Abstract : This paper analyzes the energy situation of the inlet water flow in a cooling tower and concludes that the excess energy of the inlet water flow is sufficient to drive the fan. A new type of water turbine was developed to replace the fan motor. After trial use, it was found that when the excess water head in the cooling tower is 5-8m, it can meet the requirements for driving the water turbine. This water turbine-driven fan is particularly suitable for large cooling towers. Keywords : water turbine; fan; cooling tower; energy saving The heat exchange capacity of a cooling tower is mainly determined by the air-to-water ratio. The expected temperature drop of the cooling tower can be achieved by exchanging heat with the same mass flow rate of hot water and the same mass flow rate of air. Air is generally obtained by motor-driven fans, regardless of the method used. If a water turbine is used instead, the shaft power of the water turbine can be the same as the power of the motor. The structure, shape, size, and cooling principle of the tower do not need to be changed. 1 Principle of Water-Driven Fan The inlet circulating water head of a cooling tower is generally 5-8m. From this, it can be deduced that the water flow entering the cooling tower has a head of 5-8m multiplied by the corresponding inlet water flow rate. For example, the energy consumption of a standard 100t/h cooling tower is approximately 2.2kW, meaning the actual shaft power of the fan blades used in a 100t/h standard tower is approximately 2.2kW. Higher efficiency fans consume even less than 2.2kW. A 200t/h tower consumes approximately 4.5kW, a 1000t/h tower approximately 22kW, a 4000t/h tower approximately 90kW, and so on. Since existing cooling towers possess this energy in the water flow under normal operating conditions, why not utilize it instead of wasting it? The required inlet head of a cooling tower is determined by the sum of the tower's pipe losses, tower height, and the required water jet force. The head required for the water jet force is only 0.5-1 m. These operating pressures come from the circulating water pump. The pump head selection calculation is the sum of the cooling tower's location height, pipe losses along the route, elbow and valve resistance, and the resistance of the water-using equipment. The pump's flow rate is matched to the nominal value of the cooling tower; for example, a 100t/h tower is matched with a 100t/h pump, and a 500t/h tower is matched with a 500t/h pump. The pump's head multiplied by the flow rate equals the power of the water flow. The head of the water entering the tower is the total head minus the resistance loss of the water supply system, leaving 5-8 meters. This valuable 5-8 meters can be utilized effectively. By first passing it through a water turbine to obtain output power to drive the fan, the fan motor can be completely eliminated. In industrial applications, pump head selection must consider both flow rate and pump efficiency; the head is generally allowed to be higher than it should not be lower, providing ample head for the water turbine. Therefore, for cooling towers that meet conventional design selection criteria, a water turbine can completely replace the fan motor without worrying about insufficient turbine power affecting airflow and cooling efficiency. Furthermore, the residual pressure after passing through the water turbine is sufficient to handle water distribution and other pipeline losses. Figure 1 shows the structural diagram of a water-driven fan cooling tower. The water turbine is located at the top of the water distribution system. The water head of 0.5-1 m is achieved by adjusting the water level difference between the outlet water and the distribution water after the water flows through the turbine. 2. Energy Saving of Water-Driven Fan Cooling Towers After five years of research and testing, and practical application by over one hundred users, this type of cooling tower has proven to eliminate the need for a motor, resulting in significant energy savings. Water-driven fan cooling towers have substantial energy-saving value. In China, there are approximately 500,000 standard 200t/h cooling towers. The power consumption of a standard 200t/h tower, based on the national standard of 0.04kW/t, is 7.5kW. If all of these were replaced with water turbines to drive the fan blades, 24 billion kWh of electricity could be saved. Based on an average peak-valley electricity price of 0.5 yuan/kWh in Shanghai, this translates to annual savings of 12 billion yuan. From the perspective of energy saving effect of a single tower, a 200Vh tower consumes 4.5 × 24 = 108 kWh of electricity per day, totaling 39,420 kWh per year. At an electricity cost of 0.5 yuan/kWh, this amounts to 19,710 yuan per year. For industrial electricity at 1 yuan/kWh, the cost is also 39,420 yuan. This calculation is very clear. All savings are profit. The same calculation applies to the size of the tower. 3. Development of a Micro Water Turbine To achieve such energy-saving effects, the key is how to properly match the water turbine. Most water turbines on the market are used for hydropower generation, with power outputs above 100kW, while cooling towers generally have power outputs below 100kW. Even if small-power water turbines are available, they cannot be used directly, either due to excessively high water pressure or incompatible shape and structure. Therefore, the author specifically developed a water turbine for cooling towers, as shown in Figure 2. The author calls it a miniature water turbine, a double-flow type, with a 30° inlet angle for the impeller, a chord angle of 22.5° for the blades, and 17 blades. The blade profile is designed to maximize energy utilization. The inlet head is 5-8m, completely solving the speed and shaft power requirements of the cooling fan. Actual application testing by a legally authorized testing unit showed very satisfactory results. 4. Cooling Effect of the Water-Powered Fan Cooling Tower On May 31, 2001, the Shanghai Energy Conservation Service Center tested two 200t/h cooling towers of the same type manufactured by Zhejiang Lianfeng Fiberglass Factory at the Shanghai Dairy Training Center. One tower's fan operating system only underwent water turbine modification, with other parts remaining unchanged. The two towers were operated simultaneously under identical conditions, and their thermal performance and energy-saving effects were compared. The test data after comparison are shown in Table 1 (the north tower was modified with a water turbine). The test results show that the water pump power was not increased, the head remained unchanged, but the fan motor was eliminated, therefore the power consumption was zero, achieving 100% energy saving. 5. Conclusion Whether it's retrofitting or building a new cooling tower, the advantages of using a water turbine are: ① Energy saving. This tower uses a water turbine instead of a fan motor, completely saving the operating power consumption of the fan motor and without increasing the burden on the circulating water pump. ② No noise. The energy conversion of the water turbine is completed within the water flow channel; controlling the Reynolds number of turbulence prevents the water turbine from emitting disruptive noise. ③ High efficiency. The water turbine shaft directly outputs the fan blades, eliminating the need for other reducers, and the air volume changes accordingly with the water flow, always maintaining a stable air-to-water ratio. ④ Long service life. The water turbine has a simple structure and runs smoothly; therefore, as long as the material design strength and sealing are met, its service life is long. Repairing it is also extremely simple, requiring only the replacement of some standard parts, saving much more trouble than repairing a motor or reducer. ⑤ Safety. Cooling tower motors pose potential risks of electric shock and spark explosions. Water turbines, on the other hand, do not require electricity and are lightweight, eliminating the difficulties of lifting and removing the motor reducer during work at heights, thus increasing the safety of the cooling tower's operating environment. ⑥ Applicable. Suitable for any type of cooling tower, especially extra-large ones. The larger the tower, the more reliable it is.