Note: Descriptions are shown in the official language in which they were submitted.
CA 02449576 2003-12-15
HIGH-SPEED DEFROST REFRIGERATION SYSTEM
This application is a divisional of Canadian
Patent Application No. 2,434,422, filed on July 4, 2003.
TECHNICAL FIELD
s The present invention relates to a high-speed
evaporator defrost system for defrosting refrigeration coils
of evaporators in a short period of time without having to
increase compressor head pressure.
BACKGROUND ART
to In refrigeration systems found in the food
industry to refrigerate fresh and frozen foods, it is
necessary to defrost the refrigeration coils of the
evaporators periodically, as the refrigeration systems
working below the freezing point of water are gradually
15 covered by a layer of frost which reduces the efficiency of
evaporators. The evaporators become clogged up by the
build-up of ice thereon during the refrigeration cycle,
whereby the passage of air maintaining the foodstuff
refrigerated is obstructed. Exposing foodstuff to warm
2o temperatures during long defrost cycles may have adverse
effects on their freshness and quality.
One method known in the prior art for defrosting
refrigeration coils uses an air defrost method wherein fans
blow warm air against the clogged-up refrigeration coils
2s while refrigerant supply is momentarily stopped from
circulating through the coils. The resulting defrost cycles
may last up to about 40 minutes, thereby possibly fouling
the foodstuff.
In another known method, gas is taken from the
3o top of the reservoir of refrigerant at a temperature ranging
from 80°F to 90°F and is passed through the refrigeration
coils, whereby the latent heat of the gas is used to defrost
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the refrigeration coils. This also results in a fairly
lengthy defrost cycle.
U.S. Patent No. 5,673,567, issued on October 7,
1997 to the present inventor, discloses a system wherein hot
gas from the compressor discharge line is fed to the
refrigerant coil by a valve circuit and back into the liquid
manifold to mix with the refrigerant liquid. This method of
defrost usually takes about 12 minutes for defrosting
evaporators associated with open display cases and about
20 22 minutes for defrosting frozen food enclosures. The
compressors are affected by hot gas coming back through the
suction header, thereby causing the compressors to overheat.
Furthermore, the energy costs increases with the compressor
head pressure increase.
U.S. Patent No. 6,089,033, published on July 18,
2000 to the present inventor, introduces an evaporator
defrost system operating at high speed (e. g., 1 to 2 minutes
for refrigerated display cases, 4 to 6 minutes for frozen
food enclosures) comprising a defrost conduit circuit
2o connected to the discharge line of the compressors and back
to the suction header through an auxiliary reservoir capable
of storing the entire refrigerant load of the refrigeration
system. The auxiliary reservoir is at low pressure and is
automatically flushed into the main reservoir when liquid
z5 refrigerant accumulates to a predetermined level. The
pressure difference between the low pressure auxiliary
reservoir and the typical high pressure of the discharge of
the compressor creates a rapid flow of hot gas through the
evaporator coils, thereby ensuring a quick defrost of the
3o refrigeration coils. Furthermore, the suction header is fed
with low-pressure gas to prevent the adverse effects of hot
gas and high head pressure on the compressors.
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SUMMARY OF INVENTION
It is a feature of the present invention to
provide a high-speed defrost refrigeration system that
operates a defrost of evaporators at low pressure.
s It is a further feature of the present invention
to provide a high-speed defrost refrigeration system having
a compressor dedicated to defrost cycles.
It is a still further feature of the present
invention to provide a high-speed defrost refrigeration
so system having a low-pressure defrost loop.
It is a still further feature of the present
invention to provide a method for defrosting at high-speed
refrigeration systems with low-pressure in the evaporators.
It is a still further feature of the present
15 invention to provide a method for operating a high-speed
defrost refrigeration system having a compressor dedicated
to defrost cycles.
According to the above features, from a broad
aspect, the present invention provides a defrost
2o refrigeration system of the type having a main refrigeration
circuit, wherein a refrigerant goes through at least a
compressing stage, wherein the refrigerant is compressed to
a high-pressure gas state to then reach a condensing stage,
wherein the refrigerant in the high-pressure gas state is
25 condensed at least partially to a high-pressure liquid state
to then reach an expansion stage, wherein the refrigerant in
the high-pressure liquid state is expanded to a first low-
pressure liquid state to then reach an evaporator stage,
wherein. the refrigerant in the first low-pressure liquid
ao state is evaporated at least partially to a first low-
pressure gas state by absorbing .heat, to then return to the
compressing stage. The defrost refrigeration system
comprises a first line extending from the compressing stage
to the evaporator stage and adapted to receive a portion of
3s the refrigerant in the high-pressure gas state. A first
pressure reducing device on the first line reduces a
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pressure of the portion of the refrigerant in the high-
pressure gas state to a second low-pressure gas state:
Valves stop a flow of the refrigerant in the first low-
pressure liquid state to at least one evaporator of the
s evaporator stage and direct a flow of the refrigerant in the
second low-pressure gas state to release heat to defrost the
at least one evaporator and thereby change phase at least
partially to a second low-pressure liquid state. A second
line directs the refrigerant having released heat to at
to least one of the compressing stage and the condensing stage.
According to a further broad feature of the
present invention, there is provided a defrost refrigeration
system of the type having a main refrigeration circuit,
wherein a refrigerant goes through at least a first
i5 compressor in a compressing stage, wherein the refrigerant
is compressed to a high-pressure gas state to then reach a
condensing stage wherein the refrigerant in the high-
pressure gas is condensed at least partially to a high-
pressure liquid state to then reach an expansion stage,
2o wherein the refrigerant in the high-pressure liquid state is
expanded to a first low-pressure liquid state to then reach
an evaporator stage, wherein the refrigerant in the first
low-pressure liquid state is evaporated at least partially
to a first low-pressure gas state by absorbing heat, to then
25 return to the compressing stage. The defrost refrigeration
system comprises a first line extending from the compressing
stage to the evaporator stage and is adapted to receive a
portion of the refrigerant in the high-pressure gas state.
Valves stop a flow of the refrigerant in the first low-
3o pressure liquid state to at least one evaporator of the
evaporator stage and direct a flow of the portion of the
refrigerant in the high-pressure gas state to release heat
to defrost the at least one evaporator and thereby change
phase to a second low-pressure liquid state. A dedicated
3s compressor is adapted to receive an evaporated gas portion
of the refrigerant in the second low-pressure liquid state .
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The dedicated compressor is connected to the condensing
stage for directing a discharge thereof to the condensing
stage.
According to a still further broad feature of
the present invention, there is provided a method for
defrosting evaporators of a refrigeration system of the type
having a main refrigeration circuit, wherein a refrigerant
goes through at least a compressing stage, wherein the
refrigerant is compressed to a high-pressure gas state to
to then reach a condensing stage, wherein the refrigerant in
the high-pressure gas state is condensed at least partially
to a high-pressure liquid state to then reach an expansion
stage, wherein the refrigerant in the high-pressure liquid
state is expanded to a first low-pressure liquid state to
then reach an evaporator stage, wherein the refrigerant in
the first low-pressure liquid state is evaporated at least
partially to a first low-pressure gas state by absorbing
heat, to then return to the compressing stage. The method
comprises the steps of i) stopping a flow of the refrigerant
2o in the first low-pressure liquid state to at least one
evaporator of the evaporator stage; ii) reducing a pressure
of a portion of the refrigerant in the high-pressure gas
state to a second low-pressure gas state; and iii) directing
the portion of the refrigerant in the second low-pressure
2s gas state to the at least one evaporator to release heat to
defrost the at least one evaporator and thereby changing
phase at least partially to a second low-pressure liquid
state.
According to a still further broad feature of
3o the present invention, there is provided a method for
defrosting evaporators of a refrigeration system of the type
having a main refrigeration circuit, wherein a refrigerant
goes through at least a compressing stage having at least a
first compressor, wherein the refrigerant is compressed to a
35 high-pressure gas. state to then reach a condensing stage,
wherein the refrigerant in the high-pressure gas state is
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condensed at least partially to a high-pressure liquid state
to then reach an expansion stage, wherein the refrigerant in
the high-pressure liquid state is expanded to a first low-
pressure liquid state to then reach an evaporator stage,
wherein the refrigerant in the first low-pressure liquid
state is evaporated at least partially to a first low-
pressure gas state by absorbing heat, to then return to the
compressing stage. The method comprises the steps of i)
stopping a flow of the refrigerant in the first low-pressure
to liquid state to at least one evaporator; ii) directing a
portion of the refrigerant in the high-pressure gas state to
the at least one evaporator to release heat to defrost the
at least one evaporator and thereby changing phase at least
partially to a second low-pressure liquid state; and iii)
1s directing an evaporated gas portion of the refrigerant in
the second low-pressure gas state to a dedicated compressor,
the dedicated compressor being connected to the condensing
stage for directing a discharge thereof to the condensing
stage.
20 According to a still further broad feature of
the present invention, there is provided a defrost
refrigeration system of the type having a main refrigeration
circuit, wherein a refrigerant goes through at least a
compressing stage, wherein the refrigerant is compressed to
25 a high-pressure gas state to then reach a condensing stage,
wherein the refrigerant in the high-pressure gas state is
condensed at least partially to a high-pressure liquid state
to then reach an expansion stage, wherein the refrigerant in
the high-pressure liquid state is expanded to a first low-
3o pressure liquid state to then reach an evaporator stage,
wherein the refrigerant in the first low-pressure liquid
state is evaporated at least partially to a first low-
pressure gas state by absorbing heat, to then return to the
compressing stage. The defrost refrigeration system
ss comprises a first line extending from the compressing stage
to the evaporator stage and adapted to receive a portion of
CA 02449576 2003-12-15
the refrigerant in the high-pressure gas state . Valves are
provided for stopping a flow of the refrigerant in the first
low-pressure liquid state to at least one evaporator of the
evaporator stage and directing a flow of the refrigerant in
s the high-pressure gas state to release heat to defrost the
at least one evaporator and thereby changing phase at least
partially to a second low-pressure liquid state. A second
line is provided for directing the refrigerant having
released heat to the compressing stage, and pressure control
to means in the second line for controlling a pressure of the
refrigerant reaching the compressing stage.
According to a still further broad feature of
the present invention, there is provided a defrost
refrigeration system of the type having a main refrigeration
15 circuit, wherein a refrigerant goes through at least a
compressing stage, wherein the refrigerant is compressed to
a high-pressure gas state to then reach a condensing stage,
wherein the refrigerant in the high-pressure gas state is
condensed at least partially to a high-pressure liquid state
2o to then reach an expansion stage, wherein the refrigerant in
the high-pressure liquid state is expanded to a first low-
pressure liquid state to then reach an evaporator stage,
wherein the refrigerant in the first low-pressure liquid
state is evaporated at least partially to a first low-
2s pressure gas state by absorbing heat, to then return to the
compressing stage. The defrost refrigeration system
comprises a first line extending from the compressing stage
to the evaporator stage and adapted to receive a portion of
the refrigerant in the high-pressure gas state. Valves are
so provided for stopping a flow of the refrigerant in the first
low-pressure liquid state to at least two evaporators of the
evaporator stage and directing a flow of the refrigerant in
the high-pressure gas state to release heat to defrost the
at least two evaporators and thereby changing phase at least
35 partially to a second low-pressure liquid state. A second
line is provided for directing the refrigerant having
A
CA 02449576 2003-12-15
released heat in the at least two evaporators to the
compressing stage. Temperature monitor means are adapted to
monitor an average temperature of the refrigerant in the
second line and to reverse an action of the valves when the
s temperature reaches a predetermined value to re-establish
the flow of the refrigerant in the first low-pressure liquid
state to the at least two evaporators of the evaporator
stage.
According to a still further broad feature of
to the present invention, there is provided a defrost
refrigeration system of the type having a main refrigeration
circuit, wherein a refrigerant goes through at least a
compressing stage, wherein the refrigerant is compressed to
a high-pressure gas state to then reach a condensing stage,
wherein the refrigerant in the high-pressure gas state is
condensed at least partially to a high-pressure liquid state
to then reach an expansion stage, wherein the refrigerant in
the high-pressure liquid state is expanded by an expansion
valve to a first low-pressure liquid state to then reach an
zo evaporator stage, wherein the refrigerant in the first low-
pressure liquid state is evaporated at least partially to a
first low-pressure gas state by absorbing heat, to then
return to the compressing stage. The defrost refrigeration
system comprises a first line extending from the compressing
2s stage to the expansion stage and adapted to receive a
portion of the refrigerant in the high-pressure gas state.
Valves are provided for stopping a flow of the refrigerant
in the first low-pressure liquid state to at least one
evaporator of the evaporator stage and directing a flow of
3o the refrigerant in the high-pressure gas state around the
expansion valve to the at least one evaporator of the
evaporator stage to release heat to defrost the at least one
evaporator and thereby changing phase at least partially to
a second low-pressure liquid state, to then be directed to
35 the compressing stage.
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According to a still further broad feature of
the present invention, there is provided a defrost
refrigeration system of the type having a main refrigeration
circuit, wherein a refrigerant goes through at least a
compressing stage having at least a first and a second
compressor, wherein the refrigerant is compressed to a high-
pressure gas state to then reach a condensing stage, wherein
the refrigerant in the high-pressure gas state is condensed
at least partially to a high-pressure liquid state to then
to reach an expansion stage, wherein the refrigerant in the
high-pressure liquid state is expanded to a first low-
pressure liquid state to then reach an evaporator stage,
wherein the refrigerant in the first low-pressure liquid
state is evaporated at least partially to a first low-
pressure gas state by absorbing heat, to then return to the
compressing stage. The defrost refrigeration system
comprises a first line extending from the first compressor
to the evaporator stage and adapted to receive at least a
portion of discharged low-pressure refrigerant from the
2o first compressor. Valves are provided for stopping a flow
of the refrigerant in the first low-pressure liquid state to
at least one evaporator of the evaporator stage and
directing a flow of the discharged low-pressure refrigerant
to release heat to defrost the at least one evaporator and
thereby changing phase at least partially to a second low-
pressure liquid state. A second line is provided for
directing the refrigerant having released heat to the
evaporator stage.
BRIEF DESCRIPTION OF DRAWINGS
3o A preferred embodiment of the present invention
will now be described with reference to the accompanying
drawings in which:
FIG. 1 is a block diagram showing a simplified
refrigeration system constructed in accordance with the
present invention;
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FIG. 2 is a schematic view showing a
refrigeration system constructed in accordance with the
present invention;
FIG. 3 is an enlarged schematic view of an
s evaporator unit of the refrigeration system;
FIG. 4 is an enlarged schematic view of an
evaporator unit in accordance with another embodiment of the
present invention;
FIG. 5 is a block diagram showing a simplified
to refrigeration system constructed in accordance with another;
FIG. 6 is a block diagram showing a simplified
refrigeration system constructed in accordance with still
another embodiment of the present invention; and
FIG. 7 is a schematic view showing the
15 refrigeration system of FIG. 6.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to the drawings, and more particularly
to Fig. 1, a refrigeration system in accordance with the
present invention is generally shown at 10. The
2o refrigeration system 10 comprises the components found on
typical refrigeration systems, such as compressors 12 (one
of which is 12A, for reasons to be described hereinafter), a
high-pressure reservoir 16, expansion valves 18, and
evaporators 20. The refrigeration system 10 is shown having
2s a heat reclaim unit 22, which is optional. In Fig. 1, the
refrigeration system 10 is shown having only two sets of
evaporator 20/expansion valve 18 for the simplicity of the
illustration. It is obvious that numerous other sets of
evaporator 20/expansion valve 18 may be added to the
3o refrigeration system 10.
The compressors 12 are Connected to the
condenser units 14 by lines 28. A pressure regulator 21 is
in the line 28 but is not in operation during normal
refrigeration cycles, and is thus normally open to enable
3s refrigerant flow therethrough. High-pressure gas
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refrigerant is discharged from the compressors 12 and flows
to the condenser units 14 through the line 28. A line 30
diverges from the line 28 by way of three-way valve 32. The
line 30 extends between the three-way valve 32 and the heat
s reclaim unit 22. A line 34 connects the condenser units 14
to the high-pressure reservoir 16, and a line 36 links the
heat reclaim unit 22 to the high-pressure reservoir 16. The
condenser units 14 are typically rooftop condensers that are
used to release energy of the high-pressure gas refrigerant
to discharged by the compressors 12 by a change to the liquid
phase. Accordingly, refrigerant accumulates in the high-
pressure reservoir 16 in a liquid state.
Evaporator units 17 are connected between the
high-pressure reservoir 16 and the compressors 12. Each of
15 the evaporator units 17 has an evaporator 20 and an
expansion valve 18. The expansion valves 18 are connected
to the high-pressure reservoir 16 by line 38. As known in
the art, the expansion valves 18 create a pressure
differential so as to control the pressure of liquid
2o refrigerant sent to the evaporators 20. The outlet of the
evaporators 20 are connected to the compressors 12 by lines
48. The compressors 12 are supplied with low-pressure gas
refrigerant via supply lines 48. The expansion valves 18
control the pressure of the liquid refrigerant that is sent
25 to the evaporators 20, such that the liquid refrigerant
changes phases in the evaporators 20 by a fluid, such as
air, blown across the evaporators 20 to reach refrigerated
display counters (e. g., refrigerators, freezers or the like)
at low refrigerating temperatures.
3o Refrigerant in the refrigeration system 10 is in
a high-pressure gas state when discharged from the
compressors 12. For instance, a typical head pressure of
the compressors is 200 Psi. The compressor head pressure
obviously changes as a function of the outdoor temperature
3s to which will be subject the refrigerant in the condensing
stage. The high-pressure gas refrigerant is conveyed to the
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condenser units 14 and, if applicable, to the heat reclaim
unit 22 via the line 28 and the line 30, respectively.
In the condenser units 14 and the heat reclaim
unit 22, the refrigerant releases heat so as to go from the
s gas state to a liquid state, with the pressure remaining
generally the same. Accordingly, the high-pressure
reservoir 16 accumulates high-pressure liquid refrigerant
that flows thereto by the lines 34 and 36, as previously
described.
to The compressors 12 exert a suction on the
evaporators 20 through the supply lines 48. The expansion
valves Z8 control the pressure in the evaporators 20 as a
function of the suction by the compressors 12. Accordingly,
high-pressure liquid refrigerant accumulates in the line 38
Zs to thereafter exit through the expansion valves 18 to reach
the evaporators 20 via the lines 43 in a low-pressure liquid
state. The typical pressure at an outlet of the expansion
valve 18 is 35 Psi. During a refrigeration cycle, the
refrigerant absorbs heat in the evaporators 20, so as to
2o change state to become a low-pressure gas refrigerant.
Finally, the low-pressure gas refrigerant flows through the
line 48 so as to be compressed once more by the compressors
12 to complete the refrigeration cycle.
As frost and ice build-up are frequent on the
2~ evaporators, the evaporators 20 are provided with a defrost
system for melting the frost and ice build-up. Only one of
the evaporator units l7 is shown having defrost equipment,
for simplicity of the drawings. It is obvious that all
evaporator units 17 can be provided with defrost equipment.
3o One of the evaporators 20 is supplied with refrigerant
discharged from the compressors 12 by a line 106 having a
pressure regulator 108 therein. The pressure regulator 108
creates a pressure differential in the line 106, such that
the high-pressure gas refrigerant, typically around 200 Psi,
3s is reduced to a low-pressure gas refrigerant thereafter, for
instance at about 110 Psi. The pressure regulator 108 may
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include a modulating valve in line 106. In the event that
the pressure in the evaporator 20 is lower than that of the
refrigerant conveyed thereto by the line 106 in a defrost
cycle, the modulating valve portion of the pressure
s regulator 108 will preclude the formation of water hammer by
gradually increasing the pressure in the evaporator 20.
This feature of the pressure regulator 108 will allow the
refrigeration system 10 to feed the evaporators 20 with
high-pressure refrigerant, although it is preferred to
io defrost the evaporators 20 with low-pressure refrigerant.
On the other hand, the modulating action can be effected by
the valves 118.
Valves are provided in the evaporator units 17
so as to control the flow of refrigerant in the evaporators
15 20. A valve 114 is provided in the line _38. The valve 114
is normally open, but is closed during defrosting of its
evaporator unit 17. A valve 116 is positioned on the line
48 and is normally open. The line 106 merges with the line
48 between the valve 116 and the evaporator 20. The line
20 106 has a valve 118 therein. A line 112, connecting a low-
pressure reservoir 100 to the evaporator 20, has a valve 120
therein. The valves 118 and 120 are closed during a normal
refrigeration cycle of their respective evaporators 20.
In a normal refrigeration cycle, refrigerant
25 flows in the line 38 through the valve 114, to reach the
expansion valves 18. A pressure drop in refrigerant is
caused at the expansion valve 18. The resulting low
pressure liquid refrigerant reaches the evaporators 20,
wherein it will absorb heat to change state to gas.
3o Thereafter, refrigerant flows through the low-pressure gas
refrigerant line 48 and the valve 116 therein to the
compressors 12.
During a defrost cycle of an evaporator 20, the
valves 118 and 120 are open, whereas the valves 114 and 116
35 are closed. Accordingly, the expansion valve 18 and the
evaporator 20 will not be supplied with low-pressure liquid
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refrigerant from the line 38, as it is closed by valve 114.
During the defrost cycle, low-pressure gas refrigerant
accumulated in the line 106, downstream of the pressure
regulator 108, is conveyed back into the evaporator 20
through the portion of line 48 between the valve 116 and the
evaporator 20. As the valve 116 is closed and the valve 118
is open. The closing of the valve 116 ensures that
refrigerant will not flow from the line 106 to the
compressors 12. As the low-pressure gas refrigerant flows
io through the evaporator 20, it releases heat to defrost and
melt ice build-up on the evaporator 20. This causes a
change of phase to the low-pressure gas refrigerant, which
changes to low-pressure liquid refrigerant. Thereafter, the
low-pressure liquid refrigerant flows through the line 112
and the valve 120 to reach the low-pressure reservoir 100.
The low-pressure reservoir 100 accumulates liquid
refrigerant at low pressure.
The low-pressure reservoir 100 is connected to
the compressors 12 by a line 126. The line 126 is connected
2o to a top portion of the reservoir 100 such that evaporated
refrigerant exits therefrom. As the low-pressure reservoir
100 accumulates low-pressure liquid refrigerant, evaporation
will normally occur such that a portion of the reservoir
above the level of liquid refrigerant will comprise low-
z5 pressure gas refrigerant . The pressure in the low-pressure
reservoir 100 is typically as low as 10 Psi.
However, with the present invention a compressor
is dedicated for discharging the low-pressure reservoir 100,
whereas the other compressors receive refrigerant exiting
3o from the evaporators 20. Reasons for the use of a dedicated
compressor will be described hereinafter. Accordingly, as
shown in Fig. 1, the compressor 12A will be dedicated to
discharging the low-pressure reservoir 100. A line 128
diverges from the line 126 to reach the compressor 12A. A
35 valve 130 is in the line 128, whereas a valve 132 is in the
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line 126. During operation of the dedicated compressor 12A,
the valve 132 is closed, whereas the valve 130 is open.
A bypass line 134 and a check valve 136 therein
are connected from the line 48 to the compressor 12A. The
pressure in the lines 126 and 128 is generally lower than in
the line 48. The check valve 136 therefore enables a flow
of refrigerant therethrough such that the inlet pressure at
the compressors 12 and the dedicated compressor 12A is
generally the same.
to In order to flush the liquid refrigerant in the
low-pressure reservoir 100 such that the latter does not
overflow, a flushing arrangement is provided for the
periodic flushing of the low-pressure reservoir 100. The
flushing arrangement has a line 140 having a valve 142
therein diverging from the line 28 and connecting to the
low-pressure reservoir 100. The line 140 diverges from the
line 28 upstream of the pressure regulator 21, such that
high-pressure gas refrigerant can be directed from the
compressors 12 directly to the low-pressure reservoir 100.
A line 144 having a valve 146 extends from the
low-pressure reservoir 100 to the line 28 downstream of the
pressure regulator 21, and upstream of the three-way valve
32. A line 148 having a valve 150 goes from the low-
pressure reservoir 100 to the high-pressure reservoir 16. A
periodic flush of the low-pressure reservoir 100 is
initiated by creating a pressure differential (e. g., 5 psi)
in the line 28.
The valve 142 is opened while the valves 130 and
132 are simultaneously closed, if they were open.
3o Accordingly, high-pressure gas refrigerant can be directed
to the low-pressure reservoir 100, but will be prevented
from reaching the compressors 12 and 12A. One of the valves
146 and 150 is opened, while the other remains closed. If
the valve 146 is opened, a mixture of gas and liquid
refrigerant will flow through the line 144 and to the line
28 downstream of the pressure regulator 21. It is pointed
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out that the pressure differential caused by the pressure
regulator 21 will create this flow. If the valve 150 is
opened, the gas/liquid refrigerant will flow through the
line 148 to reach the high-pressure reservoir 16, in this
case having a lower pressure than the low-pressure reservoir
100, by the insertion of compressor discharge in the low-
pressure reservoir 10o via line 140, and by the pressure
drop caused by the pressure regulator 21.
When the defrost cycle has been completed, the
?o valves are reversed so as to return the defrosted evaporator
20 to the refrigeration cycle. More specifically, the
valves 114 and 116 are opened, and the valves 118 and 120
are closed. It is preferred that the valve 116 be of the
modulating type (e. g., Mueller modulating valve,
www.muellerindustries.com), or a pulse valve. Accordingly,
a pressure differential in the line 48 between upstream and
downstream portions with respect to the valve 116 will not
cause water hammer when the valve 116 is open. The pressure
will gradually be decreased by the modulation of the valve
116. Furthermore, the refrigerant reaching the compressors
12 via the line 48 will remain at advantageously low
pressures. Although in the preferred embodiment of the
present invention the refrigerant defrosting the evaporators
20 will be at generally low pressure because of the pressure
regulator 108, the refrigeration system 10 of the present
invention may also provide high-pressure refrigerant to
accelerate the defrosting of the evaporators 20, whereby the
modulation of the valve 116 is preferred when a defrosted
evaporator 20 is returned to the refrigeration cycle. It is
obvious that equivalents of the valve 116 can be used, and
such equivalents will be discussed hereinafter.
In the warmer periods, such as summer, the
flushing is directed to the condenser units 14 via the line
144, such that the liquid content of the flush cools the
condenser units 14. In the cooler periods, the flush is
directed to the high-pressure reservoir 16. When the flush
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is completed, for instance, when the liquid level in the
low-pressure reservoir 100 reaches a predetermined low
level, the flush is stopped by the closing of the valves 142
and 146 or 150 and the deactivation of the pressure
s regulator 21. The valves 130 or 132 can also be opened if
defrosting of one of the evaporators 20 is required.
It is obvious that the control of valve
operation is preferably fully automated. As mentioned
above, the flushing of the low-pressure reservoir 100 can be
to stopped by the low-pressure reservoir 100 reaching a
predetermined low level. Similarly, the flush of the low-
pressure reservoir 100 can be initiated by the refrigerant
level reaching a predetermined high level in the low-
pressure reservoir I00. Similarly, the valve operation for
z5 controlling the defrost of evaporators 20, namely the
control of valves 114, 116, 118, 120, 130 and 132, is fully
automated. For the flushing of the low-pressure reservoir
100, and in the defrost cycles, an automation system may
also be programmed to do periodic flushing or defrost
2o cycles, respectively. It also has been thought to provide a
pump (not shown) to pump the liquid refrigerant in the low-
pressure reservoir 100 to the line 28 or to the high-
pressure reservoir 16.
It is an advantageous feature to have a
2s dedicated compressor 12A. It is known that compressors are
not adapted to receive liquids therein. However, as the
defrost cycles produce a change of phase of gas refrigerant
to liquid refrigerant, there is a risk that liquid
refrigerant reaches the compressors 12. It is thus
3o important that the low-pressure reservoir 100 does not
overflow, whereby the flushing can be actuated, as described
above, upon the low-pressure reservoir's 100 reaching a
predetermined- high level of refrigerant. An alarm system
(not shown) can also be provided in order to shut-off the
35 compressors in the event of a low-pressure reservoir
overflow. The alarm can be used to shut-off the compressors
n~
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such that liquid refrigerant cannot affect the compressors.
However, this involves a risk of fouling the foodstuff in
the refrigeration display counters. The use of a dedicated
compressor 12A, isolated from the other compressors 12, can
prevent the shutting down of all compressors or the liquid
from reaching the compressors. As described above, the
valve 132 is shut during the use of the dedicated compressor
12A such that the low-pressure reservoir 100 is isolated
from the compressors 12. On the other hand, the alarm (not
to shown) can be connected to the valve 130 in order to shut-
off the valve 130 when an overflow of the low-pressure
reservoir 100 is detected. The compressor 12A will then be
supplied with gas refrigerant from the line 48 through the
check valve 136.
15 The defrosting of one of the evaporators 20 can
be stopped according to a time delay. More precisely, a
defrost cycle of an evaporator 20 can be initiated
periodically and have its duration predetermined. For
instance, a typical defrost portion of a defrost cycle can
20 last 8 minutes for low pressures of refrigerant fed to the
evaporators 20 and can be even shorter for higher pressures.
Thereafter, a period is required to have the defrosted
evaporator 20 returned to its normal refrigeration operating
temperature, and such a period is typically up to 7 minutes
2s in duration. It is also possible to have a sensor 152
positioned downstream of the evaporator 20 in a defrost
cycle, that will control the duration of the defrost cycle
of a respective evaporator 20 by monitoring the temperature
of the refrigerant having defrosted the respective
3o evaporator 20. A predetermined low refrigerant temperature
detected by the sensor 152 could trigger an actuation of the
valves 114, 116, 118 and 120, to switch the respective
evaporator 20 to a refrigeration cycle 20.
It is known to provide the sensor 152. However,
35 these sensors have been previously provided after each
evaporator 20. Accordingly, this proves to be a costly
CA 02449576 2003-12-15
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solution. Furthermore, in systems wherein defrost is
effected for a few evaporators simultaneously, these
evaporators are often synchronized to return back to
refrigeration cycles only once all temperature sensors reach
s their predetermined -low limit. This causes unnecessarily
lengthy defrost cycles. The sensor 152 of the present
invention is thus preferably positioned so as to measure an
average temperature of the defrost refrigerant of all
evaporators defrosted simultaneously. Tn consequence
to thereof, fewer sensors 52 are necessary and the operation of
defrost cycles is more efficient.
It is obvious that the various components
enabling the defrost cycle can be regrouped in a pack so as
to be provided on site as a defrost system ready to operate.
i5 This can simplify the installation of the defrost system to
an existing refrigeration system, as the major step in the
installation would be to connect the various lines to the
defrost system.
Now that the refrigeration system 10 has been
2o described with reference to a simplified schematic figure, a
refrigeration system 10' is shown in Figs. 2 and 3 in
further detail. It is pointed out that like numerals will
designate like elements. Furthermore, the refrigeration
system 10' illustrated in Figs. 2 and 3 comprises additional
2s elements to the refrigeration system 10, and these
additional elements are common to refrigeration systems but
have been removed from Fig. 1 for clarity purposes.
As seen in Fig. 2, the compressors 12 and 12A
are connected to the line 28, which has a discharge header
30 24 to collect the discharge of all compressors 12 and 12A.
Although not shown, it is common to have an oil separator
that will remove oil contents from the high-pressure gas
refrigerant in the line 28. The three-way valve 32 is
preferably a motorized modulating valve that will prevent
3s water hammer when stopping a supply of refrigerant to the
heat reclaim unit 22.
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The refrigeration system 10' has a high-pressure
liquid refrigerant header 40 and a suction header 44. The
high-pressure liquid refrigerant header 40 is in the line 38
and thus connected to the high-pressure reservoir 16 to
supply refrigerant to the evaporators 20. The suction
header 44 is connected to inlets of the compressors 12 by
the lines 48. Refrigerant accumulates in the suction header
44 in a low-pressure gas state, and is conveyed through the
lines 48 to the compressors 12 by the pressure drop at the
Zo inlets of the compressors 12.
Numerous evaporator units 17 extend between the
high-pressure reservoir 16 and the suction header 44, but
only one is fully shown in Fig. 2 for clarify purposes.
Each of the evaporator units 17 has an evaporator 20 and an
expansion valve 18. The expansion valves 18 are connected
to the high-pressure liquid refrigerant header 40 by the
lines 38, and to the evaporators 20 by the lines 43. As
mentioned above, the expansion valves 18 create a pressure
differential so as to control the pressure of liquid
2o refrigerant sent to the evaporators 20. The expansion
valves 18 control the pressure of the liquid refrigerant
that is sent to the evaporators 20 as a function of a fluid
that is blown on the evaporators 20 (e. g., air), such that
the liquid refrigerant changes phases in the evaporators 20
z5 by the fluid, blown across the evaporators 20 to reach
refrigerated display counters (e. g., refrigerators, freezers
or the like) at low refrigerating temperatures.
The compressors 12 exert a suction on the
evaporators 20 through the suction header 44 and the lines
30 48. The expansion valves 18 control the pressure in the
evaporators 20 as a function of the suction by the
compressors 12. Accordingly, high-pressure liquid
refrigerant accumulates in the line 38 and the high-pressure
liquid refrigerant header 40 to thereafter exit through the
35 expansion valves 18 to reach the evaporators 20 in a low-
pressure liquid state.
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In the refrigeration system 10', the defrost
system has a low-pressure gas header 102 and a low-pressure
liquid header 104. The low-pressure gas header 102 is
supplied with refrigerant discharged from the compressors 12
s by a defrost line 106. As mentioned previously, the
pressure regulator 108 creates a pressure differential, such
that the high-pressure gas refrigerant is reduced to a low-
pressure gas refrigerant thereafter. The low-pressure gas
header 102 and the low-pressure liquid header 104 are
to connected by the evaporator units 17. As seen in Fig. 3,
the valve 114 is provided on the line 38, with the line 112
connected to the line 38 between the expansion valve 18 and
the valve 114. The valve 114 is normally open, but is
closed during defrosting of its evaporator unit 17. The
15 valve 116 is positioned on the line 48 and is normally open.
The line 106 merges with the line 48 between the valve 116
and the evaporator 20. The line 106 has the valve 118
therein, and the defrost outlet line 112 has the valve 120
therein. The valves 118 and 120 are closed during a normal
2o refrigeration cycle of their respective evaporators 20. A
check valve 122 is provided parallel to the expansion valve
18. It.is pointed out that the check valve 122 is not shown
in Fig. 1, yet the refrigeration system 10 of Fig. 1 and the
refrigeration system 10' of Fig. 2 operate in an equivalent
2s fashion. The check valve 122 enables the use of the line 43
and a portion of the line 38 for defrost cycles, and this
reduces the number of pipes going to the evaporators 20.
Furthermore, the check valves 122 will facilitate the
adaptation of a defrost system to an existing refrigeration
3o system.
Although, as illustrated in Fig. 3, the line 106
is preferably connected to the line 48 ~to feed the
evaporator 20 with refrigerant, whereas the line 112 is
connected to the line 38 to provide an outlet for the
35 refrigerant after having gone through the evaporator 20, it
is pointed out that the lines 106 and 112 can be
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appropriately connected. As shown in Fig. 4, the line 106
is connected to the line 38, whereas the line 112 is
connected to the line 48. In doing so, the check valve 122
of Fig. 3 is replaced by a solenoid valve 122' that will
allow refrigerant to bypass the expansion valve 18 to reach
the evaporator 20.
Therefore, as seen in Figs. 2 and 3, in a normal
refrigeration cycle, refrigerant flows in the line 38
through the valve 114. The check valve 122 blocks flow
to therethrough in that direction of flow of refrigerant, such
that refrigerant has to go through the expansion valve 18 to
reach the evaporator 20 via the line 43. Thereafter,
refrigerant flows through the line 48, including the valve
116 and the suction header 44, to reach the compressors 12.
During a defrost cycle of one of the evaporators
20, the valves 118 and 120 are open, whereas the valves 114
and 116 are closed. Accordingly, the expansion valve 18 and
the evaporator 20 will not be supplied with low-pressure
liquid refrigerant from the line portion 38, as it is closed
zo by valve 114. During the defrost cycle, low-pressure gas
refrigerant is conveyed from the line 106 to the evaporator
through a portion of the line 48. The valve 116 is
closed and the valve 118 is open. As the valve 116 is
closed, refrigerant will not flow from the line 106 to the
z5 suction header 44. As the low-pressure gas refrigerant
flows through the evaporator 20, it releases heat to defrost
and melt ice build- on the evaporator 20. This causes a
change of phase to the low-pressure gas refrigerant, which
changes to low-pressure liquid refrigerant. The check valve
122 will allow refrigerant to accumulate upstream thereof,
such that the refrigerant in the evaporator 20 has time to
release heat to melt the ice build-up on the evaporator 20.
The check valve 122 will open above a given pressure, such
that low-pressure liquid refrigerant can flow through the
line 38 to the line 112 and the valve 120 to reach the low-
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pressure liquid header 104 and the low-pressure
reservoir 100.
The low-pressure reservoir 100 is connected to
the suction header 144 by the line 126. The line 126 is
s connected to a top portion of the reservoir 100 such that
evaporated refrigerant exits therefrom.
The compressor 12A has its own portion 44A of
the header 44. The portion 44A is separated from the
suction header 44. The line 128 extends from the line 126
to to the suction header portion 44A. A valve 130 is in the
line 128, whereas the valve 132 is in the reservoir
discharge line 126. During operation of the dedicated
compressor 12A, the valve 132 is closed, whereas the valve
130 is open. The line 134 and the check valve 136 therein
15 merge with the line 128 such that the dedicated compressor
12A can be supplied with refrigerant from the suction header
44 to operate at a same pressure as the compressors 12.
A line 160 provides a valve 162 parallel to the
valve 130. The line 160 has a small diameter, and is used
2o to lower the pressure of. the gas refrigerant coming from the
low-pressure reservoir 100 after a flush of the low-pressure
reservoir 100 has been performed.
A plurality of check valves 164 and manual
valves 166 are provided through the refrigeration system 10'
25 to ensure the proper flow direction and allow maintenance of
various parts of the refrigeration system 10'.
The refrigeration system 10 of the present
invention is advantageous, as it provides a defrost system
that can readily. be adapted to existing refrigeration
3o systems. The valve configuration in the evaporator units
17, as shown in Fig. 3, provides for the use of existing
pipe of typical refrigeration systems for defrost cycles.
Also, the evaporators 20 only receive low-pressure
refrigerants therein, as opposed to known defrost systems,
35 and this ensures that most types of evaporators are
compatible with the present invention. For instance,
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aluminum coils of an evaporator may not be specified for
high refrigerant pressures that are typical to known defrost
systems. Finally, the dedicated compressor 12A is a safety
feature that will prevent costly failures and breakdown of
all compressors 12, and thus reduces the risks of fouling
foodstuff.
In Fig. 5, there is shown an alternative to the
low-pressure reservoir 100. In the refrigeration system 10'
of Fig. 5, the line 112 is connected to the line 48,
to downstream of the valve 116, for directing refrigerant
directly to the compressors after having defrosted the
evaporator 20. The refrigeration system 10' is similar to
the refrigeration system 10 of Fig. 1, whereby like elements
will bear like numerals. Pressure control means 180 are
is provided in the line 112, downstream of the valve 120. The
pressure control means 180 will ensure that defrosting
refrigerant reaching the compressors 12 is at a pressure
generally similar to that of the refrigerant flowing to the
compressors 12 after a refrigeration cycle. The pressure
2o control means 180 may consist of any one of outlet
regulating valves, modulating valves, pulse valves and a
liquid accumulator, and may also consist in a circuit having
heat exchangers (e. g., roof-top radiators) and expansion
valves, that will reduce the refrigerant pressure and change
2s the phase thereof. In the case where the pressure control
means 180 are outlet regulating valves, these may be
positioned directly after the evaporators 20, or just before
inlets of compressors 12, to prevent liquid refrigerant from
reaching the compressors 12 and to control the pressure of
3o refrigerant supplied thereto. A liquid accumulator would
preferably be positioned between suction headers (not shown)
so as to ensure that no liquid refrigerant is fed to the
compressors 12. Considering that the refrigerant having
defrosted an evaporator 20 will be generally liquid, the
3s liquid accumulator prevents excessive liquid refrigerant
from blocking the lines. The pressure control means 180
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will enable the compressors 12 to operate at low pressures,
i.e., independently from the pressure of refrigerant at the
outlet of the defrost evaporators. Therefore, more
evaporators can be defrosted at a same time as the
compressor inlet pressure is generally independent from the
number of evaporators in defrost, whereby such simultaneous
defrosting will not substantially increase the energy costs
of the compressors 12.
As mentioned previously, typical defrost periods
to with the refrigeration system 10 of the present invention
are of 8 minutes for the evaporator 20 to reach the highest
temperature, and 7 minutes for returning back to an
operating temperature. Therefore, a,total of 15 minutes is
achievable from start to finish for a defrost period with
the refrigeration system 10 of the present invention.
Referring to Figs. 6 and 7, another
configuration of the refrigeration system 10 " is shown,
wherein gas refrigerant is sent to defrost the
evaporators 20 at a lower pressure than gas refrigerant sent
to the condensing stage. The dedicated compressor 12A'
collects low pressure gas refrigerant from a suction header
204 that also supplies the other compressors 12 in
refrigerant. However, the compressor 12A' is the only
compressor supplying evaporators in defrost cycles, whereby
2s its discharge pressure can be lowered. This is performed by
having line 106' connected to the evaporators 20 by valve
116 closing to direct refrigerant via line 48 thereto (shown
connected to only one line 48 in Fig. 6 but obviously
connected to all lines 48 of all evaporators 20 requiring
3o defrost). A portion of the refrigerant discharged by the
compressor 12A' can be sent to the condensing stage, via
line 106 " that converges with the line 28. A valve 200
(e. g., a three-way modulating valve), controls the portions
of refrigerant discharge going to the lines 106' and 106 " .
35 Thereafter, the refrigerant exiting from the
defrosted evaporators 20 is injected into the evaporators 20
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in a refrigeration cycle. Line 112' collects liquid
refrigerant exiting from the evaporators 20 in defrost, and
converges with the line 38 upstream of the expansion valves
18, such that the liquid refrigerant can be injected in the
s evaporators 20 in the refrigeration cycle. A valve 202
(e. g., pressure regulating valve) ensures that a proper
refrigerant pressure is provided to the line 38, and
compensates a lack of refrigerant pressure by transferring
liquid refrigerant from the high pressure reservoir 16 to
1o the Line 38. The combination of the dedicated compressor
12A' (i.e., low pressure refrigerant feed to the defrost
evaporators, also achievable by the refrigeration system of
Fig.l) and the valve 202 enable the injection of low
pressure refrigerant, which exits from the defrost cycle, in
15 the evaporator units 17. Previously, reinjected defrost
refrigerant had to be conveyed to the condensing stage to
reach adequate conditions to be reinjected into the
evaporation cycles. As seen in Fig. 7, a subcooling system
204 can be used to ensure the proper state of the
2o refrigerant reaching the evaporator units 17. With the
refrigeration system 10 " of Figs. 6 and 7, the defrost
refrigerant can be reinjected in the evaporator units 17 at
pressures as low as 120 to 140 Psi for refrigerant 22, and
140 to 160 Psi for refrigerant 507 and refrigerant 404, even
25 though the refrigerant 22 is up to about 220 to 260 Psi in
the condenser units 14, and the refrigerant 507 and the
refrigerant 404 are up to about 250 to 340 Psi.
Although the refrigeration system l0 of the
present invention enables the defrosting of the evaporators
30 20 at high pressure, it is preferable that the pressure
regulator 108 reduce the pressure of the refrigerant fed to
the evaporators 20 in defrost cycles. In such a case, less
refrigerant is required to defrost an evaporator, whereby a
plurality of evaporators 20 can be defrosted simultaneously.
CA 02449576 2003-12-15
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It is within the ambit of the present invention
to cover any obvious modifications of the embodiments
described herein, provided such modifications fall within
the scope of the appended claims.
