Types of Cooling Towers – Plant Selection Guide

There are lots of different types of cooling towers that are used to provide efficient heat exchange in industrial and commercial cooling processes. Selecting the best tower system for your application or process requires careful consideration.  In this plant selection guide the specialists at Water Treatment Services review the most popular types of cooling tower system looking at their design, how they work, where they are commonly used, and the advantages and disadvantages of each.

Where are cooling towers used?

Cooling towers are a common sight on the skylines of many British towns and cities.

They are most commonly associated with power stations, processing plants and factories, but are not specific to one particular industry sector.

Cooling towers, as their name suggests, are designed to cool water used as part of a process where some type of air or process cooling is required.

They are also a common feature of large air conditioning systems found in modern offices, hotels and other buildings where they are used to control the quality of internal environments – usually temperature and humidity.

Whatever the reason for needing a cooling tower, the way they work is broadly the same.

How do cooling towers work?

Cooling towers work by a process of heat exchange, usually using water as the primary heat transfer medium.

Excess heat is extracted using air conditioning or air handling units from an office or production process.

The heat exchange part of the process uses water, which is heated and then pumped through pipes and into a cooling tower where the excess heat can be dealt with.

Cooling towers work by a process of heat exchange, usually using water as the primary heat transfer medium.

Once the heated water reaches the tower it is sprayed onto material known as “fill” or “tower packing” which helps to increase surface area and facilitates the cooling process.

As the flow of water through the cooling tower slows and is exposed to the air, it cools even further.

This action of water meeting air is what causes it to cool down, as the process of evaporation takes place.

Once the excess heat has been removed the cooled water then condenses and finally recirculates back into the office or production facility and the entire process repeats.

What are the different types of cooling tower?

Although cooling towers perform the same heat exchange function there are a range of different designs.

The design you select will typically depend on the type of application, the amount of cooling required, the quantity of water which needs to be cooled and a wide range of other factors.

There are three main types of cooling tower, with different designs within each group.

Crossflow cooling towers

The crossflow design of cooling tower involves water being drawn into the tower perpendicular to the flow of the water.

Water gets into the tower through the vertical faces of the tower, and the water drips downward from a basin located at the top.

This design of tower relies on gravity to do the hard work, and distributes the water evenly across the tower’s surface.

As the air passes through, it forces water into an area designed to improve contact between the air and the water.

This is the part of the process which ensures the water is cooled efficiently.

Crossflow towers are most commonly used in the chemical processing industry, and also in aluminium casting.

Advantages of crossflow cooling towers:

• • They are easy to maintain.
  • Low running costs.
  • Lower energy bills.

Disadvantages:

• • Potential issue with dirt building up on the surface, fill or packing of the tower.
  • There is a limit to how much water can be processed at any one time.

Counterflow cooling towers

The principle of this design of cooling tower is similar to the crossflow design, discussed above, but with one crucial difference; the water flows in the opposite direction to the flow of the air.

Air is pulled into the cooling tower at the bottom, and up into the tower.

Water enters at the opposite end and flows downward to meet the air coming up.

Hot air passes out of the tower to the top, and the water flows back out through the base of the tower.

Counterflow designs are one of the most efficient types of cooling tower as the design maximises water contact area, and the time of contact too.

It is a design most commonly used in large natural gas processing plants and oil refineries.

Advantages of counterflow cooling towers:

• • Design maximises the tower’s performance.
  • The droplet distribution makes for efficient water to air contact.

Disadvantages:

• • They can be noisy due to the water falling and the spraying functions.
  • Difficult to clean and can be awkward to maintain.

Natural draft cooling towers

This design of cooling tower involves water being pumped into the tower close to the top, then through a series of nozzles onto the towers fill area.

This ensures the water is evenly distributed across the tower.

At the same time, air is pulled into the bottom of the tower and flows up to meet the water coming down.

The water is cooled through the process of evaporation, with the warm water meeting the air as it descends.

The heat transfers into the air, and the cooled water collects in a basin at the base of the tower.

This type of natural draft cooling tower is typically used in power stations, and in many other larger scale industrial settings.

Advantages of natural draft cooling towers:

• • Very safe type of cooling tower.
  • Low maintenance costs.
  • Low operating costs.
  • Very efficient in terms of energy use.

Disadvantages:

• • Climate conditions may rule out the use of this type of tower.
  • Installation takes up a lot of space.
  • Very expensive to construct.

Mechanical draft cooling towers

This design of cooling tower uses a mechanism such as a mechanical blower or fan to get the air through the tower.

There are two main styles of cooling tower falling into this category are:

Forced draft cooling towers

A forced draft cooling tower has air blown into the tower using a mechanical fan.

The fan is usually located at the bottom of the tower, and the hot water inlet is at the top of the tower.

The rising air and falling water over the fill results in an effective heat transfer process.

This type of tower is a less commonly used due to issues with recirculation, but is still found in petrochemical installations and in the energy sectors.

Advantages of forced draft towers:

• • Easy to maintain.
  • Simple access to the moving parts of the cooler tower system.
  • Can be used in cases of high air resistance.

Disadvantages:

• • Large amounts of power needed to drive the fan.
  • Prone to recirculation.

Induced draft cooling towers

An induced draft cooling tower works in a very similar way to a forced draft cooling tower.

The water enters at the top, and the air from the bottom, and the water is spread across the surface of the tower using sprays.

A mechanical fan pulls air into the tower at the top, and forces it down towards the water.

This method gives a greater contact time between air and water, and this is what improves heat transfer.

An induced draft is the most commonly found method of cooling in the sugar and chemical industries, and also in large air conditioning plants.

Advantages of induced draft towers:

• • Better circulation than with the forced draft system.
  • Can be installed in a smaller space.

Disadvantages:

• • Care must be taken when installing fans, motors and other electrical components in a moist atmosphere.
  • Corrosion may be an issue.
  • Requires a fairly high level of maintenance.

Dry cooling towers

As the name suggests, this is a dry system which uses air to cool the water rather than water, without evaporation.

In order to use this sort of dry cooling, the tower needs a surface which separates the air from the heated fluid.

It is the most commonly used method of cooling processing liquids, and is often found in heat forging units.

Advantages of dry cooling towers:

• • Does not require frequent maintenance.
  • Very economical in terms of water use.
  • Reduced legionella risk.

Disadvantages:

• • Can be very noisy when in operation.

Wet cooling towers

These wet cooling towers are also sometimes known as an open circuit tower.

They use the principle of evaporative cooling.

The heated water is pumped into the tower and spread over the fill surface.

The water vapour comes into contact with the air, lowering both the temperature of the water and the air.

This cooling method is often used in the petrochemical industry, or in oil refineries and power plants.

Advantages of wet cooling towers:

• Very efficient.
• High power output.

Disadvantages:

• Can be expensive to operate.

Fluid coolers or closed circuit cooling towers

An alternative name for this type of cooler is the closed circuit cooling tower.

There are many similarities to the open circuit cooling tower but in this type of system the fluid does not come into contact with the air.

Instead, the water flows through a coil which prevents contamination from the outside air.

This cooling process is used in air conditioning systems, and in other types of ventilation and heating systems.

Advantages of fluid or closed circuit cooling towers:

• • Reduced costs for pumping.
  • Doesn’t take up much space.

Disadvantages:

• • Can be expensive to install and operate.
  • Heavier and bigger than an open circuit system.

Cooling systems training

The industrial and process water treatment specialists at Water Treatment Services have developed an extensive series of professional water and wastewater treatment training courses that includes WTS 0050 “Cooling Systems & Evaporative Cooling”.

This specialist cooling systems training course comprises an intensive one day session designed for plant operators, water treatment service engineers, facilities managers, maintenance and engineering contractors, and those with responsibility for commercial and industrial cooling towers and other cooling systems.

• Learn more about cooling systems training

Specialist industrial and commercial cooling solutions

Water Treatment Services offer a comprehensive range of innovative engineering solutions for the management of industrial and commercial cooling systems for business.

Our experts can help you optimise costs and operational efficiencies, improve plant safety and regulatory compliance, reduce downtime, achieve water and energy savings, and increase plant reliability.

With offices in London serving the South and South East England, Manchester (North West), Birmingham (Midlands), Bristol (South East England and Wales), Leeds (North and North East) and Glasgow (Scotland), supported by regional teams of specially trained technicians and consultants we can offer professional, cost effective cooling system engineering services throughout the UK and Internationally.

Contact us today to learn how our cooling tower management solutions can help you.

Further reading…

More information about our cooling water treatment services.