VDI2035 is becoming more and more recognised in the UK heating industry, I have been banging on about this method for about 8 years, so it’s good to finally see it been used more in the UK, both in the Domestic and Commercial side of our industry, but what are the requirements of VDI2035? I will try and explain these using methods used by my preferred brand Elysator, other products are available.

VDI2035 identifies 3 key parameters required to cause corrosion in heating and cooling systems

1. Dissolved Oxygen

2. System water with high conductivity

3. Low pH

Elysator products work with how metals are naturally inclined to react, not against them, harnessing the effects of these natural reactions and applying them to the benefit of system protection

The Science: let us delve a little into the science of corrosion, A typical heating system can be made up of a variety of materials, copper, brass, various forms of steel, composite and even plastics.

All metals contain negatively charged particles called electrons, the number of electrons in a metal define how stable that metal is, many metals in their refined state, do not have a stable number of electrons, instead they have a surplus of electrons and will readily give up these electrons to become stable, conversely, Oxygen requires additional electrons for it to become stable, so metals and oxygen exchange electrons to achieve greater stability.

Chemists refer to these processes as Oxidation (loss of electrons) and Reduction (gain of electrons) the more common term for this process within metals at least is corrosion and for iron and steel it is better known as rusting, the presence of oxygen in the water of a heating system therefore creates a favourable environment for corrosion to occur 

let’s look at ways we can address this naturally occurring process.

Oxygen is and always has been the enemy of a heating system, so it’s always something we should deal with, in my opinion on installation the best way to do this is good design, using good quality materials, correct expansion vessel sizing and correct pre-charge of the vessel as well as a good maintenance regime, if dissolved oxygen is a problem within the system, there are ways to address this using Elysator products, I will go into this in further detail a bit later

System water with high conductivity: a lot of the UK has hard to very hard water, water has minerals and salts in them, it is these that create the conductivity, different areas in the UK have different water hardness, so each area will have different needs, but whatever the water, if we remove these minerals and salts on filling, we lower the conductivity, basically restricting the path that is needed for the chemical reaction that is needed between metals, water and oxygen for the corrosion process to take place, so rather than adding a chemical to try and stop the natural process of chemical reaction that creates corrosion, we just remove the pathway, the best way to treat heating water on filling is using a demineralisation unit, basically a mobile cartridge that you just connect inline with the mains water fill point and the filling connection to the heating system (as in image below)

Filling the heating system with the Elysator Purotap Leader using the Nexion cartridge has the additional benefit of raising the pH of the initial fill water to around 8.4, the salts and minerals are removed from the water through an ion exchange with the resin, the Nexion cartridge has a surplus of anion resin and it removes free carbon dioxide which raises the pH of the water, this give you water suited to a heating system, with all the potentials to allow corrosion removed, so lowering the risk of system corrosion massively, without the addition of any chemicals

Purotap Leader

Ongoing protection: To ensure that the system water stays at its optimum its important to ensure any future top up water is also dimeralised, there are options for this depending on the size of the system, there are several options, I will cover the main ones. For small domestic systems there is the Purotap Micro, a small relatively cheap cartridge, that gets left on site, allowing the quick fill to be connected to it so any top up water passes through the Purotap cartridge demineralising the water before it enters the heating system, these are not designed to be left under constant pressure, so need to be disconnected after filling.

Purotap Micro

For larger systems there is the Compenso units, these can be connected to the system and can be left under pressure or connected via a pressurisation unit if required, so any water filled via the pressurisation unit is demineralised, these come in different sizes depending on system volume 2 – 50 litres 

Purotap Compenso

Continued Protection: For systems that may have oxygen ingress, or ongoing issues, or you just want to ensure the water remains at its optimum, Elysator have reaction vessels containing high-purity magnesium anodes, there are different size units which will depend on the size of the system it is connected to, there are units to suit dometic up to large commercial systems, the working principle is the same for each, so I will list the units available, then I will run through how they work, for me, now I install heat pumps, which are expensive items to spend some additional money to ensure protection of the heat pump is a no brainer in my opinion,  or commercial plant rooms where again the plant equipment is costly, it’s worth ensuring these components are fully protected.

For this Elysator have several option, for the domestic market they have the SorbOx, these are suitable for system power up to 30kW and system volumes up to 800L, and are design to be installed in the full flow, the SorbOx comes with high purity magnesium anodes and a demineralisation filter, depending on your needs, if you have an existing system that requires a little clean up, fit the demineralisation cartridge for a few days to clean up the water it will remove the salts and minerals from the circulating water, then swap for the magnesium anodes for ongoing protection

SorbOx

For larger systems up to small commercial there is the Trio range, The 10 for system volumes up to 500L, 15 for system volumes up to 1,500L & 25 for system volumes up to 5000L, these units can be fitted in the full flow or side stream, in side stream installation a flow setter should be installed and the correct flow rate needs to be set for the unit, these units provide three proven corrosion-protection measures, Degassing, Anodic Protection and magnetic protection, they have also released a new line which has the addition of a replaceable filter, so adding a fourth line of protection

TRIO

For large commercial systems Elysator have the Elysator Industrial units, these units are installed as a sidestream, starting at the 50 for volumes up to 15m3, 75 for system volumes up to 25m3, 100 for system volumes up to 35m3, 260 for system volumes up to 70m3, 500 for system volumes up to 120m3 and the 800 for system volumes up to 220m3, the principle for 3 tier protection is the same for this unit and across all the range, Degassing, Anodic protection and magnetic protection 

Elysator Industrial

All the above items offer at least three levels of protection for the system water using Magnesium Anodes, so how do these work?

Within each of Elysator units which is where the reaction occurs, whether it’s the SorbOx, Trio or Elysator Industrial units, we have the stainless steel body of the unit and the magnesium anodes inside, it is within the vessel that the exchange occurs so these units are classified as the the reaction vessels.

Magnesium is less stable than steel, so in an environment where corrosion factors are present, then the Magnesium will corrode (oxidise) first.

The more noble a metal is, the more resistant it is to corrosion when submerged in an electrolyte like water, as explained at the start, both stainless steel and magnesium have excess electrons which they want to give up to become more stable and here is where the difference in nobility becomes relevant, Stainless Steel as the more noble, has to take excess electrons from the magnesium even when it’s looking to shed its own surplus electrons and is therefore protected from oxidisation, this process of the magnesium giving up its electrons (Oxidisation) (Anodic)  and the stainless steel taking these electrons (Reduction) (Cathodic) is a chemical reaction and combining the two reactions Magnesium ions and Hydroxy ions are formed within the water in the Elysator reaction vessel combining to form Magnesium Hydroxide, 

this Magnesium Hydroxide mostly remains within the reaction tank, so any water that passes through will react with the Magnesium Hydroxide which will raise the pH of the water, this is a gradual process and continues until the entire system water pH has been increased.

As stated previously, oxygen is the enemy of a heating system, the Elysator reaction vessel will consume dissolved oxygen present in the water that passes through it. As the magnesium anodes and the stainless steel tank are connected, the electrons from the magnesium move to the surface of the stainless steel tank, as stated earlier metals want to lose electrons to make themselves more stable and because stainless steel is a more noble metal the electrons from the magnesium move to the stainless steel walls of the Elysator Reaction vessel, now as opposed to metals that want to give up electrons to become more stable, oxygen wants to gain electrons to become more stable, so any dissolved oxygen in the system water will be drawn to the walls of the reaction vessel, as there is an abundance of electrons there, when the oxygen takes these electrons a chemical reduction reaction occurs O2 + 4e- + 2H2O → 4OH- this process consumes the Oxygen, from this hydroxy ions created on the the stainless steel and magnesium ions, created on the anodes combine and produce Magnesium Hydroxide, this is a solid, which drops to the bottom of the reaction vessel, this solid Magnesium Hydroxide will get dissolved into water with a low pH as it passes through the reaction vessel, so simply put, Elysator reaction vessels consumes the dissolved oxygen and uses it to increase the pH of the system water.

These processes within the reaction vessel of Elysators are a continuous process and continues as long  as there is oxygen to consume and pH to raise, once all oxygen has been consumed and all the system water pH has been raised the system is fully protected, but if for any reason oxygen gets back into the system or  pH variation occurs, as water passes through the Elysator reaction vessel the process will recommence and is how it continuously protects the system, always consuming oxygen and raising pH to levels suited to the heating system, it is Oxygen and low pH that are the main cause of corrosion within heating systems, so these methods will protect the heating system from these issues and so prevent corrosion.

I have installed many of these systems now and I know they work, I have cleaned up many district heating systems with these methods and have long term systems out there both domestic and commercial protected with these methods that are running clean and problem free, so this post is coming from an installer experience prospective and not sales