TECHNICAL FIELD
[0001] The present invention relates to refrigeration systems each including a plurality
of utilization side heat exchangers, more particularly to a refrigeration system capable
of performing defrosting operation in a refrigeration cycle in order to defrost a
plurality of utilization side heat exchangers.
BACKGROUND ART
[0002] Refrigeration systems including refrigerant circuits operating in refrigeration cycles
are known, and are widely used in, for example, cooling machines such as chillers
or freezers for storing food and other materials and air conditioners for cooling
and heating the air in rooms.
[0003] For example, Patent Document 1 discloses an air conditioner capable of operating
in a two-stage compression refrigeration cycle. The refrigerant circuit in this air
conditioner includes a high-stage compressor, a low-stage compressor, an outdoor heat
exchanger, and an indoor heat exchanger. During heating operation of the air conditioner,
a two-stage compression refrigeration cycle in which the low-stage compressor and
the high-stage compressor are operated, the indoor heat exchanger serves as a condenser,
and the outdoor heat exchanger serves as an evaporator, is performed. The air conditioner
described above is capable of performing defrosting operation of melting frost on
the outdoor heat exchanger in winter. During this defrosting operation, only the high-stage
compressor is operated, and a refrigeration cycle (i.e., so-called reverse cycle defrosting)
in which the outdoor heat exchanger serves as a condenser and the indoor heat exchanger
serves as an evaporator is performed.
[0004] Patent Document 2 discloses a refrigeration system for cooling the interior with
a plurality of utilization side heat exchangers. In this refrigeration system, utilization
side circuits each including a plurality of utilization side heat exchangers are connected
in parallel to a heat-source side circuit including a heat-source side heat exchanger.
During cooling operation of this refrigeration system, a refrigeration cycle in which
the heat-source side heat exchanger serves as a condenser and the utilization side
heat exchangers serve as evaporators is performed. Consequently, the air in the interior
is cooled by each of the utilization side heat exchangers.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-85047
Patent Document 2: Japanese Laid-Open Patent Publication No. 2002-228297
DISCLOSURE OF INVENTION
Problems that the Invention is to Solve
[0005] In a refrigeration system including a plurality of utilization side heat exchangers
as disclosed in Patent Document 2, defrosting operation disclosed in Patent Document
1 is expected to be performed to defrost the utilization side heat exchangers at a
time. However, in defrosting operation with such reverse cycle defrosting, condensed
refrigerant may become liquid refrigerant and accumulate in the utilization side heat
exchangers to cause so-called refrigerant stagnation. Such simultaneous defrosting
of a plurality of utilization side heat exchangers as described above may increase
the total amount of refrigerant which has accumulated in the utilization side heat
exchangers, thus failing to keep a sufficient amount of refrigerant for defrosting.
This results in the problem of inefficient defrosting of the utilization side heat
exchangers.
[0006] In particular, in many refrigeration systems operating in a two-stage compression
refrigeration cycle as described above, the pressure at a low-pressure side is extremely
low, and each of the utilization side heat exchangers has a large capacity. Accordingly,
when a plurality of utilization side heat exchangers are defrosted in such a refrigeration
system, a large amount of refrigerant accumulates in each of the utilization side
heat exchangers, and thus it becomes more difficult to keep a sufficient amount of
refrigerant for defrosting.
[0007] It is therefore an object of the present invention to increase, in a refrigeration
system capable of performing defrosting operation to defrost a plurality of utilization
side heat exchangers, the efficiency in the defrosting operation by keeping a sufficient
amount of refrigerant for defrosting.
Means of Solving the Problems
[0008] A first aspect of the present invention is directed to a refrigeration system including:
a heat-source side circuit (40) including a compressor (41, 42, 43) and a heat-source
side heat exchanger (44); and a plurality of utilization side circuits (100, 120;
110, 160) respectively including utilization side heat exchangers (102, 112) and connected
in parallel to the heat-source side circuit (40). This refrigeration system is switchable
between cooling operation performed in a refrigeration cycle in which the heat-source
side heat exchanger (44) serves as a condenser and the utilization side heat exchangers
(102, 112) serve as evaporators, and defrosting operation performed in a refrigeration
cycle in which the utilization side heat exchangers (102, 112) serve as condensers
and the heat-source side heat exchanger (44) serves as an evaporator. In the refrigeration
system, the defrosting operation includes an individual defrosting process in which
part of the utilization side heat exchangers (102, 112) is operated as a condenser
and the other part of the utilization side heat exchangers (102, 112) is stopped,
the individual defrosting process being performed a plurality of times in such a manner
that each of the utilization side heat exchangers (102, 112) serves as a condenser
at least once in the defrosting operation by switching the part of the utilization
side heat exchangers (102, 112) serving as a condenser every time, and a discharge
process in which refrigerant is discharged from the part of the utilization side heat
exchangers (102, 112) stopped in the individual defrosting process.
[0009] In the refrigeration system of the first aspect, the plurality of utilization side
circuits (100, 120; 110, 160) are connected in parallel to the heat-source side circuit
(40), thereby forming a refrigerant circuit. This refrigeration system is capable
of performing cooling operation for cooling, for example, the inside of a freezer
case with the utilization side heat exchanger (102, 112) and defrosting operation
for melting frost on the surface of the utilization side heat exchanger (102, 112).
[0010] Specifically, in the cooling operation, refrigerant compressed by the compressor
(41, 42, 43) condenses in the heat-source side heat exchanger (44), is subjected to
pressure reduction at, for example, an expansion valve, and then is sent to each of
the utilization side heat exchangers (102, 112). In each of the utilization side heat
exchangers (102, 112), the refrigerant takes heat from the air, and evaporates. Consequently,
the air in the freezer case, for example, is cooled. The refrigerant that has evaporated
in the utilization side heat exchanger (102, 112) is sucked into the compressor (41,
42, 43), and is compressed again.
[0011] On the other hand, in the defrosting operation, the individual defrosting process
in which only part of the utilization side heat exchangers (102, 112) to be defrosted
serves as a condenser and the other utilization side heat exchangers (102, 112) not
to be defrosted is stopped, is performed. This individual defrosting process is now
described based on a specific example.
[0012] It is assumed that the first utilization side heat exchanger (102) is defrosted and
the second utilization side heat exchanger (112) is not defrosted in the individual
defrosting process, for example. In this case, refrigerant compressed by the compressor
(41, 42, 43) is sent only to the first utilization side heat exchanger (102), and
is not sent to the second utilization side heat exchanger (112). In the first utilization
side heat exchanger (102), the refrigerant dissipates heat to frost on the surface
of a heat exchanger pipe. Consequently, in the first utilization side heat exchanger
(102), the refrigerant condenses, and the frost on the surface of the heat exchanger
tube gradually melts to be removed. The refrigerant condensed in the first utilization
side heat exchanger (102) is subjected to pressure reduction at, for example, an expansion
valve, and then evaporates in the heat-source side heat exchanger (44). The refrigerant
that has evaporated in the heat-source side heat exchanger (44) is sucked into the
compressor (41, 42, 43), and is compressed again.
[0013] In the defrosting operation, the individual defrosting process as described above
is repeated in such a manner that the target of defrosting is sequentially switched
in a given order. Specifically, after completion of the individual defrosting process
in the above example, an individual defrosting process in which the second utilization
side heat exchanger (112) is defrosted (i.e., serves as a condenser) and the first
utilization side heat exchanger (102) is not defrosted (i.e., is stopped), is performed.
Accordingly, in this aspect of the present invention, a larger amount of refrigerant
is sent to each of the utilization side heat exchangers (102, 112) than in a case
where refrigerant is split into the utilization side heat exchangers (102, 112) and
the utilization side heat exchangers (102, 112) are defrosted at a time. Therefore,
even when refrigerant stagnates in the utilization side heat exchanger (102, 112)
in the individual defrosting process, no shortage of refrigerant for use in defrosting
of the utilization side heat exchangers (102, 112) occurs.
[0014] In addition, the defrosting operation includes the discharge process for discharging
refrigerant from part of the utilization side heat exchangers (102, 112) not to be
defrosted. Specifically, in the individual defrosting process, refrigerant may remain
in the part of the utilization side heat exchangers (102, 112) which is stopped. However,
in this aspect of the present invention, this refrigerant is discharged in the discharge
process. As a result, in the individual defrosting process, the amount of refrigerant
capable of being sent to part of the utilization side heat exchangers (102, 112) to
be defrosted can further increase.
[0015] In a second aspect of the present invention, in the refrigeration system of the first
aspect, the heat-source side circuit (40) includes the high-stage compressor (41,
42, 43), whereas the utilization side circuits (100, 120; 110, 160) respectively include
low-stage compressors (121, 122, 123; 161, 162, 163). In the cooling operation, the
high-stage compressor (41, 42, 43) and the low-stage compressors (121, 122, 123; 161,
162, 163) are driven to perform a two-stage compression refrigeration cycle, whereas
in the defrosting operation, the high-stage compressor (41, 42, 43) is driven to perform
a refrigeration cycle. In the discharge process, part of the low-stage compressors
(121, 122, 123; 161, 162, 163) of the utilization side circuits (100, 120; 110, 160)
associated with part of the utilization side heat exchangers (102, 112) not to be
defrosted is driven to send refrigerant remaining in the part of the utilization side
heat exchangers (102, 112) not to be defrosted to the part of the utilization side
heat exchangers (102, 112) to be defrosted.
[0016] The refrigeration system of the second aspect is configured to be capable of operating
in a two-stage compression refrigeration cycle. Specifically, the refrigerant circuit
of this refrigeration system includes the high-stage compressor (41, 42, 43) and the
low-stage compressors (121, 122, 123; 161, 162, 163). In the cooling operation of
this refrigeration system, refrigerant compressed in the high-stage compressor (41,
42, 43) condenses in the heat-source side heat exchanger (44), is subjected to pressure
reduction at, for example, a pressure-reducing valve, and then is sent to each of
the utilization side heat exchangers (102, 112). The refrigerant that has evaporated
in the utilization side heat exchangers (102, 112) is compressed in the low-stage
compressors (121, 122, 123; 161, 162, 163), and is sucked into the high-stage compressor
(41, 42, 43) to be further compressed.
[0017] On the other hand, in the defrosting operation of this refrigeration system, the
individual defrosting process is performed with the high-stage compressor (41, 42,
43) operated. Specifically, in the individual defrosting process, refrigerant compressed
in the high-stage compressor (41, 42, 43) is sent to, for example, the first utilization
side heat exchanger (102) to be defrosted, and is not sent to the second utilization
side heat exchanger (112) not to be defrosted. Refrigerant used for defrosting of
the first utilization side heat exchanger (102) is subjected to pressure reduction
at, for example, an expansion valve, condenses in the heat-source side heat exchanger
(44), and then is sucked into the high-stage compressor (41, 42, 43) to be compressed
again.
[0018] In the discharge process in this aspect, refrigerant is sent to part of the utilization
side heat exchangers (102, 112) to be defrosted by operating part of the low-stage
compressors (121, 122, 123; 161, 162, 163) of the utilization side circuits (100,
120; 110, 160) associated with part of the utilization side heat exchangers (102,
112) not to be defrosted in the individual defrosting process. Specifically, in the
individual defrosting process, for example, in a case where the second utilization
side heat exchanger (112) is stopped, the second low-stage compressor (161, 162, 163)
of the second utilization side circuit (110, 160) associated with the second utilization
side heat exchanger (112) is operated. Consequently, refrigerant in the second utilization
side heat exchanger (112) is sucked into the second low-stage compressor (161, 162,
163) to be compressed, and then is sent to the first utilization side heat exchanger
(102) to be defrosted. At this time, in the second utilization side circuit (110,
160), refrigerant in, for example, the pipe of the suction side of the second low-stage
compressor (161, 162, 163) is also sent to the first utilization side heat exchanger
(102). Accordingly, in the individual defrosting process, the amount of refrigerant
capable of being sent to the utilization side heat exchanger (102, 112) to be defrosted
further increases.
[0019] In a third aspect of the present invention, in the refrigeration system of the second
aspect, the utilization side circuits (100, 120; 110, 160) respectively include expansion
valves (101, 111) for reducing pressures of refrigerant at inflow ends of the utilization
side heat exchangers (102, 112) in the cooling operation, and in the individual defrosting
process, part of the expansion valves (101, 111) of the utilization side circuits
(100, 120; 110, 160) associated with the part of the utilization side heat exchangers
(102, 112) to be defrosted is opened, whereas part of the expansion valves (101, 111)
of the utilization side circuits (100, 120; 110, 160) associated with the part of
the utilization side heat exchangers (102, 112) not to be defrosted is fully closed.
[0020] In the third aspect, the utilization side circuits (100, 120; 110, 160) respectively
include the expansion valves (101, 111). In the cooling operation, refrigerant condensed
in the heat-source side heat exchanger (44) is subjected to pressure reduction at
the expansion valves (101, 111), and then is sent to the utilization side heat exchangers
(102, 112) to evaporate.
[0021] On the other hand, in the individual defrosting process, the expansion valve (101,
111) is opened in the utilization side circuit (100, 120; 110, 160) associated with
the utilization side heat exchanger (102, 112) to be defrosted. In the utilization
side circuit (100, 120; 110, 160) not to be defrosted, the expansion valve (101, 111)
is fully closed. In this state, when the high-stage compressor (41, 42, 43) is operated,
refrigerant expelled from the high-stage compressor (41, 42, 43) flows into the utilization
side heat exchanger (102, 112) to be defrosted. On the other hand, the fully-closed
expansion valve (101, 111) prevents this refrigerant from flowing in the utilization
side heat exchanger (102, 112) not to be defrosted. Accordingly, in the individual
defrosting process, a larger amount of refrigerant can be sent to the utilization
side heat exchanger (102, 112) to be defrosted.
[0022] In a fourth aspect of the present invention, in the refrigeration system of the third
aspect, in the discharge process, the part of the expansion valves (101, 111) of the
utilization side circuits (100, 120; 110, 160) associated with the part of the utilization
side heat exchangers (102, 112) not to be defrosted in the individual defrosting process
is fully closed.
[0023] In the discharge process in the fourth aspect, the expansion valve (101, 111) is
fully closed in the utilization side circuit (100, 120; 110, 160) associated with
the utilization side heat exchanger (102, 112) not to be defrosted, and the low-stage
compressor (121, 122, 123; 161, 162, 163) is operated. Specifically, for example,
in the stopped second utilization side circuit (110, 160), the second expansion valve
(111) is fully closed, and the second low-stage compressor (161, 162, 163) is operated.
Consequently, in the second utilization side circuit (110, 160), refrigerant remaining
from the fully-closed second expansion valve (111) to the suction port of the second
low-stage compressor (161, 162, 163) is sucked into the second low-stage compressor
(161, 162, 163) to be compressed, and is sent to the first utilization side heat exchanger
(102) to be defrosted. Accordingly, in the individual defrosting process, the amount
of refrigerant capable of being sent to the utilization side heat exchanger (102,
112) to be defrosted can further increase.
[0024] In addition, fully-closing the expansion valve (101, 111) in the manner described
above causes a rapid decrease in pressure at the suction side of the operating low-stage
compressor (121, 122, 123; 161, 162, 163). Accordingly, even if liquid refrigerant
has accumulated in the utilization side heat exchanger (102, 112) not to be defrosted
and pipes before and after this part, the pressure of this liquid refrigerant rapidly
decreases, and thus the liquid refrigerant is likely to evaporate. This can prevent
refrigerant in the liquid state from being sucked into the low-stage compressors (121,
122, 123; 161, 162, 163), thus avoiding a so-called liquid compression phenomenon
in the low-stage compressors (121, 122, 123; 161, 162, 163).
[0025] In a fifth aspect of the present invention, in the refrigeration system of one of
the second through fourth aspects, the utilization side circuits (100, 120; 110, 160)
respectively include bypass pipes (145, 185) connecting suction sides and discharge
sides of the low-stage compressors (121, 122, 123; 161, 162, 163) and provided with
shut-off valves (SV6, SV11) which are closed during the cooling operation, and in
the individual defrosting process, part of the shut-off valves (SV6, SV11) of the
utilization side circuits (100, 120; 110, 160) associated with the part of the utilization
side heat exchangers (102, 112) to be defrosted is opened, whereas part of the shut-off
valves (SV6, SV11) of the utilization side circuits (100, 120; 110, 160) associated
with the part of the utilization side heat exchangers (102, 112) not to be defrosted
is closed.
[0026] In the fifth aspect, the utilization side circuits (100, 120; 110, 160) respectively
include the bypass pipes (145, 185). During the cooling operation, the shut-off valves
(SV6, SV11) of the bypass pipes (145, 185) are closed. Accordingly, refrigerant that
has evaporated in the utilization side heat exchangers (102, 112) does not flow in
the bypass pipes (145, 185), but is compressed in the low-stage compressors (121,
122, 123; 161, 162, 163), and then is further compressed in the high-stage compressor
(41, 42, 43).
[0027] On the other hand, in the individual defrosting process, the shut-off valve (SV6,
SV 11) of the utilization side circuit (100, 120; 110, 160) associated with the utilization
side heat exchanger (102, 112) not to be defrosted is closed. Accordingly, this closed
shut-off valve (SV6, SV11) prevents refrigerant compressed in the high-stage compressor
(41, 42, 43) from being sent to the utilization side heat exchanger (101, 112) not
to be defrosted through the bypass pipe (145, 185). As a result, in the individual
defrosting process, a larger amount of refrigerant can be sent to the utilization
side heat exchanger (102, 112) to be defrosted.
[0028] In a sixth aspect of the present invention, in the refrigeration system of the fifth
aspect, in the discharge process, the part of the shut-off valves (SV6, SV11) of the
utilization side circuits (100, 120; 110, 160) associated with the part of the utilization
side heat exchangers (102, 112) not to be defrosted is closed.
[0029] In the discharge process in the sixth aspect, the shut-off valve (SV6, SV11) of the
utilization side circuit (100, 120; 110, 160) associated with the utilization side
heat exchanger (102, 112) not to be defrosted is closed, and the low-stage compressor
(121, 122, 123; 161, 162, 163) is operated. Specifically, for example, in the second
utilization side circuit (110, 160) associated with the stopped second utilization
side heat exchanger (112), the shut-off valve (SV 11) is closed, and the second low-stage
compressor (161, 162, 163) is operated. This prevents refrigerant expelled from the
second low-stage compressor (161, 162, 163) from returning to the suction side of
the second low-stage compressor (161, 162, 163) through the second bypass pipe (185)
in the second utilization side circuit (110, 160). Accordingly, refrigerant in the
second utilization side circuit (110, 160) can be quickly discharged, thus further
increasing the amount of refrigerant capable of being sent to the utilization side
heat exchanger (102, 112) to be defrosted in the individual defrosting process.
[0030] In a seventh aspect of the present invention, in the refrigeration system of the
fifth aspect, the utilization side circuits (100, 120; 110, 160) respectively include
vessel-like oil separators (124, 164) for causing oil in refrigerant expelled from
the low-stage compressors (121, 122, 123; 161, 162, 163) to be sucked in the low-stage
compressors (121, 122, 123; 161, 162, 163), and an end of each of the bypass pipes
(145, 185) is connected to an associated one of the oil separators (124, 164).
[0031] In the seventh aspect, the oil separators (124, 164) are respectively provided at
the discharge sides of the low-stage compressors (121, 122, 123; 161, 162, 163). This
oil separator (124, 164) separates oil from refrigerant expelled from the low-stage
compressor (121, 122, 123; 161, 162, 163) during, for example, the cooling operation.
The oil separated by the oil separator (124, 164) is sucked into the low-stage compressor
(121, 122, 123; 161, 162, 163) through, for example, an oil return pipe, and is used
for lubricating a compression mechanism, for example.
[0032] In a case where the oil separator (124, 164) is provided in the utilization side
circuit (100, 120; 110, 160), refrigerant may also accumulate in the oil separator
(124, 164) during the defrosting operation. Specifically, in the defrosting operation,
the high-stage compressor (41, 42, 43) communicates with a pipe through which refrigerant
flows in the oil separator (124, 164), and thus refrigerant expelled from the high-stage
compressor (41, 42, 43) accumulates in the oil separator (124, 164) in some cases.
This may cause shortage of refrigerant capable of being sent to the utilization side
heat exchanger (102, 112) in the defrosting operation, thus reducing the capacity
of defrosting the utilization side heat exchanger (102, 112).
[0033] To prevent this problem, according to this aspect, an end of the bypass pipe (145,
185) is connected to the oil separator (124, 164) in order to avoid accumulation of
refrigerant in the oil separator (124, 164). With this configuration, in the defrosting
operation, refrigerant expelled from the high-stage compressor (41, 42, 43) flows
into the bypass pipe (145, 185) through the oil separator (124, 164), and is sent
to the utilization side heat exchanger (102, 112) to be defrosted. Specifically, in
the defrosting operation, refrigerant in the oil separator (124, 164) is always pushed
to the bypass pipe (145, 185), and thus accumulation of refrigerant in the oil separator
(124, 164) is prevented. As a result, the amount of refrigerant capable of being sent
to the utilization side heat exchanger (102, 112) to be defrosted can further increase.
[0034] An eighth aspect of the present invention, in the refrigeration system of the seventh
aspect, an end of each of the bypass pipes (145, 185) is connected to a bottom of
an associated one of the oil separators (124, 164).
[0035] In the eighth aspect, an end of the bypass pipe (145, 185) is connected to the bottom
of the oil separator (124, 164). This configuration allows refrigerant which has accumulated
in the oil separator (124, 164) during the defrosting operation to easily flow into
the bypass pipe (145, 185). Even if refrigerant in the oil separator (124, 164) condenses
and liquid refrigerant accumulates in the bottom of the oil separator (124, 164),
this liquid refrigerant quickly flows into the bypass pipe (145, 185).
[0036] In a ninth aspect of the present invention, in the refrigeration system of one of
the first through eighth aspects, the utilization side heat exchangers (102, 112)
are placed in a case, and share a fin (102a).
[0037] In the ninth aspect, the utilization side heat exchangers (102, 112) are placed in
the same case. In addition, the utilization side heat exchangers (102, 112) share
the same fin (102a). Accordingly, in the individual defrosting process, when the utilization
side heat exchanger (102, 112) to be defrosted serves as a condenser, heat of refrigerant
in this utilization side heat exchanger (102, 112) is transmitted to the other utilization
side heat exchanger (102, 112) by way of the fin (102a). Consequently, in the individual
defrosting process, frost on the surface of the utilization side heat exchanger (102,
112) which is stopped can be melted by utilizing heat of the utilization side heat
exchanger (102, 112) serving as a condenser.
[0038] In a tenth aspect of the present invention, in the refrigeration system of one of
the first through ninth aspects, in the defrosting operation, when a degree of supercooling
of refrigerant flowing from part of the utilization side heat exchangers (102, 112)
to be defrosted reaches a given temperature or more, a target of defrosting in the
individual defrosting process is switched.
[0039] In the defrosting operation in the tenth aspect, when condensed liquid refrigerant
accumulates in the utilization side heat exchanger (102, 112) to be defrosted and
the degree of supercooling of this liquid refrigerant reaches a given temperature
or more, the target of defrosting in the individual defrosting process is switched.
Consequently, even if the individual defrosting process is repeated with the target
of defrosting appropriately switched between the utilization side heat exchangers
(102, 112), it is possible to prevent liquid refrigerant from accumulating in the
utilization side heat exchanger (102, 112). This further ensures prevention of shortage
of refrigerant for use in defrosting of the utilization side heat exchanger (102,
112).
[0040] In an eleventh aspect of the present invention, in the refrigeration system of one
of the first through ninth aspects, in the defrosting operation, when a temperature
of refrigerant flowing from part of the utilization side heat exchangers (102, 112)
to be defrosted reaches a given temperature or more, a target of defrosting in the
individual defrosting process is switched.
[0041] In the defrosting operation in the eleventh aspect, when condensed liquid refrigerant
accumulates in the utilization side heat exchanger (102, 112) to be defrosted and
the temperature of the refrigerant in the utilization side heat exchanger (102, 112)
reaches a given temperature or more, the target of defrosting in the individual defrosting
process is switched. Consequently, even if the individual defrosting process is repeated
with the target of defrosting appropriately switched between the utilization side
heat exchangers (102, 112), it is possible to prevent liquid refrigerant from accumulating
in the utilization side heat exchanger (102, 112). This further ensures prevention
of shortage of refrigerant for use in defrosting of the utilization side heat exchanger
(102, 112).
EFFECTS OF THE INVENTION
[0042] According to the present invention, in the defrosting operation, the individual defrosting
process is performed with the target of defrosting appropriately switched among the
plurality of utilization side heat exchangers (102, 112). Accordingly, a smaller amount
of refrigerant accumulates in the utilization side heat exchangers (102, 112) than
a case where defrosting is performed with all the utilization side heat exchangers
(102, 112) used as condensers. Accordingly, in this individual defrosting process,
a sufficient amount of refrigerant can be used for defrosting of the utilization side
heat exchangers (102, 112), thus increasing the efficiency in defrosting operation.
[0043] In addition, according to the present invention, the discharge process in which refrigerant
in the utilization side heat exchanger (102, 112) not to be defrosted in the individual
defrosting process is sent to the utilization side heat exchanger (102, 112) to be
defrosted, is performed. Accordingly, refrigerant in the utilization side heat exchanger
(102, 112) which is stopped can be used for defrosting of the utilization side heat
exchanger (102, 112) to be defrosted, thus further ensuring that a sufficient amount
of refrigerant is kept for defrosting of the utilization side heat exchanger (102,
112).
[0044] In the second aspect of the present invention, in the refrigeration system capable
of operating in a two-stage compression refrigeration cycle in which the utilization
side heat exchangers (102, 112) tend to have large capacities, the individual defrosting
process is performed with the target of defrosting switched. Accordingly, in this
aspect, even if a large amount of liquid refrigerant accumulates in the utilization
side heat exchanger (102, 112), a sufficient amount of refrigerant can be kept for
defrosting of the utilization side heat exchanger (102, 112).
[0045] In the discharge process of this aspect, refrigerant compressed in the low-stage
compressor (121, 122, 123; 161, 162, 163) is sent to part of the utilization side
heat exchanger (102, 112) to be defrosted. This configuration allows heat input to
the low-stage compressor (121, 122, 123; 161, 162, 163) to be used for defrosting
of the utilization side heat exchanger (102, 112) to be defrosted.
[0046] In the individual defrosting process in the third aspect of the present invention,
the expansion valve (101, 111) associated with the utilization side heat exchanger
(102, 112) not to be defrosted is fully closed. This ensures that flowing of refrigerant
in the utilization side heat exchanger (102, 112) not to be defrosted is prevented.
Accordingly, a larger amount of refrigerant can be sent to the utilization side heat
exchanger (102, 112) to be defrosted.
[0047] In particular, in the discharge process in the fourth aspect of the present invention,
the expansion valve (101, 111) associated with the utilization side heat exchanger
(102, 112) not to be defrosted is fully closed. Accordingly, refrigerant that has
accumulated between the expansion valve (101, 111) and the suction port of the low-stage
compressor (121, 122, 123; 161, 162, 163) can be sent to the utilization side heat
exchanger (102, 112) to be defrosted. This ensures that a sufficient amount of refrigerant
is used for defrosting of the utilization side heat exchanger (102, 112) to be defrosted.
In addition, fully closing the expansion valve (101, 111) changes the refrigerant
at the suction side of the low-stage compressor (121, 122, 123; 161, 162, 163) into
gas, thus preventing a liquid compression phenomenon in the low-stage compressor (121,
122, 123; 161, 162, 163).
[0048] In the fifth aspect of the present invention, the utilization side circuits (100,
120; 110, 160) respectively include bypass pipes (145, 185) connecting the suction
sides and the discharge sides of the low-stage compressors (121, 122, 123; 161, 162,
163). Accordingly, in the individual defrosting process, refrigerant expelled from
the high-stage compressor (41, 42, 43) can be sent to the utilization side heat exchanger
(102, 112) to be defrosted by way of the bypass pipe (145, 185).
[0049] In particular, in the discharge process in the sixth aspect of the present invention,
the shut-off valve (SV6, SV11) associated with the utilization side heat exchanger
(102, 112) not to be defrosted is closed. This allows refrigerant compressed in the
low-stage compressor (121, 122, 123; 161, 162, 163) to be quickly sent to the utilization
side heat exchanger (102, 112) to be defrosted in the discharge process. Accordingly,
a sufficient amount of refrigerant can be used for defrosting of the utilization side
heat exchanger (102, 112) to be defrosted.
[0050] In the seventh aspect of the present invention, an end of the bypass pipes (145,
185) is connected to an associated one of the oil separators (124, 164). This ensures
that refrigerant in the oil separator (124, 164) is sent to the utilization side heat
exchanger (102, 112) to be defrosted by way of the bypass pipe (145, 185) in the defrosting
operation. Accordingly, a sufficient amount of refrigerant can be used for defrosting
of the utilization side heat exchanger (102, 112).
[0051] In particular, in the eighth aspect of the present invention, an end of each of the
bypass pipes (145, 185) is connected to the bottom of an associated one of the oil
separators (124, 164). Accordingly, liquid refrigerant, for example, in the oil separator
(124, 164) quickly flows into the bypass pipe (145, 185), and is sent to the utilization
side heat exchanger (102, 112) to be defrosted.
[0052] In the ninth aspect of the present invention, the plurality of utilization side heat
exchangers (102, 112) share the fin (102a). Accordingly, in the individual defrosting
process, the utilization side heat exchanger (102, 112) which is stopped can be defrosted
by utilizing heat of refrigerant in the utilization side heat exchanger (102, 112)
serving as a condenser. This can reduce the time for defrosting the utilization side
heat exchanger (102, 112).
[0053] Further, in the defrosting operation in the tenth aspect of the present invention,
when the degree of supercooling of refrigerant flowing from the utilization side heat
exchanger (102, 112) to be defrosted reaches to a given temperature or more, the target
of defrosting is switched. This can prevent refrigerant stagnation in the utilization
side heat exchanger (102, 112). As a result, a sufficient amount of refrigerant can
be used for defrosting of the utilization side heat exchanger (102, 112).
[0054] In the defrosting operation in the eleventh aspect of the present invention, when
the temperature of refrigerant flowing from part of the utilization side heat exchangers
(102, 112) to be defrosted reaches to a given temperature or more, the target of defrosting
is switched. This can prevent refrigerant stagnation in the utilization side heat
exchanger (102, 112). As a result, a sufficient amount of refrigerant can be used
for defrosting of the utilization side heat exchanger (102, 112).
BRIEF DESCRIPTION OF DRAWINGS
[0055]
[FIG. 1] FIG. 1 is a piping diagram showing a schematic configuration of a refrigeration
system according to an embodiment.
[FIG. 2] FIG. 2 is a view schematically illustrating a configuration of a cooling
heat exchanger in the refrigeration system of the embodiment.
[FIG. 3] FIG. 3 is a piping diagram showing the vicinity of a low-stage oil separator
in the refrigeration system of the embodiment.
[FIG. 4] FIG. 4 is a piping diagram showing a flow of refrigerant in cooling operation
of the refrigeration system of the embodiment.
[FIG. 5] FIG. 5 is a piping diagram showing a flow of refrigerant in a pre-discharge
process of the refrigeration system of the embodiment.
[FIG. 6] FIG. 6 is a piping diagram showing a flow of refrigerant in a first individual
defrosting process of the refrigeration system of the embodiment.
[FIG. 7] FIG. 7 is a piping diagram showing a flow of refrigerant in a first discharge
process of the refrigeration system of the embodiment.
[FIG. 8] FIG. 8 is a piping diagram showing a flow of refrigerant in a second individual
defrosting process of the refrigeration system of the embodiment.
[FIG. 9] FIG. 9 is a piping diagram showing a flow of refrigerant in a second discharge
process of the refrigeration system of the embodiment.
Description of Symbols
[0056]
- 10
- refrigeration system
- 40
- outdoor circuit (heat-source side circuit)
- 41, 42, 43
- high-stage compressor (compressor)
- 44
- heat-source side heat exchanger (outdoor heat exchanger)
- 100, 120
- first freezing circuit, first booster circuit (first utilization side circuit)
- 110, 160
- second freezing circuit, second booster circuit (second utilization side circuit)
- 101, 111
- indoor expansion valve (expansion valve)
- 102, 112
- cooling heat exchanger (utilization side heat exchanger)
- 121, 161
- low-stage compressor
- 124, 164
- low-stage oil separator (oil separator)
- 145, 185
- bypass pipe
- SV6, SV11
- solenoid valve (shut-off valve)
BEST MODE FOR CARRYING OUT THE INVENTION
[0057] Hereinafter, an embodiment of the present invention will be described in detail with
reference to the drawings.
[0058] A refrigeration system (10) according to this embodiment is placed in, for example,
a convenience store, and is used to cool the interior of a freezer.
[0059] As shown in FIG. 1, the refrigeration system (10) of this embodiment includes an
outdoor unit (11), an extension unit (12), a supercooling unit (13), a freezer display
case (14), a first booster unit (15), and a second booster unit (16). The outdoor
unit (11), the extension unit (12), and the supercooling unit (13) are placed outdoors.
On the other hand, the other units (14, 15, 16) are placed in a store such as a convenience
store.
[0060] The outdoor unit (11) includes an outdoor circuit (40). The extension unit (12) includes
an extension circuit (80). The supercooling unit (13) includes a supercooling circuit
(90). The outdoor circuit (40), the extension circuit (80), and the supercooling circuit
(90) are connected in series to form a heat-source side circuit. The freezer display
case (14) includes a first freezing circuit (100) and a second freezing circuit (110).
The first booster unit (15) includes a first booster circuit (120). The second booster
unit (16) includes a second booster circuit (160). The first freezing circuit (100)
and the first booster circuit (120) are connected in series to form a first utilization
side circuit. The second freezing circuit (110) and the second booster circuit (160)
are connected in series to form a second utilization side circuit.
[0061] In this refrigeration system (10), the first utilization side circuit (100, 120)
and the second utilization side circuit (110, 160) are connected in parallel to the
heat-source side circuit (40, 80, 90) to form a refrigerant circuit in which refrigerant
circulates in a vapor compression refrigeration cycle.
[0062] Specifically, the ends of the outdoor circuit (40) are provided with a first shut-off
valve (21) and a second shut-off valve (22), respectively. The second shut-off valve
(22) is connected to an end of the extension circuit (80) through a first connection
pipe (31). The other end of the extension circuit (80) is connected to an end of the
supercooling circuit (90) through a second connection pipe (32). The other end of
the supercooling circuit (90) is connected to an end of each of the first freezing
circuit (100) and the second freezing circuit (110) through a third connection pipe
(33). The other end of the first freezing circuit (100) is connected to an end of
the first booster circuit (120) through a fourth connection pipe (34). The other end
of the second freezing circuit (110) is connected to an end of the second booster
circuit (160) through a fifth connection pipe (35). The other end of the first booster
circuit (120) is provided with a third shut-off valve (23). The other end of the second
booster circuit (160) is provided with a fourth shut-off valve (24). The third shut-off
valve (23) and the fourth shut-off valve (24) are connected to the first shut-off
valve (21) through a sixth connection pipe (36).
<<Outdoor Unit>>
[0063] The outdoor circuit (40) of the outdoor unit (11) includes a first high-stage compressor
(41), a second high-stage compressor (42), a third high-stage compressor (43), an
outdoor heat exchanger (44), a receiver (45), an internal heat exchanger (46), an
outdoor expansion valve (47), and a four-way selector valve (48).
[0064] Each of the high-stage compressors (41, 42, 43) is fully-enclosed, and is a high-pressure
domed scroll compressor. The first high-stage compressor (41) is a variable displacement
compressor which is supplied with electric power through an inverter. Specifically,
the first high-stage 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 second high-stage compressor (42)
and the third high-stage compressor (43) are fixed displacement compressors. Specifically,
the second high-stage compressor (42) and the third high-stage compressor (43) have
their respective motors always operated at constant rotational speeds, and are not
changeable in displacement.
[0065] The discharge side of the first high-stage compressor (41) is connected to an end
of a first discharge pipe (51). The discharge side of the second high-stage compressor
(42) is connected to an end of a second discharge pipe (52). The discharge side of
the third high-stage compressor (43) is connected to an end of a third discharge pipe
(53). The other ends of these discharge pipes (51, 52, 53) are connected to the four-way
selector valve (48) through a high-stage discharge pipe (54). The suction side of
the first high-stage compressor (41) is connected to an end of a first suction pipe
(55). The suction side of the second high-stage compressor (42) is connected to an
end of a second suction pipe (56). The suction side of the third high-stage compressor
(43) is connected to an end of a third suction pipe (57). The other ends of these
suction pipes (55, 56, 57) are connected to the four-way selector valve (48) through
a high-stage suction pipe (58).
[0066] The high-stage discharge pipe (54) is provided with a high-stage oil separator (59).
An end of a high-stage oil return pipe (59a) is connected to the bottom of the high-stage
oil separator (59). The other end of the high-stage oil return pipe (59a) is connected
to the high-stage suction pipe (58). The high-stage oil return pipe (59a) is provided
with a first solenoid valve (SV1) which can be appropriately opened and closed. The
high-stage oil separator (59) separates oil (i.e., refrigerating machine oil) from
the refrigerant expelled from the high-stage compressors (41, 42, 43). The oil obtained
by the high-stage oil separator (59) is sucked into the high-stage compressors (41,
42, 43) by way of the high-stage oil return pipe (59a) with the first solenoid valve
(SV1) opened.
[0067] The outdoor heat exchanger (44) is a cross-fin type fin-and-tube heat exchanger,
and is a heat-source side heat exchanger. An outdoor fan (60) is provided near the
outdoor heat exchange (44). This outdoor heat exchanger (44) performs heat exchange
between outdoor air blown from the outdoor fan (60) and the refrigerant. An end of
the outdoor heat exchanger (44) is connected to the four-way selector valve (48),
whereas the other end of the outdoor heat exchanger (44) is connected to the top of
the receiver (45) through a first liquid pipe (61).
[0068] The receiver (45) stores redundant refrigerant in a vessel. The receiver (45) has
an internal volume of about 10 L (liters). The top of the receiver (45) is connected
to the first liquid pipe (61), and the bottom of the receiver (45) is connected to
a second liquid pipe (62).
[0069] The internal heat exchanger (46) includes a first heat exchanger tube (46a) and a
second heat exchanger tube (46b), and performs heat exchange between the refrigerant
flowing in the heat exchanger tube (46a) and the refrigerant flowing in the heat exchanger
tube (46b). This internal heat exchanger (46) is, for example, a plate heat exchanger.
[0070] An end of the first heat exchanger tube (46a) is connected to the second liquid pipe
(62), and the other end of the first heat exchanger tube (46a) is connected to the
second shut-off valve (22) through a third liquid pipe (63). An end of a first branch
pipe (64) and an end of the second branch pipe (65) are connected to midpoints of
the third liquid pipe (63). The other ends of the first and second branch pipes (64,
65) are connected to midpoints of the first liquid pipe (61). The first branch pipe
(64) is provided with the outdoor expansion valve (47). The outdoor expansion valve
(47) is an electronic expansion valve controllable in opening, and is a heat-source
side expansion valve. An end of a first injection pipe (66) is connected to a midpoint
of the first branch pipe (64). The other end of the first injection pipe (66) is connected
to the high-stage suction pipe (58). The first injection pipe (66) is provided with
a first motor-operated valve (66a) which is a motor-operated valve.
[0071] An end of the second heat exchanger tube (46b) is connected to a midpoint of the
first branch pipe (64) through a second injection pipe (67), and the other end of
the second heat exchanger tube (46b) is connected to the high-stage suction pipe (58).
The second injection pipe (67) is provided with a second motor-operated valve (67a)
which is a motor-operated valve.
[0072] The four-way selector valve (48) includes first through fourth ports. In the four-way
selector valve (48), the first port is connected to the high-stage discharge pipe
(54), the second port is connected to the outdoor heat exchanger (44), the third port
is connected to the high-stage suction pipe (58), and the fourth port is connected
to the first shut-off valve (21). The four-way selector valve (48) is switchable between
a first position (i.e., the position indicated by the solid lines in FIG. 1) in which
the first and second ports communicate with each other and the third and fourth ports
communicate with each other, and a second position (i.e., the position indicated by
the broken lines in FIG. 1) in which the first and fourth ports communicate with each
other and the second and third ports communicate with each other.
[0073] The outdoor circuit (40) includes various sensors. Specifically, the first discharge
pipe (51) is provided with a first discharge temperature sensor (71), the second discharge
pipe (52) is provided with a second discharge temperature sensor (72), and the third
discharge pipe (53) is provided with a third discharge temperature sensor (73). The
discharge temperature sensors (71, 72, 73) respectively detect the temperatures of
the refrigerant discharged from the high-stage compressors (41, 42, 43). The high-stage
discharge pipe (54) is provided with a high-stage high-pressure pressure sensor (74).
The high-stage suction pipe (58) is provided with a high-stage low-pressure pressure
sensor (75). The high-stage high-pressure pressure sensor (74) detects the pressure
of the refrigerant at a high-pressure side of the outdoor circuit (40). The high-stage
low-pressure pressure sensor (75) detects the pressure of the refrigerant at a low-pressure
side of the outdoor circuit (40). Near the outdoor fan (60), an outdoor temperature
sensor (76) is provided. The outdoor-temperature sensor (76) detects the temperature
of outdoor air surrounding the outdoor heat exchanger (44).
[0074] The outdoor circuit (40) includes a plurality of check valves. Specifically, the
first discharge pipe (51) is provided with a first check valve (CV1), the second discharge
pipe (52) is provided with a second check valve (CV2), and the third discharge pipe
(53) is provided with a third check valve (CV3). The first liquid pipe (61) is provided
with a fourth check valve (CV4), the third liquid pipe (63) is provided with a fifth
check valve (CV5), and the second branch pipe (65) is provided with a sixth check
valve (CV6). These check valves and check valves which will be described later allow
the refrigerant to flow only in the direction indicated by the arrows in FIG. 1, and
prevent the refrigerant from flowing in the opposite direction.
[0075] In addition to the first shut-off valve (21) and the second shut-off valve (22),
a plurality of shut-off valves are provided in the outdoor circuit (40). Specifically,
the first liquid pipe (61) is provided with a fifth shut-off valve (25), the second
liquid pipe (62) is provided with a sixth shut-off valve (26), and the first branch
pipe (64) is provided with a seventh shut-off valve (27).
<<Extension Unit>>
[0076] The extension circuit (80) of the extension unit (12) includes a refrigerant reservoir
(81). This refrigerant reservoir (81) is an elongated vessel in the shape of a sealed
cylinder, and is configured to store the refrigerant. Specifically, the refrigerant
reservoir (81) has an internal volume of about 10 L to about 15 L. An end of a fourth
liquid pipe (82) and an end of a fifth liquid pipe (83) are connected to the circumferential
surface of the refrigerant reservoir (81) near the bottom of the refrigerant reservoir
(81). The other end of the fourth liquid pipe (82) is connected to the first connection
pipe (31), and the other end of the fifth liquid pipe (83) is connected to the second
connection pipe (32). In the extension circuit (80), the fifth liquid pipe (83) is
provided with an eighth shut-off valve (28). The refrigerant reservoir (81) is configured
to be filled with the refrigerant through this eighth shut-off valve (28).
<<Supercooling Unit>>
[0077] The supercooling circuit (90) of the supercooling unit (13) includes a supercooling
heat exchanger (91), a supercooling side compressor (92), a supercooling side outdoor
heat exchanger (93), and a supercooling side expansion valve (94). The supercooling
heat exchanger (91) includes a high-pressure side heat exchanger tube (91a) and a
low-pressure side heat exchanger tube (91b), and is configured to perform heat exchange
between the refrigerant flowing in the heat exchanger tube (91 a) and the refrigerant
flowing in the heat exchanger tube (91b). This supercooling heat exchanger (91) is,
for example, a plate heat exchanger.
[0078] An end of the high-pressure side heat exchanger tube (91 a) is connected to the second
connection pipe (32), and the other end of the high-pressure side heat exchanger tube
(91a) is connected to the third connection pipe (33). The low-pressure side heat exchanger
tube (91b) is located in a closed circuit (90a) in which the refrigerant circulates
in a vapor compression refrigeration cycle. In this closed circuit (90a), the supercooling
side compressor (92), the supercooling side outdoor heat exchanger (93), and the supercooling
side expansion valve (94) are located in this order from the outflow end of the low-pressure
side heat exchanger tube (91 b).
[0079] The supercooling side compressor (92) is a variable displacement compressor. The
supercooling side outdoor heat exchanger (93) is a cross-fin type fin-and-tube heat
exchanger. A supercooling side outdoor fan (95) is provided near the supercooling
side outdoor heat exchanger (93). The supercooling side outdoor heat exchanger (93)
performs heat exchange between outdoor air blown from the supercooling side outdoor
fan (95) and the refrigerant. The supercooling side expansion valve (94) is an electronic
expansion valve which is controllable in opening.
[0080] The closed circuit (90a) of the supercooling unit (13) includes a supercooling side
low-pressure pressure sensor (96) provided on a suction pipe of the supercooling side
compressor (92). The supercooling side low-pressure pressure sensor (96) detects the
pressure of the refrigerant at a low-pressure side of the closed circuit (90a). A
supercooling side outdoor-temperature sensor (97) is provided near the supercooling
side outdoor fan (95). The supercooling side outdoor-temperature sensor (97) detects
the temperature of outdoor air surrounding the supercooling side outdoor heat exchanger
(93).
<<Freezer Display Case>>
[0081] In the freezer display case (14), the first freezing circuit (100) and the second
freezing circuit (110) branch off from the third connection pipe (33), and are connected
in parallel with each other. The first freezing circuit (100) includes a first indoor
expansion valve (101) and a first cooling heat exchanger (102). The second freezing
circuit (110) includes a second indoor expansion valve (111) and a second cooling
heat exchanger (112). The indoor expansion valves (101, 111) are electronic expansion
valves controllable in opening, and are utilization side expansion valves.
[0082] The cooling heat exchangers (102, 112) are cross-fin type fin-and-tube heat exchangers,
and are utilization side heat exchangers. The first cooling heat exchanger (102) and
the second cooling heat exchanger (112) are placed in the same case. As shown in FIG.
2, the cooling heat exchangers (102, 112) are close to each other in such a manner
that heat exchanger tubes thereof penetrate the same fin (102a). That is, the cooling
heat exchangers (102, 112) share the fin (102a). The heat exchanger tubes of the respective
cooling heat exchangers (102, 112) may be in contact with each other, or may be spaced
apart at a given distance. In FIG. 1, the cooling heat exchangers (102, 112) are separated
from each other for convenience. Near the cooling heat exchangers (102, 112), an in-case
fan (103) is provided. Each of the cooling heat exchangers (102, 112) performs heat
exchange between in-case air blown from the in-case fan (103) and the refrigerant.
[0083] In the freezer display case (14), a drain pan (104) is placed under the cooling heat
exchangers (102, 112). The drain pan (104) is an open vessel for recovering frost
and dew condensation water which have dropped from the surfaces of the cooling heat
exchangers (102, 112). A heating pipe part (33a) that is part of the third connection
pipe (33) is provided inside the drain pan (104). The heating pipe part (33a) is formed
along the bottom plate of the drain pan (104). The heating pipe part (33a) melts frost
and ice blocks recovered in the drain pan (104) by utilizing heat of the refrigerant
flowing in the heating pipe part (33a). In FIG. 1, the in-case fan (103), the drain
pan (104), and the heating pipe part (33a) are illustrated at locations closer to
the first cooling heat exchanger (102), for convenience.
[0084] The first freezing circuit (100) includes a first refrigerant-temperature sensor
(105) and a second refrigerant-temperature sensor (106). The first refrigerant-temperature
sensor (105) is located closer to the end of the first cooling heat exchanger (102)
serving as the inflow end during cooling operation. The second refrigerant-temperature
sensor (106) is located closer to the end of the first cooling heat exchanger (102)
serving as the outflow end during cooling operation. The second freezing circuit (110)
includes a third refrigerant-temperature sensor (115) and a fourth refrigerant-temperature
sensor (116). The third refrigerant-temperature sensor (115) is located closer to
the end of the second cooling heat exchanger (112) serving as the inflow end during
cooling operation. The fourth refrigerant-temperature sensor (116) is located closer
to the end of the second cooling heat exchanger (112) serving as the outflow end during
cooling operation. Each of the temperature sensors (105, 106, 115, 116) detects the
temperature of the refrigerant flowing in the associated portion. An in-case temperature
sensor (107) is also provided near the in-case fan (103). The in-case temperature
sensor (107) detects the temperature of in-case air in the freezer display case (14).
<<First Booster Unit>>
[0085] The first booster circuit (120) of the first booster unit (15) includes a first low-stage
compressor (121), a second low-stage compressor (122), and a third low-stage compressor
(123). Each of the low-stage compressors (121, 122, 123) is fully-enclosed, and is
a high-pressure domed scroll compressor. The first low-stage compressor (121) is a
variable displacement compressor which is supplied with electric power through an
inverter. Specifically, the first low-stage compressor (121) 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. The second low-stage compressor (122) and the
third low-stage compressor (123) are fixed displacement compressors. Specifically,
the second and third low-stage compressors (122, 123) have their respective motors
always operated at constant rotational speeds, and are not changeable in displacement.
[0086] The discharge side of the first low-stage compressor (121) is connected to an end
of a fourth discharge pipe (131). The discharge side of the second low-stage compressor
(122) is connected to an end of a fifth discharge pipe (132). The discharge side of
the third low-stage compressor (123) is connected to an end of a sixth discharge pipe
(133). The other ends of these discharge pipes (131, 132, 133) are connected to the
third shut-off valve (23) through a first low-stage discharge pipe (134). The suction
side of the first low-stage compressor (121) is connected to a fourth suction pipe
(135). The suction side of the second low-stage compressor (122) is connected to a
fifth suction pipe (136). The suction side of the third low-stage compressor (123)
is connected to a sixth suction pipe (137). The other ends of these suction pipes
(135, 136, 137) are connected to the fourth connection pipe (34) through a first low-stage
suction pipe (138).
[0087] The first low-stage discharge pipe (134) is provided with a first low-stage oil separator
(124). The first low-stage oil separator (124) is in the shape of a sealed cylinder.
An end of a first low-stage oil return pipe (124a) is connected to the bottom of the
first low-stage oil separator (124). The other end of the first low-stage oil return
pipe (124a) is connected to the first low-stage suction pipe (138). The first low-stage
oil return pipe (124a) is provided with a second solenoid valve (SV2). The first low-stage
oil separator (124) separates oil (i.e., refrigerating machine oil) from the refrigerant
expelled from the first through third low-stage compressors (121, 122, 123). The oil
obtained by the first low-stage oil separator (124) is sucked into the low-stage compressors
(121, 122, 123) by way of a low-stage oil return pipe (124a) with the second solenoid
valve (SV2) opened.
[0088] First through third oil discharge pipes (141, 142, 143) are respectively connected
to the low-stage compressors (121, 122, 123) of the first booster circuit (120). An
end of each of the oil discharge pipes (141, 142, 143) opens into an oil sump in a
casing of an associated one of the low-stage compressors (121, 122, 123). The other
end of each of the oil discharge pipes (141, 142, 143) is connected to the first low-stage
discharge pipe (134). The first through third oil discharge pipes (141, 142, 143)
are provided with a third solenoid valve (SV3), a fourth solenoid valve (SV4), and
a fifth solenoid valve (SV5), respectively. In the oil discharge pipes (141, 142,
143), when the solenoid valves (SV3, SV4, SV5) are opened, redundant oil that has
accumulated in the low-stage compressors (121, 122, 123) is sent to the high-stage
compressors (41, 42, 43) in the outdoor circuit (40).
[0089] The first booster circuit (120) includes a first escape pipe (144), a first bypass
pipe (145), a first suction side injection pipe (146), and a first discharge side
injection pipe (147).
[0090] When the low-stage compressors (121, 122, 123) are stopped because of failures or
the like during cooling operation which will be described later, the first escape
pipe (144) allows the refrigerant in the suction sides of the low-stage compressors
(121, 122, 123) to be sent to the high-stage compressors (41, 42, 43) in the outdoor
circuit (40). An end of the first escape pipe (144) is connected to the suction sides
of the low-stage compressors (121, 122, 123), and the other end of the first escape
pipe (144) is connected to a point between the first low-stage oil separator (124)
and the third shut-off valve (23).
[0091] The first bypass pipe (145) allows the refrigerant to bypass the low-stage compressors
(121, 122, 123). The first bypass pipe (145) connects the suction sides and the discharge
sides of the low-stage compressors (121, 122, 123). Specifically, an end of the first
bypass pipe (145) is connected to the first low-stage suction pipe (138). On the other
hand, as illustrated in FIG. 3, the other end of the first bypass pipe (145) is connected
to the first low-stage oil return pipe (124a) so as to be connected to the bottom
of the first low-stage oil separator (124). The first bypass pipe (145) is provided
with a sixth solenoid valve (SV6).
[0092] The first suction side injection pipe (146) is configured to send liquid refrigerant
to the suction sides of the low-stage compressors (121, 122, 123). During cooling
operation, the liquid refrigerant is sucked into the low-stage compressors (121, 122,
123) as appropriate, thus adjusting the temperature of the refrigerant expelled from
the low-stage compressors (121, 122, 123). An end of the first suction side injection
pipe (146) is connected to the third connection pipe (33), and the other end of the
first suction side injection pipe (146) is connected to the first low-stage suction
pipe (138). The first suction side injection pipe (146) is provided with a third motor-operated
valve (146a) controllable in opening.
[0093] The first discharge side injection pipe (147) sends the liquid refrigerant to the
discharge sides of the low-stage compressors (121, 122, 123). During cooling operation,
the liquid refrigerant is mixed with the refrigerant expelled from the low-stage compressors
(121, 122, 123), and thus oil remaining in the expelled refrigerant can be easily
transmitted with the refrigerant. Specifically, when the refrigerant expelled from
the low-stage compressors (121, 122, 123) is excessively dried, oil in the refrigerant
is likely to stagnate in, for example, the connection pipes. However, the mixing of
the liquid refrigerant in the expelled refrigerant facilitates transmission of the
oil to the high-stage compressors (41, 42, 43) in the outdoor circuit (40). An end
of the first discharge side injection pipe (147) is connected to the third connection
pipe (33), and the other end of the first discharge side injection pipe (147) is connected
to the first low-stage discharge pipe (134). The first discharge side injection pipe
(147) is provided with a fourth motor-operated valve (147a) controllable in opening.
[0094] The first booster circuit (120) includes various sensors. Specifically, the fourth
discharge pipe (131) is provided with a fourth discharge temperature sensor (151),
the fifth discharge pipe (132) is provided with a fifth discharge temperature sensor
(152), and the sixth discharge pipe (133) is provided with a sixth discharge temperature
sensor (153). The discharge temperature sensors (151, 152, 153) respectively detect
the temperatures of the refrigerant expelled from the low-stage compressors (121,
122, 123). The first low-stage discharge pipe (134) is provided with a first low-stage
high-pressure pressure sensor (154). The first low-stage suction pipe (138) is provided
with a first low-stage low-pressure pressure sensor (155). The first low-stage high-pressure
pressure sensor (154) detects the pressure of the refrigerant at the discharge side
of the first booster circuit (120). The first low-stage low-pressure pressure sensor
(155) detects the pressure of the refrigerant at the suction side of the first booster
circuit (120).
[0095] The first booster circuit (120) includes a plurality of check valves. Specifically,
the fourth discharge pipe (131) is provided with a seventh check valve (CV7), the
fifth discharge pipe (132) is provided with an eighth check valve (CV8), and the sixth
discharge pipe (133) is provided with a ninth check valve (CV9). The first escape
pipe (144) is provided with a tenth check valve (CV 10).
<<Second Booster Unit>>
[0096] The second booster circuit (160) of the second booster unit (16) has a configuration
similar to that of the first booster circuit (120) described above, and thus detailed
description thereof is omitted. That is, the second booster circuit (160) includes
a fourth low-stage compressor (161), a fifth low-stage compressor (162), and a sixth
low-stage compressor (163). The second booster circuit (160) includes seventh through
ninth discharge pipes (171, 172, 173), a second low-stage discharge pipe (174), seventh
through ninth suction pipes (175, 176, 177), and a second low-stage suction pipe (178).
[0097] The second booster circuit (160) includes a second low-stage oil separator (164),
a second low-stage oil return pipe (164a), and fourth through sixth oil discharge
pipes (181, 182, 183). The second low-stage oil return pipe (164a) is provided with
a seventh solenoid valve (SV7). The oil discharge pipes (181, 182, 183) are respectively
provided with eighth through tenth solenoid valves (SV8, SV9, SV 10). The second booster
circuit (160) includes a second escape pipe (184), a second bypass pipe (185), a second
suction side injection pipe (186), and a second discharge side injection pipe (187).
The second bypass pipe (185) is provided with an eleventh solenoid valve (SV11), the
second suction side injection pipe (186) is provided with a fifth motor-operated valve
(186a), and the second discharge side injection pipe (187) is provided with a sixth
motor-operated valve (187a). The second booster circuit (160) further includes seventh
through ninth discharge temperature sensors (191, 192, 193), a second low-stage high-pressure
pressure sensor (194), a second low-stage low-pressure pressure sensor (195), and
eleventh through fourteenth check valves (CV 11, CV 12, CV13, CV 14).
<<Control Unit>>
[0098] The refrigeration system (10) of this embodiment includes a controller (200) as a
control unit. This controller (200) is configured to receive detection signals obtained
by, for example, the sensors in the outdoor unit (11), the supercooling unit (13),
the freezer display case (14), the first booster unit (15), and the second booster
unit (16), and to output control signals to components in these units (11, 13, 14,
15, 16).
-Operation-
[0099] Operation of the refrigeration system (10) of this embodiment is now described. This
refrigeration system (10) is capable of performing cooling operation for cooling the
inside of the freezer display case (14) and also performing defrosting operation for
defrosting the cooling heat exchangers (102, 112) in the freezer display case (14).
<Cooling Operation>
[0100] In the cooling operation shown in FIG. 4, the four-way selector valve (48) is set
at the first position. The outdoor expansion valve (47) is fully closed. The opening
of each of the supercooling side expansion valve (94), the first indoor expansion
valve (101), and the second indoor expansion valve (111) is adjusted, as appropriate.
The sixth solenoid valve (SV6) and the eleventh solenoid valve (SV11) are closed,
and the other solenoid valves are also closed in principle.
[0101] In the cooling operation, the outdoor fan (60), the supercooling side outdoor fan
(95), and the in-case fan (103) are driven. The high-stage compressors (41, 42, 43)
in the outdoor circuit (40), the low-stage compressors (121, 122, 123) in the first
booster circuit (120), the low-stage compressors (161, 162, 163) in the second booster
circuit (160) are also driven. Consequently, the refrigerant circuit in the cooling
operation operates in a two-stage compression refrigeration cycle in which the outdoor
heat exchanger (44) serves as a condenser and the cooling heat exchangers (102, 112)
serve as evaporators.
[0102] Specifically, the refrigerant expelled from the high-stage compressors (41, 42, 43)
passes through the high-stage discharge pipe (54) and the four-way selector valve
(48), and flows into the outdoor heat exchanger (44). In the outdoor heat exchanger
(44), the refrigerant dissipates heat to the outdoor air, and condenses. The refrigerant
condensed in the outdoor heat exchanger (44) passes through the receiver (45) and
the first heat exchanger tube (46a) of the internal heat exchanger (46), and flows
into the third liquid pipe (63). Part of the refrigerant flowing in the third liquid
pipe (63) is subjected to pressure reduction at the second motor-operated valve (67a)
when flowing in the second injection pipe (67), and then flows into the second heat
exchanger tube (46b) of the internal heat exchanger (46). In the internal heat exchanger
(46), heat is exchanged between the high-pressure refrigerant flowing in the first
heat exchanger tube (46a) and the low-pressure refrigerant flowing in the second heat
exchanger tube (46b). Consequently, heat of the refrigerant in the first heat exchanger
tube (46a) is taken as heat of evaporation of the refrigerant flowing in the second
heat exchanger tube (46b). That is, in the internal heat exchanger (46), the refrigerant
flowing in the first heat exchanger tube (46a) is cooled. The refrigerant evaporated
in the second heat exchanger tube (46b) flows into the high-stage suction pipe (58).
[0103] The refrigerant that has flown from the third liquid pipe (63) passes through the
refrigerant reservoir (81), and then flows into the high-pressure side heat exchanger
tube (91 a) of the supercooling heat exchanger (91). On the other hand, in the closed
circuit (90a) of the supercooling unit (13), a vapor compression refrigeration cycle
is performed. Specifically, in the closed circuit (90a), the refrigerant compressed
in the supercooling side compressor (92) condenses in the supercooling side outdoor
heat exchanger (93), then is subjected to pressure reduction in the supercooling side
expansion valve (94), and then flows into the low-pressure side heat exchanger tube
(91b) of the supercooling heat exchanger (91). In the supercooling heat exchanger
(91), heat of the refrigerant in the high-pressure side heat exchanger tube (91 a)
is taken as heat of evaporation of the refrigerant in the low-pressure side heat exchanger
tube (91b). That is, in the supercooling heat exchanger (91), the refrigerant flowing
in the high-pressure side heat exchanger tube (91a) is further cooled.
[0104] The refrigerant that has flown from the high-pressure side heat exchanger tube (91a)
of the supercooling heat exchanger (91) flows through the third connection pipe (33),
and then flows into the heating pipe part (33a). At this time, frost that has dropped
from the surfaces of the cooling heat exchangers (102, 112) and ice blocks produced
by freezing of dew condensation water has accumulated in the drain pan (104). Accordingly,
when the drain pan (104) is heated with the refrigerant flowing in the heating pipe
part (33a), frost and ice blocks in the drain pan (104) melt. Water produced by the
melting in the drain pan (104) is drained from the drain pan (104) through, for example,
the drain pipe. On the other hand, the refrigerant flowing in the heating pipe part
(33a) gives heat of melting to the frost and ice blocks in the drain pan (104), and
thus is further cooled. The refrigerant that has flown from the heating pipe part
(33a) is distributed to the first freezing circuit (100) and the second freezing circuit
(110).
[0105] The refrigerant that has flown into the first freezing circuit (100) is subjected
to pressure reduction when passing through the first indoor expansion valve (101),
and then flows into the first cooling heat exchanger (102). In the first cooling heat
exchanger (102), the refrigerant takes heat from the in-case air, and evaporates.
Consequently, the air in the freezer display case (14) is cooled. The refrigerant
that has evaporated in the first cooling heat exchanger (102) flows into the first
booster circuit (120).
[0106] In the same manner, the refrigerant that has flown into the second freezing circuit
(110) is subjected to pressure reduction when passing through the second indoor expansion
valve (111), and then flows into the second cooling heat exchanger (112). In the second
cooling heat exchanger (112), the refrigerant takes heat from the in-case air, and
evaporates. The refrigerant that has evaporated in the second cooling heat exchanger
(112) flows into the second booster circuit (160). In this manner, the air in the
freezer display case (14) is kept at, for example, -30°C.
[0107] The refrigerant that has flown into the first booster circuit (120) is sucked into
the low-stage compressors (121, 122, 123). The refrigerant compressed in the low-stage
compressors (121, 122, 123) passes through the first low-stage oil separator (124),
and flows into the sixth connection pipe (36). In the first low-stage oil separator
(124), oil is separated from the refrigerant expelled from the low-stage compressors
(121, 122, 123). The oil obtained by the separation is sucked into the low-stage compressors
(121, 122, 123) through the first low-stage oil return pipe (124a) by appropriately
opening the second solenoid valve (SV2).
[0108] In the same manner, the refrigerant that has flown into the second booster circuit
(160) is sucked into the low-stage compressors (161, 162, 163). The refrigerant compressed
by the low-stage compressors (161, 162, 163) passes through the second low-stage oil
separator (164), and flows into the sixth connection pipe (36). In the second low-stage
oil separator (164), oil is separated from the refrigerant expelled from the low-stage
compressors (161, 162, 163). The oil obtained by the separation is sucked into the
low-stage compressors (161, 162, 163) through the second low-stage oil return pipe
(164a) by appropriately opening the seventh solenoid valve (SV7).
[0109] The refrigerant merged in the sixth connection pipe (36) passes through the four-way
selector valve (48), and flows into the high-stage suction pipe (58). This refrigerant
is mixed with the refrigerant which has flown from the second heat exchanger tube
(46b) of the internal heat exchanger (46) described above, and is sucked into the
high-stage compressors (121, 122, 123) to be compressed.
<Defrosting Operation>
[0110] In defrosting operation of the refrigeration system (10), a first individual defrosting
process for defrosting the first cooling heat exchanger (102) and a second individual
defrosting process for defrosting the second cooling heat exchanger (112) are repeated.
[0111] In the refrigeration system (10), when the cooling operation described above is continuously
performed for a given period of time or longer, the cooling operation shifts to defrosting
operation. Specifically, when a timer provided in the controller (200) indicates a
given set period, it is determined that an increasing amount of frost has accumulated
in the cooling heat exchangers (102, 112), thus performing defrosting operation.
[0112] In this defrosting operation, a first individual defrosting process is performed
first. The first individual defrosting process is aimed at defrosting the first cooling
heat exchanger (102). Before starting the defrosting operation, a pre-discharge process
for recovering refrigerant in the second cooling heat exchanger (112) not to be defrosted
in the first individual defrosting process, which is performed first in the subsequent
operation, is performed.
<<Pre-discharge Operation>>
[0113] In the pre-discharge process shown in FIG. 5, the four-way selector valve (48) is
set at the first position, and the high-stage compressors (41, 42, 43) operate. The
outdoor expansion valve (47) is fully closed. The opening of the supercooling side
expansion valve (94) is adjusted. In the first utilization side circuit (100, 120)
associated with the first cooling heat exchanger (102) to be defrosted in the first
individual defrosting process, which will be described later, the opening of each
of the first indoor expansion valve (101), the third motor-operated valve (146a),
and the fourth motor-operated valve (147a) is adjusted as appropriate, and the sixth
solenoid valve (SV6) is closed. In the first utilization side circuit (100, 120),
the low-stage compressors (121, 122, 123) are operated. On the other hand, in the
second utilization side circuit (110, 160) associated with the second cooling heat
exchanger (112) not to be defrosted in the first individual defrosting process, each
of the second indoor expansion valve (111), the fifth motor-operated valve (186a),
and the sixth motor-operated valve (187a) is fully closed, and the eleventh solenoid
valve (SV11) is also closed. In the second utilization side circuit (110, 160), the
fourth low-stage compressor (161) which is a variable displacement compressor is operated.
[0114] In this pre-discharge process, the refrigerant compressed in the high-stage compressors
(41, 42, 43) condenses in the outdoor heat exchanger (44), and then is sent only to
the first utilization side circuit (100, 120). In the first utilization side circuit
(100, 120), the refrigerant subjected to pressure reduction at the first indoor expansion
valve (101) evaporates in the first cooling heat exchanger (102). Accordingly, in
this pre-discharge process, cooling of the air in the freezer display case (14) is
still continued. The refrigerant that has evaporated in the first cooling heat exchanger
(102) is compressed in the low-stage compressors (121, 122, 123) in the first booster
circuit (120), and flows into the sixth connection pipe (36).
[0115] On the other hand, in the second utilization side circuit (110, 160), the refrigerant
is sealed in between the second indoor expansion valve (111) and the suction ports
of the low-stage compressors (161, 162, 163). When the fourth low-stage compressor
(161) is driven in this state, the refrigerant that has accumulated in the second
cooling heat exchanger (112) and the refrigerant sealed in the other pipes are sucked
into the fourth low-stage compressor (161) to be compressed. This causes a rapid decrease
in the pressure at the suction side of the fourth low-stage compressor (161). Accordingly,
even if the temporarily sealed refrigerant condenses and becomes liquid, the pressure
of this refrigerant is reduced, and the refrigerant becomes gas. This can avoid a
so-called liquid compression phenomenon in which the liquid refrigerant is sucked
into the fourth low-stage compressor (161).
[0116] The refrigerant expelled from the fourth low-stage compressor (161) passes through
the second low-stage oil separator (164), and flows into the sixth connection pipe
(36). In this manner, in the second utilization side circuit (110, 160) not to be
defrosted in the first individual defrosting process, the refrigerant is discharged
outside the system with operation of the low-stage compressor (161), and is recovered
to the outdoor circuit (40). During the pre-discharge process, this refrigerant is
sent to the first cooling heat exchanger (102), and is used for cooling of the freezer
display case (14).
[0117] In addition, in the pre-discharge process, the seventh solenoid valve (SV7) is opened
as appropriate, thereby returning oil recovered in the second low-stage oil separator
(164) to the second low-stage oil return pipe (164a). Further, at this time, the eighth
solenoid valve (SV8) is opened. This causes redundant oil in the fourth low-stage
compressor (161) to be sent to the sixth connection pipe (36) by way of the fourth
oil discharge pipe (181), and is finally sucked into the high-stage compressors (41,
42, 43). As described above, in this pre-discharge process, oil recovery operation
in which oil in the low-stage compressor (161) in the second utilization side circuit
(110, 160) not to be defrosted in the first individual defrosting process is sent
to the high-stage compressors (41, 42, 43) is also performed.
[0118] In the pre-discharge process, operation capacity of the fourth low-stage compressor
(161) is controlled according to the refrigerant temperatures at the discharge sides
of the low-stage compressors (161, 162, 163) in the second utilization side circuit
(110, 160). Specifically, the fourth low-stage compressor (161) is controlled in such
a manner that the operation frequency decreases as the temperature of the expelled
refrigerant detected by the seventh discharge temperature sensor (191).
[0119] In the pre-discharge process, when the temperature detected by the seventh discharge
temperature sensor (191) reaches a given temperature or more, the fourth low-stage
compressor (161) is stopped. Consequently, the pre-discharge process is completed,
and the first individual defrosting process is performed.
<<First Individual Defrosting Process>>
[0120] In the first individual defrosting process shown in FIG. 6, the four-way selector
valve (48) is set at the second position, and the high-stage compressors (41, 42,
43). The opening of each of the outdoor expansion valve (47) and the supercooling
side expansion valve (94) is adjusted. In the first utilization side circuit (100,
120) associated with the first cooling heat exchanger (102) to be defrosted in the
first individual defrosting process, the first indoor expansion valve (101) is fully
opened, each of the third motor-operated valve (146a) and the fourth motor-operated
valve (147a) is fully closed, and the sixth solenoid valve (SV6) is opened. In the
first utilization side circuit (100, 120), the low-stage compressors (121, 122, 123)
are stopped.
[0121] On the other hand, in the second utilization side circuit (110, 160) associated with
the second cooling heat exchanger (112) not to be defrosted in the first individual
defrosting process, each of the second indoor expansion valve (111), the fifth motor-operated
valve (186a), and the sixth motor-operated valve (187a) is fully closed, and the eleventh
solenoid valve (SV11) is closed. In the second utilization side circuit (110, 160),
the low-stage compressors (161, 162, 163) are stopped.
[0122] In the first individual defrosting process, the refrigerant compressed in the high-stage
compressors (41, 42, 43) flows into the sixth connection pipe (36). The refrigerant
that has flown into the sixth connection pipe (36) passes through the first booster
circuit (120), and flows into the first low-stage oil separator (124). In the first
low-stage oil separator (124), the refrigerant that has accumulated therein is pushed
out, and flows into the first bypass pipe (145). The refrigerant flowing in the first
bypass pipe (145) flows into the first freezing circuit (100) by way of the first
low-stage suction pipe (138).
[0123] The refrigerant that has flown into the first freezing circuit (100) flows in the
first cooling heat exchanger (102). In the first cooling heat exchanger (102), frost
on the surface of the first cooling heat exchanger (102) is heated from the inside
thereof to be melted, whereas the refrigerant gives heat of melting to the frost to
condense. The refrigerant condensed in the first cooling heat exchanger (102) passes
through the fully-open first indoor expansion valve (101), and then flows in the heating
pipe part (33a) of the third connection pipe (33). Consequently, this refrigerant
heats the inside of the drain pan (104), thereby melting the frost and ice blocks
in the drain pan (104). The refrigerant that has passed through the third connection
pipe (33) is cooled in the supercooling heat exchanger (91), and then flows into the
refrigerant reservoir (81).
[0124] In this case, the refrigerant reservoir (81) stores refrigerant for increasing the
amount of refrigerant for use in defrosting the cooling heat exchangers (102, 112)
during defrosting operation. Specifically, the refrigerant may stagnate in the cooling
heat exchangers (102, 112) during defrosting operation, resulting in a deficiency
of the refrigerant for use in defrosting. However, the refrigerant reservoir (81)
stores the refrigerant in an amount enough to compensate for the deficiency. Accordingly,
when refrigerant stagnation occurs in the cooling heat exchangers (102, 112), refrigerant
in an amount corresponding to the amount of the stagnating refrigerant flows from
the refrigerant reservoir (81) into the fourth liquid pipe (82) as appropriate, thereby
adding the refrigerant in the refrigerant circuit.
[0125] The refrigerant that has flown from the refrigerant reservoir (81) is further cooled
in the internal heat exchanger (46), and then is subjected to pressure reduction in
the outdoor expansion valve (47). The refrigerant whose pressure has been reduced
in the outdoor expansion valve (47) condenses in the outdoor heat exchanger (44),
and is sucked into the high-stage compressors (41, 42, 43).
[0126] On the other hand, in the second utilization side circuit (110, 160), the second
indoor expansion valve (111), the eleventh solenoid valve (SV11), the fifth motor-operated
valve (186a), and the sixth motor-operated valve (187a) are closed. Accordingly, no
refrigerant is sent to the second utilization side circuit (110, 160), and thus the
second cooling heat exchanger (112) not to be defrosted in the first individual defrosting
process is stopped.
[0127] The first individual defrosting process as described above is completed before a
given amount of liquid refrigerant accumulates in the first cooling heat exchanger
(102). Specifically, as the first individual defrosting process continues, liquid
refrigerant accumulates in the first cooling heat exchanger (102), and thus the degree
of supercooling of the refrigerant which has flown from the first cooling heat exchanger
(102) increases. In the first individual defrosting process, the degree of supercooling
is calculated from the difference between the condensation temperature of the first
cooling heat exchanger (102) obtained from the values detected by the high-stage high-pressure
pressure sensor (74) and the first refrigerant-temperature sensor (105) and the temperature
of the refrigerant detected by the second refrigerant-temperature sensor (106). When
the obtained degree of supercooling reaches a given temperature (e.g., 5°C) or more,
the first individual defrosting process is completed.
[0128] After the completion of the first individual defrosting process, the next individual
defrosting process is performed so as to switch the cooling heat exchanger (102, 112)
to be defrosted. Specifically, after the completion of the first individual defrosting
process, the defrosting target is changed from the first cooling heat exchanger (102)
to the second cooling heat exchanger (112), and then a second individual defrosting
process is performed.
[0129] After the first individual defrosting process described above, the refrigerant remains
in the first cooling heat exchanger (102) and the pipes located before and after the
first cooling heat exchanger (102). If the second individual defrosting process was
immediately performed after this state, an insufficient amount of refrigerant might
be kept for defrosting of the second cooling heat exchanger. To prevent this, in the
refrigeration system (10) of this embodiment, before the second individual defrosting
process, a discharge process (i.e., a first discharge process) for discharging refrigerant
in the first cooling heat exchanger (102) not to be defrosted in the second individual
defrosting process is performed, in the same manner as in the pre-discharge process
described above.
<<First Discharge Process>>
[0130] In the first discharge process shown in FIG. 7, the four-way selector valve (48)
is set at the second position, and the high-stage compressors (41, 42, 43) operate.
In addition, the opening of each of the outdoor expansion valve (47) and the supercooling
side expansion valve (94) is adjusted. In the second utilization side circuit (110,
160) associated with the second cooling heat exchanger (112) to be defrosted in the
second individual defrosting process, the second indoor expansion valve (111) is fully
opened, the fifth motor-operated valve (186a) and the sixth motor-operated valve (187a)
are closed, and the eleventh solenoid valve (SV11) is opened. In the second utilization
side circuit (110, 160), the low-stage compressors (161, 162, 163) are stopped.
[0131] On the other hand, in the first utilization side circuit (100, 120) associated with
the first cooling heat exchanger (102) not to be defrosted in the second individual
defrosting process, each of the first indoor expansion valve (101), the third motor-operated
valve (146a), and the fourth motor-operated valve (147a) is fully closed, and the
sixth solenoid valve (SV6) is also closed. In the first utilization side circuit (100,
120), the first low-stage compressor (121) which is a variable displacement compressor
is operated.
[0132] In the first discharge process, the refrigerant compressed in the high-stage compressors
(41, 42, 43) flows into the sixth connection pipe (36). The refrigerant flowing in
the sixth connection pipe (36) passes through the second booster circuit (160), and
then flows into the second low-stage oil separator (164). In the second low-stage
oil separator (164), the refrigerant that has accumulated therein is pushed out, and
flows into the second bypass pipe (185). The refrigerant flowing in the second bypass
pipe (185) flows into the second freezing circuit (110) by way of the second low-stage
suction pipe (178).
[0133] The refrigerant that has flown into the second freezing circuit (110) flows into
the second cooling heat exchanger (112). In the second cooling heat exchanger (112),
frost on the surface of the second cooling heat exchanger (112) is heated from the
inside thereof to be melted, whereas the refrigerant gives heat of melting to the
frost to condense. The refrigerant condensed in the second cooling heat exchanger
(112) passes through the fully-open second indoor expansion valve (111), and flows
into the heating pipe part (33a) of the third connection pipe (33). Consequently,
this refrigerant heats the inside of the drain pan (104), thereby melting the frost
and ice blocks in the drain pan (104). The subsequent flow of the refrigerant is the
same as in the first individual defrosting process described above, and thus description
thereof is omitted.
[0134] On the other hand, in the first utilization side circuit (100, 120), the refrigerant
is sealed in between the first indoor expansion valve (101) and the suction ports
of the low-stage compressors (141, 142, 143). When the first low-stage compressor
(121) is driven in this state, the refrigerant that has accumulated in the first cooling
heat exchanger (102) and the refrigerant sealed in the other pipes are sucked into
the first low-stage compressor (141) to be compressed. This causes a rapid decrease
in the pressure at the suction side of the first low-stage compressor (121), and the
refrigerant becomes gas. Accordingly, it is possible to avoid a liquid compression
phenomenon in the first low-stage compressor (121).
[0135] The refrigerant compressed in the first low-stage compressor (121) passes through
the first low-stage oil separator (124), and flows into the sixth connection pipe
(36). This refrigerant is mixed with the refrigerant expelled from the high-stage
compressors (41, 42, 43), and is sent to the second utilization side circuit (110,
160). That is, the refrigerant discharged from the first utilization side circuit
(100, 120) is used for defrosting the second cooling heat exchanger (112). In this
case, the refrigerant discharged from the first utilization side circuit (100, 120)
is provided with heat input from the first low-stage compressor (121). Accordingly,
the capacity to defrost the second cooling heat exchanger (112) is enhanced.
[0136] In the first discharge process, the second solenoid valve (SV2) and the third solenoid
valve (SV3) are opened as appropriate, in the same manner as in the pre-discharge
process described above. Consequently, oil recovery operation in which redundant oil
in the first low-stage compressor (121) is sent to the high-stage compressors (41,
42, 43) is performed.
[0137] As the pre-discharge process described above, the first discharge process is completed
when the temperature detected by the fourth discharge temperature sensor (151) reaches
a given temperature or more, and then the second individual defrosting process is
performed.
<<Second Individual Defrosting Process>>
[0138] In the second individual defrosting process shown in FIG. 8, the four-way selector
valve (48) is set at the second position, and the high-stage compressors (41, 42,
43) operate. In addition, the opening of each of the outdoor expansion valve (47)
and the supercooling side expansion valve (94) is adjusted. In the second utilization
side circuit (110, 160) associated with the second cooling heat exchanger (112) to
be defrosted in the second individual defrosting process, the second indoor expansion
valve (111) is fully opened, each of the fifth motor-operated valve (186a) and the
sixth motor-operated valve (187a) is fully closed, and the eleventh solenoid valve
(SV11) is opened. In the second utilization side circuit (110, 160), the low-stage
compressors (161, 162, 163) are stopped.
[0139] On the other hand, in the first utilization side circuit (100, 120) associated with
the first cooling heat exchanger (102) not to be defrosted in the second individual
defrosting process, each of the first indoor expansion valve (101), the third motor-operated
valve (146a), and the fourth motor-operated valve (147a) is fully closed, and the
sixth solenoid valve (SV6) is also closed. In the first utilization side circuit (100,
120), the low-stage compressors (121, 122, 123) are stopped.
[0140] In the second individual defrosting process, the refrigerant compressed in the high-stage
compressors (41, 42, 43) flows into the sixth connection pipe (36). The refrigerant
that has flown into the sixth connection pipe (36) passes through the second booster
circuit (160), and then flows into the second low-stage oil separator (164). In the
second low-stage oil separator (164), the refrigerant that has accumulated therein
is pushed out, and flows into the second bypass pipe (185). The refrigerant that has
flown into the second bypass pipe (185) flows into the second freezing circuit (110)
by way of the second low-stage suction pipe (178).
[0141] The second freezing circuit (110) defrosts the second cooling heat exchanger (112),
in the same manner as in the first individual defrosting process described above.
The refrigerant that has flown from the second cooling heat exchanger (112) is also
used for heating the inside of the drain pan (104). The subsequent flow of the refrigerant
is the same as in the first individual defrosting process described above, and thus
description thereof is omitted.
[0142] The second individual defrosting process described above is completed before a given
amount of liquid refrigerant accumulates in the second cooling heat exchanger (112).
Specifically, in the second individual defrosting process, the degree of supercooling
is calculated from the difference between the refrigerant temperature detected by
the third refrigerant-temperature sensor (115) and the refrigerant temperature detected
by the fourth refrigerant-temperature sensor (116), for example. When the obtained
degree of supercooling reaches a given temperature (e.g., 5°C) or more, the second
individual defrosting process is completed.
[0143] After the completion of the second individual defrosting process, the first individual
defrosting process is performed again. Before this first individual defrosting process,
a process (i.e., a second discharge process) for discharging the refrigerant in the
second cooling heat exchanger (112) is performed, in the same manner as in the first
discharge process described above.
<<Second Discharge Process>>
[0144] In the second discharge process shown in FIG. 9, the four-way selector valve (48)
is set at the second position, and the high-stage compressors (41, 42, 43) operate.
In addition, the opening of each of the outdoor expansion valve (47) and the supercooling
side expansion valve (94) is adjusted. In the first utilization side circuit (100,
120) associated with the first cooling heat exchanger (102) to be defrosted in the
first individual defrosting process, the first indoor expansion valve (101) is fully
opened, the third motor-operated valve (146a) and the fourth motor-operated valve
(147a) are closed, and the sixth solenoid valve (SV6) is opened. In the first utilization
side circuit (100, 120), the low-stage compressors (121, 122, 123) are stopped.
[0145] On the other hand, in the second utilization side circuit (110, 160) associated with
the second cooling heat exchanger (112) not to be defrosted in the first individual
defrosting process, each of the second indoor expansion valve (111), the fifth motor-operated
valve (186a), and the sixth motor-operated valve (187a) is fully closed, and the eleventh
solenoid valve (SV11) is also closed. In the second utilization side circuit (110,
160), the fourth low-stage compressor (161) which is a variable displacement compressor
is operated.
[0146] In the second discharge process, the refrigerant in the second utilization side circuit
(110, 160) is discharged to outside the system, as in the first discharge process
described above. This refrigerant is sent to the first cooling heat exchanger (102),
and is used for defrosting, together with the refrigerant expelled from the high-stage
compressors (41, 42, 43).
[0147] As described above, in defrosting operation, a series of a first individual defrosting
process→a first discharge process→a second individual defrosting process→a second
discharge process→a first individual defrosting process→... is repeated after the
pre-discharge process. This defrosting operation is completed when a timer provided
in the controller (200) indicates a given set period, and then the cooling operation
starts again.
-Advantages of Embodiment-
[0148] In the above embodiment, the first individual defrosting process and the second individual
defrosting process are sequentially performed in the defrosting operation in such
a manner that the cooling heat exchangers (102, 112) are alternately defrosted. Accordingly,
in this embodiment, the amount of refrigerant that accumulates in the cooling heat
exchangers (102, 112) is smaller than in a case where the two cooling heat exchangers
(102, 112) are defrosted as condensers at a time. Consequently, in the individual
defrosting processes, it is possible to keep a sufficient amount of refrigerant for
defrosting of the cooling heat exchangers (102, 112), and thus enhancing the efficiency
in defrosting operation.
[0149] In addition, in the above embodiment, before the individual defrosting processes,
discharge operation for sending refrigerant in the cooling heat exchanger (102, 112)
not to be defrosted to the cooling heat exchanger (102, 112) to be defrosted. Accordingly,
in this embodiment, the refrigerant in the cooling heat exchanger (102, 112) to be
stopped in the subsequent individual defrosting process can be used for defrosting
of the cooling heat exchanger (102, 112) to be defrosted, thus ensuring that shortage
of the refrigerant caused by refrigerant stagnation is avoided.
[0150] Further, in the first discharge process and the second discharge process of this
embodiment, refrigerant compressed by the low-stage compressors (121, 161) is sent
to the cooling heat exchanger (102, 112) to be defrosted. Accordingly, heat input
from the low-stage compressors (121, 161) can be used for defrosting of the cooling
heat exchangers (102, 112), thus enhancing the capacity to defrost the cooling heat
exchangers (102, 112).
[0151] In the discharge processes, the indoor expansion valve (101, 111) in the utilization
side circuit (100, 120; 110, 160) not to be defrosted is fully closed. Accordingly,
the refrigerant is sealed in between the indoor expansion valve (101, 111) and the
suction ports of the low-stage compressors (121, 122, 123; 161, 162, 163), and this
refrigerant is sent to the cooling heat exchanger (102, 112) to be defrosted. When
the low-stage compressor (121, 161) is operated in this manner, the refrigerant at
the suction side is subjected to pressure reduction, and becomes gas. Accordingly,
it is also possible to avoid a liquid compression phenomenon in the low-stage compressor
(121, 161).
[0152] In addition, in the embodiment, an end of each of the bypass pipes (145, 185) is
connected to an associated one of the low-stage oil separators (124, 164). Accordingly,
in the defrosting operation, the refrigerant that has accumulated in the low-stage
oil separators (124, 164) can be sent to the cooling heat exchanger (102, 112) to
be defrosted by way of the bypass pipes (145, 185). Consequently, a sufficient amount
of refrigerant can be kept for defrosting of the cooling heat exchangers (102, 112).
In particular, since an end of each of the bypass pipes (145, 185) is connected to
the bottom of an associated one of the low-stage oil separators (124, 164), liquid
refrigerant that has accumulated in the low-stage oil separators (124, 164), for example,
can also quickly flow into the bypass pipes (145, 185).
[0153] Moreover, in the embodiment, the cooling heat exchangers (102, 112) share a fin.
Accordingly, in the individual defrosting processes, one of the cooling heat exchangers
(102, 112) which is stopped is defrosted by utilizing heat of refrigerant in the other
cooling heat exchanger (102, 112) serving as a condenser. This results in reduction
of time necessary for defrosting the cooling heat exchanger (102, 112).
[0154] Furthermore, in the defrosting operation of the embodiment, when the degree of supercooling
of the refrigerant that has flown from the cooling heat exchanger (102, 112) to be
defrosted reaches a given temperature or more, the target of defrosting is switched.
This can avoid refrigerant stagnation in the cooling heat exchangers (102, 112). As
a result, a sufficient amount of refrigerant can be kept for defrosting of the cooling
heat exchangers (102, 112).
<<Other Embodiments>>
[0155] The above embodiment may have the following configurations.
[0156] In the above embodiment, the individual defrosting processes are performed in the
refrigeration system which can operate in a two-stage compression refrigeration cycle.
Alternatively, the individual defrosting processes may be performed on a cooling heat
exchanger in a refrigeration system operating in a single-stage compression refrigeration
cycle.
[0157] In the above embodiment, two cooling heat exchangers (102, 112) are provided, and
these cooling heat exchangers (102, 112) are alternately subjected to individual defrosting
processes. However, three or more cooling heat exchangers may be provided in such
a manner that each individual defrosting process is performed on at least one of these
cooling heat exchangers selected in a given order.
[0158] In the above embodiment, the cooling heat exchangers (102, 112) are placed in the
same case. Alternatively, the cooling heat exchangers (102, 112) may be placed in
different freezer display cases in such a manner that individual defrosting processes
are respectively performed on the cooling heat exchangers (102, 112).
[0159] In the discharge processes of the above embodiment, when the temperature of the refrigerant
expelled from the low-stage compressor (121, 161) reaches a given temperature or more,
the low-stage compressor (121, 161) is stopped. Alternatively, the low-stage compressor
(121, 161) may stopped, when the pressure at the suction side of the low-stage compressor
(121, 161) decreases to a given pressure or less, for example.
[0160] In the above embodiment, when the degree of supercooling of the cooling heat exchanger
(102, 112) to be defrosted reaches a give temperature or more, the target of defrosting
is switched, and the process proceeds to the next individual defrosting process. Alternatively,
the temperature of the refrigerant flowing from the cooling heat exchanger (102, 112)
may be detected by the refrigerant temperature sensor (105, 115) such that when this
temperature reaches a given temperature or more, the target of defrosting is switched
and the next individual defrosting operation is performed. The pressure at the high-pressure
side of the outdoor circuit (40), for example, may also be detected by the high-stage
high-pressure pressure sensor (74) such that when this pressure reaches a given pressure
or more, the process shifts to the next individual defrosting process.
[0161] The foregoing embodiments are merely preferred examples in nature, and are not intended
to limit the scope, applications, and use of the invention.
INDUSTRIAL APPLICABILITY
[0162] As can be seen from the above description, the present invention relates to refrigeration
systems each including a plurality of utilization side heat exchangers, and is particularly
useful for a refrigeration system capable of performing defrosting operation in a
refrigeration cycle in which a plurality of utilization side heat exchangers are defrosted.