Air conditioning device

Abstract

To provide an air conditioning device capable of preventing drain water dripped in a defrosting operation from being frozen.SOLUTION: Freezability determination means 50 for determining whether or not there is a risk of freezing drain water dripped to a base plate 44 as a drain receiving part by performing normal cycle defrosting is provided to an outdoor side control part 29. The outdoor side control part 29 performs reverse cycle defrosting when the freezability determination means 50 determines that there is the risk of freezing the drain water. When a predetermined defrosting condition is satisfied, a detection value of an ambient air temperature sensor 28 is higher than a predetermined value T0 and the normal cycle defrosting should be performed. When it is determined that there is a risk of freezing the drain water dripped to the base plate 44 by performing the normal cycle defrosting, the reverse cycle defrosting is performed to rise temperature of the drain water dripped from an outdoor heat exchanger 24. Therefore, it can prevent constituting members in outdoor equipment 20 from being damages due to freezing of the drain water on the base plate 44.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] This invention relates to an air conditioner capable of defrosting an outdoor heat exchanger.

Background Art

[0002] Conventionally, in this type of device, a refrigerant circuit in which a compressor, an indoor heat exchanger, an expansion valve, and an outdoor heat exchanger are sequentially connected is provided, and a four-way valve capable of switching the inflow destination of the refrigerant discharged from the compressor to either the indoor heat exchanger or the outdoor heat exchanger is installed in the middle of the refrigerant circuit. When it is determined that a predetermined defrosting condition is satisfied, if the outside air temperature is higher than a predetermined value, forward cycle defrosting is performed in which the refrigerant discharged from the compressor is circulated through the indoor heat exchanger, the expansion valve, and the outdoor heat exchanger. If the outside air temperature is equal to or lower than the predetermined value, reverse cycle defrosting is performed in which the refrigerant discharged from the compressor is circulated through the outdoor heat exchanger, the expansion valve, and the indoor heat exchanger to remove the frost adhering to the outdoor heat exchanger. (For example, Patent Document 1)

[0003] In addition, a heater is provided in a drain receiving portion located below the outdoor heat exchanger, and during defrosting of the outdoor heat exchanger, the heater is driven to prevent the drain water dripping into the drain receiving portion from freezing due to defrosting. (For example, Patent Document 2)

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in this conventional device, when a predetermined defrosting condition is satisfied and normal-cycle defrosting is performed, if the temperature of the refrigerant sent from the indoor heat exchanger to the outdoor heat exchanger is low due to a low room temperature in the room where the indoor heat exchanger is installed, etc., the surface temperature of the outdoor heat exchanger during normal-cycle defrosting will decrease, and the temperature of the drain water dripping from the outdoor heat exchanger will become low. If the temperature of the drain water dripping from the outdoor heat exchanger is low, there is a possibility that the drain water will freeze in the drain receiving part. When the frozen drain water grows, the risk of damage to the components in the outdoor unit where the outdoor heat exchanger is installed increases.

[0006] As a countermeasure, there is a method of preventing the freezing of drain water by installing a heating heater in the drain receiving part as in Patent Document 2 and driving the heating heater during defrosting. However, installing a heating heater in the drain receiving part becomes a factor in increasing the cost of the product, and since the power consumption increases due to the driving of the heating heater, it is not a preferable countermeasure and there is room for improvement.

Means for Solving the Problems

[0007] In order to solve the above problems, in claim 1 of the present invention, a refrigerant circuit in which a compressor, an indoor heat exchanger, an expansion valve, and an outdoor heat exchanger are sequentially connected and refrigerant flows, A four-way valve installed in the middle of the refrigerant circuit and capable of switching the inflow destination of the refrigerant discharged from the compressor to either the indoor heat exchanger or the outdoor heat exchanger, An outdoor air temperature sensor for detecting the outdoor air temperature, Normal-cycle defrosting in which the refrigerant discharged from the compressor is circulated through the indoor heat exchanger, the expansion valve, and the outdoor heat exchanger to defrost the outdoor heat exchanger, Reverse-cycle defrosting in which the refrigerant discharged from the compressor is circulated through the outdoor heat exchanger, the expansion valve, and the indoor heat exchanger to defrost the outdoor heat exchanger, A drain receiving part that is at least located below the outdoor heat exchanger and receives the drain water dripping from the outdoor heat exchanger by performing the normal-cycle defrosting or the reverse-cycle defrosting, When a predetermined defrosting condition is satisfied, if the detected value by the outside air temperature sensor is higher than a predetermined value, the forward cycle defrosting is performed, and if it is equal to or lower than the predetermined value, the reverse cycle defrosting is performed. A control unit that switches the four-way valve is provided. The control unit is provided with a freezing possibility determination means for determining whether the drain water dripping into the drain receiving part may freeze due to the execution of the forward cycle defrosting. The control unit is characterized in that when the freezing possibility determination means determines that the drain water may freeze, the reverse cycle defrosting is performed.

[0008] In addition, in claim 2, a first temperature sensor for detecting the temperature of the medium that exchanges heat with the indoor heat exchanger is installed near the indoor heat exchanger. The freezing possibility determination means is characterized in that if the detected value by the first temperature sensor is equal to or lower than a first predetermined value, the drain water may freeze.

[0009] In addition, in claim 3, a second temperature sensor for detecting the temperature of the indoor heat exchanger is installed in the indoor heat exchanger. The freezing possibility determination means is characterized in that if the detected value by the second temperature sensor is equal to or lower than a second predetermined value, it is determined that the drain water may freeze.

[0010] In addition, in claim 4, a third temperature sensor for detecting the temperature of the outdoor heat exchanger is installed in the outdoor heat exchanger. The freezing possibility determination means is characterized in that if the detected value by the third temperature sensor is equal to or lower than a third predetermined value, it is determined that the drain water may freeze.

[0011] In addition, in claim 5, a fourth temperature sensor for detecting the temperature of the refrigerant sucked into the compressor is installed in the refrigerant circuit. The freezing possibility determination means is characterized in that if the detected value by the fourth temperature sensor is equal to or lower than a fourth predetermined value, it is determined that the drain water may freeze.

[0012] In addition, Claim 6 is provided with counting means for counting the execution time of the forward cycle defrosting, wherein the freezing possibility determination means determines that there is a possibility that the drain water freezes if the execution time of the previous forward cycle defrosting counted by the counting means is equal to or longer than a predetermined time.

Advantages of the Invention

[0013] According to the present invention, a control unit is provided with freezing possibility determination means for determining the presence or absence of the possibility that drain water dripping into a drain receiving part freezes due to the execution of forward cycle defrosting. When the control unit determines, based on the freezing possibility determination means, that there is a possibility that the drain water freezes, the control unit performs reverse cycle defrosting. Therefore, it is possible to prevent the drain water dripping into the drain receiving part from freezing without causing an increase in cost, and to prevent the components inside the outdoor unit from being damaged by the frozen drain water. As a result, the product quality is improved.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0015] Next, embodiments of the present invention will be described based on the accompanying drawings.

[0016] <Example 1> Referring to FIG. 1, 1 is an air conditioner, and the air conditioner 1 is composed of an indoor unit 10 installed indoors and an outdoor unit 20 installed outdoors. The indoor unit 10 and the outdoor unit 20 are connected by a refrigerant circuit 30 through which refrigerant circulates inside.

[0017] Inside the indoor unit 10, there are provided an indoor heat exchanger 11 having a plurality of tubes and fins through which refrigerant flows to exchange heat with indoor air, an indoor fan 12 for supplying indoor air to the indoor heat exchanger 11, a room temperature sensor 13 as a first temperature sensor for detecting the temperature of indoor air sucked into the indoor heat exchanger 11, an indoor heat exchange temperature sensor 14 as a second temperature sensor installed in the tubes constituting the indoor heat exchanger 11 for detecting the temperature of the refrigerant flowing inside the indoor heat exchanger 11, and an indoor side control unit 15 composed of a microcomputer that issues operation instructions to each actuator based on input information from each sensor. By circulating high-temperature or low-temperature refrigerant through the indoor heat exchanger 11 and driving the indoor fan 12 to supply indoor air to the indoor heat exchanger 11, air conditioning of the room where the indoor unit 10 is provided is performed.

[0018] Inside the outdoor unit 20, there are a compressor 21 that compresses the refrigerant to make it high-temperature and high-pressure, a four-way valve 22 that changes the inflow destination of the refrigerant, an expansion valve 23 that expands the refrigerant to make it low-temperature and low-pressure, an outdoor heat exchanger 24 that includes a plurality of tubes and fins and through which the refrigerant flows inside the tubes to exchange heat with the outdoor air, an outdoor fan 25 that supplies outside air toward the outdoor heat exchanger 24, an outdoor heat exchange temperature sensor 26 as a third temperature sensor installed in the tubes that constitute the outdoor heat exchanger 24 to detect the temperature of the refrigerant flowing inside the outdoor heat exchanger 24, a discharge temperature sensor 27a that detects the temperature of the refrigerant discharged from the compressor 21, a suction temperature sensor 27b as a fourth temperature sensor that detects the temperature of the refrigerant sucked into the compressor 21, an outside air temperature sensor 28 that detects the temperature of the outside air sucked into the outdoor unit 20 by the outdoor fan 25, and an outdoor side control unit 29 composed of a microcomputer that issues operation instructions to each actuator based on the input information from each sensor. By switching the direction of the four-way valve 22, it is possible to switch between cooling operation and heating operation.

[0019] The compressor 21, the four-way valve 22, the indoor heat exchanger 11, the expansion valve 23, and the outdoor heat exchanger 24 are sequentially connected by a refrigerant circuit 30. By switching the four-way valve 22, the flow direction of the refrigerant flowing in the refrigerant piping can be switched.

[0020] When an instruction to perform cooling operation, which is a type of normal operation, is issued, the four-way valve 22 is switched so that the inflow destination of the refrigerant discharged from the compressor 21 becomes the outdoor heat exchanger 24. As a result, the refrigerant made high-temperature and high-pressure by the compressor 21 exchanges heat with the outside air in the outdoor heat exchanger 24 and releases heat. At this time, when the outdoor fan 25 operates, the outside air is forcibly flowed around the outer periphery of the outdoor heat exchanger 24 to promote heat exchange. The refrigerant that has passed through the outdoor heat exchanger 24 and released heat is depressurized in the expansion valve 23, and its temperature decreases. The refrigerant with the decreased temperature is sent to the indoor unit 10.

[0021] In the indoor unit 10, air is introduced when the indoor fan 12 operates. The introduced air passes through the outer periphery of the indoor heat exchanger 11 and is blown into the room. The indoor heat exchanger 11 is supplied with the refrigerant cooled in the outdoor unit 20. The air passing through the outer periphery of the indoor heat exchanger 11 exchanges heat with the refrigerant and is cooled. The cooled air is blown into the room.

[0022] When an instruction to perform heating operation, which is a type of normal operation, is issued, the four-way valve 22 is switched so that the inflow destination of the refrigerant discharged from the compressor 21 becomes the indoor heat exchanger 11. Thereby, the refrigerant circulates in the reverse direction to that during the cooling operation, and the high-temperature refrigerant is sent to the indoor heat exchanger 11. Due to the driving of the indoor fan 12, high-temperature air is blown into the room.

[0023] Refer to FIGS. 2, 3, and 4. The outdoor unit 20 is composed of a case 40 with a box-shaped appearance, and includes a front panel 41 that covers the front and the left side, a side panel 42 that covers the right side, an upper panel 43 that covers the upper side, and a base plate 44 installed on the bottom surface and serving as a drain receiving part. In addition, an air outlet 41a is formed on the front side of the front panel 41, and the air blown by driving the outdoor fan 25 pivotally supported by the fan motor 25a is blown out. In addition, a plurality of slits 41b are formed on the left side surface side of the front panel 41, and the air around the outdoor unit 20 is sucked in through the slits 41b when the outdoor fan 25 is driven.

[0024] An L-shaped outdoor heat exchanger 24 is installed on the base plate 44 from the rear to the left side, and a drain hole 44a penetrating to the outside of the case 40 is formed near the center of the rear. Since the base plate 44 slopes downward toward the drain hole 44a, rainwater that has entered the case 40 and the drain water generated during the defrosting operation described later are discharged outside the case 40.

[0025] Refer to FIG. 5. The outdoor control unit 29 includes a freezing possibility determination means 50 that determines whether the drain water dripping from the outdoor heat exchanger 24 may freeze on the base plate 44 during positive cycle defrosting, which is a type of defrosting operation described later, and a counting means 51 that counts the execution time of the positive cycle defrosting. Further, the indoor control unit 15 and the outdoor control unit 29 are connected by a communication line, and can mutually recognize information regarding the detection values of the respective sensors and the drive counts of the actuators, etc.

[0026] Next, the defrosting operation in Embodiment 1 will be described in detail.

[0027] During the heating operation, when the temperature of the outside air passing through the outdoor heat exchanger 24 is low, frost adheres to the surface of the outdoor heat exchanger 24, and as the frost grows, the heat exchange efficiency deteriorates. Therefore, the outdoor control unit 29, during the heating operation, based on the outside air temperature detected by the outside air temperature sensor 28 and the detection value at the outdoor heat exchange temperature sensor 26, when a predetermined defrosting condition for determining that a large amount of frost has adhered to the outdoor heat exchanger 24 is satisfied, a defrosting operation for removing the frost adhering to the outdoor heat exchanger 24 is performed. The defrosting operation includes positive cycle defrosting and reverse cycle defrosting, and either one is performed at the timing when the predetermined defrosting condition is satisfied.

[0028] Positive cycle defrosting is performed by fully opening the expansion valve 23 while maintaining the refrigerant flow direction during the heating operation, and sending the high-temperature refrigerant discharged from the compressor 21 to the outdoor heat exchanger 24 via the indoor heat exchanger 11 and the expansion valve 23. It is performed when the outside air temperature is equal to or higher than a predetermined value when the predetermined defrosting condition is satisfied, and when the refrigerant sent to the outdoor heat exchanger 24 is not so high-temperature but defrosting is still possible.

[0029] Reverse cycle defrosting is performed by switching the four-way valve 22 so that the refrigerant flow direction is the same as that during the cooling operation, and sending the high-temperature refrigerant discharged from the compressor 21 to the outdoor heat exchanger 24. It is performed when the outside air temperature is lower than a predetermined value when the predetermined defrosting condition is satisfied, and when the refrigerant sent to the outdoor heat exchanger 24 is not high-temperature enough to perform sufficient defrosting.

[0030] Here, when a predetermined defrosting condition is satisfied and normal-cycle defrosting is performed, the room temperature is low shortly after the start of the heating operation, or since the indoor unit 10 has a ventilation function, it is necessary to continue driving the indoor fan 12 by blowing out the air including the outside air from the indoor unit 10 even during the defrosting operation. Therefore, the temperature of the indoor heat exchanger 11 during normal-cycle defrosting may be low. When the temperature of the indoor heat exchanger 11 is low during normal-cycle defrosting, the temperature of the refrigerant sent from the indoor heat exchanger 11 to the outdoor heat exchanger 24 becomes low. As a result, even if the frost adhering to the outdoor heat exchanger 24 can be removed, the temperature of the drain water dripping from the outdoor heat exchanger 24 due to the removal of the frost decreases, and combined with the low temperature of the outdoor heat exchanger 24, the possibility of the drain water freezing inside the base plate 44 increases.

[0031] When the drain water freezes inside the base plate 44, the drain water cannot be drained from the drain hole 44a and the frozen drain water inside the base plate 44 grows. When the frozen drain water grows, there is a higher risk that the frozen drain water comes into contact with the components installed inside the case 40 such as the outdoor heat exchanger 24 and the outdoor fan 25, leading to damage to the components. As a solution, there is a method of installing a heater on the base plate 44 and driving the heater when the drain water may freeze to prevent the drain water from freezing. However, since the installation of the heater increases the product cost and an increase in cost due to the increase in power consumption caused by driving the heater is also expected, it is not preferable.

[0032] In the present invention, when a predetermined defrosting condition is satisfied, it is determined whether the drain water dripping from the outdoor heat exchanger 24 freezes. If it is determined that there is a possibility of freezing, reverse-cycle defrosting is performed instead of normal-cycle defrosting to prevent the drain water from freezing inside the base plate 44. This will be described in detail below.

[0033] Next, the control during the defrosting operation in the first embodiment will be described based on the flowchart of FIG. 6.

[0034] During the heating operation, the outdoor control unit 29 determines whether the outside air temperature detected by the outside air temperature sensor 28 and the detected value by the outdoor heat exchanger temperature sensor 26 are below the temperature at which frost adheres to the outdoor heat exchanger 24 and a predetermined defrosting condition is satisfied (step S101). If the predetermined defrosting condition is satisfied, it proceeds to the next step. If the predetermined defrosting condition is not satisfied, the determination in step S101 is repeated.

[0035] If the outdoor control unit 29 determines in step S101 that the predetermined defrosting condition is satisfied, it determines whether the outside air temperature detected by the outside air temperature sensor 28 is higher than a predetermined value T0 (step S102). If the outside air temperature is higher than T0, the freezing possibility determination means 50 determines whether the temperature of the indoor air, which is the medium that exchanges heat with the indoor heat exchanger 11 detected by the room temperature sensor 13, is higher than a first predetermined value T1 (step S103).

[0036] If the freezing possibility determination means 50 determines in step S103 that the detected value by the room temperature sensor 13 is higher than T1, it is considered that there is no possibility of the drain water freezing during the normal cycle defrosting. Then, the outdoor control unit 29 performs the normal cycle defrosting (step S104). Also, if the freezing possibility determination means 50 determines in step S103 that the detected value by the room temperature sensor 13 is less than or equal to T1, it is considered that there is a possibility of the drain water freezing during the normal cycle defrosting. Then, the outdoor control unit 29 performs the reverse cycle defrosting (step S105).

[0037] If the outdoor control unit 29 determines in step S102 that the outside air temperature detected by the outside air temperature sensor 28 is less than or equal to the predetermined value T0, it proceeds to step S105 and performs the reverse cycle defrosting.

[0038] When the outdoor control unit 29 performs either the forward cycle defrosting in step S104 or the reverse cycle defrosting in step S105, it determines whether the defrosting end condition is satisfied because the detected value by the outdoor heat exchanger temperature sensor 26 has risen to a predetermined value or more (step S106). If it is determined that the defrosting end condition is satisfied, the heating operation is resumed (step S107). If it is determined that the defrosting end condition is not satisfied, the determination in step S106 is repeated.

[0039] As described above, when a predetermined defrosting condition is satisfied and the outside air temperature is higher than T0, but the detected value by the room temperature sensor 13, which is the temperature of the indoor air that is the medium exchanging heat with the indoor heat exchanger 11, is T1 or lower, the freezing possibility determination means 50 determines that the temperature of the drain water dripping from the outdoor heat exchanger 24 is low in the forward cycle defrosting and the drain water freezes on the base plate 44, and the outdoor control unit 29 performs the reverse cycle defrosting. When the detected value by the room temperature sensor 13 at the start of the defrosting operation is low and it is expected that the refrigerant temperature after heat exchange in the indoor heat exchanger 11 will be low, in the forward cycle defrosting, the temperature of the refrigerant flowing into the outdoor heat exchanger 24 becomes low, and the temperature of the drain water dripping from the outdoor heat exchanger 24 due to the defrosting operation decreases. Therefore, the risk of the drain water freezing in the base plate 44 increases. At this time, by performing the reverse cycle defrosting, a high-temperature refrigerant flows into the outdoor heat exchanger 24, so the temperature of the drain water dripping from the outdoor heat exchanger 24 due to the defrosting operation can be increased. Freezing of the drain water in the base plate 44 due to the implementation of the defrosting operation can be prevented, and damage to the components in the case 40 can be avoided.

[0040] Next, the effects of Example 1 will be described.

[0041] The outdoor control unit 29 is provided with a freezing possibility determination means 50 for determining whether there is a possibility that the drain water dripping onto the base plate 44 as a drain receiving part freezes due to the execution of normal cycle defrosting. When the outdoor control unit 29 determines that there is a possibility that the drain water freezes by the freezing possibility determination means 50, it executes reverse cycle defrosting. When a predetermined defrosting condition is satisfied, although the detected value by the outside air temperature sensor 28 is higher than a predetermined value T0 and normal cycle defrosting should be executed, if it is determined that there is a possibility that the drain water dripping onto the base plate 44 freezes due to the execution of normal cycle defrosting, reverse cycle defrosting is executed so that the temperature of the drain water dripping from the outdoor heat exchanger 24 becomes high. Thus, it is possible to prevent the drain water from freezing on the base plate 44 and damaging the components inside the outdoor unit 20 in advance.

[0042] Further, the freezing possibility determination means 50 determines that there is a possibility that the drain water freezes if the detected value by the room temperature sensor 13 which is the first temperature sensor is equal to or lower than a first predetermined value T1. When a predetermined defrosting condition is satisfied and the temperature of the indoor air exchanging heat with the indoor heat exchanger 11 is low and it is expected that the temperature of the refrigerant sent from the indoor heat exchanger 11 to the outdoor heat exchanger 24 becomes low during normal cycle defrosting, reverse cycle defrosting is executed so that the temperature of the drain water dripping from the outdoor heat exchanger 24 becomes high. Thus, it is possible to prevent the drain water from freezing on the base plate 44 and damaging the components inside the outdoor unit 20 in advance.

[0043] <Example 2> Next, the control during the defrosting operation in Example 2 to which the present invention is applied will be described based on the flowchart of FIG. 7. Since the configuration of Example 2 is common to that of Example 1, the description thereof will be omitted.

[0044] During the execution of the heating operation, the outdoor control unit 29 determines whether the outside air temperature detected by the outside air temperature sensor 28 and the detected value by the outdoor heat exchange temperature sensor 26 are equal to or lower than the temperature at which frost adheres to the outdoor heat exchanger 24 and a predetermined defrosting condition is satisfied (step S201). If the predetermined defrosting condition is satisfied, it proceeds to the next step. If the predetermined defrosting condition is not satisfied, the determination in step S201 is repeated.

[0045] When the outdoor control unit 29 determines in step S201 that a predetermined defrosting condition is satisfied, it determines whether the outside air temperature detected by the outside air temperature sensor 28 is higher than a predetermined value T0 (step S202). If the outside air temperature is higher than T0, the freezing possibility determination means 50 determines whether the detected value by the indoor heat exchanger temperature sensor 14 is higher than T2, which is a second predetermined value (step S203).

[0046] When the freezing possibility determination means 50 determines in step S203 that the detected value by the indoor heat exchanger temperature sensor 14 is higher than T2, the outdoor control unit 29 performs normal cycle defrosting on the assumption that there is no possibility of the drain water freezing during normal cycle defrosting (step S204). Also, when the freezing possibility determination means 50 determines in step S203 that the detected value by the indoor heat exchanger temperature sensor 14 is equal to or lower than T2, the outdoor control unit 29 performs reverse cycle defrosting on the assumption that the drain water may freeze during normal cycle defrosting (step S205).

[0047] When the outdoor control unit 29 determines in step S202 that the outside air temperature detected by the outside air temperature sensor 28 is equal to or lower than T0, it proceeds to step S205 and performs reverse cycle defrosting.

[0048] When the outdoor control unit 29 performs either the normal cycle defrosting in step S204 or the reverse cycle defrosting in step S205, it determines whether the defrosting end condition is satisfied because the detected value by the outdoor heat exchanger temperature sensor 26 has risen to a predetermined value or more (step S206). If it determines that the defrosting end condition is satisfied, it resumes the heating operation (step S207). If it determines that the defrosting end condition is not satisfied, it repeats the determination in step S206.

[0049] As described above, when the outside air temperature when a predetermined defrosting condition is satisfied is higher than T0, but the detected value by the indoor heat exchange temperature sensor 14 is T2 or lower, the freezing possibility determination means 50 determines that in normal cycle defrosting, the temperature of the drain water dripping from the outdoor heat exchanger 24 is low, and determines that the drain water freezes on the base plate 44. The outdoor control unit 29 performs reverse cycle defrosting. When the detected value by the indoor heat exchange temperature sensor 14 at the start of the defrosting operation is low and it is expected that the refrigerant temperature after heat exchange in the indoor heat exchanger 11 is low, in normal cycle defrosting, the refrigerant temperature flowing into the outdoor heat exchanger 24 becomes low, and the temperature of the drain water dripping from the outdoor heat exchanger 24 due to the defrosting operation decreases. Therefore, the risk of the drain water freezing in the base plate 44 increases. At this time, by performing reverse cycle defrosting, a high-temperature refrigerant flows into the outdoor heat exchanger 24, so that the temperature of the drain water dripping from the outdoor heat exchanger 24 due to the defrosting operation can be increased. Freezing of the drain water in the base plate 44 due to the defrosting operation can be prevented, and damage to the components in the case 40 can be prevented.

[0050] Next, the effects of Example 2 will be described. Note that the effects common to Example 1 will be omitted from the description.

[0051] The freezing possibility determination means 50 determines that there is a possibility that the drain water freezes if the detected value by the indoor heat exchange temperature sensor 14, which is the second temperature sensor, is the second predetermined value T2 or lower. When a predetermined defrosting condition is satisfied and the detected value by the indoor heat exchange temperature sensor 14 is low and it is expected that the temperature of the refrigerant sent to the outdoor heat exchanger 24 in normal cycle defrosting is low, reverse cycle defrosting is performed so that the temperature of the drain water dripping from the outdoor heat exchanger 24 becomes high. Therefore, it is possible to prevent the drain water from freezing on the base plate 44 and damage to the components in the outdoor unit 20.

[0052] <Example 3 Next, the control during the defrosting operation in Example 3 to which the present invention is applied will be described based on the flowchart of FIG. 8. Note that the configuration of Example 3 is the same as that of Example 1, so the description will be omitted.

[0053] During the heating operation, the outdoor control unit 29 determines whether the outside air temperature detected by the outside air temperature sensor 28 and the detected value of the outdoor heat exchanger temperature sensor 26 are equal to or lower than the temperature at which frost adheres to the outdoor heat exchanger 24 and a predetermined defrosting condition is satisfied (step S301). If the predetermined defrosting condition is satisfied, the process proceeds to the next step. If the predetermined defrosting condition is not satisfied, the determination in step S301 is repeated.

[0054] If the outdoor control unit 29 determines in step S301 that the predetermined defrosting condition is satisfied, it determines whether the outside air temperature detected by the outside air temperature sensor 28 is higher than a predetermined value T0 (step S302). If the outside air temperature is higher than T0, the freezing possibility determination means 50 determines whether the detected value of the outdoor heat exchanger temperature sensor 26 is higher than T3, which is a third predetermined value (step S303).

[0055] If the freezing possibility determination means 50 determines in step S303 that the detected value of the outdoor heat exchanger temperature sensor 26 is higher than T3, the outdoor control unit 29 performs positive cycle defrosting on the assumption that there is no possibility of the drain water freezing during positive cycle defrosting by the freezing possibility determination means 50 (step S304). If the freezing possibility determination means 50 determines in step S303 that the detected value of the outdoor heat exchanger temperature sensor 26 is equal to or lower than T3, the outdoor control unit 29 performs reverse cycle defrosting on the assumption that the drain water may freeze during positive cycle defrosting by the freezing possibility determination means 50 (step S305).

[0056] If the outdoor control unit 29 determines in step S302 that the outside air temperature detected by the outside air temperature sensor 28 is equal to or lower than T0, the process proceeds to step S305 to perform reverse cycle defrosting.

[0057] When the outdoor control unit 29 performs either the forward cycle defrosting in step S304 or the reverse cycle defrosting in step S305, it determines whether the defrosting end condition is satisfied because the detected value by the outdoor heat exchanger temperature sensor 26 has risen to a predetermined value or more (step S306). If it is determined that the defrosting end condition is satisfied, the heating operation is restarted (step S307). If it is determined that the defrosting end condition is not satisfied, the determination in step S306 is repeated.

[0058] As described above, when the outside air temperature when a predetermined defrosting condition is satisfied is higher than T0, but the detected value by the outdoor heat exchanger temperature sensor 26 is T3 or lower, the freezing possibility determination means 50 determines that in the forward cycle defrosting, the temperature of the drain water dripping from the outdoor heat exchanger 24 is low and the drain water freezes on the base plate 44, and the outdoor control unit 29 performs reverse cycle defrosting. When the detected value by the outdoor heat exchanger temperature sensor 26 at the start of the defrosting operation is low, in the forward cycle defrosting, a large temperature rise of the outdoor heat exchanger 24 cannot be expected, so the temperature of the drain water dripping from the outdoor heat exchanger 24 becomes low, increasing the risk of the drain water freezing in the base plate 44. At this time, by performing reverse cycle defrosting, high-temperature refrigerant flows into the outdoor heat exchanger 24, so the temperature of the drain water dripping from the outdoor heat exchanger 24 due to the defrosting operation can be increased. Freezing of the drain water in the base plate 44 due to the defrosting operation can be prevented, and damage to the components in the case 40 can be prevented.

[0059] Next, the effects of Example 3 will be described. The effects common to Example 1 will be omitted from the description.

[0060] The freezing possibility determination means 50 determines that there is a possibility that the drain water may freeze if the detected value by the outdoor heat exchanger temperature sensor 26, which is the third temperature sensor, is equal to or lower than the third predetermined value T3. When a predetermined defrosting condition is satisfied, the detected value by the outdoor heat exchanger temperature sensor 26 is low, and in the case where it is expected that the temperature of the drain water dripping from the outdoor heat exchanger 24 will be low during normal cycle defrosting, reverse cycle defrosting is performed so that the temperature of the drain water dripping from the outdoor heat exchanger 24 becomes high. Therefore, it is possible to prevent the drain water from freezing on the base plate 44 and damaging the components inside the outdoor unit 20 in advance.

[0061] <Example 4> Next, the control during the defrosting operation in Example 4 to which the present invention is applied will be described based on the flowchart of FIG. 9. Since the configuration of Example 4 is common to that of Example 1, the description thereof will be omitted.

[0062] During the heating operation, the outdoor side control unit 29 determines whether the outside air temperature detected by the outside air temperature sensor 28 and the detected value by the outdoor heat exchanger temperature sensor 26 are equal to or lower than the temperature at which frost adheres to the outdoor heat exchanger 24 and a predetermined defrosting condition is satisfied (step S401). If the predetermined defrosting condition is satisfied, the process proceeds to the next step. If the predetermined defrosting condition is not satisfied, the determination in step S401 is repeated.

[0063] If the outdoor side control unit 29 determines in step S401 that the predetermined defrosting condition is satisfied, it determines whether the outside air temperature detected by the outside air temperature sensor 28 is higher than the predetermined value T0 (step S402). If the outside air temperature is higher than T0, the freezing possibility determination means 50 determines whether the detected value by the suction temperature sensor 27b is higher than T4, which is the fourth predetermined value (step S403).

[0064] If the freezing possibility determination means 50 determines in step S403 that the detected value by the suction temperature sensor 27b is higher than T4, the freezing possibility determination means 50 determines that there is no possibility of the drain water freezing during normal cycle defrosting, and the outdoor side control unit 29 performs normal cycle defrosting (step S404). Further, if the freezing possibility determination means 50 determines that the detected value by the suction temperature sensor 27b in step S403 is T4 or less, the outdoor side control unit 29 performs reverse cycle defrosting on the grounds that drain water may freeze during normal cycle defrosting by the freezing possibility determination means 50 (step S405).

[0065] If the outdoor side control unit 29 determines that the outside air temperature detected by the outside air temperature sensor 28 in step S402 is T0 or less, it proceeds to step S405 and performs reverse cycle defrosting.

[0066] After the outdoor side control unit 29 performs either normal cycle defrosting in step S404 or reverse cycle defrosting in step S405, it determines whether the defrosting end condition is satisfied when the detected value by the outdoor heat exchanger temperature sensor 26 has risen to a predetermined value or more (step S406). If it determines that the defrosting end condition is satisfied, it resumes the heating operation (step S407). If it determines that the defrosting end condition is not satisfied, it repeats the determination in step S406.

[0067] As described above, if the outside air temperature when a predetermined defrosting condition is satisfied is higher than T0, but the detected value by the suction temperature sensor 27b is T4 or less, the freezing possibility determination means 50 determines that the temperature of the drain water dripping from the outdoor heat exchanger 24 is low during normal cycle defrosting and the drain water freezes on the base plate 44, and the outdoor side control unit 29 performs reverse cycle defrosting. When the detected value by the suction temperature sensor 27b at the start of the defrosting operation is low, it is presumed that the outdoor heat exchanger 24 is in a low temperature state because the refrigerant temperature flowing out of the outdoor heat exchanger 24 is low. During normal cycle defrosting, a large temperature rise of the outdoor heat exchanger 24 cannot be expected, and the temperature of the drain water dripping from the outdoor heat exchanger 24 becomes low, so the risk of the drain water freezing inside the base plate 44 increases. At this time, by performing reverse cycle defrosting, high-temperature refrigerant flows into the outdoor heat exchanger 24, so the temperature of the drain water dripping from the outdoor heat exchanger 24 can be increased by the defrosting operation. Freezing of the drain water inside the base plate 44 due to the defrosting operation can be prevented, and damage to the components inside the case 40 can be avoided.

[0068] Next, the effects of Example 4 will be described. Note that the effects common to Example 1 will not be described.

[0069] When the detection value at the suction temperature sensor 27b, which is the fourth temperature sensor, of the freezing possibility determination means 50 is equal to or lower than the fourth predetermined value T4, it is determined that the drain water may freeze. When the predetermined defrosting condition is satisfied, since the temperature of the refrigerant sucked into the compressor 21 is low, the temperature of the outdoor heat exchanger 24 is low, and in the case where it is expected that the temperature of the drain water dripping from the outdoor heat exchanger 24 will be low during normal cycle defrosting, reverse cycle defrosting is performed so that the temperature of the drain water dripping from the outdoor heat exchanger 24 becomes high. Therefore, it is possible to prevent the drain water from freezing on the base plate 44 and damage to the components inside the outdoor unit 20.

[0070] <Example 5> Next, the control during the defrosting operation in Example 5 to which the present invention is applied will be described based on the flowchart of FIG. 10. Note that the configuration of Example 5 is common to that of Example 1, and thus the description thereof will be omitted.

[0071] During the heating operation, the outdoor side control unit 29 determines whether the outside air temperature detected by the outside air temperature sensor 28 and the detection value at the outdoor heat exchange temperature sensor 26 are equal to or lower than the temperature at which frost adheres to the outdoor heat exchanger 24 and a predetermined defrosting condition is satisfied (step S501). If the predetermined defrosting condition is satisfied, the process proceeds to the next step. If the predetermined defrosting condition is not satisfied, the determination in step S501 is repeated.

[0072] When it is determined in step S501 that the predetermined defrosting condition is satisfied, the outdoor side control unit 29 determines whether the outside air temperature detected by the outside air temperature sensor 28 is higher than the predetermined value T0 (step S502). If the outside air temperature is higher than T0, the freezing possibility determination means 50 determines whether the execution time of the normal cycle defrosting counted and stored by the counting means 51 is shorter than the predetermined time C (step S503).

[0073] If the freezing possibility determination means 50 determines that the execution time of the normal cycle defrosting in step S503 is shorter than the predetermined time C, the freezing possibility determination means 50 determines that there is no possibility that the drain water freezes during the normal cycle defrosting. Then, the outdoor control unit 29 performs the normal cycle defrosting and counts the execution time of the normal cycle defrosting by the counting means 51 (step S504). Also, if the freezing possibility determination means 50 determines that the execution time of the normal cycle defrosting in step S503 is equal to or longer than the predetermined time C, the freezing possibility determination means 50 determines that there is a possibility that the drain water freezes during the normal cycle defrosting. Then, the outdoor control unit 29 performs the reverse cycle defrosting (step S505). If the defrosting operation immediately preceding the determination in step S503 was the reverse cycle defrosting, it is assumed that the execution time of the normal cycle defrosting is 0, and the process proceeds to step S504.

[0074] If the outdoor control unit 29 determines that the outside air temperature detected by the outside air temperature sensor 28 in step S502 is equal to or lower than T0, it proceeds to step S505 and performs the reverse cycle defrosting.

[0075] After the outdoor control unit 29 performs either the normal cycle defrosting in step S504 or the reverse cycle defrosting in step S505, it determines whether the defrosting end condition is satisfied because the detected value by the outdoor heat exchanger temperature sensor 26 has risen to a predetermined value or more (step S506). If it determines that the defrosting end condition is satisfied, it resumes the heating operation (step S507). If it determines that the defrosting end condition is not satisfied, it repeats the determination in step S506. If the outdoor control unit 29 determines that the defrosting end condition in step S506 is satisfied during the execution of the normal cycle defrosting, it stops the counting by the counting means 51 in step S507 and stores the count value.

[0076] As described above, when the outside air temperature when a predetermined defrosting condition is satisfied is higher than T0, but if the operation time of the previous normal-cycle defrosting is equal to or longer than the predetermined time C, the freezing possibility determination means 50 determines that in the normal-cycle defrosting, the temperature of the drain water dripping from the outdoor heat exchanger 24 is low and the drain water freezes on the base plate 44, and the outdoor-side control unit 29 performs reverse-cycle defrosting. At the start of the defrosting operation, when the operation time of the previous normal-cycle defrosting is equal to or longer than the predetermined time C, it is presumed that the temperature of the refrigerant sent from the indoor heat exchanger 11 to the outdoor heat exchanger 24 is low due to the low temperature of the air exchanging heat with the indoor heat exchanger 11, and thus the time of the normal-cycle defrosting is prolonged. In the normal-cycle defrosting, a large temperature rise of the outdoor heat exchanger 24 cannot be expected, and the temperature of the drain water dripping from the outdoor heat exchanger 24 becomes low, so the risk of the drain water freezing in the base plate 44 increases. In such a case, by performing reverse-cycle defrosting, a high-temperature refrigerant flows into the outdoor heat exchanger 24, so that the temperature of the drain water dripping from the outdoor heat exchanger 24 due to the defrosting operation can be increased. Freezing of the drain water in the base plate 44 due to the implementation of the defrosting operation can be prevented, and damage to the components in the case 40 can be prevented.

[0077] Next, the effects of Example 5 will be described. The effects common to Example 1 will be omitted from the description.

[0078] If the operation time of the previous normal-cycle defrosting counted by the counting means 51 is equal to or longer than the predetermined time C, the freezing possibility determination means 50 determines that there is a possibility that the drain water freezes. When a predetermined defrosting condition is satisfied, since the operation time of the previous normal-cycle defrosting is long, the temperature of the refrigerant sent from the indoor heat exchanger 11 to the outdoor heat exchanger 24 is low, and in the normal-cycle defrosting, it is expected that the temperature of the drain water dripping from the outdoor heat exchanger 24 will be low. Therefore, by performing reverse-cycle defrosting so that the temperature of the drain water dripping from the outdoor heat exchanger 24 becomes high, it is possible to prevent the drain water from freezing on the base plate 44 and the components in the outdoor unit 20 from being damaged.

[0079] In each of the embodiments, the medium that exchanges heat with the indoor heat exchanger 11 has been described as indoor air, but it is not limited to this. In the case of a system in which a circulating fluid is circulated in a heating terminal such as a floor heating panel, a liquid refrigerant heat exchanger is installed in place of the indoor heat exchanger 11 so that the indoor heat exchanger 11 can exchange heat with the circulating fluid. In this case, if the temperature of the circulating fluid flowing into the liquid refrigerant heat exchanger is low, the temperature of the refrigerant flowing into the outdoor heat exchanger 24 will decrease. Therefore, in normal cycle defrosting, the drain water dripping from the outdoor heat exchanger 24 may freeze on the base plate 44. When performing the defrosting operation, if the temperature of the liquid refrigerant heat exchanger is below a predetermined value, reverse cycle defrosting is performed, so that it is possible to prevent the drain water dripping from the outdoor heat exchanger 24 from freezing on the base plate 44, and it has the same effect as the present invention that damage to the components in the case 40 can be prevented.

[0080] Also, it is useful to apply the present invention even in a system in which the indoor heat exchanger 11 is arranged in the outside air introduction path of the whole-house ventilation and air conditioning system of a house. In the whole-house ventilation and air conditioning system of a house, since ventilation of the house is performed for 24 hours, it is necessary to continue driving the indoor fan 12 even during the defrosting operation and supply air into the room through the indoor heat exchanger 11. Especially when the indoor temperature is low, if the indoor fan 12 is continuously driven during normal cycle defrosting, the heat dissipation of the indoor heat exchanger 11 is promoted, the temperature of the refrigerant sent to the outdoor heat exchanger 24 decreases, the temperature of the drain water dripping from the outdoor heat exchanger 24 becomes low, and the risk of the drain water freezing in the base plate 44 increases. By applying the present invention, when a predetermined defrosting condition is satisfied, if the temperature of the air including the outside air sent to the indoor heat exchanger 11 is below a predetermined value, reverse cycle defrosting is performed. Therefore, it is possible to prevent the drain water dripping from the outdoor heat exchanger 24 from freezing, and it has the same effect as the present invention that damage to the components in the case 40 can be prevented.

Explanation of reference numerals

[0081] 1 Air conditioner 10 Indoor unit 11 Indoor heat exchanger 13 Room temperature sensor 14 Indoor heat exchanger temperature sensor 20 Outdoor unit 21 Compressor 22 Four-way valve 23 Expansion valve 24 Outdoor heat exchanger 26 Outdoor heat exchanger temperature sensor 27b Suction temperature sensor 28 Ambient temperature sensor 29 Outdoor control unit 30 Refrigerant circuit 44 Base plate 50 Frosting possibility determination means 51 Counting means

Claims

1. A refrigerant circuit in which a compressor, an indoor heat exchanger, an expansion valve, and an outdoor heat exchanger are sequentially connected and refrigerant flows; A four-way valve installed in the middle of the refrigerant circuit and capable of switching the inflow destination of the refrigerant discharged from the compressor to either the indoor heat exchanger or the outdoor heat exchanger; An outdoor air temperature sensor for detecting the outdoor air temperature; Forward cycle defrosting in which the refrigerant discharged from the compressor is circulated through the indoor heat exchanger, the expansion valve, and the outdoor heat exchanger to defrost the outdoor heat exchanger; Reverse cycle defrosting in which the refrigerant discharged from the compressor is circulated through the outdoor heat exchanger, the expansion valve, and the indoor heat exchanger to defrost the outdoor heat exchanger; A drain receiving portion located at least below the outdoor heat exchanger and receiving drain water dripping from the outdoor heat exchanger by performing the forward cycle defrosting or the reverse cycle defrosting; A control unit that switches the four-way valve so that when a predetermined defrosting condition is satisfied, if the detected value by the outdoor air temperature sensor is higher than a predetermined value, the forward cycle defrosting is performed, and if it is equal to or lower than the predetermined value, the reverse cycle defrosting is performed, The control unit is provided with a freezing possibility determination means for determining whether or not the drain water dripping into the drain receiving portion due to the execution of the forward cycle defrosting may freeze; The air conditioner is characterized in that when the control unit determines, by the freezing possibility determination means, that the drain water may freeze, the reverse cycle defrosting is performed.

2. A first temperature sensor for detecting the temperature of the medium that exchanges heat with the indoor heat exchanger is installed near the indoor heat exchanger; The air conditioner according to claim 1, wherein the freezing possibility determination means determines that the drain water may freeze if the detected value by the first temperature sensor is equal to or lower than a first predetermined value.

3. A second temperature sensor for detecting the temperature of the indoor heat exchanger is installed in the indoor heat exchanger; The air conditioner according to claim 1, wherein the freezing possibility determination means determines that the drain water may freeze if the detected value by the second temperature sensor is equal to or lower than a second predetermined value.

4. A third temperature sensor for detecting the temperature of the outdoor heat exchanger is installed in the outdoor heat exchanger; The air conditioner according to claim 1, wherein the freezing possibility determination means determines that the drain water may freeze if the detected value by the third temperature sensor is equal to or lower than a third predetermined value.

5. A fourth temperature sensor for detecting the temperature of the refrigerant sucked into the compressor is installed in the refrigerant circuit, The air conditioner according to claim 1, wherein the freezing possibility determination means determines that there is a possibility that the drain water freezes if the detection value by the fourth temperature sensor is equal to or less than a fourth predetermined value.

6. Comprising counting means for counting the execution time of the positive cycle defrosting, The air conditioner according to claim 1, wherein the freezing possibility determination means determines that there is a possibility that the drain water freezes if the execution time of the previous positive cycle defrosting counted by the counting means is equal to or longer than a predetermined time.

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