A Cooling Tower is defined as a device used for heat rejection in which air and water are brought into contact with one another. As direct contact occurs, water is evaporated, reducing the temperature of the water being circulated through the tower.
Industrial Water Cooling Towers are predominantly used to remove heat from various sources such as machinery or process material. Common applications include cooling water used in chemical plants, food factories, distilleries and manufacturing plants.
Cooling Towers are designed and manufactured according to the need of the site and process. They generally form part of a cooling system incorporating pipework, access systems and additional chillers and cooling units.
Towers come in varying types and sizes depending on the cooling demands of the process and other factors such as water availability, power supply and space.
How Does a Cooling Tower Work?
Evaporative Cooling Towers are the most energy efficient way of cooling water.
Water is cooled by evaporating a small proportion of the circulating water which causes the remaining water to be cooled. The evaporative process is highly efficient. Evaporative Cooling Towers are capable of cooling water to within 3 oC of the prevailing wet bulb temperature giving typical minimum cold water temperatures for the UK of 23 oC.
Heated water from an industrial process or chiller is piped to the Cooling Tower. Inside the Cooling Tower the hot water is then sprayed through nozzles onto the heat exchange surface known as ‘packing’. The pack material is designed to slow down the flow of water through the tower and increase the surface area through which the water passes to maximise contact with air. Exposure to this air, pulled through the tower via a fan evaporates a small proportion of the water producing a cooling action.
This cooled water is then pumped back to the process or chiller where it can be used and then recirculated through the system.
Crossflow Cooling Towers allow for water to flow vertically through the pack whilst air is pulled horizontally across the flow of water. Conversely, counterflow Cooling Towers are designed so that air is drawn upwards, vertically through the tower, with water falling down in the opposite direction.
What’s the Difference Between Open & Closed Cooling Towers?
An open circuit Cooling Tower can be defined as a Cooling Tower where there is no separation in the cooling loop through the process flow. The cooled water flows through the process and returns to the Cooling Tower, heated by the process, ready to be cooled again through evaporative cooling.
In Comparison, a closed circuit Cooling Tower has a primary and secondary circuit. This separates the cooling circuit from the process loop. Water is circulated over a coil within the tower, which through input from the fan delivers evaporative cooling to the process loop, which in turn, returns cool water to the application. It should be noted that it is possible to have an open circuit tower (with heat transfer pack) but create a closed circuit through the introduction of a heat exchanger, which achieves separation of the process side and cooling side of the system.
For a more in-depth look at the differences between Open & Closed Cooling Towers, take a look at our guide; Adiabatic Coolers Vs Open Cooling Towers.
Why Would You Need a Cooling Tower?
Water Cooling Towers are required in commercial and industrial processes where you need to remove heat from water. For example, in tinned food production, water is used to cook food within the can. This process demands a great deal of water at a given temperature. The Cooling Tower cools the water after use so that the process can be repeated again and again with limited evaporative loss.
How Do You Build a Cooling Tower?
Cooling Towers can be factory assembled or erected on site.
Vistech Cooling Systems Ltd is the UK agent for EWK GRP Cooling Towers, manufactured in Europe. The towers can be fully or partially assembled in the factory and then transported to the UK ready to be sited and installed as part of a complete cooling system.
The design of cooling water towers with synthetic resins differs mainly from conventional designs by its substantial cooling capacity in a reduced amount of space. The lightness in weight and small space required make the installation of these towers easier on rooftops, terraces, pedestals and other mounting sites. In general, no reinforcing of the base will be necessary to support towers.
How Expensive is a Cooling Tower?
The cost of a water Cooling Tower varies depending on the design duty characteristics and material of construction.
Purchasers should consider the total cost of ownership when buying a water Cooling Tower including, operational costs, maintenance and refurbishment costs and life span of the tower.
How to Reduce Evaporation Loss in Cooling Tower?
The method of cooling water with Cooling Towers is by the process of evaporation, it is therefore not possible to eliminate evaporation in its entirety. Nonetheless, it would be prudent to consider ways in which water loss can be limited from the system. For example, the addition of Drift Eliminators not only aids in limiting dangerous aerosols from entering the environment but also helps with water savings by returning water droplets back to the tower.
Water loss from a cooling system can also be minimised by:-
- Minimising the heat-load onto the Cooling Tower by using waste heat for other process heating requirements where possible
- Ensuring that the Cooling Tower sump operating level is correctly set to avoid overflow
- Ensuring the bleed rates are set correctly and reduced where possible without causing fouling, corrosion or scaling within the cooling system
- Using a softened water make-up particularly in hard water areas
- Ensuring that leaks are fixed
How are Cooling Towers Maintained?
Government legislation means that demonstrating proof of maintenance and cleanliness of Cooling Tower equipment is paramount.
A Cooling Tower will need to be regularly cleaned internally and externally by professional operatives who understand and have experience of the cooling equipment. This ensures the safe running and performance of the tower as well as extending its life span.
Being able to safely access plant, machinery and difficult to reach areas of your building or manufacturing site is vital for maintenance and cleaning purposes. Access to the fan and fan motor should also be provided to allow for regular maintenance and inspection.
Internally a permanent safe clean floor should be installed under the packing. This is typically in the form of an open mesh GRP grate. This has two benefits. Its primary benefit allows the operative to work at height under the Working at Height Regulation without the need to install a temporary platform and secondly provides a structure that distributes the weight of the packing – increasing its useful working life.
Ensuring the performance of the Cooling Tower packing is critical to the overall performance of the Cooling Tower. Fouled pack also presents an ideal breeding ground for harmful bacteria. Pack should be regularly inspected to check for scaling and fouling levels. Light weight, cross flow, modular packing will not only maintain the system performance but improve the maintenance regime as it is easy to remove, clean and replace as required.
Cooling Tower packing will ultimately require replacement. Overtime, it may become too fouled to clean or brittle through chemical and UV damage as well as cleaning over a sustained period.
What Are the Different Types of Cooling Solutions?
There are many combinations of cooling equipment and variations to their design.
As well as evaporative water Cooling Towers other cooling solutions include Adiabatic Coolers and Dry Air Coolers, Air Cooled and Water Cooled Chillers.
Adiabatic Cooling typically uses less than 10% of the water consumption that a traditional Cooling Tower would consume. Adiabatic cooling provides the option to cool water to within 3oC of the ambient wet bulb.
Dry coolers cool by sensible cooling only. Heat is conducted to the air from the surface of a finned coil through which the cooling water flows. They are able to cool the water to within 3 oC of the dry bulb temperature which for typical UK summer design conditions means that minimum cold water temperatures of between 35 oC to 38oC are possible. Dry coolers are advantageous in areas where water is scarce.
Air cooled and water cooled chillers are suitable for a range of applications including air conditioning, process cooling and data cooling but are substantially higher in both capital and operating costs than other forms of cooling.
Air-cooled chillers cool by a combination of refrigeration and sensible cooling of the refrigerant. In simply terms it is a refrigeration machine close coupled to an air-cooled condenser.
Water cooled chillers provide chilled water in the same way that air-cooled do but instead of the heat being rejected by air cooling the heat is rejected through a water Cooling Tower from the condenser circuit.
Water Cooled Chillers are ideal for HVAC chillers, building services chillers and comfort cooling chillers, as well as for other cooling application where a water circuit source is available to cool the condenser such as a Cooling Tower or dry air cooler.
Martin Crunden has over 40 years experience in the industrial and commercial cooling market. He has provided guidance and advice to leading industry bodies on cooling system design and technology. He is currently Managing Director of Vistech Cooling Systems Ltd based in the UK.