Abstract:
A method and apparatus for operating a discharge cooling cycle in a refrigeration system. The method includes determining a first operating condition of the refrigeration system. The method also includes, based on the determination of the operating condition, activating an evaporator fan for a first predetermined period of time, deactivating the evaporator fan for a second predetermined period of time, and repeating the activating and deactivating until a second operating condition is detected.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY 
       [0001]    The present application claims priority to commonly assigned U.S. Provisional Patent Application No. 61/343,472, filed Apr. 29, 2010, entitled “DISCHARGE COOLING”, which is hereby incorporated by reference into the present application as if fully set forth herein. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure is generally directed to refrigerated vending machines and more particularly to an apparatus and method to control a discharge gas temperature to prevent premature compressor failure. 
       BACKGROUND 
       [0003]    During operation of a refrigeration system of a refrigerated vending machine, changes in the environment inside or outside of the vending machine may cause the compressor in the system to become too hot. When the compressor overheats, the compressor may burn out, crack a valve head, or otherwise be damaged. Even if the compressor is not damaged, an overheated compressor impedes the heat: transfer by the cooling system from products contained within the vending machine. This reduced heat transfer may increase operating costs, decrease efficiency, and reduce product cooling. 
       SUMMARY 
       [0004]    According to one embodiment of the present disclosure, a method of operating a refrigeration system includes determining a first operating condition of the refrigeration system. The method also includes, based on the determination of the first operating condition, activating an evaporator fan for a first predetermined period of time, deactivating the evaporator fan for a second predetermined period of time, and repeating the activating and deactivating until a second operating condition is detected. 
         [0005]    In another embodiment, an apparatus includes a refrigeration system that includes a compressor and an evaporator fan. The apparatus also includes a controller communicatively coupled to the refrigeration system. The controller is configured to determine a first operating condition of the refrigeration system. The controller is also configured, based on the determination of the first operating condition, to activate the evaporator fan for a first predetermined period of time, deactivate the evaporator fan for a second predetermined period of time, and repeat the activation and deactivation until a second operating condition is detected. 
         [0006]    In still another embodiment, a vending machine includes a product storage area and a refrigeration system that includes a compressor and an evaporator fan, the refrigeration system configured to cool the product storage area. The vending machine also includes a controller communicatively coupled to the refrigeration system. The controller is configured to determine a first operating condition of the refrigeration system. Based on the determination of the first operating condition, the controller is also configured to activate the evaporator fan for a first predetermined period of time, deactivate the evaporator fan for a second predetermined period of time, and repeat the activation and deactivation until a second operating condition is detected. 
         [0007]    Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions and claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    For a more complete understanding of this disclosure and its features, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1  illustrates a block diagram of a vending machine according to an embodiment of the disclosure; 
           [0010]      FIG. 2  is a state diagram of refrigeration control of a vending machine according to an embodiment of the disclosure; and 
           [0011]      FIG. 3  depicts a method of using a discharge cooling cycle according to an embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIGS. 1 through 3 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged vending machine. 
         [0013]    The present disclosure provides a method and apparatus to control operation of an evaporator fan in a refrigeration system of an appliance such as a vending machine. The method and apparatus according to this disclosure offers many advantages. For example, the apparatus allows for greater flexibility, reliability, and efficiency of the refrigeration system. Also, the apparatus protects the compressor by maintaining the compressor at a stable temperature. Moreover, the apparatus may be used to enhance the energy efficiency of the evaporator. 
         [0014]    In many refrigeration systems, the evaporator is the source of the chilled air used to cool the interior of the system. Often, the evaporator resembles a radiator in physical appearance. The evaporator uses a liquid refrigerant to lower the temperature of the chilled air as described herein. 
         [0015]    When the liquid refrigerant leaves a small capillary tube, the refrigerant is injected into one or more larger tubes of the evaporator, thus causing a pressure drop. This pressure drop allows the refrigerant to expand into a gaseous state. This change of state from liquid to gas absorbs heat, thus lowering the temperature of the refrigerant. The cooled, gaseous refrigerant travels through the evaporator tubes. Air circulates across the cooled evaporator tubes, thus lowering the temperature of the air. The refrigerant then passes out of the evaporator and to the compressor to begin the circulation process again. 
         [0016]    One problem encountered in refrigeration systems is how to maintain the compressor at a suitable operating temperature. Chilled suction gas returning to the compressor from the evaporator helps to cool the compressor. However, too much air exchange at the evaporator may raise the temperature of the suction gas, thus reducing its cooling ability. This can cause the compressor to overheat. 
         [0017]    Disclosed are methods and apparatus used to cycle the evaporator fan in order to control the temperature of the suction gas returning to the compressor. By controlling the temperature of the suction gas, the system keeps the compressor temperature stable, thus protecting the compressor from excessive wear or damage. 
         [0018]    Prior methods of protecting the compressor rely on excessive amounts of condensing capacity that is only used under extreme conditions. In accordance with the disclosed methods and apparatus, regardless of the condition, the compressor is protected during abusive periods of operation, e.g. when the condenser gets dirty, if a large quantity of hot products are loaded in the vending machine, or if the ambient temperature outside the vending machine exceeds normal limits. 
         [0019]      FIG. 1  illustrates a block diagram of a vending machine according to an embodiment of the disclosure. The vending machine  100  includes a vending machine controller (VMC)  102  that operates to control functions of the vending machine  100 . Such functions include vending, payment, and refrigeration functions. 
         [0020]    The vending machine  100  includes a temperature probe  104  that is communicatively coupled to the VMC  102 . The temperature probe  104  is located in a position within the vending machine  100  that enables the temperature probe  104  to sense a temperature that is representative of either the temperature of products stored in the vending machine  100 , the temperature of the air inside the cooled portion of the vending machine  100 , or both. For example, such a location may be in a product compartment of the vending machine  100  in which products are stored, or in a return air duct for air returning from the compartment to be chilled. 
         [0021]    The vending machine  100  also includes a refrigeration system  106  that controls the temperature of the product compartment of the vending machine  100 , in which products are stored. In the refrigeration system  106 , a refrigerant is compressed in a compressor  108 . The compressed refrigerant is cooled in condenser coils and then passes through an expansion device. The low pressure refrigerant flows through evaporator coils before returning to the compressor. An evaporator fan  110  pulls air from the product compartment over the evaporator coils and pushes chilled air back into the product compartment. The compressor  108  and the evaporator fan  110  are communicatively coupled to the VMC  102 , which controls their operation. In some embodiments, the temperature probe  104  is located in a position that that enables the temperature probe  104  to sense a temperature of the evaporator coils. 
         [0022]    Typically, the product compartment of the vending machine  100  is accessible via a door for restocking products. The vending machine  100  further includes a door sensor  112  communicatively coupled to the VMC  102 . The door sensor  112  provides an indication of whether the door is open or closed. 
         [0023]    Although  FIG. 1  depicts one example of a vending machine  100 , various changes may be made to  FIG. 1 . For example, in some embodiments, the control functions of the VMC  102  may be implemented in a single microcontroller or microprocessor. In other embodiments, the control functions of the VMC  102  may be distributed across a plurality of microcontrollers or microprocessors. 
         [0024]      FIG. 2  illustrates a state diagram  200  of refrigeration control by a vending machine controller (e.g., the VMC  102 ) of a vending machine according to an embodiment of the disclosure. Often, the door that provides restocking access to the product compartment of the vending machine  100  comprises an entire sidewall or front of the compartment. As a result, a significant quantity of chilled outside air can enter the compartment when the door is opened. 
         [0025]    The introduction of outside air and unchilled products to the product compartment during restocking may cause the temperature within the compartment to rise. Similarly, when power is turned off to the vending machine  100 , the refrigeration system  106  stops functioning and the temperature within the product compartment increases. This state is illustrated in  FIG. 2  as a Door Open/Power Off state  202 . From any state of the state diagram  200 , when the door is opened, the VMC  102  enters the Door Open/Power Off state  202 . Similarly, when power to the vending machine is interrupted, the VMC  102  enters the Door Open/Power Off state  202 . 
         [0026]    When the door is closed or the power is turned back on, the vending machine  100  enters one of two modes during which the VMC  102  operates the refrigeration system  106  to quickly bring the temperature within the product compartment to a desired operating temperature. 
         [0027]    When the door sensor  112  indicates that the door is closed, the VMC  102  moves from state  202  to either a Reload state  204  or a Pulldown state  206 , according to an initial temperature in the product compartment, as sensed by the temperature probe  104 . In the exemplary embodiment, if the initial temperature is less than 73 degrees Fahrenheit, the state of VMC  102  changes to the Reload state  204 . If the initial temperature is greater than or equal to 73 degrees Fahrenheit, the state of VMC  102  changes to the Pulldown state  206 . 
         [0028]    In both the Reload state  204  and the Pulldown state  206 , the VMC  102  controls the refrigeration system  106 , including controlling the compressor  108  and the evaporator fan  110 , which are explained in more detail below. In either the Reload state  204  or the Pulldown state  206 , if the VMC  102  determines that the temperature probe  104  has reached a predetermined temperature set point, the state of the VMC  102  changes to a Steady State Temperature state  208 . During the Steady State Temperature state  208 , the VMC  102  controls the refrigeration system  106 , including the compressor  108  and the evaporator fan  110 . 
         [0029]    In some embodiments, the predetermined temperature set point is 35 degrees Fahrenheit. In other embodiments, the predetermined temperature set point is 37 degrees Fahrenheit. While particular predetermined temperature set points have been described, it will be understood that in still other embodiments, other predetermined temperature set points may be utilized. In yet other embodiments, the predetermined temperature set point is set by an operator of the vending machine  100 . 
         [0030]    Although  FIG. 2  depicts one example of a state diagram of refrigeration control of a vending machine, various changes may be made to the control flow. For example, in some embodiments, the state diagram  200  may include more or fewer states. In some embodiments, the various states may be arranged in a different order or triggered by other temperature points. 
         [0031]    In both the Reload state  204  and the Pulldown state  206 , the compressor  108  may operate continuously or may operate with duty cycles having brief “off” periods. When the compressor  108  operates continuously or with few breaks, the compressor  108  may have a tendency to overheat. To avoid or mitigate overheating at the compressor  108 , the condensing temperature of the vapor coming out of the compressor  108  (also referred to as the discharge gas temperature) is preferably monitored with one or more sensors. When the condensing temperature (discharge gas temperature) is sensed to be rising and reaching an unacceptable level, this can indicate that the compressor  108  is overheated or is in danger of overheating. 
         [0032]    In accordance with embodiments of the present disclosure, a discharge cooling cycle is used to maintain the compressor  108  at a suitable operating temperature. The discharge cooling cycle reduces the time that the evaporator fan  110  operates. In many refrigeration systems, the evaporator fan operates roughly in coordination with the compressor. Thus, whenever the compressor operates, the evaporator fan normally also operates. However, in the discharge cooling cycle disclosed herein, the evaporator fan  110  can be deactivated during periods when the compressor  108  is operating. Shutting off the evaporator fan  110  allows the compressor  108  to cool down and keep the discharge gas temperature within approved guidelines. By stopping the evaporator fan  110 , the evaporator runs at a colder temperature and the return gas to the compressor  108  should be at a lower temperature, in turn cooling the compressor  108  and reducing the discharge gas temperature. 
         [0033]    In one embodiment of the discharge cooling cycle, the evaporator fan  110  is operated using a duty cycle of approximately thirty (30) minutes “on” and approximately five (5) minutes “off”. In another embodiment, the evaporator fan  110  is operated using a duty cycle of approximately twenty (20) minutes “on” and approximately four (4) minutes “off”. Other duty cycles having other periods of “on” and “off” are possible, and can be determined and programmed in advance, or can be determined dynamically at run time. In still another embodiment, the evaporator an  110  is run on a variable basis, keying off the discharge gas temperature or a liquid line temperature. The time that the evaporator fan  110  is run may be based upon the design of the evaporator that is implemented in the refrigeration system  106 . One or more sensors (e.g., temperature probe  104 ) may be used to determine the optimum time or duty cycle for operating the evaporator fan  110 . 
         [0034]    The discharge cooling cycle may be executed whenever the compressor  108  operates for an extended period of time. Thus, the discharge cooling cycle may be executed during the Reload state  204  or the Pulldown state  206 . During the Reload state  204  or the Pulldown state  206 , the compressor  108  operates continuously or almost continuously in order to quickly reduce the temperature inside the vending machine  100 . 
         [0035]    In some embodiments, the discharge cooling cycle is executed during the Steady State Temperature state  208 . Usually, during the Steady State Temperature state  208 , the temperature inside the vending machine  100  is at or near the desired operating temperature. Thus, the compressor  108  operates using shorter cycles to maintain the desired operating temperature. However, during periods of higher ambient temperatures (e.g., in a warehouse setting, where the ambient temperature outside the vending machine can rise above 100 degrees Fahrenheit), the compressor  108  may run for extended periods simply to maintain the vending machine  100  at the desired operating temperature. Thus, during such Steady State Temperature states  208 , the discharge cooling cycle is useful in cooling the compressor  108 . 
         [0036]    In other embodiments, the discharge cooling cycle is executed in a dusty or dirty environment where the condenser  108  can get dirty quickly. Dirt buildup on or around the condenser  108  can reduce ventilation and cause the condenser  108  to overheat more quickly. 
         [0037]      FIG. 3  depicts a method of using a discharge cooling cycle according to an embodiment of the disclosure. The method shown in  FIG. 3  is for illustration only. Other embodiments of the method could be used without departing from the scope of this disclosure. 
         [0038]    First, the VMC  102  determines the occurrence of a first operating condition in the refrigeration system  106  or the vending machine  100  (block  310 ). In one embodiment, the first operating condition is the start of a Reload state  204  or a Pulldown state  206 . In another embodiment, the first operating condition is a discharge gas temperature above a certain temperature. In yet another embodiment, the first operating condition is an ambient air temperature outside the vending machine  100  above a certain temperature. 
         [0039]    Next, based on the occurrence of the first operating condition, the evaporator fan  110  is activated for an “on” period of a duty cycle (block  320 ). In an embodiment, the evaporator fan  110  is activated for approximately thirty (30) minutes. In another embodiment, the evaporator fan  110  is activated for a longer or shorter period of time. Next, after the “on” period, the evaporator fan  110  is deactivated for an “off” period of a duty cycle (block  330 ). The evaporator fan  110  may be deactivated for approximately five (5) minutes, or a longer or shorter period of time. 
         [0040]    Next, the discharge cooling cycle of the evaporator fan  110  is repeated until a second operating condition in the refrigeration system  106  or the vending machine  100  occurs (block  340 ). In an embodiment, the second operating condition is the end of a Reload state  204  or a Pulldown state  206 . In another embodiment, the second operating condition is a discharge gas temperature at or below a certain temperature. In yet another embodiment, the second operating condition is an ambient air temperature outside the vending machine  100  at or below a certain temperature. 
         [0041]    Upon the conclusion of the discharge cooling cycle, the evaporator fan  110  operates according to its standard operating practices. The standard operating practices are in coordination with the rest of the refrigeration system  106 , including the compressor  108 . 
         [0042]    Although  FIG. 3  illustrates one example of a method of using a discharge cooling cycle, various changes may be made to  FIG. 3 . For example, while shown as a series of steps, various steps in  FIG. 3  may overlap, occur in parallel, occur in a different order, or occur multiple times. 
         [0043]    Although the figures above illustrate specific systems, structures, and methods, various changes may be made to the figures. For example, various components in the systems and structures can be combined, omitted, further subdivided, or moved according to particular needs. In some embodiments, various functions described above are implemented or supported by a computer program that is formed from computer readable program code and that is embodied in a computer readable medium. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. 
         [0044]    It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. 
         [0045]    While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.