Patent ID: 12215905

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Preferred embodiments of an air conditioning apparatus disclosed in the present disclosure will be explained in detail below with reference to the accompanying drawings. Furthermore, the technology of the present disclosure is not limited to the embodiments.

[Configuration of Air Conditioning Apparatus]

FIG.1Ais a refrigerant circuit diagram illustrating an air conditioning apparatus according to the present disclosure. An air conditioning apparatus1is applied to an air conditioning apparatus that cools and heats inside a room and includes, as illustrated inFIG.1A, an outdoor unit2and an indoor unit3. The outdoor unit2is connected to the indoor unit3by a liquid pipe5and a gas pipe6. The outdoor unit2includes a compressor21, a four-way valve (channel switching unit)22, an outdoor heat exchanger23, an outdoor expansion valve24(second expansion valve), and an outdoor unit control unit200(control unit). The indoor unit3includes an indoor heat exchanger31and an indoor expansion valve (first expansion valve)32.

The compressor21includes a discharge port18as a discharge portion and an intake port19as an intake portion. The compressor21compresses, by being controlled by the outdoor unit control unit200, a refrigerant supplied from the intake port19via an intake pipe42and a four-way valve22, and then, supplies the compressed refrigerant from the discharge port18to the four-way valve22via a discharge pipe41.

The four-way valve22is connected to the discharge pipe41and the intake pipe42, is connected to the outdoor heat exchanger23via a refrigerant pipe43, and is connected to the indoor unit3via a refrigerant pipe44and the gas pipe6. The indoor unit3and the outdoor heat exchanger23are connected via a refrigerant pipe45. The four-way valve22switches, by being controlled by the outdoor unit control unit200, the air conditioning apparatus1to one of a heating mode and a cooling mode. When the air conditioning apparatus1is switched to the cooling mode, the four-way valve22supplies, to the outdoor heat exchanger23, the refrigerant discharged from the compressor21via the discharge pipe41and supplies, to the compressor21via the intake pipe42, the refrigerant flowing out from the indoor unit3. When the air conditioning apparatus1is switched to the heating mode, the four-way valve22supplies, to the indoor unit3, the refrigerant discharged from the compressor21via the discharge pipe41and supplies, to the compressor21via the intake pipe42, the refrigerant flowing out from the outdoor heat exchanger23.

The outdoor heat exchanger23is connected to the outdoor expansion valve24via the refrigerant pipe45. An outdoor fan25is arranged in the vicinity of the outdoor heat exchanger23. The outdoor fan25brings outside air into the interior of the outdoor unit2by being rotated by a fan motor (not illustrated) and releases the outside air, which is subjected to heat exchange with the refrigerant by the outdoor heat exchanger23, to the outside of the outdoor unit2. The outdoor heat exchanger23performs heat exchange, in a case of a cooling mode, between the refrigerant supplied from the four-way valve22and the outside air that is brought into the interior of the outdoor unit2, and then, supplies the refrigerant, which has been subjected to heat exchange, to the expansion valve24. The outdoor heat exchanger23performs heat exchange, in a case of a heating mode, between the refrigerant supplied from the outdoor expansion valve24and the outside air that is brought into the interior of the outdoor unit2, and then, supplies the refrigerant that has been subjected to heat exchange to the four-way valve22.

The outdoor expansion valve24is connected to the indoor expansion valve32included in the indoor unit3via the refrigerant pipe45, the liquid pipe5, and a refrigerant pipe46. The outdoor expansion valve24decompresses, in a case of a cooling mode, the refrigerant supplied from the outdoor heat exchanger23by performing adiabatic expansion, and supplies a gas-liquid two-phase refrigerant that that enters a low-temperature and low-pressure state to the indoor unit3. The outdoor expansion valve24decompresses, in a case of a heating mode, the refrigerant supplied from the indoor unit3by performing adiabatic expansion, and supplies a gas-liquid two-phase refrigerant that enters a low-temperature low-pressure to the outdoor heat exchanger23. Furthermore, the degree of opening of the outdoor expansion valve24is adjusted by being controlled by the outdoor unit control unit200and the outdoor expansion valve24adjusts, in a case of a heating mode, the flow rate of the refrigerant supplied from the indoor unit3to the outdoor heat exchanger23. In a case of a cooling mode, the outdoor expansion valve24adjusts the flow rate of the refrigerant that is supplied from the outdoor heat exchanger23to the indoor unit3.

In addition to the configuration described above, a discharge temperature sensor71that detects a temperature of the refrigerant discharged from the compressor21(discharge temperature described above) and a discharge pressure sensor72that detects a pressure are provided at the discharge pipes41included in the outdoor unit2. Furthermore, an intake temperature sensor73that detects a temperature of the refrigerant that is taken in the compressor21(intake temperature) and an intake pressure sensor74that detects a pressure are provided at the intake pipe42. Furthermore, between the outdoor expansion valve24and the outdoor heat exchanger23in the refrigerant pipe45, an outdoor-side refrigerant temperature sensor75that detects a temperature of the refrigerant passing through the subject point is arranged. Furthermore, an outdoor heat exchange intermediate temperature sensor76that detects a temperature of the refrigerant flowing inside the outdoor heat exchanger23is provided at the outdoor heat exchanger23.

The indoor unit3includes the indoor heat exchanger31, the indoor expansion valve32, and an indoor fan33. The indoor expansion valve32is connected to the indoor heat exchanger31via the refrigerant pipe46. The indoor expansion valve32decompresses, in a case of a cooling mode, the refrigerant supplied from the outdoor unit2by performing adiabatic expansion, and then, supplies a gas-liquid two-phase refrigerant that enters a low-temperature low-pressure state to the indoor heat exchanger31. The indoor expansion valve32decompresses, in a case of a heating mode, the refrigerant supplied from the indoor heat exchanger31by performing adiabatic expansion, and then, supplies a gas-liquid two-phase refrigerant that enters the low-temperature low-pressure state to the outdoor unit2.

The indoor fan33is arranged in the vicinity of the indoor heat exchanger31, brings indoor air into the interior of the indoor unit3by being rotated by a fan motor (not illustrated), and releases the indoor air that has been subjected to heat exchange with the refrigerant by the indoor heat exchanger31. The indoor heat exchanger31is connected to the four-way valve22via the refrigerant pipe44and is connected to the indoor expansion valve32via the refrigerant pipe45.

The indoor heat exchanger31is connected to the four-way valve22via a refrigerant pipe47, the gas pipe6, and the refrigerant pipe44. The indoor heat exchanger31functions as an evaporator when the air conditioning apparatus1is switched to the cooling mode, and functions as a condenser when the air conditioning apparatus1is switched to the heating mode. Namely, the indoor heat exchanger31performs heat exchange, in a case of the cooling mode, between the gas-liquid two-phase refrigerant, which is supplied from the indoor expansion valve32and is into the low-temperature low-pressure state, and indoor air, which is brought into the interior of the indoor unit3, releases the indoor air that has been subjected to heat exchange into a room, and supplies the refrigerant that has been subjected to heat exchange to the four-way valve22. The indoor heat exchanger31performs heat exchange, in a case of the heating mode, between the refrigerant that is supplied from the four-way valve22and the indoor air that is brought in the interior of the indoor unit3, releases the indoor air that has been subjected to heat exchange, and supplies the refrigerant that has been subjected to heat exchange to the indoor expansion valve32.

In addition to the configuration described above, between the indoor expansion valve32and the indoor heat exchanger31connected via the refrigerant pipe46, an indoor-side refrigerant temperature sensor77that detects a temperature of the refrigerant passing through the subject point is arranged. Furthermore, an indoor heat exchange intermediate temperature sensor78that detects a temperature of the refrigerant flowing through the interior of the indoor heat exchanger31is arranged at the indoor heat exchanger31. Furthermore, an indoor temperature sensor79that detects a room temperature, i.e., a temperature of the indoor air flowing into the interior of the indoor unit3, is arranged in the vicinity of an inlet port, which is not illustrated, of the indoor unit3.

[Configuration of Outdoor Unit Control Unit]

The outdoor unit control unit200is constituted by what is called a microcomputer and is mounted on a control substrate that is stored in an electrical component box, which is not illustrated, included in the outdoor unit2. As illustrated inFIG.1B, the outdoor unit control means200includes a CPU210, a storage unit220, a communication unit230, a sensor input unit240, and a degree-of-dryness calculating unit (degree-of-dryness calculating means)250(hereinafter, in this specification, the outdoor unit control means200is sometimes simply referred to as a control means).

The storage unit220is constituted by a flash memory and stores therein a control program of the outdoor unit2, detection values associated with respective detection signals from various sensors, a control state of, for example, the compressor21or the outdoor fan25, or the like. Furthermore, although not illustrated, the storage unit220stores therein, in advance, a rotation speed table in which the rotation speed of the compressor21is defined in accordance with a request capacity received from the indoor unit3.

The communication unit230is an interface for communicating with the indoor unit3. The sensor input unit240acquires detection results obtained from various sensors included in the outdoor unit2and outputs the acquired detection results to the CPU210. The degree-of-dryness calculating unit250calculates the degree of dryness of the refrigerant from the detection results obtained from the various sensors included in the outdoor unit2.

The CPU210acquires, via the sensor input unit240, the above described detection result obtained from each of the sensors included in the outdoor unit2. Furthermore, the CPU210acquires a control signal sent from the indoor unit3via the communication unit230. The CPU210performs drive control of the compressor21or the outdoor fan27on the basis of the acquired detection results, the control signal, or the like. Furthermore, the CPU210performs switching control of the four-way valve22on the basis of the acquired detection results or the control signal. Furthermore, the CPU210adjusts the degree of opening of the outdoor expansion valve24or the indoor expansion valve32on the basis of the acquired detection results or the control signal.

In the above, the air conditioning apparatus1according to the embodiment is configured as a single type that includes a single piece of the indoor unit3associated with a single piece of the outdoor unit2; however, the air conditioning apparatus1may also be configured as a multiple type that includes a plurality of the indoor units3associated with a single piece of the outdoor unit2.

[Operation of Air Conditioning Apparatus]

When a user of the air conditioning apparatus1adjusts a temperature of a room in which the indoor unit3is arranged, the user starts up the air conditioning apparatus1by operating a remote controller, which is not illustrated, and inputs an operation condition to an indoor-unit control unit500. When the operation condition is input, the indoor-unit control unit500sends the input operation condition and an indoor temperature to the outdoor unit control unit200. The outdoor unit control unit200performs either the heating operation or the cooling operation on the basis of the operation condition received from the indoor-unit control unit500and the indoor temperature. InFIG.1A, the flow of the refrigerant inside the refrigerant circuit at the time of the heating operation is indicated by an arrow.

[Cooling Operation]

When the outdoor unit control unit200performs the cooling operation, the outdoor unit control unit200switches the four-way valve22to the cooling mode by controlling the four-way valve22. The compressor21controlled by the outdoor unit control unit200compresses a gas refrigerant taken in from the four-way valve22via the intake pipe42. The compressor21discharges the compressed high-temperature and high-pressure gas refrigerant to the four-way valve22. When the operation is switched to the cooling mode, the four-way valve22supplies, to the outdoor heat exchanger23, the high-temperature and high-pressure gas refrigerant discharged from the compressor21. The outdoor heat exchanger23condenses the high-temperature and high-pressure gas refrigerant to liquefies the gas refrigerant by performing heat exchange between the outside air that is brought into the interior of the outdoor unit2and the high-temperature and high-pressure gas refrigerant. The outdoor heat exchanger23supplies the high-pressure liquid refrigerant to the outdoor expansion valve24.

The outdoor expansion valve24performs adiabatic expansion on the high-pressure liquid refrigerant supplied from the outdoor heat exchanger23to generate a low-temperature and low-pressure gas-liquid two-phase refrigerant. The outdoor expansion valve24supplies the low-temperature and low-pressure gas-liquid two-phase refrigerant to the indoor heat exchanger31via the indoor expansion valve32included in the indoor unit3. The indoor heat exchanger31evaporates the low-temperature and low-pressure gas-liquid two-phase refrigerant to gasify the refrigerant by performing heat exchange between the low-temperature and low-pressure gas-liquid two-phase refrigerant that is supplied from the indoor expansion valve32and the indoor air that is brought in the interior of the indoor unit3. The indoor heat exchanger31supplies a low-pressure gas refrigerant to the four-way valve22. When the four-way valve22is switched to the cooling mode, the four-way valve22supplies, to the compressor21, a low-pressure gas refrigerant flowing out from the indoor heat exchanger31.

[Heating Operation]

When the outdoor unit control unit200performs the heating operation, the outdoor unit control unit200switches the four-way valve22to the heating mode by controlling the four-way valve22. The compressor21controlled by the outdoor unit control unit200compresses the gas refrigerant taken in from the four-way valve22via the intake pipe42. The compressor21discharges the compressed high-temperature and high-pressure gas refrigerant to the four-way valve22. When the operation is switched to the heating mode, the four-way valve22supplies the high-temperature and high-pressure gas refrigerant discharged from the compressor21to the indoor heat exchanger31included in the indoor unit3. The indoor heat exchanger31condenses the high-temperature and high-pressure gas refrigerant to liquefy the gas refrigerant by performing heat exchange between the high-temperature and high-pressure gas refrigerant that is supplied from the four-way valve22to the indoor unit3and the indoor air that is brought into the interior of the indoor unit3. The indoor heat exchanger31supplies the high-pressure liquid refrigerant to the indoor expansion valve32.

The indoor expansion valve32performs adiabatic expansion on the high-pressure liquid refrigerant supplied from the indoor heat exchanger31to generate a low-temperature and low-pressure gas-liquid two-phase refrigerant. The indoor expansion valve32supplies the low-temperature and low-pressure gas-liquid two-phase refrigerant to the outdoor heat exchanger23via the outdoor expansion valve24. The outdoor heat exchanger23evaporates the low-temperature and low-pressure refrigerant to gasify the refrigerant by performing heat exchange between the outside air that is brought in the interior of the outdoor unit2and the low-temperature and low-pressure gas-liquid two-phase refrigerant that is supplied from the expansion valve24. The outdoor heat exchanger23supplies a low-pressure gas refrigerant to the four-way valve22. When the four-way valve22is being switched to the heating mode, the four-way valve22supplies, to the compressor21, a low-pressure gas refrigerant flowing out from the outdoor heat exchanger23.

[Control Performed by Outdoor Unit Control Unit (Control Means)]

In the following, a control method for controlling the outdoor expansion valve (the second expansion valve)24and the indoor expansion valve (the first expansion valve)32performed by the outdoor unit control unit (control means)200will be described in detail. Furthermore, in a description below, a control method performed by the outdoor unit control unit200at the time of the heating operation will be described and a description of the control method performed at the time of the cooling operation will be omitted. At the time of operation of the air conditioning apparatus1, an indoor-unit control unit, which is not illustrated, outputs a set temperature that is an operation condition that is input by an operation performed by a user and a request rotation speed that is stored in a storage unit, which is not illustrated, included in the indoor-unit control unit and that is defined in advance from a room temperature detected by the indoor temperature sensor79, and then, sends the set temperature and the request rotation speed to the outdoor unit control unit200. The request rotation speed is a rotation speed of the compressor21needed to set the room temperature to the set temperature and is defined in accordance with a difference between the set temperature and the room temperature. The outdoor unit control unit200performs control such that the compressor21satisfies the request rotation speed.

When the air conditioning apparatus1performs the heating operation, the indoor expansion valve32adjusts the degree of opening such that the refrigerant inside the liquid pipe5enters a gas-liquid two phase state, and the outdoor expansion valve24performs control such that the degree of its opening is a predetermined degree of opening (full open). Specifically, the outdoor unit control unit200performs degree-of-opening control of the indoor expansion valve32on the basis of target discharge temperature control. The target discharge temperature control is control of adjusting the degree of opening of the expansion valve such that a discharge temperature Td is equal to a target value (target discharge temperature Tdt) for the purpose of setting the refrigerant taken into the compressor21to be in an appropriate state.

Here, the state of the refrigerant taken into the compressor21is defined to be in an appropriate state when the degree of dryness is about 1 (for example, 0.8 to 1.0) and a degree of suction superheat SH is about 0 (for example, 0 to 5). The reason is that, when the degree of dryness falls much below 1, a liquid refrigerant is taken into the compressor21and thus the compressor21may possibly fail due to liquid compression. Furthermore, when the degree of suction superheat SH far exceeds 0, the temperature inside the compressor21excessively rises, thus leading to degradation of reliability.

The target discharge temperature Tdt is calculated on the basis of the detection results that are detected by various sensors arranged in the air conditioning apparatus1and, namely, the target discharge temperature Tdt is an estimated value of the discharge temperature Td in a case in which the refrigerant taken into the compressor21is an appropriate state.

The detection results thereof includes detection values obtained by the discharge pressure sensor72, the intake temperature sensor73, the intake pressure sensor74, the outdoor heat exchange intermediate temperature sensor76, and the indoor heat exchange intermediate temperature sensor78. The target discharge temperature Tgt is a value obtained by adding an adjusted value to a theoretical discharge temperature. The theoretical discharge temperature is a theoretical value calculated on the basis of a load condition of the air conditioning apparatus1specified by the detection results that are detected by various sensors without taking into account a pressure loss or an operating efficiency in the refrigerant circuit included in the air conditioning apparatus1. The theoretical discharge temperature is calculated from the load condition of a refrigeration cycle (a pressure and a temperature of each unit) and the degree of target superheat Tsh. The degree of target superheat Tsh is set to be 0, i.e., the degree of dryness of the refrigerant flowing into the compressor21is about 1, and furthermore, the degree of suction superheat SH is about 0.

By performing control as described above, the refrigerant is decompressed, at the time of the heating operation, by the indoor expansion valve32disposed on the upstream side of the liquid pipe5, so that it is possible to decrease the density of the refrigerant flowing inside the liquid pipe5. Consequently, it is possible to reduce the amount of refrigerant to be filled in the refrigerant circuit.

In contrast, even when the outdoor expansion valve24that is the expansion valve disposed on the downstream side of the liquid pipe5is fully opened, the pressure of the refrigerant flowing out from the outdoor expansion valve24is decreased caused by a pressure loss due to channel resistance. Furthermore, when the degree of opening of the indoor expansion valve32is changed, the degree of dryness of the refrigerant that is in the gas-liquid two phase state and that passes through the liquid pipe5and the outdoor expansion valve24and that flows into the outdoor heat exchanger23varies. When the degree of dryness varies, the refrigerant density is changed. For example, when the degree of dryness rises, the refrigerant density is decreased. When the density of the refrigerant flowing inside the liquid pipe5and the indoor expansion valve32is decreased, the flow rate of the refrigerant is increased as compared to a case in which the density of the refrigerant is high. Consequently, a pressure loss occurring when the refrigerant flows through the liquid pipe5and the outdoor expansion valve24is increased and the pressure of the refrigerant flowing out from the liquid pipe5is decreased.FIG.3is a graph illustrating a relationship based on the degree of dryness of the refrigerant that is in the gas-liquid two phase state and a pressure loss [Pa] of the refrigerant passing through the liquid pipe5and the outdoor expansion valve24when the degree of dryness is 0. In the graph, the horizontal axis indicates the degree of dryness and the vertical axis indicates the pressure loss. Furthermore, the pressure loss indicated on the vertical axis is based on the state in which the degree of dryness is 0. As illustrated in the drawing, the pressure loss of the refrigerant passing through the liquid pipe5and the outdoor expansion valve24is rapidly increased in accordance with a rise in the degree of dryness.

Namely, when the degree of dryness of the refrigerant that flows into the outdoor heat exchanger23and that is in the gas-liquid two phase state is high, when the indoor expansion valve32that is the expansion valve disposed on the upstream side of the liquid pipe5is controlled, the total amount of decompression (the indoor expansion valve32+the liquid pipe5+the outdoor expansion valve24) at the time of a change in the degree of opening of the indoor expansion valve32is increased. Consequently, controllability becomes worse. For example, when an amount of decompression per units of control variable of the expansion valve is rapidly increased, a low pressure in the refrigerant circuit in the air conditioning apparatus1is excessively decreased. Consequently, the reliability is degraded due to an excessive rise in temperature of the compressor21caused by an excessive decrease in the density of the refrigerant taken into the compressor21. Conventionally, the degree of dryness of the refrigerant flowing into the evaporator (heat exchanger disposed on the downstream side of the liquid pipe) during an operation in which the discharge temperature Td is stable in the vicinity of the target discharge temperature Tdt shifts within a range between 0.1 and 0.2. Accordingly, when the degree of dryness exceeds 0.2, the total amount of decompression (the indoor expansion valve32+the liquid pipe5+the outdoor expansion valve24) at the time of a change in the degree of opening of the indoor expansion valve32is increased, and thus, it may be said that the reliability of the compressor21possibly be degraded.

Thus, the outdoor unit control unit200includes the degree-of-dryness calculating unit250that calculates the degree of dryness of the refrigerant flowing into the heat exchanger (the outdoor heat exchanger23at the time of the heating operation) disposed on the downstream side of the liquid pipe5, and performs, when the calculation result (the degree of dryness) obtained by the degree-of-dryness calculating means250exceeds a threshold A, an inhibition mode of inhibiting control that is performed in the direction of decreasing the degree of opening of the expansion valve (the indoor expansion valve32at the time of the heating operation) disposed on the upstream side of the liquid pipe5. Consequently, even in a case in which an amount of decompression per units of control variable of the expansion valve is increased, it is possible to prevent a decrease in reliability of the compressor.

Furthermore, the outdoor unit control unit200performs target discharge temperature control of the degree of opening of the expansion valve (the outdoor expansion valve24at the time of the heating operation) disposed on the downstream side during the inhibition mode. Consequently, even during the inhibition mode, it is possible to perform control such that the refrigerant taken into the compressor21is in an appropriate state.

In the following, a control method performed by the outdoor unit control unit (control means)200according to the present disclosure will be described in detail with reference toFIG.2andFIG.3.FIG.2is a flowchart illustrating a control method performed by the outdoor unit control unit200at the time of the heating operation. During the heating operation, the outdoor unit control unit200repeatedly performs the process at Step ST01and the subsequent processes.

First, the outdoor unit control unit200judges whether the discharge temperature Td detected by the discharge temperature sensor71exceeds the target discharge temperature Tdt (ST01). The target discharge temperature Tdt is calculated, as described above, on the basis of the detection results detected by the various sensors arranged in the air conditioning apparatus1, and the detection results thereof include detection values obtained by the discharge pressure sensor72, the intake temperature sensor73, the intake pressure sensor74, the outdoor heat exchange intermediate temperature sensor76, and the indoor heat exchange intermediate temperature sensor78.

When the discharge temperature Td exceeds the target discharge temperature Tdt (YES at ST01), it is judged whether the outdoor expansion valve (the second expansion valve)24is a predetermined degree of opening, i.e., is fully opened (ST02). When the outdoor expansion valve24is fully opened (YES at ST02), the outdoor unit control unit200controls the degree of opening of the indoor expansion valve (the first expansion valve)32in the direction of opening the indoor expansion valve32(ST04), and decreases the discharge temperature Td. When the outdoor expansion valve24is not fully opened (NO at ST02), the outdoor unit control unit200controls the outdoor expansion valve24in the direction of opening the outdoor expansion valve24(ST04ST05), and decreases the discharge temperature Td. When the indoor expansion valve32is controlled in the direction of opening the indoor expansion valve32that is disposed on the upstream side of the liquid pipe5, the density of the refrigerant flowing inside the liquid pipe5rises, which is preferable when an amount of decompression can be adjusted by the outdoor expansion valve24disposed on the downstream side of the liquid pipe5.

Furthermore, when the discharge temperature Td is equal to or less than the target discharge temperature Tdt (NO at ST01), the outdoor unit control unit200judges whether the degree of dryness of the refrigerant flowing into the outdoor heat exchanger23is equal to or less than the threshold A (ST03), and, when the degree of dryness is equal to or less than the threshold A (YES at ST03), the outdoor unit control unit200controls the indoor expansion valve (the first expansion valve)32in the direction of narrowing (decreasing the degree of opening) the indoor expansion valve (the first expansion valve)32such that the discharge temperature Td is equal to the target discharge temperature Tdt (ST06). The threshold A is stored in advance in a storage unit, which is not illustrated, included in the outdoor unit control unit200. The degree of dryness of the refrigerant flowing into the outdoor heat exchanger23can be calculated from a condensation temperature (a detection value obtained by the indoor heat exchange intermediate temperature sensor78at the time of the heating operation), an evaporation temperature (a detection value obtained by the outdoor heat exchange intermediate temperature sensor76at the time of the heating operation), and a condenser outlet temperature (a detection value obtained by the indoor-side refrigerant temperature sensor77at the time of the heating operation). The threshold A is, for example, as described above, 0.2. Furthermore, an allowable value of the threshold A varies in accordance with an inner diameter or a length of the liquid pipe5, a valve diameter of the outdoor expansion valve24, or the like. Specifically, when the inner diameter of the liquid pipe5is small, the length of the liquid pipe5is long, or the valve diameter of the outdoor expansion valve24is small, a pressure loss of the refrigerant passing through the liquid pipe5and the outdoor expansion valve24is large. Accordingly, even in a case of the same degree of dryness, the threshold A is set to be a small value as compared to a case in which the inner diameter of the liquid pipe5is large, the length of the liquid pipe5is small, or the valve diameter of the outdoor expansion valve24is large. Furthermore, as the circulation volume of the refrigerant is increased, the pressure loss of the refrigerant passing through the liquid pipe5and the outdoor expansion valve24is increased. Accordingly, the threshold A may also be changed in accordance with a change in the circulation volume of the refrigerant. Specifically, as the rotation speed of the compressor21is increased, a larger value may also be set to the threshold A.

In contrast, when the degree of dryness exceeds the threshold A (NO at ST03), the outdoor unit control unit200starts an inhibition mode of inhibiting control that is performed in the direction of narrowing the indoor expansion valve32(ST07), the outdoor unit control unit200performs control the outdoor expansion valve (the second expansion valve)24(decreasing the degree of opening) instead of the indoor expansion valve32in the direction of narrowing the outdoor expansion valve (the second expansion valve)24such that the discharge temperature Td is equal to the target discharge temperature Tdt (ST08). When the degree of dryness exceeds 0.1, the refrigerant density is rapidly changed in accordance with a change in the degree of dryness. When a control is performed in the direction of narrowing the indoor expansion valve, the pressure loss of the refrigerant flowing inside the liquid pipe5and the indoor expansion valve32is increased, so that the total amount of decompression may possibly and rapidly be increased. Accordingly, by narrowing the outdoor expansion valve24disposed on the most downstream side, an increase in the total amount of decompression is prevented. After that, the outdoor unit control unit200ends the inhibition mode (ST09).

As described above, when the degree of dryness of the refrigerant flowing into the outdoor heat exchanger23is less than or equal to the threshold A, the outdoor unit control unit200performs a normal mode of controlling the indoor expansion valve (the first expansion valve)32such that the refrigerant flowing inside the liquid pipe5is in the gas-liquid two phase state, and controlling the outdoor expansion valve (the second expansion valve)24such that the degree of opening of the outdoor expansion valve (the second expansion valve)24is equal to a predetermined degree of opening (full open) (ST01to ST06). Furthermore, when the degree of dryness of the refrigerant flowing into the outdoor heat exchanger23exceeds the threshold A, the outdoor unit control unit200performs the inhibition mode of inhibiting control that is performed in the direction of decreasing the degree of opening of the indoor expansion valve (the first expansion valve)32, and controls the degree of opening of the outdoor expansion valve (the second expansion valve)24such that the refrigerant taken into the compressor21is in an appropriate state during the inhibition mode. Accordingly, even when the degree of dryness of the refrigerant flowing into the outdoor heat exchanger23is high and an amount of decompression per units of control variable of the expansion valve is increased, it is possible to prevent a decrease in reliability of the compressor. Furthermore, even during the inhibition mode, it is possible to perform control such that the refrigerant taken into the compressor21is in an appropriate state.

Furthermore, in the embodiment, a description has been given of the control method performed by the outdoor unit control unit200at the time of the heating operation; however, the technology described in the present disclosure is also applicable at the time of the cooling operation. In a case of the cooling operation, the outdoor unit control unit200includes the degree-of-dryness calculating unit250that calculates the degree of dryness of the refrigerant flowing into the indoor heat exchanger31that is the heat exchanger disposed on the downstream side of the liquid pipe5, and, when the degree of dryness exceeds the threshold A, the outdoor unit control unit200performs the inhibition mode of inhibiting control that is performed in the direction of reducing the degree of opening of the outdoor expansion valve (the second expansion valve)24that is the expansion valve disposed on the upstream side of the liquid pipe5. Accordingly, even when an amount of decompression of the units of control variable of the expansion valve is increased, it is possible to prevent a decrease in reliability of the compressor.

Furthermore, the outdoor unit control unit200controls the degree of opening of the indoor expansion valve (the first expansion valve)32that is the expansion valve disposed on the downstream side of the liquid pipe5such that the refrigerant taken into the compressor21is in an appropriate state during the inhibition mode. Accordingly, even during the inhibition mode, it is possible to perform control such that the refrigerant taken into the compressor21is in an appropriate state.

Furthermore, in the embodiment, the expansion valve (at the time of normal mode) disposed on the upstream side of the liquid pipe5and the expansion valve (at the time of inhibition mode) disposed on the downstream side of the liquid pipe5are subjected to degree-of-opening control on the basis of target discharge temperature control. However, the embodiment is not limited to this as long as the degree of opening can be adjusted such that the refrigerant inside the liquid pipe5is in a gas-liquid two phase state; therefore, it may also be possible to use a method (degree of target superheat control) for performing control such that the degree of suction superheat, instead of the discharge temperature, is equal to a target value (for example, 2 to 5). Furthermore, the degree of suction superheat is calculated from, for example, an evaporation temperature (a detection value of the indoor heat exchange intermediate temperature sensor78at the time of cooling operation and a detection value of the outdoor heat exchange intermediate temperature sensor76at the time of the heating operation) and an intake temperature (a detection value of the intake temperature sensor73).

EXPLANATION OF REFERENCE

1air conditioning apparatus2outdoor unit200outdoor unit control unit21compressor22four-way valve23outdoor heat exchanger24outdoor expansion valve (second expansion valve)25outdoor fan41discharge pipe42intake pipe43refrigerant pipe44refrigerant pipe45refrigerant pipe46refrigerant pipe47refrigerant pipe3indoor unit31indoor heat exchanger32indoor expansion valve (first expansion valve)33indoor fan71discharge temperature sensor72discharge pressure sensor73intake temperature sensor74intake pressure sensor75outdoor-side refrigerant temperature sensor76outdoor heat exchange intermediate temperature sensor77indoor-side refrigerant temperature sensor78indoor heat exchange intermediate temperature sensor79indoor temperature sensor