OPINION
THE HEAT IS ON
Kate de Selincourt (left) and Sofi e Pelsmakers argue that biomass might just be the biggest ‘sustainable’ elephant in the room
The article, ‘Burning issues’, in CIBSE Journal December 2012,
highlights several design issues associated with the specifi cation of biomass plant. The article also makes it clear that the main drive for installing biomass boilers is because of biofuel’s supposed ability to provide low-carbon heat. However, the notion that biomass is automatically low carbon is increasingly being challenged. So, a fundamental question is whether we should be heating our buildings with biomass at all? Biomass produces very large quantities of CO2
per unit of energy
when burned – more than gas or oil2 – and any notion that the fuel is low carbon depends entirely on re-uptake of CO2
through subsequent biomass
growth. But the long delay before this happens, and the immediate reduction in growth when trees are felled, means a large and long lasting pulse of CO2
is emitted for each kWh
of biomass heat produced. The Department of Energy and Climate Change (DECC) itself has admitted that, because of this, using whole trees to fuel production of heat or electricity is a higher carbon option than leaving the trees to grow and producing the energy by burning fossil fuels. This is true for at least 100 years after the energy is produced, and DECC concluded: ‘The use of harvested wood from UK managed forests exclusively for bioenergy (replacing fossil fuels) has higher relative greenhouse gas (GHG) emissions than leaving the trees unharvested in the forest. This means... there is not a strong case to produce bioenergy in this way3
.’
While DECC suggests that ‘such a scenario is very unlikely in the UK’, it is already happening. For example, in Ayrshire, pellets are made from entire logs4
, while overseas pellet 24 CIBSE Journal February 2013
Think passive before biomass: Oakmeadow Primary School achieved Passivhaus certifi cation producers also use the entire harvest5
Should we be heating our buildings with biomass at all?
.
Additionally, When a biomass boiler is specifi ed, attention tends to be diverted from a building’s fabric effi ciency, because of the belief that ‘the heat is all zero carbon anyway’. The unintended result is that actual emissions are the same as – or higher than – a conventional building, when they could have been reduced6
. Of
course, if, as reported by CIBSE, boilers are frequently operating well below optimum effi ciency, emissions will be higher still. Given that a biomass boiler
is usually the most economical option to meet the ‘low carbon’ or renewables targets set by the planning authority, biomass boilers are routinely specifi ed. Yet, increased fabric effi ciency – instead of money spent on biomass boilers – leads to genuine CO2
biomass further increases its environmental impact and CO2 emissions, and importing it from abroad raises additional ethical issues where tropical rainforest or agricultural land has been cleared for fuel crops to heat our buildings. All evidence suggests it is unwise
to believe that biomass could – or should – play any role in the UK’s carbon reduction efforts. To suggest otherwise is misleading and will increase CO2
in trees or in timber building
materials for decades (and even centuries), is by far the most robust low-carbon strategy.
References 1
reductions, lower energy
costs and better energy security over a building’s lifetime. What is really highlighted here is
the lost opportunity to deliver better buildings on the same budget. Yet prioritising fabric effi ciency over renewable generation is not in accordance with much planning policy – nor has it historically been incentivised by government – a dual scenario that leads to a misplaced focus on the role of on-site energy supply, and to inappropriate strategies. Processing and transporting
Dirtier than coal
www.rspb.org.uk/Images/ biomass_report_tcm9-326672.pdf
2
www.manomet.org/sites/manomet.org/ fi les/Manomet_Biomass_Report_Full_ LoRez.pdf
3
www.decc.gov.uk/assets/decc/11/meeting- energy-demand/bio-energy/7014-bioenergy- strategy-supplementary-note-carbon-impac. pdf
4
www.laganconstruction.com/wood-pellet- biomass-plant-successfully-completed and
www.theclaymoreproject.com/uploads/ associate/151/fi le/Low carbon wood pellet production.pdf
5
www.dogwoodalliance.org/wp-content/ uploads/2012/11/Whole-Tree-Wood-Pellet- Production-Report.pdf
6
www.aecb.net/UserFiles/File/Biomass_A_ Burning_Issue_September_2010.pdf
● KATE DE SELINCOURT is a writer and editor. SOFIE PELSMAKERS is an architect and doctoral researcher at the UCL Energy Institute.
emissions. Focusing on
effi cient building design, and locking CO2
www.cibsejournal.com
ARCHITYPE
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