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Small Scale Biomass Boilers Guidelines |
Introduction
This is one of a series of leaflets covering
biomass (wood) combustion systems in Austria, where wood provides the
greater proportion of energy for heating of domestic buildings, hotels,
etc in many regions. This may be through small furnaces and boilers as
described here, or through larger district heating systems (1 to 2 MW - see
Biomass District Heating Plants Guidelines).
The leaflet is based on the premise that
" After many years of
advisory services it became clear that information given on planning,
choice and installation of biomass heating systems in dwellings and
residential buildings has to be increased decisively. This guideline shall
provide for the basic information on the topic. First, a short summary of
the situation in Austria will be given. Furthermore the different types of
boilers available in Austria will be presented as well as the course of
action beginning with the decision-making phase until the operation of the
plant. At the end of this bioguide you will find a list of addresses where
advisory services may be obtained and a list of companies which offer
biomass heating boilers with an output of 5 to 100 kW"
IN support of biomass for domestic heating the leaflet suggests that:
"The argument that the efficiency of biomass heating boilers is
dissatisfying and that the boilers cause high emissions does no longer
apply to new boilers submitted to type tests. Their efficiency amounts to
80 and 90 %. Emissions caused by biomass heating systems are similar to
emissions caused by oil- and gas-fired furnaces. Frequent refill
operations are also a phenomenon of the past. If the furnace is fuelled by
dry logs and operated at nominal heat output refilling will only be
necessary after 6 hours. Furnaces with automatic stoking (chipped wood
furnaces and pellet furnaces) only require checking once a day. "
The leaflet then summarises the use of biomass for energy in Austria, this information is summarised in NFI/**, and not repeated here.
Analysis of demand: The guidelines indicate that:
"The
calorific value of dry wood lies at 4.3 kWh/kg. The calorific value of
recently cut wood with up to 60 % water content on the other hand ranges
from 1.6 to 2.8 kWh/kg. Therefore it is advisable to use only dry fuel for
firing. If the wood is stored in a dry and protected place the water
content can be reduced to less than 20 % over 1 or 2 years of storing.
Heating systems are constructed for the coldest days of the year. Only on
those days the nominal heat output of the boiler will be necessary. The
calculation of the heat requirement is a prerequisite for boiler
constructions. The maximum boiler heat output depends on the construction
of the walls and ceilings (roofs), the geographic position and the lowest
expected temperatures. For a one-family dwelling with 130 cu m floor space
and a normal heat insulation a nominal heat output of 15 kW will be
required. This corresponds to a maximum fuel consumption of 4.7 kg wood
per hour. Assuming 1600 hours of full load the annual fuel consumption is
easily calculated at 7,500 kg."
The guide provides the following comparison of the energy content of various types of fuel and the annual supply requirements for a single-family dwelling, with a power demand of 24,000 kWh (cu m = cubic metre; bcu m = bulk cubic metre).
| Fuel | Moisture content (%) | Energy content (kWh/unit) | Amount of fuel needed |
| log wood (beech) | 15 | 4.3 kWh/kg, 2400 kWh/cu m | ca. 7500 kg, 14 cu m |
| wood briquettes | 8 to 10 | 4.75 kWh/kg, 3090 kWh/cu m | 6700 kg, 10.4 cu m |
| chipped wood (spruce) | 30 | 3.5 kWh/kg, 750 kWh/bcu m | ca. 9100 kg, 43 bcu m |
| pellets | 3 to 10 | 4.75 kWh/kg, 3090 kWh/bcu m | 6700 kg, 10.4 bcu m |
The guide indicates that in Austria, Regulations and Standards have been set as follows
The minimal efficiency as well as the emission limits for manual and automatic residential heating systems up to a heat output of 350 kW were determined in agreements between the Federal State and the provinces under the regulations of article 15a B-VG in the law of the Federal Constitution of Austria. (Bundesgesetzblatt 388/1995; NO-Landesgesetzblatt 8208-0, 16. August 1995). The standardisation of fuels is one requirement for the establishment of a market as well as for the planning of boilers and heating systems. The following fuel standards include details about sampling, physical data (density, size, etc.) and average figures concerning the carbon content, the hydrogen content and the oxygen content.
ONORM M 7132 (Austrian standard): Energiewirtschaftliche Nutzung von Holz und Rinde als Brennstoff; Begriffsbestimmungen und brennstomechnologische Merkmale (1986); [Energy-economical utilisation of wood and bark as fuel; definitions and combustion properties].
ONORM M 7133 (Austrian standard): Holzhackgut fur energetische Zwecke -Anforderungen und Prufbestimmungen (1998); [Chipped wood for energetic purposes - Requirements and test specifications].
ONORM M 7135 (Austrian standard): Presslinge aus naturbelassenem Holz und naturbelassener Rinde - Pellets und Briketts - Anforderungen und Prufbestimmungen (1998); [Compressed wood and compressed bark in natural state - Pellets and briquettes - Requirements and test specifications].
As far as the supply of biomass is concerned the leaflet identifies fuel supply as a critical consideration for those who do not have access to their own resource. It indicates that over the last few years some provinces have set up centres co-ordinating the sale of firewood and wood chips, with information concerning supply also provided by the local Agricultural Chamber (forestry department) or the Local Farmers' Chamber. Briquettes or pellets may be bought in from various stores or shops, such as those providing building materials as well as sales outlets run by farmers' cooperative.
Concerning planning and the availability of various types of furnace the
guidelines indicate that
"Heating systems have to be authorised
by the respective authority. The building regulations of the provinces
contain all orders and requirements for the construction of furnace rooms
etc. The mayor is the first authority of the building authority. The
decision for the heating system should already be made during the planning
of the house, in order to be able to take into consideration the storage
room for the fuel, the feeder device, where the boiler shall be installed
and how much space will be needed . However, very often one has to be
satisfied with already existing locations and layout of rooms."
Three basic systems are recognised, depending on the fuel, and described
as follows.
The first group are log wood boilers, that are available
with an output range of 15 to 80 kW.
"In log wood furnaces logs up to a length of 50 cm are placed on the embers in the hopper. A fan sucks or forces the released gases through an opening into the combustion chamber, which is located directly under or beside the fuel storage tank. Secondary air is added and the wood-gas burns out. In the heat exchanger the heat is transferred to the heating water, which is pumped into the radiators in the rooms. A log wood boiler of the new generation will cost at least ATS 60,000. The efficiency of a log wood furnace can be increased considerably, if an accumulator tank is used"
Detailed calculations of the size of accumulator tanks required are given in the following standards:
ONORM M 7510-4: Uberprutung von Heizungsanlagen fur teste Brennstotte, mit einer Nenn-Warmeleistung bis 300 kW [Testing of heating systems for solid fuels with nominal heat output up to 300 kW]
EN 303-5 Heating boilers; Heating boilers for solid fuels; Hand and automatically fired; Nominal heat output of up to 300 kW; Technology, requirements, testing and marking
In chipped wood furnaces normally chipped wood with a grade of 30 mm is used as a fuel. The fuel is stored in a hopper or a storeroom and is transported into the boiler by means of a discharge device and a screw auger. The feeder device is equipped with a safety device to prevent back-burning. Chipped wood furnaces with feeder device, safety device, control device and automatic ignition cost at least ATS 150,000. The furnaces are offered with an output of 15 kW or more. For single-family or two-family houses as well as agricultural undertakings there is no limitation of the output range, as chipped wood furnaces are also produced for district heating with a boiler heat output of up to some MW.
Two different types of pellet furnaces are available on the market. One type, similar to chipped wood furnaces, is used as a central heating boiler and is equipped with a hopper or with a discharge system. The advantage of pellets compared with chipped wood is that the storeroom can be smaller and that the fuel is homogeneous. But on the other hand it is absolutely essential to ascertain that the fuel is stored in a dry place, because otherwise the pellets would soak and fall apart. The second type of pellet furnaces are stoves where the fuel is automatically stoked into the combustion chamber. They are used to heat the room in which they are installed, but they can also heat other rooms if they are equipped with a heat exchanger. Central heating boilers fuelled with pellets cost at least ATS 80,000. Pellet stoves will cost at least ATS 30,000. Pellet stoves are sold within an output range of 5 to 12 kW. The output of central heating boilers amounts to 15 kW and more.
Support measures:
Private persons get financial support for
the installation of biomass heating systems within the residential
building assistance and reconstruction measures. The amount of money will
depend on the province. Information is available at the Provincial
Governments, energy counselling services and at banks. Agricultural
undertakings can also get financial support from the Federal Ministry for
Agriculture and Forestry. Nominally the respective agricultural chamber
will co-ordinate the transactions.
The Guidelines were compiled and edited by:
Josef Rathbauer - Bundesanstalt
fur Landtechnik - A-3250 Wieselburg
The guidelines were developed in co-operation with
the following:
Mag. Susanne Geissler - Okologieinstitut, A-1070
Wien
Dipl.-lng. Andreas Grubl - OO Energiesparverband, A-4020
Linz
Dipl.-lng. Andreas Haferl - KWI Ingenieurleistungen,
A-3100 St. Polten
Ing. Leopold Lasselsberger - Bundesanstalt fur
Landtechnik, A-3250 Wieselburg
Max Lauer - Joanneum Research, IEF, A-8010 Graz
Dipl.-lng. Karl Payer - Bundesanstalt fur Landtechnik,
A-3250 Wieselbu
Dipl .-lng. Josef Plank - LWK Steiermark, A-8010 Graz
Dipl.-lng. Christian Rakos - Osterr. Akademie der
Wissenschaften, A-1010 Wien
Horst Scheuer - Landesenergieverein Steiermark, A-8010
Graz
Ing. Gunther Schwarzler - Energie- und Regionalberatung,
A-1150 Wien
Dipl.-lng. Helmut Sollinger - BM fur Umwelt, Jugend und
Familie, A-1010 Wien
Ing. Josef Strei Belberger - Agrar Plus GmbH, A-3100 St.
Polten
Ing. Werner Weiss - Arge erneuerbare Energie, A-8200
Gleisdorf
Dipl.-lnq. Manfred Worgetter - Bundesanstalt fur
Landtechnik, A-3250 Wieselburg
Contacts
Editor
Participant
© Copyright 2006 Policy Statements
Updated
by CPL Press:
03/07/2007
- biomatnet@biomatnet.org
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