Abstract:
A method of controlling a refrigerated merchandiser. The method includes providing a case that defines a product display area and an air passage that has an inlet and an outlet, positioning an evaporator in the air passage to refrigerate the air, positioning a fan in the air passage to move the air through the passage, and logging a first temperature value during frost-free operation of the evaporator. The method also includes logging a second temperature value during frosted operation of the evaporator, calculating a difference of the first and second temperature values, and defrosting the evaporator when the difference exceeds a pre-determined value. Each of the first temperature value and the second temperature value is independently associated with at least one of the air entering the inlet of the air passage, the air exiting the outlet of the air passage, and saturated evaporator temperature.

Description:
RELATED APPLICATIONS 
   This patent application is a divisional application of U.S. patent application Ser. No. 11/176,072, filed Jul. 7, 2005, entitled “METHOD OF CONTROL FOR A REFRIGERATED MERCHANDISER,” the entire contents of which are hereby incorporated by reference. 

   FIELD OF THE INVENTION 
   This invention relates generally to merchandisers, and more particularly to refrigerated merchandisers. 
   BACKGROUND OF THE INVENTION 
   In conventional practice, supermarkets and convenience stores are equipped with refrigerated merchandisers, which may be open or provided with doors, for presenting refrigerated products like fresh food or beverages to customers while maintaining the fresh food and beverages in a refrigerated environment. Typically, cold, moisture-bearing air is provided to a product display area of the merchandiser by passing an airflow over the heat exchange surface of an evaporator coil containing a suitable refrigerant. As the airflow passes through the evaporator coil, heat is transferred from the airflow to the refrigerant, which causes the refrigerant to evaporate. As a result, the temperature of the air passing through the evaporator is lowered for introduction into the product display area of the merchandiser. 
   Typically, the temperature of the air discharged into the product display area is controlled to maintain a pre-determined set point. Such a set point is typically recommended by the manufacturer of the refrigerated merchandiser, and is typically based upon data accumulated during experimental trials. 
   SUMMARY OF THE INVENTION 
   In one construction, the present invention provides a method of controlling a refrigerated merchandiser. The method includes providing a case defining a product display area and an air passage having an inlet that receives air from the product display area and an outlet that delivers air to the product display area. The method also includes positioning an evaporator in the air passage to refrigerate the air and positioning a fan in the air passage to move the air through the passage. The method further includes logging a first temperature value during frost-free operation of the evaporator, the first temperature value associated with at least one of the air entering the inlet of the air passage, the air exiting the outlet of the air passage, and saturated evaporator temperature, and logging a second temperature value during frosted operation of the evaporator, the second temperature value associated with at least one of the air entering the inlet of the air passage, the air exiting the outlet of the air passage, and saturated evaporator temperature. The method also includes calculating a difference of the first and second temperature values and defrosting the evaporator when the difference exceeds a pre-determined value. 
   Other features and aspects of the present invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a refrigerated merchandiser of the present invention incorporating multiple wired product simulators positioned in a product display area of the merchandiser. 
       FIG. 2  is a cross-sectional view of the refrigerated merchandiser of  FIG. 1 , incorporating multiple wireless product simulators positioned in the product display area of the merchandiser. 
       FIG. 3  is a graph illustrating a method of control for the refrigerated merchandiser of  FIG. 1 . 
       FIG. 4  is a graph illustrating another method of control for the refrigerated merchandiser of  FIG. 1 . 
       FIG. 5  is a graph illustrating yet another method of control for the refrigerated merchandiser of  FIG. 1 . 
       FIG. 6  is a graph illustrating another method of control for the refrigerated merchandiser of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Before any features 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 arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including”, “having”, and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of letters to identify elements of a method or process is simply for identification and is not meant to indicate that the elements should be performed in a particular order. 
   A refrigerated merchandiser  10  of the present invention is shown in  FIGS. 1 and 2 . With reference to  FIG. 1 , the merchandiser  10  includes a case  14  generally defining an interior bottom wall or shelf  18 , an interior rear wall  22 , and an interior top wall  26 . The area bounded by the interior bottom wall  18 , interior rear wall  22 , and the interior top wall  26  defines a product display area  30 , in which the refrigerated products (e.g., fresh food and/or beverages) are stored on one or more shelves  32 . The case  14  includes an open front face to allow customers access to the refrigerated products stored in the case  14 . 
   The merchandiser  10  may comprise a medium-temperature merchandiser, in which the food product temperature in the display area  30  is maintained within a standard temperature range of 28° F. to 41° F. Such merchandisers  10  may include, for example, meat merchandisers, deli and dairy merchandisers, and produce merchandisers. Alternatively, the merchandiser  10  may comprise a low-temperature merchandiser, in which the food product temperature in the display area  30  is maintained at a temperature below 28° F. Such a merchandiser  10  may include, for example, a frozen food merchandiser. 
   The merchandiser  10  may be comprised of two interconnected modules (not shown). Each module may include a case  14  having its own set of refrigeration components (e.g., an evaporator  70  and one or more fans  66 ). The separate modules may be interconnected by decorative or structural moldings to give the appearance of a single merchandiser  10 . In addition, the separate modules may be interconnected to give the appearance of a single product display area  30 . Alternatively, the merchandiser  10  may comprise a single module, or the merchandiser  10  may comprise more than two interconnected modules. For purposes of description only, a single merchandiser module is described herein. 
   The case  14  generally defines an exterior bottom wall  34  adjacent the interior bottom shelf  18 , an exterior rear wall  38  adjacent the interior rear wall  22 , and an exterior top wall  42  adjacent the interior top wall  26 . A lower flue  46  is defined between the interior bottom shelf  18  and the exterior bottom wall  34  to allow for substantially horizontal airflow throughout the lower flue  46 . The interior bottom shelf  18  includes an opening  50  to communicate with the lower flue  46  to allow surrounding air to be drawn into the lower flue  46  from the product display area  30 . A rear flue  54  is defined between the interior and exterior rear walls  22 ,  38  and is fluidly connected with and adjacent to the lower flue  46 . The rear flue  54  allows for substantially vertical airflow throughout the rear flue  54 . An upper flue  58  is defined between the interior and exterior top walls  26 ,  42  and is fluidly connected with and adjacent to the rear flue  54 . The upper flue  58  allows for substantially horizontal airflow throughout the upper flue  58 . The interior top wall  26  includes an opening  62  to communicate with the upper flue  58  to allow airflow in the upper flue  58  to be discharged from the upper flue  58  and into the product display area  30 . When combined, the lower flue  46 , the rear flue  54 , and the upper flue  58  comprise an air passage separate from the product display area  30 , in which the opening  50  provides an inlet to the air passage and the opening  62  provides an outlet for the air passage. 
   The refrigerated merchandiser  10  also includes some components of a refrigeration system (not entirely shown) therein. One or more fans  66  are located within the lower flue  46  toward the back of the case  14  to generate an airflow through the lower, rear, and upper flues  46 ,  54 ,  58 . An evaporator coil or evaporator  70  is located within the rear flue  54  toward the bottom of the case  14 . The evaporator  70  is positioned downstream of the fans  66  such that the airflow generated by the fans  66  passes through the evaporator  70 . The refrigeration system may also include other components (not shown), such as one or more compressors, one or more condensers, a receiver, and one or more expansion valves, all of which may be remotely located from the refrigerated merchandiser  10 . 
   With continued reference to  FIG. 1 , the interior rear wall  22  includes a plurality of apertures  74 . The apertures  74  fluidly connect the product display area  30  and the rear flue  54 . The apertures  74  allow some of the refrigerated air in the rear flue  54  to exit the rear flue  54  and enter the product display area  30 . Products located in the product display area  30  may then be cooled by the refrigerated air. 
   A portion of the refrigerated air is routed vertically through the rear flue  54 , and horizontally through the upper flue  58  before being discharged from the upper flue  58  via the opening  62  in the interior top wall  26 . After being discharged from the opening  62  in the interior top wall  26 , the refrigerated air moves downwardly along the open front face of the refrigerated merchandiser  10  before being drawn back into the opening  50  in the interior bottom wall  18  for re-use by the fans  66 . This portion of the refrigerated airflow is known in the art as an air curtain  78 . The air curtain  78 , among other things, helps maintain the air temperature in the product display area  30  within a temperature range determined by the products in the merchandiser  10 . 
   With continued reference to  FIG. 1 , a first product simulator  82  is positioned on the interior bottom shelf  18  adjacent the opening  50  or adjacent the inlet to the air passage. In this position, the first product simulator  82  receives refrigerated air that is returning to the lower flue  46 , which is typically the “warmest” refrigerated air in the case  14  because it has absorbed heat from products in the product display area  30  and has undergone some mixing with the ambient air outside the product display area  30 . In other words, products positioned on the interior bottom shelf  18  adjacent the opening  50  are located in the “highest temperature zone” of the product display area  30 . 
   Likewise, a second product simulator  86  is positioned on a shelf  32  adjacent the interior rear wall  22 . In this position, the second product simulator  86  receives refrigerated air discharged from the rear flue  54 , which is typically the “coolest” refrigerated air in the case  14  because it has not yet absorbed any heat from products in the product display area  30 . In other words, products positioned adjacent the interior rear wall  22  on the shelves  32  are located in the “lowest temperature zone” of the product display area  30 . 
   The first and second product simulators  82 ,  86  can each include a thermal mass (not shown) to approximate the thermal characteristics of products typically positioned in the respective highest and lowest temperature zones. The first and second product simulators  82 ,  86  can also each include a temperature probe or sensor  90  to detect the temperatures of the respective thermal masses, which approximate the actual temperature of the products positioned in the respective highest and lowest temperature zones. The first and second product simulators  82 ,  86  can be similar to those disclosed in U.S. Pat. No. 6,502,409, the entire contents of which is incorporated herein by reference. 
   Other temperature sensors can be incorporated into the refrigerated merchandiser  10 . With continued reference to  FIG. 1 , an inlet temperature sensor  94  is positioned in the lower flue  46  of the air passage to detect the temperature of the refrigerated air returning to the lower flue  46 . In the illustrated construction, the inlet temperature sensor  94  is positioned in the lower flue  46  downstream of the fan  66 . However, in alternate constructions, the inlet temperature sensor  94  may be positioned anywhere in the lower flue  46 . In addition, an outlet temperature sensor  98  is positioned in the upper flue  58  of the air passage to detect the temperature of the refrigerated air discharged from the upper flue  58 . In the illustrated construction, the outlet temperature sensor  98  is positioned adjacent the opening  62  or adjacent the outlet to the air passage. However, in alternate constructions, the outlet temperature sensor  98  may be positioned anywhere in the upper flue  58 . Further, a saturated evaporator temperature sensor  102  is tube-mounted to the evaporator  70  to detect the saturated evaporator temperature. An ambient temperature sensor (not shown) can also be incorporated into the refrigerated merchandiser  10  to detect the store ambient temperature. 
   The product simulators  82 ,  86  and the temperature sensors  94 ,  98 ,  102  all communicate with a controller  106 , which can be incorporated into the refrigerated merchandiser  10  or positioned remotely from the merchandiser  10 . The product simulators  82 ,  86  output to the controller  106  respective first and second signals representative of the temperatures of products positioned in the highest and lowest temperature zones, respectively. Similarly, the inlet temperature sensor  94 , outlet temperature sensor  98 , and saturated evaporator temperature sensor  102  output to the controller  106  an inlet temperature signal, an outlet temperature signal, and a saturated evaporator temperature signal, respectively, representative of the inlet temperature of the refrigerated air, the outlet temperature of the refrigerated air, and the saturated evaporator temperature. As shown in  FIG. 1 , the signals are transmitted to the controller  106  via a plurality of wires  110 . Alternatively, as shown in  FIG. 2 , each product simulator  82 ,  86  and temperature sensor  94 ,  98 ,  102  can include a wireless transmitter  114  and the controller  106  can include a wireless receiver  118  to transmit the signals wirelessly. 
   With reference to  FIG. 1 , a computer  122  can be used to interface with the controller  106  to modify the settings of the controller  106 . Like the controller  106 , the computer  122  can be incorporated into the merchandiser  10  or positioned remotely from the merchandiser  10 . The computer  122  and controller  106  can communicate using wires  110 , or the computer  122  and controller  106  can communicate wirelessly, as shown in  FIG. 2 . Alternatively, a computer separate from the controller  106  may not be required. 
   The combination of the product simulators  82 ,  86 , temperature sensors  94 ,  98 ,  102 , and the controller  106  allows the merchandiser  10  to utilize a control scheme that adapts the merchandiser  10  to its environment. More particularly, the controller  106  can interface with the product simulators  82 ,  86  and the refrigeration components of the merchandiser  10  to ensure that the temperature of each product simulator  82 ,  86 , and thus the temperature of the actual products positioned in the highest and lowest temperature zones, are maintained within a pre-determined temperature range (e.g., between 32° F. and 41° F. for a medium-temperature merchandiser). 
   The control scheme programmed into the controller  106  can include a “fast” portion which is responsible for maintaining the outlet temperature of refrigerated air discharged from the upper flue  58  at a desired set point. Corrections to maintain the outlet temperature can be made about every few seconds of operation of the merchandiser  10 . More particularly, corrections to maintain the outlet temperature can be made about every 1 to 3 seconds of operation of the merchandiser  10 . Alternatively, corrections to maintain the outlet temperature can be made more or less frequently than about every 1 to 3 seconds of operation of the merchandiser  10 . 
   To make corrections to the outlet temperature, the controller  106  receives the outlet temperature signal from the outlet temperature sensor  98 , and compares the “actual” outlet temperature associated with the outlet temperature signal with the pre-determined outlet temperature set point. If, for example, the actual outlet temperature is greater than the outlet temperature set point, the controller  106  can manipulate the refrigeration components of the merchandiser  10  to provide “more” refrigeration to further cool the air in the rear and upper flues  54 ,  58 . Likewise, if the actual outlet temperature is less than the outlet temperature set point, the controller  106  can manipulate the refrigeration components of the merchandiser  10  to provide “less” refrigeration to conserve energy. Although not shown in either of  FIG. 1  or  2 , the controller  106  can interface with, for example, a liquid solenoid valve (not shown) to control the flow of refrigerant through the evaporator  70  to provide more or less refrigeration to the product display area  30 . Alternatively, the controller  106  can interface with a variable speed compressor, an electronic expansion valve (“EEV”), or an electronic evaporator pressure regulating (“EEPR”) valve (not shown) to provide more or less refrigeration to the product display area  30 . Further, variable-speed fans  66  can be used to increase the flow of the refrigerated air through the rear and upper flues  54 ,  58 , effectively providing more or less refrigeration to the product display area  30 . 
   The control scheme programmed into the controller  106  can also include a “slow” portion which is responsible for periodically adjusting the outlet temperature set point. Adjustments to the outlet temperature set point can be made about every few hours of operation of the merchandiser  10 . More particularly, adjustments to the outlet temperature set point can be made about every 1 to 2 hours of operation of the merchandiser  10 . Alternatively, adjustments to the outlet temperature set point can be made more or less frequently than about every 1 to 2 hours of operation of the merchandiser  10 . 
   Adjusting the outlet temperature set point can be a desirable feature of the merchandiser  10  because it allows the merchandiser  10  to make corrections for outside factors influencing the temperature of the products in the product display area  30 . For example, in an instance when the ambient temperature in a retail store is unusually warm, drafts of the warm air may enter the product display area  30  and warm-up the products to a temperature higher than their pre-determined acceptable temperature range. Such a scenario is illustrated in  FIG. 3 .  FIG. 3  illustrates a graph comparing the temperatures of the product simulators  82 ,  86  versus time. Line (“T ps(1) ”) represents the temperature of the first product simulator  82 , while line (“T ps(2) ”) represents the temperature of the second product simulator  86 . The time axis (“t”) is situated along the X-axis of the graph, and includes two occurrences of adjusting the outlet temperature set point. The period of time between adjustments represents about every 1-2 hours of operation of the merchandiser  10 , as discussed above. The product simulator temperature axis (“T ps ”) is situated along the Y-axis of the graph. An example pre-determined acceptable temperature range (“T r ”) for products in the product display area  30  is also shown. 
   Before the first adjustment (“Adj 1 ”), the outlet temperature set point (shown as line S 1 ) may initially be in the middle of temperature range T r . However, for example, due to the outside factors discussed above, the actual temperature of the first product simulator  82  (indicated by line T ps(1) ) and the products in the highest temperature zone of the product display area  30  may be higher than the temperature range T r . Points P 1  and P 2  indicate the temperatures of the first and second product simulators  82 ,  86 , respectively, at the end of one 1-2 hour time period between adjustments. To make an adjustment to the outlet temperature set point, the controller  106  receives the first signal from the first product simulator  82  and the second signal from the second product simulator  86 , and compares the “actual” product temperatures associated with the first and second signals with the pre-determined temperature range T r . If one of the actual product temperatures is outside of the temperature range T r , the controller  106  can make an adjustment to the outlet temperature set point to bring the actual product temperature back inside the temperature range T r . 
   In the example illustrated in  FIG. 3 , the outlet temperature set point is lowered from S 1  to S 2  in an effort to lower the actual temperature of the first product simulator  82  and the actual temperature of other products situated in the highest temperature zone. For purposes of example only, the lowered outlet temperature set point S 2  may be too large of a change and cause the actual temperature of the second product simulator  86  (indicated by line T ps(2) ) to drop below the temperature range T r . Then, at the second adjustment (“Adj 2 ”), the controller  106  can again receive the signals from the product simulators  82 ,  86  at points P 3  and P 4 , and raise the outlet temperature set point from S 2  to S 3  in an effort to conserve energy and bring both temperature lines T ps(1)  and T ps(2)  within temperature range T r . If, when the time comes to make the third adjustment, the actual temperatures of the product simulators  82 ,  86  are within the temperature range T r , then no adjustment to the outlet temperature set point may be made. 
   The control scheme programmed into the controller  106  can further include a “slowest” portion which is responsible for adjusting the defrost schedule of the merchandiser  10 . Adjustments to the defrost schedule can be made about every 6 to 24 hours of operation of the merchandiser  10 . Alternatively, adjustments to the defrost schedule can be made more or less frequently than about every 6 to 24 hours of operation of the merchandiser  10 . Adjusting the defrost schedule can be a desirable feature of the merchandiser  10  because extending the time period between defrost cycles, when temperature conditions in the product display area  30  permit, can lessen the shock on the products in the product display area  30 . In other words, subjecting the products to repeated display case defrost cycles can damage the products. Such a scenario is illustrated in  FIG. 4 .  FIG. 4  illustrates a graph comparing, for example, the inlet temperature of the air returning to the lower flue  46  versus time. The time axis (“t”) is situated along the X-axis of the graph, and includes a first mark (“D off ”) indicating the end of a first defrost cycle, and a second mark (“D on ”) indicating the beginning of a second defrost cycle. The period of time (“t def ”) between the marks represents about every 6-24 hours of operation of the merchandiser  10  between defrost cycles, as discussed above. The temperature axis (“T”) is situated along the Y-axis of the graph, and line (“T in ”) represents the inlet temperature of the air returning to the lower flue  46 . 
   To make an adjustment to the defrost schedule, or an adjustment of the time t def  between defrost cycles, the controller  106  logs a first temperature value (“T 1 ”) during “frost-free” operation of the evaporator  70 , and a second temperature value (“T 2 ”) during “frosted” operation of the evaporator  70 . The evaporator  70  may operate at its optimal efficiency (i.e., without any built-up frost) for up to about one to three hours after a defrost cycle. Such frost-free operation is indicated by region (“FF”) in  FIG. 4 . After frost begins to build-up on the evaporator  70 , the evaporator  70  may operate at less than its optimal efficiency. Such frosted operation is indicated by region (“FR”) in  FIG. 4 . 
   The controller  106  may log the first temperature value T 1 , between about one to three hours after a defrost cycle, such that the first temperature value T 1  is representative of the evaporator  70  operating at its optimal efficiency (i.e., without built-up frost). After the first temperature value T 1  is logged, the controller  106  may be programmed to continuously monitor or log at discrete time intervals the value of the inlet temperature of the air returning to the lower flue  46  (represented by “T n ”). For each subsequent time interval, the controller  106  may be programmed to calculate the difference between temperature value T n  and the first temperature value T 1 . If the difference is larger than some pre-determined value, and a defrost cycle has not yet begun (i.e., if T n =T 2 ), then the controller  106  can decrease the time t def  between defrost cycles to ensure that built-up frost and ice are adequately removed from the evaporator  70 . However, if the calculated difference is less than the pre-determined value at the beginning of a scheduled defrost cycle (i.e., at D on ), then the controller  106  can increase the time t def  between defrost cycles to lessen shock on the products in the product display area  30 . 
   The controller  106  may also be configured to activate a defrost cycle when the calculated difference exceeds the pre-determined value. With reference to  FIG. 4 , the controller  106  may log the first temperature value T 1  in the frost-free operating region FF of the evaporator  70  and the second temperature value T 2  in the frosted operating region FR of the evaporator  70 . The controller  106  may calculate the difference between the first and second temperature values T 1 , T 2  and compare the calculated difference (T 2 −T 1 ) to the pre-determined value (e.g., two degrees). If the calculated difference (T 2 −T 1 ) is greater than the pre-determined value, then the controller  106  may initiate a defrost cycle. Likewise, if the calculated difference (T 2 −T 1 ) is less than the pre-determined value, then the controller  106  may continue monitoring or logging the inlet temperature T n  until the calculated difference (T 2 −T 1 ) exceeds the pre-determined value. 
   Alternatively, rather than logging the inlet temperature T n  of the air returning to the lower flue  46 , the controller  106  may continuously monitor or log the difference between the outlet temperature (“T out ”) of the air discharged from the upper flue  58  and the inlet temperature T in  of the air returning to the lower flue  46 .  FIG. 5  illustrates a graph of line (T in −T out ), which is representative of the difference between the outlet temperature T out  of the air discharged from the upper flue  58  and the inlet temperature T in  of the air returning to the lower flue  46 . As the time D on  to begin the second scheduled defrost cycle approaches, the difference between the temperatures T in  and T out  increases as a result of frost accumulating on the evaporator  70 . Specifically, built-up frost on the evaporator  70  reduces the velocity of the air moving through the evaporator  70 , therefore decreasing the effectiveness of the air curtain  78  and increasing the inlet temperature T in  of the air returning to the lower flue  46 . Using a similar method as described above, the controller  106  may calculate the difference between (T in −T out ) 2  and (T in −T out ) 1  to determine whether the defrost schedule should be adjusted or whether a defrost cycle should be initiated. 
   In addition, the controller  106  may continuously monitor or log the difference between the saturated evaporator temperature (“T sat ”) and the inlet temperature T in  of the air returning to the lower flue  46  to determine whether the defrost schedule should be adjusted or whether a defrost cycle should be initiated, using a similar method as described above.  FIG. 6  illustrates a graph of line (T in −T sat ), which is representative of the difference between the inlet temperature T in  of the air returning to the lower flue  46  and the saturated evaporator temperature T sat . As the time D on  to begin the second scheduled defrost cycle approaches, the difference between the temperatures T in  and T sat  increases as a result of frost accumulating on the evaporator  70 . As discussed above, built-up frost on the evaporator  70  reduces the velocity of the air moving through the evaporator  70 , therefore decreasing the effectiveness of the air curtain  78  and increasing the inlet temperature T in  of the air returning to the lower flue  46 . Further, the controller  106  can compare the ambient temperature, relative humidity, or dew point of the merchandiser&#39;s surroundings with similar pre-determined values to determine whether the defrost schedule should be adjusted or whether a defrost cycle should be initiated. 
   Rather than comparing the calculated values (T 2 −T 1 ), (T in −T out ) 2 −(T in −T out ) 1 , and (T in −T sat ) 2 −(T in −T sat ) 1  with a single pre-determined value, t he controller  106  can compare the calculated values with a range of pre-determined acceptable values. If the calculated values fall within the range of acceptable values, then no adjustments to the defrost schedule may be made. 
   Various features of the invention are set forth in the following claims.