CN109084392B

CN109084392B - Air conditioner

Info

Publication number: CN109084392B
Application number: CN201810582780.3A
Authority: CN
Inventors: 内藤宏治; 多田修平; 小杉真一; 渡边雅裕; 大畑亮佑
Original assignee: Hitachi Johnson Controls Air Conditioning Inc
Current assignee: Hitachi Johnson Controls Air Conditioning Inc
Priority date: 2017-06-14
Filing date: 2018-06-07
Publication date: 2021-05-18
Anticipated expiration: 2038-06-07
Also published as: CN109084392A; JP7002227B2; US20180363961A1; JP2019002620A

Abstract

The invention aims to provide an air conditioner, which shortens the time required for restarting by restraining the movement of a refrigerant from a connecting liquid pipe during stopping, improves the comfort and the reliability, and prevents the increase of the manufacturing cost caused by the enlargement of an accumulator. The air conditioner is provided with: an outdoor unit having a compressor, an outdoor heat exchanger, and an outdoor expansion valve; an indoor unit having an indoor heat exchanger and an indoor expansion valve; a liquid pipe connecting the outdoor unit and the indoor unit; and a gas pipe connecting the outdoor unit and the indoor unit, wherein one end of the outdoor heat exchanger is connected to the liquid pipe via the outdoor expansion valve, one end of the indoor heat exchanger is connected to the liquid pipe via the indoor expansion valve, and both the outdoor expansion valve and the indoor expansion valve are closed after a predetermined time has elapsed since the compressor was stopped.

Description

Air conditioner

Technical Field

The present invention relates to an air conditioner, and more particularly to a multi-type air conditioner characterized by an expansion valve control after a compressor is stopped.

Background

It is known that there is a large difference in the distribution of refrigerant in the air conditioner during operation and during stoppage. Fig. 6 is an example of refrigerant distribution in the air conditioner, and the air conditioner is roughly divided into four sections, namely, a connection liquid pipe, a connection gas pipe, an outdoor unit, and others, and the refrigerant distribution during operation and during stoppage (after a predetermined time has elapsed after stoppage) is compared. As a result, the refrigerant in the connection liquid pipe and the refrigerant in the outdoor unit are reduced and the refrigerant in the connection gas pipe is increased during stoppage as compared with the operation.

Of particular note is the large variation in the amount of refrigerant held by the connecting liquid tubes, which in the example of fig. 6, takes about six quarters in operation to reduce to about four quarters in standstill. This is because most of the refrigerant in the connection liquid pipe moves to the connection gas pipe.

Disclosure of Invention

Problems to be solved by the invention

As shown in fig. 6, when the refrigerant moves from the connection liquid pipe to the connection gas pipe during stoppage, when the air conditioner is started next, the refrigerant moving through the connection gas pipe moves to the connection liquid pipe, and it is necessary to wait for an appropriate amount of refrigerant to be accumulated again in the connection liquid pipe, which causes a problem that it takes time for the air conditioner to be effective.

Further, when the refrigerant moves from the connection liquid pipe to the outdoor unit, there is a problem that the refrigerant accumulates in the connection gas pipe, the accumulator, and the like. When restarting is performed in such a state where accumulation occurs, the risk of compressing the liquid by the compressor increases, and therefore, the risk of compressing the liquid needs to be avoided by increasing the volume of the accumulator.

The invention aims to provide an air conditioner, which shortens the time required for restarting by restraining the movement of a refrigerant from a connecting liquid pipe during stopping, improves the comfort and the reliability, and prevents the increase of the manufacturing cost caused by the enlargement of an accumulator.

Means for solving the problems

In order to solve the above problem, an air conditioner according to the present invention includes: an outdoor unit having a compressor, an outdoor heat exchanger, and an outdoor expansion valve; an indoor unit having an indoor heat exchanger and an indoor expansion valve; a liquid pipe connecting the outdoor unit and the indoor unit; and a gas pipe connecting the outdoor unit and the indoor unit, wherein one end of the outdoor heat exchanger is connected to the liquid pipe via the outdoor expansion valve, one end of the indoor heat exchanger is connected to the liquid pipe via the indoor expansion valve, and both the outdoor expansion valve and the indoor expansion valve are closed after a predetermined time has elapsed since the compressor was stopped.

Another air conditioner of the present invention includes: an outdoor unit having a compressor, an outdoor heat exchanger, and an outdoor expansion valve; an indoor unit having an indoor heat exchanger and an indoor expansion valve; a cold-hot switching unit having a high-low pressure gas pipe switching valve and a low-pressure gas pipe switching valve; a liquid pipe connecting the outdoor unit and the indoor unit; a high-low pressure gas pipe connecting the outdoor unit and the high-low pressure gas pipe switching valve; a low pressure gas pipe connecting the outdoor unit and the low pressure gas pipe switching valve; and a gas pipe connecting the indoor unit and the cold/hot switching unit, wherein one end of the outdoor heat exchanger is connected to the liquid pipe via the outdoor expansion valve, one end of the indoor heat exchanger is connected to the liquid pipe via the indoor expansion valve, and both the outdoor expansion valve and the indoor expansion valve are closed or all of the outdoor expansion valve, the high/low pressure gas pipe switching valve, and the low pressure gas pipe switching valve are closed after a predetermined time has elapsed since the compressor was stopped.

Another air conditioner of the present invention includes: an outdoor unit having a compressor, an outdoor heat exchanger, and an outdoor expansion valve; an indoor unit having an indoor heat exchanger and an indoor expansion valve; a cold-hot switching unit having a gas-liquid separator, a high-pressure pipe switching valve, a low-pressure pipe switching valve, and a hydraulic pressure regulating valve; a high pressure pipe connecting the outdoor unit and the cold/heat switching unit; a low pressure pipe connecting the outdoor unit and the cold/heat switching unit; a gas pipe connecting the indoor unit and the cold/hot switching unit; and a liquid pipe connecting the indoor unit and the cold/hot switching unit, wherein one end of the outdoor heat exchanger is connected to the high-pressure pipe via the outdoor expansion valve, one end of the indoor heat exchanger is connected to the liquid pipe via the indoor expansion valve, and the outdoor expansion valve, the indoor expansion valve, the high-pressure pipe switching valve, the low-pressure pipe switching valve, and the hydraulic pressure adjusting valve are all closed after a predetermined time has elapsed since the compressor was stopped.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, since the movement of the refrigerant from the connection liquid pipe at the time of stopping can be suppressed, the effectiveness of the heating operation or the cooling operation at the time of restarting the air conditioner can be increased, and the comfort can be improved. Further, since the possibility of compressing the liquid by the compressor can be reduced without increasing the size of the accumulator, the reliability can be improved without increasing the manufacturing cost.

Drawings

Fig. 1 shows a conventional expansion valve control at the time of heating stop in a multi-type air conditioner with cooling and heating switching.

Fig. 2 shows a conventional expansion valve control at the time of refrigeration stop of a multi-type air conditioner with cooling/heating switching.

Fig. 3 shows the stop-time expansion valve control in embodiment 1 of the multi-type air conditioner for cooling/heating switching.

Fig. 4 shows an example of the refrigerant differential pressure due to the difference in level.

Fig. 5 shows an example of refrigerant differential pressure due to an indoor/outdoor temperature difference.

Fig. 6 shows an example of refrigerant distribution during operation and during stoppage.

Fig. 7 is an isometric variation of a liquid refrigerant.

Fig. 8 shows the pressure fluctuation from the operation to the stop of the conventional technique.

Fig. 9 shows the pressure fluctuation from operation to stop during the control of the expansion valve at the time of stop.

Fig. 10 shows the pressure fluctuation from operation to stop during the control of the expansion valve at the time of stop.

Fig. 11 shows an example of the flow of the expansion valve control at the time of stop.

Fig. 12 shows a conventional stop-time expansion valve control of a simultaneous cooling and heating multi-type air conditioner.

Fig. 13 shows the stop-time expansion valve control in embodiment 2 of the simultaneous cooling and heating multi-type air conditioner.

Fig. 14 shows the control of the expansion valve during stop (opening of the cooling/heating switching unit valve) in the modification of embodiment 2 of the simultaneous cooling and heating multi-type air conditioner.

Fig. 15 shows the control of the expansion valve during stop (opening of the expansion valve in the heating chamber) in another modification of embodiment 2 of the simultaneous cooling and heating multi-type air conditioner.

Fig. 16 shows a conventional stop-time expansion valve control of a two-pipe type simultaneous cooling and heating air conditioner.

Fig. 17 shows the stop expansion valve control in the two-pipe simultaneous cooling and heating air conditioner in embodiment 3.

Fig. 18 shows the expansion valve control at the time of refrigeration stop in embodiment 4 using the configuration of the subcooling circuit.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[ example 1 ]

First, an air conditioner according to embodiment 1 of the present invention will be described with reference to fig. 1 to 5 and 7 to 11.

Expansion valve control at the time of stopping conventional heating

Fig. 1 is a diagram of a refrigeration cycle showing a conventional expansion valve control at the time of heating stop applied to a multi-type air conditioner 100 for cooling/heating switching. The air conditioner 100 shown here is configured such that the outdoor unit 10 and the indoor units 40(40a, 40b, 40c, and 40d are collectively referred to) are connected to each other through the liquid main pipe 21 and the gas main pipe 24, and each indoor unit 40 is in a heating stop state. In fig. 1, one outdoor unit 10 and four indoor units 40 are illustrated, but the number of outdoor units may be other than that.

The indoor unit 40a includes an indoor heat exchanger 41a, an indoor expansion valve 42a, and an indoor heat exchanger fan 49 a. One end of the indoor heat exchanger 41 is connected to the liquid main pipe 21 via an indoor expansion valve 42. Further, an indoor heat exchanger gas temperature sensor 45a, an indoor heat exchanger liquid temperature sensor 46a, and an indoor temperature sensor 73a are provided at the illustrated positions. The

indoor units

40b, 40c, and 40d have the same configuration, and therefore, redundant description thereof is omitted.

The outdoor unit 10 includes a compressor 11, a four-way valve 12, an outdoor heat exchanger fan 13, an outdoor heat exchanger 14, an outdoor expansion valve 15, a compressor check valve 16, and an accumulator 18. One end of the outdoor heat exchanger 14 is connected to the liquid main pipe 21 via the outdoor expansion valve 15. In addition, a discharge pressure detection sensor 55, an outdoor heat exchanger liquid temperature sensor 50, an outdoor heat exchanger gas temperature sensor 51, a liquid pressure detection device 71, and an outside air temperature sensor 72 are provided at the illustrated positions.

Next, the flow of the refrigerant during the heating operation and during the heating stop will be described. In the heating operation, the high-temperature and high-pressure gas refrigerant compressed by the compressor 11 is sent to the indoor unit 40 via the four-way valve 12 and the gas main pipe 24.

In the indoor unit 40, the gas refrigerant flowing into the indoor heat exchanger 41 exchanges heat with indoor air, condenses, becomes a high-pressure two-phase refrigerant or a high-pressure supercooled refrigerant, and is sent to the outdoor unit 10 via the indoor expansion valve 42 and the liquid main pipe 21.

In the outdoor unit 10, the flow rate of the refrigerant flowing in is adjusted by the outdoor expansion valve 15 opened to a desired opening degree, and the refrigerant exchanges heat with outdoor air in the outdoor heat exchanger 14 to be evaporated into a low-pressure gas refrigerant, which is then sent to the compressor 11 via the four-way valve 12 and the accumulator 18, thereby completing the refrigeration cycle in the heating operation. In the heating operation, the liquid main pipe 21 is substantially filled with the liquid refrigerant, and the gas main pipe 24 contains only the gas refrigerant.

When the heating is stopped, the outdoor expansion valve 15 is fully closed and the indoor expansion valve 42 is opened, as shown in fig. 1. After the compressor 11 is stopped, the pressure of the gas main pipe 24 downstream thereof is reduced, and when a certain time elapses, the pressure is balanced with the suction side pressure of the compressor 11. When the equilibrium pressure is lower than the pressure of the liquid main pipe 21, the liquid refrigerant in the liquid main pipe 21 moves to the gas main pipe 24 through the indoor expansion valve 42 and the indoor heat exchanger 41, and the refrigerant movement as shown in fig. 6 occurs. Further, the four-way valve 12, the compressor check valve 16, and the like may not be completely sealed, and the refrigerant in the gas main pipe 24 may move to the accumulator 18 and the outdoor heat exchanger 14. Therefore, when the refrigerant in the main liquid pipe 21 is distributed to each portion of the refrigeration cycle, the operation efficiency is low and it takes time to effect heating until the refrigerant is appropriately distributed to each portion of the refrigeration cycle at the next start-up.

After the heating operation is stopped, the refrigerant chamber remains in the outdoor heat exchanger 14, and at the time of start-up, the refrigerant in a gas-liquid mixed state enters the accumulator 18. The accumulator 18 separates liquid refrigerant from low-pressure refrigerant in a gas-liquid mixed state, sends gas refrigerant to the compressor 11, and prevents the liquid pressure of the compressor 11, but when the amount of liquid returned from the outdoor heat exchanger 14 is large or when refrigerant remains in the accumulator 18 itself, the function of separating liquid refrigerant is reduced, and the risk of the compressor compressing liquid increases. To prevent this, the volume of the reservoir 18 needs to be increased, which increases the manufacturing cost.

Expansion valve control at refrigeration stop

Fig. 2 is a diagram showing a refrigeration cycle in which a conventional expansion valve control during a cooling stop is applied to the air conditioner 100 having the same configuration as that of fig. 1, and the connection of the four-way valve 12 is different from that of fig. 1. The flow of the refrigerant during the cooling operation and during the cooling stop will be described with reference to the drawing. The high-temperature high-pressure gas refrigerant compressed by the compressor 11 during the cooling operation is sent to the indoor unit 40 via the four-way valve 12. The gas refrigerant flowing into the outdoor heat exchanger 14 exchanges heat with outdoor air, condenses, becomes a high-pressure two-phase refrigerant or a high-pressure supercooled refrigerant, and is sent to the indoor unit 40 via the outdoor expansion valve 15 and the liquid main pipe 21. In the indoor unit 40, the flow rate of the refrigerant flowing in is adjusted by the indoor expansion valve 42 opened to a desired opening degree, the refrigerant exchanges heat with indoor air in the indoor heat exchanger 41 and evaporates to become a low-pressure gas refrigerant, and the refrigerant is sent to the compressor 11 via the gas main pipe 24, the four-way valve 12, and the accumulator 18, thereby completing the refrigeration cycle during the cooling operation. In this cooling operation, the liquid main pipe 21 is substantially filled with the liquid refrigerant, and the gas main pipe 24 contains only the gas refrigerant.

When the cooling stop is started, the indoor expansion valve 42 is fully closed and the outdoor expansion valve 15 is opened, as shown in fig. 2. After the compressor 11 is stopped, the pressure of the outdoor heat exchanger 14 is reduced, and when a certain time elapses, the pressure is balanced with the suction-side pressure of the compressor 11. When the equilibrium pressure is lower than the pressure of the liquid main pipe 21, the liquid refrigerant in the liquid main pipe 21 moves to the outdoor heat exchanger 14 through the outdoor expansion valve 15, and therefore, the refrigerant movement as shown in fig. 6 occurs. Further, since the four-way valve 12, the compressor check valve 16, and the like are not completely sealed, the refrigerant in the indoor heat exchanger 14 may move to the accumulator 18 and the gas main pipe 24. In this way, when the refrigerant in the main liquid pipe 21 is distributed to the respective portions of the refrigeration cycle, the cooling efficiency is low and it takes time to effect cooling until the refrigerant is appropriately distributed to the respective portions of the refrigeration cycle at the next start-up.

Further, if the refrigerant chamber remains in the gas main pipe 24 after the cooling operation is stopped, the amount of liquid returning at the time of start-up increases, the liquid refrigerant separating function of the accumulator 18 decreases, and the risk of the compressor compressing the liquid increases. To prevent this, the volume of the reservoir 18 needs to be increased, which increases the manufacturing cost.

[ stop time expansion valve control of embodiment 1 ]

Fig. 3 is a diagram showing a refrigeration cycle system to which the control of the expansion valve during stoppage is applied in embodiment 1 of the air conditioner 100 having the same configuration as that of fig. 1 and 2. Although the state in which the four-way valve 12 is connected during the cooling operation (fig. 2) is illustrated here, the stop-time expansion valve control of the present embodiment can also be applied to the state in which the four-way valve 12 is connected during the heating operation (fig. 1).

In the present embodiment, when the operation is shifted from the cooling operation to the cooling stop, all of the indoor expansion valves 42 and the outdoor expansion valves 15 are closed as shown in fig. 3. As described above, in the stop-time expansion valve control of the related art, when the compressor 11 is stopped and the pressure on the outflow side of the compressor 11 is lowered, the refrigerant is dispersed to each part of the refrigeration cycle via the open expansion valves, but by closing both the expansion valves at both ends of the liquid main pipe 21 as in the present embodiment, the liquid refrigerant remaining in the liquid main pipe 21 during operation can be prevented from moving to other parts, and the cooling operation or the heating operation at the next start-up can be made effective earlier.

Next, the movement of the liquid refrigerant due to the refrigerant differential pressure between the outdoor unit 10 and the indoor unit 40 and measures against the movement will be described with reference to the schematic diagrams of fig. 4 and 5.

Fig. 4 is a schematic diagram of the air conditioner 100 in which the outdoor unit 10 is disposed below and the indoor units 40 are disposed above 10m, when the cooling operation is stopped, and is an example in which the refrigerant is likely to move downward toward the heat exchanger due to the difference in level between both ends of the liquid main pipe 21. As indicated by parenthesized numbers in the drawing, fig. 4 is also a schematic view of the air conditioner in which the indoor units 40 are disposed below and the outdoor unit 10 is disposed above during stop of heating operation.

When the expansion valve below is opened after the cooling operation is stopped, the liquid refrigerant moves toward the heat exchanger below due to the effect of the head of the liquid column. For example, the height difference between the outdoor unit 10 and the indoor unit 40 is 10m, and the liquid density of the refrigerant is 1000kg/m³When the outdoor expansion valve 15 is opened, a differential pressure of about 0.1MPa is generated in the outdoor expansion valve 15 disposed at the lower end of the main liquid pipe 21, and the refrigerant in the main liquid pipe 21 moves downward. In order to prevent this, as in the present embodiment, the expansion valve located on the lower side needs to be closed when stopped. Specifically, when the outdoor unit 10 is down and the indoor unit 40 is up, the outdoor expansion valve 15 is closed, and when the outdoor unit 10 is up and the indoor unit is down, the heating is stopped, the indoor expansion valve 42 is closed. In this way, when there is a difference in height between the installation locations of the outdoor unit 10 and the indoor unit 40, the lower expansion valve is closed during the operation stop, and thereby the liquid refrigerant can be prevented from flowing into the lower heat exchanger or the like.

Fig. 5 is a schematic diagram of the operation stop of the air conditioner 100 in which the outdoor unit 10 is disposed in the atmosphere of 17 ℃ and the indoor unit 40 is disposed in the atmosphere of 20 ℃, and illustrates an example in which the refrigerant is likely to move to the heat exchanger on the low temperature side due to the temperature difference between both ends of the liquid main pipe 21. In fig. 5, the outdoor unit 10 and the indoor unit 40 are set to have the same height, and the main liquid pipe 21 is horizontal.

Even when the operation is stopped, if there is a difference in the ambient temperature between the indoor and outdoor sides, the refrigerant and the air in the air conditioner 100 exchange heat by natural convection, and the refrigerant moves. For example, in the case where the outdoor temperature is 17 ℃ and the indoor temperature is 20 ℃, although it takes time, the liquid refrigerant in the indoor heat exchanger 41 evaporates and the gas refrigerant in the outdoor heat exchanger 14 condenses, so that the liquid refrigerant in the indoor unit 40 gradually accumulates in the outdoor unit 10. Since the saturation pressure at 20 ℃ is 1.45MPa and the saturation pressure at 17 ℃ is 1.35MPa, the differential pressure of the saturation pressure due to the temperature difference between the inside and outside of the room shown in FIG. 5, which is 3 ℃, is 0.1 MPa. This corresponds to a liquid transfer force of 10m in height difference as shown in fig. 4, and cannot be ignored. Therefore, when the temperature difference between the indoor and outdoor temperatures exceeds a predetermined value, the control of closing the expansion valve on the low temperature side may be performed in order to prevent the refrigerant from flowing out of the liquid main pipe 21.

Fig. 7 is a conceptual diagram of a liquid seal phenomenon in which a liquid pipe is filled with a liquid refrigerant. When the temperature rises after the valves at both ends of the piping are closed in a flooded state, the pressure of the liquid refrigerant rises, and when the pressure exceeds the pressure resistance of the piping, there is a problem that the piping is broken and the refrigerant leaks. Therefore, when both the indoor expansion valve 42 and the outdoor expansion valve 15 at both ends of the main liquid pipe 21 are closed as shown in fig. 3, it is desirable to close the valves at both ends after confirming that the main liquid pipe 21 is not full of liquid. For example, in the case of the heating operation, the degree of supercooling at the outlet of each indoor heat exchanger 41 is detected by the discharge pressure detection sensor 55 and the indoor heat exchanger liquid temperature sensor 46, and when the outlet temperatures of all the indoor units 40 are at the saturation temperature, the two-phase refrigerant is fed to the liquid main pipe 21, and there is a high possibility that the two-phase refrigerant is not in the full liquid state, and therefore, even if the valves at both ends are directly closed in this way, no failure occurs. Further, when the heat exchanger serving as a condenser is set down by the step construction, when the pipe length of the liquid main pipe 21 is long, or the like, the pressure at the end of the liquid pipe is likely to decrease and become a two-phase refrigerant, and therefore, even if the valves at both ends are closed in accordance with the refrigerant state, no failure occurs. It is also possible to estimate whether or not the inside of the main liquid pipe 21 is the two-phase refrigerant from the circulation state before the stop, the liquid pipe temperature, and the liquid pipe pressure.

Fig. 8 shows pressure fluctuations in the case where the conventional stop-time expansion valve control shown in fig. 1 and 2 is performed. When the air conditioner 100 stops operating, the discharge pressure and the suction pressure gradually balance to be the same pressure. At this time, since the valve at one end of the main liquid pipe 21 is opened, the liquid pressure becomes lower than or substantially equal to the discharge pressure. Here, when the discharge pressure is lower than the liquid pressure, the refrigerant in the main liquid pipe 21 moves to another device, and the pressure naturally decreases. As a result, various problems described in the explanation of fig. 1 and 2 occur.

Fig. 9 shows pressure fluctuations in the case where the stop-time expansion valve closing control of the present embodiment shown in fig. 3 is performed. As in fig. 8, the discharge pressure immediately after the stop of the air conditioner 100 becomes lower than the liquid pressure, but here, the liquid pressure in the liquid main pipe 21 remains constant because the valves at both ends of the liquid main pipe 21 are closed after the stop of the air conditioner 100.

Further, immediately after the air conditioner 100 stops, when the expansion valves at both ends of the main liquid pipe 21 are closed, the liquid pressure is maintained in a high state, and in addition to this, there is a risk that the liquid pressure rises to exceed the pressure resistance of the main liquid pipe 21 due to the influence of the liquid head difference of the high and low difference and the influence of the rise of the ambient temperature of the liquid pipe, and in order to prevent this, the expansion valves at both ends of the main liquid pipe 21 are closed after, for example, several minutes or so immediately after the stop, so that the liquid pressure at the initial stop is lowered, and the risk of the main liquid pipe 21 being damaged due to the rise of the liquid pressure can be.

Fig. 10 is an example of the case where the outside air temperature and the liquid refrigerant temperature increase with the passage of time longer than that in fig. 9, and the pressure fluctuation in the case where the expansion valve closing control is performed during the stop. If the liquid seal is not provided, the liquid pressure rises due to the pressure corresponding to the saturation pressure as the temperature rises during the day. Since the liquid main pipe 21 in the liquid sealed state has a problem that the liquid main pipe 21 is broken when the liquid pressure excessively increases, the pressure in the liquid main pipe 21 may be reduced by temporarily opening the closed expansion valve and allowing the refrigerant in the liquid main pipe 21 to flow to another device when the liquid pipe temperature detected by the liquid temperature sensor 50 of the outdoor heat exchanger or the liquid pressure detected by the liquid pressure detecting device 71 attached to the liquid main pipe 21 exceeds a predetermined threshold value. Here, the liquid pressure detecting device 71 may be a pressure sensor that detects pressure, or may be a pressure switch that generates an output when a predetermined pressure is exceeded. In the case of the pressure sensor, since the pressure is detected, the expansion valve may be closed again when the pressure drops to or below a predetermined value. In the case of the pressure switch, the expansion valve may be closed again after a predetermined time has elapsed from the time of operation.

Next, a flow of the stop-time expansion valve control used in the present embodiment will be described with reference to fig. 11. The stop-time expansion valve control described here is control after the air conditioner 100 has stopped, and therefore the expansion valve control during operation of the air conditioner 100 is omitted.

First, in step S1, it is confirmed whether the air conditioner 100 is operating or stopped. In the case of operation, the process returns to step S1 before stopping.

In step S2, it is checked whether or not a predetermined time has elapsed after the air conditioner 100 is stopped. Before the predetermined time elapses, the flow proceeds to step S5, where expansion valve control for normally stopping the opening degree, that is, expansion valve control for closing one of the expansion valves at both ends of the main liquid pipe 21 and not closing the other as shown in fig. 1 or 2, is executed. It is also confirmed at step S2 that the predetermined period of time has elapsed because, when the stop-time expansion valve control of the present embodiment shown in fig. 3 is performed after the stop, it is desirable to reduce the liquid pressure in the main liquid pipe 21 to some extent after a certain amount of time has elapsed since the high liquid pressure during operation is maintained, and then to perform the stop-time expansion valve control of the present embodiment.

When it is confirmed in step S2 that the predetermined time has elapsed, the flow proceeds to step S3, where it is confirmed whether or not the liquid pressure in the main liquid pipe 21 is equal to or less than a predetermined value. When the liquid pressure is higher than the predetermined value, the process proceeds to step S5, and expansion valve control for normally stopping the opening degree is executed. The threshold value used here is determined in consideration of the pressure resistance of the main liquid pipe 21, and by setting the threshold value to be lower than the pressure resistance of the main liquid pipe 21, it is possible to avoid breakage of the main liquid pipe 21 even when the liquid pressure of the main liquid pipe 21 increases due to an increase in the outside air temperature or the like after the stop-time expansion valve control of the present embodiment is executed. For example, when the pressure resistance of the main liquid pipe 21 is 4MPa, 2MPa, which is half of the pressure resistance, can be set as the threshold value.

When it is confirmed in step S3 that the liquid pressure in the main liquid pipe 21 is equal to or lower than the predetermined value, the flow proceeds to step S4, where it is confirmed whether or not the main liquid pipe 21 is in a liquid-tight state. In the case of the liquid-sealed state, since there is a problem that the liquid pressure in the main liquid pipe 21 significantly increases as shown in fig. 7 due to an increase in the outside air temperature or the like after the stop-time expansion valve control of the present embodiment is executed, the flow proceeds to step S5, and the expansion valve control of the normal stop opening degree is executed. Whether or not the liquid seal is established can be determined by checking whether or not there is gas refrigerant in the main liquid pipe 21, but it can be determined comprehensively from the difference in level construction, the length of the piping, the temperature of the outlet of the indoor heat exchanger during heating operation, the degree of supercooling, the temperature of the liquid pipe during cooling operation, the degree of supercooling, the temperature of the outside air during stoppage, the temperature of the liquid refrigerant, and the like.

If it is determined in step S4 that the valve is not a liquid seal, the stop time expansion valve control of the present embodiment illustrated in fig. 3 is executed. Thus, when the expansion valves at both ends of the main liquid pipe 21 are closed, the main liquid pipe 21 can be prevented from being damaged by an increase in the liquid pressure, and the refrigerant in the main liquid pipe 21 can be prevented from flowing out to other members.

Even if the flow temporarily proceeds to the stop-time expansion valve control in step S6, if it is necessary to cope with the increase in the hydraulic pressure accompanying the increase in the outside air temperature as shown in fig. 10, the flow may be returned to the expansion valve control of the normal stop opening degree in step S5, and then, if the hydraulic pressure decreases again, the stop-time expansion valve control in step S6 may be executed.

According to the present embodiment described above, since the refrigerant can be prevented from moving from the liquid main pipe to another member when the operation of the air conditioner is stopped, the heating operation or the cooling operation can be performed earlier when the air conditioner is restarted, and the comfort can be improved. Further, since the possibility of compressing the liquid by the compressor can be reduced without increasing the size of the accumulator, the reliability can be improved without increasing the manufacturing cost.

[ example 2 ]

Next, an air conditioner 200 according to embodiment 2 will be described with reference to fig. 12 to 15. Note that, the description is omitted in common with embodiment 1.

< existing expansion valve control at stop >

Fig. 12 is a diagram showing a refrigeration cycle system in which a conventional stop-time expansion valve control is applied to a simultaneous cooling and heating air conditioner 200. The air conditioner 200 shown here is configured such that the outdoor unit 10, the indoor units 40 (collectively, 40a, 40b, 40c, and 40d), and the cooling/heating unit 30 (collectively, 30a, 30b, 30c, and 30 d) existing between the indoor units 40 and the outdoor unit 10 are connected to gas pipes such as the high-low pressure gas main pipe 26, the low-pressure gas main pipe 27, and the like, and the indoor units 40a to 40d are in a state of heating high pressure stop, heating low pressure stop, cooling stop, and air supply (low pressure stop), respectively. In fig. 12, one outdoor unit 10 and four indoor units 40 are illustrated, but the number of outdoor units may be other than that.

One end of the indoor heat exchanger 41 of the indoor unit 40 is connected to the high-low pressure gas main pipe 26 or the low-pressure gas main pipe 27 via the cooling/heating switching unit 30, and the other end is connected to the liquid main pipe 21 via the indoor expansion valve 42.

The cooling/heating switching unit 30 is a branch circuit that selectively connects the indoor unit 40 to the high-low pressure gas main pipe 26 or the low-pressure gas main pipe 27, and includes a high-low pressure gas pipe expansion valve 31 (a general term for 31a, 31b, 31c, and 31 d) and a low-pressure gas pipe expansion valve 32 (a general term for 32a, 32b, 32c, and 32 d). By controlling the opening and closing of the expansion valve 31 for high-pressure and low-pressure gas pipes and the expansion valve 32 for low-pressure gas pipes, the direction of the refrigerant flowing through the indoor unit 40 can be changed, and the operation of the evaporator and the operation of the condenser of the indoor heat exchanger 41 (the general term of 41a, 41b, 41c, and 41 d) can be switched in association with the pressure reduction adjustment and the opening and closing operation of the indoor expansion valves 42 (the general terms of 42a, 42b, 42c, and 42 d).

The outdoor unit 10 includes a compressor 11, a heat exchanger-side four-way valve 12a, a high-low pressure gas pipe-side four-way valve 12b, an outdoor heat exchanger 14, an outdoor expansion valve 15, and an accumulator 18. One end of the outdoor heat exchanger 14 is connected to the liquid main pipe 21 via the outdoor expansion valve 15, and the other end is selectively connected to the discharge side and the suction side of the compressor 11 by the heat exchanger-side four-way valve 12 a. The high-low pressure gas main pipe 26 is selectively connected to the discharge side and the suction side of the compressor 11 by the high-low pressure gas pipe side four-way valve 12 b. In fig. 12, both the high-low pressure gas main pipe 26 and the outdoor heat exchanger 14 are connected to the discharge side of the compressor 11, but may be connected to the suction side depending on the operating state and the cooling/heating load ratio of the indoor unit 40.

Next, the flow of the refrigerant during operation and during stoppage will be described. During operation, a part of the high-temperature and high-pressure gas refrigerant compressed by the compressor 11 is sent to the indoor unit 40a for heating operation through the high-low pressure gas pipe side four-way valve 12b, the high-low pressure gas main pipe 26, and the high-low pressure gas pipe expansion valve 31a of the cooling/heating switching unit 30 a. In the indoor unit 40a, the gas refrigerant flowing into the indoor heat exchanger 41a exchanges heat with indoor air, condenses, becomes a high-pressure two-phase refrigerant or a high-pressure supercooled refrigerant, and is sent to the indoor expansion valve 42 and the liquid main pipe 21.

The remaining portion of the high-temperature and high-pressure gas refrigerant compressed by the compressor 11 is sent to the outdoor heat exchanger 14 via the heat exchanger-side four-way valve 12a, is condensed by heat exchange with outdoor air, becomes a high-pressure two-phase refrigerant or a high-pressure supercooled refrigerant, and is sent to the liquid main pipe 21 via the outdoor expansion valve 15.

The liquid refrigerant sent from the indoor unit 40a and the outdoor unit 10 to the liquid main pipe 21 and merged is sent to the indoor unit 40c in the cooling operation, subjected to flow rate adjustment by the indoor expansion valve 42c, subjected to heat exchange with the indoor air by the indoor heat exchanger 41c, evaporated, and turned into a low-pressure gas refrigerant. Then, the refrigerant is sent to the compressor 11 through the cold/hot switching unit 30c, the low-pressure gas pipe expansion valve 32c, and the low-pressure gas main pipe 27, and the refrigeration cycle is completed. In this operation, the liquid main pipe 21 is substantially filled with the liquid refrigerant, and only the gas refrigerant exists in the high-low pressure gas main pipe 26 and the low-pressure gas main pipe 27.

When the indoor unit 40 stops from this point, as shown in fig. 12, the indoor expansion valve 42a that stops heating is opened, the indoor expansion valve 42b that continues to stop heating is closed, the indoor expansion valve 42c that stops cooling is closed, and the indoor expansion valve 42d that sends air is closed. In the cooling/heating switching unit 30, the high-low pressure gas pipe expansion valve 31a of the cooling/heating switching unit 30a is kept open and the low-pressure gas pipe expansion valve 32b is closed according to the mode in which the indoor unit is operating. The high-and low-pressure gas

pipe expansion valves

31b, 31c, and 31d of the cold-

heat switching units

30b, 30c, and 30d are kept closed, and the low-pressure gas

pipe expansion valves

32b, 32c, and 32d are kept open. In the outdoor unit 10, the outdoor expansion valve 15 is kept open.

Immediately after the compressor 11 stops, the pressures of the outdoor heat exchanger 14 and the high-and low-pressure gas main 26 downstream thereof decrease, and when a certain amount of time has elapsed, the pressures are balanced with the suction-side pressure of the compressor 11. When the equilibrium pressure is lower than the pressure of the liquid main pipe 21, the liquid refrigerant in the liquid main pipe 21 moves to the outdoor heat exchanger 14 through the outdoor expansion valve 15, moves to the high-low pressure gas main pipe 26 through the indoor expansion valve 42a, the indoor heat exchanger 41a, and the high-low pressure gas pipe expansion valve 31a, and the refrigerant movement as shown in fig. 6 occurs. Further, since the heat-exchanger-side four-way valve 12a, the compressor check valve 16, and the like are not completely sealed, the refrigerant in the outdoor heat exchanger 14 and the high-low pressure gas main pipe 26 may move to the accumulator 18. Therefore, when the refrigerant in the main liquid pipe 21 is distributed to each portion of the refrigeration cycle, the operation efficiency is low and it takes time to be effective before the refrigerant is appropriately distributed to each portion of the refrigeration cycle at the time of restart. Further, the amount of liquid returning at the time of starting is increased, the liquid refrigerant separation function of the accumulator is reduced, and the risk of the compressor compressing liquid is increased. To prevent this, the reservoir volume needs to be increased, which increases the manufacturing cost.

< stop expansion valve control of embodiment 2 >

Fig. 13 is a diagram showing a refrigeration cycle system in which the expansion valve control at the time of stop is applied to embodiment 2 of the air conditioner 200 having the same configuration as that of fig. 12. As described above, in the stop-time expansion valve control according to the present embodiment, after the compressor 11 is stopped, all the expansion valves, that is, all the indoor expansion valves 42, all the high-low pressure gas pipe expansion valves 31, all the low-pressure gas pipe expansion valves 32, and all the outdoor expansion valves 15 are closed. This can prevent the liquid refrigerant accumulated in the liquid main pipe 21 from moving to other parts during operation, and the air conditioner 200 of the simultaneous cooling and heating type can also obtain the same effect as that of embodiment 1.

Fig. 14 is a modification of the stop-time expansion valve control of embodiment 2, and is the stop-time expansion valve control in which all of the indoor expansion valves 42 and the outdoor expansion valve 15 are closed after the compressor 11 is stopped. This can prevent the liquid refrigerant accumulated in the liquid main pipe 21 from moving to another place during operation. In the present modification, since expansion valve control of the cold-heat switching unit 30 is not required, the expansion valve can be easily manufactured as compared with fig. 13. In the present modification, the refrigerant in the indoor heat exchanger 41a for heating operation moves to the high-low pressure gas main pipe 26 via the expansion valve 31a for high-low pressure gas pipe, and the refrigerant in the indoor heat exchanger 41c for cooling operation moves to the low-pressure gas main pipe 27 via the expansion valve 32c for low-pressure gas pipe, and the amount of the moving refrigerant is not limited, and therefore, substantially the same effect as that in fig. 13 can be obtained.

Fig. 15 is another modification of the stop-time expansion valve control of embodiment 2, and is the stop-time expansion valve control in which all of the high-low pressure gas pipe expansion valves 31, all of the low-pressure gas pipe expansion valves 32, and the outdoor expansion valve 15 are closed after the compressor 11 is stopped. This can prevent the liquid refrigerant accumulated in the liquid main pipe 21 from moving to another place during operation. In the present modification, since the control of the indoor expansion valve 42 is not necessary, the present modification can be manufactured as compared with fig. 13. In addition, in the present modification, the liquid refrigerant in the liquid main pipe 21 is moved to the indoor heat exchanger 41a and the cold/heat switching unit 30a via the indoor expansion valve 42a for heating operation, but the movement to other locations can be prevented, and therefore, substantially the same effect as that of fig. 13 and 14 can be obtained.

[ example 3 ]

Next, an air conditioner according to embodiment 3 will be described with reference to fig. 16 and 17. Note that, the description of the embodiment is not repeated.

< existing expansion valve control at stop >

Fig. 16 is a diagram showing a refrigeration cycle system in which a conventional stop-time expansion valve control is applied to a two-pipe type simultaneous cooling and heating air conditioner 300. The air conditioner 300 shown here is configured such that the outdoor unit 10, the indoor units 40(40a, 40b, 40c, and 40d), and the cooling/heating switching unit 30 present between the indoor unit 40 and the outdoor unit 10 are connected by the high-pressure main pipe 28 and the low-pressure main pipe 29, and the indoor units 40 are in a state of high-pressure heating stop, low-pressure heating stop, cooling stop, and air supply (low-pressure stop), respectively. Fig. 16 shows a configuration in which there are four indoor units 40 and one outdoor unit 10, but the configuration may be other numbers.

The cold/hot switching unit 30 includes a gas-liquid separator 63, a first expansion valve 64, a second expansion valve 65, a high-pressure pipe switching valve 61 (a general term for 61a, 61b, 61c, 61 d), and a low-pressure pipe switching valve 62 (a general term for 62a, 62b, 62c, 62 d). One end of the indoor heat exchanger 41 of the indoor unit 40 is connected to the high-pressure-pipe switching valve 61 and the low-pressure-pipe switching valve 62, and the other end is connected to the lower liquid pipe of the gas-liquid separator 63 via the indoor expansion valve 42. In addition, solenoid valves are used as the high-pressure-pipe switching valve 61 and the low-pressure-pipe switching valve 62.

The cooling/heating switching means 30 changes the direction of the refrigerant flowing through the indoor unit 40 by controlling the opening and closing of the high-pressure tube switching valve 61 and the low-pressure tube switching valve 62, and switches the evaporator function and the condenser function of the indoor heat exchanger 41 in association with the pressure reduction adjustment and the opening and closing operation of the indoor expansion valve 42.

The outdoor unit 10 includes a compressor 11, a four-way valve 12, an outdoor heat exchanger fan 13, an outdoor heat exchanger 14, an outdoor expansion valve 15, a compressor check valve 16, and an accumulator 18. One end of the outdoor heat exchanger 14 is connected to the high-pressure main pipe 28 or the low-pressure main pipe 29 via the outdoor expansion valve 15. Which main pipe is communicated with differs depending on the pressure of the outdoor heat exchanger 14. Typically, the high pressure is connected to the high pressure main pipe 28, and the low pressure is connected to the low pressure main pipe 29.

Next, the flow of the refrigerant during operation and during stoppage will be described. During operation, the high-temperature and high-pressure gas refrigerant compressed by the compressor 11 is sent to the outdoor heat exchanger 14 via the four-way valve 12, exchanges heat with outdoor air, condenses, becomes a high-pressure two-phase refrigerant, and is sent to the high-pressure main pipe 28 and the cold/heat switching unit 30 through the outdoor expansion valve 15 and the check valve. The high-pressure two-phase refrigerant sent to the cold-heat switching unit 30 is separated into a gas refrigerant and a liquid refrigerant by the gas-liquid separator 63.

A part of the high-pressure gas refrigerant separated by the gas-liquid separator 63 is sent to the indoor unit 40a in the heating operation by the high-pressure pipe switching valve 61a, and is condensed by heat exchange with the indoor air by the indoor heat exchanger 41a to become a liquid refrigerant. The liquid refrigerant flows through the indoor expansion valve 42a and the check valve to the lower liquid pipe of the gas-liquid separator 63. Since the pressure of the lower liquid pipe needs to be lower than the pressure of the gas-liquid separator 63, the pressure of the lower liquid pipe is adjusted by controlling the first expansion valve 64 and the second expansion valve 65.

On the other hand, the liquid refrigerant separated by the gas-liquid separator 63 is sent to the liquid pipe through the first expansion valve. The liquid refrigerant sent from the indoor unit 40a and the gas-liquid separator 63 is sent to the indoor unit 40c performing the cooling operation, is subjected to flow rate adjustment by the indoor expansion valve 42c, is subjected to heat exchange with the indoor air by the indoor heat exchanger 41c, is evaporated, and becomes a low-pressure gas refrigerant. The low-pressure gas refrigerant is sent to the outdoor unit 10 through the low-pressure pipe switching valve 62c and the low-pressure main pipe 29.

The low-pressure gas refrigerant sent to the outdoor unit 10 is sent to the compressor 11 via the check valve, the four-way valve 12, and the accumulator 18, and the refrigeration cycle is completed. In this operation, a large amount of liquid refrigerant is present in the high-pressure main pipe 28 and the liquid piping below the gas-liquid separator 63.

When the indoor unit 40 stops from this point, as shown in fig. 16, the indoor expansion valve 42a that stops heating is opened, the indoor expansion valve 42b that continues to stop heating is closed, the indoor expansion valve 42c that stops cooling is opened, and the indoor expansion valve 42d that blows air is closed. In the cold/hot switching unit 30, the first expansion valve 64 is opened, the second expansion valve 65 is closed, and the high-pressure tube switching valve 61a and the low-pressure tube switching valve 62b are closed. Further, in the outdoor unit 10, the outdoor expansion valve 15 is kept open.

Immediately after the compressor 11 stops, the pressure of the outdoor heat exchanger 14 and the high-pressure main pipe 28 downstream thereof decreases, and when a certain amount of time has elapsed, it balances with the suction-side pressure of the compressor 11. Here, the check valve or the like used in the outdoor unit is not completely sealed, and therefore the refrigerant in the outdoor heat exchanger 14 and the high-pressure main pipe 28 may move to the accumulator 18. Therefore, when the refrigerant in the high-pressure main pipe 28 is appropriately distributed to each portion of the cycle, the operation efficiency is low and it takes time to be effective before the refrigerant is appropriately distributed to each portion of the refrigeration cycle at the time of restart. Further, the amount of liquid returning at the time of starting is increased, the liquid refrigerant separation function of the accumulator is reduced, and the risk of the compressor compressing liquid is increased. To prevent this, the reservoir volume needs to be increased, which increases the manufacturing cost.

< stop expansion valve control of embodiment 3 >

Fig. 17 is a diagram showing a refrigeration cycle system in which the expansion valve control at the time of stop is applied to embodiment 3 of an air conditioner 300 having the same configuration as that of fig. 16. As described herein, in the stop-time expansion valve control of the present embodiment, after the compressor 11 is stopped, all the valves, that is, all the indoor expansion valves 42, all the high-pressure pipe switching valves 61, all the low-pressure pipe switching valves 62, the first expansion valve 64, the second expansion valve 65, and the outdoor expansion valve 15 are closed. This prevents the liquid refrigerant accumulated in the liquid piping below the high-pressure main pipe 28 and the gas-liquid separator 63 from moving to other locations during operation, and the effect equivalent to that of embodiment 1 can be obtained also in the two-pipe type simultaneous cooling and heating air conditioner 300.

[ example 4 ]

Next, an air conditioner of example 4 will be described with reference to fig. 18. Note that, the description of the embodiment is not repeated.

Fig. 18 shows an example in which the supercooling heat exchanger 19 is used during the cooling operation. Part of the high-pressure liquid refrigerant condensed during the cooling operation is sent to the supercooling heat exchanger 19 through the supercooling expansion valve 20 for the purpose of cooling the surplus liquid refrigerant sent to the indoor space, and after cooling the surplus liquid refrigerant, is sent to the compressor suction side. In this case, even if the outdoor unit is positioned downward and the indoor unit is positioned upward by the step construction, the liquid pipe is filled with liquid even if the pipe length is long and the compression of the liquid pipe is increased. Further, since the liquid can be cooled to a temperature lower than the temperature of the outside air depending on the conditions, the liquid seal is formed when the expansion valves in front of and behind the liquid pipe are directly closed. When the temperature of the liquid refrigerant rises due to the outside air, there is a risk that the pressure of the liquid refrigerant rises.

In the case of using the supercooling heat exchanger 19 during cooling, the valve should not be closed arbitrarily. It may be closed after the liquid tube temperature rises, or after the refrigerant in the liquid tube moves to some extent towards other equipment. The pressure and the change in the movement of the refrigerant can be estimated from the temperature and the pressure of the liquid pipe during the stop.

Description of the symbols

100. 200, 300, 400-air conditioner, 10-outdoor unit, 11-compressor, 12-four-way valve, 12 a-heat exchanger side four-way valve, 12 b-high-low pressure gas pipe side four-way valve, 13-fan for outdoor heat exchanger, 14-outdoor heat exchanger, 15-outdoor expansion valve, 16-compressor check valve, 18-reservoir, 19-supercooling heat exchanger, 20-supercooling expansion valve, 21-liquid main pipe, 24-gas main pipe, 26-high-low pressure gas main pipe, 27-low pressure gas main pipe, 28-high pressure main pipe, 29-low pressure main pipe, 30a, 30b, 30c, 30 d-cold-heat switching unit, 31a, 31b, 31c, 31 d-high-low pressure gas pipe expansion valve, 32a, 32b, 32c, 32 d-low pressure gas pipe expansion valve, 40a, 40b, 40c, 40 d-indoor unit, 41a, 40b, 40d, 41b, 41c, 41 d-an indoor heat exchanger, 42a, 42b, 42c, 42 d-an indoor expansion valve, 45a, 45b, 45c, 45 d-an indoor heat exchanger gas temperature sensor, 46a, 46b, 46c, 46 d-an indoor heat exchanger liquid temperature sensor, 47-a discharge temperature sensor, 49a, 49b, 49c, 49 d-an indoor heat exchanger fan, 50-an outdoor heat exchanger liquid temperature sensor, 51-an outdoor heat exchanger gas temperature sensor, 52-a liquid pipe temperature sensor, 55-a discharge pressure detection sensor, 56-a suction pressure detection sensor, 61a, 61b, 61c, 61 d-a high-pressure pipe switching valve, 62a, 62b, 62c, 62 d-a low-pressure pipe switching valve, 63-a gas-liquid separator, 64-a first expansion valve, 65-a second expansion valve, 71-liquid pressure detecting means, 72-outside air temperature sensor, 73a, 73b, 73c, 73 d-indoor temperature sensor.

Claims

1. An air conditioner is provided with:

an outdoor unit having a compressor, an outdoor heat exchanger, and an outdoor expansion valve;

an indoor unit having an indoor heat exchanger and an indoor expansion valve;

a liquid pipe connecting the outdoor unit and the indoor unit; and

a gas pipe connecting the outdoor unit and the indoor unit,

the air conditioner is characterized in that the air conditioner is provided with a fan,

one end of the outdoor heat exchanger is connected to the liquid pipe via the outdoor expansion valve,

one end of the indoor heat exchanger is connected to the liquid pipe via the indoor expansion valve,

when the liquid pressure in the liquid pipe is equal to or lower than a predetermined value after a predetermined time has elapsed since the compressor is stopped, and the liquid pipe is not liquid-sealed, both the outdoor expansion valve and the indoor expansion valve are closed, and the refrigerant is prevented from moving from the liquid pipe to another member during the stop of the operation.

2. An air conditioner is provided with:

an indoor unit having an indoor heat exchanger and an indoor expansion valve;

a cold-hot switching unit having a high-low pressure gas pipe switching valve and a low-pressure gas pipe switching valve;

a liquid pipe connecting the outdoor unit and the indoor unit;

a high-low pressure gas pipe connecting the outdoor unit and the high-low pressure gas pipe switching valve;

a low pressure gas pipe connecting the outdoor unit and the low pressure gas pipe switching valve; and

a gas pipe connecting the indoor unit and the cold/hot switching unit,

when the liquid pressure in the liquid pipe is equal to or lower than a predetermined value after a predetermined time has elapsed since the compressor is stopped, and the liquid pressure in the liquid pipe is not equal to or lower than the predetermined value, both the outdoor expansion valve and the indoor expansion valve are closed, or all of the outdoor expansion valve, the high-low pressure gas pipe switching valve, and the low-pressure gas pipe switching valve are closed, and the refrigerant is prevented from moving from the liquid pipe to another member when the operation is stopped.

3. An air conditioner is provided with:

an indoor unit having an indoor heat exchanger and an indoor expansion valve;

a cold-hot switching unit having a gas-liquid separator, a high-pressure pipe switching valve, a low-pressure pipe switching valve, and a hydraulic pressure regulating valve;

a high pressure pipe connecting the outdoor unit and the cold/heat switching unit;

a low pressure pipe connecting the outdoor unit and the cold/heat switching unit;

a gas pipe connecting the indoor unit and the cold/hot switching unit; and

a liquid pipe connecting the indoor unit and the cold/hot switching unit,

one end of the outdoor heat exchanger is connected to the high-pressure pipe via the outdoor expansion valve,

when the liquid pressure in the liquid pipe is equal to or lower than a predetermined value after a predetermined time has elapsed since the compressor is stopped, and the liquid pressure in the liquid pipe is not liquid-sealed, all of the outdoor expansion valve, the indoor expansion valve, the high-pressure pipe switching valve, the low-pressure pipe switching valve, and the hydraulic pressure regulating valve are closed, and the refrigerant is prevented from moving from the liquid pipe to another member when the operation is stopped.

4. An air conditioner according to any one of claims 1 to 3,

when the hydraulic pressure in the liquid pipe rises after the valves are closed, any of the valves is opened.

5. An air conditioner according to any one of claims 1 to 3,

the detection of the liquid pressure in the liquid pipe is estimated based on an output of a temperature sensor or a pressure sensor provided in a refrigeration cycle, or an output of an outside air temperature sensor provided in the outdoor unit.