Patent Publication Number: US-2022214069-A1

Title: Air conditioner

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of International Application No. PCT/JP2020/034321, filed on Sep. 10, 2020. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to air conditioners. 
     BACKGROUND ART 
     There is known an air conditioner in which a drain pan where drain water is stored is irradiated with deep ultraviolet rays having a relatively short wavelength among the ultraviolet rays (see, for example, Japanese Laid-Open Patent Publication No. 2017-133700). The irradiation with deep ultraviolet rays causes denaturation or inactivation of bacteria, mold, or the like contained in the drain water (hereinafter, referred to as “sterilization”). 
     SUMMARY 
     As disclosed in Patent Literature 1, when it is determined that the air conditioner is in cooling operation, irradiation with deep ultraviolet rays is started. Accordingly, the irradiation with deep ultraviolet rays continues without stop during the cooling operation. This causes the irradiation with deep ultraviolet rays to be made for a long time, which shortens the life of an irradiation unit responsible for the irradiation with deep ultraviolet rays. 
     The present disclosure provides an air conditioner that makes the life of an irradiation unit longer. 
     An air conditioner according to an aspect of the present disclosure includes: a heat exchanger provided in an indoor unit of the air conditioner, a drain pan configured to receive drain water generated in the heat exchanger, an irradiation unit configured to irradiate the drain pan with ultraviolet rays, and a control unit configured to control ultraviolet intensity of the ultraviolet rays from the irradiation unit. The control unit controls the irradiation unit to make the ultraviolet intensity after a cooling operation larger than the ultraviolet intensity during the cooling operation. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a refrigerant circuit of an air conditioner according to an embodiment. 
         FIG. 2  is a control block diagram of the air conditioner illustrated in  FIG. 1 . 
         FIG. 3  is a schematic cross-sectional view of an indoor unit that is out of operation, the indoor unit being a component of the air conditioner illustrated in  FIG. 1 . 
         FIG. 4  is a control flowchart of irradiation with ultraviolet rays performed by the air conditioner. 
         FIG. 5  is a control flowchart of irradiation with ultraviolet rays performed by the air conditioner according to the other embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     Hereinafter, an air conditioner according to an embodiment of the present disclosure will be described with reference to the drawings. Note that the same parts in the drawings are denoted by the same reference sign, and no redundant description will be given. 
     [Overall Configuration of Air Conditioner  1 ] 
       FIG. 1  is a diagram illustrating a refrigerant circuit of an air conditioner  1  according to the embodiment of the present disclosure. As illustrated in  FIG. 1 , the air conditioner  1  includes an indoor unit  2  installed indoors and an outdoor unit  3  installed outdoors, the indoor unit  2  and the outdoor unit  3  being connected with each other via connection pipes L 1 , L 2 . The air conditioner  1  is of a type in which the indoor unit  2  is paired one-to-one with the outdoor unit  3 . 
     The indoor unit  2  is equipped with an indoor heat exchanger  4  and an indoor fan  5 . The outdoor unit  3  is equipped with a compressor  6 , a four-way switching valve  7 , an outdoor heat exchanger  8 , an outdoor fan  9 , an electric expansion valve (hereinafter, referred to as an expansion valve)  10  as an example of the decompressing mechanism, and an accumulator  11 . The outdoor unit  3  is further provided with a liquid-side shutoff valve  12  and a gas-side shutoff valve  13 . 
     The compressor  6 , the four-way switching valve  7 , the outdoor heat exchanger  8 , the expansion valve  10 , the indoor heat exchanger  4 , the accumulator  11 , and the compressor  6  are connected in this order via a refrigerant pipe and the connection pipes L 1 , L 2  to form a refrigerant circuit. The liquid-side shutoff valve  12  is interposed between the expansion valve  10  and the connection pipe L 1 , and the gas-side shutoff valve  13  is interposed between the four-way switching valve  7  and the connection pipe L 2 . 
     In the refrigerant circuit, the compressor  6  has a discharge port connected to the outdoor heat exchanger  8  via the four-way switching valve  7  and has an intake port connected to the indoor heat exchanger  4  via the four-way switching valve  7  and the accumulator  11 . 
     A remote controller  17  (hereinafter, referred to as a “remote control  17 ”) can bring the air conditioner  1  configured as described above into cooling operation, dehumidifying operation, and heating operation. The remote control  17  can further switch or stop the operations, set an indoor temperature, set a rotational speed of the indoor fan  5 , and the like. 
     During the cooling operation and the predetermined dehumidifying operation, a cooling cycle is established as indicated by solid arrows in which a refrigerant discharged from the compressor  6  sequentially flows from the four-way switching valve  7  to the indoor heat exchanger  4  through the outdoor heat exchanger  8  and the expansion valve  10  and returns to the compressor  6  through the four-way switching valve  7  and the accumulator  11 . That is, the outdoor heat exchanger  8  functions as a condenser, and the indoor heat exchanger  4  functions as an evaporator. Note that, during the predetermined dehumidifying operation, although the indoor fan  5  is driven to an extent less than during the cooling operation, the refrigerant passing through the indoor heat exchanger  4  evaporates as a result of exchanging heat with indoor air. This causes moisture in the air to be condensed and collected on a surface of the indoor heat exchanger  4 , thereby dehumidifying the air inside the room. Therefore, an operation during which condensed water is generated on the surface of the indoor heat exchanger  4  such as the cooling operation and the predetermined dehumidifying operation is herein referred to as a cooling operation. 
     On the other hand, during the heating operation, a heating cycle is established as indicated by dashed arrows in which the four-way switching valve  7  is switched to cause the refrigerant discharged from the compressor  6  to sequentially flow from the four-way switching valve  7  to the outdoor heat exchanger  8  through the indoor heat exchanger  4  and the expansion valve  10  and return to the compressor  6  through the four-way switching valve  7  and the accumulator  11 . That is, the indoor heat exchanger  4  functions as a condenser, and the outdoor heat exchanger  8  functions as an evaporator. 
     As illustrated in  FIG. 1 , the indoor unit  2  is equipped with an indoor-unit controller (control unit)  14  that controls various operations of the indoor unit  2 , and the outdoor unit  3  is equipped with an outdoor-unit controller (control unit)  15  that controls various operations of the outdoor unit  3 . The air conditioner  1  is controlled as a whole by the indoor-unit controller (control unit)  14  or the outdoor-unit controller (control unit)  15 , or under cooperation between the indoor-unit controller (control unit)  14  and the outdoor-unit controller (control unit)  15 . Therefore, at least either the indoor-unit controller  14  or the outdoor-unit controller  15  acts as a control unit  16  that controls various operations of the air conditioner  1 . 
     As illustrated in  FIG. 2 , the compressor  6 , the four-way switching valve  7 , the expansion valve  10 , the indoor fan  5 , and the outdoor fan  9  are connected to the control unit  16 . Specifically, various drive units (e.g., a motor and a solenoid) for driving such components are connected to the control unit  16 . An outdoor heat exchanger temperature sensor T 1 , an outdoor air temperature sensor T 2 , an indoor heat exchanger temperature sensor T 3 , and an indoor temperature sensor T 4  are connected to the control unit  16 . Further, an irradiation unit  40  is connected to the control unit  16 . 
     The outdoor heat exchanger temperature sensor T 1  is installed in the outdoor heat exchanger  8  to detect a temperature of the outdoor heat exchanger  8 . The outdoor air temperature sensor T 2  is installed in the outdoor unit  3  to detect an outdoor temperature. The indoor heat exchanger temperature sensor T 3  is installed in the indoor heat exchanger  4  to detect a temperature of the indoor heat exchanger  4 . The indoor temperature sensor T 4  is installed in the indoor unit  2  to detect an indoor temperature. 
     The control unit  16  includes a microcomputer, an input-output circuit, and the like. The control unit  16  controls the operation of the air conditioner  1  by performing operation processing, determination processing, or the like based on a command (such as an operation start command or an indoor temperature setting command) sent from the remote control  17  or various temperatures detected by the outdoor heat exchanger temperature sensor T 1 , the outdoor air temperature sensor T 2 , the indoor heat exchanger temperature sensor T 3 , and the indoor temperature sensor T 4 . 
     [Configuration of Indoor Unit] 
       FIG. 3  is a schematic cross-sectional view of the indoor unit  2  that is out of operation, the indoor unit  2  being a component of the air conditioner  1 . The indoor unit  2  illustrated in  FIG. 3  is of a wall-mounted type. 
     The indoor unit  2  includes a casing  30  including a casing body  31  and a front panel  32 . The casing  30  is attached to a wall surface W facing an indoor space and accommodates the indoor fan  5 , the indoor heat exchanger  4 , the drain pan  33 , and the like. 
     The casing body  31  includes a plurality of members: a front part  31   a , an upper part  31   b , a rear part  31   c , and a lower part  31   d . The front panel  32  is attached to the front part  31   a  in an openable and closable manner. Further, an intake port (not illustrated) is provided extending from the front part  31   a  to the upper part  31   b.    
     The front panel  32  is associated with the front part  31   a  of the indoor unit  2  and has, for example, a flat shape with no intake port. Further, an upper end of the front panel  32  is pivotably supported by the upper part  31   b  of the casing body  31  and thus can swing in a hinged manner. 
     The indoor fan  5  and the indoor heat exchanger  4  are attached to the casing body  31 . The indoor heat exchanger  4  exchanges heat with indoor air drawn into the casing  30  through the intake port. Further, the indoor heat exchanger  4  has an inverted V shape in a side view with both ends extending downward and a bend positioned higher. The indoor heat exchanger  4  includes a plurality of heat transfer tubes and a large number of fins. 
     The indoor fan  5  is positioned below the bend of the indoor heat exchanger  4 . The indoor fan  5  is, for example, a cross-flow fan. The indoor fan  5  forces indoor air passing through the indoor heat exchanger  4  to flow to a blow-out port  34  of the lower part  31   d  of the casing body  31 . 
     The casing body  31  is further provided with a first partition wall  35  and a second partition wall  36 . A space between the first partition wall  35  and the second partition wall  36  serves as a blow-out flow path  37  through which the indoor fan  5  and the blow-out port  34  communicate with each other. 
     The drain pan  33  is disposed below the indoor heat exchanger  4  and receives condensed water generated by condensation on the indoor heat exchanger  4 . The drain pan  33  includes an upper receiver  33   a , a lower receiver  33   b , and a connecting part (not illustrated) through which the upper receiver  33   a  and the lower receiver  33   b  are connected with each other. The condensed water drops from the indoor heat exchanger  4  into both the upper receiver  33   a  and the lower receiver  33   b . The condensed water dropped into the upper receiver  33   a  flows down to the lower receiver  33   b  through the connecting portion. The condensed water flowing down from the upper receiver  33   a  to the lower receiver  33   b  and the condensed water dropped into the lower receiver  33   b  accumulate in the lower receiver  33   b  as drain water. The drain water accumulated in the lower receiver  33   b  is drained, by its own weight, outside from a drain port  38  provided in the lower receiver  33   b  through a drain hose  39 . That is, the drain pan  33  is structured to cause the drain water to flow out by its own weight. 
     The control unit  16  controls the cooling operation to make the temperature of the indoor heat exchanger  4  measured by the indoor heat exchanger temperature sensor T 3  lower than the dew point, thereby generating drain water. The control unit  16  can estimate a water level of the drain water accumulated in the lower receiver  33   b  of the drain pan  33  based on the operation status of the cooling operation. Therefore, the control unit  16  functions as a detection unit that detects the water level of the drain water accumulated in the drain pan  33 . Some air conditioners, e.g., air conditioners installed at high places such as ceiling-embedded air conditioners and ceiling-suspended air conditioners, may have a water level sensor installed as a detection unit that detects the water level of the drain water accumulated in the drain pan  33 . 
     The irradiation unit  40  (illustrated in  FIG. 2  but not illustrated in  FIG. 3 ) is provided above the drain pan  33 . The irradiation unit  40  emits deep ultraviolet rays (hereinafter, referred to as “ultraviolet rays”) having a relatively short wavelength among ultraviolet rays to irradiate an upper surface of the drain pan  33  with the ultraviolet rays. The irradiation unit  40  is, for example, an ultraviolet LED (light emitting diode). The ultraviolet rays emitted by the irradiation unit  40  have a wavelength of, for example, 255 nm to 350 nm. 
     In order to denature or inactivate bacteria, mold, or the like contained in the drain water i.e., to perform sterilization, it is necessary to emit the ultraviolet rays by a predetermined dose. The dose of the ultraviolet rays to be emitted is determined by multiplying the ultraviolet intensity by the irradiation time, that is, by the ultraviolet intensity*the irradiation time. In order to achieve a certain predetermined dose, when the irradiation unit  40  is turned on at half the rating in accordance with a pattern B, the ultraviolet intensity becomes half the ultraviolet intensity when the irradiation unit  40  is turned on at the rating in accordance with a pattern A, and the irradiation time becomes twice the irradiation time when the irradiation unit  40  is turned on in accordance with the pattern A. Making the dose during the cooling operation and the dose after the cooling operation equal to each other makes their respective sterilization degrees equal to each other. The control unit  16  controls the ultraviolet intensity and the irradiation time of the irradiation unit  40 . 
     The irradiation unit  40  irradiates the drain pan  33  with the ultraviolet rays by the predetermined dose to sterilize the drain water accumulated in the drain pan  33 , so that propagation of bacteria, mold, or the like in the drain water accumulated in the drain pan  33  is suppressed. 
     The indoor unit  2  includes a first horizontal flap  41  and a second horizontal flap  51  disposed behind the first horizontal flap  41  (adjacent to the wall surface W). The first horizontal flap  41  and the second horizontal flap  51  adjust a vertical direction of air blowing out from the blow-out port  34  (air flowing through the blow-out flow path  37 ). The first horizontal flap  41  is pivotably attached to the lower part  31   d  of the casing body  31 . In the state illustrated in  FIG. 3 , the indoor fan  5  is stopped, the front panel  32 , the first horizontal flap  41 , and the second horizontal flap  51  are closed, and the air conditioning operation by the indoor unit  2  is stopped. Note that the first horizontal flap  41  is an example of a first horizontal blade. Further, the second horizontal flap  51  is an example of a second horizontal blade. 
     The indoor unit  2  further includes a plurality of vertical flaps (not illustrated) that adjust a lateral direction of air blowing out. The plurality of vertical flaps are arranged in the blow-out flow path  37  at predetermined intervals in a longitudinal direction of the blow-out port  34  (a direction perpendicular to the drawing sheet of  FIG. 3 ). Note that the vertical flap is an example of a perpendicular blade. 
     [Control of Irradiation with Ultraviolet Rays] 
     Next, control of irradiation with ultraviolet rays performed by the air conditioner  1  will be described with reference to  FIG. 4 .  FIG. 4  is a control flowchart of irradiation with ultraviolet rays performed by the air conditioner  1 . 
     In the air conditioner  1 , when the cooling operation is selected by operation of the remote control  17  made by the user, the control unit  16  performs the cooling operation desired by the user to place the air conditioner  1  in the cooling operation over a predetermined period of time (step S 1 ). 
     In step S 2 , the control unit  16  determines whether drain water has been generated. Specifically, drain water is generated during the normal cooling operation (YES in step S 2 ), and the process proceeds to step S 3  accordingly. 
     In step S 3 , the control unit  16  determines whether the cooling operation is stopped. When the cooling operation is not stopped (NO in step S 3 ), the process waits until the cooling operation is stopped. When the cooling operation is stopped (YES in step S 3 ), the process proceeds to step S 4 . 
     In step S 4 , the control unit  16  controls the irradiation unit  40  to turn on the irradiation unit  40 . Specifically, the control unit  16  applies, in accordance with the pattern A, a rated current and a rated voltage to the irradiation unit  40  to control the irradiation unit  40  so as to cause the irradiation unit  40  to perform irradiation with rated total radiant flux. Accordingly, the drain water accumulated in the drain pan  33  is irradiated with ultraviolet rays. 
     In step S 5 , the control unit  16  determines whether the irradiation time of the irradiation unit  40  exceeds a predetermined first time t 1  necessary for sterilization. The predetermined first time t 1  is, for example, 1 hour, but varies in a manner that depends on the intensity of the ultraviolet rays from the irradiation unit  40 . When the irradiation time is less than the predetermined first time t 1  (NO in step S 5 ), the process waits until the predetermined first time t 1  elapses. This causes the drain water accumulated in the drain pan  33  to be sterilized, and propagation of bacteria, mold, or the like in the drain water accumulated in the drain pan  33  is suppressed accordingly. When the irradiation time exceeds the predetermined first time t 1  (YES in step S 5 ), the process proceeds to step S 6 . 
     When no drain water is generated in step S 2  (NO in step S 2 ), the process proceeds to step S 11 . 
     In step S 11 , the control unit  16  determines whether a time during which no drain water is generated accumulated from the start of the cooling operation is equal to or longer than a predetermined second time t 2 . Even during the cooling operation, when an accumulated time during which the water level of the drain water is equal to or lower than a predetermined level becomes longer than the predetermined second time t 2 , bacteria, mold, or the like easily propagates. That is, when the humidity of the indoor space decreases due to long cooling operation, and as a result, the state where the drain water is low in water level continues for a predetermined time (second time t 2 ), old drain water is not replaced with new drain water, so that bacteria, mold, or the like easily propagates. The predetermined second time t 2  is in a range of, for example, 10 hours to 12 hours, but varies in a manner that depends on propagation conditions of bacteria, mold, or the like. When the accumulated time during which no drain water is generated is shorter than the predetermined second time t 2  (NO in step S 11 ), the cooling operation continues. When the accumulated time during which no drain water is generated is equal to or longer than the predetermined second time t 2  (YES in step S 11 ), the process proceeds to step S 12 . 
     In step S 12 , the control unit  16  controls the irradiation unit  40  to cause the irradiation unit  40  to perform, in accordance with the pattern B, irradiation with total radiant flux less than the rated total radiant flux during the cooling operation. Accordingly, the drain water accumulated in the drain pan  33  is irradiated with ultraviolet rays. For example, the control unit  16  controls the irradiation unit  40  to cause the irradiation unit  40  to perform, in accordance with the pattern B, irradiation with 50% of the rated total radiant flux. This makes the ultraviolet intensity after the cooling operation (pattern A) larger than the ultraviolet intensity during the cooling operation (pattern B). 
     In step S 13 , the control unit  16  determines whether the irradiation time of the irradiation unit  40  exceeds a predetermined third time t 3  necessary for sterilization. When the irradiation time is less than the predetermined third time t 3  (NO in step S 13 ), the process waits until the predetermined third time t 3  elapses. The dose of the ultraviolet rays necessary for sterilization is determined by the ultraviolet intensity*the irradiation time. Since the ultraviolet intensity during the cooling operation (pattern B) is smaller than the ultraviolet intensity after the cooling operation (pattern A), the irradiation time (third time t 3 ) during the cooling operation (pattern B) is longer than the irradiation time (first time t 1 ) after the cooling operation (pattern A). For example, when the irradiation unit  40  is controlled in accordance with the pattern B to perform irradiation with 50% of the rated total radiant flux, the irradiation time (third time t 3 ) during the cooling operation (pattern B) becomes twice the irradiation time (first time t 1 ) after the cooling operation (pattern A). Making the irradiation time during the cooling operation (pattern B) longer causes the drain water accumulated in the drain pan  33  to be sterilized, and propagation of bacteria, mold, or the like in the drain water accumulated in the drain pan  33  is suppressed accordingly. When the irradiation time exceeds the predetermined third time t 3  (YES in step S 13 ), the process proceeds to step S 6 . 
     In step S 6 , the control unit  16  controls the irradiation unit  40  to turn off the irradiation unit  40 . When the irradiation unit  40  is turned off, the control of the irradiation with ultraviolet rays is brought to an end. 
     In the air conditioner  1 , the irradiation unit  40  is controlled to make the ultraviolet intensity after the cooling operation larger than the ultraviolet intensity during the cooling operation, in other words, to make the ultraviolet intensity during the cooling operation smaller than the ultraviolet intensity after the cooling operation. This makes it possible to effectively perform sterilization after the cooling operation that requires large ultraviolet intensity and make the life of the irradiation unit  40  longer thanks to lower ultraviolet intensity during the cooling operation. 
     Other Embodiment 
     Next, control of irradiation with ultraviolet rays performed by the air conditioner  1  according to the other embodiment will be described with reference to  FIG. 5 .  FIG. 5  is a control flowchart of the irradiation with ultraviolet rays performed by the air conditioner  1  according to the other embodiment. 
     In the air conditioner  1 , when the cooling operation is selected by operation of the remote control  17  made by the user, the control unit  16  performs the cooling operation desired by the user to place the air conditioner  1  in the cooling operation over a predetermined period of time (step S 21 ). 
     In step S 22 , the control unit  16  controls the irradiation unit  40  to bring the irradiation unit  40  into a turn-off state or intermittently turn on the irradiation unit  40  during the cooling operation. Specifically, the turn-off state is to keep the ultraviolet intensity of the irradiation unit  40  at zero from the start of the cooling operation, and the intermittent turn-on is to repeat turning on and off at least once at a predetermined timing during the cooling operation. 
     In step S 23 , the control unit  16  determines whether the cooling operation is stopped. When the cooling operation is not stopped (NO in step S 23 ), the process waits until the cooling operation is stopped. When the cooling operation is stopped (YES in step S 23 ), the process proceeds to step S 24 . 
     In step S 24 , the control unit  16  controls the irradiation unit  40  to turn on the irradiation unit  40 . Specifically, the control unit  16  applies, in accordance with the pattern A, a rated current and a rated voltage to the irradiation unit  40  to control the irradiation unit  40  so as to cause the irradiation unit  40  to perform irradiation with rated total radiant flux. Accordingly, the drain water accumulated in the drain pan  33  is irradiated with ultraviolet rays. 
     In step S 25 , the control unit  16  determines whether the irradiation time of the irradiation unit  40  exceeds the predetermined first time t 1  necessary for sterilization. When the irradiation time is less than the predetermined first time t 1  (NO in step S 25 ), the process waits until the predetermined first time t 1  elapses. This causes the drain water accumulated in the drain pan  33  to be sterilized, and propagation of bacteria, mold, or the like in the drain water accumulated in the drain pan  33  is suppressed accordingly. When the irradiation time exceeds the predetermined first time t 1  (YES in step S 25 ), the process proceeds to step S 26 . 
     In step S 26 , the control unit  16  controls the irradiation unit  40  to turn off the irradiation unit  40 . When the irradiation unit  40  is turned off, the control of the irradiation with ultraviolet rays is brought to an end. 
     The air conditioner  1  makes the irradiation time of the ultraviolet rays during the cooling operation shorter, so that it is possible to make the life of the irradiation unit  40  longer by a time during which the irradiation with the ultraviolet rays is not performed during the cooling operation. 
     The embodiments of the present disclosure have been described above. However, it should be understood that specific configurations of the present disclosure are not limited to those described in the embodiments. The scope of the present disclosure is defined by not only the embodiments described above but also the appended claims and further includes equivalents of the claims and all modifications within the scope of the claims. 
     When irradiation with ultraviolet rays is performed in a state where no drain water accumulates in the drain pan  33 , the irradiation with ultraviolet rays has no effect. Therefore, in the air conditioner  1 , the irradiation unit  40  is controlled to irradiate drain water accumulated in the drain pan  33  with ultraviolet rays. This makes the irradiation time of the irradiation unit  40  short as compared with a case where the irradiation with ultraviolet rays continues without stop during the cooling operation, so that it is possible to effectively sterilize the drain water. 
     The air conditioner  1  according to the one embodiment and the other embodiment includes a detection unit  16  that detects the water level of the drain water. The control unit  16  can control the irradiation unit  40  to irradiate the drain pan  33  with the ultraviolet rays when an accumulated time during which the water level of the drain water detected by the detection unit  16  is equal to or lower than a predetermined level becomes equal to or longer than a predetermined time during the cooling operation. 
     Even during the cooling operation, when an accumulated time during which the water level of the drain water is equal to or lower than the predetermined level becomes equal to or longer than the predetermined time, bacteria, mold, or the like easily propagates due to the drain water remaining on the drain pan  33  for a long time. In the air conditioner configured as described above, the drain water is irradiated with the ultraviolet rays, so that propagation of bacteria, mold, or the like in the drain water is suppressed. 
     The air conditioner  1  according to the one embodiment and the other embodiment includes the indoor heat exchanger temperature sensor T 3  that detects a temperature of the indoor heat exchanger  4 . The control unit  16  controls the irradiation unit  40  to irradiate the drain pan  33  with the ultraviolet rays when an accumulated time during which the temperature of the indoor heat exchanger  4  detected by the indoor heat exchanger temperature sensor T 3  is equal to or higher than a dew-point temperature becomes equal to or longer than the predetermined time t 2  during the cooling operation. 
     The dew-point temperature is calculated based on, for example, an indoor temperature detected by the indoor temperature sensor T 4 , an amount of indoor moisture (for example, relative humidity) detected by a humidity sensor T 5 , and a dew-point temperature calculation table stored in a storage unit of the control unit  16 . 
     Even during the cooling operation, when an accumulated time during which the temperature of the indoor heat exchanger  4  is equal to or higher than the dew-point temperature becomes equal to or longer than the predetermined time t 2 , bacteria, mold, or the like easily propagates due to the drain water remaining on the drain pan  33  for a long time. In the air conditioner  1  configured as described above, the drain water is irradiated with the ultraviolet rays, so that propagation of bacteria, mold, or the like in the drain water is suppressed. 
     The air conditioner  1  according to the one embodiment and the other embodiment includes the indoor temperature sensor T 4  that detects an indoor temperature. The control unit  16  controls the irradiation unit  40  to emit the ultraviolet rays when a temperature difference between the indoor temperature detected by the indoor temperature sensor T 4  and a set temperature becomes equal to or less than a predetermined temperature during the cooling operation. 
     During the cooling operation, the indoor temperature approaches the set temperature and is stably maintained, which eliminates the need of cooling the indoor heat exchanger  4 . Therefore, even during the cooling operation, when the temperature difference between the indoor temperature and the set temperature is equal to or less than the predetermined temperature, cooling of the indoor heat exchanger  4  is stopped, so that the generation of drain water is suppressed. Therefore, the air conditioner  1  configured as described above makes the irradiation time of the ultraviolet rays during the cooling operation shorter, so that it is possible to make the life of the irradiation unit  40  longer. Note that the set temperature is set by the user or set by the control unit  16 . When the temperature difference between the indoor temperature and the set temperature becomes equal to or less than the predetermined temperature, the irradiation with ultraviolet rays is continuously or intermittently performed. The continuous irradiation with ultraviolet rays when the temperature difference is equal to or less than the predetermined temperature serves as the intermittent irradiation with ultraviolet rays during the cooling operation. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  air conditioner 
               2  indoor unit 
               3  outdoor unit 
               4  indoor heat exchanger (heat exchanger) 
               6  compressor 
               7  four-way switching valve 
               8  outdoor heat exchanger (heat exchanger) 
               10  expansion valve 
               11  accumulator 
               14  indoor-unit controller (control unit) 
               15  outdoor-unit controller (control unit) 
               16  control unit 
               17  remote controller (remote control) 
               30  casing 
               31  casing body 
               31   a  front part 
               31   b  upper part 
               31   c  rear part 
               31   d  lower part 
               32  front panel 
               33  drain pan 
               34  blow-out port 
               35  first partition wall 
               36  second partition wall 
               37  blow-out flow path 
               38  drain port 
               39  drain hose 
               40  irradiation unit 
               41  first horizontal flap 
               51  second horizontal flap 
             L 1 , L 2  connection pipe 
             T 1  outdoor heat exchanger temperature sensor 
             T 2  outdoor air temperature sensor 
             T 3  indoor heat exchanger temperature sensor (temperature sensor) 
             T 4  indoor temperature sensor 
             T 5  humidity sensor 
             W wall surface