Water multi-connected central air conditioning unit and water system control method thereof

Abstract

The invention discloses a water multi-connected central air conditioning unit and a water system control method thereof. The water multi-connected central air conditioning unit comprises a main machine and a tail end device which are communicated through a water system, the water system comprises a water supply pipe, a water return pipe and a plurality of branch pipes which are arranged between the water supply pipe and the water return pipe in parallel and communicated with the tail end device, a water pump is arranged on the water supply pipe, and a main path three-way valve is arranged on the water supply pipe. One port of the branch pipe is communicated with the water return pipe through a bypass, a tail end three-way valve is arranged on the water inlet side of each branch pipe, and one port of the branch pipe is communicated with the water return pipe through a bypass. Rapid cooling / heating of the system is achieved through control over the three-way valve and a bypass of the three-way valve, adjustment is rapidly responded, and the comfort level of a user is improved.

Description

Technical Field

[0001] This invention relates to the field of air conditioning technology, and in particular to a water-cooled multi-split central air conditioning unit and its water system control method. Background Technology

[0002] In recent years, people's requirements for home air conditioning have shifted from the traditional refrigerant-based multi-split central air conditioning systems to the quieter and more comfortable water-based central air conditioning systems. Water-based central air conditioning systems not only meet the cooling requirements in summer but also the heating needs of large-area underfloor heating in winter, making them an increasingly popular choice for mid-to-high-end users. Currently, water-based central air conditioning units typically use either single-pump or double-pump water circulation. In a single-pump system, a pump is installed on the main water supply pipeline, and the flow is controlled by a shut-off valve at the terminal. The advantage of the traditional single-pump system is that the system output water is directly supplied to the terminals, and the return water enters a buffer tank, making the system simple and easier to control. However, the system requires the installation of bypass and differential pressure bypass valves at appropriate locations on the supply and return ends to ensure normal water circulation even when all terminals are closed. Simultaneously, the water system constantly passes through the heat exchanger of the main unit during operation, resulting in continuous head loss and increasing system energy consumption. Secondary pump water systems are a relatively new water system control method that has emerged in recent years. This system has pumps not only on the main water supply pipeline but also on the terminal water supply pipeline. The advantage of this method is that the main equipment is easier to control. The main pump drives the intermediate water tank for cooling and heating, and the terminal side draws water from the intermediate water tank and circulates it through a secondary circulation pump. The disadvantage is that the system is relatively complex and the equipment response speed is relatively slow. At the same time, the current fan coil unit terminals are all two-way on / off switches. Once the terminal is closed or the temperature point is reached, the water flow in the entire water circuit stops, and the temperature rebound may cause repeated fluctuations in the system water temperature, which will further reduce the control accuracy.

[0003] Therefore, how to reduce the energy consumption of air conditioning units, improve the response speed, and more accurately control the indoor temperature so that water-circulating central air conditioning can be widely used is a technical problem that the industry urgently needs to solve. Summary of the Invention

[0004] This invention proposes a water-based multi-split central air conditioning unit and its control method to solve the problems of high energy consumption, slow response speed, and large indoor temperature fluctuations in existing water-based multi-split central air conditioning systems.

[0005] The water-cooled multi-split central air conditioning unit provided by the present invention includes a main unit and terminal devices connected by a water system. The water system includes a water supply pipe, a return pipe, and multiple branch pipes connected in parallel between the water supply pipe and the return pipe and connecting the terminal devices. A water pump is provided on the water supply pipe. A main three-way valve is provided on the water supply pipe, one of its interfaces being connected to the return pipe through a bypass. Terminal three-way valves are provided on the water inlet side of each branch pipe, one of its interfaces being connected to the return pipe through a bypass.

[0006] Preferably, the return water pipe is equipped with a buffer water tank.

[0007] Preferably, the terminal device is a fan coil unit and / or a floor heating coil unit.

[0008] Preferably, both the main three-way valve and the end three-way valve are three-way proportional valves.

[0009] Preferably, the water pump is a variable frequency water pump.

[0010] This invention also proposes a control method for the water system of the above-mentioned multi-split central air conditioning unit. In the control method, when the main unit receives the start command, the main three-way valve is fully opened, the water pump runs at the rated pressure difference of the operating mode for a period of time t, and then the central air conditioning unit is started and the output capacity is controlled according to the indoor load and the set temperature. When the water supply temperature is close to the set temperature, the flow rate into the fan coil / heating coil is adjusted through the terminal three-way valve.

[0011] Furthermore, when the unit is cooling, the control pressure difference P of the water pump is calculated according to the formula...

[0012] The pressure difference P is calculated using the formula P = A - (A - C) * k(1-γ). When the unit is providing heating, the pressure difference P of the water pump is calculated using the formula P = B - (BC) * k(1-γ).

[0013] Where: A is the rated differential pressure for cooling, B is the rated differential pressure for heating, C is the differential pressure of the water pump, γ is the opening degree of the main three-way valve, and k is the safety threshold.

[0014] Furthermore, the adjustment of the terminal three-way valve is based on the difference Δt between the room temperature and the outlet air temperature of the terminal device. When the difference Δt is greater than or equal to the second set temperature difference Δt2, the opening of the terminal three-way valve is increased; otherwise, it is further determined whether the difference Δt is greater than the first set temperature difference Δt1. If it is, the opening of the terminal three-way valve is reduced; otherwise, the current opening is maintained.

[0015] Furthermore, when the difference Δt is less than the first set temperature difference Δt1, the reduced opening degree β of the end three-way proportional valve is controlled according to the formula β=β+10*Δt1.

[0016] Furthermore, when the water supply temperature approaches the set temperature, the opening degree γ and minimum opening degree γ of the main three-way valve are calculated based on the real-time detected opening degrees of each end three-way valve. min And when the opening degree γ of the main three-way valve is less than or equal to the minimum opening degree γ min When the main three-way valve is open at its minimum opening, it operates at its minimum opening. min At that time, it operates according to the calculated opening degree.

[0017] Furthermore, the minimum opening degree of the main three-way valve is determined by the formula: γmin =[1-(∑β 1-n The opening degree γ of the main three-way valve is calculated according to the formula γ=γ-n[m-|To-Ti|], where n is the adjustment coefficient, m is the target temperature difference value, To is the main unit outlet water temperature, and Ti is the main unit inlet water temperature.

[0018] The control method proposed in this invention also includes the control system monitoring the operating status of the central air conditioning unit in real time. When defrosting or oil return operation mode occurs, the main three-way valve is opened to 100% in advance.

[0019] Furthermore, when the indoor temperature is close to the target temperature, all indoor three-way valves are closed to below 50°C, and the buffer water tank temperature is less than / greater than the set temperature, the main unit enters standby mode in advance.

[0020] The control method also includes initializing the water system before startup: opening both the main three-way valve and the end three-way valve to make the water pump run at a constant pressure difference and record the water flow; gradually reducing the opening of the main three-way valve and the end three-way valve, and then gradually increasing the opening of the main three-way valve and the end three-way valve, and judging whether the main three-way valve and the end three-way valve are abnormal by observing the change in water flow.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. Reduce the number of water system testing components and engineering installation components to simplify installation and commissioning costs and lower barriers to entry, ensuring that risk control does not leak out of the factory.

[0023] 2. By controlling the three-way valve and its bypass, the system can quickly provide cooling / heating and adjust rapidly, thereby improving user comfort.

[0024] 3. This allows primary pump systems to be more readily adopted in engineering practice at a lower cost. Attached Figure Description

[0025] Figure 1 This is a system diagram of an embodiment of the water-cooled multi-split central air conditioning unit proposed in this invention;

[0026] Figure 2 Flowchart of self-inspection process for water-cooled multi-split central air conditioning units before startup;

[0027] Figure 3 This is a flowchart of the water system initialization control of the present invention;

[0028] Figure 4 This is the water system operation control diagram of the present invention;

[0029] Figure 5 This is a flowchart of the main three-way valve adjustment process in this invention.

[0030] In the picture:

[0031] 1. Main unit, 2. Terminal device, 3. Water supply pipe, 4. Water return pipe, 5. Branch pipe, 6. Water pump, 7. Main three-way valve, 8. Terminal three-way valve, 9. Buffer water tank, 10. First shut-off valve, 12. Second shut-off valve. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the following specific embodiments are only used to explain the invention and do not constitute a limitation thereof.

[0033] The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention. Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of components and steps set forth in these embodiments do not limit the scope of protection of the invention.

[0034] While techniques, methods, and apparatus known to those skilled in the art are not discussed in detail herein, such techniques, methods, and apparatus should be considered part of this specification where appropriate. Any specific values ​​in this specification should be interpreted as merely exemplary and not as limiting the invention.

[0035] For ease of description, the terms used in this specification to describe position, such as "above," "to the left," and "in front," are only used to describe the spatial relationship between a component and other components in the embodiments shown in the figures. The relative position will change when the component is placed in different locations; therefore, the positional relationships in the embodiments shown in the figures should not be construed as limiting the present invention. Furthermore, it should be noted that the use of terms such as "first" and "second" in this specification is merely for distinguishing similar components and does not imply a sequential order; therefore, it should not be construed as limiting the scope of protection of this invention.

[0036] like Figure 1 As shown, the water-based multi-split central air conditioning system proposed in this invention includes a main unit 1 and multiple terminal devices 2, which are connected via a water system. The water system includes a supply pipe 3, a return pipe 4, and a water pump 6. Multiple branch pipes 5 are connected in parallel between the supply and return pipes, and the terminal devices are installed on these branch pipes. A main three-way valve 7 is also provided at the front end of the water pump 6 on the supply pipe. One port of the main three-way valve is connected to the return pipe 4 via a bypass. Terminal three-way valves 8 are respectively provided on the water inlet side of each branch pipe 5, one port of which is connected to the return pipe 4 via a bypass. To ensure system stability, a buffer water tank 9 is provided on the return pipe.

[0037] In this embodiment, two water systems are included: one for cooling and one for heating. The terminal device 2 includes a fan coil unit and a floor heating coil. The main water supply pipe splits into two branches after the water pump 6: one for cooling and the other for heating. Both supply pipes are equipped with water shut-off valves to control the water flow direction during cooling or heating. The return water pipes for cooling and heating converge into the main return water pipe and then return to the main unit 1 for heat exchange via the buffer tank 9. Afterward, the water is circulated through the main three-way valve 7 and the water pump 6.

[0038] In this embodiment, both the main three-way valve 7 and the terminal three-way valve 8 are three-way proportional valves. The water pump 6 is a variable frequency water pump.

[0039] During cooling, the water system, driven by pump 6, allows water to pass through the main unit 1 of the air conditioning equipment (including compressor, controller, heat exchanger, reversing valve, throttling device, etc., which can be considered as equipment providing heating and cooling loads). After heat exchange, the water flows to the terminal device 2 via the terminal three-way valve 8 under the guidance of the first shut-off valve 10 (while the second shut-off valve 11 is closed). In this embodiment, the terminal device uses a fan coil unit. The water in the fan coil unit exchanges heat with the air in the user's room, providing cool air to the room. Similarly, during heating, under the action of the second shut-off valve 11 (while the first shut-off valve 10 is closed), the system outlet water switches to the heating side water system. Hot water flows to the terminal device 2 via the terminal three-way valve 8. In this embodiment, underfloor heating coils (buried under the user's floor, usually exchanging heat with the upper medium) are used. Afterward, the heating water medium merges in the return pipe, flows through the buffer tank 9 to the main unit 1 for heat exchange, and then returns to the inlet of pump 6 via the main three-way valve 7 to continue circulating. This invention utilizes a main three-way valve and its bypass to improve the distribution of hot and cold water in the system by utilizing stagnant water, and stores energy through a small buffer water tank 9 to ensure the total amount of water in the system and reduce the number of times the main unit starts and stops. It is estimated that the buffer water tank in this invention, which uses a terminal three-way valve and its bypass, can reduce the water tank capacity by half compared to the traditional system.

[0040] The advantage of replacing the two-way shut-off valve with a main-line three-way valve on the water supply pipe is that it can reduce the circulating water pressure difference of the water pump and reduce operating energy consumption when the unit is on standby under partial load conditions. When the main unit is running, the water temperature of the system will continue to decrease. When it runs to the lowest frequency, it can enter standby mode. At this time, the terminal water system still needs to continue to run. Therefore, the resistance bypass can be achieved by switching the main-line three-way valve to reduce operating energy consumption.

[0041] This invention enables continuous circulation of cold / hot water at the terminal by using a three-way valve, avoiding large fluctuations in the overall system temperature during terminal startup caused by the accumulation of room-temperature water in the water system. Simultaneously, the flow rate at the terminal can be controlled by adjusting the three-way valve, and relatively precise temperature and humidity control can be achieved indoors by adjusting the valve's opening degree.

[0042] In this embodiment, the three-way valve is a three-way proportional valve, and the opening degree can be controlled by pulse voltage. The opening degree of the three-way valve is adjusted by controlling the pulse voltage. Generally, the pulse voltage duration for the three-way valve opening from 0-100% is 3 seconds. The proportional adjustment of the three-way valve is achieved by controlling the voltage duration. This part is a common technical means and will not be described in detail in this case.

[0043] The central air conditioning unit proposed in this invention requires initialization and water circuit self-checking before operation. Please refer to [link / reference]. Figure 2 When the central air conditioning unit is powered on, it automatically executes the initialization process. First, the central air conditioning unit performs self-checks on its own components, system temperature and pressure values, and electrical components. If a fault is detected, it reports the fault code and name and continues to the next test. If the system detects no abnormalities, it proceeds to the next initialization self-check normally. The unit's air conditioning unit actively communicates with the indoor units of the central air conditioning system, identifies the model of the indoor unit's terminal device and the transmitted temperature and humidity values, and judges whether there are any abnormalities. If there are, it reports the fault code and name; otherwise, it continues to the next test. If the system detects no abnormalities, it proceeds to the next initialization self-check normally. The last step is to start the water pump. The water flow rate is used to determine whether the three-way valve is abnormal, and the water pump's operating flow rate q (the flow rate when the water pump is at its rated power output) is monitored in real time. At this time, the terminal three-way valve and terminal device of the corresponding mode (cooling / heating) are open for water inlet, and the water outlet pipe and water pump are connected. The air conditioning unit judges whether the water flow switch is normal. If the water flow switch is open, there may be a water shortage, and a corresponding prompt will be displayed.

[0044] If no abnormalities are found, the water pump operates under constant pressure difference A / B control and records the water flow rate q1. The opening of the water circuit three-way valve is adjusted from 100% to 0%, and the main unit's water flow switch is checked for disconnection. The water flow rate q is analyzed for any changes. Afterward, the unit adjusts the water pump flow rate to q1, resets the water pump pressure difference C, and restores the water pump control pressure difference to A / B before adjusting it from 0% to 100% (during this initialization process, the main circuit three-way valve is positioned at two opening values, a and b, corresponding to the states when the water flow switch is disconnected and when it is restored, respectively. An abnormality is indicated when the difference between a and b is greater than α). The water pump operates under constant pressure difference A / B, while simultaneously detecting the system water flow rate. Then, the system's terminal three-way valves are closed one by one to analyze whether the terminal three-way valves and flow rates are normal. The air conditioning unit's water flow switch is observed to be normal. If the water flow rate is greater than the minimum allowable value X, the system parameters are normal, the unit completes initialization, and enters standby mode. Otherwise, a fault code and name are reported, and the user is notified to confirm whether to retry / report for repair.

[0045] In the above, A represents the rated differential pressure for cooling, B represents the rated differential pressure for heating, C represents the differential pressure of the water pump, X represents the minimum allowable flow rate, and α represents the control deviation of the three-way valve. The value range of the above parameters varies depending on the project and the main unit and terminal used. In this embodiment, A is 60 kPa, B is 55 kPa, C is 20 kPa, X is 1.5 m³ / h (taking a 16 kW air conditioning main unit as an example), and α is 10%.

[0046] Figure 3 This is the water system initialization control flowchart, including:

[0047] Step 10. When the water system initialization command is received, open the shut-off valve of the corresponding function mode, start the water pump, and fully open the main three-way valve and the end three-way valve. Operate according to the corresponding mode with constant pressure difference and record the water flow rate q1 120 seconds after it stabilizes.

[0048] Step 11. Gradually close the opening of the main three-way valve of the water system from 100% to 0, and switch the flow path from the bypass of the main three-way valve to the buffer tank. The adjustment accuracy is 0.5% / s, and the adjustment is completed in 200s.

[0049] Step 12. Determine if the difference between the real-time flow rate q and q1 is increasing. If not, report a fault. If yes, further determine if the main three-way valve is completely closed. If not, return to step 11. If yes, proceed to step 13.

[0050] Step 13. Reduce the water pump output and control the flow rate back to q1, and after stabilizing for 60 seconds, record the water pump operating pressure difference C at this time;

[0051] Step 14. Gradually open the main three-way valve from 0 to 100%, and switch the water from the buffer tank back to the main flow path. Adjust the accuracy at 0.5% per second, and complete the adjustment in 200 seconds.

[0052] Step 15. Determine if the difference between the real-time flow rate q and q1 is decreasing. If not, report a fault. If yes, further determine if the main three-way valve is fully open. If not, return to step 14; if yes, proceed to step 16.

[0053] Step 16. After running stably for 60 seconds, close the end three-way valves one by one to 50% and 0% respectively;

[0054] Step 17. After each adjustment, determine whether the difference between the real-time flow rate q and q1 is decreasing. If not, record the current fault and the terminal code (if recorded twice consecutively, it is determined to be abnormal). After completing all terminal tests, report the fault terminal code and prompt whether to retry. If yes, determine whether all terminal three-way valve verifications have been completed. If not, go to step 16. If yes, go to step 18.

[0055] Step 19. Determine whether the main unit's water flow switch is closed and whether the water flow detection value q is greater than the preset value X. If not, report a fault; if yes, the water system initialization process is completed, and the water pump and each three-way valve enter the initialization standby state. At this time, the end three-way valve is fully closed, and the water pump does not start / intermittently starts and stops.

[0056] The following section focuses on explaining the normal operation control of the waterway. For example... Figure 4 As shown, the waterway control process is as follows:

[0057] Step 21. When the unit receives the start command, it calculates the compressor operating frequency based on the room temperature and set value, the water tank temperature and set value, and then opens the main circuit and the terminal three-way valve. After that, the water pump runs under the corresponding mode pressure difference for 3 minutes.

[0058] Step 22. The unit's fan and compressor start, the throttling device adjusts automatically, and the main three-way valve of the water system remains 100% open to ensure rapid cooling / heating of the water system. When the water system temperature reaches the preset cold / hot air setpoint, the terminal three-way valve opens, and the unit handles the cooling and heating loads;

[0059] Step 23. The terminal unit refines the temperature adjustment based on room temperature and air outlet / surface temperature. When the user's target temperature approaches the set value, it adjusts the temperature via the terminal three-way valve connected to the indoor fan coil unit / underfloor heating coil. When the control temperature difference Δt of a single terminal unit is greater than or equal to the second set temperature difference Δt2, the terminal three-way valve opens H / 2 and is rounded up, and is checked again after 5 minutes. When the control temperature difference Δt of a single terminal unit is less than the second set temperature difference Δt2, it is further checked whether the control temperature difference Δt of a single terminal unit is greater than the first set temperature difference Δt1. If not, the terminal three-way valve maintains its current opening, and is checked again after 5 minutes. If so, the terminal three-way valve closes H prematurely, and is checked again after 5 minutes.

[0060] The opening degree of the terminal three-way valve can be calculated using the formula: β = β + 10 * Δt1. Typically, Δt1 is between -0.3℃ and -1℃. In cooling mode, Δt1 = actual - target; in heating mode, Δt1 = target - actual. In this embodiment, -0.5℃ is used.

[0061] Continuously monitor the outlet air temperature of the fan coil unit. When the outlet air temperature is close to the target temperature, the difference Δt is less than the first set temperature difference Δt1. If the temperature difference between the outlet air temperature and the room temperature is greater than the second set temperature difference...

[0062] At Δt2, the opening degree β of the end three-way valve is reduced by H in advance, and the detection continues after a 5-minute interval. Comfort control can be achieved in this way. Δt2 is typically set to 1-4℃, and 2℃ is used in this embodiment. Δt2 is usually set to 2-5℃, and 4℃ is used in this application. The H value is typically 5-50%, and 25% is used in this embodiment.

[0063] In step 22, the water pump operation control pressure difference P is calculated according to the formula P=A-(AC)*k(1-γ) when cooling and according to the formula P=B-(BC)*k(1-γ) when heating.

[0064] In step 23, the unit monitors the opening degree of each terminal three-way valve in real time and calculates the opening degree γ of the main three-way valve. The main three-way valve is then adjusted according to the calculated value.

[0065] In this invention, the control of the main three-way valve in the water system needs to be linked with the control of the terminal three-way valve and simultaneously identify the compressor output. The lower limit of the main three-way valve opening must meet the following requirement: γ min ≥[1-(∑β 1-n / n)]*100 and γ min ≥F / F max *100, where F is the compressor operating frequency, F max This is the compressor's maximum operating frequency.

[0066] like Figure 5 As shown, the control method for the opening γ of the main three-way valve can be as follows:

[0067] Calculate the minimum opening γ of the main three-way valve. min Calculate the opening degree γ of the main three-way valve;

[0068] γ=γ-n[m-|To-Ti|], where n is the adjustment coefficient, which is 1.1 in this embodiment, m is the target temperature difference value, which is 5 in this embodiment, To is the main unit outlet water temperature, and Ti is the main unit inlet water temperature;

[0069] Determine whether the opening degree γ of the main three-way valve is less than or equal to the minimum opening degree γ. min If so, the main three-way valve will operate at its minimum opening degree γ. min Adjust and control the valve, then make a judgment after a 5-minute interval; otherwise, adjust the main three-way valve according to the calculated value, then make a judgment after a 5-minute interval.

[0070] It is important to note that the system's operating status needs to be monitored in real time during operation. When special operating modes such as defrosting or oil return occur during system operation, the main three-way valve should be opened to 100% in advance to ensure maximum system circulation flow and avoid the risk of high and low pressure protection caused by low flow.

[0071] During system operation, it is also necessary to monitor the operation of the indoor unit terminal devices in real time. When the indoor temperature is close to the target temperature value and the three-way valves of each indoor terminal are closed to less than 50%, it indicates that the system water supply temperature meets the user's load requirements. At this time, the main unit of the equipment can enter the standby state in advance (provided that the temperature of the equipment buffer water tank is less than / greater than the predetermined set temperature by 10 / 38℃).

[0072] When the lower limit γ of the main three-way valve opening min When the value is 0, the main three-way valve must be switched after a 1-minute delay after the compressor stops. Before the compressor starts, the opening degree γ of the main three-way valve must be switched to full open 1 minute in advance. At the same time, during the proportional adjustment of the main three-way valve, the water pump control pressure difference can be adjusted downward proportionally. The specific pressure difference control method can be (taking refrigeration as an example): P=AC*k(1-γ), where k is the safety threshold and can be taken as 0.95 to avoid the pressure difference being too low.

[0073] The present invention provides a linkage control scheme for the water multi-split central air conditioning unit and the main unit, the water multi-split fan coil indoor unit, the underfloor heating coil, and the water supply proportional tee. This scheme precisely controls and solves the problem of high-risk failures that may occur in the engineering use of the primary frequency conversion pump system, such as the omission of simplified bypass equipment in the engineering process or the forgetting of recovery protection components during the special handling process.

[0074] This invention solves the problem that some installation projects in engineering use small-diameter main flow path differential pressure bypass valves, which leads to excessive pressure loss in the water system, resulting in insufficient system flow. This causes uneven distribution (bypass setting to a minimum value) or system shutdown due to excessive system resistance after the end is fully closed, seriously affecting the user experience.

[0075] The above description is merely a specific embodiment of the present invention. It should be noted that any modifications, equivalent substitutions, and variations made within the spirit and framework of the present invention should be included within the protection scope of the present invention.

Claims

1. A water-cooled multi-split central air conditioning unit, comprising a main unit and terminal devices connected via a water system, wherein the water system includes a water supply pipe, a return pipe, and multiple branch pipes connected in parallel between the water supply pipe and the return pipe and connecting the terminal devices, and a water pump is provided on the water supply pipe, characterized in that, The water supply pipe is equipped with a main three-way valve, one of which is connected to the return water pipe via a bypass. The branch pipe is equipped with an end three-way valve on the water inlet side, one of which is connected to the return water pipe via a bypass.

2. The water-cooled multi-split central air conditioning unit according to claim 1, characterized in that, A buffer water tank is installed on the return water pipe.

3. The water-cooled multi-split central air conditioning unit according to claim 1, characterized in that, The terminal device uses fan coil units and / or underfloor heating coil units.

4. The water-cooled multi-split central air conditioning unit according to claim 1, characterized in that, Both the main three-way valve and the terminal three-way valve are three-way proportional valves.

5. The water-cooled multi-split central air conditioning unit according to claim 1, characterized in that, The water pump is a variable frequency water pump.

6. The control method for the water system of a multi-split central air conditioning unit according to any one of claims 1-5, characterized in that, When the main unit receives the start command, the main three-way valve and the terminal three-way valve are fully opened. The water pump runs according to the pressure difference in the operating mode for a period of time t, and then the central air conditioning unit starts and controls the output capacity according to the indoor load and set temperature. When the water supply temperature is close to the set temperature, the flow rate into the fan coil / heating coil is adjusted through the terminal three-way valve.

7. The control method according to claim 6, characterized in that, When the unit is cooling, the control pressure difference P of the water pump is calculated according to the formula P=A - (A - C)*k(1-γ); when the unit is heating, the pressure difference P of the water pump is calculated according to the formula P=B-(B - C)*k(1-γ). Where: A is the rated differential pressure for cooling, B is the rated differential pressure for heating, C is the differential pressure of the water pump, γ is the opening degree of the main three-way valve, and k is the safety threshold.

8. The control method according to claim 6, characterized in that, The adjustment of the terminal three-way valve is based on the difference Δt between the room temperature and the outlet air temperature of the terminal device. When the difference Δt is greater than or equal to the second set temperature difference Δt2, the opening of the terminal three-way valve is increased; otherwise, it is further determined whether the difference Δt is greater than the first set temperature difference Δt1. If it is, the opening of the terminal three-way valve is reduced; otherwise, the current opening is maintained.

9. The control method according to claim 8, characterized in that, When the difference Δt is less than the first set temperature difference Δt1, the opening degree β of the end three-way proportional valve is reduced according to the formula β=β+10*Δt1.

10. The control method according to claim 6, characterized in that, When the water supply temperature approaches the set temperature, the opening degree γ and minimum opening degree γ of the main three-way valve are calculated based on the real-time detected opening degree of each terminal three-way valve. min And when the opening degree γ of the main three-way valve is less than or equal to the minimum opening degree γ min When the main three-way valve is open at its minimum opening, it operates at its minimum opening. min At that time, it operates according to the calculated opening degree.

11. The control method according to claim 10, characterized in that, The minimum opening degree of the main three-way valve is defined by the formula: γ min =[1-(∑β 1-n The opening degree γ of the main three-way valve is calculated according to the formula γ=γ-n[m-|To-Ti|], where n is the adjustment coefficient, m is the target temperature difference value, To is the main unit outlet water temperature, and Ti is the main unit inlet water temperature.

12. The control method according to claim 6, characterized in that, It also includes the control system monitoring the operating status of the central air conditioning unit in real time. When defrosting or oil return operation mode occurs, the main three-way valve is opened to 100% in advance.

13. The control method according to claim 6, characterized in that, When the indoor temperature is close to the target temperature, all indoor three-way valves are closed to below 50%, and the buffer water tank temperature is less than or greater than the set temperature, the main unit enters standby mode in advance.

14. The control method according to claim 6, characterized in that, The control method also includes initializing the water system before startup: opening both the main three-way valve and the end three-way valve to make the water pump run at a constant pressure difference and record the water flow; gradually reducing the opening of the main three-way valve and the end three-way valve, and then gradually increasing the opening of the main three-way valve and the end three-way valve, and judging whether the main three-way valve and the end three-way valve are abnormal by observing the change in water flow.

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