4 Tips for Ensuring Top Cooling Tower Performance
Expert design and timely maintenance lengthen cooling tower service life and boost efficiency.
Cooling towers are well suited for use in industrial, power generation and HVAC applications. Within these three broad categories and the many applications they encompass, cooling towers perform the same general function: They efficiently remove and reject heat from a process or building.
This article will present four tips to help ensure top cooling performance in every application. Improving the cooling equipment — from system design through long-term maintenance and upkeep — helps ensure reliable evaporative cooling. Together, these tips can help end users maintain their cooling towers so they perform as effectively and efficiently as possible.
Tip 1: Determine that Cooling Tower Technology Is Suitable
The first step toward effective, efficient cooling tower performance is to determine — before investing in the technology — if it is suitable for its intended end use.
Within the categories of industrial, power generation and HVAC applications, cooling towers are used for vastly different processes. In industrial applications, the cooling tower is used for the rejection of large amounts of heat generated in manufacturing processes, steel and paper mills, and petrochemical refining. Likewise, in power generation applications, the cooling tower rejects excess heat from power plants. In HVAC applications, the cooling tower provides comfort cooling in buildings that are too large for cost-effective air-cooled systems.
The amount of cooling required matters. In smaller applications, where less heat is generated and needs to be rejected, air cooling via condenser coils and fans is adequate to meet process or comfort cooling needs. As process heat generation or building size increases, much larger equipment becomes necessary, and these air-cooled products become less cost effective. In applications where air-cooled equipment and energy consumption are prohibitively expensive, water-cooled systems in conjunction with cooling towers offer a cost-effective, energy-efficient cooling alternative.
Cooling tower technology is especially useful in relatively low humidity, cool climates and in areas where water is readily available. In these environments, the evaporation that is at the foundation of cooling tower operation occurs more readily. Cooling towers may not be particularly well suited to smaller applications — for example, those that are less than 100 tons of cooling — because they require a significant up-front investment and support infrastructure. The operating costs and resulting total cost of ownership (TCO) of cooling towers, however, often are lower than those of air-cooled technology. In such applications, cooling towers also can deliver better economic payback as the application size increases.
Water-cooled systems with a cooling tower start becoming attractive in the 100- to 400-ton range. They become a clear-cut preference in large-scale applications of 400 tons and above. Experts at cooling technology companies can help OEMs seeking process cooling equipment determine whether cooling tower technology is suitable for a given application.
Tip 2: Establish Proper System Sizing
After determining that a cooling tower is the best choice for a given application, the next critical step toward top performance throughout the tower’s lifetime is to properly size the cooling tower. Cooling towers operate on the principle of removing heat via evaporation by spreading water across PVC heat-exchange media called fill. Because of this, the surface area available for the water-to-air interaction within the tower is the greatest factor in determining the tower’s capacity.
Proper sizing of a cooling tower requires an in-depth understanding of the process or comfort cooling needs of the given application. Experts consider these needs along with humidity, temperature and other average local weather data to calculate the surface area of water (and, therefore, size of tower) that is required.
In some instances, experts may make use of proprietary software that takes various parameters into account to provide customers with several different cooling tower options. Customers then are able to assess the options based on factors such as:
- Expected overall energy savings.
- Up-front cost and expected total cost of ownership.
- Sound levels.
- Percentage of overall capacity met.
Although proper tower sizing is the goal, process cooling equipment buyers may choose to undersize the cooling tower due to cost. This can force other pieces of equipment in the water-cooled system to work harder. For industrial and power applications, downtime can be an extremely costly risk if process water temperatures exceed the limits of the cooling tower or related equipment. Alternately, the equipment buyer may choose to oversize, perhaps paying more up-front for a system that will be large enough to handle even the extreme cooling needs projected for a given application.
Tip 3: Design for End Use
When considering the design of a cooling tower system, it is of critical importance to design for the tower’s intended end use. A large part of that is the system’s size. However, materials used, water treatment capabilities and redundancy are other important aspects of cooling tower design. All of these factors of design work together to help provide for minimal downtime and maximum process uptime in process applications.
The materials used to construct the cooling tower itself must be appropriate for the environment in which the tower will be installed. If it is to be installed on the coast, where it will be exposed to sea air, or in or near a chemical plant, the corrosive nature of the air can cause damage to the tower components. In these cases, if materials are not selected properly, components can degrade over time and structural integrity can be threatened, leading to unplanned downtime. Also of concern in chemical-plant applications is the presence of chemicals in the water used for cooling. Depending on the chemicals present in the water, this can lead to fill media being destroyed and cooling tower efficiency being severely reduced.
Customers in these environments may choose to use stainless steel instead of galvanized steel for the construction of their tower. While stainless steel is more expensive, it offers corrosion resistance and a longer lifespan. If chemical contamination of the process water is suspected, a filtration or decontamination system may be necessary to increase cooling tower service life, or the fill media may need to be replaced more frequently than in other applications. Other potential issues with water — for example, high solids if water is taken from a local freshwater source rather than municipal water supplies — can be addressed through proactive system design and careful maintenance.
A final key consideration in the design of effective cooling tower systems is the introduction of redundancy in applications such as in a power plant where it is especially necessary to avoid downtime. In these cases, the additional cost of redundancy within the cooling tower outweighs the cost of an outage or downtime from the deformation of PVC fill material due to excessive heat.
Tip 4: Inspecting and Performing Regular Maintenance
Cooling towers do not require extensive, frequent maintenance. Timely, periodic maintenance, however, can significantly lengthen cooling tower service life. The most important aspect of cooling tower maintenance is maintaining water quality. In addition, keeping mechanical parts well lubricated and inspecting the tower to ensure structural integrity are other critical maintenance steps to ensure safety and long service life.
Effective water treatment helps keep the cooling tower fill media clean and keeps scale from forming in the system’s pipes, both of which positively impact efficiency and effectiveness. Each cooling tower user has a different water supply and, therefore, different water treatment requirements. Regardless of whether filtration, UV light, chemical decontamination or another water treatment method is employed, it is important that cooling tower users are aware of their water quality and choose treatment options accordingly. Users also should remain aware of the system’s blowdown and drift. It is a recommended practice to replace a portion of the water in the system at regular intervals. This practice, known as blowdown, helps to avoid the issues of accumulated solids and improper pH balance that occur when water evaporates away from the system but leaves solids and chemicals behind.
The fan in use in a cooling tower contributes to a significant amount of the system’s overall cooling power. Users should expect to regularly grease the fan’s motor and replace the oil in its gearbox in order to keep the system operating at or near its maximum capacity.
Finally, users should perform routine inspections of the cooling tower to identify maintenance issues like fouled PVC fill material. The vibration from the moving equipment in the system can cause structural integrity issues such as bolts working loose. Such issues can cause the pitch of the fan to be incorrect.
Inspections — occurring after approximately five years on a new tower and then annually thereafter — can identify potential issues before they lead to safety concerns or damaged equipment. Additionally, periodic inspections allow users to identify issues and schedule downtime rather than waiting for problems to cause significant unplanned downtime. PC