U.S. patent application number 11/938807 was filed with the patent office on 2008-11-27 for two stage transcritical refrigeration system.
This patent application is currently assigned to HUSSMANN CORPORATION. Invention is credited to Doron Shapiro.
Application Number | 20080289350 11/938807 |
Document ID | / |
Family ID | 39133833 |
Filed Date | 2008-11-27 |
United States Patent
Application |
20080289350 |
Kind Code |
A1 |
Shapiro; Doron |
November 27, 2008 |
TWO STAGE TRANSCRITICAL REFRIGERATION SYSTEM
Abstract
The invention provides a refrigeration system including a
plurality of refrigerated display cases. Each display case has a
dedicated evaporator assembly that cools return air by evaporating
a refrigerant, and a first stage compressor assembly that is in
fluid communication with the respective evaporator assembly to
compress the refrigerant to a first pressure corresponding to a
first temperature of the refrigerant prior to discharge of the
compressed refrigerant. The refrigeration system also includes a
second stage compressor assembly that is in fluid communication
with the first stage compressor assemblies to compress the
refrigerant to a second pressure that is higher than the first
pressure, and that corresponds to a second temperature of the
refrigerant. The refrigeration system further includes a heat
exchanger that is in fluid communication with the second stage
compressor assembly to receive the refrigerant from the second
stage compressor assembly to reject heat from the refrigerant.
Inventors: |
Shapiro; Doron; (St. Louis,
MO) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH LLP
100 E WISCONSIN AVENUE, Suite 3300
MILWAUKEE
WI
53202
US
|
Assignee: |
HUSSMANN CORPORATION
Bridgeton
MO
|
Family ID: |
39133833 |
Appl. No.: |
11/938807 |
Filed: |
November 13, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60858624 |
Nov 13, 2006 |
|
|
|
Current U.S.
Class: |
62/246 ;
62/196.3; 62/510; 62/515 |
Current CPC
Class: |
F25B 7/00 20130101; F25B
9/008 20130101; F25B 25/005 20130101; F25B 2309/061 20130101; F25B
2400/0401 20130101; F25B 2400/22 20130101; F25B 43/006 20130101;
F25B 2400/06 20130101; F25B 2400/075 20130101; F25B 2400/23
20130101; F25B 1/10 20130101; F25B 2400/054 20130101; F25B 5/02
20130101; F25B 40/00 20130101 |
Class at
Publication: |
62/246 ; 62/510;
62/515; 62/196.3 |
International
Class: |
A47F 3/04 20060101
A47F003/04; F25B 1/10 20060101 F25B001/10; F25B 39/02 20060101
F25B039/02; F25B 41/00 20060101 F25B041/00 |
Claims
1. A refrigeration system comprising: a plurality of refrigerated
display cases, each of the plurality of refrigerated display cases
including a dedicated evaporator assembly adapted to cool return
air from the respective refrigerated display case by at least
partially evaporating a refrigerant, and a dedicated first stage
compressor assembly in fluid communication with the dedicated
evaporator assembly to compress the refrigerant from the dedicated
evaporator assembly to a first pressure corresponding to a first
temperature of the refrigerant, and to discharge the compressed
refrigerant into a discharge main; a second stage compressor
assembly in fluid communication with the dedicated first stage
compressor assembly of each of the plurality of refrigerated
display cases to receive the refrigerant and to compress the
refrigerant to a second pressure that is higher than the first
pressure, the second pressure corresponding to a second temperature
of the refrigerant; a heat exchanger located remotely from the
plurality of refrigerated display cases and in communication with
the refrigerated display cases via a fluid main, the heat exchanger
including an inlet in fluid communication with the second stage
compressor assembly to receive the refrigerant from the second
stage compressor assembly to reject heat from the refrigerant to an
environment, the heat exchanger further including an outlet in
fluid communication with the dedicated evaporator assembly in each
of the plurality of refrigerated display cases via the fluid
main.
2. The refrigeration system of claim 1, wherein the refrigerant
includes a carbon dioxide refrigerant.
3. The refrigeration system of claim 1, further comprising a vessel
positioned in fluid communication with the fluid main between the
refrigerated display cases and the heat exchanger to separate
liquid and gaseous phases of the refrigerant and to supply liquid
refrigerant to each dedicated evaporator assembly.
4. The refrigeration system of claim 3, wherein the discharge main
is in heat exchange relationship with the refrigerant in the
vessel, and wherein the refrigerant in the discharge main is
configured to be de-superheated by heat exchange with the
refrigerant in the vessel.
5. The refrigerated system of claim 4, further comprising a fluid
line in fluid communication with the discharge main between the
second stage compressor assembly and the vessel to direct the
de-superheated refrigerant from the discharge main toward the
second stage compressor assembly.
6. The refrigerated system of claim 5, further comprising a bypass
main coupled between the vessel and the fluid line to circulate
gaseous refrigerant from the vessel toward the second stage
compressor assembly without passing through the fluid main to the
refrigerated display cases.
7. The refrigerated system of claim 5, further comprising an outlet
line extending between the second stage compressor assembly and the
heat exchanger, and a bypass line coupled between the fluid line
and the outlet line to circulate gaseous refrigerant from the fluid
line to the heat exchanger without passing through the second stage
compressor assembly when a temperature of the refrigerant in the
discharge main is below a predetermined temperature.
8. The refrigerated system of claim 7, further comprising a check
valve positioned in the bypass line and configured to inhibit flow
of the refrigerant from the outlet line backward to the fluid
line.
9. The refrigerated system of claim 1, wherein the refrigerant
includes a critical temperature, and wherein the first temperature
is a subcritical temperature and the second temperature includes a
transcritical temperature.
10. The refrigeration system of claim 1, wherein the dedicated
evaporator assemblies are connected to the liquid main in parallel,
and wherein the dedicated compressor assemblies are connected to
the discharge main in parallel.
11. A refrigeration system comprising: a low temperature
refrigeration circuit configured to circulate a first refrigerant,
the low temperature refrigeration circuit including a plurality of
refrigerated display cases, each of the plurality of refrigerated
display cases having a dedicated evaporator assembly adapted to
cool return air from the respective refrigerated display case by at
least partially evaporating the first refrigerant, and a dedicated
first stage compressor assembly in fluid communication with the
dedicated evaporator assembly to compress the first refrigerant
from the dedicated evaporator assembly to a first pressure
corresponding to a first temperature of the first refrigerant; a
high temperature refrigeration circuit configured to circulate a
second refrigerant, the high temperature refrigeration circuit
including a second compressor assembly operable to compress the
second refrigerant to a second pressure corresponding to a second
temperature of the second refrigerant, and a heat exchanger
configured to cool the second refrigerant; and a heat exchanger in
communication with the low temperature refrigeration circuit and
the high temperature refrigeration circuit to transfer heat from
the first refrigerant to the second refrigerant to cool the first
refrigerant without mixing the first refrigerant and the second
refrigerant.
12. The refrigeration system of claim 11, wherein the first
refrigerant and the second refrigerant include carbon dioxide
refrigerant.
13. The refrigeration system of claim 11, wherein the first
refrigerant is circulated in a subcritical refrigeration cycle.
14. The refrigeration system of claim 11, wherein the low
temperature refrigeration circuit further includes a low
temperature receiver disposed between and in fluid communication
with each dedicated evaporator assembly and the heat exchanger to
separate liquid and gaseous phases of the first refrigerant and to
supply liquid refrigerant to each dedicated evaporator
assembly.
15. The refrigeration system of claim 11, wherein high temperature
refrigeration circuit further includes a high temperature receiver
disposed between and in fluid communication with the heat exchanger
and the heat exchanger to receive the cooled second refrigerant and
to direct the cooled second refrigerant to the heat exchanger.
16. The refrigeration system of claim 11, wherein the high
temperature refrigeration circuit further includes an accumulator
disposed between and in fluid communication with the second
compressor assembly and the heat exchanger to separate liquid and
gaseous phases of the second refrigerant and to supply gaseous
phase second refrigerant to the second compressor assembly.
17. The refrigeration system of claim 11, wherein the heat
exchanger is operable as a condenser for the first refrigerant, and
wherein the heat exchanger is operable as an evaporator for the
second refrigerant.
18. The refrigeration system of claim 11, wherein the second
refrigerant is circulated in a transcritical refrigeration
cycle.
19. A refrigeration system comprising: a plurality of refrigerated
display cases, each of the plurality of refrigerated display cases
including a dedicated evaporator assembly adapted to cool return
air from the respective refrigerated display case by at least
partially evaporating a refrigerant; at least one first stage
compressor assembly in fluid communication with the dedicated
evaporator assemblies to compress the refrigerant from the
dedicated evaporator assemblies to a first pressure corresponding
to a first temperature of the refrigerant; a second stage
compressor assembly in fluid communication with the at least one
first stage compressor assembly to receive the compressed
refrigerant and to compress the refrigerant to a second pressure
that is higher than the first pressure, the second pressure
corresponding to a second temperature of the refrigerant; a heat
exchanger located remotely from the plurality of refrigerated
display cases, the heat exchanger including an inlet in fluid
communication with the second stage compressor assembly to receive
the refrigerant from the second stage compressor assembly and to
reject heat from the refrigerant to an environment; a vessel
positioned between and in fluid communication with the dedicated
evaporator assemblies and the heat exchanger to separate liquid and
gaseous phases of the refrigerant; a liquid main fluidly coupled to
the dedicated evaporator assemblies and to the vessel, the liquid
main configured to supply liquid refrigerant to each dedicated
evaporator assembly; and a gas main fluidly coupled to the second
stage compressor assembly and to the vessel, the gas main
configured to direct gaseous refrigerant from the vessel to the
second stage compressor assembly without passing through the
dedicated evaporator assemblies.
20. The refrigeration system of claim 19, wherein the refrigerant
includes a carbon dioxide refrigerant.
21. The refrigerated system of claim 19, wherein the refrigerant
includes a critical temperature, and wherein the first temperature
is a subcritical temperature and the second temperature includes a
transcritical temperature.
22. A refrigeration system comprising: a closed coolant loop
configured to circulate a coolant fluid, the coolant loop including
a supply main, a distribution main, a discharge main, a heat
exchanger fluidly connected to the discharge main and the supply
main and in communication with an environment to reject heat from
the coolant fluid into the environment, and at least one coolant
pump fluidly connected to the distribution main and the discharge
main to pump the coolant fluid to the heat exchanger and through
the coolant loop; and a plurality of refrigerated display cases
coupled to the coolant loop, each of the plurality of refrigerated
display cases including a dedicated evaporator assembly adapted to
cool return air from the respective refrigerated display case by at
least partially evaporating a refrigerant, and a dedicated
refrigeration unit coupled to the evaporator assembly, the
evaporator assembly and the refrigeration unit in fluid
communication with each other and defining a closed transcritical
refrigeration circuit, the refrigeration unit including a
compressor assembly in fluid communication with the evaporator
assembly to compress the refrigerant from the evaporator assembly,
and a heat exchanger in fluid communication with the compressor
assembly and with the evaporator assembly, the heat exchanger in
heat exchange relationship with the coolant loop to reject heat
from the refrigerant to the coolant fluid.
Description
RELATED APPLICATIONS
[0001] This patent application claims priority to U.S. Patent
Application Ser. No. 60/858,624, filed Nov. 13, 2006, the entire
contents of which are hereby incorporated by reference.
BACKGROUND
[0002] The present invention relates to a refrigeration system, and
more specifically, to a transcritical refrigeration system for
refrigerating food product displayed in refrigerated display cases
in a commercial application.
[0003] A retail store, such as a supermarket, typically contains
many refrigerated display cases for displaying and cooling food
and/or beverage items for sale. Many types of refrigerated display
cases are known in the art, and are in extensive use in retail
locations. Such refrigerated display cases require a refrigeration
system to maintain a temperature within the display case that is
lower than ambient temperature inside the store.
[0004] Refrigeration systems generally include an evaporator, a
compressor, and a condenser. A refrigerant fluid flows from one
component to the next, exchanging heat so as to absorb heat from a
refrigerated area and reject heat at the condenser, typically
experiencing a phase change during the cycle.
[0005] One example of a prior art refrigeration system 10 is shown
in FIG. 1. Each refrigerated display case 15 includes an evaporator
20 for removing heat from each refrigerated display case 15.
Evaporated refrigerant is routed from the evaporators 20 via a
suction header 25 to a local bank of compressors 30 and then
through a discharge header 35 to a remotely located condenser 40 to
be condensed. Condensed refrigerant is routed from the condenser 40
via a liquid header 45 to the evaporators 20. The local bank of
compressors 30 is located either at the end of a group or directly
atop a group of refrigerated display cases 15 and contains several
compressors connected in parallel within a sound-attenuated casing
50. The suction header 25 and the discharge header 35 are partially
located within the sound-attenuated casing 50. The discharge header
35 establishes fluid communication between the local bank of
compressors 30 and the condenser 40 and is not necessarily
positioned adjacent each refrigerated display case 15. Similarly,
the liquid header 45 establishes fluid communication between the
evaporators 20 and the condenser 40, and is not necessarily
positioned adjacent each refrigerated display case 15. The local
bank of compressors 30 serves to compress heated refrigerant from
several evaporators 20. The remotely located condenser 40 receives
heated refrigerant from the single local bank of compressors
30.
SUMMARY
[0006] In one embodiment, the invention provides a refrigeration
system for use in a retail store application that includes a
plurality of refrigerated display cases. Each of the plurality of
refrigerated display cases has a dedicated evaporator assembly that
is adapted to cool return air from the respective refrigerated
display case by at least partially evaporating a refrigerant. Each
refrigerated display case also has a dedicated first stage
compressor assembly that is in fluid communication with the
dedicated evaporator assembly to compress the refrigerant from the
dedicated evaporator assembly to a first pressure that corresponds
to a first temperature of the refrigerant, and to discharge the
compressed refrigerant into a discharge main.
[0007] The refrigeration system also includes a second stage
compressor assembly and a heat exchanger. The second stage
compressor assembly is in fluid communication with the dedicated
first stage compressor assembly of each of the plurality of
refrigerated display cases to receive the refrigerant and to
compress the refrigerant to a second pressure that is higher than
the first pressure, and that corresponds to a second temperature of
the refrigerant. The heat exchanger is located remotely from the
plurality of refrigerated display cases, and is in communication
with the refrigerated display cases via a fluid main. The heat
exchanger includes an inlet that is in fluid communication with the
second stage compressor assembly to receive the refrigerant from
the second stage compressor assembly to reject heat from the
refrigerant to an environment. The heat exchanger also includes an
outlet that is in fluid communication with the dedicated evaporator
assembly in each of the plurality of refrigerated display cases via
the fluid main.
[0008] In another embodiment, the invention provides a
refrigeration system that includes a low temperature refrigeration
circuit circulates a first refrigerant, and a high temperature
refrigeration circuit circulates a second refrigerant. The low
temperature refrigeration circuit includes a plurality of
refrigerated display cases, each having a dedicated evaporator
assembly that is adapted to cool return air from the respective
refrigerated display case by at least partially evaporating the
first refrigerant. Each display case also includes a dedicated
first stage compressor assembly that is in fluid communication with
the dedicated evaporator assembly to compress the first refrigerant
from the dedicated evaporator assembly to a first pressure that
corresponds to a first temperature of the first refrigerant.
[0009] The high temperature refrigeration circuit includes a second
compressor assembly that is operable to compress the second
refrigerant to a second pressure that corresponds to a second
temperature of the second refrigerant. The high temperature
refrigeration system also includes a heat exchanger that cools the
second refrigerant. The refrigeration system also includes a heat
exchanger that is in communication with the low temperature
refrigeration circuit and the high temperature refrigeration
circuit to transfer heat from the first refrigerant to the second
refrigerant to cool the first refrigerant without mixing the first
refrigerant and the second refrigerant.
[0010] In yet another embodiment, the invention provides a
refrigeration system that includes a plurality of refrigerated
display cases, each having a dedicated evaporator assembly adapted
to cool return air from the respective refrigerated display case by
at least partially evaporating a refrigerant. The refrigeration
system also includes at least one first stage compressor assembly,
a second stage compressor assembly, and a heat exchanger. The first
stage compressor assembly is in fluid communication with the
dedicated evaporator assembly to compress the refrigerant from the
dedicated evaporator assembly to a first pressure that corresponds
to a first temperature of the refrigerant.
[0011] The second stage compressor assembly is in fluid
communication with the at least one first stage compressor assembly
to receive the compressed refrigerant and to compress the
refrigerant to a second pressure that is higher than the first
pressure, and that corresponds to a second temperature of the
refrigerant. The heat exchanger is located remotely from the
plurality of refrigerated display cases, and includes an inlet that
is in fluid communication with the second stage compressor assembly
to receive the refrigerant from the second stage compressor
assembly and to reject heat from the refrigerant to an environment.
The refrigeration system also includes a vessel that is positioned
between and in fluid communication with the dedicated evaporator
assemblies and the heat exchanger to separate liquid and gaseous
phases of the refrigerant. The refrigeration system further
includes a liquid main and a gas main. The liquid main is fluidly
coupled to the dedicated evaporator assemblies and to the vessel,
and supplies liquid refrigerant to each dedicated evaporator
assembly. The gas main is fluidly coupled to the second stage
compressor assembly and to the vessel, and directs gaseous carbon
dioxide refrigerant from the vessel to the second stage compressor
assembly without passing through the dedicated evaporator
assemblies.
[0012] In yet another embodiment, the invention provides a
refrigeration system that includes a closed coolant loop that
circulates a coolant fluid, and that includes a supply main, a
distribution main, and a discharge main. The coolant loop also
includes a heat exchanger that is fluidly connected to the
discharge main and the supply main and in communication with an
environment to reject heat from the coolant fluid into the
environment, and at least one coolant pump fluidly connected to the
distribution main and the discharge main to pump the coolant fluid
to the heat exchanger and through the coolant loop. The
refrigeration system also includes a plurality of refrigerated
display cases that are coupled to the coolant loop. Each of the
plurality of refrigerated display cases includes a dedicated
evaporator assembly that cools return air from the respective
refrigerated display case by at least partially evaporating a
refrigerant, and a dedicated refrigeration unit that is coupled to
the evaporator assembly.
[0013] The evaporator assembly and the refrigeration unit are in
fluid communication with each other, and define a closed
transcritical refrigeration circuit. The refrigeration unit
includes a compressor assembly that is in fluid communication with
the evaporator assembly to compress the refrigerant from the
evaporator assembly, and a heat exchanger in fluid communication
with the compressor assembly and with the evaporator assembly. The
heat exchanger is in heat exchange relationship with the coolant
loop to reject heat from the refrigerant to the coolant fluid.
[0014] Other aspects of the invention will become apparent by
consideration of the detailed description and accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic view of a prior art refrigeration
system for refrigerating display cases.
[0016] FIG. 2A is a schematic view of a transcritical refrigeration
system for refrigerating display cases.
[0017] FIG. 2B is a schematic view of another embodiment of a
transcritical refrigeration system that includes a cascade
refrigeration circuit for refrigerating display cases.
[0018] FIG. 3 is a schematic view of another embodiment of a
transcritical refrigeration system that includes a closed coolant
loop and a transcritical refrigeration unit for refrigerating
display cases.
[0019] FIG. 4 is a schematic view of one refrigerated display case
of FIG. 3 that includes a transcritical refrigeration unit of FIG.
3.
DETAILED DESCRIPTION
[0020] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways. Also, it is to be understood that the phraseology and
terminology used herein is for the purpose of description and
should not be regarded as limiting. The use of "including,"
"comprising," or "having" and variations thereof herein is meant to
encompass the items listed thereafter and equivalents thereof as
well as additional items. Unless specified or limited otherwise,
the terms "mounted," "connected," "supported," and "coupled" and
variations thereof are used broadly and encompass both direct and
indirect mountings, connections, supports, and couplings. Further,
"connected" and "coupled" are not restricted to physical or
mechanical connections or couplings.
[0021] FIG. 2A shows a refrigeration system 100 for use with a
building 105 that includes a shopping area 110. As used herein, the
term "shopping area 110" refers to the commonly accessible area of
a supermarket where customers may browse items for sale, and
generally does not include any areas designated as equipment,
storage, or maintenance areas.
[0022] The refrigeration system 100 is a transcritical
refrigeration system that circulates carbon dioxide refrigerant
("CO.sub.2 refrigerant") as a cooling fluid. The refrigeration
system 100 includes refrigerated display cases 115, a first stage
compressor assembly 120 attached to each of the display cases 115,
a second stage compressor assembly 125, a gas cooler or heat
exchanger 130, a vessel 135, a fluid main 140, and a discharge main
145. The refrigerated display cases 115 are positioned throughout
the shopping area 110 of the building 105 for housing and
displaying food product.
[0023] Each refrigerated display case 115 is fluidly connected to
the fluid main 140 via a liquid branch line 150. Each liquid branch
line 150 is fluidly connected to the fluid main 140 in parallel
with each of the remaining liquid branch lines 150. The
refrigerated display cases 115 are further fluidly coupled to the
discharge main 145 via discharge branch lines 155. Each discharge
branch line 155 is fluidly coupled to the discharge main 145 in
parallel with each of the remaining discharge branch lines 155.
[0024] Each of the refrigerated display cases 115 includes an
expansion device or valve 160, and an evaporator assembly 165
coupled to the related first stage compressor assembly 120. For
illustrative purposes, only the expansion device 160 and the
evaporator assembly 165 of one of the display cases 115 are shown.
The expansion device 160 is located between the fluid main 140 and
the evaporator assembly 165 to regulate a pressure of refrigerant
flowing from the fluid main 140 to the evaporator assembly 165.
[0025] The illustrated evaporator assembly 165 of each display case
115 includes a single dedicated evaporator coupled to the related
first stage compressor assembly 120. In other embodiments, the
evaporator assembly 165 may employ more than one evaporator, with
each of the evaporators connected in parallel or series between the
liquid branch line 150 and the first stage compressor assembly
120.
[0026] As used herein, the phrase "evaporator assembly 165" does
not imply the use of any particular refrigerant (i.e., a two-phase
refrigerant or a single-phase refrigerant). Rather, the terms
should be generally construed to describe a heat exchanger
assembly/coil functioning to transfer heat from an airflow passing
through/over the heat exchanger assembly/coil to a refrigerant
flowing through the heat exchanger assembly/coil.
[0027] Each first stage compressor assembly 120 is coupled to the
discharge branch line 155 between one of the display cases 115 and
the discharge main 145. The illustrated first stage compressor
assembly 120 includes a single dedicated compressor to compress
refrigerant received from the evaporator assembly 165 of the
related display case 115. Other embodiments of the first stage
compressor assembly 120 may include multiple dedicated compressors
for a single display case 115. Still other embodiments may include
one or more compressors for a small group of display cases 115.
[0028] The second stage compressor assembly 125 is located
downstream of the first stage compressor assembly 120. The
illustrated embodiment of the second stage compressor assembly 125
shows the second stage compressor assembly 120 including two
compressors 170. In other embodiments, the second stage compressor
assembly 120 may include one compressor 170, or more than two
compressors 170. In some embodiments, the compressors 170 can be
one or more variable capacity compressors. In these embodiments,
the capacity of the compressors can be varied to accommodate
pressure fluctuations that may be present within the refrigeration
system 100.
[0029] The second stage compressor assembly 125 is in fluid
communication with the first stage compressor assembly 120 via a
fluid line 172. The fluid line 172 includes an inlet 173 coupled to
an upper portion of the vessel 135, and extends between the inlet
173 and an inlet line 175 of the second stage compressor assembly
125. The second stage compressor assembly 125 further includes an
outlet line 180 that extends between an outlet of the compressor
assembly 125 and the heat exchanger 130.
[0030] A bypass line 182 is coupled between the fluid line 172 and
the outlet line 180 to circulate gaseous CO.sub.2 refrigerant from
the fluid line 172 to the heat exchanger 130 without passing
through the second stage compressor assembly 125. A check valve 183
is positioned in the bypass line 182 to allow refrigerant flow
toward the heat exchanger 130 and to limit refrigerant flow from
the outlet line 180 backward to the fluid line 172.
[0031] The heat exchanger 130 is located remotely from the shopping
area 110, and further outside the building 105 to cool the CO.sub.2
refrigerant. In some embodiments, the heat exchanger 130 may be
located inside the building 105 but remote from the shopping area
110. The heat exchanger 130 includes an inlet 185, an outlet 190,
and at least one fan 195 to cool the CO.sub.2 refrigerant. The
inlet 185 is in fluid communication with the second stage
compressor assembly 125 via the gas main 175, and the outlet 190 is
in fluid communication with the vessel 135.
[0032] The vessel 135 is in fluid communication with the fluid main
140 to separate liquid CO.sub.2 refrigerant from gaseous CO.sub.2
refrigerant, and can be located anywhere along the fluid main 140
between the heat exchanger 130 and the refrigerated display cases
115 (i.e., either inside the building 105 or outside the building
105), without departing from the scope of the invention. A bypass
main 197 is coupled between the vessel 135 and the fluid line 172
to circulate CO.sub.2 refrigerant from the vessel 135 to the second
stage compressor assembly 125 without passing through the fluid
main 140 to the display cases 115. An expansion device 198 is
disposed along the fluid main 140 downstream of the heat exchanger
130 and upstream of the vessel 135 to regulate the pressure of the
CO.sub.2 refrigerant exiting the heat exchanger 130.
[0033] In the illustrated embodiment, the fluid main 140 and the
discharge main 145 are routed throughout the building 105, such
that at least a portion of the fluid main 140 and at least a
portion of the discharge main 145 are positioned adjacent each
refrigerated display case 115 of the refrigeration system 100. A
downstream end of the discharge main 145 is in heat exchange
relationship with the vessel 135, and in fluid communication with
the inlet 173. The heat exchange between the superheated
refrigerant in the discharge main 145 and the refrigerant in the
vessel 135 adequately cools the superheated refrigerant prior to
entry into the second stage compressor assembly 125. In other
embodiments, the downstream end of the discharge main 145 may be in
fluid communication with the vessel 135. In those embodiments, the
refrigerant from the discharge main 145 can be mixed with the
refrigerant prior to being directed to the second stage compressor
assembly 125.
[0034] Positioning at least a portion of both the fluid main 140
and the discharge main 145 adjacent each refrigerated display case
115 allows the refrigerated display cases 115 to be installed at a
variety of locations in the shopping area 110 by tapping into the
fluid main 140 and the discharge main 145 with the pair of
respective liquid and discharge branch lines 150,155. In some
embodiments, the fluid and discharge mains 140,145 may be outside
the shopping area 110 adjacent a display case that is near an edge
(e.g., a wall) of the shopping area 110. In other embodiments, the
fluid and discharge mains 140, 145 may extend out into the shopping
area 110 adjacent each of a group of more centrally located display
cases 115.
[0035] In still other embodiments, the store may be divided into
"sub-loop" areas with a fluid and discharge main 140, 145 and an
air-cooled heat exchanger 130 for each sub-area of the store. For
example one set of fluid and discharge mains 140, 145 with the
air-cooled heat exchanger 130 may be positioned on a left side of
the store, and a separate set of fluid and discharge mains 140, 145
and a separate air-cooled heat exchanger 130 may be positioned on a
right side of the store. A further embodiment may use such separate
sub-loops for different types of refrigerated display cases 115.
For example, one set of fluid and discharge mains 140, 145 for the
meat area, one set for the produce area, etc. Thus, the fluid main
140 and the discharge main 145 allow the refrigerated display cases
115 to be positioned throughout the shopping area 110 of the
building 105 in a variety of configurations, without requiring
extensive routing of lengthy individual liquid and discharge branch
lines 150, 155 and thereby minimizing the length of the liquid and
discharge branch lines 150, 155.
[0036] The arrangement of the fluid main 140 and discharge main 145
throughout the building 105 may simplify the installation procedure
of refrigerated display cases 115 or allow for the refrigerated
display cases 115 to be easily moved from one location to another
within the building 105. The fluid and discharge mains 140, 145 may
be plumbed into the building 105 (e.g., under the floor or behind
walls of the shopping area 110) before any refrigerated display
cases 115 are installed. When refrigerated display cases 115 are
ready to be installed, they can be added to the refrigeration
system 100 by tapping into the fluid and discharge mains 140, 145
at a location very near the desired location for the refrigerated
display case 115. This eliminates the need for routing lengthy
liquid or discharge branch lines 150, 155 between each of the
refrigerated display cases 115 and a centralized location, remote
from the shopping area 110. This also improves the modularity of
the shopping area 110, in that the refrigerated display cases 115
can be reconfigured and moved throughout the shopping area 110
without requiring the cumbersome activity of re-routing lengthy
liquid and discharge branch lines 150, 155.
[0037] The transcritical CO.sub.2 refrigeration cycle of the
refrigeration system 100 operates in a similar fashion to the
reverse-Rankine refrigeration cycle, except the vapor CO.sub.2
refrigerant is compressed to a temperature above the thermodynamic
critical point of the CO.sub.2 refrigerant (i.e., approximately
87.7 degrees Fahrenheit). As described in detail below, the
CO.sub.2 refrigerant is compressed to a high, transcritical
pressure of about 1600 psig corresponding to a temperature above
the critical point by the second stage compressor assembly 125
prior to cooling of the refrigerant in the heat exchanger 130.
Consequently, when heat is rejected from the CO.sub.2 refrigerant
in the heat exchanger 130, the vapor CO.sub.2 refrigerant is cooled
to a cooled vapor rather than changing phases to a liquid. In the
closed circuit travel of the CO.sub.2 refrigerant, the heat
exchanger 130 cools the high-pressure CO.sub.2 vapor to a lower
temperature as a result of the forced airflow generated by the fan
195. In the illustrated embodiment, the heat exchanger 130 cools
the CO.sub.2 refrigerant from about 250 degrees Fahrenheit to about
100 degrees Fahrenheit. In other embodiments, the temperature of
the CO.sub.2 refrigerant may be cooled by the heat exchanger 130
from temperatures above or below 250 degrees Fahrenheit to
temperatures above or below 100 degrees Fahrenheit.
[0038] The cooled, high-pressure vapor CO.sub.2 refrigerant is then
throttled through the expansion device 198 to an intermediate,
subcritical pressure fluid of about 600 psig where, similar to the
reverse-Rankine refrigeration cycle, the intermediate-pressure
CO.sub.2 refrigerant changes phase to a liquid-vapor mixture prior
to entering the vessel 135. In the illustrated embodiment, the
difference between the high pressure of the refrigerant and the
intermediate pressure of the refrigerant is approximately 1000
psig. In other embodiments, the difference between the high
pressure of the refrigerant and the intermediate pressure of the
refrigerant can be above or below 1000 psig.
[0039] The liquid-vapor mixture then enters the vessel 135 where
the liquid CO.sub.2 refrigerant is separated from gaseous CO.sub.2
refrigerant. The gaseous CO.sub.2 refrigerant can flow through the
bypass main 197 to the inlet 175 of the second stage compressor
assembly 125, while the liquid CO.sub.2 refrigerant can flow
through the remaining portion of the fluid main 140 to the
refrigerated display cases 115 via the liquid branch lines 150.
[0040] The intermediate pressure CO.sub.2 refrigerant is throttled
by the expansion device 160 of each display case 115 to a
low-pressure refrigerant prior to entry into the evaporator
assembly 165. The low-pressure refrigerant boils to a vapor in the
evaporator assembly 165. In other words, the low-pressure CO.sub.2
refrigerant passing through the evaporator assembly 165 absorbs the
heat from the airflow as it is passed through the evaporator
assembly 165, thereby cooling the airflow.
[0041] The gaseous CO.sub.2 refrigerant flows from the evaporator
assembly 165 to the first stage compressor assembly 120 where the
refrigerant is compressed to the intermediate, subcritical pressure
that corresponds to a temperature generally below the critical
point. While the intermediate pressure of the refrigerant in the
illustrated embodiment is at about 600 psig, other pressures of the
refrigerant higher and lower than 600 psig are possible.
[0042] The intermediate pressure refrigerant flows from the first
stage compressor assembly 120 through the discharge branch lines
155, and accumulates in the discharge main 145. The refrigerant
flows through the discharge main 145 to the vessel 135, where the
refrigerant can be de-superheated. The refrigerant is
de-superheated prior to entering the second stage compressor
assembly 125 by heat exchange with the refrigerant in the vessel
135. The de-superheated refrigerant flows from the discharge main
145 into the fluid line 172 toward the inlet 175. The second stage
compressor assembly 125 receives the intermediate pressure
refrigerant from one or both of the discharge main 145 and the
bypass main 197 through the inlet 175. The refrigerant flowing from
the bypass main 197 from the vessel 135 is at about the same
intermediate pressure as the refrigerant flowing from the fluid
line 172.
[0043] The second stage compressor assembly compresses the CO.sub.2
refrigerant from the intermediate pressure to the high pressure.
While the high pressure refrigerant in the illustrated embodiment
is at about 1600 psig, other pressures of the refrigerant higher
and lower than 1600 psig are capable using the second stage
compressor assembly 125, and are within the scope of the invention.
The high pressure refrigerant flows from the second stage
compressor assembly 125 through the outlet line 180, and is cooled
in the heat exchanger 130 as described above.
[0044] To obtain desirable refrigeration characteristics from the
CO.sub.2 refrigerant, the transcritical CO.sub.2 refrigeration
cycle requires higher operating pressures compared to a
reverse-Rankine refrigeration cycle using R134a, for example. In
some applications, the pressure experienced in the heat exchanger
130 in the transcritical CO.sub.2 refrigeration system 100 can
exceed the pressure experienced in a condenser of a reverse-Rankine
refrigeration cycle using R134a by as much as eight-fold. Also, the
low pressure experienced in the evaporator assembly 165 in the
transcritical CO.sub.2 refrigeration cycle can exceed the pressure
experienced in an evaporator assembly in a reverse-Rankine
refrigeration cycle using R134a by as much as fifteen-fold. As a
result, the heat exchanger 130 and evaporator assembly 165 employ a
heavy-duty construction to withstand the increased pressure of the
transcritical CO.sub.2 refrigeration cycle. Such heavy-duty
construction may comprise an increased thickness of the walls of
the tubing in the evaporator assembly 165 and heat exchanger 130.
In addition, the thickness of the walls of the fluid main 140, the
discharge main 145, the liquid branch line 150, the discharge
branch line 155, and other conduit (not shown) utilized in the
refrigeration system 100 to fluidly connect the refrigeration
components may also be increased to accommodate the increased
pressure of the transcritical CO.sub.2 refrigeration cycle.
[0045] The critical temperature of CO.sub.2 refrigerant is
approximately 88 degrees Fahrenheit. In some embodiments of the
refrigeration system 100, the ambient temperature surrounding the
heat exchanger 130 may drop below the critical temperature of the
refrigerant. In those embodiments, the heat exchanger 130 may
function similarly to a condenser, cooling the high pressure
CO.sub.2 refrigerant to a liquid-vapor or a liquid-only
refrigerant. More specifically, variations in the pressure of the
refrigerant within the refrigeration system 100 are controlled by
changing the state of the second stage compressor assembly 125. For
example, when the refrigerant pressure in the discharge main 145
drops below a predetermined pressure that corresponds to a
temperature at or below the critical point of the refrigerant, the
second stage compressor assembly 125 can be shutdown such that the
refrigerant can be cycled through the system 100 using only the
first stage compressor assembly 120. When the second stage
compressor assembly 125 is shutdown, the refrigerant bypasses the
second stage compressor assembly 125 through the bypass line 182,
and flows into the heat exchanger 130. When the refrigerant
pressure in the discharge main 145 increases above the
predetermined pressure, the second stage compressor assembly can be
re-activated to accommodate the increased pressure within the
refrigeration system 100.
[0046] The second stage compressor assembly 125 capacity can be
reduced or eliminated as the ambient temperature decreases below
the critical temperature to accommodate a decrease in refrigerant
pressure within the refrigeration system 100. In embodiments where
the ambient temperature is significantly below the critical
temperature of the refrigerant, the second stage compressor
assembly 125 may be shutdown due to a low refrigerant pressure in
the discharge main 145 that corresponds to the temperature below
the critical temperature. In these embodiments, the first stage
compressor assembly 120 of each display case 115 can operate the
entire system 100, entirely bypassing the second stage compressor
assembly 125 through the bypass line 182. The check valve 183
prevents backward flow of refrigerant from the outlet line 180 to
the fluid line 172 when the second stage compressor assembly 125 is
running.
[0047] The use of the first and second stage compressor assemblies
120, 125 allows smaller compressors to be positioned adjacent the
display cases 115, which limits parasitic losses that may otherwise
occur when the compressor assembly 120 is located remotely from the
display case 115. The losses are limited because the position of
the first stage compressor assemblies 120 adjacent to the display
cases 115 allows the first stage compressor assemblies 120 to
operate at a desired suction pressure, which maintains an efficient
refrigeration system 100. In addition, the close position of the
first stage compressor assemblies 120 relative to the display cases
115 allows modulation of the capacity and/or the evaporator
temperature of each display case 115 and improves the efficiency of
the refrigeration system 100.
[0048] FIG. 2B shows another embodiment of a refrigeration system
200 for use with the building 105. Except as described below, the
refrigeration system 200 is the same as the refrigeration system
100, and common elements have been given the same reference
numerals. The refrigeration system 200 is a split-stage
transcritical refrigeration system that includes a high temperature
refrigeration circuit 205 and a low temperature refrigeration
circuit 210.
[0049] The high temperature refrigeration circuit 205 includes the
heat exchanger 130, a high temperature receiver 215, a cascade
cooler or heat exchanger 220, an accumulator 225, and a compressor
assembly 230. The receiver 215 is fluidly connected to the heat
exchanger 130 to receive cooled refrigerant. When the high
temperature refrigeration circuit 205 is operating above the
critical point for the refrigerant, only gaseous refrigerant is
stored in the receiver 215. When the high temperature refrigeration
circuit 205 is operating at or below the critical point for the
refrigerant, some liquid refrigerant may be present in the receiver
215. The expansion device 198 is positioned downstream of the
receiver 215 to control the refrigerant discharge pressure.
Refrigerant passing through the expansion device 198 flows to the
cascade cooler 220 via a fluid line 235.
[0050] The high temperature refrigeration circuit 205 is in heat
exchange relationship with the low temperature refrigeration
circuit 210 via the cascade cooler 220. The cascade cooler 220
includes a first inlet 222 that is fluidly connected to the fluid
line 235 to receive cooled refrigerant from the heat exchanger 130.
The cascade cooler 220 further includes a first outlet 224 that is
fluidly connected to the accumulator 225 via a fluid main 240 to
deliver heated refrigerant to the accumulator 225.
[0051] The refrigerant entering the cascade cooler 220 from the
refrigeration circuit 205 is cooler than the refrigerant entering
the cascade cooler 220 from the refrigeration circuit 210. As such,
the cascade cooler 220 functions similar to an evaporator for the
refrigeration circuit 205, and functions similar to a condenser for
the refrigeration circuit 210. In other words, heat from the
refrigerant in the refrigeration circuit 210 is absorbed by the
refrigerant in the refrigeration circuit 205, thereby cooling the
refrigerant in the refrigeration circuit 210 and heating the
refrigerant in the refrigeration circuit 205.
[0052] The compressor assembly 230 is located downstream of the
accumulator 225, and is dedicated to the refrigeration circuit 205.
The illustrated embodiment shows the second stage compressor
assembly 230 including two compressors 245. In other embodiments,
the first compressor assembly 230 may include one compressor 245,
or more than two compressors 245. The inlet line 175 fluidly
connects the accumulator 225 to the compressor assembly 230.
[0053] The low temperature refrigeration circuit 210 operates at a
refrigerant temperature that is at or below the critical point for
the refrigerant. The refrigeration circuit 210 includes the
refrigerated display cases 115, a receiver 250, and compressor
assemblies 255. As discussed above with regard to FIG. 2A, each
display case 115 is fluidly connected to the fluid main 140 via the
liquid branch line 150. The fluid main 140 is coupled to the
receiver 250 to distribute cooled refrigerant to the display cases
115.
[0054] The refrigerated display cases 115 are further fluidly
connected to the discharge main 145 via the discharge branch lines
155. The discharge main 145 is fluidly connected to a second inlet
260 of the cascade cooler 220 to deliver heated refrigerant from
the compressor assemblies 255 to the cascade cooler 220.
[0055] The receiver 250 is fluidly connected to the cascade cooler
220 via a distribution line 265. The distribution line 265 is
coupled to a second outlet 270 of the cascade cooler 220 to direct
cooled refrigerant into the receiver 250. The receiver 250 is
further in fluid communication with the fluid main 140 to separate
liquid refrigerant from gaseous refrigerant, and can be located
anywhere along the fluid main 140 upstream of the display cases
115.
[0056] Each compressor assembly 255 is dedicated to the
refrigeration circuit 205, and is attached to one of the cases 115.
Each compressor assembly 255 is further coupled to the discharge
branch line 155 between one of the display cases 115 and the
discharge main 145. In some embodiments, each compressor assembly
255 may be located remotely from each of the display case 115, with
adequate capacity to compress refrigerant from each display case
115. The illustrated compressor assembly 255 includes a single
dedicated compressor to compress refrigerant received from the
evaporator assembly 165 of the related display case 115. Other
embodiments of the compressor assembly 255 may include multiple
dedicated compressors for a single display case 115. Still other
embodiments may include one or more compressors for a small group
of display cases 115.
[0057] The transcritical CO.sub.2 refrigeration cycle of the
refrigeration system 200 provides cooling to the display cases 115
without mixing refrigerant between the high temperature
refrigeration circuit 205 and the low temperature refrigeration
circuit 210. Refrigerant entering the cascade cooler 220 through
the first inlet 222 is heated by heat exchange with refrigerant
flowing through the low temperature refrigeration circuit 210. The
heated refrigerant exits the cascade cooler 220 through the first
outlet 224 and flows through the fluid main 240 to the accumulator
225. When the refrigeration circuit 205 is operating at or below
the critical point for the refrigerant, some liquid refrigerant
exists in the accumulator 225. Gaseous refrigerant is separated
from the liquid refrigerant in the accumulator 225, and the gaseous
refrigerant is then directed to the compressor assembly 230. The
gaseous, heated refrigerant is then compressed by the compressor
assembly 230 prior to being cooled in the heat exchanger 130. The
cooled refrigerant flows from the heat exchanger 130 to the vessel
135, where the high temperature refrigeration circuit 205 begins
anew.
[0058] The heat exchange relationship between the high temperature
refrigeration circuit 205 and the low temperature refrigeration
circuit 210 in the cascade cooler 220 cools previously heated
refrigerant in the refrigeration circuit 210, and heats previously
cooled refrigerant in the high temperature refrigeration circuit
205. The cooled refrigerant in the low temperature refrigeration
circuit 210 flows from the second outlet 270 of the cascade cooler
220 and into the receiver 250 via the distribution line 265. The
cooled refrigerant flows to each of the display cases 115, where
the refrigerant is heated as it passes through the evaporators 165.
The heated refrigerant from each display case 115 is compressed by
the respective compressor assembly 255 prior to reaching the
discharge main 145. The heated refrigerant flows from the
compressor assembly 255 to the cascade cooler 220 through the
second inlet 260, where the low temperature refrigeration circuit
210 begins anew.
[0059] FIG. 3 shows yet another refrigeration system 300 for use
with the building 105. The refrigeration system 300 includes a
plurality of refrigerated display cases 315 that are coupled to a
coolant loop 317. Each refrigerated display case 315 includes an
evaporator assembly 320 and a refrigeration unit 325 that is
coupled to the evaporator assembly 320 (FIG. 4). The evaporator
assembly 320 is located such that air passing through the
evaporator assembly 320 is discharged to a refrigerated area 330 of
the refrigerated display case 315. The evaporator assembly 320 and
the refrigeration unit 325 are each dedicated to operate with only
one of the refrigerated display cases 315. As shown in FIG. 3, the
evaporator assembly 320 includes one evaporator 335 to provide
cooling to the refrigerated area 330. However, the quantity of
evaporators 335 depends on the cooling requirements of each
refrigerated display case 315, and additional evaporators 335 may
be included in the evaporator assembly 320 without deviating from
the scope of the invention.
[0060] FIG. 4 illustrates the refrigeration unit 325 of one
refrigerated display case 315. Each refrigeration unit 325 defines
a transcritical refrigeration cycle that circulates CO.sub.2
refrigerant to cool the refrigerated area 330. The refrigeration
unit 325 includes a compressor assembly 340 and a gas cooler or
heat exchanger 345. In some embodiments, each refrigeration unit
325 may further include a receiver (not shown) coupled to the
compressor assembly 340.
[0061] The compressor assembly 340 is coupled to the evaporator
assembly 320 to compress CO2 refrigerant received from the
evaporator assembly 320. The illustrated compressor assembly 340
includes two dedicated compressors 350 that are placed within the
transcritical refrigeration cycle in parallel with each other.
Other embodiments of the compressor assembly 340 may include one
compressor, or more than two compressors 350 in parallel or in
series with each other.
[0062] The heat exchanger 345 includes an inlet 355 that is coupled
to the compressor assembly 340, and an outlet 360 that is coupled
to the evaporator assembly 320. As shown in FIG. 3, the heat
exchanger 345 is in heat-exchange relationship with the coolant
loop 317 to reject heat from the compressed CO.sub.2 refrigerant to
a coolant fluid in the coolant loop 317. In some embodiments, an
expansion device (not shown) can be located adjacent the outlet 360
to expand the CO.sub.2 refrigerant prior to reaching the evaporator
assembly 320.
[0063] The CO.sub.2 refrigerant in the heat exchanger 345 is cooled
by heat exchange with the coolant fluid that is circulated in the
coolant loop 317. In one embodiment, the coolant fluid is a
water/glycol mixture. As shown in FIG. 3, the coolant loop 317 is a
closed circulation coolant loop, and includes an air-cooled heat
exchanger 365, a supply main 370, a distribution main 375, coolant
pumps 380, and a discharge main 385. The heat exchanger 365 is
located remotely from the shopping area 110, and is in
communication with an environment surrounding the building 105 to
cool the coolant fluid. The heat exchanger 365 includes a fan 390
to draw air across the heat exchanger 365 to cool the coolant
fluid. In some embodiments, the heat exchanger 365 is located
outside the building 105. In other embodiments, the heat exchanger
365 is located within the building 105 and remote from the shopping
area 110.
[0064] The supply main 370 is coupled to the heat exchanger 365 to
distribute coolant fluid from the heat exchanger 365 to an inlet
branch line 395 that couples the supply main 370 to the
refrigeration unit 325. The inlet branch line 395 is coupled to and
in communication with the heat exchanger 345. An outlet branch line
400 couples the heat exchanger 345 to the distribution main 375 to
deliver heated coolant fluid to the distribution main 375.
[0065] The distribution main 375 is coupled to the pumps 380 to
distribute heated coolant fluid from the outlet branch lines 400 to
the pumps 380. The illustrated pumps 380 are coupled to the
distribution main 375 and the discharge main 385 in parallel with
each other to pump coolant fluid from the distribution main 375
into the discharge main 385. In other embodiments, the pumps 380
can be connected in series with each other.
[0066] In operation, CO.sub.2 refrigerant in the refrigeration unit
325 employing a transcritical refrigeration cycle is heated in the
evaporator assembly 320 as it removes heat from the refrigerated
area 330 of each refrigerated display case 315. The compressor
assembly 340 compresses the heated refrigerant and forces it to
flow to the fluid-cooled heat exchanger 345. The fluid-cooled heat
exchanger 345 transfers heat from the CO.sub.2 refrigerant fluid to
the coolant fluid that flows through the heat exchanger 345 from
the inlet branch line 395 to the outlet branch line 400. As a
result of the heat transfer, the CO.sub.2 refrigerant cools to a
lower temperature and returns to the evaporator assembly 320 to be
heated and cooled in a cyclical manner. In embodiments of the
refrigeration unit 325 that includes the expansion device, the
CO.sub.2 refrigerant can be expanded to a lower pressure fluid
prior to entering the evaporator assembly 320.
[0067] Coolant fluid in the coolant loop 317 flows from the inlet
branch line 395 to the outlet branch line 400 in heat exchange
relationship with the CO.sub.2 refrigerant in the heat exchanger
345. The heat transfer between the heat exchanger 345 and the
coolant loop 317 increases the temperature of the coolant fluid
flowing through the coolant loop 317. The heated coolant fluid
flows through the outlet branch lines 400 and collects in the
distribution main 375. The pumps 380 pump the heated coolant fluid
from the distribution main 375 to the discharge main 385. The pumps
380 generally drive coolant fluid flow throughout the closed
coolant loop 317. The heat exchanger 365 receives the heated
coolant fluid and discharges heat from the fluid to the
environment. The cooled coolant fluid returns to the heat exchanger
345 via the supply main 370 and the inlet branch lines 395 to cool
the refrigeration units 325 in a cyclical manner.
[0068] Various features and advantages of the invention are set
forth in the following claims.
* * * * *