TECHNICAL FIELD
[0001] The present invention relates to a refrigeration apparatus using refrigerant operating
in the supercritical zone.
BACKGROUND ART
[0002] A refrigeration apparatus, using supercritical refrigerant (e.g., CO
2 refrigerant) operating in the supercritical zone as refrigerant, has been conventionally
produced (see
JP-A-2000-234814).
[0003] DE 10 2006 003 827 A1 discloses a refrigeration apparatus using a supercritical refrigerant. According
to this document, an expansion valve is opened or closed in response to a signal of
a pressure sensor and with respect to a calculated target high pressure.
DISCLOSURE OF THE INVENTION
<Technical Problem>
[0005] According to the aforementioned refrigeration apparatus, however, refrigerant in
a gas-liquid two-phase state may flow into an expansion mechanism when high pressure
of the refrigerant does not reach a fully pressurized level in the activation of the
refrigeration apparatus or when temperature of the refrigerant does not reach the
critical temperature because of low external temperature. In this case, flow sound
of the refrigerant is easily generated in a vicinity of an inlet of the expansion
mechanism. This will be a cause of noise to be produced when the refrigeration apparatus
is operated.
[0006] It is an object of the present invention to reduce generation of noise in an operation
of a refrigeration apparatus by inhibiting generation of flow sound of refrigerant
<Solution to Problem>
[0007] A refrigeration apparatus according to a first aspect of the present invention is
a refrigeration apparatus using supercritical refrigerant operating in a zone that
high pressure of the supercritical refrigerant is equal to or greater than the critical
pressure. The refrigeration apparatus includes a compressor, a gas cooler, an expansion
mechanism, an evaporator, discharge pressure detection means and a control section.
The compressor is configured to compress the supercritical refrigerant. The gas cooler
is configured to cool the supercritical refrigerant compressed by the compressor.
The expansion mechanism is configured to decompress the supercritical refrigerant.
The evaporator is configured to evaporate the supercritical refrigerant decompressed
by the expansion mechanism. The discharge pressure detection means is capable of detecting
discharge pressure of the compressor. The control section is configured to regulate
opening degree of the expansion mechanism for controlling the discharge pressure to
be equal to or greater than the critical pressure when the refrigeration apparatus
is activated and the discharge pressure is less than the critical pressure.
[0008] According to the first aspect of the present invention, the control section is configured
to regulate the opening degree of the expansion mechanism for controlling the discharge
pressure to be equal to or greater than the critical pressure when it determines that
the discharge pressure is less than the critical pressure in the activation of the
refrigeration apparatus.
[0009] Therefore, it is possible to change a state of the supercritical refrigerant in a
vicinity of an inlet of the expansion mechanism from a gas-liquid two phase state
to a supercritical state or a liquid-phase state by setting high pressure of the supercritical
refrigerant in the refrigeration cycle to be equal to or greater than the critical
pressure. Accordingly, it is possible to inhibit generation of flow sound due to a
blowout of bubbles and the like.
[0010] A refrigeration apparatus according a second aspect of the present invention is the
refrigeration apparatus according to the first aspect of the present invention, wherein
the control section is configured to execute a first control for setting the opening
degree of the expansion mechanism to be fully-closed or a slightly-opened degree when
the discharge pressure is less than the critical pressure.
[0011] According to the second aspect of the present invention, the control section is configured
to set the opening degree of the expansion mechanism to be fully-closed or a slightly
opened degree when the discharge pressure is less than the critical pressure. Therefore,
it is possible to easily set high pressure of the refrigerant in the refrigeration
cycle to be equal to or greater than the critical pressure. Consequently, it is possible
to inhibit generation of flow sound of the refrigerant in a vicinity of the inlet
of the expansion mechanism.
[0012] A refrigeration apparatus according to a third aspect of the present invention is
the refrigeration apparatus according to the second aspect of the present invention,
wherein the control section is configured to execute a second control for setting
the opening degree of the expansion mechanism to be large when the discharge pressure
is equal to or greater than the critical pressure after the first control is executed.
[0013] When the refrigerant is pressurized to be equal to or greater than the critical pressure,
the refrigerant enters a supercritical state or a liquid-phase state. In other words,
the refrigerant is not in a gas-liquid two-phase state any more. Accordingly, it is
possible to reduce generation of flow sound in a vicinity of the inlet of the expansion
mechanism without further pressurizing the refrigerant.
[0014] According to the third aspect of the present invention, the control section is configured
to execute the second control for opening the expansion mechanism when the discharge
pressure is equal to or greater than the critical pressure after execution of the
first control for easily increasing the high pressure of the refrigerant. Therefore,
it is possible to optimally control the discharge pressure without unnecessarily increasing
it. Consequently, it is possible to reduce energy consumption.
[0015] A refrigeration apparatus according to a fourth aspect of the present invention is
the refrigeration apparatus according to any of the first to third aspects of the
present invention, wherein the discharge pressure detection means is a pressure sensor
provided at the discharge side of the compressor.
[0016] According to the fourth aspect of the present invention, the pressure sensor is configured
to detect the discharge pressure and determination is made for whether or not the
refrigerant is in a supercritical state. Therefore, it is possible to directly detect
high pressure of the refrigerant in the refrigeration cycle based on the discharge
pressure. Accordingly, it is possible to proceed to the second control from the first
control while a period of time necessary for the first control is minimized. Also,
it is possible to optimally control high pressure of the refrigerant without unnecessarily
increasing it. Consequently, it is capable of reducing energy loss.
[0017] A refrigeration apparatus according to a fifth aspect of the present invention is
the refrigeration apparatus according to any of the first to fourth aspects of the
present invention, wherein the control section is configured to calculate inlet pressure
of the expansion mechanism based on the discharge pressure and operational capacity
of the compressor. Additionally, the control section is configured to regulate the
opening degree of the expansion mechanism for controlling the discharge pressure to
be equal to or greater than the critical pressure when the inlet pressure is less
than the critical pressure.
[0018] According to the fifth aspect of the present invention, the inlet pressure of the
expansion mechanism is calculated based on the discharge pressure and the compressor
capacity. The discharge pressure and the inlet pressure of the expansion mechanism
are different from each other because pressure-loss exists in the refrigerant pipe.
Therefore, it is possible to more reliably control a state of the refrigerant in the
vicinity of the inlet of the expansion mechanism (i.e., the cause of generation of
noise) from a gas-liquid two-phase state to a supercritical state or a liquid-phase
state.
[0019] A refrigeration apparatus according to a sixth aspect of the present invention is
the refrigeration apparatus according to any of the first to third aspects of the
present invention, wherein the pressure detection means is a temperature sensor capable
of detecting temperature of the supercritical refrigerant in a range from an outlet
of the gas cooler to an inlet of the expansion mechanism. Additionally, the control
section is configured to determine that the inlet pressure is less than the critical
pressure when the inlet temperature is less than the critical temperature, and is
configured to regulate the opening degree of the expansion mechanism for controlling
the inlet temperature to be equal to or greater than the critical temperature.
[0020] According to the sixth aspect of the present invention, the temperature sensor is
configured to detect refrigerant temperature in a range from the outlet of the gas
cooler to the inlet of the expansion mechanism, and determination is made for whether
or not the refrigerant is in a supercritical state. Therefore, it is possible to determine
that the refrigerant in a vicinity of the inlet of the expansion mechanism is not
in a gas-liquid two-phase state, and it is also possible to reduce a blowout sound
of bubbles and the like, which is a factor of flow sound. Furthermore, the pressure
sensor in the fourth aspect of the present invention is allowed to be replaced by
a temperature sensor, which is cheaper than the pressure sensor. Accordingly, it is
possible to reduce its production cost.
[0021] A refrigeration apparatus according to a seventh aspect of the present invention
is the refrigeration apparatus according to any of the first to sixth aspects of the
present invention, wherein the refrigeration apparatus further includes a blower.
The blower promotes cooling of the gas cooler. Additionally, the control section is
configured to control the airflow volume of the blower to be small or zero when the
refrigeration apparatus is activated and the discharge pressure is less than the critical
pressure.
[0022] According to the seventh aspect of the present invention, the control section is
configured to set the airflow volume of the blower, which is configured to blow air
to the gas cooler for promoting cooling of the gas cooler, to be small or zero when
the refrigeration apparatus is activated and the discharge pressure is less than the
critical pressure. Therefore, it is possible to weaken a cooling effect in the gas
cooler, and it is also possible to increase both temperature and pressure of the refrigerant
in the gas cooler. Accordingly, it is possible to set a state of the refrigerant at
the outlet of the gas cooler to be a supercritical state or a liquid-phase state.
Consequently, it is possible to reduce generation of flow sound in a vicinity of the
inlet of the expansion mechanism.
[0023] A refrigeration apparatus according to an eighth aspect of the present invention
is the refrigeration apparatus according to any of the first to seventh aspects of
the present invention, wherein the control section is configured to regulate the opening
degree of the expansion mechanism for controlling the discharge pressure to be equal
to or greater than the critical pressure when a normal operation is executed.
[0024] According to the eighth aspect of the present invention, the control section is configured
to control the discharge pressure to be equal to or greater than the critical pressure
not only in the activation of the refrigeration apparatus but also in the normal operation.
Therefore, it is always possible to set a state of the refrigerant in a vicinity of
the inlet of the expansion mechanism to be a supercritical state or a liquid-phase
state. Consequently, it is possible to reduce generation of flow sound at the inlet
of the expansion mechanism.
[0025] A refrigeration apparatus according to a ninth aspect of the present invention is
the refrigeration apparatus according to any of the first to seventh aspects of the
present invention, wherein the control section is configured to regulate the opening
degree of the expansion mechanism for controlling the discharge pressure to be equal
to or greater than the critical pressure even when a normal operation is executed
at a low external temperature.
[0026] When the normal operation is executed at the low external temperature, refrigerant
in a vicinity of the inlet of the expansion mechanism may be in a gas-liquid two-phase
state. According to the ninth aspect of the present invention, the control section
is configured to regulate the opening degree of the expansion mechanism for controlling
high pressure of the supercritical refrigerant to be equal to or greater than the
critical pressure even at the low external temperature. Therefore, it is possible
to set a state of the refrigerant in a vicinity of the inlet of the expansion mechanism
to be a supercritical state or a liquid-phase state.
[0027] A refrigeration apparatus according to a tenth aspect of the present invention is
the refrigeration apparatus according to the ninth aspect of the present invention,
wherein the low external temperature is defined as the external temperature equal
to or less than 20 degrees Celsius.
[0028] According to the tenth aspect of the present invention, the discharge pressure is
controlled to be equal to or greater than the critical pressure under a condition
that the supercritical refrigerant easily enters a gas-liquid two-phase state (e.g.,
a condition that the external temperature is equal to or less than 20 degrees Celsius).
Therefore, it is possible to change a state of the supercritical refrigerant in a
vicinity of the inlet of the expansion mechanism from a gas-liquid two-phase state
to a supercritical state or a liquid-phase state even when the external temperature
is equal to or less than 20 degrees Celsius.
[0029] A refrigeration apparatus according to a twelfth aspect of the present invention
is the refrigeration apparatus according to any of the first to tenth aspects of the
present invention, wherein the supercritical refrigerant is carbon dioxide (CO
2) refrigerant
[0030] According to the twelfth aspect of the present invention, the CO
2 refrigerant is used as refrigerant Ozone depletion potential (ODP) of the CO
2 refrigerant equals to zero. Therefore, the CO
2 refrigerant does not destroy the ozone layer above the earth. Furthermore, global
warming potential (GWP) of the CO
2 refrigerant equals to 1. This is much lower than GWP of fluorocarbon refrigerant
of about hundreds to ten thousand. Accordingly, the refrigerant apparatus is capable
of inhibiting worsening of global environment with use of the CO
2 refrigerant with less environmental burden.
<Advantageous Effects of Invention>
[0031] According to the refrigeration apparatus of the first aspect of the present invention,
it is possible to change a state of the supercritical refrigerant from a gas-liquid
two-phase state to a supercritical state or a liquid-phase state by setting high pressure
of the supercritical refrigerant in the refrigeration cycle to be equal to or greater
than the critical pressure. Therefore, it is possible to inhibit generation of flow
sound due to a blowout of bubbles and the like.
[0032] According to the refrigeration apparatus of the second aspect of the present invention,
it is possible to easily set high pressure of the supercritical refrigerant in the
refrigeration cycle to be equal to or greater than the critical pressure. Therefore,
it is possible to inhibit generation of flow sound due to a blowout of bubbles and
the like.
[0033] According to the refrigeration apparatus of the third aspect of the present invention,
it is possible to optimally control the discharge pressure without unnecessarily increasing
it. Consequently, it is possible to reduce energy consumption.
[0034] According to the refrigeration apparatus of the fourth aspect of the present invention,
it is possible to directly detect high pressure of the supercritical refrigerant in
the refrigeration cycle based on the discharge pressure. Therefore, it is possible
to proceed to the second control from the first control while a period of time necessary
for the first control is minimized. Also, it is possible to optimally control high
pressure of the supercritical refrigerant without unnecessarily increasing it. Consequently,
it is possible to reduce energy loss.
[0035] According to the refrigeration apparatus of the fifth aspect of the present invention,
it is possible to more reliably control a state of the refrigerant in a vicinity of
the inlet of the expansion mechanism (i.e., the cause of generation of noise) from
a gas-liquid two-phase state to a supercritical state or a liquid-phase state.
[0036] According to the refrigeration apparatus of the sixth aspect of the present invention,
it is possible to determine that the refrigerant in a vicinity of the inlet of the
expansion mechanism is not in a gas-liquid two-phase state, and it is also possible
to reduce a blowout sound of bubbles and the like, which is a factor of flow sound.
Furthermore, the pressure sensor in the fourth aspect of the present invention is
allowed to be replaced by a temperature senor, which is cheaper than the pressure
sensor. Accordingly, it is possible to reduce its production cost.
[0037] According to the refrigeration apparatus of the seventh aspect of the present invention,
it is possible to weaken a cooling effect in the gas cooler, and it is also possible
to increase both temperature and pressure of refrigerant in the gas cooler. Therefore,
it is possible to set a state of the refrigerant at the outlet of the gas cooler to
be a supercritical state or a liquid-phase state. Consequently, it is possible to
reduce generation of flow sound in a vicinity of the inlet of the expansion mechanism.
[0038] According to the refrigeration apparatus of the eighth aspect of the present invention,
it is possible to always set a state of the refrigerant in a vicinity of the inlet
of the expansion mechanism to be a supercritical state or a liquid-phase state. Therefore,
it is possible to reduce generation of flow sound at the inlet of the expansion mechanism.
[0039] According to the refrigeration apparatus of the ninth aspect of the present invention,
it is possible to set a state of the refrigerant in a vicinity of the inlet of the
expansion mechanism to be a supercritical state or a liquid-phase state even at the
low external temperature.
[0040] According to the refrigeration apparatus of the tenth aspect of the present invention,
it is possible to change a state of the supercritical refrigerant from a gas-liquid
two-phase state to a supercritical state or a liquid-phase state even when the external
temperature is equal to or less than 20 degrees Celsius.
[0041] According to the refrigeration apparatus of the twelfth aspect of the present invention,
it is possible to inhibit worsening of global environment with use of the CO
2 refrigerant with less environmental burden.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042]
Fig. 1 is a refrigeration circuit diagram of an air conditioning apparatus according
to an embodiment of the present invention.
Fig. 2 is a control block diagram of the air conditioning apparatus.
Fig. 3 is a flow chart of an activation mode.
Fig. 4 is a flow chart of a normal mode.
Fig. 5 is a time-flow chart for illustrating timing of switching between a throttle
control and a normal control.
Fig. 6 is a P-H chart (Mollier chart) of a supercritical refrigeration cycle.
Fig. 7 is a refrigeration circuit diagram of an air conditioning apparatus according
to Modification (2).
EXPLANATION OF THE REFERENCE NUMERALS
[0043]
- 1, 1a
- air conditioning apparatus (refrigeration apparatus)
- 5
- control section
- 21
- compressor
- 23
- outdoor heat exchanger (gas cooler, evaporator)
- 24
- outdoor fan (blower)
- 31
- indoor heat exchanger (gas cooler, evaporator)
- 32
- indoor fan (blower)
- P1
- discharge pressure sensor (pressure sensor)
- T2
- first liquid pipe temperature sensor (temperature sensor)
- T3
- second liquid pipe temperature sensor (temperature sensor)
- V2
- outdoor expansion valve (expansion mechanism)
- V5
- indoor expansion valve (expansion mechanism)
BEST MODE FOR CARRYING OUT THE INVENTION
[0044] An air conditioning apparatus according to an embodiment of the present invention
will be hereinafter explained with reference to the accompanying drawings.
<Structure of Air Conditioning Apparatus>
[0045] Fig. 1 is a schematic configuration diagram of an air conditioning apparatus 1 according
to an embodiment of the present invention. The air conditioning apparatus 1 is an
apparatus used for cooling and heating the indoor space of a building and the like.
In the present invention, carbon dioxide (CO
2) refrigerant, which is supercritical refrigerant, is used. The air conditioning apparatus
1 mainly includes an outdoor unit 2, an indoor unit 3 and a refrigerant communication
pipe 4. The outdoor unit 2 functions as a heat source unit. The indoor unit 3 is connected
to the outdoor unit 2, and functions as a utilization unit. The refrigerant communication
pipe 4 connects the indoor unit 3 and the outdoor unit 2. The refrigerant communication
pipe 4 is composed of a liquid refrigerant communication pipe 41 and a gas refrigerant
communication pipe 42. In other words, a refrigerant circuit 10 of the air conditioning
apparatus 1 according to the present embodiment is formed by the interconnection among
the outdoor unit 2, the indoor unit 3 and the refrigerant communication pipe 4.
(1) Outdoor Unit
[0046] The outdoor unit 2 is disposed outside a building and the like. The outdoor unit
2 is connected to the indoor unit 3 through the refrigerant communication pipe 4.
The outdoor unit 2 forms a part of the refrigerant circuit 10.
[0047] Next, structure of the outdoor unit 2 will be explained. The outdoor unit 2 mainly
includes an outdoor side refrigerant circuit 20. The outdoor side refrigerant circuit
20 forms a part of the refrigerant circuit 10. The outdoor side refrigerant circuit
20 mainly includes a compressor 21, a four-way switch valve V1, an outdoor heat exchanger
23 functioning as a heat source side heat exchanger, an outdoor expansion valve V2
functioning as an expansion mechanism, a liquid side stop valve V3 and a gas side
stop valve V4.
[0048] The compressor 21 is a compressor capable of changing its operation capacity. In
the present embodiment, the compressor 21 is a positive-displacement compressor to
be driven by a motor 22. Here, rotation speed of the motor 22 is controlled by an
inverter. Furthermore, only single compressor 21 is provided in the present embodiment.
However, the number of the compressor 21 is not limited to this. For example, two
or more compressors may be parallel-connected depending on the number of indoor units
and the like to be connected to the outdoor unit 2.
[0049] The four-way switch valve V1 is a valve provided for causing the outdoor heat exchanger
23 to function as a gas cooler and an evaporator. The four-way switch valve V1 is
connected to the outdoor heat exchanger 23, a suction side of the compressor 21, a
discharge side of the compressor 21 and the gas refrigerant communication pipe 42.
When the outdoor heat exchanger 23 is caused to function as a gas cooler, the four-way
switch valve V1 is configured to connect the discharge side of the compressor 21 and
the outdoor heat exchanger 23, and is also configured to connect the suction side
of the compressor 21 and the gas refrigerant communication pipe 42 (see a solid-line
condition in Fig. 1). On the other hand, when the outdoor heat exchanger 23 is caused
to function as an evaporator, the four-way switch valve V1 is configured to connect
the outdoor heat exchanger 23 and the suction side of the compressor 21, and is also
configured to connect the discharge side of the compressor 21 and the gas refrigerant
communication pipe 42 (see a dashed-line condition in Fig. 1).
[0050] The outdoor heat exchanger 23 is a heat exchanger allowed to function as a gas cooler
or an evaporator. In the present embodiment, the outdoor heat exchanger 23 is a cross-fin
typed fin-and-tube heat exchanger for conducting heat exchange between the refrigerant
and air functioning as a heat source. One end of the outdoor heat exchanger 23 is
connected to the four-way switch valve V1 while the other end thereof is connected
to the outdoor expansion valve V2.
[0051] The outdoor expansion valve V2 is an electric expansion valve for regulating the
pressure, the flow rate and the like of refrigerant flowing through the outdoor side
refrigerant circuit 20. The outdoor expansion valve V2 is connected between the outdoor
heat exchanger 23 and the liquid side stop valve V3 for this purpose.
[0052] Furthermore, the outdoor unit 2 includes an outdoor fan 24. The outdoor fan 24 functions
as a ventilation fan for sucking outdoor air into the outdoor unit 2 and then discharging
the air to the outside after the outdoor heat exchanger 23 conducts heat exchange
between the sucked air and the refrigerant. The outdoor fan 24 is a fan capable of
changing the flow rate of air to be supplied to the outdoor heat exchanger 23. In
the present embodiment, the outdoor fan 24 is a propeller fan to be driven by a motor
25, for instance. The motor 25 is composed of a DC fan motor.
[0053] Additionally, the outdoor unit 2 is provided with a variety of sensors. Specifically,
the outdoor unit 2 is provided with a discharge pressure sensor P1 for detecting discharge
pressure Pd of the compressor 21. The outdoor unit 2 is also provided with an external
temperature sensor T1 for detecting temperature of the outdoor air (i.e., external
temperature) flowing into the outdoor unit 2. The external temperature sensor T1 is
disposed at the outdoor-air suction side of the outdoor unit 2. In the present embodiment,
the external temperature sensor T1 is composed of a thermistor.
[0054] Moreover, the outdoor unit 2 includes an outdoor side control unit 27. The outdoor
side control unit 27 is configured to control operations of respective elements forming
the outdoor unit 2. The outdoor side control unit 27 includes a microcomputer, a memory,
an inverter circuit and the like. The microcomputer is provided for controlling the
outdoor unit 2. The inverter circuit is configured to control the motor 22 and the
like. The outdoor side control unit 27 is capable of transmitting/receiving a control
signal and the like to/from an after-mentioned indoor side control unit 34 of the
indoor unit 3 through a transmission line 51. In other words, the outdoor side control
unit 27, the indoor side control unit 34 and the transmission line 51 connecting each
of the control units 27 and 34 form a control section 5 for controlling the entire
operation of the air conditioning apparatus 1.
[0055] The elements of the control section 5 are connected for receiving detection signals
from various sensors P1 and T1 and for controlling the various devices 21, 24 and
32 and valves V1, V2 and V5, respectively, based on the detection signals and the
like. Now, Fig. 2 is a control block diagram of the air conditioning apparatus 1.
(2) Indoor Unit
[0056] The indoor unit 3 is installed by being embedded in or hanged down from the ceiling
of the indoor space of a building and the like, or hanged down on the wall thereof,
for instance. The indoor unit 3 is connected to the outdoor unit 2 through the refrigerant
communication pipe 4. The indoor unit 3 forms a part of the refrigerant circuit 10.
[0057] Next, a configuration of the indoor unit 3 will be explained. The indoor unit 3 mainly
includes an indoor side refrigerant circuit 30. The indoor side refrigerant circuit
30 forms a part of the refrigerant circuit 10. The indoor side refrigerant circuit
30 mainly includes an indoor heat exchanger 31 and an indoor expansion valve V5. The
indoor heat exchanger 31 functions as a utilization side heat exchanger. The indoor
expansion valve V5 functions as an expansion mechanism.
[0058] The indoor heat exchanger 31 is a cross-fin typed fin-and-tube heat exchanger formed
by a heat transmission tube and a plurality of fins. The indoor heat exchanger 31
is configured to function as an evaporator of the refrigerant for cooling the indoor
air in the cooling operation. On the other hand, the indoor heat exchanger 31 is configured
to function as a gas cooler of the refrigerant for heating the indoor air in the heating
operation.
[0059] The indoor expansion valve V5 is an electric expansion valve for regulating the pressure,
the flow rate and the like of the refrigerant flowing through the indoor side refrigerant
circuit 30. The indoor expansion valve V5 is connected to the liquid side of the indoor
heat exchanger 31. In this regard, the indoor expansion valve V5 is similar to the
aforementioned outdoor expansion valve V2.
[0060] Furthermore, the indoor unit 3 includes an indoor fan 32. The indoor fan 32 functions
as a ventilation fan for sucking the indoor air into the indoor unit 3 and subsequently
supplying the sucked air to the indoor space as the supply air after the indoor heat
exchanger 31 conducts heat exchange between the refrigerant and the sucked air. The
indoor fan 32 is a fan capable of changing the flow rate of air to be supplied to
the indoor heat exchanger 31. In the present embodiment, the indoor fan 32 is a centrifugal
fan, a multi-blade fan and the like to be driven by a motor 33. Here, the motor 33
is composed of a DC fan motor.
[0061] Moreover, the indoor unit 3 is provided with the indoor side control unit 34 for
controlling operations of each of the elements forming the indoor unit 3. The indoor
side control unit 34 includes a microcomputer, a memory and the like provided for
controlling the indoor unit 3. The indoor side control unit 34 is capable of transmitting/receiving
a control signal and the like to/from a remote controller (not illustrated in the
figure) for individually operating a corresponding indoor unit 3. Additionally, the
indoor side control unit 34 is capable of transmitting/receiving a control signal
and the like to/from the outdoor unit 2 through the transmission line 51, for instance.
(3) Refrigerant Communication Pipe
[0062] When the air conditioning apparatus 1 is installed in an installation place of a
building and the like, the refrigerant communication pipe 4 is attached to the air
conditioning apparatus 1 in the installation site. Any suitable refrigerant communication
pipes 4 of a variety of lengths and diameters may be used depending on an installation
condition (e.g., an installation site and a combination of the outdoor unit 2 and
the indoor unit 3).
<Operations of Air Conditioning Apparatus>
[0063] Next, operations of the air conditioning apparatus 1 according to the present embodiment
will be explained.
[0064] The air conditioning apparatus 1 according to the present embodiment is configured
to be operated in two operation modes. One of the operation modes is an activation
mode to be executed in the activation of the air conditioning apparatus 1 until the
refrigeration cycle becomes stable. The other of the operation modes is a normal mode
to be executed after the refrigeration cycle becomes stable. Furthermore, the normal
mode is classified into two operation types. One of the operation types is a cooling
operation for causing the indoor unit 3 to cool the indoor space depending on cooling
load of the indoor unit 3. The other of the operation types is a heating operation
for causing the indoor unit 3 to heat the indoor space depending on heating load of
the indoor unit 3.
[0065] Operations of the air conditioning apparatus 1 in each of the operation modes will
be hereinafter explained.
(1) Activation Mode
[0066] Fig. 3 is a flowchart for illustrating a series of control processing to be executed
in the activation mode. When the air conditioning apparatus 1 is operated for executing
either a cooling operation or a heating operation (i.e., when the compressor 21 is
activated), the activation mode is accordingly activated. The activation mode will
be hereinafter explained with reference to Fig. 3.
[0067] First, in Step S1, it is determined if the discharge pressure Pd, detected by the
discharge pressure sensor P1, is less than the critical pressure Pk of the CO
2 refrigerant. When the discharge pressure Pd is less than the critical pressure Pk,
the control processing proceeds to Step S2. On the other hand, when the discharge
pressure Pd is equal to or greater than the critical pressure Pk, the control processing
proceeds to Step S3. In Step S2, a throttle control is executed for reducing a throttle
opening degree θ1 of the outdoor expansion valve V2 in a cooling operation, whereas
a throttle control is executed for reducing a throttle opening degree θ2 of the indoor
expansion valve V5 in a heating operation. In the "throttle control" herein referred,
the throttle opening degrees θ1 and θ2 are controlled to be an opening degree α (see
Fig. 5 to be described). When the throttle opening degrees θ1 and θ2 are set to be
the opening degree α, flow sound of the gas-liquid two-phase state CO
2 refrigerant is not generated when the CO
2 refrigerant passes through the outdoor expansion valve V2 or the indoor expansion
valve V5. When the discharge pressure Pd is less than the critical pressure Pk, the
CO
2 refrigerant could be in a gas-liquid two-phase state, not in a supercritical state,
at a higher possibility. When the CO
2 refrigerant is in a gas-liquid two-phase state, flow sound of the CO
2 refrigerant is easily generated in a vicinity of the outdoor expansion valve V2 or.the
indoor expansion valve V5. Therefore, high pressure of the CO
2 refrigerant is promoted to be equal to or greater than the critical pressure Pk in
the refrigeration cycle in a shorter period of time by setting the throttle opening
degree θ1 of the outdoor expansion valve V2 or the throttle opening degree θ2 of the
indoor expansion valve V5 to be the opening degree α. When Step S2 is completed, the
control processing returns to Step S1. In Step S3, the activation mode proceeds to
the normal mode.
(2) Normal Mode
[0068] Fig. 4 is a flowchart for illustrating a series of control processing to be executed
in the normal mode. The normal mode is started after the aforementioned activation
mode is completed.
[0069] First, in Step S11, it is determined if the discharge pressure Pd, detected by the
discharge pressure sensor P1, is less than the critical pressure Pk of the CO
2 refrigerant. When the discharge pressure Pd is less than the critical pressure Pk,
the control processing proceeds to Step S12. On the other hand, when the discharge
pressure Pd is equal to or greater than the critical pressure Pk, the control processing
proceeds to Step S15. In Step S12, throttle control is executed for reducing the throttle
opening degree θ1 of the outdoor expansion valve V2 in a cooling operation, whereas
throttle control is executed for reducing the throttle opening degree θ2 of the indoor
expansion valve V5 in a heating operation. When Step S12 is completed, the control
processing proceeds to Step S13. In Step S13, it is determined if the outdoor fan
24 is being driven in the cooling operation, whereas it is determined if the indoor
fan 32 is being driven in the heating operation. When the outdoor fan 24 or the indoor
fan 32 is being driven, the control processing proceeds to Step S14. On the other
hand, when the outdoor fan 24 or the indoor fan 32 is not being driven, the control
processing returns to Step S11. In Step S14, the outdoor fan 24 or the indoor fan
32 is stopped. When Step S14 is completed, the control processing returns to Step
S11. In Step S15 to be executed when the external temperature exceeds 20 degrees Celsius
in Step S11, it is determined if throttle control is being executed with respect to
the outdoor expansion valve V2 or the indoor expansion valve V5. When throttle control
is being executed with respect to the outdoor expansion valve V2 or the indoor expansion
valve V5, the control processing proceeds to Step S16. On the other hand, when normal
control is being executed with respect to the outdoor expansion valve V2 or the indoor
expansion valve V5, the control processing returns to Step S11. In Step S16, normal
control is executed with respect to the outdoor expansion valve V2 or the indoor expansion
valve V5. Note the term "normal control" means control processing to be executed in
the after-mentioned cooling operation or the after-mentioned heating operation. When
Step S16 is completed, the control processing proceeds to Step S17. In Step S17, it
is determined if the outdoor fan 24 or the indoor fan 32 is being stopped. When the
outdoor fan 24 or the indoor fan 32 is being stopped, the control processing proceeds
to Step S18. On the other hand, when the outdoor fan 24 or the indoor fan 32 is being
driven, the control process returns to Step S11. In Step S18, the outdoor fan 24 or
the indoor fan 32 is activated, and normal control is executed with respect to the
outdoor fan 24 or the indoor fan 32. When Step S18 is completed, the control processing
returns to Step S11.
(3) Throttle Control and Normal Control
[0070] As illustrated in the aforementioned flowchart of the normal mode, the control section
5 is configured to switch controls of the outdoor expansion valve V2 or the indoor
expansion valve V5 between the throttle control and the normal control. Fig. 5 is
a time-flow chart for illustrating timing of switching the throttle control and the
normal control back and forth. In Fig. 5, the horizontal axis represents time t while
the vertical axis represents the discharge pressure Pd and the throttle opening degree
θ1 of the outdoor expansion valve V2 or the throttle opening degree θ2 of the indoor
expansion valve V5. When the activation time is assumed to be time t1 and the discharge
pressure Pd in the activation is assumed to be initial discharge pressure P0, throttle
control is started at time t1 and the throttle opening degree θ1 of the outdoor expansion
valve V2 or the throttle opening degree θ2 of the indoor expansion valve V5 is set
to be the opening degree α. Subsequently, when time t2 is elapsed and the discharge
pressure Pd is changed from the initial discharge pressure P0 to critical pressure
Pk, the throttle control is switched to the normal control. Accordingly, the throttle
opening degree θ1 of the outdoor expansion valve V2 or the throttle opening degree
θ2 of the indoor expansion valve V5 is set to be opening degree β. Furthermore, when
the discharge pressure Pd is equal to or less than the critical pressure Pk (time
t3), for instance, under a condition that the external temperature is equal to or
less than 20 degrees Celsius, the normal control is again switched to the throttle
control. At this time, the throttle opening degree θ1 of the outdoor expansion valve
V2 or the throttle opening degree θ2 of the indoor expansion valve V5 is set to be
the opening degree α.
[0071] Next, a cooling operation and a heating operation, executed in the normal control,
will be explained.
(4) Cooling Operation
[0072] First, a cooling operation will be hereinafter explained with reference to Fig. 1.
In the cooling operation, the four-way switch valve V1 in the outdoor side refrigerant
circuit 20 of the outdoor unit 2 is switched to the solid-line condition in Fig. 1.
Accordingly, the outdoor heat exchanger 23 is configured to function as a gas cooler
whereas the indoor heat exchanger 31 is configured to function as an evaporator.
[0073] When the compressor 21, the outdoor fan 24 and the indoor fan 32 are activated under
the condition of the refrigerant circuit 10, the gas refrigerant of low pressure Pl
is sucked into the compressor 21 and is therein compressed. The gas refrigerant changes
into the gas refrigerant of high pressure Ph. The gas refrigerant, compressed to the
high pressure Ph, flows into the outdoor heat exchanger 23. At this time, the outdoor
heat exchanger 23 functions as a gas cooler and cools the refrigerant by releasing
heat of the refrigerant into the outdoor air to be supplied by the outdoor fan 24.
Subsequently, the outdoor expansion valve V2 decompresses the refrigerant from the
high pressure Ph to the low pressure Pl. The refrigerant, decompressed to the low
pressure Pl, changes into gas-liquid two-phase refrigerant. The gas-liquid two-phase
refrigerant is transported to the indoor unit 3 via the liquid side stop valve V3
and the liquid refrigerant communication pipe 41.
[0074] Next, the indoor expansion valve V5 controls the flow rate of the gas-liquid two-phase
refrigerant of the low pressure Pl transported to the indoor unit 3. The indoor heat
exchanger 31 then conducts heat change between the refrigerant and the indoor air.
The refrigerant accordingly evaporates and changes into gas refrigerant of the low
pressure Pl. The gas refrigerant of the low pressure Pl is transported to the outdoor
unit 2 via the gas refrigerant communication pipe 42. The gas refrigerant is again
sucked into the compressor 21 via the gas side stop valve V4.
(5) Heating Operation
[0075] In the heating operation, the four-way switch valve V1 in the outdoor side refrigerant
circuit 20 of the outdoor unit 2 is switched to the dashed-line condition in Fig.
1. Accordingly, the outdoor heat exchanger 23 is configured to function as an evaporator
whereas the indoor heat exchanger 31 is configured to function as a gas cooler.
[0076] When the compressor 21, the outdoor fan 24 and the indoor fan 32 are activated under
the condition of the refrigerant circuit 10, gas refrigerant of the low pressure Pl
is sucked into the compressor 21 and is therein compressed. Accordingly, the refrigerant
changes into gas refrigerant of the high pressure Ph. The refrigerant is then transported
to the gas refrigerant communication pipe 42 via the four-way switch valve V1 and
the gas side stop valve V4.
[0077] The gas refrigerant of the high pressure Ph, transported to the gas refrigerant communication
pipe 42, is further transported to the indoor unit 3. The gas refrigerant of the high
pressure Ph, transported to the indoor unit 3, is further transported to the indoor
heat exchanger 31. The indoor heat exchanger 31 conducts heat exchange between the
refrigerant and the indoor air. The refrigerant is accordingly cooled, and changes
into liquid refrigerant of the high pressure Ph. Subsequently, when the refrigerant
passes through the indoor expansion valve V5, it is decompressed to the low pressure
Pl in accordance with the throttle opening degree θ2 of the indoor expansion valve
V5. The refrigerant accordingly changes into gas-liquid two-phase refrigerant.
[0078] Next, the gas-liquid two-phase refrigerant is transported to the outdoor unit 2 via
the liquid refrigerant communication pipe 41. The refrigerant flows into the outdoor
heat exchanger 23 via the liquid side stop valve V3 and the outdoor expansion valve
V2.
[0079] The outdoor heat exchanger 23 conducts heat exchange between the refrigerant and
the external air. The refrigerant accordingly evaporates and changes into gas refrigerant
of the low pressure Pl. At this time, the outdoor expansion valve V2 is fully opened.
The gas refrigerant of the low pressure Pl is again sucked into the compressor 21
via the four-way switch valve V1.
<Supercritical Refrigeration Cycle>
[0080] Next, a refrigeration cycle in the air conditioning apparatus 1 will be explained.
Fig. 6 illustrates a refrigeration cycle under the supercritical condition with a
P-H chart (Mollier chart). In Fig. 6, points A, B, C and D indicate states of refrigerant
at the corresponding points in Fig. 1 of the cooling operation. Furthermore, in Fig.
6, points (A), (F), (E) and (D) indicate states of refrigerant at the corresponding
points in Fig. 1 of the heating operation.
[0081] In the refrigerant circuit 10, the compressor 21 compresses the refrigerant and the
compressed refrigerant changes into high-temperature refrigerant of the high pressure
Ph (A→B). At this time, the gas refrigerant, CO
2, enters a supercritical state. Note the term "supercritical state" herein referred
means a state of material at temperature and pressure equal to or greater than the
critical point K. In the supercritical state, material has both gas diffusivity and
liquid solubility. In Fig. 6, the supercritical state is a state of refrigerant shown
in the area positioned rightward of a critical temperature isothermal curve Tk at
the critical pressure Pk or greater. When the refrigerant (material) enters a supercritical
state, there is no distinction between gas and liquid phases. Note the term "gas phase"
herein referred is a state of refrigerant shown in the area positioned rightward of
a saturated vapor curve Sv at the critical pressure Pk or less. Additionally, the
term "liquid phase" is a state of refrigerant shown in the area positioned leftward
of a saturated liquid curve Sl and leftward of the critical temperature isothermal
curve Tk. The outdoor heat exchanger 23, functioning as a gas cooler, releases heat
of the supercritical-state refrigerant of high temperature and the high pressure Ph
produced by the compression of the compressor 21. Accordingly, the refrigerant changes
into low-temperature refrigerant of the high pressure Ph (B→C). At this time, the
refrigerant is in a supercritical state, and therefore operates with sensible heat
changes (temperature changes) in the interior of the outdoor heat exchanger 23. Subsequently,
the refrigerant, heat of which has been released by the outdoor heat exchanger 23
is expanded by the outdoor expansion valve V2 being opened. Thus the refrigerant is
decompressed from the high pressure Ph to the low pressure Pl (C→D). The refrigerant,
decompressed by the outdoor expansion valve V2, absorbs heat and evaporates in the
indoor heat exchanger 31 functioning as an evaporator, and returns to the compressor
21 (D→A).
<Characteristics>
[0082]
- (1) According to the present embodiment, when the control section 5 determines that
the discharge pressure Pd in the refrigeration cycle is less than the critical pressure
Pk in the activation mode, it regulates the throttle opening degree θ1 of the outdoor
expansion valve V2 or the throttle opening degree θ2 of the indoor expansion valve
V5 to be very small opening degree, that is, the opening degree α, for easily controlling
the discharge pressure Pd to be equal to or greater than the critical pressure Pk.
Furthermore, similar control is executed in the normal mode.
Therefore, it is possible to change a state of the CO2 refrigerant from a gas-liquid two-phase state to a supercritical state or a liquid
phase state. As a result, it is possible to inhibit generation of flow sound of the
refrigerant in a vicinity of an inlet of the outdoor expansion valve V2 and an inlet
of the indoor expansion valve V5.
- (2) According to the present embodiment, when the discharge pressure Pd is equal to
or greater than the critical pressure Pk after the throttle control is executed, the
control section 5 is configured to execute normal control of the outdoor expansion
valve V2 or the indoor expansion valve V5. When the CO2 refrigerant is pressurized to be equal to or greater than the critical pressure Pk,
it changes into a supercritical state. Thus there is no distinction between a gas
phase and a liquid phase in the CO2 refrigerant. Accordingly, it is possible to optimally control the discharge pressure
Pd without unnecessarily increasing it. In other words, it is possible to reduce energy
loss.
- (3) According to the present embodiment, the discharge pressure sensor P1 detects
the discharge pressure Pd. Based on this, it is determined if the CO2 refrigerant of the high pressure side is in a supercritical state or a liquid state.
Therefore, it is possible to directly detect the high pressure Ph in the refrigeration
cycle based on the discharge pressure Pd. Furthermore, it is possible to proceed to
the normal control from the throttle control while a period of time (t2 - t1) necessary
for the throttle control is essentially minimized. Consequently, it is possible to
optimally control the discharge pressure Pd without unnecessarily increasing it. In
other words, it is possible to reduce energy consumption.
- (4) According to the present embodiment, the outdoor fan 24 or the indoor fan 32,
configured to blow air to the outdoor heat exchanger 23 or the indoor heart exchanger
31 functioning as a gas cooler for promoting cooling thereof, is being stopped in
the activation of the air conditioning apparatus 1. Therefore, it is possible to weaken
a cooling effect on the outdoor heat exchanger 23 or the indoor heat exchanger 31
as much as possible. In other words, it is possible to increase temperature and pressure
of the CO2 refrigerant in the outdoor heat exchanger 23 or the indoor heat exchanger 31. Therefore,
it is possible to set the refrigerant at the outlet of the outdoor heat exchanger
23 or the indoor heat exchanger 31 functioning as a gas cooler to be in a supercritical
state or a liquid phase state. As a result, it is possible to reduce generation of
flow sound of the refrigerant in a vicinity of the inlet of the outdoor expansion
valve V2 or the inlet of the indoor expansion valve V5.
- (5) According to the present embodiment, even at the low external temperature when
the external temperature is equal to or less then 20 degrees Celsius, the discharge
pressure Pd is controlled to be equal to or greater than the critical pressure Pk
by regulating the throttle opening degree θ1 of the outdoor expansion valve V2 or
the throttle opening degree θ2 of the indoor expansion valve V5. Therefore, even at
the low external temperature when the external temperature is equal to or less than
20 degrees Celsius, it is possible to set the refrigerant to be in a supercritical
state or a liquid-phase state.
- (6) According to the present embodiment, the CO2 refrigerant is used as refrigerant. The CO2 refrigerant does not destroy the ozone layer because ozone depletion potential (ODP)
thereof equals to zero. Additionally, global warming potential (GWP) of the CO2 refrigerant equals to 1. This is much lower than GWP of fluorocarbon refrigerant
of about hundreds to ten thousand. Accordingly, it is possible to inhibit worsening
of the global environment with use of the CO2 refrigerant with less environmental burden.
<Modifications>
[0083]
- (1) According to the present embodiment, the discharge pressure sensor Pl detects
the discharge pressure Pd of the compressor 21. It is then determined if the throttle
control should be executed based on whether or not the discharge pressure Pd is less
than the critical pressure Pk of the CO2 refrigerant. However, the present invention is not limited to this. The inlet pressure
in a vicinity of the inlet of the outdoor expansion valve V2 or the indoor expansion
valve V5 may be calculated based on the discharge pressure Pd and the compressor capacity
of the compressor 21. Furthermore, it may be determined if the throttle control should
be executed based on the inlet pressure.
The discharge pressure Pd and the inlet pressure of the outdoor expansion valve V2
or the indoor expansion valve V5 are different because of pressure-loss in the refrigerant
pipe disposed in the area from the discharge side of the compressor 21 to the outdoor
expansion valve V2 or the indoor expansion valve V5. In this case, it is determined
if the throttle control should be executed based on the calculated inlet pressure.
Therefore, it is possible to more reliably control the gas-liquid two-phase refrigerant
in a vicinity of the inlet of the outdoor expansion valve V2 or the inlet of the indoor
expansion valve V5, contributing to a cause of noise, to be in a supercritical state
or in a liquid-phase state.
- (2) According to the present embodiment, the discharge pressure sensor Pl detects
the discharge pressure Pd of the compressor 21. It is then determined if the throttle
control should be executed based on whether or not the discharge pressure Pd is less
than the critical pressure Pk of the CO2 refrigerant. However, the present invention is not limited to this. For example,
as illustrated in Fig. 7, a first liquid pipe temperature sensor T2 may be provided
in a first liquid refrigerant pipe 28 arranged between the outdoor heat exchanger
23 and the outdoor expansion valve V2. Furthermore, a second liquid pipe temperature
sensor T3 may be provided in a second liquid refrigerant pipe 35 arranged between
the indoor heat exchanger 31 and the indoor expansion valve V5. With the structure,
the inlet temperature in a vicinity of the inlet of the outdoor expansion valve V2
or the indoor expansion valve V5 may be detected, and it may be then determined if
the throttle control should be executed based on whether or not the inlet temperature
is less than 31 degrees Celsius, that is, the critical temperature of the CO2 refrigerant.
Therefore, it is possible to determine if the CO2 refrigerant is in a supercritical state by detecting the inlet temperature in a vicinity
of the inlet of the outdoor expansion valve V2 or the inlet of the indoor expansion
valve V5. This makes it possible to determine that the refrigerant in a vicinity of
the inlet of the outdoor expansion valve V2 or the inlet of the indoor expansion valve
V5 is not in a gas-liquid two-phase state. Consequently, it is possible to reduce
blowout sound of bubbles and the like contributing to a cause of flow sound of the
refrigerant. Furthermore, it is possible to replace a pressure sensor with a temperature
sensor cheaper than the pressure sensor. Accordingly, it is possible to reduce production
cost thereof.
- (3) In the present embodiment, the air conditioning apparatus 1 is exemplified as
an apparatus using a refrigeration apparatus. However, the apparatus using a refrigeration
apparatus is not limited to this, and may be any suitable apparatus such as a heat-pump
water heater and a refrigerator.
INDUSTRIAL APPLICABILITY
[0084] The refrigeration apparatus of the present invention achieves a working effect for
inhibiting generation of noise, and is useful as a refrigeration apparatus and the
like using refrigerant operating in the supercritical zone.
1. Kühlapparat (1), der überkritisches Kältemittel einsetzt, der in einer Zone betrieben
wird, in welcher der Hochdruck des überkritischen Kältemittels gleichwertig oder höher
als der kritische Druck ist, wobei der Kühlapparat (1) Folgendes umfasst:
einen Kompressor (21) zum Verdichten des überkritischen Kältemittels;
einen Gaskühler (23, 31) zum Kühlen des überkritischen Kältemittels, das durch den
Kompressor (21) verdichtet wird;
einen Expansionsmechanismus (V2, V5) zum Druckentlasten des überkritischen Kältemittels;
einen Verdampfer (31, 23) zum Verdampfen des überkritischen Kältemittels, das durch
den Expansionsmechanismus (V2, V5) druckentlastet wird;
Ablassdruckerfassungsmittel (P1, T2, T3), die in der Lage sind, den Ablassdruck des
Kompressors (21) zu erfassen; und
einen Steuerungsabschnitt (5), der konfiguriert ist, einen Öffnungsgrad des Expansionsmechanismus
(V2, V5) zum Steuern des Ablassdrucks derart zu regulieren, dass dieser gleichwertig
oder größer als der überkritische Druck ist, wenn der Kühlapparat (1) aktiviert und
der Ablassdruck geringer als der kritische Druck ist,
dadurch gekennzeichnet, dass der Steuerungsabschnitt (5) konfiguriert ist, einen Einlassdruck des Expansionsmechanismus
(V2, V5) basierend auf dem Ablassdruck und einer Betriebskapazität des Kompressors
(21) zu berechnen, und konfiguriert ist, den Öffnungsgrad des Expansionsmechanismus
(V2, V5) zum Steuern des Ablassdrucks derart zu regulieren, dass dieser gleichwertig
oder größer als der kritische Druck ist, wenn der Einlassdruck geringer als der kritische
Druck ist.
2. Kühlapparat (1) nach Anspruch 1, wobei der Steuerungsabschnitt (5) konfiguriert ist,
eine erste Steuerung zum Einstellen des Öffnungsgrads des Expansionsmechanismus (V2,
V5) derart auszuführen, dass dieser ein vollständig geschlossener oder ein leicht
geöffneter Grad ist, wenn der Auslassdruck geringer als der kritische Druck ist.
3. Kühlapparat (1) nach Anspruch 2, wobei der Steuerungsabschnitt (5) konfiguriert ist,
eine zweite Steuerung zum Einstellen des Öffnungsgrads des Expansionsmechanismus (V2,
V5) derart auszuführen, dass dieser groß ist, wenn der Ablassdruck gleichwertig oder
größer als der kritische Druck ist, nachdem die erste Steuerung ausgeführt worden
ist.
4. Kühlapparat (1) nach einem der Ansprüche 1 bis 3, wobei das Ablassdruckerfassungsmittel
ein Drucksensor (P1) ist, der an der Ablassseite des Kompressors (21) bereitgestellt
ist.
5. Kühlapparat (1, 1a) nach einem der Ansprüche 1 bis 4, wobei der Steuerungsabschnitt
(5) konfiguriert ist, den Öffnungsgrad des Expansionsmechanismus (V2, V5) zum Steuern
des Ablassdrucks derart zu regeln, dass dieser gleichwertig oder größer als der kritische
Druck ist, wenn ein normaler Betrieb ausgeführt wird.
6. Kühlapparat (1, 1a) nach einem der Ansprüche 1 bis 4, wobei der Steuerungsabschnitt
(5) konfiguriert ist, den Öffnungsgrad des Expansionsmechanismus (V2, V5) zum Steuern
des Ablassdrucks derart zu regeln, dass dieser gleichwertig oder größer als der kritische
Druck ist, auch wenn ein normaler Betrieb bei einer niedrigen Außentemperatur ausgeführt
wird.
7. Kühlapparat (1, 1a) nach Anspruch 6, wobei die niedrige Außentemperatur eine Außentemperatur
ist, die gleichwertig oder geringer als 20 Grad Celsius ist.
8. Kühlapparat (1, 1a) nach einem der Ansprüche 1 bis 7, wobei das überkritische Kältemittel
ein Kohlendioxid-(CO2)-Kältemittel ist.