Air conditioner

Abstract

To rapidly increase a discharge SH while reducing discomfort felt by a user.SOLUTION: An air conditioner according to an embodiment includes: a refrigerant circuit having a compressor, a condenser, an expansion valve, and an evaporator, and circulating a refrigerant; an overheat degree acquiring unit for acquiring an overheat degree of a discharge refrigerant discharged from the compressor; and a control unit which sets a rotation speed of the compressor to a prescribed rotation speed or lower and sets an opening of the expansion valve to a prescribed value so as to continue the operation of the compressor in the case where the acquired overheat degree is equal to or lower than a predetermined first threshold when thermo-off for stopping the operation of the compressor is instructed.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an air conditioner. [Background technology]

[0002] In recent years, the popularity of air conditioners for cold regions has increased, and homes in cold regions tend to be well insulated. In homes with high insulation, the air conditioner reaches the set temperature in a short time after it is turned on, and the room temperature does not drop much after that. Therefore, even in cold regions, low-load operation in which the compressor speed is reduced to reduce heating capacity is common. During such low-load operation with a low compressor speed, it is difficult to create a high-low pressure difference, which is the difference between the high-pressure side pressure and the low-pressure side pressure of the refrigerant circulating in the refrigerant circuit, and the degree of superheat of the refrigerant discharged from the compressor (discharge SH) is likely to decrease.

[0003] A decrease in the discharge SH of an air conditioner is accompanied by a decrease in the concentration of the refrigeration oil in the compressor, which induces a decrease in the sealing property, and is a factor that hinders the normal operation of the compressor. In addition, in an air conditioner, if the thermo-off command is issued and the compressor stops with the discharge SH decreased, the refrigerant is more likely to dissolve in the oil (refrigeration oil) during the stop, and the oil concentration is likely to decrease. Furthermore, if the compressor is started in this state, the refrigerant dissolved in the refrigeration oil will evaporate (oil foaming phenomenon) when the pressure inside the compressor begins to rise, and the refrigerant and refrigeration oil stored in the compressor will be carried into the refrigerant circuit, which may lead to a further decrease in the oil concentration. If the compressor operates in this state, there is a concern that the wear of the sliding parts will progress, so it is necessary to continue operation until the discharge SH becomes somewhat high before stopping the compressor.

[0004] Conventional techniques for thermo-off when the discharge SH drops include a heating control means that changes the current to each phase of the electric motor of the compressor without changing the operating speed of the compressor, or an electric heater heating means that uses an electric heating wire wound around the outer casing of the compressor to pass electricity through it, thereby quickly increasing the discharge SH and shortening the delay time for the compressor to stop. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6749471 specification Summary of the Invention [Problem to be solved by the invention]

[0006] However, while the above conventional technology can quickly increase the discharge SH, it does not change the operating speed of the compressor, which increases power consumption, and the heating capacity increases too much even though the operation should be stopped in the thermo-off state. If the heating capacity increases too much even in the thermo-off state, the room will become too warm when the air conditioner is operating, causing discomfort to the user.

[0007] The present disclosure proposes a technique that can quickly increase the discharge SH while reducing discomfort to the user. [Means for solving the problem]

[0008] The air conditioner of the present disclosure has a refrigerant circuit having a compressor, a condenser, an expansion valve and an evaporator, and comprises: a refrigerant circuit for circulating refrigerant; a superheat degree acquisition unit for acquiring the superheat degree of the refrigerant discharged from the compressor; and a control unit for setting the compressor rotation speed to a predetermined rotation speed or lower and setting the opening degree of the expansion valve to a predetermined value to continue operation of the compressor when a thermo-off command is issued to stop operation of the compressor and the acquired superheat degree is equal to or lower than a predetermined first threshold value. Effect of the Invention

[0009] According to the present disclosure, it is possible to quickly increase the discharge SH while reducing discomfort felt by the user. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing an entire air conditioner according to an embodiment. [Diagram 2] FIG. 2 is a block diagram showing an example of a functional configuration of the outdoor unit control circuit. [Diagram 3] FIG. 3 is a flowchart showing a control method during heating operation of the air conditioner according to the embodiment. [Figure 4] FIG. 4 is an explanatory diagram for explaining an overview of the heating operation of the air conditioner according to the embodiment. [Diagram 5] FIG. 5 is a flowchart showing a control method during continuous operation of the air conditioner according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an air conditioner according to an embodiment will be described with reference to the drawings. Components having the same functions in the embodiments will be given the same reference numerals, and duplicated descriptions will be omitted. Note that the air conditioner described in the following embodiment is merely an example, and does not limit the embodiment. In addition, the following embodiments may be appropriately combined within a range that does not cause contradiction.

[0012] The air conditioner according to the embodiment has a compressor, a condenser, an expansion valve, and an evaporator, and performs cooling or heating operation by a refrigerant circuit that circulates refrigerant. As the air conditioner according to the embodiment, a single type in which one indoor unit is connected to one outdoor unit and the indoor unit is configured to be able to perform cooling or heating operation will be exemplified and described. Note that the air conditioner according to the embodiment may be configured as a multi-type having multiple indoor units corresponding to one outdoor unit. FIG. 1 is a schematic diagram showing the entire air conditioner according to the embodiment.

[0013] [Air conditioning system configuration] As shown in Fig. 1, an air conditioner 1 according to an embodiment includes an outdoor unit 2, and an indoor unit 5 connected to the outdoor unit 2 via a liquid pipe 8 and a gas pipe 9. One end of the liquid pipe 8 is connected to an operation valve 25 of the outdoor unit 2, and the other end branches off and is connected to each of the liquid pipe connections 53 of the indoor unit 5. One end of the gas pipe 9 is connected to an operation valve 26 of the outdoor unit 2, and the other end branches off and is connected to each of the gas pipe connections 54 of the indoor unit 5. The refrigerant circuit 100 of the air conditioner 1 is configured as described above.

[0014] First, the outdoor unit 2 will be described. The outdoor unit 2 includes a compressor 21, a four-way valve 22, an outdoor heat exchanger 23, an expansion valve 24, an operating valve 25 connected to one end of the liquid pipe 8, an operating valve 26 connected to one end of the gas pipe 9, an accumulator 28 which is a gas-liquid separator, and an outdoor fan 27. Each of these components except for the outdoor fan 27 is connected to each other via each refrigerant pipe described later, and constitutes an outdoor unit refrigerant circuit 20 which is a part of the refrigerant circuit 100.

[0015] The compressor 21 is, for example, a rotary compressor. A refrigerant discharge side of the compressor 21 is connected to a port a of a four-way valve 22 (described later) via a discharge pipe 41. A refrigerant suction side of the compressor 21 is connected to a refrigerant outlet side of the accumulator 28 via a suction pipe (not shown). In this manner, the compressor 21 is connected to a refrigerant circuit 100 filled with refrigerant. In addition, refrigeration oil 10 is stored inside the compressor 21 as a lubricating oil for lubricating sliding parts (not shown).

[0016] The four-way valve 22 is a valve for switching the flow direction of the refrigerant, and has four ports a, b, c, and d. As described above, the port a is connected to the refrigerant discharge side of the compressor 21 by the discharge pipe 41. The port b is connected to one refrigerant inlet / outlet of the outdoor heat exchanger 23 by the refrigerant piping 43. The port c is connected to the refrigerant inlet side of the accumulator 28 by the refrigerant piping 46. And the port d is connected to the operation valve 26 by the outdoor unit gas pipe 45.

[0017] The outdoor heat exchanger 23 exchanges heat between the refrigerant and the outside air taken into the outdoor unit 2 by air blown by the outdoor fan 27 described below. One refrigerant inlet / outlet of the outdoor heat exchanger 23 is connected to the port b of the four-way valve 22 by the refrigerant piping 43 as described above, and the other refrigerant inlet / outlet is connected to the operation valve 25 via the outdoor unit liquid pipe 44. The outdoor heat exchanger 23 functions as a condenser when the indoor unit 5 performs cooling operation, and functions as an evaporator when the indoor unit 5 performs heating operation.

[0018] The expansion valve 24 is provided in the outdoor unit liquid pipe 44. The expansion valve 24 is an electronic expansion valve, and the amount of refrigerant flowing into the outdoor heat exchanger 23 or the amount of refrigerant flowing out from the outdoor heat exchanger 23 is adjusted by adjusting the opening degree of the expansion valve 24.

[0019] The outdoor fan 27 is made of, for example, a resin material, and is disposed near the outdoor heat exchanger 23. The outdoor fan 27 is rotated by a fan motor (not shown) to take in outside air from an intake port (not shown) into the outdoor unit 2, and discharges the outside air that has exchanged heat with the refrigerant in the outdoor heat exchanger 23 to the outside of the outdoor unit 2 from an exhaust port (not shown).

[0020] As described above, the refrigerant inflow side of the accumulator 28 is connected to the port c of the four-way valve 22 via the refrigerant piping 46, and the refrigerant outflow side of the accumulator 28 is connected to the refrigerant suction side of the compressor 21. In this manner, the accumulator 28 is connected to the refrigerant circuit 100 and the compressor 21. The accumulator 28 separates the refrigerant that has flowed into the accumulator 28 from the refrigerant piping 46 into a gas refrigerant and a liquid refrigerant, and causes the gas refrigerant to be sucked into the compressor 21.

[0021] In addition to the above-mentioned configuration, the outdoor unit 2 has various sensors. As shown in Fig. 1, the discharge pipe 41 is provided with a discharge pressure sensor 31 that detects the discharge pressure, which is the pressure of the refrigerant discharged from the compressor 21, and a discharge temperature sensor 33 that detects the temperature of the refrigerant discharged from the compressor 21.

[0022] An outdoor heat exchanger temperature sensor 35 is provided in the outdoor unit liquid pipe 44 between the outdoor heat exchanger 23 and the expansion valve 24 to detect the temperature of the refrigerant flowing into the outdoor heat exchanger 23 or the temperature of the refrigerant flowing out from the outdoor heat exchanger 23. An outdoor air temperature sensor 36 is provided near the suction port (not shown) of the outdoor unit 2 to detect the temperature of the outdoor air flowing into the outdoor unit 2, i.e., the outdoor air temperature.

[0023] The outdoor unit 2 also includes an outdoor unit control circuit 200. The outdoor unit control circuit 200 is a computer, and is mounted on a control board stored in an electrical equipment box (not shown) of the outdoor unit 2. The outdoor unit control circuit 200 controls the drive of the compressor 21 and the outdoor fan 27 based on the detection results and control signals detected by various sensors of the outdoor unit 2. The outdoor unit control circuit 200 also controls the switching of the four-way valve 22 and adjusts the opening degree of the expansion valve 24 based on the detection results and control signals detected by various sensors of the outdoor unit 2.

[0024] Here, the outdoor unit control circuit 200 will be described in detail with reference to Fig. 2. Fig. 2 is a block diagram showing an example of the functional configuration of the outdoor unit control circuit 200. The outdoor unit control circuit 200 is configured by a so-called microcomputer, and is mounted on a control board stored in an electrical component box (not shown) of the outdoor unit 2. The outdoor unit control circuit 200 includes a CPU 210, a storage unit 220, a communication unit 230, a sensor input unit 240, and a superheat degree acquisition unit 250. This outdoor unit control circuit 200 is an example of a control unit. In this specification, the outdoor unit control circuit 200 may be simply referred to as a control unit or a control means.

[0025] The storage unit 220 is configured with a flash memory, and stores the control program of the outdoor unit 2, detection values ​​corresponding to detection signals from various sensors, control states of the compressor 21 and the operating valve 25, etc. Although not shown, the storage unit 220 stores in advance setting information including a rotation speed table that determines the rotation speed of the compressor 21 according to the required capacity received from the indoor unit 5, a threshold value for determining the state of the discharge SH, the operation time when performing continuous operation, the opening degree of the expansion valve 24, the rotation speed of the compressor 21, etc.

[0026] The communication unit 230 is an interface that communicates with the indoor unit 5. The sensor input unit 240 takes in detection results from various sensors in the outdoor unit 2 and outputs them to the CPU 210. The superheat degree acquisition unit 250 acquires the degree of superheat of the discharged refrigerant (discharged SH) from the compressor 21 based on the detection results from the various sensors in the outdoor unit 2.

[0027] The CPU 210 takes in the detection results of the respective sensors of the outdoor unit 2 described above via the sensor input unit 240. Furthermore, the CPU 210 takes in the control signals transmitted from the indoor unit 5 via the communication unit 230. The CPU 210 performs drive control of the compressor 21 and the outdoor fan 27 based on the taken-in detection results, control signals, etc. Furthermore, the CPU 210 performs switching control of the four-way valve 22 based on the taken-in detection results and control signals. Furthermore, the CPU 210 adjusts the opening degree of the expansion valve 24 based on the taken-in detection results and control signals.

[0028] Returning to Fig. 1, the indoor unit 5 will be described. The indoor unit 5 includes an indoor heat exchanger 51, a liquid pipe connection part 53 to which the other end of the branched liquid pipe 8 is connected, a gas pipe connection part 54 to which the other end of the branched gas pipe 9 is connected, and an indoor fan 55. These parts except for the indoor fan 55 are connected to each other via refrigerant pipes described later, and constitute an indoor unit refrigerant circuit 50 that forms part of the refrigerant circuit 100.

[0029] The indoor heat exchanger 51 exchanges heat between the indoor air taken into the indoor unit 5 from an inlet (not shown) and the refrigerant by blowing air from an indoor fan 55 described below. One refrigerant inlet / outlet of the indoor heat exchanger 51 is connected to a liquid pipe connection part 53 by an indoor unit liquid pipe 71, and the other refrigerant inlet / outlet of the indoor heat exchanger 51 is connected to a gas pipe connection part 54 by an indoor unit gas pipe 72. The indoor heat exchanger 51 functions as an evaporator when the indoor unit 5 performs cooling operation, and functions as a condenser when the indoor unit 5 performs heating operation.

[0030] The indoor fan 55 is made of, for example, a resin material, and is disposed near the indoor heat exchanger 51. The indoor fan 55 is rotated by a fan motor (not shown) to take in indoor air from an intake port (not shown) into the indoor unit 5, and supplies the indoor air that has exchanged heat with the refrigerant in the indoor heat exchanger 51 to the room from an exhaust port (not shown).

[0031] In addition to the above-mentioned configuration, various sensors are provided in the indoor unit 5. An indoor temperature sensor 63 that detects the temperature of the indoor air flowing into the indoor unit 5, i.e., the suction temperature, is provided near the suction port (not shown) of the indoor unit 5. An indoor heat exchanger temperature (two-phase refrigerant temperature) sensor 61 that detects the temperature of the indoor heat exchanger 51 is provided in the indoor heat exchanger 51.

[0032] The indoor unit 5 also includes an indoor unit control circuit 500. The indoor unit control circuit 500 is a computer similar to the outdoor unit control circuit 200, and is mounted on a control board housed in an electrical component box (not shown) of the indoor unit 5. The indoor unit control circuit 500 controls the drive of the indoor fan 55 based on the detection results detected by various sensors in the indoor unit 5 and signals transmitted from the remote control and the outdoor unit 2. The control circuit of the air conditioner 1 is composed of the outdoor unit control circuit 200 and the indoor unit control circuit 500 described above.

[0033] [Air conditioning unit operation] When adjusting the temperature in the room where the indoor unit 5 is located, a user of the air conditioner 1 operates a remote controller (not shown) to start the air conditioner 1 and input the operating conditions to the indoor unit control circuit 500. When the operating conditions are input, the indoor unit control circuit 500 performs either heating operation or cooling operation based on the input operating conditions and the indoor temperature. When performing / ending heating operation or cooling operation, the indoor unit control circuit 500 transmits the operating conditions and the indoor temperature to the outdoor unit control circuit 200 together with an instruction to start / end the heating operation or cooling operation.

[0034] Furthermore, when a thermo-off condition is met, such as when the room temperature exceeds a set temperature set as an operating condition, during heating operation, the indoor unit control circuit 500 transmits a thermo-off instruction to the outdoor unit control circuit 200. Specifically, the indoor unit control circuit 500 transmits a 0 code indicating thermo-off to the outdoor unit control circuit 200. Thermo-off is a state in which the operation of the compressor 21 is stopped and heating operation is suspended until the room temperature again becomes lower than the set temperature.

[0035] Here, the flow of refrigerant in the refrigerant circuit 100 and the operation of each part during air conditioning operation of the air conditioner 1 according to the embodiment will be described. The arrows in Fig. 1 indicate the flow of refrigerant during heating operation.

[0036] As shown in Fig. 1, when the indoor unit 5 performs heating operation, the outdoor unit control circuit 200 switches the four-way valve 22 to the state shown by the solid lines in Fig. 1, that is, to communicate ports a and d of the four-way valve 22 and to communicate ports b and c. This results in a heating cycle in the refrigerant circuit 100 in which the outdoor heat exchanger 23 functions as an evaporator and the indoor heat exchanger 51 functions as a condenser.

[0037] In the heating cycle, the high-pressure refrigerant discharged from the compressor 21 flows through the discharge pipe 41 and into the four-way valve 22, and then flows from the four-way valve 22 through the outdoor unit gas pipe 45, the operating valve 26, the gas pipe 9, and the gas pipe connection part 54, in that order, before flowing into the indoor unit 5. The refrigerant that has flowed into the indoor unit 5 flows through the indoor unit gas pipe 72 and into the indoor heat exchanger 51, where it condenses by exchanging heat with indoor air taken into the indoor unit 5 by the rotation of the indoor fan 55. In this way, the indoor heat exchanger 51 functions as a condenser, and the indoor air that has been heated by exchanging heat with the refrigerant in the indoor heat exchanger 51 is blown out into the room from an air outlet (not shown), thereby heating the room in which the indoor unit 5 is installed.

[0038] The refrigerant flowing out of the indoor heat exchanger 51 flows through the indoor unit liquid pipe 71 and into the liquid pipe 8 via the liquid pipe connection part 53. The refrigerant flowing through the liquid pipe 8 flows into the outdoor unit 2 via the operation valve 25.

[0039] The refrigerant that flows into the outdoor unit 2 flows through the outdoor unit liquid pipe 44 and is decompressed by the expansion valve 24. The refrigerant that flows from the outdoor unit liquid pipe 44 into the outdoor heat exchanger 23 evaporates by exchanging heat with outside air that has been drawn into the outdoor unit 2 by the rotation of the outdoor fan 27. The refrigerant that flows out of the outdoor heat exchanger 23 flows in this order through the refrigerant piping 43, the four-way valve 22, the refrigerant piping 46, and the accumulator 28, before being sucked into the compressor 21 and compressed again.

[0040] When the indoor unit 5 performs cooling / defrosting operation, the outdoor unit control circuit 200 switches the four-way valve 22 to the state shown by the dashed lines in Fig. 1, that is, to communicate ports a and b of the four-way valve 22 and to communicate ports c and d. This results in a cooling cycle in the refrigerant circuit 100 in which the outdoor heat exchanger 23 functions as a condenser and the indoor heat exchanger 51 functions as an evaporator.

[0041] In the cooling cycle, the high-pressure refrigerant discharged from the compressor 21 flows through the discharge pipe 41 and into the four-way valve 22, and then flows from the four-way valve 22 into the outdoor heat exchanger 23 through the refrigerant piping 43. The outdoor heat exchanger 23 is heated (defrosted) by the high-pressure refrigerant discharged from the compressor 21 flowing into it. The refrigerant that has flowed into the outdoor heat exchanger 23 exchanges heat with the outdoor air taken into the interior of the outdoor unit 2 by the rotation of the outdoor fan 27, and condenses. The cooled refrigerant flows through the expansion valve 24, the operating valve 25, the liquid pipe 8, and the liquid pipe connection part 53 in this order, and flows into the indoor unit 5. The refrigerant that has flowed into the indoor unit 5 flows through the indoor unit liquid pipe 71, flows into the indoor heat exchanger 51 via the indoor unit liquid pipe 71, and exchanges heat with the indoor air taken into the interior of the indoor unit 5 by the rotation of the indoor fan 55, and evaporates. At this time, the indoor air that has been cooled by exchanging heat with the refrigerant in the indoor heat exchanger 51 is blown out into the room from an air outlet (not shown), thereby cooling the room in which the indoor unit 5 is installed.

[0042] The refrigerant flowing out of the indoor heat exchanger 51 flows through the indoor unit gas pipe 72 and into the gas pipe 9 via the gas pipe connection part 54. The refrigerant flowing through the gas pipe 9 flows into the outdoor unit 2 via the operation valve 26. The refrigerant that flows into the outdoor unit 2 flows through the outdoor unit gas pipe 45, and then through the four-way valve 22, the refrigerant piping 46, and the accumulator 28, in that order, before being sucked into the compressor 21 and compressed again.

[0043] Next, a control method of the outdoor unit control circuit 200 when a thermo-off command is issued from the indoor unit control circuit 500 during heating operation will be described with reference to Fig. 3 to Fig. 5. Fig. 3 is a flowchart showing a control method during heating operation of the air conditioner 1 according to the embodiment.

[0044] As shown in FIG. 3, after processing (heating operation) is started, when the CPU 210 receives a thermo-off instruction from the indoor unit control circuit 500 (S1), it acquires the degree of superheat of the discharged refrigerant (discharged SH) of the compressor 21 from the superheat degree acquisition unit 250 (S2).

[0045] Next, the CPU 210 judges whether the acquired discharge SH is equal to or less than a threshold value preset in the setting information of the storage unit 220 (S3). The threshold value used in this S2 is preset in order to determine the discharge SH at which the refrigeration oil concentration in the compressor 21 is likely to decrease, and is set to 10 deg as an example.

[0046] If the discharge SH is not below the threshold value (S3: No), since the discharge SH is maintained high enough not to cause a decrease in the concentration of the refrigeration oil, the CPU 210 stops the operation (motor drive) of the compressor 21, stops the heating operation (S5), and ends the processing.

[0047] If the discharge SH is equal to or less than the threshold value (S3: Yes), the discharge SH is low and the refrigerating machine oil concentration is likely to decrease, so the CPU 210 performs a continuous operation to continue the operation of the compressor 21 (S4).

[0048] Specifically, the CPU 210 refers to the rotation speed of the compressor 21 (minimum rotation speed at outside air temperature), the opening degree of the expansion valve 24 (predetermined opening degree), and the operation time of the continuous operation (maximum operation time) that are preset in the setting information of the storage unit 220. Next, the CPU 210 sets the rotation speed of the compressor 21 to the minimum rotation speed at outside air temperature, sets the opening degree of the expansion valve 24 to the predetermined opening degree, and continues operation. In the air conditioner 1, when a thermo-off command is issued, such continuous operation can suppress a decrease in the discharge SH, and enables the discharge SH to be quickly increased when operation is resumed.

[0049] The preset outdoor temperature minimum rotation speed of the compressor 21 is equal to or lower than the rotation speed when a thermo-off command is issued. The outdoor temperature minimum rotation speed may be set appropriately for each outdoor temperature so as to correspond to the outdoor temperature. The outdoor temperature minimum rotation speed may be the lower limit of a rotation speed range defined as an operating range, or a minimum rotation speed defined in advance as a specification of the compressor 21. By setting the rotation speed of the compressor 21 to such an outdoor temperature minimum rotation speed, the air conditioner 1 can reduce the heating capacity during continuous operation to prevent the room from becoming overheated, thereby reducing the discomfort of the user.

[0050] The preset opening degree of the expansion valve 24 (predetermined opening degree) may be a predetermined value (for example, a lower limit value) within the range of opening degrees during operation, or may be a minimum opening degree preset as a specification of the expansion valve 24. In order to quickly ensure the discharge SH, it is preferable to set the opening degree to the smallest opening degree within the settable range of the expansion valve opening degree according to the operating state, but it is set from a comprehensive perspective, taking into account whether the expansion valve will be in a closed state even when the variation range of the expansion valve opening degree is taken into account, whether the low pressure will not drop too much, etc. By setting the opening degree of the expansion valve 24 to such a predetermined opening degree, the air conditioner 1 can prevent the room from becoming too warm during continuous operation, thereby reducing the discomfort of the user.

[0051] During the continuous operation, the CPU 210 counts the operation time using an RTC (Real Time Clock) or the like. Next, when the elapsed operation time reaches a preset operation time, the CPU 210 stops the operation (motor drive) of the compressor 21 and ends the continuous operation.

[0052] The preset operation time differs depending on the displacement volume of the compressor 21, but is appropriately set within a predetermined range (e.g., 2 to 10 minutes) that can reliably increase the discharge SH. For example, when the operation time is set to the minimum of 2 minutes, the discharge SH can be reliably increased and an excessive increase in the discharge SH can be prevented. In addition, when the continuous operation time reaches a predetermined operation time within a predetermined range, the continuous operation is terminated, thereby making it possible to prevent wasteful continuation of the continuous operation.

[0053] Fig. 4 is an explanatory diagram outlining the heating operation of the air conditioner 1 according to the embodiment. In Fig. 4, the horizontal axis is the time axis, the vertical axis on the left side indicates the rotation speed of the compressor 21 and the opening degree of the expansion valve 24, and the vertical axis on the right side indicates the discharge SH.

[0054] 4, when a thermo-off command is issued (time t1), the discharge SH is about 0 deg, which is equal to or less than the threshold value (10 deg). Therefore, the CPU 210 sets the rotation speed of the compressor 21 to the minimum rotation speed for the outside air temperature, and sets the opening degree of the expansion valve 24 to a predetermined opening degree. When the rotation speed of the compressor 21 becomes the minimum rotation speed for the outside air temperature and the opening degree of the expansion valve 24 becomes the predetermined opening degree, the CPU 210 starts continuous operation for the longest operation time (10 minutes) (time t2).

[0055] Next, when the continuous operation reaches the longest operation time (10 minutes) (time t3), the CPU 210 stops the operation (motor drive) of the compressor 21, and ends the continuous operation.

[0056] Next, after a predetermined time (e.g., 60 seconds) set in the setting information or the like, the CPU 210 opens the expansion valve 24 to the maximum opening degree, thereby making it easier to equalize the refrigerant pressure (time t4). In this way, by equalizing the refrigerant pressure, it is possible to prevent differential pressure start-up when restarting operation.

[0057] Next, when the continuous operation ends and the next startup (when a thermo-on command is issued, time t5) occurs, the CPU 210 resumes the heating operation with the rotation speed of the compressor 21 and the opening of the expansion valve 24 according to the operating conditions.

[0058] Here, when a thermo-off command is issued (e.g., at time t1), if the acquired discharge SH is equal to or greater than a second threshold value (e.g., 5 deg) that is pre-determined to be lower than a first threshold value (e.g., 10 deg), the CPU 210 may continue operation for the shortest time (e.g., 2 minutes) within the longest operating time range.

[0059] Furthermore, the CPU 210 may stop the operation of the compressor 21 if the discharge SH is equal to or greater than the second threshold value when the operation of the compressor 21 has continued for the above-mentioned shortest time.

[0060] In addition, when a thermo-off command is issued, if the acquired discharge SH is less than a second threshold (e.g., 5 deg) that is pre-defined lower than the first threshold (e.g., 10 deg), the CPU 210 may stop operation of the compressor 21 when the acquired discharge SH during continued operation becomes equal to or greater than the second threshold.

[0061] Here, the second threshold value is preset in the setting information of the storage unit 220 in order to determine the discharge SH at which the sealing property is likely to decrease due to a decrease in the concentration of the refrigerating machine oil in the compressor 21. In other words, when the discharge SH is equal to or higher than the discharge SH at which the sealing property is unlikely to decrease to a certain extent, the air conditioner 1 limits the continuous operation time when the thermostat is off to the shortest possible time (e.g., 2 minutes), thereby reducing power consumption associated with the continuous operation and reducing discomfort to the user by suppressing an excessive increase in the discharge SH.

[0062] FIG. 5 is a flowchart showing a control method during continuous operation of the air conditioner 1 according to the embodiment, and more specifically, FIG. 5 illustrates an example of a control method during continuous operation using the above-mentioned second threshold value.

[0063] As shown in FIG. 5, when the process (continuous operation) is started, the CPU 210 determines whether or not the discharge SH is equal to or greater than 5 deg (second threshold value) (S10).

[0064] If the discharge SH is 5 deg (second threshold value) or more, the CPU 210 continues the continuous operation (S11) and determines whether the operation time has reached the shortest time within a predetermined continuous operation time (longest operation time) (S12). If the operation time has not reached the shortest time (S12: No), the CPU 210 returns the process to S11.

[0065] When the operation time reaches the shortest time (S12: Yes), the CPU 210 judges whether the discharge SH is equal to or greater than 5 deg (second threshold) (S13). When the discharge SH is equal to or greater than 5 deg (second threshold) (S13: Yes), the CPU 210 stops the operation of the compressor 21 (S14).

[0066] If the discharge SH is not 5 deg (second threshold) or more (S13: No), the CPU 210 judges whether the operation time reaches a predetermined continuous operation time (longest operation time) (S15). If the operation time reaches the predetermined continuous operation time (longest operation time) (S15: Yes), the CPU 210 stops the operation of the compressor 21 (S14). If the operation time does not reach the predetermined continuous operation time (longest operation time) (S15: No), the CPU 210 returns the process to S11.

[0067] In S10, if the discharge SH is not equal to or greater than 5 degrees (second threshold) (S10: No), the CPU 210 continues operation (S16) and determines whether the discharge SH is equal to or greater than 5 degrees (second threshold) (S17). If the discharge SH is equal to or greater than 5 degrees (second threshold) (S17: Yes), the CPU 210 stops operation of the compressor 21 (S14).

[0068] If the discharge SH is not 5 deg (second threshold) or more (S17: No), the CPU 210 judges whether the operation time reaches a predetermined continuous operation time (longest operation time) (S18). If the operation time reaches the predetermined continuous operation time (longest operation time) (S18: Yes), the CPU 210 stops the operation of the compressor 21 (S14). If the operation time does not reach the predetermined continuous operation time (longest operation time) (S18: No), the CPU 210 returns the process to S16.

[0069] As described above, the air conditioner 1 has the refrigerant circuit 100, the superheat degree acquisition unit 250, and the outdoor unit control circuit 200. The refrigerant circuit 100 has the compressor 21, a condenser (indoor heat exchanger 51), an expansion valve 24, and an evaporator (outdoor heat exchanger 23), and circulates the refrigerant. The superheat degree acquisition unit 250 acquires the superheat degree of the refrigerant discharged from the compressor 21. When a thermo-off command is issued to stop the operation of the compressor 21, if the superheat degree acquired by the superheat degree acquisition unit 250 is equal to or lower than a first threshold value determined in advance, the outdoor unit control circuit 200 sets the rotation speed of the compressor 21 to a rotation speed equal to or lower than the rotation speed when the thermo-off command is issued. In addition, when a thermo-off command is issued to stop operation of the compressor 21, if the degree of superheat acquired by the superheat degree acquisition unit 250 is equal to or lower than a predetermined first threshold value, the outdoor unit control circuit 200 sets the opening degree of the expansion valve 24 to a predetermined value to continue operation of the compressor 21.

[0070] This makes it possible for the air conditioner 1 to prevent a decrease in the discharge SH and to quickly increase the discharge SH when operation is restarted.

[0071] Furthermore, when the degree of superheat acquired by the superheat degree acquisition unit 250 is equal to or lower than a first threshold value, the outdoor unit control circuit 200 sets the rotation speed of the compressor 21 to the minimum rotation speed predetermined for the compressor 21, and sets the opening degree of the expansion valve 24 to the minimum opening degree predetermined for the operating valve 25.

[0072] As a result, the air conditioner 1 can reduce power consumption due to continuous operation, and can also reduce discomfort to the user by preventing an excessive increase in the discharge SH.

[0073] Furthermore, in the air conditioner 1, the time for which the compressor 21 continues to operate is set beforehand within a predetermined range.

[0074] As a result, the air conditioner 1 can reduce power consumption due to continuous operation, and can also reduce discomfort to the user by preventing an excessive increase in the discharge SH.

[0075] Furthermore, when a thermo-off command is issued, if the degree of superheat acquired by the superheat degree acquisition unit 250 is lower than the first threshold value and is equal to or higher than a second threshold value that is lower than the first threshold value and is determined in advance, the outdoor unit control circuit 200 continues operation of the compressor 21 for the shortest time within a predetermined range.

[0076] As a result, the air conditioner 1 can prevent a decrease in sealing performance that is likely to occur due to a decrease in the concentration of refrigerating machine oil in the compressor 21 when the thermostat is turned off.

[0077] Furthermore, when the operation of the compressor has continued for the shortest time, if the degree of superheat acquired by the superheat degree acquisition unit 250 is equal to or greater than the second threshold value, the outdoor unit control circuit 200 stops the operation of the compressor 21.

[0078] As a result, the air conditioner 1 can reduce power consumption during continuous operation while preventing deterioration of sealing performance due to a decrease in the concentration of refrigeration oil.

[0079] In addition, when a thermo-off command is issued, if the degree of superheat acquired by the superheat degree acquisition unit 250 is lower than the first threshold value and less than a predetermined second threshold value, the outdoor unit control circuit 200 stops the operation of the compressor 21 when the degree of superheat acquired while continuing to operate the compressor 21 becomes equal to or higher than the second threshold value.

[0080] This makes it possible for the air conditioner 1 to prevent the discharge SH from increasing excessively due to continued operation associated with thermo-off. [Explanation of symbols]

[0081] 1. Air conditioner 2…Outdoor unit 5…Indoor unit 8...Liquid pipe 9…Gas pipe 10...Refrigerating machine oil 20…Outdoor unit refrigerant circuit 21...Compressor 22...Four-way valve 23…Outdoor heat exchanger 24…Expansion valve 25, 26...Operating valve 27…Outdoor fan 28…Accumulator 31...Discharge pressure sensor 33...Discharge temperature sensor 35...Outdoor heat exchanger temperature sensor 36...Outside air temperature sensor 41...Discharge pipe 43…Refrigerant piping 44…Outdoor unit liquid pipe 45…Outdoor unit gas pipe 46…Refrigerant piping 50…Indoor unit refrigerant circuit 51...Indoor heat exchanger 53...Liquid pipe connection part 54…Gas pipe connection 55…Indoor fan 61...Indoor heat exchanger temperature (two-phase refrigerant temperature) sensor 63…Indoor temperature sensor 71…Indoor unit liquid pipe 72…Indoor unit gas pipe 100...Refrigerant circuit 200...Outdoor unit control circuit 210…CPU 220...Storage section 230…Communications Department 240…Sensor input section 250...Superheat degree acquisition section 500…Indoor unit control circuit a~d…Port t1~t5…time

Claims

1. a refrigerant circuit having a compressor, a condenser, an expansion valve, and an evaporator, and circulating a refrigerant; a superheat degree acquisition unit that acquires a superheat degree of a discharge refrigerant discharged from the compressor; a control unit that, when a thermo-off command is issued to stop operation of the compressor and the acquired degree of superheat is equal to or lower than a predetermined first threshold value, sets a rotation speed of the compressor to a rotation speed equal to or lower than the rotation speed when the thermo-off command is issued and sets an opening degree of the expansion valve to a predetermined value to continue operation of the compressor; An air conditioner comprising:

2. When the acquired degree of superheat is equal to or less than the first threshold value, the control unit sets the rotation speed of the compressor to a minimum rotation speed predetermined for the compressor and sets the opening degree of the expansion valve to a minimum opening degree predetermined for the expansion valve.

2. The air conditioner according to claim 1 .

3. The time for which the compressor is to continue operating is predetermined within a predetermined range.

2. The air conditioner according to claim 1 .

4. When the thermo-off command is issued, if the acquired superheat degree is lower than the first threshold value and is equal to or higher than a second threshold value that is lower than the first threshold value and is set in advance, the control unit continues the operation of the compressor for a minimum time within the predetermined range.

4. The air conditioner according to claim 3.

5. The control unit stops the operation of the compressor when the acquired superheat degree is equal to or greater than the second threshold value when the operation of the compressor is continued for the shortest time.

5. The air conditioner according to claim 4.

6. When the thermo-off command is issued, if the acquired superheat degree is lower than the first threshold and is less than a predetermined second threshold, the control unit stops the operation of the compressor when the acquired superheat degree becomes equal to or higher than the second threshold while the compressor is continuing to operate.

6. An air conditioner according to claim 1, wherein the first and second electrodes are arranged in a first direction.

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