Patent Publication Number: US-9897351-B2

Title: Air conditioner

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2014-0099194, filed on Aug. 1, 2014, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     The present disclosure relates to an air conditioner. 
     Air conditioners are appliances that maintain indoor air at the most proper state according to use and purpose thereof. In general, such an air conditioner includes a compressor, a condenser, an expansion device, and an evaporator. Thus, the air conditioner has a refrigerant cycle in which compression, condensation, expansion, and evaporation processes of refrigerant are performed to cool or heat a predetermined space. 
     The predetermined space may be variously provided according to a place at which the air conditioner is used. For example, when the air conditioner is disposed in a home or office, the predetermined space may be an indoor space of a house or building. On the other hand, when the air conditioner is disposed in a vehicle, the predetermined space may be a riding space in which a person rides. 
     When the air conditioner performs a cooling operation, an outdoor heat exchanger provided in an outdoor unit may serve as a condenser, and an indoor heat exchanger provided in an indoor unit may serve as an evaporator. On the other hand, when the air conditioner performs a heating operation, the indoor heat exchanger may serve as a condenser, and the outdoor heat exchanger may serve as an evaporator. 
       FIG. 1  is a view of an outdoor heat exchanger according to a related art. 
     Referring to  FIG. 1 , an outdoor heat exchanger  1  according to the relates art includes a plurality of refrigerant tubes  2  arranged in a plurality of rows, a coupling plate  3  coupled to an end of each of the refrigerant tubes  2  to support the refrigerant tubes  2 , and a header  4  through which refrigerant is divided to flow into the refrigerant tubes  2 , or the refrigerant passing through the refrigerant tubes  2  is mixed. 
     Also, the outdoor heat exchanger  1  may further include a return tube  7  for switching a flow direction of the refrigerant from one refrigerant tube  2  to the other refrigerant tube. For example, the return tube  7  may switch a flow direction of the refrigerant from a refrigerant tube, which is disposed in a first row, of the refrigerant tubes  2  arranged in two rows to a refrigerant tube disposed in a second row. 
     The outdoor heat exchanger  1  may further include a plurality of distributors  5  and  6 . The plurality of distributors  5  and  6  include a first distributor  5  through which the refrigerant is divided and introduced into at least one of the plurality of the refrigerant tubes  2  and a second distributor  6  through which the refrigerant is divided and introduced into the rest of the plurality of refrigerant tubes  2 . 
     In the outdoor heat exchanger  1 , the refrigerant flows in directions opposite to each other when cooling and heating operations are performed. 
     For example, when the air conditioner performs a cooling operation, the outdoor heat exchanger  1  functions as a condenser (see a solid arrow). 
     In detail, a high-pressure refrigerant compressed by the compressor is introduced into the header  4  and divided to flow into the plurality of refrigerant tubes  2 , and the divided refrigerant is heat-exchanged with outdoor air while flowing in the refrigerant tubes  2 . 
     The heat-exchanged refrigerant is mixed in the first and second distributors  5  and  6  to flow toward an indoor heat exchanger. 
     On the other hand, when the air conditioner performs a heating operation, the outdoor heat exchanger  1  functions as an evaporator (see a dotted arrow). 
     In detail, refrigerant condensed in the indoor heat exchanger may be decompressed while passing through the expansion device and then be introduced into the outdoor heat exchanger  1 . The refrigerant is divided to flow into the first and second distributors  5  and  6  at an inlet-side of the outdoor heat exchanger  1  and introduced into the refrigerant tubes  2  through a plurality of branch tubes respectively connected to the distributors  5  and  6 . 
     Here, the refrigerant may be heat-exchanged with the outdoor air while flowing in the refrigerant tubes  2 . The heat-exchanged refrigerant may be mixed in the header  4  to flow to a compressor-side. 
     When the air conditioner performs the cooling operation, the refrigerant passing through the outdoor heat exchanger  1  is in a high-temperature high-pressure gaseous state. Here, in order to increase condensation efficiency of the refrigerant, the number of branch paths branched into the outdoor heat exchanger  1  may be reduced, and the branch paths may increase in length. 
     That is, when a flow path of the refrigerant increases in length, the refrigerant increases in flow rate to reduce a condensation pressure, thereby improving condensation efficiency, i.e., a ratio in which the refrigerant changes into gaseous phase. 
     On the other hand, when the air conditioner performs a heating operation, the refrigerant passing through the outdoor heat exchanger  1  is in a two-phase state. Here, to reduce a pressure loss of the refrigerant, the number of branch paths branched into the outdoor heat exchanger  1  needs to increase, and the length of each of the branch paths needs to shorten. 
     That is, a gaseous refrigerant of the refrigerant in two-phase has a relatively large pressure loss while flowing However, when the flow path of the refrigerant has a short length, and the number of branch paths increases, the pressure loss, i.e., reduction of an evaporation pressure may be prevented to improve evaporation efficiency. 
     However, according to the structure of the outdoor heat exchanger according to the related art as illustrated in  FIG. 1 , when the air conditioner performs the cooling and heating operations, since the branch paths through which the refrigerant is divided to flow into the outdoor heat exchanger have the same number and length, the air conditioner according to the related art may be reduced in heat-exchange efficiency. 
     That is, when the cooling operation is performed, the condensation pressure in the outdoor heat exchanger increases to deteriorate condensation efficiency. When the heating operation is performed, the evaporation pressure in the outdoor heat exchanger decreases to deteriorate evaporation efficiency. 
     SUMMARY 
     Embodiments provide an air conditioner including an outdoor heat exchanger having improved heat-exchange efficiency. 
     In one embodiment, an air conditioner includes: a compressor; a flow switching part disposed at an outlet-side of the compressor to switch a flow direction of refrigerant according to a cooling or heating operation; an outdoor heat exchanger connected to the flow switching part, the outdoor heat exchanger including a plurality of refrigerant tubes for guiding the refrigerant heat exchanged with outdoor air; a main expansion valve disposed at one side of the outdoor heat exchanger; a first inlet/outlet tube extending from the flow switching part to the outdoor heat exchanger; and a second inlet/outlet tube extending from the outdoor heat exchanger to the main expansion valve, wherein the outdoor heat exchanger includes: a header defining a flow space for the refrigerant, the header including an upper header and a lower header; a check valve disposed between the upper header and the lower header to guide the refrigerant to flow in one direction; and a bypass tube extending from the lower header to the second inlet/outlet tube to guide a discharge of a liquid refrigerant existing in the lower header. 
     The air conditioner may further include first and second distribution tubes branched from the second inlet/outlet tube, and a plurality of distributors connected to the first and second distribution tubes to allow the refrigerant to be divided and introduced into the plurality of refrigerant tubes. 
     The plurality of distributors may include: a first distributor connected to the first distribution tube to communicate with the upper header; and a second distributor connected to the second distribution tube to communicate with the lower header. 
     The air conditioner may further include a plurality of capillary tubes extending from the first and second distributors to the plurality of the refrigerant tubes. 
     The air conditioner may further include a connection tube extending from the first distribution tube to the lower header to guide the refrigerant in the first distribution tube to the lower header when the cooling operation is performed. 
     The air conditioner may further include a first valve disposed in the first distribution tube; and a second valve disposed in the second distribution tube. 
     The air conditioner may further include a third valve disposed in the connection tube. 
     The bypass tube may extend from the lower header and is connected to the second inlet/outlet tube by being bent at least two times. 
     The bypass tube may extend from a bottom surface of the lower header. 
     The air conditioner may further include a plurality of refrigerant inflow tubes extending from the lower header to the plurality of refrigerant tubes, wherein the uppermost portion of the bypass tube  250  may have a height (H 1 ) lower than that (H 2 ) of the lowermost inflow tube of the plurality of refrigerant inflow tubes. 
     The height (H 1 ) of the uppermost portion of the bypass tube may be higher than that (H 3 ) of the bottom surface of the lower header. 
     In another embodiment, an air conditioner includes: a compressor; a flow switching part disposed at an outlet-side of the compressor to switch a flow direction of refrigerant according to a cooling or heating operation; an outdoor heat exchanger connected to the flow switching part, the outdoor heat exchanger including a plurality of refrigerant tubes for guiding the refrigerant heat exchanged with outdoor air; a main expansion valve disposed at one side of the outdoor heat exchanger; a first inlet/outlet tube extending from the flow switching part to the outdoor heat exchanger; and a second inlet/outlet tube extending from the outdoor heat exchanger to the main expansion valve, wherein the outdoor heat exchanger includes: a header defining a flow space for the refrigerant, the header including an upper header and a lower header; a plurality of refrigerant inflow tubes extending from the header to the plurality of refrigerant tubes; and a bypass tube extending from the lower header to an outlet-side of the outdoor heat exchanger and having a bent part. 
     The bent part of the bypass tube may include: a first bent part for changing an extension direction of the bypass tube from a lower side to an upper side; and a second bent part for changing the extension direction of the bypass tube from the upper side to the lower side. 
     The air conditioner may further include a first extension part extending downward from a lower portion of the lower header; and a second extension part extending upward from the first extension part, wherein the first bent part may be disposed between the first extension part and the second extension part. 
     The air conditioner may further include a third extension part extending downward from the second extension part, wherein the second bent part may be disposed between the second extension part and the third extension part. 
     The second bent part may have a height (H 1 ) lower than that (H 2 ) of the lowermost inflow tube of the plurality, of refrigerant inflow tubes and higher than that (H 3 ) of a bottom surface of the lower header. 
     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 of an outdoor heat exchanger according to a related art. 
         FIG. 2  is a system view of an air conditioner according to an embodiment. 
         FIG. 3  is a view of main components of an outdoor heat exchanger according to an embodiment. 
         FIG. 4  is a schematic view illustrating a bypass tube of the outdoor heat exchanger according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. 
     Hereinafter, reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, that alternate embodiments included in other retrogressive inventions or falling within the spirit and scope of the inventive concept will fully convey the concept of the invention to those skilled in the art. 
       FIG. 2  is a system view of an air conditioner according to an embodiment, and  FIG. 3  is a view of main components of an outdoor heat exchanger according to an embodiment. 
     Referring to  FIG. 2 , an air conditioner  10  according to an embodiment includes an indoor unit disposed indoors and an outdoor unit disposed outdoors. The indoor unit includes an indoor heat exchanger in which air in an indoor space is heat-exchanged. In  FIG. 2 , a configuration of the outdoor unit is illustrated. 
     The air conditioner  10  includes a plurality of compressors  110  and  112  and oil separators  120  and  122  disposed at an outlet-side of each of the plurality of compressors  110  and  112  to separate the oil from the refrigerant discharged from each of the plurality of compressors  110  and  112 . 
     The plurality of compressors  110  and  112  include a first compressor  110  and a second compressor  112 , which are connected in parallel to each other. A discharge temperature sensor  114  for detecting a temperature of the compressed refrigerant may be disposed at an outlet-side of each of the first and second compressors  110  and  112 . 
     Also, the oil separators  120  and  122  include a first oil separator  120  disposed at the outlet-side of the first compressor  110  and a second oil separator  122  disposed at the outlet-side of the second compressor  112 . 
     The air conditioner  10  includes a collection passage  116  for collecting the oil from the oil separators  120  and  122  into the compressors  110  and  112 . The collection passage  116  may extend from each of the outlet-sides of the first and second oil separators  120  and  122  and then combined with each other. Here, the combined passage may be connected to an inlet-side tube of each of the first and second compressors  110  and  112 . 
     A dryer  127  and a capillary  128  may be disposed in the collection passage  116 . 
     A high-pressure sensor  125  for detecting a discharge pressure of the refrigerant discharged from the compressors  110  and  112  and a flow switching part  130  for guiding the refrigerant passing through the high-pressure sensor  125  to the outdoor heat exchanger  200  or the indoor unit are disposed on the outlet-sides of the oil separators  120  and  122 . For example, the flow switching part  130  may include a four-way valve. 
     When the air conditioner performs a cooling operation, the refrigerant may be introduced from the flow switching part  130  into the outdoor heat exchanger  200 . On the other hand, when the air conditioner performs a heating operation, the refrigerant may flow from the flow switching part  130  into an indoor heat exchange-side of the indoor unit (not shown). 
     When the air conditioner performs a cooling operation, the refrigerant condensed in the outdoor heat exchanger  200  passes through a main expansion valve  260  (an electronic expansion valve). Here, the main expansion valve  260  is completely opened, and thus the refrigerant is not decompressed. That is, the main expansion valve  260  may be disposed at the outlet-side of the outdoor heat exchanger  200  in a cooling mode. 
     The refrigerant passing through the main expansion valve  260  passes through a heat dissipation plate  265 . The heat dissipation plate  265  may be provided in an electronic unit in which heat generation components are disposed. 
     For example, the heat generation component may include a power module (e.g., an intelligent power module (IPM)). The IPM may be understood as a module in which a driving circuit of a power device such as a power MOSFET or IGBT and a protection circuit having a self protection function is installed. 
     The condensed refrigerant is coupled to the heat dissipation plate  265  to cool the heat generation component. 
     The air conditioner  10  may further include a supercooling heat exchanger  270  in which the refrigerant passing through the heat-dissipation plate  265  is introduced and a supercooling distributor  271  disposed on an inlet-side of the supercooling heat exchanger  270  to divide the refrigerant. The supercooling heat exchanger  270  may serve as an intermediate heat exchanger in which a first refrigerant circulated into the system and a portion (a second refrigerant) of the first refrigerant are heat-exchanged with each other after the refrigerant is divided. 
     Here, the first refrigerant may be a refrigerant that is introduced into the supercooling heat exchanger  270  via the supercooling distributor  271  and thus be supercooled by the second refrigerant. On the other hand, the second refrigerant may absorb heat from the first refrigerant. 
     The air conditioner  10  includes a supercooling passage  273  disposed at an outlet-side of the supercooling heat exchanger  270  to divide the second refrigerant from the first refrigerant. 
     Also, a supercooling expansion device  275  for decompressing the second refrigerant may be disposed in the supercooling passage  273 . The supercooling expansion device  275  may include the electric expansion valve (EEV). 
     The second refrigerant of the supercooling passage  273  may be introduced into the supercooling heat exchanger  270  and then be heat-exchanged with the first refrigerant to flow to an inlet-side of a gas/liquid separator  280 . The air conditioner may further include a supercooling discharge temperature sensor  276  for detecting a temperature of the second refrigerant passing through the supercooling heat exchanger  270 . 
     The gas/liquid separator  280  may be configured to separate a gaseous refrigerant from the refrigerant before the refrigerant is introduced into the compressors  110  and  112 . The separated gaseous refrigerant may be introduced into the compressors  110  and  112 . 
     While the refrigeration cycle is driven, the evaporated refrigerant may be introduced into the gas/liquid separator  280  via the flow switching part  130 . Here, the evaporated refrigerant may be mixed with the second refrigerant passing through the supercooling heat exchanger  270  and then be introduced into the gas/liquid separator  280 . 
     A suction temperature sensor  282  for detecting a temperature of the refrigerant to be suctioned into the compressors  110  and  112  may be disposed at the inlet-side of the gas/liquid separator  280 . 
     The first refrigerant passing through the supercooling heat exchanger  270  may be introduced into the indoor unit through an indoor unit connection tube  279 . The air conditioner may further include a liquid tube temperature sensor  278  disposed at the outlet-side of the supercooling heat exchanger  270  to detect a temperature of the first refrigerant passing through the supercooling heat exchanger  270 , i.e., a temperature of the supercooled refrigerant. 
     Hereinafter, the outdoor heat exchanger  200  and peripheral components thereof will be described. 
     The air conditioner  10  includes a first inlet/outlet tube  201   a  connected from the flow switching part  130  to one side of the outdoor heat exchanger  200  and a second inlet/outlet tube  201   b  extending from the other side of the outdoor heat exchanger  200  to the main expansion device  260 . 
     For example, the first inlet/outlet tube  201   a  may be connected to an upper portion of the header  205 , i.e., an upper header  205   a , and the second inlet/outlet tube  201   b  may be connected to a lower portion of the header  205 , i.e., a lower header  205   b.    
     When the air conditioner  10  performs a cooling operation, the refrigerant is introduced into the outdoor heat exchanger  200  through the first inlet/outlet tube  201   a  and is discharged from the outdoor heat exchanger  200  through the second inlet/outlet tube  201   b.    
     On the other hand, when the air conditioner  10  performs a heating operation, the refrigerant is introduced into the outdoor heat exchanger  200  through the second inlet/outlet tube  201   b  and is discharged from the outdoor heat exchanger  200  through the first inlet/outlet tube  201   a.    
     The outdoor heat exchanger  200  includes a refrigerant tube  202  having a plurality of rows and stages. For example, the refrigerant tube  202  may be provided in plurality so that the plurality of refrigerant tubes  202  are arranged in two rows in a horizontal direction and stepped in plural stages in a vertical direction. 
     The plurality of refrigerant tubes  202  may be bent to lengthily extend. For example, in  FIG. 3 , the plurality of refrigerant tubes  202  may extend to a rear side of the ground and then extend forward. In this case, each of the plurality of refrigerant tubes  202  may have a U-shape. 
     The outdoor heat exchanger  200  may include a coupling plate  203  for supporting the refrigerant tubes  202 . The coupling plate  203  includes a first plate  203   a  having a bent shape to support one side of the refrigerant tubes  202  and a second plate  203   b  supporting the other side of the refrigerant tubes  202 . Each of the first and second plates  203   a  and  203   b  lengthily extends in a vertical direction. 
     The outdoor heat exchanger  200  may further include a return tube  204  coupled to ends of the plurality of refrigerant tubes  202  to guide refrigerant flowing in one refrigerant tube  202  to the other refrigerant tube  202 . The return tube  204  is provided in plurality and is coupled to one side of each of the first and second plates  203   a  and  203   b.    
     The outdoor heat exchanger  200  may further include the header  205  defining a flow space of the refrigerant. Through the header  205 , the refrigerant is divided and introduced into the plurality of refrigerant tubes  202 , or the refrigerant heat-exchanged in the plurality of refrigerant tubes  202  is mixed with each other. The header  205  lengthily extends in a vertical direction to correspond to a direction in which the first plate  203   a  extends. 
     A plurality of refrigerant inflow tubes  232  extend between the header  205  and the first plate  203   a . Each of the plurality of refrigerant inflow tubes  232  extends from the header  205  and then is connected to the refrigerant tube  202  supported by the first plate  203   a . Also, the plurality of refrigerant inflow tubes  232  may be vertically spaced apart from each other. 
     When the air conditioner performs a cooling operation, the refrigerant in the header  205  may be introduced into the refrigerant tubes  202  through the plurality of refrigerant inflow tubes  232 . On the other hand, when the air conditioner performs a heating operation, the refrigerant in the refrigerant tubes  202  may be introduced into the header  205  through the refrigerant inflow tube  232 . 
     The air conditioner  10  may further include a plurality of distributors  210  and  220  for dividing and introducing the refrigerant into the outdoor heat exchanger  200  when the heating operation is performed. The plurality of distributors  210  and  220  include the first distributor  210  and the second distributor  220 . 
     Also, the air conditioner  10  may further include a first distribution tube  211  and a second distribution tube  221  branched from the second inlet/outlet tube  201   b  to the first distributor  210  and the second distributor  220 . The first and second distribution tubes  211  and  221  may extend from a branch portion  201   c  to the first and second distributors  210  and  220 . 
     The air conditioner  10  may further include a first valve  215  disposed in the first distribution tube  211  to adjust a refrigerant flow rate flowing in the first distribution tube  211  and a second valve  225  disposed in the second distribution tube  221  to adjust a refrigerant flow rate flowing in the second distribution tube  221 . 
     Each of the first and second valves  215  and  225  may include an electric expansion valve (EEV) of which an opened degree is adjustable. 
     The air conditioner  10  may further include a plurality of capillary tubes  207  extending from the first and second distributors  210  and  220  to the plurality of refrigerant tubes  202 . When the air conditioner  10  performs a heating operation, the refrigerant is divided to flow into the first and second distributors  210  and  220 , and the divided refrigerant moves into the refrigerant tubes  202  through the plurality of capillary tubes  207 . 
     The air conditioner  10  may further include a branch tube  209  connecting each of the plurality of capillary tubes  207  to the refrigerant tube  202 . The branch tube  209  may divide the refrigerant flowing in the capillary tube  207  in two directions, into one refrigerant tube  202  and the other refrigerant tube  202 . For example, the branch tube  209  may include a branch tube having a Y shape. The branch tube  209  may be provided in plurality to correspond to the number of the plurality of capillary tubes  207 . 
     When the air conditioner  10  performs a heating operation, the refrigerant introduced into the refrigerant tubes  202  through the plurality of capillary tubes  207  connected to the first distributor  210  is heat-exchanged and introduced into the upper header  205   a  of the header  205 . Also, the refrigerant introduced into the refrigerant tubes  202  through the plurality of capillary tubes  207  connected to the second distributor  220  is heat-exchanged and introduced into the lower header  205   b  of the header  205 . 
     That is, the header  205  includes the upper header  205   a  communicating with the first distributor  210  and the lower header  205   b  communicating with the second distributor  220 . A virtual partition line l  1  partitioning the upper header  205   a  from the lower header  205   b  is illustrated in  FIG. 3 . 
     The air conditioner  10  may further include a check valve  240  disposed between the upper header  205   a  and the lower header  205   b . The check valve  240  may allow the refrigerant to flow from the lower header  205   b  to the upper header  205   a  and may restrict the flow of the refrigerant from the upper header  205   a  to the lower header  205   b.    
     Thus, when the air conditioner  10  performs the heating operation, the refrigerant introduced into the refrigerant tube  202  through the second distributor  220  may be heat-exchanged and then be introduced into the lower header  205   b . The refrigerant introduced into the lower header  205   b  may be guided by the check valve  240  to flow to the upper header  205   a . Also, the refrigerant introduced into the refrigerant tube  202  through the first distributor  210  may be heat-exchanged and introduced into the upper header  205   a  and then be mixed with the refrigerant introduced from the lower header  205   b  to move to the first inlet/outlet tube  201   a.    
     The air conditioner  10  may further include a connection tube  230  extending from one spot of the first distribution tube  211  to the lower header  205   b . In the connection tube  230 , a third valve  235  for adjusting a refrigerant flow rate within the connection tube  230  may be disposed. For example, the third valve  235  may include an on/off controllable solenoid valve and an EEV of which an opened degree is adjustable. 
     When the air conditioner performs a cooling operation, the refrigerant flowing from the first distributor  210  to the first distribution tube  211  may be introduced into the lower header  205   b  through the connection tube  230 . 
     The air conditioner  10  may further include a bypass tube  250  extending from a lower end of the header  205 , i.e., a lower end of the lower header  205   b  to the second inlet/outlet tube  201   b . When the air conditioner  10  performs a cooling operation, the bypass tube  250  may allow a liquid refrigerant collected in a lower portion of the header  205  to be bypassed toward the second inlet/outlet tube  201   b , i.e., the outlet-side of the outdoor heat exchanger  200 . 
     Hereinafter, a heating operation of the air conditioner and flow of the refrigerant in the air conditioner in a cooling mode will be described with reference to  FIGS. 2 and 3 . 
     First, when the air conditioner performs a heating operation, oil is separated from the high-temperature and high-pressure refrigerant compressed by the first and second compressors  110  and  112  via the first and second oil separators  120  and  122 , and the separated oil is returned into the first and second compressors  110  and  112  through the collection passage  116 . Also, the refrigerant from which the oil is separated flows toward the indoor unit via the flow switching part  130 . 
     The refrigerant introduced into the indoor unit is condensed in the indoor heat exchanger. The condensed refrigerant is introduced into the supercooling heat exchanger  270  through the indoor connection tube  279 . Here, a portion of the refrigerant may be divided to flow into a supercooling passage  273  and decompressed in a supercooling expansion device  275  and then be introduced into a supercooling heat exchanger  270 . 
     Thus, the condensed refrigerant may be heat-exchanged with the refrigerant flowing through the supercooling passage  273  to supercool the condensed refrigerant. 
     The supercooling refrigerant passing through the supercooling heat exchanger  270  may cool the heat generating component of the electronic unit while passing through the heat dissipation plate  265  and then be decompressed in the main expansion valve  260 . 
     The decompressed refrigerants may be divided to flow into the first and second distribution tubes  211  and  221  at the branch portion  201   c  and then be respectively introduced into the first and second distributors  210  and  220 . Here, each of the first and second valves  215  and  225  may be opened over a preset opening degree. For example, the first and second valves  215  and  225  may be completely opened. 
     The refrigerant flowing into the first distributor  210  is introduced into the refrigerant tube  202  via the plurality of capillary tubes  207  and then is introduced into the upper header  205   a  after being heat-exchanged. Also, the refrigerant flowing into the second distributor  220  is introduced into the refrigerant tube  202  via the plurality of capillary tubes  207  and then is introduced into the lower header  205   b  after being heat-exchanged. Here, the refrigerant may be evaporated in the heat-exchange process. 
     The refrigerant introduced into the lower header  205   b  flows into the upper header  205   a  and then is mixed with the refrigerant introduced into the upper header  205   a . Here, the refrigerant in the lower header  205   b  may flow into the upper header  205   a  via the check valve  240  (see a dotted arrow). 
     The mixed refrigerant may be discharged to the first inlet/outlet tube  201   a  connected to the upper header  205   a , and the gaseous refrigerant introduced into the gas/liquid separator  280  via the flow switching part  130  and then separated by the gas/liquid separator  280  may be absorbed into the first and second compressors  110  and  112 . This refrigeration cycle may be repeatedly performed. 
     Like this, when the air conditioner  10  performs a heating operation, the refrigerant may be introduced into the outdoor heat exchanger  200  through the first and second distributors  210  and  220  and heat-exchanged by using all of the passages at the first and second distributors sides. 
     Thus, the flow path of the refrigerant in the outdoor heat exchanger  200  is reduced in length, and the number of paths branched into the outdoor heat exchanger  200  increases. As a result, the pressure loss of the refrigerant may be reduced to prevent an evaporation pressure from being reduced, thereby improving evaporation efficiency. 
     When the air conditioner performs a cooling operation, oil is separated from the high-temperature and high-pressure refrigerant compressed by the first and second compressors  110  and  112  via the first and second oil separators  120  and  122 , and the separated oil is returned into the first and second compressors  110  and  112  through the collection passage  116 . Also, the refrigerant from which the oil is separated flows into the first inlet/outlet tube  201   a  via the flow switching part  130  and then is introduced into the header  205  of the outdoor heat exchanger  200 . 
     The refrigerant introduced into the header  205  exists in the upper header  205   a , and the introduction of the refrigerant into the lower header is restricted by the check valve  240 . 
     The refrigerant of the upper header  205   a  is introduced into the refrigerant tube  202  fixed to the first plate  203   a  through the plurality of refrigerant inflow tubes  232 . The refrigerant of the refrigerant tube  202  is heat-exchanged and flows into the plurality of capillary tubes  207  through the branch tube  209 . Here, the refrigerant may be primarily condensed in the heat-exchange process. 
     The refrigerant of the plurality of capillary tubes  207  is combined with each other in the first distributor  210  and is introduced into the lower header  205   b  through the first distribution tube  211  and the connection tube  230 . Here, the first valve  215  is closed to restrict flow of the refrigerant into the branch portion  201   c . Also, the third valve  235  is turned on or opened over a preset opened degree to allow the refrigerant to flow into the connection tube  230 . 
     The refrigerant introduced into the lower header  205   b  flows into the plurality of refrigerant tubes  202  fixed to the first plate  203   a  via the plurality of refrigerant inflow tubes  232 . Also, the refrigerant may be secondarily condensed in the process in which the refrigerant flows through the plurality of refrigerant tubes  202 . 
     The secondarily condensed refrigerant is introduced into the second distributor  220  via the branch tubes  209  and the plurality of the capillary tubes  207 . The refrigerant of the second distributor  220  flows through the second inlet/outlet passage  201   b  via the second distribution tube  221  and the branch portion  201   c  and is discharged from the outdoor heat exchanger  200 . 
     The refrigerant discharged from the outdoor heat exchanger  200  may flow toward the indoor unit via the heat dissipation plate  265  and the supercooling heat exchanger  270 . The refrigerant may be expanded and evaporated in the indoor unit and then be absorbed into the first and the second compressors  110  and  120  via the flow switching part  130  and the gas/liquid separator  280 . This refrigeration cycle may be repeatedly performed. 
     Like this, when the air conditioner  10  performs a cooling operation, the refrigerant introduced into the outdoor heat exchanger  200  may be primarily condensed in the refrigerant tube  202  connected at an upper header  205   a  side and be secondarily condensed in the refrigerant tube  202  connected to at a lower header  205   b  side. Thus, while the flow path of the refrigerant increases in length, the number of paths branched into the refrigerant tubes  202  is reduced. As a result, the refrigerant may increase in flow rate to reduce a condensation pressure, thereby improving condensation efficiency. 
     A liquid refrigerant may be filled in the lower header  205   b . In detail, since the refrigerant is primarily condensed while flowing through the refrigerant tube  202  connected to the upper header  205   a , the refrigerant may be in a two-phase state. Thus, the refrigerant introduced into the lower header  205   b  through the connection tube  230  may include a gaseous phase and a liquid phase. 
     Since the liquid refrigerant has a specific gravity greater than the gaseous refrigerant, the liquid refrigerant may be filled in a lower side of the lower header  205   b . The liquid refrigerant may be understood as a completely condensed refrigerant that does not need to be heat-exchanged any more. Thus, when the liquid refrigerant is introduced into the refrigerant tube  202  and heat-exchanged, the outdoor heat exchanger may be deteriorated in heat-exchange performance, and also pressure loss due to the liquid refrigerant may occur. 
     Thus, the current embodiment provides the bypass tube  250  for allowing the liquid refrigerant to be bypassed toward the outlet of the outdoor heat exchanger  200 . The bypass tube  250  extends from the lower header  205   b  to the second inlet/outlet tube  201   b  to discharge the refrigerant collected in the lower header  205   b  to the second inlet/outlet tube  201   b.    
     Hereinafter, a configuration of the bypass tube  250  will be described below with reference to  FIG. 4 . 
       FIG. 4  is a schematic view illustrating a bypass tube of the outdoor heat exchanger according to an embodiment. 
     Referring to  FIG. 4 , the outdoor heat exchanger  200  according to the embodiment includes the bypass tube  250  for allowing the liquid refrigerant existing in the header  205  to be bypassed toward the outlet of the outdoor heat exchanger  200 . 
     The bypass tube  250  extends from the lower portion of the lower header  205   b  of the header  205  toward the second inlet/outlet tube  201   b . The bypass tube  250  may be curved or bent at least two times. 
     In detail, the bypass tube  250  includes a first extension part  251  extending downward from the lower portion of the lower header  205   b . For example, the first extension part  251  may extend downward from a bottom surface of the lower header  205   b.    
     The bypass tube  250  may further include a second extension part  253  extending upward from the first extension part  251  and a first bent part  252  disposed at one spot between the first extension part  251  and the second extension part  253  to switch an extension direction of the bypass tube  250 . 
     The bypass tube  250  may further include a third extension part  255  extending downward from the second extension part  253  and a second bent part  254  disposed at one spot between the second extension part  253  and the third extension part  255  to switch the extension direction of the bypass tube  250 . 
     The bypass tube  250  includes at least two switching parts  252  and  254  for switching the extension direction of the bypass tube  250 . The first bent part  252  may switch the extension direction of the bypass tube  250  from a lower side to an upper side, and the second bent part  254  may switch the extension direction of the bypass tube  250  from the upper side to the lower side. 
     The outdoor heat exchanger  200  according to the current embodiment includes the plurality of refrigerant inflow tubes  232  extending from the lower header  205   b  to the plurality of refrigerant tubes  202 . The plurality of refrigerant inflow tubes  232  includes a lowermost inflow tube  232   a  disposed at the lowest position thereof and a plurality of upper inflow tubes  232   b  disposed at an upper side of the lowermost inflow tube  232   a.    
     The bypass tube  250  may have a structure in which a pressure of the refrigerant flowing in the bypass tube  250  is less than that of the refrigerant in the lowermost inflow tube  232   a.    
     For this, the lowermost inflow tube  232   a  may have a height H 2  higher than a height H 1  of an uppermost portion of the bypass tube  250 . Here, the heights H 1  and H 2  may be understood as distances from the reference line l o. For example, the reference line l o may be a base forming a lower portion of the outdoor unit or the ground. 
     The height H 1  of the uppermost portion of the bypass tube  250  may correspond to a height of the second bent part  254  of the bypass tube  250 . 
     Like this, since the height H 1  of the uppermost portion of the bypass tube  250  is lower than the height H 2  of the lowermost inflow tube  232   a , a pressure of the refrigerant in the lowermost inflow tube  232   a  may be greater than that in the bypass tube  250 . Thus, introduction of the liquid refrigerant existing in the lower header  205   b  into the lowermost tube  232   a  may be prevented. 
     Also, the bypass tube  250  may have a structure in which the gaseous refrigerant existing in the lower header  205   b  is not discharged into the bypass tube  250 . Thus, the height H 1  of the uppermost portion of the bypass tube  250  may be higher than a H 3  of the bottom surface of the lower header  205   b . The height H 3  may be understood as a distance from the reference line l o. 
     Since the height H 1  is higher than the height H 3 , a discharge of all of the liquid refrigerant existing in the lower header  205   b  through the bypass tube  250  may be restricted. Also, a level of the liquid refrigerant existing in the lower header  205   b  may correspond to the height H 1  of the uppermost portion of the bypass tube  250 . Thus, discharge of the gaseous refrigerant of the lower header  205   b  through the bypass tube  250  may be prevented. 
     According to the above-described structure, the bypass tube  250  is provided to allow the liquid refrigerant existing in the lower header  205   b  to be bypassed toward the outlet of the outdoor heat exchanger  200 , thereby improving heat exchange performance of the outdoor heat exchanger  200 . 
     Also, since the height H 1  is lower than the height H 2  and is higher than the height H 3 , introduction of the liquid refrigerant into the refrigerant inflow tube  232  may be prevented, and also a phenomenon in which the gaseous refrigerant existing in the lower header  205   b  is discharged through the bypass tube  250  may be prevented. 
     According to the embodiment, when the air conditioner performs the cooling and heating operations, since the paths through which the refrigerant passes through the outdoor heat exchanger are different in number and length, the outdoor heat exchanger may be improved in heat exchange efficiency. 
     In detail, when the air conditioner performs the cooling operation, since the number of paths through which the refrigerant is introduced into the outdoor heat exchanger is reduced, and the length of the path increases, the refrigerant may increase in flow rate to decrease the condensation pressure, thereby improving the condensation efficiency. 
     Also, when the air conditioner performs the heating operation, since the number of paths through which the refrigerant is introduced into the outdoor heat exchanger increases, and the length of the path is reduced, the refrigerant may be reduced in pressure loss to prevent the evaporation pressure from being reduced, thereby improving the evaporation efficiency. 
     Also, since the bypass tube for allowing the liquid refrigerant to be bypassed toward the outlet-side of the outdoor heat exchanger is provided at the lower side of the header of the outdoor heat exchanger, the phenomenon in which the liquid refrigerant is concentrated into the lower side of the header may be prevented. 
     As a result, since the liquid refrigerant that is already condensed and not be heat-exchanged is discharged from the outdoor heat exchanger, the outdoor heat exchanger may be improved in heat exchange performance (the condensation performance) to prevent pressure loss due to the liquid refrigerant from occurring. 
     Also, since the refrigerant flowing in the bypass tube has a pressure less than that of the refrigerant in the lowermost inflow tube of the header, the level of the liquid refrigerant may be disposed at the lower side of the lowermost inflow tube, and thus, the introduction of the liquid refrigerant into the lowermost inflow tube may be prevented. 
     Also, because the height of the uppermost portion of the bypass tube is higher than that of the lower end of the header, the liquid refrigerant within the header may be maintained over a predetermined level, and thus the discharge of the gaseous refrigerant from the outdoor heat exchanger through the bypass tube may be prevented. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.