What is VDI2035

The VDI2035 are guidelines set by the Association of German Engineers, it is their method of water quality requirements for heating water, as a comparison its equivalent in the UK would be BS7593:2019 but the VDI2035 is way more in depth and scientific than the brief coverage BS7593 gives, there are also similar requirements in Austria H öNORM IN 5195-1 and in Switzerland SWKI BT 102-01, but what is common in all these standards is the non use of inhibitors.

There are 3 parts to the VDI2035 

Part 1 deals with Scale Formation in Drinking Water  and Water heating Systems

Part 2 deals with Water-Side Corrosion

Part 3 deals with Corrosion by Fuel Gases

So for my purpose of raising awareness in heating system corrosion we will only look at Part 1 & 2,.

I will not be going into full details, just an overview so installers can understand these standards and then we can question why these methods are not more widely used in the UK

Part 1 In brief Part 1 deals with the prevention of scaling within the heating system, to prevent scaling we need to ensure the hardness of the water is within certain levels to prevent scaling forming, this is measured in Total hardness in mol/m3 h and the levels permitted in the standard will be dependent on the Total Heating Power in kW (see my website link at the end for more details) using demineralised water will acheive this.

Part 2 In brief Part 2 For the prevention of corrosion in the heating systems the main points the VDI2035 document are concerned with are pH, Conductivity and Dissolved Oxygen, pH is stated to be between 8.2 and 10 these figures are the same across the regulations in Austria and Switzerland, however in the UK in the installation manual of some manufacturers we see the figure of between 6.5-8.5 why they would ever want a pH of 6.5 in a heating system this is acidic and would certainly lead to corrosion, I would never want a system with a pH of 6.5, to control the pH the use of filling units where the water passes through a cartridge of resin, this process will alter the pH of the fill water

For conductivity they look to have a level of  <100 µS/cm. the salinity and total dissolved solids in the mains water supply will determine the conductivity of the water, high conductivity of water allows the passage of corrosion a better route to cause corrosion in the presence of oxygen, so reducing this path by lowering the conductivity of the water significantly reduces the risk of corrosion even in the presence of oxygen

Dissolved Oxygen, Oxygen virtually always enters the system during filling procedures. This is because normal drinking water contains approx. 8-11 mg of dissolved oxygen per liter of water. However this quantity is generally used up (through corrosion processes) within a short period of time without significant damage occurring. However, oxygen can be harmful if it is able to consistently enter the system from the ambient air. This may occur due to a number of factors, such as partial formation of underpressure in the system, air entrapment during filling and top up procedures, direct contact between system water and outside air, and oxygen diffusion through permeable components such as seals, plastic pipes, diaphragms and hoses.

This is just an introduction to these standards and the alternative methods to controlling corrosion in our heating systems, both domestic and commercial, it's time we started asking questions as to why other major countries in Europe do not permit the use of chemicals in their heating systems (only permitted in exceptional circumstances) and yet here in the UK we are still told that chucking chemicals in will solve all heating system problems, but we know they do not, I personally have been in the industry 38 years and I see failure after failure of systems that have been inhibited as our British Standards guidance tell us to do, but as an industry we never question this, we just keep chucking chemicals in, why do we keep doing the same thing and hope for a different outcome, I think it's high time we had a grown up conversation on this subject, the industry needs to be made aware of the better alternatives to corrosion prevention that are available to us and we need to push for these methods to be stated in our regulations.

This is the first of a series of blogs I will be doing on this subject, I will also be covering the alternative options we have available to us for corrosion prevention, how to use them and what they do.

Further details on my website https://www.vietec.com/water-treatment