Wood heating

from Wikipedia, the free encyclopedia
Mixed type of wood heating: water-bearing stove with connection to the central heating system, installation in the living room, combustion in wood gasification technology with natural draft

A wood heating system burns wood and thus generates heat for heating rooms and buildings. It is a building heater . Wood is a biogenic solid fuel .

The fuel wood (" firewood ") can be burned in the form of split logs , logs , wood briquettes , wood pellets or wood chips . Log wood has always been burned; Pellets and wood chips are burned in specially built ovens with automatic loading.

Wood heating systems can produce heat for an entire house ( central heating ) or for a single room. Some of them also serve to support heating and are only operated occasionally (e.g. chimneys ). If a system supplies a large or several buildings, it is called a heating plant or a biomass or wood heating plant .

The emissions from wood heating ( fine dust , carbon monoxide , polycyclic aromatic hydrocarbons (PAH), etc.) have increased due to the sharp increase in the use of wood as a fuel. There are (as in other areas, e.g. traffic, conventional heating ) laws and ordinances to limit these emissions. For small combustion systems in Germany, the ordinance on small and medium-sized combustion systems (1st BImSchV) specifies limit values; the last new version has been in force since March 22, 2010.

Individual room lighting

Wood stove in Klammstein Castle

Some types of wood heating are only used to heat individual rooms.

Central heating assisted ovens

Newly insulated single and two-family houses need significantly less heat than old buildings; you can heat water with a water-bearing wood-burning stove or tiled stove and store it in a buffer tank in order to feed it into the central heating later (= time-delayed). Some also allow domestic water to be heated , e.g. B. for showering or bathing. The functional principle is simple: In the heating element of the stove, water is heated on the heat exchanger surfaces and, when a set minimum temperature is reached (usually around 65 ° C), is pumped into a buffer storage tank. The buffer storage usually holds 500, 750 or 1,000 liters, depending on the performance of the water-bearing furnace or other sources (e.g. solar system), which can also be connected. Depending on the heat demand, a single-family house can be supplied with heat for a longer period of time while the stove is out of order. In the case of water-bearing stoves, two different systems have prevailed over the years:

  • Downstream heat exchangers use the flue gas temperature in the exhaust gas from the furnace insert;
  • So-called boiler devices generate the hot water directly in the combustion chamber surrounded by water .

Which system is more suitable in each individual case depends on the relationship between the heat requirement in the room where the stove is installed and the water output required. An incorrect design of the system can lead to overheating of the installation room, while the water output is too low to serve the buffer storage tank. Conversely, the buffer storage tank can become overcharged while there is not enough power available for heating in the room where the tiled stove is installed. Tiled stoves with a downstream water register are more suitable for an old building with high heat requirements in the room where the stove is installed and light heating support. Boiler devices, on the other hand, are more likely to be used in low-energy houses; A relatively low furnace output is often required there and a relatively high water output to operate a large buffer tank.

stack

A fireplace is a device for heating and subtle lighting of a room. Fireplaces are completely embedded in the wall of the room or protrude a little into the room. The combustion chamber is often open to the living room and gives off the heat directly to the room air. The high and non-controllable air supply results in a relatively large number of pollutants during combustion , which are removed via a chimney . With closed chimneys (viewing window) the air supply can be regulated; the temperature in the combustion chamber is much higher than with an open fire; as a result, the efficiency is several times higher. Fireplaces can have hot air circulation; this increases the heating output (and thus the efficiency) somewhat.

Fireplace

A stove is a stove for fossil or biogenic fuels . Most of the time, stoves are placed in front of a wall (not built into the wall) in the living room and have a closed combustion chamber. They are made of cast iron or sheet steel and often have glass panes for a clear view of the firebox. Wood- burning stoves can be designed as long-burning stoves or as time- burning stoves that are manually fired with fuel through a door. The air supply can usually be regulated using slide controls or air flaps. The efficiency of the most efficient wood-burning stoves reaches over 80%.

Tiled stove

A fireplace is a generally made of firebricks set room furnace with tiles is covered. In it you can burn logs and wood briquettes, in some also coal. A tiled stove is also called a storage stove because it has a large storage mass (e.g. clay, tiles, etc.). This mass absorbs heat, stores it and releases it to the room air at a temperature of 80 to 125 ° C. There is some time between the time of lighting and the beginning of the release of heat.

Cooking stove or heating stove

A heating stove is a wood-burning stove with an integrated hob and occasionally also with an oven. Water-bearing models can be connected to the heating system and thus supply a hot water storage tank , buffer storage tank and / or the house with heat. Heating stoves, like log fires, offer the opportunity to view the fire in the combustion chamber. According to the new First Federal Immission Control Ordinance (1st BImSchV), heating stoves in Germany have a minimum efficiency of 75%. In addition to being used in residential buildings, they are also used for complete heating in holiday homes. In Europe, the safety and emissions test is carried out uniformly in accordance with DIN EN 12815.

Efficiency improvement

The efficiency of the above Ovens can be improved with an exhaust gas heat exchanger , which integrates the ovens into the central heating system. There are also furnace pipes with cooling fins or the like; Common names are warm air exchangers , exhaust gas coolers or exhaust gas heat exchangers .

Central heating boiler

Wood chip heating, 45 kW, wood chip feed through square pipe in the picture
The burner chamber of a wood chip heating system, auger (top center) is used to return the ash to the burner chamber

Central heating is a heating system that can heat several rooms or an entire building. As a rule, water is used because of its good suitability (readily available, harmless, high specific heat capacity ) as a heat carrier or exchanger and, in buffer storage, often also as a heat store.

Wood gasification boiler

Wood gasification boilers are more efficient and have significantly lower emission values ​​than natural draft boilers , as a regulated fan ensures an optimal air supply during combustion. The wood gasification boiler is filled (“charged”) once and then burns out for several hours. The storage tank should be large enough so that the boiler can work at full load for the entire duration of the burn. The stored heat can then be accessed as required over a longer period (several days). The heating water circuit of an older single-family house can contain several hundred liters of water (large pipe diameter; radiators with a lot of water); it can also buffer part of the heat. In contrast, new buildings have relatively little water in the cycle.

Natural draft boiler

Natural draft boilers are controlled by opening a flap that is connected to a temperature controller or is set manually. You can regulate the performance; if the fire gets "too little air", incomplete combustion (=> increased emission of carbon monoxide etc.) can result. If the released heating energy is above the current demand, a buffer storage tank is needed. Natural draft boilers can be used as stand-alone heating or combined with an existing oil , gas or pellet heating system .

Wood pellet boiler

Wood pellet boilers offer the comfort of classic oil or gas heating, because the operation can be automated (feeding by a screw conveyor, ignition by hot air and boiler cleaning by shaking). Due to the defined level of residual moisture in the wood pellets and controlled combustion, small amounts of ash are produced. Modern pellet heating systems are more efficient and have lower exhaust gas values ​​than other wood-burning systems.

Wood chip boiler

Wood chip boilers also offer the convenience of classic oil or gas heating because the operation is automated ( wood chip feed by a screw conveyor, ignition by hot air and boiler cleaning by shaking). Due to the regulated combustion (using a lambda probe ), small amounts of ash are produced.

Emissions from wood heating

Exhaust plume from a wood furnace

Wood heating systems emit more fine dust , polycyclic aromatic hydrocarbons (PAH) and soot than gas or oil heating systems with comparable performance.

If the exhaust gases contain a lot of soot or ash particles, the smoke will look gray. The soot content can be estimated using the gray tone. The darker the gray, the higher the soot content. White smoke is caused by water vapor which condenses after exiting the chimney or which emerges as mist condensate - aerosol . When damp wood is burned, heat is used to evaporate the water, this lowers the flame temperature and prevents the post-combustion of volatile organic compounds (see also fireplace # air supply and tiled stove # incomplete combustion ), which causes soot and soot as a result of incomplete combustion (see also smoldering ) water vapor is produced in the cooled flue gas . Many pollutant vapors or gases - such as carbon monoxide - are colorless and therefore invisible. An exact quantitative determination of the pollutants is only possible by measurement.

When oil, gas and wood are burned, small amounts of carbon monoxide (CO) are always produced (due to incomplete combustion). It dilutes quickly in the atmosphere. Carbon monoxide occurs in natural and man-made environments. A typical concentration in the atmosphere is 0.1 ppm. In residential buildings, the normal concentration is 0.5 to 5 ppm, with concentrations of up to 15 ppm in the vicinity of gas burners. Wood fires in chimneys can release up to 5 ‰ carbon monoxide (= up to 5000 ppm).

The carbon dioxide released by wood heating was previously absorbed by the tree as it grew and is therefore part of the carbon cycle . The transport of the wood to the place of combustion may cause a certain amount of CO 2 , e.g. B. by transport with a motor vehicle.

In Europe, the increased health risk associated with the increasing use of wood firing, which is being promoted as a “sustainable” form of energy use in connection with renewable energies , is discussed above all .

Germany

From around 2000 to 2005, reductions in fine dust by means of lower-emission forms of wood combustion were nullified by an increase in wood combustion systems. According to an investigation by the Federal Environment Agency, the fine dust emissions from wood combustion systems exceeded the emissions from road traffic (incineration only) by 22,700 tons.

In order to reduce the problem of particulate matter emissions from wood combustion, the legislature in Germany has decided that plants that were last subjected to a type test before January 1, 1975 must either be retrofitted or shut down by the end of 2017. Requirements for newer systems were decided in 2010 in the First Ordinance for the Implementation of the Federal Immission Control Act (1st BImSchV).

In small wood heating systems (private chimneys or stoves up to a nominal output of 15 kW), only the fuels specified in Section 3 of the 1st BImSchV, No. 1 - 4 and 5a, i.e. natural, lumpy or pressed wood, may be used. The incineration of varnished, painted or impregnated wood is prohibited because various pollutants are generated.

The burning of treated wood can be verified retrospectively by means of a soot sample; a check can be carried out in the event of suspicion.

With the amendment to the 1st BImSchV passed on December 3, 2009, limit values ​​for fine dust (0.10 g dust / m 3 ) and other pollutants were set. Since 2015 there has been a tightening for new systems (0.02 g fine dust / m 3 ).

Limit values ​​apply to systems with an output of 4 kW or more, with the exception of single-room combustion systems. Municipalities can impose conditions on the establishment (including bans). So z. B. in Aachen in October 2010 a local solid fuel ordinance for the city area came into force.

From a technical point of view, regulation of the combustion temperature and flue gas cleaning should be considered.

Switzerland

The revised Clean Air Ordinance (LRV) has been in force since September 1, 2007 . It contains new limit values ​​for the fine dust emissions from wood-burning systems.

Share in the energy supply

Firewood is the oldest fuel known to man and has been used for around 400,000 years. The great demand led to a shortage of wood at the end of the 18th century in Central Europe, one consequence of which was the substitution of wood by fossil fuels in the 19th and 20th centuries. Today the importance of wood in this regard is increasing again.

According to an investigation by the chimney sweep trade in Germany in 2018, the total number of individual firing systems for solid fuels was around 11.3 million:

Germany

Around half (68.3 million cubic meters) of the annual raw wood volume (135.4 million cubic meters) now goes into the generation of bioenergy. In Germany, wood is currently mainly used to provide heat, with private households representing the largest energy consumers of wood (33.9 million cubic meters of wood). In the heating sector , wood is the most important source of renewable energies . In 2016, wood provided around 114.5 billion kilowatt hours (billion kWh) of heat. Around nine percent of German heat consumption in 2016 was covered by wood energy. Together with the biomass portion in the waste that was used in waste incineration plants (0.9 percent of the heat consumption), solid biomass alone provided 75 percent of the renewable heat.

In contrast, wood is only used to a lesser extent to generate electricity. In 2016, 7 percent of gross electricity generation came from bioenergy. Wood alone made up a share of 0.005 percent in 2016 with 10.9 billion kilowatt hours (billion kWh).

In the transport sector, wood has no longer played a role since the Second World War. A rediscovery of machines with wood gasifiers , for example, was experienced in agriculture during the Second World War, when there was a shortage of fuel but the fields still had to be tilled. At that time tractors (e.g. from the Lanz company) were increasingly powered by wood gasifiers. However, the consumption of 1 sterile wood per hour worked was very high.

Switzerland

After hydropower, wood is the second most important renewable energy in Switzerland.

A little more than half of the annual wood growth in Swiss forests was used in 2006/07. If the potential were exhausted, wood could cover 5% of the total energy consumption or 10% of the heating requirement.

In total, wood energy covered around 3.4% of the total energy requirement or around 7% of the heat requirement in 2005. In 2007, the installed heating systems used around 3.8 million cubic meters of wood to generate energy.

The number of automatic wood heating systems in Switzerland has almost tripled since 1990, and their wood consumption has increased by one and a half to two times. As a result, poorly operated small wood-fired furnaces in Switzerland now contribute more to fine dust pollution than road traffic.

For wood heating systems with more than 50 kW output, 19% of all systems in Switzerland are located in the wooded canton of Bern, followed by Zurich (12%) and Lucerne (11%). In terms of total installed capacity, Bern is at the top with 15%, ahead of Zurich (13%) and Lucerne (10%). This can also be explained by the fact that predominantly people from rural areas use wood for heating.

Efficiency

In general, open chimneys without heat storage mass have the lowest degree of combustion efficiency. Gradually better are stoves with heat storage mass and stoves . Most of the heat can be extracted from the flue gases by water-bearing stoves. Accordingly, low-emission water-bearing tumble - burn stoves are considered to be those with the best combustion efficiency of individual stoves for living spaces.

State of the art (more precisely the "best available technology 2018" with database from 2010) for the combustion efficiency ( related to calorific value ) for log stoves is 86%. Regardless of the efficiency of a combustion, standstill losses due to unwanted chimney drafts can reduce the overall efficiency of the heating system. Reduce the theoretical nominal efficiency significantly

The emissions from wood heating ( fine dust , carbon monoxide , polycyclic aromatic hydrocarbons (PAH) etc.) and immissions have increased due to the sharp increase in the use of wood as a fuel. Legal regulations have been issued to limit emissions, in Germany for example the ordinance on small and medium-sized combustion systems (1st BImSchV).

criticism

The fine dust emissions of all small wood burning systems in Germany exceed the exhaust emissions of road traffic of approx. 7,000 t of which around 66,000 premature deaths are derived at 18,450 tons. It is criticized that due to unrealistic measurement methods and poor market surveillance "currently valid approval tests for wood-burning stoves [...] have little to do with reality" , only stable running operation "with the best wood in the best log size" , but not unstable, high-emission heating-ups are tested - and cooling phases or with the heating behavior of the user.

Others

In February 2008 the Federal Ministry of Food, Agriculture and Consumer Protection (BMELV) founded the German Biomass Research Center .

Individual evidence

  1. ↑ The quality and quantity of fine dust can be significantly reduced with simple means ( memento of the original from October 29, 2013 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 155 kB) @1@ 2Template: Webachiv / IABot / www.lwf.bayern.de
  2. ^ Committee on Medical and Biological Effects of Environmental Pollutants: Carbon Monoxide . National Academy of Sciences, Washington, DC 1977, ISBN 0-309-02631-8 , p. 29.
  3. ↑ Green W: An Introduction to Indoor Air Quality: Carbon Monoxide (CO) . United States Environmental Protection Agency. Retrieved December 16, 2008.
  4. ↑ Doubts cast on biofuels' air quality claims report from November 15, 2011 at www.euractiv.com (English)
  5. ↑ The side effects of comfort: fine dust from the fireplace and wood stove. Background paper of the Federal Environment Agency, March 2006.
  6. ↑ 1st BImschV, version 2009 (PDF; 579 kB)
  7. ↑ Regulatory authority ordinance on the operation of single-room firing systems for solid fuels (Aachen Solid Fuel Ordinance - FBStVO) of 29 September 2010
  8. ↑ Surveys of the chimney sweep trade . Federal Association of the Chimney Sweep Crafts Central Guild Association (ZIV) - 2018
  9. ↑ Thünen 'What role does energy wood play', page 10, quoted here from Mantau 2012. (PDF) Retrieved on July 12, 2017 .
  10. ↑ Thünen, raw material monitoring wood. Retrieved July 12, 2017 .
  11. ↑ a b c AGEE Stat, time series on the development of renewable energies in Germany. (PDF) (No longer available online.) Archived from the original on May 17, 2017 ; Retrieved July 12, 2012 .
  12. ↑ AG Energiebilanzen eV, power generation according to energy sources 1990-2016. (Download as pdf). Retrieved July 12, 2017 .
  13. ↑ Possibilities for reducing emissions for small furnaces , accessed on January 28, 2012.
  14. ↑ a b Stefan Aigenbauer, Wilhelm Moser, Christoph Schmidl: final report new stoves 2020. The stove of the future - measures to implement the highest possible state of the art of stoves for lumpy wood fuel ; Report BIOENERGY 2020+; Page 36, PDF file
  15. ↑ Wood Stove 2020 research and innovation project. Development of the next generation of clean wood stoves ; TFZ technology and support center in the competence center for renewable raw materials; at tfz.bayern.de
  16. ↑ Stefan Aigenbauer, Wilhelm Moser, Christoph Schmidl: Final report new stoves 2020. The stove of the future - measures to implement the highest possible state of the art of stoves for lumpy wood fuel ; Report BIOENERGY 2020+; Page 32, PDF file
  17. ↑ Stoves: side effects of comfort ; at daserste.de
  18. ↑ The quality and quantity of fine dust can be significantly reduced with simple means ( Memento from October 29, 2013 in the Internet Archive ) (PDF; 155 kB)
  19. ↑ Fine dust emissions from small combustion systems ; at Umweltbundesamt.de
  20. ↑ fine dust and soot ; at clean-heat.eu
  21. ↑ a b wood stoves. Cozy and dangerous ; at zeit.de
  22. ↑ Archived copy ( memento of the original from October 29, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.dbfz.de

Web links

Wiktionary: Wood heating  - explanations of meanings, word origins, synonyms, translations

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