JP2010032107A - Air conditioner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air conditioner capable of securely and inexpensively detecting estimation of the frost forming state and improving comfortability during heating operation by performing appropriate defrosting. <P>SOLUTION: The air conditioner includes an indoor unit and with an outdoor unit having a compressor, an outdoor air blower, an outdoor air blower motor for driving the outdoor air blower and an outdoor heat exchanger. Based on the load of the outdoor air blower during heating operation, defrosting for removing frost adhered to the outdoor heat exchanger is started. Thus, the air conditioner can securely and inexpensively detect estimation of the frost forming state and improve comfortability during heating operation by performing appropriate defrosting. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heat pump air conditioner that performs a defrosting operation for removing frost from an outdoor heat exchanger during heating operation.

  In the heat pump type air conditioner, during the heating operation, the indoor heat exchanger becomes high temperature and the outdoor heat exchanger becomes low temperature. Therefore, when the outside air temperature is low, the temperature of the outdoor heat exchanger becomes 0 ° C. or less, and moisture in the outside air adheres to the outdoor heat exchanger and becomes frost. When the heating operation is continued with frost attached to the outdoor heat exchanger, the frost grows and deteriorates the heat exchange performance of the outdoor heat exchanger. As a result, the heating capacity decreases.

  In order to prevent this, in a general heat pump type air conditioner, when frost adheres to some extent, a defrosting operation (hereinafter referred to as “defrost”) for melting the frost is performed. Defrosting is an operation in which the operating state of the air conditioner is switched from the heating operation to the cooling operation, and a high-temperature refrigerant is allowed to flow through the outdoor heat exchanger, thereby increasing the temperature of the outdoor heat exchanger and melting the attached frost. Since the defrost is in the cooling operation, the heating operation is stopped by the user. That is, defrost becomes one of the factors that reduce the comfort during heating operation of the heat pump air conditioner.

  Therefore, in the conventional technology, the frost state is estimated from the outside air temperature and the temperature of the outdoor heat exchanger, and the defrosting is not frequently performed by providing a time limit (for example, “Patent Document 1”). reference).

  However, the conventional technology using the outside air temperature and the temperature of the outdoor heat exchanger only estimates the frost formation state, and depending on the setting of the defrost start condition, defrosting is performed even when there is little frost formation. In some cases, defrosting was not performed even though there was much frost formation. In addition, the setting of the defrost start condition must be determined from the outdoor temperature and the outdoor heat exchanger temperature in the actual frosted state, and it is necessary to consider differences in heating capacity and frosting conditions, I spent a lot of time setting up.

  Therefore, it is possible to attach a humidity sensor to the outdoor unit and detect the humidity of the outside air to improve the accuracy of estimation of the frosting state. However, there are problems with the accuracy and cost of the humidity sensor, and this is a practical solution. is not.

Japanese Patent Laid-Open No. 2-85629

  This invention makes it a subject to provide the air conditioner which made the estimation of a frost formation state cheap and reliably detectable, and improved the comfort at the time of heating operation by performing an appropriate defrost.

  An air conditioner according to the present invention includes an indoor unit, a compressor, an outdoor fan, an outdoor fan motor that drives the outdoor fan, and an outdoor unit having an outdoor heat exchanger, and the load of the outdoor fan during heating operation Based on the above, defrosting for removing frost attached to the outdoor heat exchanger is started.

  ADVANTAGE OF THE INVENTION According to this invention, the estimation of a frost formation state can be detected cheaply and reliably, and the air conditioner which improved the comfort at the time of heating operation can be provided by performing an appropriate defrost.

  In the air conditioner according to the present invention, the frost formation state of the outdoor heat exchanger is determined by monitoring the load of the outdoor fan.

  FIG. 1 is a diagram showing a change in the load of the outdoor fan depending on the presence or absence of frost on the outdoor heat exchanger. During the heating operation, the outdoor blower 7 rotates at a certain rotation speed according to the heating capacity, and the load of the outdoor blower 7 becomes a constant value if the rotation speed is constant. As shown in FIG. 1, when frost is formed on the outdoor heat exchanger 3, the amount of frost attached increases according to the heating operation time, and the ventilation resistance of the outdoor heat exchanger 3 increases. When the ventilation resistance of the outdoor heat exchanger 3 increases, the load on the outdoor blower 7 increases.

  Therefore, since the ventilation resistance of the outdoor heat exchanger 3 changes depending on the amount of frost attached to the outdoor heat exchanger 3 and the load of the outdoor fan 7 also changes, the load of the outdoor fan 7 is monitored. It is possible to determine the frosting state of the outdoor heat exchanger 3 without depending on the heat exchanger temperature. That is, it is possible to determine the start of defrosting to remove frost attached to the outdoor heat exchanger based on the load of the outdoor fan during heating operation. Embodiments according to the present invention will be described below with reference to the drawings.

A first embodiment of the present invention will be described with reference to FIGS. This embodiment is an air conditioner that includes an indoor unit, an outdoor unit having a compressor 1, an outdoor fan 7, an outdoor fan motor that drives the outdoor fan 7, and an outdoor heat exchanger 3. based on the load of the outdoor blower 7, which starts the defrosting for removing the frost on the outdoor heat exchanger 3, especially if the current I _m of the outdoor blower motor 6 exceeds the defrost start current value I _D Start defrosting.

FIG. 2 is a configuration diagram of the air conditioner according to the first embodiment. In an air conditioner including an indoor unit, an outdoor unit having a compressor 1, an outdoor fan 7, an outdoor fan motor that drives the outdoor fan 7, and an outdoor heat exchanger 3, a control device 9 is provided for the outdoor fan 7. Control the number of revolutions. Controller 9, the current I _m flowing through the outdoor blower motor 6 for driving the outdoor fan is detected by the motor current detecting means, and adjusts the motor current I _m so as to hold the rotational speed of the outdoor fan 7 constant .

FIG. 3 is a diagram showing a change in the current of the outdoor fan motor depending on the presence or absence of frost on the outdoor heat exchanger. As described above, when frost adheres to the outdoor heat exchanger 3, the amount of frost increases according to the heating operation time, and the ventilation resistance of the outdoor heat exchanger 3 increases. To increase. Accordingly, as shown in FIG. 3, on the basis of the outdoor blower motor current I _m, it is possible to determine that the frost formation amount is increasing.

FIG. 4 shows a flowchart of control in the present embodiment. First, to detect the current I _m of the outdoor blower motor 6 during the heating operation. Then, if the current I _m of the outdoor blower motor 6 is equal to or less than the defrost start current value I _D continues heating operation is detected, the outdoor blower motor 6 to the detected current I _m defrost start current value I Defrost if _D is exceeded.

According to the present embodiment, in an air conditioner including an indoor unit, an outdoor unit having a compressor 1, an outdoor fan 7, an outdoor fan motor that drives the outdoor fan 7, and an outdoor heat exchanger 3, based on the load of the outdoor blower 7 during operation, which initiates the defrost to remove the frost on the outdoor heat exchanger 3, in particular the current I _m of the outdoor blower motor 6 exceeds the defrost start current value I _D Defrost starts when Therefore, appropriate defrosting can be performed according to the frost formation amount of the outdoor heat exchanger 3, and the comfort during heating operation can be improved. Moreover, since the amount of frost formation can be determined without using the outside air temperature detection means 13, the outdoor heat exchanger temperature detection means 14, or the like, the cost can be reduced.

A second embodiment of the present invention will be described with reference to FIGS. The present embodiment is an outdoor unit having an indoor unit, a compressor 1, an outdoor fan 7, an outdoor fan motor for driving the outdoor fan 7, an outdoor heat exchanger 3, and an outdoor temperature detecting means 13 for detecting the outdoor temperature. in an air conditioner comprising, which starts the defrost when the current I _m of the outdoor blower motor 6 exceeds the defrost start current value I _D, varying the motor current I _D to initiate defrost in accordance with the outside temperature It is.

  FIG. 5 is a block diagram of the air conditioner in the second embodiment. An air conditioner comprising an indoor unit and an outdoor unit having a compressor 1, an outdoor fan 7, an outdoor fan motor for driving the outdoor fan 7, an outdoor heat exchanger 3, and an outdoor temperature detecting means 13 for detecting the outdoor temperature. The control device 9 controls the rotational speed of the outdoor blower 7.

  The outdoor heat exchanger temperature decreases as the outside air temperature decreases, but the moisture contained in the air decreases as the temperature decreases. Therefore, when the outside air temperature is low, the frost formation amount of the outdoor heat exchanger 3 is also reduced. In the prior art, using this characteristic, defrosting is performed when the outdoor heat exchanger temperature falls below a certain temperature at a predetermined outside air temperature. FIG. 6 is a diagram showing the relationship between the outside air temperature and the defrost start outdoor heat exchanger temperature.

  When the outside air temperature is low and the amount of frost adhering to the outdoor heat exchanger 3 is small, it takes time until the motor current increases. In general heat pump air conditioners, the heating capacity also decreases as the outside air temperature decreases. Therefore, even if the amount of frost adhering to the outdoor heat exchanger 3 is small, the reduction in heating capacity may be large.

FIG. 7 is a diagram showing the relationship between the outside air temperature and the defrost start motor current. As shown in FIG. 7, by using the outside air temperature detecting means 13 and changing the motor current _ID for starting defrosting according to the outside air temperature, it is appropriate under the condition that the influence of the decrease in the heating capacity due to frost formation is large. Thus, it is possible to perform defrosting and to provide an air conditioner with improved comfort performance.

FIG. 8 is a flowchart of control in this embodiment. First, the outside air temperature is detected by the outside air temperature detecting means 13 during the heating operation, and the defrost start motor current _ID corresponding to the outside air temperature is calculated. Thereafter, the motor current is detected I _m, when the motor current I _m is small continues the heating operation than the defrost start motor current I _D, is greater starts defrosting.

In addition, the outdoor heat exchanger temperature detection means 14 is also used, and the defrost start control based on the outdoor air temperature and the outdoor heat exchanger temperature (defrosting is performed when the outdoor heat exchanger temperature falls below a certain temperature at a predetermined outdoor temperature ) in combination with, the final defrosting execution start may be determined by using the relationship between the outdoor blower motor current I _m and defrost start the motor current I _D.

According to the present embodiment, the outdoor unit having the indoor unit, the compressor 1, the outdoor fan 7, the outdoor fan motor that drives the outdoor fan 7, the outdoor heat exchanger 3, and the outside air temperature detecting means 13 that detects the outside air temperature. in an air conditioner and a machine, it starts the defrost when the current I _m of the outdoor blower motor 6 exceeds the defrost start current value I _D, changes the motor current I _D to initiate defrost in accordance with the outside temperature Let Therefore, appropriate defrosting can be performed according to the frost formation amount of the outdoor heat exchanger 3, and the comfort during heating operation can be improved.

A third embodiment of the present invention will be described with reference to FIG. The present embodiment is an air conditioner including an indoor unit, an outdoor unit having a compressor 1, an outdoor fan 7, an outdoor fan motor that drives the outdoor fan 7, and an outdoor heat exchanger 3. in which deviations [Delta] I _m of the motor current I _m for a predetermined period past the motor current I ₀ starts defrosting when equal to or more than the deviation [Delta] I _D of the motor current to start defrosting.

In the first and second embodiment, to start defrosting when the current I _m of the outdoor blower motor 6 which varies according to the load of the outdoor unit fan exceeds the defrost start current value I _D. Since the current value I _m of the outdoor blower motor varies the rotation speed of the outdoor fan 7, when the rotation speed of the outdoor fan 7 is at a low rotational speed in the case of high rotational speed, the outdoor heat exchanger 3 frosting The motor current value may vary. Therefore, it is better to set the defrost start current value _ID individually according to the rotational speed of the outdoor blower 7, but generally, the rotational speed of the outdoor blower 7 to be set differs depending on the heating capacity, and the outdoor blower 7 depends on the wind speed of the indoor unit. In many cases, it is necessary to set many defrost start currents I _D.

However, when frost adheres to the outdoor heat exchanger 3, the increase in motor current is clearly increased as compared with the case where frost is not formed, regardless of the rotation speed of the outdoor fan 7. Therefore, the deviation between the motor current and the frost of the motor current when not frosted defrost start current value [Delta] I _D, for a predetermined period past the motor current I ₀ and the deviation [Delta] I _m of the current motor current I _m, [Delta] I determining the start of the defrost the relationship between _m and [Delta] I _D. Thereby, it becomes possible to start a defrost appropriately, without setting a defrost start electric current value separately according to the rotation speed of the outdoor air blower 7. FIG.

FIG. 9 is a flowchart of control in this embodiment. First, outdoor fan motor current _Im is detected at regular intervals during heating operation. Next, a deviation ΔI _m between the motor current I _m and the motor current I _{0 in} the past for a certain period is calculated. Then, as compared to the [Delta] _m and the defrost start current deviation [Delta] I _D, when [Delta] I _m is less than [Delta] I _D continues to heating operation, if it is greater, initiate defrost.

It may be changed according to the outside temperature defrosting start current deviation [Delta] I _D.

In addition to defrost initiation criteria described in Examples 1 and 2, further deviation [Delta] I _m of the motor current I _m of the current outdoor blower for a predetermined period past the motor current I ₀ starts defrosting motor You may start the defrosting when a current deviation [Delta] I _D above.

According to the present embodiment, in an air conditioner including an indoor unit, an outdoor unit having a compressor 1, an outdoor fan 7, an outdoor fan motor that drives the outdoor fan 7, and an outdoor heat exchanger 3, initiating defrost if the deviation [Delta] I _m of the motor current I _m of the blower for a predetermined period past the motor current I ₀ is equal to or greater than the deviation [Delta] I _D of the motor current to start defrosting. Accordingly, the same effects as those of the above-described embodiments can be obtained, and defrosting can be appropriately started without individually setting the defrost start current value according to the rotation speed of the outdoor blower 7.

A fourth embodiment of the present invention will be described with reference to FIGS. The present embodiment includes an indoor unit, an air compressor including an compressor 1, an outdoor fan 7, an outdoor fan motor that drives the outdoor fan 7, an overcurrent prevention control of a motor drive circuit, and an outdoor heat exchanger 3. in conditioner, overcurrent protection control of the motor drive circuit is operated, in which the rotational speed N of the outdoor blower 7 starts defrosting when it becomes less than the rotational speed N _D to start defrosting.

In the same manner as in the first embodiment, in an air conditioner including an indoor unit, and an outdoor unit including a compressor 1, an outdoor fan 7, an outdoor fan motor that drives the outdoor fan 7, and an outdoor heat exchanger 3. The device 9 controls the rotational speed of the outdoor blower 7. Controller 9, the current I _m flowing through the outdoor blower motor 6 detected by the motor current detecting means, for adjusting the motor current I _m flowing through the outdoor blower motor 6 so as to hold the rotational speed of the outdoor fan 7 constant.

  Here, when the amount of frost formation in the outdoor heat exchanger 3 increases, the load on the outdoor blower 7 increases, and the current flowing through the outdoor blower motor 6 increases, an overcurrent flows in the motor drive circuit, and the circuit is damaged. There is a possibility. In order to prevent this, when a current of a certain value or more flows in the motor drive circuit, overcurrent prevention control is performed to prevent damage to the drive circuit by lowering the motor current and lowering the rotational speed of the outdoor fan 7.

  FIG. 10 is a diagram illustrating a change in the rotational speed of the outdoor fan 7 depending on the presence or absence of frost in the outdoor heat exchanger 3 having the overcurrent prevention control of the motor drive circuit. As described above, when the outdoor heat exchanger 3 is frosted, the amount of frost increases according to the heating operation time, and the load on the outdoor blower 7 increases. When the load on the outdoor blower 7 increases, the overcurrent prevention control is activated, and the rotational speed of the outdoor blower 7 decreases. Therefore, the frost formation state of the outdoor heat exchanger 3 can be determined by detecting a decrease in the rotational speed of the outdoor fan 7.

FIG. 11 is a flowchart of control in the fourth embodiment. At the time of heating operation, and detects the current I _m of the outdoor blower motor 6, when the motor current I _m is greater than the motor drive circuit protection current I _L is controlled to decrease the motor current I _m. Then, to detect the rotational speed N of the outdoor blower 7, when the rotation speed N of the outdoor blower 7 is greater than the defrost start rotational speed N _D continues the heating operation, if it drops below N _D perform defrosting.

According to this embodiment, the indoor unit, the compressor 1, the outdoor fan 7, the outdoor fan motor for driving the outdoor fan 7, the overcurrent prevention control of the motor drive circuit, and the outdoor unit having the outdoor heat exchanger 3 are provided. in an air conditioner comprising, overcurrent prevention control of the motor drive circuit is operated, the rotational speed N of the outdoor blower 7 starts defrosting when it becomes less than the rotational speed N _D to start defrosting. Therefore, while having the same effect as each said Example, while performing the overcurrent protection of the outdoor fan motor drive circuit 8, it can perform appropriate defrost according to the amount of frost formation of the outdoor heat exchanger 3, and heating It becomes possible to improve the comfort during driving.

A fifth embodiment of the present invention will be described with reference to FIGS. The present embodiment includes an indoor unit, an air compressor including an compressor 1, an outdoor fan 7, an outdoor fan motor that drives the outdoor fan 7, an overcurrent prevention control of a motor drive circuit, and an outdoor heat exchanger 3. in conditioner, overcurrent protection control of the motor drive circuit is operated, which rotation speed N of the outdoor blower 7 starts defrosting when it becomes less than the rotational speed N _D to start defrosting, depending on the outside temperature it is intended to change the rotational speed N _D of the outdoor blower 7 to start the defrost Te.

Since the basic configuration of the air conditioner is the same as that of the fourth embodiment, detailed description thereof is omitted. FIG. 12 is a diagram showing the relationship between the outside air temperature and the rotation speed of the defrost start outdoor fan. In the present embodiment, in the same manner as in Example 2, using the outside air temperature detection means 13, as shown in FIG. 12, changes the rotational speed N _D of the outdoor blower 7 to initiate defrost in accordance with the outside temperature. By changing the rotational speed N _D of the outdoor blower 7 to initiate defrost in accordance with the outside temperature, it is possible to be a great condition the effect of lowering the heating capacity due to frost formation appropriately performed defrosting, comfortable An air conditioner with improved performance can be applied.

FIG. 13 is a flowchart of control in the fifth embodiment. During the heating operation, and detects the outdoor blower motor current I _m, when the motor current I _m is greater than the motor drive circuit protection current I _L is controlled to decrease the motor current I _m. Thereafter, the outside air temperature detecting means 13 detects the outside air temperature, and calculates a defrost start motor current _ID corresponding to the outside air temperature as shown in FIG. Then, to detect the rotational speed N of the outdoor blower 7, when the rotation speed N of the outdoor blower 7 is greater than the defrost start rotational speed N _D corresponding to the outside air temperature continues to heating operation, the rotational speed N of the outdoor blower 7 No. is less than the defrost start rotational speed N _D performs defrosting.

In addition, the outdoor heat exchanger temperature detection means 14 is also used to control the defrosting by the outdoor air temperature and the outdoor heat exchanger temperature (defrosting is performed when the outdoor heat exchanger temperature falls below a certain temperature at a predetermined outdoor temperature) ) in combination with, it may determine the final defrosting execution start by using the relationship between the rotational speed N and the defrost start rotational speed N _D of the outdoor fan 7.

Further, in the same manner as in Example 3, the number of rotations of the outdoor fan 7, and calculates the rotation speed deviation .DELTA.N a certain period, so as to start the defrosting when .DELTA.N becomes defrost start rotational speed deviation .DELTA.N _D or May be. Furthermore, it may be changed according to the outside temperature defrosting start rotational speed difference .DELTA.N _D value.

  As described above, according to each of the above embodiments, it is possible to accurately detect the frosting state of the outdoor heat exchanger, perform appropriate defrosting, and provide an air conditioner with improved comfort during heating operation. Can do.

The figure which shows the change of the load of an outdoor air blower by the presence or absence of adhesion of the frost of an outdoor heat exchanger. The block diagram of the air conditioner in a 1st Example. The figure which shows the change of the electric current of the outdoor fan motor by the presence or absence of adhesion of the frost of an outdoor heat exchanger. The control flowchart in a 1st Example. The block diagram of the air conditioner in a 2nd Example. The figure which shows the relationship between external temperature and defrost start outdoor heat exchanger temperature. The figure which shows the relationship between external temperature and a defrost start motor electric current. 7 is a control flowchart in the second embodiment. The control flowchart in a 3rd Example. The figure which shows the change of the outdoor fan rotation speed by the presence or absence of the frost of an outdoor heat exchanger at the time of providing the overcurrent prevention control of a motor drive circuit. The control flowchart in a 4th Example. The figure which shows the relationship between external temperature and a defrost start outdoor fan rotation speed. 10 is a control flowchart in the fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor 2 Four-way valve 3 Outdoor heat exchanger 4 Throttle device 5 Indoor heat exchanger 6 Outdoor fan motor 7 Outdoor fan 8 Outdoor fan motor drive circuit 9 Controller 10 Indoor fan 11 Indoor fan motor 12 Outdoor fan motor current detection means 13 Outside air temperature detecting means 14 Outdoor heat exchanger temperature detecting means

Claims (15)

  An outdoor unit having an indoor unit, a compressor, an outdoor fan, an outdoor fan motor that drives the outdoor fan, and an outdoor heat exchanger, the outdoor unit based on a load of the outdoor fan An air conditioner that starts defrosting to remove frost attached to a heat exchanger.   2. The air conditioner according to claim 1, wherein the load of the outdoor fan is at least one of a current value of the outdoor fan motor and a rotation speed of the outdoor fan. And an indoor unit, a compressor, an outdoor fan, an outdoor fan motor for driving the outdoor fan, and an outdoor unit having an outdoor heat exchanger, the air conditioner having a current value I _m of the outdoor blower motor defrost The air conditioner is characterized in that defrosting is started when the current value _ID becomes equal to or higher than the current value _ID . The air conditioner according to claim 3, wherein the current value _ID depends on an outside air temperature. 5. The deviation ΔI _m between the current value I _m of the outdoor fan motor and the current value I ₀ of the outdoor fan motor in the past for a certain time is equal to or greater than the current deviation ΔI _{D at} which defrosting starts. An air conditioner characterized by starting defrosting in case. In claim 5, the air conditioner, wherein said current deviation [Delta] I _D depends on the outside air temperature. In an air conditioner comprising an indoor unit, a compressor, an outdoor fan, an outdoor fan motor that drives the outdoor fan, and an outdoor unit having an outdoor heat exchanger, the current value I _m of the current outdoor fan motor deviation [Delta] I _m of the predetermined time the current value I ₀ of the past of the outdoor blower motor may become current deviation [Delta] I _D above to start a defrost starts defrosting for removing frost adhering to the outdoor heat exchanger and An air conditioner characterized by that. In claim 7, the air conditioner, wherein said current deviation [Delta] I _D depends on the outside air temperature. An indoor unit, a compressor, an outdoor fan, an outdoor fan motor that drives the outdoor fan, and an outdoor unit having an outdoor heat exchanger, and a control device that performs overcurrent prevention control on a drive circuit of the outdoor fan motor in the air conditioner having a rotational speed N _D of the outdoor blower motor of a predetermined value or more current flows through the driving circuit operates the overcurrent prevention control, the rotational speed N of the outdoor blower starts defrost When it becomes below, the air conditioner characterized by starting the defrost which removes the frost adhering to the said outdoor heat exchanger. In claim 9, the air conditioner, wherein the rotational speed N _D is dependent on the outside air temperature. According to claim 9 or 10, defrost if the deviation .DELTA.N between the rotational speed N of the current of the outdoor blower and a certain time the rotation speed N ₀ of the last of said outdoor blower is equal to or higher than the rotational speed deviation .DELTA.N _D to start defrosting An air conditioner characterized by starting. In claim 11, an air conditioner, wherein the rotary speed deviation .DELTA.N _D is dependent on the outside air temperature. An indoor unit, a compressor, an outdoor fan, an outdoor fan motor that drives the outdoor fan, and an outdoor unit having an outdoor heat exchanger, and a control device that performs overcurrent prevention control on a drive circuit of the outdoor fan motor in an air conditioner having a situation, when the current of the outdoor blower speed N and a predetermined time revolution speed deviation .DELTA.N _D than the deviation .DELTA.N between the rotational speed N ₀ of the last of the outdoor blower starts defrosting of The air conditioner is characterized by starting defrosting to remove frost adhering to the outdoor heat exchanger. In claim 13, an air conditioner, wherein the rotary speed deviation .DELTA.N _D is dependent on the outside air temperature.   15. The air conditioner according to claim 1, wherein defrosting is started when the temperature of the outdoor heat exchanger becomes equal to or higher than a predetermined value, and the predetermined value depends on an outside air temperature. .

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