This dry cooling tower has three air intake filters installed. (Article photos courtesy of Randy Simmons.)
Did you ever wonder what insects make that very loud buzzing sound in trees during the daytime in summer? It's a widely heard but rarely seen kind of insect called a cicada. The ones you hear every summer are nonperiodical, some of them appearing as adults every year despite requiring several years to develop to adulthood.

Unfortunately, the ones appearing as adults in the next few years can overwhelm your cooling towers, evaporative condensers, and air-handling units. They emerge as adults in 17-year intervals in large and generally nonoverlapping geographic regions of the northeastern United States.

Because of this separation in time and place, these species are called periodical cicadas, and their various widespread populations are called broods. A total of a dozen such broods are recognized, according to Dr. Thomas E. Moore, Museum of Zoology, University of Michigan, Ann Arbor, Mich., who provided all of the cicada distribution and biological information for this article.

The single largest 17-year brood, known as "Brood X" (10), is expected to appear in 16 states in 2004. (Click on the link at the bottom of this story to see a PDF of Table 1 showing state and county distribution). Another brood should appear in 2007, and a third brood in 2008. (Some states have more than one brood).

One can identify periodical cicadas by the combination of largely black bodies, reddish eyes, and reddish veins in their wings.

If your company is in a region affected by Brood X this year, you need to begin planning how you will deal with the potential problem; it could have a devastating impact on your operation if you wait until it is too late.

So What's The Big Deal?

When periodic cicadas emerge, their population density is enormous. It can exceed 1 million per square acre (several hundreds of thousands is usual).

If your facility is in a brood-infested region, and your cooling towers, evaporative condensers, and air-handling units are in or near naturally forested areas, or surrounded by trees, your system may be vulnerable.

These otherwise harmless insects can be sucked into your equipment while flying past the draft zone of the intake opening as they make their way to the nearest tree.

Units located on rooftops and away from trees or in the middle of a paved area are less likely to encounter cicada-related problems than those that are near the ground, or surrounded by trees or woody plants.

If your facility is immediately adjacent to or nestled away in affected wooded areas, your systems are likely to be at risk.

When Will They Emerge?

These insects are about the size of your little finger, measuring about 0.5 inches wide and 1.5 inches long. Three species usually emerge mixed together in the same area. Their songs are quite different, and they vary in average size.

They are expected to emerge from the soil in early May and June, and are active as adults (only males sing) for 30 to 50 days. During their short time above ground, they feed both day and night by sucking the sap of trees and other woody plants. They do not chew or bite leaves or people. The songs of males promote mating. After mating, females lay hundreds of eggs in woody tissue by making slits in the bark of pencil-sized twigs.

Shortly after mating and laying eggs, the adult cicadas die, leaving massive numbers of carcasses everywhere. In about nine weeks the eggs hatch and pale, ant-sized baby cicadas drop from the twigs to the ground, where they burrow underground and remain there for 17 years, sucking sap from the roots of plants.

Air intake filters offer a way to protect cooling towers from cicadas (above and below).

Here's What Can Happen

"The last time the periodic cicadas emerged, we had to clean our cooling tower strainers and flume several times per day," recalled one stationary steam engineer, who works at a major consumer products manufacturer in the Cincinnati area. "If we didn't clean the strainers, we would lose our chiller due to high-pressure conditions and it would shut down our cooling system.

"We had to maintain our cooling towers around the clock just to keep our systems operational."

If your facility is in an affected area and you don't anticipate the emergence of the cicadas, it can impact your annual maintenance budget and have an economic impact on your business in the following ways.

Cooling towers and evaporative condensers

  • Clog cooling tower film, reducing airflow.

  • Overwhelm sump water, increasing organic content and increasing bacteria count.

  • Increase water treatment chemical consumption and associated costs.

  • Clog strainers, reduce flow rates, and impact chiller efficiency.

  • Clog solenoid blowdown valves in the open position, resulting in increased makeup water and water treatment chemical consumption.

  • Clog heat exchangers, reducing flow rates and heat transfer efficiency.

  • Increase maintenance costs.

  • Can cause production downtime, lost productivity, and missed shipments.

    Air-handling units

  • Clog internal filters.

  • Load intake air pathways with insect debris.

  • Increase filter changes.

  • Reduce internal air quality.

  • Cause excessive service and maintenance costs.

    In short, periodic cicadas can cause real havoc to companies that are not prepared.

    How You Can Prevent Trouble

    First of all, you need to determine if you are located in an affected region. If you had a problem the last time they emerged, and if there has been little construction or disruption to the soil or forested area around your operation, then you are likely to have trouble again.

    If you are in an affected region, it is recommended that you identify your most critical systems and set extra maintenance dollars aside specifically for protecting and maintaining those systems that support production or other revenue-generating operations.

    Anticipate extra maintenance and service, increased water treatment chemical consumption, frequent filter changes on air handlers, and overtime or investment in preventive technology (such as air intake filters that stop the insects and debris from entering your systems).

    Research your alternatives. Water filtration and air intake filtration are two good options. De-pending on the level of protection you are seeking, each provides varying degrees of protection.

    Water filtration will help you manage the insects (and other airborne debris) after they have entered the cooling tower, and will protect downstream systems, including chillers and heat exchangers.

    However, water filtration cannot protect the cooling tower, where most of the maintenance will be required. Air intake filtration systems, which mount to the outside of the cooling tower or other air intake openings (as in chillers and air-handling units), will filter the air at the point of entry into your system, keeping airborne matter out of the tower in the first place and protecting the entire system (cooling tower, chiller, and heat exchanger).

    After the cicadas have gone, the air intake filters can provide long-term protection against annual airborne debris, such as cottonwood seed, small and large insects (e.g., mayflies/fishflies and ladybugs), leaves, pine needles, paper and wrappers, harvest chaff, construction debris, and birds.

    Knowing if you will be affected and developing a plan of action is the first step in reducing the impact on your operation.

    Taking a preventive approach is usually more cost effective than simply reacting when the problem occurs, and can literally save you thousands of dollars while keeping your operation running smoothly.

    Choose Your Filter Wisely

    When airborne debris becomes a serious problem, the natural tendency is to look for something to cover the intake opening to prevent entry of the debris.

    Never use window screen, roll filter media, or mesh purchased from a hardware store to cover air intake openings on cooling towers or evaporative condenser units. These materials are not designed to allow proper airflow and can drastically increase static pressure, increase energy costs, and impede cooling efficiency.

    When using air intake filtration, it should provide less than 1/10-inch drop in static pressure (as measured in inches H2O).

    Air intake filtration specifically designed for use on cooling towers and evaporative condensers and chillers is highly recommended.

    Simmons is with Air Solution Co., a manufacturer of air intake filter systems. He may be reached at 513-860-9784; 513-509-0939 (cell);; or, visit

    Publication date: 04/19/2004

    Click here to download a pdf of Table 1.