WO2022168305A1 - Air-conditioning device - Google Patents

Abstract

This air conditioning device includes: an air supply fan and an air supply path; an air return fan and an air return path; and a heat pump circuit. A first heat exchanger is disposed in the air return path, and a second heat exchanger and a third heat exchanger are disposed in the air supply path. The air conditioning device has, as operation modes, a cooling operation mode for indoor cooling and a dehumidifying operation mode for indoor dehumidifying. In the dehumidifying operation mode and the cooling operation mode, refrigerant flows through refrigerant piping in a direction of refrigerant discharged from a compressor flowing into the first heat exchanger and refrigerant flowing out from the third heat exchanger being taken into the compressor. In the cooling operation mode, the first heat exchanger acts as a condenser and the second heat exchanger and the third heat exchanger act as evaporators. In the dehumidifying operation mode, the first heat exchanger and the second heat exchanger act as condensers, and the third heat exchanger acts as an evaporator.

Description

air conditioner

The present disclosure relates to an air conditioner having a dehumidifying operation mode and a cooling operation mode.

For example, in a conventional outdoor air conditioner that ventilates a room, a heat pump circuit is known that uses a heat exchanger to recover heat from return air returning from the room to the outside. In the refrigerant flow of the heat pump circuit, high-temperature and high-pressure gas refrigerant discharged from the compressor mounted on the outdoor unit flows into the heat exchanger mounted on the indoor unit. Since the heat exchanger functions as a condenser, the inflow refrigerant is condensed in the heat exchanger to become liquid refrigerant. After that, the liquid refrigerant is depressurized by the expansion valve, and becomes a gas-liquid two-phase state in which gas refrigerant and liquid refrigerant are mixed. Then, the gas-liquid two-phase refrigerant flows into a heat exchanger mounted on the outdoor unit and functioning as an evaporator. In the heat exchanger, the liquid refrigerant of the gas-liquid two-phase refrigerant is evaporated to become a low-pressure gas refrigerant. Thereafter, the gas refrigerant sent out from the heat exchanger flows into the compressor, is compressed by the compressor, becomes high-temperature and high-pressure gas refrigerant, and is discharged from the compressor again. This cycle is then repeated.

Also, to explain the air flow, the outside air conditioner takes in outside air from the outside with a fan, cools or heats it with a heat exchanger, and supplies it to the room. Also, the outdoor air conditioner takes in return air from the room, cools or heats it with a heat exchanger, and exhausts it to the outside.

By the way, such an outside air conditioner often introduces outside air into a room maintained at an appropriate temperature by a separately installed room air circulation type air conditioner. At this time, the outdoor air conditioner adjusts the temperature and humidity of the outdoor air so that the temperature and humidity of the outdoor air are close to those of the indoor air, thereby supplying comfortable and hygienic air to the user. For this reason, outdoor air conditioners with multiple operation modes, such as an operation mode that cools and dehumidifies according to the difference in temperature and humidity between indoors and outdoors, and an operation mode that only dehumidifies and maintains a constant temperature, are known. It is

For example, the ventilation air conditioner described in Patent Document 1 is an air conditioner that has such an outside air conditioner function. The air conditioner described in Patent Document 1 has a refrigerant circuit in which the circulation direction of the refrigerant can be switched by operating a four-way valve and a solenoid valve in order to achieve both temperature control and humidity control, and an air circulation path. A plurality of operation modes are realized by using a switching device for switching.

JP 2009-58175 A

However, in the air conditioner of Patent Document 1, the circulation direction of the refrigerant is switched when switching from the cooling operation to the dehumidifying operation. Therefore, the refrigerant pressure in the heat exchanger greatly fluctuates with the switching of the circulation direction. As a result, the temperature fluctuation of the supplied air supplied from the air conditioner to the room becomes discontinuous, and the user's comfort is reduced. In addition, since it has a function of switching the circulation direction of the refrigerant and a function of switching the air circulation path, it requires a large number of driving units, which increases the possibility of functional loss due to failure of the driving units.

The present disclosure has been made to solve the above problems, and has a simple configuration that does not require switching of refrigerant flow paths when switching between cooling operation and dehumidifying operation, and when switching between cooling operation and dehumidifying operation. An object of the present invention is to provide an air conditioner capable of supplying comfortable air to a user by suppressing fluctuations in supply air temperature.

An air conditioner according to the present disclosure includes an air supply fan and an air supply path for supplying outdoor air to a room, a return air fan and a return air path for returning the indoor air to the outdoor, a compressor, A heat pump circuit in which a first heat exchanger, a second heat exchanger, a throttle device, and a third heat exchanger are connected in this order by refrigerant piping, the supply air fan, the return air fan, and the heat pump circuit. and a control unit that controls operation, wherein the first heat exchanger is arranged in the return air path, and the refrigerant and the return air flowing inside the first heat exchanger are arranged in the return air path. The second heat exchanger and the third heat exchanger are arranged in the air supply path, and the second heat exchanger and the third heat exchanger are arranged in the air supply path, respectively. Heat is exchanged between the refrigerant flowing inside the heat exchanger and the air flowing inside the air supply path, and the air conditioner has two operation modes, one for cooling the room and one for dehumidifying the room. and a dehumidifying operation mode, wherein in the dehumidifying operation mode and the cooling operation mode, the refrigerant discharged from the compressor flows into the first heat exchanger, and the refrigerant flowing out of the third heat exchanger is Refrigerant flows through the refrigerant pipe in the direction of being sucked into the compressor, and in the cooling operation mode, the first heat exchanger acts as a condenser, and the second heat exchanger and the third heat exchanger acts as an evaporator, and in the dehumidifying operation mode, the first heat exchanger and the second heat exchanger act as condensers, and the third heat exchanger acts as an evaporator.

According to the air conditioner according to the present disclosure, it is possible to continuously switch between the dehumidifying operation mode and the cooling operation mode with a simple configuration that does not require switching of the refrigerant flow path when switching between the cooling operation and the dehumidifying operation. can. As a result, fluctuations in the supply air temperature can be suppressed, and user comfort can be improved.

1 is a refrigerant circuit diagram showing an example of the configuration of an air conditioner 200 according to Embodiment 1. FIG. FIG. 4 is an explanatory diagram illustrating the flow of refrigerant and the flow of air in the cooling operation mode of the air-conditioning apparatus 200 according to Embodiment 1; 4 is a Mollier diagram showing refrigerant states in the cooling operation mode of the air-conditioning apparatus 200 according to Embodiment 1. FIG. 4 is a flowchart showing the operation of the control unit 90 in the cooling operation mode of the air conditioner 200 according to Embodiment 1. FIG. FIG. 4 is an explanatory diagram illustrating the flow of refrigerant and the flow of air in the dehumidifying operation mode of the air-conditioning apparatus 200 according to Embodiment 1; 4 is a Mollier diagram showing refrigerant states in the dehumidifying operation mode of the air-conditioning apparatus 200 according to Embodiment 1. FIG. 4 is a flow chart showing the operation of the control unit 90 in the dehumidifying operation mode in the air conditioner 200 according to Embodiment 1. FIG. 4 is an explanatory diagram showing operation mode switching operation based on the opening degree OP of the expansion device 17 in the air conditioner 200 according to Embodiment 1. FIG. 4 is a flowchart showing operation mode switching operation of the control unit 90 in the air conditioner 200 according to Embodiment 1. FIG. 2 is a side view showing the configuration of heat transfer tubes of first heat exchanger 11 and second heat exchanger 12 in air-conditioning apparatus 200 according to Embodiment 1. FIG. 2 is a plan view illustrating an example of the arrangement of second heat exchanger 12 and third heat exchanger 13 in air-conditioning apparatus 200 according to Embodiment 1. FIG. 4 is a side view illustrating a modification of the arrangement of the second heat exchanger 12 and the third heat exchanger 13 in the air conditioner 200 according to Embodiment 1. FIG. FIG. 7 is a refrigerant circuit diagram showing an example of the configuration of an air conditioner 200B according to Embodiment 2; 9 is a flow chart showing the operation of the control unit 90 in the air conditioner 200B according to Embodiment 2. FIG. FIG. 11 is a refrigerant circuit diagram showing an example of the configuration of an air conditioner 200C according to Embodiment 3; 2 is a refrigerant circuit diagram showing an example of the configuration of an air conditioner 200A that is a modification of the air conditioner 200 according to Embodiment 1. FIG.

An embodiment of an air conditioner according to the present disclosure will be described below with reference to the drawings. The present disclosure is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present disclosure. In addition, the present disclosure includes all combinations of configurations that can be combined among configurations shown in the following embodiments and modifications thereof. Also, in each figure, the same reference numerals denote the same or corresponding parts, which are common throughout the specification. In each drawing, the relative dimensional relationship, shape, etc. of each component may differ from the actual one.

Embodiment 1.
[Configuration of air conditioner 200]
First, the configuration of the air conditioner 200 according to Embodiment 1 will be described. FIG. 1 is a refrigerant circuit diagram showing an example of the configuration of an air conditioner 200 according to Embodiment 1. As shown in FIG. In Embodiment 1, the air conditioner 200 functions as an outdoor air conditioner that ventilates a room, for example. The air conditioner 200 has a cooling operation mode and a dehumidification operation mode as operation modes.

As shown in FIG. 1, the air conditioner 200 is installed, for example, at the boundary between an indoor space 300 and an outdoor space 301 . A room 300 is a space to be air-conditioned by the air conditioner 200 . The air conditioner 200 may be installed indoors 300 .

The air conditioner 200 includes a heat pump circuit including a compressor 16, an expansion device 17, a first heat exchanger 11, a second heat exchanger 12, and a third heat exchanger 13. Compressor 16, first heat exchanger 11, second heat exchanger 12, expansion device 17, and third heat exchanger 13 are connected by refrigerant pipe 18 to form a refrigerant circuit.

In the air conditioner 200, the refrigerant flows in the same direction in the cooling operation mode and the dehumidifying operation mode. Specifically, in the cooling operation mode and the dehumidifying operation mode, the refrigerant is flow in order.

As shown in FIG. 1 , the air conditioner 200 includes an air supply path 19 and an air supply fan 14 for supplying air from the outdoor 301 to the indoor 300 . The air supply fan 14 is arranged in the air supply path 19 . The air conditioner 200 also includes a return air path 20 and a return air fan 15 for returning the air in the room 300 to the outside 301 . The return air fan 15 is arranged in the return air path 20 . These components will be described below with reference to FIG.

The four arrows in FIG. 1 respectively indicate the ventilation directions of the outside air OA, the supply air SA, the return air RA, and the exhaust air EA. The outside air OA is air supplied from the outdoor 301 to the second heat exchanger 12 and the third heat exchanger 13 by the air supply fan 14, and flows in the air supply path 19 in the direction from the outdoor 301 to the indoor 300. . In addition, the supply air SA is the air supplied from the second heat exchanger 12 and the third heat exchanger 13 to the room 300 by the supply fan 14, and is directed in the air supply path 19 from the outdoor 301 to the indoor 300. flow to The return air RA is air supplied from the room 300 to the first heat exchanger 11 by the return air fan 15 and flows in the return air path 20 in the direction from the room 300 to the outside 301 . The exhaust EA is air that is discharged from the first heat exchanger 11 to the outdoor 301 by the return air fan 15 , and flows in the return air path 20 in the direction from the indoor 300 to the outdoor 301 .

The air supply path 19 is an air path that connects the outdoor 301 and the indoor 300 . The air supply path 19 is composed of, for example, a duct. The air supply fan 14 is provided in the air supply path 19 and blows air from the outdoor 301 to the indoor 300 . The air supply fan 14 supplies the outside air OA to the second heat exchanger 12 and the third heat exchanger 13 .

The return air path 20 is an air path that connects the indoor 300 and the outdoor 301 . The return air path 20 is composed of, for example, a duct. The return air fan 15 is provided in the return air path 20 and blows air from the indoor 300 to the outdoor 301 . The return air fan 15 supplies the return air RA to the first heat exchanger 11 .

The form of the supply air fan 14 and the return air fan 15 may be any of a centrifugal fan, an axial flow fan, and a cross flow fan. may be Also, the air supply fan 14 may be located upstream or downstream of the second heat exchanger 12 and the third heat exchanger 13 . Similarly, the return air fan 15 may be upstream or downstream of the first heat exchanger 11 .

The compressor 16 has a suction port and a discharge port. The compressor 16 sucks the refrigerant through the suction port, compresses the refrigerant, and discharges the compressed refrigerant through the discharge port. The compressor 16 can be configured by, for example, a rotary compressor, a scroll compressor, a screw compressor, or a reciprocating compressor. When the compressor 16 is an inverter compressor, the operating frequency may be arbitrarily changed by an inverter circuit or the like to change the refrigerant delivery capacity of the compressor 16 per unit time. In that case, the operating frequency of the compressor 16 is controlled by the controller 90, which will be described later.

The first heat exchanger 11 is connected to the discharge port of the compressor 16 via refrigerant piping 18 . High-temperature, high-pressure refrigerant discharged from the compressor 16 flows into the first heat exchanger 11 . As shown in FIG. 1 , the first heat exchanger 11 is arranged within the return air path 20 . The first heat exchanger 11 has therein heat transfer tubes through which a refrigerant flows. The first heat exchanger 11 is, for example, a fin-and-tube heat exchanger. The first heat exchanger 11 exchanges heat between the refrigerant flowing through the heat transfer tubes and the return air RA. The first heat exchanger 11 functions as a condenser in the cooling operation mode and the dehumidifying operation mode.

The second heat exchanger 12 is arranged downstream of the first heat exchanger 11 in the direction of refrigerant flow in the cooling operation mode. The refrigerant discharged from the first heat exchanger 11 flows into the second heat exchanger 12 . Also, the second heat exchanger 12 is arranged in the air supply path 19 . The second heat exchanger 12 has therein heat transfer tubes through which a refrigerant flows. The second heat exchanger 12 is, for example, a fin-and-tube heat exchanger. The second heat exchanger 12 exchanges heat between the refrigerant flowing through the heat transfer tubes and the outside air OA. The second heat exchanger 12 functions as an evaporator in the cooling operation mode, and functions as a condenser in the dehumidification operation mode.

The third heat exchanger 13 is arranged downstream of the second heat exchanger 12 in the direction of refrigerant flow in the cooling operation mode. The refrigerant discharged from the second heat exchanger 12 flows into the third heat exchanger 13 via the expansion device 17 . Also, the third heat exchanger 13 is arranged in the air supply path 19 . The third heat exchanger 13 has therein heat transfer tubes through which a refrigerant flows. The third heat exchanger 13 is, for example, a fin-and-tube heat exchanger. The third heat exchanger 13 exchanges heat between the refrigerant flowing through the heat transfer tubes and the outside air OA. The third heat exchanger 13 functions as an evaporator in the cooling operation mode and the dehumidifying operation mode.

The expansion device 17 is arranged between the second heat exchanger 12 and the third heat exchanger 13 . The expansion device 17 expands and decompresses the refrigerant that has passed through the first heat exchanger 11 and the second heat exchanger 12 . The throttle device 17 can be composed of, for example, an electric expansion valve capable of adjusting the flow rate of the refrigerant. As the expansion device 17, it is possible to apply not only the electric expansion valve but also other expansion valves such as a mechanical expansion valve employing a diaphragm as a pressure receiving portion.

In addition, as shown in FIG. 1, the air conditioner 200 has a plurality of detectors 80-88. The detection results of the detection units 80 to 88 are input to the control unit 90 . These detection units 80 to 88 will be described below.

The first temperature/humidity detector 80 is arranged in the air supply path 19 . The first temperature/humidity detector 80 is arranged downstream of the second heat exchanger 12 and the third heat exchanger 13 in the direction of air flow. The first temperature/humidity detector 80 detects the temperature and humidity of the supplied air SA. The first temperature/humidity detector 80 is composed of, for example, a temperature sensor and a humidity sensor.

The second temperature/humidity detection unit 81 is arranged in the return air path 20 . The second temperature/humidity detector 81 is arranged upstream of the first heat exchanger 11 in the direction of air flow. The second temperature/humidity detector 81 detects the temperature and humidity of the return air RA. The second temperature/humidity detector 81 is composed of, for example, a temperature sensor and a humidity sensor.

The outside air temperature detector 82 is arranged inside the air supply path 19 . The outside air temperature detector 82 is arranged upstream of the second heat exchanger 12 and the third heat exchanger 13 in the direction of air flow. The outside air temperature detector 82 detects the temperature of the outside air OA. The outside air temperature detector 82 is composed of, for example, a temperature sensor.

The first refrigerant temperature detector 83 is attached to the refrigerant pipe 18 between the first heat exchanger 11 and the second heat exchanger 12 . The first refrigerant temperature detector 83 is arranged downstream of the first heat exchanger 11 in the direction of refrigerant flow in the cooling operation mode. The first refrigerant temperature detector 83 detects the outlet refrigerant temperature of the first heat exchanger 11 . The first coolant temperature detection unit 83 is composed of, for example, a temperature sensor.

The second refrigerant temperature detector 84 is attached to the refrigerant pipe 18 between the second heat exchanger 12 and the third heat exchanger 13 . The second refrigerant temperature detector 84 is arranged, for example, downstream of the second heat exchanger 12 and upstream of the expansion device 17 in the direction of refrigerant flow in the cooling operation mode. The second refrigerant temperature detector 84 detects the outlet refrigerant temperature of the second heat exchanger 12 . The second coolant temperature detection unit 84 is composed of, for example, a temperature sensor.

The third refrigerant temperature detector 85 is attached to the refrigerant pipe 18 between the third heat exchanger 13 and the compressor 16 . The third refrigerant temperature detector 85 is arranged downstream of the third heat exchanger 13 in the direction of refrigerant flow in the cooling operation mode. The third refrigerant temperature detector 85 detects the outlet refrigerant temperature of the third heat exchanger 13 . The third coolant temperature detection unit 85 is composed of, for example, a temperature sensor.

The discharge pressure detector 86 is arranged on the discharge port side of the compressor 16 . The discharge pressure detector 86 is attached, for example, to the refrigerant pipe 18 between the compressor 16 and the first heat exchanger 11 . A discharge pressure detector 86 detects the pressure of the refrigerant discharged from the compressor 16 . The discharge pressure detection unit 86 is composed of, for example, a pressure sensor.

The suction pressure detector 87 is arranged on the suction port side of the compressor 16 . The suction pressure detector 87 is attached, for example, to the refrigerant pipe 18 between the compressor 16 and the third heat exchanger 13 . The suction pressure detector 87 detects the pressure of the refrigerant sucked into the compressor 16 . The suction pressure detection unit 87 is composed of, for example, a pressure sensor.

The discharge temperature detector 88 is arranged on the discharge port side of the compressor 16 . The discharge temperature detector 88 is attached, for example, to the refrigerant pipe 18 between the compressor 16 and the first heat exchanger 11 . A discharge temperature detector 88 detects the temperature of the refrigerant discharged from the compressor 16 . The discharge temperature detection unit 88 is composed of, for example, a temperature sensor.

Although FIG. 1 shows the refrigerant circuit configuration when the air conditioner 200 performs only the cooling operation and the dehumidifying operation, the air conditioner 200 is not limited to that case, and the air conditioner 200 may also perform the heating operation. may FIG. 16 is a refrigerant circuit diagram showing an example of the configuration of an air conditioner 200A that is a modification of the air conditioner 200 according to Embodiment 1. As shown in FIG. The air conditioner 200A has a cooling operation mode, a dehumidifying operation mode, and a heating operation mode.

As shown in FIG. 16, in the air conditioner 200A, a channel switching device 30, a second expansion device 31, and a fourth refrigerant temperature detection section 89 are added to the configuration of FIG.

The flow switching device 30 is arranged between the discharge port of the compressor 16 and the first heat exchanger 11 and the third heat exchanger 13 . The channel switching device 30 is composed of, for example, a four-way valve. The flow path switching device 30 switches the direction of refrigerant flow depending on whether the operation mode of the air conditioner 200 is the cooling operation mode or the heating operation mode. However, also in the air conditioner 200A, as in the air conditioner 200, the direction in which the refrigerant flows is the same between the cooling operation mode and the dehumidifying operation mode. 16, the solid line of the flow switching device 30 indicates the state of the flow switching device 30 in the cooling operation mode, and the broken line of the flow switching device 30 indicates the state of the flow switching device 30 in the heating operation mode. showing. That is, in the cooling operation mode, the flow switching device 30 connects the discharge port of the compressor 16 and the first heat exchanger 11 and connects the suction port of the compressor 16 and the third heat exchanger 13. Switch refrigerant flow to connect. In the heating operation mode, the flow switching device 30 connects the discharge port of the compressor 16 and the third heat exchanger 13, and connects the suction port of the compressor 16 and the first heat exchanger 11. Switch refrigerant flow to connect. As a result, the direction in which the refrigerant flows is reversed between the cooling operation mode and the heating operation mode.

In the cooling operation mode, the refrigerant discharged from the compressor 16 flows into the first heat exchanger 11 via the flow switching device 30 . That is, in the cooling operation mode, the refrigerant is the compressor 16, the flow path switching device 30, the first heat exchanger 11, the second expansion device 31, the second heat exchanger 12, the expansion device 17, the third heat exchanger 13, the flow switching device 30, and the compressor 16 in this order.

On the other hand, in the heating operation mode, the refrigerant discharged from the compressor 16 flows through the flow path switching device 30 into the third heat exchanger 13 . That is, in the heating operation mode, the refrigerant is the compressor 16, the flow path switching device 30, the third heat exchanger 13, the expansion device 17, the second heat exchanger 12, the second expansion device 31, the first heat exchanger 11, the flow switching device 30, and the compressor 16 in this order.

The second throttle device 31 is arranged between the first heat exchanger 11 and the second heat exchanger 12 . In the heating operation mode, the second expansion device 31 expands the refrigerant discharged from the second heat exchanger 12 to reduce the pressure.

The fourth refrigerant temperature detector 89 is arranged downstream of the first heat exchanger 11 in the refrigerant flow direction in the heating operation mode. The fourth refrigerant temperature detector 89 is provided, for example, in the refrigerant pipe 18 between the first heat exchanger 11 and the flow path switching device 30 . The fourth refrigerant temperature detector 89 detects the outlet refrigerant temperature of the first heat exchanger 11 in the heating operation mode. A detection result of the fourth coolant temperature detection unit 89 is input to the control unit 90 .

Thus, as shown in FIG. 16, the flow switching device 30 is added to enable the formation of a refrigerant flow in the direction opposite to that in the cooling operation mode, and the first heat exchanger 11 and the second heat exchanger 12, the air conditioner 200 can perform heating operation.

Alternatively, as described in Patent Document 1, heating operation may be performed by switching the air flow direction. That is, the switching mechanism for switching the air passages so that the first heat exchanger 11 is in the air supply passage 19 and the second heat exchanger 12 and the third heat exchanger 13 are in the return air passage 20, It may be added to the configuration of FIG.

To simplify the description, the first embodiment will be described below using the refrigerant circuit of FIG. 1 as an example.

(control unit 90)
As shown in FIG. 1 , the air conditioner 200 further includes a controller 90 . The control unit 90 controls the overall operation of the air conditioner 200, and is composed of, for example, an analog circuit, a digital circuit, a CPU, or a processing circuit in which two or more of these are combined. . When at least part of the processing circuit is a CPU (processor), each function of that part of the control unit 90 is implemented by software, firmware, or a combination of software and firmware. Software and firmware are written as programs and stored in memory. The processing circuit implements each function of the control unit 90 by reading and executing the program stored in the memory. Here, the memory means, for example, non-volatile or volatile semiconductor memory such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), magnetic disk, flexible disk, optical disk , compact discs, mini discs, and DVDs (Digital Versatile Discs).

Based on the detection results of the detection units 80 to 88, the control unit 90 controls the operation of the heat pump circuit such as the frequency of the compressor 16 and the opening of the expansion device 17, and the rotation speed of the supply fan 14 and return air. It controls the air flow such as the number of revolutions of the fan 15 . The detection results of the detection units 80 to 88 are, for example, the above-described discharge pressure detection unit 86, suction pressure detection unit 87, discharge temperature detection unit 88, first refrigerant temperature detection unit 83, second refrigerant temperature detection unit 84, and at least one of the detection results of the third refrigerant temperature detection unit 85, the first temperature/humidity detection unit 80, the second temperature/humidity detection unit 81, and the outside air temperature detection unit 82.

Further, the control unit 90 controls the frequency of the compressor 16, the number of rotations of the supply air fan 14, the number of rotations of the return air fan 15, the opening of the expansion device 17, etc. based on instructions from a remote controller (not shown). to control.

Under the control of the control unit 90, the air conditioner 200 is operated in the cooling operation mode or the dehumidifying operation mode.

Although Embodiment 1 shows the case where the control unit 90 is provided inside the air conditioner 200 , the control unit 90 may be provided outside the air conditioner 200 . Further, the control unit 90 may be composed of one control unit, or may be composed of a plurality of control units. When the control unit 90 is composed of a plurality of control units, at least one of them controls the air flow of the supply air fan 14 and the return air fan 15, and at least one of the other controls the refrigerant flow of the heat pump circuit. may be controlled.

[Operation of air conditioner 200]
As described above, in the air conditioner 200 according to Embodiment 1, the refrigerant flows in the same direction in the cooling operation mode and the dehumidifying operation mode. The differences between the cooling operation mode and the dehumidifying operation mode are as follows.

(1) The second heat exchanger 12 functions as an evaporator in the cooling operation mode, and functions as a condenser in the dehumidification operation mode.
(2) The opening degree OP of the expansion device 17 in the cooling operation mode is smaller than that in the dehumidification operation mode.
(3) In the dehumidifying operation mode, the controller 90 reduces the opening degree OP of the expansion device 17 to reduce the heating capacity of the second heat exchanger 12 for the outside air OA. Further, by increasing the opening degree OP of the expansion device 17, control is performed to increase the heating capacity of the second heat exchanger 12 for the outside air OA.

That is, in Embodiment 1, the air conditioner 200 does not need to switch the direction of refrigerant flow between the cooling operation mode and the dehumidifying operation mode due to the above (1) and (2). The controller 90 adjusts the opening degree OP of the expansion device 17 to determine whether the second heat exchanger 12 functions as an evaporator or a condenser. Therefore, it is possible to continuously transition between the dehumidifying operation mode and the cooling operation mode. Further, according to (3) above, the control unit 90 adjusts the opening degree OP of the expansion device 17, so that the heating capacity of the second heat exchanger 12 can be adjusted. As a result, in the operation in the dehumidifying operation mode, the dehumidifying operation that reduces the humidity in the room 300 while suppressing the temperature drop in the room 300 becomes possible. Details will be described below.

The operation of the air conditioner 200 will be described below together with the refrigerant flow and the air flow.

<Cooling operation>
First, among the operations performed by the air conditioner 200, the cooling operation will be described with reference to FIGS. 1 to 3. FIG. In the cooling operation, the air conditioner 200 lowers the temperature of the outdoor air 301 and supplies the indoor 300 with the air. FIG. 2 is an explanatory diagram illustrating the flow of refrigerant and the flow of air in the cooling operation mode of the air-conditioning apparatus 200 according to Embodiment 1. FIG. FIG. 3 is a Mollier diagram showing refrigerant states in the cooling operation mode of the air-conditioning apparatus 200 according to Embodiment 1. FIG. In FIG. 2 , solid line arrows indicate the direction in which the refrigerant flows, dashed line arrows indicate the direction in which air flows, and examples of temperatures of the refrigerant and air under typical conditions are appended to the arrows. In FIG. 3, the horizontal axis indicates the enthalpy of the refrigerant, and the vertical axis indicates the pressure of the refrigerant. FIG. 3 shows air temperature, refrigerant pressure, enthalpy, and refrigerant temperature. In FIG. 3, the saturated vapor line 40 and the saturated liquid line 41 are indicated by dashed curves. A critical point K is the boundary between the saturated vapor line 40 and the saturated liquid line 41 . In FIG. 3, the pressure in the state R2 and the pressure in the state R2-1 are actually the same, but for the convenience of illustration, they are not overlapped and shown separately. Here, in the heat exchange operation, the operation of the air conditioner 200 will be described by taking as an example a case where the heat exchange fluid is air and the heat exchange fluid is refrigerant.

In the cooling operation mode, the first heat exchanger 11 acts as a condenser, and the second heat exchanger 12 and the third heat exchanger 13 act as evaporators.

As shown in FIGS. 2 and 3, by driving the compressor 16, high-temperature and high-pressure gaseous refrigerant is discharged from the compressor 16 (state R1 in FIG. 3). The temperature of the coolant at this time is, for example, 70°C. The high-temperature and high-pressure gas refrigerant (single-phase) discharged from the compressor 16 flows into the first heat exchanger 11 functioning as a condenser. In the first heat exchanger 11 , heat is exchanged between the high-temperature, high-pressure gas refrigerant that has flowed in and the return air RA that is returned from the room 300 to the outside 301 by the return air fan 15 . The temperature _TR of the return air RA is, for example, 27°C. As a result, the high-temperature and high-pressure gas refrigerant is condensed into a high-pressure liquid refrigerant (single-phase) (state R2 in FIG. 3). In the cooling operation, the opening degree OP of the expansion device 17 is set smaller than that in the dehumidifying operation. As a result, the pressure P of the refrigerant in the state _R2 is increased to the value P1 to promote heat exchange, so that the temperature of the liquid refrigerant flowing out of the first heat exchanger 11 is made approximately the same as the temperature TR of the return air RA. can be lowered to The temperature of the refrigerant flowing out of the first heat exchanger 11 is, for example, 27°C. Thus, the opening degree OP of the expansion device 17 is set by the control of the control unit 90 so as to be smaller than that in the dehumidifying operation mode, which will be described later. Note that the value P1 is a value equal to or greater than the value P2 during the dehumidifying operation shown in FIG.

The high-pressure liquid refrigerant sent out from the first heat exchanger 11 exchanges heat with the outside air OA and evaporates in the second heat exchanger 12 functioning as an evaporator (state R3 in FIG. 3). Here, since the temperature of the room 300 is adjusted to be lower than the outside air OA by the air conditioner 200 or another air conditioner, the temperature _TR of the return air RA is lower than the temperature To of the outside air OA. For example, the temperature T _R of the return air RA is 27°C and the temperature T _O of the outside air OA is 35°C. The temperature of the liquid refrigerant flowing from the first heat exchanger 11 to the second heat exchanger 12 is approximately the same as the temperature _TR of the return air RA and lower than the outside air OA, as described above. Therefore, the outside air OA is cooled in the heat exchange of the second heat exchanger 12 . Therefore, the temperature T _O 1 of the outside air OA that has passed through the second heat exchanger 12 is, for example, 27°C. The liquid refrigerant evaporated and heated in the second heat exchanger 12 becomes a two-phase refrigerant of low-pressure gas refrigerant and liquid refrigerant by the throttle device 17 (state R4 in FIG. 3). The two-phase refrigerant flows into the third heat exchanger 13 functioning as an evaporator. In the third heat exchanger 13 , heat is exchanged between the flowing two-phase refrigerant and the outside air OA supplied from the outdoor 301 to the indoor 300 by the air supply fan 14 . As a result, the liquid refrigerant of the two-phase refrigerant evaporates to become a low-pressure gas refrigerant (single-phase) (state R5 in FIG. 3). The outside air OA is cooled in the third heat exchanger 13 . The temperature T _O 2 of the outside air OA that has passed through the third heat exchanger 13 is, for example, 15°C. In the air supply path 19, as shown in FIG. 2, the air that has passed through the second heat exchanger 12 and the air that has passed through the third heat exchanger 13 are mixed to form supply air SA, which is supplied to the room 300. supplied. The low-pressure gas refrigerant sent out from the third heat exchanger 13 flows into the compressor 16, is compressed into high-temperature and high-pressure gas refrigerant, and is discharged from the compressor 16 again (state R1 in FIG. 3). This cycle is then repeated.

(Operation of control unit 90 during cooling operation)
The function of the control unit 90 in the cooling operation mode will be described. The control unit 90 controls the opening degree OP of the expansion device 17 based on the discharge refrigerant pressure of the compressor 16 and the outlet refrigerant temperature of the first heat exchanger 11 so that the temperature in the room 300 reaches the set temperature. do.

FIG. 4 is a flow chart showing the operation of the control unit 90 in the cooling operation mode of the air conditioner 200 according to Embodiment 1. FIG. In step S<b>1 , the control unit 90 acquires the refrigerant pressure on the discharge port side of the compressor 16 from the discharge pressure detection unit 86 . Next, in step S2, based on the acquired refrigerant pressure, the control unit 90 calculates the saturation temperature at that pressure. Next, in step S<b>3 , the control unit 90 acquires the outlet refrigerant temperature of the first heat exchanger 11 from the first refrigerant temperature detection unit 83 . Next, in step S4, the control unit 90 calculates the degree of supercooling SC1 at the outlet of the first heat exchanger 11 based on the saturation temperature calculated in step S2 and the outlet refrigerant temperature obtained in step S3. The control unit 90 controls the opening degree OP of the expansion device 17 using the calculated outlet supercooling degree SC1 as an index. Specifically, in step S5, the controller 90 compares the outlet supercooling degree SC1 with the threshold value Th1. When the outlet supercooling degree SC1 is greater than the threshold Th1, the process proceeds to step S6, and when the outlet supercooling degree SC1 is equal to or less than the threshold Th1, the process proceeds to step S7. In step S6, the control unit 90 increases the opening degree OP of the diaphragm device 17 from the current value. On the other hand, in step S7, the controller 90 reduces the opening degree OP of the diaphragm device 17 from the current value. The amount of increase or decrease in the opening degree OP of the expansion device 17 may be set to a preset constant value, but the control unit 90 determines the amount of increase or decrease according to the difference between the outlet supercooling degree SC1 and the threshold value Th1. You may do so.

Note that the threshold Th1 may be a fixed value set in advance based on the design value of the degree of subcooling at the outlet of the first heat exchanger 11 assuming normal cooling operation (that is, the theoretical value during normal operation). can be a variable value. In that case, for example, the threshold Th1 is determined by the controller 90 based on the set value for the room temperature of the room 300 set by the user for the air conditioner 200 . As a determination method, a data table or an arithmetic expression is stored in advance in the memory, and the control unit 90 uses it to calculate the threshold value Th1. The data table stores a threshold value Th1 for each set value for room temperature. Moreover, the arithmetic expression is a function for obtaining the threshold value Th1 using the set value for the room temperature as a parameter.

Note that the opening degree OP of the expansion device 17 in the cooling operation mode is set to a smaller value than in the dehumidification operation mode. A specific description will be given. A boundary value between the opening degree OP of the expansion device 17 in the cooling operation mode and the opening degree OP of the expansion device 17 in the dehumidifying operation mode is defined as a boundary point OP _A (see FIG. 8). At this time, the opening degree OP of the expansion device 17 in the cooling operation mode is a value within the first range below the boundary point OP _A , and the opening degree OP of the expansion device 17 in the dehumidifying operation mode is greater than the boundary point OP _A. A value within the second range.

Also, in the cooling operation mode, the control unit 90 may perform the following control. The number of rotations of the supply air fan 14 and the number of rotations of the return air fan 15 are determined in advance according to the required ventilation amount of the room 300 . However, it is assumed that the rotation speeds of the supply air fan 14 and the return air fan 15 can be changed, for example, because a ventilator is provided in addition to the air conditioner 200 . In that case, the control unit 90 increases the outlet supercooling degree SC1 by increasing the rotation speeds of the supply air fan 14 and the return air fan 15, and increases the rotation speeds of the supply air fan 14 and the return air fan 15. By decreasing, the outlet supercooling degree SC1 may be decreased.

Also, the control unit 90 may control the opening degree OP of the expansion device 17 based on the suction pressure of the compressor 16 and the outlet refrigerant temperature of the third heat exchanger 13 . In this case, the controller 90 acquires the pressure of the refrigerant sucked by the compressor 16 from the suction pressure detector 87 and calculates the saturation temperature at that pressure. The control unit 90 also acquires the outlet refrigerant temperature of the third heat exchanger 13 from the third refrigerant temperature detection unit 85 . The control unit 90 calculates the outlet superheat degree SHe of the third heat exchanger 13 based on the calculated saturation temperature and the acquired outlet refrigerant temperature. When the outlet superheat degree SHe is equal to or less than a preset threshold value Th2, the control unit 90 performs control to decrease the opening degree OP of the expansion device 17 in order to prevent the liquid from being sucked into the compressor 16 . On the other hand, when the outlet superheat degree SHe is greater than the threshold value Th2, the control unit 90 maintains the opening degree OP of the expansion device 17 at the current value.

Also, the control unit 90 may control the opening degree OP of the expansion device 17 based on the discharge pressure of the compressor 16 and the temperature of the refrigerant discharged from the compressor 16 . In that case, the control unit 90 acquires the pressure of the refrigerant discharged from the compressor 16 from the discharge pressure detection unit 86 and calculates the saturation temperature at that pressure. The control unit 90 also acquires the temperature of the refrigerant discharged from the compressor 16 from the discharge temperature detection unit 88 . The control unit 90 calculates the degree of discharge superheat SHd of the compressor 16 based on the calculated saturation temperature and the acquired temperature of the refrigerant. The control unit 90 controls the opening degree OP of the throttle device 17 according to the preset threshold value Th3-1 of the ejection temperature and the threshold value Th3-2 of the ejection superheat degree SHd. When the ejection temperature detection unit 88 is equal to or higher than the threshold value Th3-1, control is performed to increase the opening degree OP of the expansion device 17 . As a result, the refrigerant at the outlet of the third heat exchanger 13 functioning as an evaporator is brought into a wet state, causing the compressor 16 to suck in a small amount of liquid refrigerant, thereby lowering the discharge temperature of the compressor 16 . When the discharge temperature detection unit 88 is less than the threshold value Th3-1, the opening degree OP of the expansion device 17 is maintained at the current value. When the degree of discharge superheat SHd is equal to or less than the threshold value Th3-2, control is performed to decrease the degree of opening OP of the throttle device 17 . As a result, excessive inflow of liquid into the compressor 16 can be prevented. When the discharge superheat SHd is greater than the threshold value Th3-2, the opening OP of the expansion device 17 is maintained at the current value.

<Dehumidification operation>
Next, among the operations performed by the air conditioner 200, the dehumidification operation will be described with reference to FIGS. 1, 5, and 6. FIG. In the dehumidifying operation, the air conditioner 200 dehumidifies the outdoor air 301 and supplies the indoor air 300 with the dehumidified air. FIG. 5 is an explanatory diagram illustrating the refrigerant flow and the air flow in the dehumidifying operation mode of the air conditioner 200 according to Embodiment 1. FIG. FIG. 6 is a Mollier diagram showing refrigerant states in the dehumidifying operation mode of the air-conditioning apparatus 200 according to Embodiment 1. FIG. In FIG. 5 , solid line arrows indicate the direction of refrigerant flow, broken line arrows indicate the direction of air flow, and the temperatures of the refrigerant and air under typical conditions are appended to the arrows. In FIG. 6, the horizontal axis indicates the enthalpy of the refrigerant, and the vertical axis indicates the pressure of the refrigerant. FIG. 6 shows air temperature, refrigerant pressure, enthalpy, and refrigerant temperature. Further, in FIG. 6, the saturated vapor line 40 and the saturated liquid line 41 are indicated by dashed curved lines. A critical point K is the boundary between the saturated vapor line 40 and the saturated liquid line 41 . Here, the operation of the air conditioner 200 will be described by taking as an example a case where the heat exchange fluid is air and the heat exchange fluid is refrigerant.

In the dehumidifying operation mode, the first heat exchanger 11 and the second heat exchanger 12 act as condensers, and the third heat exchanger 13 acts as an evaporator.

As shown in FIGS. 5 and 6, when the compressor 16 is driven, a high-temperature, high-pressure gaseous refrigerant is discharged from the compressor 16 . The high-temperature and high-pressure gas refrigerant (single-phase) discharged from the compressor 16 flows into the first heat exchanger 11 functioning as a condenser (state R1 in FIG. 6). In the first heat exchanger 11, heat is exchanged between the high-temperature and high-pressure gas refrigerant that has flowed in and the return air RA that is exhausted from the room 300 to the outside 301 by the return-air fan 15, so that the high-temperature and high-pressure gas refrigerant is It condenses into a high-pressure liquid refrigerant or two-phase refrigerant (state R2 in FIG. 6). At this time, in the dehumidifying operation mode, the control unit 90 increases the opening degree OP of the expansion device 17 compared to that in the cooling operation mode, thereby setting the pressure P in the state R2 to a value lower than the value P1 in the cooling operation mode. Make it P2. By suppressing heat exchange in this manner, the temperature of the liquid refrigerant is lowered to a temperature higher than the temperature _TO of the outside air OA. The temperature of the liquid refrigerant sent out from the first heat exchanger 11 is, for example, 45°C, and the temperature of the outside air OA is, for example, 35°C.

The high-pressure liquid refrigerant sent out from the first heat exchanger 11 flows into the second heat exchanger 12 functioning as a condenser. In the second heat exchanger 12, the liquid refrigerant exchanges heat with the outside air OA and condenses (state R3 in FIG. 6). At this time, the temperature (eg, 45° C.) of the liquid refrigerant flowing from the first heat exchanger 11 to the second heat exchanger 12 is higher than the temperature (eg, 35° C.) of the outside air OA, as described above. Therefore, the outside air OA is heated in the second heat exchanger 12 . The temperature T _O 1 of the outside air OA that has passed through the second heat exchanger 12 is, for example, 45°C. The condensed liquid refrigerant is depressurized by the expansion device 17 and becomes two-phase refrigerant of low-pressure gas refrigerant and liquid refrigerant (state R4 in FIG. 6). The two-phase refrigerant flows into the third heat exchanger 13 functioning as an evaporator. In the third heat exchanger 13, heat is exchanged between the flowing two-phase refrigerant and the outside air OA supplied from the outdoor 301 by the air supply fan 14. The refrigerant evaporates and becomes a low-pressure gas refrigerant (single-phase) (state R5 in FIG. 6). The temperature T _O 2 of the outside air OA that has passed through the third heat exchanger 13 is, for example, 15°C. The low-pressure gas refrigerant sent out from the third heat exchanger 13 flows into the compressor 16, is compressed into high-temperature and high-pressure gas refrigerant, and is discharged from the compressor 16 again (state R1 in FIG. 6). This cycle is then repeated.

In the dehumidifying operation mode, the air heated by the second heat exchanger 12 and the air cooled and dehumidified by the third heat exchanger 13 are mixed and supplied to the room 300 as supply air SA. As a result, dehumidifying operation that reduces the humidity in the room 300 while suppressing a temperature drop in the room 300 is possible.

(Operation of control unit 90 during dehumidification operation)
The operation of the control section 90 in the dehumidifying operation mode will be described. The control unit 90 controls the opening degree OP of the expansion device 17 based on the discharge refrigerant pressure of the compressor 16 and the outlet refrigerant temperature of the second heat exchanger 12 so that the temperature in the room 300 reaches the set temperature. do. By controlling the opening degree OP of the expansion device 17, the heating capacity of the second heat exchanger 12 is increased or decreased, so that the temperature of the air heated by the second heat exchanger 12 and supplied to the room 300 is can be adjusted. Thereby, the temperature in the room 300 can be maintained at the set temperature.

FIG. 7 is a flowchart showing the operation of the control unit 90 in the dehumidifying operation mode in the air conditioner 200 according to Embodiment 1. FIG. In step S<b>11 , the control unit 90 acquires the refrigerant pressure on the discharge port side of the compressor 16 from the discharge pressure detection unit 86 . Next, in step S12, the control unit 90 calculates the saturation temperature at the obtained pressure based on the obtained refrigerant pressure. Next, in step S<b>13 , the control unit 90 acquires the outlet refrigerant temperature of the second heat exchanger 12 from the second refrigerant temperature detection unit 84 . Next, in step S14, the control unit 90 calculates the outlet subcooling degree SC2 of the second heat exchanger 12 based on the saturation temperature calculated in step S12 and the refrigerant temperature obtained in step S13. The control unit 90 controls the opening degree OP of the expansion device 17 using the calculated outlet supercooling degree SC2 as an index. Specifically, in step S15, the controller 90 compares the outlet supercooling degree SC2 with the threshold value Th4. When the outlet supercooling degree SC2 is greater than the threshold Th4, the process proceeds to step S16, and when the outlet supercooling degree SC2 is equal to or less than the threshold Th4, the process proceeds to step S17. In step S16, the control unit 90 determines that the room temperature in the room 300 has decreased, and increases the opening degree OP of the expansion device 17 from the current value. As a result, the heating capacity of the second heat exchanger 12 increases, and the temperature of the outside air OA that has passed through the second heat exchanger 12 rises. On the other hand, in step S17, the controller 90 determines that the room temperature in the room 300 is high, and reduces the opening degree OP of the expansion device 17 from the current value. As a result, the heating capacity of the second heat exchanger 12 is reduced, and the temperature of the outside air OA that has passed through the second heat exchanger 12 is lowered. The amount of increase or decrease in the opening degree OP of the expansion device 17 may be set to a preset constant value, but the control unit 90 determines the amount of increase or decrease according to the difference between the outlet supercooling degree SC2 and the threshold value Th4. You may do so.

Note that the threshold Th4 may be a fixed value set in advance based on the design value of the degree of subcooling at the outlet of the second heat exchanger 12 assuming normal dehumidifying operation (that is, the theoretical value during normal operation). can be a variable value. In that case, for example, the threshold Th4 is determined by the control unit 90 based on the set value for the room temperature of the room 300 set by the user for the air conditioner 200 . As a determination method, a data table or an arithmetic expression is stored in advance in the memory, and the control unit 90 uses it to calculate the threshold value Th4. The data table stores a threshold value Th4 for each set value for room temperature. Moreover, the arithmetic expression is a function for obtaining the threshold value Th4 using the set value for the room temperature as a parameter.

In Embodiment 1, as described above, the control unit 90 controls the opening degree OP of the expansion device 17 using the outlet subcooling degree SC2 of the second heat exchanger 12 as an index. As a result, in the dehumidifying operation mode, it is possible to perform a dehumidifying operation that reduces the humidity in the room 300 while suppressing a temperature drop in the room 300 .

In addition, in the dehumidifying operation mode, the control unit 90 may perform the following control. As described above, the number of rotations of the supply air fan 14 and the number of rotations of the return air fan 15 are determined in advance according to the required ventilation amount of the room 300 . However, there are cases where the number of rotations of the supply air fan 14 and the number of rotations of the return air fan 15 can be changed, for example, because a ventilator is provided in addition to the air conditioner 200 . In that case, the outlet supercooling degree SC2 may be controlled by changing the rotation speed of the supply air fan 14 and the rotation speed of the return air fan 15 instead of the opening degree OP of the expansion device 17. FIG. In this case, when the outlet supercooling degree SC2 is equal to or less than the threshold value Th4, the control unit 90 increases the rotation speed of the supply air fan 14 and the rotation speed of the return air fan 15 to reduce the outlet supercooling degree SC2. increase. On the other hand, when the outlet supercooling degree SC2 is greater than the threshold value Th4, the controller 90 decreases the rotation speed of the supply air fan 14 and the rotation speed of the return air fan 15 to decrease the outlet supercooling degree SC2. Note that the control of the opening degree OP of the expansion device 17 and the control of the rotation speed of the supply air fan 14 and the rotation speed of the return air fan 15 may be used in combination without being limited to this case.

Also, the control unit 90 may control the opening degree OP of the expansion device 17 based on the refrigerant suction pressure of the compressor 16 and the outlet refrigerant temperature of the third heat exchanger 13 . In that case, the control unit 90 calculates the saturation temperature at the pressure based on the refrigerant suction pressure detected by the suction pressure detection unit 87 . Next, the control unit 90 calculates the outlet superheat degree SHe of the third heat exchanger 13 based on the calculated saturation temperature and the refrigerant temperature of the third refrigerant temperature detection unit 85 . The control unit 90 reduces the opening degree OP of the expansion device 17 from the current opening degree in order to prevent the liquid from being sucked into the compressor 16 when the outlet superheat degree SHe is equal to or less than the threshold value Th5. Further, when the outlet superheat degree SHe is greater than the threshold value Th5, the control unit 90 maintains the opening degree OP of the expansion device 17 at the current value.

Also, the control unit 90 may control the opening degree OP of the expansion device 17 based on the pressure of the refrigerant discharged from the compressor 16 and the temperature of the refrigerant discharged from the compressor 16 . In that case, the controller 90 calculates the saturation temperature at the pressure based on the refrigerant pressure detected by the discharge pressure detector 86 . The controller 90 calculates the discharge superheat SHd of the compressor 16 based on the calculated saturation temperature and the refrigerant temperature of the discharge temperature detector 88 . The control unit 90 controls the opening degree OP of the throttle device 17 in accordance with the preset threshold value Th6-1 for the ejection temperature and the threshold value Th6-2 for the ejection superheat degree SHd. When the ejection temperature detection unit 88 is equal to or higher than the threshold value Th6-1, control is performed to increase the opening degree OP of the expansion device 17 . As a result, the refrigerant at the outlet of the third heat exchanger 13 functioning as an evaporator is brought into a wet state, causing the compressor 16 to suck in a small amount of liquid refrigerant, thereby lowering the discharge temperature of the compressor 16 . When the discharge temperature detection unit 88 is less than the threshold value Th6-1, the opening degree OP of the expansion device 17 is maintained at the current value. When the discharge superheat SHd is equal to or less than the threshold value Th6-2, control is performed to decrease the opening degree OP of the expansion device 17 . As a result, excessive inflow of liquid into the compressor 16 can be prevented. When the degree of discharge superheat SHd is greater than the threshold value Th6-2, the opening degree OP of the expansion device 17 is maintained at the current value.

(Operation mode switching operation)
Next, the switching operation between the cooling operation mode and the dehumidifying operation mode will be described. The cooling operation mode and the dehumidifying operation mode described above can be continuously switched by the control unit 90 controlling the opening degree OP of the expansion device 17 . FIG. 8 is an explanatory diagram showing the operation mode switching operation according to the opening degree OP of the expansion device 17 in the air conditioner 200 according to Embodiment 1. FIG. In the graph of FIG. 8, the horizontal axis indicates the temperature of the refrigerant in the state R2 of FIGS. 3 and 6 and the degree of opening OP of the expansion device 17. On the horizontal axis, T _o is the temperature of the outside air OA, and T _R is the temperature of the return air RA. A boundary point OP _A of the degree of opening OP of the expansion device 17 is a boundary at which the cooling operation mode and the dehumidifying operation mode are switched. When the opening degree OP of the expansion device 17 is within a second range larger than the boundary point OP _A , the dehumidifying operation mode is entered, and when the opening degree OP of the expansion device 17 is within a first range below the boundary point OP _A , the cooling operation is performed. become a mode. In addition, in the graph of FIG. 8, the vertical axis indicates the cooling capacity and heating capacity of the second heat exchanger 12 . On the vertical axis, the area greater than 0 indicates heating capacity, and the area below 0 indicates cooling capacity.

As shown in FIG. 8, when the opening degree OP of the expansion device 17 is within the first range, the pressure in state R2 in FIGS. , heat exchange is facilitated. Therefore, the temperature of the refrigerant after heat exchange becomes approximately the same as the temperature _TR of the return air RA. At this time, since the temperature T _R of the return air RA is lower than the temperature T _O of the outside air OA, the second heat exchanger 12 acts as an evaporator. That is, the operation mode of the air conditioner 200 becomes the cooling operation mode. At this time, if the opening degree OP of the expansion device 17 is increased toward the boundary point _OPA , the pressure in the state R2 decreases and the heat exchange amount decreases as the opening degree OP increases. _As a result, when the opening degree OP of the expansion device 17 reaches the boundary point OPA, the refrigerant temperature in the state R2 becomes equal to the temperature T _O of the outside air OA. At this time, the second heat exchanger 12 does not exchange heat. Furthermore, when the opening degree OP of the expansion device 17 is increased to a value within the second range, the refrigerant temperature in the state R2 exceeds the temperature _TO of the outside air OA, so the second heat exchanger 12 functions as a condenser. works. That is, the operation mode of the air conditioner 200 becomes the dehumidification operation mode.

(Operation of control unit 90 when switching operation mode)
A switching operation of the operation mode by the control unit 90 will be described. FIG. 9 is a flowchart showing the operation mode switching operation of the control unit 90 in the air conditioner 200 according to Embodiment 1. As shown in FIG. In step S21, the control unit 90 acquires the temperature T _room and the absolute humidity X _room of the room 300, which is the space to be air-conditioned, from the second temperature/humidity detection unit 81 that detects the temperature and humidity of the return air RA. Next, in step S22, the controller 90 compares the temperature T _room of the air-conditioned space with a threshold value Th7. When the temperature T _room is higher than the threshold value Th7, the control unit 90 proceeds to the process of step S23 and operates in the cooling operation mode. On the other hand, when the temperature T _room is equal to or lower than the threshold value Th7, the control unit 90 proceeds to the process of step S24. In step S24, the controller 90 compares the absolute humidity X _room of the room 300, which is the space to be air-conditioned, with the threshold value Th8. When the absolute humidity X _room is higher than the threshold value Th8, the control unit 90 proceeds to the process of step S25 and performs operation in the dehumidifying operation mode. On the other hand, when the absolute humidity X _room is equal to or lower than the threshold Th8, the control section 90 proceeds to the process of step S26. In step S26, the control unit 90 stops the compressor 16 in the air conditioner 200 so as not to operate the heat pump circuit, and operates at least one of the return air fan 15 and the supply air fan 14 to perform only ventilation. do.

Note that the threshold Th7 may be a preset fixed value, or may be determined based on a set value for the room temperature of the room 300 set by the user for the air conditioner 200 . In addition, the threshold Th8 may be a preset fixed value, or may be determined based on a set value for the humidity of the room 300 or a set value for the room temperature set by the user for the air conditioner 200. good. The threshold Th7 and the threshold Th8 may be determined using a data table or an arithmetic expression in the same manner as the thresholds Th1 and Th4.

[Configuration of Heat Transfer Tubes of First Heat Exchanger 11 and Second Heat Exchanger 12]
10 is a side view showing the configuration of the heat transfer tubes of the first heat exchanger 11 and the second heat exchanger 12 in the air conditioner 200 according to Embodiment 1. FIG. 10(a) shows an example of the configuration of the heat transfer tubes 100 of the first heat exchanger 11, and FIG. 10(b) shows an example of the configuration of the heat transfer tubes 101 of the second heat exchanger 12. FIG.

As shown in FIG. 10(a), the heat transfer tubes 100 of the first heat exchanger 11 are arranged vertically at regular intervals. The heat transfer tube 100 has a circular tubular shape. The heat transfer tubes 100 are arranged to pass through the fins 102 .

As shown in FIG. 10(b), the heat transfer tubes 101 of the second heat exchanger 12 are arranged vertically at regular intervals. The heat transfer tubes 101 are arranged to pass through the fins 103 . The heat transfer tube 101 has a flat tube shape having a major axis and a minor axis. The short diameter of heat transfer tube 101 extends in the vertical direction, and the long diameter of heat transfer tube 101 extends in a direction perpendicular to the vertical direction (that is, in the horizontal direction). By forming the heat transfer tube 101 into a flat tube shape, it becomes possible to make the outer circumference length of the heat transfer tube per cross section longer than that of a circular tube. In Embodiment 1, heat transfer tube 101 has a longer outer circumference than heat transfer tube 100 . The heat transfer area of the heat transfer tube 101 is correspondingly larger than that of the heat transfer tube 100 .

Furthermore, FIG. 10(b) illustrates a case where the heat transfer tube 101 is made of a flat perforated tube. The inside of the heat transfer tube 101 is partitioned by the inner column 101a to form a plurality of small-diameter refrigerant flow paths 101b. On the other hand, in the circular heat transfer tube 100 shown in FIG. 10(a), one refrigerant channel 100b having a large diameter is provided. In the heat transfer tube 101 of FIG. 10(b), the contact length between the refrigerant and the inside of the tube in one cross section can be doubled or more due to the subdivision as compared with a flat tube that is not subdivided. Thereby, the heat transfer area inside the heat transfer tube 101 can be increased.

The maximum value of the heating capacity of the second heat exchanger 12 in the dehumidifying operation mode is greatly affected by the ratio of the heat transfer area to the first heat exchanger 11. In order to realize an operating state (dehumidification only) in which the heating capacity of the second heat exchanger 12 and the cooling capacity of the third heat exchanger 13 are balanced, the second heat exchanger must be It is desirable that the heat transfer area of 12 is large.

Therefore, in Embodiment 1, the heat transfer tubes 101 of the second heat exchanger 12 are made flat. Thereby, as described above, by making the outer peripheral length of the heat transfer tube 101 per cross section longer than that of the heat transfer tube 100, the heat transfer area of the heat transfer tube 101 is made larger than that of the heat transfer tube 100 of the first heat exchanger 11. also increase. Further, by subdividing the inside of the heat transfer tube 101, the heat transfer area can be further increased. In addition, the projected area of the heat transfer tubes when viewed from the direction of air flow is smaller for the flat tubes than for the circular tubes. Therefore, when designed with the same airflow resistance as that of a circular tube, the heat transfer tubes 101 can be arranged at a high density with respect to the circular tube. That is, in FIG. 10(a), four heat transfer tubes 101 can be arranged in the area where three heat transfer tubes 100 are provided, in FIG. 10(b). This increases the contact length between the heat transfer tubes 101 and the fins 103 and improves the efficiency of the fins 103 . In the case of circular heat transfer tubes 100 , the heat transfer tubes 100 are inserted into the fins 102 and then expanded so that the heat transfer tubes 100 are brought into close contact with the fins 102 . However, if even a small air layer is interposed between the heat transfer tube 100 and the fins 102, it becomes thermal resistance and the performance is lowered. On the other hand, in the case of the flat heat transfer tube 101, the fins 103 and the heat transfer tube 101 are welded together by brazing, so that the thermal resistance is reduced. For these reasons, the heat transfer area of the second heat exchanger 12 is larger than that of the first heat exchanger 11, and the heating capacity of the second heat exchanger 12 and the cooling capacity of the third heat exchanger 13 are balanced. It is possible to achieve a stable operating state (only dehumidification). The heat transfer tubes of the third heat exchanger 13 are not particularly limited, and even if they have the same flat tube shape as the heat transfer tubes 101 of the second heat exchanger 12, It may have a circular tubular shape.

Also, in the cooling operation mode, the second heat exchanger 12 is filled with liquid refrigerant, and in the dehumidifying operation mode, the second heat exchanger 12 is filled with liquid refrigerant or two-phase refrigerant. Therefore, the refrigerant charging amount required for operation differs greatly between the cooling operation mode and the dehumidifying operation mode. If the amount of refrigerant charged is appropriate for one of the operation modes, it becomes difficult to achieve stable operation in the other operation mode. Reducing the volume of the refrigerant flow path 101b of the second heat exchanger 12 is effective in suppressing fluctuations in the required amount of refrigerant due to such operation modes. Specifically, as shown in FIG. 10(b), the heat transfer tube 101 preferably has a structure having a large number of small-diameter refrigerant flow paths 101b, such as a flat perforated tube. Due to such a structure, the flat perforated pipe can achieve both a large heat transfer area and a small coolant channel volume. In this way, the second heat exchanger 12 has a smaller refrigerant passage volume than the first heat exchanger 11, thereby suppressing fluctuations in the amount of refrigerant in the heat exchanger due to differences in operation modes, The stability of the operation of the harmony device 200 can be improved. Moreover, it becomes possible for the first heat exchanger 11 to absorb excess or deficiency of the refrigerant generated in the second heat exchanger 12 .

Note that FIG. 10(b) shows an example in which the heat transfer tubes 101 of the second heat exchanger 12 have a flat tube shape. However, not limited to this case, as long as the heat transfer area where the second heat exchanger 12 performs heat exchange is larger than the heat transfer area where the first heat exchanger 11 performs heat exchange, other configurations may be In addition, in FIG.10(b), the case where the heat exchanger tube 101 of the 2nd heat exchanger 12 is comprised from a flat perforated tube is mentioned as an example, and is shown. However, it is not limited to this case. That is, if the heat transfer tube 101 of the second heat exchanger 12 has a flat tube shape, the heat transfer area where the second heat exchanger 12 performs heat exchange is Larger than the heat transfer area for heat exchange. Therefore, it is not always necessary to subdivide the inside of the heat transfer tubes 101 of the second heat exchanger 12 into perforated tubes.

FIG. 10(b) shows an example in which the heat transfer tubes 101 of the second heat exchanger 12 are made of flat perforated tubes in order to reduce the volume of the refrigerant flow path. However, the configuration is not limited to this case, and the volume of each refrigerant flow path 101b of the heat transfer tube 101 of the second heat exchanger 12 is smaller than the volume of each refrigerant flow path of the heat transfer tube 100 of the first heat exchanger 11. If so, other configurations may be used.

As described above, in Embodiment 1, the second heat exchanger 12 has a larger heat transfer area than the first heat exchanger 11 and a smaller refrigerant flow volume than the first heat exchanger 11. I explained the case where However, this is not the case when designing with a focus on the cooling operation mode.

[Arrangement of Second Heat Exchanger 12 and Third Heat Exchanger 13]
Both the second heat exchanger 12 and the third heat exchanger 13 are arranged in the air supply path 19 . Here, the arrangement of the second heat exchanger 12 and the third heat exchanger 13 in the air supply path 19 will be described.

11 is a plan view illustrating an example of the arrangement of the second heat exchanger 12 and the third heat exchanger 13 in the air conditioner 200 according to Embodiment 1. FIG. In FIG. 11, the state which looked at the 2nd heat exchanger 12 and the 3rd heat exchanger 13 from the top is shown. Further, FIG. 11(a) shows an arrangement example of the second heat exchanger 12 and the third heat exchanger 13 in Embodiment 1, and FIG. 11(b) shows a comparative example.

In FIGS. 11(a) and (b), white arrows indicate the direction in which the outside air OA flows in the air supply path 19. FIG. As shown in FIG. 11( a ), the second heat exchanger 12 and the third heat exchanger 13 are arranged side by side in a direction perpendicular to the vertical direction (that is, in the horizontal direction), and outside air OA flows. They are arranged side by side in a direction perpendicular to the direction. Accordingly, at least part of the outside air OA flowing through the air supply path 19 passes through the second heat exchanger 12 only. This can prevent the second heat exchanger 12 from acting as a condenser in the cooling operation mode.

Therefore, in Embodiment 1, it is desirable to avoid at least the serial arrangement shown in the comparative example of FIG. 11(b). In FIG. 11(b), the second heat exchanger 12 and the third heat exchanger 13 are arranged side by side along the direction of air flow. That is, one of the second heat exchanger 12 and the third heat exchanger 13 is arranged on the upstream side and the other is arranged on the downstream side in the direction of air flow. For example, as shown in FIG. 11B , if the third heat exchanger 13 is on the upstream side, the air cooled by the third heat exchanger 13 flows to the second heat exchanger 12 . In that case, the second heat exchanger 12 functions as a condenser, and operation in the cooling operation mode cannot be performed. Conversely, if the second heat exchanger 12 is on the upstream side, in the dehumidifying operation mode, after the second heat exchanger 12 warms the outside air OA, the third heat exchanger 13 cools the outside air OA, thereby dehumidifying. Insufficient quantity.

FIG. 12 is a side view explaining a modification of the arrangement of the second heat exchanger 12 and the third heat exchanger 13 in the air conditioner 200 according to Embodiment 1. FIG. FIG. 12 shows a state in which the second heat exchanger 12 and the third heat exchanger 13 are viewed from the side. You may make it arrange|position the 2nd heat exchanger 12 and the 3rd heat exchanger 13 up and down along a perpendicular direction like the modification of FIG. Specifically, the second heat exchanger 12 is arranged on the lower side, and the third heat exchanger 13 is arranged on the upper side. Also in the modified example, at least part of the outside air OA flowing through the air supply path 19 passes only through the second heat exchanger 12 . This can prevent the second heat exchanger 12 from acting as a condenser in the cooling operation mode.

As shown in FIG. 5 above, the air conditioner 200 includes one expansion device 17 and three heat exchangers 11 to 13 on the refrigerant circuit, and the first heat exchanger 11 is in the return air path 20. installed, the second heat exchanger 12 and the third heat exchanger 13 are arranged in the air supply path 19 . In the dehumidification operation, the air heated by the second heat exchanger 12 and the air cooled by the third heat exchanger 13 are mixed in the duct etc. forming the air supply path 19 before reaching the room 300. and a uniform temperature. Therefore, as shown in FIG. 12, when the second heat exchanger 12 is arranged below the third heat exchanger 13 in the vertical direction, high-temperature air rises due to buoyancy. The air that has passed through the second heat exchanger 12 rises. As a result, mixing of the air heated by the second heat exchanger 12 and the air cooled by the third heat exchanger 13 can be promoted. As a result, it is possible to provide air having a uniform temperature with little unevenness in the room 300 and improve comfort.

As described above, in the air conditioner 200 according to Embodiment 1, the refrigerant flows in the same direction in the refrigerant circuit in the cooling operation mode and the dehumidifying operation mode. In the cooling operation mode, the opening degree OP of the expansion device 17 is set within the first range, the first heat exchanger 11 acts as a condenser, and the second heat exchanger 12 and the third heat exchanger 13 are Acts as an evaporator. In the dehumidifying operation mode, the opening degree OP of the expansion device 17 is set within a second range larger than the first range, the first heat exchanger 11 and the second heat exchanger 12 act as condensers, 3 Heat exchanger 13 acts as an evaporator. As described above, the air conditioner 200 according to Embodiment 1 can continuously switch between the dehumidifying operation mode and the cooling operation mode with a simple configuration that does not require switching of the flow path. Therefore, unlike Patent Document 1 described above, it is possible to suppress fluctuations in the pressure of the refrigerant in the heat exchanger that accompany switching of the flow path. As a result, in Embodiment 1, since the temperature fluctuation of the supply air SA supplied to the room 300 by the air conditioner 200 can be suppressed, the supply air SA having a stable temperature is supplied to the room 300, and the temperature inside the room 300 is reduced. of user comfort can be improved.

Further, in the first embodiment, in the dehumidification operation mode, the control unit 90 controls the pressure of the refrigerant on the discharge side or the suction side of the compressor 16, the refrigerant temperature on the outlet side of the second heat exchanger 12, the temperature of the refrigerant on the outlet side of the second heat exchanger 12, the The opening degree OP of the throttle device 17 is controlled based on at least one of the refrigerant temperature on the outlet side of the compressor 13 and the refrigerant temperature on the discharge side of the compressor 16 . Specifically, the control unit 90 reduces the opening degree OP of the expansion device 17 from the current value within the second range so that the second heat exchanger for the outdoor air supplied by the air supply fan 14 Decrease the heating capacity of 12. Conversely, the control unit 90 increases the degree of opening of the expansion device 17 within the second range from the current value so that the outdoor air supplied by the supply fan 14 is heated by the second heat exchanger 12 . increase capacity. As a result, the temperature of the air supplied from the second heat exchanger 12 to the room 300 can be controlled, so that the dehumidification operation that reduces the humidity in the room 300 can be performed while suppressing the temperature drop in the room 300 .

Embodiment 2.
An air conditioner 200B according to Embodiment 2 will be described. FIG. 13 is a refrigerant circuit diagram showing an example of the configuration of an air conditioner 200B according to Embodiment 2. As shown in FIG. Compared with the configuration of FIG. 1 described in Embodiment 1, the configuration of FIG. Since other configurations are the same as those in FIG. 1, they are denoted by the same reference numerals, and descriptions thereof are omitted here.

The first on-off valve 21 is provided in the refrigerant pipe 18 between the first heat exchanger 11 and the second heat exchanger 12 . The opening/closing operation of the first opening/closing valve 21 is controlled by the controller 90 .

A bypass pipe 23 is a bypass pipe branched from the refrigerant pipe 18 . The bypass pipe 23 branches off from the refrigerant pipe 18 at a point C<b>1 between the first heat exchanger 11 and the first on-off valve 21 . Also, the bypass pipe 23 is connected to the refrigerant pipe 18 at a point C2 between the second heat exchanger 12 and the expansion device 17 . At this time, the second refrigerant temperature detector 84 is arranged downstream of the bypass pipe 23 .

The second on-off valve 22 is provided on the bypass pipe 23 . When the second on-off valve 22 is open, refrigerant flows through the bypass pipe 23 . The opening/closing operation of the second opening/closing valve 22 is controlled by the controller 90 .

Next, the operation of the air conditioner 200B according to Embodiment 2 will be described. In Embodiment 2, the controller 90 opens the first on-off valve 21 and closes the second on-off valve 22 in the dehumidifying operation mode. As a result, the operation in the dehumidifying operation mode of the second embodiment is the same as the operation in the dehumidifying operation mode of the first embodiment.

In the cooling operation mode, the controller 90 sets the temperature T 0 of the outside air OA to be higher than the temperature T _R of the return air RA, and the temperature difference _ΔT between the temperature T ₀ of the outside air OA and the temperature T _R of the return air RA. If it is greater than Th9, the first on-off valve 21 is opened and the second on-off valve 22 is closed. The operation in the cooling operation mode of the second embodiment in this case is the same as the operation in the cooling operation mode of the first embodiment.

The threshold Th9 is set in advance based on the design value of the temperature difference ΔT between the temperature T _O of the outside air OA and the temperature T _R of the return air RA assuming normal cooling operation (that is, the theoretical value during normal operation). It may be a fixed value, or a variable value. In that case, for example, the threshold value Th9 is a set value for the room temperature of the room 300 set by the user for the air conditioner 200 by the control unit 90, or the temperature T _O of the outside air OA and the temperature T _R of the return air RA. is determined based on the temperature difference between As a determination method, a data table or an arithmetic expression is stored in advance in the memory, and the control unit 90 uses it to calculate the threshold value Th9. The data table stores a threshold value Th9 for each set value or temperature difference with respect to the room temperature. The arithmetic expression is a function for obtaining the threshold value Th9 using the set value or the temperature difference with respect to the room temperature as a parameter.

On the other hand, in the cooling operation mode, when the temperature difference ΔT between the temperature T _O of the outside air OA and the temperature T _R of the return air RA is equal to or less than the threshold value Th9, or the temperature T _O of the outside air OA is equal to or less than the temperature T _R of the return air RA. , the controller 90 closes the first on-off valve 21 and opens the second on-off valve 22 . As a result, the refrigerant flows through the bypass pipe 23 and flows from the bypass pipe 23 through the expansion device 17 into the third heat exchanger 13 . That is, the refrigerant skips the second heat exchanger 12 and flows through the first heat exchanger 11, the bypass pipe 23, the expansion device 17, and the third heat exchanger 13 in this order. As a result, when the temperature difference ΔT between the outside air OA and the return air RA is small, the second heat exchanger 12, which originally operates as an evaporator, can be prevented from operating as a condenser in the cooling operation mode.

(control unit 90)
FIG. 14 is a flow chart showing the operation of the control unit 90 in the air conditioner 200B according to Embodiment 2. As shown in FIG. In step S31, the controller 90 determines whether the current operation mode of the air conditioner 200B is the dehumidifying operation mode or the cooling operation mode. If the current operation mode of the air conditioner 200B is the dehumidifying operation mode, the control unit 90 proceeds to the process of step S32. On the other hand, when the current operation mode of the air conditioner 200B is the cooling operation mode, the control unit 90 proceeds to the process of step S33.

At step S32, the control unit 90 opens the first on-off valve 21 and closes the second on-off valve 22. That is, the operation in the dehumidifying operation mode of the second embodiment is the same as the operation in the dehumidifying operation mode of the first embodiment.

In step S33, the controller 90 determines that the temperature T _O of the outside air OA is higher than the temperature T _R of the return air RA, and that the temperature difference ΔT between the temperature T _O of the outside air OA and the temperature T _R of the return air RA is a threshold value Th9. Determine if greater than. If all of these conditions are satisfied, the control section 90 proceeds to the process of step S34. Otherwise, the control section 90 proceeds to the process of step S35.

In step S34, the control unit 90 opens the first on-off valve 21 and closes the second on-off valve 22. The operation in the cooling operation mode of the second embodiment in this case is the same as the operation in the cooling operation mode of the first embodiment.

On the other hand, in step S35, the controller 90 determines that it is difficult to operate the second heat exchanger 12 as an evaporator, closes the first on-off valve 21, and opens the second on-off valve 22.

As described above, since the second embodiment basically has the same configuration as the first embodiment, the same effects as those of the first embodiment can be obtained. Furthermore, in Embodiment 2, as shown in FIG. 13, a first on-off valve 21, a second on-off valve 22, and a bypass pipe 23 are added to the configuration of FIG. In the second embodiment, in the cooling operation mode, when the temperature difference ΔT between the temperature T _{0 of the outside air OA and the temperature T R of} the return air RA is small, or the temperature T 0 of the outside air _OA is equal to the temperature T of the return air RA. In the case of _R or less, the control unit 90 closes the first on-off valve 21 and performs control to open the second on-off valve 22 . As a result, in the cooling operation mode, the second heat exchanger 12, which originally operates as an evaporator, can be prevented from operating as a condenser.

Embodiment 3.
An air conditioner 200C according to Embodiment 3 will be described. FIG. 15 is a refrigerant circuit diagram showing an example of the configuration of an air conditioner 200C according to Embodiment 3. As shown in FIG. 1 described in Embodiment 1 differs in that an accumulator 24 is added to the refrigerant pipe 18 between the third heat exchanger 13 and the compressor 16 in FIG. The accumulator 24 stores excess refrigerant in the refrigerant pipe 18 . Since other configurations are the same as those in FIG. 1, they are denoted by the same reference numerals, and descriptions thereof are omitted here. Although the detection units 80 to 88 are omitted in FIG. 15, they are actually provided.

In the third embodiment, in the dehumidifying operation mode, the amount of refrigerant circulating in the refrigerant pipe 18 is reduced by storing the refrigerant in the accumulator 24 .

On the other hand, in the cooling operation mode, by releasing the refrigerant stored in the accumulator 24 to the refrigerant pipe 18, the refrigerant circulating in the refrigerant pipe 18 is increased.

As a result, it is possible to obtain the effect of adjusting the substantial refrigerant charging amount according to the operation mode. The amount of refrigerant to be charged should be adjusted to the operation mode that requires the largest amount of refrigerant.

　Refrigerant is stored in and discharged from the accumulator 24 as needed. For example, consider a case where the control unit 90 controls the opening degree OP of the expansion device 17 using the outlet subcooling degree SC1 or SC2 of the refrigerant at the outlet of the first heat exchanger 11 or the second heat exchanger 12 as an index. In the cooling operation mode, when increasing the degree of subcooling SC1 at the outlet of the first heat exchanger 11, by throttling the throttling device 17, the pressure of the third heat exchanger 13 is reduced and heat exchange is promoted. Superheated gas flows into the accumulator 24 . Therefore, the liquid refrigerant in the accumulator 24 warmed by the superheated gas is released to the refrigerant pipe 18 . On the other hand, in the dehumidifying operation mode, when the outlet supercooling degree SC2 of the second heat exchanger 12 is decreased, opening the expansion device 17 increases the pressure of the third heat exchanger 13, suppressing heat exchange. As a result, liquid refrigerant flows into the accumulator 24 . Therefore, liquid refrigerant is stored in the accumulator 24 .

As described above, since the third embodiment basically has the same configuration as the first embodiment, the same effect as the first embodiment can be obtained. Furthermore, in Embodiment 3, an accumulator 24 is provided between the third heat exchanger 13 and the compressor 16 . As a result, the refrigerant is stored in the accumulator 24 in the dehumidifying operation mode, and the refrigerant stored in the accumulator 24 is released to the refrigerant pipe 18 in the cooling operation mode, thereby preventing a shortage of refrigerant.

11 1st heat exchanger, 12 2nd heat exchanger, 13 3rd heat exchanger, 14 supply air fan, 15 return air fan, 16 compressor, 17 expansion device, 18 refrigerant pipe, 19 air supply route, 20 return air path, 21 first on-off valve, 22 second on-off valve, 23 bypass pipe, 24 accumulator, 30 flow path switching device, 31 second expansion device, 40 saturated steam line, 41 saturated liquid line, 80 first temperature and humidity detection Section 81 Second temperature/humidity detection section 82 Outside air temperature detection section 83 First refrigerant temperature detection section 84 Second refrigerant temperature detection section 85 Third refrigerant temperature detection section 86 Discharge pressure detection section 87 Suction pressure detection part, 88 discharge temperature detection part, 89 fourth refrigerant temperature detection part, 90 control part, 100 heat transfer tube, 100b refrigerant flow path, 101 heat transfer tube, 101a inner column, 101b refrigerant flow path, 102 fins, 103 fins, 200 air Conditioner, 200A: Air conditioner, 200B: Air conditioner, 200C: Air conditioner, 300: Indoor, 301: Outdoor, EA: Exhaust, OA: Outside air, RA: Return air, SA: Supply air, SC1: Outlet supercooling degree of first heat exchanger 11 , SC2 Degree of subcooling at the outlet of the second heat exchanger 12, SHd Degree of superheat at the outlet of the compressor 16, SHe Degree of superheat at the outlet of the third heat exchanger 13, Th1 Threshold, Th2 Threshold, Th3-1 Threshold, Th3-2 Threshold , Th4 threshold (first threshold), Th5 threshold, Th6-1 threshold, Th6-2 threshold, Th7 threshold, Th8 threshold, Th9 threshold (second threshold).

Claims (10)

an air supply fan and an air supply path for supplying outdoor air into the room;
a return air fan and a return air path for returning the indoor air to the outdoor;
a heat pump circuit in which a compressor, a first heat exchanger, a second heat exchanger, an expansion device, and a third heat exchanger are connected in this order by refrigerant pipes;
An air conditioner comprising: a control unit that controls operations of the supply air fan, the return air fan, and the heat pump circuit,
The first heat exchanger is arranged in the return air path, and performs heat exchange between the refrigerant flowing inside the first heat exchanger and the air flowing in the return air path,
The second heat exchanger and the third heat exchanger are arranged in the air supply path, and the refrigerant flowing inside the second heat exchanger and the third heat exchanger and the air supply path, respectively heat exchange with the air flowing through the
The air conditioner has, as operation modes, a cooling operation mode for cooling the room and a dehumidifying operation mode for dehumidifying the room,
In the dehumidifying operation mode and the cooling operation mode, the direction in which the refrigerant discharged from the compressor flows into the first heat exchanger and the refrigerant discharged from the third heat exchanger is sucked into the compressor. , the refrigerant flows through the refrigerant pipe,
In the cooling operation mode, the first heat exchanger acts as a condenser, the second heat exchanger and the third heat exchanger act as evaporators,
In the dehumidification mode of operation, the first heat exchanger and the second heat exchanger act as condensers, and the third heat exchanger acts as an evaporator.
Air conditioner. In the cooling operation mode, the degree of opening of the expansion device is set to a value within a first range,
In the dehumidifying operation mode, the opening degree of the expansion device is set to a value within a second range that is larger than the first range.
The air conditioner according to claim 1. The control unit, in the dehumidifying operation mode,
reducing the opening degree of the expansion device from the current value within the second range to reduce the heating capacity of the second heat exchanger for the outdoor air supplied by the air supply fan;
By increasing the opening degree of the expansion device from the current value within the second range, thereby increasing the heating capacity of the second heat exchanger for the outdoor air supplied by the air supply fan. ,
controlling the temperature of the air supplied from the second heat exchanger into the room;
The air conditioner according to claim 2. a discharge pressure detection unit that detects the pressure on the discharge side of the compressor;
A refrigerant temperature detection unit that detects the refrigerant temperature on the outlet side of the second heat exchanger,
The control unit, in the dehumidifying operation mode,
calculating the degree of subcooling at the outlet of the second heat exchanger based on the pressure on the discharge side of the compressor and the refrigerant temperature on the outlet side of the second heat exchanger;
When the degree of supercooling at the outlet of the second heat exchanger is equal to or less than the first threshold, the opening of the expansion device is reduced from the current value within the second range to reduce the amount of air supplied by the supply fan. reducing the heating capacity of the second heat exchanger for the outdoor air,
If the outlet subcooling degree of the second heat exchanger is greater than the first threshold, the opening of the throttling device is increased from the current value within the second range so that air is supplied by the supply fan. increasing the heating capacity of the second heat exchanger for the outdoor air to be
The air conditioner according to claim 2 or 3. The heat transfer area for performing the heat exchange of the second heat exchanger is larger than the heat transfer area for performing the heat exchange of the first heat exchanger,
The air conditioner according to any one of claims 1 to 4. The first heat exchanger has therein a heat transfer tube through which the refrigerant flows,
The second heat exchanger has therein a heat transfer tube through which the refrigerant flows,
The volume of each refrigerant channel through which the refrigerant flows in the heat transfer tube of the second heat exchanger is smaller than the volume of each refrigerant channel through which the refrigerant flows in the heat transfer tube of the first heat exchanger,
The air conditioner according to any one of claims 1 to 5. a first on-off valve arranged between the first heat exchanger and the second heat exchanger;
a bypass pipe branched from between the first heat exchanger and the first on-off valve and connected between the second heat exchanger and the expansion device;
A second on-off valve provided in the bypass pipe,
The control unit
In the dehumidifying operation mode, the first on-off valve is opened, the second on-off valve is closed,
In the cooling operation mode,
When the temperature difference between the temperature of the outdoor air supplied by the supply air fan and the temperature of the indoor air returned by the return air fan is greater than a second threshold, the first on-off valve is closed. open, close the second on-off valve,
when the temperature difference is equal to or less than the second threshold, the first on-off valve is closed and the second on-off valve is opened;
The air conditioner according to any one of claims 1 to 6. The third heat exchanger and the second heat exchanger are arranged in the air supply path such that at least part of the air flowing in the air supply path passes only through the second heat exchanger.
The air conditioner according to any one of claims 1 to 7. The third heat exchanger is arranged vertically above the second heat exchanger,
The air conditioner according to any one of claims 1 to 8. An accumulator disposed between the third heat exchanger and the compressor for storing liquid refrigerant during the dehumidifying operation mode,
The air conditioner according to any one of claims 1 to 9.

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