Patent Publication Number: US-2021164665-A1

Title: Air conditioner

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2019-0158694 filed on Dec. 3, 2019 in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field 
     The disclosure relates to an air conditioner that is adjusted to have an optimum refrigerant passage according to an operation mode. 
     2. Description of the Related Art 
     In general, an air conditioner is an appliance which controls temperature, humidity, and air current distribution of an indoor space and also eliminates dust from air by using a refrigeration cycle in order to provide a comfortable indoor environment for users. As main components constituting the refrigeration cycle, a compressor, a condenser, an expansion device, and an evaporator are provided. 
     The air conditioner includes an outdoor unit and an indoor unit, and during cooling operation, heat absorbed by the indoor unit is released from the outdoor unit to lower the indoor temperature, and during heating operation, heat absorbed by the outdoor unit is released from the indoor unit to increase the indoor temperature. 
     The outdoor unit is provided with a compressor, a four-way valve, an outdoor heat exchanger, an expansion valve, and a fan, and the indoor unit is provided with an indoor heat exchanger. 
     The compressor, the four-way valve, the outdoor heat exchanger, the expansion valve, and the indoor heat exchanger are connected by a refrigerant passage to form a cooling/heating cycle. 
     During cooling operation, the outdoor heat exchanger may be used as a condenser that condenses a high temperature and high-pressure gas refrigerant into a liquid refrigerant, and during heating operation, the outdoor heat exchanger may be used as an evaporator that evaporates a low temperature and low-pressure liquid refrigerant. 
     When a plurality of outdoor heat exchangers are provided, the plurality of outdoor heat exchangers are connected in parallel regardless of the operation mode of cooling or heating, and thus the efficiency of the air conditioner may be lowered. 
     SUMMARY 
     Therefore, it is an object of the disclosure to provide an air conditioner that is varied so that a plurality of outdoor heat exchangers are connected in series or in parallel according to an operation mode to have an optimum refrigerant passage. 
     Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the disclosure. 
     According to an aspect of the disclosure, there is provided an air conditioner including: a compressor configured to compress a refrigerant and including a first compressor and a second compressor; an outdoor heat exchanger configured to have a refrigerant heat-exchanged with outdoor air, and including a first heat exchanger and a second heat exchanger; an expansion valve configured to expand a refrigerant; an indoor heat exchanger configured to have a refrigerant heat-exchanged with indoor air; a fan including a first fan and a second fan corresponding to the first heat exchanger and the second heat exchanger, respectively; and a cooling/heating conversion device controlled for the first heat exchanger and the second heat exchanger to be connected in parallel during a heating operation and controlled for the first heat exchanger and the second heat exchanger to be connected in series. 
     The cooling/heating conversion device may be a four-way valve, and the four-way valve may include a first four-way valve provided between the compressor, and the indoor heat exchanger and the first heat exchanger and a second four-way valve provided between the first heat exchanger and the second heat exchanger. 
     The first four-way valve may be controlled for the refrigerant compressed by the compressor to be moved to the indoor heat exchanger or the first heat exchanger. 
     The first four-way valve may be controlled for the refrigerant to be moved from the indoor heat exchanger or the first heat exchanger to the compressor. 
     The second four-way valve may be connected to each of the first heat exchanger, the second heat exchanger, the expansion valve, and the compressor. 
     During the heating operation, the refrigerant compressed by the compressor may be moved to the indoor heat exchanger through the first four-way valve and condensed through heat exchange with the indoor air, and the refrigerant condensed in the indoor exchanger may be moved to the expansion valve. 
     The second four-way valve may disconnect the first heat exchanger from the second heat exchanger such that the first heat exchanger and the second heat exchanger are connected in parallel. 
     A part of the refrigerant moved to the expansion valve and expanded may be moved to the first heat exchanger through the second four-way valve, and a remaining part of the refrigerant may be moved to the second heat exchanger and evaporated through heat exchange with outdoor air. 
     The refrigerant evaporated in the first heat exchanger may be moved to the compressor through the first four-way valve, and the refrigerant evaporated in the second heat exchanger may be moved to the compressor through the second four-way valve. 
     During the cooling operation, the second four-way valve may connect the first heat exchanger to the second heat exchanger such that the first heat exchanger and the second heat exchanger are connected in series and disconnects the expansion valve to the compressor. 
     The refrigerant compressed by the compressor may be moved to the first heat exchanger through the first four-way valve and condensed through heat exchange with outdoor air, and the refrigerant condensed in the first heat exchanger may be moved to the second heat exchanger through the second four-way valve and condensed through heat exchange with outdoor air. 
     The refrigerant condensed in the second heat exchanger may be moved to the expansion valve and expanded, the refrigerant expanded in the expansion valve may be moved to the indoor heat exchanger and evaporated through heat exchange with indoor air, and the evaporated refrigerant may be moved to the compressor through the first four-way valve. 
     The cooling/heating conversion device may be an on/off valve. 
     The first fan and the second fan may have different sizes. 
     The first fan and the second may have different rotation speeds. 
     According to another aspect of the disclosure, there is provided an air conditioner including: a compressor configured to compress a refrigerant, and provided in plural; an outdoor heat exchanger configured to have a refrigerant heat-exchanged with outdoor air and provided in plural; an expansion valve configured to expand a refrigerant; an indoor heat exchanger configured to have a refrigerant heat-exchanged with indoor air; a plurality of fans provided to correspond to the plurality of outdoor heat exchangers; and a cooling/heating conversion device controlled such that the plurality of outdoor heat exchangers are connected in parallel during a heating operation, and some of the plurality of outdoor heat exchangers are connected in series and remaining some of the plurality of outdoor heat exchangers are connected in parallel during a cooling operation. 
     The plurality of outdoor heat exchangers may include a first heat exchanger, a second heat exchanger, and a third heat exchanger. 
     The cooling/heating conversion device may be a four-way valve, and the four-way valve may include a first four-way valve provided between the compressor, and the indoor heat exchanger and the first heat exchanger and a second four-way valve provided between the first heat exchanger and the second heat exchanger, and the third heat exchanger may be connected to a refrigerant pipe that connects the first four-way valve to the second heat exchanger. 
     During the cooling operation, the first heat exchanger and the second heat exchanger may be connected in series, and the third heat exchanger may be connected in parallel to the first heat exchanger and the second heat exchanger. 
     The plurality of fans may have different sizes or rotation speeds. 
     Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. 
     Moreover, various functions described below can be implemented or supported by one or more computer programs, each of which is formed from computer readable program code and embodied in a computer readable medium. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer readable program code. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A “non-transitory” computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device. 
     Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
         FIG. 1  illustrates a view of a refrigerant passage during a heating operation of an air conditioner according to an embodiment of the disclosure; 
         FIG. 2  illustrates a view of the refrigerant passage during a cooling operation of the air conditioner according to the embodiment of the disclosure; 
         FIG. 3  illustrates a view of a refrigerant passage during a heating operation of an air conditioner according to another embodiment of the disclosure, showing a state in which a second four-way valve is replaced by an on/off valve; 
         FIG. 4  illustrates a view of the refrigerant passage during a cooling operation of the air conditioner according to the another embodiment of the disclosure, showing a state in which a second four-way valve is replaced by an on-off valve; 
         FIG. 5  illustrates a view of a refrigerant passage during a heating operation of an air conditioner including three outdoor heat exchangers according to another embodiment of the disclosure; and 
         FIG. 6  illustrates a view illustrating the refrigerant passage during a cooling operation of the air conditioner including three outdoor heat exchangers according to the another embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 through 6 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device. 
     Embodiments and features as described and illustrated in the disclosure are only preferred examples, and various modifications thereof may also fall within the scope of the disclosure. 
     Throughout the drawings, like reference numerals refer to like parts or components. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the disclosure. It is to be understood that the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. It will be further understood that the terms “include”, “comprise” and/or “have” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The terms including ordinal numbers like “first” and “second” may be used to explain various components, but the components are not limited by the terms. The terms are only for the purpose of distinguishing a component from another. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the disclosure. Descriptions shall be understood as to include any and all combinations of one or more of the associated listed items when the items are described by using the conjunctive term “˜and/or˜,” or the like. 
     The terms “front”, “rear”, “upper”, “lower”, “top”, and “bottom” as herein used are defined with respect to the drawings, but the terms may not restrict the shape and position of the respective components. 
     Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings. 
     In  FIGS. 1 to 6 , a broken line indicates a refrigerant passage through which a high-pressure refrigerant flows, and a solid line indicates a refrigerant passage through which a low-pressure refrigerant flows. 
       FIG. 1  illustrates a view of a refrigerant passage during a heating operation of an air conditioner according to an embodiment of the disclosure. 
     Referring to  FIG. 1 , an air conditioner may include a compressor  10  compressing a refrigerant, an outdoor heat exchanger  20  allowing a refrigerant to have heat exchanged with outdoor air, an expansion valve  30  expanding a refrigerant, an indoor heat exchanger  40  allowing a refrigerant to have heat exchanged with indoor air, a fan  50  guiding air to the outdoor heat exchanger  20 , and a cooling/heating conversion devices  60  or  70  performing conversion of heating and cooling. 
     The compressor  10  may compress a refrigerant, and include a first compressor  11  and a second compressor  13 . The first compressor  11  and the second compressor  13  may be connected in parallel to each other. 
     The outdoor heat exchanger  20  may allow a refrigerant to have heat exchanged with outdoor air. During a heating operation of the air conditioner, the outdoor heat exchanger  20  may be used as an evaporator. In this case, the indoor heat exchanger  40  may be used as a condenser. During a cooling operation of the air conditioner, the outdoor heat exchanger  20  may be used as a condenser. In this case, the indoor heat exchanger  40  may be used as an evaporator. 
     The outdoor heat exchanger  20  may be provided in plural. The outdoor heat exchanger  20  may include a first heat exchanger  21  and a second heat exchanger  23 . 
     The indoor heat exchanger  40  may allow a refrigerant to have heat exchanged with indoor air. During a heating operation of the air conditioner, the indoor heat exchanger  40  may be used as a condenser. In this case, the outdoor heat exchanger  20  may be used as an evaporator. During a cooling operation of the air conditioner, the indoor heat exchanger  40  may be used as an evaporator. In this case, the outdoor heat exchanger  20  may be used as a condenser. 
     The fan  50  may be provided to correspond to the outdoor heat exchanger  20  to guide air to the outdoor heat exchanger  20 . The fan  50  may include a first fan  51  provided to correspond to the first heat exchanger  21  and a second fan  53  provided to correspond to the second heat exchanger  23 . 
     The cooling/heating conversion device  60  may perform conversion of heating and cooling of the air conditioner. The cooling/heating conversion device  60  may be controlled such that the first heat exchanger  21  and the second heat exchanger  23  are connected in parallel during the heating operation of the air conditioner. In addition, the cooling/heating conversion device  60  may be controlled such that the first heat exchanger  21  and the second heat exchanger  23  are connected in series during the cooling operation of the air conditioner. Details thereof will be described below. 
     The cooling/heating conversion device  60  may be provided as a four-way valve  60 . The four-way valve  60  includes a first four-way valve  61  provided between the compressor  10  and the indoor heat exchanger  40  and the first heat exchanger  21  and a second four-way valve  63  provided between the first heat exchanger  21  and the second heat exchanger  23 . 
     The first four-way valve  61  may be provided between a first refrigerant passage P 1  and a second refrigerant passage P 2 . In addition, the first four-way valve  61  may be provided between an eighth refrigerant passage P 8  and a ninth refrigerant passage P 9 . That is, the first four-way valve  61  may be provided to be connected to the first refrigerant passage P 1 , the second refrigerant passage P 2 , the eighth refrigerant passage P 8 , and the ninth refrigerant passage P 9 . 
     The refrigerant passage may include a first refrigerant passage P 1  connecting the compressor  10  to the first four-way valve  61 , a second refrigerant passage P 2  connecting the first four-way valve  61  to the indoor heat exchanger  40 , a third refrigerant passage P 3  connecting the indoor heat exchanger  40  to the expansion valve  30 , a fourth refrigerant passage P 4  connecting the expansion valve  30  to the second heat exchanger  23 , a fifth refrigerant passage P 5  connecting the expansion valve  30  to the second four-way valve  63 , a sixth refrigerant passage P 6  connecting the second heat exchanger  23  to the second four-way valve  63 , a seventh refrigerant passage P 7  connecting the second four-way valve  63  to the first heat exchanger  21 , an eight refrigerant passage P 8  connecting the first heat exchanger  21  to the first four-way valve  61 , a ninth refrigerant passage P 9  connecting the first four-way valve  61  to the compressor  10 , and a tenth refrigerant passage P 10  connecting the second four-way valve  63  to the compressor  10 . 
     The second four-way valve  63  may be provided between the sixth refrigerant passage P 6  and the seventh refrigerant passage P 7 . In addition, the second four-way valve  63  may be provided between the fifth refrigerant passage P 5  and the tenth refrigerant passage P 10 . That is, the second four-way valve  63  may be provided to be connected to the sixth refrigerant passage P 6 , the seventh refrigerant passage P 7 , the fifth refrigerant passage P 5 , and the tenth refrigerant passage P 10 . 
     During a heating operation of the air conditioner, a refrigerant compressed by the compressor  10  may be moved to the indoor heat exchanger  40  through the first refrigerant passage P 1  and the second refrigerant passage P 2 . In this case, the first four-way valve  61  blocks the eighth refrigerant passage P 8  and the ninth refrigerant passage P 9  such that the refrigerant flows through the first refrigerant passage P 1  and the second refrigerant passage P 2  sequentially to the indoor heat exchanger  40 . 
     Since the indoor heat exchanger  40  is used as a condenser during the heating operation of the air conditioner, a high-temperature and high-pressure refrigerant compressed by the compressor  10  may have heat exchanged with indoor air to heat the indoor air. The refrigerant compressed by the compressor  10  is a high-temperature and high-pressure gas refrigerant, which may be easily liquefiable. The high-temperature and high-pressure gas refrigerant compressed in the compressor  10  may have heat exchanged with indoor air in the indoor heat exchanger  40  while releasing heat to the indoor air to be liquefied into a low-temperature and high-pressure liquid refrigerant. The indoor air may be warmed by the heat released. 
     The low temperature and high-pressure liquid refrigerant condensed in the indoor heat exchanger  40  may be moved to the expansion valve  30  through the third refrigerant passage P 3 . The low-temperature and high-pressure liquid refrigerant may be expanded in the expansion valve  30  to become a low-temperature and low-pressure liquid refrigerant, which may be easily evaporable. 
     A part of the low-temperature and low-pressure liquid refrigerant expanded by the expansion valve  30  may be moved to the second heat exchanger  23  through the fourth refrigerant passage P 4 . In this case, the refrigerant flowing into the second heat exchanger  23  may be in a state in which a low-temperature and low-pressure gas refrigerant and a low-temperature and low-pressure liquid refrigerant are mixed. Since the outdoor heat exchanger  20  is used as an evaporator during the heating operation of the air conditioner, the low-temperature and low-pressure liquid refrigerant moved to the second heat exchanger  23  have heat exchanged with outdoor air to absorb heat from the outdoor air. The low temperature and low-pressure liquid refrigerant may absorb heat and become a high temperature and low-pressure gas refrigerant. The high-temperature and low-pressure gas refrigerant evaporated in the second heat exchanger  23  may be introduced into the compressor  10  through the sixth refrigerant passage P 6  and the tenth refrigerant passage P 10 . In this case, the second four-way valve  63  may be controlled such that the high-temperature and low-pressure gas refrigerant moved to the sixth refrigerant passage P 6  is moved to the compressor  10  through the tenth refrigerant passage P 10 . The high-temperature and low-pressure gas refrigerant may be compressed and become a high temperature and high-pressure gas refrigerant. 
     A remaining part of the low-temperature and low-pressure liquid refrigerant expanded by the expansion valve  30  may be moved to the first heat exchanger  21  through the fifth refrigerant passage P 5  and the seventh refrigerant passage P 7 . In this case, the refrigerant flowing into the first heat exchanger  21  may be in a state in which a low-temperature and low-pressure gas refrigerant and a low-temperature and low-pressure liquid refrigerant are mixed. In this case, the second four-way valve  63  may be controlled such that the low-temperature and low-pressure liquid refrigerant moved to the fifth refrigerant passage P 6  is moved to the first heat exchanger  21  through the seventh refrigerant passage P 7 . Since the outdoor heat exchanger  20  is used as an evaporator during a heating operation of the air conditioner, the low temperature and low-pressure liquid refrigerant moved to the first heat exchanger  21  may have heat exchanged with the outdoor air to absorb heat from the outdoor air. The low temperature and low-pressure liquid refrigerant may absorb the heat and become a high temperature and low-pressure gas refrigerant. The high-temperature and low-pressure gas refrigerant evaporated in the first heat exchanger  21  may be introduced into the compressor  10  through the eighth refrigerant passage P 8  and the ninth refrigerant passage P 9 . The high temperature and low-pressure gas refrigerant introduced into the compressor  10  may be compressed to become a high temperature and high-pressure gas refrigerant. 
     As described above, during a heating operation of the air conditioner, the second four-way valve  63  may allow the first heat exchanger  21  and the second heat exchanger  23  to be connected in parallel. 
     The outdoor heat exchanger  20  is used as an evaporator during the heating operation of the air conditioner, and a decrease in system low-pressure due to a pressure drop of the refrigerant during evaporation in the first heat exchanger  21  and the second heat exchanger  23  may cause the system performance and efficiency to be degraded. In addition, with regard to defrost condition, a decrease in refrigerant temperature due to a pressure drop of the refrigerant may promote defrost, thereby causing the system performance and efficiency to be degraded. 
     In order to prevent the performance and efficiency of the system from deteriorating as described above, when the first heat exchanger  21  and the second heat exchanger  23  are connected in parallel so that a shorter refrigerant passage may be achieved, thereby reducing the pressure drop of the refrigerant. When the pressure drop of the refrigerant is reduced, the system low-pressure is increased and the defrost is delayed, so that the overall system efficiency may be improved. In a case where the outdoor heat exchanger  20  is used as an evaporator, an optimum heat exchange efficiency may be provided when the refrigerant passage has a length of 6 m to 8 m. That is, during a heating operation, in the evaporation process in the outdoor heat exchanger  20 , the refrigerant converted to a gas refrigerant is subject to flow rate increase. When the length of the refrigerant passage is shortened, the flow rate of the refrigerant is reduced, thereby improving the heat exchange efficiency. Reducing the flow rate of the refrigerant may prevent a pressure drop in the evaporation, thereby increasing the system low-pressure and improving the overall system efficiency. 
     In a case where the outdoor heat exchanger  20  is used as a condenser, the optimal heat exchange efficiency may be provided when the refrigerant passage has a length of about 15 m to 20 m. That is, during a cooling operation, in the condensation process in the outdoor heat exchanger  20 , the refrigerant converted to a liquid state is subject to flow rate decrease. When the length of the refrigerant passage is lengthened, the flow rate of the refrigerant is increased, thereby improving the heat exchange efficiency. 
     In other words, in a heating operation in which the outdoor heat exchanger  20  is used as an evaporator, the length of the refrigerant passage needs to be shortened to improve the heat exchange efficiency. In a cooling operation in which the outdoor heat exchanger  20  is used as a condenser, the length of the refrigerant passage needs to be increased to improve the heat exchange efficiency. Accordingly, in a cooling operation in which the first heat exchanger  21  and the second heat exchanger  23  are connected in series, the length of the refrigerant passage may be limited to 5 m to 30 m in consideration of the size of the outdoor unit. In a heating operation in which the first heat exchanger  21  and the second heat exchanger  23  are connected in parallel, the length of the refrigerant passage may be provided one third to two third of the length of the refrigerant passage when the first heat exchanger  21  and the second heat exchanger  23  are connected in series. 
     In addition, the system efficiency may be improved by reducing the rotation speeds of the first fan  51  and the second fan  53  provided at the rear ends of the refrigerant passages of the first heat exchanger  21  and the second heat exchanger  23  connected in parallel according to the operating load to lower the consumption input. In addition, when the sizes of the first heat exchanger  21  and the second heat exchanger  23  are different, the rotational speed reductions of the first fan  51  and the second fan  53  may be set to be different from each other to secure the optimal system efficiency. In addition, when the sizes of the first heat exchanger  21  and the second heat exchanger  23  are different, the sizes of the first fan  51  and the second fan  53  may be provided to be different from each other to correspond to the sizes of the first heat exchanger  21  and the second heat exchanger to lower the consumption input, so that the efficiency may be improved. 
       FIG. 2  illustrates a view of the refrigerant passage during a cooling operation of the air conditioner according to the embodiment of the disclosure. 
     Referring to  FIG. 2 , a refrigerant compressed in the compressor  10  during a cooling operation of the air conditioner may be moved to the first heat exchanger  21  through the first refrigerant passage P 1  and the eighth refrigerant passage P 8 . In this case, the first four-way valve  61  may block the second refrigerant passage P 2  and the ninth refrigerant passage P 9  such that the refrigerant may be moved to the first heat exchanger  21  through the first refrigerant passage P 1  and the eighth refrigerant passage P 8 . 
     Since the outdoor heat exchanger  20  is used as a condenser during the cooling operation of the air conditioner, the high temperature and high-pressure refrigerant compressed by the compressor  10  may have heat exchanged with outdoor air to release heat to the outdoor air. The refrigerant compressed by the compressor  10  is a high-temperature and high-pressure gas refrigerant, which may be easily liquefiable. The high-temperature and high-pressure gas refrigerant compressed in the compressor  10  may have heat exchanged with outdoor air in the first heat exchanger  21  while releasing heat to the outdoor air to be liquefied into a low-temperature and high-pressure liquid refrigerant. 
     The refrigerant condensed in the first heat exchanger  21  may be moved to the second heat exchanger  23  through the seventh refrigerant passage P 7  and the sixth refrigerant passage P 6 . The refrigerant moved to the second heat exchanger  23  may have heat exchanged with outdoor air to release heat to the outdoor air. Accordingly, the refrigerant passed through the second heat exchanger  23  may be a low-temperature and high-pressure liquid refrigerant having a temperature lower than that of the refrigerant passed through the first heat exchanger  21 . 
     As described above, during the cooling operation of the air conditioner, the second four-way valve  63  may allow the first heat exchanger  21  and the second heat exchanger  23  to be connected in series. 
     In the cooling operation of the air conditioner, the outdoor heat exchanger  20  is used as a condenser, and a high-temperature and high-pressure gas refrigerant is introduced into the outdoor heat exchanger  20 , so that the refrigerant in the process of being condensed in the outdoor heat exchanger  20  may be subject to flow rate decrease. Accordingly, when the length of the refrigerant passage is increased by connecting the first heat exchanger  21  and the second heat exchanger  23  in series, the heat exchange efficiency and overall system efficiency may be improved. In addition, when the rotational speed of the second fan  53  corresponding to the second heat exchanger  23  between the first fan  51  and the second fan  53  provided at the rear ends of the refrigerant passages of the first heat exchanger  21  and the second heat exchanger  23  connected in series according to the operating load is reduced, the consumption input may be lowered, thereby improving the system efficiency. This may be achieved because the first fan  51  and the second fan  53  are provided to correspond to the first heat exchanger  21  and the second heat exchanger  23 , respectively. 
     The low temperature and high-pressure liquid refrigerant condensed in the first heat exchanger  21  and the second heat exchanger  23  may be moved to the expansion valve  30  through the fourth refrigerant passage P 4 . The low-temperature and high-pressure liquid refrigerant may be expanded in the expansion valve  30  to become a low-temperature and low-pressure liquid refrigerant, which may be easily evaporated. 
     The low-temperature and low-pressure liquid refrigerant expanded by the expansion valve  30  may be moved to the indoor heat exchanger  40  through the third refrigerant passage P 3 . Since the indoor heat exchanger  40  is used as an evaporator during the cooling operation of the air conditioner, the low temperature and low-pressure liquid refrigerant introduced into the indoor heat exchanger  40  may have heat exchanged with the indoor air to absorb heat from the indoor air. The low temperature and low-pressure liquid refrigerant may absorb heat and become a high temperature and low-pressure gas refrigerant. Accordingly, the indoor air may be cooled. The high-temperature and low-pressure gas refrigerant evaporated in the indoor heat exchanger  40  may flow into the compressor  10  through the second refrigerant passage P 2  and the ninth refrigerant passage P 9 . 
       FIG. 3  illustrates a view of a refrigerant passage during a heating operation of an air conditioner according to another embodiment of the disclosure, showing a state in which a second four-way valve is replaced by an on-off valve. 
     Referring to  FIG. 3 , a cooling/heating conversion device  60  may be provided as an on-off valve. That is, a plurality of on-off valves  71 ,  73 , and  75  may be used instead of the second four-way valve  63  shown in  FIG. 1 . 
     The on-off valve  70  may include a first on-off valve  71  provided between the sixth refrigerant passage P 6  and the seventh refrigerant passage P 7 , a second on-off valve  73  provided in the fifth refrigerant passage P 5 , and a third on-off valve  75  provided in the tenth refrigerant passage P 10 . Components other than the on-off valve  70  are the same as those shown in  FIG. 1 , and thus descriptions thereof will be omitted. 
     Only parts related to the on-off valve  70  during the heating operation of the air conditioner will be described. A part of the low-temperature and low-pressure liquid refrigerant expanded in the expansion valve  30  may be moved to the second heat exchanger  23  through the fourth refrigerant passage P 4 . In this case, the refrigerant flowing into the second heat exchanger  23  may be in a state in which a low-temperature and low-pressure gas refrigerant and a low-temperature and low-pressure liquid refrigerant are mixed. Since the outdoor heat exchanger  20  is used as an evaporator during the heating operation of the air conditioner, the low-temperature and low-pressure liquid refrigerant moved to the second heat exchanger  23  may have heat exchanged with outdoor air to absorb heat from the outdoor air. The low temperature and low-pressure liquid refrigerant may absorb heat and become a high temperature and low-pressure gas refrigerant. The high-temperature and low-pressure gas refrigerant evaporated in the second heat exchanger  23  may be introduced into the compressor  10  through the sixth refrigerant passage P 6  and the tenth refrigerant passage P 10 . In this case, the first on-off valve  71  may be controlled to be closed and the third on-off valve  75  may be controlled to be opened. The high temperature and low-pressure gas refrigerant introduced into the compressor  10  may be compressed to become a high temperature and high-pressure gas refrigerant. 
     A remaining part of the low-temperature and low-pressure liquid refrigerant expanded by the expansion valve  30  may be moved to the first heat exchanger  21  through the fifth refrigerant passage P 5  and the seventh refrigerant passage P 7 . In this case, the refrigerant flowing into the first heat exchanger  21  may be in a state in which a low-temperature and low-pressure gas refrigerant and a low-temperature and low-pressure liquid refrigerant are mixed. In this case, the first on-off valve  71  may be controlled to be closed and the second on-off valve  73  may be controlled to be opened. Since the outdoor heat exchanger  20  is used as an evaporator during the heating operation of the air conditioner, the low temperature and low-pressure liquid refrigerant moved to the first heat exchanger  21  may have heat exchanged with the outdoor air to absorb heat from the outdoor air. The low temperature and low-pressure liquid refrigerant absorbs heat and become a high-temperature and low-pressure gas refrigerant. The high-temperature and low-pressure gas refrigerant evaporated in the first heat exchanger  21  may be introduced into the compressor  10  through the eighth refrigerant passage P 8  and the ninth refrigerant passage P 9 . The high-temperature and low-pressure gas refrigerant introduced into the compressor  10  may be compressed to become a high temperature and high-pressure gas refrigerant. 
     That is, when the on-off valve  70  is used as the cooling/heating conversion device, the first on-off valve  71  may be controlled to be closed during the heating operation of the air conditioner, and the second on-off valve  73  and the third on-off valve  75  may be controlled to be opened. 
       FIG. 4  illustrates a view of the refrigerant passage during a cooling operation of the air conditioner according to the another embodiment of the disclosure, showing a state in which a second four-way valve is replaced by an on-off valve. 
     Referring to  FIG. 4 , the cooling/heating conversion device  60  may be provided as an on-off valve. That is, instead of the second four-way valve  63  shown in  FIG. 2 , a plurality of on-off valves  71 ,  73 , and  75  may be used. 
     The on-off valve  70  may include a first on-off valve  71  provided between the sixth refrigerant passage P 6  and the seventh refrigerant passage P 7 , a second on-off valve  73  provided in the fifth refrigerant passage P 5 , and a third on-off valve  75  provided in the tenth refrigerant passage P 10 . Components other than the on-off valve  70  are the same as those shown in  FIG. 2 , and thus descriptions thereof will be omitted. 
     Only parts related to the on-off valve  70  during the cooling operation of the air conditioner will be described. Since the outdoor heat exchanger  20  is used as a condenser during the cooling operation of the air conditioner, a high temperature and high-pressure refrigerant compressed by the compressor  10  may have heat exchanged with outdoor air to release heat to the outdoor air. The refrigerant compressed by the compressor  10  is a high-temperature and high-pressure gas refrigerant, which may be easily liquefiable. The high-temperature and high-pressure gas refrigerant compressed by the compressor  10  may have heat exchanged with outdoor air in the first heat exchanger  21  while releasing heat to the outdoor air to be liquefied into a low-temperature and high-pressure liquid refrigerant. 
     The refrigerant condensed in the first heat exchanger  21  may be moved to the second heat exchanger  23  through the seventh refrigerant passage P 7  and the sixth refrigerant passage P 6 . In this case, the first on-off valve  71  may be controlled to be opened, and the second on-off valve  73  and the third on-off valve  75  may be controlled to be closed. The refrigerant moved to the second heat exchanger  23  may have heat exchanged with outdoor air to release heat to the outdoor air. Accordingly, the refrigerant passed through the second heat exchanger  23  may be a low-temperature and high-pressure liquid refrigerant having a temperature lower than that of the refrigerant passed through the first heat exchanger  21 . 
       FIG. 5  illustrates a view of a refrigerant passage during a heating operation of an air conditioner including three outdoor heat exchangers according to another embodiment of the disclosure. 
     Referring to  FIG. 5 , an outdoor heat exchanger  20  may include a first heat exchanger  21 , a second heat exchanger  23 , and a third heat exchanger  25 . The first heat exchanger  21 , the second heat exchanger  23 , and the third heat exchanger  25  may be provided with a first fan  51 , a second fan  53 , and a third fan  55  corresponding thereto. 
     Compared with the configuration shown in  FIG. 1 , when the outdoor heat exchanger  20  is provided to include the first heat exchanger  21 , the second heat exchanger  23  during a heating operation of the air conditioner, and the third heat exchanger  25 , the first heat exchanger  21 , the second heat exchanger  23 , and the third heat exchanger  25  may be connected in parallel. 
     That is, a part of the refrigerant expanded in the expansion valve  30  may flow into the third heat exchanger  25  through an eleventh refrigerant passage P 11  and evaporate, and may be moved to the eighth refrigerant passage P 8  through a twelfth refrigerant passage P 12 . The refrigerant moved to the eighth refrigerant passage P 8  may flow into the compressor  10  through a ninth refrigerant passage P 9 . 
     In addition, a part of the refrigerant expanded in the expansion valve  30  may flow into the second heat exchanger  23  through a fourth refrigerant passage P 4  and evaporates, and may flow into the compressor  10  through a sixth refrigerant passage P 6  and a tenth refrigerant passage P 10 . 
     In addition, a remaining part of the refrigerant expanded in the expansion valve  30  may flow into the first heat exchanger  21  through a fifth refrigerant passage P 5  and a seventh refrigerant passage P 7  and evaporates, and may flow into the compressor  10  through the eighth refrigerant passage P 8  and the ninth refrigerant passage P 9 . 
       FIG. 6  illustrates a view of the refrigerant passage during a cooling operation of the air conditioner including three outdoor heat exchangers according to the another embodiment of the disclosure. 
     Referring to  FIG. 6 , the outdoor heat exchanger  20  may include the first heat exchanger  21 , the second heat exchanger  23 , and the third heat exchanger  25 . The first heat exchanger  21 , the second heat exchanger  23  and the third heat exchanger  25  may be provided with the first fan  51 , the second fan  53 , and the third fan  55  corresponding thereto. The first fan  51 , the second fan  53 , and the third fan  55  may have different sizes or different rotational speeds, similar to the first fan  51  and the second fan  53  illustrated in  FIG. 2 . 
     Compared with the configuration shown in  FIG. 2 , when the outdoor heat exchanger  20  is provided to include the first heat exchanger  21 , the second heat exchanger  23 , and the third heat exchanger  25  during a cooling operation of the air conditioner, the first heat exchanger  21  and the second heat exchanger  23  may be connected in series, and the third heat exchanger  25  may be connected in parallel to the first heat exchanger  21  and the second heat exchanger  23 . 
     That is, a part of the refrigerant compressed by the compressor  10  may flow into the first heat exchanger  21  through the first refrigerant passage P 1  and the eighth refrigerant passage P 8 . In addition, the refrigerant condensed in the first heat exchanger  21  may flow into the second heat exchanger  23  through the seventh refrigerant passage P 7  and the sixth refrigerant passage P 6 . The refrigerant condensed in the second heat exchanger  23  may be introduced into the expansion valve  30  through the fourth refrigerant passage P 4 . 
     In addition, a remaining part of the refrigerant compressed by the compressor  10  may flow into the third heat exchanger  25  through the first refrigerant passage P 1 , the eighth refrigerant passage P 8 , and the twelfth refrigerant passage P 12 . The refrigerant condensed in the third heat exchanger  25  may be introduced into the expansion valve  30  through the eleventh refrigerant passage P 11 . 
     As is apparent from the above, according to the embodiments of the disclosure, a plurality of outdoor heat exchangers are varied to be connected in series or in parallel according to an operation mode, so that the heat exchange efficiency can be enhanced. 
     Although the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.