Cooling Towers

View A Video on Cooling Towers- A Quick Introduction

Cooling towers cool water or fluids that have been heated by an industrial manufacturing process or some other process. In some water towers, the heated water is then sprayed into the tower across a wet deck surface, or fill pack. As air flows past the water, excess heat is absorbed, lowering the temperature in the water before it is caused by gravity to return to the bottom of the chamber and be fed back into the processing plant. Airflow can be caused either by natural draft towers which depend on the characteristic of hot air to be less dense and therefore rise, creating a up flow in the chamber and moving the cold air down toward to the bottom in order to absorb heat. Other industrial cooling towers may use mechanically caused drafts through fans located on the sides of the tower, or induced draft towers which create a vacuum at one end of the tower to create air movement.

There is a variety of cooling tower systems and there are a number of factors that go into determining the most appropriate cooler tower. Particular types of cooling systems used within the tower are more suitable to some applications than others. Some of the various types include: open loop towers, closed loop towers, counter-flow and cross-flow systems. Depending on the resources available in terms of space, cool water sources, structural capacity, electrical supply and materials, one of these types or a combination of may be determined most suitable for a specific requirement. HVAC cooling towers and air conditioning cooling towers are used primarily in larger building to maintain a comfortable interior temperature. Evaporative and water cooling towers use the science of evaporation to result in the release of heat into the atmosphere and require a local water source in order to be most effective and energy efficient. Water is a naturally available resource although sources of cooling water vary according to the location of the cooling tower. These sources may include rivers, seas, wells or lakes and the cool water is used to absorb heat from heat exchangers in the tower. Chillers cooling towers incorporate refrigerant devices to achieve an even more drastic cooling effect than other towers. Closed loop cooling systems prevent contact between the cooling agent and the element being cooled, allowing for recirculation without additional filtration to remove unwanted chemicals or particles. It also eliminates the need for the coolant and processed material to be compatible with each other as they are not required to interact at any stage of the cooling process.

Water is an ideal substance to use for industrial cooling as it has a high specific heat capacity and greater thermal conductivity than many other liquids. Furthermore, when water is released into the atmosphere through the process of evaporation, it is able to be absorbed into the water cycle again. Cooling tower systems are used by industrial facilities such as power plants, oil refineries, petrochemical and natural gas processing plants, dry cleaning, plastics and nuclear power plants. These facilities each give off varying degrees and volumes of waste heat and therefore the required capacity of a cooling tower system can differ greatly. Sizes of cooling towers can vary from small roof-top units to larger hyperbolic cooling tower structures measuring 400 feet. Industrial cooling towers are typically larger and more durable than HVAC cooling towers as they are intended to operate almost continually year round and are required to cool far greater volumes of liquid.

Cooling tower design is an integral part of providing cost, energy and performance efficiency for a particular cooling tower. It is important to consider the intended location and naturally occurring environmental effects in that location, the piping capabilities of a facility, electrical source and capacity, tonnage of the finished tower, seismic events and the desired results of the cooling tower system. Cooling towers can be constructed from a number of different materials including concrete, fiberglass, stainless steel and aluminum. While there are advantages to each type of material, fiberglass cooling towers are a popular construction choice due to a number of factors. Fiberglass is durable and strong and therefore is an ideal material for a tower intended to function outside in extremes of weather and environmental conditions. It is corrosion resistant which is beneficial in a process such as this which involves almost constant contact with water and air. Furthermore, fiberglass is a lightweight material, ensuring that transport and handling of the cooling system prior to installation will be more straightforward. When selecting a cooling tower, consider industrial application, fluid type and volume. Many different cooling systems are available and many can be designed or adjusted to offer custom cooling tower systems.

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Cooling Tower Types

• Air conditioner cooling tower provide air conditioning and are fiberglass structures that cool larger buildings like hospitals, schools and some offices.
• Ceramic cooling towers have quite an attractive appearance, but are usually more expensive than other cooling towers.
  
• Chillers cooling towers are supplementary means of eliminating waste heat that is a byproduct of many processes which require the use of air and liquid chiller systems.
• Closed loop cooling towers are cooling towers in which the air and cooled water or other fluid do not have direct contact.
  
• Cooling tower design determines cost, performance, and efficiency.
  
• Cooling tower manufacturers are companies that make units that cool fluids.
  
• Cooling tower systems, sometimes referred to as heat rejection devices, provide cooling of water and other fluids through the removal of heat from the fluid.
• Counterflow cooling towers contain opposing air and water flows. The airflow moves up and the water flow moves downward.
  
• Cross flow cooling towers contain perpendicular air and water flows. The airflow is horizontal, and the water flows vertically downward.
  
• Disinfection cooling towers are used in drinking water and wastewater treatment facilities to assist in the elimination of bacteria, chemicals and other impurities in the water.
  
• Evaporative cooling towers are heat extraction devices that use the evaporation of a small amount of working fluid, typically water, to transfer heat into a moving air stream in order to cool the rest of the water stream close to the wet-bulb air temperature, a designed measurement of temperature reflecting the desired level of water vapor content of the cooling tower.
• Fiberglass cooling towers have great weather resistance, which makes them useful in harsher environmental conditions. These cooling towers also provide good corrosion resistance, which remains advantageous in applications such as water treatments, in which the tower will be exposed to chemicals.
  
• HVAC cooling towers combine a water-cooled chiller, or condenser, with a cooling tower.
• Hyperbolic cooling towers refers to a specific design and construction style for cooling towers that utilizes hyperbolic structural planning which inherently creates natural draft and employs evaporation to cool water and other fluids.
• Industrial cooling towers are heat rejection systems that are used for the cooling of water and other working fluids by means of removing process waste heat from the fluid and into the atmosphere.
• Mechanical draft cooling towers consist of forced draft towers, which contain side fans that force the air through the system, and induced draft cooling towers, which contain overhead fans that pull the air through the system. Mechanical draft cooling towers are often used in smaller cooling tower systems.
  
• Natural draft cooling towers do not utilize fans but rely on exhaust air buoyancy and natural winds to move the air through the system. Natural draft cooling towers are used in applications involving large volumes of water, such as power generation plants.
  
• Open circuit cooling towers are cooling towers in which water is internally distributed within the system with direct contact with the entering air.
  
• Water cooling towers are basic cooling systems used to cool water through contact with airflow. Applications utilizing water cooling towers include air conditioning and water/wastewater.

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Cooling Tower Terms

Ambient Temperature - The DBT as measured by a thermometer.
 
Axial Fans - Fans in which the direction of the airflow does not change. Axial fan types include propeller, tubaxial and vaneaxial.

Blowdown - Water removed from a cooling tower to prevent excessive buildup of impurities within the system. Impurities increase in concentration as water evaporates during the cooling process.
 
Blow Out - Water removed from a cooling tower through wind or splashing. Blow out is reduced or eliminated through the use of screens and other mechanisms.
 
BTU (British Thermal Unit) - The amount of heat gain or loss that is needed in order to change the temperature of one pound of water by one degree Fahrenheit.
 
Drift - Water droplets removed from a cooling tower along with the exhaust air. Drift must be controlled because, unlike the water vapor removed from the tower, drift often contains chemicals, debris and other impurities that may negatively affect the environment.
 
Drift Eliminator - A mechanism in a cooling tower that prevents drift from leaving the tower by catching the drift as it flows through the eliminator, while allowing the passage of exhausted air through the eliminator and into the atmosphere.
 
Dry Bulb Temperature (DBT) - The temperature of the air entering the cooling tower, measured in degrees Fahrenheit.
 
Entrainment - Water in the air being brought into the cooling plumes as the liquid wastes are discharged.
 
Exhaust Air - The air removed from the cooling tower during the cooling process. Exhaust air also contains water vapor that has evaporated during the cooling process.
 
Fill - A labyrinth-like packing that provides a vastly expanded air-water interface, which allows heating of the air and evaporation to occur. Film fill consists of multiple, typically vertical, wetted surfaces upon which a thin covering of water spreads, while splash fill consists of many levels of horizontal splash elements that create a cascade of tiny droplets, which have a large combined surface area.
 
Fogging - The foggy condensation of water vapor outside of a cooling tower resulting from the contact of saturated exhaust air emerging from the tower with cooler air outside of the tower.
 
Induced Draft - The process in which the fan of the cooling tower draws air from the bottom of the unit and passes it out through the top of the cooling tower.
 
Noise - Sound energy generated by the impact of falling water, movement of air by fans, the movement of fan blades within the structure and the drive belts, gearboxes and motors that is emitted by a cooling tower and recorded at a certain distance and direction.
 
Nozzle - A mechanism through which water flows into a cooling tower in either spray or stream form.
 
Plume - Exhaust air and water vapor emerging from a cooling tower. A plume may create fogging when introduced to air of a lower temperature.
 
Psychrometer - Mechanism used in a cooling tower system to measure the wet bulb temperature of the system.
 
Recirculation - The entrance into a cooling tower of previously discharged air that reenters the system along with fresh air.
 
Thermal Capacity - Cooling tower capacity representing the amount of liquid, measured in gallons per minute, that a cooling tower can process.                   
 
Wet Bulb Temperature (WBT) - The temperature within a cooling tower at which the air is saturated with water vapor, preventing the further occurrence of water evaporation.

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