Technical Field
[0001] The present disclosure relates to a refrigeration device that compresses a refrigerant
in multiple stages.
Background Art
[0002] PTL 1 discloses a refrigeration device including a two-stage compression mechanism.
Such a refrigeration device includes an electric compressor including a low-stage
compression mechanism and a high-stage compression mechanism in a sealed housing,
a condenser (gas cooler), a high-pressure expansion valve, a gas-liquid separator,
a low-pressure expansion valve, an evaporator, and a gas injection pipe. A gas refrigerant
introduced from the gas-liquid separator into the housing of the electric compressor
by the gas injection pipe is sucked into the high-stage compression mechanism together
with a refrigerant discharged into the housing from the low-stage compression mechanism.
Citation List
Patent Literature
Summary of Invention
Technical Problem
[0004] For the purpose of reducing the global warming potential (GWP) and improving the
coefficient of performance (COP), development and commercialization of a refrigeration
device that employs a refrigerant having a low GWP and includes a two-stage compression
mechanism are in progress.
[0005] In a case where a refrigerant including CO
2 is employed as the refrigerant, in order to suppress the high refrigerant discharge
temperature caused by the high-pressure operation to an allowable limit, it is effective
to introduce a gas refrigerant, which has an intermediate pressure between the high
pressure which is set in the condenser (gas cooler) and the low pressure which is
set in the evaporator, from the gas-liquid separator into a spacing between the low-stage
compression mechanism and the high-stage compression mechanism (intermediate-pressure
gas injection). According to such a configuration, the discharge temperature can be
suppressed by the injection of the gas refrigerant having a temperature which is lower
than the temperature of the refrigerant discharged from the low-stage compression
mechanism. In addition, since the liquid refrigerant is supplied from the gas-liquid
separator to the low-pressure expansion valve, an enthalpy obtained by the evaporator
is increased as compared with the case of single-stage compression. Therefore, the
cooling capacity can be increased, and the COP can be improved.
[0006] In the refrigeration device that employs the refrigerant having a low GWP, it is
desired to implement a refrigeration device having an increased COP while suppressing
the discharge temperature thereof in discharge from the compressor by further increasing
the number of stages of the compression mechanism. However, according to a test study
by the inventor of the present disclosure, the refrigeration device, in which the
number of stages of the compression mechanism is increased to for example "4", does
not operate stably depending on operating conditions such as an outside air temperature.
Such a refrigeration device includes N compression mechanisms, N expansion valves,
N-1 gas-liquid separators, and N-1 gas injection pipes.
[0007] Based on the above description, an object of the present disclosure is to provide
a refrigeration device capable of stably operating in a wide range of operating conditions
while improving the efficiency of the refrigerating cycle by increasing the number
of compression stages.
Solution to Problem
[0008] According to the present disclosure, there is provided a refrigeration device that
circulates a refrigerant in accordance with a refrigerating cycle, the refrigeration
device including: a compression portion that includes compression mechanisms which
have a plurality of stages and are connected in series, each of which compress the
refrigerant, and of which the number of stages is three or more; a first heat exchanger
that dissipates heat of the refrigerant compressed by the compression portion from
a low stage to a high stage through a plurality of steps and discharged from the compression
portion to outside air; a decompression portion that includes a plurality of decompression
mechanisms applied to each of the plurality of stages and that reduces a pressure
of the refrigerant which passes through the first heat exchanger through a plurality
of steps; a second heat exchanger that absorbs heat from a thermal load of the refrigerant
which passes through the decompression portion; a plurality of gas-liquid separators
that each are provided in a spacing between decompression mechanisms of the plurality
of decompression mechanisms; a plurality of intermediate-pressure injection flow paths
that respectively correspond to the plurality of gas-liquid separators and each supply
the gas phase refrigerant to a spacing between compression mechanisms of the plurality
of compression mechanisms from the corresponding gas-liquid separator; and a valve
that is provided in at least one of the plurality of intermediate-pressure injection
flow paths. In such a refrigeration device, the number of effective stages through
which the refrigerant circulates is configured to be variable by operating the valve.
[0009] In the present invention, the valve provided in the intermediate-pressure injection
flow path can be opened and closed during the operation of the refrigeration device
according to operating conditions for the purpose of stably operating the refrigeration
device. In addition to this, the valve can not be prevented from being closed for
other purposes such as a purpose of preventing the refrigerant from being moved in
a case where the refrigeration device is stopped.
Advantageous Effects of Invention
[0010] According to the refrigeration device of the present disclosure, the number of effective
stages through which the refrigerant circulates is configured to be variable by switching
the valve provided in at least one of the plurality of intermediate-pressure injection
flow paths to open or closed. Therefore, in a case where the operating state becomes
unstable in a case where the COP is improved by the refrigerating cycle with the maximum
number of stages and the operation is performed with the maximum number of stages,
the valve is closed during the operation to reduce the number of effective stages
with respect to the maximum number of stages. Thereby, the refrigeration device can
be stably operated.
[0011] According to the present disclosure, a cycle appropriate for each of the states of
the refrigerant under various operating conditions can be easily implemented by changing
the number of effective stages through opening and closing of the valve. Therefore,
it is possible to provide a multi-stage compression refrigeration device which can
be stably operated in a wide range of operating conditions.
Brief Description of Drawings
[0012]
Fig. 1 is a diagram showing a circuit configuration of a refrigeration device according
to a first embodiment.
Fig. 2 is a Mollier diagram in a normal operating mode of the refrigeration device
shown in Fig. 1.
Fig. 3 is a Mollier diagram in a high outside air temperature mode of the refrigeration
device shown in Fig. 1.
Fig. 4 is a diagram showing a circuit configuration of a refrigeration device according
to a modification example of the first embodiment.
Fig. 5 is a diagram showing a circuit configuration of a refrigeration device according
to a second embodiment.
Fig. 6 is a Mollier diagram in a low outside air temperature mode of the refrigeration
device shown in Fig. 5.
Fig. 7 is a diagram showing a circuit configuration of a refrigeration device according
to a modification example.
Description of Embodiments
[0013] Hereinafter, embodiments of the present disclosure will be described with reference
to the accompanying drawings.
[First Embodiment]
(Basic Elements of Refrigerating Cycle)
[0014] In the multi-stage compression type refrigeration device 1 shown in Fig. 1, thermal
loads (for example, air in a device housing and articles housed therein), which are
appropriate in a case where the outside air is used as a heat source, are cooled by
circulating a refrigerant in accordance with a refrigerating cycle.
[0015] The refrigeration device 1 has, as basic elements forming a refrigerating cycle,
a compression portion 10 that compresses the refrigerant, a condenser (gas cooler)
E1 (first heat exchanger) that dissipates heat of the refrigerant to the outside air,
a decompression portion 20 that reduces a pressure of the refrigerant, and a evaporator
E2 (second heat exchanger) that absorbs heat from the thermal loads to the refrigerant.
The refrigerant, which is compressed by the compression portion 10, flows through
the condenser (gas cooler) E1, the decompression portion 20, and the evaporator E2
in this order, and is sucked into the compression portion 10.
[0016] A refrigerant including carbon dioxide (CO
2) in at least a part thereof is sealed in the refrigerant circuit of the refrigeration
device 1 of the present embodiment. Such a refrigerant corresponds to a single refrigerant
of CO
2 or a mixed refrigerant obtained by mixing CO
2 with, for example, an R32 refrigerant at a ratio of about 10 to 20%. A GWP of carbon
dioxide is "1". A critical temperature of carbon dioxide is lower than a critical
temperature of another refrigerant (for example, hydro fluoro carbon (HFC)). Therefore,
in the normal operating mode of the refrigeration device 1, the refrigerant of the
present embodiment is compressed to a pressure greater than the critical pressure
P
C by the compression portion 10 that compresses the refrigerant through a plurality
of stages. Therefore, as compared with a case of using another refrigerant, the operation
is performed in a state where the set pressure on the high pressure side H is high.
(Compression Mechanisms and Decompression Mechanisms Having Plurality of Stages)
[0017] The compression portion 10 includes a plurality of compression mechanisms 11 to 14
connected in series. The first stage compression mechanism 11, the second stage compression
mechanism 12, the third stage compression mechanism 13, and the fourth stage compression
mechanism 14 sequentially compress the refrigerant from the low pressure side L to
the high pressure side H through a plurality of steps. The number of stages N of the
compression portion 10 is equal to or greater than 3, and for example, the number
of stages N is "4". The reference numerals of n1, n2, n3, and n4 represent first to
fourth stages.
[0018] As will be described later, the number of stages N is changed in accordance with
the operating mode of the refrigeration device 1. Fig. 2 is a Mollier diagram showing
a relationship between the specific enthalpy and the pressure of the refrigerant assumed
in the normal operating mode. Symbols such as r1 and r2 shown in Fig. 2 correspond
to the same symbols shown in Fig. 1.
[0019] The refrigeration device 1 of the present embodiment includes two electric compressors
101 and 102, a control unit 15 capable of controlling operations of the electric motor,
the expansion valve, and the like of each of the electric compressors 101 and 102,
and an intermediate cooling heat exchanger 16 which is provided between the electric
compressors 101 and 102.
[0020] The first electric compressor 101 includes the first stage compression mechanism
11 and the second stage compression mechanism 12 connected in series, a housing 101A
that houses the compression mechanisms 11 and 12, and an electric motor 101B that
rotationally drives the compression mechanisms 11 and 12.
[0021] The second electric compressor 102 includes the third stage compression mechanism
13 and the fourth stage compression mechanism 14 connected in series, a housing 102A
that houses the compression mechanisms 13 and 14, and an electric motor 102B that
rotationally drives the compression mechanisms 13 and 14.
[0022] The multi-stage compression refrigeration device 1 having the number of stages N
is implemented by combining the two electric compressors 101 and 102 each of which
is driven by the same electric motor and includes compression mechanisms having a
plurality of stages. Therefore, the control unit 15 may control rotation speeds of
the two electric motors 101B and 102B, respectively. Therefore, the control of the
refrigeration device 1 is easier than that in a case where the corresponding electric
motors individually drive the compression mechanisms 11 to 14 of the respective stages.
Further, as compared with a case where the compression portion 10 includes four compressors
each including a compression mechanism, an electric motor, and a housing, it is possible
to achieve reduction in size and weight of the refrigeration device 1.
[0023] The intermediate cooling heat exchanger 16 cools the refrigerant discharged from
the second stage compression mechanism 12 by dissipating heat to the outside air and
supplies the refrigerant to a suction portion of the third stage compression mechanism
13 (operational points r4 and r5 in Fig. 2).
[0024] The first stage compression mechanism 11 corresponds to, for example, a rotary compression
mechanism which includes a piston rotor and a cylinder. It is the same for the third
stage compression mechanism 13. The second stage compression mechanism 12 corresponds
to, for example, a scroll-type compression mechanism which includes a pair of scroll
members. It is the same for the fourth stage compression mechanism 14.
[0025] Corresponding to the case where the compression portion 10 is formed of the compression
mechanisms 11 to 14 having a plurality of stages, the decompression portion 20 includes
decompression mechanisms 21 to 24 each of which is provided to each stage (n1, n2,
n3, n4) and has the same number as the number of stages N for compression. Each of
the decompression mechanisms 21 to 24 may be an expansion valve, a capillary tube,
or the like. The fourth stage decompression mechanism 24, the third stage decompression
mechanism 23, the second stage decompression mechanism 22, and the first stage decompression
mechanism 21 sequentially reduce the pressure of the refrigerant, which passes through
the condenser (gas cooler) E1, through a plurality of steps in this order.
[0026] As shown in Fig. 2, the compression mechanisms 11 to 14 of the plurality of stages
n1, n2, n3, and n4 compress the refrigerant, and thereby the pressure of the refrigerant
is increased stepwise. Thereby, the discharge temperature of the refrigerant rises.
[0027] By lowering the temperature of the refrigerant due to the action of the intermediate
cooling heat exchanger 16 that dissipates heat of the refrigerant to the outside air
(refer to an arrow A1 in Fig. 2), it is possible to contribute to suppression of the
discharge temperature of the entire compression portion 10 as a whole.
[0028] A pressure between a pressure of suction to the first stage n1 and a pressure of
discharge from the second stage n2 is referred to as a first intermediate pressure
P
1. Similarly, a pressure between a pressure of suction to the second stage n2 and a
pressure of discharge from the third stage n3 is referred to as a second intermediate
pressure P
2, and a pressure between a pressure of suction to the third stage n3 and a pressure
of discharge from the fourth stage n4 is referred to as a third intermediate pressure
P
3. A relationship of P
1 < P
2 < P
3 is established.
[0029] The refrigerant circulates in the refrigerant circuit of the refrigeration device
1 while changing the pressure and the enthalpy with the phase change on the basis
of pressure ratios of the respective stages n1, n2, n3, and n4 determined by a set
pressure P
H of the condenser (gas cooler) E1 on the high pressure side H, a set pressure P
L of the evaporator E2 on the low pressure side L, and the intermediate pressures (P
1, P
2, P
3).
(Intermediate-Pressure Gas Injection)
[0030] The refrigeration device 1 performs gas injection for supplying the gas refrigerant
having an intermediate pressure to each spacing between the first to fourth stage
compression mechanisms 11 to 14. The gas refrigerant is obtained by gas-liquid separation
of the refrigerant in each spacing between the stages of the first to fourth stage
decompression mechanisms 21 to 24. Therefore, the refrigeration device 1 includes
N-1 gas-liquid separators 31 to 33, each of which is provided to each spacing between
the first to fourth stage decompression mechanisms 21 to 24, and N-1 intermediate-pressure
injection flow paths 41 to 43 respectively corresponding to the gas-liquid separators
31 to 33.
[0031] In the normal operating mode, the pressure (r12, r13, r14) of the refrigerant, which
is discharged from the fourth stage compression mechanism 14 and passes through the
condenser (gas cooler) E1 and the fourth stage decompression mechanism 24, that is,
the third intermediate pressure P
3 is kept equal to or less than a critical pressure P
C.
[0032] The third intermediate-pressure gas-liquid separator 33 (liquid receiver) receives
the refrigerant from the fourth stage decompression mechanism 24 into a storage tank
33A and separates the refrigerant into the gas phase and the liquid phase. As shown
in Fig. 2, this corresponds to a status change from r12 to r13 and r14.
[0033] The refrigerant inside the storage tank 33A is separated into a gas phase and a liquid
phase on the basis of a density difference. A third intermediate-pressure injection
flow path 43 is connected to a gas phase region 33B above the liquid level.
the third intermediate-pressure injection flow path 43 supplies the gas refrigerant,
which has the third intermediate pressure P
3, from the gas phase region 33B to the suction portion of the fourth stage compression
mechanism 14 (from r13 to r8). A temperature of the gas refrigerant, which is supplied
to the fourth stage compression mechanism 14 through the third intermediate-pressure
injection flow path 43, is lower than a temperature of the refrigerant which is discharged
from the third stage compression mechanism 13. Therefore, the temperature of the refrigerant
to be sucked into the fourth stage compression mechanism 14, as the entirety of the
refrigerant supplied through the third intermediate-pressure injection flow path 43
and the refrigerant discharged from the third stage compression mechanism 13, is lowered
(from r7 to r8). Then, the temperature of the refrigerant discharged from the fourth
stage compression mechanism 14 is also lowered. Therefore, the intermediate-pressure
gas injection contributes to the reduction in discharge temperature.
[0034] On the other hand, the liquid refrigerant of the third intermediate pressure P
3, which is stored in the storage tank 33A, flows out from the storage tank 33A and
is decompressed by the third stage decompression mechanism 23 (from r14 to r15). According
to a configuration in which the liquid refrigerant is supplied to the decompression
mechanisms 21 to 23 including the decompression mechanism 23, the enthalpy corresponding
to the evaporation process in the evaporator E2 is increased (refer to the arrow A2
in Fig. 2 in the third stage decompression mechanism 23). As a result, it is possible
to improve the COP.
[0035] The reduction in discharge temperature and the improvement in efficiency obtained
by increasing the enthalpy described above can be said in each of the third intermediate
pressure P
3, the second intermediate pressure P
2, and the first intermediate pressure P
1. The present invention is not limited to the four stages of the present embodiment.
By increasing the number of stages N to five or six stages, it is possible to enhance
the effect of reducing the discharge temperature and improving the efficiency.
[0036] The gas injection of each of the second intermediate pressure P
2 and the first intermediate pressure P
1 is similar to the gas injection of the third intermediate pressure P
3 described above.
[0037] The refrigerant, which passes through the third stage decompression mechanism 23,
is received by the second intermediate-pressure gas-liquid separator 32 and is separated
into the gas phase and the liquid phase, in a similar manner to the third intermediate-pressure
gas-liquid separator 33. This corresponds to a status change from r15 to r16 and r17.
[0038] A second intermediate-pressure injection flow path 42 is connected to a gas phase
region of the second intermediate-pressure gas-liquid separator 32. In a case where
the gas refrigerant of the second intermediate pressure P
2 is supplied to the suction portion of the third stage compression mechanism 13 (from
r16 to r6) through the second intermediate-pressure injection flow path 42, the gas
refrigerant of the second intermediate pressure P
2 flows out from the intermediate cooling heat exchanger 16. Thereby, the temperature
of the refrigerant sucked into the third stage compression mechanism 13 is lowered
(from r5 to r6). Between the second stage compression mechanism 12 and the third stage
compression mechanism 13, in addition to the injection action of the intermediate
pressure P
2, the action of the intermediate cooling heat exchanger 16 (from r4 to r5) also lowers
a suction temperature in suction into the third stage compression mechanism 13 is
lowered. Thus, it is possible to further suppress the discharge temperature.
[0039] The second stage decompression mechanism 22 decompress the liquid refrigerant of
the second intermediate pressure P
2 flowing out from the second intermediate-pressure gas-liquid separator 32 (from r17
to r18) .
[0040] The refrigerant, which passes through the second stage decompression mechanism 22,
is received by the first intermediate-pressure gas-liquid separator 31 and is separated
into the gas phase and the liquid phase. This corresponds to a status change from
r18 to r19 and r20.
[0041] In a case where the gas refrigerant of the first intermediate pressure P
1 is supplied to the suction portion of the second stage compression mechanism 12 through
the first intermediate-pressure injection flow path 41 connected to the gas phase
region of the first intermediate-pressure gas-liquid separator 31 (from r18 to r3),
the temperature of the refrigerant sucked into the second stage compression mechanism
12 is lowered (from r2 to r3).
[0042] The first stage decompression mechanism 21 decompress the liquid refrigerant of the
first intermediate pressure P
1 flowing out of the first intermediate-pressure gas-liquid separator 31 (from r20
to r21). The refrigerant, which passes through the first stage decompression mechanism
21, evaporates by absorbing heat from the thermal load by the evaporator E2 and is
sucked into the first stage compression mechanism 11 (from r21 to r22 and r1).
[0043] In a case where the refrigeration device 1 is operated in a state of being set to
the normal operating mode by the control unit 15, compression, expansion, and intermediate-pressure
injection corresponding to the number of stages N provided in the refrigeration device
1 are performed. In such a manner, it is possible to improve the COP while using a
refrigerant having a low GWP. In addition, it is possible to stably operate the refrigeration
device 1 while keeping the discharge temperature equal to or less than the allowable
limit.
[0044] However, for example, in a case where the outside air temperature is excessively
high with respect to the range of the outside air temperature assumed in the normal
operating mode, when the refrigeration device 1 is operated with the maximum number
of stages N, the operating state may become unstable and the refrigerant may not be
circulated.
[0045] Even though it is permissible for a temperature of the CO
2 refrigerant discharged from the compression portion 10 through the multi-stage compression
to be greater than the critical pressure P
C, the amount of heat dissipated by the refrigerant by the condenser (gas cooler) E1
decreases as the outside air temperature rises. Thereby, in a case where the third
intermediate pressure P
3 (r12, r13, r14) is greater than the critical pressure P
C, the gas-liquid separation cannot be performed since the refrigerant does not condense
in the third intermediate-pressure gas-liquid separator 33, and it is difficult to
perform stable control since the behavior of the refrigerant in the supercritical
state is not stable. It is difficult to stabilize the operating state by estimating
the pressure, temperature, flow rate, and the like of the supercritical fluid.
[0046] Therefore, in order to stably operate the refrigeration device 1 in a wide range
including an operating condition in which the outside air temperature is excessively
high or other operating conditions, the refrigeration device 1 includes a valve (V3)
provided in at least one arbitrarily selected from the intermediate-pressure injection
flow paths 41 to 43.
[0047] The refrigeration device 1 of the present embodiment includes the third intermediate-pressure
valve V3 provided in the third intermediate-pressure injection flow path 43 on the
highest pressure side H.
[0048] The third intermediate-pressure valve V3 is an electromagnetic valve, and is switched
to be open or closed on the basis of a command issued from the control unit 15.
[0049] In the normal operating mode, the refrigeration device 1 is operated while performing
the injection of first to third intermediate pressures P
1, P
2, and P
3 through the first to third intermediate-pressure injection flow paths 41 to 43 in
a state where the third intermediate-pressure valve V3 is open and while changing
the pressure and enthalpy of the refrigerant as shown in Fig. 2. In such a case, the
number of effective stages N
A as the number of stages, in which the refrigerant is circulated, is "4" corresponding
to the total number of stages N provided in the refrigeration device 1.
(High Outside Air Temperature Mode)
[0050] In a case where the outside air temperature becomes excessively higher as the pressure
of the refrigerant becomes greater than the critical pressure, the control unit 15
closes the third intermediate-pressure valve V3 and switches the operating mode of
the refrigeration device 1 to the high outside air temperature mode for performing
the intermediate-pressure injection through only the first intermediate-pressure injection
flow path 41 and the second intermediate-pressure injection flow path 42. In the high
outside air temperature mode, the refrigerant in the supercritical state even after
passing through the fourth stage decompression mechanism 24 passes through the inside
of the storage tank 33A of the third intermediate-pressure gas-liquid separator 33,
is decompressed by the third stage decompression mechanism 23, and thereafter flows
into the second intermediate-pressure gas-liquid separator 32 (from r12, r13, and
r14 to r15). In such a case, the liquid refrigerant is not stored in the storage tank
33A (corresponding to the internal state of the storage tank 33A shown in Fig. 4).
[0051] In a case where the third intermediate-pressure valve V3 is closed, the refrigerant
does not flow through the third intermediate-pressure injection flow path 43. Thus,
as a result of combining the third stage n3 and the fourth stage n4 in the normal
operating mode into one stage in the compression expansion process, the number of
effective stages N decreases to "3". As shown in the state of the refrigerant in the
high outside air temperature mode in Fig. 3, the refrigeration device 1 is operated
by a cycle of three-stage compression and three-stage expansion of n1 to n3. Since
the pressure of the refrigerant in the supercritical state is reduced by the third
stage decompression mechanism 23 (from r12, r13, and r14 to r15), the second intermediate
pressure P
2 is kept equal to or less than the critical pressure P
C. Therefore, the refrigeration device 1 is stably operated.
[0052] In the normal operating mode, the control unit 15 determines whether or not the pressure
on the high pressure side H on the map data corresponding to the detection result
of the outside air temperature is greater than the first threshold pressure T
1 (Fig. 3) which is set lower than the critical pressure P
C on the basis of estimation of a margin, by using, for example, map data or the like
indicating correspondence between the outside air temperature and the set pressure
on the high pressure side H and the outside air temperature detected by the temperature
sensor 17. In a case where the pressure on the high pressure side H on the map data
corresponding to the detection result of the outside air temperature is greater than
the first threshold pressure T
1, the control unit 15 shifts to the high outside air temperature mode from the normal
operating mode by closing the third intermediate-pressure valve V3.
[0053] The outside air temperature is continuously monitored even in the high outside air
temperature mode. For example, in a case where the pressure on the high pressure side
H on the map data corresponding to the detection result of the outside air temperature
is smaller than the second threshold pressure T
2 lower than the first threshold pressure T
1, the control unit 15 returns from the high outside air temperature mode to the normal
operating mode by opening the third intermediate-pressure valve V3.
[0054] According to the refrigeration device 1 of the first embodiment described above,
the number of effective stages N
A through which the refrigerant circulates is configured to be variable by switching
the valve V3 provided in at least one of the intermediate-pressure injection flow
paths 41 to 43 to open or closed. Therefore, in the normal operating mode, the refrigeration
device 1 can be stably operated by closing the valve V3 provided in the intermediate-pressure
injection flow path 43 on the high pressure side H to reduce the number of effective
stages N
A, in a case where the outside air temperature becomes higher as the intermediate pressure
on the high pressure side H becomes greater than the critical pressure P
C, while improving the COP by the refrigerating cycle with the maximum number of stages
N.
[0055] Consequently, according to the present embodiment, while handling the refrigerant
compressed to the supercritical state, difficult control based on the estimation of
the behavior of the refrigerant in the supercritical state is not necessary. In addition,
by changing the number of effective stages N
A through opening and closing of the valve V3, a cycle appropriate for each of the
states of the refrigerant under various operating conditions can be easily implemented.
Therefore, it is possible to provide the refrigeration device 1 with multi-stage compression
that can be stably operated in a wide range of operating conditions.
[0056] The refrigeration device 1 may include a valve provided in another intermediate-pressure
injection flow path 42 or 41 in addition to the valve V3 provided in the third intermediate-pressure
injection flow path 43. For example, as shown in Fig. 4, the valve V2, which can be
opened and closed by the control unit 15, is not prevented from being also provided
in the second intermediate-pressure injection flow path 42. In the high outside air
temperature mode shown in Fig. 4, in the intermediate-pressure valves V2 and V3, only
the third intermediate-pressure valve V3 shown in black is closed.
[Second Embodiment]
[0057] Next, a second embodiment will be described with reference to Figs. 5 and 6. The
following description will be given focusing on items that differ from those of the
first embodiment. The same reference numerals will be assigned to the same components
as those in the first embodiment.
[0058] The refrigeration device 1-2 shown in Fig. 5 includes a first intermediate-pressure
valve V1 provided in the first intermediate-pressure injection flow path 41 in order
to cope with operating conditions different from those of the refrigeration device
1 of the first embodiment. The refrigeration device 1-2 also includes the third intermediate-pressure
valve V3 provided in the third intermediate-pressure injection flow path 43, in a
similar manner to the refrigeration device 1 of the first embodiment. The refrigeration
device 1-2 of the second embodiment is configured in a similar manner to the refrigeration
device 1 of the first embodiment except that the first intermediate-pressure valve
V1 is provided.
[0059] The refrigeration device 1-2 includes the third intermediate-pressure valve V1 as
in the refrigeration device 1. Therefore, by closing only the third intermediate-pressure
valve V3 of the intermediate-pressure valves V1 and V3 to reduce the number of effective
stages N
A to "3", the above-mentioned high outside air temperature mode can be performed.
[0060] Contrary to the high outside air temperature mode, in a case where the outside air
temperature is low, a pressure ratio between the set pressure P
H on the high pressure side H and the set pressure P
L on the low pressure side L decreases. The pressure ratio is proportionally distributed
into each stage. Therefore, in a case where the operation is performed with the maximum
number of stages N as in the normal operating mode, the pressure ratios of the respective
stages n1, n2, n3, and n4 decrease. In a case where the outside air temperature becomes
lower as the pressure ratio of each stage becomes more insufficient relative to the
pressure ratios necessary for respectively transporting the refrigerant from the gas-liquid
separators 31 to 33 to the compression mechanisms 12 to 14, the refrigerant cannot
be circulated in each stage.
[0061] In such a case, the control unit 15 switches the operating mode of the refrigeration
device 1-2 from the normal operating mode to the low outside air temperature mode
(low pressure ratio operating mode) by closing both the first intermediate-pressure
valve V1 and the third intermediate-pressure valve V3. In the low outside air temperature
mode, the intermediate-pressure injection is performed only through the second intermediate-pressure
injection flow path 42.
[0062] Fig. 6 shows a state of the refrigerant in the low outside air temperature mode.
By closing the first intermediate-pressure valve V1 and the third intermediate-pressure
valve V3, the number of effective stages N
A decreases to "2", and at this time, the refrigeration device 1-2 is operated by a
cycle of two-stage compression and two-stage expansion. As the number of effective
stages N
A decreases with respect to the total number of stages N, a sufficient pressure for
transporting the refrigerant from each of the gas-liquid separators 31 to 33 to the
compression mechanisms 12 to 14 is ensured in each stage. Therefore, the refrigeration
device 1 is stably operated.
[0063] In the normal operating mode, the control unit 15 determines whether the pressure
ratio of each stage on the map data corresponding to the detection result of the outside
air temperature is larger or smaller than the first pressure ratio R
1 of each stage in consideration of the pressure ratio of each stage necessary for
the intermediate-pressure injection, by using, for example, the map data indicating
correspondence between the outside air temperature and the pressure ratio of each
stage and the outside air temperature detected by the temperature sensor 17. In a
case where the pressure ratio of each stage on the map data corresponding to the detection
result of the outside air temperature is smaller than the first pressure ratio R
1 of each stage, the control unit 15 closes the first intermediate-pressure valve V1
and the third intermediate-pressure valve V3 to shift from the normal operating mode
to the low outside air temperature mode.
[0064] The outside air temperature is continuously monitored. For example, the pressure
ratio of each stage on the map data corresponding to the detection result of the outside
air temperature is greater than a second pressure ratio R
2 (R
1 < R
2) of each stage. In such a case, the control unit 15 opens the intermediate-pressure
valves V1 and V3 to return from the low outside air temperature mode to the normal
operating mode.
[0065] According to the refrigeration device 1-2 of the second embodiment described above,
by closing at least the third intermediate-pressure valve V3 of the intermediate-pressure
valves V1 and V3 provided, one on each of the high pressure side H and the low pressure
side L, the number of effective stages N
A can be changed to three stages and two stages with respect to four stages as the
total number of stages. Then, the refrigeration device 1-2 can be stably operated
in a wider range of operating conditions with respect to the refrigeration device
1 of the first embodiment.
[0066] From the viewpoint of reducing the number of effective stages N
A, only one of the intermediate-pressure valves V1 and V3 of the second embodiment
can be closed in the low outside air temperature mode. For example, only the third
intermediate-pressure valve V3 may be closed, and a pressure ratio sufficient for
performing intermediate-pressure injection through the first intermediate-pressure
injection flow path 41 and the second intermediate-pressure injection flow path 42
may be ensured in each of the stages n1, n2, and n3. While detecting the outside air
temperature, for example, the refrigeration device 1-2 can be operated in the number
of stages which are most stable in a state where all of the intermediate-pressure
valves V1 to V3 are open (four stages), a state where only the intermediate-pressure
valve V3 is closed (three stages), and a state where both the intermediate-pressure
valves V1 and V3 are closed (two stages), among the intermediate-pressure valves V1
to V3.
[0067] Alternatively, only the first intermediate-pressure valve V1 may be closed, and a
pressure ratio sufficient for performing intermediate-pressure injection through the
third intermediate-pressure injection flow path 43 and the second intermediate-pressure
injection flow path 42 may be ensured in each of the stages n2, n3, and n4. In the
latter case, in a case where the refrigeration device 1-2 is not used in an environment
where the outside air temperature becomes higher as the third intermediate pressure
P
3 becomes greater than the critical pressure P
C, installation of the intermediate-pressure valve V3 for the third intermediate-pressure
injection flow path 43 can be omitted.
[0068] In the second embodiment, an on/off valve is not prevented from being also provided
in the second intermediate-pressure injection flow path 42. However, in the second
embodiment, the two-stage compression or two-stage expansion cycle is maintained by
constantly performing the intermediate-pressure injection through the second intermediate-pressure
injection flow path 42 in all the operating modes including the low outside air temperature
mode. Therefore, the intermediate-pressure valve is not installed in the second intermediate-pressure
injection flow path 42, and thus the device cost can be suppressed.
[0069] Even in a case where the total number of stages N is more than "4", for example,
the total number of stages N is "5" or "6", the refrigeration device can be operated
by reducing the number of stages N, in a similar manner to the second embodiment.
[0070] For example, in a case where the number of stages N is "5", the refrigeration device
includes an intermediate-pressure valve provided in at least one of the fourth intermediate-pressure
injection flow path and the third intermediate-pressure injection flow path on the
high pressure side H, and an intermediate-pressure valve provided in at least one
of a second intermediate-pressure injection flow path and a first intermediate-pressure
injection flow path on the low pressure side L.
[0071] In such a case, it is assumed that the refrigeration device includes the fourth intermediate-pressure
valve V4, the third intermediate-pressure valve V3, the second intermediate-pressure
valve V2, and the first intermediate-pressure valve V1. Then, in the low outside air
temperature mode, for example, the first intermediate-pressure valve V1, the third
intermediate-pressure valve V3, and the fourth intermediate-pressure valve V4 can
be closed and operated in a two-stage cycle, or the first intermediate-pressure valve
V1 and the fourth intermediate-pressure valve V4 can be closed and operated in a three-stage
cycle. Consequently, the number of effective stages N
A can be changed to "2" or "3".
[Modification Example]
[0072] Although not shown, it is also possible to provide intermediate-pressure valves respectively
in the first to third intermediate-pressure injection flow paths 41 to 43, that is,
in all of the intermediate-pressure injection flow paths 41 to 43. In such a case,
the number of effective stages N
A can be reduced to "1" by closing any of the three intermediate-pressure valves V1,
V2, and V3 provided in the refrigeration device.
[0073] In addition, one or two of the three intermediate-pressure valves V1, V2, and V3
provided in the refrigeration device are constantly open, and only the remaining intermediate-pressure
valves are open and closed. Thereby, the refrigeration device can be made to meet
various required operating conditions. Even the valve that is constantly open at this
time can be closed in accordance with the operating mode depending on operating conditions
such as a refrigerant used in the refrigeration device and an outside air temperature
range appropriate for the area where the refrigeration device is used. Consequently,
the same refrigerant circuit can be applied to a plurality of products having different
refrigerants, operating environment temperatures, use applications or the like.
[0074] The refrigeration device 1-3 shown in Fig. 7 does not include a plurality of stages
of electric compressors (101 and 102 in Fig. 1). Each of the compression mechanisms
11 to 13 provided in the refrigeration device 1-3 is configured as a single stage
compressor together with an electric motor 10M and a housing 10H.
[0075] The refrigeration device 1-3 includes the second intermediate-pressure valve V2 provided
in the second intermediate-pressure injection flow path 42 on the high pressure side
H, and the first intermediate-pressure valve V1 provided in the first intermediate-pressure
injection flow path 41 on the low pressure side L, in the first and second intermediate-pressure
injection flow paths 41 and 42.
[0076] Since the outside air temperature is high, if the second intermediate pressure P
2 is greater than the critical pressure P
C in a case where the intermediate-pressure injection is performed using any of the
first and second intermediate-pressure injection flow paths 41 and 42, the second
intermediate-pressure valve V2 on the highest pressure side H is closed. Thereby,
the refrigeration device 1-3 may be operated in the two-stage compression and two-stage
expansion cycle.
[0077] Further, since the outside air temperature is low, if the pressure ratio of each
of the stages is insufficient in a case where intermediate-pressure injection is performed
using both the first and second intermediate-pressure injection flow paths 41 and
42, or for another reason, one or both of the intermediate-pressure valves V1 and
V2 are closed. Thereby, the refrigeration device 1-3 may be operated in the two-stage
compression and two-stage expansion cycle or the one-stage compression and one-stage
expansion cycle.
[0078] The refrigeration device 1-3 includes the intermediate cooling heat exchanger 16,
but may not include the intermediate cooling heat exchanger 16. In order to reduce
the discharge temperature, the intermediate cooling heat exchanger 16 can be provided
in at least any of a spacing between the compression mechanisms 11 and 12 and a spacing
between the compression mechanisms 12 and 13.
[0079] Also in the refrigeration devices 1 and 1-2 described above, it is sufficient that
the intermediate cooling heat exchanger 16 is provided as necessary.
[0080] In addition to the above, it is possible to select the configurations described in
the above-mentioned embodiments or change the configurations to other configurations
as appropriate.
[0081] For example, in each of the above-mentioned embodiments, liquid level sensors can
be provided in the gas-liquid separators 31 to 33 in order to protect the compression
mechanisms 11 to 14. In a case where the liquid level sensor detects that an excessive
amount of liquid refrigerant is stored in the storage tank, the control unit 15 may
close the intermediate-pressure valve of the corresponding intermediate-pressure injection
flow path. In such a manner, it is possible to prevent damage to the compression mechanism
due to inflow of the liquid refrigerant.
[Additional Notes]
[0082] The refrigeration device described above is understood as follows.
- [1] A refrigeration device 1, 1-2, or 1-3 that circulates a refrigerant in accordance
with a refrigerating cycle, the refrigeration device 1, 1-2, or 1-3 includes: a compression
portion 10 that includes compression mechanisms 11 to 14 which have a plurality of
stages and are connected in series, each of which compress the refrigerant, and of
which the number of stages N is three or more; a first heat exchanger (E1) that dissipates
heat of the refrigerant compressed by the compression portion 10 from a low stage
to a high stage through a plurality of steps and discharged from the compression portion
10 to outside air; a decompression portion 20 that includes a plurality of decompression
mechanisms 21 to 24 applied to each of the plurality of stages and that reduces a
pressure of the refrigerant which passes through the first heat exchanger (E1) through
a plurality of steps; a second heat exchanger (E2) that absorbs heat from a thermal
load of the refrigerant which passes through the decompression portion 20; a plurality
of gas-liquid separators 31 to 33 that are respectively provided in spacings between
the decompression mechanisms among the decompression mechanisms 21 to 24; a plurality
of intermediate-pressure injection flow paths 41 to 43 that respectively correspond
to the plurality of gas-liquid separators 31 to 33 and respectively supply the gas
phase refrigerant to spacings between the compression mechanisms among the compression
mechanisms 11 to 14 from the corresponding gas-liquid separators 31 to 33; and valves
V1, V2, and V3 that are provided in at least one of the plurality of intermediate-pressure
injection flow paths 41 to 43. The number of effective stages NA through which the refrigerant circulates is configured to be variable by operating
the valves V1, V2, and V3.
- [2] The valve V3 is provided in the intermediate-pressure injection flow path 41 to
43 having a highest pressure among the plurality of intermediate-pressure injection
flow paths 41 to 43.
- [3] The refrigerant includes at least carbon dioxide in at least a part thereof.
- [4] The number of stages N is four or more. In addition, the valves V1, V2, and V3
are provided in at least one of the intermediate-pressure injection flow paths 41
to 43 on a high pressure side and at least one of the intermediate-pressure injection
flow paths 41 to 43 on a low pressure side among the plurality of intermediate-pressure
injection flow paths 41 to 43.
- [5] The refrigeration device 1, 1-2, or 1-3 further includes an intermediate cooling
heat exchanger 16 that exchanges the heat of the refrigerant, which is discharged
from the compression mechanism on a low pressure side as any one of the compression
mechanisms 11 to 14, with heat of the outside air, and that allows the refrigerant
to flow into the compression mechanism on a high pressure side as the compression
mechanism connected in series with the compression mechanism on the low pressure side.
- [6] The compression portion 10 includes multi-stage electric compressors 101 and 102
including a plurality of compression mechanisms 11, 12 (or 13, 14) that are connected
in series, a housing (101A, or the like) that houses the plurality of compression
mechanisms 11 and 12 (or 13 and 14), and an electric motor (101B, or the like) that
drives the plurality of compression mechanisms 11 and 12 (or 13 and 14).
- [7] The refrigeration devices 1, 1-2, and 1-3 include a control unit 15 that generates
a command to operate the valves V1, V2, and V3, and the control unit 15 changes the
number of effective stages NA by generating the command in accordance with a temperature of the outside air.
Reference Signs List
[0083]
1, 1-2, 1-3: refrigeration device
10: compression portion
10H: housing
10M: electric motor
11: first stage compression mechanism
12: second stage compression mechanism
13: third stage compression mechanism
14: fourth stage compression mechanism
15: control unit
16: intermediate cooling heat exchanger (intermediate heat exchanger)
17: temperature sensor
20: decompression portion
21: first stage decompression mechanism
22: second stage decompression mechanism
23: third stage decompression mechanism
24: fourth stage decompression mechanism
31: first intermediate-pressure gas-liquid separator
32: second intermediate-pressure gas-liquid separator
33: third intermediate-pressure gas-liquid separator
33A: storage tank
33B: gas phase region
41: first intermediate-pressure injection flow path
42: second intermediate-pressure injection flow path
43: third intermediate-pressure injection flow path
101: first electric compressor (multi-stage electric compressor)
101A: housing
101B: electric motor
102: second electric compressor (multi-stage electric compressor)
102A: housing
102B: electric motor
E1: condenser (gas cooler) (first heat exchanger)
E2: evaporator (second heat exchanger)
H: high pressure side
L: low pressure side
N: number of stages
NA: number of effective stages
P1: first intermediate pressure
P2: second intermediate pressure
P3: third intermediate pressure
PC: critical pressure
PH, PL: set pressure
R1, R2: pressure ratio
T1: first threshold pressure
T2: second threshold pressure
V1: first intermediate-pressure valve
V2: second intermediate-pressure valve
V3: third intermediate-pressure valve
n1 to n4: stages
r1 to r22: operational points