Have you ever seen large cylindrical or rectangular structures around industrial areas, or on top of buildings?
They are cooling towers – an underrated but crucial component used in many industries for the purpose of power generation, manufacturing, air conditioning systems (HVAC), and more.
Generally, cooling towers help remove excess heat from hot water or other fluids running through a system, transferring it to the atmosphere through evaporation. This cooling process is vital for dissipating heat from these processing systems, to ensure it runs smoothly and thus reduces the risks of breakdowns and fire hazards.
In this post, we will explore the different types of cooling towers, how they work, and what to consider when choosing a cooling tower, depending on your set of requirements.
Types of Cooling Towers
Most industries choose between two main types of cooling types – crossflow and counterflow cooling towers. The difference between them is defined by their air-to-water flow in the tower.
1. Crossflow Cooling Towers
As its namesake, crossflow cooling towers function in a way where heat transfer is done by having the flow of air perpendicular to the flow of water. Or to be more direct, the air moves horizontally across a vertical stream of water. When hot water flows down the tower with the help of gravity, it comes in contact with the cool air flowing horizontally across it. The cooled water is then collected at the bottom and reused.
A key advantage of crossflow towers is that they usually are easier to maintain, as the system is comparatively simpler in design and has a larger area for easy maintenance access.
They also consume less power and energy, making them the ideal choice if you are looking for an economic system. When sizing the water pump for a crossflow tower only the height from the pump to the top of the tower and the friction loss in the piping, including any flow control valves, need to be considered.
However, a disadvantage of a crossflow cooling tower is the footprint. Due to the method by which air interacts with the process water, the footprint of the cooling tower is larger.
2. Counterflow Cooling Towers
On the flipside, in counterflow cooling towers air is drawn upwards vertically to meet the flow of falling hot water in the fill. With the airflow moving upwards, pressurized spray nozzles are used to distribute the water evenly over the fills. The opposite direction of water and air increases the contact time of both, producing an efficient heat transfer.
Counterflow cooling towers are less prone to issues like algae growth, blowing dust, and dirt that are prevalent in a humid climate like Malaysia.
In a counterflow tower, the process water is pumped into a header, then distributed through branch arms and nozzles, creating a pressurized water distribution system. When sizing the water pump for a counterflow tower, the height from the pump to the header, the friction loss in the supply piping, and the pressure drop through the branch arms and nozzles all need to be considered.
Due to the compact design of counterflow cooling towers, there is limited space to access the components which makes maintenance and repair more complicated and time-consuming.
Type of Cooling Tower Classifications
Now that we’ve covered the different types of cooling towers by their air-to-water flow, we can further break down their classification by their difference in air flow generation – basically how airflow is introduced into the system.
1. Induced Draft
In an induced draft cooling tower, fans are located at the discharge (at the top) to draw air upwards – from the bottom, throughout the tower. Hot water is then distributed over the fill material. As air is drawn upwards, it comes into contact with the falling water to facilitate the cooling process.
Induced draft cooling towers consume less power and have a lower noise level, as it takes advantage of the natural stack effect to draw air through the tower.
Benefits of induced draft towers:
- Requires little space for installation
- Reliable and stable performance
- Reduced possibility of air recirculation
2. Forced Draft
A forced draft cooling tower is designed with fans positioned at the base of the cooling tower, forcing air into the tower with a blower-type fan. Forced airflow from the bottom of the tower travels upwards and comes in contact with hot water for heat exchange.
This type of mechanism allows for the ability to work with high static pressure. Such setups can be installed in more-confined spaces and even in some indoor situations.
However, forced draft towers consume more power than an equivalent induced draft design and are relatively more prone to recirculation if not ducted.
Benefits of forced draft towers:
- Lower noise levels
- Powerful operation
- Ability to overcome static pressure
3. Natural Draft
Natural draft cooling towers have no mechanical drivers or fans to create airflow through the cooling tower. Warm, moist air rises naturally due to the density differential compared to the dry cooler outside air. The warm moist air in the tower is less dense than the relatively cool (denser) air outside the tower. The moist air buoyancy produces an upwards current of air through the tower.
They are usually quite large and tall to induce adequate airflow from the outside environment, can cost more to build, and are usually used for applications when a large constant cooling requirement over many years is required.
A disadvantage of natural draft-type cooling towers is that they have lower reliability as they are more affected by ambient wind and temperature changes.
Advantages of natural draft cooling towers:
- Low energy costs.
- Environmentally friendly.
- Low maintenance.
How to choose a cooling tower
Now that you know the difference between the two types of cooling towers and their different mechanisms, how do you choose the right cooling tower?
It is important to consider the size and type of the tower, the climate of the area, and the specific needs of the application.
For example, a heavy-duty industrial-type cooling tower may be necessary to cool a large manufacturing facility, while a smaller tower may be sufficient for a smaller shopping mall.
Among some specific needs that should be considered:
- Desired energy efficiency
- Water consumption level
- Maintenance cost
- Space constraints
- Water quality
- Noise level restrictions
To help you get started, first, consider the type of cooling tower you need:
Considerations | Crossflow Cooling Towers | Counterflow Cooling Towers |
| Space Constraints | Suitable for areas with larger space. Two sides of air intake are required for crossflow towers. | Suitable for areas with space limitations due to its compact design. Four sides of air intake are required for counterflow towers. |
| Maintenance | With its typically larger area, it is more accessible for regular maintenance. | With a smaller footprint alongside a more efficient air and water heat transfer, it is less accessible for maintenance. |
| Power and Cost Efficiency | As it is built on a gravity-based system, this system consumes less energy and is cost-efficient. | A counterflow cooling system often requires a higher installation cost and consumes more power which leads to a higher cost to maintain in the long run. |
After deciding the type of airflow for your ideal cooling tower, go deeper into selecting the type of airflow generation mechanism you want them built with.
| Considerations | Induced Draft Cooling Towers | Forced Draft Cooling Tower |
| Installation Location | Require an open space with minimal obstruction for airflow as the air is induced through the tower. | Suitable for confined spaces with high static pressure as the air is pushed through the tower. |
| Power and Cost Efficiency | This design requires less fan power, hence lower operating costs. Economical design with low initial cost. | This design consumes more power and therefore increases the cost of operation. Equipment cost is higher. |
| Cooling Capacity | Suitable for small and large applications. | Suitable for small and large applications. |
If you’re unsure about which cooling tower system is better suited for your requirements, feel free to speak to our team. We’ll be happy to understand your needs and provide a free consultation to help you make the right decision.
Conclusion
Cooling towers are an essential component in various industries, and it’s important to choose the right type for your application.
We hope this post has given you some considerations to think about – such as cooling capacity, maintenance, power, and cost-efficiency, before settling for a cooling tower brand or type in the market.
Again, it’s always best to consult a cooling tower specialist to make an informed decision. Request for a free consultation with our Threcell team or just drop us a message.