Cooling towers and evaporative condensers tend to be looked on unfavour­ably because they are inevitably linked with legionella. Legionnaires’ disease is caused by inhalation small droplets of water, such as may be dissipated from these heat exchangers when they are contaminated by legionella bacterium. The bacterium is very common and may be found in mains water so there is no chance of preventing their access. It is only when conditions allow rapid multi­plication that there is any risk. Because of the need for mandatory inspection and fear of forced shut down on suspicion that the unit may have caused an incidence of Legionnaires’ disease, there has been a move towards air-cooled units. Controls to reduce the risk of legionella are effective in UK, but neverthe­less there remains a need for vigilance (Oughton, 1987). A type of evaporative condenser which does not require a water reservoir, known as a ‘once-through’ type, can eliminate the risk. Developments are reported by Pearson (2006).

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