EP4286767A1

EP4286767A1 - Refrigeration cycle device

Info

Publication number: EP4286767A1
Application number: EP22745917.9A
Authority: EP
Inventors: Ken Takahashi
Original assignee: Daikin Industries Ltd
Current assignee: Daikin Industries Ltd
Priority date: 2021-01-29
Filing date: 2022-01-26
Publication date: 2023-12-06
Also published as: WO2022163698A1; JP2022117024A; US20230366583A1; CN116761963A; JP7393671B2

Abstract

There is proposed a refrigeration cycle apparatus capable of suppressing a phenomenon that a condensed refrigerant accumulates in a heat source-side heat exchanger during a low-load operation. A refrigeration cycle apparatus (100) performs air conditioning of a target space. The refrigeration cycle apparatus includes a refrigerant circuit (10) and a control unit (60). The refrigerant circuit includes a compressor (21), a heat source-side heat exchanger (23), an expansion mechanism (25), a usage-side heat exchanger (52), and a flow direction switching mechanism (22). The control unit controls the compressor and the flow direction switching mechanism. The control unit executes first control of temporarily increasing the pressure of the refrigerant flowing through the heat source-side heat exchanger in a low-load operation in which the refrigerant circuit is in a low-load state with a low air conditioning load and the compressor operates at a predetermined number of rotations or less.

Description

TECHNICAL FIELD

The present disclosure relates to a refrigerant cycle apparatus.

BACKGROUND ART

Patent Literature 1 ( JP 2007-212078 A ) discloses a refrigeration cycle apparatus that shifts an opening degree of an expansion valve included in a refrigerant circuit in an opening direction to prevent occurrence of a phenomenon in which a condensed refrigerant accumulates in a heat source-side heat exchanger due to an unexpected disturbance such as a rapid temperature decrease during cooling operation at a low outside air temperature.

SUMMARY OF THE INVENTION

There is room for improvement in the control disclosed in Patent Literature 1 regarding prevention of a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger during a low-load operation.
The present disclosure proposes a refrigeration cycle apparatus capable of suppressing the phenomenon that the condensed refrigerant accumulates in the heat source-side heat exchanger during a low-load operation.

A refrigeration cycle apparatus according to a first aspect performs air conditioning of a target space. The refrigeration cycle apparatus includes a refrigerant circuit and a control unit. The refrigerant circuit includes a compressor, a heat source-side heat exchanger, an expansion mechanism, a usage-side heat exchanger, and a flow direction switching mechanism. The control unit controls the compressor and the flow direction switching mechanism. The control unit executes first control of temporarily increasing the pressure of the refrigerant flowing through the heat source-side heat exchanger in a low-load operation in which the refrigerant circuit is in a low-load state with a low air conditioning load and the compressor operates at a predetermined number of rotations or less.
According to the present refrigeration cycle apparatus, by executing the first control during the low-load operation, the pressure of the refrigerant flowing through the heat source-side heat exchanger temporarily increases, so that evaporation of a condensed refrigerant is promoted and the condensed refrigerant is pushed out from the heat source-side heat exchanger and discharged. As a result, a phenomenon that the condensed refrigerant accumulates in the heat source-side heat exchanger can be suppressed.
A refrigeration cycle apparatus according to a second aspect is the refrigeration cycle apparatus according to the first aspect, in which the control unit increases a pressure of the refrigerant flowing through the heat source-side heat exchanger by increasing a number of rotations of the compressor in the first control.
According to the present refrigeration cycle apparatus, a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger can be suppressed by simple control of increasing the number of rotations of the compressor.
A refrigeration cycle apparatus according to a third aspect is the refrigeration cycle apparatus according to the first or second aspect, and further includes a heat source-side fan that blows air to the heat source-side heat exchanger. The control unit, in the first control, increases a pressure of the refrigerant flowing through the heat source-side heat exchanger by stopping the heat source-side fan.
According to the present refrigeration cycle apparatus, a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger can be suppressed by simple control of stopping the heat source-side fan.
A refrigeration cycle apparatus according to a fourth aspect is the refrigeration cycle apparatus according to any one of the first to third aspects, in which the control unit, in the low-load operation, further executes second control of increasing an opening degree of the expansion mechanism during execution of the first control.
According to the present refrigeration cycle apparatus, the opening degree of the expansion mechanism increases during the execution of the first control, and a large amount of the refrigerant can flow out of the heat source-side heat exchanger. Therefore, the refrigerant in the heat source-side heat exchanger is easily pushed out, and a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger can be effectively suppressed.
A refrigeration cycle apparatus according to a fifth aspect is the refrigeration cycle apparatus according to any one of the first to fourth aspects, in which the control unit executes the first control over a predetermined first time period. The first time period is 10 seconds or more and 5 minutes or less.
According to the present refrigeration cycle apparatus, it is possible to prevent the first time period from being executed for a long time and prevent the execution of a cooling operation or a heating operation from being interrupted.
A refrigeration cycle apparatus according to a sixth aspect is the refrigeration cycle apparatus according to the fifth aspect, in which the control unit executes the first control at an interval of a second time period or more longer than the first time period.
According to the present refrigeration cycle apparatus, it is possible to prevent the first time period from being frequently executed for a long time and prevent the execution of a cooling operation or a heating operation from being interrupted.
A refrigeration cycle apparatus according to a seventh aspect is the refrigeration cycle apparatus according to the sixth aspect, in which the control unit determines the first time period or the second time period based on a number of rotations of the compressor.
According to the present refrigeration cycle apparatus, it is possible to suppress deterioration of comfort in the target space while suppressing a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger.
A refrigeration cycle apparatus according to an eighth aspect is the refrigeration cycle apparatus according to the sixth or seventh aspect, in which the control unit determines the first time period or the second time period based on a first temperature. The first temperature is a temperature of heat source air for heat exchange with a refrigerant in the heat source-side heat exchanger.
According to the present refrigeration cycle apparatus, it is possible to suppress deterioration of comfort in the target space while suppressing a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger.
A refrigeration cycle apparatus according to a ninth aspect is the refrigeration cycle apparatus according to any one of the first to eighth aspects, in which the control unit determines that the refrigerant circuit is in the low-load state when a difference between the first temperature and a second temperature is less than or equal to a predetermined first temperature difference. The second temperature is a temperature of the refrigerant flowing through the heat source-side heat exchanger.
A refrigeration cycle apparatus according to a tenth aspect is the refrigeration cycle apparatus according to any one of the first to ninth aspects, in which the control unit determines that the refrigerant circuit is in the low-load state when a difference between a first estimated temperature or a third temperature, and the second temperature is less than or equal to a predetermined second temperature difference. The first estimated temperature is an estimated temperature of the refrigerant flowing through the usage-side heat exchanger calculated based on the first temperature. The third temperature is a temperature of the refrigerant flowing through the usage-side heat exchanger.
A refrigeration cycle apparatus according to an eleventh aspect is the refrigeration cycle apparatus according to any one of the first to tenth aspects, in which the control unit determines that the refrigerant circuit is in the low-load state when a difference between the third temperature or a second estimated temperature, and the first temperature is less than or equal to a predetermined third temperature difference. The second estimated temperature is an estimated temperature of the refrigerant flowing through the usage-side heat exchanger calculated based on a number of rotations of the compressor.
A refrigeration cycle apparatus according to a twelfth aspect is the refrigeration cycle apparatus according to any one of the first to eleventh aspects, in which the control unit determines that the refrigerant circuit is in the low-load state when a difference between the first temperature and a sixth temperature is less than or equal to a predetermined fourth temperature difference. The sixth temperature is a temperature in the target space.
A refrigeration cycle apparatus according to a thirteenth aspect is the refrigeration cycle apparatus according to any one of the first to twelfth aspects, in which the control unit determines that the refrigerant circuit is in the low-load state when a number of rotations of the compressor is less than or equal to a predetermined number of rotations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of an air conditioning apparatus 100.
FIG. 2 is a control block diagram of a control unit 60.
FIG. 3 is a flowchart illustrating a control flow of a refrigerant discharge operation executed by the control unit 60.

DESCRIPTION OF EMBODIMENTS

(1) Overall configuration

An air conditioning apparatus 100 according to an embodiment of the present disclosure will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of the air conditioning apparatus 100.
The air conditioning apparatus 100 is an example of a refrigeration cycle apparatus. The air conditioning apparatus 100 is an apparatus using a vapor compression refrigeration cycle. The air conditioning apparatus 100 includes a refrigerant circuit 10 including a compressor 21, a heat source-side heat exchanger 23, and a usage-side heat exchanger 52. Note that the refrigeration cycle apparatus is not limited to the air conditioning apparatus. The refrigeration cycle apparatus includes, for example, a refrigerator, a freezer, a water heater, a floor heating device, and the like.
The air conditioning apparatus 100 is an air conditioning apparatus that performs a cooling operation (including a dehumidifying operation) and a heating operation of a space to be air-conditioned. However, the air conditioning apparatus 100 may not be an air conditioning apparatus capable of a cooling operation and a heating operation. For example, the air conditioning apparatus may be an air conditioning apparatus dedicated to cooling operation. Furthermore, the air conditioning apparatus 100 performs a refrigerant discharge operation for suppressing a phenomenon in which a condensed refrigerant accumulates in the heat source-side heat exchanger 23 described later while the cooling operation or the heating operation is performed. Hereinafter, details of the air conditioning apparatus 100 will be described.

(2) Air conditioning apparatus

Details of the air conditioning apparatus 100 will be described.
The air conditioning apparatus 100 mainly includes one heat source unit 20, one usage unit 50, a liquid refrigerant connection pipe 2, a gas refrigerant connection pipe 4, and a control unit 60. The liquid refrigerant connection pipe 2 and the gas refrigerant connection pipe 4 are pipes connecting the heat source unit 20 and the usage unit 50. The control unit 60 controls operations of various devices and various components of the heat source unit 20 and the usage unit 50 to achieve the cooling operation, the heating operation, and the refrigerant discharge operation.
Note that, although the air conditioning apparatus 100 of the present embodiment includes one usage unit 50, the number of usage units 50 is not limited to one and may be plural. Furthermore, although the air conditioning apparatus 100 of the present embodiment includes one heat source unit 20, the number of heat source units 20 is not limited to one and may be plural. Furthermore, the air conditioning apparatus 100 may be an integrated device in which the heat source unit 20 and the usage unit 50 are incorporated in a single unit.
The heat source unit 20 and the usage unit 50 are connected via the liquid refrigerant connection pipe 2 and the gas refrigerant connection pipe 4 to constitute a refrigerant circuit 10. A refrigerant is sealed in the refrigerant circuit 10. The refrigerant sealed in the refrigerant circuit 10 is not limited, but is, for example, a fluorocarbon refrigerant such as R32. The refrigerant circuit 10 includes the compressor 21 of the heat source unit 20, a flow direction switching mechanism 22, the heat source-side heat exchanger 23, and an expansion mechanism 25, and the usage-side heat exchanger 52 of the usage unit 50.
The air conditioning apparatus 100 has, as main operating mode modes, a cooling operating mode for executing a cooling operation and a heating operating mode for executing a heating operation. The cooling operation is an operation in which the heat source-side heat exchanger 23 functions as a radiator (condenser) of the refrigerant, the usage-side heat exchanger 52 functions as an evaporator of the refrigerant, and air in a space in which the usage unit 50 is installed is cooled. The heating operation is an operation in which the heat source-side heat exchanger 23 functions as an evaporator of the refrigerant, the usage-side heat exchanger 52 functions as a radiator of the refrigerant, and the air in the space where the usage unit 50 is installed is heated. Furthermore, during the heating operation, the air conditioning apparatus 100 may interrupt the heating operation and perform a defrost operation. The defrost operation is an operation for removing frost adhering to the heat source-side heat exchanger 23 by causing the heat source-side heat exchanger 23 to function as a radiator of a refrigerant and causing the usage-side heat exchanger 52 to function as an evaporator of the refrigerant.

(2-1) Usage unit

The usage unit 50 is a unit installed in the air conditioning target space. For example, the usage unit 50 is a ceiling-embedded type unit. However, the usage unit 50 of the air conditioning apparatus 100 is not limited to the ceiling-embedded type, and one or both of them may be a ceiling-suspended type, a wall-mounted type, or a floor-mounted type. Furthermore, the usage unit 50 may be disposed outside the air conditioning target space. For example, the usage unit 50 may be installed in an attic, a machine chamber, a garage, or the like. In this case, an air passage for supplying air heat-exchanged with the refrigerant in the usage-side heat exchanger 52 from the usage unit 50 to the air conditioning target space is provided. Examples of the air passage include a duct. However, the type of air passage is not limited to a duct, and may be appropriately selected.
As described above, the usage unit 50 is connected to the heat source unit 20 via the liquid refrigerant connection pipe 2 and the gas refrigerant connection pipe 4, and constitutes a part of the refrigerant circuit 10.
The usage unit 50 includes a usage-side refrigerant circuit 10a constituting a part of the refrigerant circuit 10. The usage-side refrigerant circuit 10a mainly includes the usage-side heat exchanger 52. The usage unit 50 includes a usage-side fan 53 driven by the motor 53a. Furthermore, the usage unit 50 includes a filter 58. The usage unit 50 includes various sensors. The sensors included in the usage unit 50 will be described later. The usage unit 50 includes a usage-side control unit 64 that controls an operation of the usage unit 50.

(2-1-1) Usage-side heat exchanger

The usage-side heat exchanger 52 causes heat exchange between a refrigerant flowing in the usage-side heat exchanger 52 and air in the air conditioning target space. The usage-side heat exchanger 52 should not be limited in terms of its type, but is exemplified by a fin- and-tube heat exchanger including a plurality of heat transfer tubes and fins (not illustrated).
The usage-side heat exchanger 52 has one end connected to the liquid refrigerant connection pipe 2 via a refrigerant pipe. The usage-side heat exchanger 52 has the other end connected to the gas refrigerant connection pipe 4 via the refrigerant pipe. During the cooling operation and the defrost operation, the refrigerant flows into the usage-side heat exchanger 52 from a side of the liquid refrigerant connection pipe 2, and the usage-side heat exchanger 52 functions as an evaporator for the refrigerant. During the heating operation, the refrigerant flows into the usage-side heat exchanger 52 from a side of the gas refrigerant connection pipe 4, and the usage-side heat exchanger 52 functions as a radiator for the refrigerant.

(2-1-2) Usage-side fan

The usage-side fan 53 is a fan that supplies air to the usage-side heat exchanger 52. In the usage unit 50, as indicated by two-dot chain line arrows in the figure, the filter 58, the usage-side heat exchanger 52, and the usage-side fan 53 are disposed in this order from an upstream side to a downstream side in a flow direction of the air generated by the usage-side fan 53. The order of the arrangement of the filter 58, the usage-side heat exchanger 52, and the usage-side fan 53 is not limited to the order illustrated in the drawing, and for example, the filter 58, the usage-side fan 53, and the usage-side heat exchanger 52 may be disposed in this order from the upstream side to the downstream side in the flow direction of the air generated by the usage-side fan 53. Examples of the usage-side fan 53 include a turbo fan. However, the type of the usage-side fan 53 is not limited to the turbo fan, and may be appropriately selected.
The usage-side fan 53 is driven by the motor 53a. The usage-side fan 53 is an air volume variable fan driven by a motor 53a whose number of rotations can be changed.

(2-1-3) Filter

The filter 58 removes foreign substances such as dust from the air supplied to the usage-side heat exchanger 52 by the usage-side fan 53. The filter 58 is disposed upstream of the usage-side heat exchanger 52 in the air flow direction generated by the usage-side fan 53.

(2-1-4) Sensor

The usage unit 50 includes a liquid-side temperature sensor 54, a gas-side temperature sensor 55, a spatial temperature sensor 56, and a heat exchange temperature sensor 57 as sensors. The type of the temperature sensor or the humidity sensor may be appropriately selected.
Note that the usage unit 50 may include only a part of the sensors 54 to 57. Furthermore, the usage unit 50 may include a sensor other than the sensors 54 to 57.
The liquid-side temperature sensor 54 is provided in a refrigerant pipe connecting a liquid side of the usage-side heat exchanger 52 and the liquid refrigerant connection pipe 2. The liquid-side temperature sensor 54 measures a temperature of the refrigerant flowing through the liquid side refrigerant pipe of the usage-side heat exchanger 52.
The gas-side temperature sensor 55 is provided in a refrigerant pipe connecting a gas side of the usage-side heat exchanger 52 and the gas refrigerant connection pipe 4. The gas-side temperature sensor 55 measures a temperature of the refrigerant flowing through the refrigerant pipe on the gas side of the usage-side heat exchanger 52.
The spatial temperature sensor 56 is provided on an air suction side of a casing (not illustrated) of the usage unit 50. The spatial temperature sensor 56 detects a temperature (space temperature Tr) of air in the air conditioning target space flowing into the casing of the usage unit 50.
The heat exchange temperature sensor 57 is provided in the usage-side heat exchanger 52. The heat exchange temperature sensor 57 is a sensor that measures a use refrigerant temperature Tar, which is a temperature of the refrigerant flowing through the usage-side heat exchanger 52. The heat exchange temperature sensor 57 measures a refrigerant temperature corresponding to a condensation temperature Tc during the heating operation, and measures a refrigerant temperature corresponding to an evaporation temperature Te during the cooling operation. The heat exchange temperature sensor 57 is, for example, a thermistor.

(2-1-5) Usage-side control unit

The usage-side control unit 64 controls operation of respective parts of the usage unit 50.
The usage-side control unit 64 includes a microcomputer provided to control the usage unit 50, a memory in which a control program executable by the microcomputer is stored, and the like. Note that the configuration of the usage-side control unit 64 described here is merely an example, and the function of the usage-side control unit 64 described below may be implemented by software, hardware, or a combination of software and hardware.
The usage-side control unit 64 is electrically connected to the usage-side fan 53, the liquid-side temperature sensor 54, the gas-side temperature sensor 55, the spatial temperature sensor 56, and the heat exchange temperature sensor 57 so as to be able to exchange control signals and information.
The usage-side control unit 64 is configured to be able to receive various signals transmitted from a remote controller (not illustrated) for operating the usage unit 50. The various signals transmitted from the remote controller include signals instructing operation or stop of the usage unit 50 and signals related to various settings. The signals related to the various settings include, for example, an operating mode switching signal, and a signal related to a set temperature Trs and a set humidity Hrs of the cooling operation and the heating operation.
The usage-side control unit 64 is connected to a heat source-side control unit 62 of the heat source unit 20 via a transmission line 66 so as to be able to exchange control signals and the like. Note that the usage-side control unit 64 and the heat source-side control unit 62 may not be connected by the physical transmission line 66, but may be connected so as to be able to communicate wirelessly. The usage-side control unit 64 and the heat source-side control unit 62 function as the control unit 60 that cooperatively controls the entire operation of the air conditioning apparatus 100. The control unit 60 will be described later.

(2-2) Heat source unit

The heat source unit 20 is disposed outside the air conditioning target space. The heat source unit 20 is installed, for example, on a rooftop of a building where the air conditioning apparatus 100 is installed or adjacent to the building.
The heat source unit 20 is connected to the usage unit 50 via the liquid refrigerant connection pipe 2 and the gas refrigerant connection pipe 4. The heat source unit 20 constitutes the refrigerant circuit 10 together with the usage unit 50.
The heat source unit 20 includes a heat source-side refrigerant circuit 10b constituting a part of the refrigerant circuit 10. The heat source-side refrigerant circuit 10b mainly includes the compressor 21, the flow direction switching mechanism 22, the heat source-side heat exchanger 23, the expansion mechanism 25, an accumulator 24, a liquid-side shutoff valve 14, and a gas-side shutoff valve 16. The heat source unit 20 includes a heat source-side fan 28 driven by a motor 28a. The heat source unit 20 includes various sensors. The sensors included in the heat source unit 20 will be described later. The heat source unit 20 includes the heat source-side control unit 62.
However, the heat source unit 20 does not necessarily have all of the above-described components, and the components of the heat source unit 20 may be appropriately selected. For example, the heat source unit 20 may not include the expansion mechanism 25, and the usage unit 50 may include a similar expansion mechanism instead of the heat source unit 20.
Furthermore, the heat source unit 20 includes a suction pipe 12a, a discharge pipe 12b, a first gas refrigerant pipe 12c, a liquid refrigerant pipe 12d, and a second gas refrigerant pipe 12e. The suction pipe 12a connects the flow direction switching mechanism 22 and a suction side of the compressor 21. The suction pipe 12a is provided with the accumulator 24. The discharge pipe 12b connects a discharge side of the compressor 21 and the flow direction switching mechanism 22. The first gas refrigerant pipe 12c connects the flow direction switching mechanism 22 and a gas side of the heat source-side heat exchanger 23. The liquid refrigerant pipe 12d connects a liquid side of the heat source-side heat exchanger 23 and the liquid refrigerant connection pipe 2. The liquid refrigerant pipe 12d is provided with the expansion mechanism 25. The liquid-side shutoff valve 14 is provided at a connection portion between the liquid refrigerant pipe 12d and the liquid refrigerant connection pipe 2. The second gas refrigerant pipe 12e connects the flow direction switching mechanism 22 and the gas refrigerant connection pipe 4. The gas-side shutoff valve 16 is provided at a connection portion between the second gas refrigerant pipe 12e and the gas refrigerant connection pipe 4.
Hereinbelow, a main configuration of the heat source unit 20 will be further described.

(2-2-1) Compressor

The compressor 21 is a device that sucks a low-pressure refrigerant in the refrigeration cycle from the suction pipe 12a, compresses the refrigerant by a compression mechanism (not illustrated), and discharges the compressed refrigerant to the discharge pipe 12b. In the present embodiment, the heat source unit 20 includes only one compressor 21, but the number of compressors 21 is not limited to one and may be plural.
The type of the compressor 21 is not limited, and is, for example, a rotary type or scroll type capacity compressor. The compression mechanism (not illustrated) of the compressor 21 is driven by a motor 21a. When the compression mechanism is driven by the motor 21a, the refrigerant is compressed by the compression mechanism. The motor 21a is a motor capable of controlling the number of rotations based on an operating frequency output from an inverter (not illustrated). The capacity of the compressor 21 is controlled by controlling the number of rotations of the motor 21a. Note that the compression mechanism of the compressor 21 may be driven by a prime mover (for example, an internal combustion engine) other than the motor.

(2-2-2) Flow direction switching mechanism

The flow direction switching mechanism 22 is a mechanism that changes a state of the refrigerant circuit 10 between a first state and a second state by switching a flow direction of the refrigerant. When the refrigerant circuit 10 is in the first state, the heat source-side heat exchanger 23 functions as a radiator for the refrigerant, and the usage-side heat exchanger 52 functions as an evaporator for the refrigerant. When the refrigerant circuit 10 is in the second state, the heat source-side heat exchanger 23 functions as an evaporator of the refrigerant, and the usage-side heat exchanger 52 functions as a radiator of the refrigerant.
In the present embodiment, the flow direction switching mechanism 22 is a four-way switching valve. However, the flow direction switching mechanism 22 is not limited to the four-way switching valve. For example, the flow direction switching mechanism 22 may be configured by combining a plurality of electromagnetic valves and refrigerant pipes so that the following switching of the flow direction of the refrigerant can be realized.
During the cooling operation and the defrost operation, the flow direction switching mechanism 22 brings the refrigerant circuit 10 into the first state. In other words, during the cooling operation and the defrost operation, the flow direction switching mechanism 22 causes the suction pipe 12a to communicate with the second gas refrigerant pipe 12e and causes the discharge pipe 12b to communicate with the first gas refrigerant pipe 12c (See a solid line in the flow direction switching mechanism 22 in FIG. 1).
During the heating operation, the flow direction switching mechanism 22 brings the refrigerant circuit 10 into the second state. In other words, during the heating operation, the flow direction switching mechanism 22 causes the suction pipe 12a to communicate with the first gas refrigerant pipe 12c and causes the discharge pipe 12b to communicate with the second gas refrigerant pipe 12e (See a broken line in the flow direction switching mechanism 22 in FIG. 1).

(2-2-3) Heat source-side heat exchanger

In the heat source-side heat exchanger 23, heat is exchanged between the refrigerant flowing inside and the air (heat source air) at the installation location of the heat source unit 20. In a case where the heat source unit 20 is installed outdoors, the heat source-side heat exchanger 23 exchanges heat between the refrigerant flowing inside and outdoor air.
The heat source-side heat exchanger 23 is, for example, but not limited to, a fin-and-tube heat exchanger having a plurality of heat transfer tubes and fins (not illustrated).
One end of the heat source-side heat exchanger 23 is connected to the liquid refrigerant pipe 12d. The other end of the heat source-side heat exchanger 23 is connected to the first gas refrigerant pipe 12c.
The heat source-side heat exchanger 23 functions as a radiator for the refrigerant during cooling operation, dehumidifying operation, and defrost operation, and functions as an evaporator for the refrigerant during heating operation.

(2-2-4) Expansion mechanism

The expansion mechanism 25 is disposed between the heat source-side heat exchanger 23 and the usage-side heat exchanger 52 in the refrigerant circuit 10. The expansion mechanism 25 is disposed in the liquid refrigerant pipe 12d between the heat source-side heat exchanger 23 and the liquid-side shutoff valve 14. In a case where the usage unit 50 includes an expansion mechanism similar to the expansion mechanism 25, instead of the expansion mechanism 25 included in the heat source unit 20, the expansion mechanism may be provided in a refrigerant pipe that connects the liquid refrigerant connection pipe 2 and the usage-side heat exchanger 52 inside the usage unit 50. The expansion mechanism 25 is an opening degree variable electronic expansion valve that adjusts the pressure and flow rate of the refrigerant flowing through the refrigerant circuit 10.

(2-2-5) Accumulator

The accumulator 24 has a gas-liquid separation function of separating the flowing refrigerant into a gas refrigerant and a liquid refrigerant. Furthermore, the accumulator 24 is a container having a function of storing a surplus refrigerant generated in response to, for example, a change in operating load of the usage unit 50. The accumulator 24 is provided in the suction pipe 12a. The refrigerant flowing into the accumulator 24 is separated into a gas refrigerant and a liquid refrigerant, and the gas refrigerant collecting in an upper space flows out to the compressor 21.

(2-2-6) Liquid-side shutoff valve and gas-side shutoff valve

The liquid-side shutoff valve 14 is a valve provided at a connection portion between the liquid refrigerant pipe 12d and the liquid refrigerant connection pipe 2. The gas-side shutoff valve 16 is a valve provided at a connection portion between the second gas refrigerant pipe 12e and the gas refrigerant connection pipe 4. The liquid-side shutoff valve 14 and the gas-side shutoff valve 16 are, for example, manually operated valves.

(2-2-7) Heat source-side fan

The heat source-side fan 28 is a fan that supplies air to the heat source-side heat exchanger 23. Specifically, the heat source-side fan 28 is a fan that sucks heat source air outside the heat source unit 20 into a casing (not illustrated) of the heat source unit 20 and supplies the air to the heat source-side heat exchanger 23, and discharges the air heat-exchanged with the refrigerant in the heat source-side heat exchanger 23 to the outside of the casing of the heat source unit 20.
The heat source-side fan 28 is, for example, a propeller fan. However, the type of the fan of the heat source-side fan 28 is not limited to the propeller fan, and may be appropriately selected.
The heat source-side fan 28 is driven by the motor 28a. The heat source-side fan 28 is a variable air volume fan driven by the motor 28a whose number of rotations can be changed.

(2-2-8) Sensor

The heat source unit 20 includes a discharge pressure sensor 30, a suction pressure sensor 31, a suction temperature sensor 32, a discharge temperature sensor 33, a heat exchange temperature sensor 34, a liquid-side temperature sensor 35, and a heat source air temperature sensor 36 as sensors. The type of the temperature sensor or the pressure sensor may be appropriately selected.
Note that the heat source unit 20 may include only a part of the sensors 30 to 36. Furthermore, the heat source unit 20 may include a sensor other than the above-described sensors 30 to 36.
The discharge pressure sensor 30 is provided in the discharge pipe 12b. The discharge pressure sensor 30 is a sensor that measures a discharge pressure Pd.
The suction pressure sensor 31 is provided in the suction pipe 12a. The suction pressure sensor 31 is a sensor that measures a suction pressure Ps.
The suction temperature sensor 32 is provided in the suction pipe 12a. The suction temperature sensor 32 is a sensor that measures a suction temperature Ts.
The discharge temperature sensor 33 is provided in the discharge pipe 12b. The discharge temperature sensor 33 is a sensor that measures a discharge temperature Td.
The heat exchange temperature sensor 34 is provided in the heat source-side heat exchanger 23. The heat exchange temperature sensor 34 is a sensor that measures a heat source refrigerant temperature Thr that is a temperature of the refrigerant flowing through the heat source-side heat exchanger 23. The heat exchange temperature sensor 34 measures a refrigerant temperature corresponding to a condensation temperature Tc during the cooling operation, and measures a refrigerant temperature corresponding to an evaporation temperature Te during the heating operation.
The liquid-side temperature sensor 35 is provided on the liquid refrigerant pipe 12d (on a liquid side of the heat source-side heat exchanger 23). The liquid-side temperature sensor 35 is a sensor that measure a temperature Tl of the refrigerant flowing through the liquid refrigerant pipe 12d. When the state of the heat source-side heat exchanger 23 is switched to the first state, a degree of subcooling SCr of the refrigeration cycle is calculated by subtracting the temperature Tl of the refrigerant measured by the liquid-side temperature sensor 35 from the condensation temperature Tc measured by the heat exchange temperature sensor 34.
The heat source air temperature sensor 36 is provided on an air suction side of a casing (not illustrated) of the heat source unit 20. The heat source air temperature sensor 36 is a sensor that measures a heat source air temperature Tha that is a temperature of the heat source air.

(2-2-9) Heat source-side control unit

The heat source-side control unit 62 controls an operation of each part constituting the heat source unit 20.
The heat source-side control unit 62 includes a microcomputer provided to control the heat source unit 20, a memory in which a control program executable by the microcomputer is stored, and the like. Note that the configuration of the heat source-side control unit 62 described herein is merely an example, and the function of the heat source-side control unit 62 described below may be implemented by software, hardware, or a combination of software and hardware.
The heat source-side control unit 62 is electrically connected to the compressor 21, the flow direction switching mechanism 22, the expansion mechanism 25, the heat source-side fan 28, the discharge pressure sensor 30, the suction pressure sensor 31, the suction temperature sensor 32, the discharge temperature sensor 33, the heat exchange temperature sensor 34, the liquid-side temperature sensor 35, and the heat source air temperature sensor 36 so as to be able to exchange control signals and information.
The heat source-side control unit 62 is connected to the usage-side control unit 64 of the usage unit 50 via the transmission line 66 so as to be able to exchange control signals and the like. The heat source-side control unit 62 and the usage-side control unit 64 function as the control unit 60 that cooperatively controls the entire operation of the air conditioning apparatus 100. The control unit 60 will be described later.

(2-3) Refrigerant connection pipe

The air conditioning apparatus 100 includes the liquid refrigerant connection pipe 2 and the gas refrigerant connection pipe 4 as refrigerant connection pipes. The liquid refrigerant connection pipe 2 and the gas refrigerant connection pipe 4 are pipes installed at an installation site of the air conditioning apparatus 100 when the air conditioning apparatus 100 is installed. The usage-side refrigerant circuit 10a of the usage unit 50 and the heat source-side refrigerant circuit 10b of the heat source unit 20 are connected by the liquid refrigerant connection pipe 2 and the gas refrigerant connection pipe 4 to constitute the refrigerant circuit 10 of the air conditioning apparatus 100.

(2-4) Control unit

The control unit 60 is configured by communicably connecting the heat source-side control unit 62 of the heat source unit 20 and the usage-side control unit 64 of the usage unit 50 via the transmission line 66. The control unit 60 controls the entire operation of the air conditioning apparatus 100 by the microcomputers of the heat source-side control unit 62 and the usage-side control unit 64 executing programs stored in the memory. FIG. 2 is a control block diagram of the control unit 60.
Note that in the present embodiment, the heat source-side control unit 62 and the usage-side control unit 64 constitute the control unit 60, but the configuration of the control unit 60 is not limited to such a form.
For example, in addition to the heat source-side control unit 62 and the usage-side control unit 64, or instead of the heat source-side control unit 62 and the usage-side control unit 64, the air conditioning apparatus 100 may include a control device that implements some or all of the functions of the control unit 60 described below. The control device may be a device dedicated to control the air conditioning apparatus 100 or a device that controls a plurality of air conditioning apparatuses including the air conditioning apparatus 100. The control device may be a server installed in a place different from a place where the air conditioning apparatus 100 is installed.
As illustrated in FIGS. 1 and 2, the control unit 60 is electrically connected to various devices of the heat source unit 20 including the compressor 21, the flow direction switching mechanism 22, the expansion mechanism 25, the heat source-side fan 28, and the usage-side fan 53, and the usage unit 50. Furthermore, as illustrated in FIGS. 1 and 2, the control unit 60 is electrically connected to the various sensors 30 to 36 provided in the heat source unit 20 and the various sensors 54 to 57 provided in the usage unit 50.
The control unit 60 controls the operation and stop of the air conditioning apparatus 100 and the operations of the various devices 21, 22, 25, 28, and 53 of the air conditioning apparatus 100 on the basis of measurement signals of the various sensors 30 to 36 and 54 to 57, commands received by the usage-side control unit 64 from a remote controller (not illustrated), and the like.

(2-5) Operation of air conditioning apparatus

The control of an operation of the air conditioning apparatus 100 during the cooling operation, the heating operation, and the refrigerant discharge operation will be described.

(2-5-1) Operation during cooling operation

When the execution of the cooling operation is instructed to the air conditioning apparatus 100, the control unit 60 sets the operating mode of the air conditioning apparatus 100 to the cooling operating mode. The control unit 60 controls the flow direction switching mechanism 22 to a state indicated by the solid line in FIG. 1 to operate the compressor 21, the heat source-side fan 28, and the usage-side fan 53 such that the refrigerant circuit 10 is in the first state described above.
During the cooling operation, the control unit 60 controls the devices of the air conditioning apparatus 100 as follows, for example. Note that the control of the operation of the air conditioning apparatus 100 during the cooling operation described here is an example, and does not limit a method of controlling the air conditioning apparatus 100 during the cooling operation by the control unit 60. For example, the control unit 60 may control the operation of various devices on the basis of variables other than those described here.
The control unit 60 controls the number of rotations of the motor 28a that drives the heat source-side fan 28 and the number of rotations of the motor 53a that drives the usage-side fan 53 to predetermined numbers of rotations. For example, the control unit 60 controls the number of rotations of the motor 28a to the maximum number of rotations. The control unit 60 appropriately controls the number of rotations of the motor 53a based on an air volume instruction input to the remote controller.
The control unit 60 adjusts an opening degree of the electronic expansion valve, which is an example of the expansion mechanism 25, so that a degree of superheating SHr of the refrigerant at a gas side outlet of the usage-side heat exchanger 52 becomes a predetermined target degree of superheating SHrs.
The control unit 60 controls an operating capacity of the compressor 21 such that the evaporation temperature Te approaches a predetermined target evaporation temperature Tes. The operating capacity of the compressor 21 is controlled by controlling the number of rotations of the motor 21a.
When the operation of the devices of the air conditioning apparatus 100 is controlled as described above during the cooling operation, the refrigerant flows through the refrigerant circuit 10 as follows.
When the compressor 21 is started, the low-pressure gas refrigerant in the refrigeration cycle is sucked into the compressor 21 and compressed by the compressor 21 to become a high-pressure gas refrigerant in the refrigeration cycle. The high-pressure gas refrigerant is sent to the heat source-side heat exchanger 23 via the flow direction switching mechanism 22, exchanges heat with the heat source air supplied by the heat source-side fan 28, and is condensed into a high-pressure liquid refrigerant. The high-pressure liquid refrigerant flows through the liquid refrigerant pipe 12d, is decompressed to a pressure close to a suction pressure of the compressor 21 in the expansion mechanism 25, becomes a refrigerant in a gas-liquid two-phase state, and is sent to the usage unit 50. The refrigerant in the gas-liquid two-phase state sent to the usage unit 50 exchanges heat with air in the air conditioning target space supplied to the usage-side heat exchanger 52 by the usage-side fan 53 in the usage-side heat exchanger 52 and evaporates to become a low-pressure gas refrigerant. The low-pressure gas refrigerant is sent to the heat source unit 20 via the gas refrigerant connection pipe 4, and flows into the accumulator 24 via the flow direction switching mechanism 22. The low-pressure gas refrigerant flowing into the accumulator 24 is again sucked into the compressor 21. On the other hand, a temperature of the air supplied to the usage-side heat exchanger 52 decreases by heat exchange with the refrigerant flowing through the usage-side heat exchanger 52, and the air cooled by the usage-side heat exchanger 52 is blown out into the air conditioning target space.

(2-5-2) Operation during heating operation

When execution of the heating operation is instructed to the air conditioning apparatus 100, the control unit 60 sets the operating mode of the air conditioning apparatus 100 to the heating operating mode. The control unit 60 controls the flow direction switching mechanism 22 to a state indicated by the broken line in FIG. 1 to operate the compressor 21, the heat source-side fan 28, and the usage-side fan 53 such that the refrigerant circuit 10 is in the above-described second state.
During the heating operation, the control unit 60 controls the devices of the air conditioning apparatus 100 as follows, for example. The control of the operation of the air conditioning apparatus 100 during the heating operation described herein is an example, and does not limit a method of controlling the air conditioning apparatus 100 during the heating operation by the control unit 60. For example, the control unit 60 may control the operation of various devices on the basis of variables other than those described here.
The control unit 60 controls the number of rotations of the motor 28a that drives the heat source-side fan 28 and the number of rotations of the motor 53a that drives the usage-side fan 53 to predetermined numbers of rotations. For example, the control unit 60 controls the number of rotations of the motor 28a to the maximum number of rotations. The control unit 60 appropriately controls the number of rotations of the motor 53a based on an air volume instruction input to the remote controller.
The control unit 60 adjusts an opening degree of the electronic expansion valve, which is an example of the expansion mechanism 25, so that the degree of subcooling SCr of the refrigerant at a liquid side outlet of the usage-side heat exchanger 52 becomes a predetermined target degree of subcooling SCrs.
The control unit 60 controls an operating capacity of the compressor 21 such that the condensation temperature Tc approaches a predetermined target condensation temperature Tcs. The operating capacity of the compressor 21 is controlled by controlling the number of rotations of the motor 21a.
When the operation of the devices of the air conditioning apparatus 100 is controlled as described above during the heating operation, the refrigerant flows through the refrigerant circuit 10 as follows.
When the compressor 21 is started, the low-pressure gas refrigerant in the refrigeration cycle is sucked into the compressor 21 and compressed by the compressor 21 to become a high-pressure gas refrigerant in the refrigeration cycle. The high-pressure gas refrigerant is sent to the usage-side heat exchanger 52 via the flow direction switching mechanism 22, exchanges heat with the air in the air conditioning target space supplied by the usage-side fan 53, and is condensed into a high-pressure liquid refrigerant. A temperature of the air supplied to the usage-side heat exchanger 52 is increased by heat exchange with the refrigerant flowing through the usage-side heat exchanger 52, and the air heated by the usage-side heat exchanger 52 is blown into the air conditioning target space. The high-pressure liquid refrigerant flowing out of the usage-side heat exchanger 52 is sent to the heat source unit 20 via the liquid refrigerant connection pipe 2, and flows into the liquid refrigerant pipe 12d. The refrigerant flowing through the liquid refrigerant pipe 12d is decompressed to a pressure close to a suction pressure of the compressor 21 when passing through the expansion mechanism 25, becomes a refrigerant in a gas-liquid two-phase state, and flows into the heat source-side heat exchanger 23. The low-pressure refrigerant in the gas-liquid two-phase state that has flowed into the heat source-side heat exchanger 23 exchanges heat with the heat source air supplied by the heat source-side fan 28, evaporates to become a low-pressure gas refrigerant, and flows into the accumulator 24 via the flow direction switching mechanism 22. The low-pressure gas refrigerant flowing into the accumulator 24 is again sucked into the compressor 21.
Note that when the operating mode of the air conditioning apparatus 100 is the heating operating mode, the control unit 60 temporarily interrupts the heating operation, temporarily switches the state of the refrigerant circuit 10 to the first state, and performs a so-called reverse cycle defrost operation. Since the defrost operation is generally known, a detailed description thereof will be omitted here.

(2-5-3) Operation during refrigerant discharge operation

(2-5-3-1) Control flow

When the air conditioning apparatus 100 is instructed to execute the cooling operation or the heating operation, the control unit 60 starts the refrigerant discharge operation simultaneously with the cooling operation or the heating operation. FIG. 3 is a flowchart illustrating a control flow of the refrigerant discharge operation executed by the control unit 60. The control flow illustrated in FIG. 3 ends when the operation of the air conditioning apparatus 100 ends.
In step S 100, the control unit 60 determines whether or not the refrigerant circuit 10 is in a low-load state with a low air conditioning load. When determining that the refrigerant circuit is in the low-load state (Yes), the control unit 60 proceeds to step S110. The control unit 60 repeats step S 100 unless determining that the refrigerant circuit 10 is in the low-load state. A criterion by which the control unit 60 determines that the refrigerant circuit 10 is in the low-load state will be described later.
In step S 110, the control unit 60 detects the number of rotations of the compressor 21, and determines whether or not the number of rotations is less than or equal to a predetermined number of rotations R1. When determining that the number of rotations of the compressor 21 is less than or equal to the number of rotations R1 (Yes), the control unit 60 proceeds to step S120. When determining that the number of rotations of the compressor 21 is not less than or equal to the number of rotations R1 (No), the control unit 60 proceeds to step S100.
The number of rotations R1 is a number of rotations at which the refrigerant condensed in the heat source-side heat exchanger 23 cannot be discharged due to the pressure of the refrigerant generated by the compressor 21 in a case where the compressor 21 rotates at a number of rotations less than the number of rotations R1. The number of rotations R1 is, for example, in a range of 1200 rpm or more and 1800 rpm or less (corresponding to 20 Hz or more and 30 Hz or less at an operating frequency). Note that hereinafter, for the sake of convenience, a state in which the refrigerant circuit 10 is in a low-load state and the compressor 21 operates at the number of rotations R1 or less is referred to as a low-load operation.
In step S120, the control unit 60 interrupts the cooling operation or the heating operation being executed, starts execution of first control, and proceeds to step S130.
The first control temporarily increases the pressure of the refrigerant flowing through the heat source-side heat exchanger 23 during the low-load operation. Specifically, in this step, the control unit 60 increases the number of rotations of the compressor 21 to a predetermined number of rotations R2 larger than the number of rotations of the compressor 21 detected in step S 110. Here, the number of rotations R2 is a number of rotations at which the refrigerant condensed in the heat source-side heat exchanger 23 can be discharged by the pressure of the refrigerant generated by the compressor 21, and is, for example, 1800 rpm or more (corresponding to 30 Hz at an operating frequency).
In step S130, the control unit 60 starts execution of second control and proceeds to step S140.
The second control is control to make an opening degree of the expansion mechanism 25 larger than the opening degree in step S 110 in the low-load operation.
In step S140, the control unit 60 determines whether or not the first control has been executed over a predetermined first time period. When determining that the first control has been executed over the first time period (Yes), the control unit 60 proceeds to step S150. When it is not determined that the first control has been executed over the first time period (No), the control unit 60 repeats step S140.
The first time period is a time period during which the first control and the second control are executed, whereby the refrigerant condensed in the heat source-side heat exchanger 23 can be discharged, and the comfort in the target space is hardly impaired even if the cooling operation or the heating operation is stopped. The first time period is, for example, 10 seconds or more and 5 minutes or less.
In step S150, the control unit 60 ends the first control and the second control, restarts the cooling and heating operation or the heating operation interrupted in step S120, and proceeds to step S160. In other words, in step S150, the control unit 60 returns the various devices of the air conditioning apparatus 100 to the state before the cooling operation or the heating operation is interrupted in step S120.
In step S160, the control unit 60 determines whether or not a predetermined second time period has elapsed since the end of the first control. When determining that the predetermined second time period has elapsed since the end of the first control (Yes), the control unit 60 proceeds to step S100. When determining that the predetermined second time period has not elapsed since the end of the first control (No), the control unit 60 repeats step S160.
The second time period is a shortest interval in a case where the first control and the second control are repeatedly executed, and is set to a time period in which the comfort in the target space is hardly impaired even in a case where the first control and the second control are repeatedly executed. The second time period is, for example, 10 minutes or more.

(2-5-3-2) Criteria for determination of low-load state

The control unit 60 can determine that the refrigerant circuit 10 is in the low-load state with a low air conditioning load based on at least one of a first criterion to a fifth criterion described below. The control unit 60 may make a determination by appropriately combining the first criterion to the fifth criterion.

(First criterion)

The control unit 60 can determine that the refrigerant circuit 10 is in the low-load state on the basis of the first criterion that a difference between the heat source air temperature Tha and the heat source refrigerant temperature Thr is less than or equal to a predetermined first temperature difference Tg1. The first temperature difference Tg1 is, for example, 2°C.
The heat source air temperature Tha is a temperature of the heat source air that exchanges heat with the refrigerant in the heat source-side heat exchanger 23. The heat source air temperature Tha is measured by the heat source air temperature sensor 36. The heat source air temperature Tha is an example of the first temperature.
The heat source refrigerant temperature Thr is a temperature of the refrigerant flowing through the heat source-side heat exchanger 23. The heat source refrigerant temperature Thr is measured by the heat exchange temperature sensor 34. The heat source refrigerant temperature Thr is an example of the second temperature.

(Second criterion)

The control unit 60 can determine that the refrigerant circuit 10 is in the low-load state based on the second criterion that a difference between a use refrigerant temperature Tar and the heat source refrigerant temperature Thr is less than or equal to a predetermined second temperature difference Tg2. The second temperature difference Tg2 is, for example, 5°C.
The use refrigerant temperature Tar is a temperature of the refrigerant flowing through the usage-side heat exchanger 52. The use refrigerant temperature Tar is measured by the heat exchange temperature sensor 57. The use refrigerant temperature Tar is an example of the third temperature.
The control unit 60 may use a first estimated use refrigerant temperature Tare 1 instead of the use refrigerant temperature Tar to the determination in the second criterion. The first estimated use refrigerant temperature Tare1 is an estimated temperature of the refrigerant flowing through the usage-side heat exchanger 52 calculated based on the heat source air temperature Tha. The first estimated use refrigerant temperature Tare1 is an example of the first estimated temperature.

(Third criterion)

The control unit 60 determines that the refrigerant circuit 10 is in the low-load state on the basis of a third criterion that a difference between the use refrigerant temperature Tar and the heat source air temperature Tha is less than or equal to a predetermined third temperature difference Tg3. The third temperature difference Tg3 is, for example, 2°C.
The control unit 60 may use a second estimated use refrigerant temperature Tare2 instead of the use refrigerant temperature Tar to the determination in the third criterion. The second estimated use refrigerant temperature Tare2 is an estimated temperature of the refrigerant flowing through the usage-side heat exchanger 52 calculated based on the number of rotations of the compressor 21. The second estimated use refrigerant temperature Tare2 is an example of the second estimated temperature.

(Fourth criterion)

The control unit 60 determines that the refrigerant circuit 10 is in the low-load state on the basis of a fourth criterion that a difference between the heat source air temperature Tha and a space temperature Tr is less than or equal to a predetermined fourth temperature difference Tg4. The fourth temperature difference Tg4 is, for example, 2°C.
The space temperature Tr is a temperature in the target space. The space temperature Tr is measured by the spatial temperature sensor 56. The space temperature Tr is an example of the sixth temperature.

(Fifth criterion)

The control unit 60 determines that the refrigerant circuit 10 is in the low-load state based on the fifth criterion that the number of rotations of the compressor 21 is less than or equal to a predetermined number of rotations. The predetermined number of rotations is 1200 rpm (corresponding to 20 Hz at an operating frequency).

(3) Characteristics

(3-1)
The air conditioning apparatus 100 performs air conditioning of the target space. The air conditioning apparatus 100 includes the refrigerant circuit 10 and the control unit 60. The refrigerant circuit 10 includes the compressor 21, the heat source-side heat exchanger 23, the expansion mechanism 25, the usage-side heat exchanger 52, and the flow direction switching mechanism 22. The control unit 60 controls the compressor 21 and the flow direction switching mechanism 22. The control unit 60 executes the first control for temporarily increasing the pressure of the refrigerant flowing through the heat source-side heat exchanger 23 during the low-load operation in which the refrigerant circuit 10 is in the low-load state with a low air conditioning load and the compressor 21 operates at a predetermined number of rotations or less.
According to the air conditioning apparatus 100, since the pressure of the refrigerant flowing through the heat source-side heat exchanger 23 temporarily increases by executing the first control during the low-load operation, evaporation of the condensed refrigerant is promoted, and the condensed refrigerant is pushed out from the heat source-side heat exchanger 23 and discharged. As a result, a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger 23 can be suppressed.
(3-2)
In the first control, the control unit 60 increases the pressure of the refrigerant flowing through the heat source-side heat exchanger 23 by increasing the number of rotations of the compressor 21.
As a result, a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger 23 can be suppressed by simple control of increasing the number of rotations of the compressor 21.
(3-3)
The control unit 60 further executes the second control for increasing the opening degree of the expansion mechanism 25 in the low-load operation.
As a result, the opening degree of the expansion mechanism 25 increases during the execution of the first control, and a large amount of the refrigerant can flow out of the heat source-side heat exchanger 23. Therefore, the refrigerant in the heat source-side heat exchanger 23 is easily pushed out, and a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger 23 can be effectively suppressed.
(3-4)
The control unit 60 executes the first control for a predetermined first time period. The first time period is 10 seconds or more and 5 minutes or less.
As a result, the first time period is executed for a long time, and the execution of the cooling operation or the heating operation is suppressed from being interrupted.
(3-5)
The control unit 60 executes the first control at an interval longer than or equal to a second time period longer than the first time period.
As a result, it is possible to prevent the first time period from being frequently executed and prevent the execution of the cooling operation or the heating operation.

(4) Modification examples

(4-1) Modification example 1A

In the air conditioning apparatus 100, the control unit 60 temporarily increases the pressure of the refrigerant flowing through the heat source-side heat exchanger 23 by increasing the number of rotations of the compressor 21 in the first control. However, the first control is not limited to this as long as the pressure of the refrigerant flowing through the heat source-side heat exchanger 23 can be temporarily increased. For example, the control unit 60 may stop the heat source-side fan 28 in the first control. The control unit 60 stops the heat source-side fan 28 to suppress heat exchange between the refrigerant in the heat source-side heat exchanger 23 and the air outside the heat source-side heat exchanger 23. As a result, since the pressure of the refrigerant flowing through the heat source-side heat exchanger temporarily increases, evaporation of the condensed refrigerant is promoted, and the condensed refrigerant is pushed out from the heat source-side heat exchanger 23 and discharged.
As a result, a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger 23 can be suppressed by simple control of stopping the heat source-side fan 28.
In the first control, the control unit 60 may simultaneously increase the number of rotations of the compressor 21 and stop the heat source-side fan 28.

(4-2) Modification example 1B

In the air conditioning apparatus 100, the first time period or the second time period may be variable. For example, the control unit 60 may determine the first time period or the second time period based on the number of rotations of the compressor 21.
Specifically, the control unit 60 can shorten the first time period and lengthen the second time period as the number of rotations of the compressor 21 increases. It is assumed that the refrigerant circuit 10 has a higher load as the number of rotations of the compressor 21 increases, and an amount of the condensed refrigerant accumulated in the heat source-side heat exchanger 23 is smaller. Therefore, in such a case, by shortening the time during which the first control and the second control are executed, it is possible to suppress impairment of comfort in the target space due to the execution of the refrigerant discharge operation.
As a result, it is possible to suppress impairment of comfort in the target space while suppressing a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger 23.

(4-3) Modification example 1C

The control unit 60 may determine the first time period or the second time period based on the heat source air temperature Tha.
Specifically, the control unit 60 can shorten the first time period and lengthen the second time period as the heat source air temperature Tha, which is a temperature of the heat source air that exchanges heat with the refrigerant in the heat source-side heat exchanger 23, is higher. It is assumed that the refrigerant circuit 10 has a higher load as the heat source air temperature Tha is higher, and an amount of the condensed refrigerant accumulated in the heat source-side heat exchanger 23 is smaller. Therefore, in such a case, by shortening the time during which the first control and the second control are executed, it is possible to suppress impairment of comfort in the target space due to the execution of the refrigerant discharge operation.
As a result, it is possible to suppress impairment of comfort in the target space while suppressing a phenomenon in which the condensed refrigerant accumulates in the heat source-side heat exchanger 23.

(4-4) Modification example D

In the refrigeration cycle apparatus, the control unit 60 executes the first control and the second control, but the control unit 60 may omit the execution of the second control.
Although the embodiments of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the present disclosure described in the claims.

REFERENCE SIGNS LIST

10: Refrigerant circuit
21: Compressor
22: Flow direction switching mechanism
23: Heat source-side heat exchanger
25: Expansion mechanism
28: Heat source-side fan
52: Usage-side heat exchanger
60: Control unit
100: Air conditioning apparatus

CITATION LIST

PATENT LITERATURE

Patent Literature 1: JP 2007-212078 A

Claims

A refrigeration cycle apparatus (100) that performs air conditioning of a target space, the refrigeration cycle apparatus comprising:
a refrigerant circuit (10) including a compressor (21), a heat source-side heat exchanger (23), an expansion mechanism (25), a usage-side heat exchanger (52), and a flow direction switching mechanism (22); and

a control unit (60) that controls the compressor and the flow direction switching mechanism, wherein

the control unit executes first control of temporarily increasing a pressure of a refrigerant flowing through the heat source-side heat exchanger in a low-load operation in which the refrigerant circuit is in a low-load state with a low air conditioning load and the compressor operates at a predetermined number of rotations or less.
The refrigeration cycle apparatus according to claim 1, wherein
the control unit increases a pressure of the refrigerant flowing through the heat source-side heat exchanger by increasing a number of rotations of the compressor in the first control.
The refrigeration cycle apparatus according to claim 1 or 2, further comprising a heat source-side fan (28) that blows air to the heat source-side heat exchanger, wherein
the control unit, in the first control, increases a pressure of the refrigerant flowing through the heat source-side heat exchanger by stopping the heat source-side fan.
The refrigeration cycle apparatus according to any one of claims 1 to 3, wherein
the control unit, in the low-load operation, further executes second control of increasing an opening degree of the expansion mechanism during execution of the first control.
The refrigeration cycle apparatus according to any one of claims 1 to 4, wherein
the control unit executes the first control over a predetermined first time period, and

the first time period is 10 seconds or more and 5 minutes or less.
The refrigeration cycle apparatus according to claim 5, wherein
the control unit executes the first control at an interval of a second time period or more longer than the first time period.
The refrigeration cycle apparatus according to claim 6, wherein
the control unit determines the first time period or the second time period based on a number of rotations of the compressor.
The refrigeration cycle apparatus according to claim 6 or 7, wherein
the control unit determines the first time period or the second time period based on a first temperature (Tha) that is a temperature of heat source air for heat exchange with a refrigerant in the heat source-side heat exchanger.
The refrigeration cycle apparatus according to any one of claims 1 to 8, wherein
the control unit determines that the refrigerant circuit is in the low-load state when a difference between a first temperature that is a temperature of heat source air for heat exchange with a refrigerant in the heat source-side heat exchanger and a second temperature (Thr) that is a temperature of the refrigerant flowing through the heat source-side heat exchanger is less than or equal to a predetermined first temperature difference (Tg1).
The refrigeration cycle apparatus according to any one of claims 1 to 9, wherein
the control unit determines that the refrigerant circuit is in the low-load state when a difference between a first estimated temperature (Tare1) of a refrigerant flowing through the usage-side heat exchanger calculated based on a first temperature that is a temperature of heat source air for heat exchange with the refrigerant in the heat source-side heat exchanger, or a third temperature (Tar) that is a temperature of the refrigerant flowing through the usage-side heat exchanger, and the second temperature is less than or equal to a predetermined second temperature difference (Tg2).
The refrigeration cycle apparatus according to any one of claims 1 to 10, wherein
the control unit determines that the refrigerant circuit is in the low-load state when a difference between a third temperature (Tar) that is a temperature of the refrigerant flowing through the usage-side heat exchanger, or a second estimated temperature (Tare2) of the refrigerant flowing through the usage-side heat exchanger calculated based on a number of rotations of the compressor, and a first temperature that is a temperature of heat source air for heat exchange with the refrigerant in the heat source-side heat exchanger is less than or equal to a predetermined third temperature difference (Tg3).
The refrigeration cycle apparatus according to any one of claims 1 to 11, wherein
the control unit determines that the refrigerant circuit is in the low-load state when a difference between a first temperature that is a temperature of heat source air for heat exchange with a refrigerant in the heat source-side heat exchanger and a sixth temperature (Tr) that is a temperature in the target space is less than or equal to a predetermined fourth temperature difference (Tg4).
The refrigeration cycle apparatus according to any one of claims 1 to 12, wherein
the control unit determines that the refrigerant circuit is in the low-load state when a number of rotations of the compressor is less than or equal to a predetermined number of rotations.