Outdoor unit of air conditioner

Abstract

This outdoor unit of an air conditioner comprises a compressor for compressing a refrigerant, a heat exchanger through which the refrigerant compressed by the compressor flows, a flow passage switching device for switching a flow direction of the refrigerant, a housing for accommodating the compressor, the heat exchanger and the flow passage switching device, a bottom plate heater which is provided on a bottom plate of the housing to heat water that has dropped from the heat exchanger, and a control device for controlling the compressor and the flow passage switching device to execute a space heating operation and a defrosting operation for removing frost attached to the heat exchanger during the space heating operation, wherein the control device controls the bottom plate heater on the basis of an outside temperature and an outside humidity during the space heating operation and the defrosting operation.

Description

Air conditioner outdoor unit

[0001] The present disclosure relates to an outdoor unit of an air conditioner that performs defrosting operation.

[0002] Generally, when an outdoor unit of an air conditioner is operated in a heating mode under a low-temperature, high-humidity environment, frost accumulates on the heat exchanger. Therefore, a technique for suppressing the growth of frost by attaching an electric heater to the metal plate on the side of the outdoor unit is known (for example, see Patent Document 1). By providing the electric heater in the outdoor unit of Patent Document 1, the frost does not block the ventilation holes formed on the side of the outdoor unit, thereby suppressing a decrease in heat exchange efficiency.

[0003] JP 2014-214983 A

[0004] However, the outdoor unit disclosed in Patent Document 1 cannot prevent the refreezing of water drained from the heat exchanger onto the bottom plate of the outdoor unit during defrosting operation. Here, an electric heater attached to the bottom plate can be energized when the outdoor temperature is low to prevent the water from dropping from the heat exchanger from freezing. However, even if the electric heater attached to the bottom plate is energized when the outdoor temperature is low, water does not necessarily accumulate on the bottom plate, resulting in wasted electricity.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to reduce the power consumption of a heater provided on a bottom plate in an outdoor unit of an air conditioner.

[0006] The outdoor unit of the air conditioner disclosed herein comprises a compressor that compresses a refrigerant, a heat exchanger through which the refrigerant sent from the compressor flows, a flow path switching device that switches the flow direction of the refrigerant, a housing that stores the compressor, the heat exchanger, and the flow path switching device, a bottom plate heater that is provided on the bottom plate of the housing and heats water that drops from the heat exchanger, and a control device that controls the compressor and the flow path switching device and performs heating operation and defrosting operation that removes frost that has adhered to the heat exchanger during heating operation, and the control device controls the bottom plate heater based on the outside air temperature and outside air humidity during heating operation and defrosting operation.

[0007] The outdoor unit of the air conditioner disclosed herein controls the base plate heater based on the outdoor temperature and humidity during heating and defrosting operations. It is known that in environments with low outdoor temperatures and humidity, little frost forms on the heat exchanger during heating operation, and almost no water is drained from the heat exchanger to the base plate. Therefore, the outdoor unit of the air conditioner disclosed herein limits the time that power is applied to the heater provided on the base plate, thereby reducing power consumption.

[0008] 1 is a refrigerant circuit diagram showing an air conditioner according to embodiment 1. FIG. 2 is an exploded perspective view showing an outdoor unit according to embodiment 1. FIG. 3 is a top view showing the interior of the outdoor unit according to embodiment 1. FIG. 4 is a diagram showing a bottom plate and a bottom plate heater of the outdoor unit according to embodiment 1. FIG. 5 is a functional block diagram of the outdoor unit according to embodiment 1. FIG. 6 is a hardware configuration diagram of a control device according to embodiment 1. FIG. 7 is a hardware configuration diagram of a control device according to embodiment 1. FIG. 8 is a flowchart showing the operation of a control device according to embodiment 1. FIG. 9 is a flowchart showing the operation of a control device according to embodiment 1.

[0009] Embodiment 1. An air conditioner 1 according to Embodiment 1 will now be described with reference to the drawings. Fig. 1 is a refrigerant circuit diagram showing an air conditioner 1 according to Embodiment 1. As shown in Fig. 1, the air conditioner 1 has an outdoor unit 2 and an indoor unit 3. The outdoor unit 2 has a compressor 11, a flow path switching device 12, a heat exchanger 13, a blower 14, and a throttling device 15. The indoor unit 3 has a heat exchanger 16. The air conditioner 1 has three operating modes: cooling operation, heating operation, and defrosting operation, which removes frost that has adhered to the heat exchanger 13 during heating operation.

[0010] The compressor 11 draws in a low-temperature, low-pressure refrigerant, compresses it, and discharges it into a high-temperature, high-pressure refrigerant. The flow path switching device 12 switches the flow direction of the refrigerant in the refrigerant circuit and is, for example, a four-way valve. The flow path switching device 12 may also be a combination of two-way and three-way valves. The heat exchanger 13 exchanges heat between the refrigerant and outdoor air and is, for example, a fin-and-tube heat exchanger. The heat exchanger 13 functions as a condenser during cooling operation and as an evaporator during heating operation. The blower 14 sends outdoor air to the heat exchanger 13. The blower 14 has a fan motor 14a, and the rotation speed of the fan motor 14a is controlled to adjust the airflow. The expansion device 15 reduces the pressure of the refrigerant and expands it and is, for example, an electronic expansion valve.

[0011] The heat exchanger 16 exchanges heat between the indoor air and the refrigerant. The heat exchanger 16 acts as an evaporator during cooling operation and as a condenser during heating operation. The indoor unit 3 may also have a blower, such as a cross-flow fan, that sends indoor air to the heat exchanger 16.

[0012] The outdoor unit 2 has a refrigerant temperature sensor 31 and an outdoor air temperature sensor 32. The refrigerant temperature sensor 31 is attached in close contact with the piping connecting the heat exchanger 13 and the throttling device 15. The refrigerant temperature sensor 31 measures the temperature of the refrigerant flowing through the piping and transmits the measurement result to the control device 21. In particular, the refrigerant temperature sensor 31 detects the temperature of the refrigerant flowing into the heat exchanger 13 of the outdoor unit 2 during heating operation and the temperature of the refrigerant passing through the heat exchanger 13 of the outdoor unit 2 during defrosting operation. The outdoor air temperature sensor 32 is provided inside a housing 40 of the outdoor unit 2, which will be described later. The outdoor air temperature sensor 32 measures the temperature of the outdoor air before heat exchange by the heat exchanger 13 and transmits the measurement result to the control device 21. The control device 21 will be described later.

[0013] Here, the operation of the air conditioner 1 will be described for each operating mode. First, cooling operation will be described. In cooling operation, the air conditioner 1 switches the flow path switching device 12 to connect the discharge side of the compressor 11 to the heat exchanger 13, as shown by the solid line. In cooling operation, the refrigerant drawn into the compressor 11 is compressed by the compressor 11 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 passes through the flow path switching device 12 and flows into the heat exchanger 13, which functions as a condenser. The refrigerant that flows into the heat exchanger 13 exchanges heat with outdoor air sent by the blower 14, condenses, and liquefies. The liquid refrigerant flows into the expansion device 15, where it is decompressed and expanded to become a low-temperature, low-pressure, two-phase gas-liquid refrigerant. The two-phase gas-liquid refrigerant flows into the heat exchanger 16, which functions as an evaporator. The refrigerant that flows into the heat exchanger 16 exchanges heat with the indoor air and evaporates and gasifies. At this time, the indoor air is cooled, thereby cooling the room. The evaporated refrigerant, now in a low-temperature, low-pressure gas state, then passes through the flow switching device 12 and is drawn into the compressor 11.

[0014] Next, heating operation will be described. In heating operation, the air conditioner 1 switches the flow path switching device 12 to connect the discharge side of the compressor 11 to the heat exchanger 16, as indicated by the dashed line. During heating operation, the refrigerant drawn into the compressor 11 is compressed by the compressor 11 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 passes through the flow path switching device 12 and flows into the heat exchanger 16, which functions as a condenser. The refrigerant that flows into the heat exchanger 16 exchanges heat with the indoor air, condenses, and liquefies. At this time, the indoor air is heated, thereby heating the room. The liquid refrigerant flows into the expansion device 15, where it is decompressed and expanded to become a low-temperature, low-pressure, two-phase gas-liquid refrigerant. The two-phase gas-liquid refrigerant flows into the heat exchanger 13, which functions as an evaporator. The refrigerant that flows into the heat exchanger 13 exchanges heat with the outdoor air sent by the blower 14, evaporating and gasifying. Thereafter, the evaporated refrigerant in a low-temperature, low-pressure gas state passes through the flow switching device 12 and is sucked into the compressor 11 .

[0015] Next, the defrosting operation will be described. In the defrosting operation, the air conditioner 1 switches the flow path switching device 12 in the same way as in the cooling operation, connecting the discharge side of the compressor 11 to the heat exchanger 13 as shown by the solid line. In the defrosting operation, the refrigerant drawn into the compressor 11 is compressed by the compressor 11 and discharged in a high-temperature, high-pressure gas state. The high-temperature, high-pressure gas state refrigerant discharged from the compressor 11 passes through the flow path switching device 12 and flows into the heat exchanger 13. The refrigerant flowing into the heat exchanger 13 exchanges heat with the frost adhering to the heat exchanger 13, condenses, and liquefies. At this time, the frost adhering to the heat exchanger 13 during the heating operation is removed. The subsequent flow of the refrigerant is the same as in the cooling operation, and therefore will not be described again.

[0016] Next, the internal configuration of the outdoor unit 2 will be described using FIGS. 2 to 4. FIG. 2 is an exploded perspective view showing the outdoor unit 2 according to the first embodiment. As shown in FIG. 2, the outdoor unit 2 includes a housing 40 housing a compressor 11, a flow switching device 12, a heat exchanger 13, a blower 14, and a throttling device 15. The housing 40 forms the exterior of the outdoor unit 2 and is composed of a bottom plate 41, a front panel 42, side portions 43, a rear portion 44, and a top panel 45. The bottom plate 41 forms the bottom of the housing 40 and is on which the compressor 11, the heat exchanger 13, and the blower 14 are mounted. The front panel 42 forms the front and side portions of the housing 40 and has an opening facing the blower 14. The front panel 42 also has a lattice-shaped fan cover 42a that covers the opening. The side portions 43 are made up of a combination of multiple parts and form the side portions of the housing 40. The rear portion 44 is also made up of a combination of multiple parts and form the rear portion of the housing 40. The components that make up the rear surface 44 are formed with a plurality of ventilation holes for air to flow to the heat exchanger 13. The top panel 45 makes up the upper part of the housing 40.

[0017] Figure 3 is a top view showing the inside of the outdoor unit 2 according to embodiment 1. In Figure 3, parts other than the bottom plate 41 of the housing 40 and the blower 14 are not shown. As shown in Figure 3, an L-shaped heat exchanger 13 is disposed along the back and side of the housing 40. In order to accurately measure the outside air temperature, the outside air temperature sensor 32 is provided at a position that takes into consideration the following first to fifth points.

[0018] First, the outdoor air temperature sensor 32 is attached so as not to be in close contact with the top panel 45 so that the measurement results are not affected by heat conduction from the top panel 45. For this reason, the outdoor air temperature sensor 32 is attached, for example, to the rear portion 44 or the top panel 45 via a support (not shown) or a dedicated holder (not shown). Second, the outdoor air temperature sensor 32 is provided directly below the top panel 45 so that snow or the like does not adhere to the sensor and prevent the outdoor temperature from being measured. In other words, the outdoor air temperature sensor 32 is covered by the top panel 45 when the outdoor unit 2 is viewed from above.

[0019] A third point is that the outdoor air temperature sensor 32 is placed as far away as possible from the heat exchanger 13 so that the measurement results are not affected by radiant heat from the heat exchanger 13. A fourth point is that the outdoor air temperature sensor 32 is placed as far away as possible from the installation surface of the outdoor unit 2 so that the measurement results are not affected by geothermal heat. And a fifth point is that the outdoor air temperature sensor 32 is placed upwind of the heat exchanger 13 so that the measurement results are not affected by the air after heat exchange, that is, to measure the temperature of the air before heat exchange.

[0020] FIG. 4 is a diagram showing the bottom plate 41 and bottom plate heater 51 of the outdoor unit 2 according to the first embodiment. Similar to FIG. 3 , FIG. 4 is a top view of the outdoor unit 2. However, in order to explain the bottom plate 41 and the bottom plate heater 51, the illustration does not include components other than the bottom plate 41 and the bottom plate heater 51. As shown in FIG. 4 , the bottom plate 41 has multiple drainage holes 41a. The drainage holes 41a are openings for draining water on the bottom plate 41 to the outside of the outdoor unit 2. Note that multiple drainage holes 41a are provided, but only one may be provided. The bottom plate 41 has a recess, and multiple drainage holes 41a are arranged in the recess. Furthermore, a slope is formed around each drainage hole 41a, decreasing in size toward the opening. This forms a drainage path in the bottom plate 41 to allow water to flow smoothly outside the outdoor unit 2.

[0021] As shown in FIG. 4 , a bottom plate heater 51 is provided on the bottom plate 41. The bottom plate heater 51 generates heat when energized. The bottom plate heater 51 prevents frost adhering to the heat exchanger 13 from melting and falling to the bottom plate 41 during heating and defrosting operations, and from refreezing. The bottom plate heater 51 is provided in a ring shape approximately directly below the heat exchanger 13. Specifically, the area on the bottom plate 41 where the bottom plate heater 51 is attached includes the area directly below the heat exchanger 13. In other words, the bottom plate heater 51 is arranged along the projection area of ​​the heat exchanger 13 onto the bottom plate 41. This allows the temperature of drainage water from the heat exchanger 13 to be increased before it comes into contact with the bottom plate 41. The bottom plate heater 51 is also provided on the drainage path of the bottom plate 41. The bottom plate heater 51 is also provided around the drainage hole 41a.

[0022] The outdoor unit 2 includes a control device 21. FIG. 5 is a functional block diagram of the outdoor unit 2 according to the first embodiment. The control device 21 switches the connection direction of the flow path switching device 12 to perform cooling or heating operation based on an operation mode instruction input by a user via a remote control (not shown) provided in the indoor unit 3. The control device 21 also controls the operating frequency of the compressor 11, the rotation speed of the fan motor 14a, and the open / close state of the expansion device 15 so that the temperature in the room where the indoor unit 3 is installed satisfies the set temperature input by the user via the remote control. As shown in FIG. 5, the control device 21 controls the operation of the bottom plate heater 51 based on the measurement results of the refrigerant temperature sensor 31 and the outdoor air temperature sensor 32.

[0023] The conditions for executing the defrost operation will be described. When a defrost start condition is satisfied during heating operation, the control device 21 switches the operation mode from heating operation to defrost operation. The defrost start condition is, for example, that the temperature indicated by the measurement result of the refrigerant temperature sensor 31 is equal to or lower than a first defrost temperature. The first defrost temperature is a temperature at which frost may form on the heat exchanger 13 when the outside air temperature is low, for example, 0°C. Furthermore, when a defrost termination condition is satisfied during defrost operation, the control device 21 switches the operation mode from defrost operation to heating operation. The defrost termination condition is, for example, that the temperature indicated by the measurement result of the refrigerant temperature sensor 31 is higher than a second defrost temperature. The second defrost temperature is a temperature at which defrosting is sufficiently expected to be completed for the refrigerant that has passed through the heat exchanger 13, for example, 0°C.

[0024] The control of the operation of the bottom plate heater 51 will now be outlined. The control device 21 controls the bottom plate heater 51 based on the outdoor temperature and outdoor humidity during heating and defrosting operations. In particular, if the control device 21 determines that the outdoor air temperature and humidity are low and that the outdoor temperature has not changed significantly since the initial heating operation, the control device 21 does not operate the bottom plate heater 51 during subsequent heating operations and operates the bottom plate heater 51 only during defrosting operations. The control device 21 determines that an outdoor temperature below a first control temperature is a low temperature. The first control temperature is a temperature at which water can freeze on the bottom plate, such as 0°C. In other words, if the outdoor air temperature is below the first control temperature, water can freeze on the bottom plate 41 unless the bottom plate heater 51 is turned on.

[0025] After the start of heating operation, the control device 21 calculates the outside air temperature as the average of the measurement results for a predetermined time period while the blower 14 is operating and air is flowing around the outside air temperature sensor 32. The predetermined time period is, for example, two or three minutes. The control device 21 monitors the outside air temperature during heating operation and measures the outside air temperature in the same manner at each determination timing.

[0026] In particular, the control device 21 determines whether the outdoor air humidity is low based on the time required for the defrosting operation. Hereinafter, the time required for the defrosting operation is referred to as the defrosting time. When the outdoor air humidity is low, very little frost forms on the heat exchanger 13. The control device 21 determines that the outdoor air humidity is low if the defrosting time is shorter than the reference time. The reference time is a defrosting time that is sufficiently long enough to ensure that only a small amount of frost forms on the heat exchanger 13, e.g., three minutes. Note that the reference time is set differently depending on the size of the heat exchanger 13. As described above, in the first embodiment, the amount of frost that forms on the heat exchanger 13 varies depending on the outdoor air humidity, and the defrosting time can be said to indirectly indicate the amount of frost. Therefore, the control device 21 determines whether the outdoor air humidity is low based on the defrosting time.

[0027] Next, a detailed description will be given of the control of the operation of bottom plate heater 51. During heating operation, if the outside air temperature is equal to or higher than the first control temperature, control device 21 always turns off bottom plate heater 51. On the other hand, during heating operation, if the outside air temperature is lower than the first control temperature, control device 21 turns on bottom plate heater 51.

[0028] When the control device 21 turns on the bottom plate heater 51 when the outside air temperature is below the first control temperature, the control device 21 continues to turn on the bottom plate heater 51 if the outside air temperature is equal to or higher than the second control temperature. The second control temperature is lower than the first control temperature, for example, -7°C. This is because the humidity in the air is particularly high in the temperature range of -7°C to 0°C. In other words, in this temperature range, there is a high possibility of a large amount of frost forming on the heat exchanger 13. On the other hand, if the outside air temperature is below the second control temperature, the humidity in the air is low, and there may be very little frost forming on the heat exchanger 13. For this reason, in this case, the control device 21 may turn off the bottom plate heater 51 in combination with other conditions.

[0029] When the outdoor air temperature is equal to or higher than the second control temperature and the bottom plate heater 51 is ON, if the defrosting time exceeds the reference time, the control device 21 continues to turn on the bottom plate heater 51. This is because, if the defrosting time is long, it is assumed that the outdoor air is not low in humidity and that a large amount of frost has formed on the heat exchanger 13. If the bottom plate heater 51 is not turned on when a large amount of frost has formed on the heat exchanger 13, water accumulated on the bottom plate 41 may freeze during heating operation after the defrosting operation.

[0030] On the other hand, if the defrosting time is less than the reference time, the control device 21 turns off the bottom plate heater 51 after the operation duration has elapsed after the defrosting operation ends. The operation duration is the time until the rotation speed of the fan motor 14a exceeds a predetermined rotation speed after the heating operation is resumed. When the heating operation is resumed after the defrosting operation, the rotation speed of the fan motor 14a of the outdoor unit 2 gradually increases as the rotation speed of the compressor 11 gradually increases. As the rotation speed of the fan motor 14a increases, the amount of heat dissipated from the surface of the bottom plate heater 51 increases, thereby reducing the ability to melt ice on the bottom plate 41. The operation duration is determined taking these factors into consideration and from the perspective of maintaining energy-saving performance, and is, for example, 5 minutes. On the other hand, when the rotation speed of the fan motor 14a is low, the air flow velocity around the bottom plate heater 51 is low, resulting in low heat transfer due to convection around the bottom plate heater 51 and low heat dissipation from the surface of the bottom plate heater 51. The reason why the rotation speed of the compressor 11 is gradually increased at the start of the heating operation is to avoid a sudden increase in speed, which would cause uneven temperature inside the compressor 11 and lead to breakdown.

[0031] Even if the control device 21 turns off the bottom plate heater 51 after the defrosting operation has been completed and the operating time has elapsed, if the change in outside air temperature since the start of heating operation is equal to or greater than the third control temperature, the control device 21 turns on the bottom plate heater 51 again. This is because even after the heating operation is initially started, a large change in outside air temperature may occur due to rainfall, snowfall, or the end of rainfall or snowfall. The third control temperature is, for example, 2°C.

[0032] On the other hand, when the operation duration has elapsed after the defrosting operation and the bottom plate heater 51 is turned off, if the change in outside air temperature since the start of the heating operation is less than the third control temperature, the bottom plate heater 51 is not operated during subsequent heating operations and is operated only during the defrosting operation. Note that the change in outside air temperature is the absolute value of the difference between the outside air temperature measured at the start of the first heating operation and the outside air temperature measured at the time of control. Furthermore, the change in outside air temperature may be calculated based on the most recent heating operation rather than the first heating operation.

[0033] Here, an example of the hardware configuration of the control device 21 will be described. Fig. 6 is a hardware configuration diagram of the control device 21 according to the first embodiment. When the various functions of the control device 21 are executed by hardware, the control device 21 is configured by a processing circuit 61 as shown in Fig. 6. The processing circuit 61 corresponds to, for example, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination thereof.

[0034] Another example of the hardware configuration of the control device 21 will now be described. FIG. 7 is a hardware configuration diagram of the control device 21 according to the first embodiment. When each function of the control device 21 is executed by software, the control device 21 is configured with a processor 62 such as a CPU and a memory 63, as shown in FIG. 7. FIG. 7 shows that the processor 62 and the memory 63 are communicably connected to each other via a bus 64. When each function is executed by software, the function of the control device 21 is realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in the memory 63. The processor 62 realizes the functions of the control device 21 by reading and executing the programs stored in the memory 63.

[0035] The memory 63 may be a non-volatile semiconductor memory such as a ROM, a flash memory, an EPROM, or an EEPROM. Alternatively, a volatile semiconductor memory such as a RAM may be used as the memory 63. Furthermore, the memory 63 may be a removable recording medium such as a magnetic disk, a flexible disk, an optical disk, a CD, an MD, or a DVD.

[0036] Here, the operation of the control device 21 will be described using Figure 8. Figure 8 is a flowchart showing the operation of the control device 21 according to the first embodiment. Here, the control of the bottom plate heater 51 when the air conditioner 1 is performing heating operation will be mainly described. First, the control device 21 determines whether the outside air temperature is equal to or higher than the first control temperature (step S1). If the outside air temperature is equal to or higher than the first control temperature (step S1: YES), the control device 21 keeps the bottom plate heater 51 OFF until the outside air temperature falls below the first control temperature.

[0037] If the outside air temperature is lower than the first control temperature (step S1: NO), the control device 21 turns on the bottom plate heater 51 (step S3). Then, the control device 21 determines whether the outside air temperature is equal to or higher than the second control temperature (step S4). If the outside air temperature is equal to or higher than the second control temperature (step S4: YES), the control device 21 performs a defrosting process (step S5).

[0038] Here, the defrosting process will be described using FIG. 9 . FIG. 9 is a flowchart showing the operation of the control device 21 according to the first embodiment. FIG. 9 is a flowchart showing the defrosting process described in FIG. 8 . First, the control device 21 determines whether the defrosting start condition is satisfied (step S11). If the defrosting start condition is not satisfied (step S11: NO), the control device 21 does not perform the defrosting operation and keeps the bottom plate heater 51 ON until a change occurs in the determination in step S1, S4, or S11. Next, the control device 21 determines whether the bottom plate heater 51 is ON (step S12). If the bottom plate heater 51 is OFF (step S12: NO), the control device 21 turns the bottom plate heater 51 ON (step S13) and starts the defrosting operation (step S14).

[0039] The control device 21 determines whether the defrost termination condition is satisfied at predetermined intervals (step S15). If the defrost termination condition is not satisfied (step S15: NO), the control device 21 continues the defrost operation until the defrost termination condition is satisfied. If the defrost termination condition is satisfied (step S15: YES), the control device 21 ends the defrost operation (step S16), and the defrosting process ends. Returning to FIG. 8, when the defrosting process in step S5 ends, the control device 21 keeps the bottom plate heater 51 ON until a change occurs in the determination in step S1 or S4.

[0040] Even if the outdoor air temperature is lower than the second control temperature, the control device 21 performs a defrosting process (step S6). The defrosting process in step S6 is the same as the defrosting process described in step S5, and therefore will not be described here. After the defrosting process in step S6 is completed, if the defrosting time exceeds the reference time (step S7: YES), the control device 21 determines that the outdoor air is not low in humidity and keeps the bottom plate heater 51 ON until a change occurs in the determination in step S1, S4, or S7.

[0041] If the defrosting time is less than the reference time (step S7: NO), the control device 21 determines that the outdoor air has low humidity and turns off the bottom plate heater 51 after the operation duration (step S8). The control device 21 then determines whether the change in outdoor air temperature is equal to or greater than the third control temperature (step S9). If the change in outdoor air temperature is equal to or greater than the third control temperature (step S9: YES), the control device 21 repeats the process from step S1. If the change in outdoor air temperature is less than the third control temperature (step S9: NO), the control device 21 repeats the process from step S4. At this time, until a change occurs in the determination in steps S1, S4, S7, or S9, the control device 21 does not operate the bottom plate heater 51 during heating operation and keeps the bottom plate heater 51 ON only during defrosting operation.

[0042] As described above, the outdoor unit 2 of the air conditioner 1 of embodiment 1 controls the base plate heater 51 based on the outdoor air temperature and outdoor air humidity during heating operation and defrosting operation. In an environment with low outdoor temperature and humidity, little frost forms on the heat exchanger 16 during heating operation, and almost no water is drained from the heat exchanger 16 to the base plate 41. For this reason, the outdoor unit 2 of the air conditioner 1 of the present disclosure can limit the time that power is applied to the heater provided on the bottom plate 41, thereby reducing power consumption.

[0043] Specifically, the control device 21 of the first embodiment operates the bottom plate heater 51 during defrosting operation, operates the bottom plate heater 51 during heating operation when it is determined that the outdoor air is at a low temperature, and stops the bottom plate heater 51 when it is determined that the outdoor air is at a low temperature and low humidity. In this way, the outdoor unit 2 of the air conditioner 1 can reduce power consumption by switching the operating state of the bottom plate heater 51 during heating operation and limiting the power-on time.

[0044] Furthermore, the control device 21 of the first embodiment operates the bottom plate heater 51 when it determines that the temperature of the outdoor air is below the first control temperature and equal to or higher than the second control temperature during heating operation, and stops the bottom plate heater 51 when it determines that the outdoor air is below the second control temperature and has low humidity. In this way, when a large amount of frost is expected, the bottom plate heater 51 is operated during heating operation to prevent water from freezing on the bottom plate 41.

[0045] Furthermore, in the first embodiment, a humidity sensor is not required because whether the outdoor air has low humidity is determined based only on the defrosting time, i.e., the amount of frost formed on the heat exchanger 13. Therefore, the humidity state of the outdoor air can be determined more inexpensively than when a humidity sensor is used.

[0046] Although the above is a description of the embodiment of the present disclosure, the present disclosure is not limited to the configuration of the above embodiment, and various modifications or combinations are possible within the scope of the technical concept. For example, the defrost start condition may be that a predetermined time has elapsed since the start of heating operation. Similarly, the defrost end condition may be that a predetermined time has elapsed since the start of defrost operation.

[0047] Furthermore, in the first embodiment, the control method for the bottom plate heater 51 was described based on the flowcharts shown in Figures 8 and 9, but the control method for the bottom plate heater 51 is not particularly limited. For example, one or more of steps S4, S5, S8, or S9 may be omitted. Even in this case, if the control device 21 determines that the outdoor air is at a low temperature and humidity based on the measurement results of the outdoor air temperature sensor 32 and the time required for defrosting operation, it does not operate the bottom plate heater 51 during heating operation and operates the bottom plate heater 51 only during defrosting operation. In other words, the outdoor unit 2 of the air conditioner 1 in the first embodiment does not operate the bottom plate heater 51 if it determines that the amount of frost on the heat exchanger 13 is small. Therefore, power consumption can be reduced by limiting the time that power is supplied to the heater provided on the bottom plate 41.

[0048] 8 may be any time set by the user. In this case, the user sets the operation duration time based on the model of the air conditioner 1 and the environment in which the air conditioner 1 is installed. The operation duration time may be set before the defrosting operation is performed, or may be set by visually checking the state of drainage from the heat exchanger 13 after the defrosting operation is completed.

[0049] The operation duration may also be determined by providing a drain sensor on the bottom plate 41. The drain sensor is, for example, attached to the lowest position of the bottom plate 41 and is a sensor that detects whether the drain sensor itself is submerged in water. After the defrosting operation, the control device 21 periodically communicates with the drain sensor. The control device 21 determines that drainage is complete when, after receiving a signal from the drain sensor indicating that the drain sensor is submerged in water, the control device 21 receives a signal indicating that the drain sensor is not submerged in water. The control device 21 may determine the operation duration as the time from the end of the defrosting operation to the completion of drainage.

[0050] Alternatively, a humidity sensor may be provided in the outdoor unit 2, and the outdoor air may be determined to be low in humidity based on the measurement results of the humidity sensor. The installation location of the humidity sensor may be determined based on, for example, the same criteria as those described for the outdoor air temperature sensor. The control device 21 determines that the outdoor air is low in humidity when the humidity of the outdoor air measured by the humidity sensor is equal to or lower than a threshold value. The threshold value may be, for example, 20%, a level at which the amount of frost formation on the heat exchanger 13 is expected to be small. The humidity sensor measurement result and the defrosting time may be combined to determine whether the outdoor air is low in humidity. In this case, the low humidity of the outdoor air can be determined more accurately. Alternatively, the determination based on the defrosting time may be omitted, and the low humidity of the outdoor air may be determined solely based on the measurement results of the humidity sensor.

[0051] REFERENCE SIGNS LIST 1 Air conditioner, 2 Outdoor unit, 3 Indoor unit, 11 Compressor, 12 Flow path switching device, 13 Heat exchanger, 14 Blower, 14a Fan motor, 15 Throttle device, 16 Heat exchanger, 21 Control device, 31 Refrigerant temperature sensor, 32 Outdoor air temperature sensor, 40 Housing, 41 Bottom plate, 41a Drainage hole, 42 Front panel, 42a Fan cover, 43 Side portion, 44 Back portion, 45 Top panel, 51 Bottom plate heater, 61 Processing circuit, 62 Processor, 63 Memory, 64 Bus.

Claims

1. A compressor that compresses a refrigerant; a heat exchanger through which the refrigerant discharged from the compressor flows; A flow path switching device that switches the flow direction of the refrigerant; a housing for housing the compressor, the heat exchanger, and the flow path switching device; a bottom plate heater provided on a bottom plate of the housing for heating water dropped from the heat exchanger; A control device that controls the compressor and the flow path switching device to perform a heating operation and a defrosting operation to remove frost adhering to the heat exchanger during the heating operation, The control device includes: During the heating operation and the defrosting operation, the bottom plate heater is controlled based on an outside air temperature and an outside air humidity. When the time required for the defrosting operation is shorter than a reference time, it is determined that the outside air humidity is low. Air conditioner outdoor unit.

2. When the control device determines that the outdoor air has a low temperature and a low humidity, the control device does not operate the bottom plate heater during the heating operation and operates the bottom plate heater only during the defrosting operation. An outdoor unit for an air conditioner according to claim 1.

3. The control device includes: Operate the bottom plate heater during the defrosting operation; During the heating operation, when it is determined that the outdoor air is at a low temperature, the bottom plate heater is operated, and when it is determined that the outdoor air is at the low temperature and at a low humidity, the bottom plate heater is stopped.

3. An outdoor unit for an air conditioner according to claim 1 or 2.

4. A compressor for compressing a refrigerant; a heat exchanger through which the refrigerant discharged from the compressor flows; A flow path switching device that switches the flow direction of the refrigerant; a housing for housing the compressor, the heat exchanger, and the flow path switching device; a bottom plate heater provided on a bottom plate of the housing for heating water dropped from the heat exchanger; A control device that controls the compressor and the flow path switching device to perform a heating operation and a defrosting operation to remove frost adhering to the heat exchanger during the heating operation, The control device includes: During the heating operation and the defrosting operation, the bottom plate heater is controlled based on an outside air temperature and an outside air humidity. When it is determined that the outdoor air has a low temperature and a low humidity, and when the temperature difference of the outdoor air after the start of the heating operation is less than a predetermined threshold value, the bottom plate heater is not operated during the heating operation, and the bottom plate heater is operated only during the defrosting operation. Air conditioner outdoor unit.

5. A compressor for compressing a refrigerant; a heat exchanger through which the refrigerant discharged from the compressor flows; A flow path switching device that switches the flow direction of the refrigerant; a housing for housing the compressor, the heat exchanger, and the flow path switching device; a bottom plate heater provided on a bottom plate of the housing for heating water dropped from the heat exchanger; A control device that controls the compressor and the flow path switching device to perform a heating operation and a defrosting operation to remove frost adhering to the heat exchanger during the heating operation, The control device includes: During the heating operation and the defrosting operation, the bottom plate heater is controlled based on an outside air temperature and an outside air humidity. Operate the bottom plate heater during the defrosting operation; During the heating operation, when it is determined that the temperature of the outdoor air is lower than a first control temperature and equal to or higher than a second control temperature that is lower than the first control temperature, the bottom plate heater is operated, and when it is determined that the outdoor air is lower than the second control temperature and has low humidity, the bottom plate heater is stopped. Air conditioner outdoor unit.

6. The control device includes: When the outdoor air temperature is lower than a first control temperature, the outdoor air temperature is determined to be a low temperature.

5. An outdoor unit for an air conditioner according to claim 1, 2 or 4.

7. The control device determines that the outside air humidity is low when the time required for the defrosting operation is shorter than a reference time.

6. An outdoor unit for an air conditioner according to claim 4 or 5.