KR20110028180A - Air conditioner and control method thereof - Google Patents

Abstract

PURPOSE: An air conditioner and a method for controlling the same are provided to eliminate the frost of an outdoor heat exchanger and improving indoor heating performance by continuously implementing a heating and defrosting operation. CONSTITUTION: An air conditioner(1) includes a compressor(10), an indoor heat exchanger(21), an expansion unit, an outdoor heat exchanger(41), a plurality of sensors, a heating unit, and a controlling unit. The compressor compresses refrigerant. The indoor heat exchanger exchanges heat between the refrigerant and indoor air. The expansion unit expands the refrigerant through the indoor heat exchanger. The outdoor heat exchanger exchanges heat between the refrigerant and outdoor air. The sensor detects the temperature of the outdoor air and outdoor heat exchanger. Based on the detected temperature, the amount of heat from the heating unit is varied. The controlling unit controls the output of the heating unit.

Description

Air conditioner and control method

An embodiment according to the present invention relates to an air conditioner and a control method thereof.

An embodiment according to the present invention relates to an air conditioner and a control method thereof, and more particularly, to an air conditioner and a control method for controlling an induction heater by sensing an amount of implantation of an outdoor heat exchanger.

In general, air conditioners are home appliances for maintaining indoor air in a state most suitable for use and purpose. For example, in the summer, the room is cooled to a cool state, in winter, the room is controlled to a warm heating state, and also the humidity of the room and the air in the room to a comfortable clean state.

As life convenience products such as air conditioners are gradually expanded and used, consumers are demanding high energy use efficiency, performance improvement and convenience products.

Such an air conditioner is divided into a separate air conditioner that separates the indoor unit and the outdoor unit, and an integrated air conditioner that combines the indoor unit and the outdoor unit into one device. And, according to the installation form of the air conditioner, it is divided into a wall-mounted air conditioner and a frame air conditioner configured to be mounted on the wall, and a slim air conditioner configured to stand in the living room.

Here, the separate air conditioner is configured to be installed indoors to supply hot or cold air into the air conditioning space, and an outdoor unit for compressing, expanding, etc. the refrigerant so that sufficient heat exchange can be performed in the indoor unit.

On the other hand, in the conventional heating operation process of the air conditioner capable of heating and cooling, when the frost occurs on the surface of the outdoor heat exchanger by the temperature sensor provided to the outdoor heat exchanger, the inverter compressor is guided to a low frequency to switch the four-way valve After this, a method of temporarily removing the idea by starting a cooling cycle was used.

However, if such a method is used, the indoor heat exchanger functions as an evaporator, and there is a problem that the room temperature is lowered because defrosting is performed in a cooled state.

In addition, the operation of the air conditioner is switched, and accordingly, since the high temperature refrigerant is provided to the outdoor heat exchanger, there is a problem that the defrosting time for defrosting takes a little longer.

The embodiment according to the present invention relates to an air conditioner and a control method thereof, and in particular, to provide an air conditioner and a method of controlling the air conditioner to improve heating and defrosting by improving the structure and control of the air conditioner. For the purpose of

In addition, an object of the present invention is to provide an air conditioner and a control method thereof by sensing the amount of heat of the heat exchanger to vary the amount of heat of the induction heater.

An air conditioner according to an embodiment of the present invention for solving the above problems includes a compressor for compressing a refrigerant; An indoor heat exchanger configured to exchange heat between the refrigerant passing through the compressor and the indoor air; An expansion device for reducing the refrigerant passing through the indoor heat exchanger; An outdoor heat exchanger configured to allow the refrigerant discharged from the expansion device to exchange heat with outside air; A plurality of sensors for sensing the temperature of the outside air and the temperature of the outdoor heat exchanger; A heater whose heat generation amount varies according to the outside air temperature sensed by the sensor and the temperature of the outdoor heat exchanger; And a controller for determining an implantation amount of the outdoor heat exchanger according to a difference between the outside air temperature and the temperature of the outdoor heat exchanger, and controlling the output of the heater according to the implantation amount.

In addition, the control method of the air conditioner according to an embodiment of the present invention, the step of comparing the room temperature with a predetermined first set temperature; Comparing the outdoor temperature with a second preset temperature according to the indoor temperature; Determining a temperature difference between the outdoor temperature and the outdoor heat exchanger; Comparing the temperature difference value with a preset reference temperature value; And adjusting the amount of heat generated by the heater according to a comparison result between the temperature difference value and the reference temperature value.

According to the embodiment of the present invention according to the above configuration, the indoor heating performance is increased by the continuous heating defrost operation so that the heating and defrosting at the same time, there is an advantage that the concept of the outdoor heat exchanger can be removed.

In addition, the amount of implantation of the outdoor heat exchanger can be determined according to the indoor / outdoor temperature and the temperature of the outdoor heat exchanger, and since the heat amount of the induction heater can be varied according to the determined amount of implantation, there is an advantage of reducing unnecessary power consumption. .

In addition, since the induction heater is provided to the accumulator, the amount of heat transfer lost to the outside air is reduced, and the time for heat transfer to the refrigerant from the induction heater is reduced.

In addition, by heating the low pressure side refrigerant of the heating cycle from the induction heater in the heating process, there is an advantage that the heating performance can be improved without additionally increasing the output of the compressor.

In addition, in the defrosting process for removing frost formed on the evaporator, by operating the induction heater it is possible to transfer more heat to the low-pressure side refrigerant, there is an advantage that the defrosting performance of the air conditioner can be improved accordingly.

Hereinafter, with reference to the drawings will be described a specific embodiment of the present invention. However, the spirit of the present invention is not limited to the embodiments presented, and those skilled in the art who understand the spirit of the present invention can easily suggest other embodiments within the scope of the same idea.

1 is a view showing the configuration of the heating cycle of the air conditioner according to an embodiment of the present invention.

Referring to FIG. 1, in the air conditioner 1 according to an embodiment of the present invention, a compressor 10 compressing a refrigerant and a refrigerant compressed at high temperature and high pressure by the compressor 10 are introduced into the air conditioner 1. An indoor heat exchanger 21 for exchanging heat, an indoor unit fan 22 for blowing heat-exchanged warm air into the room, a capillary 30 as an expansion device for expanding the heat exchanged refrigerant to low pressure, and an expanded refrigerant An outdoor heat exchanger 41 for exchanging heat with the outdoor unit and an outdoor unit fan 42 for blowing out the heat-exchanged cold air to the outside are included.

In detail, when a heating cycle is performed through an air conditioner, a condenser is applied to the indoor heat exchanger 21 to condense the refrigerant compressed by the compressor 10 to a low temperature, and the outdoor heat exchanger 41 is applied. The evaporator is applied to evaporate the refrigerant of the liquid pressure reduced through the capillary (30).

Here, the high pressure is formed before the refrigerant circulating in the heating cycle passes through the capillary 30, and the low pressure is formed after passing through the capillary 30. Hereinafter, the refrigerant before passing through the capillary 30 is called a high pressure side refrigerant, and after passing through, it is called a low pressure side refrigerant.

On the discharge side of the outdoor heat exchanger 41, a gas-liquid separator 50 is provided so that only the gaseous refrigerant of the refrigerant evaporated through the outdoor heat exchanger 41 is introduced into the compressor 10.

In the air conditioner 1, the refrigerant hot gas passing through the compressor 10 is at least bypassed to the inlet side of the outdoor heat exchanger 41 or the inlet side of the gas-liquid separator 50. Bypass flow path 81 is provided. That is, the bypass flow path 81 extends from the outlet side of the compressor 10 to the inlet side of the outdoor heat exchanger 41 and the inlet side of the compressor 10.

In addition, the bypass flow path 81 is provided with a first valve 80 to adjust the flow rate of the refrigerant to be bypassed. The first valve 80 may include a solenoid valve.

As the refrigerant passing through the compressor 10 is bypassed to the inlet side of the compressor 10, the evaporation temperature and the pressure of the inlet refrigerant of the compressor 10 may be increased, and thus, the compressor 10 may be increased. There is an advantage that the input date (load) of the is reduced. In addition, an imbalance generated between the capacity of the compressor 10 and the capacity of the indoor heat exchanger 21 is eliminated, thereby increasing the heating efficiency.

In addition, since the high temperature and high pressure refrigerant passing through the compressor 10 is bypassed to the inlet side of the outdoor heat exchanger 41, the outdoor heat exchanger 41 may be defrosted.

As the refrigerant is bypassed by the first valve 80 as described above, heating and defrosting can be simultaneously performed. This mode of operation is called continuous heating defrosting.

The first bypass flow path 81 is provided with a second valve 90 to prevent the refrigerant from flowing from the inlet side of the outdoor heat exchanger 41 to the inlet side of the gas-liquid separator 50. By the second valve 90, in the normal heating mode of the air conditioner, the refrigerant may be prevented from flowing back from the inlet side of the outdoor heat exchanger 41 to the inlet side of the gas-liquid separator 50. The second valve 90 may include a check valve.

In addition, a four-way valve 70 is provided on the discharge side of the compressor 10 to switch the flow direction of the refrigerant according to the cooling or heating mode of the air conditioner. In the heating mode, the refrigerant passing through the outdoor heat exchanger 41 is introduced into the compressor 10 through the four-way valve 70 and then compressed, and the compressed refrigerant passes through the four-way valve 70. It is introduced into the indoor heat exchanger (21). On the other hand, in the cooling mode, the refrigerant passing through the indoor heat exchanger 41 is introduced into the compressor 10 via the four-way valve 70 and then compressed, and the compressed refrigerant is the four-way valve 70. It may be introduced into the outdoor heat exchanger 41 through the).

On the other hand, outside the gas-liquid separator 50, an induction heater 100 for heating the refrigerant of the gas-liquid separator 50 is provided. The induction heater 100 may be disposed to surround the outer circumferential surface of the gas-liquid separator 50.

Here, the induction heater 100 is a heater using the induced current generated by the magnetic field as a heat source, and is composed of an electromagnet through which a high frequency alternating current can pass. The electromagnet includes a coil through which an alternating current flows.

The induction heater 100 may provide heat to the low-pressure side refrigerant, that is, the outdoor heat exchanger 41 side refrigerant in the continuous heating defrosting manner, to increase the evaporation temperature of the refrigerant, and may help to remove the frost formed. . In addition, the induction heater 100 may increase the condensation temperature by providing a heat amount to the high pressure side refrigerant, that is, the indoor heat exchanger 21 side refrigerant. As such, by the induction heater 100, heating efficiency may be improved by increasing the evaporation temperature and the condensation temperature of the refrigerant, and the defrosting efficiency may also be improved.

In addition, the induction heater 100 increases the pipe temperature of the indoor heat exchanger 21 by providing heat to the indoor heat exchanger 21 side in the normal heating mode, thereby increasing the temperature of the air blown out into the indoor space. The effect is to increase quickly.

On the other hand, the induction heater 100, an inverter method for controlling the amount of heat supplied from the heater 100 may be applied. In this case, there is an advantage that the amount of heat can be supplied to vary according to the outside temperature and the temperature of the heat exchanger requiring defrost. The control method in which the calorific value of the induction heater 100 varies according to the amount of implantation of the outdoor heat exchanger 41 will be described later with reference to the drawings.

2 is a block diagram showing the configuration of an air conditioner according to an embodiment of the present invention.

2, the air conditioner 1 according to an embodiment of the present invention, the outdoor temperature sensor 110 to detect the temperature of the outside air, and the indoor temperature sensor 120 to sense the temperature of the indoor space. And an outdoor heat exchanger sensor 130 for sensing a refrigerant pipe temperature of the outdoor heat exchanger 41, an induction heater 60 that is variably generated based on values sensed by the sensors 110, 120, and 130. The controller 100 controls the sensors 110, 120, and 130. For convenience of description, the outdoor temperature sensor 110, the indoor temperature sensor 120, and the outdoor heat exchanger sensor 130 may be a “first temperature sensor”, “second temperature sensor” and “third temperature sensor”, respectively. It may be called.

In detail, the values sensed by the sensors 110, 120, and 130 are transmitted to the controller 100, and the controller 100 reads information of the sensors 110, 120, and 130 so that the heat amount of the induction heater 60 is preset. You can control the output to.

For convenience of description, hereinafter, the value of "outdoor temperature-outdoor piping temperature" is referred to as "GAP", and the magnitude of heat output from the induction heater 60 may be classified as P1, P2 or P3 in advance. Let me know. However, according to the control method of the induction heater 60, the amount of heat output available may be more variously provided.

3 and 4 are flow charts showing how an air conditioner according to an embodiment of the present invention is controlled for a first section of room temperature, and FIG. 5 shows that the air conditioner is controlled for a second section of room temperature. Here is a flow chart that shows how.

3 to 5, a control method of an air conditioner according to an embodiment of the present invention will be described. 3 to 5 illustrate a control method in a process in which continuous heating defrosting operation is performed.

3 and 4 illustrate a method of controlling an induction heater according to an outdoor temperature and an outdoor pipe temperature when the indoor temperature is T1 or more, and FIG. 5 illustrates an induction heater according to an outdoor temperature and an outdoor pipe temperature when the indoor temperature is less than T1. The control method of is shown. Here, the temperature T1 is a preset temperature and may be formed at about 15 ° C. Of course, according to the control method of the air conditioner, the T1 may be set to a different value.

First, the indoor temperature is sensed by the indoor temperature sensor 120 (S11). If the indoor temperature is T1 or more, the outdoor temperature is sensed by the outdoor temperature sensor 110, and it is determined whether the outdoor temperature is greater than T2 (S12, S13, S14). Here, T2 is a preset temperature, it may be formed at about 0 ℃. Of course, depending on the control method of the air conditioner, the T2 may be set to a different value.

When the outdoor temperature is T2 or more, the amount of implantation of the outdoor heat exchanger 41 is determined (S15). That is, it is determined whether "GAP" (outdoor temperature-outdoor piping temperature) is formed larger than H1. In this case, the larger the GAP, the greater the amount of air condensed in the piping of the outdoor heat exchanger, and accordingly the tendency to be implanted in the piping will appear.

In detail, the refrigerant pipe temperature of the outdoor heat exchanger 41 is sensed by the outdoor heat exchanger sensor 130, and the controller 100 determines a difference value GAP of the refrigerant pipe temperature at the outdoor temperature. . At this time, the difference value and the H1 value are compared (S16). Here, H1 may be formed at about 8 ° C. as a preset temperature difference value. Of course, the H1 may be set to a different value according to the control method of the air conditioner.

When the GAP is larger than H1, the controller 100 determines that the amount of implantation of the outdoor heat exchanger 41 is large, and accordingly, the output of the induction heater 60 so that the heat generation amount of the induction heater 60 can be increased. Can be adjusted to P1 (first output value). Here, P1 may be formed at about 1200W as a preset output value (S20).

On the other hand, when the GAP is larger than H2 and has a value of H1 or less, the controller 100 determines that the amount of implantation of the outdoor heat exchanger 41 is at a normal level, and accordingly, outputs the output of the induction heater 60 to P2. (Second output value).

The H2 may be formed at about 4 ° C. different from the H1 as a preset temperature difference value, and the P2 may be formed at about 900 W smaller than the P1 as a preset output value. Of course, the H2 and P2 may be set to different values according to the control method of the air conditioner (S17, S19).

On the other hand, if it is determined that the GAP is smaller than H2, the controller 100 determines that the amount of implantation of the outdoor heat exchanger 41 is small, and accordingly, the induction heat is reduced so that the heat generation amount of the induction heater 60 is reduced. The output of the heater 60 can be adjusted to P3 (third output value). Here, the P3 may be formed at about 600W as a preset output value. However, P3 may be set to another output value smaller than P2 according to the control method of the air conditioner (S17, S18).

If the outdoor temperature is T2 or less in step S14, it is determined whether the outdoor temperature is greater than T3 and less than or equal to T2 as shown in FIG. 4 (S21). Here, the T3 may be formed at about −5 ° C., but may be preset to another temperature value according to the control method.

When the outdoor temperature is greater than T3 and less than or equal to T2, the amount of implantation of the outdoor heat exchanger 41 is determined (S22). The amount of implantation is determined depending on whether the GAP is formed larger than H3.

In detail, the refrigerant pipe temperature of the outdoor heat exchanger 41 is sensed by the outdoor heat exchanger sensor 130, and the controller 100 performs a GAP from the refrigerant pipe temperature values of the outdoor temperature and the outdoor heat exchanger 41. Judge. At this time, the difference value and the H3 value are compared (S23). Here, H3 may be formed at about 6 ° C. different from H1 and H2 as a preset temperature difference value. Of course, the H3 may be set to a different value according to the control method of the air conditioner.

When the GAP is larger than H3, the control unit 100 determines that the amount of implantation of the outdoor heat exchanger 41 is large, and accordingly, the output of the induction heater 60 to increase the heat generation amount of the induction heater 60. Can be adjusted to P1 (S20).

On the other hand, when the GAP is larger than H4 and has a value less than or equal to H3 (S24), the control unit 100 determines that the amount of implantation of the outdoor heat exchanger 41 is a normal level, and thus the induction heater 60 The output can be adjusted to P2 (S19). The H4 may be formed at about 3 ° C. as a preset temperature difference value. Of course, the H4 may be set to different values according to the control method of the air conditioner.

On the other hand, if it is determined that the GAP is less than H4 (S24), the control unit 100 determines that the amount of implantation of the outdoor heat exchanger 41 is small, and accordingly the heat generation amount of the induction heater 60 can be reduced. The output of the induction heater 60 can be adjusted to P3 so as to (S18).

In step S21, when the outdoor temperature is less than T3, the amount of implantation may be determined (S25). The amount of implantation is determined depending on whether the GAP is formed larger than H5. Here, the H5 may be formed at about 7 ℃ as a predetermined temperature difference value. Of course, the H5 may be set to a different value according to the control method of the air conditioner.

When the GAP is larger than H5 (S26), the controller 100 determines that the amount of implantation of the outdoor heat exchanger 41 is large, and accordingly, the induction heater 60 may increase the amount of heat generated by the induction heater 60. ) Can be adjusted to P1 (S20).

On the other hand, when the GAP has a value less than or equal to H5 (S26), the controller 100 determines that the amount of implantation of the outdoor heat exchanger 41 is a normal level, and accordingly, outputs the output of the induction heater 60 to P2. Can be adjusted with (S19).

As the GAP falls within a predetermined range and the outdoor temperature is low, the amount of implantation generally increases and more heat is required to remove the frost. When the outdoor temperature is less than T3, the heat amount of the induction heater 60 is reduced. At least at the P2 level.

If the indoor temperature is lower than T1 in the step S12, as shown in FIG. 5, the outdoor temperature value is determined (S31). In detail, the outdoor temperature is detected by the outdoor temperature sensor 110, and the controller 100 determines whether the outdoor temperature is greater than T2 (S32). As described above, the T2 may be formed at about 0 ° C. as a preset temperature.

When the outdoor temperature is greater than T2, the amount of implantation of the outdoor heat exchanger 41 is determined (S22). The amount of implantation is determined according to whether or not the GAP is formed larger than H6 (S33). The H6 may be formed at about 7 ° C. as a preset temperature difference value. Of course, the H6 may be set to a different value according to the control method of the air conditioner.

When the GAP is larger than H6 (S34), the control unit 100 determines that the amount of implantation of the outdoor heat exchanger 41 is large, and accordingly, the induction heater 60 may increase the heat generation amount of the induction heater 60. ) Can be adjusted to P1 (S20).

On the other hand, when the GAP has a value of H6 or less (S34), the controller 100 determines that the amount of implantation of the outdoor heat exchanger 41 is a normal level, and accordingly outputs the output of the induction heater 60. P2 can be adjusted (S19).

On the other hand, if it is determined in step S32 that the outdoor temperature is not greater than T2, it is determined whether the outdoor temperature is greater than T3 and less than T2 (S37). When it is determined that the outdoor temperature is greater than T3 and less than or equal to T2, the controller 100 determines the amount of implantation (S38).

In detail, the controller 100 determines whether the GAP is larger than H7 (S39). Here, the H7 may be formed at about 6 ℃ as a predetermined temperature difference value. Of course, the H7 may be set to a different value according to the control method of the air conditioner.

When it is determined that the GAP is larger than H7, the controller 100 determines that the amount of implantation of the outdoor heat exchanger 41 is large, and accordingly, the induction heater 60 may increase the amount of heat generated by the induction heater 60. The output of can be adjusted to P1 (S20).

However, if it is determined that the GAP is less than or equal to H7, the controller 100 determines that the amount of implantation of the outdoor heat exchanger 41 is a normal level, and accordingly, the output of the induction heater 60 may be adjusted to P2 ( S19).

In operation S37, when the outdoor temperature is less than or equal to T3, the amount of implantation may be determined (S40). The amount of implantation is determined depending on whether the GAP is formed larger than H8. Here, the H8 may be formed at about 5 ° C as a predetermined temperature difference value. Of course, the H8 may be set to a different value according to the control method of the air conditioner.

When the GAP is larger than H8 (S41), the control unit 100 determines that the amount of implantation of the outdoor heat exchanger 41 is large, and accordingly, the induction heater 60 may increase the amount of heat generated by the induction heater 60. ) Can be adjusted to P1 (S20).

On the other hand, when the GAP has a value less than or equal to H8 (S26), the controller 100 determines that the amount of implantation of the outdoor heat exchanger 41 is a normal level, and accordingly outputs the induction heater 60. P2 can be adjusted (S19).

When the room temperature is low under the same GAP condition, compared to the case where the room temperature is high, the amount of frosting in the structure of the refrigeration cycle is higher and more heat is required to remove the frost formed. When the room temperature is less than T1, The amount of heat of the induction heater 60 can be maintained at least P2 level.

As described above, H1 to H8 are reference temperatures for determining a value of "outdoor temperature"-"outdoor heat exchanger pipe temperature", that is, a value of "GAP" and may be referred to as "first reference temperature" to "eighth reference temperature." Could be. For example, H2 and H3 are referred to as the second reference temperature and the third reference temperature. As described above, the first to eighth reference temperatures may be set to different values according to indoor and outdoor temperature values.

For convenience of explanation, T1, which is a criterion for determining the indoor temperature, is referred to as "first set temperature", and T2 and T3, which is a criterion for determining outdoor temperature, are called "second set temperature".

As described above, by detecting the indoor and outdoor temperature and the outdoor heat exchanger pipe temperature, by determining the large and small amount of implantation according to the difference between the outdoor temperature and the outdoor heat exchanger pipe temperature value, by adjusting the output of the induction heater, There is an advantage that can be reduced.

That is, when the amount of frosting of the outdoor heat exchanger is large, the amount of heat generated by the induction heater is increased, and when the amount of ignition is small, the amount of heat generated by the induction heater is reduced to prevent unnecessary waste of power consumption.

1 is a view showing the configuration of the heating cycle of the air conditioner according to an embodiment of the present invention.

Figure 2 is a block diagram showing the configuration of an air conditioner according to an embodiment of the present invention.

3 and 4 are flow charts showing how an air conditioner according to an embodiment of the present invention is controlled for a first section of room temperature.

5 is a flow chart showing how the air conditioner is controlled for a second section of room temperature.

Claims (10)

A compressor for compressing the refrigerant; An indoor heat exchanger configured to exchange heat between the refrigerant passing through the compressor and the indoor air; An expansion device for reducing the refrigerant passing through the indoor heat exchanger; An outdoor heat exchanger configured to allow the refrigerant discharged from the expansion device to exchange heat with outside air; A plurality of sensors for sensing the temperature of the outside air and the temperature of the outdoor heat exchanger; A heater whose heat generation amount varies according to the outside air temperature sensed by the sensor and the temperature of the outdoor heat exchanger; And And a controller configured to determine an implantation amount of the outdoor heat exchanger according to a difference between the outside air temperature and the temperature of the outdoor heat exchanger, and to control the output of the heater according to the implantation amount. The method of claim 1, Further comprising a gas-liquid separator provided at the inlet side of the compressor, And the heater is an induction heater provided to the gas-liquid separator. The method of claim 1, A bypass flow passage through which a refrigerant is bypassed from an outlet side of the compressor to an inlet side of the outdoor heat exchanger; And And a first valve provided in the bypass passage to control the flow of the refrigerant. The method of claim 1, The heat generating amount of the heater is an air conditioner, characterized in that increases as the temperature difference between the outside air temperature and the outdoor heat exchanger increases. Comparing the room temperature with a first preset temperature; Comparing the outdoor temperature with a second preset temperature according to the indoor temperature; Determining a temperature difference between the outdoor temperature and the outdoor heat exchanger; Comparing the temperature difference value with a preset reference temperature value; And And controlling the amount of heat generated by the heater according to a result of the comparison between the temperature difference value and the reference temperature value. The method of claim 5, The control method of the air conditioner, characterized in that the reference temperature value is previously set to a different value depending on whether the room temperature is above the first set temperature. The method of claim 5, And the reference temperature value is preset to a different value depending on whether the outdoor temperature is equal to or greater than the second set temperature. The method of claim 5, And when the temperature difference value is greater than the reference temperature value, the heat generation amount of the heater is increased. The method of claim 5, The output of the heater is adjustable to a first output value, a second output value smaller than the first output value and a third output value smaller than the second output value, And the heater is controlled to output at least a second output value when the outdoor temperature is equal to or less than a preset value. The method of claim 9, And when the room temperature is lower than the first set temperature, the heater is controlled to output at least the second output value.

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