Legionella is a gram-negative bacillus, responsible of a severe infective disease called Legionnaires’ disease. Legionella survives in water and mud and it is transmitted by air. Moreover it has been ascertained its transmission by the air conditioning central system.


The Legionnaires’ disease is a pulmonary infection caused by the Legionella pneumophila bacterium, which name means exactly “Legionella lover of the lungs”. The name Legionella was coined in 1976, after an epidemic which had spread throughout the participants to a gathering of the American legion at Bellevue Stratford Hotel in Philadelphia. In this occasion 221 people contracted this kind of previously unknown pneumonia and 34 of them died. The source of the contamination was identified in the air conditioning system of the hotel.

How do you prevent Legionella?

Prevention from Legionella infections is based essentially on two main aspects:

  • on the proper projecting and realization of the technological systems which comprehend heating and/or nebulising of water (systems at risk). This comprehends water-sanitary systems, the conditioning systems with water moistening of the air, the cooling systems with evaporative towers or evaporative condensers, the systems which distribute and supply thermal water, swimming-pools and jacuzzi
  • on the adoption of preventive measures(maintenance and if needed disinfection) in order to contrast the multiplication and the diffusion of Legionella in systems at risk.
Our solutions

Our solutions satisfy the requirements of the Standard VDI 2047 Part 2 (Securing hygienically sound operation of evaporative cooling systems), this standard lists the structural, technical and organizational requirements pertaining to hygienically sound operation; these requirements concern the planning, installation and operation including the required maintenance of evaporative cooling systems. Risks posed by, e.g. legionella, for employees and third parties will be minimized if these requirements are met.

The company Thermokey has developed a system on “V-Dry coolers” and/or “V-Condensers” to work with an adiabatic system.

The AFS method employed makes use of adiabatic cooling with low water consumption by means of special nozzles developed to work with very high water pressures. The physical phenomena of the adiabatic cooling consist in creating an even diffusion of micro drops of water (Misting effect) through which is passing a current of air that will be cooled by the evaporation of the water.”

Water side:
The quality of the water supplied to the adiabatic system is tap water (according drinking water regulation). The special nozzles in the “AFS” combined with the high pressure of the water produce micro drops that are completely evaporated by the flow of air without leaving residues of water on the heat exchanger coils; no water is present in equipment and above all on the discharge of the fans or on the ground.
Water is present in the water distribution nozzles only during the operation of the “AFS”, the water distribution nozzles are emptied each time the “AFS” is not in use.
Taking this into account, there could be no legionella bacterium growth.

Air side:
The air inlet from the unit is going back to the ambient and is not used anyway for supplying air. Therefore no risk can be seen during operation.


TÜV SÜD Certified:

“With this “AFS” there is no standing water during continuous operation. Working according to the instruction manual we can state that Thermokey “Air Fresh System” carries no danger in correlation with the risk of legionnaires` disease.”