When it comes to large commercial systems, cooling towers seem to receive less attention than other system components. According to Chris Walton, assistant manager, marketing communications, Baltimore Aircoil Co., “The cooling tower is often the forgotten component of the system when it comes to maintenance.”
Yet, cooling tower maintenance is vital to ensuring overall system efficiency and preventing downtime. Todd Beard, regional operations director, Lee Co., Franklin, Tennessee, noted, “When a process or piece of cooling equipment depends on a heat-rejection device such as a cooling tower to function properly, there are not many alternatives that will work in the event the tower fails. In other words, there is typically not a cooling tower sitting in a warehouse somewhere ready to be installed at a moment’s notice. It’s not a matter of if a poorly or non-maintained tower is going to fail — it’s when.”
And, Beard added, “That is when Murphy’s Law comes into play, and the failure occurs at the most inopportune moment; it happens every time.”
To avoid these worst-case failure scenarios, mechanical systems experts recommend regular and comprehensive cooling tower maintenance.
Energy Savings and Education
To promote the importance of a cooling tower maintenance program, contractors must communicate the benefits of regular maintenance to building owners and operators.
“We find that most clients understand the importance of maintaining towers but don’t grasp the concept that good tower maintenance is multifaceted and doesn’t just consist of a good annual cleaning,” Beard said. “Cooling towers can fall into that ‘out of sight, out of mind’ category, in some cases. It’s important we continue to educate our clients on good tower maintenance. We want clients to get the most out of their investments.”
And, getting that return on investment (ROI) is not as likely when cooling towers are ignored. According to Walton, “Owners gain operating cost benefits when they implement a regular, comprehensive cooling tower maintenance program.”
Failing to maintain the cooling tower leads to higher energy usage and, therefore, higher energy costs, said Walton. “Neglecting the cooling tower will lead to higher-than-desired return water temperatures to the system, which results in higher energy usage from two perspectives,” he said. “First, the system [chiller] will consume more energy because it must operate at a higher-than-necessary condensing pressure to satisfy the load. Due to the higher fluid temperatures provided by the cooling tower, as little as 2°F higher temperature can result in 6 percent more energy consumption by the chiller. Second, the tower must operate longer at higher fan horsepower while trying to attain the design leaving water temperature.”
To avoid this scenario of higher energy use and costs created by high water return temperatures, cooling towers must be regularly maintained.”
Drew Wettlaufer, vice president, building services and energy solutions, Marble Mechanical Service, Birmingham, Michigan, said the most significant benefit of cooling tower maintenance is “consistent condenser water temperatures back to the chillers.”
Yet Wettlaufer noted that while some of Marble’s clients do follow his company’s maintenance recommendations, some do not. “The more information you can give customers, the better,” he added.
Mihir Kalyani, HVAC marketing engineer, Evapco Inc., also noted, not only does regular maintenance ensure efficient cooling, it also extends the life expectancy of the cooling tower. “The cooling tower stays corrosion-, bacteria-, and scale-free,” Kalyani said.
Keeping a cooling tower free of dangers such as bacteria and corrosion is best achieved through a regular, comprehensive maintenance program. Although recommendations for the frequency of certain actions tend to vary, a comprehensive program includes draining and cleaning, water treatment, mechanical and electrical component inspection, and winterizing.
Discussing the importance of regular cleaning, Beard noted towers should be drained and cleaned at least once a year.
“Sections of the tower that should be cleaned are the hot and cold water basins, fill, and nozzles,” he said, adding, “Nozzles, which are located in the hot water basin, sometimes get overlooked during cleaning. Maintaining the nozzles is a very important step in the cleaning process. Properly functioning nozzles ensure water will be delivered uniformly over the fill. This is important in order to achieve maximum capacity from the tower.”
Wettlaufer emphasized the importance of good water treatment.
“Without some kind of water treatment, bacteria can tend to form, which, in turn, could foul condenser tubes and reduce chiller efficiencies,” he said.
Kalyani also stressed this point, stating a systematic water treatment plan should be implemented from day one. “Makeup and recirculated quality must be checked on a regular basis, as often as weekly,” he said. “A systematic water treatment plan must be put in place to ensure prime water quality.”
Without a plan like this in effect, Kalyani warned, “Scale, corrosion, and bacteria growth can quickly deteriorate water quality.”
Beard and Walton noted some of the greatest risks stem from potential airborne impurities and biological contamination. “These threats, such as Legionella, should be controlled through the use of biocides,” Walton said. “And, such treatment should be initiated at startup and continued regularly.”
Walton also pointed to ASHRAE Guideline 12-2000, “Minimizing the Risk of Legionellosis Associated with Building Water Systems,” as an excellent resource on this topic.
The mechanical and electrical components of cooling towers also require maintenance. Walton noted cooling tower fans are typically driven by belt- or gear-driven systems.
“Both require routine maintenance to ensure reliable, trouble-free performance,” he said.
Beard added, “Regular inspection of these components cannot be overlooked when it comes to the overall maintenance of a tower.”
And, finally, Beard said, depending on the region and application of the cooling tower, it should be drained and winterized for the non-cooling season.
Benefits Can’t Be Ignored
Despite the tendency to ignore or overlook cooling towers, the benefits of an all-encompassing maintenance program cannot be overstated.
Summing up the overall importance of cooling tower maintenance, Beard said, “In the end, a poorly maintained tower is a sure and proven way to increase spending and decrease life expectancy of some of your most valuable assets.”
Publication date: 5/11/2015