Patent Publication Number: US-2016223240-A1

Title: Outdoor unit of air conditioner and air conditioner

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2015-015121 filed with the Japan Patent Office on Jan. 29, 2015, the entire content of which is hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     Embodiments of the present disclosure relate to an outdoor unit of an air conditioner including a heat exchanger with a plurality of refrigerant paths, and an air conditioner. 
     2. Description of the Related Art 
     For a known air conditioner, an outdoor unit includes an outdoor heat exchanger with a plurality of refrigerant paths vertically disposed in parallel, for example. When the air conditioner performs heating operation, the outdoor heat exchanger serves as an evaporator. Accordingly, a refrigerant brought into a gas-liquid two-phase state or a liquid state in an indoor unit flows into the outdoor heat exchanger. At that time, the liquid refrigerant flows biased toward the lower refrigerant paths under the influence of gravity. This may cause reduction in heating capacity due to degradation in evaporating performance of the outdoor heat exchanger. 
     There has been proposed a method for correcting the bias in the flow rate of the refrigerant among a plurality of refrigerant paths as described below (for example, refer to JP-A 2011-232011). According to this method, capillary tube is provided in each of the refrigerant paths of the outdoor heat exchanger. The flow passage resistance of the capillary tube in a specific refrigerant path is set to be higher than the flow passage resistances of the capillary tubes in the other refrigerant paths. At the outdoor heat exchanger as described above, for example, the flow passage resistance of the capillary tube in the lower refrigerant path is set to be higher than the flow passage resistances of the capillary tubes in the other refrigerant paths. In this case, when the outdoor heat exchanger serves as an evaporator, the amount of the liquid refrigerant flowing into the lower path is regulated by the capillary tube. This corrects the bias in the flow rate of the refrigerant among the refrigerant paths. Accordingly, it is possible to suppress degradation in evaporating performance of the outdoor heat exchanger, thereby preventing reduction in heating capacity. 
     SUMMARY 
     An outdoor unit of an air conditioner includes: an outdoor heat exchanger provided with a plurality of refrigerant paths including a flow rate-variable refrigerant path; an ambient air temperature detector that detects an ambient air temperature; and a controller that decreases a flow rate of a refrigerant flowing into the flow rate-variable refrigerant path in a case where the ambient air temperature detected by the ambient air temperature detector is equal to or higher than a threshold ambient air temperature as compared to a case where the ambient air temperature is lower than the threshold ambient air temperature, when the outdoor heat exchanger serves as an evaporator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a diagram of a refrigerant circuit in an air conditioner according to an embodiment of the present disclosure, and  FIG. 1B  is a block diagram of an outdoor unit controller in the air conditioner; 
         FIG. 2A  is a diagram illustrating a flow rate balancer in the embodiment of the present disclosure in the state where an open/close valve is open, and  FIG. 2B  is a diagram illustrating the flow rate balancer in the state where the open/close valve is closed; and 
         FIG. 3  is a flowchart of a process performed by the outdoor unit controller in the embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
     Reduction in heating capacity of the air conditioner due to decrease in the circulation volume of a refrigerant during heating operation becomes larger at lower ambient air temperatures. In particular, when the ambient air temperature is extremely low (for example, lower than −15° C.), heating capacity may decrease significantly even with a slight decrease in the circulation volume of refrigerant. This is because, in the outdoor heat exchanger serving as an evaporator, the refrigerant is more unlikely to draw heat from the ambient air at lower ambient air temperatures, and thus the evaporating performance degrades significantly even with a slight decrease in refrigerant flow rate. 
     In the outdoor heat exchanger described in JP-A 2011-232011, the flow passage resistance of the capillary tube provided in each of the refrigerant paths decrease the circulation volume of refrigerant. Accordingly, when the ambient air temperature is extremely low, the heating capacity may decrease largely due to the significant degradation in the evaporating performance of the outdoor heat exchanger. 
     An object of the present disclosure is to provide an outdoor unit of an air conditioner. The outdoor unit can suppress degradation in air conditioning performance resulting from decrease in the circulation volume of refrigerant at lower ambient air temperatures while correcting the bias in the flow rate of the refrigerant among the refrigerant paths. 
     An outdoor unit of an air conditioner according to one aspect of the present disclosure includes: an outdoor heat exchanger provided with a plurality of refrigerant paths including a flow rate-variable refrigerant path; an ambient air temperature detector that detects an ambient air temperature; and a controller that decreases a flow rate of a refrigerant flowing into the flow rate-variable refrigerant path in a case where the ambient air temperature detected by the ambient air temperature detector is equal to or higher than a threshold ambient air temperature as compared to a case where the ambient air temperature is lower than the threshold ambient air temperature, when the outdoor heat exchanger serves as an evaporator. 
     In the above described outdoor unit of an air conditioner, a controller decreases a flow rate of a refrigerant flowing into the flow rate-variable refrigerant path in a case where the ambient air temperature detected by the ambient air temperature detector is equal to or higher than a threshold ambient air temperature as compared to a case where the ambient air temperature is lower than the threshold ambient air temperature, when the outdoor heat exchanger serves as an evaporator. Consequently, the outdoor unit can suppress degradation in air conditioning performance resulting from decrease in the circulation volume of refrigerant at lower ambient air temperatures while correcting the bias in the flow rate of the refrigerant among the refrigerant paths. 
     The embodiment of the present disclosure will be described below in detail with reference to the accompanying drawings. In the air conditioner according to this embodiment, three indoor units are coupled in parallel to one outdoor unit. Using all the indoor units simultaneously can perform cooling operation or heating operation. However, the mode of the present disclosure is not limited to the following embodiment. The mode of the present disclosure can be modified in various manners without deviating from the gist of the present disclosure. 
     EXAMPLE 
     As illustrated in  FIG. 1A , an air conditioner  1  in this embodiment includes one outdoor unit  2  and three indoor units  5   a  to  5   c . The indoor units  5   a  to  5   c  are coupled in parallel to the outdoor unit  2  via pipes including a first liquid pipe  8   a , a second liquid pipe  8   b , a third liquid pipe  8   c , and a gas pipe  9 . That is, the air conditioner  1  includes the outdoor unit  2 , the indoor units  5   a  to  5   c , and the pipes coupling the outdoor unit  2  to the indoor units  5   a  to  5   c.    
     The foregoing components are coupled in a manner as described below. One end of the first liquid pipe  8   a  is coupled to a first liquid-side closing valve  27   a  of the outdoor unit  2 . The other end of the first liquid pipe  8   a  is coupled to a liquid pipe coupling portion  53   a  of the indoor unit  5   a . One end of the second liquid pipe  8   b  is coupled to a second liquid-side closing valve  27   b  of the outdoor unit  2 . The other end of the second liquid pipe  8   b  is coupled to a liquid pipe coupling portion  53   b  of the indoor unit  5   b . One end of the third liquid pipe  8   c  is coupled to a third liquid-side closing valve  27   c  of the outdoor unit  2 . The other end of the third liquid pipe  8   c  is coupled to a liquid pipe coupling portion  53   c  of the indoor unit  5   c.    
     One end of the gas pipe  9  is coupled to a gas-side closing valve  28  of the outdoor unit  2 . The other end of the gas pipe  9  is branched in three, and the gas pipe  9  has three other ends. The three other ends of the gas pipe  9  are coupled to respective gas pipe coupling portions  54   a  to  54   c  of the indoor units  5   a  to  5   c . In this manner, the outdoor unit  2  is couple to the indoor units  5   a  to  5   c  via the first liquid pipe  8   a , the second liquid pipe  8   b , the third liquid pipe  8   c , and the gas pipe  9 . These components constitutes a refrigerant circuit  10  in the air conditioner  1 . 
     The outdoor unit  2  includes a compressor  21 , a four-way valve  22 , an outdoor heat exchanger  23 , a first expansion valve  24   a , a second expansion valve  24   b , a third expansion valve  24   c , an accumulator  25 , a first flow rate balancer  26   a , a second flow rate balancer  26   b , a third flow rate balancer  26   c , the first liquid-side closing valve  27   a , the second liquid-side closing valve  27   b , the third liquid-side closing valve  27   c , the gas-side closing valve  28 , an outdoor fan  29 , and an outdoor unit controller  200 . These members except for the outdoor fan  29  and the outdoor unit controller  200  are mutually coupled via refrigerant pipes described later in detail to constitute an outdoor unit refrigerant circuit  20  as part of the refrigerant circuit  10 . 
     The compressor  21  is a capacity-variable compressor. That is, the compressor  21  is driven by a motor not illustrated controlled in rotation speed by an inverter. Accordingly, the operating capacity of the compressor  21  is variable. The refrigerant discharge opening of the compressor  21  is coupled to a port a of the four-way valve  22  described later via a discharge pipe  41 . The refrigerant intake side of the compressor  21  is coupled to the refrigerant outflow side of the accumulator  25  via an intake pipe  42 . 
     The four-way valve  22  is a valve for switching the directions in which the refrigerant flows. The four-way valve  22  includes four ports a, b, c, and d. The port a is coupled to the refrigerant discharge opening of the compressor  21  via the discharge pipe  41 . The port b is coupled to each one end of first to seventh refrigerant paths  23   a  to  23   g  included in the outdoor heat exchanger  23  described later via a refrigerant pipe  43 . The port c is coupled to the refrigerant inflow side of the accumulator  25  via a refrigerant pipe  46 . The port d is coupled to the gas-side closing valve  28  via an outdoor unit gas pipe  45 . 
     The outdoor heat exchanger  23  exchanges heat between the refrigerant and the ambient air taken into the outdoor unit  2  from an inlet not illustrated by rotation of the outdoor fan  29  described later. The outdoor heat exchanger  23  has the first refrigerant path  23   a , the second refrigerant path  23   b , the third refrigerant path  23   c , the fourth refrigerant path  23   d , the fifth refrigerant path  23   e , the sixth refrigerant path  23   f , and the seventh refrigerant path  23   g . These seven refrigerant paths are vertically disposed in parallel in order of the first refrigerant path  23   a , the second refrigerant path  23   b , , and the seventh refrigerant path  23   g  from the bottom. As described above, one end of each of the first refrigerant path  23   a  to the seventh refrigerant path  23   g  is coupled to the port b of the four-way valve  22  via the refrigerant pipe  43 . The other end of each of the first refrigerant path  23   a  to the seventh refrigerant path  23   g  is coupled to one end of each of a first liquid branch pipe  44   a  to a third liquid branch pipe  44   c  via an outdoor unit liquid pipe  44 . The outdoor heat exchanger  23  serves as a condenser when the refrigerant circuit  10  is in a cooling cycle and serves as an evaporator when the refrigerant circuit  10  is in a heating cycle. 
     The first expansion valve  24   a  is provided in the first liquid branch pipe  44   a . One end of the first liquid branch pipe  44   a  is coupled to the outdoor unit liquid pipe  44 , and the other end of the same is coupled to the first liquid-side closing valve  27   a . The second expansion valve  24   b  is provided in the second liquid branch pipe  44   b . One end of the second liquid branch pipe  44   b  is coupled to the outdoor unit liquid pipe  44 , and the other end of the same is coupled to the second liquid-side closing valve  27   b . The third expansion valve  24   c  is provided in the third liquid branch pipe  44   c . One end of the third liquid branch pipe  44   c  is coupled to the outdoor unit liquid pipe  44 , and the other end of the same is coupled to the third liquid-side closing valve  27   c.    
     The degrees of opening of the first expansion valve  24   a , the second expansion valve  24   b , and the third expansion valve  24   c  are controlled by the outdoor unit controller  200 . By controlling the degree of opening of the first expansion valve  24   a , the flow rate of the refrigerant flowing into the indoor unit  5   a  is adjusted. By controlling the degree of opening of the second expansion valve  24   b , the flow rate of the refrigerant flowing into the indoor unit  5   b  is adjusted. By controlling the degree of opening of the third expansion valve  24   c , the flow rate of the refrigerant flowing into the indoor unit  5   c  is adjusted. The first expansion valve  24   a , the second expansion valve  24   b , and the third expansion valve  24   c  are electronic expansion valves driven by a pulse motor not illustrated. The degrees of opening of the first expansion valve  24   a , the second expansion valve  24   b , and the third expansion valve  24   c  are adjusted according to the number of pulses given by the pulse motor. 
     As described above, the refrigerant inflow side of the accumulator  25  is coupled to the port c of the four-way valve  22  via the refrigerant pipe  46 . The refrigerant outflow side of the accumulator  25  is coupled to the refrigerant suction opening of the compressor  21  via the intake pipe  42 . The accumulator  25  separates the refrigerant flowing therein into a gas refrigerant and a liquid refrigerant to send the gas refrigerant to the compressor  21 . 
     The first flow rate balancer  26   a  is provided in the first refrigerant path (flow rate-variable refrigerant path)  23   a  at the four-way valve  22  side. The second flow rate balancer  26   b  is provided in the second refrigerant path (flow rate-variable refrigerant path)  23   b  at the four-way valve  22  side. The third flow rate balancer  26   c  is provided in the third refrigerant path (flow rate-variable refrigerant path)  23   c  at the four-way valve  22  side. As described above, the first refrigerant path  23   a  to the third refrigerant path  23   c  are the refrigerant paths with the first flow rate balancers  26   a  to the third flow rate balancer  26   c , respectively. 
     In this embodiment, the first flow rate balancer  26   a , the second flow rate balancer  26   b , and the third flow rate balancer  26   c  are the same in configuration. Accordingly, only the first flow rate balancer  26   a  will be described below and descriptions of the second flow rate balancer  26   b  and the third flow rate balancer  26   c  will be omitted. In  FIG. 1A , the members of the second flow rate balancer  26   b  corresponding to the members of the first flow rate balancer  26   a  are given the reference numerals given to the members of the first flow rate balancer  26   a  in which the last symbol a is replaced with b. Similarly, the members of the third flow rate balancer  26   c  corresponding to the members of the first flow rate balancer  26   a  are given the reference numerals given to the members of the first flow rate balancer  26   a  in which the last symbol a is replaced with c. 
     The first flow rate balancer  26   a  has a capillary tube  26   aa  as a flow rate regulator with a predetermined flow passage resistance, an open/close valve  26   ab  as an open/close device, and a bypass pipe  26   ac . The capillary tube  26   aa  regulates the amount of the refrigerant flowing through the first refrigerant path  23   a . That is, the capillary tube  26   aa  decreases the amount of the refrigerant flowing through the first refrigerant path  23   a  to be smaller than the amount of the refrigerant flowing through each of the fourth refrigerant path  23   d  to the seventh refrigerant path  23   g  without flow rate balancers. The bypass pipe  26   ac  is coupled to the first refrigerant path  23   a  bypassing the capillary tube  26   aa . The open/close valve  26   ab  is provided in the bypass pipe  26   ac . When being opened, the open/close valve  26   ab  allows passage of the refrigerant in the bypass pipe  26   ac . When being closed, the open/close valve  26   ab  shuts off the passage of the refrigerant in the bypass pipe  26   ac . Therefore, when the open/close valve  26   ab  is opened, the refrigerant flows into the bypass pipe  26   ac  bypassing the capillary tube  26   aa . Accordingly, the flow rate of the refrigerant is not regulated by the capillary tube  26   aa . When the open/close valve  26   ab  is closed, the refrigerant does not flow into the bypass pipe  26   ac  but flows through the capillary tube  26   aa . As a result, the flow rate of the refrigerant is regulated by the capillary tube  26   aa.    
     The outdoor fan  29  is a propeller fan made from a resin material and is disposed in the vicinity of the outdoor heat exchanger  23 . The outdoor fan  29  is rotated by a fan motor not illustrated. Accordingly, the ambient air is taken into the outdoor unit  2  from an inlet not illustrated provided in the outdoor unit  2 . Further, the ambient air having undergone heat exchange with the refrigerant flowing through the first refrigerant path  23   a  to the seventh refrigerant path  23   g  in the outdoor heat exchanger  23  is released to the outside of the outdoor unit  2  from an outlet not illustrated provided in the outdoor unit  2 . 
     Besides the members described above, the outdoor unit  2  is provided with various sensors. As illustrated in  FIG. 1A , the discharge pipe  41  is provided with a high-pressure sensor  31  and a discharge temperature sensor  33 . The high-pressure sensor  31  detects the pressure of the refrigerant discharged from the compressor  21 . The discharge temperature sensor  33  detects the temperature of the refrigerant discharged from the compressor  21 . The refrigerant pipe  46  is provided with a low-pressure sensor  32  and an intake temperature sensor  34  in the vicinity of the refrigerant inflow side of the accumulator  25 . The low-pressure sensor  32  detects the pressure of the refrigerant taken into the compressor  21 . The intake temperature sensor  34  detects the temperature of the refrigerant taken into the compressor  21 . 
     The outdoor heat exchanger  23  is provided with an outdoor heat exchange temperature sensor  35  that detects the temperature of the outdoor heat exchanger  23 . The outdoor unit liquid pipe  44  is provided with a refrigerant temperature sensor  36  that detects the temperature of the refrigerant flowing into the outdoor heat exchanger  23  or the refrigerant flowing out of the outdoor heat exchanger  23 . In addition, the outdoor unit  2  is provided with an ambient air temperature sensor  37  as an ambient air temperature detector detecting the temperature of the outdoor flowing into the outdoor unit  2 , that is, the ambient air temperature, in the vicinity of the inlet not illustrated of the outdoor unit  2 . 
     The outdoor unit  2  is also provided with the outdoor unit controller  200 . The outdoor unit controller  200  is mounted on a control substrate stored in an electrical equipment box not illustrated of the outdoor unit  2 . The outdoor unit  2  includes a CPU  210 , a storage unit  220 , a communication unit  230 , and a sensor input unit  240  as illustrated in  FIG. 1B . The CPU  210  is a controller of the outdoor unit  2 . 
     The storage unit  220  includes a ROM and a RAM. The storage unit  220  stores control programs for the outdoor unit  2 , the detection values corresponding to detection signals from the various sensors, the driving states of the compressor  21  and the outdoor fan  29 , and others. The communication unit  230  is an interface that communicates with the indoor units  5   a  to  5   c . The sensor input unit  240  obtains the results of detection by the various sensors of the outdoor unit  2  to output the same to the CPU  210 . The detection values (detection results) from the various sensors are input into the CPU  210  via the sensor input unit  240 . In addition, operation start/stop signals transmitted from the indoor units  5   a  to  5   c  and operation information signals including operation information (setting temperature, indoor temperature, and others) are input into the CPU  210  via the communication unit  230 . The CPU  210  controls, on the basis of the various kinds of input information, the degree of opening of each of the first expansion valve  24   a  to the third expansion valve  24   c , the driving of the compressor  21  and the outdoor fan  29 , and the opening/closing of the open/close valves  26   ab  to  26   cb  of the respective first flow rate balancer  26   a  to third flow rate balancer  26   c.    
     Next, the three indoor units  5   a  to  5   c  will be described. The three indoor units  5   a  to  5   c  include indoor heat exchangers  51   a  to  51   c , liquid pipe coupling portions  53   a  to  53   c , gas pipe coupling portions  54   a  to  54   c , and indoor fans  55   a  to  55   c , respectively. The indoor heat exchangers  51   a  to  51   c  are coupled respectively with the liquid pipe coupling portions  53   a  to  53   c  and the gas pipe coupling portions  54   a  to  54   c  via refrigerant pipes described later in detail to constitute indoor unit refrigerant circuits  50   a  to  50   c  as part of the refrigerant circuit  10  respectively. 
     The indoor units  5   a  to  5   c  are the same in configuration. Accordingly, only the configuration of the indoor unit  5   a  will be described below and descriptions of the other indoor units  5   b  and  5   c  will be omitted. In  FIG. 1A , the members of the indoor unit  5   b  corresponding to the members of the indoor unit  5   a  are given the reference numerals given to the members of the indoor unit  5   a  in which the last symbol a is replaced with b. Similarly, the members of the indoor unit  5   c  corresponding to the members of the indoor unit  5   a  are given the reference numerals given to the members of the indoor unit  5   a  in which the last symbol a is replaced with c. 
     The indoor heat exchanger  51   a  exchanges heat between the refrigerant and the indoor air taken into the indoor unit  5   a  from the suction opening not illustrated included in the indoor unit  5   a  by the rotation of the indoor fan  55   a  described later. One of refrigerant entry/exit openings of the indoor heat exchanger  51   a  is coupled to the liquid pipe coupling portion  53   a  via an indoor unit liquid pipe  71   a . The other refrigerant entry/exit opening of the indoor heat exchanger  51   a  is coupled to the gas pipe coupling portion  54   a  via an indoor unit gas pipe  72   a . The refrigerant pipes are coupled to the liquid pipe coupling portion  53   a  and the gas pipe coupling portion  54   a  by welding or with flare nuts or the like. The indoor heat exchanger  51   a  serves as an evaporator when the indoor unit  5   a  performs cooling operation, and serves as a condenser when the indoor unit  5   a  performs heating operation. 
     The indoor fan  55   a  is a cross-flow fan made from a resin material and is disposed in the vicinity of the indoor heat exchanger  51   a . The indoor fan  55   a  is rotated by a fan motor not illustrated. Accordingly, the indoor air is taken into the indoor unit  5   a  from a suction opening not illustrated. Further, the indoor air having undergone heat exchange with the refrigerant in the indoor heat exchanger  51   a  is supplied to the room from a blow opening not illustrated included in the indoor unit  5   a.    
     Besides the members described above, the indoor unit  5   a  is provided with various sensors. The indoor unit liquid pipe  71   a  is provided with a liquid-side temperature sensor  61   a . The liquid-side temperature sensor  61   a  detects the temperature of the refrigerant flowing into the indoor heat exchanger  51   a  or the refrigerant flowing out of the indoor heat exchanger  51   a . The indoor unit gas pipe  72   a  is provided with a gas-side temperature sensor  62   a . The gas-side temperature sensor  62   a  detects the temperature of the refrigerant flowing out of the indoor heat exchanger  51   a  or the refrigerant flowing into the indoor heat exchanger  51   a . The indoor unit  5   a  is provided with an indoor temperature sensor  63   a  in the vicinity of a suction opening. The indoor temperature sensor  63   a  detects the temperature of the indoor air flowing into the indoor unit  5   a  (that is, the indoor temperature). 
     Next, the flow of the refrigerant in the refrigerant circuit  10  and the operations of the members when the air conditioner  1  of this embodiment performs heating operation will be described with reference to  FIGS. 1A, 2A, and 2B . In the air conditioner  1  of this embodiment, the opening/closing state of each of the open/close valves  26   ab  to  26   cb  of the respective first flow rate balancer  26   a  to third flow rate balancer  26   c  vary depending on whether the ambient air temperature detected by the ambient air temperature sensor  37  is equal to or higher than a threshold ambient air temperature (for example, −15° C.) or the ambient air temperature is lower than the threshold ambient air temperature. The threshold ambient air temperature is as described below. That is, when the ambient air temperature is lower than the threshold ambient air temperature, the heating capacity of the air conditioner  1  decreases significantly due to reduction in the circulation volume of refrigerant. The threshold ambient air temperature is determined (confirmed) in advance by experiments or the like. 
     Hereinafter, descriptions will be first given as to the flow of the refrigerant in the refrigerant circuit  10  and the operations of the members in the case where the ambient air temperature detected by the ambient air temperature sensor  37  is equal to or higher than the threshold ambient air temperature. Then, descriptions will be given as to the flow of the refrigerant in the refrigerant circuit  10  and the operations of the members in the case where the ambient air temperature detected by the ambient air temperature sensor  37  is lower than the threshold ambient air temperature. 
     The following descriptions are based on the assumption that the indoor units  5   a  to  5   c  perform heating operation. The detailed descriptions of the case where the indoor units  5   a  to  5   c  perform cooling operation or dehumidifying operation will be omitted. In addition, the arrows in  FIG. 1A  indicate the flow of the refrigerant. Further,  FIGS. 2A and 2B  illustrate the opened open/close valves  26   ab  to  26   cb  in a void shape, and illustrate the closed open/close valves  26   ab  to  26   cb  in a solid filled shape. 
     &lt;The Case where the Ambient Air Temperature is Equal to or Higher than the Threshold Ambient Air Temperature&gt; 
     As illustrated in  FIG. 1A , when the indoor units  5   a  to  5   c  perform heating operation, that is, when the refrigerant circuit  10  is in the heating cycle, the CPU  210  of the outdoor unit controller  200  switches the four-way valve  22  such that the ports a and d of the four-way valve  22  communicate with each other and the ports b and c of the same communicate with each other as shown by solid lines in  FIG. 1A . Accordingly, the outdoor heat exchanger  23  serves as an evaporator and the indoor heat exchangers  51   a  to  51   c  serve as condensers. The CPU  210  activates the compressor  21  and the outdoor fan  29 . The CPU  210  further controls the opening/closing of each of the open/close valves  26   ab  to  26   cb  of the respective first flow rate balancer  26   a  to third flow rate balancer  26   c . In this example, the ambient air temperature obtained from the ambient air temperature sensor  37  is equal to or higher than the threshold ambient air temperature. Accordingly, the CPU  210  closes the open/close valves  26   ab  to  26   cb  as illustrated in  FIG. 2A . 
     The high-pressure refrigerant discharged from the compressor  21  flows from the discharge pipe  41  into the four-way valve  22 . Further, the refrigerant flows from the four-way valve  22  through the outdoor unit gas pipe  45  and enters into the gas pipe  9  via the gas-side closing valve  28 . The refrigerant having flown into the gas pipe  9  then branches and enters into the indoor units  5   a  to  5   c  via the gas pipe coupling portions  54   a  to  54   c . The refrigerant having flown into the indoor units  5   a  to  5   c  then flows through the indoor unit gas pipes  72   a  to  72   c  and enters into the indoor heat exchangers  51   a  to  51   c  respectively. The refrigerant is condensed through heat exchange with the indoor air taken into the indoor units  5   a  to  5   c  by the rotation of the indoor fans  55   a  to  55   c . In this manner, the indoor heat exchangers  51   a  to  51   c  serve as condensers to blow the indoor air having undergone heat exchange with the refrigerant in the indoor heat exchangers  51   a  to  51   c  into the room from blow openings not illustrated. Accordingly, the room with the indoor units  5   a  to  5   c  is heated. 
     The refrigerant having flown out of the indoor heat exchangers  51   a  to  51   c  flows through the respective indoor unit liquid pipes  71   a  to  71   c  and enters into the respective first liquid pipe  8   a  to third liquid pipe  8   c  via the respective liquid pipe coupling portions  53   a  to  53   c . The refrigerant having flown into the first liquid pipe  8   a  to the third liquid pipe  8   c  enters into the outdoor unit  2  via the respective first liquid-side closing valve  27   a  to third liquid-side closing valve  27   c . After that, the refrigerant is decompressed when passing through each of the first expansion valve  24   a  to the third expansion valve  24   c  while flowing through each of the first liquid branch pipe  44   a  to the third liquid branch pipe  44   c.    
     The refrigerant decompressed by each of the expansion valves flows from each of the first liquid branch pipe  44   a  to the third liquid branch pipe  44   c  into the outdoor unit liquid pipe  44  and joins together. Then, the refrigerant flows into the outdoor heat exchanger  23  and branches to the first refrigerant path  23   a  to the seventh refrigerant path  23   g . The refrigerant having entered into the outdoor heat exchanger  23  and flown through each of the first refrigerant path  23   a  to the seventh refrigerant path  23   g  is evaporated through heat exchange with the ambient air taken into the outdoor unit  2  by the rotation of the outdoor fan  29 . 
     When the refrigerant flows through each of the first refrigerant path  23   a  to the seventh refrigerant path  23   g , each of the open/close valves  26   ab  to  26   cb  of the respective first flow rate balancer  26   a  to third flow rate balancer  26   c  of the respective first refrigerant path  23   a  to third refrigerant path  23   c  is closed as illustrated in  FIG. 2A . Accordingly, the refrigerant having entered into each of the first flow rate balancer  26   a  to the third flow rate balancer  26   c  flows through the capillary tubes  26   aa  to  26   ca  respectively. 
     Accordingly, the amount of the refrigerant flowing through each of the first refrigerant path  23   a  to the third refrigerant path  23   c  is regulated by the flow passage resistance in each of the respective capillary tubes  26   aa  to  26   ca , and is lower than the amount of the refrigerant flowing through each of the other refrigerant paths (the fourth refrigerant path  23   d  to the seventh refrigerant path  23   g ) without the flow rate balancer. Therefore, even when the refrigerant in the gas-liquid two-phase state or in the liquid state enters into the outdoor heat exchanger  23 , it is possible to prevent the situation in which the liquid refrigerant flows biased toward the lower refrigerant paths (in this example, the first refrigerant path  23   a  to the third refrigerant path  23   c ) under the influence of gravity. In this manner, the flow of the refrigerant in the outdoor heat exchanger  23  is unlikely to be biased toward the lower refrigerant paths. This suppresses the degradation in evaporating performance of the outdoor heat exchanger  23 . As a result, it is possible to ensure sufficient heating capacity. 
     The refrigerant having flown out of the refrigerant pipe  43  from each of the first refrigerant path  23   a  to the seventh refrigerant path  23   g  of the outdoor heat exchanger  23  flows through the refrigerant pipe  46  and enters into the accumulator  25  via the four-way valve  22 . After that, the refrigerant is divided by the accumulator  25  into a gas refrigerant and a liquid refrigerant. The gas refrigerant having flown out of the accumulator  25  flows through the intake pipe  42  to be sucked into the compressor  21  and compressed again there. 
     &lt;The Case where the Ambient Air Temperature is Lower than the Threshold Ambient Air Temperature&gt; 
     When the ambient air temperature detected by the ambient air temperature sensor  37  is lower than the threshold ambient air temperature, the flowing of the refrigerant and the operations of the refrigerant circuit  10  except for the flowing of the refrigerant and the operations related to the opening/closing control of the open/close valves  26   ab  to  26   cb  of the respective first flow rate balancer  26   a  to third flow rate balancer  26   c , are the same as those in the foregoing case where the ambient air temperature is equal to or higher than the threshold ambient air temperature, and therefore descriptions thereof will be omitted. Hereinafter, the flow of the refrigerant in each of the first flow rate balancer  26   a  to the third flow rate balancer  26   c  and its effect will be described. 
     In this case, the ambient air temperature obtained from the ambient air temperature sensor  37  is lower than the threshold ambient air temperature. Accordingly, as illustrated in  FIG. 2B , the CPU  210  opens the open/close valves  26   ab  to  26   cb . In this state, when the refrigerant flows through each of the refrigerant paths of the outdoor heat exchanger  23 , the refrigerant having entered into each of the first flow rate balancer  26   a  to the third flow rate balancer  26   c  does not flow through each of the respective capillary tubes  26   aa  to  26   ca  but flows through each of the respective bypass pipe  26   ac  to  26   cc  as illustrated in  FIG. 2B . Accordingly, the amount of the refrigerant flowing through each of the first refrigerant path  23   a  to the third refrigerant path  23   c  is not regulated. Thus, the amount of the refrigerant flowing through each of the first flow rate balancer  26   a  to the third flow rate balancer  26   c  is unlikely to decrease. Therefore, it is possible to suppress reduction in the circulation volume of the refrigerant in the refrigerant circuit  10 . As a result, it is possible to suppress degradation in heating capacity resulting from the reduction in the circulation volume of the refrigerant. 
     Next, the process performed by the CPU  210  of the outdoor unit controller  200  when the air conditioner  1  according to this embodiment performs heating operation will be described with reference to the flowchart of  FIG. 3 . In the flowchart of  FIG. 3 , the symbol ST indicates the steps in the process and the numbers following the symbol ST indicate the step numbers.  FIG. 3  describes the process mainly related to control on the circulation volume of the refrigerant depending on the ambient air temperature. Descriptions of other processes, for example, general processes related to the air conditioner  1  such as controls under operating conditions specified by the user when heating operation is performed will be omitted. 
     First, the CPU  210  determines whether the operating instruction from the user is an instruction for heating operation (ST 1 ). When the instruction is not an instruction for heating operation (ST 1 -No), the CPU  210  controls cooling operation or dehumidifying operation (ST 12 ), and then returns the process to ST 1 . The control of cooling operation or dehumidifying operation means a general control during cooling operation or dehumidifying operation. For example, the CPU  210  operates the four-way valve  22  to switch a refrigerant circuit  10  such that the outdoor heat exchanger  23  serves as a condenser and the indoor heat exchangers  51   a  to  51   c  serve as evaporators. The CPU  210  also activates the compressor  21  and the outdoor fan  29  at the rotation speed according to the performance required by the indoor units  5   a  to  5   c  during cooling operation or dehumidifying operation. 
     When determining that the instruction from the user is an instruction for heating operation (ST 1 -Yes), the CPU  210  makes preparations for heating operation (ST 2 ). At the preparations for heating operation, the CPU  210  operates the four-way valve  22  to switch the refrigerant circuit  10  such that the outdoor heat exchanger  23  serves as an evaporator and the indoor heat exchangers  51   a  to  51   c  serve as condensers. That is, the CPU  210  brings the refrigerant circuit  10  into the state illustrated in  FIG. 1A . 
     Next, the CPU  210  activates the compressor  21  and the outdoor fan  29  (ST 3 ). Specifically, the CPU  210  activates the compressor  21  and the outdoor fan  29  at the rotation speed according to the performance required by the indoor units  5   a  to  5   c.    
     Next, the CPU  210  obtains the ambient air temperature detected by the ambient air temperature sensor  37  via the sensor input unit  240  (ST 4 ). The CPU  210  stores the obtained ambient air temperature in the storage unit  220 . 
     Next, the CPU  210  determines whether the obtained ambient air temperature is lower than the threshold ambient air temperature (ST 5 ). When the obtained ambient air temperature is lower than the threshold ambient air temperature (ST 5 -Yes), the CPU  210  opens the open/close valves  26   ab  to  26   cb  of the respective first flow rate balancer  26   a  to third flow rate balancer  26   c  (ST 6 ), and then moves the process to ST 8 . 
     When determining at ST 5  that the obtained ambient air temperature is not lower than the threshold ambient air temperature (ST 5 -No), the CPU  210  closes the open/close valves  26   ab  to  26   cb  of the respective first flow rate balancer  26   a  to third flow rate balancer  26   c  (ST 7 ), and then moves the process to ST 8 . 
     After ST 6  or ST 7 , the CPU  210  performs a heating operation control (ST 8 ). At the heating operation control, the CPU  210  receives via the communication unit  230  an operation information signal including operation information (setting temperature, indoor temperature, and others) transmitted from the indoor units  5   a  to  5   c . The CPU  210  further controls the driving of the compressor  21  and the outdoor fan  29  and the degree of opening of each of the first expansion valve  24   a  to the third expansion valve  24   c  on the basis of the operation information signal. 
     Next, the CPU  210  determines whether there is an instruction for switching operation from the user (ST 9 ). The instruction for switching operation is an instruction for switching from the current operation to another operation, for example, switching from heating operation to cooling operation or dehumidifying operation. When there is an instruction for switching operation (ST 9 -Yes), the CPU  210  returns the process to ST 1 . 
     When there is no instruction for switching operation (ST 9 -No), the CPU  210  determines whether there is an instruction for stopping operation (ST 10 ). The instruction for stopping operation is an instruction for stopping the operation of each of the indoor units  5   a  to  5   c.    
     When there is no instruction for stopping operation (ST 10 -No), the CPU  210  returns the process to ST 4 . When there is an instruction for stopping operation (ST 10 -Yes), the CPU  210  performs an operation stopping process (ST 11 ), and terminates the process. At the operation stopping process, the CPU  210  stops the compressor  21  and the outdoor fan  29 . 
     As described above, at the air conditioner  1  in this embodiment, when the outdoor heat exchanger  23  serves as an evaporator, that is, when the air conditioner  1  performs heating operation, the CPU  210  opens each of the open/close valves  26   ab  to  26   cb  so as not to regulate the amount of the refrigerant flowing through each of the first refrigerant path  23   a  to third refrigerant path  23   c  in the case where the ambient air temperature detected by the ambient air temperature sensor  37  is lower than the predetermined threshold ambient air temperature. In contrast, in the case where the ambient air temperature detected by the ambient air temperature sensor  37  is equal to or higher than the predetermined threshold ambient temperature, the CPU  210  closes each of the open/close valves  26   ab  to  26   cb  to regulate the amount of the refrigerant flowing through each of the first refrigerant path  23   a  to third refrigerant path  23   c . Accordingly, it is possible to suppress degradation in heating capacity resulting from reduction in the circulation volume of the refrigerant at lower ambient air temperatures while correcting the bias of the flow rate of refrigerant among the refrigerant paths. 
     The CPU  210  may regulate to some extent the amount of the refrigerant flowing through each of the first refrigerant path  23   a  to the third refrigerant path  23   c  even in the case where the ambient air temperature detected by the ambient air temperature sensor  37  is equal to or higher than the threshold ambient air temperature. Accordingly, in the case where the ambient air temperature is equal to or higher than the threshold ambient air temperature, the CPU  210  decreases the amount of the refrigerant flowing through each of the first refrigerant path  23   a  to the third refrigerant path  23   c  as compared to the case where the ambient air temperature is lower than the threshold ambient air temperature. In this case, when the ambient air temperature is equal to or higher than the threshold ambient air temperature, the CPU  210  may adjust the amount of the refrigerant flowing through each of the first refrigerant path  23   a  to the third refrigerant path  23   c  to be equal to or lower than (or almost the same as) the amount of the refrigerant flowing through each of the fourth refrigerant path  23   d  to the seventh refrigerant path  23   g . This adjustment can be made by use of flow rate adjustment valves described later, for example. 
     In the embodiment described above, the first flow rate balancer  26   a  to the third flow rate balancer  26   c  have the capillary tubes  26   aa  to  26   ca , the open/close valves  26   ab  to  26   cb , and the bypass pipes  26   ac  to  26   cc  respectively. Instead of this, the first flow rate balancer  26   a  to the third flow rate balancer  26   c  may be flow rate adjustment valves (for example, electronic expansion valves). In this case, when the ambient air temperature is lower than the threshold ambient air temperature, the CPU  210  may open fully the flow rate adjustment valves, for example. When the ambient air temperature is equal to or higher than the threshold ambient air temperature, the CPU  210  may set the degree of opening of each flow rate adjustment valve to a predetermined value. For example, the CPU  210  may adjust the degree of opening of the flow rate adjustment valve such that the amount of the refrigerant flowing through the refrigerant path provided with the flow rate adjustment valve are equal to or lower than (or almost the same as) the amount of the refrigerant flowing through the refrigerant path not provided with the flow rate balancer. 
     In this embodiment, the capillary tubes  26   aa  to  26   ca  of the respective first flow rate balancer  26   a  to third flow rate balancer  26   c  have the same flow passage resistance. Instead of this, the flow passage resistance of the capillary tube  26   aa  included in the lowest first refrigerant path  23   a  may be higher than the flow passage resistance of each of the other capillary tubes  26   ba  and  26   ca . In this manner, by making uneven the flow passage resistances of the capillary tubes  26   aa  to  26   ca  (for example, setting the flow passage resistances to be different from one another), the regulated flow rates of the refrigerant in the refrigerant paths may be made uneven (for example, made different from each other). That is, the flow passage resistances of the capillary tubes  26   aa  to  26   ca  may be selected such that the regulated flow rates of the refrigerant flowing through the first refrigerant path  23   a  to the third refrigerant path  23   c  become uneven. 
     When the first flow rate balancer  26   a  to the third flow rate balancer  26   c  are flow rate adjustment valves (expansion valves), the CPU  210  may set the degree of opening of the flow rate adjustment valve included in the lowest first refrigerant path  23   a  to be smaller than the degree of opening of each of the other flow rate adjustment valves. In this manner, the CPU  210  may make uneven the degrees of opening of the flow rate adjustment valves to make uneven the regulated flow rates of the refrigerant flowing through the refrigerant paths. That is, the CPU  210  may control the degrees of opening of the flow rate adjustment valves such that the regulated flow rates of the refrigerant flowing through the first refrigerant path  23   a  to the third refrigerant path  23   c  become uneven. 
     In this embodiment, the flow rate balancer is included in each of the first refrigerant path  23   a  to the third refrigerant path  23   c . The flow rate balancer may be included in at least the lowest first refrigerant path  23   a  out of the refrigerant paths vertically disposed in parallel. 
     The first refrigerant path  23   a  to the third refrigerant path  23   c  may be the same in structure as the fourth refrigerant path  23   d  to the seventh refrigerant path  23   g  except for including the respective first flow rate balancer  26   a  to third flow rate balancer  26   c.    
     The first refrigerant path  23   a  to the third refrigerant path  23   c  do not necessarily have to include the first flow rate balancer  26   a  to the third flow rate balancer  26   c . The first refrigerant path  23   a  to the third refrigerant path  23   c  merely need to be flow rate-variable refrigerant paths structured to be capable of being regulated in flow rate by the CPU  210 . The flow rate-variable refrigerant path may be disposed in at least the lowest one of the refrigerant paths vertically disposed in parallel. 
     The air conditioner according to the embodiment of the present disclosure may be any one of the following first to fifth air conditioners. 
     The first air conditioner is an air conditioner having an outdoor heat exchanger with a plurality of refrigerant paths and an ambient air temperature detection unit detecting the ambient air temperature. At least one of the plurality of refrigerant paths has a flow rate balancing unit that switches operations on whether or not to regulate the flow rate of a refrigerant flowing through the refrigerant path. When the outdoor heat exchanger serves as an evaporator, the flow rate balancing unit does not regulate the flow rate of the refrigerant in the case where the ambient air temperature detected by the ambient air temperature detection unit is lower than a predetermined threshold ambient air temperature. When the outdoor heat exchanger serves as an evaporator, the flow rate balancing unit regulates the flow rate of the refrigerant in the case where the ambient air temperature detected by the ambient air temperature detection unit is higher than the threshold ambient air temperature. 
     In the second air conditioner according to the first air conditioner, the flow rate balancing unit has a flow rate regulation unit that regulates the flow rate of the refrigerant flowing through the refrigerant path with the flow rate balancing unit and a bypass pipe that includes an open/close unit and bypasses the flow rate regulation unit. When the outdoor heat exchanger serves as an evaporator, the open/close unit is opened in the case where the ambient air temperature detected by the ambient air temperature detection unit is lower than the threshold ambient air temperature. When the outdoor heat exchanger serves as an evaporator, the open/close unit is closed in the case where when the ambient air temperature detected by the ambient air temperature detection unit is equal to or higher than the threshold ambient air temperature. 
     In the third air conditioner according to the first or second air conditioner, when the flow rate balancing unit is provided in a plurality of refrigerant paths, the flow rate regulation unit is selected such that the regulated flow rates of the refrigerant are different among the plurality of paths. 
     In the fourth air conditioner according to the first air conditioner, the flow rate balancing unit is composed of a flow rate adjustment valve. When the outdoor heat exchanger serves as an evaporator, the flow rate adjustment valve is fully opened in the case where the ambient air temperature detected by the ambient air temperature detection unit is lower than the threshold ambient air temperature. When the outdoor heat exchanger serves as an evaporator, the flow rate adjustment valve is opened at a predetermined degree in the case where the ambient air temperature detected by the ambient air temperature detection unit is equal to or higher than the threshold ambient air temperature. When the flow rate balancing unit is provided in a plurality of refrigerant paths, the degree of opening of the flow rate adjustment valve is controlled such that the regulated flow rates of the refrigerant are different among the plurality of paths. 
     In the fifth air conditioner according to the first to fourth air conditioners, the outdoor heat exchanger has the plurality of refrigerant paths vertically disposed in parallel and the flow rate balancing unit provided in at least the lowest refrigerant path. 
     The foregoing detailed description has been presented for the purposes of illustration and description. Many modifications and variations are possible in light of the above teaching. It is not intended to be exhaustive or to limit the subject matter described herein to the precise form disclosed. Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims appended hereto.