JP2020176732A - Air conditioner - Google Patents

Abstract

To provide an air conditioner capable of avoiding frost formation on an outdoor heat exchanger.SOLUTION: A control device (40) which an air conditioner (1) includes executes frost formation avoiding operation control processing for controlling valve devices (51, 52) so that the lower a refrigerant temperature (Tdef) is, the larger the flow rate of a refrigerant flowing in a bypass pipe (38) becomes, in the case where a state continues for predetermined time in which the refrigerant temperature (Tdef) detected by refrigerant temperature sensors (61, 62) during a heating operation is below a frost formation avoiding reference temperature (T0) that is determined in advance as an upper limit value of the temperature at which frost formation to an outdoor heat exchanger (13) is expected.SELECTED DRAWING: Figure 2

Description

The present invention relates to an air conditioner.

The outdoor heat exchanger provided in the air conditioner is configured so that the outside air can exchange heat with the refrigerant flowing inside the air conditioner. Further, when the air conditioner is performing the heating operation, the refrigerant flowing through the outdoor heat exchanger evaporates by removing heat from the outside air. That is, the outdoor heat exchanger functions as an evaporator during the heating operation. In order for the refrigerant to take heat from the outside air in the outdoor heat exchanger, the temperature of the refrigerant flowing through the outdoor heat exchanger must be set lower than the outside air temperature. Therefore, in some cases, the refrigerant temperature is set to less than 0 ° C. When the refrigerant temperature becomes less than 0 ° C., frost is formed on the outdoor heat exchanger. When frost is formed on the outdoor heat exchanger, the ventilation area of the outside air passing through the outdoor heat exchanger becomes small, so that the heat exchange efficiency decreases. Therefore, when the outdoor heat exchanger is frosted, the defrosting operation is performed to melt the frost that has formed on the outdoor heat exchanger.

The general defrosting operation is performed by switching the operating state from the heating operation state to the cooling operation state. As a result, the discharge port of the compressor and the outdoor heat exchanger are connected via a four-way valve. Therefore, a high-temperature and high-pressure gas refrigerant flows into the outdoor heat exchanger from the compressor, the refrigerant is condensed in the outdoor heat exchanger, and heat of condensation is generated to defrost (see, for example, Patent Document 1). Further, a defrosting operation has also been proposed in which a part of the gas refrigerant discharged from the compressor is directly flowed into the outdoor heat exchanger while the operating state is maintained in the heating operation state during the defrosting operation (for example, Patent Document 2). reference)

Japanese Unexamined Patent Publication No. 07-174441 International Publication No. 2016/170680

(Problems to be solved by the invention)
According to the defrosting method described in Patent Documents 1 and 2, the outdoor heat exchanger is defrosted by using all or a part of the gas refrigerant discharged from the compressor, so that the amount of refrigerant that can be used for air conditioning is increased. Decrease. Therefore, the heating efficiency during the defrosting operation is lowered. In addition, it takes a long time to melt a large amount of frost adhering to the outdoor heat exchanger. Therefore, the defrosting operation should not be carried out as much as possible.

In order to avoid the defrosting operation, it is necessary to take measures to avoid frost formation on the outdoor heat exchanger, but conventionally, no measures have been taken to avoid frost formation on the outdoor heat exchanger. Therefore, an object of the present invention is to provide an air conditioner capable of avoiding frost formation on an outdoor heat exchanger.

The present invention includes a compressor (11) including an inlet (11a) and an outlet (11b), a first port (12a), a second port (12b), a third port (12c), and a fourth port ( It has 12d), the first port is connected to the discharge port of the compressor via the first pipe (31), the first port and the second port communicate with each other during the heating operation, and the third port and the fourth port A four-way valve (12) and four-way valve (12) configured so that the communication state of each port can be switched so that the first port and the third port communicate with each other and the second port and the fourth port communicate with each other during the communication and cooling operation. An indoor heat exchanger (17) connected to the second port of the valve via the second pipe (32), and an intermediate pipe (13) connected to the third port of the four-way valve via the third pipe (33). An outdoor heat exchanger (13) connected to the indoor heat exchanger via 34) and an accumulator outlet pipe (36) connected to the fourth port of the four-way valve via an accumulator inlet pipe (35). The accumulator (15) connected to the suction port of the compressor via the bypass pipe (38) connecting the first pipe and the accumulator inlet pipe, and the flow rate of the refrigerant flowing through the bypass pipe intervening in the bypass pipe. A control device including an adjustable valve device (51, 52), a control device (40) for controlling the valve device, and a refrigerant temperature sensor (61, 62) for detecting the temperature of the refrigerant flowing through the outdoor heat exchanger. Is defined as a state in which the refrigerant temperature detected by the refrigerant temperature sensor during the heating operation is less than the frosting avoidance reference temperature (T0), which is predetermined as the upper limit of the temperature at which frost is predicted to frost on the outdoor heat exchanger. Air configured to perform frost avoidance operation control processing that controls the valve device so that the lower the refrigerant temperature detected by the refrigerant temperature sensor, the greater the flow rate of the refrigerant flowing through the bypass pipe when the time continues. The harmonizer (1) is provided.

According to the present invention, the frost formation avoidance operation is carried out by executing the frost formation avoidance operation control process. In this frost formation avoidance operation, a part of the high temperature and high pressure gas refrigerant discharged from the discharge port of the compressor is sucked into the suction port of the compressor through the bypass pipe. Therefore, the temperature of the refrigerant sucked from the suction port of the compressor rises, which raises the temperature of the refrigerant flowing in the refrigerant circuit. Therefore, the temperature of the refrigerant passing through the outdoor heat exchanger also rises. As a result, frost formation on the outdoor heat exchanger can be avoided, or frost can be quickly removed when the outdoor heat exchanger is slightly frosted.

In addition, in the frosting avoidance operation control process, the temperature of the refrigerant flowing through the outdoor heat exchanger detected by the refrigerant temperature sensor is the frost on the outdoor heat exchanger, not when the outdoor heat exchanger is actually frosted. It is executed when the state of being lower than the frost formation avoidance reference temperature predetermined as the upper limit of the temperature predicted in the future continues for a predetermined time. Therefore, at the start of the frost formation avoidance operation, it is considered that the outdoor heat exchanger is not yet frosted or the outdoor heat exchanger is slightly frosted. In other words, the frost formation avoidance operation is not a defrosting operation that removes a large amount of frost that has already adhered to the outdoor heat exchanger, but the refrigerant is in a state where the outdoor heat exchanger is not frosted or slightly frosted. It is an operation to raise the temperature. Therefore, the refrigerant temperature is likely to be raised as compared with the defrosting operation performed when the outdoor heat exchanger to which frost is attached is defrosted, and therefore the operation is completed in a short time. Therefore, comfort during heating operation can be ensured.

Further, in the frost formation avoidance operation control process, the valve device interposed in the bypass pipe is controlled so that the lower the temperature of the refrigerant flowing through the outdoor heat exchanger, the larger the flow rate of the refrigerant flowing through the bypass pipe. Therefore, the amount of refrigerant used to avoid frost formation in the outdoor heat exchanger can be minimized. Therefore, frost formation on the outdoor heat exchanger can be avoided without significantly reducing the heating efficiency.

The frost avoidance operation control process is performed when the refrigerant temperature detected by the refrigerant temperature sensor is equal to or higher than the frost avoidance end temperature (Ts), which is predetermined as the temperature at which it can be determined that the outdoor heat exchanger does not frost. It is preferable to end the process when (S42: Yes) or when the execution time of the frost formation avoidance operation control process has elapsed a predetermined set time (τ2th) (S41: Yes). According to this, the comfort of air conditioning can be ensured by promptly ending the frost avoidance operation and shifting to the normal heating operation based on the preset refrigerant temperature condition or the preset execution time. ..

In the control device, the outside air temperature (Tout) is lower than the predetermined temperature at which frost formation avoidance unavoidable temperature is determined as the temperature at which frost formation on the outdoor heat exchanger cannot be avoided by executing the frost formation avoidance operation control process. At a certain time (S12: No), it is preferable that the frost formation avoidance operation control process is not executed. When the outside air temperature is extremely low, even if the frost formation avoidance operation control process according to the present invention is executed, the refrigerant temperature becomes less than 0 ° and there is a high possibility that frost will form on the outdoor heat exchanger. Therefore, in such a case, by executing the defrosting operation without executing the frost formation avoidance operation control process, the outdoor heat exchanger can be quickly defrosted as a result.

The valve device may have a flow control valve (52) and an on-off valve (51) connected in parallel to the bypass pipe. In this case, the control device may adjust the flow rate of the refrigerant flowing through the bypass pipe by combining the opening / closing operation of the on-off valve and the adjustment of the opening degree of the flow rate adjusting valve during the execution of the frost formation avoidance operation control process. According to this, the adjustment range of the flow rate of the refrigerant flowing through the bypass pipe can be increased by combining the opening / closing operation of the on-off valve and the adjustment of the opening degree of the flow rate adjusting valve.

FIG. 1 is a diagram showing a schematic configuration of an air conditioner according to the present embodiment. FIG. 2 is a flowchart showing the flow of the frost formation avoidance operation start determination processing routine. FIG. 3 is a flowchart showing the flow of the frost formation avoidance operation control processing routine. FIG. 4 is a diagram showing an example of a flow rate control valve control map. FIG. 5 is a flowchart showing the flow of the frost formation avoidance operation end determination processing routine.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an air conditioner according to the present embodiment. As shown in FIG. 1, the air conditioner 1 includes a compressor 11, a four-way valve 12, an outdoor heat exchanger 13, a sub heat exchanger 14, an accumulator 15, an outdoor electronic expansion valve 16, and an indoor. It includes a heat exchanger 17, an indoor electronic expansion valve 18, an engine 20, a plurality of refrigerant pipes 31 to 38, and a control device 40. The above components excluding the engine 20 and the control device 40 are the first pipe 31, the second pipe 32, the third pipe 33, the intermediate pipe 34, the accumulator inlet pipe 35, the accumulator outlet pipe 36, and the branch pipe 37 as the refrigerant pipe. , Connected by bypass pipe 38. In this way, the refrigerant circuit is configured.

The compressor 11 is connected to the output shaft of the engine 20 and operates by receiving a driving force from the engine 20. The compressor 11 has a suction port 11a and a discharge port 11b. When the compressor 11 operates, the refrigerant gas is sucked from the suction port 11a, the refrigerant gas is internally compressed, and the compressed refrigerant gas is discharged from the discharge port 11b.

The discharge port 11b of the compressor 11 is connected to one end of the first pipe 31. A four-way valve 12 is connected to the other end of the first pipe 31. The four-way valve 12 has a first port 12a, a second port 12b, a third port 12c, and a fourth port 12d. The discharge port 11b of the compressor 11 is connected to the first port 12a of the four-way valve 12 via the first pipe 31. The indoor heat exchanger 17 is connected to the second port 12b of the four-way valve 12 via the second pipe 32. The outdoor heat exchanger 13 is connected to the third port 12c of the four-way valve 12 via the third pipe 33. Further, the outdoor heat exchanger 13 is connected to the indoor heat exchanger 17 via the intermediate pipe 34. The accumulator 15 is connected to the fourth port 12d of the four-way valve 12 via the accumulator inlet pipe 35.

The four-way valve 12 has a heating switching state in which the first port 12a communicates with the second port 12b and the third port 12c communicates with the fourth port 12d, and the first port 12a communicates with the third port 12c. It is configured so that the switching state at the time of cooling in which the second port 12b communicates with the fourth port 12d can be selectively realized.

The outdoor heat exchanger 13 connected to the third port 12c of the four-way valve 12 via the third pipe 33 exchanges heat between the refrigerant flowing inside the outdoor heat exchanger and the outside air. Further, the indoor heat exchanger 17 connected to the second port 12b of the four-way valve 12 via the second pipe 32 exchanges heat between the refrigerant flowing inside the indoor heat exchanger and the indoor air.

Further, the portion of the intermediate pipe 34 connecting the outdoor heat exchanger 13 and the indoor heat exchanger 17 from the position A to the position B is branched into two pipes (pipe L1 and pipe L2). A one-way valve 19 is interposed in the pipe L1, and an outdoor electronic expansion valve 16 is interposed in the pipe L2. During the cooling operation, the refrigerant flows through the pipe L1, and during the heating operation, the refrigerant flows through the pipe L2. The one-way valve 19 allows the flow of refrigerant from position A to position B and blocks the flow of refrigerant from position B to position A. The outdoor electronic expansion valve 16 expands the refrigerant flowing therethrough. The outdoor electronic expansion valve 16 is a flow rate adjusting valve whose opening degree can be adjusted.

The accumulator 15 connected to the fourth port 12d of the four-way valve 12 via the accumulator inlet pipe 35 is further connected to the suction port 11a of the compressor 11 via the accumulator outlet pipe 36. The accumulator 15 introduces a refrigerant from the accumulator inlet pipe 35 side, and gas-liquid separates the introduced refrigerant. The gas refrigerant separated from the liquid refrigerant in the accumulator 15 is sucked into the suction port 11a of the compressor 11 via the accumulator outlet pipe 36.

Further, the accumulator inlet pipe 35 and the intermediate pipe 34 are connected by a branch pipe 37. A sub heat exchanger 14 is interposed in the branch pipe 37. The refrigerant flowing through the branch pipe 37 enters the sub heat exchanger 14, and the sub heat exchanger 14 cools the engine 20 to exchange heat with the heated cooling water. The flow rate of the refrigerant flowing through the branch pipe 37 is adjusted by the branch flow rate adjusting valve 37a interposed in the branch pipe 37.

Further, the first pipe 31 and the accumulator inlet pipe 35 are connected by a bypass pipe 38. The bypass pipe 38 is branched into a first bypass pipe 381 and a second bypass pipe 382 between the position C and the position D in the middle of the bypass pipe 38. Then, an electromagnetic on-off valve 51 is interposed in the middle of the first bypass pipe 381, and a flow rate adjusting valve 52 is interposed in the middle of the second bypass pipe 382. Therefore, the electromagnetic on-off valve 51 and the flow rate adjusting valve 52 are connected in parallel to the bypass pipe 38. The electromagnetic on-off valve 51 and the flow rate adjusting valve 52 correspond to the valve device of the present invention.

The electromagnetic on-off valve 51 can be set to an open state or a closed state, and when the electromagnetic on-off valve 51 is in the open state, the flow of the refrigerant into the first bypass pipe 381 is permitted, and when the electromagnetic on-off valve 51 is in the closed state, the first bypass is allowed. The flow of the refrigerant into the pipe 381 is blocked. The flow rate adjusting valve 52 is configured so that the opening degree can be adjusted and the flow rate of the refrigerant flowing in the second bypass pipe 382 can be adjusted.

The control device 40 mainly comprises a microcomputer composed of a CPU, ROM, RAM, etc., and at least drives the engine 20 and the compressor 11, switches the four-way valves 12, opens the expansion valves 16 and 18, and opens and closes electromagnetically. The open / closed state of the valve 51, the opening degree of the flow rate adjusting valve 52, and the opening degree of the branch flow rate adjusting valve 37a are controlled.

In addition, temperature sensors and pressure sensors are attached to various parts of the refrigerant circuit. These various sensors include a first temperature sensor 61, a second temperature sensor 62, and an outside air temperature sensor 63. The first temperature sensor 61 is provided at a position near the outdoor heat exchanger 13 in the intermediate pipe 34, and detects the temperature of the refrigerant flowing through the intermediate pipe 34. The second temperature sensor 62 is provided at a position near the outdoor heat exchanger 13 in the third pipe 33, and detects the temperature of the refrigerant flowing through the third pipe 33. The outside air temperature sensor 63 detects the outside air temperature in the vicinity of the outdoor heat exchanger 13. The temperature information detected by each temperature sensor is input to the control device 40.

Next, the air conditioning operation of the air conditioner 1 having the above configuration will be described. The air conditioner 1 according to the present embodiment allows the user to set whether the air conditioning mode is the heating mode (heating operation state) or the cooling mode (cooling operation state) by operating a remote controller or the like. Has been made. Then, the air conditioning device 1 operates in air conditioning according to the set air conditioning mode.

Further, when the air conditioning mode of the air conditioning device 1 is the heating mode, the control device 40 controls the switching operation of the four-way valve 12 so that the switching state of the four-way valve 12 becomes the switching state during heating. Further, when the air conditioning mode of the air conditioner 1 is the cooling mode, the control device 40 controls the switching operation of the four-way valve 12 so that the switching state of the four-way valve 12 becomes the switching state during cooling. In FIG. 1, the main flow of the refrigerant during the cooling operation (operation in the cooling mode) is indicated by a solid arrow, and the main flow of the refrigerant during the heating operation (operation in the heating mode) is indicated by a dotted arrow. Is done.

First, the heating operation will be described. When the compressor 11 is operated by driving the engine 20, the compressor 11 sucks the low-pressure gas refrigerant in the accumulator outlet pipe 36 from the suction port 11a and compresses the sucked low-pressure gas refrigerant to generate a high-temperature high-pressure gas refrigerant. .. Then, the generated high-temperature high-pressure gas refrigerant is discharged from the discharge port 11b. The high-temperature high-pressure gas refrigerant discharged from the discharge port 11b flows through the first pipe 31 and enters the first port 12a of the four-way valve 12. During normal heating operation, the electromagnetic on-off valve 51 interposed in the bypass pipe 38 connected to the first pipe 31 is closed and the flow rate adjusting valve 52 is fully closed.

Since the switching operation of the four-way valve 12 is controlled by the control device 40 so that the four-way valve 12 is in the heating switching state when the air conditioning mode of the air conditioning device 1 is the heating mode, the first of the four-way valves 12 during the heating operation. The port 12a communicates with the second port 12b. Therefore, the high-temperature high-pressure gas refrigerant that has entered the first port 12a of the four-way valve 12 from the first pipe 31 flows out of the four-way valve 12 from the second port 12b and flows into the second pipe 32.

The refrigerant in the second pipe 32 flows into the indoor heat exchanger 17. The high-temperature and high-pressure gas refrigerant that has flowed into the indoor heat exchanger 17 exchanges heat with the indoor air while flowing through the indoor heat exchanger 17, and discharges heat into the room to condense it. That is, the indoor heat exchanger 17 functions as a condenser during the heating operation. At this time, the room air is warmed by the heat discharged from the high-temperature high-pressure gas refrigerant, and the room is heated.

The refrigerant that has been condensed by discharging heat into the indoor air is partially liquefied and flows out from the indoor heat exchanger 17 to the intermediate pipe 34. Then, the voltage is increased by expanding with the indoor side electronic expansion valve 18 interposed in the intermediate pipe 34, and further flows through the pipe L2 of the intermediate pipe 34, and the outdoor electronic expansion valve 16 interposed in the pipe L2 is provided. By passing through, the pressure of the refrigerant is reduced. The refrigerant that has passed through the outdoor electronic expansion valve 16 flows into the outdoor heat exchanger 13. The refrigerant that has flowed into the outdoor heat exchanger 13 takes away the heat of the outside air and evaporates while flowing through the outdoor heat exchanger 13. That is, the outdoor heat exchanger 13 functions as an evaporator during the heating operation.

The refrigerant that has taken the heat of the outside air and evaporated is partially vaporized and flows out from the outdoor heat exchanger 13 to the third pipe 33, and then enters the third port 12c of the four-way valve 12. When the air conditioning mode is the heating mode, the third port 12c of the four-way valve 12 communicates with the fourth port 12d, so that the refrigerant that has entered the third port 12c of the four-way valve 12 from the third pipe 33 is the fourth port. The four-way valve 12 flows out from 12d and flows through the accumulator inlet pipe 35. The refrigerant flowing through the accumulator inlet pipe 35 is introduced into the accumulator 15. In the accumulator 15, the introduced refrigerant is gas-liquid separated. Of the gas-liquid separated refrigerants, the gas refrigerant flows out to the accumulator outlet pipe 36. Then, the gas refrigerant in the accumulator outlet pipe 36 returns to the suction port 11a of the compressor 11. By repeating such a circulation cycle of the refrigerant, the room heating is continued.

Next, the cooling operation will be described. When the compressor 11 operates, the high-temperature high-pressure gas refrigerant is discharged from the discharge port 11b of the compressor 11 to the first pipe 31. The high-temperature high-pressure gas refrigerant flows through the first pipe 31 and enters the first port 12a of the four-way valve 12.

Since the switching operation of the four-way valve 12 is controlled by the control device 40 so that the four-way valve 12 is in the switching state during cooling when the air conditioning mode of the air conditioner is the cooling mode, the first port of the four-way valve 12 is controlled during the cooling operation. 12a communicates with the third port 12c. Therefore, the high-temperature high-pressure gas refrigerant that has entered the first port 12a of the four-way valve 12 from the first pipe 31 flows out of the four-way valve 12 from the third port 12c and flows into the third pipe 33. The high-temperature high-pressure gas refrigerant flowing through the third pipe 33 flows into the outdoor heat exchanger 13. The refrigerant that has flowed into the outdoor heat exchanger 13 discharges heat to the outside air and condenses while flowing through the outdoor heat exchanger 13. That is, the outdoor heat exchanger 13 functions as a condenser during the cooling operation.

Part of the condensed refrigerant that discharges heat to the outside air is liquefied and flows out from the outdoor heat exchanger 13 to the intermediate pipe 34. The liquid refrigerant (or gas-liquid two-phase refrigerant) flowing out to the intermediate pipe 34 passes through the indoor electronic expansion valve 18 via the one-way valve 19 interposed in the pipe L1 and the pipe L1. The pressure is lowered so that the refrigerant easily evaporates as the refrigerant expands in the indoor electronic expansion valve 18. After that, the refrigerant flows into the indoor heat exchanger 17. The refrigerant flowing into the indoor heat exchanger 17 takes heat from the indoor air and evaporates while flowing through the indoor heat exchanger 17. That is, the indoor heat exchanger 17 functions as an evaporator during the cooling operation. At this time, the refrigerant takes heat from the room air, so that the room air is cooled and the room is cooled.

The refrigerant that has taken the heat of the indoor air and evaporated is partially vaporized, flows out from the indoor heat exchanger 17 to the second pipe 32, and further enters the second port 12b of the four-way valve 12. When the air conditioning mode is the cooling mode, the second port 12b of the four-way valve 12 communicates with the fourth port 12d, so that the refrigerant that has entered the second port 12b of the four-way valve 12 from the second pipe 32 is the fourth. The four-way valve 12 flows out from the port 12d and flows into the accumulator inlet pipe 35. The refrigerant flowing through the accumulator inlet pipe 35 is introduced into the accumulator 15. In the accumulator 15, the introduced refrigerant is gas-liquid separated, and the separated low-temperature low-pressure gas refrigerant flows out to the accumulator outlet pipe 36. Then, the gas refrigerant that has flowed from the accumulator 15 into the accumulator outlet pipe 36 returns to the suction port 11a of the compressor 11. By repeating such a circulation cycle of the refrigerant, indoor cooling is continued.

By the way, during the air conditioning operation in the heating mode, that is, during the heating operation, the outdoor heat exchanger 13 functions as a refrigerant evaporator as described above. In order for the refrigerant flowing through the outdoor heat exchanger 13 to take heat from the outside air and evaporate, the temperature of the refrigerant flowing through the outdoor heat exchanger 13 must be set lower than that of the outside air. Further, since the heating operation is usually carried out in winter, the outside air temperature during the heating operation is low, and in some cases, the outside air temperature may be about 0 ° C. or lower. Therefore, when the outside air temperature is about 0 ° C. or lower, the temperature of the refrigerant flowing through the outdoor heat exchanger 13 may be lower than 0 ° C. When the temperature of the refrigerant flowing through the outdoor heat exchanger 13 becomes less than 0 ° C., frost is formed on the outdoor heat exchanger 13. When the heating operation is continued with the outdoor heat exchanger 13 frosted, the heat exchange efficiency of the outdoor heat exchanger 13 deteriorates. Therefore, in a normal air conditioner, the defrosting operation is performed when the frost formation of the outdoor heat exchanger is confirmed. However, since the heating efficiency is lowered during the defrosting operation, there is a demand to avoid the defrosting operation as much as possible. Regarding this point, in the present embodiment, the frost formation avoidance operation is carried out not when the frost formation of the outdoor heat exchanger 13 is confirmed but when the frost formation on the outdoor heat exchanger 13 is predicted. As a result, frost formation on the outdoor heat exchanger 13 is avoided, or even if frost is slightly formed on the outdoor heat exchanger 13, frost is quickly removed. This will be described below.

During the heating operation, the control device 40 executes a frost formation avoidance operation start determination process. FIG. 2 is a flowchart showing the flow of the frost formation avoidance operation start determination processing routine executed by the control device 40. When this routine is activated, first, in the control device 40, the latest outside air temperature Tout detected by the outside air temperature sensor 63 in step 11 of FIG. 2 (hereinafter, step is abbreviated as S) is 2 ° C. or higher. Judge whether or not. If it is determined by this determination that the outside air temperature Tout is less than 2 ° C. (S11: No), the control device 40 proceeds to S12. On the other hand, when it is determined by this determination that the outside air temperature Tout is 2 ° C. or higher (S11: Yes), the control device 40 proceeds to S14.

In S12, it is determined whether or not the latest outside air temperature Tout detected by the outside air temperature sensor 63 is within the range of −5 ° C. or higher and lower than 2 ° C. If it is determined by this determination that the outside air temperature Tout is not within the range of −5 ° C. or higher and less than 2 ° C. (S12: No), the control device 40 proceeds to S18. In S18, the control device 40 determines that the frost formation avoidance operation start condition is not satisfied. After that, the control device 40 ends this routine.

When the judgment result of S12 is No, it means that the outside air temperature is less than −5 ° C. When the outside air temperature is very low as described above, it is determined that frost formation on the outdoor heat exchanger 13 cannot be avoided by executing the frost formation avoidance operation control process described later. Therefore, in this case, the frost formation avoidance operation control process is not executed, and the defrosting operation is performed when frost formation on the outdoor heat exchanger 13 is confirmed. The outside air temperature of −5 ° C. in the present embodiment corresponds to the temperature at which frost formation cannot be avoided according to the present invention. Therefore, the control device 40 determines in advance that the outside air temperature Tout cannot avoid frosting on the outdoor heat exchanger 13 by executing the frosting avoidance operation control process. When the temperature is lower than (-5 ° C. in the present embodiment), the frost formation avoidance operation control process is not executed. In the defrosting operation, the switching state of the four-way valve 12 is changed to the switching state during cooling. Therefore, the high-temperature and high-pressure refrigerant discharged from the compressor 11 flows into the outdoor heat exchanger 13. The refrigerant flowing into the outdoor heat exchanger 13 is condensed in the outdoor heat exchanger 13 to generate heat of condensation. The outdoor heat exchanger 13 is heated by the generated heat of condensation. As a result, the outdoor heat exchanger 13 is defrosted.

When it is determined in S12 that the outside air temperature Tout is within the range of −5 ° C. or higher and lower than 2 ° C. (S12: Yes), the control device 40 proceeds to S13. In S13, the control device 40 determines whether or not the frost formation avoidance operation priority mode is selected. Here, the control device 40 is provided with a switch (for example, a DIP switch) capable of selecting whether or not to preferentially carry out the frost formation avoidance operation described later. When the user or the operator turns on this DIP switch, the frost formation avoidance operation priority mode is selected. On the other hand, when the user or the operator turns off the DIP switch, the frost avoidance operation non-priority mode is selected.

When it is determined in S13 that the frost avoidance operation priority mode is not selected (that is, the frost avoidance operation non-priority mode is selected) (S13: No), the control device 40 proceeds to S18. Therefore, it is determined that the frost formation avoidance operation start condition is not satisfied. After that, the control device 40 ends this routine. On the other hand, when it is determined in S13 that the frost formation avoidance operation priority mode is selected (S13: Yes), the control device 40 proceeds to S14.

The control device 40 has a case where the judgment result of S11 is Yes (when the outside air temperature Tout is 2 ° C. or higher) and a case where the judgment result of S13 is Yes (the outside air temperature is −5 ° C. or higher) as described above. When the temperature is lower than 2 ° C. and the frost formation avoidance operation priority mode is selected), the process proceeds to S14. In the process of S14, the counting of the timer τ1 is started. Next, in S15, the control device 40 determines whether or not the defrost temperature Tdef is lower than the frost formation avoidance reference temperature T0. Here, the defrost temperature Tdef is the temperature T1 detected by the first temperature sensor 61 and the temperature T2 detected by the second temperature sensor 62, whichever is lower. During the heating operation, the temperature T1 detected by the first temperature sensor 61 is the temperature of the liquid refrigerant flowing into the outdoor heat exchanger 13, and the temperature T2 detected by the second temperature sensor 62 is the temperature T2 of the outdoor heat exchanger 13. It is the temperature of the gas refrigerant flowing out from. Therefore, it can be said that the defrost temperature Tdef is the temperature of the refrigerant flowing through the outdoor heat exchanger 13. Further, the frost formation avoidance reference temperature T0 is an upper limit value of a temperature predetermined as a defrost temperature in which frost formation on the outdoor heat exchanger 13 is predicted in the future during the heating operation. That is, it is considered that the outdoor heat exchanger 13 is not frosted at present, but if the temperature continues, it is judged that there is a high possibility that the outdoor heat exchanger 13 will be frosted. The upper limit of Tdef is the frost formation avoidance reference temperature T0. The frost formation avoidance reference temperature T0 is a temperature of 0 ° C. or higher, which is the temperature at which frost is almost certainly formed on the outdoor heat exchanger 13. Further, when the defrost temperature Tdef exceeds 2 ° C., the possibility of frost on the outdoor heat exchanger 13 is considerably reduced. Therefore, the frost formation avoidance reference temperature T0 is preferably 2 ° C. or lower. That is, the frost formation avoidance reference temperature T0 is preferably 0 ° C. or higher and 2 ° C. or lower. More preferably, the frost formation avoidance reference temperature T0 is 1 ° C. or higher and 2 ° C. or lower.

When it is determined in S15 that the defrost temperature Tdef is equal to or higher than the frost formation avoidance reference temperature T0 (S15: No), the control device 40 has a relatively high refrigerant temperature (defrost temperature Tdef) flowing through the outdoor heat exchanger 13. Therefore, it is determined that the possibility of frost formation on the outdoor heat exchanger 13 is low, the process proceeds to S18, and it is determined that the frost formation avoidance operation start condition is not satisfied. After that, the control device 40 ends this routine. On the other hand, when it is determined in S15 that the defrost temperature Tdef is less than the frost formation avoidance reference temperature T0 (S15: Yes), the control device 40 proceeds to S16.

In S16, the control device 40 determines whether or not the time measured by the timer τ1 is equal to or greater than the threshold time τ1th corresponding to the predetermined time of the present invention. The threshold time τ1th can be set arbitrarily. For example, the threshold time τ1th can be set to 25 minutes. When the measurement time τ1 by the timer is less than the threshold time τ1th (S16: No), the control device returns the process to S15. On the other hand, when the measurement time τ1 by the timer is equal to or longer than the threshold time τ1th (S16: Yes), the control device 40 proceeds to S17 and determines that the frost formation avoidance operation start condition is satisfied. After that, the control device 40 ends this routine.

As can be seen from the above-mentioned flow of the frost avoidance operation start determination process, the frost avoidance operation start condition is defined as a state in which the outside air temperature is -5 ° C or higher and the defrost temperature Tdef is lower than the frost avoidance reference temperature T0. It holds when the time (threshold time τ1th) continues.

When the control device 40 determines that the frost avoidance operation start condition is satisfied in the above-mentioned frost avoidance operation start determination process, the control device 40 executes the frost avoidance operation control process for executing the frost avoidance operation. FIG. 3 is a flowchart showing the flow of the frost formation avoidance operation control processing routine. When this routine is activated, the control device 40 first outputs a closing operation signal to the electromagnetic on-off valve 51 interposed in the bypass pipe 38 in S21 of FIG. As a result, the electromagnetic on-off valve 51 is closed. If the electromagnetic on-off valve 51 is already in the closed state, the closed state is maintained.

Next, the control device 40 acquires the latest defrost temperature Tdef in S22, and subsequently acquires the control amount U of the flow rate adjusting valve 52 in S23 with reference to the flow rate adjusting valve control map.

FIG. 4 is a diagram showing an example of a flow rate control valve control map. The horizontal axis of FIG. 4 represents the defrost temperature Tdef, and the vertical axis represents the controlled variable U. According to the flow control valve control map shown in FIG. 4, the control amount U is set to + S2 when the defrost temperature Tdef is less than the temperature Ta, and the control amount is when the defrost temperature Tdef is the temperature Ta or more and less than the temperature Tb. When U is set to + S1 (<S2), the control amount U is set to 0 when the defrost temperature Tdef is equal to or higher than the temperature Tb and lower than the temperature Tc, and the defrost temperature Tdef is equal to or higher than the temperature Tc and lower than the temperature Td. The control amount U is set to −S1, and the control amount U is set to −S2 (<−S1) when the defrost temperature Tdef is equal to or higher than the temperature Td. Here, the opening degree of the flow rate adjusting valve 52 in the present embodiment is adjusted by the stepping motor, and the control amount U represents the number of steps for increasing / decreasing from the current number of steps of the stepping motor.

The control device 40 acquires the control amount U by referring to the flow rate control valve control map as described above in S23, then proceeds to process in S24, and the flow rate adjustment valve 52 of the flow rate adjustment valve 52 is based on the acquired control amount U. Adjust the opening. Specifically, in the control device 40, the number of steps of the stepping motor for adjusting the opening degree of the flow rate adjusting valve 52 in S24 is represented by the control amount U acquired in S23 from the current number of steps. Increase or decrease only. For example, when the control quantities U acquired in S23 are + S1 and + S2, the stepping motor rotates in the positive direction by S1 step or S2 step. As a result, the opening degree of the flow rate adjusting valve 52 increases. Further, when the control amounts U acquired in S23 are −S1 and −S2, the stepping motor rotates in S1 step or S2 step in the opposite direction. As a result, the opening degree of the flow rate adjusting valve 52 is reduced. When the control amount U is 0, the stepping motor does not rotate. Therefore, the current opening degree of the flow rate adjusting valve 52 is maintained.

By adjusting the opening degree of the flow rate adjusting valve 52 in S24 in this way, when the electromagnetic on-off valve 51 is opened via the flow rate adjusting valve 52 or by the process of S28 described later, the electromagnetic on-off valve A part of the high-temperature and high-pressure gas refrigerant discharged from the compressor 11 flows through the bypass pipe 38 via the 51 and the flow rate adjusting valve 52. The high-temperature and high-pressure gas refrigerant that has flowed through the bypass pipe 38 flows into the accumulator inlet pipe 35 from the bypass pipe 38, and is further introduced into the suction port 11a of the compressor 11 through the accumulator 15 and the accumulator outlet pipe 36. As a result, the pressure of the refrigerant on the suction side of the compressor 11 rises, so that the evaporation temperature of the refrigerant rises, and the temperature of the refrigerant flowing in the refrigerant circuit rises. As a result, the temperature of the refrigerant flowing through the outdoor heat exchanger 13 also rises. By raising the temperature of the refrigerant flowing through the outdoor heat exchanger 13 in this way, frost formation on the outdoor heat exchanger 13 is avoided, or when the outdoor heat exchanger 13 is slightly frosted, it is promptly performed. Is defrosted.

The control device 40 whose opening degree of the flow rate adjusting valve 52 is adjusted in S24 subsequently determines in S25 whether or not the flow rate adjusting valve 52 is fully open. When the flow rate adjusting valve 52 is fully open (S25: Yes), the control device 40 proceeds to S28 to fully close the flow rate adjusting valve 52 and open the electromagnetic on-off valve 51. Here, when the flow rate adjusting valve 52 is in the fully open state, the flow rate of the refrigerant flowing through the bypass pipe 38 through the flow rate adjusting valve 52 and the flow rate of the refrigerant flowing through the bypass pipe 38 through the electromagnetic on-off valve 51 in the open state are approximately the same. The opening diameter of the flow rate adjusting valve 52 and the opening diameter of the electromagnetic on-off valve 51 are set so as to be equal. Therefore, even when the process of S28 is executed, the amount of the refrigerant flowing through the bypass pipe 38 does not change. After executing the process of S28, the control device 40 proceeds to the process of S30.

Further, when it is determined in S25 that the flow rate adjusting valve 52 is not fully open (S25: No), the control device 40 proceeds to S26 and determines whether or not the flow rate adjusting valve 52 is fully closed. To do. When the flow rate adjusting valve 52 is not fully closed (S26: No), that is, when the flow rate adjusting valve 52 is neither fully open nor fully closed, the control device proceeds to S30. On the other hand, when the flow rate adjusting valve 52 is fully closed (S26: Yes), the control device 40 proceeds to S27 to determine whether or not the electromagnetic on-off valve 51 is in the open state. When the electromagnetic on-off valve 51 is not in the open state, that is, when the electromagnetic on-off valve 51 is in the closed state (S27: No), the control device 40 proceeds to S30. In this case, both the electromagnetic on-off valve 51 and the flow rate adjusting valve 52 are closed, so that the refrigerant does not flow in the bypass pipe 38. Since it is considered that such a situation does not occur during the frost formation avoidance operation control process, the process of S27 may be omitted.

On the other hand, when it is determined in S27 that the electromagnetic on-off valve 51 is in the open state (S27: Yes), the control device 40 proceeds to S29. In S29, the control device 40 fully opens the flow rate adjusting valve 52 and closes the electromagnetic on-off valve 51. Here, as described above, when the flow rate adjusting valve 52 is in the fully open state, the refrigerant flows through the bypass pipe 38 through the flow rate adjusting valve 52 and flows through the bypass pipe 38 through the electromagnetic on-off valve 51 in the open state. The opening diameter of the flow rate adjusting valve 52 and the opening diameter of the electromagnetic on-off valve 51 are set so that the refrigerant flow rates are substantially equal. Therefore, even when the process of S29 is executed, the amount of the refrigerant flowing through the bypass pipe 38 does not change. After executing the process of S29, the control device 40 advances the process to S30.

When the determination results of S26 and S27 are No, the process of S28 is executed, and the process of S29 is executed, the control device 40 advances the process to S30. In S30, the control device 40 determines whether or not the control cycle has been reached. This control cycle can be set arbitrarily. For example, the control cycle can be set to 30 seconds. If the control cycle is too short, the processing of S28 and the processing of S29 may be frequently executed, and the life of the electromagnetic on-off valve 51 may be shortened. Therefore, the control cycle is preferably about 30 seconds.

When it is determined in S30 that the control cycle has not been reached (S30: No), the control device 40 repeats the process of S30. Then, when it is determined in S30 that the control cycle has been reached (S30: Yes), the control device 40 returns the process to S22 and executes the process after S22 again.

The frost formation avoidance operation is carried out by the control device 40 executing the above-mentioned frost formation avoidance operation control process. In this frost formation avoidance operation, the flow rate of the high-temperature and high-pressure gas refrigerant flowing from the discharge port 11b of the compressor 11 to the accumulator 15 through the bypass pipe 38 is adjusted according to the defrost temperature Tdef. Specifically, the flow rate adjusting valve 51 is controlled so that the opening degree of the flow rate adjusting valve 51 increases as the defrost temperature Tdef decreases. By adjusting the opening degree of the flow rate adjusting valve 51 and opening / closing the electromagnetic on-off valve 51 according to the opening state of the flow rate adjusting valve 51, the lower the defrost temperature Tdef, the greater the flow rate of the gas refrigerant flowing in the bypass pipe 38. The open / closed state of the electromagnetic on-off valve 51 and the opening degree of the flow rate adjusting valve 52 are controlled so as to increase the number. Therefore, the minimum amount of gas refrigerant necessary for avoiding frost formation on the outdoor heat exchanger 13 can flow through the bypass pipe 38. In other words, during the frost formation avoidance operation, the minimum gas refrigerant is used to avoid frost formation on the outdoor heat exchanger 13, and the remaining gas refrigerant is used for the heating operation to achieve heating efficiency (outdoor heat exchanger). It is possible to avoid frost formation on the outdoor heat exchanger 13 or to remove frost slightly adhering to the outdoor heat exchanger 13 without significantly reducing the heat exchange efficiency of the outdoor heat exchanger 13.

Further, the bypass pipe 38 according to the present embodiment serves as a bypass circuit for directly sending the gas refrigerant discharged from the compressor 11 to the accumulator 15 in order to avoid a low pressure state of the refrigerant circuit, that is, as a so-called hot gas bypass. , Conventionally provided. By connecting the flow rate adjusting valve to the hot gas bypass in parallel with the on-off valve, that is, by improving the existing hot gas bypass, frost formation on the outdoor heat exchanger 13 can be avoided at low cost.

Further, the opening degree of the flow rate adjusting valve 52 interposed in the bypass pipe 38 according to the present embodiment can be adjusted even in a situation other than the above-mentioned frost formation avoidance operation. For example, when adjusting the capacity of the refrigerant flowing in the refrigerant circuit, the opening degree of the flow rate adjusting valve 52 can be adjusted. This has the additional effect that the capacity of the refrigerant can be adjusted without changing the compressor to an expensive variable capacity type compressor.

Further, in the frost formation avoidance operation control process according to the present embodiment, when the flow rate adjusting valve 52 is fully opened while the electromagnetic on-off valve 51 is closed, the electromagnetic on-off valve 51 is opened and the flow rate adjusting valve 52 is opened. Fully closed. As a result, when it becomes necessary to further increase the flow rate of the refrigerant flowing in the bypass pipe 38 after that, the need can be dealt with by increasing the opening degree of the flow rate adjusting valve 52. Further, when the flow rate adjusting valve 52 is fully closed while the electromagnetic on-off valve 51 is open, the electromagnetic on-off valve 51 is closed and the flow rate adjusting valve 52 is fully opened. As a result, when it becomes necessary to further reduce the flow rate of the refrigerant flowing in the bypass pipe 38 after that, the need can be dealt with by reducing the opening degree of the flow rate adjusting valve 52. That is, according to the present embodiment, the control device 40 uses the opening / closing operation of the electromagnetic on-off valve 51 and the opening / closing operation of the flow rate adjusting valve 52 together during the execution of the frost formation avoidance operation control process, so that the inside of the bypass pipe 38 The adjustment range of the flow rate of the refrigerant flowing through the water can be increased.

The control device 40 executes the frost avoidance operation end condition determination process at a predetermined cycle during the execution of the above frost avoidance operation control process. FIG. 5 is a flowchart showing the flow of the frost formation avoidance operation end determination processing routine. When this routine is activated, the control device 40 first determines in S41 of FIG. 5 whether the elapsed time from the start of the frost avoidance operation, that is, the frost avoidance operation time τ2 has reached the predetermined set time τ2th. Judge whether or not. The set time τ2th can be set arbitrarily. The set time τ2th is preferably a time between 10 minutes and 25 minutes.

When it is determined in S41 that the frost formation avoidance operation time τ2 has reached the set time τ2th (S41: Yes), the control device 40 proceeds to S43. On the other hand, when it is determined in S41 that the frost formation avoidance operation time τ2 has not reached the set time τ2th (S41: No), the control device 40 proceeds to S42. In S42, the control device 40 determines whether or not the defrost temperature Tdef is equal to or higher than the frost formation avoidance end temperature Ts. The frost formation avoidance end temperature Ts is preset as a temperature at which it can be determined that frost does not form on the outdoor heat exchanger 13 for the time being. The frost formation avoidance end temperature Ts is preferably set to a temperature between 7 ° C. and 10 ° C.

When it is determined in S42 that the defrost temperature Tdef is less than the frost formation avoidance end temperature Ts (S42: No), the control device 40 determines that the avoidance of frost on the outdoor heat exchanger 13 has not been completed. Then, this routine is terminated without ending the frost avoidance operation. On the other hand, when it is determined that the defrost temperature Tdef is equal to or higher than the frost formation avoidance end temperature Ts (S42: Yes), the control device 40 proceeds to S43. In S43, the control device 40 ends the frost formation avoidance operation control process. As a result, the frost avoidance operation is completed. Next, the control device 40 closes the electromagnetic on-off valve 51 in S44 (S44), and further closes the flow rate adjusting valve 52 (S45). After that, the control device 40 ends this routine.

When the defrost temperature Tdef is raised to the frost avoidance end temperature Ts or higher by executing the above-mentioned frost avoidance operation end determination process, or when the execution time of the frost avoidance operation control process elapses the set time τ2th. , The frost avoidance operation is completed. If the defrost temperature Tdef is sufficiently increased, the temperature of the refrigerant flowing through the outdoor heat exchanger 13 is likely to be higher than the outside air temperature, so that the refrigerant flowing through the outdoor heat exchanger 13 takes heat from the outside air. Can't. In this case, the opening degree of the branch flow rate adjusting valve 37a is increased to increase the flow rate of the refrigerant flowing through the branch pipe 37. Since the sub heat exchanger 14 is interposed in the branch pipe 37, the refrigerant flowing through the branch pipe 37 exchanges heat with the engine cooling water in the sub heat exchanger 14 and evaporates. In this way, by using the sub heat exchanger 14 as a substitute for the outdoor heat exchanger 13, the refrigerant can be evaporated, thereby compensating for the decrease in the heating efficiency of the outdoor heat exchanger 13.

As described above, according to the air conditioner 1 according to the present embodiment, when the frost formation avoidance operation is performed, the lower the temperature of the refrigerant flowing through the outdoor heat exchanger 13 (defrost temperature Tdef), the more the bypass pipe 38 is connected. The valve device (electromagnetic on-off valve 51, flow rate adjusting valve 52) is controlled so that the flow rate of the flowing refrigerant increases. As a result, frost formation on the outdoor heat exchanger 13 is avoided, or frost slightly adhering to the outdoor heat exchanger 13 is removed. Further, the flow rate of the gas refrigerant flowing through the bypass pipe 38 during the frost formation avoidance operation can be minimized by adjusting the flow rate according to the defrost temperature Tdef. Therefore, it is possible to avoid frost formation on the outdoor heat exchanger 13 without significantly lowering the heating efficiency.

Further, the above-mentioned frost formation avoidance operation is not when it is confirmed that the outdoor heat exchanger 13 has actually been frosted, but when it is predicted that the outdoor heat exchanger 13 will be frosted in the future, specifically. It is started when the state in which the defrost temperature Tdef is lower than the frost formation avoidance reference temperature T0 continues for a predetermined time. Therefore, it is considered that the outdoor heat exchanger 13 has not yet been frosted or has been slightly frosted at the start of the frost avoidance operation. That is, the frost formation avoidance operation according to the present embodiment is not a defrosting operation that removes a large amount of frost adhering to the outdoor heat exchanger 13 at once, but the outdoor heat exchanger 13 is not or slightly frosted. Since this operation is for raising the temperature of the refrigerant in the refrigerant circuit in the frosted state, the operation is completed in a short time as compared with the normal defrosting operation. Therefore, it is possible to shorten the time during which the heating operation is performed so as to reduce the efficiency of the heating operation, and as a result, the comfort during the heating operation can be ensured.

Although the embodiments of the present invention have been described above, the present invention should not be limited to the above embodiments. For example, the value of each temperature and the value of each time shown in the above embodiment can be appropriately set according to the situation. As described above, the present invention is deformable as long as it does not deviate from the gist thereof.

1 ... Air conditioner, 11 ... Compressor, 11a ... Suction port, 11b ... Discharge port, 12 ... Four-way valve, 12a ... First port, 12b ... Second port, 12c ... Third port, 12d ... Fourth port, 13 ... Outdoor heat exchanger, 14 ... Sub heat exchanger, 15 ... Accumulator, 16 ... Outdoor electronic expansion valve, 17 ... Indoor heat exchanger, 18 ... Indoor side electronic expansion valve, 20 ... Engine, 31 ... First piping , 32 ... 2nd pipe, 33 ... 3rd pipe, 34 ... Intermediate pipe, 35 ... Accumulator inlet pipe, 36 ... Accumulator outlet pipe, 37 ... Branch pipe, 38 ... Bypass pipe, 381 ... 1st bypass pipe, 382 ... Two bypass pipes, 40 ... control device, 51 ... electromagnetic on-off valve (on-off valve), 52 ... flow control valve, 61 ... first temperature sensor (fuel refrigerant temperature sensor), 62 ... second temperature sensor (fuel refrigerant temperature sensor), 63 ... outside temperature sensor, T0 ... frost avoidance reference temperature, Tdef ... defrost temperature, Tout ... outside air temperature, Ts ... frost avoidance end temperature, τ1th ... threshold time (predetermined time), τ2th ... set time

Claims (4)

A compressor with a suction port and a discharge port,
It has a first port, a second port, a third port, and a fourth port, and the first port is connected to the discharge port of the compressor via a first pipe, and is connected to the first port during heating operation. The second port communicates with the third port and the fourth port communicates with each other so that the first port and the third port communicate with each other and the second port and the fourth port communicate with each other during cooling operation. In addition, a four-way valve that can switch the communication state of each port,
An indoor heat exchanger connected to the second port of the four-way valve via a second pipe,
An outdoor heat exchanger connected to the third port of the four-way valve via a third pipe and connected to the indoor heat exchanger via an intermediate pipe.
An accumulator connected to the fourth port of the four-way valve via an accumulator inlet pipe and connected to the suction port of the compressor via an accumulator outlet pipe.
A bypass pipe connecting the first pipe and the accumulator inlet pipe,
A valve device that is interposed in the bypass pipe and can adjust the flow rate of the refrigerant flowing through the bypass pipe.
A control device that controls the valve device and
A refrigerant temperature sensor that detects the temperature of the refrigerant flowing through the outdoor heat exchanger, and
With
The control device is in a state where the refrigerant temperature detected by the refrigerant temperature sensor during the heating operation is lower than the frost formation avoidance reference temperature predetermined as an upper limit value of the temperature at which frost is predicted to be formed on the outdoor heat exchanger. Is continued for a predetermined time, the frost-prevention operation control process for controlling the valve device is executed so that the lower the refrigerant temperature detected by the refrigerant temperature sensor, the larger the flow rate of the refrigerant flowing through the bypass pipe. An air conditioner that is configured. In the air conditioner according to claim 1,
In the frost avoidance operation control process, when the refrigerant temperature detected by the refrigerant temperature sensor is equal to or higher than a predetermined frost avoidance end temperature as a temperature at which it can be determined that frost does not form on the outdoor heat exchanger. Or, an air conditioner that ends when the execution time of the frost formation avoidance operation control process elapses a predetermined set time. In the air conditioner according to claim 1 or 2.
In the control device, the outside air temperature is lower than a predetermined temperature at which frost formation avoidance unavoidable temperature is determined as a temperature at which frost formation on the outdoor heat exchanger cannot be avoided by executing the frost formation avoidance operation control process. An air conditioner configured to not perform the frost avoidance operation control process at one time. In the air conditioner according to any one of claims 1 to 3, the air conditioner
The valve device has a flow rate adjusting valve and an on-off valve connected in parallel to the bypass pipe.
The control device adjusts the flow rate of the refrigerant flowing through the bypass pipe by combining the opening / closing operation of the on-off valve and the adjustment of the opening degree of the flow rate adjusting valve during the execution of the frost formation avoidance operation control process. Harmonizer.

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