EP2299206B1

EP2299206B1 - Air conditioner and method for controlling the same

Info

Publication number: EP2299206B1
Application number: EP10251464.3A
Authority: EP
Inventors: Hwan Jong Choi; Byoung Jin Ryu; Seung Hyun Jung
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2009-09-11
Filing date: 2010-08-19
Publication date: 2019-02-06
Anticipated expiration: 2030-08-19
Also published as: CN102022807A; WO2011031014A3; WO2011031014A2; KR101605901B1; CN102022807B; KR20110028180A; EP2299206A1

Description

BACKGROUND

The present disclosure relates to an air conditioner and a method for controlling the air conditioner. In general, an air conditioner refers to an appliance, for example a home appliance, to maintain the optimum condition of indoor air according to use and purpose. For instance, the air conditioner may cool the air in summer while heating the air in winter. Also, the air conditioner may control the indoor humidity to thereby maintain freshness of the indoor air.
As convenience products, such as the air conditioner, are getting more prevalent, consumers' demands have been growing for more energy-efficient, high-functional and user-friendly products.
The air conditioner may be classified into a split air conditioner in which an indoor unit and an outdoor unit are separated from each other, and an integral air conditioner in which an indoor unit and an outdoor unit are combined as one module. According to an installation type, on the other hand, the air conditioner may be classified into a wall mount air conditioner and a picture frame air conditioner to be hung on the wall, and a slim air conditioner to be stood on a floor.
More specifically, the split air conditioner includes an indoor unit that is installed indoors to supply warm air or cold air into a space being air-conditioned, and an outdoor unit that compresses and expands refrigerant to facilitate the heat exchange in the indoor unit.
During a heating mode of a heating and cooling air conditioner of the related art, if it is determined using a temperature sensor that frost is formed on a surface of an outdoor heat exchanger, the frost is removed by lowering the frequency of an inverter compressor and switching a 4-way valve to temporarily drive a refrigeration cycle.
In such a method, however, an indoor heat exchanger has to operate as an evaporator for defrosting in a cooling mode, which decreases the indoor temperature.
Furthermore, when the air conditioner is converted to the cooling mode, defrost may be retarded since it takes a predetermined time for high-temperature refrigerant to reach the outdoor heat exchanger.
US5,845,502 discloses an air conditioner comprising a compressor, an indoor heat exchanger, an expansion device, an outdoor heat exchanger, a gas liquid separator, an outdoor temperature sensor and a heater. This documents discloses also a method to defrost an exterior heat exchanger. EP0299361 discloses a demand defrost control method and apparatus for a heat pump in which a controller compares the temperature of an outdoor heat exchanger coil with an enable temperature.

SUMMARY

Embodiments provide an air conditioner improved in the structure and a control method for efficient defrosting and heating, and a method for controlling the air conditioner.
Embodiments also provide an air conditioner capable of sensing quantity of frost formed at a heat exchanger and accordingly varying heat quantity of an induction heater, a method for controlling the same.
The present invention provides an air conditioner and a method for controlling an air conditioner as set out in claims 1 and 3 respectively.
In one embodiment, an air conditioner includes: a compressor that compresses refrigerant an indoor heat exchanger in which heat exchange between the refrigerant passed through the compressor and indoor air is performed, an expansion device that decompresses the refrigerant passed through the indoor heat exchanger, an outdoor heat exchanger in which heat exchange between the refrigerant supplied from the expansion device and outdoor air is performed, a plurality of sensors that sense temperature of the outdoor heat exchanger, indoor temperature and, outdoor temperature, respectively, a heater that generates heat variably according to the outdoor temperature and the outdoor heat exchanger temperature detected by the sensors, and a controller that determines quantity of frost formed on the outdoor heat exchanger by comparing a preset reference temperature (or reference value) with a temperature difference between the outdoor temperature and the outdoor heat exchanger temperature, and controls output of the heater according to the determined frost quantity.
In another embodiment, a method for controlling an air conditioner comprising a compressor, an indoor heat exchanger, an expansion device and an outdoor heat exchanger for a refrigeration cycle, includes: comparing indoor temperature with a first preset temperature, comparing outdoor temperature with a second preset temperature according to a result of the comparison between the indoor temperature and the first preset temperature, determining a temperature difference between the outdoor temperature and temperature of an outdoor heat exchanger, comparing the temperature difference with a preset reference temperature (or reference value) and controlling heat quantity of a heater that defrosts the outdoor heat exchanger, according to a result of the comparison between the temperature difference and the reference temperature.
In further another embodiment, a control method for an air conditioner comprising a compressor, a condenser, an expansion device and an evaporator that are used for driving a refrigeration cycle, and a heater to defrost the evaporator, includes: comparing indoor and outdoor temperatures with preset temperatures, detecting a pipe temperature of an outdoor heat exchanger, obtaining a temperature difference between the outdoor temperature and temperature of the outdoor heat exchanger, determining frost quantity on the evaporator by the temperature difference, and controlling heat quantity of the heater in proportion to the frost quantity.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a view showing the structure of a heating cycle of an air conditioner according to an embodiment.
Fig. 2 is a block diagram showing the structure of the air conditioner according to the embodiment.
Figs. 3 and 4 are flowcharts illustrating a method of controlling the air conditioner in a first range of the indoor temperature; and
Fig. 5 is a flowchart illustrating a method of controlling the air conditioner in a second range of the indoor temperature.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 is a view showing the structure of a heating cycle of an air conditioner 1 according to an embodiment.
Referring to Fig. 1, the air conditioner 1 of the current embodiment includes a compressor 10 that compresses refrigerant, an indoor heat exchanger 21 in which high-temperature high-pressure refrigerant compressed in the compressor 10 is supplied for heat exchange with indoor air, an indoor heat exchanger fan 22 supplying the air heated through the heat exchange into an indoor space, an expansion device (for example, a capillary tube 30) that expands the refrigerant to a low pressure after the heat exchange, an outdoor heat exchanger 41 in which heat exchange between the expanded refrigerant and outdoor air is performed, and an outdoor heat exchanger fan 42 supplying the air cooled through the heat exchange to the outside.
More particularly, for the operation of the heating cycle of the air conditioner, the indoor heat exchanger 21 operates as a condenser to condense at low temperature the refrigerant compressed in the compressor 10 whereas the outdoor heat exchanger 41 operates as an evaporator to evaporate the refrigerant decompressed and condensed through the capillary tube 30.
Here, the refrigerant circulating during the heating cycle has a high pressure before passing through the capillary tube 30 and has a low pressure after passing through the capillary tube 30. Hereinafter, the refrigerant before passage through the capillary tube 30 will be referred to as 'high-pressure side refrigerant' while the refrigerant after passage through the capillary tube 30 will be referred to as 'low-pressure side refrigerant'.
An indoor heat exchanger heater 23 is provided at one side of the indoor heat exchanger 21. The indoor heat exchanger heater 23 may supplement the heating capability of the indoor heat exchanger 21, which may be decreased when the outside temperature is too low owing to the configuration of the heating cycle.
Also, the indoor heat exchanger heater 23 is capable of maintaining a predetermined temperature of the conditioned air blown to the indoor space during a 'defrosting with continuous heating' operation.
The 'defrosting with continuous heating' operation is herein defined as the operation in which a defrosting operation for the outdoor heat exchanger 41 is performed simultaneously with a heating operation of the air conditioner. The defrosting operation for the outdoor heat exchanger 41 may be performed as high-temperature high-pressure refrigerant passed through the compressor 10 is bypassed toward an inlet of the outdoor heat exchanger 41.
A gas liquid separator 50 is disposed at an outlet of the outdoor heat exchanger 41. The gas liquid separator 50 extracts liquid refrigerant from the entire refrigerant evaporated through the outdoor heat exchanger 41, and guides only gaseous refrigerant into the compressor 10.
Additionally, the air conditioner 1 further includes a bypass path 81 that bypasses hot gas of the refrigerant passed through the compressor 10 toward at least one of the inlet of the outdoor heat exchanger 41 and an inlet of the gas liquid separator 50. More specifically, the bypass path 81 may extend from an outlet of the compressor 10 to the inlet of the outdoor heat exchanger 41 and to the inlet of the compressor 10.
The bypass path 81 includes a first valve 80 that controls quantity of the bypassing refrigerant. The first valve 80 may include a solenoid valve.
As the refrigerant passed through the compressor 10 is bypassed to the inlet of the compressor 10, the evaporating temperature and pressure of the refrigerant at the inlet of the compressor 10 may be increased, thereby reducing a work input (load) of the compressor 10. Moreover, imbalance of capacities between the compressor 10 and the indoor heat exchanger 21 may be reduced, accordingly improving the heating efficiency.
In addition, the outdoor heat exchanger 41 may be defrosted by bypassing the high-temperature high-pressure refrigerant passed through the compressor 10 to the inlet of the outdoor heat exchanger 41.
In other words, the defrosting with continuous heating operation is carried out as the refrigerant is bypassed by the first valve 80.
A second valve 90 is disposed on the bypass path 81 to prevent the refrigerant from flowing from the inlet of the outdoor heat exchanger 41 to the inlet of the gas liquid separator 50. In a general heating mode, the second valve 90 may prevent backflow of the refrigerant from the inlet of the outdoor heat exchanger 41 to the inlet of the gas liquid separator 50 through the bypass path 81. Here, the second valve 90 may include a check valve.
A 4-way valve 70 is disposed near the outlet of the compressor 10 in order to change a flow direction of the refrigerant according to whether the air conditioner is in a heating mode or a cooling mode.
In the heating mode, the refrigerant passed through the outdoor heat exchanger 41 is guided into the compressor 10 through the 4-way valve 70 and then compressed. The compressed refrigerant is passed through the 4-way valve 70 and guided into the indoor heat exchanger 21. On the other hand, in the cooling mode, the refrigerant passed through the indoor heat exchanger 21 is guided into the compressor 10 through the 4-way valve 70 and then compressed. The compressed refrigerant may be guided into the outdoor heat exchanger 41 through the outdoor heat exchanger 41.
A heater, such as an induction heater 60, is provided at the outside of the gas liquid separator 50 to heat the refrigerant in the gas liquid separator 50. The induction heater 60 may be configured to enclose an outer circumference of the gas liquid separator 50.
Specifically, the induction heater 60 is a heater that uses an induced current generated by a magnetic field as a heat source. The induction heater 60 includes an electromagnet that conducts a high-frequency alternating current. The electromagnet includes coils conducting alternating currents.
The induction heater 60 supplies heat to the low-pressure side refrigerant, that is, the refrigerant at the outdoor heat exchanger 41 during the defrosting with continuous heating operation, consequently increasing the evaporating temperature of the refrigerant. In addition, defrost for the outdoor heat exchanger 41 may be promoted.
Also, the induction heater 60 heats the refrigerant at the inlet of the compressor 10. Therefore, the induction heater 60 supplies heat to the high-pressure side refrigerant, that is, the refrigerant at the indoor heat exchanger 21, and thereby increases a condensing temperature. Thus, the evaporating temperature and the condensing temperature of the refrigerant are increased, and therefore the heating efficiency and the defrosting efficiency may both be improved.
Furthermore, the induction heater 60 supplies heat to the indoor heat exchanger 21 in the general heating mode, thereby increasing a pipe temperature of the indoor heat exchanger 21. As a result, the air to be blown into the indoor space may be rapidly heated.
An inverter system may be applied to the induction heater 60 to control the heat quantity of the induction heater 60. In this case, the supplied heat quantity is adjustable according to the outdoor temperature and the temperature of a heat exchanger requiring defrosting. A method of controlling the heat quantity of the induction heater 60 according to frost quantity on the outdoor heat exchanger 41 will be described hereinafter with reference to the accompanying drawings.
Fig. 2 is a block diagram showing the structure of the air conditioner according to the embodiment.
Referring to Fig. 2, the air conditioner 1 includes an outdoor temperature sensor 110 detecting the outdoor temperature, an indoor temperature sensor 120 detecting temperature of an indoor space, and an outdoor heat exchanger sensor 130 detecting a refrigerant pipe temperature of the outdoor heat exchanger 41.
The air conditioner 1 further includes a controller 100 that receives signals from the sensors 110, 120 and 130 and controls the induction heater 60 which generates heat by variable degrees according to values detected by the sensors 110, 120 and 130.
For a convenient explanation, the outdoor temperature sensor 110, the indoor temperature sensor 120, and the outdoor heat exchanger sensor 130 will be referred to as a first temperature sensor, a second temperature sensor, and a third temperature sensor, respectively.
More particularly, values detected by the sensors 110, 120 and 130 are transmitted to the controller 100. The controller 100 may analyze data transmitted from the sensors 110, 120 and 130 and control the induction heater 60 to generate a preset quantity of heat.
Hereinafter, an "outdoor temperature - outdoor heat exchanger pipe temperature" value (a temperature difference) may be referred to as "GAP." In addition, quantities of heat generated from the induction heater 60 may be classified into P1, P2 and P3. However, more various quantities of heat output may be applied according to the control method of the induction heater 60.
Fig. 3 and Fig. 4 are flowcharts illustrating a method of controlling the air conditioner in a first indoor temperature range. Fig. 5 is a flowchart illustrating a method of controlling the air conditioner in a second indoor temperature range.
The control method of the air conditioner according to the embodiment will now be explained with reference to Fig. 3 to Fig. 5. The flowcharts of Fig. 3 to Fig. 5 show the control method during the defrosting with continuous heating operation.
More specifically, Figs. 3 and 4 show a method of controlling the induction heater according to the outdoor temperature and the outdoor heat exchanger pipe temperature in a case where the indoor temperature is not less than a preset temperature T1 (preset indoor reference temperature). Fig. 5 shows the control method in a case where the indoor temperature is less than T1.
T1 may be preset to about 15°C, but is not limited thereto. That is, T1 may be varied according to the control method of the air conditioner.
First, the indoor temperature is detected by the indoor temperature sensor 120 (S11). When the indoor temperature is not less than T1, the outdoor temperature is detected by the outdoor temperature sensor 110, and it is determined whether the outdoor temperature is greater than a preset temperature T2 (S12, S13, and S14). The preset temperature T₂ may also be referred to as a preset outdoor reference temperature.
Here, T2 may be set to about 0°C, but not limited thereto. That is, T2 may be varied according to the control method of the air conditioner.
The quantity of frost (or a parameter indicative of the amount of frost) formed on the outdoor heat exchanger 41 is determined when the outdoor temperature is not less than T2 (S15). The frost quantity on the outdoor heat exchanger 41 may be determined based on whether the "GAP" (outdoor temperature-outdoor heat exchanger pipe temperature) is greater than a preset temperature difference H1. As the GAP becomes greater, condensed air quantity at the pipe of the outdoor heat exchanger 41 may increase. Consequently, frost is more likely to form on the pipe.
More particularly, temperature of the refrigerant pipe of the outdoor heat exchanger 41 is detected by the outdoor heat exchanger sensor 130. Next, the controller 100 determines the GAP, that is, a difference between the outdoor temperature and the refrigerant pipe temperature. The difference is compared to H1.
Here, H1 may be preset to about 8°C, but not limited thereto. That is, H1 may be varied according to the control method of the air conditioner (S16).
When the GAP is greater than H1, the controller 100 determines that the frost quantity on the outdoor heat exchanger 41 is large. According to this, the controller 100 controls the output of the induction heater 60 to a first output P1 so that the heat quantity of the induction heater 60 is increased. P1 may be preset to about 1200W (S20).
When the GAP is greater than a preset temperature difference H2 and not greater than H1, the controller 100 determines that the frost quantity on the outdoor heat exchanger 41 is medium and, accordingly, controls the output of the induction heater 60 to a second output P2.
Here, H2 may be preset to 4°C different from H1. P2 may be preset to 900W less than P1. However, not limited to those values, H2 and P2 values may be varied according to the control method of the air conditioner (S17 and S19).
On the other hand, when the GAP is determined to be less than H2, the controller 100 determines that the frost quantity on the outdoor heat exchanger 41 is small. According to this, the controller 100 may control the output of the induction heater 60 to a third output P3 so that the heat quantity of the induction heater 60 is reduced.
Here, P3 may be preset to about 600W. However, P3 may be set to any other value as long as less than P2, according to the control method of the air conditioner (S18).
When the outdoor temperature is not greater than T2 in operation S14, it is determined whether the outdoor temperature is greater than a preset temperature T3 and not greater than T2 as shown in Fig. 4 (S21). Here, T3 may be set to about -5°C, but not limited to this, may be varied according to the control method.
When the outdoor temperature is greater than T3 and not greater than T2, the frost quantity on the outdoor heat exchanger 41 is determined (S22). The frost quantity may be determined by whether the GAP is greater than a preset temperature difference H3.
More specifically, the refrigerant pipe temperature of the outdoor heat exchanger 41 is detected by the outdoor heat exchanger sensor 130. The controller 100 determines the GAP through the outdoor temperature and the refrigerant pipe temperature of the outdoor heat exchanger 41. The GAP is compared to the H3 (S23).
Here, H3 may be preset to about 6°C which is different from H1 and H2 values. H3 may be varied according to the control method of the air conditioner.
When the GAP is greater than H3, the controller 100 may determine that the frost quantity on the outdoor heat exchanger 41 is large and accordingly control the output of the induction heater 60 to the first output P1 so that the heat quantity of the induction heater 60 is increased (S20).
When the GAP is greater than a preset temperature difference H4 and not greater than H3 (S24), the controller 100 may determine the frost quantity on the outdoor heat exchanger 41 is medium and accordingly control the output of the induction heater 60 to the second output P2 (S19).
Here, H4 may be preset to about 3°C, but not limited thereto. That is, H4 may be varied according to the control method of the air conditioner.
On the other hand, when the GAP is determined to be less than H4 (S24), the controller 100 may determine that the frost quantity on the outdoor heat exchanger 41 is small and, accordingly, control the output of the induction heater 60 to the third output P3 so that the heat quantity of the induction heater 60 is reduced (S18).
The frost quantity may be determined when the outdoor temperature is not greater than T3 in operation S21 (S25). The frost quantity may be determined based on whether the GAP is greater than a preset temperature difference H5. Here, H5 may be preset to about 7°C, but not limited thereto. That is, H5 may be varied according to the control method of the air conditioner.
When the GAP is greater than H5 (S26), the controller 100 determines that the frost quantity on the outdoor heat exchanger 41 is large and accordingly control the output of the induction heater 60 to the first output P1 so that the heat quantity of the induction heater 60 is increased (S20).
When the GAP is not greater than H5 (S24), the controller 100 may determine the frost quantity on the outdoor heat exchanger 41 is medium and accordingly control the output of the induction heater 60 to the second output P2 (S19).
When the GAP is in a predetermined range, as the outdoor temperature decreases, the frost quantity generally increases, thereby requiring more heat quantity for defrosting. Therefore, when the outdoor temperature is not greater than T3, the output heat quantity of the induction heater 60 may be maintained not less than P2.
When the indoor temperature is less than T1 in operation S12, the outdoor temperature value is determined as shown in Fig. 5 (S31). More particularly, the outdoor temperature is detected by the outdoor temperature sensor 110. The controller 100 determines whether the detected outdoor temperature is greater than T2 (S32). As described above, T2 may be preset to about 0°C.
When the outdoor temperature is greater than T2, the frost quantity on the outdoor heat exchanger 41 is determined. Here, the frost quantity is determined by whether the GAP is greater than a preset temperature difference H6 (S32 and S33).
H6 may be set to about 7°C, but not limited to this. That is, H6 may be varied according to the control method.
When the GAP is greater than H6 (S34), the controller 100 may determine that the frost quantity on the outdoor heat exchanger 41 is large and accordingly control the output of the induction heater 60 to the first output P1 so that the heat quantity of the induction heater 60 is increased (S20).
On the other hand, when the GAP is not greater than H6 (S34), the controller 100 may determine that the frost quantity on the outdoor heat exchanger 41 is medium and accordingly control the output of the induction heater 60 to the second output P2 (S19).
When the outdoor temperature is not greater than T2 in operation S32, it is determined whether the outdoor temperature is greater than T3 and not greater than T2 (S37). When the outdoor temperature is greater than the T3 and not greater than T2, the controller 100 determines the frost quantity (S38).
More specifically, the controller 100 determines whether the GAP is greater than a preset temperature difference H7 (S39). Here, H7 may be preset to about 6°C, but not limited to this, may be varied according to the control method.
When it is determined that the GAP is greater than H7, the controller 100 may determine that the frost quantity on the outdoor heat exchanger 41 is large and, accordingly, control the output of the induction heater 60 to the first output P1 so that the heat quantity of the induction heater 60 is increased (S20).
On the other hand, when it is determined that the GAP is not greater than H7, the controller 100 may determine that the frost quantity on the outdoor heat exchanger 41 is medium and, accordingly, control the output of the induction heater 60 to the second output P2 (S19).
The frost quantity may be determined when the outdoor temperature is not greater than T3 in operation S37 (S40). Here, the frost quantity may be determined by whether the GAP is greater than a preset temperature difference H8. H8 may be preset to about 5°C, but not limited to this, may be varied according to the control method.
When the GAP is greater than H8 (S41), the controller 100 may determine that the frost quantity on the outdoor heat exchanger 41 is large and, accordingly control the output of the induction heater 60 to the first output P1 so that the heat quantity of the induction heater 60 is increased (S20).
On the other hand, when the GAP is not greater than H8, the controller 100 may determine that the frost quantity on the outdoor heat exchanger 41 is medium and, accordingly, control the output of the induction heater 60 to the second output P2 (S19).
Under the condition of the same GAP value, the frost quantity increases as the indoor temperature is low due to the structure of the refrigeration cycle. Accordingly, more heat quantity is required to remove the frost. To this end, when the outdoor temperature is not greater than T1, the output heat quantity of the induction heater 60 may be maintained not less than P2.
In the above description, the H1 to H8 may be referred to as a "first reference temperature" to "eighth reference temperature," respectively, as reference temperatures to determine the GAP obtained through a calculation of "outdoor temperature-outdoor heat exchanger pipe temperature." For example, H2 and H3 may be the second reference temperature and the third reference temperature. As aforementioned, the first to the eighth reference temperatures may be set to respectively different values in accordance with the indoor temperature and the outdoor temperature.
For a convenient explanation, T1 serving as a reference to determine the indoor temperature will be referred to as a "first preset temperature" while T2 and T3 serving as references to determine the outdoor temperature will be referred to as "second preset temperatures." Out of the second preset temperatures, T2 and T3 may be distinguished into a first temperature and a second temperature.
According to the above-described embodiment, the GAP value to determine the frost quantity on the outdoor heat exchanger may be differently set according to temperature ranges including the indoor temperature and the outdoor temperature. Therefore, whether the frost quantity is large or small may be determined by comparing the GAP value to a temperature difference between the detected outdoor temperature and the outdoor heat exchanger pipe temperature.
According to the above-described control method, the frost quantity may be accurately determined under the condition of various indoor and outdoor temperatures and the outdoor heat exchanger pipe temperature.
Furthermore, waste output of the induction heater may be prevented since the output of the induction heater is varied based on whether the frost quantity on the outdoor heat exchanger is large or small. As a result, the efficiency of power consumption may be enhanced.
More specifically, the waste output of the induction heater can be prevented by increasing the heat quantity of the induction heater when the frost quantity on the outdoor heat exchanger is large and decreasing the heat quantity when the frost quantity is small.
As can be appreciated from the above description, the embodiment may improve the indoor heating efficiency through the defrosting with continuous heating operation during which heating and defrosting are simultaneously performed, also achieving defrost of the outdoor heat exchanger.
Quantity of frost formed on the outdoor heat exchanger may be determined in accordance with indoor and outdoor temperatures and the outdoor heat exchanger temperature. In addition, heat quantity of the induction heater may be variably applied according to the frost quantity determined. Therefore, waste of electricity can be reduced.
The induction heater provided to an accumulator reduces outward heat loss, also shortening time for heat transfer from the induction heater to the refrigerant.
Furthermore, because heat of the induction heater is applied to the low-pressure side refrigerant in the heating cycle during the heating operation, the heating efficiency may be improved without the necessity of increasing output of the compressor.
Also, more heat may be transferred to the low-pressure side refrigerant by driving the induction heater during the defrosting operation that removes frost from the evaporator. As a result, the defrosting efficiency of the air conditioner may be improved.

Claims

An air conditioner (1) comprising:
a compressor (10) arranged to compress refrigerant;

an indoor heat exchanger (21) arranged to heat exchange between the refrigerant passed through the compressor (10) and indoor air; an expansion device (30) arranged to decompress the refrigerant passed through the indoor heat exchanger (21);

an outdoor heat exchanger (41) arranged to heat exchange between the refrigerant supplied from the expansion device (30) and outdoor air;

a gas liquid separator (50) provided at an inlet of the compressor (10) to separate liquid refrigerant;

a bypass path (81) arranged to bypass the refrigerant from an outlet of the compressor toward at least one of an inlet of the outdoor heat exchanger (41) and an inlet of the gas liquid separator (50);

a first valve (80) disposed on the bypass path to control a flow of the refrigerant;

a plurality of sensors (110, 120, 130) arranged to sense temperature of the outdoor heat exchanger, indoor temperature and outdoor temperature, respectively;

a heater (60) arranged to generate heat variably according to the outdoor temperature and the outdoor heat exchanger temperature detected by the sensors, the heater (60) comprising an induction heater located at the outside of the gas liquid separator; and

a controller (100) arranged to determine a quantity indicative of the amount of frost formed on the outdoor heat exchanger by comparing a reference temperature (H1) with a temperature difference (GAP) between the outdoor temperature and the outdoor heat exchanger temperature, and controls output of the heater (60) according to the determined frost quantity,

wherein the output of the heater (60) is increased as the temperature difference (GAP) increases and the indoor temperature is greater than a first preset temperature (T1).
The air conditioner according to claim 1, wherein the plurality of sensors comprise an outdoor temperature sensor (110) that detects outdoor temperature, and the output of the heater (60) is controlled according to whether the detected outdoor temperature is greater than a second preset temperature (T2).
A method for controlling an air conditioner comprising a compressor (10), an indoor heat exchanger (21), an expansion device (30), and an outdoor heat exchanger (41) for a refrigeration cycle, a bypass valve arranged to bypass a refrigerant from an outlet of the compressor toward an inlet of the outdoor heat exchanger (41) and a heater (60) located at the outside of a gas liquid separator (50) to heat the refrigerator in the gas liquid separator (50), the method comprising:
comparing indoor temperature with a first preset temperature (T1);

determining a temperature difference (GAP) between the outdoor temperature and a temperature of an outdoor heat exchanger;

comparing the temperature difference (GAP) with a reference temperature (H1); and

controlling heat quantity of a heater (60) arranged to defrost the outdoor heat exchanger, according to a result of the comparison between the temperature difference (GAP) and the reference temperature (H1),

wherein the output of the heater (60) is increased as the temperature difference (GAP) increases and the indoor temperature is greater than the first preset temperature (T1).
The method according to claim 3, further comprising:
comparing outdoor temperature with a second preset temperature (T2) according to a result of the comparison between the indoor temperature and the first preset temperature (T1).
The method according to claim 4, wherein the reference temperature is set to different values (H3,H7) according to whether the indoor temperature is not less than the first preset temperature (T1).
The method according to claim 4 or 5, wherein the reference temperature is set to different values (H1,H3) according to whether the outdoor temperature is not less than the second preset temperature (T2).
The method according to any of claims 3 to 6, wherein the heat quantity of the heater is increased when the temperature difference is greater than the reference temperature.
The method according to any of claims 3 to 7, wherein the heater (60) is adapted to be controlled to provide a first output (P1), a second output (P2) less than the first output, and a third output (P3) less than the second output, and
the heater is controlled to generate heat quantity of at least the second output (P2) when the outdoor temperature is not greater than a second preset temperature (T2).
The method according to claim 8, wherein the heater is controlled to generate heat quantity of at least the second output (P2) when the indoor temperature is less than the first preset temperature.
The method according to claim 9, wherein the step of comparing against a reference temperature includes comparing against a first reference temperature (H1) and a second reference temperature (H2) which is less than the first reference temperature, and under the condition where the outdoor temperature is greater than the second preset temperature,
the heater outputs the first output (P1) when the temperature difference is greater than the first reference temperature,
the heater outputs the second output (P2) when the temperature difference is greater than the second reference temperature but not greater than the first reference temperature, and
the heater outputs the third output (P3) when the temperature difference is not greater than the second reference temperature.
The method according to any of claims 3 to 10, wherein, while an indoor space is heated by the operation of the refrigeration cycle, defrosting of the outdoor heat exchanger is simultaneously performed by bypassing refrigerant from an outlet of the compressor (10) to an inlet of the outdoor heat exchanger (41).