U.S. patent application number 12/044732 was filed with the patent office on 2008-09-18 for refrigeration system.
This patent application is currently assigned to Johnson Controls Technology Company. Invention is credited to Alexander C. Pachai, John Ritmann.
Application Number | 20080223074 12/044732 |
Document ID | / |
Family ID | 39523843 |
Filed Date | 2008-09-18 |
United States Patent
Application |
20080223074 |
Kind Code |
A1 |
Pachai; Alexander C. ; et
al. |
September 18, 2008 |
REFRIGERATION SYSTEM
Abstract
Refrigeration systems are provided which include a first
refrigeration system and a second refrigeration system that share a
common heat exchanger. The heat exchanger includes a vessel that
operates as a condenser for the second refrigeration system. A coil
disposed in the vessel operates as an evaporator for the first
refrigeration system. A method of operating a refrigeration system
is also provided that includes exchanging energy between the
refrigerant of the first refrigeration system and the refrigerant
of the second refrigeration system.
Inventors: |
Pachai; Alexander C.;
(Skoedstrup, DK) ; Ritmann; John; (Hoerning,
DK) |
Correspondence
Address: |
Johnson Controls, Inc.;c/o Fletcher Yoder PC
P.O. Box 692289
Houston
TX
77269
US
|
Assignee: |
Johnson Controls Technology
Company
Holland
MI
|
Family ID: |
39523843 |
Appl. No.: |
12/044732 |
Filed: |
March 7, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60894052 |
Mar 9, 2007 |
|
|
|
60917175 |
May 10, 2007 |
|
|
|
Current U.S.
Class: |
62/513 ; 62/115;
62/515 |
Current CPC
Class: |
F28D 2021/0071 20130101;
F04C 23/001 20130101; F25B 2339/024 20130101; F28F 2009/226
20130101; F28F 2220/00 20130101; F04C 29/042 20130101; F25B 2309/06
20130101; F25B 2339/047 20130101; F25B 2339/046 20130101; F25B
2400/16 20130101; F04C 18/16 20130101; F25B 2400/23 20130101; F28F
2280/02 20130101; F04C 18/02 20130101; F25B 9/008 20130101; F25B
7/00 20130101; F25B 25/005 20130101 |
Class at
Publication: |
62/513 ; 62/515;
62/115 |
International
Class: |
F25B 41/00 20060101
F25B041/00; F25B 39/02 20060101 F25B039/02; F25B 1/00 20060101
F25B001/00 |
Claims
1. A refrigeration system comprising: a first refrigeration system
configured to implement a refrigeration cycle with a first
refrigerant, and a second refrigeration system configured to
implement a refrigeration cycle with a carbon dioxide refrigerant;
a heat exchanger common to the first and second refrigeration
systems, the heat exchanger comprising a vessel configured to
operate as a condenser for the carbon dioxide refrigerant and a
coil disposed in the vessel and configured to operate as an
evaporator for the first refrigerant.
2. The system of claim 1, wherein the vessel is configured to
receive vapor phase carbon dioxide refrigerant in an interior
volume disposed about the coil.
3. The system of claim 2, wherein the vessel is configured to
retain a volume of liquid carbon dioxide refrigerant within the
interior volume.
4. The system of claim 1, comprising a carbon dioxide refrigeration
system coupled to the vessel and configured to cool carbon dioxide
refrigerant within the vessel during operation.
5. The system of claim 1, wherein the second refrigeration system
comprises an expansion device and an evaporator configured to
provide cooling at an application via evaporation of liquid carbon
dioxide.
6. The system of claim 5, wherein vapor phase carbon dioxide
refrigerant is directed from the evaporator to the interior volume
of the vessel.
7. The system of claim 1, wherein the second refrigeration system
comprises a plurality of expansion devices associated with
respective evaporators configured to provide cooling to different
temperatures at a plurality of applications via evaporation of
liquid carbon dioxide.
8. The system of claim 7, wherein a circuit comprising one of the
evaporators operating at a lower temperature than the other
evaporator includes a compressor configured to compress vapor phase
carbon dioxide refrigerant prior to returning the carbon dioxide
refrigerant to the vessel.
9. The system of claim 1, wherein the first refrigerant is an
ammonia based refrigerant, a hydrocarbon based refrigerant, or a
hydrofluorocarbon based refrigerant.
10. A refrigeration system comprising: a first stage system
comprising a compressor, a condenser, an expansion device and an
evaporator, the first stage system configured to implement a
refrigeration cycle with a first refrigerant; and a second stage
system comprising an expansion device, an evaporator, a receiver
and a pump, the second stage system configured to implement a
refrigeration cycle with a carbon dioxide refrigerant; the first
stage evaporator being disposed within the receiver.
11. The system of claim 10 wherein the receiver is configured to
operate as a condenser for the carbon dioxide refrigerant.
12. The system of claim 10, wherein the receiver is configured to
retain a volume of liquid carbon dioxide refrigerant within an
interior volume in which the first stage evaporator is
disposed.
13. The system of claim 10, comprising a carbon dioxide
refrigeration system coupled to the receiver and configured to cool
carbon dioxide refrigerant within the vessel during operation.
14. The system of claim 10, wherein the second refrigeration system
comprises an expansion device and an evaporator configured to
provide cooling at an application via evaporation of liquid carbon
dioxide.
15. The system of claim 14, wherein vapor phase carbon dioxide
refrigerant is directed from the evaporator to an interior volume
of the receiver.
16. The system of claim 10 wherein the second refrigeration system
comprises a plurality of expansion devices associated with
respective evaporators configured to provide cooling to different
temperatures at a plurality of applications via evaporation of
liquid carbon dioxide.
17. The system of claim 16, wherein a circuit comprising one of the
evaporators operating at a lower temperature than the other
evaporator includes a compressor configured to compress vapor phase
carbon dioxide refrigerant prior to returning the carbon dioxide
refrigerant to the receiver.
18. A method for operating a refrigeration system, comprising:
circulating a first refrigerant in a first refrigeration system and
through a coil disposed in a vessel; and circulating a carbon
dioxide refrigerant in a second refrigeration system and through
the vessel; wherein the first refrigerant and the carbon dioxide
refrigerant exchange energy with one another in the vessel to
vaporize the first refrigerant in the coil and to condense the
carbon dioxide refrigerant in the vessel.
19. The method of claim 18, wherein the first refrigerant is an
ammonia based refrigerant, a hydrocarbon based refrigerant, or a
hydrofluorocarbon based refrigerant.
20. The method of claim 18, comprising cooling two different
applications at different temperatures via evaporation of the
carbon dioxide refrigerant at two different pressures.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims priority from and the benefit
of U.S. Provisional Application No. 60/894,052, entitled SYSTEMS
AND METHODS OF USING CO2 IN REFRIGERATION AND AIR CONDITIONING
APPLICATIONS, filed Mar. 9, 2007, and U.S. Provisional Application
No. 60/917,175, entitled SYSTEMS AND METHODS OF USING NATURAL
REFRIGERANTS, filed May 10, 2007, which are hereby incorporated by
reference.
BACKGROUND
[0002] The invention relates generally to refrigeration
systems.
[0003] Many applications exist for refrigeration systems including
residential, commercial, and industrial applications. For example,
a commercial refrigeration system may be used to cool an enclosed
space such as a cooler or a freezer. In another example, an
industrial refrigeration system may be used to preserve, process,
and store food. Very generally, refrigeration systems may include
circulating a fluid through a closed loop between an evaporator
where the fluid absorbs heat and a condenser where the fluid
releases heat. The fluid flowing within the closed loop is
generally formulated to undergo phase changes within the normal
operating temperatures and pressures of the system so that
considerable quantities of heat can be exchanged by virtue of the
latent heat of vaporization of the fluid.
[0004] In some applications, two or more closed refrigeration loops
may be interconnected to form a multistage refrigeration system.
Multistage refrigeration systems (also referred to as cascade
refrigeration systems or multi-pressure systems) may be used to
provide cooling to multiple environments with different temperature
requirements, such as a refrigerated case and a storage freezer.
Multistage refrigeration systems also may be used to provide
cooling temperatures that are lower that that attainable by a
single-stage system, such as a vapor compression system.
SUMMARY
[0005] The present invention relates to a refrigeration system
including a first refrigeration system configured to implement a
refrigeration cycle with a first refrigerant, a second
refrigeration system configured to implement a refrigeration cycle
with a carbon dioxide refrigerant, and a heat exchanger common to
the first and second refrigeration systems. The heat exchanger
includes a vessel configured to operate as a condenser for the
carbon dioxide refrigerant and a coil disposed in the vessel that
is configured to operate as an evaporator for the first
refrigerant.
[0006] The present invention also relates to a refrigeration system
including a first stage system configured to implement a
refrigeration cycle with a first refrigerant and a second stage
system configured to implement a refrigeration cycle with a carbon
dioxide refrigerant. The first stage system includes a compressor,
a condenser, an expansion device, and an evaporator. The second
stage system includes an expansion device, an evaporator, a
receiver, and a pump. The first stage evaporator is disposed within
the receiver.
[0007] The present invention further relates to a method for
operating a refrigeration system that includes circulating a first
refrigerant in a first refrigeration system and through a coil
disposed in a vessel and circulating a carbon dioxide refrigerant
in a second refrigeration system and through the vessel. The first
refrigerant and the carbon dioxide refrigerant exchange energy with
one another in the vessel to vaporize the first refrigerant in the
coil and to condense the carbon dioxide refrigerant in the
vessel.
DRAWINGS
[0008] FIG. 1 is an illustration of an exemplary embodiment of a
commercial application incorporating a refrigeration system.
[0009] FIG. 2 is an illustration of an exemplary embodiment of an
industrial application incorporating a refrigeration system.
[0010] FIG. 3 is a perspective view of an exemplary refrigeration
system.
[0011] FIG. 4 is a front elevational view of the refrigeration
system of FIG. 3.
[0012] FIG. 5 is a diagrammatical representation of an exemplary
embodiment of a multistage refrigeration system.
[0013] FIG. 6 is a somewhat more detailed diagrammatical
representation of the multistage refrigeration system of FIG.
5.
[0014] FIG. 7 is a diagrammatical representation of an exemplary
embodiment of a multistage refrigeration system.
DETAILED DESCRIPTION
[0015] FIG. 1 illustrates an exemplary embodiment of a commercial
application incorporating a refrigeration system 10 that provides
both refrigeration and freezing capacity for a supermarket 12.
Refrigeration system 10 includes a first stage system and a second
stage system, each with their own closed refrigeration loop.
Refrigerated display cases 14, which may contain refrigerated
grocery items, such as milk and cheese, are maintained at a preset
refrigeration temperature while freezer display cases 16, which may
contain frozen grocery items, such as ice cream and pizza, are
maintained at a preset freezer temperature. According to an
exemplary embodiment, the refrigeration temperature may be between
about 2 deg C. and about 7 deg 7 C, and the freezer temperature may
be between about -20 deg C. and about -30 deg C. An evaporator 18,
located in a freezer storage area 20, may be used to cool display
cases 16 to the preset freezer temperature. An evaporator 20,
located in a refrigerated storage area 24, may be used to cool
display cases 14 to the preset refrigeration temperature.
Evaporators 18 and 20 also may be used to cool freezer storage area
20 and refrigerated storage area 24 to the preset freezer
temperature and the preset refrigeration temperature, respectively.
Grocery items may be stored in storage areas 20 and 24 prior to
placement within display cases 14 and 16. According to an exemplary
embodiment, evaporators 18 and 20 are both part of the second stage
system and are operated at different pressures to maintain the
preset refrigeration temperature and the present freezer
temperature.
[0016] FIG. 2 illustrates an exemplary embodiment of an industrial
application incorporating refrigeration system 10 into an
industrial building 26. Building 26 houses manufacturing
operations, such as a food packaging and processing operations,
that employ a plate freezer 28 to rapidly freeze flat products,
such as pastries, fish fillets, and beef patties, as well as
irregular-shaped items such as vegetables packaged in brick-shape
containers. Horizontal or vertical plates 30 may be used to freeze
and shape the products. Plates 30 are cooled to subfreezing
temperatures by internally circulating refrigerant through thin
channels within plates 30. Generally, the internal construction of
plates 30 allows for a high rate of heat transfer between the
products and plates 30. According to an exemplary embodiment,
plates 30 are part of the second stage system are cooled to
temperature of between about -20 deg C. and about -50 deg C.
[0017] FIG. 3 is a perspective view of an exemplary multistage
refrigeration that includes a first stage system circulating a
first fluid and a second stage system circulating a second fluid.
The equipment used in the multistage refrigeration system includes,
among other things, a heat exchanger 36, a compressor 38 and
condenser 40 used in the first stage system, one or more
compressors 48 used in the second stage system, a receiver 52, and
a pump 54. Heat exchanger 36 is used by both the first stage system
and the second stage system. For example, according to an exemplary
embodiment, heat exchanger 36 may be used to vaporize liquid
refrigerant circulating within the first stage system and condense
vapor refrigerant circulating within the second stage system. Heat
exchanger 36 may be a plate heat exchanger, a shell and tube heat
exchanger, a plate and shell heat exchanger, or any other suitable
type of heat exchanger. Compressors 38 and 48 receive vapor phase
refrigerant flowing within each stage and reduce the volume
available for the refrigerant, consequently, increasing the
pressure and temperature of the refrigerant. The compressors may be
any suitable compressor such as a screw compressor, reciprocating
compressor, rotary compressor, swing link compressor, scroll
compressor, or turbine compressor. According to an exemplary
embodiment, compressor 38 compresses the vaporized refrigerant of
the first stage system after it exits heat exchanger 36. Condenser
40 receives the compressed vapor and condenses the vapor into a
liquid that after expansion is ready to enter heat exchanger 36 to
begin the refrigeration cycle again. Receiver 52 may be used to
store the liquid refrigerant within first stage system before the
refrigerant enters heat exchanger 36.
[0018] The refrigerant circulating within the second stage system
exits heat exchanger 36 as a liquid that flows to one or more
evaporators (not shown). In the evaporators, the liquid phase
refrigerant absorbs heat and vaporizes into a vapor phase
refrigerant or a mixed vapor and liquid phase refrigerant. The
refrigerant circulating within the evaporators absorbs heat from an
external fluid allowing the evaporator to provide a cooled fluid,
such as water or air, to an environment. According to an exemplary
embodiment, the vapor phase refrigerant exiting one of the
evaporators enters compressor 48 where it is compressed and ready
to enter heat exchanger 36 to begin the refrigeration cycle again.
Although only a few pieces of equipment are described, the
multistage refrigeration may include numerous pieces of equipment
such as multiple condensers, compressors, expansion devices,
receivers, and evaporators, or combination thereof.
[0019] FIG. 4 depicts a front view of the multistage refrigeration
system of FIG. 3 and shows heat exchanger 36, compressors 38 and
48, and receiver 52. FIG. 4 also depicts a pump 54 that may be used
to circulate refrigerant within the second stage system.
[0020] FIG. 5 shows a multistage refrigeration system 56 that
includes a first stage system 58 and a second stage system 60. The
first and second stage systems each include a closed refrigeration
loop for circulating a fluid within each system. According to an
exemplary embodiment, a carbon dioxide refrigerant (R-744) may be
circulated within the second stage system and ammonia (R-717) may
be circulated within the first stage system. According to another
exemplary embodiment, any fluid capable of performing as a
refrigerant in a high temperature and pressure system, such as
hydrocarbon based refrigerants or hydrofluorocarbon based
refrigerants, may be circulated within the first stage system.
[0021] Heat exchanger 36 is utilized by both first and second stage
systems 58 and 60. Heat exchanger 36 includes a receiver or vessel
62 configured to operate as a condenser for the second stage
refrigerant and a coil 64 configured to operate as an evaporator
for the first stage refrigerant. Coil 64 is disposed within vessel
62 and configured to circulate the first stage refrigerant within
an interior volume 66. Although coil 64 is shown with a generally
serpentine shape, other exemplary embodiments may include other
suitable coil configurations. Furthermore, according to exemplary
embodiments, the coil may be replaced by a plate, tube, or series
thereof.
[0022] Liquid phase refrigerant 68 exits first stage system 58 and
enters coil 64. As the refrigerant flows through coil 64, the
refrigerant absorbs heat from the second stage refrigerant
contained within interior volume 66. The heat causes the
refrigerant within coil 64 to vaporize, creating vapor phase
refrigerant 70 that exits heat exchanger 36 and enters first stage
system 58. Within first stage system 58, the refrigerant completes
the refrigeration cycle to change phase back to liquid phase
refrigerant 68 that is ready to enter heat exchanger 36.
[0023] Vapor phase refrigerant 72 exits second stage system 60 and
enters interior volume 66. Within interior volume 66, the vapor
phase refrigerant transfers heat to the refrigerant in coil 64. The
loss of heat causes the refrigerant within interior volume 66 to
condense, creating liquid phase refrigerant 74 that exits heat
exchanger 36 and enters second stage system 60. Within second stage
system 60, the refrigerant completes the refrigeration cycle to
change phase back to vapor phase refrigerant 72 that is ready to
enter heat exchanger 36. A pool of liquid second stage refrigerant,
in this case, carbon dioxide, will collect in the vessel with vapor
phase carbon dioxide being resident above the liquid.
[0024] FIG. 6 shows the portions of the refrigeration cycles that
occur within first stage system 58 and second stage system 60.
Referring to first stage system 58, vapor phase refrigerant 70
exiting heat exchanger 36 enters compressor 38 where the
refrigerant is compressed into a relatively high temperature and
pressure vapor. The compressed vapor enters condenser 40 and
transfers heat to a fluid, such as water from a cooling tower,
flowing through condenser 40. The heat transfer causes the vapor
phase refrigerant to condense into a liquid phase. The liquid phase
refrigerant then flows into an expansion device 80 where the
refrigerant expands, thereby reducing its temperature and pressure.
According to an exemplary embodiment, the expansion device may be a
thermal expansion valve; however, any suitable expansion device may
be used. After exiting expansion device 80, the refrigerant enters
coil 64 within heat exchanger 36 to begin the refrigeration cycle
again.
[0025] Referring to second stage system 60, liquid phase
refrigerant 74 exiting heat exchanger 36 enters pump 54 for
circulation through second stage system 60. Pump 54 circulates the
refrigerant to expansion valve 84 where the refrigerant expands to
become a relatively low pressure and temperature liquid. The
refrigerant then enters evaporator 82 and absorbs heat from a
fluid, such as air or products in contact with the surface of
evaporator 82. The heat transfer causes some, or all, of the liquid
phase refrigerant to vaporize into a vapor phase refrigerant. The
vapor phase refrigerant then enters interior volume 66 of heat
exchanger 36 to begin the refrigeration cycle again. It should be
noted that the equipment described in FIG. 5 is not intended to be
limiting. Other equipment such as receivers, controllers, oil
separators, fans, motors, and additional evaporators, condensers,
and pumps, among other things may be used in the refrigeration
cycles of first stage 58 and second stage 60 depending on factors
such as the cooling capacity required, system sizes, and
environmental temperatures.
[0026] FIG. 7 depicts an exemplary embodiment of a multistage
refrigeration system that includes two evaporators 88 and 90 for
cooling two environments at two different temperatures. Evaporators
88 and 90 each have a valve 92 or 94 located upstream to allow
regulation of the pressure and temperature of the refrigerant
entering each evaporator 88 and 90. Valves 92 and 94 allow each
evaporator to provide cooling to a different temperature. For
example, according to an exemplary embodiment, valve 94 may be a
thermal expansion valve configured to reduce the pressure and
temperature of the refrigerant that enters evaporator 90. In this
embodiment, the refrigerant enters valve 94 as a relatively high
pressure and temperature fluid and exits valve 94 at a reduced
temperature and pressure. Within valve 94, a portion of the liquid
refrigerant may be evaporated, which may cool the remaining liquid
refrigerant. In this embodiment, valve 92 may be a solenoid valve
configured to distribute the refrigerant into evaporator 88. Where
operating pressures permit, the liquid refrigerant may flow through
valve 92 and enter evaporator 88 at a temperature and pressure that
are substantially the same as the temperature and pressure reigning
in vessel 62. According to an exemplary embodiment, evaporator 90
receives refrigerant at a much lower pressure than the refrigerant
entering evaporator 88. For example, according to an exemplary
embodiment, evaporator 90 may receive refrigerant at a temperature
of approximately -30 deg C. and a pressure of approximately 12 bar
allowing evaporator 90 to provide cooling to a temperature close to
-30 deg C. depending on, among other things, evaporator efficiency.
In the same embodiment, evaporator 88 may receive refrigerant at a
temperature of approximately -10 deg C. and a pressure of
approximately 28 bar allowing evaporator 88 to provide cooling to a
temperature close to -10 deg C. depending on, among other things,
evaporator efficiency
[0027] First stage system 58 and second stage system 60 share heat
exchanger 36, as described with respect to FIG. 5. Referring to
second stage system 60, vapor phase refrigerant in interior volume
66 is condensed into a liquid phase refrigerant. According to an
exemplary embodiment, the liquid phase refrigerant within interior
volume 66 may collect in the bottom of vessel 62 to form a liquid
reservoir. Liquid phase refrigerant 74 exiting heat exchanger 36 is
circulated through second stage system 60 by pump 54. While any
type of pump can be used, the pump is generally selected to have
very low or no net positive suction head. An optional filter 96 may
be included to receive a diverted portion of liquid refrigerant
exiting pump 54. Filter 96 is positioned within a minimum flow line
disposed lower than the refrigeration line that exits pump 54.
Filter 96 filters the refrigerant to reduce sediment, small
particles, and water entrained within the refrigerant (e.g., by
absorption of water).
[0028] The refrigerant not diverted to filter 96 flows to a heat
exchanger 98 where the refrigerant is cooled, and in exemplary
embodiments may be sub-cooled. According to exemplary embodiments,
heat exchanger 98 is a dual coil heat exchanger that includes a
coil 100 that receives liquid phase refrigerant from pump 54 and a
coil 102 that receives vapor phase refrigerant from evaporator 90.
The liquid phase refrigerant exiting heat exchanger 98 flows to
evaporator 88 or 90 through valve 92 or 94, respectively. Valves 92
and 94 allow regulation of the pressure and temperature of the
refrigerant entering evaporators 88 and 90 to allow each evaporator
88 or 90 to provide cooling to a different temperature. Although
evaporators 88 and 90 are used to cool environments to different
temperatures, evaporators 88 and 90 also may be used to cool
environments to similar temperatures.
[0029] The liquid refrigerant flowing through valve 92 enters
evaporator 88 where the refrigerant absorbs heat from a fluid
flowing through evaporator 88 causing some, or all, of the
refrigerant to vaporize. The vapor phase refrigerant (or in some
exemplary embodiments, the vapor and liquid phase refrigerant
mixture) exits evaporator 88 and enters interior volume 66 of heat
exchanger 36 where it condenses into a liquid to begin the
refrigeration cycle again. Liquid phase refrigerant, which may
enter interior volume 66 as part of a vapor phase and liquid phase
mixture, may be collected in the bottom portion of vessel 62.
According to exemplary embodiments, evaporator 88 is typically
operated using refrigerant of a relatively high temperature (about
0 deg C. or less) and consequently high pressure, and, therefore,
the refrigerant exiting evaporator 88 is able to flow directly back
to heat exchanger 36 without being compressed. In these
embodiments, the high pressure refrigerant returning directly to
heat exchanger 36 may correspond to the pressure within vessel 62.
However, in other exemplary embodiments, evaporator 88 may be
operated using a lower temperature and pressure refrigerant and the
refrigerant may enter a compressor prior to returning to heat
exchanger 36.
[0030] The liquid phase refrigerant flowing through valve 94 enters
evaporator 90 where the refrigerant absorbs heat causing the liquid
to vaporize. According to exemplary embodiments, evaporator 90 is
typically operated using refrigerant of a relatively low
temperature (about -56 deg C. or more) and consequently low
pressure, and, therefore, typically undergoes superheating and
compression prior to returning to heat exchanger 36. The vapor
phase refrigerant exiting evaporator 90 flows through coil 102
within heat exchanger 98 where the vapor phase refrigerant is
heated, and in exemplary embodiment may by superheated. After
exiting heat exchanger 98, the refrigerant enters compressor 48.
Compressor 48 reduces the volume available for the vapor phase
refrigerant, consequently, increasing the pressure and temperature
of the vapor phase refrigerant. An optional heat exchanger 106 may
receive the compressed vapor phase refrigerant exiting compressor
48. Heat exchanger 106 may be used to de-superheat the vapor phase
refrigerant, thereby allowing some of the heat from the vapor
refrigerant to be used to heat another environment or device. As
the refrigerant flows within heat exchanger 106, a fan 108 draws
air across heat exchanger 106. The fan may push or pull air across
the heat exchanger. Heat transfers from the refrigerant to the air,
producing heated air and cooling the refrigerant. Fan 108 is driven
by a motor 110. According to exemplary embodiments, the fan may be
replaced by a pump that circulates a fluid, such as water, through
heat exchanger 106. According to an exemplary embodiment, the fluid
may be freeze protected (e.g. by glycol or brine) to reduce the
risk of cooling the fluid below its freezing point. After exiting
heat exchanger 106, the refrigerant returns to interior volume 66
where it condenses into liquid to begin the refrigeration cycle
again.
[0031] It may be noted that check valves or other arrangements may
be provided around valves 92 and 94 to permit the return of
refrigerant to the vessel, such as in the even flow to the
evaporators is stopped, trapping liquid refrigerant that may
vaporize in an otherwise confined volume.
[0032] Referring to first stage system 58, liquid phase refrigerant
flowing within coil 64 is vaporized producing vapor phase
refrigerant. The vapor phase refrigerant exiting heat exchanger 36
flows to a heat exchanger 112 where the refrigerant is heated, and
in exemplary embodiments may be superheated. According to exemplary
embodiments, heat exchanger 112 is a dual coil heat exchanger that
includes a coil 114 that receives vapor phase refrigerant from heat
exchanger 36 and a coil 116 that receives liquid phase refrigerant
from receiver 52. The vapor phase refrigerant exiting heat
exchanger 112 flows to compressor 38 where it is compressed to
increase the temperature and pressure of the vapor phase
refrigerant. The compressed vapor phase refrigerant enters heat
exchanger 118 where the refrigerant is de-superheated before
entering condenser 40. Within condenser 40, the vapor phase
refrigerant transfers heat to a fluid, such as water, flowing
through condenser 40. The heat transfer causes the vapor phase
refrigerant to condense into a liquid. The liquid phase refrigerant
exiting condenser 40 enters receiver 52 where it is stored prior to
entering heat exchanger 112. According to an exemplary embodiment,
receiver 52 may cause some of the uncondensed vapor phase
refrigerant (if any is present) exiting condenser 40 to condense
into a liquid. After exiting receiver 52, the refrigerant may flow
through coil 116 of heat exchanger 112 where the refrigerant is
cooled, and in an exemplary embodiment is sub-cooled. The
refrigerant then enters expansion device 80 where the temperature
and pressure is reduced before returning the refrigerant to coil 64
of heat exchanger 36 to begin the refrigeration cycle again. It may
be noted that heat exchanger 116, which may be of a type sometimes
referred to as a "suction line" heat exchanger, may not be used in
all systems and with all refrigerants. For example, if the first
refrigerant is ammonia, this heat exchanger may be eliminated,
while it may be more useful with refrigerants such as
hydrocarbons.
[0033] First stage system 58 also may include an optional closed
loop 122 that is circulated through heat exchanger 118. Closed loop
122 allows heat absorbed from the vapor phase refrigerant within
heat exchanger 118 to be transferred to a device 124. Device 124
may be any device that utilizes an input of heat. For example,
device 124 may be a water heater or a furnace. A pump 126
circulates a fluid, such as water or any suitable refrigerant,
within closed lop 122. According to an exemplary embodiment, the
fluid may be freeze protected (e.g. by glycol or brine) to reduce
the risk of cooling the fluid below its freezing point. The fluid
flows through a coil 128 within device 124 and transfers heat to an
interior volume 130. A fluid, such as air or water, may be
circulated through interior volume 130 to transfer the heat
absorbed to a suitable environment.
[0034] In accordance with an exemplary embodiment, the fluid
circulated within second stage system 60 may be carbon dioxide. An
optional coil 132 may be disposed within interior volume 66 to
maintain the temperature within the interior volume in the case of
a power failure or other equipment malfunction. Coil 132 may be
used to decrease the temperature, and consequently, the pressure,
within vessel 66 if the temperature and pressure exceed a specified
value. For example, in the case of a power failure, coil 132 may be
used to maintain the pressure within vessel 62 to prevent the
carbon dioxide refrigerant from evaporating. A separate
refrigeration unit (sometimes referred to as a stand still cooler)
134 may maintain the temperature of coil 132.
[0035] It should be noted that a number of additions and
adaptations may be made to the vessel, as well as combinations of
certain of the components and functions described above. For
example, a level monitoring arrangement (e.g., electrical,
mechanical or electromechanical) may be included for monitoring the
level of liquid carbon dioxide in the vessel. In the event the
level drops below a desired level, remedial measures may be taken,
such as preventing operation of the pump of the second system. A
signal or alarm may also be generated and conveyed to a system
interface, controller, operator, or other recipient to signal such
conditions.
[0036] Certain system components may be selected or placed in the
vessel to further improve operation of the system, as well as to
reduce the potential for loss of refrigerant and to improve
packaging. For example, the pump utilized for the second system may
be selected or designed to permit a reduced inlet head, thereby
reducing the overall height of the system. Similarly, the pump may
be placed in the vessel, thereby reducing or eliminating any need
to otherwise cool a motor associated with the pump. The filter may
also be placed in the vessel, where appropriate, to reduce external
components.
[0037] A pressure limiting arrangement may also be included for
limiting the pressure in the vessel to a high pressure, a low
pressure, or both. In general, a pressure relief valve may form
part of this arrangement to release vapor in the event of a high
pressure situation (e.g., to avoid consequences that may be caused,
for example, by washdown of an evaporator or system components by
an operator). Low pressures may be avoided to avoid creation of ice
that could affect operation of the pump.
[0038] It may be seen, then, that the vessel and its associated
components may become one of the central elements of the combined
(i.e., multistage) refrigeration system. By including as much
functionality and as many components into this arrangement, then,
the overall system may be made more robust and integrated.
[0039] The refrigeration systems may find application in a variety
of applications. However, the systems are particularly well-suited
to cooling two environments where each environment needs to be
cooled to a different temperature. The systems are also
particularly well-suited to cooling environments requiring
temperatures within a range from about -54 deg C. to about 10 deg
C. The systems may be used in the refrigeration systems described
in P.C.T. Patent Application No. ______ (Attorney Docket No.
26427-0007) to Alexander Pachai et al., filed on Mar. 7, 2008, and
P.C.T. Patent Application No. ______ (Attorney Docket No.
26427-0011) to Alexander Pachai et al., filed on Mar. 7, 2008,
which are incorporated herein by reference in their entirety for
all purposes. Other aspects that could be used in conjunction with
the refrigeration systems are described in P.C.T. Patent
Application No. ______ (Attorney Docket No. 26427-0003) to Holger
Tychsen, filed on Mar. 7, 2008, P.C.T. Patent Application No.
______ (Attorney Docket No. 26427-0004) to Alexander Pachai et al.,
filed on Mar. 7, 2008, P.C.T. Patent Application No. ______
(Attorney Docket No. 26427-0005) to Alexander Pachai et al., filed
on Mar. 7, 2008, P.C.T. Patent Application No. ______ (Attorney
Docket No. 26427-0006) to Alexander Pachai et al., filed on Mar. 7,
2008, P.C.T. Patent Application No. ______ (Attorney Docket No.
26427-0008) to Alexander Pachai et al., filed on Mar. 7, 2008,
P.C.T. Patent Application No. ______ (Attorney Docket No.
26427-0009) to Alexander Pachai et al., filed on Mar. 7, 2008, and
P.C.T. Patent Application No. ______ (Attorney Docket No.
26427-0010) to Alexander Pachai et al., filed on Mar. 7, 2008,
which are incorporated herein by reference in their entirety for
all purposes.
[0040] While only certain features and embodiments of the invention
have been illustrated and described herein, many modifications and
changes may occur to those skilled in the art (e.g., variations in
sizes, dimensions, structures, shapes and proportions of the
various elements, values of parameters (e.g., temperatures,
pressures, etc.), mounting arrangements, use of materials, colors,
orientations, etc.) without materially departing from the novel
teachings and advantages of the subject matter recited in the
claims. The order or sequence of any process or method steps may be
varied or re-sequenced according to alternative embodiments. It is,
therefore, to be understood that the appended claims are intended
to cover all such modifications and changes as fall within the true
spirit of the invention. Furthermore, in an effort to provide a
concise description of the exemplary embodiments, all features of
an actual implementation may not have been described (i.e., those
unrelated to the presently contemplated best mode of carrying out
the invention, or those unrelated to enabling the claimed
invention). It should be appreciated that in the development of any
such actual implementation, as in any engineering or design
project, numerous implementation specific decisions may be made.
Such a development effort might be complex and time consuming, but
would nevertheless be a routine undertaking of design, fabrication,
and manufacture for those of ordinary skill having the benefit of
this disclosure, without undue experimentation.
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