Of all the chemical elements, hydrogen is the most plentiful in the universe. It is the first element in the periodic table and has the atomic number 1. It is a component of water and most organic compounds such as natural gas, oil and sugar – and alongside oxygen and natural gas, is the fuel that the Vitovalor combined heat and power (CHP) unit runs on.
In relation to mass, hydrogen has the highest energy density – 33.33 kWh/kg – of all fuels. By way of comparison, methane has a mass-related energy density of 13.9 kWh/kg whilst petrol has 12 kWh/kg. One litre of hydrogen therefore contains almost as much energy as three litres of petrol.
Hydrogen is also the lightest gas. Its volume-related energy density is just 3 kWh/Nm3; that of petrol on the other hand is 8800 kWh//Nm3. The standard volume given here as Nm3 is a unit of measurement for gas volumes at identical pressure and temperature levels. When used as a fuel, hydrogen is therefore either highly compressed or condensed.
In contrast to natural gas, crude oil and coal, which are considered primary energy sources, hydrogen is used as a secondary energy source. This is because it does not occur in nature in its pure form; this must first be produced. It has many further differences to other fuels. Pure hydrogen as an energy source is:
Hydrogen has already proven its suitability as an energy source for fuel cells in vehicles and ships many times over. It is also being used more and more often in residential settings. In Japan alone, where technology is valued very highly, sales of fuel cells for stationary applications have risen to more than 200,000 since 2009. One of the heating appliances that makes use of this clean and futureproof technology is the Vitovalor. It is the result of a joint project between Viessmann and Japanese technology giant Panasonic. Hydrogen is obtained in a gas reformer in the presence of a catalyst. The source material for this is the cleanest of the fossil fuels, natural gas.
In an electrochemical process, the hydrogen, which has been separated from the source fuel, is split and at the same time, oxygen is added. This results in the generation of both power and heat. The type of combustion that takes place in conventional condensing boilers does not occur. This electrochemical process is also referred to as cold combustion. Experts are of the opinion that CO2 is one of the main factors causing global warming. Hydrogen on the other hand releases mainly water during the process in the fuel cell, making it very environmentally responsible. Its use also reduces the consumption of limited fossil fuel reserves.
As mentioned in the previous section, hydrogen can be used for many applications. As a lifting gas for airships, as was the case 100 years ago, or as an energy source for welding as is still the case today: to put it simply, hydrogen is no more dangerous than conventional fossil fuels – quite the reverse. After all, compared to gas and oil, hydrogen stands out on account of its very positive properties. Moreover, hydrogen is not carcinogenic and burns without leaving any residues.
Contrary to popular public belief, hydrogen per se is not explosive and therefore not automatically dangerous. It is only dangerous in the presence of an oxidiser such as oxygen and an active ignition source. The risk of an explosion involving hydrogen is generally low – especially where the Vitovalor is concerned, since there is no fuel store as is the case with conventional boilers. Instead, hydrogen is produced from the source fuel – natural gas – as needed and only in the required quantity. Furthermore, cold combustion involves splitting hydrogen atoms, which automatically precludes the possibility of an explosive oxyhydrogen reaction. The hydrogen in the Vitovalor can therefore be considered as no more dangerous than commercially available natural gas. You will also find more information about hydrogen in the Guide to the Vitovalor.