阅读说明：本技术 一种轨道车辆用co2空调系统及其控制方法 (CO for railway vehicle2Air conditioning system and control method thereof ) 是由 李敬茂 金甜甜 佘凯 王森林 于 2020-12-31 设计创作，主要内容包括：本发明涉及一种轨道车辆用CO-2空调系统及其控制方法,包括由压缩机、气体冷却器、主膨胀阀、蒸发器和气液分离器通过管路依次连接形成的循环主路,还包括循环支路,所述循环支路的一端接入气体冷却器的出口侧,所述循环支路的另一端接入气液分离器的入口侧,在所述循环支路中串接有支路膨胀阀和支路换热器,所述支路膨胀阀设置在支路换热器的入口侧,所述支路换热器中的冷媒与气体冷却器中的冷媒进行热交换,空调系统运行制冷模式时,控制支路膨胀阀导通,通过循环支路对压缩机补充低温低压的气态冷媒。本发明不但系统结构简单,且有利于降低压缩机的排气温度和高压压力,拓宽系统高温运行范围。(The invention relates to a CO for a rail vehicle 2 The air conditioning system comprises a main circulation path formed by sequentially connecting a compressor, a gas cooler, a main expansion valve, an evaporator and a gas-liquid separator through pipelines, and further comprises a circulation branch, wherein one end of the circulation branch is connected to the outlet side of the gas cooler, the other end of the circulation branch is connected to the inlet side of the gas-liquid separator, and a branch expansion valve and a branch heat exchanger are connected in series in the circulation branchThe branch expansion valve is arranged on the inlet side of the branch heat exchanger, the refrigerant in the branch heat exchanger exchanges heat with the refrigerant in the gas cooler, and when the air-conditioning system operates in a refrigeration mode, the branch expansion valve is controlled to be switched on, and the compressor is supplemented with low-temperature and low-pressure gaseous refrigerant through the circulating branch. The invention has simple system structure, is beneficial to reducing the exhaust temperature and the high pressure of the compressor and widening the high-temperature operation range of the system.)

1. CO for railway vehicle₂Air conditioning system, include the circulation main road that is formed by compressor, gas cooler, main expansion valve, evaporimeter and vapour and liquid separator connect gradually through the pipeline, its characterized in that: the gas cooler is characterized by further comprising a circulating branch, one end of the circulating branch is connected to the outlet side of the gas cooler, the other end of the circulating branch is connected to the inlet side of the gas-liquid separator, a branch expansion valve and a branch heat exchanger are connected in series in the circulating branch, the branch expansion valve is arranged on the inlet side of the branch heat exchanger, and heat exchange is carried out between refrigerant in the branch heat exchanger and refrigerant in the gas cooler.

2. CO for a rail vehicle according to claim 1₂Air conditioning system, its characterized in that: the gas cooler and the branch heat exchanger are integrated into a whole and comprise two groups of pipelines, wherein one group of pipelines is connected to the main circulation path, and the other group of pipelines is used as the branch heat exchanger to be connected to the branch circulation path;

or, the branch heat exchanger comprises two groups of pipelines, wherein one group of pipelines is connected to the circulating branch, and the other group of pipelines is connected to the circulating main path between the outlet end of the gas cooler and the inlet end of the main expansion valve.

3. CO for a rail vehicle according to claim 2₂Air conditioning system, its characterized in that: the refrigerant in the two groups of pipelines flows in the reverse direction or the forward direction.

4. CO for a rail vehicle according to claim 1₂Air conditioning system, its characterized in that: the flow of the circulating branch accounts for 0.1-0.25 of the total circulating flow.

5. CO for a rail vehicle according to any one of claims 1-4₂Air conditioning system, its characterized in that: the electric control system also comprises a first electric three-way valve and a second electric three-way valve;

and pipelines on the exhaust side of the compressor, the inlet side of the gas cooler and the outlet side of the evaporator are respectively connected into three ports of the first electric three-way valve, and three ports of the second electric three-way valve are respectively connected into pipelines between the outlet side of the evaporator and the first electric three-way valve, between the inlet side of the gas cooler and the first electric three-way valve and between the outlet side of the branch heat exchanger and the inlet side of the gas-liquid separator through pipelines.

6. CO for a rail vehicle according to any one of claims 1 to 5₂The control method of the air conditioning system is characterized by comprising the following steps:

s1, detecting the operation mode of the air conditioner system;

s2, when the air conditioning system runs in a refrigeration mode, controlling the conduction of the circulation branch, and supplementing a low-temperature and low-pressure gaseous refrigerant to the compressor through the circulation branch;

and S3, when the air-conditioning system operates in the heating mode, controlling the circulation branch to be closed.

7. The control method according to claim 6, characterized in that: in the above step S2, the method further comprises the step of adjusting the temperature T according to the suction temperature of the compressor_{Air suction}The step of controlling the opening of the branch expansion valve specifically comprises the following steps:

s21, when the suction temperature T of the compressor_{Air suction}Greater than saturation temperature T corresponding to suction pressure of compressor_{Saturation of}When the branch expansion valve is opened, the branch expansion valve is controlled to be communicated;

s22, when the suction temperature T of the compressor_{Air suction}Less than or equal to saturation temperature T corresponding to suction pressure of compressor_{Saturation of}And when the branch expansion valve is closed, the branch expansion valve is controlled to be closed.

8. The control method according to claim 7, characterized in that: in step S21, the method further includes the step of controlling the opening degree of the bypass expansion valve according to the following formula;

n＝K1*N*((T_{air suction-}T_{Saturation of})/T_{Air suction})*(T_{Exhaust of gases}/T_{Protection of}) (1)；

Wherein n is the regulating step number of the branch expansion valve;

k1 is the coefficient;

n is the total step number of the branch expansion valve;

T_{exhaust of gases}Is the compressor discharge temperature;

T_{protection of}Is the protection temperature of the compressor.

9. The control method according to claim 8, characterized in that: the K1 is in the range of 0.5-1.

10. The control method according to claim 7, characterized in that: in the above step S21, the method further comprises the step of_{Air suction-}T_{Saturation of}Is less than or equal to the setting value delta T_{Setting up}And (5) controlling the branch expansion valve to be closed.

Technical Field

The invention relates to the technical field of air conditioning of railway vehicles, in particular to CO for a railway vehicle₂Air conditioning system simultaneously relates to this air conditioning system's control method.

Background

In the present environment, people are dedicated to searching for environment-friendly and reliable refrigerant, CO₂The refrigerant with GWP of 1 is the first choice to replace the traditional Freon working medium.

In order to increase the refrigeration capacity and energy efficiency ratio of the carbon dioxide cycle, a regenerator cycle is typically employed. However, this cycle is prone to high suction and discharge temperatures, which can result in failure to operate at high temperatures.

In order to solve the problem that the exhaust temperature of a carbon dioxide circulating air-conditioning system is too high, so that the system cannot operate in a high-temperature environment, a driver room CO2 variable-frequency air conditioner is provided in the Chinese patent with the patent number of 202010352316.2, an economizer and a heat regenerator are additionally arranged in a circulating pipeline of the air conditioner, the effect of cooling a high-temperature side refrigerant is achieved by reducing in an air supplementing mode, but the air-conditioning system is complex in structure and high in cost, and cannot be compatible with CO₂The heating function of the refrigerant.

Disclosure of Invention

The invention mainly solves the technical problem of providing the CO for the railway vehicle, which has a simple system structure, is favorable for reducing the exhaust temperature and the high pressure of a compressor and widening the high-temperature operation range of the system₂A heat pump air conditioning system and a control method of the heat pump air conditioning system are also provided.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

CO for railway vehicle₂The air conditioning system comprises a main circulation path formed by sequentially connecting a compressor, a gas cooler, a main expansion valve, an evaporator and a gas-liquid separator through pipelines, and further comprises a circulation branch, wherein one end of the circulation branch is connected with a gas coolerThe other end of the circulating branch is connected to the inlet side of the gas-liquid separator, a branch expansion valve and a branch heat exchanger are connected in series in the circulating branch, the branch expansion valve is arranged on the inlet side of the branch heat exchanger, and the refrigerant in the branch heat exchanger exchanges heat with the refrigerant in the gas cooler.

Further, the gas cooler and the branch heat exchanger are integrated into a whole and comprise two groups of pipelines, wherein one group of pipelines is connected to the main circulation path, and the other group of pipelines is used as the branch heat exchanger to be connected to the branch circulation path;

or, the branch heat exchanger comprises two groups of pipelines, wherein one group of pipelines is connected to the circulating branch, and the other group of pipelines is connected to the circulating main path between the outlet end of the gas cooler and the inlet end of the main expansion valve.

Furthermore, the refrigerant in the two groups of pipelines flows in the reverse direction or the forward direction.

Furthermore, the flow of the circulation branch accounts for 0.1-0.25 of the total circulation flow.

Further, the device also comprises a first electric three-way valve and a second electric three-way valve;

and pipelines on the exhaust side of the compressor, the inlet side of the gas cooler and the outlet side of the evaporator are respectively connected into three ports of the first electric three-way valve, and three ports of the second electric three-way valve are respectively connected into pipelines between the outlet side of the evaporator and the first electric three-way valve, between the inlet side of the gas cooler and the first electric three-way valve and between the outlet side of the branch heat exchanger and the inlet side of the gas-liquid separator through pipelines.

The other provided technical scheme of the invention is as follows:

CO for railway vehicle₂The control method of the air conditioning system comprises the following steps:

s1, detecting the operation mode of the air conditioner system;

s2, when the air conditioning system runs in a refrigeration mode, controlling the conduction of the circulation branch, and supplementing a low-temperature and low-pressure gaseous refrigerant to the compressor through the circulation branch;

and S3, when the air-conditioning system operates in the heating mode, controlling the circulation branch to be closed.

Further, step S2 includes a step of adjusting the temperature T of the compressor_{Air suction}The step of controlling the opening of the branch expansion valve specifically comprises the following steps:

s21, when the suction temperature T of the compressor_{Air suction}Greater than saturation temperature T corresponding to suction pressure of compressor_{Saturation of}When the branch expansion valve is opened, the branch expansion valve is controlled to be communicated;

s22, when the suction temperature T of the compressor_{Air suction}Less than or equal to saturation temperature T corresponding to suction pressure of compressor_{Saturation of}And when the branch expansion valve is closed, the branch expansion valve is controlled to be closed.

Further, the step S21 includes the step of controlling the opening degree of the bypass expansion valve according to the following formula;

n＝K1*N*((T_{air suction-}T_{Saturation of})/T_{Air suction})*(T_{Exhaust of gases}/T_{Protection of}) (1)；

Wherein n is the regulating step number of the branch expansion valve;

k1 is the coefficient;

n is the total step number of the branch expansion valve;

T_{exhaust of gases}Is the compressor discharge temperature;

T_{protection of}Is the protection temperature of the compressor.

Further, the K1 is in the range of 0.5-1.

Further, step S21 includes the step of when T is reached_{Air suction-}T_{Saturation of}Is less than or equal to the setting value delta T_{Setting up}And (5) controlling the branch expansion valve to be closed.

In summary, the present invention provides a CO for rail vehicles₂Compared with the prior art, the air conditioning system and the control method thereof have the following advantages:

(1) the invention has simple structure, and the circulating branch is arranged between the outlet side of the gas cooler and the inlet side of the compressor to supplement low-temperature and low-pressure gaseous refrigerant to the compressor, thus being beneficial to reducing the exhaust temperature and high-pressure of the compressor and widening the high-temperature operation range of the system.

(2) The invention further reduces the temperature of the refrigerant in the gas cooler by using the low-temperature refrigerant in the circulating branch, is beneficial to improving the energy efficiency ratio of the system in a high-temperature environment and improves the refrigerating capacity and the heating capacity.

(3) The invention accurately controls the opening of the branch expansion valve, and is beneficial to further improving the energy efficiency ratio of the system in a high-temperature environment.

(4) The two electric three-way valves are arranged in the system, so that the system can realize air supplement of the compressor and can also have heating operation.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention, are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention without limiting the invention to the right. It is obvious that the drawings in the following description are only some embodiments, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.

FIG. 1 is a schematic diagram of the air conditioning system of the present invention during cooling operation;

FIG. 2 is a schematic diagram of the air conditioning system of the present invention during heating operation;

fig. 3 is a flowchart of a control method of the air conditioning system of the present invention.

As shown in fig. 1 to 3, a compressor 1, a gas cooler 2, a main expansion valve 3, an evaporator 4, a gas-liquid separator 5, a first electric three-way valve 6, a second electric three-way valve 7, a bypass heat exchanger 8, a bypass expansion valve 9, a discharge pressure sensor 10, a suction pressure sensor 11, a discharge temperature sensor 12, and a suction temperature sensor 13.

It should be noted that the drawings and the description are not intended to limit the scope of the inventive concept in any way, but to illustrate it by a person skilled in the art with reference to specific embodiments.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and the following embodiments are used for illustrating the present invention and are not intended to limit the scope of the present invention.

The first embodiment is as follows:

as shown in fig. 1 and 2, the present embodiment provides a CO for a railway vehicle₂The air conditioning system comprises a circulating main path formed by sequentially connecting a compressor 1, a gas cooler 2, a main expansion valve 3, an evaporator 4 and a gas-liquid separator 5 through pipelines. During the refrigeration operation, the high-temperature and high-pressure refrigerant discharged by the compressor 1 is subjected to heat exchange with the outdoor environment through the gas cooler 2 to cool the refrigerant, the cooled liquid refrigerant is throttled by the main expansion valve 3 to form a low-temperature and low-pressure refrigerant, then enters the evaporator 4 to perform heat exchange with the indoor environment, and the evaporated refrigerant flows back to the compressor 1 through the gas-liquid separator 5.

An exhaust pressure sensor 10 and an exhaust temperature sensor 12 are installed on an exhaust pipeline of the compressor 1, and an intake pressure sensor 11 and an intake temperature sensor 13 are installed on an intake pipeline of the compressor 1, and are respectively used for detecting the exhaust pressure, the exhaust temperature, the intake pressure and the intake temperature of the compressor 1.

The air conditioning system also comprises a circulating branch, one end of the circulating branch is connected into a pipeline on the outlet side of the gas cooler 2, the other end of the circulating branch is connected into a pipeline on the inlet side of the gas-liquid separator 5, a branch expansion valve 9 and a branch heat exchanger 8 are connected in series in the circulating branch, and the branch expansion valve 9 is arranged on the inlet side of the branch heat exchanger 8.

In this embodiment, the refrigerant in the bypass heat exchanger 8 exchanges heat with the refrigerant in the gas cooler 2, and preferably, the bypass heat exchanger 8 is integrated with the gas cooler 2, the gas cooler 2 employs a double pipe heat exchanger, one group of pipes in the double pipe heat exchanger is connected to the main circulation path, and the other group of pipes in the double pipe heat exchanger is used as the bypass heat exchanger 8 connected to the branch circulation path. Of course, the gas cooler 2 and the branch heat exchanger 8 are integrated, and other heat exchanger structures such as a plate heat exchanger and the like which can realize heat exchange between the refrigerants in the two sets of pipelines can be adopted.

The air conditioning system also comprises a first electric three-way valve 6 and a second electric three-way valve 7, so that the air conditioning system can also realize heating operation.

The discharge side of the compressor 1 is connected to a port 6a of the first electric three-way valve 6 via a pipe, the inlet side of the gas cooler 2 is connected to a port 6b of the first electric three-way valve 6 via a pipe, and the outlet side of the evaporator 4 is connected to a port 6c of the first electric three-way valve 6 via a pipe.

A port 7a of the second electric three-way valve 7 is connected to a pipeline between the outlet side of the evaporator 4 and the first electric three-way valve 6 through a pipeline, a port 7b of the second electric three-way valve 7 is connected to a pipeline between the inlet side of the gas cooler 2 and the first electric three-way valve 6 through a pipeline, and a port 7c of the second electric three-way valve 7 is connected to a pipeline between the outlet side of the bypass heat exchanger 8 and the inlet side of the gas-liquid separator 5 through a pipeline.

As shown in fig. 1, in the cooling operation, the controller of the air conditioning system controls the first electric three-way valve 6 to communicate with two ports 6a and 6b connected to the discharge side of the compressor 1 and the inlet side of the gas cooler 2, and the port 6c connected to the outlet side of the evaporator 4 is closed. Meanwhile, the second electric three-way valve 7 is controlled to be connected between the outlet side of the evaporator 4 and the first electric three-way valve 6, and ports 7a and 7c of the piping between the outlet side of the bypass heat exchanger 8 and the inlet side of the gas-liquid separator 5 are communicated, and the port 7b of the piping connected between the inlet side of the gas cooler 2 and the first electric three-way valve 6 is closed.

During refrigeration operation, a high-temperature and high-pressure refrigerant discharged from the compressor 1 enters the port 6a of the first electric three-way valve 6 through a pipeline, flows out of the other port 6b of the first electric three-way valve 6 to enter the gas cooler 2, is condensed and cooled by the gas cooler 2, and is divided into two paths, wherein one path enters the main expansion valve 3 along the main circulation path for throttling, and the other path enters the branch expansion valve 9 along the branch circulation path for throttling.

The liquid refrigerant in the main circulation path is throttled by the main expansion valve 3 to form a low-temperature low-pressure refrigerant, then enters the evaporator 4 to exchange heat with the indoor environment, and the evaporated refrigerant enters the port 7a of the second electric three-way valve 7, flows out of the port 7c, enters the gas-liquid separator 5 and finally flows back to the compressor 1.

The liquid refrigerant in the circulation branch is throttled by the branch expansion valve 9 to form a low-temperature low-pressure refrigerant, then enters the branch heat exchanger 8 to exchange heat with the high-temperature refrigerant in the gas cooler 2, the refrigerant after heat exchange enters the gas-liquid separator 5, and is mixed with the refrigerant flowing back in the main circulation path in the gas-liquid separator 5 to cool the refrigerant entering the compressor 1, reduce the suction temperature of the compressor 1, and finally enter the compressor 1. The suction temperature of the compressor 1 is reduced, so that the exhaust temperature of the compressor 1 is reduced, the air conditioning system can normally operate in a high-temperature environment, the refrigeration energy efficiency ratio of the air conditioning system is ensured, and the high-temperature operation range of the air conditioning unit is widened.

As shown in fig. 2, during heating, the controller of the air conditioning system controls the first electric three-way valve 6 to communicate with the discharge side of the compressor 1 and the two ports 6a and 6c connected to the outlet side of the evaporator 4, and the port 6b connected to the inlet side of the gas cooler 2 is closed. At the same time, the second electric three-way valve 7 is controlled to be communicated with the port 7b connected to the pipe between the inlet side of the gas cooler 2 and the first electric three-way valve 6 and the port 7c connected to the pipe between the outlet side of the bypass heat exchanger 8 and the inlet side of the gas-liquid separator 5, and the port 7a connected to the pipe between the outlet side of the evaporator 4 and the first electric three-way valve 6 is closed.

During heating operation, the air conditioning system controller controls the branch expansion valve 9 to be closed, namely the circulation branch is disconnected. High-temperature and high-pressure refrigerant discharged by the compressor 1 enters a port 6a of the first electric three-way valve 6 through a pipeline, flows out of the other port 6c of the first electric three-way valve 6 and enters the evaporator 4, is subjected to heat exchange with an indoor environment in the evaporator 4, enters the main expansion valve 3 for throttling after heat exchange, enters the gas cooler 2 for heat exchange with an outdoor environment, enters a port 7b of the second electric three-way valve 7 and flows out of the port 7c, enters the gas-liquid separator 5 and then flows back to the compressor 1.

In this embodiment, the refrigerant in the two sets of pipelines in the double pipe heat exchanger may flow in opposite directions or in forward directions. In the embodiment, the refrigerant flow directions in the main circulation path and the branch circulation path in the double-pipe heat exchanger are preferably opposite, so that on one hand, the refrigerant in the branch circulation path is completely gasified before entering the gas-liquid separator 5, and the exhaust temperature of the compressor 1 can be reduced by 10-15%; on the other hand, the temperature of the refrigerant flowing out of the gas cooler 2 is reduced. Test data indicate that a counter-flow double-pipe heat exchanger is used.

In this embodiment, the flow rate of the refrigerant in the circulation branch is preferably controlled to be between 0.1 and 0.25 of the total circulation flow rate, and more preferably, the flow rate of the refrigerant in the circulation branch accounts for 0.2 to 0.25 of the total circulation flow rate, so as to achieve the optimal cooling effect.

As shown in FIG. 3, the present embodiment also provides a CO for railway vehicles₂The control method of the heat pump air conditioning system comprises the following steps:

s1, detecting the operation mode of the air conditioner system;

s2, when the air conditioning system runs in a refrigeration mode, controlling the conduction of the circulation branch, namely controlling the conduction of the branch expansion valve 9, and supplementing a low-temperature and low-pressure gaseous refrigerant to the compressor 1 through the circulation branch;

s3, when the air conditioning system is operating in the heating mode, the control of the closing of the circulation branch is preferably performed by controlling the branch expansion valve 9 to close and disconnect the circulation branch.

Step S2 includes the step of adjusting the temperature T of the compressor 1_{Air suction}The step of controlling the opening degree of the branch expansion valve 9 specifically includes:

s21, when the suction temperature T of the compressor 1_{Air suction}Greater than saturation temperature T corresponding to suction pressure of compressor_{Saturation of}When the air conditioner is used, the branch expansion valve 9 is controlled to be communicated so as to reduce the air suction temperature of the delta compressor 1;

in the step S21, the method further comprises the step of detecting T after a period of operation_{Air suction-}T_{Saturation of}Is less than or equal to the setting value delta T_{Setting up}And (4) controlling the branch expansion valve 9 to be closed.

S22, when the suction temperature T of the compressor 1_{Air suction}Less than or equal to saturation temperature T corresponding to suction pressure of compressor_{Saturation of}In the meantime, the branch expansion valve 9 is controlled to be closed, and the temperature of the suction gas of the compressor 1 does not need to be reduced.

In the above step S21, the method further includes the step of controlling the opening degree of the bypass expansion valve 9, which is the initial opening degree of the bypass expansion valve 9, according to the following formula;

n＝K1*N*((T_{air suction-}T_{Saturation of})/T_{Air suction})*(T_{Exhaust of gases}/T_{Protection of}) (1)

Wherein n is the regulating step number of the branch expansion valve;

k1 is the coefficient;

n is the total step number of the branch expansion valve;

T_{exhaust of gases}Is the compressor discharge temperature;

T_{protection of}Is the protection temperature of the compressor.

Among them, K1 is preferably in the range of 0.5 to 1.

One example is shown in table 1:

TABLE 1

K1

TEnvironment(s)

TExhaust of gases

TAir suction

TSaturation of

N

TProtection of

0.8

30℃

90℃

40℃

10℃

500 steps

120℃

Wherein, T_{Environment(s)}The outdoor ambient temperature is calculated by a formula, and the opening degree of the branch expansion valve 9 is controlled to be 225 steps at this time.

The invention has the following advantages:

(1) the air conditioning system is simple in structure, and the circulating branch is arranged between the outlet side of the gas cooler and the inlet side of the compressor to supplement low-temperature and low-pressure gaseous refrigerants to the compressor, so that the exhaust temperature and the high-pressure of the compressor are reduced, and the high-temperature operation range of the system is widened.

(2) The air conditioning system further reduces the temperature of the refrigerant in the gas cooler by using the low-temperature refrigerant in the circulating branch, is favorable for improving the energy efficiency ratio of the system in a high-temperature environment, and improves the refrigerating capacity and the heating capacity.

(3) The air conditioning system determines the opening degree of the branch expansion valve according to the outdoor environment temperature, the suction temperature of the compressor, the exhaust temperature and other parameters, realizes intelligent regulation and control, and is favorable for further improving the energy efficiency ratio of the system in the high-temperature environment.

(4) This air conditioning system makes the system both can realize the compressor tonifying qi through set up two electronic three-way valves in the system, can have the operation of heating simultaneously again concurrently.

Example two:

the difference from the first embodiment is that the bypass heat exchanger 8 is a double pipe heat exchanger, one set of pipes in the double pipe heat exchanger is connected to the circulation bypass, and the other set of pipes in the double pipe heat exchanger is connected to the circulation main between the outlet end of the gas cooler 2 and the inlet end of the main expansion valve 3. Of course, the branch heat exchanger 8 may also adopt other heat exchanger structures such as a plate heat exchanger, etc. which can realize the heat exchange between the refrigerants in the two sets of pipelines.

During refrigeration operation, a high-temperature and high-pressure refrigerant discharged from the compressor 1 enters a port 6a of the first electric three-way valve 6 through a pipeline, flows out of the other port 6b of the first electric three-way valve 6 to enter the gas cooler 2, is condensed and cooled by the gas cooler 2, and is divided into two paths, wherein one path enters the main expansion valve 3 for throttling through a group of pipelines in the branch heat exchanger 8 along a main circulation path, and the other path enters the branch expansion valve 9 for throttling along a branch circulation path.

The liquid refrigerant in the main circulation path is throttled by the main expansion valve 3 to form a low-temperature low-pressure refrigerant, then enters the evaporator 4 to exchange heat with the indoor environment, and the evaporated refrigerant enters the port 7a of the second electric three-way valve 7, flows out of the port 7c, enters the gas-liquid separator 5 and finally flows back to the compressor 1.

The liquid refrigerant in the circulation branch is throttled by a branch expansion valve 9 to form a low-temperature low-pressure refrigerant, then enters a branch heat exchanger 8 to exchange heat with a high-temperature refrigerant flowing out of the gas cooler 2 and entering the double-pipe heat exchanger, the refrigerant after heat exchange enters a gas-liquid separator 5, and is mixed with the refrigerant flowing back in the main circulation path in the gas-liquid separator 5 to cool the refrigerant entering the compressor 1, reduce the suction temperature of the compressor 1, and finally enter the compressor 1.

In this embodiment, the refrigerant in the two sets of pipelines in the double pipe heat exchanger may flow in opposite directions or in forward directions.

Example three:

the difference from the first embodiment is that the air conditioning system is a single-cooling air conditioning system, the first electric three-way valve 6 and the second electric three-way valve 7 in the first embodiment are omitted, the exhaust pipeline of the compressor 1 is directly connected to the inlet end of the gas cooler 2, and the outlet side of the bypass heat exchanger 8 is directly connected to the pipeline between the outlet side of the evaporator 4 and the gas-liquid separator 5.

Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.