Cooling and air-conditioning waterBWT offers the perfect solution for the effective
treatment of cooling and air-conditioning water.

Cooling and air-conditioning water

Closed loops (such as cold water circulation in conditioning systems)

Softened or desalinated water is generally adequate for filling when a corrosion-resistant pipe material (i.e. plastic) is used, and with a single filling. However, some filling water treatment may be required, depending on the water quality and operating conditions.


Open re-cooling systems (all systems with cooling towers)

As only pure water is evaporated in cooling towers, the concentration of salt in the circulation water is constantly rising. Excessive salinity may lead to calcification and corrosion in the cooling tower and the circulation water pipes. The formation of algae and dust particles from the ambient air can also disrupt the system. Water treatment is therefore necessary in almost all cases to ensure the cooling tower operates economically and reliably.


The VDI 3803 standard stipulates that the quality of the circulation water must be suitable for the materials used in the cooling circuit. The thresholds are defined in the table below:


Recommended thresholds for the quality of re-cooling circulation water


Materials in contact with the cooling tower water  Conductivity  Calcium content  Chlorid content   Sulphate content
    Ca Cl  SO4
  µS/cm mg/l  mg/l mg/l
Steel and non-ferrous metals < 2200 > 20 < 200 < 325
Steel and coated metals < 2500 > 20 < 250 < 400
Plastic and stainless steel < 3000   < 400

< 600


The circulation water should be as clear and colourless as possible, and contain no sediment. Carbonate hardness should be < 4° dH, with chemical hardness stabilisation of < 20° dH. A biocide should be added intermittently with a bacterial count of > 100,000/ml.


The following malfunctions may occur if the above thresholds are not maintained:

  • Deterioration of the heat or cold transfer

  • Increased loss of pressure through sectional constriction

  • Blocking of nozzles, valves and cooling ducts


This can result in:

  • Higher energy and water consumption

  • Malfunction and production outages

  • Increased maintenance

  • Destruction of important system components


Air-conditioning water (e.g. in humidification units in air-conditioning systems)

Humidifiers in air-conditioning systems are used in many buildings, because humans require a minimum level of air humidity. Inadequate or improperly implemented air humidity can seriously affect the health and comfort of the building occupants. Hygiene considerations play a central role in the planning and operation of humidifiers, and the current VDI 6022 standard contains valuable recommendations in this respect.


Various processes are used to humidify air and, for each process, the correct treatment of the humidification water is crucial. Reverse osmosis systems for desalinating drinking water are becoming increasingly popular for this purpose and in some cases are supplemented with disinfection systems.


We can provide technical support, from the project planning for reliable and cost-efficient systems to regular maintenance of the installed system.