Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02518553 2005-09-08
EVAPORATION CIRCUIT FOR ALTERNATIVE REFRIGERANT
IN A REFRIGERATION SYSTEM
CROSS-REFERENCE TO RELATED APPLICATION
This patent application claims priority on United
States Application No. 10/937,365, filed on September 10,
2004, by the present applicant.
TECHNICAL FIELD
The present invention generally relates to
refrigeration systems and, more particularly, to
refrigeration systems having circuits used in conjunction
with a main refrigeration circuit.
BACKGROUND ART
With the constant evolution of technology, the
demand for electricity has greatly increased in
industrialized countries over the last decades. A major
portion of households and offices of industrialized
countries are now equipped with electrical appliances that
did not exist a few decades ago. Computers, air-
conditioning units, microwave ovens and home entertainment
systems are a few of these appliances that are widely used
in the industrialized countries.
In these industrialized countries, a major portion
of the industries have adopted a Monday-to-Friday daytime
work schedule. As a consequence, a generally corresponding
part of the population has similar hours of activity and
this has created peak-hour periods for energy demand.
Accordingly, electricity consumption is higher during these
hours of activity. In typical supply-and-demand logic
following this peaked daytime demand, power companies have
adopted two-way electricity tariffs, with cheaper rates at
night.
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It is however of concern to reduce the quantity of
some types of refrigerants, which are considered to some
level harmful for the environment. For instance, some types
of fluorine-based refrigerants are subjected to
environmental concerns. This factor must therefore be
considered when designing refrigeration systems which are
energy efficient, but that increase the volume of conduits
of refrigerant.
SUMMARY OF INVENTION
Therefore, it is a feature of the present
invention to provide a novel refrigeration system.
It is a further feature of the present invention
to provide a refrigeration system having an evaporation
circuit that relates evaporators of the refrigeration
cabinets to a main refrigeration cycle.
It is a still further feature of the present
invention to provide a refrigeration system with energy
storage.
It is a still further feature of the present
invention to provide a method for storing energy.
Therefore, in accordance with the present
invention, there is provided an evaporator circuit for a
second refrigerant used in conjunction with a refrigeration
circuit of the type operating a refrigeration cycle having a
compression stage, a condensation stage, an expansion stage,
and an evaporation stage with a first refrigerant,
comprising a heat exchange stage having at least one heat
exchanger in a refrigerant accumulator in which the second
refrigerant is in heat-exchange relation with the first
refrigerant circulating in the heat exchanger in the
evaporation stage of the refrigeration circuit, the heat
exchanger being positioned in the refrigerant accumulator so
as to be immersed in the second refrigerant such that the
second refrigerant releases heat to the first refrigerant
circulating in the heat exchanger, and an evaporator stage
having at least one evaporator in which the second
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refrigerant absorbs heat from a fluid passing through the
evaporator, so as to cool the fluid, whereby the second
refrigerant circulates between the heat exchange stage and
the evaporator stage.
Further in accordance with the present invention,
there is provided a refrigeration system of the type having
a refrigeration circuit having a compression stage, a
condensation stage, an expansion stage and an evaporation
stage through which a first refrigerant circulates, further
comprising an evaporator circuit through which circulates a
second refrigerant between a heat exchange stage having at
least one heat exchanger in a refrigerant accumulator in
which the second refrigerant is in heat-exchange relation
with the first refrigerant circulating in the heat exchanger
in the evaporation stage of the refrigeration circuit, the
heat exchanger being positioned in the refrigerant
accumulator so as to be immersed in the second refrigerant
such that the second refrigerant releases heat to the first
refrigerant circulating in the heat exchanger, and an
evaporator stage having at least one evaporator in which the
second refrigerant absorbs heat from a fluid passing through
the evaporator, so as to cool the fluid for refrigeration,
whereby the second refrigerant circulates between the heat
exchange stage and the evaporator stage.
Still further in accordance with the present
invention, there is provided a refrigeration system of the
type having a refrigeration circuit having a compression
stage, a condensation stage, an expansion stage and an
evaporation stage through which a first refrigerant
circulates, comprising at least one compressor at the
compression stage, the compressor being a magnetic-bearing
compressor, and pressure increasing means upstream of the
expansion stage, so as to increase the pressure of the first
refrigerant for subsequently being fed to the expansion
stage .
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BRIEF DESCRIPTION OF DRAWINGS
A preferred embodiment of the present invention
will now be described with reference to the accompanying
drawings in which:
Fig. 1 is a schematic view of a refrigeration
system in accordance with a first embodiment of the present
invention, in which an evaporation circuit is pressurized
for refrigerant circulation;
Fig. 2 is a schematic view of a refrigeration
system in accordance with a second embodiment of the present
invention, in which an evaporation circuit operates with
pumps for refrigerant circulation;
Fig. 3 is a schematic view of a refrigeration
system in accordance with a third embodiment of the present
invention, without any auxiliary energy accumulator;
Fig. 4 is a perspective view of a transfer
accumulator with plate heat-exchangers in accordance with
the embodiments of the present invention, having a wall
thereof removed to show an interior thereof; and
Fig. 5 is a perspective view of coil heat-
exchanger to be used with the transfer accumulator of the
present invention, as an alternative to a plate heat
exchanger.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to the drawings, and more particularly
to Fig. 1, a refrigeration system in accordance with a first
embodiment of the present invention is generally shown at
10. The refrigeration system 10 has a main circuit 11 in
which a first refrigerant circulates from stage to stage of
a refrigeration cycle.
More specifically, the main circuit 11 has a
compression stage 12, in which the first refrigerant will be
compressed. The main circuit 11 has a condensing stage 14
and, optionally, a heat-reclaim stage 15, in which heat will
be released from the compressed first refrigerant.
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Thereafter, the main circuit 11 has an expansion stage 16,
in which the first refrigerant in the main circuit 11 will
be expanded in view of the subsequent evaporation. The main
circuit 11 has an evaporation stage 18, in which the first
refrigerant will absorb heat. The first refrigerant then
returns to the compression stage 12 to complete the
refrigeration cycle.
In addition to the main circuit 11, the
refrigeration system 10 has an evaporator circuit 19 and a
defrost circuit 54. The main circuit 11 and the evaporator
circuit 19 interact at the evaporation stage 18, as will be
described hereinafter. As the main circuit 11 and the
evaporator circuit 19 are closed with respect to one
another, the refrigerant (hereinafter the second
refrigerant) in the evaporator circuit 19 is physically
separated from the first refrigerant in the main circuit 11.
The first refrigerant of the main circuit 11 is typically a
fluorine-based refrigerant, as it will go through a complete
refrigeration cycle (and be exposed to outdoor temperature
variations), whereas the refrigerant in the evaporator
circuit 19 is preferably an alcohol-based refrigerant, such
as a mixture of glycol and water, as it will be subjected to
less temperature variation in its use.
MAIN CIRCUIT 11
The compression stage 12 has compressors, such as
the compressors 20 in Fig. 1. The compressors 20 compress
the first refrigerant of the main circuit 11. The first
refrigerant is conveyed from the compression stage 12 to the
condensing stage 14 and/or the heat-reclaim stage 15. More
specifically, lines 22 interconnect the compressors 20 to
the condensing stage 14. Line 24 diverges from the lines 22
so as to reach the heat-reclaim stage 15. It is pointed out
that valves and/or controllers are provided in the lines 22
and/or 24 in order to control the quantity of the first
refrigerant reaching the condensing stage 14 versus the
heat-reclaim stage 15. Moreover, systems such as an oil
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recuperator are used in conjunction with the lines 22 and/or
24 to ensure optimal operating parameters of the first
refrigerant.
The condensing stage 14 has a condenser 40, at
which heat will be released from the first refrigerant. As
is well known in the art, the first refrigerant is typically
compressed as a function of the fluid that is in heat
exchange relation with the condenser 40 (e. g., air blown
across the condenser 40), so as to release heat therefrom.
The heat-reclaim stage 15 has a heat exchanger 50
in which the first refrigerant is in heat-exchange relation
with a second refrigerant circulating in the defrost circuit
54, or, alternatively, a medium that will absorb heat from
the first refrigerant (e. g., air from a ventilation duct,
water heater, or the like). Lines 52 connect downstream
ends of the condenser 40 and heat exchanger 50 to a
reservoir 62 (i.e., a receiver). The lines 52 will convey
the first refrigerant to transfer accumulators 80 and 80' of
the evaporation stage 18, and have expansion valves 60
thereon of the expansion stage 16.
The transfer accumulators 80 and 80' will be
described in further detail hereinafter. The transfer
accumulators 80 and 80' represent the evaporation stage 18
of the main circuit 11, as the first refrigerant circulating
in lines 52 will absorb heat therein. Thereafter, lines 82
relate the transfer accumulators 80 and 80' to the
compressors 20, whereby the main circuit 11 is closed and
the refrigeration is completed.
EVAPORATOR CIRCUIT 19
The transfer accumulators 80 and 80' are heat-
exchanger reservoirs (i.e., refrigerant accumulators) that
will receive the second refrigerant. The first refrigerant
will circulate through a reservoir portion of the transfer
accumulators 80 and 80' by way of heat exchangers (such as
coils). Accordingly, the first refrigerant will absorb heat
from the second refrigerant by circulating through the
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transfer accumulators 80 and 80', whereby evaporation of the
first refrigerant will occur in this heat-exchange stage.
The reservoir portion of the transfer accumulators
80 and 80' is part of the evaporator circuit 19 in which the
second refrigerant circulates. More specifically, the
transfer accumulators 80 and 80' are each connected to a
feed line 84 that will supply evaporators 86 (only one of
which is shown in Fig. 1) with the second refrigerant. The
feed line 84 has a feed header 92.
The refrigeration system 10 is typically used to
cool refrigerators, foodstuff refrigerated cabinets,
freezers and the like. One of the evaporators present in
these enclosures is illustrated at 86 in Fig. 1. For
clarity of the figures, only one of the evaporators 86 is
illustrated, but the refrigeration system 10 typically has a
plurality of evaporators 86. Lines 88, incorporating return
header 93, collect the second refrigerant out of the
evaporators 86, and return the second refrigerant to the
transfer accumulators 80 and 80', whereby the cycle of the
second refrigerant in the evaporator circuit 19 is
completed, following this evaporator stage.
In the first embodiment of the present invention,
a pressure source 90 in conjunction with a control system
(e.g. , solenoid valves and a controller) are provided so as
to control the feed of the second refrigerant to the
evaporators 86. The pressure of the pressure source 90 will
cause a displacement of the second refrigerant in the
evaporator circuit 19. More specifically, the pressure
source 90 is connected to pressure lines 91, which are
connected to the transfer accumulators 80 and 80', as well
as the feed header 92 and the return header 93 of the
evaporator circuit 19. Moreover, the pressure lines 91 are
also connected to the energy accumulator 94, as will be
described hereinafter. Valves A1, A2, Bl, B2, C1, C2, D1;
D2, El, E2 and Fl are provided in the pressure lines 91 or
evaporator circuit 19 and are associated with a controller
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that controls the feed of refrigerant in the evaporator
circuit 19.
OPERATING SEQUENCE
Referring to Fig. 1, the operating sequence of the
refrigeration system 10 for the feed of the second
refrigerant to the evaporators 86 is now described.
A first one of the transfer accumulators, e.g.,
transfer accumulator 80, will be used to supply the
evaporators 86 with the second refrigerant, whereas the
other transfer accumulator 80 will be in heat-exchange
relation with the first refrigerant passing therethrough to
release heat to the first refrigerant, and hence be cooled
down for a subsequent feed to the evaporator 86. In this
case, valve A2 on the pressure line 91, valve B2 on the feed
line 84, and valve C1 on the line 88, will all be open,
while valves A1 on the pressure line 91, B1 on the feed line
84, and C2 on the line 88 are all closed.
Therefore, the pressure from the pressure source
90 will increase the pressure in the transfer accumulator
80, whereby the second refrigerant accumulated in a cool
state therein (as it has released heat to the first
refrigerant beforehand), exits the transfer accumulator 80
through the feed line 84.
The second refrigerant is conveyed in the feed
line 84, through the feed header 92, to reach the
evaporators 86, in which the second refrigerant will absorb
heat to cool the refrigerated cabinets.
Thereafter, the second refrigerant in a heated
state, having gone through the evaporators 86, will be
conveyed in lines 88, through the return header 93, as a
result of the pressure from the pressure source 90 and the
network of valves. The second refrigerant reaches the
transfer accumulator 80' through the line 88. Therefore,
the transfer accumulator 80' will accumulate the second
refrigerant in the heated state, having absorbed heat in the
evaporators 86 to cool the refrigerated cabinets. The
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second refrigerant in its heated state gathers in the
transfer accumulator 80', and is in heat exchange with the
first refrigerant such that the second refrigerant is cooled
down to a cool state. Therefore, the second refrigerant in
the transfer accumulator 80' reaches suitable conditions so
as to be sent subsequently to the evaporators 86 to absorb
heat.
The transfer accumulators 80 and 80' are provided
with level detectors (not shown) that are interconnected to
the controller. When the transfer accumulator 80 reaches a
low level of the second refrigerant, the valves are actuated
so as to switch the duty of supplying the evaporators 86
with the second refrigerant in its cool state to the
transfer accumulator 80', while the transfer accumulator 80
collects the second refrigerant from the evaporators 86.
More specifically, for this second sequence, the valves A2,
B2 and C1 are closed, while the valves Al, B1 and C2 are
opened.
The refrigeration system 10 described above has
the advantage of reducing the amount of fluorine-based
refrigerant when compared to refrigeration systems of
similar capacity, but without evaporation circuits.
Refrigeration systems typically have nonnegligible lengths
of piping that will interrelate the evaporators of the
evaporation state to the remainder of the refrigeration
cycle. This is due to the fact that refrigerated cabinets
are often spread out on the surface of a store. With the
refrigeration system 10 of the present invention, the
transfer accumulators 80 and 80' are, for instance, adjacent
to the pack of compressors and headers, whereby the main
line of the first refrigerant extends from the condensing
stage 14 to the mechanical room that contains the pack.
As the second refrigerant in the evaporator
circuit 19 is generally subjected to constant conditions of
heat exchange in and the transfer accumulators 80 and 80',
as well as in the evaporators 86, the second refrigerant
does not undergo pressure-change phases such as compression
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and expansion, whereby alcohol-based refrigerant, such as
glycol mixed with water, can be used. It is noted that the
second refrigerant is preferably environmentally sound.
DEFROST CIRCUIT 54
Referring to Fig. l, the heat-reclaim stage 15 has
a heat exchanger 50 by which the first refrigerant is
condensed in heat reclaim. In accordance with the first
embodiment of the present invention, the refrigeration
system 10 uses the heat-reclaim stage 15 so as to provide
refrigerant for the defrost of the evaporators 86.
Accordingly, the heat-reclaim stage 15 has a defrost circuit
54. The defrost circuit 54 has a defrost accumulator 55
and, optionally, heat-reclaim coils 56. The defrost circuit
54 has lines 57 by which the various components of the
defrost circuit 54, namely the defrost accumulator 55 and
the heat reclaim coils 56, a feed header 58 and a return
header 59, are connected to the heat exchanger 50. Pumps
and other devices, such as valves, are provided in order to
convey refrigerant in the defrost circuit 54, in a selected
sequence. For instance, refrigerant in the defrost circuit
54 may be sent directly to the heat-reclaim coils 56 so as
to heat ventilation ducts or a water reservoir.
Alternatively, the refrigerant may be sent directly to the
defrost accumulator 55 after having absorbed heat from the
first refrigerant through the heat exchanger 50. Finally,
and as will be described hereinafter, the refrigerant may be
sent to the feed header 58 so as to return through the
return header 59 in a defrost of the evaporators of the
refrigeration cabinets.
The feed header 58 taps into the feed line 84, and
has valves that are controlled to open the feed header 58 to
the feed line 84, and hence to the evaporators 86.
Similarly, the return header 59 is connected to the lines
88, and has valves that are controlled to open the return
header 59 for the line 88.
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DEFROST OPERATING SEQUENCE
As the refrigerant that will be used for the
defrost cycle of the evaporators 86 will be using the same
lines as the evaporator circuit 19, it is preferred to
provide the defrost circuit 54 with the second refrigerant
(e. g., glycol/water mixture), like the evaporator circuit
19, so as to avoid potential contamination.
In order to lessen energy loss, the refrigeration
system 10 operates a flushing sequence by which the second
l0 refrigerant in heat-absorbing refrigerating condition, as is
present in the lines 84, 88 and the evaporators 86, is
flushed out therefrom prior to the second refrigerant in
heat-releasing defrosting condition being fed to the
evaporators 86 and lines 88, thereby avoiding the mixture of
the second refrigerant in these two conditions. In order to
do so, valve D1 (normally closed) on the pressure line 91
will be opened, while valve D2 (normally closed) is kept
closed, so as to supply the feed header 92 with pressure
from the pressure source 90. Selected evaporators 86 will
remain open such that the pressure will flush the
refrigerant out of these selected evaporators 86, while
others that do not require defrost will be closed to avoid
the flush pressure. Although unidentified in Fig. l,
controllable valves (e.g., solenoid valves) are
appropriately provided upstream and downstream of each of
the evaporators 86 to enable the selection of some
evaporators 86 for defrost.
Therefore, the flush pressure will cause the flush
of the evaporators 86 of the second refrigerant in the heat
absorbing refrigerating condition. The second refrigerant
in the heat-absorbing refrigerating condition will leave the
selected evaporators 86 to return to either one of the
transfer accumulators 80 and 80', depending on the sequence
which the evaporator circuit 19 is at. Once the selected
evaporators 86 have been flushed out of the second
refrigerant in the heat-absorbing refrigerating condition,
valve D1 is closed such that the second refrigerant in the
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defrost circuit 54 (i.e., in the heat-releasing defrosting
condition) may reach the selected evaporators 86 through the
feed header 58. The return header 59 defines a path by
which the defrost second refrigerant will return from the
selected evaporators 86 to the defrost accumulator 55. The
unidentified valves of Fig. 1 that enable the feed of
refrigerant to the evaporators 86 are controlled to stop the
feed of the second refrigerant in the heat-absorbing
refrigerating condition to the selected evaporators 86, and
enable the feed of the second refrigerant in the heat-
absorbing refrigerating condition from the feed header 58 to
the selected evaporators 86. The refrigeration system 10
therefore enables the simultaneous defrost and refrigeration
cycles to operate in the evaporation stage, with some of the
evaporators 86 being used to cool air, while others are
being defrosted.
Once the selected evaporators 86 have been
defrosted, a flush of the selected evaporators 86 is
performed so as to remove the hot second refrigerant from
the selected evaporators 86 for the subsequent feed of cool
second refrigerant (from the evaporator circuit 19) to the
selected evaporators 86. Accordingly, the flush prevents
the mixture of the cool second refrigerant of the evaporator
circuit 19 with the hot second refrigerant of the defrost
circuit 54. To perform the flush of the defrost second
refrigerant, valve D2 is opened while valve D1 is kept
closed, and only the selected evaporators 86 are opened for
fluid communication with the headers 58, 59. Accordingly,
pressure from the pressure source 90 will build in feed
header 58, so as to flush the hot second refrigerant from
the selected evaporators 86, such that the hot second
refrigerant exits through the return header 59 and gathers
thereafter in the defrost accumulator 55 or other apparatus
of the defrost circuit 54.
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ENERGY ACCUMULATOR CIRCUIT PORTION
Referring to Fig. 1, the evaporator circuit 19
optionally has an energy accumulator circuit portion. The
energy accumulator circuit portion has an energy accumulator
94 that is in fluid communication with the transfer
accumulator 80 through lines 95. Valves E1 and E2 are
provided in lines 95. Moreover, the energy accumulator 94
is connected to the pressure lines 91 and separated
therefrom by valve F1. In the embodiment of Fig. l,
l0 pressure differential is used to transfer refrigerant
between the energy accumulator 94 and the transfer
accumulators 80 and 80', with appropriate valve operating
sequences for valves E1, E2 and Fl. Alternatively, pumps
may be provided on the lines 95 so as to convey refrigerant
from the transfer accumulator 80 to the energy
accumulator 94.
For instance, the energy accumulator circuit
portion operates at night when the demand for refrigerant
from the evaporators 86 is low (e. g., cooler outdoor
temperature, refrigerated cabinets are not opened up, stores
are closed, etc.), but when tariffs are also low, so as to
store a greater amount of energy than would be possible with
the transfer accumulators 80 and 80'. The transfer
accumulator 80 cools the second refrigerant, which is sent
for storage to the energy accumulator 94. Moreover, warm
refrigerant from the energy accumulator 94 may be sent to
the transfer accumulator so as to be cooled.
Thereafter, the pressure source 90 is used in
order to convey the second refrigerant from the energy
accumulator 94 to the transfer accumulator 80, when there is
demand from the evaporators 86. Accordingly, valves E1 and
E2 are operated to enable circulation of refrigerant between
the transfer accumulator 80 and the energy accumulator 94.
ALTERNATIVE EMBODIMENTS
Referring to Fig. 2, a refrigeration system in
accordance with an alternative embodiment of the present
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invention is generally shown at 10'. The refrigeration
system 10' of Fig. 2 is similar to the refrigeration system
of Fig. 1, whereby like elements will bear like reference
numerals. Elements of the refrigeration system 10 that are
5 different from that of the refrigeration system 10' will
have reference numerals between 100 and 199, inclusively.
The refrigeration system 10' has an evaporation
circuit 119 that differs from the evaporator circuit 19 of
Fig. 1, in that the second refrigerant in the evaporation
10 circuit 119 is pumped to the evaporators 86, rather than
being entrained by pressure differential. More
specifically, line 84, which interrelates the transfer
accumulators 80 and 80' to the evaporators 86 (only one of
which is shown in Fig. 2), is provided with a pump 100,
which induces the flow of the second refrigerant from the
transfer accumulators 80 and 80' to the evaporators 86, and
back to the transfer accumulators 80 and 80'. The above-
described sequence of having one of the transfer
accumulators 80 and 80' feeding the evaporators 86, while
the other of the transfer accumulators 80 and 80' is in
heat-exchange with the main circuit 11 for cooling the
second refrigerant, is followed. Therefore, a set of
valves, not shown in Fig. 2, is controlled to ensure the
sequence is followed.
The refrigeration system 10' has a pressure source
190, which differs from the pressure source 90 of Fig. 1, in
that it is used for the flushing operations when defrost of
some of the evaporators 86 is required, as described above
for the refrigeration system 10. Therefore, the line 91
connects the pressure source 190 to the line 84, to flush
the second refrigerant in the heat-absorbing refrigerating
condition back into the transfer accumulators 80 and 80',
and to the line 57, to flush the second refrigerant in the
heat-releasing defrosting condition back into the defrost
accumulator 55. The valves Dl and D2 are controlled to
cause the above-described flushes.
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The energy accumulator 94 is connected to both
transfer accumulators 80 and 80' by line 195. A pump 102 is
provided on the line 195 to induce circulation of the second
refrigerant between the transfer accumulators 80 and 80',
and the energy accumulator 94.
The use of pumps in the refrigeration system 10' ,
as opposed to compressed air in the refrigeration system 10
(Fig. 1), is advantageous in that the transfer accumulators
80 and 80', and the energy accumulator 94 need not be
adapted to maintain the second refrigerant pressurized.
Because of the volume of the transfer accumulators 80 and
80', and the energy accumulator 94, and the relatively high
pressure (i.e., above atmospheric pressure) necessary to
induce the circulation of the second refrigerant in the
refrigeration system 10 of Fig. 1, the various accumulators
80, 80' and 94 must have the structural integrity to operate
under such conditions, whereby the use of pumps represents a
cost-efficient alternative.
Referring to Fig. 3, a refrigeration system in
accordance with another embodiment of the present invention
is generally at 10" . The refrigeration system 10" of
Fig. 3 is similar to the refrigeration system 10 of Fig. 1,
and the refrigeration system 10' of Fig. 2, whereby like
elements will bear like reference numerals.
The refrigeration system 10" has an evaporation
circuit 219, essentially similar to the evaporator circuit
19 of the refrigeration system 10 of Fig. 1, but without an
energy accumulator. Therefore, the refrigeration system
10" does not have an additional reservoir to accumulate
energy, for instance when fuel/electricity tariffs are low'.
Energy may be stored in the transfer accumulators 80
and 80'.
In Figs. 2 and 3, the refrigeration systems 10'
and 10" , respectively, have compressors 120' that differ
form the compressors 20 of the refrigeration system 10 of
Fig. 1. More specifically, the compressors 120' are
compressors that can operate at lower minimum compression
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ratios than typical compressors. For instance, Turbocor
(www.turbocor.com) has designed an oil-free magnetic-bearing
compressor that can safely operate at the aforementioned
compression ratios.
At such low compression ratios, typical
compressors have been subjected to failure. For this
reason, the refrigerant has been over-compressed to a
minimum operating pressure in view of the subsequent
condensing stages, when the outdoor temperatures are low.
The Turbocor compressor may thus compress the first
refrigerant to pressures better suited for cold outdoor
temperatures (i.e., lower pressures), thereby causing
reductions in energy consumption, as previous compressors
typically have a minimum operating pressure at which they
operate for cold outdoor temperatures. However, the
expansion valves of the expansion stage 16 require minimum
refrigerant pressures to operate, whereby it is contemplated
to provide pumps 104 to increase the refrigerant pressure
upstream of the expansion stage 16, to ensure the first
refrigerant is in an appropriate condition for expansion.
Electronic/automatic expansion valves could be used as an
alternative to the pumps 104, as pressure increasing means.
TRANSFER ACCUMULATORS
Referring to the drawings and, more particularly,
to Fig. 4, a transfer accumulator, such as the transfer
accumulators 80 and 80', is generally shown at 300. The
transfer accumulator 300 is shown having a wall thereof
removed to illustrate its interior.
The transfer accumulator 300 has a vessel body
302 that accumulates the second refrigerant of the
evaporator circuit 19 (Figs. 1-3), which circulates through
the vessel body 302 by the inlets 303 and outlets 305. A
heat exchanger 304 passes through the vessel body 302, and
is immersed in the second refrigerant accumulated in the
vessel body 302. The first refrigerant of the main circuit
11 (Figs. 1-3) circulates through the heat exchanger 304 so
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as to be in a heat-exchange relation with the second
refrigerant in the vessel body 302, as described above for
Figs. 1-3. The heat exchanger 304 is a plate heat
exchanger, having a plurality of plates 306 through which
the first refrigerant circulates, through inlets 308 and
outlets 310.
Accordingly, the second refrigerant accumulating
in the vessel body 302 is preferably subjected to a phase
change, according to its nature. For instance, a
l0 glycol/water mixture used as second refrigerant typically
becomes slushy at the heat-exchange conditions in the
vessel body 302. Therefore, as illustrated in Fig. 4,
moving knives 312 are mounted onto the plates 306, and are
displaceable along direction A so as to break any solid
build-up on the plates 306. The displacement of the moving
knives 312 may be actuated using compressed air from the
pressure source 90 (Figs. 1 and 3), or the pressure source
190 (Fig. 2). The moving knives 312 may alternatively be
motorized.
In Fig. 5, there is shown an alternative
configuration for the heat exchanger 304, in that the
plates 306 of Fig. 4 are substituted by coils 314.
Therefore, the moving knives 312 are equipped to break
solid build-ups between the passes of the coils 314.
In the event that the transfer accumulator 300 is
used in the refrigeration systems of Figs. 1 and 3, the
vessel body 302, must be a pressure chamber, capable of
sustaining the pressure supplied by the pressure source 90.
In such as case, a bleed valve 316 is provided to ensure
the pressure within the vessel body 302 remains below
expected levels.
In the embodiments of Figs. 1 to 3, there are a
pair of transfer accumulators according to the sequence of
steps through which the second refrigerant goes. In order
to provide feedback to a controller to ensure the proper
operation of the evaporator circuit 19, level detectors
(e.g., optical, mechanical) are typically provided in the
CA 02518553 2005-09-08
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vessel body 302 to signal when it is required to shift the
feeding sequence from one accumulator to another.
It is contemplated to provide alternative
solutions to embody the heat-exchange relation between the
first and the second refrigerant. For instance, a slush
making machine, having a rotary knife that prevents solid
build-ups on the heat exchangers, may be used in accordance
with the embodiments of the present invention.
It is within the ambit of the present invention to
l0 cover any obvious modifications of the embodiments described
herein, provided such modifications fall within the scope of
the appended claims.
