Chilled water bypass device of central air conditioning system and control method

Abstract

The invention relates to the field of air conditioning, and discloses a chilled water bypass device of a central air conditioning system and a control method.The device comprises an air conditioner chilled water bypass pipe, a bypass water pump is arranged on the air conditioner chilled water bypass pipe and is a variable-frequency water pump, and an electric water valve is arranged at an outlet of the variable-frequency water pump; the bypass water pump is linked with the electric water valve, and when the bypass water pump is started, the bypass water pump is started after receiving a signal that the electric water valve is opened in place; when the bypass water pump is closed, the bypass water pump is closed firstly, and after a certain time is delayed, the electric water valve is closed; a flow sensor is arranged on the chilled water return main pipe, and the bypass water pump is started or stopped according to signals of the flow sensor, so that water flow flowing through the water chilling unit is not smaller than safety flow of the water chilling unit. And the power frequency flow of the bypass water pump is the same as the safety flow of the water chilling unit. The scheme that the bypass water pump replaces a differential pressure bypass valve is adopted, and the beneficial effects of being convenient to debug and easy to control are achieved.

Description

Technical Field

[0001] This invention relates to the field of air conditioning, specifically to a chilled water bypass device and control method for a centralized air conditioning system, applicable to air conditioning systems that use chilled water for cooling and dehumidification. Background Technology

[0002] In centralized air conditioning systems using chilled water cooling, reduced cooling demand on the user side leads to a decrease in the opening degree of the electric two-way valves at the terminals, resulting in a decrease in chilled water flow on the user side and an increase in water system network resistance. To prevent excessively low chilled water flow on the user side, where the flow rate through the chiller evaporator falls below the chiller's safe flow rate, triggering the chiller's shutdown protection, a chilled water bypass pipe is typically installed between the chiller's supply and return main pipes. This bypass pipe is equipped with a differential pressure bypass device that opens or closes based on pressure differences between the main chilled water supply and return pipes.

[0003] Differential pressure bypass devices typically come in two types: electrically operated differential pressure bypass valves and self-operated differential pressure bypass valves. The electrically operated differential pressure bypass valve consists of a differential pressure controller and an electrically operated regulating valve. Its working principle is that the differential pressure controller monitors the system's differential pressure. When the opening of the user-side electrically operated two-way valve decreases, and the differential pressure between the chilled water supply and return increases and exceeds the controller's set value, the controller will control the electrically operated differential pressure bypass valve to open wider. Some circulating chilled water will then flow through the bypass valve, increasing the chilled water flow rate through the chiller unit's evaporator. Conversely, when the user's cooling demand increases, the opening of the terminal electrically operated two-way valve increases, and the system's differential pressure falls below the set value; in this case, the controller will close the electrically operated valve.

[0004] The self-operated differential pressure bypass valve has a pressure-sensing diaphragm inside. This diaphragm senses the pressure difference between the chilled water supply and return mains through a pressure guide orifice. When the pressure difference exceeds a set value, the diaphragm drives the valve stem to open the valve plug, allowing some circulating chilled water to flow through the bypass valve to ensure the unit's flow rate is not less than the minimum safe flow rate. Conversely, if the user's cooling demand increases, the terminal electric two-way valve opens wider, and the system's pressure difference falls below the set value. The self-operated differential pressure bypass valve then automatically closes or shuts off.

[0005] In summary, the setting of the opening pressure of the differential pressure bypass device is an important factor affecting the system operation. In actual engineering, the process of determining the opening pressure of the differential pressure bypass device is complicated: (1) After the hydraulic balance of the pipeline network is completed, the differential pressure bypass valve is closed when the air conditioning system is running at full load; (2) When the system is under partial load, the terminal electric two-way valve gradually closes, and the chilled water pump runs at a reduced speed; (3) When the chilled water pump is reduced to the minimum set value, one of the chilled water pumps and the corresponding chiller unit is stopped, and so on, until only one chilled water pump and chiller unit are running; (4) When the chiller unit is running at the minimum flow rate, the differential pressure of the chilled water supply and return main pipe is tested at this time, and this value is the differential pressure set value. When the differential pressure of the chilled water supply and return main pipe exceeds the set value, the differential pressure bypass device opens, and the circulating chilled water flows into the chiller unit through the bypass pipe to meet the minimum flow rate requirement of the chiller unit. There are problems such as complicated commissioning process and difficulty in determining the opening pressure. Summary of the Invention

[0006] To address the problems of complex commissioning and difficulty in determining the opening pressure of chilled water differential pressure bypass devices in centralized air conditioning systems, this invention aims to provide a chilled water bypass device and control method for centralized air conditioning systems. The solution employs a bypass water pump instead of a differential pressure bypass valve, offering advantages such as convenient commissioning and simple control.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a chilled water bypass device for a centralized air conditioning system, comprising an air conditioning chilled water bypass pipe, a chilled water return main pipe and a chiller unit, wherein a bypass water pump is provided on the air conditioning chilled water bypass pipe, the bypass water pump is a variable frequency water pump and an electric water valve is provided at its outlet. The bypass water pump is linked to the electric water valve. When the bypass water pump starts, it starts only after receiving a signal that the electric water valve is fully open. When the bypass water pump stops, it stops first and then closes the electric water valve after a 30-second delay. A flow sensor is installed on the chilled water return main pipe. The bypass water pump starts or stops according to the flow sensor signal to ensure that the water flow through the chiller unit is not less than the safe flow of the chiller unit. The bypass water pump operates at a variable frequency, and its power frequency flow rate is the same as the safe flow rate of the chiller unit.

[0008] The present invention further includes an air conditioning chilled water circulation system, which includes a chiller unit, chilled water supply circulation pipes, air conditioning terminals, an electric two-way valve, chilled water return circulation pipes, and a chilled water pump. The equipment and pipes installed in the machine room are on the machine room side, and the rest are on the user side. All equipment is connected by pipes.

[0009] The present invention further includes a control cabinet, which is connected to the bypass water pump, the electric water valve, and the flow sensor via control cables.

[0010] A second aspect of the present invention provides a control method for a chilled water bypass device in a central air conditioning system, comprising the following steps: (1) When the user’s cooling demand decreases, the opening of the electric two-way valve decreases, the frequency of the chilled water pump and the output cooling capacity of the chiller unit decreases or shuts down until only one chilled water pump and chiller unit are running. This process is controlled by the air conditioning energy-saving control system. (2) The flow signal monitored by the flow sensor is transmitted to the control cabinet through the control cable. If the flow signal monitored by the flow sensor is less than or equal to the safe flow of the chiller, the control cabinet outputs a signal to open the electric water valve. After the electric water valve is opened and delayed for 30 seconds, the bypass water pump is started and runs at 35 Hz. (3) If the user’s cooling demand decreases further, the flow rate monitored by the flow sensor will decrease further, and the control cabinet will output a signal to increase the operating frequency of the bypass pump until the bypass pump operates at the power frequency. At this time, the flow rate of the bypass pump is the same as the safe flow rate of the chiller unit. (4) When the user’s cooling demand increases, the opening of the electric two-way valve increases. When the flow signal monitored by the flow sensor is greater than the safe flow of the chiller, the control cabinet outputs a signal to reduce the operating frequency of the bypass water pump. When the operating frequency of the bypass water pump is as low as 35Hz, the control cabinet outputs a signal to shut down the chilled water pump. After a delay of 30 seconds, the electric water valve is shut down.

[0011] Optionally, the safe flow rate of the chiller unit is the minimum allowable flow rate of the chiller unit.

[0012] Preferably, the criteria for determining a decrease in user-side cooling demand are that the chilled water return temperature is lower than a set value and the chilled water supply-return temperature difference is lower than a set value.

[0013] Preferably, the criterion for determining if the user's cooling demand is further reduced is that after steps (1) and (2), the chilled water return temperature is still lower than the set value, and the chilled water supply and return temperature difference is still lower than the set value.

[0014] Preferably, the frequency of the bypass pump is increased to +5 Hz / hour per cycle.

[0015] Preferably, the reduced bypass pump operating frequency is -5 Hz / hour per cycle.

[0016] Furthermore, the data from the flow sensor is collected every 15 minutes, and the hourly average is taken, with adjustments made once per hour.

[0017] Compared with differential pressure-based chilled water flow bypass technology, this invention has the following significant advantages: This invention eliminates the need for debugging. Traditional bypass devices based on differential pressure between chilled water supply and return water require gradual adjustments after the system's hydraulic balance has been established. This invention, however, uses a bypass system based on chilled water flow rate, allowing the bypass pump's opening flow rate to be set directly to the chiller's safe flow rate (the chiller's minimum permissible flow rate), eliminating the need for debugging.

[0018] This invention directly controls the bypass system and the water flow into the chiller unit based on the chilled water flow rate. Compared with the traditional indirect bypass device based on the pressure difference between the chilled water supply and return main pipes, it is more responsive, has higher control accuracy, and effectively avoids the chiller unit from shutting down due to insufficient chilled water flow. Attached Figure Description

[0019] Figure 1 A schematic diagram of a chilled water bypass device for a centralized air conditioning system; Figure 2 This is a schematic diagram of the control principle of the chilled water bypass device in a centralized air conditioning system.

[0020] Explanation of reference numerals in the attached figures: 1-Air conditioning chilled water bypass pipe; 2-Bypass water pump; 3-Chiller water return main pipe; 4-Flow sensor; 5-Electric water valve; 6-Chiller unit; 7-Chiller water supply circulation pipe; 8-Air conditioning terminal; 9-Electric two-way valve; 10-Chiller water return circulation pipe; 11-Chiller water pump; 12-Control Cabinet: 12.1-Circuit Breaker, 12.2-Motor Protector, 12.3-PLC, 12.4-Frequency Inverter, 12.5-Contactor, 12.6-Signal Acquisition Terminal. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 A chilled water bypass device for a centralized air conditioning system, see Figure 1 , Figure 2The system includes a bypass pump, an electric water valve, a flow sensor, a control cabinet, and control cables. The chilled water bypass pipe 1 is located on the machine room side and connects to the chilled water supply circulation pipe 7 (blue solid line) and the chilled water return main pipe 3 (green solid line). A bypass pump 2 is installed on the chilled water bypass pipe 1 (red solid line), and a flow sensor 4 is installed on the chilled water return main pipe 3 (green solid line). The flow sensor 4 is located between the chilled water bypass pipe 1 and the chilled water pump 11. The bypass pump 2 starts or stops based on the signal from the flow sensor 4, ensuring that the water flow through the chiller unit 6 is not less than the chiller unit's safe flow rate (the minimum allowable flow rate of the chiller unit). The bypass pump 2 is linked to the electric water valve 5 installed at its outlet. When the bypass pump 2 starts, it starts only after receiving a signal from the electric water valve 5 indicating that the valve is fully open. When the bypass pump 2 closes, it closes first and then, after a 30-second delay, closes the electric water valve 5. Bypass pump 2 is a variable frequency pump. When it is running, its power frequency flow rate is the same as the safe flow rate of chiller unit 6. When bypass pump 2 is started, it first runs at 35 Hz. Based on the data monitored by flow sensor 4 and the comparison with the safe flow rate value of chiller unit, the operating frequency of bypass pump 2 is increased or decreased.

[0023] See Figure 1 , Figure 2 The device also includes an air conditioning chilled water circulation system, which includes chiller units 6, chilled water supply circulation pipes 7 (blue solid line), air conditioning terminals 8, electric two-way valves 9, chilled water return circulation pipes 10 (green solid line), chilled water pumps 11, etc. The chiller units 6 are connected to each user-measured air conditioning terminal 8 via the chilled water supply circulation pipes 7 (blue solid line), and each air conditioning terminal 8 is connected to each chiller unit 6 on the machine room side via the chilled water return circulation pipes 10 (green solid line). Simultaneously, electric two-way valves 9 are installed near each air conditioning terminal 8 on the chilled water return circulation pipes 10, and chilled water pumps 11 are installed near each chiller unit 6 on the chilled water return circulation pipes 10 (green solid line). The equipment and pipes located in the machine room are on the machine room side, and the rest are on the user side. All equipment is connected via pipes. The air conditioning chilled water circulation system uses existing technology, which will not be described in detail here.

[0024] See Figure 2The device also includes a control cabinet 12, which is connected to the bypass water pump 2, the electric water valve 5, and the flow sensor 4 via control cables. Specifically, the control cabinet 12 includes components such as a circuit breaker 12.1, a motor protector 12.2, a frequency converter 12.4, a PLC 12.3, a contactor 12.5, and a signal acquisition terminal 12.6. The circuit breaker 12.1 is responsible for connecting / disconnecting the power supply circuit of the entire control cabinet 12; the motor protector 12.2 is a protection element specifically for the bypass water pump motor, which can issue a protection signal or directly cut off the power supply to the motor to prevent the motor from burning out; the frequency converter 12.4 adjusts the speed of the bypass water pump; the PLC 12.3 receives feedback signals from the flow sensor and other sources from the signal acquisition terminal 12.6, performs calculations and judgments according to the program logic, and outputs control commands to the actuators; the contactor 12.5 is an actuator switching element used to control the on / off state of the equipment's power supply circuit; the signal acquisition terminal 12.6 is an interface element for signal conversion and preprocessing, which normalizes the current, voltage, or switch signals output by the sensors and transmits them to the PLC 12.3.

[0025] The power supply link connection method for the control cabinet is as follows: External power supply → Circuit breaker 12.1 → Branch power supply to inverter 12.4, motor protector 12.2, PLC 12.3, contactor 12.5 coil → Inverter / contactor main circuit → Bypass water pump 2, electric water valve 5.

[0026] The control cabinet control link connection method is as follows: Detection end: Flow sensor 4 → Signal acquisition terminal 12.6 → PLC 12.3 (PLC receives flow feedback signal); Operational control terminal: PLC 12.3 outputs instructions to frequency converter 12.4 (to adjust water pump speed) and contactor 12.5 (to control the start and stop of water pump / water valve) according to the program logic. Protection terminal: The motor protector is connected in series in the water pump motor circuit. Its protection signal is fed back to PLC 12.3 and contactor 12.5. In case of abnormality, the power supply to the load is cut off. Circuit breaker 12.1 serves as the upper-level protection, covering the power supply circuit of the entire control cabinet and external equipment.

[0027] Example 2 A control method for a chilled water bypass device in a centralized air conditioning system, see [link / reference] Figure 1 , Figure 2 This includes the following steps: (1) When the user's cooling demand decreases (the chilled water return temperature is lower than the set value, and the chilled water supply and return temperature difference is lower than the set value), the opening of the electric two-way valve 9 decreases, the frequency of the chilled water pump 11 and the output cooling capacity of the chiller unit 6 decrease or shut down, until only one chilled water pump 11 and chiller unit 6 are running. This process is controlled by the air conditioning energy-saving control system (central air conditioning systems are equipped with energy-saving control systems, which can adjust and control the operating status of chilled water pumps, chiller units, air conditioning terminals, etc. according to the temperature and flow rate of chilled water and cooling water, indoor air temperature, etc., which will not be elaborated here). (2) The flow signal monitored by the flow sensor 4 is transmitted to the control cabinet 12 through the control cable. If the flow signal monitored by the flow sensor 4 is less than or equal to the safe flow of the chiller (the minimum flow allowed by the chiller), the control cabinet 12 outputs a signal to open the electric water valve 5. After the electric water valve 5 is opened and delayed for 30 seconds, the bypass water pump 2 is started and runs at 35 Hz. (3) If the user's cooling demand is further reduced (after steps (1) and (2), the chilled water return temperature is still lower than the set value, and the chilled water supply and return temperature difference is still lower than the set value), the flow rate monitored by the flow sensor 4 is further reduced, and the control cabinet 12 outputs a signal to increase the operating frequency of the bypass pump (single +5 HZ / hour, the data of the flow sensor is collected every 15 minutes, the hourly average value is taken, and it is adjusted once per hour), until the bypass pump 2 operates at the power frequency (50 Hz), at which time the flow rate of the bypass pump 2 is the same as the safe flow rate of the chiller unit 6; (4) When the user's cooling demand increases (the chilled water return temperature is higher than the set value, and the chilled water supply and return temperature difference is higher than the set value), the opening of the electric two-way valve 9 increases. When the flow signal monitored by the flow sensor 4 is greater than the safe flow of the chiller (the minimum flow allowed by the chiller), the control cabinet 12 outputs a signal to reduce the operating frequency of the bypass pump 2 (single time -5 HZ / hour, the data of the flow sensor is collected every 15 minutes, the hourly average value is taken, and it is adjusted once per hour). When the operating frequency of the bypass pump 2 is as low as 35 HZ, the control cabinet 12 outputs a signal to shut down the chilled water pump 11. After a delay of 30 seconds, the electric water valve 5 is shut down.

[0028] The above description is merely a specific embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any transformations or substitutions that can be conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A chilled water bypass device for a centralized air conditioning system, comprising an air conditioning chilled water bypass pipe, a chilled water return main pipe, and a chiller unit, characterized in that, A bypass water pump is installed on the air conditioning chilled water bypass pipe. The bypass water pump is a variable frequency water pump, and an electric water valve is installed at its outlet. The bypass water pump is linked to the electric water valve. When the bypass water pump starts, it starts only after receiving a signal that the electric water valve is fully open. When the bypass water pump stops, it stops first and then closes the electric water valve after a 30-second delay. A flow sensor is installed on the chilled water return main pipe. The bypass water pump starts or stops according to the flow sensor signal to ensure that the water flow through the chiller unit is not less than the safe flow of the chiller unit. The bypass water pump operates at a variable frequency, and its power frequency flow rate is the same as the safe flow rate of the chiller unit.

2. The chilled water bypass device for a centralized air conditioning system according to claim 1, characterized in that, It also includes an air conditioning chilled water circulation system, which includes a chiller unit, chilled water supply circulation pipes, air conditioning terminals, electric two-way valves, chilled water return circulation pipes, and chilled water pumps. The equipment and pipes installed in the machine room are on the machine room side, and the rest are on the user side. All equipment is connected by pipes.

3. The chilled water bypass device for a centralized air conditioning system according to claim 1, characterized in that, It also includes a control cabinet, which is connected to the bypass water pump, electric water valve, and flow sensor via control cables.

4. A control method for a chilled water bypass device in a centralized air conditioning system according to any one of claims 1-3, characterized in that, Includes the following steps: (1) When the user’s cooling demand decreases, the opening of the electric two-way valve decreases, the frequency of the chilled water pump and the output cooling capacity of the chiller unit decreases or shuts down until only one chilled water pump and chiller unit are running. This process is controlled by the air conditioning energy-saving control system. (2) The flow signal monitored by the flow sensor is transmitted to the control cabinet through the control cable. If the flow signal monitored by the flow sensor is less than or equal to the safe flow of the chiller, the control cabinet outputs a signal to open the electric water valve. After the electric water valve is opened and delayed for 30 seconds, the bypass water pump is started and runs at 35 Hz. (3) If the user’s cooling demand decreases further, the flow rate monitored by the flow sensor will decrease further, and the control cabinet will output a signal to increase the operating frequency of the bypass pump until the bypass pump operates at the power frequency. At this time, the flow rate of the bypass pump is the same as the safe flow rate of the chiller unit. (4) When the user’s cooling demand increases, the opening of the electric two-way valve increases. When the flow signal monitored by the flow sensor is greater than the safe flow of the chiller, the control cabinet outputs a signal to reduce the operating frequency of the bypass water pump. When the operating frequency of the bypass water pump is as low as 35 Hz, the control cabinet outputs a signal to shut down the chilled water pump. After a delay of 30 seconds, the electric water valve is shut down.

5. The control method for the chilled water bypass device of the centralized air conditioning system according to claim 4, characterized in that, The safe flow rate of the chiller unit is the minimum allowable flow rate of the chiller unit.

6. The control method for the chilled water bypass device of the centralized air conditioning system according to claim 4, characterized in that, The criteria for determining a decrease in user-side cooling demand are that the chilled water return temperature is lower than the set value and the chilled water supply-return temperature difference is lower than the set value.

7. The control method for the chilled water bypass device of the centralized air conditioning system according to claim 5, characterized in that, The criterion for determining if the user's cooling demand is further reduced is that after steps (1) and (2), the chilled water return temperature is still lower than the set value, and the chilled water supply and return temperature difference is still lower than the set value.

8. The control method for the chilled water bypass device of the centralized air conditioning system according to claim 4, characterized in that, The frequency of the bypass pump is increased to +5 Hz / hour.

9. The control method for the chilled water bypass device of the centralized air conditioning system according to claim 4, characterized in that, The frequency of the bypass pump is reduced to -5 Hz / hour per cycle.

10. The control method for the chilled water bypass device of the centralized air conditioning system according to claim 8 or 9, characterized in that, The data from the flow sensor is collected every 15 minutes, and the hourly average is taken. The data is adjusted once per hour.

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