A Case Study in Rx for Maintenance-Intensive Cooling Towers

By Consulting Specifying Engineer Staff June 24, 2005

Metal cooling towers lined with galvanizing or other coatings have been around for a long time—in many instances, far too long. Like an aging fighter, decades-old metal cooling towers frequently become high-maintenance, while performance drops off sharply. Over time, these towers are increasingly thin-skinned and inefficient, and can cause unscheduled process disruptions.

Secondary damage can also be caused by chronic “leakers,” and outdated tower fans and motors often consume more energy than necessary. All of this adds up to a classic “money pit” for facility maintenance personnel that rely on cooling towers to support HVAC equipment.

In the past, the prevailing cure for a leaking or corroding cooling tower was simple (although not easy). You either repaired it or replaced it. However, repairs such as re-skinning or coating tower linings often take weeks and shut down critical processes if maintenance isn’t already scheduled. Welding patches on galvanized linings might work, but typically not for long.

”We were spending between $5,000 and $10,000 a year on cooling tower repairs—patching metal, putting in rubber seals and gasketing. In other words, Band-aid fixes just to keep the tower from leaking,” says Marvin Richer, owner of the Crystal Lake University Center, a facility using the cooling tower on an absorption-chiller.

On the other hand, replacing towers is time-consuming and expensive, as is the installation of additional towers to increase cooling capacity.

”Given our choices, we were most likely going to install a new tower similar to the old one,” Richer says. “But first I wanted to look into a new plastic type of cooling tower that was said to be more reliable and require less maintenance than the old-fashioned metal-lined models.”

What Richer was looking for has become a new prescription for replacing ailing cooling towers or adding capacity: engineered molded plastic cooling towers. Just as advanced plastics have replaced metal in many high-tech and industrial applications, plastics also offer a remarkably comprehensive solution to the chronic deficiencies of metal-skinned cooling towers.

When selecting cooling towers, the focus of any engineer beyond efficiently meeting duty requirements is on reliability, reduced maintenance and ease of installation. Given these considerations and a choice between metal and plastic towers, many engineers are opting for the latter, which are now high-capacity, lightweight, and often more energy efficient.

”As the tower got older not only did we have ongoing leak problems, we started to have a structural problem,” Richer explains. “Water is pretty heavy, and the tanks that hold the water on the bottom were getting heavier and heavier as we added more and more materials to fix the leaks. All that weight was beginning to bend the structural members that held the cooling tank together.”

Metal cooling towers like Brock Equipment’s are also subjected to constant changes in pH, requiring chemical treatments that attack the galvanized metal lining, essentially wearing it out in just a year or so. Environmental conditions such as sunlight, pollution, salt air, and harsh process chemicals may also contribute to galvanized steel’s early demise. With this inherent vulnerability, metal-lined cooling towers generally carry only a one-year warranty.

In the past, plastic cooling towers were considered “too small” for many comfort cooling applications. For that reason, galvanized metal cooling towers were deemed the primary choice for packaged applications above 250 tons. Unfortunately, over time these galvanized metal towers have recurring maintenance costs and costly process downtime.

However, factory-assembled plastic towers can now be combined to provide up to 2,000 cooling tons in a single, modularized unit. Modular cooling towers also facilitate an extra margin of cooling capacity that can be advantageous in adjusting to operational heat load or outflow changes, or in upgrading to meet future cooling requirements.

The modular design of plastic cooling towers has also introduced new flexibility in conserving valuable real estate. By molding towers in a rectangular shape, some manufacturers enable users to cluster cooling towers in a group that occupies a much smaller footprint.

”With the new system we actually got more cooling with less tower,” says Richer. “Our old 45x20x18 metal cooling tower was replaced by a lightweight plastic model that is only half that size, yet has slightly greater cooling capacity.”

For more information on plastic cooling towers from Delta, click here .