Since the air contains particles of dust and dirt of various kinds, (depending upon the local environment), the recirculating water becomes contaminated with a variety of materials. This creates fouling on the inside surfaces of the condenser system which can lead to under-deposit corrosion and loss of heat-transfer efficiency increasing energy consumption. In addition, air dissolves in the water making it saturated with corrosive oxygen at all times during tower operation and creating conditions that are ideal for corrosion. Corrosion of condenser system components such as chillers, circulating pumps, and cooling towers can be very costly in terms of service disruption, tenant complaints, loss of production, increased maintenance and capital equipment replacement.
Since towers contain warm water, are open to sunlight and trap a variety of life forms and nutrient sources, they are perfect breeding grounds for algae, fungi and bacteria. Some of these forms circulate throughout the condenser system, while others attach themselves to convenient surfaces. Corrosion is frequently found beneath these deposits as a result of under-deposit corrosion or direct attack from species that consume iron in order to propagate.
Cooling towers have been found to provide ideal breeding conditions for pathogenic bacteria such as Legionella pneumophila which is responsible for Legionnaires’ Disease. Legionnaires' Disease is a potentially fatal form of pneumonia thought to be transmitted to humans via airborne water droplets. The forced air design of cooling towers creates droplets of the correct size to be easily drawn into heating and cooling ducts and transported to working and living areas.
Implementing a properly designed chemical treatment program involves maintaining adequate levels of corrosion inhibitors, scale inhibitors and biocides in the condenser water system. The treatment plan should be carefully chosen to suit the local conditions under which the tower operates which consists of the raw water quality, air quality, and materials of construction.
In order for the treatment program to work effectively they must also be properly fed into the system. Corrosion and scale inhibitors should be maintained at a constant level at all times, whereas biocides are most effective when applied in slug doses on a product-alternated basis. Even if the cooling tower is not used during the winter months, chemical levels must still be maintained and provision made for circulation of the condenser water at least once daily.
Regular testing of the condenser water and observation of the condition of the equipment is necessary to maintain adequate chemical levels and to ensure prompt action in the case of sudden system disruptions. Remember, it is much easier to keep a system under control than to get it back under control.