Utilities Manager: Cutting Costs In Process Cooling
Kathy | November 1, 2007
New to North America, this proven technology soon may change the way you approach process cooling in your operations.
Although some technologies are constantly changing, at least one has remained virtually unchanged for decades: cooling tower systems. New technology in this arena, however, has at last hit the United States—and it’s changing everything about the way many people approach process cooling. As a utility manager, you might find you want to change your approach, too.
Ecodry is a closed-loop, dry-cooling system that nearly eliminates wastewater problems and drastically lowers energy bills. It does so by completely eliminating traditional cooling towers and the typical hassles associated with them.
The current situation
For over 80 years, cooling towers have been at the center of industrial cooling despite the ongoing expense of water treatment, regular heat-exchanger cleaning, difficult cold-weather operation and substantial water and energy consumption. Traditional cooling towers rely on constant evaporation of water passing through the air, resulting in an ever-increasing concentration of contaminants and dissolved solids. Until recently, cooling tower maintenance professionals have accepted these problems as inevitable. This new system, from the Italian company Frigel, offers an alternative.
While new to North America, the Ecodry system has been proven in well over 5000 installations worldwide. The concept originated in Europe, where energy is more expensive and water quality has been a huge challenge, making the perfection of this technology imperative.
In place of a traditional cooling tower, the Ecodry features a closed-circuit fluid cooler. The water returning from the process is pumped into heat exchangers and cooled with ambient air flow. This process provides clean water at the right temperature to process machines year-round.
The closed-loop design keeps heat exchangers scale-free, minimizing the need for costly chemical consumption and disposal. The ultimate result is a modular, flexible, preengineered system that produces the lowest operating cost and highest reliability for installation anywhere.
The endless water challenges related to cooling tower systems include high levels of consumption, chemical treating needs and disposal issues.
Over-consumption occurs as water either evaporates or is dumped down a drain. Both events are inevitable with traditional tower systems, whereas the new closedloop system described here never exposes water to the elements—making it possible to use the same clean water over and over again. The reduced water consumption, when compared to conventional cooling towers, is up to 95%.
Most facilities’ incoming process water is not what you would call ideal. That’s why, in an open cooling tower system, continuous water treatment becomes an expensive part of everyday operations. It’s common for a local chemical representative to visit a plant every couple of months to test and adjust the water. In closed-loop, dry cooling, adjustments are made up front if needed. The time and resources spent on regular testing and treating are completely eliminated.
Many facilities also are struggling with local government regulations on contaminated water disposal. These facilities face large dumping fees, fines or the need to call a service to haul away chemically treated wastewater.
This type of closed-loop system minimizes environmental impact by using the same clean water continuously and not disposing chemically treated water into the ground, lakes and streams. With evaporation virtually eliminated, the Ecodry’s technology poses the lowest risk of refrigerant gas emission into the atmosphere.
According to Frigel, the Ecodry system can reduce energy consumption significantly by eliminating big pump tanks and using efficient fans that only run when needed.
One of the key energy-saving components is the advanced microprocessor featuring an easy-to-use, remote interface. It not only controls functions of the system but makes the adjustments needed for the system to run at optimum efficiency. Based on ambient temperature and process water temperature, the controller adjusts fan speed and initiates evaporative functions to generate the required cooling capacity in the most efficient way possible. The microprocessor also manages the pumping stations to save energy and boost equipment longevity by controlling water pressure and pump rotation.
To power the fans, the system uses highly efficient, brushless, variable-speed DC servo motors with individual automatic speed control. These maintenance-free motors are 30% more efficient than traditional motors, feature quiet operation (less than 57 dBa), allow any fan to be changed while the equipment is running and offer increased reliability and durability. Overall, the average annual energy consumption of this closed loop system is 0.05 kWh/ton.
How the system works
Besides continuous maintenance, chemical expenses and wasted water, cooling towers also fall short of optimum performance when ambient temperatures soar above 85 F or drop below freezing.
When ambient air reaches 85 F or above, the Ecodry system automatically switches into “adiabatic” mode. Air passes through an adiabatic chamber before reaching the heat exchanger. A fine mist of tap water is “pulsed” into the incoming air stream inside the chamber and humidified air drops the water temperature to, at or below 95 F—even with ambient temperatures as high as 120 F.
The pulsed water evaporates instantly, cooling the air before it impinges on the cooling coils that carry the process water. The coil fins remain dry, thus the term “dry cooling.” To ensure consistent cooling, an advanced control panel continuously adjusts the amount of water sprayed.
Units can deliver heat loads of 17 tons or can be daisychained to deliver capacity up to 3500 tons.
What happens if ambient air dips below 32 F when the plant is not running or a power outage occurs? The Ecodry system’s copper pipes are automatically drained by gravity to protect the unit and avoid icing. Furthermore, it is done without the need for valves, antifreeze or any manual interaction with the system at all. The self-draining process provides completely safe operation in extreme weather conditions.
This function also allows the system to be used for applications where contact with glycol is not tolerated. For facilities in cold-weather climates, partial glycol supplement is an option if the user requests it. It’s not preferred, however, because pure water has the best heat-transfer properties.
For colder weather, Frigel’s technology includes builtin freeze protection that monitors ambient and return water temperatures. In a pure-water system, if the leaving water temperature drops below the setpoint, the controller halts the pumps circulating to the outdoor heat exchanger (made entirely of non-corrosive copper, aluminum, bronze and stainless steel) and the Ecodry automatically drains its water back to an indoor reservoir. The central system then circulates cool water from its indoor tank until it becomes sufficiently warmed to permit sending it outdoors again to the heat exchanger.
Central chiller replacement
The closed-loop system also can be used in conjunction with chiller/temperature control units (Microgels) for individual control of chilled or heated water at each process machine. A single set of uninsulated pipes supplies the process water without heat loss to the chiller/ temperature control unit at each machine. These units offer high flow, precise temperature control and a builtin valve that provides automatic “free cooling” when ambient temperatures are lower than process setpoint.
“This setup is really great. In the winter we get free cooling because we’re sending water outside to cool down to temperature,” said Steve Streff, president of SK Plastics, whose company uses Frigel’s technology (see sidebar below). “Sometimes, the compressors don’t even run because the water’s already cool enough. So, we’re saving money and energy on several fronts.”
Free cooling means using the closed-loop fluid cooler or other non-refrigeration cooling methods in place of the chiller/refrigeration method. The Ecodry can provide free cooling to a variety of processes/devices based on process setpoint and local ambient conditions. This can save up to 80% on energy costs and improve processes the water is serving because of the precise water temperature delivered at individual process machines. This can have quite a positive impact on productivity. UM
SK Plastics Molding Inc. in Monroe, WI, once had a conventional cooling tower system, as so many in the industry do. The company always was having trouble with contaminants in the water, dumping that chemically treated water into the environment and then needing to add more chemicals all over again. When it came time to look for a new system as part of plant expansion, company leaders were determined to consider alternatives.
“We’re in a rural area. The water’s terrible,” says Steve Streff, SK’s president. “There’s dust in it, lime, lily pads and dandelions. The water treatment people have to come in and bleed-off all the chemicals added to it. Our heat exchangers were getting plugged and our molds were starting to lime up.”
Streff met with representatives from Frigel North America to discuss their closed-loop, dry-cooling system. What he learned soon started to make sense for his operation. While he was at first skeptical about a system so different from the one to which he was accustomed, the fact that the Ecodry didn’t require constantly adding water and chemicals had significant appeal.
“We’re now running just one waterline into the new room that breaks off into chillers. And there’s no tower,” Streff notes. “We just have two little 500-gallon tanks out back. When we shut down, there’s nothing to drain. And the Ecodry looks like a big radiator; it’s not up on the roof, so it’s easy to service. Our maintenance guy loves it.”
Streff also points out that with the Ecodry system in place, SK Plastics even has eliminated checking or cleaning the hydraulic heat exchangers when the company conducts its annual maintenance teardowns.