METHOD AND APPARATUS TO CONTROL DISCHARGE COOLING IN A REFRIGERATION SYSTEM

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

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

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

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

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.

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.

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.

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

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:

FIG. 1 illustrates a block diagram of a vending machine according to an embodiment of the disclosure;

FIG. 2 is a state diagram of refrigeration control of a vending machine according to an embodiment of the disclosure; and

FIG. 3 depicts a method of using a discharge cooling cycle according to an embodiment of the disclosure.

DETAILED DESCRIPTION

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Claims

1. A method of operating a refrigeration system, the method comprising:

determining a first operating condition of the refrigeration system; and

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.

2. The method of claim 1, wherein the first operating condition is a start of a pulldown state or a reload state, and the second operating condition is an end of the pulldown state or the reload state.

3. The method of claim 1, wherein the first operating condition is a discharge gas temperature above a first predetermined level.

4. The method of claim 3, wherein the second operating condition is the discharge gas temperature below a second predetermined level.

5. The method of claim 1, wherein the first operating condition is an ambient temperature outside the refrigeration system above a predetermined level and the second operating condition is the ambient temperature outside the refrigeration system at or below the predetermined level.

6. The method of claim 1, wherein the first predetermined period of time is approximately thirty minutes and the second predetermined period of time is approximately five minutes.

7. The method of claim 1, wherein the refrigeration system is disposed in a vending machine.

8. An apparatus, comprising:

a refrigeration system comprising a compressor and an evaporator fan; and

a controller communicatively coupled to the refrigeration system, the controller configured to:

determine a first operating condition of the refrigeration system; and

based on the determination of the first operating condition, 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.

9. The apparatus of claim 8, wherein the first operating condition is a start of a pulldown state or a reload state, and the second operating condition is an end of the pulldown state or the reload state.

10. The apparatus of claim 8, wherein the first operating condition is a discharge gas temperature above a first predetermined level.

11. The apparatus of claim 10, wherein the second operating condition is the discharge gas temperature below a second predetermined level.

12. The apparatus of claim 8, wherein the first operating condition is an ambient temperature outside the refrigeration system above a predetermined level and the second operating condition is the ambient temperature outside the refrigeration system at or below the predetermined level.

13. The apparatus of claim 8, wherein the first predetermined period of time is approximately thirty minutes and the second predetermined period of time is approximately five minutes.

14. The apparatus of claim 8, wherein the apparatus is disposed in a vending machine.

15. A vending machine, comprising:

a product storage area;

a refrigeration system comprising a compressor and an evaporator fan, the refrigeration system configured to cool the product storage area; and

a controller communicatively coupled to the refrigeration system, the controller configured to:

determine a first operating condition of the refrigeration system; and

based on the determination of the first operating condition, 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.

16. The apparatus of claim 15, wherein the first operating condition is a start of a pulldown state or a reload state, and the second operating condition is an end of the pulldown state or the reload state.

17. The apparatus of claim 15, wherein the first operating condition is a discharge gas temperature above a first predetermined level.

18. The apparatus of claim 17, wherein the second operating condition is the discharge gas temperature below a second predetermined level.

19. The apparatus of claim 15, wherein the first operating condition is an ambient temperature outside the product storage area above a predetermined level and the second operating condition is the ambient temperature outside the product storage area at or below the predetermined level.

20. The apparatus of claim 15, wherein the first predetermined period of time is approximately thirty minutes and the second predetermined period of time is approximately five minutes.