Introduction
5
1.1 How the Condensing
Wood Pellet Boiler Operates
During the combustion process,
hydrogen and oxygen combine to
produce heat and water vapour. The
water vapour produced is in the form of
superheated steam in the heat
exchanger. This superheated steam
contains sensible heat (available heat)
and latent (heat locked up in the flue
gas). A conventional boiler cannot
recover any of the latent heat and this
energy is lost to the atmosphere
through the flue.
The Grant SPIRA Condensing wood
pellet boiler contains an extra
(secondary) heat exchanger which is
designed to recover the latent heat
normally lost by a conventional boiler. It
does this by cooling the flue gases to
below 90°C thus extracting more
sensible heat and some of the latent
heat. This is achieved by cooling the
flue gases to their dew point.
The boiler has been independently
tested to BS EN303-5 and will achieve
the following full load efficiencies when
both the boiler and system are correctly
set:
To ensure maximum efficiency from the
Grant SPIRA boiler, the boiler return
temperature should be 55°C or less
(but NOT less than 40°C) at
maximum operating temperature.
This will enable the latent heat to be
condensed out of the flue gases.
The boiler is capable of a maximum
flow temperature of 75°C.
To achieve the required return
temperature (55°C or less), it is
recommended that the heating system
is designed and balanced to operate
with a temperature differential of 20°C
between flow and return. The use of
modulating circulating pumps (now
widely available) and effective control
systems should be considered.
Grant SPIRA condensing wood pellet
boilers will still operate at extremely
high efficiencies even when not in
condensing mode and are therefore
suitable for fitting to an existing heating
system without alteration to the radiator
sizes.
1.2 Boiler Description
The Grant SPIRA boiler uses a drop
feed type burner with modulated heat
output. The burner output is
determined by varying the feed and
pause time of the pellet feed auger
supplying pellets to the burner. See
Section 8 for details of burner operation.
The boiler is suitable for use on a
sealed or open vented central heating
system. When commissioned and set
correctly, Grant SPIRA condensing
wood pellet boilers will operate
automatically, using a typical heating
control system.
All models are supplied with the control
panel and burner factory fitted. The
combined fan box & flue starter, pellet
feed auger and hopper are supplied
separately and are fitted by the installer.
See Section 4 for boiler installation.
The boiler needs to be connected to a
conventional flue system. There is no
provision for connection to a balanced
flue system as there is draft stabilizer
fitted to the appliance.
The boiler is not designed specifically
for operation on a system with a buffer
tank/ thermal store, however when
used on such a system there is no
effect on the boiler performance.
!
NOTE
Model Nominal Reduced
Output Output
SPIRA 6-26 97.4% 96.4%
SPIRA 9-36 93.1% 98.1%
The only flue suitable for use with
the Grant SPIRA condensing wood
pellet boiler is the Grant ‘Black’
twin-wall insulated conventional flue
system. This 125mm (5”) diameter,
black powder coated stainless steel
flue system is suitable for both
6-26kW and 9-36kW Spira models.
For the 52kW, 62kW and 72kW
double boiler installations each
boiler must have a separate flue
system. Refer to Section 7.
Product
Code Model Description
WPS626RH110 6-26 1 x 6-26kW boiler + 110kg right hand hopper
WPS626LH110 6-26 1 x 6-26kW boiler + 110kg left hand hopper
WPS626RH200 6-26 1 x 6-26kW boiler + 200kg right hand hopper
WPS626LH200 6-26 1 x 6-26kW boiler + 200kg left hand hopper
WPS936RH110 9-36 1 x 9-36kW boiler + 110kg right hand hopper
WPS936LH110 9-36 1 x 9-36kW boiler + 110kg left hand hopper
WPS936RH200 9-36 1 x 9-36kW boiler + 200kg right hand hopper
WPS936LH200 9-36 1 x 9-36kW boiler + 200kg left hand hopper
WPS1252 12-52 2 x 6-26kW boilers + 140kg double boiler hopper
WPS1562 15-62 1 x 6-26kW boiler and 1 x 9-36kW boiler
+ 140kg double boiler hopper
WPS1872 18-72 2 x 9-36kW boilers + 140kg double boiler hopper
1.3 Boiler Models
The Grant SPIRA condensing wood
pellet boiler is available in eleven
different models:
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