Note: Descriptions are shown in the official language in which they were submitted.
CA 02897081 2015-07-10
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10.3
TRANSCRITICAL R744 REFRIGERATION SYSTEM WITH GAS
COOLER OUTLET VAPORS USED AS A HEAT SOURCE FOR THE
DEHUMIDIFYING COIL
FIELD OF THE INVENTION
5 [0001] The present invention relates to transcritical R-744 refrigeration
systems,
and more specifically to transcritical R-744 refrigeration systems for
supermarkets and the like, which use multiple compressors and multiple
evaporators to refrigerate and/or to maintain in frozen conditions perishable
food products. The refrigeration system used is transcritical R744 system
10 having heat reclaim and dehumidifying capability.
BACKGROUND OF THE INVENTION
[0002] During some periods of the year when the ambient temperatures and
humidity are elevated, it is necessary to provide, in addition to the air
conditioning, a system which will reduce the relative air humidity in the
supermarket. Failing to do so will result in high air relative humidity inside
the
store, frequent defrosts, frosting of the surface of the food products and
discomfort for the customers.
[0003] The most frequently used dehumidifying method in supermarkets is to
install heating coil downstream of the air conditioning coil. The air from the
outlet of the air conditioning coil has low temperature and very high relative
humidity. By reheating this air to a comfortable temperature level the
relative
humidity is lowered to acceptable level (around 40%). Most often the heat of
the high pressure compressed refrigerant that vapors directly from the
discharge outlet of the compressors is used as a heat source for the heating
coil. This method provides sufficient heat for the dehumidification process
but in
the case of R744 transcritical system, having into consideration that the
dehumidification process is used mainly during the summer period, does not
provide increase of efficiency of the transcritical refrigeration system which
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during the summer period is significantly lower than that of the freon
refrigeration systems.
[0004] The need to improve the cycle efficiency during the warmer periods of
the year is obvious.
5 [0005] Accordingly, there is a need for an improved transcritical R-744
refrigeration system.
SUMMARY OF THE INVENTION
[0006] It is therefore a general object of the present invention to provide an
improved transcritical R-744 refrigeration system and method.
10 [00071 An advantage of the present invention is that the transcritical R-
744
refrigeration system and method, instead of using the high pressure
compressed refrigeration vapors directly from the discharge outlet of the
compressors as a heat source for the heating coil, uses the vapors from the
outlet of the gas cooler are as a heat source for the heating coil.
[0008] Another advantage of the present invention is that the transcritical R-
744
refrigeration system and method.uses only one heat exchanger for heat reclaim
and dehumidifying purposes.
[0009] A further advantage of the present invention is that the transcritical
R-744 refrigeration system and method, by using the vapors from the outlet of
the gas cooler as a heat source for dehumidification, a significant amount of
subcooling capacity is provided thus increasing the efficiency of the system
without installing additional equipment and without adding to the power
consumption of the system.
[0010] Still another advantage of the present invention is that the
transcritical
R-744 refrigeration system and method, by feeding vapors with lower
temperature through the dehumidifying heat exchanger, reduces the thermal
stress to the heat exchanger thus increasing the reliability and the useful
Fife of
the dehumidifying system.
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[0011] According to an aspect of the present invention, there is provided a
transcritical R-744 refrigeration system for supermarket with dehumidifying
capability, the transcritical R-744 refrigeration system having a vapor of a R-
744
refrigerant circulating from a compressor to a heat reclaim /dehumidifying
heat
5 exchanger, a gas cooler, a receiver and an evaporator, and back to the
compressor via a plurality of conduits and a plurality of valves, the
transcntical
R-744 refrigeration system comprising a modulating valve allowing heat of at
least a portion of the R-744 refrigerant leaving the gas cooler to directly
reach
and dehumidify the heat reclaim /dehumidifying heat exchanger before
10 circulating to the receiver.
[0012] In one embodiment, one of the plurality of conduits is a conduit
junction
located between the gas cooler and the receiver, one of the plurality of
valves is
a second valve located between the conduit junction and the receiver, and the
modulating valve is located between the conduit junction and the heat reclaim
/dehumidifying heat exchanger, wherein the modulating valve allowing heat of
all of the R-744 refrigerant leaving the gas cooler to directly reach and
dehumidify the heat reclaim /dehumidifying heat exchanger before circulating
to
the receiver when the modulating valve is open and the second valve is closed.
[0013] According to another aspect of the present invention, there is provided
a
method of dehumidifying a heat reclaim /dehumidifying heat exchanger of a
transcritical R-744 refrigeration system, the transcritical R-744
refrigeration
system having a vapor of a R-744 refrigerant circulating from a compressor to
a
heat reclaim /dehumidifying heat exchanger, a gas cooler, a receiver and an
evaporator, and back to the compressor via a plurality of conduits and a
plurality
of valves, the method comprising the step of: modulating a modulating valve to
allow heat of at least a portion of the R-744 refrigerant leaving the gas
cooler to
directly reach and dehumidify the heat reclaim /dehumidifying heat exchanger
before circulating to the receiver.
100141 In one embodiment, one of the plurality of conduits is a conduit
junction
located between the gas cooler and the receiver, one of the plurality of
valves is
a second valve located between the conduit junction and the receiver, the
modulating valve is located between the conduit junction and the heat reclaim
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/dehumidifying heat exchanger, wherein the method further comprising the step
of: dosing the second valve as to allow all of the R-744 refrigerant leaving
the
gas cooler to directly reach and dehumidify the heat reclaim /dehumidifying
heat
exchanger before circulating to the receiver.
5 [0015] Other objects and advantages of the present invention will become
apparent from a careful reading of the detailed description provided herein,
with
appropriate reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Further aspects and advantages of the present invention will become
10 better understood with reference to the description in association with
the
following Figure, wherein:
[0017] Figure 1 is a schematic view of a transcritical R-744 refrigeration
system
having the gas cooler outlet vapors used as a heat source for the
dehumidifying
the heating coil in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0018] With reference to the annexed drawings the preferred embodiment of the
present invention will be herein described for indicative purpose and by no
means as of limitation.
[0019] Referring to Figure 1, there is schematically shown a transcritical R-
744
refrigeration system 30 having the gas cooler outlet vapors used as a heat
source for the dehumidifying the heating coil in accordance with an embodiment
of the present invention.
[0020] The refrigeration system shown on Figure 1 is a simplified schematic of
the transcritical R-744 system 30 with the low temperature compressors and all
evaporators not being specifically shown since they are not participating
directly
into the dehumidifying and heat reclaim process.
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[0021] If heat reclaim or dehumidifying are not required, the compressed
refrigerant vapors from corn pressors 11 are fed through conduit 12 and
conduit
18 to the gas cooler 5, and then through conduit 19 and conduit 20 to the
throttling device 9 and then to the receiver (flash tank) 10. During this
5 operational configuration, valves 25 and 7 are fully open, while valves
3, 4, 6
and 8 are completely closed. Valve 7, the 'second valve', is located between
the gas cooler 5 and the receiver 10, downstream of a conduit junction 26
allowing the refrigerant vapors leaving the gas cooler 5 to circulate to a
heat
reclaim /dehumidifying heat exchanger 1 for the dehumidification thereof, as
10 further explained herein below.
[0022] If heat reclaim is required, valve 25 is adjusted to maintain a
pressure
higher than the pressure maintained by valve 3. Valve 4 is completely open.
The compressed vapors from compressors 11 are fed through conduit 12, valve
4 and conduit 13 to the heat reclaim /dehumidifying heat exchanger 1 where the
15 heat of the vapors is transferred to the air flowing through the heat
exchanger.
The valve 3 maintains the necessary pressure in order to provide maximum
efficiency. From heat exchanger 1, the vapors are fed through valve 3, conduit
14, conduit 16, conduit 17 and conduit 18 to the gas cooler 5. Valve 6 and 8
are
completely closed and valve 7 is completely open. From the gas cooler 5, the
20 vapors and/or liquid refrigerant, depending on the operation conditions,
are fed
through conduit 19 and conduit 20 to the throttling device 9 and from there to
the receiver 10.
[0023] If dehumidifying is required, valve 25 is completely open, valves 3, 4
and
7 are completely closed and valves 6 and 8 are completely open. The
25 compressed refrigeration vapors from compressors are fed through conduit
12,
valve 25 and conduit 18 to the gas cooler 5. The vapors from the outlet of the
gas cooler 5 are fed through conduit 19, junction 26, valve 6, conduit 22,
conduit
23, conduit 24 and conduit 13 to the heat reclaim /dehumidifying heat
exchanger 1. Cooled by the air-conditioning heat exchanger 2, air is reheated
30 by the dehumidifying heat exchanger 1, using the heat of the vapors from
the
gas cooler 5 outlet, thus reducing its relative humidity. From heat exchanger
1,
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the refrigerant is fed through conduit 14, conduit 15, conduit 21 and valve 8
to
conduit 20 and then to throttling device 9 and receiver 10.
[0024] An embodiment of the present invention is a method of dehumidifying a
heat reclaim /dehumidifying heat exchanger 1 of a transcritical R-744
5
refrigeration system 30. The method includes the step of modulating the
modulating valve 6 to allow heat of at least a portion of the R-744
refrigerant
leaving the gas cooler 5 to directly reach and dehumidify the heat reclaim
/dehumidifying heat exchanger 1 before circulating to the receiver 10.
[0025] Preferably, the method includes the step of closing the second valve 7
10 as to allow
all of the R-744 refrigerant leaving the gas cooler 5 to directly reach
and dehumidify the heat reclaim /dehumidifying heat exchanger 1 before
circulating to the receiver 10.
[0026] Although the present invention has been described with a certain degree
of particularity, it is to be understood that the disclosure has been made by
way
of example only and that the present invention is not limited to the features
of
the embodiments described and illustrated herein, but includes all variations
and modifications within the scope of the invention as hereinabove described
and hereinafter claimed.
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