JP7268773B2 - air conditioner - Google Patents

Description

TECHNICAL FIELD The present invention relates to an air conditioner, and more particularly to an air conditioner provided with a gas-liquid separator on the high pressure side.

Some air conditioners have a gas-liquid separator in a liquid pipe that connects an outdoor heat exchanger of an outdoor unit and an indoor heat exchanger of an indoor unit (for example, Patent Document 1). In such an air conditioner, gas-liquid two-phase refrigerant (refrigerant in a state where gas refrigerant and liquid refrigerant are mixed) that flows from the indoor unit to the outdoor unit during heating operation flows through the liquid pipe to the gas-liquid separator. and separated into gas refrigerant and liquid refrigerant by the gas-liquid separator. Then, the separated liquid refrigerant flows out from the gas-liquid separator into the liquid pipe and flows to the outdoor heat exchanger. Also, the separated gas refrigerant flows out from the gas-liquid separator and flows to the compressor via the suction pipe.

By the way, in recent years, from the viewpoint of prevention of global warming, a refrigerant with a small global warming potential, for example, R32 refrigerant, is filled in the refrigerant circuit. However, since these refrigerants are combustible refrigerants, the amount of refrigerant charged into the refrigerant circuit is reduced in order to reduce the amount of leakage when the refrigerant leaks from the refrigerant circuit.

JP 2004-278825 A

In the air conditioner provided with the gas-liquid separator described above, the refrigerant that flows from the gas-liquid separator to the outdoor heat exchanger during heating operation is liquid refrigerant. At this time, if the refrigerant flowing out of the gas-liquid separator is a saturated liquid (a state in which gas refrigerant is not mixed), the refrigerant pipe between the liquid refrigerant outlet of the gas-liquid separator and the outdoor heat exchanger is liquid. It will be filled with refrigerant. If such an air conditioner is filled with a combustible refrigerant with a low global warming potential and the filling amount is reduced, the refrigerant piping between the liquid refrigerant outlet of the gas-liquid separator and the outdoor heat exchanger during heating operation is filled with liquid refrigerant, compared to the case where the refrigerant pipe is filled with gas-liquid two-phase refrigerant, the condensation capacity of the indoor heat exchanger functioning as a condenser is reduced and the heating capacity is reduced. I was afraid to.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems, and to provide an air conditioner in which the heating capacity does not decrease during heating operation even if the amount of refrigerant charged is reduced.

In order to solve the above problems, the air conditioner of the present invention comprises a compressor, an indoor heat exchanger, a first expansion valve, a gas-liquid separator, a second expansion valve, and an outdoor heat exchanger in this order during heating operation. It has a refrigerant circuit through which refrigerant circulates, and a bypass pipe that is provided with a third expansion valve and guides the refrigerant from the gas-liquid separator to the compressor. The degree of opening of the first expansion valve is adjusted so that the temperature difference between the temperature of the refrigerant flowing into the second expansion valve and the temperature of the refrigerant flowing out of the second expansion valve becomes a predetermined target value. The degree of opening of the valve is adjusted so that the discharge temperature, which is the temperature of the refrigerant discharged from the compressor, reaches a predetermined target temperature. The refrigerant that is adjusted to be a gas refrigerant and flows out from the second expansion valve is a gas-liquid two-phase refrigerant having a high ratio of liquid refrigerant to gas refrigerant.

According to the air conditioner of the present invention configured as described above, the refrigerant that flows out of the gas-liquid separator and flows to the outdoor heat exchanger during heating operation is a gas-liquid two-phase refrigerant having a high ratio of liquid refrigerant to gas refrigerant. It can be used as a refrigerant. As a result, even if the amount of refrigerant charged is reduced, it is possible to suppress a decrease in the condensation capacity of the indoor heat exchanger that functions as a condenser during heating operation, thereby suppressing a decrease in the heating capacity.

1 is a refrigerant circuit diagram of an air conditioner in an embodiment of the present invention; FIG. FIG. 3 is a Mollier diagram showing a refrigeration cycle during heating operation in the embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. As an embodiment, an air conditioner in which one outdoor unit and one indoor unit are connected by two refrigerant pipes will be described as an example. The present invention is not limited to the following embodiments, and various modifications can be made without departing from the gist of the present invention.

As shown in FIG. 1, an air conditioner 1 in this embodiment includes an outdoor unit 2 installed outdoors, and an indoor unit 3 installed indoors and connected to the outdoor unit 2 by a liquid pipe 4 and a gas pipe 5. I have. Specifically, the closing valve 25 of the outdoor unit 2 and the liquid pipe connection portion 33 of the indoor unit 3 are connected by the liquid pipe 4 . Also, the closing valve 26 of the outdoor unit 2 and the gas pipe connection portion 34 of the indoor unit 3 are connected by the gas pipe 5 . As described above, the refrigerant circuit 10 of the air conditioner 1 is formed.

<Configuration of outdoor unit>
First, the outdoor unit 2 will be explained. The outdoor unit 2 includes a compressor 21, a four-way valve 22, an outdoor heat exchanger 23, an outdoor fan 24, a closing valve 25 to which one end of the liquid pipe 4 is connected, and one end of the gas pipe 5. A closing valve 26, a first expansion valve 27a, a second expansion valve 27b, a third expansion valve 27c, a gas-liquid separator 28, an on-off valve 29, a first check valve 30a, and a second check and a valve 30b. These devices other than the outdoor fan 24 are connected to each other by refrigerant pipes, which will be described in detail below, to form an outdoor unit refrigerant circuit 10a forming a part of the refrigerant circuit 10. FIG.

The compressor 21 is a variable capacity compressor whose operating capacity can be changed by controlling the rotation speed by an inverter (not shown). A refrigerant discharge side of the compressor 21 and the port a of the four-way valve 22 are connected by a discharge pipe 61 . A refrigerant suction side of the compressor 21 and the port c of the four-way valve 22 are connected by a suction pipe 66 .

The four-way valve 22 is a valve for switching the direction of refrigerant flow, and has four ports a, b, c, and d. The port a is connected to the refrigerant discharge side of the compressor 21 by the discharge pipe 61 as described above. The port b is connected to one refrigerant inlet/outlet of the outdoor heat exchanger 23 by a refrigerant pipe 62 . The port c is connected to the refrigerant suction side of the compressor 21 by the suction pipe 66 as described above. The port d is connected to the closing valve 26 and the outdoor unit gas pipe 64 .

The outdoor heat exchanger 23 exchanges heat between the refrigerant and outside air taken into the outdoor unit 2 by the rotation of the outdoor fan 24, which will be described later. One refrigerant inlet/outlet of the outdoor heat exchanger 23 is connected to the port b of the four-way valve 22 by the refrigerant pipe 62 as described above, and the other refrigerant inlet/outlet is connected to the shutoff valve 25 by the outdoor unit liquid pipe 63. The outdoor heat exchanger 23 functions as a condenser when the air conditioner 1 performs the cooling operation, and functions as an evaporator when the air conditioner 1 performs the heating operation.

The first expansion valve 27 a is an electronic expansion valve, for example, and is provided in the outdoor unit liquid pipe 63 . The amount of refrigerant flowing through the indoor unit 3 is adjusted by adjusting the opening degree of the first expansion valve 27a. A specific method for adjusting the degree of opening of the first expansion valve 27a will be described later.

The outdoor fan 24 is made of a resin material and arranged near the outdoor heat exchanger 23 . The outdoor fan 24 is rotated by a fan motor (not shown) to take outside air into the outdoor unit 2 from a suction port (not shown) of the outdoor unit 2, and heat-exchanged with the refrigerant in the outdoor heat exchanger 23. It is discharged to the outside of the outdoor unit 2 from an air outlet (not shown).

The gas-liquid separator 28 is a substantially cylindrical closed container, and separates the inflowing gas-liquid two-phase refrigerant into a gas refrigerant and a liquid refrigerant. A first liquid branch pipe 67 connects between the refrigerant inlet provided on the top surface of the sealed container of the gas-liquid separator 28 and the outdoor heat exchanger 23 and the first expansion valve 27a in the outdoor unit liquid pipe 63. During heating operation, a gas-liquid two-phase refrigerant flows into the gas-liquid separator 28 from the first liquid branch pipe 67 . In addition, the liquid refrigerant outlet provided on the lower side of the sealed container of the gas-liquid separator 28 and the connection between the first liquid branch pipe 67 and the outdoor heat exchanger 23 in the outdoor unit liquid pipe 63 are the second liquid. They are connected by a branch pipe 68 , and the liquid refrigerant separated by the gas-liquid separator 28 and collected at the bottom of the sealed container flows out to the second liquid branch pipe 68 . A gas refrigerant outlet provided on the bottom surface of the gas-liquid separator 28 and the intake pipe 66 are connected by a bypass pipe 69, and the gas refrigerant separated by the gas-liquid separator 28 flows out to the bypass pipe 69. do. A part of the bypass pipe 69 is inserted into the gas-liquid separator 28 through the gas refrigerant outlet, and the end of the bypass pipe 69 that opens inside the gas-liquid separator 28 extends from the liquid refrigerant outlet. is placed at a higher position.

The on-off valve 29 is provided in the first liquid branch pipe 67 . The on-off valve 29 is closed during cooling operation and opened during heating operation. The first check valve 30a is provided between the connecting portion of the first liquid branch pipe 67 and the connecting portion of the second liquid branch pipe 68 in the outdoor unit liquid pipe 63, and connects the outdoor unit liquid pipe 63 to the outdoor heat exchanger. 23 to the first expansion valve 27a. The second check valve 30b is provided in the second liquid branch pipe 68, and allows the refrigerant to flow through the second liquid branch pipe 68 only in the direction from the gas-liquid separator 28 to the outdoor unit liquid pipe 63. .

The second expansion valve 27b is, for example, an electronic expansion valve, is provided between the liquid refrigerant outlet of the gas-liquid separator 28 in the second liquid branch pipe 68 and the second check valve 30b, and It is arranged in the vicinity of the 28 liquid refrigerant outlet. By adjusting the degree of opening of the second expansion valve 27b, the amount of liquid refrigerant flowing from the gas-liquid separator 28 to the outdoor unit liquid pipe 63 is adjusted. The third expansion valve 27 c is, for example, an electronic expansion valve, is provided in the bypass pipe 69 and is arranged near the gas refrigerant outlet of the gas-liquid separator 28 . By adjusting the degree of opening of the third expansion valve 27c, the amount of gas refrigerant flowing from the gas-liquid separator 28 to the suction pipe 66 is adjusted. A specific method for adjusting the degree of opening of each of the second expansion valve 27b and the third expansion valve 27c will be described later.

In addition to the configuration described above, the outdoor unit 2 is provided with various sensors. As shown in FIG. 1, the discharge pipe 61 has a discharge pressure sensor 71 for detecting the pressure of the refrigerant discharged from the compressor 21 and a discharge temperature sensor 73 for detecting the temperature of the refrigerant discharged from the compressor 21. is provided. The suction pipe 66 is provided with a suction temperature sensor 74 that detects the temperature of the refrigerant sucked into the compressor 21 .

A heat exchanger temperature sensor 75 for detecting the temperature of the refrigerant flowing through the intermediate portion of the refrigerant flow path, that is, the temperature of the outdoor heat exchanger 23 is provided in the middle portion of the refrigerant flow path (not shown) of the outdoor heat exchanger 23. ing. An outside air temperature sensor 76 for detecting the temperature of the outside air flowing into the inside of the outdoor unit 2, ie, the outside air temperature, is provided near the suction port (not shown) of the outdoor unit 2 .

Between the gas-liquid separator 28 and the second expansion valve 27b in the second liquid branch pipe 68, the outflow liquid refrigerant temperature, which is the temperature of the liquid refrigerant flowing out from the gas-liquid separator 28 to the second liquid branch pipe 68, is detected. An effluent coolant temperature sensor 78 is provided. At the refrigerant outlet side of the third expansion valve 27c in the bypass pipe 69, the outflow gas refrigerant pressure, which is the pressure of the gas refrigerant that flows out from the gas-liquid separator 28 to the bypass pipe 69 and is decompressed by the third expansion valve 27c, is detected. An outflow gas refrigerant pressure sensor 72 and an outflow gas refrigerant temperature sensor 78 that detects the outflow gas refrigerant temperature, which is the temperature of the gas refrigerant that has flowed out of the gas-liquid separator 28 into the bypass pipe 69 and has been decompressed by the third expansion valve 27c. are provided.

<Indoor unit configuration>
Next, the indoor unit 3 will be described with reference to FIG. The indoor unit 3 includes an indoor heat exchanger 31, an indoor fan 32, a liquid pipe connection portion 33 to which the other end of the liquid pipe 4 is connected, and a gas pipe connection portion 34 to which the other end of the gas pipe 5 is connected. I have it. These devices other than the indoor fan 32 are connected to each other by refrigerant pipes, which will be described in detail below, to form an indoor unit refrigerant circuit 10b forming a part of the refrigerant circuit 10. FIG.

The indoor heat exchanger 31 exchanges heat between a refrigerant and indoor air taken into the interior of the indoor unit 3 from a suction port (not shown) of the indoor unit 3 by rotation of an indoor fan 32, which will be described later. The entrance/exit is connected to the liquid pipe connection portion 33 by the indoor unit liquid pipe 91 , and the other refrigerant entrance/exit is connected to the gas pipe connection portion 34 by the indoor unit gas pipe 92 . The indoor heat exchanger 31 functions as an evaporator when the air conditioner 1 performs the cooling operation, and functions as a condenser when the air conditioner 1 performs the heating operation. At the liquid pipe connection portion 33 and the gas pipe connection portion 34, each refrigerant pipe is connected by welding, a flare nut, or the like.

The indoor fan 32 is made of a resin material and arranged near the indoor heat exchanger 31 . The indoor fan 31 is rotated by a fan motor (not shown) to take indoor air into the interior of the indoor unit 3 from a suction port (not shown) of the indoor unit 3, and heat-exchange the indoor air with the refrigerant in the indoor heat exchanger 31. It blows into the room from the air outlet (not shown) of the machine 3 .

In addition to the configuration described above, the indoor unit 3 is provided with various sensors. The indoor unit liquid pipe 91 is provided with a liquid side temperature sensor 81 that detects the temperature of the refrigerant flowing into or out of the indoor heat exchanger 31 . The indoor unit gas pipe 92 is provided with a gas-side temperature sensor 82 that detects the temperature of the refrigerant flowing out of or flowing into the indoor heat exchanger 31 . A room temperature sensor 83 for detecting the temperature of indoor air flowing into the interior of the indoor unit 3, that is, the room temperature, is provided near the suction port (not shown) of the indoor unit 3 .

<Operation of refrigerant circuit>
Next, the flow of the refrigerant in the refrigerant circuit 10 and the operation of each part during the air conditioning operation of the air conditioner 1 according to the present embodiment will be described. In the following description, first, the case where the indoor unit 3 performs the cooling operation will be described using FIG. 1, and then the case where the indoor unit 3 performs the heating operation will be described using FIGS. 1 and 2. FIG.

<Behavior of the refrigerant circuit during cooling operation>
When the air conditioner 1 performs a cooling operation, the refrigerant circuit 10 is arranged such that the four-way valve 22 is in a state indicated by a broken line as shown in FIG. Switching is performed so that port c and port d communicate. As a result, the refrigerant circulates in the direction indicated by the dashed arrow in the refrigerant circuit 10, forming a cooling cycle in which the outdoor heat exchanger 23 functions as a condenser and the indoor heat exchanger 31 functions as an evaporator. As described above, the on-off valve 29 is closed during the cooling operation. Both the second expansion valve 27b and the third expansion valve 27c are fully opened.

The high-pressure refrigerant discharged from the compressor 21 flows through the discharge pipe 61 into the four-way valve 22 , flows from the four-way valve 22 through the refrigerant pipe 62 , and flows into the outdoor heat exchanger 23 . The refrigerant that has flowed into the outdoor heat exchanger 23 exchanges heat with the outside air taken into the outdoor unit 2 by the rotation of the outdoor fan 24, and is condensed.

The refrigerant flowing out from the outdoor heat exchanger 23 to the outdoor unit liquid pipe 63 passes through the first check valve 30a and flows to the first expansion valve 27a. At this time, the refrigerant that has flowed out from the outdoor heat exchanger 23 to the outdoor unit liquid pipe 63 does not flow to the second liquid branch pipe 68 due to the second check valve 30b. Further, since the on-off valve 29 is closed, the refrigerant that has flowed out from the outdoor heat exchanger 23 to the outdoor unit liquid pipe 63 does not flow to the first liquid branch pipe 67 .

The opening of the first expansion valve 27a is adjusted so that the discharge temperature detected by the discharge temperature sensor 73 reaches a predetermined target temperature according to the outside air temperature and the cooling capacity required by the indoor unit 3. there is Specifically, when the detected discharge temperature is higher than the target temperature, the degree of opening of the first expansion valve 27a is made larger than the current degree of opening. By increasing the opening degree of the first expansion valve 27a, the amount of refrigerant returning from the refrigerant circuit 10 to the compressor 21 increases, and the discharge temperature decreases. On the other hand, when the detected discharge temperature is lower than the target temperature, the degree of opening of the first expansion valve 27a is made smaller than the present degree of opening. The discharge temperature rises by reducing the degree of opening of the first expansion valve 27a. The refrigerant decompressed when passing through the first expansion valve 27 a flows through the outdoor unit liquid pipe 63 and flows out to the liquid pipe 4 via the closing valve 25 . The refrigerant that has flowed through the liquid pipe 4 and flowed into the indoor unit 3 via the liquid pipe connection portion 33 flows through the indoor unit liquid pipe 91 and flows into the indoor heat exchanger 31 .

The refrigerant that has flowed into the indoor heat exchanger 31 exchanges heat with the indoor air taken into the indoor unit 3 by the rotation of the indoor fan 32 and evaporates. In this way, the indoor heat exchanger 31 functions as an evaporator, and in the case of cooling operation, the indoor air that has undergone heat exchange with the refrigerant in the indoor heat exchanger 31 is blown into the room from an outlet (not shown). , the room in which the indoor unit 3 is installed is cooled.

The refrigerant flowing out of the indoor heat exchanger 31 flows through the indoor unit gas pipe 92 and flows out to the gas pipe 5 via the gas pipe connecting portion 34 . The refrigerant flowing through the gas pipe 5 and into the outdoor unit 2 through the closing valve 26 flows through the outdoor unit gas pipe 64, the four-way valve 22, and the suction pipe 66, is sucked into the compressor 21, and is compressed again.

<Behavior of the refrigerant circuit during heating operation>
Next, the operation of the refrigerant circuit 10 during heating operation will be described with reference to FIGS. 1 and 2. FIG. As described above, the on-off valve 29 is opened during the heating operation. In the Mollier diagram shown in FIG. 2, the vertical axis is pressure (unit: MPa), the horizontal axis is specific enthalpy (unit: kJ / kg), the condensation pressure is Ph (MPa), and the evaporation pressure is Pl (MPa). In this Mollier diagram, points A to G shown on the diagram respectively correspond to the states of the refrigerant at points A to G shown in the refrigerant circuit 10 of FIG. The point X is a critical point on the saturation curve. The saturated liquid line is on the side of the point X with a smaller specific enthalpy, and the saturated vapor line is on the side of the point X with a larger specific enthalpy. Point Y is the point on the saturated steam line where the specific enthalpy changes with respect to the pressure change. Specifically, when the pressure is higher than point Y, the specific enthalpy decreases as the pressure increases. , when the pressure is lower than point Y, the lower the pressure, the lower the specific enthalpy.

When the indoor unit 3 performs a heating operation, the refrigerant circuit 10 is in a state in which the four-way valve 22 is indicated by a solid line as shown in FIG. and port c. As a result, the refrigerant circulates in the direction indicated by the solid arrow in the refrigerant circuit 10, and a heating cycle is established in which the outdoor heat exchanger 23 functions as an evaporator and the indoor heat exchanger 31 functions as a condenser. As described above, the on-off valve 29 is opened during the heating operation.

Refrigerant compressed by the compressor 21 to a high pressure (refrigerant in the state of point B in FIG. 2) is discharged from the compressor 21 to the discharge pipe 61, flows through the discharge pipe 61, and flows into the four-way valve 22. , from the four-way valve 22 through the outdoor unit gas pipe 64 and into the gas pipe 5 via the closing valve 26 . The refrigerant flowing through the gas pipe 5 flows into the indoor unit 3 via the gas pipe connection portion 34 .

The refrigerant that has flowed into the indoor unit 3 flows through the indoor unit gas pipe 92 and into the indoor heat exchanger 31, exchanges heat with the indoor air taken into the indoor unit 3 by the rotation of the indoor fan 32, and condenses. do. In this way, the indoor heat exchanger 31 functions as a condenser, and the indoor air that has undergone heat exchange with the refrigerant in the indoor heat exchanger 31 is blown out into the room from an air outlet (not shown), whereby the indoor unit 3 is installed. The room is heated.

The refrigerant that has flowed out of the indoor heat exchanger 31 (refrigerant in the state of point C in FIG. 2) flows through the indoor unit liquid pipe 91 and flows into the liquid pipe 4 via the liquid pipe connection portion 33 . The refrigerant that has flowed through the liquid pipe 4 and flowed into the outdoor unit 2 via the closing valve 25 flows through the outdoor unit liquid pipe 63 to the first expansion valve 27a. The degree of opening of the first expansion valve 27a is adjusted so that the discharge temperature detected by the discharge temperature sensor 73 reaches a predetermined target temperature according to the outside air temperature and the heating capacity required by the indoor unit 3. there is A specific method for adjusting the degree of opening of the first expansion valve 27a is the same as the method described for the cooling operation, so detailed description thereof will be omitted.

Refrigerant in a gas-liquid two-phase state (refrigerant in the state of point D in FIG. 2), which is decompressed when passing through the first expansion valve 27a and has a large ratio of liquid refrigerant to gas refrigerant, is supplied to the outdoor unit. It flows from the liquid pipe 63 to the first liquid branch pipe 67 and flows into the gas-liquid separator 28 via the opened on-off valve 29 . The gas-liquid two-phase refrigerant that has flowed into the gas-liquid separator 28 is separated into liquid refrigerant and gas refrigerant inside the gas-liquid separator 28 .

The saturated liquid refrigerant separated inside the gas-liquid separator 28 (refrigerant in the state of point E in FIG. 2. The reason why it becomes the saturated liquid refrigerant will be described later) flows out to the second liquid branch pipe 68. and flows to the second expansion valve 27b. The second expansion valve 27b has a predetermined temperature difference between the outflow liquid refrigerant temperature detected by the outflow liquid refrigerant temperature sensor 77 and the temperature of the refrigerant flowing out of the second expansion valve 27b detected by the heat exchanger temperature sensor 75. The degree of opening is adjusted to the target value.

Specifically, when the temperature difference is greater than the target value, the degree of opening of the second expansion valve 27b is made larger than the current degree of opening. As the degree of opening of the second expansion valve 27b increases, the degree to which the liquid refrigerant passing through the second expansion valve 27b is decompressed decreases. temperature difference becomes smaller. On the other hand, when the temperature difference is smaller than the target value, the degree of opening of the second expansion valve 27b is made smaller than the present degree of opening. The smaller the degree of opening of the second expansion valve 27b, the greater the degree to which the liquid refrigerant passing through the second expansion valve 27b is decompressed. The temperature difference from the liquid refrigerant temperature increases.

Here, the above-described target value is a value that is determined to achieve a desired ratio of the gas refrigerant to the liquid refrigerant in the refrigerant flowing out from the second expansion valve 27b. Specifically, if priority is given to reducing the amount of refrigerant charged in the refrigerant circuit 10 over reducing the pressure loss when the refrigerant flows through the refrigerant flow path (not shown) of the outdoor heat exchanger 23, the target value is increased. By adjusting the degree of opening of the second expansion valve 27b so as to achieve this target value, the ratio of gas refrigerant to liquid refrigerant in the refrigerant flowing from the second expansion valve 27b to the outdoor heat exchanger 23 is increased. On the other hand, if priority is given to reducing the pressure loss when the refrigerant flows through the refrigerant passage (not shown) of the outdoor heat exchanger 23 over reducing the amount of refrigerant charged in the refrigerant circuit 10, the target value is set to a small value. By adjusting the degree of opening of the second expansion valve 27b so as to achieve this target value, the ratio of gas refrigerant to liquid refrigerant in the refrigerant flowing from the second expansion valve 27b to the outdoor heat exchanger 23 is reduced.

However, when determining the target value, it is necessary to determine the pressure at point G shown in FIG. 2 so as not to exceed the pressure at point Y. Although details will be described later, when the pressure at point G exceeds the pressure at point Y, the opening degree of the third expansion valve 27c is adjusted so that the degree of superheat of the refrigerant at the refrigerant outlet side of the third expansion valve 27c is 0 deg. Moreover, even if the saturated gas refrigerant has a dryness of 1, the refrigerant before being decompressed by the third expansion valve 27c, that is, the refrigerant that flows out from the gas-liquid separator 28 into the bypass pipe 69 and flows into the third expansion valve 27c. The state is a superheated gas state in which the value of the specific enthalpy of the refrigerant is greater than the value of the specific enthalpy on the saturated vapor line. In the present invention, the state of the refrigerant flowing into the third expansion valve 27c is not a superheated gas state, but a state in which a small amount of liquid refrigerant is mixed with the gas refrigerant. Set a target value so as not to exceed it.

The refrigerant that has passed through the second expansion valve 27b and has been depressurized to become a gas-liquid two-phase refrigerant with a high proportion of liquid refrigerant (refrigerant in the state of point F in FIG. 2) flows through the second liquid branch pipe 68, It flows into the outdoor unit liquid pipe 63 through the second check valve 30b. The refrigerant flowing through the outdoor unit liquid pipe 63 and flowing into the outdoor heat exchanger 23 exchanges heat with the outside air taken into the outdoor unit 2 by the rotation of the outdoor fan 24 and evaporates. The refrigerant flowing out from the outdoor heat exchanger 23 to the refrigerant pipe 62 flows through the four-way valve 22 and the suction pipe 66, is sucked into the compressor 21, and is compressed again.

On the other hand, the gas refrigerant separated inside the gas-liquid separator 28 flows out to the bypass pipe 69 and flows to the third expansion valve 27c. The third expansion valve 27c detects a value obtained by subtracting the refrigerant temperature calculated using the pressure detected by the outflow gas refrigerant pressure sensor 72 from the outflow gas refrigerant temperature detected by the outflow gas refrigerant temperature sensor 78 (hereinafter referred to as the outflow gas The degree of opening is adjusted so that the superheating degree of the refrigerant) becomes 0 deg, that is, the refrigerant flowing out to the bypass pipe 69 becomes saturated gas refrigerant. Specifically, when the degree of superheating of the outflowing gas refrigerant obtained is greater than 0 deg, the degree of opening of the third expansion valve 27c is made larger than the present degree of opening. On the other hand, if the outflow gas refrigerant superheat degree obtained is 0 deg, the degree of opening of the third expansion valve 27c is made smaller than the present degree of opening.

Here, how the state of the refrigerant inside the gas-liquid separator 28 and the refrigerant flowing out to the second liquid branch pipe 68 and the bypass pipe 69 change due to changes in the degree of opening of the third expansion valve 27c will be described. do. As described above, the refrigerant that has flowed into the gas-liquid separator 28 is in the state indicated by point D in FIG.

First, when the opening degree of the third expansion valve 27c is small, the amount of gas refrigerant flowing out from the gas-liquid separator 28 to the bypass pipe 69 is less than the amount of gas refrigerant in the refrigerant flowing into the gas-liquid separator 28. , and only the gas refrigerant flows out to the bypass pipe 69 . Therefore, when the degree of opening of the third expansion valve 27c is small, the state of the gas refrigerant flowing out from the gas-liquid separator 28 to the bypass pipe 69 is a saturated gas state (Fig. 2 is on the saturated steam line). On the other hand, the state of the refrigerant flowing out from the gas-liquid separator 28 to the second liquid branch pipe 68 is a state in which a slight amount of gas refrigerant is mixed with the liquid refrigerant (a state in which point E in FIG. 2 is slightly closer to point D). Become.

Next, as the opening degree of the third expansion valve 27c is increased, the state of the gas refrigerant flowing out from the gas-liquid separator 28 to the bypass pipe 69 remains unchanged (saturated gas refrigerant with a degree of superheat of 0 deg). , the amount of gas refrigerant flowing out to the bypass pipe 69 increases, and the same amount of gas refrigerant as that in the refrigerant flowing into the gas-liquid separator 28 at a certain degree of opening of the third expansion valve 27c becomes gas-liquid. Out of the separator 28 is a bypass pipe 69 . At this time, the state of the refrigerant flowing out from the gas-liquid separator 28 to the second liquid branch pipe 30b becomes a saturated liquid state (state indicated by point E in FIG. 2) that does not contain gas refrigerant.

When the degree of opening of the third expansion valve 27c is further increased from the above value, the amount of gas refrigerant flowing out from the gas-liquid separator 28 to the bypass pipe 69 flows into the gas-liquid separator 28. The amount of gas refrigerant remaining in the gas-liquid separator 28, which is greater than the amount of gas refrigerant in the refrigerant, also flows into the bypass pipe 69. As shown in FIG. As a result, inside the gas-liquid separator 28, the amount of liquid refrigerant retained increases, the liquid level rises, the liquid level reaches the opening of the bypass pipe 69 inside the gas-liquid separator 28, and the gas-liquid A small amount of liquid refrigerant is contained in the gas refrigerant flowing from the separator 28 to the bypass pipe 69 (the state indicated by point G in FIG. 2).

In the air conditioner 1 of the present embodiment, the state of the refrigerant inside the gas-liquid separator 28 changes due to the change in the opening degree of the third expansion valve 27c described above, and the second liquid branch pipe 68 and the bypass pipe 69, the opening degree of the third expansion valve 27c is adjusted, and the outflow gas refrigerant temperature detected by the outflow gas refrigerant temperature sensor 78 is detected by the outflow gas refrigerant pressure sensor 72. The value obtained by subtracting the temperature of the refrigerant obtained using the detected pressure (hereinafter referred to as the outflow gas refrigerant superheat degree) is 0 deg (state indicated by point A in FIG. 2), that is, the saturated gas state to By making the refrigerant flowing out of the third expansion valve 27c into a saturated gas refrigerant, the state of the refrigerant before being decompressed by the third expansion valve 27c, that is, the refrigerant flowing out from the gas-liquid separator 28 to the bypass pipe 69 is changed. , the state indicated by point G in FIG. 2, that is, the state in which the liquid refrigerant is slightly mixed with the gas refrigerant.

As described above, when the gas refrigerant flowing from the gas-liquid separator 28 to the bypass pipe 69 contains a small amount of liquid refrigerant, the amount of liquid refrigerant retained inside the gas-liquid separator 28 increases. As a result, the liquid level rises and reaches the opening of the bypass pipe 69 inside the gas-liquid separator 28 . If the amount of liquid refrigerant until the liquid level reaches the opening of the bypass pipe 69 remains inside the gas-liquid separator 28, it is provided below the side surface of the closed container of the gas-liquid separator 28. The refrigerant that flows out from the liquid refrigerant outlet to the second liquid branch pipe 30b is surely saturated liquid refrigerant that does not contain gas refrigerant.

As described above, if the degree of opening of the third expansion valve 27c is adjusted so that the refrigerant flowing out from the third expansion valve 27c becomes the saturated gas refrigerant, the liquid level of the liquid refrigerant inside the gas-liquid separator 28 is The height can be near the opening of the bypass pipe 69 (a state where the liquid level reaches and slightly does not reach the opening of the bypass pipe 69 depending on the degree of opening of the third expansion valve 27c). By setting the height to the vicinity of the opening of the bypass pipe 69, the refrigerant flowing out from the gas-liquid separator 28 to the second liquid branch pipe 68 can be saturated liquid refrigerant. Therefore, by reducing the pressure of the saturated liquid refrigerant that has flowed out to the second liquid branch pipe 68 by the second expansion valve 27b, the state of the refrigerant that flows out from the second expansion valve 27b to the second liquid branch pipe 68 can be changed from the gas refrigerant to the liquid state. A gas-liquid two-phase state (state indicated by point F in FIG. 2) with a large proportion of the refrigerant can be ensured. As a result, even if the amount of refrigerant with which the refrigerant circuit 10 is filled is reduced, it is possible to prevent a reduction in the heating capacity due to a reduction in the condensation capacity of the indoor heat exchanger 31 functioning as a condenser during the heating operation.

The present invention is more effective when the outdoor heat exchanger is a micro-channel heat exchanger. Compared to ordinary heat exchangers such as fin-and-tube heat exchangers, microfluidic heat exchangers are smaller and have higher heat transfer properties. can be reduced by comparison. On the other hand, since the cross-sectional area of the refrigerant channel of the micro-channel heat exchanger is smaller than that of a normal heat exchanger, when the refrigerant flows through the micro-channel heat exchanger, The pressure drop increases as the proportion of gaseous refrigerant in the refrigerant entering the microchannel heat exchanger increases.

Therefore, when the outdoor heat exchanger is a micro-channel heat exchanger, it is preferable that the refrigerant flowing into the micro-channel heat exchanger during heating operation is a liquid refrigerant. However, as described above, if the refrigerant flowing into the microchannel heat exchanger during heating operation is liquid refrigerant, the space between the gas-liquid separator and the microchannel heat exchanger is filled with liquid refrigerant, resulting in There is a possibility that the condensation capacity of the heat exchanger 31 will be reduced and the heating capacity will be reduced.

However, in the air conditioner 1 of the present invention, as described above, the liquid refrigerant that has flowed out of the gas-liquid separator 28 during heating operation is transferred to the second expansion unit disposed near the liquid refrigerant outlet of the gas-liquid separator 28. The valve 27b allows the gas-liquid two-phase state with a high proportion of the liquid refrigerant to flow to the outdoor heat exchanger 23 . Therefore, even if the outdoor heat exchanger 23 is a microchannel heat exchanger, the pressure loss from the gas-liquid separator 28 to the outdoor heat exchanger 23 is minimized when the refrigerant flows through the microchannel heat exchanger. By filling the space with the liquid refrigerant, it is possible to prevent the occurrence of a state in which the condensation capacity in the indoor heat exchanger 31 is lowered and the heating capacity is lowered.

Further, in the embodiment described above, the opening degree of the first expansion valve 27a is adjusted so that the discharge temperature detected by the discharge temperature sensor 73 becomes a predetermined target temperature, and the opening degree of the second expansion valve 27b is adjusted. is adjusted so that the temperature difference from the temperature of the refrigerant flowing out of the second expansion valve 27b detected by the heat exchanger temperature sensor 75 becomes the target value. However, the effects of the present invention are exhibited even if the method of adjusting the degree of opening of the first expansion valve 27a and the method of adjusting the degree of opening of the second expansion valve 27b are interchanged.

1 air conditioner 2 outdoor unit 3 indoor unit 10 refrigerant circuit 21 compressor 22 four-way valve 23 outdoor heat exchanger 27a first expansion valve 27b second expansion valve 27c third expansion valve 28 gas-liquid separator 29 on-off valve 30a first Check valve 30b Second check valve 31 Indoor heat exchanger 67 First liquid branch pipe 68 Second liquid branch pipe 69 Bypass pipe 72 Outflow gas refrigerant pressure sensor 75 Heat exchange temperature sensor 77 Outflow liquid refrigerant temperature sensor 78 Outflow gas refrigerant temperature sensor

Claims (1)

a refrigerant circuit in which refrigerant circulates in the order of the compressor, the indoor heat exchanger, the first expansion valve, the gas-liquid separator, the second expansion valve, and the outdoor heat exchanger during heating operation;
a bypass pipe that has a third expansion valve and guides refrigerant from the gas-liquid separator to the compressor;
An air conditioner having
The degree of opening of the first expansion valve is adjusted so that the temperature difference between the temperature of the refrigerant flowing into the second expansion valve and the temperature of the refrigerant flowing out of the second expansion valve becomes a predetermined target value,
The degree of opening of the second expansion valve is adjusted so that the discharge temperature, which is the temperature of the refrigerant discharged from the compressor, reaches a predetermined target temperature,
The degree of opening of the third expansion valve is adjusted so that the refrigerant flowing out of the third expansion valve becomes saturated gas refrigerant, and the refrigerant flowing out of the second expansion valve has a ratio of liquid refrigerant to gas refrigerant. High gas-liquid two-phase refrigerant,
An air conditioner characterized by:

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