Patent Publication Number: US-9851134-B2

Title: Air-conditioning apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. national stage application of International Application No. PCT/JP2012/003078 filed on May 11, 2012, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to an air-conditioning apparatus that performs air conditioning by using, for example, a zeotropic refrigerant mixture. 
     BACKGROUND ART 
     For reasons such as enhanced operational efficiency and environmental considerations, there are air-conditioning apparatuses that perform air conditioning by using a zeotropic refrigerant mixture in which a plurality of refrigerants with different boiling points are mixed. For example, in some conventional air-conditioning apparatuses using a zeotropic refrigerant mixture such as multi-air-conditioning apparatuses for buildings, a composition-sensing bypass circuit is added to the main refrigerant circuit to sense the composition (circulating composition) of a zeotropic refrigerant mixture circulating through the refrigerant circuit. For example, the composition-sensing bypass circuit is formed by composition-sensing heat exchangers and an expansion device, with temperature and pressure sensors attached in the flow path. A part of the refrigerant discharged from the compressor is caused to flow through the composition-sensing heat exchanger (high-pressure side), the expansion device, and the composition-sensing heat exchanger (low-pressure side) in the order named, and bypassed to the suction portion (suction-side pipe) of the accumulator. At this time, the temperature of the refrigerant in a supercooled liquid state (supercooled liquid refrigerant) at the outlet of the composition-sensing heat exchanger (high-pressure side), the temperature of the refrigerant that is in a two-phase state (two-phase refrigerant) after passing through the expansion device, and the pressure (low-pressure side pressure) at the suction portion of the accumulator are detected by the temperature and pressure sensors. Then, the circulating composition is computed on the basis of the temperature of the supercooled liquid refrigerant, the two-phase refrigerant temperature, and the low-pressure side pressure (see, for example, Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2003-314914 (FIG. 1 and the like) 
     SUMMARY OF INVENTION 
     Technical Problem 
     As described above, conventional air-conditioning apparatuses using a zeotropic refrigerant mixture perform control by deriving the circulating composition by computation on the basis of the temperature of the supercooled liquid refrigerant, the two-phase refrigerant temperature, and the low-pressure side pressure. In this regard, various operational states exist as represented by operation modes such as cooling operation and heating operation, operating conditions such as outdoor temperature and indoor temperature, the number of indoor units to be operated, and so on. For this reason, depending on the operational state, the refrigerant at the high-pressure-side outlet of the composition detection heat exchanger does not always become a supercooled liquid state, or the refrigerant that has passed through the expansion device does not always become a two-phase state. Computing the circulating composition in such an operational state may sometimes result in the computed result being significantly different from the real circulating composition. Controlling an air-conditioning apparatus on the basis of such a different circulating composition may lead to the possibility of deterioration in efficiency. 
     The present invention has been made in view of the above-mentioned problem, and accordingly the present invention provides an air-conditioning apparatus that can operate efficiently on the basis of an appropriate circulating composition. 
     Solution to Problem 
     An air-conditioning apparatus according to the present invention is An air-conditioning apparatus in which a refrigerant circuit is formed by connecting, by a refrigerant pipe, a compressor that discharges a refrigerant, which is a zeotropic refrigerant mixture including a plurality of components with different boiling points, an outdoor-side heat exchanger that exchanges heat between air outside an air-conditioning target space and the refrigerant, a first expansion device that regulates a pressure of the refrigerant, and a load-side heat exchanger that exchanges heat between air in the air-conditioning target space and the refrigerant, the air-conditioning apparatus comprising a controller, the controller including: a composition computing function unit configured to compute a circulating composition, the circulating composition representing a value of composition of each of components in the refrigerant circulating through the refrigerant circuit; and a composition determining function unit configured to determine whether or not a computation result of the composition computing function unit is correct, adopt a predetermined value set in advance and related to composition as the circulating composition if the computation result is determined as incorrect, and adopt the computation result as the circulating composition if the computation result is determined as correct. 
     Advantageous Effects of Invention 
     With the air-conditioning apparatus according to the present invention, in the controller, the composition determining function unit determines whether or not the computation result of the composition computing function unit is appropriate, and if the computation result is determined as not appropriate, the composition determining function unit adopts a previously set predetermined value as the circulating composition. Therefore, a control based on an appropriate circulating composition can be performed, thereby making it possible to obtain an air-conditioning apparatus with good operational efficiency. As a result, energy saving can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating an example of the apparatus configuration of an air-conditioning apparatus according to Embodiment 1 of the present invention. 
         FIG. 2  illustrates a flow of refrigerant in cooling operation mode of an air-conditioning apparatus  100 . 
         FIG. 3  illustrates a flow of refrigerant in heating operation mode of the air-conditioning apparatus  100 . 
         FIG. 4  is a p-h diagram of a zeotropic refrigerant mixture. 
         FIG. 5  is a flowchart illustrating a procedure of processing executed by a composition computing function unit  40 A for computing the composition of a refrigerant mixture. 
         FIG. 6  is a flowchart illustrating a procedure of processing in a composition determining function unit  40 B according to Embodiment 1 of the present invention. 
         FIG. 7  is a p-h diagram for explaining processing in the composition determining function unit  40 B according to Embodiment 1. 
         FIG. 8  is a flowchart illustrating processing of a control operation of a controller  40 . 
         FIG. 9  is a flowchart illustrating a procedure of processing in the composition determining function unit  40 B according to Embodiment 2 of the present invention. 
         FIG. 10  is a p-h diagram for explaining processing in the composition determining function unit  40 B according to Embodiment 2. 
         FIG. 11  is a flowchart illustrating a procedure of processing in the composition determining function unit  40 B according to Embodiment 3 of the present invention. 
         FIG. 12  is a p-h diagram for explaining processing in the composition determining function unit  40 B according to Embodiment 2. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
       FIG. 1  is a schematic diagram illustrating an example of the apparatus configuration of an air-conditioning apparatus according to Embodiment 1 (hereinafter, referred to as air-conditioning apparatus  100 ). A configuration of the air-conditioning apparatus  100  will be described with reference to  FIG. 1 . In the following description, when a temperature, a pressure, or the like is described as being high, low, or the like, this is not determined in relation to a specific absolute value but is determined relatively depending on the state, operation, or the like of the apparatus or the like. 
     The air-conditioning apparatus  100  according to Embodiment 1 is an apparatus that performs air conditioning using a refrigeration cycle by circulating a zeotropic refrigerant mixture made up of a plurality of refrigerants with different boiling points (for example, a refrigerant in which an R32 refrigerant and an R1234yf refrigerant are mixed at mass ratios of 44 wt % (percent by weight) and 56 wt % (percent by weight)). In the air-conditioning apparatus  100  according to Embodiment 1, an outdoor unit  1  and an indoor unit  2  are connected by a refrigerant main pipe  3  to form a refrigerant circuit. As for the operation mode, it is possible to select a cooling operation mode in which the indoor unit  2  to be operated performs cooling, and a heating operation mode in which the indoor unit  2  to be operated performs heating. 
     &lt;Outdoor Unit  1 &gt; 
     The outdoor unit  1  includes a compressor  10 , a refrigerant flow switching device  11  such as a four-way valve, an outdoor-side heat exchanger  12 , and an accumulator  13 , which are connected by a refrigerant pipe  4 . 
     The compressor  10  sucks a low-temperature, low-pressure refrigerant, compresses the refrigerant into a high-temperature, high-pressure state, and discharges the resulting refrigerant. The compressor  10  is preferably configured by, for example, an inverter compressor whose capacity can be controlled, although the compressor  10  is not particularly limited to this. The refrigerant flow switching device  11  is a device that switches between the flow of refrigerant in cooling operation mode and the flow of refrigerant in heating operation mode. 
     The outdoor-side heat exchanger  12  functions as a condenser in cooling operation, and as an evaporator in heating operation. The outdoor-side heat exchanger  12  exchanges heat between air supplied from an outdoor fan (air-sending device)  12 A and the refrigerant. The outdoor fan  12 A supplies air to the outdoor-side heat exchanger  12  in order to promote heat exchange between the refrigerant and air in the outdoor-side heat exchanger  12 . The rotation speed of the outdoor fan  12 A can be varied on the basis of control by a controller  40 . The accumulator  13  is provided on the suction side of the compressor  10 . The accumulator  13  accumulates surplus refrigerant produced owing to the difference in operational state between cooling operation and heating operation or surplus refrigerant for transient changes in operation. 
     The air-conditioning apparatus  100  has a composition detection circuit  20  provided in the main refrigerant circuit. The composition detection circuit  20  has a first pipe  21 , a second pipe  22 , a composition detection heat exchanger  23 , and a second expansion device  24 . The first pipe  21  is a pipe that is branched from the refrigerant pipe  4  that connects the discharge portion of the compressor  10  and the refrigerant flow switching device  11 , and used to bypass a part of the refrigerant discharged from the compressor  10 . The second pipe  22  is a pipe that is branched from the refrigerant pipe  4  that connects the refrigerant flow switching device  11  and the accumulator  13 , and used to merge a refrigerant flow with the refrigerant flowing on the suction side of the compressor  10 . The composition detection heat exchanger  23  exchanges heat between the flow of refrigerant through the first pipe  21  and the flow of refrigerant through the second pipe  22 . The second expansion device  24  is provided between the composition detection heat exchanger  23  and the second pipe  22 . Although the second expansion device  24  is depicted as a capillary tube in  FIG. 1 , the second expansion device  24  may be configured by any device as long as the second expansion device  24  reduces the pressure of refrigerant so that the refrigerant expands, such as a fixed-throttle pressure reducing valve that operates by another principle, or an electronic expansion valve that is driven by a stepping motor and whose opening degree varies. 
     The outdoor unit  1  has a first pressure detecting device  30  and a second pressure detecting device  31  as pressure detecting devices (pressure sensors). The first pressure detecting device  30  serving as a high-pressure side pressure detecting device is provided in the refrigerant pipe  4  that connects the compressor  10  and the refrigerant flow switching device  11 . The first pressure detecting device  30  detects the pressure (high-pressure side pressure) of a high-temperature, high-pressure refrigerant compressed and discharged by the compressor  10 , as a detection value P 1 . The second pressure detecting device  31  serving as a low-pressure side pressure detecting device is provided in the refrigerant pipe  4  that connects the refrigerant flow switching device  11  and the accumulator  13 . The second pressure detecting device  31  detects the pressure (low-pressure side pressure) of a low-temperature, low-pressure refrigerant sucked by the compressor  10  as a detection value P 2 . 
     The composition detection circuit  20  has a first temperature detecting device  32  and a second temperature detecting device  33  as temperature detecting devices (temperature sensors). The first temperature detecting device  32  serving as a supercooled liquid temperature detecting device is provided in the first pipe  21  connected to the upstream side of the second expansion device  24 . The first temperature detecting device  32  detects, a detection value T 1 , the temperature (supercooled liquid refrigerant temperature) of a supercooled liquid refrigerant at high pressure that has flowed out of the composition detection heat exchanger  23 . The second temperature detecting device  33  serving as a two-phase refrigerant temperature detecting device is provided in the second pipe  22  connected to the downstream side of the second expansion device  24 . The second temperature detecting device  33  detects, as a detection value T 2 , the temperature (two-phase refrigerant temperature) of a low-pressure refrigerant in a two-phase gas-liquid state whose pressure has been reduced by the second expansion device  24 . In this regard, the first temperature detecting device  32  and the second temperature detecting device  33  may each be configured by, for example, a thermistor. 
     The air-conditioning apparatus  100  according to Embodiment 1 has a controller  40  provided in the outdoor unit  1 . The controller  40  executes processing on the basis of, for example, an instruction inputted from a remote controller, or detection values detected by various detecting devices, and controls devices that constitute the air-conditioning apparatus  100 . Examples of the control of devices includes control of the frequency of the compressor  10 , the rotation speed (including ON/OFF) of the outdoor fan  12 A, switching of the refrigerant flow switching device  11 , and the opening degree of a first expansion device  51 . 
     The controller  40  according to Embodiment 1 has, in particular, a composition computing function unit  40 A and a composition determining function unit  40 B. The composition computing function unit  40 A is configured to compute the composition of refrigerant components in a refrigerant mixture that circulates within the refrigerant circuit at least from the detection value T 1  detected by the first temperature detecting device  32 , the detection value T 2  detected by the second temperature detecting device  33 , and the detection value P 2  detected by the second pressure detecting device  31 . The composition determining function unit  40 B determines whether or not it is possible to sense the composition of the refrigerant flowing on the upstream side of the second expansion device  24 , on the basis of the detection value T 1  detected by the first temperature detecting device  32  and the detection value P 1  detected by the first pressure detecting device  31 . Further, the composition determining function unit  40 B determines whether or not it is possible to sense the composition of refrigerant flowing on the downstream side of the second expansion device  24 , on the basis of the detection value T 2  detected by the second temperature detecting device  33 , and the detection value P 2  detected by the second pressure detecting device  31 . Then, the rotation speed of the compressor  10  or/and the outdoor fan  12 A is controlled on the basis of the composition computed by the composition computing function unit  40 A, the result of the determination by the composition determining function unit  40 B as to whether or not sensing of the composition is possible, and the detection value P 1  and the detection value P 2 . While the controller  40  is provided in the outdoor unit  1  in this example, the controller  40  may be provided in the indoor unit  2 . Further, the controller  40  may be provided in each of the outdoor unit  1  and the indoor unit  2 . 
     With regard to the controller  40 , the controller  40  may be configured solely by a dedicated device (hardware). Further, for example, the hardware may be configured by computation control means (computer) configured mainly of a central processing unit (CPU). Procedures executed by the composition computing function unit  40 A, the composition determining function unit  40 B, and the like may be defined as programs in advance and stored as software, firmware, or the like in, for example, storage means or the like provided in the controller  40 , and the computation control means may execute the programs to thereby execute processing of various units. 
     &lt;Indoor Unit  2 &gt; 
     The indoor unit  2  is equipped with a load-side heat exchanger  50 , and the first expansion device  51 . The indoor unit  2  connects to the outdoor unit  1  via the refrigerant main pipe  3 , and refrigerant enters and flows out of the indoor unit  2 . The load-side heat exchanger  50  exchanges heat between, for example, the air supplied from an indoor fan (not illustrated) and the refrigerant, and generates heating air or cooling air that is to be supplied to an air-conditioning target space. The first expansion device  51  functions as a pressure reducing valve or an expansion valve, and reduces the pressure of refrigerant to cause the refrigerant to expand. The first expansion device  51  is preferably configured by, for example, an electronic expansion valve whose opening degree can be variably controlled. 
     The indoor unit  2  is also provided with a third temperature detecting device  60  for detecting the temperature of refrigerant entering the load-side heat exchanger  50  in cooling operation, a fourth temperature detecting device  61  for detecting the temperature of flow of refrigerant out of the load-side heat exchanger  50 , and a fifth temperature detecting device  62  for detecting indoor air temperature. The third temperature detecting device  60  is provided in the pipe that connects the first expansion device  51  and the load-side heat exchanger  50 . The fourth temperature detecting device  61  is provided in the pipe located on the side opposite to the first expansion device  51  with respect to the load-side heat exchanger  50 . The fifth temperature detecting device  62  is provided in the air suction portion of the load-side heat exchanger  50 . Each of these temperature detecting devices is preferably configured by, for example, a thermistor. 
     &lt;Cooling Operation Mode&gt; 
       FIG. 2  illustrates a flow of refrigerant in cooling operation mode of the air-conditioning apparatus  100 . In  FIG. 2 , the flow direction of refrigerant is indicated by solid arrows. In  FIG. 2 , the cooling operation mode will be described with respect to a case where a cooling load is generated in the load-side heat exchanger  50 . 
     In the case of the cooling operation mode illustrated in  FIG. 2 , a low-temperature, low-pressure refrigerant is compressed by the compressor  10 , and discharged as a high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor  10  is branched into a flow of refrigerant through the main refrigerant circuit which enters the refrigerant flow switching device  11 , and a flow of refrigerant that is bypassed to the first pipe  21 . The flow of refrigerant through the main refrigerant circuit enters the outdoor-side heat exchanger  12  via the refrigerant flow switching device  11 . The high-temperature/high-pressure gas refrigerant that has entered the outdoor-side heat exchanger  12  condenses and turns into a high-pressure liquid refrigerant while rejecting heat to the outdoor air. Then, the high-pressure liquid refrigerant that has flowed out of the outdoor-side heat exchanger  12  flows out of the outdoor unit  1 , passes through the refrigerant main pipe  3 , and enters the indoor unit  2 . The high-pressure liquid refrigerant that has entered the indoor unit  2  is reduced in pressure into a low-temperature, low-pressure two-phase refrigerant by the first expansion device  51 , enters the load-side heat exchanger  50  serving as an evaporator, cools the indoor air while removing heat from the indoor air, and turns into a low-temperature, low-pressure gas refrigerant. The low-temperature, low-pressure gas refrigerant that has flowed out of the load-side heat exchanger  50  passes through the refrigerant main pipe  3  and enters the outdoor unit  1 . The refrigerant that has entered the outdoor unit  1  passes through the refrigerant flow switching device  11  and the accumulator  13 , and is sucked into the compressor  10 . 
     At this time, the controller  40  controls the opening degree of the first expansion device  51  so that the superheat (degree of superheat) obtained as the difference between the saturation temperature of refrigerant, which is calculated from the pressure detected by the second pressure detecting device  31  and the composition of refrigerant passing through the composition detection circuit  20 , and the temperature detected by the fourth temperature detecting device  61  becomes constant. 
     Meanwhile, a part of the high-temperature, high-pressure gas refrigerant discharged from the compressor  10  which is branched to the first pipe  21  enters the composition detection heat exchanger  23 . The high-temperature, high-pressure gas refrigerant that has entered the composition detection heat exchanger  23  turns into a high-pressure supercooled liquid refrigerant by rejecting heat to the low-temperature, low-pressure two-phase refrigerant whose pressure has been reduced by the second expansion device  24 , and then the high-pressure supercooled liquid refrigerant enters the second expansion device  24 . Then, after the high-pressure supercooled liquid refrigerant is reduced in pressure by the second expansion device  24  into a low-temperature, low-pressure two-phase refrigerant, the low-temperature, low-pressure two-phase refrigerant enters the composition detection heat exchanger  23  again, and turns into a low-pressure gas refrigerant by removing heat from the high-temperature, high-pressure gas flow of refrigerant through the first pipe  21 . The low-pressure gas refrigerant that has passed through the composition detection heat exchanger  23  passes through the second pipe  22  and merges with the refrigerant pipe  4  located on the upstream side of the accumulator  13 . 
     &lt;Heating Operation Mode&gt; 
       FIG. 3  illustrates a flow of refrigerant in heating operation mode of the air-conditioning apparatus  100 . In  FIG. 3 , the flow direction of refrigerant is indicated by solid arrows. In  FIG. 3 , the heating operation mode will be described with respect to a case where a heating load is generated in the load-side heat exchanger  50 . 
     In the case of the heating operation mode illustrated in  FIG. 3 , a low-temperature, low-pressure refrigerant is compressed by the compressor  10 , and discharged as a high-temperature, high-pressure gas refrigerant. The high-temperature, high-pressure gas refrigerant discharged from the compressor  10  is branched into a flow of refrigerant through the main refrigerant circuit which enters the refrigerant flow switching device  11 , and a flow of refrigerant that is bypassed to the first pipe  21 . The flow of refrigerant through the main refrigerant circuit passes through the refrigerant main pipe  3  via the refrigerant flow switching device  11 , and enters the indoor unit  2 . The high-temperature, high-pressure gas refrigerant that has entered the indoor unit  2  rejects heat to the indoor air in the load-side heat exchanger  50 , turns into a high-pressure liquid refrigerant, and enters the first expansion device  51 . Then, after the high-pressure liquid refrigerant is reduced in pressure into a low-temperature, low-pressure two-phase refrigerant by the first expansion device  51 , the low-temperature, low-pressure two-phase refrigerant flows out of the indoor unit  2 , passes through the refrigerant main pipe  3 , and enters the outdoor unit  1 . The low-temperature, low-pressure two-phase refrigerant that has entered the outdoor unit  1  turns into a low-temperature, low-pressure gas refrigerant by removing heat from the outdoor air in the outdoor-side heat exchanger  12 . The low-temperature, low-pressure gas refrigerant that has flowed out of the outdoor-side heat exchanger  12  passes through the refrigerant flow switching device  11  and the accumulator  13 , and is sucked into the compressor  10 . 
     At this time, the controller  40  controls the opening degree of the first expansion device  51  so that the subcooling (supercooling) obtained as the difference between the saturation temperature of refrigerant, which is calculated from the pressure detected by the first pressure detecting device  30  and the composition of refrigerant passing through the composition detection circuit  20 , and the temperature detected by the third temperature detecting device  60  becomes constant. 
     Meanwhile, a part of the high-temperature, high-pressure gas refrigerant discharged from the compressor  10  which is branched to the first pipe  21  flows in the same manner as in cooling operation mode. The refrigerant branched to the first pipe  21  flows through the composition detection heat exchanger  23 , the second expansion device  24 , the composition detection heat exchanger  23 , and the second pipe  22  in the order named, and merges with the main flow of refrigerant in the portion upstream of the accumulator  13 . 
       FIG. 4  is a p-h diagram of the zeotropic refrigerant mixture. Because the zeotropic refrigerant mixture is made up of a plurality of refrigerant components with different boiling points, the temperature of saturated liquid refrigerant and the temperature of saturated gas refrigerant at the same pressure differ from each other. Therefore, once the pressure, the temperature, and the composition of the refrigerant mixture are given, the state of the refrigerant is determined at a single point even when the refrigerant is in a two-phase state. 
       FIG. 5  is a flowchart illustrating a procedure of processing executed by the composition computing function unit  40 A for computing the composition of the refrigerant mixture. Next, processing in the composition computing function unit  40 A of the controller  40  will be described. First, in step A 1 , detection values T 1 , T 2 , and P 2  are inputted from the first temperature detecting device  32 , the second temperature detecting device  33 , and the second pressure detecting device  31 , respectively. Next, in step A 2 , for each component of the refrigerant mixture, its circulating composition X i  is assumed. At this time, the suffix “i” indicates that the composition in question relates to the component of the type “i” of the refrigerant mixture. Next, in step A 3 , the supercooled liquid enthalpy H 1  on the high-pressure side is computed from the circulating composition X i  assumed in step A 2 , and the detection value T 1  detected by the first temperature detecting device  32 . Next, in step A 4 , the enthalpy H 2  of refrigerant on the low-pressure side is computed from the circulating composition X i , the detection value T 2  detected by the second temperature detecting device  33 , and the detection value P 2  detected by the second pressure detecting device  31 . Next, in step A 5 , the supercooled liquid enthalpy H 1  on the high-pressure side and the enthalpy H 2  of refrigerant on the low-pressure side are compared with each other. If the two enthalpies are not equal, the processing returns to step A 2 , and the assumption of the circulating composition is repeated until the two enthalpies become equal. Finally, in step A 6 , the value at which H 1  and H 2  become equal is determined as the circulating composition X i  obtained by computation. 
     Now, with regard to the composition computing function unit  40 A of the controller  40 , the high-pressure supercooled liquid enthalpy H 1  in step A 3  is calculated by Equation (1) below. Further, the enthalpy H 2  of the low-pressure refrigerant in step A 4  is calculated by Equation (2) below.
 
 H   1   =H   1 ( T   1   ,X   i )  (1)
 
 H   2   =H   2 ( T   2   ,P   2   ,X   i )  (2)
 
       FIG. 6  is a flowchart illustrating a procedure of processing in the composition determining function unit  40 B according to Embodiment 1. Next, processing in the composition determining function unit  40 B of the controller  40  will be described. First, in step B 1 , the respective detection values T 1 , T 2 , P 1 , and P 2  detected by the first temperature detecting device  32 , the second temperature detecting device  33 , the first pressure detecting device  30 , and the second pressure detecting device  31  are read. Next, in step B 2 , the charged composition of the refrigerant mixture (the composition when the refrigerant is charged into the refrigerant circuit) Y i , which is set to a predetermined value, is read from storage means. At this time, the suffix “i” indicates that the composition in question relates to the component of the type “i” of the refrigerant mixture. 
     Next, in step B 3 , a high-pressure supercooled liquid enthalpy F 1  in the portion upstream of the second expansion device  24  is computed from the charged composition Y i  read in step B 2 , and the detection values T 1  and P 1  respectively detected by the first temperature detecting device  32  and the first pressure detecting device  30 . Further, in step B 4 , a high-pressure saturated liquid enthalpy F L1  in the portion upstream of the second expansion device  24  is computed from the charged composition Y i  read in step B 2 , and the detection value P 1  detected by the first pressure detecting device  30 . 
     In step B 5 , the enthalpy F 2  of a low-pressure refrigerant in the portion downstream of the second expansion device  24  is treated as being equal to the high-pressure supercooled liquid enthalpy F 1 . Further, in step B 6 , a low-pressure saturated liquid enthalpy F L2  in the portion downstream of the second expansion device  24  is computed from the charged composition Y i  read in step B 2 , and the detection value P 2  detected by the second pressure detecting device  31 . 
     Then, in step B 7 , it is determined whether or not the high-pressure supercooled liquid enthalpy F 1  is less than the high-pressure saturated liquid enthalpy F L1 , and the enthalpy F 2  of the low-pressure refrigerant is greater than the low-pressure saturated liquid enthalpy F L2 . If it is determined that the above-mentioned determination condition is satisfied, the composition computation result is determined as “correct” (step B 8 ). If it is determined that the determination condition is not satisfied, the composition computation result is determined as “incorrect” (step B 9 ). 
     Now, with regard to the composition determining function unit  40 B of the controller  40 , the high-pressure supercooled liquid enthalpy F 1  in step B 3  is calculated by Equation (3) below. The enthalpy F L1  of the low-pressure refrigerant in step B 4  is calculated by Equation (4) below. The low-pressure saturated liquid enthalpy F L2  in step B 6  is calculated by Equation (5) below.
 
 F   1   =H   2 ( T   1   ,P   1   ,Y   i )  (3)
 
 F   L1   =H   2 ( P   1   ,Y   i )  (4)
 
 F   L2   =H   2 ( P   2   ,Y   i )  (5)
 
       FIG. 7  is a p-h diagram for explaining processing in the composition determining function unit  40 B according to Embodiment 1. The processing in the composition determining function unit  40 B of the controller  40  according to Embodiment 1 described above will be described on the basis of a specific example. In this case, it is supposed that the charged composition Y R32  of R32 in the refrigerant mixture is 44 wt %. It is also supposed that the detection value P 1  detected by the first pressure detecting device  30  is 2.7 MPa abs , and the detection value P 2  detected by the second pressure detecting device  31  is 0.70 MPa abs . Further, it is supposed that the detection value T 1  detected by the first temperature detecting device  32  is 45° C., and the detection value T 2  detected by the second temperature detecting device  33  is 2° C. For calculation of physical property values described below, values described in REFPROP Version9.0 sold by the National Institute of Standards and Technology (NIST) are used (the same applies hereinafter). 
     First, in step B 1 , the detection value P 1 =2.7 MPa abs  is read from the first pressure detecting device  30 , the detection value P2=0.70 MPa abs  is read from the second pressure detecting device  31 , the detection value T 1 =45° C. is read from the first temperature detecting device  32 , and the detection value T 2 =2° C. is read from the second temperature detecting device  33 . Further, the charged composition Y R32 =44 wt % is read in step B 2 . Next, in step B 3 , the high-pressure supercooled liquid enthalpy F 1  is calculated from the detection value T 1 =45° C. detected by the first temperature detecting device  32 , the detection value P 1 =2.7 MPa abs  detected by the first pressure detecting device  30 , and the charged composition Y R32 =44 wt %. At this time, the high-pressure supercooled liquid enthalpy F 1  becomes equal to 196 kJ/kg. The high-pressure supercooled liquid enthalpy F 1  corresponds to the enthalpy at point B in the p-h diagram illustrated in  FIG. 7 . 
     Next, in step B 4 , the high-pressure saturated liquid enthalpy F L1  is calculated from the detection value P 1 =2.7 MPa abs  detected by the first pressure detecting device  30  and the detection value of the charged composition Y R32 =44 wt %. At this time, the high-pressure saturated liquid enthalpy F L1  becomes equal to 207 kJ/kg. The high-pressure saturated liquid enthalpy F L1  corresponds to the enthalpy at point A in the p-h diagram illustrated in  FIG. 7 . 
     Next, in step B 5 , the supercooled liquid enthalpy F 1 =196 kJ/kg is assigned into the enthalpy F 2  of the low-pressure refrigerant. The enthalpy F 2  of the low-pressure refrigerant corresponds to the enthalpy at point C in the p-h diagram illustrated in  FIG. 7 . Next, in step B 6 , the low-pressure saturated liquid enthalpy F L2  is calculated from the detection value P 2=0.70  MPa abs  detected by the second pressure detecting device  31 , and the charged composition Y R32 =44 wt %. At this time, the low-pressure saturated liquid enthalpy F L2  becomes equal to 120 kJ/kg. The low-pressure saturated liquid enthalpy F L2  corresponds to the enthalpy at point D in the p-h diagram illustrated in  FIG. 7 . 
     Next, in step B 7 , the supercooled liquid enthalpy F 1  and the high-pressure saturated liquid enthalpy F L1  are compared with each other. Further, the enthalpy F 2  of the low-pressure refrigerant and the low-pressure saturated liquid enthalpy F L2  are compared with each other. In this example, F 1 =196 kJ/kg&lt;F L1 =207 kJ/kg, and F 2 =207 kJ/kg&gt;F L2 =120 kJ/kg. Therefore, it is determined that the determination condition is satisfied, and the processing proceeds to step B 8 . In step B 8 , the composition computation result is determined as “correct”. 
     When the composition determining function unit  40 B determines whether or not the composition computation result of the composition computing function unit  40 A is correct, the determination is performed by using the charged composition Y i  of the refrigerant mixture. Therefore, the computation result of enthalpies used in the determination formula include errors against a case where the actual circulating composition is used, and measurement errors introduced by the pressure detecting devices and the temperature detecting devices. For this reason, there is a possibility that the computation result of the composition computing function unit  40 A may be determined as correct even through the computation result is actually incorrect. Accordingly, it is possible to reduce the possibility of erroneous composition detection by adding a margin for error to the determination formula used for the correct/incorrect determination performed by the composition determining function unit  40 B. 
     For example, the determination formula F 1 &lt;F L1  and F 2 &gt;F L2  with no margin added is changed to the following form: F 1 &lt;F L1 ×α and F 2 &gt;F L2 ×β. At this time, α and β are margins on the high-pressure side and the low-pressure side, respectively. By defining α and β as such values that α&lt;1 and β&gt;1, point A in  FIG. 7  is moved to the left side, and point D is moved to the right side, thereby enabling more rigorous and stable correct/incorrect determination of the composition computation result. 
     Setting too small a value as the margin α on the high-pressure side increases the region in which the composition computation result is determined as incorrect even through the computation result is correct. Further, setting too large a value as the margin β on the low-pressure side increases the region in which the composition computation result is determined as incorrect even through the computation result is correct. Therefore, the respective values of the margins α and β on the high-pressure side and the low-pressure side need to be determined by taking into account errors due to the composition, errors due to the temperature detecting devices, and errors due to the pressure detecting devices. For example, in a case where the errors in enthalpy computation due to the composition, the temperature detecting devices, and the pressure detecting devices are each estimated to be 1%, it is preferable to set α=0.97 and β=1.03. 
     Next, a description will be given of an example of how to compute each enthalpy on the basis of the result obtained by the composition computing function unit  40 A and the result obtained by the composition determining function unit  40 B. To compute an enthalpy, data representing the relationship between temperature, composition, and supercooled liquid enthalpy, data representing the relationship between pressure, composition, and saturated liquid enthalpy, and data representing the relationship between temperature, pressure, composition, and enthalpy are each previously stored in a table format in storage means (not illustrated) included in the controller  40 . Then, it is preferable to employ such a method that allows an enthalpy to be derived from a composition and a detection value of each detecting device. In this regard, as can be appreciated from the p-h diagram of a refrigerant mixture in  FIG. 4 , the isothermal line in the supercooled state is substantially parallel to the axis that represents pressure. This indicates a characteristic that the temperature does not vary significantly with varying pressure. Accordingly, as for the data representing the relationship between temperature, composition, and supercooled liquid enthalpy, by creating a simplified table in advance so that its value becomes the same irrespective of pressure, the data size can be reduced. Further, the stored data about the relationship between temperature, pressure, and composition may be interpolated as required to thereby compute enthalpy. 
       FIG. 8  is a flowchart illustrating processing of a control operation of the controller  40 . A control operation of devices executed by the controller  40  according to Embodiment 1 will be described. First, in step C 1 , detection values P 1  and P 2  respectively detected by the first pressure detecting device  30  and the second pressure detecting device  31  are read. Next, in step C 2 , as previously described, a circulating composition X i  is computed by the composition computing function unit  40 A. 
     Further, in step C 3 , as previously described, a correct/incorrect determination with respect to the composition computation result is performed by the composition determining function unit  40 B. Then, in step C 4 , it is determined whether or not the correct/incorrect determination result with respect to the composition computation result is “correct”. If it is determined that the correct/incorrect determination result with respect to the composition computation result is “correct”, the computed circulating composition X i  is adopted as correct (step C 5 ). On the other hand, if it is determined that the correct/incorrect determination result with respect to the composition computation result is “incorrect”, the computed circulating composition X i  is determined as not reflecting the actual circulating composition. Then, a predetermined value (cooling operation mode: X ci , heating operation mode: X hi ) previously set in accordance with the operation mode is adopted as the circulating composition X i  (step C 6 ). In this regard, in cooling operation mode, refrigerant accumulates in the outdoor-side heat exchanger  12 , and surplus refrigerant is unlikely to accumulate in the accumulator  13 , with the result that the circulating composition during operation becomes close to the charged composition Y i . Accordingly, the predetermined value X ci  for the cooling operation mode is set as the charged composition Y i . In heating operation mode, the amount of refrigerant that accumulates in the load-side heat exchanger  50  is small, and surplus refrigerant accumulates in the accumulator  13 , with the result that the circulating composition during operation contains a large proportion of low boiling point components. Accordingly, the predetermined value X hi  for the heating operation mode is set to such a value that the resulting composition contains a larger proportion of components with low boiling points than does the charged composition Y i . 
     Next, in step C 7 , a condensing temperature T c  is computed from the circulating composition X i  and the detection value P 1  detected by the first pressure detecting device  30 . Further, an evaporating temperature T e  is computed from the circulating composition X i  and the detection value P 2  detected by the second pressure detecting device  31 . At this time, in calculation of the condensing temperature T c  and the evaporating temperature T e , data representing the relationship between pressure, composition, and saturation temperature may be stored in storage means (not illustrated) in advance so that a saturation temperature can be derived from a composition and a value detected by a pressure detecting device. 
     Next, in step C 8 , ΔT c , which is a value obtained by subtracting a target value T cm  of condensing temperature from the condensing temperature T c , and ΔT e , which is a value obtained by subtracting a target value T em  of evaporating temperature from the evaporating temperature T e , are calculated. At this time, the values calculated in step C 7  are used as the condensing temperature T c  and the evaporating temperature T e . Further, for the target value T cm  of condensing temperature and the target value T em  of evaporating temperature, values stored as data in storage means (not illustrated) in accordance with the outdoor temperature and the indoor temperature are used. 
     Next, in step C 9 , the frequency f of the compressor  10  and the rotation speed F of the outdoor fan  12 A are controlled so that ΔT c  and ΔT e  approach 0 (zero). For example, in a case where the outdoor-side heat exchanger  12  serves as a condenser, when ΔT c  has a positive value, the frequency f of the compressor  10  is controlled so as to become lower, or/and the rotation speed F of the outdoor fan  12 A is controlled so as to become higher. When ΔT c  has a negative value, the frequency f of the compressor  10  is controlled so as to become higher, or/and the rotation speed F of the outdoor fan  12 A is controlled so as to become lower. In a case where, for example, the outdoor-side heat exchanger  12  serves as an evaporator, when ΔT e  has a positive value, the frequency f of the compressor  10  is controlled so as to become higher, or/and the rotation speed F of the outdoor fan  12 A is controlled so as to become lower. When ΔT e  has a negative value, the frequency f of the compressor  10  is controlled so as to become lower, or/and the rotation speed F of the outdoor fan  12 A is controlled so as to become higher. 
     As described above, with the air-conditioning apparatus according to Embodiment 1, in the controller  40 , the composition determining function unit  40 B evaluates the computation result of the composition computing function unit  40 A, and if it is determined that the computation result is not appropriate, the composition determining function unit  40 B adopts a previously set predetermined value as the circulating composition X i . Therefore, a control based on an appropriate circulating composition can be performed, thereby making it possible to obtain an air-conditioning apparatus with good operational efficiency. As a result, energy saving can be achieved. At this time, the predetermined value X ci  for cooling operation and the predetermined value X hi  for heating operation are set independently, thereby enabling a control based on a more appropriate circulating composition. 
     Embodiment 2 
     Next, the air-conditioning apparatus  100  according to Embodiment 2 of the present invention will be described. Here, differences from Embodiment 1 will be mainly described. The configuration of the air-conditioning apparatus  100  according to Embodiment 2 is the same as that according to Embodiment 1. The air-conditioning apparatus  100  according to Embodiment 2 differs from the air-conditioning apparatus  100  according to Embodiment 1 in the processing executed in the composition determining function unit  40 B of the controller  40 . 
     In Embodiment 2, with regard to the composition determining function unit  40 B, the saturation temperature on each of the high-pressure side and the low-pressure side is calculated. Then, the relative magnitudes of the calculated value of saturated liquid temperature, the detection value T 1  detected by the first temperature detecting device  32 , and the detection value T 2  detected by the second temperature detecting device  33  are compared with each other to thereby determine whether or not the circulating composition computed in the composition computing function unit  40 A is correct. 
       FIG. 9  is a flowchart illustrating a procedure of processing in the composition determining function unit  40 B according to Embodiment 2. Next, operation of the composition determining function unit  40 B according to Embodiment 2 will be described. First, in step D 1 , detection values T 1 , T 2 , P 1 , and P 2  are read from the first temperature detecting device  32 , the second temperature detecting device  33 , the first pressure detecting device  30 , and the second pressure detecting device  31 , respectively. Next, in step D 2 , the charged composition Y i  of a refrigerant mixture, which is set to a predetermined value and stored in advance, is read. At this time, the suffix “i” indicates that the composition in question relates to the component of the type “i” of the refrigerant mixture. 
     Next, in step D 3 , a high-pressure saturated liquid temperature T L1  in the portion upstream of the second expansion device  24  is computed from the charged composition Y i  read in step D 2 , and the detection value P 1  detected by the first pressure detecting device  30 . Further, in step D 4 , a low-pressure saturated liquid temperature T L2  in the portion downstream of the second expansion device  24  is computed from the charged composition Y i  read in step D 2 , and the detection value P 2  detected by the second pressure detecting device  31 . 
     Next, in step D 5 , it is determined whether or not the detection value T 1  detected by the first temperature detecting device  32  is less than the high-pressure saturated liquid temperature T L1 , and the detection value T 2  detected by the second temperature detecting device  33  is greater than the low-pressure saturated liquid temperature T L2 . If it is determined that the above-mentioned determination condition is satisfied, the composition computation result is determined as “correct” (step D 6 ). If it is determined that the above-mentioned determination condition is not satisfied, the composition computation result is determined as “incorrect” (step D 7 ). 
     Now, with regard to operation of the composition determining function unit  40 B according to Embodiment 2, the high-pressure saturated liquid temperature T L1  in step D 3  is calculated by Equation (6) below. The low-pressure saturated liquid temperature T L2  in step D 4  is calculated by Equation (7) below.
 
 T   L1   =T   L ( P   1   ,Y   i )  (6)
 
 T   L2   =T   L ( P   2   ,Y   i )  (7)
 
       FIG. 10  is a p-h diagram for explaining processing in the composition determining function unit  40 B according to Embodiment 2. The processing in the composition determining function unit  40 B of the controller  40  according to Embodiment 2 described above will be described on the basis of a specific example. In this case, it is supposed that the charged composition Y R32  of R32 in the refrigerant mixture is 44 wt %. It is also supposed that the detection value P 1  detected by the first pressure detecting device  30  is 2.7 MPa abs , and the detection value P 2  detected by the second pressure detecting device  31  is 0.70 MPa abs . Further, it is supposed that the detection value T 1  detected by the first temperature detecting device  32  is 45° C., and the detection value T 2  detected by the second temperature detecting device  33  is 2° C. 
     First, in step D 1 , the detection value P 1 =2.7 MPa abs  is read from the first pressure detecting device  30 , the detection value P 2 =0.70 MPa abs  is read from the second pressure detecting device  31 , the detection value T 1 =45° C. is read from the first temperature detecting device  32 , and the detection value T 2 =2° C. is read from the second temperature detecting device  33 . At this time, the detection value T 1  detected by the first temperature detecting device  32  corresponds to the temperature at point B in the p-h diagram illustrated in  FIG. 10 . The detection value T 2  detected by the second temperature detecting device  33  corresponds to the temperature at point C in  FIG. 10 . Further, the charged composition Y R32 =44 wt % is read in step D 2 . 
     Next, in step D 3 , the high-pressure saturated liquid temperature T L1  is calculated from the detection value P 1 =2.7 MPa abs  detected by the first pressure detecting device  30  and the detection value of the charged composition Y R32 =44 wt %. At this time, the high-pressure saturated liquid temperature T L1  becomes equal to 50° C. The high-pressure saturated liquid temperature T L1  corresponds to the temperature at point A in the p-h diagram illustrated in  FIG. 10 . 
     Next, in step D 4 , the low-pressure saturated liquid temperature T L2  is calculated from the detection value P 2 =0.70 MPa abs  detected by the second pressure detecting device  31  and the charged composition Y R32 =44 wt %. At this time, the low-pressure saturated liquid temperature T L2  becomes equal to −1° C. The low-pressure saturated liquid temperature T L2  corresponds to the temperature at point D in the p-h diagram illustrated in  FIG. 10 . 
     Next, in step D 5 , the detection value T 1  detect by the first temperature detecting device  32  and the high-pressure saturated liquid temperature T L1  are compared with each other. Further, the detection value T 2  detect by the second temperature detecting device  33  and the low-pressure saturated liquid temperature T L2  are compared with each other. In this example, T 1 =45° C.&lt;T L1 =50° C., and T 2 =2° C.&gt;T L2 =−1° C. Therefore, it is determined that the determination condition in step D 5  is satisfied, and the processing proceeds to step D 6 . In step D 6 , the composition computation result is determined as “correct”. 
     In this regard, in Embodiment 2, as in Embodiment 1, it is possible to reduce the possibility of erroneous composition detection by adding a margin for error to the determination formula used for the correct/incorrect determination performed by the composition determining function unit  40 B. 
     For example, the determination formula T 1 &lt;T L1  and T 2 &gt;T L2  with no margin added is changed to the following form: T 1 &lt;T L1 ×α and T 2 &gt;T L2 ×β. At this time, α and β are margins on the high-pressure side and the low-pressure side, respectively. By defining α and β as such values that α&lt;1 and β&gt;1, point A in  FIG. 10  is moved to the left side, and point D is moved to the right side, thereby enabling more rigorous and stable correct/incorrect determination of the composition computation result. 
     Setting too small a value as the margin α on the high-pressure side increases the region in which the composition computation result is determined as incorrect even through the computation result is correct. Further, setting too large a value as the margin β on the low-pressure side increases the region in which the composition computation result is determined as incorrect even through the computation result is correct. Therefore, the respective values of the margins α and β on the high-pressure side and the low-pressure side need to be determined by taking errors due to the composition, errors due to the temperature detecting devices, and errors due to the pressure detecting devices into account. 
     As described above, with the air-conditioning apparatus  100  according to Embodiment 2, the composition determining function unit  40 B evaluates the computation result of the composition computing function unit  40 A on the basis of the high-pressure saturated liquid temperature T L1  and the low-pressure saturated liquid temperature T L2 . Therefore, processing steps can be reduced, thereby enabling a control based on the circulating composition more easily. 
     Embodiment 3 
     Next, the air-conditioning apparatus  100  according to Embodiment 3 of the present invention will be described. Here, differences from Embodiment 1 and Embodiment 2 will be mainly described. The configuration of the air-conditioning apparatus  100  according to Embodiment 2 is the same as that according to Embodiment 1. The air-conditioning apparatus  100  according to Embodiment 3 differs from the air-conditioning apparatus  100  according to Embodiment 1 in the processing related to determination executed in the composition determining function unit  40 B of the controller  40 . 
     In Embodiment 3, the quality of refrigerant in each of the portions upstream and downstream of the second expansion device  24  is calculated by using detection values detected by the first pressure detecting device  30 , the second pressure detecting device  31 , the first temperature detecting device  32 , and the second temperature detecting device  33 , and the charged composition Y i  of refrigerant. Then, whether or not the computed circulating composition of refrigerant is correct is determined by determining whether the state of the refrigerant is a two-phase state or a liquid state. 
       FIG. 11  is a flowchart illustrating a procedure of processing in the composition determining function unit  40 B according to Embodiment 3. Next, operation of the composition determining function unit  40 B according to Embodiment 3 will be described. First, in step E 1 , the respective detection values T 1 , T 2 , P 1 , and P 2  detected by the first temperature detecting device  32 , the second temperature detecting device  33 , the first pressure detecting device  30 , and the second pressure detecting device  31  are read. Next, in step E 2 , the charged composition Y i  of a refrigerant mixture, which is set to a predetermined value and stored in advance, is read. At this time, the suffix “i” indicates that the composition in question relates to the component of the type “i” of the refrigerant mixture. 
     Next, in step E 3 , the quality X 1  of refrigerant in the portion upstream of the second expansion device  24  is computed from the charged composition Y i  read in step E 2 , the detection value T 1  detected by the first temperature detecting device  32 , and the detection value P 1  detected by the first pressure detecting device  30 . Further, in step E 4 , the quality X 2  of refrigerant in the portion downstream of the second expansion device  24  is computed from the charged composition Y i  read in step E 2 , the detection value T 2  detected by the second temperature detecting device  33 , and the detection value P 2  detected by the second pressure detecting device  31 . 
     Next, in step E 5 , it is determined whether or not the quality X 1  of refrigerant in the portion upstream of the second expansion device  24  is less than or equal to 0, and the quality X 2  of refrigerant in the portion downstream of the second expansion device  24  is greater than 0. If it is determined that the above-mentioned determination condition is satisfied, the composition computation result is determined as “correct” (step E 6 ). If it is determined that the above-mentioned determination condition is not satisfied, the composition computation result is determined as “incorrect” (step E 7 ). 
     At this time, the quality X 1  of refrigerant in the portion upstream of the second expansion device  24  is calculated by Equation (8) below. The quality X 2  of refrigerant in the portion downstream of the second expansion device  24  is calculated by Equation (9) below. A high-pressure saturated gas enthalpy F G1  included in each of Equation (8) and Equation (9) is calculated from Equation (10) from the detection value P 1  detected by the first pressure detecting device  30  and the charged composition Y i  of the refrigerant mixture. Further, a low-pressure saturated gas enthalpy F G2  is calculated from Equation (11) from the detection value P 2  detected by the second pressure detecting device  31  and the charged composition Y i  of the refrigerant mixture. The definitions of the other enthalpies are as described above with reference to Embodiment 1.
 
 X   1 =( F   1   −F   L1 )/( F   G1   −F   L1 )  (8)
 
 X   2 =( F   2   −F   L2 )/( F   G2   −F   L2 )  (9)
 
 F   G1   =H   q ( P   1   ,Y   i )  (10)
 
 F   G2   =H   q ( P   2   ,Y   i )  (11)
 
       FIG. 12  is a p-h diagram for explaining processing in the composition determining function unit  40 B according to Embodiment 2. The processing in the composition determining function unit  40 B of the controller  40  according to Embodiment 3 described above will be described on the basis of a specific example. In this case, it is supposed that the charged composition Y R32  of R32 in the refrigerant mixture is 44 wt %. It is also supposed that the detection value P 1  detected by the first pressure detecting device  30  is 2.7 MPa abs , and the detection value P 2  detected by the second pressure detecting device  31  is 0.70 MPa abs . Further, it is supposed that the detection value T 1  detected by the first temperature detecting device  32  is 45° C., and the detection value T 2  detected by the second temperature detecting device  33  is 2° C. 
     First, in step E 1 , the detection value P 1 =2.7 MPa abs  is read from the first pressure detecting device  30 , the detection value P 2 =0.70 MPa abs  is read from the second pressure detecting device  31 , the detection value T 1 =45° C. is read from the first temperature detecting device  32 , and the detection value T 2 =2° C. is read from the second temperature detecting device  33 . Further, the charged composition Y R32 =44 wt % is read in step D 2 . 
     Next, in step E 3 , the quality X 1  of refrigerant in the portion upstream of the second expansion device  24  is calculated from the detection value T 1 =45° C. detected by the first temperature detecting device  32 , the detection value P 1 =2.7 MPa abs  detected by the first pressure detecting device  30 , and the charged composition Y R32 =44 wt %. At this time, the quality X 1  becomes equal to −0.08. The quality X 1  of refrigerant in the portion upstream of the second expansion device  24  corresponds to point B in the p-h diagram illustrated in  FIG. 12 . 
     Further, in step E 4 , the quality X 2  of refrigerant in the portion downstream of the second expansion device  24  is calculated from the detection value T 2 =2° C. detected by the second temperature detecting device  33 , the detection value P 2 =0.70 MPa abs  detected by the second pressure detecting device  31 , and the charged composition Y R32 =44 wt %. At this time, the quality X 2  becomes equal to −0.35. The quality X 2  of refrigerant in the portion downstream of the second expansion device  24  corresponds to point C in the p-h diagram illustrated in  FIG. 12 . 
     Then, in step E 5 , it is determined whether or not the quality X 1  of refrigerant in the portion upstream of the second expansion device  24  is less than or equal to 0, and the quality X 2  of refrigerant in the portion downstream of the second expansion device  24  is greater than 0. In this example, the quality X 1 =−0.08≦0 and the quality X 2 =−0.35&gt;0. Therefore, it is determined that the determination condition in step E 5  is satisfied, and the processing proceeds to step E 6 . In step E 6 , the computation result is determined as “correct”. 
     In this regard, in Embodiment 3, as in Embodiments 1 and 2, it is possible to reduce the possibility of erroneous composition detection by adding a margin for error to the determination formula used for the correct/incorrect determination performed by the composition determining function unit  40 B. 
     For example, the determination formula X 1 &lt;0 and X 2 &gt;0 with no margin added is changed to the following form: X 1 &lt;0+α and X 2 &gt;0+β. At this time, α and β are margins on the high-pressure side and the low-pressure side, respectively. By defining α and β as such values that α&lt;0 and β&gt;0, point A in  FIG. 10  is moved to the left side, and point D is moved to the right side, thereby enabling more rigorous and stable correct/incorrect determination of the composition computation result. 
     Setting too small a value as the margin α on the high-pressure side increases the region in which the composition computation result is determined as incorrect even through the computation result is correct. Further, setting too large a value as the margin β on the low-pressure side increases the region in which the composition computation result is determined as incorrect even through the computation result is correct. Therefore, the respective values of the margins α and β on the high-pressure side and the low-pressure side need to be determined by taking errors due to the composition, errors due to the temperature detecting devices, and errors due to the pressure detecting devices into account. 
     As described above, with the air-conditioning apparatus  100  according to Embodiment 3, the composition determining function unit  40 B evaluates the computation result of the composition computing function unit  40 A on the basis of the qualities of refrigerant X 1  and X 2  in the portions upstream and downstream of the second expansion device  24 , respectively. Therefore, processing steps can be reduced, thereby enabling a control based on the circulating composition more easily. 
     Embodiment 4 
     For example, in the air-conditioning apparatus  100  illustrated in  FIG. 1 , a single indoor unit  2  and the outdoor unit  1  are connected via the refrigerant main pipe  3 . However, the number of indoor units  2  to be connected is not limited to one but a plurality of indoor units  2  may be connected. 
     Further, a system in which a plurality of indoor units  2  are connected is not limited to a system in which all of the indoor units  2  connected perform cooling or heating operation but may be a system that performs mixed operation in which each individual indoor unit  2  performs cooling operation and heating operation simultaneously. 
     A plurality of outdoor units  1  may be connected, in which case a representative outdoor unit  1  may be determined. 
     While the air-conditioning apparatus  100  according to Embodiment 1 and the like mentioned above is directed to the case of a direct expansion circuit in which the outdoor unit  1  and the indoor unit  2  are connected in series by the refrigerant main pipe  3 , this should not be construed restrictively. For example, the air-conditioning apparatus  100  includes a heat medium relay unit provided at a position spaced apart from the outdoor unit  1 . The heat medium relay unit includes an intermediate heat exchanger that exchanges heat between a refrigerant mixture and a heat medium different from the refrigerant mixture, and the first expansion device  51 . Further, the air-conditioning apparatus may be configured so that a heat medium that is heated or cooled through heat exchange with the refrigerant is circulated through the load-side heat exchanger  50 . 
     While Embodiment 1 and the like mentioned above are directed to the case of a refrigerant in which an R32 refrigerant and an R1234yf refrigerant are mixed at mass ratios of 44 wt % and 56 wt %, this should not be construed restrictively. As long as the zeotropic refrigerant mixture used is such that a plurality of refrigerants are mixed and the saturated gas temperature and the saturated liquid temperature at the same pressure are different, the same effect is obtained even if the kinds and mixing ratios of the refrigerants to be mixed differ from those of the refrigerant mixture described with reference to the embodiments mentioned above. 
     While Embodiment 1 and the like mentioned above are directed to the case where the outdoor unit  1  has a single compressor  10 , the outdoor unit  1  may have a plurality of compressors. 
     While Embodiment 1 and the like mentioned above are directed to the case where the outdoor unit  1  has a single accumulator  13 , the outdoor unit  1  may have a plurality of accumulators  13 . Further, for example, in the air-conditioning apparatus  100  to which a plurality of indoor units  2  are connected, the circulating composition of a refrigerant mixture flowing through a refrigerant circuit may sometimes change for reasons such as the refrigerant accumulating in the indoor unit  2  that has stopped. Accordingly, the same effect is obtained even in a case where the outdoor unit  1  is not equipped with the accumulator  13 . 
     While Embodiment 1 and the like mentioned above are directed to the case of the air-conditioning apparatus  100  having the refrigerant flow switching device  11  provided in the outdoor unit  1 , the present invention can be also applied to the air-conditioning apparatus  100  that does not include the refrigerant flow switching device  11  and performs only one of cooling operation and heating operation. 
     While Embodiment 1 and the like mentioned above are directed to the case of the air-conditioning apparatus  100  having the composition detection circuit  20  provided in the outdoor unit  1 , this should not be construed restrictively. The composition detection circuit  20  may not necessarily be provided as long as there are detecting devices that detect a high-pressure side pressure that is a pressure on the upstream side of the first expansion device  51 , a low-pressure side pressure that is a pressure on the downstream side of the first expansion device  51 , a temperature on the high-pressure side upstream of the first expansion device  51  (the temperature of a supercooled liquid refrigerant), and the temperature of refrigerant on the low-pressure side downstream of the first expansion device  51 . 
     For example, the low-pressure side pressure as a pressure on the downstream side of the first expansion device  51  can be substituted for by a value close to the low-pressure side pressure. For example, the pressure on the suction side of the compressor  10 , or the pressure on the suction side of the accumulator  13  may be used instead. 
     REFERENCE SIGNS LIST 
       1  outdoor unit,  2  indoor unit,  3  refrigerant main pipe,  4  refrigerant pipe,  10  compressor,  11  refrigerant flow switching device,  12  outdoor-side heat exchanger,  13  accumulator,  20  composition detection circuit,  21  first pipe,  22  second pipe,  23  composition detection heat exchanger,  24  second expansion device,  30  first pressure detecting device,  31  second pressure detecting device,  32  first temperature detecting device,  33  second temperature detecting device,  40  controller,  40 A composition computing function unit,  40 B composition determining function unit,  50  load-side heat exchanger,  51  first expansion device,  60  third temperature detecting device,  61  fourth temperature detecting device,  62  fifth temperature detecting device,  100  air-conditioning apparatus