Fireplace

from Wikipedia, the free encyclopedia
Fireplace stove with glass ceramic fire door

A wood-burning stove, fireplace or Swedish stove is a stove for fossil or biogenic fuels that is located in front of or next to the chimney and is connected to it with a stove pipe . It is to be distinguished from an open fireplace in that it has a combustion chamber that is closed except for air inlet openings and it is usually not built in. Transparent glass ceramic is used for doors with a window . This material, which is heat-resistant up to around 700 ° C, has been around since the 1970s.

construction

A stove is usually made of cast iron or sheet steel. It often has one pane (sometimes several) for a clear view of the combustion chamber. A wood-burning stove emits the heat energy partly in the form of radiation to the room and partly by conduction to the room air, where it is then distributed by convection . Basic stoves (synonym storage stoves ) emit most of the heat through radiation. The heat transfer to the ambient air and the heat transfer through the materials of the furnace (steel, fireclay, natural stone, glass) depend on the temperature in the furnace.

Air supply

The fuel in the furnace needs air in order to be able to burn.

  1. So-called primary air passes the ash pan through the grate and enters the combustion chamber from below.
  2. Secondary air is sucked in past the ash drawer through air ducts. These vertical channels are heated by fire; the air rising in them is preheated. The channels usually end up in the combustion chamber near the glass pane (s); the panes are washed behind and heated, so that the panes do not fog up with condensable substances and become cloudy. The secondary air helps burn the combustible gases that have escaped from the wood.
  3. Tertiary air can also promote the afterburning of the gases. The more completely the gases burn, the fewer unburned flue gas components are emitted .

Water-bearing stoves

Water-bearing stove with 19 kW heating output and hob

Water-bearing stoves feed a large part of their heat into the water circuit of the central heating by means of heat exchangers . In addition, they (and the stove pipe between the stove and the transition to the chimney) heat the room in which they are located. They distribute the energy evenly in the house, act like a heating system and can also guarantee the hot water supply. They relieve (or replace) the heating system through the water flow. In connection with the hot water storage tank of the heating system, the energy from the fire can be used later in the evening (e.g. for showering the next morning). In Germany, a thermal discharge safety device is prescribed for pressurized, water-bearing stoves : if the power to the circulation pump fails, excess heat is dissipated in an emergency by the drinking water that then flows through the stove. Water-bearing wood-burning stoves that are operated as open, pressureless systems do not require a thermal discharge safety device, since pressure cannot build up due to increased temperatures despite a power failure and these wood-burning stoves are intrinsically safe by design .

A water-bearing stove that also has a hob and / or an oven is called a water-bearing heating stove or a cooking stove . In addition to water-bearing wood-burning stoves, there are also water-bearing pellet stoves that can even surpass classic water-bearing wood-burning stoves in terms of functionality and handling. The handling of a pellet stove, regardless of whether it is water-bearing or not, is easy. This applies to heating up and also to ongoing operation. Thanks to the automatic pellet feed and the programmability, heat can also be provided in absence and the regular refilling of wood, as is necessary with a fireplace, is no longer necessary. Water-bearing pellet stoves are funded by BAFA .

Downfire furnaces

In furnaces with a lower burnout (mostly log boilers and solid fuel boilers), the firewood (fuel) is heated before burning. Outgassing volatile compounds are drawn together with the fresh air through the invisible combustion zone (surrounded by heating coils). The turbulence and combustion are usually more complete.

Open fireplaces and most woodburning stoves are top burn stoves where the wood burns like a campfire and this can be viewed through a sight glass. However, outgassing wood components can also be partially burned or unburned in the exhaust gas (which is harmful to the environment and you can smell around a house that is heated in this way).

In order to combine the advantages of an upper burnout (visible cozy flames) with the lower burnout (improved complete combustion), flue-fire stoves were developed as "natural draft gasifiers" (without induced draft fan as in boilers), in which the outgassing substances from a "wood drying chamber" with the fresh air into a chamber with a shop window downstairs.

Emissions

In Germany, wood-burning stoves with a nominal output of 4 kW or more are subject to the regulations of the ordinance on small and medium-sized combustion systems . Depending on the model, the emissions can differ significantly. Fireplace stoves with particularly low emissions can be awarded the Blue Angel .

Fireplace stoves that are fed with renewable energies such as firewood , wood briquettes or wood pellets do not contribute to the greenhouse effect in contrast to stoves that are charged with fossil fuels , provided that the fuel comes from the annual growth or offspring. Only substances are burned that would otherwise have rotted away in nature and released the CO 2 bound in the wood .

If chimney or pellet stoves are operated with wood, wood-like substances or coal, they can be used as dioxin emitters . The table salt contained in it combines at the low combustion temperatures with lignin containing hydrocarbons (wood) or maceral and residual moisture (coal) to form dioxin.

Also PAHs (polycyclic aromatic hydrocarbons) are found in the exhaust gas of chimney and pellet under the same formation conditions, but without NaCl (sodium chloride) as reactant.

The Federal Environment Agency of Austria led in 1997 and measurements. a. on an old cast iron stove. When heating with wood, it emitted far fewer pollutants than when heating with coal.

According to an estimate, wood stoves in Germany emitted 19,000 t of fine dust in 2005 ; In 2012 it should have been around 27,000 t. The Federal Environment Agency has suggested that emissions will decrease to 20,000 t per year as a result of the requirements adopted in 2010. The 15 million stoves and chimneys in Germany thus emitted more fine dust than road traffic. With small wood-fired fires, however, around 80 percent of the fine dust emissions can be avoided by using the correct lighting method (ignite above).

In 2016, in the event of inversion weather conditions in Stuttgart, the operators of chimney stoves were asked not to operate them (“ fine dust alarm ”). The state government issued the 'Air Quality Ordinance - Small Firing Systems' on January 31, 2017. Since then, the operation of comfort chimneys (single-room firing systems for solid fuels that supplement an existing heating system and do not cover the basic need for heat) has been prohibited on days with a fine dust alarm.

Correct lighting

The lighting method “from above” is better than the method “from below”. To do this, one or two thick logs are placed on the grate, a ball of dry paper on top and this is covered with a few dry wood chips like a pyramid. Burning paper with rapid heat causes the chimney effect in the chimney due to the strong buoyancy . At the same time, the wood chips are ignited. The first heat evaporates volatile substances (combustible and residual moisture) in the logs and, due to the chimney draft, are drawn through the hot fire zone and burned effectively and more efficiently. When a layered pile of firewood is lit "from below", the heat evaporates volatile substances from above, but they are usually only partially, i.e. incompletely, burned. This creates more smoke and soot and carbon monoxide in the exhaust gas during the heating-up phase and the flames are cooled (by binding the heat of evaporation ); heating up and incomplete combustion take longer.

Fuels

One (1) cubic meter of dry, seasoned hardwood weighs around 500 kg and has a calorific value of around 2100 kWh. This corresponds to 210 l (approx. 170 kg) EL heating oil or 200 m³ (166 kg) natural gas. Air-dried logs (residual moisture 10–20%) have a calorific value of 3.9–4.6 kWh / kg. The calorific value depends somewhat on the type of wood (softwood or hardwood). Manufacturers of wood briquettes indicate a calorific value of around 4.5 kWh / kg. Bioethanol has about 8 kWh / kg.

A good combustion can be recognized by the light gray ash that no longer contains any fuel residues. The ashes from untreated wood can be used as fertilizer in the garden or added to the compost, as they are made of minerals such as B. There is lime, for dosage see ash # use .

Light furnace

The modern wood-burning stove with its typically large window is historically based on the cast-iron light stove that came from the USA and became popular in Europe around 1910. Its name comes from the fact that, for the first time, larger windows filled with highly transparent mica sheets, especially in the oven door, allowed light and heat radiation from the flames to radiate outwards.

Previously, only small openings - for example in ornaments - allowed a permanent control view through the closed furnace door at least in the dark, at the cracks of a small inner door of the combustion chamber. Before the openings could be glazed, the risk of large pieces of embers jumping out of the furnace, causing fire, had to be countered.

These mica sheets of the luminous furnace are temperature-resistant up to 600 ° C, typically 0.2 mm thin, at most 25 × 25 cm in size, because they split off from manually mined mineral crystals. They were often installed with a somewhat uniaxial curve (cylindrical), which means that they withstand pressure surges from the combustion chamber and manual contact better than flat.

history

Orders under Palatine Count Karl IV. From 1772 also served to prevent fire in connection with domestic fireplaces. According to simultaneous building regulations, no more wooden chimneys were allowed to be erected, no more wooden hoses were allowed to be built in to conduct the smoke from the fireplace to the fireplace, just as it was forbidden to lead stovepipes out of the window.

See also

literature

Web links

Individual evidence

  1. ↑ Martin Kaltschmitt, Hans Hartmann, Hermann Hofbauer: Energy from biomass: Fundamentals, techniques and processes . Gabler Wissenschaftsverlage, 2001 ( full text / preview in Google book search).
  2. ↑ Wood burning stoves. In: blau-engel.de. Retrieved January 13, 2020 .
  3. ↑ Blue Angel for wood-burning stoves. In: Umweltbundesamt.de . December 13, 2019, accessed January 13, 2020 .
  4. ↑ Gerhard Tanner, Wolfgang Moche: Emission of Dioxins, PCBs and PAHs from Small Firings pdf, p. 3. ISBN 3-85457-625-0 PDF (Note: a stove from the 1980s is very different from the stoves sold today Newly approved stoves in Germany since January 1, 2015 must meet the Federal Immission Control Ordinance ("Level 2").)
  5. ↑ vdi-nachrichten.com: Even state-of-the-art ovens can produce a lot of dust , November 7, 2014.
  6. ↑ Leibniz Institute for Tropospheric Research, Biomass Combustion Can Contribute to Fine Dust Pollution, February 4, 2013 .
  7. ↑ spiegel.de August 17, 2014: Pollution from fine dust .
  8. ↑ Good for the climate - bad for the air? In: bafu.admin.ch . December 16, 2019, accessed December 20, 2019 .
  9. ↑ stuttgart.de: stuttgart.de Feinstaubalarm , accessed on December 14, 2016.
  10. ↑ Information on the ban on operating comfort fireplaces
  11. ↑ Technology and Support Center in the Competence Center for Renewable Raw Materials (TFZ): Correct heating, The operation of chimney stoves July 2015 (pdf, 20 MB).
  12. ↑ TFZ: Correct lighting of a fireplace , 09/2012.
  13. ↑ youtube.com: Department of Economics of the Canton of Bern, Heating with wood, but without smoke , November 2, 2008.
  14. ↑ Federal Environment Agency: Heating with wood, a guide to correct and clean heating ( Memento from March 6, 2015 in the Internet Archive ) (1 MB, 2013).
  15. ↑ Bavarian State Office for the Environment : Heating with wood in chimney stoves ( Memento from January 29, 2016 in the Internet Archive ) (2010).
  16. ↑ Mila Schrader: Cast iron ovens and cookers: history, technology, fascination - a historical review ; edition elsewhere, October 2001, accessed on June 21, 2014, u. a. P. 112
  17. ^ Franz-Josef Sehr : The fire extinguishing system in Obertiefenbach from earlier times . In: Yearbook for the Limburg-Weilburg district 1994 . The district committee of the Limburg-Weilburg district, Limburg-Weilburg 1993, p. 151-153 .