Many choices are available for designing and customizing a cooling system for process cooling. The most basic choice is whether to choose an open- or closed-loop system for the application. Factors such as reliability, ease of operation, energy efficiency, water usage and total cost of ownership can come into play when choosing a system. While there are many options, with the proper planning and strategy, a closed-loop system can bring benefits not attainable by traditional open-loop systems.
Reliability and Ease of Operation
The main focuses of any process cooling application are keeping the equipment up and running and decreasing scheduled and emergency downtime, which can have a tremendous impact on a cooling system as well as the bottom line. System maintainability and reliability directly impact the ability to maximize uptime.
The fundamental advantage of a closed-circuit cooling tower and a closed-loop system is keeping the whole system cleaner. The closed loop makes the eases system easier maintenance and improves reliability and performance, protecting the other components in the system against fouling. An open cooling tower can introduce dirt and other contaminants to the process fluid. Over time, these can build up inside the cooling loop, or worse: directly within the equipment if a heat exchanger is not installed. This requires the arrangement of all the connected equipment, including pumps and filters, to be selected for operation in a contaminated environment. A system running a closed loop prevents the introduction of dirt and debris to the process fluid by isolating the fluid inside the coil of the closed-circuit cooling tower. This allows the fluid to maintain a higher level of quality, which protects the system’s equipment and minimizes fouling.
With easy-to-maintain equipment, the system is more likely to receive the routine maintenance it needs to stay operational. By closing the loop, maintenance of the cooling system has been simplified while reliability has increased.
Once it has been determined that the closed-circuit cooling system provides reliable performance, it is important to consider how efficiently the system can operate. Water and energy usage are the primary drivers when evaluating a system’s efficiency. By addressing these factors everyday performance of the system can be optimized.
Water is used throughout the cooling system, but the limiting factor for water quality typically is determined by the composition of the process fluid. The total suspended solids, total dissolved solids, pH and other aspects of the process fluid can require much more attention to detail than water used for makeup or other side-stream applications.
Because a traditional open cooling tower does not separate the process fluid, it puts a larger burden on water usage. The cycles of concentration must be carefully monitored and the quality control of the water becomes a critical aspect of system performance. The process fluid is separated from the spray water, which allows for lower quality makeup water at higher cycle of concentrations when the system is closed. This reduces water usage of the system while promoting conditions that achieve peak performance and provide higher quality fluid in the loop.
In addition to contaminants, an open cooling tower can introduce excess air into the cooling system. Air trapped in the process fluid negatively affects its ability to transfer heat. If a heat exchanger is used to protect the process loop from air or contaminants, this will result in thermal performance losses. As the thermal performance decreases, energy usage increases to maintain the specified fluid temperature.
Air-cooled systems rely solely on sensible heat transfer and operate at considerable lower thermal efficiencies than evaporative cooling systems, which make the loss in performance more clear. Because they are dependent upon the ambient dry-bulb temperature, they supply higher temperature fluid than evaporative cooling equipment. If the temperature of process fluid supplied to a chiller increases by 1°F, this can result in 3 percent loss in efficiency for the chiller. Using an evaporative cooled system maximizes system performance while minimizing energy consumption.
Reducing Energy Costs
The total cost of ownership for purchasing, operating and maintaining a system is directly related to its efficiency. There is a clear connection between energy efficiency and energy costs. As the energy use decreases, the operation costs for purchasing the energy also decrease.
The water costs for the cooling process have more variables that depend on many different aspects of the system. In a closed-loop system, the ability to use lower quality spray water means that less makeup water is needed. This saves not only on the supply cost of water, but it also saves on the chemical treatment associated with that water. Because spray water quality can be lower, it may be possible to reclaim the source of makeup water from another process. This saves on both supply and sewage costs incurred for water in the closed-circuit cooling tower. Additionally, with a reduction in fouling in the process loop, the lifespans of all the downstream components are maximized. This saves on maintenance and replacement costs for individual pieces of equipment throughout the lifecycle of the system.
In addition to the reoccurring operating costs, it is possible to save on initial installation costs. Keeping the process fluid in a closed system allows you to prioritize which components need upgraded materials of construction. This means a stainless steel, open cooling tower may be needed for a given application, but when using a closed-loop system, it may be possible to use a traditional galvanized, closed-circuit cooling tower. In addition to simplifying the materials, it may be possible to reduce the total number of components needed in a system. For example, since the process side is kept isolated, the heat exchange loop may be eliminated. This saves money on equipment such as the heat exchanger and pump and the installation labor for installing and balancing the system.
Beyond the more traditional ways of cost savings, there are creative solutions for using a closed-circuit cooling tower to save on first costs and annuals costs of the system. These tend to be a case-by-case basis, but everything from the specific process to the local environment can present opportunities for savings. Facilities with rigorous maintenance schedules can explore cleanable coils, removable headers or other service friendly options that can help reduce labor. Buildings located in cooler climates might be able to take advantage of dry winter operation. Areas with elevated water costs can optimize energy and water usage by utilizing a hybrid closed-circuit cooling tower offering optional wet, dry or adiabatic operation.
|See the related web exclusive content, An Optimized Solution for Closed-Loop Cooling|
In conclusion, every application has multiple solutions that can address specific needs. Selecting the right system based on its benefits can better align which solution is right for a given application. Closed-loop systems provide increased flexibility for isolating critical components and removing interruptions within the cooling loop. Utilizing these solutions that flow through the entire system can provide greater opportunities to increase the reliability of equipment, simplify system operation, optimize efficiency and lower costs, all while reducing the risk of downtime.
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