Dry/wet cooling systems
Sometimes referred to as hybrid or adiabatic coolers
In recent years there has been increasing use of dry/wet cooling systems which are described in HSG274 Legionella Technical Guidance Part 1, paragraphs 1.18-1.21. These are designed to operate both in dry air cooled mode and wet evaporative cooling mode. There are different types of dry/wet cooling systems, sometimes referred to as "hybrid" or "adiabatic" coolers, and these can have a wide range of risk profiles.
The Water Management Society, endorsed by HSE, has published a document which supplements HSG274 Part 1 with more detailed information to help evaluate between different designs and risk profiles of dry/wet cooling equipment. This guidance is to help dutyholders, which includes employers, those in control of premises and those with health and safety responsibilities for others, to comply with their legal duties and gives practical guidance on how to assess and control the risks due to legionella bacteria in dry/wet cooling systems.
This guidance is freely available to download from the Water Management Society.