JP2004183913A - Air conditioner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air conditioner capable of developing sufficient heating capacity and high operating efficiency even if an outside air temperature is -10°C or under. <P>SOLUTION: This air conditioner comprises a low stage compressor allowing the regulation of rotational speed, a high stage compressor allowing the regulation of rotational speed independently of the low stage compressor, a condenser, a first pressure reducing device, and an evaporator which are connected to each other in order. An intercooler is installed between the condenser and the first pressure reducing device. Refrigerant flowing out of the condenser is branched, the refrigerant pressure-reduced to an intermediate pressure through a second pressure reducing device makes heat exchange in the intercooler and flows into the suction side of the high stage compressor to form a heat pump cycle. Thus, even when the outside air temperature is low, highly efficient heating operation can be performed. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an air heat source type heat pump air conditioner, and more particularly to an air conditioner that improves the heating capacity when the outside air temperature is low.
[0002]
[Prior art]
Normally, in cold regions where the outside air is below -10 ° C, heating is performed by the combustion heat of kerosene, gas and the like. This is because, in general, in the case of heat pump heating that obtains evaporation heat from the outside air, under a low outside air condition, the heating capacity becomes insufficient and the coefficient of performance (heating capacity / power consumption) decreases, and a satisfactory heating operation cannot be performed. However, since cooling using heat pumps is widely used in summer, there is a strong demand for air conditioning and cooling both by using heat pumps from the viewpoint of equipment costs and installation space for air conditioners. In order to meet this demand, various proposals for improving the heating capacity and the efficiency under low outside air conditions have been made.
[0003]
In a conventional air conditioner, a compressor having an injection port is used. During low outside air heating, the liquid refrigerant is injected during the compression process to increase the condenser-side refrigerant flow rate, thereby increasing heating capacity and improving operating efficiency. There are things. (For example, see Patent Document 1)
[0004]
In another conventional air conditioner, as a heat pump cycle for performing gas injection, two expansion valves are provided between a condenser and an evaporator, and a gas-liquid separator is provided between the expansion valves. In some cases, the gas refrigerant separated by the separator is injected during the compression process to increase the flow rate of the refrigerant. (For example, see Patent Document 2)
[0005]
[Patent Document 1]
JP-A-8-210709 (page 4-7, FIG. 2)
[Patent Document 2]
JP 2001-116373 A (pages 3-4, FIG. 1)
[0006]
[Problems to be solved by the invention]
However, when liquid refrigerant is injected into the compressor, the effect of improving the heating capacity by increasing the flow rate of the refrigerant is obtained.However, since the heat for evaporating the injected liquid refrigerant is provided by the compressor input, the operating efficiency is reduced. Occurs. Further, the refrigerant enthalpy difference on the evaporator side is exactly the same as the case where no injection is performed, and the amount of heat absorbed from the outside air cannot be improved.
[0007]
In the case of gas injection, since the refrigerant flowing to the evaporator side due to gas-liquid separation becomes a medium-pressure saturated liquid, the refrigerant is smaller than the refrigerant enthalpy at the outlet of the condenser, and the refrigerant enthalpy difference at the refrigerant inlet and outlet of the evaporator does not cause injection. Be larger. As a result, the amount of heat absorbed from the outside air can be increased, and the operation efficiency can be improved.However, a change in refrigerant circulation amount difference between the evaporator side and the condenser side occurs due to a change in compressor speed or load fluctuation. Then, the amount of refrigerant stored in the gas-liquid separator changes, and a large amount of liquid refrigerant may enter the liquid bag or the gas injection pipe. This becomes more remarkable when a refrigeration cycle is constituted by two compressors and the rotation speed is controlled independently of each other.
[0008]
When a non-azeotropic refrigerant mixture is used for gas injection, the concentration of the low-boiling-point refrigerant component in the gas phase in the gas-liquid separator is high, so that the low-boiling-point refrigerant concentration is high on the condenser side, while the evaporator side is high. , The high-boiling-point refrigerant concentration increases. Therefore, the density of the compressor suction gas flowing out of the evaporator decreases, and the amount of heat absorbed by the flow rate of the refrigerant becomes insufficient, resulting in a problem that the operation efficiency is reduced.
[0009]
Therefore, the present invention has been made to solve the above problems, and in a heat pump air conditioner using air as a heat source, sufficient heating capacity and high operating efficiency even when the outside air is -10 ° C or less. The aim is to obtain an air conditioner that can demonstrate
[0010]
[Means for Solving the Problems]
An air conditioner according to the present invention includes a low-stage compressor whose rotation speed can be adjusted, a high-stage compressor whose rotation speed can be adjusted independently of the low-stage compressor, a condenser, a first pressure reducing device, and an evaporator. In an air conditioner that forms a refrigeration cycle by sequentially connecting the condensers, an intercooler is provided between the condenser and the first decompression device, and the refrigerant that has flowed out of the condenser is branched and interposed through the second decompression device. The refrigerant depressurized to a pressure exchanges heat in the intercooler, and then flows into the suction side of the high-stage compressor.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
Hereinafter, an air conditioner according to Embodiment 1 of the present invention will be described with reference to FIGS.
FIG. 1 is a refrigerant circuit diagram showing a configuration of the air conditioner of the present invention. A plurality of indoor units are connected to the outdoor unit 1 in parallel via a liquid pipe 3 and a gas pipe 4. In this refrigeration cycle, R407C refrigerant (23 wt% of R32, 25 wt% of R125, and 52 wt% of R134a) is used as the refrigerant.
[0012]
The outdoor unit 1 has two compressors that are connected in series from the low-stage compressor 5 to the high-stage compressor 6 and that can independently adjust the rotation speed. In order to return oil separated from the oil separator 7 provided on the discharge side pipe between the high-stage compressor 6 and the four-way valve 9, an oil return pipe 8 connected from the lower part of the oil separator 7 is provided with a capillary. It is connected to the suction side of the low-stage compressor 5 via a pressure reducing means such as a tube. Further, the gas refrigerant compressed by the low-stage compressor 5 and the high-stage compressor 6 flows into the four-way valve 9 from the discharge pipe of the high-stage compressor 6 via the oil separator 7, from which the heating operation is performed. In this case, the gas flows to the indoor unit 2 via the gas pipe 4. On the other hand, during the cooling operation, the four-way valve 9 is switched (dotted line in FIG. 1), and the refrigerant is guided to the outdoor heat exchanger 10 which becomes an evaporator during the heating operation and a condenser during the cooling operation. The fourth pipe from the four-way valve 9 is connected to an accumulator 16 connected to the suction pipe of the low-stage compressor 5.
[0013]
A part of the mainstream refrigerant is branched into the refrigeration cycle liquid-side pipe of the outdoor unit 1 connected to the liquid-side pipe of the indoor unit 2 via the liquid pipe 3, and the branched flow is injected into a second decompression device, the injection expansion. An intercooler 11 that exchanges heat with a mainstream refrigerant via a valve 12 is provided. This intercooler 11 is constituted by, for example, a double tube heat exchanger. After the branched refrigerant is decompressed by the injection expansion valve 12, the refrigerant is returned from the intermediate pressure side pipe outlet of the intercooler 11 to the compressor through the injection pipe 15 connected to the suction of the high-stage compressor 6. Further, between the outdoor heat exchanger 10 and the intercooler 11, there is a motor-operated expansion valve 13 as a first pressure reducing device during heating and a check valve for preventing a flow from the intercooler 11 to the outdoor heat exchanger 10. 14 is installed and configured by parallel pipe connection. The accumulator 16 has a function of storing surplus refrigerant during a refrigeration cycle operation.
[0014]
The plurality of indoor units 2 are connected by pipes from the gas pipe 4 side, respectively. An indoor heat exchanger 18 that serves as a condenser during a heating operation and an evaporator during a cooling operation, and a flow control unit that is a first decompression device during cooling. The motor-operated expansion valve 17 is connected in series in order, and is connected to the liquid pipe 3 from the outdoor unit 1.
[0015]
In the air conditioner of the present embodiment configured as described above, it is possible to operate with sufficient heating capacity and a high coefficient of performance even in a low outside air condition where the outside air temperature is about −20 ° C. Hereinafter, the operation of the air conditioner during the heating operation will be described with reference to FIGS. 1 and 2. FIG. 2 is a Ph diagram showing the refrigeration cycle operation during the heating operation. The horizontal axis represents specific enthalpy [kJ / kg], and the vertical axis represents pressure [MPa]. The points A to J in the figure correspond to the points shown on the refrigerant circuit diagram in FIG.
[0016]
In the heating operation, the high-temperature and high-pressure gas refrigerant (state A) discharged from the high-stage compressor 6 is oil-separated by the oil separator 7 and then flows through the four-way valve 9 to the gas pipe 4 to be indoors. Unit 2 is reached. In the indoor heat exchanger 18, the high-temperature and high-pressure gas refrigerant radiates heat to indoor air to be condensed and liquefied, and becomes a high-pressure liquid refrigerant (state B). Then, the liquid refrigerant (state C), which has passed through the electric expansion valve 17 which is a flow control means controlled to be fully opened and has a slight pressure drop, flows out of the indoor unit 2 and passes through the liquid pipe 3 to the outdoor unit 1 again. And return.
[0017]
The high-pressure liquid refrigerant (state C) returned from the liquid pipe 3 connecting the indoor and outdoor units to the outdoor unit 1 passes through the intercooler 11, but a part of the refrigerant passes through the injection expansion valve 12 to the intermediate pressure. The state is reduced to a state H in which the gas-liquid two phases are mixed. In the intercooler 11, the high-pressure liquid refrigerant (state C) is in a state where the degree of supercooling is further increased (state D), flows to the electric expansion valve 13 which is a pressure reducing device, and becomes a low-pressure two-phase refrigerant (state E). . Then, the low-pressure two-phase refrigerant (state E) flows into the outdoor heat exchanger 10, absorbs heat from low-temperature outside air, evaporates, and becomes a low-pressure gas refrigerant (state F). This low-pressure gas refrigerant flows into the accumulator 16 via the four-way valve 9. When it flows out of the accumulator 16 and is sucked into the low-stage compressor 5, it merges with the refrigerating machine oil separated by the oil separator 7. The medium-pressure gas refrigerant pressurized and discharged by the low-stage compressor 5 (state G) merges with the medium-pressure two-phase refrigerant (state I) flowing from the intercooler 11, and a dry refrigerant before and after a saturated gas (state G). J), the air is sucked into the high-stage compressor 6, and the same cycle is repeated again to perform the heating operation under the low outside air condition.
[0018]
Here, in the air conditioner of the present embodiment, the points A, F, and I shown on the refrigerant circuit of FIG. 1, the state A (corresponding to the internal pressure of the condenser) of FIG. A pressure sensor for detecting the working refrigerant pressure in each of the state I (intermediate pressure in the injection circuit) and state I (intermediate pressure in the injection circuit) and a temperature sensor for detecting the working refrigerant temperature in state A (point A of the refrigerant circuit) are provided. (Not shown). In the operation state of the low-stage compressor 5 and the high-stage compressor 6, the respective rotation speeds are controlled by the detection values of the pressure sensors. For example, in the high-stage compressor 6, the discharge pressure is controlled to be a predetermined pressure, and in the low-stage compressor 5, the compression ratio on the lower stage is higher than that on the higher stage. On the other hand, the injection expansion valve 12 changes the current discharge temperature (detected value of the temperature sensor in the state A) to a target appropriate discharge temperature calculated from the pressures in the states A and I and the rotation speed of the high-stage compressor 6. The opening is controlled so as to approach.
[0019]
With the above operation, a predetermined heating capacity can be exhibited even when the outside air temperature is extremely low, such as about −20 ° C. In other words, when the outside air temperature becomes low, the evaporating pressure decreases, and in order to maintain the heating capacity, the compression ratio becomes abnormally large in the single-stage compression refrigeration cycle. Since the compressor is divided into two, a relatively high compression temperature can be obtained without abnormally increasing the compression ratio of each of the compressors in the lower stage and the higher stage, and the intercooler 11 is connected via the injection expansion valve 12. And heat exchange, thereby increasing the refrigerant flow rate in the high-stage compressor by the injection action of the high-dryness refrigerant, and enabling operation without abnormally increasing the discharge temperature.
[0020]
In the refrigeration cycle in which the liquid refrigerant is injected, the specific enthalpy of the refrigerant at the outlet of the condenser (state B) is equal to the specific enthalpy of the refrigerant at the inlet of the evaporator (state E). Since the difference in evaporator enthalpy can be increased by heat exchange in the intercooler, the amount of heat that can absorb heat from the outside air can be increased, and the heating capacity can be increased and the operation efficiency can be improved.
[0021]
In a gas injection cycle using a gas-liquid separator having an intermediate pressure, the gas phase in the gas-liquid separator has a large amount of low-boiling-point refrigerant (R32, R125) components, and the liquid phase has a large amount of a high-boiling-point refrigerant (R134a) component. Thus, the R134a-rich refrigerant flows into the evaporator. Since the gas density of R134a at the same temperature is smaller than that of R407C, in order to obtain the same evaporating capacity, when the refrigerant temperature is the same, the R134a-rich gas has a lower low pressure, the operating differential pressure of the compressor increases, and the COP deteriorates. . However, in the present invention, since the gas-liquid separation at the intermediate pressure is not performed, there is no change in the refrigerant composition on the high stage side and the low stage side, and such a problem does not occur.
[0022]
Furthermore, in the gas injection cycle, when the load fluctuates or the compressor speed changes, the imbalance occurs between the flow rates of the low-stage and high-stage compressors and the ratio of gas to liquid flowing out of the gas-liquid separator. While the liquid level in the liquid separator becomes unstable, in the present invention, the main pressure reducing means between the condensing side and the evaporating side of the refrigeration cycle is one expansion valve (expansion valve 17 during heating). Since a two-stage compression injection circuit using the intercooler 11 and the injection expansion valve 12 is formed, such a problem does not occur.
[0023]
At this time, the rotation speed of the low-stage compressor 5 is controlled so as to have a higher compression ratio than that of the high-stage compressor 6. By doing so, the oil discharge amount of the low-stage compressor 5 becomes larger than the oil discharge amount of the high-stage compressor 6, and as a result, more oil than the discharge amount of the high-stage compressor 6 becomes lower. It is supplied from the stage compressor 5. In the low-stage compressor 5, the refrigerating machine oil discharged from the high-stage compressor 6 and separated from the refrigerant by the oil separator 7 is supplied from the oil return pipe 8 to the suction side. The operation can be performed without a significant decrease.
[0024]
Further, since the low-stage compressor 5 has the same suction volume as the high-stage compressor 6, the low-stage compressor 5 having a smaller suction gas refrigerant density has a larger rotation speed than the high-stage compressor 6. Driven by numbers. The different rotational speeds are controlled on the higher stage side according to the required capacity required by the indoor unit, for example, according to the difference between the target indoor temperature and the actual indoor temperature. On the other hand, since the intermediate pressure is determined by the balance between the compressor speed on the high stage side and the compressor speed on the low stage side, the rotational speed is controlled so that the compression ratio is higher on the lower stage than on the higher stage. For example, as shown in FIG. 3, the compression ratio (intermediate pressure / evaporation pressure) on the lower stage is adjusted so as to increase as the overall compression ratio (condensation pressure / evaporation pressure) increases. FIG. 3 is a graph of the high-stage low-stage compression ratio showing the operation control state of the air conditioner, in which the horizontal axis represents the overall compression ratio of the air conditioner, the vertical axis represents the high-stage and low-stage compression ratios, and the solid line represents the solid line. The low-stage compression ratio and the dotted line indicate the high-stage compression ratio.
[0025]
However, this does not apply if the required heating capacity cannot be obtained even when the rotation speed of the low-stage compressor reaches the upper limit. The high-stage compressor 6 is operated so as to obtain a large capacity without maintaining the relationship as shown in FIG. In other words, the rotational speed control of the compressor is switched from efficiency priority to capacity priority.
[0026]
Up to this point, the operation during the heating operation has been described. Next, the operation during the cooling operation will be described with reference to FIGS. 1 and 4. In the cooling operation, the four-way valve 9 is switched in the direction of the dashed line, and the gas refrigerant (state A) discharged from the high-stage compressor 6 radiates heat to the outside air in the outdoor heat exchanger 10 to condense, and the liquid refrigerant ( State E) is reached and flows through the check valve 14. The high-pressure liquid refrigerant is branched from the outlet thereof in the intercooler 11, exchanges heat with the refrigerant (state H) depressurized to the intermediate pressure by the electric expansion valve 12, and further increases the degree of supercooling (state C). ) And flows to the indoor unit 2 via the liquid pipe 3.
[0027]
The high-pressure two-phase refrigerant (state C) is decompressed by the electric expansion valve 17 in the indoor unit 2, becomes a low-pressure two-phase refrigerant (state B), and flows into the indoor heat exchanger 18. Here, heat is absorbed from the indoor air, evaporated and changed to a low-pressure gas refrigerant (state F), and returns to the outdoor unit 1 again. In the outdoor unit 1, the air flows through the four-way valve 9 to the accumulator 16, is drawn into the low-stage compressor 5, and is compressed to an intermediate pressure. The medium-pressure superheated gas refrigerant (state G) merges with the medium-pressure two-phase refrigerant (state I) flowing from the injection pipe 15 to become a gas refrigerant having a dryness of about 1 and sucked into the high-stage compressor 6 again. Is done.
[0028]
Here, in order to increase the efficiency in the cooling operation, it is important to increase the degree of supercooling of the refrigerant state C at the outlet of the intercooler 11 from the outdoor heat exchanger 10 to the indoor heat exchanger 18 as much as possible. is there. This is because the enthalpy difference between the refrigerant state B at the evaporator inlet and the refrigerant state F at the evaporator outlet becomes large, and when compared with the same cooling capacity, the flow rate of the refrigerant flowing to the indoor unit 2 becomes small. This is because the pressure loss on the low pressure side due to the four-way valve 9 is suppressed, and highly efficient operation can be performed. Therefore, the intermediate pressure in the cooling operation is different from that in the low-temperature heating operation, and the compressor speed of each of the high and low stages is controlled so that the low-stage side compression ratio becomes small.
[0029]
However, this does not apply to the case where the outside air is abnormally high in the cooling operation, or under the operating load condition where the evaporation temperature is abnormally lowered. Eventually, the compressor speed is controlled so as to have a relationship between the overall compression ratio and the low-stage and high-stage compression ratios shown in FIG.
[0030]
Embodiment 2 FIG.
Embodiment 2 of the present invention will be described with reference to FIG.
FIG. 5 is a refrigerant circuit diagram showing a configuration of the air conditioner. In the figure, reference numeral 19 denotes a low-pressure shell-type high-stage compressor having an oil separation function, which corresponds to the configuration in which the oil separator 7 is provided in the middle of the outlet pipe of the high-stage compressor 6 in FIG. are doing. The same or corresponding parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. Note that the indoor unit side connected to the liquid pipe 3 and the gas pipe 4 is completely the same as in the first embodiment, and is not shown.
[0031]
Next, the operation will be described. The low-stage compressor 5 draws low-pressure gas refrigerant from the accumulator 16, compresses it to an intermediate pressure, and discharges it. This discharge gas merges with the medium-pressure two-phase refrigerant flowing out from the intermediate pressure side that has passed through the injection electric expansion valve 12 of the intercooler 11, and flows into the high-stage compressor 19 in a state close to a saturated gas. The high-stage compressor 19 is of a low-pressure shell type, and the inside of this container is filled with medium-pressure gas. Refrigeration oil is stored at the bottom of the compressor shell. An oil return pipe 8 is attached to the shell at a predetermined oil level of the high-pressure side compressor 19, and when the oil level becomes higher than this level, the oil return pipe 8 is connected to the lower stage side through the oil return pipe 8. The refrigerating machine oil stored in the suction side of the compressor 5 is returned.
[0032]
Also, as described above, since the rotation speed is controlled so that the oil discharge amount of the low-stage compressor 5 is always larger than the oil discharge amount of the high-stage compressor 19, the oil level of the high-stage compressor 19 decreases. Also, when the oil level of the high-stage compressor 19 is higher than a predetermined level, the oil is directly supplied to the low-stage compressor 5, so that the oil level of the low-stage compressor does not drop below a predetermined level. .
[0033]
With such a configuration, it is possible to secure the oil levels of the high-stage compressor and the low-stage compressor without separately installing an oil separator, so that the cost can be reduced.
[0034]
【The invention's effect】
As described above, the air conditioner according to the present invention includes a low-stage compressor whose rotation speed can be adjusted, a high-stage compressor whose rotation speed can be adjusted independently of the low-stage compressor, a condenser, In an air conditioner that forms a refrigeration cycle by sequentially connecting a decompression device and an evaporator, an intercooler is provided between the condenser and the first decompression device, and the refrigerant flowing out of the condenser is branched to form a second decompression device. After the refrigerant decompressed to the intermediate pressure via the intercooler exchanges heat with the intercooler, it flows into the suction side of the high-stage compressor, so that the difference in evaporator enthalpy can be made larger than in the liquid injection cycle, thereby lowering the outside air temperature. It is possible to perform a high-efficiency heating operation even at the time, and, unlike gas injection, even if a non-azeotropic refrigerant mixture is used, the high-boiling-point refrigerant composition of the refrigerant drawn into the low-stage compressor increases. And high-efficiency operation It can be carried out. Furthermore, since a gas-liquid separator is not used, an air conditioner that can operate stably even when the refrigerant distribution in the refrigeration cycle has a load change or the like can be obtained.
[0035]
Further, since the working fluid enclosed in the refrigeration cycle is a mixture of two or more types of refrigerant, it is possible to avoid insufficient evaporation capacity due to a change in the composition of the circulating refrigerant generated in the gas injection cycle by the gas-liquid separator, Time capacity and operation efficiency can be improved.
[0036]
Further, since the pressure reduction amount of the second pressure reducing device is adjusted so that the discharge temperature of the high-stage compressor becomes the target discharge temperature, an abnormal increase in the discharge temperature of the high-stage compressor can be prevented.
[0037]
In addition, since the low-stage compressor has the same suction volume as the high-stage compressor, it must be operated at an appropriate intermediate pressure during both high compression ratio operation during low-temperature heating and during cooling operation at a relatively low compression ratio. Can be.
[0038]
An oil separator is installed between the high-stage compressor and the condenser, and the oil return pipe is connected to the suction side of the low-stage compressor, so both the low-stage compressor and the high-stage compressor are required. Refrigerator oil can be secured.
[0039]
Also, the high-stage compressor is a low-pressure shell-type compressor, which has an oil return pipe at a predetermined oil level of the compressor shell and is connected to the suction side of the low-stage compressor. The required amount of refrigerating machine oil can be secured for both the low-stage compressor and the high-stage compressor without providing a separator, and a low-cost air conditioner can be obtained.
[0040]
In addition, the air conditioner includes condensing pressure detecting means, evaporating pressure detecting means, and intermediate pressure detecting means, and is operated such that the compression ratio of the low-stage compressor is smaller than the compression ratio of the high-stage compressor during the cooling operation. During the heating operation, the operation is performed such that the compression ratio of the low-stage compressor is higher than the compression ratio of the high-stage compressor, so that cooling and heating can be realized with high operation efficiency both in the low compression ratio operation and in the high compression operation.
[Brief description of the drawings]
FIG. 1 is a refrigerant circuit diagram of an air conditioner according to Embodiment 1 of the present invention.
FIG. 2 is a Ph diagram showing a heating operation of the air conditioner according to Embodiment 1 of the present invention.
FIG. 3 is a graph of a high-stage low-stage compression ratio showing an operation control state of the air conditioner according to Embodiment 1 of the present invention.
FIG. 4 is a Ph diagram showing a cooling operation of the air conditioner according to Embodiment 1 of the present invention.
FIG. 5 is a refrigerant circuit diagram of an air conditioner according to Embodiment 2 of the present invention.
[Explanation of symbols]
1 outdoor unit, 2 indoor unit, 3 liquid pipe, 4 gas pipe, 5 low-stage compressor, 6 high-stage compressor, 7 oil separator, 8 oil return pipe, 9 four-way valve, 10 outdoor heat exchanger, 11 intermediate Cooler, 12, 13 Electric expansion valve, 14 Check valve, 15 Injection pipe, 16 Accumulator, 17 Electric expansion valve, 18 Indoor heat exchanger, 19 Low pressure shell type high stage compressor.

Claims (7)

A refrigeration cycle by sequentially connecting a low-stage compressor whose rotation speed is adjustable, a high-stage compressor whose rotation speed is adjustable independently of the low-stage compressor, a condenser, a first pressure reducing device, and an evaporator. In the air conditioner to be configured, an intermediate cooler is provided between the condenser and the first decompression device, and the refrigerant that has flowed out of the condenser and that has been decompressed to an intermediate pressure through the second decompression device is provided. An air conditioner characterized by flowing into the suction side of the high stage compressor after heat exchange in the intercooler. The air conditioner according to claim 1, wherein the working fluid sealed in the refrigeration cycle is a mixed refrigerant of two or more types. Discharge temperature detecting means for detecting the discharge temperature of the high-stage compressor, high / low pressure detecting means for detecting the temperature or pressure of the condenser and the evaporator, and a target based on information obtained by the detecting means. Calculating means for calculating a discharge temperature, wherein the pressure reducing amount of the second pressure reducing device is adjusted so that the discharge temperature detected by the discharge temperature detecting means becomes the target discharge temperature. Or the air conditioner according to claim 2. 4. The air conditioner according to claim 1, wherein a suction volume of the low-stage compressor is equal to that of the high-stage compressor. 5. An oil separator is provided between the high-stage compressor and the condenser, and an oil return pipe is connected to return the refrigerating machine oil separated by the oil separator to the suction side of the low-stage compressor. The air conditioner according to any one of claims 1 to 4, wherein The high-stage compressor is a low-pressure shell-type compressor that fills a shell with a suction refrigerant, and has an oil return pipe at a predetermined oil level of the shell. The air conditioner according to any one of claims 1 to 4, wherein the air conditioner is connected to a suction side of a side compressor. High pressure detection means for detecting the condensation pressure in the condenser, low pressure detection means for detecting the evaporation pressure in the evaporator, and medium pressure detection means for detecting the intermediate pressure; Operating so that the compression ratio of the high-stage compressor becomes smaller than the compression ratio of the high-stage compressor, and operating during the heating operation so that the compression ratio of the low-stage compressor becomes larger than the compression ratio of the high-stage compressor. The air conditioner according to any one of claims 1 to 6, wherein:

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