Did you ever wonder what insects make that loud buzzing sound in trees during the daytime in summer? Well, it’s a widely heard but rarely seen kind of insect called a cicada. The ones you hear every summer are non-periodical, which means some appear every year despite requiring several years to develop to adulthood. The cicadas appearing as adults in the next few years -- the ones that can overwhelm your cooling towers, evaporative condensers and air-handling units -- emerge in 17-year intervals in large and generally non-overlapping geographic regions of the northeastern United States.
Because of this separation in time and place, these species are called periodic cicadas, and their various widespread populations are called broods. A dozen such broods are recognized. The single largest 17-year brood, known as “Brood X” (X, the Roman numeral for 10), is expected to appear in 16 states in 2004 (figure 1). Another 17-year brood should appear in four states in 2007, and yet another in 12 states in 2008.
You can identify periodic cicadas by the combination of large 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 can have a drastic impact on your operation if you wait until it is too late.
When periodic cicadas emerge, their population density is enormous and can exceed 1 million per square acre (several hundred thousand 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.
Is Your System at Risk?
Where your equipment is located will determine your company’s risk. 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.
Cicadas are about the size of your little finger, measuring about 0.5" wide and 1.5" 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 for 30 to 50 days. During their short time above ground, they feed 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 (only the males sing) 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 plant roots.
What Can Happen
As one stationary steam engineer at a manufacturing plant in Cincinnati put it, “The last time the periodic cicadas emerged, we had to clean our cooling tower strainers and flume several times per day. If we didn't clean the strainers, we would lose our chiller due to high-pressure conditions, and it would shutdown 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 do not anticipate emergence of the cicadas, it can impact your annual maintenance budget and have an economic impact on your business.
Cooling towers and evaporative condensers can be affected in many ways. A large infiltration of cicadas can:
- Clog cooling tower fill, reducing airflow.
- Overwhelm sump water, increasing organic content and increasing bacteria count.
- Increase water treatment chemical consumption and associated cost.
- Clog strainers, reduce flow rate 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 rate and heat transfer efficiency.
- Cause production downtime, lost productivity and missed shipments.
- Increase maintenance cost.
Air-handling units also can be affected. A large infiltration of cicadas can:
- Clog internal filters.
- Load intake air ducts 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 to Prevent Trouble
Determine if your county is an affected region (figure 2). If you had a problem the last time they emerged and there has been little development 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, identify your most critical systems and consider setting extra maintenance dollars aside specifically for protecting and maintaining those systems. Systems that support production or other revenue-generating operations are key. Anticipate extra maintenance and service, increased water treatment chemical consumption, frequent filter changes on air-handlers, overtime or investment in preventive technology.
Research your alternatives. Water filtration and air-intake filtration are two good options. Depending on the level of protection your plant will need, each provides varying degrees of protection. Water filtration will help you to manage the insects and other airborne debris after it has entered the cooling tower and will protect downstream systems, including the chiller and heat exchanger. However, water filtration alone does not protect the cooling tower, where much of the maintenance will be required. Air-intake filtration systems that 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, protecting the entire cooling system.
Anticipation and prevention are key. Knowing if you will be affected and developing a plan of action are important. Taking a preventive approach is usually more cost effective than simply reacting when the problem occurs. Prevention can not only save you money, but it will keep your operation running smoothly.
What Not To Do. 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 cost and impede cooling efficiency. When using air-intake filtration, it should provide less than 0.1" w.c. drop in static pressure. Air-intake filtration specifically designed for use on cooling towers and evaporative condensers and chillers is recommended to achieve the most efficient results.