Four-pipe unit and control method thereof

Abstract

According to the four-pipe unit and the control method thereof, in the four-pipe unit, an exhaust port is connected with a D port, an E port is connected with a T port, a first throttling element is arranged on a first branch, the first branch is connected with a P port and an R port, a second branch is connected with an O port and an air suction port, an S port is connected with the second branch, a C port is connected with an M port, and a third branch is connected with an N port and the first branch; a first switch valve is arranged on the fourth branch, the fourth branch is connected with the N port and the low-pressure injection inlet, a second switch valve is arranged on the fifth branch, the fifth branch is connected with the exhaust port and the high-pressure injection inlet, and the mixing outlet is connected with the air suction port. According to the four-pipe unit and the control method thereof, the refrigerant in the balance heat exchanger is recycled into the refrigerant circulation loop through the ejector, and the problem that the refrigerant in the system circulation loop is insufficient can be solved.

Description

Technical Field

[0001] This application relates to the field of air conditioning unit technology, and in particular to a four-pipe unit and its control method. Background Technology

[0002] Four-pipe units can simultaneously provide chilled and hot water, making them particularly suitable for applications requiring both cold and heat sources. They are increasingly used in hospitals, archives, high-end hotels, and temperature- and humidity-controlled factories. A typical four-pipe unit includes a chilled water heat exchanger, a hot water heat exchanger, a balance heat exchanger, and a four-way valve. By switching the connection state of the four-way valve, the four-pipe unit can switch between chilled water mode, hot water mode, and a chilled water + hot water mode. When the four-pipe unit is in chilled water + hot water mode, the chilled water and hot water heat exchangers are engaged, while the balance heat exchanger is idle. In winter, when the ambient temperature is low, the pressure inside the balance heat exchanger is low, making it easy for refrigerant to migrate through the four-way valve into the balance heat exchanger under pressure differential. This leads to insufficient refrigerant circulation in the system, a sharp drop in evaporation pressure, and consequently, decreased unit output and energy efficiency. In more severe cases, it may even cause the chilled water heat exchanger to freeze and crack. Summary of the Invention

[0003] Therefore, it is necessary to provide a four-pipe unit to solve the problems of refrigerant migrating into the balance heat exchanger through the four-way valve, resulting in insufficient circulating refrigerant in the system and a sharp drop in evaporation pressure.

[0004] A four-pipe unit includes a compressor, a four-way valve, a hot water heat exchanger, a cold water heat exchanger, a balance heat exchanger, a first throttling element, an ejector, a first branch, a second branch, a third branch, a fourth branch, and a fifth branch. The compressor has a discharge port and a suction port. The four-way valve has ports D, E, S, and C. The hot water heat exchanger has ports T and P. The cold water heat exchanger has ports R and O. The balance heat exchanger has ports M and N. The ejector has a high-pressure ejector inlet and a low-pressure ejector inlet. The system includes an exhaust port and a mixing outlet; the exhaust port is connected to port D, port E is connected to port T, a first throttling element is located on the first branch, and the first branch is connected to port P and port R, the second branch is connected to port O and the intake port, port S is connected to the second branch, port C is connected to port M, the third branch is connected to port N and the first branch, a first switching valve is located on the fourth branch, and the fourth branch is connected to port N and the low-pressure ejector inlet, a second switching valve is located on the fifth branch, and the fifth branch is connected to the exhaust port and the high-pressure ejector inlet, and the mixing outlet is connected to the intake port.

[0005] In one embodiment, a fifth check valve is provided between port S and the second branch, allowing unidirectional flow from port S to the second branch.

[0006] In one embodiment, the first branch includes a first segment, a second segment, a third segment, and a fourth segment connected sequentially from port P to port R. The second segment is provided with a first check valve that allows unidirectional flow from the first segment to the third segment. The third segment is provided with a liquid reservoir and a dryer filter connected in series. The liquid reservoir is positioned closer to the first check valve than the dryer filter. A first throttling element is located in the fourth segment. The end of the third branch away from port N is connected to the junction of the second and third segments, and the third branch is provided with a second check valve that allows unidirectional flow from port N to the third segment.

[0007] In one embodiment, the four-control unit further includes a sixth branch and a second throttling element. The second throttling element is located on the sixth branch. One end of the sixth branch is connected to the connection between the third and fourth sections, and the other end is connected to the N port. A third one-way valve is provided on the sixth branch for unidirectional flow from the sixth branch to the N port.

[0008] In one embodiment, the four-pipe unit further includes a seventh branch, one end of which is connected between the second throttling element and the third check valve, and the other end is connected to the connection between the first section and the second section. The seventh branch is provided with a fourth check valve that allows one-way flow from the second throttling element to the first section.

[0009] In one embodiment, the third section is further provided with an economizer assembly, and the compressor also has a gas inlet; the economizer assembly includes a main liquid pipe, a secondary liquid pipe and a connecting pipe, the inlet of the main liquid pipe is connected to a dryer filter, the outlet of the main liquid pipe is connected to a first branch, the connecting pipe is provided with a third throttling element, and one end of the connecting pipe is connected between the outlet of the main liquid pipe and the first branch, and the other end is connected to the inlet of the secondary liquid pipe, and the outlet of the secondary liquid pipe is connected to the gas inlet.

[0010] A control method for controlling the operation of a four-pipe chiller unit as described in any of the above embodiments, the control method comprising: upon receiving a command to switch to chilled water + hot water mode, acquiring the compressor's saturation temperature T. pe and the outlet water temperature T of the cold water heat exchanger o And calculate the deviation value Δ=T O -T pe Adjust the on / off states of the first and second switching valves to keep the deviation value Δ less than ΔT. e , where ΔT e This represents the target deviation value.

[0011] In one embodiment, the on / off states of the first and second switching valves are adjusted so that the deviation value Δ remains less than ΔT. e Specifically, this includes: when the deviation value Δ ≥ ΔT e Start timing and maintain the deviation value Δ≥ΔT e When the preset time t is reached, the first and second switching valves are opened; when the deviation value Δ < ΔTe When -T is applied, the first and second switching valves are closed.

[0012] In one embodiment, 8℃≤ΔT e ≤13℃, 1℃≤T≤6℃, 8s≤t≤300s.

[0013] In one embodiment, the saturation temperature T of the compressor is obtained. pe include:

[0014] Obtain the compressor's suction pressure P e According to the inhalation pressure P e Calculate the corresponding saturation temperature T pe .

[0015] Compared with existing technologies, the four-pipe unit and its control method provided in this application, when the four-pipe unit is in chilled water + hot water mode, the refrigerant circulation loop is: compressor discharge port - port D - port E - hot water heat exchanger - first throttling element - chilled water heat exchanger - compressor suction port. When refrigerant migrates into the balance heat exchanger through the four-way valve, the first and second switching valves can be opened to allow the high-temperature, high-pressure refrigerant vapor discharged from the compressor discharge port to enter the mixing chamber through the high-pressure ejector inlet, and to eject the low-speed, low-energy refrigerant in the balance heat exchanger through the low-pressure ejector inlet into the mixing chamber. In the mixing chamber, the two refrigerants mix to form a relatively uniform flow of refrigerant, thereby timely recovering the refrigerant that has migrated into the balance heat exchanger back into the refrigerant circulation loop, thus avoiding insufficient refrigerant in the refrigerant circulation loop, which could lead to problems such as decreased evaporation pressure, reduced unit output, and decreased energy efficiency. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic diagram of the four-control unit of Embodiment 1 provided in this application;

[0018] Figure 2 A schematic diagram of the four-control unit of Embodiment 2 provided in this application;

[0019] Figure 3 A schematic diagram of the four-pipe chiller unit's chilled water mode according to Embodiment 1 of this application;

[0020] Figure 4A schematic diagram of the hot water production mode of the four-pipe unit in Embodiment 1 provided in this application;

[0021] Figure 5 A schematic diagram of the four-pipe unit in the chilled water + hot water production mode of Embodiment 1 provided in this application;

[0022] Figure 6 This is a schematic diagram of the defrosting mode of the four-pipe unit in Embodiment 1 provided in this application.

[0023] Reference numerals: 100, Four-pipe unit; 10, Compressor; 11, Exhaust port; 12, Inlet port; 13, Make-up port; 20, Four-way valve; 30, Hot water heat exchanger; 40, Cold water heat exchanger; 50, Balanced heat exchanger; 60, Ejector; 61, High-pressure ejector inlet; 62, Low-pressure ejector inlet; 63, Mixing outlet; 71, First branch; 710, First throttling element; 711, First stage; 712, Second stage; 701, First check valve; 702, Liquid receiver; 703, Dryer filter; 713, Third section; 714, Fourth section; 72, Second branch; 73, Third branch; 731, Second check valve; 74, Fourth branch; 741, First switching valve; 75, Fifth branch; 751, Second switching valve; 76, Sixth branch; 761, Second throttling element; 762, Third check valve; 77, Seventh branch; 771, Fourth check valve; 78, Fifth check valve; 90, Economizer assembly; 91, Main liquid pipe; 92, Secondary circuit liquid pipe; 93, Connecting pipe; 931, Third throttling element. Detailed Implementation

[0024] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0025] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on the other component or there may be an intermediate component. When a component is considered to be "connected to" another component, it can be directly connected to the other component or there may be an intermediate component present. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application's specification are for illustrative purposes only and do not represent the only possible implementation.

[0026] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0027] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature and the second feature are in indirect contact through an intermediate medium. Furthermore, "above," "over," and "on top" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0028] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items.

[0029] Please see Figure 1 This application provides a four-pipe unit 100, which includes a compressor 10, a four-way valve 20, a hot water heat exchanger 30, a cold water heat exchanger 40, a balancing heat exchanger 50, a first throttling element 710, an ejector 60, a first branch 71, a second branch 72, a third branch 73, a fourth branch 74, and a fifth branch 75. The compressor 10 has an exhaust port 11 and an intake port 12, the four-way valve 20 has ports D, E, S, and C, the hot water heat exchanger 30 has ports T and P, the cold water heat exchanger 40 has ports R and O, the balancing heat exchanger 50 has ports M and N, and the ejector 60 has a high-pressure ejector inlet 61, a low-pressure ejector inlet 62, and a mixing outlet 63. Exhaust port 11 is connected to port D, port E is connected to port T, a first throttling element 710 is provided on the first branch 71, and the first branch 71 is connected to port P and port R, the second branch 72 is connected to port O and intake port 12, port S is connected to the second branch 72, port C is connected to port M, the third branch 73 is connected to port N and the first branch 71, the fourth branch 74 is provided with a first switching valve 741, and the fourth branch 74 is connected to port N and low-pressure ejector inlet 62, the fifth branch 75 is provided with a second switching valve 751, and the fifth branch 75 is connected to exhaust port 11 and high-pressure ejector inlet 61, and the mixing outlet 63 is connected to intake port 12.

[0030] It should be noted that the ejector 60 is a device that uses a high-speed, high-energy flow to eject another low-speed, low-energy flow. Its working principle is based on Bernoulli's principle, specifically: the ejector 60 has a mixing chamber inside. A high-speed, high-energy flow (e.g., compressed steam, air) enters the mixing chamber through the high-pressure ejector inlet 61, and another low-speed, low-energy flow is ejected through the low-pressure ejector inlet 62 into the mixing chamber. Inside the mixing chamber, the two fluids are thoroughly mixed, and the resulting high-energy fluid has its velocity reduced and static pressure increased by a diffuser, ultimately forming a relatively uniform flow that exits from the mixing outlet 63. In this application, when the four-pipe unit 100 is in chilled water + hot water mode, the refrigerant circulation loop is: compressor 10 discharge port 11 - port D - port E - hot water heat exchanger 30 - first throttling element 710 - chilled water heat exchanger 40 - compressor 10 suction port 12. When refrigerant migrates into the balance heat exchanger 50 through the four-way valve, the first switching valve 741 and the second switching valve 751 can be opened to allow the high-temperature and high-pressure refrigerant vapor discharged from the compressor 10 discharge port 11 to enter the mixing chamber through the high-pressure ejector inlet 61, and to eject the low-speed and low-energy refrigerant in the balance heat exchanger 50 through the low-pressure ejector inlet 62 into the mixing chamber. In the mixing chamber, the two refrigerants mix to form a relatively uniform flow of refrigerant, thereby timely recovering the refrigerant that has migrated into the balance heat exchanger 50 back into the refrigerant circulation loop, so as to avoid insufficient refrigerant in the refrigerant circulation loop, which would lead to problems such as a drop in evaporation pressure, reduced unit output and energy efficiency.

[0031] Optionally, the first switching valve 741 and the second switching valve 751 are respectively equipped with solenoid valves.

[0032] A fifth check valve 78 is provided between port S and the second branch 72, allowing one-way flow from port S to the second branch 72. This helps to prevent the refrigerant in the chilled water heat exchanger 40 from entering port M of the balance heat exchanger 50 via port O-port-port S-port when the four-pipe unit 100 is in chilled water + hot water mode.

[0033] The first branch 71 includes a first segment 711, a second segment 712, a third segment 713, and a fourth segment 714 connected sequentially from port P to port R. The second segment 712 is provided with a first one-way valve 701 that allows unidirectional flow from the first segment 711 to the third segment 713. The third segment 713 is provided with a liquid reservoir 702 and a dryer filter 703 connected in series. The liquid reservoir 702 is positioned closer to the first one-way valve 701 relative to the dryer filter 703. A first throttling element 710 is located in the fourth segment 714. The end of the third branch 73 away from port N is connected to the junction of the second segment 712 and the third segment 713, and the third branch 73 is provided with a second one-way valve 731 that allows unidirectional flow from port N to the third segment 713.

[0034] The four-pipe unit 100 also includes a sixth branch 76 and a second throttling element 761. The second throttling element 761 is provided on the sixth branch 76. One end of the sixth branch 76 is connected to the connection between the third section 713 and the fourth section 714, and the other end is connected to the N port. The sixth branch 76 is provided with a third one-way valve 762 that allows unidirectional flow from the sixth branch 76 to the N port.

[0035] The four-pipe unit 100 also includes a seventh branch 77, one end of which is connected between the second throttling element 761 and the third one-way valve 762, and the other end is connected to the connection between the first section 711 and the second section 712. The seventh branch 77 is provided with a fourth one-way valve 771 that allows unidirectional flow from the second throttling element 761 to the first section 711.

[0036] Please see Figure 2 In one embodiment, the third segment 713 is further provided with an economizer assembly 90, and the compressor 10 also has a gas supply port 13. The economizer assembly 90 includes a main liquid pipe 91, a secondary loop liquid pipe 92, and a connecting pipe 93. The inlet of the main liquid pipe 91 is connected to a dryer filter 703, and the outlet of the main liquid pipe 91 is connected to a first branch 71. Specifically, the outlet of the main liquid pipe 91 is connected between a second throttling element 761 and a first throttling element 710. The connecting pipe 93 is provided with a third throttling element 931, and one end of the connecting pipe 93 is connected between the outlet of the main liquid pipe 91 and the first branch 71, while the other end is connected to the inlet of the secondary loop liquid pipe 92. The outlet of the secondary loop liquid pipe 92 is connected to the gas supply port 13.

[0037] Thus, the refrigerant from the dryer filter 703 enters the main liquid pipe 91 and is divided into two parts. One part enters the connecting pipe 93 and is further cooled by thermal expansion after being throttled by the third throttling element 931. Then it flows into the secondary loop liquid pipe 92 and exchanges heat with the refrigerant in the main liquid pipe 91, making the refrigerant in the main liquid pipe 91 subcooled. The refrigerant in the secondary loop liquid pipe 92 enters the gas injection port 13 of the compressor 10 in a gaseous state. The other part flows to the first throttling element 710 and enters the chilled water heat exchanger 40 for cooling after being throttled by the first throttling element 710.

[0038] The first throttling element 710, the second throttling element 761 and the third throttling element 931 are all configured as throttling elements with a shut-off function. For example, they can be configured as a combination of an electronic expansion valve and a thermal expansion valve.

[0039] The following describes several operating modes of the four-pipe unit 100:

[0040] Cooling water mode

[0041] Please see Figure 1 and Figure 3When the four-pipe unit 100 is in chilled water mode, port D is connected to port C, port E is connected to port S, the first throttling element 710 is open, and the second throttling element 761 is closed. The refrigerant circulation loop is as follows: compressor 10 discharge port 11 - port D - port C - balance heat exchanger 50 - second one-way valve 731 - liquid receiver 702 - dryer filter 703 - first throttling element 710 - chilled water heat exchanger 40 - compressor 10 suction port 12.

[0042] Hot water mode

[0043] Please see Figure 1 and Figure 4 When the four-pipe unit 100 is in hot water production mode, port D is connected to port E, port C is connected to port S, the first throttling element 710 is closed, and the second throttling element 761 is open. The refrigerant circulation loop is as follows: compressor 10 discharge port 11 - port D - port E - hot water heat exchanger 30 - first one-way valve 701 - second one-way valve 731 - liquid receiver 702 - dryer filter 703 - second throttling element 761 - third one-way valve 762 - balance heat exchanger 50 - port C - port S - fifth one-way valve 78 - compressor 10 suction port 12.

[0044] Cooling water + hot water mode

[0045] Please see Figure 1 and Figure 5 Port D is connected to Port E, and Port C is connected to Port S. The first throttling element 710 is open, and the second throttling element 761 is closed. The refrigerant circulation loop is as follows: compressor 10 discharge port 11 - port D - port E - hot water heat exchanger 30 - first one-way valve 701 - liquid receiver 702 - dryer filter 703 - first throttling element 710 - cold water heat exchanger 40 - compressor 10 suction port 12.

[0046] Defrosting mode

[0047] Please see Figure 1 and Figure 6 Port D is connected to Port C, and Port E is connected to Port S. The first throttling element 710 is closed, and the second throttling element 761 is open. The refrigerant circulation loop is as follows: Discharge port 11 of compressor 10 - Port D - Port C - Balance heat exchanger 50 - Second one-way valve 731 - Liquid receiver 702 - Dryer filter 703 - Second throttling element 761 - Fourth one-way valve 771 - Hot water heat exchanger 30 - Port E is connected to Port S - Fifth one-way valve 78 - Inlet port 12 of compressor 10.

[0048] This application also provides a control method for a four-pipe generator set 100, which is used to implement the operation control of the four-pipe generator set 100 described in any of the above embodiments. Specifically, the control method includes:

[0049] Step S1: When a command to switch to chilled water + hot water mode is received, the saturation temperature T of compressor 10 is obtained. pe and the outlet water temperature T of the cold water heat exchanger 40 O And calculate the deviation value Δ=T O -T pe ;

[0050] Step S2: Adjust the on / off state of the first switching valve 741 and the second switching valve 751 to keep the deviation value Δ less than ΔT. e , where ΔT e This represents the target deviation value.

[0051] It should be noted that receiving the command to switch to chilled water + hot water mode specifically means connecting port D to port E, port C to port S, opening the first throttling element 710, and closing the second throttling element 761, causing the four-pipe unit 100 to start operating in chilled water + hot water mode. The deviation value Δ reflects the heat exchange efficiency of the evaporator and is an important parameter for evaluating evaporator performance. Keeping the deviation value Δ within the preset range helps ensure efficient heat exchange. If the deviation value Δ exceeds the normal range, it indicates insufficient refrigerant in the refrigerant circulation loop. By opening the first switching valve 741 and the second switching valve 751, the ejector 60 can recover the refrigerant from the balancing heat exchanger 50 back into the refrigerant circulation loop.

[0052] Optionally, in one embodiment, step S1 involves obtaining the saturation temperature T of the compressor 10. pe Specifically, this includes: obtaining the suction pressure P of compressor 10. e According to the inhalation pressure P e Calculate the corresponding saturation temperature T pe .

[0053] Optionally, in one embodiment, step S2 specifically includes: when the deviation value Δ ≥ ΔT e Start timing and maintain the deviation value Δ≥ΔT e When the preset time t is reached, the first switching valve 741 and the second switching valve 751 are opened; when the deviation value Δ < ΔT e When -T is applied, the first switching valve 741 and the second switching valve 751 are closed.

[0054] It is understandable that the maintenance deviation value Δ≥ΔT is set. eThe first switching valve 741 and the second switching valve 751 are only opened after a preset time t is reached, which can prevent a sudden increase in the deviation value Δ caused by fluctuations in the operation of the four-pipe unit 100. After the first switching valve 741 and the second switching valve 751 are opened, the ejector 60 recovers the refrigerant in the balancing heat exchanger 50 into the refrigerant circulation loop, so that as the four-pipe unit 100 operates, the deviation value Δ gradually decreases and approaches the target deviation value ΔT. e By setting Δ < ΔT e The first switching valve 741 and the second switching valve 751 are closed only when -T is reached, which helps to ensure that the ejector 60 recovers as much refrigerant as possible from the balance heat exchanger 50 into the refrigerant circulation loop.

[0055] In one embodiment, for example, 8°C ≤ ΔT e ≤13℃, 1℃≤T≤6℃, 8s≤t≤300s.

[0056] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. Therefore, the patent protection scope of this application should be determined by the appended claims.

Claims

1. A four-pipe unit, characterized in that, The four-pipe unit includes a compressor (10), a four-way valve (20), a hot water heat exchanger (30), a cold water heat exchanger (40), a balancing heat exchanger (50), a first throttling element (710), an ejector (60), a first branch (71), a second branch (72), a third branch (73), a fourth branch (74), and a fifth branch (75). The compressor (10) has an exhaust port (11) and an intake port (12). The four-way valve (20) has ports D, E, S, and C. The hot water heat exchanger (30) has ports T and P. The cold water heat exchanger (40) has ports R and O. The balancing heat exchanger (50) has ports M and N. The ejector (60) has a high-pressure ejector inlet (61), a low-pressure ejector inlet (62), and a mixing outlet (63). The exhaust port (11) is connected to the D port, the E port is connected to the T port, the first throttling element (710) is provided on the first branch (71), and the first branch (71) is connected to the P port and the R port, the second branch (72) is connected to the O port and the intake port (12), the S port is connected to the second branch (72), the C port is connected to the M port, the third branch (73) is connected to the N port and the first branch (71), the fourth branch (74) is provided with a first switching valve (741), and the fourth branch (74) is connected to the N port and the low-pressure ejector inlet (62), the fifth branch (75) is provided with a second switching valve (751), and the fifth branch (75) is connected to the exhaust port (11) and the high-pressure ejector inlet (61), and the mixing outlet (63) is connected to the intake port (12).

2. The four-pipe unit according to claim 1, characterized in that, A fifth check valve (78) is provided between the S port and the second branch (72) to allow one-way flow from the S port to the second branch (72).

3. The four-pipe unit according to claim 1, characterized in that, The first branch (71) includes a first section (711), a second section (712), a third section (713), and a fourth section (714) connected sequentially from the P port to the R port. The second section (712) is provided with a first one-way valve (701) that unidirectionally flows from the first section (711) to the third section (713). The third section (713) is provided with a reservoir (702) and a dryer filter (703) connected in series. The reservoir (702) is located close to the first one-way valve (701) relative to the dryer filter (703). The first throttling element (710) is located in the fourth section (714). The third branch (73) is connected at the end away from the N port to the connection between the second segment (712) and the third segment (713), and the third branch (73) is provided with a second one-way valve (731) that allows one-way flow from the N port to the third segment (713).

4. The four-pipe unit according to claim 3, characterized in that, The four-control unit also includes a sixth branch (76) and a second throttling element (761). The second throttling element (761) is provided on the sixth branch (76), one end of the sixth branch (76) is connected to the connection between the third section (713) and the fourth section (714), and the other end is connected to the N port. The sixth branch (76) is provided with a third one-way valve (762) that allows one-way flow from the sixth branch (76) to the N port.

5. The four-pipe unit according to claim 4, characterized in that, The four-pipe unit also includes a seventh branch (77), one end of which is connected between the second throttling element (761) and the third one-way valve (762), and the other end is connected to the connection between the first section (711) and the second section (712). The seventh branch (77) is provided with a fourth one-way valve (771) that allows one-way flow from the second throttling element (761) to the first section (711).

6. The four-pipe unit according to any one of claims 3-5, characterized in that, The third section (713) is also provided with an economizer assembly (90), and the compressor (10) is also provided with an air inlet (13); The economizer assembly (90) includes a main liquid pipe (91), a secondary loop liquid pipe (92), and a connecting pipe (93). The inlet of the main liquid pipe (91) is connected to the dryer filter (703), and the outlet of the main liquid pipe (91) is connected to the first branch (71). The connecting pipe (93) is provided with a third throttling element (931). One end of the connecting pipe (93) is connected between the outlet of the main liquid pipe (91) and the first branch (71), and the other end is connected to the inlet of the secondary loop liquid pipe (92). The outlet of the secondary loop liquid pipe (92) is connected to the air supply port (13).

7. A control method, characterized in that, The control method is used to implement the operation control of the four-pipe unit as described in any one of claims 1-6, and the control method includes: When a command to switch to chilled water + hot water mode is received, the saturation temperature T of the compressor (10) is obtained. pe and the outlet water temperature T of the cold water heat exchanger (40) O And calculate the deviation value Δ=T O -T pe ; Adjust the on / off states of the first switching valve (741) and the second switching valve (751) to keep the deviation value Δ less than ΔT. e , where ΔT e This represents the target deviation value.

8. The control method according to claim 7, characterized in that, Adjust the on / off states of the first switching valve (741) and the second switching valve (751) to keep the deviation value Δ less than ΔT. e Specifically, it includes: When the deviation value Δ≥ΔT e Start timing and maintain the deviation value Δ≥ΔT e When the preset time t is reached, the first switching valve (741) and the second switching valve (751) are opened; When the deviation value Δ < ΔT e When -T, the first switching valve (741) and the second switching valve (751) are closed.

9. The control method according to claim 8, characterized in that, 8℃≤ΔT e ≤13℃,1℃≤T≤6℃,8s≤t≤300s。 10. The control method according to claim 7, characterized in that, Obtain the saturation temperature T of the compressor (10) pe include: Obtain the suction pressure P of the compressor (10) e According to the inhalation pressure P e Calculate the corresponding saturation temperature T pe .

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