U.S. patent application number 11/661609 was filed with the patent office on 2007-10-25 for refrigeration system.
Invention is credited to Azuma Kondo, Takenori Mezaki, Kazuyoshi Nomura, Yoshinari Oda, Satoru Sakae, Masaaki Takegami.
Application Number | 20070245768 11/661609 |
Document ID | / |
Family ID | 36000175 |
Filed Date | 2007-10-25 |
United States Patent
Application |
20070245768 |
Kind Code |
A1 |
Sakae; Satoru ; et
al. |
October 25, 2007 |
Refrigeration System
Abstract
A pressure regulating valve (71) is connected to the discharge
side of a low stage compressor (55) to make the pressure in the
suction side of high stage compressors (11, 12) lower than the
pressure in a dome of the low stage compressor (55). Further, an
oil return path (72) is connected to the dome of the low stage
compressor (55) at one end and to the suction side of the high
stage compressors (11, 12) by bypassing the pressure regulating
valve (71) at the other end. With this configuration, refrigeration
oil accumulated in the dome of the low stage compressor (55) is
returned to the high stage compressors (11, 12).
Inventors: |
Sakae; Satoru; (Osaka,
JP) ; Mezaki; Takenori; (Osaka, JP) ;
Takegami; Masaaki; (Osaka, JP) ; Nomura;
Kazuyoshi; (Osaka, JP) ; Kondo; Azuma; (Osaka,
JP) ; Oda; Yoshinari; (Osaka, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
36000175 |
Appl. No.: |
11/661609 |
Filed: |
September 2, 2005 |
PCT Filed: |
September 2, 2005 |
PCT NO: |
PCT/JP05/16123 |
371 Date: |
March 1, 2007 |
Current U.S.
Class: |
62/470 |
Current CPC
Class: |
F25B 2600/021 20130101;
F25B 2400/0751 20130101; F25B 2313/007 20130101; Y02B 30/70
20130101; F25B 1/10 20130101; F25B 13/00 20130101; F25B 2500/01
20130101; Y02B 30/741 20130101; F25B 2400/22 20130101; F25B
2313/02741 20130101; F25B 31/004 20130101 |
Class at
Publication: |
062/470 |
International
Class: |
F25B 43/02 20060101
F25B043/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 2, 2004 |
JP |
2004-255303 |
Claims
1. A refrigeration system having a refrigerant circuit (6)
including a low stage compressor (55) and high stage compressors
(11, 12) which are connected in series to perform a two-stage
compression refrigeration cycle, wherein the refrigeration system
(1) comprises an oil return means (70) for returning refrigeration
oil from the low stage compressor (55) to the high stage
compressors (11, 12).
2. The refrigeration system of claim 1, wherein the low stage
compressor (55) is configured to accumulate the refrigerant oil in
a high-pressure part thereof and the oil return means (70) is
configured to return the refrigeration oil accumulated in the
high-pressure part of the low stage compressor (55) to the high
stage compressors (11, 12).
3. The refrigeration system of claim 2, wherein the oil return
means (70) is provided on the discharge side of the low stage
compressor (55) and includes a pressure reducing means (71) and an
oil return path (72), the pressure reducing means (71) making the
pressure in the suction side of the high stage compressors (11, 12)
lower than the pressure in the high-pressure part of the low stage
compressor (55) and the oil return path (72) being connected to the
high pressure part of the low stage compressor (55) at one end and
to the suction side of the high stage compressors (11, 12) by
bypassing the pressure reducing means (71) at the other end.
4. The refrigeration system of claim 1, wherein the low stage
compressor (55) is configured to accumulate the refrigeration oil
in a dome thereof where the pressure is high and the oil return
means (70) is configured to return the refrigeration oil
accumulated in the dome of the low stage compressor (55) to the
high stage compressors (11, 12).
5. The refrigeration system of claim 4, wherein the oil return
means (70) is provided on the discharge side of the low stage
compressor (55) and includes a pressure reducing means (71) and an
oil return path (72), the pressure reducing means (71) making the
pressure in the suction side of the high stage compressors (11, 12)
lower than the pressure in the dome of the low stage compressor
(55) and the oil return path (72) being connected to the dome of
the low stage compressor (55) at one end and to the suction side of
the high stage compressors (11, 12) by bypassing the pressure
reducing means (71) at the other end.
6. The refrigeration system of claim 2, 3, 4 or 5, wherein the low
stage compressor (55) includes a plurality of low stage compressors
(55a, 55b, 55c) connected parallel to each other, the oil return
means (70) is configured to return the refrigeration oil from one
of the low stage compressors (55a) to the high stage compressors
(11, 12), the one of the low stage compressors (55a) being in
charge of returning the refrigeration oil to the high stage
compressors (11, 12), and the oil return means (70) includes oil
delivery paths (67a, 67b) for sending the refrigeration oil to the
low stage compressor (55a) in charge from the other low stage
compressors (55b, 55c) than the low stage compressor (55a) in
charge.
7. The refrigeration system of claim 1, wherein an oil separator
(64) is provided on the discharge side of the low stage compressor
(55) to trap the refrigeration oil discharged from the low stage
compressor (55) and the oil return means (70) includes a pressure
reducing means (71) and an oil return path (72), the pressure
reducing means (71) being closer to the high stage compressors (11,
12) than to the oil separator (64) to make the pressure in the
suction side of the high stage compressors (11, 12) lower than the
pressure in the oil separator (64) and the oil return path (72)
being connected to the oil separator (64) at one end and to the
suction side of the high stage compressors (11, 12) by bypassing
the pressure reducing means (71) at the other end.
Description
TECHNICAL FIELD
[0001] The present invention relates to a refrigeration system
having a refrigerant circuit including a low stage compressor and a
high stage compressor which are connected in series to perform a
two-stage compression refrigeration cycle. In particular, the
invention relates to a mechanism for returning refrigeration oil to
the compressor.
BACKGROUND ART
[0002] A common example of conventional refrigeration systems
performs a vapor compression refrigeration cycle by circulating a
refrigerant in a refrigerant circuit. Another known example of the
refrigeration system of this kind executes a two-stage compression
refrigeration cycle by compressing the refrigerant in two
stages.
[0003] The two-stage compression refrigeration system includes a
low stage compressor and a high stage compressor. A low pressure
gaseous refrigerant from an evaporator is sucked into the low stage
compressor and compressed to intermediate pressure. Then, the
refrigerant discharged from the low stage compressor is delivered
to the high stage compressor for further compression. The
refrigerant discharged out of the high stage compressor is then
sent to a condenser. Thus, the refrigeration cycle is
performed.
[0004] The refrigerant used in the refrigeration system is likely
to dissolve refrigeration oil used for lubricating the compressors.
Therefore, the refrigeration oil contained in the refrigerant gas
discharged from the compressor is dissolved into condensate in the
condenser. When the refrigerant liquid flows into the evaporator
and evaporates therein, the oil is separated. However, unless the
piping is designed for easy return of the oil to the compressor,
the oil remains accumulated in a low pressure part of the
refrigerant circuit. In this case, the compressors are not
lubricated enough, which leads to seizing of them.
[0005] For example, Patent Publication 1 discloses a refrigeration
system which includes an oil separator and an oil return path. The
oil separator separates the refrigeration oil from the refrigerant
discharged from the high stage compressor and the oil return path
returns the refrigeration oil to each of the high and low stage
compressors.
[0006] Further, Patent Publication 2 discloses another
refrigeration system which includes a gas-liquid separator and an
oil return path. The gas-liquid separator separates the
refrigeration oil from the refrigerant discharged from the low
stage compressor and the oil return path returns the refrigeration
oil from the gas-liquid separator to the low stage compressor.
[0007] Patent Publication 1: Publication of Unexamined Japanese
Patent Application No. H7-260263
[0008] Patent Publication 2: Pamphlet of International Publication
No. 02/46663
DISCLOSURE OF THE INVENTION
Problem that the Invention is to Solve
[0009] For both of the refrigeration systems according to Patent
Publications 1 and 2, it is impossible to return the refrigeration
oil accumulated in the low stage compressor to the high stage
compressor. Therefore, it is necessary to fill additional
refrigeration oil to prevent the high stage compressor from seizing
caused by the deficiency of the refrigeration oil in the high stage
compressor. Therefore, time and effort are required to fill the
refrigeration oil, which is disadvantageous from the aspect of
cost.
[0010] The present invention has been achieved in view of the
foregoing problem. An object of the present invention is to provide
a simple structure that makes it possible to distribute the
refrigeration oil between the low and high stage compressors,
thereby lubricating the compressors with a minimum amount of the
refrigeration oil and preventing failure from occurring.
Means of Solving the Problem
[0011] In order to achieve the above-described object, according to
the configuration of the present invention, refrigeration oil is
returned from a low stage compressor (55) to high stage compressors
(11, 12).
[0012] More specifically, a first aspect of the present invention
is directed to a refrigeration system (1) having a refrigerant
circuit (6) including a low stage compressor (55) and high stage
compressors (11, 12) which are connected in series to perform a
two-stage compression refrigeration cycle.
[0013] The refrigeration system (1) further includes an oil return
means (70) for returning refrigeration oil from the low stage
compressor (55) to the high stage compressors (11, 12).
[0014] To be more specific, in the refrigeration system (1)
including the refrigerant circuit (6) which performs the two-stage
compression refrigeration cycle, the refrigeration oil for
lubricating the compressors (11, 12, 55) is likely to accumulate in
the low stage compressor (55) where the pressure is low. With the
above-described configuration, the refrigeration oil accumulated in
the low stage compressor (55) is returned to the high stage
compressors (11, 12) by the oil return means (71).
[0015] According to a second aspect of the invention related to the
first aspect, the low stage compressor (55) is configured to
accumulate the refrigerant oil in a high-pressure part thereof and
the oil return means (70) is configured to return the refrigeration
oil accumulated in the high-pressure part of the low stage
compressor (55) to the high stage compressors (11, 12).
[0016] With this configuration, the refrigeration oil is returned
from the high-pressure part of the low stage compressor (55) where
it accumulates to the high stage compressors (11, 12) by the oil
return means (70).
[0017] According to a third aspect of the invention related to the
second aspect, the oil return means (70) is provided on the
discharge side of the low stage compressor (55) and includes a
pressure reducing means (71) and an oil return path (72). The
pressure reducing means (71) makes the pressure in the suction side
of the high stage compressors (11, 12) lower than the pressure in
the high-pressure part of the low stage compressor (55) and the oil
return path (72) is connected to the high pressure part of the low
stage compressor (55) at one end and to the suction side of the
high stage compressors (11, 12) by bypassing the pressure reducing
means (71) at the other end.
[0018] With this configuration, the pressure reducing means (71)
makes the pressure in the suction side of the high stage
compressors (11, 12) lower than the pressure in the high-pressure
part of the low stage compressor (55). Therefore, the refrigeration
oil accumulated in the high-pressure part of the low stage
compressor (55) is ejected to the suction side of the high stage
compressors (11, 12) through the oil return path (72) bypassing the
pressure reducing means (71).
[0019] According to a fourth aspect of the invention related to the
first aspect, the low stage compressor (55) is configured to
accumulate the refrigeration oil in a dome thereof where the
pressure is high and the oil return means (70) is configured to
return the refrigeration oil accumulated in the dome of the low
stage compressor (55) to the high stage compressors (11, 12).
[0020] With this configuration, the refrigeration oil is returned
from the dome of the low stage compressor (55) where it accumulates
to the high stage compressors (11, 12) by the oil return means
(70).
[0021] According to a fifth aspect of the invention related to the
fourth aspect, the oil return means (70) is provided on the
discharge side of the low stage compressor (55) and includes a
pressure reducing means (71) and an oil return path (72). The
pressure reducing means (71) makes the pressure in the suction side
of the high stage compressors (11, 12) lower than the pressure in
the dome of the low stage compressor (55) and the oil return path
(72) is connected to the dome of the low stage compressor (55) at
one end and to the suction side of the high stage compressors (11,
12) by bypassing the pressure reducing means (71) at the other
end.
[0022] With this configuration, the pressure reducing means (71)
makes the pressure in the suction side of the high stage
compressors (11, 12) lower than the pressure in the dome of the low
stage compressor (55). Therefore, the refrigeration oil accumulated
in the dome of the low stage compressor (55) is ejected to the
suction side of the high stage compressors (11, 12) through the oil
return path (72) bypassing the pressure reducing means (71).
[0023] According to a sixth aspect of the invention related to the
second, third, fourth or fifth aspect, the low stage compressor
(55) includes a plurality of low stage compressors (55a, 55b, 55c)
connected parallel to each other, the oil return means (70) is
configured to return the refrigeration oil from one of the low
stage compressors (55a) to the high stage compressors (11, 12), the
one of the low stage compressors (55a) being in charge of returning
the refrigeration oil to the high stage compressors (11, 12), and
the oil return means (70) includes oil delivery paths (67a, 67b)
for sending the refrigeration oil to the low stage compressor (55a)
in charge from the other low stage compressors (55b, 55c) than the
low stage compressor (55a) in charge.
[0024] With this configuration, the refrigeration oil accumulated
in the other low stage compressors (55b, 55c) than the low stage
compressor (55a) in charge is sent to the low stage compressor
(55a) through the oil delivery paths (67a, 67b). Then, the
refrigeration oil in the low stage compressor (55a) in charge is
returned to the high stage compressors (11, 12). That is to say,
according to the sixth aspect of the invention, the refrigeration
oil is gathered in the low stage compressor (55a) in charge, and
then returned to the high stage compressors (11, 12).
[0025] According to a seventh aspect of the invention related to
the first aspect, an oil separator (64) is provided on the
discharge side of the low stage compressor (55) to trap the
refrigeration oil discharged from the low stage compressor (55) and
the oil return means (70) includes a pressure reducing means (71)
and an oil return path (72). The pressure reducing means (71) is
closer to the high stage compressors (11, 12) than to the oil
separator (64) to make the pressure in the suction side of the high
stage compressors (11, 12) lower than the pressure in the oil
separator (64) and the oil return path (72) is connected to the oil
separator (64) at one end and to the suction side of the high stage
compressors (11, 12) by bypassing the pressure reducing means (71)
at the other end.
[0026] With this configuration, the pressure reducing means (71)
makes the pressure in the suction side of the high stage
compressors (11, 12) lower than the pressure in the oil separator
(64). Therefore, the refrigeration oil trapped in the oil separator
(64) is ejected to the suction side of the high stage compressors
(11, 12) through the oil return path (72) bypassing the pressure
reducing means (71). Thus, the refrigeration oil is returned from
the low stage compressor (55) to the high stage compressors (11,
12).
EFFECT OF THE INVENTION
[0027] As described above, according to the present invention, the
refrigeration system (1) including the refrigerant circuit (6)
which performs the two-stage compression refrigeration cycle is
configured such that the refrigeration oil, which is likely to
accumulate in the low stage compressor (55) where the pressure is
low, is returned from the low stage compressor (55) to the high
stage compressors (11, 12) by the oil return means (70). Therefore,
the high stage compressors (11, 12) will never be short of the
refrigeration oil, thereby eliminating the need of filling
additional refrigeration oil and saving time and effort to fill the
refrigeration oil. Further, since the refrigeration oil is
prevented from being accumulated in the low stage compressor (55),
rotational resistance caused by the refrigeration oil in the low
stage compressor (55) is reduced. Thus, the system is operated with
improved efficiency.
[0028] According to the third aspect of the invention described
above, the pressure reducing means (71) is provided on the
discharge side of the low stage compressor (55) and the pressure in
the suction side of the high stage compressors (11, 12) is made
lower than the pressure in the high-pressure part of the low stage
compressor (55). Further, the oil return path (72) is connected to
the high-pressure part of the low stage compressor (55) at one end
and to the suction side of the high stage compressors (11, 12) by
bypassing the pressure reducing means (71) at the other end such
that the refrigeration oil accumulated in the high-pressure part of
the low stage compressor (55) is returned to the high stage
compressors (11, 12). With such a simple structure, time and effort
to additionally fill the refrigeration oil are saved and the
refrigeration system (1) is operated efficiently with a minimum
amount of the refrigeration oil.
[0029] According to the fifth aspect of the invention, the pressure
reducing means (71) is provided on the discharge side of the low
stage compressor (55) and the pressure in the suction side of the
high stage compressors (11, 12) is made lower than the pressure in
the dome of the low stage compressor (55). Further, the oil return
path (72) is connected to the dome of the low stage compressor (55)
at one end and to the suction side of the high stage compressors
(11, 12) by bypassing the pressure reducing means (71) at the other
end. As a result, the refrigeration oil accumulated in the dome of
the low stage compressor (55) is returned to the high stage
compressors (11, 12). With such a simple structure, time and effort
to additionally fill the refrigeration oil are saved and the
refrigeration system (1) is operated efficiently with a minimum
amount of the refrigeration oil.
[0030] According to the sixth aspect of the invention, even if the
plurality of low stage compressors (55a, 55b, 55c) are provided,
the oil return means (70) returns the refrigeration oil from one of
the low stage compressors (55a) to the high stage compressors (11,
12). The one of the low stage compressors (55a) is in charge of
returning the refrigeration oil to the high stage compressors (11,
12). That is, it is no longer necessary to return the refrigeration
oil from each of the low stage compressors (55a, 55b, 55c) to the
high stage compressors (11, 12). Thus, the oil return means (71) is
achieved with a simple structure.
[0031] According to the seventh aspect of the invention, the
pressure reducing means (71) is provided closer to the high stage
compressors (11, 12) than to the oil separator (64) and the
pressure in the suction side of the high stage compressors (11, 12)
is made lower than the pressure in the oil separator (64). Further,
the oil return path (72) is connected to the oil separator (64) at
one end and to the suction side of the high stage compressors (11,
12) by bypassing the pressure reducing means (71) at the other end.
As a result, the refrigeration oil trapped in the oil separator
(64) is returned to the high stage compressors (11, 12). With such
a simple structure, time and effort to additionally fill the
refrigeration oil are saved and the refrigeration system (1) is
operated efficiently with a minimum amount of the refrigeration
oil.
BRIEF DESCRIPTION OF DRAWINGS
[0032] FIG. 1 is a refrigerant circuit diagram of a refrigeration
system according to an embodiment of the present invention.
[0033] FIG. 2 is an enlargement of an oil return means.
[0034] FIG. 3 is a Mollier chart of a refrigeration cycle according
to the embodiment.
[0035] FIG. 4 is a refrigerant circuit diagram of a refrigeration
system according to a first modification of the embodiment of the
present invention.
[0036] FIG. 5 is a refrigerant circuit diagram of a refrigeration
system according to a second modification of the embodiment of the
present invention.
[0037] FIG. 6 is a refrigerant circuit diagram of a refrigeration
system according to a third modification of the embodiment of the
present invention.
[0038] FIG. 7 is a refrigerant circuit diagram of a refrigeration
system according to the third modification of the embodiment of the
present invention.
EXPLANATION OF REFERENCE NUMERALS
[0039] 6 Refrigerant circuit [0040] 11 First compressor (high stage
compressor) [0041] 12 Second compressor (high stage compressor)
[0042] 55 Freezer compressor (low stage compressor) [0043] 55a
First freezer compressor (low stage compressor) [0044] 55b Second
freezer compressor (low stage compressor) [0045] 55c Third freezer
compressor (low stage compressor) [0046] 64 Oil separator [0047]
67a First oil equalizing pipe (oil delivery path) [0048] 67b Second
oil equalizing pipe (oil delivery path) [0049] 70 Oil return means
[0050] 71 Pressure regulating valve (pressure reducing means)
[0051] 72 Oil return path
BEST MODE FOR CARRYING OUT THE INVENTION
[0052] Hereinafter, explanation of an embodiment of the present
invention is provided with reference to the drawings. The following
embodiment is given as a preferable example of the present
invention and does not limit the invention and the scope of
application and use thereof.
Structure of Refrigeration System
[0053] As shown in FIG. 1, a refrigeration system (1) of the
present embodiment is used for room air conditioning, as well as
cold storage and freezing of food and drink. For example, it is
used in convenience stores. The refrigeration system (1) includes a
refrigerant circuit (6) realized by connecting an outdoor unit (2),
an indoor unit (3), a cold storage unit (4) and a freezer unit
(5).
[0054] The outdoor unit (2) includes first and second compressors
(11, 12), an outdoor heat exchanger (13) and a receiver (14). The
first and second compressors (11, 12) are connected parallel to
each other and serve as high stage compressors. The first
compressor (11) is an inverter compressor capable of varying the
capacity. The second compressor (12) is a non-inverter compressor
whose capacity is fixed. A four-pass switching valve (15) is
provided on the discharge side of the compressors (11, 12).
Discharge pipes of the compressors (11, 12) are connected to a
first port of the four-pass switching valve (15). An oil separator
(16), a temperature sensor (81) and a pressure sensor (82) are
provided between the compressors (11, 12) and the four-pass
switching valve (15). The discharge pipe of the first compressor
(11) has a high pressure switch (40). The first and second
compressors (11, 12) have a suction pipe (17), on which a pressure
sensor (83) is provided. An oil return pipe (18) connects the
suction pipe (17) to the oil separator (16) and has a solenoid
valve (19). An oil equalizing pipe (20) of the compressors (11, 12)
is connected to the side of the second compressor (12) at one end
and to the suction pipe (22) of the first compressor (11) at the
other end. The oil equalizing pipe (20) has a solenoid valve
(21).
[0055] The outdoor heat exchanger (13) is connected to a second
port of the four-pass switching valve (15) via a refrigerant pipe
(30) at one end and to the receiver (14) via a refrigerant pipe
(24) at the other end. A liquid pipe (25) of the receiver (14) is
connected to the refrigerant pipe (24) via a bypass pipe (26). The
bypass pipe (26) is provided with an electronic expansion valve
(27).
[0056] The liquid pipe (25) of the receiver (14) is connected to a
refrigerant pipe (35) extending to the outside of the outdoor unit
(2). The refrigerant pipe (35) is connected to an end of the
refrigerant pipe (24) closer to the receiver (14) via a refrigerant
pipe (41). The refrigerant pipes (41) and (24) are provided with
check valves (CV) for blocking a flow of refrigerant from the
receiver (14), respectively.
[0057] The suction pipe (17) of the compressors (11, 12) is
connected to a third port of the four-pass switching valve (15).
The suction pipe (17) is provided with a temperature sensor (37). A
refrigerant pipe (38) extending to the outside of the outdoor unit
(2) is connected to part of the suction pipe (17) between the
four-pass switching valve (15) and the temperature sensor (37).
[0058] A fourth port of the four-pass switching valve (15) is
connected to a refrigerant pipe (39) extending to the outside of
the outdoor unit (2). The four-pass switching valve (15) is
switchable between the first and second states described below. In
the first state, the first and second ports are communicated with
each other, and so are the third and fourth ports. In the second
state, the first and fourth ports are communicated with each other,
and so are the second and third ports.
[0059] The outdoor unit (2) further includes an outdoor fan (23)
for feeding air to the outdoor heat exchanger (13) and a
temperature sensor (50) for sensing the temperature of outside
air.
[0060] An indoor unit (3) performs indoor air conditioning and
includes an indoor heat exchanger (42), an indoor electronic
expansion valve (43) and an indoor fan (44). The indoor heat
exchanger (42) is connected to the refrigerant pipe (39) at one
end, and to the refrigerant pipe (35) at the other end. The indoor
electronic expansion valve (43) is provided in the refrigerant pipe
(35). The indoor heat exchanger (42) and the refrigerant pipe (39)
are provided with temperature sensors (45) and (46), respectively.
A temperature sensor (51) is provided to sense the temperature of
indoor air.
[0061] The cold storage unit (4) is used to keep food and drink in
cold storage and includes a cold storage cooling coil (47), a cold
storage electronic expansion valve (48) and a cold storage fan
(49). The cold storage cooling coil (47) is connected to a
refrigerant pipe (36) which is joined with the refrigerant pipe
(35) at one end, and to the refrigerant pipe (38) at the other end.
The cold storage electronic expansion valve (48) is provided in the
refrigerant pipe (36). The cold storage cooling coil (47) and the
refrigerant pipe (38) are provided with temperature sensors (53)
and (54), respectively. The cold storage unit (4) further includes
a temperature sensor (52) for sensing the temperature in a cold
storage chamber.
[0062] The freezer unit (5) is used to freeze food and drink and
includes a freezer compressor (55) serving as a low stage
compressor, a freezer cooling coil (56), a freezer electronic
expansion valve (57) and a freezer fan (58). The freezer unit (5)
is connected to a refrigerant pipe (59) branched from the
refrigerant pipe (36) and a refrigerant pipe (60) branched from the
refrigerant pipe (38). The freezer electronic expansion valve (57),
the freezer cooling coil (56) and the freezer compressor (55) are
connected in this order. The freezer electronic expansion valve
(57) is connected to the refrigerant pipe (59) and the discharge
side of the freezer compressor (55) is connected to the refrigerant
pipe (60). A temperature sensor (61) is provided in the freezer
cooling coil (56) and a temperature sensor (62) is provided in a
pipe on the exit side of the freezer cooling coil (56) (i.e., a
pipe between the freezer cooling coil (56) and the freezer
compressor (55)). The freezer unit (5) further includes a
temperature sensor (63) for sensing the temperature in a freezer
chamber.
[0063] The freezer compressor (55) is a high-pressure dome type
inverter compressor capable of varying the volume. The freezer
compressor (55) has an oil separator (64) on a discharge pipe
thereof. The oil separator (64) has an oil return pipe (65), which
is connected to a suction pipe (68) of the freezer compressor (55).
The oil return pipe (65) is provided with a capillary tube (69)
serving as a pressure reducing system. Refrigerant sucked into the
dome of the freezer compressor (55) through the suction pipe (68)
is compressed by a compressor mechanism (not shown) in the dome and
discharged in space inside the dome. Therefore, the dome becomes a
high pressure part as the high pressure refrigerant is discharged
therein. The freezer compressor (55) is configured to accumulate
refrigeration oil at the bottom of the high-pressure dome.
[0064] As shown in an enlargement of FIG. 2, a pressure regulating
valve (71) serving as a pressure reducing means is provided in part
of the discharge pipe of the freezer compressor (55) downstream of
the oil separator (64). This configuration is a characteristic
feature of the present invention. Refrigerant discharged from the
freezer compressor (55) is reduced in pressure when it passes
through the pressure regulating valve (71). Therefore, the pressure
becomes lower in the suction side of the first and second
compressors (11, 12) than in the dome of the freezer compressor
(55). The pressure reducing means may be realized by, for example,
a capillary tube, an oil separator, a filter, a muffler, a check
valve, a long pipe or the like in place of the pressure regulating
valve (71), as long as it functions as resistance against the
refrigerant flow.
[0065] An oil return path (72) is connected to a certain position
of the dome of the freezer compressor (55) at one end such that the
level of the refrigeration oil in the dome corresponds to a
predetermined height H. The other end of the oil return path (72)
bypasses the pressure regulating valve (71) and is connected to the
refrigerant pipe (60). The oil return path (72) has a solenoid
valve (73). The pressure regulating valve (71) and the oil return
path (72) function as an oil return means (70) of the present
invention.
[0066] In FIG. 1, (CV) and (F) represent check valves and filters,
respectively.
Operation of Refrigeration System
[0067] In cooling operation, the four-pass switching valve (15)
enters the first state where the first and second ports are
communicated with each other, and so are the third and fourth
ports. The electronic expansion valve (27) of the outdoor unit (2)
is fully opened. Accordingly, refrigerant in the refrigerant
circuit (6) flows along the arrows depicted in FIG. 1. Explanation
of heating operation is omitted from the description.
[0068] More specifically, the refrigerant discharged from the
compressors (11, 12) is condensed in the outdoor heat exchanger
(13) and flows into the receiver (14). The refrigerant in the
receiver (14) flows out of the outdoor unit (2), and is branched
into the indoor unit (3), the cold storage unit (4) and the freezer
unit (5). The refrigerant entered the indoor unit (3) is reduced in
pressure as it passes through the indoor electronic expansion valve
(43) and then evaporated in the indoor heat exchanger (42), thereby
cooling the indoor air. The refrigerant entered the cold storage
unit (4) is reduced in pressure to first predetermined pressure PL1
as it passes through the cold storage electronic expansion valve
(48) (see FIG. 3), and then evaporated in the cold storage cooling
coil (47), thereby cooling the air in the cold storage chamber.
[0069] Further, the refrigerant entered the freezer unit (5) is
reduced in pressure down to second predetermined pressure PL2 which
is lower than the first predetermined pressure PL1 as it passes
through the freezer electronic expansion valve (57). The
refrigerant with reduced pressure is evaporated in the freezer
cooling coil (56), thereby cooling the air in the freezer chamber.
The refrigerant flows from the freezer cooling coil (56) to the
freezer compressor (55), where the refrigerant pressure is
increased to the first predetermined pressure PL1. Then, the
refrigerant flows into the outdoor unit (2) together with the
refrigerant flowing from the cold storage cooling coil (47). The
refrigerant entered the outdoor unit (2) is sucked into the
compressors (11, 12) together with the refrigerant flowing back to
the outdoor unit (2) from the indoor unit (3).
[0070] The refrigerant sucked into the compressors (11, 12) is
compressed by the compressors (11, 12). After that, the
above-described circulation is repeated. In this operation, a
two-stage compression refrigeration cycle as shown in FIG. 3 is
achieved in the refrigerant circuit (6).
[0071] In the freezer unit (5), the refrigeration oil trapped in
the oil separator (64) is returned to the suction pipe (68) via the
oil return path (65), and then collected in the freezer compressor
(55).
[0072] By the effect of the pressure regulating valve (71), the
pressure is in the suction side of the high stage compressors (11,
12) becomes lower than that in the dome of the low stage compressor
(55). Therefore, when the solenoid valve (73) is opened, the
refrigeration oil which is accumulated in the dome over the
predetermined height H is ejected to the suction side of the first
and second compressors (11, 12) through the oil return path (72)
bypassing the pressure regulating valve (71). Thus, the level of
the refrigeration oil in the dome of the freezer compressor (55) is
maintained not to exceed the predetermined height H. Further, the
first and second compressors (11, 12) are prevented from being
short of the refrigeration oil.
Effect of the Embodiment
[0073] According to the present embodiment, the oil return means
(70) makes it possible to return the refrigeration oil accumulated
in the dome of the freezer compressor (55) to the first and second
compressors (11, 12). Therefore, the first and second compressors
(11, 12) will never be short of the refrigeration oil, thereby
eliminating the need of filling additional refrigeration oil and
saving time and effort to fill the refrigeration oil. Further,
since the refrigeration oil is prevented from being accumulated in
the freezer compressor (55) over the predetermined height H,
rotational resistance caused by the refrigeration oil in the
freezer compressor (55) is reduced. Thus, the system is operated
with improved efficiency.
[0074] The pressure regulating valve (71) is provided on the
discharge side of the freezer compressor (55) and the pressure on
the suction side of the first and second compressors (11, 12) is
made lower than the pressure in the dome of the freezer compressor
(55). Further, the oil return path (72) is connected to the dome of
the freezer compressor (55) at one end and to the suction side of
the first and second compressors (11, 12) at the other end. As a
result, the refrigeration oil accumulated in the dome of the
freezer compressor (55) is returned to the first and second
compressors (11, 12). With such a simple structure, time and effort
to fill the refrigeration oil are saved and the refrigeration
system is operated efficiently with a minimum amount of the
refrigeration oil.
FIRST MODIFICATION OF EMBODIMENT
[0075] Explanation of a first modification of the embodiment is
provided below. FIG. 4 shows a refrigeration circuit diagram of a
refrigeration system (1) according to the first modification. The
refrigeration system (1) of the first modification is different
from that the above-described embodiment in that the oil return
path (72) is connected to a different part of the freezer
compressor (55).
[0076] More specifically, the oil return path (72) is connected to
the oil return pipe (65) connected to the oil separator (64) at one
end and to the refrigerant pipe (60) by bypassing the pressure
regulating valve (71) at the other end. The oil return path (72) is
provided with a solenoid valve (73) in the same manner as the above
embodiment. Further, the oil return pipe (65) is also provided with
a solenoid valve (66), which is different from the above
embodiment.
[0077] According to the first modification, the solenoid valve (66)
of the oil return pipe (65) and the solenoid valve (73) of the oil
return path (72) are controlled such that the refrigeration oil
trapped in the oil separator (64) is returned to either the freezer
compressor (55) or the first and second compressors (11, 12). More
specifically, when the refrigeration oil is returned from the oil
separator (64) to the freezer compressor (55), the solenoid valve
(66) of the oil return pipe (65) is opened and the solenoid valve
(73) of the oil return path (72) is closed. On the other hand, when
the refrigeration oil is returned from the oil separator (64) to
the first and second compressors (11, 12), the solenoid valve (66)
of the oil return pipe (65) is closed and the solenoid valve (73)
of the oil return path (72) is opened.
SECOND MODIFICATION OF EMBODIMENT
[0078] Explanation of a second modification of the present
embodiment is provided below. FIG. 5 shows a refrigeration circuit
diagram of a refrigeration system (1) according to the second
modification. In the refrigeration system (1) of the second
modification, the oil return means (70) includes a first oil return
path (72a) and a second oil return path (72b). The first oil return
path (72a) is connected to the freezer compressor (55) in the same
manner as the oil return path of the above-described embodiment,
while the second oil return path (72b) is connected to the freezer
compressor (55) in the same manner as the oil return path of the
first modification.
[0079] According to the second modification, the refrigeration oil
is usually returned from the freezer compressor (5) to the first
and second compressors (11, 12) through the first oil return path
(72a) as the oil return means (70). That is to say, a solenoid
valve (73a) of the first oil return path (72a) is opened, while a
solenoid valve (73b) of the second oil return path (72b) is closed.
The second oil return path (72b) is used when the solenoid valve
(73a) of the first oil return path (72a) fails to operate
properly.
THIRD MODIFICATION OF EMBODIMENT
[0080] Explanation of a third modification of the embodiment is
provided. FIG. 6 shows a refrigeration circuit diagram of a
refrigeration system (1) according to the third modification.
Different from the above embodiment, the refrigeration system (1)
of the third modification includes a plurality of freezer
compressors (55a, 55b, 55c) as the low stage compressor of the
freezer unit (5). In the third modification, three freezer
compressors (55a, 55b, 55c) are provided in the refrigerant circuit
(6). However, the number of the freezer compressors (55a, 55b, 55c)
is given as an example. Therefore, two or four or more freezer
compressors (55a, 55b, 55c) may be provided in the refrigerant
circuit (6).
[0081] More specifically, the freezer unit (5) includes a first
freezer compressor (55a), a second freezer compressor (55b) and a
third freezer compressor (55c) arranged parallel to each other
between the freezer condenser (56) and the oil separator (64).
Refrigerant pipes of the freezer compressors (55a, 55b, 55c) on the
discharge side are joined together and connected to the oil
separator (64). Refrigerant pipes, which are branched from the
suction pipe (68) connected to the freezer condenser (56) at one
end, are connected to the suction side of the freezer compressors
(55a, 55b, 55c).
[0082] Referring to FIG. 6, the first freezer compressor (55a) on
the left side has a refrigerant pipe on the suction side thereof
connected to a dome of the second freezer compressor (55b) located
in the middle with a first oil equalizing pipe (67a). The second
freezer compressor (55b) has a refrigerant pipe on the suction side
thereof connected to a dome of the third freezer compressor (55c)
on the right side with a second oil equalizing pipe (67b). The oil
equalizing pipes (67a, 67b) function as an oil return path for
returning the refrigeration oil from the second and third freezer
compressors (55b, 55c) to the first freezer compressor (55a). The
oil equalizing pipes (67a, 67b) are connected to certain positions
of the domes of the second and third freezer compressors (55b,
55c), respectively, such that the level of the refrigeration oil in
the dome corresponds to the predetermined height H. The oil
equalizing pipes (67a, 67b) are provided with solenoid valves (74a,
74b), respectively.
[0083] An oil return path (72) is connected to a dome of the first
freezer compressor (55a), which is a low stage compressor in charge
of returning the refrigeration oil to the high stage compressor. In
the same manner as the above embodiment, the oil return path (72)
is connected to a certain position of the first freezer compressor
(55a) at one end such that the level of the refrigeration oil in
the dome corresponds to the predetermined height H. The other end
of the oil return path (72) bypasses the pressure regulating valve
(71) and is connected to the refrigerant pipe (60).
[0084] The oil return pipe (65) is connected to the refrigerant
pipe on the suction side of the third freezer compressor (55c). The
refrigeration oil separated from the refrigerant in the oil
separator (64) is sent to the refrigerant pipe on the suction side
of the third freezer compressor (55c) through the oil return pipe
(65), and then sucked into the third freezer compressor (55c)
together with the refrigerant.
[0085] According to the third modification, the amounts of the
refrigeration oil in the freezer compressors (55a, 55b, 55c) are
equalized using the solenoid valves (74a, 74b). When the solenoid
valve (74b) of the second oil equalizing pipe (67b) is opened, the
refrigeration oil accumulated in the dome of the third freezer
compressor (55c) over the predetermined height H flows into the
refrigerant pipe on the suction side of the second freezer
compressor (55b) through the second oil equalizing pipe (67b), and
is sucked into the second freezer compressor (55b) together with
the refrigerant. On the other hand, when the solenoid valve (74a)
of the first oil equalizing pipe (67a) is opened, the refrigeration
oil accumulated in the dome of the second freezer compressor (55b)
over the predetermined height H flows into the refrigerant pipe on
the suction side of the first freezer compressor (55a) through the
first oil equalizing pipe (67a), and is sucked into the first
freezer compressor (55a) together with the refrigerant.
[0086] Further, according to the third modification, in the same
manner as the above embodiment, the solenoid valve (73) of the oil
return path (72) is used to return the refrigeration oil from the
first freezer compressor (55a) to the first and second compressors
(11, 12). When the solenoid valve (73) is opened, the refrigeration
oil accumulated in the dome of the first freezer compressor (55a)
over the predetermined height H flows into the oil return path (72)
bypassing the pressure regulating valve (71) and sent to the
suction side of the first and second compressors (11, 12).
[0087] According to the third modification, as described above, the
refrigeration oil accumulated in the domes of the second and third
freezer compressors (55b, 55c) is collected in the first freezer
compressor (55a), and then returned to the first and second
compressors (11, 12) as the high stage compressors.
[0088] In the present modification, the oil return pipe (65) may be
connected to the refrigerant pipe on the suction side of the second
freezer compressor (55b) as shown in FIG. 7. In the refrigerant
circuit (6) shown in FIG. 7, the second and third freezer
compressors (55b, 55c) are constant-speed compressors whose volume
is fixed. Further, an end of the second oil equalizing pipe (67b)
on the discharge side is connected to part of the first oil
equalizing pipe (67a) downstream of the solenoid valve (74a). When
the solenoid valve (74a) of the first oil equalizing pipe (67a) is
opened, the refrigerant oil accumulated in the dome of the second
freezer compressor (55b) is sent to the suction side of the first
freezer compressor (55a). On the other hand, when the solenoid
valve (74b) of the second oil equalizing pipe (67b) is opened, the
refrigeration oil accumulated in the dome of the third freezer
compressor (55c) is sent to the suction side of the first freezer
compressor (55a). Further, the refrigeration oil separated from the
refrigerant in the oil separator (64) flows into the refrigerant
pipe on the suction side of the second freezer compressor (55b)
through the oil return pipe (65) and is sucked into the second
freezer compressor (55b) together with the refrigerant.
OTHER EMBODIMENTS
[0089] The above-described embodiment of the present invention may
be configured as follows.
[0090] In the present embodiment, the refrigeration system (1)
includes the refrigerant circuit (6) realized by connecting the
outdoor unit (2), the indoor unit (3), the cold storage unit (4)
and the freezer unit (5). However, the present invention is also
applicable to any refrigeration system as long as it includes a
refrigerant circuit (6) including a low stage compressor (55) and
high stage compressors (11, 12) which are connected in series to
perform the two-stage compression refrigeration cycle.
INDUSTRIAL APPLICABILITY
[0091] Thus, as described above, the present invention is useful as
a refrigeration system which includes a refrigeration circuit
capable of performing a two-stage compression refrigeration cycle
and is generally used in convenience stores and supermarkets.
* * * * *