Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS TO CONTROL DISCHARGE COOLING IN A
REFRIGERATION SYSTEM
TECHNICAL FIELD
[0001] 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
[0002] 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.
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SUMMARY
[0003] 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.
[0004] 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.
[0005] 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
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for a second predetermined period of time, and repeat the
activation and deactivation until a second operating condition
is detected.
[00061 Other technical features may be readily apparent to
one skilled in the art from the following figures,
descriptions and claims.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0007] 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:
[0008] FIGURE 1 illustrates a block diagram of a vending
machine according to an embodiment of the disclosure;
[0009] FIGURE 2 is a state diagram of refrigeration control
of a vending machine according to an embodiment of the
disclosure; and
[0010] FIGURE 3 depicts a method of using a discharge
cooling cycle according to an embodiment of the disclosure.
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DETAILED DESCRIPTION
[0011] FIGURES 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
5 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.
[0012] 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.
[0013] 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.
[0014] 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
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of the evaporator and to the compressor to begin the
circulation process again.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] FIGURE 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.
[0019] 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
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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.
[0020] 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.
[0021] 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.
[0022] Although FIGURE 1 depicts one example of a vending
machine 100, various changes may be made to FIGURE 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
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of the VMC 102 may be distributed across a plurality of
microcontrollers or microprocessors.
[0023] FIGURE 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 unchilled outside air can
enter the compartment when the door is opened.
[0024] 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 FIGURE 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.
[0025] 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.
[0026] 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
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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.
[0027] 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.
[0028] 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.
[0029] Although FIGURE 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.
[0030] In both the Reload state 204 and the Pulldown state
206, the compressor 108 may operate continuously or may
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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
5 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
10 indicate that the compressor 108 is overheated or is in danger
of overheating.
[0031] 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.
[0032] 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
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(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 fan 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.
[0033] 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.
[0034] 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.
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[0035] 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.
[0036] FIGURE 3 depicts a method of using a discharge
cooling cycle according to an embodiment of the disclosure.
The method shown in FIGURE 3 is for illustration only. Other
embodiments of the method could be used without departing from
the scope of this disclosure.
[0037] 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.
[0038] 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.
[0039] 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
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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.
[0040] 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.
[0041] Although FIGURE 3 illustrates one example of a
method of using a discharge cooling cycle, various changes may
be made to FIGURE 3. For example, while shown as a series of
steps, various steps in FIGURE 3 may overlap, occur in
parallel, occur in a different order, or occur multiple times.
[0042] 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.
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[0043] 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.
[0044] 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.
