when controlling the merchandiser  45  based on the sensed data. 
         [0036]    If the control unit  165  determines that the sensor data is invalid (i.e. “Yes” at step  235 ), the control unit  165  de-energizes the merchandiser  45  at step  225 , energizes the fans  137  and/or the blower  145  at step  245 , and activates the alarm indicators  175 , as necessary, as described above. If the control unit  165  determines that the sensor data is valid (i.e. “No” at step  235 , the control process proceeds to step  240  to determine whether the sensor  160  has detected a refrigerant-gas mixture that reaches or exceeds a predetermined value or threshold over a third predetermined time. That is, the control process determines at step  240  whether any refrigerant has leaked from the secondary circuit  20 , and whether the amount of leaked refrigerant creates a potential hazard. 
         [0037]    In particular, the control unit  165  determines whether the amount of refrigerant mixed with the air reaches a lower flammability limit (“LFL”) based on the type of refrigerant being used in the secondary circuit  20 . The LFL defines the lowest percentage threshold at which a gaseous refrigerant mixed with air becomes flammable. As described herein, the LFL is expressed as the threshold percentage of refrigerant that, when mixed with air, becomes flammable. For example, when propane is used as the second refrigerant, the LFL of a propane air-refrigerant mixture is approximately 2% by volume of refrigerant in the air. In other words, when the air-refrigerant mixture is comprised of approximately 2% propane by volume, the mixture is defined as a flammable mixture. 
         [0038]    The illustrated sensor  160  monitors the air within the merchandiser  45  (i.e. the sensor  160  is initiated to determine whether refrigerant is present in the air) every 3 seconds, although the sensor  160  can monitor the air continuously or at intervals shorter or longer than 3 seconds. With continued reference to  FIG. 7 , the illustrated control process determines whether the sensor  160  has detected a air-refrigerant mixture comprised of a quantity or volume of refrigerant that reaches a first predetermined percentage of the LFL (e.g., 25% of the LFL) for a predetermined time (e.g., 30 seconds, which equates to ten consecutive sensing cycles of the illustrated sensor  160 ), or a second predetermined percentage of the LFL (e.g., 50% of the LFL) for a predetermined time ( 6  seconds, which equates to two consecutive cycles of the sensor  160 ). Generally, the control process more quickly de-energizes the merchandiser  45  when the volume of refrigerant reaches a higher predetermined percentage of the LFL to avoid a scenario in which the volume of refrigerant reaches or exceeds 100% of the LFL and, as a result, the air-refrigerant mixture becomes flammable. 
         [0039]    In other constructions, the control unit  165  can control the merchandiser  45  based on a detected volume of refrigerant that reaches other predetermined percentages of the LFL (e.g., 10% of the LFL, 25% of the LFL, 33% of the LFL, 50% of the LFL, 60% of the LFL, 75%, 90%, etc.) for an associated period of time that is based on the likelihood the air-refrigerant mixture may become flammable. Generally, the amount of time that the merchandiser  45  is operational after detecting a volume of refrigerant in the air within the merchandiser  45  depends on the volume of refrigerant detected. 
         [0040]    When the control unit  165  determines at step  240  that 1) no refrigerant is detected by the sensor  160 , 2) the volume of refrigerant detected by the sensor  160  has not exceeded the first predetermined percentage of the LFL, or 3) the volume of refrigerant detected by the sensor  160  has not exceeded the first or second predetermined percentages of the LFL for the associated predetermined time, the control unit  165  proceeds to step  210  to control the merchandiser  45  based on normal operating conditions. Stated another way, the control unit  165  determines at step  240  that the merchandiser  45  can be operated normally because there is a minimal or no risk of flammability. 
         [0041]    If the control unit  165  determines at step  240  that a volume of refrigerant has been detected within the air in the merchandiser  45  (i.e. the air-refrigerant mixture has been detected) and that the refrigerant volume is at or has exceeded either the first predetermined percentage of the LFL or the second predetermined percent of the LFL for the associated predetermined time, the control unit proceeds to step  225  to de-energize the merchandiser  45 . The fans  137  and/or the blower  145  are energized to clear the air in the merchandiser  45 . In particular, the exhaust fans  137  dryer out of the case  100 , whereas the illustrated blower  145  pushes air into the case  100  to quickly clear the air-refrigerant mixture from the merchandiser  45 . The control unit  165  also initiates an alarm via the alarm indicators  175  at step  252  alert people adjacent the merchandiser  45 , and in some cases, people remote from the merchandiser  45 , that an alarm condition exists in the merchandiser  45 . The control process then proceeds to step  200  and repeats. 
         [0042]      FIG. 8  illustrates another exemplary control process for the system that, except as described below, is the same as the control process described with regard to  FIG. 7 . With reference to  FIG. 8 , if the control unit  165  determines at step  240  that the refrigerant volume is at or has exceeded either the first predetermined percentage of the LFL or the second predetermined percent of the LFL for the associated predetermined time, as described above, the control process proceeds to step  255  to determine whether an ignition source is present in or adjacent the merchandiser  45 . If no ignition source is detected (i.e. “No” at step  255 ), the control process proceeds to step  260  to energize the fans  137  or the blower  145  to assist with reducing or clearing the air-refrigerant mixture that is present in the case  100 . The control process then proceeds to step  210  to operate the merchandiser  45  normally before returning to step  200 . If the control unit  165  detects an ignition source (i.e. “Yes” at step  255 ), the control process proceeds to step  225  to de-energize the system as described above. 
         [0043]    In some constructions, the control unit  165  can activate one or both of the fans  137  and the blower  145  periodically, even when a flammable mixture is not detected in the merchandiser  45 , to remove debris that may accumulate in the blower  145  or to limit icing of the blower  145  due to cold air that may enter the blower  145  during inactivity. Also, other controls can be incorporated into the control unit  165  to operate the merchandiser  45  and to maintain the product display area  65  within normal operating conditions. 
         [0044]    Several secondary circuits  20  can be coupled together and cooled through the pump circuit  25  where the third refrigerant is cooled through the primary circuit  20  or external heat exchanger  90 . The closed secondary circuit  20  within each merchandiser  45  reduces the charge of hydrocarbon refrigerant in the merchandiser  45  without sacrificing cooling capacity for the product display area  65 . The risk of ignition in the merchandiser  45  is mitigated by minimizing the charge of the hydrocarbon refrigerant that is present in the secondary circuit  20 . Also, in the unlikely event that a air-refrigerant mixture ignites in one merchandiser  45 , the closed secondary circuit  20  assists with limiting any damage that may occur by isolating the ignition to that merchandiser  45 . As described with regard to  FIGS. 7 and 8 , the control unit  165  is programmed to control the merchandiser  45  based in part on the volume of refrigerant, if any, that is detected within the case  100  by shutting down at least some electrical components of the merchandiser  45 . The control unit  165  is further programmed to initiate one or more fans  137  or the blower  145  to expel the air-refrigerant mixture out of the merchandiser  45  and to initiate an alarm via the alarm indicators  175  so that people adjacent the merchandiser  45 , and possibly others, are aware that an ignition risk may exist. 
         [0045]    Various features and advantages of the invention are set forth in the following claims.