CN106766371B

CN106766371B - two-stage compressor heat pump and oil return control system and control method thereof

Info

Publication number: CN106766371B
Application number: CN201611075943.6A
Authority: CN
Inventors: 梁尤轩; 沈军; 赵桓; 谭锋; 卢耀汕
Original assignee: Gree Electric Appliances Inc of Zhuhai
Current assignee: Gree Electric Appliances Inc of Zhuhai
Priority date: 2016-11-29
Filing date: 2016-11-29
Publication date: 2019-12-10
Anticipated expiration: 2036-11-29
Also published as: CN106766371A

Abstract

the invention provides a double-stage compressor heat pump and an oil return control system and method thereof, wherein the double-stage compressor heat pump comprises an indoor heat exchanger, an outdoor heat exchanger, a low-pressure compressor (1) and a high-pressure compressor (2), an exhaust port of the low-pressure compressor (1) is communicated with an air suction port of the high-pressure compressor (2) through a medium-pressure pipeline (17), an exhaust end of the high-pressure compressor (2) is also connected with an oil separator (3), oil separated by the oil separator (3) is branched into two paths through an oil return pipeline (18), one path is connected to an air suction end of the low-pressure compressor (1) through a low-pressure oil return pipeline (19), and the other path is connected to an air suction end of the high-pressure compressor (2) through a high-pressure oil. According to the invention, the low-pressure compressor and the high-pressure compressor can be respectively returned with oil according to requirements, so that the oil return of the low-pressure compressor and the oil return of the high-pressure compressor are uniform; the abnormal shutdown phenomenon caused by the abrasion of the cylinder body is effectively prevented, the service life of the compressor is prolonged, and the performance of the heat pump is improved.

Description

Two-stage compressor heat pump and oil return control system and control method thereof

Technical Field

the invention belongs to the technical field of air-conditioning heat pumps, and particularly relates to a two-stage compressor heat pump and an oil return control system and method thereof.

Background

The existing double-stage compression air-supplying enthalpy-increasing technology is one of mainstream technologies for solving low-temperature heating, and has large heating capacity and high energy efficiency at low temperature; on the other hand, compared with a single-stage system, the two-stage compression can reduce the high-low pressure ratio and the exhaust temperature, and is beneficial to improving the unit performance and prolonging the service life of the compressor. In an air conditioning system, a compressor is an important part of system performance and reliability, and lubricating oil directly affects one of the key factors of the compressor. When the two-stage compression system connected in series operates, the difference between the suction pressure and the exhaust pressure of the two compressors is large, and the oil return of the two compressors is uneven along with the increase of the operation time. When the condition of uneven oil return is serious, the low-pressure compressor is rich in oil, the refrigerant compression and the performance of the whole machine are influenced, the high-pressure compressor is lack of oil, the service life is shortened, and even the cylinder body is abraded to stop abnormally. In addition, when the compressor is operated at a low rotation speed and is used for low-temperature heating (the rotation speed of the compressor is not reduced during low-temperature heating, but the flow of the refrigerant is relatively reduced), the refrigerant is operated at a low rotation speed, the oil return amount of the compressor is reduced, and the oil return unevenness of the two compressors is aggravated.

The invention provides a two-stage compressor heat pump and an oil return control system and a control method thereof, which are researched and designed because the two-stage heat pump system in the prior art has the technical problems that the performances of the compressor and the heat pump system are affected due to uneven oil return among the compressors.

Disclosure of Invention

Therefore, the technical problem to be solved by the present invention is to overcome the defect of uneven oil return between compressors in a two-stage heat pump system in the prior art, so as to provide an oil return method and an oil return control system for a two-stage compression heat pump.

the invention provides a double-stage compressor heat pump which comprises an indoor heat exchanger, an outdoor heat exchanger, a low-pressure compressor and a high-pressure compressor, wherein an exhaust port of the low-pressure compressor is communicated with an air suction port of the high-pressure compressor through a medium-pressure pipeline, an exhaust end of the high-pressure compressor is also connected with an oil separator, oil separated by the oil separator is branched into two paths through an oil return pipeline, one path is connected to an air suction end of the low-pressure compressor through a low-pressure oil return pipeline, and the other path is connected to an air suction end of the high-pressure compressor through a high-pressure.

preferably, a first oil return valve is further arranged on the low-pressure oil return pipeline;

And/or a second oil return valve is also arranged on the high-pressure oil return pipeline.

Preferably, a first check valve which only allows fluid to flow towards a suction port of the low-pressure compressor is further arranged on the low-pressure oil return pipeline;

and/or a second one-way valve which only allows the fluid to flow towards the suction port of the high-pressure compressor is arranged on the high-pressure oil return pipeline.

Preferably, an oil equalizing pipeline for equalizing oil between the low-pressure compressor and the high-pressure compressor is also arranged in a communicating manner,

an oil equalizing valve is also arranged on the oil equalizing pipeline; and/or a third one-way valve which only allows fluid to flow from the low-pressure compressor to the high-pressure compressor is arranged on the oil equalizing pipeline.

Preferably, an intermediate heat exchanger is further disposed on the main circulation pipeline between the indoor heat exchanger and the outdoor heat exchanger;

A branch pipeline is connected between the indoor heat exchanger or the outdoor heat exchanger and the intermediate heat exchanger through a branch point, the branch pipeline penetrates through the intermediate heat exchanger and then is connected to the intermediate pressure pipeline, and heat exchange is carried out between the main circulation pipeline and the branch pipeline in the intermediate heat exchanger;

and a first throttling device is also arranged between the branch point and the intermediate heat exchanger on the branch pipeline.

preferably, a second throttling device is further arranged on the oil return pipeline.

preferably, the air conditioner further comprises a four-way valve for controlling the heat pump to switch between a cooling mode and a heating mode.

The invention also provides an oil return control system suitable for the double-stage compressor heat pump, which is characterized in that: the device comprises a detection unit, a control unit and a control unit, wherein the detection unit is used for detecting the discharge pressure PH of a high-pressure compressor and the suction pressure PL of a low-pressure compressor;

the judging unit is used for judging the size relation between the ratio of the high-pressure exhaust pressure PH to the low-pressure suction pressure PL and a preset value;

and the control unit is used for controlling the low-pressure oil return pipeline and the high-pressure oil return pipeline to be alternately opened for different time according to the judgment result of the judgment unit.

preferably, when the two-stage compressor heat pump further comprises a first oil return valve, the control unit further comprises the first oil return valve;

And/or, when the dual-stage compressor heat pump further comprises a second oil return valve, the control unit further comprises the second oil return valve;

and/or, when the dual-stage compressor heat pump comprises an oil equalizing valve and/or a third check valve, the control unit further comprises the oil equalizing valve and/or the third check valve.

preferably, when the two-stage compressor heat pump further comprises an intermediate heat exchanger, the detection unit further comprises a unit for detecting whether the first throttling device is opened;

The judging unit is also used for judging whether the heat pump is in an air supply opening state or an air supply closing state according to whether the first throttling device is opened or not detected by the detecting unit;

The control unit is also used for controlling the low-pressure oil return pipeline and the high-pressure oil return pipeline to be alternately opened for different time according to the state that the judging unit judges whether the heat pump is in the state of air supply opening or air supply closing.

preferably, when the two-stage compressor heat pump further comprises a four-way valve, the detection unit is further configured to detect a state of the four-way valve being powered on or powered off;

The judging unit is also used for judging whether the heat pump is in a cooling mode or a heating mode according to the state that the detecting unit detects that the four-way valve is powered on or powered off;

The control unit is also used for controlling the low-pressure oil return pipeline and the high-pressure oil return pipeline to be alternately opened for different time according to the judgment unit that the heat pump is in the refrigeration mode or the heating mode.

Preferably, the detection unit is further configured to detect an outdoor ambient temperature;

The judging unit is also used for judging the magnitude relation between the outdoor environment temperature and the set environment temperature;

the control unit is also used for controlling the low-pressure oil return pipeline and the high-pressure oil return pipeline to be alternately opened for different time according to the magnitude relation between the outdoor environment temperature and the set environment temperature.

The invention also provides an oil return control method suitable for the double-stage compressor heat pump, which is characterized by comprising the following steps of: the method comprises a detection step, a control step and a control step, wherein the detection step is used for detecting the exhaust pressure PH of a high-pressure compressor and the suction pressure PL of a low-pressure compressor;

A judging step, which is used for judging the size relation between the ratio of the high-pressure exhaust pressure PH to the low-pressure suction pressure PL and a preset value;

And a control step for controlling the low-pressure oil return pipeline and the high-pressure oil return pipeline to be alternately opened for different time according to the size relation.

Preferably, when the two-stage compressor heat pump further comprises an intermediate heat exchanger, the detecting step further comprises detecting whether the first throttling device is open;

The judging step is also used for judging whether the heat pump is in an air supply opening state or an air supply closing state according to whether the first throttling device is opened or not detected in the detecting step;

And the control step is also used for controlling the low-pressure oil return pipeline and the high-pressure oil return pipeline to be alternately opened for different time according to the state that whether the heat pump is in the state of air supply opening or air supply closing judged by the judging step.

preferably, when the two-stage compressor heat pump further comprises a four-way valve, the detecting step is further for detecting whether the four-way valve is in a power-on or power-off state;

the judging step is also used for judging whether the heat pump is in a cooling mode or a heating mode according to the state that whether the four-way valve is electrified or not detected by the detecting step;

And the control step is also used for controlling the low-pressure oil return pipeline and the high-pressure oil return pipeline to be alternately opened for different time according to whether the heat pump judged by the judging step is in a refrigerating mode or a heating mode.

preferably, the detecting step is also used for detecting the outdoor environment temperature;

the judging step is also used for judging the magnitude relation between the outdoor environment temperature and the set environment temperature;

And the control step is also used for controlling the low-pressure oil return pipeline and the high-pressure oil return pipeline to be alternately opened for different time according to the magnitude relation between the outdoor environment temperature and the set environment temperature.

Preferably, when the first and second return valves are included, and the air make-up valve is open, and the heat pump is in cooling operation:

(1) when the PH/PL is greater than 4, the second oil return valve is opened for 20-30min, the first oil return valve is closed, then the second oil return valve is closed for 10-20min, and the first oil return valve is opened;

(2) When the PH/PL <4 is 2, the second oil return valve is opened for 10-20min, the first oil return valve is closed, then the second oil return valve is closed for 20-60min, and the first oil return valve is opened;

(3) when PH/PL <2, the second oil return valve is opened for 5-10min, the first oil return valve is closed, then the second oil return valve is closed for 60-120min, and the first oil return valve is opened.

Preferably, when the first and second return valves are included, and the air make-up valve is open, and the heat pump is in heating operation:

a. When outdoor ambient temperature T >5 ℃:

(1) when the PH/PL is greater than 4, the second oil return valve is opened for 20-30min, the first oil return valve is closed, then the second oil return valve is closed for 10-60min, and the first oil return valve is opened;

(2) when the PH/PL <4 is 2, the second oil return valve is opened for 10-20min, the first oil return valve is closed, then the second oil return valve is closed for 60-120min, and the first oil return valve is opened;

(3) when PH/PL <2, the second oil return valve is opened for 5-10min, the first oil return valve is closed, then the second oil return valve is closed for 120-240min, and the first oil return valve is opened;

b. when outdoor ambient temperature-15 ℃ < T <5 ℃:

c. When the outdoor environment temperature T < -15 ℃:

(1) When the PH/PL is greater than 2, opening the second oil return valve for 20-40min, closing the first oil return valve, then closing the second oil return valve for 20-30min, and opening the first oil return valve;

(2) And when the PH/PL is less than 2, the second oil return valve is opened for 10-20min, the first oil return valve is closed, then the second oil return valve is closed for 10-30min, and the first oil return valve is opened.

Preferably, when the first oil return valve and the second oil return valve are included and the air supply is closed, the first oil return valve is opened for 20-60min, the second oil return valve is closed, then the first oil return valve is closed, the second oil return valve is opened for 20-60min, and the steps are repeated.

Preferably, when the dual-stage compressor heat pump further comprises and/or a third check valve, the oil equalizing valve and/or the third check valve are kept normally open.

The two-stage compressor heat pump and the oil return control system and the oil return control method thereof provided by the invention have the following beneficial effects:

1. according to the two-stage compressor heat pump and the oil return control system and the control method thereof, oil separated by the oil separator is branched into two paths through the oil return pipeline, one path is connected to the air suction end of the low-pressure compressor through the low-pressure oil return pipeline, the other path is connected to the air suction end of the high-pressure compressor through the high-pressure oil return pipeline, the low-pressure compressor and the high-pressure compressor can be respectively returned according to needs, and particularly, targeted oil return is performed on the two compressors according to the condition that the oil distribution between the low-pressure compressor and the high-pressure compressor is uneven;

2. According to the two-stage compressor heat pump and the oil return control system and the control method thereof, oil separated by the oil separator is branched into two paths through the oil return pipeline, one path is connected to the air suction end of the low-pressure compressor through the low-pressure oil return pipeline, and the other path is connected to the air suction end of the high-pressure compressor through the high-pressure oil return pipeline, so that the refrigerant compression of the compressor can be further effectively ensured, the abnormal shutdown phenomenon caused by the abrasion of a cylinder body can be prevented, the service life of the compressor is prolonged, and the performances of the compressor and the heat pump;

3. According to the double-stage compressor heat pump and the oil return control system and the oil return control method thereof, the structure of the intermediate heat exchanger, the branch pipeline and the first throttling device is arranged, so that the effects of air supply and enthalpy increase can be achieved for the double-stage compressor, the running performance of the heat pump is improved when the working load is heavy and/or the outdoor environment temperature is too high or too low, and the exhaust temperature and the pressure ratio of the compressor are reduced;

4. According to the two-stage compressor heat pump and the oil return control system and method thereof, the structure of the four-way valve is arranged, so that the heat pump can be adjusted to be switched between the cooling mode and the heating mode, meanwhile, the cooling and the heating are used as influence factors, and the ambient temperature is required to be introduced into the oil return control method during the heating, because the pressure difference of two stages of the heating is large under different ambient temperatures relative to the cooling, the oil return between the two compressors can be controlled to be as uniform as possible under the condition of different ambient temperatures.

drawings

Fig. 1 is a schematic view of the construction of a two-stage compressor heat pump of the present invention.

The reference numbers in the figures denote:

1-a low-pressure compressor, 2-a high-pressure compressor, 3-an oil separator, 4-a four-way valve, 5-an indoor heat exchanger, 6-a first electronic expansion valve, 7-an intermediate heat exchanger, 8-a first throttling device, 9-a second electronic expansion valve, 10-an outdoor heat exchanger, 11-a gas-liquid separator, 12.1-a first oil return valve, 12.2-a second oil return valve, 13.1-a first one-way valve, 13.2-a second one-way valve, 13.3-a third one-way valve, 14-an oil equalizing valve, 15.1-a first filter, 15.2-a second filter, 16-a second throttling device, 17-a medium-pressure pipeline, 18-an oil return pipeline, 19-a low-pressure oil return pipeline, 20-a high-pressure oil return pipeline, 21-an oil equalizing pipeline, 22-a main circulation pipeline, 23-a branch point, and 24-a branch pipeline.

Detailed Description

Example 1

As shown in fig. 1, the present invention provides a two-stage compressor heat pump, which comprises indoor and outdoor heat exchangers 5, 10, a low-pressure compressor 1 and a high-pressure compressor 2, wherein an exhaust port of the low-pressure compressor 1 is communicated with an air suction port of the high-pressure compressor 2 through a medium-pressure pipeline 17, an exhaust end of the high-pressure compressor 2 is further connected with an oil separator 3, oil separated by the oil separator 3 is branched into two paths through an oil return pipeline 18, one path is connected to an air suction port of the low-pressure compressor 1 through a low-pressure oil return pipeline 19, and the other path is connected to the medium-pressure pipeline through a high-pressure oil return pipeline 20 and is further communicated to an air suction port of the. (it should be explained here that the low pressure, the medium pressure and the high pressure mentioned in the present invention are relative concepts, in the present invention, the pressure of the low pressure < the pressure of the medium pressure < the pressure of the high pressure, the low pressure compressor, i.e. the low pressure stage compressor, the high pressure compressor, i.e. the high pressure stage compressor, and the pressure of the low pressure compressor < the pressure of the high pressure compressor).

The oil separated by the oil separator is branched into two paths through an oil return pipeline, one path is connected to the air suction end of the low-pressure compressor through a low-pressure oil return pipeline, the other path is connected to the air suction end of the high-pressure compressor through a high-pressure oil return pipeline, oil return can be respectively carried out on the low-pressure compressor and the high-pressure compressor according to needs, and particularly targeted oil return is carried out on the two compressors according to the condition that the oil distribution between the low-pressure compressor and the high-pressure compressor is uneven; the refrigerant compression of the compressor can be further effectively ensured, the abnormal shutdown phenomenon caused by the abrasion of the cylinder body can be prevented, the service life of the compressor is prolonged, and the performances of the compressor and the heat pump are improved.

preferably, a first oil return valve 12.1 is further arranged on the low-pressure oil return line 19;

and/or a second oil return valve 12.2 is also arranged on the high-pressure oil return pipeline 20.

Through the structure that sets up first time oil valve and second time oil valve, be one kind respectively to the low pressure return oil pipe way with high pressure return oil pipe way control switching preferred control form, can open first time oil valve when the low pressure returns oil pipe way that needs are opened, open the second time oil valve when the high pressure returns oil pipe way that needs are opened. The first and second return valves are preferably solenoid valves.

This technical scheme designs returning oil pipe way, controls the compressor oil return through two oil distributing valves to in avoiding series system, the phenomenon of rich oil or lack of oil appears in high low pressure level compressor, compromise the unit performance simultaneously, satisfy the unit under different operational mode, and move under the different ambient temperature, solve the oil distributing problem of two compressors, improve unit performance and reliability, extension compressor life-span. On one hand, the two compressors are both provided with oil pipe structures, and on the other hand, oil return of the compressors is respectively controlled through the two electromagnetic valves on the oil return pipeline on the high-pressure side, so that the oil uniformity of the two compressors is improved.

the technical scheme of the invention is suitable for conventional air-conditioning heat pump systems (including household, commercial and automobile air conditioners), can solve the problem of unbalanced oil return of the series connection of the double compressors, particularly reduces the operation times of the oil return of the system at low frequency and low temperature, not only improves the reliability of a unit, but also can improve the performance of the system.

Example 2

In this embodiment, on the basis of embodiment 1, the low-pressure oil return line 19 is further provided with a first check valve 13.1 which only allows fluid to flow towards the suction port of the low-pressure compressor 1;

and/or a second one-way valve 13.2 which only allows the fluid to flow towards the suction port of the high-pressure compressor 2 is arranged on the high-pressure oil return line 20.

the first one-way valve is arranged on the low-pressure oil return pipeline, so that fluid (including oil and refrigerant) can only flow into the low-pressure compressor from the oil separator, and the refrigerant or the oil can be effectively prevented from flowing back from the low-pressure compressor.

Example 3

In this embodiment, on the basis of embodiment 1 and/or 2, preferably, an oil equalizing pipeline 21 for equalizing oil between the low pressure compressor 1 and the high pressure compressor 2 is further communicatively provided,

an oil equalizing valve 14 is also arranged on the oil equalizing pipeline 21; and/or a third check valve 13.3 which only allows the fluid to flow from the low-pressure compressor 1 to the high-pressure compressor 2 is arranged on the oil equalizing pipeline 21.

through still being provided with the structural style of oil-sharing pipeline and oil-sharing valve between high, low pressure compressor, can make two compressors carry out the mutual distribution of oil each other, especially can promote the oil mass that enters into high pressure compressor from the oil in the low pressure compressor (because the oil mass in the low pressure compressor is greater than high pressure compressor usually) to make the oil content between two compressors tend to evenly, further reach the purpose and the effect of oil-sharing. Further, a third one-way valve 13.3 which only allows fluid to flow from the low-pressure compressor to the high-pressure compressor is arranged on the oil-balancing pipeline, so that oil can be further effectively guaranteed to only allow the fluid to flow from the low-pressure compressor to the high-pressure compressor, and further effective guarantee is provided for achieving the oil-balancing degree between the two compressors.

Example 4

In this embodiment, on the basis of embodiments 1 and/or 2 and/or 3, preferably, an intermediate heat exchanger 7 is further disposed on the main circulation pipeline 22 between the indoor heat exchanger 5 and the outdoor heat exchanger 10;

a branch pipeline 24 is further connected at any position between the indoor heat exchanger 5 or the outdoor heat exchanger 10 and the intermediate heat exchanger 7 through a branch point 23, the branch pipeline penetrates through the intermediate heat exchanger and then is connected to the intermediate pressure pipeline 17, and heat exchange is carried out between the main circulation pipeline 22 and the branch pipeline 24 in the intermediate heat exchanger 7;

and a first throttle device 8 is also provided on the branch line 24 between the branch point and the intermediate heat exchanger 7. The first restriction means is preferably an electronic expansion valve.

Through the structure that sets up middle heat exchanger, branch pipeline and first throttling arrangement, can play the effect of tonifying qi enthalpy gain to the double stage compressor, improve the heat pump operating performance when work load is heavier and/or outdoor ambient temperature is too high or low excessively, reduce compressor exhaust temperature and pressure ratio.

example 5

Preferably, a second throttle device 16 is also provided on the return line 18. Preferably a throttled capillary. Since the oil separator 3 is connected to the discharge end of the high-pressure compressor, and the pressure ratio thereof is high, in order to prevent the oil from rapidly flowing to the suction end of the low-pressure and/or high-pressure compressor, so that the oil can be uniformly returned, the second throttling device is provided to effectively release the pressure of the high-pressure oil, thereby ensuring uniform oil return.

Example 6

Preferably, the air conditioner further comprises a four-way valve 4 for controlling the heat pump to switch between a cooling mode and a heating mode. As shown in fig. 1, four ends of the four-way valve 4 are respectively connected to the oil separator 3, the gas-liquid separator 11, the indoor heat exchanger 5 and the outdoor heat exchanger 10, and the heat pump can be adjusted to effectively switch between a cooling mode and a heating mode by the arrangement of the four-way valve, so that the requirements of users on cooling and heating are met.

Example 7

the invention also provides an oil return control system suitable for the double-stage compressor heat pump, which comprises a detection unit, a control unit and a control unit, wherein the detection unit is used for detecting the exhaust pressure PH of the high-pressure compressor and the suction pressure PL of the low-pressure compressor;

The pressure ratio of the two-stage compressor can be obtained by detecting the high-pressure exhaust pressure and the low-pressure suction pressure of the two-stage compressor and comparing the high-pressure exhaust pressure and the low-pressure suction pressure, the higher the pressure ratio is, the higher the compression capacity of the high-pressure compressor is, the higher the high-pressure exhaust pressure is, the more difficult the oil enters the high-pressure compressor, the more the oil shortage in the high-pressure compressor is, the more the deposited oil in the low-pressure compressor is, the more uneven the oil content between the high-pressure compressor and the low-pressure compressor is, and therefore the pressure ratio is used as one of main parameters for judging; the control unit can selectively control more oil entering the high-pressure compressor or more oil entering the low-pressure compressor according to the magnitude relation between the pressure ratio and the preset value, so that the aim of equalizing the oil of the two-stage compressor is fulfilled by intelligently controlling the two-stage compressor.

the oil distribution device has the advantages that the first oil return valve can play a role in controlling the on-off of a low-pressure oil return pipeline, the second oil return valve can play a role in controlling the on-off of a high-pressure oil return pipeline, the oil distribution valve can play a role in controlling the on-off of an oil distribution pipeline, the third one-way valve can play a role in controlling fluid (mainly oil) to flow into the high-pressure compressor from the low-pressure compressor, and conditions are provided for realizing oil distribution control.

Example 8

the intermediate heat exchanger can play a role in air supply and enthalpy increase for the two-stage compressor, so that the performance of the compressor under heavy load is improved, the exhaust temperature of the compressor is reduced, the pressure ratio is reduced, and because the non-air supply and enthalpy increase is suitable for the condition that the working load of the heat pump is light, the high-low pressure ratio is small at the moment, the oil content difference between the two compressors is not very large, and compared with the adjustment that the oil balance needs to be increased in force under the condition of air supply and enthalpy increase, the oil balance is relatively easy to realize under the condition of non-air supply. Therefore, the air supplement or the air non-supplement is introduced into the adjustment of the oil balancing control of the double-stage compressor as an influence factor, so that the intelligent oil balancing adjustment and control functions of the two compressors can be effectively performed according to the situation.

example 9

The structure of the four-way valve can adjust the heat pump to switch between a refrigeration mode and a heating mode, and simultaneously, refrigeration and heating are introduced into oil return control as influence factors, because the oil content between two compressors of a two-stage compressor for heating and refrigeration is different, the loads of the two compressors are different, and the control means required by oil equalization are different, so that the refrigeration and heating modes can be treated respectively, and the oil return between the two compressors is controlled to be as uniform as possible in different operation modes.

example 10

The oil return control system is introduced by introducing the ambient temperature, because the differential pressure difference of the two-stage compressor under different ambient temperatures is very large particularly under the heating condition, the oil contents of the two compressors under different ambient temperatures are different and even very large, so that the two compressors can be respectively treated under different ambient temperatures, and the oil return between the two compressors is controlled to be as uniform as possible.

example 11

the invention also provides an oil return control method suitable for the double-stage compressor heat pump,

The method comprises a detection step, a control step and a control step, wherein the detection step is used for detecting the exhaust pressure PH of a high-pressure compressor and the suction pressure PL of a low-pressure compressor;

example 12

example 13

example 14

Example 15

The refrigerant is compressed by the low-pressure compressor 1, mixed with the make-up air, then enters the second compressor 2, then is compressed to obtain high-temperature and high-pressure gas, enters the four-way valve 4 through the oil separator 3, wherein a part of the refrigerant and oil are separated by the oil separator 3, and then enter the compressors through oil return branches after being decompressed by the second throttling device 16 (preferably a capillary tube). Note: if the second oil return valve 12.2 is opened, the first oil return valve 12.1 is closed; if the second oil return valve 12.2 is closed, the first oil return valve 12.1 is opened, so as to ensure the control certainty and accuracy of the oil return direction, and avoid the situations of air leakage and difficult control.

The second oil return valve and the first oil return valve are controlled to be switched according to the high-low pressure ratio:

(1) when the PH/PL is more than 3.5-4, the second oil return valve is opened for 20-30min, the first oil return valve is closed, then the second oil return valve is closed for 10-20min, and the first oil return valve is opened; repeating the cycling of the above controls until the pH/PL <4 (or 3.5);

(2) when the PH/PL is 2-3 < 3.5-4, the second oil return valve is opened for 10-20min, the first oil return valve is closed, then the second oil return valve is closed for 20-60min, and the first oil return valve is opened; repeating the above control cycle until pH/PL <2 (or 3);

(3) and when the PH/PL is less than 2-3, the second oil return valve is opened for 5-10min, the first oil return valve is closed, then the second oil return valve is closed for 60-120min, and the first oil return valve is opened. And repeating the control.

the specific oil return control step during air supply and refrigeration operation of the two-stage compression heat pump effectively realizes oil equalization control between the two compressors.

example 16

Preferably, when the first and second return valves are included, and the air make-up valve is open, and the heat pump is in heating operation: the second oil return valve and the first oil return valve are controlled to be switched according to the ambient temperature and the high-low pressure ratio:

a. when the outer ring temperature T is >0-5 ℃:

(1) when the PH/PL is more than 3.5-4, the second oil return valve is opened for 20-30min, the first oil return valve is closed, then the second oil return valve is closed for 10-60min, and the first oil return valve is opened; repeating the cycling of the above controls until the pH/PL <4 (or 3.5);

(2) When the PH/PL is 2-3 < 3.5-4, the second oil return valve is opened for 10-20min, the first oil return valve is closed, then the second oil return valve is closed for 60-120min, and the first oil return valve is opened; repeating the above control cycle until pH/PL <2 (or 3);

(3) When the PH/PL is less than 2-3, the second oil return valve is opened for 5-10min, the first oil return valve is closed, then the second oil return valve is closed for 120-240min, and the first oil return valve is opened; repeating the above control;

b. when the temperature of the outer ring is-15 ℃ to-10 < T < 0-5 ℃:

(1) when the PH/PL is more than 3-4, the second oil return valve is opened for 20-30min, the first oil return valve is closed, then the second oil return valve is closed for 10-20min, and the first oil return valve is opened; repeating the above control cycle until pH/PL <4 (or 3);

(2) When the PH/PL is 2-3 < 3-4, the second oil return valve is opened for 10-20min, the first oil return valve is closed, then the second oil return valve is closed for 20-60min, and the first oil return valve is opened; repeating the above control cycle until pH/PL <3 (or 2);

(3) when the PH/PL is less than 2-3, the second oil return valve is opened for 5-10min, the first oil return valve is closed, then the second oil return valve is closed for 60-120min, and the first oil return valve is opened; and repeating the control.

c. When the outer ring temperature T < -15 ℃:

(1) when the PH/PL is more than 2-3, opening the second oil return valve for 20-40min, closing the first oil return valve, then closing the second oil return valve for 20-30min, and opening the first oil return valve; repeating the above control cycle until pH/PL <3 (or 2);

(2) and when the PH/PL is less than 2-3, the second oil return valve is opened for 10-20min, the first oil return valve is closed, then the second oil return valve is closed for 10-30min, and the first oil return valve is opened. And repeating the control.

The specific oil return control step during air supply and heating operation of the two-stage compression heat pump effectively realizes oil equalization control between the two compressors; when the temperature of the outer ring is in the condition of a, the temperature of the outer ring is higher, the power consumption of the compressor is relatively lower than the power consumption in the refrigeration mode, the pressure ratio is relatively smaller, the oil content difference between the two compressors is smaller, and therefore the closing time of the second oil return valve (namely the opening time of the first oil return valve) is relatively longer; and when the outer ring temperature is in the condition c, the outer ring temperature is lower, the power consumption of the compressor is higher than that in the refrigeration mode, the pressure ratio is relatively larger, the oil content difference between the two compressors is larger, and therefore the closing time of the second oil return valve (namely the opening time of the first oil return valve) is relatively longer.

example 17

preferably, when the first and second oil return valves are included and the air make-up is closed (the first throttling device 8 is closed), the first oil return valve is opened for 20-60min, the second oil return valve is closed, then the first oil return valve is closed, the second oil return valve is opened for 20-60min, and the above steps are repeated. The specific oil return control step of the double-stage compression heat pump without air supply effectively realizes the oil equalization control between the two compressors, and the opening time of the first oil return valve and the second oil return valve is controlled to be the same because the pressure ratio is smaller when the air supply is closed and the oil content between the two compressors has little difference.

the closing of the air supply condition comprises: when the work load is lighter, the temperature of the refrigerating outer ring is lower than 27 ℃ or the temperature of the heating outer ring is higher than 15 ℃, the high-low pressure ratio is small, the air supplement amount is small, the performance is not obviously improved, and the air supplement is closed to ensure the reliability of the unit; or the unit system judges that air supply is closed due to the reasons of air supply liquid carrying, reverse flow and the like; or when the compressor runs at low frequency, the high-low pressure ratio is too low, and the air supply is closed. At the moment, the refrigerant enters the high-pressure compressor 2 after passing through the low-pressure compressor 1, is compressed again to obtain high-temperature and high-pressure gas, and enters the four-way valve 4 through the oil separator 3; similarly, a part of the refrigerant and oil are separated by the oil separator 3, and then are decompressed by the capillary tube 16 and enter the compressor through each oil return branch. The oil equalizing valve 14 is normally open, the first oil return valve 12.1 is open, and the second oil return valve 12.2 is closed; after 20-60min, the first oil return valve 12.1 is closed, the second oil return valve 12.2 is opened, and the control is repeated.

When the unit operates, on one hand, the oil equalizing valve is normally opened, which is beneficial to oil equalizing of the double compressors; on the other hand, according to the real-time running state of the unit, the first oil return valve 12.1 and the second oil return valve 12.2 are controlled in a combined mode, so that the double compressors are in an oil equalizing state, the phenomenon of oil enrichment or oil shortage of the high-low pressure stage compressor is avoided, the service life of the compressors is prolonged, the oil return times of the unit are reduced, and the refrigerating and heating performance and reliability of the unit are improved.

example 18

preferably, when the dual-stage compressor heat pump further comprises an oil equalizing valve and/or a third check valve, the oil equalizing valve and/or the third check valve is kept normally open. The oil quantity distribution between the two compressors can be further promoted by opening the oil equalizing valve, so that the aim of equalizing oil is fulfilled; the third check valve can further enable the oil to flow from the low-pressure compressor with high oil content to the high-pressure compressor, so that the situation that oil flows from the high-pressure compressor to the low-pressure compressor due to high pressure in the high-pressure compressor is prevented, sufficient oil content in the high-pressure compressor is guaranteed, and the purpose of oil balancing is achieved.

It is readily understood by a person skilled in the art that the advantageous ways described above can be freely combined, superimposed without conflict.

the above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention. The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

Claims

1. the utility model provides an oil return control system of doublestage compressor heat pump which characterized in that:

The two-stage compressor heat pump includes: the indoor and outdoor heat exchanger, low-pressure compressor (1) and high-pressure compressor (2), the exhaust outlet of the said low-pressure compressor (1) is linked with the suction inlet of the said high-pressure compressor (2) through the medium-pressure pipeline (17), still connect and have the oil separator (3) in the exhaust end of the said high-pressure compressor (2), the oil separated by the said oil separator (3) is branched into two routes through the oil return pipeline (18), one route links to the suction end of the low-pressure compressor (1) through the low-pressure oil return pipeline (19), another route links to the suction end of the high-pressure compressor (2) through the high-pressure oil return pipeline (20);

The oil return control system comprises a detection unit, a control unit and a control unit, wherein the detection unit is used for detecting the exhaust pressure PH of the high-pressure compressor and the suction pressure PL of the low-pressure compressor; the device also comprises a judging unit, a judging unit and a control unit, wherein the judging unit is used for judging the size relation between the ratio of the high-pressure exhaust pressure PH to the low-pressure suction pressure PL and the preset value; the control unit is used for controlling the low-pressure oil return pipeline and the high-pressure oil return pipeline to be alternately opened for different time according to the judgment result of the judgment unit, and a first oil return valve (12.1) is further arranged on the low-pressure oil return pipeline (19); a second oil return valve (12.2) is also arranged on the high-pressure oil return pipeline (20); wherein the mutually alternate opening for different times is: when the air supply is opened, the second oil return valve is opened, the first oil return valve is closed, and then the second oil return valve is closed and the first oil return valve is opened.

2. the oil return control system of a two-stage compressor heat pump of claim 1, wherein: the low-pressure oil return pipeline (19) is also provided with a first one-way valve (13.1) which only allows fluid to flow towards a suction port of the low-pressure compressor (1);

and/or a second one-way valve (13.2) which only allows fluid to flow towards the suction port of the high-pressure compressor (2) is arranged on the high-pressure oil return pipeline (20).

3. The oil return control system of a two-stage compressor heat pump of claim 1, wherein: an oil equalizing pipeline (21) for equalizing oil between the low-pressure compressor (1) and the high-pressure compressor (2) is also arranged between the low-pressure compressor and the high-pressure compressor in a communicating manner,

An oil equalizing valve (14) is also arranged on the oil equalizing pipeline (21); and/or a third one-way valve (13.3) which only allows fluid to flow from the low-pressure compressor (1) to the high-pressure compressor (2) is arranged on the oil equalizing pipeline (21).

4. the oil return control system of a two-stage compressor heat pump of claim 1, wherein: an intermediate heat exchanger (7) is also arranged on a main circulation pipeline (22) between the indoor heat exchanger (5) and the outdoor heat exchanger (10);

A branch pipeline (24) is connected between the indoor heat exchanger (5) or the outdoor heat exchanger (10) and the intermediate heat exchanger (7) through a branch point (23), the branch pipeline penetrates through the intermediate heat exchanger and then is connected to the medium-pressure pipeline (17), and heat exchange is carried out between the main circulation pipeline (22) and the branch pipeline (24) in the intermediate heat exchanger (7);

and a first throttle device (8) is also arranged on the branch line (24) between the branch point and the intermediate heat exchanger (7).

5. The oil return control system of a two-stage compressor heat pump of claim 1, wherein: and a second throttling device (16) is also arranged on the oil return pipeline (18).

6. the oil return control system of a two-stage compressor heat pump of claim 1, wherein: the heat pump is characterized by further comprising a four-way valve (4) used for controlling the heat pump to switch between a cooling mode and a heating mode.

7. The oil return control system of the two-stage compressor heat pump according to any one of claims 1-6, wherein: when the dual stage compressor heat pump further comprises a first oil return valve, the control unit further comprises the first oil return valve;

8. The oil return control system of the two-stage compressor heat pump according to any one of claims 1-6, wherein: when the two-stage compressor heat pump further comprises an intermediate heat exchanger, the detection unit further comprises a unit for detecting whether the first throttling device is opened;

9. The oil return control system of the two-stage compressor heat pump according to any one of claims 1-6, wherein: when the two-stage compressor heat pump further comprises a four-way valve, the detection unit is further used for detecting whether the four-way valve is in a power-on or power-off state;

10. the oil return control system of the two-stage compressor heat pump according to any one of claims 1-6, wherein: the detection unit is also used for detecting the outdoor environment temperature;

11. An oil return control method suitable for the two-stage compressor heat pump according to any one of claims 1 to 10, characterized by: the method comprises a detection step, a control step and a control step, wherein the detection step is used for detecting the exhaust pressure PH of a high-pressure compressor and the suction pressure PL of a low-pressure compressor;

a control step for controlling the low-pressure oil return pipeline and the high-pressure oil return pipeline to be alternately opened for different time according to the size relation; wherein the mutually alternate opening for different times is: when the air supply is opened, the second oil return valve is opened, the first oil return valve is closed, and then the second oil return valve is closed and the first oil return valve is opened.

12. the oil return control method according to claim 11, characterized in that: when the dual stage compressor heat pump further comprises an intermediate heat exchanger, the detecting step further comprises detecting whether the first throttling device is open;

13. the oil return control method according to any one of claims 11 to 12, characterized in that: when the two-stage compressor heat pump further comprises a four-way valve, the detecting step is further used for detecting whether the four-way valve is in a power-on or power-off state;

14. The oil return control method according to any one of claims 11 to 12, characterized in that: the detecting step is also used for detecting the outdoor environment temperature;

15. The oil return control method according to claim 13, characterized in that: when the first oil return valve and the second oil return valve are included, the air supplementing valve is opened, and the heat pump is in refrigerating operation:

16. the oil return control method according to claim 14, characterized in that: when the first oil return valve and the second oil return valve are included, the air replenishing is opened, and the heat pump is in heating operation:

a. When outdoor ambient temperature T >5 ℃:

b. when outdoor ambient temperature-15 ℃ < T <5 ℃:

(3) When PH/PL <2, the second oil return valve is opened for 5-10min, the first oil return valve is closed, then the second oil return valve is closed for 60-120min, and the first oil return valve is opened;

c. When the outdoor environment temperature T < -15 ℃:

17. The oil return control method according to claim 12, characterized in that: when the first oil return valve and the second oil return valve are included and air supply is closed, the first oil return valve is opened for 20-60min, the second oil return valve is closed, then the first oil return valve is closed, the second oil return valve is opened for 20-60min, and the steps are repeated.

18. The oil return control method according to any one of claims 15 to 17, characterized in that: when the dual-stage compressor heat pump further comprises an oil equalizing valve and/or a third check valve, keeping the oil equalizing valve and/or the third check valve normally open.