Technical Field
[0001] The present invention relates to a refrigerant circuit that is applied to an air
conditioning apparatus, a refrigerator, a hot water supply system or the like, which
uses a refrigerating cycle in which carbon dioxide (CO
2) serves as a refrigerant.
Background Art
[0002] Conventionally, in a refrigerant circuit (refer to FIG. 9A and FIG. 9B) that uses
an HFC refrigerant, surplus refrigerant can be held as a saturated liquid refrigerant
by providing a receiver at the condenser outlet. Note that in the refrigerant circuit
that is shown in FIG. 9A, reference numeral 1 indicates a compressor, 2 indicates
an accumulator, 3 indicates a condenser, 4 indicates a receiver, 5 indicates a restriction
mechanism, and 6 indicates a evaporator. The state at the positions that are indicated
by "a" to "d" in the figures corresponds to those in the Mollier diagram that is shown
in FIG. 9B.
[0003] However, in a supercritical refrigerating cycle that uses carbon dioxide as a refrigerant,
a conventional condenser unit is supercritical and there is no liquid refrigerant,
and thus, it is impossible to hold any surplus refrigerant. In addition, in the case
of carbon dioxide refrigerant, the theoretical coefficient of performance (COP) significantly
falls when the evaporator outlet temperature is high.
In order to improve this, in a supercritical refrigerating cycle that uses carbon
dioxide as a refrigerant, 1) a two-stage compression two-stage expansion cycle (gas-liquid
separation method) and 2) a two-stage compression one-stage expansion cycle (intercooler
method) and the like are used.
[0004] FIG. 10A is a refrigerant circuit for a two-stage compression two-stage expansion
cycle (gas-liquid separation method), a restriction mechanism 5A is additionally provided
between the condenser 3 and the receiver 4, and the space between the receiver 4 and
the compressor 1 is connected by a refrigerant pipe. Note that the state at the positions
that are indicated by "a" to "f" in the figure corresponds to those in the Mollier
diagram in FIG. 10B.
[0005] FIG. 11A is a refrigerating circuit for a two-stage compression one-stage expansion
cycle (intercooler method), and an intercooler 7 is placed between the condenser 3
and the restriction mechanism 4. This intercooler 7 is connected to the compressor
1 by a refrigerant pipe, and furthermore, it is connected to a refrigerant pipe that
branches upstream of the intercooler 7 and is provided with a restriction mechanism
5B. Note that the state at the positions that are indicated by "a" to "g" in the figure
corresponds to those in the Mollier diagram that is shown in FIG. 11B.
[0006] In addition, as a prior application related to a refrigerant apparatus that uses
a two-stage compression one-stage expansion cycle (intercooler method) using carbon
dioxide as a refrigerant, there is a patent application that improves performance
by improving the refrigeration capacity in the evaporator of a refrigeration device
(refer, for example, to Patent Citation 1).
In addition, there is a prior application related to an operation method and apparatus
for a supercritical evaporation-compression cycle that can operate normally under
supercritical conditions by controlling the refrigeration and heating capacity of
an apparatus by using the thermodynamic characteristics of the supercritical state
(refer, for example, to Patent Citation 2).
Patent Citation 1: Japanese Unpublished Patent Application, First Publication, No.
2006-242557
Patent Citation 2: Japanese Published Patent Application, Second Publication, No.
H7-18602
Disclosure of Invention
[0007] However, in the conventional refrigerating cycle described above, the refrigerant
after expansion is a gas-liquid two-phase flow. Thus, in the case in which a liquid
refrigerant is necessary, the following shortcomings and problems occur in an air
conditioning apparatus:
- 1. The processing of surplus refrigerant due to necessary refrigerant amount differences
that depend on the operation state such as refrigerating operation or heating operation
and the like.
- 2. The refrigerant distribution to a plurality of indoor units.
- 3. Ensuring a pipe for high pressure liquid in an indoor unit that carries out a mixed
refrigerating and heating operation.
- 4. Ensuring the supercooling refrigerating condenser when reheating and dehumidifying
are carried out.
- 5. Enlargement of the fluid pipe diameter to accommodate pipe pressure loss and increase
in the case in which the refrigerant pipe is a long pipe.
[0008] In this manner, in a supercritical refrigerating cycle that uses carbon dioxide as
a refrigerant, because the refrigerant after expanding changes to a gas-liquid two
phase flow, resolving such problems as the holding of surplus refrigerant produced
when a liquid refrigerant is desirable.
In consideration of the problems described above, it is an object of the present invention
to provide, in a refrigerant circuit for a supercritical cycle that uses carbon dioxide
as a refrigerant, a refrigerant circuit that can hold an amount of surplus refrigerant.
[0009] The invention uses the following solutions to solve the problems described above.
The refrigerant circuit of the present invention includes, in a refrigerant circuit
of a refrigerating cycle in which carbon dioxide is used as a refrigerant, an intercooler
that is provided at the wake flow side of a condenser and an intermediate pressure
receiver provided via a restriction mechanism at the wake flow side of the intercooler.
[0010] According to such a refrigerant circuit, due to providing an intercooler that is
provided at the wake flow side of the condenser and an intermediate pressure receiver
that is provided via restriction mechanism at the wake flow side of the intercooler,
the refrigerant that is cooled by the intercooler is liquefied due to a reduction
in pressure caused by the restriction mechanism, and this refrigerant can be held
in the receiver as a liquid phase refrigerant.
[0011] In the refrigerant circuit described above, the intercooler and the intermediate
pressure receiver are preferably provided with a bridge circuit that forms a predetermined
refrigerant path depending on the refrigerant circulation direction that is switched
by a four-way valve, and thereby, a liquid phase refrigerant can be held in the receiver
during both a refrigerating operation or a heating operation.
[0012] In the refrigerant circuit described above, preferably a reheating condenser is provided
at the wake flow side of the intermediate pressure receiver, and thereby, reheating
and dehumidifying become possible by using the reheating condenser as a supercooling
condenser.
[0013] In the refrigerant circuit described above, preferably two or more evaporators are
provided so as to be arranged in parallel, and thereby, the liquid phase refrigerant
can be suitably distributed between the plural evaporators.
[0014] In the refrigerant circuit described above, preferably a supercooling heat exchanger
is provided at the wake flow side of the intermediate pressure receiver, and thereby,
even in the case in which the refrigerant piping is long and the pressure loss in
the liquid phase refrigerant piping is large, an appropriate distribution of the liquid
refrigerant becomes possible without making the pipe diameter large.
[0015] In a refrigerant circuit of a refrigeration cycle that can carry out a mixed refrigeration
and heating operation using carbon dioxide as a refrigerant, the refrigerant circuit
of the present invention is provided with an intercooler that is provided at the wake
flow side of an outdoor heat exchanger and an intermediate pressure receiver that
is provided via a restriction mechanism at the wake flow side of the intercooler,
and at the wake flow side of the intermediate pressure receiver, a supercooling heat
exchanger is provided in each of the indoor heat exchangers that are arranged in parallel.
[0016] According to such a refrigerant circuit, due to providing an intercooler that is
provided at the wake flow side of the outdoor heat exchanger and an intermediate pressure
receiver that is provided via a restriction mechanism at the wake flow side of the
intercooler, and a supercooling heat exchanger is provided for each of the plural
indoor heat exchangers arranged in parallel at the wake flow side of the intermediate
pressure receiver, the surplus portion of the refrigerant that has exited from the
plural indoor heat exchangers, which are used as evaporators and condensers, can be
held in a receiver as a saturated liquid.
[0017] According to the present invention described above, in a refrigerant circuit having
a supercritical cycle that uses carbon dioxide as a refrigerant, an amount of surplus
refrigerant can be held in a receiver as a liquid single-phase.
Brief Description of Drawings
[0018]
[FIG. 1A]
FIG. 1A is a refrigerant circuit diagram that shows a first embodiment of the refrigerant
circuit according to the present invention.
[FIG. 1B]
FIG. 1B is a Mollier diagram of the refrigerant circuit diagram that is shown in FIG.
1A.
[FIG. 2A]
FIG. 2A is a refrigerant circuit diagram that shows a second embodiment of the refrigerant
circuit according to the present invention.
[FIG. 2B]
FIG. 2B is a Mollier diagram of the refrigerant circuit diagram that is shown in FIG.
2A.
[FIG. 3A]
FIG. 3A is a refrigerant circuit diagram that shows a third embodiment of the refrigerant
circuit according to the present invention.
[FIG. 3B]
FIG. 3B is a Mollier diagram of the refrigerant circuit diagram that is shown in FIG.
3A.
[FIG. 4]
FIG. 4 is a refrigerant circuit diagram that shows a fourth embodiment of the refrigerant
circuit according to the present invention.
[FIG. 5A]
FIG. 5A is a refrigerant circuit diagram that shows a fifth embodiment of the refrigerant
circuit according to the present invention.
[FIG. 5B]
FIG. 5B is a Mollier diagram of the refrigerant circuit diagram that is shown in FIG.
5A.
[FIG. 6A]
FIG. 6A is a refrigerant circuit diagram in a simultaneous refrigerant state showing
a sixth embodiment of the refrigerant circuit according to the present invention.
[FIG. 6B]
FIG. 6B is a Mollier diagram of the refrigerant circuit diagram that is shown in FIG.
6A.
[FIG. 7A]
FIG. 7A is a refrigerant circuit diagram in a simultaneous heating state showing a
seventh embodiment of the refrigerant circuit according to the present invention.
[FIG. 7B]
FIG. 7B is a Mollier diagram of the refrigerant circuit diagram that is shown in FIG.
7A.
[FIG. 8A]
FIG. 8A is a refrigerant circuit in a mixed refrigerating and heating state showing
a seventh embodiment of the refrigerant circuit according to the present invention.
[FIG. 8B]
FIG. 8B is a Mollier diagram of the refrigerant circuit diagram that is shown in FIG.
8A.
[FIG. 9A]
FIG. 9A is a refrigerant circuit diagram in which a conventional HFC refrigerant is
used.
[FIG. 9B]
FIG. 9B is a Mollier diagram of the refrigerant circuit diagram that is shown in FIG.
9A
[FIG. 10A]
FIG. 10A is a refrigerant circuit diagram of a two-stage compression two-phase expansion
cycle (gas-liquid separation method) .
[FIG. 10B]
FIG. 10B is a Mollier diagram of the refrigerant circuit diagram that is shown in
FIG. 10A.
[FIG. 11A]
FIG. 11A is a refrigerant circuit diagram of a two-stage compression one-stage expansion
cycle (intercooler method).
[FIG. 11B]
FIG. 11B is a Mollier diagram of the refrigerant circuit that is shown in FIG. 11A.
Explanation of Reference:
[0019]
- 1:
- compressor
- 2:
- accumulator
- 3:
- condenser
- 4:
- intermediate pressure receiver
- 5, 5A, 5B:
- restriction mechanism
- 6:
- evaporator
- 7:
- intercooler
- 8:
- four-way valve
- 9:
- bridge circuit
- 10, 10A - E:
- refrigerant circuit
- 20:
- reheating condenser
- 30:
- supercooling heat exchanger
Best Mode for Carrying Out the Invention
[0020] Below, embodiments of the refrigerant circuit according to the present invention
will be explained with reference to the figures. Note that the refrigerant circuits
in each of the embodiments described below forms a refrigeration cycle that uses carbon
dioxide as the refrigerant.
First Embodiment
[0021] In the refrigerant circuit 10 for the refrigeration cycle that is shown in FIG. 1A,
reference numeral 1 indicates a compressor, 2 indicates an accumulator, 3 indicates
a condenser, 4 indicates a receiver, 5, 5A, and 5B indicate a restriction mechanism,
6 indicates an evaporator, and 7 indicates an intercooler. Note that the state at
the positions that are indicated by "a" to "h" in FIG. 1A corresponds to those in
the Mollier diagram that is shown in FIG. 1B.
[0022] In the illustrated refrigerant circuit 10, the gas-phase refrigerant that has been
compressed to a supercritical state "a" by the compressor 1 changes from state "a"
to state "b" after the enthalpy has decreased by heat exchange being carried out by
the condenser 3 at an equal pressure.
The flow of the refrigerant in state "b" is divided into the main refrigerant flow
that is directly conducted to the intercooler 7 and then toward the restriction mechanism
5A, and reduced pressure refrigerant flow that is conducted to the intercooler 7 via
the restriction mechanism 5B.
[0023] In the intercooler 7, the main refrigerant flow and the reduced pressure refrigerant
flow undergo heat exchange. During this heat exchange, the pressure of the main refrigerant
flow is reduced to a state "c" by the restriction mechanism 5B, and this main refrigerant
flow is cooled to a state "e" due to the reduced pressure refrigerant flow which has
imparted thereto a two-phase gas-liquid state, and the enthalpy is thereby reduced.
The temperature of the two-phase gas-liquid reduced pressure refrigerant flow that
cooled the main refrigerant flow is raised due to heat adsorption, and thus, the main
refrigerant flow is drawn into the compressor 1 after changing to the gas-phase "d".
[0024] The main refrigerant flow in state "e", which has been cooled by the intercooler
7, changes to the liquid-phase state "f" by expanding after an initial pressure reduction
due to the restriction mechanism 5A. Because the intermediate pressure receiver 4
is provided at the wake flow side of the restriction mechanism 5A, at which the main
refrigerant flow becomes state "f", when there is surplus refrigerant in the liquid-phase
main refrigerant flow, this surplus refrigerant is held in the intermediate pressure
receiver 4 as surplus refrigerant.
In addition, the main refrigerant flow, which excludes the refrigerant that is held
in the intermediate pressure receiver 4 as surplus refrigerant, expands to state "g"
due to another pressure reduction by the restriction mechanism 5 after passing through
the intermediate pressure receiver 4. The temperature of this main refrigerant flow
of this state "g" increase because of absorbing heat due to heat exchange in the process
of passing through the evaporator 6, and enters the compressor 1 after becoming a
gas-phase state "h".
[0025] Thus, the gas-phase refrigerant (state "d" and state "h") that is drawn into the
compressor 1 is compressed to the supercritical state "a" due to being pressurized
by the compressor 1.
Therefore, the refrigerant in state "a" circulates through the refrigerant circuit
10 after passing through subsequent similar processes, and thus, a refrigeration cycle
is formed by carrying out refrigerating by the evaporator using refrigerant that has
repeatedly circulated through the state changes 6. In addition, the refrigerant circuit
10 formed in this manner arranges an intermediate pressure receiver 4 at the wake
flow side, in which the refrigerant that has been cooled by the intercooler 7 expands
to an intermediate pressure due to the restriction mechanism 5A, and thus, liquid-phase
surplus refrigerant can be held in the intermediate pressure receiver 4.
Second Embodiment
[0026] Next, a second embodiment of the refrigerant circuit according to the present invention
will be explained with reference to FIG. 2A and 2B. Note that identical reference
symbols indicate parts that are identical to those of the embodiment described above,
and the detailed explanations thereof are omitted.
The refrigerant circuit 10A of the refrigeration cycle that is shown in FIG. 2A can
selectively switch between, for example, a refrigerating operation and a heating operation
of an air conditioner. Thus, a four-way valve 8 and a bridge circuit 9 are added to
the refrigerant circuit 10 described above. In this refrigerant circuit 10 as well,
the refrigerant states during the refrigerating operation, which are indicated by
"a" to "h" in FIG. 2A, correspond to those in the Mollier diagram that is shown in
FIG. 2B.
[0027] This refrigerant circuit 10 reverses the functions of the condenser 3 and the evaporator
6 by reversing the circulation direction of the refrigerant, and thus, switching between
the refrigerating operation and the heating operation becomes possible. Specifically,
the circulation direction of the gas-phase refrigerant that is fed from the compressor
1, after being changed to a supercritical state "a", is switched by the operation
of the four-way valve 8. As shown by the arrows in the figures, during a refrigerating
operation, the refrigerant flows from the four-way valve 8 toward the condenser 3,
and after passing through the condenser 3, flows so as to be divided between the intercooler
7 and the restriction mechanism 5B after passing through the bridge circuit 9, which
is a combination of check valves.
[0028] In contrast, during a heating operation, the four-way valve 8 is operated, and the
refrigerant in state "a", having been compressed by the compressor 1, flows toward
the evaporator 6 side, and thus, in this case, the evaporator 6 serves as a heat exchanger
that functions as a condenser. Therefore, the refrigerant radiates heat when passing
through the heat exchanger (the evaporator 6 in the figure) that functions as a condenser,
and after the temperature thereof falls to state "b", passes through the bridge circuit
9 and flows so as to be divided between the intercooler 7 and the restriction mechanism
5B. Note that during the heating operation, the condenser 3 in the figure serves as
a heat exchanger that absorbs heat as an evaporator.
[0029] The liquid-phase surplus portion of the refrigerant that has been distributed between
the intercooler 7 and the restriction mechanism 5B is held in the receiver 4 after
passing through processes similar to those in the first embodiment described above.
Specifically, in either of the operation states during the heating operation or the
refrigerating operation, the liquid-phase surplus refrigerant can be held in the intermediate
pressure receiver 4.
Note that in the refrigerant circuit 10A, in the case in which the refrigerant states
during a heating operation differs from that during a refrigerating operation, the
positions "a" to "h" of the refrigerant states corresponding to those in the Mollier
diagram are shown in parentheses in FIG. 2A.
Third Embodiment
[0030] Next, a third embodiment of the refrigerant circuit according to the present invention
will be explained with reference to FIG. 3A and FIG. 3B. Note that identical reference
symbols indicate parts that are identical to those of the embodiment described above,
and the detailed explanations thereof are omitted.
The refrigerant circuit 10B of the refrigeration cycle that is shown in FIG. 3A adds
a reheating condenser 20 to the first embodiment described above. This reheating condenser
20 is arranged between the receiver 4 and the restriction mechanism 5. In this refrigerant
circuit 10B as well, the refrigerant states during the refrigerating operation, which
are indicated by "a" to "i" in FIG. 3A, correspond to those in the Mollier diagram
that is shown in FIG. 3B.
[0031] The reheating condenser 20 that is added in this embodiment is a heat exchanger having
the function of a condenser that absorbs heat from the refrigerant in the state "f",
which is a liquid-phase state, to lower the temperature to the state "g". As a result,
in the case of an air-conditioning apparatus that dehumidifies, the reheating condenser
20 can be used as a supercooling condenser. Specifically, in an air conditioning apparatus
that uses carbon dioxide refrigerant, by adding the reheating condenser 20, in addition
to holding surplus refrigerant, dehumidification becomes possible.
Fourth embodiment
[0032] Next, a fourth embodiment of the refrigerant circuit according to the present invention
will be explained with reference to FIG. 4. Note that identical reference symbols
indicate parts that are identical to those of the embodiment described above, and
the detailed explanations thereof are omitted.
In the refrigerant circuit 10C shown in this embodiment, plural sets of restriction
mechanisms 5 and evaporators 6 are arranged in parallel at the wake flow side of the
receiver 4. Specifically, in contrast to the refrigerant circuit 10 in FIG. 1, a structure
is used in which the restriction mechanism 5' and the evaporator 6' are arranged parallel
to the restriction mechanism 5 and the evaporator 6, and plural indoor units are arranged
in parallel.
[0033] In this manner, because the refrigerant circuit 10C, in which two or more sets of
restriction mechanisms 5 and evaporators 6 are arranged at the wake flow side of the
intermediate pressure receiver 4, can supply a liquid single-phase from the intermediate
pressure receiver 4, refrigerant can be suitably distributed. Therefore, by applying
this refrigerant circuit 10C to an air conditioning apparatus in which plural indoor
units are arranged in parallel, operation in which suitable refrigerant distribution
is carried out becomes possible.
In addition, this embodiment may be formed such that the reheating condenser 20, which
was explained in the third embodiment described above, is added between the restriction
mechanisms 5 and 5' and the intermediate pressure receivers 4 that are disposed in
parallel.
Fifth Embodiment
[0034] Next, a fifth embodiment of the refrigerant circuit according to the present invention
will be explained with reference to FIG. 5A and FIG. 5B. Note that identical reference
symbols indicate parts that are identical to those of the embodiment described above,
and the detailed explanations thereof are omitted.
In the refrigerant circuit 10C that is exemplified in this embodiment, a supercooling
heat exchanger 30 is added along with the restriction mechanism 5C downstream of the
intermediate pressure receiver 4. This supercooling heat exchanger 30 is a heat exchanger
that applies supercooling by refrigerating the liquid phase refrigerant downstream
of the intermediate pressure receiver 4.
[0035] The refrigerant circuit 10D having such a structure is capable of an operation in
which liquid refrigerant is appropriately distributed without the diameter of pipes
for the liquid refrigerant enlarging even in an air conditioning apparatus disposed
such that pressure loss increases because the refrigerant pipes through which the
liquid refrigerant flows becomes long due to providing a supercooling heat exchanger
30 downstream of the intermediate pressure receiver 4.
Sixth embodiment
[0036] Next, a sixth embodiment of the refrigerant circuit according to the present invention
will be explained with reference to FIG. 6A to FIG. 8B. Note that identical reference
symbols indicate parts that are identical to those of the embodiment described above,
and the detailed explanations thereof are omitted.
This embodiment is applied, in an indoor unit disposed in plurality, to a refrigerant
circuit 10E that enables mixed refrigerating and heating operation, in which a different
operation for each unit is selected from among the refrigerating operation and the
heating operation, and operated simultaneously. Note that in this embodiment, the
condenser 3 is referred to as an "indoor heat exchanger", and the evaporators 6 and
6' are referred to as "outdoor heat exchangers".
[0037] In order to enable the mixed refrigeration and heating operation, the illustrated
refrigerant circuit 10E connects one side of the outdoor heat exchanger 3 to two refrigeration
paths provided with flow path switching valves 41 and 42, and in addition, the two
refrigerant flow paths, which are provided with flow path switching valves 43, 44,
45, and 46, are respectively connected to one among two indoor heat exchangers 6 and
6' arranged in parallel. In addition, the refrigerant circuit 10E is provided with
an intercooler 7 that is provided at the wake flow side of the outdoor heat exchanger
3, and an intermediate pressure receiver 4 that is provided via the restriction mechanism
5A at the wake flow side of the intercooler 7. Furthermore, the refrigerant circuit
10E is provided with supercooling heat exchangers 30 and 30', which are provided in
each of the indoor heat exchangers 6 and 6' that are arranged in parallel at the wake
flow side of the intermediate pressure receiver 4.
[0038] In the refrigerant circuit 10E that is structured in this manner, in the case in
which the two indoor heat exchangers 6 and 6' both carry out refrigerating operations
(refer to FIG. 6A), the refrigerant flows as shown by the arrows in the figure. The
open and closed state of each of the flow path switching valves 41 and 44 at this
time is shown, where a closed valve is shown in black. In this refrigerant circuit
10E as well, the refrigerant states during the refrigeration operation, which are
indicated by "a" to "i" in FIG. 6A, correspond to those in the Mollier diagram that
is shown in FIG. 6B.
During such plural and simultaneous refrigeration operations, the refrigerant flows
in a manner that is substantially identical to that of the fifth embodiment described
above, and thus, the Mollier diagram that shows the refrigerant states is also identical.
Therefore, the liquid phase surplus refrigerant can be held in the intermediate pressure
receiver 4.
[0039] The refrigerant circuit 10E shown in FIG. 7A illustrates the case in which two indoor
heat exchangers 6 and 6' both carry out the refrigeration operation, and the refrigerant
flows as shown by the arrows. The open and closed state of each of the flow path switching
valves 42, 43, and 45 at this time are shown, where a closed valve is shown in black.
In this refrigerant circuit 10E as well, the refrigerant states during the heating
operation, which are shown by "a" to "f" in FIG. 7A, correspond to those in the Mollier
diagram shown in fig. 7B.
During such plural simultaneous heating operation, the refrigerant that has passed
through the indoor heat exchangers 6 and 6', which function as condensers, is cooled
by the supercooling heat exchangers 30 and 30', and the refrigerant changes to a supercooled
liquid phase. Therefore, if there is a surplus of this refrigerant, this surplus can
be held in the intermediate pressure receiver 4 at the wake flow side of the supercooling
heat exchangers 30 and 30'.
[0040] The refrigerant circuit 10E that is shown in FIG. 8A illustrates the case of a mixed
refrigeration and heating operation, in which two indoor heat exchangers 6 and 6'
are respectively carrying out a refrigeration operation and a heating operation, and
the refrigeration and heating loads are substantially identical. The refrigerant flows
as shown by the arrows in the figure. In the illustrated example, the indoor heat
exchanger 6 is carrying out a refrigeration operation and the indoor heat exchanger
6' is carrying out a heating operation. The open and closed states of each of the
flow path switching valves 41, 42, 44, 45, and 5A at this time are shown, where a
closed valve is shown in black. In this refrigerant circuit 10E as well, the refrigerant
states during a mixed refrigeration and heating operation, which are shown by "a"
to "f" in FIG. 8A, correspond to those in the Mollier diagram that is shown in FIG.
8B.
During such mixed refrigeration and heating operation, in the case in which the refrigeration
and the heating loads are balanced, the indoor heat exchanger 6' radiates heat as
a condenser, and the indoor heat exchanger 6 absorbs heat as an evaporator. In addition,
the refrigerant that has passed through the indoor heat exchanger 6', which functions
as a condenser, is cooled by the supercooling heat exchanger 30', and thus, at the
outlet of the supercooling heat exchanger 30', the refrigerant changes from a two-phase
to a supercooled liquid phase due to the amount of heat exchange. Thus, if there is
surplus refrigerant, this surplus refrigerant can be held in the intermediate pressure
receiver 4, which is at the wake flow side of the supercooling heat exchanger 30'.
[0041] In this manner, according to the present invention described above, in a critical
cycle refrigerant circuit that uses carbon dioxide as a refrigerant, an intercooler
is provided at the wake flow side of the condenser, and the refrigerant that has been
cooled forms a region (liquid phase) of saturated fluid due to the pressure being
reduced by the added restriction mechanism. Thus, an amount of surplus refrigerant
can be held as a liquid single-phase in an intermediate pressure receiver that is
located at the wake flow of the restriction mechanism.
Note that the present invention is not limited by the embodiments described above,
and suitable modifications are possible within a range that do not depart from the
spirit of the present invention.