Patent Publication Number: US-9897355-B2

Title: Refrigeration apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 14/404,307 filed on Nov. 26, 2014, which is a National Stage application of International Patent Application No. PCT/JP2013/061597 filed on Apr. 19, 2013. The entire disclosure of U.S. patent application Ser. No. 14/404,307 is hereby incorporated herein by reference. 
    
    
     The present invention relates to a refrigeration apparatus, and more specifically, a refrigeration apparatus that uses R32 as a refrigerant. 
     BACKGROUND ART 
     In the conventional art, among refrigeration apparatuses such as air conditioning apparatuses and like, are apparatuses that use R32 as the refrigerant. When using R32 as the refrigerant, the discharge temperature of the compression mechanism tends to be higher in comparison to the case of using R410A or R22 as the refrigerant. Recognizing this problem, an air conditioning apparatus that lowers the refrigerant discharge temperature while using R32 is described in Japanese Laid-open Patent Application No. 2009-127902. In this air conditioning apparatus, part of the liquid refrigerant exiting from a gas liquid separator disposed in a high-pressure line is caused to bypass to a compression mechanism, that bypassed refrigerant then being converted to a flash gas state in an internal heat exchanger. That refrigerant, bypassed to the compression mechanism and converted into a flash gas is injected, lowering the enthalpy of refrigerant in an intermediate-pressure state in the compressor, causing a decrease in the discharge temperature of refrigerant in the compression mechanism. 
     SUMMARY 
     Technical Problem 
     If the refrigerant from the high-pressure main refrigerant channel is caused to bypass and is depressurized, and then that refrigerant is evaporated in an internal heat exchanger and supplied to a compressor, it is certainly possible to lower the discharge temperature of the compressor. 
     However, in the case in which the outdoor unit of an air conditioning apparatus is positioned higher in comparison to the indoor unit, the pressure of refrigerant coming out of the gas liquid separator of the outdoor unit during the heating operation may become very low. Further, in the case in which the refrigerant communication tubes joining the outdoor unit and the indoor unit are long, it is conceivable that the pressure of refrigerant coming out of the gas liquid separator will decrease. When the pressure of such refrigerant that is caused to bypass is low, the room for depressurizing the refrigerant that is caused to bypass prior to entry into the internal heat exchanger decreases and the temperature difference between the refrigerant that is caused to bypass and the refrigerant flowing in the main refrigerant channel in the internal heat exchanger becomes small, causing concern that the quantity of flash gas or the dryness may not be maintained. In order to prevent these problems it becomes necessary to increase the size of the internal heat exchanger, which then raises production costs and makes it necessary to increase the size of the outdoor unit. 
     An object of the present invention is to provide a refrigeration apparatus having a heat exchanger that exchanges heat between refrigerant flowing in the main refrigerant channel and refrigerant diverged from the main refrigerant channel, in which the refrigerant diverged from the main refrigerant channel is supplied to a compressor or a suction pipe, lowering the discharge temperature of the compressor, while minimizing increase in the size of the heat exchanger and maintaining the function of reducing the discharge temperature of the compressor. 
     Solution to the Problem 
     A refrigeration apparatus according to a first aspect of the present invention uses R32 as the refrigerant, and is provided with a compressor, a condenser, an expansion mechanism, an evaporator, a branch flow channel, a first opening adjustable valve, a heat exchanger for injection, a first injection channel, a refrigerant storage tank, and a second injection channel. The compressor sucks in low-pressure refrigerant from a suction passage, compresses the refrigerant and discharges high-pressure refrigerant. The condenser condenses high-pressure refrigerant discharged from the compressor. The expansion mechanism expands the high-pressure refrigerant that comes out of the condenser. The evaporator evaporates the refrigerant expanded by the expansion mechanism. The branch flow channel is a channel that branches from the main refrigerant channel joining the condenser and the evaporator. The first opening adjustable valve is disposed in the branch flow channel, and the degree of opening can be adjusted. The heat exchanger for injection exchanges heat between the refrigerant that flows in the main refrigerant channel and refrigerant that passes through the first opening adjustable valve of the branch flow channel. The first injection channel guides refrigerant that flows in the branch flow channel and exits from the heat exchanger for injection, to the compressor or the suction passage. The refrigerant storage tank is disposed along the main refrigerant channel. The second injection channel guides the gas component of refrigerant accumulated inside the refrigerant storage tank to the compressor or the suction passage. 
     This refrigeration apparatus according to the present invention, furnished with the heat exchanger for injection and the first injection channel, depressurizes refrigerant branched from the main refrigerant channel connecting the condenser and the evaporator at the first opening adjustable valve of the branch flow channel, and heats the refrigerant in the heat exchanger for injection. The depressurized, heated refrigerant, that has become flash gas in a gas-liquid two-phase state, saturated gas or superheated gas, is flowed to the compressor or the suction passage by passing through the first injection channel, enabling the discharge temperature of the compressor to be lowered. On the other hand, as the refrigeration apparatus is further furnished with the refrigerant storage tank and the second injection channel, the gas component (saturated gas) of refrigerant accumulated inside the refrigerant storage tank, is flowed to the compressor or the suction passage via the second injection channel, which also enables the discharge temperature of the compressor to be lowered. Thus, as there are two injection routes, in the refrigeration apparatus according to the present invention, even in the case in which the pressure of the refrigerant diverged from the main refrigerant channel is low, and the dryness and quantity of refrigerant flowing to the compressor is unable to be maintained even after being heated at the heat exchanger for injection, it is possible to lower the discharge temperature of the compressor using the refrigerant from the refrigerant storage tank. Further, as it is possible to use either of the two routes, it becomes unnecessary to increase the size of the heat exchanger for injection in order to maintain the dryness of refrigerant flowing to the compressor, regardless of the refrigerant state, thereby minimizing an increase in the size of the heat exchanger, and enabling the function of reducing the discharge temperature of the compressor to be maintained. 
     A refrigeration apparatus according to a second aspect of the present invention is the refrigeration apparatus according to the first aspect of the present invention further provided with a control unit. The control unit switches between a first injection control that flows refrigerant to primarily the first injection channel, and a second injection control that flows refrigerant to primarily the second injection channel. 
     Here, when the first injection control is performed, refrigerant diverged from the main refrigerant channel joining the condenser and the evaporator, is depressurized by the first opening adjustable valve of the branch flow channel, and heated in the heat exchanger for injection. Then, the depressurized, heated refrigerant that is a gas-liquid two-phase flash gas, saturated gas or superheated gas, passes through the first injection channel, flowing to the compressor or the suction passage, serving to lower the discharge temperature of the compressor. On the other hand, when the second injection control is performed, the gas component (saturated gas) of refrigerant accumulated in the refrigerant storage tank passes through the second injection channel and flows to the compressor or the suction passage, serving to lower the discharge temperature of the compressor. In this way, this refrigeration apparatus according to the present invention is configured to enable switching between the first injection control that flows refrigerant to primarily the first injection channel and the second injection control that flows refrigerant to primarily the second injection channel. Accordingly, even in the case in which the pressure of the refrigerant diverged from the main refrigerant channel is low, and the dryness and quantity of refrigerant flowing to the compressor is unable to be maintained even after being heated at the heat exchanger for injection, it is possible to switch to the second injection control and lower the discharge temperature of the compressor. Further, as it is possible to use the second injection control as well as the first injection control, regardless of the state of the refrigerant, it becomes unnecessary to increase the size of the heat exchanger for injection in order to maintain the dryness of refrigerant flowing to the compressor, thereby minimizing an increase in the size of the heat exchanger, while enabling the function of reducing the discharge temperature of the compressor to be maintained. 
     The first injection control is control for lowering the discharge temperature of the compressor through refrigerant flowing in primarily the first injection channel. The first injection control operates such that almost no refrigerant flows in the second injection channel or the quantity of refrigerant that flows in the second injection channel is less than the quantity of refrigerant that flows in the first injection channel. The second injection control is control for lowering the discharge temperature of the compressor with refrigerant flowing in primarily the second injection channel. The second injection control operates such that almost no refrigerant flows in the first injection channel or the quantity of refrigerant that flows in the first injection channel is less than the quantity of refrigerant that flows in the second injection channel. 
     A refrigeration apparatus according to a third aspect of the present invention is the refrigeration apparatus according to the second aspect of the present invention, in which the control unit switches between the first injection control and the second injection control based on the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism. 
     Here, in the case in which the pressure is low in the refrigerant flowing via the first opening adjustable valve and the heat exchanger for injection to the compressor or the suction passage, given that it is not possible to maintain the quantity and dryness of refrigerant exiting from the heat exchanger for injection, the switching between the first injection control and the second injection control is performed based on the pressure of refrigerant in the main refrigerant channel that is diverged by the branch flow channel (basically, the pressure of refrigerant between the condenser and the expansion mechanism). Accordingly, even in the case in which injection using the first injection channel largely cannot be performed, the discharge temperature of the compressor can be lowered. 
     Note that the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism can be directly detected by for example, installing a pressure gauge. Further, by obtaining the quantity of circulating refrigerant from the compressor frequency, the pressure of low-pressure refrigerant in the suction passage or the pressure of high-pressure refrigerant discharged from the compressor, and calculating the amount of depressurization in the expansion mechanism of the main refrigerant channel, it is possible to calculate the pressure of refrigerant in the main refrigerant channel from the amount of depressurization of the expansion mechanism and the difference between the high and low pressures. For the pressure of high-pressure refrigerant or of low-pressure refrigerant, it is suitable to detect these using a pressure gauge, and it is also suitable to calculate from the refrigerant saturation temperature or the like. 
     Moreover, the switching between the first injection control and the second injection control performed based on the pressure of refrigerant in the main refrigerant channel diverged by the branch flow channel, includes switching performed based on a detected value or estimated value of the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism, and also includes switching performed based on a detected value related to the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism. 
     A refrigeration apparatus according to a fourth aspect of the present invention is the refrigeration apparatus according to either the second aspect or the third aspect of the present invention further provided with a second opening adjustable valve. The second opening adjustable valve is disposed along the second injection channel and the degree of opening can be adjusted. The first injection channel and the second injection channel cause the refrigerant to merge with intermediate-pressure refrigerant of the compressor. The control unit, in the first injection control, causes refrigerant from primarily the first injection channel to merge with intermediate-pressure refrigerant of the compressor, and in the second injection control, causes refrigerant from primarily the second injection channel to merge with intermediate-pressure refrigerant of the compressor. 
     Here, as the refrigerant flowing in each of the injection channels is caused to merge with intermediate-pressure refrigerant of the compressor, it is possible to suppress the rotational speed of the compressor while maintaining capacity, thereby improving the efficiency of the refrigeration apparatus. Further, during the first injection control the first opening adjustable valve is adjusted, and during the second injection control the second opening adjustable valve is adjusted, such that the discharge temperature of the compressor can be lowered through performing the appropriate injection. 
     A refrigeration apparatus according to a fifth aspect of the present invention is the refrigeration apparatus according to the second aspect of the present invention, in which the control unit switches between the first injection control, the second injection control and a third injection control, the third injection control being a control that flows refrigerant to both the first injection channel and the second injection channel. 
     Here, in addition to the first injection control that flows refrigerant to primarily the first injection channel and the second injection control that flows refrigerant to primarily the second injection channel, the third injection control is provided. The control unit, through the third injection control, flows refrigerant to the first injection channel and the second injection channel. That is, the third injection control flows refrigerant from the heat exchanger for injection via the first injection channel to the compressor or the suction passage, and also flows refrigerant from the refrigerant storage tank via the second injection channel to the compressor or the suction passage. In this way, as the first, second and third injection controls are provided, the appropriate injection control is selected based on the operating condition and installation conditions of the refrigeration apparatus, leading to improved operating capacity and a reduction in the discharge temperature of the compressor. 
     A refrigeration apparatus according to a sixth aspect of the present invention is the refrigeration apparatus according to the fifth aspect of the present invention, in which the control part, in the third injection control, changes the ratio between the quantity of refrigerant flowed to the first injection channel and the quantity of refrigerant flowed to the second injection channel, based on the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism. 
     If the pressure of refrigerant in the main refrigerant channel between the condenser and the expansion mechanism decreases, depending on the size of the heat exchanger for injection, the dryness and quantity of refrigerant flowing from the heat exchanger for injection to the first injection channel may not reach the desired levels. Further, if the pressure of refrigerant in the main refrigerant channel decreases, in the case in which there is substantial difference between the height of the position of the condenser and the height of the position of the evaporator, such that there is substantial difference between the elevation of the condenser and the evaporator, it is not preferable to control accumulation (control that further decreases the pressure) of the gas component of the refrigerant in the refrigerant storage tank. 
     However, in the third injection control of the refrigeration apparatus according to the sixth aspect of the present invention that flows refrigerant from the heat exchanger for injection and the refrigerant storage tank simultaneously to the compressor and the like, the ratio of the quantity of refrigerant subject to injection that flows from the heat exchanger for injection to the first injection channel and the quantity of refrigerant subject to injection that flows from the refrigerant storage tank to the second injection channel, is changed based on the pressure of refrigerant in the main refrigerant channel. Control implemented in this way enables injection to be implemented as appropriate and prevents adverse effects occurring at other places in the refrigeration apparatus due to injection of refrigerant. 
     A refrigeration apparatus according to a seventh aspect of the present invention is the refrigeration apparatus according to the second aspect of the present invention, in which the control unit switches between the first injection control, the second injection control, and non-injection control. The non-injection control is control such that refrigerant does not flow in the first injection channel or the second injection channel. 
     Here, as the discharge temperature is low, it is not necessary to decrease the temperature of the compressor through suction injection or intermediate injection, moreover, in the case for example in which the rotational speed of the compressor is low as low capacity is required, the control unit can switch to non-injection control. If the switch to non-injection control is made, increase of capacity through suction injection or intermediate injection and the occurrence of substantially decreased operating efficiency are minimized, enabling operating efficiency to be maintained while fulfilling the requirement of low capacity. 
     Advantageous Effects of Invention 
     The refrigeration apparatus according to the first aspect of the present invention uses refrigerant from the refrigerant storage tank, thereby enabling the discharge temperature of the compressor to be reduced, even in the case in which the pressure of refrigerant diverged from the main refrigerant line is low and though heated by the heat exchanger for injection, the dryness and quantity of the refrigerant flowed to the compressor cannot be maintained. 
     The refrigeration apparatus according to the second aspect of the present invention switches to the second injection control thereby enabling the discharge temperature of the compressor to be reduced, even in the case in which the pressure of refrigerant diverged from the main refrigerant line is low and though heated by the heat exchanger for injection, the dryness and quantity of the refrigerant flowed to the compressor cannot be maintained. 
     The refrigeration apparatus according to the third aspect of the present invention switches to the second injection control, such that appropriate operation to reduce the discharge temperature of the compressor is performed even in the case in which due to the refrigerant pressure injection using the first injection channel is largely unable to be performed. 
     The refrigeration apparatus according to the fourth aspect of the present invention merges the refrigerant from the injection channel with intermediate-pressure refrigerant of the compressor, thereby improving the efficiency of the refrigeration apparatus, and enabling the appropriate injection to be performed by adjusting the degree of opening of each opening adjustable valve. 
     The refrigeration apparatus according to the fifth aspect of the present invention selects the appropriate injection control based on the operating condition and installation conditions of the refrigeration apparatus, leading to improved operating capacity and a reduction in the discharge temperature of the compressor. 
     The refrigeration apparatus according to the sixth aspect of the present invention enables injection to be performed as appropriate and suppresses adverse effects occurring at other places in the refrigeration apparatus due to injection of refrigerant. 
     In the refrigeration apparatus according to the seventh aspect of the present invention, increase of capacity through suction injection or intermediate injection and the occurrence of decreased operating efficiency are minimized, enabling operating efficiency to be maintained while fulfilling the requirement of low capacity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the refrigerant piping system of an air conditioning apparatus according to the first embodiment of the present invention. 
         FIG. 2  is a control block diagram of the control unit of the air conditioning apparatus. 
         FIG. 3  is a plan view of the soundproof material wound around the compressor. 
         FIG. 4  shows the refrigerant piping system of the air conditioning apparatus according to Modification C. 
         FIG. 5  shows the refrigerant piping system of the air conditioning apparatus according to the second embodiment of the present invention. 
         FIG. 6A  illustrates the injection control flow of the air conditioning apparatus according to the second embodiment. 
         FIG. 6B  illustrates the injection control flow of the air conditioning apparatus according to the second embodiment. 
         FIG. 6C  illustrates the injection control flow of the air conditioning apparatus according to the second embodiment. 
         FIG. 6D  illustrates the injection control flow of the air conditioning apparatus according to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     (1)  FIG. 1  shows the refrigerant piping system of an air conditioning apparatus  10 , being a refrigeration apparatus according to the first embodiment of the present invention. The air conditioning apparatus  10  is a distributed refrigerant piping system air conditioning apparatus, that cools and heats each room inside a building by vapor compression type refrigerant cycle operation. The air conditioning apparatus  10  is provided with an outdoor unit  11  as a heat source unit, a plurality of indoor units  12  as usage-side units, and a liquid refrigerant communication pipe  13  and gas refrigerant communication pipe  14  as refrigerant communication pipes that connect the outdoor unit  11  to the indoor units  12 . That is, the refrigerant circuit of the air conditioning apparatus  10  shown in  FIG. 1 , is configured such that the outdoor unit  11 , the indoor units  12 , the liquid refrigerant communication pipe  13  and the gas refrigerant communication pipe  14  are connected. The liquid refrigerant communication pipe  13  and the gas refrigerant communication pipe  14  are, in the case of a long piping configuration, 150 m long or longer. The total length of the piping of the liquid refrigerant communication pipe  13  and the gas refrigerant communication pipe  14  in order to connect the plurality of indoor units  12  with the single outdoor unit  11  can be up to 1000 m. Further, although it is envisaged that there may be a difference in the elevations in which the outdoor unit  11  and the indoor units  12  are installed, in the case that the outdoor unit  11  is installed in a low place and the indoor units  12  are installed in a higher place, the difference in elevation between the highest positioned indoor unit  12  and the outdoor unit  11  can be up to 40 m. On the other hand, in the case in which the outdoor unit  11  is installed in a high place such as on a roof or the like, and the indoor units  12  are installed in a low place, the difference in elevation between the lowest positioned indoor unit  12  and the outdoor unit  11  can be up to 90 m. 
     Refrigerant is sealed in the refrigerant circuit shown in  FIG. 1 , and as described subsequently, is subjected in that circuit to the operations of a refrigerant cycle in which the refrigerant is compressed, cooled and condensed, depressurized, then heated and evaporated, after which the refrigerant is compressed again. R32 is used as the refrigerant. R32 is a low GWP refrigerant with a low warming coefficient, a type of HFC refrigerant. Further, an ether-based synthetic oil having some degree of compatibility with R32 is used as the refrigerator oil. 
     (2) Detailed Configuration of the Air Conditioning Apparatus 
     (2-1) Indoor Units 
     The indoor units  12  are installed on the ceiling or a side wall in each room and are connected to the outdoor unit  11  via the refrigerant communication pipes  13  and  14 . The indoor unit  12  has primarily, an indoor expansion valve  42  that is a pressure reducer and an indoor heat exchanger  50  as a usage-side heat exchanger. 
     The indoor expansion valve  42  is an expansion mechanism that depressurizes the refrigerant, being an electric valve having an adjustable opening. One end of the indoor expansion valve  42  is connected to the liquid refrigerant communication pipe  13  and the other end is connected to the indoor heat exchanger  50 . 
     The indoor heat exchanger  50  is a heat exchanger that functions as an evaporator or a condenser of refrigerant. One end of the indoor heat exchanger  50  is connected to the indoor expansion valve  42  and the other end is connected to the gas refrigerant communication pipe  14 . 
     The indoor unit  12  has an indoor fan  55  for sucking in indoor air and resupplying the air indoors, facilitating exchange of heat between the indoor air and the refrigerant flowing in the indoor heat exchanger  50 . 
     Further, the indoor unit  12  has an indoor controller  90   b  for controlling the operation of each part that configures the indoor unit  12  and each kind of sensor. The indoor controller  90   b  has a microcomputer or memory or the like installed for controlling the indoor unit  12 , exchanges control signals or the like with a remote control unit (not shown in the drawing) to facilitate individual operation of the indoor unit  12 , and exchanges control signals or the like via a transmission line  90   c  with an outdoor controller  90   a  of the outdoor unit  11 , described subsequently. The various sensors include an indoor liquid pipe temperature sensor  97  and an indoor gas pipe temperature sensor  98  that are installed in the indoor unit  12 . The indoor liquid pipe temperature sensor  97  is attached to a refrigerant pipe that connects the indoor expansion valve  42  and the indoor heat exchanger  50 . The indoor gas pipe temperature sensor  98  is attached to a refrigerant pipe extending from the indoor heat exchanger  50  to the gas refrigerant communication pipe  14 . 
     (2-2) Outdoor Unit 
     The outdoor unit  11  is installed either outside or in the basement of the building having each room in which the indoor unit  12  is deployed, and is connected to the indoor units  12  via the refrigerant communication pipes  13  and  14 . Primarily, the outdoor unit  11  has a compressor  20 , a four-way switching valve  15 , an outdoor heat exchanger  30 , an outdoor expansion valve  41 , a bridge circuit  70 , a high-pressure receiver  80 , a first electric injection valve  63 , a heat exchanger for injection  64 , a second electric injection valve  84 , a liquid-side shut off valve  17  and a gas-side shut off valve  18 . 
     The compressor  20  is a hermetically sealed compressor driven by a compressor motor. In this embodiment there is one compressor  20 , however this embodiment is not limited to this number, and it is suitable to have two or more compressors  20  connected in parallel, depending on the number of connected indoor unit  12 . The compressor  20  sucks the gas refrigerant from a suction passage  27  via a vessel  28  appurtenant to the compressor  20 . A discharge pressure sensor  91  for detecting the pressure of discharged refrigerant, and a discharge temperature sensor  93  for detecting the temperature of discharged refrigerant are mounted to a discharge-side refrigerant pipe  29  of the compressor  20 . Further, an intake temperature sensor  94  for detecting the temperature of the refrigerant sucked into the compressor  20  is mounted to the suction passage  27 . Note that the compressor  20  has an intermediate injection port  23  described subsequently. 
     The four-way switching valve  15  is a mechanism for switching the direction of refrigerant flow. The four-way switching valve  15  connects the discharge-side refrigerant pipe  29  of the compressor  20  and one end of the outdoor heat exchanger  30 , and connects the suction passage  27  of the compressor  20  (including the vessel  28 ) to the gas-side shut off valve  18  (refer the solid line of the four-way switching valve  15  in  FIG. 1 ), such that during the cooling operation, the outdoor heat exchanger  30  is caused to function as a condenser of refrigerant compressed by the compressor  20  and the indoor heat exchanger  50  is caused to function as an evaporator of refrigerant cooled in the outdoor heat exchanger  30 . Further, the four-way switching valve  15  connects the discharge-side refrigerant pipe  29  of the compressor  20  and the gas-side shut off valve  18 , and connects the suction passage  27  to one end of the outdoor heat exchanger  30  (refer the dashed line of the four-way switching valve  15  in  FIG. 1 ), such that during the heating operation, the indoor heat exchanger  50  is caused to function as a condenser of refrigerant compressed by the compressor  20  and the outdoor heat exchanger  30  is caused to function as an evaporator of refrigerant cooled in the indoor heat exchanger  50 . In this embodiment, the four-way switching valve  15  is a four-way valve connected to the suction passage  27 , the discharge-side refrigerant pipe  29  of the compressor  20 , the outdoor heat exchanger  30  and the gas-side shut off valve  18 . 
     The outdoor heat exchanger  30  is a heat exchanger that functions as an evaporator or a condenser of the refrigerant. One end of the outdoor heat exchanger  30  is connected to the four-way switching valve  15  and the other end is connected to the outdoor expansion valve  41 . An outdoor liquid pipe temperature sensor  95  is mounted to the refrigerant pipe connecting the outdoor heat exchanger  30  and the outdoor expansion valve  41 , in order to detect the temperature of the refrigerant flowing in that pipe. 
     The outdoor unit  11  has an outdoor fan  35  that sucks in outdoor air into the unit and expels the air again outdoors. The outdoor fan  35  facilitates exchange of heat between outdoor air and the refrigerant flowing in the outdoor heat exchanger  30 , and is driven by an outdoor fan motor. Note that the heat source of the outdoor heat exchanger  30  is not limited to outside air and it is suitable to use a different heating medium such as water or the like. 
     The outdoor expansion valve  41  is an expansion mechanism for depressurizing the refrigerant, and is an electric valve having an adjustable opening. One end of the outdoor expansion valve  41  is connected to the outdoor heat exchanger  30  and the other end is connected to the bridge circuit  70 . 
     The bridge circuit  70  has four check valves,  71 ,  72 ,  73  and  74 . The inlet check valve  71  allows the refrigerant from the outdoor heat exchanger  30  to flow only toward the high-pressure receiver  80 . The outlet check valve  72  allows the refrigerant from the high-pressure receiver  80  to flow only toward the indoor heat exchanger  50 . The inlet check valve  73  allows the refrigerant from the indoor heat exchanger  50  to flow only toward the high-pressure receiver  80 . The outlet check valve  74  allows the refrigerant from the high-pressure receiver  80  to flow only toward the indoor heat exchanger  30  via the outdoor expansion valve  41 . That is, the inlet check valves  71  and  73  fulfill the function of flowing refrigerant from one of the outdoor heat exchanger  30  and the indoor heat exchanger  50  to the high-pressure receiver  80 , while the outlet check valves  72  and  74  fulfill the function of flowing refrigerant from the high-pressure receiver  80  to the other of the outdoor heat exchanger  30  and the indoor heat exchanger  50 . 
     The high-pressure receiver  80  is a container disposed between the outdoor expansion valve  41  and the liquid-side shut off valve  17  that functions as a refrigerant storage tank. During the cooling operation and during the heating operation, the high-pressure receiver  80 , into which high-pressure refrigerant has flowed, is not subject to the occurrence of the adverse phenomena in which excess refrigerant, including refrigerator oil, separates into two layers, with the refrigerator oil accumulating in the upper portion, because the surplus refrigerant that accumulates in the high-pressure receiver  80  is kept at a relatively high temperature. 
     Further, normally liquid refrigerant resides in the lower part of the internal space of the high-pressure receiver  80  and gas refrigerant resides in the upper part. A second injection channel  82  extends from the upper part of that internal space toward the compressor  20 . The second injection channel  82  fulfills the function of guiding the gas component of refrigerant accumulated inside the high-pressure receiver  80  to the compressor  20 . An adjustable opening second electric injection valve  84  is provided in the second injection channel  82 . 
     A heat exchanger for injection  64  is provided between the outlet of the high-pressure receiver  80  and the outlet check valves  72  and  74  of the bridge circuit  70 . A branch flow pipe  62  branches from a part of the main refrigerant channel  11   a  connecting the outlet of the high-pressure receiver  80  and the heat exchanger for injection  64 . The main refrigerant channel  11   a  is the main channel for liquid refrigerant, and connects the outdoor heat exchanger  30  and the indoor heat exchanger  50 . The high-pressure receiver  80  is disposed between the outdoor expansion valve  41  and the liquid-side shut off valve  17  along the main refrigerant channel  11   a.    
     A first electric injection valve  63  having an adjustable opening, is disposed in the branch flow pipe  62 . The branch flow pipe  62  is connected to a second flow path  64   b  of the heat exchanger for injection  64 . That is, when the first electric injection valve  63  is open, the refrigerant diverged from the main refrigerant channel  11   a  to the branch flow pipe  62  is depressurized at the first electric injection valve  63  and flows to the second channel  64   b  of the heat exchanger for injection  64 . 
     The refrigerant depressurized at the first electric injection valve  63  and flowed to the second channel  64   b  of the heat exchanger for injection  64 , is subject to heat exchange with refrigerant flowing in a first channel  64   a  of the heat exchanger for injection  64 . The first channel  64   a  of the heat exchanger for injection  64  configures a part of the main refrigerant channel  11   a . The refrigerant that has flowed through the branch flow pipe  62  and the second channel  64   b  after heat exchange at the heat exchanger for injection  64 , is delivered toward the compressor  20  by means of a first injection channel  65 . A first injection temperature sensor  96  for detecting the temperature of the refrigerant that has been subject to heat exchange after passing through the second channel  64   b  of the heat exchanger for injection  64 , is mounted to the first injection channel  65 . 
     The heat exchanger for injection  64  is an internal heat exchanger employing a double tube structure that performs heat exchange between the refrigerant flowing in the main refrigerant channel  11   a  that is the main path, and the refrigerant diverged from the main refrigerant channel  11   a  for injection, as described above. One end of the first channel  64   a  of the heat exchanger for injection  64  is connected to the outlet of the high-pressure receiver  80 , while the other end connects to the outlet check valves  72  and  74  of the bridge circuit  70 . 
     The liquid-side shut off valve  17  is a valve connected to the liquid refrigerant communication pipe  13  that functions to exchange refrigerant between the outdoor unit  11  and the indoor unit  12 . The gas-side shut off valve  18  is a valve connected to the gas refrigerant communication pipe  14  that functions to exchange refrigerant between the outdoor unit  11  and the indoor unit  12 , the gas-side shut off valve  18  being connected to the four-way switching valve  15 . Here, the liquid-side shut off valve  17  and the gas-side shut off valve  18  are three-way valves provided with service ports. 
     The vessel  28  is arranged in the suction passage  27  between the four-way switching valve  15  and the compressor  20 , and fulfills the function of preventing liquid refrigerant from being sucked into the compressor  20  when refrigerant that includes excessive liquid component flows in. Here, while the vessel  28  is provided, it is also suitable to additionally deploy in the suction passage  27 , an accumulator for preventing liquid flow back to the compressor  20 . 
     As described above, the intermediate injection port  23  is provided in the compressor  20 . The intermediate injection port  23  is a port that introduces refrigerant in order to flow refrigerant from outside into the intermediate-pressure refrigerant in the course of compression in the compressor  20 . The above described first injection channel  65  and second injection channel  82  are connected to an intermediate injection pipe  23   a  that is connected to the intermediate injection port  23 . When the first electric injection valve  63  is open, intermediate injection is performed that flows refrigerant to the intermediate injection port  23  from the first injection channel  65 , and when the second electric injection valve  84  is open, intermediate injection is performed that flows refrigerant to the intermediate injection port  23  from the second injection channel  82 . Note that it is possible to replace the compressor  20  with two compressors connected in series and connect the intermediate injection pipe  23   a  to the refrigerant piping connecting the discharge port of a low stage compressor and the suction port of a high-stage compressor. 
     As shown in  FIG. 3 , soundproof material  20   a  is wound around the compressor  20 . A notch  20   b  that prevents contact with the intermediate injection pipe  23   a  is formed in the soundproof material  20   a . The soundproof material  20   a  is divided into two parts in consideration of the difficulties that would be incurred in attaching and removing the soundproof material  20   a  if the whole of the soundproof material  20   a  around the notch  20   b  were a single integrated body, when another member such as a casing member of the outdoor unit  11  or the like is provided around the intermediate injection pipe  23   a . Specifically, the soundproof material  20   a  is divided into a main body section  20   c  and a small piece section  20   d . The small piece section  20   d  attaches to the main body section  20   c  via a plurality of hook and loop fasteners  20   e . When the soundproof material  20   a  is removed from the compressor  20  for a reason such as performing maintenance or the like, firstly the small piece section  20   d  is detached from the main body section  20   c , then the main body section  20   c  is slid to the left side in  FIG. 3 , removing the soundproof material  20   a  from the intermediate injection pipe  23   a  and the compressor  20 . 
     Further, the outdoor unit  11  has various sensors, and an outdoor controller  90   a . The outdoor controller  90   a  is provided with memory or a microcomputer or the like, for performing control of the outdoor unit  11 , and exchanges control signals and the like via a transmission line  8   a  with the indoor controller  90   b  of the indoor unit  12 . The various sensors include the discharge pressure sensor  91 , the discharge temperature sensor  93 , the intake temperature sensor  94 , the outdoor liquid pipe temperature sensor  95  and the first injection temperature sensor  96  described above, a receiver outlet pressure sensor  92 , and an outdoor air temperature sensor  99  for detecting the outside air temperature. The receiver outlet pressure sensor  92 , mounted to a part of the main refrigerant channel  11   a  between the outlet of the high-pressure receiver  80  and the heat exchanger for injection  64 , is a sensor for detecting the pressure of refrigerant exiting the high-pressure receiver  80 . 
     (2-3) Refrigerant Communication Pipes 
     The refrigerant communication pipes  13  and  14  are refrigerant pipes that are installed on site when the outdoor unit  11  and the indoor units  12  are installed on location. 
     (2-4) Controller 
     The controller  90 , control device for performing the various operation controls of the air conditioning apparatus  10 , comprises the outdoor controller  90   a  and the indoor controller  90   b  joined via a transmission line  90   c  as shown in  FIG. 1 . As shown in  FIG. 2 , the controller  90  receives detection signals from the above described various sensors  91 - 99 , and implements control of the various devices including the compressor  20 , the outdoor fan  35 , the outdoor expansion valve  41 , the indoor fan  55 , the first electric injection valve  63 , the second electric injection valve  84  and the like, based on these detection signals. 
     The controller  90  is provided with function parts including a cooling operation control part for when the cooling operation is performed, that uses the indoor heat exchanger  50  as an evaporator, a heating operation control part for when the heating operation is performed, that uses the indoor heat exchanger  50  as a condenser, and an injection control part that performs injection control for the cooling operation or the heating operation. 
     (3) Operation of the Air Conditioning Apparatus 
     The operation of the air conditioning apparatus  10  according to this embodiment will now be described. The controls for each operation explained subsequently are performed from the controller  90  that functions as a device for operation control. 
     (3-1) Basic Operations for the Cooling Operation 
     During the cooling operation the four-way switching valve  15  is in the condition indicated by the solid line in  FIG. 1 , that is, liquid refrigerant discharged from the compressor  20  flows to the outdoor heat exchanger  30 , moreover the suction passage  27  is connected to the gas-side shut off valve  18 . With the outdoor expansion valve  41  fully open, the indoor expansion valve  42  comes to be adjusted. Note that the shut off valves  17  and  18  are in the open condition. 
     With the refrigerant circuit in this condition, the high-pressure gas refrigerant discharged from the compressor  20  is delivered via the four-way switching valve  15  to the outdoor heat exchanger  30  functioning as a condenser of refrigerant, where the refrigerant is cooled by being subjected to heat exchange with outdoor air supplied from the outdoor fan  35 . The high-pressure refrigerant cooled in the outdoor heat exchanger  30  and liquefied, becomes refrigerant in a supercooled state at the heat exchanger for injection  64 , and is then delivered via the liquid refrigerant communication pipe  13  to each of the indoor units  12 . The refrigerant delivered to each of the indoor units  12  is depressurized by the respective indoor expansion valves  42 , becoming low-pressure refrigerant in a gas-liquid two-phase state, and is then subjected to heat exchange with indoor air in the indoor heat exchanger  50 , functioning as an evaporator of refrigerant, becoming evaporated, and becoming low-pressure gas refrigerant. The low-pressure gas refrigerant heated in the indoor heat exchanger  50  is delivered via the gas refrigerant communication pipe  14  to the outdoor unit  11  and sucked into the compressor  20  again via the four-way switching valve  15 . This is how the air conditioning apparatus cools indoors. 
     In the case in which some of the indoor units  12  from among the indoor units  12  are not operating, the indoor expansion valve  42  of the indoor unit  12  that is not operating has the opening closed (for example completely closed). In this case, almost no refrigerant passes through the indoor unit  12  that has stopped operating and the cooling operation is only carried out in the indoor unit  12  that is operating. 
     (3-2) Basic Operations During the Heating Operation 
     During the heating operation the four-way switching valve  15  is in the condition indicated by the dashed line in  FIG. 1 , that is, the discharge-side refrigerant pipe  29  of the compressor  20  is connected to the gas-side shut off valve  18 , moreover, the suction passage  27  is connected to the outdoor heat exchanger  30 . The outdoor expansion valve  41  and the indoor expansion valve  42  come to be adjusted. Note that the shut off valves  17  and  18  are in the open condition. 
     With the refrigerant circuit in this condition, the high-pressure gas refrigerant discharged from the compressor  20  is delivered via the four-way switching valve  15  and the gas refrigerant communication pipe  14  to each of the indoor units  12 . The high-pressure gas refrigerant delivered to each of the indoor units  12  is cooled by being subjected to heat exchange with indoor air in the respective indoor heat exchangers  50 , each functioning as a condenser of refrigerant. Thereafter the refrigerant passes through the indoor expansion valve  42  and is delivered via the liquid refrigerant communication pipe  13  to the outdoor unit  11 . As the refrigerant is subjected to heat exchange with indoor air and cooled, the indoor air is heated. The high-pressure refrigerant delivered to the outdoor unit  11  is separated into liquid and gas at the high-pressure receiver  80 , the high-pressure liquid refrigerant comes into a subcooled state at the heat exchanger for injection  64 , being depressurized by the outdoor expansion valve  41  to become low-pressure refrigerant in a gas-liquid two-phase state, which is then flowed into the outdoor heat exchanger  30 , functioning as an evaporator of refrigerant. The low-pressure refrigerant in a gas-liquid two-phase state flowed into the outdoor heat exchanger  30  is subjected to heat exchange with outdoor air supplied from the outdoor fan  35  and heated, becoming evaporated, low-pressure refrigerant. The low-pressure gas refrigerant exiting from the outdoor heat exchanger  30  is sucked into the compressor  20  again via the four-way switching valve  15 . This is how the air conditioning apparatus warms indoors. 
     (3-3) Injection Control for Each Operation 
     During the cooling operation and during the heating operation, the injection control part comprising one of the function parts of the controller  90 , selectively performs either the first injection control that flows refrigerant to primarily the first injection channel  65 , or the second injection control that flows refrigerant to primarily the second injection channel  82 . These injection controls are performed in order to reduce the discharge temperature as there is a tendency for the discharge temperature of the compressor  20  using R32 as refrigerant to be high, the refrigerant being delivered to the intermediate injection port  23  of the compressor  20  using the first injection channel  65  or the second injection channel  82 , reducing the discharge temperature of the compressor  20 . The intermediate-pressure refrigerant delivered to the intermediate injection port  23  is of lower temperature than intermediate-pressure refrigerant in the course of compression in the compressor  20 , thereby reducing the discharge temperature of the compressor  20 . 
     The controller  90  normally performs the first injection control. The first injection control flows refrigerant to primarily the first injection channel  65  and is therefore a control that performs intermediate injection. During the first injection control the first electric injection valve  63  functions as an expansion valve, the opening normally being adjusted based on the detected temperature Tsh from the first injection temperature sensor  96 . At this time, the opening of the first electric injection valve  63  is adjusted such that the refrigerant flowing in the first injection channel  65  becomes superheated gas, that is, such that the refrigerant becomes refrigerant gas superheated as required. In this way, the discharge temperature of the compressor  20  is reduced and the operating efficiency of the air conditioning apparatus  10  is improved. 
     The controller  90 , in the first injection control monitors the discharge temperature Tdi of the compressor  20  detected by the discharge temperature sensor  93 , and if the discharge temperature Tdi exceeds a first upper limit value, stops adjusting the degree of the opening of the first electric injection valve  63  based on the detected temperature Tsh of the first injection temperature sensor  96  and transitions to adjustment of the degree of opening of the first electric injection valve  63  based on the detected temperature Tdi of the discharge temperature sensor  93 . At this time the opening of the first electric injection valve  63  is adjusted such that the refrigerant flowing in the first injection channel  65  becomes humid gas (flash gas). If the detected temperature Tdi of the discharge temperature sensor  93  is below the first upper limit value, the controller  90  returns to adjusting the degree of opening of the first electric injection valve  63  based on the detected temperature Tsh of the first injection temperature sensor  96  again. On the other hand, if the detected temperature Tdi of the discharge temperature sensor  93  exceeds a second upper limit value that is higher than the first upper limit value, droop control of the compressor  20  commences, reducing the rotational speed of the compressor  20 , moreover if the detected temperature Tdi exceeds a third upper limit value that is still higher than the second upper limit value, an instruction is issued to stop the compressor  20 . 
     Basically, the first injection control lowers the discharge temperature of the compressor  20  and improves the operating efficiency of the air conditioning apparatus  10  as described above, however, the controller  90 , through the receiver outlet pressure sensor  92 , constantly monitors the pressure Ph 2  (outdoor liquid pipe pressure Ph 2 ) of the refrigerant in the vicinity of the connection point of the main refrigerant channel  11   a  with the branch flow pipe  62 . When the outdoor liquid pipe pressure Ph 2  of the main refrigerant channel  11   a  is lower than a threshold value, the controller  90  switches from the first injection control to the second injection control. This is because if the outdoor liquid pipe pressure Ph 2  becomes low, it becomes necessary to considerably reduce the opening degree of the first electric injection valve  63  in order that the refrigerant flowing in the first injection channel  65  becomes superheated gas, and it is not possible to maintain the quantity of injected refrigerant (the quantity of refrigerant flowing into the intermediate injection port  23 ). In the second injection control, performed when the outdoor liquid pipe pressure Ph 2  is below the threshold value, the first electric injection valve  63  is closed and the second electric injection valve  84  is opened instead, the gas component of the refrigerant accumulated inside the high-pressure receiver  80  passes through the second injection channel  82 , being supplied from the intermediate injection port  23  to the compressor  20 . Because the outdoor liquid pipe pressure Ph 2  is low, it often occurs that refrigerant returning to the outdoor unit  11  from the indoor unit  12  is flashed, with the gas component of the refrigerant residing in the high-pressure receiver  80 . 
     In this second injection control it may be possible for the first electric injection valve  63  to not be closed, and to continue adjustment of the opening of the first electric injection valve  63  based on the detected temperature Tsh of the first injection temperature sensor  96 . However, as the outdoor liquid pipe pressure Ph 2  is below the threshold value, in the second injection control the quantity of refrigerant flowing in the second injection channel  82  becomes larger than the quantity of refrigerant flowing in the first injection channel  65 . Further, in the second injection control, the opening of the second electric injection valve  84  is adjusted based on the detected temperature Tdi of the discharge temperature sensor  93 . 
     Note that even when the air conditioning apparatus  10  is started up, in the case in which a small number of the indoor units  12  are operated, as it is envisaged that the discharge temperature of the compressor  20  will rise, intermediate injection is performed at times when predetermined conditions are met. Specifically, the determination on whether or not to implement intermediate injection is dependent on the outside air temperature conditions or conditions of the capacity for thermo-on (the total capacity of the indoor units  12  that flow refrigerant with the indoor expansion valve  42  open). In this case in which intermediate injection is implemented at startup, the control operates such that the opening of the first electric injection valve  63  is gradually increased in order that the compressor  20  does not cause liquid compression. 
     (4) Characteristics of the Air Conditioning Apparatus 
     (4-1) 
     The air conditioning apparatus  10  according to this embodiment of the present invention, when performing the first injection control, primarily depressurizes at the first electric injection valve  63  of the branch flow pipe  62 , the refrigerant diverged from the main refrigerant channel  11   a , and heats the refrigerant in the heat exchanger for injection  64 . The depressurized, heated refrigerant that has become flash gas in a gas-liquid two-phase state, saturated gas or superheated gas, flows through the first injection channel  65  to the compressor  20 , the discharge temperature of the compressor  20  being reduced. On the other hand, when the second injection control is performed, primarily, the gas component (saturated gas) of the refrigerant accumulated inside the high-pressure receiver  80  is flowed through the second injection channel  82  to the compressor  20 , operating to lower the discharge temperature of the compressor  20 . In this way, the air conditioning apparatus  10  is configured so as to be capable of switching between the first injection control that flows refrigerant primarily in the first injection channel  65 , and the second injection control that flows refrigerant primarily in the second injection channel  82 . 
     Accordingly, even in the case in which the pressure of the liquid refrigerant in the outdoor unit  11  that has been diverged from the main refrigerant channel  11   a  is low, and though the refrigerant is heated in the heat exchanger for injection  64  it is not possible to maintain the quantity of the refrigerant flowing from the first injection channel  65  to the compressor  20 , it is possible to switch to the second injection control and lower the discharge temperature of the compressor  20 . Further, as it is possible to perform the second injection control in addition to the first injection control, it becomes unnecessary to substantially increase the size of the heat exchanger for injection  64  so that the dryness of the refrigerant flowing to the compressor  20  is maintained, regardless of the refrigerant condition, thereby minimizing any increase in the size of the heat exchanger for injection  64  and enabling the function of reducing the discharge temperature of the compressor  20  to be maintained. 
     (4-2) 
     In the air conditioning apparatus  10  according to this embodiment, as the quantity of refrigerant required for the cooling operation is sealed in the refrigerant circuit, during the heating operation, while also depending on the condition of load, the high-pressure refrigerant that returns to the outdoor unit  11  flashes easily. However, in the case in which the pressure of the refrigerant about to be flowed to the compressor  20  via the first electric injection valve  63  and the heat exchanger for injection  64  is low (the pressure of refrigerant prior to depressurization at the first electric injection valve  63 ), it is conceivable that it would not be possible to maintain the dryness and quantity of refrigerant exiting the heat exchanger for injection  64 . 
     In light of this, in the air conditioning apparatus  10 , the switching between the first injection control and the second injection control is performed based on the pressure of the refrigerant of the main refrigerant channel  11   a  diverged by the branch flow pipe  62 . Specifically, the pressure Ph 2  (outdoor liquid pipe pressure Ph 2 ) of the refrigerant in the vicinity of the connection point of the main refrigerant channel  11   a  and the branch flow pipe  62 , is constantly monitored by the receiver outlet pressure sensor  92 , and when the outdoor liquid pipe pressure Ph 2  of the main refrigerant channel  11   a  is below the threshold value, the controller  90  switches from the first injection control to the second injection control. The receiver outlet pressure sensor  92  is disposed in the part of the main refrigerant channel  11   a  between the indoor expansion valve  42  in the role of an expansion mechanism and the outdoor heat exchanger  30  in the role of a condenser in the cooling operation. Further, the receiver outlet pressure sensor  92  is disposed in the part of the main refrigerant channel  11   a  between the outdoor expansion valve  41  in the role of an expansion mechanism and the indoor heat exchanger  50  in the role of a condenser in the heating operation. That is, in the air conditioning apparatus  10 , switching between the first injection control and the second injection control is performed based on the pressure of refrigerant in the main refrigerant channel  11   a  between the condenser and the expansion mechanism. 
     In this way, even in the case in which intermediate injection using the first injection channel  65  is largely not able to be performed, the gas component of the refrigerant accumulated in the high-pressure receiver  80  comes to be supplied after passing through the second injection channel  82 , to the intermediate injection port  23  of the compressor  20 , thereby enabling the discharge temperature of the compressor  20  to be lowered. This air conditioning apparatus  10  envisages switching from the first injection control to the second injection control particularly in the heating operation. 
     Note that the controller  90 , basically through the first injection control, reduces the discharge temperature of the compressor  20  and improves the operating efficiency of the air conditioning apparatus  10 . This is because by adjusting the opening of the first electric injection valve  63 , the refrigerant that flows in the first injection channel  65  and is subject to intermediate injection, can be made into superheated gas and can also be made into humid gas (flash gas). The controller  90 , in the first injection control, stops adjusting the opening degree of the first electric injection valve  63  based on the detected temperature Tsh of the first injection temperature sensor  96  if the discharge temperature Tdi exceeds the first upper limit value, and transitions to adjusting the opening degree of the first electric injection valve  63  based on the detected temperature Tdi of the discharge temperature sensor  93 , such that humid gas that has high cooling effect flows in the first injection channel  65  and is subject to intermediate injection. Further, the second injection control, in the case in which the pressure of high-pressure refrigerant returning to the outdoor unit  11  becomes low, could be said to be the preferable control as it enables gas to be simply ensured at the high-pressure receiver  80 , on the other hand because only saturated gas can be subject to intermediate injection, the cooling effect is low. Moreover, in the case of intentionally dropping the pressure of high-pressure refrigerant that is returned to the outdoor unit  11  for the purpose of the second injection control, when the indoor expansion valve  42  cannot shut perfectly, a large amount of the refrigerant will flow at different pressures in an indoor unit  12  in the thermo-off condition or an indoor unit  12  that is stopped in the heating operation, leading to wasteful energy consumption due to superfluous heating. Accordingly, the air conditioning apparatus  10  according to this embodiment, primarily through the first injection control, reduces the discharge temperature of the compressor  20  and improves the operating efficiency of the air conditioning apparatus  10 . 
     (4-3) 
     The air conditioning apparatus  10  according to this embodiment of the present invention operates such that refrigerant flowing in each of the first injection channel  65  and the second injection channel  82  is caused to merge with intermediate-pressure refrigerant inside the compressor  20 , thereby suppressing the rotational speed of the compressor  20  while maintaining capacity, providing improved operating efficiency. 
     (5) Modifications 
     (5-1) Modification A 
     In the air conditioning apparatus  10  according to the above described embodiment, the pressure Ph 2  (outdoor liquid pipe pressure Ph 2 ) of the refrigerant is continually monitored by the receiver outlet pressure sensor  92  in the vicinity of the connection point of the main refrigerant channel  11   a  and the branch flow pipe  62 , and switching between the first injection control and the second injection control is performed based on that outdoor liquid pipe pressure Ph 2 . It is also possible however, to not have the receiver outlet pressure sensor  92  installed and to estimate the outdoor liquid pipe pressure. For example, it is possible to obtain the quantity of circulating refrigerant from the operating frequency of the compressor  20 , the pressure of low-pressure refrigerant in the suction passage  27  or the pressure of high-pressure refrigerant discharged from the compressor  20  (detected value from the discharge pressure sensor  91 ), calculate the amount of depressurization in the indoor expansion valve  42  or the outdoor expansion valve  41 , then calculate the refrigerant pressure in the vicinity of the heat exchanger for injection  64  of the main refrigerant channel  11   a  from that amount of depressurization and the difference between the high and low pressures. It is also possible to install a pressure gauge to detect the pressure of low-pressure refrigerant in the suction passage  27 , or to calculate from the refrigerant saturation temperature or the like. 
     (5-2) Modification B 
     In the above described embodiment, switching between the first injection control and the second injection control is performed based on the pressure of the refrigerant (outdoor liquid pipe pressure Ph 2 ) in the vicinity of the connection point of the main refrigerant channel  11   a  and the branch flow pipe  62 , however it is also possible for the switching to be performed based on a detected value related to the outdoor liquid pipe pressure Ph 2 , rather than being based on an estimated value or detected value of the outdoor liquid pipe pressure Ph 2  itself. For example, in the case in which it is determined from the temperature (value detected by the first injection temperature sensor  96 ) and the pressure of refrigerant after depressurized at the first electric injection valve  63  and the refrigerant has been subject to heat exchange at the heat exchanger for injection  64 , that the dryness of refrigerant or the quantity of refrigerant flow at the intermediate injection from the first injection channel  65  is outside the desired range, it is possible to recognize that the outdoor liquid pipe pressure Ph 2  is decreased and to change from the first injection control to the second injection control. 
     (5-3) Modification C 
     In the air conditioning apparatus  10  according to the above described embodiment, intermediate injection is performed in which refrigerant flowing in each of the injection channels  65  and  82  is flowed into the intermediate injection port  23  of the compressor  20 , however as shown in  FIG. 4 , it is also possible to reduce the discharge temperature of the compressor  20  by flowing the refrigerant flowing in each of the injection channels  65  and  82  into the suction passage  27 . 
     An air conditioning apparatus  110  shown in  FIG. 4  replaces the outdoor unit  11  of the air conditioning apparatus  10  in the above described embodiment with an outdoor unit  111 . The outdoor unit  111  has a compressor  120  instead of the compressor  20  of the outdoor unit  11 , and changes the connecting ends of the first injection channel  65  and the second injection channel  82  to the suction passage  27 . 
     The compressor  120  of the outdoor unit  111  sucks in refrigerant gas from the suction passage  27  via the vessel  28  appurtenant to the compressor and discharges compressed, high-pressure refrigerant to the refrigerant pipe  29 , such that an intermediate injection port is not provided. Further, in the outdoor unit  111 , the end of the second injection channel  82  extending toward the compressor  120  from the high-pressure receiver  80  and the end of the first injection channel  65  extending towards the compressor  120  from the heat exchanger for injection  64 , connect to a merge pipe  27   a . As shown in  FIG. 4 , the end of the merge pipe  27   a  connects to the suction passage  27 . Thus the refrigerant that has flowed through each of the injection channels  65  and  82  merges with low-pressure gas refrigerant flowing in the suction passage  27  and comes to be sucked into the compressor  120 . In this case also, it is possible to reduce the discharge temperature of the compressor  120  using injection control. Further, the switch between the first injection control and the second injection control can be performed in the same way as in the above described embodiment, moreover, the same effects as are achieved in the above described embodiment are realized. 
     Second Embodiment 
     (1) Configuration of the Air Conditioning Apparatus 
     In the air conditioning apparatus according to the second embodiment of the present invention, the outdoor unit  11  of the air conditioning apparatus  10  in the above described first embodiment using R32 as the refrigerant, is replaced by an outdoor unit  211  shown in  FIG. 5 . In this air conditioning apparatus according to the second embodiment, the outdoor unit  211  is disposed in a position lower than the indoor unit  12 , and there is a substantial difference between the positional height of the outdoor unit  211  and the positional height of the highest part of the indoor unit  12 , such that there is substantial difference in their respective elevations. The outdoor unit  211  will now be described, some of those elements which are substantially similar to the corresponding elements of the outdoor unit  11  in the first embodiment described above will be given the same reference numerals in the figures and their description is omitted. 
     The outdoor unit  211  has primarily, the compressor  20 , the four way switching valve  15 , the outdoor heat exchanger  30 , the outdoor expansion valve  41 , the bridge circuit  70 , a high-pressure receiver  280 , a first electric injection valve  263 , a heat exchanger for injection  264 , a second electric injection valve  284 , an intermediate injection switching valve  266 , a suction injection switching valve  268 , the liquid-side shut off valve  17  and the gas-side shut off valve  18 . 
     The compressor  20 , the vessel  28  appurtenant to the compressor, the suction passage  27 , the discharge-side refrigerant pipe  29  of the compressor  20 , the discharge temperature sensor  93 , the intermediate injection port  23 , the four-way switching valve  15 , the liquid-side shut off valve  17 , the gas-side shut off valve  18 , the outdoor heat exchanger  30 , the outdoor expansion valve  41 , the outdoor fan  35  and the bridge circuit  70  are the same as their corresponding members in the first embodiment, accordingly their descriptions are omitted. 
     The high-pressure receiver  280  is a vessel that functions as a refrigerant storage tank, and is disposed between the outdoor expansion valve  41  and the liquid-side shut off valve  17 . The high-pressure receiver  280 , into which high-pressure refrigerant flows during the cooling operation and during the heating operation, does not have the problem in which the excess refrigerant including refrigerant oil separates into two layers, with the refrigerant oil collecting in the upper portion, as the temperature of excess refrigerant accumulated therein is maintained relatively high. A receiver outlet pressure sensor  292  is provided to the receiver outlet pipe that extends from the lower portion of the high-pressure receiver  280  to the heat exchanger for injection  264 . The receiver outlet pipe is part of the main refrigerant channel  211   a  described subsequently. The receiver outlet pressure sensor  292  is a sensor that detects a pressure value (high-pressure value) for high-pressure liquid refrigerant. 
     Liquid refrigerant normally resides in the lower part of the internal space of the high-pressure receiver  280 , and gas refrigerant normally resides in the upper part of that space, while a bypass channel  282  extends from that upper part of the internal space toward the compressor  20 . The bypass channel  282  is a pipe that plays the role of guiding the gas component of refrigerant accumulated inside the high-pressure receiver  280  to the compressor  20 . A second bypass electric injection valve  284  having an adjustable opening, is provided in the bypass channel  282 . When this second bypass electric injection valve  284  opens, gas refrigerant flows via a common injection tube  202  to an intermediate injection channel  265  or a suction injection channel  267  described subsequently. 
     A heat exchanger for injection  264  is provided between the outlet check valves  72  and  74  of the bridge circuit  70  and the outlet of the high-pressure receiver  280 . Further, a branch flow pipe  262  branches from a part of the main refrigerant channel  211   a  that connects the outlet of the high-pressure receiver  280  and the heat exchanger for injection  264 . The main refrigerant channel  211   a  is the main channel for liquid refrigerant, and connects the outdoor heat exchanger  30  and the indoor heat exchanger  50 . 
     The first electric injection valve  263 , having an adjustable opening, is disposed in the branch flow pipe  262 . The branch flow pipe  262  is attached to a second flow path  264   b  of the heat exchanger for injection  264 . That is, when the first electric injection valve  263  is open, refrigerant diverged from the main refrigerant channel  211   a  to the branch flow pipe  262  is depressurized at the first electric injection valve  263  and flows to the second flow path  264   b  of the heat exchanger for injection  264 . 
     The refrigerant depressurized at the first electric injection valve  263  and flowed to the second flow path  264   b  of the heat exchanger for injection  264  is subject to heat exchange with refrigerant flowing in a first flow path  264   a  of the heat exchanger for injection  264 . The refrigerant that flows through the branch flow pipe  262  after heat exchange at the heat exchanger for injection  264 , flows via the shared injection tube  202  and into the intermediate injection channel  265  or the suction injection channel  267  described subsequently. An injection temperature sensor  296  for detecting the temperature of refrigerant after heat exchange at the heat exchanger for injection  264 , is mounted to the down flow side of the heat exchanger for injection  264  of the branch flow pipe  262 . 
     The heat exchanger for injection  264  is an internal heat exchanger employing a double tube structure. One end of the first flow path  264   a  connects to the outlet of the high-pressure receiver  280 , and the other end of the first flow path  264   a  connects to the outlet check valves  72  and  74  of the bridge circuit  70 . 
     The common injection tube  202  is a pipe connecting to an end of the bypass channel  282  extending from the high-pressure receiver  280  and an end of the branch flow pipe  262  extending from the main refrigerant channel  211   a  via the heat exchanger for injection  264 , and connecting to the intermediate injection switching valve  266  and the suction injection switching valve  268 . If at least one from among the first electric injection valve  263  and the second bypass electric injection valve  284  is open, and either the intermediate injection switching valve  266  or the suction injection switching valve  268  opens, refrigerant flows in the common injection tube  202 , and intermediate injection or suction injection is implemented. 
     The intermediate injection channel  265  extends from the intermediate injection switching valve  266  connected to the common injection tube  202 , to the compressor  20 . Specifically, one end of the intermediate injection channel  265  is connected to the intermediate injection switching valve  266 , and the other end of the intermediate injection channel  265  is connected to the intermediate injection port  23  of the compressor  20 . 
     The suction injection channel  267  extends from the suction injection switching valve  268  connected to the common injection tube  202  to the suction passage  27 . Specifically, one end of the suction injection channel  267  is connected to the suction injection switching valve  268 , and the other end of the suction injection channel  267  is connected to the part of the suction passage  27  connecting the vessel  28  appurtenant to the compressor and the compressor  20 . 
     The intermediate injection switching valve  266  and the suction injection switching valve  268  are solenoid valves that switch between an open condition and a closed condition. 
     (2) Operation of the Air Conditioning Apparatus 
     The operation of the air conditioning apparatus according to the second embodiment of the present invention will now be described. The controls for each operation explained subsequently are performed by the control unit of the outdoor unit  211  that functions as a means for operation control. 
     (2-1) Basic Operations for the Cooling Operation 
     During the cooling operation the four-way switching valve  15  is in the condition indicated by the solid line in  FIG. 5 , that is, gas refrigerant discharged from the compressor  20  flows to the outdoor heat exchanger  30 , moreover the suction passage  27  is connected to the gas-side shut off valve  18 . With the outdoor expansion valve  41  in the fully open condition, the degree of opening of the indoor expansion valve  42  comes to be adjusted. Note that the shut off valves  17  and  18  are in the open condition. 
     With the refrigerant circuit in this condition, the high-pressure gas refrigerant discharged from the compressor  20  is delivered via the four-way switching valve  15  to the outdoor heat exchanger  30  functioning as a condenser of refrigerant, where the refrigerant is cooled by being subjected to heat exchange with outdoor air supplied from the outdoor fan  35 . The liquefied high-pressure refrigerant cooled in the outdoor heat exchanger  30 , becomes refrigerant in a subcooled state at the heat exchanger for injection  264 , and is then delivered to each of the indoor units  12 . The operation of each of the indoor units  12  is the same as in the first embodiment described above. Low-pressure gas refrigerant returning to the outdoor unit  11  from each of the indoor units  12  is sucked into the condenser  20  again, via the four-way switching valve  15 . Basically, this is how the air conditioning apparatus cools indoors. 
     (2-2) Basic Operations for the Heating Operation 
     During the heating operation the four-way switching valve  15  is in the condition shown by the dashed line in  FIG. 5 , that is the discharge-side refrigerant pipe  29  of the compressor  20  is connected to the gas-side shut off valve  18 , moreover the suction passage  27  is connected to the outdoor heat exchanger  30 . The degrees of opening of the outdoor expansion valve  41  and the indoor expansion valve  42  come to be adjusted. Note that the shut off valves  17  and  18  are in the open condition. 
     With the refrigerant circuit in this condition, high-pressure gas refrigerant discharged from the compressor  20  passes via the four-way switching valve  15  and the gas refrigerant communication pipe  14  and is delivered to each of the indoor units  12 . The operation of each of the indoor units  12  is the same as for the first embodiment described above. The high-pressure refrigerant returning to the outdoor unit  11  again, passes via the high-pressure receiver  280  and becomes refrigerant in a subcooled state at the heat exchanger for injection  264 , flowing to the outdoor expansion valve  41 . The refrigerant depressurized at the outdoor expansion valve  41  and now low-pressure refrigerant in a gas-liquid two-phase state, flows into the outdoor heat exchanger  30  functioning as an evaporator. The low-pressure, gas-liquid two-phase state refrigerant that flows into the outdoor heat exchanger  30  is heated by being subject to heat exchange with outdoor air supplied from the outdoor fan  35 , and is evaporated, becoming low-pressure refrigerant. The low-pressure gas refrigerant coming out of the outdoor heat exchanger  30  passes via the four-way switching valve  15  and is sucked into the compressor  20  again. Basically, this is how the air conditioning apparatus heats indoors. 
     (2-3) Injection Control for Each Operation 
     During the cooling operation and during the heating operation, the control unit performs intermediate injection or suction injection, the object being to improve operating capacity or decrease the discharge temperature of the compressor  20 . Intermediate injection means that the refrigerant that has flowed into the common injection tube  202  from the heat exchanger for injection  264  and/or the high-pressure receiver  280 , flows through the intermediate injection channel  265  and is injected into the intermediate injection port  23  of the compressor  20 . Suction injection means that the refrigerant that has flowed into the common injection tube  202  from the heat exchanger for injection  264  and/or the high-pressure receiver  280 , is injected into the suction passage  27  by way of the suction injection channel  267  and caused to be sucked into the compressor  20 . Both intermediate injection and suction injection have the effect of decreasing the discharge temperature of the compressor  20 . Intermediate injection has the further effect of improving operating capacity. 
     The control unit performs injection control based on the rotational speed (or frequency) of the inverter controlled compressor  20 , the discharge temperature Tdi of refrigerant detected from the discharge temperature sensor  93  with respect to refrigerant discharged from the compressor  20 , and the temperature of injected refrigerant as detected by the injection temperature sensor  296  to the downstream side of the heat exchanger for injection  264 . Specifically, the control unit implements intermediate injection control that causes intermediate injection, or implements suction injection control that causes suction injection. Further, when the conditions are such that the control unit should not perform either intermediate injection or suction injection, neither form of injection is performed and operations are carried out in the non-injection condition. In other words, the control unit may selectively perform intermediate injection control, suction injection control, or non-injection control, in which neither form of injection is implemented. 
     The flow of injection control from the control unit will now be described with reference to  FIG. 6A  through  FIG. 6D . 
     Firstly, at step S 21 , the control unit determines whether the rotational speed of the compressor  20  is above or below a predetermined threshold. The predetermined threshold is set for example, at a significantly low rotational speed, a value below which a lower rotational speed could not be set, or, a value at which, were the rotational speed to be lowered even further, there would be a decrease in the efficiency of the compressor motor. 
     (2-3-1) Intermediate Injection Control 
     If the control unit determines at step S 21  that the rotational speed of the compressor  20  is greater than or equal to the threshold, the control unit transitions to step S 22  to determine whether the air conditioning apparatus is performing the cooling operation or the heating operation. In the case of the heating operation, intermediate injection is performed, that flows gas refrigerant taken from primarily the high-pressure receiver  280 , to the intermediate injection channel  265 . 
     (2-3-1-1) Intermediate Injection Control During Heating 
     If the determination at step S 22  is that the air conditioning apparatus is in the heating operation, the control unit transitions to step S 23  and determines whether or not the discharge temperature Tdi of refrigerant discharged from the compressor  20  as detected by the discharge temperature sensor  93 , is higher than the first upper limit value. The first upper limit value can be set at for example 95° C. If the discharge temperature is not higher than the first upper limit value, the control unit transitions to step S 24  and puts the intermediate injection switching valve  266  into the open condition and the suction injection switching valve  268  into the closed condition. If those valves are already in those respective conditions, the valves are maintained as they are. Further, at step S 24  the respective degrees of opening of the first electric injection valve  263  and the second bypass electric injection valve  284  are adjusted. As the discharge temperature Tdi is in the normal range, the opening of the first electric injection valve  263  is adjusted, in accordance with basic heating operation control, such that liquid refrigerant out from the high-pressure receiver  280  and flowing in the main refrigerant channel  211   a  reaches a predetermined degree of subcooling. Moreover, the opening of the second bypass electric injection valve  284  is adjusted such that the gas refrigerant in the high-pressure receiver  280 , flows to the intermediate injection channel  265 . On the other hand, if, at step S 23 , the control unit determines that the discharge temperature Tdi is higher than the first upper limit value, step S 25  is transitioned to. Here, as it is necessary to reduce the discharge temperature Tdi, the respective openings of the first electric injection valve  263  and the second bypass electric injection valve  284  are adjusted based on that discharge temperature Tdi. Specifically, at step S 25 , moisture control is performed that moistens gas refrigerant to be subject to intermediate injection such that the discharge temperature Tdi can be swiftly brought below the first upper limit value. That is, in order to raise the cooling effect of intermediate injection, the opening of the first electric injection valve  263  and the like is adjusted such that gas refrigerant for intermediate injection becomes gas-liquid, two-phase flash gas. 
     (2-3-1-2) Intermediate Injection Control During Cooling 
     If the determination at step S 22  is that the air conditioning apparatus is in the cooling operation, the control unit transitions to step S 26  and determines whether or not the discharge temperature Tdi is higher than the first upper limit value. If the discharge temperature Tdi is higher than the first upper limit value, the control unit transitions to step S 27 , and in order to perform moisture control that moistens gas refrigerant to be subject to intermediate injection, refrigerant flows from primarily the heat exchanger for injection  264  to the intermediate injection channel  265 . Specifically, at step S 27 , the intermediate injection switching valve  266  is put into the open condition and the suction injection switching valve  268  is put into the closed condition, further, the degree of opening of the first electric injection valve  263  is controlled based on the discharge temperature Tdi. Moreover, at step S 27 , the second bypass electric injection valve  284  is opened as required. At this step S 27 , moist gas refrigerant in a gas-liquid two-phase state from the heat exchanger for injection  264  is subject to intermediate injection to the compressor  20 , and the elevated discharge temperature Tdi can be expected to decrease rapidly. 
     At step S 26 , if the discharge temperature Tdi is lower than the first upper limit value the control unit determines there is no necessity to lower the discharge temperature Tdi, and intermediate injection is performed using both refrigerant from the high-pressure receiver  280  and refrigerant from the heat exchanger for injection  264 . Specifically, the system transitions via step S 28  or step S 29  to step S 30 , the intermediate injection switching valve  266  is put into the open condition, the suction injection switching valve  268  is put into the closed condition, moreover the degree of opening of the first electric injection valve  263  and the degree of opening of the second bypass electric injection valve  284  are adjusted. At step S 28  the control unit determines whether or not a high-pressure value of liquid refrigerant detected by the receiver outlet pressure sensor  292  at the outlet of the high-pressure receiver  280  is below a threshold value. This threshold value is an initially set value, based on for example the elevational difference (difference in the height of their respective places of installation) between the outdoor unit  211  and the indoor unit  12  of the air conditioning apparatus, and is set such that if the high-pressure value is lower than this threshold value, prior to passing through the indoor expansion valve  42  of the indoor unit  12 , the refrigerant would become refrigerant in a flash gas state and the sound of passing refrigerant would increase substantially. If it is determined at step S 28  that the high-pressure value is below the threshold value, as it is necessary to increase the high-pressure value, the outdoor expansion valve  41  in a state of being slightly constricted, is opened more, relieving the degree of depressurization by the outdoor expansion valve  41 . Thus, the gas component of refrigerant in the high-pressure receiver  280  is reduced, the quantity of gas refrigerant from the high-pressure receiver  280  comprising the total quantity of refrigerant for injection decreases, and the ratio of injection from the high-pressure receiver  280  becomes smaller. On the other hand, if at step S 28  the high-pressure value exceeds the threshold value, the system transitions to step S 30  maintaining that injection ratio. At step S 30 , in the same manner as above, the intermediate injection switching valve  266  is open, and both refrigerant flowing from the high-pressure receiver  280  and refrigerant flowing from the heat exchanger for injection  264  flow from the intermediate injection channel  265  to the intermediate injection port  23  of the compressor  20 . Moreover at step S 30  the degree of opening of the first electric injection valve  263  is adjusted based on the temperature Tsh of refrigerant used for injection, to the down flow side of the heat exchanger for injection  264 , further, based on the injection ratio, the opening of the second bypass electric injection valve  284  is adjusted in conjunction with the degree of opening of the outdoor expansion valve  41 . 
     (2-3-2) Control to Maintain Low Capacity 
     From step S 22  up to step S 30  above, relates to control when it is determined at step S 21  that the rotational speed of the compressor  20  is greater than or equal to the threshold value, however as there is room to drop the rotational speed of the compressor  20  further lowering capacity, basically improved operating capacity is achieved through injection. Accordingly, intermediate injection is selected and not suction injection. 
     However, if at step S 21  it is determined that the rotational speed of the compressor  20  is less than the threshold value, this means that the compressor  20  has already dropped to low capacity, and as raising the operating capacity right up would be contrary to the needs of users, control is implemented to maintain the capacity of the compressor  20  as it is, in that low capacity condition. 
     (2-3-2-1) Suction Injection Control 
     If at step S 21  it is determined that the rotational speed of the compressor  20  is below the threshold value, the control unit transitions to step S 31  and the determination is made whether or not the discharge temperature Tdi is higher than the first upper limit value. If the discharge temperature Tdi is higher than the first upper limit value, as it is needed to lower the discharge temperature Tdi, step S 33  or step S 34  is transitioned to, and suction injection is implemented. 
     (2-3-2-1-1) Suction Injection Control During the Heating Operation 
     If it is determined at step S 31  that the discharge temperature Tdi is higher than the first upper limit value, moreover at step S 32  it is determined that the heating operation is being performed, suction injection is performed in which primarily refrigerant from the high-pressure receiver  280  flows from the suction injection channel  267  to the suction passage  27 . Specifically, at step S 33 , the intermediate injection switching valve  266  is put into the closed condition and the suction injection switching valve  268  is put into the open condition. Then, based on the discharge temperature Tdi, the degree of opening of the second bypass electric injection valve  284  is adjusted such that gas refrigerant accumulated in the high-pressure receiver  280  in the heating operation flows mostly to the suction injection channel  267 , further, the degree of opening of the first electric injection valve  263  is adjusted such that refrigerant flowing from the heat exchanger for injection  264  to the suction injection channel  267  becomes flash gas. 
     (2-3-2-1-2) Suction Injection Control During the Cooling Operation 
     If it is determined at step S 31  that the discharge temperature Tdi is higher than the first upper limit value, moreover at step S 32  it is determined that the cooling operation is being performed, suction injection is performed in which primarily refrigerant from the heat exchanger for injection  264  flows to the suction injection channel  267 . Specifically, at step S 34 , the intermediate injection switching valve  266  is put into the closed condition and the suction injection switching valve  268  is put into the open condition. Then, based on the discharge temperature Tdi, the degree of opening of the first electric injection valve  263  is adjusted such that refrigerant flowing from the heat exchanger for injection  264  to the suction injection channel  267  becomes flash gas. Further at step S 34 , the second bypass electric injection valve  284  is opened as necessary. 
     (2-3-2-2) Non-Injection Control 
     If at step S 31  the discharge temperature Tdi is lower than the first upper limit value, it is determined that it is not necessary to reduce the discharge temperature Tdi, and the control unit selects the non-injection condition. That is, intermediate injection and suction injection in order to lower the discharge temperature Tdi and intermediate injection in order to improve operation capacity are not required, and as it is desirable to stop those forms of injection, the non-injection condition is implemented. At step S 35 , the control unit puts the intermediate injection switching valve  266  and the suction injection switching valve  268  into the closed condition, and adjusts the degree of opening of the first electric injection valve  263  and the degree of opening of the second bypass electric injection valve  284  to the minimum. When the minimum degree of opening is zero, the first electric injection valve  263  and the second electric injection valve  284  are in the completely closed condition. 
     Thus, in the air conditioning apparatus according to this second embodiment of the present invention, it is not necessary to lower the discharge temperature of the compressor  20  by intermediate injection or suction injection as the discharge temperature Tdi is low, moreover, in the case in which the rotational speed of the compressor  20  is decreased as low capacity is required, the non-injection control is selected and implemented. Thus, increase of capacity through intermediate injection or suction injection and the occurrence of decreased operating efficiency are minimized, and in this air conditioning apparatus according to the second embodiment, it is possible to maintain operating efficiency while satisfying the requirement of low capacity.