A cooling tower allows building owners and operators to take advantage of low cooling water temperatures and higher rates of heat rejection per square meter inherent in evaporative cooling systems.
A well maintained cooling tower enables cooling systems to perform at optimum efficiency, reliably and cost-effectively, with contractors who maintain cooling systems able to service their customers with comprehensive and routine cooling tower maintenance programs that should maintain cooling performance for many years.
Humble cooling tower
Unfortunately, the humble cooling tower is often the forgotten component of the water cooling system when it comes to maintenance, but extremely high up the table when it comes to safety, so while certain tasks are regularly carried out others can be overlooked.
A well maintained cooling tower should be able to reliably deliver its design fluid temperature
A well maintained cooling tower should be able to reliably deliver its design fluid temperature and flow rate relative to the ambient condition indefinitely, but since its heat transfer operation creates a natural ‘air-scrubber’ environment, removing impurities from the cooling air as well as the circulating water, the cooling tower needs regular routine inspections and maintenance to continue performing at its best, and a small deterioration in performance should be expected, but easily managed. Cooling towers use large volumes of ambient air to take heat away from a process through sensible and non-sensible cooling.
Critical maintenance activities
Non-sensible cooling is a term that describes heat rejection through evaporation, where air will gain moisture until it reaches saturation, which is when the air is fully laden with water at 100% RH. This increase in water content requires energy to occur and this is obtained by taking heat out of the circulating water, reducing the temperature of the water in the process.
Sensible cooling also occurs, which is where the colder inlet air reduces the temperature of the water due the difference in the air and water temperature, and in turn heats up as it travels through the heat exchange media. Because of this, one of the most critical maintenance activities of cooling systems is to ensure that the heat transfer has the best conditions to occur.
Air moving equipment
Maintenance on the air moving equipment will focus on the condition of the fans themselves
The best conditions mean that the airflow is optimal, the heat exchange surfaces are clean and correctly installed, and the water distribution is balanced and operating correctly. Unless it is a natural draft cooling tower, the airflow will be created by fans which are driven by motors that are either directly attached to the fans or operate through gearboxes or fan belts.
Maintenance on the air moving equipment will focus on the condition of the fans themselves, ensuring that the blade angles are set to achieve the necessary airflow if they can be adjusted and that the gearboxes or belts are operating properly with sufficient lubrication in bearings and gearboxes.
Heat exchange media
The heat exchange media in the cooling tower should be selected to offer the best trade-off between the tendency to foul and the amount of heat exchange surface. Maintenance on these components focuses first on the cleanliness of the heat exchange surfaces, as well as ensuring that the correct type of heat exchange media is being used and that it is properly fitted.
The distribution systems in cooling towers are also essential to efficient operation
Incorrect fill type or poor installation can lead to the packs becoming blocked quickly or could result in higher pressure drops reducing airflow. Poorly fitted fill packs can lead to air bypassing the water through gaps in the fill pack and results in loss of thermal performance and higher drift rates. The distribution systems in cooling towers are also essential to efficient operation.
Heat exchange surfaces
Heat exchange surfaces are only effective if there is a steady flow of water over them, blocked or broken nozzles can lead to an imbalance of water flow which results in variations of wetting rates or even dry spots throughout the fill where the airflow will be less effective.
Water flow, airflow and heat exchange surface are the essential ingredients in cooling tower thermal performance, but these three critical subsystems don’t make up the entire system. The remaining systems are related to safety, access and containment, which carry a significant importance when concerned with the safe and effective operation of a cooling tower.
Preventing direct sunlight
Cooling towers are ultimately maintainable through a series of interconnected subsystems
These systems include drift eliminators that prevent harmful water droplets from leaving the cooling tower, air inlet honeycombs that prevent direct sunlight from entering the cooling tower and reduce airside contamination, access systems that allow safe access for maintenance and the general fabric of tower to provide containment of fluids and protection to operators.
All these things should be considered in a comprehensive maintenance plan which goes beyond cleanliness to ensure that you have not only a safe system but a high performing system.
Cooling towers are ultimately maintainable through a series of interconnected subsystems that can all be relatively easily and cost effectively replaced. By allowing correctly maintained systems to operate at peak efficiency, they will work safely for many years.
