Central Can Co., a Chicago-based maker of containers for food, industrial, automotive and consumer uses, needed a central chilling system for a new injection-molding operation at its facility. The company’s did not want to use a cooling tower because the evaporative cooling method air left concentrations of contaminants and dissolved solids in the water.
Instead, in late 2005, Central Can selected a closed-loop, dry-cooling system from Frigel, a process cooling company based in Italy. That system, called Ecodry, originated in Europe, where features such as the ability use less energy and provide clean process water are especially attractive due to higher energy costs and poorer water quality compared to the United States.
Central Can evaluated the options and chose to use the closed-loop system in conjunction with individual chiller/temperature controllers rather than cooling towers and chillers. The system promised to provide a dramatic reduction in water and energy consumption as well as additional savings from the almost maintenance-free operation.
Operating PrinciplesCentral Can uses a dry cooling Ecodry unit and individual chiller/temperature controllers called Microgels at each press.
The Ecodry technology starts with a closed-circuit fluid cooler instead of the evaporation-based design of a traditional cooling tower, said Steve Petrakis, president of Frigel North America, Lake Zurich, Ill. The water returning from the process is pumped into heat exchangers and cooled with ambient airflow. This process provides clean water at the proper temperature to process machines year round. The built-in control systems of the closed-circuit dry cooling technology allow operation in extreme hot or cold temperatures.
When the ambient air reaches 85°F (29°C) or higher, the system switches automatically into “adiabatic” mode. In this mode, air passes through an adiabatic chamber (in which no heat is transferred) before reaching the heat exchanger. A fine mist of city water is “pulsed” into the incoming airstream inside the chamber.
According to Petrakis, 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, hence the term “dry cooling.” To ensure consistent cooling, an advanced control panel continuously adjusts the amount of water sprayed. The humidified air precools the air passing over the coils, which drops the water temperature to 95°F (35°C) or below, even with ambient temperatures as high as 120°F (49°C).
The closed-circuit dry cooling system uses a self-draining process to avoid icing when ambient air dips below 32°F (0°C) or a power outage occurs in the winter.
“Gravity automatically drains the system’s copper pipes to protect the unit,” Petrakis explained. “The self-draining process does not require valves or any manual interaction, which ensures safe operation in extreme weather.”
The system also has built-in freeze protection that monitors ambient and return water temperatures. When the leaving water temperature drops below the setpoint, the controller halts the pumps circulating to the outdoor heat exchanger, and the system 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.
At Central Can, these automatic controls were a welcome addition for the maintenance staff, where the average tenure with the company is 15 years, said Bill Ruba, vice president of manufacturing.
“My maintenance people love the equipment because you don’t have to do anything,” Ruba said. “What more could you ask for?”
A typical injection-molding facility using cooling towers or chillers might spend as much as 5 to 10 hr in maintenance each week repairing temperature controller valves and heaters; heat exchangers on the molding machines; and condensers due to poor water quality. The closed-circuit dry cooling system eliminates these maintenance requirements. The only preventive maintenance steps required are periodic checks of water levels and filter changes while the system remains in operation.
Free Cooling CapabilitiesThe system’s design replaces the chiller/refrigeration method with free cooling, which is achieved using the closed-circuit dry fluid cooler or other nonrefrigeration cooling methods. The closed-circuit system can provide free cooling to a range of processes and devices based on the process setpoint and local ambient conditions.
In Chicago, for example, where Central Can is located, the ambient temperature is below 50°F (10°C) for 50 percent of the year (figure 1). A process requiring 60°F (16°C) cooling water (assuming a ∆T of 10°F [6°C]) would be able to take advantage of free cooling for an average of six months every year.
“The system also can be used with chiller/temperature control units for individual control of chilled or heated water at each process machine,” Petrakis added. “A single set of uninsulated pipes supplies the process water without heat loss to each chiller/temperature control unit. These units offer high flow, precise temperature control and a built-in valve that provides automatic cooling when ambient temperatures are lower than the process setpoint.”
This design can save up to 80 percent on energy costs. It also can improve processes being served by the water; the precise water temperature delivered at individual process machines positively affects productivity.
Solving the Water ProblemA significant benefit for Central Can and other manufacturers is how the system handles water consumption, disposal and treatment.
The process water in most facilities contains dust, lime, dandelions and even lily pads, which makes continuous water treatment challenging and potentially expensive. The closed design of the dry cooling system minimizes these problems and thereby reduces filtration and maintenance requirements, Petrakis said.
Continuous water consumption also is a costly issue for many facilities. Many local governments are imposing high disposal costs for concentrated and contaminated fluids. In some areas, cooling tower wastewater requires specialized hazardous disposal handling. Companies have to consider these costs when they work on cooling system installations or upgrades because these imposed fees are becoming more prevalent.
A closed-loop system minimizes environmental impact by using less water and avoiding disposal of chemicals into the ground, lakes and streams. With evaporation virtually eliminated, the closed-circuit technology poses a low risk of refrigerant gas emission into the atmosphere. Additionally, while a conventional 100-ton cooling tower might use as much as 1 million to 1.5 million gal/yr of water, a closed-circuit dry cooling system with the same capacity requires only 20,000 to 40,000 gal/yr. Water consumption is reduced by 95 percent or more compared to cooling towers.
In addition to the system’s ability to provide free cooling, further energy savings come from the elimination of big pump tanks.
“A typical 100-ton central chiller system operates with about 0.8 to 1.2 kWh/ton energy consumption, with most of the energy going to the pumping system,” Petrakis said. “Because the closed-circuit dry cooling system requires less pumping to circulate much less water, energy requirements are lower.”
Additional energy savings are obtained from the system’s use of the fans only when needed. The dry cooling system uses brushless, variable-speed DC motors to power the fans with individual automatic speed control. The motors are more efficient than traditional motors, have quiet operation (less than 57 dBa), and allow any fan to be changed while equipment is running. Overall, the average annual energy consumption of a 100-ton closed-circuit dry cooling system is 0.05 kWh/ton.
While the energy and water savings were a welcome improvement at Central Can, the system’s easy maintenance and cleanliness were the primary reasons the company chose this technology over typical tower and chilling systems, Ruba said. The system also has allowed the company to improve cycle times.
For more information from Frigel North America, Lake Zurich, Ill., a manufacturer of the closed-circuit dry cooling system, call (847) 540-0160 or visit www.frigel.com.