Biomass heating has great potential to cuts costs and
carbon emissions in the industrial sector. In this article,
Martin Murrish, technical manager with Hoval, explains
how the company approached the process of switching to
biomass heating for its factory

While there are a number of
renewable energy options
available to building operators, it
is clear that wood fuel biomass is proving
particularly popular in the UK. The concept
of burning a fuel is clearly familiar and wellunderstood,
retrofitting biomass to an
existing heating system is relatively
straightforward and there are opportunities
for extra revenue through the government’s
Renewable Heat Incentive (RHI).

In retrofit projects where a fossil fuel
boiler is being replaced or supplemented by
a biomass boiler, a key advantage is that the
biomass boiler will use the same flow and
return water temperatures as the previous
boiler. Consequently there is no need to
change heat emitters, pumps, pressurisation
sets and other ancillary items.

Nevertheless, there are some important
factors to consider; these can be illustrated
through the procedures we followed in
installing biomass heating at our factory in
Newark-on-Trent. This is the factory where
our latest generation STU wood pellet
biomass boilers are manufactured and we
have two STUs installed at the factory. One
600kW unit replaces the previous gas-fired
boiler to deliver hot water (80°C flow/60°C
return) to fan coil units mounted in each of
the three factory spaces. This boiler is sized
to meet all space heating requirements
throughout the year and is coupled to a heat
meter for the RHI.

In addition, a 195kW STU boiler has been
installed for training and demonstration
purposes, connected to a small, separate
heating system so as not to interfere with
metering for the RHI.

The latest STUs use a standardised skid
mounted design that includes pumps, fans
and fuel delivery augers to reduce footprint,
so finding a space for them was straightforward
However, we also needed to find
space for storage of the fuel as close to the
boilers as feasible to keep delivery simple.

The most appropriate solution was to opt
for a 35m3 GRP silo just outside the
building, connected to the boilers with
flexible augers; planning permission was
gained for this. The silo holds 20-25 tonnes
of wood pellets and uses load cells to track
fuel reserves. The system can be set up to
send an SMS message to the fuel supplier
when reserves reach a predetermined level.

Fuel is delivered in a ‘blower’ vehicle and
blown directly into the silo, so there was no
need to make special provision for delivery
access.

Flueing is another consideration as
biomass boilers have slightly different flue
specifications to gas and oil fired boilers. In
the event the existing flue for the gas boiler
was suitable for the 600kW STU, but we
needed to install a new flue for the 195kW
model. To optimise performance we have
also installed a 6000L thermal store, which
helps to spread the residual heat when the
boiler switches off. Also, when the water has
reached design temperature the boiler will
not fire again until the temperature falls to
75°C. So the thermal store acts as a buffer to
maintain flow temperatures while reducing
the firing of the boiler. It retains much of its
heat through the night, which accelerates
the warm-up times in the mornings.

For maximum efficiency and control,
STU boilers are optimised to run on wood
pellets produced to the EN+ A1 standard,
thus achieving a close marriage between
controls, hardware and fuel to get as close to
complete combustion as possible. This avoids
problems of inconsistent combustion
efficiency caused by the variable moisture
content and dimensions of wood chips and
some low quality wood pellets.

Given the benefits of using biomass
heating, it is certainly worth considering. It
also makes sense to work with a supplier
that has the technical expertise and practical
knowledge to ensure the system delivers
maximum performance at every level.