Control System For A Refrigerated Merchandiser

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.

Claims

1. A method of controlling a refrigerated merchandiser, the method comprising: 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.

2. The method of claim 1, further comprising de-energizing electrical components of the merchandiser in response to detecting the presence of an air-refrigerant mixture.

3. The method of claim 2, further comprising activating the fan and de-energizing the electrical components in response to the detected air-refrigerant mixture reaching a predetermined threshold.

4. The method of claim 1, further comprising activating an alarm in response to detecting the air-refrigerant mixture.

5. The method of claim 3, wherein the refrigerant is a hydrocarbon refrigerant, and wherein the predetermined threshold is approximately 25% of a lower flammability limit of the hydrocarbon refrigerant.

6. The method of claim 1, wherein at least partially evacuating the interior includes blowing air into the interior from outside the merchandiser.

7. The method of claim 1, further comprising determining a presence of an ignition source prior to activating the fan.

8. A method of controlling a refrigerated merchandiser, the method comprising: refrigerating a product display area of the merchandiser using a refrigerant; detecting a presence of an air-refrigerant mixture in the refrigerated merchandiser; initiating an action in response to the detected air-refrigerant mixture reaching a predetermined threshold relative to a lower flammability limit of the refrigerant. at least one of activating a fan and de-energizing one or more electrical components of the merchandiser in response to the detected air-refrigerant mixture reaching a predetermined threshold relative to a lower flammability limit of the refrigerant

9. The method of claim 8, wherein initiating an action includes at least one of activating a fan, de-energizing one or more electrical components of the merchandiser, and activating an alarm.

10. The method of claim 9, further comprising de-energizing the one or more components; activating the fan after the one or more components are de-energized; and at least partially evacuating an interior of the merchandiser of the detected air-refrigerant mixture in response to fan activation.

11. The method of claim 8, further comprising determining a presence of an ignition source prior to initiating the action.

12. The method of claim 11, further comprising activating a fan to clear an interior of the merchandiser of the detected air-refrigerant mixture regardless of whether an ignition source is detected.

13. The method of claim 8, further comprising determining whether a predetermined time has elapsed after detecting the presence of the air-refrigerant mixture reaching the predetermined threshold before initiating the action.

14. A refrigerated merchandiser comprising: a case defining a product display area; a refrigeration system including an evaporator coupled to the case and through which a hydrocarbon refrigerant is circulated to condition the product display area; a sensor 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; and a controller 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.

15. The refrigerated merchandiser of claim 14, wherein the controller is in communication with at least one of 1) a fan to clear an interior of the merchandiser of the detected air-refrigerant mixture, 2) one or more electrical components of the merchandiser to selectively de-energize the components, and 3) an alarm indicator to signal the presence of an air-refrigerant mixture in the merchandiser.

16. The refrigerated merchandiser of claim 15, wherein the controller is programmed to activate the fan after the one or more electrical components are de-energized.

17. The refrigerated merchandiser of claim 14, wherein the controller is programmed to initiate the action after a predetermined time has elapsed.

18. The refrigerated merchandiser of claim 14, wherein the predetermined threshold is approximately 25% of the lower flammability limit.

19. The refrigerated merchandiser of claim 14, wherein the controller is further programmed to determine the presence of an ignition source prior to initiation of the action.

20. The refrigerated merchandiser of claim 19, wherein the controller is programmed to activate a fan to clear an interior of the merchandiser of the detected air-refrigerant mixture regardless of whether the presence of an ignition source is detected.