Water Treatment

As most of you are aware I am not a fan of chemicals been used in heating systems, we have other options, these options are widely used in Europe, yet the UK chooses to ignore these proven methods and continue to push the chemical option.

We had an interesting conversation on Twitter regarding water treatment, but what I realised is many UK installers are unaware of the alternative options, so i thought I would share the different methods available, these follow the German VDI2035 methods

Softened Water
Some people have mentioned using softened water to fill a heating system, here are the fact on this.

By softening of filling water via ion-exchange the total hardness of the heating system make-up water is reduced.

By removing calcium and magnesium out of the water the total hardness is lowered. This basically comes up to the demands according to VDI2035 guidelines. But replacing calcium and magnesium against sodium ions does not lower the electrical conductivity of the heating water. In most cases the electrical conductivity of the softened water rises due to technical reasons in comparison with the untreated raw water.

This critical factor makes softened water unsuitable for heating-system make-up water, if there is a higher amount of oxygen to be expected in the heating system there would be need for water with a conductivity of <100 µS/cm.

In systems with higher temperatures, a high pH above 10 may occur, if the system has been filled with softened water. As the sodium has exchanged its position with calcium it is dissolved in the water in form of sodium-hydrogen carbonate – its partner in solution is carbon dioxide. As soon as the water is heated up above 60°C, the solubility of gases in the water is lowered and carbon dioxide changes from the aqueous to the gaseous phase. Sodium stays in the water mainly in form of sodium hydroxide which might results in a pH >10.

Due to these technical based restrictions a filling water treatment with water softening does not cover all demands of the common guidelines for heating water treatment.

Demineralisation 

The de-ionisation by ion-exchange follows the same principle as water softening, but the de-ionisation of the heating-system filling water lowers the electrical conductivity and the total hardness.

At the process of de-ionisation the ion-exchanger consists of two components – the cation- and the anion-exchanger.

The difference to water softening is the cation exchanger is not loaded with sodium-salts, but with hydrogen-ions. As soon as water comes in contact with the cation exchanger all positive charged ions (potassium, sodium, calcium, magnesium) change their position with hydrogen-ions.

The anion-exchanger is loaded with hydronium-ions. These swap their position with any negative charged ions in the water (carbon dioxide, silica, chlorides, sulphates, nitrates).

The treated water thus contains H+ and OH- ions – ions where water molecules are made from. The H+ and OH- ions combine to H2O – pure water.
The de-ionisation of heating-system make-up water generates a water, which has a low electrical conductivity of <10 µS/cm, a total hardness of ~0,1°dH and a neutral pH of ~7-8. All salts, even chlorides, sulphates and nitrates are completely removed from the water.

But with this ion-exchange principle, the pH can cause problems. Improper use of the ion-exchanger salts of silica and carbon dioxide are not removed properly. As a result the pH of the treated water drops and the water becomes slightly acidic with a pH of 4-5. Even correct use of de-ionisation the pH can drop as soon as there is an acidic reaction in the system. De-ionised water is rather sensitive to outside influences as there are no dissolved salts that can act as a buffer against such influences.

In ordinary heating-systems without disturbing impurities and without constructive deficiency the pH of the de-ionised water normally rises to approx. 8.2 after one or two weeks of operation. This assumes that the water is heated up to >60°C and that the system is de-aerated properly so that residues of carbon dioxide can be vented. This and some metal hydroxides results in a rise of the pH.

Demineralisation with pH control

There are also water filter system available, for the reduction of total hardness and electrical conductivity as well as stabilisation of the pH of the heating system water.

The pH is raised by constant dosing of suitable salts. In the first stage in the chamber the water is adjusted to a specific level by use of a special resin. In a second filter stage suitable salts are dosed to the water depending on the volume flow, which results in a rise of the pH. By use of a special salt-resin mixture the pH can be limited. The result is a water with an electrical conductivity of 1-100 µS/cm, a total hardness of ~0.01°dH and a pH of 8.5. Regardless of the raw water quality such filters create water that fully complies to the demands of VDI2035 guidelines for heating-system water quality. Products which provides such water treatment are the CLARIMAX 1200 HW water filter system and the Elysator Purotap Leader with the Nexion cartridge.

Electrochemical solutions

The use of electrochemical water-treatment will results in an increase of the pH-value, constant oxygen consumption and cleaning of the system water. A cyclonic water flow and separation plates installed inside of the unit enhance the separation of impurities and the venting of the heating system by an air-vent. In addition, a strong magnetic filter rod of rare-earth provides the effective removal of magnetic particles from the heating water. Protection of the metals in the system by a water quality which supports the formation of natural protective layers and passivation (corrosion protection) The electrochemical water treatment is a well known method for an eco-logical corrosion protection in central heating systems and is a recommended method for refurbishment and protection of central heating systems in the case of water containing oxygen resulting in corrosion.  The increase of the pH-value by electrochemically formed hydroxide is state of the art technology and a safe way to operate a central heating in combination with demineralised water in a low-salt operation style according to VDI 2035. these units come in varying sizes and are particularly useful in large commercial systems suffering from corossion, as they can be fitted into the system with minimum of disruption and will treat the water over time, bringing it to a clean and non corrosive condition

System Top Up

If these methods are used its important to use conditioned water for any top ups, cartridges are available that can be connected to the quick fill of the heating system, which ensure any top up water is the same quality water that you filled the system with.

There is much more to this, but I have tried to keep it as brief as possible