How to clean a heating system and how to prevent corrosion and sludge (magnetite) from forming in radiators are very common questions. Inhibitors can be used but UK heating engineers are now learning about best practice in Germany and the VDI 2035. Magnetic, a German company, are bringing demineralisation technology and the VDI 20135 to the UK.
In this interview we meet one of Nathan's favourite engineers Si Poskett; Joe Sharpe, head of content for Installer Online Magazine and Michael Grimm who is the Director of Business Development at Magnetic.
By taking the ions (both cations and anions) out of the water we fill heating systems with we can help to prevent corrosion. This is because it reduces the conductivity of the water.
Corrosion is an electrochemical process that relies on the heating water to be conductive - an electrolyte. Rather than adding chemical inhibitors the mineral salts (ions) can be exchanged using mixed resin.
Heating systems, whether using a boiler or a heat pump, become inefficient if corrosion is allowed to continue.
Oxygen, electrical conductivity and pH are all factors which can contribute to corrosion. By reducing the conductivity the system water is able to withstand higher concentrations of oxygen O2. However, with a higher conductivity even low concentrations of dissolved oxygen can cause corrosion.
pH is discussed in this interview and how heating systems will naturally alkalise, sometimes referred to as self alkalisation. Heating systems prefer an alkaline water and the VDI standard sets this at 8.2 to 10. aluminium in heating systems tends to prefer 8.2 to 8.5. Magnetic decided not set their resin to fill heating systems to a pH of 8.3. They were concerned self alkalisation may take it over 8.5 which would then start to become outside the preferred parameters of aluminium. Instead the fill water enters the system around neutral and over time will self alkalise to within the VDI limits.
CONDUCTIVITY:
Conductivity is measured in microsiemens per centimetre. It is a measure of how well a solution conducts an electric current between two electrodes which are placed a cm apart. The current flows by ion transport. The more ions present in the water the higher the conductivity. If ions are removed there is higher resistance to current flow. Microsiemens is written using the symbol "S" for Siemens and the greek letter µ means "micro". The VDI 2035 requires system water to be below 100µS/cm (microsiemens per centimetre)
By passing ordinary tap water through a mixed bed resin which exchanges positively charged cations and negatively charged anions the water reduces its conductivity.
OXYGEN
Water is known as the universal solvent, which means it's basically good at dissolving stuff such as salts. It is these salts that form the cations and ions that resin from Magnetic removes. But as well as solids water dissolves air. It's the dissolved oxygen which can be harmful to metals in the heating system. When we heat water, even by just a few degrees, the air comes out of solution and the micro bubbles can also cause more damage through erosion. This is why a competent heating engineer will run a system as hot as possible when commissioning to seperate this air from solution and vent it off. It is vented off not with an automatic air vent (AAV) but a deaeration device, sometimes known as a deaerator or air separator.
What is a deaeration device on a heating system?
These devices are common in Europe and the US but in the UK they are only starting to catch on. Yet on a closed loop sealed central heating system they are considered quite vital.
It is hoped more engineers will adopt VDI 2035 methods and be able to explain to customers the importance for checking water hardness, pH and conductivity. For more info