Note: Descriptions are shown in the official language in which they were submitted.
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C02 REFRIGERATION SYSTEM
FOR ICE-PLAYING SURFACES
FIELD OF THE APPLICATION
The present application relates to refrigeration
systems used in industrial refrigeration applications, such
as rinks, curling centers and arenas, to refrigerate an ice-
skating or ice-playing surface, and more particularly to
such refrigeration systems using CO2 refrigerant.
BACKGROUND OF THE ART
With the growing concern for global warming, the
use of chlorofluorocarbons (CFCs) and hydrochlorofluoro-
carbons (HCFCs) as refrigerant has been identified as having
a negative impact on the environment. These chemicals have
non-negligible ozone-depletion potential and/or global-
I5 warming potential.
As alternatives to CFCs and HCFCs, ammonia, hydro-
carbons and CO2 are used as refrigerants. Although ammonia
and hydrocarbons have negligible ozone-depletion potential
and global-warming potential as does CO2, these refrigerants
are highly flammable and therefore represent a risk to local
safety. On the other hand, CO2 is environmentally benign
and locally safe.
Ice-playing surfaces typically have large-scale
heat exchangers disposed under the ice surface to
refrigerate the ice surface. Considering the specific use
of such refrigeration systems, and thus the requirement for
a refrigerant at a precise range of temperature, brine is
currently used in such refrigeration systems. The brine
circulates in a closed circuit and is in a heat-exchange
relation with a refrigeration circuit. However, these
refrigeration circuits often use refrigerants that are
harmful to the environment.
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SUMMARY OF THE APPLICATION
It is therefore an aim of the present disclosure
to provide a CO2 refrigeration system for ice surfaces, that
addresses issues associated with the prior art.
Therefore, in accordance with the present applica-
tion, there is provided a CO2 refrigeration system
comprising a CO2 condensation reservoir in which CO2
refrigerant is accumulated and circulates between a supra-
compression loop and an evaporation loop; the supra-
compression loop comprising a compression stage in which CO2
refrigerant from at least the CO2 condensation reservoir is
compressed to at least a supracompression state, a cooling
stage in which the CO2 refrigerant from the compression
stage releases heat, and a pressure-regulating unit in a
line extending from the cooling stage to the CO2
condensation reservoir to maintain a pressure differential
therebetween; and the evaporation loop comprising an
evaporation stage in which the CO2 refrigerant from at least
the CO2 condensation reservoir absorbs heat in a heat
exchanger, the heat exchanger being connected to an ice-
playing surface refrigeration circuit in which cycles a
second refrigerant, such that the CO2 refrigerant absorbs
heat from the second refrigerant in the heat exchanger.
Further in accordance with the present
application, there is provided a CO2 refrigeration system
comprising a CO2 condensation exchanger for heat exchange
between a supracompression loop of CO2 refrigerant and an
evaporation loop of CO2 refrigerant; the supracompression
loop comprising a compression stage in which CO2 refrigerant
having absorbed heat in the condensation exchanger is
compressed to at least a supracompression state, a cooling
stage in which the CO2 refrigerant from the compression
stage releases heat, and a pressure-regulating unit in a
line extending from the cooling stage to the condensation
exchanger to maintain a pressure differential therebetween;
and the evaporation loop comprising a condensation reservoir
in which CO2 refrigerant having released heat in the
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condensation exchanger is accumulated in a liquid state, and
an evaporation stage in which the CO2 refrigerant from the
condensation reservoir absorbs heat to cool an ice-playing
surface, to then return to one of the condensation reservoir
and the condensation exchanger.
Still further in accordance with the present
application, there is provided a CO2 refrigeration system
comprising a CO2 condensation reservoir in which CO2
refrigerant is accumulated and circulates between a supra-
compression loop and an evaporation loop; the supra-
compression loop comprising a compression stage in which CO2
refrigerant from at least the CO2 condensation reservoir is
compressed to at least a supracompression state, a cooling
stage in which the CO2 refrigerant from the compression
stage releases heat, and a pressure-regulating unit in a
line extending from the cooling stage to the CO2
condensation reservoir to maintain a pressure differential
therebetween; the evaporation loop comprising an evaporation
stage of pipes under an ice-playing surface in which
circulates the CO2 refrigerant to absorb heat to cool an
ice-playing surface, to then return to the CO2 condensation
reservoir; and a geothermal well loop in heat-exchange
relation with the CO2 refrigerant, the geothermal well loop
having a geothermal heat exchanger for heat exchange between
the CO2 refrigerant of one of the evaporation loop and the
compression loop and another refrigerant absorbing heat from
the CO2 refrigerant, the geothermal well loop extending to a
geothermal well in which the other refrigerant releases heat
geothermally.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram of a CO2 refrigeration
system for skating surfaces in accordance with a first
embodiment;
Fig. 2 is a block diagram of a CO2 refrigeration
system for skating surfaces in accordance with a second
embodiment;
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Fig. 3 is a block diagram of a CO2 refrigeration
system with a geothermal well in accordance with a third
embodiment;
Fig. 4 is a block diagram of a CO2 refrigeration
system with a geothermal well in accordance with a fourth
embodiment; and
Fig. 5 is a schematic view of a modulated
pressure-relief system for use with the CO2 refrigeration
systems of the previous figures.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Fig. 1, a CO2 refrigeration system in
accordance with an embodiment is illustrated at 1. The CO2
refrigeration system 1 has a CO2 refrigeration circuit
comprising a CO2 condensation reservoir 12. The
condensation reservoir 12 accumulates CO2 refrigerant in a
liquid and gaseous state, and may be in a heat-exchange
relation with a closed condensation circuit that absorbs
heat from the CO2 refrigerant, with examples given
hereinafter.
Line 14 directs CO2 refrigerant from the
condensation reservoir 12 to an evaporation stage via
pump(s) 15 or expansion valve(s). As is shown in Fig. 1,
the CO2 refrigerant is supplied in a liquid state by the
condensation reservoir 12 into line 14. The pump 15 ensures
a suitable flow of liquid CO2 refrigerant to the evaporation
exchanger 16. In some instances, expansion valve(s) 15 may
be used to control the pressure of the CO2 refrigerant,
which is then fed to the evaporation exchanger 16. Any
appropriate means may be used to put the CO2 refrigerant in
suitable condition, such as heat exchangers to vaporize the
refrigerant.
The evaporation exchanger 16 features the heat
exchange between the CO2 refrigerant and the refrigerant of
the ice-playing surface. The ice-playing surface
refrigerant circulating in the ice-playing surface is
typically brine, but may be other types of fluid, such as
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alcohol-based fluid (e.g., glycol) or the like. In one
embodiment, the CO2 circulates in pipes upon which fins are
provided. The pipes of the evaporator exchanger 16 are
typically positioned in a bath of the ice-playing surface
refrigerant. In another embodiment, the refrigeration
system 1 is retrofitted to an existing ice-playing surface
refrigeration circuit 17. It is pointed out that the
expansion valve(s) 15 may be part of a refrigeration pack in
the mechanical room, as opposed to being at the evaporation
exchanger 16.
The CO2 refrigerant exiting the evaporation stage
16 is returned to the condensation reservoir 12 via line 18.
Alternatively, the CO2 refrigerant may be directed to the
inlet of compressors of the transcritical circuit or loop,
via line 19. In such a case, it may be required to provide
some form of protection in line 19 to vaporize the CO2
refrigerant fed to the inlet of the compressors, such as an
evaporator, a heat exchanger or source of heat, valves,
among numerous possibilities.
The transcritical circuit or loop (i.e., supra-
compression circuit) is provided to compress the CO2
refrigerant exiting from the condensation reservoir 12 to a
transcritical state, for heating purposes, or supra-
compressed state. In both compression states, the CO2
refrigerant is pressurized with a view to maintaining the
condensation reservoir 12 at a high enough pressure to allow
vaporized CO2 refrigerant to be circulated in the
evaporation stage 16, as opposed to liquid CO2 refrigerant.
In one embodiment, the pressure is high enough for the CO2
refrigerant to circulate to the evaporation exchanger 16 via
the action of the pump 15.
A line 30 (using valve 30A) relates the
condensation reservoir 12 to a heat exchanger 31 and
subsequently to a supracompression stage 32. The heat
exchanger 31 or any other appropriate means may be provided
to vaporize the CO2 refrigerant fed to the supracompression
stage 32 (e.g., feed from a top of the condensation
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reservoir 12, multiple reservoirs in specific arrangement,
etc) . The supracompression stage 32 features one or more
compressors (e.g., BockTM, DorinTM), that compress the CO2
refrigerant to a supracompressed or transcritical state.
In the supracompressed or transcritical state, the
CO2 refrigerant is used to heat a secondary refrigerant via
heat-reclaim exchanger 34, or may be used directly in a
heating unit, with a fluid such as air blown thereon to heat
parts of the building related to the ice-playing surface.
In the heat-reclaim exchanger 34, the CO2 refrigerant is in
a heat-exchange relation with the secondary refrigerant
circulating in the secondary refrigerant circuit 35, or with
a fluid blown on the heat exchanger 34. In the event that a
secondary refrigerant is used, the secondary refrigerant is
preferably an environmentally sound refrigerant, such as
water or glycol, that is used as a heat-transfer fluid.
Because of the supracompressed or transcritical state of the
CO2 refrigerant, the secondary refrigerant circulating in
the circuit 35 reaches a high temperature. Accordingly, due
to the high temperature of the secondary refrigerant, lines
of smaller diameter may be used for the secondary
refrigerant circuit 35. It is pointed out that the
secondary refrigerant circuit 35 may be the largest of the
circuits of the refrigeration system 1 in terms of quantity
of refrigerant. Therefore, the compression of the CO2
refrigerant into a transcritical state by the transcritical
circuit allows the lines of the secondary refrigerant
circuit 35 to be reduced in terms of diameter. It is
pointed out that heat-reclaim exchanger 34 may include
individual heating units used to produce heat locally. Such
heating units 35 are typically a coil and fan assembly. The
control of the amount of refrigerant sent to each heating
unit 35 is described hereinafter.
A gas-cooling stage 36 is provided in the
transcritical circuit. The gas-cooling stage 36 absorbs
excess heat from the CO2 refrigerant in the transcritical
state, with a view to re-injecting the CO2 refrigerant into
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the condensation reservoir 12. Although it is illustrated
in a parallel relation with the heat-reclaim exchanger 34,
the gas-cooling stage 36 may be in series therewith, or in
any other suitable arrangement. Although not shown,
appropriate valves are provided so as to control the amount
of CO2 refrigerant directed to the gas-cooling stage 36, in
view of the heat demand from the heat-reclaim exchanger 34.
In warmer climates in which the demand for heat is
smaller, the CO2 refrigerant is compressed to a supra-
compressed state, namely at a high enough pressure to allow
the expansion of the CO2 refrigerant at the exit of the
condensation reservoir 12, so as to reduce the amount of CO2
refrigerant circulating in the refrigeration circuit. A by-
pass line is provided to illustrate that the heat-reclaim
exchanger 34 and the gas-cooling stage 36 may be optional
for warmer climates.
The gas-cooling stage 36 may feature a fan blowing
a gas refrigerant on coils. The speed of the fan may be
controlled as a function of the heat demand of the heat-
reclaim exchanger 34. For an increased speed of the fan,
there results an increase in the temperature differential at
opposite ends of the gas-cooling stage 36.
Lines 37 and 38 return the CO2 refrigerant to the
condensation reservoir 12, and thus to the refrigeration
circuit. The line 37 may feed the heat exchanger 31 such
that the CO2 refrigerant exiting the stages 34 and 36
releases heat to the CO2 refrigerant fed to the supra-
compression stage 32, for the CO2 refrigerant fed to the
supracompression stage 32 to be in a gaseous state.
In the case of transcritical compression, a CO2
transcritical pressure-regulating valve 39 is provided to
maintain appropriate pressures at the stages 34 and 36, and
in the condensation reservoir 12. The CO2 transcritical
pressure-regulating valve 39 is for instance a DanfossTM
valve. Any other suitable pressure-control, pressure-
regulating, pressure-reducing device may be used as an
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alternative to the valve 39, such as any type of valve or
loop.
The condensation circuit and the supracompression
circuit allow the condensation reservoir 12 to store
refrigerant at a relatively medium pressure. The pump 15
then ensures the circulation of the CO2 refrigerant in the
evaporation exchanger 16. In the embodiment featuring
expansion valve 15, as CO2 refrigerant is vaporized
downstream of the expansion valve 15, the amount of CO2
refrigerant in the refrigeration circuit is reduced,
especially if the expansion valve 15 is in the refrigeration
pack.
It is considered to operate the supracompression
circuit (i.e., supracompression 32) with higher operating
pressure. CO2 refrigerant has a suitable efficiency at a
higher pressure. More specifically, more heat can be
extracted when the pressure is higher.
Referring now to Fig. 2, there is illustrated a
CO2 refrigeration system 2 for ice-playing surfaces. The CO2
refrigeration system 2 is similar to the CO2 refrigeration
system 1 of Fig. 1, whereby like elements will bear like
reference numerals. One difference between refrigeration
systems 1 and 2 is that the refrigeration system 2 features
two closed circuits of refrigerant in addition to the ice-
playing surface refrigeration circuit 17. More
specifically, the CO2 refrigeration circuit 2 of Fig. 2 has
a condensation exchanger 50 by which the refrigerant
circulating in the main refrigeration circuit 40 (i.e., CO2
or other refrigerants, if suitable) is in a heat-exchange
relation with CO2 refrigerant circulating in the
transcritical/supracompression circuit. Accordingly, in the
condensation exchanger 50, the CO2 refrigerant circulating
in the supracompression/transcritical circuit is used to
absorb heat from the refrigerant circulating in the main
refrigeration circuit 40. In an embodiment, both
refrigerants are CO2.
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Referring to Fig. 3, there is illustrated a CO2
refrigeration system 3 similar to the CO2 refrigeration
systems 1 and 2, whereby like elements and components will
bear like reference numerals. The valve 30A in line 30 may
be an expansion valve, evaporative pressure-regulating
valve, control valve or the like so as to ensure that the
compressors 32 are fed with vaporized CO2 refrigerant. The
refrigeration system 3 has one or more heating units 35 at
the outlet of the supracompression stage 32, in any given
arrangement with the exchanger 34 and gas-cooling stage 36.
The heating units 35 are typical direct-heating units,
having coils in which CO2 refrigerant circulates and upon
which air is blown for heating purposes.
According to an embodiment, there are a plurality
of the heating units 35. In another embodiment, the heating
units 35 are in a parallel relation, and they may or may not
be fed with CO2 refrigerant as a function of the heating
requirements. Moreover, the speed of the fans of the
heating units 35 may also be controlled for this purpose. A
valve or valves 35A are used to control the amount of CO2
refrigerant sent to each of the heating units 35 and/or to
heat-reclaim exchanger 34. For instance, if two of the
heating units 35 cover two different zones having different
heating requirements, the valves 35A and fans of each unit
may be adjusted to meet the local heating requirements. One
configuration is to have thermostats for the various zones
to adjust the amount of refrigerant sent to the heating
units 35 via the adjustment of the valves 35A.
A reservoir 55 may be provided between lines 37
and 38 to receive CO2 refrigerant, and ensure it is fed in
suitable condition to the condensation exchanger 50. For
instance, the line 38 may tap into a bottom of the reservoir
55 to direct liquid CO2 refrigerant to the condensation
exchanger 50. A valve 56 (e.g., expansion valve) may be
provided to ensure that the CO2 refrigerant is in a suitable
state to absorb heat from the CO2 refrigerant. In an
embodiment, valve 56 is used as pressure differential valve
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instead of valve 39 (not required in such a case to reduce
the pressure), with the supracompression pressure maintained
upstream of valve 56. With this configuration, the pressure
of the CO2 refrigerant in the main refrigeration circuit 40
may be kept lower, or other refrigerants may be used in the
main refrigeration circuit 40.
Still referring to Fig. 3, a heat exchanger 60 is
illustrated as extending from the condensation reservoir 12
and in fluid communication therewith so as to receive a feed
of CO2 refrigerant. The heat exchanger 60 is in fluid
communication with a geothermal well 61 by a geothermal
circuit. A refrigerant (e.g., glycol, or any appropriate
refrigerant such as alcohol-based refrigerants or the like)
circulates in the geothermal circuit, so as to absorb heat
from the CO2 refrigerant in the heat exchanger 60 and
release the heat in the well 61. Appropriate pumps 62
and/or 63 or flow controlling means may be used to ensure
that there is a suitable flow of refrigerant to the heat
exchanger 60. The pumps 62 and 63 are variably controlled.
In Fig. 3, although the refrigeration system 3 is
shown with an evaporation exchanger 16 and ice-rink cooling,
the refrigeration system 3 may be used for any appropriate
type of refrigeration, with or without an evaporation
exchanger 16. Moreover, the refrigeration system 3 may be
operated without a geothermal well in appropriate
conditions.
Referring to Fig. 4, a CO2 refrigeration system 4
similar to the CO2 refrigeration systems 1, 2 and 3 is
illustrated, whereby like elements and components will bear
like reference numerals. The refrigeration system 4
features a geothermal well loop, but does not have a
condensation exchanger 50 as does the refrigeration system
3. The CO2 refrigeration system 4 may be used to
refrigerate a skating rink or the like. For simplicity
purposes, the evaporation stage is generally shown as 17.
In the embodiment in which the CO2 refrigerant is sent
directly in the pipes of the ice-playing surface as part of
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the evaporation stage 17, the pump(s) 15 is well suited to
induce a suitable flow of liquid CO2 refrigerant into the
pipes of the ice-playing surface.
The refrigeration systems 1-3 may be used with
existing ice-playing surface piping, or as part of new ice-
rink refrigeration systems. The evaporation exchanger 16 is
modified to receive CO2 refrigerant. It may be required
that the coils be modified in view of the specifications of
the CO2 refrigerant versus the brine or other refrigerant
used in the ice-playing surface piping. The CO2
refrigeration systems 1-3 advantageously use the existing
hardware related to the ice-playing surface refrigeration.
It is pointed out that the CO2 refrigeration systems 1-3
need not be used only in a retrofit configuration.
Referring to Fig. 5, there is illustrated a
modulated pressure-relief system which may be used with any
one of the CO2 refrigeration systems 1-4 of the previous
figures, if appropriate. The modulated pressure-relief
system has a line 70 that is in fluid communication with the
evaporators of the refrigeration system. A pair of valves
71 and 72 are in a parallel arrangement with the line 70,
and are part of exhaust lines opened to the atmosphere, for
exhausting CO2 refrigerant. Valve 71 is a modulating valve,
automatically operable from a set point pressure. The
modulating valve 71 therefore gradually opens upon the
pressure in the line reaching the set point pressure. Any
other gradually-opening type of valve may be used as valve
71. For instance, valve 71 may be operated by a controller
(e.g., central processing unit of the CO2 refrigeration
systems), or may be a mechanical valve with an appropriate
controlled-opening mechanism.
Valve 72 is a pressure-relief valve. The
pressure-relief valve 72 has its own set point pressure,
which is higher than the set point pressure of the
modulating valve 71. The pressure-relief valve 72 opens
when the set point pressure is reached. Accordingly, if the
pressure is high in the evaporators, but not at the set
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point of relief, the pressure increase in the evaporators 70
will be modulated to reduce the pressure increase. The
opening of valve 72 in a relief condition may be controlled
so as to be a slow release to limit the release of
refrigerant to the atmosphere. Valve 72 may be any
appropriate type of relief valve, such as a mechanical
valve, or a valve controlled by the controller of the CO2
refrigeration system.
The CO2 refrigeration systems described above for
Figs. 1-4 are generally separated into a supracompression
loop and an evaporation loop. The supracompression loop
comprises the supracompression stage, while the evaporation
loop comprises the evaporation stage. The loops may be
separated from one another by the condensation exchanger 50
(Figs. 2 and 3) , in which case the CO2 refrigerant does not
circulate between loops. In Figs. 1 and 4, the loops are
interrelated by the condensation reservoir 12, in which case
the CO2 refrigerant circulates between loops.
The CO2 refrigeration systems described above for
Figs. 1-4 are used for ice-playing surfaces, which may
include ice-skating surfaces of arenas or of outdoor
applications, skating rinks (e.g., speed skating), the
playing surface of curling centers, or any other application
in which a relatively large-scale refrigerated surface is
used. Moreover, although the word "ice" is used (and thus
water), it is understood that the medium used for the
surface may be any appropriate fluid reaching a solid state.
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