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From top to bottom

By positioning fans at the bottom of cooling towers, Tower Tech claims to have greatly reduced the potential for legionella growth

One major concern with cooling towers is that they are susceptible to growing and spreading legionella. The water in cooling tower basins moves fairly slow, often just 1 foot per second, and many basins have stagnant zones.

The water is also exposed to sunlight, and the elements, since they are open water basins. This all contributes to sediment build-up in the basin, which can be an ideal breeding ground for legionella bacteria to grow, especially at certain water temperatures.

To make matters worse, water from inside the cooling tower is sprayed outside of the cooling tower by what is called ‘drift’. Drift is caused by small particles of water that splash up inside the cooling tower, getting caught in the high exit velocity caused by the top-mounted fans of the cooling tower.

Drift makes it possible for any legionella bacteria that may be in the cooling tower water to spread outside the cooling tower.   

Although internal cleaning of cooling towers is recommended by the manufacturers, many operators have difficulty keeping up with the recommended cleaning schedules. This is frequently due to ever-decreasing maintenance budgets and the inability to shut down processes as often as recommended for proper cleaning.

To combat this issue, various governmental agencies (including Australia) are requiring the owners of cooling towers to shut down and clean their kit on a regular basis. Most cooling tower owners don’t do this because of the cost and impact to their business – if you have a process that requires cold water, your entire process is down for as long as the cooling tower is down.

If you are running a hospital in London, you would need an additional cooling tower in order to comply, because you can’t shut it down to clean it during the summer months, as it could result in loss of life, since surgical units require the cooling tower to provide certain temperatures.

Also, if you have a brewery in a suburb that can’t shut down its process for six months once it starts because it takes days or weeks to get the formula just right when you first start the process, you are in the same difficult position.

Shutting down an entire cooling tower for cleaning on such a short-term re-occurring basis can be seen  as sticking a plaster on the situation, rather than truly addressing the problem, which is the growth and spread of legionella.

Upside down

Because cooling towers are often the most efficient way to extract heat from a large process (for example, power generation, food, oil/gas, chemical, HVAC  and so on), Tower Tech in the US has developed new technology to combat this and other major sustainability concerns associated with cooling  towers. With nearly 4,000 units in operations, the technology is well proven. 

To achieve this, we’ve turned cooling towers upside down – literally. The fans are now located at the bottom of the cooling tower. With reduced internal splash-up and a lower exit velocity, due to bottom-mounted fans, the Tower Tech design has a drift rate 92 per cent lower than most conventional designs. Keeping the water inside the cooling tower makes it more difficult for any legionella inside the tower to spread outside.

The Tower Tech design also reduces the potential for formation of legionella by way of a totally enclosed water basin that eliminates water contact with sunlight and the elements. This basin design also eliminates stagnant zones, while greatly increasing the velocity of water in the basin to 5-7 feet per second. The combination of these key innovations in basin design makes it less likely that legionella will breed.

When coupling reduced potential for legionella formation with 92 per cent less drift, and therefore potential for transmission, the Tower Tech design greatly reduces the risk of legionella associated with cooling towers.

Dan Coday is sales manager at Tower Tech


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