U.S. patent application number 12/308016 was filed with the patent office on 2009-07-09 for multi-stage compressor unit for refrigeration system.
This patent application is currently assigned to Carrier Corporation. Invention is credited to Wayne P. Beagle, James W. Bush, Biswajit Mitra.
Application Number | 20090175748 12/308016 |
Document ID | / |
Family ID | 38801929 |
Filed Date | 2009-07-09 |
United States Patent
Application |
20090175748 |
Kind Code |
A1 |
Bush; James W. ; et
al. |
July 9, 2009 |
Multi-stage compressor unit for refrigeration system
Abstract
A multi-stage compressor unit for a refrigeration system
configured to circulate a refrigerant comprises a first compressor
sub-unit having a first stage and a second stage, and a second
compressor sub-unit in parallel with the first compressor sub-unit
and having a first stage. The first and second stages of the first
compressor sub-unit each have a suction port and a discharge port.
The first compressor sub-unit is configured to receive and compress
a first portion of the refrigerant from an evaporator. The first
stage of the second compressor sub-unit is configured to compress a
second portion of the refrigerant.
Inventors: |
Bush; James W.;
(Skaneateles, NY) ; Beagle; Wayne P.;
(Chittenango, NY) ; Mitra; Biswajit; (Liverpool,
NY) |
Correspondence
Address: |
KINNEY & LANGE, P.A.
THE KINNEY & LANGE BUILDING, 312 SOUTH THIRD STREET
MINNEAPOLIS
MN
55415-1002
US
|
Assignee: |
Carrier Corporation
Farmington
CT
|
Family ID: |
38801929 |
Appl. No.: |
12/308016 |
Filed: |
June 1, 2006 |
PCT Filed: |
June 1, 2006 |
PCT NO: |
PCT/US2006/021123 |
371 Date: |
December 4, 2008 |
Current U.S.
Class: |
418/5 ;
62/510 |
Current CPC
Class: |
F25B 2309/061 20130101;
F25B 1/10 20130101; F25B 9/008 20130101; F25B 2400/13 20130101;
F25B 2400/075 20130101 |
Class at
Publication: |
418/5 ;
62/510 |
International
Class: |
F04C 23/00 20060101
F04C023/00; F25B 1/10 20060101 F25B001/10 |
Claims
1. A multi-stage compressor unit for a refrigeration system
configured to circulate a refrigerant, the multi-stage compressor
unit comprising: a first compressor sub-unit having a first stage
and a second stage, wherein the first and second stages of the
first compressor sub-unit each have a suction port and a discharge
port, and wherein the first compressor sub-unit is configured to
receive and compress a first portion of the refrigerant from an
evaporator; and a second compressor sub-unit in parallel with the
first compressor sub-unit and having a first stage, wherein the
first stage of the second compressor sub-unit has a suction port
and a discharge port, and wherein the second compressor sub-unit is
configured to compress a second portion of the refrigerant prior to
the compressed second portion being combined with the compressed
first portion.
2. The multi-stage compressor unit of claim 1, wherein the first
stage of the second compressor sub-unit is configured to receive
the second portion of the refrigerant from a second evaporator.
3. The multi-stage compressor unit of claim 1, wherein the first
stage of the second compressor sub-unit is configured to receive
the second portion of the refrigerant from a first economizer
circuit.
4. The multi-stage compressor unit of claim 3, wherein the first
compressor sub-unit further comprises an interstage port disposed
between the discharge port of the first stage and the suction port
of the second stage, and wherein the interstage port is configured
to receive a third portion of the refrigerant from a second
economizer circuit.
5. The multi-stage compressor unit of claim 1, wherein the first
compressor sub-unit and the second compressor sub-unit comprise
reciprocating compressors.
6. The multi-stage compressor unit of claim 1, wherein the
refrigerant is a transcritical refrigerant.
7. The multi-stage compressor unit of claim 1, and further
comprising an intercooler configured to cool the first portion of
the refrigerant between the first and second stages of the first
compressor sub-unit.
8. The multi-stage compressor unit of claim 1, wherein the second
compressor sub-unit is configured to discharge into an interstage
port of the first compressor sub-unit.
9. The multi-stage compressor unit of claim 1, wherein the second
compressor sub-unit further comprises a second stage having a
suction port and a discharge port, and wherein the first and second
stages of the second compressor sub-unit are connected in
series.
10. A multi-stage compressor unit for a refrigeration system having
a first economizer circuit and configured to circulate a
refrigerant, the multi-stage compressor unit comprising: a first
compressor sub-unit having a first stage and a second stage,
wherein the first compressor sub-unit is configured to receive and
compress a first portion of the refrigerant from an evaporator; and
a second compressor sub-unit in parallel with the first compressor
sub-unit, wherein the second compressor sub-unit is configured to
compress a second portion of the refrigerant from the first
economizer circuit prior to the compressed second portion being
combined with the compressed first portion.
11. The multi-stage compressor unit of claim 10, and further
comprising an intercooler configured to cool the first portion of
the refrigerant between the first and second stages of the first
compressor sub-unit.
12. The multi-stage compressor unit of claim 10, wherein the first
compressor sub-unit is configured to discharge refrigerant at a
first exit pressure, and wherein the second compressor sub-unit is
configured to discharge refrigerant at a second exit pressure.
13. The multi-stage compressor unit of claim 12, wherein the first
and second exit pressures are substantially equivalent.
14. The multi-stage compressor unit of claim 10, wherein the first
compressor sub-unit further comprises an interstage port disposed
between the first and second stages and configured to receive a
third portion of the refrigerant from a second economizer circuit,
and wherein the second stage of the first compressor sub-unit is
configured to compress a mixture of the first and third portions of
the refrigerant.
15. The multi-stage compressor unit of claim 10, wherein the second
compressor sub-unit is a single-stage compressor.
16. The multi-stage compressor unit of claim 10, wherein the second
compressor sub-unit is a two-stage compressor.
17. The multi-stage compressor unit of claim 16, wherein the second
compressor sub-unit further comprises an interstage port configured
to receive a fourth portion of the refrigerant from a third
economizer circuit.
18. A multi-stage compressor unit for a refrigeration system
configured to circulate a refrigerant, the multi-stage compressor
unit comprising: a first compressor sub-unit having a first stage,
a second stage, and an interstage port disposed between the first
and second stages, wherein the first stage of the first compressor
sub-unit is configured to compress a first portion of the
refrigerant to an intermediate pressure, and wherein the second
stage of the first compressor sub-unit is configured to compress
the first portion of the refrigerant to an exit pressure of the
first compressor sub-unit; and a second compressor sub-unit having
a first stage, wherein the second compressor sub-unit is configured
to compress a second portion of the refrigerant to an exit pressure
of the second compressor sub-unit prior to the compressed second
portion being combined with the compressed first portion.
19. The multi-stage compressor unit of claim 18, wherein the exit
pressures of the first compressor sub-unit and the second
compressor sub-unit are substantially equivalent.
20. The multi-stage compressor unit of claim 18, wherein the second
compressor sub-unit discharges the second portion of the
refrigerant into the interstage port of the first compressor
sub-unit, and wherein the exit pressure of the second compressor
sub-unit is substantially equivalent to the intermediate pressure
of the first compressor sub-unit.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to compressors used
in refrigeration systems. More particularly, the present invention
relates to a multi-stage compressor unit for a refrigeration system
that includes at least one two-stage compressor sub-unit.
[0002] A typical refrigeration system includes an evaporator, a
compressor, a condenser, and a throttle valve. A refrigerant, such
as a hydrofluorocarbon (HFC), typically enters the evaporator as a
two-phase liquid-vapor mixture. Within the evaporator, the liquid
portion of the refrigerant changes phase from liquid to vapor as a
result of heat transfer into the refrigerant. The refrigerant is
then compressed within the compressor, thereby increasing the
pressure of the refrigerant. Next, the refrigerant passes through
the condenser, where it changes phase from a vapor to a liquid as
it cools within the condenser. Finally, the refrigerant expands as
it flows through the throttle valve, which results in a decrease in
pressure and a change in phase from a liquid to a two-phase
liquid-vapor mixture.
[0003] While natural refrigerants such as carbon dioxide have
recently been proposed as alternatives to the presently used HFCs,
the high side pressure of carbon dioxide typically ends up in the
supercritical region where there is no transition from vapor to
liquid as the high pressure refrigerant is cooled. For a typical
single stage vapor compression cycle, this leads to poor efficiency
due to the loss of the subcritical constant temperature
condensation process and to the relatively high residual enthalpy
of supercritical carbon dioxide at normal high side
temperatures.
[0004] Thus, there exists a need for a compressor unit for a
refrigeration system that is capable of utilizing any refrigerant,
including a transcritical refrigerant, while helping to maintain a
high level of system efficiency.
BRIEF SUMMARY OF THE INVENTION
[0005] The present invention is a multi-stage compressor unit for a
refrigeration system configured to circulate a refrigerant. The
multi-stage compressor unit comprises a first compressor sub-unit
having a first stage and a second stage, and a second compressor
sub-unit in parallel with the first compressor sub-unit and having
a first stage. The first and second stages of the first compressor
sub-unit each have a suction port and a discharge port. The first
compressor sub-unit is configured to receive and compress a first
portion of the refrigerant from an evaporator. The first stage of
the second compressor sub-unit has a suction port and a discharge
port. The second compressor sub-unit is configured to compress a
second portion of the refrigerant
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1A illustrates a schematic diagram of a first
alternative embodiment of a multi-stage compressor unit connected
to a refrigeration system.
[0007] FIG. 1B illustrates a graph relating enthalpy to pressure
for the refrigeration system of FIG. 1A.
[0008] FIG. 2A illustrates a schematic diagram of a second
alternative embodiment of a multi-stage compressor unit connected
to a refrigeration system.
[0009] FIG. 2B illustrates a graph relating enthalpy to pressure
for the refrigeration system of FIG. 2A.
[0010] FIG. 3A illustrates a schematic diagram of a third
alternative embodiment of a multi-stage compressor unit connected
to a refrigeration system.
[0011] FIG. 3B illustrates a graph relating enthalpy to pressure
for the refrigeration system of FIG. 3A.
[0012] FIG. 4A illustrates a schematic diagram of a fourth
alternative embodiment of a multi-stage compressor unit connected
to a refrigeration system.
[0013] FIG. 4B illustrates a graph relating enthalpy to pressure
for the refrigeration system of FIG. 4A.
[0014] FIG. 5A illustrates a schematic diagram of a fifth
alternative embodiment of a multi-stage compressor unit connected
to a refrigeration system.
[0015] FIG. 5B illustrates a graph relating enthalpy to pressure
for the refrigeration system of FIG. 5A.
[0016] FIG. 6A illustrates a schematic diagram of a sixth
alternative embodiment of a multi-stage compressor unit connected
to a refrigeration system.
[0017] FIG. 6B illustrates a graph relating enthalpy to pressure
for the refrigeration system of FIG. 6A.
DETAILED DESCRIPTION
[0018] FIG. 1A illustrates a schematic diagram of multi-stage
compressor unit 10A connected to refrigeration system 20A, which
includes heat rejecting heat exchanger 24, first economizer circuit
25A, main expansion valve 26, evaporator 27, and sensor 31. First
economizer circuit 25A includes first economizer heat exchanger
28A, expansion valve 30A, and sensor 31A. Although first economizer
heat exchanger 28A is depicted as a parallel flow tube-in-tube heat
exchanger, multi-stage compressor unit 10A is useful in
refrigeration systems utilizing other types of economizer heat
exchangers including, but not limited to, counter flow tube-in-tube
heat exchangers, shell-in-tube heat exchangers, flash tanks, and
brazed plate heat exchangers.
[0019] Multi-stage compressor unit 10A includes two-stage
compressor sub-unit 32 and single-stage compressor sub-unit 34. As
shown in FIG. 1, two-stage compressor sub-unit 32 is a
reciprocating compressor and includes cylinders 36A and 36B
connected in series. Similarly, single-stage compressor sub-unit 34
is also a reciprocating compressor and includes cylinder 36C.
Although two-stage compressor sub-unit 32 and single-stage
compressor sub-unit 34 are shown as reciprocating compressors,
other types of compressors (in various combinations) may be used
including, but not limited to, scroll, screw, rotary vane, standing
vane, variable speed, hermetically sealed, and open drive
compressors. However, for purposes of example, embodiments of the
present invention will be described as including reciprocating-type
compressor units having multiple stages represented by compression
cylinders.
[0020] In refrigeration system 20A, two distinct refrigerant paths
are formed by connection of the various elements in the system. A
main refrigerant path is created by a loop defined by the points 1,
2, 3, 4, and 5. A first economized refrigerant path is created by a
loop defined by the points 4A, 5A, 6A, and 7A. It should be
understood that the paths are all closed paths that allow for
continuous flow of refrigerant through refrigeration system
20A.
[0021] In reference to the main refrigerant path, after refrigerant
exits two-stage compressor sub-unit 32 at high pressure and
enthalpy through discharge port 39 (point 3), the refrigerant loses
heat in heat rejecting heat exchanger 24, exiting heat rejecting
heat exchanger 24 at low enthalpy and high pressure (point 4A). The
refrigerant then splits into two flow paths 40A and 42A prior to
entering first economizer heat exchanger 28A. The main path
continues along path 40A through first economizer heat exchanger
28A (point 4). As the refrigerant in path 40A flows through first
economizer heat exchanger 28A, it is cooled by the refrigerant in
path 42A of the first economized path.
[0022] Refrigerant from path 40A is then throttled in main
expansion valve 26. Main expansion valve 26, along with economizer
expansion valve 30A, is preferably a thermal expansion valve (TXV)
or an electronic expansion valve (EXV). After going through an
expansion process within main expansion valve 26 (point 5), the
refrigerant is a two-phase liquid-vapor mixture and is directed
toward evaporator 27. After evaporation of the remainder of the
liquid (point 1), the refrigerant enters two-stage compressor
sub-unit 32 through suction port 37. The refrigerant is compressed
within cylinder 36A, which is the first stage of two-stage
compressor sub-unit 32, and is then directed out discharge port 50
(point 2). After the second stage of compression, the refrigerant
is discharged through discharge port 39 (point 3).
[0023] In reference to the first economized path, after refrigerant
exits heat rejecting heat exchanger 24 at low enthalpy and high
pressure (point 4A) and splits into two flow paths 40A and 42A, the
first economized path continues along path 42A. In path 42A, the
refrigerant is throttled to a lower pressure by economizer
expansion valve 30A (point 5A) prior to flowing through first
economizer heat exchanger 28A. The refrigerant from path 42A that
flowed through first economizer heat exchanger 28A (point 6A) is
then directed along economizer return path 46A and injected into
suction port 52 of single-stage compressor sub-unit 34 for
compression in single-stage compressor sub-unit 34. After
compression within single-stage compressor sub-unit 34, refrigerant
is discharged through discharge port 54 (point 7A) where it merges
with the refrigerant discharged from two-stage compressor sub-unit
32.
[0024] Refrigeration system 20A also includes sensor 31 disposed
between evaporator 27 and multi-stage compressor unit 10A along the
main refrigerant path. In general, sensor 31 acts with expansion
valve 26 to sense the temperature of the refrigerant leaving
evaporator 27 and the pressure of the refrigerant in evaporator 27
to regulate the flow of refrigerant into evaporator 27 to keep the
combination of temperature and pressure within some specified
bounds. In a preferred embodiment, expansion valve 26 is an
electronic expansion valve and sensor 31 is a temperature
transducer such as a thermocouple or thermistor. In another
embodiment, expansion valve 26 is a mechanical thermal expansion
valve and sensor 31 includes a small tube that terminates in a
pressure vessel filled with a refrigerant that differs from the
refrigerant running through refrigeration system 20A. As
refrigerant from evaporator 27 flows past sensor 31 on its way
toward multi-stage compressor unit 10A, the pressure vessel will
either heat up or cool down, thereby changing the pressure within
the pressure vessel. As the pressure in the pressure vessel
changes, sensor 31 sends a signal to expansion valve 26 to modify
the pressure drop caused by the valve. Similarly, in the case of
the electronic expansion valve, sensor 31 sends an electrical
signal to expansion valve 26 which responds in a similar manner to
regulate refrigerant flow. For example, if a return gas coming from
evaporator 27 is too hot, sensor 31 will then heat up and send a
signal to expansion valve 26, causing the valve to open further and
allow more refrigerant per unit time to flow through evaporator 27,
thereby reducing the heat of the refrigerant exiting evaporator
27.
[0025] Economizer circuit 25A also includes sensor 31A that
operates in a similar manner to sensor 31. However, sensor 31A
senses temperature along economizer return path 46A and acts with
expansion valve 30A to control the pressure drop within expansion
valve 30A instead. It should also be noted that sensors other than
the ones previously described may be substituted for sensors 31 and
31A.
[0026] By controlling the expansion valves 26 and 30A, the
operation of refrigeration system 20A can be adjusted to meet the
cooling demands and achieve optimum efficiency. In addition to
adjusting the pressure drops associated with expansion valves 26
and 30A, the displacements of cylinders 36A, 36B, and 36C may also
be adjusted to help achieve optimum efficiency of refrigeration
system 20A.
[0027] FIG. 1B illustrates a graph relating enthalpy to pressure
for the refrigeration system 20A of FIG. 1A. Vapor dome V is formed
by a saturated liquid line and a saturated vapor line, and defines
the state of the refrigerant at various points along the
refrigeration cycle. Underneath vapor dome V, all states involve
both liquid and vapor coexisting at the same time. At the very top
of vapor dome V is the critical point. The critical point is
defined by the highest pressure where saturated liquid and
saturated vapor coexist. In general, compressed liquids are located
to the left of vapor dome V, while superheated vapors are located
to the right of vapor dome V.
[0028] Once again, in FIG. 1B, the main refrigerant path is the
loop defined by the points 1, 2, 3, 4, and 5, and the first
economized path is the loop defined by the points 4A, 5A, 6A, and
7A. The cycle begins in the main path at point 1, where the
refrigerant is at a low pressure and high enthalpy prior to
entering multi-stage compressor unit 10A. After a first stage of
compression within cylinder 36A of two-stage compressor sub-unit
32, both the enthalpy and pressure increase as shown by point 2.
After a second stage of compression within cylinder 36B, the
refrigerant exits multi-stage compressor unit 10A at high pressure
and even higher enthalpy, as shown by point 3. Then, as the
refrigerant flows through heat rejecting heat exchanger 24,
enthalpy decreases while pressure remains constant. Prior to
entering first economizer heat exchanger 28A, the refrigerant
splits into a main portion and a first economized portion as shown
by point 4A. The main portion is then throttled in main expansion
valve 26, decreasing pressure as shown by point 5. Finally, the
main portion of the refrigerant is evaporated, exiting evaporator
27 at a higher enthalpy as shown by point 1.
[0029] As stated previously, the first economized portion splits
off of the main portion as indicated by point 4A. The first
economized portion is throttled to a lower pressure in expansion
valve 30A as shown by point 5A. The first economized portion of the
refrigerant then exchanges heat with the main portion in first
economizer heat exchanger 28A, cooling down the main portion of the
refrigerant as indicated by point 4, and heating up the first
economized portion of the refrigerant as indicated by point 6A. The
first economized portion is then compressed within single-stage
compressor sub-unit 34 and merged with the main portion of the
refrigerant discharged from two-stage compressor sub-unit 32, as
shown by point 7A.
[0030] As shown in FIG. 1B, cylinders 36A, 36B, and 36C of
multi-stage compressor unit 10A are configured to receive and
compress refrigerant to different pressures. In particular,
cylinder 36A receives and compresses refrigerant from the main
refrigerant path to an intermediate pressure, as indicated by point
2. Then, cylinder 36B receives and compresses the refrigerant from
an intermediate pressure to an exit pressure, as indicated by point
3. Similarly, cylinder 36C receives and compresses refrigerant from
the first economized refrigerant path to an exit pressure, as
indicated by point 7A. As shown in FIG. 1B, the exit pressure of
cylinder 36C is substantially equivalent to the exit pressure of
cylinder 36B. In refrigeration system 20A, the exit pressures are
determined by the inlet pressure required by heat rejecting heat
exchanger 24.
[0031] FIG. 2A illustrates a schematic diagram of multi-stage
compressor unit 10B connected to refrigeration system 20B.
Multi-stage compressor unit 10B is similar to multi-stage
compressor unit 10A. However, as will be discussed in more detail
below, two-stage compressor sub-unit 32 further includes interstage
port 48 configured to receive refrigerant from an economizer
circuit to cool down the refrigerant in the main refrigerant path
prior to a second stage of compression. Refrigeration system 20B is
similar to refrigeration system 20A, but further includes second
economizer circuit 25B. Second economizer circuit 25B includes
second economizer heat exchanger 28B, expansion valve 30B, and
sensor 31B.
[0032] In refrigeration system 20B, three distinct refrigerant
paths are formed by connection of the various elements in the
system. A main refrigerant path is created by a loop defined by the
points 1, 2, 3, 4, 5, and 6. A first economized refrigerant path is
created by a loop defined by the points 5A, 6A, 7A, 3, and 4.
Finally, a second economized refrigerant path is created by a loop
defined by the points 5B, 6B, 7B, and 8B.
[0033] In reference to the main refrigerant path, after refrigerant
exits two-stage compressor sub-unit 32 at high pressure and
enthalpy through discharge port 39 (point 4), the refrigerant loses
heat in heat rejecting heat exchanger 24, exiting heat rejecting
heat exchanger 24 at low enthalpy and high pressure (point 5A). The
refrigerant then splits into two flow paths 40A and 42A prior to
entering first economizer heat exchanger 28A. The main path
continues along paths 40A and 40B through first economizer heat
exchanger 28A (point 5B) and second economizer heat exchanger 28B
(point 5), respectively. As the refrigerant in path 40A flows
through first economizer heat exchanger 28A, it is cooled by the
refrigerant in path 42A of the first economized path. Similarly, as
the refrigerant in path 40B flows through second economizer heat
exchanger 28B, it is cooled by the refrigerant in path 42B of the
second economized path.
[0034] Refrigerant from path 40B is then throttled in main
expansion valve 26. After going through an expansion process within
main expansion valve 26 (point 6), the refrigerant is a two-phase
liquid-vapor mixture and is directed toward evaporator 27. After
evaporation of the remainder of the liquid (point 1), the
refrigerant enters two-stage compressor sub-unit 32 through suction
port 37. The refrigerant is compressed within cylinder 36A, which
is the first stage of two-stage compressor sub-unit 32, and is then
directed out of discharge port 50 (point 2), where it merges with
the cooler refrigerant from economizer return path 46A that is
injected into interstage port 48 (point 3). Thus, the refrigerant
from economizer return path 46A functions to cool down the
refrigerant discharged from cylinder 36A prior to the second stage
of compression within cylinder 36B. After the second stage of
compression, the refrigerant is discharged through discharge port
39 (point 4).
[0035] In reference to the first economized path, after refrigerant
exits heat rejecting heat exchanger 24 at low enthalpy and high
pressure (point 5A) and splits into two flow paths 40A and 42A, the
first economized path continues along path 42A. In path 42A, the
refrigerant is throttled to a lower pressure by economizer
expansion valve 30A (point 6A) prior to flowing through first
economizer heat exchanger 28A. The refrigerant from path 42A that
flowed through first economizer heat exchanger 28A (point 7A) is
then directed along economizer return path 46A and injected into
interstage port 48 of two-stage compressor sub-unit 32 where it
merges with refrigerant flowing through the main path to cool down
the refrigerant (point 3) prior to a second stage of compression in
cylinder 36B.
[0036] In reference to the second economized path, after being
cooled in the higher pressure first economizer heat exchanger 28A
(point 5B), the refrigerant in path 40A splits into two flow paths
40B and 42B. The second economized path continues along flow path
42B where the refrigerant is throttled to a lower pressure by
economizer expansion valve 30B (point 6B) prior to flowing through
second economizer heat exchanger 28B. The refrigerant from path 42B
that flowed through second economizer heat exchanger 28B (point 7B)
is then directed along economizer return path 46B and injected into
suction port 52 of single-stage compressor sub-unit 34 for
compression in single-stage compressor sub-unit 34. After
compression within single-stage compressor sub-unit 34, refrigerant
is discharged through discharge port 54 (point 8B) where it merges
with the refrigerant discharged from two-stage compressor sub-unit
32.
[0037] FIG. 2B illustrates a graph relating enthalpy to pressure
for the refrigeration system 20B of FIG. 2A. As shown in FIG. 2B,
the main refrigerant path is the loop defined by the points 1, 2,
3, 4, 5, and 6; the first economized path is the loop defined by
the points 5A, 6A, 7A, 3, and 4; and the second economized path is
the loop defined by the points 5B, 6B, 7B, and 8B.
[0038] As shown in FIG. 2B, cylinders 36A, 36B, and 36C of
multi-stage compressor unit 10B are configured to receive and
compress refrigerant to different pressures. In particular,
cylinder 36A receives and compresses refrigerant from the main
refrigerant path to an intermediate pressure, as indicated by point
2. Then, cylinder 36B receives and compresses refrigerant from the
main refrigerant path and the first economized path from an
intermediate pressure to an exit pressure, as indicated by point 4.
Similarly, cylinder 36C receives and compresses refrigerant from
the second economized refrigerant path to an exit pressure, as
indicated by point 8B. As shown in FIG. 2B, the exit pressure of
cylinder 36C is substantially equivalent to the exit pressure of
cylinder 36B.
[0039] FIG. 3A illustrates a schematic diagram of multi-stage
compressor unit 10C connected to refrigeration system 20C.
Multi-stage compressor unit 10C is similar to multi-stage
compressor unit 10B. However, as will be discussed in more detail
below, single-stage compressor sub-unit 34 is configured to
discharge into first economizer return path 46A instead of into
heat rejecting heat exchanger 24, as depicted by multi-stage
compressor unit 10B of FIG. 2A.
[0040] In refrigeration system 20C, three distinct refrigerant
paths are formed by connection of the various elements in the
system. A main refrigerant path is created by a loop defined by the
points 1, 2, 3, 4, 5, and 6. A first economized refrigerant path is
created by a loop defined by the points 5A, 6A, 7A, 3, and 4.
Finally, a second economized refrigerant path is created by a loop
defined by the points 5B, 6B, 7B, 8B, 3, and 4.
[0041] In reference to the main refrigerant path, after refrigerant
exits two-stage compressor sub-unit 32 at high pressure and
enthalpy through discharge port 39 (point 4), the refrigerant loses
heat in heat rejecting heat exchanger 24, exiting heat rejecting
heat exchanger 24 at low enthalpy and high pressure (point 5A). The
refrigerant then splits into two flow paths 40A and 42A prior to
entering first economizer heat exchanger 28A. The main path
continues along paths 40A and 40B through first economizer heat
exchanger 28A (point 5B) and second economizer heat exchanger 28B
(point 5), respectively. As the refrigerant in path 40A flows
through first economizer heat exchanger 28A, it is cooled by the
refrigerant in path 42A of the first economized path. Similarly, as
the refrigerant in path 40B flows through second economizer heat
exchanger 28B, it is cooled by the refrigerant in path 42B of the
second economized path.
[0042] Refrigerant from path 40B is then throttled in main
expansion valve 26. After going through an expansion process within
main expansion valve 26 (point 6), the refrigerant is a two-phase
liquid-vapor mixture and is directed toward evaporator 27. After
evaporation of the remainder of the liquid (point 1), the
refrigerant enters two-stage compressor sub-unit 32 through suction
port 37. The refrigerant is compressed within cylinder 36A, which
is the first stage of two-stage compressor sub-unit 32, and is then
directed out discharge port 50 (point 2), where it merges with the
cooler refrigerant from economizer return path 46A that is injected
into interstage port 48 (point 3). Thus, the refrigerant from
economizer return path 46A functions to cool down the refrigerant
discharged from cylinder 36A prior to the second stage of
compression within cylinder 36B. After the second stage of
compression, the refrigerant is discharged through discharge port
39 (point 4).
[0043] In reference to the first economized path, after refrigerant
exits heat rejecting heat exchanger 24 at low enthalpy and high
pressure (point 5A) and splits into two flow paths 40A and 42A, the
first economized path continues along path 42A. In path 42A, the
refrigerant is throttled to a lower pressure by economizer
expansion valve 30A (point 6A) prior to flowing through first
economizer heat exchanger 28A. The refrigerant from path 42A that
flowed through first economizer heat exchanger 28A (point 7A) is
then directed along economizer return path 46A and injected into
interstage port 48 of two-stage compressor sub-unit 32 where it
merges with refrigerant flowing through the main path to cool down
the refrigerant (point 3) prior to a second stage of compression in
cylinder 36B.
[0044] In reference to the second economized path, after being
cooled in the higher pressure first economizer heat exchanger 28A
(point 5B), the refrigerant in path 40A splits into two flow paths
40B and 42B. The second economized path continues along flow path
42B where the refrigerant is throttled to a lower pressure by
economizer expansion valve 30B (point 6B) prior to flowing through
second economizer heat exchanger 28B. The refrigerant from path 42B
that flowed through second economizer heat exchanger 28B (point 7B)
is then directed along economizer return path 46B and injected into
suction port 52 of single-stage compressor sub-unit 34 for
compression in single-stage compressor sub-unit 34. After
compression within single-stage compressor sub-unit 34, the
refrigerant is discharged through discharge port 54 where it is
mixed with the refrigerant in economizer return path 46A (point 8B)
prior to injection into interstage port 48 of two-stage compressor
sub-unit 32 (point 3).
[0045] FIG. 3B illustrates a graph relating enthalpy to pressure
for the refrigeration system 20C of FIG. 3A. As shown in FIG. 3B,
the main refrigerant path is the loop defined by the points 1, 2,
3, 4, 5, and 6; the first economized path is the loop defined by
the points 5A, 6A, 7A, 3, and 4; and the second economized path is
the loop defined by the points 5B, 6B, 7B, 8B, 3, and 4.
[0046] As shown in FIG. 3B, cylinders 36A, 36B, and 36C of
multi-stage compressor unit 10C are configured to receive and
compress refrigerant to different pressures. In particular,
cylinder 36A receives and compresses refrigerant from the main
refrigerant path to an intermediate pressure, as indicated by point
2. Similarly, cylinder 36C receives and compresses refrigerant from
the second economized refrigerant path to an exit pressure, as
indicated by point 8B. Then, cylinder 36B receives and compresses
refrigerant from the main refrigerant path, the first economized
path, and the second economized path to an exit pressure, as
indicated by point 4. As shown in FIG. 3B, the exit pressure of
cylinder 36C is substantially equivalent to the intermediate
pressure of cylinder 36A.
[0047] FIG. 4A illustrates a schematic diagram of multi-stage
compressor unit 10D connected to refrigeration system 20D.
Multi-stage compressor unit 10D is similar to multi-stage
compressor unit 10A. However, multi-stage compressor unit 10D
further includes single-stage compressor sub-unit 35 having
cylinder 36D.
[0048] Refrigeration system 20D is similar to refrigeration system
20C, except that interstage port 48 is replaced by intercooler 49,
which is configured to cool the main portion of the refrigerant
between the first and second stages of compression in two-stage
compressor sub-unit 32.
[0049] In refrigeration system 20D, three distinct refrigerant
paths are formed by connection of the various elements in the
system. A main refrigerant path is created by a loop defined by the
points 1, 2, 3, 4, 5, and 6. A first economized refrigerant path is
created by a loop defined by the points 5A, 6A, 7A, and 8A.
Finally, a second economized refrigerant path is created by a loop
defined by the points 5B, 6B, 7B, and 8B.
[0050] In reference to the main refrigerant path, after refrigerant
exits two-stage compressor sub-unit 32 at high pressure and
enthalpy through discharge port 39 (point 4), the refrigerant loses
heat in heat rejecting heat exchanger 24, exiting heat rejecting
heat exchanger 24 at low enthalpy and high pressure (point 5A). The
refrigerant then splits into two flow paths 40A and 42A prior to
entering first economizer heat exchanger 28A. The main path
continues along paths 40A and 40B through first economizer heat
exchanger 28A (point 5B) and second economizer heat exchanger 28B
(point 5), respectively. As the refrigerant in path 40A flows
through first economizer heat exchanger 28A, it is cooled by the
refrigerant in path 42A of the first economized path. Similarly, as
the refrigerant in path 40B flows through second economizer heat
exchanger 28B, it is cooled by the refrigerant in path 42B of the
second economized path.
[0051] Refrigerant from path 40B is then throttled in main
expansion valve 26. After going through an expansion process within
main expansion valve 26 (point 6), the refrigerant is a two-phase
liquid-vapor mixture and is directed toward evaporator 27. After
evaporation of the remainder of the liquid (point 1), the
refrigerant enters two-stage compressor sub-unit 32 through suction
port 37. The refrigerant is compressed within cylinder 36A, which
is the first stage of two-stage compressor sub-unit 32, and is then
directed out discharge port 50 (point 2), where it flows through
intercooler 49 prior to a second stage of compression in cylinder
36B. Intercooler 49 is configured to cool down the refrigerant
discharged from cylinder 36A prior to the second stage of
compression within cylinder 36B. After the second stage of
compression, the refrigerant is discharged through discharge port
39 (point 4).
[0052] In reference to the first economized path, after refrigerant
exits heat rejecting heat exchanger 24 at low enthalpy and high
pressure (point 5A) and splits into two flow paths 40A and 42A, the
first economized path continues along path 42A. In path 42A, the
refrigerant is throttled to a lower pressure by economizer
expansion valve 30A (point 6A) prior to flowing through first
economizer heat exchanger 28A. The refrigerant from path 42A that
flowed through first economizer heat exchanger 28A (point 7A) is
then directed along economizer return path 46A and injected into
suction port 52 of single-stage compressor sub-unit 34 for
compression in single-stage compressor sub-unit 34. After
compression within single-stage compressor sub-unit 34, the
refrigerant is discharged through discharge port 54 (point 8A)
where it merges with the refrigerant discharged from two-stage
compressor sub-unit 32 and single-stage compressor sub-unit 35.
[0053] In reference to the second economized path, after being
cooled in the higher pressure first economizer heat exchanger 28A
(point 5B), the refrigerant in path 40A splits into two flow paths
40B and 42B. The second economized path continues along flow path
42B where the refrigerant is throttled to a lower pressure by
economizer expansion valve 30B (point 6B) prior to flowing through
second economizer heat exchanger 28B. The refrigerant from path 42B
that flowed through second economizer heat exchanger 28B (point 7B)
is then directed along economizer return path 46B and injected into
suction port 56 of single-stage compressor sub-unit 35 for
compression in single-stage compressor sub-unit 35. After
compression within single-stage compressor sub-unit 35, the
refrigerant is discharged through discharge port 58 (point 8B)
where it merges with the refrigerant discharged from two-stage
compressor sub-unit 32 and single-stage compressor sub-unit 34.
[0054] FIG. 4B illustrates a graph relating enthalpy to pressure
for the refrigeration system 20D of FIG. 4A. As shown in FIG. 4B,
the main refrigerant path is the loop defined by the points 1, 2,
3, 4, 5, and 6; the first economized path is the loop defined by
the points 5A, 6A, 7A, and 8A; and the second economized path is
the loop defined by the points 5B, 6B, 7B, and 8B.
[0055] As shown in FIG. 4B, cylinders 36A, 36B, 36C, and 36D of
multi-stage compressor unit 10D are configured to receive and
compress refrigerant to different pressures. In particular,
cylinder 36A receives and compresses refrigerant from the main
refrigerant path to an intermediate pressure, as indicated by point
2. After being cooled within intercooler 49, cylinder 36B receives
and compresses refrigerant from the main refrigerant path from an
intermediate pressure to an exit pressure, as indicated by point 4.
Cylinder 36C receives and compresses refrigerant from the first
economized refrigerant path to an exit pressure, as indicated by
point 8A. Similarly, cylinder 36D receives and compresses
refrigerant from the second economized refrigerant path to an exit
pressure, as indicated by point 8B. As shown in FIG. 4B, the exit
pressures of cylinders 36C and 36D are substantially equivalent to
the exit pressure of cylinder 36B.
[0056] FIG. 5A illustrates a schematic diagram of multi-stage
compressor unit 10E connected to refrigeration system 20E. In
addition to two-stage compressor sub-unit 32, multi-stage
compressor unit 10E further includes two-stage compressor sub-unit
70. Two-stage compressor sub-unit 70 includes cylinders 36E and 36F
connected in series. Refrigeration system 20E is similar to
refrigeration system 20D, except that third economizer circuit 25C
is added to the system.
[0057] In refrigeration system 20E, four distinct refrigerant paths
are formed by connection of the various elements in the system. A
main refrigerant path is created by a loop defined by the points 1,
2, 3, 4, 5, and 6. A first economized refrigerant path is created
by a loop defined by the points 5A, 6A, 7A, 3, and 4. A second
economized refrigerant path is created by a loop defined by the
points 5B, 6B, 7B, 9, and 10. Finally, a third economized
refrigerant path is created by a loop defined by the points 5C, 6C,
7C, 8C, 9, and 10.
[0058] In reference to the main refrigerant path, after refrigerant
exits two-stage compressor sub-unit 32 at high pressure and
enthalpy through discharge port 39 (point 4), the refrigerant loses
heat in heat rejecting heat exchanger 24, exiting heat rejecting
heat exchanger 24 at low enthalpy and high pressure (point 5A). The
refrigerant then splits into two flow paths 40A and 42A prior to
entering first economizer heat exchanger 28A. The main path
continues along paths 40A, 40B, and 40C through first economizer
heat exchanger 28A (point 5B), second economizer heat exchanger 28B
(point 5C), and third economizer heat exchanger 28C (point 5),
respectively. As the refrigerant in path 40A flows through first
economizer heat exchanger 28A, it is cooled by the refrigerant in
path 42A of the first economized path. As the refrigerant in path
40B flows through second economizer heat exchanger 28B, it is
cooled by the refrigerant in path 42B of the second economized
path. Finally, as the refrigerant in path 40C flows through third
economizer heat exchanger 28C, it is cooled by the refrigerant in
path 42C of the third economized path.
[0059] Refrigerant from path 40C is then throttled in main
expansion valve 26. After going through an expansion process within
main expansion valve 26 (point 6), the refrigerant is a two-phase
liquid-vapor mixture and is directed toward evaporator 27. After
evaporation of the remainder of the liquid (point 1), the
refrigerant enters two-stage compressor sub-unit 32 through suction
port 37. The refrigerant is compressed within cylinder 36A, which
is the first stage of two-stage compressor sub-unit 32, and is then
directed out discharge port 50 (point 2), where it merges with the
cooler refrigerant from economizer return path 46A that is injected
into interstage port 48 (point 3). Thus, the refrigerant from
economizer return path 46A functions to cool down the refrigerant
discharged from cylinder 36A prior to the second stage of
compression within cylinder 36B. After the second stage of
compression, the refrigerant is discharged through discharge port
39 (point 4).
[0060] In reference to the first economized path, after refrigerant
exits heat rejecting heat exchanger 24 at low enthalpy and high
pressure (point 5A) and splits into two flow paths 40A and 42A, the
first economized path continues along path 42A. In path 42A, the
refrigerant is throttled to a lower pressure by economizer
expansion valve 30A (point 6A) prior to flowing through first
economizer heat exchanger 28A. The refrigerant from path 42A that
flowed through first economizer heat exchanger 28A (point 7A) is
then directed along economizer return path 46A and injected into
interstage port 48 of two-stage compressor sub-unit 32 where it
merges with refrigerant flowing through the main path to cool down
the refrigerant (point 3) prior to a second stage of compression in
cylinder 36B.
[0061] In reference to the second economized path, after being
cooled in the higher pressure first economizer heat exchanger 28A,
the refrigerant in path 40A splits into two flow paths 40B and 42B
(point 5B). The second economized path continues along flow path
42B where the refrigerant is throttled to a lower pressure by
economizer expansion valve 30B prior to flowing through second
economizer heat exchanger 28B (point 6B). The refrigerant from path
42B that flowed through second economizer heat exchanger 28B (point
7B) is then directed along economizer return path 46B and injected
into interstage port 72 of two-stage compressor sub-unit 70 where
it mixes with refrigerant exiting discharge port 74 (point 9) to
cool down the refrigerant prior to a second stage of compression in
cylinder 36F.
[0062] In reference to the third economized path, after being
cooled in the higher pressure second economizer heat exchanger 28B,
the refrigerant in path 40B splits into two flow paths 40C and 42C
(point 5C). The third economized path continues along flow path 42C
where the refrigerant is throttled to a lower pressure by
economizer expansion valve 30C prior to flowing through third
economizer heat exchanger 28C (point 6C). The refrigerant from path
42C that flowed through third economizer heat exchanger 28C (point
7C) is then directed along economizer return path 46C and injected
into suction port 76 of two-stage compressor sub-unit 70. After a
first stage of compression in cylinder 36E (point 8C), the
refrigerant is cooled prior to a second stage of compression by the
refrigerant from economizer return path 46B that was injected into
interstage port 72 (point 9). After the second stage of compression
in cylinder 36F, the refrigerant is discharged through discharge
port 78 (point 10), where it merges with the compressed refrigerant
discharged from two-stage compressor sub-unit 32.
[0063] FIG. 5B illustrates a graph relating enthalpy to pressure
for the refrigeration system 20E of FIG. 5A. As shown in FIG. 5B,
the main refrigerant path is the loop defined by the points 1, 2,
3, 4, 5, and 6; the first economized path is the loop defined by
the points 5A, 6A, 7A, 3, and 4; the second economized path is the
loop defined by the points 5B, 6B, 7B, 9, and 10; and the third
economized path is the loop defined by the points 5C, 6C, 7C, 8C,
9, and 10.
[0064] As shown in FIG. 5B, cylinders 36A, 36B, 36E, and 36F of
multi-stage compressor unit 10E are configured to receive and
compress refrigerant to different pressures. In particular,
cylinder 36A receives and compresses refrigerant from the main
refrigerant path to an intermediate pressure, as indicated by point
2. Then, cylinder 36B receives and compresses refrigerant from the
main refrigerant path and the first economized path from the
intermediate pressure to an exit pressure, as indicated by point 4.
Similarly, cylinder 36E receives and compresses refrigerant from
the third economized refrigerant path to an intermediate pressure,
as indicated by point 8C. Cylinder 36F then receives and compresses
refrigerant from the second and third economized paths from the
intermediate pressure to an exit pressure, as indicated by point
10. As shown in FIG. 5B, the exit pressure of cylinder 36B is
substantially equivalent to the exit pressure of cylinder 36F.
[0065] Although each of the embodiments of a multi-stage compressor
unit shown and described above have been connected to a
refrigeration system that includes one or more economizer circuits,
the multi-stage compressor unit of the present invention may also
be used in refrigerating systems that do not include economizer
circuits. FIG. 6A illustrates a schematic diagram of multi-stage
compressor unit 10F connected to refrigeration system 20F, which
includes heat rejecting heat exchanger 24, first expansion valve
26, first evaporator 27, first sensor 31, second expansion valve
126, second evaporator 127, and second sensor 131. Multi-stage
compressor unit 10F includes two-stage compressor sub-unit 32 and
single-stage compressor sub-unit 34. Two-stage compressor sub-unit
32 includes cylinders 36A and 36B connected in series, while
single-stage compressor sub-unit 34 includes cylinder 36C.
[0066] In refrigeration system 20F, two distinct refrigerant paths
are formed by connection of the various elements in the system. A
first main refrigerant path is created by a loop defined by the
points 1, 2, 3, 4, and 5. A second main refrigerant path is created
by a loop defined by the points 4, 5A, 6A, and 7A.
[0067] In reference to the first main refrigerant path, after
refrigerant exits two-stage compressor sub-unit 32 at high pressure
and enthalpy through discharge port 39 (point 3), the refrigerant
loses heat in heat rejecting heat exchanger 24, exiting heat
rejecting heat exchanger 24 at low enthalpy and high pressure
(point 4). The refrigerant in the main path is then throttled in
first expansion valve 26. After going through an expansion process
within first expansion valve 26 (point 5), the refrigerant is a
two-phase liquid-vapor mixture and is directed toward first
evaporator 27. After evaporation of the remainder of the liquid
(point 1), the refrigerant enters two-stage compressor sub-unit 32
through suction port 37. The refrigerant is compressed within
cylinder 36A, which is the first stage of two-stage compressor
sub-unit 32, and is then directed out discharge port 50 (point 2).
After the second stage of compression in cylinder 36B, the
refrigerant is discharged through discharge port 39 (point 3).
[0068] In reference to the second main refrigerant path, after
exiting heat rejecting heat exchanger 24, the refrigerant is
throttled in second expansion valve 126. After going through an
expansion process within second expansion valve 126 (point 5A), the
refrigerant is a two-phase liquid-vapor mixture and is directed
toward second evaporator 127. After evaporation in second
evaporator 127 (point 6A), the refrigerant enters single-stage
compressor sub-unit 34 through suction port 52. The refrigerant is
compressed within cylinder 36C, and is then directed out discharge
port 54 point 7A) where it mixes with the refrigerant discharged
through discharge port 39 of two-stage compressor sub-unit 32.
[0069] FIG. 6B illustrates a graph relating enthalpy to pressure
for the refrigeration system 20F of FIG. 6A. As shown in FIG. 6B,
the first main refrigerant path is the loop defined by the points
1, 2, 3, 4, and 5, and the second main refrigerant path is the loop
defined by the points 4, 5A, 6A, and 7A.
[0070] As shown in FIG. 6B, cylinders 36A, 36B, and 36C of
multi-stage compressor unit 10F are configured to receive and
compress refrigerant to different pressures. In particular,
cylinder 36A receives and compresses refrigerant from the first
main refrigerant path to an intermediate pressure, as indicated by
point 2. Then, cylinder 36B receives and compresses the refrigerant
from the intermediate pressure to an exit pressure, as indicated by
point 3. Similarly, cylinder 36C receives and compresses
refrigerant from the second main refrigerant path to an exit
pressure, as indicated by point 7A. As shown in FIG. 6B, the exit
pressure of cylinder 36C is substantially equivalent to the exit
pressure of cylinder 36B.
[0071] While the alternative embodiments of the multi-stage
compressor unit have been described as including a number of
compressor sub-units ranging from two to three, it should be
understood that a multi-stage compressor unit with more than three
compressor sub-units is within the intended scope of the present
invention. Furthermore, although the embodiments of the multi-stage
compressor unit were described as including only single-stage and
two-stage compressor sub-units, compressor sub-units having more
than two stages are within the intended scope of the present
invention. Thus, single-stage and two-stage compressor sub-units
were shown merely for purposes of example and not for limitation.
In addition, alternative embodiments that include compressor
sub-units connected in various combinations other than those
depicted above are also contemplated.
[0072] Although the multi-stage compressor unit of the present
invention is useful to increase system efficiency in a
refrigeration system using any type of refrigerant, it is
especially useful in refrigeration systems that utilize
transcritical refrigerants, such as carbon dioxide. Because carbon
dioxide is such a low critical temperature refrigerant,
refrigeration systems using carbon dioxide typically run
transcritical. Furthermore, because carbon dioxide is such a high
pressure refrigerant, there is more opportunity to provide multiple
pressure steps between the high and low pressure portions of the
circuit to include multiple economizers and multiple compressor
cylinders, each of which contributes to increase the efficiency of
the system. Thus, the multi-stage compressor unit of the present
invention may be used to increase the efficiency of systems
utilizing transcritical refrigerants such as carbon dioxide, making
their efficiency comparable to that of typical refrigerants.
However, the multi-stage compressor unit of the present invention
is useful to increase the efficiency in refrigeration systems using
any refrigerant, including those that run subcritical as well as
those that run transcritical.
[0073] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *