U.S. patent application number 11/922579 was filed with the patent office on 2009-02-05 for refrigeration system.
Invention is credited to Koichi Kita, Azuma Kondo, Kazuyoshi Nomura, Yoshinari Oda, Masaaki Takegami, Kenji Tanimoto, Takeo Ueno.
Application Number | 20090031737 11/922579 |
Document ID | / |
Family ID | 37636975 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090031737 |
Kind Code |
A1 |
Ueno; Takeo ; et
al. |
February 5, 2009 |
Refrigeration System
Abstract
A refrigerant circuit (20) includes a low stage compressor (101,
102, 121, 122), a high stage compressor (41, 42, 43), an outdoor
heat exchanger (44) and a utilization side heat exchanger (83, 93).
During a defrosting operation of the refrigeration system (10), the
high stage compressor (41, 42, 43) is driven. Refrigerant
discharged from the high stage compressor (41, 42, 43) is pumped
into the utilization side heat exchanger (83, 93) to heat frost on
it from its inside. Thereafter, the refrigerant evaporates in the
outdoor heat exchanger (44), is then compressed by the high stage
compressor (41, 42, 43) and is sent again to the utilization side
heat exchanger (83, 93).
Inventors: |
Ueno; Takeo; (Osaka, JP)
; Takegami; Masaaki; (Osaka, JP) ; Kita;
Koichi; (Osaka, JP) ; Tanimoto; Kenji; (Osaka,
JP) ; Oda; Yoshinari; (Osaka, JP) ; Nomura;
Kazuyoshi; (Osaka, JP) ; Kondo; Azuma; (Osaka,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
37636975 |
Appl. No.: |
11/922579 |
Filed: |
July 3, 2006 |
PCT Filed: |
July 3, 2006 |
PCT NO: |
PCT/JP2006/313233 |
371 Date: |
December 20, 2007 |
Current U.S.
Class: |
62/151 ;
62/196.1; 62/291; 62/470; 62/510 |
Current CPC
Class: |
F25B 2400/13 20130101;
F25B 2400/0401 20130101; F25B 2400/075 20130101; F25B 13/00
20130101; F25B 47/025 20130101; F25B 2313/02741 20130101; F25B
2313/0233 20130101; F25B 1/10 20130101; F25B 2313/006 20130101;
F25B 2400/22 20130101 |
Class at
Publication: |
62/151 ; 62/510;
62/470; 62/196.1; 62/291 |
International
Class: |
F25D 21/06 20060101
F25D021/06; F25B 1/10 20060101 F25B001/10; F25B 41/00 20060101
F25B041/00; F25D 21/14 20060101 F25D021/14; F25B 43/02 20060101
F25B043/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 8, 2005 |
JP |
2005-200240 |
Dec 12, 2005 |
JP |
2005-357686 |
Claims
1. A refrigeration system including a refrigerant circuit in which
a low stage compressor, a high stage compressor, a heat-source side
heat exchanger and a utilization side heat exchanger are connected,
the refrigeration system being operable in a two-stage compression
refrigeration cycle by driving the low stage compressor and the
high stage compressor during a cooling operation in which the
heat-source side heat exchanger serves as a condenser and the
utilization side heat exchanger serves as an evaporator, wherein
the refrigeration system is configured to be switchable between the
cooling operation and a defrosting operation for defrosting the
utilization side heat exchanger and operate, during the defrosting
operation, in a refrigeration cycle in which the high stage
compressor is driven, the utilization side heat exchanger serves as
a condenser and the heat-source side heat exchanger serves as an
evaporator.
2. The refrigeration system of claim 1, wherein the refrigeration
system is configured to keep the low stage compressor off during
the defrosting operation.
3. The refrigeration system of claim 2, further including a bypass
pipe that connects the suction side and the discharge side of the
low stage compressor and includes a shut-off valve, the shut-off
valve being open during the defrosting operation and being closed
during the cooling operation.
4. The refrigeration system of claim 2 or 3, wherein a drain pan is
disposed below the utilization side heat exchanger, the refrigerant
circuit comprises a utilization side expansion valve connected
upstream of the utilization side heat exchanger in the cooling
operation and a drain pan heating pipe connected upstream of the
utilization side expansion valve in the cooling operation and
disposed along the drain pan, and the refrigeration system is
configured so that, during the cooling operation, refrigerant
condensed in the heat-source side heat exchanger flows through the
drain pan heating pipe, is then reduced in pressure by the
utilization side expansion valve and is then fed into the
utilization side heat exchanger.
5. The refrigeration system of claim 4, wherein the refrigerant
circuit includes a heat-source side expansion valve disposed
upstream of the heat-source side heat exchanger in the defrosting
operation, and the refrigeration system is configured so that,
during the defrosting operation, refrigerant condensed in the
utilization side heat exchanger flows through the fully-open
utilization side expansion valve and the drain pan heating pipe, is
then reduced in pressure by the heat-source side expansion valve
and is then fed into the heat-source side heat exchanger.
6. The refrigeration system of claim 1, wherein the refrigeration
system is configured, during the defrosting operation, to operate
in a refrigeration cycle in which refrigerant discharged from the
high stage compressor is further compressed by the low stage
compressor, the utilization side heat exchanger serves as a
condenser and the heat-source side heat exchanger serves as an
evaporator.
7. The refrigeration system of claim 6, wherein the refrigeration
system is configured so that, during the defrosting operation, part
of refrigerant discharged from the high stage compressor is further
compressed by the low stage compressor and then returned to the
discharge side of the high stage compressor.
8. The refrigeration system of claim 7, wherein the refrigeration
system is configured to return, during the defrosting operation,
part of refrigerant condensed in the utilization side heat
exchanger to the suction side of the low stage compressor.
9. The refrigeration system of claim 1, further including a liquid
return pipe connecting the suction side and the discharge side of
the low stage compressor, the refrigeration system being
configured, after the completion of the defrosting operation, to
perform a refrigerant recovery action by driving only the high
stage compressor to allow the high stage compressor to suck
refrigerant built up in the utilization side heat exchanger through
the liquid return pipe.
10. The refrigeration system of claim 9, further including: an oil
separator disposed to the discharge side of the low stage
compressor; and an oil return pipe for sending refrigerating
machine oil recovered by the oil separator to the suction side of
the low stage compressor, the oil return pipe serving also as the
liquid return pipe during the refrigerant recovery action.
11. The refrigeration system of claim 10, wherein the oil separator
is configured, during the refrigerant recovery action, to separate
gas refrigerant from refrigerant flowing thereinto from the liquid
return pipe and send the gas refrigerant to the suction side of the
high stage compressor.
Description
TECHNICAL FIELD
[0001] This invention relates to refrigeration systems operating in
a two-stage compression refrigeration cycle and particularly
relates to techniques for defrosting a utilization side heat
exchanger for cooling the internal air in a freezer or the
like.
BACKGROUND ART
[0002] Refrigeration systems are conventionally known that include
a refrigerant circuit operating in a refrigeration cycle and they
are widely used as cooling machines for chillers or freezers for
storing food and other materials.
[0003] For example, Patent Document 1 discloses a refrigeration
system for cooling the internal air of a freezer such as in a
convenience store. Connected in the refrigerant circuit of this
refrigeration system are a low stage compressor, a high stage
compressor, an outdoor heat exchanger (heat-source side heat
exchanger) and a cooling heat exchanger (utilization side heat
exchanger). This refrigeration system operates in a so-called
two-stage compression refrigeration cycle in which the cooling heat
exchanger serves as an evaporator, the heat-source side heat
exchanger serves as a condenser and the refrigerant is compressed
in two stages by driving the low stage compressor and the high
stage compressor.
[0004] In the refrigeration system, the evaporation temperature of
refrigerant in the cooling heat exchanger is set at a relatively
low temperature. This causes a problem that moisture in the air
adheres to the cooling heat exchanger and freezes on it and the
frost on it prevents the cooling of the internal air in the
freezer. Therefore, such a refrigeration system must perform an
operation of melting the frost on the cooling heat exchanger, i.e.,
a defrosting operation for the cooling heat exchanger.
[0005] The defrosting operation is commonly carried out using an
electric heater as disclosed, for example, in Patent Document 2. In
this defrosting operation, air heated by the electric heater is
supplied to the cooling heat exchanger to heat the frost on the
cooling heat exchanger with the air and thereby melt it.
Patent Document 1: Published Japanese Patent Application No.
2002-228297
[0006] Patent Document 2: Published Japanese Patent Application No.
H09-324978
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0007] However, since, in the defrosting operation in the above
Patent Document 2, the frost on the cooling heat exchanger is
melted by supplying air heated by the electric heater to the
cooling heat exchanger, the heated air may flow into the freezer
and raise the internal temperature of the freezer. Furthermore, the
frost on the cooling heat exchanger must be heated with air from
the outside surface of the cooling heat exchanger. Therefore, it
takes a long time (for example, 40 minutes or more) to defrost the
cooling heat exchanger, which invites another problem that the
power consumption is large and the running cost of the
refrigeration system thereby increases.
[0008] The present invention has been made in view of the foregoing
points and an object thereof is that the refrigeration system
operating in a two-stage compression refrigeration cycle reduces
the time taken to defrost the utilization side heat exchanger and
reduces the power consumption during the defrosting operation.
Means to Solve the Problems
[0009] A first aspect of the invention is directed to a
refrigeration system including a refrigerant circuit (20) in which
a low stage compressor (101, 102, 121, 122), a high stage
compressor (41, 42, 43), a heat-source side heat exchanger (44) and
a utilization side heat exchanger (83, 93) are connected, the
refrigeration system being operable in a two-stage compression
refrigeration cycle by driving the low stage compressor (101, 102,
121, 122) and the high stage compressor (41, 42, 43) during a
cooling operation in which the heat-source side heat exchanger (44)
serves as a condenser and the utilization side heat exchanger (83,
93) serves as an evaporator. Furthermore, the refrigeration system
is configured to be switchable between the cooling operation and a
defrosting operation for defrosting the utilization side heat
exchanger (83, 93) and operate, during the defrosting operation, in
a refrigeration cycle in which the high stage compressor (41, 42,
43) is driven, the utilization side heat exchanger (83, 93) serves
as a condenser and the heat-source side heat exchanger (44) serves
as an evaporator.
[0010] During the cooling operation in the first aspect of the
invention, the refrigerant circuit (20) operates in a two-stage
compression refrigeration cycle, whereby air in a freezer or the
like is cooled by the utilization side heat exchanger (83, 93)
serving as an evaporator. Specifically, refrigerant compressed by
the high stage compressor (41, 42, 43) is condensed in the
heat-source side heat exchanger (44) and then reduced in pressure,
for example, by an expansion valve. The refrigerant evaporates in
the utilization side heat exchanger (83, 93), while the air in the
freezer or the like gives heat of evaporation to the refrigerant
and is thereby cooled. The refrigerant having evaporated in the
utilization side heat exchanger (83, 93) is compressed by the low
stage compressor (101, 102, 121, 122). The refrigerant discharged
from the low stage compressor (101, 102, 121, 122) is sucked into
and further compressed by the high stage compressor (41, 42, 43)
and then sent again to the heat-source side heat exchanger
(44).
[0011] During the defrosting operation in this aspect of the
invention, the high stage compressor (41, 42, 43) is put into
operation so that the utilization side heat exchanger (83, 93) is
defrosted. Specifically, refrigerant compressed by the high stage
compressor (41, 42, 43) is pumped in a high-temperature and
high-pressure state into the utilization side heat exchanger (83,
93). In the utilization side heat exchanger (83, 93), frost
adhering to its surface is melted by heat from its inside. On the
other hand, the refrigerant gives heat of melting to the frost and
thereby condenses. The refrigerant having condensed in the
utilization side heat exchanger (83, 93) is reduced in pressure,
for example, by an expansion valve, and then flows through the
heat-source side heat exchanger (44). In the heat-source side heat
exchanger (44), the refrigerant takes heat from air and thereby
evaporates. The refrigerant having evaporated in the heat-source
side heat exchanger (44) is compressed again by the high stage
compressor (41, 42, 43).
[0012] A second aspect of the invention is the refrigeration system
according to the first aspect of the invention, wherein the
refrigeration system is configured to keep the low stage compressor
(101, 102, 121, 122) off during the defrosting operation.
[0013] In the second aspect of the invention, during the defrosting
operation, the low stage compressor (101, 102, 121, 122) is shut
off and the high stage compressor (41, 42, 43) is put into
operation, whereby the defrosting operation is performed as in the
first aspect of the invention.
[0014] A third aspect of the invention is the refrigeration system
according to the second aspect of the invention, further including
a bypass pipe (119, 139) that connects the suction side and the
discharge side of the low stage compressor (41, 42, 43) and
includes a shut-off valve (SV-2, SV-4), the shut-off valve (SV-2,
SV-4) being open during the defrosting operation and being closed
during the cooling operation.
[0015] During the cooling operation in the third aspect of the
invention, the shut-off valve (SV-2, SV-4) of the bypass pipe (119,
139) is closed to interrupt communication between the suction side
and the discharge side of the low stage compressor (83, 93).
Therefore, the refrigerant having evaporated in the utilization
side heat exchanger (83, 93) is sucked into the low stage
compressor (101, 102, 121, 122) through the suction side thereof,
compressed therein and then sent to the high stage compressor (41,
42, 43).
[0016] On the other hand, during the defrosting operation in this
aspect of the invention, the shut-off valve (SV-2, SV-4) of the
bypass pipe (119, 139) is open to provide communication between the
suction side and the discharge side of the low stage compressor
(83, 93). Therefore, the refrigerant sent from the high stage
compressor (41, 42, 43) to the discharge side of the low stage
compressor (101, 102, 121, 122) is sent via the bypass pipe (119,
139) to the suction side of the low stage compressor (101, 102,
121, 122). In other words, during the defrosting operation, the
refrigerant discharged from the high stage compressor (41, 42, 43)
bypasses the low stage compressor (101, 102, 121, 122) and is sent
to the utilization side heat exchanger (83, 93).
[0017] A fourth aspect of the invention is the refrigeration system
according to the second or third aspect of the invention, wherein a
drain pan (85, 95) is disposed below the utilization side heat
exchanger (83, 93), the refrigerant circuit (20) comprises a
utilization side expansion valve (82, 92) connected upstream of the
utilization side heat exchanger (83, 93) in the cooling operation
and a drain pan heating pipe (81, 91) connected upstream of the
utilization side expansion valve (82, 92) in the cooling operation
and disposed along the drain pan (85, 95), and the refrigeration
system is configured so that, during the cooling operation,
refrigerant condensed in the heat-source side heat exchanger (44)
flows through the drain pan heating pipe (81, 91), is then reduced
in pressure by the utilization side expansion valve (82, 92) and is
then fed into the utilization side heat exchanger (83, 93).
[0018] In the fourth aspect of the invention, a drain pan (85, 95)
is disposed below the utilization side heat exchanger (83, 93). The
drain pan (85, 95) recovers dew condensation water dropping from
the surface of the utilization side heat exchanger (83, 93) and
frost falling off from it. Furthermore, a drain pan heating pipe
(81, 91) is disposed close to the drain pan (85, 95).
[0019] In this case, during the cooling operation in this aspect of
the invention, refrigerant condensed in the heat-source side heat
exchanger (44) flows through the drain pan heating pipe (81, 91).
As a result, frost recovered in the drain pan (85, 95) and ice
blocks produced by freezing of dew condensation water in the drain
pan (85, 95) melt with heat from the refrigerant flowing through
the drain pan heating pipe (81, 91). On the other hand, the
refrigerant flowing through drain pan heating pipe (81, 91) gives
heat of melting to the frost and ice blocks and is thereby cooled.
In other words, the refrigerant gradually decreases its enthalpy as
it flows through the drain pan heating pipe (81, 91). Thereafter,
the refrigerant is reduced in pressure by the utilization side
expansion valve (82, 92) and then evaporates in the utilization
side heat exchanger (83, 93). As a result, air in a freezer or the
like is cooled by the utilization side heat exchanger (83, 93).
[0020] A fifth aspect of the invention is the refrigeration system
according to the fourth aspect of the invention, wherein the
refrigerant circuit (20) includes a heat-source side expansion
valve (48) disposed upstream of the heat-source side heat exchanger
(44) in the defrosting operation, and the refrigeration system is
configured so that, during the defrosting operation, refrigerant
condensed in the utilization side heat exchanger (83, 93) flows
through the fully-open utilization side expansion valve (82, 92)
and the drain pan heating pipe (81, 91), is then reduced in
pressure by the heat-source side expansion valve (48) and is then
fed into the heat-source side heat exchanger (44).
[0021] During the defrosting operation in the fifth aspect of the
invention, the refrigerant condensed by heating frost adhering to
the utilization side heat exchanger (83, 93) from its inside flows
through the fully-open utilization side expansion valve (82, 92)
and then flows through the drain pan heating pipe (81, 91). As a
result, frost recovered in the drain pan (85, 95) and ice blocks
produced in the drain pan (85, 95) melt with heat from the
refrigerant flowing through the drain pan heating pipe (81, 91).
Thereafter, the refrigerant is reduced in pressure by the
heat-source side expansion valve (48) and then flows through the
heat-source side heat exchanger (44). In the heat-source side heat
exchanger (44), the refrigerant takes heat from air and thereby
evaporates. The refrigerant having evaporated in the heat-source
side heat exchanger (44) is compressed by the high stage compressor
(41, 42, 43) and sent again to the utilization side heat exchanger
(41, 42, 43).
[0022] A sixth aspect of the invention is the refrigeration system
according to the first aspect of the invention, wherein the
refrigeration system is configured, during the defrosting
operation, to operate in a refrigeration cycle in which refrigerant
discharged from the high stage compressor (41, 42, 43) is further
compressed by the low stage compressor (101, 102, 121, 122), the
utilization side heat exchanger (83, 93) serves as a condenser and
the heat-source side heat exchanger (44) serves as an
evaporator.
[0023] In the sixth aspect of the invention, unlike the second
aspect of the invention, both the high stage compressor (41, 42,
43) and the low stage compressor (101, 102, 121, 122) are put into
operation during the defrosting operation. Specifically,
refrigerant compressed by the high stage compressor (41, 42, 43) is
further compressed by the low stage compressor (101, 102, 121, 122)
and then sent to the utilization side heat exchanger (83, 93) for
use in defrosting it. Since, during the defrosting operation in
this aspect of the invention, refrigerant is thus compressed by
both the high stage compressor (41, 42, 43) and the low stage
compressor (101, 102, 121, 122), this increases the amount of heat
given to the refrigerant during the defrosting operation.
[0024] A seventh aspect of the invention is the refrigeration
system according to the sixth aspect of the invention, wherein the
refrigeration system is configured so that, during the defrosting
operation, part of refrigerant discharged from the high stage
compressor (41, 42, 43) is further compressed by the low stage
compressor (101, 102, 121, 122) and then returned to the discharge
side of the high stage compressor (41, 42, 43).
[0025] During the defrosting operation in the seventh aspect of the
invention, part of the high stage compressor (41, 42, 43) is sucked
into the low stage compressor (101, 102, 121, 22) and further
compressed therein. The refrigerant compressed by the low stage
compressor (101, 102, 121, 122) is mixed with the refrigerant
discharged from the high stage compressor (41, 42, 43), and the
mixed refrigerant is sent to the utilization side heat exchanger
(83, 93) for use in defrosting it. Since, during the defrosting
operation in this aspect of the invention, part of refrigerant
discharged from the high stage compressor (41, 42, 43) is
compressed by the low stage compressor (101, 102, 121, 122), this
increases the amount of heat given to the refrigerant during the
defrosting operation.
[0026] An eighth aspect of the invention is the refrigeration
system according to the seventh aspect of the invention, wherein
the refrigeration system is configured to return, during the
defrosting operation, part of refrigerant condensed in the
utilization side heat exchanger (83, 93) to the suction side of the
low stage compressor (101, 102, 121, 122).
[0027] In the eighth aspect of the invention, during the defrosting
operation in the seventh aspect of the invention, part of
refrigerant liquefied by condensation in the utilization side heat
exchanger (83, 93) is sent to the suction side of the low stage
compressor (101, 102, 121, 122). In other words, during the
defrosting operation in this aspect of the invention, so-called
liquid injection is carried out for the low stage compressor (101,
102, 121, 122). As a result, the refrigerant sucked in the low
stage compressor (101, 102, 121, 122) is cooled.
[0028] A ninth aspect of the invention is the refrigeration system
according to the first aspect of the invention, further including a
liquid return pipe (141, 142) connecting the suction side and the
discharge side of the low stage compressor (101, 102, 121, 122),
the refrigeration system being configured, after the completion of
the defrosting operation, to perform a refrigerant recovery action
by driving only the high stage compressor (41, 42, 43) to allow the
high stage compressor (41, 42, 43) to suck refrigerant built up in
the utilization side heat exchanger (83, 93) through the liquid
return pipe (141, 142).
[0029] The refrigerant circuit (20) in the ninth aspect of the
invention is provided with a liquid return pipe (141, 142)
connecting the suction side and the discharge side of the low stage
compressor (101, 102, 121, 122). Furthermore, in performing the
cooling operation again after the completion of the defrosting
operation, the refrigeration system according to this aspect of the
invention performs a refrigerant recovery action in order to
prevent liquid refrigerant from being sucked into the low stage
compressor (101, 102, 121, 122).
[0030] Specifically, when the above defrosting operation is carried
out, refrigerant in the utilization side heat exchanger (83, 93)
releases heat of melting for defrosting and thereby gradually
condenses. Therefore, after the completion of the defrosting
operation, liquid refrigerant may be built up in the utilization
side heat exchanger (83, 93). If in this state the above cooling
operation is carried out by driving both the low stage compressor
(101, 102, 121, 122) and the high stage compressor (41, 42, 43),
liquid refrigerant built up in the utilization side heat exchanger
(83, 93) will be sucked into the low stage compressor (101, 102,
121, 122) to cause a so-called liquid compression phenomenon
(liquid back phenomenon), which may break down the low stage
compressor (101, 102, 121, 122).
[0031] To cope with this, in this aspect of the invention, the
following refrigerant recovery action is carried out after the
completion of the defrosting operation. In the refrigerant recovery
action, only the high stage compressor (41, 42, 43) is driven and
the low stage compressor (101, 102, 121, 122) is shut off. Thus,
refrigerant sent to the utilization side heat exchanger (83, 93) by
driving the high stage compressor (41, 42, 43) flows out of the
utilization side heat exchanger (83, 93) together with liquid
refrigerant built up in the utilization side heat exchanger (83,
93). The refrigerant flows through the liquid return pipe (141,
142) so as to bypass the low stage compressor (101, 102, 121, 122)
in off state and is then sucked into the high stage compressor (41,
42, 43).
[0032] As described above, in this aspect of the invention, liquid
refrigerant built up in the utilization side heat exchanger (83,
93) is sucked via the liquid return pipe (141, 142) into the high
stage compressor (41, 42, 43) after the completion of the
defrosting operation. Therefore, it can be surely avoided that
after the restart of the cooling operation after the defrosting
operation, a liquid compression phenomenon occurs in the low stage
compressor (101, 102, 121, 122).
[0033] Furthermore, when such a refrigerant recovery action is
carried out, liquid refrigerant having flowed out of the
utilization side heat exchanger (83, 93) is sucked via the liquid
return pipe (141, 142) and the other connection pipes into the high
stage compressor (41, 42, 43). Therefore, the liquid refrigerant
can easily take heat from the air surrounding the pipes to
evaporate when flowing through the pipes. Hence, it can be also
avoided that during the refrigerant recovery action, liquid
refrigerant is sucked into the high stage compressor (41, 42,
43).
[0034] A tenth aspect of the invention is the refrigeration system
according to the ninth aspect of the invention, further including
an oil separator (143, 144) disposed to the discharge side of the
low stage compressor (101, 102, 121, 122) and an oil return pipe
(141, 142) for sending refrigerating machine oil recovered by the
oil separator (143, 144) to the suction side of the low stage
compressor (101, 102, 121, 122), the oil return pipe (141, 142)
serving also as the liquid return pipe during the refrigerant
recovery action.
[0035] In the tenth aspect of the invention, an oil separator (143,
144) is disposed to the discharge side of the low stage compressor
(101, 102, 121, 122). When refrigerant discharged from the low
stage compressor (101, 102, 121, 122) flows into the oil separator
(143, 144) during the above cooling operation, oil is separated
from the refrigerant in the oil separator (143, 144) and recovered
therein. The refrigerant after oil separation is sent to the high
stage compressor (41, 42, 43) and further compressed therein, while
the recovered oil is sent via the oil return pipe (141, 142) to the
suction side of the low stage compressor (101, 102, 121, 122) and
used again to lubricate sliding parts of the low stage compressor
(101, 102, 121, 122).
[0036] In this aspect of the invention, the oil return pipe (141,
142) serves also as the oil return pipe in the ninth aspect of the
invention. In other words, in the above refrigerant recovery
action, the liquid refrigerant having flowed out of the utilization
side heat exchanger (83, 93) is sent via the oil return pipe (141,
142) and the oil separator (143, 144) to the high stage compressor
(41, 42, 43).
[0037] An eleventh aspect of the invention is the refrigeration
system according the tenth aspect of the invention, wherein the oil
separator (143, 144) is configured, during the refrigerant recovery
action, to separate gas refrigerant from refrigerant flowing
thereinto from the liquid return pipe (141, 142) and send the gas
refrigerant to the suction side of the high stage compressor (41,
42, 43).
[0038] In the eleventh aspect of the invention, during the
refrigerant recovery action, the oil separator (143, 144) functions
as a gas-liquid separator. Specifically, in the refrigerant
recovery action in this aspect of the invention, when refrigerant
including liquid refrigerant built up in the utilization side heat
exchanger (83, 93) flows via the oil return pipe (141, 142) into
the oil separator (143, 144), the refrigerant separates, in the oil
separator (143, 144), into gas refrigerant and liquid refrigerant.
Furthermore, in the refrigerant recovery action, only the gas
refrigerant separated in the oil separator (143, 144) is sent to
the high stage compressor (41, 42, 43). This effectively avoids a
liquid compression phenomenon in the high stage compressor (41, 42,
43) during the refrigerant recovery action.
EFFECTS OF THE INVENTION
[0039] According to the present invention, during the defrosting
operation, frost adhering to the surface of the utilization side
heat exchanger (83, 93) is heated from the inside of the
utilization side heat exchanger (83, 93) by feeding the refrigerant
discharged by the high stage compressor (41, 42, 43) into the
utilization side heat exchanger (83, 93). Therefore, the
utilization side heat exchanger (83, 93) can be effectively
defrosted, which reduces the time taken to defrost it.
[0040] Furthermore, according to the present invention, since
during the defrosting operation the heat-source side heat exchanger
(44) serves as an evaporator, heat given from air to refrigerant
can be used to defrost the utilization side heat exchanger (83,
93). In other words, according the present invention, heat given to
refrigerant by the high stage compressor (41, 42, 43) and heat
given to refrigerant by the heat-source side heat exchanger (44)
are both used to defrost the utilization side heat exchanger (83,
93). This reduces the defrosting time and in turn reduces the power
consumption of the refrigeration system during the defrosting
operation.
[0041] Particularly, since in the second aspect of the invention
the defrosting operation is carried out with the low stage
compressor (101, 102, 121, 122) off, this reduces the operating
power during the defrosting operation.
[0042] Furthermore, according to the third aspect of the invention,
by opening and closing the shut-off valve (SV-2, SV-4) of the
bypass pipe (119, 139), the refrigeration system can easily switch
between the cooling operation of compressing refrigerant evaporated
by the utilization side heat exchanger (83, 93) in two stages,
i.e., in the low stage compressor (101, 102, 121, 122) and the high
stage compressor (41, 42, 43), and the defrosting operation of
allowing refrigerant discharged from the high stage compressor (41,
42, 43) to bypass the low stage compressor (101, 102, 121, 22) and
sending the refrigerant to the utilization side heat exchanger (83,
93).
[0043] Furthermore, in the fourth aspect of the invention, during
the cooling operation, refrigerant condensed in the heat-source
side heat exchanger (44) is allowed to flow through the drain pan
heating pipes (81, 91) before being reduced in pressure by the
utilization side expansion valve (82, 92). Therefore, according to
this aspect of the invention, heat of condensation of refrigerant
can be used to melt frost and ice blocks in the drain pan (85, 95)
and the water thus obtained can be promptly drained as drainage
away from the drain pan (85, 95). Furthermore, the refrigerant
flowing through the drain pan heating pipe (81, 91) gives heat to
frost and ice blocks in the drain pan (85, 95) and thereby
gradually increases its degree of supercooling. Therefore, the
enthalpy of refrigerant flowing into the utilization side heat
exchanger (83, 93) can be reduced, which increases the air cooling
effect of the utilization side heat exchanger (83, 93).
[0044] Furthermore, in the fifth aspect of the invention, during
the defrosting operation, the refrigerant used to defrost the
utilization side heat exchanger (83, 93) is sent, without reducing
its pressure with the utilization side expansion valve (82, 92), to
the drain pan heating pipe (81, 91). Therefore, according to this
aspect of the invention, also during the defrosting operation, heat
of refrigerant flowing through the drain pan heating pipe (81, 91)
can be used to melt frost and ice blocks in the drain pan (85,
95).
[0045] On the other hand, the refrigerant having flowed through the
drain pan heating pipe (81, 82) is reduced in pressure by the
heat-source side expansion valve (48) and then flows through the
heat-source side heat exchanger (44). Therefore, in the heat-source
side heat exchanger (44), heat of evaporation of refrigerant is
taken from air and therefore can be used to not only defrost the
utilization side heat exchanger (83, 93) but also heat the drain
pan (85, 95). This reduces the power consumption during the
defrosting operation of the refrigeration system.
[0046] Furthermore, in the sixth and seventh aspects of the
invention, during the defrosting operation, refrigerant is
compressed by both the high stage compressor (41, 42, 43) and the
low stage compressor (101, 102, 121, 122). Therefore, according to
these aspects of the invention, the amount of heat given to
refrigerant during the defrosting operation increases, which
enhances the capacity to defrost the utilization side heat
exchanger (83, 93). Hence, the utilization side heat exchanger (83,
93) can be effectively defrosted by the defrosting operation in
these aspects of the invention even in such a case that the
refrigeration system might cause a shortage of defrosting capacity,
for example, during the defrosting operation in the second aspect
of the invention.
[0047] Furthermore, in the eighth aspect of the invention, the
refrigerant to be sucked in the low stage compressor (101, 102,
121, 122) is cooled during the defrosting operation by returning
liquid refrigerant to the suction side of the low stage compressor
(101, 102, 121, 122). Therefore, according to the eighth aspect of
the invention, the temperature of refrigerant to be discharged from
the low stage compressor (101, 102, 121, 122) can be prevented from
abnormally increasing, which ensures the protection of the low
stage compressor (101, 102, 121, 122).
[0048] In ninth aspect of the invention, after the completion of
the defrosting operation, the refrigeration system performs a
refrigerant recovery action for allowing the high stage compressor
(141, 142) to suck liquid refrigerant built up in the utilization
side heat exchanger (83, 93). Therefore, according to this aspect
of the invention, it can be surely avoided that in performing the
cooling operation again after the defrosting operation, liquid
compression occurs in the low stage compressor (101, 102, 121,
122). On the other hand, since the liquid refrigerant is thus sent
to the high stage compressor (41, 42, 43), the total length of
pipes through which the liquid refrigerant flows can be increased
as compared with the case where the liquid refrigerant is sent to
the low stage compressor (101, 102, 121, 122). Therefore, according
to this aspect of the invention, the liquid refrigerant can be
evaporated using heat of the air surrounding the pipes between exit
of the liquid refrigerant from the utilization side heat exchanger
(83, 93) and sucking thereof into the high stage compressor (141,
142). Hence, according to this aspect of the invention, it can be
avoided that during the refrigerant recovery action, liquid
compression occurs in the high stage compressor (141, 142).
[0049] In the tenth aspect of the invention, an oil separator (143,
144) is disposed to the discharge side of the low stage compressor
(101, 102, 121, 122). Therefore, according to this aspect of the
invention, during the cooling operation, oil having flowed out of
the low stage compressor (101, 102, 121, 122) can be surely
returned to the low stage compressor (101, 102, 121, 122), which
eliminates the shortage of refrigerating machine oil in the low
stage compressor (101, 102, 121, 122).
[0050] In addition, in this aspect of the invention, the oil return
pipe (141, 142) for returning oil recovered by the oil separator
(143, 144) to the low stage compressor (101, 102, 121, 122) is used
also as a liquid return pipe. Therefore, according to this aspect
of the invention, the refrigerant circuit (20) can be
simplified.
[0051] In the eleventh aspect of the invention, during the
refrigerant recovery action, liquid refrigerant built up in the
utilization side heat exchanger (83, 93) is sent to the oil
separator (143, 144) and gas refrigerant separated in the oil
separator (143, 144) is sent to the high stage compressor (41, 42,
43). Therefore, according to this aspect of the invention, it can
be surely avoided that during the refrigerant recovery action,
liquid compression occurs in the high stage compressor (41, 42,
43). In addition, in this aspect of the invention, the oil
separator (143, 144) used to separate oil during the cooling
operation is used as a gas-liquid separator during the refrigerant
recovery action. Therefore, according to this aspect of the
invention, it can be avoided that liquid compression occurs in the
high stage compressor (41, 42, 43) during the refrigerant recovery
action, without the need to additionally provide a gas-liquid
separator.
BRIEF DESCRIPTION OF DRAWINGS
[0052] FIG. 1 is a piping diagram showing a schematic configuration
of a refrigeration system according to Embodiment 1.
[0053] FIG. 2 is a piping diagram showing the behavior of a cooling
operation of the refrigeration system according to Embodiment
1.
[0054] FIG. 3 is a piping diagram showing the behavior of a
defrosting operation of the refrigeration system according to
Embodiment 1.
[0055] FIG. 4 is a piping diagram showing a schematic configuration
of a refrigeration system according to Embodiment 2.
[0056] FIG. 5 is a piping diagram showing the behavior of a second
defrosting operation of the refrigeration system according to
Embodiment 2.
[0057] FIG. 6 is a piping diagram showing a schematic configuration
of a refrigeration system according to Embodiment 3.
[0058] FIG. 7 is an enlarged schematic structural diagram of an oil
separator and its surroundings in the refrigeration system
according to Embodiment 3.
[0059] FIG. 8 is a piping diagram showing the behavior of a cooling
operation of the refrigeration system according to Embodiment
3.
[0060] FIG. 9 is a piping diagram showing the behavior of a
defrosting operation of the refrigeration system according to
Embodiment 3.
[0061] FIG. 10 is a piping diagram showing a refrigerant recovery
action of the refrigeration system according to Embodiment 3.
[0062] FIG. 11 is a piping diagram showing a schematic
configuration of a refrigeration system according to a modification
of Embodiment 3.
LIST OF REFERENCE NUMERALS
[0063] 10 refrigeration system [0064] 20 refrigerant circuit [0065]
41, 42, 43 high stage compressor [0066] 44 heat-source side heat
exchanger (outdoor heat exchanger) [0067] 48 heat-source side
expansion valve [0068] 81, 91 drain pan heating pipe [0069] 82, 92
utilization side expansion valve [0070] 83, 93 utilization side
heat exchanger (cooling heat exchanger) [0071] 85, 95 drain pan
[0072] 101, 102, 121, 122 low stage compressor [0073] 119, 139
bypass pipe [0074] 141, 142 oil return pipe (liquid return pipe)
[0075] 143, 144 oil separator
BEST MODE FOR CARRYING OUT THE INVENTION
[0076] Embodiments of the present invention will be described below
in detail with reference to the drawings.
Embodiment 1
[0077] A refrigeration system (10) of Embodiment 1 is placed, for
example, in a convenience store and used to cool the interiors of a
plurality of freezers. As shown in FIG. 1, the refrigeration system
(10) of Embodiment 1 includes an outdoor unit (11), a first freezer
display case (12), a second freezer display case (13), a first
booster unit (14) and a second booster unit (15). The outdoor unit
(11) is placed outdoors. On the other hand, the other units (12,
13, 14, 15) are all placed in a store, such as a convenience
store.
[0078] The outdoor unit (11), the first freezer display case (12),
the second freezer display case (13), the first booster unit (14)
and the second booster unit (15) include an outdoor circuit (40), a
first freezing circuit (80), a second freezing circuit (90), a
first booster circuit (100) and a second booster circuit (120),
respectively. In this refrigeration system (10), a refrigerant
circuit (20) operable in a vapor compression refrigeration cycle is
constituted by connecting these circuits (40, 80, 90, 100, 120) via
pipes.
[0079] The first freezing circuit (80) and the first booster
circuit (100) are connected in series to each other to form a first
cooling circuit. The second freezing circuit (90) and the second
booster circuit (120) are connected in series to each other to form
a second cooling circuit. The first and second cooling circuits are
connected in parallel to the outdoor circuit (40).
[0080] Specifically, a first shut-off valve (21) and a second
shut-off valve (22) are disposed at ends of the outdoor circuit
(40), a third shut-off valve (23) is disposed at an end of the
first booster circuit (100) and a fourth shut-off valve (24) is
disposed at an end of the second booster circuit (120). The first
shut-off valve (21) is connected to one end of a liquid connection
pipe (31). The other end of the liquid connection pipe (31) is
divided into two branch lines, one branch line connected to an end
of the first freezing circuit (80) and the other connected to an
end of the second freezing circuit (90). The second shut-off valve
(22) is connected to one end of a gas connection pipe (32). The
other end of the gas connection pipe (32) is divided into two
branch lines, one branch line connected to the third shut-off valve
(23) and the other connected to the fourth shut-off valve (24).
[0081] <<Outdoor Unit>>
[0082] The outdoor circuit (40) of the outdoor unit (11) includes a
first variable displacement compressor (41), a first fixed
displacement compressor (42), a second fixed displacement
compressor (43), an outdoor heat exchanger (44), a receiver (45), a
supercooling heat exchanger (46), a first outdoor expansion valve
(47), a second outdoor expansion valve (48) and a four-way selector
valve (49).
[0083] The first variable displacement compressor (41), the first
fixed displacement compressor (42) and the second fixed
displacement compressor (43) are all fully-enclosed, high-pressure
domed scroll compressors and constitute high stage compressors of
the refrigerant circuit (20). The first variable displacement
compressor (41) is supplied with electric power through an
inverter. The first variable displacement compressor (41) is
configured to be changeable in displacement by changing the output
frequency of the inverter to change the rotational speed of a motor
for the compressor. On the other hand, the first fixed displacement
compressor (42) and the second fixed displacement compressor (43)
have their respective motors always operated at constant rotational
speeds and are not changeable in displacement.
[0084] The suction side of the first variable displacement
compressor (41) is connected to a first suction pipe (61), the
suction side of the first fixed displacement compressor (42) is
connected to one end of a second suction pipe (62), and the suction
side of the second fixed displacement compressor (43) is connected
to one end of a third suction pipe (63). The other ends of these
suction pipes (61, 62, 63) are connected via a high stage suction
pipe (64) to the four-way selector valve (49).
[0085] The discharge side of the first variable displacement
compressor (41) is connected to a first discharge pipe (65), the
discharge side of the first fixed displacement compressor (42) is
connected to a second discharge pipe (66), and the discharge side
of the second fixed displacement compressor (43) is connected to a
third discharge pipe (67). The other ends of these discharge pipes
(65, 66, 67) are connected via a high stage discharge pipe (68) to
the four-way selector valve (49).
[0086] The outdoor heat exchanger (44) is a cross-fin type
fin-and-tube heat exchanger and constitutes a heat-source side heat
exchanger. Disposed close to the outdoor heat exchanger (44) is an
outdoor fan (50). The outdoor heat exchanger (44) provides heat
exchange between refrigerant therein and outdoor air blown by the
outdoor fan (50). One end of the outdoor heat exchanger (44) is
connected via a fifth shut-off valve (25) to the four-way selector
valve (49). On the other hand, the other end of the outdoor heat
exchanger (44) is connected via a first liquid pipe (71) to the top
of the receiver (45).
[0087] The supercooling heat exchanger (46) includes a
high-pressure channel (46a) and a low-pressure channel (46b) and
provides heat exchange between refrigerants flowing through the
channels (46a, 46b). The supercooling heat exchanger (46) is
composed of, for example, a plate heat exchanger.
[0088] The inflow end of the high-pressure channel (46a) is
connected to the bottom of the receiver (45). Furthermore, the
outflow end of the high-pressure channel (46a) is connected via a
second liquid pipe (72) to the first shut-off valve (21). On the
other hand, the inflow end of the low-pressure channel (46b) is
connected via a first branch pipe (73) to a midpoint of the second
liquid pipe (72). Furthermore, the outflow end of the low-pressure
channel (46b) is connected to the high stage suction pipe (64).
[0089] The second liquid pipe (72) is connected at a point between
the junction with the first branch pipe (73) and the first shut-off
valve (21) to one end of a second branch pipe (74). The other end
of the second branch pipe (74) is connected to the first liquid
pipe (71) midway between the outdoor heat exchanger (44) and the
receiver (45).
[0090] The first branch pipe (73) is provided with the first
outdoor expansion valve (47). The first outdoor expansion valve
(47) is composed of an electronic expansion valve controllable in
opening. Furthermore, the first branch pipe (73) is connected at a
point upstream of the first outdoor expansion valve (47) to one end
of a third branch pipe (75). The other end of the third branch pipe
(75) is connected to the first liquid pipe (71) midway between the
junction with the second branch pipe (74) and the outdoor heat
exchanger (44). The third branch pipe (75) is provided with the
second outdoor expansion valve (48). The second outdoor expansion
valve (48) is an electronic expansion valve controllable in opening
and constitutes a heat-source side expansion valve.
[0091] The four-way selector valve (49) is connected at a first
port thereof to the high stage discharge pipe (68), connected at a
second port thereof to the high stage suction pipe (64), connected
at a third port thereof to the outdoor heat exchanger (44) and
connected at a fourth port thereof to the second shut-off valve
(22). The four-way selector valve (49) is switchable between a
first position (the position shown in the solid lines in FIG. 1) in
which the first and third ports are communicated with each other
and the second and fourth ports are communicated with each other
and a second position (the position shown in the broken lines in
FIG. 1) in which the first and fourth ports are communicated with
each other and the second and third ports are communicated with
each other.
[0092] The outdoor circuit (40) is provided also with various kinds
of sensors and pressure switches. Specifically, the high stage
suction pipe (64) is provided with a first suction temperature
sensor (151) and a first suction pressure sensor (152). The first
discharge pipe (65) is provided with a first high-side pressure
switch (153), a first discharge temperature sensor (154) and a
first discharge pressure sensor (155). The second discharge pipe
(66) is provided with a second high-side pressure switch (156) and
a second discharge temperature sensor (157). The third discharge
pipe (67) is provided with a third high-side pressure switch (158)
and a third discharge temperature sensor (159). Disposed close to
the outdoor fan (50) for the outdoor heat exchanger (44) is an
outdoor air temperature sensor (160). The second liquid pipe (72)
is provided with a liquid temperature sensor (161).
[0093] Furthermore, the outdoor circuit (40) is provided also with
a plurality of check valves for allowing refrigerant flow in one
direction and prohibiting refrigerant flow in the opposite
direction. Specifically, the first discharge pipe (65), the second
discharge pipe (66) and the third discharge pipe (67) are provided
with a check valve (CV-1), a check valve (CV-2) and a check valve
(CV-3), respectively. Furthermore, the first liquid pipe (71) has a
check valve (CV-4) provided between the junction thereof with the
third branch pipe (75) and the junction thereof with the second
branch pipe (74). The second liquid pipe (72) has a check valve
(CV-5) provided between the junction thereof with the first branch
pipe (73) and the junction thereof with the second branch pipe
(74). The second branch pipe (74) is provided with a check valve
(CV-6). These check valves (CV-1, CV-2, . . . ) are configured to
allow only refrigerant flow in the direction of the arrows
accompanying the signs indicating the check valves in FIG. 1.
[0094] <<Freezer Display Case>>
[0095] The first freezing circuit (80) in the first freezer display
case (12) includes, in the order from its liquid side end towards
its gas side end, a first drain pan heating pipe (81), a first
indoor expansion valve (82) and a first cooling heat exchanger
(83).
[0096] The first indoor expansion valve (82) is an electronic
expansion valve controllable in opening and constitutes a
utilization side expansion valve. Furthermore, the first cooling
heat exchanger (83) is a cross-fin type fin-and-tube heat exchanger
and constitutes a utilization side heat exchanger. Disposed close
to the first cooling heat exchanger (83) is a first in-case fan
(84). The first cooling heat exchanger (83) provides heat exchange
between refrigerant therein and in-case air blown by the first
in-case fan (84). Disposed below the first cooling heat exchanger
(83) is a first drain pan (85). The first drain pan (85) is
configured to recover frost and dew condensation water dropped from
the surface of the first cooling heat exchanger (83).
[0097] The first drain pan heating pipe (81) is composed of a
refrigerant pipe disposed along the bottom surface of the first
drain pan (85). The first drain pan heating pipe (81) is configured
to use heat from refrigerant to melt frost recovered by the first
drain pan (85) and ice blocks produced by freezing of liquid drops
in the first drain pan (85).
[0098] The first freezing circuit (80) is provided with three
temperature sensors. Specifically, the heat exchanger tube of the
first cooling heat exchanger (83) is provided with a first
refrigerant temperature sensor (162). Disposed close to the gas
side end of the first freezing circuit (80) is a first gas
temperature sensor (163). Disposed close to the first in-case fan
(84) is a first in-case temperature sensor (164).
[0099] The second freezing circuit (90) in the second freezer
display case (13) has the same structure as the first freezing
circuit (80). Specifically, the second freezing circuit (90)
includes, like the first freezing circuit (80), a second drain pan
heating pipe (91), a second indoor expansion valve (92), a second
cooling heat exchanger (93), a second in-case fan (94) and a second
drain pan (95). Furthermore, the second freezing circuit (90) is
provided, like the first freezing circuit (80), with a second
refrigerant temperature sensor (165), a second gas temperature
sensor (166) and a second in-case temperature sensor (167).
[0100] <<Booster Unit>>
[0101] The first booster circuit (100) in the first booster unit
(14) is connected via a first booster connection pipe (33) to the
gas side end of the first freezing circuit (80). The first booster
circuit (100) includes a second variable displacement compressor
(101) and a third fixed displacement compressor (102).
[0102] The second variable displacement compressor (101) and the
third fixed displacement compressor (102) are both fully-enclosed,
high-pressure domed scroll compressors and constitute low stage
compressors of the refrigerant circuit (20). The second variable
displacement compressor (101) is supplied with electric power
through an inverter. The second variable displacement compressor
(101) is configured to be changeable in displacement by changing
the output frequency of the inverter to change the rotational speed
of a motor for the compressor. On the other hand, the third fixed
displacement compressor (102) has its motor always operated at a
constant rotational speed and is not changeable in
displacement.
[0103] The suction side of the second variable displacement
compressor (101) is connected to one end of a fourth suction pipe
(111) and the suction side of the third fixed displacement
compressor (102) is connected to one end of a fifth suction pipe
(112). The other ends of these suction pipes (111, 112) are
connected via a first low stage suction pipe (113) to the first
booster connection pipe (33).
[0104] The discharge side of the second variable displacement
compressor (101) is connected to one end of a fourth discharge pipe
(114) and the discharge side of the third fixed displacement
compressor (102) is connected to one end of a fifth discharge pipe
(115). The other ends of these discharge pipes (114, 115) are
connected via a first low stage discharge pipe (116) to the third
shut-off valve (23).
[0105] The first booster circuit (100) further includes a first oil
discharge pipe (117), a first escape pipe (118) and a first bypass
pipe (119).
[0106] The first oil discharge pipe (117) is connected at its one
end to an oil discharge port of the second variable displacement
compressor (101) and connected at the other end to the first low
stage discharge pipe (116). The first oil discharge pipe (117) is
provided with a solenoid valve (SV-1). The solenoid valve (SV-1) is
turned open when refrigerating machine oil in the second variable
displacement compressor (101) becomes excessive. As a result, the
refrigerating machine oil flows through the first oil discharge
pipe (117) into the outdoor circuit (40) and is then sucked into
the first variable displacement compressor (41) and the first and
second fixed displacement compressors (42, 43).
[0107] The first escape pipe (118) is connected at its one end to
the first low stage suction pipe (113) and connected at the other
end to the first low stage discharge pipe (116). For example, when
the second variable displacement compressor (101) or the third
fixed displacement compressor (102) goes out of order, the first
escape pipe (118) sends refrigerant flowing through the first low
stage suction pipe (113) to the outdoor circuit (40) via the first
low stage discharge pipe (116), thereby allowing the first variable
displacement compressor (41) and the first and second fixed
displacement compressor (42, 43) to suck the refrigerant.
[0108] The first bypass pipe (119) is connected at its one end to
the first escape pipe (118) and connected at the other end to the
first low stage discharge pipe (116). The first bypass pipe (119)
is provided with a solenoid valve (SV-2). The solenoid valve (SV-2)
is held open during a cooling operation of the refrigeration system
(10) and held closed during a defrosting operation thereof
(detailed operational behavior of the defrosting operation will be
described later).
[0109] The first booster circuit (100) is provided also with
various kinds of sensors and pressure switches. Specifically, the
first low stage suction pipe (113) is provided with a second
suction temperature sensor (168) and a second suction pressure
sensor (169). The fourth discharge pipe (114) is provided with a
fourth high-side pressure switch (170) and a fourth discharge
temperature sensor (171). The fifth discharge pipe (115) is
provided with a fifth high-side pressure switch (172) and a fifth
discharge temperature sensor (173). The first low stage discharge
pipe (116) is provided with a second discharge pressure sensor
(174).
[0110] The first booster circuit (100) is provided also with a
plurality of check valves. Specifically, the fourth discharge pipe
(114), the fifth discharge pipe (115) and the first escape pipe
(118) are provided with a check valve (CV-7), a check valve (CV-8)
and a check valve (CV-9), respectively.
[0111] The second booster circuit (120) in the second booster unit
(15) is connected via a second booster connection pipe (34) to the
gas side end of the second freezing circuit (90). The second
booster circuit (120) has the same configuration as the first
booster circuit (100). Specifically, the second booster circuit
(120) includes, like the first booster circuit (100), a third
variable displacement compressor (121) and a fourth fixed
displacement compressor (122).
[0112] The second booster circuit (120) further includes, like the
first booster circuit (100), a sixth suction pipe (131), a seventh
suction pipe (132), a second low stage suction pipe (133), a sixth
discharge pipe (134), a seventh discharge pipe (135), a second low
stage discharge pipe (136), a second oil discharge pipe (137), a
second escape pipe (138) and a second bypass pipe (139). The second
oil discharge pipe (137) and the second bypass pipe (139) are
provided with a solenoid valve (SV-3) and a solenoid valve (SV-4),
respectively.
[0113] Furthermore, the second booster circuit (120) is provided,
like the first booster circuit (100), also with various kinds of
sensors and pressure switches. Specifically, the second low stage
suction pipe (133) is provided with a third suction temperature
sensor (175) and a third suction pressure sensor (176). The sixth
discharge pipe (134) is provided with a sixth high-side pressure
switch (177) and a sixth discharge temperature sensor (178). The
seventh discharge pipe (135) is provided with a seventh high-side
pressure switch (179) and a seventh discharge temperature sensor
(180). The second low stage discharge pipe (136) is provided with a
third discharge pressure sensor (181).
[0114] The second booster circuit (120) is provided also with a
plurality of check valves. Specifically, the sixth discharge pipe
(134), the seventh discharge pipe (135) and the second escape pipe
(138) are provided with a check valve (CV-10), a check valve
(CV-11) and a check valve (CV-12), respectively.
[0115] --Operational Behavior--
[0116] A description is given below of the operational behavior of
the refrigeration system (10) of Embodiment 1.
[0117] <Cooling Operation>
[0118] In the cooling operation of this refrigeration system (10),
the interiors of the first freezer display case (12) and the second
freezer display case (13) are cooled.
[0119] As shown in FIG. 2, in the outdoor circuit (40) during the
cooling operation, the four-way selector valve (49) is selected to
the first position. In addition, the second outdoor expansion valve
(48) is fully closed and the opening of the first outdoor expansion
valve (47) is adjusted as appropriate. In the first freezing
circuit (80), the opening of the first indoor expansion valve (82)
is adjusted as appropriate. In the second freezing circuit (90),
the opening of the second indoor expansion valve (92) is adjusted
as appropriate. In the first booster circuit (100), the solenoid
valve (SV-1) and the solenoid valve (SV-2) are selected to their
closed positions. In the second booster circuit (120), the solenoid
valve (SV-3) and the solenoid valve (SV-4) are selected to their
closed positions. During the cooling operation, the compressors
(41, 42, 43) in the outdoor circuit (40), the compressors (101,
102) in the first booster circuit (100) and the compressors (121,
122) in the second booster circuit (120) are driven. As a result,
the outdoor heat exchanger (44) provides a condenser and the
cooling heat exchangers (83, 93) provide evaporators, so that the
refrigerant circuit (20) operates in a two-stage compression
refrigeration cycle.
[0120] The refrigerant discharged from the first variable
displacement compressor (41) and the first and second fixed
displacement compressors (42, 43) flows through the high stage
discharge pipe (68), then the four-way selector valve (49) and then
the outdoor heat exchanger (44). In the outdoor heat exchanger
(44), the refrigerant is given heat from the outdoor air and
thereby condenses.
[0121] The refrigerant having condensed in the outdoor heat
exchanger (44) flows through the first liquid pipe (71), the
receiver (45) and the high-pressure channel (46a) of the
supercooling heat exchanger (46) and then flows into the second
liquid pipe (72). Part of the refrigerant having flowed into the
second liquid pipe (72) is distributed to the first branch pipe
(73) and the rest flows into the liquid connection pipe (31).
[0122] The refrigerant having flowed into the first branch pipe
(73) flows through the first outdoor expansion valve (47) to reduce
its pressure and then flows through the low-pressure channel (46b)
of the supercooling heat exchanger (46). In the supercooling heat
exchanger (46), heat is exchanged between high-pressure refrigerant
flowing through the high-pressure channel (46a) and low-pressure
refrigerant flowing through the low-pressure channel (46b). As a
result, heat of the refrigerant flowing through the high-pressure
channel (46a) is taken as heat of evaporation of refrigerant
flowing through the low-pressure channel (46b). In other words, in
the supercooling heat exchanger (46), the refrigerant flowing
through the high-pressure channel (46a) is supercooled. The
refrigerant evaporated in the low-pressure channel (46b) in the
supercooling heat exchanger (46) flows into the high stage suction
pipe (64).
[0123] On the other hand, the refrigerant having flowed into the
liquid connection pipe (31) is distributed to the first freezing
circuit (80) and the second freezing circuit (90). The refrigerant
having flowed into the first freezing circuit (80) flows through
the first drain pan heating pipe (81). At this time, the first
drain pan (85) has accumulated frost dropped from the surface of
the first cooling heat exchanger (83) and ice blocks produced by
freezing of recovered dew condensation water. Therefore, as the
refrigerant flowing through the first drain pan heating pipe (81)
heats around the first drain pan (85), the frost and ice blocks in
the first drain pan (85) melt. The water obtained in the above
manner is drained as drainage away from the first drain pan
(85).
[0124] On the contrary, the refrigerant flowing through the first
drain pan heating pipe (81) gives heat of melting to frost and ice
blocks in the first drain pan (85) and is thereby cooled. As a
result, the refrigerant flowing through the first drain pan heating
pipe (81) is further supercooled.
[0125] The refrigerant having flowed out of the first drain pan
heating pipe (81) flows through the first indoor expansion valve
(82) to reduce its pressure and then flows through the first
cooling heat exchanger (83). In the first cooling heat exchanger
(83), the refrigerant takes heat from the in-case air to evaporate.
As a result, the in-case air in the first freezer display case (12)
is cooled and the in-case temperature is held, for example, at
-20.degree. C.
[0126] The refrigerant having evaporated in the first cooling heat
exchanger (83) flows via the first booster connection pipe (33)
into the first booster circuit (100), then flows through the first
low stage suction pipe (113) and is then sucked into the second
variable displacement compressor (101) and the third fixed
displacement compressor (102). The refrigerant compressed by the
compressors (101, 102) flows through the first low stage discharge
pipe (116) and then into the gas connection pipe (32).
[0127] The refrigerant having flowed into the second freezing
circuit (90) flows through the second drain pan heating pipe (91).
At this time, the second drain pan (95) has accumulated frost
dropped from the surface of the second cooling heat exchanger (93)
and ice blocks produced by freezing of recovered dew condensation
water. Therefore, as the refrigerant flowing through the second
drain pan heating pipe (91) heats around the second drain pan (95),
the frost and ice blocks in the second drain pan (95) melt. The
water obtained in the above manner is drained as drainage away from
the second drain pan (95).
[0128] On the contrary, the refrigerant flowing through the second
drain pan heating pipe (91) gives heat of melting to frost and ice
blocks recovered in the second drain pan (95) and is thereby
cooled. As a result, the refrigerant flowing through the second
drain pan heating pipe (91) is further supercooled.
[0129] The refrigerant having flowed out of the second drain pan
heating pipe (91) flows through the second indoor expansion valve
(92) to reduce its pressure and then flows through the second
cooling heat exchanger (93). In the second cooling heat exchanger
(93), the refrigerant takes heat from the in-case air to evaporate.
As a result, the in-case air in the second freezer display case
(13) is cooled and the in-case temperature is held, for example, at
-20.degree. C.
[0130] The refrigerant having evaporated in the second cooling heat
exchanger (93) flows via the second booster connection pipe (34)
into the second booster circuit (120), then flows through the
second low stage suction pipe (133) and is then sucked into the
third variable displacement compressor (121) and the fourth fixed
displacement compressor (122). The refrigerant compressed by the
compressors (121, 122) flows through the second low stage discharge
pipe (136) and then into the gas connection pipe (32).
[0131] The refrigerant combined in the gas connection pipe (32)
flows through the four-way selector valve (49) and then into the
high stage suction pipe (64). The combined refrigerant is further
combined with the refrigerant having evaporated in the low-pressure
channel (46b) of the supercooling heat exchanger (46) and then
sucked into the first variable displacement compressor (41) and the
first and second fixed displacement compressors (42, 43).
[0132] <Defrosting Operation>
[0133] During the defrosting operation of the refrigeration system
(10), the first cooling heat exchanger (83) and the second cooling
heat exchanger (93) are simultaneously defrosted.
[0134] As shown in FIG. 3, in the outdoor circuit (40) during the
defrosting operation, the four-way selector valve (49) is selected
to the second position. In addition, the first outdoor expansion
valve (47) is fully closed and the opening of the second outdoor
expansion valve (48) is adjusted as appropriate. In the first
freezing circuit (80), the first indoor expansion valve (82) is
fully opened. In the second freezing circuit (90), the second
indoor expansion valve (92) is fully opened. In the first booster
circuit (100), the solenoid valve (SV-1) is selected to its closed
position and the solenoid valve (SV-2) is selected to its open
position. In the second booster circuit (120), the solenoid valve
(SV-3) is selected to its closed position and the solenoid valve
(SV-4) is selected to its open position.
[0135] During the defrosting operation, the compressors (41, 42,
43) in the outdoor circuit (40) are driven while the compressors
(101, 102) in the first booster circuit (100) and the compressors
(121, 122) in the second booster circuit (120) are shut off. As a
result, the outdoor heat exchanger (44) provides an evaporator and
the cooling heat exchangers (83, 93) provide condensers, so that
the refrigerant circuit (20) operates in a refrigeration cycle.
[0136] The refrigerant discharged from the first variable
displacement compressor (41) and the first and second fixed
displacement compressors (42, 43) flows through the high stage
discharge pipe (68) and then the four-way selector valve (49) and
then into the gas connection pipe (32). The refrigerant having
flowed into the gas connection pipe (32) is distributed to the
first booster circuit (100) and the second booster circuit
(120).
[0137] The refrigerant having flowed into the first booster circuit
(100) flows midway through the first low stage discharge pipe
(116), then flows through the first bypass pipe (119) and the first
low stage suction pipe (113) and then flows into the first freezing
circuit (80). In other words, the refrigerant having flowed into
the first booster circuit (100) bypasses the shut-off second
variable displacement compressor (101) and third fixed displacement
compressor (102) and then flows out of the first booster circuit
(100).
[0138] The refrigerant having flowed into the first freezing
circuit (80) flows through the first cooling heat exchanger (83).
In the first cooling heat exchanger (83), frost on its surface is
melted by heat from its inside while the refrigerant gives heat of
melting to the frost to condense. The refrigerant having condensed
in the first cooling heat exchanger (83) flows through the
fully-opened first indoor expansion valve (82) and then the first
drain pan heating pipe (81). As a result, the refrigerant heats
around the first drain pan (85) to melt the frost and ice blocks in
the first drain pan (85). On the contrary, the refrigerant flowing
through the first drain pan heating pipe (81) gives heat of melting
to frost and ice blocks in the first drain pan (85). Thereafter,
the refrigerant having flowed through the first freezing circuit
(80) flows into the liquid connection pipe (31).
[0139] On the other hand, the refrigerant having flowed into the
second booster circuit (120) flows midway through the second low
stage discharge pipe (136), then flows through the second bypass
pipe (139) and the second low stage suction pipe (133) and then
flows into the second freezing circuit (90). In other words, the
refrigerant having flowed into the second booster circuit (120)
bypasses the shut-off third variable displacement compressor (121)
and fourth fixed displacement compressor (122) and then flows out
of the second booster circuit (120).
[0140] The refrigerant having flowed into the second freezing
circuit (90) flows through the second cooling heat exchanger (93).
In the second cooling heat exchanger (93), frost on its surface is
melted by heat from its inside while the refrigerant gives heat of
melting to the frost to condense. The refrigerant having condensed
in the second cooling heat exchanger (93) flows through the
fully-opened second indoor expansion valve (92) and then the second
drain pan heating pipe (91). As a result, the refrigerant heats
around the second drain pan (95) to melt the frost and ice blocks
in the second drain pan (95). On the contrary, the refrigerant
flowing through the second drain pan heating pipe (91) gives heat
of melting to frost and ice blocks in the second drain pan (95).
Thereafter, the refrigerant having flowed through the second
freezing circuit (90) flows into the liquid connection pipe
(31).
[0141] The refrigerant combined in the liquid connection pipe (31)
flows midway through the second liquid pipe (72) and then flows
through the second branch pipe (74), then the receiver (45) and
then the high-pressure channel (46a) of the supercooling heat
exchanger (46). The refrigerant flows through the first branch pipe
(73), then flows through the second outdoor expansion valve (48) of
the third branch pipe (75) to reduce its pressure and then flows
through the outdoor heat exchanger (44). In the outdoor heat
exchanger (44), the refrigerant takes heat from the outdoor air to
evaporate. The refrigerant having evaporated in the outdoor heat
exchanger (44) flows through the four-way selector valve (49) and
then into the high stage suction pipe (64) and is then sucked into
the first variable displacement compressor (41) and the first and
second fixed displacement compressors (42, 43).
Effects of Embodiment 1
[0142] According to Embodiment 1, during the defrosting operation,
frost adhering to the surfaces of the cooling heat exchangers (83,
93) are heated from the insides of the cooling heat exchangers (83,
93) by feeding the refrigerant discharged by the high stage
compressors (41, 42, 43) into the utilization side heat exchangers
(83, 93). Therefore, the cooling heat exchangers (83, 93) can be
effectively defrosted, which reduces the time taken to defrost
them.
[0143] Furthermore, according to Embodiment 1, since during the
defrosting operation the outdoor heat exchanger (44) serves as an
evaporator, heat given from air to refrigerant is used to defrost
the utilization side heat exchangers (83, 93). In other words,
according to Embodiment 1, heat given to refrigerant by the high
stage compressors (41, 42, 43) and heat given to refrigerant by the
outdoor heat exchanger (44) are both used to defrost the cooling
heat exchangers (83, 93). This reduces the time required for
defrosting and in turn reduces the power consumption of the
refrigeration system (10) during the defrosting operation.
[0144] Furthermore, in Embodiment 1, during the cooling operation,
refrigerant condensed in the outdoor heat exchanger (44) is allowed
to flow through the drain pan heating pipes (81, 91). Therefore,
according to Embodiment 1, heat of refrigerant can be used to melt
frost and ice blocks in the drain pans (85, 95) and the melted
moisture can be promptly drained as drainage. Furthermore, in this
case, the refrigerant flowing through the drain pan heating pipes
(81, 91) gives heat of melting to frost and ice blocks in the drain
pans (85, 95) and is thereby supercooled. Therefore, during the
cooling operation, the enthalpy difference between air and liquid
refrigerant in the utilization side heat exchangers (83, 93)
becomes large, which increases the air cooling effect of the
utilization side heat exchangers (83, 93).
[0145] Furthermore, in Embodiment 1, during the defrosting
operation, the refrigerant used to defrost the cooling heat
exchangers (83, 93) is sent, without reducing its pressure with the
indoor expansion valves (82, 92), to the drain pan heating pipes
(81, 91). Therefore, heat of condensation of refrigerant flowing
through the drain pan heating pipes (81, 91) can be used to melt
frost and ice blocks in the drain pans (85, 95).
Embodiment 2
[0146] A refrigeration system (10) of Embodiment 2 is different
from that of Embodiment 1 in the configuration of the refrigerant
circuit (20) and the behavior during the defrosting operation. A
description is given below of different points from Embodiment
1.
[0147] As shown in FIG. 4, the refrigerant circuit (20) in
Embodiment 2 includes two liquid injection pipes (190, 192). One
end of the first liquid injection pipe (190) is connected to the
first freezing circuit (80) midway between the first cooling heat
exchanger (83) and the first indoor expansion valve (82). The other
end of the first liquid injection pipe (190) is connected to the
first low stage suction pipe (113) in the first booster circuit
(100). The first liquid injection pipe (190) is provided with a
first liquid injection valve (191). The first liquid injection
valve (191) is composed of an electronic expansion valve
controllable in opening. On the other hand, one end of the second
liquid injection pipe (192) is connected to the second freezing
circuit (90) midway between the second cooling heat exchanger (93)
and the second indoor expansion valve (92). The other end of the
second liquid injection pipe (192) is connected to the second low
stage suction pipe (133) in the second booster circuit (120). The
second liquid injection pipe (192) is provided with a second liquid
injection valve (193). The second liquid injection valve (193) is
composed of an electronic expansion valve controllable in
opening.
[0148] --Operational Behavior--
[0149] The refrigeration system (10) of Embodiment 2 selectively
performs the above-mentioned defrosting operation in Embodiment 1
(first defrosting operation) and the after-mentioned defrosting
operation (second defrosting operation). The selection between
these two defrosting operations is made according to the detected
temperatures of the first refrigerant temperature sensor (162) and
the second refrigerant temperature sensor (165) provided at the
first cooling heat exchanger (83) and the second cooling heat
exchanger (93), respectively.
[0150] Specifically, when the refrigeration system (10) of
Embodiment 2 defrosts the cooling heat exchangers (83, 93), it
performs the first defrosting operation like Embodiment 1. During
the first defrosting operation, the compressors (41, 42, 43) in the
outdoor circuit (40) is driven while the compressors (101, 102) in
the first booster circuit (100) and the compressors (121, 122) in
the second booster circuit (120) are shut off, whereby the cooling
heat exchangers (83, 93) are defrosted in the above manner. On the
other hand, if the first defrosting operation may cause a shortage
of capacity to defrost the cooling heat exchangers (83, 93) and,
thus, it may take a long time to defrost the cooling heat
exchangers (83, 93), the second defrosting operation is performed
in the following manner.
[0151] Specifically, if during the first defrosting operation the
detected temperature of the first refrigerant temperature sensor
(162) or the second refrigerant temperature sensor (165) does not
readily reach a specified temperature, the refrigeration system
(10) is determined to be lacking in the capacity to defrost the
cooling heat exchangers (83, 93). As a result, the refrigeration
system (10) switches from the first defrosting operation to the
second defrosting operation.
[0152] In the second defrosting operation, as in the first
defrosting operation, the four-way selector valve (49) in the
outdoor circuit (40) is selected to the second position. In
addition, the first outdoor expansion valve (47) is fully closed
and the opening of the second outdoor expansion valve (48) is
adjusted as appropriate. In the first freezing circuit (80), the
first indoor expansion valve (82) is fully opened. In the second
freezing circuit (90), the second indoor expansion valve (92) is
fully opened. In the first booster circuit (100), the solenoid
valve (SV-1) is selected to its closed position and the solenoid
valve (SV-2) is selected to its open position. In the second
booster circuit (120), the solenoid valve (SV-3) is selected to its
closed position and the solenoid valve (SV-4) is selected to its
open position.
[0153] In contrast to the first defrosting operation, during the
second defrosting operation, the compressors (41, 42, 43) in the
outdoor circuit (40) are driven and the compressors (101, 102) in
the first booster circuit (100) and the compressors (121, 122) in
the second booster circuit (120) are also driven. As a result, the
outdoor heat exchanger (44) provides an evaporator and the cooling
heat exchangers (83, 93) provide condensers, so that the
refrigerant circuit (20) operates in a refrigeration cycle.
[0154] The refrigerant discharged from the first variable
displacement compressor (41) and the first and second fixed
displacement compressors (42, 43) flows through the high stage
discharge pipe (68) and then the four-way selector valve (49) and
then into the gas connection pipe (32). The refrigerant having
flowed into the gas connection pipe (32) is distributed to the
first booster circuit (100) and the second booster circuit
(120).
[0155] The refrigerant having flowed into the first booster circuit
(100) flows midway through the first low stage discharge pipe (116)
and then flows through the first bypass pipe (119). Part of the
refrigerant having flowed through the first bypass pipe (119) is
sucked via the first low stage suction pipe (113) into the second
variable displacement compressor (101) and the third fixed
displacement compressor (102). The refrigerant compressed by the
compressors (101, 102) is sent again to the first bypass pipe (119)
to combine with the refrigerant discharged from the high stage
compressors (41, 42, 43). The rest of the refrigerant having flowed
through the first bypass pipe (119) flows into the first freezing
circuit (80). In other words, in the first booster circuit (100),
part of the refrigerant circulates therethrough while being
compressed by the second variable displacement compressor (101) and
the third fixed displacement compressor (102) and heat input from
these compressors (101, 102) is given to the refrigerant.
[0156] The refrigerant having flowed into the first freezing
circuit (80) flows through the first cooling heat exchanger (83).
In the first cooling heat exchanger (83), frost on its surface is
melted by heat from its inside while the refrigerant gives heat of
melting to the frost to condense. The refrigerant having condensed
in the first cooling heat exchanger (83) flows through the
fully-opened first indoor expansion valve (82) and then the first
drain pan heating pipe (81). As a result, the refrigerant heats
around the first drain pan (85) to melt the frost and ice blocks in
the first drain pan (85). On the contrary, the refrigerant flowing
through the first drain pan heating pipe (81) gives heat of melting
to frost and ice blocks in the first drain pan (85). Thereafter,
the refrigerant having flowed through the first freezing circuit
(80) flows into the liquid connection pipe (31).
[0157] On the other hand, the refrigerant having flowed into the
second booster circuit (120) flows midway through the second low
stage discharge pipe (136) and then flows through the second bypass
pipe (139). Part of the refrigerant having flowed through the
second bypass pipe (139) is sucked via the second low stage suction
pipe (133) into the third variable displacement compressor (121)
and the fourth fixed displacement compressor (122). The refrigerant
compressed by the compressors (121, 122) is sent again to the
second bypass pipe (139) to combine with the refrigerant discharged
from the high stage compressors (41, 42, 43). The rest of the
refrigerant having flowed through the second bypass pipe (139)
flows into the second freezing circuit (90). In other words, in the
second booster circuit (120), part of the refrigerant circulates
therethrough while being compressed by the third variable
displacement compressor (121) and the fourth fixed displacement
compressor (122) and heat input from these compressors (101, 102)
is given to the refrigerant.
[0158] The refrigerant having flowed into the second freezing
circuit (90) flows through the second cooling heat exchanger (93).
In the second cooling heat exchanger (93), frost on its surface is
melted by heat from its inside while the refrigerant gives heat of
melting to the frost to condense. The refrigerant having condensed
in the second cooling heat exchanger (93) flows through the
fully-opened second indoor expansion valve (92) and then the second
drain pan heating pipe (91). As a result, the refrigerant heats
around the second drain pan (95) to melt the frost and ice blocks
in the second drain pan (95). On the contrary, the refrigerant
flowing through the second drain pan heating pipe (91) gives heat
of melting to frost and ice blocks in the second drain pan (95).
Thereafter, the refrigerant having flowed through the second
freezing circuit (90) flows into the liquid connection pipe
(31).
[0159] The refrigerant combined in the liquid connection pipe (31)
flows midway through the second liquid pipe (72) and then flows
through the second branch pipe (74), then the receiver (45) and
then the high-pressure channel (46a) of the supercooling heat
exchanger (46). The refrigerant flows through the first branch pipe
(73), then flows through the second outdoor expansion valve (48) of
the third branch pipe (75) to reduce its pressure and then flows
through the outdoor heat exchanger (44). In the outdoor heat
exchanger (44), the refrigerant takes heat from the outdoor air to
evaporate. The refrigerant having evaporated in the outdoor heat
exchanger (44) flows through the four-way selector valve (49) and
then into the high stage suction pipe (64) and is then sucked into
the first variable displacement compressor (41) and the first and
second fixed displacement compressors (42, 43).
[0160] In the second defrosting operation, part of the refrigerant
compressed by the high stage compressors (41, 42, 43) in the
outdoor circuit (40) is further compressed by the low stage
compressors (101, 102, 121, 122) in the booster circuits (100,
120). Therefore, if such operation is continued, the temperature of
refrigerant discharged from the low stage compressors (101, 102,
121, 122) may significantly rise up to break down these compressors
(101, 102, 121, 122). Hence, in order to prevent the breakdown of
the compressors (101, 102, 121, 122), the refrigeration system (10)
of Embodiment 2 performs the following liquid injection action.
[0161] Specifically, during the second defrosting operation, the
opening of the first liquid injection valve (191) is controlled
according to the degree of superheat of refrigerant to be sucked
into the second variable displacement compressor (101) and the
third fixed displacement compressor (102). The degree of superheat
of the refrigerant is properly calculated based on the detected
values of the second suction temperature sensor (168) and the
second suction pressure sensor (169). If, for example, the degree
of superheat is higher than a specified degree of superheat, the
opening of the first liquid injection valve (191) is increased. As
a result, part of the refrigerant having condensed in the first
cooling heat exchanger (83) is sent via the first liquid injection
pipe (190) to the suction sides of the second variable displacement
compressor (101) and the third fixed displacement compressor (102).
Thus, the refrigerant to be sucked into the compressors (101, 102)
is cooled, which prevents the temperature of refrigerant discharged
by the compressors (101, 102) from abnormally increasing.
[0162] Likewise, the opening of the second liquid injection valve
(193) is appropriately controlled according to the degree of
superheat of refrigerant to be sucked into the third variable
displacement compressor (121) and the fourth fixed displacement
compressor (122). As a result, the temperature of refrigerant
discharged by the compressors (121, 122) is prevented from
abnormally increasing.
Effects of Embodiment 2
[0163] According to Embodiment 2, like Embodiment 1, during the
defrosting operation, frost adhering to the surfaces of the cooling
heat exchangers (83, 93) are heated from the insides of the cooling
heat exchangers (83, 93) by feeding the refrigerant discharged by
the high stage compressors (41, 42, 43) into the cooling heat
exchangers (83, 93). Therefore, the cooling heat exchangers (83,
93) can be effectively defrosted, which reduces the time taken to
defrost them.
[0164] Furthermore, in Embodiment 2, the refrigeration system (10)
can selectively perform the first defrosting operation and the
second defrosting operation. According to Embodiment 2, when during
the first defrosting operation the refrigeration system (10) is
lacking in the capacity to defrost the cooling heat exchangers (83,
93), the low stage compressors (101, 102, 121, 122) are also
driven. Therefore, according to Embodiment 2, the amount of heat
given to refrigerant can be increased by the second defrosting
operation, which enhances the capacity to defrost the cooling heat
exchangers (83, 93). Hence, the second defrosting operation
provides effective defrosting of the cooling heat exchangers (83,
93).
[0165] Furthermore, in Embodiment 2, the refrigerant to be sucked
in the low stage compressors (101, 102, 121, 122) is cooled during
the second defrosting operation by returning liquid refrigerant to
the suction sides of the low stage compressors (101, 102, 121,
122). This prevents the temperature of refrigerant to be discharged
from the low stage compressors (101, 102, 121, 122) from abnormally
increasing, which ensures the protection of the low stage
compressors (101, 102, 121, 122).
Embodiment 3
[0166] A refrigeration system (10) of Embodiment 3 is different
from those of Embodiments 1 and 2 in the configuration of the
booster units (14, 15). A description is given below of different
points from Embodiments 1 and 2.
[0167] As shown in FIG. 6, the first booster circuit (100) in the
first booster unit (14) includes a first oil separator (143)
disposed to the discharge sides of the second variable displacement
compressor (101) and the third fixed displacement compressor (102).
Likewise, the second booster circuit (120) in the second booster
unit (15) includes a second oil separator (144) disposed to the
discharge sides of the third variable displacement compressor (121)
and the fourth fixed displacement compressor (122).
[0168] As shown in FIG. 7, each oil separator (143, 144) is formed
of a so-called demister oil separator. Each oil separator (143,
144) includes a hermetic oil recovery vessel (145) and a demister
(146). Each oil recovery vessel (145) is formed in the shape of a
hollow cylinder, in which its upper interior space constitutes a
gas reservoir (147) and its lower interior space constitutes a
liquid reservoir (148). Each demister (146) is disposed in the gas
reservoir (147). The demister (146) separates refrigerating machine
oil from gas refrigerant by trapping oil in the gas
refrigerant.
[0169] The first oil separator (143) is connected to a first oil
return pipe (141), a first low stage discharge pipe (116a) and a
first discharge connection pipe (116b). The second oil separator
(144) is connected to a second oil return pipe (142), a second low
stage discharge pipe (136a) and a second discharge connection pipe
(136b).
[0170] Each oil return pipe (141, 142) is connected to the bottom
of the oil recovery vessel (145) of the associated oil separator
(143, 144). One end of each oil return pipe (141, 142) opens into
the liquid reservoir (148) of the associated oil separator (143,
144). The other end of each oil return pipe (141, 142) is connected
to the associated low stage suction pipe (113, 133). Furthermore,
the oil return pipes (141, 142) are provided with solenoid valves
(SV-5, SV-6), respectively, that can be appropriately opened and
closed.
[0171] Each low stage discharge pipe (116a, 136a) is connected to
the peripheral wall of the oil recovery vessel (145) of the
associated oil separator (143, 144). Each low stage discharge pipe
(116a, 136a) opens into the gas reservoir (147) of the associated
oil separator (143, 144). Each discharge connection pipe (116b,
136b) is connected to the top of the oil recovery vessel (145) of
the associated oil separator (143, 144). Each discharge connection
pipe (116b, 136b) opens into the gas reservoir (147) of the
associated oil separator (143, 144).
[0172] The booster circuits (100, 120) are connected to bypass
pipes (119, 139), respectively, like Embodiments 1 and 2. The first
bypass pipe (119) is connected at its one end to the first low
stage suction pipe (113) and connected at the other end to a
midpoint of the first oil return pipe (141). The second bypass pipe
(139) is connected at its one end to the second low stage suction
pipe (133) and connected at the other end to a midpoint of the
second oil return pipe (142). The bypass pipes (119, 139) are
provided, like Embodiments 1 and 2, with solenoid valves (SV-2,
SV-4), respectively, that can be appropriately opened and
closed.
[0173] Each oil return pipe (141, 142) serves also as a liquid
return pipe for allowing, during a refrigerant recovery action,
liquid refrigerant accumulated in the associated cooling heat
exchanger (83, 93) to bypass the associated low stage compressors
(101, 102, 121, 122) to the suction sides of the high stage
compressors (41, 42, 43). Furthermore, each oil separator (143,
144) constitutes a gas-liquid separator for separating gas
refrigerant from refrigerant flowing thereinto via the associated
oil return pipe (141, 142) during the refrigerant recovery action
to send only the gas refrigerant to the high stage compressors (41,
42, 43).
[0174] The details of the refrigerant recovery action will be
described later.
[0175] --Operational Behavior--
[0176] The refrigeration system (10) of Embodiment 3, like
Embodiment 1, selectively performs the cooling operation and the
defrosting operation. Furthermore, the refrigeration system (10) of
Embodiment 3 performs, after the completion of the defrosting
operation, a refrigerant recovery action for recovering liquid
refrigerant built up in each cooling heat exchanger (83, 93).
[0177] <Cooling Operation>
[0178] In the cooling operation of the refrigeration system (10) of
Embodiment 3, like Embodiments 1 and 2, the interiors of the first
freezer display case (12) and the second freezer display case (13)
are cooled.
[0179] As shown in FIG. 8, in the outdoor circuit (40) during the
cooling operation, the four-way selector valve (49) is selected to
the first position. In addition, the second outdoor expansion valve
(48) is fully closed and the opening of the first outdoor expansion
valve (47) is adjusted as appropriate. In the first freezing
circuit (80), the opening of the first indoor expansion valve (82)
is adjusted as appropriate. In the second freezing circuit (90),
the opening of the second indoor expansion valve (92) is adjusted
as appropriate. In the first booster circuit (100), the solenoid
valve (SV-1) and the solenoid valve (SV-2) are selected to their
closed positions while the solenoid valve (SV-5) is opened or
closed as appropriate. In the second booster circuit (120), the
solenoid valve (SV-3) and the solenoid valve (SV-4) are selected to
their closed positions while the solenoid valve (SV-6) is opened or
closed as appropriate.
[0180] During the cooling operation, the compressors (41, 42, 43)
in the outdoor circuit (40), the compressors (101, 102) in the
first booster circuit (100) and the compressors (121, 122) in the
second booster circuit (120) are driven. As a result, the outdoor
heat exchanger (44) provides a condenser and the cooling heat
exchangers (83, 93) provide evaporators, so that the refrigerant
circuit (20) operates in a two-stage compression refrigeration
cycle.
[0181] The refrigerant discharged from the first variable
displacement compressor (41) and the first and second fixed
displacement compressors (42, 43) flows through the high stage
discharge pipe (68), then the four-way selector valve (49) and then
the outdoor heat exchanger (44). In the outdoor heat exchanger
(44), the refrigerant is given heat from the outdoor air and
thereby condenses.
[0182] The refrigerant having condensed in the outdoor heat
exchanger (44) flows through the first liquid pipe (71), the
receiver (45) and the high-pressure channel (46a) of the
supercooling heat exchanger (46) and then flows into the second
liquid pipe (72). Part of the refrigerant having flowed into the
second liquid pipe (72) is distributed to the first branch pipe
(73) and the rest flows into the liquid connection pipe (31). In
the supercooling heat exchanger (46), like Embodiment 1, the
refrigerant flowing through the high-pressure channel (46a) is
supercooled.
[0183] On the other hand, the refrigerant having flowed into the
liquid connection pipe (31) is distributed to the first freezing
circuit (80) and the second freezing circuit (90). The refrigerant
having flowed into the first freezing circuit (80) melts ice blocks
in the first drain pan (85), is then reduced in pressure by the
first indoor expansion valve (82) and then flows through the first
cooling heat exchanger (83). In the first cooling heat exchanger
(83), the refrigerant takes heat from the in-case air to evaporate.
As a result, the in-case air in the first freezer display case (12)
is cooled.
[0184] The refrigerant having evaporated in the first cooling heat
exchanger (83) flows via the first booster connection pipe (33)
into the first booster circuit (100), then flows through the first
low stage suction pipe (113) and is then sucked into the second
variable displacement compressor (101) and the third fixed
displacement compressor (102). The refrigerant compressed by the
compressors (101, 102) flows through the first low stage discharge
pipe (116a) and then into the first oil separator (143).
[0185] In the first oil separator (143), refrigerant in the oil
recovery vessel (145) flows upward while passing through the
demister (146). As the refrigerant passes through the demister
(146), oil in the refrigerant is trapped by the demister (146). The
oil trapped by the demister (146) is recovered by the liquid
reservoir (148) in the oil recovery vessel (145). On the other
hand, gas refrigerant separated from oil flows via the first
discharge connection pipe (116b) into the gas connection pipe
(32).
[0186] The oil recovered in the first oil separator (143) is
returned to the suction sides of the second variable displacement
compressor (101) and the third fixed displacement compressor (112)
as appropriate. In other words, the solenoid valve (SV-5) of the
first oil return pipe (141) is appropriately opened according to
the setting time of a timer, the liquid level of oil accumulated in
the oil recovery vessel (145) or other specified conditions. As a
result, oil accumulated in the liquid reservoir (148) flows through
the first oil return pipe (141) and is then sent to the first low
stage suction pipe (113). The oil is sucked into the second
variable displacement compressor (101) and the third fixed
displacement compressor (112) and used to lubricate sliding parts
of the compressors (101, 112).
[0187] The refrigerant having flowed into the second freezing
circuit (90) melts ice blocks in the second drain (95), is then
reduced in pressure by the second indoor expansion valve (92) and
then flows through the second cooling heat exchanger (93). In the
second cooling heat exchanger (93), the refrigerant takes heat from
the in-case air to evaporate. As a result, the in-case air in the
second freezer display case (13) is cooled.
[0188] The refrigerant having evaporated in the second cooling heat
exchanger (93) flows via the second booster connection pipe (34)
into the second booster circuit (120), then flows through the
second low stage suction pipe (133) and is then sucked into the
third variable displacement compressor (121) and the fourth fixed
displacement compressor (122). The refrigerant compressed by the
compressors (121, 122) flows through the second low stage discharge
pipe (136a) and then flows into the second oil separator (144).
[0189] In the second oil separator (144), like in the first oil
separator (143), oil in the gas refrigerant is trapped by the
demister (146) and the trapped oil is then recovered in the liquid
reservoir (148). The gas refrigerant separated from oil flows via
the second discharge connection pipe (136b) into the gas connection
pipe (32). The oil in the second oil separator (144) is returned to
the suction sides of the third variable displacement compressor
(121) and the fourth fixed displacement compressor (122) by
appropriately opening the solenoid valve (SV-6) of the second oil
return pipe (142).
[0190] The refrigerant combined in the gas connection pipe (32)
flows through the four-way selector valve (49) and then into the
high stage suction pipe (64). The combined refrigerant is further
combined with the refrigerant having evaporated in the low-pressure
channel (46b) of the supercooling heat exchanger (46) and then
sucked into the first variable displacement compressor (41) and the
first and second fixed displacement compressors (42, 43).
[0191] <Defrosting Operation>
[0192] During the defrosting operation of the refrigeration system
of Embodiment 3, like Embodiments 1 and 2, the first cooling heat
exchanger (83) and the second cooling heat exchanger (93) are
simultaneously defrosted.
[0193] As shown in FIG. 9, in the outdoor circuit (40) during the
defrosting operation, the four-way selector valve (49) is selected
to the second position. In addition, the first outdoor expansion
valve (47) is fully closed and the opening of the second outdoor
expansion valve (48) is adjusted as appropriate. In the first
freezing circuit (80), the first indoor expansion valve (82) is
fully opened. In the second freezing circuit (90), the second
indoor expansion valve (92) is fully opened. In the first booster
circuit (100), the solenoid valve (SV-1) and the solenoid valve
(SV-5) are selected to their closed positions and the solenoid
valve (SV-2) is selected to its open position. In the second
booster circuit (120), the solenoid valve (SV-3) and the solenoid
valve (SV-6) are selected to their closed positions and the
solenoid valve (SV-4) is selected to its open position.
[0194] During the defrosting operation, the compressors (41, 42,
43) in the outdoor circuit (40) are driven while the compressors
(101, 102) in the first booster circuit (100) and the compressors
(121, 122) in the second booster circuit (120) are shut off. As a
result, the outdoor heat exchanger (44) provides an evaporator and
the cooling heat exchangers (83, 93) provide condensers, so that
the refrigerant circuit (20) operates in a refrigeration cycle.
[0195] The refrigerant discharged from the first variable
displacement compressor (41) and the first and second fixed
displacement compressors (42, 43) flows through the high stage
discharge pipe (68) and then the four-way selector valve (49) and
then into the gas connection pipe (32). The refrigerant having
flowed into the gas connection pipe (32) is distributed to the
first booster circuit (100) and the second booster circuit
(120).
[0196] The refrigerant having flowed into the first booster circuit
(100) flows via the first discharge connection pipe (116b) into the
first oil separator (143). The gas refrigerant having flowed into
the oil recovery vessel (145) of the first oil separator (143)
flows through the gas reservoir (146) and then the liquid reservoir
(148) and then flows out to the first oil return pipe (141). During
the time, oil and liquid refrigerant accumulated in the liquid
reservoir (148) also flows out to the first oil return pipe (141),
together with the gas refrigerant. The refrigerant having flowed
out to the first oil return pipe (141) flows through the first
bypass pipe (119) and then the first low stage suction pipe (113)
and then flows into the first freezing circuit (80).
[0197] In the second booster circuit (120), as in the first booster
circuit (100), gas refrigerant flows through the second oil
separator (144), then flows through the second oil return pipe
(142), the second bypass pipe (139) and the second low stage
suction pipe (133) and then flows into the second freezing circuit
(90).
[0198] The refrigerant having flowed into each freezing circuit
(80, 90) is used, like Embodiment 1, to defrost the associated
cooling heat exchanger (83, 93) and melt ice blocks in the
associated drain pan (85, 95).
[0199] The refrigerant flows having flowed out of the freezing
circuits (80, 90) are combined together in the liquid connection
pipe (31), and the combined refrigerant flow flows through the
second liquid pipe (72), the second branch pipe (74), the receiver
(45) and the first branch pipe (73) in this order. Thereafter, the
refrigerant flows through the second outdoor expansion valve (48)
of the third branch pipe (75) to reduce its pressure and then flows
through the outdoor heat exchanger (44). In the outdoor heat
exchanger (44), the refrigerant takes heat from the outdoor air to
evaporate. The refrigerant having evaporated in the outdoor heat
exchanger (44) flows through the four-way selector valve (49) and
then into the high stage suction pipe (64) and is then sucked into
the first variable displacement compressor (41) and the first and
second fixed displacement compressors (42, 43).
[0200] <Refrigerant Recovery Action After Defrosting
Operation>
[0201] In each freezer display case (12, 13), when the above
defrosting operation is performed, liquid refrigerant obtained by
condensation in defrosting the associated cooling heat exchangers
(83, 93) may build up in the cooling heat exchangers (83, 93). If
under this condition the above cooling operation is restarted,
liquid refrigerant built up in the cooling heat exchangers (83, 93)
will be sucked into the low stage compressors (101, 102, 121, 122)
in the booster circuits (100, 120). As a result, a so-called liquid
compression phenomenon may occur to break down the low stage
compressors (101, 102, 121, 122).
[0202] Therefore, in order to avoid such liquid compression in the
low stage compressors (101, 102, 121, 122), the refrigeration
system of Embodiment 3 performs the following refrigerant recovery
action in restarting the cooling operation after the completion of
the defrosting operation.
[0203] As shown in FIG. 10, during the refrigerant recovery action,
as during the cooling operation, the four-way selector valve (49)
is selected to the first position. In addition, the second outdoor
expansion valve (48) is fully closed and the opening of the first
outdoor expansion valve (47) is adjusted as appropriate. In the
first freezing circuit (80), the opening of the first indoor
expansion valve (82) is adjusted as appropriate. In the second
freezing circuit (90), the opening of the second indoor expansion
valve (92) is adjusted as appropriate. In the first booster circuit
(100), the solenoid valve (SV-1) and the solenoid valve (SV-2) are
selected to their closed positions while the solenoid valve (SV-5)
is opened. In the second booster circuit (120), the solenoid valve
(SV-3) and the solenoid valve (SV-4) are selected to their closed
positions while the solenoid valve (SV-6) is opened or closed as
appropriate.
[0204] Furthermore, during the refrigerant recovery action, the
high stage compressors (41, 42, 43) in the outdoor circuit (40) are
driven while the low stage compressors (101, 102, 121, 122) in the
booster circuits (100, 120) are shut off.
[0205] In the outdoor circuit (40) during the refrigerant recovery
action, refrigerant compressed by the high stage compressors (41,
42, 43) flows through the same path as during the above cooling
operation. Specifically, in the outdoor circuit (40), high-pressure
refrigerant is condensed in the outdoor heat exchanger (44) and the
condensed refrigerant flows into the liquid connection pipe (31)
and is then distributed to the freezing circuits (80, 90).
[0206] The refrigerant having flowed into the first freezing
circuit (80) is reduced in pressure by the first indoor expansion
valve (82) and then flows through the first cooling heat exchanger
(83). In the first cooling heat exchanger (83), the refrigerant
takes heat from the in-case air to evaporate. Concurrently, the
liquid refrigerant built in the first cooling heat exchanger (83)
is forced out of the first cooling heat exchanger (83) by the gas
refrigerant.
[0207] Thereafter, the refrigerant flows into the first booster
circuit (100). The refrigerant flows through the first oil return
pipe (141) serving as a liquid return pipe and then flows into the
first oil separator (143). In the first oil separator (143), the
refrigerant is separated, in the oil recovery vessel (145), into
liquid refrigerant and gas refrigerant. The liquid refrigerant
after the separation accumulates in the liquid reservoir (148) in
the oil recovery vessel (145). On the other hand, the gas
refrigerant after the separation accumulates in the gas reservoir
(147) and flows out of the oil recovery vessel (145) through the
first discharge connection pipe (116b).
[0208] Likewise, the refrigerant having flowed into the second
freezing circuit (90) evaporates in the second cooling heat
exchanger (93) and is sent to the second booster circuit (120)
while carrying liquid refrigerant accumulated in the second cooling
heat exchanger (93). The refrigerant flows via the second oil
return pipe (142) serving as a liquid return pipe into the second
oil separator (144). Also in the second oil separator (144), the
refrigerant is separated into gas refrigerant and liquid
refrigerant and only the gas refrigerant flows out of the oil
recovery vessel (145) through the second discharge connection pipe
(136b).
[0209] The refrigerant having flowed out of each booster circuit
(100, 120) flows through the gas connection pipe (32). At this
time, if liquid refrigerant still remains in the refrigerant
flowing through the gas connection pipe (32), it takes heat from
the air surrounding the gas connection pipe (32) to evaporate. The
gas refrigerant having flowed out of the gas connection pipe (32)
flows into the outdoor circuit (40) and is sucked into the high
stage compressors (41, 42, 43).
Effects of Embodiment 3
[0210] In Embodiment 3, after the completion of the defrosting
operation, the refrigeration system (10) performs a refrigerant
recovery action for allowing the high stage compressors (141, 142)
to suck liquid refrigerant built up in each cooling heat exchanger
(83, 93). Therefore, according to this embodiment, it can be surely
avoided that in performing the cooling operation again after the
defrosting operation, liquid compression occurs in the low stage
compressors (101, 102, 121, 122). On the other hand, since the
liquid refrigerant is thus sent to the high stage compressors (41,
42, 43), the total length of pipes through which the liquid
refrigerant flows can be increased as compared with the case where
the liquid refrigerant is sent to the low stage compressors (101,
102, 121, 122). Specifically, in Embodiment 3, the liquid
refrigerant having flowed out of the cooling heat exchangers (83,
93) is sucked via the associated refrigerant pipes, such as the oil
return pipes (141, 142) and the gas connection pipe (32), into the
high stage compressors (141, 142). Therefore, according to
Embodiment 3, liquid refrigerant remaining in the refrigerant in
each refrigerant pipe can be evaporated using heat of the air
surrounding the refrigerant pipe. Hence, it can be avoided that
during the refrigerant recovery action, liquid compression occurs
in the high stage compressors (141, 142).
[0211] Furthermore, in Embodiment 3, the oil separators (143, 144)
are disposed to the discharge sides of the associated low stage
compressors (101, 102, 121, 122). Therefore, during the cooling
operation of Embodiment 3, oil having flowed out of the low stage
compressors (101, 102, 121, 122) can be surely returned to the low
stage compressors (101, 102, 121, 122), which eliminates the
shortage of refrigerating machine oil in the low stage compressors
(101, 102, 121, 122).
[0212] In addition, in Embodiment 3, the oil return pipes (141,
142) for returning oil recovered by the oil separators (143, 144)
to the low stage compressors (101, 102, 121, 122) are used also as
liquid return pipes. Therefore, according to this embodiment, the
refrigerant circuit (20) can be simplified.
[0213] Furthermore, during the refrigerant recovery action of
Embodiment 3, liquid refrigerant built up in the cooling heat
exchangers (83, 93) is sent to the associated oil separators (143,
144) and gas refrigerant separated in the oil separators (143, 144)
is sent to the high stage compressors (41, 42, 43). Therefore,
according to Embodiment 3, it can surely be avoided that during the
refrigerant recovery action, liquid compression occurs in the high
stage compressors (41, 42, 43). In addition, in Embodiment 3, the
oil separators (143, 144) used to separate oil during the cooling
operation are used as gas-liquid separators during the refrigerant
recovery action. Therefore, according to Embodiment 3, it can be
avoided that liquid compression occurs in the high stage
compressors (41, 42, 43) during the refrigerant recovery action,
without the need to additionally provide gas-liquid separators.
Modifications of Embodiment 3
[0214] The oil separators (143, 144) and the oil return pipes (141,
142) described in Embodiment 3 may be applied to the refrigeration
systems (10) of Embodiments 1 and 2 so that the refrigeration
systems (10) can perform a similar cooling operation, a similar
defrosting operation and a similar refrigerant recovery action to
those in Embodiment 3. Furthermore, for example, in the booster
circuits (100, 120) in Embodiment 3 shown in FIG. 9, the bypass
pipes (119, 139) may be connected at their one ends to the
discharge connection pipes (116b, 136b), respectively, and
connected at the other ends to the low stage suction pipes (113,
133), respectively. According to this configuration, during the
defrosting operation, the cooling heat exchangers (83, 93) can be
defrosted, without sending high-pressure refrigerant into the oil
separators (143, 144), by directly introducing it into the bypass
pipes (119, 139).
[0215] Furthermore, for example, as shown in FIG. 11, the oil
return pipes (141, 142) may be configured to serve also as bypass
pipes (119, 139) for use in the defrosting operation. Specifically,
in this modification, during the cooling operation, the solenoid
valves (SV-5, SV-6) of the oil return pipes (141, 142) are opened
or closed as appropriate, whereby oil recovered in the oil
separators (143, 144) is returned via the associated oil return
pipes (141, 142) to the associated low stage compressors (101, 102,
121, 122). Furthermore, during the defrosting operation in this
modification, the solenoid valves (SV-5, SV-6) are opened, whereby
high-pressure refrigerant sent from the outdoor circuit (40) is
sent via the associated oil return pipes (141, 142) to the
associated freezing circuits (80, 90). In other words, during the
defrosting operation in this modification, the oil return pipes
(141, 142) function as bypass pipes described above. Furthermore,
during the refrigerant recovery action after the defrosting
operation in this modification, the solenoid valves (SV-5, SV-6)
are held open, whereby liquid refrigerant built up in the cooling
heat exchangers (83, 93) flows via the associated oil return pipes
(141, 142) into the associated oil separators (143, 144) and gas
refrigerant separated in the oil separators (143, 144) is sent to
the high stage compressors (41, 42, 43). Since, in this
modification shown in FIG. 11, the oil return pipes (141, 142) for
oil return serve also as both of bypass pipes during the defrosting
operation and liquid return pipes during the refrigerant recovery
action in the above manner, the configuration of the refrigerant
circuit (20) can be further simplified.
Other Embodiments
[0216] The above embodiments may have the following
configurations.
[0217] Although in Embodiments 1 and 2 all the high stage
compressors (41, 42, 43) are driven during the cooling operation
and the defrosting operation, only one or two of these high stage
compressors (41, 42, 43) may be driven during each operation.
[0218] Furthermore, although in Embodiment 2 both the low stage
compressors (101, 102, 121, 122) in each booster circuit (100, 120)
are driven during the second defrosting operation, only one of both
the low stage compressors (101, 102, 121, 122) may be driven during
it.
[0219] Furthermore, although during the second defrosting operation
the openings of the liquid injection valves (191, 193) are
appropriately controlled according to the degree of superheat of
refrigerant to be sucked into the compressors (101, 102, 121, 122),
they may be appropriately controlled according to the temperature
of refrigerant discharged from the low stage compressors (101, 102,
121, 122), instead of the degree of superheat. Also in this case,
the temperature of refrigerant discharged from the low stage
compressors (101, 102, 121, 122) can be prevented from abnormally
increasing.
[0220] Furthermore, although in Embodiment 2 the refrigeration
system decreases the discharge temperatures of the compressors
(101, 102, 121, 122) in the booster circuits (100, 120) by
performing liquid injection, it may be configured not to perform
the liquid injection. In this case, for example, the operating
frequency of the second variable displacement compressor (101) or
the third variable displacement compressor (121) may be reduced to
decrease the temperature of discharged refrigerant, or either one
of both the low stage compressors (101, 102, 121, 122) in each
booster circuit (100, 120) may be shut off.
[0221] Furthermore, although in the refrigeration systems (10) of
the above embodiments the refrigerant circuit (20) includes a
plurality of cooling heat exchangers (83, 93) to simultaneously
cool the interiors of a plurality of freezer display cases (12,
13), the refrigerant circuit (20) may include a single cooling heat
exchanger to cool the interior of a single freezer display
case.
[0222] 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
[0223] As can be seen from the above description, the present
invention relates to refrigeration systems operating in a two-stage
compression refrigeration cycle and is particularly useful for
techniques for defrosting a utilization side heat exchanger for
cooling the internal air in a freezer or the like.
* * * * *