Cooling Towers

A cooling tower is a specialised industrial heat exchanger that is used to remove heat from buildings, or to remove heat from other industrial processes. Often, commercial buildings generate a substantial amount of heat through normal everyday activities, because of the number of people in a building and from other things that produce heat, such as computers, and also any other industrial processes taking place.

Cooling towers are the answer: the cooling system expels hot air into the atmosphere, and returns colder water to the chiller, which in turn means cool, fresh air can be circulated throughout a building.

Water that’s been heated by the various processes around a building is circulated through a cooling tower, where it is exposed to cool, dry air, which in turn cools the water. Heat leaves the circulating water by evaporative cooling as some of the water evaporates into the air stream, and the colder water exits the cooling tower basin and reenters the air conditioning system. This is a continuous process; hot moist air is expelled outside and cooled water returns to air conditioning equipment for recirculation. An industrial cooling tower can be larger than one for an HVAC system and is a highly effective solution to keeping the temperature of industrial processes at the desired level for operation.

As a key component of many refrigeration systems, cooling towers are found wherever cooling is necessary; for example, they’re found in chemical processing, manufacturing companies, power plants and steel mills. Also, commercial cooling towers can be used to provide cooling for large commercial buildings like airports, hospitals, hotels, or schools.

In New Zealand, cooling towers that are installed need to be compliant under NZS-3666 standard as this has been devised to minimise the risk of legionella. Cool, fresh air has many health benefits alongside the priority of eliminating this risk.

There are a range of reputable brands in the cooling tower industry. In all cases, a reputable engineer will be able to get you the best fit for your needs.

Types of cooling towers

There are three basic types of cooling tower.

1) An induced draft tower draws air up through a falling water stream using an axial fan. Typically, these sit higher than the other types, but have a smaller footprint.

2) A cross flow tower draws air sideways through (normally) two chambers of falling water. These sit lower than an induced draft tower but are long and narrow. They therefore suit certain installations where the width is restricted.

3) A forced draft tower operates with an overpressure and blows a stream of air through a falling stream of water. Both axial and centrifugal fans can be used.

The cooling tower fans produce a noise profile that needs to be verified against local requirements. For many buildings, and particularly hospitals, it is necessary for the noise level to not exceed certain limits. These requirements are normally outlined in tender or request for quotation documents. Some manufacturers have low noise fan options and these may be necessary to employ when the required noise levels are most stringent.

The fan motors may be direct drive or belt drive. The size of the motor (kW rating) and speed of operation are carefully selected to optimise both performance and to achieve the required sound profile.


Towers for HVAC systems are generally manufactured in fibreglass or steel. For certain industrial applications, wood or concrete may also be used. The structural frame is either galvanised steel or stainless steel.

For most applications, it is best to use stainless steel for all the hardware holding the components of the tower together.

The tower fill or packing is key to the efficiency of the tower operation. There are two types of fill: splash fill which interrupts the water flow and causes splashing, and film fill, which is made up of sheets of material that the water travels across.


Cooling towers are built with an access panel which allows you to inspect the tower or undertake maintenance. Because of this, access doors are necessary to enable the tower to be inspected and to replace the fill when necessary.

Under New Zealand legislation the water basin that collects the water, after it has passed through the tower fill media, must have smooth surfaces without joins or dead spots, and must be readily cleaned manually. There are requirements for the frequency of testing of the tower water and the frequency of cleaning to ensure the basin remains clean and does not become a source of contamination, especially with legionella spores.

Access is required to the fan motor to allow maintenance to be carried out. This may require the installation of ladders and platforms, especially with induced draft towers that stand higher as a rule.