Whilst everyone is aware of, and manages the risks associated with cooling towers, often the related adiabatic or wet/dry cooling systems are overlooked.
There are various types of these systems but essentially, they work in the same way, using ambient air to cool via a heat exchanger and when demand increases, the introduction of water via spray nozzles assists the cooling process.
An adiabatic chiller will generally use around 80-90% less water than a traditional cooling tower and unlike cooling towers do not always recirculate water, so risks from Legionella bacteria are lower, however they do still need to be managed as they do create aerosols when used ‘wet’.
We know that the primary nutrient source for Legionella is ferric iron, so periodic checks on the physical condition of the system should be carried out to make sure that corrosion does not become an issue, either in wet or dry mode. Not only is corrosion a food source for bacteria, but it will also contribute to the overall degradation of the system leading to a decline in performance.
The spray nozzles creating the aerosols used for wet cooling should be checked and cleaned to remove scale (a direct result of the evaporative cooling process), as scale is a safe harbour for Legionella bacteria. Additionally, scaled up spray nozzles will reduce the cooling efficiency. As with all other water systems, any dead legs should either be removed or flushed at least weekly, and the whole system itself if not isolated when not needed, should be flushed through. All these checks should be documented.
Your Legionella risk assessment should include a review of the adiabatic cooling system, and the control measures required as, although these systems are not generally notifiable, there is still a risk which should be kept as low as is reasonably practicable.
If you need any support with managing your adiabatic or wet/dry cooling systems, please get in touch.