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1.1 How the Condensing Wood
Pellet Boiler Operates
On start up, the auger feeds the wood
pellets from the hopper into the burner
where they are lit by an ignition element.
The burner output is modulated
to achieve the set temperature by
controlling the feed rate of pellets.
The fan in the burner propels hot
gases generated from the fuel into
the Spira’s primary heat exchanger.
The heat energy is then transferred to
water from the central heating system,
before being circulated around the
property to radiators/underfloor heating.
It is important to note that in non-
condensing biomass boilers, up to 20%
of the energy that is produced is lost to
the atmosphere through waste gases
exhausted by the flue system.
The Spira contains a unique extra
(secondary) condensing heat
exchanger which has been designed to
capture some of this lost heat energy
that would otherwise be lost, so it
maintains extremely high efficiencies.
It does this by cooling the flue gases
to their dew point (below 55°C) thus
extracting more sensible heat.
The boiler has been independently
tested to BS EN303-5 and will achieve
the following full load (nett) 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 with a maximum set
point 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 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 times of the
pellet feed auger supplying pellets to
the burner. See Section 9 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
fan box, 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 draught stabiliser 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.
The only flue suitable for use with
the Grant Spira condensing wood
pellet boiler is the Grant Biomass
twin-wall insulated conventional flue
system.
This 125mm (5”) diameter flue
system is suitable for the 5-18kW,
6-26kW and 9-36kW Spira models.
For the 44kW, 52kW, 62kW and
72kW double boiler installations
each boiler must have a separate
flue system. Refer to Section 7.
1.3 Boiler Models
The Grant Spira condensing wood
pellet boiler is available in sixteen
different models:
!
NOTE
Model
Nominal
Reduced
output output
Spira 5-18
95.5%
90.2%
Spira 6-26
97.4%
96.4%
Spira 9-36
93.1%
98.1%
Product code
Model
Description
WPS518 RH110
5-18
1 x 5-18kW 110kg right hand hopper
WPS518 LH110
5-18
1 x 5-18kW 110kg left hand hopper
WPS518 RH200
5-18
1 x 5-18kW 200kg right hand hopper
WPS518 LH200
5-18
1 x 5-18kW 200kg left hand hopper
WPS626 RH110
6-26
1 x 6-26 110kg right hand hopper
WPS626 LH110
6-26
1 x 6-26 110kg left hand hopper
WPS626 RH200
6-26
1 x 6-26 200kg right hand hopper
WPS626 LH200
6-26
1 x 6-26 200kg left hand hopper
WPS936 RH110
9-36
1 x 9-36 110kg right hand hopper
WPS936 LH110
9-36
1 x 9-36 110kg left hand hopper
WPS936 RH200
9-36
1 x 9-36 200kg right hand hopper
WPS936 LH200
9-36
1 x 9-36 200kg left hand hopper
WPS1144
11-44
1 x 5-18kW and 1 x 6-26kW b 140kg double boiler
hopper
WPS1252
12-52
2 x 6-26kW b 140kg double boiler hopper
WPS1562
15-62
1 x 6-26kW and 1 x 9-36kW b 140kg double boiler
hopper
WPS1872
18-72
2 x 9-36kW b 140kg double boiler hopper
