Air conditioner

Abstract

To suppress an overheat state of a refrigerant during heating operation.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 outdoor air temperature acquiring unit for acquiring an outdoor air temperature; a discharge temperature acquiring unit for acquiring a discharge temperature of the refrigerant discharged from the compressor; a compression ratio acquiring unit for acquiring a compression ratio of the refrigerant in the compressor; and a control unit. The control unit executes discharge temperature control for controlling an opening of the expansion valve so that the acquired discharge temperature is restricted to a first threshold or lower under a first condition that the acquired compression ratio is equal to or higher than a prescribed value when the operation is performed by circulating the refrigerant at the acquired outdoor air temperature equal to or lower than a prescribed low outdoor air temperature.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In an air conditioner, when operating in heating mode under low outdoor air temperatures such as -15°C or below, the density of the refrigerant (gas-liquid mixed refrigerant) sucked into the compressor decreases, and the expansion valve opening during heating mode tends to become smaller, so that the amount of liquid refrigerant present in the condenser tends to be excessive, and the amount of refrigerant present in the evaporator decreases. If a large amount of liquid refrigerant exists in the condenser in this way, some of it will remain, and the amount of refrigerant flowing through the refrigeration cycle during heating mode will decrease.

[0003] For this reason, during heating operation under low outdoor temperature conditions, the relationship between the distribution rates of the refrigerant in the condenser and the evaporator changes, and the amount of refrigerant in the condenser tends to increase and the amount of refrigerant in the evaporator tends to decrease, which reduces the amount of refrigerant drawn into the compressor and makes the refrigerant more likely to overheat. When the compressor draws in a refrigerant with low density and advanced overheating, the cooling effect of the refrigerant on the sliding parts and oil (refrigeration oil) decreases, and the oil temperature rises. The increase in oil temperature causes changes in the oil characteristics due to a decrease in sealing performance caused by a decrease in oil viscosity, changes in characteristics due to tribochemical reactions caused by the high temperature of the sliding surfaces of the compressor, and the consumption of additives, which can hinder the normal operation of the compressor.

[0004] A known conventional technique for preventing such an overheating of the refrigerant involves setting a target discharge temperature based on the evaporation temperature and condensation temperature of the refrigerant and the length of the connecting piping of the refrigeration cycle device, and controlling the discharge temperature from the compressor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-294295 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in low outdoor air temperature conditions, the superheated state of the suctioned refrigerant is greatly affected by the amount of refrigerant distributed in the condenser and evaporator and the compression ratio. Therefore, it may be difficult to prevent the suctioned refrigerant from being overheated by the conventional method of limiting the discharge temperature using the connecting pipe length as an index.

[0007] The present disclosure proposes a technique that can prevent the refrigerant from overheating during heating operation under low outside air temperature conditions. [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 circulating a refrigerant, an outdoor air temperature acquisition unit acquiring an outdoor air temperature, a discharge temperature acquisition unit acquiring a discharge temperature of the refrigerant discharged from the compressor, a compression ratio acquisition unit acquiring a compression ratio of the refrigerant in the compressor, and a control unit. When the acquired outdoor air temperature is equal to or lower than a predetermined low outdoor air temperature and the air conditioner is operating by circulating the refrigerant, the control unit performs discharge temperature control that controls the opening degree of the expansion valve so as to limit the acquired discharge temperature to a first threshold value or lower under a first condition where the acquired compression ratio is equal to or higher than a predetermined value. Effect of the Invention

[0009] According to the present disclosure, it is possible to prevent the refrigerant from becoming overheated during heating operation. [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 the limit of the discharge temperature of the refrigerant. [Diagram 5] FIG. 5 is an explanatory diagram for explaining the limit of the discharge temperature of the refrigerant. [Figure 6] FIG. 6 is a block diagram showing a first modified example of the functional configuration of the outdoor unit control circuit. [Figure 7] FIG. 7 is a block diagram showing a second modified example of the functional configuration of the outdoor unit control circuit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the air conditioner of the present disclosure will be described with reference to the drawings. Components having the same functions in the embodiments are 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 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 a discharge pressure, which is the pressure of the refrigerant discharged from the compressor 21, a suction pressure sensor 32 that detects a suction pressure, which is the pressure of the refrigerant sucked into the compressor 21, a discharge temperature sensor 33 that detects the discharge temperature of the refrigerant discharged from the compressor 21, and a suction temperature sensor 34 that detects the temperature of the refrigerant sucked into 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 equipment box (not shown) of the outdoor unit 2. In this embodiment, the outdoor unit control circuit 200 includes a CPU 210, a storage unit 220, a communication unit 230, a sensor input unit 240, and an outdoor air temperature acquisition unit 250, but these do not necessarily have to be included in the outdoor unit control circuit 200. This outdoor unit control circuit 200 is an example of a control unit. In this specification, the outdoor unit control circuit 200 may simply be 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 for 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 setting information in advance, 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, and a rotation speed-circulation amount table that determines the correspondence between the rotation speed of the compressor 21 and the circulation amount of the refrigerant flowing through the refrigerant circuit 100 per unit time.

[0026] The communication unit 230 is an interface that communicates with the indoor unit 5. The sensor input unit 240 receives detection results from various sensors of the outdoor unit 2 and outputs them to the CPU 210.

[0027] The outdoor air temperature acquisition unit 250 acquires the outdoor air temperature based on the detection result by the outdoor air temperature sensor 36 of the outdoor unit 2 .

[0028] The discharge temperature acquisition unit 251 acquires the discharge temperature of the refrigerant discharged from the compressor 21 based on the detection result of the discharge temperature sensor 33 of the outdoor unit 2.

[0029] The compression ratio acquisition unit 252 acquires the compression ratio of the refrigerant in the compressor 21 based on the suction pressure measured by the suction pressure sensor 32 and the discharge pressure measured by the discharge pressure sensor 31. The compression ratio is equal to a value obtained by dividing the discharge pressure by the suction pressure or the absolute pressure.

[0030] The compression ratio acquisition unit 252 may acquire the compression ratio after converting the detected temperature of the refrigerant measured by the outdoor heat exchanger temperature sensor 35, the indoor heat exchanger temperature (two-phase refrigerant temperature) sensor 61, etc. into a suction pressure and a discharge pressure. Specifically, the compression ratio acquisition unit 252 converts the detected temperature (evaporation temperature) by the outdoor heat exchanger temperature sensor 35 of the outdoor heat exchanger 23 into a pressure (low pressure). The compression ratio acquisition unit 252 also converts the detected temperature (condensation temperature) by the indoor heat exchanger temperature sensor 61 of the indoor heat exchanger 51 into a pressure (high pressure). Next, the compression ratio acquisition unit 252 acquires the compression ratio of the refrigerant in the compressor 21 based on the low pressure and the high pressure converted from the detected temperature of the refrigerant.

[0031] The refrigerant circulation amount acquisition unit 253 acquires the circulation amount of the refrigerant flowing through the refrigerant circuit 100 per unit time. Specifically, the refrigerant circulation amount acquisition unit 253 refers to a rotation speed-circulation amount table included in the setting information of the storage unit 220, and calculates the circulation amount of the refrigerant (volume amount per unit time (cc / s)) based on the current rotation speed of the compressor 21. When calculating such a circulation amount, calibration may be performed based on the temperature of the refrigerant (discharge temperature, intake temperature) measured by the discharge temperature sensor 33 and the intake temperature sensor 34. For example, under low outside air temperature conditions such as -15°C or lower, the density change of the refrigerant with respect to temperature becomes small. Therefore, under low outside air temperature conditions, priority is given to the simplicity of control described later, and the circulation amount to be acquired may be the volume amount. Also, the refrigerant circulation amount acquisition unit 253 may directly acquire the circulation amount of the refrigerant flowing through the refrigerant circuit 100 per unit time (mass per unit time (mg / s)) by a mass flow meter installed on the refrigerant circuit 100. Alternatively, if a low-pressure sensor or an intake temperature sensor is installed or a method for calculating the amount of pressure loss on the low-pressure side is included in the control program, the density of the refrigerant sucked into the compressor can be known, and the mass flow rate can be calculated from that.

[0032] The condensation temperature acquisition unit 254 acquires the condensation temperature of the refrigerant in the condenser (the indoor heat exchanger 51 during heating operation). Specifically, the condensation temperature acquisition unit 254 acquires the temperature of the indoor heat exchanger 51 detected by the indoor heat exchanger temperature sensor 61 and notified by the indoor unit 5 during heating operation, that is, the condensation temperature of the refrigerant.

[0033] 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 control signals and the like transmitted from the indoor unit 5 via the communication unit 230. The CPU 210 controls the drive of the compressor 21 and the outdoor fan 27 based on the taken-in detection results and control signals. Furthermore, the CPU 210 controls the switching 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.

[0034] 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.

[0035] 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.

[0036] 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).

[0037] In addition to the above-mentioned configuration, various sensors are provided in the indoor unit 5. An indoor temperature sensor 63 is provided near the intake port (not shown) of the indoor unit 5 to detect the temperature of the indoor air flowing into the indoor unit 5, i.e., the intake temperature. An outlet temperature sensor 64 is provided near the outlet port (not shown) of the indoor unit 5 to detect the temperature of the air that exchanges heat with the refrigerant in the indoor heat exchanger 51 and is released into the room from the indoor unit 5, i.e., the outlet temperature. The indoor heat exchanger 51 is provided with an indoor heat exchanger temperature sensor 61 that detects the temperature of the indoor heat exchanger 51.

[0038] 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.

[0039] [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 executes either heating operation or cooling operation based on the input operating conditions and the indoor temperature. When executing / ending heating operation or cooling operation, the indoor unit control circuit 500 transmits the operating conditions (heating operation / cooling operation and the required capacity during operation) and the detection results detected by various sensors in the indoor unit 5 (indoor temperature, temperature (condensing temperature) of the indoor heat exchanger 51, etc.) to the outdoor unit control circuit 200.

[0040] The outdoor unit control circuit 200 switches the four-way valve 22 based on the operating conditions (heating operation / cooling operation) transmitted from the indoor unit 5. The outdoor unit control circuit 200 also drives the compressor 21 at a rotation speed according to the required capacity, referring to a rotation speed table included in the setting information of the storage unit 220. The outdoor unit control circuit 200 also controls the opening degree of the expansion valve 24 so that the refrigerant temperature becomes the target discharge temperature corresponding to the indoor temperature transmitted from the indoor unit 5. For example, when the discharge temperature measured by the discharge temperature sensor 33 is higher than the target discharge temperature, the outdoor unit control circuit 200 reduces the opening degree of the expansion valve 24. When the discharge temperature measured by the discharge temperature sensor 33 is lower than the target discharge temperature, the outdoor unit control circuit 200 also increases the opening degree of the expansion valve 24.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] [Control method during heating operation] Here, a detailed description will be given of a control method of the outdoor unit control circuit 200 during heating operation. When the outdoor unit control circuit 200 is operating by circulating the refrigerant at an outdoor air temperature acquired by the outdoor air temperature acquisition unit 250 that is equal to or lower than a predetermined low outdoor air temperature, the outdoor unit control circuit 200 determines whether or not a first condition is satisfied, that is, the compression ratio acquired by the compression ratio acquisition unit 252 is equal to or higher than a predetermined value.

[0050] The predetermined low outdoor temperature is preset in the setting information of the storage unit 220 according to the type of refrigerant as the outdoor temperature at which the relationship between the distribution ratio of the refrigerant present in the condenser and the evaporator during heating operation tends to increase the amount of refrigerant in the condenser and decrease the amount of refrigerant in the evaporator. Specifically, for example, when the refrigerant is R32, the temperature is set to minus 15 degrees or lower, or to a temperature at which the saturated gas density of the refrigerant is 60% or lower compared to when it is 0°C.

[0051] Regarding the value of the compression ratio related to the first condition, a predetermined value (e.g., compression ratio ≧10) for detecting high compression ratio operation in which the difference between the high pressure and the low pressure becomes large when the compressor 21 is operating is preset in the setting information of the memory unit 220.

[0052] When the first condition is satisfied, the outdoor unit control circuit 200 performs discharge temperature control to control the opening degree of the expansion valve 24 so as to limit the discharge temperature acquired by the discharge temperature acquisition unit 251 to a first threshold value or less (first discharge temperature limit).

[0053] Regarding the first threshold value, for example, an upper limit temperature (e.g., 80°C) is preset in the setting information of the memory unit 220 to limit the refrigerant drawn into the compressor from becoming overheated, thereby preventing a change in the characteristics of the refrigeration oil 10 from occurring due to a reduction in the cooling effect of the refrigerant around the sliding parts.

[0054] By this discharge temperature control, in the air conditioner 1, during heating operation at low outdoor temperatures, it is possible to prevent overheating of the refrigerant drawn into the compressor, and to make it difficult for changes in the characteristics of the refrigerating machine oil 10 to occur.

[0055] In addition, when the outdoor unit control circuit 200 is operating by circulating the refrigerant at the outdoor air temperature acquired by the outdoor air temperature acquisition unit 250, which is the above-mentioned predetermined low outdoor air temperature, the outdoor unit control circuit 200 determines whether or not a second condition based on the circulation amount acquired by the refrigerant circulation amount acquisition unit 253 is satisfied.

[0056] Regarding the circulation amount for the second condition, a value for detecting a state in which a portion of the liquid refrigerant remains in the condenser, and the amount of refrigerant distributed in the condenser becomes uneven, changing the refrigerant distribution ratio in the condenser and the evaporator, and reducing the amount of refrigerant flowing through the refrigeration cycle, is preset in the setting information of memory unit 220 through experiments, etc.

[0057] When the second condition is satisfied, the outdoor unit control circuit 200 performs discharge temperature control to control the opening degree of the expansion valve 24 so as to limit the discharge temperature acquired by the discharge temperature acquisition unit 251 to a second threshold value or less (second discharge temperature limit).

[0058] Regarding the second threshold, for example, the setting content of "discharge temperature≦high-pressure converted temperature (two-phase refrigerant temperature in the condenser)+A° C." is preset in the setting information of the storage unit 220.

[0059] The high-pressure converted temperature (two-phase refrigerant temperature in the condenser) corresponds to the condensation temperature of the refrigerant in the condenser (indoor heat exchanger 51 during heating operation). That is, the outdoor unit control circuit 200 sets the second threshold value (high-pressure converted temperature (two-phase refrigerant temperature in the condenser) + A°C) based on the condensation temperature of the refrigerant acquired by the condensation temperature acquisition unit 254.

[0060] By this discharge temperature control, in the air conditioner 1, it is possible to make it difficult for the characteristics of the refrigerating machine oil 10 to change during heating operation at low outdoor temperatures.

[0061] Here, A°C may be a fixed value, but may also be set (adjusted) to an optimal value based on at least one of the refrigerant circulation volume and the outdoor air temperature. Specifically, the outdoor unit control circuit 200 sets the value of A based on at least one of the values ​​of the outdoor air temperature acquired by the outdoor air temperature acquisition unit 250 and the circulation volume acquired by the refrigerant circulation volume acquisition unit 253 (details will be described later). This allows the air conditioner 1 to control the discharge temperature in accordance with the refrigerant circulation volume or the outdoor air temperature.

[0062] Next, an example of the above control method 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. Fig. 4 and Fig. 5 are explanatory diagrams for explaining limitations on the discharge temperature of the refrigerant.

[0063] 3, when processing (heating operation) is started, the outdoor unit control circuit 200 acquires the outdoor air temperature from the outdoor air temperature acquisition unit 250 and the refrigerant circulation amount from the refrigerant circulation amount acquisition unit 253. Next, the outdoor unit control circuit 200 acquires the outdoor air temperature range (lower than a predetermined low outdoor air temperature) and the value of the refrigerant circulation amount (circulation amount related to the second condition) used for judgment from the setting information in the storage unit 220. Next, the outdoor unit control circuit 200 judges whether the acquired outdoor air temperature is within a predetermined outdoor air temperature range and whether the acquired circulation amount is within the predetermined refrigerant circulation amount range of the second condition (S1).

[0064] If the determination in S1 is positive (Yes), the outdoor unit control circuit 200 acquires the compression ratio from the compression ratio acquisition unit 252. Next, the outdoor unit control circuit 200 acquires the value of the compression ratio related to the first condition (predetermined compression ratio) from the setting information in the storage unit 220. Next, the outdoor unit control circuit 200 determines whether or not the acquired compression ratio is an operation exceeding the predetermined compression ratio (S2).

[0065] If the determination in S2 is positive (Yes), the outdoor unit control circuit 200 acquires the first threshold value and the second threshold value from the setting information in the storage unit 220.

[0066] Here, the outdoor unit control circuit 200 calculates the second threshold value as "discharge temperature≦high-pressure converted temperature (two-phase refrigerant temperature in the condenser)+A° C." based on the condensation temperature of the refrigerant acquired by the condensation temperature acquisition unit 254. In addition, the outdoor unit control circuit 200 sets the value of A to an optimal value for limiting the discharge temperature based on the outdoor air temperature acquired by the outdoor air temperature acquisition unit 250 and the circulation amount acquired by the refrigerant circulation amount acquisition unit 253.

[0067] As an example, as shown in FIG. 4, the outdoor unit control circuit 200 sets THP (high pressure equivalent temperature)+55° C. or THP+45° C. based on the values ​​of the outdoor air temperature (horizontal axis) and the circulation amount (vertical axis).

[0068] Next, the outdoor unit control circuit 200 performs operation with the discharge temperature limit set to the lower of the first and second threshold values ​​(first and second discharge temperature limits) as the target discharge temperature (S4).

[0069] The vertical axis in FIG. 4 indicates the amount of refrigerant circulating. In this embodiment, the volumetric flow rate [CC / S] is used as an example. For example, when heating operation is started, the compressor rotation speed increases and the amount of refrigerant circulating increases. In this case, the amount of refrigerant circulating on the left vertical axis is used as a parameter. Also, when the heating capacity is reduced, that is, when the compressor rotation speed decreases, the amount of refrigerant circulating also decreases. In this case, the amount of refrigerant circulating on the right vertical axis is used as a parameter.

[0070] As an example, when the refrigerant circulation amount increases, for example, when the outside air temperature is −22° C. and the refrigerant circulation amount is 900 [CC / S], the second threshold (second discharge temperature limit) is THP+55° C.=85° C., and the first threshold (first discharge temperature limit) 80° C. is lower than the second threshold (second discharge temperature limit). In this case, as shown in FIG. 5, the outdoor unit control circuit 200 operates with the refrigerant discharge temperature limited to the first threshold of 80° C. when the compression ratio is ≧10. In contrast, for example, when the outside air temperature is similarly −22° C. and the refrigerant circulation amount is 800 [CC / S], the second threshold (second discharge temperature limit) is THP+45° C.=75° C., and when the second threshold is lower than the first threshold, the outdoor unit control circuit 200 operates with the refrigerant discharge temperature limited to the second threshold of 75° C. even when the compression ratio is ≧10.

[0071] If the determination in S2 is negative (No), the outdoor unit control circuit 200 acquires a second threshold value (second discharge temperature limit), and performs operation with the discharge temperature limit set to the second threshold value as the target discharge temperature (S3).

[0072] If the determination in S1 is negative (No), the outdoor unit control circuit 200 acquires the compression ratio from the compression ratio acquisition unit 252. Next, the outdoor unit control circuit 200 acquires the value of the compression ratio related to the first condition (predetermined compression ratio) from the setting information in the storage unit 220. Next, the outdoor unit control circuit 200 determines whether or not the acquired compression ratio is greater than the predetermined compression ratio (S5).

[0073] If the determination in S5 is positive (Yes), the outdoor unit control circuit 200 acquires a first threshold value (first discharge temperature limit) from the setting information in the memory unit 220. Next, the outdoor unit control circuit 200 performs operation with the discharge temperature limit set to the first threshold value as the target discharge temperature (S6). If the determination in S5 is negative (No), the outdoor unit control circuit 200 leaves the target discharge temperature unchanged and returns the process to S1.

[0074] Following S4, S3, and S6, the outdoor unit control circuit 200 determines whether or not the operation has ended based on whether or not an instruction to end the heating operation has been notified from the indoor unit 5 (S7). If the operation has not ended (S7: No), the outdoor unit control circuit 200 returns the process to S1. If the operation has ended (S7: Yes), the outdoor unit control circuit 200 stops the operation of the compressor 21 and ends the process.

[0075] [Variations] In the above-described embodiment, a configuration example has been described in which the discharge temperature is limited by a first threshold (first discharge temperature limit) when the first condition (compression ratio) is satisfied, and the discharge temperature is limited by a second threshold (second discharge temperature limit) when the second condition (refrigerant amount) is satisfied. In contrast, in Modifications 1 and 2, configuration examples will be described in which the discharge temperature control is performed by a first or second threshold (first or second discharge temperature limit) when the first or second condition is satisfied.

[0076] 6 is a block diagram showing a first modified example of the functional configuration of the outdoor unit control circuit. The outdoor unit control circuit 200A of the first modified example differs from the outdoor unit control circuit 200 described above in that it does not have a refrigerant circulation amount acquisition unit 253. The condensation temperature acquisition unit 254 is provided in the configuration of a general air conditioner 1, but may not be required in the control of the first modified example.

[0077] In the outdoor unit control circuit 200A, when the outdoor air temperature acquired by the outdoor air temperature acquisition unit 250 is below a predetermined low outdoor air temperature and the refrigerant is circulated during operation, the outdoor unit control circuit 200A determines whether or not a first condition is satisfied, that is, the compression ratio acquired by the compression ratio acquisition unit 252 is equal to or greater than a predetermined value. If the first condition is satisfied, the outdoor unit control circuit 200A performs discharge temperature control to control the opening degree of the expansion valve 24 so as to limit the discharge temperature acquired by the discharge temperature acquisition unit 251 to a first threshold value or less (first discharge temperature limit). In this way, the outdoor unit control circuit 200A may determine only whether or not the first condition is satisfied, and perform the first discharge temperature control if the condition is satisfied.

[0078] 7 is a block diagram showing a functional configuration of an outdoor unit control circuit according to Modification 2. An outdoor unit control circuit 200B according to Modification 2 differs from the outdoor unit control circuit 200 described above in that it does not have a compression ratio acquisition unit 252.

[0079] In the outdoor unit control circuit 200B, when the outdoor air temperature acquired by the outdoor air temperature acquisition unit 250 is below a predetermined low outdoor air temperature and the refrigerant is circulated during operation, the outdoor unit control circuit 200B determines whether or not a second condition is satisfied, in which the circulating amount acquired by the refrigerant circulation amount acquisition unit 253 is equal to or greater than a predetermined value. If the second condition is satisfied, the outdoor unit control circuit 200B performs discharge temperature control to control the opening degree of the expansion valve 24 so as to limit the discharge temperature acquired by the discharge temperature acquisition unit 251 to a second threshold value or less (second discharge temperature limit). In this way, the outdoor unit control circuit 200B may determine only whether or not the second condition is satisfied, and perform the second discharge temperature control if the condition is satisfied.

[0080] As described above, the air conditioner 1 in the first modification has the refrigerant circuit 100, the outdoor air temperature acquisition unit 250, the discharge temperature acquisition unit 251, the compression ratio acquisition unit 252, and the outdoor unit control circuit 200 including them. The refrigerant circuit 100 has the compressor 21, the condenser (indoor heat exchanger 51), the expansion valve 24, and the evaporator (outdoor heat exchanger 23), and circulates the refrigerant. The outdoor air temperature acquisition unit 250 acquires the outdoor air temperature. The discharge temperature acquisition unit 251 acquires the discharge temperature of the refrigerant discharged from the compressor 21. The compression ratio acquisition unit 252 acquires the compression ratio of the refrigerant in the compressor 21. When the outdoor unit control circuit 200 is operating by circulating the refrigerant when the acquired outdoor air temperature is equal to or lower than a predetermined low outdoor air temperature, the outdoor unit control circuit 200 performs discharge temperature control to control the opening degree of the expansion valve 24 so as to limit the acquired discharge temperature to a first threshold value or lower under a first condition where the acquired compression ratio is equal to or higher than a predetermined value.

[0081] This makes it possible to prevent the refrigerant from overheating during heating operation when the air conditioner 1 is operating by circulating the refrigerant when the outdoor temperature is equal to or lower than a predetermined low outdoor temperature. Also, by preventing the refrigerant from overheating in this way, it is possible to prevent changes in oil characteristics that could lead to a breakdown in the compressor 21, such as a decrease in oil viscosity due to an increase in the temperature of the refrigeration oil 10.

[0082] The air conditioner 1 in the embodiment of the present invention has a refrigerant circuit 100, an outdoor air temperature acquisition unit 250, a discharge temperature acquisition unit 251, a refrigerant circulation amount acquisition unit 253, and an outdoor unit control circuit 200. The refrigerant circulation amount acquisition unit 253 acquires the amount of refrigerant circulating per unit time flowing through the refrigerant circuit 100. When the acquired outdoor air temperature is equal to or lower than a predetermined low outdoor air temperature and the outdoor unit control circuit 200 is operating by circulating the refrigerant, the outdoor unit control circuit 200 performs discharge temperature control that controls the opening degree of the expansion valve 24 so as to limit the acquired discharge temperature to a second threshold value or less under a second condition where the acquired circulation amount is equal to or lower than a predetermined value.

[0083] As a result, when the air conditioner 1 is operating by circulating the refrigerant when the outdoor air temperature is below a predetermined low outdoor air temperature, even if the amount of refrigerant circulating decreases and the refrigerant is prone to overheating, the discharge temperature can be limited to below the second threshold value to prevent the refrigerant from overheating.

[0084] In addition, in variant example 2, when the outdoor unit control circuit 200 is operating by circulating refrigerant when the acquired outdoor air temperature is below a predetermined low outdoor air temperature, under a first condition in which the acquired compression ratio is equal to or higher than a predetermined value, it performs discharge temperature control to control the opening of the expansion valve 24 so as to limit the acquired discharge temperature to a first threshold value or less, and under a situation in which both the first and second conditions exist, it performs discharge temperature control to limit the discharge temperature to the lower of the first and second threshold values.

[0085] As a result, when both the first and second conditions are met, the air conditioner 1 limits the discharge temperature to below the lower of the first and second thresholds, allowing for control that is more tailored to the situation and reliably preventing the refrigerant from overheating.

[0086] Moreover, the air conditioner 1 further includes a condensation temperature acquisition unit 254 that acquires the condensation temperature of the refrigerant in the condenser. The outdoor unit control circuit 200 sets a second threshold value based on the acquired condensation temperature.

[0087] As a result, the air conditioner 1 limits the discharge temperature to below the second threshold value corresponding to the condensation temperature of the refrigerant, thereby enabling the prevention of overheating of the refrigerant to be appropriately performed in accordance with the state of the condensation temperature of the refrigerant. [Explanation of symbols]

[0088] 1. Air conditioner 2…Outdoor unit 5…Indoor unit 8...Liquid pipe 9…Gas pipe 10...refrigeration 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 32...Suction pressure sensor 33...Discharge temperature sensor 34…Intake 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 64...Air outlet temperature sensor 71…Indoor unit liquid pipe 72…Indoor unit gas pipe 100...Refrigerant circuit 200, 200A, 200B...Outdoor unit control circuit 210…CPU 220...Storage section 230…Communications Department 240…Sensor input section 250…Outside temperature acquisition section 251...Discharge temperature acquisition section 252…Compression ratio acquisition section 253…Refrigerant circulation amount acquisition unit 254…Condensation temperature acquisition unit 500…Indoor unit control circuit a~d…Port

Claims

1. a refrigerant circuit having a compressor, a condenser, an expansion valve, and an evaporator, and circulating a refrigerant; an outside air temperature acquisition unit that acquires an outside air temperature; a discharge temperature acquisition unit that acquires a discharge temperature of the refrigerant discharged from the compressor; a compression ratio acquisition unit that acquires a compression ratio of a refrigerant in the compressor; A control unit, The control unit performs discharge temperature control to limit the acquired discharge temperature to a first threshold value or less under a first condition where the acquired compression ratio is a predetermined value or more when the acquired outside air temperature is a predetermined low outside air temperature or less and the refrigerant is circulated and the operation is performed. An air conditioner characterized by the above.

2. The low outside air temperature is a temperature below minus 15 degrees Celsius or a temperature at which the saturated gas density of the refrigerant is 60% or less of that at 0° C.

2. The air conditioner according to claim 1 .

3. a refrigerant circuit having a compressor, a condenser, an expansion valve, and an evaporator, and circulating a refrigerant; an outside air temperature acquisition unit that acquires an outside air temperature; a discharge temperature acquisition unit that acquires a discharge temperature of the refrigerant discharged from the compressor; a refrigerant circulation amount acquisition unit that acquires a circulation amount per unit time of the refrigerant flowing through the refrigerant circuit; a control unit that performs discharge temperature control to limit the acquired discharge temperature to a second threshold value or less under a second condition based on the acquired circulation amount when the acquired outside air temperature is equal to or lower than a predetermined low outside air temperature and the refrigerant is circulated during operation; An air conditioner comprising:

4. A compression ratio acquisition unit that acquires a compression ratio of the refrigerant in the compressor, The control unit performs discharge temperature control to limit the acquired discharge temperature to a first threshold value or less under a first condition where the acquired compression ratio is a predetermined threshold value or more when the acquired outside air temperature is equal to or less than a predetermined low outside air temperature and the refrigerant is circulated during operation, and performs discharge temperature control to limit the discharge temperature to a lower threshold value of the first threshold value and the second threshold value or less under a situation where the first condition and the second condition are both satisfied.

4. The air conditioner according to claim 3.

5. a condensation temperature acquisition unit that acquires a condensation temperature of the refrigerant in the condenser, The control unit sets the second threshold value based on the acquired condensation temperature.

5. The air conditioner according to claim 3 or 4.

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