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Principles of wood combustion for generating heat
The diagram shows the dependency of the net calorific value on the
water content, using spruce as an example. With a water content of
20 % (moisture level 25 %), the net calorific value is 4.0 kWh/kg.
The net calorific value of timber stored over several years is approx.
twice that of freshly cut timber.
Storage
Not only is the combustion of moist wood uneconomical, it also leads
to low combustion temperatures and high emissions plus tar deposits
inside the chimney.
Information on storing firewood
■ Split round logs from a diameter of 10 cm upwards. Enlarging the
surface area enables the wood gases to be expelled more quickly
and simply. The drying process is also accelerated during storage.
■ Stack the logs in a ventilated and preferably sunny spot underneath
a rain canopy.
1.2 Minimum wood fuel requirements
Wood remnants, coarse woodchips and compressed shavings can be
used in the Pyromat Eco. The Pyromat Eco is ideal for the combustion
of logs. The wood should have an edge length between 45 and 50 cm
or up to 100 cm (depending on the boiler type: boilers for 50 cm logs
or 100 cm logs). The rated wood boiler heating output will only be ach-
ieved with dry wood with maximum 20 % water content (air-dried
wood). Wood of poorer quality and higher moisture content also
reduces the rated heating output and the length of combustion.
Substances
When procuring wood for combustion in a Pyromat Eco, ensure that
foreign objects (e.g. stones, metal parts, pieces of brick, plastics etc.)
are avoided. These would change the composition of the fuel and
therefore the critical parameters of the combustion process.
Chlorine Cl
Sulphur S
Total Cl, S
Ash content total
Alkali oxides in the ash (K
O and Na
2
SB start of ash sintering
Exceeding the above limits will shorten the service life of the combus-
tion chamber and wood boiler. This also means that maintenance work
is increased and service intervals are reduced.
Origin, treatment and storage
Depending on the origin, wood can be natural wood (e.g. forest wood
and waste from sawmills), residual wood from wood processing plants
or waste wood (building rubble, furniture). The wood must be obtained
and cut to the desired size, and foreign objects deal with appropriately.
In addition to the requirement to adhere to ÖNorm M 7133, a max.
proportion of 5 % outliers in the fuel should be observed.
Size of the woodchips
The Pyromat Eco is also suitable for the combustion of coarse woodchips. To prevent increased maintenance work, appropriate coarse wood-
chips in accordance with ÖNorm M 7133 should be used.
PYROMAT ECO
mg/kg
mg/kg
mg/kg
g/kg
O)
g/kg
2
°C
(cont.)
■ Stack the logs with generous air gaps to enable the flowing air to
carry off the dissipating moisture.
■ A hollow should be created underneath the wood pile (e.g. in the
form of support timbers) to allow moist air to escape downwards.
■ Never store freshly cut wood in a cellar, as air and sunshine are
required for drying. However, dried wood can be stored in a well
ventilated cellar.
When using softwood (e.g. spruce), note that the energy per volume
unit is lower than with hardwood (e.g. beech). Softwood is therefore
suitable for "initial heat-up" - however, its use shortens the intervals
between recharging considerably and increases the volume to be used
(up to 44 %). Observe the requirements specified in the next chapter
relating to non-combustible substances and their limits for warranty
period claims. Deviations are only possible through written, system-
specific manufacturer declarations.
The values must not exceed or fall below the following limits (per kg of
dry fuel) for the non-combustible content (ash at an analysis temper-
ature of 815 °C):
Limit
Comparison with natural wood from forests
max. 300
max. 1000
max. 1000
max. 15.0
max. 1.0
min. 1000
The proportion of dust-like and fine-grained materials should also be
minimised (in accordance with ÖNORM M 7133).
The length of the outliers must not exceed 16 cm (with a cross-section
of max. 5 cm²). The surface of the fuels should be roughened where
possible (e.g. through shredder, etc.). When using briquettes, ensure
compression is matched to charging. The maximum diameter is
60 mm.
1
10
120
130
5.0
0.35
approx. 1200
5
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