Sustainable solutions for heat generation are more in demand today than ever. Energy from renewable raw materials is the order of the day. The standardized small compacts made of wood are all the rage when it comes to renewable energy. And actually they are a Swiss solution.
Especially in old buildings with flow temperatures between 75 and 90 °C, solutions with natural and low-CO2 raw materials as heat carriers should definitely be included in the energy considerations. So that, for example, a heat pump can be operated economically, large sums have to be invested in the renovation of the building envelope. In order to be able to reduce flow temperatures, the surfaces of radiators would have to be enlarged, which would also be associated with high costs. Pellet heating is a very good alternative. In existing technical rooms there is usually enough space for a complete pellet heating system.
Example of a refurbishment of a historic building
Historic building fabric is aesthetic and exudes a touch of the magic of days gone by. That's a good thing - until renovation work is due. Then there are not only high costs, but also the home protection or monument protection has an important say. When evaluating a new heating solution, you get to feel the pitfalls of old building fabric. But there are also ideal solutions for buildings worthy of protection. As in this example of a hotel in central Switzerland that is over a hundred years old.
When the periodic heating oil tank renovation and further investments in the building infrastructure were due, the right time had come to finally say goodbye to fossil fuels. The location directly on the lake actually spoke for a water-water heat pump. But in historical buildings with poor insulation, the system temperatures are usually high and a heat pump could not be operated economically. The choice fell on the renewable and CO2-neutral fuel wood. Since a hotel needs a heating system that is highly reliable, ultimately only the pellet heating system met the complex catalog of requirements.
New use of space
The oil tank with a capacity of several thousand liters was housed in a separate room next to the technical room. That's when the idea came up to place the pellet silo outside the hotel complex and convert the space that was freed up as a result into a fitness studio for the guests. Today the silo is on the outside wall of the boiler room and can be easily filled with the pellet tanker at any time. The volume of the silo is 22 m3 or 15 tons of pellets, which corresponds to a six-month supply. The existing stone fireplace was demolished, thereby expanding the space available. The elegant new stainless steel chimney, color matched to the building, requires little space and in no way disturbs the picturesque image of the hotel.
Easy maintenance - good for the environment
Boiler specialists such as Windhager or Meier Tobler have years of experience with pellet heating systems and offer excellent products. They are equipped with proven combustion technology, the highest levels of efficiency and are very convenient to operate. Burners with the latest technology ensure an optimal combustion process with a stable bed of embers. Efficiencies of up to 98% can be achieved and the limit values for fine dust emissions are clearly undercut. The high technological standard of the firing technology enables combustion with practically no ash residue and guarantees trouble-free operation even with fluctuating pellet qualities. The reliable operation of modern pellet boilers is comparable to oil or gas boilers - only much more environmentally friendly.
Do these little energy miracles really come from Switzerland, or is the starting material delivered from distant forests? A conversation with Peter Lehmann, Head of Sales at AEK Pellet AG, Balsthal, gives an insight into the domestic production of the fuel from wood.
Pellets «Made in Switzerland»
AEK pellets are made in-house from local wood. Only sawdust, shavings and wood chips are processed, delivered from regional sawmills and wood companies. The local added value is therefore high. Pellets have a high level of environmental compatibility, are CO2-neutral and the raw material grows back. They are crisis-proof and less dependent on the international fuel market. As a domestic added value, pellets correspond to the ideas of the Swiss population, the short transport routes are economical.
Pellets have a high calorific value of around 4.8 kWh/kg. The annual requirement is around 400 kg per kW heating load. In a nutshell: it is the most convenient way to heat with wood. The energy required to produce pellets is around 3% of the energy content of pellets (heating oil around 15%).
The idea of producing pellets was triggered by the storm of the century "Lothar" in 1999. The uprooted trees had to be put to good use. Today, AEK Pellet AG is the market leader with a production of over 60,000 tons. This amount is enough to heat 12,000 single-family homes.
How these little energy miracles are created
Damp wood chips are dried and crushed. Before dry sawdust is processed into pellets, another quality control is carried out. If it is bark-free, the colour, smell and water content are correct. Then the basic material comes into the production hall. Spruce and fir wood is very suitable for production and is available in large quantities in Swiss forests. The starting material is stored in the buffer store and from there a conveyor belt takes it to the magnetic and heavy-parts separator. What does not belong in the wood mass is removed here. The next step is the hammer mill, where 132 little hammers grind the material as finely as necessary at 3,000 revolutions per minute.
The three presses each have a throughput of 4 tons per hour. The perforated die ring creates the shape: the finely ground raw material is heated to around 100 degrees Celsius and pressed through the die. The heating dissolves lignin, a natural glue in the wood, connects the wood particles and thus strengthens the pellets. The natural, shiny shell around the pellet also offers protection. At the end of the matrix ring, the rods are separated into the standardized length. The quality is monitored throughout the production process and samples are taken every hour.
Proper storage
The storage of the pellets plays an important role in maintaining the quality. Proper ventilation of the warehouse is also essential. If a fuel storage room already exists, for example when converting from oil to pellets, this can be converted into a pellet storage room. The volume of the room is usually sufficient for the required amount of pellets during a renovation. So-called textile silos can be used, for example. This type of storage offers a maximum of spatial flexibility. They are easy to install and do not require any special structural precautions. A flexible, air-permeable but dust-proof and anti-static fabric ensures optimal storage and dust-free delivery. Depending on the fuel requirement, silo sizes with a capacity of up to 12 t of pellets are available.
The full article was published in p+i 01/22
