Fluorine refrigerating system, double-cold-source air conditioning unit and control method

Abstract

The invention discloses a fluorine refrigerating system, a double-cold-source air conditioning unit and a control method, and relates to the technical field of machine room air conditioners, the fluorine refrigerating system comprises a compressor, at least two evaporators and a condenser, the compressor, the evaporators and the condenser are connected to form a refrigerant circulation loop, the number of the evaporators is at least two, and the evaporators are arranged in parallel; an expansion valve group is connected in series on a circulating loop between the evaporator and the condenser; and the expansion valve group at least comprises two electronic expansion valves which are connected in parallel. By means of the electronic expansion valve set with the small flow hole diameter, the problem that the superheat degree changes suddenly during high and low load switching of the evaporator is solved on the basis that the operation requirements of the low-load working condition and the high-load working condition of the evaporator are met.

Description

Technical Field

[0001] The present application relates to the technical field of computer room air conditioning, and in particular to a fluorine refrigeration system, a dual-cold source air conditioning unit and a control method. Background Art

[0002] A fluorine system is a common type of air conditioning system that uses a refrigerant (usually Freon or another type of refrigerant) as a medium to transfer cooling or heat.

[0003] In the process of implementing the present invention, the inventors found that the prior art has at least the following problems:

[0004] The evaporator in the existing fluorine system is usually connected in series with only one expansion valve, and the pressure and flow of the refrigerant entering the evaporator are adjusted by the opening of the expansion valve. In order to meet the high evaporation pressure when the evaporator is running at high load, an expansion valve with a larger flow aperture is usually selected. However, when the evaporator is switched between high and low loads, due to the larger flow aperture of the expansion valve, under the same opening change, the expansion valve with a large flow aperture can adjust a larger flow range, which will cause a sudden increase in superheat, resulting in hot spots at the air outlet, affecting the stable operation of the fluorine system.

[0005] Therefore, in response to the above technical problems, how to make the expansion valve meet the high-load and low-load operation requirements of the evaporator while avoiding sudden changes in superheat when the evaporator switches between high and low loads is a technical problem that technical personnel in this field need to solve. Summary of the invention

[0006] The purpose of the present application is to provide a fluorine refrigeration system, a dual-cold source air-conditioning unit and a control method, which solves the problem of sudden change in superheat when the evaporator is switched between high and low loads by using an electronic expansion valve group with a small flow aperture while ensuring the operating requirements of the evaporator under low load and high load conditions.

[0007] To achieve the above-mentioned purpose, the present application provides a fluorine refrigeration system, including a compressor, an evaporator and a condenser, wherein the compressor, the evaporator and the condenser are connected to form a circulation loop of the refrigerant, the number of the evaporators is at least two, and the evaporators are arranged in parallel, and an expansion valve group is connected in series on the circulation loop between the evaporator and the condenser, and the expansion valve group includes at least two parallel electronic expansion valves.

[0008] Preferably, the expansion valve group is connected in series on the parallel branch corresponding to each evaporator, and the expansion valve groups connected in series with different evaporators are arranged in parallel.

[0009] Preferably, in any group of the expansion valve groups, the expansion valve group includes a first electronic expansion valve and a second electronic expansion valve connected in parallel, the first electronic expansion valve and the second electronic expansion valve have the same specifications, and the path lengths of the refrigerant flowing from the first electronic expansion valve and the second electronic expansion valve to the corresponding evaporator are the same.

[0010] Preferably, the expansion valve group includes a third electronic expansion valve, a fourth electronic expansion valve and a fifth electronic expansion valve, the third electronic expansion valve is connected in series on a parallel branch of one of the evaporators, the fourth electronic expansion valve is connected in series on a parallel branch of another of the evaporators, and the fifth electronic expansion valve is connected in parallel with both the third electronic expansion valve and the fourth electronic expansion valve.

[0011] Preferably, the third electronic expansion valve and the fourth electronic expansion valve have the same specifications, and at the same opening degree, the flow rate of the fifth electronic expansion valve is greater than the flow rate of the third electronic expansion valve or the fourth electronic expansion valve.

[0012] Preferably, the first end of the fifth electronic expansion valve is connected to the first end of the third electronic expansion valve and the first end of the fourth electronic expansion valve, respectively, and the second end of the fifth electronic expansion valve is connected to the second end of the third electronic expansion valve and the second end of the fourth electronic expansion valve through the first one-way valve and the second one-way valve, respectively;

[0013] Among them, the first ends of the third electronic expansion valve, the fourth electronic expansion valve, and the fifth electronic expansion valve are connected to the condenser; the flow direction of the first one-way valve is the direction from the second end of the fifth electronic expansion valve to the branch where the third electronic expansion valve is located, and the flow direction of the second one-way valve is the direction from the second end of the fifth electronic expansion valve to the branch where the fourth electronic expansion valve is located.

[0014] A dual-cold-source air-conditioning unit, comprising:

[0015] A chilled water system, comprising a chilled water circulation loop and a chilled water coil and a cooling unit arranged on the chilled water circulation loop;

[0016] Fluorine refrigeration system, which is the fluorine refrigeration system described above;

[0017] The evaporator of the fluorine refrigeration system is an evaporating coil, the evaporating coil corresponds to the position of the chilled water coil, and a plurality of the evaporating coils and the chilled water coils are arranged in series in the air flow direction.

[0018] A control method is applied to the above-mentioned dual cold source air conditioning unit, the control method comprising:

[0019] Operate the chilled water system and / or fluorine refrigeration system according to the cooling demand of the computer room;

[0020] When the fluorine refrigeration system is running, obtaining a first evaporation pressure of a corresponding evaporator of one of the electronic expansion valves in the expansion valve group when the evaporator is fully loaded at a low pressure ratio;

[0021] The current second evaporation pressure of the evaporator is detected by a pressure sensor. If the second evaporation pressure is less than the first evaporation pressure, only one of the electronic expansion valves is opened, and the opening of the electronic expansion valve is adjusted according to the second evaporation pressure; if the second evaporation pressure is greater than or equal to the first evaporation pressure, the other electronic expansion valve is opened, and the two electronic expansion valves provide refrigerant to the corresponding evaporator at the same time.

[0022] Preferably, when the fluorine refrigeration system is running, the first electronic expansion valve is automatically opened, the first evaporation pressure of the corresponding evaporator when the first electronic expansion valve is fully loaded at a low pressure ratio is detected, and based on the relationship between the first evaporation pressure and the second evaporation pressure, it is determined whether to open the second electronic expansion valve.

[0023] Preferably, when the fluorine refrigeration system is running, the third electronic expansion valve and the fourth electronic expansion valve are automatically opened, and the first evaporation pressure of the corresponding evaporator of the third electronic expansion valve or the fourth electronic expansion valve when it is fully loaded at a low pressure ratio is detected, and according to the relationship between the first evaporation pressure and the second evaporation pressure, it is determined whether to open the fifth electronic expansion valve.

[0024] Compared with the prior art, the technical solution provided by this application has at least the following beneficial effects:

[0025] The present application replaces the traditional large-flow aperture expansion valve with an expansion valve group. The expansion valve group uses at least two parallel electronic expansion valves. On the basis of a certain maximum flow of the fluorine refrigeration system, the flow aperture of the parallel electronic expansion valve is significantly smaller. When the evaporator is under low load, only one electronic expansion valve can be opened to ensure the normal opening of the electronic expansion valve. When the low pressure ratio of the opened electronic expansion valve is fully loaded, another electronic expansion valve in parallel can be opened. In this way, the normal opening of the small valve can be achieved at low load, and the high-load operation requirements can be met. At the same time, the present application uses parallel small-flow aperture electronic expansion valves. Therefore, when the evaporator is switched between high and low loads, when the opening of the small-flow aperture electronic expansion valve changes, the system superheat is less affected, avoiding the sudden change of superheat, and improving the operation stability of the fluorine refrigeration system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0027] FIG1 is a schematic diagram of the configuration structure of a first expansion valve group of a fluorine refrigeration system provided in an embodiment of the present application;

[0028] FIG. 2 is a schematic diagram of the second expansion valve group configuration structure of the fluorine refrigeration system provided in an embodiment of the present application.

[0029] In the figure: 1- compressor; 2- evaporator; 3- condenser; 4- circulation loop; 5- expansion valve group; 51- first electronic expansion valve; 52- second electronic expansion valve; 53- third electronic expansion valve; 54- fourth electronic expansion valve; 55- fifth electronic expansion valve; 6- chilled water coil; 7- cooling unit; 8- chilled water circulation loop. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] It should be noted that in this embodiment, the directions or positional relationships indicated by "upper", "lower", "front", "back", etc. are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present application. In addition, "first", "second", "third", and "fourth" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0032] In order to enable those skilled in the art to better understand the present application, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0033] Referring to FIG. 1 and FIG. 2, a fluorine refrigeration system is provided in this embodiment, and the fluorine refrigeration system includes a compressor 1, an evaporator 2 and a condenser 3. The compressor 1, the evaporator 2 and the condenser 3 are connected to form a circulation loop 4 of the fluorine refrigerant. In this embodiment, the number of evaporators 2 in the fluorine refrigeration system is at least two, and the evaporators 2 are arranged in parallel. When one of the evaporators 2 fails or is maintained, the other evaporators 2 connected in parallel can still work normally, thereby ensuring the cooling capacity of the machine room and avoiding the temperature rise of the machine room.

[0034] On the basis of the parallel arrangement of the evaporators 2, an expansion valve group 5 is connected in series on the circulation loop 4 between the evaporator 2 and the condenser 3. Specifically, the expansion valve group 5 can be connected in series on the parallel branch of each evaporator 2. At this time, the number of the expansion valve groups 5 and the evaporator 2 are consistent; please refer to Figure 1, the expansion valve groups 5 connected in series with different evaporators 2 are arranged in parallel, and each expansion valve seat can adjust the flow rate of the fluorine refrigerant on the corresponding parallel branch.

[0035] Furthermore, in any group of expansion valve groups 5, the expansion valve group 5 includes a first electronic expansion valve 51 and a second electronic expansion valve 52 connected in parallel. Considering that when the evaporator 2 is under low load, one of the first electronic expansion valve 51 and the second electronic expansion valve 52 can be opened to meet the low load requirement of the evaporator 2, the first electronic expansion valve 51 and the second electronic expansion valve 52 can be set as electronic expansion valves of the same specification to ensure that regardless of whether the first electronic expansion valve 51 or the second electronic expansion valve 52 is opened, the flow control of the fluorine refrigerant is the same when the opening degree changes to a certain extent, that is, when the first electronic expansion valve 51 or the second electronic expansion valve 52 is opened alone, the flow control of the refrigerant is consistent in both cases, thereby ensuring the control stability of the fluorine refrigeration system.

[0036] The specifications of the first electronic expansion valve 51 and the second electronic expansion valve 52 include flow aperture, control accuracy, working pressure, etc.

[0037] In addition, in order to further improve the consistency of the flow control by the first electronic expansion valve 51 and the second electronic expansion valve 52, the path lengths of the fluorine refrigerant flowing from the first electronic expansion valve 51 and the second electronic expansion valve 52 to the corresponding evaporator 2 can be made the same, thereby avoiding the situation where different refrigerant resistances are caused by different path lengths. Different refrigerant resistances will also cause certain deviations in the flow control by the first electronic expansion valve 51 and the second electronic expansion valve 52.

[0038] As mentioned above, when the evaporator 2 is under load, only the first or second electronic expansion valve 52 can be opened, but when the opened electronic expansion valve is under full load, another electronic expansion valve connected in parallel can be opened, so that the normal opening of the small valve can be achieved at low load and the high load operation requirements can be met. At the same time, the expansion valve group 5 can control the refrigerant amount of the corresponding evaporator 2 independently, so that each expansion valve group 5 can be accurately adjusted according to the evaporation pressure of each evaporator 2.

[0039] In another embodiment, an expansion valve group 5 is connected in series on the circulation loop 4 between the evaporator 2 and the condenser 3, and the expansion valve group 5 is also connected in series in two parallel branches. Please refer to Figure 2. The expansion valve group 5 of this embodiment includes a third electronic expansion valve 53, a fourth electronic expansion valve 54 and a fifth electronic expansion valve 55; specifically, the third electronic expansion valve 53 is connected in series on the parallel branch of one evaporator 2, and the fourth electronic expansion valve 54 is connected in series on the parallel branch of another evaporator 2, and the fifth electronic expansion valve 55 is connected in parallel with the third electronic expansion valve 53 and the fourth electronic expansion valve 54 at the same time.

[0040] The fifth electronic expansion valve 55 can also serve as a backup valve for the third electronic expansion valve 53 and the fourth electronic expansion valve 54. When the two evaporators 2 are running at a low load, only the third electronic expansion valve 53 and the fourth electronic expansion valve 54 can be opened, and the two electronic expansion valves can be kept at a normal opening. At this time, the opening of the electronic expansion valve on the corresponding parallel branch can be automatically adjusted according to the evaporation pressure of the evaporator 2; when the third electronic expansion valve 53 and the fourth electronic expansion valve 54 are fully loaded at a low pressure ratio, the fifth electronic expansion valve 55 can be opened, and the fifth electronic expansion valve 55 can replenish fluorine refrigerant for the two evaporators 2 at the same time, thereby adapting to the high-load operation requirements of the evaporator 2.

[0041] It should be noted that, since the fifth electronic expansion valve 55 can replenish the fluorine refrigerant for the two evaporators 2 at the same time after opening, the evaporation pressures of the two evaporators 2 should be roughly the same, so that after replenishing the fluorine refrigerant, both evaporators 2 can meet the high-load operation. On this basis, the third electronic expansion valve 53 and the fourth electronic expansion valve 54 should also maintain the same specifications to ensure that when the evaporation pressures of the two evaporators 2 are roughly the same, the fifth electronic expansion valve 55 can provide roughly the same amount of fluorine refrigerant for the two evaporators 2 as a backup valve.

[0042] At the same time, the expansion valve group 5 uses at least parallel electronic expansion valves. On the basis of a certain maximum flow rate of the fluorine refrigeration system, the flow aperture of the parallel electronic expansion valves is obviously smaller, so that the electronic expansion valves can provide more precise flow control. On this basis, the flow apertures of the third electronic expansion valve 53 and the fourth electronic expansion valve 54 are relatively small. In order to meet the maximum flow rate of the fluorine refrigeration system, the flow aperture of the fifth electronic expansion valve 55 should also be large enough, so that sufficient supplementary refrigerant can be provided for the two evaporators 2 at the same time. In some embodiments, under the same opening condition, the flow rate of the fifth electronic expansion valve 55 is greater than the flow rate of the third electronic expansion valve 53 or the fourth electronic expansion valve 54, thereby ensuring that sufficient supplementary refrigerant can be provided for the two evaporators 2.

[0043] Please refer to FIG. 2 , the first end of the fifth electronic expansion valve 55 is connected to the first end of the third electronic expansion valve 53 and the first end of the fourth electronic expansion valve 54, respectively, and the second end of the fifth electronic expansion valve 55 is connected to the second end of the third electronic expansion valve 53 and the second end of the fourth electronic expansion valve 54, respectively, through the first one-way valve and the second one-way valve. Among them, the first ends of the third electronic expansion valve 53, the fourth electronic expansion valve 54, and the fifth electronic expansion valve 55 are connected to the condenser 3; the flow direction of the first one-way valve is the direction from the second end of the fifth electronic expansion valve 55 to the branch where the third electronic expansion valve 53 is located, and the flow direction of the second one-way valve is the direction from the second end of the fifth electronic expansion valve 55 to the branch where the fourth electronic expansion valve 54 is located; by setting the first one-way valve and the second one-way valve, the refrigerants in the corresponding parallel branches of the two evaporators 2 can be prevented from flowing mutually, so as to ensure the stable operation of the two evaporators 2.

[0044] In summary of the above embodiments, the present application replaces the traditional large flow aperture expansion valve with the expansion valve group 5. The expansion valve group 5 adopts at least two parallel electronic expansion valves. On the basis of the certain maximum flow of the fluorine refrigeration system, the flow aperture of the parallel electronic expansion valve is obviously smaller. When the evaporator 2 is underloaded, only one electronic expansion valve can be opened to ensure the normal opening of the electronic expansion valve. When the low pressure ratio of the opened electronic expansion valve is fully loaded, another electronic expansion valve in parallel can be opened, so that the normal opening of the small valve can be achieved at low load and the high load operation requirements can be met. At the same time, the present application adopts parallel small flow aperture electronic expansion valves. Therefore, when the evaporator 2 is switched between high and low loads, when the opening of the electronic expansion valve with a small flow aperture changes, the influence on the system superheat is smaller, avoiding the situation of sudden changes in superheat, and improving the operation stability of the fluorine refrigeration system.

[0045] The present application also provides a dual-cold source air-conditioning unit, please refer to Figure 1 or Figure 2, the air-conditioning unit includes a chilled water system and a fluorine refrigeration system, the freezer water system includes a chilled water circulation loop 8 and a chilled water coil 6 and a cooling unit 7 arranged on the chilled water circulation loop 8; the fluorine refrigeration system is the above-mentioned fluorine refrigeration system. Among them, the evaporator 2 of the fluorine refrigeration system is an evaporating coil, and the position of the evaporating coil corresponds to the position of the chilled water coil 6, so that multiple evaporating coils can be arranged in series with the chilled water coil 6 in the airflow direction, that is, series ventilation; series connection in the airflow direction means that the return airflow of the machine room can flow through the evaporating coil and the chilled water coil 6 in sequence, or through the chilled water coil 6 and the evaporating coil in sequence, so that according to the actual cooling demand of the machine room, the chilled water system or the fluorine refrigeration system can be operated separately, or the two systems can be operated simultaneously.

[0046] Since the dual-cold-source air-conditioning unit includes a fluorine refrigeration system, the air-conditioning unit also has the beneficial effects of the expansion valve group 5 in the fluorine refrigeration system.

[0047] The present application also provides a control method, which can be applied to the above-mentioned dual cold source air conditioning unit, and the control method includes:

[0048] Operate the chilled water system and / or fluorine refrigeration system according to the cooling demand of the computer room;

[0049] When the fluorine refrigeration system is running, the first evaporation pressure of the corresponding evaporator 2 of one of the electronic expansion valves of the expansion valve group 5 when fully loaded at a low pressure ratio can be obtained through the corresponding pressure sensor;

[0050] At the same time, when the fluorine refrigeration system is running, the evaporation pressure of the evaporator 2 will change to a certain extent according to the cooling demand of the machine room, so the opening degree of the corresponding electronic expansion valve will also change; on this basis, the current second evaporation pressure of the evaporator 2 can be detected by the pressure sensor. If the second evaporation pressure is less than the first evaporation pressure, it means that one electronic expansion valve can meet the current load requirement of the evaporator 2. At this time, only one electronic expansion valve needs to be opened, and the opening degree of the electronic expansion valve can be adjusted according to the second evaporation pressure; if the second evaporation pressure is greater than or equal to the first evaporation pressure, it means that the electronic expansion valve that has been opened at this time cannot meet the high-load operation demand of the evaporator 2, so it is necessary to open another electronic expansion valve in parallel to supplement the evaporator 2 with sufficient fluorine refrigerant to meet the high-load operation demand of the evaporator 2.

[0051] By using a small flow aperture electronic expansion valve in parallel, when the evaporator 2 switches between high and low loads, when the opening of the small flow aperture electronic expansion valve changes, the impact on the system superheat is smaller, avoiding sudden changes in superheat.

[0052] In the first embodiment, the expansion valve group 5 includes a first electronic expansion valve 51 and a second electronic expansion valve 52. When the fluorine refrigeration mode is running, the first electronic expansion valve 51 can be automatically opened, and the opening of the first electronic expansion valve 51 can be automatically adjusted according to the evaporation pressure of the evaporator 2; according to the above control method, it is also necessary to detect the first evaporation pressure of the corresponding evaporator 2 when the first electronic expansion valve 51 is fully loaded at a low pressure ratio, and determine whether to open the second electronic expansion valve 52 according to the magnitude relationship between the first evaporation pressure and the second evaporation pressure. Specifically, when the second evaporation pressure is less than the first evaporation pressure, the evaporator 2 is under low load, so only the first electronic expansion valve 51 can be kept open; when the second evaporation pressure is greater than or equal to the first evaporation pressure, it means that the first electronic expansion valve 51 is under low pressure ratio and fully loaded. At this time, the second electronic expansion valve 52 needs to be opened, so that the two electronic expansion valves provide refrigerant for the corresponding evaporator 2 at the same time. In this way, the normal opening of the first electronic expansion valve 51 when the evaporator 2 is under low load can be achieved, and the operation requirements of the evaporator 2 under high load can be met.

[0053] Of course, when the fluorine refrigeration mode is running, the second electronic expansion valve 52 can also be automatically opened. The second electronic expansion valve 52 and the first electronic expansion valve 51 can be equivalently replaced. Please refer to the above content for the subsequent steps of opening the second electronic expansion valve 52, which will not be repeated here.

[0054] In the second embodiment, the expansion valve group 5 includes a third electronic expansion valve 53, a fourth electronic expansion valve 54 and a fifth electronic expansion valve 55. When the fluorine refrigeration system is running, the third electronic expansion valve 53 and the fourth electronic expansion valve 54 are automatically opened to meet the normal operation of the two evaporators 2 and ensure the normal opening of the third electronic expansion valve 53 and the fourth electronic expansion valve 54. According to the above control method, it is also necessary to detect the first evaporation pressure of the corresponding evaporator 2 when the third electronic expansion valve or the fourth electronic expansion valve 54 is fully loaded at a low pressure ratio, and determine whether to open the fifth electronic expansion valve 55 according to the magnitude relationship between the first evaporation pressure and the second evaporation pressure. Specifically, when the second evaporation pressure is less than the first evaporation pressure, the evaporator 2 is under low load, so only the third electronic expansion valve 53 and the fourth electronic expansion valve 54 can be kept open; when the second evaporation pressure is greater than or equal to the first evaporation pressure, it means that the third electronic expansion valve 53 or the fourth electronic expansion valve 54 is under low pressure ratio and fully loaded. At this time, the fifth electronic expansion valve 55 needs to be opened, so that the fifth electronic expansion valve 55 can provide refrigerant for the two evaporators 2 at the same time to meet the high load operation requirements.

[0055] From the above, it can be seen that the control method of the present application can meet the operating requirements of the evaporator 2 under low-load conditions and high-load conditions. At the same time, it can also control the opening of the corresponding electronic expansion valve and control the opening and closing of different electronic expansion valves according to the evaporation pressure of the evaporator 2, thereby reducing the impact on the system superheat through the electronic expansion valve with a small flow aperture and improving the operating stability of the fluorine refrigeration system.

[0056] It should be noted that, in this specification, relational terms such as first and second are merely used to distinguish one entity from other entities, but do not necessarily require or imply any actual relationship or order between these entities.

[0057] Specific examples are used herein to illustrate the principles and implementation methods of the present application, and the description of the above embodiments is only used to help understand the method and core ideas of the present application. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A fluorine refrigeration system, characterized in that: The invention comprises a compressor (1), an evaporator (2) and a condenser (3), wherein the compressor (1), the evaporator (2) and the condenser (3) are connected to form a circulation loop (4) of a refrigerant, the number of the evaporators (2) is at least two, and the evaporators (2) are arranged in parallel, and an expansion valve group (5) is connected in series on the circulation loop (4) between the evaporator (2) and the condenser (3), and the expansion valve group (5) comprises at least two electronic expansion valves connected in parallel.

2. The fluorine refrigeration system according to claim 1, characterized in that: The expansion valve group (5) is connected in series to the parallel branch corresponding to each evaporator (2), and the expansion valve groups (5) connected in series to different evaporators (2) are arranged in parallel.

3. The fluorine refrigeration system according to claim 2, characterized in that: In any group of the expansion valve groups (5), the expansion valve group (5) comprises a first electronic expansion valve (51) and a second electronic expansion valve (52) connected in parallel, the first electronic expansion valve (51) and the second electronic expansion valve (52) have the same specifications, and the path lengths of the refrigerant flowing from the first electronic expansion valve (51) and the second electronic expansion valve (52) to the corresponding evaporator (2) are the same.

4. The fluorine refrigeration system according to claim 1, characterized in that: The expansion valve group (5) comprises a third electronic expansion valve (53), a fourth electronic expansion valve (54) and a fifth electronic expansion valve (55); the third electronic expansion valve (53) is connected in series to a parallel branch of one of the evaporators (2); the fourth electronic expansion valve (54) is connected in series to a parallel branch of another of the evaporators (2); and the fifth electronic expansion valve (55) is connected in parallel to both the third electronic expansion valve (53) and the fourth electronic expansion valve (54).

5. The fluorine refrigeration system according to claim 4, characterized in that: The third electronic expansion valve (53) and the fourth electronic expansion valve (54) have the same specifications, and at the same opening degree, the flow rate of the fifth electronic expansion valve (55) is greater than the flow rate of the third electronic expansion valve (53) or the fourth electronic expansion valve (54).

6. The fluorine refrigeration system according to claim 5, characterized in that: The first end of the fifth electronic expansion valve (55) is respectively connected to the first end of the third electronic expansion valve (53) and the first end of the fourth electronic expansion valve (54), and the second end of the fifth electronic expansion valve (55) is respectively connected to the second end of the third electronic expansion valve (53) and the second end of the fourth electronic expansion valve (54) via the first one-way valve and the second one-way valve; The first ends of the third electronic expansion valve (53), the fourth electronic expansion valve (54) and the fifth electronic expansion valve (55) are connected to the condenser (3); the flow direction of the first one-way valve is the direction in which the second end of the fifth electronic expansion valve (55) flows toward the branch where the third electronic expansion valve (53) is located, and the flow direction of the second one-way valve is the direction in which the second end of the fifth electronic expansion valve (55) flows toward the branch where the fourth electronic expansion valve (54) is located.

7. A dual cold source air conditioning unit, characterized in that: include: A chilled water system, comprising a chilled water circulation loop (8) and a chilled water coil (6) and a cooling unit (7) arranged on the chilled water circulation loop (8); A fluorine refrigeration system, which is the fluorine refrigeration system according to any one of claims 1 to 6; The evaporator (2) of the fluorine refrigeration system is an evaporating coil, the evaporating coil corresponds to the position of the chilled water coil (6), and a plurality of the evaporating coils and the chilled water coil (6) are arranged in series in the airflow direction.

8. A control method, characterized in that: Applied to the dual cold source air conditioning unit according to claim 7, the control method comprises: Operate the chilled water system and / or fluorine refrigeration system according to the cooling demand of the computer room; When the fluorine refrigeration system is running, obtaining a first evaporation pressure of the corresponding evaporator (2) of one of the electronic expansion valves of the expansion valve group (5) when the evaporator is fully loaded at a low pressure ratio; The current second evaporation pressure of the evaporator (2) is detected by a pressure sensor. If the second evaporation pressure is less than the first evaporation pressure, only one of the electronic expansion valves is opened, and the opening of the electronic expansion valve is adjusted according to the second evaporation pressure. If the second evaporation pressure is greater than or equal to the first evaporation pressure, the other electronic expansion valve is opened, and the two electronic expansion valves simultaneously provide refrigerant for the corresponding evaporator (2).

9. The control method according to claim 8, characterized in that: When the fluorine refrigeration system is in operation, the first electronic expansion valve (51) is automatically opened, the first evaporation pressure of the corresponding evaporator (2) when the first electronic expansion valve (51) is fully loaded at a low pressure ratio is detected, and according to the relationship between the first evaporation pressure and the second evaporation pressure, it is determined whether to open the second electronic expansion valve (52).

10. The control method according to claim 8, characterized in that: When the fluorine refrigeration system is in operation, the third electronic expansion valve (53) and the fourth electronic expansion valve (54) are automatically opened, the first evaporation pressure of the corresponding evaporator (2) of the third electronic expansion valve (53) or the fourth electronic expansion valve (54) is detected when the third electronic expansion valve (53) or the fourth electronic expansion valve (54) is fully loaded at a low pressure ratio, and whether to open the fifth electronic expansion valve (55) is determined based on the relationship between the first evaporation pressure and the second evaporation pressure.

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