Most bulk materials and
labour were sourced within a 50 mile
radius of
the site, enabling the completed embodied carbon to compare favourably
with that of a volume housebuilder's industry standard product -
despite having thicker walls and considerably higher thermal mass.
BedZED is just about large enough to merit its own on site water
treatment plant and woodchip fuelled combined heat and power plant.
Although the plant can be accurately sized to meet demand, staff
maintenance costs on an isolated island site of this size can become
prohibitive, although this problem will be overcome as both these
community scale technologies become more commonplace in south London.
Biomass chp works very well on mixed use zero heating specification
developments, as the thermal demand is for hot water only, and remains
consistent all year, withoversize hot water storage tanks that can meet
peak demands whilst still allowing trickle recharging throughout the
day. This allows the power plant to more or less match average
electrical demand, exporting to grid when surplus power is generated on
site - and importing to meet peak demand.
On balance over a year, if
the plant performs reliably, with only its planned maintenance downtime
- then slightly more power is generated than is actually required on
site. If this surplus power is between 5 and 15 % of annual demand, it
should be possible to pay off both the embodied initial construction
carbon and the planned maintenance / replacement carbon footprint.
The advantage of the biomass chp system is that very similar amounts of
biomass are burnt compared to a conventional heat only boiler, as the
electricity is generated from flue gases that would be unlikely to have
been harnessed to the same efficiency in a more conventional combustion
process. This make it much easier to stay within the national biomass
quota, whilst still inhabiting higher density urban infrastructure
