Thinking Energy Savings? Think Advanced Closed-Loop Process Cooling Systems

By Al Fosco

Manufacturers that rely on process cooling water to consistently produce quality products at competitive prices are regularly challenged to find cost-savings measures wherever possible, including methods to lower ever-increasing energy rates. Thankfully, closed-loop process cooling systems continue to evolve to give decision-makers more opportunities to reduce energy costs -- as well as provide other ways to improve profitability.

Straightforward Operation

With a closed-loop system, process water is never exposed to outdoor ambient air for contamination or evaporation like it is with an open cooling tower. Instead, the systems continuously reuse water without continuous evaporation.

Shown (on right) is a Frigel Microgel chiller/TCU combination unit, which can provide process cooling water temperatures from 48˚F to 195˚F with accuracy of ±0.5˚F.

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. Sometimes referred to as an "adiabatic" process, it uses heat exchangers and an internationally patented adiabatic chamber to cool water circulated to it from process machines.

In the 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. This drops the temperature at or below the setpoint, and cooled water is then recirculated to a facility's process machines. A microprocessor-based controller automatically maintains targeted cooling temperatures.

A primary advantage of closed-loop systems is often substantial water savings and associated costs. They also eliminate concerns associated with airborne diseases, such as Legionella. Other advantages compared to a traditional cooling tower include lower costs for chemical treatment and system maintenance.

Most manufacturers use closed-loop systems to deliver cooling water temperatures that range between 90 and 95 degrees Fahrenheit (32–35 degrees Celsius). The systems are typically installed when designing a new plant or renovating an existing facility.

Any operation that relies heavily on process water for cooling equipment is an ideal candidate for such a system. They are especially appealing to operations where water is in short supply but are equally attractive to companies looking to get ahead of the eventual water shortage curve and the challenges it can bring.

More Flexible Options

Many companies currently rely on a dated cooling tower/central chiller approach to meet their process cooling needs. But closed-loop systems offer more energy-efficient and flexible options.

The cooling tower/central chiller method incorporates the use of large compressors associated with the chillers to cool water for process cooling. However, since this is an evaporative approach, it uses high amounts of energy and water. Often, the system labors to deliver the same cooling water temperatures system-wide, which creates inefficiencies since not all machines require water at the same low temperature.

This Frigel Ecodry closed-loop central cooler helps SELA reduce water consumption and ensures the delivery of clean water.

Technologically advanced closed-loop systems do away with the "one-temperature-fits-all" approach, offering flexibility when it comes to energy-saving options. In fact, four different stages offer 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 cooled air and outgoing heated air. The heat exchangers and exhaust fans together are all that's needed to cool process water.
• Adiabatic cooling: As mentioned, 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, still without the use of a central chiller.
• 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.

Additional energy savings come from variable speed fans that reduce fan energy use by as much as 25 percent compared to typical on/off fans, as well as high-efficiency pumps that can also reduce energy consumption.

Taken together, these capabilities mean that a closed-loop adiabatic process cooling system can reduce energy consumption by as much as 50 percent compared to a conventional cooling tower/central chiller system.

Reaping the Benefits

Forward-thinking SELA Inc. took an advanced approach to process cooling in 2007 when it added a third extrusion line to its plant in York, S.C. At the time, the company wanted to achieve more precise temperature control of its extruder lines and cut costs without sacrificing quality.

Founded in 1983, SELA produces liquid-sampling devices for a number of industries and mainly manufactures corrugated drinking straws for businesses worldwide. The company continues to grow at a healthy pace, thanks to demand for its products and a dedicated and talented workforce. It is currently working on the addition of a fourth extrusion line and plant expansion.

After exploring traditional process cooling options, the company opted to replace two 5-ton air-cooled chillers with an integrated system from Frigel that includes a 32-ton Ecodry central cooler and Microgel chiller/TCU units. The Ecodry unit cools each of the three extruders as well as the chiller/TCU units located at each line. The central cooler also feeds a dual-zone Microgel dedicated to an injection molding machine that produces straw tips. The Microgel units are used specifically to maintain proper and consistent temperature control at the extrusion tanks and injection molding machine.

With the closed-loop system, SELA drastically reduced the need for municipal water for process cooling. It also reduced energy costs since it eliminated the air-cooled chillers and capitalized on the new system's free cooling capability. In all, the integrated system saves SELA approximately $10,000 per year in water and energy savings when compared to the alternative of a cooling tower/central chiller setup, which it originally considered for the same purpose. This would also have added more costs for maintenance and chemicals to treat water.

Cost savings aside, the approach allows SELA to maintain a stable heat profile from start to finish to ensure dimensional stability on its extrusion lines, as well as the desired color and clarity of products. Additionally, the company has increased throughput on its extrusion lines by as much as 15 percent -- all while maintaining the same high level of quality its customers have come to expect. SELA is currently adding another Ecodry central cooler to its plant to achieve further savings and provide system redundancy.

All About Planning

An advanced closed-loop process cooling system represents a significant opportunity for energy-efficiency improvements. The key is to plan ahead when given the importance of the application and the technology involved. Toward that end, look to a proven supplier that not only has the cooling technologies expertise but also a clear understanding of both the manufacturing process involved and the goals of the operation.

About the Author: Al Fosco is the Global Marketing Manager for Frigel North America. He has a Masters degree in Heat Transfer and Fluid Mechanics Engineering from the University of Illinois.