Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
I
TITLE OF THE INVENTION
MECHANICAL SUBCOOLING OF TRANSCRITICAL R744 REFRIGERATION
SYSTEMS USING SEPARATE R-744 OR OTHER REFRIGERANTS UNITS
FOR MECHANICAL SUBCOOLING AND AS A HEAT PUMP FOR HEAT
RECLAIM PURPOSES
TECHNICAL FIELD
[0001] The present disclosure concerns refrigeration systems, and more
particularly R-744 transcritical refrigeration systems with mechanical
subcooling,
heat pump heat reclaim and floating head pressure.
BACKGROUND OF THE INVENTION
[0002] R-744 transcritical refrigeration systems are used in supermarkets to
refrigerate or to maintain perishable products in a frozen state, such as
foodstuff.
[0003] A major disadvantage of a transcritical R-744 refrigeration system is
its
low energy efficiency ratio (EER) during the warmer periods of the year
(critical
point 87/61 F).
[0004] When the outside air temperature is such that the R-744 vapors cooled
by
an exterior heat exchanger (gas cooler) have a temperature higher than the
critical point, there will be no condensation. Therefore, in order to obtain a
liquid
state, the cooled R-744 vapors are fed though a throttling device, thus
reducing
the pressure and the temperature of the vapors. The result is a mixture of
liquid
and vapor which, at an ambient temperature of 90 F, will have a ratio of 55%
liquid and 45% vapor. It is evident that the mass flow of the compressor in
transcritical operation has to be almost doubled in order to obtain the
required
refrigeration capacity. Hence, there is a necessity for a system and method
for
increasing the efficiency of an R-744 transcritical refrigeration system.
SUMMARY OF THE INVENTION
[0005] It is an object of the present disclosure to provide an improved
transcritical
R-744 refrigeration system with a higher energy efficiency ratio.
Date Recue/Date Received 2020-10-30
2
[0006] It is a further object of the present disclosure to provide a
transcritical
refrigeration system with an energy efficiency ratio (EER) of a level
comparable to
that of refrigeration systems using common refrigerants operating in
subcritical
mode, by means of a separate subcooling system using R-744 or other
refrigerants, connected to the transcritical R-744 system by means of heat
exchangers.
[0007] Accordingly, the present disclosure provides a mechanical subcooling
system for use with a transcritical R-744 refrigeration system having at least
one
first compressor for compressing R-744 vapors directed to a cooler operatively
connected to a throttling device, for reducing the pressure and temperature of
the
R-744 vapors to a level required for the normal operation of the R-744
refrigeration system, through a first heat exchanger, the first heat exchanger
being operatively connected to the at least one compressor to provide the R-
744
vapors to the at least one first compressor and to receive compressed R-744
vapors from the at least one first compressor, a by-pass valve for maintaining
a
required flow of R-744 vapors through the first heat exchanger, a first
receiver for
receiving the R-744 vapors from the first throttling device, and a condenser,
the
mechanical subcooling system comprising a second heat exchanger operatively
connected between the first heat exchanger and the first receiver for
subcooling
the R-744 exiting the gas cooler, a first pressure regulating valve (flash gas
bypass valve) for feeding R-744 vapors from the first receiver to the at least
one
first compressor, and at least one second compressor for mechanically
subcooling of R-744 vapors leaving the cooler through the second heat
exchanger, wherein the mechanical subcooling system is operatively connectable
to the R-744 refrigeration system.
[0008] Conveniently, the mechanical subcooling system further comprises a
second pressure regulating valve operatively connected between the at least
one
second compressor and the condenser.
[0009] Conveniently, the transcritical R-744 refrigeration system further
including
a third heat exchanger operatively connected between the at least one second
compressor and the condenser for transferring heat to a circulation system to
be
used during warm periods for dehumidification purposes.
Date Recue/Date Received 2020-10-30
3
[0010] Conveniently, the mechanical subcooling system further comprises a
second pressure regulating device operatively connected between the third heat
exchanger and the condenser.
[0011] In an embodiment, conveniently, the mechanical subcooling system
further comprises a fourth heat exchanger operatively connected between the at
least one first compressor and the cooler, wherein the at least one second
compressor for mechanically subcooling of R-744 vapors leaving the cooler
through the second heat exchanger or, conveniently, for heat reclaim through
the
fourth heat exchanger.
[0012] Conveniently, the mechanical subcooling system further comprises a
first
motorized valve operatively connected between the second heat exchanger and
the at least one second compressor and a second motorized valve operatively
connected between the fourth heat exchanger and the at least one second
compressor.
[0013] Conveniently, when subcooling is required, the first motorized valve is
open and the second motorized valve is closed.
[0014] Conveniently, the mechanical subcooling system further comprises a
first
expansion valve operatively connected between a second receiver and the
second heat exchanger, and a second expansion valve operatively connected
.. between the second receiver and the fourth heat exchanger.
[0015] Conveniently, when subcooling is not required, the first expansion
valve
and the first motorized valve are closed, and the second expansion valve and
the
second motorized valve are opened.
[0016] Conveniently, the mechanical subcooling system further comprises a
third
throttling device, wherein the subcooling system uses R-744 as its
refrigerant, the
condenser is replaced by a gas cooler, and, conveniently the subcooling system
is operable as a transcritical R-744 system.
[0017] The present disclosure also provides a transcritical R-744
refrigeration
system having at least one first compressor for compressing R-744 vapors
directed to a cooler operatively connected to a throttling device, for
reducing the
pressure and temperature of the R-744 vapors to a level required for the
normal
Date Recue/Date Received 2020-10-30
4
operation of the R-744 refrigeration system, through a first heat exchanger,
the
first heat exchanger being operatively connected to the at least one first
compressor to provide the R-744 vapors to the at least one first compressor
and
to receive compressed R-744 vapors from the at least one first compressor, a
by-
pass valve for maintaining a required flow of R-744 vapors through the first
heat
exchanger, a receiver for receiving a R-744 mix of vapour and liquid from the
throttling device, and the transcritical R-744 refrigeration system comprising
and
being operatively connectable to a mechanical subcooling system as above.
[0018] The present disclosure also provides a method for improving the energy
efficiency ratio of a transcritical R-744 refrigeration system having at least
one
compressor for compressing R-744 vapors directed to a cooler operatively
connected to a throttling device, for reducing the pressure and temperature of
the
R-744 vapors to a level required for the normal operation of the R-744
refrigeration system, through a first heat exchanger, the first heat exchanger
being operatively connected to the at least one compressor to provide the R-
744
vapors to the at least one first compressor and to receive compressed R-744
vapors from the at least one first compressor, a by-pass valve for maintaining
a
required flow of R-744 vapors through the first heat exchanger, and a receiver
for
receiving a R-744 mix of vapour and liquid from the throttling device, the
method
comprising mechanically subcooling of the R-744 vapors leaving the cooler by
an
operatively connectable a mechanical subcooling system as above.
[0019] All of the foregoing and still further objects and advantages of the
invention will become apparent from a study of the following specification,
taken
in connection with the accompanying drawings wherein like characters of
reference designate corresponding parts throughout the several views.
BRIEF DESCRIPTION OF THE FIGURES
[0020] Embodiments of the disclosure will be described by way of examples only
with reference to the accompanying drawing, in which:
[0021] FIG. 1 is a schematic diagram of a typical transcritical R-744
refrigeration
system;
Date Recue/Date Received 2020-10-30
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[0022] FIG. 2 is a schematic diagram of the transcritical R-744 refrigeration
system of FIG. 1 with mechanical subcooling system incorporated into the main
refrigeration system;
[0023] FIG. 3 is a schematic diagram of the transcritical R-744 refrigeration
system of FIG. 1 with separate mechanical subcooling system using other than
R-744 refrigerants; and
[0024] FIG. 4 is a schematic diagram of the transcritical R-744 refrigeration
system of FIG. 1 with separate mechanical subcooling system using R-744
refrigerant.
.. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] R-744 transcritical refrigeration system
[0026] Referring to FIG. 1, there is shown a typical R-744 transcritical
refrigeration system 50. R-744 vapors are compressed by compressors 1 and
directed through conduit 34, oil separator 31, conduit 19, heat exchanger 5
and
conduit 20 to cooler 11, for example a gas cooler. The heat from the
compressed
R-744 vapors from compressors 1 is transferred in heat exchanger 5 to, for
example, a glycol circulation system through conduits 41 and 42, to be used
during the warm periods of the year for dehumidification purposes. From the
cooler lithe cooled transcritical R-744 vapors are directed through conduit
21,
heat exchanger 12 and fed through conduit 30 to throttling device 16 where its
pressure and temperature are reduced to a level required for the normal
operation of the refrigeration system 50 both at low and medium temperatures
and then is fed to receiver 17, which is operatively connected to defrost
compressors 18. R-744 vapors from heat exchanger 12 are directed through
conduit 29 and conduit 32 to the suction of compressors 1, which are connected
through conduit 33 and conduit 28 to heat exchanger 12 where a heat transfer
between R-744 vapors from the cooler 11 and the R-744 vapors from the suction
of the compressors 1 takes place in order to insure stable suction temperature
at
a desired level. The by-pass valve 15 maintains the required flow of suction
vapors through heat exchanger 12 in order to insure the required temperature
of
the suction vapors.
Date Recue/Date Received 2020-10-30
6
[0027] R-744 transcritical refrigeration system with mechanical subcooling
where
the subcoolinq unit is an inteqral part of the main refriqeration system (FIG.
2)
[0028] Referring now to FIG. 2, there is shown a transcritical R-744
refrigeration
system with mechanical subcooling 60 which is basically the transcritical R-
744
refrigeration system 50 of FIG. 1 to which mechanical subcooling 62 is added
as
an integral part of the system 50. The R-744
vapors compressed by
compressors 1 are directed through conduit 34, oil separator 31, conduit 19,
heat
exchanger 4, conduit 35 and conduit 20 to cooler 11. From the cooler 11 the
cooled transcritical R-744 vapors are directed through conduit 21, heat
exchanger 12, conduit 22, heat exchanger 3 and throttling device 13 to
receiver
14 where a separation of R-744 vapors and liquid occurs. The R-744 vapors
from receiver 14 are fed through conduit 36 and pressure regulating valve
(flash
gas by-pass valve) 37 to conduit 33 and to conduit 32, and to the suction of
compressors 1. The suction of compressors 1 is connected through conduit 33
and conduit 28 to heat exchanger 12 where a heat transfer between R-744
vapors from the cooler 11 and the R-744 vapors from the suction of the
compressors 1 take place in order to insure stable suction temperature at a
desired level. The by-pass valve 15 maintains the required flow of suction R-
744
vapors through heat exchanger 12 in order to insure the required temperature
of
.. the suction vapors.
[0029] The compressors 2 are used for mechanical subcooling of the R-744
refrigerant leaving the cooler 11 through heat exchanger 3 or for heat reclaim
through heat exchanger 4. Additional subcooling is provided for R-744
refrigerant
leaving the receiver 14 by means of heat exchanger 43. The suction ports of
.. compressors 2 are connected through motorized valves 9 and 44, and through
conduits 26 and 48 to heat exchangers 3 and 43 or through motorized valve 10
and conduit 27 to heat exchanger 4.
[0030] When subcooling is required, valves 9 and 44 are open, and valve 10 is
closed. Liquid R-744 is fed through conduits 23, 46 and 24 to expansion valves
8
and 45. The evaporation of the liquid R-744 in heat exchangers 3 and 43
absorbs heat from the R-744 refrigerant flowing through the other side of heat
exchangers 3 and 43 (vapors in heat exchanger 3 and liquid in heat exchanger
43), thus reducing its temperature. The liquid R-744 is then fed through
conduit
30 to throttling device 16 where its pressure and temperature are reduced to a
Date Recue/Date Received 2020-10-30
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level required for normal operation of the transcritical R-744 system 60 both
at
low and medium temperatures, and then is fed to receiver 17, which is
operatively
connected to the defrost compressors 18.
[0031] The evaporated R-744 refrigerant from heat exchangers 3 and 43 is fed
through conduits 26 and 48, and through motorized valves 9 and 44 to the
suction ports of compressors 2. The
compressed R-744 vapors from
compressors 2 are fed through heat exchanger 5 and conduit 39 to pressure
regulating valve 6. From the pressure regulating valve 6 the R-744 vapors are
fed through conduits 40 and 20 to cooler 11. The heat from the compressed
R-744 vapors from compressors 2 is transferred in heat exchanger 5 to, for
example, a glycol circulation system through conduits 41 and 42, and is used
during the warm periods of the year for dehumidification purposes or water
heating.
[0032] During colder periods of the year, where subcooling is not required,
valves
8, 9, 44 and 45 are closed. Valves 7 and 10 are opened. Liquid R-744 is fed
through conduits 23 and 47 to the expansion valve 7 and then to heat exchanger
4 where it evaporates and absorbs heat from the compressed R-744 vapors from
compressors 1, which are fed through conduit 34, oil separator 31 and conduit
19
to heat exchanger 4.
[0033] The heat is then, by means of compressors 2, transferred in heat
exchanger 5 to, for example, a glycol circulation system through conduits 41
and
42, and is used for comfort heating of the premises.
[0034] R-744 transcritical refrigeration system with mechanical subcooling
where
the subcooling unit is not an integral part of the main refrigeration system
and
uses other than R-744 refrigerants (FIG. 3)
[0035] Referring now to FIG. 3, there is shown a transcritical R-744
refrigeration
system with mechanical subcooling where the subcooling unit is not an integral
part of the main refrigeration system and uses refrigerants other than R-744,
in
accordance with an illustrative embodiment of the present disclosure. In such
an
embodiment, the mechanical subcooling system 62 is operatively connectable
and subsequently removable from an existing R-744 refrigeration system, and
thus is not required to be designed and built in conjunction with an R-744
refrigeration system. The R-744 vapors compressed by compressors 1 are
Date Recue/Date Received 2020-10-30
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directed through conduit 34, oil separator 31, conduit 19, heat exchanger 4,
conduit 35 and conduit 20 to cooler 11. From the cooler 11 the cooled
transcritical R-744 vapors are directed through conduit 21, heat exchanger 12,
conduits 22 and 38, heat exchanger 3, conduit 30 and throttling device 16 to
receiver 17 where a separation of R-744 vapors and liquid occurs. The R-744
vapors from receiver 17 are fed through conduit 36 and pressure regulating
valve
(flash gas by-pass valve) 37 to conduit 33 and conduit 28 to heat exchanger 12
where a heat transfer between R-744 vapors from the cooler 11 and the R-744
vapors from the suction of the compressors 1 take place in order to insure
stable
suction temperature at a desired level. The by-pass valve 15 maintains the
required flow of suction R-744 vapors through heat exchanger 12 in order to
insure the required temperature of the suction vapors.
[0036] The compressors 2 are used for mechanical subcooling of the R-744
refrigerant leaving the cooler 11 through heat exchanger 3 or optionally for
heat
reclaim through heat exchanger 4. The suction ports of compressors 2 are
connected through motorized valve 9, and through conduit 26 to heat exchanger
3 or through motorized valve 10 and conduit 27 to heat exchanger 4.
[0037] When subcooling is required, valves 9 is open, and valve 10 is closed.
Liquid refrigerant is fed through conduits 23 and 24 to expansion valve 8. The
evaporation of the liquid refrigerant in heat exchanger 3 absorbs heat from
the
R-744 refrigerant flowing through the other side of heat exchanger 3 thus
reducing its temperature. Expansion valve 8 is operatively connected between
receiver 51 and heat exchanger 3. Expansion valve 7 is operatively connected
between receiver 51 and heat exchanger 4. The R-744 is then fed through
conduit 30 to throttling device 16 where its pressure and temperature are
reduced
to a level required for normal operation of the transcritical R-744 system 60
both
at low and medium temperatures, and then is fed to receiver 17.
[0038] The evaporated refrigerant from heat exchanger 3 is fed through
conduits
26, through motorized valve 9 and through conduit 48 to the suction ports of
compressors 2. The compressed refrigerant vapors from compressors 2 are fed
through heat exchanger 5 and conduit 39 to pressure regulating valve 6. From
the pressure regulating valve 6 the refrigerant vapors are fed through
conduits 40
to condenser 49. The heat from the compressed refrigerant vapors from
compressors 2 is transferred in heat exchanger 5 to, for example, a glycol
Date Recue/Date Received 2020-10-30
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circulation system through conduits 41 and 42, and is used during the warm
periods of the year for dehumidification purposes or water heating.
[0039] During colder periods of the year, in the event it is applicable, where
subcooling is not required, valve 8 is closed. Valves 7 and 10 are opened.
Liquid refrigerant is fed through conduits 23, 25 and 47 to the expansion
valve 7
and then to heat exchanger 4 where it evaporates and absorbs heat from the
compressed R-744 vapors from compressors 1, which are fed through conduit
34, oil separator 31 and conduit 19 to heat exchanger 4.
[0040] The heat is then, by means of compressors 2, transferred in heat
exchanger 5 to, for example, a glycol circulation system through conduits 41
and
42, and is used for comfort heating of the premises.
[0041] When the glycol circulation system is not used, the heat exchanger 5 is
eliminated and the hot compressed vapors from compressors 2 are fed to a set
of
heat reclaim coils ensuring direct heat transfer from the refrigerant vapors
to the
surrounding air.
[0042] R-744 Transcritical refrigeration system with mechanical subcoolinq
where
the subcooling unit is not an integral part of the main refrigeration system
and
uses R-744 as refrigerant (FIG .4)
[0043] The transcritical R-744 system shown on FIG. 4 operates exactly as the
system shown in FIG. 3 with the following differences:
- The subcooling system uses R-744 as its refrigerant;
- The heat exchanger 49 here is a gas cooler and not a condenser; and
- There is additional throttling device 6A which is necessary to insure the
operation of the subcooling system as a transcritical R-744 system.
[0044] Eneray Efficiency
[0045] By using mechanical subcooling as disclosed above with a transcritical
R-744 refrigeration system 60, the EER may go up to, for example, about 9.27
compared to the EER of a typical transcritical R-744 refrigeration system 50,
which is about 6.09. The compressors 2 used for the mechanical subcooling
have an energy efficiency ratio of about 14.00 due to their favorable
operating
conditions.
Date Recue/Date Received 2020-10-30
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[0046] It is clear that the mechanical subcooling of R-744 transcritical
refrigeration systems eliminates their major disadvantage of having low energy
efficiency.
[0047] During the cold periods of the year, a transcritical R-744
refrigeration
system with mechanical subcooling 60 can operate as a subcritical R-744
refrigeration system 50 and its energy efficiency then becomes similar to the
energy efficiency of a Freon refrigeration system when the ambient air
temperature is lower than about 12 C (53.6 F). No mechanical subcooling
should be required during these periods. What is important, however, is that
there is a need for heat recuperation for comfortable heating of the premises.
The R-744 will provide heat but at a low temperature level of around 70 F,
which
is not appropriate for space heating.
[0048] During these periods the compressors 2 used for subcooling operate as a
heat pump extracting heat from the refrigeration compressors 1 and elevate
this
heat to usable temperatures for space heating.
[0049] The scope of the claims should not be limited by the preferred
embodiments set forth in the examples, but should be given the broadest
interpretation consistent with the description as a whole.
Date Recue/Date Received 2020-10-30
