EP3431903A1

EP3431903A1 - Air-conditioning apparatus and method for operating the same

Info

Publication number: EP3431903A1
Application number: EP18183852.5A
Authority: EP
Inventors: Masayuki Takigawa; Takahiro Kato; Tatsuhiro Yasuda; Tomohiro SAKAGUCHI
Original assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Current assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2017-07-20
Filing date: 2018-07-17
Publication date: 2019-01-23
Also published as: JP2019020080A

Abstract

An air-conditioning apparatus is provided that can prevent a shortage of lubricating oil supplied to a sliding part of a compressor. The air-conditioning apparatus includes a compressor 21 placed inside an outdoor unit 2 and compressing a refrigerant, an oil supply pump supplying lubricating oil to a sliding part in accordance with a rotational speed of the compressor 21, a bypass pipe 57 bypassing an outdoor heat exchanger 24 and an indoor heat exchanger 71 to connect a discharge side and a suction side of the compressor 21, a bypass valve 58 provided in the bypass pipe 57, and a control unit 10 controlling operation of the bypass valve 58, wherein the control unit 10 opens the bypass valve 58 when a low-pressure refrigerant pressure on the suction side is greater than or equal to a predetermined value.

Description

[Technical Field]

The present invention relates to an air-conditioning apparatus and a method for operating the same.

[Background Art]

A multi-type air-conditioning apparatus including a plurality of indoor units connected to one outdoor unit is known (see PCT International Publication No. WO 2012/042573 , hereinafter referred to as " WO 2012/042573 ").
WO 2012/042573 discloses a high-low pressure bypass pipe that connects a discharge side and a suction side of a compressor. A bypass expansion device is disposed in the high-low pressure bypass pipe and composition of a mixed refrigerant is obtained using state quantity before and after the bypass expansion device.

[Summary of Invention]

[Technical Problem]

Incidentally, when an outdoor temperature is high, such as during summer, it is necessary to decrease a rotational speed of an electric compressor by reducing its input so as not to exceed a use temperature limit of electrical components in an outdoor unit. However, when the rotational speed of the compressor decreases, lubricating oil supplied to a sliding part in accordance with the rotational speed of the compressor becomes insufficient, and this may cause failure of the compressor.
The present invention has been achieved in light of such a situation, and an object thereof is to provide an air-conditioning apparatus that can prevent a shortage of lubricating oil supplied to a sliding part of a compressor and a method for operating the air-conditioning apparatus.

[Solution to Problem]

In order to solve the above-described problems, an air-conditioning apparatus and a method for operating the same according to the present invention employ the following solutions.
Specifically, an air-conditioning apparatus according to the present invention includes a compressor placed inside an outdoor unit and compressing a refrigerant, a lubricating oil supply unit supplying lubricating oil to a sliding part in accordance with a rotational speed of the compressor, a bypass flow path bypassing a condenser and a evaporator to connect a discharge side and a suction side of the compressor, an on-off valve provided in the bypass flow path, and a control unit controlling operation of the on-off valve, wherein the control unit opens the on-off valve when a pressure on the suction side is greater than or equal to a predetermined value.
The bypass flow path bypassing the condenser and the evaporator to connect the discharge side and the suction side of the compressor is provided. Opening the on-off valve provided in the bypass flow path returns part of a high-pressure refrigerant discharged from the compressor back to the suction side, to reduce a high-low pressure difference before and after the compressor, reduce a load on the compressor, and increase the rotational speed of the compressor.
When the outdoor temperature is high, the pressure on the suction side of the compressor becomes high, and therefore it is necessary to limit the rotational speed of the compressor to a predetermined value or less for electrical components protection. Limiting the rotational speed of the compressor may cause a shortage of lubricating oil supplied by the lubricating oil supply unit. Therefore, the control unit opens the on-off valve when the pressure on the suction side of the compressor exceeds the predetermined value. Accordingly, the rotational speed of the compressor increases to eliminate the shortage of the lubricating oil supplied by the lubricating oil supply unit.
For the predetermined value of the pressure on the suction side, a pressure value used for protection control to protect the compressor from failure can be used, for example.
Moreover, in the air-conditioning apparatus according to the present invention, the control unit opens the on-off valve when the rotational speed of the compressor is less than or equal to a predetermined value.
When the rotational speed of the compressor is less than or equal to the predetermined value, the shortage of the supplied lubricating oil may be caused, and accordingly the on-off valve is opened. In addition, the determination of whether the on-off valve is opened is made in combination with the pressure on the suction side of the compressor, thereby avoiding unnecessarily actuating the on-off valve to be opened.
For the predetermined value of the rotational speed of the compressor, a rotational speed which may cause the shortage of the lubricating oil supplied by the lubricating oil supply unit is used, for example. This rotational speed is predetermined in accordance with types, capacity, and the like of the compressor.
Further, in the air-conditioning apparatus according to the present invention, the control unit opens the on-off valve when an ambient temperature of the compressor is greater than or equal to a predetermined value.
When the ambient temperature of the compressor is greater than or equal to the predetermined value, the pressure on the suction side of the compressor rises, and accordingly the timing of opening the on-off valve is determined in accordance with the ambient temperature of the compressor. In addition, the determination of whether the on-off valve is opened is made in combination with the pressure on the suction side of the compressor and the rotational speed of the compressor, thereby avoiding unnecessarily actuating the on-off valve to be opened.
For the ambient temperature of the compressor, a temperature measured by an outdoor unit temperature sensor provided in the outdoor unit can be used.
For the predetermined value of the ambient temperature of the compressor, a temperature corresponding to the pressure value used for protection control to protect the compressor from failure is used, for example.
Furthermore, in the air-conditioning apparatus according to the present invention, the control unit closes the on-off valve when the pressure on the suction side is less than or equal to a predetermined value.
When the on-off valve is opened, the rotational speed of the compressor rises, and accordingly the pressure on the suction side drops. When the pressure on the suction side falls below the predetermined value, the protection control of the compressor is avoided, and thus it is preferable that the on-off valve be closed to return the air-conditioning apparatus to normal operation. Thus, when the pressure on the suction side is less than or equal to the predetermined value, the on-off valve is closed.
Further, a method for operating an air-conditioning apparatus according to the present invention is a method for operating an air-conditioning apparatus including a compressor placed inside an outdoor unit and compressing a refrigerant, a lubricating oil supply unit supplying lubricating oil to a sliding part in accordance with a rotational speed of the compressor, a bypass flow path bypassing a condenser and an evaporator to connect discharge side and suction side of the compressor, and an on-off valve provided in the bypass flow path, wherein the on-off valve is opened when a pressure on the suction side is greater than or equal to a predetermined value.

[Advantageous Effects of Invention]

It is possible to prevent the shortage of the lubricating oil supplied to the sliding part of the compressor by opening the on-off valve in the bypass flow path to increase the rotational speed of the compressor.

[Brief Description of Drawings]

[Fig. 1]
Fig. 1 is a diagram showing a schematic configuration of a refrigerant circuit of a multi-type air-conditioning apparatus according to an embodiment of the present invention.
[Fig. 2]
Fig. 2 is a perspective view showing a compressor of Fig. 1.
[Fig. 3]
Fig. 3 is a schematic block diagram showing a control unit of the multi-type air-conditioning apparatus of Fig. 1.
[Fig. 4]
Fig. 4 is a vertical sectional view showing the compressor of Fig. 1.

[Description of Embodiments]

Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.
Fig. 1 illustrates a schematic configuration of a refrigerant circuit of a multi-type air-conditioning system (air-conditioning apparatus) 1 according to the embodiment.
A multi-type air-conditioning system 1 includes one outdoor unit 2, a gas-side pipe 4 and a liquid-side pipe 5 that are led out from the outdoor unit 2, a plurality of indoor units 7A, 7B connected in parallel between the gas-side pipe 4 and the liquid-side pipe 5 via respective branch units 6, and a control unit 10. In Fig. 1, the two indoor units 7A, 7B are shown, but the number thereof may be three or more. Unless each of the indoor units 7A, 7B needs to be distinguished from one another, reference numeral 7 is hereinafter used and the indoor unit is described as the indoor unit 7.
The outdoor unit 2 includes an inverter-driven compressor 21 that compresses a refrigerant, an oil separator 22 that separates chiller oil from refrigerant gas, a four-way change-over valve 23 changing over a circulation direction of the refrigerant, an outdoor heat exchanger 24 that exchanges heat between the refrigerant and outdoor air, a supercooling coil 25 configured integrally with the outdoor heat exchanger 24, an outdoor electronic expansion valve for heating (EEVH) 26, a receiver 27 that stores therein a liquid refrigerant, a supercooling heat exchanger 28 that supercools the liquid refrigerant, an electronic expansion valve for supercooling (EEVSC) 29 that controls an amount of the refrigerant branched to the supercooling heat exchanger 28, an accumulator 30 that separates the liquid refrigerant from the refrigerant gas absorbed into the compressor 21 so as to absorb only gas refrigerant into the compressor 21, a gas-side operating valve 31, and a liquid-side operating valve 32. An outdoor fan 35 that sends the outdoor air to the outdoor heat exchanger 24 is provided at a position facing a heat transfer surface of the outdoor heat exchanger 24.
The constituent elements of the outdoor unit 2 described above are connected to one another via refrigerant pipes such as a discharge pipe 33A, a gas pipe 33B, a liquid pipe 33C, a gas pipe 33D, a suction pipe 33E, and a supercooling branch pipe 33F, and constitute an outdoor refrigerant circuit 34.
The suction pipe 33E is provided with a low-pressure refrigerant pressure sensor 54 that measures the pressure of low-pressure gas refrigerant. Low-pressure refrigerant pressure LP measured by the low-pressure refrigerant pressure sensor 54 is transmitted to the control unit 10.
The outdoor unit 2 includes inside thereof an outdoor unit temperature sensor 55 that measures a temperature inside the outdoor unit 2. An outdoor temperature Tout measured by the outdoor unit temperature sensor 55 is transmitted to the control unit 10. An ambient temperature of the compressor 21 is estimated on the basis of the outdoor temperature Tout.
A parallel circuit constituted by a first oil return circuit 37 that includes a fixed throttle (throttle) 36 such as a capillary tube and a second oil return circuit 60 that includes a solenoid valve 38 and a fixed throttle (throttle) 39 such as a capillary tube is connected between the oil separator 22 and the suction pipe 33E connected to the compressor 21, so as to return the chiller oil separated from the discharged refrigerant gas within the oil separator 22 to the compressor 21 by a predetermined amount at a time.
Between the discharge side and the suction side of the compressor 21, a bypass pipe (bypass flow path) 57 is provided. The bypass pipe 57 is provided to bypass the outdoor heat exchanger 24 and indoor heat exchangers 71. More specifically, as shown in Fig. 2, the bypass pipe 57 is provided between a discharge chamber 45 of the compressor 21 and an intermediate position of a housing 40 of the compressor 21 in a height direction. The compressor 21 is a low-pressure housing-type compressor as described below with reference to Fig. 4. Therefore, the intermediate position of the housing 40 in the height direction is suction side of the gas refrigerant.
The bypass pipe 57 includes a bypass valve 58. The bypass valve 58 is an on-off valve and actuated to be opened/closed in accordance with a command from the control unit 10.
It should be noted that the bypass pipe 57 connects the discharge side and the suction side of the compressor 21 in common with the aforementioned oil return circuits 37, 60 but is separately provided from the oil return circuits 37, 60. The bypass pipe 57 is not for oil return and accordingly does not include a throttle mechanism like the oil return circuits 37, 60.
The gas-side pipe 4 and the liquid-side pipe 5 are the refrigerant pipes connected to the gas-side operating valve 31 and the liquid-side operating valve 32 of the outdoor unit 2. At a time of installing the multi-type air-conditioning system 1 on site, lengths of the gas-side pipe 4 and the liquid-side pipe 5 are set depending on distances between the outdoor unit 2 and the indoor units 7A, 7B connected to the outdoor unit 2. An appropriate number of branch units 6 are provided halfway along the gas-side pipe 4 and the liquid-side pipe 5, and an appropriate number of indoor units 7A, 7B are each connected to the gas-side pipe 4 and the liquid-side pipe 5 via these branch units 6. A closed one-system refrigerant cycle 3 is thereby constituted.
Each of the indoor units 7A, 7B includes the indoor heat exchanger 71 that exchanges heat between the refrigerant and indoor air to be used for indoor air-conditioning, an indoor electronic expansion valve for cooling (EEVC) 72, and an indoor fan 73 that circulates the indoor air through the indoor heat exchanger 71. The indoor units 7A and 7B are connected to the respective branch units 6 via a corresponding indoor-side branch gas pipe 4A or 4B and a corresponding indoor-side branch liquid pipe 5A or 5B.
For example, as shown in Fig. 3, the control unit 10 is constituted by a microcomputer mainly including a CPU (Central Processing Unit) 11 that executes programs, main storage 12 such as RAM (Random Access Memory) that temporarily stores calculation results and the like by the CPU 11, auxiliary storage 13 that stores the programs executed by the CPU 11, an input/output interface 14 such as digital I/O, and a communication interface 15.
As shown in Fig. 4, the compressor 21 is a hermetic electric scroll compressor. The compressor 21 includes the vertical cylindrical housing 40 constituting a shell and having sealing structure, and a scroll compression mechanism 41 is assembled in an upper portion of the housing 40. The scroll compression mechanism 41 includes a pair of a fixed scroll 42 and an orbiting scroll 43 and is assembled via a bearing member 44 securely arranged within the housing 40. The high-pressure refrigerant gas compressed by the scroll compression mechanism 41 is discharged to the discharge chamber 45 and is sent out toward the refrigerant cycle 3 via the discharge pipe 33A.
A motor 48 including a stator 46 and a rotor 47 is securely arranged under the scroll compression mechanism 41 in the housing 40. A drive shaft 49 is integrally coupled to the rotor 47 of the motor 48. A crank pin provided on an upper end of the drive shaft 49 is coupled to a back surface of the orbiting scroll 43 of the scroll compression mechanism 41 via a drive bush and a slewing bearing, and thereby the scroll compression mechanism 41 can be driven.
The motor 48 is controlled by the control unit 10 (see Fig. 1) and a rotational speed of the motor 48 can be changed by inverter control. The control unit 10 acquires the rotational speed of the motor 48 (rotational speed of the compressor) at all times.
The drive shaft 49 is supported by the bearing member 44 at its upper end and is supported by a bearing member 50 provided in a lower portion of the housing 40 at its lower end. An oil supply pump 51 is provided between this lower end of the drive shaft 49 and the bearing member 50, and lubricating oil stored in an oil sump 52 in the inner bottom of the housing 40 can be supplied to a sliding part of the scroll compression mechanism 41 via an oil supply port 53 provided inside the drive shaft 49. Such oil supply mechanism (lubricating oil supply unit) employs the oil supply pump 51 operated in accordance with the rotational speed of the drive shaft 49, that is, the rotational speed of the compressor 21, and therefore the amount of supplied oil varies in accordance with the rotational speed of the compressor 21. In other words, when the rotational speed of the compressor 21 is low, the amount of supplied oil decreases, whereas when the rotational speed of the compressor 21 is high, the amount of supplied oil increases.
The suction pipe 33E is provided on a side wall of the housing 40 to be opened in a space between the motor 48 and the scroll compression mechanism 41. The low-pressure gas refrigerant is led via the suction pipe 33E. Therefore, the compressor 21 is a low-pressure housing-type compressor and maintains low-pressure atmosphere in the housing 40.
It should be noted that the compressor 21 is not necessarily a hermetic electric scroll compressor as described above and may be an open-type scroll compressor having an oil sump inside its housing or may also be a different type of a compressor rather than a scroll compressor. In addition, the oil supply mechanism supplying the lubricating oil to the sliding part of the compressor 21 is not limited to the aforementioned configuration, and any type of oil supply mechanism in which the amount of supplied oil is determined in accordance with the rotational speed of the compressor 21 may be used.

[Cooling operation]

In the aforementioned multi-type air-conditioning system 1, cooling operation is performed as follows.
The high-temperature and high-pressure refrigerant gas compressed by the compressor 21 is discharged to the discharge pipe 33A, and the oil separator 22 separates the chiller oil contained in the refrigerant. Thereafter, the refrigerant gas circulates toward the gas pipe 33B via the four-way change-over valve 23, exchanges heat with the outdoor air sent by the outdoor fan 35 and is condensed into a liquid refrigerant in the outdoor heat exchanger 24. After being further cooled by the supercooling coil 25, this liquid refrigerant passes through the outdoor electronic expansion valve 26 and is temporarily stored in the receiver 27.
The liquid refrigerant of a circulating amount regulated in the receiver 27 is branched in part to the supercooling branch pipe 33F while being distributed through the supercooling heat exchanger 28 via the liquid pipe 33C. The resultant liquid refrigerant exchanges heat with the refrigerant expanded by the electronic expansion valve for supercooling (EEVSC) 29 and is thereby supercooled. This liquid refrigerant is led out from the outdoor unit 2 to the liquid-side pipe 5 via the liquid-side operating valve 32. The liquid refrigerant led out to the liquid-side pipe 5 is further branched to the branch liquid pipes 5A, 5B of the respective indoor units 7A, 7B by the branch units 6.
The liquid refrigerant branched to the branch liquid pipes 5A, 5B flows into the indoor units 7A, 7B and is expanded by the respective indoor electronic expansion valves (EEVC) 72, in each of which the liquid refrigerant flows, as a gas-liquid two-phase flow, into the indoor heat exchanger 71. In each of the indoor heat exchangers 71, the indoor air circulated by the indoor fan 73 exchanges heat with the refrigerant, and the indoor air is cooled and used for indoor cooling. On the other hand, the refrigerant is transformed into gas, the gas refrigerant reaches the branch units 6 via the branch gas pipes 4A, 4B, and the gas refrigerant meets with the refrigerant gas from the other indoor unit in the gas-side pipe 4.
The refrigerant gas meeting together in the gas-side pipe 4 returns toward the outdoor unit 2, reaches the suction pipe 33E via the gas-side operating valve 31, the gas pipe 33D, and the four-way change-over valve 23, meets with the refrigerant gas from the branch pipe 33F, and is then led into the accumulator 30. In the accumulator 30, the liquid refrigerant contained in the refrigerant gas is separated and only the gas refrigerant is absorbed into the compressor 21. This refrigerant is compressed again in the compressor 21. Thus, the cooling operation is performed by repeating the aforementioned cycle.

[Heating operation]

Meanwhile, heating operation is performed as follows.
The high-temperature and high-pressure refrigerant gas compressed by the compressor 21 is discharged to the discharge pipe 33A, the oil separator 22 separates the chiller oil contained in the refrigerant, and then the refrigerant gas circulates toward the gas pipe 33D by the four-way change-over valve 23. This refrigerant is led out from the outdoor unit 2 via the gas-side operating valve 31 and the gas-side pipe 4, and further led into the indoor units 7A, 7B via the branch units 6 and the respective indoor-side branch gas pipes 4A, 4B.
The high-temperature and high-pressure refrigerant gas led into the indoor units 7A, 7B exchanges heat with the indoor air circulated by the indoor fan 73 in the indoor heat exchanger 71, and the indoor air is heated and used for indoor heating. The liquid refrigerant resulting from condensation in the indoor heat exchanger 71 reaches the branch units 6 via the indoor electronic expansion valve (EEVC) 72 and the branch liquid pipe 5A, 5B, meets with the refrigerant from the other indoor unit, and then returns to the outdoor unit 2 via the liquid-side pipe 5.
The refrigerant returned to the outdoor unit 2 reaches the supercooling heat exchanger 28 via the liquid-side operating valve 32 and the liquid pipe 33C and is supercooled similarly to the cooling operation. Thereafter, the resultant refrigerant flows into the receiver 27 and is temporarily stored in the receiver 27, and thereby the circulating amount of the refrigerant is regulated in the receiver 27. This liquid refrigerant is supplied to the outdoor electronic expansion valve (EEVH) 26 via the liquid pipe 33C and expanded in the outdoor electronic expansion valve (EEVH) 26, and the liquid refrigerant then flows into the outdoor heat exchanger 24 via the supercooling coil 25.
In the outdoor heat exchanger 24, the refrigerant exchanges heat with the outdoor air sent from the outdoor fan 35, and the refrigerant absorbs the heat from the outdoor air and is evaporated into gas. This refrigerant led out from the outdoor heat exchanger 24 meets with the refrigerant from the supercooling branch pipe 33F via the gas pipe 33B, the four-way change-over valve 23, and the suction pipe 33E, and is led into the accumulator 30. In the accumulator 30, the liquid refrigerant contained in the refrigerant gas is separated and only the gas refrigerant is absorbed into the compressor 21. This refrigerant is compressed again by the compressor 21. Thus, the heating operation is performed by repeating the aforementioned cycle.
During the cooling operation or the heating operation described above, the chiller oil separated from the discharged refrigerant gas in the oil separator 22 is returned toward the compressor 21 via the first oil return circuit 37 including the fixed throttle 36 and the second oil return circuit 60 including the solenoid valve 38 and the fixed throttle 39 that are connected to each other in parallel. This secures a certain amount of the chiller oil in the compressor 21 and allows slide portions in the compressor 21 to be lubricated. The solenoid valve 38 provided in the second oil return circuit 60 is configured to be able to regulate a returning amount of the oil separated in the oil separator 22 toward the compressor 21 by being actuated to be opened/closed at appropriate timing during the steady cooling operation or heating operation.

[Bypass valve control]

Next, control on the bypass valve 58 provided in the bypass pipe 57 will be described.
When an outdoor temperature is high, such as during summer, the low-pressure refrigerant pressure LP on the suction side of the compressor 21 becomes high, and therefore it is necessary to limit the rotational speed of the compressor 21 to a predetermined value or less for electrical components protection. Limiting the rotational speed of the compressor 21 may cause a shortage of the lubricating oil supplied by the oil supply mechanism using the oil supply pump 51 (see Fig. 4). Thus, the control unit 10 opens the bypass valve 58 being closed when the pressure on the suction side of the compressor 21 exceeds a predetermined value. Specifically, when the low-pressure refrigerant pressure LP measured by the low-pressure refrigerant pressure sensor 54 (see Fig. 1) exceeds the predetermined value, the bypass valve 58 is opened. This returns part of the high-pressure refrigerant discharged from the compressor 21 back to the suction side to reduce a high-low pressure difference before and after the compressor 21, reduce a load on the compressor 21, and increase the rotational speed of the compressor 21. By increasing the rotational speed of the compressor 21, the shortage of the lubricating oil supplied by the oil supply pump 51 can be eliminated.
It should be noted that for the predetermined value of the pressure on the suction side for opening the bypass valve 58, a pressure value used for protection control to protect the compressor 21 from failure (e.g., 1.2 MPa) can be used, for example.
To the condition of opening the bypass valve 58, it may be added that the rotational speed of the compressor 21 is less than or equal to a predetermined value. For the predetermined value of the rotational speed of the compressor 21, a rotational speed which may cause the shortage of the lubricating oil supplied by the oil supply pump 51 (e.g., 33 rps) is used, for example. This rotational speed is predetermined in accordance with types, capacity, and the like of the compressor.
Moreover, to the condition of opening the bypass valve 58, it may be added that the outdoor temperature Tout measured by the outdoor unit temperature sensor 55 is greater than or equal to a predetermined value. For the predetermined value of the outdoor temperature Tout, a temperature corresponding to the pressure value used for protection control to protect the compressor 21 from failure (e.g., 46°C) is used, for example.
The control unit 10 monitors the pressure on the suction side, that is, the low-pressure refrigerant pressure LP measured by the low-pressure refrigerant pressure sensor 54 and closes the bypass valve 58 when the low-pressure refrigerant pressure LP is less than or equal to a predetermined value. For this predetermined value, the pressure value used when the bypass valve 58 is opened or a different value around the pressure value may be used.
According to the embodiment, the following effects are exerted.
When the low-pressure refrigerant pressure LP of the compressor 21 exceeds the predetermined value, the bypass valve 58 is opened. Accordingly, the rotational speed of the compressor 21 increases to eliminate the shortage of the lubricating oil supplied by the oil supply pump 51.
When the rotational speed of the compressor 21 is less than or equal to the predetermined value, the shortage of the supplied lubricating oil may be caused, and accordingly the bypass valve 58 is opened. In addition, the determination of whether the bypass valve 58 is opened is made in combination with the low-pressure refrigerant pressure LP of the compressor 21, thereby avoiding unnecessarily actuating the bypass valve 58 to be opened.
When the outdoor temperature Tout is greater than or equal to the predetermined value, the pressure on the suction side of the compressor 21 rises, and accordingly the timing of opening the bypass valve 58 is determined. In addition, the determination of whether the bypass valve 58 is opened is made in combination with the low-pressure refrigerant pressure LP and the rotational speed of the compressor 21, thereby avoiding unnecessarily actuating the bypass valve 58 to be opened.
When the bypass valve 58 is opened, the rotational speed of the compressor 21 rises, and accordingly the low-pressure refrigerant pressure LP being the pressure on the suction side drops. When the low-pressure refrigerant pressure LP falls below the predetermined value, the protection control of the compressor 21 is avoided, and thus the bypass valve 58 is closed to return the multi-type air-conditioning system 1 to normal operation. This makes it possible to continue effective operation while preventing the shortage of the supplied lubricating oil.
It should be noted that in the aforementioned embodiment, the bypass pipe 57 is configured to connect the discharge chamber 45 and the side of the housing 40 of the compressor 21 but the present invention is not limited to this configuration, so long as the bypass pipe 57 connects the discharge side and the suction side of the compressor 21 to decrease the high-low pressure difference before and after the compressor 21. That is, the bypass pipe 57 may be configured to connect the discharge pipe 33A and the suction pipe 33E, for example.

[Reference Signs List]

1 multi-type air-conditioning system (air-conditioning apparatus)
2 outdoor unit
7 indoor unit
10 control unit
21 compressor
51 oil supply pump (lubricating oil supply unit)
53 oil supply port (lubricating oil supply unit)
54 low-pressure refrigerant pressure sensor
55 outdoor unit temperature sensor
57 bypass pipe (bypass flow path)

Claims

An air-conditioning apparatus comprising:
a compressor placed inside an outdoor unit and compressing a refrigerant;

a lubricating oil supply unit supplying lubricating oil to a sliding part in accordance with a rotational speed of the compressor;

a bypass flow path bypassing a condenser and an evaporator to connect a discharge side and a suction side of the compressor;

an on-off valve provided in the bypass flow path; and

a control unit controlling operation of the on-off valve,

wherein the control unit opens the on-off valve when a pressure on the suction side is greater than or equal to a predetermined value.
The air-conditioning apparatus according to claim 1,
wherein the control unit opens the on-off valve when a rotational speed of the compressor is less than or equal to a predetermined value.
The air-conditioning apparatus according to claim 1 or 2,
wherein the control unit opens the on-off valve when an ambient temperature of the compressor is greater than or equal to a predetermined value.
The air-conditioning apparatus according to any one of claims 1 to 3,
wherein the control unit closes the on-off valve when a pressure on the suction side is less than or equal to a predetermined value.
A method for operating an air-conditioning apparatus comprising:
a compressor placed inside an outdoor unit and compressing a refrigerant;

a lubricating oil supply unit supplying lubricating oil to a sliding part in accordance with a rotational speed of the compressor;

a bypass flow path bypassing a condenser and an evaporator to connect a discharge side and a suction side of the compressor; and

an on-off valve provided in the bypass flow path,

wherein the on-off valve is opened when a pressure on the suction side is greater than or equal to a predetermined value.