Cooling towers are very efficient at extracting and rejecting heat from HVAC systems.
However, as with any equipment that involves the storage of water, there is always a risk of Legionella (a pathogenic group of bacterium that causes Legionnaires Disease).
Good maintenance therefore becomes essential, although safe maintenance processes are often time consuming, expensive and more likely to prompt facilities managers to ask whether it is possible to streamline engineering time and cost whilst minimising the risk of bacterial growth.
The science behind cooling towers
Cooling towers make use of a moving air stream to evaporate water stored inside HVAC systems and cool the entire water system in the process. In addition, their daily operation will remove large volumes of dirt, dust, pollen, bacteria, stack emissions and other airborne matter from the surrounding air.
Typically, 75 to 80 per cent of heat rejection is achieved through evaporation, with the remainder removed by the large volume of air passing over a unit. With sometimes large volumes of stored water, it is vital that cooling tower systems should be maintained adequately, since this ensures units deliver required volumes of heat transfer at maximum efficiency and also prevents the proliferation of bacteria.
Left unmaintained, a warm cooling tower with large volumes of dissolved airborne particulates and debris will become the ideal environment for the growth of microorganisms which can cause significant waterborne contamination issues.
Existing maintenance schemes generally involve the use of treatment chemicals and biocides in order to inhibit bacteria and algae growth. Not only is this costly, but time consuming too and for many building managers, engineering time has become a valuable commodity on site as a consequence of workforce streamlining, contract cutbacks and increasing client-side 'value-for-money' expectations. With this in mind, the solution is simple: Prevent airborne debris and microbiological contaminants from being drawn into the system at the source using air filtration.
Introduced to the UK market in 2012, air intake screens are long lasting, purpose-designed filter mesh screens which can be affixed to the external air intakes on cooling towers, condensers, air handling units and chillers. With a lifespan of up to 15 years, air intake screens act as a cost effective protective component of any cooling tower treatment program and, by removing airborne particulates and debris from recirculating water, the potential for bacterial deposits is significantly reduced. This helps keep cooling systems operating at maximum design efficiency, enabling them to achieve their specified heat rejection capability and reducing strain placed upon the unit. More importantly, this means that the serviceable life of the plant is extended and the likelihood of mechanical downtime is significantly reduced.
An air intake screen can also assist in the preventing microbiological bacteria and their food supply from entering the cooling tower's water. By stopping insects, leaves and associated biological matter from being drawn into the system through the use of a filtered mesh, air intake screens also contribute towards a significant reduction in the potential for microbiological growth. In turn, this helps to reduce biocide costs which can be an excellent means of cost reduction on site.
Unscheduled maintenance and unit downtime can also be extremely costly to any facility. Maintaining clean, recirculating water is not only sound preventive maintenance but also reduces heat exchanger and tower cleaning costs. Rather than waiting for airborne waste products to enter the system before cleaning it, air intake screens can be cleaned simply and efficiently using a soft brush, hose or vacuum. In cases of severe clogging, they can be easily removed for more thorough cleaning using a jet wash.