BACKGROUND
The following description relates to chillers and, more particularly, to
sorption-based subcoolers.
Currently, chillers typically include an ejector for pressure recovery. In an
exemplary case, a compressor compresses a refrigerant and outputs the refrigerant
in superheated form to a gas cooler and then, in some cases, to an ejector. When
an ejector is provided, the ejector is used for work recovery or pressure recovery
of the refrigerant and can outputs the refrigerant in cooled form to an evaporator
and the compressor.
Until now, the refrigerant has often been a fluid with either a high
greenhouse warming potential (GWP) characteristic or a high ozone depletion
potential (ODP) characteristic. This is changing, however, and there is an
increasing demand for the use of natural, non-toxic, low-GWP and ODP
refrigerants leading to the use of carbon dioxide and other similar fluids as
refrigerants in supermarket cooling systems.
These systems can, in certain cases, have low coefficients of performance
(COP) at high ambient conditions in which the carbon dioxide moves into
supercritical/transcritical fluid zones.
BRIEF DESCRIPTION
According to an aspect of the disclosure, a cooling system is provided and
includes a compressor, an expansion valve, a gas cooler through which a
refrigerant received from the compressor passes toward the expansion valve in a
supercritical state, an evaporator interposed between the expansion valve and the
compressor and a vapor sorption subcooling system. The vapor sorption
subcooling system includes a desorber disposed to remove heat from refrigerant
flowing from the gas cooler toward the expansion valve.
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In accordance with additional or alternative embodiments, an ejector is
downstream from the desorber.
In accordance with additional or alternative embodiments, the vapor
sorption subcooling system includes a vapor absorption subcooling system.
In accordance with additional or alternative embodiments, a subcooling
refrigerant of the vapor absorption subcooling system includes a natural, low
greenhouse warming potential (GWP), low ozone depletion potential (ODP) and
non-flammable refrigerant.
In accordance with additional or alternative embodiments, a subcooling
refrigerant of the vapor absorption subcooling system includes carbon dioxide.
In accordance with additional or alternative embodiments, the vapor
absorption subcooling system includes a subcooling compressor, which is
receptive of subcooling refrigerant from the desorber, an absorber for subcooling
refrigerant absorption by an absorbent, a subcooling gas cooler through which the
subcooling refrigerant received from the subcooling compressor passes toward the
absorber in a supercritical state and a pump configured to pump at least the
absorbent from the desorber to the absorber.
In accordance with additional or alternative embodiments, the absorbent
includes an ionic liquid.
In accordance with additional or alternative embodiments, the vapor
sorption subcooling system includes a vapor adsorption subcooling system.
In accordance with additional or alternative embodiments, a subcooling
refrigerant of the vapor adsorption subcooling system includes a natural, low
greenhouse warming potential (GWP), low ozone depletion potential (ODP) and
non-flammable refrigerant.
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In accordance with additional or alternative embodiments, a subcooling
refrigerant of the vapor adsorption subcooling system includes carbon dioxide.
In accordance with additional or alternative embodiments, the vapor
adsorption subcooling system includes a subcooling compressor, which is
receptive of subcooling refrigerant from the desorber, an adsorber disposed in
parallel with the desorber for subcooling refrigerant adsorption by an adsorbent
and a subcooling gas cooler through which the subcooling refrigerant received
from the subcooling compressor passes toward the adsorber and the desorber in a
supercritical state.
In accordance with additional or alternative embodiments, the adsorbent
includes a solid adsorbent and the solid adsorbent includes activated carbon or a
metal organic framework (MOF).
According to an aspect of the disclosure, a vapor absorption subcooling
system is provided and includes a desorber in which a first refrigerant is cooled, a
subcooling compressor, which is receptive of subcooling refrigerant from the
desorber, an absorber for subcooling refrigerant absorption by an absorbent, a
subcooling gas cooler through which the subcooling refrigerant received from the
subcooling compressor passes toward the absorber in a supercritical state and a
pump configured to pump at least the absorbent from the desorber to the absorber.
In accordance with additional or alternative embodiments, the subcooling
refrigerant includes a natural, low greenhouse warming potential (GWP), low
ozone depletion potential (ODP) and non-flammable refrigerant.
In accordance with additional or alternative embodiments, the subcooling
refrigerant includes carbon dioxide.
In accordance with additional or alternative embodiments, the absorbent
includes an ionic liquid.
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According to another aspect of the disclosure, a vapor adsorption
subcooling system is provided and includes a desorber in which a first refrigerant
is cooled, a subcooling compressor, which is receptive of subcooling refrigerant
from the desorber, an adsorber disposed in parallel with the desorber for
subcooling refrigerant adsorption by an adsorbent and a subcooling gas cooler
through which the subcooling refrigerant received from the subcooling
compressor passes toward the adsorber and the desorber in a supercritical state.
In accordance with additional or alternative embodiments, the subcooling
refrigerant includes a natural, low greenhouse warming potential (GWP), low
ozone depletion potential (ODP) and non-flammable refrigerant.
In accordance with additional or alternative embodiments, the subcooling
refrigerant includes carbon dioxide.
In accordance with additional or alternative embodiments, the adsorbent
includes a solid adsorbent and the solid adsorbent includes activated carbon or a
metal organic framework (MOF).
In accordance with additional or alternative embodiments, the desorber
includes multiple desorbers, the adsorber includes multiple adsorbers, each one of
the multiple adsorbers is paired with a corresponding one of the multiple
desorbers to form respective combined beds and each of the combined beds is
independently operable at a different adsorption stage.
These and other advantages and features will become more apparent from
the following description taken in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter, which is regarded as the disclosure, is particularly
pointed out and distinctly claimed in the claims at the conclusion of the
specification. The foregoing and other features, and advantages of the disclosure
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are apparent from the following detailed description taken in conjunction with the
accompanying drawings in which:
FIG. 1 is a schematic diagram illustrating a vapor absorption subcooling
system of a cooling system in accordance with embodiments;
FIG. 2 is a graphical depiction of a coefficient of performance capability
of the vapor absorption subcooling system of the cooling system of FIG. 1;
FIG. 3 is a schematic diagram illustrating a vapor adsorption subcooling
system of a cooling system in accordance with embodiments;
FIG. 4 is a schematic diagram showing another embodiment of a vapor
adsorption subcooling system of a cooling system in which the vapor adsorption
subcooling system has more than two sorption beds operating at different stages
of adsorption and desorption in accordance with embodiments; and
FIG. 5 is a schematic diagram of a controller of the cooling systems of at
least the embodiments of FIGS. 1, 3 and 4.
These and other advantages and features will become more apparent from
the following description taken in conjunction with the drawings.
DETAILED DESCRIPTION
As will be described below, a cooling system for use in a supermarket
cooling system, for example, is provided and uses a natural, non-toxic, low-GWP
and ODP refrigerant. This refrigerant can be carbon dioxide, which is paired with
an absorbent, such as one or more ionic liquids, or a solid adsorbent. The cooling
system includes a gas cooler, a vapor absorption/adsorption-based subcooler and a
desorber component that provides subcooling to refrigerant exiting the gas cooler.
In the particular case of the refrigerant being carbon dioxide and the absorbent
being an ionic liquid, the ionic liquid absorbs the carbon dioxide in an exothermic
process in which the heat of absorption is rejected to ambient in order to sustain
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absorption processes (this is similar to the heat of compression needing to be
rejected to ambient in a conventional gas cooler).
With reference to FIG. 1, a cooling system 101 is provided. The cooling
system 101 includes a first, low temperature compressor 110 and a second, high
temperature compressor 111. The first, low temperature compressor is configured
to compress low temperature refrigerant and to output compressed refrigerant to
the second, high temperature compressor 111. The second, high temperature
compressor 111 is configured to compress high temperature refrigerant and the
compressed refrigerant received from the first, low temperature compressor into
compressed or supercritical refrigerant. The cooling system 101 further includes a
gas cooler 120, which is disposed downstream from the second, high temperature
compressor 111 and which is receptive of the compressed or supercritical
refrigerant from the second, high temperature compressor 111. Within the gas
cooler 120, the compressed or supercritical refrigerant is cooled slightly before
flowing through a desorber 160, an ejector 155 and first and second expansion
valves 131 and 132 toward a first, low temperature evaporator 140, which is
associated with and upstream from the first, low temperature compressor 110, or
through the first expansion valve 131 toward a second, high temperature
evaporator 141, which is associated with and upstream from the second, high
temperature compressor 111.
The cooling system 101 also includes a vapor sorption subcooling system
150. The vapor sorption subcooling system 150 can be provided as a vapor
absorption subcooling system 151 and includes the desorber 160, which is
disposed between the gas cooler 120 and the first and second expansion valves
131 and 132 and which is configured to remove heat from the refrigerant flowing
from the gas cooler 120 toward the first and second expansion valves 131 and
132. A subcooling refrigerant of the vapor absorption subcooling system 151 can
include a natural, low greenhouse warming potential (GWP), low ozone depletion
potential (ODP) and non-flammable refrigerant. More particularly, the subcooling
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refrigerant of the vapor absorption subcooling system 151 can include carbon
dioxide.
The cooling system 101 can further include the ejector 155 disposed
downstream from the desorber 160. The cooling system 101 in such cases would
have subcooling capability from the vapor sorption subcooling system 150 and
pressure recovery using the ejector 155. This would result in the cooling system
101 having increased COPs. It is to be understood that the ejector 155 is optional
and that embodiments exist in which the ejector 155 is not present in the cooling
system 101.
As shown in FIG. 1, in addition to the desorber 160, the vapor absorption
subcooling system 151 includes a subcooling compressor 170, which is receptive
of subcooling refrigerant from the desorber 160, an absorber 180 for subcooling
refrigerant absorption by an absorbent 182, a subcooling gas cooler 190 through
which the subcooling refrigerant that is received from the subcooling compressor
170 passes toward the absorber 180 in a supercritical state and a pump 200. The
vapor absorption subcooling system 151 further includes a first valve 210, which
is disposed immediately downstream from the subcooling gas cooler 190 and
immediately upstream from the absorber 180, and a second valve 211, which is
disposed immediately downstream from the absorber 180 and immediately
upstream from the desorber 160.
The absorber 180 includes an enclosure 181 and the absorbent 182, which
is contained within the enclosure 181. In accordance with embodiments, the
absorbent 182 may include an ionic liquid (see below for example of ionic
liquids). While this absorbent 182 (i.e., ionic liquid) is contained within the
enclosure 181, it can be used to dissolve the subcooling refrigerant (i.e., carbon
dioxide).
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Table 1, Literature values of CO2 absorption by ionic liquids
Where the absorbent 182 includes an ionic liquid, the ionic liquid can be
immobilized in an adsorbent. In such cases, the vapor absorption subcooling
system 151 is similar to an adsorption system (to be discussed below) where pores
of an adsorbent are filled with the ionic liquid (sometimes referred to as an
immobilized ionic liquid).
During an operation of the vapor absorption subcooling system 151, the
desorber 160 provides subcooling to the refrigerant exiting the gas cooler 120.
This is accomplished as follows.
Within the absorber 180, the subcooling refrigerant flowing into the
absorber 180 from the subcooling gas cooler 190 is absorbed into the absorbent
182 (i.e., absorption by the subcooling refrigerant being dissolved into the
absorbent 182 within the enclosure 182) as part of an exothermic process. The
Desorption Absorption
Cation Anion
Temperature
[K]
Pressure
[bar] xCO2
Temperature
[K]
Pressure
[bar] xCO2
Delta
xCO2
[BMIM]+ [BF4]- 293.65 41 0.458 313.35 105 0.61 0.152
[BMIM]+ [BF4]- 298.2 42.1 0.4902 313.3 84.02 0.5289 0.0387
[BMIM]+ [PF6]- 298.2 42 0.4905 313.3 84.01 0.5941 0.1036
[BMIM]+ [PF6]- 298.2 42 0.4905 313.3 95.47 0.5991 0.1086
[BMIM]+ [Tf2N]- 298.2 44.27 0.6181 313.3 110.25 0.742 0.1239
[BMIM]+ [SCN]- 303.15 37.5 0.345 313.15 122.5 0.422 0.077
[BMIM]+ [C(CN)3]- 303.15 37.9 0.502 313.15 104.6 0.633 0.131

[HMIM]+ [Tf2N]- 298.2 42.34 0.6282 313.3 97.92 0.7478 0.1196
[HMIM]+ [BF4]- 303.63 49.1 0.498 313.07 104.6 0.602 0.104
[HMIM]+ [PF6]- 303.48 33.7 0.41 318.11 93.4 0.599 0.189

[EMIM]+ [Tf2N]- 298.15 32.54 0.533 323.15 100.81 0.711 0.178
[EMIM]+ [Tf2N]- 293.05 43 0.6448 314.05 90.5 0.7043 0.0595
[EMIM]+ [Tf2N]- 298.15 38.72 0.619 323.15 102.81 0.701 0.082
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heat of absorption gets rejected to ambient. The absorbent 182 with the subcooling
refrigerant absorbed therein flows through the second valve 211 to the desorber
160, which is at a lower pressure than the absorber 180. Within the desorber 160,
the subcooling refrigerant desorbs from the absorbent 182 in an endothermic
process and provides cooling through a heat transfer surface to the refrigerant
flowing from the gas cooler 120. The subcooling refrigerant that desorbs is
recompressed by the subcooling compressor 170. At least the absorbent 182 or a
mixture of the absorbent 182 and a portion of the subcooling refrigerant is
pumped back into the absorber 180 in order to complete the cycle by the pump
200.
In accordance with embodiments, the absorber 180 and the desorber 160
can be operated in a cyclic mode.
As shown in FIG. 2, the cooling system 101 in combination with the vapor
absorption subcooling system 151 has a high COP due to the high heat of
desorption which can be 1-10 times higher than the heat of vaporization
depending on the absorbent. In particular, with an ionic liquid as the absorbent
182, a subcooler cycle of the vapor absorption subcooling system 151 subcools
WKHUHIULJHUDQWE\DERXWÛ&DQGRSHUDWHVEHWZHHQ-7 MPa.
With reference to FIG. 3, the cooling system 101 is provided with the
vapor sorption system 150. Here, the vapor sorption subcooling system 150 can be
provided as a vapor adsorption subcooling system 301 and includes the desorber
160, which is disposed between the gas cooler 120 and the first expansion valve
131 and which is configured to remove heat from the refrigerant flowing from the
gas cooler 120 toward the first and second expansion valves 131 and 132. A
subcooling refrigerant of the vapor adsorption subcooling system 301 can include
a natural, low greenhouse warming potential (GWP), low ozone depletion
potential (ODP) and non-flammable refrigerant. More particularly, the subcooling
refrigerant of the vapor adsorption subcooling system 301 can include carbon
dioxide.
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As shown in FIG. 3, in addition to the desorber 160, the vapor adsorption
subcooling system 301 includes the subcooling compressor 170, which is
receptive of subcooling refrigerant from the desorber 160, an adsorber 310 for
subcooling refrigerant adsorption by an adsorbent 312, a subcooling gas cooler
190 through which the subcooling refrigerant that is received from the subcooling
compressor 170 passes toward the adsorber 310 in a supercritical state and a valve
system 320. The valve system 320 includes first and second valves 321 and 322,
which are respectively disposed upstream from the adsorber 310 and the desorber
160 and which respectively control subcooling refrigerant flows into the adsorber
310 and the desorber 160, as well as third, fourth and fifth valves 323, 324 and
325, which are respectively downstream from the adsorber 310 and the desorber
160 and which are respectively configured to control flows of the subcooling
refrigerant to the subcooling compressor 170.
Within the adsorber 310, the subcooling refrigerant flowing into the
adsorber 310 from the subcooling gas cooler 190 is adsorbed into the adsorbent
312 as part of an exothermic process. The heat of adsorption gets rejected to
ambient.
In accordance with embodiments, adsorption and desorption beds of the
adsorber 310 and the desorber 160, respectively, can be operated in a cyclic mode.
In addition, the adsorber 310 can include two or more adsorbent beds.
The adsorber 310 includes an enclosure 311 and a solid adsorbent 312
contained within the enclosure 311. In accordance with some embodiments, the
solid adsorbent 312 can include or be provided as activated carbon and metal
organic frameworks (MOFs).
With reference to FIG. 4 and in accordance with further embodiments, the
cooling system 101 is provided with the vapor sorption system 150 and the vapor
sorption subcooling system 150 can be provided as a vapor adsorption subcooling
system 501. The vapor adsorption subcooling system 501 is similar to the vapor
adsorption subcooling system 301 but is characterized in that the desorber 160
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includes multiple desorbers 160, the adsorber 180 includes multiple adsorbers 180
and each one of the multiple adsorbers 180 is paired with a corresponding one of
the multiple desorbers 160 in respective desorber/adsorber beds 4101, 4102 and
4103 that are fed by valve system 420.
The respective desorber/adsorber beds 4101, 4102 and 4103 are operable at
different stages of adsorption and desorption to mitigate a potential issue of
intermittency in which the desorber 160 switches from desorption mode to
adsorption mode. With the presence of the multiple desorbers 160, cooling loads
can be maintained by having the different multiple desorbers 160 at different
stages of desorption. As one of the multiple desorbers 160 switches from
desorption mode to adsorption mode, the other of the multiple desorbers 160 are
available to provide cooling effects to satisfy extra cooling requirements.
With reference to FIG. 5 and in accordance with further embodiments, a
controller 501 can be provided to control various components of the cooling
system 101 of at least the embodiments of FIGS. 1, 3 and 4. The controller 501
can include a processing unit 510, a memory unit 520, a networking unit 530, a
servo control unit 540 and an input/output (I/O) bus 550 by which the processing
unit 510, the memory unit 520, the networking unit 530 and the servo control unit
540 are communicative. The networking unit 530 is configured to enable
communications between the processing unit 510 and various sensing elements
disposable throughout the cooling system 101 as well as external computing
systems. The servo control unit 540 is responsive to instructions issued by the
processing unit 510 to thereby control operations of the first and second expansion
valves 131 and 132, the first and second valves 210 and 211 of the embodiments
of FIG. 1, the pump 200 of the embodiments of FIG. 1, the valve system 320 of
FIG. 3 and the valve system 420 of FIG. 4. The memory unit 520 has executable
instructions stored thereon, which are readable and executable by the processing
unit 510 such that, when the executable instructions are read and executed by the
processing unit 510, the executable instructions cause the processing unit 510 to
generate and issue the commands to the servo control unit 540.
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Technical effects and benefits of the features described herein are the
provision of a vapor sorption subcooling system that uses a natural, low ODP, low
GWP, non-flammable refrigerant like carbon dioxide for the subcooler system
that, when combined with a current cooling system, shows 10% increase in COP.
While the disclosure is provided in detail in connection with only a limited
number of embodiments, it should be readily understood that the disclosure is not
limited to such disclosed embodiments. Rather, the disclosure can be modified to
incorporate any number of variations, alterations, substitutions or equivalent
arrangements not heretofore described, but which are commensurate with the
spirit and scope of the disclosure. Additionally, while various embodiments of the
disclosure have been described, it is to be understood that the exemplary
embodiment(s) may include only some of the described exemplary aspects.
Accordingly, the disclosure is not to be seen as limited by the foregoing
description, but is only limited by the scope of the appended claims.

We Claim:
1. A cooling system, comprising:
a compressor;
an expansion valve;
a gas cooler through which a refrigerant received from the compressor
passes toward the expansion valve in a supercritical state;
an evaporator interposed between the expansion valve and the compressor;
and
a vapor sorption subcooling system comprising a desorber disposed to
remove heat from refrigerant flowing from the gas cooler toward the expansion
valve.
2. The cooling system according to claim 1, further comprising an
ejector downstream from the desorber.
3. The cooling system according to claim 1, wherein the vapor
sorption subcooling system comprises a vapor absorption subcooling system.
4. The cooling system according to claim 3, wherein a subcooling
refrigerant of the vapor absorption subcooling system comprises a natural, low
greenhouse warming potential (GWP), low ozone depletion potential (ODP) and
non-flammable refrigerant.
5. The cooling system according to claim 3, wherein a subcooling
refrigerant of the vapor absorption subcooling system comprises carbon dioxide.
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6. The cooling system according to claim 3, wherein the vapor
absorption subcooling system comprises:
a subcooling compressor, which is receptive of subcooling refrigerant
from the desorber;
an absorber for subcooling refrigerant absorption by an absorbent;
a subcooling gas cooler through which the subcooling refrigerant received
from the subcooling compressor passes toward the absorber in a supercritical
state; and
a pump configured to pump at least the absorbent from the desorber to the
absorber.
7. The cooling system according to claim 6, wherein the absorbent
comprises an ionic liquid.
8. The cooling system according to claim 1, wherein the vapor
sorption subcooling system comprises a vapor adsorption subcooling system.
9. The cooling system according to claim 8, wherein a subcooling
refrigerant of the vapor adsorption subcooling system comprises a natural, low
greenhouse warming potential (GWP), low ozone depletion potential (ODP) and
non-flammable refrigerant.
10. The cooling system according to claim 8, wherein a subcooling
refrigerant of the vapor adsorption subcooling system comprises carbon dioxide.
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11. The cooling system according to claim 8, wherein the vapor
adsorption subcooling system comprises:
a subcooling compressor, which is receptive of subcooling refrigerant
from the desorber;
an adsorber disposed in parallel with the desorber for subcooling
refrigerant adsorption by an adsorbent; and
a subcooling gas cooler through which the subcooling refrigerant received
from the subcooling compressor passes toward the adsorber and the desorber in a
supercritical state.
12. The cooling system according to claim 11, wherein the adsorbent
comprises a solid adsorbent and the solid adsorbent comprises activated carbon or
a metal organic framework (MOF).
13. The cooling system according to claim 11, wherein two or more
sorption beds are used as adsorbers and desorbers to provide subcooling
13. A vapor absorption subcooling system, comprising:
a desorber in which a first refrigerant is cooled;
a subcooling compressor, which is receptive of subcooling refrigerant
from the desorber;
an absorber for subcooling refrigerant absorption by an absorbent;
a subcooling gas cooler through which the subcooling refrigerant received
from the subcooling compressor passes toward the absorber in a supercritical
state; and
a pump configured to pump at least the absorbent from the desorber to the
absorber.
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14. The vapor absorption subcooling system according to claim 13,
wherein the subcooling refrigerant comprises a natural, low greenhouse warming
potential (GWP), low ozone depletion potential (ODP) and non-flammable
refrigerant.
15. The vapor absorption subcooling system according to claim 13,
wherein the subcooling refrigerant comprises carbon dioxide.
16. The vapor absorption subcooling system according to claim 13,
wherein the absorbent comprises an ionic liquid.
17. A vapor adsorption subcooling system, comprising:
a desorber in which a first refrigerant is cooled;
a subcooling compressor, which is receptive of subcooling refrigerant
from the desorber;
an adsorber disposed in parallel with the desorber for subcooling
refrigerant adsorption by an adsorbent; and
a subcooling gas cooler through which the subcooling refrigerant received
from the subcooling compressor passes toward the adsorber and the desorber in a
supercritical state.
18. The vapor adsorption subcooling system according to claim 17,
wherein the subcooling refrigerant comprises at least one of:
a natural, low greenhouse warming potential (GWP), low ozone depletion
potential (ODP) and non-flammable refrigerant; and
carbon dioxide.
19. The vapor adsorption subcooling system according to claim 17,
wherein the adsorbent comprises a solid adsorbent and the solid adsorbent
comprises activated carbon or a metal organic framework (MOF).
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20. The vapor adsorption subcooling system according to claim 17,
wherein:
the desorber comprises multiple desorbers,
the adsorber comprises multiple adsorbers,
each one of the multiple adsorbers is paired with a corresponding one of
the multiple desorbers to form respective combined beds, and
each of the combined beds is independently operable at a different
adsorption stage.