Air conditioner and control method

Abstract

This air conditioner has a refrigerant circuit through which refrigerant circulates and in which a variable-speed compressor, an expansion valve, and a heat exchanger including an outdoor heat exchanger and an indoor heat exchanger are connected via refrigerant piping, the air conditioner comprising: an indoor unit having at least the indoor heat exchanger; an outdoor unit having at least the compressor and the outdoor heat exchanger; a discharge pressure sensor for detecting a discharge pressure, which is the pressure of the refrigerant discharged from the compressor; a discharge temperature sensor for detecting a discharge temperature, which is the temperature of the refrigerant discharged from the compressor; a heat exchanger temperature sensor for detecting a heat exchanger temperature, which is the temperature of the refrigerant flowing through the heat exchanger functioning as a condenser; and a control unit that, after starting the compressor, controls the speed of the compressor so that the heat exchanger temperature is the saturation temperature of the discharge pressure calculated on the basis of the discharge pressure during a period until discharge superheating, which is a value obtained by subtracting the saturation temperature from the discharge temperature, becomes equal to or greater than a preset threshold value.

Description

Air conditioner and control method

[0001] The present disclosure relates to an air conditioner and a control method.

[0002] During heating operation of an air conditioner, the compressor may be started in a refrigerant-stagnation state, where liquid refrigerant is stored inside the hermetic compressor due to low outdoor temperatures. In such cases, the refrigeration oil stored inside the compressor is carried out into the refrigerant circuit outside the compressor by the rapidly gasified refrigerant, causing a drop in the oil level inside the compressor and resulting in poor lubrication of the compressor's sliding parts.

[0003] Various measures have been proposed to solve the problem of a drop in the compressor oil level immediately after starting heating operation. For example, two oil separators, a main and a sub, are connected in parallel downstream of the compressor in the refrigerant flow, and during start-up when a large amount of refrigerant oil has dissolved in the refrigerant, the refrigerant is also flowed into the sub oil separator, the refrigerant and refrigerant oil are separated in the two oil separators, and the separated refrigerant oil is returned to the low-pressure piping on the suction side of the compressor, thereby preventing a drop in the oil level (see, for example, Patent Document 1).

[0004] JP 2010-112639 A

[0005] However, in the conventional technology described in Patent Document 1, when starting up a heating operation, which results in a large amount of refrigerant oil being carried out, two oil separators are used to separate the refrigerant and the refrigerant oil, and the refrigerant oil that flows out of the compressor together with the refrigerant is returned to the compressor, which requires the addition of another oil separator to the outdoor unit. As a result, this conventional technology leads to an increase in the size of the outdoor unit and requires the addition of an oil separator that is used only when starting up a heating operation. Furthermore, the conventional technology described in Patent Document 1 is a countermeasure taken after the refrigerant oil has flowed out of the compressor, making it difficult to prevent the refrigerant oil from being discharged outside the compressor together with the refrigerant.

[0006] The present disclosure has been made to solve the above problems, and its purpose is to provide an air conditioner and control method that can prevent refrigeration oil from leaking outside the compressor and improve the reliability of the compressor.

[0007] In order to solve the above problems, one aspect of the present disclosure is an air conditioner having a refrigerant circuit in which a refrigerant circulates, in which a compressor with a variable rotation speed, an expansion valve, and a heat exchanger including an outdoor heat exchanger and an indoor heat exchanger are connected by refrigerant piping, and the air conditioner includes an indoor unit having at least the indoor heat exchanger, and an outdoor unit having at least the compressor and the outdoor heat exchanger, and the air conditioner is also equipped with a discharge pressure sensor that detects a discharge pressure, which is the pressure of the refrigerant discharged from the compressor, a discharge temperature sensor that detects a discharge temperature, which is the temperature of the refrigerant discharged from the compressor, and a heat exchanger temperature sensor that detects a heat exchanger temperature, which is the temperature of the refrigerant flowing through the heat exchanger that functions as a condenser, and a control unit that executes a startup control process to control the rotation speed of the compressor so that the heat exchanger temperature detected by the heat exchanger temperature sensor becomes the saturation temperature after the compressor is started, during a period until a discharge superheat, which is the value obtained by subtracting a saturation temperature of the discharge pressure detected by the discharge pressure sensor from the discharge temperature detected by the discharge temperature sensor, becomes equal to or exceeds a predetermined threshold.

[0008] Furthermore, one aspect of the present disclosure is an air conditioner having a refrigerant circuit in which a refrigerant circulates, in which a compressor with a variable rotation speed, an expansion valve, and a heat exchanger including an outdoor heat exchanger and an indoor heat exchanger are connected by refrigerant piping, and the air conditioner includes an indoor unit having at least the indoor heat exchanger, and an outdoor unit having at least the compressor and the outdoor heat exchanger, and the air conditioner is also equipped with a discharge pressure sensor that detects a discharge pressure, which is the pressure of the refrigerant discharged from the compressor, a discharge temperature sensor that detects a discharge temperature, which is the temperature of the refrigerant discharged from the compressor, and a control unit that executes a startup control process to control the rotation speed of the compressor so that the discharge pressure becomes a target discharge pressure, which indicates the pressure at which a predetermined set temperature is saturated, during a period after the compressor is started, until a discharge superheat, which is the value obtained by subtracting a saturation temperature of the discharge pressure calculated based on the discharge pressure detected by the discharge pressure sensor from the discharge temperature detected by the discharge temperature sensor, becomes equal to or exceeds a predetermined threshold.

[0009] Furthermore, one aspect of the present disclosure is an air conditioner having a refrigerant circuit in which a refrigerant circulates, in which a compressor with a variable rotation speed, an expansion valve, and a heat exchanger including an outdoor heat exchanger and an indoor heat exchanger are connected by refrigerant piping, and the air conditioner includes an indoor unit having at least the indoor heat exchanger, and an outdoor unit having at least the compressor and the outdoor heat exchanger, and the air conditioner is also equipped with a discharge pressure sensor that detects the discharge pressure, which is the pressure of the refrigerant discharged from the compressor, a discharge temperature sensor that detects the discharge temperature, which is the temperature of the refrigerant discharged from the compressor, a space temperature sensor that detects the air temperature in the space in which the heat exchanger functioning as a condenser is installed, and a control unit that executes a startup control process to control the rotation speed of the compressor so that the discharge pressure becomes a target discharge pressure indicating the pressure at which the space temperature detected by the space temperature sensor becomes a saturation temperature, during a period after the compressor is started, until a discharge superheat, which is the value obtained by subtracting a saturation temperature of the discharge pressure detected by the discharge temperature sensor from the discharge temperature detected by the discharge pressure sensor, becomes equal to or exceeds a predetermined threshold.

[0010] Furthermore, one aspect of the present disclosure is a control method for an air conditioner having a refrigerant circuit in which a refrigerant circulates, in which a compressor whose rotation speed is changeable, an expansion valve, and a heat exchanger including an outdoor heat exchanger and an indoor heat exchanger are connected by refrigerant piping, and the air conditioner is equipped with an indoor unit having at least the indoor heat exchanger, an outdoor unit having at least the compressor and the outdoor heat exchanger, a discharge pressure sensor detecting a discharge pressure that is the pressure of the refrigerant discharged from the compressor, a discharge temperature sensor detecting a discharge temperature that is the temperature of the refrigerant discharged from the compressor, and a heat exchanger temperature sensor detecting a heat exchanger temperature that is the temperature of the refrigerant flowing through the heat exchanger functioning as a condenser, in which, after starting the compressor, a control unit executes a startup control process to control the rotation speed of the compressor so that the heat exchanger temperature detected by the heat exchanger temperature sensor becomes the saturation temperature during a period until a discharge superheat, which is a value obtained by subtracting a saturation temperature of the discharge pressure calculated based on the discharge pressure detected by the discharge pressure sensor from the discharge temperature sensor, becomes equal to or exceeds a predetermined threshold.

[0011] Furthermore, one aspect of the present disclosure is a control method for an air conditioner having a refrigerant circuit in which a refrigerant circulates, in which a compressor whose rotation speed is changeable, an expansion valve, and a heat exchanger including an outdoor heat exchanger and an indoor heat exchanger are connected by refrigerant piping, and the air conditioner is equipped with an indoor unit having at least the indoor heat exchanger, an outdoor unit having at least the compressor and the outdoor heat exchanger, a discharge pressure sensor that detects a discharge pressure that is the pressure of the refrigerant discharged from the compressor, and a discharge temperature sensor that detects a discharge temperature that is the temperature of the refrigerant discharged from the compressor, in which, after starting the compressor, a control unit executes a start-up control process to control the rotation speed of the compressor so that the discharge pressure becomes a target discharge pressure that indicates the pressure at which a predetermined set temperature is saturated during a period until a discharge superheat, which is a value obtained by subtracting a saturation temperature of the discharge pressure calculated based on the discharge pressure detected by the discharge pressure sensor from the discharge temperature detected by the discharge temperature sensor, becomes equal to or exceeds a predetermined threshold.

[0012] and a space temperature sensor that detects the air temperature in a space in which the heat exchanger, which functions as a condenser, is installed. The control method includes a control unit that, after starting the compressor, executes a startup control process to control the rotation speed of the compressor so that the discharge pressure becomes a target discharge pressure that indicates the pressure at which the space temperature detected by the space temperature sensor becomes a saturation temperature during a period until a discharge superheat, which is a value obtained by subtracting a saturation temperature of the discharge pressure calculated based on the discharge pressure detected by the discharge pressure sensor from the discharge temperature sensor, becomes equal to or exceeds a predetermined threshold value.

[0013] According to the present disclosure, it is possible to suppress leakage of refrigeration oil to the outside of the compressor, thereby improving the reliability of the compressor.

[0014] FIG. 1 is a configuration diagram showing an example of an air conditioner according to a first embodiment. FIG. 2 is a flowchart showing an example of operation of the air conditioner according to the first embodiment. FIG. 3 is a diagram explaining an example of operation of the air conditioner according to the first embodiment. FIG. 4 is a flowchart showing an example of operation of the air conditioner according to a second embodiment. FIG. 5 is a diagram explaining an example of operation of the air conditioner according to the second embodiment. FIG. 6 is a flowchart showing an example of operation of the air conditioner according to a third embodiment. FIG. 7 is a diagram explaining an example of operation of the air conditioner according to the third embodiment. FIG. 8 is a diagram explaining an example of the hardware configuration of each control unit in an embodiment of the present disclosure.

[0015] An air conditioner and a control method according to an embodiment of the present disclosure will be described below with reference to the drawings.

[0016] [First embodiment] Fig. 1 is a configuration diagram showing an example of an air conditioner 1 according to a first embodiment. As shown in Fig. 1, the air conditioner 1 includes an outdoor unit 10 and an indoor unit 20, and has a refrigerant circuit RC.

[0017] The refrigerant circuit RC includes a compressor 11, an outdoor heat exchanger 13, a pressure vessel 15, a liquid pipe shutoff valve 16, a gas pipe shutoff valve 17, an internal heat exchanger 18, an expansion valve 19, an indoor expansion valve 21, and an indoor heat exchanger 22, which are connected by refrigerant piping, and the refrigerant sealed in the piping circulates.

[0018] The indoor unit 20 is an example of a user unit that supplies cold or hot heat to a space to be air-conditioned (e.g., a room) through heat exchange of a refrigerant. The indoor unit 20 and the outdoor unit 10 are connected by refrigerant piping. The indoor unit 20 includes an indoor expansion valve 21, an indoor heat exchanger 22, an indoor fan 23, an indoor unit control unit 40, an indoor heat exchanger temperature sensor 41, and an indoor unit temperature sensor 42.

[0019] The indoor expansion valve 21 is disposed on the refrigerant circuit RC and reduces the pressure of the refrigerant to expand it within the indoor unit 20. The indoor heat exchanger 22 is a user-side heat exchanger (an example of a heat exchanger) that supplies cold or hot heat to the space to be air-conditioned by heat exchange with the refrigerant. The indoor heat exchanger 22 is disposed on the refrigerant circuit RC and exchanges heat between the indoor air and the refrigerant. The indoor heat exchanger 22 functions as an evaporator during cooling operation and as a condenser during heating operation.

[0020] The indoor fan 23 is, for example, a sirocco fan, and is a blower that blows air to the indoor heat exchanger 22. The rotation speed of the indoor fan 23 can be changed under the control of the indoor unit control unit 40.

[0021] The indoor heat exchanger temperature sensor 41 detects a heat exchanger temperature Tc1 (Tc), which is the temperature of the refrigerant flowing through the indoor heat exchanger 22. The indoor heat exchanger temperature sensor 41 detects, for example, the outlet temperature of the indoor heat exchanger 22 (the outlet temperature of the condenser during heating operation) as the heat exchanger temperature Tc1 (Tc). The outdoor heat exchanger temperature sensor 34 outputs the detected heat exchanger temperature Tc1 (Tc) to the indoor unit control unit 40. The indoor heat exchanger temperature sensor 41 is an example of a heat exchanger temperature sensor that detects the heat exchanger temperature Tc (Tc1), which is the temperature of the refrigerant flowing through the heat exchanger (indoor heat exchanger 22) that functions as a condenser. The indoor heat exchanger 22 has a heat transfer tube through which the refrigerant flows, and the indoor heat exchanger temperature sensor 41 may also detect the surface temperature of the heat transfer tube of the indoor heat exchanger 22.

[0022] The indoor unit temperature sensor 42 detects an indoor temperature Tm1 (an example of air temperature Tm), which is the air temperature around the indoor unit 20. The indoor unit temperature sensor 42 detects, for example, the air temperature at the intake port of the indoor unit 20. The indoor unit temperature sensor 42 outputs the detected indoor temperature Tm1 to the indoor unit control unit 40. The indoor unit temperature sensor 42 is an example of a space temperature sensor that detects the air temperature Tm (Tm1) in the space where a heat exchanger (indoor heat exchanger 22) functioning as a condenser is installed during heating operation.

[0023] The indoor unit control unit 40 is configured with, for example, a processor including a CPU (Central Processing Unit), and controls the indoor unit 20. The indoor unit control unit 40 controls each part of the indoor unit 20 and is capable of mutual communication with the outdoor unit 10. The indoor unit control unit 40 controls the refrigerant circuit RC in cooperation with the outdoor unit control unit 30, which will be described later.

[0024] The outdoor unit 10 is a heat source unit that generates heat to be supplied to the indoor units 20, and functions as a heat source side unit. The outdoor unit 10 includes a compressor 11, a four-way valve 12, an outdoor heat exchanger 13, an outdoor fan 14, a pressure vessel 15, a liquid pipe shutoff valve 16, a gas pipe shutoff valve 17, an internal heat exchanger 18, an expansion valve 19, an outdoor unit control unit 30, a discharge temperature sensor 31, a discharge pressure sensor 32, an outdoor unit outdoor air temperature sensor 33, an outdoor heat exchanger temperature sensor 34, an outdoor unit liquid pipe outlet temperature sensor 35, and a suction pressure sensor 36.

[0025] The compressor 11 is a device that compresses the refrigerant, and its operating capacity can be varied by changing its rotation speed. That is, the rotation speed (frequency) of the compressor 11 can be changed to change the operating capacity. The rotation speed (frequency) of the compressor 11 is controlled by the outdoor unit control unit 30. The compressor 11 contains refrigeration oil as a lubricant inside.

[0026] The four-way valve 12 is connected to the output side (discharge side) of the compressor 11 in the refrigerant circuit RC and serves to switch the direction of refrigerant flow in the refrigerant circuit RC. In Fig. 1, the four-way valve 12 is connected in the cooling operation direction when shown by solid lines, and in the heating operation direction when shown by dashed lines. The four-way valve 12 is switched between the cooling operation direction and the heating operation direction under the control of the outdoor unit control unit 30.

[0027] The outdoor heat exchanger 13 is an example of a heat exchanger that exchanges heat between outside air and a refrigerant. The outdoor heat exchanger 13 functions as a condenser during cooling operation and as an evaporator during heating operation.

[0028] The outdoor fan 14 is, for example, a propeller fan, and is a blower that blows air to the outdoor heat exchanger 13. The outdoor fan 14 can change its rotation speed under the control of the outdoor unit control unit 30.

[0029] The pressure vessel 15 is disposed on the suction side of the compressor 11, and stores excess refrigerant in the vessel to prevent liquid refrigerant from flowing into the compressor 11. In this embodiment, the pressure vessel 15 is an accumulator.

[0030] The liquid pipe shutoff valve 16 is an example of a shutoff valve and is arranged on the refrigerant circuit RC between the outdoor heat exchanger 13 and the internal heat exchanger 18 and the indoor unit 20. The gas pipe shutoff valve 17 is arranged on the refrigerant circuit RC between the four-way valve 12 and the indoor unit 20 and is an example of a shutoff valve.

[0031] The internal heat exchanger 18 is disposed between the outdoor heat exchanger 13 and the liquid pipe shutoff valve 16 on the refrigerant circuit RC, and exchanges heat between the refrigerant flowing in the refrigerant circuit RC and the refrigerant flowing through the bypass pipe BP1.

[0032] The bypass pipe BP1 connects the suction port side of the pressure vessel 15 to an internal heat exchanger 18 between the outdoor heat exchanger 13 and the liquid pipe shutoff valve 16, forming a bypass refrigerant circuit. The expansion valve 19 decompresses a portion of the refrigerant branched from the refrigerant circuit RC.

[0033] The discharge temperature sensor 31 detects a discharge temperature Td, which is the temperature of the refrigerant discharged from the compressor 11. The discharge temperature sensor 31 outputs the detected discharge temperature Td to the outdoor unit control unit 30. Note that the discharge temperature sensor 31 may also be configured to detect the surface temperature of the discharge pipe of the compressor 11.

[0034] The discharge pressure sensor 32 detects a discharge pressure Pd, which is the pressure of the refrigerant discharged from the compressor 11. The discharge pressure sensor 32 outputs the detected discharge pressure Pd to the outdoor unit control unit 30.

[0035] The outdoor unit outside air temperature sensor 33 detects an outside air temperature Tm2 (an example of a space temperature Tm), which is the air temperature around the outdoor unit 10. The outdoor unit outside air temperature sensor 33 detects, for example, the air temperature at the intake port of the outdoor unit 10. The outdoor unit outside air temperature sensor 33 outputs the detected outside air temperature Tm2 to the outdoor unit control unit 30. The outdoor unit outside air temperature sensor 33 is an example of a space temperature sensor that detects the air temperature Tm (Tm2) in the space in which a heat exchanger (outdoor heat exchanger 13) functioning as a condenser is installed during cooling operation.

[0036] The outdoor heat exchanger temperature sensor 34 detects a heat exchanger temperature Tc2 (Tc), which is the temperature of the refrigerant flowing through the outdoor heat exchanger 13. The outdoor heat exchanger temperature sensor 34 detects, for example, the outlet temperature of the outdoor heat exchanger 13 (the outlet temperature of the condenser during cooling operation) as the heat exchanger temperature Tc2 (Tc). The outdoor heat exchanger temperature sensor 34 outputs the detected heat exchanger temperature Tc2 (Tc) to the outdoor unit control unit 30. The outdoor heat exchanger temperature sensor 34 is an example of a heat exchanger temperature sensor that detects the heat exchanger temperature Tc (Tc2), which is the temperature of the refrigerant flowing through a heat exchanger that functions as a condenser. Note that the outdoor heat exchanger 13 has a heat transfer tube through which the refrigerant flows, and the outdoor heat exchanger temperature sensor 34 may also detect the surface temperature of the heat transfer tube of the outdoor heat exchanger 13.

[0037] The outdoor unit liquid pipe outlet temperature sensor 35 detects the temperature of the refrigerant passing through the liquid pipe shutoff valve 16 during cooling operation. The outdoor unit liquid pipe outlet temperature sensor 35 outputs the detected temperature to the outdoor unit control unit 30. Note that the outdoor unit liquid pipe outlet temperature sensor 35 may also detect the surface temperature of the refrigerant pipe between the liquid pipe shutoff valve 16 and the internal heat exchanger 18.

[0038] The suction pressure sensor 36 is disposed on the suction side of the pressure vessel 15, and detects the suction pressure, which is the pressure of the refrigerant sucked into the compressor 11. The suction pressure sensor 36 outputs the detected suction pressure to the outdoor unit control unit 30.

[0039] The outdoor unit control unit 30 (an example of a control unit) is configured, for example, with a processor including a CPU, and controls the outdoor unit 10. The outdoor unit control unit 30 controls each part of the outdoor unit 10 and is capable of mutual communication with the indoor unit 20. The outdoor unit control unit 30 cooperates with the indoor unit control unit 40 to control the refrigerant circuit RC.

[0040] For example, after starting the compressor 11, the outdoor unit control unit 30 executes a startup control process to control the rotation speed of the compressor 11 so that the heat exchanger temperature Tc detected by a heat exchanger temperature sensor (e.g., the indoor heat exchanger temperature sensor 41 during heating operation and the outdoor heat exchanger temperature sensor 34 during cooling operation) becomes equal to the saturation temperature Th of the discharge pressure of the compressor 11 during a period until the discharge superheat (Shd) becomes equal to or higher than a preset threshold (e.g., 3 degrees or higher). Here, the discharge superheat is the value (Shd = Td - Th) obtained by subtracting the saturation temperature Th of the discharge pressure Pd calculated based on the discharge pressure Pd detected by the discharge pressure sensor 32 from the discharge temperature Td detected by the discharge temperature sensor 31.

[0041] The outdoor unit control unit 30 acquires the discharge pressure Pd detected by the discharge pressure sensor 32 and calculates the saturation temperature Th of the discharge pressure Pd based on the acquired discharge pressure Pd. The outdoor unit control unit 30 subtracts the calculated saturation temperature Th from the discharge temperature Td detected by the discharge temperature sensor 31 to calculate the discharge superheat (Shd).

[0042] For example, during heating operation, the outdoor unit control unit 30 controls the rotation speed of the compressor 11 so that the heat exchanger temperature Tc (Tc1) detected by the indoor heat exchanger temperature sensor 41 becomes the saturation temperature Th of the discharge pressure of the compressor 11. The control by the outdoor unit control unit 30 during heating operation will be described below.

[0043] In the startup control process, when the heat exchanger temperature Tc (Tc1) is higher than the saturation temperature Th (Tc>Th), the outdoor unit control unit 30 executes control to increase the rotation speed (frequency) of the compressor 11. In addition, in the startup control process, when the heat exchanger temperature Tc (Tc1) is lower than the saturation temperature Th (Tc<Th), the outdoor unit control unit 30 executes control to decrease the rotation speed (frequency) of the compressor 11.

[0044] Furthermore, in the startup control process, when the heat exchanger temperature Tc (Tc1) is equal to the saturation temperature Th (Tc=Th), the outdoor unit control unit 30 executes control to maintain the current rotation speed (frequency) of the compressor 11.

[0045] The outdoor unit control unit 30 may perform the above-described startup control process by providing a margin of ±α (for example, ±0.5°C). That is, the outdoor unit control unit 30 may, for example, reduce the rotation speed of the compressor 11 when (Tc<Th-α), increase the rotation speed of the compressor 11 when (Tc>Th+α), and maintain the current rotation speed of the compressor 11 when (Th+α≧Tc≧Th-α). Furthermore, the outdoor unit control unit 30 may set a lower limit value for the rotation speed of the compressor 11 when performing the startup control process.

[0046] Furthermore, when the discharge superheat (Shd) reaches a preset threshold value Tth1 or higher (e.g., 3 degrees or higher) ((Td-Th)>Tth1), the outdoor unit control unit 30 transitions to normal control processing. In normal control processing, the outdoor unit control unit 30 controls the rotation speed of the compressor 11 in accordance with the air conditioning load of the heat exchanger (e.g., the indoor heat exchanger 22). That is, in normal control processing, the outdoor unit control unit 30 controls the rotation speed of the compressor 11 so that the temperature (e.g., room temperature) of the air-conditioned space in which the indoor unit 20 is installed becomes a set temperature.

[0047] The outdoor unit control unit 30 may also be configured to execute the above-described startup control process after a certain period of time (e.g., 3 minutes) has elapsed since starting the compressor 11. The outdoor unit control unit 30 may also set an upper limit time (e.g., 20 minutes) for the period during which the startup control process is executed. In this case, when the upper limit time is reached, the outdoor unit control unit 30 ends the startup control process and transitions to normal control process even if the discharge superheat (Shd) has not reached or exceeded the preset threshold value Tth1.

[0048] In addition, during cooling operation, the outdoor unit control unit 30 performs startup control processing in the same manner as during heating operation described above, using the heat exchanger temperature Tc2 detected by the outdoor heat exchanger temperature sensor 34 instead of the heat exchanger temperature Tc1 detected by the indoor heat exchanger temperature sensor 41 as the heat exchanger temperature Tc.

[0049] That is, when the air conditioner 1 is performing heating operation, the heat exchanger temperature Tc is the temperature (heat exchanger temperature Tc1) of the refrigerant flowing through the indoor heat exchanger 22. When the air conditioner 1 is performing cooling operation, the heat exchanger temperature Tc is the temperature (heat exchanger temperature Tc2) of the refrigerant flowing through the outdoor heat exchanger 13.

[0050] Next, the operation of the air conditioner 1 according to this embodiment will be described with reference to the drawings. Fig. 2 is a flowchart showing an example of the operation of the air conditioner 1 according to this embodiment.

[0051] 2, the air conditioner 1 first starts operation (step S101). The outdoor unit control unit 30 and the indoor unit control unit 40 of the air conditioner 1 start air conditioning operation.

[0052] Next, the outdoor unit control unit 30 starts the operation of the compressor 11 (step S102).

[0053] Next, the outdoor unit control unit 30 determines whether a certain period of time has elapsed since startup (step S103). The outdoor unit control unit 30 determines whether a certain period of time (3 minutes), for example, has elapsed since startup. If the certain period of time has elapsed since startup (step S103: YES), the outdoor unit control unit 30 proceeds to step S104. If the certain period of time has not elapsed since startup (step S103: NO), the outdoor unit control unit 30 returns the process to step S103.

[0054] In step S104, the outdoor unit control unit 30 determines whether the heat exchanger temperature Tc is lower than the saturation temperature Th. The outdoor unit control unit 30 acquires the discharge pressure Pd detected by the discharge pressure sensor 32 and calculates the saturation temperature Th of the discharge pressure Pd based on the acquired discharge pressure Pd. During heating operation, the outdoor unit control unit 30 acquires the heat exchanger temperature Tc1 detected by the indoor heat exchanger temperature sensor 41 as the heat exchanger temperature Tc. During cooling operation, the outdoor unit control unit 30 acquires the heat exchanger temperature Tc2 detected by the outdoor heat exchanger temperature sensor 34 as the heat exchanger temperature Tc. The outdoor unit control unit 30 compares the heat exchanger temperature Tc with the saturation temperature Th to determine whether the heat exchanger temperature Tc is lower than the saturation temperature Th. If the heat exchanger temperature Tc is lower than the saturation temperature Th (Tc<Th) (step S104: YES), the outdoor unit control unit 30 proceeds to step S105. If the heat exchanger temperature Tc is not lower than the saturation temperature Th (step S104: NO), the outdoor unit control unit 30 proceeds to step S106.

[0055] In step S105, the outdoor unit control unit 30 executes control to lower (reduce) the rotation speed of the compressor 11. After the process of step S105, the outdoor unit control unit 30 advances the process to step S109.

[0056] In step S106, the outdoor unit control unit 30 determines whether the heat exchanger temperature Tc is greater than the saturation temperature Th. If the heat exchanger temperature Tc is greater than the saturation temperature Th (Tc > Th) (step S106: YES), the outdoor unit control unit 30 proceeds to step S107. If the heat exchanger temperature Tc is not greater than the saturation temperature Th (Tc = Th) (step S106: NO), the outdoor unit control unit 30 proceeds to step S108.

[0057] In step S107, the outdoor unit control unit 30 executes control to increase (control to increase) the rotation speed of the compressor 11. After the process of step S107, the outdoor unit control unit 30 advances the process to step S109.

[0058] In step S108, the outdoor unit control unit 30 executes control to maintain the rotation speed (control to maintain the current state) of the compressor 11. After the process of step S108, the outdoor unit control unit 30 advances the process to step S109.

[0059] In step S109, the outdoor unit control unit 30 determines whether (discharge temperature Td - saturation temperature Th) is equal to or greater than threshold value Tth1. The outdoor unit control unit 30 acquires the discharge temperature Td detected by the discharge temperature sensor 31 and calculates the discharge superheat (Shd) by subtracting the saturation temperature Th from the acquired discharge temperature Td. The outdoor unit control unit 30 determines whether the discharge superheat (Shd = Td - Th) is equal to or greater than threshold value Tth1. If the discharge superheat (Shd) is equal to or greater than threshold value Tth1 (Td - Th ≧ Tth1) (step S109: YES), the outdoor unit control unit 30 proceeds to step S110. If the discharge superheat (Shd) is less than threshold value Tth1 (Td - Th < Tth1) (step S109: NO), the outdoor unit control unit 30 returns the process to step S104.

[0060] In step S110, the outdoor unit control unit 30 transitions to normal control. That is, the outdoor unit control unit 30 transitions from the startup control process to normal control process in which the rotation speed of the compressor 11 is controlled in accordance with the air conditioning load of the heat exchanger (e.g., the indoor heat exchanger 22), and then ends the process.

[0061] Next, an example of the operation of the air conditioner 1 according to this embodiment will be described with reference to Fig. 3. Fig. 3 is a diagram illustrating an example of the operation of the air conditioner 1 according to this embodiment.

[0062] The graph shown in Figure 3 shows an example of the startup control process of the air conditioner 1, with the horizontal axis representing time and the vertical axis representing temperature (°C) or rotation speed (frequency Hz). In Figure 3, waveform W1 represents changes in heat exchanger temperature Tc, waveform W2 represents changes in saturation temperature Th, waveform W3 represents changes in the rotation speed of the compressor 11, and waveform W4 represents changes in discharge superheat (Shd).

[0063] Furthermore, during a period TR1 from the start of the compressor 11 to time T1 (e.g., 3 minutes), the outdoor unit control unit 30 does not execute the startup control process. Furthermore, time T2 is the time when the discharge superheat (Shd = Td - Th) reaches the threshold value Tth1, and the outdoor unit control unit 30 executes the startup control process during a period TR2 from time T1 to time T2. During the period TR2, the outdoor unit control unit 30 controls the rotation speed of the compressor 11 so that the heat exchanger temperature Tc becomes the saturation temperature Th (so that the heat exchanger temperature Tc coincides with the saturation temperature Th).

[0064] Specifically, during period TR2, as shown by waveform W3, the outdoor unit control unit 30 executes control to increase (raise) the rotation speed of the compressor 11 when the heat exchanger temperature Tc is greater (higher) than the saturation temperature Th (Tc > Th), and executes control to decrease (lower) the rotation speed of the compressor 11 when the heat exchanger temperature Tc is less (lower) than the saturation temperature Th (Tc < Th).

[0065] Furthermore, period TR3 is a period from time T2 onwards (Shd≧Tth1) and is a period for normal control processing. At time T2, the outdoor unit control unit 30 transitions from the startup control processing to the normal control processing, and executes the normal control processing during period TR3.

[0066] As described above, the air conditioner 1 according to this embodiment has a refrigerant circuit RC and includes an indoor unit 20 having at least an indoor heat exchanger 22, and an outdoor unit 10 having at least a compressor 11 and an outdoor heat exchanger 13. The refrigerant circuit RC includes a variable-speed compressor 11, an indoor expansion valve 21, and heat exchangers including the outdoor heat exchanger 13 and the indoor heat exchanger 22, all connected by refrigerant piping, through which refrigerant circulates. The air conditioner 1 also includes a discharge pressure sensor 32, a discharge temperature sensor 31, a heat exchanger temperature sensor (indoor heat exchanger temperature sensor 41 during heating operation and outdoor heat exchanger temperature sensor 34 during cooling operation), and an outdoor unit control unit 30. The discharge pressure sensor 32 detects the discharge pressure Pd, which is the pressure of the refrigerant discharged from the compressor 11. The discharge temperature sensor 31 detects the discharge temperature Td, which is the temperature of the refrigerant discharged from the compressor 11. The heat exchanger temperature sensor (indoor heat exchanger temperature sensor 41 during heating operation, outdoor heat exchanger temperature sensor 34 during cooling operation) detects the heat exchanger temperature Tc, which is the temperature of the refrigerant flowing through the heat exchanger functioning as a condenser (indoor heat exchanger 22 during heating operation, outdoor heat exchanger 13 during cooling operation). After starting the compressor 11, the outdoor unit control unit 30 (controller) executes a start-up control process to control the rotation speed of the compressor 11 so that the heat exchanger temperature Tc detected by the heat exchanger temperature sensor (indoor heat exchanger temperature sensor 41 during heating operation, outdoor heat exchanger temperature sensor 34 during cooling operation) becomes equal to the saturation temperature Th during a period (e.g., period TR2) until the discharge superheat (Shd) becomes equal to or greater than a predetermined threshold value Tth1. Here, the discharge superheat (Shd) is the value obtained by subtracting the saturation temperature Th of the discharge pressure Pd calculated based on the discharge pressure Pd detected by the discharge pressure sensor 32 from the discharge temperature Td detected by the discharge temperature sensor 31.

[0067] The inventors discovered through startup experiments and oil level observations of the compressor 11 that increasing the rotation speed of the compressor 11 when the heat exchanger temperature Tc is lower (smaller) than the saturation temperature Th (Tc<Th) causes refrigeration oil to suddenly flow out of the compressor, resulting in a drop in the oil level. This is presumably because this is the timing when the refrigerant begins to subcool in the condenser and the amount of refrigerant carried out from the compressor 11 increases. If the rotation speed is increased more than necessary at this timing, the amount of refrigerant carried out increases rapidly, leading to oil depletion. Therefore, by not increasing the rotation speed of the compressor 11 when the heat exchanger temperature Tc is lower (smaller) than the saturation temperature Th (Tc<Th), it is believed that the drop in the oil level immediately after startup can be suppressed.

[0068] As a result, the air conditioner 1 according to this embodiment, having the above-described configuration, controls the rotation speed of the compressor 11 so that the heat exchanger temperature Tc becomes the saturation temperature Th, thereby avoiding the situation that leads to oil depletion described above. Therefore, the air conditioner 1 according to this embodiment can prevent refrigeration oil from leaking out of the compressor 11, thereby improving the reliability of the compressor 11. Furthermore, because the air conditioner 1 according to this embodiment can prevent refrigeration oil from leaking out of the compressor 11, there is no need to add an oil separator as in Patent Document 1.

[0069] Furthermore, in this embodiment, in the startup control process, the outdoor unit control unit 30 executes control to increase the rotation speed of the compressor 11 when the heat exchanger temperature Tc is higher than the saturation temperature Th (Tc>Th). In addition, in the startup control process, the outdoor unit control unit 30 executes control to decrease the rotation speed of the compressor 11 when the heat exchanger temperature Tc is lower than the saturation temperature Th (Tc<Th). In addition, when the discharge superheat (Shd) becomes equal to or higher than the threshold value Tth1, the outdoor unit control unit 30 transitions to normal control process, in which the rotation speed of the compressor 11 is controlled in accordance with the air conditioning load of the heat exchanger (e.g., the indoor heat exchanger 22).

[0070] As a result, the air conditioner 1 according to this embodiment can appropriately suppress the leakage of refrigerating machine oil to the outside of the compressor 11 by using a simple control method, thereby improving the reliability of the compressor 11.

[0071] In this embodiment, when the air conditioner 1 is performing heating operation, the heat exchanger temperature Tc is the temperature (e.g., Tc1) of the refrigerant flowing through the indoor heat exchanger 22. When the air conditioner 1 is performing cooling operation, the heat exchanger temperature Tc is the temperature (e.g., Tc2) of the refrigerant flowing through the outdoor heat exchanger 13.

[0072] As a result, the air conditioner 1 according to this embodiment can be used in both heating and cooling operations, preventing refrigeration oil from leaking out of the compressor 11, thereby improving the reliability of the compressor 11.

[0073] Furthermore, in this embodiment, the outdoor unit control unit 30 executes the startup control process after a certain period of time (e.g., three minutes) has elapsed since starting the compressor 11. As a result, the air conditioner 1 according to this embodiment can prevent erroneous control from being performed by not executing the startup control process for a certain period of time (e.g., three minutes) in a situation where the refrigerant pressure is unstable, for example, when restarting the air conditioner 1 after stopping operation or from a thermo-off state.

[0074] Furthermore, in this embodiment, the outdoor unit control unit 30 can set an upper limit time (e.g., 20 minutes) for the period during which the startup control process is executed. This allows the air conditioner 1 according to this embodiment to prevent a delay in transition to normal control process due to a longer startup process control time. Therefore, the air conditioner 1 according to this embodiment can suppress a loss of comfort for occupants in the air-conditioned space caused by a delay in transition to normal control process.

[0075] Furthermore, the control method according to this embodiment is a control method for an air conditioner 1 having the above-mentioned refrigerant circuit RC and an indoor unit 20 having at least an indoor heat exchanger 22, an outdoor unit 10 having at least a compressor 11 and an outdoor heat exchanger 13, a discharge pressure sensor 32, a discharge temperature sensor 31, and a heat exchanger temperature sensor (indoor heat exchanger temperature sensor 41 during heating operation and outdoor heat exchanger temperature sensor 34 during cooling operation) that detects the heat exchanger temperature Tc, which is the temperature of the refrigerant flowing through the heat exchanger that functions as a condenser (indoor heat exchanger 22 during heating operation and outdoor heat exchanger 13 during cooling operation), and includes control steps. In the control step, after the outdoor unit control unit 30 starts the compressor 11, the outdoor unit control unit 30 executes a start-up control process to control the rotation speed of the compressor 11 so that the heat exchanger temperature Tc detected by the heat exchanger temperature sensor (the indoor heat exchanger temperature sensor 41 during heating operation and the outdoor heat exchanger temperature sensor 34 during cooling operation) becomes equal to the saturation temperature Th during the period until the discharge superheat (Shd) becomes equal to or greater than a predetermined threshold value Tth1. Note that the discharge superheat (Shd) is a value obtained by subtracting the saturation temperature Th of the discharge pressure Pd, which is calculated based on the discharge pressure Pd detected by the discharge pressure sensor 32, from the discharge temperature Td detected by the discharge temperature sensor 31.

[0076] As a result, the control method according to this embodiment has the same effect as the air conditioner 1 described above, and can suppress the leakage of refrigeration oil to the outside of the compressor 11, thereby improving the reliability of the compressor 11.

[0077] Second Embodiment Next, an air conditioner 1 according to a second embodiment will be described with reference to the drawings. In the air conditioner 1 according to the second embodiment, a modified example will be described in which the rotation speed of the compressor 11 is controlled so that the discharge pressure Pd becomes the target discharge pressure Pdm1, using a target discharge pressure Pdm1 that is a preset set temperature as the saturation temperature instead of the saturation temperature Th.

[0078] The hardware configuration of the air conditioner 1 according to this embodiment is the same as that of the first embodiment shown in Fig. 1, and therefore a description thereof will be omitted here. In the air conditioner 1 according to this embodiment, the control processing of the outdoor unit control unit 30 differs from that of the first embodiment, and the difference in the control processing of the outdoor unit control unit 30 will be described below.

[0079] In this embodiment, the outdoor unit control unit 30 (an example of a control unit) executes a startup control process to control the rotation speed of the compressor 11 after starting the compressor 11, so that the discharge pressure Pd becomes a target discharge pressure Pdm1 indicating the pressure at which a preset set temperature (space temperature Tm) becomes a saturated temperature, during the period until the discharge superheat (Shd) becomes equal to or higher than a preset threshold value Tth1 (e.g., 3 degrees or higher). Note that, as in the first embodiment, the discharge superheat is a value (Shd = Td - Th) obtained by subtracting the saturation temperature Th of the discharge pressure Pd, which is calculated based on the discharge pressure Pd detected by the discharge pressure sensor 32, from the discharge temperature Td detected by the discharge temperature sensor 31.

[0080] When the air conditioner 1 is performing heating operation, the air temperature Tm is the temperature in the space where the indoor unit 20 is installed, and the set temperature is set to, for example, 20° C. When the air conditioner 1 is performing cooling operation, the air temperature Tm is the outdoor air temperature around where the outdoor unit 10 is installed, and the set temperature is set to, for example, 35° C.

[0081] The set temperature is determined with reference to the guaranteed operating temperature range of the compressor 11. The outdoor unit control unit 30 sets a target discharge pressure Pdm1 corresponding to the set temperature (corresponding to the air temperature Tm).

[0082] In the startup control process, when the discharge pressure Pd of the compressor 11 is lower than the target discharge pressure Pdm1 (Pd<Pdm1), the outdoor unit control unit 30 executes control to increase the rotation speed (frequency) of the compressor 11. In addition, in the startup control process, when the discharge pressure Pd of the compressor 11 is higher than the target discharge pressure Pdm1 (Pd>Pdm1), the outdoor unit control unit 30 executes control to decrease the rotation speed (frequency) of the compressor 11.

[0083] Furthermore, in the startup control process, when the discharge pressure Pd of the compressor 11 is equal to the target discharge pressure Pdm1 (Pd=Pdm1), the outdoor unit control unit 30 executes control to maintain the current rotation speed (frequency) of the compressor 11.

[0084] The outdoor unit control unit 30 may perform the above-described startup control process by providing a margin ±β. That is, for example, the outdoor unit control unit 30 may increase the rotation speed of the compressor 11 when (Pd<Pdm1-β), decrease the rotation speed of the compressor 11 when (Pd>Pdm1+β), and maintain the current rotation speed of the compressor 11 when (Pdm1+β≧Pd≧Pdm1-β). Furthermore, when performing the startup control process, the outdoor unit control unit 30 may set a lower limit value for the rotation speed of the compressor 11, as in the first embodiment.

[0085] Furthermore, other processes of the outdoor unit control unit 30 in this embodiment are the same as those in the first embodiment, and therefore descriptions thereof will be omitted here.

[0086] Next, the operation of the air conditioner 1 according to this embodiment will be described with reference to Figures 4 and 5. Figure 4 is a flowchart showing an example of the operation of the air conditioner 1 according to this embodiment.

[0087] In FIG. 4, the processes from step S201 to step S203 are the same as the processes from step S101 to step S103 shown in FIG. 2 described above, and therefore a description thereof will be omitted here.

[0088] In step S203, if a certain period of time has elapsed since startup (step S203: YES), the outdoor unit control unit 30 proceeds to step S204. In addition, if the certain period of time has not elapsed since startup (step S203: NO), the outdoor unit control unit 30 returns the process to step S203.

[0089] In step S204, the outdoor unit control unit 30 determines whether the discharge pressure Pd is greater than the target discharge pressure Pdm1. The outdoor unit control unit 30 acquires the discharge pressure Pd detected by the discharge pressure sensor 32. The outdoor unit control unit 30 also pre-calculates, from the set temperature, the pressure at which the set temperature becomes the saturation temperature as the target discharge pressure Pdm1. The outdoor unit control unit 30 compares the discharge pressure Pd with the target discharge pressure Pdm1 to determine whether the discharge pressure Pd is greater than the target discharge pressure Pdm1. If the discharge pressure Pd is greater than the target discharge pressure Pdm1 (Pd > Tdm1) (step S204: YES), the outdoor unit control unit 30 proceeds to step S205. If the discharge pressure Pd is not greater than the target discharge pressure Pdm1 (step S204: NO), the outdoor unit control unit 30 proceeds to step S206.

[0090] In step S205, the outdoor unit control unit 30 executes control to lower (reduce) the rotation speed of the compressor 11. After the process of step S205, the outdoor unit control unit 30 advances the process to step S209.

[0091] In step S206, the outdoor unit control unit 30 determines whether the discharge pressure Pd is smaller than the target discharge pressure Pdm1. If the discharge pressure Pd is smaller than the target discharge pressure Pdm1 (Pd<Pdm1) (step S206: YES), the outdoor unit control unit 30 proceeds to step S207. If the discharge pressure Pd is not smaller than the target discharge pressure Pdm1 (Pd=Pdm1) (step S206: NO), the outdoor unit control unit 30 proceeds to step S208.

[0092] In step S207, the outdoor unit control unit 30 executes control to increase (control to increase) the rotation speed of the compressor 11. After the process of step S207, the outdoor unit control unit 30 advances the process to step S209.

[0093] In step S208, the outdoor unit control unit 30 executes control to maintain the rotation speed (control to maintain the current state) of the compressor 11. After the process of step S208, the outdoor unit control unit 30 advances the process to step S209.

[0094] The processes in steps S209 and S210 are similar to the processes in steps S109 and S110 shown in FIG. 2, and therefore, description thereof will be omitted here.

[0095] In step S209, if the discharge superheat (Shd) is equal to or greater than the threshold value Tth1 (Td-Th≧Tth1) (step S209: YES), the outdoor unit control unit 30 proceeds to step S210. If the discharge superheat (Shd) is less than the threshold value Tth1 (Td-Th<Tth1) (step S209: NO), the outdoor unit control unit 30 returns the process to step S204.

[0096] Next, an example of the operation of the air conditioner 1 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a diagram illustrating an example of the operation of the air conditioner 1 according to this embodiment.

[0097] The graph shown in Fig. 5 shows an example of the startup control process of the air conditioner 1, with the horizontal axis representing time and the vertical axis representing pressure (MPaG) or rotation speed (frequency Hz). In Fig. 5, waveform W5 represents changes in the target discharge pressure Pdm1, and waveform W6 represents changes in the discharge pressure Pd of the compressor 11. Furthermore, waveform W7 represents changes in the rotation speed of the compressor 11, and waveform W8 represents changes in the discharge superheat (Shd).

[0098] Furthermore, time T1, time T2, period TR1, period TR2, and period TR3 are the same as those in FIG. 3 of the first embodiment.

[0099] Furthermore, during a period TR1 from the start of the compressor 11 to time T1 (e.g., 3 minutes), the outdoor unit control unit 30 does not execute the startup control process. Furthermore, the outdoor unit control unit 30 executes the startup control process described above during a period TR2 from time T1 to time T2. During period TR2, the outdoor unit control unit 30 controls the rotation speed of the compressor 11 so that the discharge pressure Pd becomes the target discharge pressure Pdm1 (so that the discharge pressure Pd matches the target discharge pressure Pdm1).

[0100] Specifically, during period TR2, as shown by waveform W7, the outdoor unit control unit 30 executes control to increase (raise) the rotation speed of the compressor 11 when the discharge pressure Pd is smaller (lower) than the target discharge pressure Pdm1 (Pd < Pdm1), and executes control to decrease (lower) the rotation speed of the compressor 11 when the discharge pressure Pd is larger (higher) than the target discharge pressure Pdm1 (Pd > Pdm1).

[0101] At time T2, the outdoor unit control unit 30 transitions from the startup control process to the normal control process, and executes the normal control process during period TR3.

[0102] As described above, the air conditioner 1 according to this embodiment has the above-described refrigerant circuit RC and includes the indoor unit 20 having at least the indoor heat exchanger 22, and the outdoor unit 10 having at least the compressor 11 and the outdoor heat exchanger 13. The air conditioner also includes a discharge pressure sensor 32, a discharge temperature sensor 31, and an outdoor unit control unit 30 (control unit). The discharge pressure sensor 32 detects the discharge pressure Pd, which is the pressure of the refrigerant discharged from the compressor 11. The discharge temperature sensor 31 detects the discharge temperature Td, which is the temperature of the refrigerant discharged from the compressor 11. After starting the compressor 11, the outdoor unit control unit 30 executes a startup control process to control the rotation speed of the compressor 11 so that the discharge pressure Pd becomes a target discharge pressure Pdm1, which indicates the pressure at which the predetermined set temperature Tm is saturated, during the period until the discharge superheat (Shd) becomes equal to or greater than a predetermined threshold (e.g., 3 degrees or greater). Here, the discharge superheat (Shd) is the value obtained by subtracting the saturation temperature Th of the discharge pressure Pd calculated based on the discharge pressure Pd detected by the discharge pressure sensor 32 from the discharge temperature Td detected by the discharge temperature sensor 31.

[0103] As a result, the air conditioner 1 according to this embodiment can achieve the same effects as the first embodiment by replacing the timing in the first embodiment where the heat exchanger temperature Tc is less than the saturation temperature Th with the timing where the discharge pressure Pd is greater than the target discharge pressure Pdm1. That is, the air conditioner 1 according to this embodiment controls the rotation speed of the compressor 11 so that the discharge pressure Pd becomes equal to the target discharge pressure Pdm1, thereby avoiding a situation where oil runs out. Therefore, the air conditioner 1 according to this embodiment can suppress the leakage of refrigeration oil to the outside of the compressor 11 and improve the reliability of the compressor 11.

[0104] Furthermore, in this embodiment, in the startup control process, the outdoor unit control unit 30 executes control to increase the rotation speed of the compressor 11 when the discharge pressure Pd is lower than the target discharge pressure Pdm1 (Pd<Pdm1). In addition, in the startup control process, the outdoor unit control unit 30 executes control to decrease the rotation speed of the compressor 11 when the discharge pressure Pd is higher than the target discharge pressure Pdm1 (Pd>Pdm1). In addition, when the discharge superheat (Shd) becomes equal to or higher than the threshold value Tth1, the outdoor unit control unit 30 transitions to normal control process in which the rotation speed of the compressor 11 is controlled in accordance with the air conditioning load of the heat exchanger (e.g., the indoor heat exchanger 22).

[0105] As a result, the air conditioner 1 of this embodiment, like the first embodiment, can appropriately suppress the leakage of refrigerant oil outside the compressor 11 through a simple control division method, thereby improving the reliability of the compressor 11.

[0106] In this embodiment, when the air conditioner 1 is performing heating operation, the set temperature (Tm) is a temperature set as the air temperature in the space where the indoor unit 20 is installed. When the air conditioner 1 is performing cooling operation, the set temperature (Tm) is a temperature set as the outdoor air temperature around where the outdoor unit 10 is installed.

[0107] As a result, the air conditioner 1 according to this embodiment can be used in both heating and cooling operations, preventing refrigeration oil from leaking out of the compressor 11, thereby improving the reliability of the compressor 11.

[0108] Furthermore, a control method according to this embodiment is a control method for an air conditioner 1 having the above-described refrigerant circuit RC, an indoor unit 20 having at least an indoor heat exchanger 22, an outdoor unit 10 having at least a compressor 11 and an outdoor heat exchanger 13, a discharge pressure sensor 32, and a discharge temperature sensor 31, and includes a control step. In the control step, after starting the compressor 11, the outdoor unit control unit 30 executes a startup control process to control the rotation speed of the compressor 11 so that the discharge pressure Pd becomes a target discharge pressure Pdm1, which indicates the pressure at which the predetermined set temperature Tm becomes the saturation temperature, during a period until the discharge superheat (Shd) becomes equal to or greater than a predetermined threshold (e.g., 3 degrees). Here, the discharge superheat (Shd) is a value obtained by subtracting the saturation temperature Th of the discharge pressure Pd, which is calculated based on the discharge pressure Pd detected by the discharge pressure sensor 32, from the discharge temperature Td detected by the discharge temperature sensor 31.

[0109] As a result, the control method according to this embodiment has the same effect as the air conditioner 1 described above, and can suppress the leakage of refrigeration oil to the outside of the compressor 11, thereby improving the reliability of the compressor 11.

[0110] [Third Embodiment] Next, an air conditioner 1 according to a third embodiment will be described with reference to the drawings. In the air conditioner 1 according to the third embodiment, the air temperature Tm in the space in which the heat exchanger is installed is used instead of the set temperature of the second embodiment. In the air conditioner 1 according to the third embodiment, a target discharge pressure Pdm2 is calculated as the pressure at which the air temperature Tm becomes the saturation temperature, and the calculated target discharge pressure Pdm2 is used to control the rotation speed of the compressor 11 so that the discharge pressure Pd becomes the target discharge pressure Pdm2.

[0111] The hardware configuration of the air conditioner 1 according to this embodiment is the same as that of the first embodiment shown in Fig. 1, and therefore a description thereof will be omitted here. In the air conditioner 1 according to this embodiment, the control processing of the outdoor unit control unit 30 differs from that of the first and second embodiments, and the difference in the control processing of the outdoor unit control unit 30 will be described below.

[0112] In this embodiment, the outdoor unit control unit 30 (an example of a control unit) executes a startup control process to control the rotation speed of the compressor 11 so that the discharge pressure Pd becomes a target discharge pressure Pdm2 indicating the pressure at which the space temperature Tm becomes the saturation temperature, during a period after starting the compressor 11 until the discharge superheat (Shd) becomes equal to or higher than a preset threshold value Tth1 (for example, 3 degrees or higher). Note that, as in the first embodiment, the discharge superheat is a value (Shd = Td - Th) obtained by subtracting the saturation temperature Th of the discharge pressure Pd, which is calculated based on the discharge pressure Pd detected by the discharge pressure sensor 32, from the discharge temperature Td detected by the discharge temperature sensor 31.

[0113] The space temperature Tm is the temperature detected by the space temperature sensor. The space temperature sensor is the indoor unit temperature sensor 42 during heating operation, and the outdoor unit outside air temperature sensor 33 during cooling operation. That is, during heating operation, the indoor temperature Tm1, which is the air temperature around where the indoor unit 20 is installed and detected by the indoor unit temperature sensor 42, is used as the air temperature Tm. During cooling operation, the outside air temperature Tm2, ​​which is the air temperature around where the outdoor unit 10 is installed and detected by the outdoor unit outside air temperature sensor 33, is used as the air temperature Tm.

[0114] Thus, in this embodiment, when the air conditioner 1 is performing heating operation, the air temperature Tm is the temperature in the space in which the indoor unit 20 is installed (indoor temperature Tm1), and when the air conditioner 1 is performing cooling operation, the air temperature Tm is the outdoor air temperature Tm2 in the vicinity in which the outdoor unit 10 is installed.

[0115] Furthermore, the outdoor unit control unit 30 calculates, based on the air temperature Tm, a target discharge pressure Pdm2 that indicates the pressure at which the space temperature Tm becomes the saturation temperature.

[0116] In the startup control process, when the discharge pressure Pd of the compressor 11 is lower than the target discharge pressure Pdm2 (Pd<Pdm2), the outdoor unit control unit 30 executes control to increase the rotation speed (frequency) of the compressor 11. In addition, in the startup control process, when the discharge pressure Pd of the compressor 11 is higher than the target discharge pressure Pdm2 (Pd>Pdm2), the outdoor unit control unit 30 executes control to decrease the rotation speed (frequency) of the compressor 11.

[0117] Furthermore, in the startup control process, when the discharge pressure Pd of the compressor 11 is equal to the target discharge pressure Pdm2 (Pd=Pdm2), the outdoor unit control unit 30 executes control to maintain the current rotation speed (frequency) of the compressor 11.

[0118] The outdoor unit control unit 30 may perform the above-described startup control process by providing a margin ±β, as in the second embodiment. That is, the outdoor unit control unit 30 may increase the rotation speed of the compressor 11 when (Pd<Pdm2-β), decrease the rotation speed of the compressor 11 when (Pd>Pdm2+β), and maintain the current rotation speed of the compressor 11 when (Pdm2+β≧Pd≧Pdm2-β). Furthermore, the outdoor unit control unit 30 may set a lower limit value for the rotation speed of the compressor 11 when performing the startup control process, as in the first embodiment.

[0119] Furthermore, other processes of the outdoor unit control unit 30 in this embodiment are the same as those in the first embodiment, and therefore descriptions thereof will be omitted here.

[0120] Next, the operation of the air conditioner 1 according to this embodiment will be described with reference to Figures 6 and 7. Figure 6 is a flowchart showing an example of the operation of the air conditioner 1 according to this embodiment.

[0121] In FIG. 6, the processes from step S301 to step S303 are the same as the processes from step S201 to step S203 shown in FIG. 4 described above, and therefore the description thereof will be omitted here.

[0122] In step S303, if a certain period of time has elapsed since startup (step S303: YES), the outdoor unit control unit 30 proceeds to step S304. In addition, if the certain period of time has not elapsed since startup (step S303: NO), the outdoor unit control unit 30 returns the process to step S303.

[0123] In step S304, the outdoor unit control unit 30 determines whether the discharge pressure Pd is greater than the target discharge pressure Pdm2. The outdoor unit control unit 30 acquires the discharge pressure Pd detected by the discharge pressure sensor 32. During heating operation, the outdoor unit control unit 30 acquires the indoor temperature Tm1 from the indoor unit temperature sensor 42 as the space temperature Tm, and during cooling operation, acquires the outdoor air temperature Tm2 from the outdoor unit outdoor air temperature sensor 33 as the space temperature Tm. From the space temperature Tm, the outdoor unit control unit 30 calculates the pressure that makes the space temperature Tm the saturation temperature as the target discharge pressure Pdm2.

[0124] The outdoor unit control unit 30 compares the discharge pressure Pd with the target discharge pressure Pdm2 and determines whether the discharge pressure Pd is greater than the target discharge pressure Pdm2. If the discharge pressure Pd is greater than the target discharge pressure Pdm2 (Pd > Tdm2) (step S304: YES), the outdoor unit control unit 30 proceeds to step S305. If the discharge pressure Pd is not greater than the target discharge pressure Pdm2 (step S304: NO), the outdoor unit control unit 30 proceeds to step S306.

[0125] In step S305, the outdoor unit control unit 30 executes control to lower (reduce) the rotation speed of the compressor 11. After the process of step S305, the outdoor unit control unit 30 advances the process to step S309.

[0126] In step S306, the outdoor unit control unit 30 determines whether the discharge pressure Pd is smaller than the target discharge pressure Pdm2. If the discharge pressure Pd is smaller than the target discharge pressure Pdm2 (Pd<Pdm2) (step S306: YES), the outdoor unit control unit 30 proceeds to step S307. If the discharge pressure Pd is not smaller than the target discharge pressure Pdm2 (Pd=Pdm2) (step S306: NO), the outdoor unit control unit 30 proceeds to step S308.

[0127] In step S307, the outdoor unit control unit 30 executes control to increase (control to increase) the rotation speed of the compressor 11. After the process of step S207, the outdoor unit control unit 30 advances the process to step S309.

[0128] In step S308, the outdoor unit control unit 30 executes control to maintain the rotation speed (control to maintain the current state) of the compressor 11. After the process of step S308, the outdoor unit control unit 30 advances the process to step S309.

[0129] The processes in steps S309 and S310 are similar to the processes in steps S209 and S210 shown in FIG. 4, and therefore, description thereof will be omitted here.

[0130] In step S309, if the discharge superheat (Shd) is equal to or greater than the threshold value Tth1 (Td-Th≧Tth1) (step S309: YES), the outdoor unit control unit 30 proceeds to step S310. If the discharge superheat (Shd) is less than the threshold value Tth1 (Td-Th<Tth1) (step S309: NO), the outdoor unit control unit 30 returns the process to step S304.

[0131] Next, an example of the operation of the air conditioner 1 according to this embodiment will be described with reference to Fig. 7. Fig. 7 is a diagram illustrating an example of the operation of the air conditioner 1 according to this embodiment.

[0132] The graph shown in Fig. 7 shows an example of the startup control process of the air conditioner 1, with the horizontal axis representing time and the vertical axis representing pressure (MPaG) or rotation speed (frequency Hz). In Fig. 7, waveform W9 represents changes in the target discharge pressure Pdm2, and waveform W10 represents changes in the discharge pressure Pd of the compressor 11. Furthermore, waveform W11 represents changes in the rotation speed of the compressor 11, and waveform W12 represents changes in the discharge superheat (Shd).

[0133] Furthermore, time T1, time T2, period TR1, period TR2, and period TR3 are the same as those in FIGS. 3 and 5 of the first embodiment.

[0134] Furthermore, during a period TR1 from the start of the compressor 11 to time T1 (e.g., 3 minutes), the outdoor unit control unit 30 does not execute the startup control process. Furthermore, the outdoor unit control unit 30 executes the startup control process described above during a period TR2 from time T1 to time T2. During period TR2, the outdoor unit control unit 30 controls the rotation speed of the compressor 11 so that the discharge pressure Pd becomes the target discharge pressure Pdm2 (so that the discharge pressure Pd matches the target discharge pressure Pdm2).

[0135] Specifically, during period TR2, as shown by waveform W11, the outdoor unit control unit 30 executes control to increase (raise) the rotation speed of the compressor 11 when the discharge pressure Pd is smaller (lower) than the target discharge pressure Pdm2 (Pd < Pdm2), and executes control to decrease (lower) the rotation speed of the compressor 11 when the discharge pressure Pd is larger (higher) than the target discharge pressure Pdm2 (Pd > Pdm2).

[0136] At time T2, the outdoor unit control unit 30 transitions from the startup control process to the normal control process, and executes the normal control process during period TR3.

[0137] As described above, the air conditioner 1 according to this embodiment has the above-described refrigerant circuit RC and includes the indoor unit 20 having at least the indoor heat exchanger 22, and the outdoor unit 10 having at least the compressor 11 and the outdoor heat exchanger 13. The air conditioner also includes a discharge pressure sensor 32, a discharge temperature sensor 31, a space temperature sensor, and an outdoor unit control unit 30 (controller). The discharge pressure sensor 32 detects the discharge pressure Pd, which is the pressure of the refrigerant discharged from the compressor 11. The discharge temperature sensor 31 detects the discharge temperature Td, which is the temperature of the refrigerant discharged from the compressor 11. The space temperature sensor detects the air temperature Tm in the space where the heat exchanger functioning as a condenser is installed. The space temperature sensor is the indoor unit temperature sensor 42 during heating operation and the outdoor unit outdoor air temperature sensor 33 during cooling operation. After starting the compressor 11, the outdoor unit control unit 30 executes a startup control process to control the rotation speed of the compressor 11 so that the discharge pressure Pd becomes a target discharge pressure Pdm2 indicating the pressure at which the air temperature Tm becomes the saturation temperature during the period until the discharge superheat (Shd) becomes equal to or higher than a preset threshold value (e.g., 3 degrees or higher). Here, the discharge superheat (Shd) is a value obtained by subtracting the saturation temperature Th of the discharge pressure Pd, which is calculated based on the discharge pressure Pd detected by the discharge pressure sensor 32, from the discharge temperature Td detected by the discharge temperature sensor 31.

[0138] As a result, the air conditioner 1 according to this embodiment can achieve the same effects as the first embodiment by replacing the timing in which the heat exchanger temperature Tc is less than the saturation temperature Th in the first embodiment with the timing in which the discharge pressure Pd is greater than the target discharge pressure Pdm2. That is, the air conditioner 1 according to this embodiment controls the rotation speed of the compressor 11 so that the discharge pressure Pd becomes equal to the target discharge pressure Pdm2, thereby avoiding a situation in which oil runs out. Therefore, the air conditioner 1 according to this embodiment can suppress the leakage of refrigeration oil to the outside of the compressor 11 and improve the reliability of the compressor 11.

[0139] Furthermore, in this embodiment, in the startup control process, the outdoor unit control unit 30 executes control to increase the rotation speed of the compressor 11 when the discharge pressure Pd is lower than the target discharge pressure Pdm2 (Pd<Pdm2). In addition, in the startup control process, the outdoor unit control unit 30 executes control to decrease the rotation speed of the compressor 11 when the discharge pressure Pd is higher than the target discharge pressure Pdm2 (Pd>Pdm2). In addition, when the discharge superheat (Shd) becomes equal to or higher than the threshold value Tth1, the outdoor unit control unit 30 transitions to normal control process in which the rotation speed of the compressor 11 is controlled in accordance with the air conditioning load of the heat exchanger (e.g., the indoor heat exchanger 22).

[0140] As a result, the air conditioner 1 of this embodiment, like the first embodiment, can appropriately suppress the leakage of refrigerant oil outside the compressor 11 through a simple control division method, thereby improving the reliability of the compressor 11.

[0141] Furthermore, in this embodiment, when the air conditioner 1 is performing heating operation, the air temperature Tm is the temperature in the space in which the indoor unit 20 is installed (indoor temperature Tm1), and when the air conditioner 1 is performing cooling operation, the air temperature Tm is the outdoor air temperature Tm2 in the vicinity in which the outdoor unit 10 is installed.

[0142] As a result, the air conditioner 1 according to this embodiment can be used in both heating and cooling operations, preventing refrigeration oil from leaking out of the compressor 11, thereby improving the reliability of the compressor 11.

[0143] Furthermore, a control method according to this embodiment is a control method for an air conditioner 1 including the above-described refrigerant circuit RC, an indoor unit 20 including at least an indoor heat exchanger 22, an outdoor unit 10 including at least a compressor 11 and an outdoor heat exchanger 13, a discharge pressure sensor 32, a discharge temperature sensor 31, and a space temperature sensor, and includes a control step. The space temperature sensor detects the air temperature Tm in the space where the heat exchanger functioning as a condenser is installed. The space temperature sensor is the indoor unit temperature sensor 42 during heating operation and the outdoor unit outdoor air temperature sensor 33 during cooling operation. In the control step, after starting the compressor 11, the outdoor unit control unit 30 executes a start-up control process to control the rotation speed of the compressor 11 so that the discharge pressure Pd becomes a target discharge pressure Pdm2, which indicates the pressure at which the air temperature Tm becomes a saturation temperature, during a period until the discharge superheat (Shd) reaches or exceeds a predetermined threshold (e.g., 3 degrees). Here, the discharge superheat (Shd) is the value obtained by subtracting the saturation temperature Th of the discharge pressure Pd calculated based on the discharge pressure Pd detected by the discharge pressure sensor 32 from the discharge temperature Td detected by the discharge temperature sensor 31.

[0144] As a result, the control method according to this embodiment has the same effect as the air conditioner 1 described above, and can suppress the leakage of refrigeration oil to the outside of the compressor 11, thereby improving the reliability of the compressor 11.

[0145] Fig. 8 is a diagram illustrating the hardware configuration of each control unit of the air conditioner 1. The control unit shown in Fig. 8 illustrates the hardware configuration of each control unit (outdoor unit control unit 30, indoor unit control unit 40) of the air conditioner 1.

[0146] As shown in FIG. 8, each control unit (outdoor unit control unit 30, indoor unit control unit 40) of the air conditioner 1 includes a communication device H11, a memory H12, and a processor H13.

[0147] The communication device H11 is, for example, a communication device such as a LAN card that can be connected to the network NW1, or a communication device that performs wired or wireless communication. The memory H12 is, for example, a storage device such as a RAM, a flash memory, or an HDD, and stores various information and programs used by each control unit (the outdoor unit control unit 30, the indoor unit control unit 40).

[0148] The processor H13 is a processing circuit including, for example, a CPU, etc. The processor H13 executes various processes of each control unit (outdoor unit control unit 30, indoor unit control unit 40) by executing programs stored in the memory H12.

[0149] The present disclosure is not limited to the above-described embodiments and may be modified within the scope of the present disclosure. For example, in the above-described embodiments, the air conditioner 1 is described as being connected to one indoor unit 20 and one outdoor unit 10. However, the present disclosure is not limited to this, and multiple indoor units 20 or multiple outdoor units 10 may be connected. In this case, the heat exchanger temperature Tc1 (or Tc2) may be the minimum, maximum, average, etc., of the multiple indoor units 20. Similarly, the air temperature Tm (indoor temperature Tm1 or outdoor air temperature Tm2) may be the minimum, maximum, average, etc., of the multiple indoor units 20 or multiple outdoor units 10.

[0150] In each of the above embodiments, the air conditioner 1 may be provided with a plurality of pressure sensors and temperature sensors. In this case, the outdoor unit control unit 30 may execute control processing using the minimum, maximum, average, etc. of the detected values ​​of the plurality of sensors.

[0151] Furthermore, in each of the above embodiments, if the air conditioner 1 does not have each pressure sensor, the outdoor unit control unit 30 may use the temperature detected by the temperature sensor and perform control processing using the pressure converted from that temperature.

[0152] In addition, in each of the above embodiments, an example has been described in which a margin (tolerance value) of ±α or ±β is provided for the saturation temperature Th or the target discharge pressure (Pdm1, Pdm2), but this is not limited to this, and the margin value may be changed above and below, for example, +α1, −α2, or +β1, −β2. In this case, the outdoor unit control unit 30 can perform control such as reducing the rotation speed earlier.

[0153] In the second embodiment, the set temperature may be changed depending on, for example, the season or the outside air temperature.

[0154] In the second and third embodiments, the target discharge pressure Pdm1 or Pdm2 may be increased gradually over time, or may be increased at a specific gradient over time. Alternatively, the target discharge pressure Pdm1 or Pdm2 may be increased after a specific time has elapsed.

[0155] Each of the components of the air conditioner 1 described above has an internal computer system. A program for realizing the functions of each of the components of the air conditioner 1 described above may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed to perform processing in each of the components of the air conditioner 1 described above. Here, "reading a program recorded on a recording medium into a computer system and executing it" includes installing the program into a computer system. The term "computer system" here includes hardware such as an OS and peripheral devices.

[0156] Furthermore, a "computer system" may include multiple computer devices connected via a network, including communication lines such as the Internet, WAN, LAN, and dedicated lines. Furthermore, a "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into a computer system. Thus, the recording medium storing the program may be a non-transitory recording medium such as a CD-ROM.

[0157] The recording medium also includes internal or external recording media accessible from a distribution server for distributing the program. The program may be divided into multiple parts, downloaded at different times, and then combined by the components of the air conditioner 1, or each divided program may be distributed by a different distribution server. Furthermore, the term "computer-readable recording medium" also includes a medium that stores a program for a certain period of time, such as volatile memory (RAM) within a computer system that acts as a server or client when a program is transmitted over a network. The program may also be a program that realizes part of the above-described functions. Furthermore, the program may be a so-called differential file (differential program) that can realize the above-described functions in combination with a program already stored in the computer system.

[0158] 1...air conditioner, 10...outdoor unit, 11...compressor, 12...four-way valve, 13...outdoor heat exchanger, 14...outdoor fan, 15...pressure vessel, 16...liquid pipe shut-off valve, 17...gas pipe shut-off valve, 18...internal heat exchanger, 19...expansion valve, 20...indoor unit, 21...indoor expansion valve, 22...indoor heat exchanger, 23...indoor fan, 30...outdoor unit control unit, 31...discharge temperature sensor, 32...discharge pressure sensor, 33...outdoor unit outdoor air temperature sensor, 34...outdoor heat exchanger temperature sensor, 35...outdoor unit liquid pipe outlet temperature sensor, 36...suction pressure sensor, 40...indoor unit control unit, 41...indoor heat exchanger temperature sensor, 42...indoor unit temperature sensor, BP1...bypass piping, RC...refrigerant circuit

Claims

1. An air conditioner comprising an indoor unit having at least the indoor heat exchanger and an outdoor unit having at least the compressor and the outdoor heat exchanger, wherein the heat exchanger, including an outdoor heat exchanger and an indoor heat exchanger, is connected by refrigerant piping and has a refrigerant circuit through which the refrigerant circulates, and the air conditioner comprises an indoor unit having at least the indoor heat exchanger and an outdoor unit having at least the compressor and the outdoor heat exchanger, A discharge pressure sensor for detecting the discharge pressure, which is the pressure of the refrigerant discharged from the compressor, A discharge temperature sensor for detecting the discharge temperature, which is the temperature of the refrigerant discharged from the compressor, A heat exchanger temperature sensor detects the heat exchanger temperature, which is the temperature of the refrigerant flowing through the heat exchanger that functions as a condenser. After starting the compressor, a control unit executes a start-up control process to control the rotation speed of the compressor so that the heat exchanger temperature detected by the heat exchanger temperature sensor becomes the saturation temperature during the period until the discharge superheat, which is the value obtained by subtracting the saturation temperature of the discharge pressure calculated based on the discharge pressure detected by the discharge pressure sensor from the discharge temperature detected by the discharge temperature sensor, becomes equal to or greater than a preset threshold. An air conditioner equipped with [a specific feature].

2. The control unit, in the startup control process, When the heat exchanger temperature is greater than the saturation temperature, control is performed to increase the rotational speed of the compressor. When the heat exchanger temperature is lower than the saturation temperature, control is performed to reduce the rotational speed of the compressor. When the discharged superheat exceeds the threshold, the system transitions to a normal control process that controls the rotational speed of the compressor according to the air conditioning load of the heat exchanger. The air conditioner according to claim 1.

3. When the air conditioner is operating in heating mode, the heat exchanger temperature is the temperature of the refrigerant flowing through the indoor heat exchanger. When the air conditioner is operating in cooling mode, the heat exchanger temperature is the temperature of the refrigerant flowing through the outdoor heat exchanger. An air conditioner according to claim 1 or claim 2.

4. An air conditioner comprising an indoor unit having at least the indoor heat exchanger and an outdoor unit having at least the compressor and the outdoor heat exchanger, wherein the heat exchanger, including an outdoor heat exchanger and an indoor heat exchanger, is connected by refrigerant piping and has a refrigerant circuit through which the refrigerant circulates, and the air conditioner comprises an indoor unit having at least the indoor heat exchanger and an outdoor unit having at least the compressor and the outdoor heat exchanger, A discharge pressure sensor for detecting the discharge pressure, which is the pressure of the refrigerant discharged from the compressor, A discharge temperature sensor for detecting the discharge temperature, which is the temperature of the refrigerant discharged from the compressor, After starting the compressor, a control unit executes a start-up control process to control the rotation speed of the compressor so that the discharge pressure becomes a target discharge pressure, which is the pressure at which the saturation temperature is set to a predetermined temperature, during the period until the discharge superheat, which is the value obtained by subtracting the saturation temperature of the discharge pressure calculated based on the discharge pressure detected by the discharge pressure sensor from the discharge temperature detected by the discharge temperature sensor, exceeds a predetermined threshold, so that the discharge pressure becomes a target discharge pressure that is the pressure at which the saturation temperature is set to a predetermined temperature. An air conditioner equipped with [a specific feature].

5. An air conditioner comprising an indoor unit having at least the indoor heat exchanger and an outdoor unit having at least the compressor and the outdoor heat exchanger, wherein the heat exchanger, including an outdoor heat exchanger and an indoor heat exchanger, is connected by refrigerant piping and has a refrigerant circuit through which the refrigerant circulates, and the air conditioner comprises an indoor unit having at least the indoor heat exchanger and an outdoor unit having at least the compressor and the outdoor heat exchanger, A discharge pressure sensor for detecting the discharge pressure, which is the pressure of the refrigerant discharged from the compressor, A discharge temperature sensor for detecting the discharge temperature, which is the temperature of the refrigerant discharged from the compressor, A spatial temperature sensor that detects the air temperature in the space where the heat exchanger, which functions as a condenser, is installed, After starting the compressor, a control unit executes a start-up control process to control the rotation speed of the compressor so that, during the period until the discharge superheat, which is the value obtained by subtracting the saturation temperature of the discharge pressure calculated based on the discharge pressure detected by the discharge pressure sensor from the discharge temperature detected by the discharge temperature sensor, exceeds a preset threshold, the discharge pressure becomes a target discharge pressure that represents the pressure at which the air temperature detected by the ambient temperature sensor becomes the saturation temperature. An air conditioner equipped with [a specific feature].

6. When the air conditioner is operating in heating mode, the air temperature is the temperature in the space where the indoor unit is installed. When the air conditioner is operating in cooling mode, the air temperature is the ambient temperature of the surrounding area where the outdoor unit is installed. The air conditioner according to claim 5.

7. The control unit, in the startup control process, If the discharge pressure is less than the target discharge pressure, control is performed to increase the rotational speed of the compressor. If the discharge pressure is greater than the target discharge pressure, control is performed to reduce the rotational speed of the compressor. When the discharged superheat exceeds the threshold, the system transitions to a normal control process that controls the rotational speed of the compressor according to the air conditioning load of the heat exchanger. An air conditioner according to any one of claims 4 to 6.

8. The control unit executes the startup control process after a certain period of time has elapsed since the compressor was started. An air conditioner according to claim 1 and any one of claims 4 to 6.

9. A control method for an air conditioner comprising: an indoor unit having at least the indoor heat exchanger; an outdoor unit having at least the compressor and the outdoor heat exchanger; an outdoor heat exchanger having at least the compressor and the outdoor heat exchanger; a discharge pressure sensor for detecting the discharge pressure, which is the pressure of the refrigerant discharged from the compressor; a discharge temperature sensor for detecting the discharge temperature, which is the temperature of the refrigerant discharged from the compressor; and a heat exchanger temperature sensor for detecting the heat exchanger temperature, which is the temperature of the refrigerant flowing through the heat exchanger that functions as a condenser; After the control unit starts the compressor, it performs a start-up control process to control the rotation speed of the compressor so that the heat exchanger temperature detected by the heat exchanger temperature sensor becomes the saturation temperature, during the period until the discharge superheat, which is the value obtained by subtracting the saturation temperature of the discharge pressure (calculated based on the discharge pressure detected by the discharge pressure sensor) from the discharge temperature detected by the discharge temperature sensor, exceeds a preset threshold. Control method.

10. A control method for an air conditioner comprising: an indoor unit having at least the indoor heat exchanger; an outdoor unit having at least the compressor and the outdoor heat exchanger; an outdoor heat exchanger having at least the compressor and the outdoor heat exchanger; a discharge pressure sensor for detecting the discharge pressure, which is the pressure of the refrigerant discharged from the compressor; and a discharge temperature sensor for detecting the discharge temperature, which is the temperature of the refrigerant discharged from the compressor; After the control unit starts the compressor, it performs a start-up control process to control the rotation speed of the compressor so that the discharge pressure becomes a target discharge pressure, which is the pressure at which the saturation temperature is set to a predetermined temperature, during the period until the discharge superheat, which is the value obtained by subtracting the saturation temperature of the discharge pressure calculated based on the discharge pressure detected by the discharge pressure sensor from the discharge temperature detected by the discharge temperature sensor, exceeds a predetermined threshold. Control method.

11. An air conditioner comprising: an indoor unit having at least the indoor heat exchanger; an outdoor unit having at least the compressor and the outdoor heat exchanger; an outdoor heat exchanger having at least the compressor and the outdoor heat exchanger; a discharge pressure sensor for detecting the discharge pressure, which is the pressure of the refrigerant discharged from the compressor; a discharge temperature sensor for detecting the discharge temperature, which is the temperature of the refrigerant discharged from the compressor; and a space temperature sensor for detecting the air temperature in the space in which the heat exchanger, which functions as a condenser, is installed, wherein the heat exchanger has a rotational speed that can be changed; an expansion valve; and a heat exchanger including an outdoor heat exchanger and an indoor heat exchanger are connected by refrigerant piping and have a refrigerant circuit through which the refrigerant circulates, and further comprising: an indoor unit having at least the indoor heat exchanger; an outdoor unit having at least the compressor and the outdoor heat exchanger; a discharge pressure sensor for detecting the discharge pressure, which is the pressure of the refrigerant discharged from the compressor; a discharge temperature sensor for detecting the discharge temperature, which is the temperature of the refrigerant discharged from the compressor; and a space temperature sensor for detecting the air temperature in the space in which the heat exchanger, which functions as a condenser, is installed, After the compressor is started, the control unit performs a start-up control process to control the rotation speed of the compressor so that the discharge superheat, which is the value obtained by subtracting the saturation temperature of the discharge pressure (calculated based on the discharge pressure detected by the discharge pressure sensor) from the discharge temperature detected by the discharge temperature sensor, becomes equal to or greater than a preset threshold, so that the discharge pressure becomes a target discharge pressure that represents the pressure at which the air temperature detected by the ambient temperature sensor becomes the saturation temperature. Control method.