Environmental Engineering Reference
In-Depth Information
there is no loss of comfort due to the frequent fi ring-up of the system during the
day. The boiler rated output can therefore be designed specifi cally for the heat
energy needs of a building. A buffer storage facility is still useful as it prevents a
boiler from fi ring up too frequently and ensures that the heating is working at its
rated load most of the time. The system then burns at an optimal level and produces
a minimal emission of noxious substances.
Unlike fi rewood, wood pellets are usually stored in a special area within a building.
It is not possible for the pellets to be stored outdoors as they will absorb moisture
and may be damaged. An area of three to fi ve square metres should normally be
suffi cient as the pellet store for a standard single-family new-build home. Older
buildings need more space, whereas three-litre houses require considerably less.
The transport system for the pellets is on the fl oor of the store (Figure 12.17). A
slanted shelf will ensure that the pellets slide down to the transport system even
when the fi lling level is low. However, slanted shelves create a void that reduces
the useable storage volume to about two-thirds of the space volume. As the price
of wood pellets varies throughout the year, the store should hold at least a year's
worth of fuel. Pellets can then always be bought at times when prices are low.
Figure 12.17
Cross-section of a wood pellet store.
Size of Wood Pellet Store
If the annual heat requirement
Q
H
of a house and the boiler effi ciency
boiler
are
known, this can be used to calculate the necessary store volume
V
S
including the
void:
η
Q
H
V
=
.
S
2
3
kg
m
kWh
kg
⋅
η
⋅
650
⋅
5
boiler
3
