Note: Descriptions are shown in the official language in which they were submitted.
REFRIGERATION SYSTEM WITH REVERSE FLOW DEFROST
Related Application Data
This application claims benefit under 35 U.S.C. Section 119(e) of U.S.
Provisional Application No. 60/529,301 filed December I2, 2003.
Background
The present invention relates generally to a refrigeration system. More
particularly, the present invention relates to a refrigeration system that
includes a defrost
cycle.
Refrigeration systems cool a space by supplying cold refrigerant to an
evaporator.
Water vapor in the space being cooled sometimes condenses onto the outer
surface of the
evaporator and forms layers of ice. These layers of ice reduce the efficiency
of the
evaporator and make it difficult to maintain the desired temperature within
the space.
Summary
In one embodiment, the invention provides a refrigeration system including a
compressor operable to discharge compressed refrigerant. A first heat
exchanger is
operable to cool the compressed refrigerant. The first heat exchanger includes
a first
inlet, an outlet, and a second inlet disposed between the first inlet and the
outlet. A
second heat exchanger is disposed adjacent a cool space. A valve is movable
between a
first position to direct the compressed refrigerant to the first inlet and
then to the second
heat exchanger to cool the second heat exchanger and a second position to
direct the
compressed refrigerant to the second heat exchanger and then to the second
inlet to heat
the second heat exchanger.
CA 02489970 2004-12-09
-2-
In another embodiment, the invention provides a refrigeration system including
a
plurality of compressors. Each compressor is operable to discharge compressed
refrigerant. A first heat exchanger is operable to cool the compressed
refrigerant. The
first heat exchanger includes a first inlet, an outlet, and a second inlet
between the first
inlet and the outlet. The system also includes a plurality of evaporators and
a receiver in
fluid communication with the first heat exchanger and in selective fluid
communication
with each of the plurality of evaporators. The system further includes a hot
gas header
and a valve that is movable between a first position to direct the compressed
refrigerant
to the first inlet and a second position to direct the compressed refrigerant
to the hot gas
header. A plurality of defrost valves are movable between a first position to
place the
receiver in fluid communication with one of the plurality of evaporators to
cool the
evaporator and a second position to place the hot gas header in fluid
communication with
the one of the plurality of evaporators to heat the evaporator. The evaporator
discharges
refrigerant to the second inlet when the defrost valve is in the second
position.
In yet another embodiment, the invention provides a method of operating a
refrigeration system including operating a compressor to deliver compressed
refrigerant.
The method also includes directing the compressed refrigerant to a first inlet
of a first
heat exchanger and condensing the compressed refrigerant within the t7rst heat
exchanger. The method further includes expanding a portion of the compressed
refrigerant and passing the portion of the expanded compressed refrigerant
through a
second heat exchanger to cool the heat exchanger. The method also includes
manipulating a valve to redirect the compressed refrigerant to the second heat
exchanger
to heat the second heat exchanger and directing the compressed refrigerant to
a second
inlet of the first heat exchanger. The second inlet is disposed downstream of
the first
inlet.
CA 02489970 2004-12-09
-3-
Brief Description of the Drawings
The detailed description particularly refers to the accompanying figures in
which:
Fig. 1 is a circuit diagram for a refrigeration system illustrating the flow
paths in a
refrigeration mode; and
Fig. 2 is a circuit diagram for a refrigeration system illustrating the flow
paths in a
defrost mode.
Detailed Description
Before any embodiments of the invention are explained in detail, it is to be
understood that the invention is not limited in its application to the details
of construction
and the arrangement of components set forth in the following description or
illustrated in
the following figures. The invention is capable of other embodiments and of
being
practiced or of being carried out in various ways. Also, it is to be
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," "comprising," or "having" and
variations thereof herein is meant to encompass the items listed thereafter
and equivalents
thereof as well as additional items. Unless specified or limited otherwise,
the terms
"mounted," "connected," "supported," and "coupled" and variations thereof are
used
broadly and encompass both direct and indirect mountings, connections,
supports, and
couplings. Further, "connected" and "coupled" are not restricted to physical
or
mechanical connections or couplings.
The basic configuration of a refrigeration system 10 generally includes the
conventional components of a vapor-compression or refrigeration cycle (i.e.,
compressors) 15, condensers) 20, evaporators) 25, a receivers) 30, and
expansion
valves) 35). As one of ordinary skill will realize, refrigeration systems may
incorporate
multiple compressors 15, evaporators 25, and/or condensers 20 in paral~l or in
series to
CA 02489970 2004-12-09
-4-
accomplish the goals ofthe particular system. As such, the invention should
not be
limited to systems that include components arranged or numbered as illustrated
herein. It
should be understood that the invention hereinafter described is not dependent
upon the
number or size of such components.
Before describing the figures in detail, it should also be noted that the
figures
have been simplified for the purpose of illustration. Components such as check
valves,
drain and fill valves, pressure taps, flow meters, sensors, parallel piping,
as well as other
types of components have been omitted for clarity.
Figs. 1 and 2 show the basic layout of one arrangement of a refrigeration
system
10 incorporating a reverse flow defrost. Fig. 1 shows the flow through a
portion of the
system when operating in a refrigeration mode and Fig. 2 illustrates the same
portion of
the system operating in a defrost mode.
With reference to Fig. 1, the flow in refrigeration mode begins when one or
more
compressors 15 draw superheated refrigerant vapor (e.g., R12, ammonia, CFCs,
HCFCs,
HFCs, etc.) from a suction header 40. The term "superheated" as used herein
includes
any refrigerant that contains vapor at or above the saturation temperature for
the
refrigerant at the particular pressure. The compressor 15 compresses the vapor
to
produce a flow of superheated, high-pressure refrigerant. The vapor passes
through a
defrost differential valve 45 that is maintained in an open position when
operating in
refrigeration mode. From the defrost differential valve 45, the flow passes
through the
condenser 20, entering through a condenser inlet 50 and exiting through a
condenser
outlet 55. In the condenser 20, the flow cools and condenses to produce a
higl~pressure
flow of cool liquid refrigerant that is directed into the receiver 30. From
the receiver 30,
liquid refrigerant is directed to a liquid header 60 that is positioned to
supply refrigerant
to one, or more than one, of a plurality of cooling paths 65. It shouldbe
noted that the
CA 02489970 2004-12-09
-5-
term "header" should be read broadly to include structures as simple as a pipe
or
manifold that are able to deliver or receive a fluid to/from a plurality of
flow paths.
For the sake of simplicity, only one complete cooling path 65 is illustrated
in
Figs. 1 and 2. The remaining cooling paths 65 are similar to the illustrated
path 65. Each
cooling path 65 includes an expansion valve 35 and the evaporator 25. The
expansion
valve 35 expands the flow of vapor to reduce the temperature and pressure of
the flow
prior to its entry into the evaporator 25. After the flow passes through the
evaporator 25,
it is returned to the suction header 40 and the cycle repeats.
Each evaporator 25 is positioned to cool a space. Alternatively, multiple
evaporators may be used to cool a single space if necessary. The cold
refrigerant passes
through the evaporator 25 and is heated by the environment in which the
evaporator 25 is
positioned. Typically, air or another fluid moves across the evaporator 25 aid
is cooled
by the refrigerant as the refrigerant is heated. In some constructions, fans
(not shown)
are used to move the air across the evaporator 25. The refrigerant is usually
heated such
that it leaves the evaporator 25 as superheated refrigerant, while the air is
cooled and
returned to the cool space. Depending on the environment in which the
evaporator 25 is
positioned, the cold temperature of the evaporator 25 may cause some of the
water vapor
in the air to condense and freeze onto the evaporator 25. The freezing water
forms layers
of ice that reduce the efficiency of the heat exchange between the environment
being
cooled and the refrigerant within the evaporator 25. To improve the evaporator
efficiency, the layers of ice generally need to be removed.
To remove the ice, the refrigeration system 10 periodically transitions into a
defrost mode. The flows within the refrigeration system 10 when in the defrost
mode are
illustrated in Fig. 2. A portion of the hot compressed gas exiting the
compresses is
directed to a hot gas header 70. The defrost differential valve 45 at least
partially
controls the quantity of hot compressed gas that is directed to the hot gas
header 70. For
CA 02489970 2004-12-09
-6-
example, when additional hot gas is required in the hot gas header 70,the
defrost
differential valve is closed slightly or closed completely to reduce the size
of the flow
path to the condenser 20. The reduced flow path effectively redirects an
increased
quantity of hot gas to the hot gas header 70. As one of ordinary skill will
realize, other
constructions could position the defrost differential valve 45 differently.
For example,
one construction places the defrost differential valve 45 in the flow path to
the hot gas
header 70. In this position, opening the valve increases the flow to the hot
gas header 70.
The hot gas header 70 is selectively connected with each of the cooling paths
65.
A defrost valve 72 is positioned within each cooling path 65 to inhibit the
flow of
refrigerant to the hot gas header 70 when in the cooling mode, In the
illustrated
construction, a solenoid-operated valve is used as the defrost valve 72 in
each cooling
path 65. However, other constructions may use other types of valves or other
actuation
means (e.g., manual) for the defrost valves 72. To transition one of the
cooling paths 65
from the refrigeration mode to the defrost mode, the system may close the
defrost
differential valve 45 to direct additional hot compressed refrigerant to the
hot gas header
70 if necessary. The defrost valve 72 corresponding to the cooling path 65 to
be heated is
opened to direct a flow of hot compressed refrigerant to the evaporator. In
addition, an
isolation valve 74 is closed to inhibit flow of hot gas from the hot gas
header 70 directly
to the suction header 40.
As with the refrigeration mode, the defrost cycle begins when the compressor
15
draws superheated refrigerant vapor from the suction header 40. However, with
the
defrost differential valve 45 reducing or completely preventing flow to the
condenser 20,
part or all of the flow is redirected to the hot gas header 70. The hot gas
header 70
directs the flow of superheated, high-pressure refrigerant vapor through the
evaporator 25
in the opposite direction it would flow if in the refrigeration mode. The
superheated
CA 02489970 2004-12-09
high-pressure vapor heats the evaporator 25 and melts the accumulated ice.
After passing
through the evaporator 25, the refrigerant collects in a hot gas return header
75.
The hot gas return header 75 directs the refrigerant to the condenser 20. The
flow
enters the condenser 20 at a defrost inlet 80 located downstream of the
condenser inlet
50. After passing through the condenser 20, the now cooled liquid flows into
the receiver
tank 30. In an alternative construction, a separate heat exchanger (not
shown), having the
ability to remove heat (heat removed via air/water or other means) and
condense the
refrigerant from a vapor to a liquid, receives the flow of refrigerant vapor
from the hot
gas return header 75 and directs the condensed refrigerant to a reentry point
at or after the
condenser outlet 55.
As one of ordinary skill will realize, operation in defrost mode directs vapor
from
the suction header 40 to the hot gas header 70, through the evaporator 25
being defrosted,
through the condenser 20, and finally to the receiver tank 30. However, if
none of the
evaporators 25 in the system are operating in refrigeration mode, none of the
refrigerant
will be drawn from the receiver tank 30. As such, no refrigerant will flow to
the suction
header 40, and eventually no refrigerant will be available to the compressors
15. As
such, at least one cooling path 65 is generally maintained in the
refrigeration mode
during a defrost cycle to assure that refrigerant is always available to the
compressors 15.
With at least one evaporator 25 operating in refrigeration mode, refrigerant
is drawn from
the receiver tank 30 and returned to the suction header 40, thus completing
the defrost
cycle.
For the sake of clarity, only one evaporator 25 is illustrated herein.
However, it
should be understood that multiple evaporators 25 are typically employed in
systems of
this type. In fact, to operate in the defrost mode for a long duration, one
evaporator 25
should be operated in the refrigeration mode as just descried to prevent the
depletion of
the refrigerant. Typically, several evaporators 25 within the system operate
in
CA 02489970 2004-12-09
_g_
refrigeration mode with the remaining evaporators 25 operating in defrost
mode. Of
course, all of the evaporators 25 can be operated in refrigeration mode at the
same time if
desired.
Although the invention has been described in detail with reference to certain
preferred embodiments, variations and modifications exist within the scope and
spirit of
the invention. Thus, the invention provides, among other things, a new and
useful system
and method of cooling multiple spaces and defrosting the individual
evaporators. The
constructions of the system and the methods of operation of the system
described above
and illustrated in the figures are presented by way of example only and are
not intended
as a limitation upon the concepts and principles of the invention. Various
features and
advantages of the invention are set forth in the following claims.
CA 02489970 2004-12-09
