Abstract:
An air conditioner includes a heat generating member, an electromagnetic induction heating unit, an air conditioning target space temperature detecting unit, an outdoor air temperature detecting unit, and a control unit. The heat generating member thermally contacts a refrigerant piping and/or refrigerant that flows through the refrigerant piping. The electromagnetic induction heating unit includes a magnetic field generating part that generating part generates a magnetic field in order to heat the heat generating member by induction heating. The control unit, when the refrigeration cycle is performing heating operation or defrosting operation, inhibits the generation of the magnetic field by the magnetic field generating part when the temperature of the space to be air conditioned and the outside air temperature do not satisfy a first prescribed condition or when a difference between a target set temperature and the temperature of the space does not satisfy a second prescribed condition.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. National stage application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2009-069102, filed in Japan on Mar. 19, 2009, the entire contents of which are hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an air conditioner that comprises: a refrigerant circuit, which connects a compressing mechanism, a condenser, an expansion mechanism, and an evaporator; and a heating unit, which heats a refrigerant inside the refrigerant circuit. 
     BACKGROUND ART 
     In the conventional art of air conditioners that are capable of heating operation, an air conditioner that comprises a refrigerant heating function for the purpose of increasing heating capacity has been proposed. For example, in an air conditioner according to Japanese Laid-open Patent Application Publication No. H06-26696, a refrigerant that flows through a refrigerant heater, which functions as an evaporator, is heated by a burner during heating operation. Here, in the air conditioner recited in Japanese Laid-open Patent Application Publication No. H06-26696, the amount of fuel that the burner burns is controlled during heating operation in accordance with a temperature difference between the temperature of the refrigerant on the inlet side of the refrigerant heater, which functions as an evaporator, and the temperature of the refrigerant on the outlet side of the refrigerant heater. 
     SUMMARY 
     Technical Problem 
     In the art described in Japanese Laid-open Patent Application Publication No. H06-26696, the amount of fuel that the burner burns during heating operation is adjusted in accordance with the temperature difference; however, because the burner burns continuously, there is a possibility that the burner will burn wastefully. For example, it is desirable to reduce the amount of heating output by the burner when the heating load is such that the refrigeration cycle alone—without any heating of the refrigerant—can sufficiently cover heating operation, but the burner performs heating anyway. 
     An object of the present invention is to provide an air conditioner that can prevent wasteful heating of a refrigerant in accordance with the heating load and can quickly perform heating operation either when the heating load is large or when the load demanded by defrosting operation is large, and thereby can make a space to be air conditioned comfortable. 
     Solution to Problem 
     An air conditioner according to a first aspect of the present invention is an air conditioner that comprises a refrigerant circuit, which connects a compressing mechanism, a heat source side heat exchanger, an expansion mechanism, and a utilization side heat exchanger, and wherein performing a refrigeration cycle that uses the refrigerant circuit air conditions a space to be air conditioned such that the temperature of the space to be air conditioned approaches a target set temperature. Furthermore, the air conditioner of the present invention comprises a heat generating member, an electromagnetic induction heating unit, an air conditioning target space temperature detecting unit, an outdoor air temperature detecting unit, and a control unit. The heat generating member thermally contacts a refrigerant piping and/or a refrigerant that flows through the refrigerant piping. The electromagnetic induction heating unit comprises a magnetic field generating part. The magnetic field generating part generates a magnetic field in order to heat the heat generating member by induction heating. The air conditioning target space temperature detecting unit detects the temperature of the space to be air conditioned. The outdoor air temperature detecting unit detects an outside air temperature. The control unit, when the refrigeration cycle is performing heating operation or defrosting operation, inhibits the generation of the magnetic field by the magnetic field generating part in the case wherein the temperature of the space to be air conditioned and the outside air temperature do not satisfy a first prescribed condition or the case wherein the temperature difference between the target set temperature and the temperature of the space to be air conditioned does not satisfy a second prescribed condition. 
     The air conditioner of the present invention comprises a refrigerant circuit that comprises an electromagnetic induction heating unit that, by virtue of the magnetic field generating part heating the heat generating member by induction heating, heats the refrigerant piping, which thermally contacts the heat generating member, and/or the refrigerant that flows through the refrigerant piping. Namely, in this air conditioner, the refrigerant that flows through the refrigerant piping can be heated by causing the electromagnetic induction heating unit to operate. In the present invention, in such an air conditioner, the control unit permits the electromagnetic induction heating unit to be operated (i.e., permits the magnetic field generating part to generate a magnetic field) if the temperature of the space to be air conditioned and the outside air temperature satisfy the first prescribed condition and the temperature difference between the target set temperature and the temperature of the space to be air conditioned satisfies the second prescribed condition. 
     Thus, the control unit determines the magnitude of the heating load of the space to be air conditioned or the load demanded by defrosting operation by determining whether the temperature of the space to be air conditioned and the outside air temperature satisfy the first prescribed condition and whether the temperature difference between the target set temperature and the temperature of the space to be air conditioned satisfies the second prescribed condition. Accordingly, the control unit can cause the electromagnetic induction heating unit to operate only when the heating load or the load demanded by defrosting operation is large and heating of the refrigerant by the electromagnetic induction heating unit is necessary. Consequently, if the heating load or the load demanded by defrosting operation is large, then the operation of heating the space to be air conditioned can be performed quickly and thereby a comfortable space can be provided for the user. In addition, because the electromagnetic induction heating unit is not operated wastefully, it is possible to reduce energy consumption. 
     An air conditioner according to a second aspect of the present invention is the air conditioner according to the first aspect of the present invention, wherein the heat generating member includes a ferromagnetic material. 
     In this air conditioner, heating by electromagnetic induction can be performed efficiently because the magnetic field generating part is caused to generate a magnetic field in a portion that includes the ferromagnetic material. 
     An air conditioner according to a third aspect of the present invention is the air conditioner according to the first or second aspects of the present invention, wherein the case wherein the temperature of the space to be air conditioned and the outside air temperature satisfy the first prescribed condition is the case wherein the temperature of the space to be air conditioned and the outside air temperature are in a first temperature region at the startup of the heating operation or during the defrosting operation. The case wherein the temperature difference satisfies the second prescribed condition is the case wherein the temperature difference exceeds a first prescribed temperature at the startup of the heating operation or during defrosting operation. 
     In the air conditioner of the present invention, the control unit determines that the heating load of the space to be air conditioned or the load demanded by the defrosting operation is large if, at the startup of heating operation or during defrosting operation, the temperature of the space to be air conditioned and the outside air temperature are in the first temperature region and the temperature difference exceeds the first prescribed temperature. 
     Accordingly, the control unit can cause the electromagnetic induction heating unit to operate at the startup of heating operation and during defrosting operation only when the heating load is large and heating of the refrigerant by the electromagnetic induction heating unit is necessary. Consequently, if the heating load is large, then the operation of heating the space to be air conditioned can be performed quickly and thereby a comfortable space can be provided for the user. In addition, because the electromagnetic induction heating unit is not operated wastefully, it is possible to reduce energy consumption. 
     An air conditioner according to a fourth aspect of the present invention is the air conditioner according to the third aspect of the present invention, wherein the control unit further inhibits the generation of the magnetic field by the magnetic field generating part if the rotational frequency of the compressing mechanism is less than or equal to a prescribed frequency at the startup of the heating operation or during defrosting operation. 
     Accordingly, the control unit can cause the electromagnetic induction heating unit to operate at the startup of heating operation or during defrosting operation only when the heating load is large and it is necessary for the electromagnetic induction heating unit to heat the refrigerant. Consequently, during the startup of heating operation, supplementary heating can be performed only if the heating load is large, and consequently heating operation can be started up quickly. In addition, during defrosting operation, supplementary heating can be performed only if the load demanded by defrosting operation is large, and consequently the time needed to perform defrosting operation can be shortened. In addition, because the electromagnetic induction heating unit is not operated wastefully, it is possible to reduce energy consumption. 
     An air conditioner according to a fifth aspect of the present invention is the air conditioner according to the third or fourth aspects of the present invention, wherein the control unit further inhibits the generation of the magnetic field by the magnetic field generating part during heating operation, excepting at the startup of the heating operation, in the case wherein the rotational frequency of the compressing mechanism is less than or equal to the prescribed frequency or the case wherein the temperature of the space to be air conditioned and the outside air temperature deviate from a second temperature region. 
     In the air conditioner of the present invention, the control unit determines that the heating load of the space to be air conditioned is large if, during heating operation excepting at the startup of heating operation, the rotational frequency of the compressing mechanism exceeds the prescribed frequency and the temperature of the space to be air conditioned and the outside air temperature are in the second temperature region. 
     Accordingly, the control unit can cause the electromagnetic induction heating unit to operate during heating operation excepting at the startup of heating operation (i.e., during regular heating operation) only when the heating load is large and heating of the refrigerant by the electromagnetic induction heating unit is necessary. Consequently, if the heating load is large, then the operation of heating the space to be air conditioned can be performed quickly and thereby a comfortable space can be provided for the user. In addition, because the electromagnetic induction heating unit is not operated wastefully, it is possible to reduce energy consumption. 
     An air conditioner according to a sixth aspect of the present invention is the air conditioner according to the fifth aspect of the present invention, wherein the second temperature region is narrower than the first temperature region. 
     In the air conditioner of the present invention, the electromagnetic induction heating unit is operated under stricter conditions during regular heating operation than at the startup of heating operation. During regular heating operation, the compressor is in the state wherein it is already running, and consequently is in a warmer state than at the startup of heating operation. Consequently, regardless of whether it is determined, that heating of the refrigerant is necessary or unnecessary in the second temperature region at the startup of heating operation, which is narrower than the first temperature region, the heating load can be made to track heating capacity sufficiently and quickly during regular heating operation. 
     Thus, by making the determination during regular heating operation using a temperature condition that is narrower than that used at the startup of heating operation, the control unit can prevent the wasteful heating of the refrigerant more than would be the case if the magnitude of the heating load were determined using the same temperature region for the startup of the heating operation as for regular heating operation. Consequently, energy consumption can be reduced. 
     Advantageous Effects of Invention 
     In the air conditioner according to the first aspect of the present invention, the control unit determines the magnitude of the heating load of the space to be air conditioned or the load demanded by defrosting operation by determining whether the temperature of the space to be air conditioned and the outside air temperature satisfy the first prescribed condition and whether the temperature difference between the target set temperature and the temperature of the space to be air conditioned satisfies the second prescribed condition. Accordingly, the control unit can cause the electromagnetic induction heating unit to operate only when the heating load or the load demanded by defrosting operation is large and heating of the refrigerant by the electromagnetic induction heating unit is necessary. Consequently, if the heating load or the load demanded by defrosting operation is large, then the operation of heating the space to be air conditioned can be performed quickly and thereby a comfortable space can be provided for the user. In addition, because the electromagnetic induction heating unit is not operated wastefully, it is possible to reduce energy consumption. 
     In the air conditioner according to the second aspect of the present invention, heating by electromagnetic induction can be performed efficiently because the magnetic field generating part is caused to generate a magnetic field in a portion that includes the ferromagnetic material. 
     In the air conditioner according to the third aspect of the present invention, the control unit can cause the electromagnetic induction heating unit to operate at the startup of heating operation and during defrosting operation only when the heating load is large and heating of the refrigerant by the electromagnetic induction heating unit is necessary. Consequently, if the heating load is large, then the operation of heating the space to be air conditioned can be performed quickly and thereby a comfortable space can be provided for the user. In addition, because the electromagnetic induction heating unit is not operated wastefully, it is possible to reduce energy consumption. 
     In the air conditioner according to the fourth aspect of the present invention, the control unit can cause the electromagnetic induction heating unit to operate at the startup of heating operation or during defrosting operation only when the heating load is large and it is necessary for the electromagnetic induction heating unit to heat the refrigerant. Consequently, during the startup of heating operation, supplementary heating can be performed only if the heating load is large, and consequently heating operation can be started up quickly. In addition, during defrosting operation, supplementary heating can be performed only if the load demanded by defrosting operation is large, and consequently the time needed to perform defrosting operation can be shortened. In addition, because the electromagnetic induction heating unit is not operated wastefully, it is possible to reduce energy consumption. 
     In the air conditioner according to the fifth aspect of the present invention, the control unit can cause the electromagnetic induction heating unit to operate during heating operation excepting at the startup of heating operation (i.e., during regular heating operation) only when the heating load is large and heating of the refrigerant by the electromagnetic induction heating unit is necessary. Consequently, if the heating load is large, then the operation of heating the space to be air conditioned can be performed quickly and thereby a comfortable space can be provided for the user. In addition, because the electromagnetic induction heating unit is not operated wastefully, it is possible to reduce energy consumption. 
     In the air conditioner according to the sixth aspect of the present invention, by making the determination during regular heating operation using a temperature condition that is narrower than that used at the startup of heating operation, the control unit can prevent the wasteful heating of the refrigerant more than would be the case if the magnitude of the heating load were determined using the same temperature region for the startup of the heating operation as for regular heating operation. Consequently, energy consumption can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a refrigerant circuit diagram of an air conditioner that uses a refrigeration apparatus according to one embodiment of the present invention. 
         FIG. 2  is an external oblique view of an outdoor unit, viewed from the front surface side. 
         FIG. 3  is an external oblique view of the outdoor unit, viewed from the rear surface side. 
         FIG. 4  is an oblique view of the outdoor unit with the right side surface panel and the rear surface panel removed. 
         FIG. 5  is a plan view of the outdoor unit with only the bottom plate and the machine chamber remaining. 
         FIG. 6  is a cross sectional view of an electromagnetic induction heating unit. 
         FIG. 7  is a graph that shows, as temperature regions, a heating operation permitted condition, an electromagnetic induction heating unit operation permitted condition at startup and during defrosting operation, and an electromagnetic induction heating unit operation permitted condition during regular heating operation based on the relationship between an outside air temperature and an indoor temperature. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments of the present invention will now be explained, referencing the drawings. Furthermore, the embodiments below are merely illustrative examples of the present invention and do not limit its technical scope. 
     &lt;Air Conditioner&gt; 
       FIG. 1  is a block diagram of an air conditioner that uses a refrigeration apparatus according to one embodiment of the present invention. In an air conditioner  1  in  FIG. 1 , an outdoor unit  2 , which serves as a heat source unit, and an indoor unit  4 , which serves as a utilization unit, are connected by refrigerant pipings, and thereby a refrigerant circuit  10  that performs a vapor compression type refrigeration cycle is formed. 
     The outdoor unit  2  houses a compressor  21 , a four-way switching valve  22 , an outdoor heat exchanger  23 , a motor operated expansion valve  24 , an accumulator  25 , outdoor fans  26 , a hot gas bypass valve  27 , a capillary tube  28 , and an electromagnetic induction heating unit  6 . The indoor unit  4  houses an indoor heat exchanger  41  and an indoor fan  42 . 
     The refrigerant circuit  10  comprises a discharge pipe  10   a , a gas pipe  10   b , a liquid pipe  10   c , an outdoor side liquid pipe  10   d , an outdoor side gas pipe  10   e , an accumulator pipe  10   f , a suction pipe  10   g , and a hot gas bypass  10   h.    
     The discharge pipe  10   a  connects the compressor  21  and the four-way switching valve  22 . The gas pipe  10   b  connects the four-way switching valve  22  and the indoor heat exchanger  41 . The liquid pipe  10   c  connects the indoor heat exchanger  41  and the motor operated expansion valve  24 . The outdoor side liquid pipe  10   d  connects the motor operated expansion valve  24  and the outdoor heat exchanger  23 . The outdoor side gas pipe  10   e  connects the outdoor heat exchanger  23  and the four-way switching valve  22 . 
     The accumulator pipe  10   f  connects the four-way switching valve  22  and the accumulator  25 . The electromagnetic induction heating unit  6  is mounted to one portion of the accumulator pipe  10   f . At least the portion of the accumulator pipe  10   f  that is covered by the electromagnetic induction heating unit  6  and is to be heated is a copper pipe wrapped in a stainless steel pipe. Of the piping that constitutes the refrigerant circuit  10 , the portion outside of the stainless steel pipe is copper pipe. 
     The suction pipe  10   g  connects the accumulator  25  and the inlet side of the compressor  21 . The hot gas bypass  10   h  connects a branching point A 1 , which is provided along the discharge pipe  10   a , and a branching point D 1 , which is provided along the outdoor side liquid pipe  10   d.    
     The hot gas bypass valve  27  is disposed along the hot gas bypass  10   h . To switch between the state wherein the flow of the refrigerant through the hot gas bypass  10   h  is permitted and the state wherein it is not permitted, a control unit  11  opens and closes the hot gas bypass valve  27 . In addition, the capillary tube  28 , wherein the cross sectional area of the refrigerant channel is reduced, is provided on the downstream side of the hot gas bypass valve  27 ; furthermore, during defrosting operation, a constant ratio of the refrigerant that flows through the outdoor heat exchanger  23  to the refrigerant that flows through the hot gas bypass  10   h  is maintained. 
     The four-way switching valve  22  can switch between a cooling operation cycle and a heating operation cycle. In  FIG. 1 , solid lines indicate the connection state for performing heating operation, and dotted lines indicate the connection state for performing cooling operation. During heating operation, the indoor heat exchanger  41  functions as a condenser, and the outdoor heat exchanger  23  functions as an evaporator. During cooling operation, the outdoor heat exchanger  23  functions as a condenser, and the indoor heat exchanger  41  functions as an evaporator. 
     The outdoor fans  26 , which deliver outdoor air to the outdoor heat exchanger  23 , are provided in the vicinity of the outdoor heat exchanger  23 . The indoor fan  42 , which delivers indoor air to the indoor heat exchanger  41 , is provided in the vicinity of the indoor heat exchanger  41 . 
     In addition, various sensors are provided to the outdoor unit  2  and the indoor unit  4 . 
     Specifically, the outdoor unit  2  is provided with: a discharge pressure sensor Ps, which detects a discharge pressure (i.e., a high-pressure pressure Ph) of the compressor  21 ; a discharge temperature sensor T 21 , which detects a discharge temperature Td of the compressor  21 ; a first liquid side temperature sensor T 22 , which detects a temperature of the refrigerant in the liquid state or the vapor-liquid two-phase state on the liquid side of the outdoor heat exchanger  23 ; an outdoor heat exchanger sensor T 23 , which detects a temperature (i.e., an outdoor heat exchanger temperature Tm) of the outdoor heat exchanger  23 ; and an inlet temperature sensor T 25 , which detects an inlet temperature (i.e., a suction temperature Tsu) of the accumulator  25 . In addition, an outdoor temperature sensor T 24 , which detects the temperature of the outdoor air that flows into the outdoor unit  2  (i.e., the outdoor air temperature Ta), is provided to the outdoor air suction port side of the outdoor unit  2 . 
     In addition, in the indoor unit  4 , a second liquid side temperature sensor T 41 , which detects the temperature of the refrigerant (i.e., the condensing temperature during the heating operation or the refrigerant temperature that corresponds to the evaporating temperature during the cooling operation), is provided to the liquid side of the indoor heat exchanger  41 . An indoor temperature sensor T 42 , which detects the temperature of the indoor air (i.e., an indoor temperature Tr) that flows into the indoor unit  4 , is provided to the indoor air suction port side of the indoor unit  4 . In the present embodiment, the discharge temperature sensor T 21 , the first liquid side temperature sensor T 22 , the outdoor heat exchanger temperature sensor T 23 , the outdoor temperature sensor T 24 , the inlet temperature sensor T 25 , the second liquid side temperature sensor T 41 , and the indoor temperature sensor T 42  are each a thermistor. 
     The control unit  11  comprises an outdoor control unit  11   a  and an indoor control unit  11   b . The outdoor control unit  11   a  and the indoor control unit  11   b  are connected by a communication line  11   c . Furthermore, the outdoor control unit  11   a  controls equipment disposed inside the outdoor unit  2 , and the indoor control unit  11   b  controls equipment disposed inside the indoor unit  4 . Furthermore, the control unit  11  is connected such that it can receive detection signals of the various sensors Ps, T 21 -T 25 , T 41 , T 42  and such that it can control various valves and equipment  6 ,  21 ,  22 ,  24 ,  26 ,  42  based on those detection signals and the like. 
     (External Appearance of Outdoor Unit) 
       FIG. 2  is an external oblique view of the outdoor unit  2 , viewed from the front surface side, and  FIG. 3  is an external oblique view of the outdoor unit  2 , viewed from the rear surface side. In  FIG. 2  to  FIG. 5 , a shell of the outdoor unit  2  is formed as a substantially rectangular parallelepiped by a top plate  2   a , a bottom plate  2   b , a front panel  2   c , a left side surface panel  2   d , a right side surface panel  2   f , and a rear surface panel  2   e.    
     (Interior of the Outdoor Unit) 
       FIG. 4  is an oblique view of the outdoor unit  2  with the right side surface panel and the rear surface panel removed. In  FIG. 4 , a partition plate  2   h  partitions the outdoor unit  2  into a fan chamber and a machine chamber. The outdoor heat exchanger  23  and the outdoor fans  26  (refer to  FIG. 1 ) are disposed in the fan chamber, and the electromagnetic induction heating unit  6 , the compressor  21 , and the accumulator  25  are disposed in the machine chamber. 
     (Structure of Vicinity of Bottom Plate of Outdoor Unit) 
       FIG. 5  is a plan view of the outdoor unit  2  with only the bottom plate  2   b  and the machine chamber remaining. Furthermore, in  FIG. 5 , chain double-dashed lines are used to represent the outdoor heat exchanger  23  so that its position is known. The hot gas bypass  10   h  is disposed above the bottom plate  2   b , extends from the machine chamber, wherein the compressor  21  is positioned, to the fan chamber, makes a circuit through the fan chamber, and then returns to the machine chamber. Approximately half of the overall length of the hot gas bypass  10   h  lies below the outdoor heat exchanger  23 . In addition, water discharge ports  86   a - 86   e , which pass through the bottom plate  2   b  in the plate thickness directions, are formed in portions of the bottom plate  2   b  that are positioned below the outdoor heat exchanger  23 . 
     (Electromagnetic Induction Heating Unit) 
       FIG. 6  is a cross sectional view of the electromagnetic induction heating unit  6 . In  FIG. 6 , the electromagnetic induction heating unit  6  is disposed such that the portion  11   f  of the accumulator pipe  10   f  that is to be heated is covered from the outer side in the radial directions and heated by electromagnetic induction. The portion  11   f  of the accumulator pipe  10   f  to be heated has a double pipe structure comprising a copper pipe on the inner side and a stainless steel pipe  100   f  on the outer side. Ferritic stainless steel that contains 16%-18% chrome or precipitation hardening stainless steel that contains 3%-5% nickel, 15%-17.5% chrome, and 3%-5% copper is used as the stainless steel material of the stainless steel pipe  100   f.    
     First, the electromagnetic induction heating unit  6  is positioned at the accumulator pipe  10   f ; next, the vicinity of the upper end of the electromagnetic induction heating unit  6  is fixed by a first hex nut  61 ; lastly, the vicinity of the lower end of the electromagnetic induction heating unit  6  is fixed by a second hex nut  66 . 
     A coil  68  is wound helically around the outer side of a bobbin main body  65 , with the directions in which the accumulator pipe  10   f  extends being the axial directions of the winding. The coil  68  is housed on the inner side of a ferrite case  71 . The ferrite case  71  further houses first ferrite parts  98  and second ferrite parts  99 . 
     The first ferrite parts  98  are formed from ferrite, which has high magnetic permeability; furthermore, when an electric current flows to the coil  68 , the first ferrite parts  98  capture the magnetic flux generated even in portions outside of the stainless steel pipe  100   f  and form a path for that magnetic flux. The first ferrite parts  98  are positioned on both end sides of the ferrite case  71 . 
     Although their placement positions and shapes differ from those of the first ferrite parts  98 , the second ferrite parts  99  function in the same manner as the first ferrite parts  98  and are positioned in the housing part of the ferrite case  71  in the vicinity of the outer side of the bobbin main body  65 . 
     &lt;Operation of Air Conditioner&gt; 
     In the air conditioner  1 , the four-way switching valve  22  is capable of switching between cooling operation and heating operation. 
     (Cooling Operation) 
     In cooling operation, the four-way switching valve  22  is set to the state indicated by the dotted lines in  FIG. 1 . When the compressor  21  is operated in this state, a vapor compression refrigeration cycle is performed in the refrigerant circuit  10  wherein the outdoor heat exchanger  23  becomes a condenser and the indoor heat exchanger  41  becomes an evaporator. 
     The outdoor heat exchanger  23  exchanges the heat of the high pressure refrigerant discharged from the compressor  21  with the outdoor air, whereupon the refrigerant condenses. When the refrigerant that passed through the outdoor heat exchanger  23  passes through the expansion valve  24 , the refrigerant&#39;s pressure is reduced; subsequently, the indoor heat exchanger  41  exchanges the heat of the refrigerant with the indoor air, whereupon the refrigerant evaporates. Furthermore, the indoor air, whose temperature has dropped owing to the exchange of its heat with the refrigerant, is blown out to a space to be air conditioned. The refrigerant that passed through the indoor heat exchanger  41  is suctioned into the compressor  21  and compressed. 
     (Heating Operation) 
     In the heating operation, the four-way switching valve  22  is set to the state indicated by the solid lines in  FIG. 1 . When the compressor  21  is operated in this state, the vapor compression refrigeration cycle is performed in the refrigerant circuit  10 , wherein the outdoor heat exchanger  23  becomes an evaporator and the indoor heat exchanger  41  becomes a condenser. 
     The indoor heat exchanger  41  exchanges the heat of the high pressure refrigerant discharged from the compressor  21  with the indoor air, whereupon the refrigerant condenses. Furthermore, the indoor air, whose temperature has risen owing to the exchange of its heat with the refrigerant, is blown out to the space to be air conditioned. When the condensed refrigerant passes through the expansion valve  24 , the refrigerant&#39;s pressure is reduced; subsequently, the outdoor heat exchanger  23  exchanges the heat of the refrigerant with the outdoor air, whereupon the refrigerant evaporates. The refrigerant that passed through the outdoor heat exchanger  23  is suctioned into the compressor  21 , where it is compressed. 
     In heating operation, capacity shortfall can be supplemented at startup, particularly when the compressor  21  is not sufficiently warmed up, by the electromagnetic induction heating unit  6  heating the refrigerant. 
     (Defrosting Operation) 
     When the outdoor air temperature is between −5° C. and +5° C. and heating operation has been performed, moisture contained in the air either condenses on the surface of the outdoor heat exchanger  23  and then turns to frost or freezes and covers the surface of the outdoor heat exchanger  23 , in both cases reducing heat exchange performance. The defrosting operation is performed to melt the frost or ice adhered to the outdoor heat exchanger  23 . The defrosting operation is performed with the same cycle as that of the cooling operation. 
     The heat of the high pressure refrigerant discharged from the compressor  21  is exchanged with the outdoor air by the outdoor heat exchanger  23 , whereupon the refrigerant condenses. The heat radiated from that refrigerant melts the frost or ice covering the outdoor heat exchanger  23 . When the condensed refrigerant passes through the expansion valve  24 , its pressure is reduced; subsequently, the indoor heat exchanger  41  exchanges the heat of the refrigerant with the indoor air, whereupon the refrigerant evaporates. At this time, the indoor fan  42  is stopped. This is because if the indoor fan  42  were operating, then cooled air would be blown out to the space to be air conditioned, which would adversely affect user comfort. Furthermore, the refrigerant that passed through the indoor heat exchanger  41  is suctioned into the compressor  21  and compressed. 
     In addition, during defrosting operation, the electromagnetic induction heating unit  6  heats the accumulator pipe  10   f , and thereby the compressor  21  can compress the heated refrigerant. As a result, the temperature of the gas refrigerant discharged from the compressor  21  rises, and the time needed to melt the frost decreases. Furthermore, the time needed to return from the defrosting operation back to the heating operation shortens. 
     In addition, during defrosting operation, the high pressure refrigerant discharged from the compressor  21  flows also to the hot gas bypass  10   h . Even if ice grows on the bottom plate  2   b  of the outdoor unit  2 , that ice is melted by the heat radiated from the refrigerant that passes through the hot gas bypass  10   h . The water produced at that time is discharged via the water discharge ports  86   a - 86   e . In addition, the hot gas bypass  10   h  also heats the water discharge ports  86   a - 86   e , which prevents the water discharge ports  86   a - 86   e  from freezing and getting plugged up. 
     &lt;Electromagnetic Induction Heating Unit Operation Permitted Condition&gt; 
     If the heating load during heating operation is large or if the load demanded by the defrosting operation is large, then the control unit permits the operation of the electromagnetic induction heating unit  6 . Namely, only if the heating load is large or the load demanded by the defrosting operation is large, then the electromagnetic induction heating unit  6  is permitted to heat the refrigerant and thereby to supplement the heating capacity or to supplement the defrosting capacity of defrosting operation. In the air conditioner  1  according to the present embodiment, the conditions under which the electromagnetic induction heating unit  6  is permitted to operate differs for the case of heating operation startup or defrosting operation and for the cases other than heating operation startup (i.e., regular heating operation). 
     Incidentally, heating operation performed by the air conditioner  1  according to the present embodiment is performed under the temperature condition enclosed by the solid lines in  FIG. 7 . Here,  FIG. 7  shows as temperature regions a heating operation permitted condition, an electromagnetic induction heating unit operation permitted condition at startup and during defrosting operation, and an electromagnetic induction heating unit operation permitted condition during regular heating operation based on the relationship between an outside air temperature and an indoor temperature. Furthermore, if the outside air temperature Ta is high and the indoor temperature Tr is low (e.g., if the outside air temperature Ta is 15° C. and the indoor temperature Tr is 10° C.), then heating operation is not permitted and the temperature region of the heating operation permitted condition in  FIG. 7  is a quadrilateral with a missing corner, namely, a pentagon. The heating operation permitted region is incomplete because, in the missing region, the outside air temperature Ta is high and the indoor temperature Tr is low and consequently the indoor temperature Tr can be increased by taking in the outside air as is without performing heating operation. Accordingly, energy consumption can be reduced by permitting heating operation in such a temperature region. 
     The text below separately explains, referencing  FIG. 7 , the electromagnetic induction heating unit operation permitted condition for two cases: at heating operation startup or during defrosting operation; and during regular heating operation. 
     (Operation Permitted Condition at Heating Operation Startup or During Defrosting Operation) 
     At heating operation startup or during defrosting operation, the control unit  11  permits the operation of the electromagnetic induction heating unit  6  if the range of the outside air temperature Ta is Ta&lt;8° C. (refer to the broken line in  FIG. 7 ); the range of the indoor temperature Tr is Tr&lt;21° C. (refer to the broken line in  FIG. 7 ); a temperature difference ΔTrs calculated by subtracting the indoor temperature Tr detected by the indoor temperature sensor T 42  from the indoor set temperature Tse, which serves as the indoor space target set temperature set by an inputting unit (not shown) such as a remote control, exceeds 1K; and the rotational frequency of the compressor  21  exceeds a maximum frequency (in the present embodiment, 184 Hz). Conversely, if the operation permitted condition is not satisfied, then it is determined that the heating load or the load demanded by defrosting operation is small and therefore operation of the electromagnetic induction heating unit  6  is inhibited. Furthermore, “at the startup of heating operation” refers to the interval of ten minutes since the user started heating operation via the inputting unit (not shown) such as a remote control. Namely, operation transitions to regular heating operation after ten minutes have elapsed since heating operation started. 
     (Operation Permitted Condition During Regular Heating Operation) 
     During regular heating operation, the control unit  11  permits the operation of the electromagnetic induction heating unit  6  if the range of the outside air temperature Ta is Ta&lt;−5° C. (refer to the chain single-dashed line in  FIG. 7 ); the range of the indoor temperature Tr is Tr&lt;21° C. (refer to the chain single-dashed line in  FIG. 7 ); the temperature difference ΔTrs calculated by subtracting the indoor temperature Tr detected by the indoor temperature sensor T 42  from the indoor set temperature Tse, which serves as the indoor space target set temperature set via an inputting unit (not shown) such as a remote control, exceeds 1K; and the rotational frequency of the compressor  21  exceeds the maximum frequency (in the present embodiment, 184 Hz). Conversely, if the operation permitted condition is not satisfied, then it is determined that the heating load is small and therefore the operation of the electromagnetic induction heating unit  6  is inhibited. 
     &lt;Characteristics&gt; 
     In the air conditioner  1  of the present embodiment, at heating operation startup or during defrosting operation, the control unit  11  determines that the heating load is large or the load demanded by defrosting operation is large and permits the operation of the electromagnetic induction heating unit  6  if the range of the outside air temperature Ta is Ta&lt;8° C.; the range of the indoor temperature Tr is Tr&lt;21° C.; the temperature difference ΔTrs calculated by subtracting the indoor temperature Tr detected by the indoor temperature sensor T 42  from the indoor set temperature Tse, which serves as the indoor space target set temperature set by an inputting unit such as a remote control, exceeds 1K; and the rotational frequency of the compressor  21  exceeds a maximum frequency. 
     In addition, in the air conditioner  1 , during regular heating operation, the control unit  11  determines that the heating load is large and permits the operation of the electromagnetic induction heating unit  6  if the range of the outside air temperature Ta is Ta&lt;−5° C.; the range of the indoor temperature Tr is Tr&lt;21° C.; the temperature difference ΔTrs calculated by subtracting the indoor temperature Tr detected by the indoor temperature sensor T 42  from the indoor set temperature Tse, which serves as the indoor space target set temperature set via an inputting unit (not shown) such as a remote control, exceeds 1K; and the rotational frequency of the compressor  21  exceeds the maximum frequency (in the present embodiment, 184 Hz). 
     Thus, the control unit  11  determines the magnitude of the heating load of the indoor space or the load demanded by defrosting operation. In addition, the control unit  11  divides the condition for determining the magnitude of the heating load during heating operation into two cases: at startup and during regular heating operation. Accordingly, the control unit  11  can cause the electromagnetic induction heating unit  6  to operate only when the heating load or the load demanded by defrosting operation is large and heating of the refrigerant by the electromagnetic induction heating unit  6  is necessary. Consequently, if the heating load or the load demanded by defrosting operation is large, then the operation of heating the indoor space can be performed quickly and thereby a comfortable space can be provided for the user. In addition, because the electromagnetic induction heating unit  6  is not operated wastefully, it is possible to reduce energy consumption. 
     &lt;Modified Examples&gt; 
     (1) 
     In the air conditioner  1  according to the abovementioned embodiment, the operation permitted condition for the electromagnetic induction heating unit  6  during regular heating operation is set, but does not particularly have to be set. This is because it is conceivable that there are fewer opportunities for the electromagnetic induction heating unit  6  to operate than would be the case at heating operation startup and during defrosting operation. Nevertheless, even during regular heating operation, as in the air conditioner  1  of the present embodiment, determining the operation permitted condition of the electromagnetic induction heating unit  6  and causing the electromagnetic induction heating unit  6  to operate accordingly is effective in that the indoor space is made comfortable for the user when the heating load is large. 
     (2) 
     In the air conditioner  1  according to the abovementioned embodiment, under the operation permitted condition at heating operation startup or during defrosting operation, the control unit  11  permits the operation of the electromagnetic induction heating unit  6  if the range of the outside air temperature Ta is Ta&lt;8° C. (refer to the broken line in  FIG. 7 ); the range of the indoor temperature Tr is Tr&lt;21° C. (refer to the broken line in  FIG. 7 ); the temperature difference ΔTrs calculated by subtracting the indoor temperature Tr detected by the indoor temperature sensor T 42  from the indoor set temperature Tse, which serves as the indoor space target set temperature set by an inputting unit (not shown) such as a remote control, exceeds 1K; and the rotational frequency of the compressor  21  exceeds the maximum frequency (in the present embodiment, 184 Hz); however, this does not necessarily include the condition wherein the rotational frequency of the compressor  21  exceeds the maximum frequency (in the present embodiment, 184 Hz). This applies also to the operation permitted condition during regular heating operation. 
     INDUSTRIAL APPLICABILITY 
     The present invention is useful in an air conditioner for cold regions.