Cooling tower group energy-saving control method based on actual heat dissipation capacity of cooling tower

Abstract

The application discloses a cooling tower group energy-saving control method based on actual heat dissipation capacity of cooling towers, wherein the energy-saving control device comprises a frequency converter, a flowmeter, a regulating valve, a water temperature sensor, a wet bulb temperature sensor and a control unit. The energy-saving control method comprises the following steps: firstly, distributing the cooling water evenly; then, comparing the water outlet branch pipe temperature of each cooling tower with the total water outlet pipe temperature, and actively adjusting the water quantity of each tower until the water outlet branch pipe temperature of all the towers is equal to (the total water outlet pipe temperature-pipeline temperature rise±insensitive temperature), so that the water quantity of the cooling towers is distributed according to the heat dissipation capacity; and then, according to the feedback of the total water outlet pipe temperature of the cooling tower, the frequency of all the fans is synchronously adjusted until the total water outlet pipe temperature of the cooling tower is equal to (the wet bulb temperature+wet bulb approximation degree set value±insensitive temperature). Finally, the water outlet temperature of each tower is close to uniform, all the fans run at the same frequency, and the total water outlet temperature reaches the high-efficiency energy-saving operation of the best wet bulb temperature approximation degree.

Description

Technical Field

[0001] This invention belongs to the field of cooling tower technology, and in particular relates to an energy-saving control method for cooling tower groups based on the actual heat dissipation capacity of cooling towers. Background Technology

[0002] For central air conditioning, refrigeration units, water-cooled air compressor units, and other devices that use open cooling towers, when there are many inlet branch pipes in the cooling tower, uneven water distribution often occurs, resulting in some towers having excessive flow and others having insufficient flow, thus failing to utilize the full cooling capacity of the cooling tower.

[0003] Currently, there are hydraulic pressure stabilizers on the market for uniform water distribution. They utilize the U-tube principle to ensure uniform water distribution across multiple inlet branches, greatly improving cooling tower efficiency. However, the arrangement of cooling towers, wind direction, external obstructions, and air mixing within the towers result in varying actual cooling capacities for each tower during operation. This only addresses the issue of uniform water distribution and does not maximize the cooling tower's capacity, leading to a still relatively low efficiency for the cooling tower group. The cooling water temperature cannot reach the optimal wet-bulb temperature, thus failing to achieve maximum energy savings for the system.

[0004] Traditional energy-saving control methods achieve an even distribution of cooling tower water volume. However, the actual electric-to-air ratio and heat dissipation capacity of cooling towers cannot be uniform due to the influence of their layout, obstruction, surrounding heat sources, and seasonal wind direction. For example, if a group of towers located in the middle with insufficient spacing is severely obstructed and has insufficient airflow, the water volume of this group of towers will be the same as that of the group of towers on the outside with sufficient airflow. Adjusting the frequency according to the water temperature will inevitably lead to the frequency of the obstructed tower group being higher than that of other towers, and even reaching the power frequency will not be able to control the water temperature. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a highly efficient energy-saving control method for cooling tower groups based on the actual heat dissipation capacity of the cooling towers, thereby improving the energy-saving effect of the cooling tower groups.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: an energy-saving control method for a cooling tower group based on the actual heat dissipation capacity of the cooling towers, wherein the energy-saving control device includes a frequency converter, a flow meter, a regulating valve, a water temperature sensor, a wet-bulb temperature sensor, and a control unit; the frequency converter is installed in the cooling tower distribution cabinet to control the frequency of the cooling tower fans and provide feedback on the fan operating status; the flow meter is installed on the main outlet pipe of the cooling tower group and the inlet and outlet branch pipes of the cooling towers to provide feedback on the total flow rate of the system and the inlet and outlet water volume of each cooling tower; the regulating valve is installed before the flow meter on the inlet and outlet branch pipes of the cooling towers to control the flow rate; the water pipe temperature sensor is installed on the outlet branch pipe and the main outlet pipe of the cooling towers to provide feedback on the outlet water temperature of each tower and the total outlet water temperature of the cooling tower group; the control unit includes a human-machine interface and a data communication module to receive water temperature sensor data, wet-bulb temperature sensor data, operating data of each cooling tower fan, data from each flow meter, and to provide feedback and adjust the opening degree of each regulating valve and the frequency converter frequency.

[0007] Energy-saving control methods include the following steps:

[0008] S1. Cooling tower water volume equal distribution adjustment:

[0009] Upon receiving the signal to start the water pump, all cooling tower fans are turned on and run at full frequency. All cooling tower regulating valves are opened to 100%. Based on the flow rate of the main inlet pipe of the cooling tower group and the number of cooling towers, the average flow rate allocated to each cooling tower is calculated and set as the average flow rate value. The regulating valves of the cooling tower inlet pipes are adjusted according to the flow rate value fed back by the flow meter of the cooling tower inlet branch pipe until the inlet flow rate value of each cooling tower = the average flow rate value ± the insensitivity deviation.

[0010] S2. Cooling tower inlet and outlet water flow balance adjustment:

[0011] Adjust the regulating valve of the outlet branch pipe according to the feedback value of the flow meter of the inlet and outlet branch pipes of the cooling tower until the inlet and outlet water flow of the cooling tower are balanced.

[0012] S3, Cooling tower outlet water temperature equalization adjustment:

[0013] After S1 and S2 adjustments are completed, the controller reads the data of the outlet branch pipe temperature and the outlet main pipe temperature of each cooling tower, keeps the fan frequency constant, adjusts the cooling tower inlet regulating valve (opening degree decreases) for cooling towers with [outlet branch pipe temperature > (outlet main pipe - pipe temperature rise ± insensitive temperature)] to reduce the water inflow; adjusts the cooling tower inlet regulating valve (opening degree increases) for cooling towers with [outlet branch pipe temperature < (outlet main pipe - pipe temperature rise ± insensitive temperature)] to increase the water inflow; until the outlet branch pipe temperature of all towers equals (outlet main pipe - pipe temperature rise ± insensitive temperature).

[0014] S4. Cooling tower fan frequency adjustment:

[0015] Based on the feedback of the cooling tower main outlet water temperature, the frequency of all fans is adjusted synchronously until the cooling tower main outlet water temperature equals (wet-bulb temperature + wet-bulb approximation setpoint ± insensitive temperature). After each execution of S4, the system executes S3 again, and so on.

[0016] Furthermore, integrated operation of cooling towers: In order to ensure that the heat dissipation area of ​​the cooling towers is fully utilized and to minimize the fan frequency and cooling water temperature, all cooling towers are integrated into a variable frequency operation.

[0017] The cooling tower is fully automated during operation: During operation, the control unit receives real-time feedback on various operating parameters and operating status of the cooling tower fans. When the number of fans changes, or if a fan stops running due to a fault or is manually stopped during maintenance, the control device will readjust from S1, achieving full life cycle operation of the cooling tower without manual intervention.

[0018] Depending on the arrangement and design of the tower, there are various forms of inlet and outlet water pipes for cooling towers. Existing conventional inlet and outlet water pipe designs can control the inlet and outlet water volume of each cooling tower by setting flow meters and regulating valves. For ease of explanation, this embodiment takes a single cooling tower as the basic unit.

[0019] This invention can be used for high-efficiency energy-saving control of open cooling towers in civil and industrial buildings, and has the following beneficial effects:

[0020] 1. This control device connects to the frequency converters of all cooling tower fans, enabling the cooling tower group to operate in a unified frequency conversion manner. It adjusts the frequency of the fans according to the optimal wet-bulb temperature approximation law, utilizes the entire heat dissipation area, and ensures that the fans operate uniformly in the highest efficiency range. The optimal operating efficiency range of the fans is the range with the largest electric-to-air ratio. In the environment of multiple cooling towers and long working cycles of the cooling tower group, the energy-saving effect is obvious.

[0021] 2. All cooling towers actively adjust the water flow according to their heat dissipation capacity to ensure that the outlet water temperature is the same, thereby maximizing the efficiency of the cooling tower group.

[0022] 3. This control device actively and precisely controls the water flow of each cooling tower through the flow meter and regulating valve of the cooling tower inlet and outlet pipes, so as to achieve uniform water distribution, water distribution according to cooling capacity, and balance of inlet and outlet water volume. It effectively avoids the overflow and underflow situation in traditional control tower groups, saves water consumption and chemical dosage, and saves operating costs. At the same time, it eliminates the need to install traditional balancing pipes, saving material and construction costs.

[0023] 4. When the number of operating fans changes, the device can automatically adjust during operation, achieving full life cycle of the cooling tower without manual intervention. Attached Figure Description

[0024] Figure 1This is a schematic diagram of the structure of the energy-saving control device for a cooling tower group according to an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of the connection relationship of the control unit of the energy-saving control device for a cooling tower group according to an embodiment of the present invention.

[0026] Figure 3 The diagram shows the operating efficiency of the cooling tower fan in the energy-saving control method for cooling tower groups according to an embodiment of the present invention. Detailed Implementation

[0027] To facilitate understanding by those skilled in the art, the present invention will be further described below in conjunction with embodiments and accompanying drawings.

[0028] The control device in this embodiment consists of a main inlet flow meter for the tower group, inlet and outlet branch flow meters for a single tower, inlet and outlet branch regulating valves, outdoor wet-bulb temperature sensor, outlet branch temperature sensor, cooling tower fan frequency converter, control unit, etc. When in use, the administrator sets the cooling water wet-bulb temperature approximation (if not set, the default is 2℃). After operation, no other manual intervention is required.

[0029] like Figure 1-2 As shown, the frequency converter is installed in the cooling tower distribution cabinet to control the frequency of the cooling tower fan; the flow meter is installed in the inlet and outlet branch pipes of the cooling tower; the regulating valve is installed before the flow meter; the water pipe temperature sensor is installed in the outlet branch pipe of the cooling tower; the control unit includes a data communication unit and a program logic controller, which receive data from the water temperature sensor, wet bulb temperature sensor, each flow meter data, each valve opening feedback, the frequency converter frequency feedback, and adjust the output valve opening and frequency converter frequency.

[0030] The control unit can be operated locally by administrators via a touchscreen with one click, or it can be started remotely. After starting, upon receiving a signal to start the water pump, all cooling tower fans will be turned on and run at industrial frequency. All cooling tower regulating valves will be opened to 100%. Based on the total pipe flow rate and the number of cooling towers, the average flow rate allocated to each cooling tower will be calculated. The inlet regulating valve of the cooling tower will be adjusted according to the flow rate feedback from the inlet branch pipe flow meter, adjusting the flow rate of each cooling tower to the set value ± non-sensitive deviation. At the same time, the outlet regulating valve will be adjusted according to the feedback value from the outlet branch pipe flow meter, until the inlet and outlet water flow rates of the cooling towers are the same.

[0031] Depending on the arrangement and design of the tower, there are various forms of inlet and outlet water pipes for cooling towers. Existing conventional inlet and outlet water pipe designs can control the inlet and outlet water volume of each cooling tower by setting flow meters and regulating valves. For ease of explanation, this embodiment takes a single cooling tower as the basic unit.

[0032] After the water volume distribution of the cooling tower group is adjusted evenly, the controller reads the temperature data of the outlet branch pipe and the outlet main pipe of each cooling tower. Keeping the fan frequency constant, the controller adjusts the cooling tower inlet regulating valve (decreasing the opening) for cooling towers where the outlet branch pipe temperature is greater than (outlet main pipe - pipe temperature rise ± insensitive temperature) to reduce the water intake; and adjusts the cooling tower inlet regulating valve (increasing the opening) for cooling towers where the outlet branch pipe temperature is less than (outlet main pipe - pipe temperature rise ± insensitive temperature) to increase the water intake; until the outlet branch pipe temperature of all towers equals (outlet main pipe - pipe temperature rise ± insensitive temperature).

[0033] Cooling tower fan frequency adjustment:

[0034] Based on feedback from the cooling tower main outlet water temperature, the frequency of all fans is synchronously adjusted until the cooling tower main outlet water temperature equals (wet-bulb temperature + wet-bulb approximation setpoint ± insensitive temperature). After each cooling tower fan frequency adjustment, the system performs cooling tower outlet water temperature equalization adjustment again, and this cycle repeats.

[0035] Fully automated cooling tower regulation:

[0036] During operation, the control unit receives real-time feedback on various operating parameters and operating status of the cooling tower fans. When the number of fans in operation changes, or if a fan stops operating due to a fault or is manually stopped during maintenance, the control device will start from S1 again to perform the above adjustment, so that the cooling tower can be operated without manual intervention throughout its entire life cycle.

[0037] Given n = 60f / p, Q' / Q = n' / n, N' / N = (n' / n) 3 Therefore, N' / N = (f' / f) 3 =(Q' / Q) 3 ;

[0038] Where n and n' are the rated speed of the fan motor and the speed of the fan after frequency adjustment, respectively;

[0039] f and f' are the rated frequency of the fan motor and the frequency of the fan after frequency adjustment, respectively.

[0040] p is the number of pole pairs of the motor; for example, p = 2 for a four-pole motor.

[0041] Q' and Q' are the air volume after frequency adjustment of the fan and the rated air volume of the fan, respectively.

[0042] N' and N are the power of the fan after frequency regulation and the rated power of the fan, respectively.

[0043] Actual measurements show that after applying the control device of this embodiment, the overall frequency of the cooling tower group fans is 3 to 5 Hz lower on average than that of traditional energy-saving control, which is about 6% to 10% of the rated frequency of the motor. According to the above formula, N' / N = (f' / f) 3=(0.94f / f) 3 =0.83, which means that it saves more than 17% of energy compared with traditional energy-saving control, saving about 1% of the energy consumption of the entire central air conditioning system. At the same time, due to the joint operation of the cooling towers, the heat dissipation area is fully utilized. When the outdoor wet-bulb temperature is ≤ design wet-bulb temperature, the wet-bulb temperature of the cooling water is ≤2℃, which is 1-2℃ lower than traditional energy-saving control. This can bring about a 5% increase in the COP of the main unit, which accounts for about 4% of the energy consumption of the entire central air conditioning system. In summary, by adopting the energy-saving control device of this tower group, more than 5% of the energy consumption of the central air conditioning system can be saved.

[0044] This control device monitors the operating parameters and status of the cooling tower fans in real time. When the number of fans in operation changes, or if a fan stops operating due to a fault or is manually stopped during maintenance, the device will automatically readjust, achieving full life cycle operation of the cooling tower without manual intervention.

[0045] This control device achieves water balance by using flow meters and regulating valves in the cooling tower's inlet and outlet pipes. This effectively avoids overflow and underflow situations that occur in traditional control tower groups, saving water consumption and chemical dosage, and reducing operating costs. At the same time, it eliminates the need for traditional balancing pipes, saving on material and construction costs.

[0046] This control device connects to the frequency converters of all cooling tower fans, enabling the cooling tower group to operate as a unified frequency converter, utilizing the entire heat dissipation area, and ensuring that the fans operate uniformly in their highest efficiency range. Figure 3 As shown, the optimal operating efficiency zone for the fans is the zone with the highest electro-air ratio, concentrated between 25 and 42 Hz. Traditional energy-saving control methods achieve even distribution of cooling tower water volume. However, the actual electro-air ratio and heat dissipation capacity of the towers cannot be uniform due to the influence of their layout, obstruction, surrounding heat sources, and seasonal wind direction. For example, if a group of towers located in the middle with insufficient spacing is severely obstructed, the airflow will be insufficient. In this case, the water volume of this group of towers will be the same as that of the towers on the outside with sufficient airflow. Frequency adjustment based on water temperature will inevitably lead to the frequency of the obstructed towers being higher than that of other towers, even reaching the power frequency without being able to control the water temperature. This embodiment uses flow meters and regulating valves to actively and precisely control the inlet and outlet water volume of each cooling tower, achieving uniform water distribution, water distribution according to cooling capacity, and balance of inlet and outlet water volume. All cooling towers actively adjust their water volume according to their heat dissipation capacity to ensure that their outlet water temperature is the same, achieving the maximum efficiency of the cooling tower group. When the number of operating fans changes, automatic recirculation adjustment can be performed, achieving the goal of no manual intervention throughout the entire life cycle of the cooling towers. If the fan frequency is reduced simply to save energy, the inlet water temperature will increase significantly under high load.

[0047] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A method for energy-saving control of cooling tower groups based on the actual heat dissipation capacity of cooling towers, characterized in that: The energy-saving control device for the cooling tower group includes a frequency converter, flow meters, regulating valves, water temperature sensors, wet-bulb temperature sensors, and a control unit. The frequency converter is installed in the cooling tower distribution cabinet to control the frequency of the cooling tower fans and provide feedback on the fan operating status. The flow meters are installed on the main outlet pipe, inlet branch pipes, and outlet branch pipes of the cooling tower group to provide feedback on the total system flow and the inlet and outlet water volume of each cooling tower. The regulating valves are installed before the flow meters on the inlet and outlet branch pipes of the cooling towers to control the flow rate. The water pipe temperature sensors are installed on the outlet branch pipes and main outlet pipe of the cooling towers to provide feedback on the outlet water temperature of each tower and the total outlet water temperature of the cooling tower group. The control unit includes a human-machine interface and a data communication module to receive data from the water temperature sensors, wet-bulb temperature sensors, the operating data of each cooling tower fan, and the flow meter data; to provide feedback and adjust the opening of each regulating valve; and to provide feedback and adjust the frequency converter frequency. The energy-saving control method for cooling tower groups is as follows: S1. Cooling tower water volume equal distribution adjustment: After receiving the water pump start signal, all cooling tower fans are turned on and all are running at industrial frequency. Based on the flow rate of the main water inlet pipe of the cooling tower group and the number of cooling towers, the average flow rate of each cooling tower is calculated and set as the average flow rate value. The water inlet pipe regulating valve of the cooling tower is adjusted according to the flow rate value fed back by the flow meter of the cooling tower water inlet branch pipe until the water inlet flow rate of each cooling tower = average flow rate value ± insensitive deviation. S2. Cooling tower inlet and outlet water balance adjustment: Adjust the outlet branch pipe regulating valve according to the feedback value of the flow meter of the outlet branch pipe of the cooling tower to balance the inlet and outlet water of the cooling tower. S3. Cooling Tower Outlet Water Temperature Balancing Adjustment: The controller reads the temperature data of each cooling tower's outlet branch pipe and outlet main pipe, keeping the fan frequency constant. If the outlet branch pipe temperature of a cooling tower is greater than (outlet main pipe - pipe temperature rise ± insensitive temperature), the cooling tower inlet regulating valve is adjusted to reduce the water intake. If the outlet branch pipe temperature of a cooling tower is less than (outlet main pipe - pipe temperature rise ± insensitive temperature), the cooling tower inlet regulating valve is adjusted to increase the water intake. This continues until the outlet branch pipe temperature of all towers equals (outlet main pipe - pipe temperature rise ± insensitive temperature). S4. Based on the feedback of the cooling tower main outlet water temperature, synchronously adjust the frequency of all fans until the cooling tower main outlet water temperature = (wet bulb temperature + wet bulb approximation setpoint ± insensitive temperature); after each execution of S4, execute S3 again.

2. The energy-saving control method for cooling tower groups based on the actual heat dissipation capacity of cooling towers according to claim 1, characterized in that: The cooling tower is integrated with a variable frequency drive, and the fans operate at the same frequency. During operation, the control unit receives real-time feedback on various operating parameters and operating status of the cooling tower fans. When the number of fans in operation changes, the control device will readjust from S1 to ensure that the cooling tower outlet water temperature remains the same.

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