Cooling Towers: Not So Cool?

Frederick M. Lowther

Anyone who has been in a tall building looking down on shorter buildings has seen the usual array of mechanical “boxes” with large spinning fans. Those “cooling towers” sit atop tens of thousands of buildings across the country, from hotels to office buildings, hospitals, university and government buildings, and residential towers. Cooling towers also sit adjacent to many industrial facilities, such as petrochemical plants, where cooling by exhaustion of heat is part of the industrial process. More recently, there is the advent of truly enormous data centers, which are the guts of operations of “public cloud” companies, such as Google, Amazon, Apple, Microsoft, Facebook, Oracle, IBM, etc. In many cases, these data centers rely on water-based cooling towers, which control temperatures for the large spaces housing computers/servers, and which are often adjacent to thousands of people. It is now estimated that there are as many as two million cooling towers operating in the United States.

Many of us may recall the crisis in 1976, at a hotel in Philadelphia, where an outbreak of a virulent form a pneumonia (dubbed Legionnaire’s Disease) felled dozens of people at an American Legion convention. The outbreak, caused by a bacterium later aptly named legionella pneumophila, caused great concern because of the high and rapid mortality (within a week, more than 130 people had been hospitalized and 25 had died). The bacterium was traced to the hotel’s cooling tower. Since then, legionella has become a very serious concern because the number of incidents has spiraled. More than 5,000 cases of legionella are now being reported annually, and the mortality rate is ranged between five and 30 percent. On October 26, 2017, a cluster of 12 legionella cases was reported in New York City, traced to cooling tower systems in the community. The next day, the cooling towers at Disneyland in Anaheim, California were found to be the likely cause of a sudden legionella outbreak in the Anaheim area. The legionella issue now has the attention of the U.S. Center for Disease Control (“CDC”) in Atlanta, both with regard to the sources and the diagnosis and treatment of the disease. One of CDC’s apparent concerns is that “pneumonia” is being treated reflexively with antibiotics without determining whether the cause is legionella, potentially leading to underreporting of the disease.

Further, the U.S. Environmental Protection Agency (“EPA”) is now focusing on so-called “chemical clouds” being generated by cooling towers, where harsh chemicals are being used to control operating and biological issues. Since cooling towers use the evaporation of water to expel heat, the chemicals added to the water to minimize mineral “scaling” and growth of viruses and bacteria find their way into the water particles and are being expelled into the atmosphere by the tower.

The root of the problem with cooling towers is the fact that they use local sources of often untreated or poorly treated water as the base for the evaporative cooling process. The water, whether it comes from groundwater, rivers and streams, or municipal wastewater systems, is rife with minerals and other contaminants that tend to precipitate out and cause a film of scale inside the tower. The buildup of scale over time reduces the operating efficiency of the tower, but perhaps more importantly, creates an environment in which biological contamination—viruses, bacteria (including legionella), and other living organisms— can thrive. Chemicals such as sulphur dioxide and chlorine are often added to the water in order to soften the minerals and kill some portion of the biological contamination. As noted above, those chemicals—and surviving biological contaminants—find their way into the water molecules, which evaporate and are expelled by large fans into the atmosphere. When the cooling towers sit atop or alongside hotels, office buildings, residential towers, and large complexes, such as data centers, literally thousands of people are unsuspectingly exposed to these dangers.

As is often the case when these types of crises occur, the scientific and entrepreneurial communities are hard at work seeking solutions. While no “silver bullet” has yet been found, at least one promising technology has been awarded key patents and is approaching the crucial proof-of-concept/pilot phase and may well provide an effective answer. By design, the emerging technologies do not involve use of strong chemicals, but instead use ozone, shock waves (electric fields, heat from plasma streamers, ultraviolet light, and biocidal metal ions), electromagnetic pulses, and other non-toxic systems to minimize harmful scaling and to kill nearly 100 percent of biological contaminants. These technologies are also designed to operate flexibly so that they can adapt in real time to the static and dynamic circumstances of each cooling tower.

Unfortunately, as is also often the case, technology development is starved for capital and it behooves the entities that operate large scale cooling towers to get behind these efforts quickly. If government and private industry can come together to accelerate emerging technologies so that they can be deployed in the market, it may obviate the need for harsh mandates that could impact the myriad business and institutions that rely on cooling towers. With CDC and EPA now involved at high levels and with a clear sense of urgency, a focused and aggressive attack on the problem is called for.


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