FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
REFRIGERATION CYCLE APPARATUS;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED AND
EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION
AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
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DESCRIPTION
Title of Invention
REFRIGERATION CYCLE APPARATUS
Technical Field5
[0001]
The present disclosure relates to a refrigeration cycle apparatus, such as an air-
conditioning apparatus.
Background Art
[0002]10
A known refrigeration cycle apparatus, such as an air-conditioning apparatus,
includes a high-pressure gauge and a low-pressure gauge in a refrigerant circuit and
controls actuators, for example, the operating frequency of a compressor, the rotation
speed of a fan, and the opening degree of a valve, on the basis of readings of the
pressure gauges. If refrigerant used in the apparatus is at high pressure, the15
apparatus may include a pressure reducing device to produce an intermediate pressure
in the refrigerant circuit and an intermediate-pressure gauge to measure the
intermediate pressure.
[0003]
Specifically, if an outdoor unit is installed at a position higher than that of an20
indoor unit, the pressure of refrigerant in pipes in the indoor unit may increase due to a
liquid head difference, causing a pipe stress in the indoor unit to exceed an allowable
value. As a way to prevent such a problem, a pressure reducing device, such as a
linear expansion valve (LEV), can be disposed at an outlet of the outdoor unit to reduce
the pressure of refrigerant flowing into the indoor unit. In such a case, the opening25
degree of the pressure reducing device disposed at the outlet of the outdoor unit is
controlled based on the pressure (i.e., intermediate pressure) of refrigerant flowing into
the indoor unit. For that reason, the intermediate-pressure gauge to measure the
intermediate pressure is disposed at the outlet of the outdoor unit.
[0004]30
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However, installing the intermediate-pressure gauge in addition to the high-
pressure gauge and the low-pressure gauge results in an increase in the number of
parts. In addition, installation operation, management, maintenance, and the like of the
pressure gauge are also required. This contributes to an increase in cost for installing
the refrigeration cycle apparatus. As a measure against such a problem, as disclosed5
in Patent Literature 1, two of the three pressures or high, intermediate, and low
pressures, are directly measured, and the other one pressure is determined through
calculation. Specifically, in an air-conditioning apparatus disclosed in Patent Literature
1, the intermediate pressure is calculated in such a manner that a saturation
temperature of refrigerant flowing through a high-pressure portion of an internal heat10
exchanger including a plate heat exchanger is calculated from the quantity of heat
transferred in the internal heat exchanger and the calculated saturation temperature is
converted to pressure. The air-conditioning apparatus disclosed in Patent Literature 1
achieves a reduction in cost for installing the air-conditioning apparatus as well as a
reduction in costs associated with procurement, installation, and management of parts15
included in the air-conditioning apparatus.
Citation List
Patent Literature
[0005]
Patent Literature 1: Japanese Unexamined Patent Application Publication No.20
2007-101069
Summary of Invention
Technical Problem
[0006]
As described in Patent Literature 1, the pressure reducing device to produce an25
intermediate pressure is disposed upstream of the internal heat exchanger in a
refrigerant flow direction (i.e., between the internal heat exchanger and an outdoor heat
exchanger). However, the pressure reducing device disposed upstream of the internal
heat exchanger causes refrigerant passing through the pressure reducing device to turn
into a two-phase state, which may cause abnormal noise in the pressure reducing30
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device. To keep the refrigerant passing through the pressure reducing device from
turning into a two-phase state, the pressure reducing device can be disposed
downstream of the internal heat exchanger (i.e., between the internal heat exchanger
and the indoor unit). In this case, if the saturation temperature is calculated from the
quantity of heat transferred in the internal heat exchanger as in Patent Literature 1, the5
intermediate pressure may fail to be calculated because of a change in pressure caused
by the pressure reducing device.
[0007]
The present disclosure intends to solve the above problem and provides a
refrigeration cycle apparatus that achieves a reduction in cost even with a configuration10
in which a pressure reducing device is disposed between an internal heat exchanger
and an indoor unit.
Solution to Problem
[0008]
A refrigeration cycle apparatus according to an embodiment of the present15
disclosure includes an outdoor unit, an indoor unit connected to the outdoor unit, and a
controller. The outdoor unit includes a compressor configured to compress and
discharge refrigerant, an outdoor heat exchanger configured to exchange heat of
refrigerant discharged from the compressor, an internal heat exchanger configured to
exchange heat of refrigerant flowing from the outdoor heat exchanger, and a pressure20
reducing device disposed between the internal heat exchanger and the indoor unit and
configured to reduce a pressure of refrigerant flowing into the indoor unit. The
controller is configured to calculate an intermediate pressure that is the pressure of
refrigerant flowing into the indoor unit by using a high pressure that is a pressure of
refrigerant on a discharge side of the compressor, a flow rate of refrigerant flowing25
through the pressure reducing device, a Cv value of the pressure reducing device, and
a density of liquid refrigerant.
Advantageous Effects of Invention
[0009]
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In the refrigeration cycle apparatus according to the embodiment of the present
disclosure, the intermediate pressure can be obtained without an intermediate-pressure
sensor even in a configuration in which the pressure reducing device is disposed
between the internal heat exchanger and the indoor unit. This leads to a reduction in
cost.5
Brief Description of Drawings
[0010]
[Fig. 1] Fig. 1 is a schematic diagram of the configuration of a refrigeration cycle
apparatus according to Embodiment 1.
[Fig. 2] Fig. 2 is a control block diagram of the refrigeration cycle apparatus10
according to Embodiment 1.
[Fig. 3] Fig. 3 is a flowchart illustrating an intermediate pressure calculation
method in Embodiment 1.
[Fig. 4] Fig. 4 is a control block diagram of a refrigeration cycle apparatus
according to Embodiment 2.15
[Fig. 5] Fig. 5 is a flowchart illustrating an intermediate pressure calculation
method in Embodiment 2.
[Fig. 6] Fig. 6 is a schematic diagram of the configuration of a refrigeration cycle
apparatus according to Embodiment 3.
[Fig. 7] Fig. 7 is a control block diagram of the refrigeration cycle apparatus20
according to Embodiment 3.
[Fig. 8] Fig. 8 is a flowchart illustrating an intermediate pressure calculation
method in Embodiment 3.
[Fig. 9] Fig. 9 is a schematic diagram of the configuration of a refrigeration cycle
apparatus according to Modification 1.25
[Fig. 10] Fig. 10 is a schematic diagram of the configuration of a refrigeration
cycle apparatus according to Modification 2.
[Fig. 11] Fig. 11 is a flowchart illustrating an intermediate pressure calculation
method in Modification 2.
Description of Embodiments30
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[0011]
Embodiments will be described below with reference to the drawings. Note that
components designated by the same reference signs in the figures are the same
components or equivalents. This note applies to the entire description herein.
Furthermore, note that the relationship between the sizes of components in the5
following figures may differ from that of actual ones. The terms "high temperature",
"low temperature", "high pressure", "intermediate pressure", and "low pressure" as used
hereinafter are intended to refer to relative temperatures and pressures of refrigerant in
a refrigerant circuit, rather than absolute temperatures and pressures of the refrigerant.
[0012]10
Embodiment 1.
Fig. 1 is a schematic diagram of the configuration of a refrigeration cycle
apparatus 100 according to Embodiment 1. The refrigeration cycle apparatus 100
according to Embodiment 1 is an air-conditioning apparatus to cool an indoor space.
The refrigeration cycle apparatus 100 includes an outdoor unit 1 disposed outside the15
indoor space and an indoor unit 2 disposed in the indoor space. The outdoor unit 1
and the indoor unit 2 are connected by pipes and lines such as power lines or signal
lines. Although a single indoor unit 2 is connected to the outdoor unit 1 in Fig. 1,
multiple indoor units 2 may be connected to the outdoor unit 1.
[0013]20
The outdoor unit 1 includes a compressor 11, an oil separator 12, a check valve
13, an outdoor heat exchanger 14, an outdoor fan 15, an internal heat exchanger 16, a
bypass pressure reducing device 17, a first pressure reducing device 18, an
accumulator 19, and a controller 5. The indoor unit 2 includes an indoor heat
exchanger 21, an indoor fan 22, and a second pressure reducing device 23. The25
configuration of the indoor unit 2 is not limited to the example in Fig. 1.
[0014]
The compressor 11, the oil separator 12, the check valve 13, the outdoor heat
exchanger 14, the internal heat exchanger 16, the bypass pressure reducing device 17,
the first pressure reducing device 18, the second pressure reducing device 23, the30
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indoor heat exchanger 21, and the accumulator 19 are connected by pipes, thus
forming a refrigerant circuit. Refrigerant circulating through the refrigerant circuit of the
refrigeration cycle apparatus 100 is, for example, a natural refrigerant, such as carbon
dioxide, hydrocarbon, or helium, a chlorine-free refrigerant, such as HFC-410A or HFC-
407C, or a fluorocarbon-based refrigerant, such as R-22 or R-134a.5
[0015]
The compressor 11 sucks low-pressure gaseous refrigerant, compresses the
refrigerant into high-pressure gaseous refrigerant, and discharges the refrigerant.
Examples of the compressor 11 used include reciprocating, rotary, scroll, and screw
compressors.10
[0016]
The oil separator 12 separates refrigerating machine oil from the refrigerant
discharged from the compressor 11 and returns the refrigerating machine oil to the
compressor 11. The oil separator 12 has an inlet that is connected to a discharge
outlet of the compressor 11 and through which vapor-phase refrigerant and the15
refrigerating machine oil flow into the oil separator 12, a first outlet that is connected to
the check valve 13 and through which the vapor-phase refrigerant flows out of the oil
separator 12, and a second outlet that is connected to a suction inlet of the compressor
11 and through which the refrigerating machine oil flows out of the oil separator 12.
[0017]20
The check valve 13 is connected to the first outlet of the oil separator 12 and
prevents backflow of the refrigerant to the compressor 11. The oil separator 12 and
the check valve 13 are not essential components and may be omitted.
[0018]
The outdoor heat exchanger 14 is, for example, a fin-and-tube heat exchanger,25
and exchanges heat between the refrigerant flowing through circular tubes or flat tubes
and air supplied by the outdoor fan 15. The outdoor heat exchanger 14 operates as a
condenser in a cooling operation.
[0019]
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The outdoor fan 15 draws in outdoor air and blows the air through the outdoor
heat exchanger 14 to an outdoor space. The outdoor fan 15 is, for example, a motor-
driven fan, such as a propeller fan, a sirocco fan, or a cross-flow fan.
[0020]
The internal heat exchanger 16 is, for example, a double pipe heat exchanger or5
a plate heat exchanger. The internal heat exchanger 16 includes a first passage 61
connected to an outlet of the outdoor heat exchanger 14 and a second passage 62
diverted at an outlet of the first passage 61, and exchanges heat between refrigerant
flowing through the first passage 61 and refrigerant flowing through the second passage
62. The internal heat exchanger 16 is provided to prevent two-phase refrigerant from10
flowing into the indoor unit 2.
[0021]
The bypass pressure reducing device 17 is, for example, an electronic linear
expansion valve with a controllable opening degree. The bypass pressure reducing
device 17 is disposed at an inlet of the second passage 62 of the internal heat15
exchanger 16 and reduces the pressure of refrigerant flowing into the second passage
62. The bypass pressure reducing device 17 may be a capillary tube.
[0022]
The first pressure reducing device 18 is, for example, an electronic linear
expansion valve with a controllable opening degree. The first pressure reducing20
device 18 is disposed between the indoor unit 2 and the outlet of the first passage 61 of
the internal heat exchanger 16, or downstream of the internal heat exchanger 16 in a
refrigerant flow direction, and reduces the pressure of refrigerant flowing into the indoor
unit 2. Hereinafter, the pressure of refrigerant reduced in pressure through the first
pressure reducing device 18 and flowing into the indoor unit 2 will be referred to as an25
"intermediate pressure Pm".
[0023]
The accumulator 19 stores excess refrigerant. The accumulator 19 is connected
to the suction inlet of the compressor 11 and an outlet of the indoor heat exchanger 21.
The accumulator 19 separates refrigerant flowing from the indoor heat exchanger 2130
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into gaseous refrigerant and liquid refrigerant, stores the liquid refrigerant, and causes
the gaseous refrigerant to flow to the compressor 11. An insufficient degree of
superheat at an outlet of the indoor unit 2 may cause liquid backflow to the compressor
11, leading to a failure of the compressor 11. However, the accumulator 19 located on
a suction side of the compressor 11 can reduce or eliminate liquid backflow to the5
compressor 11. The accumulator 19 is not an essential component and may be
omitted.
[0024]
The indoor heat exchanger 21 is, for example, a fin-and-tube heat exchanger,
and exchanges heat between refrigerant flowing through circular tubes or flat tubes and10
air supplied by the indoor fan 22. The outdoor heat exchanger 14 operates as an
evaporator in the cooling operation.
[0025]
The indoor fan 22 draws in indoor air and blows the air through the indoor heat
exchanger 21 to the indoor space. The indoor fan 22 is, for example, a motor-driven15
fan, such as a propeller fan, a sirocco fan, or a cross-flow fan.
[0026]
The second pressure reducing device 23 is, for example, an electronic linear
expansion valve with a controllable opening degree. The second pressure reducing
device 23 is disposed between the first pressure reducing device 18 and the indoor heat20
exchanger 21. The second pressure reducing device 23 reduces the pressure of
refrigerant flowing into the indoor heat exchanger 21.
[0027]
The refrigeration cycle apparatus 100 further includes a high-pressure sensor 31
disposed on a discharge side of the compressor 11 and a low-pressure sensor 3225
disposed on the suction side of the compressor 11. The high-pressure sensor 31 is a
pressure gauge that measures the pressure of refrigerant on a high-pressure side of the
refrigerant circuit. The low-pressure sensor 32 is a pressure gauge that measures the
pressure of refrigerant on a low-pressure side of the refrigerant circuit. Hereinafter, the
pressure measured by the high-pressure sensor 31 will be referred to as a "high30
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pressure Pd", and the pressure measured by the low-pressure sensor 32 will be
referred to as a "low pressure Ps". The positions of the high-pressure sensor 31 and
the low-pressure sensor 32 are not limited to those in the example of Fig. 1.
[0028]
Furthermore, the refrigeration cycle apparatus 100 may include a temperature5
sensor or a pressure sensor other than the high-pressure sensor 31 and the low-
pressure sensor 32. For example, the refrigeration cycle apparatus 100 may include
an outdoor air temperature sensor that measures the temperature of air in the outdoor
space where the outdoor unit 1 is installed or an indoor temperature sensor that
measures the temperature of air in the indoor space where the indoor unit 2 is installed.10
Additionally, the refrigeration cycle apparatus 100 may include a sensor that measures
any of a suction temperature that is the temperature of refrigerant to be sucked into the
compressor 11, the temperature of refrigerant flowing through the outdoor heat
exchanger 14 or the indoor heat exchanger 21, and the temperature of air blown from
the indoor unit 2.15
[0029]
The controller 5 includes a processor, such as a central processing unit (CPU),
and a memory. Alternatively, the controller 5 may include a processing circuit, such as
an application specific integrated circuit (ASIC) or a field-programmable gate array
(FPGA). The controller 5 controls an operation of the entire refrigeration cycle20
apparatus 100 on the basis of an instruction inputted by a user through a remote control
(not illustrated) and, for example, measurement results of the high-pressure sensor 31
and the low-pressure sensor 32. Although the controller 5 is disposed in the outdoor
unit 1 in Fig. 1, the controller 5 may be disposed in the indoor unit 2. Separate
controllers 5 may be disposed in the outdoor unit 1 and the indoor unit 2 such that the25
controllers are communicative with each other. Alternatively, the controller 5 may be
disposed in a location away from the outdoor unit 1 and the indoor unit 2.
[0030]
Fig. 2 is a control block diagram of the refrigeration cycle apparatus 100
according to Embodiment 1. As illustrated in Fig. 2, the controller 5 of the refrigeration30
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cycle apparatus 100 includes an operation control unit 51, a flow rate calculation unit
52, a Cv value calculation unit 53, an intermediate pressure calculation unit 54, and a
storage unit 55. The operation control unit 51, the flow rate calculation unit 52, the Cv
value calculation unit 53, and the intermediate pressure calculation unit 54 are
functional modules implemented by programs executed by the processor of the5
controller 5. Alternatively, at least any of the operation control unit 51, the flow rate
calculation unit 52, the Cv value calculation unit 53, and the intermediate pressure
calculation unit 54 may be implemented by a processing circuit, such as an ASIC or an
FPGA.
[0031]10
The operation control unit 51 controls an operation of the refrigeration cycle
apparatus 100 on the basis of, for example, a set temperature inputted by the user,
readings of the sensors, and an intermediate pressure calculated by the intermediate
pressure calculation unit 54. Specifically, the operation control unit 51 controls the
operating frequency of the compressor 11, the opening degrees of the bypass pressure15
reducing device 17, the first pressure reducing device 18, and the second pressure
reducing device 23, and the rotation speeds of the outdoor fan 15 and the indoor fan 22.
[0032]
The flow rate calculation unit 52 calculates a flow rate Grc of refrigerant
discharged from the compressor 11 on the basis of the high pressure Pd, the low20
pressure Ps, a rotation speed N of the compressor 11, and the machine characteristics
of the compressor 11 or the like. Furthermore, the flow rate calculation unit 52
calculates a flow rate Grh of refrigerant flowing through the bypass pressure reducing
device 17 to the second passage 62 on the basis of the high pressure Pd, the low
pressure Ps, a Cv value Cvb of the bypass pressure reducing device 17, and a25
refrigerant density ρ. In addition, the flow rate calculation unit 52 calculates a flow rate
Gr of refrigerant flowing through the first pressure reducing device 18 to the indoor unit
2 on the basis of the flow rate Grc of refrigerant discharged from the compressor 11 and
the flow rate Grh of refrigerant flowing through the bypass pressure reducing device 17
to the second passage 62.30
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[0033]
The Cv value calculation unit 53 calculates the Cv value Cvb of the bypass
pressure reducing device 17 on the basis of the characteristics and opening degree of
the bypass pressure reducing device 17. Furthermore, the Cv value calculation unit 53
calculates a Cv value Cv1 of the first pressure reducing device 18 on the basis of the5
characteristics and opening degree of the first pressure reducing device 18.
[0034]
The intermediate pressure calculation unit 54 calculates an intermediate pressure
Pm, which is the pressure of refrigerant leaving the first pressure reducing device 18, on
the basis of the high pressure Pd, the flow rate Gr of refrigerant flowing through the first10
pressure reducing device 18 to the indoor unit 2, the Cv value Cv1 of the first pressure
reducing device 18, and the refrigerant density ρ.
[0035]
The storage unit 55 is, for example, a volatile or nonvolatile memory, such as a
random access memory (RAM), a read-only memory (ROM), or a flash memory. The15
storage unit 55 stores, for example, the programs executed by the controller 5, various
parameters used in the programs, and table data.
[0036]
A flow of refrigerant in the cooling operation of the refrigeration cycle apparatus
100 according to Embodiment 1 will now be described with reference to Fig. 1. In Fig.20
1, the refrigerant flow direction is represented by arrows. High-pressure gaseous
refrigerant compressed and discharged by the compressor 11 passes through the oil
separator 12 and the check valve 13 and then enters the outdoor heat exchanger 14.
The refrigerant that has entered the outdoor heat exchanger 14 transitions from a
gaseous state to a two-phase state and then to a liquid state by releasing heat to the air25
sent from the outdoor fan 15 while passing through the outdoor heat exchanger 14.
After that, the refrigerant flows out of the outdoor heat exchanger 14 and passes
through the first passage 61 of the internal heat exchanger 16. At a branch B1, the
refrigerant is divided into two streams, a major stream F1 flowing to the indoor unit 2
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and a minor stream F2 flowing to the second passage 62 of the internal heat exchanger
16.
[0037]
The refrigerant in the minor stream F2 is reduced in pressure into a low-
temperature, low-pressure two-phase state by the bypass pressure reducing device 175
and then passes through the second passage 62 of the internal heat exchanger 16.
Thus, the refrigerant flowing through the second passage 62 exchanges heat with
refrigerant flowing through the first passage 61 of the internal heat exchanger 16. The
refrigerant flowing through the second passage 62 receives heat from the refrigerant
flowing through the first passage 61 and thus turns into a gaseous state. Then, the10
refrigerant enters the accumulator 19. The refrigerant flowing through the first passage
61 loses heat to the refrigerant flowing through the second passage 62 and thus turns
into a lower-temperature liquid state.
[0038]
The flow rate of refrigerant diverted from the branch B1 to the second passage 6215
of the internal heat exchanger 16 (i.e., the flow rate of refrigerant in the minor stream
F2) is changed by controlling the opening degree of the bypass pressure reducing
device 17. If a sufficient degree of subcooling is not provided by heat exchange
through the outdoor heat exchanger 14, the controller 5 can increase the flow rate of
refrigerant in the minor stream F2 to cause the refrigerant flowing into the indoor unit 220
to have a sufficient degree of subcooling. The refrigerant in the major stream F1 is
reduced in pressure by the first pressure reducing device 18 and then flows into the
indoor unit 2.
[0039]
The opening degree of the first pressure reducing device 18 is controlled based25
on the pressure of refrigerant flowing into the indoor unit 2, or the intermediate pressure
Pm. In Embodiment 1, the operation control unit 51 of the controller 5 controls the
opening degree of the first pressure reducing device 18 on the basis of the intermediate
pressure Pm calculated by the intermediate pressure calculation unit 54. For example,
the operation control unit 51 reduces the opening degree of the first pressure reducing30
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device 18 in response to the intermediate pressure Pm at or above a reference value.
This increases a reduction in pressure of the refrigerant flowing into the indoor unit 2.
Thus, the pressure of the refrigerant flowing into the indoor unit 2 can be kept from
exceeding an allowable stress for the pipes in the indoor unit 2. Furthermore, the
controller 5 increases the opening degree of the first pressure reducing device 18 in5
response to the intermediate pressure Pm below the reference value. This reduces a
reduction in pressure of the refrigerant flowing into the indoor unit 2, leading to improved
cooling capacity.
[0040]
The refrigerant that has entered the indoor unit 2 is reduced in pressure into a10
two-phase state by the second pressure reducing device 23 and then enters the indoor
heat exchanger 21. The refrigerant passing through the indoor heat exchanger 21
receives heat from the indoor air sent from the indoor fan 22 and thus turns into a high-
temperature, low-pressure gaseous state. Thus, the air passing through the indoor
heat exchanger 21 is cooled, thereby cooling the indoor space. The refrigerant leaving15
the indoor heat exchanger 21 enters the outdoor unit 1. The refrigerant that has
returned to the outdoor unit 1 joins the refrigerant flowing from the second passage 62
of the internal heat exchanger 16 at a junction B2. Then, the refrigerant passes
through the accumulator 19 and is then sucked into the compressor 11.
[0041]20
A method of calculating the intermediate pressure in the refrigeration cycle
apparatus 100 according to Embodiment 1 will now be described. As described above,
the pressure (intermediate pressure Pm) of refrigerant flowing into the indoor unit 2 is
changed by controlling the opening degree of the first pressure reducing device 18. In
the related art, an intermediate-pressure sensor configured to measure an intermediate25
pressure would be provided at, for example, an outlet of the outdoor unit 1.
[0042]
In contrast, the refrigeration cycle apparatus 100 according to Embodiment 1
obtains the intermediate pressure Pm through calculation, instead of actual
measurement through the intermediate-pressure sensor. Fig. 3 is a flowchart30
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illustrating an intermediate pressure calculation method in Embodiment 1. The method
of the flowchart of Fig. 3 is executed by the controller 5 during the cooling operation.
[0043]
Firstly, the flow rate calculation unit 52 of the controller 5 obtains the high
pressure Pd, the low pressure Ps, and the rotation speed N of the compressor 11 (S1).5
The high pressure Pd is a pressure value measured by the high-pressure sensor 31.
The low pressure Ps is a pressure value measured by the low-pressure sensor 32.
The rotation speed N of the compressor 11 may be obtained from the operating
frequency of the compressor 11 or may be detected with a rotation speed detector, such
as a Hall element, included in the compressor 11.10
[0044]
Then, the flow rate calculation unit 52 calculates the flow rate Grc of refrigerant
discharged from the compressor 11 using the obtained high pressure Pd, low pressure
Ps, the rotation speed N of the compressor 11, and the machine characteristics of the
compressor 11 or the like (S2). Specifically, the flow rate calculation unit 52 obtains15
the flow rate Grc from the high pressure Pd, the low pressure Ps, and the rotation speed
N of the compressor 11 using a table. Then, the flow rate calculation unit 52 multiplies
the flow rate Grc obtained using the table by a correction factor determined based on
the degree of suction superheat, thereby calculating a final flow rate Grc. The degree
of suction superheat is obtained from the suction temperature and the low pressure Ps.20
The table and the correction factor for each type of the compressor 11 are generated in
advance through, for example, tests or simulation, and are stored in the storage unit 55.
[0045]
The flow rate calculation unit 52 may calculate the flow rate Grc using the
following equation (1).25
[Math. 1]
where V is a stroke volume [m3] determined based on the machine characteristics of the
compressor 11, N is the rotation speed of the compressor 11, ρs is a suction refrigerant
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density [kg/m3], which can be calculated from the low pressure Ps and the suction
temperature at the compressor 11, and η is a volumetric efficiency, which can be
calculated from the low pressure Ps and the high pressure Pd.
[0046]
Then, the Cv value calculation unit 53 calculates the Cv value Cvb of the bypass5
pressure reducing device 17 from the characteristics of the bypass pressure reducing
device 17 (S3). The Cv value Cvb of the bypass pressure reducing device 17 is a
function of the opening degree of the bypass pressure reducing device 17. For that
reason, an approximation equation to convert the opening degree of the bypass
pressure reducing device 17 to Cv value is obtained in advance based on the10
specifications of the bypass pressure reducing device 17 and is stored in the storage
unit 55. The Cv value calculation unit 53 obtains the opening degree of the bypass
pressure reducing device 17 and inputs the obtained opening degree into the stored
approximation equation to calculate the Cv value Cvb of the bypass pressure reducing
device 17.15
[0047]
The flow rate calculation unit 52 uses, as inputs, the high pressure Pd and the
low pressure Ps obtained in step S1, the Cv value Cvb of the bypass pressure reducing
device 17 calculated in step S3, and the refrigerant density ρ and calculates the flow
rate Grh of refrigerant flowing through the bypass pressure reducing device 17 using the20
following equation (2) (S4). In the following and subsequent equations, "A" is a
correction factor set in advance for each type of the pressure reducing device and is
stored in the storage unit 55.
[Math. 2]
25
[0048]
The flow rate Grh of refrigerant flowing through the bypass pressure reducing
device 17 can be calculated from a pressure difference between an inlet and an outlet
of the bypass pressure reducing device 17, the Cv value of the bypass pressure
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reducing device 17, and the specific gravity of a fluid, as generally known. The
pressure difference between the inlet and the outlet of the bypass pressure reducing
device 17 is calculated using the difference between the high pressure Pd and the low
pressure Ps. Strictly speaking, the pressure difference between the inlet and the outlet
of the bypass pressure reducing device 17 differs from the difference between the high5
pressure Pd and the low pressure Ps because of a pressure drop in, for example, the
check valve 13, the outdoor heat exchanger 14, and the pipes. However, such a
difference is not so large as to significantly reduce the degree of accuracy needed to
calculate the intermediate pressure Pm. Furthermore, while the density ρ changes
depending on the state of refrigerant, the density ρ of refrigerant in a liquid state is used10
for this calculation because refrigerant that has passed through the internal heat
exchanger 16 has a sufficient degree of subcooling. In the equations in the present
disclosure, the flow rate is in units of [kg/h], the density is in units of [kg/m3], and the
pressure is in units of [kgf/cm2(G)].
[0049]15
The flow rate calculation unit 52 calculates the flow rate Gr of refrigerant flowing
through the first pressure reducing device 18 to the indoor unit 2 (S5). The flow rate Gr
of refrigerant flowing to the indoor unit 2 is obtained by subtracting the flow rate Grh of
refrigerant flowing through the bypass pressure reducing device 17 from the flow rate
Grc of refrigerant discharged from the compressor 11.20
[0050]
The Cv value calculation unit 53 calculates the Cv value Cv1 of the first pressure
reducing device 18 from the characteristics of the first pressure reducing device 18 (S6).
The Cv value of the first pressure reducing device 18 is a function of the opening
degree of the first pressure reducing device 18. For that reason, an approximation25
equation to convert the opening degree of the first pressure reducing device 18 to Cv
value is obtained in advance based on the specifications of the first pressure reducing
device 18 and is stored in the storage unit 55. The Cv value calculation unit 53 obtains
the opening degree of the first pressure reducing device 18 and inputs the obtained
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opening degree into the stored approximation equation to calculate the Cv value Cv1 of
the first pressure reducing device 18.
[0051]
The intermediate pressure calculation unit 54 uses, as inputs, the high pressure
Pd, the flow rate Gr of refrigerant flowing through the first pressure reducing device 185
to the indoor unit 2, the Cv value Cv1 of the first pressure reducing device 18, and the
refrigerant density ρ and calculates the intermediate pressure Pm using the following
equation (3) (S7).
[Math. 3]
10
[0052]
Although the high pressure Pd is strictly different from a pressure at an inlet of the
first pressure reducing device 18, the value of the high pressure Pd is used as an
approximation as in the equation (2). Because liquid refrigerant enters the first
pressure reducing device 18 located downstream of the internal heat exchanger 16, the15
refrigerant density ρ of refrigerant in a liquid state can be used. Thus, the intermediate
pressure Pm, which is the pressure of refrigerant flowing into the indoor unit 2, is
obtained. The intermediate pressure Pm is used to control the first pressure reducing
device 18 as described above.
[0053]20
As described above, in the refrigeration cycle apparatus 100 according to
Embodiment 1, the pressure (intermediate pressure) of refrigerant flowing into the
indoor unit 2 can be calculated even in the configuration in which the first pressure
reducing device 18 to reduce the pressure of refrigerant flowing into the indoor unit 2 is
disposed between the internal heat exchanger 16 and the indoor unit 2. This can25
eliminate an intermediate-pressure sensor, leading to simplification of the refrigeration
cycle apparatus 100 and lower cost thereof. Furthermore, the first pressure reducing
device 18 disposed downstream of the internal heat exchanger 16 can provide a
sufficient degree of subcooling at the inlet of the first pressure reducing device 18, thus
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keeping the refrigerant from turning into a two-phase state. This reduces or eliminates
abnormal noise in the first pressure reducing device 18. Additionally, this eases
restrictions on the placement of the first pressure reducing device 18 on the design of
the refrigerant circuit.
[0054]5
Furthermore, in the related art, it is necessary to calculate an enthalpy from
measurements of pressure and temperature or calculate a pressure from a saturation
temperature. In Embodiment 1, an intermediate pressure is obtained from a flow rate
and a Cv value. Therefore, the storage unit 55 does not need to store information on
the properties of refrigerant used for enthalpy calculation. This allows the storage unit10
55 to have a smaller capacity than in the related art. For the intermediate pressure
calculation method in Embodiment 1, information on the machine characteristics of the
compressor 11 is stored for calculation of the flow rate Grc of refrigerant discharged
from the compressor 11. The information on the machine characteristics of the
compressor 11 is used for another control in the refrigeration cycle apparatus 100 and is15
necessary regardless of whether an intermediate pressure is calculated or not.
Therefore, this information is not a factor that burdens the storage capacity.
[0055]
Embodiment 2.
A refrigeration cycle apparatus 100A according to Embodiment 2 will be20
described. An intermediate pressure calculation method in the refrigeration cycle
apparatus 100A according to Embodiment 2 differs from that in Embodiment 1. The
refrigeration cycle apparatus 100A according to Embodiment 2 has the same
configuration as that in Embodiment 1.
[0056]25
In Embodiment 1, the high pressure Pd measured by the high-pressure sensor 31
is used as a pressure at the inlet of the bypass pressure reducing device 17 and that of
the first pressure reducing device 18. Strictly speaking, however, each of the
pressures at the bypass pressure reducing device 17 and the first pressure reducing
device 18 is lower than the high pressure Pd because of a pressure drop in the check30
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valve 13, the outdoor heat exchanger 14, and the pipes to the inlets of the pressure
reducing devices. For example, if the outdoor heat exchanger 14 used is a heat
exchanger with a relatively large pressure drop, such as a parallel-flow heat exchanger
(PFC), such a difference may be non-negligible. The refrigeration cycle apparatus
100A according to Embodiment 2 obtains an intermediate pressure in consideration of a5
pressure drop in the check valve 13 and the outdoor heat exchanger 14.
[0057]
Fig. 4 is a control block diagram of the refrigeration cycle apparatus 100A
according to Embodiment 2. A controller 5A of the refrigeration cycle apparatus 100A
includes a pressure calculation unit 56 in addition to the same functional modules as10
those in Embodiment 1. The pressure calculation unit 56 is a functional module
implemented by a program executed by a processor of the controller 5A. The pressure
calculation unit 56 may be implemented by a processing circuit, such as an ASIC or an
FPGA.
[0058]15
The pressure calculation unit 56 calculates a pressure Pcv of refrigerant leaving
the check valve 13 on the basis of a Cv value Cvcv of the check valve 13, the high
pressure Pd, the flow rate Grc of refrigerant discharged from the compressor 11, and a
density ρg of gaseous refrigerant. Furthermore, the pressure calculation unit 56
calculates a pressure Phex of refrigerant at the outlet of the outdoor heat exchanger 1420
on the basis of the pressure Pcv of refrigerant leaving the check valve 13, the flow rate
Grc of refrigerant discharged from the compressor 11, and the characteristics of the
outdoor heat exchanger 14.
[0059]
Fig. 5 is a flowchart illustrating the intermediate pressure calculation method in25
Embodiment 2. The method of the flowchart of Fig. 5 is executed by the controller 5A
during the cooling operation. Operations in steps S11 to S16 in Fig. 5 are the same as
those in steps S1 to S6 in Embodiment 1. The pressure calculation unit 56 calculates
the pressure Pcv of refrigerant leaving the check valve 13 from the Cv value Cvcv of the
check valve 13, the high pressure Pd, the flow rate Grc of refrigerant discharged from30
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the compressor 11, and the density ρg of gaseous refrigerant using the following
expression (4) (S17). The density of gaseous refrigerant is used because refrigerant
passing through the check valve 13 is typically in a gaseous state. The Cv value Cvcv
of the check valve 13 is dictated by the specifications of the check valve 13 and is
stored in advance in the storage unit 55.5
[Math. 4]
[0060]
The pressure calculation unit 56 calculates the pressure Phex of refrigerant at the
outlet of the outdoor heat exchanger 14 from the pressure Pcv of refrigerant leaving the10
check valve 13, the flow rate Grc of refrigerant discharged from the compressor 11, and
the characteristics of the outdoor heat exchanger 14 (S18). A pressure drop caused by
the outdoor heat exchanger 14 can be calculated as a function of the flow rate of
refrigerant flowing through the outdoor heat exchanger 14. For that reason, a
conversion equation to convert the flow rate of refrigerant flowing through the outdoor15
heat exchanger 14 to pressure drop is theoretically or experimentally derived from the
diameter and length of the tubes in the outdoor heat exchanger 14 and a coefficient of
friction or the like, and is stored in advance in the storage unit 55. The pressure Phex
of refrigerant at the outlet of the outdoor heat exchanger 14 is calculated by subtracting
a pressure drop caused by the outdoor heat exchanger 14, which is converted from the20
flow rate Grc of refrigerant discharged from the compressor 11 using the stored
conversion equation, from the pressure Pcv of refrigerant leaving the check valve 13.
[0061]
The intermediate pressure calculation unit 54 uses, as inputs, the pressure Phex
of refrigerant leaving the outdoor heat exchanger 14, the flow rate Gr of refrigerant25
flowing to the indoor unit 2, the Cv value Cv1 of the first pressure reducing device 18,
and the density ρ of liquid refrigerant and calculates the intermediate pressure Pm using
the following equation (5) (S19).
[Math. 5]
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Thus, the intermediate pressure Pm is obtained and is used by the operation
control unit 51 to control the first pressure reducing device 18.
[0062]
As described above, in the refrigeration cycle apparatus 100A according to5
Embodiment 2, the pressure (intermediate pressure) of refrigerant flowing into the
indoor unit 2 can be calculated even in the configuration in which the first pressure
reducing device 18 is disposed between the internal heat exchanger 16 and the indoor
unit 2. This can eliminate an intermediate-pressure sensor, leading to simplification of
the refrigeration cycle apparatus 100A and lower cost thereof. Furthermore, this eases10
restrictions on the placement of the first pressure reducing device 18 on the design of
the refrigerant circuit. In addition, it is unnecessary to calculate an enthalpy from
measurements of pressure and temperature or calculate a pressure from a saturation
temperature. This allows the storage unit 55 to have a smaller capacity than in the
related art. Additionally, since the intermediate pressure Pm is calculated in15
consideration of a pressure drop in the check valve 13 and the outdoor heat exchanger
14, the accuracy of calculating the intermediate pressure Pm is improved compared to
Embodiment 1.
[0063]
In Embodiment 2, either S17 or S18 of operations in the flowchart of Fig. 5 may20
be omitted. If S18 is omitted, the intermediate pressure Pm can be calculated using
the equation (5) and the pressure Pcv of refrigerant leaving the check valve 13, instead
of the pressure Phex of refrigerant leaving the outdoor heat exchanger 14. If S17 is
omitted, the pressure Phex of refrigerant leaving the outdoor heat exchanger 14 can be
obtained by subtracting a pressure drop in the outdoor heat exchanger 14 from the high25
pressure Pd. In this case, the accuracy of calculating the intermediate pressure Pm is
improved compared to Embodiment 1.
[0064]
Embodiment 3.
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A refrigeration cycle apparatus 100B according to Embodiment 3 will be
described. The configuration of an outdoor unit 1A and an intermediate pressure
calculation method in the refrigeration cycle apparatus 100B according to Embodiment
3 differ from those in Embodiment 1. The rest of the configuration of the refrigeration
cycle apparatus 100B according to Embodiment 3 is the same as that in Embodiment 1.5
[0065]
Fig. 6 is a schematic diagram of the configuration of the refrigeration cycle
apparatus 100B according to Embodiment 3. As illustrated in Fig. 6, the outdoor unit
1A of the refrigeration cycle apparatus 100B according to Embodiment 3 includes a first
temperature sensor 41, a second temperature sensor 42, and a third temperature10
sensor 43 in addition to the same components as those in Embodiment 1.
[0066]
The first temperature sensor 41, the second temperature sensor 42, and the third
temperature sensor 43 are, for example, thermistors. The first temperature sensor 41
measures the temperature of refrigerant at an inlet of the first passage 61 of the internal15
heat exchanger 16. The second temperature sensor 42 measures the temperature of
refrigerant at the outlet of the first passage 61 of the internal heat exchanger 16. The
third temperature sensor 43 measures the temperature of refrigerant at an outlet of the
second passage 62 of the internal heat exchanger 16.
[0067]20
Fig. 7 is a control block diagram of the refrigeration cycle apparatus 100B
according to Embodiment 3. A controller 5B of the refrigeration cycle apparatus 100B
includes an enthalpy obtaining unit 57 in addition to the same functional modules as
those in Embodiment 1. The enthalpy obtaining unit 57 is a functional module
implemented by a program executed by a processor of the controller 5B. The pressure25
calculation unit 56 may be implemented by a processing circuit, such as an ASIC or an
FPGA.
[0068]
The enthalpy obtaining unit 57 obtains an inlet enthalpy H1 and an outlet enthalpy
H2 at the first passage 61 and an inlet enthalpy H3 and an outlet enthalpy H4 at the30
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second passage 62 on the basis of measurement results of the first to third temperature
sensors 41 to 43, the high pressure Pd, and the low pressure Ps.
[0069]
Fig. 8 is a flowchart illustrating the intermediate pressure calculation method in
Embodiment 3. In Fig. 8, operations in steps S21 and S22 are the same as those in5
steps S1 and S2 in Embodiment 1. The enthalpy obtaining unit 57 obtains an inlet
temperature T1 and an outlet temperature T2 at the first passage 61 of the internal heat
exchanger 16 and an outlet temperature T3 at the second passage 62 (S23). The inlet
temperature T1 at the first passage 61 is the temperature of refrigerant at the inlet of the
first passage 61 measured by the first temperature sensor 41. The outlet temperature10
T2 is the temperature of refrigerant at the outlet of the first passage 61 measured by the
second temperature sensor 42. The outlet temperature T3 at the second passage 62
is the temperature of refrigerant at the outlet of the second passage 62 measured by the
third temperature sensor 43.
[0070]15
The enthalpy obtaining unit 57 obtains the inlet and outlet enthalpies H1 to H4 at
the first passage 61 and the second passage 62 of the internal heat exchanger 16 using
the inlet temperature T1 and the outlet temperature T2 at the first passage 61, the outlet
temperature T3 at the second passage 62, the high pressure Pd, and the low pressure
Ps (S24). An enthalpy can be obtained from the properties of refrigerant if pressure20
and temperature are known. For that reason, a table for conversion from pressure and
temperature, serving as inputs, to enthalpy is stored in advance in the storage unit 55.
The enthalpy obtaining unit 57 obtains the enthalpies H1 to H4 using the stored table.
[0071]
The inlet enthalpy H1 at the first passage 61 is obtained from the temperature T125
and the high pressure Pd. The outlet enthalpy H2 at the first passage 61 is obtained
from the temperature T2 and the high pressure Pd. Because a passage from the outlet
of the first passage 61 to the inlet of the second passage 62 has only a change in
pressure, such as a reduction in pressure caused by the bypass pressure reducing
device 17, the inlet enthalpy H3 at the second passage 62 is equal to the outlet enthalpy30
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H2 at the first passage 61. The outlet enthalpy H4 at the second passage 62 is
obtained from the temperature T3 and the low pressure Ps.
[0072]
The flow rate calculation unit 52 inputs the flow rate Grc of refrigerant discharged
from the compressor 11 and the enthalpies H1 to H4 to the following equation (6) to5
calculate the flow rate Grh of refrigerant leaving the bypass pressure reducing device 17
(S25). The equation (6) is derived from equality in the quantity of heat exchanged
between the first passage 61 and the second passage 62 of the internal heat exchanger
16.
[Math. 6]10
[0073]
Operations in the subsequent steps S26 to S28 are the same as those in steps
S5 to S7 in Embodiment 1. The intermediate pressure Pm is obtained in that manner
and is used by the operation control unit 51 to control the first pressure reducing device15
18.
[0074]
As described above, in the refrigeration cycle apparatus 100B according to
Embodiment 3, the pressure (intermediate pressure) of refrigerant flowing into the
indoor unit 2 can be calculated even in the configuration in which the first pressure20
reducing device 18 is disposed between the internal heat exchanger 16 and the indoor
unit 2. This can eliminate an intermediate-pressure sensor, leading to simplification of
the refrigeration cycle apparatus 100B and lower cost thereof. Furthermore, this eases
restrictions on the placement of the first pressure reducing device 18 on the design of
the refrigerant circuit. Additionally, since the Cv value of the bypass pressure reducing25
device 17 does not need to be used to obtain the flow rate Grh of refrigerant leaving the
bypass pressure reducing device 17 in Embodiment 3, a calculation program to
calculate an intermediate pressure can be used irrespective of the specifications of the
bypass pressure reducing device 17.
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[0075]
In Embodiment 3, the intermediate pressure Pm may be obtained using the
pressure Phex of refrigerant leaving the outdoor heat exchanger 14, instead of the high
pressure Pd, in consideration of a pressure drop caused by the check valve 13 and the
outdoor heat exchanger 14 as in Embodiment 2.5
[0076]
Although the embodiments have been described above, the present disclosure is
not intended to be limited to the above-described embodiments. Various modifications
or combinations of the embodiments can be made without departing from the spirit and
scope of the present disclosure. For example, the refrigeration cycle apparatus 100 is10
not limited to a direct expansion air-conditioning apparatus in Embodiment 1 described
above. The refrigeration cycle apparatus 100 may be, for example, a refrigerator or a
heat pump chiller using cold or hot water for air conditioning.
[0077]
Although the refrigeration cycle apparatus 100 according to Embodiment 115
performs only the cooling operation, the present disclosure is not limited to this
example. Fig. 9 is a schematic diagram of the configuration of a refrigeration cycle
apparatus 100C according to Modification 1. As illustrated in Fig. 9, an outdoor unit 1B
of the refrigeration cycle apparatus 100C may include a flow switching valve 10 so that
the cooling operation and a heating operation can be performed.20
[0078]
The flow switching valve 10 switches between the cooling operation in which the
outdoor heat exchanger 14 operates as a condenser and the heating operation in which
the outdoor heat exchanger 14 operates as an evaporator. The flow switching valve 10
is, for example, a four-way valve, and is controlled by the controller 5. In the cooling25
operation, as represented by solid lines in Fig. 9, the flow switching valve 10 is switched
such that refrigerant discharged from the compressor 11 flows into the outdoor heat
exchanger 14. In the heating operation, as represented by broken lines in Fig. 9, the
flow switching valve 10 is switched such that refrigerant discharged from the
compressor 11 flows into the indoor heat exchanger 21.30
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[0079]
In Modification 1, in the cooling operation, the intermediate pressure Pm can be
obtained by using an intermediate pressure calculation method similar to any of those in
Embodiments 1 to 3.
[0080]5
Furthermore, although the refrigeration cycle apparatus 100 according to
Embodiment 1 is configured such that the refrigerant in the minor stream F2 diverted at
the outlet of the first passage 61 of the internal heat exchanger 16 flows through the
second passage 62, the present disclosure is not limited to this example. Fig. 10 is a
schematic diagram of the configuration of a refrigeration cycle apparatus 100D10
according to Modification 2. As illustrated in Fig. 10, the refrigeration cycle apparatus
100D may be configured such that refrigerant leaving the indoor heat exchanger 21 in
the indoor unit 2 flows through the second passage 62 of the internal heat exchanger 16
in an outdoor unit 1C.
[0081]15
In this case, the bypass pressure reducing device 17 is omitted. The inlet of the
second passage 62 is connected to the outlet of the indoor heat exchanger 21 in the
indoor unit 2, and the outlet of the second passage 62 is connected to an inlet of the
accumulator 19. In the internal heat exchanger 16, refrigerant leaving the outdoor heat
exchanger 14 and flowing through the first passage 61 exchanges heat with refrigerant20
leaving the indoor heat exchanger 21 and flowing through the second passage 62.
[0082]
Fig. 11 is a flowchart illustrating an intermediate pressure calculation method in
Modification 2. The method of the flowchart of Fig. 11 is executed by the controller 5
during the cooling operation. The flow rate calculation unit 52 of the controller 525
obtains the high pressure Pd, the low pressure Ps, and the rotation speed N of the
compressor 11 (S31).
[0083]
Then, the flow rate calculation unit 52 calculates the flow rate Grc of refrigerant
discharged from the compressor 11 from the obtained high pressure Pd, low pressure30
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Ps, and rotation speed N of the compressor 11, and the machine characteristics of the
compressor 11 (S32). The Cv value calculation unit 53 calculates the Cv value Cv1 of
the first pressure reducing device 18 from the characteristics of the first pressure
reducing device 18 (S33). The intermediate pressure calculation unit 54 calculates the
intermediate pressure Pm using the high pressure Pd, the flow rate Grc of refrigerant5
discharged from the compressor 11, the Cv value Cv1 of the first pressure reducing
device 18, and the density ρ of liquid refrigerant (S34).
[0084]
In Modification 2, the flow of refrigerant is not divided upstream of the first
pressure reducing device 18, and the bypass pressure reducing device 17 is omitted.10
Therefore, the flow rate Grh of refrigerant flowing through the bypass pressure reducing
device 17 to the second passage 62 is equal to 0. For that reason, the intermediate
pressure calculation unit 54 calculates the intermediate pressure Pm by using the
above-described equation (2) and substituting the flow rate Grc of refrigerant
discharged from the compressor 11 for the flow rate Gr of refrigerant flowing through the15
first pressure reducing device 18 to the indoor unit 2. Modification 2 is based on an
assumption that the internal heat exchanger 16 provides a sufficient degree of
subcooling and the refrigerant flowing through the first pressure reducing device 18 is in
a liquid state.
[0085]20
The pressures and flow rates obtained in the above-described embodiments are
not limited to those obtained in the above-described manner. For example, the
temperature of two-phase refrigerant leaving the second pressure reducing device 23
may be measured by using a temperature sensor, the measured temperature may be
converted to pressure, and the pressure may be used as an approximation of the low25
pressure Ps. The flow rate of refrigerant may be measured by using a flowmeter.
Reference Signs List
[0086]
1, 1A, 1B, 1C: outdoor unit, 2: indoor unit, 5, 5A, 5B: controller, 10: flow switching
valve, 11: compressor, 12: oil separator, 13: check valve, 14: outdoor heat exchanger,30
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15: outdoor fan, 16: internal heat exchanger, 17: bypass pressure reducing device, 18:
first pressure reducing device, 19: accumulator, 21: indoor heat exchanger, 22: indoor
fan, 23: second pressure reducing device, 31: high-pressure sensor, 32: low-pressure
sensor, 41: first temperature sensor, 42: second temperature sensor, 43: third
temperature sensor, 51: operation control unit, 52: flow rate calculation unit, 53: Cv5
value calculation unit, 54: intermediate pressure calculation unit, 55: storage unit, 56:
pressure calculation unit, 57: enthalpy obtaining unit, 61: first passage, 62: second
passage, 100, 100A, 100B, 100C, 100D: refrigeration cycle apparatus
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We Claim :
[Claim 1]
A refrigeration cycle apparatus comprising:
an outdoor unit;
an indoor unit connected to the outdoor unit; and5
a controller,
the outdoor unit including
a compressor configured to compress and discharge refrigerant,
an outdoor heat exchanger configured to exchange heat of refrigerant
discharged from the compressor,10
an internal heat exchanger configured to exchange heat of refrigerant
flowing from the outdoor heat exchanger, and
a pressure reducing device disposed between the internal heat exchanger
and the indoor unit, the pressure reducing device being configured to reduce a pressure
of refrigerant flowing into the indoor unit,15
the controller being configured to calculate an intermediate pressure that is the
pressure of refrigerant flowing into the indoor unit by using a high pressure that is a
pressure of refrigerant on a discharge side of the compressor, a flow rate of refrigerant
flowing through the pressure reducing device, a Cv value of the pressure reducing
device, and a density of liquid refrigerant.20
[Claim 2]
The refrigeration cycle apparatus of claim 1, wherein the controller is configured
to control, based on the intermediate pressure, the pressure reducing device.
[Claim 3]
The refrigeration cycle apparatus of claim 1 or 2, wherein25
the internal heat exchanger includes a first passage connected to the outdoor
heat exchanger and a second passage branching from the first passage, the internal
heat exchanger being configured to exchange heat between refrigerant flowing through
the first passage and refrigerant flowing through the second passage,
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the outdoor unit further includes a bypass pressure reducing device configured to
reduce a pressure of refrigerant flowing into the second passage, and
the controller is configured to subtract a flow rate of refrigerant flowing through
the bypass pressure reducing device from a flow rate of refrigerant discharged from the
compressor to obtain the flow rate of refrigerant flowing through the pressure reducing5
device.
[Claim 4]
The refrigeration cycle apparatus of claim 3, wherein the controller is configured
to obtain the flow rate of refrigerant flowing through the bypass pressure reducing
device by using an inlet enthalpy and an outlet enthalpy at the first passage and an inlet10
enthalpy and an outlet enthalpy at the second passage.
[Claim 5]
The refrigeration cycle apparatus of any one of claims 1 to 4, wherein
the outdoor unit further includes a high-pressure sensor configured to measure
the pressure of refrigerant on the discharge side of the compressor, and15
the controller is configured to calculate the intermediate pressure by using, as the
high pressure, the pressure measured by the high-pressure sensor.
[Claim 6]
The refrigeration cycle apparatus of any one of claims 1 to 4, wherein the
controller is configured to calculate the intermediate pressure by using, as the high20
pressure, a pressure of refrigerant leaving the outdoor heat exchanger.
[Claim 7]
The refrigeration cycle apparatus of any one of claims 1 to 4, wherein
the outdoor unit further includes a check valve disposed on the discharge side of
the compressor, and25
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the controller is configured to calculate the intermediate pressure by using, as the
high pressure, a pressure of refrigerant leaving the check valve.