U.S. patent application number 12/302605 was filed with the patent office on 2009-09-17 for refrigeration system.
Invention is credited to Hiroto Nakajima, Satoru Sakae, Iwao Shinohara, Masaaki Takagami.
Application Number | 20090229301 12/302605 |
Document ID | / |
Family ID | 38778614 |
Filed Date | 2009-09-17 |
United States Patent
Application |
20090229301 |
Kind Code |
A1 |
Sakae; Satoru ; et
al. |
September 17, 2009 |
REFRIGERATION SYSTEM
Abstract
A refrigeration system (1) includes first to third compressors
(11a, 11b, 11c) connected in parallel and an oil separator for
separating a refrigeration oil from a refrigerant discharged from
the compressors (11a, 11b, 11c). A main suction pipe (55) in which
a refrigerant to be sucked into the compressors (11a, 11b, 11c)
flows includes a primary curved portion (101) and a primary branch
element (102) assembled to part of the main suction pipe (55)
downstream of a junction with an oil return pipe (71) for returning
the refrigeration oil separated by the oil separator. The main
suction pipe (55) is branched by the primary branch element (102)
into a first suction pipe branch (61a) of the first compressor
(11a) and a connecting suction pipe (56). In the primary branch
element (102), the first suction pipe branch (61a) is at the
bottommost position and the outermost position in the direction of
a radius of curvature of the primary curved portion (101).
Inventors: |
Sakae; Satoru; (Osaka,
JP) ; Takagami; Masaaki; (Osaka, JP) ;
Nakajima; Hiroto; (Osaka, JP) ; Shinohara; Iwao;
(Osaka, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
38778614 |
Appl. No.: |
12/302605 |
Filed: |
May 29, 2007 |
PCT Filed: |
May 29, 2007 |
PCT NO: |
PCT/JP2007/060873 |
371 Date: |
November 26, 2008 |
Current U.S.
Class: |
62/470 ; 62/500;
62/510 |
Current CPC
Class: |
F25B 31/004 20130101;
F25B 2400/075 20130101; F25B 13/00 20130101; F25B 41/40
20210101 |
Class at
Publication: |
62/470 ; 62/500;
62/510 |
International
Class: |
F25B 43/02 20060101
F25B043/02; F25B 1/06 20060101 F25B001/06; F25B 1/10 20060101
F25B001/10 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2006 |
JP |
2006-151480 |
Claims
1. A refrigeration system comprising a refrigerant circuit (10)
including a plurality of compressors (11a, 11b, 11c) connected in
parallel and an oil separator (70) for separating a refrigeration
oil from a refrigerant discharged from the compressors (11a, 11b,
11c), the refrigerant circuit (10) including a main suction pipe
(55) in which a refrigerant to be sucked into the compressors (11a,
11b, 11c) flows, suction pipe branches (61a, 61b, 61c) for
distributing the refrigerant in the main suction pipe (55) to the
compressors (11a, 11b, 11c) and an oil return pipe (71) for
returning the refrigeration oil separated by the oil separator (70)
to the main suction pipe (55), wherein a primary flow biasing
element (110) for biasing the flow of the refrigeration oil is
assembled to part of the main suction pipe (55) downstream of a
junction of the main suction pipe (55) and the oil return pipe (71)
so that a larger amount of the refrigeration oil flows into the
suction pipe branch (61a) of the first compressor (11a) previously
chosen from the compressors (11a, 11b, 11c).
2. A refrigeration system comprising a refrigerant circuit (10)
including a plurality of compressors (11a, 11b, 11c) connected in
parallel and an oil separator (70) for separating a refrigeration
oil from a refrigerant discharged from the compressors (11a, 11b,
11c), the refrigerant circuit (10) including a main suction pipe
(55) in which a refrigerant to be sucked into the compressors (11a,
11b, 11c) flows, suction pipe branches (61a, 61b, 61c) for
distributing the refrigerant in the main suction pipe (55) to the
compressors (11a, 11b, 11c) and an oil return pipe (71) for
returning the refrigeration oil separated by the oil separator (70)
to the main suction pipe (55), wherein a primary curved portion
(101) and a primary branch element (102) for branching the main
suction pipe (55) into the suction pipe branches (61a, 61h, 61c)
are assembled to part of the main suction pipe (55) downstream of a
junction of the main suction pipe (55) and the oil return pipe
(71), the primary branch element (102) being located downstream of
the primary curved portion (101), and the suction pipe branch (61a)
of the first compressor (11a) previously chosen from the
compressors (11a, 11b, 11c) is at the outermost position in the
primary branch element (102) in the direction of a radius of
curvature of the primary curved portion (101).
3. A refrigeration system comprising a refrigerant circuit (10)
including a plurality of compressors (11a, 11b, 11c) connected in
parallel and an oil separator (70) for separating a refrigeration
oil from a refrigerant discharged from the compressors (11a, 11b,
11c), the refrigerant circuit (10) including a main suction pipe
(55) in which a refrigerant to be sucked into the compressors (11a,
11b, 11c) flows, suction pipe branches (61a, 61b, 61c) for
distributing the refrigerant in the main suction pipe (55) to the
compressors (11a, 11b, 11c) and an oil return pipe (71) for
returning the refrigeration oil separated by the oil separator (70)
to the main suction pipe (55), wherein the suction pipe branch
(61a) of the first compressor (11a) previously chosen from the
compressors (11a, 11b, 11c) is at the bottommost position in a
primary branch element (102) for branching the main suction pipe
(55) into the suction pipe branches (61a, 61b, 61c).
4. The refrigeration system of claim 2, wherein the suction pipe
branch (61a) of the first compressor (11a) is at the bottommost
position in the primary branch element (102).
5. The refrigeration system of claim 1, wherein the plurality of
compressors (11a, 11b, 11c) are first to third compressors (11a,
11b, 11c), the main suction pipe (55) is branched into the suction
pipe branch (61a) of the first compressor (11a) and a connecting
suction pipe (56) which is branched into the suction pipe branch
(61b) of the second compressor (11b) and the suction pipe branch
(61c) of the third compressor (11c), and a secondary flow biasing
element (120) for biasing the flow of the refrigeration oil in the
connecting suction pipe (56) is provided so that more refrigeration
oil flows into the suction pipe branch (61b) of the second
compressor (11b) than into the suction pipe branch (61c) of the
third compressor (11c).
6. The refrigeration system of claim 2, wherein the plurality of
compressors (11a, 11b, 11c) are first to third compressors (11a,
11b, 11c), the main suction pipe (55) is branched by the primary
branch element (102) into the suction pipe branch (61a) of the
first compressor (11a) and a connecting suction pipe (56) which is
branched by a secondary branch element (104) into the suction pipe
branch (61b) of the second compressor (11b) and the suction pipe
branch (61c) of the third compressor (11c), the connecting suction
pipe (56) is provided with a secondary curved portion (103) and the
suction pipe branch (61b) of the second compressor (11b) is
positioned outside the suction pipe branch (61c) of the third
compressor (11c) in the secondary branch element (104) in the
direction of a radius of curvature of the secondary curved portion
(103).
7. The refrigeration system of claim 2, wherein the plurality of
compressors (11a, 11b, 11c) are first to third compressors (11a,
11b, 11c), the main suction pipe (55) is branched by the primary
branch element (102) into the suction pipe branch (61a) of the
first compressor (11a) and a connecting suction pipe (56) which is
branched by a secondary branch element (104) into the suction pipe
branch (61b) of the second compressor (11b) and the suction pipe
branch (61c) of the third compressor (11c), and the suction pipe
branch (61b) of the second compressor (11b) is positioned lower
than the suction pipe branch (61c) of the third compressor (11c) in
the secondary branch element (104).
8. The refrigeration system of claim 6, wherein the suction pipe
branch (61b) of the second compressor (11b) is positioned lower
than the suction pipe branch (61c) of the third compressor (11c) in
the secondary branch element (104).
9. The refrigeration system of claim 2, wherein the plurality of
compressors (11a, 11b, 11c) are first to third compressors (11a,
11b, 11c), the main suction pipe (55) is branched by the primary
branch element (102) into the suction pipe branch (61a) of the
first compressor (11a) and a connecting suction pipe (56) which is
branched by a secondary branch element (104) into the suction pipe
branch (61b) of the second compressor (11b) and the suction pipe
branch (61c) of the third compressor (11c), and the suction pipe
branch (61b) of the second compressor (11b) is positioned outside
the suction pipe branch (61c) of the third compressor (11c) in the
secondary branch element (104) in the direction of a radius of
curvature of the primary curved portion (101) of the main suction
pipe (55).
10. The refrigeration system of claim 1, further comprising oil
equalizers (72, 73) for supplying the refrigeration oil accumulated
in a casing of the first compressor (11a) to the other compressors
(11b, 11c).
11. The refrigeration system of claim 1, further comprising oil
equalizers (72, 73, 74) for equalizing the amounts of the
refrigeration oil accumulated in casings of the compressors (11a,
11b, 11c).
12. The refrigeration system of claim 5, further comprising a first
oil equalization pipe (72) for supplying the refrigeration oil
accumulated in a casing of the first compressor (11a) to the
connecting suction pipe (56) or the suction pipe branch (61b) of
the second compressor (11b), a second oil equalization pipe (73)
for supplying the refrigeration oil accumulated in a casing of the
second compressor (11b) to the suction pipe branch (61c) of the
third compressor (11c) and a third oil equalization pipe (74) for
supplying the refrigeration oil accumulated in a casing of the
third compressor (11c) to the main suction pipe (55) or the oil
return pipe (71).
13. The refrigeration system of claim 1, wherein the first
compressor (11a) is a capacity invariable compressor.
14. The refrigeration system of claim 1, wherein each of the
compressors (11a, 11b, 11c) is so configured that the refrigeration
oil is accumulated in high pressure space in the casing.
15. The refrigeration system of claim 1, wherein liquid injection
pipes (86, 86a, 86b, 86c) for introducing a portion of a liquid
refrigerant flowing in a liquid pipe (84) on a high pressure side
of the refrigerant circuit (10) to the suction pipe branches (61a,
61b, 61c) of the compressors (11a, 11b, 11c) are connected to the
suction pipe branches (61a, 61b, 61c).
16. The refrigeration system of claim 1, further comprising oil
collecting pipes (75, 76, 77) connected to the suction pipe
branches (61a, 61b, 61c) of the compressors (11a, 11b, 11c) at one
end, respectively, and connected to each other at the other
end.
17. A refrigeration system comprising a refrigerant circuit (10)
including a plurality of compressors (11a, 11b, 11c) connected in
parallel and an oil separator (70) for separating a refrigeration
oil from a refrigerant discharged from the compressors (11a, 11b,
11c), the refrigerant circuit (10) including a main suction pipe
(55) in which a refrigerant to be sucked into the compressors (11a,
11b, 11c) flows, suction pipe branches (61a, 61b, 61c) for
distributing the refrigerant in the main suction pipe (55) to the
compressors (11a, 11b, 11c) and an oil return pipe (71) for
returning the refrigeration oil separated by the oil separator (70)
to the main suction pipe (55), wherein oil collecting pipes (75,
76, 77) connected to the suction pipe branches (61a, 61b, 61c) of
the compressors (11a, 11b, 11c) at one end, respectively, and
connected to each other at the other end are provided.
18. The refrigeration system of claim 16, wherein each of the
suction pipe branches (61a, 61b, 61c) has an oblique portion (59)
extending obliquely upward in the downstream direction from a
certain position of a barrel of the suction pipe branch (61a, 61b,
61c) and an oil storing portion (58) formed upstream of the oblique
portion (59) and the one ends of the oil collecting pipes (75, 76,
77) are connected to the oil storing portions (58).
19. The refrigeration system of claim 17, wherein the suction pipe
branch (61a, 61b, 61c) has an oblique portion (59) extending
obliquely upward in the downstream direction from a certain
position of a barrel of the suction pipe branch (61a, 61b, 61c) and
an oil storing portion (58) formed upstream of the oblique portion
(59) and the one ends of the oil collecting pipes (75, 76, 77) are
connected to the oil storing portions (58).
20. The refrigeration system of claim 6, further comprising a first
oil equalization pipe (72) for supplying the refrigeration oil
accumulated in a casing of the first compressor (11a) to the
connecting suction pipe (56) or the suction pipe branch (61b) of
the second compressor (11b), a second oil equalization pipe (73)
for supplying the refrigeration oil accumulated in a casing of the
second compressor (11b) to the suction pipe branch (61c) of the
third compressor (11c) and a third oil equalization pipe (74) for
supplying the refrigeration oil accumulated in a casing of the
third compressor (11c) to the main suction pipe (55) or the oil
return pipe (71).
21. The refrigeration system of claim 7, further comprising a first
oil equalization pipe (72) for supplying the refrigeration oil
accumulated in a casing of the first compressor (11a) to the
connecting suction pipe (56) or the suction pipe branch (61b) of
the second compressor (11b), a second oil equalization pipe (73)
for supplying the refrigeration oil accumulated in a casing of the
second compressor (11b) to the suction pipe branch (61c) of the
third compressor (11c) and a third oil equalization pipe (74) for
supplying the refrigeration oil accumulated in a casing of the
third compressor (11c) to the main suction pipe (55) or the oil
return pipe (71).
Description
TECHNICAL FIELD
[0001] The present invention relates to a refrigeration system
including a plurality of compressors connected in parallel.
BACKGROUND ART
[0002] Among conventional refrigeration systems performing
refrigeration cycles, there are refrigeration systems having a
plurality of compressors connected in parallel so that compressor
capacity is varied in a wide range in response to the operating
state of a utilization side (e.g., Patent Literature 1).
[0003] The refrigeration system of Patent Literature 1 includes an
indoor unit having an indoor heat exchanger and performing indoor
air conditioning, a cold storage unit having a cold-storage heat
exchanger and cooling a cold storage showcase, a freezing unit
having a freezing heat exchanger and cooling a freezing showcase,
and an outdoor unit having an outdoor heat exchanger and three
compressors.
[0004] For cooling only the cold-storage and freezing showcases by
the refrigeration system, an inverter compressor and a first
non-inverter compressor connected in parallel, which are two of the
compressors of the outdoor unit, are operated. In this operation, a
refrigerant discharged out of the two compressors is condensed in
the outdoor heat exchanger and distributed to the cold storage unit
and the freezing unit. The distributed flows of the refrigerant are
expanded by expansion valves in the cold storage unit and the
freezing unit, respectively, and then evaporate in the
corresponding heat exchangers as they absorb heat of the air in the
showcases. As a result, the showcases are cooled. Then, the flows
of the refrigerant discharged from the cold storage unit and the
freezing unit are united and the united flow enters the outdoor
unit. After passing through a main suction pipe, the united flow is
distributed to suction pipe branches of the compressors to enter
the compressors.
[0005] In the refrigeration system, a discharge pipe in which the
flows of the refrigerant discharged from the two compressors are
united is provided with an oil separator for separating
refrigeration oil from the discharged refrigerant. The
refrigeration oil separated by the oil separator is supplied to the
main suction pipe through an oil return pipe, and then distributed
to the suction pipe branches and supplied to the compressors.
[0006] Each of the two compressors is provided with an oil
equalization pipe connected to part of a casing of the compressor
at a certain height at one end and connected to the suction pipe
branch of the other compressor at the other end. Each of the oil
equalization pipes is provided with a solenoid valve. As the
solenoid valves of the oil equalization pipes are opened
alternately at predetermined time intervals, the refrigeration oil
accumulated in the casing of one of the compressors is supplied to
the casing of the other compressor through the oil equalization
pipe so as to equalize the amounts of the refrigeration oil in the
compressors.
Patent Literature 1: Publication of Japanese Patent Application No.
2004-353996
DISCLOSURE OF THE INVENTION
Problem that the Invention is to Solve
[0007] According to the refrigeration system of Patent Literature
1, the refrigeration oil separated by the oil separator is merely
returned to the main suction pipe. That is, control of the
refrigeration oil is not achieved to a sufficient degree. This may
lead to a problem of decrease in reliability of the compressor.
[0008] In view of the foregoing, the present invention has been
achieved. With respect to the refrigeration system having a
plurality of compressors connected in parallel, an object of the
present invention is to control the oil in the compressors in an
adequate manner.
Means of Solving the Problem
[0009] According to a first aspect of the present invention, a
refrigeration system includes a refrigerant circuit (10) including
a plurality of compressors (11a, 11b, 11c) connected in parallel
and an oil separator (70) for separating a refrigeration oil from a
refrigerant discharged from the compressors (11a, 11b, 11c), the
refrigerant circuit (10) including a main suction pipe (55) in
which a refrigerant to be sucked into the compressors (11a, 11b,
11c) flows, suction pipe branches (61a, 61b, 61c) for distributing
the refrigerant in the main suction pipe (55) to the compressors
(11a, 11b, 11c) and an oil return pipe (71) for returning the
refrigeration oil separated by the oil separator (70) to the main
suction pipe (55), wherein a primary flow biasing element (110) for
biasing the flow of the refrigeration oil is assembled to part of
the main suction pipe (55) downstream of a junction of the main
suction pipe (55) and the oil return pipe (71) so that a larger
amount of the refrigeration oil flows into the suction pipe branch
(61a) of the first compressor (11a) previously chosen from the
compressors (11a, 11b, 11c).
[0010] According to the conventional refrigeration system, it is
impossible to grasp the amounts of the refrigeration oil returned
from the oil separator to the parallel-connected compressors
through the main suction pipe. Therefore, in the oil equalizing
operation, the unwanted step of opening the solenoid valve of the
oil equalization pipe for supplying the refrigeration oil from a
casing of the compressor containing enough refrigeration oil to a
casing of the compressor lacking the refrigeration oil. Due to the
unwanted step, the refrigeration oil is not quickly supplied to the
compressor lacking the refrigeration oil. That is, according to the
conventional refrigeration system, the unwanted step is performed
in addition to the suitable oil equalizing operation to supply the
refrigeration oil from the compressor containing a sufficient
amount of the refrigeration oil to the compressor containing a
small amount of the refrigeration oil through the oil equalization
pipe. Therefore, the amount of the refrigeration oil may always be
insufficient in a certain compressor.
[0011] According to a first aspect of the invention, the primary
flow biasing element (110) allows more refrigeration oil to flow
into the suction pipe branch (61a) of the first compressor (11a) so
that the largest amount of the refrigeration oil is returned to the
first compressor (11a) among the plurality of compressors (11a,
11b, 11c). In this way, the refrigeration oil is surely accumulated
in the casing of the first compressor (11a). The refrigeration oil
is supplied from the first compressor (11a) to the other
compressors (11b, 11c) to suitably equalize the amounts of the
refrigeration oil in the compressors.
[0012] According to a second aspect of the invention, a
refrigeration system includes a plurality of compressors (11a, 11b,
11c) connected in parallel and an oil separator (70) for separating
a refrigeration oil from a refrigerant discharged from the
compressors (11a, 11b, 11c), the refrigerant circuit (10) including
a main suction pipe (55) in which a refrigerant to be sucked into
the compressors (11a, 11b, 11c) flows, suction pipe branches (61a,
61b, 61c) for distributing the refrigerant in the main suction pipe
(55) to the compressors (11a, 11b, 11c) and an oil return pipe (71)
for returning the refrigeration oil separated by the oil separator
(70) to the main suction pipe (55), wherein a primary curved
portion (101) and a primary branch element (102) for branching the
main suction pipe (55) into the suction pipe branches (61a, 61b,
61c) are assembled to part of the main suction pipe (55) downstream
of a junction of the main suction pipe (55) and the oil return pipe
(71), the primary branch element (102) being located downstream of
the primary curved portion (101), and the suction pipe branch (61a)
of the first compressor (11a) previously chosen from the
compressors (11a, 11b, 11c) is at the outermost position in the
primary branch element (102) in the direction of a radius of
curvature of the primary curved portion (101).
[0013] According to the second aspect of the invention, centrifugal
force is exerted on the refrigerant and the refrigeration oil as
they pass through the primary curved portion (101) of the main
suction pipe (55). In part of the main suction pipe (55) downstream
of the primary curved portion (101), the refrigerant flows in an
inside region and the refrigeration oil flows in an outside region
in the direction of a radius of curvature of the primary curved
portion (101) due to the difference in centrifugal force exerted on
the refrigerant and the refrigeration oil. As the suction pipe
branch (61a) of the first compressor (11a) is at the outermost
position in the primary branch element (102) in the direction of a
radius of curvature of the primary curved portion (101), the
refrigeration oil running in the outside region in the main suction
pipe (55) flows into the suction pipe branch (61a) of the first
compressor (11a). In this way, a larger amount of the refrigeration
oil is returned to the first compressor (11a) among the plurality
of the compressors (11a, 11b, 11c). The refrigeration oil is
supplied from the first compressor (11a) to the other compressors
(11b, 11c) to suitably equalize the amounts of the refrigeration
oil in the compressors.
[0014] According to a third aspect of the invention, a
refrigeration system includes a refrigerant circuit (10) including
a plurality of compressors (11a, 11b, 11c) connected in parallel
and an oil separator (70) for separating a refrigeration oil from a
refrigerant discharged from the compressors (11a, 11b, 11c), the
refrigerant circuit (10) including a main suction pipe (55) in
which a refrigerant to be sucked into the compressors (11a, 11b,
11c) flows, suction pipe branches (61a, 61b, 61c) for distributing
the refrigerant in the main suction pipe (55) to the compressors
(11a, 11b, 11c) and an oil return pipe (71) for returning the
refrigeration oil separated by the oil separator (70) to the main
suction pipe (55), wherein the suction pipe branch (61a) of the
first compressor (11a) previously chosen from the compressors (11a,
11b, 11c) is at the bottommost position in a primary branch element
(102) for branching the main suction pipe (55) into the suction
pipe branches (61a, 61b, 61c).
[0015] According to the third aspect of the invention, the
refrigerant flows in an upper region in the main suction pipe (55)
and the refrigeration oil flows in a lower region in the main
suction pipe (55) due to the difference in gravity exerted on the
refrigerant and the refrigeration oil. As the suction pipe branch
(61a) of the first compressor (11a) is at the bottommost position
in the primary branch element (102), the refrigeration oil running
in the lower region in the main suction pipe (55) flows into the
suction pipe branch (61a) of the first compressor (11a). In this
way, a larger amount of the refrigeration oil is returned to the
first compressor (11a) among the plurality of compressors (11a,
11b, 11c). The refrigeration oil is supplied from the first
compressor (11a) to the other compressors (11b, 11c) to suitably
equalize the amounts of the refrigeration oil in the
compressors.
[0016] According to a fourth aspect of the invention, a
refrigeration system includes a refrigerant circuit (10) including
a plurality of compressors (11a, 11b, 11c) connected in parallel
and an oil separator (70) for separating a refrigeration oil from a
refrigerant discharged from the compressors (11a, 11b, 11c), the
refrigerant circuit (10) including a main suction pipe (55) in
which a refrigerant to be sucked into the compressors (11a, 11b,
11c) flows, suction pipe branches (61a, 61h, 61c) for distributing
the refrigerant in the main suction pipe (55) to the compressors
(11a, 11b, 11c) and an oil return pipe (71) for returning the
refrigeration oil separated by the oil separator (70) to the main
suction pipe (55), wherein a primary curved portion (101) and a
primary branch element (102) for branching the main suction pipe
(55) into the suction pipe branches (61a, 61b, 61c) are assembled
to part of the main suction pipe (55) downstream of a junction of
the main suction pipe (55) and the oil return pipe (71), the
primary branch element (102) being located downstream of the
primary curved portion (101), and the suction pipe branch (61a) of
the first compressor (11a) previously chosen from the compressors
(11a, 11b, 11c) is at the bottommost position and the outermost
position in the primary branch element (102) in the direction of a
radius of curvature of the primary curved portion (101).
[0017] That is, according to the fourth aspect of the present
invention related to the second aspect of the invention, the
suction pipe branch (61a) of the first compressor (11a) is at the
bottommost position in the primary branch element (102).
[0018] According to the fourth aspect of the invention, the
refrigerant and the refrigeration oil running through the main
suction pipe (55) experience gravity and centrifugal force caused
in the primary curved portion (101). In part of the main suction
pipe (55) downstream of the primary curved portion (101), the
refrigerant flows in an upper inside region of the main suction
pipe (55) in the direction of a radius of curvature of the primary
curved portion (101), while the refrigeration oil flows in a lower
outside region of the main suction pipe (55) in the direction of a
radius of curvature of the primary curved portion (101). As the
suction pipe branch (61a) of the first compressor (11a) is at the
bottommost position and the outermost position in the primary
branch element (102) in the direction of a radius of curvature of
the primary curved portion (101), the refrigeration oil running in
the lower outside region in the main suction pipe (55) flows into
the suction pipe branch (61a) of the first compressor (11a). In
this way, a larger amount of the refrigeration oil is returned to
the first compressor (11a) among the plurality of compressors (11a,
11b, 11c). The refrigeration oil is supplied from the first
compressor (11a) to the other compressors (11b, 11c) to suitably
equalize the amounts of the refrigeration oil in the
compressors.
[0019] According to a fifth aspect of the invention related to the
first aspect of the invention, the plurality of compressors (11a,
11b, 11c) are first to third compressors (11a, 11b, 11c), the main
suction pipe (55) is branched into the suction pipe branch (61a) of
the first compressor (11a) and a connecting suction pipe (56) which
is branched into the suction pipe branch (61b) of the second
compressor (11b) and the suction pipe branch (61c) of the third
compressor (11c), and a secondary flow biasing element (120) for
biasing the flow of the refrigeration oil in the connecting suction
pipe (56) is provided so that more refrigeration oil flows into the
suction pipe branch (61b) of the second compressor (11b) than into
the suction pipe branch (61c) of the third compressor (11c).
[0020] According to the fifth aspect of the invention, the
secondary flow biasing element (120) allows the second largest
amount of the refrigeration oil returning to the second compressor
(11b) among the three compressors (11a, 11b, 11c). In this way, the
largest, the second largest and the smallest amounts of the
refrigeration oil are returned to the first, second and third
compressors (11a, 11b, 11c), respectively. The refrigeration oil is
supplied from the compressors (11a, 11b) containing a larger amount
of the refrigeration oil to the compressors (11b, 11c) containing a
smaller amount of the refrigeration oil so as to suitably equalize
the amounts of the refrigeration oil in the compressors.
[0021] According to a sixth aspect of the invention related to any
one of the second to fourth aspects of the invention, the plurality
of compressors (11a, 11b, 11c) are first to third compressors (11a,
11b, 11c), the main suction pipe (55) is branched by the primary
branch element (102) into the suction pipe branch (61a) of the
first compressor (11a) and a connecting suction pipe (56) which is
branched by a secondary branch element (104) into the suction pipe
branch (61b) of the second compressor (11b) and the suction pipe
branch (61c) of the third compressor (11c), the connecting suction
pipe (56) is provided with a secondary curved portion (103) and the
suction pipe branch (61b) of the second compressor (11b) is
positioned outside the suction pipe branch (61c) of the third
compressor (11c) in the secondary branch element (104) in the
direction of a radius of curvature of the secondary curved portion
(103).
[0022] According to the sixth aspect of the invention, centrifugal
force is exerted on the refrigerant and the refrigeration oil as
they pass through the secondary curved portion (103) of the
connecting suction pipe (56). In part of the connecting suction
pipe (56) downstream of the secondary curved portion (103), the
refrigerant flows in an inside region and the refrigeration oil
flows in an outside region in the direction of a radius of
curvature of the secondary curved portion (103) due to the
difference in centrifugal force exerted on the refrigerant and the
refrigeration oil. As the suction pipe branch (61b) of the second
compressor (11b) is positioned outside the suction pipe branch
(61c) of the third compressor (11c) in the secondary branch element
(104), more refrigeration oil is returned to the second compressor
(11b) than to the third compressor (11c) from the connecting
suction pipe (56). In this way, the largest, the second largest and
the smallest amounts of the refrigeration oil are returned to the
first, second and third compressors (11a, 11b, 11c), respectively.
The refrigeration oil is supplied from the compressors (11a, 11b)
containing a larger amount of the refrigeration oil to the
compressors (11b, 11c) containing a smaller amount of the
refrigeration oil so as to suitably equalize the amounts of the
refrigeration oil in the compressors.
[0023] According to a seventh aspect of the invention related to
any one of the second to fourth aspects of the invention, the
plurality of compressors (11a, 11b, 11c) are first to third
compressors (11a, 11b, 11c), the main suction pipe (55) is branched
by the primary branch element (102) into the suction pipe branch
(61a) of the first compressor (11a) and a connecting suction pipe
(56) which is branched by a secondary branch element (104) into the
suction pipe branch (61b) of the second compressor (11b) and the
suction pipe branch (61c) of the third compressor (11c), the
suction pipe branch (61b) of the second compressor (11b) is
positioned lower than the suction pipe branch (61c) of the third
compressor (11c) in the secondary branch element (104).
[0024] According to the seventh aspect of the invention, due to the
difference in gravity exerted on the refrigerant and the
refrigeration oil as they pass through the connecting suction pipe
(56), the refrigerant flows in an upper region and the
refrigeration oil flows in a lower region in the connecting suction
pipe (56). As the suction pipe branch (61b) of the second
compressor (11b) is positioned lower than the suction pipe branch
(61c) of the third compressor (11c) in the secondary branch element
(104), more refrigeration oil is returned to the second compressor
(11b) than to the third compressor (11c) from the connecting
suction pipe (56). In this way, the largest, the second largest and
the smallest amounts of the refrigeration oil are returned to the
first, second and third compressors (11a, 11b, 11c), respectively.
The refrigeration oil is supplied from the compressors (11a, 11b)
containing a larger amount of the refrigeration oil to the
compressors (11b, 11c) containing a smaller amount of the
refrigeration oil so as to suitably equalize the amounts of the
refrigeration oil in the compressors.
[0025] According to an eighth aspect of the invention related to
any one of the second to fourth aspects of the invention, the
plurality of compressors (11a, 11b, 11c) are first to third
compressors (11a, 11b, 11c), the main suction pipe (55) is branched
by the primary branch element (102) into the suction pipe branch
(61a) of the first compressor (11a) and a connecting suction pipe
(56) which is branched by a secondary branch element (104) into the
suction pipe branch (61b) of the second compressor (11b) and the
suction pipe branch (61c) of the third compressor (11c), the
connecting suction pipe (56) is provided with a secondary curved
portion (103) and the suction pipe branch (61b) of the second
compressor (11b) is positioned lower than and outside the suction
pipe branch (61c) of the third compressor (11c) in the secondary
branch element (104) in the direction of a radius of curvature of
the secondary curved portion (103).
[0026] That is, according to the eighth aspect of the invention
related to the sixth aspect of the invention, the suction pipe
branch (61b) of the second compressor (11b) is positioned lower
than the suction pipe branch (61c) of the third compressor (11c) in
the secondary branch element (104).
[0027] According to the eighth aspect of the invention, the
refrigerant and the refrigeration oil running through the
connecting suction pipe (56) experience gravity and centrifugal
force caused in the secondary curved portion (103). Therefore, in
part of the connecting suction pipe (56) downstream of the
secondary curved portion (103), the refrigerant flows in an upper
inside region and the refrigeration oil flows in a lower outside
region in the direction of a radius of curvature of the secondary
curved portion (103). As the suction pipe branch (61b) of the
second compressor (11b) is positioned lower than and outside the
suction pipe branch (61c) of the third compressor (11c) in the
secondary branch element (104) in the direction of a radius of
curvature of the secondary curved portion (103), more refrigeration
oil is returned to the second compressor (11b) than to the third
compressor (11c) from the connecting suction pipe (56). In this
way, the largest, the second largest and the smallest amounts of
the refrigeration oil are returned to the first, second and third
compressors (11a, 11b, 11c), respectively. The refrigeration oil is
supplied from the compressors (11a, 11b) containing a larger amount
of the refrigeration oil to the compressors refrigeration oil
compressors (11b, 11c) containing a smaller amount of the
refrigeration oil so as to suitably equalize the amounts of the
refrigeration oil in the compressors.
[0028] According to a ninth aspect of the invention related to the
second or fourth aspect of the invention, the plurality of
compressors (11a, 11b, 11c) are first to third compressors (11a,
11b, 11c), the main suction pipe (55) is branched by the primary
branch element (102) into the suction pipe branch (61a) of the
first compressor (11a) and a connecting suction pipe (56) which is
branched by a secondary branch element (104) into the suction pipe
branch (61b) of the second compressor (11b) and the suction pipe
branch (61c) of the third compressor (11c), and the suction pipe
branch (61b) of the second compressor (11b) is positioned outside
the suction pipe branch (61c) of the third compressor (11c) in the
secondary branch element (104) in the direction of a radius of
curvature of the primary curved portion (101) of the main suction
pipe (55).
[0029] According to the ninth aspect of the invention, the
refrigerant flows in an inside region and the refrigeration oil
flows in an outside region in the connecting suction pipe (56) in
the direction of a radius of curvature of the primary curved
portion (101) due to the difference in centrifugal force exerted on
the refrigerant and the refrigeration oil in the connecting suction
pipe (56) as they pass through the primary curved portion (101) of
the main suction pipe (55). As the suction pipe branch (61b) of the
second compressor (11b) is positioned outside the suction pipe
branch (61c) of the third compressor (11c) in the secondary branch
element (104) in the direction of a radius of curvature of the
primary curved portion (101) of the main suction pipe (55), more
refrigeration oil is returned to the second compressor (11b) than
to the third compressor (11c) from the connecting suction pipe
(56). In this way, the largest, the second largest and the smallest
amounts of the refrigeration oil are returned to the first, second
and third compressors (11a, 11b, 11c), respectively. The
refrigeration oil is supplied from the compressors (11a, 11b)
containing a larger amount of the refrigeration oil to the
compressors refrigeration oil compressors (11b, 11c) containing a
smaller amount of the refrigeration oil so as to suitably equalize
the amounts of the refrigeration oil in the compressors.
[0030] According to a tenth aspect of the invention related to any
one of the first to ninth aspects of the invention, the
refrigeration system further includes oil equalizers (72, 73) for
supplying the refrigeration oil accumulated in a casing of the
first compressor (11a) to the other compressors (11b, 11c).
[0031] According to the tenth aspect of the invention, the oil
equalizers (72, 73) supply the refrigeration oil accumulated in the
casing of the first compressor (11a) to the other compressors (11b,
11c) containing a smaller amount of the refrigeration oil than the
first compressor (11a) so as to suitably equalize the amounts of
the refrigeration oil in the compressors.
[0032] According to an eleventh aspect of the invention related to
any one of the first to tenth aspects of the invention, the
refrigeration system further includes oil equalizers (72, 73, 74)
for equalizing the amounts of the refrigeration oil accumulated in
casings of the compressors (11a, 11b, 11c).
[0033] According to the eleventh aspect of the invention, the oil
equalizers (72, 73, 74) equalize the amounts of the refrigeration
oil accumulated in the casings of the compressors (11a, 11b,
11c).
[0034] According to a twelfth aspect of the invention related to
any one of the fifth, eighth and ninth aspects of the invention,
according to a twentieth aspect of the invention related to the
sixth aspect of the invention, and according to a twenty-first
aspect of the invention related to the seventh aspect of the
invention, the refrigeration system further includes a first oil
equalization pipe (72) for supplying the refrigeration oil
accumulated in a casing of the first compressor (11a) to the
connecting suction pipe (56) or the suction pipe branch (61b) of
the second compressor (11b), a second oil equalization pipe (73)
for supplying the refrigeration oil accumulated in a casing of the
second compressor (11b) to the suction pipe branch (61c) of the
third compressor (11c) and a third oil equalization pipe (74) for
supplying the refrigeration oil accumulated in a casing of the
third compressor (11c) to the main suction pipe (55) or the oil
return pipe (71).
[0035] According to the twelfth, twentieth and twenty-first aspects
of the invention, the refrigeration oil is supplied from the first
compressor (11a) containing the largest amount of the refrigeration
oil to the second compressor (11b) containing the second largest
amount of the refrigeration oil through the first oil equalization
pipe (72). Thus, the to refrigeration oil is surely accumulated in
the second compressor (11b). As the refrigeration oil is surely
accumulated in the second compressor (11b), the refrigeration oil
is supplied from the second compressor (11b) to the third
compressor (11c) containing the smallest amount of the
refrigeration oil through the second oil equalization pipe (73).
Thus, the refrigeration oil is surely accumulated in the third
compressor (11c). A surplus of the refrigeration oil in the third
compressor (11c) is returned to the first compressor (11a).
[0036] According to a thirteenth aspect of the invention related to
any one of the first to twelfth, twentieth and twenty-first aspects
of the invention, the first compressor (11a) is a capacity
invariable compressor (11a).
[0037] If the first compressor (11a) is a capacity variable
compressor, the amount of the refrigeration oil returned to the
first compressor (11a) varies as the capacity of the first
compressor (11a) varies, even if more refrigeration oil is allowed
to flow into the suction pipe branch (61a) of the first compressor
(11a). Therefore, according to the thirteenth aspect of the
invention, the capacity of the first compressor (11a) is
invariable. As a result, more refrigeration oil is surely returned
to the first compressor (11a) than to the other compressors as long
as the first compressor (11a) is working. In a like manner,
according to the fifth to ninth aspects of the invention, in the
case where one of the second compressor (11b) and the third
compressor (11c) is a capacity invariable compressor and the other
is a capacity variable compressor, the second compressor (11b) is
configured as the capacity invariable compressor.
[0038] According to a fourteenth aspect of the invention related to
any one of the first to thirteenth, twentieth and twenty-first
aspects of the invention, each of the compressors (11a, 11b, 11c)
is so configured that the refrigeration oil is accumulated in high
pressure space in the casing.
[0039] In low-pressure dome compressors, the refrigeration oil is
accumulated in low pressure space in the casings of the
compressors. Therefore, the casings (oil storing portions) of the
compressors may be connected directly by the oil equalization pipe
so as to equalize the amounts of the refrigeration oil. In this
case, the oil amount equalization among the low-pressure dome
compressors is performed in a suitable manner irrespective of the
amounts of the refrigeration oil returned to the compressors.
[0040] In high-pressure dome compressors or high/low-pressure dome
compressors, the refrigeration oil is accumulated in high pressure
space in the casings of the compressors. Therefore, the amounts of
the refrigeration oil returned to the compressors (11a, 11b, 11c)
are equalized only by supplying the refrigeration oil from the
compressors (11a, 11b, 11c) to the suction pipe branches (61a, 61b,
61c) of the other compressors (11a, 11b, 11c). In this case, there
is a need of adjusting the amounts of the refrigeration oil
returned to the compressors (11a, 11b, 11c) for suitable oil amount
equalization. Therefore, according to the fourteenth aspect of the
invention, the compressors (11a, 11b, 11c) are so configured that
the refrigeration oil is accumulated in high pressure space in the
casings of the compressors (11a, 11b, 11c).
[0041] According to a fifteenth aspect of the invention related to
the first to fourteenth, twentieth and twenty-first aspects of the
invention, liquid injection pipes (86, 86a, 86b, 86c) for
introducing a portion of a liquid refrigerant flowing in a liquid
pipe (84) on a high pressure side of the refrigerant circuit (10)
to the suction pipe branches (61a, 61b, 61c) of the compressors
(11a, 11b, 11c) are connected to the suction pipe branches (61a,
61b, 61c).
[0042] When the liquid refrigerant is injected into the main
suction pipe (55), the liquid refrigerant is dissolved in the
refrigeration oil so that more liquid refrigerant is supplied to
the suction pipe branch (61a) of the first compressor (11a) than to
the suction pipe branches (61b) of the other compressors (11b,
11c). Therefore, according to the fifteenth aspect of the
invention, the liquid refrigerant is injected to the suction pipe
branches (61a, 61b, 61c) through the liquid injection pipes (86,
86a, 86b, 86c) in an individual manner.
[0043] According to a sixteenth aspect of the invention related to
the first to fifteenth, twentieth and twenty-first aspects of the
invention, oil collecting pipes (75, 76, 77) connected to the
suction pipe branches (61a, 61b, 61c) of the compressors (11a, 11b,
11c) at one end, respectively, and connected to each other at the
other end.
[0044] The refrigeration oil separated by the oil separator (70) is
returned to the main suction pipe (55). Therefore, when any one of
the compressors (the compressor (11a)) is stopped, the
refrigeration oil is accumulated in the suction pipe branch (61a)
of the stopped compressor (11a). In particular when the first
compressor (11a) is stopped most frequently among the plurality of
compressors, a great amount of the refrigeration oil is accumulated
in the suction pipe branch (61a) of the first compressor (11a).
[0045] According to the sixteenth aspect of the invention, the
refrigeration oil accumulated in the suction pipe branch (61a) of
the stopped compressor (11a) is sucked into the working compressors
(11b, 11c) through the oil collecting pipes (75, 76, 77). As a
result, the stopped compressor (11a) does not suck the great amount
of the refrigeration oil in the liquid state upon restart.
[0046] According to a seventeenth aspect of the invention, a
refrigeration system includes a refrigerant circuit (10) including
a plurality of compressors (11a, 11b, 11c) connected in parallel
and an oil separator (70) for separating a refrigeration oil from a
refrigerant discharged from the compressors (11a, 11b, 11c), the
refrigerant circuit (10) including a main suction pipe (55) in
which a refrigerant to be sucked into the compressors (11a, 11b,
11c) flows, suction pipe branches (61a, 61b, 61c) for distributing
the refrigerant in the main suction pipe (55) to the compressors
(11a, 11b, 11c) and an oil return pipe (71) for returning the
refrigeration oil separated by the oil separator (70) to the main
suction pipe (55), wherein oil collecting pipes (75, 76, 77)
connected to the suction pipe branches (61a, 61b, 61c) of the
compressors (11a, 11b, 11c) at one end, respectively, and connected
to each other at the other end are provided.
[0047] More specifically, the refrigeration oil separated by the
oil separator (70) is returned to the main suction pipe (55).
Therefore, for example, when the compressor (11a) is stopped, the
refrigeration oil and the refrigerant are accumulated in the
suction pipe branch (61a) of the stopped compressor (11a).
[0048] According to the seventeenth aspect of the invention, the
refrigeration oil accumulated in the suction pipe branch (61a) of
the stopped compressor (11a) is sucked into the working compressors
(11b, 11c) through the oil collecting pipes (75, 76, 77). As a
result, the stopped compressor (11a) does not suck the great amount
of the refrigeration oil in the liquid state upon restart.
[0049] According to an eighteenth aspect of the invention related
to the sixteenth aspect of the invention, and according to a
nineteenth aspect of the invention related to the seventeenth
aspect of the invention, each of the suction pipe branches (61a,
61b, 61c) has an oblique portion (59) extending obliquely upward in
the downstream direction from a certain position of a barrel of the
suction pipe branch (61a, 61b, 61c) and an oil storing portion (58)
formed upstream of the oblique portion (59) and the one ends of the
oil collecting pipes (75, 76, 77) are connected to the oil storing
portions (58).
[0050] According to the eighteenth and nineteenth aspects of the
invention, the oil storing portion (58) of the suction pipe branch
(61a, 61b, 61c) is positioned lower than the oblique portion (59).
Therefore, when the compressors (11a, 11b) are stopped, the
refrigeration oil is accumulated in the oil storing portions (58).
The one ends of the oil collecting pipes (75, 76, 77) are connected
to the oil storing portions (58) of the suction pipe branches (61a,
61b, 61c). Therefore, when one compressor (11a) is stopped, the
refrigeration oil accumulated in the suction pipe branch (61a) of
the stopped compressor (11a) is surely sucked into the working
compressors (11b, 11c) through the oil collecting pipes (75, 76,
77).
EFFECT OF THE INVENTION
[0051] According to the first aspect of the invention, the largest
amount of the refrigeration oil is returned to the first compressor
(11a) among the plurality of compressors (11a, 11b, 11c) by the
primary flow biasing element (110). Therefore, the refrigeration
oil is surely accumulated in the casing of the first compressor
(11a) and the refrigeration oil in the first compressor (11a) is
distributed to the other compressors (11b, 11c). Thus, the oil
amounts in the compressors (11a, 11b, 11c) are checked with
accuracy, thereby improving the reliability of the compressors
(11a, 11b, 11c).
[0052] According to the second aspect of the invention, the largest
amount of the refrigeration oil is returned to the first compressor
(11a) by making use of the difference in centrifugal force exerted
on the refrigerant and the refrigeration oil as they pass through
the primary curved portion (101) of the main suction pipe (55).
Accordingly, the refrigeration oil is surely accumulated in the
casing of the first compressor (11a) and the refrigeration oil in
the first compressor (11a) is distributed to the other compressors
(11b, 11c). Thus, the oil amounts in the compressors (11a, 11b,
11c) are checked with accuracy, thereby improving the reliability
of the compressors (11a, 11b, 11c).
[0053] According to the third aspect of the invention, the largest
amount of the refrigeration oil is returned to the first compressor
(11a) by making use of the difference in gravity exerted on the
refrigerant and the refrigeration oil as they pass through the main
suction pipe (55). Accordingly, the refrigeration oil is surely
accumulated in the casing of the first compressor (11a) and the
refrigeration oil in the first compressor (11a) is distributed to
the other compressors (11b, 11c). Thus, the oil amounts in the
compressors (11a, 11b, 11c) are checked with accuracy, thereby
improving the reliability of the compressors (11a, 11b, 11c).
[0054] According to the fourth aspect of the invention, the largest
amount of the refrigeration oil is returned to the first compressor
(11a) by making use of the difference in gravity exerted on the
refrigerant and the refrigeration oil as they pass through the main
suction pipe (55) and the difference in centrifugal force exerted
on the refrigerant and the refrigeration oil as they pass through
the primary curved portion (101) of the main suction pipe (55).
Therefore, the refrigeration oil is surely accumulated in the
casing of the first compressor (11a) and the refrigeration oil in
the first compressor (11a) is distributed to the other compressors
(11b, 11c). Thus, the oil amounts in the compressors (11a, 11b,
11c) are checked with accuracy, thereby improving the reliability
of the compressors (11a, 11b, 11c).
[0055] According to the fifth aspect of the invention, the second
largest amount of the refrigeration oil is returned to the second
compressor (11b) among the three compressors (11a, 11b, 11c) by the
secondary flow biasing element (120). That is, the largest, the
second largest and the smallest amounts of the refrigeration oil
are returned to the first, second and third compressors (11a, 11b,
11c), respectively. Therefore, the refrigeration oil is supplied
from the compressors (11a, 11b) containing a larger amount of the
refrigeration oil to the compressors (11b, 11c) containing a
smaller amount of the refrigeration oil. Thus, the oil amounts in
the compressors (11a, 11b, 11c) are checked with accuracy, thereby
improving the reliability of the compressors (11a, 11b, 11c).
[0056] According to the sixth aspect of the invention, the second
largest amount of the refrigeration oil is returned to the second
compressor (11b) among the three compressors (11a, 11b, 11c) by
making use of the difference in centrifugal force exerted on the
refrigerant and the refrigeration oil as they pass through the
secondary curved portion (103) of the connecting suction pipe (56).
That is, the largest, the second largest and the smallest amounts
of the refrigeration oil are returned to the first, second and
third compressors (11a, 11b, 11c), respectively. Therefore, the
refrigeration oil is supplied from the compressors (11a, 11b)
containing a larger amount of the refrigeration oil to the
compressors (11b, 11c) containing a smaller amount of the
refrigeration oil. Thus, the oil amounts in the compressors (11a,
11b, 11c) are checked with accuracy, thereby improving the
reliability of the compressors (11a, 11b, 11c).
[0057] According to the seventh aspect of the invention, the second
largest amount of the refrigeration oil is returned to the second
compressor (11b) among the three compressors (11a, 11b, 11c) by
making use of the difference in gravity exerted on the refrigerant
and the refrigeration oil as they pass through the connecting
suction pipe (56). That is, the largest, the second largest and the
smallest amounts of the refrigeration oil are returned to the
first, second and third compressors (11a, 11b, 11c), respectively.
Therefore, the refrigeration oil is supplied from the compressors
(11a, 11b) containing a larger amount of the refrigeration oil to
the compressors (11b, 11c) containing a smaller amount of the
refrigeration oil. Thus, the oil amounts in the compressors (11a,
11b, 11c) are checked with accuracy, thereby improving the
reliability of the compressors (11a, 11b, 11c).
[0058] According to the eighth aspect of the invention, the second
largest amount of the refrigeration oil is returned to the second
compressor (11b) among the three compressors (11a, 11b, 11c) by
making use of the difference in gravity exerted on the refrigerant
and the refrigeration oil as they pass through the connecting
suction pipe (56) and the difference in centrifugal force exerted
on the refrigerant and the refrigeration oil as they pass through
the secondary curved portion (103). That is, the largest, the
second largest and the smallest amounts of the refrigeration oil
are returned to the first, second and third compressors (11a, 11b,
11c), respectively. Therefore, the refrigeration oil is supplied
from the compressors (11a, 11b) containing a larger amount of the
refrigeration oil to the compressors (11b, 11c) containing a
smaller amount of the refrigeration oil. Thus, the oil amounts in
the compressors (11a, 11b, 11c) are checked with accuracy, thereby
improving the reliability of the compressors (11a, 11b, 11c).
[0059] According to the ninth aspect of the invention, the second
largest amount of the refrigeration oil is returned to the second
compressor (11b) among the three compressors (11a, 11b, 11c) by
making use of the difference in centrifugal force exerted on the
refrigerant and the refrigeration oil as they pass through the
primary curved portion (101) of the main suction pipe (55). That
is, the largest, the second largest and the smallest amounts of the
refrigeration oil are returned to the first, second and third
compressors (11a, 11b, 11c), respectively. Therefore, the
refrigeration oil is supplied from the compressors (11a, 11b)
containing a larger amount of the refrigeration oil to the
compressors (11b, 11c) containing a smaller amount of the
refrigeration oil. Thus, the oil amounts in the compressors (11a,
11b, 11c) are checked with accuracy, thereby improving the
reliability of the compressors (11a, 11b, 11c).
[0060] According to the tenth aspect of the invention, the
refrigeration oil accumulated in the casing of the first compressor
(11a) is supplied to the other compressors (11b, 11c) through the
oil equalizers (72, 73) so as to suitably equalize the amounts of
the refrigeration oil in the compressors. Therefore, lack of the
refrigeration oil in the compressors (11a, 11b, 11c) is
prevented.
[0061] According to the eleventh aspect of the invention, the oil
equalizers (72, 73, 74) make it possible to suitably equalize the
amounts of the refrigeration oil accumulated in the casings of the
compressors (11a, 11b, 11c). Therefore, lack of the refrigeration
oil in the compressors (11a, 11b, 11c) is prevented.
[0062] According to the twelfth, twentieth and the twenty-first
aspects of the invention, the refrigeration oil accumulated in the
casing of the first compressor (11a) is supplied to the second
compressor (11b) and the refrigeration oil accumulated in the
casing of the second compressor (11b) is supplied to the third
compressor (11c) and a surplus of the refrigeration oil in the
third compressor (11c) is returned to the first compressor (11a).
As a result, the refrigeration oil is sequentially supplied to the
compressors (11a, 11b) containing a larger amount of the
refrigeration oil to the compressors (11b, 11c) containing a
smaller amount of the refrigeration oil so as to suitably equalize
the amounts of the refrigeration oil. Further, a surplus of the
refrigeration oil is circulated in the compressors (11a, 11b, 11c).
Therefore, the oil amounts in the compressors (11a, 11b, 11c) are
checked with accuracy.
[0063] According to the thirteenth aspect of the invention, the
first compressor (11a) is a capacity invariable compressor (11a).
Therefore, when the first compressor (11a) is working, a larger
amount of the refrigeration oil is surely returned to the first
compressor (11a).
[0064] According to the fourteenth aspect of the invention, each of
the compressors (11a, 11b, 11c) is so configured that the
refrigeration oil is accumulated in high pressure space in the
casing. Therefore, the effect of improving the reliability due to
the suitable equalization of the oil amounts in the compressors
(11a, 11b, 11c) is expressed more significantly.
[0065] According to the fifteenth aspect of the invention, liquid
injection pipes (86, 86a, 86b, 86c) are connected to the suction
pipe branches (61a, 61b, 61c) of the compressors (11a, 11b, 11c).
Therefore, the liquid refrigerant is surely supplied to the suction
pipe branches (61a, 61b, 61c). Further, the flows of the
refrigerant discharged from the compressors (11a, 11b, 11c) are
surely reduced in temperature, thereby preventing excessive
temperature rise in the compressors (11a, 11b, 11c). Thus, the
compressors (11a, 11b, 11c) are further improved in
reliability.
[0066] According to the sixteenth aspect of the invention, the oil
collecting pipes (75, 76, 77) are provided. Therefore, when a
certain compressor (11a) among the plurality of the compressors
(11a, 11b, 11c) is stopped, the refrigeration oil accumulated in
the suction pipe branch (61a) of the stopped compressor (11a) is
sucked into the other working compressors (11h, 11c). Therefore,
the stopped compressor (11a) is prevented from sucking a large
amount of the refrigeration oil in the liquid state and performing
the liquid compression upon restart. As a result, the compressor
(11a) is further improved in reliability.
[0067] In particular when the first compressor (11a) is stopped
most frequently among the plurality of the compressors, the effect
of improving the reliability due to the suitable equalization of
the oil amounts in the compressors (11a, 11b, 11c) is expressed
more significantly.
[0068] According to the seventeenth aspect of the invention, the
oil collecting pipes (75, 76, 77) are provided. Therefore, when a
certain compressor (11a) among the plurality of the compressors
(11a, 11b, 11c) is stopped, the refrigeration oil accumulated in
the suction pipe branch (61a) of the stopped compressor (11a) is
sucked into the other working compressors (11b, 11c). Therefore,
the stopped compressor (11a) is prevented from sucking a large
amount of the refrigeration oil in the liquid state and performing
the liquid compression upon restart. As a result, the compressor
(11a) is further improved in reliability.
[0069] According to the eighteenth and nineteenth aspects of the
invention, the oil collecting pipes (75, 76, 77) are connected to
the oil storing portions (58) of the suction pipe branches (61a,
61b, 61c). Therefore, the refrigeration oil accumulated in the
suction pipe branch (61a) of the stopped compressor (11a) is surely
sucked into the other working compressors (11b, 11c).
BRIEF DESCRIPTION OF DRAWINGS
[FIG. 1]
[0070] FIG. 1 is a piping diagram of a refrigerant circuit in a
refrigeration system according to Embodiment 1.
[FIG. 2]
[0071] FIG. 2 is a schematic perspective view of refrigerant pipes
on a suction side of compressors according to Embodiment 1.
[FIG. 3]
[0072] FIG. 3 is a piping diagram illustrating the direction of
refrigerant circulation in the refrigeration system according to
Embodiment 1 during a cooling operation.
[FIG. 4]
[0073] FIG. 4 is a schematic perspective view of refrigerant pipes
on a suction side of compressors according to Embodiment 2.
[FIG. 5]
[0074] FIG. 5 is a schematic view illustrating refrigerant pipes on
a suction side of compressors according to Embodiment 3.
EXPLANATION OF REFERENCE NUMERALS
[0075] 1 Refrigeration system [0076] 10 Refrigerant circuit [0077]
11a First compressor [0078] 11b Second compressor [0079] 11c Third
compressor [0080] 55 Main suction pipe [0081] 56 Connecting suction
pipe [0082] 58 Oil storing portion [0083] 59 Oblique portion [0084]
61a First suction pipe branch (suction pipe branch) [0085] 61b
Second suction pipe branch (suction pipe branch) [0086] 61c Third
suction pipe branch (suction pipe branch) [0087] 70 Oil separator
[0088] 71 Oil return pipe [0089] 72 First oil equalization pipe
[0090] 73 Second oil equalization pipe [0091] 74 Third oil
equalization pipe [0092] 84 Fourth liquid pipe (liquid pipe) [0093]
101 Primary curved portion [0094] 102 Primary branch element [0095]
103 Secondary curved portion [0096] 104 Secondary branch element
[0097] 110 Primary flow biasing element [0098] 120 Secondary flow
biasing element
BEST MODE FOR CARRYING OUT THE INVENTION
[0099] Embodiments of the present invention will now be described
with reference to the drawings.
Embodiment 1
[0100] According to Embodiment 1 of the present invention, a
refrigeration system (1) for performing an operation of cooling a
cooling chamber includes an outdoor unit (2), a cold storage unit
(3) and a controller (100) as shown in FIG. 1.
[0101] In the refrigeration system (1), the outdoor unit (2)
includes an outdoor circuit (20) and the cold storage unit (3)
includes a cold-storage circuit (30). In the refrigeration system
(1), a gas end of the outdoor circuit (20) is connected to a gas
end of the cold-storage circuit (30) by a gas-end connecting pipe
(22). A liquid end of the outdoor circuit (20) is connected to a
liquid end of the cold-storage circuit (30) by a liquid-end
connecting pipe (21). In this way, a refrigerant circuit (10) for
performing vapor compression refrigerating cycles is formed.
[0102] (Outdoor Unit)
[0103] The outdoor circuit (20) of the outdoor unit (2) includes
three compressors (11a, 11b, 11c), an outdoor heat exchanger (13),
a receiver (14), a refrigerant heat exchanger (50), a first
expansion valve (45), a second expansion valve (46) and a third
expansion valve (47). The outdoor circuit (20) further includes a
four-way switch valve (12), a liquid-end stop valve (53) and a
gas-end stop valve (54). In the outdoor circuit (20), one end of
the liquid-end connecting pipe (21) is connected to the liquid-end
stop valve (53) and one end of the gas-end connecting pipe (22) is
connected to the gas-end stop valve (54).
[0104] The three compressors (11a, 11b, 11c) are connected in
parallel in the refrigerant circuit (10). Each of the three
compressors (11a, 11b, 11c) is a high-pressure dome scroll
compressor. A first compressor (11a) and a second compressor (11b)
are capacity invariable compressors, while a third compressor (11c)
is a capacity variable compressor to which power is supplied
through an inverter and which is capable of varying the operation
capacity by changing the output frequency of the inverter. When the
refrigeration system (1) is working, the third compressor (11c) is
predominantly driven among the three compressors (11a, 11b, 11c).
Then, in response to the operating state of a utilization side of
the refrigeration system (1), the second compressor (11b) and the
first compressor (11a) are sequentially driven in this order.
[0105] To the suction sides of the first to third compressors (11a,
11b, 11c), a main suction pipe (55) is connected via suction pipe
branches (61a, 61b, 61c). More specifically, the main suction pipe
(55) is connected to the four-way switch valve (12) at one end and
to a primary branch element (102) at the other end. One end of the
first suction pipe branch (61a) and one end of a connecting suction
pipe (56) are connected to the primary branch element (102) of the
main suction pipe (55), and the other end of the first suction pipe
branch (61a) is connected to the suction side of the first
compressor (11a). The connecting suction pipe (56) has a secondary
branch element (104) connected to the other end thereof. To the
secondary branch element (104), one end of a second suction pipe
branch (61b) and one end of a third suction pipe branch (61c) are
connected. The other end of the second suction pipe branch (61b) is
connected to the suction side of the second compressor (11b). The
other end of the third suction pipe branch (61c) is connected to
the suction side of the third compressor (11c). As a feature of the
present invention, the main suction pipe (55) is provided with a
primary flow biasing element (110) and the connecting suction pipe
(56) is provided with a secondary flow biasing element (120). Their
specific structures are described later in more detail with
reference to FIG. 2.
[0106] To the discharge sides of the three compressors (11a, 11b,
11c), a main discharge pipe (64) is connected. More specifically,
one end of the main discharge pipe (64) is connected to the
four-way switch valve (12) and the other end thereof is branched
into a first discharge pipe branch (64a), a second discharge pipe
branch (64b) and a third discharge pipe branch (64c). The first
discharge pipe branch (64a) is connected to the discharge side of
the first compressor (11a). The second discharge pipe branch (64b)
is connected to the discharge side of the second compressor (11b).
The third discharge pipe branch (64c) is connected to the discharge
side of the third compressor (11c). The discharge pipe branches
(64a, 64b, 64c) have check valves (CV-1, CV-2, CV-3), respectively.
Each of the check valves passes only a refrigerant flow traveling
from the corresponding compressor (11a, 11b, 11c) to the four-way
switch valve (12).
[0107] The outdoor heat exchanger (13) is a cross-fin type
fin-and-tube heat exchanger which performs heat exchange between
the refrigerant and outdoor air. One end of the outdoor heat
exchanger (13) is connected to the four-way switch valve (12) and
the other end thereof is connected to the top of the receiver (14)
via a first liquid pipe (81). The first liquid pipe (81) is
provided with a check valve (CV-4) which passes only a refrigerant
flow traveling from the outdoor heat exchanger (13) to the receiver
(14). One end of a second liquid pipe (82) is connected to the
bottom of the receiver (14).
[0108] The refrigerant heat exchanger (50) is a plate-shaped heat
exchanger and performs heat exchange between refrigerants. The
refrigerant heat exchanger (50) includes a first flow path (50a)
and a second flow path (50b). One end of the first flow path (50a)
of the refrigerant heat exchanger (50) is connected to the other
end of the second liquid pipe (82) and the other end of the first
flow path (50a) is connected to one end of a third liquid pipe
(83). The other end of the third liquid pipe (83) is connected to
one end of the liquid-end connecting pipe (21) by the liquid-end
stop valve (53). The third liquid pipe (83) is provided with a
check valve (CV-5) which passes only a refrigerant flow traveling
from the other end of the first flow path (50a) to the liquid-end
stop valve (53).
[0109] One end of a fourth liquid pipe (84) is connected to part of
the third liquid pipe (83) upstream of the check valve (CV-5) and
the other end of the fourth liquid pipe (84) is connected to one
end of the second flow path (50b) of the refrigerant heat exchanger
(50). The fourth liquid pipe (84) is provided with a second
expansion valve (46). The second expansion valve (46) is an
electronic expansion valve whose degree of opening is
adjustable.
[0110] The other end of the second flow path (50b) of the
refrigerant heat exchanger (50) is connected to the barrel of the
main suction pipe (55) by a gas injection pipe (85). The gas
injection pipe (85) functions to inject refrigerant gas to the
suction side of the compressor (11a, 11b, 11c).
[0111] One end of a fifth liquid pipe (88) is connected to part of
the third liquid pipe (83) between the check valve (CV-5) and the
liquid-end stop valve (53). The other end of the fifth liquid pipe
(88) is connected to part of the first liquid pipe (81) between the
check valve (CV-4) and the receiver (14). The fifth liquid pipe
(88) is provided with a check valve (CV-6) which passes only a
refrigerant flow traveling from the one end to the other end of the
fifth liquid pipe (88).
[0112] One end of a sixth liquid pipe (89) is connected to part of
the fourth liquid pipe (84) between the one end of the fourth
liquid pipe (84) and the second expansion valve (46). The other end
of the sixth liquid pipe (89) is connected to part of the first
liquid pipe (81) between the other end of the outdoor heat
exchanger (13) and the check valve (CV-4). The sixth liquid pipe
(89) is provided with a first expansion valve (45). The first
expansion valve (45) is an electronic expansion valve whose degree
of opening is adjustable.
[0113] One end of a communicating pipe (78) is connected to part of
the first liquid pipe (81) between the check valve (CV-4) and the
junction with the fifth liquid pipe (88). The other end of the
communicating pipe (78) is connected to the main discharge pipe
(64). The communicating pipe (78) is provided with a check valve
(CV-7) which passes only a refrigerant flow traveling from the
receiver (14) to the main discharge pipe (64).
[0114] The four-way switch valve (12) is configured so that a first
port is connected to the main discharge pipe (64), a second port is
connected to the main suction pipe (55), a third port is connected
to the one end of the outdoor heat exchanger (13) and a fourth port
is connected to the gas-end stop valve (54). The four-way switch
valve (12) is switchable between a first state where the first and
third ports communicate with each other and the second and fourth
ports communicate with each other (a state depicted by a solid line
in FIG. 1) and a second state where the first and fourth ports
communicate with each other and the second and third ports
communicate with each other (a state depicted by a broken line in
FIG. 1).
[0115] The outdoor circuit (20) includes the oil separator (70). As
a feature of the present invention, the outdoor circuit (20)
further includes three oil equalization pipes (72, 73, 74), liquid
injection pipes (86, 86a, 86b, 86c) and three oil collecting pipes
(75, 76, 77).
[0116] The oil separator (70) is connected to the main discharge
pipe (64) to separate refrigeration oil from the flows of the
refrigerant discharged from the compressors (11a, 11b, 11c). The
oil separator (70) is connected to part of the main suction pipe
(55) downstream of the junction with the gas injection pipe (85) by
an oil return pipe (71). The oil return pipe (71) is provided with
a solenoid valve (SV-1). As the solenoid valve (SV-1) is opened,
the refrigeration oil separated by the oil separator (70) is
returned to the main suction pipe (55).
[0117] The three oil equalization pipes (72, 73, 74) are a first
oil equalization pipe (72), a second oil equalization pipe (73) and
a third oil equalization pipe (74). They function as oil
equalizers. One end of the first oil equalization pipe (72) is
connected to part of a casing of the first compressor (11a) at a
certain height and the other end thereof is connected to the
connecting suction pipe (56) and has a solenoid valve (SV-2). One
of the second oil equalization pipe (73) is connected to part of a
casing of the second compressor (11b) at a certain height and the
other end thereof is connected to the third suction pipe branch
(61c) by a third liquid injection pipe branch (86c) to be described
later and has a solenoid valve (SV-3). One end of the third oil
equalization pipe (74) is connected to part of a casing of the
third compressor (11c) at a certain height and the other end
thereof is connected to the oil return pipe (71) and has a solenoid
valve (SV-4). The first oil equalization pipe (72) may be connected
to the main suction pipe (55), the second oil equalization pipe
(73) may be connected to the second suction pipe branch (61b) and
the third oil equalization pipe (74) may directly be connected to
the third suction pipe branch (61c).
[0118] The liquid injection pipes (86, 86a, 86b, 86c) include a
main liquid injection pipe (86) and first to third liquid injection
pipe branches (86a, 86b, 86c). One end of the main liquid injection
pipe (86) is connected to part of the fourth liquid pipe (84)
between the one end of the fourth liquid pipe (84) and the junction
with the sixth liquid pipe (89). The other end of the main liquid
injection pipe (86) is branched in two for connection with one end
of the second liquid injection pipe branch (86b) and one end of the
third liquid injection pipe branch (86c). The main liquid injection
pipe (86) is provided with a third expansion valve (47). The third
expansion valve (47) is an electronic expansion valve whose degree
of opening is adjustable. One end of the first liquid injection
pipe branch (86a) is connected to the barrel of the second liquid
injection pipe branch (86b). The first to third liquid injection
pipe branches (86a, 86b, 86c) have capillary tubes (87a, 87b, 87c),
respectively, and the other ends of them are connected to the
suction pipe branches (61a, 61b, 61c) of the first to third
compressors (11a, 11b, 11c), respectively. Accordingly, a liquid
refrigerant running through the third liquid pipe (83) flows into
the liquid injection pipe branches (86a, 86b, 86c) via the fourth
liquid pipe (84) and the main liquid injection pipe (86) and is
supplied to the suction pipe branches (61a, 61b, 61c) of the
compressors (11a, 11b, 11c).
[0119] The three oil collecting pipes (75, 76, 77) are a first oil
collecting pipe (75), a second oil collecting pipe (76) and a third
oil collecting pipe (77). One end of the first oil collecting pipe
(75) is connected to part of the first suction pipe branch (61a) of
the first compressor (11a) between the junction with the first
liquid injection pipe branch (86a) and the other end of the first
suction pipe branch (61a). One end of the second oil collecting
pipe (76) is connected to part of the second suction pipe branch
(61b) of the second compressor (11b) between the junction with the
second liquid injection pipe branch (86b) and the other end of the
second suction pipe branch (61b). One end of the third oil
collecting pipe (77) is connected to part of the third suction pipe
branch (61c) of the third compressor (11c) between the junction
with the third liquid injection pipe branch (86c) and the other end
of the third suction pipe branch (61c). The other ends of the oil
collecting pipes (75, 76, 77) are connected to each other.
[0120] The outdoor circuit (20) further includes various sensors
and pressure switches (95a, 95b, 95c, 95d). More specifically, a
suction pressure sensor (25) and a suction temperature sensor (24)
are assembled to the main suction pipe (55). A discharge pressure
sensor (23) is assembled to the main discharge pipe (64). Discharge
temperature sensors (19a, 19b, 19c) are assembled to the discharge
pipe branches (64a, 64b, 64c), respectively. A temperature sensor
(51) is assembled to part of the third liquid pipe (83) near the
junction with the first flow path (50a) of the refrigerant heat
exchanger (50). Pressure switches (95a, 95b, 95c, 95d) are
assembled to a pipe between the gas-end stop valve (54) and the
four-way switch valve (12) and the discharge pipe branches (64a,
64b, 64c), respectively.
[0121] The outdoor unit (2) further includes an outside temperature
sensor (13a) and an outdoor fan (13f). Outdoor air is sent to the
outdoor heat exchanger (13) by the outdoor fan (131).
[0122] (Refrigerant Pipes on the Suction Side of the
Compressors)
[0123] As a feature of the present invention, the structure of the
refrigerant pipes (60a, 60b, 61a, 61b, 61c) on the suction sides of
the three compressors (11a, 11b, 11c) will be described in more
detail with reference to FIG. 2. In FIG. 2, the third oil
equalization pipe (74), the discharge pipe branches (64a, 64b, 64c)
and parts of the first and second oil equalization pipes (72, 73)
connected to the casings of the compressors (11a, 11b) are
omitted.
[0124] The refrigerant pipes (60a, 60b, 61a, 61b, 61c) on the
suction sides of the compressors (11a, 11b, 11c) are provided as
described above. The main suction pipe (55) is branched by the
primary branch element (102) into the first suction pipe branch
(61a) and the connecting suction pipe (56). The connecting suction
pipe (56) is branched by the secondary branch element (104) into
the second suction pipe branch (61b) and the third suction pipe
branch (61c).
[0125] Part of the main suction pipe (55) downstream of the
junction with the oil return pipe (71) extends horizontally and has
a primary flow biasing element (110). The primary flow biasing
element (1110) includes a primary curved portion (101) and the
primary branch element (102).
[0126] The primary curved portion (101) is an elbow joint that
connects pipes on the upstream and downstream sides of the primary
curved portion (101) at an angle of 90.degree.. Accordingly, a
refrigerant running through the main suction pipe (55) in the
direction from the right back to the front in FIG. 2 turns at a
substantially right angle at the primary curved portion (101) and
flows to the left side.
[0127] The primary branch element (102) is a branch joint that
divides a refrigerant flow into two flows and has a first branch
port (102a) and a second branch port (102b). In the primary branch
element (102), the first branch port (102a) is positioned obliquely
below the second branch port (102b) at an angle of 45.degree. and
positioned outside the second branch port (102b) in the direction
of a radius of curvature of the primary curved portion (101). The
first suction pipe branch (61a) of the first compressor (11a) is
connected to the first branch port (102a) and the connecting
suction pipe (56) is connected to the second branch port (102b).
Accordingly, in the primary branch element (102), the first suction
pipe branch (61a) is at the bottommost position and the outermost
position in the direction of a radius of curvature of the primary
curved portion (101).
[0128] One end of the first suction pipe branch (61a) is connected
to the first branch port (102a) of the primary branch element (102)
and the other end thereof is connected to the first compressor
(11a). More specifically, the first suction pipe branch (61a)
includes a horizontally extending linear oil storing portion (58)
connected to the first branch port (102a) of the primary branch
element (102) at one end, an oblique portion (59) connected to the
other end of the oil storing portion (58) at one end and extends
obliquely upward in the downstream direction and a vertical portion
(60) extending vertically downward from the top of the oblique
portion (59) and connected to the first compressor (11a). Further,
the first liquid injection pipe branch (86a) is connected to the
top wall of the oil storing portion (58) of the first suction pipe
branch (61a), and the first oil collecting pipe (75) is connected
to the bottom wall of the oil storing portion (58) to be located
downstream of the first liquid injection pipe branch (86a).
[0129] The connecting suction pipe (56) extends horizontally and
has a secondary flow biasing element (120). The secondary flow
biasing element (120) includes a secondary curved portion (103) and
the secondary branch element (104). The first oil equalization pipe
(72) is connected to part of the connecting suction pipe (56)
downstream of the secondary curved portion (103).
[0130] The secondary curved portion (103) is an elbow joint that
connects pipes on the upstream and downstream sides of the
secondary curved portion (103) at an angle of 90.degree..
Accordingly, a refrigerant flowing from one end of the connecting
suction pipe (56) to the left side in FIG. 2 turns at a
substantially right angle at the secondary curved portion (103) and
flows to the back.
[0131] The secondary branch element (104) is a branch joint that
divides a refrigerant flow into two flows and has a first branch
port (104a) and a second branch port (104b). In the secondary
branch element (104), the first branch port (104a) is positioned
obliquely below the second branch port (104b) at an angle of
45.degree. and positioned outside the second branch port (104b) in
the direction of a radius of curvature of the secondary curved
portion (103). The second suction pipe branch (61b) of the second
compressor (11b) is connected to the first branch port (104a) and
the third suction pipe branch (61c) of the third compressor (11c)
is connected to the second branch port (1044b).
[0132] One end of the second suction pipe branch (61b) is connected
to the first branch port (104a) of the secondary branch element
(104) and the other end thereof is connected to the suction side of
the second compressor (11b). More specifically, the second suction
pipe branch (61b) includes a horizontally extending linear oil
storing portion (58) connected to the first branch port (104a) of
the secondary branch element (104) at one end, an oblique portion
(59) connected to the other end of the oil storing portion (58) at
one end and extends obliquely upward in the downstream direction
and a vertical portion (60) extending vertically downward from the
top of the oblique portion (59) and connected to the second
compressor (12a). Further, the second liquid injection pipe branch
(86b) and the second oil collecting pipe (76) are connected to the
top and bottom walls of the oil storing portion (58),
respectively.
[0133] One end of the third suction pipe branch (61c) is connected
to the second branch port (104b) of the secondary branch element
(104) and the other end thereof is connected to the suction side of
the third compressor (11c). The third suction pipe branch (61c)
does not have the oil storing portion (58) and the oblique portion
(59). The third suction pipe branch (61c) extends horizontally in
the direction from the one end to the other end and is bent
vertically downward at the other end. The third liquid injection
pipe branch (86c) and the second oil equalization pipe (73)
combined with each other are connected to the horizontal top wall
of the third suction pipe branch (61c), and the third oil
collecting pipe (77) is connected to the bottom wall of the third
liquid injection pipe branch (86c) to be located downstream of the
junction with the third liquid injection pipe branch (86c) and the
second oil equalization pipe (73).
[0134] The other ends of the first to third oil collecting pipes
(75, 76, 77) are connected with each other immediately below the
junction of the second suction pipe branch (61b) with the second
oil collecting pipe (76).
[0135] (Cold Storage Unit)
[0136] As shown in FIG. 1, a cold-storage circuit (30) of the cold
storage unit (3) includes two cold-storage heat exchangers (16,
17), two drain pan heaters (26, 27) and two cold-storage expansion
valves (15a, 15b).
[0137] The cold-storage heat exchangers (16, 17) are cross-fin type
fin-and-tube heat exchangers, each of which performs heat exchange
between the refrigerant and air in the cooling chamber. Each of the
cold-storage heat exchangers (16, 17) is connected to one end of
the corresponding drain pan heater (26, 27) by the corresponding
cold-storage expansion valve (15a, 15b) at one end, and is
connected to one end of a corresponding gas-end pipe branch (22a,
22b) at the other end. The other ends of the gas-end pipe branches
(22a, 22b) are united with each other and connected to the other
end of the gas-end connecting pipe (22).
[0138] The cold-storage expansion valves (15a, 15b) are electronic
expansion valves whose degree of opening is adjustable. The
cold-storage heat exchangers (16, 17) have first refrigerant
temperature sensors (16b, 17b) for measuring the temperature at
which the refrigerant evaporates, respectively. The cold-storage
heat exchangers (16, 17) further have second refrigerant
temperature sensors (18a, 18b) assembled to the other ends thereof,
respectively. The degree of opening of the cold-storage expansion
valves (15a, 15b) is adjustable so that the temperature measured by
the second refrigerant temperature sensors (18a, 18b) is higher
than the evaporation temperature of the refrigerant measured by the
first refrigerant temperature sensors (16b, 17b) by a predetermined
temperature value (e.g., 5.degree. C.).
[0139] The drain pan heaters (26, 27) are assembled to drain pans
(not shown) of the cold-storage heat exchangers (16, 17) and heat
the drain pans as a high-temperature and high-pressure refrigerant
flows through the drain pan heaters so that frost and ice are not
formed on the drain pans. The other ends of the drain pan heaters
(26, 27) are connected to the one ends of liquid-end pipe branches
(21a, 21b), respectively. The other ends of the liquid-end pipe
branches (21a, 21b) are combined with each other and connected to
the other end of the liquid-end connecting pipe (21).
[0140] The cold storage unit (3) further includes cooling chamber
temperature sensors (16a, 17a) and cooling chamber fans (16f, 17f).
The air in the cooling chamber is sent to the cold-storage heat
exchangers (16, 17) by the cooling chamber fans (16f, 17f).
[0141] (Controller)
[0142] The controller (100) switches the valves (SV-1, SV-2, SV-3,
SV-4, 12, 46, 47, 48, 15a, 15b) provided in the refrigerant circuit
(10) and adjusts the degree of opening of the valves. The
controller (100) also drives the compressors (11a, 11b, 11c) and
the fans (13f, 16f, 17f) to control the operation of the
refrigeration system (1).
[0143] --Operation--
[0144] Now, the operation of the refrigeration system (1) according
to the present embodiment is explained.
[0145] The refrigeration system (1) performs a cooling operation
for cooling the air in the cooling chamber to the chosen
temperature of 5.degree. C., for example, and temporarily stops the
cooling operation to perform a defrosting operation.
[0146] (Cooling Operation)
[0147] For the cooling operation, as shown in FIG. 3, the
controller (100) puts the four-way switch valve (12) of the outdoor
circuit (20) into the first state and the first expansion valve
(45) is fully opened. In this state, the first to third compressors
(11a, 11b, 11c) are driven, and the cold-storage expansion valves
(15a, 15b), the second expansion valve (46) and the third expansion
valve (47) are opened to a suitable degree of opening to circulate
the refrigerant in the direction of solid arrows indicated in FIG.
3. At the same time, the outdoor fan (13f) and the cold-storage
fans (16f, 17f) are driven. The controller (100) allows the
solenoid valve (SV-1) of the oil return pipe (71) to open or close
as required and controls the solenoid valves of the oil
equalization pipes (72, 73, 74) so that, for example, the solenoid
valve (SV-2) of the first oil equalization pipe (72), the solenoid
valve (SV-3) of the second oil equalization pipe (73) and the
solenoid valve (SV-4) of the third oil equalization pipe (74) are
sequentially opened in this order.
[0148] The flows of the refrigerant discharged out of the first to
third compressors (11a, 11b, 11c) run through the discharge pipe
branches (64a, 64b, 64c), respectively, to flow into the main
discharge pipe (64), and then sent to the outdoor heat exchanger
(13) through the four-way switch valve (12). In the outdoor heat
exchanger (13), the refrigerant is condensed and liquefied as it
dissipates heat to the outdoor air. The liquefied refrigerant
enters the first liquid pipe (81), passes through the receiver (14)
and the second liquid pipe (82), and then flows into the first flow
path (50a) of the refrigerant heat exchanger (50). The liquefied
refrigerant runs through the first flow path (50a) and the third
liquid pipe (83), while a portion of which flows into the fourth
liquid pipe (84) as indicated in FIG. 3 by broken line arrows (a,
b).
[0149] A portion of the refrigerant flowed into the fourth liquid
pipe (84) as indicated by the broken line arrow (a) is reduced in
pressure as it passes through the second expansion valve (46).
Then, it flows into the second flow path (50b) of the refrigerant
heat exchanger (50) and exchanges heat with the liquid refrigerant
in the first flow path (50a) to evaporate, thereby cooling the
liquid refrigerant in the first flow path (50a) to a predetermined
low temperature. After being cooled by the branched flow of the
refrigerant in the second flow path (50b) to 15.degree. C., for
example, the liquid refrigerant in the first flow path (50a) passes
through the third liquid pipe (83), the liquid-end stop valve (53)
and the liquid-end connecting pipe (21) and flows into the
cold-storage circuit (30). The branched flow of the liquid
refrigerant in the second flow path (50b) evaporates and is
injected into the main suction pipe (55) through the gas injection
pipe (85).
[0150] The other portion of the refrigerant flowed into the fourth
liquid pipe (84) runs through the main liquid injection pipe (86)
as indicated by the broken line arrow (b) and passes through the
third expansion valve (47) opened to a suitable degree. Then, it is
distributed into the liquid injection pipe branches (86a, 86b, 86c)
and supplied the suction pipe branches (61a, 61b, 61c) of the
compressors (11a, 11b, 11c).
[0151] In the cold-storage circuit (30), a liquid refrigerant of
15.degree. C. is distributed into the liquid-end pipe branches
(21a, 21b). The distributed flows of the refrigerant run through
the drain pan heaters (26, 27) to prevent frosting on the drain
pans and surely melt frost fell on the drain pans from the
cold-storage heat exchangers (16, 17). The liquid refrigerant flows
discharged out of the drain pan heaters (26, 27) are reduced in
pressure and expanded as they pass through the cold-storage
expansion valves (15a, 15b) and enter the cold-storage heat
exchangers (16, 17). In each of the cold-storage heat exchangers
(16, 17), the refrigerant absorbs heat of the air in the cooling
chamber and evaporates at an evaporation temperature of, for
example, about -5.degree. C. In this way, in the cold storage unit
(3), the air cooled by the cold-storage heat exchangers (16, 17) is
supplied to the cooling chamber to keep the temperature in the
cooling chamber to the chosen temperature of 5.degree. C.
[0152] The flows of refrigerant gas resulting from the evaporation
in the cold-storage heat exchangers (16, 17) run through the
gas-end pipe branches (22a, 22b) and are united in the gas-end
connecting pipe (22). Then, the united flow of the refrigerant gas
runs through the gas-end connecting pipe (22) and the four-way
switch valve (12) to enter the main suction pipe (55). The
refrigerant flowed through the main suction pipe (55) is
distributed into the first suction pipe branch (61a) and the
connecting suction pipe (56). The refrigerant flowed into the first
suction pipe branch (61a) is sucked into the first compressor (11a)
and compressed. The refrigerant flowed into the connecting suction
pipe (56) is distributed into the second suction pipe branch (61b)
and the third suction pipe branch (61c). The refrigerant entered
the second suction pipe branch (61b) is sucked into the second
compressor (11b) and compressed. The refrigerant entered the third
suction pipe branch (61c) is sucked into the third compressor (11c)
and compressed.
[0153] (Refrigeration Oil Returning Operation)
[0154] When all the three compressors (11a, 11b, 11c) are working
for the cooling operation, the refrigeration oil is returned from
the main suction pipe (55) to the first, second and third
compressors so that the largest, the second largest and the
smallest amounts of the refrigeration oil are returned to the
first, second and third compressors, respectively. The
refrigeration oil is supplied from the compressors (11a, 11b) which
receive a larger amount of the returned refrigeration oil to the
compressors (11b, 11c) which receive a smaller amount of the
returned refrigeration oil through the oil equalization pipes (72,
73, 74) so as to equalize the amounts of the refrigeration oil in
the compressors (11a, 11b, 11c).
[0155] More specifically, as shown in FIG. 2, the refrigeration oil
separated from the discharged refrigerant by the oil separator (70)
is supplied to the main suction pipe (55) through the oil return
pipe (71). In part of the main suction pipe (55) downstream of the
oil return pipe (71), the refrigerant and the refrigeration oil
flow in a mixed state. In this state, gravity is exerted on the
refrigerant and the refrigeration oil as they flow in the main
suction pipe (55) and centrifugal force is exerted on the
refrigerant and the refrigeration oil as they flow in the primary
curved portion (101). Accordingly, in the downstream part of the
primary curved portion (101), the refrigerant flows in an upper
inside region in the primary curved portion (101) in the direction
of a radius of curvature of the primary curved portion (101), and
the refrigeration oil flows in a lower outside region in the
primary curved portion (101) in the direction of a radius of
curvature of the primary curved portion (101). Since the first
suction pipe branch (61a) of the first compressor (11a) is at the
bottommost and outermost position in the primary branch element
(102) in the direction of a radius of curvature of the primary
curved portion (101), most of the refrigeration oil in the main
suction pipe (55) flows into the first suction pipe branch (61a).
Further, as the first compressor (11a) is a capacity invariable
compressor, the refrigeration oil flowed into the first suction
pipe branch (61a) is surely sucked into and accumulated in the
first compressor (11a).
[0156] The refrigerant flowed into the connecting suction pipe (56)
contains a small amount of refrigeration oil. The refrigerant and
the refrigeration oil experience gravity as they flow in the
connecting suction pipe (56) and centrifugal force as they flow in
the secondary curved portion (103). Accordingly, in the downstream
part of the secondary curved portion (103), the refrigerant flows
in an upper inside region in the secondary curved portion (103) in
the direction of a radius of curvature of the secondary curved
portion (103), and the refrigeration oil flows in a lower outside
region in the secondary curved portion (103) in the direction of a
radius of curvature of the secondary curved portion (103). In the
secondary branch element (104), the second suction pipe branch
(61b) of the second compressor (11b) is positioned lower than and
outside the third suction pipe branch (61c) of the third compressor
(11c) in the direction of a radius of curvature of the secondary
curved portion (103). Therefore, most of the refrigeration oil in
the connecting suction pipe (56) flows into the second suction pipe
branch (61b). Further, as the second compressor (11b) is a capacity
invariable compressor, the refrigeration oil flowed into the second
suction pipe branch (61b) is surely sucked into and accumulated in
the second compressor (11b).
[0157] The refrigerant and the rest of the refrigeration oil flow
into the third suction pipe branch (61c) of the third compressor
(11c) and sucked into the third compressor (11c). In this way, the
largest, the second largest and the smallest amounts of the
refrigeration oil are returned to the first, second and third
compressors, respectively.
[0158] Then, a liquid refrigerant is injected to the suction pipe
branches (61a, 61b, 61c) through the liquid injection pipe branches
(86a, 86b, 86c), respectively. If the liquid refrigerant is
injected into the main suction pipe (55) or the connecting suction
pipe (56), the liquid refrigerant is dissolved in the refrigeration
oil and the largest, the second largest and the smallest amounts of
the refrigeration oil are returned to the first, second and third
compressors, respectively. However, as long as the refrigerant is
injected to the suction pipe branches (61a, 61b, 61c),
respectively, the flows of the refrigerant discharged from the
compressors (11a, 11b, 11c) are surely reduced in temperature,
thereby preventing excessive temperature rise in the compressors
(11a, 11b, 11c).
[0159] As described above, the controller (100) controls the
solenoid valves of the oil equalization pipes (72, 73, 74) to open,
for example, in the order of the solenoid valve (SV-2) of the first
oil equalization pipe (72), the solenoid valve (SV-3) of the second
oil equalization pipe (73), and the solenoid valve (SV-4) of the
third oil equalization pipe (74).
[0160] First, the solenoid valve (SV-2) of the first oil
equalization pipe (72) is opened to supply the refrigeration oil
accumulated in the casing of the first compressor (11a) to the
connecting suction pipe (56) through the first oil equalization
pipe (72). The refrigeration oil supplied to the connecting suction
pipe (56) runs through a lower region in the connecting suction
pipe (56) due to the difference in weight between the refrigerant
and the refrigeration oil. As a result, most of the refrigeration
oil flows into the second suction pipe branch (61b). In this way,
the refrigeration oil is supplied from the first compressor (11a)
to the second compressor (11b) through the first oil equalization
pipe (72) and surely accumulated in the second compressor
(11b).
[0161] The first oil equalization pipe (72) may be connected to
part of the connecting suction pipe (56) upstream of the secondary
curved portion (103). In this case, most of the refrigeration oil
supplied to the connecting suction pipe (56) through the first oil
equalization pipe (72) flows into the second suction pipe branch
(61b) due to the gravity and the centrifugal force exerted thereon
in the secondary curved portion (103). Alternatively, the first oil
equalization pipe (72) may be connected not to the connecting
suction pipe (56) but to the second suction pipe branch (61b).
[0162] With a large amount of the refrigeration oil accumulated in
the casing of the second compressor (11b), the solenoid valve
(SV-3) of the second oil equalization pipe (73) is opened. As a
result, the refrigeration oil accumulated in the casing of the
second compressor (11b) is supplied to the third suction pipe
branch (61c) through the second oil equalization pipe (73) and
flows into the third compressor (11c). In this way, the
refrigeration oil is surely accumulated in the third compressor
(11c).
[0163] With a large amount of the refrigeration oil accumulated in
the casing of the third compressor (11c), the solenoid valve (SV-4)
of the third oil equalization pipe (74) is opened. As a result, a
surplus of the refrigeration oil in the third compressor (11c) is
supplied to the oil return pipe (71) through the third oil
equalization pipe (74) and returned to the first compressor (11a)
through the main suction pipe (55).
[0164] The operation of the first compressor (11a) may be stopped
depending on the operating state of a utilization side (cooling
load). In this case, the refrigeration oil and the liquid
refrigerant injected through the liquid injection pipes (86, 86a)
remain in the oil storing portion (58) of the suction pipe branch
(61a) of the first compressor (11a). As the second and third
compressors (11b, 11c) are working, the refrigeration oil and the
liquid refrigerant remaining in the oil storing portion (58) of the
first suction pipe branch (61a) are introduced to the suction pipe
branches (61b, 61c) of the second and third compressors (11b, 11c)
through the oil collecting pipes (75, 76, 77) and sucked into the
second and third compressors (11b, 11c). Therefore, the stopped
first compressor (11a) does not suck a large amount of the
refrigeration oil in the liquid state upon restart. That is, there
is no possibility that the compressor (11a) performs liquid
compression immediately upon restart.
[0165] Even when the second compressor (11b) is stopped with the
first compressor (11a) being stopped, the refrigeration oil and the
liquid refrigerant remaining in the oil storing portions (58) of
the first and second suction pipes (61a, 61b) is sucked into the
working third compressor (11c) through the oil collecting pipes
(75, 76, 77).
[0166] (Defrosting Operation)
[0167] For a defrosting operation, though not shown, the four-way
switch valve (12) is set to the second state and the cold-storage
expansion valves (15a, 15b) and the second expansion valve (46) are
fully opened. The first and second expansion valves (45, 46) are
opened to a suitable degree of opening. In this state,
reverse-cycle defrosting is performed by circulating the
refrigerant in the direction opposite to the circulating direction
during the cooling operation.
[0168] More specifically, the flows of the refrigerant discharged
from the three compressors (11a, 11b, 11c) run through the
cold-storage heat exchangers (16, 17) and the drain pan heaters
(26, 27) and are condensed and liquefied as they dissipate heat to
the frost on the cold-storage heat exchangers (16, 17) and the
drain pans. The liquefied refrigerant flows into the outdoor
circuit (20) through the liquid-end connecting pipe (21). Then, it
passes through the fifth liquid pipe (88), the receiver (14) and
the first flow path (50a) of the refrigerant heat exchanger (50).
Then, the refrigerant is expanded by the first expansion valve (45)
as it flows in the sixth liquid pipe (89), condensed in the outdoor
heat exchanger (13) and flows into the main suction pipe (55)
through the four-way switch valve (12). Then, the refrigerant is
distributed into the suction pipe branches (61a, 61b, 61c) and
sucked into the compressors (11a, 11b, 11c).
[0169] Also in the defrosting operation, the largest, the second
largest and the smallest amounts of the refrigeration oil are
returned to the first, second and third compressors, respectively.
Among the compressors (11a, 11b, 11c), the amount of refrigeration
oil is equalized suitably by sequentially supplying the
refrigeration oil from the compressors (11a, 11b) which receive a
larger amount of the returned refrigeration oil to the compressors
(11b, 11c) which receive a smaller amount of the returned
refrigeration oil through the oil equalization pipes (72, 73,
74).
Effect of Embodiment 1
[0170] In the refrigeration system (1), the largest amount of the
refrigeration oil is returned to the first compressor (11a) by
making use of the difference in gravity and centrifugal force
exerted on the refrigerant and the refrigeration oil as they pass
through the main suction pipe (55). Therefore, the refrigeration
oil is surely accumulated in the casing of the first compressor
(11a). Further, with the help of the difference in gravity and
centrifugal force exerted on the refrigerant and the refrigeration
oil as they pass through the connecting suction pipe (56), a larger
amount of the refrigeration oil is returned to the second
compressor (11b) than to the third compressor (11c). Thus, the
largest, the second largest and the smallest amounts of the
refrigeration oil are returned to the first, second and third
compressors, respectively.
[0171] Through the first oil equalization pipe (72), the
refrigeration oil accumulated in the casing of the first compressor
(11a) containing the largest amount of the refrigeration oil is
supplied to the second compressor (11b) so that the refrigeration
oil is also accumulated in the second compressor (11b). Then, the
refrigeration oil accumulated in the casing of the second
compressor (11b) is supplied to the third compressor (11c) through
the second oil equalization pipe (73) so that the refrigeration oil
is also accumulated in the third compressor (11c). Further, through
the third oil equalization pipe (74), a surplus of the
refrigeration oil in the third compressor (11c) is returned to the
first compressor (11a). In this way, the refrigeration oil is
sequentially supplied from the compressors (11a, 11b) which receive
a larger amount of the returned refrigeration oil to the
compressors (11b, 11c) which receive a smaller amount of the
returned refrigeration oil and a surplus of the refrigeration oil
in each casing is circulated among the compressors (11a, 11b, 11c)
so as to suitably equalize the amounts of the refrigeration
oil.
[0172] When only the first compressor (11a) is stopped or the first
and second compressors (11a, 11b) are stopped, the refrigeration
oil and the liquid refrigerant remaining in the oil storing portion
(58) of the suction pipe branch (61a, 61b) of the stopped
compressor (11a, 11b) is sucked into the other working compressors
(11b, 11c) through the oil collecting pipes (75, 76, 77).
Therefore, the stopped compressor (11a) does not suck a large
amount of the refrigeration oil and the refrigerant in the liquid
state upon restart. This allows preventing the stopped compressor
(11a) from performing liquid compression immediately upon restart.
In particular, according to the present embodiment, the largest,
the second largest and the smallest amounts of the refrigeration
oil are returned to the first, second, third suction pipe branches
(61a, 61b, 61c) of the first, second and third compressors,
respectively. Then, as the cooling load is reduced during the
operation, the first, second and third compressors are stopped in
this order. Thus, the effect of the oil collecting pipes (75, 76,
77) is significantly exerted.
[0173] As described above, the refrigeration system (1) is able to
prevent lack of the refrigeration oil in the compressors (11a, 11b,
11c). Even when the first and second compressors (11a, 11b) are
stopped when the refrigeration system (1) is working, the stopped
compressors are prevented from performing liquid compression upon
restart. That is, according to the refrigeration system (1), the
oil amounts in the compressors (11a, 11b, 11c) are checked with
accuracy, thereby improving the reliability of the compressors
(11a, 11b, 11c).
Embodiment 2
[0174] In Embodiment 1, the primary flow biasing element (110)
includes the primary curved portion (101) and the primary branch
element (102) and the secondary flow biasing element (120) includes
the secondary curved portion (103) and the secondary branch element
(104). According to the present embodiment shown in FIG. 4,
different from Embodiment 1, the primary flow biasing element (110)
is formed of the primary branch element (102) only and the
secondary flow biasing element (120) is formed of the secondary
branch element (104) only. More specifically, according to the
present embodiment, centrifugal force is not exerted on the
refrigerant and the refrigeration oil as they pass through the
curved portions (101, 103) of the pipes (55, 56) on the suction
side. Only by making use of the difference gravity exerted on the
refrigerant and the refrigeration oil, the largest, the second
largest and the smallest amounts of the refrigeration oil are
returned to the first, second and third compressors, respectively.
In FIG. 4, the liquid injection pipe branches (86a, 86b, 86c) are
omitted.
[0175] More specifically, as shown in FIG. 4, the main suction pipe
(55) extends horizontally in part thereof downstream of the
junction with the oil return pipe (71) and is connected to a
primary branch element (102) serving as the primary flow biasing
element (110) at the most downstream end thereof.
[0176] The primary branch element (102) includes a first branch
port (102a) and a second branch port (102b). The first branch port
(102a) is positioned obliquely below the second branch port (102b)
at an angle of 45.degree.. The first suction pipe branch (61a) of
the first compressor (11a) is connected to the first branch port
(102a) and the connecting suction pipe (56) is connected to the
second branch port (102b). That is, the first suction pipe branch
(61a) is at the bottommost position in the primary branch element
(102).
[0177] One end of the first suction pipe branch (61a) is connected
to the first branch port (102a) of the primary branch element (102)
and the other end thereof is connected to the suction side of the
first compressor (11a). More specifically, the first suction pipe
branch (61a) includes a descending portion (63) connected to the
first branch port (102a) of the primary branch element (102) at one
end and extends obliquely downward to be away from the connecting
suction pipe (56), a horizontally extending linear oil storing
portion (58) connected to the other end of the descending portion
(63) at one end, an oblique portion (59) connected to the other end
of the oil storing portion (58) at one end and extends obliquely
upward in the downstream direction and a vertical portion (60)
extending vertically downward from the top of the oblique portion
(59) and connected to the first compressor (11a). One end of a
first oil collecting pipe (75) is connected to the bottom wall of
the oil storing portion (58) at the most downstream end of the oil
storing portion (58) of the first suction pipe branch (61a).
[0178] One end of the connecting suction pipe (56) is connected to
the second branch port (102h) of the primary branch element (102)
and the other end thereof is connected to a secondary branch
element (104) serving as the secondary flow biasing element (120).
The connecting suction pipe (56) extends horizontally in the
direction from one end to the other end thereof with a first oil
equalization pipe (72) connected to the barrel thereof.
[0179] The secondary branch element (104) includes a first branch
port (104a) and a second branch port (104b). The first branch port
(104a) is positioned obliquely below the second branch port (104b)
at an angle of 45.degree.. One end of the second suction pipe
branch (61b) of the second compressor (11b) is connected to the
first branch port (104a) and the third suction pipe branch (61c) of
the third compressor (11c) is connected to the second branch port
(104b).
[0180] One end of the second suction pipe branch (61b) is connected
to the first branch port (104a) of the secondary branch element
(104) and the other end thereof is connected to the suction side of
the second compressor (11b). More specifically, the second suction
pipe branch (61b) includes a horizontally extending linear oil
storing portion (58) connected to the first branch port (104a) of
the secondary branch element (104) at one end, an oblique portion
(59) connected to the other end of the oil storing portion (58) at
one end and extends obliquely upward in the downstream direction, a
horizontally extending horizontal portion (62) connected to the top
of the oblique portion (59) at one end and a vertical portion (60)
connected to the other end of the horizontal portion (62) at one
end and extends vertically downward and connected to the second
compressor (12a). One end of a second oil collecting pipe (76) is
connected to the bottom wall of the oil storing portion (58) at the
most downward end of the oil storing portion (58) of the second
suction pipe branch (61b).
[0181] One end of the third suction pipe branch (61c) is connected
to the second branch port (104b) of the secondary branch element
(104) and the other end thereof is connected to the suction side of
the third compressor (11c). The third suction pipe branch (61c)
does not have the oil storing portion (58) and the oblique portion
(59), but extends horizontally in the direction from the one end to
the other end and is bent vertically downward at the other end. A
second oil equalization pipe (73) is connected to the top wall of
the horizontal part of the third suction pipe branch (61c) and one
end of a third oil collecting pipe (77) is connected to the bottom
wall of the horizontal part to be located downstream of the second
oil equalization pipe (73).
[0182] According to the present embodiment, the refrigerant flows
in an upper region and the refrigeration oil flows in a lower
region in the main suction pipe (55) due to the difference in
gravity exerted on the refrigerant and the refrigeration oil. Since
the suction pipe branch (61a) of the first compressor (11a) is at
the bottommost position in the primary branch element (102), most
of the refrigeration oil flowing in the lower region in the main
suction pipe (55) flows into the suction pipe branch (61a) of the
first compressor (11a).
[0183] The refrigerant flowed into the connecting suction pipe (56)
contains a small amount of refrigeration oil. The refrigerant flows
in an upper region and the refrigeration oil flows in a lower
region in connecting suction pipe (56) due to the difference in
gravity exerted on the refrigerant and the refrigeration oil. Since
the second suction pipe branch (61b) of the second compressor (11b)
is positioned lower than the third suction pipe branch (61c) of the
third compressor (11c) in the secondary branch element (104), most
of the refrigeration oil running through the connecting suction
pipe (56) flows into the second suction pipe branch (61b).
[0184] The refrigerant and the rest of the refrigeration oil flow
into the third suction pipe branch (61c) of the third compressor
(11c) and sucked into the third compressor (11c). In this way, the
largest, the second largest and the smallest amounts of the
refrigeration oil are returned to the first, second and third
compressors, respectively.
[0185] The refrigeration oil in the casing of the first compressor
(11a) is supplied to the connecting suction pipe (56) through the
first oil equalization pipe (72). The supplied refrigeration oil
flows in the lower region in the connecting suction pipe (56) due
to the difference in gravity exerted on the refrigerant and the
refrigeration oil. As a result, most of the refrigeration oil flows
into the second suction pipe branch (61b). That is, the
refrigeration oil is supplied from the first compressor (11a) to
the second compressor (11b) through the first oil equalization pipe
(72) and the refrigeration oil is surely accumulated in the second
compressor (11b).
[0186] The refrigeration oil in the casing of the second compressor
(11b) is supplied to the third suction pipe branch (61c) through
the second oil equalization pipe (73) and sucked into the third
compressor (11c). In this manner, the refrigeration oil is supplied
from the second compressor (11b) to the third compressor (11c) and
the refrigeration oil is surely accumulated in the third compressor
(11c). A surplus of the refrigeration oil in the third compressor
(11c) is supplied to the oil return pipe (71) through the third oil
equalization pipe (not shown) and returned to the first compressor
(11a) through the main suction pipe (55). In this way, the amounts
of the refrigeration oil in the compressors (11a, 11b, 11c) are
suitably equalized.
[0187] When only the first compressor (11a) is stopped or the first
and second compressors (11a, 11b) are stopped, the refrigeration
oil remaining in the oil storing portions (58) of the suction pipe
branches (61a, 61b) of the stopped compressors (11a, 11b) is sucked
into the other working compressors (11b, 11c) through the oil
collecting pipes (75, 76, 77). This prevents the stopped
compressors (11a, 11b) from sucking a large amount of the
refrigeration oil in the liquid state and performing liquid
compression upon restart.
[0188] Except the above, the structure and the effect of Embodiment
2 are the same as those of Embodiment 1.
Embodiment 3
[0189] In Embodiment 1, the secondary flow biasing element (120)
includes the secondary curved portion (103) and the secondary
branch element (104) assembled to the connecting suction pipe (56).
According to the present embodiment as shown in FIG. 5, different
from Embodiment 1, the secondary flow biasing element (120) is
formed of the primary curved portion (101) assembled to the main
suction pipe (55) and the secondary branch element (104) assembled
to the connecting suction pipe (56). More specifically, according
to the present embodiment, centrifugal force caused in the primary
curved portion (101) of the main suction pipe (55) is used to bias
the flow of the refrigeration oil running through the connecting
suction pipe (56). In FIG. 5, the liquid injection pipe branches
(86a, 86b, 86c) are omitted.
[0190] More specifically, as shown in FIG. 5, in part of the main
suction pipe (55) downstream of the junction with the oil return
pipe (71), a primary curved portion (101) and a primary branch
element (102) are provided as the primary flow biasing element
(110). The piping downstream of the primary branch element (102) is
the same as that of Embodiment 2 shown in FIG. 4.
[0191] According to this structure, in the refrigeration system
(1), the refrigerant flows in an upper inside region and the
refrigeration oil flows in a lower outside region in the main
suction pipe (55) in the direction of a radius of curvature of the
primary curved portion (101) due to the difference in gravity
exerted on the refrigerant and the refrigeration oil and the
difference in centrifugal force exerted on the refrigerant and the
refrigeration oil as they pass through the primary curved portion
(101). The suction pipe branch (61a) of the first compressor (11a)
is at the bottommost and outermost position in the primary branch
element (102) in the direction of a radius of curvature of the
primary curved portion (101). Therefore, most of the refrigeration
oil in the main suction pipe (55) flows into the suction pipe
branch (61a) of the first compressor (11a).
[0192] The refrigerant flowed into the connecting suction pipe (56)
contains a small amount of refrigeration oil. Due to the difference
in gravity exerted on the refrigerant and the refrigeration oil and
the difference centrifugal force exerted on the refrigerant and the
refrigeration oil as they pass through the primary curved portion
(101) of the main suction pipe (55), the refrigerant flows in an
upper inside region and the refrigeration oil flows in a lower
outside region in the connecting suction pipe (56) in the direction
of a radius of curvature of the primary curved portion (101). Since
the suction pipe branch (61b) of the second compressor (11b) is
positioned lower than and outside the suction pipe branch (61c) of
the third compressor (11c) in the direction of a arduous of
curvature of the primary curved portion (101) of the main suction
pipe (55), more refrigeration oil in the connecting suction pipe
(56) flows into the suction pipe branch (61c) of the second
compressor (11b) than into the suction pipe branch (61c) of the
third compressor (11c).
[0193] The refrigerant and the rest of the refrigeration oil flow
into the third suction pipe branch (61c) of the third compressor
(11c). In this way, the largest, the second largest and the
smallest amounts of the refrigeration oil are returned to the
first, second and third compressors, respectively.
[0194] Except the above, the structure and the effect of Embodiment
3 are the same as those of Embodiment 1.
Other Embodiments
[0195] The above-described embodiments may be modified in the
following manner.
[0196] According to Embodiments 1 to 3, the first branch ports
(102a, 104a) are positioned lower than the second branch ports
(102b, 104b) in the primary branch element (102) and the secondary
branch element (104). However, the first branch ports (102a, 104a)
and the second branch ports (102b, 104b) may be arranged
horizontally on the same level. Even in this case, the first branch
port (102a) of the primary branch element (102) is positioned
outside the second branch port (102b) in the direction of a radius
of curvature of the primary curved portion (101) and the first
branch port (104a) of the secondary branch element (104) is
positioned outside the second branch port (104b) in the direction
of a radius of curvature of the secondary curved portion (103) or
the primary curved portion (101). Therefore, only by making use of
the centrifugal force caused in the curved portions (101, 103), the
largest, the second largest and the smallest amounts of the
refrigeration oil are returned to the first, second and third
compressors, respectively.
[0197] In each of the embodiments described above, the
refrigeration system (1) includes three compressors. However, the
number of the compressors is not limited to three. For example, two
compressors are connected in parallel and more refrigeration oil
may be returned to one of the compressors.
[0198] The structure of the flow biasing elements (110, 120) is not
limited to those described in the embodiments. The structure of the
main suction pipe (55) branched into the suction pipe branches
(61a, 61b, 61c) is not limitative. For example, the suction pipe
branch (61c) of the third compressor (11c) may be branched off the
upstream part of the main suction pipe (55), and then the suction
pipe branches (61a, 61b) of the first compressor (11a) and the
second compressor (11b) may be branched off the downstream part of
the main suction pipe (55). In this case, the largest amount of the
refrigeration oil is supplied from the main suction pipe (55) to
suction pipe branch (61a) to the first compressor (11a). Further in
this case, the largest, the second largest and the smallest amounts
of the refrigeration oil are returned to the first, second and
third compressors, respectively.
[0199] The refrigeration system (1) of Embodiment 1 includes the
refrigerant circuit (10) which performs one-stage refrigerant
compression by vapor compression refrigerating cycles. However, the
refrigeration system (1) may include a refrigerant circuit which
performs two-stage refrigerant compression. In this case, a
plurality of compressors (first to third compressors) may be
connected in parallel in each of a low-stage compressor mechanism
and a high-stage compressor mechanism for the two-stage
compression. In each of the compressor mechanisms the largest, the
second largest and the smallest amounts of the refrigeration oil
may be returned to the first, second and third compressors,
respectively. Further, in each of the compressor mechanisms, the
refrigeration oil may be supplied from the compressor which
receives a larger amount of the refrigeration oil to the compressor
which receives a smaller amount of the refrigeration oil through
the oil equalization pipe. In the low-stage compressor mechanism,
the refrigeration oil in the casing of the third compressor which
receives the smallest amount of the refrigeration oil may be
supplied to the suction side of the high-stage compressor mechanism
through the oil equalization pipe.
[0200] The above embodiments are merely preferred embodiments in
nature and are not intended to limit the scope, applications and
use of the invention.
INDUSTRIAL APPLICABILITY
[0201] As described above, the present invention is useful for
refrigeration systems including a plurality of compressors
connected in parallel.
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