Closed-loop process cooling systems are gaining attention among food processors in North America as a growing number of companies realize the efficiencies they provide in cooling plant equipment, especially when compared with traditional cooling towers.
Here’s what to know about closed-loop systems and how they differ from cooling towers — along with tips for how to ensure the best return on the investment, which can include water efficiencies, cost savings and improved sustainability.
Closed-loop process cooling: a primer
A closed-loop process cooling system uses ambient air to cool process water. The technology is a proven water- and energy-saving alternative to traditional cooling towers, which many companies use for process cooling.
The operation of closed-loop systems is straightforward. The system features a central cooler that provides clean water at the right temperature to processes year round. It uses heat exchangers and an internationally patented adiabatic chamber to cool water circulated to it from process machines.
In the central cooler’s adiabatic chamber, a fine mist of water is pulsed into the incoming air stream during high ambient temperature conditions. The mist evaporates instantly, cooling the air before it impinges on the cooling coils that carry the process water. The process drops the temperature at or below the setpoint. Cooled water is then re-circulated to the facility’s process machines. A microprocessor-based controller automatically maintains targeted cooling temperatures.
Closed-loop system advantages
The biggest and most obvious benefit of the closed loop? Resource efficiency – particularly in the form of water savings.
A closed-loop system reuses water, often translating into water savings of up to 98 percent. A cooling tower, conversely, is open-loop system that does not reuse water. The result is water waste in the form of evaporation.
Cooling tower systems also leave the water exposed to outside elements and surrounding communities exposed to waterborne illnesses such as Legionella, all while requiring costly chemical treatment and disposal. Closed-loop systems, conversely, minimize these issues – along with all the related maintenance costs.
Another advantage of a closed-loop system is the ability to adapt it
to for optimum performance based on the local climate. Depending on the system, there are as many as four different stages with varying levels of energy use depending on ambient conditions and setpoint requirements:
- Dry cooling – In moderate temperatures, the central cooler continuously routes water returning from the process through heat exchangers. Exhaust fans at the top of the central cooler ensure a steady stream of incoming cool air and outgoing heated air. The heat exchangers and exhaust fans together are all that’s needed to cool process water.
- Adiabatic cooling – This function only activates in hot weather as needed to meet cooling needs.
- Increased adiabatic cooling – A patent-pending “adiabatic booster system” enables the unit to deliver even lower process cooling water temperatures in the hottest climates.
- “Free cooling” – The system automatically shuts down any chillers and lets the central cooler provide all the cool process water needed via ambient air flow, conditions permitting.
Taken together, these capabilities mean that a closed-loop system can reduce energy consumption for process cooling by as much as 50 percent compared to a conventional cooling tower/central chiller system.
System design 101
A range of factors influences the design of a closed-loop system and its performance. When planning, consider:
- System sizing: It requires an analysis of the cooling load required, as well as the process temperature to be maintained. A rule of thumb is for the system to provide 20 percent to 30 percent more capacity than needed. The calculation should also account for unclean cooling water because it can limit system performance.
- Plant location: System performance is dependent on ambient conditions. All things being equal, a system in New Orleans will typically call for more cooling capacity than a system in Chicago.
- Future plans: Whether a plant expansion is imminent or a remote possibility, the system design should support the potential need for more cooling capacity down the road.
- Available footprint: Even though it can be located on the roof or the side of the facility, consider available space for the system. Also account for acceptable noise levels and other details, such as the requirements for UL-listed electrical panels.
As the popularity of closed-loop systems grows so does the number of equipment choices. Here’s a checklist of key considerations:
- Modularity of auxiliary components: Some systems require more time to expand due to the need to connect manifolds, reservoirs and piping in the field whereas a self-contained modular system expedites installation. Also eliminated with a modular “package” is the need to drain water from the system. The net result is less worry about plant downtime during an upgrade or expansion.
- Cooling in unique conditions: Systems differ in how they cool process water in the hottest climates when high ambient temperatures routinely prevent water from reaching 90-95 degrees F (32-35 C), or in situations when the application requires water temperature in the 85 degrees F range (30 degrees C). Some systems spray extra water directly on the heat exchanger, which can lead to exchanger pitting and premature maintenance. Conversely, a system that temporarily floods heat exchanger surfaces and also drains (and reuses) the excess water reduces the potential for pitting for system longevity.
- Friendliness of programmable controls: The microprocessor-based control should be intuitive since it controls all functions. They also make it easier to optimize system performance and plan for routine maintenance. Check to see if the supplier provides remote internet monitoring services if a higher level of support is the goal.
- Use of protective materials: The materials used to construct system components vary by supplier. The shell of a central cooler, for example, might be built with galvanized steel, which doesn’t provide the same level of protection against the elements as stainless steel. Or, the heat exchangers might call for a more-resistive acrylic coating (standard on some brands) for use in harsh environments. Understanding the options and investing in protective materials often saves in the long run.
Functionality in tight spaces: A system might need to fit in a tight space, which is fine as long as airflow is unrestricted. Ensure the system is available with space-saving options, such as roof panels that allow multiple central cooling units to be positioned more closely together. Another example is extended legs that support the cooler to provide ample airflow in smaller confines, sometimes even side-by-side.
Putting the needs of the operation first
Selecting a closed-loop process cooling system for a new or existing facility requires careful planning given the importance of the application and the technology involved. Often the best advice is to partner with a proven supplier that not only has the cooling technologies expertise, but also a clear understanding of both the plant processes involved and the goals of the operation.