HVAC - Comprehensive Knowledge You Must Know about Cooling Towers

A cooling tower is a device that uses the contact between water and air to dissipate the waste heat generated in industrial processes or in refrigeration and air conditioning systems through the process of evaporation. The waste heat generated during industrial production or in the refrigeration process generally needs to be carried away by cooling water. A certain amount of water is drawn from natural water bodies such as rivers, lakes, seas, etc. as cooling water. The cooling process equipment absorbs the waste heat, causing the water temperature to rise, and then the water is discharged back into rivers, lakes, seas, etc. This cooling method is called direct current cooling. When the conditions for direct current cooling are not available, a cooling tower is required for cooling. The function of a cooling tower is to conduct heat exchange between the cooling water carrying waste heat and the air inside the tower, transferring the waste heat to the air and dissipating it into the atmosphere.

I. Basic Working Principle of the Cooling Tower
After being drawn by the fan, dry (low enthalpy value) air enters the cooling tower through the air inlet mesh. High-temperature water molecules with a high partial pressure of saturated steam flow towards the air with a lower pressure, and hot and humid (high enthalpy value) water is sprayed into the tower. When water droplets come into contact with the air, on the one hand, there is direct heat transfer between the air and the water, and on the other hand, due to the pressure difference between the surface of the water vapor and the air, an evaporation phenomenon occurs under the action of pressure, taking away the heat in the water, that is, evaporative heat transfer, thus achieving the purpose of cooling.

II. The Working Process of the Cooling Tower
Taking the working process of a circular counterflow cooling tower as an example:
The hot water from the main engine room is pumped by a water pump under a certain pressure through pipes, horizontal pipes, elbow pipes, and the central pipe to the water distribution system of the cooling tower. The water is evenly sprayed onto the packing through the small holes on the water distribution pipes. The dry air with a low enthalpy value enters the tower from the bottom air inlet mesh under the action of the fan. When the hot water flows through the surface of the packing, a water film is formed and heat exchange occurs with the air. The hot and humid air with a high humidity and high enthalpy value is drawn out from the top, and the cooled water droplets fall into the bottom basin and flow into the main engine through the outlet pipe.
Under normal circumstances, the air entering the tower is dry air with a low wet bulb temperature. There is obviously a concentration difference and a kinetic energy pressure difference of water molecules between the water and the air. When the fan is in operation, under the action of the static pressure inside the tower, water molecules continuously evaporate into the air and become water vapor molecules. The average kinetic energy of the remaining water molecules will decrease, thus reducing the temperature of the circulating water.
From the above analysis, it can be seen that as long as water molecules can continuously evaporate into the air, the water temperature will decrease. However, the evaporation of water into the air will not continue indefinitely. When the air in contact with the water is unsaturated, water molecules continuously evaporate into the air. But when the air on the water-air contact surface reaches saturation, the water molecules cannot evaporate anymore and are in a state of dynamic equilibrium. The number of water molecules that evaporate is equal to the number of water molecules that return from the air to the water, and the water temperature remains unchanged. Thus, it can be seen that the drier the air in contact with the water, the easier the evaporation process will be, and the easier it is for the water temperature to decrease.

III. Classification of Cooling Towers

IV. Composition of Cooling Towers
1. Water Distribution Packing: The water (hot water) that needs to be cooled is splashed into water droplets or formed into a water film multiple times to increase the contact area and time between the water and the air, promoting the heat exchange between the water and the air. The cooling process of water mainly takes place in the water distribution packing.
2. Water Distribution System: Evenly distributes the hot water over the entire water distribution packing. Whether the hot water is evenly distributed has a great impact on the cooling effect. If the water distribution is uneven, it will not only directly reduce the cooling effect but also cause some cooling water droplets to splash and drift outside the tower.
3. Ventilation Equipment: In a mechanical ventilation cooling tower, a ventilation fan is used to generate the expected air flow rate to ensure the required cooling effect.
4. Air Distribution Device: Devices such as air inlets, louvers, and air guide plates are used to guide the air to be evenly distributed across the entire cross-section of the cooling tower.
5. Ventilation Cylinder: The function of the ventilation cylinder is to create good aerodynamic conditions, reduce ventilation resistance, and send the hot and humid air discharged from the cooling tower to a high altitude to reduce the backflow of hot and humid air. The ventilation cylinder of a mechanical ventilation cooling tower is also called the air duct. The ventilation cylinder of a natural draft cooling tower with an air duct serves the functions of ventilation and sending the hot and humid air to a high altitude.
6. Water Eliminator: Separates the water droplets carried in the discharged hot and humid air from the air, reducing the loss of water escaping and the impact on the surrounding environment.
7. Tower Body: The external enclosure structure of the cooling tower. The tower bodies of mechanical ventilation cooling towers and natural draft cooling towers with air ducts are closed, playing the functions of support, maintenance, and organizing a suitable air flow. The tower body of an open cooling tower is open along its height to allow natural wind to enter the tower.
8. Collection Basin: Located at the lower part of the cooling tower, it collects the cooling water falling from the water distribution packing. Sometimes, the collection basin also has a certain reserve volume, playing the role of regulating the flow rate.
9. Water Conveyance System: The inlet pipe sends the hot water to the water distribution system, and a valve is installed on the inlet pipe to regulate the water inlet volume of the cooling tower. The outlet pipe sends the cooled water to the water-using equipment or the circulating water pump. In the collection basin, supplementary water pipes, sewage pipes, overflow pipes, emptying pipes, etc. are also installed. When necessary, a connecting pipe can also be installed between multiple cooling towers.
10. Other Facilities: Including access doors, access ladders, walkways, lighting, electrical control, lightning protection devices, and flight obstruction signs set when necessary, etc. Sometimes, test components for the cooling tower are also set up for testing needs.
The different combinations of the above components form various forms and purposes of cooling towers: open dripping cooling towers, natural draft cooling towers with air ducts, induced draft (or forced draft) counterflow cooling towers, induced draft crossflow cooling towers, etc.

V. Scope of Application of Cooling Towers
The waste heat generated during industrial production or in the refrigeration process generally needs to be carried away by cooling water. The function of a cooling tower is to conduct heat exchange between the cooling water carrying waste heat and the air inside the tower, transferring the waste heat to the air and dissipating it into the atmosphere.

For example, in a thermal power plant, the boiler heats water into high-temperature and high-pressure steam, which drives the steam turbine to do work and generate electricity by the generator. The waste steam after the steam turbine has done work is discharged into the condenser, where it exchanges heat with the cooling water and condenses into water, which is then pumped back to the boiler for recycling. In this process, the waste heat of the exhaust steam is transferred to the cooling water, causing the water temperature to rise. The cooling water carrying the waste heat transfers the heat to the air in the cooling tower and is discharged into the atmospheric environment from the air duct.
Scope of Application of Cooling Towers: Mainly applied in air conditioning cooling systems, refrigeration series, injection molding, leather making, foaming, power generation, steam turbines, aluminum profile processing, air compressors, industrial water cooling, and other fields. The most common applications are in the air conditioning cooling, refrigeration, and plastic chemical industries.
VI. Installation Reference for Cooling Towers
(1) Environmental Selection
1. Avoid installing the cooling tower in waterproof passages or near high walls that easily reflect sound. It should be installed on the roof or in a well - ventilated area.
2. When using two or more cooling towers together, pay attention to the spacing between the tower bodies.
3. Do not install the cooling tower in a place surrounded by outer walls or in an air - tight area. Also, pay attention to the spacing between the tower body and the outer walls.
4. Avoid installing the cooling tower in areas with a lot of soot and dust to prevent the film from being blocked.
5. Keep the cooling tower away from hot areas such as kitchens and boiler rooms.
(2) Installation Key Points
1. The foundation should be level and not inclined. The center line of the cooling tower should be perpendicular to the horizontal plane; otherwise, it will affect water distribution and the operation of the motor.
2. For cooling towers with a capacity of over 175t, supports should be installed for the inlet and outlet water pipes.
3. When using pumps for two or more cooling towers, a balancing water pipe should be added.
4. It is advisable to use shock - absorbing hoses for the connection of the circulating inlet and outlet water.
5. The clearance between the fan blades of the cooling tower and the tower wall should be consistent.
6. Regularly inspect the motor and the reducer. Check the oil level in the reducer.
(3) Startup Inspection
1. Check if all screws are tightened and if there are any debris inside the tower.
2.

Ensure that the fan and the water spraying system rotate smoothly.
3. Check if the power supply voltage matches the motor voltage.
4. Verify if the belt combination is installed correctly.
5. Open the water supply valve to completely fill the water basin and pipes. The water level should be 25mm below the full - water pipe.
6. When starting, turn on the water pump first and then the fan. Check the wind direction and air volume, and make timely adjustments until the requirements are met.
7. When stopping, turn off the fan first and then the water pump.
(4) Operation Inspection
1. Keep the inside of the cooling tower clean and perform regular water quality treatment.
2. After running for about 60 hours, re - check the belt tension to ensure it is normal.

3. Check the oil level in the gear reducer and replace the lubricating oil after running for 150 hours.
VII. Basis for Cooling Tower Selection
Usually, the selection of a cooling tower is based on its cooling capacity. The circulating water volume of the cooling tower in an air - conditioning refrigeration system is determined by the refrigeration capacity of the chiller and the temperature difference between the inlet and outlet of the cooling water. The temperature difference between the inlet and outlet usually refers to the design under standard working conditions, i.e., the inlet water temperature is 37°C, the outlet water temperature is 32°C, and the wet - bulb temperature is 28°C.
When the wet - bulb temperature in the area where the cooling tower is located is not the standard working condition and the inlet and outlet water temperatures also change, the approach (the approach is the difference between the outlet water temperature and the wet - bulb temperature) will also change. For example, in Beijing, the wet - bulb temperature is 26.4°C, the inlet water temperature is 35°C, and the outlet water temperature is 29.5°C, with an approach of 3°C.
The approach directly affects the cooling capacity of the cooling tower. The smaller the approach, the smaller the cooling capacity; conversely, the larger the approach, the greater the cooling capacity. A standard 100 - ton cooling tower can cool 100 tons of water when the approach is 4°C. When the approach is 3°C, it can only cool 85 tons of water. To cool 100 tons of water, a standard 125 - ton cooling tower must be selected.
VIII. Analysis and Solutions for Common Problems and Failures of Cooling Towers
IX. Correct Operation Method of Cooling Towers
Although the cooling tower is an auxiliary device in the air - conditioning refrigeration system, it undertakes the important task of dissipating the total heat absorbed by the entire system. Therefore, whether the cooling tower is operated correctly is directly related to the refrigeration effect and energy saving of the entire air - conditioning system. Since the incorrect operation of the cooling tower mentioned above is quite common and exists throughout the process from startup to shutdown, its harm is great, and relevant operators and managers should pay high attention to it.
The correct operation methods and requirements for the cooling tower are as follows:
1. The number of cooling towers in use should match the number of operating units.
2. Close the inlet and outlet valves of the cooling towers with non - operating fans to prevent cooling water from flowing through the unused towers.
3. After turning off the temporarily added cooling tower fan, do not forget to close the inlet and outlet valves of that tower.
4. Check the operation of the cooling towers after each shift starts. If cooling water is found flowing through a cooling tower with a non - operating fan, close the inlet and outlet valves of that tower in time and adjust the water level in the water tray. Some units of the condenser, evaporator, and screw - type chiller in the air - conditioning system are equipped with electric valves, but electric valves are prone to failure and malfunction, so inspection should be strengthened to ensure the normal and correct operation of the system. The refrigeration process is actually a heat - exchange process. The heat - exchange of the chiller is more complex than that of window - type, split - type, and cabinet - type air conditioners. The former is indirect refrigeration, while the latter is direct refrigeration.
X. Noise Control of Cooling Towers
(1) Sound Source Analysis
Cooling towers are widely used in the cooling water circulation systems of urban hotels, restaurants, shopping malls, office buildings, etc., and are also widely used in industrial enterprises such as petroleum, chemical, power generation, and metallurgy.
(2) The noise sources of the cooling tower consist of the following parts:
1. Fan intake and exhaust noise;
2. Water - spraying noise;
3. Noise from the fan reducer and the motor;
4. Noise from the cooling tower water pump, piping, and valves.
The operation of the cooling fan generates rotational noise, vortex noise, and mechanical noise. Their noise spectra all have broadband characteristics. Although the noise level is not very high, it has strong penetrability and can affect the surrounding residents and buildings. It is also one of the reasons for the formation of other noise sources. Among them, the main noise sources are the intake and exhaust noise during fan operation and the water - spraying noise. The fan radiates noise outward through the intake and exhaust ports and the tower body. The exhaust port noise is about 5 - 10 dB(A) higher than the intake port noise. Its spectral characteristic is a continuous spectrum dominated by low frequencies, belonging to low - frequency noise. When the circulating hot water falls from the water - spraying device and hits the accumulated water in the water - receiving tray at the bottom of the tower, the generated water - spraying sound belongs to high - frequency noise. The size of the water - spraying sound is related to the water - spraying height and the water flow rate per unit time. The overall noise of the cooling tower is a continuous spectrum dominated by low frequencies, without prominent noise, generally between 31.5 - 2000Hz, and the noise level is about 55 - 85dB(A).
(3) Control Methods
1. Control the noise at the inlet and outlet of the cooling tower. Select different noise - reduction equipment such as silencers and sound barriers according to the situation.
2. Control the water - spraying noise of the tower body. Use different noise - reduction equipment such as sound - insulation rooms and sound barriers according to different situations.
3. Control the noise of water falling into the water - collection tray. Use different noise - reduction equipment such as noise - absorbing water pads and water - falling silencers according to the situation.
4. Control the vibration of the cooling tower. Use vibration - reduction equipment such as vibration dampers and rubber flexible joints.
Special Note: While controlling the noise of the cooling tower, fully consider the ventilation requirements for the operation of the cooling tower according to the actual situation to ensure that the installation of the noise - reduction equipment does not affect the operation of the cooling tower.