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BCD SPECIAL REPORT ON
HERITAGE RETROFIT
FIRST ANNUAL EDITION
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often necessary to seek specialist guidance
and take precautions to avoid affecting
significant archaeological finds, which
can include whole Saxon villages. This
can make it problematic to excavate large
areas of a site to develop schemes such as
ground source heat pumps.
Choosing the most appropriate
type of energy for some National Trust
properties can be a difficult challenge.
For example, the trust’s historic art and
house collections at Beningborough
Hall in North Yorkshire require lower
heat levels and would only need a 90kW
biomass boiler, but this option may not
be financially viable, especially following
substantial reductions in payments made
under the Renewable Heat Incentive in
2015/16 for biomass heating installations
of less than 200kW. On the other hand,
a heat pump might not provide the
right solution either, because the heat
emitters are too small. Ground-source
heat pumps work most efficiently with
underfloor heating systems due to the
lower temperature requirements of a large
emitter, but installation is rarely possible
due to both conservation issues and
financial constraints.
WOOD FUEL
Log heating systems such as stoves
and boilers are ideal for houses but
in larger properties they require
more frequent refilling so in these
environments other types of wood
fuel such as wood chips and pellets are
mostly used in automated systems.
Wood chips can be made from
virtually any kind of woody biomass,
including whole trees, by a chipping
machine. This makes it possible
for the trust to supply fuel from
its own estates. Wood chips are
typically used in automated systems
making them a clean and convenient
heating option for the trust.
Pellets are relatively new in the UK
but they have been used in central Europe
for some time. They are produced from
wood by-products such as sawdust
and have a better calorific value which
means the energy to weight ratio is very
favourable, so they are more appropriate
for smaller spaces.
The visitor building at Penrhyn Castle
in Wales has a new wood pellet space
heater with a hot-air convector built in,
which heats the whole building.
In simple carbon dioxide emission
terms the log stove at another trust
property, Llanerchaeron tea room, emits
considerably less carbon dioxide per kWh
than the new high-tech pellet stove at
Penrhyn. Research has shown that log
stoves emit around 4g of carbon dioxide
per kWh compared to 34g per kWh for a
wood pellet system (and around 500g per
kWh for an electric heater using power
from the grid).
Deciding whether a pellet stove or a
log stove is more suitable for a particular
site can come down to the ability to
manage the stoves. Cutting, hauling,
drying and splitting logs, or just supplying
them, as well as loading and cleaning
the stove are all time-consuming and
members of staff have other tasks to
carry out. It can come down to the simple
question: ‘Do you have the space to store
the fuel and the time to manage the fire?’
Expense can also be a consideration.
The Tigchelaar wood-fired storage heater
or ‘masonry stove’ at Llanerchaeron
is over 90 per cent efficient and a very
good space heater but it is also twice
the price of some stoves. On the other
hand, there is a simple Clearview
stove space heater in Colby Woodland
Garden which is significantly cheaper
than the masonry stove, and far
cheaper than any pellet system.
Fuel is important and the trust
ensures that its wood fuels are produced
in the UK from FSC timber and from as
local a supplier as possible, if not from its
own estates. Wood chip and pellets must
also conform to the relevant standards
(including DIN 66 165).
In some cases, using the natural
resources that properties and estates have
access to creates additional conservation
wins. The biomass system at Croft Castle
in Herefordshire uses wood from conifer
trees on the estate to heat the property.
Removing the conifers has exposed
ancient wood pasture and led to an
increase in biodiversity.
CASE STUDY 1:
A wood pellet range cooker
in a farmhouse in Snowdonia
At Hafod y Llan in Snowdonia, the trust
experimented with a Klover 120 wood
pellet range cooker. The requirement
was for a viable, economic, manageable
biomass cooker and central heating
appliance which could simply replace
the host of oil-fired range cookers (Aga,
Stanley, Rayburn, Esse, etc) used in many
similar farmhouses and cottages.
The building is a fairly typical three-
bedroom farm-house with moderate
levels of insulation, draught-proofing
and retrofitted windows. The appliance
had no problem at all heating it. When
used all day, two 20kg bags of pellets
were consumed and this fell to one bag
a day if the property was heated only in
the morning and evening. In the summer
months just half a bag a day was used for
hot water. A fossil-fuel boiler was retained
as a backup, but it has never been needed.
In winter-heating mode the fuel was
burning much more cleanly and only
leaving a very fine ash. In summer there
was some partially burnt pellet but this
was not an issue. The daily and weekly
controls were not very intuitive at first but
are adequate once members of staff get
used to them.
As a cooker it performed well
overall, if a little less refined than
an Aga. The oven could be a tad hot
(200°C+ top and 180°C bottom of the
oven), and it was a matter of trial and
error at the start. Using the hob plate
also took some practice, with a range
of temperatures across the surface.
A simple slot-in electric plate
cooker was also provided for minor
cooking requirements (boiling an egg for
Wood-fired storage heater or ‘masonry stove’ at
Llanerchaeron, Ceredigion