Pellet heating System
Heating with pellet stoves & pellet boilers
- The pellet boiler, which is used as central heating and which is usually located in a heating room. Pellet boilers are differentiated into semi-automatic and fully-automatic pellet heating systems. Of late, wall-mounted pellet appliances which work with low-temperature technology are on the market.
- The pellet stove, which are used as individual room heating based on air as well as central heating using an integral heat exchanger and installed in living rooms.
The area of application of a pellet heating system is very varied and broad based. Pellet heating systems are especially suitable for detached and semi-detached houses as well as apartments of every size. The use in larger living complexes is also optimal, as well as in the commercial, communal and industrial sectors. As a result of the various technologies, performance sectors from 5 kW up to 100 kW heating output in cascade connection are possible.
Combined or hybrid pellet heating systems can be additionally fuelled with split logs or wood chips. A pellet heating system can be controlled to approx. 30% of its nominal heating output. Heating operation together with a heat buffer system is ideal for the efficiency of the complete system.
The method of charging and combustion of the pellet fuel is divided into 5 technologies.
- Pellet heating system with roller grate system: The pellets fall from above onto several slow-turning steel plates with small clearances. A skimmer cleans the clearance spaces with every revolution so that the ash can fall down unhindered and combustion air can be fed through upwards.
- Pellet heating system with underfeed firing: The pellets are pressed from below into a burn plate by an auger where they are burnt and the ash that remains falls over the edge of the plate into the ash pan below.
- Pellet heating system with side-fed firing: This technology functions similarly to the underfeed firing except that the fuel is pressed via an auger onto the burn plate from the side. At the same time the burn plate as well as the air supply can be configured to match partial performances.
- Pellet heating system with drop chute firing: With this system the pellets slide down a drop chute into a burn pot. By using a burn pot the combustion area is exactly defined, combustion can therefore be exactly controlled. With this technology the least rest ash remains compared with other systems and can be carried out of the burn pot by cleaning mechanisms. This type of charging is usually used for pellet stoves.
- Pellet heating system with suction technology: The 100% burnback security of the drop-chute system combined with a solid metal rotary valve, prevents coating of the cyclone or suction turbine with dust. The narrow and high cyclone cleans the return air of dust and thereby guarantees maximum service life of the turbine. The variable control firebed possible with the drop principle, together with the high combustion chamber temperatures, makes unique modulation characteristics possible.
In order to optimize efficiency and pollutant content of exhausted air, modern pellet heating systems control combustion either via a temperature or flame space sensor in combination with an infinitely variable input of combustion air via a suck-blow fan or a lambda probe. The hot flue gases are led into the chimney via a heat exchanger with manual or automatic cleaning of the reheating surfaces.
Most pellet stoves are equipped with burnback protection. Generally good pellet heating systems are configured for very safe and almost fully-automatic operation, so that cleaning and maintenance work are only necessary at intervals of several weeks or months depending on the type of system involved. Several pellet heating systems achieve maintenance intervals of once per annum and are therefore almost as convenient as comparable oil or gas-fired heating systems. Some manufacturers of pellet stoves recommend daily cleaning of the burn pot for safety reasons.
For modern pellet heating systems, the emission of fine dust is approx. 8 mg per MJ heat quantity equal to 29 mg/kWh. In the meantime pellet heating systems have been developed which by means of optimized combustion, can undercut the specified emission limits and can also be installed where tighter specifications are applicable. Such heating systems operate with condensing technology and have relatively dust and soot free flue gases (approx. 4 mg fine dust per MJ). In comparison, fine dust emissions for single stoves (fireplaces, tiled stoves) are approx. 150 mg/MJ, for wood-burning boilers approx. 90 mg/MJ, and for oil-fired heating systems approx. 3 mg/MJ.